Single Crystal Orientation Research Articles

Bushveld symplectic and sieve-textured chromite is a result of coupled dissolution-reprecipitation: a comparison with xenocrystic chromite reactions in arc basalt

Textures of Bushveld chromite from thin seams and accessory disseminations in the Platreef and the northernmost Waterberg Project area were compared with textures of xenocrystic chromite from mantle xenoliths found in Neogene basalt in the Kurile Island Arc. The sieve-textured to symplectic rims around the resorbed chromite in the Kurile samples resulted from the reaction between chromite and chromite-undersaturated basaltic melt, with the inclusions in chromite being entrapped during episodes of chromite primary growth, chemical dissolution, and reprecipitation or secondary growth. The relics of the lattice-oriented etch tunnels suggest that the dissolution preferentially developed along the crystallographic planes and defects. The Bushveld chromites exhibiting similar textures are interpreted as reaction-textured chromites, by analogy with the Kurile samples. The Bushveld sieve-textured, fish-hook to symplectic and amoeboidal to atoll-like chromites, are believed to have been formed due to coupled dissolution-reprecipitation of the earlier cumulus or xenocrystic chromite during interaction with chromite-undersaturated evolved melt. The electron backscattered diffraction data confirm the same single-crystal crystallographic orientation of all domains of the reaction-textured chromites as well as their clustered semi-dissolved relics. Therefore, Bushveld inclusion-rich chromite might have captured different populations of melt inclusions during its discontinuous out-of-equilibrium growth with fast episodic resorption and regeneration. The occurrence of reaction-textured chromites indicates a zone of interaction between dynamic magmatic influxes where chemical equilibrium was not achieved whereas a complete re-equilibration between chromite and the stagnant and sequestered interstitial liquid was attained during the formation of the massive chromitites.

Effect of strain hardening on subgrain formation during ECAP process

The effect of strain hardening on the grain refinement in the Equal Channel Angular Pressing (ECAP) is studied by applying various hardening models and the ratio of the latent hardening to self-hardening in the form of the latent hardening matrix in the elasto-viscoplastic material model. The initial and final orientations of pure nickel single crystals after a single pass are evaluated to study subgrain formation during the ECAP extrusion. The pole figures show that all hardening models predict almost the same trends in the grain refinement as observed in experiments. The results demonstrate that with increasing latent hardening ratios the orientations are heterogeneously scattered around the initial orientation. Also the analysis of the misorientation distribution reveals that the grain fragmentation has occurred with both high and low angle grain boundaries. The reconstruction of the microstructure after the deformation shows that when the active and latent slip systems harden equally, the number of subgrains is minimum, and with increasing latent hardening ratios (the active systems harden faster than other systems) the number of subgrains is increasing.

VUV/O3 activated direct heterogeneous bonding towards high-performance LiNbO3-based optical devices

The combination of lithium niobate (LiNbO3) and glass without an intermediate layer is an essential component of micro/nanofluidics and optical waveguides. Direct bonding is a popular method for joining homo/heterogeneous materials into a single composite. However, direct bonding of LiNbO3 and glass is extremely difficult due to the chemical inertness of LiNbO3 and the large mismatch of the coefficients of thermal expansion of these materials. In this work, we realized direct bonding of LiNbO3 and glass via VUV/O3 activation at 150 °C. Focused ion beam microfabrication tests and observation by scanning electron microscopy and transmission electron microscopy confirmed the strong LiNbO3/glass bonding interfaces. The excellent transmittance and piezoelectric properties of the direct bonded pairs and the single-crystal orientation of the LiNbO3 close to the glass demonstrated that the VUV/O3 activated direct bonding method was suitable for the fabrication of high-performance surface acoustic wave (SAW)-actuated LiNbO3-based devices. Additionally, we investigated the bonding mechanism through water contact angles, atomic force microscopy, Raman spectroscopy, FTIR spectroscopy, and adhesion measurements.

Texture in Superconducting Magnet Constituent Materials and Its Effect on Elastic Anisotropy

The materials used in superconducting magnet coils and in the structural magnet constituents are textured to various extents. This causes an angular dependence of the Young's moduli that needs to be taken into account when predicting the stress and strain distribution in the magnets. We have measured by neutron diffraction the texture in metallic materials typically used in superconducting magnets. Based on the neutron diffraction data the elastic anisotropy of the different materials has been calculated. Among the materials studied, the extruded Al oxide dispersion strengthened Cu coil wedges exhibit the strongest elastic anisotropy of 37%. The Young's moduli calculated from single crystal elastic constants and grain orientation distributions are compared with highly accurate Young's moduli derived experimentally from resonance tests.

Correction to: Prediction of strain distribution and four, six, or eight ears depending on single-crystal orientation using a new single crystal criterion

Correction to: Prediction of strain distribution and four, six, or eight ears depending on single-crystal orientation using a new single crystal criterion

Effect of annealing parameters on optoelectronic properties of highly ordered ZnO thin films

In the present work, tuning in optoelectronic properties of sputter deposited zinc oxide (ZnO) thin films on ITO coated glass substrate have been investigated as a function of annealing parameters. Although, the annealing treatment is needed to tune the optoelectronic properties of ZnO layer but it can also modify the electrical properties {a drastic change in sheet resistance (13 Ω/sq. to 23 ohm/sq.) was observed at an annealing temperature of 200 °C} of underlying ITO substrate, which restricted maximum annealing temperature to 200 °C for ZnO at ITO. Vertically standing array of ZnO nano-pipes having single crystal orientation (002) with hexagonal structure, large crystallite size (∼24 nm), lowest lattice strain (0.621%), highest surface roughness (∼16 nm), and lowest Rsh (12.3 KΩ/sq.) were obtained for sample annealed at 200 °C for 60 min. The XPS study also revealed that the sample annealed at 200 °C for 60 min contains lowest oxygen related vacancy (23.7), which favors the facile electrons transport when ZnO is used as an electron transport layer (ETL). SE and UV–Vis results revealed best optical parameters i.e., highest transmittance (T∼ 89%), refractive index (n = 1.98 at 480 nm), and band gap (Eg = 3.30 eV), for the sample annealed at 200 °C for 60 min. These results indicated that ZnO nano-pipes based ETL may be a promising candidate for low temperature, high mobility, and cost-effective optoelectronic devices.

Matrix material structure dependence of the embedded electron spin decoherence.

In this article, we present the novel application of the nuclear spin bath model and the cluster correlation expansion method on studying the matrix material structure via embedded electron spin decoherence. Profiles of embedded electron spin decoherence under the Carr-Purcell-Meiboom-Gill dynamical decoupling pulse series in a model system for organic solids (malonic acid) are calculated for different structures. Resulting decay profiles exhibit a strong correlation to the variations of an adjacent proton environment among them. In addition, the decoherence behavior of embedded spin in proton spin bath(s) of organic solids is found to be significantly different from bath models with other nuclei through the violation of the even-odd pulse parity, which characterizes the influence of large dipolar coupling between protons at the quantum level. Theoretical predictions of decoherence profiles in polycrystalline, the relative distribution of Hahn echo signal decay time scales among single crystal orientations, and the reduction in Hahn echo signal decay time scale by disorder are positively verified by experiments.

Investigating the M(hkl)| ionic liquid interface by using laser induced temperature jump technique

The interface between several Room Temperature Ionic Liquids (RTILs) in contact with both Au(hkl) basal planes and Pt(111) was studied by using cyclic voltammetry and Laser Induced Temperature Jump Technique (LITJT). Three RTILs, based on the imidazolium cation and the [Tf2N] anion were investigated: [Emmim][Tf2N], [Emim][Tf2N] and [Bmmim][Tf2N]. These three RTILs were selected with the aim to analyse how the balance between the different ion-ion interactions influences the interfacial properties of the M(hkl)|RTIL interface. It was found that the voltammetric response of the Au(hkl)|[Emmim][Tf2N] was highly sensitive to the geometry of the active surface sites, displaying sharp spikes superimposed to a capacitive voltammetric current. Conversely, these sharp spikes disappeared when [Bmmim][Tf2N] replaced [Emmim][Tf2N], although the capacitive voltammetric current profile was essentially maintained. This result is most likely related to the increase of the van der Waals interactions in the [Bmmim][Tf2N]. When [Emim][Tf2N] was analysed, the increase of the hydrogen bond interactions due to the hydrogenation of C2 (second carbon at the imidazolium ring) resulted also in the disappearance of the voltammetric spikes. The laser measurements showed that the highest values of the potential of maximum entropy (pme) in RTIL media correspond to the atomically closest packet surface structures, following the order: Au(111)>Au(100)>Au(110), in agreement with work function values. The measurement with Pt(111) revealed that the voltammetric profiles for this surface are featureless in all cases. However, the laser experiments showed that solvent restructuration, as a function of both value and direction of the applied potential, is dependent on the type of cation.Finally, the interface Au(hkl)|Choline chloride:urea Deep Eutectic Solvent (DES) was also investigated by using cyclic voltammetry and LITJT. The voltammetric response of DES was also sensitive to the orientation of the Au single crystal, and the cyclic voltammograms displayed distinct sharp and characteristic features. Nevertheless, the laser response could not provide a value of the pme for the Au(hkl)|DES interface, likely due to the complex chemical structure of the DES which, in addition, strongly adsorbs on Au(hkl).

Blistering and hydrogen retention in poly- and single- crystals of aluminum by a joint experimental-modeling approach

Abstract Aluminum samples have been exposed to a hydrogen plasma generated by a low-pressure – high-density microwave reactor. Aluminum has been chosen as a surrogate for Beryllium. The fluence was kept below 4 × 1024 ions/m2, in order to study the first steps of nucleation and growth of surface and bulk defects, i.e. blisters and bubbles. Experimental analyzes and macroscopic rate equation (MRE) modeling on poly- and single- crystals were made to investigate the role played by grains boundaries in the hydrogen retention. Temperature programmed desorption (TPD) on Al poly-crystals revealed the production of aluminum hydrides (alanes) as majority species in the desorption flux. Comparison of microscopy observations for three different single-crystal orientations (〈100〉, 〈110〉 and 〈111〉) allowed to determine preferential orientations able to attenuate the formation of blisters.

An Anisotropic Elastoviscoplasticity Model of Thermomechanical Responses of Shocked β‐HMX and α‐RDX Single Crystals

AbstractAn anisotropic elastoviscoplasticity constitutive model for β‐cyclotetramethylene tetranitramine (β‐HMX) and α‐cyclotrimethylene trinitramine single crystals (α‐RDX) is developed to analyze the thermomechanical responses under shock loading. The model considers nonlinear, pressure and temperature dependent elasticity, and dislocation‐based plasticity which incorporate regenerative multiplication and heterogeneous nucleation mechanisms. The proposed model is calibrated against experimental wave profiles of (011), (010), (100), , and orientations of HMX single crystals and (210), (100), , and (111) orientations of RDX single crystals. The model can well capture elastoplastic double wave structure, stress relaxation after the Hugoniot elastic limit as well as the arrival of plastic wave. Moreover, pressure, accumulated shear strain, and temperature contours of both HMX and RDX show obvious anisotropy and non‐uniform spatial distribution, which is explained by analyzing dislocation activity with corresponding resolved shear stress on slip systems. Results provide insights into understanding ignition mechanisms and predicting ignition sensitivity of explosive single crystals as well as polymer bonded explosives at the mesoscale.

Kinetic model of anisotropic stress assisted diffusion of nitrogen in nitrided austenitic stainless steel

The influence of elastic anisotropy of austenite on the transport of nitrogen in austenitic stainless steel (ASS) during the expanded austenite formation is analyzed by the presented kinetic model. The model is based on the thermodynamics involving the anisotropic lattice expansion due to nitrogen insertion. Thus, a diffusion behavior of nitrogen is affected by not only nitrogen concentration but also the anisotropic stress induced by nitrogen atom expanding the lattice of the steel. Developed model describes well known experimental results for polycrystalline and single crystal ASSs. Using presented model, we studied the effect of crystallographic orientations of single crystal on nitrogen penetration depth and surface concentration during formation of the expanded austenite. It was shown, that the thickness of the nitrided layer depends on the crystalline orientation and the diffusion rate is found to be highest for (100) orientation. Furthermore, anisotropic surface energies of different oriented crystals lead to anisotropy of nitrogen adsorption process. As a result, the (100) crystalline orientation is most favorable for nitrogen diffusion.

Orientation dependence of superelasticity in FeMnAlNi single crystals under compression

The orientation dependence of the martensitic transformation characteristics and superelasticity were investigated in the Fe43.5Mn34Al15Ni7.5 single crystalline shape memory alloy along the [100], [111] and [123] orientations under compression. Solution heat treated samples exhibited a strong orientation dependence of the slopes for the stress vs. temperature phase diagrams (i.e. Clausius-Clapeyron slopes), while peak-aged samples demonstrated reduced orientation dependence. Maximum superelastic strains determined in the experiments along various single crystal orientations match well with the theoretical predictions.

Deformation Microstructure of a Copper Single Crystal after Loading by Spherically Converging Shock Waves

A layer by layer study of the structure of a 34-mm ball of a copper single crystal after loading by spherically converging shock waves has been performed using transmission electron microscopy. The deformation microstructure along directions \(\left\langle {100} \right\rangle \) and \(\left\langle {110} \right\rangle \) has been studied. It has been revealed that the character of the deformation microstructure substantially depends on both the direction of the shock-wave propagation and on the depth of the layer location in the sample. In the near-surface layers of the ball that are located perpendicular the \(\left\langle {100} \right\rangle \) direction, a well-pronounced cellular dislocation structure is present; in the layers located perpendicular to the \(\left\langle {110} \right\rangle \) direction, no formation of the cellular structure occurs; there is only a high density of homogeneously distributed dislocations. Regardless of the single-crystal orientation, microbands, microtwins, banded structures, and recrystallized grains are detected along with the dislocations. Dislocation vacancy loops are observed in all layers of the ball.

Efficient Si-ZnO-ZnMgO heterojunction solar cell with alignment of grown hexagonal nanopillar

The bulk heterojunction (BHJ) grown with nanopillar has been predicted to be high performance solar cell due to having high photon and electron collection capability. Here, we report a reproducible high efficient Si-ZnO-ZnMgO BHJ solar cell having nanopillar structure (efficiency >20.9%). Due to its tendency to formation of single crystal orientation (002) in its structure and reduced contact and series resistance, long term stability is guaranteed as the device maintains its initial efficiency for 2400 h at 75% stability/reliability.

Prediction of strain distribution and four, six, or eight ears depending on single-crystal orientation using a new single crystal criterion

Significant progress has been achieved on modeling the influence of plastic anisotropy on forming of polycrystalline metal sheets. In contrast, the effect of crystal orientation on forming of single-crystal sheets has been largely unexplored. In this paper, using a recently developed single crystal criterion, it is shown that the single-crystal orientation has a very strong influence on forming. Results of F.E. simulations of cup drawing and hole expansion are reported. The same set of values of the anisotropy coefficients, which correspond to Al single crystal (with 5% Cu) is used in all simulations. It is predicted that for the {100}〈001〉 orientation four ears develop whereas for the $$ \left\{111\right\}\left\langle 1\overline{1}0\right\rangle $$ and $$ \left\{122\right\}\left\langle 1\overline{1}0\right\rangle $$ crystal orientations six, and eight ears form. Moreover, correlations between the location of the ears and the variation of the Lankford coefficients in the plane of the respective single-crystal sheets are established. F.E. analysis of hole expansion also show a strong influence of crystal orientation on the distribution of thickness strains and strain localization.

Influence of long-lasting electric field on the formation of monodomain polymer stabilized blue phase liquid crystals

Blue phase liquid crystals (BPLCs) are emerging as a promising candidate for tunable three-dimensional (3D) photonic crystals. Uniform monodomain BPLCs with a large temperature range are needed to achieve higher performance for photonic applications. Here, we experimentally demonstrated monodomain polymer stabilized blue phase liquid crystals (PS-BPLCs) induced by a long-lasting electric field. The PS-BPLCs with a single crystal orientation can be obtained with appropriate electrical treatment, and they also possess a large temperature range of 70 °C including room temperature. The physical mechanism behind their spectral properties, phase transition temperature, and the morphology of crystal growth process under different electric fields are investigated with detailed experimental analysis. This work helps further understanding of crystal nucleation and growth of PS-BPLCs in electric field and also can expedite the development of PS-BPLC based tunable 3D photonic crystal devices.

Modeling of energy-dispersive X-ray diffraction for high-symmetry crystal orientation.

The methods for X-ray crystal orientation are rapidly evolving towards versatility, fewer goniometry measurements, automation, high accuracy and precision. One method that attracts a lot of attention is energy-dispersive X-ray diffraction (EDXRD) which is based on detecting reflections from crystallographic planes in a crystal at fixed angles of a parallel polychromatic X-ray incident beam. In theory, an EDXRD peak can move in a diffraction pattern as a function of a crystallographic plane d-spacing and its orientation relative to a fixed direction in space can change also. This is equivalent to the possibility of measuring the orientation of single crystals. The article provides a modeling for the EDXRD method whose main feature is the nonmoving crystal in the sense of traditional goniometry where the angle measurements of diffracting planes are a must. The article defines the equation of orientation for the method and shows the derivation in great detail. It is shown that the exact solutions of the equations can be obtained using the generalized reduced gradient method, a mathematical subroutine that is implemented in Excel software. The significance and scientific impact of the work are discussed along with the validated tested results.

Low-cost Cu-based shape memory single crystals obtained by abnormal grain growth showing excellent superelasticity

Metal single crystals are generally obtained by directional solidification with sophisticated equipment and process. This method is not only very expensive but also very time-consuming. In this study, we report a new approach to produce Cu-Al-Mn-Mo shape memory alloys with single crystals through annealing cast polycrystalline alloys. The microstructure of the cast alloys has a common characteristic that the L21-Cu2AlMn parent is completely coherent with bcc A2(Mo) precipitates due to bcc phase separation. The dissolution of bcc A2(Mo) nanoparticles during annealing process results in abnormal grain growth because of the formation of a continuous misorientation gradient within the grains. The single crystals obtained from large grains exhibit excellent superelasticity. When the orientation of single crystals is close to [−210], the largest full superelasticity is up to 10%, and the largest superelastic strain is up to 6.7%. It is expected that such microstructural design can also be applied to the production of large grains and even single crystals of other alloy systems with phase separation.

Microstructure and mechanical properties of a MoSi2-Mo5Si3 eutectic composite processed by laser surface melting

Laser surface melting (LSM) of a single-crystal substrate of a MoSi2-Mo5Si3 eutectic composite has been performed to check the feasibility of mechanical property improvement through microstructure refinement and seeded growth of the eutectic composite on top of the seed composite single crystal by additive manufacturing processes using scanned laser beam. LSM is proved to be capable of obtaining a eutectic composite maintaining the eutectic script-lamellar microstructure as well as crystallographic orientations of the substrate single crystal. The eutectic script-lamellar microstructure is considerably refined from several micrometers (the substrate) to several tenths nanometers (43 ± 7 nm) after LSM processing while maintaining the orientation relationship. Due to the microstructure refinement, the hardness increases by about 38% from 11.60 ± 0.04 GPa (substrate) to 15.96 ± 0.42 GPa (LSMed region) and the fracture toughness increases by about 34% from 3.8 ± 0.3 MPa m1/2 (substrate) to 5.1 ± 1.5 MPa m1/2 (LSMed region).

Crystallographic orientation errors in mechanical exfoliation

We evaluate the effect of mechanical exfoliation of van der Waals materials on crystallographic orientations of the resulting flakes. Flakes originating from a single crystal of graphite, whose orientation is confirmed using STM, are studied using facet orientations and electron back-scatter diffraction (EBSD). While facets exhibit a wide distribution of angles after a single round of exfoliation (), EBSD shows that the true crystallographic orientations are more narrowly distributed (), and facets have an approximately error from the true orientation. Furthermore, we find that the majority of graphite fractures are along armchair lines, and that the cleavage process results in an increase of the zigzag lines portion. Our results place values on the rotation caused by a single round of the exfoliation process, and suggest that when a 1–2 degree precision is necessary, the orientation of a flake can be gauged by the orientation of the macroscopic single crystal from which it was exfoliated.