Exfoliation of Graphene onto Si(111)-7 × 7 under Ultrahigh Vacuum Provides Some Protection against Exposure to Air.

Abstract

The investigation of graphene as a protective coating for different materials has been an area of active research for well over a decade. However, graphene's ability to protect clean, reconstructed silicon from ambient gases has remained uninvestigated. Here, we describe the use of a clean ultrahigh vacuum transfer method to deposit graphene onto the Si(111)-7 × 7 reconstruction. Using a combination of X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM), we confirmed the successful transfer of graphene onto the surface. We then exposed the graphene-protected surface to 120 L of ambient air in the vacuum chamber and found that although the reconstruction is destroyed on unprotected terraces, clean and ordered silicon can be imaged through the transferred graphene. Exposing the sample to ambient air at atmospheric pressure for 2 days produces a strong signature of oxidation in XPS, and STM images revealed that although graphene can still be identified, the regions beneath the graphene appear amorphous. This work demonstrates that graphene provides some protection against the oxidation of Si(111)-7 × 7 by air, but that this protective ability is not sufficient to forestall oxidation during prolonged exposure to atmospheric conditions.