A novel CuS thin film deposition method by laser-assisted spray photolysis deposition and its application to EGFET

Abstract

Several studies have deposited copper sulphide (CuS) thin films via spray pyrolysis using a heater. In this study, the spray pyrolysis deposition of CuS thin films was carried out using two processes; the first process called pyrolytic process to deposit CuS thin film on glass, ITO, Si and tungsten substrates using CW CO2 laser beam (10.6μm, 40W) as the heat source rather than a heater, while the second process called photolytic process to deposit CuS thin film on glass substrate by apply the laser directly on the droplet after leaving the nozzle. Copper chloride and sodium thiosulfate were used as precursor materials for the preparation of CuS. Deionized water was used to dissolve 0.4M concentration of copper chloride and sodium thiosulfate, separately. In pyrolytic process, the glass, ITO, Si and tungsten substrates were placed on a rotator fan to provide large surface area coating, and to ensure uniform distribution of laser beam heat and the sprayed solution through deposition. Hence, homogenous films of CuS nanocrystallites with covellite phase with good structural and morphological characteristics were obtained. In photolytic process, the glass substrate was placed on the heater and the laser was guided toward the droplet exactly after leaving the nozzle, to achieve resonant absorption of the laser by aerosols. The structure of this film was differ from the previous films, it contains S element in addition to the pure CuS covellite phase. The membrane surface parameters (number of ions, crystallite size, surface-to-volume ratio of these crystallites and contact angle) were investigated to determine the pH sensor applicability of the CuS membranes deposited by CO2 laser beam. The CuS membrane deposited onto glass substrate showed the optimum pH sensing performance: 31.7mV/pH with linearity of 99.56% & hysteresis 1.65mV (pyrolytic process), and 40mV/pH with 97.78% & hysteresis 0.53mV (photolytic process), respectively.