Tues. seminar

[CM ICTP - Trieste]

JOINT ICTP/SISSA CONDENSED MATTER SEMINARS





Seminar Room - ICTP Leonardo Building   (first floor)







Tuesday, 17 February -     11:00 a.m.




P. KHOMYAKOV    ( University of Twente )



"Doping graphene with metal contacts"



Abstract



Measuring the transport of electrons through a graphene sheet  
necessarily involves contacting it with metal electrodes. We study  
the adsorption of graphene on metal substrates using first-principles  
calculations at the level of density functional theory.  The bonding  
of graphene to Al, Ag, Cu, Au and Pt(111) surfaces is so weak that  
its unique "ultrarelativistic'' electronic structure is preserved.  
The interaction does, however, lead to a charge transfer that shifts  
the Fermi level by up to 0.5 eV with respect to the conical points.  
The crossover from p-type to n-type doping occurs for a metal with a  
work function ~5.4 eV, a value much larger than the work function of  
free-standing graphene, 4.5 eV.  We develop a simple analytical model  
that describes the Fermi level shift in graphene in terms of the  
metal substrate work function. Graphene interacts with and binds more  
strongly to Co, Ni, Pd and Ti. This chemisorption involves  
hybridization between graphene p_z-states and metal d-states that  
opens a band gap in graphene. The graphene work function is as a  
result reduced considerably. In a current-in-plane device geometry  
this should lead to n-type doping of graphene.