The (3$\times$3)-SiC-($\bar{1}\bar{1}\bar{1}$) Reconstruction: Atomic Structure of the Graphene Precursor Surface from a Large-Scale First-Principles Structure Search

TL;DR

This paper presents a new atomic model for the (3×3)-SiC-(1̅1̅1̅) surface reconstruction, crucial for understanding graphene growth on SiC, derived from large-scale first-principles searches and validated by STM simulations.

Contribution

The study introduces a novel atomic structure model for the (3×3) SiC surface phase using ab initio random structure search and density functional theory, clarifying its atomic arrangement.

Findings

The structure features five Si adatoms on a C-terminated substrate.

Simulated STM images match experimental data.

The model reveals a formally unsaturated C atom per unit cell.

Abstract

Silicon carbide (SiC) is an excellent substrate for growth and manipulation of large scale, high quality epitaxial graphene. On the carbon face (the ($\bar{1}\bar{1}\bar{1}$) or $(000\bar{1}$) face, depending on the polytype), the onset of graphene growth is intertwined with the formation of several competing surface phases, among them a (3$\times$3) precursor phase suspected to hinder the onset of controlled, near-equilibrium growth of graphene. Despite more than two decades of research, the precise atomic structure of this phase is still unclear. We present a new model of the (3$\times$3)-SiC-($\bar{1}\bar{1}\bar{1}$) reconstruction, derived from an {\it ab initio} random structure search based on density functional theory including van der Waals effects. The structure consists of a simple pattern of five Si adatoms in bridging and on-top positions on an underlying, C-terminated substrate layer, leaving one C atom per (3$\times$3) unit cell formally unsaturated. Simulated scanning tunneling microscopy (STM) images are in excellent agreement with previously reported experimental STM images.