INVESTIGATION OF MOLYBDENUM-DISULFIDE USING A SCANNING TUNNELING MICROSCOPE UNDER IRRADIATION OF MONOCHROMATED UV-VIS

By monochromatically illuminating the tunnel junction between molybden um disulphide and the tip of a scanning tunneling microscope (STM), th e photo-induced tunneling current (Delta I) was detected. By measuring dl as a function of wavelength, the local absorption spectra of the m olybdenum disulphide bulk crystal were obtained. This Delta I was dete cted only when the potential of the sample was positively biassed. The modulation-frequency(f) dependence of Delta I, i.e., the Delta I-f ch aracteristic, and the tunnel gap separation (s) dependence of the tunn eling current (I) and Delta I, i.e., the I-s and Delta I-s characteris tics, respectively, were measured, and the effects of the thermal expa nsion and capacitance of the tunnel junction were evaluated. The resul t 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 dl and the surface topography of the adsorbed iron phthalocyanine molecules were simultaneously obtained.