Investigation of Molybdenum Disulphide Using a Scanning Tunneling Microscope under Irradiation of Monochromated UV-VIS

Abstract

By monochromatically illuminating the tunnel junction between molybdenum disulphide and the tip of a scanning tunneling microscope (STM), the photo-induced tunneling current (ΔI) was detected. By measuringΔI as a function of wavelength, the local absorption spectra of the molybdenum disulphide bulk crystal were obtained. This ΔI was detected only when the potential of the sample was positively biassed. The modulation-frequency(f) dependence of ΔI, i.e., the ΔI-f characteristic, and the tunnel gap separation (s) dependence of the tunneling current (I) and ΔI, i.e., the I-s and ΔI-s characteristics, respectively, were measured, and the effects of the thermal expansion and capacitance of the tunnel junction were evaluated. The result revealed that the thermal effect can be neglected, while the effect of capacitance is non-negligible at a large-s region. Furthermore, the spatial distribution of ΔI and the surface topography of the adsorbed iron phthalocyanine molecules were simultaneously obtained.