Yu-Tai Shih

Effects of Na content on the luminescence behavior, conduction type, and crystal structure of Na-doped ZnO films

This study investigates the effect of Na content on the structural, optical, and electrical properties of sol-gel Na-doped ZnO films using x-ray diffraction, photoluminescence, and conductivity measurements. It is shown that a p-type conversion of the Na-doped ZnO film might be due to a combined effect of the increased substitutional-Na density and the decreased oxygen-vacancy (VO) density. However, excess Na incorporation into ZnO shows an ambiguous carrier type due to the increase in the donorlike VO density. These results indicate that compensation effects limit the hole concentration in the Na-doped ZnO films. In addition, when more Na is substituted into the ZnO system, the difference in the ionic radii of Zn2+ and Na+ starts playing an increasingly important role, causing the presence of tensile stress in the Na-doped ZnO film.

Effects of Li content on the structural, optical, and electrical properties of LiZnMgO films

This study investigates the effect of Li content on the structural, optical, and electrical properties of sol-gel LiZnMgO films by x-ray diffraction, scanning electron microscopy, photoluminescence, and conductivity measurements. A dependence of crystallite size and conduction type upon Li content has been found. The abnormal shift of the (002) diffraction peak position determined from x-ray diffraction measurements and conduction type determined by Hall effect measurements are closely related to the defects/different defect types. It is shown that n-type conversion of LiZnMgO films is a result of the increase in the donor density based on the change in stoichiometry.

Influence of Y-doped induced defects on the optical and magnetic properties of ZnO nanorod arrays prepared by low-temperature hydrothermal process

One-dimensional pure zinc oxide (ZnO) and Y-doped ZnO nanorod arrays have been successfully fabricated on the silicon substrate for comparison by a simple hydrothermal process at the low temperature of 90°C. The Y-doped nanorods exhibit the same c-axis-oriented wurtzite hexagonal structure as pure ZnO nanorods. Based on the results of photoluminescence, an enhancement of defect-induced green-yellow visible emission is observed for the Y-doped ZnO nanorods. The decrease of E2(H) mode intensity and increase of E1(LO) mode intensity examined by the Raman spectrum also indicate the increase of defects for the Y-doped ZnO nanorods. As compared to pure ZnO nanorods, Y-doped ZnO nanorods show a remarked increase of saturation magnetization. The combination of visible photoluminescence and ferromagnetism measurement results indicates the increase of oxygen defects due to the Y doping which plays a crucial role in the optical and magnetic performances of the ZnO nanorods.

Structural Dependence of Photoluminescence and Room-Temperature Ferromagnetism in Lightly Cu-Doped ZnO Nanorods

Well-defined 1-D ZnO and ZnO:Cu semiconductor nanostructures have been fabricated by a low temperature solution process. Cu (0.073 nm) is chosen as a dopant due to the similar ionic radius with Zn (0.074 nm). The radius of ZnO:Cu nanorods observed by FE-SEM is lager than that of pure ZnO which indicates the growth rate of the nanorods can be obviously enhanced by the light doping of Cu. The XRD patterns of both compositions with single diffraction peak (002) show the same wurtzite hexagonal structure. Photoluminescence spectra show a red-shift of the UV emission peak position and a decrease of the luminescence intensity in green-yellow region. From the room temperature hysteresis loop, ferromagnetism is observed and the saturation magnetization decreases with the increase of the Cu concentration for ZnO:Cu nanorods.

Induced increase in surface work function and surface energy of indium tin oxide-doped ZnO films by (NH4)2Sx treatment

The effects of (NH4)2Sx treatment on the surface electronic properties of the thin indium tin oxide (ITO)-doped ZnO films have been examined in this study. According to the experimental results, we found that the formation of S-metal bonds and the removal of oxygen vacancies near the (NH4)2Sx-treated ITO-doped ZnO surface could lead to an increase in the surface energy and the work function, meaning that (NH4)2Sx treatment might be more helpful to form the uniform deposition of the organic semiconductor on ITO-doped ZnO surfaces and improve the efficiency of ZnO-based organic devices.

MAGNETIC PROPERTIES OF La-DOPED AND Cu-DOPED ZnO NANOWIRES FABRICATED BY HYDROTHERMAL METHOD

La-doped and Cu-doped ZnO nanowires have been prepared to compare the substitution effect on the microstructural and magnetic properties. The XRD patterns of both compositions with single diffraction peak (002) show the same wurtzite hexagonal structure. The growth rate of the ZnO nanowires were enhanced by Cu doping, which were different from the suppression of growth rate by La doping. Room temperature ferromagnetism is observed for all ZnO, Cu-doped ZnO and La-doped ZnO nanowires. The saturation magnetizations are 0.102, 0.232 and 0.04 emu/g for ZnO, Cu-doped ZnO and La-doped ZnO nanowires, respectively. The results showed that the ferromagnetism is restrained by Cu doping, but enhanced by the La doping.

Effect of the Polyimide Concentration on the Memory Stability of the Silica-Nanoparticle-Doped Hybrid Aligned Nematic Cell

We investigate the stability of the memory state of the silica-nanoparticle-doped hybrid aligned nematic (SN-HAN) cell. The memory stability of the cell is attributed to the employed planar substrate, which is coated with a homogeneous polyimide (H-PI) film. A H-PI film with a low H-PI solid concentration gives the cell high memory stability. This is because the low H-PI solid concentration causes the film to have a high polar surface energy, trapping polar silica nanoparticles on the planar substrate tightly. The low H-PI solid concentration also gives the substrate a bumpy surface, which has a large surface area for trapping silica nanoparticles.

MAGNETIC PROPERTIES OF ONE-DIMENSIONAL Sm-DOPED ZnO NANOSTRUCTURES FABRICATED BY HYDROTHERMAL METHOD

Well-defined ZnO and Sm-doped nanorods have been successfully fabricated by a low temperature hyderthermal process. The XRD patterns of both compositions with single diffraction peak (002) show the same wurtzite hexagonal structure. The radius of Sm-ZnO nanorods observed by FE-SEM is smaller than that of pure ZnO indicating the reduction of growth rate by the doping of Sm. Ferromagnetism is observed from the results of magnetization measurement. The increase of the saturation magnetization and decrease of coercivity reveal an association with the increase of oxygen vacancies induced by the doping of the Sm in the nanorods.

GRAIN SIZE EFFECT ON THE COLOSSAL MAGNETORESISTANCE IN GRANULAR PEROVSKITE La0.7Pb0.3MnO3

Magnetic behaviors and transport properties in granular perovskite La0.7Pb0.3MnO3 with different grain sizes have been synthesized. The results show that magnetic susceptibility, ferromagnetic ordering temperature and magnetoresistance are affected by the grain size. These compounds with different grain sizes exhibit two kinds of magnetoresistance origins, intragrain double exchange and intergrain interfacial tunneling. With the increasing grain size, the intrinsic transport is dominant while the extrinsic tunneling gradually disappears. Thus, the basis of magnetotransport mechanism is the result of competition between the double exchange interaction and the interfacial tunneling effect.

Construction of concepts and proposition statements in high school nanotechnology curriculum

To develop the high school nanotechnology curriculum and to enhance the understanding of nanotechnology concepts for high school students in Taiwan, we organized a research team consisting of nanotechnology experts, science education experts and senior high school teachers. The expert validity was checked by external experts and senior high school teachers. We obtained an expert concept map of high school nanotechnology, and developed propositional statements with the nanotechnology concept map. Finally, the learning objectives of cognitive development were provided for the nanotechnology high school curriculum. This work will have long-term effects on nanotechnology concept education in high schools an on societys understanding of nanotechnology concepts.