Chung-Jen Ou

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.

Variable-Range Hopping and Thermal Activation Conduction of Y-Doped ZnO Nanocrystalline Films

ZnO and Y-doped ZnO nanocrystalline films were separately fabricated on the glass substrates by sol-gel spin-coating method. X-ray diffraction patterns of the films show the same wurtzite hexagonal structure and (0 0 2) preferential orientation. Scanning electron microscope images show that grain size and thickness of the nanocrystalline films decrease with increasing doping concentration. The decrease of optical bandgap with the increase of Y doping is deduced from the transmittance spectra. Temperature-dependent resistivity reveals a semiconductor transport behavior for all ZnO and Y-doped ZnO nanocrystalline films. The resulting conductivity originates from the combination of thermal activation conduction and Mott variable-range hopping (VRH) conduction. In the high-temperature range, the temperature-dependent resistivity can be described by the Arrhenius equation, σ (T) = σ0 exp[ -(Ea/kT)], which shows the thermal activation conduction. The activation energy Ea increases from 0.47 meV for ZnO film to 0.83 meV for Zn0.98Y0.02O film. On the contrary, in the low-temperature range, the temperature-dependent resistivity can be fitted well by the relationship, σ(T) = σh 0exp[-(T0/T)1/4], which indicates the behavior of Mott VRH. The results demonstrate that the crystallization and the corresponding carrier transport behavior of the ZnO and Y-doped ZnO nanocrystalline films are affected by Y doping.

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.

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.

Fresnel-like prism structure generating algorithm on a curved surface with iterative and noniterative forms.

A Fresnel-like structure is required for various kinds of applications, such as contact lenses in the biomedical field, solar concentrators in the energy industry, wave-front correctors for display technology, and beam shaping for illumination systems. In this report, the author provides a simple iterative algorithm that can generate prism structures on arbitrary curved surfaces in an analytical form. Using this algorithm, a spreadsheet program can easily generate the profile of prism structures for optical software simulation. Moreover, a noniterative formulation is derived in order to reduce the design procedures. Comparisons between iterative and noniterative formulations prove the feasibility and robustness of the present approach.

Cell Illuminating Apparatus for Photo-Stimulation of Neuron Gates

We present a cost-effective optogenetic experimental setup for investigation of synaptic gating (neuron gate). The setup consists of a cell illuminating system containing a common micro-display of a commercial word processor and light emitting diode (LED) semiconductor materials instead of optogenetic cells. The performance is verified by illuminating the LED materials and measuring the induced electric potential.

Temperature dependence carrier transport behavior of transparent ZnO:Y nanocrystalline films

The Y-doped ZnO nanocrystalline films were deposited on the glass substrates by sol-gel method. X-ray diffraction measurements of the films showed the same wurtzite hexagonal structure and preferential orientation along the c-axis. The grain size of the ZnO films was decreased by the doping of Y. Temperature dependence resistivity showed a semiconductor transport behavior for the nanocrystalline films. At low temperature region, the resistivity can be fitted well with the behavior of Mott variable range hopping, σ(T)=σ_h0 exp[-(T₀/T)ⁿ] with n=1/4. On the contrary, at high temperature region, the transport mechanism can be fitted with semiconductor behavior by Arrhenius equation, σ(T)=σ₀ exp[-(E_a/kT)^m] with m=1. The activation energy E_a is increased from 0.47 meV for nondoped ZnO film to 0.83 meV for Zn_0.98Y_0.02O film obtained from equation. The results demonstrate that the crystallization and the corresponding carrier transport behavior of the Y-doped ZnO films are affected by the doping of Y.

An associative memory based on the immune networks: perspectives on internal image with antibody dynamics

Immune memory can be regarded as an equilibrium state of immune network system with nonlinear dynamical behavior. The rapid response of immune systems to the second-time antigen is owing to the stable structure of memory state forming by a closed idiotypic immune network. Internal image of an antigen is defined while memory state is formed via such network. A dynamical system of cell population based on antibody chains and tree structure is proposed which explains how the memory state is formed in the immune network. We also propose a network dynamics model of idiotypic immune network based on cross-reactive correlation matrix to fill the gap of weaker assumption for artificial immune memory. Mathematical theory of associative memory is also explored, particularly, combining network structure and dynamical systems are some breakthrough in this paper. We realize that cyclic idiotypic immune network and dynamical systems can be a cooperative description for immune memory.

NOVEL APPROACH FOR t–J MODEL WITH ELECTRON SCATTERINGS

This report proposes a graphical-like approach for simulating the Hamiltonian of the t–J model. The two spin states are modeled by the two emitting layer, the kinematics of the electrons and the causalities between the operators are satisfied through the event cone. Operators and the event cone are integrated together, and the results indicate that this approach can provide information during the evolution of the t–J model. In addition, parameters that can be accessed by this approach are consistent with general requirements on values of t and J in the t–J model. Furthermore, our approach also includes the solution with vanishing hopping amplitude (tij = 0) and the H∞ solution.

Artificial Immune Memory: Perspectives on Internal Image with Antibody Dynamics

Immune memory can be regarded as an equilibrium state of immune network system with nonlinear dynamical behavior. The rapid response of immune systems to the second-time antigen is owing to the stable structure of memory state forming by a closed idiotypic immune network. Internal image of an antigen is defined while memory state is formed via such network. A dynamical system of cell population based on antibody chains and tree structure is proposed which explains how the memory state is formed in the immune network.