A team of researchers, led by Suneel Kodambaka, assistant professor of materials science and engineering, have found that the electronic properties of graphene, a one-atom-thick sheet of graphite, depend on its crystallinity and the metal contact. Large-scale fabrication of graphene devices will, therefore, require a precise control over graphene quality and metal contact. The team included researchers from UCLA Engineering, Sandia National Laboratories/California, and Colorado School of Mines.
Graphene has generated considerable attention owing to its ultra-thin geometry, high carrier mobility and tunable band gap, with potential applications in high-performance low-power electronics and as transparent electrodes. Since graphene-based devices require metal (or metallic) contacts, knowledge of the electronic properties, for example, nature of the contact (Ohmic or Schottky) and electron transport at the metal-graphene interfaces is essential.
Using Palladium , or Pd (111), as a model substrate, the research group focused on understanding the influence of metal substrate and the in-plane orientation of graphene on its work function. Using a combination of in-situ low-energy electron microscopy (LEEM) and density functional theory (DFT) calculations they show that monolayer graphene on Palladium exhibits a work function that varies significantly with domain orientation, a result of spatial variations in charge transfer at the graphene-Pd interface.
For the sizeable community interested in growth and characterization of graphene and graphene-based devices, these results show that the in-plane orientation plays an important role on the nature of contact. The results suggest that a precise control over graphene orientation with respect to the metal contacts is essential for the realization of large-scale graphene electronics.
The work was published in the October 7 issue of Applied Physics Letters, and is available online here: http://apl.aip.org/resource/1/applab/v97/i14/p143114_s1.