Tailoring Kinetics on a Topological Insulator Surface by Defect-Induced Strain: Pb Mobility on Bi2Te3

TL;DR

This study demonstrates that local strain induced by defects on Bi2Te3 surfaces can significantly modify Pb adatom mobility, revealing a unique strain-dependent diffusion behavior with implications for interface control in topological insulator films.

Contribution

It introduces a novel strain-dependent diffusion mechanism for Pb on Bi2Te3, combining experimental STM, DFT calculations, and kinetic Monte Carlo simulations to understand adatom behavior.

Findings

Pb adatom mobility is tunable by local strain.

Diffusion barrier E_d shows a cusp-like dependence on strain.

Experimental and simulation results are in good agreement.

Abstract

Heteroepitaxial structures based on Bi$_{2}$Te$_{3}$-type topological insulators (TIs) exhibit exotic quantum phenomena. For optimal characterization of these phenomena, it is desirable to control the interface structure during film growth on such TIs. In this process, adatom mobility is a key factor. We demonstrate that Pb mobility on the Bi$_{2}$Te$_{3}$(111) surface can be modified by the engineering local strain, {\epsilon}, which is induced around the point-like defects intrinsically forming in the Bi$_{2}$Te$_{3}$(111) thin film grown on a Si(111)-7 $\times$ 7 substrate. Scanning tunneling microscopy observations of Pb adatom and cluster distributions and first-principles density functional theory (DFT) analyses of the adsorption energy and diffusion barrier E$_{d}$ of Pb adatom on Bi$_{2}$Te$_{3}$(111) surface show a significant influence of {\epsilon}. Surprisingly, E$_d$ reveals a cusp-like dependence on {\epsilon} due to a bifurcation in the position of the stable adsorption site at the critical tensile strain {\epsilon}$_{c}$ $ \approx $ 0.8%. This constitutes a very different strain-dependence of diffusivity from all previous studies focusing on conventional metal or semiconductor surfaces. Kinetic Monte Carlo simulations of Pb deposition, diffusion, and irreversible aggregation incorporating the DFT results reveal adatom and cluster distributions compatible with our experimental observations.