Crystals

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Crystal Dislocations

by Ronald W. Armstrong

Crystals 2016, 6(1), 9; https://doi.org/10.3390/cryst6010009 - 6 Jan 2016

Cited by 1 | Viewed by 6193

Abstract

Crystal dislocations were invisible until the mid-20th century although their presence had been inferred; the atomic and molecular scale dimensions had prevented earlier discovery. Now they are normally known to be just about everywhere, for example, in the softest molecularly-bonded crystals as well [...] Read more.

Crystal dislocations were invisible until the mid-20th century although their presence had been inferred; the atomic and molecular scale dimensions had prevented earlier discovery. Now they are normally known to be just about everywhere, for example, in the softest molecularly-bonded crystals as well as within the hardest covalently-bonded diamonds. The advent of advanced techniques of atomic-scale probing has facilitated modern observations of dislocations in every crystal structure-type, particularly by X-ray diffraction topography and transmission electron microscopy. The present Special Issue provides a flavor of their ubiquitous presences, their characterizations and, especially, their influence on mechanical and electrical properties. Full article

(This article belongs to the Special Issue Crystal Dislocations)

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Research

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6349 KiB

Open AccessArticle

Study of Dislocations in the Minicrystallized Regions in Multicrystalline Silicon Grown by the Directional Solidification Method

by Nan Chen, Shenyu Qiu, Jianhua Huang, Guoping Du and Guihua Liu

Crystals 2016, 6(10), 130; https://doi.org/10.3390/cryst6100130 - 12 Oct 2016

Cited by 3 | Viewed by 4384

Abstract

Directionally solidified multicrystalline silicon (mc-Si)-based solar cells have dominated the global photovoltaic market in recent years. The photovoltaic performance of mc-Si solar cells is strongly influenced by their crystalline defects. The occurrence of minicrystallization results in much smaller grain size and, therefore, a [...] Read more.

Directionally solidified multicrystalline silicon (mc-Si)-based solar cells have dominated the global photovoltaic market in recent years. The photovoltaic performance of mc-Si solar cells is strongly influenced by their crystalline defects. The occurrence of minicrystallization results in much smaller grain size and, therefore, a larger number of grain boundaries in mc-Si ingots. Dislocations in the minicrystallized regions have been rarely investigated in the literature. In this work, optical microscopy was used to investigate dislocations in the mincrystallized regions in mc-Si ingots grown by the directional solidification method. The distribution of dislocations was found to be highly inhomogeneous from one grain to another in the mincrystallized regions. High inhomogeneity of dislocation distribution was also observed in individual grains. Serious shunting behavior was observed in the mc-Si solar cells containing minicrystallized regions, which strongly deteriorates their photovoltaic properties. The shunting was found to be highly localized to the minicrystallized regions. Full article

(This article belongs to the Special Issue Crystal Dislocations)

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1008 KiB

Open AccessArticle

Technique for High-Quality Protein Crystal Growth by Control of Subgrain Formation under an External Electric Field

by Haruhiko Koizumi, Satoshi Uda, Kozo Fujiwara, Masaru Tachibana, Kenichi Kojima and Jun Nozawa

Crystals 2016, 6(8), 95; https://doi.org/10.3390/cryst6080095 - 16 Aug 2016

Cited by 10 | Viewed by 5689

Abstract

X-ray diffraction (XRD) rocking-curves were measured for tetragonal hen egg white (HEW) lysozyme crystals grown with and without application of an external electric field, and the crystal quality was assessed according to the full width at half-maximums (FWHMs) of each rocking-curve profile. The [...] Read more.

X-ray diffraction (XRD) rocking-curves were measured for tetragonal hen egg white (HEW) lysozyme crystals grown with and without application of an external electric field, and the crystal quality was assessed according to the full width at half-maximums (FWHMs) of each rocking-curve profile. The average FWHMs for tetragonal HEW lysozyme crystals grown with an external electric field at 1 MHz were smaller than those for crystals grown without, especially for the 12 12 0 reflection. The crystal homogeneity of the tetragonal HEW lysozyme crystals was also improved under application of an external electric field at 1 MHz, compared to that without. Improvement of the crystal quality of tetragonal HEW lysozyme crystals grown under an applied field is discussed with a focus on subgrain formation. In addition, the origin of subgrain misorientation is also discussed with respect to the incorporation of impurities into protein crystals. Full article

(This article belongs to the Special Issue Crystal Dislocations)

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10592 KiB

Open AccessArticle

Dislocation Nucleation on Grain Boundaries: Low Angle Twist and Asymmetric Tilt Boundaries

by Erman Guleryuz and Sinisa Dj. Mesarovic

Crystals 2016, 6(7), 77; https://doi.org/10.3390/cryst6070077 - 5 Jul 2016

Cited by 15 | Viewed by 9697

Abstract

We investigate the mechanisms of incipient plasticity at low angle twist and asymmetric tilt boundaries in fcc metals. To observe plasticity of grain boundaries independently of the bulk plasticity, we simulate nanoindentation of bicrystals. On the low angle twist boundaries, the intrinsic grain [...] Read more.

We investigate the mechanisms of incipient plasticity at low angle twist and asymmetric tilt boundaries in fcc metals. To observe plasticity of grain boundaries independently of the bulk plasticity, we simulate nanoindentation of bicrystals. On the low angle twist boundaries, the intrinsic grain boundary (GB) dislocation network deforms under load until a dislocation segment compatible with glide on a lattice slip plane is created. The half loops are then emitted into the bulk of the crystal. Asymmetric twist boundaries considered here did not produce bulk dislocations under load. Instead, the boundary with a low excess volume nucleated a mobile GB dislocation and additional GB defects. The GB sliding proceeded by motion of the mobile GB dislocation. The boundary with a high excess volume sheared elastically, while bulk-nucleated dislocations produced plastic relaxation. Full article

(This article belongs to the Special Issue Crystal Dislocations)

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8340 KiB

Open AccessArticle

Electronic and Optical Properties of Dislocations in Silicon

by Manfred Reiche and Martin Kittler

Crystals 2016, 6(7), 74; https://doi.org/10.3390/cryst6070074 - 30 Jun 2016

Cited by 13 | Viewed by 10970

Abstract

Dislocations exhibit a number of exceptional electronic properties resulting in a significant increase of the drain current of metal-oxide-semiconductor field-effect transistors (MOSFETs) if defined numbers of these defects are placed in the channel. Measurements on individual dislocations in Si refer to a supermetallic [...] Read more.

Dislocations exhibit a number of exceptional electronic properties resulting in a significant increase of the drain current of metal-oxide-semiconductor field-effect transistors (MOSFETs) if defined numbers of these defects are placed in the channel. Measurements on individual dislocations in Si refer to a supermetallic conductivity. A model of the electronic structure of dislocations is proposed based on experimental measurements and tight binding simulations. It is shown that the high strain level on the dislocation core—exceeding 10% or more—causes locally dramatic changes of the band structure and results in the formation of a quantum well along the dislocation line. This explains experimental findings (two-dimensional electron gas and single-electron transitions). The energy quantization within the quantum well is most important for supermetallic conductivity. Full article

(This article belongs to the Special Issue Crystal Dislocations)

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7908 KiB

Open AccessArticle

Optical and X-Ray Topographic Studies of Dislocations, Growth-Sector Boundaries, and Stacking Faults in Synthetic Diamonds

by Moreton Moore, Stuart G. Nailer and Wojciech K. Wierzchowski

Crystals 2016, 6(7), 71; https://doi.org/10.3390/cryst6070071 - 24 Jun 2016

Cited by 16 | Viewed by 7129

Abstract

The characterization of growth features and defects in various high-pressure high-temperature (HPHT) synthetic diamonds has been achieved with optical and X-ray topographic techniques. For the X-ray studies, both characteristic and synchrotron radiation were used. The defects include dislocations, stacking faults, growth banding, growth [...] Read more.

The characterization of growth features and defects in various high-pressure high-temperature (HPHT) synthetic diamonds has been achieved with optical and X-ray topographic techniques. For the X-ray studies, both characteristic and synchrotron radiation were used. The defects include dislocations, stacking faults, growth banding, growth sector boundaries, and metal inclusions. The directions of the Burgers vectors of many dislocations (edge, screw, and mixed 30°, 60°, and 73.2°), and the fault vectors of stacking faults, were determined as <110> and 1/3 <111> respectively. Some dislocations were generated at metallic inclusions; and some dislocations split with the formation of stacking faults. Full article

(This article belongs to the Special Issue Crystal Dislocations)

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3205 KiB

Open AccessArticle

Control of Cellular Arrangement by Surface Topography Induced by Plastic Deformation

by Aira Matsugaki and Takayoshi Nakano

Crystals 2016, 6(6), 73; https://doi.org/10.3390/cryst6060073 - 22 Jun 2016

Cited by 10 | Viewed by 4981

Abstract

The anisotropic microstructure of bone tissue is crucial for appropriate mechanical and biological functions of bone. We recently revealed that the construction of oriented bone matrix is established by osteoblast alignment; there is a quite unique correlation between cell alignment and cell-produced bone [...] Read more.

The anisotropic microstructure of bone tissue is crucial for appropriate mechanical and biological functions of bone. We recently revealed that the construction of oriented bone matrix is established by osteoblast alignment; there is a quite unique correlation between cell alignment and cell-produced bone matrix orientation governed by the molecular interactions between material surface and cells. Titanium and its alloys are one of the most attractive materials for biomedical applications. We previously succeeded in controlling cellular arrangement using the dislocations of a crystallographic slip system in titanium single crystals with hexagonal close-packing (hcp) crystal lattice. Here, we induced a specific surface topography by deformation twinning and dislocation motion to control cell orientation. Dislocation and deformation twinning were introduced into α-titanium polycrystals in compression, inducing a characteristic surface structure involving nanometer-scale highly concentrated twinning traces. The plastic deformation-induced surface topography strongly influenced osteoblast orientation, causing them to align preferentially along the slip and twinning traces. This surface morphology, exhibiting a characteristic grating structure, controlled the localization of focal adhesions and subsequent elongation of stress fibers in osteoblasts. These results indicate that cellular responses against dislocation and deformation twinning are useful for controlling osteoblast alignment and the resulting bone matrix anisotropy. Full article

(This article belongs to the Special Issue Crystal Dislocations)

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633 KiB

Open AccessArticle

The Adhesive Properties of Coherent and Semicoherent NiAl/V Interfaces Within the Peierls-Nabarro Model

by Yaoyao Linghu, Xiaozhi Wu, Rui Wang, Weiguo Li and Qing Liu

Crystals 2016, 6(4), 32; https://doi.org/10.3390/cryst6040032 - 25 Mar 2016

Cited by 7 | Viewed by 4967

Abstract

The work of adhesion and the interface energy of NiAl/V coherent interface systems have been investigated using first-principles methods. The adhesion of the Ni-terminated interface is larger than the Al-terminated interface. The difference in charge density and the density of states show that [...] Read more.

The work of adhesion and the interface energy of NiAl/V coherent interface systems have been investigated using first-principles methods. The adhesion of the Ni-terminated interface is larger than the Al-terminated interface. The difference in charge density and the density of states show that the Ni-terminated interface is dominated by metallic bonds, and the Al-terminated interface is dominated by metallic and covalent bonds. To account for the effects of misfit dislocations on the semicoherent interfaces, the Peierls–Nabarro model combined with generalized stacking fault energy is employed to determine the interface energy. It is found that misfit dislocations can reduce the adhesion of the interface, and the reduction increases with the maximum of the restoring force. Full article

(This article belongs to the Special Issue Crystal Dislocations)

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Review

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Open AccessReview

Strategies to Approach Stabilized Plasticity in Metals with Diminutive Volume: A Brief Review

by Tao Hu, Lin Jiang, Amiya K. Mukherjee, Julie M. Schoenung and Enrique J. Lavernia

Crystals 2016, 6(8), 92; https://doi.org/10.3390/cryst6080092 - 9 Aug 2016

Cited by 5 | Viewed by 4652

Abstract

Micrometer- or submicrometer-sized metallic pillars are widely studied by investigators worldwide, not only to provide insights into fundamental phenomena, but also to explore potential applications in microelectromechanical system (MEMS) devices. While these materials with a diminutive volume exhibit unprecedented properties, e.g., strength values [...] Read more.

Micrometer- or submicrometer-sized metallic pillars are widely studied by investigators worldwide, not only to provide insights into fundamental phenomena, but also to explore potential applications in microelectromechanical system (MEMS) devices. While these materials with a diminutive volume exhibit unprecedented properties, e.g., strength values that approach the theoretical strength, their plastic flow is frequently intermittent as manifested by strain bursts, which is mainly attributed to dislocation activity at such length scales. Specifically, the increased ratio of free surface to volume promotes collective dislocation release resulting in dislocation starvation at the submicrometer scale or the formation of single-arm dislocation sources (truncated dislocations) at the micrometer scale. This article reviews and critically assesses recent progress in tailoring the microstructure of pillars, both extrinsically and intrinsically, to suppress plastic instabilities in micrometer or submicrometer-sized metallic pillars using an approach that involves confining the dislocations inside the pillars. Moreover, we identify strategies that can be implemented to fabricate submicrometer-sized metallic pillars that simultaneously exhibit stabilized plasticity and ultrahigh strength. Full article

(This article belongs to the Special Issue Crystal Dislocations)

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2286 KiB

Open AccessFeature PaperReview

Dislocation Motion and the Microphysics of Flash Heating and Weakening of Faults during Earthquakes

by Elena Spagnuolo, Oliver Plümper, Marie Violay, Andrea Cavallo and Giulio Di Toro

Crystals 2016, 6(7), 83; https://doi.org/10.3390/cryst6070083 - 22 Jul 2016

Cited by 7 | Viewed by 6286

Abstract

Earthquakes are the result of slip along faults and are due to the decrease of rock frictional strength (dynamic weakening) with increasing slip and slip rate. Friction experiments simulating the abrupt accelerations (>>10 m/s²), slip rates (~1 m/s), and normal stresses [...] Read more.

Earthquakes are the result of slip along faults and are due to the decrease of rock frictional strength (dynamic weakening) with increasing slip and slip rate. Friction experiments simulating the abrupt accelerations (>>10 m/s²), slip rates (~1 m/s), and normal stresses (>>10 MPa) expected at the passage of the earthquake rupture along the front of fault patches, measured large fault dynamic weakening for slip rates larger than a critical velocity of 0.01–0.1 m/s. The dynamic weakening corresponds to a decrease of the friction coefficient (defined as the ratio of shear stress vs. normal stress) up to 40%–50% after few millimetres of slip (flash weakening), almost independently of rock type. The microstructural evolution of the sliding interfaces with slip may yield hints on the microphysical processes responsible for flash weakening. At the microscopic scale, the frictional strength results from the interaction of micro- to nano-scale surface irregularities (asperities) which deform during fault sliding. During flash weakening, the visco-plastic and brittle work on the asperities results in abrupt frictional heating (flash heating) and grain size reduction associated with mechano-chemical reactions (e.g., decarbonation in CO₂-bearing minerals such as calcite and dolomite; dehydration in water-bearing minerals such as clays, serpentine, etc.) and phase transitions (e.g., flash melting in silicate-bearing rocks). However, flash weakening is also associated with grain size reduction down to the nanoscale. Using focused ion beam scanning and transmission electron microscopy, we studied the micro-physical mechanisms associated with flash heating and nanograin formation in carbonate-bearing fault rocks. Experiments were conducted on pre-cut Carrara marble (99.9% calcite) cylinders using a rotary shear apparatus at conditions relevant to seismic rupture propagation. Flash heating and weakening in calcite-bearing rocks is associated with a shock-like stress release due to the migration of fast-moving dislocations and the conversion of their kinetic energy into heat. From a review of the current natural and experimental observations we speculate that this mechanism tested for calcite-bearing rocks, is a general mechanism operating during flash weakening (e.g., also precursory to flash melting in the case of silicate-bearing rocks) for all fault rock types undergoing fast slip acceleration due to the passage of the seismic rupture front. Full article

(This article belongs to the Special Issue Crystal Dislocations)

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