Characteristic responses of a semiconductor gas sensor depending on the frequency of a periodic temperature change

A novel gas-sensing system based on a dynamic nonlinear response is reported to enhance the selectivity toward sample gases using a single detector. A periodic temperature change was applied to a semiconductor gas sensor and the resulting conductance of the sensor was evaluated by fast Fourier transformation (FFT). The dynamic nonlinear response to the sample gases was further characterized depending on the frequency of the temperature change. The characteristic sensor response under the application of a temperature change was theoretically simulated by considering the kinetics of gas molecules on the semiconductor surface.     

Photoinduced electron transfer in some photosensitive molecules-incorporated semiconductor/zeolites: New photocatalytic systems

An intramolecular charge transfer (ICT) molecule,p-N,N-dimethyl-aminobenzoic acid (DMABA) has been studied in zeolite and colloidal media. The ratio of ICT to normal emission (ICT/LE) is greatly enhanced in zeolites compared to that in polar solvents. The ICT emission of DMABA was quenched by increasing the concentration of TiO₂ colloids, while the normal emission was slightly enhanced. Upon illumination of the heteropoly acid (HPA) incorporated TiO₂ colloids, interfacial electron transfer takes place from the conduction band of TiO₂ to the incorporated HPA which is also excited to catalyze the photoreduction of Methyl Orange. It is found that the interfacial electron transfer mechanism of HPA/TiO₂ is quite analogous to the Z-scheme mechanism for plant photosynthetic systems. In DMABA-adsorbed TiO₂/Y-zeolite the ICT/LE ratio of DMABA is quite small implying that electron transfer takes place from DMABA to the conduction band of TiO₂. This results in drastic enhancement in the photocatalytic activity of DMABA-adsorbed TiO₂/Y-zeolite compared to free TiO₂/Y-zeolite.     

Pressure-induced phase transition of zinc-blende AlN: An ab initio molecular dynamics study

An ab initio constant pressure technique is carried out to study the pressure-induced phase transition of the zinc blende AlN (aluminum nitride). A first order phase transformation into a rock salt structure is observed in the constant pressure simulations. The transformation is accompanied by an initial tetragonal distortion and a subsequent shearing, similar to that found in the other zinc blende structured materials. This phase transition should occur around 6.2 GPa based upon the enthalpy calculations.     

Modular synthesis of ruthenium tripodal system with variable anchoring groups positions for semiconductor sensitization

We describe an improved synthetic approach to access tripodal compounds with variable footprints and anchor groups. Two ruthenium(II) bipyridine tripodal complexes with three carboxylic acid groups in meta (Ru-m-COOH, 1) and para (Ru-p-COOH, 2) positions, and with large (180-250 Å²) footprints were synthesized and bound to the surface of nanostructured TiO₂. Selected properties of 1 and 2 in solution and bound are reported.     

Synthesis, crystal structure, and properties of the rhombohedral modification of the thiospinel CuZr1.86(1)S4

The rhombohedral modification of the thiospinel, CuZr_1.86(1)S₄, has been synthesized by the reaction of the constituent elements in an alkali metal halide flux and structurally characterized by single crystal X-ray diffraction techniques. The title compound crystallizes in the rhombohedral space group (#166, a=7.3552(2) Å, c=35.832(2) Å, V=1678.76(13) Å³, Z=12, and R/wR=0.0239/0.0624). The structure is composed of close packed S layers, with a stacking order of ?ABCBCABABCACAB?·along the c axis. The Zr and Cu atoms occupy the octahedral and tetrahedral holes between S layers, respectively. Three different kinds of S-M-S layers exist in the structure: layer I has fully occupied Zr and Cu sites, layer II has fully occupied Zr sites but no Cu, and layer III has partially occupied Zr and fully occupied Cu sites. Transport and optical properties indicate that the title compound is a small band gap (1.26 eV) n-type semiconductor.     

Properties of a vector soliton laser passively mode-locked by a fiber-based semiconductor saturable absorber operating in transmission

We experimentally demonstrate a passively mode-locked fiber laser employing a fiber-based semiconductor saturable absorber (SSA) operating in transmission. Polarization rotation locked vector solitons are observed in the laser. Due to the intrinsic dynamic feature of the laser, period-doubling of these vector solitons has also been observed. Furthermore, extra spectral sidebands are formed on the optical spectrum, caused by the energy exchange between the two orthogonal polarization components of the vector solitons. By careful reduction of the pump power together with fine adjustment to the cavity birefringence, period-one state can further be obtained. Additionally, the phase noise properties of the vector soliton fiber laser have also been characterized experimentally and analytically.     

EAM-SOA millimeter-wave frequency up-converter for radio-over-fiber applications

We present an optical scheme for photonic frequency up-conversion at the millimeter-wave bands based on Semiconductor Optical Amplifier. The proposed scheme modulates the bias current with the Intermediate Frequency in order to achieve frequency mixing of an incoming optical signal modulated with the Local Oscillator. Theory indicates that the proposed scheme supports data bandwidths in the tens of GHz for LO values above 10 GHz. This scheme allows for photonic integration of the considered optical devices. A laboratory demonstration of the scheme for up-conversion to the 40 GHz band, using narrow-band IF signals, showed relatively low thresholds for the optical input power and bias current level to achieve error free operation: − 14.5 dBm 100 mA for a 64-QAM signal. Spurious-Free Dynamic Range showed an acceptable performance, with a linearity about 52.5 dB·Hz^2/3 for an optical input power of − 6 dBm.     

A novel all optical method of implementing an n-bit wavelength encoded complete digital data comparator using nonlinear semiconductor optical amplifiers

Data comparator is the integral part of arithmetic and logical unit of any electronic or optical data processor. Due to some inherent limitations of electronics it cannot be possible to obtain a super fast operation (over terahertz limit) from electronic comparators. Again wavelength encoding technique has been established as an excellent one over other existing optical data encoding techniques. Semiconductor optical amplifier (SOA) technologies have shown their strong potentiality of realizing many all-optical systems. In this communication the authors have proposed a new scheme of developing all-optical wavelength encoded n bit binary comparator exploiting the four-wave mixing, wavelength filtering, wavelength conversion and nonlinear polarization rotation capabilities property of nonlinear semiconductor optical amplifiers. The scheme can be used for comparing signed and unsigned optical binary data of any bit wide numbers as well. The comparator is especially suitable for use as a building block in a larger optical circuit, such as in an all optical telecommunications switch.     

基于典型工况的半导体制冷系统优化方式探讨

半导体制冷的特殊性,使制冷优化探讨对其工程应用具有重要指导意义.文中阐述了作为制冷片工作参数优化依据的最大效率E、等增量I、等功率P、综合最佳S、最大制冷量Q和最大温差T六种典型制冷工况.工况对比分析指出,温差亦是影响制冷性能的重要因素.在讨论各工况应用场合和制冷片损坏机理的基础上.探讨了温差优化和供电与控制方式优化措...     

半导体制冷电脑CPU恒温散热研究

用风冷的方法给CPU降温存在着降温效率低、反应速度慢、风扇的机械转动可靠性差、噪音大等弊病.因此,这里设计了一种用半导体制冷降温的装置来提高CPU的散热效率.它用温度传感器检测电脑CPU温度,当CPU温度超过设定温度的时侯,控制电路供电使半导体制冷块制冷,使CPU温度保持恒定.为防止冷凝结露,采用绝热材料密封导热铜板及...