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NanoDevices and NEMS

Nano Devices

• Nano devices are in the early stages in

development.

• Lithography; optical, electron beam and X-

ray each has practical problems and

constraints.

• A major obstacle facing nanotechnology is

the lack of effective processes for building

the nanoscale structures.

Nanodevices

• Nano-imprint lithography can produce patterns on a surface having 10-nm resolution at low cost and high rates. It does not required the use of sophisticated radiation beam generating patterns.

• Scanning tunneling microscope (STM) and atomic force microscope (AFM) have been used to build nano sized structures atom by atom on the surface of materials.

• The nanomanipulation with scanning probe microscopes (SPMs) provide an effective approach for constructing nanostructures from the bottom up, by assembling building blocks that result from chemical synthesis.

• Single-tip SPM manipulation is useful for fabrication of prototypedesigns. Long time before the mass production of any nanodevice, prototyping is needed to ensure that the device will work as intended, and to optimize its parameters, like geometry.

• Single-tip SPM may also be used to repair or modify structures built by other techniques.

Methods of Synthesis

• 1. Top-Down Approach

– Lithography

• 2. Bottom-Up Approach

– Assemble from units

– Compact powders

– Solid-Solution precipitation

– Deposition and Coatings

– Electro-depositions

Nanoparticles Nanowires

• Scanning probe instruments like Atomic Force Microscope (AFM)

• Lithography Techniques:– Dip-Pen Lithography

– E-Beam Lithography

– Ion-Beam Lithography

– Soft Lithography (nano printing)

• Plasma arcing

• Laser Ablation

• Chemical Vapor Deposition

• Electro-deposition

• Sol gel synthesis

• Ball milling, and the use of natural nanoparticles

• Self Assembly techniques


Application of the nanowires in electronics, optics,

mechanics, and sensing technology is very broad. These

days they are the building blocks for many nano devices.

They have been used as a master in nano-imprinting, and

as a masking layer for dry etching into other materials.

They are used as a template in a self-assembly technology,

e.g., Au nanowires are used to assemble biological

species.


• As nanowires with various materials with

different propertied are produced, makes

the potential applications of nanowires

unlimited.

Sensing Applications

Materials Applications

AuDetection of Mecurry in water,

Biosensors , green house gases,

Ag Explosive and drug sensors

Single crystalline siliconBiological and chemical sensors for life sciences, health care,

pharmacy

Pd H2 gas sensor

Semiconducting oxides: ZnO, SnO2, and In2O3 CH4, NH3, CO, NOx, O2 gas sensors

BiMagnetic field sensor,

Biomagnetic sensors

silicon nanowires

functionalized with palladiumHydrogen gas

Nanowires and Energy

materials Applications

ZnO Piezoelectricity

Graphene coated with ZnO Solar cell

Semiconductor nanowires grown on

gold nanoparticles

Solar cell

Copper nanowires Flexible conductors

Semiconductor nanowires Light concentrator

CdS nanowires coated with CuS Solar cell

Silicon nanowires Hydrogen storage

Silicon nanowires grown on Stainless

steel

High capacity batteries

Doped ZnO nanowires Color centers, Single Photon Lasers

Nanowires and Elctronics

Gold nanowires Electronic contacts

Conducting nanowires Flat panel displays to be flexible

Metallic and semiconductor nanowires transistors

Nanowires made of iron –nickel alloys Dense memory devices

Applications

• Nanoelectronic Devices.

• Optoelectronic Devices Based on

Nanostructures

• Sensors

• Actuators

• NEMS

• Molecular and Biological Devices.

Application of nano particles

• Optical: Nanoparticles could be

engineered and used for anti-reflection

product coatings, producing a refractive

index for various surfaces, and also

providing light based sensors for use in

diagnosing cancer.

• .


• Magnetic. Nanoparticles have the potential

to increase the density of various storage

media, and also when magnetized they

can improve the detail and contrast of MRI

images as previously alluded to.


• Thermal. Specifically engineered particles

could improve the transfer of heat from

collectors of solar energy to their storage

tanks. They could also enhance the

coolant system currently used by

transformers in these types of processes.


• Mechanical. Nanoparticles could provide

improved wear and tear resistance for

almost any mechanical device. They could

also give these devices previously unseen

anti-corrosion abilities, as well as creating

entirely new composites and structural

materials that are both lighter and stronger

than those we use today.


• Electronic. Because of their tiny size,

nanoparticles are inherently poised to aid

in the production of high performance

delicate electronics; they may provide not

only materials with a high rate of

conductivity, but also sleeker parts for

small consumer electronics like cell

phones. And when it comes to advertising,

nanoparticle electronics can create digital

displays that are more electricity-efficient,

less expensive to produce, brighter in

Nanoparticles and Energy

• Nanoparticle batteries would be longer-lasting and have

a higher energy density than those we use today.

• Metal nanoparticle clusters could also have revolutionary

applications for hydrogen storage

• They could also produce extremely efficient fuel cells by

acting as electrocatalysts for these devices.

• Nanoparticles may also pave the way for practical and

renewable energy; they have already demonstrated an

ability to improve solar panel efficiency many times over.

Nanoparticles and Biomedical

You may soon find that your wounds are

dressed with antibacterial coatings of silver

nanoparticles. Nanoparticles have also been

used to produce “quantum dots,” which can

detect diseases, as well as interactive foods

and drinks that change flavor and color

based on your tastes, or in some cases may

even alter their nutrient content based on

your state of health.

•Nanoparticles in polymer composite materials for application in baseball

structure to cars, .. airplane, satellites…

•Nanoparticles additives to or surface treatments of fabrics help them resist

wrinkling, staining, and bacterial growth,

•Nanoparticles or nanoscale thin films on eyeglasses, computer and camera

displays, windows, and other surfaces ..

•Nanoparticles materials in cosmetic products provide greater clarity or

coverage; cleansing..

•Nanoparticle materials in the food industry ..

•Nanosensors built into plastic packaging can warn against spoiled food.

•Nanoparticles are used to develop sensors to detect salmonella, pesticides,

and other contaminates on food

•Nanoparticle materials in automotive products include high-power rechargeable

battery systems and extended range.

•Nanoparticle materials make superior household products such as degreasers and

stain removers; environmental sensors, alert systems, air purifiers and filters;

antibacterial cleansers; and specialized paints and sealing products.

•Nanostructured ceramic coatings exhibit much greater toughness than

conventional wear-resistant coatings for machine parts. In 2000, the U.S. Navy

qualified such a coating for use on gears of air-conditioning units for its ships,

saving $20 million in maintenance costs over 10 years. Such coatings can extend

the lifetimes of moving parts in everything from power tools to industrial machinery.

•

•Nanoparticles are used increasingly in catalysis to boost chemical reactions.

•Nanoscale transistors that are faster, more powerful, and increasingly

energy-efficient; soon your computer’s entire memory may be stored on a

single tiny chip.

•Magnetic random access memory (MRAM) enabled by nanometer‐scale

magnetic tunnel junctions that can quickly and effectively save even

encrypted data during a system shutdown or crash, enable resume‐play

features, and gather vehicle accident data.

•Displays for many new TVs, laptop computers, cell phones, digital cameras,

and other devices incorporate nanostructured polymer films known as

organic light-emitting diodes, or OLEDs. OLED screens offer brighter images

in a flat format, as well as wider viewing angles, lighter weight, better picture

density, lower power consumption, and longer lifetimes.

•Other computing and electronic products include Flash memory chips for

iPod nanos; ultrar esponsive hearing aids; antimicrobial/antibacterial coatings

•Nanostructured materials are being pursued to greatly improve hydrogen

membrane and storage materials and the catalysts needed to realize fuel cells

for alternative transportation technologies at reduced cost. Researchers are also

working to develop a safe, lightweight hydrogen fuel tank.

•Various nanoscience-based options are being pursued to convert waste heat in

computers, automobiles, homes, power plants, etc., to usable electrical power.

•An epoxy containing carbon nanotubes is being used to make windmill blades

that are longer, stronger, and lighter-weight than other blades to increase the

amount of electricity that windmills can generate.

•Researchers are developing wires containing carbon nanotubes to have much

lower resistance than the high-tension wires currently used in the electric grid

and thus reduce transmission power loss.

•To power mobile electronic devices, researchers are developing thin-film solar

electric panels that can be fitted onto computer cases and flexible piezoelectric

nanowires woven into clothing to generate usable energy on-the-go from light,

friction, and/or body heat.

•Energy efficiency products are increasing in number and kinds of application.

In addition to those noted above, they include more efficient lighting systems

for vastly reduced energy consumption for illumination; lighter and stronger

vehicle chassis materials for the transportation sector; lower energy

consumption in advanced electronics; low-friction nano-engineered lubricants

for all kinds of higher-efficiency machine gears, pumps, and fans; light-

responsive smart coatings for glass to complement alternative heating/cooling

schemes; and high-light-intensity, fast-recharging lanterns for emergency

crews.

• Nanotechnology has the real potential to revolutionize a wide array of

medical and biotechnology tools and procedures so that they are more

personalized, portable, cheaper, safer, and easier to administer. Below are

some examples of important advances in these areas.

• Quantum dots are semiconducting nanocrystals that can enhance biological

imaging for medical diagnostics. When illuminated with ultraviolet light, they

emit a wide spectrum of bright colors that can be used to locate and identify

specific kinds of cells and biological activities. These crystals offer optical

detection up to 1,000 times better than conventional dyes used in many

biological tests, such as MRIs, and render significantly more information.

• Nanotechnology has been used in the early diagnosis of atherosclerosis, or

the buildup of plaque in arteries. Researchers have developed an imaging

technology to measure the amount of an antibody-nanoparticle complex that

accumulates specifically in plaque. Clinical scientists are able to monitor the

development of plaque as well as its disappearance following treatment

(see image).

Nanoelectronics DevicesCarbon nanotube field effect transistors (CNFET)

• A carbon nanotube device is similar to a MOSFET where a gate is used to control the flow of current through the device by varying the field through a channel. The new idea here is the mechanism of transport of electrons from the source to drain. Instead of having a channel whose field can be controlled by a gate electrode, these devices have a tiny tubular structure of carbon nanotube. Carbon nanotube with diameter 2nm have extremely low resistance and thus can carry large current without heating, so it could be use as interconnectors. It also has very high thermal conductivity means that they can also serve as heat sink i.e. allows heat to be rapidly transferred away from the chip.

Carbon Nanotube Single-Electron Transistor (SET)

Single-electron transistors (SETs) are transistors whose drain to source

current is composed of only one electron. With only one electron

traveling, the power consumption is greatly reduced.

It has been discovered that SETs will have a very tough time replacing

MOSFETs because of their low gain, high impedance, and higher

sensitivity to background noise

The SETs contribution is high charge sensitivity, while the MOSFETs

provide the gain and low impendence needs for real life application.

Another important application for SETs is charge-sensing applications

such as the readouts for both memories and charge-coupled devices in

metrology and astronomy where precision charge measurements are

required.

Electronic Devices

A Carbon nanotube field effect transistors (CNFET)

Electronic Devices

Single-Electron Transistors

Coulomb Blockade

V<VthV>Vth

I-V characteristic of the SET

EF

The first gate is of a standard planar design that is used for the input of the transistor. The

second gate is a parallel plate type of gate, used to tune the background charge. The

arrows point to the small points where the source and drain make contact. These contact

points are the tunneling junctions that isolate the conduction island.

pnp device

ε is steepness of the barrier

CNT Switches

• Due to the thermal activation of electrons over the energy gap results in empty valence states and occupied conduction states.

• The off-state conductance of semiconductor CNT is non-zero, and it is depend on the temperature and the band gap.

Effects of Doping on CNT Structure

• The geometry, band structure, and binding

energies of CNT is strongly depend on the

doping of some atoms or molecules.

• The effects of hydrogen doping is very

depend on the pattern of hydrogenation.

Effects of Doping on CNT

O. Gulseren, et al. 2002

T. Yildirim, Phys. Rev.B, 64, pp

75404-1/, 2001

Hydrogen

Optoelectronic Devices

• Light emission from CNTs

IRThe transistor has two Schottky

barriers at the source and drain.

Electron and holes can inject into

the intrinsic CNT, inducing light

emission with wavelength of 1.5 -

2 micron. It was found that IR

luminescence emitted from a

very small region. Its position can

be controlled by applied gate

voltage. The intensity and the

shape of IR spot can be

monitored.

The IRL is optimized

when VG = VD/2 and the

source is grounded

Nanowires and Optoelectronic Devices

substrate

Semiconductor

NW

P type SNW

N type SNW GaN CdS CdSeelectrodes

ZnO NW

light

Buckytube Electro-

mechanical

NanoActuators

Baughman et al., Science 284, 1340 (1999)

~1% length change per volt

Memory device based on 2 layers of carbon nanotubes,

in which the top layer is suspended above the lower

layer. A 3D view, gold structures are the contacts, and

the black cubes are nonconductive supports

Conductivity and molecular perfection

allows nanotubes to be used as switches

and memory elements.

NEMS

• NEMS research involves design

prototyping, fabrication, control,

programming, and applications.

• Design of any NEMS or MEMS involves

Sensors, Actuators, and Control.

NEMS

• Sensors, which sense chemicals,

mechanical, electrical, and any other

physical changes, had so far very little

progress.

NEMS

• Sensing Methods

Chemical, due to interaction of nanostructures with environment, impurities, oxidation,..

Electrical, effect of environment on electrical properties of nanostructures

Mechanical, tactile, pressure, stress,..

Optical, effect of environment on optical properties like photoluminescence, spectroscopic parameters

Biological, use of bacteria to detect some chemical or physical properties

Smart Materials, PZT, PVDF

Sensors

• Tactile sensing using functionalized SPM cantilevers is investigated.

• Fluorescent probes with nano sizes are reported.

• Biological species like bacteria may be used to sense light or magnetic fields.

• Sensors technologies, in particular chemical and biochemical sensing are evolving very fast.

Sensors

• Nanotubes and nanowires are used to sense the chemicals and gases.

• Chemical sensors based on microscopic cantilevers are investigated. The detection mechanism is based on either by detecting the deflection of a cantilever caused by surface stresses that arise when a chemical species binds to one of the two opposing sides of the cantilever, or by measuring the shift in the resonance frequency of a vibrating cantilever when its mass increases because of the deposition of the molecules being detected.

Gas SensorsHow does a gas sensor work?

• Gaseous species are adsorbed at the

surface of materials (catalysts)

• Some physical properties of catalysts are

changed upon adsorption of gases

• By monitoring those physical parameters,

one can detect the gas type and measure

its concentration

Gas Ionization Sensors

1. The precise breakdown voltage provides the fingerprint for the gas to be identified; it is well established that at constant temperature and pressure every gas has a unique breakdown electric field.

2. Because this technique does not involve adsorption / desorption of gases, the sensor displays a fast response and is not limited by considerations of reversibility and recovery.

Methods of Operation

Breakdown Voltage

(Vb)

Blunt-tip AuNRs

or

Whisker/Al2O3-covered AuNRs

at the cathode

Tunneling Field-Ion Current

IFI = f(UI)

Whisker/Al2O3-covered AuNRs

at the anode

AuNRs are used as field-enhancing elements

(a) (b)

A

A

DC

DC

Ic or Ia

Ia or IcSMU #1

SMU #2

Device Schematic

Counter electrode

Gas vents

Au nanowires

Ag/Ti coated Si substrate

Positive corona / Field-Ion currentNegative corona / Field-Emission current

Electron avalanche current

Geometrical Field Enhancement

d

VFM macroscopic field

V

d

Geometrical/Mathematical models for

field enhancing: (top) definition of the

macroscopic field in a parallel-plate

capacitor; (right) enhancement factor

on a hemisphere on a post structure

resembling a nanotube or nanowire

R.G. Forbes et al.

Ultramicroscopy 95, 57–65 (2003).

M

loc

F

F

L

9.015.22.1

field-enhancement

factor

protrusion length to

base ratio

V

dFloc

2

L

VFloc field factor

200

250

300

350

400

450

500

550

0 2 4 6 8 10

Pressure (P ) [torr]

Bre

akd

ow

n v

olta

ge

(V

b)

[V]

0.E+00 1.E-04 2.E-04 3.E-04 4.E-04 5.E-04 6.E-04

Concentration [mol/liter]

O

Air

N

Ar

2

2

Sensor #1

Breakdown characteristics of Au-only device

Vb–P curves of the NWGIS (AuNWs at the cathode) for Ar, N2, Air and O2.

The minimum breakdown voltage (Vb)min, observed here, occurred within a

pressure range of 0.3 < P < 0.5 torr which is far less than the pressures at

which Vb is minimum in uniform fields.

R. B. Sadeghian & M. Kahrizi,

SNA 137, 248–255, (2007).

The Two-Step Field Enhancement Approach

rt2

l2

l1

r t1

1 1 1 1, t appE l r E

2 2 2 2 1 1 1, ,t t appE l r l r E

appE V d

d

Tunneling Field Ionization

He Atom

He+ ion

rtip

R

Cathode

Anode

He Atom

rtip

He+ ion

12

3

tipr

RM

Theory

µ-spheres

100 nm

Nanowhiskers

Tunneling Field Ionization on Semiconductors

EC

EV

EF

fS

f fS UI

atom

xc

Valence band

ES = Evac' erEvac

surface

states

lS

e-

c

T.T. Tsong, Surf. Sci. 85, 1–18 (with modifications).

Ic SU Ex ff

l

ef r

S

E

1/ 21/ 2exp I cD A U BE x

Theory

Anodized Aluminum Oxide (AAO)or

Porous Anodic Alumina (PAA)

Expansion of aluminum during anodic

oxidation. On the left the level of the

unoxidized metal surface is depicted.

O. Jessensky et al.,

APL 72, 1173–1175, (1998).

SEM micrographs of cell configuration in barrier layer with

different intervals of 100 nm (a), 150 nm (b), and 200 nm (c).

Anodization voltage were 40 V (a), 60 V (b), and 80 V (c).

Anodization was conducted in 0.3 M oxalic acid of 17 °C for

(a) and (b), and 0.04 M oxalic acid of 3 °C for (c). Thickness

of the oxide films was approximately 3 mm.

H. Masuda et al.

Appl. Phys. Lett., 71,

2770–2772, (1997).

Nanowires

The template-assisted electrochemical

growth

PAA membrane nanopores

Sputtered Au

Electrochemical growth

Template removal

Nanowires

Self-Standing AuNWs

Nanowires

Super tips Tubular Structures

Nanowhiskers

Nanowires

Photographs

Film of vertically aligned freestanding

gold nanowire/nanorods bonded on an

Ag-Ti coated silicon substrate, after the

embedding template has been removed

A snapshot of the

Gas Ionization Sensor

Breakdown characteristics

200

250

300

350

400

450

500

550

0.01 0.1 1 10


Bre

akdow

n v

oltage (

Vb

) [V

]

O

air

N

Ar

2

2

36

37

38

39

40

41

42

0.0001 0.001 0.01 0.1 1


Bre

akdow

n V

oltage (

Vb

) [V

]

He

Ar

O2

Room temperature Vb – P characteristics of our sensor, in O2

, air, N2 and Ar, when the embedding template is completely

removed (semilog scale). The dashed lines show the average

Vb of each gas for P 1 torr.

Room temperature Vb – P characteristics of our sensor, in He,

Ar and O2, when the dissolution treatment was incomplete

(semilog scale). The breakdown voltages are considerably

reduced compared to the former case due to presence of

alumina on AuNWs.

Au-only Au/Al2O3 with whiskers

0

1

2

3

4

5

6

7

8

9

10

0 10 20 30 40 50

V (V)

I (

10

-5 A

)4E-06

0.01

0.09

37

Sensor #7

Full range I – V

(AuNWs at the cathode)

Fowler-

Nordheim

tunneling

Quasiballistic

emission

Formation of

coronabreakdown

Results

ZnO nanowires

Applications

E-Nose

Explosive & Poisonous

gases

Control

air quality

Vacuum

control

Device Optimization

I1 I2 I3 ...

DC

High FieldLow Field

Improved Vents Tilted Counter Electrode

Multigrid Electrode

Applications: Odor Sensors, Explosive &

Poisonous Gases, …

Grid of

Sensors

Pattern

Recognition

System

Analysis & Control

System

PreprocessorGas Flow

(Odor)

66

Biosensors

• AFM of Au-PS

colloidal crystal (Au

can’t be seen here –

too small)

• Ordered multilayers of

composites 18-20

layers

PS microspheres: 510 nm; Au: 5 nm

Vertical deposition 55oC, 3 days

Morphology of Au Nanostructures

67

• Sample prepared with 700 nm PS

Spheres – not annealed

• Nanorings and nanoholes present

• Aggregation effects around holes

•Size of holes is less than the size of

spheres

Results

Morphology cont’d

• Fabricated many samples – PS sphere sizes: 100 nm, 200 nm, 500 nm and 700 nm

• Resulted in hole and ring structures

• Ring structures are not continuous ring structures - made of nanoparticles which do not touch one another

• Some samples were annealed and some were not

• Observed aggregation effects around holes for certain samples

• Observed PS spheres not completely removed in some cases

• Nanohole/nanoring array prepared with 530 nm PS and 20 nm Au – more rings

• Sample annealed at 900C for 20 min

• Inset: enlarged image of a region where PS spheres were not completely removed. - Au nanoparticles are around and on the top of the spheres

68

Results

Morphology cont’d



• Nanohole present – evenly

distributed



• Nanoholes present – some imperfections

Gold Nanostructures

71

Results

UV-VIS Spectrum of a Nanohole/Nanoring Array -

Sensitivity of the Structure (l/n)

A) In water and B) 2-PROPANOL (sample annealed for 30 min at

110C)

Au LSPR band red-shifted by 8 nm in 2-propanol S = 340 nm/RIU

72

Results

Biomolecular Interactions cont’d

• ADDL deposited on

functionalized gold

structures

• Left in contact with

sensor platform for

24 hours

• Large shift of

LSPR band

observed Δλ = 30nm

Δλ = λ in PBS without ADDL – λ in

PBS with ADDL

73


Spectra corresponding to the protein-antibody interaction:

A) spectrum of the functionalized substrate using Au that

was prepared in the lab B) spectrum of the antibody

adsorbed on the substrate C) spectrum of the previously

absorbed antibody followed by the adsorption of the protein

on the substrate

• Observed shift of +10 nm when antibody adsorbed

• After protein adsorption no additional shift but observed

shoulder around 600 nm

74

Spectrum corresponding to the protein sandwiched between two antibody

layers: A) Spectrum of the functionalized substrate with antibody and protein

adsorption – using Au that was prepared in the lab B) spectrum when an

additional antibody layer is adsorbed on the system corresponding to trace A


Additional antibody layer results in shift of +10 nm

NEMS

• Actuators, are moving parts of any micro or nano devices.

• Powers are mechanical, electrical, optical or chemical, which among them electrical and optical are most convenient.

• CNT, nanowires, nano-cantilevers,… can be used as the actuators.

• Molecular actuators either from a single molecules or supramolecules are fabricated using chemical synthesis. They are atomically precise.

Nano cantilever

NEMS

• Electrical &Electromagnetic Actuators

Coulomb interactions including weak interactions

Capacitive interactions

Dipole- Dipole interactions

Dipole Interaction with Electric Field

Magnetic Field Interactions

Magnetic dipole-dipole interactions

Magnetostrictive Materials (ferromagnetic materials)

NEMS, Electrical Actuators

• Coulomb interaction between two charged particles

• Superposition effect

• The electric field induced by a charge like Q

• Forces exerted on a charge by electric field

2

21

r

qqkF

...321 FFFFT

2r

QkE

qEF


• The distribution of charges in a body is characterized by a parameter called dipole moment

p = LQ (p is a vector

directed from –ve

charge toward +ve

charge)

Applying electric field induces a torque T = p x E (T, p, and E are vectors)


F+ = EQsin(θ)

F- =- EQsin(θ) The net force is

zero, and as a

result of this

torque the rod will

rotate around

centerT =∑ r x F = -1/2 L Q Esin(θ) -1/2LQEsin(θ)

= - LQ E sin(θ)


• The energy of the two

dipoles p1 and p2 at

angles θ1and θ2

measured from the

line connecting the

dipoles is given by

3

21

3

21int

).)(.(3.

r

rprp

r

ppE eraction


• Similar to electric dipoles, there exist a magnetic dipole between the two magnetic poles.

• A current carrying loop of radius a induces a magnetic dipole moment m

• Electrons orbit around nucleus also induces current and dipole moments

2aIm

r

qvI

2

2

qvrIAm


• Torque on a current loop is a twisting force or moment about an axis.

N = r x F = m x B (vectors)

N is the torque, m is magnetic dipole moment and B is the field strength

( The electric dipole lines up parallel to the direction of E, the magnetic dipole lines up parallel to the direction of B due to the action of the torque)


+-

-

-

- +

+

+

+

+

-

Electrophoresismigration of dispersed particles on a fluid under the influence of

an uniform electric field

Coulomb Interaction


+

+

+

+

+ - - - - - -

-

-+

+

Dielectrophoresismigration of dispersed particles in a fluid under the influence

of a non-uniform electric field


0o

27

0o

180o

90o

-Q Q+

E

Electrorotation

NEMS, Optical forces

• Optical actuation is due to:

Direct conversion of optical energy to mechanical (thermal) energy

The interaction of Electric component of light with the charged particles

( Laser tweezers and laser spanners)

Molecular or Structural changes in nanostructures, cis-transisomerization

Photostrictive Materials (opto-piozoelectric)

Photorefractive crystals; Actuation occurs as a result of mechanical deformation of the crystal caused by photogenerated electric charge distribution due to piezoelectric effect.

NEMS

Isomerization

• Isomers are molecules having the same

atoms and the same bonds but different

equilibrium structure (geometry).

• Isomers can switch from one structure to

other if they subjected to external stimuli

like light, electric field, heat,…

NEMS

• The rotation happens as the light causes a cis-

trans isomerization. The resulting conformation

is unstable and spontaneously changes to a

more energetically-favorable conformation,

continuing the rotation.

• [cis-trans is a change of shape of the molecule

from a state in which two groups (of atoms) are

on the same side of a bond (cis) to another in

which the groups are on opposite sides of the

bond (trans)]

NEMS

Difficulties:

These actuators are synthesized and exist in solutions. You can

not address them individually.

They must be attached to any other structure in order to actuate

continuously, and this is difficult.

The yield of operation is very low.

Difficulties with powers

NEMS

Cantilevers

• An essential components to MEMS/NEMS is a cantilever which can actuate and be controlled by applied actuation forces.

• The actuation force could be electrostatic, electromagnetic or optical.

• The cantilever can be integrated with associated electronic/optoelectronic of a system.

NEMS

• Electrostatic is most used to actuate the cantilevers. Applying a voltage V between the cantilever and a metallic plate can induce attractive/repulsive forces between them.

• Electromagnetic forces applied when a large deflections are needed.

• Optical forces applied for a very small actuations.

NEMS

Figure: G. Kovacs, 1998.

NEMS

Many formula applied for micro structures are not adequate for structures in nano scale among them:

a) Van der Waals forces: has a significant contribution to actuation process of nano cantilever, it is attractive or repulsive in nature. It is strongly sensitive to the geometry of the structure.

b) Casimir force: understood through Quantum Field Theory. According to this theory the vacuum is not empty, filled with virtual particles, continuously created and annihilated. This fluctuation induce a force between bodies separated by distances less than a micron. Again is strongly depended on the geometry and boundary conditions.

NEMS

Micro and Nano cantilevers

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oth wLkhV e27/8 333 4/ LwEtK

K is the spring constant & E is

the Young’s modulus

The equilibrium is maintained

up to h/3. After that the

cantilever will collapse.

h

NEMS

3

3

,360d

cRF spherecas

4

2

,240d

cSF platecas

F(cas)

Casmir force between two metallic plates (S

is their area and d is their separation

distance)

Casmir force between a sphere and a

plate (R is the radius of the sphere)

])1(720/[)()2/( 33222

oo xxcxKxU oxxx /

40 nm

U/Uo

x/xo

RTD characteristic

NEMS

• Casmir force is dependent on the geometry of

the structures. Can be engineered to make nano

devices.

• As an example a nonlinear mechanical

oscillators and switches can be fabricated using

a sphere placed over a plate. As the plate moves

under elastic forces the structure oscillates

around the equilibrium (local minima) and can

switch between the minimum and maximum

positions.

NEMS

Micro and Nano cantilevers

Y(max)

Quantized motion of nanocantilever

Nano cantilever when are double-

clamped the van der Waals has a

very little effect however another

characteristic will show up. The

quantized mechanical movement of

the cantilever. Each time an electron

tunnel through the CNT (an

additional electrostatic

contribution), its deflection changes

in discrete steps.

NEMS

• Control:

• It is demonstrated that with the

combinations of sensors and power

sources one can control the behavior of

these nanodevices

• A technique of making objects invisible TO RADAR

• Scientifically known as Low Observatory

• Prevent the detection of aircrafts or planes from radar systems.

• Modifying the shape of the airplane

• Engines hidden in body of wing

• Exhaust ducts placed on top of aircrafts

Radar Cross-Section Reductions

(Measure the detectability of an object by a radar.

RCS= Cross Section of the object X Reflectivity x Directivity)

Radar Cross-Section Reductions

• RADAR Absorbing Material (RAM)

Painting the aircraft with the material that can

absorb the Radar signals.

• CNT based RAM

CNTs can be deployed as constituents in RAM to

achieve high desirable effects.

Production:

Carbon nanotube type used : CM95/MWNT

Diameter : 0.01-0.015 μm

Length : 10-20 μm

Formulations used : 0.1, 0.5 and 1.0% (w/w) of CNT

dispersed in the epoxy resin.

To achieve more homogenous dispersion, ultrasonic

homogenizer shoud be used.

Resin/CNT Composites

Resin/CNT Composites; SEM image

Electromagnetic Properties

Attenuation of nanostructured composites processed with epoxy resin and

different formulations of carbon nanotubes

CNT/epoxy absorbed 50 to 99.7% of the incident electromagnetic

radiation, using only 0.5% (w/w) of CNT.

• Cathode– Generally made of graphite

and other conductive additives.

• Anode– a layered transition metal

oxide

(Lithium cobalt oxide etc. )

• Electrolyte– Through which lithium ions

shuttles between the cathode and anode

Nanotechnology and Batteries

Improvements

• More energy storage and long duration of

power supply.

• Shorter charging times.

• Durability.

• Resistance to fire hazards.

Applying Nanotechnology

• Faster intercalation of Li ions can be facilitated by using nanosized materials for electrodes, which offer high surface areas and short diffusion paths, and hence faster storage and delivery of energy

• Nanosizing the anode materials can make the anode to have short mass and charge pathways to allow easier transport of both lithium ions and electrons, resulting in high reverse capacity and deliver at a faster rate.

• Nanostructuring of solid electrolytes has proven to improve the lithium ion conductivity, – for example, when the conventional bulk lithium thiophosphate

electrolyte was made nanoporous, it could conduct lithium ions 1000 times faster.

Nanotechnology and Hydrogen Storage

Advantages

• Higher energy per unit mass (>142 MJ kg-1 compare to 47 MJ kg-1 for a liquid hydrocarbon)

• Cleanest energy carrier (H2O is burning by-product compare to CO2 for hydrocarbons)

Disadvantages

• Low energy density per unit volume as it is a low density gas.

• Challenging onboard storage

Hydrogen Storage: physisorption

• Accumulation of hydrogen molecules on and between surfaces of

materials without any chemical reaction. H2 molecules are adsorbed

to host material surface by van der Waals force

Hydrogen Storage: Chemisorption

• Hydrogen atoms penetrate into interstitial site of the host materials

LaNi5, ZrNi, Mg2Ni; metallic hydride.

• Hydrogen atoms form covalent bonds with host material atoms like

Si, ZnO; complex hydride.

• b: hydrogen molecules split into atoms in

presence of catalyst

• c: in moderate pressure H atom take random

locations

• d: in high pressure they would fill all the

interstitial sites.

Nanowries and hydrogen storage

• The problem with the physisorption method is that

they can only occur at cryogenic temperatures which

are difficult to reach.

• On the other hand, the chemisorption methods are

fast and they need to be controlled so that they can be

used for practical purposes.

• The percentage of hydrogen that can be stored

depends upon individual type of nanowires like for

ZnO, ZnS, Ge, Si etc.

Hydrogen Storage: Silicon Nanowires

• It can be seen in the figure that the body of structures is made of closely stacked

nano plates, make them suitable for the hydrogen storage. The hydrogen can be

stored via physisorption (in space between the nano plates), as well as chemisorption

(attached to the dangling bonds on the surface of nano plates).

a) b) c)

Potential Material for Hydrogen chemisorption

Hydrogen capacity of pure ZnO, Al and Sb doped ZnO under 5Mpa at 100°C

3wt% for Al-doped ZnO. high crystalline

defects induced by aluminum, so hydrogen

atoms can penetrate into interstitial sites of

the nanostructure.

Under ambient pressure 80% of

adsorbed hydrogen on Al-ZnO

desorbs and the remaining 20%

releases under elevated temperature

(125-210°C)*“Investigation of hydrogen storage capabilities of ZnO-based nanostructures,” J. Phys. Chem. C, vol. 114, pp. 2560–2565, 2010. 115

Hydrogen Storage

. Hydrogen Storage in Mg Nanowires

Nanotechnology and Solar Cell:

Effect of metal nanoparticles on polymers solar cell

Colloidal solutions of gold nanopartcles

Ag and Au nanoparticles

Local Surface Plasmonic Rresonance

Absorption bands of gold NP in water

Numbers represent 2R (nm)

Molecular Devices

• This is an inter/multidisciplinary research

field, engineering, biology, chemistry, and

physics.

• So we skip all (most of) the

chemical/biological terms.

• In this field most terms related to atomic

structures in semiconductors will be

replaced by molecular structures.

Molecular Devices

For example in band structures:

• Ec will be replaced by highest occupied molecular orbit (HOMO)

• Ev will be replaced by lowest unoccupied molecular orbit (LUMO)

• Metallic contacts are replaced by conjugated linear polymeric systems.

• Chemical substitutions will replace the doping in semiconductors.

• Molecular orbitals define the band gap.

• Individual atoms and the replacement will control all physical, mechanical, chemical, optical properties of the devices.

Molecular Devices

• Unlike the semiconductor electronic circuits

where adding a branch does not change the

electrical properties of the individual elements,

adding a new branch to a molecule creates a

new molecule with different electrical properties.

• So, the Ohm’s law and Kirchhoff's law can not

be applied for molecular circuits.

• As a result, the electrical properties of molecular

systems can be easily engineered.

Molecular Transistor

LUMO HOMO

Molecular Machines

• In common with their macroscopic counterparts,

a molecular machine is characterized by several

criteria. These are:

• the type of energy needed to make it work

• the nature of the movement during which work is

done or energy is transformed

• the way it can be controlled

• the ability to repeat its operation

• the time needed for a useful action.

Molecular Machines

• Catenanes, Rotaxanes and knots are

topologically molecular objects which are

well known to chemists for a long time.

However, these novel chemical species

received special attention in recent years

as it was found their places in the area of

nanosciences and nanotechnology, and an

emerging new field of research called

molecular machines and motors.

Molecular Machines

Molecular Machines

• Catenanes: Structures are joined bracelets

linked through each other. Their polymers, which

consist of chained together are called

polycatenanes

• Thus a [2] catenane has two rings and a [3]

polycatenane has three rings. Two-bracelet

catenanes ([2] catenanes) are useful because

each bracelet can be rotated around the other.

Molecular Machines

• Rotaxane: In this structure a central rod holds the axle to the superstructure through a collar, and dumbbell structures are at each end to stop the collar falling off. The molecular equivalents of these structures are called rotaxanes. Rotaxanes are of particular interest because the collar structure can often be moved by some external force and used as a molecular switch . The principle behind using rotaxanes as molecular switches is the ability to move the collar under some external influence. If the collar can be switched back and forth from each site 's' then it acts as a switch.

Molecular Machines

Rotaxane Catenane

S S

S S

Molecular Machines (Motors)

• A molecular machine is a multicomponent system in which the reversible movement of the components can be controlled by an external stimulus (S). Known examples of molecular machines includes nondegenerate rotaxanes (Type I), nondegenerate catenanes (Type II), as well as pseudorotaxanes (Type III). Control of the motions of the components in those systems has been introduced, which results in a change in properties which produce a signal that allows the operation of the machine to be monitored. The outside stimuli can be photons, electrons, or chemical species, to generate photochemically-, electrochemically- and chemically-driven molecular machines, respectively.

Molecular Machines

Molecular Machines

• Researches are done on the switches composed from the single molecules called molecular switches.

• There are various molecular switches that work using electricity, light, heat, protons or ions as external stimuli.

• Attentions are paid to catenanes which have a structure of two macrocycles which mechanically interlocked and move from the state A to the Bby the external stimulus.

Molecular Machines

The chemically and electrochemically triggered redox switching of 2 catenanes.

Molecular Machines

CN-

Cu+

Molecular Machines

Isomerization of 2 catenanes

Molecular Machines

CH3OC

H3

S

CH3

H3C

Molecular Machines

• Parts of molecular machines: a molecular

paddle system,

Molecular Machines

Molecular Machines

Cl2CO

Et3N

NaBH(OEt)3

Molecular Machines

CH3OC

H3

S

hv, 300nm

hv, 250nm

X

X

M-CisP-trans

M-transP-Cis

Molecular Machines

CH3

H3C

hv>

280nm

hv>280nm

heat

heat

PP-Cis

MM-CisMM-trans

PP-

trans

Molecular Machines

+NH3

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