Lattice Dislocations Research Articles

Revealing the interface structure of {111} type I twin in Ti-Ni-Hf shape memory alloy composite

• The interface of martensite twins in Ti-Ni-Hf shape memory alloy composite was studied. • The formation mechanisms of {111} type I twins in Ti-Ni-Hf alloy was revealed. • The lattice dislocations and misfit dislocations of the interface of martensite variant are identified. In the present study, the interface of martensite twins in Ti-Ni-Hf shape memory alloy composite was studied by high resolution transmission electron microscopy in terms of atomic structure. The results reveal that two varieties of interface structure for {111} type I twins are observed, which is determined by the interior substructure (001) compounds twin. The formation of {111} type I twins can be attributed to the interaction between the misfit dislocations on (001) plane and ( 1 ¯ 11) twin boundary. In addition, the corresponding characteristic parameters of misfit dislocation were calculated in theory. The theoretical value of disregistry factor and average spacing for the misfit dislocations are well in good agreement with the experimental results.

Mechanisms and Performance Analysis of GaN-Based Micro-LED Grown on Pattern Sapphire Substrate by Laser Lift-Off Process

The laser lift-off (LLO) process was employed to fabricate a monochromatic GaN-based green micro-light-emitting-diode (Micro-LED) 14 × 14 arrays grown on pattern sapphire substrate (PSS) in this research. A new experimental phenomenon and internal mechanism of some epitaxial residues on the top and sidewalls of PSS protrusion after laser stripping were deeply discussed. In addition, the reasons for the formation of micro lattice dislocation of epitaxial layer crystal caused by laser were also analyzed. The leakage current of the array devices after LLO was 200 times higher that before LLO under the same voltage, but the light output current efficiency was discovered to be 109.7% higher under the 500 cd m−2 brightness. The results indicate peak wavelength was blue shift 3 nm once the LLO process had been performed. Furthermore, the optical pattern from a “heart-shaped” distribution before LLO was changed into the maximum intensity directly above the array devices. The luminous angle was also reduced from ±75° to ±65°, which indicates that the collimation of the light after LLO process was increased. The results are high important for understanding the optical properties of Micro-LED array devices after LLO process.

Initiation Mechanism of Localized Corrosion Induced by Al2O3-MnS Composite Inclusion in Low-Alloy Structural Steel

The present work systematically investigated the initiation mechanism of localized corrosion induced by Al2O3-MnS composite inclusion in E690 steel under a simulated marine environment. The results showed that a micro-gap exists between the Al2O3-MnS inclusion and the matrix, and electron backscattered diffraction (EBSD) analysis revealed significant lattice dislocation zones around the Al2O3-MnS composite inclusion. The presence of the micro-gap and the lattice dislocation both promoted the localized corrosion initiation. The Volta potential of Al2O3 detected by scanning Kelvin probe force microscopy (SKPFM) was approximately 149.33 mV higher than that of the steel matrix, and the Volta potential of MnS was 10 mV lower than that of the steel matrix. The current-sensing atomic force microscopy (CSAFM) results showed that the Al2O3 was not conductive, while the MnS had good conductive properties. Therefore, it was not possible for a galvanic couple to be formed between Al2O3 and the adjacent steel matrix. A galvanic couple effect between the MnS and the adjacent steel matrix was directly demonstrated for the first time. The MnS acted as the anode phase for preferential dissolution in the corrosion process. The in situ immersion experiments and the Pourbaix diagram results confirmed that the dissolution of MnS was an electrochemical reaction process and the dissolution of Al2O3 was a chemical reaction.

Enhanced dielectric and optical performance of (Cu, Ag) co-doped ZnO nanostructures for electronic applications

ABSTRACT Pure and Cu/Ag co-doped ZnO nanoparticles were synthesised by the co-precipitation method. The phase and structural analysis of ZnO nanoparticles were examined by using XRD and Williamson-Hall plots. XRD spectra revealed that prepared samples exhibit hexagonal wurtzite structure of ZnO. The change in lattice parameters, bond length, dislocation density and strain indicates that Cu and Ag were successfully incorporated. UV vis studies indicated the red shift in the absorption band attributed to defects induced after dopant additions. The dielectric measurements showed that the dielectric constant was found to increase and the dielectric loss decreases with increase in dopant percentage. Additions of Cu and Ag in ZnO lattice may lead to supplement grain boundary defects which can increase polarisation. The relatively higher values of ac conductivity were also found due to modulation of charge carrier density after dopant additions which suggest that the diffusion controlled charge carrier hopping mechanism is involved.

Elastically non-linear discrete model for core of edge dislocation

To facilitate the modeling of crystal defects on their core scales, the present paper introduces a discrete stress balance equation that admits non-linear elasticity of the defected crystal cell and its arbitrary boundary conditions. Thus, the cell may be free or embedded into continuum. In the latter case, when considering a sufficiently large domain tractable by the proposed method, boundary forces can be related to long-range stresses of the defect. For a case study, an edge dislocation in the primitive cubic lattice is simulated to assess influence of the crystal dimensions and elastic properties on the microscopic discrete core.

Do some virtual bound states carry torsion trace?

This paper presents theoretical arguments that certain virtual bound states carry the trace component of affine torsion. The motivation for this work is that Einstein–Cartan theory, which extends general relativity by including torsion to model intrinsic angular momentum, is becoming more credible. We are not aware of any situation for which there is evidence or substantial argument for the presence of torsion trace, except in the continuum theory of edge dislocations in crystals. The main evidence for the hypothesis consists of analogies between the structure of virtual bound states and (a) geometry of dislocations in crystal lattices, which are modeled with torsion; and (b) modeling of intrinsic angular momentum by torsion in Einstein–Cartan theory and the theory of micro-elasticity. The work focuses on conjectured presence of torsion in para-positronium, which intermediates annihilation of an electron and a positron with opposite z-spins. If the virtual bound state carries torsion, then the local law of conservation of angular momentum can hold over the spacelike separation during annihilation.

RETRACTED: Improving the Structural, Optical and Photovoltaic Properties of Sb- and Bi- Co-Doped MAPbBr3 Perovskite Solar Cell

We prepared 1% Bi- and (0, 0.5%, 1% and 1.5%) Sb- co-doped MAPbBr3 films by a sol-gel spin coating technique. For the first time, the detailed structural properties including grain size, dislocation line density, d-spacing, lattice parameters, and volume of co-doped MAPbBr3 films have been investigated. XRD confirmed the cubic structure of MAPbBr3 with high crystallinity and co-doping of Bi and Sb. The 1% Bi and 1% Sb co-doping have a surprising effect in MAPbBr3 structures, such as large grain size (59.5 nm), d-space value (6.23 Å), small dislocation line dislocation (2.79 × 1018 m−2), and small lattice parameters (a = b = c = 6.3 Å) and volume of unit cell. The detailed optical properties, including energy band gap (Eg), refractive index (n), extinction coefficient (k) and dielectric constant (Ɛ), which are very important for optoelectronics applications, were investigated by UV-Vis spectroscopy. The film of 1% Bi and 1% Sb co-doped MAPbBr3 showed good optical response including small Eg, high n, low value of k, high real and low imaginary parts of dielectric constant, making it good for solar cell applications. Solar cells were fabricated from these films. The cell fabricated with pure MAPbBr3 has Jsc of 8.72 mA cm−2, FF of 0.66, Voc of 1.29 V, and η of 7.5%. All the parameters increased by co-doping of Bi and Sb in MAPbBr3 film. The cell fabricated with 1% Bi and 1% Sb co-doped MAPbBr3 film had high current density (12.12 mA-cm−2), open circuit voltage (Voc), fill factor (0.73), and high efficiency (11.6%). This efficiency was 65% larger than a pure MAPbBr3-based solar cell.

Structural, morphological and optical characterizations of spray pyrolyzed nickel oxide thin films

A simple spray pyrolysis technique was used to prepare thin nickel oxide films on glass substrates at different substrate temperatures (350 °C, 400 °C, and 450 °C). Hydrated Nickel Acetate (Ni(CH3COO)2·4H2O) salt solution was used as a precursor to producing these thin films. The structural properties of the films were characterized by X-ray Diffraction (XRD) spectroscopy. The XRD curve confirms that the films were crystalline, and their preferred growth orientation was along the (111) plane. The values of the lattice parameter, dislocation density, and microstrain were changed with the temperature of the substrate. Scanning Electron Microscope (SEM) micrographs of the surface of the prepared thin films showed uniform morphology with nanorings. A UV-visible Spectrophotometer was used to detect absorption and transmission spectra in the spectral region of 300 nm–900 nm. The films deposited at 400 °C and 450 °C have 80% transparency in the visible wavelength region, while the films deposited at 350 °C have lower transparency. The optical bandgap of the films was varied with substrate temperatures and the values were from 3.55 to 3.65 eV. Other optical metrics, including extinction coefficient, refractive index, optical conductivity, and electron energy loss functions, were also affected by substrate temperature.

Phosphorization-Introduced Defect-Rich Phosphorus-Doped Co3O4 with Propelling Adsorption–Catalysis Transformation of Polysulfide

Cathodic polysulfide electrocatalysts are introduced to confidently accelerate the polysulfide conversion to propel the increased practical density of lithium–sulfur (Li–S) batteries. Defect engineering as an advanced functional strategy has been confirmed to have the competent capability of optimizing the electrocatalytic kinetics. In this work, the conventional phosphorization process is used to process Co3O4 anchored on nitrogen-doped carbon nanotubes. Unexpectedly, there is no phase change, only phosphorus doping with rich lattice dislocation on Co3O4. With the combined characterization of X-ray diffraction, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy, it is found that phosphorus doping transfers part of the oxygen vacancies to the lattice oxygen of Co3O4, which can induce the catalytic active species Co–O–P. The concomitant lattice dislocations can strengthen the chemical adsorption of phosphorus-doped Co3O4 for polysulfides and even elevate more catalytically active sites. With the use of defect-rich phosphorus-doped Co3O4 embedded in a nitrogen-doped carbon nanotube (P-Co3O4/NCNT) as an electrocatalyst, Li–S batteries showcase enhanced oxidation and reduction kinetics and an improved rate performance. This work provides new insight into the rational design of the electrocatalyst of heteroatom-doped metal compounds for high-performance Li–S batteries.

Alpha-to-gamma phase transformation self-reinforcing of Alumina Ceramic Slit Array in Nd:YAG Laser Cutting Based on Vapor-to-melt Ratio Controlling

The greatest challenge in the subsequent processing of alumina ceramic slit arrays is the strength of the cutting wall. Because of its high brittleness, the fracture toughness of the wall has become one of the most important factors limiting the cutting quality. In the process of laser cutting alumina ceramics, α-γ reverse phase transformation is caused by the lattice dislocation effect due to instantaneous impact of high-energy beam, which can be induced in the heating/melting process and retained in the rapid cooling process. Generally speaking, due to the metastable characteristics of γ-Al2O3 lattice structure, the density, hardness and mechanical strength of the phase change products are obviously lower than α-Al2O3. However, the looser structure endows γ-Al2O3 with higher shear deformation component and fracture toughness, which potentially generates self-reinforcing effect when attached to the substrate. By controlling the material removal mode, i.e. vapor-to-melt ratio, the effects of different phase transformation content and distribution on the wall of slit array is discussed to reveal the phenomenon and mechanism of α-γ phase transformation self-reinforcing. The results show that the thickness of phase transformation layer and mass fraction of γ-Al2O3 both decrease with the increase of rvmr and the existence of phase transformation layer will slightly reduce the Vickers hardness of residual molten layer. However, a thinner phase transformation layer can simultaneously enhance the fracture toughness of the slit wall. Through the observation of the micromorphology and the comprehensive evaluation of the mechanical properties of the slit wall, it can be concluded that, under the appropriate vapor-to-melt ratio parameters (stable state of the molten layer and good cutting quality), the material is removed in time, and a small amount of phase transformation products contained in the residual molten layer can produce a self-reinforcing effect on the cutting slit.

Lattice rotation effect on the dislocation pattern of Cu deformed in tension

ABSTRACT The dislocation pattern of cold deformed FCC metals follows an orientation-dependent rule. However, only final orientation after deformation has been considered in related studies, i.e. without considering lattice rotation effect, although metals have undergone heavy lattice rotation during plastic deformation. In this work, the lattice rotation effect on the dislocation structures of Cu is investigated by combining electron backscatter diffraction, focused ion beam lift-out and scanning transmission electron microscopy techniques. The dislocation patterns of [110]-[110], [111]-[111] and [110]-[111] type grains deformed in tension under room temperature are compared. The notation [h1k1l1]-[h2k2l2] represents the lattice rotation history of a grain, meaning that the grain rotates from [h1k1l1] corner to [h2k2l2] corner during tension. It is found that for a given strain range, the dislocation cell structure is observed in [111]-[111] grain, while the dislocation cell block structure is dominant in [110]-[111] grain. This demonstrates that for Cu grains with a final orientation near [111] corner, dislocation pattern type is influenced by the lattice rotation feature. Same with [110]-[111] type grain, cell block structure is the main feature found in [110]-[110] grain, indicating that for grain with initial orientation near [110] corner, lattice rotation has a marginal effect on the dislocation structure. The relation between the dislocation structure, lattice rotation, slip system and strain level of Cu is discussed.

A Comparative Investigation of the Effect of Microstructure and Crystallographic Data on Stress-Oriented Hydrogen Induced Cracking Susceptibility of API 5L X70 Pipeline Steel

In this research, stress-oriented hydrogen induced cracking (SOHIC) test was carried out on a 50 mm thickness of a commercial API 5L X70 steel plate. The evolution of microscopic features such as phase, boundary, interface, grain, and crystallographic data was analyzed before and after SOHIC, in order to comprehend the effect of crystallographic orientation on SOHIC propagation. Chemical composition and previous thermomechanical processing even finish rolling temperature and cooling rate determine the ferrite matrix microstructure. A recrystallized ultrafine ferrite grain with about 3–5% degenerated pearlite dispersed in the microstructure was characterized, called as-received specimen. The average lattice strain and dislocation density was calculated first using multiple Gaussian peak-fitting method from XRD pattern. Electrochemically charged combination mixed H2S-CO2 solution, constant hydrogen injection, and external loading were applied to tensile specimen, in order to simulate the H2S and CO2 environment. The results show that local misorientation and Taylor factor analyses predicted the possibility of hydrogen crack nucleation especially at boundaries and interfaces. Moreover, SOHIC crack propagation occurred along the mid-thickness of the cross section of steel plate along the ferritic boundaries, pearlitic colonies, and ferrite-cementite interfaces. Moreover, the crack propagated along distorted {110} and {001} grains, indicating a strong strain gradient towards the boundaries. The analysis of XRD patterns of SOHIC tested specimen by multiple Gaussian peak-fitting method estimated about 68% increment in micro-deformation and approximately 170% increase in dislocation density.

The tensile properties and microstructure evolution of cold-rolled Fe–Mn–C TWIP steels with different carbon contents

Fe–18Mn-1.0C and Fe–18Mn-0.6C twinning-induced plasticity steels are cold rolled at various rolling reductions, and their tensile properties, evolution of dislocation density, and twinning behavior during tensile deformation were systemically investigated. With increasing the cold rolling reduction, the yield strength and tensile strength of both steels increase obviously, especially for Fe–18Mn-1.0C steel; concurrently, the elongation to fracture decreases largely while this decrease is not as significant for Fe–18Mn-1.0C steel as for Fe–18Mn-0.6C steel. Furthermore, dislocation density and the amount of deformation twins increase with increasing rolling reduction and tensile strain. Such increase is more obvious for Fe–18Mn-1.0C steel than for Fe–18Mn-0.6C steel. A maximum (or saturation) dislocation density and a maximum (or saturation) amount of deformation twins are observed in specimens when they are deformed to fracture. Compared with Fe–18Mn-0.6C steel, the saturation values of dislocation density and amount of deformation twins are obviously larger in Fe–18Mn-1.0C steel, regardless of cold rolling reductions. The contributions of lattice friction stress, dislocations, twins and dynamic strain ageing (DSA) to flow stress were quantitatively analyzed using a parametric model. Dislocation strengthening and twin boundaries strengthening are found to play a dominant role in increasing the flow stress during tensile deformation, and the contribution from DSA is negligibly small.

Moiré Pattern Dislocation in Continuous Atomic Lattice of Monolayer h-BN

Moiré Pattern Dislocation in Continuous Atomic Lattice of Monolayer h-BN

Deformation behavior during hot torsion of an ultrahigh carbon steel containing 1.3 wt.% C

Abstract The torsion behavior of an ultrahigh carbon steel containing 1.3 wt.% C has been studied at high strain rates (2 – 26 s –1) and high temperatures (900 – 1200 °C). Adiabatic heating strongly affects the shape of the stress– strain curves. Grain size measurements at strains of ε = 2 and ε = 5 reveal that the austenite grain size does not change between these two strains and is finer than the initial austenite grain size. This is an indication that a recrystallization process took place in the interval of strains between ε peak and ε = 2 and that the deformation state associated to the strains of ε = 2 and ε = 5 can be considered as steady state. Stress–strain rate relations have been analysed for ε peak, ε = 2 and ε = 5. It has been found that data obtained at ε peak correlate well with a lattice diffusion-controlled dislocation creep process. On the other hand, analysis of the stress –strain rate relations found at the steady state indicated that the deformation occurs by the contribution of two independent mechanisms: grain boundary sliding controlled by pipe diffusion and slip creep controlled by lattice diffusion.

Strain-size features of bare ZnSe:Cu and ZnSe:Cu@ZnS core/shell quantum dots from extensive X-ray diffraction analysis, and their photoluminescence properties

ZnSe:Cu d-dots and ZnSe:Cu@ZnS core/shell quantum dots (QDs) were synthesized under different synthesis regimes of Cu-dopant content, microwave irradiation time (MWIRT) and over-coating of ZnSe:Cu by ZnS shell in order to optimize their structural and photoluminescence (PL) properties. The morphological and microstructural characterizations broadly done by transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD), revealed the spherical shape, synthesis-condition tunable and almost uniform size distribution of bare and core/shell QDs. Extended X-ray diffraction analysis (XDA) was performed by employing both Williamson-Hall (W–H) and Williamson-Smallman (W–S) approaches in order to validate these methods and obtain lattice strain (ε), dislocation density (δ) and particle size. The results indicated that all the QDs had cubic zinc-blend structure with an average crystallite size of ∼1.5 nm, and shift of peak positions shift toward higher angles for core/shells compared with bare QDs. W–S and W–H's outputs for bare and core/shell QDs showed similar trends, i.e. the optimal Cu-content of 0.1 mol% with higher crystalline quality. In addition, bare and core/shell QDs were investigated by Ultraviolet–Visible and PL spectroscopy. The blue-shift of band gap for the synthesized ZnSe QDs (∼3.5 eV) in comparison with bulk counterpart (∼2.7 eV) confirmed the formation of nano-sized particles. It was found that these QDs exhibited PL emission in the range of 423–559 nm. After changing the experimental variables during the experiment, the samples with optimal PL were identified. In reasonable relation to the microstructural aspects, ZnSe:Cu(1.5%) under MWIRT = 6 min has the highest band-edge PL intensity, which was associated with increased particle size, reduced lattice strain and higher atomic order raised from MWIR. Among the core/shell QDs, ZnSe:Cu(1.5%)@ZnS under MWIR indicated the highest band-edge emission intensity, which besides the microstructural parameters, may be a result of the morphological change from spherical to nanorod as certified by TEM. In addition, ZnSe@ZnS under MWIR showed the highest trap-defect emission intensity. In brief, due to the strong experimental condition-dependence of studied features, which is very important in tuning the properties, the studied bare and core/shells can be promising agents in green-blue luminescent photometric-biological applications.

Microwear mechanism of monocrystalline germanium

Germanium (Ge), as a higher mobility material, presents great merits for future semiconductor field-effect transistor devices. Extremely smooth Ge surface is required for high-performance devices, which depends on mechanical surface planarization. However, the defects generated during surface manufacturing usually degrade device performance, which are desired to be minimized to improve the performance and service life of Ge-based products. In this paper, when a light normal load was applied on monocrystalline Ge surface by an atomic force microscope (AFM), the pile-up was generated in the scratched area under line-scan mode by a diamond tip. The formation of the pile-up intensely depends on the contact pressure, and the threshold is about 10.7 GPa, which is close to the microhardness of Ge. Unlike the formation of anodized hillock, the amorphization of Ge was found to be the main contributor to the pile-up induced by the scratch, rather than the oxidation. Based on chemical composition and microstructure detections, it suggests that the pile-up is constructed by thin oxide layer (possibly GeOx (x≤2)) on the surface, thick amorphous layer in the middle and deformed Ge (lattice dislocations excluding amorphization) at the bottom. These findings provide a fundamental understanding of the light-load machining process on monocrystalline Ge surface.

STRUCTURAL CHARACTERIZATION OF BRASS BY Au-ION IMPLANTATION: SURFACE ANALYSIS

Brass has been tested for the modification in its structural, electrical properties as well as hardness using Au-ion implantation. Four ion doses were devised as follows: [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] ions/cm2. SRIM/TRIM software helped to predict Au-ion distribution inside the brass. The alloy was then characterized using X-ray diffraction (XRD), microhardness, four-point probe testing and scanning electron microscopy (SEM) analysis. The microstructure parameters from XRD analysis were determined and used for the calculation of lattice parameter, crystallite size, microstrain and dislocation density. The microhardness value was observed to be changed from 106[Formula: see text]HV to 119[Formula: see text]HV with the maximum increase as 12.26%. A noticeable decrease occurred in the crystallite size from 44[Formula: see text]nm to 34[Formula: see text]nm for the plane (2 2 0) due to increase in dislocation density, and the corresponding change in ([Formula: see text]/[Formula: see text] is also noted. The electrical conductivity is overall found to be decreased, whereas the [Formula: see text]-spacing values fluctuated with ion dose. SEM analysis helped observing the microstructural changes, which occurred in the form of particulates and defects, namely pores, voids, cavities and craters. The relationships between microstructure and these properties are important for developing new materials for future prospects.

High Thermoelectric Performance Achieved in Sb-Doped GeTe by Manipulating Carrier Concentration and Nanoscale Twin Grains.

Lead-free and eco-friendly GeTe shows promising mid-temperature thermoelectric applications. However, a low Seebeck coefficient due to its intrinsically high hole concentration induced by Ge vacancies, and a relatively high thermal conductivity result in inferior thermoelectric performance in pristine GeTe. Extrinsic dopants such as Sb, Bi, and Y could play a crucial role in regulating the hole concentration of GeTe because of their different valence states as cations and high solubility in GeTe. Here we investigate the thermoelectric performance of GeTe upon Sb doping, and demonstrate a high maximum zT value up to 1.88 in Ge0.90Sb0.10Te as a result of the significant suppression in thermal conductivity while maintaining a high power factor. The maintained high power factor is due to the markable enhancement in the Seebeck coefficient, which could be attributed to the significant suppression of hole concentration and the valence band convergence upon Sb doping, while the low thermal conductivity stems from the suppression of electronic thermal conductivity due to the increase in electrical resistivity and the lowering of lattice thermal conductivity through strengthening the phonon scattering by lattice distortion, dislocations, and twin boundaries. The excellent thermoelectric performance of Ge0.90Sb0.10Te shows good reproducibility and thermal stability. This work confirms that Ge0.90Sb0.10Te is a superior thermoelectric material for practical application.

Influence of temperature on twinning dominated pop-ins during nanoindentation of a magnesium single crystal

The present paper examines the temperature sensitivity of tensile twinning in a magnesium single crystal during nanoindentation of the prismatic plane. High temperature indentations from 25 °C to 250 °C were employed on a well polished magnesium single crystal {10-10} plane. For a indentation curve displaying a pop-in, a single twin was seen on the sample surface using Atomic Force Microscopy (AFM) imaging. For indentations that produced no pop-in, no twinning was observed. We thus conclude the pop-in arises from a twinning event in the present case. With increasing temperature, the mean pop-in load (measured from 200 repeat indentations of each testing temperature) drops markedly. This is interpreted by the thermal activation of nucleation of lattice dislocations, which immediately trigger a twinning event. Thermal activation analysis yields activation energies that are consistent with this idea. With increasing temperature the pop-ins became deeper and the twins, after further indentation, showed more growth. It is likely that non-basal slip is activated in the stress concentrations that arise during twinning and the thermal activation of this slip accounts for the observed temperature effects. It is concluded that in interpreting the temperature sensitivity of twinning stresses, any associated lattice dislocation activity must be considered.