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Three-dimensional (3D) heterogeneous integration has shown great promise in increasing integration density and reducing parasitic capacitance, which micro through vias on insulators are highly desired. In this work, femtosecond laser bidirectional drilling of crack-free micro through-sapphire-vias has been demonstrated. Mechanisms of material removal and defect suppression during the drilling process were studied. The bottom surface was drilled first and followed by the top surface drilling. A blind hole prefabricated by the bottom surface drilling can effectively suppress the edge collapse and extensive ablation damage on the bottom surface during subsequent top surface drilling with high pulse energy laser. Effects of incident laser parameters on the surface quality, morphology, diameter, and taper of the through hole at different drilling stages were systematically studied. Under given strategy, hole diameter down to ~50 μm on 400 μm-thick sapphire wafers can be achieved directly, showing great prospects in 3D heterogeneous integration. [ABSTRACT FROM AUTHOR]

Ultrasonic vibration has a certain effect on the crack propagation tendency during sapphire grinding, but the mechanism of the effect on the crack propagation tendency has not yet been elucidated. In this study, tangential ultrasonic vibratory scratching and normal scratching sapphire processes were simulated using the discrete element method, and the expansion tendency of sub-surface cracks in the scratching sapphire process was analyzed in terms of cutting forces and stresses. The results of the study show that the crack depth decreases with increasing scratch speed and increases with increasing scratch depth; The greater the variation in cutting force, the greater the number of cracks formed and the crack propagation is mainly distributed near the maximum residual tensile stress; The introduction of tangential ultrasonic vibration induces a decrease in residual tensile stresses and an increase in residual compressive stresses, thus inhibiting subsurface crack propagation; The suppression of subsurface cracks becomes more pronounced as the amplitude increases. Finally, tangential ultrasonic vibratory scratching and normal scratching sapphire experiments were comparatively studied and the experimental results were in agreement with the simulation results. This study provides some theoretical guidance for the suppression of subsurface cracks in sapphire materials during the grinding process. [ABSTRACT FROM AUTHOR]

This paper presents the initial results of the synthesis of β-Ga2O3 luminescent ceramics via plasma gas-thermal spraying synthesis, where low-temperature plasma of an argon and nitrogen mixture was employed. A direct current electric arc generator of high-enthalpy plasma jet with a self-aligning arc length and an expanding channel of an output electrode served as a plasma source. The feedstock material consisted of a polydisperse powder of monocrystalline β-Ga2O3 with particle sizes ranging from 5 to 50 μm. The study presents the results of both theoretical and experimental studies on the heating rate and average temperature of gallium oxide particles in a plasma jet. The results of computational modelling of the synthesis process of β-Ga2O3 via plasma gas-thermal spraying are shown. The obtained ceramic samples were characterized using scanning electron microscopy and X-ray diffraction analysis. Our results indicate that the synthesis process yielded ceramics with a layered texture. The stoichiometric composition of ceramics exhibited a shift towards gallium-rich content. X-ray diffraction data demonstrated a reduction in the lattice parameters and unit cell volume of β-Ga2O3 ceramic structure. Radioluminescence spectra of β-Ga2O3 ceramics revealed an intensive emission band with a maximum at ~360 nm and non-exponential decay. The synthesized β-Ga2O3 ceramics possess potential applications in scintillation detectors. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of High Pressure Physics is the property of Chinese Journal of High Pressure Physics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Decreasing the scale of vanadium dioxide (VO2) structures is one of the ways to enhance the switching speed of the material. We study the properties of VO2 films of altered thicknesses in the range of 20–170 nm prepared on c-sapphire substrates with a TiO2 sublayer by pulsed laser deposition (PLD) method. The synthesis regime to design a TiO2 film was preliminarily optimized based on XRD data. XRD patterns reveal an epitaxial growth of the VO2 films with distortion of the monoclinic cell to hexagonal symmetry. The positions of the lattice vibration modes in Raman spectra are similar to those in bulk VO2 when the film thickness is greater than ∼ 3 0 nm. For VO2 films thicker that ∼ 2 0 nm, a lattice strain results in the modes' positions and intensity change. However, the electrically triggered transition in a ∼ 5 0 nm thick VO2 film reveals forward and reverse switching times as short as 20 ns and 400 ns, correspondingly. [ABSTRACT FROM AUTHOR]

In this work, selected numerical simulation aspects are analyzed in terms of their effect on predictions of the m-c interface. The fixed-grid enthalpy porosity phase change model, which is highly attractive in the field of modeling sapphire crystallization processes, is examined for its sensitivity to the mushy zone parameter as well as the grid resolution. A further focus is set to the simulation of thermal transport including internal radiation in the crystal and the melt via the finite volume method. Depending on the purpose of the investigation, different requirements on the angular resolutions are relevant. While most of the m-c interface as well as the temperature distribution remain practically unchanged at reasonable resolutions, a high sensitivity of the m-c interface in the near-wall region is demonstrated. This sensitivity is also observed in terms of radiative transport and, hence, the total heat transfer. [ABSTRACT FROM AUTHOR]

Single-crystal sapphire (α-Al2O3) has a wide range of applications in a variety of extreme environments due to its excellent mechanical and chemical properties as well as its stability under extreme service conditions. In addition, sapphire is a hard and brittle material, which makes it difficult to avoid the introduction of subsurface damage during processing, and the existence of a subsurface damage layer seriously affects the performance of the optical system. Therefore, this study focuses on the mechanism of subsurface damage in sapphire grinding, the suppression of damage depth, and the accurate and fast prediction of damage depth. A subsurface damage model for ultrasonic vibration–assisted grinding of sapphire was established by combining ultrasonic vibration single abrasive grain kinematics and dynamics analysis. The mechanism of ultrasonic vibration–assisted grinding was investigated by combining force and acoustic emission (AE) signals. And the effects of ultrasonic vibration–assisted grinding on the surface quality, subsurface damage form, and depth were analyzed. A comprehensive prediction model of SSD based on surface roughness (Sz) was established by combining indentation fracture mechanics and Gaussian process regression. Finally, by analyzing the influence law of each process parameter on the subsurface damage depth (SSD), the grinding process parameters were optimized, and the subsurface damage suppression strategy was proposed. This study provides theoretical guidance for the high-efficiency and low-damage grinding of sapphire. [ABSTRACT FROM AUTHOR]

Metal–organic vapor phase epitaxy of GaN on sapphire (0001) substrates without using low‐temperature (LT) buffer layers is demonstrated. The growth of GaN is achieved by pretreatment of sapphire with trimethylaluminum (TMA) at a high temperature (1050 °C) in a H2 + N2 gas mixture. The TMA pretreatment forms AlN, which acts as nucleation seeds for the subsequent growth of GaN at the same temperature. When AlN created by the TMA pretreatment is three‐dimensional, similar to conventional LT buffer layers, the GaN layers exhibit good structural properties such as atomically smooth surfaces and narrow X‐ray diffraction line widths, comparable to those of GaN on LT buffer layers. In addition, the growth evolution of GaN on TMA‐pretreated sapphire is similar to that on GaN or AlN LT buffer layers. These similarities between the TMA pretreatment and conventional LT buffer‐layer technologies might offer an opportunity to further generalize the heteroepitaxy growth model of GaN. [ABSTRACT FROM AUTHOR]

Brazing of sapphire or ceramic with metal is an essential manufacturing process for sensor and ultra-high vacuum applications. For an efficient brazing of such materials with metals, a prerequisite of metallization of sapphire with titanium (Ti) layers with good adhesion is required. In this direction, the present work is carried out to investigate the phenomena occurring at the interface of titanium–sapphire during metallization process and observe the strength of joint of sapphire with respect to Ti layer. To carry out such study, a model was constructed using molecular dynamics simulation (MDS) for both sapphire and Ti. The MDS model showed that the chemical reaction between Ti and sapphire takes place to form new chemical bonds of Ti–O, Ti–O–Al–O–Ti, and Al–O–Ti. These new bonds are much stronger than the chemical bonds of parent materials and they are the key factor for brazing of sapphire surface using Ti layer. This study shows that chemical reaction in the metallization is a spontaneous and exothermic process which increases the temperature of Ti layer by 450 K. Moreover, it is also observed that the metallization quality mainly depends on the extent of proximity between sapphire and Ti, and it is possible by surface heating up to 1,200 K. The present work is for the understanding and optimization of metallization process, which could be useful toward an efficient execution of brazing between sapphire and metal. [ABSTRACT FROM AUTHOR]

One of the urgent tasks of modern medicine is to detect microcirculation disorder during surgery to avoid possible consequences like tissue hypoxia, ischemia, and necrosis. To address this issue, in this article, we propose a compact probe with sapphire tip and optical sensing based on the principle of spatially resolved diffuse reflectance analysis. It allows for intraoperative measurement of tissue effective attenuation coefficient and its alteration during the changes of tissue condition, caused by microcirculation disorder. The results of experimental studies using (1) a tissue‐mimicking phantom based on lipid emulsion and hemoglobin and (2) a model of hindlimb ischemia performed in a rat demonstrated the ability to detect rapid changes of tissue attenuation confirming the feasibility of the probe to sense the stressful exposure. Due to a compact design of the probe, it could be useful for rather wide surgical operations and diagnostic purposes as an auxiliary instrument. [ABSTRACT FROM AUTHOR]

The high surface area and transfer-less growth of graphene on dielectric materials is still a challenge in the production of novel sensing devices. We demonstrate a novel approach to graphene synthesis on a C-plane sapphire substrate, involving the microwave plasma-enhanced chemical vapor deposition (MW-PECVD) technique. The decomposition of methane, which is used as a precursor gas, is achieved without the need for remote plasma. Raman spectroscopy, atomic force microscopy and resistance characteristic measurements were performed to investigate the potential of graphene for use in sensing applications. We show that the thickness and quality of graphene film greatly depend on the CH4/H2 flow ratio, as well as on chamber pressure during the synthesis. By varying these parameters, the intensity ratio of Raman D and G bands of graphene varied between ~1 and ~4, while the 2D to G band intensity ratio was found to be 0.05–0.5. Boundary defects are the most prominent defect type in PECVD graphene, giving it a grainy texture. Despite this, the samples exhibited sheet resistance values as low as 1.87 kΩ/□. This reveals great potential for PECVD methods and could contribute toward efficient and straightforward graphene growth on various substrates. [ABSTRACT FROM AUTHOR]

The paper presents the results of a comparative analysis of sapphire-bearing placers in South Primorye (Shkotovo Plateau, Russia) and in the adjacent Heilongjiang Province (the Muling deposit, China). The placers are confined to intraplate alkali basalts with similar geochemical characteristics and age. It was found that the same minerals from placers in Russia and China are very similar, although with some differences, the most apparent of which being the predominance of fancy-colored gemstones and rubies among Muling corundums and blue-green-yellow sapphires (BGY sapphires) in the Primorye placers. The minerals of the megacryst assemblage, including gem corundum, bear traces of magmatic corrosion and have an affinity with the host alkali basaltic melt. Magma chambers of an alkali basaltic volcano provide the conditions necessary for the growth of large and transparent crystals. It is suggested that the sapphires formed from gaseous aluminum chloride in miarolitic cavities. Megacrysts are rapidly transported to the surface owing to the explosive eruptions of basaltic volcanoes. Further erosion of megacryst-bearing rocks and redeposition of minerals in alluvium lead to the formation of zircon- and sapphire-bearing placers. The publication emphasizes economic importance of placers of gem corundum and zircon in alkali basalts and, hence, the need for their further study. [ABSTRACT FROM AUTHOR]

Montana hosts the largest sapphire deposits in the US, but the genesis of and connection among the various secondary and primary sapphire occurrences remains cryptic. In situ SIMS measurements of oxygen isotopes in sapphires and zircon inclusions in sapphires provide an opportunity to study the isotope and trace element geochemistry in order to understand sapphire-forming protoliths (i.e. crustal setting and alteration). Sapphire from Montana was transported as xenocrysts in carrier (host) magmas that resorbed sapphire exteriors during transport. The timing and nature of sapphire genesis is elucidated by SIMS measurements of trace elements and U–Pb from discrete zones in zircon inclusions with rims that are interpreted to be syngenetic with host sapphire. Montana sapphires exhibit a large range of δ18O values, from −3‰ to +12‰ VSMOW. However, all but two anomalous crystals fall in the range of 0‰ to 8‰. There is significant crystal-to-crystal variability yet averages at most deposits are consistent with high-temperature equilibration with the mantle (δ18O(Crn) = 4.4‰ to 5.7‰), with the exception of the commercial sapphire deposits at Rock Creek that average 2.7‰. Ruby analyses are limited, but typically have lower δ18O values compared to sapphires from the same detrital localities. Homogeneity within individual crystals (avg. 2 s = ±0.2‰) indicates the absence of isotopically distinct fluid or melt during crystallization. But intercrystalline δ18O ranges by up to 7‰ at a single locality, suggesting sapphire variability at a deposit reflects heterogeneity in the original protolith. Oxygen isotope fractionations between zircon rims and surrounding sapphire suggest comagmatic zircon inclusions and corundum equilibrated at high temperature. No correlation is seen for the degree of radiation damage and alteration of δ18O(Zrc) when zircon inclusions are surrounded and armored by sapphire. U–Pb ages and trace elements were measured in a small subset of syngenetic zircon inclusions in Dry Cottonwood Creek sapphires, revealing a Proterozoic (1778 ± 9 Ma) age for the protolith of sapphires at this locality and a likely polygenetic history. Previous work has suggested formation of these sapphires through partial melting of anorthosites and several anorthosites occur locally and match the age of zircon inclusion cores—the Boehls Butte anorthosite (~180 km NW of Rock Creek) and the Bitterroot anorthosite (~55 km W of Rock Creek) could correlate with Al-rich protoliths at depth. Proterozoic U–Pb ages of zircon from the Boehls Butte anorthosite (1787 ± 2 Ma) match well with the age of zircon inclusion cores in Dry Cottonwood Creek sapphires and suggest genesis in these or similar protoliths. Zircon rims with Tera-Wasserburg lower intercept ages of 110 ± 9 Ma are consistent with previous observations of a xenocrystic relationship to the ~50 Ma Eocene volcanic rocks. Corundum that formed over 50 Ma prior to being scavenged by Eocene magmas likely originated by the anatexis of Precambrian anorthosites and possibly other aluminum-rich rocks at depth. [ABSTRACT FROM AUTHOR]

Diamond coating were deposited on serrated blade by hot filament chemical vapor deposition (HFCVD) method. The lapping experiments of sapphire wafer were carried out by using diamond coated tools. The diamond coatings and machined surface of the sapphire wafer were characterized by scanning electron microscopy (SEM), laser confocal microscope and Raman spectrum. The results show that the lapped sapphire chips are small irregular chips and long thread-like debris. During the lapping process, there is graphitization of diamond crystal. A low surface roughness can be obtained using a spherical grain diamond coated tool. [ABSTRACT FROM AUTHOR]

The introduction of ultrasonic vibration had a significant effect on the expansion tendency of sub-surface microcracks, but the reason for influencing the expansion tendency of microcracks is not clear. In this study, the vertical ultrasonic vibration cutting process of sapphire was simulated by the discrete element method, and the reasons for the expansion of sub-surface microcracks during the cutting process were revealed from the viewpoint of cutting force and stress. The results of the study show that the sub-surface microcracks in the cutting process are mainly caused by tensile stresses, and the tensile stresses increase with the increase of amplitude and frequency; as the amplitude and frequency increase, the degree of cutting force fluctuation, the depth of the sub-surface cracks, and the number of cracks increase more drastically; the tensile stress at smaller amplitudes is smaller than in normal cutting, and the location of the maximum tensile stress is closer to the machined surface, which inhibits the expansion of the sub-surface cracks. Finally, the vertical ultrasonic vibratory cutting and normal cutting sapphire experiments were comparatively studied, and the experimental results were in agreement with the simulation results. This research provides theoretical guidance for the realization of low damage and efficient processing of sapphire materials. [ABSTRACT FROM AUTHOR]

Copyright of Geologia USP: Série Científica is the property of Geologia USP and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The aim of this study was to explore the feasibility of quantitatively evaluating a sapphire's color by analyzing gemstone images. The color characteristics of gemstones through photography and color extraction were accurately captured, and the key color parameters for different color regions of gemstones were extracted. Then, the color of sapphires was simulated by statistical method and function simulation method. The results indicate that the brightness value of the bright area was the highest and the chroma value of the "fire" area was the highest. The chroma (C) of the sapphires was linearly positively correlated with the absolute value of its b value, and the brightness (L) showed a quadratic correlation with its chromaticity parameters (b or C). The function simulation method with an average of b as the main independent variable had a larger standard deviation, which proves that this method has a stronger ability to distinguish the differences in a sapphire's color. This method can be extended to the color evaluation of other colored gemstones, and it can be used to form a gemstone color evaluation system. [ABSTRACT FROM AUTHOR]

The paper presents experimental data on the kinetics of charging and cathodoluminescence (CL) of single-crystal sapphire under electron irradiation. We give a new explanation for the previously found effect of the delay in surface potential development during charging of single-crystal sapphire by an electron beam, and simultaneous increasing of CL intensity. Such a delay can be explained by a gradual accumulation of negative charge in the sapphire volume, which volume is larger than the initial electron-solid interaction region, together with high secondary electron emission. Such charge spreading leads to an increase in the CL intensity throughout the surface potential delay. A hypothesis is suggested that the delay time is determined by the initial number of electron traps. Subsequently, when sufficient charge is accumulated, a retarding electric field arises inside the sample, leading to a decrease of the region of negative charge localization and almost complete neutralization of the positive charge.

Decreasing the scale of vanadium dioxide (VO2) structures is one of the ways to enhance the switching speed of the material. We study the properties of VO2 films of altered thicknesses in the range of 20–170[Formula: see text]nm prepared on c-sapphire substrates with a TiO2 sublayer by pulsed laser deposition (PLD) method. The synthesis regime to design a TiO2 film was preliminarily optimized based on XRD data. XRD patterns reveal an epitaxial growth of the VO2 films with distortion of the monoclinic cell to hexagonal symmetry. The positions of the lattice vibration modes in Raman spectra are similar to those in bulk VO2 when the film thickness is greater than [Formula: see text][Formula: see text]nm. For VO2 films thicker that [Formula: see text][Formula: see text]nm, a lattice strain results in the modes’ positions and intensity change. However, the electrically triggered transition in a [Formula: see text][Formula: see text]nm thick VO2 film reveals forward and reverse switching times as short as 20[Formula: see text]ns and 400[Formula: see text]ns, correspondingly.

Sapphire exhibits typical anisotropy due to its unique crystal structure, and there are significant property differences in different processing areas during the machining of curved sapphire component, making it essential to investigate the anisotropy in the removal process of sapphire materials for efficient curved surface machining. In this study, the force and acoustic emission (AE) signals were monitored at different scratch stages and orientations, and the anisotropic characteristics of ductile-brittle transition (DBT) depths, material removal morphology, and subsurface crack propagation direction were analyzed. The results indicate that the anisotropy of force signals and DBT depths is mainly reflected in the differences between crystal planes. In addition, the removal morphology of materials with different crystal orientations showed smooth scratch grooves with unclear anisotropic characteristics during the ductile removal (DR) stage, while the crack propagation direction with different scratch orientations during the DBT stage showed significant anisotropic characteristics. The brittle removal (BR) stage is characterized by brittle spalling in the form of shell-like, blocky, and fishbone spalling, and there is a significant anisotropic difference in the spalling shapes on both sides of the scratch. The original AE signals, Fast Fourier Transform (FFT), and Short Time Fourier Transform (STFT) results show that the AE frequencies of different crystal planes are different, and the differences in different scratch orientations on the same crystal plane are reflected in the peak amplitude. Finally, the propagation directions of subsurface cracks with different directions are anisotropic due to different scratching crystal planes, and propagate mainly along directions of 15°, 29°, 32°, 58°, and 105°.

To understand the relationship between the damage mechanism of sapphire and the anisotropic characteristic of its crystal structure, in-situ scratch tests under the confocal laser scanning microscope (CLSM) were performed along different directions of C-plane sapphire wafer. The relation between in-situ images and normal/lateral forces was established. Craters in front of the contact region (CR) between the indenter and the material, and subsurface special cracks separated from CR were observed. As the scratch direction changed, these special cracks and craters initiated and propagated on the left front, front, and right front of the CR, respectively. The scratch phenomena in different scratch directions exhibited triple symmetric characteristic around the c-axis. The probability of slip/twinning activation and the theoretical stress field in front of the indenter were calculated to investigate the fracture mechanism of sapphire. Craters and those special cracks appeared in the region with the highest probability of rhombohedral twinning and basal twinning activation, respectively. According to the theoretical stress field, the material ahead of the indenter axis was separated into regions I and II. Craters in front of the CR and those special cracks separated from the CR appeared in these two regions, respectively.

GHz burst-mode femtosecond (fs) laser, which emits a series of pulse trains with extremely short intervals of several hundred picoseconds, provides distinct characteristics in materials processing as compared with the conventional irradiation scheme of fs laser (single-pulse mode). In this paper, we take advantage of the moderate pulse interval of 205 ps (4.88 GHz) in the burst pulse for high-quality and high-efficiency micromachining of single crystalline sapphire by laser induced plasma assisted ablation (LIPAA). Specifically, the preceding pulses in the burst generate plasma by ablation of copper placed behind the sapphire substrate, which interacts with the subsequent pulses to induce ablation at the rear surface of sapphire substrates. As a result, not only the ablation quality but also the ablation efficiency and the fabrication resolution are greatly improved compared to the other schemes including single-pulse mode fs laser direct ablation, single-pulse mode fs-LIPAA, and nanosecond-LIPAA.

Sapphire has various applications in photonics due to its broadband transparency, high-contrast index, and chemical and physical stability. Photonics integration on the sapphire platform has been proposed, along with potentially high-performance lasers made of group III–V materials. In parallel with developing active devices for photonics integration applications, in this work, silicon nitride optical waveguides on a sapphire substrate were analyzed using the commercial software Comsol Multiphysics in a spectral window of 800~2400 nm, covering the operating wavelengths of III–V lasers, which could be monolithically or hybridly integrated on the same substrate. A high confinement factor of ~90% near the single-mode limit was obtained, and a low bending loss of ~0.01 dB was effectively achieved with the bending radius reaching 90 μm, 70 μm, and 40 μm for wavelengths of 2000 nm, 1550 nm, and 850 nm, respectively. Furthermore, the use of a pedestal structure or a SiO2 bottom cladding layer has shown potential to further reduce bending losses. The introduction of a SiO2 bottom cladding layer effectively eliminates the influence of the substrate's larger refractive index, resulting in further improvement in waveguide performance. The platform enables tightly built waveguides and small bending radii with high field confinement and low propagation losses, showcasing silicon nitride waveguides on sapphire as promising passive components for the development of high-performance and cost-effective PICs. [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]

Pressure sensors prepared from sapphire exhibit excellent characteristics, including high-temperature resistance, high hardness, and resistance to electromagnetic interference. A Fast Fourier Transform and Mean Square Error (FFT-MSE) demodulation algorithm was employed to demodulate a sapphire sandwich-structure Fabry–Perot (F-P) pressure sensor. Through simulation analysis, the experimental results indicated that the demodulation error of the air cavity length in the range of 206 μm to 216 μm was less than 0.0008%. Compared to single demodulation methods and combined demodulation methods based on FFT or Minimum Mean Square Error (MMSE), the method proposed in this work reduced the demodulation error by more than three times and increased accuracy by more than six times. The algorithm was utilized to demodulate the sapphire sandwich-structure F-P pressure sensor, and the test results indicated that the fitting error of the sensor was less than 0.025% within the pressure range of 0 MPa to 10 MPa. The repeatability error was less than 0.066%, the zero-point deviation was 1.26%, and the maximum stability deviation was 0.0063% per 30 min. The algorithm effectively demodulated the actual cavity length variation in the sapphire sandwich-structure F-P pressure sensor, providing a solution for the performance evaluation of the sapphire sandwich-structure F-P pressure sensor. [ABSTRACT FROM AUTHOR]

Residual stress is a key factor affecting the properties of ceramic/metal brazed joints. In this work, the residual stress of sapphire/Ti6Al4V alloy joints brazed with CuTi+B composite filler after cooling and reheated to 400 °C was calculated by finite element numerical simulation method. The effect of the B content in the filler and the filler thickness on the residual stress distribution of brazed joints after cooling was studied. The results show that the residual stress is mainly concentrated in the area near the filler layer. The maximum von Mises stress is located in the filler layer and a large Z-axial (the direction perpendicular to the brazed surface) tensile stress is on the sapphire near the filler layer. The B content and the filler thickness have no significant effect on the distribution of residual stress, but they have a certain effect on the value of residual stress of the sapphire near the filler layer. The von Mises stress and the Z-axial stress of this area increase with the increase of B content, and they decrease first and then increases with the increase of filler thickness. When the sapphire/Ti6Al4V joint is reheated to 400 °C, its residual stress significantly reduces and the residual stress on the periphery of the filler layer changes from compressive stress to tensile stress. As the B content is 1 and 3 wt%, the sapphire/Ti6Al4V joint with a smaller residual stress can be obtained. The microstructure observation and shear tests of the joints show that cracks appear in the high stress concentration area and the fracture starts from the area with maximum axial tensile stress, which verifies the accuracy of the simulation results. [ABSTRACT FROM AUTHOR]

The ultrashort pulsed (USP) laser microwelding of sapphire/lnvar36 alloy controlled by the surface roughness of metal was investigated for the first time. The surface roughness (Sa) of Invar alloys gradually decreased from 0.944 to 0.029 μm from the prime surface to grounded and polished surface. However, the joint shear strength first increased and then decreased with the lowered Sa, the maximum shear strength reached 107.87 MPa at the Sa ∼ 0.131 μm. Compared to other surfaces with low Sa, the relatively high surface roughness enhanced the interfacial thermal deposition both spatially and temporally which in turn promoted the diffusion of interface elements and the formation of jagged mechanical interlocking structures. Therefore, the appropriate rough metal surface was beneficial for the enhancement of sapphire/metal dissimilar joints. This report is of great significance in simplifying the surface preparation process in the USP laser microwelding of transparent hard and brittle materials with metals, therefore promoting this technique from lab to industry. [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]

The joining of YSZ and sapphire was achieved through the utilization of nanosecond laser pulses. The microstructure, mechanical properties and forming process of the YSZ/Sapphire joint were systematically studied. The joint consists of an amorphous region guided by the temperature gradient and a dendritic recrystallization region. The amorphous region is situated centrally within the joint, while the recrystallization region surrounds it in a distributed manner. The reason for this phenomenon lies in the fact that the welding process occurring in the central region of the joint, and the extreme cooling prevents Al3+, Zr4+ and O2- ions from forming regular crystal phases. During this study when the laser power is set at 9 W and the scanning speed is adjusted to 80 mm/s, optimal welding interface performance can be achieved, resulting in a maximum joint shear strength of 32 MPa. This study provides a new idea for rapid and efficient welding of advanced ceramic. [ABSTRACT FROM AUTHOR]

In this study, we investigated the effect of adding cerium oxide (CeO2) particles to the cutting fluid on the machining mechanism when slicing sapphire wafers using an electrodeposited diamond wire tool. The results showed that the added CeO2 acted to suppress wire tool deflection and promote initial wear of the nickel plating to rapidly expose the abrasive grains. In addition, elemental analysis of the shed wear particles suggested that they were adsorbed particles of nickel plating and sapphire. It was statistically confirmed that the CeO2 slurry reduced the size of the wear particles. In addition, the machining force was measured, and it was found that the CeO2 slurry reduced the machining force. Based on these results, it is the CeO2 slurry likely changed the wear mode from severe to mild and suppressed the lifting of the tool because smaller wear particle were formed. This suppressed wire tool deflection and stabilized the machining pressure to make the abrasive grains uniformly contact and remove material from the workpiece. Therefore, the number of cutting grains increased and the depth of cut per grain was kept small, which likely resulted in a transition to the crack-free ductile mode. [ABSTRACT FROM AUTHOR]

C-plane sapphire (α-Al 2 O 3) is a commonly used substrate material for integrated circuits and Light-emitting diodes (LEDs). Efficient, stable, and low-damage lapping processes are used to ensure surface smoothness and meet application requirements. Fixed abrasive pads (FAPs) are typically used for the lapping of sapphire substrates, but the pads are prone to be glazed or even failed. In this study, loose alumina grains were used for in-situ reconditioning of fixed diamond abrasive pads. The material removal rate and surface roughness of the lapped sapphire substrate were calculated, the types and size distributions of the wear debris were analyzed, the surface morphology of the FAP after lapping was examined, and an online monitoring system was used to track the friction coefficient between the FAP and the sapphire substrate. In order to determine the ideal size and concentration of loose grains and to reveal the in-situ reconditioning mechanisms for the fixed diamond abrasive pads, the effects of the size and concentration of loose alumina grains in the lapping slurry on the in-situ reconditioning of the FAP were investigated. This was done by examining the wear behavior of loose alumina grains during the lapping processes of sapphire substrates. • In-situ reconditioning mechanism for fixed abrasive pads based on the wear behavior of loose grains is discussed. • Loose alumina abrasives improve lapping efficiency and stability of fixed diamond abrasive pads. • Three-body wear of alumina grains on the pad enhances self-conditioning ability of fixed diamond abrasive pads. • Size of loose alumina grains should be close to the maximum protrusion height of the diamond abrasives. [ABSTRACT FROM AUTHOR]

This work describes a sapphire cryo-applicator with the ability to sense tissue freezing depth during cryosurgery by illumination of tissue and analyzing diffuse optical signals in a steady-state regime. The applicator was manufactured by the crystal growth technique and has several spatially resolved internal channels for accommodating optical fibers. The method of reconstructing freezing depth proposed in this work requires one illumination and two detection channels. The analysis of the detected intensities yields the estimation of the time evolution of the effective attenuation coefficient, which is compared with the theoretically calculated values obtained for a number of combinations of tissue parameters. The experimental test of the proposed applicator and approach for freezing depth reconstruction was performed using gelatin-based tissue phantom and rat liver tissue in vivo. It revealed the ability to estimate depth up to 8 mm. The in vivo study confirmed the feasibility of the applicator to sense the freezing depth of living tissues despite the possible diversity of their optical parameters. The results justify the potential of the described design of a sapphire instrument for cryosurgery. [ABSTRACT FROM AUTHOR]

The main purpose of this study was to develop observation techniques and processing technology for the electrochemical discharge machining (ECDM) of sapphire wafers. To measure the effect of gas-film thickness, discharge-spark conditions, and droplet sliding frequency on machining quality and efficiency in ECDM, this research utilized high-speed cameras to observe the gas film thickness and formation of the gas film during ECDM. Additionally, this study observed the machining-gap phenomena during ECDM. The formation mechanism and machining characteristics of the gas film were understood through experiments. The machining parameters included the liquid level, working voltage, rotation speed, and duty factor. This study analyzed and discussed the effect of each machining parameter on the gas-film thickness, current, electrode consumption, and droplet sliding frequency. Moreover, this study aimed to obtain optimized machining parameters to overcome the difficulty of machining sapphire. The experimental results indicated that utilizing a high-speed camera to capture the phenomena between electrodes during electrochemical discharge could effectively observe the gas-film thickness and the coverage of the gas film. A higher bubble coalescence rate enhanced the machining capability and reduced the lateral discharge. Therefore, this study could obtain better machining-hole depths through observation and analysis to improve gas-film stability and machining capability. This study demonstrated that a liquid level of 700 µm, a working voltage of 48 V, a duty factor of 50%, and a tool electrode rotational speed of 200 rpm could achieve a hole depth of 86.7 µm and a hole diameter of 129.5 µm. [ABSTRACT FROM AUTHOR]

Multi-wire swing reciprocating sawing technology is the main machining method used to cut sapphire crystal bars into wafer substrates, while normal force is an important index that reflects the processing stability. In this paper, the normal force（\begin{document}$ {F}_{\mathrm{n}} $\end{document}）during multi-wire swing reciprocating wire saw cutting sapphire crystal bars was measured, and the change in normal force at different positions and cutting depths of the sapphire crystal bars was tracked. The influence of various process parameters on the stability of the machining process was tracked by using the rangeability of normal force（\begin{document}$ \mathrm{\Delta }{F}_{\mathrm{n}} $\end{document}）as the index. The experimental results show that \begin{document}$ {F}_{\mathrm{n}} $\end{document} is closely correlated with the reciprocating motion of the wire saw and the rocking motion of the workpiece, and Δ\begin{document}$ {F}_{\mathrm{n}} $\end{document} in the front of the sapphire crystal bar is significantly different from that in the middle and back. Process parameters such as the wire saw speed（Vs）, maximum swing angle (θmax), single piece wire consumption (Md), tensioning force (Fw), and total cutting time (T) have different effects on Δ\begin{document}$ {F}_{\mathrm{n}} $\end{document}. The fluctuation degree of Δ\begin{document}$ {F}_{\mathrm{n}} $\end{document} is closely related to the wear of the wire saw.

A novel Ti–Al-Diamond metal matrix composite (MMC) material has been recently developed for fabricating diamond blade that is an indispensable tool for the mechanical dicing of optoelectronic devices. This work aims to achieve a deep understanding of the influence of sintering temperature on the microstructure, the mechanical and frictional properties, and the grinding and dicing performances on hard-and-brittle materials. Firstly, the microstructures and the mechanical and frictional properties of Ti–15Al-25 vol% Diamond metal matrix composites (MMCs) sintered at 750, 850, and 950 °C were investigated. The upraising of sintering temperature results in the enhancement of the diffusion between constitute elements, which consequently increases the hardness and bending strength, but reduces the porosity of sintered MMCs. Then, Ti–15Al-25 vol% Diamond blades were sintered at 750, 850, and 950 °C for dicing of sapphire. The increase in sintering temperature was found to be responsible for the compromise of the self-sharpness capability of diamond blades, resulting in an inferior dicing quality in terms of the chipping size, the kerf width, and the surface roughness, but an improved dicing ratio. Results obtained in this work indicate that sufficient porosity and self-sharpening capability play the most determinant role in satisfying the dicing quality of sapphire.

Nanoindentation test method is widely used to measure the material hardness, which is a standard test and the effect of measurement error is limited. However, the measured results of the nano-hardness for the same plane of single crystal materials, such as sapphire, were very different. The possible reason for the difference of nano-hardness is induced by the anisotropy of single crystal materials. In this study, nanoindentation tests were carried out to obtain the nano-hardness of C-plane sapphire. The tests with two different indenter orientations were designed as follow. On C-plane, one edge of the Berkovich indenter was indented parallel to the direction [101‾0], as well as one edge indented perpendicular to the direction [101‾0] for comparison. The average hardness was 25.58 GPa and 29.64 GPa respectively. Molecular dynamics simulation was employed to reveal the generation mechanism of anisotropy in nanoindentation process. The results showed that the distribution of subsurface dislocations and the activation of slip systems were affected by indenter orientations, which resulted in the difference in nano-hardness. When one edge of the Berkovich indenter was indented perpendicular to the direction [101‾0], C-plane sapphire had a stronger ability to resist deformation, showing a higher hardness on the macroscopic level.

The article discusses promising penetrators with non-removable transparent and removable opaque windows, created mainly from corundum and ice composite, respectively. Their use will expand the scientific research program due to visualization capabilities for video recording of the movement of the penetrator in the subsurface layers of soil and their optical methods of studying, as well as direct contact with them. The calculation method and the calculated values of damage to these windows from the impact of spherical particles of lunar regolith with diameters of 1,0 and 1,5 mm, colliding with them at speeds of up to 1 km/s in the angular range from 70° to 80°, obtained using numerical modeling or based on an engineering model, are discussed.

Although the hardness of sapphire is very high, in some applications, for example, working as panels in mobile phones and watches as well as optical windows in various military optical sensors, it still suffers from the destruction of being scratched and marked as well as mechanical failure by fracture. Here we reported that the technique of high‐temperature rolling we developed recently could be exploited to sapphire to enhance its hardness and fracture toughness. After rolling at 1200°C, Vickers' hardness and fracture toughness of sapphire increase by 4%–6% and 13%–27%, respectively. The enhancement of fracture toughness was explained by the residual compressive stress layer that was introduced in sapphire during rolling. The improvement of hardness was thought to be related to the hardening effect of dislocations. This work provides a new strategy for the mechanical property enhancement of sapphire in further applications. [ABSTRACT FROM AUTHOR]

Sapphires crystals were identified in the corundum-bearing xenoliths in Miocene (Upper to Middle Sarmathian) andesites of the Slanské vrchy Mountains, eastern Slovakia at the Záhradné, Hubošovce and Vechec localities. The sapphire crystals occur in (1) micaceous xenoliths, which are built mostly of dark mica from annite-phlogopite series (biotite), K-feldspars, plagioclase with abundant inclusions of hercynite, ilmenite and Ti-rich magnetite, locally with pyroxenes of enstatite-ferosilite series at the localities Záhradné and Hubošovce. Less abundant are sapphires occurring in cordieritic xenoliths (2), dominantly consisting of cordierite, plagioclase and sillimanite with minor hercynite and ilmenite inclusions discovered in the Vechec quarry. Sapphires are dark blue to light blue with vitreous to diamond lustre and no visible pleochroic colour change forming mostly pseudohexagonal tabular, locally more complex euhedral to subhedral crystals up to 2.0 mm in size with triangular-shaped patterns on crystal faces. Raman spectroscopy showed characteristic corundum peaks at 419 cm-1 A1g mode and 384 cm-1 Eg mode with other peaks assigned to Al2O3 crystal vibrations. Chemical composition (EPMA, LA-ICP-MS) shows typical content of 98.12-99.60 wt. % Al2O3 with increased concentrations of Fe, Ti, Cr, V, Mg and Ga, locally also Na, Ca, K, B and Li. Genesis of corundum-bearing xenoliths interpreted from paragenetic observations and geochemical data shows clear metamorphic trend. Formation of sapphires was caused by incorporation of Al-rich precursor metasediments depleted in silica into the magmatic reservoir, which caused thermal overprint of the precursor mineral assemblage and led to the formation of high temperature mineral association suitable for corundum crystallization. Furthermore, sapphire crystals from the Hubošovce quarry exhibit spinel coronas, which are typically developed from destabilization of corundum during their retrograde development. [ABSTRACT FROM AUTHOR]

Portezuelo de Pajas Blancas' primary metasomatic deposits host sapphires that differ in size, colour, and colour distribution through different lithological units. The discovery of sapphire-bearing secondary aeolian placer deposits enabled a detailed analysis of sapphire types to determine the causes of this heterogeneity. Representative single sapphires from the primary and secondary deposits were analysed using various techniques, including SEM-CL, OM-CL, Micro-XRF, Raman spectroscopy, and polarised transmitted light multi-focus optical microscopy. Based on the results, seven sapphire types were identified according to their colours and colour distribution. Fe and Ti concentrations mainly contribute to the colour and micro-textures occurrence. The primary growth textures include cores, progressive, oscillatory, and diffusion zoning, whereas the secondary alteration features correspond to micro-brecciation, re-arrangement, and overgrowth. Inclusions such as euhedral andalusite, anhedral anhydrite, and anhedral rutile were identified in the sapphires. The formation of Portezuelo de Pajas Blancas sapphires can be divided into five genetic stages: (i) core growth development; (ii) chemical imbalance due to open system behaviour that produces progressive and oscillatory zoning; (iii) low-temperature deformations that produce micro-brecciation; (iv) re-arrangement of pre-formed sapphire fragments and subsequent sapphire overgrowth; (v) diffusion zoning that produce Fe- and Ti-enriched outer rims. In conclusion, the Portezuelo de Pajas Blancas' sapphires were formed through at least five stages of oxidised contact metasomatism at varying temperatures and low pressures, where a heterogeneous forming condition predominates during sapphire formation. [ABSTRACT FROM AUTHOR]