Ätzuntersuchungen an natürlichen Spaltflächen von (Ga,Al) As/GaAs-Heterostrukturen

This communication reports on etching of {110} cleaved faces of (Ga,Al)As/GaAs heterostructures with and without an additional pn-junction. The etching agents are dilute HNO₃ and mixtures of NH₃ and H₂O₂. The lines appearing in the etch patterns are attributed to the related steep changes in the physicochemical features of the crystals. The etch patterns can be correlated with the aluminum concentration profiles throughout the epitaxial layers as obtained by electron microprobe analysis. The optimum temperatures, times and compositions of the etch solutions are given. Preferential etching of GaAs by NH₃/H₂O₂ mixtures is 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.     

Biscyclopentadienides with transition metal-mercury bonds. II: Dithiocarbamato derivatives of molybdenum and tungsten,and X-ray structure of (η5-C5H5)2Mo[HgS2CN(C2H5)2]2

The reactions in THF or benzene between Cp₂ M (HgX)₂ ·x HgX ₂ (M = Mo or W; O ?x ? 1;X ^? = Cl^?, Br^?, I^?, SCN^?, OAc^?) and sodium diethyl-dithiocarbamate $$\begin{gathered} Cp_2 M\left( {HgX} \right)_2 .xHgX_2 + \left( {2 + x} \right)Nadtc \rightleftharpoons Cp_2 M\left( {Hgdtc} \right)_2 \hfill \\ + xHg\left( {dtc} \right)_2 + \left( {2 + x} \right)NaX \hfill \\ \end{gathered} $$ as well as between Cp₂ MH₂ and mercury diethyldithiocarbamate $$x2Cp_2 MH_2 + 2Hg\left( {dtc} \right)_{2 - } Cp_2 M\left( {Hgdtc} \right)_2 + \left\{ {Cp_2 Mdtc} \right\}dtc + 2H_2 $$ give the compound Cp₂ M(Hgdtc)₂ (dtc is diethyldithiocarbamate anion). The structure of the molybdenum complex determined by the X-ray method (a = 12.776(4),b = 7.835(4),c = 27.397(7) Å β = 111.18(2) °; space groupC2/c (No. 15);Z = 4) consists of discrete molecules occupying special positions on two-fold axes. A short Mo-Hg distance of 2.643(8) Å and a rather long Hg-S one of 2.50(2) Å were found. The diethyldithiocarbamate anion behaves like a monodentate ligand. IR and¹H,¹³C NMR results agree with the molecular structure determination and confirm a weak bond between mercury and dithiocarbamate and strong molybdenum-mercury bond. A considerable solvent effect (C₆D₆ vs. CDCl₃ solutions) has been observed on the¹H chemical shifts of both dtc and Cp ligands. The {Cp₂Modtc}⁺ X ^? (X = dtc and PF₆) complexes, although not obtained in a pure form, were included in the discussion of the spectroscopic features of those with theM-Hg bonds.     

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.     

Synthesis,Crystal Structure and Spectroscopic Characterization of {6-[2-(2-chlorophenyl)-1,3-thiazol-4-yl]-2-oxo-1,3-benzothiazol-3(2<Emphasis Type="Italic">H</Emphasis>)-yl}acetic acid

Abstract  

The title compound {6-[2-(2-chlorophenyl)-1,3-thiazol-4-yl]-2-oxo-1,3-benzothiazol-3(2H)-yl}acetic acid was prepared and characterized by elemental analyses, FT-IR, ¹H NMR spectroscopy, X-ray diffraction. A quantum-chemical calculation was performed using the CNDO method. In the title compound, C₁₈H₁₁ClN₂O₃S₂, the crystal structure is stabilized by intermolecular hydrogen bonds (C–H···O=C) to form centrosymmetric R₂² R_{2}^{2} (16) dimers and the C–H···O, O–H···N, and C–H···N interactions generating the graph set motifs R₂² R_{2}^{2} (9) and R₂² R_{2}^{2} (22).     

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.     

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.     

Structural Etching of {001} and {110} Faces of Various AIIIBV Compounds

The present paper discusses the use of selective photoetching with H₃PO₄:H₂O₂ for characterizing various A^IIIB^V compounds and detecting misfit dislocations in transition layers. For GaP, the results obtained are compared with those realized with the use of an AB etchant for which suitable conditions for the structural etching of {001} material and the characterization of cleavage faces are given. The direction of the dislocation line is inferred from the shape and orientation of etch pits. The etch figures of different types of misfit dislocations are discussed.     

Controls on Morphology of Analcime-Pollucite in Natural Minerals,Synthetic Phases,and Nuclear Waste Products

Crystals of the analcime-pollucite series (NaAlSi₂O₆ · H₂O CsAlSi₂O₆) exhibit tetragon-trioctahedral {211} and hexahedral {100} morphology, with rare modification by tetrahexahedral {210} or rhombic dodecahedral {110} forms. Under weakly acidic to weakly basic conditions {100} is dominant; with increasing alkalinity (cation concentration), basicity (pH), and temperature {211} is dominant over {100}, with minor development of {210}. The morphology does not appear to be influenced by broad ranges in Si/Al (from 2.0 to 2.6 in the natural minerals) and Na-Cs contents between analcime and pollucite, by substitutions of univalent cations Li, K, Rb, and Tl, or by small amounts of divalent cations Mg, Mn, Ni, Zn, Fe. Larger amounts of Ca, however, and possible substitutions for framework Al and Si seem to produce a more complex morphology.     

Twin Structure of (La,Nd)GaO3 Solid Solutions

For La_1‐xNd_xGaO₃ crystals the La‐Nd substitution leads to decrease of spontaneous strains and for composition with x≈0.32 the six possible twin states of orthorhombic phase (m3mFmmm) may be degenerated in three twin states inhered in m3mF4/mmm species when a distorted perovskite pseudocell becomes tetragonal. The {110} and {112} reflection twins and axial twins with compositional planes close to (211) and (21‐1) (S‐walls) were identified in La_1‐xNd_xGaO₃ (x=0.07, 0.12, 0.20) solid solutions crystals. All observed twins are typical for crystals with GdFeO₃ type perovskite‐like structure. It has been shown that for x≤0.2 and x≥0.5 orientations of S‐walls weakly depend on La/Nd ratio, whereas in the range of 0.2<x<0.5 they depend strongly on the solid solution composition. The tilt angle between two twin states across twin boundary in La_1‐xNd_xGaO₃ (x<0.6) solid solutions is smaller than that between two twins in pure LaGaO₃ or NdGaO₃.     

Single crystal synthesis and properties of lithium-gallium-, lithium-aluminium-oxide and mixed compounds (I) growing of LiGaO2-, LiAlO2- and LiAlxGa1−x crystals from fluxes

LiGaO₂ forms a single eutectic with PbO/B₂O₃ (molar ratio 9:4). A nearly linear slope of the liquidus curve is followed by a steep rise of the temperature coefficient of solubility. The solvent power at 1300°C is 0.35 g LiGaO₂/g PbO, B₂O₃; from 1000 to 1300°C there exist only poor differences in solubility of LiGaO₂ and LiAlO₂ in PbO/B₂O₃. LiGaO₂ crystals up to 1 p in weight grew spontaneously by slow cooling from fluxes or by evaporation of the solvent, those of about 1–1.5 p from seeds by cooling stirred fluxes. LiAlO₂ crystals are essentially smaller (6 mm). – By partial substitution of Ga₂O₃ by Al₂O₃ mixed crystals LiAl_xGa_1−xO₂ result. In the case of x ≦ 0.5 the coefficient of segregation remains ≦1. The al concentrations along the polar axis decrease by more than 25 p.c., perpendicular to [001] they keep constant till to the crystal surface. – Crystals show hypermorphism from mm2 to mmm. With high initial exceedings only {110} and {011}, with lower ones also {120}, {130}, {210} and {310} as well as the reduced {100}, {010} combinations are observed. – LiGaO₂ crystals grow by nucleous, sceletal or faceted growth resp. during the cooling period. – Primarily at 1270°C formed nuclei up to 1150°C grow to critical dimensions (≈0.5 mm) and develop to the main branch along [001]. Primary branches deflect to [010]. The convex secondary branches intergrow along (110), often including flux. With decreasing temperature a new crystallisation front is formed at the periphery leading to a stable faceted growth at about 1000°C.     

The synthesis and molecular structures of 2,5-diarylpyrroles, [{\text{pyr}}^{{\text{Ar}}_{\text{2}} } ]H (Ar = Ph, 2,4-Xyl)

2,5-Di(2,4-xylyl)pyrrole, H, has been synthesized by reaction of the diketone [XylC(O)CH₂]₂ with NH₄OAc in AcOH; the diketone itself is obtained by condensation of XylC(O)Me with XylC(O)CH₂Br in the presence of Ti(OPrⁱ)₄. The molecular structures of both H and H have been determined by single crystal X-ray diffraction, thereby demonstrating that an ortho methyl substituent increases the dihedral angle between the aryl and pyrrolyl groups from 14.5° in H to 24.1° in H.     

Crystal and Molecular Structure of Bis{2,6‐bis(hydroxymethyl)pyridine‐O,O,N}{μ‐bis(2‐hydroxymethylpyridyl)methanolate‐O,N}dicopper(II)di(propionate). First example of non‐coordinate propionate anoins

Bis{2,6‐bis (hydroxymethyl) pyridine‐O,O,N} {μ‐bis(2‐hydroxymethylpyridyl) methanolate‐O,N} dicopper(II) di(propionate) (CCDC 143763) has been prepared and studied by single‐crystal X‐ray diffraction methods at 293(2) K. The crystal structure consists of dimeric complex cation, [Cu₂(μ‐bhmp)₂(bhmpH)₂]⁺² and propionate anions (bhmp ‐ 2,6‐bis(hydroxymethyl) pyridine; bhmpH ‐ 2‐(6‐hydroxymethylpyridyl) methanolate ) and propionate anions. The complex cation contains two neutral and two monodeprotonated bhmp molecules, each coordinate to one Cu(II) atom in a tridentate chelating manner, via two O atoms and N atom. The monodeprotonated bmph molecules are also tridentate coordinate via N atom and only one O atom, which serve as bridge between two CuO₄N₂ moieties. The propionate anions are “ fixed” to the complex by the hydrogen bonds.     

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.     

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.     

The nature of spontaneous twisting of (NH4)2SO4 crystals at the curie point

Spontaneous twisting of (NH₄)₂SO₄ crystals at the phase transition from the paraelectric phase Pnam to the ferroelectric phase Pna2 (T _C = 223 K) was studied using the method of low-frequency torsion pendulum. It is shown that the macroscopic twisting of samples is caused by the rearrangement of ferroelastic twins with the {011} and {031} twinning planes existing in both the paraelectric and ferroelectric phases. A model interpreting the effect of the spontaneous twisting below the ferroelectric Curie point is proposed.     

Synthesis,characterization and single crystal x-ray analysis of a complex of iron(II) bis(2,4-dimethylphenyl)dithiophosphate with 4-ethylpyridine

Complex of iron(II) bis(2,4-dimethylphenyl)dithiophosphate with 4-ethylpyridine [{(2,4- (CH₃)₂C₆H₃O)2PS2}2Fe{NC₅H₄(C₂H₅)-4}₂] is synthesized and characterized by elemental analysis, magnetic moment, IR spectroscopy and single crystal X-ray analysis. Complex crystallizes in the monoclinic sp. gr. P2₁/n, Z = 2. Crystal structure consists of mononuclear units with Fe(II) ion chelated by four S atoms of the two diphenyldithiophosphate ligands in bidentate manner. N atoms from two 4-ethylpyridine ligands are axially coordinated to the Fe(II) atom leading to an octahedral geometry.     

Magnetic properties of the CrSxTe1−x (x = 0−0.2) solid solutions

On the basis of X-ray, magnetic and neutron diffraction measurements the range of solubility in the CrS_xTe_1−x (x = 0−0.2) system has been established and the magnetic phase diagram of the system has been plotted. The decrease of magnetization at low temperature and the additional reflections in the neutron diffraction patterns are associated with the formation of noncollinear magnetic structure which is characterized by the antiferromagnetic component of the magnetic moments. This component has the orthorhombic unit cell with \documentclass{article}\pagestyle{empty}\begin{document}$ a_M = \sqrt {3a_0 } $\end{document}, b_M = a₀, c_M = c₀. The character of the exchange interactions giving rise to this magnetic structure is discussed.     

Twinning Morphologies and Mechanisms of β-BaB2O4 (BBO) Crystal Grown by TSSG Method

The twinning morphology of β-BaB₂O₄ crystal grown by TSSG has been studied on the basis of crystallography. It was found that the faces R{101-2} and r{011-4} are often intergrown together by either r{011-4} intergrown in R{101-2} or in reverse, two individuals mostly take X(112-0) and occasionally take Y(011-0) as twin boundary; and that two individuals in the twin could take the same or opposite crystallographic polarity, this was identified by surface etched figures and the piezoelectric measurements. The formation of the twinned crystals are discussed from the crystallographic structural characteristics and the energetic considerations. The experimental factors such as crystal seed quality are suggested to reduce or eliminate the twin formation and to improve the crystal quality.     

The Morphology of Hydrothermally Grown Plagioclase

Plagioclase crystals Ab₂₀An₀₀ and nearly pure anorthite were grown on the surface of artificial melts by hydrothermal treatment at 2 kb. The average crystal size was 0.002 to 0.008 mm. In the temperature range of 400° to 600°C a pseudohexagonal habit was observed for anorthite while a lath-like habit due to the prevalence of {010} was found for the Ab₂₀An₈₀ composition. Dominating faces are {010} {130} {110} {100} {110} {130} in the zone [001] and {021} {111} {111} {021} {111} {111} together with {001}.