Photonic crystal vertical-cavity surface-emitting laser based on GaAs material

A photonic crystal vertical-cavity-surface-emitting laser ( PC-VCSEL) with a wavelength of about 850 nm was realized. The direct-current electrically-driven PC-VCSELs with a minimum threshold current of 2 mA and a maximum threshold current of 13.5 mA were obtained. We fabricated a series of PC-VCSEL chips whose lattice constants are in the range from 0.5 to 3 mu m with different filling factors, and found that the laser characterization depends on the lattice constant, the filling factor, the size of cavity, etc.

Stability improvement of selective oxidation during the fabrication of InGaAs/GaAs vertical cavity surface emitting laser

The effects of the carrier gas flow and water temperature on the oxidation rate for different reaction temperatures were investigated. The optimum conditions for stable oxidation were obtained. Two mechanisms of the oxidation process are revealed. One is the flow-controlling process, which is unstable. The other is the temperature-controlling process, which is stable. The stable region decreases for higher reaction temperatures. The simulation results for the stable oxidation region are also given. With optimum oxidation conditions, the stability and precision of the oxidation can be dramatically improved.

HIGH-EFFICIENCY TOP SURFACE-EMITTING LASERS FABRICATED BY 4 IMPLANTATION USING TUNGSTEN WIRE AS MASK

We report the results of a high efficiency room temperature continuous wave (cw) vertical-cavity surface-emitting laser. The structure is obtained by four deep H+ implantation using tungsten wires as the mask. The fabrication process is the simplest ever reported in vertical-cavity surface-emitting laser fabrication. The largest differential quantum efficiency of 65% and maximum cw light output power over 4 mW have been achieved for the 15X15 mu m(2) device. (C) 1995 American Institute of Physics.

Array for 980nm Vertical Cavity Surface Emitting Diodes and Detectors

Both the vertical cavity surface emitting diodes and detectors are fabricated by using the epitaxial wafer with resonant cavity structure. Their characteristics are analyzed. The light emitters have high spectral purity of 4.8nm and high electroluminescence intensity of 0.7mW while injection current is 50mA. A 1*16 array of surface emitting light device is tested on line by probes and then used for module. The light detectors have wavelength selectivity and space selectivity. The required difference in input mirror reflectivity between emitters and detectors can easily be achieved though varying the numbers of top DBR period by etching.

Stability improvement of selective oxidation during the fabrication of InGaAs/GaAs vertical cavity surface emitting laser

The effects of the carrier gas flow and water temperature on the oxidation rate for different reaction temperatures were investigated. The optimum conditions for stable oxidation were obtained. Two mechanisms of the oxidation process are revealed. One is the flow-controlling process, which is unstable. The other is the temperature-controlling process, which is stable. The stable region decreases for higher reaction temperatures. The simulation results for the stable oxidation region are also given. With optimum oxidation conditions, the stability and precision of the oxidation can be dramatically improved.

X-ray spectra induced by slow highly charged Arq+ ions in collision with Nb surface

The X-ray spectra of Nb surface induced by Arq+ (q = 16,17) ions with the energy range from 10 to 20 keV/q were studied by the optical spectrum technology. The experimental results indicate that the multi-electron excitation occurred as a highly charged Ar16+ ion was neutralized below the metal surface. The K shell electron of Ar16+ was excited and then de-excited cascadly to emit K X-ray. The intensity of the X-ray emitted from K shell of the hollow Ar atom decreased with the increase of projectile kinetic energy. The intensity of the X-ray emitted from L shell of the target atom Nb increased with the increase of projectile kinetic energy. The X-ray yield of Ar17+ is three magnitude orders larger than that of Ar16+.

Surface modelling of soil pH

In addition to classical methods, namely kriging, Inverse Distance Weighting (IDW) and splines, which have been frequently used for interpolating the spatial patterns of soil properties, a relatively more accurate surface modelling technique is being developed in recent years, namely high accuracy surface modelling (HASM). It has been used in the numerical tests, DEM construction and the interpolation of climate and ecosystem changes. In this paper, HASM was applied to interpolate soil pH for assessing its feasibility of soil property interpolation in a red soil region of Jiangxi Province, China. Soil pH was measured on 150 samples of topsoil (0-20 cm) for the interpolation and comparing the performance of HASM, kriging. IDW and splines. The mean errors (MEs) of interpolations indicate little bias of interpolation for soil pH by the four techniques. HASM has less mean absolute error (MAE) and root mean square error (RMSE) than kriging, IDW and splines. HASM is still the most accurate one when we use the mean rank and the standard deviation of the ranks to avoid the outlier effects in assessing the prediction performance of the four methods. Therefore, HASM can be considered as an alternative and accurate method for interpolating soil properties. Further researches of HASM are needed to combine HASM with ancillary variables to improve the interpolation performance and develop a user-friendly algorithm that can be implemented in a GIS package. (C) 2009 Elsevier B.V. All rights reserved.

Surface-modified Nafion membranes with mesoporous SiO2 layers via a facile dip-coating approach for direct methanol fuel cells

In this study. Nafion (R) 117 membrane is surface-modified with mesoporous silica layers through in situ surfactant-templated sol-gel reaction. The reaction makes use of tetraethyl orthosilicate (TEOS) under acidic condition via dip-coating technique on both sides. Scanning electron microscopy (SEM), Fourier transformation infrared (FTIR), and thermogravimetric analysis (TGA) are employed to characterize the resultant membranes. Proton conductivity and methanol permeability of the membranes are also studied.

Glucose biosensor based on gold nanoparticle-catalyzed luminol electrochemiluminescence on a three-dimensional sol-gel network

An electrochemiluminescent glucose biosensor was proposed based on gold nanoparticle-catalyzed luminol electrochemiluminescence (ECL). Gold nanoparticles were self-assembled onto silica sol-gel network, and then glucose oxidase was adsorbed on the surface of gold nanoparticles. The surface assembly process and the electrochemistry and ECL behaviors of the biosensor were investigated. The assembled gold nanoparticles could efficiently electrocatalyze luminol ECL ECL intensity of the biosensor depended on scan rate, luminol concentration, and size of gold nanoparticles.

Surface modification of bioactive glass nanoparticles and the mechanical and biological properties of poly(L-lactide) composites

Novel bioactive glass (13G) nanoparticles/poly(L-lactide) (PLLA) composites were prepared as promising bone-repairing materials. The BG nanoparticles (Si:P:Ca = 29:13:58 weight ratio) of about 40 run diameter were prepared via the sol-gel method. In order to improve the phase compatibility between the polymer and the inorganic phase, PLLA (M-n = 9700 Da) was linked to the surface of the BG particles by diisocyanate. The grafting ratio of PLLA was in the vicinity of 20 wt.%. The grafting modification could improve the tensile strength, tensile modulus and impact energy of the composites by increasing the phase compatibility.

STRUCTURAL EVOLUTION AND COMPOSITION CHANGE IN THE SURFACE REGION OF POLYPROPYLENE/CLAY NANOCOMPOSITES ANNEALED AT HIGH TEMPERATURES

A model experiment was done to clear the formation mechanism of protective layers during combustion of polypropylene (PP)/organically modified montmorillonite (OMMT) nanocomposites. The investigation was focused on the effects of annealing temperature on the structural changes and protective layer formation. The decomposition of OMMT and degradation of PP/OMMT nanocomposites were characterized by means of thermogravimetric analysis (TGA). The structural evolution and composition change in the surface region of PP/OMMT nanocomposites during heating were monitored by means of X-ray photoelectron spectroscopy (XPS), ATR-FTIR and field emission scanning electron microscopy (FESEM).

Pt Nanoparticles Supported on TiO2 Colloidal Spheres with Nanoporous Surface: Preparation and Use as an Enhancing Material for Biosensing Applications

An easy surface-modified method has been developed to link -NH2 groups to the TiO2 colloidal spheres with nanoporous surface (f-TiO2). It was found that the as-prepared f-TiO2 is positively charged in neutral conditions and could act as an electrostatic anchor for nanosructures with opposite charge, Furthermore, platinum nanoparticles (Pt NPs) are successfully assembled on the f-TiO2 mainly via electrostatic interaction to fabricate a new kind of Pt NPs/TiO2 hybrid nanomaterial (f-TiO2-Pt NPs). The morphology, structure, and composition of the hybrids were characterized by the means of diverse techniques such as transmission electron microscopy, scanning electron microscopy, X-ray powder diffraction, and Raman spectra. Electrochemical experiments indicate the electrode modified with f-TiO2-Pt NPs shows prominent electrocatalytic activity toward the oxidation of hydrogen peroxide.

Preparation, Surface Properties and Biological Activity of the Composite of Poly (lactide-co-glycolide) and Bioglass Nanoparticles Surface Grafted with Poly(L-lactide)

SiO2-CaO-P2O5 gel bioglass (BG) nanoparticles with the diameter of 40 nm were synthesized by sol-gel approach. The surface of BG nanoparticles was grafted through the ring-open polymerization of the L-lactide to yield poly (L-lactide) (PLLA) grafted gel particle (PLLA-g-BG). The PLLA-g-BG was further blended with poly(lactide-co-glycolide) (PLGA) to prepare the nanocomposites of PLLA-g-BG/PLGA with the various blend ratios of two phases. PLLA-g-BG accounted 10%, 20% and 40% in the composite, respectively. TGA, ESEM and EDX were used to analyze the graft ratio of PLLA-g-BG, the dispersion of nano-particles and the surface elements of the composites respectively. The rabbit osteoblasts were seeded and cultured on the thin films of composites in vitro. The cell adhesion, spreading and growth of osteoblasts were analyzed with FITC staining, NIH Image J software and MTT assay. The change of cell cycle was monitored by flow cytometry (FCM). The results demonstrated that the Surface modification of BG with PLLA could significantly improve the dispersing of the particles in the matrix of PLGA. The nanocomposite with 20% PLLA-g-BG exhibited superior surface properties, including roughness and plenty of silicon, calcium and phosper, to enhance the adhesion, spreading and proliferation of osteoblasts.

NOVEL COMPOSITES OF POLY(L-LACTIDE) AND SURFACE MODIFIED BIOACTIVE SiO2-CaO-P2O5 GEL NANOPARTICLES: MECHANICAL AND BIOLOGICAL PROPERTIES

Bioactive SiO2-CaO-P2O5 gel (BAG) nanoparticles with 40 nm in diameter were synthesized by the sol-gel route and further modified via the ring-opening polymerization of lactide on the surface of particles. Surface modified BAG (mBAG) was introduced in poly(L-lactide) (PLLA) matrix as bioactive filler. The dispersibility of mBAG in PLLA matrix was much higher than that of rough BAG particles. Tensile strength of the mBAG/PLLA composite could be increased to 61.2 MPa at 2 wt% filler content from 53.4 MPa for pure PLLA. The variation of moduli of the BAG/PLLA and mBAG/PLLA composites always showed an enhancement tendency with the increasing content of filler loading. The SEM photographs of the fracture surfaces showed that mBAG could be homogeneously dispersed in the PLLA matrix, and the corrugated deformation could absorb the rupture energy effectively during the breaking of materials. In vitro bioactivity tests showed that both BAG and mBAG particles could endow the composites with ability of the calcium sediment in SBF, but the surface modification of BAG particles could weaken this capability to some extent. Biocompatibility tests showed that both BAG and mBAG particles could facilitate the attachment and proliferation of the marrow cells on the surface of the composite.

Sol-gel synthesis and photoluminescence properties of spherical SiO2@LaPO4 : Ce3+/Tb3+ particles with a core-shell structure

LaPO4: Ce3+ and LaPO4: Ce3+, Tb3+ phosphor layers have been deposited successfully on monodispersed and spherical SiO2 particles of different sizes ( 300, 500, 900 and 1200 nm) through a sol - gel process, resulting in the formation of core - shell structured SiO2@ LaPO4: Ce3+/ Tb3+ particles. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microcopy (SEM), transmission electron microscopy (TEM), and general and time-resolved photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting SiO2@ LaPO4: Ce3+/ Tb3+ samples. The XRD results demonstrate that the LaPO4: Ce3+, Tb3+ layers begin to crystallize on the SiO2 templates after annealing at 700 degrees C, and the crystallinity increases on raising the annealing temperature. The obtained core - shell phosphors have perfectly spherical shape with a narrow size distribution, non-agglomeration, and a smooth surface. The doped rare-earth ions show their characteristic emission in the core - shell phosphors, i.e. Ce3+ 5d - 4f and Tb3+5D4 - F-7(J) (J = 6 - 3) transitions, respectively. The PL intensity of the Tb3+ increased on increasing the annealing temperature and the SiO2 core particle size.