graphene - web.stanford.eduweb.stanford.edu/~sidaw/projects/graphene.pdfpotential applications...
TRANSCRIPT
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Graphene
Sida Wang
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Overview
• Overview– Current Research– Current Research
– Potential Application
• My Work– Theoretical
– Experimental
– Patterns
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Graphene: Overview of Properties
• Graphene has many impressive properties
– It is not supposed to exist (Landau and Peierls)
– zero-gap semiconductor
– Its charge carriers mimic relativistic particles– Its charge carriers mimic relativistic particles
– Ballistic electrons
– Non-diminishing conductivity
– Room temperature quantum hall effect
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Stabilization Mechanism
• Small deformation in the third dimension
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Potential Applications
� Graphene based electronics
� Battery (High surface to volume ratio)
� Light weight micromechanical resonator
� Sensitive chemical detector� Sensitive chemical detector
� Molecular Sieves
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My Work: Making Graphene
• Background
• Experimental Work
• The goal: observe photocurrent in • The goal: observe photocurrent in graphene as predicted by E. J. Mele, Petr Kra´l, David Toma´nek
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Methods
• Micromechanical Exfoliation
• Chemical Synthesis (222 carbons)
• Decomposition of SiC wafer
• Reduction of graphene oxide
Pealing with tape
• Reduction of graphene oxide
• Other Sophisticated Methods
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Detection Methods
• AFM is the only direct detection method
– Limited by scanning range, and speed
• Optical detection was crucial to the discovery of graphenediscovery of graphene
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Optical Contrast
• The thickness of graphene is ~0.3 nm
• Transparent in air
• The contrast is high only for specific substrates (300nm of SiO on Si)substrates (300nm of SiO2 on Si)
• P. Blake et al, Making graphene visible
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The Problem
Contrast = (R2 – R1)/R1
graphene
R2R1
SiO2
Si
graphene
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The Abstract Problem
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The Simpler Problem
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The Solution
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ResultsPlot of Contrast
Wavelength (nm)
Contrast = (R2 – R1)/R1
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Designing New Substrate
• A good substrate with higher contrast must be possible.
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More Contrast
• Changing n of the substrate(n0=5.4-0.4i)
n=2.2-0.4i
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More Contrast
• By changing n of the thinfilm (n0=1.41)
n=2.3
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Experimental Work
• There is a 10% contrast
• But there are other troubles experimentallyA
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Experimental Concerns
• The probability distribution number of layers
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Another Unhelpful Distribution
• The probability distribution area
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A Beneficial Distribution
• Probability of spotting the sample in 1 sec
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Mostly random but certain things help
• Parameters
– Pressure (strength and time and what type)
– Number of cleave
– Surface treatment of wafer– Surface treatment of wafer
– Other details
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My Samples
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Analysis
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Intensity Analysis
Intensity vs. Position
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Errors In Intensity Analysis
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Some Patterns
• Patterns are interesting
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On the graphite
59 degrees
60 degrees
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SEM Image of Graphene
A. K. GEIM, K. S. NOVOSELOV, Rise of graphene, Nature
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Graphene Industries and UBC Samples
Graphene industries UBC
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Folding
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The graphite
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Angles and Straight Edges
120 degrees
118 degrees117 degrees
118 degrees
120 degrees122 degrees
30 microns
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Upper Limit in Size
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Current Price of Graphene
• Graphene Industries sold a 900µm2 piece for £400 = $820
• $ 1,227,000,000,000,000 per gram
– Lasts 3 million years at a rate of spending of 1 – Lasts 3 million years at a rate of spending of 1 million dollars a day
– 36m x 36m =1300m2 in area
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Future Works
• More and larger samples
• Reliably characterizing the samples
• Shoot the samples with a laser
• Placing electrodes on the samples• Placing electrodes on the samples
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Summary
• Current Research
– Properties and potential applications of graphene
• My Work• My Work
– Theoretical, multilayer reflection problem
– Experimental, making samples
– Patterns on the samples
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I sincerely thank
• Prof. van Driel for this opportunity
• Everyone for being very nice and very helpful
• Ryan for patiently explaining a lot of things• Ryan for patiently explaining a lot of things
• Thank you!
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Extra Slides
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Stronger than modelled
• Heats of hydrogenation
– 29 kilocalories
3x29=87 > 50
– 50 kilocalories
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Features of Contrast Function
• The contrast between n layer and n+1 layers remains approximately constant when n is small. And approaches 0 when n is large.n is large.
• High contrast at low reflectivity
• Linear