THE SCANNING MICROSCOPE FOR SEMICONDUCTOR CHARACTERIZATION (SMSC) - STUDY OF THE INFLUENCE OF SURFACE-MORPHOLOGY ON THE PHOTOELECTROCHEMICAL BEHAVIOR OF AN N-MOSE2 SINGLE-CRYSTAL ELECTRODE BY PHOTOCURRENT AND ELECTROLYTE ELECTROREFLECTANCE IMAGING

Photocurrent and electrolyte electroreflectance (EER) measurements hav e been carried out, on a microscopic scale, in order to characterize t he photoelectrochemical behavior of an n-MoSe2 single crystal as a fun ction of its surface morphology. Digital images of the surface distrib ution of these photoeffects have been obtained with the help of the sc anning microscope for semiconductor characterization (SMSC). From the mathematical expressions describing both photoeffects, it is shown tha t the corresponding images yield complementary information about the s emiconductor (sc)/electrolyte interface, which can be related to the s emiconductor topology. A comparative study is made on three different types of surface: (1) ''as grown'', produced just after growing the si ngle crystal; (2) ''aged'', which results from the as-grown surface af ter working the electrode in the photoelectrochemical cell for some ti me; and (3) ''freshly-peeled'', which is obtained by peeling off the u pper sandwich layers of the aged sample. In the case of the aged surfa ce, it is observed that electrochemical corrosion is detrimental for t he photoelectrochemical behavior of the semiconductor, except on the s harp defects of its van der Waals surface. An explanation of this agin g effect is proposed on the basis of the high anisotropy and structura l parameters of this material. From EER images of the sc/electrolyte i nterface, the spatial distribution of the drop of the applied voltage at the Helmholtz layer is shown for the first time.