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

Potentiostatic coulometry is used in conjunction with electrochemical quart z-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 limitatio ns, are illustrated using the example of electrosynthesized Ag,Se thin film s, successfully used previously for developing ion-selective sensors for Ag (I), cyanide and Hg(II). Well-defined flowing electrolyte conditions are ac hieved by the EQCM/submerged wall jet (SWJ) cell arrangement. The electroly te flow rate through the nozzle is maintained constant between 5.5 and 250 cm(3) min (-1) . The hydrodynamic control makes it possible to extend the r ange of the combined EQCM/coulometric approach to greater layer thickness c onsistent with that of membranes practically used in sensor preparation. Th e stoichiometric coefficient (gamma) profile of Ag,Se 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 gamma = 2.24 +/- 0.06 is determined for the deposited layers, which is in good agreement with the values previously obtained by ex situ energy disper sive X-ray fluorescent microanalysis (EDAX). (C) 2000 Elsevier Science S.A. All rights reserved.