Miscellaneous “Hot” Topics
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Transcript of Miscellaneous “Hot” Topics
Miscellaneous “Hot” Topics
• Molecular Electronics
• Photonic Crystals
• Spintronics* *Sorry, there will be no time for this!
Topics
Molecular ElectronicsFrom Wikipedia:
“Molecular Electronics (sometimes called moletronics) involves the study and application of molecular building blocks for the fabrication of electronic components. This includes both passive and active electronic components. Molecular electronics is a branch of nanotechology.”
Wikipedia Continued“An interdisciplinary pursuit, molecular electronics spans physics, chemistry, and materials science. The unifying feature is the use of molecular building blocks for the fabrication of electronic components. This includes both passive (e.g. resistive wires) and active components such as transistors and molecular-scale switches. Due to the prospect of size reduction in electronics offered by molecular-level control of properties, molecular electronics has aroused much excitement both in science fiction and among scientists. Molecular electronics provides means to extend “Moore's Law” beyond the foreseen limits of small-scale conventional silicon integrated circuits.
Molecular electronics is split into two related but separate subdisciplines:
1. Molecular materials for electronics utilizes the properties of the molecules to affect the bulk properties of a material.
2. Molecular scale electronics focuses on single-molecule applications.
Prophecies of the Future of Technology are Risky!! For example:
“I think there is a world market for maybe five computers.” - T.J. Watson,
President & CEO, IBM Corporation, 1941-1956
“640K ought to be enough for everybody.”--- Bill Gates, co-Founder, Microsoft Corporation.
One of the wealthiest men in the world.
“There is no reason anyone would want a computer in their home”. --- Ken Olson, co-Founder, Digital Equipment Corporation (DEC)
“There is not the slightest indication that nuclear energy will ever be obtainable.”--- Albert Einstein, Nobel Laureate
& one of the greatest scientists who ever lived!
Source: Quantum Computing: “A short Course from Theory to Experiment, Joachim Stolze and Dieter Suter.
Source: Quantum Computing. 2004. A Short Course from Theory to Experiment. Joachim Stoltze and Dieter Stuter.
Moore’s “Law”
• The number of transistors that can be fabricated on a silicon integrated circuit--and therefore the computing speed of such a circuit--is doubling every 18 to 24 months.
• After four decades, solid-state microelectronics has advanced to the point at which 100 million transistors, with feature size measuring 180 nm can be put onto a few square centimeters of silicon
Source: European Commission. Community Research. 2004. Nanotechnology. Innovation for tomorrow’s world.
Silicon and Moore’s Law• Heat dissipation.
– At present, a state-of-the-art 500 MHz microprocessor with 10 million transistors emits almost 100 watts--more heat than a stove-top cooking surface.
• Leakage from one device to another. – The band structure in silicon provides a wide range of allowable electron energies.
Some electrons can gain sufficient energy to hop from one device to another, especially when they are closely packed.
• Capacitive coupling between components.• Fabrication methods (Photolithography).
– Device size is limited by diffraction to about one half the wavelength of the light used in the lithographic process.
• ‘Silicon Wall.’– At 50 nm and smaller it is not possible to dope silicon uniformly. (This is the end of
the line for bulk behavior.)
Moore’s “Second Law"
Plant cost Mask cost
generationX
100
0$
Silicon and Moore’s Law• Moore’s second law.
– Continued exponential decrease in silicon device size is achieved by exponential increase in financial investment. $200 billion for a fabrication facility by 2015.
• Transistor densities achievable under the present and foreseeable silicon format are not sufficient to allow microprocessors to do the things imagined for them.
Electronics Development Strategies
• Top-Down. – Continued reduction in size of bulk semiconductor devices.
• Bottom-up (Molecular Scale Electronics).– Design of molecules with specific electronic function.– Design of molecules for self assembly into supramolecular
structures with specific electronic function.– Connecting molecules to the macroscopic world.
Bottom-Up (Why Molecules?)• Molecules are small.
– With transistor size at 180 nm on a side, molecules are some 30,000 times smaller.• Electrons are confined in molecules.
– Whereas electrons moving in silicon have many possible energies that will facilitate jumping from device to device, electron energies in molecules and atoms are quantized - there is a discrete number of allowable energies.
• Molecules have extended pi systems. – Provides thermodynamically favorable electron conduit - molecules act as wires.
• Molecules are flexible.– pi conjugation and therefore conduction can be switched on and off by changing
molecular conformation providing potential control over electron flow.• Molecules are identical.
– Can be fabricated defect-free in enormous numbers.• Some molecules can self-assemble.
– Can create large arrays of identical devices.
Molecules as Electronic Devices: Historical Perspective
• 1950’s: Inorganic Semiconductors
• To make p-doped material, one dopes Group IV (14) elements (Silicon, Germanium) with electron-poor Group III elements (Aluminum, Gallium, Indium)
• To make n-doped material, one uses electron-rich dopants such as the Group V elements nitrogen, phosphorus, arsenic.
• 1960’s: Organic Equivalents.– Inorganic semiconductors have their organic molecular counterparts.
Molecules can be designed so as to be electron-rich donors (D) or electron-poor acceptors (A).
– Joining micron-thick films of D and A yields an organic rectifier (unidirectional current) that is equivalent to an inorganic pn rectifier.
– Organic charge-transfer crystals and conducting polymers yielded organic equivalents of a variety of inorganic electronic systems: semiconductors, metals, superconductors, batteries, etc.
• BUT: they weren’t as good as the inorganic standards. – more expensive– less efficient
Molecules as Electronic Devices: Historical Perspective
Molecules as Electronic Devices: Historical Perspective
•1970’s: Single Molecule Devices? • In the 1970’s organic synthetic techniques start to grow up prompting the idea that device function can be combined into a single molecule.
• Aviram and Ratner suggest a molecular scale rectifier. (Chem. Phys. Lett. 1974)
• But, no consideration as to how this molecule would be incorporated into a circuit or device.
•1980’s Single Molecule Detection.
How to image at the molecular level. How to manipulate at the molecular level.
• Scanning Probe Microsopy. STM (IBM Switzerland, 1984)AFM
Molecules as Electronic Devices: Historical Perspective
1990’s: Single Molecule Devices.
• New imaging and manipulation techniques
• Advanced synthetic and characterization techniques
• Advances in Self-Assembly »» Macroscopic/Supramolecular ChemistryThese developments have finally allowed scientists to address the question:
“How can molecules be synthesized and assembled into structures that function in the same way as solid state silicon electronic devices and how can these structures be integrated with the macroscopic regime?”
Molecules as Electronic Devices: Historical Perspective
Molecular Wire
Mechanically-Controlled Break Junction
Resistance is a few megohms. (Schottky Barrier)
Molecular Junction
Alkyl Tunnel Barriers
Conduction between the two ends of the moleculedepends on pi orbital overlap which in turn relies on a planar arrangement of the phenyl rings.
Resonant Tunneling Diode
mNDR = molecular Negative Differential ResistanceMeasured using a conducting AFM tip
Negative Differential Resistance
One electron reduction provides a charge carrier. A second reduction blocks conduction. Therefore, conduction occurs only between the two reduction potentials.
Voltage-DrivenConductivity Switch
Applied perpendicular field favorszwitterionic structure which is planarBetter pi overlap, better conductivity.
Dynamic Random Access Memory
Voltage pulse yieldshigh conductivityState - data bit stored
Bit is read as highin low voltage region
Device is fabricated by sandwiching a layerof catenane between an polycrystalline layer of n-dopedsilicon electrode and a metal electrode. The switch isopened at +2 V, closed at -2 V and read at 0.1 V.
Voltage-Driven Conductivity Switch
High/Low Conductivity Switching DevicesRespond to I/V Changes
Voltage-Driven Conductivity Switch
n-type
Voltage-Driven Conductivity Switch
Molecular Wire Crossbar Interconnect(MWCB)
Nanotube conductivity is quantized.Nanotubes found to conduct current ballistically and do not dissipate heat. Nanotubes are typically 15 nanometers wide and 4 micrometers long.
Carbon Nanotubes
Gentle contact needed
Molecular Self-Assembly
• Self-Assembly on Metals – (e.g., organo-sulfur compounds on
gold)
• Assembly Langmuir-Blodgett Films– Requires amphiphilic groups for
assembly
• Carbon Nanotubes– Controlling structure
Cyclic Peptide Nanotubes as Scaffolds for Conducting DevicesHydrogen-bonding interactions promote stacking of cyclic peptidesPi-systems stack face-to-face to allow conduction along the length of the tube
Cooper and McGimpsey - to be submittedCYCLIC BIOSYSTEMS
Spontaneous self-directed chemical growth allowing parallel fabrication of identical complex functional structures.
Molecular Electronics:Measuring single molecule conduction
Kushmerick et al. PRL 89 (2002) 086802
Cross-wire
Wang et al. PRB 68 (2003)
035416
Nanopore STM Break Junction
B. Xu & N. J. Tao Science (2003) 301, 1221
Electromigration
H. S. J. van der Zant et al. Faraday Discuss. (2006)
131, 347
Nanocluster
Dadosh et al. Nature 436 (2005) 677
Scanning Probe
Cui et al. Science
294 (2001) 571
Reichert et al. PRL 88 176804
Mechanical Break Junction
Single-Molecule ConductivityL
ELECTRODER
ELECTRODEMOLECULE
L ELECTRODE
R ELECTRODE
MOLECULE
Fermi energy
Molecular Orbitals
eV
V
L ELECTRODE
R ELECTRODE
MOLECULE
I
Molecular Orbitals
Elastic
InelasticV
h/e V
h/e V
h/e V
IdI
/dV
d2 I/dV2
h/e
Finding a true molecular signature:Inelastic Electron Tunnelling Spectroscopy (IETS)
Molecular level structure between electrodes
en ergy
LUMO
HOMO
“The resistance of a single octanedithiol molecule was 900 50 megaohms, based on measurements on more than 1000 single molecules. In contrast, nonbonded contacts to octanethiol monolayers were at least four orders of magnitude more resistive, less reproducible, and had a different voltage dependence, demonstrating that the measurement of intrinsic molecular properties requires chemically bonded contacts”.
Cui et al (Lindsay), Science 294, 571 (2001)
-1
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2
3
4
5
6
-1 -0.5 0 0.5 1
I / a
rb. u
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0.0 - 0.5
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V (V)
Ratner and Troisi, 2004
Dynamics of current voltage switching response of single bipyridyl-dinitro oligophenylene ethynylene dithiol (BPDN-DT) molecules between gold contacts. In A and B the voltage is changed relatively slowly and bistability give rise to telegraphic switching noise. When voltage changes more rapidly (C) bistability is manifested by hysteretic behavior
Lortscher et al (Riel), Small, 2, 973 (2006)
Chem. Commun., 2006, 3597 - 3599, DOI: 10.1039/b609119aUni- and bi-directional light-induced switching of
diarylethenes on gold nanoparticlesTibor Kudernac, Sense Jan van der Molen, Bart J. van Wees and Ben L.
Feringa
“In conclusion, photochromic behavior of diarylethenesdirectly linked to gold nanoparticles via an aromatic spacer hasbeen investigated. Depending on the spacer, uni- (3) or bidirectionality(1,2) has been observed.”
Switching with light
Current–voltage data (open circles) for (a) openmolecules 1o and (b) closed molecules 1c
Nanotechnology 16 (2005) 695–702Switching of a photochromic molecule on gold electrodes: single-moleculemeasurementsJ. He, F. Chen, P. Liddell, J. Andr´easson, S D Straight, D. Gust, T. A. Moore,A. L. Moore, J. Li, O. F Sankey and S. M. Lindsay
Temperature and chain length dependence
Giese et al, 2002
Michel-Beyerle et al
Selzer et al 2004
Xue and Ratner 2003
Electron transfer in DNA
DNA-news-1
DNA-news-4
DNA-news-2
Conjugated vs. Saturated Molecules: Importance of Contact Bonding
Kushmerick et al., PRL
(2002)
2 -vs. 1-side Au-S bonded conjugated system gives at most 1 order of magnitude current increase compared to 3 orders
for C10 alkanes !
SS S/AuAu/S
10-4
10-3
10-2
10-1
100
101
102
0.0 0.2 0.4 0.6 0.8 1.0
Current (nA)
Tip bias (V)
Curre
nt (n
A)
SS S/AuAu//
Au//CH3(CH2)7S/Au
Au/S(CH2)8SAu
Positive bias
negative bias
Lindsay & Ratner 2007
Where does the potential bias falls, and how?
•Image effect•Electron-electron interaction (on the Hartree level)Vacuu
mExcess electron density
Potential profile
Xue, Ratner (2003)
Galperin et al 2003
L
Galperin et al JCP 2003
Experiment Theoretical Model
Experimental i/V behavior
Experimental (Sek&Majda)
junction Ratio of current: i(-1.0 V)/i(+1.0 V)a
Hg-SC12/C12S-Au 0.98 0.13
Hg-SC12/C10S-Au 1.03 0.07
Hg-SC16/C12S-Au 1.22 0.16
Hg-SC12/C9S-Au 1.44 0.20
Hg-SC16/C10S-Au 1.34 0.19
Hg-SC16/C9S-Au 2.03 0.27
aCurrent at the negative bias refers to the measurement with the Hg side of the junction biased negative relative to the Au side.
Cui et al (Science 2001):
The sulfur atoms (red dots) ofoctanethiols bind to a sheet of gold atoms (yellow dots), and theoctyl chains (black dots) form a monolayer. The second sulfuratom of a 1,8-octanedithiol molecule inserted into themonolayer binds to a gold nanoparticle, which in turn is contacted by the gold tip of the conducting AFM.
J. G. Kushmerick et al., Nano Lett. 3, 897 (2003). A. S. Blum, J. G. Kushmerick, et al., The J. Phys. Chem. B 108, 18124 (2004).
1-nitro-2,5-di(phenylethynyl-4’-mercapto)benzene
Y. Selzer et al., Nano Letters 5, 61 (2005).
Red – single molecule; black – molecular layer. Dashed black is molecular layer per molecule
Red – single molecule; black – molecular layer per molecule
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Resonant tunneling?
Carbon Nano Tubes (CNT)
Issues:•Production of Single Walled CNTs yield a mixture of types (dimensions to less than 1nm)
• Metallic• Semiconductive
•Separation of types is time consuming
Potential Solutions•Continue development efforts
Benefits:•Novel electronic devices•High temperature applications•Improved microscopy
Solar Cells (Organic)
Issues:•Efficiencies•Material development•Manufacturing processes
Potential Solutions•Development of organic plastics with improved efficiency•Development of adsorptive dyes•Flexible conductors•Enhanced property covering material
Benefits:•Low cost energy•Inexpensive to manufacture yielding to wide spread applications
Credit: Nicole Cappello and the Georgia Institute of Technology
New Material Properties
Issues:•Unanticipated properties are being found in nano materials – Example:
• Thirteen atoms of Silver have been shown theoretically to be magnetic
• Thirteen atoms of Platinum have been experimentally shown to be magnetic
Potential Solutions:•Quantify and classify the material properties in the range between bulk material properties and quantum phenomena•Establish a program to employ theoretical projections to verify experimental data
Benefits:•Improve the time to develop nano based devices, due to eliminating the duplication of research efforts•Creation of new products based on applying novel nano propertiesExample: The creation of new memory devices that are 100x more dense than current technology
Silver properties reported May 30, 2006 in NanoTechWebPlatinum experiments reported by University of Stuttgart
Metrology
Issues:•Imaging realm is at limits of resolution, in the 1nm range•Time per image is long >one hour•Effective imaging applications require multiple images in minutes or less
Potential Solutions:•New solutions for metrology•Enhancements to equipment•New technologies
Benefits:•Improved resolution of material properties•Capability to employ in manufacturing processes•If one can not measure something, it can not be manufactured
Aberration Corrected HR-TEM Korgel Group Si Nanowire
Au dot structure&
Nanowire Twinning
Metrology
Issues:•Imaging is slow and computations are time consuming•Unique structures can not be verified•No validation results•Dimensions extend to below 1nm
Potential Solutions•Development and execution of validation plan•Improved algorithms•Improved equipment for rapid imaging
Benefits:•Improved understanding of materials•Ability to identify unique nano structures•Ability to create and verify novel materials
Not corrected
Corrected
Sloan, et al., MRS Bulletin, April 2004
Aberration Corrected TEM ImagingAberration Corrected TEM Imaging
K & I in nanotube
Proposal for Molecular Computers Nanotechnology+ cheap+ high-density+ low-power– unreliable
Computer architecture+ vast body of knowledge – expensive– high-power
Reconfigurable Computing+ defect tolerant+ high performance– low density
++++ ++
__
_
_
Reconfigurable Computing• Back to ENIAC-style computing
• Synthesize one machine to solve one problem
Defect Tolerance
Despite having >70% of the chips defective, Teramac works flawlessly.
Compilation has two phases:• defect detection through self-testing• placement for defect-avoidance
Lattice of covalently bonded carbon atoms
Single-walled Carbon Nanotube d d = 0.4nm -
10nm
L
L = ?
Nano-wires
• carbon nanotubues, Si, metal• >2nm diameter, up to mm length• excellent electrical properties
A carbon nanotube: one molecule
Independent Claims
1. A transistor that uses a carbon nanotube ring as a semiconductor material, the carbon nanotube ring having semiconductor characteristics.
12. A transistor that uses a carbon nanotube ring as an electrode material, the carbon nanotube ring having conductivity or semiconductor characteristics.
18. A carbon nanotube ring having p-type semiconductor characteristics.
19. A semiconductor device in which a carbon nanotube ring having p-type semiconductor characteristics is placed on an n-type semiconductor substrate thereof.
Alternatives for transistors Carbon nanotube transistors Single electron transistors (SET)
Memory devices MRAM (various different approaches Phase change RAMPhotonicsNano-electromechanical system (NEMS)Fuel cellsThermo-photovoltaicsQuantum computersSoftware
Nanotechnology in Electronics
Nano-switch
Nano-switch Between Nano-wires
Self-assembly