Line and Point Defects in MoSe2 Bilayer Studied by Scanning Tunneling Microscopy and Spectroscopy

TL;DR

This study uses STM/S to analyze line and point defects in bilayer MoSe2 films, revealing defect networks, quantum confinement effects, and ionization phenomena relevant for device applications.

Contribution

It provides detailed atomic-scale characterization of defects in bilayer MoSe2, highlighting differences from monolayer films and insights into defect states and their electronic properties.

Findings

Networks of inversion domain boundary defects observed in both layers.

Quantum confinement effects in defect states identified.

Ionization of point defects by electric field demonstrated.

Abstract

Bilayer (BL) MoSe2 films grown by molecular-beam epitaxy (MBE) are studied by scanning tunneling microscopy and spectroscopy (STM/S). Similar to monolayer (ML) films, networks of inversion domain boundary (DB) defects are observed both in the top and bottom layers of BL MoSe2, and often they are seen spatially correlated such that one is on top of the other. There are also isolated ones in the bottom layer without companion in the top-layer and are detected by STM/S through quantum tunneling of the defect states through the barrier of the MoSe2 ML. Comparing the DB states in BL MoSe2 with that of ML film reveals some common features as well as differences. Quantum confinement of the defect states is indicated. Point defects in BL MoSe2 are also observed by STM/S, where ionization of the donor defect by the tip-induced electric field is evidenced. These results are of great fundamental interests as well as practical relevance of devices made of MoSe2 ultrathin layers.