Morphology and Structure of Thermally Induced Microdefects in High-Temperature Treated Czochralski-Silicon

The morphology and structure of amorphous precipitates grown by thermal annealing in the temperature range from 1100 °C to 1200 °C are investigated by means of highvoltage electron microscopy. It is shown that there exist some characteristic morphological types which are equivalent to the equilibrium forms of the cubic diamond structure itself or which can be derived from these. For the growth process an oxygen diffusion-controlled mechanism is deduced. Structural aspects are discussed on the basis of this mechanism.     

X-ray electrono-optical and SIMS characterization of Si crystals implanted with Bi ions before and after rapid thermal annealing

The purpose of the presented paper is to find out what kinds of information on surface layer structure of implanted silicon after rapid thermal annealing can be acquired by such non-destructive methods as X-ray diffractometry and its complementary RHEED technique. The experiments were performed on Si crystals implanted with Bi ions. The studies showed that using the anomalous X-ray transmission of the wavelength of 1.54 Å we are able to determine the defect concentration introduced by ion implantation with different doses as well as the effects of defect annealing. It was also shown using the REED that the surface layer of ca. 50 Å thick remains amorphous after RTA probably due to the oxidation. The measurements by using SIMS pointed also out that at the crystal surface there was a small amount of Bi atoms accumulated after RTA.     

Dilatometric Studies of Thermal Expansion of Anthracene Crystals

The thermal expansion of anthracene plates cut along the cleavage plane and having different crystalographic orientations was studied by means of a quartz dilatometer. The expansion tensor cross-section in cleavage plane has been determined. It is shown that there is a correlation between the compressibility tensor orientation and the thermal expansion.     

The effect of boron addition on texture and structure of NiMo/Al2O3 catalysts

The effect of support (Al₂O₃) modification with borate ions and the effect of their concentration on the texture and structure of nickel-molybdena catalysts were studied. The surface area and pore volume of the samples were determined using the BET method, whereas pores distribution – besides the BET method also by mercury porosimetry. FT-IR, derivatographic, and diffractometric studies were also performed. Modification with borate ions does not bring about any change in the type of the support pores, nor does it change its crystallic structure. However, a considerable decrease in the surface area of the support was observed. It was shown that modification with borate ions leads to a decrease in thermal stability of catalysts, yet increase in concentration of borate ions raises the thermal stability of the samples. It was found that on the catalyst surface borate ions form a well-dispersed monolayer structure.     

热屏间距对泡生法蓝宝石单晶生长影响研究

太空、军事和科研等高科技领域的持续发展极大促进了对蓝宝石晶体的需求,泡生法是蓝宝石晶体的主要制造方法之一;热场结构对所得蓝宝石晶体的质量具有重要影响.本文对采用泡生法工艺制造蓝宝石单晶过程中,具有内置7层氧化锆外置8层钼金属的新型热屏结构间距进行研究.通过数值模拟考察热屏间距对单晶炉功率、固-液界面形状和晶体热应力的影响确定了合理的热场结构;并与试验生产结果进行对比验证.结果表明:热屏间距增大使得单晶炉功率明显提升,并引起固-液界面凸度增大;而蓝宝石晶体热应力出现减小.综合考察三个影响因素的影响,最后确定热屏间距为5 mm时单晶炉能耗较低,可用于制造高质量的蓝宝石晶体.     

Vibrational spectra of the YbB<Subscript>12</Subscript> Kondo insulator

The density of phonon states for the YbB₁₂ Kondo insulator is calculated from the inelastic neutron scattering spectra of this compound. It is established that thermal vibrations of rare-earth atoms predominantly occur in the low-energy range. These atoms are most weakly bound in the crystal structure of the YbB₁₂ Kondo insulator. The high-energy part of the vibrational spectrum is determined by thermal vibrations of the boron atoms forming a rigidly connected structure of the compound. It is revealed that the temperature dependence of the intensity of the phonon peak attributed to thermal vibrations of the ytterbium atoms exhibits an anomalous behavior. This circumstance suggests that the magnetoelastic coupling occurring in the structure of the YbB₁₂ Kondo insulator is relatively strong and can contribute to the magnetic excitation spectrum of this compound.     

Effects of carbon structure orientation on the performance of glucose sensors fabricated from electrospun carbon fibers

High-performance enzyme-based glucose sensors were prepared by electrospinning carbon fibers. The efficiency of the glucose sensor was assessed based on efficient enzyme immobilization and electrical resistance transfer by examining improved porosity and electrical properties, respectively. The porosity of the electrospun carbon fiber electrode was improved by physical activation to increase the immobilization sites of the glucose oxidase enzyme. The electrical properties were improved by a thermal treatment, which caused carbon orientation effects because of the high thermal energy. The glucose oxidase enzyme immobilization was developed based on improved specific surface area and pore volume, which were studied by pore structure and image analyzers. The glucose sensor was evaluated by amperometric measurements and cyclic voltammetry. The measured current increased with higher glucose concentrations based on the effects of the developed pore structure and the electrical properties. The enzymatic kinetics were also studied using the Lineweaver–Burk equation. The sensitivity of the glucose sensor was improved significantly with increased maximum current, whereas the GOD enzyme activity was diminished by efficient GOD immobilization. It is concluded that a high-performance glucose sensor was obtained using electrospun carbon fibers based on the effects of efficient GOD enzyme immobilization and electrical resistance transfer.     

X-ray and cathodoluminescence study on the effect of intentional long time annealing of the InGaN/GaN multiple quantum wells grown by MOCVD

GaN-based InGaN/GaN multiple quantum wells (MQWs) structure having a high-quality epilayer and coherent periodicity was grown by metalorganic chemical vapor deposition. After thermal annealing of InGaN/GaN MQWs, the increase in temperature and annealing time caused the intermixing between the barrier and the wells, which in turn caused a decrease in periodicity on the high-resolution X-ray diffraction patterns. Thereby, we confirmed that the structural performance of InGaN MQWs is successively degrading with increasing thermal annealing temperature. Especially, InGaN MQWs of the sample annealed at 950 °C were profoundly damaged. The cathodoluminescence (CL) measurement indicated that MQWs emission intensity decreases with increasing thermal annealing temperature. Thus, the integrated CL intensity ratio of InGaN MQWs to GaN dramatically decreased while thermal annealing temperatures increased. This result caused the intermixing in MQWs to deteriorate the active layer performance. Furthermore, the peak position of MQWs showed a tendency of the red shift after high thermal annealing. It is suggested that the annealing-induced red shift in MQWs is attributed to the reduction of the inhomogeneity of the In content in the MQWs leading to the reduction of the quantized energies. Consequently, it indicates that the high temperature and the long-time thermal annealing would be inevitably followed by the structural destruction of InGaN MQWs.     

近化学计量比LiNbO3晶体各向畴形态的研究

本文对采用双坩埚提拉法生长的近化学计量比LiNbO3晶体沿其各向切块腐蚀后通过直接观察和在金相显微镜下观察,对其各个面的畴结构进行了分析.我们发现晶体a面上由于镜相对称不反映畴结构,b面和c面上的腐蚀形貌则完全显露而且按一定的方向整齐地排列,证明我们生长的SLN晶体是完全单畴结构的晶体.     

6英寸低位错锗单晶生长热场设计

锗片作为衬底材料已在空间太阳电池领域得到广泛的应用,新型锗基空间太阳能电池对锗片的需求由4英寸(1英寸=2.54 cm)提高到6英寸后,低位错锗单晶的生长难度增大.本文设计开发了一种适用于直拉法生长大尺寸、低位错锗单晶的双加热器热场系统,模拟研究了不同形状主加热器的热场分布,从而得到最优的热场环境.研究发现:渐变长度为...     

X-ray Investigations of Shape Memory Alloys

The investigation aims to analyse the influence of different kinds of thermal treating on the structure of martensite. Maxima of the X-value are observed at 60–70 minutes for the sample aged at 200°C and 90 minutes for that aged at 375 °C and minima for Y after almost the same time. We consider that with these results the discussion on the processes occurring during short ageing times will be activated, because in the literature there is lack of such a results.     

X-Ray Study of the Structure and Thermal Properties of Ba1–xKxBiO3 at Different Temperatures

The crystal structure as well as the temperature and composition dependences of the lattice parameters, the thermal expansion coefficients in the high-temperature superconducting Ba_1–xBiO₃ system were determined by an X-ray powder diffraction method at temperatures between 80 and 650 K. The character of variation of intensity, profiles, and line widths of the diffraction lines for different perovskite structures as a function of the content x and temperatures was found. The correlation between the behaviour of the thermal expansion coefficients and potassium content was revealed at different temperatures. It is shown that the thermal expansion coefficients vary inversely with rising x at any temperature in the range from 80 to 400 K.     

Formation of structure in small lead clusters under thermal effect

The thermal effect on lead clusters with radii up to 5.5 nm has been investigated by the molecular dynamics method using a modified tight-binding potential TB-SMA. The melting of Pb nanoparticles of these sizes is strictly homogeneous, without the formation of a surface liquidlike layer. The primary fcc phase in the particles is retained upon heating in the overwhelming majority of model experiments. An analysis of the structure formation during crystallization has shown that structures with pentagonal symmetry are preferred for lead clusters in this case. It is noted that an increase in the nanoparticle size leads to the dominance of the dodecahedral structure over the icosahedral one.     

Regularities of thermal deformations in Monoclinic Crystals

The results of calculations of thermal deformation tensor and its analysis are given for eleven silicates and vanadates of clinopyroxenic structure. It is shown that the level of thermal deformation anisotropy in monoclinity plane is in stable correlation with velocity of monoclimity angle change. The correlation is explained by considerable contribution of shear component into deformations. Considering the shears it is possible to understand, to separate the thermal deformations in monoclinic crystals into components and to summarize them from those components. The given regularities permit generalisations for triclinic crystals as well as for pressure and chemical (compositional) deformations.     

A 3-D numerical heat transfer model for silica aerogels based on the porous secondary nanoparticle aggregate structure

A 3-D finite volume numerical model based on the porous secondary nanoparticle random aggregate structure was developed to predict the total thermal conductivity of silica aerogels. An improved 3-D diffusion-limited cluster–cluster aggregation (DLCA) method was used to generate an approximately real silica aerogel structure. The model includes the effects of the random and irregular nanoparticle aggregate structure for silica aerogels, solid–gas coupling, combined conduction and radiation, nanoparticle and pore sizes, secondary nanoparticle porosity and contact length between adjacent nanoparticles. The results show that the contact length and porosity of the secondary aerogel nanoparticle significantly affect the aerogel microstructure for a give density and, thus, greatly affect the total thermal conductivity of silica aerogels. The present model is fully validated by experimental results and is much better than the model based on a periodic cubic array of full density primary nanoparticles, especially for higher densities. The minimum total thermal conductivity for various silica aerogel microstructures can be well predicted by the present model for various temperatures, pressures and densities.     

Three-dimensional global analysis of thermal stress and dislocations in a silicon ingot during a unidirectional solidification process with a square crucible

A three-dimensional global model was used to obtain the solution of a thermal field within the entire furnace during a unidirectional solidification process of multicrystalline silicon with a square crucible. Then the thermal stress distribution in the silicon ingot was solved. Based on the solution of thermal stress, relaxation of stress and multiplication of dislocations were performed by using the Haasen–Alexander–Sumino model (HAS model). The influence of crucible constraint on stress levels and dislocations was investigated. It was found that the crucible constraint had significant influence on the thermal stresses and dislocations in the ingot. The results indicated that it is important to reduce the crucible constraint in order to relax thermal stresses and reduce dislocations in a silicon ingot during the solidification process.     

Photoemission (UPS and XPS) study of local structures of amorphous GeTe and GeSe films

In situ photoemission (UPS and XPS) measurements have been performed for amorphous GeTe and GeSe films deposited onto a cooled substrate during thermal annealing and crystallization of the films. It has been found that an amorphous film prepared at room temperature has a 4-2 coordinated local structure while a highly disordered film deposited onto a 77 K substrate is largely 3-3 coordinated and relaxes into the 4-2 coordinated structure upon thermal annealing.     

Liquid phase separation in immiscible Ag-Ni-Nb alloy and formation of crystalline/amorphous composite

Phase decomposition in liquid miscibility gap presents a unique opportunity for designing amorphous/crystalline composites with a multilayer structure. One of typical monotectic systems, Ag-Ni alloy, is selected, and element Nb is added in the Ag-Ni alloy. The new ternary Ag-Ni-Nb monotectic alloys are rapidly quenched by using melt spinning technique. It is revealed that the ternary alloy undergoes a liquid-liquid phase decomposition and forms two immiscible Ag-rich and NiNb-rich liquids. Subsequently, the immiscible liquids solidify into Ag-rich crystalline and NiNb-based amorphous phases, respectively. Self-assembled amorphous/crystalline composites with double layer and sandwich type structures have been developed. The structure of the alloy ribbons with a dependence on the composition changes from a particle-dispersed structure to double layer structure and to sandwich type structure. The phase formation and thermal property of the quenched alloys are investigated. The formation mechanism of the crystalline/amorphous composite structures has been discussed.     

The crystal structure and chemistry of several palygorskite samples with different geneses

The structure, chemical composition, and properties of palygorskites from several deposits in the Russian Federation, Ukraine, Uzbekistan, and Slovakia have been investigated by transmission electron microscopy, microanalysis, X-ray diffraction, IR spectroscopy, and thermal analysis. It is shown that the palygorskites formed under different physicochemical conditions may significantly differ in chemical composition, morphology, and defect structure. Depending on the formation conditions, palygorskites decompose differently upon heating.     

The behavior of thermal conductivity in the chaotic phase of [N(CH<Subscript>3</Subscript>)<Subscript>4</Subscript>]<Subscript>2</Subscript>ZnCl<Subscript>4</Subscript> crystal

A thermal investigation of the modulated structure dynamics at the transition between metastable states in the incommensurate phase of [N(CH₃)₄]₂ZnCl₄ crystal have been performed. It is established that the anomalous behavior of the thermal conductivity in the absence of a defect-density wave is due to the inelastic scattering of thermal phonons from critical phonons of the soft optical branch. In the presence of a defect-density wave, the anomalous increase in thermal conductivity is caused by the existence of a chaotic phase and is related to the contribution that soft optical phonons make to the heat transfer due to the increase in their group velocity.