Ming Hu

Study of residual stress in porous silicon during drying

Porous silicon has been extensively researched as an interesting photoluminescent material for photoelectric device integration. Residual stress often occurs due to capillary force during drying and results in warp, fracture and failure of the devices. Micro-Raman spectroscopy (MRS) has many special advantages of nondestructive, non-contact, high spatial resolution (1μm), broad spectrum range, Raman shift unaffected by the frequency of laser source, and ability to focus on a specific layer of sample. Furthermore, Raman spectrum is a powerful tool for the study of residual stress for its sensitivity to strain in the sample, which make it possible to measure residual stress directly. The underlying basis of micro-Raman spectroscopy for strain measurement is that Raman shift reflects the atomic spacing change, namely the strain information. The residual stress was measured during drying using Micro-Raman spectrum technology, the maxim is 3.6GPa. The relation of residual stress and Raman shift, drying times and FWHM were analysed, the capillary effect and the residual stress evolution from wetting to drying stages of porous silicon were investigated using phonon confinement model.

Effects of Ti addiction in WO3 thin film ammonia gas sensor prepared by dc reactive magnetron sputtering

WO3 sensing films (1500 Å) were deposited using dc reactive magnetron sputtering method on alumina substrate on which patterned interdigital Pt electrodes were previously formed. The additive Ti was sputtered with different thickness (100-500 Å) onto WO3 thin films and then the films as-deposited were annealed at 400°C in air for 3h. The crystal structure and chemical composition of the films were characterized by XRD and XPS analysis. The effect of Ti addition on sensitive properties of WO3 thin film to the NH3 gas was then discussed. WO3 thin films added Ti revealed excellent sensitivity and response characteristics in the presence of low concentration of NH3 (5-400 ppm) gas in air at 200°C operating temperature. Especially,in case 300 Å thickness of additive Ti, WO3 thin films have a promotional effect on the response speed to NH3 and selectivity enhanced with respect to other gases (CO, C2H5OH, CH4). The influence of different substrates, including alumina, silicon and glass, on sensitivity to NH3 gas has also been investigated.