Browsing by Subject "crystal"
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Item Long-Wavelength Reflecting Filters Found in the Larval Retinas of One Mantis Shrimp Family (Nannosquillidae)(Elsevier B.V., 2019-09-23) Feller, Kathryn D.; Wilby, David; Jacucci, Gianni; Vignolini, Silvia; Mantell, Judith; Wardill, Trevor J.; Cronin, Thomas W.; Roberts, Nicholas W.Both vertebrates and invertebrates commonly exploit photonic structures adjacent to their photoreceptors for visual benefits. For example, use of a reflecting structure (tapetum) behind the retina increases photon capture, enhancing vision in dim light [1, 2, 3, 4, 5]. Colored filters positioned lateral or distal to a photoreceptive unit may also be used to tune spectral sensitivity by selective transmission of wavelengths not absorbed or scattered by the filters [6, 7, 8]. Here we describe a new category of biological optical filter that acts simultaneously as both a transmissive spectral filter and narrowband reflector. Discovered in the larval eyes of only one family of mantis shrimp (stomatopod) crustaceans (Nannosquillidae), each crystalline structure bisects the photoreceptive rhabdom into two tiers and contains an ordered array of membrane-bound vesicles with sub-wavelength diameters of 153 ± 5 nm. Axial illumination of the intrarhabdomal structural reflector (ISR) in vivo produces a narrow band of yellow reflectance (mean peak reflectivity, 572 ± 18 nm). The ISR is similar to several synthetic devices, such as bandgap filters, laser mirrors, and (in particular) fiber Bragg gratings used in optical sensors for a wide range of industries. To our knowledge, the stomatopod larval ISR is the first example of a naturally occurring analog to these human-made devices. Considering what is known about these animals’ visual ecology, we propose that these reflecting filters may help improve the detection of pelagic bioluminescence in shallow water at night.Item Low Temperature Flux Growth of 2H-SiC and β-Gallium OxideSingh, N. B.; Choa, Fow-Sen; Su, Ching-Hua; Arnold, Bradley; Kelly, LisaWe present brief overview of our study on the low temperature flux growth of two very important novel wide bandgap materials 2H-SiC and β-gallium oxide (β-Ga₂O₃). We have synthesized and grown 5mm to 1cm size single crystals of β-gallium oxide (β-Ga₂O₃). We used a flux and semi wet method to grow transparent good quality crystals. In the semi-wet method Ga₂O₃ was synthesized with starting gallium nitrate solution and urea as a nucleation agent. In the flux method we used tin and other metallic flux. This crystal was placed in an alumina crucible and temperature was raised above 1050 ºC. After a time period of thirty hours, we observed prismatic and needle shaped crystals of gallium oxide. Scanning electron microscopic studies showed step growth morphology. Crystal was polished to measure the properties. Bandgap was measured 4.7eV using the optical absorption curve. Another wide bandgap hexagonal 2H-SiC was grown by using Si-Al eutectic flux in the graphite crucible. We used slight AlN also as the impurity in the flux. The temperature was raised up to 1050C and slowly cooled to 850C. Preliminary characterization results of this material are also reported.