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Transparent Ceramics
Published in Debasish Sarkar, Ceramic Processing, 2019
Samuel Paul David, Debasish Sarkar
To give a better insight into the need for transparent ceramics over conventional crystalline media, a brief look into the development differences between YAG single crystals and YAG ceramics for laser applications is provided. Rare earth-doped yttrium aluminum garnet is still the most promising laser-gain media of last 50 years after the first laser demonstration by Geusic et al. in Bell Laboratories in 1964 [3]. Single crystals of YAG are generally grown by Czochralski or Bridgman methods using expensive iridium crucible because of the high melting point of YAG (~1940°C). The growth period usually demands several days to grow to a large size (growth rate ~1 mm/h) crystals (>10 cm) which are essential to build high-power solid-state lasers. Adding to the woes, thermal stress caused during the growth process creates stress-induced birefringence in the crystal, as in Figure 3.2, that limits the usable material to less than 60% of the grown boule.
Detector Fabrication
Published in Alan Owens, Semiconductor Radiation Detectors, 2019
For epitaxial produced material, the end product is a wafer of semiconducting material between 2 inches and 8 inches in diameter, although for most compound semiconductors, wafer sizes are limited to 2 inches. Once processed and patterned with particular device structures, on-wafer testing of each chip is carried out and the wafer is separated into individual chips, commonly referred to as wafer dicing. Depending on the wafer material and its thickness, dicing is achieved by (i) scribing along selected crystallographic planes and breaking, (ii) cutting with a high precision diamond blade or (iii) laser cutting. For melt grown crystals, the ingot or boule is first sliced into wafers using a diamond tip or wire saw and the surfaces lapped and polished prior to patterning and dicing. All other operations beyond this point are identical.
An Assorted Outlook on the Versatility of Thermoluminescence Techniques
Published in Sanjay J. Dhoble, B. Deva Prasad Raju, Vijay Singh, Phosphors Synthesis and Applications, 2018
Sumedha Tamboli, S. J. Dhoble, B. C. Bhatt
In this method crystals are grown by slow cooling of a small molten zone. It is a method of purifying crystals, in which a narrow region of a crystal is molten, and this molten zone is moved along the crystal. The crystal is formed with a preferential orientation under these conditions. The principle is that the segregation coefficient, which is the ratio of an impurity in the solid phase to that in the liquid phase, usually is less than 1. Therefore, at the solid-liquid boundary, the impurity atoms will diffuse to the liquid region. Thus, by passing a crystal boule through a thin section of a furnace slowly, such that only a small region of the boule is molten at any time, the impurities will be segregated at the end of the crystal. Because of the lack of impurities in the leftover regions, which solidify, the boule can grow as a perfect single crystal if a seed crystal is placed at the base to initiate a chosen direction of crystal growth. When high purity is required, such as in the semiconductor industry, the impure end of the boule is cut off and the refining is repeated. In zone refining, solutes are segregated at one end of the ingot in order to purify the remainder or to concentrate the impurities. Lithium fluoride has been produced by using this method by Soifer et al. (1965) [77].
Correlated Debye model for atomic motions in metal nanocrystals
Published in Philosophical Magazine, 2018
The expressions derived so far implicitly refer to crystals of large dimension: the VDOS in Figure 2, for example, was measured on a single crystal of Pd, specifically grown for neutron scattering measurements in the shape of a boule, 3′′ long by ca 0.75′′ diameter [21].