Single Crystal Planes Research Articles

Unveiling the temperature-dependent deformation mechanisms of single crystal gallium nitride in nanoscratching

The surface grinding process of single crystal gallium nitride (GaN) is intricate, and localized high temperature generated during interactions between the workpiece and the abrasives on grinding wheel is inevitable. Elevated temperatures significantly affect the deformation mechanisms of GaN, which remains inadequately elucidated. In this study, nanoscratching experiments were systematically conducted on the (0001) plane of GaN single crystal across a temperature range up to 500 ℃, and the resultant deformation patterns were thoroughly characterized. The results indicate that temperature elevation delays the brittle-to-ductile transitions in GaN and enhance its anisotropy. Additionally, GaN exhibits increased plasticity as temperature rises, leading to distinct scratch-induced subsurface deformation patterns at varying temperatures: at room temperature, the thickness of the subsurface damaged layer is primarily influenced by the penetration depth of cross slips, whereas at 500 ℃, basal slipping predominantly defines the thickness of the subsurface damaged layer. The plastic deformation patterns at both room temperature and 500 ℃ mainly involve phase transition, polycrystal formation, slips, stacking faults, dislocations and lattice distortions. The discrepancies in deformations at varying temperatures were thoroughly investigated by transmission electron microscopy and molecular dynamics simulations, and the underlying mechanisms were elucidated.

Reactivity of Resorcinol on Pt(511) Single-Crystal Surface and Its Effect on the Kinetics of Underpotentially Deposited Hydrogen and Hydrogen Evolution Reaction in 0.1 M NaOH Electrolyte.

This article presents cyclic voltammetry, Tafel polarization, and ac. impedance spectroscopy examinations of resorcinol (RC) ion reactivity on Pt(511) single-crystal plane and the effect of surface-electrosorbed RC ions on the kinetics of UPD H (underpotentially deposited hydrogen) and HER (hydrogen evolution reaction) processes in 0.1 M NaOH solution. Obtained data delivered a proof for the RC ion surface adsorption and its later electroreduction over the potential range characteristic for the UPD H. A favourable role of platinum-adsorbed resorcinol anions on the kinetics of the UPD H and HER processes is also discussed. The above was explained via the recorded capacitance and charge-transfer resistance parameters (the presence of resorcinol at 1.5 × 10-3 M in 0.1 M NaOH caused significant reduction in the resistance parameter values by 3.9 and 2.6 times, correspondingly, for the UPD of H at 50 mV and the HER process, examined at -50 mV vs. RHE) along with the charge transients, produced by injecting small amounts of RC-based 0.1 M NaOH solution to initially RC-free base electrolyte on the Pt(511) electrode plane (a large cathodic charge-transient density of -90 µC cm-2 was recorded at the electrode potential of 50 mV).

Electro-Reactivity of Resorcinol on Pt(111) Single-Crystal Plane and Its Influence on the Kinetics of Underpotentially Deposited Hydrogen and Hydrogen Evolution Reaction Processes in 0.1 M NaOH Solution

This article primarily presents cyclic voltammetry, Tafel polarization and ac. impedance spectroscopy electrochemical examinations of resorcinol (RC) electro-reactivity on the Pt(111) surface and its influence on the kinetics of UPD H (underpotentially deposited hydrogen) and the HER (hydrogen evolution reaction) in a 0.1 M NaOH supporting solution. The collected data provided evidence of the RC-ion’s surface adsorption and its further electroreduction in the presence of surface-adsorbed H radicals along with their primary beneficial role on the kinetics of the UPD H process. The above was elucidated through an evaluation of the associated charge-transfer resistance and capacitance parameters, and was carried out on the platinum (111) electrode plane, comparatively, for the RC-free and resorcinol-modified NaOH electrolyte. In addition, the recorded cathodic charge transients (obtained by injecting small amounts of RC-based 0.1 M NaOH solution to initially resorcinol-free electrolyte, carried out at the constant electrode potential characteristic to the UPD H potential zone) provided evidence that the RC species undergoes electrocatalytic reduction through the involvement of the Pt(111)-chemisorbed hydrogen radicals.

Crystal Face-Dependent Behavior of Single-Atom Pt: Construct of SA-FLP Dual Active Sites for Efficient NO2 Detection.

The strong potential of platinum single atom(PtSA) in gas sensor technology is primarily attributed to its high atomic economy. Nevertheless, it is imperative to conduct further exploration to understand the impact of PtSAon the active sites. In this study,the evolution of PtSAon (100)CeO2and (111)CeO2 is examined, revealing notable disparities in the position and activity of surface PtSAon different crystal planes.The PtSAin (100)CeO2surfacecan enhancethe stability of Ce3+and construct a frustrated Lewis pair (FLP) to form a double active site by combining the steric hindrance effect of oxygen vacancies, whichincreases the response value from 1.8 to 27 and reducethe response-recovery time from 140-192s to 25-26s toward five ppm NO2at room temperature.Conversely,PtSAtends to bind to terminal oxygen on the surface of (111)CeO2and become an independent reaction site.The response valueofPtSA-(111)CeO2surface onlyincreased from 1.6 to 3.8.This research underscores the correlation between single atoms and crystal plane effects, laying the groundwork for designing and synthesizing ultra-stable and efficient gas sensors.

Understanding platinum-based H2 adsorption/ desorption kinetics during catalytic hydrogenation or hydrogen storage-related reactions

Hydrogen is among the most promising energy carriers and plays an important role on the way to sustainable technologies. Platinum holds great promise for unlocking the potential of renewable hydrogen, as it is an essential component of proton exchange membrane technologies and in various hydrogenation reactions. For the variety of applications of energy harvesting, conversion, and storage, the optimization and reduction of Pt loading is crucial. In view of this, a platinum catalyst using a stable SiO2 support is synthesized to investigate the adsorption/desorption behavior of hydrogen on platinum nanoparticles of different sizes, obtained by treating the sample at different calcination temperatures. Pulsed chemisorption and subsequent temperature-programmed desorption are described mathematically to obtain kinetic parameters. It is shown that higher adsorption capacities could be obtained using smaller particles. However, for particles smaller than 2.4 nm, higher Pt2+ content decreases H2 adsorption. Adsorption inhibition due to the presence of monatomic Pt cannot be excluded. The size of the Pt nanoparticles does not significantly affect the desorption/adsorption energy, but there is evidence that the hydrogen adsorbed per Pt atom at the surface varies with size: about 1 for single crystal planes and 2 for nanoparticles <3 nm.

Macroscopic low-friction via twinning assisted lattice reconstruction in magnesium

One-fourth of the global energy losses are spent to overcome friction, making it particularly important to reduce and minimize friction between contacting materials. Hexagonal close-packed (HCP) metals are an important class of structural materials. It has not been possible to reduce their friction, primarily because of friction-induced dislocation slip and twinning. Here, we find particularly low friction when sliding perpendicular to the a-axis on the basal plane in HCP Mg single crystals. This is in contrast to the common belief that friction is small along the preferred dislocation slip direction (a-axis). This macroscopic low-friction stems from twinning assisted lattice reconstruction sharing a common rotation axis, confirmed by atomistic simulations and strain energy analysis. While sliding along the a-axis and other directions, 〈c + a〉 dislocation activity accounts for high frictional resistance. By unambiguously decoupling the contributions of dislocation slip and twinning, this discovery reveals potential opportunities in mitigating the energy dissipation at tribological interfaces of HCP metals, e.g. through crystallographic texture design.

Comprehensive realization of the crystal growth perfection of the uni-indexed, bi-indexed and tri-indexed planes of single crystals grown by unidirectional technique- A case study on potassium dihydrogen phosphate

Over the years, even though several research publications have been made on uni-directional crystal growth technique, the plane-dependent crystal growth such as uni-indexed (100), bi-indexed (101) and tri-indexed (111) planes, their crystalline perfection remains to be unclear. On these lines, the present work brings in a possible correlation between them such that it is highly required to extend the applications of the above-mentioned crystal growth technique as well as to understand better the growth kinetics of crystals with respect to their planes. In this work, we have made a systematic comparative analysis of the crystal growth perfection of the uni-indexed (200), bi-indexed (101) and tri-indexed (111) planes of potassium dihydrogen phosphate (KDP) single crystals which were grown by unidirectional crystal growth technique known as the Sankaranarayanan-Ramasamy (SR) method. For the existing uni-indexed (200), bi-indexed (101) and tri-indexed (332) planes of KDP results, the required data have been procured from the reported results. According to the conventional powder X-ray diffraction (XRD) results, the values of full width at half maximum of the (200), (101) and (332) planes are 0.0402, 0.8656, and 6.016 degrees, respectively. Based on the obtained XRD and high resolution X-Ray diffraction (HR-XRD) results, it is established that the uni-indexed grown crystals yield a high degree of crystalline perfection while to a certain extent, the bi-indexed crystals, but tri-indexed crystals grow with a lower degree of crystalline nature. Similar types of logical results on crystalline perfection have also been found for the previously reported ammonium dihydrogen phosphate (ADP) and benzophenone single crystals grown by unidirectional crystal growth technique. Analyzing the observed results, uni-indexed crystal planes such as (100), (010), and (001) are more favorable candidates for producing a high degree of crystalline perfection in materials grown by the SR method which are very much required for nonlinear optical applications.

The anisotropy of deformation behaviors in (100) and (010) plane of monoclinic β-Ga2O3 single crystals

β-Ga2O3 is an ultrawide bandgap (UWBG) semiconductor with excellent ensemble of attributes. To optimize the machining technologies and improve the mechanical performances, the plastic deformation mechanism of β-Ga2O3 is necessary to thoroughly understand. In this work, nanoindentation experiments were conducted on (100) and (010) oriented β-Ga2O3 to study the incipient plasticity with small indentation depths. It is indicated that the yield strength, elastic modulus and hardness for the (100) plane are higher than those of the (010) plane. Observations in the deformation morphology confirms that the deformed zone of the (100) plane is constrained in a hemispherical volume below the indentation with a radius about ten times larger than the indentation depth. However, for the (010) plane, a “one dimensional” plastic zone is formed in front of the tip with near one hundred times deeper than the penetration depth of the indenter. The deformation behavior is dominated by stacking faults, twins and dislocations for the (100) plane, while only dislocations are responsible for the plastic deformation of the (010) plane.

Synthesis, crystal growth, and its characterization of 2-amino-4-methylpyridinium oxalate

The 2-amino 4-methyl pyridinium oxalate (2A4MPO) compound was synthesized using methanol and water as a solvent in an equimolar ratio (1:1) by the slow evaporation solution growth method. Single crystal X-ray diffraction analysis for the grown crystal sample has been carried out to unfold the structural information. It reveals that the grown crystal belongs to the monoclinic crystal system with a space group of P21/n. The obtained unit cell parameters are; a = 7.1853 (7) Å, b = 9.5314 (9) Å, c = 11.0896 (11) Å, α = 90°, β = 105.665 (3)°, γ = 90° and V = 731.27 (12) Å3. The various (hkl) planes of 2A4MPO single crystal have been identified by the Powder X-ray diffraction measurement. The high-resolution XRD result shows the structural perfection of the grown crystal is quite good. The various functional groups associated with the synthesized compound have been investigated through FTIR spectroscopy measurements. The thermal stability of the grown crystal was studied by using thermogravimetry analysis (TGA) anddifferential scanning calorimetry(DSC) measurements. The electrical properties have been investigated by the dielectric measurement with frequency ranges from 1 KHz to 5 MHz region. The third-order nonlinear optical properties were analyzed by the Z-scan measurements using a He-Ne laser 632.8 nm. The foregoing results suggest that the title compound can be considered for third-order NLO applications.

Mechanism of the surface-preferred crystal plane of CsPbBr3 single crystals in different solvents

CsPbBr3 single crystals have been grown by using solution method with hydrobromic acid (HBr) and dimethyl sulfoxide (DMSO), respectively. The same orthorhombic phase of crystals grown in these two solvents was confirmed by X-ray powder diffraction (XRD). A very interesting phenomenon is that the surface-preferred crystal plane of the CsPbBr3 single crystal would be (200) in HBr solution, while that would be (101) in DMSO solution. Remarkably, this growth mechanism can be explained effectively by the principle of opposite charges attraction, which would be likely to provide an approach to be extended to the regulation of surface-preferred crystal plane of other perovskite single crystals grown in different solvents, especially using solvent with original perovskite solute ions.

Impact of nanosecond UV laser pulses on the surface of germanium single crystals

For the first time, a detailed comprehensive study of the "dry" etching of dislocation and dislocation-free germanium samples on the {111}, {110} and {100} planes has been carried out. Etching was carried out by exposure to pulses of nanosecond UV laser radiation of subthreshold intensity (wavelength 355 nm, duration ~ 10 ns, energy density ~ 0.5–1.3 J/cm2, pulse repetition rate 100 Hz, divergence 1–2 mrad). Before and after laser heat treatment of the surface, the samples were examined using a Zygo optical profilometer and a scanning electron microscope. Features of the nature of damage to surfaces corresponding to different crystallographic planes of single crystals of industrial dislocation germanium are revealed. They are compared with data on subthreshold damages of typical dislocation-free crystals.It is shown that in dislocation samples of germanium on the {111} plane, it is possible to create a regime of exposure to radiation, leading to the formation of etch pits that are outwardly identical to dislocation pits detected during selective chemical etching. Their concentration corresponds in order of magnitude to the density of dislocations.On the {100} plane of dislocation samples, etching results were also found, which clearly have a crystallographic nature. At an energy density of the acting radiation ≥ 0.4 J/cm2, on the surfaces of dislocation ({100} plane) and dislocation-free germanium ({111}, {100}, {110} planes), only individual spots ~ 50 μm in size were registered, as well as individual microcraters ~ 0.1–1 μm in size, which do not have crystallographic features. The possibility of environmentally friendly detection of dislocations in germanium without the use of chemical reagents is shown.

Influence of UO2 crystal orientation on laser ablation performance

Crystallographic orientation dependence deteriorates the performance of surface analysis methods such as secondary ion mass spectrometry (SIMS) and focused ion beam (FIB). This study explores the corresponding potential challenges of laser ablation (LA) as a powerful sampling tool for inductively coupled plasma-mass spectrometry (ICP-MS). To this end, three UO2 single crystals of different orientation as well as polycrystalline UO2 were produced and characterized. Subsequently, a ns-laser ablation system was employed to study laser-matter interaction in detail. Firing the laser continuously at 1Hz with various single shot fluence (2, 4, 6, 8, 12Jcm-2) for diverse periods created LA craters impacted by cumulative fluence between 50 and 650Jcm-2. Repeated LA experiments on the (100) plane of a UO2 single crystal at the beginning and end of the entire study revealed highly reproducible (<3%) LA rates, only limited by the fluctuation of the laser energy output of the ns-LA system. After thorough cleaning of the ablated samples, surface roughness and average depth of LA craters were determined using confocal laser scanning profilometry. Both LA rate and average depth of craters decreased exponentially with increasing single shot fluence independently of the crystal orientation. Surface roughness increased linearly with increasing cumulative fluence having largest intensification for lowest single shot fluence. Scanning electron microscope (SEM) images not only revealed the conical silhouette of LA craters, but also identified a convex meniscus at its bottom. This particular shape of the crater bottom with a deeper ring surrounding the central region is a result of melted and re-solidified UO2 generated during the LA process and the main limiting factor for the achievable depth resolution. The rapid re-solidification of the liquid phase after each single laser shot created tiles of different shape and orientation, depending on UO2 crystal orientation. Three different types of ejected particles radially distributed around the LA craters were identified by SEM, providing profound insights into laser-UO2 interaction.

Surface-Dependent Hydrogen Evolution Activity of Copper Foil

Single-crystal planes are ideal platforms for catalytic research. In this work, rolled copper foils with predominantly (220) planes were used as the starting material. By using temperature gradient annealing, which caused grain recrystallization in the foils, they were transformed to those with (200) planes. In acidic solution, the overpotential of such a foil (10 mA cm-2) was found to be 136 mV lower than that of a similar rolled copper foil. The calculation results show that hollow sites formed on the (200) plane have the highest hydrogen adsorption energy and are active centers for hydrogen evolution. Thus, this work clarifies the catalytic activity of specific sites on the copper surface and demonstrates the critical role of surface engineering in designing catalytic properties.

Two types of etching pits in (100) β-Ga2O3 single crystals grown by casting method

Two types of micron-sized etching pits were observed on (100) plane of β-Ga2O3 single crystals grown by casting method. Type A etching pits were elongated along [010] direction with a density of 105/cm2. Using FIB and HRTEM, the atomic structure under the pits bottom remained complete but exhibited continuous microscopic strain, which could be attributed to strain-related. On the other hand, type B etching pits represented different geometric parameters, with 2 times larger and 6 times deeper than type A. Edge dislocations with clearly dislocation lines which perpendicular to b = <100> were observed. The origins of etching pits were clarified, especially the co-exist strain-related pits. After annealing at 1200 °C for 3 h in air, we found varying degrees of reduction in the density of both etching pits, which could be owing to partial stress release and dislocations slip at the oxygen-containing ambient during elevated temperature.

The anisotropy dependence of deformation mechanism of cleavage planes in β-Ga2O3 single crystal

β-Ga2O3 is a promising ultra-wide bandgap semiconductor. The deformation of β-Ga2O3 was few investigations, especially on the cleavage planes which hindered the high-efficiency and low-damage manufacturing of β-Ga2O3 wafers. Here, the anisotropy dependence of mechanical response and deformation mode of the (100) and (001) cleavage planes in β-Ga2O3 single crystal were studied by the nanoindentation method. The results showed that a broad deformation zone was formed on the subsurface of the β-Ga2O3 wafer after unloading, which was dominated by slippage, dislocations, stacking faults, and cracks. Cross stacking faults were found on the subsurface of the (100) plane. Under the same load condition, the damaged zone depth of the (001) plane was twice that of the (100) plane. At the same time, two kinds of cracks with different angles were found on the subsurface. The direction of the crack is related to stress distribution. The crack propagation mechanism transitioned to brittle cleavage fracture within the loading process. The crack did not extend to the indentation surface of the (100) plane. These results revealed the mechanism of deformation and damage in the manufacturing of low-symmetry β-Ga2O3 wafers.

Directional growth of quasi-2D Cu2O monocrystals on rGO membranes in aqueous environments.

The preparation technology of unconventional low-dimensional Cu2O monocrystals, which exhibit specific crystal planes and present significantly unique interfacial and physicochemical properties, is attracting increasing attention and interest. Herein, by integrating a high-temperature oxidation process under vacuum and a pure-water incubation process under ambient conditions, we propose the self-assembled growth and synthesis of quasi-two-dimensional Cu2O monocrystals on reduced graphene oxide (rGO) membranes. The prepared Cu2O crystals have a single (110) crystal plane, regular rectangular morphology, and potentially well conductivity. Experimental and theoretical results suggest that this assembly is attributed to the pre-nucleation clusters aggregation and directional attachment of Cu and O on the rGO membranes in aqueous environment and cation-π interactions between the (110) crystal plane of Cu2O and rGO surface. Our findings offer a potential avenue for the discovery and design of advanced low-dimensional single-crystal materials with specific interfacial properties in a pure aqueous environment.

Practice of the Visual Determination of the Direction of the Rotation of the Light Polarization Plane in Gyrotropic Uniaxial Single Crystals

Practice of the Visual Determination of the Direction of the Rotation of the Light Polarization Plane in Gyrotropic Uniaxial Single Crystals

One-step method to prepare coccinellaseptempunctate-like silver nanoparticles for high sensitivity SERS detection

The surface morphology of metal particles can be adjusted by the annealing process to enhance the activity of Raman substrate and achieve an ultra-low concentration detection limitation. In this study, a surface-enhanced Raman scattering (SERS) substrate of coccinellaseptempunctate-like silver nanospheres coated with a silver nanoisland structure (Ag NI@Ag NSs) was prepared using a simple annealing process. Numerous silver nanospheres were dispersed on the surface of the silver nanoislands, which exhibited a single crystal plane (111) orientation. The SERS substrate had an enhancement factor of 108 for Rhodamine B (Rh B) and was highly sensitive to phosphoethanolamine (PETA). The SERS response toward PETA showed excellent correlation during the range of 5 × 10−7 - 1 × 10−5 mol/L with the detection limitation as low as 5 × 10−7 mol/L, and the correlation coefficient is 0.9918. The simulated high-pressure test showed that the SERS response could be still observed at 1100 m sub ocean pressure even with a PETA concentration of 1 mM. The test results of selectivity, reproducibility, and accuracy indicated that the Ag NI@Ag NS sensor possessed potential applications in the deep-sea analytical and other related fields.

Adsorption of iodide ions at the Bi(1 1 1) | propylene carbonate + dimethyl carbonate interface

• The interface Bi | PC + DMC was studied by impedance measurements. • Adsorption of I - anions was studied at the Bi(1 1 1)| PC + DMC interface. • The adsorption parameters of I - anions have been calculated. • Adsorption of anions is stronger from pure carbonates than from solvent mixtures. The adsorption of I - anions on the Bi(1 1 1) single crystal plane from mixed solutions of propylene carbonate and dimethyl carbonate (1:1) has been investigated with impedance measurements. Both electrode charge and electrode potential were applied as the independent electrical variables in the calculations of the ionic charge due to the specific adsorption following the mixed-electrolyte method. The Gibbs energy of I - anions adsorption has been calculated using the virial adsorption isotherm. It was found that under comparable conditions, the standard Gibbs energy values obtained at constant electrode potential and at constant electrode charge, are coincident and the Gibbs energy of I - anion adsorption in the mixture is only slightly lower than in the pure propylene carbonate or ethylene carbonate solutions. However, at higher concentrations of iodide ions, the specific adsorption charge values in the mixture are remarkably lower than in pure propylene carbonate caused by different lateral repulsion values of iodide ions on the electrode surface in different systems. The electrosorption valency values have been calculated and it was found that this parameter is higher in the mixture than in pure propylene carbonate or in other organic carbonate solvents.

De-channeling in terms of instantaneous transition rates: computer simulations for 855 MeV electrons at (110) planes of diamond

Monte-Carlo simulation calculation have been performed for 855 MeV electrons channeling in (110) planes of a diamond single crystal. The continuum potential picture has been utilized. Both, the transverse potential and the angular distributions of the scattered electrons at screened atoms are based on the Doyle–Turner scattering factors which were extrapolated with the functional dependence of the Molière representation to large momentum transfers. Scattering cross-sections at bound electrons have been derived for energies less than 30 keV from the double differential cross-section as function of both, energy and momentum transfer, taking into account also longitudinal and transverse excitations. For energies above 30 keV the Møller cross-section is used. The dynamics of the particle in the continuum transverse potential has been described classically. Results of the channeling process are presented in terms of instantaneous transition rates as function of the penetration depth, indicating that channeling can be described by a single exponential function only after about 15 mu m when the equilibration phase has been reached. As a byproduct, improved drift and diffusion coefficients entering the Fokker–Planck equation have been derived with which its predictive power can be improved.Graphic abstract