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The electrodeposition of Ag at MoSe2 has been investigated, in situ, by electrochemical scanning tunneling microscopy (EC-STM). The process was investigated by observing MoSe2 at fixed electrode potentials which were referenced to the onset potential in the cyclic voltammograms of Ag electrodeposition at MoSe2. When an electrode potential more negative than the onset potential was applied to MoSe2, continuous Ag bulk deposition occurred. Consistently, the scanning tunneling microscopy (STM) image showed Ag deposits which exhibit a growth mode between island and layer growth. In the STM images taken near the onset potential, a small amount of Ag, presumably with sub-monolayer level coverage, was thought to be deposited. This initial deposition occurred so as to make the MoSe2 surface smooth in the STM images. STM imaging was difficult in the electrode potential region positive of the onset potential because the applied bias voltage became small. However, the STM images acquired during Ag deposition after a...

Surface modification of MoSe2 has been accomplished in an electrochemical environment by a combined technique of scanning tunneling microscopy (STM) indentation with the following etching reaction. The artificial holes (defects), amde by STM indentation, could successfully serve as sites that initiated the electrochemical etching reaction that resulted in growth of the holes. The etching progressed in a highly anisotropic way, mainly occurring toward directions within the basal plane of the MoSe2, and predominantly leaving the step edges with equilateral triangular shapes. The etched holes had depths of a few van der Waals layers of the MoSe2, irrespective of the depths of the artificially made initial holes. The present technique could provide favorable opportunities not only for nanometer scale lithography in solution but also for fundamental studies on the mechanism of the etching processes at layered transition metal dichalcogenide materials.

The surface of a p-MoSe 2 electrode has been observed in 0.05 M HNO 3 , in situ, by electrochemical scanning tunneling microscopy (ECSTM). Randomly oriented nanometer size spots have been observed on the surface. The STM images of the p-MoSe 2 surface have been found to change with the electrode potential. That is, the nanometer size spots appeared as a dark contrast under a smaller band bending condition (0.2 V versus SCE) while the spots disappeared or further appeared as bright contrast under a larger band bending condition (0 and -0.2 V versus SCE). This is presumed to result from whether the acceptor level, within the band gap of the p-MoSe 2 , is occupied or not. In addition, it will depend on the electrode potential, which determines the amount of the band bending.