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Growth of the World's Largest Sapphire Crystals
Abstract
Sapphire crystals up to 34 cm diameter, 65 kg, are grown in production using the heat exchanger method (HEM). The properties of sapphire that are important for high technology applications make it difficult to grow as large high-quality single crystal boules. The HEM has been adapted and efforts to grow 50 cm diameter sapphire crystals are in progress. Current applications require the upper limits of sapphire properties to meet current systems demands of the combination of size, purity, crystal perfection with optimum optical and mechanical properties.
... The main difference between HDC and the horizontal Bridgman method is the presence of a localized melt zone (1/3 of the container length) and its slow movement along a container during crystal growth. Compared to the methods of Bridgman [2], heat exchange method (HEM) [3], and temperature gradient technique (TGT) [5], the HDC method offers the advantage of visual monitoring of seed crystal melting and the location of the crystal-melt boundary (CMB). Most commonly, this method produces eutectic ceramics [6,7], crystalline functional materials based on sapphire [8], Y3Al5O12 [9], and beryllium aluminate [10], as well as doped with rare earth and transition elements [11][12][13][14], including gradient doping [15]. ...
... Most commonly, this method produces eutectic ceramics [6,7], crystalline functional materials based on sapphire [8], Y3Al5O12 [9], and beryllium aluminate [10], as well as doped with rare earth and transition elements [11][12][13][14], including gradient doping [15]. The contemporary level of HDC method development has made it possible to significantly increase the size and optical quality of the grown crystals and, in the case of sapphire, to reach record sizes of 457×914×38 mm 3 [16]. The current state of this method is based on research into new refractory structural materials and various crystallization atmospheres, ensuring the formation of large crystals as well as identifying the conditions for the production of optical materials [17][18][19][20]. ...
In order to determine the stability of crystallization conditions, four experimental processes of sapphire crystal growth by the horizontal directional crystallization (HDC) method were carried out. The heater power was regulated based on real-time crystal-melt boundary position data obtained using video monitoring, which provided a stable crystal growth rate. The obtained curves of the dependence of the heater power on the length of the growing crystal indicate the similarity of physical phenomena regardless of the degree of melting of the seed crystal, the length of the container, and the effectiveness of thermal shielding. The analysis of the heat flow balance revealed that heat transfer from the heater is dependent on the melt surface area.
... Owing to its high hardness, dielectric constant in line with the capacitive screen requirements, sapphire crystal can be used in the field of wearable equipment window [7][8][9]. Because of its special characteristics of the atomic level transition, titanium-doped sapphire single crystal was used in highpower laser gain media [10,11]. With the rapid development of these industries, the growth of largesized and high-quality sapphire single crystal has become particularly urgent [12][13][14].As well known, the temperature field is the core part of the large-size sapphire single crystal furnace. ...
... The 0, 5,8,11,15 and 20layer of molybdenum screen were replaced by an equal thickness alumina fiber module, respectively. The radial temperature variation curve of side thermal insulation system can be shown in Figure 4. ...
In this paper, the properties of the combined temperature field of zirconia, alumina and metal have been studied by using the simulation software CGSim. For the first time, a thermal insulation system with the combination of molybdenum, zirconia and alumina screen has been proposed. By keeping the side of the screen thickness unchanged, the heat preservation effect of temperature field turns out to be worse when the molybdenum screen with the same thickness is replaced with alumina. To ensure internal molybdenum screen layers unchanged, the insulation effect of temperature field is significantly enhanced with increasing the thickness of alumina or zirconia, the power consumption is decreased. However, the decrease of power consumption slows down when the thickness of alumina or zirconia increase to a certain thickness.
... The HEM achieves an almost negligible temperature gradient. Notably, the HEM has made significant advancements in producing large, high-quality sapphire crystals [8,9], achieving growth diameters exceeding 200 mm [10,11]. ...
... Heat is extracted by a heat exchanger block in contact with the crucible bottom and is supplied by top and side heaters, Silicon promoting directional solidification [2,[8][9][10]. The heat transfer control achieved by using an independent source and sink of heat in the block-casting process is based on a concept similar to that in the heat exchanger method (HEM) [11], adopted for growing several types of crystals, including Si [12][13][14]. ...
Experiments on directional solidification were carried out to investigate how purification of metallurgical-grade silicon in cast furnaces is affected by changes in heat extraction from and heat supply to their melts. A reference condition analogous to that in the block-casting process was established using top/side heaters to supply heat and a water-cooled base to extract heat from the bottom of a graphite-clay crucible. This condition was modified by (a) changing the crucible bottom material to graphite, (b) increasing the length of the resulting ingot from 100 to 130 mm, and (c) turning off the heaters. Temperatures were measured within the melt and in the furnace environment. The grain macro-microstructures and the macrosegregation of impurities of the ingots were revealed. The cooling rates and solid–liquid interface velocity calculated with a mathematical model increase relative to the reference experiment when the graphite crucible bottom is used or when the top/side heaters are absent. The vertical temperature gradients also increase with the graphite bottom, but significantly decrease without the heaters. Most of the ingots exhibit a purified lower region of columnar grains with straight boundaries, free from intermetallic particles, and an upper region with mixed long and short columnar grains with serrated boundaries, precipitated particles, and higher impurity concentrations. Changing the crucible bottom material from graphite-clay to graphite increases the length of the purified region from 70 (reference condition) to 97 mm, whereas turning off the heaters completely eliminates this region. Although the graphite crucible bottom (with the top/side heaters) yields the longest purified region, the graphite-clay bottom (also with the heaters) gives the lowest impurity concentrations.
... Specifically, its corundum structure R 3c space group ensures stability and availability in high-quality, large-scale wafers, thanks to the cost-effective melt-based growth techniques. 14,15 While high-quality Al 2 O 3 can be grown efficiently in largescale wafers, fabricating nanoscale devices demands meticulous control over defects and impurities, as pristine surface quality is critical. In Al 2 O 3 , any defects, including native defects and impurities, contribute to defect levels in the band structure, a phenomenon well-documented across numerous studies. ...
α-Al2O3 is renowned for its extensive bandgap and diverse applications in electronic and optoelectronic devices. Employing density-functional theory-based methods, this study investigates the feasibility of chalcogen doping (S, Se, Te) in α-Al2O3. Standard modeling tools are utilized to construct α-Al2O3 supercells, focusing on the calculations of individual chalcogen-related and native point defects resulting from single-atom doping. Our analysis systematically explores the formation energies and transition levels associated with chalcogen (S, Se, Te) doping in oxygen (or aluminum) sites in Al-rich (or O-rich) limits. We observe a trend where increasing atomic number (from S to Te) correlates with a higher difficulty in forming anion-doped α-Al2O3, but a lower barrier to cationic doping. The results indicate a preferential substitution of chalcogen atoms for aluminum in O-rich environments. Specifically, in varying oxygen conditions, the dominant defect types, their prevalence, and defect formation energies in α-Al2O3 are significantly altered following chalcogen doping, offering new insights into defect processes in α-Al2O3.
... The applied pressure can be well correlated with the nonlinear model of resonance frequency variation using experimental detection [74]. Sapphire crystals have a unique crystal configuration, good stress resistance, and the ability to withstand high temperatures, making them essential in the production of various components [75,76]. In 2017, John E. Rogers and Yong-Kyu Yoon designed a platinum capacitive component-based pressure sensor for microelectromechanical systems using sapphire, which has high thermal conductivity, high melting temperature, and high resistivity physical properties at high temperatures. ...
In recent years, passive wireless sensors have been studied for various infrastructure sectors, making them a research and development focus. While substantial evidence already supports their viability, further effort is needed to understand their dependability and applicability. As a result, issues related to the theory and implementation of wireless sensors still need to be resolved. This paper aims to review and summarize the progress of the different materials used in different passive sensors, the current status of the passive wireless sensor readout devices, and the latest peripheral devices. It will also cover other related aspects such as the system equipment of passive wireless sensors and the nanogenerators for the energy harvesting for self-powered sensors for applications in contemporary life scenarios. At the same time, the challenges for future developments and applications of passive wireless are discussed.
... Single crystal form of aluminum oxide (Al 2 O 3 ) is called sapphire while polycrystalline form is also known as α-Al 2 O 3 . Single crystal Alumina or sapphire crystals possess some critical properties like better thermodynamic stability, chemical inertness, hardness and shock resistance [1][2][3]. It has wide range of applications in opto-electronic devices, laser-based hosts and nano-electronic devices [4] and geo sciences [5]. ...
Elastic-plastic response of M-plane single crystal sapphire was explored via a nano-indenter with a Berkovich tip. Elastic-plastic transition was observed with eight different points (ranging from 0.30-0.55 mN) subject to respective peak load. Mechanical properties i.e., Oliver-Pharr hardness and elastic modulus were also determined in the onset elastic and elastic-plastic regions. Stable value of elastic modulus estimated from Oliver-Pharr nanoindentation experiments was around 430 ± 15.0 GPa. However, Oliver-Pharr hardness in purely elastic and elastic–plastic (ISE) regions was approximately 2.19 and 2.0 times greater than the non-ISE hardness values respectively. Values of hardness in the non-ISE region were also in compliance with the depth independent hardness calculated through Nix-Gao and proportional specimen resistance models. Additionally, principal stresses and maximum shear stress were estimated on pop-in burst using Hertzian contact theory. Values of the critical resolved shear stress (CRSS) and maximum possible shear strength were also calculated at the first pop-in burst. Moreover, plastic zone size enhanced 1.36 times by shifting of critical load from 0.30 to 0.55 mN. Multiplication of Schmid factor and interplanar spacing indicated two slip systems i.e., prism {011¯1¯} <101¯1¯> and pyramidal {112¯0} <1¯100>, which are verified in the Transmission electron microscopy (TEM) images. Estimated values of maximum contact pressures at respective critical loads were much lower in comparison to phase transformation pressure of sapphire. Maximum tensile stress was also calculated using Hertzian contact theory relations. Obtained value of maximum tensile strength was 3.58 times lower than cleavage fracture stress at the first pop-in.
... C-plane sapphire is an excellent mother substrate for the preparation of Cu(111) films, because it has an acceptable lattice mismatch of 8.6% with the Cu(111) lattice, allowing epitaxial growth of single-crystal Cu film (Figure 19a). [132][133][134] The sufficiently different lattice mismatch provides the stresses required for easy peel-off, reliably providing a flat surface (in direct contact with the sapphire) to achieve a uniform, easily reduced, and exclusively Cu(111)-oriented film. In addition, sapphire has a relatively low cost is available in sizes up to 15 in., has excellent tailorable interfacial properties, and its insulating properties make it compatible with electrochemical processes. ...
Grain boundaries produced during material synthesis affect both the intrinsic properties of materials and their potential for high‐end applications. This effect is commonly observed in graphene film grown using chemical vapor deposition and therefore caused intense interest in controlled growth of grain‐boundary‐free graphene single crystals in the past ten years. The main methods for enlarging graphene domain size and reducing graphene grain boundary density are classified into single‐seed and multiseed approaches, wherein reduction of nucleation density and alignment of nucleation orientation are respectively realized in the nucleation stage. On this basis, detailed synthesis strategies, corresponding mechanisms, and key parameters in the representative methods of these two approaches are separately reviewed, with the aim of providing comprehensive knowledge and a snapshot of the latest status of controlled growth of single‐crystal graphene films. Finally, perspectives on opportunities and challenges in synthesizing large‐area single‐crystal graphene films are discussed. Comprehensive knowledge of and recent progress in controlled growth of single‐crystal graphene films using chemical vapor deposition are presented. The main methods for enlarging graphene domain size and reducing graphene grain‐boundary density are classified into single‐seed and multiseed approaches, based on which detailed synthesis strategies, related mechanisms, key parameters, and limiting factors are summarized.
... The combination of these properties makes it (Al2O3) suitable for a wide range of product applications [Bruni (2013)]. Sapphire shaped crystals are very required in the development of modern science and technology [Duffar (2010)], and they have several medical, military and industrial applications [Duffar (2010); Chandra and Schmid (2001)]: lasers and optical systems, cellular phone glasses, optical fibers, wave guides for surgery, needles for laser therapy and medical power delivery systems [Duffar (2010)]. Czochralski (Cz) growth technique is widely used for producing sapphire oxide single crystals Al2O3 and many other crystals such as, YAG, LiNbO3, GGG, BGO, BaBrCl-BaBrCl: Eu and LGT [Tavakoli (2014); Yan, Shalapska and Bourret (2016); Stelian, Nehari, Lasloudji et al. (2017)] which have many applications in different technologies such as lasers, nonlinear optics, and substrates [Tavakoli (2008)]. ...
In this work we have performed a three-dimensional numerical investigation in order to find the optimal conditions for growing efficiently high quality sapphire crystals with good thermal properties. We have studied thermal instabilities near the melt-crystal interface and the convective heat transfer under the Czochralski (Cz) process. We performed 3-D CFD simulation in cylindrical coordinates and used the Fast Fourier Transform method to analyze the temperature fluctuations. We present a detailed investigation on the effects of the crystal rotation speed and the temperature distribution on thermal instabilities of sapphire melt under forced convection. Where the melt forced convection, the radiative heat transfer and the Marangoni convection, were conducted for Al2O3 melt in the Cz crucible. We have been able to determine the optimal rotation speed giving a planar crystal-melt interface where the symmetry of the flow in the crucible is conserved witch is found to be 13 rpm for the studied case. On the other hand we achieved a visualization of the temperature fluctuations just below the interface. These fluctuations give precious information about the melt-crystal interface, which plays an important role on the quality of the pulled crystal.
... Sapphire (Al2O3) is a very important material because of its specific structure and its exceptional optical, thermal and electrical properties, [1]. In different and various systems and applications, Al2O3 is used widely in optical systems, needles for laser therapy and medical power delivery systems watch windows, cellular phone glasses, optical fibers, and in wave guides for surgery [2,3]. We also cite the use of this material as a optical window material and, filter material for thermal neutron beams and a substrate material for the epitaxial deposition [4]. ...
A three-dimensional numerical study of the convection heat transfer in a simulated Czochralski system is conducted .In this work, the numerical investigation were performed to analyze the free convection in the Czochralski crucible and the temperature fluctuations(thermal instabilities) just below the melt-crystal interface. We used the Finite Volume Method in cylindrical coordinates and the Fast Fourier Transform method for study the free convection, the temperature fluctuations 2 mm near the interface by taking into account the case of non-rotating crystal. In this study the heat transfer, thermal instabilities, melt natural convection, radiative heat transfer, Marangoni convection were conducted for Al2O3 melt in the crucible. Our objective is to show the fluctuations of temperature just below the interface by taking into account the effect of Rayleigh number for determining the crucible heating temperature value, and display the problem and his solution of the natural convection in the Czochralski crucible.
... Owing to its high hardness, dielectric constant in line with the capacitive screen requirements, sapphire crystal can be used in the field of wearable equipment window [7][8][9]. Because of its special characteristics of the atomic level transition, titaniumdoped sapphire single crystal was used in high-power laser gain media [10,11]. With the rapid development of these industries, the growth of large-sized and high-quality sapphire single crystal has become particularly urgent [12][13][14][15][16]. Therefore, the temperature field study of the large-size sapphire single crystal furnace has great application value. ...
In this paper, the temperature field of large-sized (120kg, 200kg and 300kg grade) sapphire single crystal furnace was simulated. By keeping the crucible diameter ratio and the insulation system unchanged, the power consumption, axial and radial temperature gradient, solid-liquid surface shape, stress distribution and melt flow were studied. The simulation results showed that with the increase of the single crystal furnace size, the power consumption increased, the temperature field insulation effect became worse, the growth stress value increased and the stress concentration phenomenon occurred. To solve these problems, the middle and bottom insulation system should be enhanced during designing the large-sized sapphire single crystal furnace. The appropriate radial and axial temperature gradient was favorable to reduce the crystal stress and prevent the occurrence of cracking. Expanding the interface between the seed and crystal was propitious to avoid the stress accumulation phenomenon.
... Many researchers had made a great number of attempts for B removal from silicon with different slags, especially for Na 2 O-SiO 2 and CaO-SiO 2 in general. CaO-SiO 2 [16] , CaO-SiO 2 -Na 2 O [17] , CaO-SiO 2 -CaCl 2 [18][19][20][21] , CaO-SiO 2 -Al 2 O 3 -CaF 2 [22] and Na 2 O-SiO 2 [23][24][25] were performed to refine MG-Si. Tomlinson et al. [26] found that silicate slags of CaO-SiO 2 have much higher density than liquid silicon, which are inconvenient for continuous operation during the furnace run under industrial conditions. ...
Boron (B) removal by slag refining using Na2O-SiO2 was investigated in industrial applications. The experimental results showed that the reasonable ratio range of slag to silicon is about 0.7–0.8; the suitable holding time is about 30 min; the concentration of B is reduced from 1.90 ppmw to 0.17 ppmw by three times slag refining; and the removal efficiency of B reaches 91.1%. Moreover, it is discussed that B in silicon is more inclined to be oxidized by Na2O than SiO2 according to thermodynamic analysis and then volatilized to the atmosphere in the form of Na2B2O4 according to kinetic analysis.
... This unique capability, combined with the ability to control cooling to room temperature, allows this method to be used to grow sapphire boules up to 380 mm in diameter (Khattak and Schmid, 2001;Khattak et al., 2003) and weighing 130 kg ( Figure 5). A program to extend HEM for growth of sapphire crystals up to 500 mm diameter was initiated. ...
... The ability to engineer three significantly different microstructures from the same starting material is also technologically very advantageous. Each microstructure class provides useful properties: single crystal sapphire can be used for high strength armor windows [18] or substrates for LED applications [19], a bimodal microstructure in many materials can enhance toughness as compared to a microstructure with a unimodal grain size distribution [20], and ultra-fine grain alumina can have higher strength and ductility as compared to coarse-grained alumina [21]. ...
Grain boundaries and other interfaces can undergo complexion transitions from one thermodynamic state to another, resulting in discontinuous changes in interface properties such as diffusivity, mobility, and cohesive strength. The kinetics of such complexion transitions has been largely overlooked until recently. Just as with bulk phase transformations, complexion transition kinetics can be represented on time-temperature-transformation (TTT) diagrams. An experimental complexion TTT diagram is presented here for polycrystalline Eu-doped spinel annealed at 1400–1800 °C. This material developed a microstructure with a bimodal grain size distribution, indicating that a complexion transition occurs within this temperature range. The time and temperature dependence of this complexion transition was analyzed and used to produce a grain-boundary complexion TTT diagram for this system. Complexion TTT diagrams have the potential to be remarkably useful tools for manipulating the properties of internal interfaces in polycrystalline metals and ceramics. The development of experimental complexion TTT diagrams is likely to have an important impact on the field of grain-boundary engineering, and hence the development of these experimental diagrams should be an intense area of focus in the coming years.
... Two kinds of sapphire wafers are inspected: one grown by the Kyropoulos method (KYM) and the other optical grade sapphire grown by the heat exchanger method (HEM) (Khattak & Schmid, 2001). The crystal quality of these two kinds of sapphire wafers was verified using X-ray topography and the dislocation densities were measured. ...
Hard X-ray Fabry–Perot resonators (FPRs) made from sapphire crystals were constructed and characterized. The FPRs consisted of two crystal plates, part of a monolithic crystal structure of Al2O3, acting as a pair of mirrors, for the backward reflection (0 0 0 30) of hard X-rays at 14.3147 keV. The dimensional accuracy during manufacturing and the defect density in the crystal in relation to the resonance efficiency of sapphire FPRs were analyzed from a theoretical standpoint based on X-ray cavity resonance and measurements using scanning electron microscopic and X-ray topographic techniques for crystal defects. Well defined resonance spectra of sapphire FPRs were successfully obtained, and were comparable with the theoretical predictions.
... This unique capability, combined with the ability to control cooling to room temperature, allows this method to be used to grow sapphire boules up to 380 mm in diameter (Khattak and Schmid, 2001;Khattak et al., 2003) and weighing 130 kg ( Figure 5). A program to extend HEM for growth of sapphire crystals up to 500 mm diameter was initiated. ...
The main techniques of bulk sapphire crystal growth (i.e., Verneuil, Czochralski, Kyropoulos, HEM – heat exchange method, GSM – gradient solidification method, and horizontal directed crystallization method are described shortly. Melt growth techniques for production of sapphire crystals with predetermined or variable cross-section (i.e., Stepanov, EFG – edge-defined film-fed growth, GES – growth from an element of shape, VST – variable shaping technique, and NCS – noncapillary shaping technique) are shown. After that typical growth techniques for production of sapphire fiber crystals (i.e., EFG, micro zone floating, micro pulling down, ICM – internal crystallization method, and µ-PD – micro pulling down technique) also are presented.
... , Kyropoulos(KY)[4,5]exchange method(HEM)[6]등 다양한 방법들이 시도되고 있다. 이 중 CZ 공법의 경우 용융상에서 단결정 seed를 천천히 끌어올려 성장시키는 방법으로 기존의 Si, Ge 등 의 금속계 단결정을 만드는 데 일반적으로 널리 사용되어 온 공정이다. ...
Sapphire single crystals have been highlighted for epitaxial of gallium nitride films in high-power laser and light emitting diode industries. Among the many crystal growth methods, vertical Bridgman process is an excellent commercial method for growing high quality sapphire crystals with c-axis. In this study, the thermally induced stress in Sapphire during the vertical Bridgman crystal growth process was investigated using a finite element model. A vertical Bridgman process of 2-inch Sapphire was considered for the model. The effects of vertical and transverse temperature gradients on the thermal stress during the process were discussed based on the finite element analysis results.
... phase, nitrogen was used as a carrier gas while growing the InGaN multiple Quantum well to increase the indium incorporation rate[24]. Next, the samples were annealed at 735 o C for 40mins in N 2 ambient to activate the Mg-doped p type GaN layers. ...
This research produces a highly efficient energy saving electroluminescent enhanced blue light emitting diode. The fabrication of this enhanced blue LED involves the growth of a complex semiconductor crystal with advanced heterostructure bandgap design and absolute optimization of the light out-coupling to maximize efficiency. This research discusses innovative ideas which enhance the efficiency of the white light source by critically analyzing the processes involved. It covers the fabrication of blue GaN LED chip, channeled at improving the efficacy of each building block stage from Substrates, Buffers and Epitaxy, to Physics, Processing and Devices, to Lamps, Luminaires and Systems.
... Then, the corresponding nanowires are nucleated at the solid-liquid interface via the vapor-liquid-solid (VLS) mechanism [13][14][15][16][17]. Therefore, the size, density, and shape of the nanowires are directly determined by the diameter, density, and shape of the Au NPs. Meanwhile, owing to the high chemical stability [18,19], wide bandgap, and high thermal tolerance [20], sapphire has been widely adapted in optical and optoelectronic devices such as optical lenses [18,19] and LEDs [21]. In the previous works, various metal films had been studied on oxide surfaces [22][23][24][25]. ...
Au nanoparticles (NPs) have been utilized in a wide range of device applications as well as catalysts for the fabrication of nanopores and nanowires, in which the performance of the associated devices and morphology of nanopores and nanowires are strongly dependent on the size, density, and configuration of the Au NPs. In this paper, the evolution of the self-assembled Au nanostructures and NPs on sapphire (0001) is systematically investigated with the variation of annealing temperature (AT) and dwelling time (DT). At the low-temperature range between 300 and 600 °C, three distinct regimes of the Au nanostructure configuration are observed, i.e., the vermiform-like Au piles, irregular Au nano-mounds, and Au islands. Subsequently, being provided with relatively high thermal energy between 700 and 900 °C, the round dome-shaped Au NPs are fabricated based on the Volmer-Weber growth model. With the increased AT, the size of the Au NPs is gradually increased due to a more favorable surface diffusion while the density is gradually decreased as a compensation. On the other hand, with the increased DT, the size and density of Au NPs decrease due to the evaporation of Au at relatively high annealing temperature at 950 °C.
Keywords: Au nanoparticle; Au piles; Nano-mounds; Annealing temperature; Dwelling time
... LED 기판용 사파이어 잉곳 제조 방법은 아직까지 정형화되어 있지 않고, 제조 방법이 유사한 반 도체 기판용 단결정 잉곳의 제조법을 기반으로 다양한 방법들이 응용되고 있다. 단결정 잉곳의 성장 방법은 매 우 다양하지만, 대구경화가 용이하고 대량생산이 가능한 방법으로는 대표적으로 HEM[3] ...
Sapphire single crystals have been highlighted for epitaxial gallium nitride films in high-power laser and light emitting diode (LED) industries. Among the many crystal growth methods, the Kyropoulos process is an excellent commercial method for growing larger, high-optical-quality sapphire crystals with fewer defects. Because the properties and growth behavior of sapphire crystals are influenced largely by the temperature distribution and convection of molten sapphire during the manufacturing process, accurate predictions of the thermal fields and melt flow behavior are essential to design and optimize the Kyropoulos crystal growth process. In this study, computational fluid dynamic simulations were performed to examine the effects of the crucible geometry aspect ratio on melt convection during Kyropoulos sapphire crystal growth. The results through the evolution of various growth parameters on the temperature and velocity fields and convexity of the crystallization interface based on finite volume element simulations show that lower aspect ratio of the crucible geometry can be helpful for the quality of sapphire single crystal.
The article reviews current state of the art in growing large sapphire crystals used for epitaxial substrates of GaN light-emitting diodes and optical windows. Results of crystal growth with the Czochralski, Kyropoulos, heat-exchanger methods, horizontal directional crystallization, and edge-defined film-fed growth are demonstrated and discussed, along with recommendations of useful tools to increase crystal size.
The attractive physical and chemical properties of corundum lend to this material’s importance in both its natural and synthetic forms. However, much of the quantitative work performed on this material is plagued by unknown inaccuracy as non‐matrix matched reference materials are used. To conduct accurate quantitative analysis using SIMS, matrix‐specific relative sensitivity factors (RSFs) were determined for eighteen trace elements in corundum using dose‐verified ion‐implants. The RSF values ranged from 2.56 × 10²² cm⁻¹ to 3.29 × 10²⁴ with total combined uncertainty values ranging from 7–10%. The RSF values, which are related to ionisation potentials, showed trends consistent with expectations for an insulating oxide. The developed values were applied to calibrate reference materials for LA‐ICP‐MS and to study other natural and synthetic corundum samples. A measurement reference material calibrated for Mg, Si, Ti, V, Fe and Ga produced consistent results over ten sessions in four years with relative standard deviations per trace element of 5% or less, confirming the repeatability of our process. A key finding was that calibrating LA‐ICP‐MS with NIST SRM 610 and 612 glasses to analyse corundum resulted in under‐reporting trace elements Be, Ti, V, Fe, Co, Ni and Ga compared with using matrix‐matched reference materials.
The Cryogenic Sapphire Oscillator (CSO) is currently the best available technology that can provide a relative frequency stability better than 10^-15 for integration times between 1 s and 10,000 s. But, the CSO remains a complex instrument requiring multiple loop controls to achieve the best frequency stability. The possibility to use of the sapphire resonator in a self-sustained MASER oscillator constitutes an elegant alternative to the CSO. Here, the sustaining amplification is achieved through the interaction between a high-Q factor whispering gallery mode and the paramagnetic Fe3+ ions, which are present in small concentration in the sapphire crystal. The Fe3+ ion exhibits three energy states enabling to realize a self-sustaining solid-state maser. Although, this principle has been already experimentally demonstrated few years ago, its development as a truly usable ultra-stable source has not yet been completed, mainly due to the lack of control of the complex physical phenomena involved. This paper completes the previous theoretical work based on the rate equations model. Here we derive the full quantum equations describing the evolution of the Fe3+ ions inside the sapphire lattice and submitted to a pump and a maser signal. The influence of the ions concentration and spin-spin relaxation time will be pointed out.
Sapphire single crystals have been highlighted for epitaxial of gallium nitride films in high-power laser and light emitting diode industries. In this study, the evolution of thermally induced stress in sapphire during the vertical Bridgman crystal growth process was investigated using a finite element model that simplified the real Bridgman process. A vertical Bridgman process of cylindrical sapphire crystal with a diameter of 50 mm was considered for the model. The solidification history effect during the growth was modeled by the quite element technique. The effects of temperature gradient, seeding interface shape and seeding position on the thermal stress during the process were discussed based on the finite element analysis results.
The ideal form of a compact all-optical frequency conversion in a photonic circuit is a monolithical intracavity and resonant nonlinear fiber scheme. However, integrating nonlinear crystalline material that provides significant gain and realizes enhanced second-order nonlinearity (χ⁽²⁾) remains challenging to date. This challenge is due to the inherent conflict in achieving crystallization of nonlinear crystals in a rather unstable state, while attaining a sufficient thermal stability for glass fiber drawing. In addition, existing nano-fabrication techniques, such as the e-beam and focused ion beam, are not necessarily suitable for fabricating such large-scale three-dimensional metamaterials throughout the fiber. We therefore propose and demonstrate, for the first time, a new platform toward an enhanced χ⁽²⁾, where a large-scale harmonic crystal (Si⁴⁺:γ-Al2O3) is monolithically integrated in a hybrid crystal-glass metamaterial fiber cavity. Through a comprehensive nano-scale investigation, along with nonlinear optical measurement, we confirmed a detailed growth mechanism for non-centrosymmetric harmonic crystal directly derived from a centrosymmetric sapphire template. The key to this accomplishment lies in the development of a simple and scalable laser-based fiber drawing that involves the interplay of the inter-crystalline layer forming, the crystal core phase separation, and considerable defective centers. The proof-of-concept developed in this study can be applied to any nonlinear optical fiber comprised of hybrid materials, depending on the practical applications.
During crystal growth in heat exchanger method (HEM) system, the shape of the growth interface changes with the proceeding of the growth process, which limits the crystal size and reduces the quality of the crystal. In this paper, a modified HEM system is proposed to control the interface shape for growth of sesquioxide crystals. Numerical simulation is performed to predict heat transfer, melt flow and interface shape during growth of high melting sesquioxide crystals by the heat exchanger method. The results show that a flat or slightly convex interface shape is beneficial to reduce the solute pileup in front of the melt/crystal interface and decrease the radial temperature gradient inside the crystal during growth of sesquioxide crystals. The interface shape can be controlled by adjusting the gap size d and lower resistance heater power during growth. The growth rate and the melt/crystal interface position can be obtained by two measured temperatures.
Heat transfer and thermal stress during sapphire crystal growth using the heat exchanger method is numerically studied based on two radiation models: the no-slip Rosseland diffusion approximation and the finite volume method (FVM). The results indicate that at the full-diameter growth stage the Rosseland model gives almost the same melt-crystal interface shape and stream function for melt flow as the rigorous FVM. However, it over-predicts the heat transfer through the sapphire domain and fails completely to capture the steep variation in temperature, and the consequent high temperature gradient and thermal stress in the narrow bottom region of the crystal. The temperature gradient and thermal stress in this region predicted by the Rosseland approximation gradually approach the FVM predictions as the optical thickness is increased. However, disparities remain even at a very large optical thickness.
Stochastic simulation (Monte Carlo method) has been used to evaluate the Mo–Al2O3 system at T = 2400 K and p = 1 × 105 Pa in a controlled Ar + H2 atmosphere. The results demonstrate that the qualitative and quantitative compositions of the system differ markedly from those in an inert (Ar) atmosphere: the presence of hydrogen in the system leads to the formation of hydrogen-containing vapor species (OH, H2O, AlOH, AlOOH, AlH, AlH2, and smaller amounts of H2O2, HO2, and AlH3). Increasing the hydrogen concentration in a controlled atmosphere leads to a reduction in the total concentration of oxygen and molybdenum oxides, accompanied by an increase in the concentration of elemental Al in the vapor phase. We have identified the main chemical processes that take place in the system and have shown that such processes have a cyclic nature and involve repeated interactions with the participation of the basic components of the system.
Metal nanoparticles (NPs) with controllable size, density and configuration can significantly enhance the energy conversion efficiency, detection sensitivity and catalytic activity as witnessed in various optoelectronic, optical sensing and electro-catalytic devices due to their shape and size dependent properties. In this work, we systematically investigate the evolution of the size, density and configuration of Pt nanostructures on sapphire (0001). In particular, we have demonstrated four different configuration and evolution of Pt nanostructures with the systematic control of deposition amount (DA) based on the Volmer-Weber growth model in conjunction with the surface energy minimization mechanism, diffusion and coalescence. The various size and configuration of Pt nanostructures with respect to DA are (i) nucleation of mini-sized round shaped Pt NPs (1 ≤ DA ≤ 5 nm), (ii) growth of large sized Pt NPs (10 ≤ DA ≤ 15 nm), (iii) isolated irregular nanostructures (20 ≤ DA ≤ 30 nm) and (iv) coalesced Pt nanostructures (DA ≥ 40). On the other hand, with the increased dwelling time (DT), irregular Pt NPs are fabricated with the increased size and improved uniformity between 0 and 450 s of annealing. The growth of Pt NPs is saturated when the dwelling time reaches the critical value between 900 and 1800 s, which can be attributed to the Ostwald ripening.
Yield improvement and advanced defect control can be identified as the driving forces for modeling of industrial bulk crystal growth. Yield improvement is mainly achieved by upscaling of the whole crystal growth apparatus and increased processing windows with more tolerances for parameter variations. Advanced defect control means on one hand a reduction of the number of deficient crystal defects and on the other hand the formation of beneficial crystal defects with a uniform distribution and well defined concentrations in the whole crystal. This 'defect engineering' relates to the whole crystal growth process as well as the following cooling and optional annealing processes respectively. These topics were illustrated by examples of modeling and experimental results of bulk growth of silicon (Si), gallium arsenide (GaAs), indium phosphide (InP) and calcium fluoride (CaF2). These examples also involve the state of the art of modeling of the most important melt growth techniques, crystal pulling (Czochralski methods) and vertical gradient freezing (Bridgman-type methods).
Advances in CMP Polishing Technologies demystifies scientific developments and technological innovations, opening them up for new applications and process improvements in the semiconductor industry and other areas of precision engineering.
Sapphire single crystals are used widely in a number of modern high-tech applications, such as a substrate material for the epitaxial deposition, optical window material and a filter material for thermal neutron beams. In particular, sapphire single crystals have been highlighted for epitaxial gallium nitride films in high-power laser and light emitting diode (LED) industries. Among the many crystal growth methods, the Kyropoulos process is an excellent commercial method for growing larger, highoptical-quality sapphire crystals with fewer defects. Because the properties and growth behavior of sapphire crystals are influenced largely by the temperature distribution and convection of molten sapphire during the manufacturing process, accurate predictions of the thermal fields and melt flow behavior are essential to design and optimize the Kyropoulos crystal growth process. In this study, computational fluid dynamic simulations were performed to examine the effects of the thermal conditions and geometry on melt convection during Kyropoulos sapphire crystal growth. The evolution of various growth parameters on the temperature, pressure, and velocity profiles were examined using three-dimensional, quantitative, finite volume element-based simulations.
The bubbles were observed as one of the main defects in the as-grown sapphire crystal grown by modified heating exchange method(HEM). The influence of helium flux on thermal field and solid-liquid interface shape in the crucible during growth process were studied using numerical simulation. The influence of Helium flux on the size, shape and distribution of bubbles in the crystal were studied by considering simulation results and experimental results.
A sapphire single crystal growth process by the Vertical-Horizontal Gradient Freezing (VHGF) method was studied by a numerical analysis technique. The heater power was controlled in order to follow the given arbitrary target heater temperature profile through the whole series of the process. Due to the influence of radiation heat transfer, the heater had spatial temperature deviation in spite of the fact that the heater power was imposed uniformly through its whole body. As a structural feature of the VHGF method, temperature at the lower part of crucible was lower than that at the upper part of crucible because it was cooler at the bottom of the furnace. Thus, the movement of the solid/liquid interface was driven in the bottom-to-top direction.
For some applications, ceramic materials must be prepared as single crystals. When used as substrates for thin-film growth [e.g., silicon-on-sapphire (SOS) technology or the growth of superconductor thin films], it is the crystalline perfection of a single crystal that is the important requirement. In optical applications [e.g., the use of ruby and yttrium aluminum garnet (YAG) for laser hosts and quartz and sapphire for optical windows], single crystals are used to minimize scattering or absorption of energy. In piezoelectric materials (e.g., quartz), the optimum properties are obtained in single-domain single crystals. Table 29.1 lists some of the applications that utilize the desirable optical, electrical, magnetic, or mechanical properties of ceramic single crystals.
The formation of blocks in shaped sapphire rods of two crystallographic orientations has been investigated. It is shown that, when growth occurs in the direction of the optical c axis, blocks are formed with a higher probability than in the case of growth in the a direction. A model of formation of blocks in rods of different orientations is proposed. The distribution of residual stresses over sapphire rod cross sections is measured by conoscopy. It is found that stresses increase from the middle of a rod to its periphery and reach 20 MPa.
The Heat Exchanger Method (HEM) of crystal growing was combined with the Fixed Abrasive Slicing Technology (FAST) to produce low-cost, high-quality sapphire substrates for deposition of the GaN family of compounds. Production quantities of 2-inch diameter blanks have been supplied, and 3-inch diameter material has been qualified. Current technology can be used to prepare sapphire blanks up to 6-inch diameter.
Morphologies of metallic inclusions observed in sapphire crystals grown by the vertical Bridgman (VB) technique using a tungsten (W) crucible were investigated. Square- or hexagonal-shaped inclusions 2-5 mu m in size were observed in sapphire crystals around the interface between the seed and the grown crystal. It was found that such inclusions consisted of W metal used for the crucible. The morphology of some of the inclusions reflects a rhombic dodecahedron which is based on the cubic structure of W and is surrounded by {110} faces. It is probable that inclusions form in the sapphire melt during the crystal growth process, and then sink in the melt to the growth interface due to the high density of W.
Ti:sapphire single crystals are important tunable laser materials. Recent researches are focusing on how to grow large-size and high-quality Ti:sapphire crystals to meet the demand of high-energy laser development. 30 kg grade Ti:sapphire of 0.2% ion concentrations has been successfully grown by the Kyropoulos (KY) technique through the optimization of the growth process. The experimental tests show that the crystal has a homogeneous titanium distribution and good optical performance. Meanwhile, the figure of merit (FOM) value of the crystal is larger than 200. The present paper is of great importance for the growth and laser application of large-size Ti:sapphire crystal.
In this study, the process of magnetic abrasive polishing (MAP), installed permanent magnet to improved magnetic force on surface of wafer, was used for planarization of sapphire wafer. The surface roughness and polished area were investigated according to polishing time. The results showed that the improving strategy of magnetic force was helpful to improvethe roughness of sapphire and the polished area was gradually increased according to polishing time since the frictional heat between magnetic abrasives and wafer surface caused the improvement of fluidity for magnetic abrasive. In addition to, for using medium based on oil, the better improvement of surface roughness was achieved comparing to silicone gel medium of high viscosity.
A new technique is proposed in the traditional vertical Bridgman growth of sapphire crystals, in which thin-neck formation follows the initial seeding. Low-angle grain boundaries generated at the periphery of the seeding interface were eliminated at the thin neck, and the c-axis sapphire crystals with main bodies free from low-angle grain boundaries were grown. (C) 2014 Published by Elsevier B.V.
We present a simple approach to improving the quality of CVD grown graphene, exploiting a Cu(111) foil catalyst. The catalyst is epitaxially grown by evaporation on a single crystal sapphire substrate, thickened by electroplating, and peeled off. The exposed surface is atomically flat, easily reduced, and exclusively of (111) orientation. Graphene grown on this catalyst under atmospheric CVD conditions and without wet chemical prereduction produces single crystal domain sizes of several hundred micrometers in samples that are many centimeters in size. The graphene produced in this way can easily be transferred to other substrates using well-established techniques. We report mobilities extracted using field-effect (as high as 29 000 cm(2) V(-1) s(-1)) and Hall bar measurement (up to 10 100 cm(2) V(-1) s(-1)).
The anisotropic growth of large-size sapphire single crystals along different pulling directions was studied on the basis of the chemical bonding theory of single crystal growth and practical Czochralski growth. The projection of thermodynamic morphology of sapphire single crystal respectively along [210], [110], [001], and [001] rotated 57.62° directions can be used to confirm the growth directions of surfaces that are preferred to be exposed thermodynamically in Czochralski growth. Starting from these thermodynamically preferred directions, the possible radial directions that are normal to the four typical pulling directions by kinetic controls have been identified by anisotropic chemical bonding distributions of sapphire single crystal. Chemical bonding calculations demonstrate that the lower pulling rate should be designed when Raxial/Rradial > 1, whereas the higher pulling rate should be designed when Raxial/Rradial < 1. The anisotropic chemical bonding conditions demonstrate the lowest chemical bonding density along the radial directions of sapphire single crystal when it grows along the [001] pulling direction. Taking [001] as the pulling direction in practical growth, a 2″ sapphire single crystal was grown via the Czochralski method with a growth rate of 2–3 mm/h. Our present work shows the effect of anisotropy on the Czochralski growth of large-size single crystals, which can provide a theoretical guide in practical growth from both thermodynamic and kinetic viewpoints.
Quite often sapphire shaped crystals contain specific defects called bubbles of average diameter higher than 100 μm or microbubbles of diameter smaller than 10 μm. These defects strongly affect the crystal properties. Bubbles of 100 μm in diameter have been observed in the molten zone during micropulling-down of sapphire fibers. Before their incorporation inside the crystal, they show a periodic oscillation and consequently deform the crystallization interface. These observations are discussed with reference to the available literature.
Based on the growth of 3-inch diameter c-axis sapphire using the vertical Bridgman (VB) technique, numerical simulations were made and used to guide the growth of a 6-inch diameter sapphire. A 2D model of the VB hot-zone was constructed, the seeding interface shape of the 3-inch diameter sapphire as revealed by green laser scattering was estimated numerically, and the temperature distributions of two VB hot-zone models designed for 6-inch diameter sapphire growth were numerically simulated to achieve the optimal growth of large crystals. The hot-zone model with one heater was selected and prepared, and 6-inch diameter c-axis sapphire boules were actually grown, as predicted by the numerical results.
Boron removal from metallurgical grade silicon (MG-Si) using a calcium silicate slag was studied. The results show that it is impossible basically to remove boron using a pure SiO2 refining. The oxidizing ability of CaO–SiO2 slag for boron removal was characterized by establishing the thermodynamic relationship between the distribution coefficient of boron (LB) and the activities of SiO2 and CaO. The experimental results show that the distribution coefficient and the removal efficiency of boron are greatly improved with the increase of CaO proportion in the slag. The maximal value of LB reaches 1.57 with a slag composition of 60%CaO-40%SiO2 (mass fraction). The boron content in the refined silicon is reduced from 18×10−6 to 1.8×10−6 using slag refining at 1600 °C for 3 h with a CaO–SiO2/MG-Si ratio of 2.5, and the removal efficiency of boron reaches 90%.
The growth of sapphire by the traditional vertical Bridgman (VB) method was studied by using various shapes of seed crystals and tungsten (W) crucibles shaped to match the seeds. Approximately 2-in. diameter, c-axis sapphire single crystals were reproducibly grown from three kinds of seed: thin, tapered and full diameter. Factors relating seed type to single-crystal growth are discussed, including the reproducibility of seeding processes, and the generation and elimination of low-angle grain boundaries (LAGBs). What was learned facilitated the subsequent growth of large-diameter, 3-, 4- and 6-in., c-axis single-crystal sapphires from full-diameter seeds.
Large sapphire boules, up to 34 cm diameter, 65 kg, are being grown by the heat exchanger method (HEM) and even larger sizes are sought to meet future requirements of advanced optical systems. These boules, especially in large sizes, exhibit lattice distortion and light scatter in a very narrow range. A qualitative grading system has been developed to characterize sapphire. Windows of five grades and different orientations were prepared and measured for refractive index homogeneity to evaluate transmitted wavefront distortion. The data showed that the refractive index homogeneity for all samples was in the 10-7 (0.1 ppm) range. The fact that lattice distortion does not affect the transmitted wavefront allows fabrication of large sapphire windows in production mode at low cost. Bibtex entry for this abstract Preferred format for this abstract (see Preferences) Find Similar Abstracts: Use: Authors Title Abstract Text Return: Query Results Return items starting with number Query Form Database: Astronomy Physics arXiv e-prints
The titanium-doped sapphire (Ti:Al2O3) laser is a relatively recent addition to the class of widely tunable lasers. Recent material growth has provided samples of high optical quality and high figure of merit. Cross sections, tuning methods, and large boule evaluation of heat exchanger method growth runs are discussed.
Spectroscopic measurements and laser performance of Ti:Al2O3 are discussed in detail. Data on absorption and fluorescence spectra and fluorescence lifetime as a function of temperature are presented. Laser characteristics observed with pulsed-dye-laser, frequency-doubled Nd:YAG-laser, and argon-ion-laser pumping are covered and show that nearly quantum-limited conversion of pump radiation can be achieved, along with tuning over the wavelength range 660–986 nm.
The crystal growth of high melting point oxide crystals by the Czochralski technique is described. The group of crystals was selected with emphasis on laser hosts and includes Ti**3** plus -doped sapphire, gadolinium scandium gallium garnet, and its aluminum analog, yttrium aluminum garnet. Material preparation, growth experiments design considerations, consideration for scaling up the crystal size, and crystal evaluation are included. Results of work leading to growth of 3 in. diam YAG crystals are presented. The paper presents a general approach to crystal growth including crucible material selection, atmosphere control, and fluid dynamics.
No longer considered an exotic material, sapphire has been made useful for applications across the spectrum by improved crystal growth and fabrication techniques.
Large sapphire boules are grown free of light scatter by Heat Exchange Method (HEM). Sapphire optical components of various sizes, shapes, and orientations can be fabricated out of this material to produce scatter-free optics. The process has also been adapted for growth of doped-sapphire crystals for solid-state laser applications.
The Schmid-Viechnicki technique which has been developed specifically to provide large, high quality single crystals for industry, is described. Its scale-up and various crystals that have been successfully grown are covered. The Schmid-Viechnicki technique is distinct from all other techniques in that the solid/liquid interface advances three dimensionally. Variously shaped crystals can be grown by solidifying in crucibles with the desired configuration.
Sapphire has a unique combination of desirable mechanical and optical properties. The Heat Exchanger Method has been developed to produce large-sized, high-quality sapphire for industrial applications. Fabrication technology has been developed to produce large optical components with super flat and smooth surfaces for IR and VUV optics.
The Heat Exchanger Method (HEM), a new crystal growth process, is in commercial production for 20 cm diameter sapphire crystals and 40 cm diameter silicon ingots for optical applications. The simplicity of the HEM combined with a very high degree of control of the submerged, solid-liquid interface allows growth of high-quality crystals. The HEM is also being adapted for the growth of Co:MgF2, Ti:A1203 and Cr:A1203 crystals for laser applications.
The book treats the spectroscopic and generational characteristics of
activated dielectric laser crystals, and examines the theoretical
aspects of stimulated emission from these crystals. Topics discussed
include the Stark structure of the levels of activated ionic crystals,
and the luminescence-generational characteristics of Y2O3-Al2O3
crystals. A wavelength index is presented for activated dielectric solid
state laser emission, and a table is given summarizing the
characteristics of the activated crystals.
Recently, the U.S. Army Research Laboratory (ARL) has focused increased attention on the development of transparent armor material systems for a variety of applications. Future combat and non-combat environments will require lightweight, threat adjustable, multifunctional, and affordable armor. Current glass/polycarbonate technologies are not expected to meet the increased requirements. Results over the past few years indicate that the use of transparent crystalline ceramics greatly improve the performance of a system. These results coupled with recent processing and manufacturing advances have revitalized the interest in using transparent ceramics for armor systems. The materials currently under investigation at ARL are magnesium aluminate spinel (MgAl2O4), aluminum oxynitride spinel (AlON), single crystal sapphire (Al2O3), glasses, and glass-ceramics. The polymers under investigation are polycarbonate (PC) and polyurethane (PU). An overview of current ARL efforts in these areas, including the motivation for using transparent ceramics, the requirements, the potential applications, and the ongoing processing research will be reviewed.
Heat treatments of finished sapphire compression and biaxial flexure specimens increased sapphire's high temperature strength. Heat treatments of sapphire specimens at 1450 degrees C for 48 hours in an air atmosphere enriched with oxygen increased the compression strength by 60 percent and biaxial flexure strength at 600 degrees C by 45 percent over untreated samples.
Recent interest in monitoring systems requires very large optical windows that are transmitting over a wide spectral range. Some of the other requirements involve durability, high strength and robustness to withstand severe environments. Therefore, sapphire has been required for these applications. The Heat Exchanger Method (HEM)TM has been used to produce very large sapphire crystals primarily for optical applications. Crystals of 20 cm and 25 cm diameter have been produced in production for over 20 years. Presently, 34 cm diameter boules have been adopted in production, and 50 cm diameter sapphire growth is currently in development. Results of progress and characterization data of the boules will be presented.
Sapphire is an ideal visible-MWIR window due to its excellent optical and mechanical properties and its availability in large sizes up to 340-mm diameter boules. Anticipated applications for new, high performance optical systems call for even larger, 450-750 mm diameter, windows. The present effort has focused on producing 500-mm diameter sapphire boules using the Heat Exchanger Method. Three experimental growth runs demonstrated the feasibility of producing 500-mm diameter sapphire boules. Completely crack- free boules have not been grown, but large size sapphire pieces up to 400 mm by 280 mm have yielded from these experimental runs.
The strength of sapphire decreases more rapidly with increasing temperature than does the strength of polycrystalline alumina and many other ceramics. Twinning on the rhombohedral plane (1102) at elevated temperature induced by compression along the crystallographic c-axis [0001] appears to initiate failure and accounts for the decreased strength. The tensile strength of sapphire along the (alpha) - [1120] or c-axes is constant to within approximately 30% between 20 degree(s) and 800 degree(s)C. Compressive strength along the (alpha) -axis is also constant to within approximately 20%. However, compressive strength along the c-axis falls by > 95% (from 2000 MPa to less than 100 MPa) between 20 degree(s) and 800 degree(s)C.
Sapphire is an ideal optical material and is in used for window and dome applications. The anisotropic properties of sapphire affect the production of high-quality components. Out of the three major orientations, c-axis, a-axis or m- axis, the c-axis is preferred for optical applications as it is the zero birefringence orientation. This orientation is difficult to grow with high quality. Therefore, components are fabricated by sectioning from the sides of a- or m- boules. The anisotropic properties also present problems in grinding and polishing windows for precision optical applications. The degree of difficulty varies with the orientation selected. For hemispherical domes involving polishing of several orientations, it is difficult to achieve a good figure. The choice for larger diameter windows is limited to a- or m-orientation; the m-orientation may be preferable due to the geometry of fabrication-induced stress.
Crack-free near-net-shaped [0001] orientation sapphire blanks of nearly hemispherical shape and 8 cm diameter have been produced directly from the melt by the heat exchanger method. Molybdenum preforms placed in the crucible did not perturb the solid-liquid interface during growth. The inside and outside curvature of these blanks can be accurately controlled.
Single crystal Al2O3 (sapphire) is a candidate material for various window applications. A gradient furnace technique has been developed for the growth of large sapphire disks, 7.3 cm in diameter and 1.5 cm thick, from the melt in molybdenum crucibles. The disks are free of gas bubbles and inclusions and consist of several large pie-shaped grains. Within the grains dislocation densities of 100,000/sq.cm. have been measured. The disks are essentially transparent to radiation from wavelengths of 0.25 micrometers in the ultraviolet spectrum to 4.5 micrometers in the infrared spectrum.
Sapphire optical materials have limited index of refraction homogeneity. This homogeneity can limit the degree of transmitted wavefront error achievable with current, conventional optical finishing practices. Current practices can not typically compensate well for the localized inhomogeneities in the sapphire substrates resulting in limited transmitted wavefront values. Emerging transmitted wavefront requirements exceed those achievable with current practices. Hughes Danbury Optical Systems recently completed a successful demonstration program in which computer controlled polishing was applied to the fabrication of very low transmitted wavefront error sapphire window. This technique involves measuring the windows in transmission and then polishing them in localized areas to remove the wavefront errors arising from the material index inhomogeneity. The net effect of each localized correction is a high fidelity transmitted wavefront over each subaperture. In the demonstration completed, we stated with windows fabricated to the limit of current, conventional practices. Applying computer controlled polishing, the transmitted wavefront quality was rapidly improved by a factor of up to five over the starting value. These results not only satisfied emerging requirements, but the process also resulted in satisfying parallel requirements of extreme surface smoothness and scatter as defined by the bi- directional transmittance distribution function. This paper addresses the process developed, its results, benefits and applications.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
Sapphire is an ideal visible-MWIR window due to its excellent optical and mechanical properties and its availability in large sizes up to 340-mm diameter boules. Anticipated applications for new, high performance optical systems call for even larger, 450-750 mm diameter, windows. The present effort has focused on producing 500-mm diameter sapphire boules using the Heat Exchanger Method. Three experimental growth runs demonstrated the feasibility of producing 500-mm diameter sapphire boules. Completely crack- free boules have not been grown, but large size sapphire pieces up to 400 mm by 280 mm have yielded from these experimental runs.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
We report a set of optical absorption measurements on x-irradiated high-purity sapphire. The results of the photothermal deflection absorption measurements at 1064 nm show an increase of the absorption at the x-irradiated areas. The x-ray damage recovery is achieved through annealing, where the absorption level at 1064 nm is brought from an average level of ~80 ppm cm-1 to ~24 ppm cm-1 . UV-Vis spectroscopy results suggest that the residual absorption at 1064 nm is due to complex clusters of Ti and Fe ions and oxygen vacancies. We suggest that a further reduction of Ti and Fe in sapphire (<0.1 ppm) as well as oxygen vacancies (through post growth oxidizing annealing) would further reduce the absorption. Moreover, the absorption level of 20 ppm cm-1 remains within the requirements of the second generation laser interferometric gravitational-wave detectors.
Measurements are reported on the optical absorption of various samples of monocrystalline sapphire from various manufacturers, at 1 μm wavelength. The lowest observed absorption coefficient was 3.1 ppm/cm comparable to the best optical glass materials. The absorption coefficient showed variations within samples ∼ 30% and was not correlated with metal impurity concentration.
Nearly stoichiometric MgAl 2 O 4 spinel single crystals can be grown by a gradient furnace technique in molybdenum crucibles with an inert‐gas atmosphere of industrial‐grade argon, high‐purity argon, or technical‐grade helium. There is a reaction between MgO in the melt and the molybdenum crucibles which results in bands of molybdenum metal inclusions in the boule, although molybdenum concentration away from the bands is less than 100 ppm. This reaction can be minimized by ensuring that the starting materials are well reacted by high‐temperature heat treatment to form MgAl 2 O 4 before melting. Similarly, a greenish‐brown discoloration which arises from oxygen deficiency in the boules may be eliminated by reacting the starting materials completely to MgAl 2 O 4 . A loss of nearly 2 mole% MgO generally occurs during the growth of a boule. This loss results in the formation of a ``skin'' of nonstoichiometric spinel on the outside of the boule. This ``skin'' is the last material to solidify and is highly strained upon cooling. It cracks and these cracks propagate throughout the boule. The loss of MgO also causes the formation of a second phase, α‐Al 2 O 3 , when the spinel is annealed at 1150 and/or 1550°C for periods of time that are less than 30 h. This second‐phase precipitate causes variations in the Knoop 100 hardness of spinel between 1360 and 1820 kg/mm2. Because of the difficulty in controlling composition, cracking, and the changes in hardness upon annealing at temperatures where silicon is commonly deposited on single‐crystal insulating substrates, it is questionable whether spinel will find widespread applicability as an insulating substrate material.
We present a feasibility study of using sapphire beamsplitters and test masses in laser interferometer gravitational wave detectors. The internal thermal noise, optical losses and birefringence effects are analysed. Suspension losses are investigated. Experimental data on birefringence is presented. The conclusions are generally positive.
Tezisy dokladov na IV Vses. Soveslich, po rostu kristallov, Chast II (Summaries of reports presented to the Fourth All-Union Conference on the Growth of Crystals, Part II)
- Bagdasarov
- S Kh
Bagdasarov, Kh.S. Tezisy dokladov na IV Vses. Soveslich, po rostu kristallov, Chast II (Summaries of reports presented to the Fourth All-Union Conference on the Growth of Crystals, Part II), Izdvo Arm.SSR, Erevan, 1972, p. 6.
Infrared (IR) window and domes data base
- K Kogler
- R Lane
K. Kogler, R. Lane, Infrared (IR) window and domes data base, Proceedings of 8th DoD Electromagnetic Windows Symposium, 2000, p. 434.