Papers by Author: Ming Hu

Abstract: WO₃ nano-films were deposited on Al₂O₃ substrate by dc reactive magnetron sputtering method. The effects of preparing conditions, such as the discharge gas ratio (Ar:O2), working pressure, sputtering time and annealing temperature on microstructure, crystalline state and NO2-sensing properties of WO₃ nano-films were investigated by orthogonal trial experiment method. The optimum technological conditions were determined by orthogonal test and extreme difference analysis. The crystallization, morphology and composition of WO₃ thin film obtained at the optimal parameters were studied by XRD, SEM and XPS. The gas sensing mechanism was also studied. WO₃ nano-film shows high sensitivity, fast response, good selectivity at the best operating temperature 200°C.

Abstract: Extensive research has been done on porous silicon (PS) and its applications in optoelectronics since the discovery of its light emitting properties. Porous silicon technology is also used for silicon micro machining. However, porous films can be seriously strained and this often causes mechanical curling, fracture and device failures. In the present study an optical apparatus based on substrate curvature method was developed for intrinsic stress measurement of thin films, which offered a lot of advantages as overall field, non-contact, high precision, nondestructive, easy operation and quick response. Using the apparatus, the residual stress in porous silicon layers prepared by electrochemical etching was obtained. The residual stresses in the films were determined by measuring the curvature of the Si substrate before and after etching. It is found that the residual tensile stress tends to increase with the porosity increasing and the doping concentration of the silicon wafer increasing. The results show that there is a deep connection between the microstructure PS and the residual stress distribution.