Journal articles: 'Crystals – Defects'

1

Zhao, Xiaoji, Yanlu Li, and Xian Zhao. "Density Functional Theory Study of the Point Defects on KDP (100) and (101) Surfaces." Molecules 27, no. 24 (December 17, 2022): 9014. http://dx.doi.org/10.3390/molecules27249014.

Full text

Abstract:

Surface defects are usually associated with the formation of other forms of expansion defects in crystals, which have an impact on the crystals’ growth quality and optical properties. Thereby, the structure, stability, and electronic structure of the hydrogen and oxygen vacancy defects (VH and VO) on the (100) and (101) growth surfaces of KDP crystals were studied by using density functional theory. The effects of acidic and alkaline environments on the structure and properties of surface defects were also discussed. It has been found that the considered vacancy defects have different properties on the (100) and (101) surfaces, especially those that have been reported in the bulk KDP crystals. The (100) surface has a strong tolerance for surface VH and VO defects, while the VO defect causes a large lattice relaxation on the (101) surface and introduces a deep defect level in the band gap, which damages the optical properties of KDP crystals. In addition, the results show that the acidic environment is conducive to the repair of the VH defects on the surface and can eliminate the defect states introduced by the surface VO defects, which is conducive to improving the quality of the crystal surface and reducing the defect density. Our study opens up a new way to understand the structure and properties of surface defects in KDP crystals, which are different from the bulk phase, and also provides a theoretical basis for experimentally regulating the surface defects in KDP crystals through an acidic environment.

APA, Harvard, Vancouver, ISO, and other styles

2

Filip, Octavian, Boris M. Epelbaum, Juan Li, Matthias Bickermann, Xian Gang Xu, and Albrecht Winnacker. "Growth on Rhombohedral (01-1n) Plane: An Alternative for Preparation of High Quality Bulk SiC Crystals." Materials Science Forum 600-603 (September 2008): 23–26. http://dx.doi.org/10.4028/www.scientific.net/msf.600-603.23.

Full text

Abstract:

Results on bulk growth of SiC crystals along rhombohedral [01-1n] directions are presented. 6H- and 4H-crystals were grown on rhombohedral planes, which make angles of about 45o with the (0001) plane. Etching features on three differently oriented planes cut from characteristic crystals were compared. Utmost care was concentrated on defect development in the case of non-conventional growth orientation using the seed cut from a “standard” (0001) crystal, containing a typical (standard for [0001] growth) set of crystal defects. We clearly distinguished between a transient layer adjacent to the seed and the main crystal body grown at latter stages. The defect selection and/or transformation in the transient layer appeared strongly depending on the SiC polytype and growth direction. This study brings directly the information on stability of particular defects in the chosen crystal orientation and allows us to distinguish between defects characteristic for [0001] and rhombohedral growth.

APA, Harvard, Vancouver, ISO, and other styles

3

Tuomisto, Filip. "Vacancy Defects in Bulk and Quasi-Bulk GaN Crystals." Crystals 12, no. 8 (August 9, 2022): 1112. http://dx.doi.org/10.3390/cryst12081112.

Full text

Abstract:

In-grown vacancy defects in bulk and quasi-bulk GaN crystals have been extensively studied with positron annihilation spectroscopy. High concentrations of Ga-vacancy-related defects are found irrespective of the growth method used in crystals with a high O contamination or intentional O doping, and they act as the dominant compensating native defect for n-type conductivity. Low-temperature crystal growth also leads to high concentrations of Ga-vacancy-related defects. Ga vacancies are present in the crystals as a part of the different types of complexes with O, H, and/or VN, depending on the growth conditions.

APA, Harvard, Vancouver, ISO, and other styles

4

Smirnov, Maxim, Diana Manukovskaya, Nikolay Sidorov, and Mikhail Palatnikov. "Features of the Defect Structure and Luminescence of Nominally Pure Lithium Niobate Crystals Produced Using Different Technologies." Materials 16, no. 1 (December 27, 2022): 255. http://dx.doi.org/10.3390/ma16010255.

Full text

Abstract:

We have established that luminescence in lithium niobate crystals both congruent and near-stoichiometric (R≈1) is due to point defects in the cationic sublattice and intraconfigurational transitions in the oxygen-octahedral NbO6 clusters. We have also determined that the main contribution to the luminescence in the visible and near IR regions is made by luminescence centers with the participation of NbLi defects: the NbLi-NbNb bipolaron pair and the NbLi-O defect in a congruent crystal. The minimum intensity of bipolaron luminescence has been observed in stoichiometric crystals obtained using different technologies. Weak luminescence of the NbLi-NbNb bipolaron pair indicates a small number of NbLi defects in the crystal structure. The number of NbLi defects in the crystal structure indicates a deviation of the crystal composition from stoichiometry.

APA, Harvard, Vancouver, ISO, and other styles

5

Zhang, Hongdan, Ludan Zhu, Jun Cheng, Long Chen, Chuanqi Liu, and Shuanglong Yuan. "Photoluminescence Characteristics of Sn2+ and Ce3+-Doped Cs2SnCl6 Double-Perovskite Crystals." Materials 12, no. 9 (May 8, 2019): 1501. http://dx.doi.org/10.3390/ma12091501.

Full text

Abstract:

In recent years, all-inorganic lead-halide perovskites have received extensive attention due to their many advantages, but their poor stability and high toxicity are two major problems. In this paper, a low toxicity and stable Cs2SnCl6 double perovskite crystals were prepared by aqueous phase precipitation method using SnCl2 as precursor. By the XRD, ICP-AES, XPS, photoluminescence and absorption spectra, the fluorescence decay curve, the structure and photoluminescence characteristics of Ce3+-doped and undoped samples have been investigated in detail. The results show that the photoluminescence originates from defects. [ S n S n 4 + 2 + +VCl] defect complex in the crystal is formed by Sn2+ substituting Sn4+. The number of defects formed by Sn2+ in the crystal decreases with Ce3+ content increases. Within a certain number of defects, the crystal luminescence is enhanced with the number of [ S n S n 4 + 2 + +VCl] decreased. When Ce3+ is incorporated into the crystals, the defects of [ C e 3 + S n 4 + +VCl] and [ S n S n 4 + 2 + +VCl] were formed and the crystal show the strongest emission. This provides a route to enhance the photoluminescence of Cs2SnCl6 double perovskite crystals.

APA, Harvard, Vancouver, ISO, and other styles

6

Pond, R. C. "TEM studies of line defects in interfaces." Proceedings, annual meeting, Electron Microscopy Society of America 46 (1988): 586–87. http://dx.doi.org/10.1017/s0424820100104996.

Full text

Abstract:

Line defects are ubiquitious features in interfaces, and have important structural and mechanistic role. Recently, a crystallographic theory of such defects has been presented which appears to offer a comprehensive framework for their classification. The object of the present paper is firstly to outline the characterisation and classification of defects according to this treatment. Secondly, we illustrate examples of defects in the distinctive classes observed using tern, and discuss the various imaging techniques which have been employed.In the absence of a rigorous treatment of line defects in single crystals and interfaces, which would require the development of a discrete field theory, approximate methods of defect characterisation are used. The most popular method involves mapping a contour, initially constructed around a defect of interest, into a reference space. For defeats in single crystals this Burgers circuit method, introduced by Frank, is very helpful, but suffers from certain procedural inconveniences in the case of interfacial defects.

APA, Harvard, Vancouver, ISO, and other styles

7

Zhang, Ji Zhong, Wei Qiang Wang, and Na Li. "Self-Organization Behavior of Sub-Micron CdO Grains Grown during Vapour-Solid Transition." Defect and Diffusion Forum 278 (July 2008): 45–54. http://dx.doi.org/10.4028/www.scientific.net/ddf.278.45.

Full text

Abstract:

Various deposits of CdO grains were observed on the surface of N 100 silicon crystals heated at 580 °C and 620 °C for 1 hour in an evaporation-deposition device, respectively. The ball-shaped crystals, and regular-prism-shaped crystals were found on top of bush-like long crystals. Two types of CdO self-organization aggregates were also observed, that is, regular circular-shaped dense aggregate and long-chainshaped aggregate. The self-organization aggregates were composed of numerous submicron CdO grains. The relationship between self-organization aggregates and surface defects of virgin N 100 silicon crystal was investigated. The results showed that the CdO self-organization aggregates were related to surface defects of the virgin N 100 silicon crystal, and a defect induced aggregation (DIA) model is suggested.

APA, Harvard, Vancouver, ISO, and other styles

8

Kato, Tomohisa, Kazutoshi Kojima, Shin Ichi Nishizawa, and Kazuo Arai. "Defect Characterization of 4H-SiC Bulk Crystals Grown on Micropipe Filled Seed Crystals." Materials Science Forum 483-485 (May 2005): 315–18. http://dx.doi.org/10.4028/www.scientific.net/msf.483-485.315.

Full text

Abstract:

We report defects study in 4H-SiC bulk crystals grown by sublimation method on micropipe filled seed crystals oriented (0001) on-axis. The seed crystals of 1~3 inch in diameter were prepared from the large 4H-SiC bulk crystals. Before the sublimation growth, micropipes of the seed crystals were filled with epilayers grown by micropipe filling technique of CVD method. We confirmed about 95% of micropipes perfectly disappeared in the grown crystal. The mechanism of the micropipe extinction was also defined by defect analysis.

APA, Harvard, Vancouver, ISO, and other styles

9

Giles, N. C., and L. E. Halliburton. "Native Defects in the Ternary Chalcopyrites." MRS Bulletin 23, no. 7 (July 1998): 37–40. http://dx.doi.org/10.1557/s0883769400029079.

Full text

Abstract:

Ternary-chalcopyrite crystals contain a variety of point defects—the most common of which are vacancies, antisite ions, and impurities. Usually these defects are isolated, but they can also appear as complexes involving two or more of the simple defects. Depending on the material, the concentrations of these defects may vary from a few hundred parts per billion to a few hundred parts per million. Many of the point defects in the ternary chalcopyrites have associated optical-absorption bands with significant oscillator strengths. It is these absorption features that become important when the crystals are exposed to intense laser beams during device operation. Even a small amount of absorption will seriously degrade the performance of the device if any of the wavelengths of the various propagating beams happen to overlap an absorption band. This phenomenon can be a problem for both second-harmonic-generator and optical-parametric-oscillator applications. In general the absorption leads to heating of the crystal and results in-thermal lensing (due to temperature dependence of the index of refraction) and dephasing of the beams, and it can ultimately lead to thermal fracturing of the crystal. Thus it is important to develop a fundamental understanding of the defect structure of the ternary-chalcopyrite crystals if they are to serve as the critical component in midinfrared frequency-conversion devices. Once the nature and behavior of the point defects are established, processes can be developed to remove the defects from the crystals either during the growth itself or during post-growth treatments.

APA, Harvard, Vancouver, ISO, and other styles

10

Cheredov, V. N., and A. E. Petrakov. "Determination of the orientation of internal linear defects in isotropic optical crystals." Industrial laboratory. Diagnostics of materials 85, no. 2 (March 1, 2019): 29–32. http://dx.doi.org/10.26896/1028-6861-2019-85-2-29-32.

Full text

Abstract:

Study of the structure of optical crystals and defects in them is one of the most important problems in crystal physics, crystallography and material science. Nowadays, study of the nanostructures, including the linear defects in crystals is of particular importance. Defects, and first and foremost linear imperfections of the crystal structure, significantly reduce the operational physical properties of optical crystals. Analysis of the properties of those defects, their orientation in the crystal lattice, as well as developing of the methods for determination of the crystallographic orientation of linear defects are the most important in view of the possibility of improving the properties of optical crystals. A method for rapid determination of the crystallographic orientation of linear defects (dislocations, clusters, linearly extended bulk inclusions, etc.) in optical crystals is presented. The orientation of a linearly extended micropore in an isotropic optical transparent fluorite crystal was determined using an optical microscope. The readings of the scale of the eyepiece drum were recorded when rotating the crystal fixed in the crystal holder of the microscope. Corrections for the refraction of light in the bulk of the crystal were taken into account analytically. The crystallographic orientation of the microporous in a transparent fluorite crystal was studied in detail. Crystallographic indices of micropore orientation corresponded to [100]. We developed an efficient rapid procedure for determination of the orientation of internal linear defects (imperfections) in optically isotropic crystals using an optical microscope. The restrictions imposed on the angles of crystal rotation depending on the value of the refractive index are considered for the given method of determination.

APA, Harvard, Vancouver, ISO, and other styles

11

Barry, J. C., and E. F. Bres. "HRTEM of hydroxyapatite in carious human tooth enamel." Proceedings, annual meeting, Electron Microscopy Society of America 45 (August 1987): 170–71. http://dx.doi.org/10.1017/s0424820100125786.

Full text

Abstract:

Human dental enamel is composed 98% by weight of small, densely packed carbonated hydroxyapatite (HAP) crystals. These crystals have an unusual morphology and often contain a “central dark line” (CDL) defect. The HAP crystals in carious enamel are preferentially dissolved at the CDL defect. Bres et al. have identified three types of disorder in human tooth enamel crystallites near to the crystal midline: a) regions of lattice buckling and departure from hexagonal symmetry, b) dislocations and c) grain and twin boundaries. Nelson et al. have obtained very clear images of planar defects, similar to the CDL defects in human enamel, at the centers of crystals of certain synthetic carbonated apatites. In this present study HRTEM images have been obtained from carious regions of tooth enamel, and an analysis of the results is attemped in the light of previous work.

APA, Harvard, Vancouver, ISO, and other styles

12

Jiang, X. N., and D. Xu. "Surface morphology and defect formation of the {100} face of ZnCd(SCN)4crystals investigated by AFM." Journal of Applied Crystallography 36, no. 6 (November 15, 2003): 1448–51. http://dx.doi.org/10.1107/s0021889803022738.

Full text

Abstract:

Surface morphology and defect formation of the prismatic {100} face of ZCTC crystals were investigated by atomic force microscopy (AFM). Both screw-dislocation-controlled growth and two-dimensional nucleation growth occur on the face at a supersaturation of 0.03. Steps advance with strong kinetic anisotropy along theb-axis direction, probably because different parts of the ZCTC molecules are exposed along different crystallographic directions. By comparing heights of elementary steps with the structure of the ZCTC crystal, it is deduced that the growth of ZCTC crystals occurs mostly by direct incorporation of monomers or dimers of ZCTC molecules into the crystal. Defects of hollow channels, negative crystals and cracks that are oriented preferentially along the direction of theborcaxis were observed. The formation of the defects is mainly related to the growth mechanism and structural features of the ZCTC crystal.

APA, Harvard, Vancouver, ISO, and other styles

13

Kirste, Lutz, Karolina Grabianska, Robert Kucharski, Tomasz Sochacki, Boleslaw Lucznik, and Michal Bockowski. "Structural Analysis of Low Defect Ammonothermally Grown GaN Wafers by Borrmann Effect X-ray Topography." Materials 14, no. 19 (September 22, 2021): 5472. http://dx.doi.org/10.3390/ma14195472.

Full text

Abstract:

X-ray topography defect analysis of entire 1.8-inch GaN substrates, using the Borrmann effect, is presented in this paper. The GaN wafers were grown by the ammonothermal method. Borrmann effect topography of anomalous transmission could be applied due to the low defect density of the substrates. It was possible to trace the process and growth history of the GaN crystals in detail from their defect pattern imaged. Microscopic defects such as threading dislocations, but also macroscopic defects, for example dislocation clusters due to preparation insufficiency, traces of facet formation, growth bands, dislocation walls and dislocation bundles, were detected. Influences of seed crystal preparation and process parameters of crystal growth on the formation of the defects are discussed.

APA, Harvard, Vancouver, ISO, and other styles

14

Zou, Jiaona, Alex Fauler, Alexander S. Senchenkov, Nikolai N. Kolesnikov, Lutz Kirste, Merve Pinar Kabukcuoglu, Elias Hamann, Angelica Cecilia, and Michael Fiederle. "Characterization of Structural Defects in (Cd,Zn)Te Crystals Grown by the Travelling Heater Method." Crystals 11, no. 11 (November 18, 2021): 1402. http://dx.doi.org/10.3390/cryst11111402.

Full text

Abstract:

Structural defects and compositional uniformity remain the major problems affecting the performance of (Cd, Zn)Te (CZT) based detector devices. Understanding the mechanism of growth and defect formation is therefore fundamental to improving the crystal quality. In this frame, space experiments for the growth of CZT by the Travelling Heater Method (THM) under microgravity are scheduled. A detailed ground-based program was performed to determine experimental parameters and three CZT crystals were grown by the THM. The structural defects, compositional homogeneity and resistivity of these ground-based crystals were investigated. A ZnTe content variation was observed at the growth interface and a high degree of stress associated with extensive dislocation networks was induced, which propagated into the grown crystal region according to the birefringence and X-ray White Beam Topography (XWBT) results. By adjusting the growth parameters, the ZnTe variations and the resulting stress were efficiently reduced. In addition, it was revealed that large inclusions and grain boundaries can generate a high degree of stress, leading to the formation of dislocation slip bands and subgrain boundaries. The dominant defects, including grain boundaries, dislocation networks and cracks in the interior of crystals, led to the resistivity variation in the crystals. The bulk resistivity of the as-grown crystals ranged from 109 Ωcm to 1010 Ωcm.

APA, Harvard, Vancouver, ISO, and other styles

15

Darmon, Alexandre, Michael Benzaquen, David Seč, Simon Čopar, Olivier Dauchot, and Teresa Lopez-Leon. "Waltzing route toward double-helix formation in cholesteric shells." Proceedings of the National Academy of Sciences 113, no. 34 (August 4, 2016): 9469–74. http://dx.doi.org/10.1073/pnas.1525059113.

Full text

Abstract:

Liquid crystals, when confined to a spherical shell, offer fascinating possibilities for producing artificial mesoscopic atoms, which could then self-assemble into materials structured at a nanoscale, such as photonic crystals or metamaterials. The spherical curvature of the shell imposes topological constraints in the molecular ordering of the liquid crystal, resulting in the formation of defects. Controlling the number of defects, that is, the shell valency, and their positions, is a key success factor for the realization of those materials. Liquid crystals with helical cholesteric order offer a promising, yet unexplored way of controlling the shell defect configuration. In this paper, we study cholesteric shells with monovalent and bivalent defect configurations. By bringing together experiments and numerical simulations, we show that the defects appearing in these two configurations have a complex inner structure, as recently reported for simulated droplets. Bivalent shells possess two highly structured defects, which are composed of a number of smaller defect rings that pile up through the shell. Monovalent shells have a single radial defect, which is composed of two nonsingular defect lines that wind around each other in a double-helix structure. The stability of the bivalent configuration against the monovalent one is controlled by c = h/p, where h is the shell thickness and p the cholesteric helical pitch. By playing with the shell geometry, we can trigger the transition between the two configurations. This transition involves a fascinating waltz dynamics, where the two defects come closer while turning around each other.

APA, Harvard, Vancouver, ISO, and other styles

16

Horichok, I. V., L. I. Nykyruy, T. O. Parashchuk, S. D. Bardashevska, and M. P. Pylyponuk. "Thermodynamics of defect subsystem in zinc telluride crystals." Modern Physics Letters B 30, no. 16 (June 20, 2016): 1650172. http://dx.doi.org/10.1142/s0217984916501724.

Full text

Abstract:

Using method on the base of minimizing of thermodynamic potential in “crystal-vapor” system as a function of defect concentration the equilibrium concentration of point defects and free charge carriers in zinc telluride (ZnTe) crystals have been calculated depending on the technological factors of two-temperature annealing (annealing temperature [Formula: see text] and vapor pressure [Formula: see text] of zinc or [Formula: see text] of tellurium). It is shown that the dominant defects are zinc vacancies the charge state of which depends on the technological conditions of annealing.

APA, Harvard, Vancouver, ISO, and other styles

17

Shiran, N. "Defects related luminescence in yttrium-aluminum garnet crystals." Functional materials 23, no. 2 (June 15, 2016): 191–96. http://dx.doi.org/10.15407/fm23.02.191.

Full text

APA, Harvard, Vancouver, ISO, and other styles

18

Smalc-Koziorowska, Julita. "Defects in Crystals." Crystals 10, no. 10 (October 9, 2020): 915. http://dx.doi.org/10.3390/cryst10100915.

Full text

APA, Harvard, Vancouver, ISO, and other styles

19

Ludwig, W., P. Cloetens, J. Härtwig, J. Baruchel, B. Hamelin, and P. Bastie. "Three-dimensional imaging of crystal defects by `topo-tomography'." Journal of Applied Crystallography 34, no. 5 (September 25, 2001): 602–7. http://dx.doi.org/10.1107/s002188980101086x.

Full text

Abstract:

A new technique, `topo-tomography', suitable for the characterization of the three-dimensional defect structure in bulk crystals, is proposed. The technique consists of the combination of diffraction topography and microtomography. It is applicable to high-quality single crystals, provided that the `direct image' is the dominant contrast mechanism. In this case, crystal defects give rise to locally enhanced intensity compared with the perfect-crystal matrix. The additional intensities sum along the diffracted-beam direction and yield projections of the local Bragg reflectivity. Like in the case of absorption tomography, the three-dimensional distribution of this reflectivity can be reconstructed from a large number of projections. The first experimental results of this technique, applied to a synthetic diamond crystal, are presented.

APA, Harvard, Vancouver, ISO, and other styles

20

Xu, Guogang, Jing Li, Yongjie Guo, Shujuan Han, and Jiyang Wang. "Crystal growth and defects in Ga3PO7 crystals." Crystal Research and Technology 45, no. 6 (April 9, 2010): 600–602. http://dx.doi.org/10.1002/crat.201000080.

Full text

APA, Harvard, Vancouver, ISO, and other styles

21

Huang, Pei-Hsing, and Chi-Ming Lu. "Effects of Vacancy Cluster Defects on Electrical and Thermodynamic Properties of Silicon Crystals." Scientific World Journal 2014 (2014): 1–8. http://dx.doi.org/10.1155/2014/863404.

Full text

Abstract:

A first-principle plane-wave pseudopotential method based on the density function theory (DFT) was employed to investigate the effects of vacancy cluster (VC) defects on the band structure and thermoelectric properties of silicon (Si) crystals. Simulation results showed that various VC defects changed the energy band and localized electron density distribution of Si crystals and caused the band gap to decrease with increasing VC size. The results can be ascribed to the formation of a defect level produced by the dangling bonds, floating bonds, or high-strain atoms surrounding the VC defects. The appearance of imaginary frequencies in the phonon spectrum of defective Si crystals indicates that the defect-region structure is dynamically unstable and demonstrates phase changes. The phonon dispersion relation and phonon density of state were also investigated using density functional perturbation theory. The obtained Debye temperatureθDfor a perfect Si crystal had a minimum value of 448 K atT= 42 K and a maximum value of 671 K at the high-temperature limit, which is consistent with the experimental results reported by Flubacher. Moreover, the Debye temperature decreased with increases in the VC size. VC defects had minimal effects on the heat capacity (Cv) value when temperatures were below 150 K. As the temperature was higher than 150 K, the heat capacity gradually increased with increasing temperature until it achieved a constant value of 11.8 cal/cell·K. The heat capacity significantly decreased as the VC size increased. For a 2 × 2 × 2 superlattice Si crystal containing a hexagonal ring VC (HRVC10), the heat capacity decreased by approximately 17%.

APA, Harvard, Vancouver, ISO, and other styles

22

Larson, Bennett C. "Historical Perspective on Diffraction Line-Profile Analyses for Crystals Containing Defect Clusters." Crystals 9, no. 5 (May 17, 2019): 257. http://dx.doi.org/10.3390/cryst9050257.

Full text

Abstract:

Deviations of crystal diffraction line profiles from those predicted by the dynamical theory of diffraction for perfect crystals provide a window into the microscopic distributions of defects within non-perfect crystals. This overview provides a perspective on key theoretical, computational, and experimental developments associated with the analysis of diffraction line profiles for crystals containing statistical distributions of point defect clusters, e.g., dislocation loops, precipitates, and stacking fault tetrahedra. Pivotal theoretical developments beginning in the 1940s are recalled and discussed in terms of their impact on the direction of theoretical and experimental investigations of lattice defects in the 1960s, the 1970s, and beyond, as both experimental and computational capabilities advanced. The evolution of experimental measurements and analysis techniques, as stimulated by theoretical and computational progress in understanding the distortion fields surrounding defect clusters, is discussed. In particular, consideration is given to determining dislocation loop densities and separate size distributions for vacancy and interstitial type loops, and to the internal strain and size distributions for coherent precipitates.

APA, Harvard, Vancouver, ISO, and other styles

23

Klunnikova, Yu V., S. P. Malyukov, A. V. Filimonov, and N. Zhang. "Analysis of heat transfer processes for sapphire growth by horizontal directed crystallization method." Journal of Advanced Dielectrics 10, no. 01n02 (February 2020): 2060001. http://dx.doi.org/10.1142/s2010135x20600012.

Full text

Abstract:

This research summarizes the analytical and experimental results of heat-transfer processes influence on defects formation during sapphire crystal growth by horizontal directed crystallization method (HDC). The shape of solid-melt interface significantly influences the process of sapphire crystals growth by this method. We receive the Stefan problem solution for sapphire crystals growth. It allows investigating the crystal growth process and the related factors (thermal stresses on different stages of growth process), their influence on defects formation. We investigate the main reasons for the formation of defective structures of the solid phase of sapphire crystals and the influence of thermal unit construction, the crystal geometry on the quality of the resulting sapphire crystal. We study the structure formation process, impurity distribution, and the nature of the defects in the crystal during it growth.

APA, Harvard, Vancouver, ISO, and other styles

24

Dupraz, Maxime, Guillaume Beutier, David Rodney, Dan Mordehai, and Marc Verdier. "Signature of dislocations and stacking faults of face-centred cubic nanocrystals in coherent X-ray diffraction patterns: a numerical study." Journal of Applied Crystallography 48, no. 3 (April 16, 2015): 621–44. http://dx.doi.org/10.1107/s1600576715005324.

Full text

Abstract:

Crystal defects induce strong distortions in diffraction patterns. A single defect alone can yield strong and fine features that are observed in high-resolution diffraction experiments such as coherent X-ray diffraction. The case of face-centred cubic nanocrystals is studied numerically and the signatures of typical defects close to Bragg positions are identified. Crystals of a few tens of nanometres are modelled with realistic atomic potentials and `relaxed' after introduction of well defined defects such as pure screw or edge dislocations, or Frank or prismatic loops. Diffraction patterns calculated in the kinematic approximation reveal various signatures of the defects depending on the Miller indices. They are strongly modified by the dissociation of the dislocations. Selection rules on the Miller indices are provided, to observe the maximum effect of given crystal defects in the initial and relaxed configurations. The effect of several physical and geometrical parameters such as stacking fault energy, crystal shape and defect position are discussed. The method is illustrated on a complex structure resulting from the simulated nanoindentation of a gold nanocrystal.

APA, Harvard, Vancouver, ISO, and other styles

25

Lukáč, František, Jakub Čížek, Marián Vlček, Ivan Procházka, Martin Vlach, Wolfgang Anwand, Gerhard Brauer, et al. "Hydrogen Interaction with Defects in ZnO." Materials Science Forum 733 (November 2012): 228–31. http://dx.doi.org/10.4028/www.scientific.net/msf.733.228.

Full text

Abstract:

In the present work hydrothermally grown ZnO single crystals were electrochemically charged with hydrogen. The influence of hydrogen on ZnO microstructure was investigated by positron annihilation spectroscopy (PAS) combined with X-ray diffraction (XRD) using synchrotron radiation. Hydrogen concentration in the samples was determined by nuclear reaction analysis (NRA). It was found that a high concentration of hydrogen can be introduced into ZnO by electrochemical loading. At low concentrations, absorbed hydrogen causes elastic volume expansion of ZnO crystal. At higher concentration, hydrogen-induced stresses exceed the yield stress in ZnO and plastic deformation of the crystal takes place leading to formation of a defected subsurface layer in the crystals.

APA, Harvard, Vancouver, ISO, and other styles

26

Абишев, Н. М., Э. И. Байбеков, Б. З. Малкин, М. Н. Попова, Д. С. Пыталев, and С. А. Климин. "Деформационное уширение и тонкая структура спектральных линий в оптических спектрах диэлектрических кристаллов, содержащих редкоземельные ионы." Физика твердого тела 61, no. 5 (2019): 898. http://dx.doi.org/10.21883/ftt.2019.05.47589.22f.

Full text

Abstract:

AbstractThe procedure of calculation of the spectral line shape in optical spectra of rare-earth ions in crystals with the inclusion of random deformations of an elastically anisotropic crystal lattice caused by point defects is developed. The distribution function of components of the random strain tensor in the case of a low defect concentration is obtained as the generalized six-dimensional Lorentz distribution. The distribution function parameters are represented by the integral functional of the strain tensor components on a sphere of unit radius containing an isotropic point defect in its center. The numerical calculations of the strain tensors induced by point defects and the parameters of the distribution functions of random strains in LiLuF_4 and LaAlO_3 crystals have been performed. The calculated envelope with the doublet structure corresponding to the Γ_2(^3 H _4) → Γ_34(^3 H _5) singlet–doublet transition in the absorption spectrum of Pr^3+ ions in the LiLuF_4 crystal agrees well with the data of the measurements.

APA, Harvard, Vancouver, ISO, and other styles

27

McPherson, Alexander, and Yurii G. Kuznetsov. "Mechanisms, kinetics, impurities and defects: consequences in macromolecular crystallization." Acta Crystallographica Section F Structural Biology Communications 70, no. 4 (March 29, 2014): 384–403. http://dx.doi.org/10.1107/s2053230x14004816.

Full text

Abstract:

The nucleation and growth of protein, nucleic acid and virus crystals from solution are functions of underlying kinetic and thermodynamic parameters that govern the process, and these are all supersaturation-dependent. While the mechanisms of macromolecular crystal growth are essentially the same as for conventional crystals, the underlying parameters are vastly different, in some cases orders of magnitude lower, and this produces very different crystallization processes. Numerous physical features of macromolecular crystals are of serious interest to X-ray diffractionists; the resolution limit and mosaicity, for example, reflect the degree of molecular and lattice order. The defect structure of crystals has an impact on their response to flash-cooling, and terminal crystal size is dependent on impurity absorption and incorporation. The variety and extent of these issues are further unique to crystals of biological macromolecules. All of these features are amenable to study using atomic force microscopy, which provides direct images at the nanoscale level. Some of those images are presented here.

APA, Harvard, Vancouver, ISO, and other styles

28

Vasilev, Evgeny. "Defects of diamond crystal structure as an indicator of crystallogenesis." Записки Горного института 250 (September 29, 2021): 481–91. http://dx.doi.org/10.31897/pmi.2021.4.1.

Full text

Abstract:

Based on the study of a representative collections of diamonds from diamondiferous formations of the Urals and deposits of the Arkhangelsk and Yakutian diamond provinces, we established patterns of zonal and sectoral distribution of crystal structure defects in crystals of different morphological types, identified the specifics of crystals formed at different stages of crystallogenesis and performed a comprehensive analysis of constitutional and population diversity of diamonds in different formations. We identified three stages in the crystallogenesis cycle, which correspond to normal and tangential mechanisms of growth and the stage of changing crystal habit shape. At the stage of changing crystal habit shape, insufficient carbon supersaturation obstructs normal growth mechanism, and the facets develop from existing surfaces. Due to the absent stage of growth layer nucleation, formation of new {111} surfaces occurs much faster compared to tangential growth mechanism. This effect allows to explain the absence of cuboids with highly transformed nitrogen defects at the A-B1 stage: they have all been refaceted by a regenerative mechanism. Based on the revealed patterns, a model of diamond crystallogenesis was developed, which takes into account the regularities of growth evolution, thermal history and morphological diversity of the crystals. The model implies the possibility of a multiply repetitive crystallization cycle and the existence of an intermediate chamber; it allows to explain the sequence of changes in morphology and defect-impurity composition of crystals, as well as a combination of constitutional and population diversity of diamonds from different geological formations.

APA, Harvard, Vancouver, ISO, and other styles

29

Zhang, Haobin, Jinjiang Xu, Shichun Li, Jie Sun, and Xiaolin Wang. "Characterization of Nano-Scale Parallel Lamellar Defects in RDX and HMX Single Crystals by Two-Dimension Small Angle X-ray Scattering." Molecules 27, no. 12 (June 16, 2022): 3871. http://dx.doi.org/10.3390/molecules27123871.

Full text

Abstract:

Nano-scale crystal defects extremely affect the security and reliability of explosive charges of weapons. In this work, the nano-scale crystal defects of 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) single crystals were characterized by two-dimension SAXS. Deducing from the changes of SAXS pattern with sample stage rotating, we firstly found the parallel lamellar nano-scale defects in both RDX and HMX single crystals. Further analysis shows that the average diameter and thickness of nano-scale lamellar defects for RDX single crystal are 66.4 nm and 19.3 nm, respectively. The results of X-ray diffraction (XRD) indicate that the lamellar nano-scale defects distribute along the (001) in RDX and the (011) in HMX, which are verified to be the crystal planes with the lowest binding energy by the theoretical calculation.

APA, Harvard, Vancouver, ISO, and other styles

30

O'Rourke, Mary Jane E., and Edwin L. Thomas. "Morphology and Dynamic Interaction of Defects in Polymer Liquid Crystals." MRS Bulletin 20, no. 9 (September 1995): 29–36. http://dx.doi.org/10.1557/s0883769400034904.

Full text

Abstract:

The liquid crystal phase is an anisotropic mesophase, intermediate in order between the liquid and crystal phases. Liquid crystals have less translational order than crystals and more rotational order than isotropic liquids. The liquid crystal phase does not support finite shear stresses and thus behaves like a fluid. Molecules that display a liquid crystal phase are referred to as mesogenic. Mesogenic molecules exhibit shape anisotropy: either large length to diameter ratio (needlelike) or large diameter to thickness ratio (disklike). Because of their shape anisotropy, all liquid crystals display orientational order of their molecular axes.Until 1956, all known examples of liquid crystals were low molecular weight compounds. Robinson was the first to identify liquid crystallinity in a liquid crystalline polymer (LCP) as the explanation for “a birefringent solution” of a polymeric material, poly-y-benzyl-L-glutamate, in chloroform, previously observed by Elliott and Ambrose. Chemists soon discovered that LCPs may be readily synthesized by covalently stitching small mesogenic units (e.g., rigid monomers) together into a chain using short flexible spacers. Mainchain or sidechain liquid crystal polymers may be formed (Figure 1). An example of a polymer molecule possessing a liquid crystal phase is shown in Figure 2. Liquid crystals may be thermotropic, where liquid crystallinity is exhibited over a range of temperatures, or lyotropic, where nonmesogenic solvent molecules are present in addition to the mesogens, and liquid crystallinity is observed over a range of concentrations as well.

APA, Harvard, Vancouver, ISO, and other styles

31

Luo, Jinping, Chenyang Zhou, Qihang Li, and Lijun Liu. "Thermodynamic Formation Properties of Point Defects in Germanium Crystal." Materials 15, no. 11 (June 6, 2022): 4026. http://dx.doi.org/10.3390/ma15114026.

Full text

Abstract:

Point defects are crucial in determining the quality of germanium crystals. A quantitative understanding of the thermodynamic formation properties of the point defects is necessary for the subsequent control of the defect formation during crystal growth. Here, molecular dynamics simulations were employed to investigate the formation energies, total formation free energies and formation entropies of the point defects in a germanium crystal. As far as we know, this is the first time that the total formation free energies of point defects in a germanium crystal have been reported in the literature. We found that the formation energies increased slightly with temperature. The formation free energies decreased significantly with an increase in temperature due to the increase in entropy. The estimated total formation free energies at the melting temperature are ~1.3 eV for self-interstitial and ~0.75 eV for vacancy, corresponding to a formation entropy of ~15 kB for both types of point defects.

APA, Harvard, Vancouver, ISO, and other styles

32

Luo, Jinping, Chenyang Zhou, Qihang Li, and Lijun Liu. "Thermodynamic Formation Properties of Point Defects in Germanium Crystal." Materials 15, no. 11 (June 6, 2022): 4026. http://dx.doi.org/10.3390/ma15114026.

Full text

Abstract:

Point defects are crucial in determining the quality of germanium crystals. A quantitative understanding of the thermodynamic formation properties of the point defects is necessary for the subsequent control of the defect formation during crystal growth. Here, molecular dynamics simulations were employed to investigate the formation energies, total formation free energies and formation entropies of the point defects in a germanium crystal. As far as we know, this is the first time that the total formation free energies of point defects in a germanium crystal have been reported in the literature. We found that the formation energies increased slightly with temperature. The formation free energies decreased significantly with an increase in temperature due to the increase in entropy. The estimated total formation free energies at the melting temperature are ~1.3 eV for self-interstitial and ~0.75 eV for vacancy, corresponding to a formation entropy of ~15 kB for both types of point defects.

APA, Harvard, Vancouver, ISO, and other styles

33

Liliental-Weber, Z., M. Benamara, W. Swider, J. Washburn, I. Grzegory, S. Porowski, R. D. Dupuis, and C. J. Eiting. "Mg Segregation, Difficulties of P-Doping in GaN." MRS Internet Journal of Nitride Semiconductor Research 5, S1 (2000): 500–506. http://dx.doi.org/10.1557/s1092578300004695.

Full text

Abstract:

Transmission electron microscopy has been used to study defects formed in Mg-doped GaN crystals. Three types of crystals have been studied: bulk crystals grown by a high pressure and high temperature process with Mg added to the Ga solution and two types of crystals grown by metal-organic chemical vapor deposition (MOCVD) where Mg was either delta-doped or continuously doped. Spontaneous ordering was observed in bulk crystals. The ordering consists of Mg rich planar defects on basal planes separated by 10.4 nm and occurs only for growth in the N to Ga polar direction (000 N polarity). These planar defects exhibit the characteristics of stacking faults with a shift vector of a 1/3 [1 00] +c/2 but some other features identify these defects as inversion domains. Different type of defects were formed on the opposite site of the crystal (Ga to N polar direction), where the growth rate is also an order of magnitude faster compared to the growth with N-polarity. These defects are three-dimensional: pyramidal and rectangular, empty inside with Mg segregation on internal surfaces. The same types of defects seen for the two growth polarities in the bulk crystals were also observed in the MOCVD grown GaN samples with Mg delta doping, but were not observed in the crystals where Mg was added continuously.

APA, Harvard, Vancouver, ISO, and other styles

34

Malinowska, Agnieszka, Maria Lefeld-Sosnowska, and Jürgen Härtwig. "Contrast in transmission X-ray diffraction topographs of growth defects in the core of SrLaGaO4single crystals." Journal of Applied Crystallography 46, no. 1 (January 17, 2013): 48–54. http://dx.doi.org/10.1107/s0021889812050522.

Full text

Abstract:

Defects in the core of SrLaGaO4single crystals, grown by the Czochralski method using a [001]-oriented seed, were studied by transmission X-ray diffraction projection topography. Topographs were taken with radiation from a laboratory source and with high-energy radiation available at the ESRF beamline ID19 in Grenoble. The contrast of the investigated defect images was analysed for various diffraction vectorsgand for various values of the product μ0t(μ0is the linear absorption coefficient andtthe crystal thickness). This allowed the contrast formation to be studied as a function of absorption. The results of the analysis confirm the model of crystal lattice deformation around rod-like volume defects in SrLaGaO4crystals.

APA, Harvard, Vancouver, ISO, and other styles

35

Suzuki, Ryo, Seiki Baba, Nobuhiro Mizuno, Kazuya Hasegawa, Haruhiko Koizumi, Kenichi Kojima, Takashi Kumasaka, and Masaru Tachibana. "Radiation-induced defects in protein crystals observed by X-ray topography." Acta Crystallographica Section D Structural Biology 78, no. 2 (January 21, 2022): 196–203. http://dx.doi.org/10.1107/s205979832101281x.

Full text

Abstract:

The characterization of crystal defects induced by irradiation, such as X-rays, charged particles and neutrons, is important for understanding radiation damage and the associated generation of defects. Radiation damage to protein crystals has been measured using various methods. Until now, these methods have focused on decreased diffraction intensity, volume expansion of unit cells and specific damage to side chains. Here, the direct observation of specific crystal defects, such as dislocations, induced by X-ray irradiation of protein crystals at room temperature is reported. Dislocations are induced even by low absorbed doses of X-ray irradiation. This study revealed that for the same total absorbed dose, the formation of defects appears to critically depend on the dose rate. The relationship between dislocation energy and dose energy was analyzed based on dislocation theory associated with elasticity theory for crystalline materials. This demonstration of the crystal defects induced by X-ray irradiation could help to understand the underlying mechanisms of X-ray-induced radiation damage.

APA, Harvard, Vancouver, ISO, and other styles

36

CAO, Y. J., and Y. Z. LI. "SYMMETRY AND COUPLING EFFICIENCY OF THE DEFECT MODES IN TWO-DIMENSIONAL PHONONIC CRYSTALS." Modern Physics Letters B 21, no. 22 (September 20, 2007): 1479–88. http://dx.doi.org/10.1142/s0217984907013754.

Full text

Abstract:

We study theoretically the symmetric property and coupling efficiency of the defect modes in a two-dimensional phononic crystal by calculating band structures, field distributions and transmission coefficients of the defect modes. The results show that the point defect could act as a microcavity surrounded by the phononic crystal, and the confining ability of the phononic crystal to the resonant modes strongly depends on the thickness of the phononic crystal. By investigating the transmission spectra, we also find that the defect modes cannot be absolutely excited by the normally incident plane waves. The transmission coefficients are calculated by using the eigen-mode match theory method under the supercell technique, which is applied to the phononic crystals with the defects for the first time.

APA, Harvard, Vancouver, ISO, and other styles

37

Лебедев, А. А., И. П. Никитина, Н. В. Середова, Н. К. Полетаев, С. П. Лебедев, В. В. Козловский, and А. В. Зубов. "Исследование влияния структурных дефектов на спектры фотолюминесценции в n-3C-SiC." Письма в журнал технической физики 45, no. 11 (2019): 28. http://dx.doi.org/10.21883/pjtf.2019.11.47820.17755.

Full text

Abstract:

AbstractPhotoluminescence (PL) spectra have been studied in 3 C -SiC/4 H -SiC heterostructures and 3 C ‑SiC single crystals. It was shown that epitaxial 3 C -SiC layers grown on 4 H -SiC substrates have a markedly poorer crystal perfection than do 3 C -SiC single crystals. It was found that doping with aluminum gives rise to a characteristic PL both in epitaxial layers and in 3 C -SiC single crystals. At the same time, the electron irradiation of epitaxial layers does not give rise to defect-related PL, in contrast to what is observed for single crystals. An assumption is made that the twin boundaries existing in epitaxial 3 C -SiC layers can serve as getters of radiation defects that are components of donor–acceptor pairs responsible for the “defect-related” PL.

APA, Harvard, Vancouver, ISO, and other styles

38

Cooke, Jacqueline, Praneeth Ranga, Arkka Bhattacharyya, Xueling Cheng, Yunshan Wang, Sriram Krishnamoorthy, Michael A. Scarpulla, and Berardi Sensale-Rodriguez. "Sympetalous defects in metalorganic vapor phase epitaxy (MOVPE)-grown homoepitaxial β-Ga₂O₃ films." Journal of Vacuum Science & Technology A 41, no. 1 (January 2023): 013406. http://dx.doi.org/10.1116/6.0002303.

Full text

Abstract:

We report a new type of structural defect in β-Ga2O3 homoepitaxial thin films grown by metalorganic vapor phase epitaxy, which we have dubbed as “sympetalous defects.” These consist of a line defect (for example, a nanotube defect) in the underlying substrate combined with a multi-faceted inverted polycrystalline pyramid in the epitaxial film, which may also be decorated with twinned polycrystalline grains. In plan-view atomic force, scanning electron, or optical microscopies, the sympetalous defects appear similar in shape to polygonal etch pits observed for single crystals. Photoluminescence microscopy exposed spots of polarization-dependent luminescence at these defects, different from the single crystal films' luminescence. Furthermore, some of the defects exhibited circular dichroism in their luminescence that we correlated with partial helices formed within the pits by the arrangement of linearly dichroic polycrystalline grains. Finally, the density of sympetalous defects agrees with the etch pit densities of the substrates. Understanding and controlling these defects will be of importance as they modify the local properties of films, affect fabricated device yields, and influence characterization experiments.

APA, Harvard, Vancouver, ISO, and other styles

39

Hu, Yucheng, Yang Qu, and Pingwen Zhang. "On the Disclination Lines of Nematic Liquid Crystals." Communications in Computational Physics 19, no. 2 (February 2016): 354–79. http://dx.doi.org/10.4208/cicp.210115.180515a.

Full text

Abstract:

AbstractDefects in liquid crystals are of great practical importance and theoretical interest. Despite tremendous efforts, predicting the location and transition of defects under various topological constraint and external field remains to be a challenge. We investigate defect patterns of nematic liquid crystals confined in three-dimensional spherical droplet and two-dimensional disk under different boundary conditions, within the Landau-de Gennes model. We implement a spectral method that numerically solves the Landau-de Gennes model with high accuracy, which allows us to study the detailed static structure of defects. We observe five types of defect structures. Among them the 1/2-disclination lines are the most stable structure at low temperature. Inspired by numerical results, we obtain the profile of disclination lines analytically. Moreover, the connection and difference between defect patterns under the Landau-de Gennes model and the Oseen-Frank model are discussed. Finally, three conjectures are made to summarize some important characteristics of defects in the Landau-de Gennes theory. This work is a continuing effort to deepen our understanding on defect patterns in nematic liquid crystals.

APA, Harvard, Vancouver, ISO, and other styles

40

Wunderlich, Bernhard, and Stefan N. Kreitmeier. "Defects in Polymer Crystals." MRS Bulletin 20, no. 9 (September 1995): 17–22. http://dx.doi.org/10.1557/s0883769400034886.

Full text

Abstract:

The development of early knowledge about crystals of flexible macromolecules (usually called simply “polymers”) and their defects was reviewed in Reference. Much of the initial research followed the information gathered on crystals of small molecules, metals, salts, and ceramics. Very quickly, however, the special nature of polymers became obvious. It was suggested some time ago to describe semicrystalline polymers with the help of zero- to three-dimensional defects. The present status of this scheme is summarized in this article.Crystallized polymers are rarely in equilibrium. Therefore, the phase rule, which permits the presence of only one phase with two degrees of freedom (temperature and pressure) for a onecomponent material, does not apply. This nonequilibrium state is kept metastable by restrictions caused by the molecules that cross the interfaces (two-dimensional defects). The strain propagated to the noncrystalline areas produces three-dimensional defects of limited mobility. The overall structure can also be described as being microphase-separated.Often the sizes of the different phases can be as small as the nanometer scale. One-dimensional or line defects, also called dislocations, became obvious in polymers with the first observations of solution-grown crystals of polyethylene that showed frequent growth spirals. Because of the molecular chain struc ture, many of these dislocations are sessile (immobile) and cannot participate for example, in deformation mecha nisms. Until recently, zero-dimensiona or point defects were understood largely because of molecular-mechanics calculations.

APA, Harvard, Vancouver, ISO, and other styles

41

Yin, Hongbing, Peizhen Deng, and Fuxi Gan. "Defects in YAG:Yb crystals." Journal of Applied Physics 83, no. 7 (April 1998): 3825–28. http://dx.doi.org/10.1063/1.366612.

Full text

APA, Harvard, Vancouver, ISO, and other styles

42

Kleman, M. "Defects in liquid crystals." Reports on Progress in Physics 52, no. 5 (May 1, 1989): 555–654. http://dx.doi.org/10.1088/0034-4885/52/5/002.

Full text

APA, Harvard, Vancouver, ISO, and other styles

43

Karpov, S. V., I. L. Isaev, A. P. Gavrilyuk, V. S. Gerasimov, and A. S. Grachev. "Defects of colloidal crystals." Colloid Journal 71, no. 3 (June 2009): 329–39. http://dx.doi.org/10.1134/s1061933x09030065.

Full text

APA, Harvard, Vancouver, ISO, and other styles

44

KLEMAN, M., and A. PAVLOVITCH. "DEFECTS IN APERIODIC CRYSTALS." Le Journal de Physique Colloques 47, no. C3 (July 1986): C3–229—C3–236. http://dx.doi.org/10.1051/jphyscol:1986324.

Full text

APA, Harvard, Vancouver, ISO, and other styles

45

Dissanayake, S. E., and K. A. I. L. Wijewardena Gamalath. "Point Defects in GaAs Photonic Crystals." International Letters of Chemistry, Physics and Astronomy 43 (January 2015): 91–102. http://dx.doi.org/10.18052/www.scipress.com/ilcpa.43.91.

Full text

Abstract:

Applying plane wave expansion method to one dimensional multilayer system formed from alternating layers of GaAs and air, a defect mode was artificially introduced by removing a GaAs layer at the centre of a supercell and the band structures and mode field distributions were obtained. The defect mode normalized frequency was 0.28. The parameters for developing a Febry-Perot filter in the visible frequencies are given. The point defects in a two dimensional square lattice formed from GaAs rods of radius 0.16a in air was created by removing one GaAs rod at the centre of a supercell and also by increasing the centre GaAs rod radius to 0.5a. The removal of the rod folded the band structure 25 times creating a localized evanescent defect mode. The increment of the centre GaAs rod radius led to five defect bands inside the band gap with one degenerate state creating a monopole, two quadrupoles and two hexapoles. Evolution of the defect modes with the variation of the radius of GaAs rod is also presented.

APA, Harvard, Vancouver, ISO, and other styles

46

Dissanayake, S. E., and K. A. I. L. Wijewardena Gamalath. "Point Defects in GaAs Photonic Crystals." International Letters of Chemistry, Physics and Astronomy 43 (January 4, 2015): 91–102. http://dx.doi.org/10.56431/p-43shde.

Full text

Abstract:

Applying plane wave expansion method to one dimensional multilayer system formed from alternating layers of GaAs and air, a defect mode was artificially introduced by removing a GaAs layer at the centre of a supercell and the band structures and mode field distributions were obtained. The defect mode normalized frequency was 0.28. The parameters for developing a Febry-Perot filter in the visible frequencies are given. The point defects in a two dimensional square lattice formed from GaAs rods of radius 0.16a in air was created by removing one GaAs rod at the centre of a supercell and also by increasing the centre GaAs rod radius to 0.5a. The removal of the rod folded the band structure 25 times creating a localized evanescent defect mode. The increment of the centre GaAs rod radius led to five defect bands inside the band gap with one degenerate state creating a monopole, two quadrupoles and two hexapoles. Evolution of the defect modes with the variation of the radius of GaAs rod is also presented.

APA, Harvard, Vancouver, ISO, and other styles

47

Wang, Kunpeng, Jianxiu Zhang, Jiyang Wang, Changshui Fang, Wentao Yu, Xian Zhao, and Hongyan Xu. "Growth defects and infrared spectra analysis of CePO4single crystals." Journal of Applied Crystallography 38, no. 4 (July 13, 2005): 675–77. http://dx.doi.org/10.1107/s0021889805017528.

Full text

Abstract:

High-quality CePO4single crystals (monazite) were grown by the flux TSSG (top-seeded-solution growth) slow-cooling method. The X-ray powder diffraction pattern shows good crystalline quality of the crystals and the various peaks were assigned. The unit-cell parameters were calculated using theDICVOL90andTERORcomputer programs. The concentrations of all elements in the crystals were measured by electron probe microanalysis. Growth habits were deduced by the Bravais–Friedel Donnay–Harker (BFDH) method and macro-defects in the crystals are discussed. An infrared spectrum of the crystal was recorded in the frequency range of 300 to 1600 cm−1and all vibration frequency peaks were assigned.

APA, Harvard, Vancouver, ISO, and other styles

48

ZHEN, XIHE, QIANG LI, and YUHENG XU. "STRUCTURE AND OPTICAL DAMAGE RESISTANCE IN In:Mn:Fe:LiNbO3 CRYSTALS." Modern Physics Letters B 18, no. 16 (July 10, 2004): 841–46. http://dx.doi.org/10.1142/s0217984904007347.

Full text

Abstract:

A series of In : Mn : Fe : LiNbO 3 crystals were prepared with fixed concentrations of Fe 2 O 3, MnCO 3 and various concentrations of In 2 O 3. Their ultraviolet-visible (UV-Vis) absorption spectra were measured in order to investigate their defect structure. The optical damage resistance of In : Mn : Fe : LiNbO 3 crystals was characterized by the transmitted beam pattern distortion method. It increases remarkably when the concentration of In 2 O 3 is over its threshold concentration. The optical damage resistance of In (3.0 mol %): Mn : Fe : LiNbO 3 crystal is two orders of magnitude higher that of the Mn : Fe : LiNbO 3 crystal. The dependence of the defects on the optical damage resistance of the In : Mn : Fe : LiNbO 3 crystals was discussed.

APA, Harvard, Vancouver, ISO, and other styles

49

Zakharova, Maria I., and Vladimir P. Tarasikov. "The effects of neutron irradiation on the physicomechanical properties of refractory metals." Nuclear Energy and Technology 6, no. 2 (June 25, 2020): 117–23. http://dx.doi.org/10.3897/nucet.6.55230.

Full text

Abstract:

Studying the interaction of radiation defects with defects in the crystal lattice in the initial state makes it possible to distinguish the contribution of each type of defect to changes in the physicomechanical properties of materials exposed to irradiation. When comparing the changes in the properties of the metals with the body-centered cubic (BCC) lattice (Mo, W, V, Nb) and hexagonal close-packed (HCP) lattice (Re), we see common features and differences in their behavior under irradiation: − both HCP and BCC crystals show an orientation dependence of their properties; at the same time, the metals with the BCC lattice are characterized by an increase in the size of the sample in all crystallographic directions, whereas, for the HCP crystals, the sample is narrowed along the <0001> direction, perpendicular to the plane with the closest packing of atoms, and expanded along other directions; − for the BCC samples, the elastic moduli decrease; for the HCP samples, the shear modulus increases significantly as a result of irradiation; − electrical resistance for the metals of Group 6 (Mo, W) and rhenium as a result of irradiation increases; for the metals of Group 5 (V, Nb), it decreases: this decrease in electrical resistance is associated with the release of interstitial impurity atoms to radiation defects; − for the BCC crystals, relaxation processes occur both in the unirradiated and irradiated samples, whereas, in the HCP crystals, only irradiation and post-irradiation annealing cause the temperature dependence of internal friction (TDIF) and the appearance of a relaxation maximum due to a change in the point symmetry of the defect; and − during isochronous annealings up to 0.7×Тm, behavior features associated with the crystal lattice structure are retained.

APA, Harvard, Vancouver, ISO, and other styles

50

Okrepka, G. M., and V. М. Tomashik. "Selective Etching of ZnхCd1-хTe Single Crystals." Фізика і хімія твердого тіла 16, no. 4 (December 15, 2015): 711–15. http://dx.doi.org/10.15330/pcss.16.4.711-715.

Full text

Abstract:

Selective etching is an express method to identify the defects of crystal structure of semiconductors. It reveals the dislocations density, type of conductivity, crystal’s orientation, inclusions/precipitates, twins. This article is the review of selective etching of ZnxCd1-xTe single crysrals. All informations has been generalized in the table. Qualitative and quantitative compositions of etchants and information about defect structure of ZnxCd1-xTe after etchant treatment have been represented in the table.

APA, Harvard, Vancouver, ISO, and other styles

Journal articles on the topic 'Crystals – Defects'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles