Published in Phys. Rev. Materials 3, 084006 (2019).

Formation of Graphene atop a Si adlayer on the C-face of SiC

Jun Li1, Qingxiao Wang2, Guowei He1, Michael Widom1, Lydia Nemec3, Volker Blum4, Moon Kim2, Patrick Rinke3,5, and Randall M. Feenstra1
1Dept. Physics, Carnegie Mellon University, Pittsburgh, PA 15213, USA
2Dept. Materials Science and Engineering, The University of Texas at Dallas, Richardson, TX 75080, USA
3Fritz-Haber-Institut der Max-Planck-Gesellschaft, D-14195, Berlin, Germany
4Dept. Mechanical Engineering and Materials Science, Duke University, Durham, NC 27708 USA
5Dept. Applied Physics, Aalto University, P.O. Box 11100, Aalto FI-00076, Finland

Abstract

The structure of the SiC(000-1) surface, the C-face of the {0001} SiC surfaces, is studied as a function of temperature and of pressure in a gaseous environment of disilane (Si2H6). Various surface reconstructions are observed, both with and without the presence of an overlying graphene layer (which spontaneously forms at sufficiently high temperatures). Based on cross-sectional scanning transmission electron microscopy measurements, the interface structure that forms in the presence of the graphene is found to contain 1.4 – 1.7 monolayers (ML) of Si, a somewhat counter-intuitive result since, when the graphene forms, the system is actually under C-rich conditions. Using ab initio thermodynamics, it is demonstrated that there exists a class of Si-rich surfaces containing about 1.3 ML of Si that are stable on the surface (even under C-rich conditions) at temperatures above about 400 K. The structures that thus form consist of Si adatoms atop a Si adlayer on the C-face of SiC, with or without the presence of overlying graphene.

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