S.Y. Ma

Blue-green emission mechanism and spectral shift of Al-doped ZnO films related to defect levels

The crystal structure, surface morphology, chemical state and optical properties of Al-doped ZnO films grown at different sputtering powers are studied. Results indicated that compressive stress related to defects exists in all the samples measured by X-ray diffraction. Blue-green emission mechanisms and a blue-shift were explored based on defects sites. The peak at 458 nm comes from the electron transition from interstitial Zn to the top of the valence band and transition from the conduction band to misplaced oxygen defects. The peak at 490 nm comes from the electron transition from interstitial Zn to Zn vacancies or interstitial O and transition from a complex defect level of O vacancies and interstitial Zn to the valence band. The existence of compressive stress related to the defects in Al-doped ZnO plays a significant role in the blue-green emission and blue-shift.

Microstructures and optical absorption of Ti-doped ZnO films

Undoped and Ti-doped ZnO films were deposited using radio frequency reactive magnetron sputtering at various sputtering powers. The crystal structures, surface morphology, chemical state of titanium, zinc, and oxygen and optical properties in Ti-doped ZnO films were systematically investigated via X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and ultraviolet visible (UV-Vis)spectrophotometer. ZnO films showed a stronger preferred orientation toward c-axis and became smoother after Ti doping. The intensity of Ti-doped ZnO (002) peak further increased and surface showed more lattice defects as sputtering power increased from 100 W to 150 W. The XPS spectrum confirmed that Zn exists only in the oxidized state and the sample is a mixture of ZnO and TiO2. In addition, the UV absorption edge of ZnO films shifted to a longer wavelength as sputtering power increased.

Design of automatic system for multiple-gas sensing

This paper presents the design of the automatic system for detecting harmful gases. It uses PC, NI LabWindows/CVI, commercially available data acquisition hardware, and circuit boards specially designed for fluctuation-enhanced gas sensing. The system can not only be used for laboratory research and teaching, but also used for detecting CH4 and CO in coal mines. Our initial test results with commercial sensor support the feasibility of developing this prototype into a cost effective product used for multiple-gas sensing.