1. APS -- March Meeting 2011 Graphene nanoelectronics from ab initio theory Jesse Maassen, Wei Ji and Hong Guo Department of Physics, McGill University, Montreal, Canada

2. 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.

3. APS -- March Meeting 2011 Experimental works: Nature Nanotechnology 3, 486 (2008)Phys. Rev. B 79, 245430 (2009) Photocurrent experiments Motivation (of studying a graphene/metal contact)

4. APS -- March Meeting 2011 Experimental works: Nature Nanotechnology 3, 486 (2008)Phys. Rev. B 79, 245430 (2009) Photocurrent experiments Motivation (of studying a graphene/metal contact)

5. APS -- March Meeting 2011 Our goal Parameter-free transport calculation of a graphene / metal interface

6. 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 H KS  1 Jeremy Taylor, Hong Guo and Jian Wang, PRB 63, 245407 (2001). System Left lead Right lead -- ++ Simulation Box ++ --

7. 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 (1 st C on metal, 2 nd C on hollow site). After relaxation Metal

8. 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

9. APS -- March Meeting 2011 Graphene-metal interface  Double minimum T.  T almost perfectly described by pure graphene at T MIN. Appl. Phys. Lett. 97, 142105 (2010) Transport properties: graphene | Cu(111) junction

10. APS -- March Meeting 2011 EFEF kk EE Graphene-metal interface Transport properties: graphene | Cu(111) E = 0.2 eV Transmission kxkx kzkz  Momentum filtering kk Nano. Lett. 11, 151 (2011)

11. APS -- March Meeting 2011 Graphene-metal interface  One Dirac point pinned, while other moves with V.  Peak in conductance  doping level of graphene Appl. Phys. Lett. 97, 142105 (2010) Transport properties: graphene | Cu(111) junction

12. 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(p z ) : B-site C(p z ) : Ni(d Z2 )

13. APS -- March Meeting 2011 Graphene-metal interface Nano. Lett. 11, 151 (2011) Transport properties : graphene-Ni(111) system

14. APS -- March Meeting 2011 Graphene-metal interface Transport properties : graphene-Ni(111) system Nano. Lett. 11, 151 (2011)

15. 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)

16. 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

17. APS -- March Meeting 2011 Thank you ! Questions? Computation facilities: RQCHP Financial support: NSERC, FQRNT and CIFAR