Dislocation Growth Research Articles

Screw dislocation assisted spontaneous growth of single-crystalline α-Al2O3 microrods

Abstract Herein we reported a simple chemical vapor deposition approach to synthesize single crystal α-Al 2O3 microrods with diameters of 2–4 μm and lengths of 10–30 μm on the as-prepared SiC-Si-Al2O3 ceramics based on the screw dislocation growth. Two types of evidence for screw dislocation growth have been conclusively observed in the as-synthesized microrods: scanning electron microscopy analysis reveals that the representative morphology feature of the screw dislocation growth is the stepwise spiral terrace configuration and the growth kinetics of the as-synthesized microrods follows the prediction of the dislocation growth mechanism as described by Burton-Cabrera-Frank theory. This work provides not only a new method for synthesizing Al 2O3 microrods but also a new insight into the growth mode for Al2O3 microrods.

Polymorphic Smooth Interfaces Formation Based on the Biphasic BaTeMo2O9 Using Top Multi-Seeded Growth

An interesting phenomenon of two polymorphic heterojunctions is reported in this paper. The selective growth of the individual phases of high-quality α- and β-BaTeMo2O9 (BTM) crystals was successfully achieved using an optimized flux system and growth parameters. A biphasic BTM crystal based on a multiseeding technique used to control the nucleation and subsequent growth was realized in a one-flux system. The formation of a grain boundary, similar to a heterojunction, between the α- and β-BTM crystals emerged as an unavoidable consequence of this process, and the factors that led to the formation of the grain boundaries in the multiseeds were examined. Lattice mismatch and interfacial binding energy calculation verified that the BTM crystals were grown together rather than being physically adhered, and the chains at the grain boundary were linked by O5Mo–O–MoO5 dioctahedrons corner-sharing O atoms at the eutectic boundary. The screw dislocation growth mechanism was confirmed for β-BTM with the growth unit...

Structural defects in ZnGeP2single crystals revealed by X-ray topography

The results of X-ray transmission topography and diffraction analysis of a ZnGeP2single crystal grown by the vertical Bridgman method in the [001] direction are presented and discussed. The FWHM of rocking curves over a large area of a (100) longitudinal slice is about 12′′, which is indicative of the high quality of the examined sample. Glow discharge mass spectrometry does not show significant content of foreign chemical elements. X-ray topography reveals growth striations and dislocations. The predominant defects are single dislocations and their pile-ups. Near to the growth-axis region, curved dislocation bundles passing through the entire crystal are observed, on which precipitates are formed. In the initial part of the crystal, dislocations are located chaotically, while towards the middle of the sample they are aligned along the growth striae. In the final part of the crystal, the dislocation density increases.

Injuries of the Sportsman’s Hand

Injuries of the Sportsman’s Hand

The Relationship of Femoral Tunnel Positioning in Medial Patellofemoral Ligament Reconstruction on Clinical Outcome and Postoperative Complications

To analyze the relation of the femoral tunnel (FT) positioning on clinical outcome. Patients with recurrent patellar dislocation who underwent medial patellofemoral ligament (MPFL) reconstruction with or without tibial tubercle osteotomy between 1998 and 2012 were included in this retrospective study. Strict postoperative lateral radiographs were mandatory. Knees with previous osseous stabilization surgery, fixed lateral patellar dislocation, valgus knee (>5°), or open growth plates were excluded. The distance between the FT and the validated radiographic landmark (the "Schoettle point") was measured. An FT with a distance greater than 10mm was considered as malpositioned. The distance was correlated to subjective outcome measurements (patient satisfaction and Kujala score) and postoperative complications (a loss of range of motion and revision surgery). Sixty-three knees in 60 patients (aged 23.7 ± 7.5years at the time of surgery, 79.4% female) were included with a mean follow-up of 5.7 ± 3.3years. The FT showed an average distance of 13.3mm (±6.0mm; 95% confidence interval [CI]: 11.7-14.8) to the Schoettle point, and 45 of 63 knees (71.4%) were deemed malpositioned. The postoperative Kujala score of malpositioned FT (75.9 points; 95% CI: 71.2-80.7) was not significantly inferior to knees with an FT within 10mm (80.5; 95% CI: 73.7-87.3, P= .315). However, all 5 knees that underwent revision surgery showed an FT outside the 10-mm area. Malpositioning of the FT in MPFL reconstruction is associated with postoperative complications. However, a malpositioned FT in MPFL reconstruction will not necessarily lead to an unsatisfactory subjective or objective clinical outcome. Other factors, such assurgical indication or graft tensioning, might also significantly influence postoperative outcome. Level IV, case-control study.

Atomistic simulation analysis of the effects of void interaction on void growth and coalescence in a metallic system

Material deformation caused by the interaction between defects is a significant factor of material fracture failure. The present study employs molecular dynamics simulations of single-void and double-void crystalline Ni atomic systems to investigate inter-void interactions. Furthermore, simulations showing the evolution of dislocations for three different crystallographic orientations are conducted to study the void growth and coalescence. The simulations also consider the effect of the radius of the secondary void on dislocation evolution. The results show that double-void systems are more prone to yield than single-void systems. Further microstructural analysis indicates that the interaction between voids is realized by dislocation reactions. The simulation results of the dislocation evolution of the three orientations reveal that a relationship exists between the evolution of the dislocation density and the stress-strain curve. At the initial stage of dislocation, the dislocation grows slowly, and consists of Shockley partial dislocation. The dislocation growth rate then increases significantly in the sharply declining stage of the stress-strain curve, where most of dislocations are Shockley partial dislocation. Analysis of the dislocation length during the overall simulation indicates that the dislocation length of the [110] orientation is the longest, followed by that of the [111] orientation and the [100] orientation, which has the shortest dislocation length.

Radiation resistance of oxide dispersion strengthened alloys: Perspectives from in situ observations and rate theory calculations

Here, in situ ion irradiation and rate theory calculations were employed to directly compare the radiation resistance of an oxide dispersion strengthened alloy with that of a conventional ferritic/martensitic alloy. Compared to the rapid buildup of dislocation loops, loop growth, and formation of network dislocations in the conventional ferritic/martensitic alloy, the superior radiation resistance of the oxide dispersion strengthened alloy is manifested by its stable dislocation structure under the same irradiation conditions. The results are consistent with rate theory calculations, which show that high-density nanoparticles can significantly reduce freely migrating defects and suppress the buildup of clustered defects.

New insights into microstructural evolution of epitaxial Ni–Mn–Ga films on MgO (1 0 0) substrate by high-resolution X-ray diffraction and orientation imaging investigations

In this work, a detailed investigation has been performed on hetero-epitaxial growth and microstructural evolution in highly oriented Ni–Mn–Ga (1 0 0) films grown on MgO (1 0 0) substrate using high-resolution X-ray diffraction and orientation imaging microscopy. Mosaicity of the films has been analysed in terms of tilt angle, twist angle, lateral and vertical coherence length and threading dislocation densities by performing rocking curve measurements and reciprocal space mapping. Density of edge dislocations is found to be an order of magnitude higher than the density of screw dislocations, irrespective of film thickness. X-ray pole figure measurements have revealed an orientation relationship of || (1 0 0)MgO; || [0 0 1]MgO between the film and substrate. Microstructure predicted by X-ray diffraction is in agreement with that obtained from electron microscopy and atomic force microscopy. The evolution of microstructure in the film with increasing thickness has been explained vis-à-vis dislocation generation and growth mechanisms. Orientation imaging microscopy observations indicate evolutionary growth of film by overgrowth mechanism. Decrease in coercivity with film thickness has been explained as an interplay between stress field developed due to crystal defects and magnetic domain pinning due to surface roughness.

Spontaneous growth of hexagonal ZrB2 nanoplates driven by a screw dislocation mechanism

Hexagonal ZrB2 nanoplates had been successfully synthesized by a facile molten-salt assisted borothermal reduction technique based on the screw dislocation growth mechanism for the first time.

Low threading dislocation density GaAs growth on on-axis GaP/Si (001)

We report a systematic study of high quality GaAs growths on on-axis (001) GaP/Si substrates using molecular beam epitaxy. Various types of dislocation filter layers and growth temperatures of initial GaAs layer were investigated to reduce the threading dislocation densities in GaAs on GaP/Si. Electron channeling contrast imaging techniques revealed that an optimized GaAs buffer layer with thermal cycle annealing and InGaAs/GaAs dislocation filter layers has a threading dislocation density of 7.2 × 106 cm−2, which is a factor of 40 lower than an unoptimized GaAs buffer. The root-mean-square surface roughness was greatly decreased from 7.8 nm to 2.9 nm after the optimization process. A strong enhancement in photoluminescence intensity indicates that the optimized GaAs template grown on on-axis (001) GaP/Si substrates is a promising virtual substrate for Si-based optoelectronic devices.

Crystal growth and viscous flow in barium disilicate glass

Decoupling between the diffusion coefficients that control crystal growth (DU) and viscous flow (Dη) in deeply supercooled glass-forming liquids is one of the most celebrated, still unsolved, phenomena in glass science because it strongly impacts the analysis and prediction of crystallization kinetics. To further understand the decoupling phenomenon, we measured viscosity and crystal growth rates (of the crystalline surface layer growth and internally nucleated crystals) of a supercooled liquid with barium disilicate composition. We performed all measurements using glass samples from the same batch, a rare case that we call a “clean” experiment. This type of analysis is uncommon, and its aim is to minimize the uncertainty due to the composition variation that is inherent in laboratory glass production. The decoupling temperature (Td), the glass transition temperature (Tg), the melting point (Tm), and the liquid fragility index were obtained and successfully used to test a recently derived relationship which allows one to estimate Td by knowing only Tm and the viscosity curve. We also show, for the first time, that the reduced decoupling parameter, which gauges the degree of deviation between DU and Dη, does not depend on the crystal growth mechanism for the cases of Normal or Screw Dislocation growth.

Growth and characterization of high quality N-type GaSb/GaAs heterostructure by IMF growth mode using MOCVD for low power application

In this study, we demonstrate the growth of a 150-nm-thick GaSb layer on a GaAs substrate with excellent film quality using the interfacial misfit dislocation growth mode by the Metal–Organic Chemical Vapor Deposition technique. The n-type GaSb epilayer grown on the GaAs substrate has a low threading dislocation density of 3.2 × 106 cm−2 and a surface roughness of approximately 0.8 nm. A high carrier mobility up to 4600 cm2 V−1 s−1 with a carrier concentration of 1.2 × 1017 cm−3 is achieved in this study. The fabricated Al2O3/GaSb/GaAs MOSCAP demonstrated excellent capacitance–voltage (C–V) characteristics with a small frequency dispersion of approximately 2.8%/decade. The results demonstrate the potential of high-mobility Sb-based materials on GaAs for p-type channel CMOS applications in the future.

Microstructure and texture evolution of electrodeposited coatings of nickel in the industrial electrolyte

Nickel is an important strategic metal material, which has been widely used in modern industry. The different electrolyte systems and main parameters have a great effect on microstructure and mechanical properties of electrodeposited coatings. In order to investigate the evolution of texture and preferential orientation of nickel electro-crystallization in sulfide nickel soluble anode/sulfate solution, and grain size, microstructure of electrodeposited coatings of nickel were characterized by electrochemical workstation, XRD and SEM methods.The results show that nickel electro-crystallization conforms to the classical nucleation theory and crystal growth theory. The preferential orientation of electrodeposited coatings of nickel can be changed initially from (111) and (200) planes to (220) plane after 16h. The surface morphology changes slowly from pyramid to cellular structure, while the growth mechanism changes from screw dislocation growth to cumulative growth model. The cross sectional microstructure of electrodeposited coatings is non-uniform and mostly grains are columnar and perpendicular to the sheet. The distribution of grains abides by stepwise distribution along the thickness. The microstructure of electrodeposited coatings is fine equiaxed grain region and coarse columnar grain region, which are perpendicular to starting sheet when the electrodeposition time is 144h. Angle grain boundary is related to grain size, whereas the coincidence site lattice (CSL) is associated with preferential orientation. Therefore the grain boundary misorientation are mainly above 15°, being more than angle grain boundaries and coincidence site lattice Σ3 appearing highest frequency.

Characterization of screw dislocation-driven growth in nickel micro-nanostructure electrodeposition process by AFM

In this study, nickel coating with micro-nanostructure feature was fabricated by a simple two-step method during electrodeposition process. To evaluate surface morphology characteristics, the histogram and power spectral density analyses of atomic force microscopy data were extracted from two different morphologies of nickel films. Results showed that boric acid plays an important role in the control of nucleation and the growth of micro-nanostructures. With clear observation of growth steps in atomic force microscopy characterization, terrace width and spiral growth proved the existence of screw dislocation growth.

Dislocation loop formation in model FeCrAl alloys after neutron irradiation below 1 dpa

FeCrAl alloys with varying compositions and microstructures are under consideration for accident-tolerant fuel cladding, but limited details exist on dislocation loop formation and growth for this class of alloys under neutron irradiation. Four model FeCrAl alloys with chromium contents ranging from 10.01 to 17.51 wt % and aluminum contents of 4.78 to 2.93 wt % were neutron irradiated to doses of 0.3–0.8 displacements per atom (dpa) at temperatures of 335–355 °C. On-zone STEM imaging revealed a mixed population of black dots and larger dislocation loops with either a/2〈111〉 or a〈100〉 Burgers vectors. Weak composition dependencies were observed and varied depending on whether the defect size, number density, or ratio of defect types was of interest. Results were found to mirror those of previous studies on FeCrAl and FeCr alloys irradiated under similar conditions, although distinct differences exist.

Demonstrating antiphase domain boundary-free GaAs buffer layer on zero off-cut Si (0 0 1) substrate for interfacial misfit dislocation GaSb film by metalorganic chemical vapor deposition

High quality 40 nm GaSb thin film was grown on the zero off-cut Si (0 0 1)-oriented substrate using metalorganic chemical vapor deposition with the temperature-graded GaAs buffer layer. The growth time of the GaAs nucleation layer, which was deposited at a low temperature of 490 °C, is systematically investigated in this paper. Cross-sections of the high resolution transmission electron microscopy images indicate that the GaAs compound formed 3D-islands first before to quasi-2D islands, and finally formed uniform GaAs layer. The optimum thickness of the 490 °C-GaAs layer was found to be 10 nm to suppress the formation of antiphase domain boundaries (APDs). The thin GaAs nucleation layer had a root-mean-square surface roughness of 0.483 nm. This allows the continued high temperature GaAs buffer layer to be achieved with low threading dislocation density of around 7.1 × 106 cm−2 and almost invisible APDs. Finally, a fully relaxed GaSb film was grown on the top of the GaAs/Si heterostructure using interfacial misfit dislocation growth mode. These results indicate that the GaSb epitaxial layer can be grown on Si substrate with GaAs buffer layer for future p-channel metal-oxide-semiconductor field effect transistors (MOSFETs) applications.

Critical thickness of GaN on AlN: impact of growth temperature and dislocation density

Critical thickness and strain relaxation of c-plane GaN layers grown by molecular beam epitaxy on AlN were studied as a function of growth temperature and threading dislocation density (TDD). For this purpose we used AlN/sapphire templates and AlN single crystals with TDDs of ∼109 cm−2 and ∼103 cm−2, respectively. Whereas at high growth temperature (900 °C) the critical thickness for plastic relaxation is only 3 monolayers (MLs) for both substrates, this value drastically increases when decreasing the growth temperature. It reaches ∼30 MLs when GaN is deposited at 750 °C on AlN single crystals. We also observed that the strain relaxation rate strongly depends on TDD. These results exemplify the lack of efficient gliding planes in III-nitrides when grown along the c-axis, which, combined with low kinetics, allows for plastic relaxation to be frozen out. Achieving pseudomorphic GaN layers on AlN is of interest for two-dimensional electron gases based on AlN/GaN/AlN heterostructures lattice-matched to AlN single crystal substrates.

The growth and perfection of β-cyclotetramethylene-tetranitramine (HMX) studied by laboratory and synchrotron X-ray topography

An examination has been made of the defect structure of crystals of the energetic material β-cyclotetramethylene-tetranitramine (HMX) using both Laboratory (Lang method) and Synchrotron (Bragg Reflection and Laue method) techniques. The results of the three methods are compared with particular attention to the influence of potential radiation damage caused to the samples by the latter, more energetic, technique. The comparison shows that both techniques can be confidently used to evaluate the defect structures yielding closely similar results. The results show that, even under the relatively casual preparative methods used (slow evaporation of unstirred solutions at constant temperature), HMX crystals of high perfection can be produced. The crystals show well defined bulk defect structures characteristic of organic materials in general: growth dislocations, twins, growth sector boundaries, growth banding and solvent inclusions. The distribution of the defects in specific samples is correlated with the morphological variation of the grown crystals. The results show promise for the further evaluation and characterisation of the structure and properties of dislocations and other defects and their involvement in mechanical and energetic processes in this material.

Growth of Oxygen Precipitates and Dislocations in Czochralski Silicon

The impact of oxygen precipitates and dislocations on carrier recombination is investigated on thick silicon slabs cut vertically from a Czochralski-grown silicon ingot. Using a combination of photoluminescence imaging, photoluminescence spectroscopy, and Fourier transform infrared spectroscopy, we investigate the impact of pre-anneal on their recombination activity. We show that the vacancy concentration during precipitate growth affects the recombination activity of oxygen precipitates. Finally, we demonstrate the impact of nonequilibrium point defect concentrations on precipitate and dislocation growth.

Incorporation of the Organic Additives during the Damascene or TSV Process: Influence of the Applied Waveform

The today increase demand for high-performance microelectronic products requires new reliable interconnection metallization for microelectronic packaging. Copper electroplating is a cost-effective technology, mainly adopted to manufacture interconnects in integrated semiconductor devices [1-3]. In copper 3D interconnections, Damascene or Through Silicon Via (TSV) technologies; numerous factors have an influence on the filling and microstructural results, as the copper bath composition, the applied current density and waveform, the plating cell hydrodynamics…, conditioning the final resistivity of the copper layer. These parameters must be more and more optimised to achieve the filling of a large challenging range via dimensions and very aggressive aspect–ratio. Nevertheless whatever the design of the vias, the substrate composition, the plating cell and other parameters, the free-defect filling of interconnections is obtained only by bottom-up mechanism, where the copper deposition is promoted by superfilling effect and limited on the top, thanks to the addition of two or three organic additives. Without organic additives, only conformal or sub-conformal platings can be grown, causing voids, defects, lack of adherence and poor compactness. The superfilling mechanisms, depending on the additive composition, their relative concentration and the competition between them, are well described and simulated by the curvature-enhanced acceleration accumulation (CEAC) mechanism [4]. Determined first from steady-state measurements, this model permit to predict the evolution of via filling by copper [5], with no information concerning additives incorporation or signature throughout this layer. Indeed, the use of additives introduces also impurities and additives breakdown products during the copper growing. These contaminating agents create defects during the crystallisation like vacancies or dilatation sites of dislocation and limit grain boundary motion and growth during the self-annealing of the copper layer. These phenomena are well deal in the works of Koh et al. [6], and Stangl et al. [7] and particularly well observed with the use of aged bathes. Strangl et al. [7] have demonstrated the incorporation differences between a regular plated copper film and a pulse plated. Favry et al. [5] have also investigated the organic adsorption and inclusion during the copper growing as a function of the additive concentrations or current density. By the combination of electrochemical measurements and SIMS analysis, they have proved an increase of organic inclusion during a regime modification in the plating process. In this present research work, the influence of the applied waveform on the organic additives incorporations is discussed. The work focuses on the organic trace analyses by complementary analysis methods: XPS and SIMS. Firstly, XPS for X-ray photoelectron spectroscopy is a surface (10 nm) sensitive quantitative technique. The resulting spectrum allows the determination of the elementary and chemical composition of the analysed material and the concentration of the different detected elements. The XPS sensitivity is around 0.1 at.%, allowing a chemical cartography of the sample surface composition just after the bath extraction, with the determination of additive adsorptions during an OCP time. Then thanks to an ionic abrasion during the acquisition, a depth analysis is possible, profiling the elements concentration in the bulk material and not only on the surface. Secondly, based on heavy ions bombardment, SIMS for secondary ion mass spectrometry allows a surface composition analysis by sputtering, collecting and mass analysing of ejected secondary ions. This destructive method enables the determination of the elemental, isotopic and molecular composition of a surface or a bulk. The SIMS sensitivity is around 10-4 and 1 at%, but the quantitative analyse is limited. After electrochemical considerations concerning the influence of applied current density waveforms, this research work presents a comparative study of organic incorporations by XPS and SIMS analyses for different copper layers, taking into account the applied waveforms and the bath composition. [1] M. Paunovic at al, Fundamental Considerations in Modern Electroplating 5th edition, edited by M. Schlesinger and M. Paunovic, Wiley edition (2010) [2] M. Datta, Electrochemical processing technologies and their impact in microelectronic packaging in Microelectronic Packaging, edited by M. Datta, T. Osaka and J.W. Schultze, CRC Press edition (2005) [3] J.W. Dini et al, Electrodeposition of copper in Modern Electroplating 5th edition, edited by M. Schlesinger and M. Paunovic, Wiley edition (2010) [4] P.M. Vereecken et al, IBM J. Res. & Dev., 49 1 (2005) [5] E. Favry et al, Electrochimica Acta 53 (2008) 7004-7011 [6] L.T. Koh et al, Microelectronics Journal 33 (2002) 229-234 [7] M. Stangl et al, Microelectronic Engineering 84 (2007) 54-59 Figure 1