Hydrothermal etching as a method of quartz quality control of density and distribution of dislocations

Abstract

In this paper the effective non-destructive method of hydrothermal etching of crystals is considered to carry out estimation of density and place of dislocations in large scaled crystals of synthetic quartz. In this process of etching there are specific etch figures which appear as faceted holes of a millimetre up to several millimetres in size on all quartz facets. The size of holes depends on concentration of solution, duration of the process of etching and degree of solution saturation by silicon dioxide. The configuration of the holes on the facets of different indexes is various. Pits of symmetry, having facets, correspond to each facet there. Zcrystals are basic in quartz production. In sectional operation the expedients of defection of dislocations in pits generated on a facet are considered (0001).     

Grain-boundary faceting at a = 3, [110]/{112} grain boundary in a cubic zirconia bicrystal

The atomic structure of a = 3, [110]/{112} grain boundary in a yttria-stabilized cubic zirconia bicrystal has been investigated by high-resolution transmission electron microscopy (HRTEM). It was found that the grain boundary migrated to form periodic facets, although the bicrystal was initially joined so as to have the symmetric boundary plane of {112}. The faceted boundary planes were indexed as {111}/{115}. The structure of the {111}/{115} grain boundary was composed of an alternate array of two types of structure unit: {112}- and {111}-type structure units. HRTEM observations combined with lattice statics calculations verified that both crystals were relatively shifted by (α/4)[110] along the rotation axis to form a stable grain-boundary structure. A weak-beam dark-field image revealed that there was a periodic array of dislocations along the grain boundary. The grain-boundary dislocations were considered to be introduced by the slight misorientation from the perfect = 3 orientation. The fact that the periodicity of the facets corresponded to that of the grain-boundary dislocations must indicate that the introduction of the grain-boundary dislocations is closely related to the periodicity of the facets. An atomic flipping model has been proposed for the facet growth from the initial = 3, {112} grain boundary.     

Coupled motion of [10−10] tilt boundaries in magnesium bicrystals

Magnesium bicrystals were grown with symmetric and asymmetric tilt boundaries about the [10–10] axis using the vertical Bridgman technique. Isothermal constant load tensile tests were conducted on these bicrystals in the temperature range 300–500°C and relative displacements of the two grains were measured to obtain an appreciation for grain boundary motion characteristics. Coupled grain boundary motion was noted in almost all cases with the degree of tangential motion versus migration changing with tilt misorientation, temperature and applied stress. Specifically, within the family of symmetric bicrystals evaluated, a minimum in grain boundary displacement in the specimen plane was observed at a tilt misorientation of 20°. In specific stress/temperature regimes, rigid body sliding was observed for the particular case of a 35° asymmetric tilt misorientation. The ease of basal and prism slip in magnesium at the temperatures considered and the consequential impingement of intragranular dislocations on the bicrystal boundary and their decomposition and motion along the boundary are thought to play an important role in the observed coupled motion of these tilt boundaries.     

Solid-state morphology of aromatic-aliphatic polyester crystallized from smectic liquid crystal

The solid-state morphology of poly(hexamethylene p,p'-bi-benzoate) (BB-6) and its dependence on the texture of the smectic liquid crystal state from which it crystallized were studied using electron microscopy, polarizing optical microscopy, and small-angle x-ray diffractometry. Thin films of BB-6 suitable for the microscopy were prepared by casting a hot solution of the polymer in tetrabromoethane onto mica at 150°C. The as-cast film of BB-6 was first heated to 260°C, maintained in the smectic range (210°C), and then cooled gradually to room temperature. A number of types of defect structures—such as Dupan cyclides, edge dislocation, tilt walls, and disclinations — were observed in the solid BB-6 formed from the smectic melt. On the basis of the electron microscopy and small-angle x-ray diffractometry, it is suggested that folded-chain crystals are formed during the crystallization from the smectic melt. Electron microscopic observations of the solid BB-6 and its orientation behavior under shear can be reasonably explained by assuming the presence of a precursory chain-folded layer structure in the smectic liquid crystal of BB-6.     

Thermally stimulated luminescence origin in LiF crystals irradiated in a reactor at different temperatures

Thermally stimulated luminescence as well as optical absorption and emission spectra have been studied in LiF crystals irradiated in a reactor at different temperatures. It was shown that aggregate colour centres give rise to thermally stimulated luminescence peaks registered below 450°C. Peak at 470°C is observed only in crystals that have been irradiated at standard temperature of the reactor experimental channels. The peak is caused by interaction of dislocations and F centres.     

Accommodation of the Lattice Mismatch at the VCx-WC Interface

A VC doped WC-Co alloy is investigated using high resolution transmission electron microscopy. The VC grain growth inhibitor induces the presence of a thin layer on the surfaces of the WC grains in contact with Co and precipitates in the corners of Co pockets. These (VW)C_x compounds adopt an epitaxial orientation relationship with regards to the (0001) base facets of the WC crystals. Due to the small difference in lattice parameters, misfit dislocations are expected in the interfaces. Unlike the thin layers where no defects are observed, two kinds of dislocations are pointed out for larger precipitates. 1/6〈112〉_VC interfacial dislocations are sometimes present while more often 1/2〈1¯10〉_VC dislocations lying above the interface in the (VW)C_x phase are visible.     

Multiple quantum well structures and high-power lasers of gaas- algaas grown by metalorganic vapor phase epitaxy (MOVPE)1

GaAs/AlGaAs GRIN-SCH type multiple quantum well lasers with four wells of 11 nm GaAs, grown in an MOVPE chimney reactor, exhibit an output power as high as 110 mW/facet (CW, 30°C; 5 μm stripe) and 1.3 W/facet (pulsed, 30°C; 53 μm stripe) until catastrophic optical damage occurs. 2000 hours life tests conducted at 60°C and 15 mW CW show no noticeable degradation for the 5 μm stripe laser with a reflective coating on both facets. Raman spectroscopy on similar multiple quantum well structures with 65 GaAs wells is used to ascertain that the wells have minimum residual aluminum- content.     

Crystallographic analysis of lightly facetted cylindrical crystals

A method is described for determining the crystallographic orientation of cylindrical crystals from the geometry of surface facets. The method is applied to individual grains in polycrystalline wire samples having a bamboo structure, where classical methods of orientation determination, such as electron and X-ray diffraction, are inapplicable. In addition to providing information on the orientation of grains, the methods identifies the crystallographic orientation of the facets, which is of potential importance in studies of facet formation.     

Generation of dislocations introduced by bending stress in a Si wafer

Distribution and morphology for dislocations introduced in (001) Si wafers subjected to bending stress at 800°, 900°, and 1100°C were investigated. For wafers bent around a [110] axis at 900° and 1100°C, straight dislocations appeared along the [110] direction only near the neutral plane, and were absent at the surfaces where bending stress is greatest. However, for wafers bent at 800 °C, such straight dislocations were not formed. Dependence of the dislocation distribution and morphology on heat treatment temperature is explained on the basis of interaction between bending stress and SiO₂ precipitates introduced in bulk. Also, it was found that the straight [110] dislocations remained still near the neutral plane, even when additional reverse bending stress was applied around an axis parallel to the dislocations, but were transfered toward the tensile surface by bending around an axis normal to the dislocation direction.     

Ordinary dislocation configurations in high Nb-containing TiAl alloy deformed at high temperatures

Abstract

High Nb-containing TiAl (Nb–TiAl) alloys possess mechanical properties at elevated temperatures superior to conventional TiAl alloys. However, the strengthening mechanisms induced by Nb addition have been discussed controversial for a long time. In the present study, the dislocation structures in a polycrystalline high Nb–TiAl alloy after tensile tests at 700 and 900 °C were investigated by transmission electron microscope (TEM) observation. The results show that abundant double cross slip of ordinary dislocations is activated in the samples deformed at 700 °C. The dislocations are pinned at the jogs and numerous dipoles are observed. Debris can be commonly observed in the vicinity of screw dislocations. Trace analysis shows that the cross-slip plane is (1?1?0)γ at 700 °C but (1?1?1)γ octahedral plane at 900 °C. Three-dimensional (3D) dislocation structures, caused by cross-slip and annihilation of ordinary dislocations, were observed along the screw orientation. The dipoles and debris produced by high-temperature cross slip can be important for the strengthening of high Nb–TiAl alloys.     

The interactions between dislocations and ferroelectric domains in KNbO3 crystals

It is found that it is rather easy to introduce dislocations into KNbO₃. With transmission electron microscopy we have determined the slip plane to be (110) and the Burgers vector of dislocations to be [110]. Using hot stage in a JEM-200CX electron microscope, we have made in situ observations during phase transitions at 435°C (cubic-tetragonal) and 225°C (tetragonal-orthorhombic). We have found evidence indicating the interactions between dislocations and ferroelectric domains. Especially during phase transitions, the new ferroelectric phase first appear in the vicinity of dislocations showing that the stress field of dislocations may raise Curie point of the crystals.     

Dislocation content of geometrically necessary boundaries aligned with slip planes in rolled aluminium

Previous studies have revealed that dislocation structures in metals with medium-to-high stacking fault energy, depend on the grain orientation and therefore on the slip systems. In the present work, the dislocations in eight slip-plane-aligned geometrically necessary boundaries (GNBs) in three grains of near 45° ND rotated cube orientation in lightly rolled pure aluminium are characterized in great detail using transmission electron microscopy. Dislocations with all six Burgers vectors of the ½?1?1?0? type expected for fcc crystals were observed but dislocations from the four slip systems expected active dominate. The dislocations predicted inactive are primarily attributed to dislocation reactions in the boundary. Two main types of dislocation networks in the boundaries were identified: (1) a hexagonal network of the three dislocations in the slip plane with which the boundary was aligned; two of these come from the active slip systems, the third is attributed to dislocation reactions (2) a network of three dislocations from both of the active slip planes; two of these react to form Lomer locks. The results indicate a systematic boundary formation process for the GNBs. Redundant dislocations are not observed in significant densities.     

High-resolution transmission electron microscopy study of crystallography and morphology of TiC precipitates in tempered steel

In spite of the significance of NaCl-type transition-metal carbides in steels, their crystallography and morphology have not been understood on an atomic scale. High-resolution electron microscopy was employed in the present work to examine the crystallography and morphology of TiC particles that precipitated in the quenched and tempered 0.05?wt%?C–0.20?wt%?Ti–2.0?wt%?Ni steel. Plate-like TiC precipitates with a thickness ranging from a couple of atomic layers to 20?nm were observed in steels by tempering at 550, 600 and 800°C. It was found that the Baker–Nutting orientation relationship is always satisfied with the ferrite matrix within about 5° for both the nanosized and the coarse TiC particles. The habit plane of the TiC precipitate is the (100) ferrite plane. A moderate tendency for the faceting of lateral interfaces on the {001} and {011} ferrite planes was found. The presence of interfacial misfit dislocations was revealed by examining the excess lattice fringes terminating at the interfaces between the TiC platelet and the ferrite matrix. The location and number of the excess lattice fringes terminating at the broad plane and the lateral interface were consistent with the mismatch in the atomic arrangement between the Baker–Nutting orientation relationship related TiC and ferrite.     

硅中位错与蚀斑的对应关系

通过实验肯定了硅单晶的化学侵蚀定向方法,找出抛光液的最佳配比及抛光时间。确定了所选定的位错侵蚀剂的侵蚀规范;此侵蚀剂对晶面无选择性,能显示出刃型和螺型位错,以及“新”、“旧”位错。通过长时间侵蚀、逐层侵蚀、劈裂面蚀斑的对应、小角晶界上蚀斑的观察、形变硅单晶中蚀斑排列以及弯曲形变样品中蚀斑密度与曲率半径间的关系的研究等方法,证明了用此侵蚀剂所得的蚀斑确实与位错一一对应。     

Indentation studies of alkali halides at elevated temperatures

The hardness of NaCl and KCl crystals has been estimated from the lengths of dislocation rosette formed around indentation at various temperatures up to 400°C. The hardness decreases with increasing temperature. This is due to the softening of the crystals at elevated temperatures which results in the easy movement of dislocations. The results are discussed using a few available relations which connect hardness to temperature. Arms of indentation dislocation rosette are well defined up to 300°C but around 400°C the rosette pattern is spread over a circular region. A possible mechanism is discussed.     

Metallic thin film growth on vicinal Cu substrates

In this study we have investigated the heteroepitaxial growth of nickel and silver on vicinal copper substrates. Nickel was deposited onto a (211) substrate. The low lattice mismatch between copper and nickel of 2.5% enables epitaxial bidimensional growth in the substrate's orientation, where the strain can be accommodated in the overlaying film. On the contrary, copper and silver have a much larger mismatch of about 13% which usually cannot be accommodated in the film. In general, Ag is known to form alloys or to induce faceting on a stepped Cu surfaces. Here, silver was deposited onto a Cu(311) facet covered with a monatomic layer of NaCl. For the first time we show that Ag can be grown as ultrathin film in the substrates's orientation on a stepped surface using NaCl as a novel surfactant material.     

Characterization of dislocation interactions in olivine using electron tomography

We have investigated by electron tomography, in a transmission electronic microscope, the interactions between dislocations in olivine single crystals and polycrystals deformed in axial compression at T < 1000 °C (T < 0.5T_m). Dislocations are mostly of the [0?0?1] type, except in the polycrystal where [1?0?0] and [0?0?1] dislocations have been activated. A few 〈1?0?1〉 junctions have been found and characterized. Many collinear interactions have been identified either involving direct interactions between crossing dislocations of opposite Burgers vectors or indirect interactions between dislocations gliding in parallel planes and sessile dislocation loops. We suggest that collinear interaction, already identified as the primary source of strain hardening in FCC metals, is the main dislocation interaction mechanism in olivine deformed at temperatures below 1000 °C.     

Die Verfestigungserholung von plastisch verformten Steinsalzeinkristallen

Cylindrical rock salt single crystals have been plastically deformed by compression in the [001]-direction at room temperature to shear stresser τ _E of 200 N/cm² and 350 N/cm², respectively. Isochronal annealing experiments reveal, that workhardening recovers at >300° C. The characteristic annealing temperature was found between 400° C and 450° C. At 600° C the residual workhardening still amounts to 15–20%. The isochronal reduction of screw dislocation density between 400 and 600° C shows qualitatively the same behaviour as recovery of workhardening. From the isothermal annealing curves of the samples deformed to 200 N/cm² the activation energy for recovery of workhardening was found to be about 1 eV. Assuming that the kinetics of recovery can be explained by processes distributed in activation energy, an approximate spectrum of activation energies (with a maximum arising at ～1 eV) has been evaluated. The results show that recovery of workhardening after low deformation (stage I of the stress strain curve) is mainly due to the dislocations.     

Isochronal annealing study of neutron induced defects in single and poly crystals of molybdenum

In single crystals the positron [arameter shoes a stabilization of voids till 650°C followed by coarsing and annealing between 650 and 1050°C. In poly crystals, migration of monovacancies and formation of vacancy clusters between 200 and 500°C and a two step vacancy cluster annealing between 500 and 850°C have been observed.     

On the formation of lamellae during annealing of extended chain crystals of radiation-polymerized trioxane

The structure changes of radiation-polymerized trioxane taking place during annealing have been studied by means of electron microscopy, X-ray small- and wide-angle scattering, and differential thermal analysis. The original fibrillar crystals, supposedly consisting of extended chains, change into lamellar crystals due to annealing at temperatures between 150° and 190°C. Lamella formation can be connected with the appearance of a long period of about 200A which is not observed in the unannealed sample.

During annealing within the same temperature range the X-ray reflections due to the twin structure of the original polytrioxane disappear, whereas the orientation of the fraction with its c-axis parallel to the c-axis of the parent trioxane remains unaltered.

The melting point of the lamellar crystals obtained by annealing is 186°-187°C and, therefore, considerably higher than the melting point (175°C) of crystals grown during cooling of a polytrioxane melt. The equilibrium melting point of an undisturbed extended-chain poly-oxymethylene single crystal must be still higher and may even approach 200°C.

On the basis of the electron-microscopical observations and the X-ray results, it is supposed that the process of lamella formation takes place continuously by reorganization of the whole structure including the already grown lamellae. The rate of this process is the faster the higher the annealing temperature. Some possible mechanisms are discussed but the final reasons for the observed structure changes are not known.