Surface Crystal Orientation Research Articles

Effect of microstructure on outer surface roughening of magnesium alloy tubes in die-less mandrel drawing

The crystal orientation and outer surface roughening of magnesium alloy tubes were evaluated to clarify the effect of the mandrel on the microstructure and outer surface roughness in die-less mandrel drawing. Locally heated ZM21 tubes with an outer diameter of 6.0 mm and an inner diameter of 3.8 mm were drawn with and without a mandrel. The outer surface roughness and crystal orientation were evaluated in the same measurement area. The results indicated that the outer surface becomes rougher in the die-less mandrel drawing than in die-less drawing for a given outer circumferential strain. The outer surface roughness developed when there was large difference in the pyramidal slip system Schmid factor. Therefore, the slip deformation of the pyramidal slip system seems to be mainly responsible for the outer surface roughening in the die-less mandrel drawing. Furthermore, the crystal grain with the {2 1 ¯ 1 ¯ 0} crystal plane vertical to the normal direction of outer surface had a larger Schmid factor than the other crystal grains. The large number of crystal grains with the {2 1 ¯ 1 ¯ 0} crystal plane in the die-less mandrel drawing is one of the reasons that the outer surface roughness develops more in the die-less mandrel drawing than in die-less drawing for a given outer circumferential strain. These results will contribute significantly to the development of fabrication process of the microtube with high surface quality, which prevents rapid corrosion of biomedical applications.

Seed surface orientation dependence of the defect formation at the initial stage of physical vapor transport growth of 4H-SiC crystals

The influence of the seed crystal surface orientation on the defect formation at the initial stage of physical vapor transport (PVT) growth of 4H-SiC crystals was investigated using X-ray topography and Raman scattering microscopy. To examine the detailed influence of the seed surface orientation, a seed crystal having a groove on the growth surface was used for PVT growth; the seed crystal with a groove provides a continuously varying seed surface orientation from (0 0 0 1¯) (on-axis c-face growth) to (1 1 2¯ 0) (a-face growth), and using the seed crystal, the effect of the seed surface orientation can be examined in a single growth experiment. X-ray topography observations revealed that a number of threading screw dislocations (TSDs) were formed at the bottom corners of the groove, while their formation was largely suppressed at the bottom of the groove, indicating that an off-oriented (0 0 0 1¯) seed crystal surface tends to generate TSDs. Characteristic dopant striations were also observed in the crystal portions grown on the off-oriented seed crystal surface, and the generated TSDs were found to propagate along the boundaries of these dopant striations. Based on these results, we discuss the TSD formation mechanism on an off-oriented (0 0 0 1¯) seed crystal surface at the initial stage of PVT growth of 4H-SiC crystals and suggest an important role of macrostep formation on the surface.

Liquid Diffused Separation Induced Crystallization to efficiently grow centimeter-sized diamond-like Cs4PbBr6 crystals for light-emitting applications

Large-size single crystal (SCs) is an excellent platform for studying the optoelectronic properties of materials. However, growing high-quality crystals has always been a challenge. Here we develop a liquid-induced diffusion (LDSC) method for high-efficiency and low-cost growth of centimeter-sized Cs4PbBr6 crystals. All-sized crystals with a special diamond-like appearance exhibit strong green photoluminescence (PL) and good stability. In addition, X-ray diffraction (XRD) reveals that the diamond-like Cs4PbBr6 crystal exhibits a different crystal surface orientation from the rhombic SCs. More importantly, different from the CsPbBr3 impurity-induced photoluminescence mechanism, the strong green PL of the as-prepared diamond-like Cs4PbBr6 crystal originates from its defect state: Br vacancies (VBr). Furthermore, high-efficiency white light-emitting diodes (WLED) devices are prepared by using high-luminous intensity Cs4PbBr6 crystals as green light emitters. The optimized devices generate high-quality white light with luminous efficiency of ∼54 lm W−1, which is much better than that of conventional perovskite nanocrystals-based LED devices. Our work demonstrates that the Cs4PbBr6 crystal devices possess higher luminous efficiency, better stability and great application potential in display backlighting.

Surface evolution of crystalline SrTiO3, LaAlO3 and Y3Al5O12 targets during pulsed laser ablation

Pulsed laser ablation and deposition find applications in various technological and scientific fields, where precise control of the laser target interaction is crucial for achieving reproducible results. In this work, we investigated pulsed laser ablation of single crystalline (001), (011) and (111) oriented SrTiO3 (STO), (102) LaAlO3 (LAO) and (001) Y3Al5O12 (YAG) targets. The morphology, oxygen loss, and crack formation on the target surfaces after irradiation with a series of KrF excimer laser pulses will be discussed. The target surface morphology was imaged by atomic force, scanning electron microscopy and confocal laser scanning microscopy. Electron backscatter diffraction analysis and energy-dispersive X-ray spectroscopy were used to analyze the crystallographic changes of the surface and the elemental composition. The target material STO shows a significant crack formation and layer separation increasing with surface crystal orientation from (001) through (011) to (111) and laser pulse fluence. In contrast, the laser-ablated surfaces of LAO show only thin hairline cracks and YAG stays free of cracks in the whole laser fluence range investigated but presents large chipped areas.

Disordering of β-Ga2O3 upon irradiation with Si+ ions: Effect of surface orientation

Development of gallium oxide-based devices is one of the most promising areas of modern electronic technology. The method of ion implantation is widely used in electronic engineering; however, it has not yet been sufficiently studied for gallium oxide from a physical point of view. One of the interesting questions is the possible impact of surface orientation of β-Ga2O3 single crystals on the structural damage upon ion irradiation. In this work, the effect of Si+ ion irradiation on the structural properties of β-Ga2O3 crystals with (−201) and (010) surface orientations has been investigated by X-ray diffraction and small-angle reflection electronography. It is established that mechanical stresses in the irradiated layer depend on surface orientation: in the case of (−201) orientation, the stress in lateral to the surface direction is compressive, while it is tensile for the (010) orientation. At one and the same irradiation dose, the degree of damage for (010) orientation is shown to be stronger than that for (−201). Possible explanation is suggested for the surface orientation effect.

Molecular dynamics study on the contribution of 4H–SiC surface morphology and crystal orientation to the wetting behavior of molten Al droplet

AlSiC composites is a common material to make IGBT substrate due to its adjustable coefficient of thermal expansion which can be well matched with the chip and ceramic substrate to prevent the fatigue failure. Understanding the role of SiC surface morphology or crystal orientation might have an important influence on the proper control of the solid-liquid interface transmission in the process of preparing SiC reinforced aluminum matrix composites. To quantify the solid-liquid interaction, the molecular dynamics study is performed on the wetting characteristics of molten aluminum droplets on the 4H–SiC surface. Two SiC surface structures including rectangular-groove and wedge-groove are firstly adopted to analyze the effect of surface morphology on the wettability. Then, the wetting characteristics of Al droplets on two SiC crystal orientations including (110) plane and (111) plane are studied. The corresponding contact angles θ in the four Al/SiC systems are 124.81°, 126.65°, 105.72° and 97.35° respectively. It is found that the atomic surface morphology and crystal orientation playing important roles in the wettability of 4H–SiC. High hydrophobic is observed on the rectangular-groove and wedge-groove surface, while the wettability of the (110) plane and (111) plane is between wetting and hydrophobicity.

Temperature dependent magnetostatic and dynamic properties of soft magnetic FeGaB/Al2O3 thin films for microwave applications

Iron Gallium Boron (FeGaB) thin film is one of the low-loss self-biased soft magnetic films. In this report, the temperature dependent magnetostatic and dynamic properties of FeGaB/Al2O3 composite soft magnetic thin films were studied. The analysis of surface roughness, crystal orientation and magnetostatic properties indicate that the grain size and anisotropy of the thin film increase after annealing which temperature is from 573 K to 773 K. The ferromagnetic resonance spectra of different annealed thin films suggest the damping factor, linewidth and resonance magnetic fields all increase with the increased annealing temperature, which is attributed to the change of film crystallization. Moreover, the angle dependent anisotropic magnetoresistance and planar Hall effect show the percentage of magnetoresistance change increased due to the high annealing temperature.

Improved epitaxy of ZnO films by regulating the layers of graphene

Growth of ZnO film on graphene buffered sapphire substrate by plasma assisted molecular beam epitaxy (PAMBE) was investigated. Specifically, the surface morphology, crystal orientation and crystal quality of ZnO epitaxial layer and nucleation layer deposited on graphene with various thickness were analyzed by atomic force microscope (AFM), scanning electron microscope (SEM), high resolution X-ray diffraction (HRXRD), and high-resolution transmission electron microscope (HRTEM). The experiments showed that after buffered with double-layer graphene (DLG), six-fold symmetrical pits with the same orientation appeared on the successive ZnO film surface and the full width of half maximum (FWHM) of ZnO (002) plane rocking curve decreased to 769.3 arcsec. By comparing ZnO nucleation layer on graphene with different layers and checking the graphene by Raman spectroscopy, the mechanism for improving crystal quality of ZnO film grown on DLG was revealed. This study demonstrates the potential that high-crystal-quality ZnO film can be grown on graphene by plasma-assisted remote heteroepitaxy without limitation of the crystal mismatch and thermal mismatch between epitaxial film and substrate. It could be meaningful for the development of simplified growth technology of ZnO based films and devices.

Novel homo-epitaxial approaches in solvothermal synthesis for preparing surface tethered uni-directionally oriented zinc oxide micro and nano structured arrays

Surface aligned, uni-directionally grown, hexagonal nanorod bundles and microrod pillared arrays of zinc oxide (ZnO), were synthesized through a simple, homo-epitaxial growth approach. A uniform layer of ZnO seed was initially prepared on cleaned glass substrates by dip coating and calcination. Uni-directionally oriented ZnO micro– nano structures were subsequently developed on the seeded glass substrates through solvothermal methods, by employing equi-molar solutions of zinc nitrate and hexamethylenetetramine. The reaction parameters that control the surface morphologies and crystal orientations were explored. A solution exchange process was also carried out to prepare perpendicularly aligned ZnO nanorod arrays. The structural and functional features of the resultant samples were studied and discussed with the help of X-ray diffractometry, scanning electron microscopy, high-resolution transmission electron microscopy and photoluminescence spectrophotometry. A plausible structure dependent growth mechanism of the morphologically varied ZnO was also proposed.

Molecular dynamics study of crystal orientation effect on surface generation mechanism of single-crystal silicon during the nano-grinding process

Crystal orientation of the crystalline materials surfaces significantly affects the surface generation and subsurface damage of the materials during the ultra-precision machining. This work is based on the molecular dynamics (MD) simulation method to study the nano-grinding process of the single-crystal silicon workpiece with three different types of surface crystal orientations. And the MD simulation results are compared with the experimental results. The results show that the machined surface quality of workpieces with different surface crystal orientations is similar, but the degree of subsurface damage, processing force, phase transition, and internal residual stress is quite different. By comparing all the three types of the workpiece, the surface and subsurface quality of the single-crystal silicon workpiece with {110} surface crystal orientation has a better processing effect. This work reveals the evolution of the crystal structure of single-crystal silicon with different surface crystal orientations and the mechanism of subsurface damage from the atomic point of view.

The fabrication of Ti4O7 particle composite modified PbO2 coating electrode and its application in the electrochemical oxidation degradation of organic wastewater

A novel Ti/PbO2 electrode modified with Ti4O7 was synthesized through electrochemical deposition method. The surface morphology and electrochemical performance of the as-prepared electrodes were characterized by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Transmission Electron Microscope (TEM), Cyclic Voltammetry (CV), Linear Sweep Voltammetry (LSV), Electrochemical Impedance Spectroscopy (EIS), etc. The characterization results indicated that Ti4O7 composite modification improved the surface morphology and crystal plane orientation of the PbO2 coating electrodes and reduced the interplanar spacing of PbO2. Phenol was chosen as the model pollutant to evaluate electrochemical activity of the electrode. The Ti4O7 with 1.0 g L−1 below 500 mesh modification electrodes presented the highest removal efficiency (97.8%) on degradation of phenol, which could be attributed to its high oxygen evolution potential (OEP) and more electrode active sites.

Pure titanium fabrication with spatter-less selective laser melting in vacuum

Selective laser melting (SLM), which is an additive manufacturing technology, is attractive due to its ability to freely form shapes. SLM forms a 3D material by building it layer-by-layer from a metal powder. However, some issues have yet to be resolved, including dimensional accuracy, surface finish, processing time, and mechanical properties such as surface roughness, hardness, and crystal orientation. We demonstrate that pure titanium (Ti), which is clinically used for artificial bone and hard tissue implants because it is lightweight and biocompatible, can be fabricated by the SLM process in vacuum to develop a spatter-less process. The amount of spatter was dependent on the laser scanning rate; at 10 mm/s and an output power of 200 W, the spatter was minimized so that the surface roughness was reduced to 4.2 µm from 50 µm with a laser scanning rate of 50 mm/s. Defects such as pores, voids and delamination were found to be caused with an increase in the amount of spatter.

Coverage-dependent adsorption and stability of functionalized Ge(1 0 0) and (1 1 1) surfaces

The coverage-dependent adsorption and stability of functionalized Ge(100) and (111) surfaces terminated with X and XH (X = –F, –Cl, –Br, -I, –CH3, and –OH) are systematically investigated by employing density functional theory calculations. The chemical bond Ge-X slightly decreases with the increase of surface coverage for Ge(100) and Ge(111) surfaces and much less depends on the surface crystal orientation. The adsorption energy indicates that different chemical species adsorption on Ge surface are favorable thermodynamically. Ge(111) surface shows stronger adsorption stability over the entire coverage range compared with Ge(100) surface. The Bader population analysis shows that the charge transfer from the Ge atoms to the chemical species X results in local dipole moment at the surfaces. The surface reconstruction and the electronegativity difference between the adsorbate and substrate atoms lead to the charge redistribution, which give rise to a significant influence on the surface or interface properties. The study of coverage-dependent adsorption and stability of functionalized Ge surfaces terminated with different chemical groups may pave the way for Ge device application in the fields of optoelectronics, bioelectronics, and electronics.

Evaluation of oxidation suppression of multilayer graphene synthesized using fluorene as a solid source

Multilayer graphene (MLG) on a Cu substrate was successfully fabricated via a solid-source chemical vapor deposition process using fluorene as the solid source. The surface coverage of graphene was greater than 98% even at 6 min, and the MLG ratio was ∼97%, indicating that our growth method selectively promoted MLG growth from the beginning of graphene growth. The oxidation suppression characteristics of MLG were confirmed using electron back-scattered diffraction (EBSD) analysis. Cu crystal orientations were identified only under areas covered by graphene, indicating that the oxidation of Cu did not proceed at the interface between Cu and graphene. We confirmed using EBSD techniques that MLG suppresses the surface oxidation of a Cu substrate. Furthermore, we showed that EBSD was an effective tool for evaluating surface oxidation as well as surface crystal orientations.

Material removal mechanism of FCC single-crystalline materials at nano-scales: Chip removal & ploughing

In machining operations, investigating the transformation between chip removal and ploughing is crucial to understand the material removal mechanism, which is also the basis for analyzing the machining process, such as calculating cutting force and predicting minimum uncut chip thickness (MUCT). In this study, an analytical model was proposed to predict the chip thickness and ploughing width for FCC crystal materials under arbitrary crystal orientations in nano-machining. The molecular dynamics (MD) simulation methods and the nano-scratching experiments were conducted to verify the theoretical model under two representative crystal orientations. The results indicate that the crystal orientation determines the transformation between chip removal and ploughing. Moreover, according to surface crystal orientation, machining direction, tool radius, and uncut chip thickness, the chip thickness and ploughing width can be calculated in nano-machining. The model can be applied to the nano-machining process of FCC crystals that achieve the plastic deformation by the (110){111} slip system, where tool size and uncut chip thickness are at the nanoscale.

The initial wet oxidation process on Fe-Cr alloy surface: Insights from ReaxFF molecular dynamic simulations

The durable use of stainless steels depends on the formation of a protective chromium-rich oxide layer. To better understand the atomistic mechanism of surface oxide film formed on Fe-Cr alloy, the initial wet oxidation process on Fe-Cr alloy surface was investigated using ReaxFF molecular dynamic simulations. The oxidation process initiates from the adsorption and local dissociation of the water molecules near Cr atoms, followed by the segregation of Cr and the formation of cation vacancies on alloy surface. Meanwhile, the dissociated O and H atoms diffuse into the alloy substrate, which consequently facilitates to form a Cr-rich oxide layer. The compositions of oxide film possess distribution from Cr hydrates and hydroxides, Fe hydroxides and oxides to hydrogen ions with negative charge along depth. It was also demonstrated that there is a charge transfer between the metal atoms and hydrogen atoms. The effects of Cr content (0–20 at.%) and crystal surface orientation on the initial wet oxidation process were further discussed. These results can provide a microstructural understanding of the wet oxidation process on the surface of stainless steels from an atomistic point of view.

Effect of crystal orientation on inner surface roughness of micro metal tubes in hollow sinking

The crystal deformation behavior of the micro tube was investigated to clarify the crystal orientation, which suppresses the development of the inner surface roughness during the hollow sinking. Stainless steel tubes with an outer diameter of 1.50 mm and a wall thickness of 0.045 mm were drawn without an inner tool. The inner surface roughness and crystal orientation were examined using the same measurement area. The results indicated that the crystal grains with the {102} crystal planes vertical to the normal direction to the inner surface (ND) suppressed the increase in the height of the unevenness of the surrounding crystal grains, including themselves. The height deviation of the unevenness of the wall-thickened tube was larger than that of the wall-thinned one. Meanwhile, the number of crystal grains with the {102} crystal plane vertical to ND of the wall-thinned tube was larger than that of the wall-thickened one. Therefore, it was considered that this crystal orientation suppressed the development of the inner surface roughness during the hollow sinking. The development of the inner surface roughness was suppressed with decreasing wall thickness because the crystal grains rotated so that the normal direction of {102} crystal plane was parallel to the ND: meanwhile the tensile and compressive stresses were applied to the inner surface of the micro tube in the drawing and transversal directions, respectively.

The influence of morphology and crystal orientation of spangles on hot-dip Zn-0.5Sn alloy coating

The study on the surface morphology and crystal orientation of the Zn-0.5Sn coating could offer some guidance to improve the surface performance of the hot-dip galvanizing coating. In this paper, a scanning electron microscope (SEM) and an energy dispersive spectrometer (EDS) were used to analyze the typical morphology and the element distribution of spangles. The surface texture of the coating was analyzed by X-ray diffraction (XRD). Electron backscatter diffraction (EBSD) was used to analyze the crystal orientation of spangles. The results show that Sn segregates among the spangle dendrites while a metastable divorced eutectic structure can be maintained in the tin-rich phase, where the composition tends to be very similar. The crystal orientation of spangles affects their morphology, leading to the formation of feathery, ridged, and orthogonal dendrite arm spangles. When the angle among the <0001> orientation of the spangle crystal and the normal of the steel base surface changes from 0? to 90?, feathery spangles change to orthogonal dendrite arms spangles. The misorientation within a spangle is small while that among spangles is quite large. The orientation changes in the direction of the dendrite arm are relatively smooth and low, while the orientation changes which are perpendicular to the dendrite arm have a saltatory and irregular fluctuation.

Effect of hexamethylenetetramine on surface smoothness of electroplated copper coating

In this paper, hexamethyltetramine is introduced into the electroplating bath to improve the surface morphology of electrodeposited copper. The cyclic voltammetry (CV) and dynamic polarization curves are used to study the effect of Cu(Ⅰ) and hexamethyltetramine on the electrochemical behaviors of electroplating solution. After implementing the electrodeposited copper experiment, scanning electron microscope (SEM) and X-ray diffraction (XRD) are used to explore the influence of Cu(Ⅰ) and hexamethyltetramine on the Surface morphology and crystal plane orientation of the electrodeposited copper. The results show that 5ppm hexamethyltetramine and 7.5ppm hexamethyltetramine can solve the problem of the loose and uneven surface of the electroplated copper layer caused by Cu(Ⅰ).

Mo-doping induced crystal orientation reconstruction and oxygen vacancy on BiVO4 homojunction for enhanced solar-driven water splitting

• A facile CVD method was employed to introduce Mo doping on BiVO 4 photoanode. • Mo doping will induce the reconstruction of BiVO 4 surface, thereby forming a homojunction. • Oxygen vacancies will be generated by Mo doping, which is beneficial for OER reaction. • The CoPi/Graphene/Mo:BiVO 4 photoanode exhibits excellent OER activity. • This work provide a promising strategy for designing high-performance BiVO 4 photoelectrodes. Fabrication junction and doping are the two major methods to improve the charge separation and transfer efficiency of BiVO 4 (BVO) photoanode to boost its photoelectrochemical water splitting performance. Most of the reported methods require complicated fabrication steps, therefore increasing the usage of hazardous chemicals and cost as well. Herein, we report a BiVO 4 homojunction with abundant oxygen vacancies fabricated by a surface crystal orientation reconstruction induced by one step Mo doping method. After Mo doping, a few nanometer BVO with crystal orientation of (1 2 1) is formed on BVO (1 1 0) surface with abundant oxygen vacancies on BVO photoanode. Mo doped BiVO 4 photoanode (Mo:BVO) exhibits an obvious improvement of photocurrent (∼1.63 folds) compared with the pristine BVO. Using graphene as the hole extraction layer and CoPi as the cocatalysts, CoPi/Gr/Mo:BVO photoanode shows a high oxygen evolution reaction (OER) activity with the onset potential of 0.3 V vs. RHE and photocurrent of 4.36 mA cm −2 at 1.23 V vs. RHE under AM 1.5 G illumination. This work provides a promising strategy for the design of high-performance BiVO 4 photoelectrodes.