graphene and nanowires--petar petrov and kevin babb.ppt

7/27/2019 Graphene and Nanowires--Petar Petrov and Kevin Babb.ppt

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Graphene &

Nanowires:

ApplicationsKevin Babb & Petar PetrovPhysics 141A PresentationMarch 5, 2013


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What is a Nanowire? One-dimensional structure

o Diameter: 1-100 nanometers (10-9 m)

o Length: microns (10-6 m)

Exhibits crystal structureo Unlike quantum dots (0-dimensional)

Many different materialso Metals, semiconductors, oxides

Kevin Babb & Petar PetrovPhysics 141ASpring 2013 2


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Features of Nanowires Smallest dimension which can transport charge

carriers (e-, h+)o Can act as both nanoscale devices and wiring

o Unique density of states

Controlled synthesiso Diameter, length, composition

o Electronic structure (band gap, doping)

Sizeo Quantum confinement

Present in some, absent in others

Unique magnetic & electronic properties

o Millions more transistors per microprocessor

o Probe microscopic systems (e.g. cells)



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Graphene Reminder Graphene is a 2-d from of

pure carbon

Band gap depends onstructureo

Large area monolayerso Bilayers

o Nanoribbons


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Solar Cells Currently: silicon wafers, thin films

Application of graphene:o Transparent conducting electrodes

Robust, conductive, abundant

Cheaper than ITO

Application of nanowires:o Enhanced light trapping

o Efficient charge transport (1D)



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Graphene-NanowireSolar Cells

A new design:o Layer of graphene (transparent cathode)

o Conductive polymer (maintains integrity)

o ZnO nanowire layer (electron transport)

o PbS quantum dots (hole transport)

o Au layer (anode)

Efficiency approaches ITO-basedsolar cellso 4.2% conversion efficiency (5.1% for ITO)

o

Cheaper to produce



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Field Effect Transistors Challenges to scaling

o Lower transconductance

o Manufacturing difficulties

o Quantum effects

o Gate capacitance


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Graphene FETs Challenges

o Low on-off ratios

o High graphene-electrode contactresistance

o Tradeoff betweenmobility and bandgap

Advantages

High roomtemperaturemobility

Thinner than

traditional MOSFETs


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Nanowire FETs Advantages

o Many differentnanowires withdifferent properties

o High mobilityo Bottom up

synthesis

Challenges

o Integrating NW intocircuit

o Control of growthand dopants


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Light-Emitting Diodes LEDs versus conventional lighting:

o Efficient: less heat, lower power consumption

o Long lifetime

o Cheap

o No mercury

How nanowires help:o Various geometries of p-n junctions available

Coaxial wires

Thin film/wire combinations

Crossed-wire junction arrays

o Unique carrier transport properties

Natural waveguiding cavities

o Improve extraction efficiency of light

High surface area improves conductivity



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Artificial Photosynthesis Simulate natural photosynthetic process

o Convert CO2 and H2O into fuels, O2

H2O oxidation

CO2 reduction

How nanowires help: photoelectrodeso High surface area for reaction sites

o High charge mobility due to small diameter

o Can be grown in large quantities



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Touch Screen Devices Graphene is strong, transparent, highly

conductive, and cheaper than traditionalITO


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This is scalable!


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Ultracapacitors Graphene

advantages:o High surface area to weight

ratio (2600 m2 /g)

o High conductivity

o Measured specific

capacitance 135 F/g

Uses:o Electric vehicles

o Backup powering

o High power capability

o Cell phones


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References Physical Foundations of Solid State Devices, E. F. Schubert

Y. J. Hwang, et al., Nano Lett., 2012, 12, 16781682

A. Hochbaum, Chem. Rev., 2010, 110, 527546

H. Park, et al., Nano Lett., 2013, 13, 233-239

E. Lai, et al., Nano Res., 2008, 1, 123-128 D. Siburly, et al.,J. Phys. Chem, 2005, 109, 15190-15213

F. Schwarz, Nature Nanotechnology, 2010, 5, 487496

S. Bae, et al., Nature Nanotechnology, 2010, 5, 574578

M. Stoller, et al., Nano Lett., 2008, 8, 34983502 Y. Zhang, et al., Nature, 2009, 459, 820-823


graphene and nanowires--petar petrov and kevin babb.ppt

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