Synthesis and temperature-dependent near-band-edge emission of chain-like Mg-doped ZnO nanoparticles

Chain-like Mg-doped ZnO nanoparticles were prepared using a wet chemical method combined with subsequent heat treatment. The blueshifted near-band-edge emission of the doped ZnO sample with respect to the undoped one was investigated by temperature-dependent photoluminescence. Based on the energy shift of the free-exciton transition, a band gap enlargement of similar to 83 meV was estimated, which seems to result in the equivalent shift of the bound-exciton transition. At 50 K, the transformation from the donor-acceptor-pair to free-to-acceptor emissions was observed for both the undoped and doped samples. The results show that Mg doping leads to the decrease of the acceptor binding energy. (c) 2006 American Institute of Physics.

Conduction band offset and electron effective mass in GaInNAs/GaAs quantum-well structures with low nitrogen concentration

We have investigated the optical transitions in Ga1-yInyNxAs1-x/GaAs single and multiple quantum wells using photovoltaic measurements at room temperature. From a theoretical fit to the experimental data, the conduction band offset Q(c), electron effective mass m(e)*, and band gap energy E-g were estimated. It was found that the Q(c) is dependent on the indium concentration, but independent on the nitrogen concentration over the range x=(0-1)%. The m(e)* of GaInNAs is much greater than that of InGaAs with the same concentration of indium, and increases as the nitrogen concentration increases up to 1%. Our experimental results for the m(e)* and E-g of GaInNAs are quantitatively explained by the two-band model based on the strong interaction of the conduction band minimum with the localized N states. (C) 2001 American Institute of Physics.

Strain effect on the band structure of InAs/GaAs quantum dots

The strain effect on the band structure of InAs/GaAs quantum dots has been investigated. 1 mu m thick InGaAs cap layer was added onto the InAs quantum dot layer to modify the strain in the quantum dots. The exciton energies of InAs quantum dots before and after the relaxation of the cap layer were determined by photoluminescence. When the epilayer was lifted off from the substrate by etching away the sacrifice layer (AlAs) by HF solution, the energy of exciton in the quantum dots decreases due to band gap narrowing resulted from the strain relaxation. This method can be used to obtain much longer emission wavelength from InAs quantum dots.

Correlation Between Lattice Strain and Energy Gap Bowing of AlxGa1-xN Epitaxial Thin Films

The correlation between the energy band-gap of AlxGa1-xN epitaxial thin films and lattice strain was investigated using both High Resolution X-ray Diffraction (HRXRD) and Spectroscopic Ellipsometry (SE). The Al fraction, lattice relaxation, and elastic lattice strain were determined for all AlxGa1-xN epilayers, and the energy gap as well. Given the type of intermediate layer, a correlation trend was found between energy band-gap bowing parameter and lattice mismatch, the higher the lattice mismatch is, the smaller the bowing parameter (b) will be.

Valence band offset of ZnO/BaTiO3 heterojunction measured by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy has been used to measure the valence band offset of the ZnO/BaTiO3 heterojunction grown by metal-organic chemical vapor deposition. The valence band offset (VBO) is determined to be 0.48 +/- 0.09 eV, and the conduction band offset (CBO) is deduced to be about 0.75 eV using the band gap of 3.1 eV for bulk BaTiO3. It indicates that a type-II band alignment forms at the interface, in which the valence and conduction bands of ZnO are concomitantly higher than those of BaTiO3. The accurate determination of VBO and CBO is important for use of semiconductor/ferroelectric heterojunction multifunctional devices.

Pressure Controlled Self-Assembly of High Quality Three-Dimensional Colloidal Photonic Crystals

A concise pressure controlled isothermal heating vertical deposition (PCIHVD) method is developed, which provides an optimal growing condition with better stability and reproducibility for fabricating photonic crystals (PCs) without the limitation of colloidal sphere materials and sizes. High quality PCs are fabricated with PCIHVD from polystyrene spheres with diameters ranging from 200 nm to 1 mu m. The deep photonic band gap and steep photonic band edge of the samples are most favorable for realizing ultrafast optical devices, photonic chips, and communications. This method makes a meaningful advance in the quality and diversity of PCs and greatly promotes their wide applications.

The Key Factors In Fabrication Of High-Quality Ordered Macroporous Copper Film

The template-directed fabrication of highly-ordered porous film is of significant importance in implementation of the photonic band gap structure. The paper reports a simple and effective method to improve the electrodeposition of metal porous film by utilizing highly-ordered polystyrene spheres (PSs) template. By surface-modification method, the hydrophobic property of the PSs template surfaces was changed into hydrophilic one. It was demonstrated that the surface modi. cation process enhanced the permeability of the electrolyte solution in the nanometer-sized voids of the colloidal template. The homogeneously deposited copper film with the highly-ordered voids in size of less than 500 nm was successfully obtained. In addition, it was found that large defects, such as microcracks in the template, strongly influenced the macroporous films quality. An obvious preferential growth in the cracked area was observed. (C) 2008 Elsevier B. V. All rights reserved.

Transport Properties And Induced Voltage In The Structure Of Water-Filled Single-Walled Boron-Nitrogen Nanotubes

Density functional theory/molecular dynamics simulations were employed to give insights into the mechanism of voltage generation based on a water-filled single-walled boron-nitrogen nanotube (SWBNNT). Our calculations showed that (1) the transport properties of confined water in a SWBNNT are different from those of bulk water in view of configuration, the diffusion coefficient, the dipole orientation, and the density distribution, and (2) a voltage difference of several millivolts would generate between the two ends of a SWBNNT due to interactions between the water dipole chains and charge carriers in the tube. Therefore, this structure of a water-filled SWBNNT can be a promising candidate for a synthetic nanoscale power cell as well as a practical nanopower harvesting device.

Transport properties and induced voltage in the structure of water-filled single-walled boron-nitrogen nanotubes

Density functional theory/molecular dynamics simulations were employed to give insights into the mechanism of voltage generation based on a water-filled single-walled boron-nitrogen nanotube (SWBNNT). Our calculations showed that (1) the transport properties of confined water in a SWBNNT are different from those of bulk water in view of configuration the diffusion coefficient the dipole orientation and the density distribution and (2) a voltage difference of several millivolts would generate between the two ends of a SWBNNT due to interactions between the water dipole chains and charge carriers in the tube. Therefore this structure of a water-filled SWBNNT can be a promising candidate for a synthetic nanoscale power cell as well as a practical nanopower harvesting device.

Ultrafast dynamics in ZnO thin films irradiated by femtosecond lasers

The damage morphologies, threshold fluences in ZnO films were studied with femtosecond laser pulses. Time-resolved reflectivity and transmissivity have been measured by the pump-probe technique at different pump fluences and wavelengths. The results indicate that two-phase transition is the dominant damage mechanism, which is similar to that in narrow band gap semiconductors. The estimated energy loss rate of conduction electrons is 1.5 eV/ps. (c) 2005 Elsevier Ltd. All rights reserved.

Scattering by two degenerate anisotropic modes in square-lattice dielectric photonic crystals

We systematically investigate the square-lattice dielectric photonic crystals that have been used to demonstrate flat slab imaging experimentally. A right-handed Bloch mode is found in the left-handed frequency region by using the plane wave expansion method to analyze the photonic band structure and equifrequency contours. Using the multiple scattering theory, numerical simulations demonstrate that the left-handed mode and the right-handed mode are excited simultaneously by a point source and result in two kinds of transmitted waves. Impacted by the evanescent waves, superposition of these transmitted waves brings on complicated near field distributions such as the so-called imaging and its disappearance.

Influence of thermal annealing on optical properties and surface morphology of NiOx thin films

NiOx thin films were deposited by reactive DC-magnetron sputtering from a nickel metal target in Ar + O-2 with the relative O-2 content of 5%. Thermal annealing effects on optical properties and surface morphology of NiOx, films were investigated by X-ray photoelectron spectroscopy, thermogravimetric analysis, scanning electron microscope and optical measurement. The results showed that the changes in optical properties and surface morphology depended on the temperature. The surface morphology of the films changed obviously as the annealing temperature increased due to the reaction NiOx -> NiO + O-2 releasing O-2. The surface morphology change was responsible for the variation of the optical properties of the films. The optical contrast between the as-deposited films and 400 degrees C annealed films was about 52%. In addition, the relationship of the optical energy band gap with the variation of annealing temperature was studied. (c) 2006 Elsevier B.V. All rights reserved.

掺铒钙铝硅玻璃的光学带隙

玻璃中稀土掺杂的离子的光谱性质受其周围的玻璃结构和在玻璃基质中的分布影响很大。利用熔融法制备了组分为9SiO2·26Al2O3·65CaO·1．0Er2O3·0．3Yb2O3和分别加入MgO以及La2O3的掺铒钙铝硅玻璃，并研究了其吸收边和光学带隙。计算得出离子填充比随玻璃的平均摩尔质量的增大而减小，同时利用Judd—Ofelt模型计算出该玻璃体系的Ω2，Ω4和Ω6参数，并进行了分析。随着MgO或La2O3的加入，吸收边向短波长移动，光学带隙增大，同时Ω2和Ω6值也增大。对ln（α）和hω的曲线进行线性拟

Photoluminescence of undoped and B-doped ZnO in silicate glasses

Photoluminescence of undoped and B-doped ZnO in silicate glasses was investigated by varying the concentration of ZnO (3550 mol%) and B dopant (0-10 mol%) in the glass matrices. The broad and intense near band edge emissions were observed while the visible light emission was very weak. UV luminescence in all samples was red-shifted relative to the exciton transition in bulk ZnO and enhanced by decreased ZnO concentration due to higher degree of structural integrity and the lower aggregation degree of ZnO. Donor B dopant played the double roles of filling conduction bands to broaden band gap when its concentration was lower than 5 mol%, and emerging with conduction bands to narrow the gap when B dopant exceeded this value. (c) 2007 Elsevier B.V. All rights reserved.

Growth and characterization of new transparent conductive oxides single crystals beta-Ga2O(3): Sn

Tin oxide doped beta-Ga2O3 single crystals are recognized as transparent conductive oxides (TCOs) materials. They have a larger band gap (4.8 eV) than any other TCOs, thus can be transparent in UV region. This property shows that they have the potential to make the optoelectronic device used in even shorter wavelength than usual TCOs. beta-Ga2O3 single crystals doped with different Sn4+ concentrations were grown by the floating zone technique. Their optical properties and electrical conductivities were systematically studied. It has been found that their conductivities and optical properties were influenced by the Sn4+ concentrations and annealing. (c) 2006 Elsevier Ltd. All rights reserved.