Yang Guo-Zhen

Unit-Cell by Unit-Cell Epitaxial Growth of SrTiO3 and BaTiO3 Thin Films by Laser Molecular Beam Epitaxy

Atomically regulated unit-cell by unit-cell homoepitaxial SrTiO3 and heteroepitaxial BaTiO3 films were fabricated on SrTiO3(100) substrates by laser molecular beam epitaxy. The fine streak patterns and more than 1000 cycles undamping intensity oscillation were obtained by in situ reflection high-energy electron diffraction with precisely controlled intermittence between each unit-cell layer. The surface morphology of the films was examined by atomic force microscopy. The root-mean-square surface roughness of the films is about 0.1 nm.

Large Third-Order Nonlinear Optical Susceptibility of Rh-Doped BaTiO3 Thin Films Prepared by Pulsed Laser Deposition

Rh-doped barium titanate (BaTiO3) epitaxial thin films have been fabricated on SrTiO3 (100) substrates by pulsed laser deposition. The nonlinear optical properties of the films were determined using the z-scan method at a wavelength of 532 nm with a laser duration of 10 ns. The real and imaginary parts of the third-order nonlinear susceptibility χ(3) were 5.71×10-7 esu and 9.59×10-8 esu, respectively. The real part value of χ(3) of the Rh:BaTiO3 films is about one order larger than that of Ce-doped BaTiO3 thin films. The results show that Rh:BaTiO3 thin films have great potential applications for nonlinear optical devices.

Antitrace Maps and Light Transmission Coefficients for Generalized Fibonacci Multilayers

By using antitrace map method, we investigate the light transmission for a generalized Fibonacci multilayers. Analytical results are obtained for transmission coefficients in some special cases. We find that the transmission coefficients possess two-cycle property or six-cycle property. The cycle properties of the trace and antitrace are also obtained. PACS numbers: 61.44.Br, 05.45.-a, 42.25.Dd, 71.23.Ft Typeset using REVTEX 1 The transmission of light through the multilayers arranged by the Fibonacci [1–3], nonFibonacci sequence [4,5], Thue-Morse sequence [6], and the generalized Thue-Morse sequence [7] was studied in the literature. Schwartz [8] suggested a possibility of quasiperiodic multilayers as optical switches and memories. Huang et al [9] and Yang et al [10] have found an interesting switch-like property in the light transmission through Fibonacci-class sequences. On the other hand, the trace-map technique, first introduced in 1983 [11], has proven to be a powerful tool to investigate the properties of various aperiodic systems. However, as pointed by Dulea et al [4], we must know the so-called “antitrace map” when we evaluate the light transmission coefficients through aperoidic sequences. Here, the so-called “antitrace” of a 2×2 matrix

Label-Free and High-Throughput Detection of Protein Microarrays by Oblique-Incidence Reflectivity Difference Method

We label-free detected the biological process of preparing a microarray that includes 400 spots of mouse immunoglobulin G (IgG) as well as the specific hybridization between mouse IgG and goat anti-mouse IgG by an oblique-incidence reflectivity difference (OI-RD) method. The detection results after each process including printing, washing, blocking, and hybridization, demonstrate that the OI-RD method can trace the preparation process of a microarray and detect the specific hybridization between antigens and antibodies. OI-RD is a promising method for label-free and high-throughput detection of biological microarrays.

Superconducting MgB2 Thin Films with Tc≈39 K Grown by Pulsed Laser Deposition

Superconducting MgB2 thin films were fabricated on Al2O3(0001) substrates under ex situ processing conditions. Boron thin films were deposited by pulsed laser deposition followed by a post-annealing process. Resistance measurements of the deposited MgB2 films show Tc of ~39 K, while scanning electron microscopy and x-ray diffraction analysis indicate that the films consist of well-crystallized grains with a highly c-axis-oriented structure.Superconducting MgB2 thin films were fabricated on Al2O3(0001) substrates under an ex-situ processing conditions. Boron thin films were deposited by pulsed laser deposition followed by a post-annealing process. Resistance measurements of the deposited MgB2 films show Tc of about 39K, while scanning electron microscopy and x-ray diffraction analysis indicate that the films consist of well-crystallized grains with a highly c-axis-oriented structure.

Laser Molecular Beam Epitaxy Growth of BaTiO3 in Seven Thousands of Unit-Cell Layers

BaTiO3 thin films in seven thousands of unit-cell layers have been successfully fabricated on SrTiO3 (001) substrates by laser molecular beam epitaxy. The fine streak pattern and the undamping intensity oscillation of reflection high-energy electron diffraction indicate that the BaTiO3 film was layer-by-layer epitaxial growth. The measurements of scanning electron microscopy and atomic force microscopy show that surfaces of the BaTiO3 thin film are atomically smooth. The measurements of x-ray diffraction and transmission electron microscopy, as well as selected-area electron diffraction reveal that the BaTiO3 thin film is a c-oriented epitaxial crystalline structure.

Enhanced nonlinear optical properties of laser deposited Ag/BaTiO3 nanocomposite films

The composite films containing Ag particles embedded in BaTiO3 matrix were deposited on MgO (100) substrates by using the pulsed laser deposition technique and characterized by x-ray diffraction and x-ray photoelectron spectroscopy. The absorption peak resulting from the surface plasmon resonance of Ag particles is found at the wavelength of 430 nm. The third-order nonlinear optical characteristics of the films are determined by z-scan technique using a nanosecond laser. The results show that the Ag/BaTiO3 nanocomposite films exhibit great optical nonlinearities and the real and imaginary parts of the third-order nonlinear susceptibility χ(3) are calculated to be 4.544×10-6 esu and 2.352×10-7 esu, respectively. The enhancement mechanism of χ(3) is discussed.

Photoelectric Characteristic of La0.9Sr0.1MnO3/SrNb0.01Ti0.99O3 p–n Heterojunctions

Good rectifying current–voltage characteristics and nanosecond photoelectric effects are observed in the p–n heterojunctions of La0.9Sr0.1MnO3/SrNb0.01Ti0.99O3 fabricated by laser molecular beam epitaxy. The rise time is about 26 ns and the full width at half maximum is about 125 ns for the open-circuit photovoltaic pulses when the La0.9Sr0.1MnO3 film in the heterojunction is irradiated by a laser operated at wavelength 308 nm with pulse duration of about 25 ns. A qualitative explanation is presented, based on an analysis of the photoelectric effect of p–n heterojunction.

Experimental study on the chirped structure of the white-light continuum generation by femtosecond laser spectroscopy

The chirped structure of the white-light continuum generation (WLCG) pulse produced by focusing 800nm laser pulse with a pulse duration of 150fs (FWHM: full-width-at-half-maximum) onto a 2.4 mm thick sapphire plate was investigated by the optical Kerr gate technique with normal hexane as the optical Kerr gate medium. The observed WLCG was positively chirped, the measured anti-Stokes spectrum of WLCG ranges from 449 to 580nm with a temporal span of 2.56ps. When using metal reflecting mirrors to eliminate the group velocity dispersion (GVD) effect, we found that a span of 1.3ps still remained, indicating that the chirped pulse cannot be accounted for simply by GVD of the pulse propagation in the dispersive media. Our results suggest that the light-induced refractive index change due to the third-order nonlinear optical effect leads to an additional positive group velocity dispersion, which contributes to an important portion of the observed temporal broadening of the chirped WLCG. In addition to using reflective optical elements instead of dispersive optical elements, an effective way of reducing the chirp is to minimize the optical path length of the WLCG medium.

Simulation of Anisotropic Resistivity for Mixed-Phase Manganite La2/3Ca1/3MnO3 Thin Films

We utilize the random network model based on phase separation scenario to simulate the conductive behaviour and anisotropic characteristics of resistivity for La2/3Ca1/3MnO3 (LCMO) thin films. The simulated results agree well with our experimental data, showing a metal-to-insulator transition from a high-T paramagnetic (PM) insulating phase to a low-T ferromagnetic (FM) metallic phase in both the untilted film deposited on a (001) SrTiO3 (STO) substrate and the tilted film grown on a vicinal cut STO substrate. It is found that the resistivity of the tilted sample is higher than that of the untilted one, displaying prominent anisotropic characteristics. The studies reveal that the tilting not only decreases the conduction of the FM domains, but also increases the activation energy of the PM regions, inducing the enhancement of resistivity. All those results suggest that the intrinsic inhomogeneity in the phase separation system plays a significant role in the electrical conductivity and the resistive anisotropy is related to the structure of the crystal lattice.