THIN-LAYER CHEMICAL SENSORS BASED ON CHEMICALLY DEPOSITED AND MODIFIED CHALCOGENIDE GLASSES

A new type of chemically deposited and modified thin-layer sensors has been prepared and investigated. Amorphous As2S3 and AsSe thin films obtained by the spin-coating technique and doped with silver were used as membrane materials of these sensors. It was found that the temperature of preliminary annealing of the films is crucial for doping efficiency. As-prepared films annealed above 120-degrees-C remain insulating after silver doping with subsequent annealing and/or light irradiation. XPS measurements indicated some kind of decomposition of arsenic chalcogenides in this case. Properly prepared and modified thin layers are mixed conductors with a final resistivity of about 10(5) OMEGA cm for As2Se-based and almost-equal-to 10(3) OMEGA cm for AsSe-based films. Electrochemical measurements in AgNO3 solutions revealed a reasonable sensitivity of doped AsSe films to silver ions. The ionic response of doped As2S3 films was found to be significantly poorer. High electronic conductivity giving rise to competitive interfacial redox processes seems to be one reason for such behaviour. The redox response of the films was studied in solutions of potassium hexacyanoferrate(II)/(III) with total redox concentration from 0.1 to 0.001 M. The parameters of the redox response of selenide glass thin-layer sensors are close to those of platinum electrode at high total redox concentration and even better in dilute solutions.