APS -- March Meeting 2011

Graphene nanoelectronics from ab initio theory

Jesse Maassen, Wei Ji

and Hong Guo

Department of Physics,

McGill University, Montreal, Canada

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

APS -- March Meeting 2011

Motivation(of studying a graphene/metal contact)

Graphene has interesting properties (i.e., 2D material, zero gap, linear dispersion bands, …).

For electronics, all graphene sheets must unavoidably be

electrically contacted to a metal (source/drain).

Can the graphene/metal interface largely influence the global response of the device?

Subject of much experimental and theoretical research.

APS -- March Meeting 2011

Experimental works:

Nature Nanotechnology 3, 486 (2008) Phys. Rev. B 79, 245430 (2009)

Photocurrentexperiments

Motivation(of studying a graphene/metal contact)

APS -- March Meeting 2011

Experimental works:

Nature Nanotechnology 3, 486 (2008) Phys. Rev. B 79, 245430 (2009)

Photocurrentexperiments

Motivation(of studying a graphene/metal contact)

APS -- March Meeting 2011

Our goal

Parameter-free

transport calculation

of a graphene /

metal interface

APS -- March Meeting 2011

Theoretical method

• Density functional theory (DFT) combined with nonequilibrium Green’s functions (NEGF)1

• Two-probe geometry under finite bias

NEGF

DFT

HKS

1 Jeremy Taylor, Hong Guo and Jian Wang, PRB 63, 245407 (2001).

SystemLeftlead

Rightlead

- +

Simulation Box

+

-

APS -- March Meeting 2011

Atomic structure

Which metals? What configuration at the interface?

Cu, Ni and Co (111) have in-place lattice constants that almost match that of graphene (PRL 101, 26803 (2008)).

Found most stable configuration (1stC on metal, 2ndC on hollow site).

After relaxation

Metal

APS -- March Meeting 2011

Appl. Phys. Lett. 97, 142105 (2010)

Graphene-metal interface

Bandstructure of hybrid

graphene | Cu(111) system

Graphene states in black Weak hybridization n-type graphene

Metal

APS -- March Meeting 2011

Graphene-metal interface

Double minimum T.

T almost perfectly described by pure graphene at TMIN.

Appl. Phys. Lett. 97, 142105 (2010)

Transport properties:

graphene | Cu(111) junction

APS -- March Meeting 2011

EF

k

E

Graphene-metal interface

Transport properties:

graphene | Cu(111) E = 0.2 eV

Tra

nsm

issi

on

kx

kz

Momentum filteringk

Nano. Lett. 11, 151 (2011)

APS -- March Meeting 2011

Graphene-metal interface

One Dirac point pinned, while other moves with V.

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Peak in conductance doping level of graphene

Appl. Phys. Lett. 97, 142105 (2010)

Transport properties:

graphene | Cu(111) junction

APS -- March Meeting 2011

Graphene-metal interface

Band structure : graphene-Ni(111) system

Strong hybridization with metal

No more linear bands

Spin-dependent band gaps

Nano. Lett. 11, 151 (2011)

: A-site C(pz): B-site C(pz)

: Ni(dZ2)

APS -- March Meeting 2011

Graphene-metal interface

Nano. Lett. 11, 151 (2011)

Transport properties : graphene-Ni(111) system

APS -- March Meeting 2011

Graphene-metal interface

Transport properties : graphene-Ni(111) system

Nano. Lett. 11, 151 (2011)

APS -- March Meeting 2011

Graphene-metal interface

Transport properties : graphene-Ni(111) system

• Spin-dependent band gaps large spin filtering

Nano. Lett. 11, 151 (2011)

APS -- March Meeting 2011

Performed a parameter-free calculation of electronic transport through a graphene/metal interface.

Cu merely n-dopes the graphene resulting in:

• Double T minimum

• Similar trends for Al, Ag, Au & Pt

• Simple modeling

Ni & Co create spin-dependent (pseudo-) band gaps in

graphene. Large spin injection efficiencies ~80%.

Graphene-metal interface

SUMMARY

APS -- March Meeting 2011

Thank you !

Questions?

Computation facilities: RQCHP

Financial support: NSERC, FQRNT and CIFAR