Crystal Surface Research Articles

Tailoring selenization dynamics: How heating rate manipulates nucleation and growth boosts efficiency in kesterite solar cells.

Kesterite Cu2ZnSn(S,Se)4 (CZTSSe) has emerged as a promising photovoltaic material due to its low cost and high stability. The CZTSSe film for high-performance solar cells can be obtained by annealing the deposited CZTS precursor films with selenium (a process known as selenization). The design of the selenization process significantly affects the quality of the absorber layer. In this work, we systematically investigate the impact of heating rate on the selenization kinetics and the microstructural characteristics of the films using a two-step selenization method. The results indicate that a slow heating rate promotes surface crystallization, resulting in a thick and dense layer of large grains at the film surface that impedes the diffusion of Se vapor. Conversely, a rapid heating rate enhances the diffusion of Se into the interior of the film, synthesizing more low-melting-point intermediate compounds that facilitate grain growth and reduce the thickness of fine grains at the film bottom. Ultimately, a CZTSSe solar cell with an efficiency of 10.17% was fabricated at a heating rate of 200 °C/min. This research deepens the understanding of thin film growth mechanisms and advances the development of high-performance solar cells.

Investigating charge dynamics at lead halide perovskite single crystal surfaces

Investigating charge dynamics at lead halide perovskite single crystal surfaces

High‐voltage electron microscopy analyses for crack‐tip dislocations and their shielding effect on fracture toughness in MgO and Si crystals

AbstractIn this study, characteristics of dislocation structures around a crack‐tip in both crystals of MgO and Si were investigated using high‐voltage electron microscopy (HVEM). The interaction between a crack and dislocations was analyzed to discuss the effect of crack‐tip plasticity on fracture toughness. The present paper first demonstrates a dislocation configuration around a crack‐tip in a MgO thin crystal, where the plastic zone called 45°‐shear type is dominant under the plane stress condition. Then, the slip systems necessary for brittle‐to‐ductile transition in ionic crystals with the rock‐salt structure are discussed based on the temperature dependence of stress‐strain relationships and the aspect of crack front observed in NaCl crystals. Second, crack‐tip dislocations near the surface of bulk Si crystals are exhibited based on the 3D analyses using HVEM tomography. We focus on a newfound plastic zone being perpendicular to the crack plane, which is different from either 45°‐shear type or the hinge type generally well‐known. The dislocation loops observed in this plastic zone fundamentally have a crack‐tip shielding effect to increase fracture toughness. Still, in addition, they contribute to activating crack‐tip dislocations by their localized antishielding field. These analyses reveal a fundamental toughening mechanism for crystalline materials.

Fabrication of MoS2@Fe3O4 Magnetic Catalysts with Photo-Fenton Reaction for Enhancing Tetracycline Degradation

Tetracycline (TCs) is widely used in the treatment of human and animal infectious disease. TCs gives rise to a growing threat to the human health and environment protection due to its overuse. Therefore, it is important to remove TCs contaminants from waste effluents. In this work, MoS2@Fe3O4 catalytic material was fabricated by the simple hydrothermal method, which was applied in the photo-Fenton system to degrade TCs. The crystal structure, surface morphology, elemental composition, chemical state, electrochemical properties, and separability of MoS2@Fe3O4 catalytic materials were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), conventional and high-resolution transmission electron microscopy (TEM/HRTEM), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), and vibrating sample magnetometry (VSM). Furthermore, MoS2@Fe3O4 could degrade 98.6% of TCs within 60 min under the optimum reaction conditions (the catalyst dosage of 3 g/L, H2O2 concentration of 5 mmol/L, the initial TCs concentration of 50 mg/L, and the initial pH of 5), which was a significant increase compared with pure Fe3O4. MoS2 can accelerate the Fe3+/Fe2+ cycle through electron transfer from Mo4+ to Fe3+, resulting in the improvement in the degradation efficiency of TCs. The quenching and electron paramagnetic resonance (EPR) results showed that OH• and photogenic hole h+ was the main active species in the photo-Fenton system. What is more, MoS2@Fe3O4 catalytic materials had remarkable stability and reusability, and can be handily regained via magnetic separation technology in a real scenario.

Electrochemical Oxidative Desorption of Adsorbed Sulfur Species on (111) Surfaces of Single Crystals of Pure Pt and Pt-Based Bimetallic Alloys

Electrochemical Oxidative Desorption of Adsorbed Sulfur Species on (111) Surfaces of Single Crystals of Pure Pt and Pt-Based Bimetallic Alloys

Peptidomics & Molecular Simulation-Based Specific Screening of Antifreeze Peptides from Evynnis japonica Scale and the Action Mechanism.

This study aims to explore the cryoprotective mechanisms of food-derived hydrolyzed peptides and develop novel cryoprotectants to enhance the quality of frozen foods. Evynnis japonica scale antifreeze peptides (Ej-AFP) were prepared using enzymatic hydrolysis, which had a 4-fold increase in protection efficiency for surimi compared to traditional cryoprotectants. Furthermore, Ej-AFP was able to control 63.60% of the ice crystals to sizes below 600 μm2. Three antifreeze peptide sequences were purified by using ice-affinity techniques and peptidomics. These sequences demonstrated a 21.75% enhancement in antifreeze activity and an increase of 1 °C in thermal hysteresis activity compared to Ej-AFP. Molecular simulation-elucidated ice-binding surface interacts with ice crystals through hydrogen bonds, while the nonice-binding surface disrupts the orderly arrangement of water molecules. This results in a tightly structured hydration layer around the peptide, increasing the curvature of the ice crystal surface and thereby demonstrating significant antifreeze activity in controlling ice crystal growth.

Construction of Mn-Defective S/Mn0.4Cd0.6S for Promoting Photocatalytic N2 Reduction.

Improving catalytic performance by controlling the microstructure of materials has become a hot topic in the field of photocatalysis, such as the surface defect site, multistage layered morphology, and exposed crystal surface. Due to the differences in the metal atomic radius (Mn and Cd) and solubility product constant (MnS and CdS), Mn defect easily occurred in the S/Mn0.4Cd0.6S (S/0.4MCS) composite. To optimize the photocatalytic performance in N2 fixation, the effects of the synthesis conditions and reaction conditions for S/0.4MCS were explored and systematically studied. Combined with the experimental characterization and theoretical calculation, not only the photocatalytic reaction pathway but also the key steps of N2 reduction were explored. Moreover, the transfer mechanism of photogenerated charge carriers (PCCs) formed between S and 0.4MCS was studied, which enhanced the utilization rate of photogenerated electrons (e-) and holes (h+). This work detailedly discusses the relationship between microstructure and photocatalytic performance, which is beneficial for the design of efficient photocatalyst.

Research on Controllable Synthesis and Growth Mechanism of Sodium Vanadium Fluorophosphate Nanosheets.

Sodium vanadium fluorophosphate is a sodium ion superconductor material with high sodium ion mobility and excellent cyclic stability, making it a promising cathode material for sodium-ion batteries. However, most of the literature and patents report preparation through traditional methods, which involve complex processes, large particle sizes, and low electronic conductivity, thereby limiting development progress. Aiming at the limitation of high cost and poor performance of vanadium sodium fluorophosphate cathode material, the low temperature and high-efficiency nano preparation technology was developed. This study uses a homogenizer with high dispersion and shear force to directionally control the collision of sodium vanadium fluorophosphate nanoparticles with higher specific surface energy during the initial nucleation stage, forming nanosheet structures. The growth mechanism of these nanosheets was analyzed using SEM, XRD, AFM, and DFT simulation. Results indicate that the crystal surfaces with higher surface energy undergo directional collisions in the early nucleation stage, gradually reducing the surface energy and stabilizing the system, resulting in sodium vanadium fluorophosphate nanosheets. Due to the larger specific surface area and pore structure, these nanosheets exhibit excellent rate performance and cycle stability, making them suitable for application and promotion in the field of fast-charging energy storage.

High-concentration diamond nitrogen vacancy color center fabricated by microwave plasma chemical vapor deposition and its properties

Diamond nitrogen vacancy (NV) color centers have good stability at room temperature and long electron spin coherence time, and can be manipulated by lasers and microwaves, thereby becoming the most promising structure in the field of quantum detection. Within a certain range, the higher the concentration of NV color centers, the higher the sensitivity of detecting physical quantities is. Therefore, it is necessary to dope sufficient nitrogen atoms into diamond single crystals to form high-concentration NV color centers. In this study, diamond single crystals with different nitrogen content are prepared by microwave plasma chemical vapor deposition (MPCVD) to construct high-concentration NV color centers. By doping different amounts of nitrogen atoms into the precursor gas, many problems encountered during long-time growth of diamond single crystals under high nitrogen conditions are solved. Diamond single crystals with nitrogen content of about 0.205, 5, 8, 11, 15, 36, and 54 ppm (1ppm –10<sup>–6</sup>) are prepared. As the nitrogen content increases, the width of the step flow on the surface of the diamond single crystal gradually widens, eventually the step flow gradually disappears and the surface becomes smooth. Under the experimental conditions in this study, it is preliminarily determined that the average ratio of the nitrogen content in the precursor gas to the nitrogen atom content introduced into the diamond single crystal lattice is about 11. Fourier transform infrared spectroscopy shows that as the nitrogen content inside the CVD diamond single crystal increases, the density of vacancy defects also increases. Therefore, the color of CVD high nitrogen diamond single crystals ranges from light brown to brownish black. Compared with HPHT diamond single crystal, the CVD high nitrogen diamond single crystal has a weak intensity of absorption peak at 1130 cm<sup>–1</sup> and no absorption peak at 1280 cm<sup>–1</sup>. Three obvious nitrogen-related absorption peaks at 1371, 1353, and 1332 cm<sup>–1</sup> of the CVD diamond single crystal are displayed. Nitrogen atoms mainly exist in the form of aggregated nitrogen and single substitutional N<sup>+</sup> in diamond single crystals, rather than in the form of C-defect. The PL spectrum results show that defects such as vacancies inside the diamond single crystal with nitrogen content of 54 ppm are significantly increased after electron irradiation, leading to a remarkable increase in the concentration of NV color centers. The magnetic detection performance of the NV color center material after irradiation is verified, and the fluorescence intensity is uniformly distributed in the sample surface. The diamond single crystal with nitrogen content of 54 ppm has good microwave spin manipulation, and its longitudinal relaxation time is about 3.37 ms.

Advanced photonic crystal fiber-based surface plasmon resonance biosensors for transformative RI sensing

Advanced photonic crystal fiber-based surface plasmon resonance biosensors for transformative RI sensing

Effect of SiO2 monocrystalline substrate orientation on the crystal structure and properties of VO2 film

The VO2 films were deposited on the AT-, X-, Y- and Z-SiO2 monocrystalline substrates with the magnetron sputtering. The effects of the substrate crystal planes, (011), (2—10), (100) or (001), on the crystal structure, surface morphology, optical properties and phase transformation characteristics of the VO2 film were investigated. The crystal structure differences among the VO2 films deposited on the four substrates were attributed to the lattice mismatch between the SiO2 monocrystalline substrate and the VO2 film, which led to the generation of internal stress within the VO2 film, causing the VO2 to present a diversity of crystal plane and phase at the interface. Among them, the VO2 film exhibited the M-phase on the AT- and X-SiO2 substrates, while a mixture of the M-phase and the R-phase on the Z- and Y-SiO2 substrates. The complex crystal structure resulted in the various surface morphologies, the VO2 particles on the Z- and Y-SiO2 substrates presented a smaller size and gap, as well as a more uniform distribution than those on the AT- and X-SiO2 substrates. All the VO2 films exhibited the metal-insulator phase transition during both the thermal cycling and the laser irradiation cycling processes. The Z-SiO2 substrate had a positive effect on the phase transition performance of the VO2 film, which got a thermochromic phase transition threshold of 64.62 ℃ and an infrared switching ratio of 78.99% at the wavelength of 2500nm. And its photoinduced phase transition threshold was 36.43W/cm², and its infrared switching ratio reached 59.00% under the 1989 nm laser irradiation.

Investigating the impact of crystal face on SnO2/GO-A humidity sensor via adsorption kinetics and DFT calculations

Ranging from monitoring indoor air quality to controlling processes in the food, pharmaceutical, and electronics industries, humidity-sensitive sensors play a pivotal role in various industrial and environmental applications. The crystallographic orientation of their surfaces is one of the key factors influencing the performance of metal oxide-based humidity sensors. However, the study of different crystal faces of metal oxides is rarely discussed, such as surface energy, charge distribution and reactivity, which can significantly affect their water absorption behavior and thus affect the sensitivity and response time of the humidity sensor. Hence, the present study introduces a meticulously designed SnO2/GO-A sensor that not only validates the successful fabrication of SnO2/GO-A sensor featuring optimized crystal alignment but also delves into the intricate water absorption mechanisms operative across various SnO2 crystal faces. The First-principles results show that (110) face of SnO2 is more sensitive to the water molecule than others. Consequently, due to the (110) crystal surface growth with annealing process, the SnO2/GO-A sensor demonstrates significant performance enhancements, especially in response speed, recovery time, linearity, and repeatability. In particular, the SnO2/GO-A sensor exhibiting faster response and recovery times of 20s and 18s, respectively, which is higher than SnO2 and SnO2/GO sensor. This advantage makes SnO2/GO-A sensor a potential candidate for humidity sensing applications.

Kinetics of decomposition of 1,1-diamino-2,2-dinitroethylene (FOX-7). 6. The induction period at the early stages of the reaction in the solid state

The kinetics of thermal decomposition of FOX-7 compound at 155 °C under semi-open conditions in vessels with a volume of V = 0.8–0.9 cm3 in an air atmosphere and the degree of filling of the vessel with substances m/V = 0.03–0.72 g/cm3 has been studied by gravimetric method. It was found that at the largest m/V, an induction period is observed at the early stages of the reaction, during which the rate of mass loss of the sample is ten times less than the rate of decomposition of FOX-7 in the solid phase. With a decrease in m/V, the induction period is shortened and at m/ V = 0.04 g/cm3 disappears altogether. The appearance of the induction period is due to the fact that nitronic acid, which is the only product of the first stage of decomposition of FOX-7, is well adsorbed on the surface of FOX-7 crystals. At the same time, it almost completely loses its reactivity. As a result, until the end of the adsorption process, the decomposition of FOX-7 proceeds without the formation of gaseous products, and the reaction rate is not fixed by the gravimetric method suitable for studying the kinetics of the reaction at the early stages of decomposition FOX-7.

Trapezoidal back projection for positron emission tomography reconstruction.

In the back projection step of the 3D PET reconstruction, all Lines of Responses (LORs) that go through a given voxel need to be identified and included in an integral. The standard Monte Carlo solution to this task samples stochastically the surfaces of the detector crystals and the volume of the voxel to search for valid LORs. To get a low noise Monte Carlo estimate, the number of samples needs to be very high, making the computational cost of the projection significant. In this paper, a novel deterministic projection algorithm called trapezoidal back projection (TBP) is proposed that replaces the extensive Monte Carlo sampling. Its goal is to determine all LORs that contribute to a given voxel together with their exact contribution weights. This is achieved by trapezoidal rasterization and a pre-computed look-up table. The precision and speed of the proposed TBP algorithm were compared to that of the Monte Carlo back projection of 1000, 10,000 and 100,000 samples. Measurements were run on a National Electrical Manufacturers Association (NEMA) NU 4-2008 image quality phantom as well as on a mouse acquisition. Results show that the TBP algorithm achieves the same low noise level (2.5 Uniformity %STD) as the Monte Carlo method with the highest sample number, but 13 times faster-the highest-precision Monte Carlo back projection takes 31.3 s, while TBP takes only 2.3 s on the NEMA NU 4-2008 image quality phantom of voxels. The proposed deterministic TBP algorithm achieves a low noise level in a short runtime, thus it can be a promising solution for the back projection of the 3D PET reconstruction. Its performance advantage could be used to reduce either the reconstruction time, the data acquisition time, or the noise level of the image.

Experimental Study on Softening High-Calcium Sulfate Reverse Osmosis Concentrate Using Induced Crystallization Method

Reverse osmosis (RO) concentrate often contains high levels of sulfate and calcium ions due to the use of antiscalants, leading to significant calcium sulfate supersaturation and creating favorable conditions for induced crystallization. This study utilized a combination of static and dynamic experiments to investigate the key factors influencing the removal of calcium sulfate from RO concentrate via induced crystallization. The static experiments examined the effects of seed crystal concentration, stirring speed, reaction temperature, and the molar ratio of SO42− to Ca2+ on removal efficiency, with response surface methodology (RSM) employed to analyze the interactions among these factors. In the dynamic experiments, gypsum particles were used as seed crystals in a fluidized bed reactor to study the impact of initial seed crystal dosage and influent flow rate on the removal performance. Optimization strategies for stable operation were also explored. The static experiments revealed that seed crystal concentration was the most critical factor affecting removal efficiency. Under optimal conditions, the calcium ion concentration in the treated water could be reduced to 453 mg/L, achieving a removal rate of 63.8%. In the dynamic experiments, the effluent calcium ion concentration was reduced to 724 mg/L, with a removal rate of 52.5%. However, prolonged continuous operation led to a gradual increase in effluent calcium ion levels, which could be mitigated by recycling seed crystals from the settling zone back to the reaction zone. Characterization of the induced seed crystals and simulation calculations demonstrated that Ca2+ and SO42− reacted to form calcium sulfate crystals, primarily as CaSO4·2H2O, which adhered to the seed crystal surfaces. The growth of the seed crystals, indicated by an increase in particle size, correlated with the volume of water treated. This study provides valuable insights and data for the application of calcium sulfate-induced crystallization as a method to reduce sulfate and calcium ion concentrations in RO concentrate, offering a viable approach to water softening and resource recovery.

Investigation of Appropriate Collector Selection for Hematite Removal from Pyrolusite and the Adsorption Mechanism on the Crystal Surface

This study examined the appropriate hematite (Fe2O3) collector for the concentration of pyrolusite (MnO2) in a reverse flotation. Actual ore flotation studies were performed to determine how sodium oleate, sodium dodecyl sulfonate, and oxidized paraffin soap affect hematite removal during reverse flotation of pyrolusite ore. In order to explore the flotation mechanism, simulation experiments were carried out. Firstly, the crystal models of pyrolusite and hematite were established. Then, in order to verify the reliability of the simulation results, the simulated XRD spectra of the crystal model were compared with the measured spectra. Finally, density functional theory and molecular dynamics modeling were used to study the interaction between collector molecules and mineral surfaces. The flotation test results show that oxidized paraffin soap is the best hematite collector and promotes its flotation, removing iron from pyrolusite. Molecular dynamics simulations and density functional theory show that the three collectors (oxidized paraffin soap, sodium oleate, and sodium dodecyl sulfonate) have a much stronger interaction with hematite than with pyrolusite. Therefore, it is possible to separate pyrolusite and hematite through flotation. The simulation results also show that oxidized paraffin soap has the highest adsorption strength and selectivity for hematite. This characteristic makes oxidized paraffin soap an excellent collector for effectively removing hematite from pyrolusite in the reverse flotation process.

Mechanical constraint to extend the operational range of (011)-oriented Mn-doped PIN–PMN–PT single crystals

AbstractWe investigated mechanical stress-dependent behaviors of (011)-oriented Mn-doped PIN–PMN–PT single crystals to further improve their stabilities for high-power piezoelectric applications. In contrast to the common belief that mechanical constraint induces depolarization of active piezoelectric materials, the (011)-oriented single crystals demonstrated up to 44% of enhancements in their coercive field when mechanical stress is loaded on the specific flank surfaces of the single crystals. Furthermore, the suggested strategy is also feasible over practical operational temperatures for electroacoustic sensors (5–60 °C), which is beneficial to high-temperature applications. Nevertheless, consistent with the generally accepted trade-off, their electromechanical responses are inevitably degraded at constrained states due to less shear deformation which is key in piezoelectricity of relaxor-PT single crystals. We hope that the current work will elucidate mechanical stress-dependent behaviors of domain-engineered anisotropic relaxor-PT single crystals and provide a clue for a proper selection of prestress levels to achieve better performances of electroacoustic transducers in a variety of environments.

In-Situ Growth of One-Dimensional Blocking Layer to Mitigate Deficient Surface of Single-Crystal Perovskites.

Organic-inorganic halide perovskite (OIHP) single crystals are promising for optoelectronic application, but their high surface trap density and associated ion migration hinders device performance and stability. Herein, a one-dimensional (1D) perovskites are designed and proposed as blocking layer at the crystal/electrode interface to mitigate the surface issues. As a model system, the interface ion migration in Cs0.05FA0.95PbI3 (FA=formamidinium) single-crystal perovskite solar cells (PSCs) is obviously suppressed, leading to increase of T90 lifetime from 260 to 1000 hours, five times better than previously reported results. Besides, the reduction of surface iodide ion vacancies inhibits nonradiative recombination, thus increasing the efficiency from 22.1 % to 23.8 %, which is one of the highest values for single-crystal PSCs. Since the deficient crystal surface is a universal and open issue, our strategy is instructive for optimizing diverse single-crystal perovskite devices.

High Rate Performance of Single‐Crystalline NCM Upcycled from Spent Lithium‐Ion Batteries Via Direct Recovery and Modification

AbstractThe global expansion of spent lithium‐ion batteries (LIBs) presents both an urgent environmental issue and a significant economic opportunity, driving the development of diverse recycling processes worldwide. Direct regeneration is a promising method for recovering materials from spent LIBs. However, most existing direct regeneration methods focus solely on recovering cathodes without addressing further improvements in their performance. Herein, a direct regeneration method is reported to upcycle single‐crystalline lithium nickel manganese cobalt oxides (NCM) from spent polycrystalline NCM based on a facile phosphoric acid etching approach. Moreover, the Li3PO4 coating and PO43− polyanion doping are simultaneously achieved on the surface of single‐crystal NCM during the upcycling single‐crystalline process. The enlarged lattice spacing and fast ionic conductor coating layer enhance Li+ diffusion and mitigate phase transformations during delithiation/lithiation. Benefiting from the synergistic effect of single crystal structure and surface modification, the upcycled single‐crystalline LiNi0.65Co0.2Mn0.15O2 demonstrates excellent electrochemical performances, including large reversible capacity (≈186 mAh g−1 at 0.1C), high‐rate capability (≈142 mAh g−1 at 10C), and excellent cycling stability (≈99% retention for 100 cycles). This approach provides a novel and effective upcycling pathway to transform the spent LIBs into value‐added cathode materials, achieving a win–win situation for environmental protection and resource conservation.

New surface waves in a hyperbolic graded-index crystal

The transverse electric surface waves propagating along the surface of the crystal characterized by a spatial dependence of the dielectric permittivity are theoretically described. A hyperbolic profile of the dielectric permittivity of the crystal is used to obtain an exact analytical solution to the wave equation, which is expressed by Whittaker function. The influence of the parameters of the hyperbolic profile of the dielectric constant on the localization of the electric field near the crystal surface is analyzed. The dependencies of the effective refractive index on the parameters of a hyperbolic profile of the dielectric permittivity are explored. The way to effectively control the localization and intensity of the surface waves by changing the values of the parameters of the hyperbolic profile using the obtained exact solution is found.