the fingerprinto of graphene - ferrari prezzo
DESCRIPTION
Presentation on Raman of grapheneTRANSCRIPT
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The Raman Fingerprint of GrapheneA. C. Ferrari1, J. C. Meyer2, V. Scardaci1, C. Casiraghi1,
M. Lazzeri3, F. Mauri3, S. Piscanec1, D. Jiang4, K. S.Novoselov4, S. Roth2, A. K. Geim4
1Department of Engineering, University of Cambridge, Cambridge, UK2Max Planck Institute for Solid State Research, Stuttgart 70569, Germany3Institut de Mineralogie et de Physique des Milieux Condenses, Paris, France4Department of Physics and Astronomy, University of Manchester, UK
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NanoTube-Evolution-Nagano 06
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NanoTube-Evolution-Nagano 06
“Cut…. Get graphene”Eklund-Sensei NT06
“Press (50GPa)…Get Diamond-like Carbon!”
S. Saito-Sensei CCNT06
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Graphene
•Electron transport described by the (relativistic-like) Dirac equation Access to the rich and subtle physics of quantum electrodynamics in a relatively simple condensed matter experiment
•Scalability of graphene devices to true nanometre dimensions makes it a promising candidate for future electronic applications, because of its ballistic transport at room temperature combined with chemical and mechanical stability.
•Graphene is the two-dimensional (2d) building block for carbon allotropes of every other dimensionality
….big hype recently…
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Transistor: Graphene Ribbon
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Drawing:(micro) mechanical cleavage of graphite
How to Make Graphene?
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ELECTRONIC DEVICES AND MATERIALS GROUPindividual atomic sheets: do they exist?
How to Make Graphene?
GRAPHITE ISSTRONGLY LAYERED
SLICE DOWN TO ONE ATOMIC PLANE
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SEM
1 μm
0Å 9Å 13Å
Free-Standing GrapheneAFM
1 μm
single layer of atoms visible by “naked” eyeonly on 300 nm SiO2
OPTICS
Key: Visual Identification
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HoweverNeed Extremely
Good Eye To Spot!!!
Single Layer
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TwoLayers
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One Comment…
However…Low yield, messy, not scalable
Better to grow graphenedirectly on substrate
This can be done…But…not the subject of this talk
Mechanical cleavage is nice and simple
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Another Comment
AFM thickness of single layer is0.5-1.5 nm! Due to chemical contrast
We want to be 150% sure
TEM
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Free-Hanging graphene sheets
500nm
1 layer of graphene !
J. C. Meyer
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Preparation1. Graphene sheet on substrate
2µm
2. Metal grid patterned ontothe flake
10µm
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Preparation
3. Etching of substrate
10µmFlake remainsin metal grid
4. TEM and electron diffraction analysis
500nm
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Electron diffraction:
Highly crystalline samples
Number of layers?Diffraction tilt series!
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Sheets fold back at the edges, and sometimes show a wrinkle within the sheet. HRTEM analysis of the folding allows to verify the layer count.
2nm
2nm
One-layer graphene
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Two-layer graphene
2nm
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Two-Layer Graphene
2 Layers
Stacking A/B
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8 layers
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We Need High Throughput Non Destructive
Quick Substrate Independent
Identification Technique
Raman Spectroscopy
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1500 2000 2500 3000
Inte
nsity
Raman shift (cm-1)
514nm
Graphene
Graphite
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2500 2600 2700 2800 2900 30000
10000
20000
30000
40000
Graphene
Inte
nsity
(a. u
.)
Raman shift (cm-1)
514 nm
Graphite G’ Peak
(2D peak)
Clear Fingerprint
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1800 2400
Inte
nsity
(A.U
.)
Raman Shift (cm-1)
Graphene
1200 1300 1400 1500 1600 1700 1800
Inte
nsity
(A.U
.)
Raman Shift (cm-1)
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1800 2400
Inte
nsity
(A.U
.)
Raman Shift (cm-1)
Graphene
1200 1300 1400 1500 1600 1700 1800
Inte
nsity
(A.U
.)
Raman Shift (cm-1)
D peak intensityNOT related to Number of Layers
Disorder (in the widest possible meaning)
See Tuinstra Koening 1970…
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1500 2000 2500 3000
Inte
nsity
(A.U
.)
Raman Shift (cm-1)
Graphene
On Substrate
Suspended
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1500 2000 2500 3000
Inte
nsity
(A.U
.)
Raman Shift (cm-1)
2-Layers
514 nm
2600 2640 2680 2720 2760 2800
Inte
nsity
(A.U
.)
Raman Shift (cm-1)
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1500 1550 1600 16501500 1550 1600 1650
10 layers
5 layers
Inte
nsity
(a. u
.)
Raman shift (cm-1)
1 layer
2 layers
graphite
Raman shift (cm-1)
514nm 633 nm
Slight Upshift ~ 5cm-1
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2600 2700 28002600 2700 2800
10 layers
5 layers
2 layers
Inte
nsity
(a. u
.)
Raman shift (cm-1)
1 layer
graphite
514nm
633 nm
Raman shift (cm-1)
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2550 2600 2650 2700 2750 28000
5000
10000
15000
200002D2B2D2A
2D1A
Inte
nsity
(A.U
.)
Raman Shift (cm-1)
E) 2 Layer
514.5 nm
633 nm
2D1B
1300 1350 14000
500
1000
1500
2000
2500Edge Graphite
D2
Inte
nsity
(A. U
.)
Raman Shift (cm-1)
D
D) 514.5 nm
D1
Edge 1 Layer
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The Origin of G’ (2D) Peak
BUT it is the second order of D peak
Nothing to do with G peak
Named G’ since is one of the 2 biggest peaks in graphite
D forbidden in perfect crystal By Raman Fundamental Selection Rule q~0
However 2nd order always allowed: q+(-q)=0
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D Peak Dispersion Vidano et al. (1981)
Pocsik et al. (1998)
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Active by double resonance(Baranov 1988, Thomsen-Reich 2000)
D peak comes from LO phonons(Ferrari Robertson 2000)
Strongly dispersive due to Kohn Anomaly at K(Piscanec et al. 2004)
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Second order no defect scattering necessary
However…
In principle ALL phonons activeBUT
Double resonant phonons enhanced due to resonance and strong
electron-phonon coupling
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Previous double resonance modelspredict multiple D peaks for graphene
Double structure of 2D peak in graphitenever explained
Traditional interpretation (1980)2 Maxima in graphite
Phonon Density of States at K and MWRONG since 2D disperses with excitation
KEY: Evolution of Electron Bands with number of layers
in contrast with experiments
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Three Possible Processes
However: only 1 contributes
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Three Possible Processes
However: only 1 contributes
Small:Trigonal Warping
Forbidden:EPC=0
OK!
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Trigonal Warping Effect
• q > K Strong EPC and large portion of the phase-space • q < K Strong EPC but small portion of the phase-space • q ~ K EPC~0
Adapted from: Kurti et al., Phys. Rev. B 65 165433 (2002)
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1 Component D and 2D peaks
2500 2600 2700 2800 2900 3000
Graphene
Inte
nsity
(a. u
.)Raman shift (cm-1)
514 nm2D
1 3 0 0 1 3 5 0 1 4 0 0
Inte
nsity
(A. U
.)
R a m a n S h if t (c m -1 )
5 1 4 .5 n m
E d g e 1 L a y e r
D
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0.8 0.7 0.6 0.5
1300
1320
1340
1360
1380
1400
1420
Μ Κ Γ
q = (ξ,0,0)
ve Vector (2π/a0)
Two-layer GrapheneTwo possibilities:
1) Phonon Splitting
2) Band splitting
Phonon SplittingK-M is Minor
PRL 93, 185503 (2004)
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Band Splitting Main Effect
2550 2600 2650 2700 2750 28000
5000
10000
15000
200002D2B2D2A
2D1A
Inte
nsity
(A.U
.)
Raman Shift (cm-1)
2 Layer
514.5 nm
633 nm
2D1B
4 components2 Most intense
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Origin of Small Upshift of G peak
1 5 0 0 1 5 5 0 1 6 0 0 1 6 5 0
Inte
nsity
(a. u
.)
R a m a n sh ift (cm -1 )
1 la ye r
g ra p h ite
-0.1 0.0 0.11570
1580
1590
1600
q = (0,ξ,0)
Γ
~5 cm-1 Upshift
IRRaman GrapheneRaman Graphite
PRL 93, 185503 (2004)
Kohn Anomaly
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Phonon-Linewidths and EPCIn a perfect crystal, phonon linewidths determined byInteraction with other elementary excitations:
EPCan γγγ +=γan : anharmonic contribution, due to interactionWith other phonons. Determined by anharmonicterms in interatomic potential.
γEPC: interaction with electron-hole pairs. Determinedby EPC and present in systems with null electron gap
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Γ-E2gLO Phonon Decay Processes
From the Fermi Golden Rule:
2
2)(2 β
γ Γ∝
−Γ
EPCEPCE LO
g
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Γ-E2gLO : Graphite Raman G Peak
1000 1200 1400 1600 1800 2000
Inte
nsity
(A. U
.)
Raman Shift (cm-1)
FWHM(G)= 13.5 cm-1
Single Crystal Graphite
No D Peak
No extra broadening due to disorder
No FWHM(G) increase with temperature
γan≤1.5 cm-1
(spectrometer resolution)
EPC(Γ)=45.5 (eV/Ą)2
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And… Single layer graphene…
1200 1400 1600 1800 2000
FWHM(G)= 14 cm-1
Inte
nsity
(A.U
.)
Raman Shift (cm-1)
Similar EPC
PRB 73, 155426 (2006)
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Implications for NanotubesSingle 2D peak graphene ⇒
Single 2D peak in Single Wall CNT
Curvature and confinement give diameter dependence
2D(SWNT)~2D (graphene)- A/d
2D position in Graphite should not be used to scale
Distribution of SWNTs of different diameters, distribution of 2D peaks
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What about Multi-Wall?
First approximation each wall gives a 2D peak
DWNT two 2D peaks (inner and outer wall)
HOWEVER, inter-wall interactions Can change simple picture
Further splitting, Less peaks!
Details to follow…
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ConclusionsIdentified unique features of Raman spectrum, which fingerprintsgraphene amongst all other carbon allotropes.
The Raman spectrum evolution with increasing number of layers reflects the evolution of the electronic structure and electron-phonon interactions
Raman spectroscopy is a quick, high-throughput, non-destructive technique for the unambiguous identification of graphene layers.
Raman+Graphene is Good Fun!
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Funding:• EU FAMOUS & CANAPE project• Marie Curie Fellowship IHP-HPMT-CT-2000-00209• The Royal Society• EPSRC GR/S97620/01•The Leverhulme Trust
CPU:• HPCF, Cambridge UK• IDRIS, Orsay France
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Reference