Scanning tunneling microscopy and spectroscopy of graphene on semiconducting surfaces

In order to better understand the perturbation of the physical and electronic structure of graphene monolayers and bilayers due to interactions with the supporting substrate, we have utilized scanning tunneling microscopy (STM) and spectroscopy (STS) to probe the graphene-substrate interaction for graphene on several different semiconducting substrates in ultrahigh vacuum (UHV). The Si(100) ??? 2??1:H, GaAs(110), InAs(110), and Si(111) ??? 7??7 surfaces used in this study were prepared in the UHV-STM chamber. We deposited monolayer and bilayer graphene features on the surfaces through a dry contact transfer (DCT) technique in the UHV system. The graphene-substrate interaction for the surfaces used in this study varied from quite inert and non-perturbing for the Si(100) ??? 2??1:H surface to highly disruptive and strongly interacting for the Si(111) ??? 7??7 surface. Graphene monolayer features on the GaAs(110), InAs(110), and Si(111) ??? 7??7 surfaces exhibit a semi-transparency effect wherein the atomic structure of the substrate beneath the graphene is clearly resolved through the graphene monolayer. Bilayer graphene features on the GaAs(110) and InAs(110) surfaces do not show this behavior; however, bilayer graphene features on the Si(111) ??? 7??7 surface do show the same effect. STM scans of the features at varying tip-sample biases reveal the different graphene-substrate interactions for the GaAs(110) and InAs(110) surfaces and the Si(111) ??? 7??7 surface. STS measurements of monolayer graphene quantum dots on the Si(100) ??? 2??1:H surface show an energy band gap with a scaling inversely proportional to the average lateral dimension of the features. STS measurements of graphene on the Si(111) ??? 7??7 surface show metallic behavior, which is expected for the feature sizes studied on this surface