Theoretical and practical achievements in the electric melting of glass

New information concerning electric power and temperature fields and their influence on the flow of glass will be shown.

Methods of calculation of resistances between electrodes, physical, mathematical and other types of new modelling techniques will be described. The optimal connections of electrodes with the multiphase sources of power and ways of protection of electrodes against corrosion by glasses will be discussed. Furnaces for melting different types of glasses and new processes using electricity for melting will be mentioned.     

Characterization of the carrot defect in 4H-SiC epitaxial layers

Characterization of the epitaxial defect known as the carrot defect was performed in thick 4H-SiC epilayers. A large number of carrot defects have been studied using different experimental techniques such as Nomarski optical microscopy, KOH etching, cathodoluminescence and synchrotron white beam X-ray topography. This has revealed that carrot defects appear in many different shapes and structures in the epilayers. Our results support the previous assignment of the carrot defect as related to a prismatic stacking fault. However, we have observed carrot defects with and without a visible threading dislocation related etch pit in the head region, after KOH etching. Polishing of epilayers in a few μm steps in combination with etching in molten KOH and imaging using Nomarski optical microscope has been used to find the geometry and origin of the carrot defects in different epilayers. The defects were found to originate both at the epi-substrate interface and during the epitaxial growth. Different sources of the carrot defect have been observed at the epi-substrate interface, which result in different structures and surfaces appearance of the defect in the epilayer. Furthermore, termination of the carrot defect inside the epilayer and the influence of substrate surface damage and growth conditions on the density of carrot defects are studied.     

Analytical complex at the PIK reactor for studying the supra-atomic structure and dynamics of materials by neutron scattering

A project of the center for studying reactor materials and solving problems of materials science is presented which will be equipped with the following neutron instruments: a small-angle Membrana diffractometer, a spin-echo spectrometer, and a time-of-flight spectrometer. It is proposed to irradiate materials in the PIK reactor core and use neutron-scattering tools to analyze the structure and dynamics of these materials and investigate radiative defects in the complete experimental cycle (initial material-irradiation-strength tests, thermal loads, and other effects) using materials science techniques.     

Scientific opportunities for the study of amorphous solids using pulsed neutron sources

The use of pulsed-neutron-scattering techniques for the investigation of amorphous solids is reviewed in the light of current problems in amorphous solid-state physics and chemistry. The broad areas in which neutron scattering can contribute are those of structure and dynamics, both atomic and magnetic. Possible applications for the new generation of pulsed neutron sources are discussed, and it is concluded that not only will these play a vital role in future studies but also that an important step forward will be made with the extension of measurements into hitherto inaccessible regions of ω-Q space.     

Nondestructive three-dimensional observation of defects in semi-insulating 6H-SiC single-crystal wafers using a scanning laser microscope (SLM) and infrared light-scattering tomography (IR-LST)

Peripheral and central areas of a semi-insulating 6H-SiC single-crystal wafer were examined using a scanning laser microscope (SLM) and infrared light-scattering tomography (IR-LST). The form and density of the defects in each area were observed by SLM. We reconstructed three-dimensional (3D) IR-LST images of scatterers by stacking 2D layer-by-layer IR-LST images on different planes. Using these 3D IR-LST images, variations in the defect distribution with depth were observed for the first time. To study the defect distribution and defect form in detail, we observed the defect configuration in the same volume as for 3D IR-LST images by magnified SLM and merged the images from the two techniques. Information on defects obtained using this approach will be very important in the development of high-quality semi-insulating silicon carbide (SiC) substrates.     

KDP晶体体缺陷和损伤的观测方法研究

采用激光散射诊断法和显微镜相衬法对磷酸二氢钾(KH2PO4、KDP)晶体中的缺陷和损伤进行观测,发现散射法可以对晶体中的缺陷和损伤进行灵敏观测,并可以即时判断损伤;而显微镜相衬法可以对损伤形貌清晰观测,两种方法结合使用可以更好地观测晶体的缺陷和损伤并有助于了解晶体损伤的机理.     

Revealing extended defects in HVPE-grown GaN

In this communication we will summarize the results of a complementary study of structural and chemical non-homogeneities that are present in thick HVPE-grown GaN layers. It will be shown that complex extended defects are formed during HVPE growth, and are clearly visible after photo-etching on both Ga-polar surface and on any non-polar cleavage or section planes. Large chemical (electrically active) defects, such as growth striations, overgrown or empty pits (pinholes) and clustered irregular inclusions, are accompanied by non-uniform distribution of crystallographic defects (dislocations). Possible reasons of formation of these complex structures are discussed. The nature of defects revealed by selective etching was subsequently confirmed using TEM, orthodox etching and compared with the CL method. The non-homogeneities were studied in GaN crystals grown in different laboratories showing markedly different morphological characteristics.     

The possibility of identifying the spatial location of single dislocations by topo-tomography on laboratory setups

The spatial arrangement of single linear defects in a Si single crystal (input surface {111}) has been investigated by X-ray topo-tomography using laboratory X-ray sources. The experimental technique and the procedure of reconstructing a 3D image of dislocation half-loops near the Si crystal surface are described. The sizes of observed linear defects with a spatial resolution of about 10 μm are estimated.     

High-density ultracold neutron sources for the WWR-M and PIK reactors

It is proposed to equip the PIK and WWR-M research reactors at the Petersburg Nuclear Physics Institute (PNPI) with high-density ultracold neutron (UCN) sources, where UCNs will be obtained based on the effect of their accumulation in superfluid helium (due to the specific features of this quantum fluid). The maximum UCN storage time in superfluid helium is obtained at temperatures on the order of 1 K. These sources are expected to yield UCN densities of 10³–10⁴ cm^–3, i.e., approximately three orders of magnitude higher than the density from existing UCN sources throughout the world. The development of highest intensity UCN sources will make PNPI an international center of fundamental UCN research.     

Impurity incorporation in orientation patterned GaAs grown by low pressure HVPE

Orientation-patterned GaAs (OP-GaAs) has shown promise as an efficient frequency-shifted laser source over the range of 2–12 μm. In order to make OP-GaAs a viable source, efficiency and output power must be significantly increased, which requires minimizing major sources of loss. Low pressure HVPE has been adopted as the most suitable technique for regrowth of thick high quality GaAs layers on OP templates. We have explored process parameters in bulk and OP material to identify and control the sources of point defects, a key contributor to optical losses. Growth on OP templates with periodic [001] and [00?1] domains results in domain specific surface orientation, which should have inhomogeneous defect incorporation. Hall measurements, SIMS depth profiling, and cathodoluminescence (CL) were used to identify point defects in bulk and OP-GaAs. It was found that Si impurities are the primary source of donors, while V_Ga were identified as the primary source of acceptors. In order to study the incorporation of impurities in OP-GaAs samples, we intentionally doped samples with Si to increase CL and SIMS detectability. Spatially resolved CL and SIMS revealed regions with significant differences in the defect concentration, which can affect device output.     

反蛋白石结构光子晶体制备技术

光子晶体是一种具有光子带隙的新型材料,由于其可以控制和抑制光子运动的特性,在光通讯领域具有广阔的应用前景.反蛋白石结构是光子晶体一种重要的结构,由于其制备方法简便、成本低廉而受到人们的普遍关注.本文在介绍目前常用的几种制备光子晶体技术的基础上,详细阐述了制备反蛋白石结构光子晶体的各种技术和方法、以及利用这些制备技术和方法在反蛋白石结构光子晶体上制备一维和二维缺陷的最新进展.     

硅片加工表面层损伤检测技术的试验研究

单晶硅片超精密加工表面层损伤较小,检测评价比较困难.为了确定合适的检测技术,对多种硬脆材料表面层质量检测技术进行了系统的试验研究.结果表明,硅片加工表面宏/ 微观形貌可采用各种显微镜及3D表面轮廓仪等进行检测,表面损伤分布可采用择优腐蚀法和分步蚀刻法检测;粗加工和半精加工硅片的损伤深度宜采用角度抛光法检测,而精加工硅片的损伤深度较小,宜采用截面Raman光谱分析和恒定腐蚀速率法检测;损伤层的微裂纹、位错、非晶及多晶相变等微观结构可采用分步蚀刻法、平视和剖视TEM分析法及显微Raman光谱仪检测;表面层宏观残余应力分布可用显微Raman光谱仪检测,其微观应变可采用高分辨X射线衍射仪的双品摇摆曲线的半高宽值来衡量.综合以上检测技术可以对硅片加工表面层损伤进行系统的评价.     

The role of dislocations in the formation of mechanical stresses during annealing of gallium arsenide single crystals

The effect of dislocations on the change of mechanical stresses in undoped semi-insulating gallium arsenide single crystals has been studied during their annealing in vacuum and in the arsenic atmosphere. The phenomena observed are explained by the effect of dislocations playing the role of channels for arsenic diffusion on the concentration of intrinsic point defects in the crystal regions surrounding dislocations. The mechanism of arsenic diffusion over dislocations allows one to consider dislocations as sources and sinks of arsenic without the translational and twinning processes and, thus, makes the well-known data on the reactions of dislocation interaction with point defects and the experimental structural data for single crystals more consistent.     

Thermal stability of light-induced defects in hydrogenated amorphous silicon: Effect on defect creation kinetics and role of network microstructure

The kinetics of light-induced defect creation in a-Si:H is studied in early-time limit and as function of pre-existing defects of different thermal stability by electron spin resonance and optical spectroscopy techniques. Both for cw and for laser pulse exposures, the early-time kinetics follows sublinear t^β time dependences, similar to the long-time limit. In addition, the overall defect creation rate is not a single function of the total defect number. Instead, it depends on the thermal stability, or annealing energy distribution, of the defects present in the film. Furthermore, creation of the thermally less stable defects is unaffected by the presence of a large number of stable defects introduced by pre-exposure at a higher temperature. These findings question the existing defect creation models. Thermal stability of the light-induced defects depends on the network microstructure, the less stable defects being created in a-Si:H deposited near microcrystalline transition.     

Defects in natural diamonds: Recent observations by new methods

The observations presented concern both grown-in defects and those which develop after growth. They will deal principally with impurity platelets precipitated on {100} planes and with dislocations. The former defects are a notable feature in the most common variety of natural diamond (Type Ia.) The experimental techniques used are of the direct-imaging, topographic type and include ultraviolet absorption topography, X-ray topography, cathodoluminescence topography (both with visible and near infrared wavelengths) and transmission electron microscopy at 100 kV, 120 kV and 1 MeV. Spectrography and colour photography are informative in cathodoluminescence studies. The cathodolumisnecent images of individual dislocation lines can be photographed, whether the dislocations be grown-in or arise from plastic deformation post growth, provided that they lie in matrices sufficiently free from point defects acting as strong electron-hole recombination centres. In practice this requirement implies a low concentration of nitrogen impurity much of which is distributed in “small clusters” which give rise to the bright blue cathodoluminescent emission characteristic of Type Ia diamonds. The luminescence from individual dislocation lines may be either a violet-coloured emission, or an emission which is dominantly a system (known as “H3”) having a zero-phonon line at 2.46 eV and stretching from green to orange in the visible spectrum. The violet dislocation emission is strongly polarised with E vector parallel to the dislocation line. New observations on platelets have been mainly concerned with those attaining diameters of 1 μm or more which can be observed individually by X-ray topography and cathodoluminescence topography. However, evidence from electron and X-ray diffraction contrast indicates that these “giant platelets” produce the same matrix lattice displacements as the more familiar submicrometre-sized platelets in Type Ia diamond and may be presumed to have essentially the same structure and composition. Near infrared cathodoluminescence has been recorded from individual large platelets and it has been discovered that this emission is highly polarised with the E vector in the platelet plane. Available evidence on the structure and properties of the platelets weighs against a currently mooted hypothesis that they are composed of interstitial carbon, and does not conflict with an older idea, that they are composed of nitrogen impurity.     

Selective epitaxy and lateral overgrowth of 3C-SiC on Si – A review

This review article attempts to present a comprehensive picture of the progress in selective epitaxial growth (SEG) of cubic silicon carbide (3C-SiC) to make it a cheap and practical material for high temperature and high power, high frequency and MEMS (Micro Electromechanical Systems) applications. Selective epitaxial growth followed by epitaxial lateral overgrowth (ELO) is a suitable approach to minimize the interfacial defects and other planar defects in case of thin film growth. Different techniques of SEG and its application to Si, GaAs and III–V nitrides are reviewed briefly in the first section of this article. Various SEG techniques like epitaxial lateral overgrowth, pyramidal growth and pendeo epitaxial growth, etc. have been discussed extensively for growing 3C-SiC on Si, together with the characterization of the grown films. The influence of various experimental parameters such as temperature of growth, choice of mask material, influence of an etchant, pattern shape and size, etc. is also discussed. On the basis of these data, it is believed that SEG and related techniques are a promising approach for heteroepitaxial growth of 3C-SiC films useful for devices and MEMS applications.     

Atomic Force Microscopy Studies on Growth Mechanisms and Defect Formations on {110} Faces of Cadmium Mercury Thiocyanate Crystals

Growth mechanisms and defect formations on {110} faces of cadmium mercury thiocyanate crystals grown at 30°C (σ=0.24) were investigated by using atomic force microscopy (AFM). It was found that, under this condition, spiral dislocation controlled mechanism and 2D nucleation mechanism operates simultaneously and equally during growth, which is completely different from the traditional 2D nucleation and dislocation source controlled mechanisms. A number of 2D nucleus are formed at the large step terraces generated by dislocation sources, leading to the unequal growth rates of the elementary steps and thereby “step bunches” arecaused. Various defects are formed under this growth condition, which is assumed to result from the incongruence between the steps generated by different sources. A new kind of 2D defect, corresponding to one growth layer in height, was observed for the first time.     

Role of transmission electron microscopy in the semiconductor industry for process development and failure analysis

Transmission electron microscope (TEM) based techniques offer superior spatial resolution and highly sensitive elemental analysis capabilities that can be exploited for metrology and materials characterization of sub-nanometer sized device features in advanced semiconductor technologies. TEM based techniques are suited for evaluating interfacial details, dimensions of device structures, and defects or flaws that arise during the fabrication process. In this work, TEM based techniques that are commonly used for physical characterization, compositional analysis, and failure analysis of semiconductor device structures are reviewed. Sample preparation methods, based on focused ion beam milling that is capable of site specific sample preparation, are also reviewed. The strength of these methods as well as problems, such as focused ion beam induced damage and gallium contamination, and methods to control them are described. Examples are presented from case studies that are required for process development, yield enhancement, and failure analysis of semiconductor manufacturing. Challenges faced due to introduction of alternative gate structures, nano-sized features, high-K gate dielectrics, and new materials needs in the integration of device structures are addressed.     

Small-angle X-ray scattering,synchrotron radiation,and the structure of bio- and nanosystems

Small-angle X-ray scattering is a universal diffraction method for studying the supra-atomic structure of matter. The potential of this technique has greatly increased in recent years due to the development of bright synchrotron radiation sources. The extensive use of these sources, in combination with new techniques for analyzing scattering data and structure modeling, made small-angle scattering one of the most effective analytical methods for studying nanoscale structures. In this review, after a brief outline of the basic principles of small-angle scattering by isotropic dispersed nanosystems, we consider two areas of nanodiagnostics, in which the progress in the small-angle experiment and the latest techniques for interpreting scattering data has become pronounced in recent years. These areas—the analysis of the structure of biological macromolecules in a solution and structural studies of metal nanoparticles synthesized in polymer and aqueous media—are illustrated by examples of practical biological and nanotechnologycal applications.