Microstructures of Tin Iodide Single Crystals Grown in Silica Gels

Single crystals of tin iodide (SnI₂) have been grown in silica gels. A detailed microtopographical study of {100} faces have been described. Horizontal striations are predominant on these faces for most of the crystals, while few of them show vertical striations. The horizontal striations are associated with the two-dimensional nucleation theory whereas the vertical striations relate to the growth fronts. Growth layers modified by the presence of misaligned microcystals have been illustrated. The natural etch pits on {100} faces of the crystal are attributed to the dissolution of crystals in the acid set gel. In the light of these observations, the mechanism of the development and growth of these faces have been assessed and the implications are discussed.     

Beiträge zum Ätzen von Galliumarsenid (I) Strukturtheoretische Diskussion der erzeugten Ätzmorphologien

{111}-, {110}- and {100}-plates of GaAs have been etched in various etching solutions followed by comparing the obtained etching structures. The fundamentals of the discussion is the existing correlation between the morphology of etch pits and crystal structure. It is shown that a qualitative interpretation of the manifold etching phenomena on the above faces in a structure characteristic for GaAs can be given by including 1. the presence of primary defects as a constitutive property of real crystals and 2. the consideration of recordable influences of the surroundings.     

X-ray topographic investigation of growth defects in natural calcium fluoride crystals

Calcium fluoride crystals have been cleaved along {111} faces and the freshly cleaved faces have been chemically etched in 2.6 N nitric acid solution. The etched faces have been optically studied. One-to-one correspondence of dislocation etch pits have been established on the matched cleavage faces and on the opposite sides of thin flakes. The same crystal has been studied using X-ray topographic technique. By using 022 - and 02 2 reflections, stereopair projection topographs were studied and compared with the optical micrographs. The close resemblance between dislocation etch pits and dislocation out-crop images has been established. The orientation of the Burgers vectors of the dislocation lines has been identified using AgKα radiation with 111 -, 11 1- and 1 11 reflections. It has been confirmed that Burgers vectors of dislocation lines lie parallel to 〈110〉 directions. The implications are discussed.     

Ätzuntersuchungen an Alaunen mit nichtwäßrigen Lösungsmitteln. Will Kleber zum Gedenken

This paper presents investigations on etching of KAl-, NH₄Al-, KCr- and K(Al, Cr)-alum crystals. The etchant was a solution of tartaric acid in ethyl alcohol which produces well-defined etch pits on {111} faces. The correspondence of etch pits with dislocations was investigated by KAl-alum crystals. Between microscopic holes in the crystals and dislocations are not stated.     

Chiral Etch Pits on Sodium Chlorate Crystals

Microtopography of {100}, {110}, {111}, and {210} surfaces of sodium chlorate crystals etched in various solvents has been studied by optical microscopy. It has been established that etch pits formed on left- and right-handed crystals are chiral, and directions of dissolution steps reveal bond chains of the structure.     

Shape of thermal etch pits and crystal structure in tellurium crystals

During the systematic study of thermal etching of tellurium crystals, various shaped thermal etch pits were observed on the {101 0} cleavage faces of this crystal. An attempt has been made to explain the shape of non-dislocation and dislocation etch pits. A simple model based on crystal structure and bonding of atoms has been suggested to explain the shape of etch pits.     

水热法BSO晶体腐蚀像及与晶体对称的关系

对水热法生长的两种不同结晶习性的 BSO晶体进行了腐蚀像的观察研究,得到了{100}、{110}、{211}、{111}晶面的腐蚀形貌特征,建立了BSO晶体腐蚀像在三维空间分布的立体模型。研究发现不同单形晶面的蚀坑形态不同,但都体现了晶体的对称性。不同晶面腐蚀难易程度与晶体结构有关。     

Etching of CaF2 single crystals in silica gels

Etching of {111} cleavage faces of CaF₂ crystals in aqueous solution of 50% HCl is carried out in citric acid set silica gel, and the kinetics of growth of etch pits at the sites of dislocations is investigated as a function of temperature, time of etching and height of gel column above the crystal surface. It is observed that the transient period required to initiate etch pit at the sites of a dislocation decreases (1) at particular temperature, with a decrease in gel height, and (2) for a particular gel height, with an increase in the temperature of etching. It is also observed that the morphology of dislocation etch pits remains triangular irrespective of the gel height and the temperature of etching. The results are compared with those of solution etching and discussed.     

硫镓银晶体(112)面蚀坑形貌研究

本文报道了一种能在室温下对硫镓银晶体(112)面进行择优腐蚀的新腐蚀液配方,采用新腐蚀液对改进的Bridgman法生长的AgGaS2晶体进行腐蚀,用扫描电镜对蚀坑进行了观察,得到了清晰的(112)面蚀坑形貌,形状为三角锥形.初步解释了蚀坑的形成原因.AgGaS2晶体低指数的{100}面的腐蚀速度较慢,在腐蚀过程中逐渐显露出来,最终使晶体(112)面呈现出三角锥形蚀坑形貌.     

Zur Ätzstruktur von Silizium-Einkristallen,besonders in versetzungsfreien Bereichen

In silicon crystals a real etching structure can be visualized by means of a suitable method of etching also in the domains free from dislocations. The shapes of etch pits are chiefly dependent on the orientation of the grinding faces. It may be that the etching structure comes from growth domains, bordered by faces {111}, at which impurities are segregated or adsorbed.     

Causes of the formation of etch pits of different size and morphology on {100} faces of CsI crystals

Causes of the formation of dislocation etch pits of different shape and size on {100} faces of cesium iodide crystals by an etchant composed from 25–35 mg/1 CuCl₂ · 2 H₂O in 96% ethanol are studied. It is shown that one of the reasons of the change in the morphology of etch pits is the segregation of excessive iodine at dislocations.     

Zum Nachweis von Versetzungen in β-Kupferphthalocyanin-Einkristallen

An etching technique was developed to investigate dislocations in β-copper phthalocyanine single crystals. Considering the expected content of dislocations and the etch pit symmetry the symmetric etch pits are correlated to [010]-edge dislocations on {201 }- and {001}-lattice planes with (001)- and (201 )-slip planes. Asymmetric etch pits on {001}- and {201 }-planes are connected with [010]-edge dislocations related to (100)- and (101 )-slip planes. The dislocation density on growth planes and cleavage planes is commonly lower than 100 cm⁻². [010]-screw dislocations are not observed, but their existence could not be excluded.     

Evidence of slip in calcium fluoride single crystals

Natural single crystals of calcium fluoride have been cleaved along (111) planes and the cleavage faces have been etched in 0.2 N nitric acid solution. Etching produces rows of equally spaced etch pits running in <110>directions. One-to-one correspondence of glide bands has been established on the matched faces and on the three different flakes of the same crystal. This is further confirmed by studying the rosette structure produced on a (111) cleavage plane by indenting that plane itself. The active slip planes are found to be {110}. The implications are discussed.     

Studies on etching behaviour of {101} faces of natural mesolite crystals

Etching behaviour of {101} habit faces of natural mesolite crystals is reported. Rectangular, truncated and elliptical etch pits are illustrated, and mechanism of their formation is assessed. Factors influencing kinetics of etching are discussed. From Arrhenius plots activation energy and pre-exponential factor are computed and reported.     

Growth‐Sector Boundaries and Growth‐Rate Dispersion in Potassium Alum Crystals

Crystals of potassium alum, pure and slightly doped with Cr³⁺, were grown from aqueous solution by slow temperature lowering. In addition, short re‐dissolution periods were introduced in order to provoke growth defects and changes of growth rates. Crystal slices of about 1 mm thickness were studied by conventional LANG X‐ray diffraction topography using MoKα radiation. For Cr‐doped crystals, boundaries between {100}, {100} and {111} growth sectors appear by pronounced dynamical X‐ray topographic contrast similar to that of stacking faults. Re‐dissolution experiments provoke the formation of inclusions on {100} faces, followed by an increase of the {100} growth rate by the factor of about six, relative to the neighboured {111} faces. X‐ray topographs show that this increase is correlated with the formation of dislocations, which interestingly have pure‐edge character. During further growth these dislocations penetrate the {100}‐{111} growth sector boundary and vanish from the {100} face, which slows down and finally adopts its former growth rate before re‐dissolution.     

Microtopographical studies of ‘a’-faces of natural analcite crystals

Vertical striation, isolated elliptical natural etch pits, natural etch grooves, flat-bottomed natural etch pits on ‘a’-(prism) faces of natural analcite crystals are illustrated and described. Freshly exposed surfaces due to general dissolution of these faces are reported. Isolated, well defined eccentric rhombus shaped natural etch pits are illustrated and, it is established that they are nucleated at sites of emergence of inclined dislocations on the face. Rows of tiny rhombus shaped etch pits along horizontal lines perpendicular to c-axis are illustrated and explained.     

In situ Observed Twin Formation on ZnSe Crystals Growing by Sublimation

ZnSe crystals were grown by sublimation in closed ampoules between 1335 K and 1365 K. The growth was observed in situ with a video camera after an abrupt change of the supersaturation. The crystals developed preferably {110} faces. Repeatedly a nucleus was formed in ortho-twin position on a small {111} face which truncated the corner of three adjacent {110} faces. The repeated twin formation led to a preferred growth into the relevant 〈111〉 direction. The twinning already occurred at a low supercooling of less than 1 K and accelerated the growth distinctly.     

Growth and etching of calcite crystals

Single crystals of calcite (CaCO₃) have been grown by the method employed by GRUZENSKY , using an aquoeus solution of CaCl₂ and a solid (NH₄)₂SO₃, The chemical reaction takes place according to the following equation: CaCl₂ + (NH₄)₂SO₃ CaCO₃ + 2 NH₄Cl The crystals grown by this method are about 0.2 to 0.8 mm in edge dimensions. Synthetic calcite crystals have been cleaved along (100) planes and the cleavage surfaces have been studied by multiple beam interferometry. The interferograms have revealed that the cleavages are quite flat. The cleavage faces have also been chemically etched and the etch patterns studied optically. By etching a cleavage successively for three different periods it was found that the bottoms of the point-bottomed pits follow a linear etch path. By etching a cleavage pair, one face in one etchant and the other face in a different etchant and by comparing the etch patterns produced, before and after polishing a cleavage face it has been shown that the etch pits nucleate at the sites of dislocations in the crystal. The etch patterns have also been compared with those produced on the cleavage faces of natural crystals. The density of dislocations in the syntheitc calctie crystals was generally less than the density of dislocations in the natural calcite crystals. The implications have been discussed.     

Growth and dissolution of BaFCl crystals

Single crystals of BaFCl have been growth by flux technique using BaF₂ and BaCl₂. Etching with formic acid revealed dislocation etch pits on (001) cleavage faces of the crystals, at room temperature. The influence of etching parameters such as undersaturation, temperature and concentration of poison in the etchant is studied. Decreasing the undersaturation of formic acid by reducing the percentage of water and increasing the temperature of the etchant were found not to have any effect on the morphology of etch pits. However, as the CdCl₂ poison concentration is gradually increased, the orientation of the pits change from 〈100〉 to 〈110〉 at high concentration.     

H3PO4 — etching of {001}-faces of InP, (GaIn)P,GaP, and Ga(AsP)

This paper shows that hot H₃PO₄ is a suitable etchant for the production of dislocation etch pits on {001}-InP, (InGa)P, GaP, Ga(AsP), and {111}-GaP. The effects upon etch pit morphology of the misorientation of samples and the type of dislocations are investigated in detail.