Influence of deposition parameters on composition and refractive index of femtosecond and nanosecond pulsed laser deposited gallium lanthanum oxysulphide

The influence of the deposition parameters on femtosecond and nanosecond pulsed laser deposited gallium lanthanum oxysulphide (GLSO) glass films has been investigated. A comparison between films deposited by femtosecond and nanosecond pulsed laser deposition (PLD) shows that the compositional range of each ablation regime varies significantly; in particular, femtosecond PLD shows a unique potential for selective fabrication of films with a high lanthanum content well outside the conventional glass-melting region. We demonstrate how manipulation of the PLD growth parameters can influence the stoichiometric transfer of the PLD process, leading to films with compositions that differ significantly from the GLSO target material. We also reveal how the refractive index of as-deposited films is dependent upon the composition and briefly discuss the thermal properties of bulk GLSO material of various compositions which indicate the potential for films grown by PLD to be used in optical data-storage device applications.     

基于ISOMAP-DE-SVM的Cz单晶硅等径阶段掉苞预测

针对目测法无法及时发现直拉单晶硅在等径生长阶段发生的掉苞问题,本文提出一种基于ISOMAP-DE-SVM的掉苞预测模型,可以在掉苞现象发生之前发出警告。首先剔除方差较小的参数,采用斯皮尔曼相关系数法剔除冗余参数,采用最大互信息法检验剩余参数的非线性相关性;然后将关键参数的均值和标准差作为等度量映射和多维放缩的输入,得到两份样本数据;最后将这两份样本数据分别输入到经过差分算法、遗传算法优化的支持向量机预测模型,得到4份预测结果。预测结果表明：基于ISOMAP-DE-SVM的预测模型具有收敛速度快、准确度高的特点,平均预测准确率可以达到96%;同时,所使用的方法揭示了单晶硅等径阶段的数据具有非线性特点。通过实际应用验证表明模型具有一定的工程实用价值。     

Thermodynamic and experimental studies of the CVD of A-15 superconductors I. Nb3Ga

This paper deals with the experimental and thermodynamic study of the CVD synthesis of Nb₃Ga layers on various metallic and insulting substrates using the coreduction of mixed halides by hydrogen. Thermodynamic equilibrium in the seven-components system Nb-Ga-H-Cl-Si-O-Ar has been calculated using the method of minimization of the system Gibbs free energy as a function of the variables directly available in the CVD system. The chosen variables were the chloride ratio, the reduction and dilution parameters and the temperature of the deposition zone. The equilibrium compositions were calculated for the two composition limits of the A-15 phase: NbGa_0.15 and Nb₃Ga. They are presented in the form of CVD phase diagrams. A CVD reactor has been set up and more than one hundred measurements have been made in order to check the validity of the equilibrium calculations. The comparisons between equilibrium and experimental results show a good agreement and lead to a better understanding of the chemistry and thermodynamics of the system.     

Influence of laser treatment on thermodynamic and kinetic parameters of lithium intercalation process into nanosized SiO2

Amorphous nanosized SiO₂ powder has been modified by laser treatment. The influence of this treatment on the structure and parameters of a process of Li⁺ electrochemical intercalation into cathodes based on SiO₂ has been studied by means of an X-ray analysis, infrared spectroscopy, electro-motive force and impedance spectroscopy methods.     

Dynamic stability analysis of the solidification of binary melts in the presence of a mushy region: changeover of instability

A dynamic linear instability analysis of steady-state binary melt solidification with a mushy region has been carried out. Such an instability differs from a conventional morphological one of a planar solid–liquid interface and is connected with the perturbations in the steady-state solidification velocity. Solidification with a narrow mushy region has been revealed to be absolutely unstable with a monotonous instability of a “hard” type. An increase of the mushy region width leads to an instability changeover from the “hard” type to the oscillatory “soft” one. Both the critical changeover width and the neutral stability curves have been determined as the functions of relevant physical and operating parameters. The steady-state solidification regime with a broad mushy region is absolutely stable. Thus, the mushy region width has been shown to represent a stabilizing factor.     

On the morphological instability of the growing crystals (III). Micro-interferometric investigations of the morphological stability of KDP crystals growing from aqueous solutions

The paper is aimed at the elucidation of the limits to which the faceted forms of KDP crystals preserve their stability and beyond which a skeletal growth from stagnant solutions takes place. In order to avoid the natural convections the experiments were performed in two-dimensional cells. On the basis of quantitative criteria, it has been shown that the kinetic regime of growth has been replaced by a diffusion one when the concentration on the crystal surface drops with respect to the bulk value with 0.1% to 0.2%. The critical size above which the KDP crystal no longer retains its polyhedral growth mode in a diffusion regime since a gross morphological defect in the form of a depression appears on its (010) face has been compared with the theoretical expressions derived by Cahn and Chernov.     

Specific features of the formation of terrace-step nanostructures on the (0001) surface of sapphire crystals

The terrace-step structures on atomically smooth vicinal surfaces of sapphire crystals subjected to thermal annealing after mechanical and chemical treatments have been investigated by atomic-force microscopy. The influence of the vicinal angles and conditions of thermal treatment (including annealings in air and vacuum) of sapphire plates on the metric parameters of terrace-step structures has been analyzed. It is shown that steps with a height from monoatomic (0.22 nm) to 3 nm or more can be formed on the sapphire surface by changing the vicinal angle and thermal-treatment conditions. The results are interpreted in terms of the minimum surface energy and surface diffusion processes.     

Influence of the chemical nature of implanted ions on the structure of a silicon layer damaged by implantation

The influence of the implantation of silicon single crystals by fluorine, nitrogen, oxygen, and neon ions on the distribution of strain and the static Debye-Waller factor in the crystal lattice over the implanted-layer depth has been investigated by high-resolution X-ray diffraction. The density depth distribution in the surface layer of native oxide has been measured by X-ray reflectometry. Room-temperature implantation conditions have ensured the equality of the suggested ranges of ions of different masses and the energies transferred by them to the target. It is convincingly shown that the change in the structural parameters of the radiation-damaged silicon layer and the native oxide layer depend on the chemical activity of the implanted ions.     

Influence of the surface on the properties of macro-and nanocrystals

The influence of the surface energy on the properties of macro-and nanocrystals has been considered. It is shown that the properties of small crystals (several microns and less) depend on their dimensions, which is explained by an increase of the number of surface atoms in the total number of all the atoms in a crystal. On the basis of the energy criterion of crystalline substance amorphization, a formula relating the surface energy of a crystal to its crystal-lattice parameters is derived. The surface energies of elemental crystals are calculated. It is assumed that anisotropy in contact-melting temperature of single crystals can be observed experimentally.     

Mathematical modelling of the SSD-process

In order to achieve a better agreement between the calculated and experimental results of crystal production by the SSD-process, it was essential to extend the application of the modell presented earlier (Weinert et al.). The thermal and geometrical conditions, which vary strongly during the course of the process and influence the GaP crystallisation, have never been taken into consideration. It has been attempted, in the present work, to consider these changes by dividing the total time of crystallisation into so small durations (Δt), that the evaluation model presented earlier for instant times can be successfully applied. The results of crystallisation for the total period can then be obtained through a mathematical analysis named as sequence correction of process parameters. It has been shown that an exact knowledge of the temperature distribution in the furnace will yield results which are in very good agreement with the experimental values. Moreover, the changes in the process parameters during the whole time of crystallisation have been represented graphically. — Application of this model to other systems, for example to GaAs, is also possible.     

Effect of mixing on the crystal size distribution of borax decahydrate in a batch cooling crystallizer

The effect of the impeller speed upon the metastable zone width, supersaturation level, crystal growth and the crystal size distribution of borax decahydrate have been investigated to find operating conditions of a batch cooling crystallizer. The importance of impeller speed was studied in baffled stirred crystallizer with a volume of about 2 dm³, equipped with four straight blade turbine (4-SBT) cooling at a constant cooling rate. The metastable zone width was determined by visual method, while concentration changes during the process were monitored in line using ion-selective electrode. The crystal size distribution was determined by optical microscope and sieve analysis respectively. The power consumption measurements were performed for all impeller speeds examined as well. On the basis of the experimental results and observations it is evident that in an agitated batch crystallizer the above mentioned parameters are significantly influenced by hydrodynamic regime in the system determined by impeller used and its revolution speed.     

基于ISIGHT的二维手性声子晶体带隙最优设计

本文首先利用有限元仿真软件COMSOL计算了二维手性声子晶体的带隙,分析了散射体参数与韧带涂层参数变化对带隙的影响规律。在此基础上,确定手性声子晶体带隙最优设计的有效参数设计空间;然后基于ISIGHT优化设计平台嵌入遗传算法,开展二维手性声子晶体带隙的最优设计。在带隙的最优设计过程中,先以二维手性声子晶体的有效构型参数为设计变量,相对带隙宽度最大为目标,设计手性声子晶体单胞构型。再以此优化单胞构型为初始构型,以手性声子晶体的有效材料参数为设计变量,相对带隙宽度最大为目标,进一步实现二维手性声子晶体带隙的最优设计。本工作极大限度地挖掘了二维手性声子晶体带隙最优设计潜能,为充分发挥手性声子晶体在减振降噪中的作用提供了可靠有效的分析设计方法。     

Influence of gas flow direction on DC glow-discharge deposited a-Si films

Influence of the electrical and of the aerodynamical parameters of a DC glow discharge in silane on the properties of a-Si films deposited in different sites of the glow-discharge has been investigated. It has been found that the electric as well as aerodynamic asymmetry of the DC discharge influence considerably the film properties. Under certain conditions it is possible to obtain semimetallic films without photoeffect.     

On the hypomorphism of ADP crystals

The morphology and symmetry of spheres of ADP crystals has been studied. Faces as well as bands were observed. In contrast to the 2m symmetry as determined from X-ray and neutron diffraction studies, the bands on the spheres displayed a 222 symmetry. It is shown that this reduced symmetry either is the bulk symmetry or is induced by stereospecific interactions at the surface. The influence of several parameters on the stability of the bands and the symmetry of the spheres has been studied. At pH = 6.15 the symmetry reduction was found to be absent.     

The effect of changes in relative humidity on the hydration rate of Pachuca obsidian

The effect of relative humidity on the hydration rate of obsidian and other glasses has been debated since the early work of [I. Friedman, R. Smith, Am. Antiquity 25 (1960) 476]. While more recent work has been in general agreement that a relative humidity dependence does exist, hydration profiles as a function of relative humidity have not been obtained. In this paper we present the results of a study in which samples of Pachuca obsidian were hydrated for approximately 5 days at 150 °C at relative humidities ranging from 21% to 100%, and the resultant profiles were measured by secondary ion mass spectrometry (SIMS). The results suggest that the hydration rate is, indeed, a function of relative humidity, but for the relative humidity levels commonly observed in most soils the effects on hydration dating are expected to be relatively small. In addition, analysis of the surface values as sorption isotherms and comparisons with nitrogen sorption isotherms suggests that water is relatively strongly bound to the obsidian surface. By assuming a situation in which the ‘surface’ refers to active centers within the glass we have shown that an adsorption model provides a useful approach to modeling the diffusive process.     

Influence of lithium ions on the NLO properties of KDP single crystals

Potassium Dihydrogen Phosphate (KDP) and its isomorphous deuterated form are popular due to their applications in frequency converters and electro‐optic modulation. Different attempts have been made to dope KDP with inorganic additives, organic materials and amino acids. Since many of the metal ions possess more electro negativity which increases the non centrosymmetry, it is of interest to dope them in KDP. The influence of lithium ion (Li⁺) on NLO properties of KDP crystal has been studied in the present investigation. Single crystal of Lithium ion doped Potassium Dihydrogen Phosphate (KDP) was grown by slow evaporation technique. The enhancement in SHG efficiency after addition of ion Lithium (Li⁺) was observed by Kurtz Powder SHG test. It was found that the SHG efficiency of KDP after addition of Lithium ion is 1.33 times more than pure KDP. The crystal structure and cell parameters of grown crystal were determined by X‐ray diffraction. The Energy Dispersive X‐ray analysis (EDAX) gives the chemical composition of grown crystal. The functional groups were identified by FT‐IR spectral analysis. The presence of Lithium in the material of grown crystal was detected by Atomic absorption spectroscopy (AAS). The optical absorption and transmission studies were done by UV‐Visible spectral analysis. The grown crystal was subjected to thermogravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC). (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of the influence of electron irradiation on the properties of cobalt nanotubes

Cobalt nanotubes have been synthesized by electrochemical deposition in pores of ion track membranes. The structures obtained have been studied by scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction analysis, and gas permeability method. The influence of electron irradiation on the cobalt nanotube structure has been investigated. It is shown that an increase in the irradiation dose leads to the transformation of the sample crystal structure. This fact can be explained by the simultaneous reduction of the β-Co metastable phase and relaxation of the microstress formed by the fcc phase in the lattice. The degree of sample texturing along the [100] direction increases under electron irradiation. The dependences of the resistive and magnetic properties of cobalt nanotubes on the irradiation dose have been analyzed.     

ZrO2陶瓷显微结构对绿光飞秒激光加工过程的协同效应

氧化锆(ZrO₂)陶瓷因其性能优异,常被应用于医学与工业等领域.通过表面微纳加工可进一步发挥其性能优势,扩大应用范围.实验采用绿光飞秒激光对具有不同显微结构的ZrO₂陶瓷基体进行微孔加工,结合显微结构差异对材料物理性能的影响,系统研究了激光加工功率与加工时间等工艺参数对微孔形貌、直径及深度等不同维度下形貌学特征的作用效果.结果表明,同一加工参数下,晶粒更小、显微结构更均匀、热导率更低的ZrO₂具有更高的加工效率;通过对比微孔直径与深度随激光加工工艺参数的变化,发现材料显微结构的差异对微孔轴向的影响比径向更加显著.     

Influence of crystalline volume fraction on the performance of high mobility microcrystalline silicon thin-film transistors

The influence of the crystalline volume fraction of hydrogenated microcrystalline silicon on the device performance of thin-film transistors fabricated at temperatures below 200 °C was investigated. Transistors employing microcrystalline silicon channel material prepared close to the transition to amorphous growth regime exhibit the highest charge carrier mobilities exceeding 50 cm²/V s. The device parameters like the charge carrier mobility, the threshold voltage and the subthreshold slope will be discussed with respect to the crystalline volume fraction of the intrinsic microcrystalline silicon material.     

Influence of order-domain size on the optical gain of AlGaInP laser structures

Ordered AlGaInP bulk layers and double quantum well laser structures have been grown by metalorganic vapor phase epitaxy at various growth temperatures. The dependence of the degree of ordering and the domain structure on the growth temperature and the aluminum content have been examined by photoluminescence excitation and transmission electron microscopy, respectively. We investigate the influence of these parameters on the optical gain and the threshold current density of ordered lasers. According to band structure calculations for the optical gain, CuPt_B-type ordering is supposed to enhance laser performance. However, up to now this has not been observed. We will show that the domain structure can be made responsible for the diminished laser performance of ordered structures. By changing the growth temperature within the epitaxial run, we introduce a method to separately control the degree of ordering and the domain size. By this manner, we were able to fabricate a highly ordered laser structure with improved performance.