Effect of high temperature band gap of GaN annealing on strain and nanoparticles

<正>Black-coloured GaN nanoparticles with an average grain size of 50 nm have been obtained by annealing GaN nanoparticles under flowing nitrogen at 1200℃for 30 min.XRD measurement result indicates an increase in the lattice parameter of the GaN nanoparticles annealed at 1200℃,and HRTEM image shows that the increase cannot be ascribed to other ions in the interstitial positions.If the as-synthesised GaN nanoparticles at 950℃are regarded as standard,the thermal expansion changes nonlinearly with temperature and is anisotropic;the expansion below 1000℃is smaller than that above 1000℃.This study provides an experimental demonstration for selecting the proper annealing temperature of GaN.In addition,a large blueshift in optical bandgap of the annealed GaN nanoparticles at 1200℃is observed,which can be ascribed to the dominant transitions from the C（Γ₇） with the peak energy at 3.532 eV.     

Indium distribution and light emission in wurtzite InGaN alloys: Several-atom In-N clusters

Considering various In distributions, we investigate electronic structures and light emission of wurtzite In_xGa_1 − xN (0?x?1) alloys. We find In_xGa_1 − xN forms a random alloy, in which many several-atom In-N clusters and short In-N- chains can exist. Small In-N clusters, especially in-plane ones, strongly localize valence electrons and dominate light emission in Ga-rich In_xGa_1 − xN alloys, which is consistent with experiments.     

Lithography-free fabrication of large-area plasmonic nanostructures using colloidal gold nanoparticles

We report simple and efficient fabrication of large-area gold nanostructures using solution-processible gold nanoparticles, where lithography and vacuum evaporation techniques are not involved in the fabrication processes. These gold nanoisland structures exhibit strong particle plasmon resonance that is characterized by optical extinction spectroscopy in the visible spectral range. The tunability of the optical response is realized by controlling the annealing temperature and by changing the concentration of the colloidal solutions of gold nanoparticles. This enables a low-cost route for exploiting new photonic devices, biosensors, and optoelectronic devices with localized field-enhancement.     

High performance uncooled InAsSbP/InGaAs photodiodes for the 1.8–3.4 μm wavelength range

Room temperature In_0.97Ga_0.03As photodiodes with an InAs_0.36Sb_0.20P_0.44 transparent window layer operating in the mid-infrared region over the wavelength range 1.8–3.4 μm are reported. The InAs_0.36Sb_0.20P_0.44/In_0.97Ga_0.03As heterojunction photodiodes were grown on p-type (100) InAs substrates by liquid phase epitaxy (LPE). Basic detector characteristics have been measured and compared with other detectors in this wavelength range. The typical detectivity of the photodiodes is 1.2 × 10¹⁰ cm Hz^1/2/W at room temperature, which compares very favourably with that of TE cooled HgCdTe and is at least three times that of cooled PbSe photoconductors. The InAs_0.36Sb_0.20P_0.44/In_0.97Ga_0.03As heterojunction photodiodes offer the advantage of increased sensitivity and extended wavelength response at room temperature compared with that of currently available commercial photodetectors, making them an attractive alternative for a number of mid-infrared applications including optical gas sensors and infrared spectrometers.     

Preparation and microwave-absorbing properties of NiFe2O4-polystyrene composites

NiFe₂O₄ nanoparticles were synthesized by the polyacrylamide gel method with acrylamide as the monomer and N,N′-methylenediacrylamide as lattice agent. The average crystallite sizes of the nickel ferrites annealed at 500, 600 and 800 °C are about 10, 30 and 50 nm, respectively. Ferrite-polystyrene composites were made by hot pressing, and microwave-absorbing properties of the composites with different contents of 35, 45, 55 and 65 wt% ferrite were investigated by testing complex permeability and complex permittivity in the X-band (8.2-12.4 GHz) frequency range. All the parameters, ε′, ε″, μ′ and μ″, increase with increasing ferrite content. The reflection losses were calculated based on a model of a single-layered plane wave absorber backed by a perfect conductor. The composite with 65 wt% ferrite content shows a minimum reflection loss of −13 dB at 11.5 GHz with a −10 dB bandwidth over the extended frequency range of 10.3-13 GHz for an absorber thickness of 2 mm.     

Ti(SO_4)_2水解-水热法制备锐钛型纳米TiO_2及其光催化性能

以Ti(SO4)2水溶液为原料,在水热条件下直接水解合成了锐钛型纳米TiO2颗粒。利用透射电镜(TEM)、X射线衍射(XRD)、BET低温吸附和紫外-可见光谱(UV-Vis)等方法对产物进行了表征,并研究了样品光催化降解甲基橙(MO)的性能。结果表明所制得纳米TiO2颗粒为锐钛矿型,晶型良好,平均粒径为24 nm,BET比表面积约为56.20 m2.g-1。光催化活性与商品纳米TiO2(P25)相近,具有良好的工业应用前景。     

Thermal-induced nonlinear optical characteristics of ethanol solution doped with silver nanoparticles

The investigation of nonlinear optical characteristics of ethanol solution doped with is presented. A large thermal-induced third-order nonlinear refractive index up to silver nanoparticles 1.941× 10^-7 cm2/W is obtained from the mixed solution under 488-nm continue wave （CW） laser irradiation, which may result from surface plasmon resonance （SPR） enhancement effect of silver nanoparticles as well as high thermo-optic coefficient and low thermal conductivity of ethanol. Obvious spatial self-phase modulation and influence of thermal-induced negative lens effect are observed when a beam propagates through this solution, indicating promising applications such as optical limiting, beam flattening, and so on.     

Spectral structure of 510.6 and 578.2 nm lines in?a?CuBr?vapor?laser

Considering the hyperfine structure and the isotopic splitting of copper active atomic levels, the temporal behavior of the spectral structure of amplified spontaneous emission at 510.6 nm line was calculated. The spectral line shapes of 510.6 and 578.2 nm laser lines were measured and compared with the calculated results at different experimental configurations, i.e., without cavity mirrors, with the back mirror, and with cavity mirrors. The results of the 578.2 nm line revealed that the mode competition was involved in the formation of laser oscillation.     

纳米银组装结构上罗丹明B的表面增强荧光效应

采用表面自组装技术,在玻璃表面构筑银纳米粒子的二维组装结构。银纳米粒子组装结构的表面等离子共振光谱中偶极子表面等离子体共振对组装结构更为敏感而表现出较大位移。组装银纳米粒子可极大增强罗丹明B的荧光。荧光的表面增强效应主要来自银纳米粒子对荧光分子所处区域的局部电磁场增强,银纳米粒子的表面分子修饰对其表面增强效应有较大的影响。     

Phonon spectrum boron nitrideof single-wallednanotubes

Based on a force constant model, we investigated the phonon spectrum and then specific heat of single-walled boron nitride nanotubes. The results show that the frequencies of Raman and infrared active modes decrease with increasing diameter in the low frequency, which is consistent with the results calculated by density functional theory. The fitting formulae for diameter and chirality dependence of specific heat at 300K are given.