Graphene

Sida Wang

Overview

• Overview– Current Research– Current Research

– Potential Application

• My Work– Theoretical

– Experimental

– Patterns

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

Stabilization Mechanism

• Small deformation in the third dimension

Potential Applications

� Graphene based electronics

� Battery (High surface to volume ratio)

� Light weight micromechanical resonator

� Sensitive chemical detector� Sensitive chemical detector

� Molecular Sieves

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

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

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

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

The Problem

Contrast = (R2 – R1)/R1

graphene

R2R1

SiO2

Si

graphene

The Abstract Problem

The Simpler Problem

The Solution

ResultsPlot of Contrast

Wavelength (nm)

Contrast = (R2 – R1)/R1

Designing New Substrate

• A good substrate with higher contrast must be possible.

More Contrast

• Changing n of the substrate(n0=5.4-0.4i)

n=2.2-0.4i

More Contrast

• By changing n of the thinfilm (n0=1.41)

n=2.3

Experimental Work

• There is a 10% contrast

• But there are other troubles experimentallyA

Experimental Concerns

• The probability distribution number of layers

Another Unhelpful Distribution

• The probability distribution area

A Beneficial Distribution

• Probability of spotting the sample in 1 sec

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

My Samples

Analysis

Intensity Analysis

Intensity vs. Position

Errors In Intensity Analysis

Some Patterns

• Patterns are interesting

On the graphite

59 degrees

60 degrees

SEM Image of Graphene

A. K. GEIM, K. S. NOVOSELOV, Rise of graphene, Nature

Graphene Industries and UBC Samples

Graphene industries UBC

Folding

The graphite

Angles and Straight Edges

120 degrees

118 degrees117 degrees

118 degrees

120 degrees122 degrees

30 microns

Upper Limit in Size

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

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

Summary

• Current Research

– Properties and potential applications of graphene

• My Work• My Work

– Theoretical, multilayer reflection problem

– Experimental, making samples

– Patterns on the samples

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!

Extra Slides

Stronger than modelled

• Heats of hydrogenation

– 29 kilocalories

3x29=87 > 50

– 50 kilocalories

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