Electron Emission Properties of Self-Assembling Nanodiamond‒Polymer Nanocomposite Coatings

Crystallography Reports - The formation of thin-film coatings from detonation nanodiamond (DND) suspensions on atomically ordered conducting Ni–W substrates by self-assembly in an evaporating...     

纳米金刚石的结构、光学性能和热稳定性研究

纳米金刚石兼具纳米材料和金刚石的双重特性,呈现出与微米金刚石、块体金刚石截然不同的特点。本文以不同尺寸金刚石样品为研究对象,采用扫描电镜、X射线衍射、光谱学、热重分析技术对其结构、光学性能和热稳定性进行研究。结果显示样品尺寸分别为300 μm、30 μm和100 nm,大尺寸样品结晶质量较好,富含孤氮杂质,为Ⅰb型金刚石。纳米金刚石样品结晶较差,含有少量石墨残留,并含有H₂O、N—H和C—H键,说明其表面存在诸多有机活性基团。大尺寸金刚石样品存在中性和带负电荷的氮空位缺陷,产生较强荧光,而纳米金刚石由于存在诸多的有机基团和表面缺陷,形成非辐射中心,导致荧光猝灭。大尺寸样品在300~525 nm具有较强吸收,而纳米金刚石样品在紫外-可见-近红外整个区域均呈现出较强吸收,透过率显著较低。随着颗粒尺寸的减小,金刚石的起始氧化温度逐渐下降,氧化速率降低,因此大颗粒尺寸金刚石样品具有更好的热稳定性。     

Growth of KCl crystal by Czochralski method and influence of nanodiamond impurity on its hardness and optical properties

KCl alkali halide crystal with different nanodiamond impurity was grown by Czochralski method. X‐Ray diffraction of the outcome samples reveals that they are still single crystal. Also crystal hardness observation reveals that the hardness of KCl single crystal has been increased by adding different percentage of nanodiamond impurity. In addition, the study of FTIR spectrums of the pure and doped crystals represents that the KCl optical properties has not changed.     

纳米金刚石薄膜的合成、表征及应用

纳米金刚石薄膜具有众多优异性能,在众多领域有广泛的应用.本文在详细介绍纳米金刚石薄膜合成的基础上,着重阐述了对纳米金刚石薄膜的表征,介绍了近边X射线的吸收光谱可有效地用于鉴别大面积纳米金刚石薄膜.     

X-ray diffraction study of the structure of detonation nanodiamonds

The spatial structure of aggregates formed by detonation nanodiamonds is investigated using the wide-angle and small-angle X-ray scattering techniques. The effective sizes of crystallites and the crystallite size distribution function are determined. The shape of scattering aggregates is restored from the small-angle X-ray scattering data. An analysis of the results obtained allowed the conclusion that the nanodiamond aggregates have an extended spatial structure composed of nine to ten clusters, each involving four to five crystallites with a crystal lattice of the diamond type.     

Structure and chemical composition of LiB3O5 surfaces

The electronic and structural properties of LiB₃O₅ (LBO) surfaces have been studied by X‐ray photoemission spectroscopy (XPS) and reflectance high‐energy electron diffraction (RHEED). The as‐grown (110) crystal face and mechanically polished (001) surfaces have been investigated comparatively. Electronic structure of LBO has been determined on as‐grown (110) crystal face previously cleaned by chemical etching with RHEED control. The correlation of valence band structure and measured binding energies with earlier reported results has been discussed. Core‐level spectroscopy reveals strong enriching of mechanically polished LBO surface with carbon, when nanodiamond powder is used as an abrasive. So high carbon level as C:B = 0.7 has been observed at the surface while the ratio Li:B:O remains according to LBO chemical composition. The association of LBO Kikuchi‐lines with strong background has been shown by RHEED analysis of the surface. Thus, the polished LBO surface constitutes a high structure quality LBO with the inclusions of some amorphous carbon compound. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Rotating magnetic fields as a means to control the hydrodynamics and heat transfer in single crystal growth processes

The paper discusses a possibility to use different types of rotating magnetic fields (RMF) and combinations of these to control the hydrodynamics and heat/mass transfer in the processes of bulk semiconductor single crystal growth. Some factors contributing to the efficiency of RMF and their influence on different technologies are analyzed. Their specific practical application is illustrated by some examples.     

Laser damage of glycidoxypropyltrimethoxysilane based hybrid materials

The preparation of solid samples, having specific optical properties, is one of the main goals for the realization of devices in the photonic field. To this end, it is important to attain the best control of the optical properties in the final materials. The sol-gel technique is a powerful synthesis method allowing the preparation of matrices with high stability, mechanical resistance and high optical quality. The use of hybrid organic-inorganic precursors permits samples with different thicknesses, ranging from films of hundreds of nanometers to bulk samples of millimeters, to be obtained. The control of the synthesis protocol and the choice of precursors and catalyst allows the control of the final matrix microstructure, which is related to optical properties, like the laser damage threshold. In this work four different matrices, based on glycidoxypropyltrimethoxysilane and Zr alcoxide, have been prepared through sol-gel synthesis. An interpenetrating organic and inorganic network, controlled by the synthesis protocol, characterizes these matrices. The obtained materials show high resistance to the optical damage and long term stability.     

Crystal pulling with a floating nonwetted shaper

In crystal growth by pulling from the melt, the crystal cross-section can be controlled with the help of a shaper, which in the case of semiconductor and metal single crystals is usually lighter than and not wetted by the melt. In order to better control the crystal cross-section, we controlled the temperature near the aperture of the shaper during crystal growth. Graphite was used as a floating shaper and in order to allow close observation of crystal growth, a low melting-point material, i.e., Sn, was chosen as the melt. Single crystals were grown with excellent control over the cross-sectional shape and size. Single crystals were also grown under two other conditions, i.e., no temperature control and crucible temperature control. The control over the crystal cross-section in these two cases, however, was inferior to that in the case of shaper (aperture) temperature control. This difference was explained with the help of knowledge of the shaper (aperture) temperature, which was measured in each of the three cases.     

基于贝叶斯参数优化的无模型自适应硅单晶直径控制

直拉硅单晶的生长过程涉及多场多相耦合与复杂的物理化学变化,其中工艺参数的波动是导致晶体直径不均匀的重要原因,如何实现工艺参数的控制以获得理想的、均匀的晶体直径具有重要的研究意义。本文分析现有控制方法存在不稳定以及控制效果不佳的问题后,提出基于贝叶斯参数优化的无模型自适应控制模型来控制硅单晶生长过程中的晶体直径。首先以坩埚上升速度与加热器的功率作为控制输入参数,晶体直径作为输出,搭建无模型自适应控制模型,并分析算法的稳定性。其次将控制模型进行仿真实验,发现硅单晶直径控制模型中不同的超参数设定会影响控制过程的迭代次数以及控制效果。最后,利用贝叶斯优化超参数的取值范围,并进行最终的仿真实验,结果表明,经贝叶斯参数优化后的控制模型计算快、迭代次数少,输出的晶体直径稳定,同时将生长工艺参数控制在实际生产要求范围内。因此,基于贝叶斯参数优化的无模型自适应控制实现了硅单晶直径均匀稳定的有效控制,具有结合工程背景的实际应用前景。     

Growth characteristics of ultra long double-ended acicular ZnO synthesized by a hydrothermal process

Double-ended acicular ZnO structure can be synthesized via a hydrothermal process with tetramethylammonium hydroxide and zinc acetate as precursors and polyvinyl alcohol (PVA) as a structure-directing agent. The as-prepared ZnO products show the well crystalline wurtzite structure with growth direction along [0 0 0 1]. For the first time, PVA is found to be employed as a reservoir of Zn²⁺ ions in the present study, and can control the concentration of Zn²⁺ in reaction solution, and the acicular morphology can be formed at the two ends of the 1-D ZnO structure, due to the effect of secondary growth that occurs as the sufficient concentration of Zn²⁺ ions chelated by PVA releasing to the reaction solution. Furthermore, the size of the 1-D ZnO structure can be tuned by different amounts of PVA addition.     

Lysozyme crystallization in a precision-controlled temperature gradient

The possibility to control the crystallization process of biomaterials by the temperature was examined by the mathematical simulation of lysozyme crystallization. The precision-temperature control with creation of a local temperature gradient in solution was demonstrated to allow the growth of lysozyme crystals with high structural perfection.     

Enhanced Automatic Diameter Control System of Czochralski-grown Crystals

The automatic diameter control system with two ways of the crystal diameter determination is described. The correction of temperature oscillations during the growth process is applied in the describing system. Also, it allows to estimate the crystal quality already during the growth process. The control system is intended for the growth of crystals with different physical properties.     

Synthesis of sulfated-zirconia aerogel: effect of the chemical modification of precursor on catalyst porosity

Sulfated-zirconia aerogels were prepared by a one-step sol–gel synthesis combined with the supercritical drying technique using zirconium propoxide starting material with three different modifiers to control the hydrolysis reaction. The present study discloses a way to exert a significant degree of control on the morphology of zirconia sulfate catalysts. By an appropriate choice of the modifier one can deeply affect the porosity of these materials, in particular at low precursor concentration.     

In-process monitoring and control of doping gas concentration during vapor phase silicon epitaxial growth by using a flame photometric detector

An in-process monitoring and control method of the doping gas concentration during epitaxial growth of Si was developed. A flame photometric detector (FPD) can be used as a monitor for the PH₃ and B₂H₆ dopant concentrations in the injected doping gases. A combination of this dopant monitor with an automatic control system of the silicon source (SiHCl₃) gas concentration using an infrared spectrophotometer as a monitor, makes possible an automatic in-process control of the concentrations of dopant and of silicon source gas supplied to the reactor. The present system provides an accurate and reproducible control of impurity concentrations in Si epitaxial layers. Good correlation between the monitored signal (or the doping gas concentration) and the impurity concentration incorporated into the growth layers was confirmed for PH₃ (n-type) and B₂H₆ (p-type) doping. For the B₂H₆ doping, a divergence from the linear relationship between the doping gas concentration and the impurity concentration in the layers was observed in the level of acceptor concentration below about 10¹⁵ atoms/cm³. The transient response of the present system was measured by growing epitaxial layers with increasing and decreasing step-changes in the dopant gas flow during continuous deposition of the layers. Some interesting, but complicated, transient responses of impurity concentration in the growth layer were observed. The responses are different between the PH₃ doping and the B₂H₆ doping, and also different between increasing and decreasing steps especially for the B₂H₆ doping.     

In situ determination of metastable zone width by a simple optical probe

The metastable zone width (MSZW), which denotes the region between the solubility curve and the onset of nucleation, is an important control parameter for successful operation of a solution crystallization process as it defines an operating boundary for the crystallization process. The MSZW can be approximated as the gap between the loci of cloud points that correspond to onset of nucleation and clear points that closely represent solubility. This work presents the design and application of a simple optical probe consisting of a line laser source, a light‐dependent resistor, and a simple processing circuit for in situ determination of onset of nucleation of a crystallization process. Three different crystallization processes, namely, cooling crystallization of glycine, cooling crystallization of L‐asparagine monohydrate, and anti‐solvent crystallization of glycine, are investigated to assess the performance of the in situ probe. In all the cases, the cloud points and clear points are conveniently detected by sharp changes in output voltage of the probe with reasonable accuracy. The presented optical probe can be used as a simple and inexpensive alternative tool in the area of crystallization process monitoring.     

Thermal radiation and low-temperature-vapour growth of HgI2 crystal in production furnace

Heat exchanges in a sealed ampoule in the LTVG (low temperature vapour growth) furnace have been modelled in order to compute temperature fields and control the growth of HgI₂ crystals from vapour phase at low temperatures. We use a coupled conductive-radiative model to determine the shapes of the source and the crystal at different equilibrium states (i.e. without growth rate). The model involves conductivity anisotropy in the crystal and radiative exchanges between grey and diffuse surfaces (source and crystal interfaces, Pyrex walls), which are considered as opaque. Internal buoyancy effect is not taken into account as the pressure inside the ampoule is very small. The source temperature is fixed. For different undercoolings, i.e. for different cold finger temperatures, the “equilibrium” isotherm between the source/gas and crystal/gas interface has been numerically obtained. This “equilibrium” isotherm, which is associated with the stop of the growing process, gives a crystal shape. This shape is compared with experimental results given by the ETH-Zürich group. The model would permit a better understanding and control of the future HgI₂ crystal growth experiment. The computations are performed using a finite element package (FIDAP).     

Excluded-volume corrections to the single-chain static properties of a polymer melt: Temperature,density and potential effects

Excluded-volume effects on single-chain statics are introduced by analytic corrections to the Rouse results. The final expressions do not depend on free parameters. They are compared with numerical simulations of a polymer melt for different values of the temperature, the density and the interaction potential. Density and interactions control the energy landscape of the system, whereas the temperature selects the accessible regions. The agreement between the theory and the Rouse modes does not depend markedly on the temperature with some improvement for the first modes (large length scales). Differently, increasing the packing and the stiffness of the monomer–monomer interaction reduces the deviations for the first modes, but it leaves the magnitude of the deviations for the high-indexes modes (short length scales) nearly unaffected or with some tendency to increase. The scaling properties of the corrections are briefly discussed.     

Photoluminescence of a new polycrystalline scintillator based on stilbene

Abstract

Photoluminescence and excitation spectra of stilbene single crystals, polycrystals, and solutions are investigated in the temperature range of 5-280 K. With the increase in the temperature, the photoluminescence bands shift to the short-wavelength region by 600?cm^?1, which indicates the existence of Gaussian-distributed localized states. Such states are associated both with different arrangements of the benzene rings with respect to the C?=?C bond and with different molecule environments in the crystal lattice. The photoluminescence intensity of the polycrystals depends on the grain size and reaches 87% of the single crystal photoluminescence intensity, when the grain size is 2.5?mm.     

Development of a solvate as an active pharmaceutical ingredient: Developability,crystallisation and isolation challenges

The preclinical development of an active pharmaceutical ingredient (API) begins with the selection of a solid state form. A solvate may be selected for development if it is sufficiently stable and if the solvent quantity administered to the patient is lower than the tolerated potential daily exposure (PDE). The selection and process development of a solvate is presented here. The initial crystallisation process gave poor control over the particle size distribution (PSD) and inclusion of additional crystallisation solvent in the crystal lattice. These two API attributes were controlled using micronised seeds and optimising the crystallisation conditions. After filtration, slurry washing with a second solvent was used to replace the high boiling point crystallisation solvent to improve the drying efficiency. The slurry washing was modelled and studied in the laboratory to control the level of unbound crystallisation solvent in the API. The API desolvation during slurry washing was studied by considering thermodynamics, by construction of the ternary phase diagram, and kinetics aspects. This work provides useful approaches and considerations to assess the risks specific to the controlled production of a solvate that are rarely presented in the literature.