Real-time stoichiometry monitoring of electrodeposited chalcogenide films via coulometry and electrochemical quartz-crystal microgravimetry with hydrodynamic control. Ag2+Se case

Abstract

Abstract Potentiostatic coulometry is used in conjunction with electrochemical quartz-crystal microgravimetry (EQCM) with controlled hydrodynamics to develop a new electroanalytical protocol for in situ composition monitoring of metal chalcogenide thin films. The approach, its application scope and limitations, are illustrated using the example of electrosynthesized AgySe thin films, successfully used previously for developing ion-selective sensors for Ag(I), cyanide and Hg(II). Well-defined flowing electrolyte conditions are achieved by the EQCM/submerged wall jet (SWJ) cell arrangement. The electrolyte flow rate through the nozzle is maintained constant between 5.5 and 250 cm3 min−1. The hydrodynamic control makes it possible to extend the range of the combined EQCM/coulometric approach to greater layer thickness consistent with that of membranes practically used in sensor preparation. The stoichiometric coefficient (y) profile of AgySe is monitored in situ for comparatively thick electrodeposited films (up to 800 nm). Two distinct features are clearly distinguished in the electrochemical formation of non-stoichiometric layers: in the zone adjacent to the substrate (i.e. between 170 and 270 nm) and for greater thickness (up to 800 nm). A mean value for y=2.24±0.06 is determined for the deposited layers, which is in good agreement with the values previously obtained by ex situ energy dispersive X-ray fluorescent microanalysis (EDAX).