Surface and interface structure of quasi-free standing graphene on SiC

TL;DR

This study investigates the surface and interface structure of hydrogen-intercalated graphene on SiC, revealing changes in electronic properties, defect formation, and demonstrating SERS as a useful tool for interface analysis.

Contribution

The paper introduces the use of surface-enhanced Raman scattering (SERS) to analyze the interface structure of hydrogen-intercalated graphene, providing new insights into defect formation and electronic property changes.

Findings

Hydrogen intercalation converts graphene to quasi-free standing form with p-type carriers.

SERS detects Si-H and C-H bonds, confirming successful intercalation and defect formation.

Mobility increases fourfold after intercalation, but decreases with defect formation in bilayer graphene.

Abstract

We perform local nanoscale studies of the surface and interface structure of hydrogen intercalated graphene on 4H-SiC(1000). In particular, we show that intercalation of the interfacial layer results in the formation of quasi-free standing one layer graphene (QFS 1LG) with change in the carrier type from n- to p-type, accompanied by a more than four times increase in carrier mobility. We demonstrate that surface enhanced Raman scattering (SERS) reveals the enhanced Raman signal of Si-H stretching mode, which is the direct proof of successful intercalation. Furthermore, the appearance of D, D+D' as well as C-H peaks for the quasi-free standing two layer graphene (QFS 2LG) suggests that hydrogen also penetrates in between the graphene layers to locally form C-H sp3 defects that decrease the mobility. Thus, SERS provides a quick and reliable technique to investigate the interface structure of graphene which is in general not accessible by other conventional methods. Our findings are further confirmed by Kelvin probe force microscopy and X-ray photoelectron spectroscopy.