ALOK MISHRA(I120003) 26-10-2016MOHAMMED ARSHAD(I120110)SHARATH V(I120117)VARUN K V(I120118)VIVEK C(I120121) ASSIGNMENT NO:1

LEAD-FREE SOLDERS

ABSTRACT

The reliability of electronic assemblies is highly dependent on the quality ofsolder joints, and the latter’s response to temperature excursions. Finite ele-ment modeling (FEM) has been widely used for the estimation of the lifetimeof solder joints subjected to temperature cycling. Thanks to the expertise ofdecades, a significant number of companies, universities and research insti-tutes were able to have a relatively accurate estimation of life time for SnPbsolder. For the leadfree solder materials, first attempts for correlation modelsshow up but there are several problems. First of all, there is a wide rangeof alloys and alloy compositions, which have a different material behavior(Emodulus, CTE) but also a different resistance to thermal fatigue. Sec-ond, it is shown in several papers that lead-free solders have different failuremodes compared to SnPb. In particular at low temperatures , some lead-free materials show brittle behavior and this is not covered by the currentsimulation models based on creep fatigue at high temperature. Experimentsshow that the trends in lead-free solder joint reliability are cycling-conditionand package dependent. In this paper, the simulation results for commonlyused solder alloys are presented and the thermal fatigue reliability of leadfreesolder joints has been investigated. An isothermal fatigue test method wasused in this study to improve the efficiency of fatigue study, and two differentlead-free solder alloys, Sn-Ag-Cu, Sn-Ag were investigated. It was found thatthe lead-free solder alloy was more reliable compared to the lead alloy andthis is package dependent.

INTRODUCTION

EVOLUTION OF SOLDER

Soldering is a metallurgical joining method using solder with a melting pointof below 3150C as filler. Also, soldering can be explained as any of variousalloys fused and applied to the joint between metal objects to unite themwithout heating the objects to the melting point . In year 1921, Ernst Sachs

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(founder of ERSA) was the first man who invented the first electric andmass-produces soldering iron for industry.

Callister states that solders are metal alloys that are used to bond or jointwo or more components (usually other metal alloys). They are used ex-tensively in the electronics industry to physically hold assemblies together .Furthermore, they must allow expansion and contraction of the various com-ponents, must transmit electrical signals, and also dissipate any heat thatis generated. The bonding action is accomplished by melting solder mate-rial, allowing it to flow among and make contact with the components to bejoined; which do not melt . Finally, upon solidification, a physical bond withall of these components is formed . As shown in Figure 1, Sn-Pb has loweutectic temperature of 1830C. Great strength and good ductility makes itcan endure thermal cycling . Pb is an adequate solubility but it combinesrapidly with Sn . In board level packaging the solder used is primarily 63Sn-37Pb, a eutectic composition, or 60Sn-40Pb, a near eutectic composition .Since Sn-Pb is used as primary components of eutectic solders, Pb providesmany technical advantages, which includes the following Sn-Pb solders: Pbreduces the surface tension of pure tin, which is 550N/m at 2320C, and thelower surface tension of 63Sn-37Pb solder (470mN/m at 2800C) facilitateswetting.

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A good understanding of the behaviour of Sn-Pb solders has enabled currentboard level technology to assemble and create small geometry solder joints,approaching 75µm in size, in high volume, and at a competitive cost .Metallic lead and its alloys have been used for productions without concern-ing the risk and consequences. Before, lead is used to make plates, bowls,drinking glasses and many more .In recent times, health and environment matter have been taken seriously.The first serious concern started with the lead-containing pigments used inpaint [1]. Electronic and electrical waste devices may wind up in the refuseheap. Therefore, lead may spread into the air particle and may be affectedto the environment, such as, air pollution [16]. Next, effect of lead to humancan be listed as below:1. Harm to foetus including brain damage or death.2. High blood pressure.3. Digestive issues.4. Nerve disorders .5. Muscle and joint pain.Due to the negativities of lead to human and environment, a legislation oflead usage has been enacted.

LEAD-FREE SOLDERS

In today’s society,the following three problems such as over-population, re-source crisis, and environmental pollution are the point of increasing world-wide attention since entering the 21st century. Among them, the environmen-tal pollution is becoming more and more serious. Since China is the biggestone among the developing countries in the world, the task of environmentalprotection is of extreme significance for it. With the rapid development ofelectronic technology, the electronic products are updating constantly in ourdaily life. However, most of the abandoned electronic products are directlydiscarded or buried which lead to a new kind of pollution, namely, heavymetal pollution. Till recently, solders used in electronics, based on suitabil-ity and knowledge-base developed over a period of time, remained to be tolead-based. Successive rapid advances in microelectronic devices make themobsolete within a very short period after their introduction resulting in sig-nificant quantities of electronic wastes in landfills. Leaching of toxic leadfrom such electronic wastes can result in contamination of the human foodchain causing serious health hazards.As a consequence, several European andPacific Rim countries have passed legislation warranting elimination of leadfrom electronic solders by specific fast approaching deadlines. Then, thestandard of lead-free solders for production is proposed that the lead con-

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tent in the electronic devices should not be more than 0.1 percentage whichcan reduce the pollution caused by the waste device . Modern society hasentered into an information age with the development of science and tech-nology, however, the information level of discretion to measure a country hasalso became an important symbol of comprehensive national strength.

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The development of modern electronic industry puts forward increasinghigh demand. Volume miniaturization, components multi-function, high re-liability, and low cost are needed for new electronic products. Due to thetechnology limitation in miniaturization of the semiconductor chip size, inrecent years, related electronic packing technology and materials are consid-ered to be the dominating direction in microelectronic industry technologycompetition . Microelectronic technology, in which chip manufacturing andelectronic packing are the two keys, respectively, is the indispensable basein the electronic information industry and various hightechnology applica-tions.However, electronic packing is a complex of system engineering involv-ing craft, material, and design, evaluation analytical technology systems.Electronic packing generally can be divided into three levels, first-level pack-age, second-level package, and third-level package, respectively, (see Fig.2,Scheme of three levels in electronic packaging).First-level package is chip encapsulation, mainly silicon chip in the substrate,second-level package is the connection between electronic devices and printedcircuit board, and the third-level package is the connection, seal, and quar-antine from the external environment. Micro- connection technology in theelectronic package plays an essential role in the whole process. Solderingis the preferred method of joining components to printed circuit boards in

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electronics. It is generally a relatively low temperature (¡2500C) process,therefore, avoiding thermal damage to the polymeric materials of the PCBsor the components [5]. Sn-Pb alloys are the primary solders used widely inmanufacturing because of their unique combination of material propertiesand low cost. The electronic industry has been using Pb-bearing solders forinterconnection applications for over fifty years, however, the presence of leadin the actual solders is considered to be very dangerous for the environmentdue to the huge amounts of printed circuit board and electronic devices tobe recycled from municipal waste dumps. There are several pending nationaland international legislation proposals forbidding the wide use of Pb in sol-ders such as Sn95Pb and Sn37Pb solder because of the toxicity of lead andits harm to the environment and human health; thus these Sn-Pb solders arenot allowed to be used in the electronic products.The European Community, the U.S., and Japan, as well as electronic industrycompanies launched initiatives to look for lead-free solders having physical,chemical, and technological properties comparable to or better than the Sn-Pb alloys in use [9]. The development of lead-free solders has been a pressingtask for material scientists due to the health and environment concerns overthe lead content of conventional solders used in electronic industry widely.The new lead-free solder alloys, which has been used in the electronic indus-try and attracted extensive attention, need to meet a variety of propertiessuch as good wettability, low soldering temperature, low-cost, environmentalfriendly, adequate strength, good thermal fatigue resistance and so on whichare superior to or even consistent with that of conventional Sn-Pb soldersat least. Internationally, the lead-free solder is defined as based of Sn dueto its good conductance which is doped with Ag, Cu, Zn, Bi, In to formbinary, ternary, or even quaternary eutectic alloys to improve the perfor-mances of pure Sn, in addition, the Pb-content is less than 0.1percentage.Global concern over the environmental impact and health effects of Pb-basedsolders in consumer electronics has led to the development of lead-free sol-ders alternatives. Leadfree solders were never an industry choice until recentUK legislation has enforced their use since the introduction of Eu RoHS di-rective. As a consequence, a specific family of alloys has emerged that arelikely to become industry standard for surface mount reflow solder joints.The SAC(Tin- Silver-Copper) family of solder alloys are recommended bymost of the electronics industries governing bodies own to superior mechani-cal properties, good wettability, improved creep resistance and long thermalfatigue life, but the Sn- Ag-Cu eutectic composition is still in question suchas the liquidus temperature of the Sn-Ag-Cu solders is about 300C higherthan that of the Sn- 37Pb (187 0C) solder which would bring serious oxida-tion problem to the solder surface and decrease the wettability between the

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solder and substrate. So the research of new lead-free solders with equivalentmechanical performances and microstructural stability to eutectic tin-leadsolder is an urgent task.

THE RESEARCH STATUS OF LEAD-FREE SOLDERS

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Considerable effort has been made to explore various solders and thedesign of reliable joints with newly developed lead-free solders in order tounderstand completely their mechanical properties and deformation mech-anism. The role of solder joints in electronic products is not limited byinterconnection of the electronic components only, but also they ensure thestructural reliability of the electronic package. Nano-soldering is a promis-ing technique for nano-scale joining and interconnect formation for manynewly emerging nano-fabrication processes and nano-building blocks. Withthe burst of nanotechnology in the last two decades, has improved signifi-cantly. There is an increasing technology interest for low melting point alloysuitable for use in soldering with lead-free materials. Surojit Pande adopteda straightforward route to gram level synthesis of pure phase of the Sn-Agnano-alloy in an eutectic composition (96.5:3.5) in a mixture of ethylene gly-col and silicone oil using hydrazine as the reductant and then the directreduction of Sn(II) acetate and Ag(I) nitrate gave the Sn-Ag nano-solder.Smaller particles with a melting point as low as 1280C were obtained whenthe nano-alloy disintegrates by sonication and reforms by heating. Zou fo-cused on the research aimed to lower the melting temperature of the lead-freesolder alloy through decreasing the particle size down to nanometer level us-ing the tin()2-ethylhexanote, silver nitrate, copper() ethoxide monohydrateas the starting materials, anhydrous ethanol as the solvent, sodium boro-

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hydride as the reductant and the 1,10-phenanthroline as the surfactant bychemical reduction method. The Sn3.5Ag and Sn3.5Ag0.5Cu nanoparticles(average size about 30 nm) are obtained by adjusting the drops rate of re-ductant, the concentration of surfactant and reactant. The results showedthat the larger ratio of the weight of surfactant to the precusor leading tosmaller particle size and size distribution due to the capping effect caused bythe surfactant molecules coordinating with the nano-clusters. Fig. 2 depictsthe relationship of the different particle sizes and average diameter with sur-factant. When the addition rate of reductant is decreased, the particle sizesand size distribution showed the same result. Also, the melting temperatureof lead-free solder showed strong size-dependent tendency and the meltingtemperature of Sn3.5Ag and Sn3.5Ag0.5Cu nano-particles with average sizeof 30 nm was 2100C and 2010C, much lower than that of bulk alloy. Theo-retical analytical showed that the melting temperature can be as low as thatof eutectic Sn-Pb solder alloy when the particle size was decreased to 10 nm.Gao synthesized nano-scale Sn/Ag, Sn, and In lead-free solders directly ontomulti segmented metal nano wires by an electro deposition method in nanoporous templates. The diameter of nano-solder nano wires ranges from 30to 200 nm and the length from 1 to 10 micrometer. The thermal propertiesof the solders were treated using a temperature- programmable furnace tubunder a controlled atmosphere, it was found that nitrogen plays an essentialrole in the solder reflow process. Base layer, diffusion barrier layer, and wet-ting layer effect on solderreflow were studied and Nickel/gold surface finishingwas found to be effective for the nanowires. Solderjoints were formed whenthe nanosolder were reflowed in a liquid medium, which showed the great po-tential based self-assembly technology to integrate nanowires into 2D or 3Dfunctional structures or other electronic devices. Intermetallic compounds(IMCs) are formed when interconnections in integrated circuit (IC) packages

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figure : 3

figure : 3are joined with solder.Although IMCs are not present in large amounts, theyusually have a dominant influence on the reliability of the interconnectionbecause of their material properties . Xu et al. studied systematically theformation and evolution of intermetallic compounds (IMCs) layer betweentheSn-3.7Ag-1In-0.9Zn lead-free solder and Ni/Cu substrate at different re-flow times. The evolution of the interfacial structures was divided into threestages: a thin Ni3Sn4was formed at the interface at the early reflow stageowing to the presence of the thin plated Ni layer (Ni+Sn Ni3Sn4). As thereflow time went on, an intermediate Sn-Ni-Cu ter- nary compound was ob-served when the Ni layer was consumed completely, because of the reactionof the Ni3Sn4 and diffused Cu (Ni3Sn4+Cu Sn-Ni-Cu) ternary compound.Finally, the Sn-Ni-Cu ternary compound changed into Cu6Sn5 (Sn-Ni-Cuternary compound+Cu Cu6Sn5). The effect of surfactant concentration onthe vari- ous shape nanostructures was analyzed using a simple surfactant-assisted method, see Fig. 4. As shown in Figs. 4a and 4b, polydispersedspherical tin nanoparticles are synthesized at low SDS con- centrations of

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0.5 and 4 mM, however, high-yield, uniform tin nanorods are formed with afurther in- crease of SDS concentration up to 10 mM (see Fig. 4c). Whenthe concentration increases up to 15 mM, the nanorods turn into a less uni-form mixture containing nanoparticles and nanorods (see Fig. 4d). Theresults obtained indicate that these nanotubes are promising candidate fornanoscale soldering. Generally, the reasons of Sn-Zn solders bad wetting is ahigh interfacial tension between the solder and substrate and the hinderingeffect of high interfacial tension of solder and accumulation of oxide . Wuprepared new solders doped with small amounts of Cu or Ni to improve theperformances of Sn-Zn solders. The oxidation resistance of the solders onCu substrate was evaluated using colorimetric analysis; mechanical proper-ties were also tested. Experimental results showed that the addition of Cuand Ni into Sn-Zn-Al solders improve the wettability, in contrast to basiccompositions, it has no significant effect on the oxidation resistance. Mostperspective candidates for lead-free solder alloys are based on eutectic Sn-3.5Ag solder with some additional elements aimed to decrease high meltingtemperature and improve wetting ability. When Ga is added into the Sn-9Znlead-free solders, the effects of Ga on melting temperature, wetting proper-ties as well as the mechanical properties of soldered joints were investigated,respectively. In general, the optimum additive amount of Ga in Sn- 9Zn sol-der is about 0.5percentage.The influence of rare earth elements Ce, Er, Y, and Sc on physical, wetting,and mechanical properties of Sn-Ag-Cu alloy with Sn-3.0Ag-0.5Cu based sol-der as master alloy was analyzed. The test results show that RE elementswould affect the properties of the solder in different ways. The properties canbe further improved by the addition of trace rare earth Ce into the solder .Sn whisker growth is a serious reliability concern for electronic devices withhigh-density packing since Sn whisker as a conductive metal wire should leadto many potential risks such as short circuiting, metal vapor arcing, and in-terference with other components and finally results in the failure of devices.It is found that many various lengths of needle-like Sn whisker originatespontaneously from the Sn Printer metallic compounds of the solder

0.5Ga-0.7Pr bulk solder at ambient conditions for a few hours as shownin Fig. 5. It is proposed that the driving force for whisker formation inthe bulk solder is related to the compressive stress owing to the oxidation ofSn-Pr phase and so the free Sn atoms released from the oxidation reactionfeed the growth of Sn whisker during the exposure . In addition, the effect ofnano-TiO2 particles on the interfacial microstructures and bonding strengthof Sn3.5Ag0.5 Cu composite solder joints in ball grid array package with im-mersion Sn surface finishes have been investigated by J.C. Leong. Metallogra-phy reveals that the addition of nano-TiO2 particles retarded wicker-Cu6Sn5

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IMC formed in the Sn3.5Ag0.5Cu composite solder joints. The thickness ofthe interfacial intermetallic compounds of the solder joint was decreased withthe increased addition of nano-TiO2 particles (0.25-1.0 wt.percentage), how-ever, further addition up to 1.25 wt.percentage decreased the beneficial influ-ence which suggests that the presence of small amount of nano-TiO2 particlesis effective for suppressing the growth of the compounds layer. Also, the shearstrength of the solder joints was enhanced by larger nano-TiO2 occurring at1.0 wt.percentage of nano-TiO2 into the solder.Therefore, we think doped inthe lead-free solders, but also try to other appropriate metal oxides to obtainmore preferable solders. The lead-freewelding theory and practice both be-long to the soldering technology fields. In the process of transformation fromlead-bearing to lead-free solders gradually, the implementation of lead-freesolder is still a long-term and hard task. However, at present, the solder-ing development is in the coexistence state of lead-containing and lead-freeleading to a serious lead pollution.Another problem is a higher melting tem-perature which can do damage to other electronic components. There is agreat increasing promise for the development of lead-free solders, but whenthey are used in practical applications still facing a lot of problems such ashigh cost, the collage between components and substrate, the performance ofreflow furnace tube, the exploitation types of lead-free solders and the jointsreliability to the lead-free solders and so on. Therefore, more efforts and re-search need to be paid to accelerate the process and improve the propertiesof lead-free solders to satisfy the needs of electronic industry. We stronglybelieve that lead-free solders must replace the lead-bearing solders with thefurther research and requirements to the environmental protection in thenear future.

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[3) M,B. nail. Electronic Packaging Engineering (Tsirqhua UniYefiIy Press, 2003)

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Quantum Nanophotonics andQuantum Optical Devices.

Recent advances in the synthesis and understanding of material properties atnano scale addition to the development of the nanofabrication techniques hasenabled researchers to control and manipulate photons at nanometre scales. Thesehave given the birth of an emerging hybrid technology with multi-facets appliedinterests, popularly known as nanophotonics.The field nanophotonics deals with a number of interestingly important opics inphotonics and materials structures at nm length scales and their applications ingeneral. Waves in the form of electromagnetic and quantum mechanical, andmaterials as semiconductors and metals are the focus. Different approaches toconfine these waves and devices employing such confinement are the key issue innanophotonics. Localization of light and applications to metallic mirrors, photoniccrystals, optical waveguides, microresonators, plasmonics are gaining tremendousapplied interest. Localization of quantum mechanical waves in low dimensionalstructures such as quantum wells, wires and dots has been demonstrated. Devicesincorporating localization of both electromagnetic andquantum mechanical waves, such as resonant cavity quantum well lasers and micro-cavitybased single photon sources are on the way of commercialization. Somesystem-level applications of the introduced concepts, such as opticalcommunications, biochemical sensing and quantum cryptography are targeted forthe near future.

Classification of Nanophotonics

Nanophotonics can be defined as the science and engineering of light-matterinteractions. These interactions, which take, place, on the one hand, within the lightwavelength and sub-wavelength scales and, on the other hand, are determined bythe physical, chemical and structural nature of artificially or natural nanostructuredmatter. It is envisaged that nanophotonics has the potential to provide ultra-smalloptoelectronic components, high speed and greater bandwidth. Nanophotonics hassignificant potential applications in the field of science and technology. Some ofthem are sensors, lasers, optoelectronic chips, optical communications, opticalmicroscopy (by overcoming the usual diffraction limit), bio-imaging, targetedtherapy, barcodes, harvesting solar energy. Nanophotonics are classified into threemain branches as illustrated in the block diagram depicting variousprocess andtechniques in nanophotonics including plasmonic

Objectives of Quatum nanophotonicsThe main objectives of quantum nanophotonics research is to control the

optical energy and its conversion on the nanometer scale by combining the properties ofmetal, organic, semiconductor, organo-metallic, polymers and dielectric materials tocreate new, combined states of light and matter often called meta-materials. Specificexamples of scientist’s targets are:

Controlled quantum coupling at the nanoscale:The ability to prepare coupled nanostructures presents tremendousopportunity to induce and control the interactions of photons, plasmons,polarons, polaritons and excitons, thereby producing new elementaryexcitations that have no bulk counterpart. Basic scientific research on theseexcitations is performed, with application to many disciplines such as solar

energy conversion, nanoscale photonic devices, new photochemicalprocesses, communications, sensing, imaging and quantum logic. Understanding ultrafast processes at ultra-small length scales:

The outcome of ultrafast processes can be very different in nanoscaleversus bulk materials, with potentially great impact on the physicalproperties and photochemical products of the nanoscale system. Research hasbeen continuously performed to understand, manipulate, optimize.

Nanoscale Quantum Optics

The investigation of quantum phenomena in nanophotonics systems may lead tonew scales of quantum complexity and constitutes the starting point for developingphotonic technologies that deliver quantum-enhanced performances in real-worldsituations. This ambition demands new physical insight as well as cutting-edgeengineering, with an interdisciplinary approach and a view towards how suchgroundbreaking technologies may be implemented and commercialized. The Actionaims at promoting and coordinating forefront research in nanoscale quantum optics(NQO) through a competitive and organized network, which will define new andunexplored pathways for deploying quantum technologies in nanophotonics deviceswithin the European research area. The main vision is to establish a fruitful andsuccessful interaction among scientists and engineers from academia, research centersand industry, focusing on quantum science & technology, nanoscale optics &photonics, and materials science. The Action will address fundamental challenges inNQO, contribute to the discovery of novel phenomena and define new routes forapplications in information & communication technology, sensing & metrology, andenergy efficiency. Gathering a critical mass of experts the Action will serve as aplatform in NQO and as such it will cooperate with industry and academia to promoteinnovation and education in a forefront research field.

Quantum confinement

Nano scale quantum confiment Limiting interactions between light and matter to thenanoscale In general, confinement produces a blue shift of the band-gap. Location of

discrete energy levels depends on the size and nature of confinement.

This implies increase of optical transition probability. This happens anytime theenergy levels are squeezed into a narrow range, resulting in an increase of energydensity. The oscillator strengths increase as the confinement increases from Bulk toQuantum Well to Quantum Wire to Quantum Dot.

The micro scale confinement of photons and the nano scale confinements ofelectrons can be compered. The structures of traditional optical waveguides cannotbe smaller than 1/ʎ wave guiding along bent guides causes dramatic loss. Theproblem associated with loss is overcome in photonic band gap structures, apotential candidate for nanophotonics device as already mentioned. However, thedimensions of the structures are still limited by the wavelength of light. Thisrestriction can be overcome by wave guiding of the plasmonic excitation in closelyplaced metal nanoparticles.

Hybrid quantum systems

Hybrid approach aims to combine useful features of dissimilar systems Directstrong coupling with tightly localized photons, phonons new approaches to quantum

optics and quantum information Control, measurements at sub-micron scales newpossibilities for sensing, metrology at nanoscales.With an assortment of narrow line-width transitions spanning the visible and IRspectrum and long spin coherence times, rare-earth doped crystals are the leadingmaterial system for solid-state quantum memories. Integrating these materials in anon-chip optical platform would create opportunities for highly integrated light-matter interfaces for quantum communication and quantum computing. Nano-photonic resonators with high quality factors and small mode volumes are requiredfor efficient on-chip coupling to the small dipole moment of rare-earth iontransitions. However, direct fabrication of optical cavities in these crystals withcurrent nanofabrication techniques is difficult and unparallelized, as either exoticetch chemistries or physical milling processes are required. We fabricated hybriddevices by mechanically transferring a nanoscale membrane of gallium arsenide(GaAs) onto a neodymium-doped yttrium silicon oxide (Y2SiO5) crystal and thenusing electron beam lithography and standard III-V dry etching to pattern nanobeamphotonic crystalcavities and ring resonator cavities, a technique that is easily adapted to otherfrequency ranges for arbitrary dopants in any rare earth host system. Singlecrystalline GaAs was chosen for its low loss and high refractive index at thetransition wavelength. We demonstrated the potential to evanescently couplebetween the cavity field and the 883 nm 4I9/2-4F3/2 transition of nearbyneodymium impurities in the host crystal by examining transmission spectrathrough a waveguide coupled to the resonator with a custom-built confocalmicroscope. The prospects and requirements for using this systemfor scalable quantum networks are discussed.

Gallium arsenide devices

To fabricate these GaAs resonators, we developed two separate techniques.For the nanobeam resonators, we started with a gallium arsenide wafer that, usingmolecular beam epitaxy, had an epitaxially grown Al0.8Ga0.2As sacrificial layergrown on it, and an epitaxial GaAs membrane grown on top of that. Electronbeam lithography was then used to pattern the one-dimensional photonic crystalin a positive electron beam resist, and a chlorine/argon chemistry was used totransfer the pattern into the top GaAs layer using ICP etching. These beams arethen undercut and tested before being fully undercut and transferred in solution to

the YSO substrate

Amorphous silicon devices

Lastly developed an alternative material system for resonances in the nearinfrared. Amorphous silicon (a-Si) is deposited using plasma enhancedchemical vapor deposition with silane. The a-Si can be deposited directly onthe YSO substrate, with devices patterned using electron beam lithographyand etched with sulfur hexafluoride and octofluorobutane dry etch. Theresults of some of these fabricated devices.

Nanophotonics for quantum optics using nitrogen-vacancycenters in diamond.

Optical microcavities and waveguides coupled to diamond are needed to enableefficient communication between quantum systems such as nitrogen-vacancycenters which are known already to have long electron spin coherence lifetimes.This paper describes recent progress in realizing microcavities with low loss andsmall mode volume in two hybrid systems: silica microdisks coupled to diamondnanoparticles, and gallium phosphide microdisks coupled to single-crystal diamond.A theoretical proposal for a gallium phosphide nanowire photonic crystal cavitycoupled to diamond is also discussed. Comparing the two material systems, silicamicrodisks are easier to fabricate and test. However, at low temperature, nitrogen-vacancy centers in bulk diamond are spectrally more stable, and we expect that in

the long term the bulk diamond approach will be better suited for on-chipintegration of a photonic network.

Diamond is an attractive material for some electronic and photonic applicationsbecause of its high thermal conductivity, excellent chemical stability and highcarrier mobility. Diamond appears to be an excellent material for quantuminformation and magnetic sensing applications as well, with hundreds of knownoptically active centers , many of which are paramagnetic. Few of these impuritieshave been studied in detail, but at least one of them, the nitrogenvacancy (NV)center, is optically addressable and can exhibit electron spin coherence lifetimesexceeding 1 ms at room temperature. This long-lived coherence is usually attributedto the nuclear spin-zero environment of the diamond lattics which can be furtherimproved with isotopic purification. These capabilities have recently allowed forsome remarkable demonstrations in thissystem such as controlled coupling between single electronicand nuclear spins .

For quantum information applications, a logical next step would be to connectmultiple diamond impurities such as NV centers together optically, to enable long-distance quantum communication through repeaters , or to test one-wayquantum computation approaches . However, currently it is rather difficult tofabricate structures such as waveguides and cavities in diamond. One of the chiefdifficulties at present isthat one cannot commercially obtain a wafer containing a thinlayer of high-qualitysingle-crystal diamond on top of a lower index insulator, analogous to silicon-on-insulator wafers. One can make similar structures by growing polycrystallinediamond on other materials, and optical structures have beenmade in this way , but these polycrystalline films have high scattering loss, and sofar there are no reports of these films containing optically active impuritieswithgood spin coherence properties. Nevertheless, there have been several recent effortsto surmount these problems using other approaches, and

here we shall describe two such approaches attempted in our own laboratory, onebased on coupling diamond nanoparticles to silica microdisk structures, and theother based on higher-index gallium phosphide structures attached to bulksingle-crystal diamond . In both cases, coupling between NV centers andwhispering-gallery-type cavity modes has been demonstrated. The most seriousremaining technical challenges involve the properties of the NV centers in thesestructures.

Quantum dot light emitting diodes

QD LED or QLED is considered as a next generation display technology afterOLED-Displays. QLED means Quantum dot light emitting diodes and are a form oflight emitting technology and consist of nano-scale crystals that can provide analternative for applications such as display technology. The structure of a QLED isvery similiar to the OLED technology. But the difference is that the light emittingcenters are cadmium selenide (CdSe) nanocrystals, or quantum dots. A layer ofcadmium-selenium quantum dots is sandwiched between layers of electron-transporting and hole-transporting organic materials. An applied electric fieldcauses electrons and holes to move into the quantum dot layer, where they arecaptured in the quantum dot and recombine, emitting photons. The spectrum ofphoton emission is narrow, characterized by its full width at half the maximumvalue.

QLEDs advantages:

Pure color — Will deliver 30-40% luminance efficiency advantage over organic lightemitting diodes (OLEDs) at the same color point.

Low power consumption — QLEDs have the potential to be more than twice as powerefficient as OLEDs at the same color purity.

Low-cost manufacture — The ability to print large-area QLEDs on ultra-thin flexiblesubstrates will reduce luminaire manufacturing cost.

Ultrathin, transparent, flexible form factors — QLEDs will enable designers to developnew display and lighting forms not possible with existing technologies.

There are two major fabrication techniques for QD-LED, called phase separation and contact-printing. QLEDs are a reliable, energy efficient, tunable color solution for display and lightingapplications that reduce manufacturing costs, while employing ultra-thin, transparent or flexiblematerials.

Optical Biosensors

The dimension of biomolecules is of few nanometers, so the biomoleculardevices ought to be of that range so a better understanding about the performance ofthe electronic biomolecular devices can be obtained at nanoscale. Development ofoptical biomolecular device is a new move towards revolution of nano-bioelectronics. Optical biosensor is one of such nano-biomolecular devices that hasa potential to pave a new dimension of research and device fabrication in the fieldof optical and biomedical fields. This paper is a very small report about opticalbiosensor and its development and importance in various fields.

The advantages of optical biosensors are their speed, the immunity of the signal toelectrical or magnetic interference, and the potential for higher information content(spectrum of information available) but the main drawback can be the high cost ofsome instrumentation. Optical biosensor in the last decade has developed to a greatextent in every field but there is still a long way to replace completely theconventional methods of the optical biosensor technology in many fields and,specially, in biomedical field. To achieve such objective, we still need to developoptical biosensors able to detect, in a direct way at very low levels (picomolar tofemtomolar) of a great number of substances in the areas of environmental

monitoring, industrial and food process, health care, biomedical technology, clinicalanalysis

Superconducting Single-Photon Detectors.

Superconducting single photon detectors consist of a current carryingsuperconducting nanowire that can become normal due to the absorption of a singlephoton at optical frequencies. We do optical experiments at cryogenic temperaturesand investigate the physical mechanisms that are important for photon detection.

To unveil the physics we use different materials, different detector geometries andexplore the use of a sharp metal tip to locally enhance photon absorption. Inaddition we use a technique called ‘quantum detector tomography’ to extract thequantum response of the detector. The recorded count rates as a function of theaverage power in a laser beam is inverted to a response of the detector to quantumstates with exactly one, two, three etc. photons. This gives a wealth of informationabout the detector and allows to explore the physics of these devices.

The current understanding of NbN nanowires is that entry of magnetic vortices playan important role. This renders the detectors more susceptible to detection ofphotons at the edges. Very recently we have observed the signature of this effect inthe polarization dependent response of detectors. Outstanding challenges are to

directly observe the effect or to explore MoGe material where vortices can movethrough the material with much less dissipation.

Laser cooling

The simple mechanical oscillator, canonically consisting of a coupled mass–spring system, is used in a wide variety of sensitive measurements, includingthe detection of weak forces1 and small masses On the one hand, a classicaloscillator has a well-defined amplitude of motion; a quantum oscillator, on theother hand, has a lowest-energy state, or ground state, with a finite-amplitudeuncertainty corresponding to zero-point motion. On the macroscopic scale ofour everyday experience, owing to interactions with its highly fluctuatingthermal environment a mechanical oscillator is filled with many energy quantaand its quantum nature is all but hidden. Recently, in experiments performedat temperatures of a few hundredths of a kelvin, engineered nanomechanicalresonators coupled to electrical circuits have been measured to be oscillatingin their quantum ground state

.

These experiments , in addition to providing a glimpse into the underlyingquantum behaviour of mesoscopic systems consisting of billions of atoms,represent the initial steps towards the use of mechanical devices as tools forquantum metrology or as a means of coupling hybrid quantum systems Herewe report the development of a coupled, nanoscale optical and mechanicalresonator formed in a silicon microchip, in which radiation pressure from alaser is used to cool the mechanical motion down to its quantum ground state(reaching an average phonon occupancy number of ). This coolingis realized at an environmental temperature of 20 K, roughly one thousand

times larger than in previous experiments and paves the way for opticalcontrol of mesoscale mechanical oscillators in the quantum regime.

Submitted by,

ARAVIND P. BABU.KIRAN S KUMAR.DEVIKA T.CHRISTY MARIA JOY.

BIOMEMS, DIODES AND NANOWIRE TRANSISTOR

BIOMEMS: Microelectromechanical systems MEMS, also written as micro-electro-mechanical, MicroElectroMechanical or microelectronic and microelectromechanical systems and the related micromechatronics is the technology of microscopic devices, particularly those with moving parts. It merges at the nano-scale into nanoelectromechanical (NEMS) and nanotechnology. Bio MEMS orBiological microelectromechanical systems has emerged as a subset of MEMS devices for applications in biomedical research and medical microdevices. MEMS are made up of components between 1 and 100 micrometres in size (i.e. 0.001 to 0.1 mm), and MEMS devices generally range in size from 20 micrometres to a millimetre. BioMEMS are devices constructed using techniques inspired by micro/ nanoscale fabrication, that are used for performing identification, immobilization, growth, separation, purification and manipulation of single or multiple cells. The fabrication of MEMS evolved from the process in semiconductor device fabrication, i.e. the basic techniques are depositions of materiallayers, patterning by photolithography and etching to produce the required shapes. BioMEMS is theapplication of MEMS technology in the field of Biomedical and health sciences. BioMEMS has applications in the field of microfluidics, smart drug delivery, microsurgical tools etc. BioMEMS device used to detect the presence of bacterial cultures within micronsize chambers and confinements. BioMEMS need to interact with biological systems such as cells or even single molecules. Strategies for developing bioMEMS involve adapting traditional microfabrication materials and process resulting in system fabricated using non degradable materials including silicon and polydimethylsiloxane. It is a subset of microelectromechanical systems and microtechnology. BioMEMS applies to biological systems in general and to human health. The use of microtechnology particularly MEMS is changing medical applications for areas such as detection, diagnostics, monitoring and drug delivery. For example potential health problems can now be detected early by having the patient wear a non invasive heart monitor. Bio MEMS is a general term for any MEMS used in biological applications. The advantage of bioMEMS is sensitivity, portability, clinical convenience. Polymer is BioMEMS material because polymers are biocompatible, cheaper and stable.

BioMEMS applications: a) MEMS Pressure Sensors The first MEMS devices to be used in the biomedical industry were reusable blood pressure sensors in the 1980s. MEMS pressure sensors have the largest class of applications including disposable blood pressure, intraocular pressure (IOP), intracranial pressure (ICP), intrauterine pressure, and angioplasty. Some manufacturers of MEMS pressure sensors for biomedical applications include CardioMEMS, Freescale semiconductors, GE sensing, Measurement Specialties, Omron, Sensimed AG and Silicon Microstructures. MEMS implantable pressure sensors are used for continuous IOP monitoring in Glaucoma patients. A normal eye maintains a positive IOP in the range of 10-22 mmHg. Abnormal elevation (> 22 mmHg) and fluctuation of IOP are considered the main risk factors for glaucoma. Glaucoma, often without any pain or significant symptoms, can cause an irreversible and incurable damage to the optic nerve. This initially affects the peripheral vision and possibly leads to blindnesswithout timely lifetime treatment. Therefore, it is critical to accurately monitor IOP and provide prompt treatments at the early stages of glaucoma development. It consists of a disposable contact lens with a MEMS strain-gage pressure sensor element, an embedded loop antenna, and an ASIC microprocessor (2mmx2mm chip). The MEMS sensor includes a circular active outer ring and passive strain gages to measure corneal curvature changes in response to IOP. The loop antenna in the lens receives power from the external monitoring system and sends information back to the system.

b) MEMS Inertial Sensors: MEMS accelerometers are used in defibrillators and pacemakers. Some patients exhibit unusually fast or chaotic heart beats and thus are at a high risk of cardiac arrest or a heart attack. An implantable defibrillator restores a normal heart rhythm by providing electrical shocks to the heart during abnormal conditions. Some peoples’ hearts beat too slowly, and this may be related to the natural aging process or a genetic condition. A pacemaker maintains a proper heart beat by transmitting electrical impulses to the heart. Conventional pacemakers were fixed rate. Modern pacemakers employ MEMS accelerometers and are capable of adjusting heart rate in accordance with the patient’s physical activity. Medtronic is a leading manufacturer of MEMS based defibrillators and pacemakers.

c) MEMS Hearing-Aid Transducer A hearing-aid is an electroacoustic device used to receive, amplify and radiate sound into the ear. The goal of a hearing aid is to compensate for the hearing loss and thus make audio communication more intelligible for the user. In the US, hearing aids are considered medical devices and are regulated by the FDA. According to NIH, approximately 17 percent (36 million) of American adults report some degree of hearing loss. There is a strong relationship between age and reported hearing loss. Also, about 2 to 3 out of every 1,000 children inthe United States are born deaf or hard-of-hearing.

According to statistics, 80% of those who could benefit from a hearing-aid chose not to use one. The reasons include reluctance to recognize hearing loss and social stigma associated with common misconceptions about wearing hearing aids. Thus, it is highly desirable to miniaturize hearing-aids without compromising performance. MEMS technology enables reduction of form factor, cost, and power consumption compared to conventional hearing-aid solutions.

g) Microsurgical tools Surgery is treatment of diseases or other ailments through manual and instrumental methods. In surgery, the majority of trauma to the patient is caused by the surgeon’s incisions to gain access to the surgical site. Minimally invasive surgical (MIS) procedure aims to

provide diagnosis, monitoring, or treatment of diseases by performing operations with very small incisions or sometimes through natural orifices. Advantages of MIS over conventional open surgeryincludes less pain, minimal injury to tissues, minimal scarring, reduced recovery time, shorter hospital visits, faster return to normal activities and often lower cost to the patient. Common MIS procedures include angioplasty, catheterization, endoscopy, laparoscopy, and neurosurgery. MEMS based microsurgical tools have been identified as a key enabling technology for MIS [6]. A pair of silicon MEMS based microtweezers and metal MEMS based biopsy forceps are shown in Figure 12. It should be noted that some of these feasibility demonstrations have yet to be qualified for clinical applications.

h)Oral drug delivery system by bioMEMS: BioMEMS is the emerging approach in the field of oraldrug delivery system. They have significant potential to overcome some of the barriers of oral drug delivery through fabrication of asymmetrical devices with precise control over size and shape. Apartfrom drug delivery devices, microfabrication approaches can also enhance the field of oral drug delivery by designing biomimetic in vitro GI tract model systems that can aid in better prediction ofdrug absorption in vivo. Thus MEMS technique is used in the development of oral drug delivery system and in vitro cell culture models that can be used to evaluate the drug delivery efficacy.

DIODES: A diode is a specialized electronic component with two electrodes called the anode and the cathode. Most diodes are made with semiconductors materials such as silicon, germanium, or selenium. Some diodes are comprised of metal electrodes in a chamber evacuated or filled with a pure elemental gas at low pressure. Diodes can be used as rectifiers, signal limiters, voltage regulators, switches, signal modulators, signal mixers, signal demodulators, and oscillators.The fundamental property of a diode is its tendency to conduct electric current in only one direction. When the cathode is negatively charged relative to the anode at a voltage greater than a certain minimum called forward breakover, then current flows through the diode. If the cathode is positive with respect to the anode, is at the same voltage as the anode, or is negative by an amount less than the forward breakover voltage, then the diode does not conduct current. The forward breakover voltage is approximately six tenths of a volt (0.6 V) for silicon devices, 0.3 V for

germanium devices, and 1 V for selenium devices. The above general rule notwithstanding, if the cathode voltage is positive relative to the anode voltage by a great enough amount, the diode will conduct current. The voltage required to produce this phenomenon, known as the avalanche voltage, varies greatly depending on the nature of the semiconductor material from which the device is fabricated. The avalanche voltage can range from a few volts up to several hundred volts.

When an analog signal passes through a diode operating at or near its forward breakover point, the signal waveform is distorted. This nonlinearity allows for modulation, demodulation, and signal mixing. Diodes of this type, with the application of a voltage at the correctlevel and the polarity, generate analog signals at microwave radio frequencies.

Semiconductor diodes can be designed to produce direct current (DC) when visible light, infrared transmission (IR), or ultraviolet (UV) energy strikes them. These diodes are known asphotovoltaic cells and are the basis for solar electric energy systems and photosensors. Yet another form of diode, commonly used in electronic and computer equipment, emits visible light or IR energy when current passes through it. Such a device is the familiar light-emitting diode (LED).

The most common function of a diode is to allow an electric current to pass in one direction (called the diode's forward direction), while blocking current in the opposite direction (the reverse direction). This unidirectional behavior is called rectification, and is used to convert alternating current(AC) to direct current (DC), including extraction of modulation from radio signals in radio receivers—these diodes are forms of rectifiers.

A semiconductor diode's current–voltage characteristic can be tailored by selecting the semiconductor materials and the doping impurities introduced into the materials during manufacture. These techniques are used to create special-purpose diodes that perform many different functions. For example, diodes are used to regulate voltage Zener diodes, to protect circuits from high voltage surges avalanche diodes, to electronically tune radio and TV receivers (varactor diodes), to generate radio frequency oscillations (tunnel diodes, Gunn diodes, IMPATT diodes), and to produce light (light emitting diodes). Tunnel, Gunn and IMPATT diodes exhibit negative resistance, which is useful in microwave and switching circuits.Diodes, both vacuum and semiconductor, can be used as short noise generators

The n side will have a large number of electrons and very few holes (due to thermal excitation) whereas the p side will have a high concentration of holes and very few electrons. Due to this, a process called diffusion takes place. In this process free electrons from the n side will diffuse (spread) into the p side and combine with holes present there, leaving a positive immobile (not moveable) ion in the n side. Hence, few atoms on the p side are converted into negative ions. Similarly, few atoms on the n-side will get converted to positive ions. Due to this large number of positive ions and negative ions will accumulate on the n-side and p-side respectively. This region soformed is called as depletion region. Due to the presence of these positive and negative ions a static electric field called as "barrier potential" is created across the p-n junction of the diode. It is called as "barrier potential" because it acts as a barrier and opposes the further migration of holes and electrons across the junction.

In a PN junction diode when the forward voltage is applied i.e. positive terminal of a source is connected to the p-type side, and the negative terminal of the source is connected to the n-

type side, the diode is said to be in forward biased condition. We know that there is a barrier potential across the junction. This barrier potential is directed in the opposite of the forward applied voltage. So a diode can only allow current to flow in the forward direction when forward applied voltage is more than barrier potential of the junction. This voltage is called forward biased voltage. For silicon diode, it is 0.7 volts. For germanium diode, it is 0.3 volts. When forward applied voltageis more than this forward biased voltage, there will be forward current in the diode, and the diode will becombecome short circuited. Hence, there will be no more voltage drop across the diode beyond this forward biased voltage, and forward current is only limited by the external resistance">resistance connected in series with the diode. Thus, if forward applied voltage increasesfrom zero, the diode will start conducting only after this voltage reaches just above the barrier potential or forward biased voltage of the junction. The time taken by this input voltage to reach that value or in other words the time taken by this input voltage to overcome the forward biased voltage is called recovery time.

Now if the diode is reverse biased i.e. positive terminal of the source is connected to the n-type end, and the negative terminal of the source is connected to the p-type end of the diode, there will be no current through the diode except reverse saturation current. This is because at the reverse biased condition the depilation layer of the junction becomes wider with increasing reverse biased voltage. Although there is a tiny current flowing from n-type end to p-type end in the diode due to minority carriers. This tiny current is called reverse saturation current. Minority carriers are mainly thermally generated electrons and holes in p-type semiconductor and n-type semiconductor respectively. Now if reverse applied voltag across the diode is continually increased, then after certain applied voltage the depletion layer will destroy which will cause a huge reverse current to flow through the diode. If this current is not externally limited and it reaches beyond the safe value, the diode may be permanently destroyed. This is because, as the magnitude of the reverse voltage increases, the kinetic energy of the minority charge carriers also increase. These fast moving electrons collide with the other atoms in the device to knock-off some more electrons from them. The electrons so released further release much more electrons from the atoms by breaking the covalent bonds. This process is termed as carrier multiplication and leads to a considerable increase in the flow of current through the p-n junction. The associated phenomenon is called Avalanche Breakdown.

Some of the typical applications of diodes include:

• Rectifying a voltage, such as turning AC into DC voltages

• Isolating signals from a supply

• Voltage Reference

• Controlling the size of a signal

• Mixing signals

• Detection signals

• Lighting

• Lasers diodes

Diodes and capacitors can also be used to create a number of types of voltage multipliers to take a small AC voltage and multiply it to create very high voltage outputs. Both AC and DC outputs are possible using the right configuration of capacitors and diodes.

The most common use for diodes is to remove the negative component of an AC signal so it can be worked with easier with electronics. Since the negative portion of an AC waveform is usually identical to the positive half, very little information is effectively lost in this process. Signal demodulation is commonly used in radios as part of the filtering system to help extract the radio signal from the carrier wave.

Diodes also function well as protection devices for sensitive electronic components. When used as voltage protection devices, the diodes are non-conducting under normal operating conditions but immediately short any high voltage spike to ground where it cannot harm an integrated circuit. Specialized diodes called transient voltage suppressors are designed specifically for over-voltage protection and can handle very large power spikes for short time periods, typical characteristics of a voltage spike or electric shock, which would normally damage components and shorten the life of an electronic product.

The basic application of diodes is to steer current and make sure it only flows in the proper direction. One area where the current steering capability of diodes is used to good effect is inswitching from power from a power supply to running from a battery. When a device is plugged in and charging, for example, a cell phone or uninterruptible power supply, the device should be drawing power only from the external power supply and not the battery and while the device is plugged in the battery should be drawing power and recharging. As soon as the power source is removed, the battery should power the device so no interruption in noticed by the user.

NANOWIRE TRANSISTORS: is a nanowire-based transistor that has no gate junction.Junctions are difficult to fabricate, and, because they are a significant source of current leakage, they waste significant power and heat. Eliminating them held the promise of cheaper and denser microchips. The JNT uses a simple nanowire of silicon surrounded by an electrically isolated "wedding ring" that acts to gate the flow of electrons through the wire.

The combination of n-doped nanowire and the p-doped channel forms a p-n junction and depletion layer is formed. Due to heavy concentration of the dopant atom in both nanowire and gate the depletion region is so large that virtually no carriers are present to conduct the current.When a forward bias voltage is applied the thickness of the depletion region is reduced and gradually the channel forms which causes the current to flow again.The JNT uses bulk conduction instead of surface channel conduction. The current drive is controlled by doping concentration and not by gate capacitance.Germanium has been used instead of silicon nanowires.

Si nanowire used to make complementary inverter circuit. These inverter circuits are made from lightly doped si nano wires. The nanowires are very sensitive to gating action enabling full depletion. These circuits need low static power dispersion. In comparison a single nanowire devices requires 10^3-10^4 times larger dissipation.

Nanowire transistors are of particular interest for future display devices because of their several unique and interesting features: 1) enhanced field effect mobility compared with bulk mobility for the same semiconductor. 2) amenability to low temperature processing, and 3) optical transparency and mechanical flexibility. In2O3 and ZnO nanowires are particularly promising candidates for transistor active channels since these materials are both transparent and mechanicallyrobust/flexible. In2O3 Nanowire transistors on glass substrates exhibit 82% visible transparency. Fully flexible and transparent In2O3 Nanowire transistor with optical transmission of 81% have also been fabricated. Ozone treatment to the nanowire surface, which removes defects and contamination and enhances the charge injection by modifiying the work function.

The ability to prepare nanowires with diameter <20nm made it possible for the first time to produce devices that could approach a 1-D limit desirable for high perforamance FETs.

CVD Growth of SiNWs: The development of CVD based nanowire growth has led to much better control over the doping level and electrical properties of SiNWs and correspondingly, the realization of high performance p and n channel SiNW FETs as shown in fig. SiNW is depositedon a SiO2/degenerately doped si substrate with the Si substrate serving as the back gate. Metal electrodes are fabricated through e-beam or photolithography and serve as the source adn drain electrodes that complete the FET structure.

In a study on boron-doped Si nanowires, it was found that the I-V curves became more linear and symmetric at low bias and the transport behavior became more stable after annealing. The contact resistances can greatly influence the performance of NWFETs. The contact resistance effect has been observed in both p- and n- type SiNWs.

InAs Nanowires: InAs nanowires have widely been studied as a building block fo n-type FETs. InAs is an attractive material for several reasons. First, its small effective electron mass results in high electron mobility in bulk materials. Second, an electron gas layer is known to form at the surface of planar InAs due to Fermi level pinning in the conduction band at the surface. Third, the formation of an electron gas combined with the small band gap should yield transparent contacts to InAs nanowire devices. InAs nanowires can be grown using the nanocluster catalyzed process in

which the reactant species are delivered by metal organic CVD.

Submitted by S. Mouniya A. Mydhili Y. Vanisree R. Karthika R. Prameela

NANO CATALYST AND NANOPHOROUS ZEOLITES

BY

K.SANDHYA(I120114)

T.KEERTHANA(I120109)

V.VINU(I120119)

R.SARANYA(I120115)

A.BHARATHI PRIYA(I120105)

IMSC PHYSICS 5TH YEAR. INTRODUCTION: Nanomaterial-based catalysts are usually heterogeneous catalysts broken up into metal

nanoparticles in order to speed up the catalytic process. Metal nanoparticles have a higher

surface area so there is increased catalytic activity because more catalytic reactions can

occur at the same time. Nanoparticle catalysts can also be easily separated and recycled

with more retention of catalytic activity than their bulk counterparts. These catalysts can

play two different roles in catalytic processes: they can be the site of catalysis or they can

act as a support for catalytic processes. They are typically used under mild conditions to

prevent decomposition of the nanoparticles at extreme conditions.

Functionalized nanoparticles:

Functionalized metal nanoparticles are more stable in solution compared to non-

functionalized metal nanoparticles. In liquid solutions, the metal nanoparticles are close

enough together to be affected by van der Waals force. If there isn’t anything to oppose

these forces, then the nanoparticles will aggregate, which will lead to a decrease in catalytic

activity by lowering the surface area. For organometallic functionalized nanoparticles,

ligands are coordinated to the metal center to prevent aggregation. Using different ligands

alters the properties and sizes of the nanoparticle catalysts. Nanoparticles can also be

functionalized with polymers or oligomers to sterically stabilize the nanoparticles by

providing a protective layer that prevents the nanoparticles from interacting with each

other. Alloys of two metals, called bimetallic nanoparticles, are used to create synergistic

effects on catalysis between the two metals.

Applications:

Dehalogenation and hydrogenation:

Nanoparticle catalysts can be used in the hydrogenolysis of C-Cl bonds such as

polychlorinated biphenyls.Hydrogenation of halogenated aromatic amines is also important

for the synthesis of herbicides and pesticides as well as diesel fuel.In organic chemistry,

hydrogenation of a C-Cl bond with deuterium is used to selectively label the aromatic ring

for use in experiments dealing with the kinetic isotope effect. Buil et al. created rhodium

complexes that generated rhodium nanoparticles. These nanoparticles catalyzed the

dehalogenation of aromatic compounds as well as the hydrogenation of benzene to

cyclohexane. Polymer-stabilized nanoparticles can also be used for the hydrogenation of

cinnamaldehyde and citronellal found that the ruthenium nanocatalysts are more selective

in the hydrogenation of citronellal compared to the traditional catalysts used.

Hydrosilylation reactions:

The Reduction of gold, cobalt, nickel, palladium, or platinum organometallic complexes with

silanes creates a catalytically active metal nanoparticle that catalyzes the hydrosilylation

reaction, which is important for the synthesis of optically active alcohols. BINAP

functionalized palladium nanoparticles and gold nanoparticles have been used for the

hydrosilylaytion of styrene under mild conditions; they were found to be more catalytically

active and more stable than non-nanoparticle Pd-BINAP complexes. The reaction may also

be catalyzed by a nanoparticle that consists of two metals.

Organic redox reactions:

(Oxidation reaction of cyclohexane to synthesize adiapic acid)

An oxidation reaction to form adipic acid is shown in above dig and it can be catalyzed by cobalt

nanoparticles. This is used in an industrial scale to produce the nylon 6,6 polymer. Other examples of

oxidation reactions that are catalyzed by metallic nanoparticles include the oxidation of cyclooctane,

the oxidation of ethene, and glucose oxidation.

C-C coupling reactions:

(Heck coupling reaction)

Metallic nanoparticles can catalyze C–C coupling reactions such as the hydroformylation of

olefins,the synthesis of vitamin E and the Heck coupling and Suzuki coupling reactions.

Palladium nanoparticles were found to efficiently catalyze heck coupling reactions. It was

found that increased electronegativity of the ligands on the palladium nanoparticles

increased their catalytic activity.

The compound Pd2(dba)3 is a source of Pd(0), which is the catalytically active source of

palladium used for many reactions, including cross coupling reactions. Pd2(dba)3 was

thought to be a homogeneous catalytic precursor, but recent articles suggest that palladium

nanoparticles are formed, making it a heterogeneous catalytic precursor.

Alternative fuels:

Much research on nanomaterial-based catalysts has to do with maximizing the effectiveness

of the catalyst coating in fuel cells. Platinum is currently the most common catalyst for this

application, however, it is expensive and rare, so a lot of research has been going into

maximizing the catalytic properties of other metals by shrinking them to nanoparticles in

the hope that someday they will be an efficient and economic alternative to platinum. Gold

nanoparticles also exhibit catalytic properties, despite the fact that bulk gold is unreactive.

Fuel cells take advantage of the reaction between hydrogen and oxygen but catalysts are

needed to facilitate this reaction. Nanomaterial catalysts can be used to improve energy

production. In one experiment, yttrium stabilized zirconium nanoparticles were found to

increase the efficiency and reliability of a solid oxide fuel cell. Nanomaterial

ruthenium/platinum catalysts could potentially be used to catalyze the purification of

hydrogen for hydrogen storage. Palladium nanoparticles can be functionalized with

organometallic ligands to catalyze the oxidation of CO and NO to control air pollution in the

environment. Carbon nanotube supported catalysts can be used as m;mm;m;a cathode

catalytic support for fuel cells and metal nanoparticles have been used to catalyze the

growth of carbon nanotubes. Platinum-cobalt bimetallic nanoparticles combined with

carbon nanotubes are promising candidates for direct methanol fuel cells since they

produce a higher stable current electrode.

Medicine:

In magnetic chemistry, nanoparticles can be used for catalyst support for medicinal use.

Nanozymes:

Besides conventional catalysis, nanomaterials have been explored for mimicking natural

enzymes. The nanomaterials with enzyme mimicking activities are termed as nanozymes.

Lots of nanomaterials have been used to mimic varieties of natural enzymes, such as

oxidase, peroxidase, catalase, SOD, nuclease, etc. The nanozymes have found wide

applications in many areas, from biosensing and bioimaging to therapeutics and water

treatment.

Characterization of nanoparticles:

Some techniques that can be used to characterize functionalized nanomaterial catalysts

include X-ray photoelectron spectroscopy, transmission electron microscopy, circular

dichroism spectroscopy, nuclear magnetic resonance spectroscopy, UV-visible spectroscopy

and related experiments.

NANOPOROUS ZEOLITES

INTRODUCTION:

Nanoporous materials consist of a regular organic or inorganic framework supporting a

regular, porous structure. The size of the pores is generally 100 nanometers or smaller.

Most nanoporous materials can be classified as bulk materials or membranes. Activated

carbon and zeolites are two examples of bulk nanoporous materials, while cell membranes

can be thought of as nanoporous membranes.

There are many natural nanoporous materials, but artificial materials can also be

manufactured. One method of doing so is to combine polymers with different melting

points, so that upon heating one polymer degrades. A nanoporous material with

consistently sized pores has the property of letting only certain substances pass through,

while blocking others.

DIVISION:

Nanoporous materials can be subdivided into 3 categories, set out by IUPAC:

Microporous materials: 0.2–2 nm

Mesoporous materials: 2–50 nm.

Properties and occurrence:

Zeolites have a porous structure that can accommodate a wide variety of cations, such as

Na+, K+, Ca2+, Mg2+ and others. These positive ions are rather loosely held and can readily

be exchanged for others in a contact solution. Some of the more common mineral zeolites

are analcime, chabazite, clinoptilolite, heulandite, natrolite, phillipsite, and stilbite. An

example of the mineral formula of a zeolite is: Na2Al2Si3O10·2H2O, the formula for

natrolite.

Natural zeolites form where volcanic rocks and ash layers react with alkaline groundwater.

Zeolites also crystallize in post-depositional environments over periods ranging from

thousands to millions of years in shallow marine basins. Naturally occurring zeolites are

rarely pure and are contaminated to varying degrees by other minerals, metals, quartz, or

other zeolites. For this reason, naturally occurring zeolites are excluded from many

important commercial applications where uniformity and purity are essential.

Zeolites are the aluminosilicate members of the family of microporous solids known as

"molecular sieves." The term molecular sieve refers to a particular property of these

materials, i.e., the ability to selectively sort molecules based primarily on a size exclusion

process. This is due to a very regular pore structure of molecular dimensions. The maximum

size of the molecular or ionic species that can enter the pores of a zeolite is controlled by

the dimensions of the channels. These are conventionally defined by the ring size of the

aperture, where, for example, the term "8-ring" refers to a closed loop that is built from

eight tetrahedrally coordinated silicon (or aluminium) atoms and 8 oxygen atoms. These

rings are not always perfectly symmetrical due to a variety of effects, including strain

induced by the bonding between units that are needed to produce the overall structure, or

coordination of some of the oxygen atoms of the rings to cations within the structure.

Therefore, the pores in many zeolites are not cylindrical.

The sequence of silica-rich volcanic rocks commonly progresses from:

Clay → quartz → mordenite–heulandite → epistilbite → stilbite → thomsonite–

mesolite-scolecite → chabazite → calcite.

The sequence of silica-poor volcanic rocks commonly progresses from:

Cowlesite → levyne–offretite → analcime → thomsonite–mesolite-scolecite →

chabazite → calcite.

Production:

Industrially important zeolites are produced synthetically. Typical procedures entail heating

aqueous solutions of alumina and silica with sodium hydroxide. Equivalent reagents include

sodium aluminate and sodium silicate. Further variations include changes in the cations to

include quaternary ammonium cations.

Synthetic zeolites hold some key advantages over their natural analogues. The synthetic

materials are manufactured in a uniform, phase-pure state. It is also possible to produce

zeolite structures that do not appear in nature. Zeolite A is a well-known example. Since the

principal raw materials used to manufacture zeolites are silica and alumina, which are

among the most abundant mineral components on earth, the potential to supply zeolites is

virtually unlimited.

Natural occurrence:

Natrolite from Poland:

Conventional open-pit mining techniques are used to mine natural zeolites. The overburden

is removed to allow access to the ore. The ore may be blasted or stripped for processing by

using tractors equipped with ripper blades and front-end loaders. In processing, the ore is

crushed, dried, and milled. The milled ore may be air-classified as to particle size and

shipped in bags or bulk. The crushed product may be screened to remove fine material

when a granular product is required, and some pelletized products are produced from fine

material.

As of 2016 the world's annual production of natural nano zeolite approximates 3 million

tonnes. Major producers in 2010 included China (2 million tonnes), South Korea (210,000 t),

Japan (150,000 t), Jordan (140,000 t), Turkey (100,000 t) Slovakia (85,000 t) and the United

States (59,000 t).[7] The ready availability of zeolite-rich rock at low cost and the shortage of

competing minerals and rocks are probably the most important factors for its large-scale

use. According to the United States Geological Survey, it is likely that a significant

percentage of the material sold as zeolites in some countries is ground or sawn volcanic tuff

that contains only a small amount of zeolites. Some examples of such usage include

dimension stone (as an altered volcanic tuff), lightweight aggregate, pozzolanic cement, and

soil conditioners.

Artificial synthesis:

Synthetic nano zeolite:

There are several types of synthetic zeolites that form by a process of slow crystallization of

a silica-alumina gel in the presence of alkalis and organic templates. One of the important

processes used to carry out zeolite synthesis is sol-gel processing. The product properties

depend on reaction mixture composition, pH of the system, operating temperature, pre-

reaction 'seeding' time, reaction time as well as the templates used. In sol-gel process, other

elements (metals, metal oxides) can be easily incorporated. The silicalite sol formed by the

hydrothermal method is very stable. The ease of scaling up this process makes it a favorite

route for zeolite synthesis.

Uses:

1.NANO Zeolites are widely used as ion-exchange beds in domestic and commercial water

purification, softening, and other applications. In chemistry, zeolites are used to separate

molecules (only molecules of certain sizes and shapes can pass through), and as traps for

molecules so they can be analyzed.

2.NANO Zeolites are also widely used as catalysts and sorbents. Their well-defined pore

structure and adjustable acidity make them highly active in a large variety of reactions.[9]

3.NANO Zeolites have the potential of providing precise and specific separation of gases,

including the removal of H2O, CO2 and SO2 from low-grade natural gas streams. Other

separations include noble gases, N2, O2, freon and formaldehyde.

4.On-board oxygen generating systems (OBOGS) and Oxygen concentrators use zeolites in

conjunction with pressure swing adsorption to remove nitrogen from compressed air in

order to supply oxygen for aircrews at high altitudes, as well as home and portable oxygen

supplies.

Industry:

Synthetic zeolites are widely used as catalysts in the petrochemical industry, for instance in

fluid catalytic cracking and hydrocracking. Zeolites confine molecules in small spaces, which

causes changes in their structure and reactivity. The hydrogen form of zeolites (prepared by

ion-exchange) are powerful solid-state acids, and can facilitate a host of acid-catalyzed

reactions, such as isomerisation, alkylation, and cracking. The specific activation modality of

most zeolitic catalysts used in petrochemical applications involves quantum-chemical Lewis

acid site reactions.[citation needed]

Catalytic cracking uses reactor and a regenerator. Feed is injected onto hot, fluidized

catalyst where large gasoil molecules are broken into smaller gasoline molecules and

olefins. The vapor-phase products are separated from the catalyst and distilled into various

products. The catalyst is circulated to a regenerator where air is used to burn coke off the

surface of the catalyst that was formed as a by product in the cracking process. The hot

regenerated catalyst is then circulated back to the reactor to complete its cycle.

Nano Zeolites have uses in advanced reprocessing methods, where their micro-porous

ability to capture some ions while allowing others to pass freely, allowing many fission

products to be efficiently removed from nuclear waste and permanently trapped. Equally

important are the mineral properties of zeolites. Their alumino-silicate construction is

extremely durable and resistant to radiation even in porous form. Additionally, once they

are loaded with trapped fission products, the zeolite-waste combination can be hot pressed

into an extremely durable ceramic form, closing the pores and trapping the waste in a solid

stone block. This is a waste form factor that greatly reduces its hazard compared to

conventional reprocessing systems. Zeolites are also used in the management of leaks of

radioactive materials. For example, in the aftermath of the Fukushima Daiichi nuclear

disaster, sandbags of zeolite were dropped into the seawater near the power plant to

adsorb radioactive caesium which was present in high levels.

The German group Fraunhofer e.V. announced that they had developed a zeolite substance

for use in the biogas industry for long-term storage of energy at a density 4x more than

water.Ultimately, the goal is to be able to store heat both in industrial installations and in

small combined heat and power plants such as those used in larger residential buildings.

Commercial and domestic:

Zeolites can be used as solar thermal collectors and for adsorption refrigeration. In these

applications, their high heat of adsorption and ability to hydrate and dehydrate while

maintaining structural stability is exploited. This hygroscopic property coupled with an

inherent exothermic (energy releasing) reaction when transitioning from a dehydrated to a

hydrated form make natural zeolites useful in harvesting waste heat and solar heat energy.

Zeolites are also used as a molecular sieve in cryosorption style vacuum pumps.

The largest single use for zeolite is the global laundry detergent market. This amounted to

1.44 million metric tons per year of anhydrous zeolite A in 1992.Synthetic zeolites are used

as an additive in the production process of warm mix asphalt concrete. The development of

this application started in Germany in the 1990s. They help by decreasing the temperature

level during manufacture and laying of asphalt concrete, resulting in lower consumption of

fossil fuels, thus releasing less carbon dioxide, aerosols, and vapours. The use of synthetic

zeolites in hot mixed asphalt leads to easier compaction and, to a certain degree, allows

cold weather paving and longer hauls.

When added to Portland cement as a pozzolan they can reduce chloride permeability and

improve workability. They reduce weight and help moderate water content while allowing

for slower drying which improves break strength.[14] When added to lime mortars and

lime-metakaolin mortars, synthetic zeolite pellets can act simultaneously as pozzolanic

material and water reservoir.

In Biological:

Research into and development of the many biochemical and biomedical applications of

nano zeolites, particularly the naturally occurring species heulandite, clinoptilolite and

chabazite has been ongoing.

Zeolite-based oxygen concentrator systems are widely used to produce medical-grade

oxygen. The zeolite is used as a molecular sieve to create purified oxygen from air using its

ability to trap impurities, in a process involving the adsorption of nitrogen, leaving highly

purified oxygen and up to 5% argon.

QuikClot brand hemostatic agent, which is used to stop severe bleeding, contains a calcium-

loaded form of zeolite found in kaolin clay.

In agriculture:

clinoptilolite (a naturally occurring zeolite) is used as a soil treatment. It provides a source

of slowly released potassium. If previously loaded with ammonium, the zeolite can serve a

similar function in the slow release of nitrogen. Zeolites can also act as water moderators, in

which they will absorb up to 55% of their weight in water and slowly release it under the

plant's demand. This property can prevent root rot and moderate drought cycles.

Clinoptilolite has also been added to chicken food, the absorption of water and ammonia by

the zeolite made the birds droppings drier, less odoriferous and hence easier to handle.

Pet stores market zeolites for use as filter additives in aquaria. In aquaria, zeolites can be

used to adsorb ammonia and other nitrogenous compounds. However, due to the high

affinity of some zeolites for calcium, they may be less effective in hard water and may

deplete calcium. Zeolite filtration is used in some marine aquaria to keep nutrient

concentrations low for the benefit of corals adapted to nutrient-depleted waters.

Assignment 1: Nanoparticle coatings for electrical productsShashikant V, Sabarigresan M, Spandana K, Vijendran

M.Tech (Material Science), First Year

During the past several years, advances in nanomaterials have allowed nanoparticles to be formulated into numerous applications. The majority of these applications sought performance improvements that were previously unobtainable. Examples of such applications containing nanomaterials that have been commercialised for coatings electrical products such as fuel cells, FET’s, solar cells and sensors. Nanoparticles have one dimension that measures 100 nanometers or less. The properties of many conventional materials change when formed from nanoparticles. This is typically because nanoparticles have a greater surface area per weight than larger particles which causes them to be more reactive to some other molecules.Nanoparticles are used, or being evaluated for use, in many fields. The list below introduces several of the uses under development.

1. NOMFET’s2. Corrosion Protection of Electrically Conductive Surfaces 3. Nanotechnology in Fuel Cells4. Silicon nanoparticles coating anodes of lithium-ion batteries5. Nanotechnology in Solar Cells6. Nano coated Sensors (Palladium Coated Hydrogen sensor)7. Nanotetrapods

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1. NOMFET is a nanoparticle organic memory field-effect transistor. The transistor is designed to mimic

the feature of the human synapse known as plasticity, or the variation of the speed and strength of the

signal going from neuron to neuron. The transistor uses gold nano-particles of about 5—20 nm set with pentacene to emulate the change in voltages and speed within the signal.

The recent creation of this novel transistor gives prospects to better recreation of certain types of human

cognitive processes, such as recognition and image processing. When the NOMFET is eventually applied, it should be able to replicate the functionality of plasticity that previously required groups of several

transistors to emulate and thus continue to decrease the size of the processor that would be attempting to utilize the computational advantages of a pseudo-synaptic operation.

Source: O. Bichler et al., Fig. 1. Physical structure of the NOMFET transistor

2. Corrosion Protection of Electrically Conductive Surfaces

The basic function of the electrically conductive surface of electrical contacts is electrical conduction. The electrical conductivity of contact materials can be largely reduced by corrosion and in order to avoid corrosion, protective coatings must be used. Fretting corrosion is the degradation mechanism of surface material, which causes increasing contact resistance. Fretting corrosion occurs when there is a relative movement between electrical contacts with surfaces of ignoble metal. Avoiding fretting corrosion is therefore extremely challenging in electronic devices with pluggable electrical connections.

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Gold is one of the most commonly used noble plating materials for high performance electrical contacts because of its high corrosion resistance and its good and stable electrical behavior. There different ways to minimize the consumption of gold for electrical contacts and to improve the performance of gold plating. Other plating materials often used for corrosion protection of electrically conductive surfaces are tin, nickel, silver and palladium. Gold alloys fundamentally possess the combination of desired properties for the overall protection of electrically conductive surfaces, having a very high corrosion resistance, a high wear resistance, a high fretting corrosion resistance and a high and stable electrical conductivity.

Nanoparticle enhanced gold coatings displayed a higher potential than gold alloys. However, the statistical lifetime spread of these coatings is large and there are many more parameters with nanoparticles which influence the properties of coatings.

Fig. 2. Effect of different nanoparticles on the lifetime of electrically conductive surfaces in fretting corrosion tests Source: Jian Song et. al Corrosion Protection of Electrically Conductive Surfaces, Metals, 2012

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3. Nanotechnology in Fuel CellsFuel cells convert chemical energy directly into electrical energy. They consist of an anode, which oxidizes the fuel (such as hydrogen), and a cathode, which reduces oxygen to water. A polymer membrane separates the electrodes. Fuel cell-powered cars in production today use pure platinum to catalyze the oxygen reduction reaction in the cathode side. While platinum is the most efficient catalyst available today for the oxygen reduction reaction, its activity is limited, and it is rare and expensive.

The spacing between platinum nanoparticles affects the catalytic behavior, and that by controlling the packing density of the platinum nanoparticles it is possible to reduce the amount of platinum needed as a catalyst in fuel cells.The catalyst is made from a sheet of graphene coated with cobalt nanoparticles.A catalyst using platinum-cobalt nanoparticles produces 12 times more catalytic activity than pure platinum. In order to achieve this performance, annealing the nanoparticles will form a crystalline lattice which will reduce the spacing between platinum atoms on the surface, increasing their reactivity.

4. Silicon nanoparticles coating anodes of lithium-ion batteries

Silicon is an earth abundant element, and is fairly inexpensive to refine to high purity. When alloyed with lithium it has a theoretical capacity of ~3,600 milliampere hours per gram (mAh/g),

Fig 3. The self-discharging is driven by the internal compressive stress generated inside the lithiated SiNPs

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which is nearly 10 times the energy density of graphite electrodes (372 mAh/g). One of silicon's inherent traits, unlike carbon, is the expansion of the lattice structure by as much as 400% upon full lithiation (charging). For bulk electrodes, this causes great structural stress gradients within the expanding material, inevitably leading to fractures and mechanical failure, which significantly limits the lifetime of the silicon anodes. Thus, the challenges of Si-based anodes for lithium ion batteries is the large volume change upon lithiation and delithiation, which commonly leads to electrochemi-mechanical degradation and subsequent fast capacity fading. Recent studies have shown that applying nanometer-thick coating layers on Si nanoparticle (SiNPs) enhances cyclability and capacity retention. However, it is far from clear how the coating layer function from the point of view of both surface chemistry and electrochemi-mechanical effect. When studied further using transmission electron microscopy to investigate the lithiation/delithiation kinetics of SiNPs coated with a conductive polymer, polypyrrole (PPy). We discovered that this coating layer can lead to “self-delithiation” or “self-discharging” at different stages of lithiation.

The self-discharging is driven by the internal compressive stress generated inside the lithiated SiNPs due to the constraint effect of the coating layer. It is also noticed that the critical size of lithiation-induced fracture of SiNPs is increased from ∼150 nm for bare SiNPs to ∼380 nm for the

PPy-coated SiNPs, showing a mechanically protective role of the coating layer. These observations demonstrate both beneficial and detrimental roles of the surface coatings, shedding light on rational design of surface coatings for silicon to retain high-power and high capacity as anode for lithium ion batteries.Cu2+1O coated Si nanoparticles were investigated as an anode material for lithium-ion battery. The coating of Cu2+1O on the surface of Si particles remarkably improves the cycle performance of the battery than that made by the pristine Si. The battery exhibits an initial reversible capacity of 3063 mAh/g and an initial columbic efficiency (CE) of 82.9 %. With a current density of 300 mA/g, its reversible capacity can remains 1060 mAh/g after 350 cycles, corresponding to a CE ≥ 99.8 %. It is believed that the Cu2+1O coating enhances the electrical conductivity, and the elasticity of Cu2+1O further helps buffer the volume changes during lithiation/delithiation processes. Experiment results indicate that the electrode maintained a highly integrated structure after 100 cycles and it is in favor of the formation of stable solid electrolyte interface (SEI) on the Si surface to keep the extremely high CE during long charge and discharge cycles.

5. Nanotechnology in Solar Cells Solar panel conversion efficiency, typically in the 20 percent range, is reduced by dust, grime, pollen, and other particulates that accumulate on the solar panel. A dirty solar panel can reduce its

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power capabilities by up to 30 percent in high dust/pollen or desert areas. Cleaning dirty panels with commercial detergents can be time-consuming, costly, hazardous to the environment, or even corrode the solar panel frame. Ideally solar panels should be cleaned every few weeks to maintain peak efficiency, which is especially hard to do for large solar-panel arrays

Passive (Non-Reactive) CoatingTo obtain a self-cleaning property, nanohydrophobic material is coated on the solar panel to maintain peak efficiency over longer periods of time.The coating itself is very robust, an actual covalent linkage holds it to surface of the panel, creating a strong chemical bond. This is a big advantage over spray-on coatings, which gradually degrade with time. The principle behind a hydrophobic coating is that the layer forms a barrier so that water accumulates on the surface in an almost spherical shape, but is blocked from adhering to the surface by the barrier. This means that when a treated surface is tilted at an angle, the water rolls

Fig. 4 Passive (Non-Reactive) Coating

off the surface like a sphere rolling down a slide.

Active coating in Solar cells:

Solar cells that can be installed as a coating on windows or other building materials, referred to as "Building Integrated Photovoltaic's".Solar cell using graphene coated with zinc oxide nanowires. The researchers believe that this method will allow the production of low cost flexible solar cells at high enough efficiency to be competive. Coatable Solar Cells Organic solar cells that can be applied by spray painting, possibly

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turning the surface of a car into a solar cell. The material is composed of metal nanoparticles (diameters ~ 10 nm) embedded in a transparent composite matrix.(A Norwegian company EnSol AS has patented a ground breaking, novel thin film solar cell technology which they seek to develop commercially by 2017.) Solar cells that can be installed as a coating on windows or other building materials, referred to as "Building Integrated Photovoltaic's".

How else can nanotechnology improve solar cells?Using nanoparticles in the manufacture of solar cells has the following benefits: Reduced manufacturing costs as a result of using a low temperature process similar to printing instead of the high temperature vacuum deposition process typically used to produce conventional cells made with crystalline semiconductor material.Reduced installation costs achieved by producing flexible rolls instead of rigid crystalline panels. Cells made from semiconductor thin films will also have this characteristic.Currently available nanotechnology solar cells are not as efficient as traditional ones, however their lower cost offsets this. In the long term nanotechnology versions should both be lower cost and, using quantum dots, should be able to reach higher efficiency levels than conventional ones.

6. Nano coated Sensors (Palladium Coated Hydrogen sensor)

A kind of chemical coating used to dramatically enhances the sensitivity and reaction time of hydrogen sensors. Hydrogen sensor technology is a critical component for safety and other practical concerns in the proposed hydrogen economy. For example, hydrogen sensors will detect leaks from hydrogen-powered cars and fueling stations long before the gas becomes an explosive hazard. Scientists have demonstrated that the enhanced sensor design shows a rapid and reversible response to hydrogen gas that is repeatable over hundreds of cycles

The sensor material is made by depositing a discontinuous palladium thin film on a glass slide coated with a grease-like self-assembled monolayer of siloxane anchored to the surface. By adding the siloxane self-assembled monolayer, the thin film dynamics can be changed. Other sensors have a response time of several seconds upon exposure to 2 percent hydrogen; this new nano coated sensor works in tens of milliseconds. It is reported that the enhanced sensors are sensitive enough to detect hydrogen levels as low as 25 parts per million (ppm), far below hydrogen's lower explosive limit around 40,000 ppm. Their sensitivity and speed are superior to any available commercial sensors.

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Palladium is an ideal material for hydrogen sensing because it selectively absorbs hydrogen gas and forms a chemical species known as a palladium hydride. Thick-film hydrogen sensor designs rely on the fact that palladium metal hydride's electrical resistance is greater than the metal's resistance. In such systems, the absorption of hydrogen is accompanied by a measurable increase in electrical resistance. However, a palladium thin-film sensor is based on an opposing property that depends on the nanoscale structures within the thin film. In the thin film, nanosized palladium particles swell when the hydride is formed, and in the process of expanding, some of them form new electrical connections with their neighbors. The increased number of conducting pathways results in an overall net decrease in resistance.

Palladium spreads across the glass in puddle-like clusters a few nanometers thick and tens of nanometers across. After pre-coating the glass with the siloxane monolayer, the Argonne scientists saw a remarkable shift in the size and spatial distribution of the palladium. Like water beading on the surface of a freshly waxed car, the palladium formed granular clusters just a few nanometers across. The gaps between neighboring palladium clusters on the siloxane-coated glass were more numerous and ten times smaller on average than the gaps between the much larger, spread-out clusters on the bare glass. The shorter gap distance is important for giving you a fast, sensitive response. It is also proven that the surface treatment of the glass reduces the adhesion – or “stiction” – between the metal and glass that hinders the expansion and contraction of the palladium nanoparticles on bare glass. This effect contributes to the increased speed of the sensor response.

6. NanotetrapodsHybrid thin film solar cell based on all-inorganic nanoparticles is a new member in the family of photovoltaic devices. In this work, a novel and performance-efficient inorganic hybrid nanostructure with continuous charge transportation and collection channels is demonstrated by introducing CdTe nanotetropods (NTs) and CdSe quantum dots (QDs). Hybrid morphology is characterized, demonstrating an interpenetration and compacted contact of NTs and QDs. Electrical measurements show enhanced charge transfer at the hybrid bulk heterojunction interface of NTs and QDs after ligand exchange which accordingly improves the performance of solar cells. Photovoltaic and light response tests exhibit a combined optic-electric contribution from both CdTe NTs and CdSe QDs through a formation of interpercolation in morphology as well as a type II energy level distribution. The NT and QD hybrid bulk heterojunction is applicable and promising in other highly efficient photovoltaic materials such as PbS QDs.

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Fig. 5. Nanoterapods

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1

NANOMATERIALS AND

NANOTECHNOLOGY

aSSIGNMENT ON PHOTOVOLTAIC CELL

SUBMITTED BY:

Akshay Govind

Angelina Eliz Shaji

Anoja Tony Tharakan

Archana . R

Sabin Hashmi .K.K

2

PHOTOVOLTAIC CELL

A Solar cell also called as Photovoltaic cell is an electrical device that covers the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect. Solar cells are described as being photovoltaic irrespective of whether the source is sunlight or an artificial light. They are used as a photodetector (for example infrared detectors), detecting light or other electromagnetic radiation near the visible range, or measuring light intensity. Photovoltaics are best known as a method for generating electric power by using solar cells to convert energy from the sun into a flow of electrons. The photovoltaic effect refers to photons of light exciting electrons into a higher state of energy, allowing them to act as charge carriers for an electric current. The photovoltaic effect was first observed by Alexandre-Edmond Becquerel in 1839. Photovoltaic cells are an integral part of solar-electric energy systems, which are becoming increasingly important as alternative sources of utility power. SOLAR CELL SOLAR PANEL

3

CONSTRUCTION AND COMPONENTS OF PHOTOVOLTAIC CELL

The first PV cells were made of silicon combined, or doped, with other elements to affect the behavior of electrons or holes (electron absences within atoms). Other materials, such as copper indium diselenide (CIS), cadmium telluride (CdTe), and gallium arsenide (GaAs), have been developed for use in PV cells. There are two basic types of semiconductor material, called positive (or P type) and negative (or N type). In a PV cell, flat pieces of these materials are placed together, and the physical boundary between them is called the P-N junction. The device is constructed in such a way that the junction can be exposed to visible light, IR, or UV. When such radiation strikes the P-N junction, a voltage difference is produced between the P type and N type materials. Electrodes connected to the semiconductor layers allow current to be drawn from the device. Large sets of PV cells can be connected together to form solar modules, arrays, or panels.

Components of photovoltaic system

4

The process of fabricating conventional single and polycrystalline silicon PV cells begins with very pure semiconductor grade polysilicon. The polysilicon is then heated to melting temperature, and trace amounts of boron are added to the melt to create a P-type semiconductor material. Next, an ingot, or block of silicon is formed, commonly using one of two methods:

1) by growing a pure crystalline silicon ingot from a seed crystal drawn from the molten polysilicon

2) by casting the molten polysilicon in a block, creating a polycrystalline silicon material.

Individual wafers are then sliced from the ingots using wire saws and then subjected to a surface etching process. After the wafers are cleaned, they are placed in a phosphorus diffusion furnace, creating a thin N-type semiconductor layer around the entire outer surface of the cell. Next, an anti-reflective coating is applied to the top surface of the cell, and electrical contacts are imprinted on the top (negative) surface of the cell. An aluminized conductive material is deposited on the back (positive) surface of each cell, restoring the P-type properties of the back surface by displacing the diffused phosphorus layer. Each cell is then electrically tested, sorted based on current output, and electrically connected to other cells to form cell circuits for assembly in PV modules.

+

5

Working Principle of Photovoltaic Cell

When light falls on silicon crystal , some portion of light is reflected, some portion is transmitted through the crystal and rest is absorbed by the crystal. If the intensity of incident light is high enough, sufficient numbers of photons are absorbed by the crystal and these photons in turn excite some of the electrons of covalent bonds. These excited electrons then get sufficient energy to migrate from valence band to conduction band. As the energy level of these electrons is in conduction band they leave from the covalent bond leaving a hole in the bond behind each removed electron. These are called free electrons and they move randomly inside the crystal structure of the silicon. These free electrons and holes have vital role in creating electricity in photovoltaic cell. These electrons and holes are hence called light-generated electrons

and holes respectively.

6

Potential Difference

In n-type semiconductor mainly the free electrons carry negative charge and in p-type semiconductor mainly the holes in turn carry positive charge.

There is always a potential barrier between n-type and p-type material. When light ray strikes on the crystal some portion of the light is absorbed by the crystal and consequently some of the valance electrons are excited and come out from the covalent bond resulting free electron-hole pairs. If light strikes on n-type semiconductor the electrons from such light-generated electron-hole pairs are unable to migrate to p-region since they are not able to cross the potential barrier due to repulsion of electric field across depletion layer. At the same time the light-generated holes cross the depletion region due to attraction of electric field of depletion layer where they recombine with electrons and then the lack of electrons here is compensated by valance electrons of p-region and this makes as many number of holes in the p-region. As such light generated holes are shifted to p-region where they are trapped because once they come to the p-region cannot be able to come back to n-type region due to repulsion of potential barrier. As the negative charge (light generated electrons) is trapped in one side and positive charge (light generated holes) is trapped in opposite side of a cell there will be a potential difference between these two sides of the cell. This potential difference is typically 0.5 V.

7

The electrical characteristics of solar cells

Exposing it to solar radiation the cell behaves like a current generator, whose functioning may be described in terms of its voltage-current characteristic. Generally speaking the characteristic of a photovoltaic cell depends on three basic variables; intensity of solar radiation, temperature and area of the cell. The intensity of solar radiation has no significant effect on the open circuit voltage; vice versa the intensity of the short-circuit current varies in proportion to the varying intensity of the irradiation, increasing as this increases. Temperature has no significant effect on the reading of the short-circuit current. On the contrary, this is proportional to the open circuit voltage, the voltage decreasing as the temperature increases. The cell's area has no effect on the reading of the voltage. Vice versa this is directly proportional to the available current.

In closed circuit conditions the current generated is maximum (Isc), while in open circuit conditions the voltage is maximum (Voc). In open and closed circuit conditions zero power will be generated as, applying the equation P=V x I, there will be zero current in the first case and zero voltage in the second. At other points power will increase with an increase in voltage, reaching a maximum and decreasing rapidly in proximity to the Voc.

8

Crystalline-Silicon Solar Panels

Crystalline silicon (c-Si) solar cells are currently the most common solar cells in use mainly because c-Si is stable, it delivers efficiencies in the range of 15% to 25% ,it relies on established process technologies with an enormous database.

A basic c-Si cell consists of essentially seven layers .A transparent adhesive holds a protective glass cover over the anti- reflective coating that ensures all of the light filters through to the silicon crystalline layers. Similar to semiconductor technology, an N layer sandwiches against a P layer and the entire package is held together with two electrical contacts: positive topside and negative below. Two types of c-Si are in common use: monocrystalline and multicrystalline silicon.

c-Si SOLAR PANEL

9

Nanotechnology in Solar Cells

As the applications of nanotechnology has spread its branches overall walks of life it has also crept into non-conventional energy production.

Now we are using thin film solar cell.

Thin-film solar cell

10

A thin-film solar cell is a second generation solar cell that is made by depositing one or more thin layers, or thin film (TF) of photovoltaic material on a substrate, such as glass, plastic or metal. Thin-film solar cells are commercially used in several technologies, including cadmium telluride (CdTe), copper indium gallium diselenide(CIGS), and amorphous thin-film silicon (a-Si, TF-Si).

Cells made from these materials tend to be less efficient than bulk silicon, but are less expensive to produce. Their quantum efficiency is also lower due to reduced number of collected charge carriers per incident photon.

The performance and potential of thin-film materials are high, reaching cell efficiencies of 12–20%.

Thin Film Solar Cell

11

Thin-Film Solar Panels

Thin-film solar cells are potentially cheaper than traditional panels but less efficient, in the realm of 20% to 30% of light-to-voltage conversion.

Typical thin-film solar cells are one of four types depending on the material used:

amorphous silicon (a-Si) and thin-film silicon (TF-Si); cadmium telluride (CdTe); copper indium gallium deselenide (CIS or CIGS); dye-sensitized solar cell (DSC) plus other organic materials.

Thin-film solar cells consist of about six layers. In this case, a transparent coating covers the antireflective layer. These are followed by the P- and N-type materials, followed by the contact plate and substrate. And, obviously, the operating principle (photovoltaic) is the same as c-Si cells.

Advantages of Thin Film Solar Panel

Using nanoparticles in the manufacture of solar cells has the following benefits:

Reduced manufacturing costs as a result of using a low temperature process similar to printing instead of the high temperature vacuum deposition process typically used to produce conventional cells made with crystalline semiconductor material.

Reduced installation costs achieved by producing flexible rolls instead of rigid crystalline panels. Cells made from semiconductor thin films will also have this characteristic.

12

Currently available nanotechnology solar cells are not as efficient as traditional ones, however their lower cost offsets this. In the long term nanotechnology versions should both be lower cost and, using quantum dots, should be able to reach higher efficiency levels than conventional ones.

Advantages of Photovoltaic Cell

PV panels provide clean – green energy. During electricity generation with PV panels there is no harmful greenhouse gas emissions thus solar PV is environment friendly.

Solar energy can be made available almost anywhere there is sunlight.

Solar energy is especially appropriate for smart energy networks with distributed power generation.

Photovoltaic panels, through photoelectric phenomenon, produce electricity in a direct electricity generation way.

Operating and maintenance costs for PV panels are considered to be low, almost negligible, compared to costs of other renewable energy systems.

PV panels are totally silent, producing no noise at all. Residential solar panels are easy to install on rooftops or on the

ground.

13

Disadvantages of Photovoltaic Cell

Solar energy panels require additional equipment (inverters) to convert direct electricity (DC) to alternating electricity (AC) in order to be used on the power network.

In case of land-mounted PV panel installations, they require relatively large areas for deployment.

Solar panels efficiency levels are relatively low (between 14%-25%) compared to the efficiency levels of other renewable energy systems.

They are fragile and can be damaged relatively easily.

Conclusion

The time to depend on non conventional energy production has encroached upon us in our world which is being fast depleted of its non- renewable resources. The best solution to the problem is the sun . If we could manage to harness the full potential of the solar radiation the earth receives we wouldn’t need to look any further for our energy needs. This is where solar cells come-in .The traditional solar cells are rather rigid, fragile and expensive to install. The solar cells which employ nanotechnology on the other hand are flexible, portable and comparably inexpensive.

ASSIGNMENT

TOPIC : ELECTRIC DOUBLE LAYER CAPACITOR

Submitted by

Y Ramya Koteswari

R Nivetha

Karthikeyan

V K Puvinila

Shanmuga Priya

CONTENTS

What is a capacitor ?

What is an electric double layer capacitor(EDLC)?

Use of ELDC over capacitors

Principle of electric double layer capacitor

Structure of ELDC

Electronic characteristics of ELDC

Benefits of using ELDC

Weaknesses

Examples of applications

Future of supercapacitors

Comparison of ELDC to batteries

What is a capacitor ?

A capacitor is an energy storage device that, unlike a battery, generates an electrical field

between two parallel conductor plates. As electrons move from one plate to the other, they

build potential energy that can be channeled for use in an associated circuit. The accumulation

of e ergy is k o as hargi g, a d apa itors are generally measured by the quantity,

density, and rate of their charge.

What is an electric double layer capacitor(EDLC)?

An electric double-layer capacitor, or supercapacitor, is capable of charging and storing energy

at an exponentially higher density than standard capacitors. For comparison, a typical

apa itor’s energy storage is measured in nano- or micro-farads, while a supercapacitor can be

rated in farads.

Use of ELDC over capacitors

A apa itor’s e ergy apa ity is deter i ed y its a ou t of stored charges and the potential

for charging between its plates. The charge potential is greatly influenced by the quality of the

aterial through hi h the ele tri field a e sustai ed, other ise k o as the diele tri . In an electric double-layer capacitor, the dielectric is typically suspended in a high surface area

carbon material, rendering the dielectric medium exceptionally thin. The large surface area,

o i ed ith a arro ediu , results i ery high harge pote tial, or apa ita e, i a

relatively small-sized de i e; he e the ter super apa itor.

While the layers in a double-layer capacitor are electrically conductive, they have a somewhat

low tolerance for voltage (usually no more than one volt). Inclusion of an organic electrolyte

can increase voltage reception, as can connecting multiple supercapacitors in a serial array. The

material used in the dielectric can also affect capacitor efficiency. Activated carbon, for

instance, has a much greater surface area than aluminum, which is traditionally used in

standard capacitors. Research to develop newer and more effective dielectric substances is

continuously underway.

Principle of electric double layer capacitor

In ELDC ,an electrolyte (solid or liquid) is filled between two electrodes (see figure 1) . Electric

double-layer capacitors are based on the operating principle of the electric double-layer that is

formed at the interface between activated charcoal and an electrolyte. Capacitance is

proportional to the surface area of the electrical double layer. Therefore using activated carbon

which has large surface area for electrodes, enables EDLC to have high capacitance. The

activated charcoal is used as an electrode, and the principle behind the capacitor is shown in

Figure 1. Activated charcoal is used in its solid form, and the electrolytic fluid is liquid. When

these materials come in contact with each other, the positive and negative poles are distributed

relative to each other over an extremely short distance. Such a phenomenon is known as an

electric double-layer. When an external electric field is applied, the electric double-layer that is

formed in the vicinity of the activated charcoal's surface within the electrolytic fluid is used as

the fundamental capacitor structure. The mechanism of ion absorption and desorption to the

electrical double layer contributes to charge and discharge of EDLC.

By applying voltage to the facing electrodes, ions are drawn to the surface of the electrical

double layer and EDLC is charged. Conversely, they move away when discharging EDLC. This is

how EDLC is charged and discharged (see figure 2).

Figure 1

Structure of ELDC

EDLC consists of electrodes, electrolyte (and electrolyte salt) , and the separator, which

prevents facing electrodes from contacting each other. Activated carbon powder is applied to

the electricity collector of the electrodes. The electrical double layer is formed on the surface

where each powder connects with an electrolyte (see figure 2).

Considering this structure as a simple equivalent circuit, EDLC is shown by anode and cathode

capacitors (C1, C2) , separator, inter-electrode resistance which consists of resistance of

separator and electrolyte (Rs) , electrode resistance which consists of activated carbon

electrode and collector (Re) ,and isolation resistance (R) (see figure 3)

Figure 2

Activated carbon electrodes consist of a various amount of powder with holes on their

respective surfaces. The electrical double layer is formed on the surface where each powder

contacts with the electrolyte. Therefore, equivalent circuit electrode resistance (Re) and

resistance caused by ion moving (Rs) are shown by a complicated equivalent circuit where

various resistances are connected to capacitors in series to capacitors .

Figure 3

Electronic characteristics of ELDC

Because EDLC has high capacitance, it can be used as an energy supply device for backup or

peak power. Unlike a battery, the electric potential of EDLC becomes low by discharging

electricity. Therefore, energy stored in EDLC is shown by half of Q(electricity) x V(voltage).

However, EDLC consists of complicated equivalent circuit as shown in figure 4. As such, actual

measured capacitance value varies depending on charge or discharge condition.

Figure 4

Charge current

As shown in figure 4, EDLC is an assembly of several capacitors which have various R values.

Whe EDLC’s CR alue is s all, it a e harged i a short ti e. O the other ha d, he CR value is large, it needs a long charging time. Therefore, the sum of In is considered as leakage

current (LC). The current value that flows through RLC (the actual leakage current component)

is too small to be measured.

Figure 5

Constant Voltage Charge

When charging EDLC at a low current, it takes a longer time than the charging time calculated

according to the nominal capacitance. On the contrary, when discharging at low current, it may

provide a longer discharging time than calculated discharging time(figure 6).

IIXIIO ,------------,

1001

v

Rn Cn

+- lic

Figure 6

Calculating of discharge time

Unlike a secondary battery, the voltage of EDLC drops according to discharge current. The

voltage also drops proportionately because of the internal resistance (ESR) of the capacitor.

These voltage drops affect output, especially when EDLC is used with high discharge current

and a decrease in voltage. Therefore, it is necessary to calculate the needed characteristics

(capacitance, ESR, series or parallel numbers of capacitors) considering the voltage drop.

Calculation formulas are shown below.

Figure 7

• " ,

" " • ~ • , •

>5

05

0 0

1/

./-' ./ 10flCMcula • ....:!

./ lOOOC-.olat<KI

lkCl Cakula, 1KI

ff 100 Mo<>.:>sur<Kl

I' __ IOOOMoioasur<KI

l k!lMoMs",<>d

Tlmel....:')

Constant Voltage Charge

I ~ Comtant

Dio;chil rglng Tlm ... I(~K)

Discharging at (on stant current

I-l-l-I-

Discharging time (t )

C t; -1- (V, -V,)

Formula 5

l oad Current (consUlnl) : t Discharging time: t Charge vol tage: Vc ( .. pilChor voltage: VI Capuitance: C

Figure 8

Figure 9

Energy loss by Internal resisitance

When discharging EDLC at high current, high power, or low ESR, it is necessary to consider

energy loss caused by capacitor resistance. When output power or current becomes larger,

discharge efficiency becomes low and in some cases EDLC cannot provide enough discharging

time. When discharging time is not enough, please use several EDLC in series or in parallel.

"r-_

Discharging at Constant Power

v<

~ ,;: • • ~ ;; j •

Reo.;stanc" jRI = Con,tant

·1 , Disch"'cin& ti m" t (sec)

Discharging at Constant Resistance

Discharging time (t )

t = 21p (CV,' - CV,')

Formula 6

Power (constant): P Discharging time: t Charge Yoltagl!: Vc Capacitor voltage: Vt Capacitance: C

Discharging time (t l

V, t = -C X R X In ( Vc )

Fo rmula 7

Resistance (constant): R Discharging time: t Charge voltage:Vc Capacitor voltage: Vt Capacitance: C

Figure 10

Benefits of using ELDC

The electric double-layer design does not have the solid dielectric that is used in the previous

designs, nor does it have the chemical reactions such as are found in batteries during charging

and discharging. Rather this design has the following characteristics:

1. This design allows farad-order capacitance in a small device (When activated charcoal,

with its large surface area, is used the thickness of the dielectric is extremely thin).

2. There is no need for special charging circuits or for control during discharge.

3. Overcharging or over discharging does not have a negative effect on the lifespan, as it

does with batteries.

4. This technology is extremely "clean energy" in terms of environmental friendliness.

5. Because the electronic parts can be soldered, there are no problems with unstable

contacts as there are with batteries.

Weaknesses

1. The lifespan is limited because of the use of electrolyte.

2. The electrolyte may leak if the capacitor is used incorrectly.

3. When compared to aluminum electrolytic capacitors, these capacitors have high internal

resistances and thus cannot be used in AC circuits.

Examples of Application

Taking advantage of the benefits described above, electric double-layer capacitors are used

broadly in applications such as the following:

1. Memory backup for timers, programs, etc., in video and audio equipment.

2. Backup power sources when changing batteries for portable electronic equipment.

3. Power sources for equipment that uses solar cells, such as watches and display lights.

4. Starters for small motors and cell motors.

Future of supercapacitors

While today’s supercapacitor has a limited range of applications, advances in design might

eventually expand the produ t’s utility. For example, researchers continue to develop and

experiment with newer forms of dielectric materials, such as carbon nanotubes, polypyrrole,

and barium titanate, which may improve capacitance and energy density. The concept of

combining supercapacitors with alternative energy sources to replace car batteries has gained

appeal within the current "green" movement, and several public transportation systems have

created pilot trials for capacitor-run buses and trains. If these and other developments yield

successful results, the electric double-layer capacitor may achieve greater functionality and gain

a larger role within the energy industry.

Comparison of ELDC to batteries

This special type of capacitor has properties that are about halfway between regular capacitors

and rechargeable (secondary) batteries. While a battery stores an electrical charge through a

chemical reaction, the EDLC stores charge by means of an electric double layer formed by ions

adhering to the surface of an activated carbon electrode. Whereas charging a rechargeable

battery requires several hours, an electric double layer capacitor can be charged in a matter of

seconds.

Figure 11

PAGE 1

Nanomaterials and Nanotechnology

Assignment-1

Fuel Cells and Batteries

GROUP MEMBERS:

R VARUNAA MUKESH KUMAR CHOUDHARY

VISHNU SUDARSANAN

ANU MARIA AUGUSTINE ARUNAV DAS

PAGE 2

Fuel cell

Fuel cell is a device that converts chemical energy into electrical energy (along with

water and heat as a by-product) through electrochemical reactions. Conversion of the fuel to

energy takes place through an electrochemical process (not combustion) and it is a clean, quiet

and highly efficient process and two to three times more efficient than burning fuel in engines.

Fuel cells are different from batteries in requiring a continuous source of fuel and

oxygen or air to sustain the chemical reaction, whereas in a battery the chemicals present in the

battery react with each other to generate an electromotive force (emf). Fuel cells can produce

electricity continuously for as long as these inputs are supplied.

A fuel cell consists of two catalyst coated electrodes surrounding an electrolyte one

electrode is an anode and the other is a cathode. The process begins when hydrogen molecules

enter the anode. The catalyst coating on the anode separates hydrogen’s negatively charged electrons from the positively charged protons.

Anode Reaction: 2H2 + 2O2-

2H2O + 4e-

Cathode Reaction: O2 + 4e- 2O

2-

The electrolyte allows the protons to pass through the

cathode, but not the electrons. Instead the electrons are directed

through an external circuit which creates an electrical current.

While the electrons pass through the external circuit, oxygen

molecules pass through the cathode. The oxygen and the protons

combine there with the electrons after they have passed through the external circuit in the

presence of a second catalyst at the cathode. When the oxygen and the protons

combine with the electrons it produces water and heat.

Net Reaction: 2H2 + O2 2H2O

This reaction in a single fuel cell produces only about 0.7 V. Individual fuel cells can

then be placed in a series to form a fuel cell stack. The stack can be used in a system to power a

vehicle or to provide stationary power to a building.

A typical fuel cell produces a voltage from 0.6 V to 0.7 V at full rated load. Voltage

decreases as current increases, due to several factors:

1. Activation loss

2. Ohmic loss (voltage drop due to resistance of the cell components and interconnections)

3. Mass transport loss (depletion of reactants at catalyst sites under high loads, causing rapid

loss of voltage).

PAGE 3

Types of fuel cells:

(i) Proton exchange membrane fuel cells (PEMFCs): The proton exchange membrane fuel

cells have a solid polymer membrane as an electrolyte. Due to membrane limitations, PEMs

usually operate at low temperatures (60-100oC), but new developments have produced higher

temperature PEMs (up to 200oC). Since platinum is the most chemically active substance for low

temperature hydrogen separation, it is used as the catalyst. Hydrogen fuel is supplied as

hydrogen gas or is reformed from methanol, ethanol, natural gas or liquefied petroleum gas and

then fed into the fuel cell. The power range of existing PEMs is about 50W to 150kW. The

advantages of using PEM fuel cells include:

1) low weight and volume with good power-to-weight ratio,

2) low temperature operation, so less thermal wear to components, and

3) quick starts, with full power available in minutes or less.

(ii) Direct methanol fuel cells (DMFCs): DMFCs differ from PEMs because they use

unreformed liquid methanol fuel rather than hydrogen. DMFCs operate at slightly higher

temperatures than PEMs (50-120oC) and achieve around 40% efficiency. Since they are

refuelable and do not run down, DMFCs are directed toward small mobile power applications

such as laptops and cell phones, using replaceable methanol cartridges at power ranges of 1-50

Watts. Many of the major electronics companies are demonstrating miniature DMFCs powering

their equipment and smaller fuel cell companies are partnering with military and

communications contractors.

(iii) Phosphoric acid fuel cell (PAFC): In these cells phosphoric acid is used as a non-

conductive electrolyte to pass positive hydrogen ions from the anode to the cathode. These cells

commonly work in temperatures of 150 to 200 degrees Celsius. This high temperature will cause

heat and energy loss if the heat is not removed and used properly. This heat can be used to

produce steam for air conditioning systems or any other thermal energy consuming system.

Using this heat in cogeneration can enhance the efficiency of phosphoric acid fuel cells from 40–50% to about 80%. Phosphoric acid, the electrolyte used in PAFCs, is a non-conductive liquid

acid which forces electrons to travel from anode to cathode through an external electrical circuit.

Since the hydrogen ion production rate on the anode is small, platinum is used as catalyst to

increase this ionization rate. A key disadvantage of these cells is the use of an acidic electrolyte.

This increases the corrosion or oxidation of components exposed to phosphoric acid.

(iv) Solid acid fuel cell (SAFC): Solid acid fuel cells (SAFCs) are characterized by the use of a

solid acid material as the electrolyte. At low temperatures, solid acids have an ordered molecular

structure like most salts. At warmer temperatures (between 140 to 150 degrees Celsius for

CsHSO4), some solid acids undergo a phase transition to become highly disordered

"superprotonic" structures, which increases conductivity by several orders of magnitude. The

first proof-of-concept SAFCs were developed in 2000 using cesium hydrogen sulfate (CsHSO4).

Current SAFC systems use cesium dihydrogen phosphate (CsH2PO4) and have demonstrated

lifetimes in the thousands of hours.

(v) Solid oxide fuel cells (SOFCs): These are one of the high temperature fuel cells, operating at

800-1000oC. High temperature operation eliminates the need for precious metal catalysts and can

PAGE 4

reduce cost by recycling the waste heat from internal steam reformation of hydrocarbon fuels.

SOFCs are tolerant to CO poisoning, allowing CO derived from coal gas to also be employed as

source of fuel. These fuel cells use a solid ceramic electrolyte and produce a power output of 2-

100 kW and can attain 220 kW-300 kW when used in a SOFC/gas turbine hybrid system.

Demonstrated electrical efficiencies are 45-55%, with total efficiencies of 80-85% with

cogeneration of waste heat. SOFCs are well-suited for medium-to-large scale, on-site power

generation or CHP (hospitals, hotels, universities), and are also being marketed for

telecommunications back up and as auxiliary power units (APUs) for military vehicle on-board

equipment.

(vi) Molten carbonate fuel cells (MCFCs): These fuel cells operate at 600-750oC and use a

molten alkali carbonate mixture for an electrolyte. MCFCs typically range between 75-250 kW,

but when using combined units, have produced up to 5 MW of power. Electrical efficiencies are

50-60%, with total efficiencies of 80-85% with cogeneration of waste heat. To date, MCFCs

have operated on hydrogen, carbon monoxide, natural gas, propane, landfill gas, marine diesel,

and simulated coal gasification products.

Fuel Cell Applications

As a result of the inherent size flexibility of fuel cells, the technology may be used in

applications with a broad range of power needs. This is a unique feature of fuel cells and their

potential application ranges from systems of a few watts to megawatts Fuel cell applications may

be classified as being either mobile or stationary applications. The mobile applications primarily

include transportation systems and portable electronic equipment while stationary applications

primarily include combined heat and power systems for both residential and commercial needs.

In the following, fuel cell applications for transportation, portable electronic equipment, and

combined heat and power systems are addressed.

Transportation Applications

Cars

All the world leading car manufacturers have designed at least one prototype vehicle using fuel

cells. Some of the car manufacturers (Toyota, Ford) have chosen to feed the fuel cell with

methanol, while others have preferred to use pure hydrogen (Opel has used liquid hydrogen,

General Motors has stored hydrogen in hydride form). In the short term there is a general trend

for the car manufacturers to use reformed methanol as the fuel type for the fuel cell. However,

over in the long term hydrogen remains the fuel of choice for the majority of the car

manufacturers. Since 1994, Daimler-Benz working in collaboration with Ballard, built a series of

PAGE 5

PEMFC powered cars. The first of such vehicles was fuelled with hydrogen, and in 1997

Daimler-Benz released a methanol fuelled car with a 640 km range. Plans are to offer a

commercial vehicle by 2004 . In 1996, Toyota built a hydrogen-fuelled (metal hydride storage)

fuel cell/battery hybrid passenger car, which was followed, in 1997 by a methanol-fuelled car

built on the same RAV4 platform. Renault and PSA-Peugeot Citroën are currently working on an

improved design based on the results obtained from the FEVER prototype. General Motors,

Volkswagen, Volvo, Honda, Chrysler, Nissan, and Ford have also announced plans to build

prototype PEMFC cars operating on hydrogen, methanol, or gasoline. International Fuel Cells,

Plug Power, and Ballard Power Systems are each participating in separate programs to build 50

to 100 kW fuel cell systems for cars . NECAR Program The NECAR program, initiated in 1994,

was designed in 4 phases leading to 4 prototypes of electric vehicles. The aim of this program

was to show the feasibility of such a vehicle and then to improve the technology during each of

the design phases. The latest in the series is NECAR 4, which uses the 5-seater Mercedes Class

A vehicle as the platform. Incorporating a PEMFC using hydrogen stored in a cryogenic tank, it

offers a maximum speed of 145 km/h and an operating range of 450 km. A compressor maintains

the fuel cell under pressure. Air and hydrogen pass through a humidifier and a thermal exchanger

before enter to the fuel cell. A condenser recovers the water produced by the fuel cell. An air

radiator evacuates excessive heat. NECAR 4 can accelerate from 0 to 60 km/h in 6 seconds.

Buses

In 1993, Ballard Power Systems demonstrated a 10 m light-duty transit bus with a 120 kW fuel

cell system, followed by a 200 kW, 12 meter heavy-duty transit bus in 1995. These buses use no

traction batteries and operate on compressed hydrogen as the on-board fuel. In 1997, Ballard

provided 205 kW PEMFC units for a small fleet of hydrogen-fuelled, full-size transit buses for

demonstrations in Chicago, Illinois, and Vancouver, British Columbia.

The marketing phase is envisaged for Portable Electronic Equipment

In addition to large-scale power production, miniature fuel cells could replace batteries that

power consumer electronic products such as cellular telephones, portable computers, and video

cameras. Small fuel cells could be used to power telecommunications satellites, replacing or

augmenting solar panels. Micro-machined fuel cells could provide power to computer chips.

PAGE 6

Finally, minute fuel cells could safely produce power for biological applications, such as hearing

aids and pacemakers . Unlike transportation applications where fuel cells are competing with the

internal combustion engines to indirectly produce a mechanical output, in portable electronic

equipment fuel cells are in competition with devices such as batteries to produce an electrical

output. As a result fuel cells can offer a viable alternative to batteries and several low power fuel

cells are currently being manufactured for this application.

Combined Heat and Power Systems

The primary stationary application of fuel cell technology is for the combined generation of

electricity and heat, for buildings, industrial facilities or stand-by generators. Because the

efficiency of fuel cell power systems is nearly unaffected by size, the initial stationary plant

development has focused on the smaller, several hundred kW to low MW capacity plants. “The

plants are fuelled primarily with natural gas, and operation of complete, self-contained,

stationary plants has been demonstrated using PEMFC, AFC, PAFC, MCFC, SOFC technology”

Fuel Cell Efficiency

Since fuel cells use materials that are typically burnt to release their energy, y the fuel cell

efficiency is described as the ratio of the electrical energy produced to the heat that is produced

by burning the fuel (its enthalpy of formation or Δhf). From the basic definition of efficiency:

From the basic definition of efficiency: η =W/Qin where W is given by ΔG (or NFE)

Qin is the enthalpy of formation of the reaction taking place. Since two values can often be

computed depending on the state of the reactant, the larger of the two values ( the two values (

higher “higher heating value heating value )” is used (HHV) is used (HHV).

η = ΔG/ HHV = NFE /HHV

where E is the cell voltage and I is the current

N = number of electrons transferred

F = Faraday’s constant = 96,493 coloumbs

Maximum Fuel Cell Efficiency

PAGE 7

The maximum efficiency occurs under open circuit conditions (reversible) when the highest cell

voltage is obtained when the highest cell voltage is obtained.

ηmax = ΔGo/ HHV = NFE

o /HHV

Difference between fuel cell and Battery

1. The fuel cell is a kind of energy conversion devices, at work must have an energy (fuel) input,

to output power. Common battery is an energy storage device, power must first be stored in the

battery, only output power at work, do not need to enter the energy at work, nor does it generate

electricity, the essential difference is a fuel cell and a normal cell.

2. as soon as the technical performance of the fuel cell is finalized, it can produce the electricity

and fuel supply related, as long as the supply of fuel to generate power, the discharge

characteristics are continuous. After the technical performance of the ordinary battery to

determine, only in the context of its rated output power, and must be a duplicate charge may only

after repeated use, the discharge characteristics are ongoing.

3. fuel battery ontology of quality and volume and not, but fuel battery needs a fuel store device

or fuel conversion device and subsidiary device, to get hydrogen, and these fuel store device or

fuel conversion device and subsidiary device of quality and volume far over fuel battery itself, in

work process in the, fuel will as fuel battery power of produced gradually consumption, quality

gradually reduce (means car limited fuel). Common battery no other auxiliary equipment, after

the technical performance, whether it is fully charged or drain, battery quality and volume is

essentially the same.

4. fuel cells are the chemical energy into electricity, General batteries turn chemical energy into

electrical energy, which is their common, but when fuel cells generate electricity, participate in

the reaction of the substance after reaction, constant consumption is no longer reused, therefore,

demands to enter the substance. Normal active substance with battery charging and discharging

of the battery change, repeated reversible chemical active substances, active substances not

consumed, only need to add electrolyte, and so on.

Battery - principles and operation

Batteries operate by converting chemical energy into electrical energy through electrochemical

discharge reactions. Batteries are composed of one or more cells, each containing a positive

electrode, negative electrode, separator, and electrolyte.

Batteries are classified into primary and secondary forms:

Primary batteries are designed to be used until exhausted of energy then discarded. Their

chemical reactions are generally not reversible, so they cannot be recharged. When the

PAGE 8

supply of reactants in the battery is exhausted, the battery stops producing current and is

useless.

Secondary batteries can be recharged; that is, they can have their chemical reactions

reversed by applying electric current to the cell. This regenerates the original chemical

reactants, so they can be used, recharged, and used again multiple times.

Some types of primary batteries used, for example, for telegraph circuits, were restored to

operation by replacing the electrodes. Secondary batteries are not indefinitely rechargeable due to

dissipation of the active materials, loss of electrolyte and internal corrosion.

Primary

Primary batteries, or primary cells, can produce current immediately on assembly. These are

most commonly used in portable devices that have low current drain, are used only

intermittently, or are used well away from an alternative power source, such as in alarm and

communication circuits where other electric power is only intermittently available. These have

higher energy densities than rechargeable batteries. Common types of disposable batteries

include zinc–carbon batteries and alkaline batteries.

Secondary

Secondary batteries, also known as secondary cells, or rechargeable batteries, must be charged

before first use; they are usually assembled with active materials in the discharged state.

Rechargeable batteries are (re)charged by applying electric current, which reverses the chemical

reactions that occur during discharge/use. Devices to supply the appropriate current are called

chargers.

The oldest form of rechargeable battery is the lead–acid battery. This technology contains liquid

electrolyte in an unsealed container. Common application of lead acid battery is the modern car

battery, which can, in general, deliver a peak current of 450amperes.

The sealed valve regulated lead–acid battery (VRLA battery) is popular in the automotive

industry as a replacement for the lead–acid wet cell. The VRLA battery uses an

immobilized sulphuric acid electrolyte, reducing the chance of leakage and extending shelf

life. VRLA batteries immobilize the electrolyte. The two types are:

Gel batteries (or "gel cell") use a semi-solid electrolyte.

Absorbed Glass Mat (AGM) batteries absorb the electrolyte in a special fiberglass

matting.

Other portable rechargeable batteries include several sealed "dry cell" types, that are useful in

applications such as mobile phones and laptop computers. Cells of this type (in order of

increasing power density and cost) include nickel–cadmium (NiCd), nickel–zinc (NiZn), nickel

metal hydride (NiMH), and lithium-ion (Li-ion) cells. Li-ion has by far the highest share of the

dry cell rechargeable market. NiMH has replaced NiCd in most applications due to its higher

capacity, but NiCd remains in use in power tools, two-way radios, and medical equipment.

PAGE 9

Cell Types

Many types of electrochemical cells have been produced, with varying chemical processes and

designs, including galvanic cells, electrolytic cells, fuel cells, flow cells and voltaic piles.

Wet cell

A wet cell battery has a liquid electrolyte. Wet cells were a precursor to dry cells and are

commonly used as a learning tool for electrochemistry. Wet cells may be primary cells (non-

rechargeable) or secondary cells (rechargeable).

Dry cell

A dry cell uses a paste electrolyte, with only enough moisture to allow current to flow. Unlike a

wet cell, a dry cell can operate in any orientation without spilling, as it contains no free liquid,

making it suitable for portable equipment. A common dry cell is the zinc–carbon battery.

Molten salt

Molten salt batteries are primary or secondary batteries that use a molten salt as electrolyte. They

operate at high temperatures and must be well insulated to retain heat.

Capacity and discharge

"Battery capacity" is a measure (typically in Amp-hr) of the charge stored by the battery, and is

determined by the mass of active material contained in the battery. The battery capacity

represents the maximum amount of energy that can be extracted from the battery under certain

specified conditions. However, the actual energy storage capabilities of the battery can vary

significantly from the "nominal" rated capacity, as the battery capacity depends strongly on the

age and past history of the battery, the charging or discharging regimes of the battery and the

temperature.

The energy stored in a battery, called the battery capacity, is measured in either watt-hours (Wh),

kilowatt-hours (kWh), or ampere-hours (Ahr). The most common measure of battery capacity is

Ah, defined as the number of hours for which a battery can provide a current equal to the

discharge rate at the nominal voltage of the battery.

In many types of batteries, the full energy stored in the battery cannot be withdrawn (in other

words, the battery cannot be fully discharged) without causing serious, and often irreparable

damage to the battery. The Depth of Discharge (DOD) of a battery determines the fraction of

power that can be withdrawn from the battery. For example, if the DOD of a battery is given by

the manufacturer as 25%, then only 25% of the battery capacity can be used by the load.

PAGE 10

C rate

The C-rate is a measure of the rate at which a battery is being discharged. It is defined as the

discharge current divided by the theoretical current draw under which the battery would deliver

its nominal rated capacity in one hour. A 1C discharge rate would deliver the battery's rated

capacity in 1 hour. A 2C discharge rate means it will discharge twice as fast (30 minutes).

Battery Life Time

That batteries have a finite life is due to occurrence of the unwanted chemical or physical

changes to, or the loss of, the active materials of which they are made. Battery Calendar Life is

the elapsed time before a battery becomes unusable whether it is in active use or inactive. There

are two key factors influencing calendar life, namely temperature and time. Battery Shelf Life

like calendar life is the time an inactive battery can be stored before it becomes unusable, usually

considered as having only 80% of its initial capacity. Battery Cycle Life is defined as the

number of complete charge - discharge cycles a battery can perform before its nominal capacity

falls below 80% of its initial rated capacity. Key factors affecting cycle life are time t and the

number N of charge-discharge cycles completed.

Factors Affecting the Battery Life

Chemical Changes

Batteries are electrochemical devices which convert chemical energy into electrical energy or

vice versa by means of controlled chemical reactions between a set of active chemicals.

Unfortunately the desired chemical reactions on which the battery depends are usually

accompanied by unwanted, parasitic chemical reactions which consume some of the active

chemicals or impede their reactions. Even if the cell's active chemicals remain unaffected over

time, cells can fail because unwanted chemical or physical changes to the seals keeping the

electrolyte in place.

Temperature effects

The hotter the battery, the faster chemical reactions will occur. High temperatures can thus

provide increased performance, but at the same time the rate of the unwanted chemical reactions

will increase resulting in a corresponding loss of battery life. The Arrhenius equation defines the

relationship between temperature and the rate at which a chemical action proceeds. It is given by:

k = A e-(E

A / RT)

K : rate of chemical reaction

A : frequency factor ( usually taken as a constant over small temperature ranges}.

PAGE 11

EA : activation constant (the minimum energy needed for the reaction to occur) R : Universal Gas Constant

T : temperature in degrees Kelvin

even small increases in temperature will have a major influence on battery performance affecting

both the desired and undesired chemical reactions.

Depth Of Discharge (DOD)

At a given temperature and discharge rate, the amount of active chemicals transformed with each

charge - discharge cycle will be proportional to the depth of discharge. The relation between the

cycle life and the depth of discharge appears to be logarithmic.

Charging Rate

Battery life is also influenced by the charging rate. The capacity reduction at high discharge rates

occurs because the transformation of the active chemicals cannot keep pace with the current

drawn. The result is incomplete or unwanted chemical reactions and an associated reduction in

capacity and battery life.

Cell Ageing

During the lifetime of the cell, even if there is no undesirable change in the chemical

composition of the materials, the morphology of the active components will continue to change,

usually for the worse. The result is that the performance of the cell gradually deteriorates until

eventually the cell becomes unserviceable.

Cyclic Mechanical Stresses

In Lithium ion cells the insertion or ejection of the Lithium ions into and out of the intercalation

spaces during charging and discharging causes the electrode materials to swell or contract.

Repetitive cycling can weaken the electrode structure reducing its adhesion to the current

collector causing the cell to swell. This can lead to reduction in charge capacity and ultimately

failure of the cell.

Memory Effect The so called "Memory Effect" is another manifestation of the changing morphology of the cell

components with age. It appears that some Nickel based cells particularly NiCads could

"remember" how much discharge was required on previous discharges and would only accept

that amount of charge in subsequent charges. What happens in fact is that repeated shallow

charges cause the crystalline structure of the electrodes to change as noted above and this causes

the internal impedance of the cell to increase and its capacity to be reduced.

Self-discharge

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Disposable batteries typically lose 8 to 20 percent of their original charge per year when stored at

room temperature (20–30 °C). This is known as the "self-discharge" rate, and is due to non-

current-producing "side" chemical reactions that occur within the cell even when no load is

applied.

Corrosion

Internal parts may corrode and fail, or the active materials may be slowly converted to inactive

forms.

How to Store Batteries

The recommended storage temperature for most batteries is 15°C (59°F); the extreme allowable

temperature is –40°C to 50°C (–40°C to 122°F) for most batteries. While lead acid must always

be kept at full charge during storage, nickeland lithium-based batteries should be stored at

around a 40 percent state-of-charge (SoC). This minimises age-related capacity loss while

keeping the battery operational and allowing for some self-discharge.

Storage induces two forms of losses: Self-discharge that can be refilled with charging before use,

and non-recoverable losses that permanently lower the capacity.

Li-ion has higher losses if stored fully charged rather than at a SoC of 40 percent.

Simple Guidelines for Storing Batteries:

• Primary batteries store well. Alkaline and primary lithium batteries can be stored for 10 years

with moderate loss capacity.

• When storing, remove the battery from the equipment and place in a dry and cool place. • Avoid freezing. Batteries freeze more easily if kept in discharged state.

• Charge lead acid before storing and monitor the voltage or specific gravity frequently. • Nickel-based batteries can be stored for 3–5years, even at zero voltage. The capacity drop that occurs during storage is partially reversible with priming. Nickel-cadmium stores well.

• Lithium-ion must be stored in a charged state, ideally at 40 percent. This prevents the battery

from dropping below 2.50V/cell, triggering sleep mode.

• Discard Li-ion if kept below 2.00/V/cell for more than a week. Also discard if the voltage does not recover normally after storage.

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PAGE 14

For humans, both lead and cadmium

can be taken only by ingestion or inhalation. Mercury another harmful

metals can even be absorbed through the skin, although this metal's

use in batteries has declined greatly

due to laws and regulations that have

been put in place. These harmful

substances permeate into the soil,

groundwater and surface water

through landfills and also release

toxins into the air when they are burnt

in municipal waste combustors. Moreover, cadmium is easily taken up

by plant roots and accumulates in

fruits, vegetables and grass. The

impure water and plants in turn are consumed by animals and human

beings, who then fall prey to a host of

ill-effects. Studies indicate that

nausea, excessive salivation, abdominal pain, liver and kidney

damage, skin irritation, headaches,

asthma, nervousness, decreased IQ in

children and sometimes even cancer

can result from exposure to such

metals for a sufficient period of time. In addition, potassium, if it leaks, can

cause severe chemical burns thereby

affecting the eyes and skin. Landfills

also enerate methane gas leading to

the greenhouse effect and global

climatic changes With the ever-

growing usage of batteries in today s times, their disposal issues have come

to occupy the center stage due to thei

r deteriorating effects on human ealth

and environment. Much attention

needs to be paid to solve this problem

especially by developin countries so

that a cleaner, greener and healthy world is what we and our future

generations get to live in!

Inorganic lead dust is the most significant health exposure in battery manufacture. Lead can be absorbed into the body by inhalation and ingestion. Inhalation of airborne lead is generally the most important source of occupational lead absorption. Once in the blood stream, lead is circulated throughout the body and stored in various organs and body tissues (e.g., kidney, liver, brain,

bone marrow, bones and teeth). Thus it can affect the Central Nervous System, Urinary System and also the Reproductive System Additional chemical hazards in battery manufacturing include possible exposure to toxic metals, such as antimony (stibine), arsenic (arsine), cadmium, mercury, nickel, selenium, silver, and zinc, and reactive

chemicals, etc.

PAGE 15

References

1Thomas, S. & Zalbowitz,M. “Fuel Cells- Green Power”, Los Alamos National

Laboratory, http://education.lanl.gov/resources/fuelcells/fuelcells.pdf

2Fuel Cell Technology.pdf 3Larmanie, J. & Dicks, A. 2000 Fuel Cell Systems

Explained, John Wiley & Sons