Vacancy diffusion on a brominated Si(100) surface: Critical effect of the dangling bond charge state

TL;DR

This study investigates how the charge state of silicon dangling bonds influences vacancy diffusion on a brominated Si(100) surface, revealing that positively charged vacancies are mobile while neutral and negative ones are not, with implications for surface imaging and atom manipulation.

Contribution

It demonstrates the critical role of the dangling bond charge state in vacancy diffusion, combining experimental STM observations with density functional theory calculations.

Findings

Positively charged vacancies diffuse at positive bias.

Neutral and negatively charged vacancies do not diffuse.

Positively charged vacancies have a lower activation barrier.

Abstract

Silicon dangling bonds (DBs) on an adsorbate-covered Si(100) surface can be created in a scanning tunneling microscope (STM) with high precision required for a number of applications. However, vacancies containing DBs can diffuse, disrupting precisely created structures. In this work, we study the diffusion of Br vacancies on a Si(100)-2$\times$1-Br surface in an STM under typical imaging conditions. In agreement with previous work, Br vacancies diffuse at a positive sample bias voltage. Here, we demonstrated that only vacancies containing a positively charged DB hop across the two atoms of a single Si dimer, while vacancies containing neutral and negatively charged DBs do not. Calculations based on the density functional theory confirmed that positively charged Br (and Cl) vacancies have a minimum activation barrier. We propose that diffusion operates by both one-electron and two-electron mechanisms depending on the applied voltage. Our results show that the DB charge has a critical effect on the vacancy diffusion. This effect should be taken into account when imaging surface structures with charged DBs, as well as when studying the diffusion of other atoms and molecules on the Si(100) surface with vacancies in an adsorbate layer.