Tip-Induced Etching and Vacancy Island Evolution on 2H-TaS2 Revealed by STM

TL;DR

This paper shows how scanning tunneling microscopy can etch and reshape 2D TaS2 surfaces, leading to controlled vacancy island formation and potential for nanolithography.

Contribution

The study introduces a new understanding of tip-induced etching and vacancy island evolution in 2H-TaS2 using real-space STM and AI analysis.

Findings

Vacancy islands on 2H-TaS2 grow with linear perimeter and parabolic area rates.

Tip-induced etching mechanisms include chemistry, water adsorbates, and native defects.

Redeposited surface islands contribute to the etching process.

Abstract

Recent research on 2D materials using scanning probe
microscopy
reveals that the surface of transition metal dichalcogenides can be
etched during the measurement via either a tunneling-field-driven
or a scanning probe-driven process. The tip-induced manipulation of
the surface structure and defects is a first step toward nanolithography
using scanning probes. Real-space scanning tunneling microscopy experiments
provide a surface defect inventory, which includes linear and point
defects for 2H-TaS2 grown by chemical vapor transport.
Extended periods of imaging trigger the formation of vacancy islands
that grow and coalesce over time, leading to the sequential removal
of entire layers. The growth kinetics of vacancies were observed over
extended periods and quantified using AI and conventional image analysis
tools. The vacancy islands have a linear growth rate of their perimeter
and corresponding parabolic growth rates in the area for isolated
islands. The growth rate variance of individual islands is discussed
in the framework of etching mechanisms including tip-induced chemistry,
etching by water adsorbates, and native defects that support vacancy
island nucleation in the TaS2 surface. New vacancy islands
emerge rapidly in newly exposed layers after the top layer is removed.
Small and mobile surface islands that are redeposited are revealed
to participate in the tip-induced etching mechanism. The quantitative
analysis of etching kinetics is a first step toward automated nanostructuring
of TaS2 surfaces. This work paves the way to use scanning
tunneling microscopy to build more complex 2D material structures.

Figures