Growth and characterization of ferromagnetic shape memory alloy Co50Ni20FeGa29 single crystals

Single crystals of Co₅₀Ni₂₀FeGa₂₉ with B2 phase have been obtained in a deep supercooling condition. The interface-facets and the segregation effect lead to the formation of ordered defects that store a directional internal stress. These defects give to a large energy barrier that leads to a very sharp martensitic transformation within a temperature window of only 2 K. The single crystals show good shape memory effect and superelasticity, which are anisotropic between the growth direction [0 0 1] and its equivalent direction [0 1 0]. The anisotropic behaviors are attributed to the directional internal stress caused by the ordered defects.     

水热法白宝石晶体和籽晶界面研究

用分光光度计研究发现水热法白宝石晶体和籽晶界面使晶体透过率降低,用大视场偏光显微镜和原子力显微镜分析了该界面的包裹物分布以及界面的显微结构.结果表明平行于(1123)面的籽晶和生长层晶体界面包裹物含量少.界面的缺陷主要来自于晶格畸变及生长初期的温场不稳定所引起的结构缺陷,这也是引起晶体透过率下降的主要因素.     

PVT法生长SiC过程生长界面形状对热应力的影响

PVT法生长SiC过程中晶体内部的热应力是其位错产生的主要原因,而生长界面的形状对晶体热应力及缺陷的产生都有一定影响.本文对不同生长界面晶体的温场及应力场进行了数值分析,结果显示相对于凸出及平整界面的晶体,微凹界面晶体的轴向温差最小,同时产生缺陷的切应力Τrz及引起开裂的径向正应力σrr值都为最小.     

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.     

声光晶体TeO2的生长及缺陷研究

本文研究了直接ＴeO２晶体中的主要晶体缺陷形成机理,讨论分析了Ｔ eO2单晶生长的工艺参数对晶体缺陷的影响,结果表明：晶体裂缝的主要与温度梯度有关,温度梯度大于２０－２５℃/cm及出现界面翻转时,易造成晶全的开裂,位错密度增加,晶体中的包裹体主要为气态包裹全,它的形成主要与籽晶的转速和晶体的提拉速率有关,转速１５－１８r/min,拉速０.55mm/h,固液界面微凹,可以减少晶体中的气态包裹体,晶体台阶由晶体生长过程中温度和生长速度的引起伏引起,当台阶间距较宽时,易形成包裹体。     

Structure of Diamond-Like Silicon–Carbon Films Alloyed by Vanadium

The structure of diamond-like silicon–carbon films formed on silicon substrates by magnetron and plasmatron codeposition using a closed-field magnetron and a plasmatron activated by tungsten cathode has been studied by transmission electron microscopy. The main feature of the films alloyed by vanadium to concentrations of 12–31 at % was found to be a layered structure of the film cross section. It was established that vanadium alloying leads to the formation of vanadium carbide (VC) nanocrystals; the nanocrystal size increases from 1–2 to 10 nm. At the maximum vanadium content, VC nanocrystals have an anisotropic shape: they are extended in the direction perpendicular to the film–substrate interface.     

High-resolution electron microscopy of microstructure of SrTiO3/BaZrO3 bilayer thin films on MgO substrates

SrTiO₃/BaZrO₃ heterofilms as buffer layers are deposited on (0 0 1) MgO substrates by an RF-sputtering technique. The atomic structure and the defect configuration at the interfaces are investigated by means of aberration-corrected high-resolution transmission electron microscopy. At the BaZrO₃/MgO interface, two types of interfacial structures, MgO/ZrO₂-type and MgO/BaO-type, are observed. Antiphase boundaries and dislocations are found at the BaZrO₃/MgO interface. The formation of these lattice defects is discussed in terms of film growth and structural imperfections of the substrate surface. At the SrTiO₃/BaZrO₃ interface, a high density of misfit dislocations is observed with different configurations. The formation of these dislocations contributes both to the relaxation of the large misfit strain and to stopping of the further propagation of lattice defects which are formed in the BaZrO₃ layer into the SrTiO₃ layer.     

3D simulation of the effects of growth parameters on the growth of sapphire crystals using heat exchanger method

3D simulations using the commercial CFDRC and FIDAP code, which are based on finite element techniques, were performed to investigate the effects of anisotropic conductivity on the convexity of the melt–crystal interface and the hot spots of sapphire crystal in a heat‐exchanger‐method crystal growth system. The convection boundary conditions of both the energy input to the crucible by the radiation as well as convection inside the furnace and the energy output through the heat exchanger are modeled. The cross‐sectional flow pattern and the shape of the melt–crystal interface are confirmed by comparing the 3‐D modeling results with previous 2D simulation results. In the 3D model, the “hot spots” in the corners of the crucible are donut shaped, and the shape changes with the value of the conductivity of anisotropic crystal. The outline of the crystal becomes more convex as the conductivity in the z direction (k_sz) increases. The outline of melt–crystal interface is elliptical when the anisotropic conductivity is moving in the radial direction (k_sx and k_sy). The portion at the outline touching the bottom of the crucible is smaller than the maximum outline of the crystal, meaning that the shape at the “hot spot”, changes with the value of the conductivities of anisotropic crystal. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Atomic layer deposition of high-k dielectrics on III–V semiconductor surfaces

The goal of this article is to provide an overview of the state of knowledge regarding the Atomic Layer Deposition (ALD) of metal oxides on III–V semiconductor surfaces. An introduction to ALD, the band structure, various defects present on the III–V surface and how they relate to Fermi level pinning are discussed. Surface passivation approaches are examined in detail in conjunction with experimental and computational results. The “interface clean-up” reaction that leads to the formation of a sharp gate oxide/semiconductor interface is related to the surface chemistry and the transport of the surface oxides through the growing dielectric film. Finally, the deposition of metal oxides on semiconductors is discussed in the context of interface quality and some examples of devices using III–V channels and ALD metal oxides are given.     

Selective etching and epitaxial refilling of silicon wells in the system SiH4/HCl/H2

Wells were etched in (100) silicon by different kinds of selective etching and were selectively refilled by using different gas systems. Masking materials were SiO₂ and Si₃N₄; for the refilling the systems SiCl₄/H₂ and SiH₄/HCl/H₂ were studied. By using a combination of weak anisotropic gas etching with HCl (Si₃N₄ films as mask) and of SiH₄/HCl/H₂ as refilling system, plane surfaces without ridges at the boundary of the mask and without nuclei on the mask were reached. The results were obtained by SEM, light microscopic and profile investigations and are compared with the other kinds of etching and refilling.     

改进热交换法生长蓝宝石晶体的气泡研究

采用改进的热交换法生长的蓝宝石晶体,气泡是其主要缺陷之一.本文采用数值模拟研究了晶体生长过程中氦气流量对坩埚内温场、固液界面形状的影响.并结合晶体生长实验结果,分析了在实际的晶体生长过程中,氦气流量的线性增加对晶体内气泡的尺寸、形态和分布的影响.     

Factors affecting the formation of misoriented domains in 6H‐SiC single crystals grown by PVT method

Misoriented domains (MDs) are common defects in 6H‐SiC single crystals. We performed an experimental study on the formation of MDs in 2‐inch 6H‐SiC single crystals. Micro‐Raman spectroscopy revealed that the polytype of MDs was mainly 4H‐SiC. By changing growth conditions, it was found that the MDs' formation was closely related to growth rate and the position of highest temperature relative to growth interface. When the growth rate of ingots was relatively high the MDs were more likely to form. Furthermore, the nearer growth interface the position of highest temperature was, the larger the size of the MDs. Based on our experimental findings we suggested that the MDs' formation and the polytype switching from 6H‐ to 4H‐SiC were due to too large axial and/or radial temperature gradients.The results would be helpful to improve the quality of SiC single crystals grown by PVT technique. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

光子晶体多组元缺陷态问题研究

缺陷态光子晶体可以用于制作良好的谐振器、偏振器、滤光器等光学器件,具有重要的应用价值。本文发展了光子晶体缺陷态问题的PG有限元界面问题计算方法,有效地处理了各种不同组元体系、几何结构、界面形状、材料属性以及模态的光子晶体缺陷态问题。数值结果表明,二组元结构单点缺陷对带隙的影响较小,只是使局部范围内的波继续传播而产生一条缺陷带,多点缺陷使一些特定范围内的波可以传播而产生多条缺陷带,线缺陷产生的影响较大,可以使整个禁带消失。结合线缺陷与点缺陷,波导结构中的侧点缺陷可以有效地应用于光子晶体阻带内诱导窄通带或在波导的通带内诱导非常窄的阻带。三组元结构引入了不均匀介质、复杂介质形状以及不同几何结构的缺陷态。通过计算与分析发现Ω₃区域的介质形状对结果影响比较有限,表面层越不光滑禁带越窄,n型缺陷态在TM模中的高频区域更容易产生禁带。对于TE模来说,n型与v型的缺陷态更容易产生禁带。     

Effect of magnetic field on lyotropic nematic in the vanadium pentoxide (V2O5)-water system

The optical textures of anisotropic phases of dispersed aqueous vanadium pentoxide solutions have been studied. It was established that the application of a magnetic field to these phases results in the formation of transient magnetohydrodynamic domains. The evaluation of the Freedericksz threshold field for the S-effect provided the determination of the elastic constant, K ₁ ≈ 3.6 × 10^?7 dyn. It is concluded that the studied anisotropic phases can be related to nematics.     

The crystal growth and perfection of 2,4,6-trinitrotoluene

Large crystals of TNT were grown from ethyl acetate solution by both temperature lowering and solvent evaporation. The perfection of crystals grown from seeds under carefully controlled conditions was generally higher than those prepared by uncontrolled solvent evaporation. Examination by X-ray topography revealed the crystals to have a characteristic growth induced defect structure comprising growth sectors and boundaries, growth banding, solvent inclusions and dislocations. Twins and stacking faults (SF) were also observed. Many of the defects noted in the topographs can be attributed to impurities. The influence of the highly anisotropic crystal structure on the nature of growth defects is discussed. A structural model proposed to explain twinning and SF formation is partially supported by topographic evidence.     

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.     

Elastic interaction of point defects and volume defects near interfaces

The paper contains a generalization of previous works of the author dealing with the calculation of the interaction energy of point defects and more or less extended volume defects near a solid surface. Formulae for the interaction energy of two defects between each other and with an interface are derived. For special cases the well-known results of BACON for dilatation centres have been generalized to extended defects with arbitrary shape and size.     

New approach to capacitance spectroscopy for interface characterization of a-Si:H/c-Si heterojunctions

A new technique for characterization of interface defects in a-Si:H/c-Si heterostructure solar cells from capacitance spectroscopy measurements under illumination at forward bias close to open-circuit voltage is described. The proposed method allows to significantly increase the sensitivity to interface defects compared to conventional capacitance measurements at zero or small negative bias. Results of numerical modelling as well as experimental data obtained on n-type a-Si:H/p-type c-Si heterojunctions are presented. The sensitivity of the proposed method to interface states and the influence of various parameters like band mismatch, density of interface defects, recombination velocity at the back contact are discussed.     

Texture growth and screw dislocations in smectic A phases

The formation of the textures of smectic A phases was investigated. In planar oriented samples the A phases grow in the shape of rods without defects. The velocity of growth is strongly anisotropic with its maximum normal to the director orientation. In non oriented samples the smectic A texture is growing in batonnets with defect structure to give focal conic textures. The maximum growth velocity of the batonnets is parallel to the director orientation. Since this would contradict to the Wulff theorem we assume a growth mechanism with a screw dislocation.     

Modelling of point defects in monoclinic zirconia

We present the results of plane wave density functional theory calculations of oxygen vacancies and interstitial oxygen atoms in monoclinic zirconia. After calculating the incorporation energies and structures of interstitial oxygen atoms and formation energies of neutral oxygen vacancies, we consider the electron affinities and ionisation potentials of these defects. These properties are especially important at the silicon/oxide interface in MOSFET devices, where silicon may serve as an electron and hole source. The results demonstrate that interstitial oxygen atoms and positively charged oxygen vacancies can trap electrons if the electron source (band offset) is higher than ∼2 eV above the top of the zirconia valence band.