Dislocation Etch Pits Research Articles

Influence of impurities on the etching of NaCl crystals

The effect of CdCl2, CuCl2·2H2O, MnCl2·4H2O and FeCl3·6H2O impurities and undersaturation on the rates of macroscopic dissolution,vp, lateral etching away from a dislocation line,vt, and normal etching along the dislocation line,vn, and on the surface micromorphology of the {100} face of NaCl single crystals in water, methanol and 96% ethanol is investigated. The dependence of etch rates on impurity concentration,ci, showed that the addition of a salt to the solvent always leads to a decrease invp, which attains a minimum value after a particular value ofci. The concentration dependence ofvt andvn is relatively complex, but often both decrease or increase simultaneously. A change in etch-pit morphology is caused by increasing the concentrations of all additives in ethanol and methanol. The dependence of etch rates on the undersaturation of methanol and methanol containing 10−3 M CdCl2 showed that dislocation etch pits are formed only for undersaturations greater than 0.02 and 0.06, respectively. These results as well as the roughening of etched surfaces at low impurity concentrations, the formation of terraced etch pits and the difference between etch pits at aged and fresh dislocations are discussed.

Surface Defects on MBE-Grown GaAs

The most common macroscopic defects in GaAs layers grown by MBE, i.e. oval defects, were studied. TEM observation shows that oval defects include stacking faults and that the crystalline quality is considerably inferior around these stacking faults. The successive optical microscopic observation of step-etched surfaces reveals that for an epitaxial layer with an oval defect density of more than 104/cm2, the majority of the oval defects originate in the epitaxial layer, while for an epitaxial layer with an oval defect density of less than 103/cm2, they originate at the interface between the epitaxial layer and the substrate. X-ray topography and observation of the dislocation etch pits clearly show that substrate dislocations are not responsible for the oval defects.

LPE growth and characterization of InP photodiodes

Advances have been made in understanding high-purity LPE growth, and several important materials parameters have been determined from measurements on high performance InP APD's. In particular, for the former, sulfur contamination resulting from opening the growth system to air can occur via adsorption on and re-evaporation from graphite. Also the type of fused silica used in the growth tube affects the rate of approach to equilibrium during baking. From the study of high performance InP APD's with grown p-n junctions we have determined the hole diffusion length L p ≈ 12 μm, appropriate to LPE material with N D− N A≈1 ×10 16 cm -3, by fitting the calculated to measured photocurrent versus voltage and versus n-layer thickness. This is an order of magnitude higher than L p's determined from EBIC, a technique that is not well suited to these long diffusion lengths. Messurements of dark current versus dislocation etch pit density show no correlation between these parameters; this is in contrast to work reported by other authors on junctions formed by diffusion. Impact ionization measurements have been made for the electric field parallel to 〈100〉 and 〈110〉 directions, and excess noise versus multiplication data have also been analyzed for these directions as well as <111. We find that there is not a measurable orientational dependence of the ratio of hole to electron impact ionization coefficients.

Plastic deformation and dislocation structure of single crystal mercuric iodide

A systematic investigation of plasticity in single crystal mercuric iodide was carried out. Over eighty compression tests were performed on single crystal specimens oriented variously with respect to the axis of loading. Three characteristic loading responses were observed and classified according to crystal orientation, as follows: (a) the direction of load was perpendicular to the [001] axis, (b) the loading direction was parallel to [001] and (c) the load was neither parallel nor perpendicular to [001]. In cases a and b, under sufficient load, the samples always exhibited brittle failure (without prior plastic deformation) whereas, in case c, the samples were always easily plastically deformed by slip of (001) planes. The case c plastic deformation also exhibited work hardening. A dislocation model for plasticity in mercuric iodide is induced from the experimental results. The model consists of “easy glide” dislocations, the cores of which are parallel to (001) planes, and “hard glide” dislocations that intersect the (001) planes. Movement of the easy glide dislocations causes the (001) slip in case c, whereas interactions between the easy and hard glide dislocations account for the work hardening. The results of other experiments (including creep, annealing, microscopic observation of dislocation etch pits, and bending) are consistent with the model. Deformation during large angle bending tests is a particularly remarkable phenomenon.

Influence of temperature upon dislocation mobility and elastic limit of single crystal HgI 2

The practical importance of studying mechanical properties and dislocation structure of HgI 2 is reviewed briefly. Specifically, the performance of single crystal HgI 2 radiation detectors is evidently sensitive to crystalline imperfections, including dislocations. The dislocation structure, in turn, may be altered during crystal growth and detector fabrication; the nature of such alterations depends upon the mechanical properties of the crystal and the stresses to which the crystal is subjected. This work examines the influence of temperature upon dislocation mobility and plasticity in vapor grown single crystals of mercuric iodide. Dislocation mobility is determined by measuring the lengths of the longest arms of dislocation etch pit rosettes on (001) surfaces following microhardness indentation and chemical etch. Measurements were made at temperatures ranging from room temperature to the phase transition temperature of 127°C. Dislocation mobility was found to increase with temperature, with the effect accelerating as the 127°C phase transition is approached. Increasing temperature was also found to lower the critical resolved shear stress for plastic deformation or slip on (001) planes. In these contexts, the vapor grown crystals are clearly “softer” at their elevated growth temperatures. The results are discussed in terms of a dislocation model involving “soft” and “hard” glide dislocations.

X-ray topographic investigations of solid state reactions. I. Changes in surface and bulk substructure during incipient thermal decomposition in sodium chlorate monocrystals

On heating, sodium chlorate monocrystals undergo a limited degree of thermal decomposition in the solid state (0.1-1 % mass loss) between 450 K and the melting point,ca. 535 K. The degree to which this occurs depends on the perfection of the sample, the more perfect crystals suffering lower mass loss. Examination of thermally treated pristine surfaces with a microscope reveals distributions of decomposition sites characteristic of the reaction initiating where emergent dislocations intersect the crystal surface. There is little correlation, however, between dislocation etch-pits and decomposition centres. X-ray topographic studies of changes in bulk substructure during thermal treatment confirm that ‘grown in’ dislocations play little or no part in the nucleation of the decomposition process in the bulk. There is some evidence, however, that they may contribute to the surface reaction. In the bulk, the potential nuclei are strained regions in the lattice. From these, and possibly as a consequence of decomposition, dislocation loops are punched out into the surrounding lattice along &lt;100&gt; and &lt;110&gt; directions. Similar defects are emitted from localized regions at the surface and it is possible that these give rise to the surface decomposition patterns. Impurity doped crystals show considerably enhanced decomposition.

Chemical etching of deformation sub-structures in quartz

Chemical etching of dislocations has been studied in natural and synthetic quartz single crystals, in deformed synthetic quartz and in naturally and experimentally deformed quartzites. The ability of different etchants to produce polished or preferentially etched surfaces on quartz is described. Dislocation etching was achieved on all crystal planes examined by using a saturated solution of ammonium bifluoride as the etchant. Appropriate etching times were determined for etching quartzites for grain size, subgrain boundaries, deformation lamellae, dislocations and twins. Growth and polished surfaces of synthetic single crystal quartz were similarly etched and dislocation etch pits, characteristic of various orientations were found. The use of ammonium bifluoride proved to be expecially advantageous for the basal plane, producing a polished surface with etch pits, suitable for dislocation etch pit counting. “Double” etch pits have been found on Dauphine twin boundaries on the basal plane and the first order prism, using this etchant. Slip lines and deformation bands were suitably etched on deformed synthetic crystal surfaces for identification of the slip planes. Other acidic etchants have been explored and their application to the study of deformation structures in quartz crystals is discussed.

Growth and dissolution of BaFCl crystals

AbstractSingle 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.

Surface morphology of the {010} faces of potassium hydrogen phthalate crystals

A detailed surface microtopographic study with the aid of highly sensitive differential interference and phase contrast microscopy has been carried out for the {010} faces of potassium hydrogen phthalate single crystals. Two types of growth hillocks could be identified: (i) macroscopic hillocks, emitting steps of considerable height (100–2500 A) from their centres, and (ii) shallow hillocks, being sources of growth steps of 14 A, which corresponds to one unit lattice translation. From a relationship between hillock centres and dislocation etchpits, the macroscopic hillocks were identified as a group of cooperating spirals, whereas the shallow hillocks are single spirals originating from single dislocations of unit height. Several properties of both spiral types are described, among which a relation between inclusion strings and the occurence of some of the macroscopic hillocks, the phenomenon of bunching of lower steps to higher steps, the formation of liquid inclusions via macrostep overhangs and the equivalence in advancement rates of steps of different heights.

Dissolution kinetics of MgO crystals in aqueous acidic salt solutions

The revelation and morphology of dislocation etch pits as well as the rates of macroscopic dissolution and selective etching on the {1 0 0} plane of MgO crystals in aqueous solutions of various inorganic salts are investigated in relation to the nature and concentration of salt in solution and the etching temperature. It is found that addition of a salt generally facilitates etch pit formation and that the rates of surface dissolution and selective etching increase with additive concentration, etchant temperature and character and ageing of dislocations, while the etch pit morphology depends on the concentration and chemical nature of an impurity, etching temperature and the ageing of the dislocations. It is also observed that some fast etching solutions produce very shallow etch pits at screw dislocations. The results are discussed from a consideration of solution pH, standard electrode potentials of metals and stability of complexes present in solution. The importance of the surface entropy factor in revealing etch pits at screw dislocations is pointed out.

Dislocation etch pit formation on non-metallic crystals

Experimental results available in the literature on selective etch pit formation on non-metallic crystals (excluding semiconductors) are discussed against the background of thermodynamic and topochemical adsorption theories of etching. The main purpose of the article is to deduce general principles involved in the formation of dislocation etch pits, and to better define the role of addition of salts to a solvent, of reaction products and solvents in etch pit formation. In addition, attention is focussed on the need for experimental determination of the absolute values of the parameters involved in thermodynamic theories in order to explain the results quantitatively.

On the morphology of dislocation etch-pits on cube faces of MgO in acids

On the morphology of dislocation etch-pits on cube faces of MgO in acids

X-ray topographic analysis of dislocation line defectsin calcium fluoride crystals

One-to-one correspondence of dislocation etch pits have been established on the matched cleavage faces and on the opposite sides of thin flakes of calcium fluoride crystals. By selecting 022 and 022 reflections and MoKα1 radiation, stereopair projection x-rays topographs were studied and critically compared with optical micrographs. The dislocation etch pits and dislocation out crop images show a close resemblance. The orientation of the Burgers vectors of the dislocation lines has been identified and these lines lie parallel to the <110> directions. The growth history of the stratigraphical pattern has been studied using x-ray topographic technique.

On the selective etching of KDP crystals

The etching characteristics of [100] and [101] surfaces of KDP in water, alcohols, acetone, organic acids and in their mixtures are investigated. It is found that a fast dissolving solvent produces better contrasting dislocation etch pits and is insensitive to surface orientation. The results are briefly analysed from theoretical considerations. Finally, some comments are made on the composition of selective etchants used for the crystals of dihydrogen phosphate group by previous workers.

X-ray topographic analysis of dislocation line defects in 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 and studied optically. One-to-one correspondence of dislocation etch pits has been established on the matched cleavage faces and on the opposite sides of thin flakes. The same crystal has been studied using an X-ray topographic technique. By selecting 0 2 2 and 02 2 reflections using Mo Kα 1 radiation, stereo pair projection topographs were studied and critically compared with the optical micrographs. The close resemblance between dislocation etch pits and dislocation outcrop images has been established. The orientations of the Burgers vectors of the dislocation lines have been identified using Ag Kα 1 radiation at 11 1 , 1 1 1 and 1 11 reflections. By using the dislocation contrast condition it has been confirmed that Burgers vectors of dislocation lines lie parallel to 〈110〉 directions. The growth history of the stratigraphical pattern has been studied using the X-ray topographic technique and the implications are discussed.

Cu結晶の(111)面転位ピットの形態変化について

Dislocation etch pits on the (111) surface of Cu crystals have been observed to study the effects of the composition, stirring rate and temperature of etchants and the small addition of Al in Cu. The etchants are Young’s solutions containing (NH4)2S2O8, NH4OH and NH4Br. The dislocation etch pit morphology strongly depends on the composition of the etchants. It is shown that the pit size varies with the concentration of the etchant and the pit shape varies with the ratio of each components in the etchant. At a ratio (NH4)2S2O8:NH4OH:NH4Br nearly equal to 1∼1.5:6:0.3, the triangular pyramid pits surrounded with 〈110〉 sides are produced, while, off this ratio, the etch pits tend to become more or less rounded. On the other hand, the stirring of the etchant increases the pit size remaining its shape unchanged. Such a tendency is also indicated with an increase of etchant temperature from 260 to 300 K, except a slight rounding of etch pit at 300 K. Moreover, with the addition of Al, the etch pits become small and rounded, though the straight-sided pits are revealed when etched with etchant containing high concentration of (NH4)2S2O8. Some discussions about the effects of the etching condition are given in connection with the kink nucleation and motion at the surface steps.

Crystal defects and dissolution

Potassium perchlorate crystals were grown in silica gel by reaction between perchloric acid in the gel and potassium chloride diffusing into the gel from a layer of solution on the gel surface. The crystals were harvested at depths from the surface of 0–1, 2–3, 4–6 cm. X-Ray diffraction and DSC thermograms showed that the crystals were identical and no impurities were detected by X-ray energy analysis. Octahedral crystals were selected, cleaved to expose the (001) plane and etched with a mixture of sodium sulfite and sulfuric acid. The dislocation etch pits were counted under surface illumination using a differential interference contrast microscope. Dislocation densities were approximately normally distributed with the mean densities being greatest at the 0–1 cm level where the growth rate was fastest and lowest at the 4–6 cm growth level where the growth rate was slowest. Bulk dissolution measurements, carried out under sink conditions in 95% ethanol using the USP rotating basket method, showed a positive correlation between the observed dissolution rate constant, K' obs, and the dislocation density. Dissolution rates increased with the number of dislocations such that an approximately 3-fold increase in mean dislocation density produced a 21% increase in K' obs.

Crystallographic polarity and chemical etching of CdxHg1−xTe

The absolute crystallographic polarity of CdxHg1−xTe crystals (x?0.2) has been determined using the anomalous scattering of x rays and correlated with the chemical etching characteristics. It is shown that Cr Kα radiation adequately distinguishes 333 and 3̄3̄3̄ reflections, and that the reflected intensities agree closely with theoretical calculations. Using a range of chemical etchants it is reported that dislocation etch pits are revealed on the (111) or A face, i.e., the face terminating with triply bonded Cd (Hg) atoms or singly bonded Te atoms, and not on the (1̄1̄1̄) or B face.

Dislocation activity in single crystal Hgl2

An etchant of 5% alcohol in trichloroethylene (TCE) allows greater resolution of dislocation etch pits in vapour-grown single crystals of Hgl2 than the “traditional” alcohol etches. The improved etchant has made possible the identification of etch pits, on the (001) faces of single-crystal Hgl2, that are associated with dislocations on {100}-type slip planes. The evidence for this conclusion includes (a) the geometric and crystallographic features of the etch pits, (b) the manner in which they are induced by deformation, and (c) their regularity in passing through the crystal, perpendicular to the (001) plane.

Defect‐Revealing Etches on GaAs : A Comparison of the AHA with the A/B and KOH Etches

AHA etch‐revealed features on {100} N+ wafers were compared to defects revealed by the well‐characterized A/B and molten etches on the same sample areas. It was demonstrated that the AHA etch technique reveals dislocation line segments, growth striae, and microdefects as does the A/B etch. Unlike the A/B etch the AHA etch did not result in a “memory” effect. A 1:1 correlation between molten dislocation etch pits and AHA‐revealed dislocation line segments was demonstrated.