presentation-14-ver3.pptx [Last saved by user]vpopov/Grapnene-properties-and... · 2019-09-20 · Graphene production Graphene dot, flakes, ribbons, sheets…: graphene electronics-Mechanical

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Graphene: Properties and Application

ISSP-INERA-30-06-2014

Valentin PopovFaculty of Physics, Sofia University

[email protected]://www.phys.uni-sofia.bg/~vpopov

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IntroductionPropertiesApplicationOutlook

Outline

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Outline

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FULLERENESKCS, 1985NP 1996

0D

Introduction

GN, NP 2010“…for groundbreaking experiments regarding the two-dimensional material graphene…"

NANOTUBESIijima, 1991

1D

GRAPHENEGeim, Novoselov,

Science 306, 666 (2004)

Graphene is a perspective material for atomic-thin metallic field-effect transistors which would havesmaller size, lesser power consumption, higher operation frequencies.

GRAPHITE3D

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Outline

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Properties

P. R. Wallace, 1947

Wallace model

( ) | |FE v± ≈ ±k k

( ) ( )E t f± = ±k k

( ) 3 2cos( ) 4cos( / 2)cos( 3 / 2)y y xf k a k a k a= + +k

( ),

ˆˆ ˆ . .i ji j

H t a b h c+= − +∑

±→ electrons/ holes

FLG - SWM model for graphite: Slonczewski and Weiss, 1958; J.W. McClure, 1957.

Dirac cones, Dirac points

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PropertiesWeyl equation

( ) ( )Fi v Eψ ψ− ⋅∇ =σ r r

/2

, /2

1( )2

i

K i

ee

θ

θψ

−

±

⎛ ⎞= ⎜ ⎟

±⎝ ⎠

k

kk

arctan( / )x yk kθ =k

± → electrons/ holes

Helicity operator ½ħσ·k/|k| → helicity ±½ for e/h

“QED on a table”: Klein tunneling, Zitterbewegung…

Semenoff, 1984Haldane, 1988

Two-component wavefunction → spinor → pseudospin

Observation of Dirac cones by ARPES: Zhou et al., Nature Physics 2006.

спиралност

A

B

ψψ

ψ⎛ ⎞

= ⎜ ⎟⎝ ⎠

ψψ

ψ↑

↓

⎛ ⎞= ⎜ ⎟⎝ ⎠

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PropertiesKlein tunneling

Theory: Katsnelson, Nature Physics 2006; Observation: Stander, PRL 2009, Young, Nature Physics 2009

The electrons can tunnel through potential barrier with probability of unity (Klein paradox).

ϕ – incident angleqx – electron momentum

V0 = 200 meV (blue)V0 = 285 meV (red)

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PropertiesElectrical transport

Scanning electron microscope image of the experimental device

Schematic of the experimental device

Novoselov et al., Science 306, 666 (2004)

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PropertiesZero-field transport

Novoselov et al., Science 306, 666 (2004)

Ambipolar field effect in 2D zero-gap semiconductor:

ρ(Vg) – sharp peak, σ(Vg) – linear dependence

ρ-1 = σ = neμ, n ~ Vg (theory) → σ ~ Vg (exptl.) μ - weak dependence on T, mainly limited by defects; μ = 3,000 - 10,000 cm2/V.s

σmin ≈ e2/h

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PropertiesAnomalous quantum Hall effect

Landau quantization

Novoselov et al., Science, 2007

Novoselov et al., Nature, 2005

Zhang et al., Nature, 2005

Quantum Hall effect Shubnikov – de Haas oscillations

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PropertiesGraphene quantum dots

Single electron transistor (SET)

Ponomarenko et al., Science, 2008

Coulomb blockade < 10 K

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PropertiesOptical absorption

Graphene is almost transparent

Mak et al., SSC, 2012

Absorbance πα ≈ 2.3%, α=πe2/ħc≈1/137

Nair et al., Science, 2008

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PropertiesPhonon dispersion

Raman-active phonon E2g

Wirtz et al., SSC, 2004

E2g

Malard et al., PR, 2009

Raman scattering

- first-order spectra – the G band- second-order spectra – two-phonon and

defect-induced bands excited by the double-resonance mechanism

Experimental data: inelastic neutron scattering, high resolution electron energy loss spectroscopy, double-resonance Raman scattering, inelastic x-ray scattering.

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PropertiesDoping effects

G band damping and energy renormalization

Yan et al., PRL, 2007

LO/TO branch @Γ and TO branch @K damping and renormalization

Popov et al., PRB, 2010

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PropertiesSpecific heat

Specific heat:saturates to the Dulong-Petit limit of 2.1 J/gK at high temperatures

Pop et al., MRS Bull., 2012

Theory:Electronic contribution - negligiblePhonon contribution: C ~ T2 for ω ~ q (LA, TA phonons)C ~ T for ω ~ q2 (ZA phonons)ω(ZA) < ω(LA,TA) → C ~ T below ~100 K

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PropertiesThermal expansion

Negative thermal expansion coefficient Experiment: < 350 K; Bao, 2009Theory: < 2300 K; Mounet, 2005

Bao et al., Nature Nanotechnology, 2009

This behavior is explained by the negative Grüneisen parameter of the ZA phonon mode γ (γ ~ α). This effect was predicted in membranes by Lifshitz, 1952.

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PropertiesThermal conductivity

Intrinsic thermal conductivity limited by only phononsdiamond ~2000 W/mKCNT ~2300 W/mKsuspended graphene ~2000 W/mK

Extrinsic thermal conductivity limited by defects, impurities, boundariesamorphous carbon ~0.01 W/mKsupported graphene ~600 W/mK

2j j j

j

K C v dτ ω=∑∫

Theory:Electronic contribution - negligiblePhonon contribution:

Chen, Nature Materials, 2012

Seol, Science, 2010

Pop et al., MRS Bull., 2012

Thermoelectricity:FoM: ZT = S2σT/KS ~ 100 µV/K (Zuev, PRL 2009)Increase ZT by suppressing thermal conductivityPredicted ZT~4 in graphene ribbons, not measured

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Density: 0.77 mg/m2; 1 m2 -> 0.77 mg

Optical transparency: almost transparentabsorbs only πα ≈ 2.3%

Mechanical strength:42 N/m; 1 m2 -> 4 kg100 times stronger than steel (same thickness)

Electrical conductivity:2D conductivity σ = enμμ = 200,000 cm2V-1s-1 limited by acoustic phonons at n = 1012 cm-2

2D sheet resistivity ρ = 31 Ω/3D conductivity: 0.96 x 106 Ω-1cm-1 higher than for copper of 0.60 x 106 Ω-1cm-1

Thermal conductivity:2D thermal conductivity: 5000 Wm-1K-1 dominated by phonons, higher than for copper of 400 Wm-1K-1

PropertiesSummary

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Outline

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ApplicationGraphene production

Graphene dot, flakes, ribbons, sheets…: graphene electronics

-Mechanical exfoliation of HOPG (low yield, mainly for basic research) (Novoselov et al., Science 306, 666 (2004))

-Thermal exfoliation (graphene nanoribbons) (Wang et al., Science 319, 1229 (2008)).

-Electrochemical exfoliation (processing with sulphuric acid – high-quality, large-area, large yield of unoxidized defect-free few-layer graphene) (Paton et al., Nature Mater. (2014))

-Thermal decomposition of SiC (graphitization of Si-terminated SiC wafer) (Emtsev et al., Nature Mater. 8, 203 (2009)).

-Chemical vapor deposition (decomposition of hydrocarbons – large-scale production of few-layer graphene on copper and nickel foils; etching for removal of catalyst) (Kim et al., Nature 457, 706 (2009)).

Zhang et al., Accounts Chem. Res. 46, 2329 (2012)

CVD

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ApplicationGraphene production

Graphene oxide: composites, energy conversion and storage

-Graphene oxide GO) – produced by Hummer and Offeman method (mixture of sulphuric acid H2SO4, sodium nitrite NaNO3, and potassium permanganate KMnO4 as an oxidizing agent) (J. Am. Chem. Soc., 1958). GO structure – not established well: Hofmann, 1939 (repeat unit, epoxide groups C2O); Ruess, 1946 (incl. hydroxyl groups -OH); Lerf-Klinowski, 1998 (amorphous model, may include carboxyl groups -CO2H)

-Reduced graphene oxide (rGO) – chemical reduction with sodium borohydride (NaBH4) or hydrazine (N2H4), thermal reduction, electrochemical reduction, microwave-assisted reduction… resulting in partial removal of oxygen and recovery of aromatic rings.

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ApplicationGraphene composites

Rafiee et al., ACS Nano, 2009

Composites with improved mechanical properties

0.1% graphene filler in epoxy matrix → >20% increase of Young’s modulus and tensile strength

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Composites with improved electrical properties

Φc ~0.1vol% percolation threshold for polystyrene-graphene compositeandσc ~0.1S/m – sufficient for many electrical applications

Stankovich et al., Nature, 2006

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Composites with improved thermal properties

Verdejo et al., J.Mater.Chem., 2008

0.25 vol% graphene filler in silicon foam matrix→ ~6% increase of thermal conductivity

Composites with metals, metal oxides, nanoparticles (attaching nanoparticles to graphene, wrapping nanoparticles in graphene) for various applications

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ApplicationTransparent electrodes

Transparent electrodes are needed for LCD displays, touch panel displays, LEDs, solar cells, sensors, detectors, etc.

Most popular material for transparent electrodes is ITO (indium tin oxide).-Advantages: transparent, conducting-Drawbacks: rare element, brittle, poor adhesion to organic materials, expensive production technique by magnetron sputtering

Challenges:-Cheaper production technique, e.g., by chemical vapor deposition or deposition from solution-Cheaper materials, e.g., conductive polymers, metallic nanowires, nanowire-polymer composites, carbon nanotubes, graphene-Flexible electrodes

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material Sheet resistance Ω/ Transparency %

ITO on glass ~20 ~90

ITO on PET ~40-80 ~80PEDOT on PET ~200 ~90

Nanowires on glass/PET ~10 ~85Graphene on PET (CVD) ~30 ~90

Yong et al., Nature Nanotechnology, 2010; Hu et al., ACS Nano, 2010

PET=polyethylene terephthalate PEDOT=poly(3,4-ethylenedioxythiophene)

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Bae et al., Nature Nanotechnology, 2010; CVD at 1000 °C for 16 h, PET film of size 100 m x 0.2 mKim et al., APL, 2011, PECVD, at 500 °C

Chemical vapor deposition (CVD) method. ‐Decomposition of hydrocarbons, mainly methane and ethylene, in the presence of transition metal catalysts, mainly copper or nickel. Solubility problems with nickel. ‐Transfer of the graphene by etching the catalyst, removing graphene using polymer film (PET, PMMA, PDMS) by pressing the film, pressing the film onto target substrate, and removing the polymer film.

PMMA=poly(methyl methacrylatePDMS=polydimethylsiloxane

Graphene-based electrodes for ITO replacement

Improvement of electrical conductivity by doping with nitric acid (HNO3) – sheet resistance of 30 Ω/ at 90%.

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Bae et al., Nature Nanotechnology, 2010

Touchscreen displays:

a. Copper foil wrapping around a 7.5-inch quartz tube to be inserted into an 8-inch quartz reactor. The lower image shows the stage in which the copper foil reacts with CH4 and H2 gases at high temperatures.b. Roll-to-roll transfer of graphene films from a

thermal release tape to a PET film at 120 °C.c. A transparent ultralarge-area graphene film transferred on a 35-inch PET sheet.d. Screen printing process of silver paste electrodes on graphene/PET film. The inset shows 3.1-inch graphene/PET panels patterned with silver electrodes before assembly.e. An assembled graphene/PET touch panel showing outstanding flexibility.f. A graphene-based touch-screen panel connected to a computer with control software.

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Zhu et al., ACS Nano, 2011

Graphene layer was grown on copper foil by CVD and transferred on top of a metal grid of size ~0.1 mm x 0.1 mm prepared on glass or PET films. Sheet resistance: 20 Ω/ at 90%

Graphene-based electrodes for ITO replacement

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ApplicationSolar cells

Handbook of Photovoltaic Sci. & Eng., ed. A. Luque and S. Hegedus, John Willey & Sons, 2003

Theoretical limit of the efficiency of single-junction solar cell: max ~32% at band gap of 1.1 eV (Shockley).The efficiency is limited by blackbody radiation losses, radiative recombination, and incident light spectrum losses.

Shockley and Queisser, JAP, 1961

Conventional solid state solar cells implement a p-n junction between two electrodes; at least one of the electrode should be transparent; incident photon creates an electron-hole pair, which travel to the electrodes; the e.m.f. is equal to the quasi-Fermi level separation.

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Electrochemical solar cells (Grätzel cells) use a photosensitizer; incident photons are absorbed by the photosensitizer, which is excited; the excited electrons are injected into the TiO2 electrode, thus oxidizing the photosensitizer; the electrons travel over the circuit to the other electrode, where they reduce the photosensitizer. Also: perovskite sensitizer; Mitzi et al., Nature, 1994

*Grätzel, Nature, 1991

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Solar Cell Efficiency %

SiliconSi (crystalline) 25Si (multicryst., thin film) 20Si (amorphous) 10III-VGaAs (thin film) 29GaS (multicrystalline) 18InP (crystalline) 22

Solar Cell Efficiency %

Thin-film chalcogenideCIGS 20CdTe 20MultijunctionInGaP/GaAs/InGaAs 44OrganicDye sensitized 12Perovskite sensitized 14

Green et al., Prog. Photovolt: Res. Appl. 2014

Challenges:-Cheaper production method of the solar cells,-Cheaper materials,-Flexible electrodes

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Graphene as ITO replacement

Ramuz et al., ACS Nano. 2012

P3DDT=poly(3-dodecylthiophene-2,5-diyl)

Active layer: Sc-SWNT(absorber and p-type)/C60(n-type)

Silver cathode+ITOEfficiency ~0.46%

All-carbonEfficiency ~0.004%

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Park et al., Nano Lett.. 2013

P3HT=poly(3-hexylthiophene)

Active layer: PbS QD (P3HT) (absorber and p-type)/ZnO(n-type)

PbS QD (P3HT) Efficiency 4.2% (0.5%)

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Park et al., Nature Sci. Rep., 2013

PEDOT:PSS=poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)PEDOT:PEG (PC)=poly(3,4-ethylenedioxythiophene)-block-poly(ethylene glycol) (perchlorate)

Anode: grapheneActive layer: PEDOT:PSS (absorber and p-type)/C60(n-type)

Efficiency 10-15% of ITO

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Wang et al., Nano Lett.. 2014

Active layer: Perovskite(absorber and p-type)/graphene-TiO2(n-type)

Efficiency 15.6%

Superstructured perovskite solar cellSolution-based fabrication at < 150 ºC

FTO=fluorine doped tin oxide coated glassPerovskite=Al2O3/CH3NH3PbI3-xClx

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ApplicationFuel cells

Proton exchange membrane (PEM) fuel cell: hydrogen enters the cell at the anode, where it is oxidized to ions and electrons; the electrons travel from anode to cathode, the hydrogen ions pass through the PEM to the cathode, where they meet oxygen and are reduced to water. Variant: Direct Methanol Fuel Cells. Catalyst of redox reactions: platinum

Advantages:-high energy density,-cheap fuelDrawback: -Pt is very expensive!

Challenges: replacement of bulk Pt with-Pt nanoparticles-cheaper metal catalyst-non-metal catalyst

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ApplicationFuel cells

Graphene as Pt nanoparticles support: advantage - higher surface area, lower production costs

Seger, J. Phys. Chem. C Lett., 2009

Pt nanoparticles on rGO support:Increase of catalyst activity by 80%

Non-platinum catalysts:N-doped graphene (Liang, Nature Mater., 2011)

Non-metal catalysts:edge-halogenated (Cl, Br, I) graphene nanoplatelets (Jeon, Nature Sci. Rep., 2013)

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ApplicationSupercapacitors

Electrochemical capacitors (supercapacitors):Double-layer capacitors: electrostatic storage through charge separation in a Helmholzdouble layer at each electrode;Pseudocapacitors: Electrochemical storage through faradaic charge transfer via redox reactions; desolvated alkali metal cations pervade the double layer, adsorb on the transition metal oxide layer (RuO2, MnO2, etc.) of the anode and transfer charge to it.Hybrid supercapacitors: capacitors with asymmetric electrodes (Li-ion capacitor).

←→ Helmholz double layer, formed by the electrode, solvent and solvated ions of the electrolyte

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Ragone (1968) chart

Advantages: -fast charging,-unlimited cycle life,-quick operation mode.Drawback:-low energy density-rapid voltage drop

Challenge:-increase the energy density by increasing surface-to-volume ratio of anode for redox reactions

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Yoo et al., Nano Lett. 2011

Transition-metal-oxide nanowire/single-walled carbon nanotubes thin-film electrodes: capacitance of 184 F/g, energy density of 25.5 Wh/kg (Chen et al., ACS Nano, 2010).

Vertically aligned and electrochemically oxidized carbon nanotube electrodes: capacitance of ~158 F/g and energy density of ~53 Wh/kg (Kim et al., Nanotechnology, 2012).

Graphene oxide electrodes: capacitance of 154 F/g and energy density of 85.6 Wh/kg (Liu et al., Nano Lett. 2011). (Also: Zhu et al., Science, 2011)

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ApplicationBatteries

Li-ion batteries (Sony, 1991): consist of a graphite anode, transition metal oxide cathode (LiXO2, X = Mn, Fe, Co, Ni), and an electrolyte (Li salt, such as LiPF6, LiBF4, or LiClO4, in an organic solvent, such as ether). The storage is based on a faradaic redox reaction. Upon charging Li ions percolate the anode and are reduced on it, upon discharge Li ions percolate back to the cathode and are oxidized on it.

Advantages: -high energy density-low self discharge-no memory effect.Drawback:-special charging and exploitation conditions-expensive

Challenge:-cheaper production-increase of charging cycles-increase of energy density

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Kucinskis et al. , J. Power Sources, 2013

The electrochemical activity can be improved by anchoring, mixing, wrapping or encapsulating the active cathode material particles in graphene, which forms a 3D conducting network

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Song, Nano Lett., 2013

The Li-S batteries: increase of electrochemical activity by using sulphur as cathode constituent; advantages – sulphur is nontoxic, safe, and inexpensive ; reduction of deterioration with cetyltrimethyl ammonium bromide (CTAB)-modified sulfur-graphene oxide nanocomposite cathode; twice larger energy density than Li-ion batteries.

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ApplicationGas sensors

Field effect transistors based on graphene are promising devices for high signal-to-noise ratio detection of various local electrical and chemical influences due to high carrier mobility and low intrinsic noise of graphene.

Schedin et al., Nature Mater., 2007

Measurement of NO2: resistance – 1 ppb, Hall resistance – 1 molecule!Optimal device size ~ 1 μm

Measurement of NH3, NO2, CO, CO2, O2, etc.Potyrailo, Chem. Rev. 2011.

Precise discrimination between the different gases by analyzing the low-frequency noiseRumyantsev et al., Nano Lett. 2012.

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ApplicationCharge sensors

Charge sensor: device, consisting of a quantum dot and a single electron transistor, fabricated by oxygen reactive ion etching of single layer graphene (dark areas).

Wang et al., Appl. Phys. Lett. 2010

Measurement of charges at the QD: once an electron occupies the QD, it is detected by the SET because of capacitive coupling with the dot: the conductance of the SET changes by ~ 30%.

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ApplicationHumidity sensors

Sreeprasad et al., Nano. Lett. 2013

Humidity sensor: graphene nanoribbons were assembled into polyallylminehydrochloride (PAH) nanofibers to form a percolating network

Measurement of humidity and temperature: graphene oxide is deposited by drop casting or spray coating on silver electrodes printed on a polyethylene naphthalate (PEN) substrate;. device resistance is proportional to temperature and humidity in the range 10-40 °C and 30-80%.Borini et al., ACS Nano 2012

Measurement of humidity and pressure: fibers swell on absorbing water, fiber volume increases,tunneling distance increases, current decreases;Pressure is proportional to water-to-fiber ratio.humidity range 0-40%.

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ApplicationTransistors

Schwierz, Nature Nanotech. 2010

Planar field-effect transistor (FET): the planar FET consists of a gate, a channel connecting source and drain electrodes, and a barrier separating the gate from the channel; application in digital logic (FoM = Ion/Ioff ratio) and radiofrequency devices (FoM = cut-off frequency).

Moore’s Law (1965):Component density doubles every 18 months (blue line). Reducing gate length and pitch is accompanied by increasing current leakage. Limit on gate length ~ 20 nm.

Solution: FinFET

Graphene – an option for post-silicon electronics?

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E=2.2 V/nm, ∆=130 meV, Ion/Ioff~100 @RT; Xia et al., Nano Lett. 2010

Graphene field-effect transistor for logic circuit devices

Challenge: high Ion/Ioff ratio → bandgap

Electric field Graphene nanoribbons

W=15 nm, ∆=200 meVHan et al., PRB 2007

Zhang et al., Nature 2009

W=10 nm, ∆=80 meVIon/Ioff~107 @RTLi et al., Science 2008

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Lin et al., Science 2010

Gate=240 nm, f=100 GHz Gate=40 nm, f=133 GHz

Wu et al., Nature 2011

Graphene field-effect transistor for r.f. applications

Challenge: high cut-off frequency

Gate=140 nm, f=300 GHz

Duan et al., Nature, 2010

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ApplicationOther applications

Light-emitting diodesEM radiation sensorsStrain sensorsEtc.

NTT

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Outline

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OutlookGraphene publications (Web of Knowledge, June 2014)

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OutlookGraphene dreams

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Acknowledgments

This work was supported by Project #316309: INERA— Research and Innovation Capacity Strengthening of ISSP-BAS in Multifunctional Nanostructures.

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Thank you!

Documents

presentation-14-ver3.pptx [Last saved by user]vpopov/Grapnene-properties-and... · 2019-09-20 · Graphene production Graphene dot, flakes, ribbons, sheets…: graphene electronics-Mechanical