m120128 ec seminarppt_2013

GRAPHENE AS A REPLACEMENT FOR

SILICON

RICHU JOSE CYRIAC

M120128EC

WONDER MATERIAL???

MOTHER OF ALL GRAPHITIC FORM

GRAPHENE -SYNTHESIS

Exfoliation method

GRAPHENE –SYNTHESIS...(CONTD)

Chemical vapor deposition Transition metal layers (e.g. Ir, Pd, Ni, Cu) Furnace to be heated to 1000º C in a hydrocarbon gas Catalyzes decomposition of hydrocarbon gas the dissociated carbon

atoms Later cooling, Carbon atom precipitates to surface and graphene is

formed. large area, high quality, controllable number of layers and low defects.

GRAPHENE -SYNTHESIS...(CONTD)

Epitaxial growth

Annealing of SiC crystal at a very elevated temperature (~2000 K) in ultra-high vacuum.

Thermal desorption of Si from the top layers of SiC. Time or temperature of the heating treatment is a limiting factor.

STRUCTURE OF GRAPHENE

STRUCTURE OF GRAPHENE

ELECTRONIC BAND STRUCTURE

THEORY OF RELATIVITY A stationary particle (p=0) has rest energy

A particle in motion is described by relativistic

dispersion relation

Velocity:

222 )()( cpmcE

2mcE

22 )()( cpmc

cpc

dP

dEv

Massive particle(e.g. electron)

Non-relativistic limit(v‹‹c)

Massless particle(e.g. photon)

....2

22

m

pmcE

0m

cv pcE

222 )()( cpmcE

CHIRAL DIRAC FERMIONS Massless Dirac fermions: Charged massless particles Relativistic Quantum particles Spin directed only along the direction of propagation-

pseudospin A projection pseudospin on the direction of motion-

Chirality

KLEIN TUNNELING

Weak electrostatic confinement. It cannot be used as a digital switch.

GRAPHENE-DOPING Hetero atom doping

B and N –substitutional doping-similar atomic size Arc discharge

High current between graphene electrodes in presence of H2 + B2 H6 or N2 + NH3

Chemical vapour deposition

Cu film on silicon substrate as a catalyst in H2 atmosphere and CH4+NH3

Ion-irradiation

Defects are introduced through positive nitrogen ions and the samples are annealed in NH3 . In the process of annealing defects are restored ,getting N doping

Chemical modification process NO2 and NH3 creates holes and electrons respectively.Adsorption of water molecules-inexpensive, cheap, easier to

control-but performance degradationOrganic molecules

Napthalalediamene – n doping

9,10-Dibromo anthracene- p doping

Electrostatic field tuning

OTHER METHODS-OPENING BANDGAP

Applying strain to graphene Biasing bilayer graphene

APPLICATIONS

CONCLUSION Can achieve high speed in electronic devices,

which is transparent and flexible. As if now cannot be used as a digital switch

owing to Klein tunneling. Can be used in RF devices.

It is surely a candidate material to replace silicon in near future.

REFERENCE The rise of Graphene, A.K. Geim and K.S. Novoselov

The elementary electronic properties of Graphene, Qinlong Luo

Graphene: carbon in two dimensions, Mikhail I. Katsnelson

Graphene: Is It the Future for Semiconductors?An Overview of the Material, Devices, and Applications, Yaw Obeng and Purushothaman Srinivasan

Graphene Doping: A Review ,Beidou Guo ,Liang Fang, Baohong Zhang, Jian Ru Gong

THANK YOU

APPENDIX Analytical description of π band

yyx

yyx

ka

ka

ka

s

ka

ka

ka

kE

2cos4

2cos

23

cos411

2cos4

2cos

23

cos41)(

20

2