退火对Si(111)衬底上ZnO薄膜的结构和发光特性的影响

采用磁控溅射法在硅(111)衬底上制备了C轴高度取向的ZnO薄膜,并研究了退火温度和氧气气氛对ZnO薄膜晶体质量、晶粒度大小和光致发光谱的影响.X射线衍射表明,所有薄膜均为高度C轴择优取向,当退火温度低于900℃时,随着退火温度的升高,薄膜的取向性和结晶度都明显提高.室温下对ZnO薄膜进行了光谱分析,退火后的样品均可观测到明显的紫光发射.在一定的退火温度范围内,还可以观测到明显的紫外双峰.空气中退火的样品,当退火温度达到或高于600℃还可观测到绿光发射.实验结果表明,发光峰强度随退火温度和氧气气氛不同而不同,通过改变退火时的温度和氧气气氛可以改变ZnO薄膜的微结构和发光性质.     

退火对硫化方法制备ZnS薄膜特性的影响

以反应磁控溅射方法沉积ZnO薄膜,然后在空气和H2S气氛中退火制备了六方相ZnS薄膜.用X射线衍射仪(XRD)、紫外-可见透射光谱和扫描电子显微镜(SEM)对薄膜进行表征.提高空气退火温度能够改善ZnS薄膜结晶性,而空气退火温度超过500℃则会降低ZnS薄膜结晶性.另外,当硫化退火温度低于400℃时,ZnO只能部分转变为ZnS,只有硫化温度等于或大于400℃时,ZnO才能全部转变为ZnS.硫化前后薄膜晶粒尺寸有显著变化.所得ZnS薄膜在可见光范围的透过率约为80;,带隙为3.61 ～3.70 eV.     

溶胶-凝胶法制备ZnO薄膜及其微结构特性研究

采用溶胶-凝胶法(Sol-Gel)制备氧化锌(ZnO)薄膜,研究镀膜层数和退火温度对ZnO薄膜晶体结构、光谱性质及表面形貌的影响.X射线衍射谱测试表明,退火温度为600℃、镀膜层数为10层时制备样品的晶粒尺寸最大,结晶度最好.紫外-可见透过谱发现,样品退火后其透过率曲线变得陡直,光学带隙随退火温度升高而逐渐减小.光致发光谱测试显示,ZnO薄膜的发光谱包含388 nm和394 nm附近的两个主要发光峰,分别对应于本征发射和缺陷发射,其强度随退火温度升高呈现相反的变化.原子力显微照片则显示了随退火温度的升高制备样品表面晶粒的分布趋于均匀而致密.     

用快速光热退火制备多晶硅薄膜的研究

用等离子体增强型化学气相沉积先得到非晶硅(a-Si:H)薄膜,再用卤钨灯照射的方法对其进行快速光热退火(RPTA),得到了多晶硅薄膜.然后,进行XRD衍射谱、暗电导率和拉曼光谱等的测量.结果发现,a-Si:H薄膜在RPTA退火中,退火温度在750℃以上,晶化时间需要2min,退火温度在650℃以下,晶化时间则需要2.5h;晶化后,晶粒的优先取向是(111)晶向;退火温度850℃时,得到的晶粒最大,暗电导率也最大;退火温度越高,晶化程度越好;退火时间越长,晶粒尺寸越大;光子激励在RPTA退火中起着重要作用.     

基于PECVD制备多晶硅薄膜研究

基于PECVD以高纯SiH4为气源研究制备多晶硅薄膜,在衬底温度550℃、射频(13.56MHz)电源功率为20W直接沉积获得多晶硅薄膜.采用X射线衍射仪(XRD) 和场发射扫描电子显微镜(SEM) 对多个样品薄膜的结晶情况及形貌进行分析,薄膜结晶粒取向均为<111>、<220>、<311>晶向.对550℃沉积态薄膜在900℃、1100℃时进行高温退火处理,硅衍射峰明显加强.结果表明,退火温度越高,退火时间越长,得到多晶硅薄膜表面晶粒趋于平坦,择优取向为<111>晶向,晶粒也相对增大.     

空气退火对ZnS薄膜结构和光学特性的影响

采用X射线衍射、扫描电子显微镜和光致发光等技术研究了空气退火对ZnS薄膜的结构和光学特性的影响.薄膜在500℃以下退火后结晶质量得到改善,仍呈ZnS立方相结构.退火温度达到550℃时,薄膜中出现ZnO六方相结构.薄膜退火后,大气中的氧掺入薄膜中,出现ZnS-ZnO复合层.随退火温度升高,薄膜晶粒尺寸增大,透过率增加,带隙逐渐接近ZnO带隙.薄膜光致发光结果表明,复合层内ZnS和ZnO绿色发光的叠加替代了来自ZnS缺陷能级间的绿色发光.     

退火温度和涂膜层数对溶胶-凝胶法制备ZnO薄膜微结构及光学特性的影响

采用溶胶-凝胶法在玻璃基片上制备了ZnO薄膜,研究了退火温度和涂膜层数对ZnO薄膜结晶性和光学特性的影响.扫描电镜(SEM)结果表明,退火温度的升高使得薄膜致密性和均匀性均得到改善.旋涂10层以上的薄膜其表面形貌明显要好于旋涂5层的薄膜样品,但旋涂10层和20层的薄膜其形貌和微结构差异并不显著.XRD图谱表明所有样品都具有纤锌矿结构,随着热处理温度的升高,各衍射峰强度增大,晶粒尺寸变大.光致发光(PL)测量显示,退火温度越高,涂膜层数越少,其PL谱发光强度越强.紫外-可见透过谱发现,涂膜层数越少,透射率越高;而提高退火温度也有助于改善薄膜透射率.结合已得到的微结构信息,对观察到的光学性能进行了合理解释,综合认为旋涂10层并在600℃退火是溶胶凝胶法制备ZnO薄膜的最佳生长条件.     

退火温度对Co掺杂CeO2稀磁氧化物薄膜的结构和铁磁性能的影响

采用溶胶-凝胶法,在Si(100)和石英玻璃衬底上制备了3;Co掺杂CeO2稀磁氧化物薄膜,研究了不同退火温度(500 ℃, 600 ℃和700 ℃)对薄膜结构和铁磁性能的影响.XRD 和拉曼光谱结果表明,随着退火温度的升高,薄膜晶化度明显提高.不同退火温度下的3;Co掺杂CeO2薄膜为多晶薄膜,且未破坏CeO2原有的结构.随着退火温度的升高, 晶粒尺寸逐渐增大.另外,3;Co掺杂CeO2薄膜在可见光范围内都有很好的透射率,其室温下的光学带隙Eg随退火温度增加而减小.超导量子干涉磁强计(SQUID)测量表明所有样品都表现出室温铁磁性,随着退火温度的升高,饱和磁化强度和矫顽力增大,700 ℃退火的薄膜具有最大的饱和磁化强度和最大的矫顽力.不同退火温度导致样品的磁性有了明显的变化,这源于磁性产生的不同机理.可见薄膜的结构最终影响了其铁磁性能.     

Si(111)衬底上ZnO薄膜的磁控溅射法制备及表征

采用磁控溅射法在(111)单晶硅衬底上沉积了ZnO薄膜,并研究了退火温度对ZnO薄膜晶体质量、晶粒度大小、应力和光致发光谱的影响.X射线衍射(XRD)表明薄膜为高度c轴择优取向.不同退火温度下的ZnO薄膜应力有明显变化,应力分布最为均匀的退火温度为500℃.室温下对ZnO薄膜进行了光谱分析,可观测到明显的紫光发射(波长为380nm左右).实验结果表明,用磁控溅射法在单晶硅衬底上能获得高质量的ZnO薄膜.     

单晶硅衬底上Ge填埋层低温应力诱导重结晶制备多晶硅薄膜

本文采用电子束蒸发法,室温下在Si(400)的基片上生长含锗(Ge)填埋层的非晶硅薄膜,其结构为a-Si/Ge/Sisubstrate,并在真空中进行后续退火.采用Raman散射(Raman Scattering)、X射线衍射(X-ray Diffraction)、高分辨电子扫描显微镜(HRSEM)、光学显微镜和热重差热分析(DSC)等手段,研究退火后样品晶化特性和晶化机理.结果表明,室温下生长的含有250 nm Ge填埋层的生长态样品在400℃退火5h,薄膜基本全部实现晶化,并表现出明显的Si (111)择优取向.样品分别在400℃、500℃、600℃和700℃退火后薄膜的横向光学波的波峰均在519cm-1附近,半高宽大约为6.1 cm-1,且均在Si(111)方向高度择优生长.退火温度为600℃的样品对应的晶粒尺寸约为20 μm.然而,在相同的薄膜结构(a-Si/Ge/Si substrate)的前提下,当把生长温度提高到300℃时,温度高达到700℃退火时间5h后,薄膜依然是非晶硅状态.差热分析表明,室温生长的样品,在后续退火过程中伴随界面应力的释放,从而诱导非晶硅薄膜重结晶成多晶硅薄膜.     

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.