适用于高动态平台的TDM/FDMA+令牌环卫星混合多址接入协议

对卫星通信中比较常用的多址接入方式进行了比较,提出了一种固定分配与自由分配相结合的卫星混合多址接入协议,对指标性能进行了分析。试验结果表明,该协议具有业务接入灵活、卫星频带利用率高、系统实现简单等特点,适用于高动态平台卫星通信。研究内容对相关工程应用具有一定的参考价值。     

Poly(4-styrenesulfonic acid) doped polypyrrole/tungsten oxide/reduced graphene oxide nanocomposite films based surface acoustic wave sensors for NO sensing behavior

Poly(4-styrenesulfonic acid) (PSSA) doped polypyrrole (PPy)/tungsten oxide (WO₃)/reduced graphene oxide (rGO) hybrid nanocomposite have been successfully synthesized using appropriate amounts of PSSA, pyrrole monomer, WO₃, and rGO dispersed in aqueous solution through in situ chemical oxidation polymerization. Here, a simple spin coating method was used to fabricate a nitric oxide (NO) gas sensor composed of the aforementioned nanocomposite on a surface acoustic wave (SAW) resonator. This sensor can detect NO gas at concentrations of 1–110 parts per billion (ppb) at room temperature in dry air, with a sensitivity of 12 Hz/ppb and response and recovery times of <2 min. Moreover, its limit of detection (LOD) is 0.31 ppb for a signal to noise ratio of 3. It demonstrates repeatability, fast response, and recovery at room temperature. Moreover, its sensory performance remains highly stable over 30 days with only a 6.3% decrease in sensitivity. In addition, the sensor is highly selective for NO, even when nitrogen dioxide, ammonia, and carbon dioxide are applied as interfering gases. The inclusion of rGO (with large specific surface area) and the synergic effect of n-type WO₃ nanoparticles in the p-type PPy matrix (leading to p-n heterojunction region formation) possibly underlie the efficient sensing performance of our sensor.     

沿[001]c极化0.70Pb(Mg_(1/3)Nb_(2/3))O_3-0.30PbTiO_3单晶的声表面波传播特性研究

以室温下弛豫铁电单晶0.70Pb(Mg_(1/3)Nb_(2/3))O_3-0.30PbTiO_3(PMN-30%PT)的材料参数为基础,研究了该晶体沿[001]c极化情况下,不同切型的声表面波传播特性.研究发现,X-切型的PMN-30%PT单晶是一种具有低相速度和高机电耦合系数的材料,同时存在许多能流角为零的传播方向,综合来看,X-切型的127°左右方向是声表面波的最佳传播方向.     

GaAs表面及Al_xGa_（1－x）As／GaAsHBT外基区表面（NH_4）_2S／SiN_x钝化工艺研究

分析了ＡｌｘＧａ１－ｘＡｓ／ＧａＡｓＨＢＴ外基区表面复合电流及外基区表面复合速度对直流增益的影响，用光致发光（ＰＬ）谱和Ａｌ／ＳｉＮｘ－Ｓ／ＧａＡｓＭＩＳ结构Ｃ－Ｖ特性，研究了ＧａＡｓ表面（ＮＨ４）２Ｓ／ＳｉＮｘ钝化工艺的效果及其稳定性。结果表明，ＥＣＲ－ＣＶＤ淀积ＳｉＮｘ覆盖并在Ｎ２气氛中退火有助于改善ＧａＡｓ表面硫钝化效果的稳定性。在此基础上形成了一套包括（ＮＨ４）２Ｓ处理、ＳｉＮｘＥＣＲ－ＣＶＤ淀积及退火并与现有ＨＢＴ工艺兼容的外基区表面钝化工艺，使发射区面积为４×１０μｍ２的器件增益比钝化前提高了４倍，且６０天内不退化。     

Al薄膜对(002)ZnO/Al/Si结构基片中ZnO薄膜特性影响的实验研究

采用射频磁控溅射法沉积制备了(002)ZnO/A l/Si复合结构。研究了Al薄膜对(002) ZnO/Al/Si复合结构的声表面波器件(SAWD)基片性能影响以及当ZnO 薄膜厚度一定时的Al膜最佳厚度。采用X射线衍射(XRD)对Al和ZnO薄膜进行了结构表征 ,采用 扫描电镜(SEM)对ZnO薄膜进行表面形貌表征,并从薄膜生长机理角度进行了分析。结果 表明,加Al薄膜有利于ZnO薄膜按(002)择优取向生长,并且ZnO 薄膜的结晶性能提高;与(002)ZnO/Si结构基片相比,当Al薄膜 厚为100nm时,(002)ZnO/Al/Si结构中ZnO薄 膜的机电耦合系数提高 了65%。     

Young’s modulus evaluation by SAWs for porous silica low-k film with cesium doping

Young’s moduli of porous silica low-k films with cesium (Cs) doping are determined by surface acoustic waves (SAWs) in this study. Four low-k samples doped with 0-30 ppm wt% Cs in the precursor solution are investigated to check the mechanical promotion of the porous silica films. The SAW determination process is performed on these ultra-thin porous films. The detected signals with the signal-to-noise ratio of 50:1 are achieved in our measurements. The signal process with combination of wavelet and FIR filter is proposed to effectively restrain the high and low frequency noises and the “Gibbs effect” of the detected signals. The smooth experimental dispersive curves with frequency range from 20 to 150 MHz, which is qualified for the data fitting process with the theoretical dispersion curves, are obtained for these detected thin low-k films. The determination results show that the mechanical property is improved with the pretreatment of cesium doping, which confirms that the degree of siloxane cross-linkage of the porous silica film is promoted by cesium doping.     

数字移动通信体制的新动向—扩频码分多址（SS／CDMA）

本文主要讨论数字移动通信中扩频码分多址技术，介绍了国外关于ＣＤＭＡ数字移动通信研究的动态，阐明了ＣＤＭＡ体制的优越之处，分析了ＣＤＭＡ的关键技术，并就我国数字移动通信体制提出建议。     

关于Ni（100）面上C复盖的LEED和STM研究

本文叙述了Ｃ／Ｎｉ（１００）系统的ＬＥＥＤ和ＳＴＭ的研究结果，并讨论了该系统的表面结构模型。     

Anisotropic Surface Roughness in Molecular-Beam Epitaxy CdTe (211)B/Ge(211)

We characterize the surface of molecular-beam epitaxy (MBE)-grown CdTe(211)B/Ge(211) by atomic-force microscopy (AFM), optical interference microscopy, and generalized ellipsometry (GE). We find that, for substrate temperatures above 300°C, the surface is rough and hazy; the AFM root-mean-square roughness is of the order of 150 Å. It appears from GE that the optical response is anisotropic, the principal axes of anisotropy being along the $ [\overline{1} 11] We characterize the surface of molecular-beam epitaxy (MBE)-grown CdTe(211)B/Ge(211) by atomic-force microscopy (AFM), optical interference microscopy, and generalized ellipsometry (GE). We find that, for substrate temperatures above 300°C, the surface is rough and hazy; the AFM root-mean-square roughness is of the order of 150 ?. It appears from GE that the optical response is anisotropic, the principal axes of anisotropy being along the and directions. For a substrate temperature of approximately 300°C, the surface is smooth and mirror-like and the AFM roughness is as low as 45 ?. The sample is still anisotropic, even though the magnitude of the cross-polarized reflection coefficients are very small in this case. It appears that the anisotropy originates from the surface roughness, not the bulk.     

Optimizing back surface field for improving Voc of(Al)GaInP solar cell

GaInP and AlGaInP solar cells were grown by metal organic chemical vapor deposition (MOCVD), and theoretical analysis demonstrated that hetero-interface recombination velocity plays an important role in the optimizing of cell performance, especially the interface between base layer and back surface field (BSF). Measurements including lattice-matched growth and pseudo-BSF were taken to optimize BSF design. Significant improvement of V_oc in GaInP and AlGaInP solar cells imply that the measures we took are effective and promising for performance improvement in the next generation high efficiency solar cells.     

In0.53Ga0.47As(1 0 0) native oxide removal by liquid and gas phase HF/H2O chemistries

The native oxide removal, surface termination, and stoichiometry of InGaAs(1 0 0) surfaces using liquid and gas phase HF/H₂O etching were studied using X-ray photoelectron spectroscopy. Oxide removal in liquid phase HF stopped at the As layer, producing either elemental or H-terminated As. The surface oxidized upon air exposure, forming a 4.8 Å As₂O₃ layer on an As rich InGaAs sub-surface (17% In, 16% Ga, 66% As). A sub atmospheric gas phase HF/H₂O process (100 Torr, 29 °C, 0.5 min) completely removed As₂O₃ and produced mainly In and Ga fluorides, since As fluoride is volatile at these experimental conditions. Once enough F accumulated on the surface, the water sticking probability decreased and the etching reaction proceeded at a much lower rate. The highest oxide removal (4.2 Å residual oxide) was achieved after 5 min of etching. As₂O₃ and As₂O₅ were completely removed and considerably more InF₃ and GaF₃ were produced. The surface contained a group III-fluoride rich overlayer (34% In, 36% Ga) on a slightly As rich bulk (21% In, 21% Ga, and 58% As). The As rich InGaAs sub-surface produced with both liquid and the longer gas phase HF treatments is intrinsic to HF-InGaAs chemistry, although the oxide removal mechanism is likely different.