Etching and kinetics of dissolution of Mo1−x WxSe2 single crystals

The dislocation etchant has been established for single crystals of Mo_1−xW_xSe₂ system. Effect of concentration of an etchant on the etch rate has been discussed. The morphology of etch pits is also described. The etch activation energies for all the compositions of these crystals for a particular concentration (7 N) of an etchant has been found out. The etch activation energies for a particular composition (x = 0.4) of crystals with different concentrations of an etchant have been investigated and the results have been discussed.     

Etching studies of tungstenite (WS2) crystals in acids

Single crystals of tungstenite (WS₂) have been grown by direct vapour transport or sublimation method. An etchant capable of revealing the sites of dislocations has been developed. The effects of etching time, etchant concentration and temperature on the selective etch rate have been worked out. It is seen that the etch rate is independent on time, but is influenced by the temperature and concentration of the etchant. The values of activation energy determined from the etch rate against temperature plots established that the process of etching in chromic acid is chemical reaction rate controlled. The effect of addition of HF to the above etchant has led to some further interesting results.     

Etch pit morphology and calcium sulphate growth on {111} faces of calcium fluoride crystals etched in sulphuric acid

An investigation of the etching behaviour of cleaved octahedral faces of calcium fluoride crystals in sulphuric acid of different concentrations and at various temperatures is carried out. It is observed that the morphology of dislocation etch pits depends on the temperature and concentration of the acid. With an increase in the acid concentration, growth of whiskers, elongated platelets, hexagonal and dice-shaped elevations, spherulites and sheaves is observed. Temperature of the etchant also has an effect on their formation. By X-ray diffraction techniques, the compounds forming the whiskers and elongated platelets, and hexagonal and dice-shaped features are identified as CaSO₄ · 2 H₂O and CaSO₄, respectively. The mechanism of the growth of CaSO₄ · 2 H₂O and CaSO₄ and the change in the morphology of selective etch pit are discussed.     

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.     

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.     

Crystal growth and dislocation structure of gallium antimonide

Single crystals of GaSb have been grown by the Czochralski method under reducing conditions. Crystals were grown in the 〈100〉, 〈111〉, and 〈112〉 directions. The 〈111〉 growth direction was found to be the most suitable for the successful and reliable crystal growth. Dislocation densities in 〈111〉 oriented crystals were examined by chemical etching. The etch pits density in these crystals didn't exceed the value of 1 × 10² cm⁻².     

Chemical kinetics of dissolution of BaMoO4 crystals

An etchant capable of revealing the sites of dislocations in the flux-grown crystals of BaMoO₄ has been established. Using this etchant (HNO₃), effect of etching time, acid concentration and temperature on the selective etch rate is demonstrated. It is established that the process of dissolution in unstirred HNO₂ solutions is one of the diffusion rate controlled; an empirical equation governing the kinetics has been suggested.     

Change in morphology and dislocation Etch Pits on the (010) Surface of Magnesium Orthosilicate Crystals

Investigations made on the etching behaviour of magnesium orthosilicate crystals in hydrochloric acid and melts of potassium and sodium hydroxides are described. It is shown that the morphology and orientation of the etch pits depend upon the concentration, composition and temperature of the etchant used. At low concentrations of HCl acid solution, the boat shaped pits produced are oriented along [100] direction while in concentrated acid, the hexagonal pits produced are oriented along [001] direction. At intermediate concentrations of about 5 N HCl acid the pits are square. KOH melt at 400 °C is found to produce rectangular pits with their longer sides parallel to [100] direction. The effect of a mixture of KOH and NaOH in different proportions in the melt is investigated. It is observed that square pits are obtained in melt of the mixture of KOH and NaOH in the proportion of 6:4 respectively. The mechanism responsible for the change in orientation of etch pits have been explained. The implications are discussed.     

Eccentricity of symmetrical and asymmetrical etch pits on calcite cleavages

There are two types of chemical eccentric etch pits.

• (1) Deepest points are always lying on the shorter diagonal. – Symmetrical etch pits the deepest points of which lying on the diagonals show dislocation lines in the plane (110). Eccentricity of symmetrical etch pits along the [110] direction is depending on the concentration of the etchant and on the inclination of the dislocation line in the plane (110).
• (2) Depth points do not lie on any diagonals. Eccentricity of asymmetrical etch pits along the [110] direction is depending on the concentration of the etchant and on the inclination of the dislocation line in the plane (110).

     

Selective etching of ZnTe in HF:H2O2:H2O solution: Interpretation of extended defect‐related etch figures

HF:H₂O₂:H₂O solution (40%wt.HF: 30wt.%H₂O₂: H₂O, 3:2:1 by volume) was used to reveal extended defects (line, face and volume defects) in bulk ZnTe crystals grown from Te solution. The etch patterns were analyzed based on their size, shape and distribution. The etch figures, both in the shape of pits and hillocks with high resolution, show forms controlled by the symmetries of the respective faces were produced. Two different sizes of pits were observed, the larger‐size pits correspond to dislocations penetrating the surface, however, the smaller‐size texture pits are produced on the defect‐free region, which serve as standard pits on respect faces. The face defects, such as grain boundaries, sub‐grain boundaries, dislocation walls, twins and stacking faults, can be all displayed clearly. Another essential feature of the etchant is that, it can effectively dissolve Te‐rich phase (Te inclusion/precipitates), which makes it promising to reveal the shape of this volume defect.     

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.     

Dislocation etching of tin iodide single crystals

Single crystals of tin-iodide (SnI₂) have been grown using the controlled reaction between SnCl₂ and KI by diffusion process in gel medium. As grown (010) surfaces of the crystals have been optically studied. Characteristic etch pits have been observed on them. This suggests that SnI₂ crystals might go into dissolution in the acid-set gel. By successively etching (010) surfaces in a mixture of ammonia, acetic acid, and CdCl₂ solution, it is established that the pits indicate the site of dislocations in the crystals. This is further confirmed by comparing the etch patterns before and after chemically polishing (010) surfaces. The average dislocation density in the crystals have been evaluated and found to be 3.2 × 10³ cm⁻² and the implications are discussed.     

Dislocation etch pits in anhydrous diglycine sulfate

New dislocation etchants for anhydrous diglycine sulfate single crystals have been developed and the etching results are reported. Dichloroacetic acid, glacitel acetic acid and their mixtures work as dislocation etchants on the cleavage plane of the crystal. Morphology of the etch pits was found to vary with the etchant composition.     

碲锌镉单晶体的(110)面蚀坑形貌观察

本文报道了一种能够在室温下择优腐蚀碲锌镉(CZT)单晶体(110)晶面的腐蚀液配方,并对富Cd生长的CZT晶体蚀坑形貌进行了扫描电镜观察.结果表明晶体(110)面腐蚀坑形状为三角形,并初步对蚀坑的成因进行了分析,估算出CZT(110)面蚀坑密度约为103～105/cm2数量级.这说明富Cd原料的改进布里奇曼法可以生长出低蚀坑密度的CZT单晶体.     

Etching Studies on Potassium Dichromate (KBC) Crystals

An investigation of the revelation of dislocations in potassium dichromate (KBC) crystals by etching in water, alcohls, and in inorganic acids mixes with acetone and alcohols is carried out. It is observed that several solutions including water, alcohols and organic acids produce disslocation etch pits on various faces of KBC crystals. Observations of twining and dissolution anisotorpy of (001) faces are also presented. Etching of (001) cleavage faces of same crystals in an etchant composed from 1 part HNO₃ and 3 parts acetone indicates the possible growth of another phase at low temperatures.     

Controlled synthesis of Cu2O cubic and octahedral nano‐ and microcrystals

Cubic and octahedral Cu₂O nano‐ and microcrystals were selectively synthesized via a simple wet chemical reduction route at room temperature, with CuCl₂ and NaOH as starting reactants, and ascorbic acid or hydrazine hydrate as the reducer. Hydrazine hydrate could be preferentially adsorbed on different crystal faces of Cu₂O, affecting the growth rate along the 〈100〉 to that along the 〈111〉 direction, which resulted in the formation of octahedral Cu₂O crystals. When ascorbic acid was used as the reducer, the growth rate along the 〈100〉 to that along the 〈111〉 direction was different, which resulted in the formation of cubic Cu₂O crystals. The size of cubic and octahedral Cu₂O crystals could be varied by adjusting the molar ratio of OH^– to Cu²⁺. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dislocation studies by chemical etching on solution-grown NaSbF4 and Na3Sb4F15 single crystals

An attempt has been made to study the etch pit dislocations of isolated as well as matched pairs of cleavage planes of solution grown NaSbF₄ and Na₃Sb₄F₁₅ single crystals when etched with analar grade methyl alcohol and ethyl alcohol. On etching of cleavage faces the pits nucleate at the intersection sites of dislocations with the cleavage face. On successive etching of a cleavage face, arrays of triangular shape etch pits are observed. After prolonged etching some of the etch pits disappear. These pits are curved and terminated indicating that they are crystallographically non-oriented. One-to-one correspondence with respect to number, shape, position and structure of the pits has been established by etching of a matched cleavage face. The etch pit densities of both NaSbF₄ and Na₃Sb₄F₁₅ crystals are found to be 10³ per cm².     

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.     

Growth of Li2CO3 Single Crystals by Zone Melting Technique

Li₂CO₃ single crystals have been grown by zone melting technique in carbondioxide atmosphere. The diameter of the grown crystal depends on the growth rate. The quality of the crystal depends on the growth rate, temperature of the molten zone, choice of the seed and the temperature of the auxiliary furnace. The crystal shows cleavage plane. The etch studies on cleavage planes show that the etch pits are always triangular in character.     

Effect of Impurities on the Etching of Sodium Chloride Crystals

The results of a study of the effect of HgCl₂, ZnCl₂, PbCl₂ and CaCl₂ on the surface micro-morphology and kinetics of etching of {100} planes of NaCl crystals in methanol and ethanol are described and discussed. It was found that addition of an impurity to the solvent leads to the formation of contrasting dislocation etch pits, and that the overall dissolution rate in a solvent decreases with an increase in additive concentration. In the case of HgCl₂ impurity added to methanol terraced etch pits are observed, but their terracing behaviour diminishes with the increasing impurity concentration.