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semiconductor-electrolyte boundaries; tungsten compounds; molybdenum compounds; selenium compounds; electrochemistry; voltage distribution; capacitance; adsorbed layers; electroreflectance; electrical conductivity; space charge
Abstract:
The voltage distribution at the n-WSe2 and n-MoSe2/electrolyte interface is obtained from electroreflection and capacitancemeasurements. Variations in the electroreflection signal intensity with electrode potential are used as a direct probeto locate the band position as a function of potential. Capacitance measurements are consistent with and complement theelectroreflection results. As expected, a variety of Fe3+/2+ based mid-gap redox couples have no significant effect on thevoltage distribution across either dichalcogenide/electrolyte interface. In the presence of the strongly oxidizing ceriumredox couple, the authors observed flatband shifts/double-layer charging, and conclude that Ce4+ adsorption rather thanhole injection is the cause. There is a common threshold of 0.4 V above either dichalcogenide's flat-band potential beforethe double layer begins to charge. Then, for more positive biases, it is the double layer that charges while the space chargevoltage remains relatively unaffected. Finally, above about 0.7 and 1.1 V respectively, double-layer charging ceases, andthe applied voltage again appears predominantly across the space-charge region. We estimate that Ce4+ adsorption saturateswith a coverage on the order of 0.1 monolayer.
