Liang-Yao Chen

MICROSTRUCTURE, MAGNETIC, AND MAGNETO-OPTICAL PROPERTIES OF CHEMICAL SYNTHESIZED CO-RE (RE=HO, ER, TM, YB, LU) FERRITE NANOCRYSTALLINE FILMS

The sol-gel synthesis of Co–RE (RE=Ho, Er, Tm, Yb, Lu) ferrite nanocrystalline films was accomplished on monocrystalline silicon substrates, and the influence of RE ions on structure, magnetic, and magneto-optical (MO) properties of the resultant ferrites was examined. The results obtained reveal that, when x⩽0.2, the CoFe2−xRExO4 ferrite films have pure spinel phase with slightly enlarged cell constants and lattice distortion due to the large radii of RE ions. The RE ions tend to decrease the room-temperature magnetization as well as the Curie point of products, and may have a certain contribution to coercive force except for a nonmagnetic Lu3+ ion. For the present optical structure in which MO layers are substrated on silica, Co–RE ferrite films show the peak Kerr rotation at a shorter wavelength than the CoFe2O4 film, and Er or Tm doped samples exhibit an interesting enhancement of the MO effect.

Design of a scanning ellipsometer by synchronous rotation of the polarizer and analyzer

We have designed and constructed a new type of spectroscopic ellipsometer to study the optical properties of materials in the 3500-8000-Å wavelength range. In the system, the analyzer and polarizer are driven 10(4) steps/revolution by two stepping motors that have hollow shafts and rotate synchronously with a speed ratio of 2:1, i.e., A = 2P. Both the polarizer and analyzer are mounted directly on the shafts to avoid mechanical transmission and vibration problems entirely and make the system simple and reliable. An additional source polarizer was placed in the optical path to reduce the slight polarization effects of the light source. The light intensity finally received by the detector contained five components, one dc and four ac, with frequencies of ω(0), 2ω(0), 3ω(0), and 4ω(0), respectively. One can independently obtain the ellipsometric parameters of ψ and Δ as well as the optical constants by calculating any one of the two sets of ac signals, with a raw data self-consistency of better than 0.5%. The incident angle, aligned precisely by a laser beam, was continuously variable through a mechanical system with a computercontrolled resolution of 0.001° or a visual resolution of 0.005°. The system operations, including data acquisition and reduction, high-voltage control of the photomultiplier, incident angle, as well as wavelength setting and scanning, were fully and automatically controlled by a 386-based microcomputer. We self-calibrated the system by adjusting and setting precisely the initial azimuthal angles of the prisms. The results from the measured spectra of the complex refractive index for a gold-film sample are presented, and we show that the data obtained at three different incident angles of 65°, 70°, and 75° are remarkably consistent with one another. A comparison of the two results from the ellipsometry and reflectance measurements is given. The experimental skills and system error reduction are discussed in detail.

Layer by Layer Immobilized Horseradish Peroxidase on Zinc Oxide Nanorods for Biosensing

Using zinc powders as source material, ZnO nanorods (ZnONR) were fabricated on gold wire by a hydrothermal reaction without any other surfactant. The gold wire end was coated by a thin layer of Zn-Au alloy to improve the nucleation for growth of ZnO nanostructures and to further improve the performance of the biosensor, which was constructed by alternatively immobilizing poly(sodium 4-styrenesulfonate) (PSS) and horseradish peroxidase (HRP) on the ZnONR. Electrochemical measurement, ultraviolet-visible spectrum, zeta-potential, and scanning electron microscopic analysis demonstrated that PSS and HRP were stably adsorbed layer by layer on the ZnONR surface, and the HRP kept bioactivity for H(2)O(2) detection without an electron transfer mediator. The multilayered HRP sensors exhibited a wide linear range and low detection limit. The sensitivity of the biosensor increased with the immobilized HRP layers from the lowest value of 36.28 microA mM(-1) for a monolayer.

Nanostructure magneto-optical thin films of rare earth (RE=Gd,Tb,Dy) doped cobalt spinel by sol–gel synthesis

Nanocrystalline CoFe1.9RE0.1O4 [rare earth (RE=Gd,Tb,Dy)] films have been prepared by the sol–gel route, and their polar magneto-optical (MO) Kerr rotation and ellipticity have been determined in the spectral range of 4000–8000 A. The films are composed of nanometer grains with the spinel structure. RE doped cobalt spinel ferrites are found to have dramatic changes in magnetic and MO properties, with increases in their coercive force and enhancement of the MO rotation in the Tb3+ doped sample.

Tyrosinase Immobilization on ZnO Nanorods for Phenol Detection

Directly using zinc powders as source material, ZnO nanorods were fabricated on gold wire by hydrothermal reaction without any other surfacant and stabilizing agent. The gold wire was skillfully treated to improve the nucleation for growth of ZnO nanostructures and to further improve the performance of the biosensor, which was construct by immobilizing tyrosinase (Tyr) on the ZnO nanorods for phenol detection. Electrochemical measurement, Fourier transform infrared and scanning electron microscopic analyses demonstrated that the Tyr was stably adsorbed on the ZnO nanorods surface with bioactivity for phenol oxidization. The biosensor reached 95% of steady-state current within 5s, and the sensitivity was as high as 103.08 microA/mM at C(phenol) > 20 microM and was 40.76 microA/mM at C(phenol) < 20 microM. The detection limit of 0.623 microM was obtained at a signal/noise ratio of 3.

Optical properties of cubic Ti3N4, Zr3N4, and Hf3N4

A systematic theoretical study is presented for the electronic, mechanical, and optical properties of cubic Ti3N4, Zr3N4, and Hf3N4 with the Th3P4 structure in the framework of density functional theory. The calculated band structures of Ti3N4, Zr3N4, and Hf3N4 show the indirect band gaps of 0.268, 0.909, and 1.00eV, respectively. Furthermore, the optical properties for all three materials were calculated and analyzed in detail. The calculated results are well consistent with available experimental data. Also, it is shown that all these materials have relatively large static dielectric constants at zero frequency, rendering them potential applications in microelectronic devices.

Improved rotating analyser-polarizer type of scanning ellipsometer

Abstract A new type of spectroscopic ellipsometer in which the analyser and polarizer rotate synchronously has been designed and constructed. For the system, the analyser and polarizer were driven 10 4 steps per revolution by two stepping motors with a speed ratio of 2:1. A second polarizer was placed in the optical path to eliminate the source polarization effect. The light intensity thus contains four a.c. components, having frequencies of ω 0 , 2ω 0 , 3ω 0 and 4ω 0 . The ellipsometric parameters ψ and Δ, as well as the optical constants, can be independently obtained by calculating any one of the two sets of a.c. signals. The system was self-calibrated, and was fully and automatically controlled by a 386-based microcomputer. The results of measured spectra of the complex refractive index for a 3000 A thick Au film sample are given. An equation for calculating directly the principal angle to obtain the highest precision of the optical constants is presented.

High solar absorption of a multilayered thin film structure

We report a structure with 4 thin film layers composed of pure metal and dielectric materials and prepared by sputtering. The reflectance and transmittance are lower than 5% with the absorption to be achieved higher than 95% in the 400-1000nm wavelength region as match to the solar radiance spectrum. The thermal emittance of the structure is in the range of 0.063-0.10 through data analysis. The good reproducibility and stability of spectral data associated with the deposition process imply the advantage of the solar energy absorber which is cost-effective in application.

Influence of nanocrystal size on dielectric functions of Si nanocrystals embedded in SiO2 matrix

The complex dielectric functions of Si-nanocrystals (nc-Si) with different sizes embedded in SiO2 matrix synthesized by SiOx/SiO2 superlattice approach is obtained by spectroscopic ellipsometry. The Maxwell–Garnett effective medium approximation and the Lorentz oscillator model are employed in the spectra fitting. The dependence of the dielectric functions on the nc-Si size is observed. A significant suppression in amplitude of the dielectric functions with respect to bulk crystalline silicon, and a large influence of the nc-Si size on the E1 and E2 critical points are observed and discussed.

Triple-band perfect metamaterial absorption, based on single cut-wire bar

In general metamaterial perfect absorber, the single meta-pattern makes the single absorption band. Therefore, the multi-absorption bands need the corresponding kinds of meta-patterns. Here, we introduce the triple-band metamaterial perfect absorber utilizing only single kind of pattern. We also demonstrate the absorption mechanism of the triple perfect absorption. The first and the second absorption bands were induced by the fundamental magnetic resonance of the major and the minor axes, respectively, of cut-wire bar. The third peak was caused by the third-harmonic magnetic resonance of the major axis. Additionally, the unexpected third band was formed, which was the overlapping of the third absorption peak with another absorption peak, which was made by pairs of antiparallel currents parallel or antiparallel to the incident electromagnetic wave.