Atomic-scale structures and electronic states of defects on Ar+-ion irradiated MoS2

We observed MoS2 surfaces bearing defects generated by Ar+-ion bombardment at the density of 2.75 x 10(-3) ions/nm(2) by scanning tunneling microscopy (STM) and measured local electronic state by scanning tunneling spectroscopy (STS). Two types of concave surface defects, one with a bright feature and one without, were observed in STM images. STS revealed that the two features have different spectra. We elucidated the origins of these defects by comparison of the experimental results with electronic states obtained from density functional theory (DFT) calculation. The dI/dV curve measured at the center of the bright feature has a mid-gap state, which can be assigned to Mo beneath the feature. The bright feature was composed of several S vacancies, leaving a surface with metallic character. The concave defect without the bright feature is interpreted as being formed by layer-by-layer removal of MoS2. The dI/dV curve measured at the center of this type of concave defect showed a semiconducting property similar to that of a clean MoS2 surface, and the edge of the concave region shows a peak at -0.5 V from the Fermi level. (C) 2012 Elsevier B.V. All rights reserved.