Application of scanning electrochemical microscopy for investigation of CuxS layers

Abstract

Scanning electrochemical microscopy (SECM) is powerful tool for investigation of surfaces of different conductivity [1]. From current vs distance dependencies it is possible to extract information about surface reactivity, by calculating kinetic constant [2]. The easiest way to perform these experiments is to measure oxygen reduction current [3]. While approaching the surface, the measured signal depends on the conductivity of the surface and (i) if the surface is conducting then close to the surface current signal is increasing, (ii) if the surface is non-conducting then the signal is decreasing. If surface is semiconducting the current vs dependence can be observed between these two characteristics. Out of many different semiconductor layers copper sulfide is interesting one, due to their metal-like electrical conductivity, chemical-sensing capability and ideal characteristics for solar energy conversion. Consequently, copper sulfides modified polymers are used: (i) as the conductive substrates for the deposition of metal and semiconductors; (ii) as gas sensors functioning at temperatures tending to room temperature; (iii) as polarizers of infrared radiation; and (iv) as active absorbents of radio waves. Electrically conductive CuxS layers can be prepared by the sorption-diffusion method, described earlier [4]. By this method, the surface of a polymer is initially treated by the solution containing sulfurization agent, and then by the aqueous solution of metal salt. Each step of deposition of different layers can be investigated by SECM. The main aim of this work was to investigate differently modified electrically conductive CuxS layers. Normalized current dependence on distance from CuxS differently modified surface. Oxygen reduction current at -500 mV was measured by moving ultramicroelectrode (radius of 5 μm) in three electrodes electrochemical cell, with platinum counter and Ag/AgCl reference electrode.