Sapphire Research Articles

Effects of surface coating materials on cutting forces and ductile-to-brittle transition in orthogonal cutting of monocrystalline sapphire

Ductile regime cutting has been studied to process brittle materials without cracking. The predominant material response during cutting can be tuned to the ductile range under certain conditions. This study aims to explore and reveal the effects of workpiece surface coatings on promoting the ductile cutting regime. Despite of several attempts on applying surface coatings, the effects of coating properties on material behaviors and cutting forces are not yet well-understood. Here, the effects of surface coatings on the cutting forces during ductile regime cutting of monocrystalline sapphire were investigated from the perspectives of types of coating materials and crystal orientation. Flexible elastomers, hard coatings, and a lubricant were applied to the surface, and the cutting force behaviors were observed. Coatings effectively promoted ductile cutting regime, but the effects varied by coating type and crystal orientation. The cutting forces and ductile cutting regime were significantly influenced by types of coating materials and dominant deformation/fracture mechanisms of sapphire crystal. The machining characteristics were analyzed based on the modified slip-fracture model; this explained the varying effects per different cutting direction. This study aids identification of effective coatings under various cutting conditions and is expected to contribute to wider utilization of ductile regime cutting in processing of brittle materials.

Influence of diamond parameters on microstructure and properties of copper-based diamond composites manufactured by Fused Deposition Modeling and Sintering (FDMS)

As an additive manufacturing technology, Fused Deposition Modeling and Sintering (FDMS) technology can give diamond tools some creative structures to be applied in more fields. To explore the influence of diamond parameters on diamond tools manufactured by FDMS, copper-tin-diamond composite samples with different diamond concentrations and particle size were prepared by FDMS technology in this paper. During the study, the morphological characteristics of diamond particles inside the samples during the debinding and sintering process are summarized and the influence of diamond parameters on the mechanical properties and structure of the samples was further explored. These influence laws were also verified by cutting experiments. The results show that most diamond particles are in an incomplete coating state because of the volatilization of the binder. Meanwhile, a higher concentration of diamond will lead to more pores and cavities in the samples; and the cavities can be connected to form a large area of cavity zone by the print layer, thereby resulting in a serious loss in the performance of the samples. On the other hand, a small diamond particle size can lead to agglomeration of particles. Subsequently, this will result in void generation and regional weakening of the holding ability. However, agglomeration and some pores or cavities will increase the wear of the matrix, expose more diamond particles, and finally improve the cutting efficiency of the dicing blades when cutting sapphire crystal. Excessive wear may reduce the life of the diamond tool, but improved of sharpness can be better applied in the field of precision machining.

Transverse-pumping approach for a powerful single-mode Ti:sapphire laser for near infrared lidar applications.

We present a design of a transversely pumped and powerful Ti:sapphire laser, suitable for laser remote sensing in the near infrared (NIR) spectrum. Examining multiple pump configurations revealed that transversal pumping of Ti:sapphire crystals with a Nd:YAG laser (532 nm) from one or two sides yields maximum output power. Together with an optimized bow-tie resonator setup, we were able to extract up to 3 W (30 mJ, 100 Hz) of narrowband NIR laser emission from a cuboid 50 mm long Ti:sapphire crystal. Beam quality and divergence were determined as Mx2=1.1, My2=1.7, φx=0.5mrad, and φy=0.8mrad. The spectral purity (seeded, Pseed≥170µW) was better than 99.8%. Additionally, we show a two-wavelength setup applicable to atmospheric water vapor lidar. The principle performance of this theory of operation suggests a good chance of scalability towards significantly enhanced power of future Ti:sapphire lasers.

Study of Natural and Synthetic Yellow–Orange Sapphires Based on the CIE 1976 L*a*b* Uniform Colour Space

The natural and synthetic yellow–orange sapphires are researched in a new angle of gemstone chromaticity. The relationship between spectrum and composition and colour was studied by UV-Visible spectroscopy and Laser Ablation Inductively Coupled Plasma Mass Spectrometer (LA-ICP-MS) testing. The results show that synthetic yellow–orange sapphires for this article are co-coloured by nickel and chromium, and differ from natural yellow–orange sapphires. The lightness L* of synthetic sapphires is mainly influenced by the chromium, and the hue angle h° is influenced by nickel and chromium, in addition to the ratio of chromium to nickel content. In the UV-Visible spectroscopy, the hue angle of natural sapphire is influenced by the wavelength that corresponds to the trough in the blue–violet area, while the absorption band at 555 nm in the ultraviolet-visible spectrum of synthetic sapphire influences the hue angle. The lightness of the sapphire is higher under A than under D65; the chroma decreases with the change of light source from D65 to A for the yellow sapphire and increases for the rest; the hue angle is generally higher under D65 than under A, and as the red hue continues to increase, the hue angle is higher under A than under D65.

Cavity Etching Behavior on the M‐Plane of Sapphire Crystal

AbstractWet etching has been a fundamental process for the fabrication of sapphire crystal substrates with critical position in the current semiconductor devices industry. The present work reveals the etching behaviors of cavities on the M‐plane {100} of sapphire crystal by the hot KOH etchant. It is shown that the boundary of cavities changes from smooth circle to octagon‐like and the edges evolve sharper as the etching temperature increases. Carefully analyzing the structure of the etched cavities suggests they are partially framed by low index planes (20) (20), (100), (010), and (110).

Effect of Reduction Annealing on the Coloration Mechanism of Yellow Sapphire with High Iron Content

The color of yellow sapphire from Africa characterized by high iron content and low levels of other transition metal elements was changed from yellow to grayish-blue after high-temperature reduction annealing. Before reduction annealing, the optical absorption spectra showed that the outer d–d electron transitions of Fe3+ were the main coloring cause of yellow sapphires, but the charge transfer between O2− and Fe3+ may have a greater contribution. The change in lattice parameter indicates that Fe3+ is reduced to Fe2+ during reduction annealing, and adjacent Fe2+ and Fe3+ form an Fe2+-Fe3+ ion pair. The absorption caused by intervalence charge transfer of Fe2+-Fe3+ is the essential reason for the grayish-blue appearance of yellow sapphires after reduction annealing. The charge compensation mechanism of Fe2+-Fe3+ in natural sapphire is also discussed, and oxygen vacancy is considered to be the most suitable charge compensator for Fe2+-Fe3+.

Optical and interfacial characteristics of a heterojunction between (2¯01)-oriented single-domain β-(In0.072Ga0.928)2O3 and α-Al2O3 crystals

In this article, we determine the band alignment at the thermodynamically stable heterointerface between a ( 2 ¯ 01 )-oriented single-domain β-(In0.072Ga0.928)2O3 crystal and bulk c-plane sapphire, namely, (0001)-oriented α-Al2O3. The β-(In0.072Ga0.928)2O3 layer was deposited on the bulk sapphire crystal using pulsed laser deposition. The β-(In0.072Ga0.928)2O3 and α-Al2O3 valence and conduction band offsets (VBO and CBO, respectively) were found to be 0 ± 0.1 and 4.87 ± 0.1 eV, respectively. Accordingly, we identified a type-I α-Al2O3/β-(In0.072Ga0.928)2O3 heterojunction. X-ray diffraction measurements confirmed ( 2 ¯ 01 )-oriented single-domain β-(In0.072Ga0.928)2O3 high-quality films with in-plane rotations of every 120 ∘ , whereas Rutherford backscattering spectrometry was employed to verify the bulk composition. We employed high-resolution X-ray photoelectron spectroscopy to measure the core level binding energies of Al 2p and Ga 2p3/2 with respect to the valence band maxima of the β-(In0.072Ga0.928)2O3 and α-Al2O3 layers, respectively. Then, we measured the energy separation between the Al 2p and Ga 2p3/2 core levels at the interface of the heterojunction. β-(InGa)2O3 is a wide-bandgap semiconductor, while α-Al2O3 is a well-known dielectric. Together, they can be employed to fabricate reliable and efficient power electronic devices. We also combined high-resolution transmission electron microscopy, X-ray diffraction, and fast Fourier transform algorithms to characterize the dislocations at the interface.

Radiance properties of corundum and feldspar minerals under X-ray induced luminescence

The paper reports the characteristics of luminescence spectra under X-ray excitations of corundum (sapphire and ruby) and feldspar (amazonite and labradorite) group to identify the natural gemstones. Compositional, structural and optical properties were investigated to confirm gemstones' identification. The structural studies of both blue sapphire and ruby using XRD technique showed a single phase of α-Al2O3 structural. While the amazonite and labradorite reveal the mixed-phase of microcline and plagioclase phase, corresponding to the Al2O3 and SiO2, which are the primary element composition of feldspar mineral confirmed by EDXRF studies. The optical absorption spectra were investigated in the ultraviolet and visible regions from around 300 to 1000 nm. The X-ray induced luminescence (XIL) spectra of corundum observed that the luminescence arises from Cr3+ transition in both blue sapphire and ruby, showing the narrow and intense red emission (693 nm). Meanwhile, blue sapphire's emission spectrum arises from both Cr3+ and Ti3+ transitions. The XIL spectra of feldspar centered at 446–472 nm have generally been attributed to recombination at an intrinsic defect Al–O--Al center whereas, the longer wavelength emissions spectra at around 560, 736–755 and 885 nm have been associated unequivocally with the presence of Mn, Fe and Pb impurity, respectively. This research shows that a complete characterization of blue sapphire, ruby, amazonite and labradorite stones can be successfully achieved through XIL technique, which is a fast process and non-destructive. Accordingly, XIL technique is a reliable tool for characterizing the corundum and feldspar minerals.

Feasibility Analysis of Sapphire Compound Refractive Lenses for Advanced X-Ray Light Sources

The compound refractive lens (CRL) is a commonly used X-ray optical component for photon beam conditioning and focusing on the beamlines of the X-ray facilities. The normal preparation materials are beryllium, aluminum, silicon of current lenses, and they all suffered from high heat load fatigue and short pulse damage risks. Hard materials based CRL is engaged attention for the advanced X-ray application. Sapphire crystal has the advantages of high density, high melting point, low thermal expansion coefficient. In this paper, properties of the refraction and absorption ratio of Sapphire and parameters of Sapphire lenses of effective aperture, transmittance, resolution, number of lenses needed for a certain focus, are taken into account for the CRL design, comparing with those of several common materials as well. The calculation results show that the performance of the sapphire lens is better than that of the aluminum lens and silicon lens, and inferior to that of the beryllium lens and diamond lens, but the number of lenses used is less. In the meantime, performances of sapphire lenses focusing are simulated and thermal effects on lenses are analyzed. Analysis and discussion are carried out under the same conditions as the metal Aluminum ones. The focusing simulation shows that the sapphire lenses can obtain a smaller spot with more intensity. The thermal analysis indicates that the temperature during use of the sapphire lens is much lower than the melting point of sapphire, and the thermal deformation is negligible.

Mechanical and Metallurgical Evaluation of 3 Different Nickel-Titanium Rotary Instruments: An In Vitro and In Laboratory Study.

An in-depth evaluation of the mechanical and metallurgical properties of NiTi instruments is fundamental to assess their performance and to compare recently introduced instrument with widespread ones. According to this, since there are no data on this topic, the aim of the study was to mechanically and metallurgically evaluate an instrument recently introduced into the market (ZenFlex (ZF)), by comparing it with two well-known instruments with similar characteristics: Vortex Blue (VB) and EdgeSequel Sapphire (EES). According to this, 195 instruments were selected: 65 ZF, 65 VB and 65 EES. Each group was divided in subgroups according to the mechanical tests (i.e., cyclic fatigue resistance, torsional resistance and bending ability; (n = 20)) and the metallurgical test (differential scanning calorimetry (n = 5)). A scanning electron microscopy was performed to verify the causes of fracture after mechanical tests (cyclic fatigue and torsional tests). According to results, VB showed the highest flexibility and cyclic fatigue resistance in comparison to the other instruments, with a statistically significant difference (p < 0.05). Regarding torsional resistance, EES showed the lowest value of torque at fracture, with a statistically significant difference, whilst the comparison between ZF and VB showed no statistically significant difference (p > 0.05). DSC analysis pointed out that VB had the highest austenite start and finish temperatures, followed by ESS and then ZF. ESS sample showed the highest martensite start and finish temperatures followed by VB and ZF. Considering the results, it can be concluded that VB showed the best mechanical performance during static tests in comparison to ESS and ZF. This is fundamentally due to the interaction of parameters such as instrument design and heat-treatments that are able to enhance its mechanical performance.

CONTROL OF THE OPTICAL SURFACE PURITY OF THE ELEMENTS BY THE ELLIPSOMETRIC METHOD

The possibility of controlling the chemical purity of the surface of optical elements by the ellipsometric method has been analyzed. The rationale of the possibility of measuring the parameters of contaminating films on the optical surface of elements by the ellipsometric method has been given simplification has been&#x0D; shown of the process of determining the thickness of the contaminating film while expanding the possibility of its measurement on an optical element made of different materials. Ellipsometric studies of freshly polished and used metal mirrors made of copper and copper alloy (zirconium bronze), aluminum and its alloys AMG-6, AL-9, AL-24 have been carried out. Research has also been conducted on elements made of K-8 and&#x0D; K-108 (State Standard 3514-94) optical glasses, which are the most typical materials used for manufacture of optical parts for laser technique of visible and near IR-range, from single crystals of NaCl, BaF2 and sapphire (Al2O3). Parameters of contaminating films on the surface of these elements have been measured.&#x0D; It has been concluded that it is advisable to use the ellipsometry method during the input (before carrying out physicochemical cleaning) and during the output (after cleaning) control of the optical element to assess the contamination of the optical surface and also for the quantitative analysis of the concentration of contaminants on the optical surface of the elements while working off the technology of their physicochemical cleaning.

High-Efficiency Continuous-Wave Ti:Sapphire Laser with High-Intensity Pumping Using a Commercially Available Crystal

Despite the importance of improving the efficiency of lasers in order to expand their utility range, the improvement of the efficiency of Ti:sapphire lasers has not progressed due to their high crystal losses. Therefore, we improved the efficiency of CW Ti:sapphire lasers by high-intensity pumping, which is one of the most effective methods of suppressing the efficiency reduction due to losses. Using a easily commercially available 0.25 wt.%, figure of merit (FOM) 200 Ti:sapphire crystal, optics and a pump source, we achieved an optical-to-optical conversion efficiency of 32.4% with a slope efficiency of 42.5% at an incident pump power of 5.0 W which corresponds the maximum pumping intensity of 860 kW/cm2. Furthermore, we ensured the reliability of our theoretical analysis by reproducing the experimental results. From this reliable theory, double-pass pumping and increasing the pump power to 25 W resulted in the highest optical-to-optical conversion and slope efficiencies for the incident pump power of 55.9% and 59.6%, respectively, at a high intrinsic residual loss of 4.0%. Even if losses doubled or deviated from the optimum condition for the highest efficiency, the efficiency reduction due to these factors was only a few percent. These results show that with high-intensity pumping, lasers with efficiencies well exceeding half of the quantum limit can be achieved even if all components, including Ti:sapphire crystals, are easily commercially available.

A Hybrid Self-Seeded Ti:sapphire Laser with a Pumping Scheme Based on Spectral Beam Combination of Continuous Wave Diode and Pulsed DPSS Lasers

A wide variety of applications require high peak laser intensity in conjunction with a narrow spectral linewidth. Typically, injection-locked amplifiers have been employed for this purpose, where a continuous wave oscillator is amplified in a secondary external resonant amplifier cavity using a pulsed pump laser. In contrast, here we demonstrate a setup that combines a CW Ti:sapphire oscillator and pulsed amplifier in a single optical cavity, resulting in a compact system. Dichroic beam combination of blue wavelength semiconductor diodes and the green wavelength of a Nd:YAG laser allowed the simultaneous excitation of the Ti:sapphire crystal by both continuous wave and pulsed pump sources. A linewidth of &lt;2 MHz is achieved in continuous wave operation, while the linewidth increases to about 10 MHz in the combined CW+pulsed mode with a pulse duration of 73 ns. A peak pulse intensity of 0.2 kW is achieved, which should enable efficient single-pass second harmonic generation in a nonlinear crystal.

Experimental research on surface characteristics and subsurface damage behavior of monocrystal sapphire induced by helical micro abrasive tools

Sapphire crystals have been widely used in the fields of national defense and optical devices due to good chemical stability and high temperature resistance. In this study, the surface quality, edge fracture characteristic and subsurface damage behavior of sapphire induced by helical micro abrasive tools were experimentally investigated. Effects of geometrical structure of helix micro abrasive tool and process parameters on surface topography, section profile height and surface roughness of sapphire were analyzed. To reveal formation mechanism of subsurface damage of sapphire induced by micro-grinding process, the high temperature chemical corrosion was used to etch sapphire workpiece, and the transformation law of surface morphology and crack layer information with corrosion time were obtained. Besides, effects of geometrical structure of helix micro abrasive tool and process parameters on edge collapse feature and surface fracture length for sapphire crystals were discussed. Furthermore, the ratio of etching surface defect area was put forward to qualitatively the degree of subsurface damage and experimental results indicated that the ratio of etching surface defect area of sapphire was increased with the increase of feed speed and grinding depth. This research can supply a theoretical basis for understanding surface feature and subsurface damage behaviors of monocrystal sapphire involved in micro-grinding process and provide important guidance for high surface quality and low subsurface damage grinding of hard brittle materials.

Naryn-Gol Creek Sapphire Placer Deposit, Buryatia, Russia

A new gem corundum occurrence has been discovered in the Naryn-Gol Creek placer of the Dzhida volcanic field (Russia). In this placer deposit, sapphire associates with large crystals of garnet, spinel, augite, olivine, enstatite, ilmenite, Ti-magnetite, and alkali feldspar. Such a combination of minerals is typical for the placer deposits associated with alkali basalts widely distributed in Southeastern Asia and Australia. We have also found sapphire crystals in phonotephrites of the nearby Cenozoic alkali-basalt paleovolcano Barun Khobol Pravyi, and in basalt sample and trachybasalt from the valley flood basalts. The chemical composition of sapphire is generally typical for ‘basalt’ corundum: it is rich in Fe, and depleted in Ti and Cr. The δ18O SMOW values of corundum and related megacrysts range from 4.6 to 6.8 ‰, thus corresponding to the isotopic signature of igneous rocks. Etched and corroded surfaces of sapphire and other megacrysts indicate that they are in non-equilibrium with their host alkali basalts. Volatile components, CO2 in particular, played a significant role during sapphire formation as gas inclusions reveal.

Thermally Polarized Solid-State Spin Sensor

Quantum sensors based on spin defect ensembles have seen rapid development in recent years, with a wide array of target applications. Historically, these sensors have used optical methods to prepare or read out quantum states. However, these methods are limited to optically polarizable spin defects, and the spin ensemble size is typically limited by the available optical power or acceptable optical heat load. We demonstrate a solid-state sensor employing a nonoptical state preparation technique, which harnesses thermal population imbalances induced by the defects' zero-field splitting. Readout is performed using the recently demonstrated microwave cavity readout technique, resulting in a sensor architecture that is entirely nonoptical and broadly applicable to all solid-state paramagnetic defects with a zero-field splitting. The implementation in this work uses ${\mathrm{Cr}}^{3+}$ defects in a sapphire (${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$) crystal and a simple microwave architecture where the host crystal also serves as the high quality-factor resonator. This approach yields a near-unity filling factor and high single-spin-photon coupling, producing a broadband magnetometer with a minimum sensitivity of $9.7\phantom{\rule{0.2em}{0ex}}\mathrm{pT}/\sqrt{\mathrm{Hz}}$ near 5 kHz.

Thermodynamic Calculations of Ti Ion Concentrations and Segregation Coefficients during Ti:Sapphire Crystal Growth

Thermodynamic Calculations of Ti Ion Concentrations and Segregation Coefficients during Ti:Sapphire Crystal Growth

Color Genesis and Compositional Characteristics of Color-Change Sapphire from Fuping, China

The color-change sapphire occurs in sillimanite-biotite gneiss in Fuping County Hebei province, China, is one of most famous sapphire deposits in China. However, the color genesis, mechanisms of color changing and compositional characteristics of the sapphire remain enigmatic. In this contribution, the coloration in the Fuping sapphire, color changing mechanisms and, compositional characteristics were studied by conventional gemological instruments in conjunction with ultraviolet-visible spectroscopy and Laser ablation inductively coupled plasma mass spectrometer. The results show that the Fuping sapphire is characterized by purple-blue-to-purple-red changed effect and column-shaped, waist drum-shaped with higher degree of euhedral crystal. Reddish brown rutile inclusions with 120° crossed cleavage are commonly observed. The dominant coloring element of the Fuping sapphire is Fe3+, and subordinate elements are Fe2+, Cr3+ and V3+. The color-change effect is caused by trace elements Cr3+ and V3+. The chemical compositions of Fuping color-change sapphires are analogous to those of metamorphic blue sapphires. When geochemically compared with sapphires from Isalo/Ilakaka deposit in Madagascar, Ratnapura deposit in Sri Lanka and Mogok in Myanmar, the Fuping color-change sapphires have distinctly higher rare element contents of Fe, Cr and Ga.

Ultra‐Low Threshold Titanium‐Doped Sapphire Whispering‐Gallery Laser

AbstractTitanium doped sapphire (Ti:sapphire) is a laser gain material with broad gain bandwidth benefiting from the material stability of sapphire. These favorable characteristics of Ti:sapphire have given rise to femtosecond lasers and optical frequency combs. Shaping a single Ti:sapphire crystal into a millimeter sized high quality (Q) whispering gallery mode resonator (Q ≈ 108) reduces the lasing threshold to 14.2 mW and increases the laser slope efficiency to 34%. The observed lasing can be both multi‐mode and single‐mode. This is the first demonstration of a Ti:sapphire whispering‐gallery laser. Furthermore, a novel method of evaluating the gain in Ti:sapphire in the near infrared region is demonstrated by introducing a probe laser with a central wavelength of 795 nm. This method results in decreasing linewidth of the modes excited with the probe laser, consequently increasing their Q. These findings open avenues for the usage of whispering gallery mode resonators as cavities for the implementation of compact Ti:sapphire lasers. Moreover, Ti:sapphire whispering‐gallery laser can also be utilized as an amplifier inside its gain bandwidth by implementing a pump–probe configuration.

Cathodoluminescent Analysis of Sapphire Surface Etching Processes in a Medium-Energy Electron Beam.

Sapphire crystals are widely used in optics and optoelectronics. In this regard, it is important to study the stability of crystals under external influence and the possibility of modifying their surfaces by external influence. This work presents the results of studying the processes of the action of an electron beam with an average energy of 70 keV or less under vacuum conditions on the surfaces of sapphire substrates of various orientations. The effect of etching a sapphire surface by an electron beam in vacuum at room temperature was discovered. The highest etching rate was observed for A-plane sapphire (the average pit etching rate was 10−6 µm3/s). It was shown that the rate of etching of a sapphire surface increased many times over when gold is deposited. An in situ method for studying the process of etching a sapphire surface using cathodoluminescence analysis was considered. Possible mechanisms of sapphire etching by a beam of bombarding electrons were considered. The results obtained could be important in solving the problem of the stability of sapphire windows used in various conditions, including outer space. In addition, the proposed method of metal-stimulated etching of a sapphire surface can be widely used in patterned sapphire substrate (PSS) technology and further forming low-dislocation light-emitting structures on them.