Electronic properties of monolayer copper selenide with one-dimensional moir\'e patterns

TL;DR

This study combines experimental STM/S and DFT calculations to explore how uniaxial strain and moiré patterns affect the electronic properties of monolayer CuSe, revealing a 1.28 eV band gap and strain-dependent electronic modulation.

Contribution

It provides a systematic investigation of strain effects on CuSe monolayer's electronic properties, highlighting the role of 1D moiré patterns and domain defects, which is novel in 2D material research.

Findings

CuSe monolayer exhibits a 1.28 eV band gap.

1D moiré patterns cause periodic electronic modulation.

Strain influences conduction band peak positions.

Abstract

Strain engineering is a vital way to manipulate the electronic properties of two-dimensional (2D) materials. As a typical representative of transition metal mono-chalcogenides (TMMs), a honeycomb CuSe monolayer features with one-dimensional (1D) moir\'e patterns owing to the uniaxial strain along one of three equivalent orientations of Cu(111) substrates. Here, by combining low-temperature scanning tunneling microscopy/spectroscopy (STM/S) experiments and density functional theory (DFT) calculations, we systematically investigate the electronic properties of the strained CuSe monolayer on the Cu(111) substrate. Our results show the semiconducting feature of CuSe monolayer with a band gap of 1.28 eV and the 1D periodical modulation of electronic properties by the 1D moir\'e patterns. Except for the uniaxially strained CuSe monolayer, we observed domain boundary and line defects in the CuSe monolayer, where the biaxial-strain and strain-free conditions can be investigated respectively. STS measurements for the three different strain regions show that the first peak in conduction band will move downward with the increasing strain. DFT calculations based on the three CuSe atomic models with different strain inside reproduced the peak movement. The present findings not only enrich the fundamental comprehension toward the influence of strain on electronic properties at 2D limit, but also offer the benchmark for the development of 2D semiconductor materials.