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• Cathodoluminescence imagery and Ti-zoning of corundum crystals ("Carmel Sapphire") record growth from a silicate melt in an evolving open system at very low oxygen fugacity (Oliveira et al., [19]). These spectacular structures are only one form of TiN in the Carmel sapphire; it also occurs in large inclusions coexisting with Fe-Ti silicides and TiB SB 2 sb , and as regular crystals that appear to have crystallised directly from Fe-Ti silicide melts (Griffin I et al. i , [10], [11], [12]). We thank the Galuskins for their detailed study of the explosion breccias and the nitrides included in corundum aggregates from Mt Carmel; space considerations have limited our previous publication of such detailed data on this interesting aspect of these important samples. We suggest that the report of böhmite /bauxite represents analyses of spots consisting of amorphous carbon plus micro-inclusions of corundum; this would be consistent with the apparently higher C content of the EDS spectrum. [Extracted from the article]

iBeam Materials is developing a revolutionary new technology to fabricate large‐area inexpensive sheets of GaN‐based LEDs and devices directly on large‐area metal foils. This new technology is based on using ion‐beam crystal alignment to fabricate templates for epitaxial GaN films on flexible metal foil, that are lattice‐matched, as well as thermally highly conductive and thermally matched to GaN. The ion beam assisted deposition (IBAD) texturing process is used to prepare biaxially aligned films as templates for GaN epitaxy. Epitaxial GaN films have been grown on these engineered flexible metal substrates. We have achieved GaN films of several microns in thickness on polycrystalline metal foils that have typical threading dislocation densities of 4 – 8 x 108/cm2. We then used these epitaxial GaN films on IBAD/polycrystalline metal foil as templates to deposit epitaxial multi‐quantum well light emitting diode (LED) InGaN structures. InGaN LED devices were successfully fabricated and patterned into MicroLED arrays on metal foil. We observe photoluminescence from these LED structures with 70% of the intensity compared to LEDs fabricated on sapphire. We discuss how these LED devices could be manufactured using a roll‐to‐roll process and cost reductions that result from this. Large‐area LED sheets can then be used to monolithically integrate MicroLEDs into paper‐thin and flexible displays. [ABSTRACT FROM AUTHOR]

A novel red LED using Eu‐doped GaN is a promising component for next‐generation micro‐LED displays with small‐size, full‐color, and ultrahigh‐definition. The red LED exhibits narrow‐band red emission and the wavelength is almost independent of ambient temperature and injected current, and the efficiency remains almost constant even at a ultrasmall chip. Monolithic vertically stacked full‐color LEDs on a sapphire substrate is demonstrated. [ABSTRACT FROM AUTHOR]

Narrow-gap InN is a desirable candidate for near-infrared (NIR) optical communication applications. However, the absence of lattice-matched substrates impedes the fabrication of high-quality InN. In this paper, we employed Molecular Beam Epitaxy (MBE) to grow nanostructured InN with distinct growth mechanisms. Morphological and quality analysis showed that the liquid phase epitaxial (LPE) growth of hexagonal InN nanopillar could be realized by depositing molten In layer on large lattice-mismatched sapphire substrate; nevertheless, InN nanonetworks were formed on nitrided sapphire and GaN substrates through the vapor-solid process under the same conditions. The supersaturated precipitation of InN grains from the molten In layer effectively reduced the defects caused by lattice mismatch and suppressed the introduction of non-stoichiometric metal In in the epitaxial InN. Photoluminescence and electrical characterizations demonstrated that high-carrier concentration InN prepared by vapor-solid mechanism showed much stronger band-filling effect at room temperature, which significantly shifted its PL peak to higher energy. LPE InN displayed the strongest PL intensity and the smallest wavelength shift with increasing temperature from 10 K to 300 K. These results showed enhanced optical properties of InN nanostructures prepared on large lattice mismatch substrates, which will play a crucial role in near-infrared optoelectronic devices. [ABSTRACT FROM AUTHOR]

With the growing demand for the fabrication of microminiaturized components, a comprehensive understanding of material removal behavior during ultra-precision cutting has become increasingly significant. Single-crystal sapphire stands out as a promising material for microelectronic components, ultra-precision lenses, and semiconductor structures owing to its exceptional characteristics, such as high hardness, chemical stability, and optical properties. This paper focuses on understanding the mechanism responsible for generating anisotropic crack morphologies along various cutting orientations on four crystal planes (C-, R-, A-, and M-planes) of sapphire during ultra-precision orthogonal cutting. By employing a scanning electric microscope to examine the machined surfaces, the crack morphologies can be categorized into three distinct types on the basis of their distinctive features: layered, sculptured, and lateral. To understand the mechanism determining crack morphology, visualized parameters related to the plastic deformation and cleavage fracture parameters are utilized. These parameters provide insight into both the likelihood and direction of plastic deformation and fracture system activations. Analysis of the results shows that the formation of crack morphology is predominantly influenced by the directionality of crystallographic fracture system activation and by the interplay between fracture and plastic deformation system activations. ARTICLE HIGHLIGHTS: • Crack morphologies are categorized into three types: sculptured, layered, and lateral cracks. • The parameters of slip and fracture activation are investigated in relation to the crystallographic properties of sapphire. • The mechanism of crack formation is studied through an analysis of the directions of fracture activation and their interaction with slip systems. [ABSTRACT FROM AUTHOR]

The document is a contents list for the journal CrystEngComm. It provides information about the articles and papers included in the issue, as well as details about the journal's focus on the design and understanding of solid-state and crystalline materials. The document also includes information about the editorial board, submission guidelines, and contact information for the journal. [Extracted from the article]

Phase-change alloy Ge 2 Sb 2 Te 5 (GST) forms a favorable material platform for modern optics, photonics, and electronics thanks to a pronounced increase in conductivity with thermally induced phase transitions from amorphous (a-GST) into cubic (c-GST) and then hexagonal (h-GST) crystalline states at the temperatures of ≃ 150 and ≃ 300 ° C, respectively. Nevertheless, the data on broadband electrodynamic response of distinct GST phases are still missing, which hamper the design and implementation of related devices and technologies. In this paper, a-, c-, and h-GST films on a sapphire substrate are studied using broadband dielectric spectroscopy. For all GST phases, complex dielectric permittivity is retrieved using Drude and Lorentz models in the frequency range of 0.06 – 50 THz or the wavelength range of ≃ 5000 – 6 μ m. A contribution from the free charge-carriers conductivity and vibrational modes to the broadband response of an analyte is quantified. In this way, the Drude model allows for estimation of the static (direct current—DC) and dynamic (at 1.0 THz) conductivity values, caused by motions of free charges only, which are as high as σ DC ≃ 15 and 40 S/cm and σ 1.0 THz ≃ 8.8 and 28.6 S/cm for the c- and h-GSTs, respectively. This overall agrees with the results of electrical measurements of GST conductivity using the four-point probe technique. The broadband electrodynamic response models obtained for the three GST phases are important for further research and developments of GST-based devices and technologies. [ABSTRACT FROM AUTHOR]

Advancements in astronomical telescopes and cutting-edge technologies, including deep ultraviolet (DUV) and extreme ultraviolet (EUV) lithography, have escalated demands and imposed stringent surface quality requirements on optical system components. Achieving near-ideal optical components requires ultra-smooth surfaces with sub-nanometer roughness, no sub-surface damage, minimal surface defects, low residual stresses, and intact lattice integrity. This necessity has driven the rapid development and diversification of ultra-smooth surface fabrication technologies. This paper summarizes recent advances in ultra-smooth surface processing technologies, categorized by their material removal mechanisms. A subsequent comparative analysis evaluates the roughness and polishing characteristics of ultra-smooth surfaces processed on various materials, including fused silica, monocrystalline silicon, silicon carbide, and sapphire. To maximize each process's advantages and achieve higher-quality surfaces, the paper discusses tailored processing methods and iterations for different materials. Finally, the paper anticipates future development trends in response to current challenges in ultra-smooth surface processing technology, providing a systematic reference for the study of the production of large-sized freeform surfaces. [ABSTRACT FROM AUTHOR]

Ultraprecision positioning to better than nanometer in accuracy is of a great interest in various applications. The paper reports on recent pre-rolling experimental measurements of the moment friction during the phase of pre-rolling, i.e., at the start and at the finish. To discuss the case properly, the experiments are set for pure rolling without any external effect nor any slippage at the contact patch. The pendulum was designed to secure pure pre-rolling without slippage. Beside the fact that the experiments have shown extremely low values of rolling coefficients in the order of (× 10–7), it is possible to establish the appearance of real hysteresis curves showing the dependance of the friction moment on the displacement. The sensitivity of the measurement of rolling friction moments is in the order of 10–10 Nm, the measurement error does not exceed 10% with 125 nm minimum displacement of the ball peel adhesion density evaluated as 2.2 × 10–4 J/m2. [ABSTRACT FROM AUTHOR]

Sapphire has increasing demand toward optoelectrical devices like LED; its big challenge is to find reasonable growth mechanisms for high quality large size single crystals. In this paper, we proposed both theoretical and experimental studies to clarify multiscale behaviors within the Al2O3 growth system. Molecular dynamics simulation for sapphire crystal growth along c-, a-, and m-axes, and solid–liquid interface structure, and grown 2″ sapphire via the Czochralski method along the c-axis, were reported herein. Our studies show that α-Al2O3 growth behaviors along different crystal directions are different, which is different from the amorphous Al2O3 phase transition at the various α-Al2O3 planes. α-Al2O3 crystal growth in the c-axis system may be a complex process involving solid–liquid and solid–solid transformations, rather than a single solid–liquid transformation that happened in the systems growing along the a- and m-axes. Within the time scale of simulation, the crystals cannot be grown by the lattice period of the seed crystal along the c-axis and transform into γ-Al2O3 rather than α-Al2O3, while it is opposite along the a- and m-axes. This may be the microscopic reason why it is difficult to grow sapphire along the c-axis in the experiment. An abrupt change in the interfacial structure is the key reason to inhibit the transformation of liquid Al2O3 into α-Al2O3 along the c-axis. [ABSTRACT FROM AUTHOR]

During the diamond wire saw cutting process of sapphire crystals, warpage is one of the key parameters for evaluating wafer quality. Based on the thermoelasticity theory and diamond wire saw cutting theory, a finite element model for thermal analysis of diamond wire saw cutting sapphire crystals was established in this paper. The variation laws and internal connections of the temperature field and thermal deformation displacement field of the wafer during the sawing process were analyzed. A calculation and analysis model for the warpage of sapphire crystal wafer cut by wire saw was established based on the node thermal deformation displacement field of the wafer, and the rationality of the simulation results was verified through sawing experiments. This simulation calculation model constructs the mapping relationship between the process parameters of diamond wire sawing and the sapphire wafer warpage during sawing. The influence of wafer thickness, diamond wire speed, feed rate, diamond wire diameter, and tension on the warpage of the wafer was studied using the simulation model. The results indicate that the highest temperature occurs in the sawing area during cutting. The wafer thickness decreases and the warpage increases. The wafer warpage decreases with the increase of the diamond wire tension and diameter, and increases with the increase of diamond wire speed and feed rate. The research results provide a reference for understanding the variation of wafer warpage during sawing and optimizing sawing process parameters. [ABSTRACT FROM AUTHOR]

The issue of brightness in strong ambient light conditions is one of the critical obstacles restricting the application of augmented reality (AR) and mixed reality (MR). Gallium nitride (GaN)-based micro-LEDs, renowned for their exceptional brightness and stability, are considered the foremost contenders for AR applications. Nevertheless, conventional heteroepitaxial growth micro-LED devices confront formidable challenges, including substantial wavelength shifts and efficiency droop. In this paper, we firstly demonstrated the high-quality homoepitaxial GaN-on-GaN micro-LEDs micro-display, and thoroughly analyzed the possible benefits for free-standing GaN substrate from the material-level characterization to device optoelectronic properties and micro-display application compared with sapphire substrate. The GaN-on-GaN structure exhibits a superior crystal quality with ultra-low threading dislocation densities (TDDs) of ~ 105 cm−2, which is three orders of magnitude lower than that of GaN-on-Sapphire. Through an in-depth size-dependent optoelectronic analysis of blue/green emission GaN-on-GaN/ Sapphire micro-LEDs from 100 × 100 shrink to 3 × 3 μm2, real that a lower forward voltage and series resistance, a consistent emission wavelength (1.21 nm for blue and 4.79 nm for green @ 500 A/cm2), coupled with a notable reduction in efficiency droop ratios (15.6% for blue and 28.5% for green @ 500 A/cm2) and expanded color gamut (103.57% over Rec. 2020) within GaN-on-GaN 10 μm micro-LEDs. Last but not least, the GaN-on-GaN micro-display with 3000 pixels per inch (PPI) showcased enhanced display uniformity and higher luminance in comparison to its GaN-on-Sapphire counterpart, demonstrating significant potentials for high-brightness AR/MR applications under strong ambient light. [ABSTRACT FROM AUTHOR]

Double-sided planetary grinding (DSPG) with a fixed abrasive is widely used in sapphire substrate processing. Compared with conventional free abrasive grinding, it has the advantages of high precision, high efficiency, and environmental protection. In this study, we propose a material removal rate (MRR) model specific to the fixed-abrasive DSPG process for sapphire substrates, grounded in the trajectory length of abrasive particles. In this paper, the material removal rate model is obtained after focusing on the theoretical analysis of the effective number of abrasive grains, the indentation depth of a single abrasive grain, the length of the abrasive grain trajectory, and the groove repetition rate. To validate this model, experiments were conducted on sapphire substrates using a DSPG machine. Theoretical predictions of the material removal rate were then juxtaposed with experimental outcomes across varying grinding pressures and rotational speeds. The trends between theoretical and experimental values showed remarkable consistency, with deviations ranging between 0.2% and 39.2%, thereby substantiating the model's validity. Moreover, leveraging the insights from this model, we optimized the disparity in the material removal rate between two surfaces of the substrate, thereby enhancing the uniformity of the machining process across both surfaces. [ABSTRACT FROM AUTHOR]

We discuss the structure of threading dislocations in α-Ga2O3 thin films grown on c- and m-plane sapphire substrates. The thickness-dependent threading dislocation density in both films directly affects the electrical properties of the films including carrier concentration and mobility. Two distinct types of threading dislocations are identified for each of the c- and m-plane α-Ga2O3 thin films. The c-plane α-Ga2O3 thin film shows Burgers vectors of 1 / 3 [ 1 1 ¯ 01 ] and 1 / 3 [ 11 2 ¯ 0 ] , while the m-plane α-Ga2O3 thin film displays Burgers vectors of 1 / 3 [ 2 1 ¯ 1 ¯ 0 ] and 1 / 3 [ 1 1 ¯ 01 ]. This paper presents a detailed structure of the threading dislocations in α-Ga2O3, which has been little disclosed thus far mainly due to the difficulty in synthesizing the metastable α-Ga2O3. [ABSTRACT FROM AUTHOR]

High-quality seeding is the key to ensure the preparation of high-quality sapphire single crystals. The strength and direction of the melt flow control the crystal seeding shape and bubble movement and will directly affect the quality of crystal seeding. To improve the crystal seeding quality under complex convection, based on the lattice Boltzmann method, an optimization method of seed crystal rotation was proposed before crystal seeding, and the unsteady melt flow rate, internal temperature of the melt and crystal rotation speed were calculated and analyzed. The coupling relationship between the Grashof number and the Reynolds number is analyzed. The results show that the optimization method of crystal rotation can effectively restrain the convection of the melt and improve the temperature distribution on the surface of the melt. Compared with the multi-frame intercomparison visual inspection detection method and artificial seeding method, the method proposed in this paper is helpful to improve the quality of sapphire seeding. [ABSTRACT FROM AUTHOR]

In general, β-Ga2O3 films with (2¯01) out-of-orientation have been widely obtained and reported on (0001) sapphire substrates by various growth methods. In this paper, the unusual (3¯10)-oriented β-Ga2O3 films have been epitaxially grown on (0001) sapphire substrates with high crystal-quality under Ga-rich conditions by halide vapor phase epitaxy (HVPE). The out-of-plane epitaxial relationship as (3¯10) β-Ga2O3//(0001) α-Al2O3 has been confirmed by XRD and HRTEM analysis. Under most growth conditions, β-Ga2O3 films exhibit the coexistence of (3¯10) and (2¯01) out-of-plane orientation domains, and increasing the growth temperatures and HCl flow-rates can enhance the growth of (3¯10)-oriented β-Ga2O3. Off-angled (0001) sapphire substrates with off-angles (Δa) toward 〈112¯0〉 have been introduced to control the in-plane domains. It was indicated that the (2¯01)-oriented domains have been gradually eliminated with increasing the off-angles, and pure (3¯10)-oriented β-Ga2O3 films with the best crystal quality reported so far have been obtained while the off-angle was ∼7°. The decrease of the domain boundaries and defects caused by the in-plane rotational domains have led to the improvement of the crystal quality of the as-grown films. [ABSTRACT FROM AUTHOR]

In this paper, the design of different dielectric advanced ceramic materials of RF windows for dual-band K-band and Q-band Gyro-TWT has been described. The design methodology of quartz, magnesium aluminate (MgAl2O4) and sapphire dielectric windows of operating TE01 mode for K-band and Q-band Gyro-TWT has been discussed. The simulation result predicts that these windows can handle 100 kW output power and return loss −58.5 dB and insertion loss −0.02 dB. This paper presents the electrical design and thermal analysis of K-band and Q-band dual-band Gyro-TWT amplifier. In the thermal analysis, the maximum temperature has been obtained at the centre of the dielectric disc. The electro-mechanical analysis has also been carried out on the different dielectric windows to achieve stress and displacement. A new type and unique advance transparent dielectric material magnesium aluminate (MgAl2O4) disc window has been used to improve the bandwidth performance of Gyro-TWT. [ABSTRACT FROM AUTHOR]

Hydrogen energy is the clean energy with the most potential in the 21st century. The microchannel reactor for methanol steam reforming (MSR) is one of the effective ways to obtain hydrogen. Ceramic materials have the advantages of high temperature resistance, corrosion resistance, and high mechanical strength, and are ideal materials for preparing the catalyst support in microchannel reactors. However, the structure of ceramic materials is hard and brittle, and the feature size of microchannel is generally not more than 1 mm, which is difficult to process using traditional processing methods. Diamond wire saw processing technology is mainly used in the slicing of hard and brittle materials such as sapphire and silicon. In this paper, a microchannel with a periodic corrugated microstructure was fabricated on a ceramic plate using diamond wire sawing, and then as a catalyst support when used in a microreactor for MSR hydrogen production. The effects of wire speed and feed speed on the amplitude and period size of the periodic corrugated microstructure were studied using a single-factor experiment. The microchannel surface morphology was observed via SEM and a 3D confocal laser microscope under different processing parameters. The microchannel samples obtained under different processing parameters were supported by a multiple impregnation method. The loading strength of the catalyst was tested via a strong wind purge experiment. The experimental results show that the periodic corrugated microstructure can significantly enhance the load strength of the catalyst. The microchannel catalyst support with the periodic corrugated microstructure was put into the microreactor for a hydrogen production experiment, and a good hydrogen production effect was obtained. The experimental results have a positive guiding effect on promoting ceramic materials as the microchannel catalyst support for the development of hydrogen energy. [ABSTRACT FROM AUTHOR]

Nitrides are the leading semiconductor material used for the fabrication of high electron mobility transistors (HEMTs). They exhibit piezoelectric properties, which, coupled with their high mechanical stiffness, expand their versatile applications into the fabrication of piezoelectric devices. Today, due to advances in device technology that result in a reduction in the size of individual transistor elements and due to increased structural complexity (e.g., multi-gate transistors), the integration of piezoelectric materials into HEMTs leads to an interesting occurrence, namely acoustic emission from the transistor gate due to piezoelectric effects. This could affect the device's performance, reliability, and durability. However, this phenomenon has not yet been comprehensively described. This paper aims to examine this overlooked aspect of AlGaN/GaN HEMT operation, that is, the acoustic emission from the gate region of the device induced by piezoelectric effects. For this purpose, dedicated test structures were designed, consisting of two narrow 1.7 μm-wide metallization strips placed at distances ranging from 5 μm to 200 μm fabricated in AlGaN/GaN heterostructures to simulate and examine the gate behavior of the HEMT transistor. For comparison, the test device structures were also fabricated on sapphire, which is not a piezoelectric material. Measurements of acoustic and electrical interactions in the microwave range were carried out using the "on wafer" method with Picoprobe's signal–ground–signal (SGS)-type microwave probes. The dependence of reflectance |S11| and transmittance |S21| vs. frequency was investigated, and the coupling capacitance was determined. An equivalent circuit model of the test structure was developed, and finite element method simulation was performed to study the distribution of the acoustic wave in the nitride layers and substrate for different frequencies using Comsol Multiphysics software. At frequencies up to 2–3 GHz, the formation of volume waves and a surface wave, capable of propagating over long distances (in the order of tens of micrometers) was observed. At higher frequencies, the resulting distribution of displacements as a result of numerous reflections and interferences was more complicated. However, there was always the possibility of a surface wave occurrence, even at large distances from the excitation source. At small gate distances, electrical interactions dominate. Above 100 µm, electrical interactions are comparable to acoustic ones. With further increases in distance, weakly attenuated surface waves will dominate. [ABSTRACT FROM AUTHOR]

Electroplated diamond wire sawing is widely used as a processing method to cut hard and brittle difficult-to-machine materials. Currently, obtaining the sawing capability of diamond wire saw through the wire bow is still difficult. In this paper, a method for calculating the sawing capability of diamond wire saw in real-time based on the wire bow is proposed. The influence of the renewed length per round trip, crystal orientation of sapphire, wire speed, and feed rate on the wire sawing capability has been revealed via slicing experiments. The results indicate that renewing the diamond wire saw, and reducing the wire speed and feed rate can delay the reduction in sawing capability. Furthermore, controlling the value of renewed length per round trip can make the diamond wire saw enter a stable cutting state, in which the capability of the wire saw no longer decreases. The sawing capability of diamond wire saw cutting in the A-plane of the sapphire is smaller than that of the C-plane, and a suitable feed rate or wire speed within the range of sawing parameters studied in this study can avoid a rapid decrease in the sawing capability of the wire saw during the cutting process. The knowledge obtained in this study provides a theoretical basis for monitoring the performance of the wire saw, and guidance for the wire cutting process in semiconductor manufacturing. In the future, it may even be possible to provide real-time performance parameters of diamond wire saw for the digital twin model of wire sawing. [ABSTRACT FROM AUTHOR]

This work investigated the impact of periodic thickness and doping region on the doping efficiency of the P-type AlGaN superlattice. In this paper, the band structure of the simulated superlattice was analyzed. The superlattice structure of Al0.1Ga0.3N/Al0.4Ga0.6N, and the AlGaN buffer on the sapphire substrate, achieved a resistivity of ~3.3 Ω·cm. The results indicate that barrier doping and low periodic thickness offer significant advantages in introducing a reduction of the resistivity of P-type AlGaN superlattice structures. [ABSTRACT FROM AUTHOR]

Lift-off processes have been developed as the enabling technology to free the epitaxial III-nitride thin film from a conventional growth substrate such as sapphire and silicon in order to realize a variety of novel device designs and structures not otherwise possible. An epitaxial lift-off (ELO) process can be adopted to transfer the entire film to an arbitrary foreign substrate to achieve various functions, including enhancement of device performance, improvement of thermal management, and to enable flexibility among others. On the other hand, partial ELO techniques, whereby only a portion of the thin-film is detached from the substrate, can be employed to realize unconventional device structures or geometries, such as apertured, pivoted, and flexible devices, which may be exploited for various photonic structures or optical cavities. This paper reviews the development of different lift-off strategies and processes for III-nitride materials and devices, followed by a perspective on the future directions of this technology. [ABSTRACT FROM AUTHOR]

In this paper, the Monte Carlo simulation for sapphire in wet etching is optimized, which improves the accuracy and efficiency of simulated results. Firstly, an eight-index classification method is proposed to classify the kinds of surface atoms, which can make assigned removal probabilities more accurately for surface atoms. Secondly, based on the proposed classification method of surface atoms, an extended removal probability equation (E-RPE) is proposed, which makes the errors between simulated and experimental rates smaller and greatly improves the accuracy of the simulated result of the etch rate distribution under the experimental condition (H2SO4:H3PO4 = 3:1, 236 °C). Thirdly, a modified removal probability equation (ME-RPE) considering the temperature dependence is proposed based on the error analysis between the simulated and experimental rates under different temperature conditions, which can simulate etch rates under the different temperature conditions through a group of optimized energy parameters and improve the simulation efficiency. Finally, small errors between the simulated and experimental rates under the different temperature conditions (H2SO4:H3PO4 = 3:1, 202 °C and 223 °C) verify the validity of the ME-RPE for temperature change. The optimization methods for the Monte Carlo simulation of sapphire in wet etching proposed in this paper will provide a reference for the simulation of other crystal materials. [ABSTRACT FROM AUTHOR]

Femtosecond laser processing technology is an advanced sub-micro-processing technique that enables the non-contact processing of various materials. This technology can be used to apply sub-micro structures for purposes such as hydrophilicity enhancement, optical transmittance improvement, and photonics detection. However, when it comes to processing micro/nanostructures on highly brittle materials using femtosecond lasers, there are challenges such as low processing efficiency, generation of debris, and microcracking. In this paper, we propose a method called the out-of-focus femtosecond laser direct writing technique combined with wet etching. This method offers simplicity, speed, and flexibility in preparing dense, large-area sub-microstructured surfaces on the brittle material sapphire. Our detailed investigation focuses on the impact of laser processing parameters (direct writing period, distance of focusing, direct writing speed, etc.) on the sub-microstructures of Al2O3 surfaces. The results demonstrate that this method successfully creates embedded sub-microstructures on the sapphire surface. The microholes, with a diameter of approximately 2.0 μm, contain sub-micro structures with a minimum width of 250 ± 20 nm. Additionally, we conducted experiments to assess the optical transmittance of sapphire nanostructures in the range of 350–1200 nm, which exhibited an average transmittance of approximately 77.0%. The water contact angle (CA) test yielded a result of 52 ± 2°, indicating an enhancement in the hydrophilicity of the sapphire nanostructures with only a slight reduction in optical transmittance. Our efficient fabrication of sub-microstructures on the sapphire surface of highly brittle materials offers a promising method for the production and application of brittle materials in the field of micro-optics. [ABSTRACT FROM AUTHOR]

The document is a contents list for the journal CrystEngComm, which focuses on the design and understanding of solid-state and crystalline materials. The contents list includes various articles on topics such as the growth of gold-based nanostructures, the synthesis of energetic pentazolate salt, and the investigation of additives on calcium carbonate crystallization. The journal is published by The Royal Society of Chemistry, a leading chemistry community. The document also mentions other journals in the field of environmental science and provides information about the organization's charitable work. [Extracted from the article]

In quest of achieving compact and economic PW-level Ti:Sapphire (Ti:sa) lasers with a sub-15 fs pulse duration, a modified hybrid amplification scheme, which combines the optical parametric chirped pulse amplifier (OPCPA) and the chirped pulse amplifier (CPA), is presented and numerically investigated in this paper. The key characteristic of this scheme is that the conventional Ti:sa regenerative amplifier and preamplifier are replaced by a dual-crystal OPCPA front-end, which is spectrally matched with the upstream seed source and the downstream Ti:sa amplifiers and, therefore, can realize a broader spectrum. Moreover, some useful laser techniques are also applied to suppress the spectral gain narrowing and redshift in the Ti:sa CPA chain and to control the residual dispersion in the laser system. This way, fewer amplification stages and pump lasers are required to reach PW-level peak power compared with traditional all-CPA Ti:sa lasers. Numerical results indicate that pulse energy and spectral bandwidth can reach up to ∼22 J and ∼125 nm at full width at half maximum (FWHM), respectively, only by employing three-stage amplifiers. After compression, PW-level lasers with a ∼13.3 fs pulse duration are expected. This work can offer a promising route for the development of compact and economic PW-level Ti:sa lasers. [ABSTRACT FROM AUTHOR]

The diamond wire sawing technology has been widely used in cutting sapphire crystal, and the surface roughness and morphology of as-sawn sapphire wafers are important indexes of the cutting quality. With the development of diamond wire saw cutting technology to high wire speed, this paper conducted diamond wire sawing sapphire crystal experiments within the industrial high saw wire speed of 1000–1600 m/min, and the effect of cutting parameters on the as-sawn wafers surface roughness and morphology was analyzed. Furthermore, a diamond wire saw cutting numerical calculation model was established based on the wire sawing mechanism and sapphire crystal material removal mechanism, and the model was verified by sawing experiments. The influences of abrasive density and size on the surface roughness of the as-sawn wafers were predicted using the sawing model which provides a theoretical reference for the rationally adopting saw wire parameters to improve the cutting quality of sapphire crystal under industrial cutting parameters. The results show that within the range of parameters studied in this paper, the sapphire crystal material is mainly removed in brittle mode. Increasing saw wire speed from 1000 to 1400 m/min and decreasing specimen feed speed from 0.5 to 0.05 mm/min, increasing the abrasive density, and decreasing the abrasive size are all beneficial to decrease the as-sawn wafers surface roughness. Increasing the saw wire speed and decreasing the feed speed are beneficial to reduce the number of brittle pits and saw marks, the period of waviness on the as-sawn wafer surface, and improve the as-sawn wafer surface morphology. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to present a numerical study of atomic structure for aluminium nitride (AlN) when the crystal was assumed grown on different orientation of sapphire substrate. The change of the AlN atomic structure with sapphire orientation was associated to the interface between the AlN and the sapphire. The results from this study would provide a guideline in selecting suitable orientation of sapphire for obtaining desirable AlN crystals, in particular, for reducing threading dislocation density in the AlN/sapphire templates for developing UV LEDs. Design/methodology/approach: The approach of atomic structure by visualization for electronic and structural analysis numerical method to develop shape of atomic geometry to evaluate which plane are more suitable for the AlGaN technology UV-LED based. Findings: The calculation based on ratio on first and second layers can be done by introduction of lattice constant. Research limitations/implications: With plane's color of cutting plane on bulky materials, all the shape looks the same. Practical implications: By implementing this method, the authors can save time to find the most suitable plane on the growth structure. Originality/value: All authors of this research paper have directly participated in the planning, execution or analysis of the study; all authors of this paper have read and approved the final version submitted; the contents of this manuscript have not been copyrighted or published previously; the contents of this manuscript are not now under consideration for publication elsewhere; the contents of this manuscript will not be copyrighted, submitted or published elsewhere, whereas acceptance by the journal is under consideration. [ABSTRACT FROM AUTHOR]

Abrasive single crystal diamond (SCD) grit is widely used in the machining process of sapphire. The wear of SCD grit has a significant influence on the surface quality of sapphire. In this paper, smooth particle hydrodynamics (SPH) method is employed to reveal the wear mechanism of SCD grit with Steinberg constitutive equation and Grüneisen state equation. The wear morphology, wear volume and scratching forces are measured and analyzed by combination of SPH simulations and experiments. The results show that the scratching forces fluctuate in a certain range and decrease with the increasing of workpiece material removal volume. Different degrees of cleavage and fracture appear in the front and rear of SCD grit. The shear stress and extrusion stress are the main stresses of SCD grit during the scratching process. The wear progress and wear form are mainly determined by the stress state. Different stress state leads to different wear progress of the SCD grit. The SPH method is able to reflect and illustrate the wear characteristics of SCD grit scratching on sapphire. [ABSTRACT FROM AUTHOR]

Lithium niobate is a material of special interest for its challenging functional properties, which can suit various applications. However, high quality 200‐mm LixNb1‐xO3 thin film grown on sapphire substrate have never been reported so far which limits these potential applications. This paper reports the efficient optimization of high quality LiNbO3 thin film deposition on sapphire (001) substrate through chemical beam vapor deposition in a combinatorial configuration. With this technique, flow ratio of Li/Nb can be tuned from ≈0.25 to ≈2.45 on a single wafer. Various complementary characterizations (by means of diffraction, microscopy and spectroscopy techniques) have been performed at different areas of the film (different cationic ratios) in order to investigate the impact of the cationic stoichiometry deviation on the film properties. Close to cationic stoichiometry (LiNbO3), the epitaxial films are of high quality (single phase in spite of two in‐plane domains, low mosaicity of 0.04°, low surface roughness, refractive index and band gap close to bulk values). Deviating from the stoichiometry conditions, secondary phases are detected (LiNb3O8 for Nb‐rich flow ratios, and Li3NbO4 with partial amorphization for Li‐rich flow ratios). LiNbO3 films are of high interest for various key applications in data communications among others. [ABSTRACT FROM AUTHOR]

In high-sensitive laser interferometers, such as the gravitational-wave detector KAGRA, ultra-high-quality mirrors are essential. In the case of KAGRA, where cavity mirrors are cooled down to 20 K, large-size Sapphire crystals are used as the substrate for the main mirrors to achieve both a good optical quality (i.e., low absorption and uniform refractive index) and optimized thermal behavior under cryogenic temperatures. To implement the very tight optical specifications required by this demanding application, it is mandatory to test the optical homogeneity of different substrates. In order to characterize refractive-index inhomogeneities of large-size uniaxial samples such as the KAGRA Sapphire test masses, we developed a dedicated setup, allowing to resolve birefringence changes with a sensitivity in the order of Δ n ≈ 2 × 10 - 10 and a spatial resolution of 1 mm 2 . Moreover, the same setup allows us to simultaneously record residual absorption maps, thus allowing for a comparison between birefringence and absorption features. In this paper, we will present for the first time measurements on a KAGRA-sized Sapphire substrate which has been characterized in terms of absorption already in an earlier work. Both birefringence inhomogeneities and absorption distributions will be compared and correlations discussed. [ABSTRACT FROM AUTHOR]

The document is a contents list for the journal CrystEngComm. It provides information about the articles and authors featured in the journal's latest issue. The journal focuses on the design and understanding of solid-state and crystalline materials. The document also includes information about the journal's editorial board and submission guidelines for authors. [Extracted from the article]

With excellent mechanical and optical properties, sapphire substrate becomes a very important industrial material especially for LED manufacturing. Its quality control requires two tasks, double-sided surface profiling and defect detection. In this paper, a 3D surface scanning system is proposed as a platform for sapphire substrate inspection. During the scanning process, the height information of both upper and lower surfaces is measured by a chromatic confocal probe. For lateral positioning feedback, an in-house developed sensor, namely, image grating, is introduced in this paper. For these inspection processes, there are three challenges: 1) the motion error in the vertical direction, 2) simultaneous measurement of both upper and lower surfaces, and 3) lateral positioning error in a large scanning area. To address these challenges, three key technologies were developed: 1) real-time motion error compensation based on a fringe interferometer, 2) a double-sided measurement for transparent specimen without the pre-knowledge of its refractive index, and 3) planar image grating pair for accurate 2D displacement feedback. The experimental results showed that the proposed measurement system was able to achieve 50 nm accuracy of the standard deviation when measuring the step height of gauge blocks. When the system measured 4-inch double-sided polished sapphire substrate, the measurement repeatability of TTV (Total Thickness Variation) was within 60 nm; and that of warpage was within 10 nm. As a side product, refractive index can also be measured using the proposed system, and experimental results showed respectable consistency. • A motion error compensation system is proposed based on film interferometry. • By setting up a pair of image gratings, lateral positioning errors and 2D Abbe error can be minimised. • The proposed technology is able to achieve nanometer repeatability in measuring thickness variation and warpage. • This system is able to simultaneously measure transparent specimens without having to know the refractive index. • The proposed system can also be used for general surface topography measurement purposes. [ABSTRACT FROM AUTHOR]

Ultrasonic-assisted chemical mechanical polishing (UA-CMP) can greatly improve the sapphire material removal and surface quality, but its polishing mechanism is still unclear. This paper proposed a novel model of material removal rate (MRR) to explore the mechanism of sapphire UA-CMP. It contains two modes, namely two-body wear and abrasive-impact. Furthermore, the atomic force microscopy (AFM) in-situ study, computational fluid dynamics (CFD) simulation, and polishing experiments were conducted to verify the model and reveal the polishing mechanism. In the AFM in-situ studies, the tip scratched the reaction layer on the sapphire surface. The pit with a 0.22 nm depth is the evidence of two-body wear. The CFD simulation showed that abrasives could be driven by the ultrasonic vibration to impact the sapphire surface at high frequencies. The maximum total velocity and the air volume fraction (AVF) in the central area increased from 0.26 to 0.55 m/s and 20% to 49%, respectively, with the rising amplitudes of 1–3 µm. However, the maximum total velocity rose slightly from 0.33 to 0.42 m/s, and the AVF was nearly unchanged under 40–80 r/min. It indicated that the ultrasonic energy has great effects on the abrasive-impact mode. The UA-CMP experimental results exhibited that there was 63.7% improvement in MRR when the polishing velocities rose from 40 to 80 r/min. The roughness of the polished sapphire surface was Ra = 0.07 nm. It identified that the higher speed achieved greater MRR mainly through the two-body wear mode. This study is beneficial to further understanding the UA-CMP mechanism and promoting the development of UA-CMP technology. [ABSTRACT FROM AUTHOR]

In this paper, we present the preparation of few-layer MoS2 films on single-crystal sapphire, as well as on heteroepitaxial GaN templates on sapphire substrates, using the pulsed laser deposition (PLD) technique. Detailed structural and chemical characterization of the films were performed using Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction measurements, and high-resolution transmission electron microscopy. According to X-ray diffraction studies, the films exhibit epitaxial growth, indicating a good in-plane alignment. Furthermore, the films demonstrate uniform thickness on large areas, as confirmed by Raman spectroscopy. The lateral electrical current transport of the MoS2 grown on sapphire was investigated by temperature (T)-dependent sheet resistance and Hall effect measurements, showing a high n-type doping of the semiconducting films (ns from ~1 × 1013 to ~3.4 × 1013 cm−2 from T = 300 K to 500 K), with a donor ionization energy of Ei = 93 ± 8 meV and a mobility decreasing with T. Finally, the vertical current injection across the MoS2/GaN heterojunction was investigated by means of conductive atomic force microscopy, showing the rectifying behavior of the I-V characteristics with a Schottky barrier height of ϕB ≈ 0.36 eV. The obtained results pave the way for the scalable application of PLD-grown MoS2 on GaN in electronics/optoelectronics. [ABSTRACT FROM AUTHOR]

The influence of birefringence on rays entering and exiting a non-isotropic medium is a complex process that depends on its dielectric tensor, the orientation and geometry of the medium, the surrounding material, and the inclination of the incident ray. Thus, when aiming for a calculation of the effects, many parameters need to be taken into account while simplifications are generally not applicable. Moreover, the complexity of the general issue makes it almost impossible to find an analytical solution for backward calculations of stress-birefringence from polarization measurements. In this paper, a report is given on the formulation of a birefringence ray-tracing program in Python for the convenient evaluation of optical effects inside uniaxial crystals under stress. The aim thereby is to have an easily applicable tool that can be used in interferometer commissioning for current and future gravitational-wave detectors. Results from test simulations using realistic parameters for a sapphire mirror as used in the gravitational-wave detector KAGRA are implemented and show the capabilities of this tool. [ABSTRACT FROM AUTHOR]

We present source design and process results of a linearly scalable ribbon ion beam for modifying materials by an ion implantation technique. Our source technology enables beam currents up to 30 mA/cm2 and ion implant energies up to 60keV enabling economically viable large format and high throughput processing. In this paper, we demonstrate application of this ion source towards the production of glass and sapphire substrates with durable broadband anti‐reflection surfaces with reflectance <0.5% in the visible spectra. In addition, the anti‐reflection surface is shown to remain after subsequent tempering and chemical strengthening processes. [ABSTRACT FROM AUTHOR]

This paper discusses the results of high temperature resistivity and Hall effect studies of Mg-doped GaN and AlxGa1−xN epilayers (0.05 < x < 0.23). The studied samples were grown by molecular beam epitaxy on low temperature buffers of GaN and AlN deposited on a sapphire substrate. The experiments were carried out at temperatures ranging from 300 up to 1000 K. Up to a certain critical temperature TC (around 800 K), a typical increase of the conduction processes due to the excitation of impurity states has been observed with an activation energy of about EA = 200 meV. However, at this critical temperature TC, an annealing effect was observed in all the investigated samples. At this critical temperature, the increase in the free carrier concentration as a function of time leads to an irreversible decrease in the samples' resistivity of more than 60%. The observed temperature dependences of the electrical transport properties are analyzed in the frame of an impurity model including shallow donors and Mg-related acceptors (with EA ∼ 200 meV). In some cases, an additional conduction channel not related to free carriers in the valence band must be taken into account. This can lead to an incorrect determination of hole concentration in the valence band, an important parameter in the process of radiative recombination. [ABSTRACT FROM AUTHOR]

The Cryogenic Sapphire Oscillator (CSO) is today recognized for its unprecedented frequency stability, mainly coming from the exceptional physical properties of its resonator made in a high-quality sapphire crystal. With these instruments, the fractional frequency measurement resolution, currently of the order of 10 − 16 , is such that it is possible to detect very small phenomena such as residual resonator environmental sensitivities. Thus, we highlighted an unexpected magnetic sensitivity of the CSO at low magnetic fields. The fractional frequency sensitivity has been preliminarily evaluated to be 10 − 13 / G, making this phenomenon a potential cause of frequency stability limitations. In this paper, we report the experimental data related to the magnetic sensitivity of the quasi-transverse magnetic Whispering Gallery (WGH) modes excited in sapphire crystals differing from their paramagnetic contaminant concentration. The magnetic behavior of the WGH modes does not follow the expected theory combining the Curie law and the Zeeman effect affecting the electron spin resonance of the paramagnetic ions present in the crystal. [ABSTRACT FROM AUTHOR]

Sapphire crystal with excellent properties is widely used as substrate materials for optoelectronics and microelectronics industries. Subsurface crack damage (SSD) will occur in the diamond wire saw slicing process of the sapphire wafer, which is related to the quality of the as-sawn wafer and the cost of subsequent processing. Therefore, rapid and effective detection of SSD is required in production. However, current detection methods are time-consuming and labor-intensive, thus requiring a fast, effective, and low-carbon evaluation method. In this paper, based on the current diamond wire saw slicing process parameters range of sapphire crystal in actual production, sawing experiments were carried out to study the surface and subsurface crack damage morphology characteristics, evolution law of surface roughness (Rz), and SSD. Furthermore, the mapping relationship between Rz and SSD was established by the numerical fitting method. The results show that, in the range of processing parameters for practical industrial applications, the surface of the as-sawn wafer was mainly formed by material brittleness removal, the subsurface presented a small number of micro-cracks and brittle fracture damage, and the median crack propagation direction was shifted. Within the range of process parameters used in this study, the maximum SSD value of the sapphire wafer is 20.07 µm, the minimum value is 11.67 µm, and the corresponding Rz values are 11.13 µm and 8.12 µm, respectively. Both SSD and Rz decreased with the increase in saw wire speed and the decrease in specimen feed speed. There is a nonlinear relationship of monotone increase between the two, which is SSD = 0.15Rz3 − 4.87Rz2 + 55.49Rz − 195.23. The research results can be used to evaluate SSD quickly and effectively by measuring as-sawn sapphire wafer Rz that can provide an experimental reference for wire-sliced SSD evaluation, wafer quality improvement, and processing parameter optimization. [ABSTRACT FROM AUTHOR]

Sapphire fibers are becoming a research hotspot for high-temperature sensing in extreme environments due to their high melting point, wide transmission band and superior thermal stability. Nevertheless, the preparation of high-quality, few-mode, large-length sapphire fibers is still a major challenge for further application. Here, we have successfully fabricated high-quality sapphire fibers with a minimum diameter of ∼16 μm and a maximum length of more than 50 m using a state-of-the-art laser-heated pedestal growth system, which, to the best of our knowledge, is the size record for single-crystal fibers. Besides, the anisotropic growth behavior and mechanical properties were investigated in detail, demonstrating that c-oriented sapphire fibers present higher high-temperature tensile strength and superior creep resistance compared with a- and m-oriented sapphire fibers. Further reasearch demonstrates that the tensile strength increases dramatically with decreasing diameter, with the 30 μm-diameter sapphire fibers achieving a tensile strength of more than 8000 MPa and a maximum strain over 20 000 με, both of which are more than twice those of conventional sapphire fibers. Furthermore, a fiber Bragg grating was fabricated within a 30 μm-diameter sapphire fiber for the first time by the femtosecond laser line-by-line scanning method, exhibiting few-mode and stable spectral response in the range of 20–1600 °C with a maximum sensitivity of 40.45 pm °C−1 at 1600 °C. This work provides a feasible approach for the preparation of sapphire fibers without size limitation, and demonstrates huge potential of ultra-fine sapphire fibers for applications in harsh environments and strain sensing. [ABSTRACT FROM AUTHOR]

A three-dimensional-micro-pulling-down (3D-μ-PD) method was developed for the growth of 3D shaped single crystals, and spring-shaped sapphire single crystals were grown by the 3D-μ-PD method using Mo crucibles with different dies. The shape of the die significantly affected the growth stability and shape control of the spring-shaped single crystals. Spring-shaped sapphire single crystals with a smaller helical pitch and larger helical radius were obtained easily using a Mo crucible with a sharp conical die compared to that with a blunt conical die. However, spring-shaped sapphire single crystals grown using a Mo crucible with an inverse conical die can be obtained with smaller helical pitches, and the shape of the cross-sectional plane is a horizontally extended elliptical shape. The difference in the shape of the cross-sectional plane for spring-shaped sapphire single crystals affects the crystallinity and mechanical properties. Furthermore, crystals grown using the Mo crucible with the inverse conical die exhibited a larger shrinkage rate in the compression test. [ABSTRACT FROM AUTHOR]

During the operation of the waste liquid incinerator, the alkali metal slag might adhere to the surface of the refractory material to form an inhomogeneous solid slag layer, causing the furnace lining to be simultaneously corroded by three phases of alkali metals: vapor, molten salt, and slag. This phenomenon intensifies the damage to the refractory material. Therefore, this paper investigates the mass transfer and permeation process, phase change process and corrosion rate of Na 2 CO 3 inside corundum refractory materials in three phases: Na vapor, molten Na 2 CO 3 and Na-slag. The results showed that alkali vapor penetrated the interior through the pores, and the NaAlO 2 and β-Al 2 O 3 generated by the reaction led to the volume expansion and microcracks. Na vapor continued to penetrate the interior along the cracks and eroded the sample, and the higher the temperature the greater Na vapor penetration. In vapor phase corrosion, the effect of corrosion time on the erosion resistance of corundum refractories is less than that of temperature, and the increase in corrosion time does not lead to the formation of additional new phases. In the molten salt corrosion experiments, it was found that the molten salt corrosion was accompanied by vapor phase corrosion at 1100 °C, and the amount of Na 2 CO 3 has a greater effect on the corroded mass than the temperature. Comparing the corrosion of refractory materials by the three phases of Na 2 CO 3 , the molten salt corrosion rate was the highest, followed by the vapor phase corrosion, and finally the slag corrosion. It is concluded that the slag layer can effectively prevent the corrosion of the refractory material by alkali metal molten salts and vapors, thus prolonging the service life of refractories. [ABSTRACT FROM AUTHOR]

In the paper, experimental and numerical results of the wear of a molybdenum disulfide coated on a titanium alloy disk are reported. The coating is in contact with a sapphire ball. The experiments are conducted for ambient temperatures varying from 20 to 350 ∘ C. The results indicate that the wear profile becomes increasingly pronounced at the growth of the temperature up to 350 ∘ C. A numerical model is proposed to describe the results of the experiment. The central assumption is the thermal steady state forming in the interface area. The resulting stress field serves as input for the simulation of wear. A good agreement can be observed between the experimental findings and the FE calculations. [ABSTRACT FROM AUTHOR]

In this paper, we report light ion (H+) implantation-induced effect on a-plane GaN epitaxial layer on the sapphire substrate. Non-polar (NP) a-plane GaN (11–20) epitaxial layer is grown on an r-plane sapphire substrate by the metal–organic chemical vapour deposition (MOCVD) technique. The H+ ion-implanted NP (11–20) GaN epitaxial layer (dose 1 × 1017 cm−2 and 170 keV energy) is annealed by the rapid thermal annealing (RTA) process. The un-implanted a-GaN, H+ ion-implanted and annealed samples are investigated structurally and optically by High-resolution X-ray diffraction (HRXRD), Atomic force microscopy (AFM), Raman spectroscopy and Emission characterisation techniques. HRXRD analysis infers that implanted GaN sample is hydrostatically strained up to implanted depth. Raman scattering study by green laser excitation found defect-activated Raman scattering (DARS) due to lattice distortion by ion implantation in the implanted sample and annealed out partially after annealing. The Raman peak intensity ratio between the E2 (high) and LO peak of the above bandgap excited laser (~ 266 nm) was around 3.92 in the un-implanted GaN layer whilst after implantation, the ratio was reduced to ~ 0.97 because implantation induces the defect-activated centre which increased the LO peak intensity. After annealing, the ratio between E2 (high) and LO peak was increased by ~ 2.5. After annealing due to partial recovery and reduction in the implantation-induced defected activated centre, the a-plane GaN thin layer can be transferred to the other substrate easily by exfoliation or ion-cutting process and can be used in electronics and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Composite materials used in dental restorations are considered resistant, long-lasting and aesthetic. As the wear of restorations is an important element in long-term use, the aim of this study was to evaluate the surface condition of nanohybrid and microfilled composite resins, after being subjected to the erosive action of dental bleaching protocols. This paper reflects a comparative study between one nanofilled composite and three microfilled composites used in restorations. For each composite, three sets of samples (under the form of composite discs) were created: a control group, an "office bleach" group with discs bleached with 40% hydrogen peroxide gel, and a "home bleach" group with discs bleached with 16% carbamide peroxide gel. Wear was numerically determined as the trace and the coefficients of friction obtained using a tribometer, the ball-on-disk test method, and two balls: alumina and sapphire. For all composite groups, there were statistically significant differences between the wear corresponding to the control and bleaching groups, for both testing balls. Regarding the composite type, the largest traces were recorded for GC Gradia direct anterior, for all groups, using the alumina ball. In contrast, for the sapphire ball, 3M ESPE Filtek Z550 was characterized by the largest traces. With respect to the friction coefficients, the "office bleach" group recorded the largest values, no matter the composite or the ball type used. The 3M ESPE Valux Plus composite recorded the largest friction coefficients for the alumina ball, and 3M ESPE Filtek Z550 for the sapphire ball. Overall, the "office bleach" group was characterized by higher composite wear, compared to the "home bleach" protocol or control group. Nanofilled composite resins showed superior wear resistance to microfilled resins after undergoing a bleaching protocol. [ABSTRACT FROM AUTHOR]

The sapphire crystal, the most commonly used LED substrate material, has excellent optical and chemical properties and has rapidly developed in recent years. However, the challenge of growing large–size sapphire crystals remains. This paper presents a novel approach using alumina nanoparticles synthesized with abietic acid as a template to enhance sapphire growth via the heat exchange method. This study explores the effects of temperature, time, and template amount on the structure and morphology of the synthesized alumina nanoparticles. The results show that the morphology of the raw material, particularly spherical alumina nanoparticles, positively affects the quality and yield stability of sapphire products. Furthermore, the light output power of GaN–based LED chips made with the experimentally fabricated sapphire substrate increased from 3.47 W/µm2 to 3.71 W/µm2, a 6.9% increase compared to commercially available sapphire substrates. This research highlights the potential of using abietic acid as a template for alumina nanoparticle synthesis and their application in sapphire growth for LED production. [ABSTRACT FROM AUTHOR]

The paper presents the results of studies of the influence on the optical transmission of defects in the structure of a sapphire tube grown by the method of A.V. Stepanov, changes in the transparency of a single crystal after mechanical surface treatment, and ultraviolet and radiation exposure. [ABSTRACT FROM AUTHOR]

In this paper, an active dual-control electromagnetically induced transparency (EIT) analog is realized by using vanadium dioxide (VO2) metasurface on a sapphire substrate. The unit cell of the metasurface is a composite-split-ring-resonator (CSRR) composed of two resonators, one of which containing gold pattern and VO2 is named as VSRR and the other containing two T-type resonators is called TTR. The resonant frequency of VSRR and that of TTR are located at 0.43 and 0.75 THz, respectively. While, the CSRR have two resonant frequencies at 0.39 and 0.72 THz, and an EIT-like band has a central frequency at 0.56 THz. When the metasurface is electrically stimulated, the insulator-to-metal-transition (IMT) of VO2 can result in the reconstruction of the metasurface. Therefore, the EIT resonance can be controlled by bias voltages. At central frequency of 0.56 THz, a modulation depth of 87.7% and a group delay of 2.7 ps are obtained. The EIT mechanism is further explained by using a coupled Lorentz model, and theoretical calculation and simulation show good agreement with the experiment. Moreover, by mechanically adjusting the incidence angle, the adjustable EIT-like phenomenon is also observed and the modulation depth achieves 73%. This work paves a way for the development of THz modulators, switches, and slow light devices. [ABSTRACT FROM AUTHOR]

Natural gas hydrate (GH) is a significant potential energy source due to its large reserves, wide distribution, high energy density and low pollution. However, the gas production rate of past gas hydrate production tests is much lower than the requirement of commercial gas production. Reservoir stimulation technologies like hydraulic fracture provide one potential approach to enhance gas production from GH. The reservoir reformation behaviour of the hydrate-bearing sediments (HBS), particularly sediments with a high clay content, is a complex process during a hydraulic fracturing operation, which has been poorly understood and thus hardly predictable. This paper presents an experimental facility that was developed to analyze the hydraulic fracture mechanism in synthesized HBS. This facility can be used to form GH in sediments, conduct visual observation of hydraulic fracturing experiments, and measure the permeability of HBS under high pressure (up to 30 MPa) and low-temperature conditions (from 253.15 K to 323.15 K). It is mainly composed of a pressure control and injection unit, a low temperature and cooling unit, a cavitation unit, a visual sapphire reactor, and a data acquisition and measurement unit. The hydraulic fracture module is consisting of a gas cylinder, fracturing pump, hopper, proppants warehouse and valves. The sapphire reservoir chamber is applied to observe and measure the fracture of HBS during hydraulic fracturing. The permeability test module is composed of a constant-flux pump and pressure sensors, which can evaluate the permeability performance before and after hydraulic fracture in HBS. The fundamental principles of this apparatus are discussed. Some tests were performed to verify hydraulic fracture tests and permeability tests could be practically applied in the HBS exploitation. [ABSTRACT FROM AUTHOR]