Crystals

The mechanisms of AlGaN device buffer layer growth were studied. Gallium residues in the reactor chamber may be harmful to the quality of the AlN strain modulation layer, which eventually worsens the AlGaN buffer layer. By restraining the gallium residues, the crystalline quality of the AlGaN layer is markedly improved. In addition, enhancing stress relief in nucleation and coalescence stages will reduce the edge dislocations induced by strain relaxation in the 2D growth stage. A slower precursor flow rate can promote the stress relief in nucleation and coalescence stages. By comparison, a suitable suppression of Al atoms’ surface migration can decrease surface roughness, which can be realized by increasing the precursor flow rate. Eventually, we obtained a AlGaN buffer layer having both low edge dislocation density and a flat surface using a two-step growth method. Full article

FeO is a low-price material with high charge storage capacity, biocompatibility and other characteristics. It has been applied in the fields of catalysts, capacitors, electrodes and composite materials. However, the current method of preparing FeO needs to control the temperature and reducing atmosphere, which increase the production difficulty and cost. In this experiment, the molten salt electrolysis method was used to prepare FeO by using the NaCl-KCl molten salt system and Fe₂O₃ and Al₂O₃ as raw materials, and the influence of temperature on the preparation process was explored. The results showed that the electrolysis process of Fe₂O₃ to FeO is mainly divided into the following three stages: the electric double-layer charging process, Fe₂O₃ to Fe₃O₄ process and Fe₃O₄ to FeO process. The increase in temperature can improve the reaction speed and strengthen the electrolysis effect. The higher the temperature, the less Fe₃O₄ and more FeO in the sample. Through analysis, it was found that the increase in temperature will affect the theoretical voltage of the electrolytic reaction in thermodynamics, resulting in the increase in the overall potential provided by the power supply. In terms of kinetics, the increase in temperature will affect the viscosity of molten salt, so that O²⁻ transport has better kinetic conditions. Full article

Electronic-grade polysilicon is the cornerstone of the information industry. Considering the demand for this material in the semiconductor industry, any technological improvement has great potential benefits. Due to the quality requirements of electronic polysilicon, its preparation process is characterized by low raw material utilization and high cost. Simply increasing the deposition rate by increasing the chemical reaction rate will easily lead to a reduction in the proportion of dense materials. For the first time, a coupled furnace scheme is proposed to improve the utilization of raw materials while maintaining the same deposition quality. The deposition conditions on the surface of silicon rods with different base plate designs were modeled and analyzed using the software PolySim, and a design characterized by a high flow rate and the use of 9 mm and 15 mm nozzles was selected for the coupling scheme. In coupling mode, the simulation results show that the utilization of raw materials is increased by 17.5%, and the deposition rate is increased by 44.9%, while the deposition quality and uniformity remain approximately unchanged. The results show that the coupling scheme with high feed flow is beneficial for significantly improving the deposition conditions and the utilization rate of raw materials, which also provides guidance for material preparation processes with similar principles. Full article

Precision laser spectroscopy of the 229-thorium nuclear isomer transition in a solid-state environment would represent a significant milestone in the field of metrology, opening the door to the realization of a nuclear clock. Working toward this goal, experimental methods require knowledge of various properties of a large band-gap material, such as calcium fluoride doped with specific isotopes of the heavy elements thorium, actinium, cerium, neptunium, and uranium. By accurately determining the atomic structure of potential charge compensation schemes by using a generalized gradient approximation within the ab-initio framework of density functional theory, calculations of electric field gradients on the dopants become accessible, which cause a quadrupole splitting of the nuclear-level structure that can be probed experimentally. Band gaps and absorption coefficients in the range of the 229-thorium nuclear transition are estimated by using the $G_0{W}_0$ method and by solving the Bethe–Salpeter equation. Full article

In this paper, the different Ti:Sapphire crystal configurations of the final amplifiers, depending on the Chirped Pulse Amplification laser system parameters, such as the repetition rates and pulse energy, are discussed. Restrictions placed on the final Ti:Sa amplifiers with a high repetition rate are discussed. The repetition rate of these systems is limited due to the crystal overheating, which leads to stress fracturing or significant beam distortion. The heating density threshold leading to stress fracturing was calculated and taken as the limit of the upper level of the possible pump average power. On the basis of these calculations, the highest repetition rates and corresponding thermolens focal distances were estimated for conventional crystal geometry of the most suitable thicknesses. It was demonstrated that conventional crystal shapes, such as a thin disc, can be used for systems with repetition rates below a few hundred Hz if several Joules of the output pulse energy are required. The rectangular thin crystal plate geometry was more suitable for Ti:Sa amplifiers with repetition rates above 1 kHz. Finally, the parameters of rectangular thin crystal plate Ti:Sa laser amplifier with an output energy above 3 J per pulse for a laser system with more than 100 TW pulse power and 1 kHz repetition rates are presented. Full article

Plastic damage assessment in 316 austenitic steel was performed in this research by using the misorientation parameters derived from an in situ EBSD technique. With the increase in plastic strain, the misorientation parameters, such as the Grain Reference Orientation Deviation (GROD), Grain Orientation Spread (GOS), the Grain Orientation Spread over the grain Diameter (GOS/D), and Geometrically Necessary Dislocation (GND) density presented a growing trend. Nevertheless, the variation in GROD did not show a monotony trend, and the relative increase in the amplitude of GOS and GND density was less in the late plastic stage. Compared with the above parameters, the (GOS)/D exhibited a near-linear increase during the plastic tensile stage. As the specimen was stretched to a strain of 56.99%, the (GOS)/D increased 8.9 times compared with the original specimen. The results showed that the (GOS)/D parameter has the potential of becoming an indicator for the assessment of plastic damage in 316 steel. Full article

In this paper, a symmetric power-exponent prismatic phononic crystal configuration was proposed for the vibration reduction of thin plate structures, and the mechanism of bandgap generation and the influencing factors of the band gaps were analyzed. The results showed that the proposed symmetric power-exponent prismatic phononic crystal structure has three complete band gaps of bending waves, where the width of the second band gap can go up to 1639 Hz. The band gaps of bending waves of the phononic crystal were verified using a combination of numerical simulations and experimental methods, and subsequently, the bandgap characteristics and energy-focusing effect of the phononic crystals were effectively used to suppress the bending vibration of the thin plate. With the increase in prismoid height of the structure, the width of the first band gap expanded, while the bandwidths of the other two band gaps narrowed down. It was observed that an increase in the power of the power-exponent prismoid would reduce the starting and ending frequencies of the band gaps, whereas an increase in the prismoid edge thickness would weaken the energy-focusing effect and narrow the band gaps gradually. Our research results provide a new technique and a pathway to realize vibration reduction in thin plate structures. Full article

In this study, the microstructure evolution and mechanical properties of CoFeNiMnMox high-entropy alloy after adding Mo were investigated. With the increase in Mo content, Mo atoms occupied lattice sites and the microstructure changed from hypoeutectic of primary FCC-phase to Laves phase particles of FCC-phase, and Vickers microhardness increased steadily from 193 to 357. The yield strength increased from 187 MPa when the Mo content was 0.25 to 537 MPa when the Mo content was 1.0. The microstructure formation can be explained by atomic size difference δ and parameter Δχ_A. δ ≥ 3.87% and Δχ_A ≥ 5.24% criterion is proposed to better predict the microstructure formation of the coexistence of (FCC + Laves) phases. Full article

This study investigates the thermal decomposition of acetyl acetonates of Ni(II) and Fe(III) via a sonochemical process at 20 kHz for 50 min. In the absence of magnetic fields the reactions of Ni(II) and Fe(III) acetyl acetonates under ultrasonic treatment produce Ni(OH)₂ and FeO(OH) nanoparticles coated with carbon. The synthesized materials with different Ni-Fe stoichiometries, Ni90-Fe10, Ni80-Fe20, and Ni50-Fe50 wt%, were subjected to catalytic activity for dye decolorization of Reactive Black 5 (RB5, 100 mg/L) at room temperature using visible radiation. The correlation between the structural and optoelectronic properties and the catalytic performance of the Ni-Fe system with different stoichiometries is reported. Full article

An intriguing but rare silicon-centered spirocyclic compound, spiro[5.5]octaferrocenylpentasiloxane (4) featuring silicon fused six-membered ferrocenyl-functionalized siloxane rings, has been obtained during the thermally induced transformation of triferrocenylsilane Fc₃Si–H (1) into triferrocenylsilanol Fc₃Si–OH (2), when N,N-dimethylformamide (DMF) was used as a solvent in the presence of the metal carbonyl Mo(CO)₆. The unexpected formation of the maximally ferrocenyl substituted silicon centered spirocyclic 4 involves the obtention, and subsequent condensation, of different ferrocenylsilanol intermediates. Spirocyclic silicate 4 has been characterized using a combination of MALDI-TOF mass spectrometry, elemental analysis, and single crystal X-ray diffraction analysis. Full article

One of the greatest challenges in the design of shape-memory elements (mostly binary Nickel-Titanium wires) is to ensure that the required travel (stroke) is achieved, as this is subject to variation due to various influencing factors. One way of predicting the stroke is to use a suitable energy model. In the past, for example, a model was developed by Oelschläger with which the stroke can be calculated on the basis of the electrical energy. However, so far no model takes into account the change of the phase transformation temperature. In this study, the model of Oelschläger is extended and verified to consider the degradation behavior over the whole lifetime. For this purpose, fatigue tests of 52 wires (2 different load scenarios) were performed. Based on these tests and the application of statistical methods (distribution models, goodnes-of-fit tests etc.), a target model was developed for each load scenario, which is used to verify the extended energy model. The energy model was applied to wires of both load scenarios to simulate the stroke progression. The verification of the extended simulation model shows that it is possible to simulate the longterm behavior of the stroke for one of the two load scenarios. The second load scenario shows deviations between the target model and the simulation, which is due to problems in the area of measurement equipment, convection, and temperature distribution in the wire. Nevertheless, a decisive modeling approach could be developed, which can be used to consider the long-term behavior of the phase transformation temperature of wires in simulations. Full article

The crystal structure of sergeysmirnovite, MgZn₂(PO₄)₂·4H₂O (orthorhombic, Pnma, a = 10.6286(4), b = 18.3700(6), c = 5.02060(15) Å, V = 980.26(6) ų, Z = 4), a new member of the hopeite group of minerals, was determined and refined to R₁ = 0.030 using crystals from the Këster mineral deposit in Sakha-Yakutia, Russia. Similar to other members of the hopeite group, the crystal structure of sergeysmirnovite is based upon [Zn(PO₄)]^– layers interlinked via interstitial [MO₂(H₂O)₄]^2– octahedra, where M = Mg²⁺. The layers are parallel to the (010) plane. Within the layer, the ZnO₄ tetrahedra share common corners to form chains running along [001]. Sergeysmirnovite is a dimorph of reaphookhillite, a mineral from the Reaphook Hill zinc deposit in South Australia. The relations between sergeysmirnovite and reaphookhillite are the same as those between hopeite and parahopeite. Topological and structural complexity analysis using information theory shows that the hopeite (sergeysmirnovite) structure type is more complex, both structurally and topologically, than the parahopeite (reaphookhillite) structure type. Such complexity relations contradict the general observation that more complex polymorphs possess higher physical density and higher stability, since parahopeite is denser than hopeite. It could be hypothesized that hopeite is metastable under ambient conditions and separated from parahopeite by a structural and topological reconstruction that requires an essential energy barrier that is difficult to overcome. Full article

Aluminium alloys are becoming increasingly popular due to the demands for high-performance lightweight components, and semi-solid metal processing (SSM) is a technique for forming near-net-shape and complex components with far fewer defects associated with turbulent filling. The deformation mechanisms of semi-solid 7075 aluminium alloy were studied through the direct partial re-melting method using as-extruded billets. It is found that inter-granular and intra-granular deformation occur simultaneously during compression under the semi-solid condition; the deformation of solid primary α-Al grains can compensate for the shrinkage of inter-granular liquid and increase the integrity of shaped parts. The intra-granular deformation at the final stage of SSM can change the morphology of spherical solid grains and induces sub-grain boundaries. Full article

High temperature superconducting (HTS) magnets often work at high energy density and have slow quench propagation speed, so a quench will present a serious risk to the safety of magnets. The quench protection method based on the dump resistance can effectively reduce the current and release the energy in the HTS magnets. However, too large dump resistance may cause excessive voltage across the magnets. A quench protection system consisting of dump resistances and metal discs has been proposed. Copper discs are often embedded in HTS magnets for conducting cooling and mechanical support. In the discharging process of HTS magnets, the copper discs can absorb energy from the magnets through magnetic coupling, thus accelerating the current decay of the magnets. This quench protection method is more effective than using dump resistance alone. In this paper, the effect of different copper discs on the discharging process of HTS coils is discussed. Eight types of copper with different residual resistivity ratios (RRR) are applied. The results show that with the increase of the RRR of the copper disc, the current decay rate of the coil increases, and the energy absorbed by the copper disc from the coil increases. The role of different copper discs in the fast quench protection of the coil can be sorted as: RRR = 300 > RRR = 100 > RRR = 80 > RRR = 60 > RRR = 40 > RRR = 30 > RRR = 20 > RRR = 10. The copper disc with RRR of 300 shows the best performance in quench protection of HTS coils. Full article

Graphene has been widely explored as an ideal platform for gas sensing owing to exceptional properties, such as its atom-thin two-dimensional conjugated structure and large specific surface area. Herein, we report that, by introducing covalent C-F bonds via site-selective ion-beam-induced fluorination, graphene sensing response to ammonia gas can be considerably improved due to the enhanced gas adsorption on the surface of fluorinated graphene. The response to the ammonia gas increased by a factor of eight together with the limit of detection approaching 65 ppb. The absorption kinetics between the ammonia gas and fluorinated graphene were analyzed by using the Langmuir isotherm model and the result shows that the enhanced sensitivity is mainly attributed to the strong binding energy of fluorinated graphene to ammonia gas molecules, which is consistent with previous theoretical predictions. Full article

In this work, we measure polarization-resolved photoluminescence spectra from excitonic complexes in tens of single InAs/GaAs quantum dots (QDs) at the telecom O-band with strain-coupled bilayer structure. QDs often show fine-structure splitting (FSS) ~100 μeV in uniform anisotropy and valence-band mixing of heavy holes (HH) and light holes (LH); the biaxial strain also induces LH excitons with small FSS (especially XX, <5 μeV, 70% of QDs); delocalized LH reduces the Coulomb interaction between holes V_hh and enhances population on LH excitons XX, XX₁₁, X₁₁⁺ and XX₂₁⁺. Full article

Devices based on ferroelectric hafnium oxide are of major interest for sensor and memory applications. In particular, Si-doped hafnium oxide layers are investigated for the application in the front-end-of-line due to their resilience to high thermal treatments. Due to its very confined doping concentration range, Si:HfO₂ layers based on thermal atomic layer deposition often exhibited a crossflow pattern across 300 mm wafer. Here, plasma enhanced atomic layer deposition is explored as an alternative method for producing Si-doped HfO₂ layers, and their ferroelectric and pyroelectric properties are compared. Full article

The present work focuses on the effect of multistage solution heat treatment (MSHT) and artificial aging on two-stage stir-cast LM4 + TiB₂ (1, 2, and 3 wt.%) composites on the mechanical properties as compared to as-cast and single-stage solution heat-treated (SSHT) composites. Two novel tests, viz. the confirmation hardness test and the chemical analysis test, were performed to ensure the soundness of the casting and uniform distribution of TiB₂ within the matrix. Samples subjected to MSHT + aging at 100–200 °C displayed the highest hardness and UTS values compared to as-cast and SSHT + aging at 100–200 °C samples. Compared to as-cast alloy, peak-aged samples of 1–3 wt.% (MSHT + aging at 100 °C), hardness values improved from 107–150%, and UTS values improved from 47–68%. The presence of metastable phases (θ′-Al₂Cu and θ″-Al₃Cu) and of hard TiB₂ particles are the reason for the improvement in the properties. Peak aged LM4 + 3 wt.% TiB₂ composite displayed the highest hardness of 175 VHN and UTS of 251 MPa. Fracture analysis of the LM4 alloy showed dimple rupture, and its composites revealed quasi-cleavage fracture. Based on the overall results, the inclusion of TiB₂, MSHT, and artificial aging treatment on the LM4 alloy significantly influenced the composites’ mechanical properties. Full article

In this study, an Er:YAG laser pumped intra-cavity Tm:YAG-Ho:GdVO₄ laser was built and debuted at room temperature. At an incident pump power of 9.2 W, this laser obtained a maximum output power of 1.6 W with a slope efficiency of 28.0%. Additionally, the M² factors at the maximum output power were measured to be 1.06 and 1.03 in the x and y directions, respectively. The results showed that the intra-cavity pumping method of combining thulium and holmium crystals as the gain medium was an effective way to obtain a 2 μm laser with near diffraction limited beam quality. Full article