Inducing Electronic Changes in Graphene through Silicon (100) Substrate Modification

We have performed scanning tunneling microscopy and spectroscopy (STM/STS) measurements as well as ab initio calculations for graphene monolayers on clean and hydrogen(H)-passivated silicon (100) (Si(100)/H) surfaces. In order to experimentally study the same graphene piece on both substrates, we develop a method to depassivate hydrogen from under graphene monolayers on the Si(100)/H surface. Our work represents the first demonstration of successful and reproducible depassivation of hydrogen from beneath monolayer graphene flakes on Si(100)/H by electron-stimulated desorption. Ab initio simulations combined with STS taken before and after hydrogen desorption demonstrate that graphene interacts differently with the clean and H-passivated Si(100) surfaces. The Si(100)/H surface does not perturb the electronic properties of graphene, whereas the interaction between the clean Si(100) surface and graphene changes the electronic states of graphene significantly. This effect results from the covalent bonding between C and surface Si atoms, modifying the π-orbital network of the graphene layer. The local density of states shows that the bonded C and Si surface states are highly disturbed near the Fermi energy.