多孔硅层的剥离及反射率研究

通过改变电化学腐蚀电流密度的大小成功剥离了多孔硅层,并分析了多孔硅层的剥离机理,测量了多孔硅层的反射率曲线.结果表明:影响多孔硅层剥离的主要因素是多孔硅的形成临界电流密度,当电化学腐蚀的电流密度增大到100mA/cm2时,已经大于多孔硅的临界形成电流,从而发生了硅片表面的电化学抛光,并且多孔硅层对从近紫外到近红外的整个波段反射率都较低.     

多孔硅吸杂对单晶硅片电性能的影响

多孔硅吸杂是减少晶体硅中杂质和缺陷,提高太阳能电池转换效率的有效方法.本文采用电化学腐蚀方法在单晶硅片上制备多孔硅.通过观察多孔硅的形貌、孔隙率、多孔层厚度及单晶硅片的电阻率变化,研究不同的腐蚀时间对制备多孔硅的吸杂效果的影响,并分析多孔硅吸杂的机理.结果表明,在J=100 mA/cm2条件下腐蚀时间为30 min、40 min、50 min、60 min吸杂处理后,电阻率均提高,且随着腐蚀时间的增加,电阻率相应增加,与多孔硅的形貌、孔隙率和多孔层厚度的变化趋势一致.多孔硅形成伴随弹性机械应力出现,随腐蚀时间增加,应力增加,晶格常数相应增加,这都有利于缺陷和金属杂质在多孔硅层-基底界面处迁移和富集,导致单晶硅吸杂后电阻率增大.     

镁离子掺杂多孔硅的蓝光发射

用电化学方法对多孔硅薄膜进行了镁离子的化学掺杂.用荧光分光光度计分析了样品的光致发光特性,发现镁掺杂增强了多孔硅的蓝光发射,当镁离子浓度增大到0.002mol/L时,可使蓝光强度达到多孔硅红光强度的一半.红外吸收谱表明,掺镁多孔硅的表面形成较完整的Si-O-Si网络结构,分析结果认为,多孔硅的蓝光光激发主要发生在多孔硅的纳米硅粒中,光发射主要发生在多孔硅中包裹纳米硅SiOx层中的发光中心上,对实验结果进行了合理的解释.     

多孔硅-Au/Ag枝晶复合材料研究进展

基于金属包裹的多孔硅衬底具有制备成本低、检测能力强的优点。自20世纪表面增强拉曼散射(SERS)现象被发现以来,多孔硅-Au/Ag复合材料逐渐展现出作为SERS衬底的优势,被广泛应用于生物、化学、医疗等领域。本文综述了近些年来基于多孔硅复合Au/Ag纳米颗粒混合平台的研究,重点讨论了将贵金属Ag/Au复合于多孔硅衬底上的制备方法,介绍了它们在不同制备条件下枝晶结构的生长形貌和检测性能,并对多孔硅-Ag/Au枝晶复合结构作为SERS衬底的未来发展进行简要分析。     

低温AlN插入层降低硅基GaN膜微裂

为了降低MOCVD外延硅基GaN膜层中的应力、减少硅基厚GaN层的微裂;在高温GaN层中插入低温AlN.低温AlN插入层可平衡HT-GaN生长和降温过程引起的张应力,降低厚膜外延层的微裂,已研制出厚度超过1.8微米无微裂GaN外延层.本文重点研究了低温AlN生长温度对HT-GaN材料的影响,给出了较佳的LT-AlN生长温度.采用扫描电子显微镜(SEM),原子力显微镜(AFM)和高分辨率双晶X射线衍射(DCXRD),对样品进行了测试分析.试验和测试结果表明低温AlN的生长温度至关重要,生长温度过低影响GaN晶体质量,甚至不能形成晶体;生长温度过高同样会影响GaN结晶质量,同时降低插入层的应力平衡作用;实验结果表明最佳的LT-AlN插入层的生长温度为680℃左右.     

一维多孔硅声子晶体的带隙研究

多孔硅的力学性质随多孔度有较大变化,因此可以用多孔硅材料来构建声子晶体结构.本文将在理论上讨论一维多孔硅声子晶体的带隙,设计出宽禁带声子晶体结构,分析其相关的物理特性.计算结果表明薄的高孔度插入层将获得宽的带隙,而声子晶体异质结能够获得更宽带隙.     

ZnO/SnO2复合透明导电膜性能的研究

采用直流磁控溅射工艺在SnO:透明导电玻璃上沉积一层ZnO膜,制备出ZnO/SnO2复合透明导电膜,作为硅薄膜太阳电池前电极.比较了具有不同ZnO厚度的复合膜氢轰击前后的光电性能,发现适当控制ZnO膜的厚度至关重要.研究了快速热退火(RTA)对薄膜的结构及光电性能的影响,发现400℃退火能够改善薄膜的光学性能.     

多孔硅形成机理的逆结晶学模型

本文概述了多孔硅形成机理和现有模型.通过观察和分析多晶多孔硅化学腐蚀机理提出了一个新模型:多孔硅形成机理的逆结晶学模型.这个模型指出多晶多孔硅均匀形貌具有自选择性,而此自选择性受结晶学原理控制.此模型的提出对研究晶体生长有用.     

多孔硅基WO3气敏传感器的制备与性能研究

以钨酸钠和氯化钠为原料,采用水热法在硅基多孔硅上原位生长WO3纳米棒薄膜,制成p型多孔硅基-n型WO3复合结构气敏传感器.为了获得最大比表面积的复合形貌,详细研究了水热反应时间和温度对多孔硅基WO3复合结构显微组织表面形貌的影响.利用扫描电镜、粉末衍射等表征手段测试并分析了多孔硅基表面WO3纳米棒薄膜的形貌以及晶体结构,并测试了复合结构传感器在不同工作温度下的气敏响应特性,结果表明:该气敏传感器在室温下便对有毒气体NO2具有高灵敏度以及稳定的重复性.     

多孔硅制备研究进展及其在锂离子电池方面的应用

多孔硅具有比表面积大、发光性能良好等特点,目前对于多孔硅的研究已经涉及到生物与化学传感器、药物递送、光催化、能源等领域。多孔硅中的孔隙可有效缓解硅在锂化时的体积膨胀,缩短锂离子从电解液向硅本体扩散的距离,促进高电流密度下的充放电过程。因此,多孔硅在储能领域得到了广泛研究与发展。但是一些挑战仍然存在,如制备成本、刻蚀机理、多孔结构的调控、多孔硅的电化学性能等还不能满足商业化应用的要求。本文对目前国内外多孔硅制备方法的研究进行了综述,并详细介绍了多孔硅在锂离子电池领域的应用。最后,对多孔硅材料在储能领域的发展进行了展望。     

A review of measurement of thermophysical properties of silicon melt

Measurements of thermophysical properties of Si melt and supplementary study of X-ray scattering/diffraction by the authors' group were reviewed. The values obtained differed variously from those of literature. Density was 2–3% larger, surface tension 20–30% smaller, viscosity up to 40% larger, electrical conductivity 8% smaller, spectral emissivity more or less in good agreement with literature values, and thermal diffusivity a few percent larger. An anomalous density jump was found near the melting point. Surface tension and viscosity also showed anomaly. A strange time-dependent change of density was observed over 3 h after melting. X-ray analyses suggested a slight change in local atom ordering, but showed no sign of cluster formation. An addition of 0.1 at% gallium caused the density jump to disappear, while that of boron caused no change. An EXAFS study of the former melt indicated a strong interaction between Ga and Si atoms as if molecules of GaSi₃ existed. The implications of the measured properties are a possibility of soft-turbulence in an Si melt in a relatively large crucible, a more complicated manner of intake of oxygen depleted molten Si from the free surface region to underneath the growing crystal, and a relaxation of the melt after melting arising from trapped gas species.     

Effect of alumina on enthalpy of mixing of mixed alkali silicate glasses

The enthalpy of mixing of mixed alkali (Na₂O and K₂O) silicate glasses containing various concentrations of alumina was determined using an ion-exchange equilibrium method. For glasses with a constant alkali concentration, the enthalpy of mixing was found to become less negative with alumina addition. Consistent with our previous results on the enthalpy of mixing of alumina-free mixed alkali silicate glasses, the magnitude of enthalpy of mixing exhibited a good correlation with the molar volume mismatch of the corresponding two single alkali glasses as well as with the extent of conductivity mixed alkali effect, e.g. excess activation energy of conductivity, ΔE. The reduction of the magnitude of the enthalpy of mixing with alumina addition can be attributed to the reduction of non-bridging oxygen and ionic field strength. Combining the present results with results obtained earlier, the magnitude of the enthalpy of mixing for all mixed alkali (Na₂O and K₂O) silicate glasses with and without alumina was expressed by a simple function of a modified Tobolsky parameter, which takes into account the alkali concentration and the difference in cation-to-effective anion distances. The enthalpy of mixing data of the mixed alkali glasses was then compared with reported experimental data on the conductivity of mixed alkali aluminosilicate glasses. What appears to be conflicting experimental data can be understood in terms of the magnitude of the enthalpy of mixing and we can conclude that the mixed alkali effect is closely correlated with the negative enthalpy of mixing.     

Mesomorphism Dependence on the Position of Substitution of a Pair of Esters

A novel homologous series of ethylene derivatives of thermotropic liquid crystals has been synthesized. The methoxy to octyloxy derivatives are nematogenic, the decyloxy to tetradecyloxy derivatives are smectogenic, in addition to nematogenic, and the hexadecyloxy homologue is smectogenic only. All the members of the series are enantiotropically mesogenic. Thermotropic behavior was determined by an optical polarizing microscope equipped with a heating stage and Differential Scanning Calorimetry (DSC) study. Analytical and spectral data confirm the molecular structures of homologues (infrared, nuclear magnetic resonance, mass spectra, X-ray, and DSC data). Textures of the nematic phase are threaded or Schlieren and that of smectic phase are focal conic fan-shaped of smectic A or C. Transition curves of the phase diagram behave in a normal manner except one or two deviations from the normal trend. The mesophase range (Sm+N) varies from 3°C to 44°C. The average thermal stability for smectic is 93°C and that for nematic 117.4°C. The LC behavior of the novel series is compared with a structurally similar known series.     

原位氮化法制备TiN纳米粉体

用溶胶凝胶法合成的纳米TiO2粉体作为原料,将该粉体在氨气中进行原位氮化制备了TiN纳米粉体.用XRD,TEM,化学分析等手段对合成的TiN纳米粉体的物相组成、形貌、成分进行了分析.实验分析表明:在1000℃和1100℃下分别氮化5h,可以制备粒径大约为40nm和80nm的TiN粉体,其TiN的含量分别为95.40;和98.37;;而在1000℃条件下氮化时间减少到2h时,TiN的含量仅为58.36;.氮化温度和氮化时间是合成纳米TiN的重要因素,提高合成温度和延长氮化时间均可形成纯度较高的TiN纳米粉体,但延长氮化时间更有利于获得粒径小的氮化钛粉体.     

立方晶系晶体本征铁弹相变序参量的选取

在本征铁弹相变的软模理论的基础上,依据弹性本构关系和居里原理,给出了立方晶系晶体所有可能的自发应变的种类,研究了立方晶系晶体本征铁弹相变序参量的选取问题.以Th群和Oh群为例,阐明了不同类的序参量导致晶体对称性变化相同的的原因,提出了该情况下序参量选取的“就少不就多”的原则.得到了发生本征铁弹相变时所有可能的序参量及晶体的对称性的变化.     

On the influence of structural features of DNA on the possibility of metabolic transfer of electrons

Abstract

A fragment of a DNA molecule is considered as one of the channels of metabolic electron transfer. The heterogeneity of the complementary chains is effectively taken into account. This made it possible to find the speed of the electron injected into the DNA conduction band and the current density that it creates. Estimates of electron mobility in nucleic acid chains are made. They were an order of magnitude smaller than that of typical semiconductors. For the specific conductivity of nucleic acid chains, estimates provide a conductivity of one to two orders of magnitude lower than in graphite.     

Features of transformations in REE-containing systems of nitrate precursors in preparatory processes of formation of multifunctional oxide materials

Abstract

The complex study provides a reliable idea of ??the trends in the joint behavior of structural components in the water-salt systems of nitrate precursors of REE, alkaline, alkaline earth metals in the preparatory stages of the processes of forming multicomponent oxide polyfunctional materials on their basis with thermal activation. Stages of such transformations are revealed; The regularities of complex and phase formation in systems and factors influencing them are determined; A number of physicochemical properties of the intermediate phases formed - coordination lanthanides nitrates: their composition, types of compounds, atomic-crystalline structure, regularities of transformations during heat treatment were studied.     

Growth and characterization of semicarbazone of cyclohexanone

A new organic single crystal of semicarbazone of cyclohexanone (SCCH) has been synthesized and grown as a bulk single crystal by low temperature solution growth technique for the first time in the literature. The grown crystal has been confirmed by X‐ray diffraction and proton nuclear magnetic resonance spectral analyses and also characterized by FT‐ir and FT‐Raman studies. Thermal properties of the grown crystals were studied by thermogravimetric and differential thermal analyses. Optical transmittance was studied by ultraviolet‐visible spectrum and the second harmonic generation property was tested by using Q switched Nd: YAG laser as a source. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of density of states on optical properties of GaSe thin film

A systematic investigation on the effect of substrate temperature on the structure, optical absorption and density of states of vacuum evaporated gallium monoselenide (GaSe) thin films is reported. The X‐ray diffraction analysis shows an occurrence of amorphous to polycrystalline transformation in the films deposited at higher‐temperature substrates (573K). The compositional analysis is made with Auger Electron Spectroscopy (AES). The thickness of the film (175nm) is measured by a multiple beam interferometery. Optical characteristics of the GaSe sample have been analyzed using spectrophotometer in the photon energy range of 1.0 ‐ 4 eV. The absorption mechanism has been recognized and the allowed indirect as well as forbidden direct transitions have been found. As‐deposited films show two indirect and allowed transitions due to spin‐orbit splitting of the valence band, as reported here for the first time. Low field conduction have enabled us to determine the density of states in amorphous and poly‐GaSe films. The amorphous and polycrystalline GaSe thin films have localized states density values of N (E_F) = 1.686 × 10¹⁷ cm^‐3 eV^‐1 and 1.257 × 10¹⁵ cm^‐3 eV^‐1 respectively. The experimental results are interpreted in terms of variations in the density of localized states due to progressive decrease of the unsaturated bonds during deposition. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

电子显微分析在表征纳米晶体化学组分中的应用

纳米材料的化学组分及含量影响其光、电、声、热、磁等物理性能,电子显微分析是表征纳米晶体化学组分的重要方法之一.本文综述了X-射线能谱(EDS)、X-射线波谱(WDS)、电子能量损失谱(EELS)和选区电子衍射(SAED)等现代电子显微分析技术在表征纳米晶体化学组分、形貌、尺寸和结构等方面的应用及其研究进展,并比较了这些分析方法存在的差异,提出了其应用中存在的不足及今后的研发方向.