Properties of Surface Layers in Single Crystals of Calomel

Within the framework of the systematic study of differences in physical properties of the calomel (Hg₂Cl₂) single crystals before and after surface treatment, the differences in the microhardness, the residual stress in the surface layer, and the chemical etching rate were investigated on the (110) and (001) crystal faces. It has turned out that Beilby layer (B-layer) formed during surface treatment is softer, and, on the cleavage surface is harder than the underlying bulk material. The thickness of the B-layer in these samples ranged between 5 anf 7 m̈m. Further it has been found that a tensile residual stress s̀ = 14 Nm^-2 prevails in the surface layer of a polished (110) face to a depth of 70 m̈m and, after grinding, to a depth from 90 to 200 m̈m. On the other hand, a compressive stress has been found in the natural cleavage plane. Experiments on etching the Hg₂Cl₂ crystals with HCl + HNO₃ etching solution have shown that the rate of chemical etching is 2 to 4 times larger on the (110) face than on the (001) face. Differences are very strongly dependent on the experimental conditions and on the real structure of a given surface.     

CsB_3O_5晶体潮解机理及防潮研究

三硼酸铯(CsB3O5)晶体在Nd:YAG 1064 nm激光三倍频转换方面具有优良的性能,限制该晶体器件实用化的一个重要因素是其在空气中较易潮解.本文用化学侵蚀法研究了CsB3O5晶体的潮解取向,并从晶体结构上给予了解释:由于CsB3O5晶体的B-O骨架在(010)方向存在较大的通道,水分子较易沿(010)方向进入晶体而导致晶体潮解.采用了用光学增透膜结合疏水保护膜的方法防止CsB3O5晶体潮解的技术手段,使CBO晶体器件能够在常规环境中保存及使用.     

Domain structure in main crystallographic planes of orthoferrites at spin reorientation

The behaviour peculiarities of the domain structure of the single crystal samarium-terbium-erbium and samarium-terbium-thulium orthoferrites in the spin reorientation range in three crystallographic planes (001), (110) and (100) are investigated. In the (001)-plane the temperature-induced bubble domain lattice formation is observed. The formation kinetics of these domains is similar to the process of nucleation and that of growth with spontaneous crystallization. In the (110) plane the inclined domains formation is noted. The canting angle depends on temperature at spin reorientation. The values of remagnetization fields are measured as a function of temperature in the indicated crystallographic planes. From the measured changes of the domain structure the temperature dependences of the first anisotropy constant and the domain wall density are determined.     

Growth of YBa2Cu3O7 films with [110] tilt of CuO planes to surface on SrTiO3 crystals

YBa₂Cu₃O₇ films with the CuO plane tilted to the surface have been grown on SrTiO₃ crystalline substrates by pulsed laser deposition. This tilt was obtained by rotating the film lattice with respect to the substrate surface around its [110] axis oriented parallel to the surface. The zero tilt of the CuO plane was implemented at the orientation of the SrTiO₃ crystal surface parallel to the (100) plane. The rotation angles were varied in the range from 0° to 70°. It is found that, being tilted at any angle, the CuO planes of the film remain parallel to one or several crystallographic planes of the (100)-type substrate. In the range of tilt angles from 0° to 49°, the film has a single-crystal structure. Above 49° the film is transformed into a three-domain texture and its surface roughness sharply increases.     

Growth and some properties of TeO<Subscript>2</Subscript> single crystals with a large diameter

Large-diameter single crystals of TeO₂ are grown by the Czochralski method in specially designed setups with automatic monitoring of the crystal growth. The degree of perfection of the grown crystals is examined using selective etching and X-ray topography (the Shultz method). The temperature dependence of the microhardness of TeO₂ single crystals is investigated for different crystallographic planes, namely, (001), (100), and (110).     

Reducing Inversion Twinning in Single Crystal Growth of GaPO4

Gallium orthophosphate (GaPO₄) single crystals were grown by the reverse temperature gradient method from phosphoric acid solutions under hydrothermal conditions. Twins after (110) were studied by etching faces having been cut perpendicular to one of the twofold axes. Based on the determination of the twin boundary position as well as on the knowledge of the growth rates of different crystallographic forms, a few faces have been chosen to be quite promising for growing high‐quality GaPO₄ single crystals if they are offered at the referring seed crystal. From the characterization of the grown crystals conditions have been found, which may lead to the reduction of the inversion twin number during the growth process.     

In situ mesa etching and immediate regrowth in a HVPE reactor for buried heterostructure device fabrication

Mesa etching in a hydride vapour-phase epitaxy (HVPE) reactor has been studied. Etched depth, underetching and shape of the mesas have been analysed as a function of partial pressures of active gases (HCl, PH₃ and InCl), stripe orientation and etching temperature. The experimental results show that the depth and undercut can be etched independently. We propose qualitative mechanisms for etching each of the emerging crystallographic planes ((0 0 1), (1 1 0) and {1 1 1}). In situ mesa etching with immediate regrowth was applied to the fabrication of buried heterostructure Fabry–Perot lasers. No surface contamination due to exposure to ambient and low process time are advantages of this technique.     

Surface morphology of iron specimens boronized with BCl3-H2 mixtures (II) investigation of short-time gas phase boronized iron surfaces

Specimens made of armco iron or pure iron were boronized during a time ≦; 1 minute with 1.1 vol.% BCl₃ in H₂, and then their surfaces were investigated by scanning electron microscopy and X-ray diffraction. The boride particles consist of FeB and Fe₂B, they crow oriented on the substrate surface, e.g. the Fe₂B (110) crystallographic plane is situated parallel to the (111) plane of α-iron. The polycrystalline substrates are decorated by growing boride particles so that grains, twinning, etc. can be seen. There is a correlation between number per area and size of boride particles in early stages of layer formation and surface morphology in advanced layer growth.     

Changes in Structure of ZnS Crystals Due to Mechanical Stresses

Using the direct X-ray diffraction method which was worked out for the case of lattices built up of translationally equivalent layers for the determination of the rat of occurrences of structure elements in crystal regions consisting of 3, 4 and 5 layers, respectively, structure changes in ZnS crystals due to mechanical stresses were investigated. Forces acting parallel to the [110] direction induced a decrease in the number of stackings containing hexagonal elements and increase in the number of cubic stackings. A lattice region of a ZnS crystal having originally pure 4 H structure became heavily stacking faulted when polished parallel to the (110) plane; repeated polishing results in a twinned cubic structure.     

Surface diffusion length of Ga adatoms in molecular-beam epitaxy on GaAs(100)-(110) facet structures

By the molecular-beam epitaxial (MBE) growth of GaAs on [001]-mesa stripes patterned on GaAs(100) substrates, (110) facets were formed on the mesa edges defining (100)-(110) facet structures. The surface diffusion length of Ga adatoms along the [010] direction on the mesa stripes was obtained for a variety of growth conditions by in-situ scanning microprobe reflection high-energy electron diffraction (μ-RHEED). Using these values and the corresponding growth rate on the GaAs(110) facets, the diffusion length on the (110) plane was estimated. We found that the Ga diffusion length on the (110) plane is longer than that on the (100) and (111)B planes. The long diffusion length on the (110) plane is discussed in terms of the particular surface reconstruction on this plane.     

The texture of GaSb ingots grown by the bridgman method

Crystallographic features of GaSb grown by the Bridgman procedure were investigated by scanning electron microscopy. Chemical etching and the electron channelling method were used to determine the position and crystallographic orientation of crystallites. A pronounced 〈110〉 texture was detected which was misaligned by 5÷28° with respect to the main axes of the ingots. Boundaries were categorized according to the orientation change accross them. Results were compared. The majority of small angle boundaries are probably caused by thermal stresses induced dislocation migration.     

Dislocation Etching Behaviour of Hydrothermal and Organic Acid Etchants on Natrolite Crystals

Studies on etching of (110) cleavages of natrolite crystals in organic acids (viz., succinic acid, formic acid, and phthalic acid) and stream under high hydrostatic pressures have been made. It is observed that on successive etching of matched cleavages in any of these organic etchants, the pits get bigger both in regard to depth as well as lateral dimensions. Study of matched cleavages etched in any of these etchants indicates 1:1 correspondence of point bottomed pits. Similar results are obtained when matched cleavages are etched by the hydrothermal method. In contrast to such results, it is observed that the etch pit density on a cleavage etched by the hydrothermal method is always higher when compared with its matched cleavage etched in any of the given organic acids. Through a series of experiments, it is found that while corresponding to every etch pit due to any of these organic acids there is a pit due to hydrothermal etching, the converse is not true. It is suggested that the hydrothermal etching is more reliable so far as dislocation density estimation on (101) cleavages of natrolite is concerned.     

Growth Mechanism and Crystal Form of Potassium Dichromate

The structure of potassium dichromate (P-1, Z = 4) consists of two layers parallel to (001), between which no crystallographic symmetry relation exists. These layers are nearly coincident with each other when rotated through 90° about c*. One question remained unanswered: do the crystals grow parallel to {001} with d(002) or d(001) layers? The pseudo-fourfold axis does not run parallel to a crystallographic direction and acts only between two layers. This means that crystal growth parallel to {001} occurs in d(001) layers, which corresponds to the occurrence of one-sided intergrowths on (00-1). The layers are also nearly coincident with each other through pseudo-twofold axes parallel to [110] and [-110]. These axes do not act in the (100) or (010) projections. In the projections along the [110] and [-110] directions, the lattice directions are then extended by a factor of approximately 1.414, and the formula units in the cell of the d(002) layer are doubled. This indicates a further possible growth mechanism. The theoretical growth forms of the crystals were calculated with the Fourier transform method of morphology.     

Single-crystal spectrum of 5-anilinopentadienylidenanilinium bromide,C17H17BrN2

The visible and ultraviolet absorption spectra of crystalline 5-anilinopenta-dienylidenaniliniumbromide have been measured with a microreflexion spectrometer, using polarized light. The (110) crystal plane shows exceptional dichroism, which is interpreted from the results of X-ray structure analysis as being due to the approximately parallel arrangement of the molecular oscillators.     

CdTe(110)表面原子与电子结构的第一性原理研究

采用基于密度泛函理论的第一性原理计算了CdTe(110)表面的原子和电子性质.结果表明,CdTe(110)理想表面在禁带中出现两个明显的表面态,弛豫后表层Cd原子和Te原子p态电子发生转移,Cd原子趋向于sp2平面杂化构型,Te原子趋向p3杂化的锥形构型.经过表面弛豫大大降低了表面能,增大了表面功函数,表面占据态和表面空态分别被推进价带顶之下和导带底之上,导致弛豫表面没有明显的表面态.     

Investigation of X‐ray Satellite Reflections Attributed to Antiphase Boundaries in Epitaxial (Ga,In)P Layers grown on (001) GaAs Substrates

We report on the analysis of additional X‐ray reflections that probably arise from antiphase domain boundaries within (Ga,In)P/(001) GaAs heteroepitaxial layers. Due to the preferred cation ordering along the crystallographic directions [1‐1 1] and [‐1 1 1] which belong to the [110] zone the original sphalerite‐type structure of (Ga,In)P changes into a CuPt‐like of the cation sublattice. This ordering phenomenon causes a loss of symmetry, i.e. the cubic structure is converted into a rhombohedral one. The antiphase boundaries between ordered domains are assumed to behave similar to lattice planes at X‐ray diffraction. Therefore, additional reflections may occur spatially neighboured to the [001] direction. The presented results of X‐ray experiments are discussed in relation to TEM experiments published in the literature in order to explain the origin of the satellite reflections. In the case of the investigated samples (grown on GaAs substrates misoriented 2° towards the azimuthal [010] direction) the APBs run preferentially in directions tilted up to angles of 20° with respect to growth direction. A preferential occurrence of satellite reflections in <13 2 1> directions was observed coinciding with {13 2 1} "lattice planes" whose normals enclose the same angle to the [001] growth direction as the normals of the average planes characterized by APBs. The appearence of the phenomenon in other directions that are also spatially neighboured to the <13 2 1> directions was determined on the basis of the shift of the reflection positions due to tilting the sample around an axis geometrically included in the scattering plane.     

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)     

Modification of birefringence properties of nanostructured silicon with a change in the level of substrate doping with boron

Birefringence of porous-silicon films prepared by electrochemical etching of boron-doped Si(110) wafers with a resistivity of 25–45 mΘ cm has been studied. The samples are found to exhibit the properties of a negative uniaxial crystal with the optical axis oriented along the [1 $\bar 1$ 0] crystallographic direction. The possibility of using porous-silicon films as phase plates for light-polarization control in the near and mid-IR ranges is demonstrated.     

自支撑氮化硅膜结构制备工艺优化

自支撑氮化硅膜结构一般是基于微纳加工技术来制备的。为了提高膜结构的品质,本文分别对自支撑氮化硅膜结构制备中的干法刻蚀参数和各向异性湿法腐蚀参数进行了研究和优化,其中干法刻蚀参数主要包括反应气体配比和刻蚀时间,各向异性湿法腐蚀参数主要包括腐蚀剂浓度和腐蚀温度。在不同的参数组合下进行实验,使用光学显微镜观察并比较不同样品的表面形貌,得到了较理想的参数组合。在干法刻蚀的反应气体中加入少量O₂可改善刻蚀效果,反应气体配比V(SF₆)∶V(CHF₃)∶V(O₂)=6∶37∶3,刻蚀时间2 min。湿法腐蚀中腐蚀剂在质量分数25%处达到最大的硅腐蚀速率,同时氮化硅表面形貌也较理想。     

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.