Concentration Of Stacking Faults Research Articles

Effect of N and Al Doping on 3C-SiC Stacking Faults

This study offers a comprehensive examination of the behavior of 3C-SiC crystals grown on 4° off-axis (100) Si substrates with different off-axis angles along <110> and <100> for N and Al doping, respectively. The investigation takes advantage of molten KOH etching to conduct an in-depth investigation of the average density and size of the SFs inside the crystal for both n- and p-type doped 3C-SiC epitaxial layers. Moreover, 3C-SiC grown on a <100> off-cut substrate was revealed to have a greater concentration of SFs due to the absence of self-annihilation along the plane (-1-10). Considering two different doping ranges suitable for IGBTs and MOSFETs development, the impact of doping and off-angle on the crystal quality, concentration, and length distribution of SFs was then investigated in order to quantify the influence of N and Al incorporation on the structural and optical characteristics of the semiconductor. It turned out that under heavy nitrogen doping (~1019 cm-3), when the dopant concentration grew, the average length of the stacking faults (SFs) expanded while their density dropped.

Detailed microscopic observations of the structure of bulk colloidal crystals grown by sedimentation

Since the actual and microscopic structure of hard-sphere-type colloidal crystals has not been fully understood, we performed detailed microscopic structural characterization of the sedimentation-grown opal-type colloidal crystals by conventional optical microscopy, laser conforcal microscopy, and secondary electron microscopy. It is directly proved for the first time, to the best of our knowledge, that iridescent striations originate from the repetition of twin structures and stacking faults in crystal structures. We propose “subdomain” as an intrinsic constitutional unit of a monocolored iridescent “domain” and the subdomain boundary is defined as the envelope of the edges of stacking faults. Every domain forming the bulk crystal contains a high concentration of slanted stacking faults at various tilt angles inherent to the domain. These observations show that the bulk colloidal crystals can be described in terms of five stages of hierarchical structure units, bulk crystal, domains, sub-domains, pristine single-crystal lamellae, and silica particles.

Phase controlled synthesis and cathodoluminescence properties of ZnS nanobelts synthesized by PVD

Zinc sulfide (ZnS) nanobelts were synthesized via physical vapor deposition to explore the electronic properties of optoelectronic nano-devices. It was determined that the mass ratio of wurtzite (WZ) phase to zincblende (ZB) phase and the preferential orientation (100) are related to the carrier-gas flow rate. The high concentration of planar defects within the phase boundary enhances phase transition. Cathodoluminescence measurements show a red shift of the 337 nm band-gap emission due to stacking and twin faults. We find a direct correlation between the magnitude of the red shift and the mass ratio of ZB phase. With an increase in the ZB phase, there is an increase in the concentration of stacking and twin faults introduced by the phase transformation, as indicated by an increasing red shift in the data. The absorption peaks at 666 and 719 nm were found by UV–vis absorption spectrum, which is attributed to surface defects. This work would help to better understand the important roles of planar defects in the phase transition and also provide us with a feasible route to control phase ratio and cathodoluminescence properties of ZnS nanobelts and other II-VI semiconductor nanostructures.

X-ray radiography investigation of structural conditions of Fe-15Cr-35Ni- 11 W steel irradiated by ion-plasma fluxes

It was found that structural-phase transformations induced by radiation in the highly doped heat resistant Fe-15Cr-35Ni-11 W alloy under the effects of treatment with ion-plasma beams differ from the transformations in steels of types 0 × 18H10T and 0 × 16N15M3B widely used in nuclear power engineering. Presence of these differences was established by performing X-ray radiography analysis, which demonstrated that additional reflections on the X-ray patterns of irradiated samples of Fe-15Cr-35Ni-11 W alloy appear from the side of large angles relative to the reflections for the initial solid solution. Detailed X-ray diffraction studies carried out by the authors showed that additional peaks appeared from the side of smaller angles in the X-ray diffraction patterns of iron-chromium alloys of type 0 × 18 (10–30) H additionally doped with Ti, Mo, Nb, Al to the amount of 1–3% and irradiated with ion-plasma beams.In both cases the phase thus formed is of isomorphic matrix type and is thermally metastable and, in contrast to 0 × 18H10T steel, Fe-15Cr-35Ni-11 W alloy undergoes softening. The analysis of published data on the possible causes inflicting similar structural-phase transformations in materials subjected to intensive ion-plasma treatment was performed. Concentrations of crystalline lattice stacking faults in Fe-15Cr-35Ni-11 W alloy and in 0 × 18H10T steel in the deformed state were determined by X-ray diffraction analysis. It was found that concentration of structural stacking faults in this state is 4 times higher for 0 × 18H10T steel, which indicates the lower stacking fault energy in this steel. Conclusion was made that the observed effects are associated with the mechanism of radiation-induced plastic deformation. Structural-phase changes in Fe-15Cr-35Ni-11 W alloy are associated with deformation by twinning, in contrast to 0 × 18H10T steel, where the observed transformations are due to slip deformation.

Structure and Mechanical Properties of Nitrogen Austenitic Steel after Ultrasonic Forging

Electron microscopy and X-ray diffraction have been used to investigate a nitrogen 07Kh17AG18 steel with an austenitic structure after the surface deformation treatment—ultrasonic forging. During ultrasonic forging, an austenitic structure transforms into a new structure with an elevated concentration of deformation-induced stacking faults, a lot of deformation microtwins, e-martensite crystals. The austenite lattice parameter is found to be decreased in the surface layer. After ultrasonic forging, nitrided steel exhibits enhanced strength properties with retained high plasticity.

Effect of Ag doping on the microstructure and photoluminescence of ZnO nanostructures

ZnO nanostructures were obtained by metal-organic chemical vapor deposition via Ag catalyst-assisted growth in a temperature range of 200–500 °C. Growth at temperatures above 500 °C resulted in vertically aligned ZnO nanorods (NLs). Ag incorporation into ZnO up to 0.4 at.% promoted creation of basal plane stacking fault (BSF) defects and corrugation of the side facets of the NLs. The presence of BSFs give rise to an additional photoluminescence peak with a wavelength of ∼386 nm, which is slightly red-shifted compared to the commonly observed NBE emission at ∼375 nm. The observed emission was found to be specifically observed from the side facets of the NLs. It is suggested that this emission is due to a high concentration of BSFs in the ZnO as a result of an incorporation of Ag as acceptor dopant. SEM image of an Ag-doped ZnO nanorod with corrugated side facets. The observed corrugation is accompanied by a high concentration of basal plane stacking faults.

Characterization of a‐plane GaN templates grown by HVPE and high efficiency deep UV emitting AlGaN/AlN MQWs grown by MBE on such templates

AbstractThick GaN templates (>50 µm) were grown by hydride‐vapor‐phase epitaxy (HVPE) on the r‐plane of sapphire. While X‐ray diffraction indicates that the GaN grows with its a‐plane parallel to the r‐plane of sapphire, the surface has a triangular morphology of 120º, which is the result of the faster growth rate of the a‐plane compared to the m‐plane. Electron microscopy studies indicate that these GaN templates have a high concentration of threading defects (>1010 cm–2) and basal plane stacking faults (7x105 cm–1). Several identical deep‐UV emitting Al0.7Ga0.3N/AlN multiple quantum wells (MQWs) were grown on such GaN templates by molecular‐beam epitaxy (MBE). The wells were grown under more gallium than required by stoichiometry, which changes the growth mode from physical vapor deposition to liquid phase epitaxy. This growth mode leads to deep band structure potential fluctuations. The structure and microstructure of these MQWs were evaluated by transmission electron microscopy (TEM) and found to have even higher density of threading defects than the GaN template. In spite of this, the internal quantum efficiency (IQE) of these MQWs was estimated from the temperature dependence of the cathodoluminescence spectra to be 87%. This remarkable result was attributed to the deep band structure potential fluctuations introduced by the liquid‐phase epitaxy growth mode as well as the high concentration of basal plane stacking faults. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Microstructure dependence of the c-axis critical current density in second-generation YBCO tapes

C-axis current flow in high temperature superconductor (HTS) tape-shaped wires arises in configurations where the local wire axis is not perpendicular to the local magnetic field, such as in power cables with helically wound HTS tapes. The c-axis critical current density Jcc has been recently found to be orders of magnitude lower than the ab-plane critical current density Jcab. Here we report on Jcc (77 K, sf) values of various YBa2Cu3O7-based (YBCO) tapes with different microstructures. Our results show that the value of Jcc (77 K, sf) decreases significantly with increasing concentration of ab-plane stacking faults in YBCO thin films and that the critical current anisotropy γ = Jcab/Jcc can reach values as high as 2070, implying that in the highest-anisotropy tape, ∼20% of the tape width carries c-axis current in a helically wound power cable.

Metal organic vapor phase epitaxy growth of single crystalline GaN on planar Si(211) substrates

We present metal organic vapor phase epitaxy growth of polarization reduced, wurtzitic gallium nitride layers with an 18° inclination of the c-axis to the surface normal on planar Si(211) substrates. The growth of this layer is performed as c-axis oriented growth on the naturally occurring Si(111) planes of the Si(211) substrate. Cathodoluminescence measurements on a ∼1.2 μm thick structure reveals that it has a low concentration of basal plane stacking faults and no prismatic stacking fault luminescence.

Peculiarities of the X-Ray Powder Diffraction Patterns from FCC Crystals Containing a High Concentration of Random Deformation Stacking Faults

Peculiarities of the X-Ray Powder Diffraction Patterns from FCC Crystals Containing a High Concentration of Random Deformation Stacking Faults

High oxygen pressure generation of flux-pinning centers in melt-textured YBa2Cu3O7

A strong enhancement of the critical current density, Jcab(H,T), has been generated in melt-textured YBa2Cu3O7/Y2BaCuO5 composites by means of high oxygen pressure (≈100 bar, ∼400 °C). Enhancement factors as high as 180% have been found at low temperatures leading high sample performances at 77 K (Jcab≈1.2×105 A/cm2 at null field). Transmission electron microscopy studies show a high concentration of dendritic-like stacking faults generated as a consequence of the strong nonequilibrium conditions of the transformation from YBa2Cu3O7 to YBa2Cu4O8. The high concentration of 1/6〈031〉 partial dislocations within the (001) planes are proposed as point-defect pinning centers enhancing Jcab(H,T) for the H∥c configuration.

The Monte Carlo simulation of random stacking faults in close-packed structures

A new approach to the estimation of the concentration of random stacking faults in close-packed structures (and also multilayers) is presented. It is based on the Monte Carlo computer simulation of the arrangement of stacking faults in a crystal, given by an appropriate h-k sequence. Thus the corresponding intensity (structure-factor) distribution along the streaked reciprocal-lattice rows may be calculated from nearly the same expression as for a perfect multilayer structure. In particular, good agreement is observed with the computations on the basis of the intensity equations derived for several particular cases. Some peculiarities in the diffracted intensity distribution of crystals with multilayer structures containing random stacking faults of different types, or having different dimensions of the hexagonal unit cell, are pointed out.

Structural characteristics of cobalt particles in a 9.5%Co-ZSM-5 catalyst

A detailed structural study of cobalt particles in a 9.5%Co-ZSM-5 catalyst was made using X-ray diffraction and analytical transmission electron microscopy. The results obtained from these two techniques show that the cobalt particles contain a high concentration of basal plane stacking faults. On the average one out of every 12 basal planes is faulted. It is suggested that atoms of a particle which lie at positions on the surface where intersection stacking faults exist may be the origin of active sites.

Fine structure of steel 5Kh3V3MFS after LTMT and standard heat treatment

1. Plastic deformation of austenite in the metastable temperature range leads to a reduction in the effective size of coherent scattering regions. With increasing strain rates the effective size of blocks decreases. 2. The true size of coherent scattering regions averages 20% smaller after LTMT than after standard heat treatment. With increasing rates of plastic deformation the true size of coherent scattering regions remains unchanged. 3. The concentration of deformation and twin stacking faults after LTMT increases with increasing deformation and increasing strain rates. When the strain rate is increased by two orders the concentration of deformation stacking faults doubles. 4. The variation of the dislocation density with deformation is linear. With increasing strain rates the dislocation density decreases. 5. The inversely proportional relationship between the dislocation density and strain rate in LTMT is due to dynamic strain aging of austenite.

An X-ray diffraction study on the lattice imperfections in vapour-deposited FCC (Ag-4.5 at.% Ge) alloy films

Fourier analyses of both multiple and single-order reflections in FCC (Ag-4.5 at.% Ge) alloy films (68 to 238 nm thick) indicated appreciable coherent domain size and lattice strain effects with slight lattice contraction and significant compressive long-range residual stress. The study further reveals large concentrations of growth twin stacking faults but none that were intrinsic or extrinsic. The films showed a high dislocation density and a strong preferential texture along (111).

An X-ray investigation of growth and deformation faults in a vapour grown 2H SiC crystal

Single crystals of 2H SiC grown by hydrogen reduction of methyltrichlorosilane at 1400°C frequently contain a high concentration of random stacking faults in their hexagonal closepacked | AB | AB | … structure. This given rise to diffuse streaks along reciprocal lattice rows parallel to the c ∗ axis for h − k ≠ 0 mod 3. To investigate the nature of stacking faults in these crystals, the intensity distribution along the 10. l reciprocal lattice row of a 2H SiC crystal was recorded on a 4-circle computer-controlled single crystal diffractometer. The halfwidths of 10. l reflections with l even and l odd were found to be 0.36 and 0.24 reciprocal units respectively. It is observed (i) that the 10. l reflections with l even are highly broadened and (ii) that the halfwidths of l even and l odd reflections are in the ratio of 3 : 2. This suggests that the stacking faults present are predominantly growth and deformation faults. Since the fault concentration is very high, exact theoretical expressions for the halfwidths of 10. l reflections were used to calculate the growth and deformation fault probabilities (α and β) from the observed half widths, without neglecting the second and higher order terms in α and β. It is found that α = 0.11 and β = 0.20. The deformation fault probability (β) is surprisingly high for hard and brittle material like SiC which does not undergo plastic deformation easily. It is suggested that several deformation fault configurations have resulted from a clustering of growth faults.

An X-ray diffraction profile analysis of vacuum-evaporated copper films: normal and oblique vapour incidence

A detailed study of copper films was made in the thickness range 80-330 nm for the 111, 200, 220, 311 and 222 reflections. Only high concentrations of growth-twin stacking faults have been observed. The line-shift analysis has shown the existence of small lattice parameter changes and appreciable residual stresses, tensile in nature, for the films deposited from an oblique vapour beam. The line-broadening analyses considering multiple-order and single-order ('linlog') reflections have shown the presence of small coherent domain sizes lying in the range 45-175 AA and an appreciable amount of total RMS strain resulting in a density of dislocations rho approximately 1011 cm-3. The effective coherent domain size De and RMS strain values obtained from the 'linlog' method show considerable anisotropy and the average ratio (De)111/(De)100 approximately 2.0 signifies a fairly large contribution of stacking faults to the domain size broadening. For all the films more than 100 nm thick the 'apparent' orientation factor R approximately=3.0-4.0 indicates a preferential orientation of (111) planes parallel to the film surface.

A model for the growth of anomalous polytype structures in vapour grown SiC

A number of polytype structures observed in vapour grown SiC crystals have a unit-cell which is an integral multiple of the unit-cell of the basic 6H, 15R or 4H structure. The growth of such anomalous structures cannot be understood in terms of spiral growth round a single screw dislocation in a basic matrix. However many of these polytype crystals display a single growth spiral on their (0001) face indicating that they have resulted from spiral growth round a single screw dislocation. It is shown that this anomaly can be resolved if the basic matrix is assumed to contain stacking faults near the surface at the time of the origin of the screw dislocation ledge. This possibility, overlooked in the earlier deduction of polytype structures, must be taken into consideration since vapour grown SiC crystals frequently contain a high concentration of random stacking faults, producing continuous streaks on their X-ray diffraction photographs. The most probable fault configurations that can occur in 6H, 15R and 4H structures of SiC have been deduced from a calculation of their stacking fault energy. These fault configurations are then considered to lie at different distances from the surface at the time of the origin of a screw dislocation ledge. Such a faulted ledge gives rise to polytype structures during subsequent spiral growth even if the screw dislocation has an integral Burgers vector. The most probable series of polytype structures that can result from such a faulted matrix model are deduced. It is shown that nearly all the polytype structures of SiC hitherto regarded as anomalous (such as 36H, 54H, 66H, 45R, 90R etc.) are among the expected structures and there is no need to postulate a complicated configuration of cooperating dislocations to account for their growth.

An X-ray line profile analysis in vacuum-evaporated silver films

An X-ray Fourier line profile analysis from multiple-order and single-order reflections has been performed considering 111, 200, 220, 311 and 222 reflections recorded in a counter X-ray diffractometer from eight vapour-deposited thin films in the range of thickness 58-212 nm. Detailed analysis of line shift, line asymmetry and Fourier line shapes measurements have been found to yield large concentrations of growth twin stacking faults only in the thin film range with a total absence of intrinsic and extrinsic ones for the entire range. Measurements of the domain size, dislocation density, RMS strains and orientation factors were made, and their dependence on the film thickness investigated.

The Preparation and Crystal Structure of TlMnCl3, TlFeCl3, TlCoCl3 and TlNiCl3

AbstractThe compounds TlMnCl3, TlFeCl3, TlCoCl3 and TlNiCl3 were prepared by heating T1C1 with the corresponding transition metal dichloride in an evacuated ampoule. Atomic positions were determined from powder photographs. All four compounds were found to be related to the perovskite type structure. TlMnCl3 has a cubic structure, space group Pm3m, with ao = 5.025 Å. The other three compounds are hexagonal, probable space group P63mc, with cell dimensions (in Å) a0 = 6.976 and c0 = 6.008 for the Fe compound, a0 = 6.907 and c0 = 5.981 for the Co compound and a0 = 6.863 and c0 = 5.881 for the Ni compound. The three hexagonal compounds are isomorphous. A measureable concentration of basal plane stacking faults was found to occur in TlFeCl3 and also, to a lesser degree, in TlCoCl3.