m120128 ec seminarppt_2013
TRANSCRIPT
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