Crystal Orientation Research Articles

Heteroepitaxy of ε‐Ga2O3 thin film for artificial synaptic device

AbstractEmerging‐wide bandgap semiconductor Ga2O3 shows distinct characteristics for optoelectronic applications and a stable crystal phase of Ga2O3 is highly desired. Herein, we have first reported a metal‐semiconductor‐metal structure photonic synaptic device based on the ε‐Ga2O3 thin film. The ε‐Ga2O3 epilayer is grown on the c‐sapphire with a low temperature nucleation layer, which presents a crystal orientation relationship with the c‐sapphire (ε‐Ga2O3 <010> // c‐sapphire <1–100> and ε‐Ga2O3 <001> // c‐sapphire <0001>). The ε‐Ga2O3 photonic device was stimulated by UV pulses at different pulse widths, pulse intervals, and reading voltages. Under the UV pulse excitation, the photonic device exhibits primary synaptic functions including excitatory postsynaptic current, short term memory, pair pulse facilitation, long term memory, and STM‐to‐LTM conversion. In addition, stronger and repeated stimuli can naturally contribute to the higher learning capability, thus prolonging the memory time.

Study on the uniaxial tensile mechanical behavior of two-dimensional single-crystal aluminum nitride

Abstract To investigate the tensile behavior and mechanical properties of single-crystal aluminum nitride (AlN) at the microscopic level, molecular dynamics simulations were used to study the effects of crystal orientation, strain rate, environmental temperature, and hole defect size on fracture strength, fracture mechanism, and potential energy during uniaxial tensile. The results show that the tensile strength of AlN in the [100] crystal direction is stronger. The anisotropic behavior characteristics of Al-N bonds fracture mechanism, crack growth rate, and cracking degree are significant when stretched along the [100], [010], and [110] crystal directions. Under high temperature condition, the lattice structure undergoes changes, causing grain boundaries to move and slip. This facilitates the breaking of bonds, leading to a decrease in tensile strength and a reduction in stored potential energy. Hole defects cause more lattice damage, reducing the energy required for Al-N bonds breakage and facilitating the propagation of microcracks. Additionally, it was found that the strain rate affects the stress-strain behavior of the model. An increase in strain rate leads to an increase in breaking stress, and the rapid deformation of AlN results in more energy being stored in the lattice in the form of potential energy. Therefore, the tensile strength and potential energy are improved.

Mechanical and high-temperature steam oxidation properties of Cr coatings deposited via high-power impulse magnetron sputtering

Applying protective coatings to Zr alloy cladding surfaces is one of the better methods to design fuel tolerant materials. In this study, the surface of a Zr-4 alloy was coated with Cr using high-power impulse magnetron sputtering. Furthermore, the mechanisms by which bias voltages affect the mechanical characteristics, resistance to high-temperature steam oxidation, and coating structure were elucidated. The coating exhibits a strong (200) weave structure with coarse grains at a bias voltage of -100 V. With increasing bias, the energy of deposited particles increases, grains continue to grow, (200) preferential growth orientation disappears, and the coating exhibits a (110) crystal orientation. The growth structure of the coating first shows a tendency to be dense and then loose. For the Cr coating with a (200) crystal orientation, a dense oxide layer is preferentially formed after oxidation, which can effectively block the internal diffusion of O. With increasing oxidation time, coarse Cr grains can effectively block the external diffusion of Zr. Furthermore, the Cr coating exhibiting a (110) crystal orientation was severely oxidized after oxidation, resulting in the formation of cracks at the film base; this accelerated the outward diffusion of Zr.

Synthesis of Multifunctional Organic Molecules via Michael Addition Reaction to Manage Perovskite Crystallization and Defect

AbstractAdditive engineering plays a pivotal role in achieving high‐quality light‐absorbing layers for high‐performance and stable perovskite solar cells (PSCs). Various functional groups within the additives exert distinct regulatory effects on the perovskite layer. However, few additive molecules can synergistically fulfill the dual functions of regulating crystallization and passivating defects. Here, we custom‐synthesized 2‐ureido‐4‐pyrimidone (UPy) organic small molecules with diverse functional groups as additives to modulate crystallization and defects in perovskite films via the Michael addition reaction. Theoretical and experimental investigations demonstrate that the −OH groups in UPy exhibit significant effects in fixing uncoordinated Pb2+ ions, passivation of lead‐iodide antisite defects, alleviating hysteresis, and reducing non‐radiative recombination. Furthermore, the enhanced C=O and −NH2 motifs interact with the A‐site cation via hydrogen bonding, which relieves residual strain and adjusts crystal orientation. This strategy effectively controls perovskite crystallization and passivates defects, ultimately enhancing the quality of perovskite films. Consequently, the open‐circuit voltage of the UPy‐based p‐i‐n PSCs reaches 1.20 V, and the fill factor surpasses 84 %. The champion device delivers a power conversion efficiency of 25.75 %. Remarkably, the unencapsulated device maintained 96.9 % and 94.5 % of its initial efficiency following 3,360 hours of dark storage and 1,866 hours of 1‐sun illumination, respectively.

Comparison between carrier transport property and crystal quality of TlBr semiconductors

Thallium bromide (TlBr) semiconductor detectors are being developed as promising candidates for high-detection-efficiency, high-energy-resolution, and room-temperature gamma-ray spectrometers. This study presents methods for evaluating TlBr crystal quality and carrier transport characteristics using neutron Bragg-dip imaging and the time-of-flight method for pulsed-laser-induced carriers, respectively. Neutron Bragg-dip imaging effectively determines the crystal orientation distribution, revealing crystal imperfections and grain boundaries. Time-of-flight measurements provide a spatial distribution of carrier mobility. In this study, two samples obtained from both the upstream and downstream region in the crystal ingot were evaluated. Although both samples show similar crystal quality, the upstream sample showed high carrier mobility across all areas, whereas the downstream sample exhibits low mobility in some areas. These findings suggest that, at least within the range of carrier mobility currently obtained, the effect of crystal integrity on carrier mobility is less significant than that of impurities. In conclusion, combining neutron Bragg-dip imaging with carrier mobility measurements offers a comprehensive approach to evaluating and improving TlBr detectors.

Improved Charge‐Transfer Doping in Crystalline Polymer for Efficient and Stable Perovskite Solar Cells

AbstractPerovskite solar cells (PSCs) have significant potential for next‐generation photovoltaic technology applications. However, the instability of hole transport layers (HTLs) becomes the major obstacle to long‐term operational devices, which are affected by the intrinsic thermal instability and loose structure of hole transport materials, as well as the hygroscopicity and migration of dopants. Here, poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) is used as a model crystalline polymer to thoroughly investigate effective p‐type doping strategies and the underlying mechanism. According to Hard–Soft‐Acid–Base theory, the soft base P3HT is more likely to form a stable Lewis acid–base adduct with the reactive soft acid radical, resulting in a strong charge‐transfer interaction, thereby enhancing conductivity and regulating the energy band of the HTL. Meanwhile, the radical cation salt can promote pre‐nucleation to optimize the crystallization orientation of P3HT. The resulting PSCs exhibited the efficiency of 25.16%, which is the highest efficiency reported so far based on doped P3HT. In addition, the resulting devices demonstrated excellent stability, maintaining 96.5%, 96%, and 91% of their initial efficiency after aging under continuous illumination for 2028 h, at 85 °C for 1080 h, and at maximum power point (MPP) tracking under continuous 1 Sun illumination at 85 °C for 528 h, respectively.

Study of the effect of SMAW welding speed on the microstructure and crystal stability of X70 steel using X-ray diffraction

This study investigates the impact of manual electric arc welding (SMAW) speed on the microstructure of X70 steel. Welding was performed at two distinct speeds: S1 = 20 mm/min and S2 = 35 mm/min, at the COSIDER BISKRA workshop in Algeria. X-ray diffraction (XRD) analysis was conducted on the welded zones to examine crystal orientation, size, dislocation density, and structural stability across different welding areas, including the base metal (MB), heat-affected zones (HAZ1 and HAZ2), and weld zones (WZ1 and WZ2). The XRD results revealed that key crystal peaks, such as {110} and {200}, retained their positions at both welding speeds, though variations in {110} peak intensity were noted. The lower welding speed (S1) resulted in a higher heat input, which enhanced crystal stability, increased crystal size, and reduced dislocation density. On the other hand, the higher speed (S2) produced lower heat input, leading to smaller crystal sizes, increased residual stresses, and a greater number of defects due to rapid cooling. These findings underscore the critical influence of welding speed on heat input, cooling rates, and their consequent effects on microstructure. The study highlights the importance of optimizing welding parameters to balance microstructural integrity, mechanical performance, and production efficiency.

Anisotropy of radiation-induced defects in Yb-implanted β-Ga2O3

RE-doped β-Ga2O3 seems attractive for future high-power LEDs operating in high irradiation environments. In this work, we pay special attention to the issue of radiation-induced defect anisotropy in β-Ga2O3, which is crucial for device manufacturing. Using the RBS/c technique, we have carefully studied the structural changes caused by implantation and post-implantation annealing in two of the most commonly used crystallographic orientations of β-Ga2O3, namely the (-201) and (010). The analysis was supported by advanced computer simulations using the McChasy code. Our studies reveal a strong dependence of the structural damage induced by Yb-ion implantation on the crystal orientation, with a significantly higher level of extended defects observed in the (-201) direction than for the (010). In contrast, the concentration and behavior of simple defects seem similar for both oriented crystals, although their evolution suggests the co-existence of two different types of defects in the implanted zone with their different sensitivity to both, radiation and annealing. It has also been found that Yb ions mostly occupy the interstitial positions in β-Ga2O3 crystals that remain unchanged after annealing. The location is independent of the crystal orientations. We believe that these studies noticeably extend the knowledge of the radiation-induced defect structure, because they dispel doubts about the differences in the damage level depending on crystal orientation, and are important for further practical applications.

Nanoscale Wet Etching of Molybdenum Interconnects with Organic Solutions.

Molybdenum (Mo) has emerged as a promising material for advanced semiconductor devices, especially in the design and fabrication of interconnects requiring sub-10nm metal nanostructures. However, current wet etching methods for Mo using aqueous solutions struggle to achieve smooth etching profiles at such scales. To address this problem, we explore wet chemical etching of patterned Mo nanowires (NWs) using an organic solution: ceric ammonium nitrate (CAN) dissolved in acetonitrile (ACN). In this study, we demonstrate two distinct etching pathways by controlling the reaction temperature: i) digital cyclic scheme at room temperature, with a self-limiting Mo recess per cycle of ≈1.6nm, and ii) direct etching at elevated temperature (60°C), with a time-controlled Mo recess of ≈2nm min-1. These methods not only offer a highly controllable nanoscale Mo etching but also ensure smooth and uniform etching profiles independent of the crystal grain orientation of the metal.

Analytical insight into caffeine extraction from typica coffee leaves based on crystallinity enhancement, optical phonon vibration upshift, and morphological evolution.

Caffeine extracted from callus cultures by in vitro technique induced from typica coffee (Coffea arabica L. var. typica) leaves was successfully carried out by a simple Soxhlet method. Analysis of X-ray diffraction patterns showed an increase in crystallinity fraction from leaves (13.56%) to callus (14.46%) and then to caffeine (39.18%). Crystallite size also varied, with average sizes of 18±6, 69±51, and 32.5±17 nm for leaves, callus, and caffeine, respectively. Fourier transmission infrared absorption data confirmed the presence of hydroxyl (OH) groups bound to carbon (C─COH), indicating caffeine content. The high stability of the C─COH is indicated by the broad optical phonon vibrations of the leaves: 247cm-1 to caffeine: 963cm-1. Quantitative analysis of dielectric function and electron loss function intensity peaks of each sample showed that leaves efficiently capture and store light energy while caffeine has less potency. Scanning electron microscopy analysis showed irregular shapes of leaves, oval round shapes for callus, and rectangular crystals for caffeine due to crystal orientation during transformation and had a strong correlation with crystallinity fraction. Finally, the structure-based identification, chemistry, optical-dielectric function, and micro-surface properties have been fully studied, thus unmasking the phenomenon of slow transformation from leaves to caffeine form. PRACTICAL APPLICATION: The result of this study can be applied to uncover new methodologies related to the classification, and biotechnological utilization of callus culture based on structural properties, optical-dielectric function, and micro-surface analysis. Methodologically, the resulting callus culture provides a sustainable and controllable supply of plant material for caffeine extraction, thereby reducing traditional methods involving field-grown plants and avoiding the use of pesticides.

Wrinkled Rhenium Disulfide for Anisotropic Nonvolatile Memory and Multiple Artificial Neuromorphic Synapses.

Two-dimensional materials are emerging as potential solutions for high-density nonvolatile memory and efficient neuromorphic computing. However, integrating multidimensional memory and an ideal linear weight updating synapse in a simple device configuration to achieve versatile biomimetic neuromorphic systems remains challenging. Here, we introduce a wrinkled rhenium disulfide (ReS2) transistor, where the wrinkled structure facilitates the carrier trapping/detrapping at the dielectric interface, thus enabling the fusion of nonvolatile memory and both electronic and optoelectronic synaptic functionalities. As a nonvolatile memory, anisotropic wrinkled ReS2 can yield three distinct sets of data across three crystal orientations under identical programming operations. Each set demonstrates exceptional retention and endurance properties. As a neuromorphic synapse, it realizes the linear and symmetric updates of conductance states up to 9 bits and 8 bits, the ultra-low-energy consumption of 75 fJ and 2.5 pJ under the electrical and optical stimuli, respectively. The artificial neural network (ANN) based on electronic synapses gives a superior recognition accuracy of 92.9% for the original handwritten digits. The anisotropic synaptic responses and multiwavelength sensitivities of optoelectronic synapses enable them to execute advanced memory and recognition functions for complex images that encompass a variety of pattern features or color information. This underscores its substantial potential for integration into efficient biomimetic visual systems.

Atomistic insights into cold welding process of high-entropy alloy nanowires

This research applied molecular dynamics (MD) simulations to investigate the influences of contact pressure, temperature, crystal orientation, and chemical composition on the characteristics of the cold welding joints of CoNiCrFeMn high-entropy alloy (HEA) nanowires. The findings indicate that defect-free cold welded joints can be successfully formed within a contact pressure range of 10 to 10,000 Pa. In addition, changing the contact orientation could cause a significant change in the structure transformation level. The dislocation distribution is continuous when the top and lower blocks are oriented in the same direction. Dislocation lines, on the other hand, stop at the interfacial area and have a discontinuous shape when the weld joints are formed from different orientations. Furthermore, creating from the same orientations leads to a higher ultimate tensile strength (UTS) value than the different orientation cases. In the temperature range of 150 K–350 K, the deformation behaviors of the cold weld joint are stable. Besides, there was no noticeable change in the weld joint when the composition changed. Because of the strong crystal structure of the cold welding joints, the UTS values of the cold-welded joints range from 13.2 to 17.4 GPa, comparable to the bulk samples.

On influence of microstructural anisotropy of additive manufactured structures upon machining dynamics: An example of milling of Ti6Al4V thin-walled parts

Thin-walled structures, as common component specification for aerospace components, easily experience deformation and chatter issues during machining (e.g. milling) operations. With Additively Manufactured (AM) materials being increasingly applied in these areas, it is found that their microstructural anisotropy can lead to varied mechanical properties and machinability in different directions. However, former research on thin-walled parts mainly focused on bulk materials, while the machining performance of these thin-wall structures produced from AM processes remains unclear. In this view, this research aims to reveal the effect of microstructural anisotropy resulting from AM process on the machining (deformation and stability) of thin-walled parts by taking Ti6Al4V as an example. Three kinds of AM Ti6Al4V thin-walled parts were fabricated with different laser scanning strategies, in which the prior columnar β grains were found to grow along the building direction and led to a variation in mechanical properties. Owing to this, the deformation and machining stability varied in the AM thin-walled parts with different β phase crystallization orientations on the same milling directions, which could be attributed to the changes of cutting force and dynamic parameters (e.g., frequency, stiffness (determined by elastic modulus), damping ratio) in different orientations. This investigation could provide a reference for the selection of printing strategies and follow-up machining process of AM thin-walled parts when considering their microstructural anisotropy.

Atomistic understanding on the surface formation mechanism of nanoscale scratches along different crystal orientations of silicon carbide

Single crystal silicon carbide has been widely used in many fields due to its excellent physical and chemical properties. However, these special properties of silicon carbide can lead to surface defects and subsurface damage in precision machining processes. In this research, high-speed scratching experiments and molecular dynamics simulations were used to study the surface formation mechanism of nanoscale scratches along the [1-210] and [1-100] crystal orientations of silicon carbide. For both the simulations and experiments, different scratching crystal orientations result in the formation of different amorphous patterns. The angle between the scratching orientation [1-210] and the amorphous pattern is 60°, while the angle between scratching orientation [1-100] and the amorphous pattern is 30°. The stress concentration during the scratching process along the orientations [1-210] and [1-100] is mainly located at the two edges and one edge of the amorphous patterns, respectively. The amorphous patterns along the < 1-210 > directions on the (0001) plane are caused by dislocations and slips on the {10-10} plane. This study reveals the material deformation mechanism and removal mechanism of silicon carbide along different crystal orientations scratching, providing theoretical guidance for the nanoscale machining of silicon carbide.

Ultrahigh thermal stability and piezoelectricity of lead-free KNN-based texture piezoceramics

The contradiction between high piezoelectricity and uniquely poor temperature stability generated by polymorphic phase boundary is a huge obstacle to high-performance (K, Na)NbO3 -based ceramics entering the application market as Pb-based substitutes. We possess the phase boundary by mimicking Pb(Zr, Ti)O3’s morphotropic phase boundary structure via the synergistic optimization of diffusion phase boundary and crystal orientation in 0.94(Na0.56K0.44)NbO3−0.03Bi0.5Na0.5ZrO3−0.03(Bi0.5K0.5)HfO3 textured ceramics. As a result, a prominent comprehensive performance is obtained, including giant d33 of 550 ± 30 pC/N and ultrahigh temperature stability (d33 change rate less than 1.2% within 25-150 °C), representing a significant breakthrough in lead-free piezoceramics, even surpassing the Pb-based piezoelectric ceramics. Within the same temperature range, the d33 change rate of the commercial Pb(Zr, Ti)O3−5 ceramics is only about 10%, and more importantly, its d33 (~ 350 pC/N) is much lower than that of the (K, Na)NbO3-based ceramics in this work. This study demonstrates a strategy for constructing the phase boundary with MPB feature, settling the problem of temperature instability in (K, Na)NbO3-based ceramics.

Influence of ultrasonic assistance on the microstructure and friction properties of laser cladded Ni60/WC composite coatings

The effects of different ultrasonic vibration powers on the distribution, phase structure, friction and wear properties of WC reinforced particles in laser melted Ni60/WC composite coatings are investigated. The effects of ultrasonic vibration on the microstructure, elemental distribution, crystal orientation, friction and wear properties of the fused coatings are analyzed. The experimental results show that the deposition of WC particles in the lower and middle parts of the coating is significantly improved after the introduction of ultrasonic vibration during the fusion cladding process. In particular, at 600 W ultrasonic power, not only the distribution uniformity of tungsten carbide particles in the coating is optimal, but also the composite coating shows better wear resistance. However, too much ultrasonic power increases the possibility of particle agglomeration. In addition, although the phase pattern of the coating does not change after ultrasonic vibration, the width of the columnar crystalline region of the coating is reduced, and the coating is covered by a homogeneous lamellar nanoscale eutectic structure with the phase compositions of the γ-(Fe, Ni) and M23C6 phases. The ultrasonic vibration improves elemental segregation of the coating, reduces the large number of precipitated phases in the coating, weakens the grain growth orientation, and relieves the local stress concentration in the coating. In addition, the mechanism of the influence of WC particles on the microstructure evolution and wear resistance of the composite coatings is discussed.

Plasma photonic crystal ‘kaleidoscope’ with flexible control of topology and electromagnetism

Continuous development of photonic crystals (PCs) over the last 30 years has carved out many new scientific frontiers. However, creating tunable PCs that enable flexible control of geometric configurations remains a challenge. Here we present a scheme to produce a tunable plasma photonic crystal (PPC) ‘kaleidoscope’ with rich diversity of structural configurations in dielectric barrier discharge. Multi-freedom control of the PPCs, including the symmetry, dielectric constant, crystal orientation, lattice constant, topological state, and structures of scattering elements, has been realized. Four types of lattice reconfigurations are demonstrated, including transitions from periodic to periodic, disordered to ordered, non-topological to topological, and striped to honeycomb Moiré lattices. Furthermore, alterations in photonic band structures corresponding to the reconstruction of various PPCs have been investigated. Our system presents a promising platform for generating a PPC ‘kaleidoscope’, offering benefits such as reduced equipment requirements, low cost, rapid response, and enhanced flexibility. This development opens up new opportunities for both fundamental and applied research.Graphical

Elucidating Heterogeneous Li Insertion Using Single-Crystalline and Freestanding Layered Oxide Thin Film.

The kinetics of interfacial ion insertion govern the uniformity of electrochemical reactions, playing a crucial role in lithium-ion battery performance. In two-dimensional lithium-conducting layered-oxide battery particles, variation in insertion rates across insertion channels remains unclear due to poorly defined crystal orientation at the solid-liquid interface and solid-state-lithium-diffusion length. This ambiguity complicates understanding inhomogeneous lithium-insertion channels activation. A systematic study requires crystallographically predefined interfaces and in situ lithium-concentration mapping. Here, we fabricated a freestanding, (104)-oriented-LiNi1/3Mn1/3Co1/3O2 single-crystal thin film using dissolution-induced release and performed in situ scanning-transmission-X-ray-microscopy to spatially resolve lithium-insertion at well-defined-interfaces. We observed heterogeneous lithium-concentration evolution due to channel-by-channel insertion rate variation, despite the potential for homogeneous lithium distribution via a solid-solution-phase at equilibrium in NMC111. Increasing current density exacerbates this heterogeneity, highlighting channel-by-channel variation. Our findings provide critical insights into battery electrode utilization and lifetime management, potentially guiding the design of more efficient and durable lithium-ion batteries.

Achieving High Thermoelectric Performance in Bi2(Te, Se)3 Thin Film with (00l)-Oriented by Incorporating Tellurization and Selenization Processes.

Flexible thermoelectric (TE) generators have received great attention as a sustainable and reliable option to convert heat from the human body and other ambient sources into electricity. This study provides a synthesis route that involves thermally induced diffusion to introduce Te and Se into Bi, fabricating an n-type Bi-Te-Se flexible thin film on a flexible substrate. This specific synthesis alters the crystal orientation (00l) of the thin film, improving in-plane electrical transportation and optimizing carrier concentration. Consequently, BixTeySe0.42 enhanced both the Seebeck coefficient and electrical conductivity, achieving a power factor of 17.1 μW cm-1 K-2 at room temperature. The TE device assembled with p-type Sb2Te3 exhibited exceptional flexibility with only a 26.2% change in resistance after 1000 times of bending at a radius of about 6 mm. The resistance change was further reduced to 7.5% after the application of a vinyl laurate coating. The fabricated TE device generated an ultrahigh output power of 792 nW with a temperature difference of 30 K.

Tuning Crystalline Preferred Orientation of SnSe2 Anode by Co-doping to Enhance Pseudocapacitive Behaviors for High-Performance Sodium Storage.

SnSe2 has attracted great attention due to its unique 2D-layered structure, which makes it capable of sodium ion storage and higher theoretical capacities compared to traditional anode materials like hard carbon for sodium ion batteries (SIBs). However, SnSe2-based materials will cause structural damage due to volume expansion during ion storage, leading to poor cycle stability and rate capacity. In this work, Co-doped SnSe2 (Co-SnSe2) with preferred crystal orientation was fabricated by a one-step solvothermal method. It has been found that after doping Co, the lower (001) crystal plane located at 14.4° replaced the higher (101) plane at 30.7° as the dominant crystal plane in Co-SnSe2, which significantly promoted ion diffusion and enhanced the pseudocapacitance behavior. Therefore, this Co-SnSe2 anode achieves a high capacity of 504 mAh g-1 at 1 A g-1, and a high-rate cycle stability, delivering a reversible capacity of 302 mAh g-1 at 5 A g-1 after 1800 cycles with a retained capacity rate of 94%. Moreover, the Na3V2(PO4)3||Co-SnSe2 full cell exhibits a stable cycle performance of over 300 cycles at 1 A g-1, demonstrating great promise for practical applications. This work provides an effective reference for the exploration of high-performance sodium storage anode materials.