Modulated STM images of ultrathinMoSe2films grown onMoS2(0001) studied by STM/STS

Abstract

The ${\mathrm{MoSe}}_2$/${\mathrm{MoS}}_2$ system is investigated by scanning tunneling microscope (STM) and by its spectroscopic mode, scanning tunneling spectroscopy (STS). STM images show a hexagonal wagon-wheel-like pattern, which is made of bright lines and dark triangles. High-resolution STM images show that the bright line consists of twin lines separated by about 1 nm and that the hexagonal pattern is often skewed. These features are not explained by the simple moiré effect due to the lattice mismatch between the overlayer and the substrate materials. The STS spectra show that the bright area results mainly from electron waves derived from chalcogen orbitals running parallel to the interface between ${\mathrm{MoSe}}_2$ and ${\mathrm{MoS}}_2$ layers. A mechanism of the pattern formation is proposed, in which scattered electron waves produce the bright wagon-wheel-like pattern.