Radiation damage in Si1−x Ge x heteroepitaxial devices

Results are presented of an extended study on the induced lattice defects and their effects on the degradation of Si_1−x Ge _x devices, subjected to a 20 MeV alpha-ray, 1 MeV electron, 1 MeV fast neutron, and 20 and 86 MeV proton irradiations. The degradation of the electrical device performance increase with increasing fluence, while it decreases with increasing germanium content. In the Si_1−x Ge _x epitaxial layers, electron capture levels associated with an interstitial-substitutional boron complex are induced. The radiation source dependence of performance degradation is attributed to the difference of mass and the probability of nuclear collision for the formation of lattice defects.     

锂离子电池用非晶态Si/Al/Si薄膜负极材料

采用磁控溅射法在铜箔集流体上沉积了具有“三明治”结构的Si/Al/Si三层薄膜. 高分辨率透射电镜(HRTEM)和选区电子衍射(SAED)分析结果表明, 该薄膜为非晶态. 扫描电镜(SEM)和能量散射X射线能谱(EDS)结果表明, 该薄膜总厚度约为4.0 μm, 循环100周后体积膨胀率为225％. 在1.5~0.005 V(vs. Li+/Li)和0.1 mA/cm2条件下, 该薄膜电极前5周衰减较快, 而后趋于平缓. 首次放锂量为0.88 mA·h/cm2, 循环5周后, 放锂量为0.71 mA·h/cm2, 100周后的放锂量仍能保持在0.61 mA·h/cm2. 研究结果表明, Al的加入有效地抑制了Si膜的体积膨胀, 使之具有良好的循环寿命. 交流阻抗结果表明, 随着循环次数的增加, 极化电阻首先从46.9 Ω·cm2(第1周)降低到36.2 Ω·cm2(第50周), 而后又升高到47.3 Ω·cm2(第100周). Al的加入提高了Si膜的导电性, 有效地降低了其极化电阻, 改善了Si膜的电压滞后现象.     

Transition between direct gap and indirect gap in two dimensional hydrogenated honeycomb Si x Ge1−x alloys

Using first-principles calculations, we have explored the structural and electronic properties of fully hydrogenated honeycomb Si _x Ge_1?x H alloys. Finite band gaps are opened by hydrogenation for x in the whole range from 0 to 1, while their nature and values can be tuned by x. When x is <0.7, the band gap is direct (from Γ to Γ). And when x is ≥0.7, the gap turns into indirect (from Γ to M). For all the computed compositions, the two kinds of energy differences between valence band and conduction band, Γ–Γ and Γ–M, are described well by two polynomial functions of x. The smaller of the two functions gives a good prediction for the overall band gap at any x. The two curves cross at x = 0.7, leading to the change of band gap type. At PBE level, the values of band gap for different x spread from 1.09 to 2.29 eV. These findings give a new route to tune the electronic properties of these materials and may have potential applications in nanoscale optoelectronics.     

镓在裸Si系和SiO2/Si系掺杂效应

Based on the diffusion action of gallium in silicon and SiO2 ,a diffusion model of gallium doping in bare silicon system and SiO_2/Si system is first presented in this paper ,the gallium doping effect in the two systems is analyzed theoretically. Experiments and applications have proved that the use of the open-tube gallium deffusion in SiO2/Si system can substantially improve diffusion quality and device characteristics .     

Hydrogen content in proton-conducting perovskites CaZr1 − x Sc x O3 − x /2 (x = 0.0–0.2)

The hydrogen content in CaZr_{1 ? x} Sc _x O_{3 ? x/2} (x = 0.00–0.20) and BaZr_0.9Y_0.1O_3-α (for comparison) was studied by powder nuclear microanalysis. The samples were saturated with heavy water (D₂O) vapors at 350 and 400°C in air. The chemical expansion of the CaZr_0.95Sc_0.05O_3-α and BaZr_0.95Y_0.05O_3-α samples at 700°C was measured at different water vapor pressures. A model was suggested to explain the lowered hydrogen content in oxides based on CaZrO₃.     

SYNTHESIS OF ORGANOMETALLIC PRECURSORS FOR Si/Zr/C/N-BASED CERAMICS

A new kind of organometallic precursor for Si/Zr/C/N-based ceramics was synthesized from the amine exchangereaction of hexamethylcyclotrisilazane (D_3~N) and tetrakis(diethylamino) zirconium (Zr[NEt_2]_4). Pyrolysis was performedunder nitrogen at 800℃ in a tube furnace equipped with a temperature program controller. The highest pyrolytic yield was67.5%.     

PAni/Si/G/C复合材料的制备及电化学性能

通过球磨及高温固相法制得了Si/C复合材料,并氧化合成聚苯胺包覆于硅碳复合材料的表面. 采用XRD、SEM、红外和热重分析观察复合材料形貌、分析样品结构,循环伏安法和充放电测试表征PAni/Si/G/C电极电化学性能. 结果表明,PAni/Si/C复合材料表面覆盖了较为完整的片层状结构的聚苯胺膜,可逆容量高达784 mAh.g^-1,50次周期循环后,嵌锂容量保持在690 mAh?g-1.     

锂离子电池用“三明治”型Si/Fe/Si薄膜负极材料的制备及其性能

采用磁控溅射法在铜箔集流体上沉积得到了具有“三明治”结构的Si/Fe/Si薄膜. 高分辨率透射电镜(HRTEM)和选区电子衍射(SAED)分析表明, 该薄膜为非晶态. 扫描电镜(SEM)和能量散射X射线能谱(EDXS)结果表明, 该薄膜循环前总厚度为3.2 μm, 循环200 周后体积膨胀率为265%. 在1.5-0.005 V(vs Li+/Li)和0.1 mA·cm-2条件下, 该薄膜电极首次吸锂量为1.85 mAh·cm-2, 70周后放锂量达最大值0.84 mAh·cm-2, 200周后放锂量仍维持在0.55 mAh·cm-2, 为最高放锂量的66%. 惰性材料铁的加入一方面提高了薄膜的导电性和电极的面积比容量, 有效抑制了电压滞后效应; 另一方面有效抑制了活性物质硅的体积膨胀, 保持了薄膜较好的循环充、放电性能.     

Glycolate Ti1 − x Fe x (OCH2CH2O)2 − x/2 as a precursor for the preparation of quasi-one-dimensional (1D) solid solutions Ti1 − x Fe x O2 − 2x/2 (0 ≤ x ≤ 0.1)

Quasi-one-dimensional (1D) solid solutions Ti_{1 ? x} Fe _x (OCH₂CH₂O)_{2 ? x/2} (0 < x ≤ 0.1) with the structure of anatase were prepared by heating the glycolate Ti_{1 ? x} Fe _x (OCH₂CH₂O)_{2 ? x/2} in an atmosphere of air at a temperature of >450°C. The conditions of formation and the properties of the new glycolate Ti₃Fe₂(OCH₂CH₂O)₉ were described. It was found that the synthesized Ti_{1 ? x} Fe _x O_{2 ? 2x/2} solid solutions exhibit photocatalytic activity in the reaction of hydroquinone oxidation in an aqueous solution on irradiation with UV light. A correlation between the rate of oxidation of hydroquinone and the concentration of iron in the catalyst was established. A procedure for the preparation of titanium dioxide with the structure of anatase doped with iron and carbon (Ti_{1 ? x} Fe _x O_{(2 ? x/2) ? yCy)} and also composites on its basis, which contain an excess amount of carbon, was proposed.     

Ti/ZrN2/Si薄膜界面扩散反应的研究

利用直流磁控反应溅射法在Si基底上制备了Ti/ZrN2/Si多层薄膜，利用俄歇深度剖析和线形分析研究了真空热处理前后膜层间的界面状态及相互作用.研究结果表明，Ti膜和ZrN2膜均在沉积过程中发生了界面扩散作用，真空热处理可以显著地增强Ti/ZrN2/Si膜层间的界面扩散和化学反应，并分别在界面层生成了TiNx和SiNx等物种.     

Fe/Ti/Si复合纳米微粒光催化降解NO-2

采用溶胶－凝胶法制备了Ti/Si和不同浓度Fe^3 掺杂的Fe/Ti/Si复合纳米粉末,并利用XRD、BET、UV－vis等技术手段研究了Ti/Si复合微粒的表面结构形态变化,以及对污染物NO2^-光催化降解的影响。研究表明,Fe/Ti/Si复合微粒的催化活性高于Ti/Si体系,并且Fe/Ti/Si[ω（Fe^3 )=1.5%,m(Ti):m(Si)=2:1]具有最佳活性,样品呈晶化度较低的锐钛矿结构。Fe^3 掺杂导致晶粒的增大,稳定性降低,大大提高了半导体的光催化活性,有利于对低浓度NO2^-的光催化降解。     

Fe/Ti/Si复合微粒的表面结构与催化活性

利用UV-vis,FT-IR,XRD,XPS,Raman等手段研究了Ti/Si,Fe/Ti,Fe/Ti/Si复合微粒的表面结构与催化活性。研究表明:Ti/Si复合微粒的光催化活性明显高于TiO~2微粒,TiO~2微粒以晶化度较低的锐钛矿相高度分散在SiO~2网络中,粒径约为10nm;并与SiO~2形成Si-O-Ti桥氧结构;提高了TiO~2微晶的热稳定性、比表面积和表面缺陷;有利于吸附降解有机污染物、半导体光生电子-空穴的分离及提高催化剂的光催化活性。Fe/Ti复合微粒具有Ti-O-Fe网络结构,粒径约为12nm,样品呈晶化度较低的锐钛矿和金红石混晶形式,这种结构有利于促进半导体光生电子-空穴的分离与活性.OH基团的生成;并能在半导体TiO~2中形成杂质中间能级,扩大光响应范围及提高半导体的光催化活性。但是,杂质Fe^3^+的掺入促进了TiO~2微粒的晶格畸变,晶粒增大。所研究的复合微粒中,Fe/Ti/Si体系具有最高的光催化活性。这种体系兼有Ti/Si,Fe/Ti复合微粒的优点,包含Si-O-Si,Si-O-Ti,Ti-O-Ti,Ti-O-Fe多种网络结构的Fe~2O~3,Fe~3O~4,FeO多种物种,具有很高的比表面积和表面缺陷;大大提高了半导体的光催化活性。是一种极具有实用价值的新型光催化剂。     

Gd2CuO4薄膜与Si, SiO2/Si基底界面相互作用研究

采用XRD和俄歇电子能谱（AES）等技术研究了钙钛矿型Gd2CuO4薄膜与基底Si和SiO2/Si的界面相互作用,发现衬底对Gd2CuO4薄膜的晶化特性有很大影响,以单晶Si为基镀时,Gd2CuO4薄膜经600℃热处理1h即可形成钙钛矿型晶体结构,而以SiO2/Si为基底时,经700℃热处理1h能形成较完善的钙钛矿型晶体结构,Gd2CuO4薄膜的晶粒度随热处理温度的升高而增大,热处理时间对晶粒度则影响较小,AES深度剖析表明,形成的薄膜组成均匀,在界面上有一定程度的扩散,以Si为基底时,Gd2CuO4与基底Si相互扩散,以SiO2/Si为基底时则主要是薄膜中Gd,Cu向SiO2层中的扩散,AES线性分析表明,在薄膜与基底的界面上,各元素的俄歇电子动能发现位移,表明基底作用使界面上元素的化学环境发生了变化。     

不同Si/Al比对Mo/ZSM-5催化性能的影响

采用浸渍法在不同Si／Al比的HZSM-5上制备了3种MoO3含量相同的Mo／ZSM-5样品，并在相同的实验条件下对其进行了活性测试，同时运用XRD、XPS、NO—TPD等技术分别对催化剂的体相和表面结构进行了表征．实验结果表明，Si／Al比对Mo／ZSM-5上NO的选择性催化还原性能有明显的影响，Si／Al比为28的1#样品其转化率在530℃达到94％以上，而Si／Al比较大的2#和3#样品最高转化率只有48％和41％．对3种Mo／ZSM-5样品的XRD表征只发现有HZSM-5和MoO3两种物相存在，分子筛骨架差异不大；而XPS表征却发现1#样品的表面M03d5／2含量远大于2#和3#样品，并且有Mo^4 和(或)Mo＼ 5 存在，表明3种样品的表面性质存在很大差异．在3种样品中，1#样品具有最大的NO吸附能力，这与表面特性差异相吻合．     

Phase equilibriums, oxygen exchange kinetics and diffusion in oxides CaZr1 ? x Sc x O3 ? x/2 ? δ

Oxides CaZr_{1 ? x} Sc _x O_{3 ? x/2 - ??} (x = 0.00?C0.20) were synthesized according to the ceramic technology. The solubility boundary of scandium with formation of solid solutions on the basis of calcium zirconate CaZrO_{3 ? ??} corresponds to x = 0.07?C0.08. The second phase of CaSc₂O₄ is present in the samples with scandium content of x = 0.10, 0.15, 0.20. Its fraction grows at an increase in x. The method of full-profile Rietveld analysis was used to calculate the structure parameters for oxides CaZr_0.99Sc_0.01O_{2.995 ? ??} and CaZr_0.95Sc_0.05O_{2.975 ? ??}. The method of isotopic exchange with gas phase analysis was used to study the kinetics of gas-phase oxygen interaction with the CaZr_0.95Sc_0.05O_{2.975 ? ??} oxide in the temperature range of 700?C850°C and at oxygen pressures of 0.13?C6.67 kPa. The values of effective activation energies of the oxygen exchange and diffusion processes were 1.36 ± 0.32 and 1.92 ± 0.21 eV, accordingly. The dependence of the interphase exchange rate on the pressure of oxygen corresponds to the power law with the exponent of 0.31 ± 0.04 at the temperature of 750°C.     

TiO_2/Si复合材料的制备及其性能研究

为了提高单晶硅表面的光学利用效率,本文采用水热法在其表面生长一层平均棒长为900±50 nm,直径为100±20 nm的金红石相Ti O2纳米棒阵列。通过积分球反射光谱对这种Ti O2/Si复合材料进行抗反射性能表征,发现这种复合材料具有较好的抗反射性能;通过测量Ti O2/Si复合材料的光电流性能,发现其具有高效的光电转化效率,可有效提高太阳光的利用率;通过探讨Ti O2/Si复合材料对亚甲基蓝的降解,发现其在光催化降解染料效率方面具有显著的提高效果。     

Si/石墨复合负极材料的制备方法研究进展

目前,锂离子电池被广泛地应用于移动电子设备、电动汽车以及混合动力汽车,因此,对高比容量以及长循环寿命的需求也愈加迫切.石墨类负极材料具有优异的循环性能,但理论比容量较低（372 mA·h·g^-1）,难以满足日益增长的高能量密度需求.Si负极材料因具有较高的可逆比容量（3579 mA·h·g^-1）而引起广泛关注.但是,巨大的体积膨胀限制了Si负极的使用.纳米化可以有效的释放Si体积膨胀带来的应力变化,提高其电化学性能.然而,单独的纳米材料具有很高的比表面会引起诸多副反应,阻碍其实际应用.将纳米Si与石墨复合制备Si/石墨复合材料,可充分利用纳米Si和石墨的优点,有望成为新一代高能量密度和长循环寿命锂离子电池负极材料.截至目前,多种技术手段被应用于制备纳米Si/石墨的复合材料,其核心问题是保证纳米Si和石墨的均匀分散以及稳定的结合.根据石墨与纳米Si的复合过程可以将该类材料的制备方法分为：固相法、液相法、以及气相沉积法.本综述对现有文献报道的Si/石墨复合材料制备方法以及所面临的主要问题进行简要总结概括.     

Novel red-emitting phosphors, (Mg(1−x−y)MnxDyy)Al2Si2O8 and (Mg(1−x−y)MnxTmy)Al2Si2O8

Mn⁴⁺ doped and Dy³⁺, Tm³⁺ co-doped MgAl₂Si₂O₈-based phosphors were prepared by conventional solid state reaction at 1,300 °C. They were characterized by thermogravimetry, differential thermal analysis, X-ray powder diffraction, photoluminescence, and scanning electron microscopy. The luminescence mechanism of the phosphors, which showed broad red emission bands in the range of 600–715 nm and had a different maximum intensity when activated by UV illumination, was discussed. Such a red emission can be attributed to the ²E → ⁴A₂ transitions of Mn⁴⁺.     

Chemical pressure and rare-earth orbital contributions in mixed rare-earth silicides La(5-x)Y(x)Si4 (0 ≤ x ≤ 5)

A crystallographic study and theoretical analysis of the structural and La/Y site preferences in the La(5-x)Y(x)Si(4) (0 ≤ x ≤ 5) series prepared by high-temperature methods is presented. At room temperature, La-rich La(5-x)Y(x)Si(4) phases with x ≤ 3.0 exhibit the tetragonal Zr(5)Si(4)-type structure (space group P4(1)2(1)2, Z = 4, Pearson symbol tP36), which contains only Si-Si dimers. On the other hand, Y-rich phases with x = 4.0 and 4.5 adopt the orthorhombic Gd(5)Si(4)-type structure (space group Pnma, Z = 4, Pearson symbol oP36), also with Si-Si dimers, whereas Y(5)Si(4) forms the monoclinic Gd(5)Si(2)Ge(2) structure (space group P2(1)/c, Z = 4, Pearson symbol mP36), which exhibits 50% "broken" Si-Si dimers. Local and long-range structural relationships among the tetragonal, orthorhombic, and monoclinic structures are discussed. Refinements from single crystal X-ray diffraction studies of the three independent sites for La or Y atoms in the asymmetric unit reveal partial mixing of these elements, with clearly different preferences for these two elements. First-principles electronic structure calculations, used to investigate the La/Y site preferences and structural trends in the La(5-x)Y(x)Si(4) series, indicate that long- and short-range structural features are controlled largely by atomic sizes. La 5d and Y 4d orbitals, however, generate distinct, yet subtle effects on the electronic density of states curves, and influence characteristics of Si-Si bonding in these phases.     

Lithium-cation Conduction and Crystallochemical Features of Solid Solutions La2/3 – x Li3x□4/3 – 2x Nb2O6 with the Structure of Fault Perovskite

Transport properties and crystallochemical features of lithium-containing lanthanum metaniobates La_{2/3 – x} Li_{3x4/3 – 2x} Nb₂O₆ with the structure of fault perovskite are studied. The materials studied have high conductivity by lithium ions. A correlation between the conductivity magnitude, chemical composition, and crystallographic parameters is found.