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Sample records for a-axis sapphire substrates

  1. Birefringence measurements in single crystal sapphire and calcite shocked along the a axis

    NASA Astrophysics Data System (ADS)

    Tear, Gareth R.; Chapman, David J.; Eakins, Daniel E.; Proud, William G.

    2017-01-01

    Calcite and sapphire were shock compressed along the <10 1 ¯0 > direction (a axis) in a plate impact configuration. Polarimetery and Photonic Doppler Velocimetery (PDV) were used to measure the change in birefringence with particle velocity in the shock direction. Results for sapphire agree well with linear photoelastic theory and current literature showing a linear relationship between birefringence and particle velocity up to 310 m s-1. A maximum change in birefringence of 5% was observed. Calcite however showed anomolous behaviour with no detectable change in birefringence (less than 0.1%) over the range of particle velocities studied (up to 75 m s-1).

  2. Optical waveguide formed by cubic silicon carbide on sapphire substrates

    NASA Technical Reports Server (NTRS)

    Tang, Xiao; Wongchotigul, Kobchat; Spencer, Michael G.

    1991-01-01

    Optical confinement in beta silicon carbide (beta-SiC) thin films on sapphire substrate is demonstrated. Measurements are performed on waveguides formed by the mechanical transfer of thin beta-SiC films to sapphire. Recent results of epitaxial films of SiC on sapphire substrates attest to the technological viability of optoelectronic devices made from silicon carbide. Far-field mode patterns are shown. It is believed that this is the first step in validating a silicon carbide optoelectronic technology.

  3. Integrated Optical Pumping of Cr & Ti-Doped Sapphire Substrates With III-V Nitride Materials

    DTIC Science & Technology

    2005-08-24

    the Cr in sapphire could also permit the construction of white light LEDs . Ultimately, an integrated III-V Nitride optical pump for Ti:Sapphire could...substrates by MOCVD. 2. Characterization of doped sapphire/ InGaN structures byPL to simulate electrical injection by laser or LED device structures Part 2 1...Cr:sapphire substrate. Solid line is the spectrum of blue and red light emitted by InGaN LED epitaxially grown on Cr:sapphire substrate. The light was collected

  4. Lattice-Matched Semiconductor Layers on Single Crystalline Sapphire Substrate

    NASA Technical Reports Server (NTRS)

    Choi, Sang; King, Glen; Park, Yeonjoon

    2009-01-01

    SiGe is an important semiconductor alloy for high-speed field effect transistors (FETs), high-temperature thermoelectric devices, photovoltaic solar cells, and photon detectors. The growth of SiGe layer is difficult because SiGe alloys have different lattice constants from those of the common Si wafers, which leads to a high density of defects, including dislocations, micro-twins, cracks, and delaminations. This innovation utilizes newly developed rhombohedral epitaxy of cubic semiconductors on trigonal substrates in order to solve the lattice mismatch problem of SiGe by using trigonal single crystals like sapphire (Al2O3) as substrate to give a unique growth-orientation to the SiGe layer, which is automatically controlled at the interface upon sapphire (0001). This technology is different from previous silicon on insulator (SOI) or SGOI (SiGe on insulator) technologies that use amorphous SiO2 as the growth plane. A cubic semiconductor crystal is a special case of a rhombohedron with the inter-planar angle, alpha = 90 deg. With a mathematical transformation, all rhombohedrons can be described by trigonal crystal lattice structures. Therefore, all cubic lattice constants and crystal planes (hkl) s can be transformed into those of trigonal crystal parameters. These unique alignments enable a new opportunity of perfect lattice matching conditions, which can eliminate misfit dislocations. Previously, these atomic alignments were thought to be impossible or very difficult. With the invention of a new x-ray diffraction measurement method here, growth of cubic semiconductors on trigonal crystals became possible. This epitaxy and lattice-matching condition can be applied not only to SiGe (111)/sapphire (0001) substrate relations, but also to other crystal structures and other materials, including similar crystal structures which have pointgroup rotational symmetries by 120 because the cubic (111) direction has 120 rotational symmetry. The use of slightly miscut (less than

  5. Increased effective reflection and transmission at the GaN-sapphire interface of LEDs grown on patterned sapphire substrates

    NASA Astrophysics Data System (ADS)

    Dongxue, Wu; Ping, Ma; Boting, Liu; Shuo, Zhang; Junxi, Wang; Jinmin, Li

    2016-10-01

    The effect of patterned sapphire substrate (PSS) on the top-surface (P-GaN-surface) and the bottom-surface (sapphire-surface) of the light output power (LOP) of GaN-based LEDs was investigated, in order to study the changes in reflection and transmission of the GaN-sapphire interface. Experimental research and computer simulations were combined to reveal a great enhancement in LOP from either the top or bottom surface of GaN-based LEDs, which are prepared on patterned sapphire substrates (PSS-LEDs). Furthermore, the results were compared to those of the conventional LEDs prepared on the planar sapphire substrates (CSS-LEDs). A detailed theoretical analysis was also presented to further support the explanation for the increase in both the effective reflection and transmission of PSS-GaN interface layers and to explain the causes of increased LOP values. Moreover, the bottom-surface of the PSS-LED chip shows slightly increased light output performance when compared to that of the top-surface. Therefore, the light extraction efficiency (LEE) can be further enhanced by integrating the method of PSS and flip-chip structure design. Project supported by the National High Technology Program of China (No. Y48A040000) and the National High Technology Program of China (No. Y48A040000).

  6. Layer matching epitaxy of NiO thin films on atomically stepped sapphire (0001) substrates

    PubMed Central

    Yamauchi, Ryosuke; Hamasaki, Yosuke; Shibuya, Takuto; Saito, Akira; Tsuchimine, Nobuo; Koyama, Koji; Matsuda, Akifumi; Yoshimoto, Mamoru

    2015-01-01

    Thin-film epitaxy is critical for investigating the original properties of materials. To obtain epitaxial films, careful consideration of the external conditions, i.e. single-crystal substrate, temperature, deposition pressure and fabrication method, is significantly important. In particular, selection of the single-crystal substrate is the first step towards fabrication of a high-quality film. Sapphire (single-crystalline α-Al2O3) is commonly used in industry as a thin-film crystal-growth substrate, and functional thin-film materials deposited on sapphire substrates have found industrial applications. However, while sapphire is a single crystal, two types of atomic planes exist in accordance with step height. Here we discuss the need to consider the lattice mismatch for each of the sapphire atomic layers. Furthermore, through cross-sectional transmission electron microscopy analysis, we demonstrate the uniepitaxial growth of cubic crystalline thin films on bistepped sapphire (0001) substrates. PMID:26402241

  7. Layer matching epitaxy of NiO thin films on atomically stepped sapphire (0001) substrates

    NASA Astrophysics Data System (ADS)

    Yamauchi, Ryosuke; Hamasaki, Yosuke; Shibuya, Takuto; Saito, Akira; Tsuchimine, Nobuo; Koyama, Koji; Matsuda, Akifumi; Yoshimoto, Mamoru

    2015-09-01

    Thin-film epitaxy is critical for investigating the original properties of materials. To obtain epitaxial films, careful consideration of the external conditions, i.e. single-crystal substrate, temperature, deposition pressure and fabrication method, is significantly important. In particular, selection of the single-crystal substrate is the first step towards fabrication of a high-quality film. Sapphire (single-crystalline α-Al2O3) is commonly used in industry as a thin-film crystal-growth substrate, and functional thin-film materials deposited on sapphire substrates have found industrial applications. However, while sapphire is a single crystal, two types of atomic planes exist in accordance with step height. Here we discuss the need to consider the lattice mismatch for each of the sapphire atomic layers. Furthermore, through cross-sectional transmission electron microscopy analysis, we demonstrate the uniepitaxial growth of cubic crystalline thin films on bistepped sapphire (0001) substrates.

  8. Microwave properties of peeled HEMT devices sapphire substrates

    NASA Technical Reports Server (NTRS)

    Young, Paul G.; Alterovitz, Samuel A.; Mena, Rafael A.; Smith, Edwyn D.

    1992-01-01

    The focus of this research is to demonstrate the first full radio frequency characterization of high electron mobility transistor (HEMT) device parameters. The results of this research are used in the design of circuits with peeled HEMT devices, e.g. 10 GHz amplifiers. Devices were fabricated using two HEMT structures grown by molecular beam epitaxy methods. A 500 A AlAs release layer for 'peel off' was included under the active layers of the structure. The structures are a homogeneously doped Al(0.3)GA(0.7)As/GaAs and a delta doped square well Al(.23)Ga(.77)As/GaAs HEMT structure. Devices were fabricated using a mesa isolation process. Contacts were done by sequentially evaporating Au/Ge/Au/Ni/Au followed by rapid thermal anneal at 400 C for 15 seconds. Gates were wet etch recessed and 1 to 1.4 micron Ti/Au gate metal was deposited. Devices were peeled off the GaAs substrate using Apiezon wax to support the active layer and a HF:DI (1:10) solution to remove the AlAs separation layer. Devices were then attached to sapphire substrates using van der Waals bonding.

  9. Impurity effects on the adhesion of aluminum films on sapphire substrates

    SciTech Connect

    Schneider, J.A.; Guthrie, S.E.; Clift, W.M.; Moody, N.R.; Kriese, M.D.

    1998-05-01

    The adhesion of aluminum (Al) films onto sapphire substrates in the presence of controlled contaminants is being investigated. In this study, adhesion strength is evaluated by continuous scratch and nanoindentation tests to induce delamination of the Al film from the sapphire substrate. If delamination blisters or spallations can be induced, then fracture mechanics based models can be used to calculate the fracture energy or work of adhesion based on the radius of the blister. Initial specimens of 178 nm thick Al films were vapor deposited onto (0001) oriented sapphire substrates with a 5--19 nm layer of carbon sputter deposited onto the sapphire surface of selected samples. Continuous scratch tests promoted blistering of the film in specimens with carbon on the sapphire surface. Delamination blisters could not be induced by continuous indentation testing in samples with or without carbon at the interface. An overlayer of sputtered tantalum (Ta) was then used on a second set of 500 nm thick Al films with and without 10--20 nm of sputtered carbon on the sapphire surface to promote delaminations. With Ta overlayers, continuous nanoindentation techniques induced larger diameter delamination blisters in the specimens with carbon, than in the specimens without carbon. Resistance to blistering, or smaller induced blisters, indicates a higher interfacial strength.

  10. Heteroepitaxy mechanisms of AlN on nitridated c- and a-plane sapphire substrates

    NASA Astrophysics Data System (ADS)

    Funato, Mitsuru; Shibaoka, Mami; Kawakami, Yoichi

    2017-02-01

    We investigate the metalorganic vapor phase epitaxy of c-oriented AlN on c- and a-plane sapphire substrates, focusing on the effect of sapphire nitridation on the AlN structure. Prior to AlN growth, the sapphire surface is subjected to nitridation via an in-situ NH3 treatment. We demonstrate that nitridation without H2 thermal etching treatment realizes high quality AlN on both c- and a-plane sapphires, indicating that a reaction between NH3 and oxygen on the sapphire surface is a critical factor in the material growth. It is proposed that nitridation initially creates nanometer-scale inversion domains in the AlN epilayer, but as growth proceeds, the N-polar domains are annihilated, leaving voids. Such growth behaviors can be regarded as spontaneous selective area growth with strain-adsorbing void formation, and lead to crack-free, ˜5 μm thick AlN layers, which produce x-ray line widths as narrow as 180 and 483 arc sec for the (0002) and ( 10 1 ¯ 2 ) reflections, respectively, on c-plane sapphire, and 237 and 433 arc sec for these reflections on a-plane sapphire.

  11. Crystal orientation mechanism of ZnTe epilayers formed on different orientations of sapphire substrates by molecular beam epitaxy

    SciTech Connect

    Nakasu, T. Yamashita, S.; Aiba, T.; Hattori, S.; Sun, W.; Taguri, K.; Kazami, F.; Kobayashi, M.

    2014-10-28

    The electrooptic effect in ZnTe has recently attracted research attention, and various device structures using ZnTe have been explored. For application to practical terahertz wave detector devices based on ZnTe thin films, sapphire substrates are preferred because they enable the optical path alignment to be simplified. ZnTe/sapphire heterostructures were focused upon, and ZnTe epilayers were prepared on highly mismatched sapphire substrates by molecular beam epitaxy. Epitaxial relationships between the ZnTe thin films and the sapphire substrates with their various orientations were investigated using an X-ray diffraction pole figure method. (0001) c-plane, (1-102) r-plane, (1-100) m-plane, and (11-20) a-plane oriented sapphire substrates were used in this study. The epitaxial relationship between ZnTe and c-plane sapphire was found to be (111) ZnTe//(0001) sapphire with an in-plane orientation relationship of [−211] ZnTe//[1-100] sapphire. It was found that the (211)-plane ZnTe layer was grown on the m-plane of the sapphire substrates, and the (100)-plane ZnTe layer was grown on the r-plane sapphire. When the sapphire substrates were inclined from the c-plane towards the m-axis direction, the orientation of the ZnTe thin films was then tilted from the (111)-plane to the (211)-plane. The c-plane of the sapphire substrates governs the formation of the (111) ZnTe domain and the ZnTe epilayer orientation. These crystallographic features were also related to the atom arrangements of ZnTe and sapphire.

  12. Gallium Nitride Light Emitter on a Patterned Sapphire Substrate for Improved Defectivity and Light Extraction Efficiency

    DTIC Science & Technology

    2010-01-01

    Gallium nitride light emitter on a patterned sapphire substrate for improved defectivity and light extraction efficiency Michael A. Mastro a,*, Byung ...Phys. 47 (2008) 7827. [6] B.J. Kim, H. Jung, J. Shin , M.A. Mastro, C.R. Eddy Jr., J.K. Hite, S.H. Kim, J. Bang, J. Kim, Thin Solid Films 517 (2009

  13. Fabrication of a new substrate for atomic force microscopic observation of DNA molecules from an ultrasmooth sapphire plate.

    PubMed

    Yoshida, K; Yoshimoto, M; Sasaki, K; Ohnishi, T; Ushiki, T; Hitomi, J; Yamamoto, S; Sigeno, M

    1998-04-01

    A new stable substrate applicable to the observation of DNA molecules by atomic force microscopy (AFM) was fabricated from a ultrasmooth sapphire (alpha-Al2O3 single crystal) plate. The atomically ultrasmooth sapphire as obtained by high-temperature annealing has hydrophobic surfaces and could not be used for the AFM observation of DNA. However, sapphire treated with Na3PO4 aqueous solution exhibited a hydrophilic character while maintaining a smooth surface structure. The surface of the wet-treated sapphire was found by x-ray photoelectron spectroscopy and AFM to be approximately 0.3 nm. The hydrophilic surface character of the ultrasmooth sapphire plate made it easy for DNA molecules to adhere to the plate. Circular molecules of the plasmid DNA could be imaged by AFM on the hydrophilic ultrasmooth sapphire plate.

  14. Fabrication of a new substrate for atomic force microscopic observation of DNA molecules from an ultrasmooth sapphire plate.

    PubMed Central

    Yoshida, K; Yoshimoto, M; Sasaki, K; Ohnishi, T; Ushiki, T; Hitomi, J; Yamamoto, S; Sigeno, M

    1998-01-01

    A new stable substrate applicable to the observation of DNA molecules by atomic force microscopy (AFM) was fabricated from a ultrasmooth sapphire (alpha-Al2O3 single crystal) plate. The atomically ultrasmooth sapphire as obtained by high-temperature annealing has hydrophobic surfaces and could not be used for the AFM observation of DNA. However, sapphire treated with Na3PO4 aqueous solution exhibited a hydrophilic character while maintaining a smooth surface structure. The surface of the wet-treated sapphire was found by x-ray photoelectron spectroscopy and AFM to be approximately 0.3 nm. The hydrophilic surface character of the ultrasmooth sapphire plate made it easy for DNA molecules to adhere to the plate. Circular molecules of the plasmid DNA could be imaged by AFM on the hydrophilic ultrasmooth sapphire plate. PMID:9545030

  15. Deep UV AlGaN light emitting diodes grown by gas source molecular beam epitaxy on sapphire and AlGaN/sapphire substrates

    NASA Astrophysics Data System (ADS)

    Nikishin, S.; Borisov, B.; Kuryatkov, V.; Usikov, A.; Dmitriev, V.; Holtz, M.

    2006-02-01

    We report the electrical and optical properties of deep ultraviolet light emitting diodes (LEDs) based on digital alloy structures (DAS) of AlN/Al 0.08Ga 0.92N grown by gas source molecular beam epitaxy with ammonia on sapphire substrates and AlGaN/sapphire templates. AlGaN/sapphire templates were grown by recently developed stress controlled hydride vapor phase epitaxy (HVPE). For DAS with effective bandgap of 5.1 eV we obtain room temperature electron concentrations up to 1x10 19 cm -3 and hole concentrations of 1x10 18 cm -3. Based on these results we prepared double heterostructure (DHS) LEDs operating in the range of 250 to 290 nm. The emission wavelengths were controlled through the effective bandgap of the active region. The possible ways for increase of LED's efficiency are discussed. We observed significant improvement in the room temperature luminescence efficiency (by factor of 100) of AlGaN quantum wells when a transition growth mode is induced by reduced flux of ammonia. We found that active layer grown on HVPE AlGaN/sapphire substrates have higher luminescence efficiency (by factor of 3) than DAS grown on sapphire.

  16. Fabrication of wafer-scale nanopatterned sapphire substrate through phase separation lithography

    NASA Astrophysics Data System (ADS)

    Guo, Xu; Ni, Mengyang; Zhuang, Zhe; Dai, Jiangping; Wu, Feixiang; Cui, Yushuang; Yuan, Changsheng; Ge, Haixiong; Chen, Yanfeng

    2016-04-01

    A phase separation lithography (PSL) based on polymer blend provides an extremely simple, low-cost, and high-throughput way to fabricate wafer-scale disordered nanopatterns. This method was introduced to fabricate nanopatterned sapphire substrates (NPSSs) for GaN-based light-emitting diodes (LEDs). The PSL process only involved in spin-coating of polystyrene (PS)/polyethylene glycol (PEG) polymer blend on sapphire substrate and followed by a development with deionized water to remove PEG moiety. The PS nanoporous network was facilely obtained, and the structural parameters could be effectively tuned by controlling the PS/PEG weight ratio of the spin-coating solution. 2-in. wafer-scale NPSSs were conveniently achieved through the PS nanoporous network in combination with traditional nanofabrication methods, such as O2 reactive ion etching (RIE), e-beam evaporation deposition, liftoff, and chlorine-based RIE. In order to investigate the performance of such NPSSs, typical blue LEDs with emission wavelengths of ~450 nm were grown on the NPSS and a flat sapphire substrate (FSS) by metal-organic chemical vapor deposition, respectively. The integral photoluminescence (PL) intensity of the NPSS LED was enhanced by 32.3 % compared to that of the FSS-LED. The low relative standard deviation of 4.7 % for PL mappings of NPSS LED indicated the high uniformity of PL data across the whole 2-in. wafer. Extremely simple, low cost, and high throughput of the process and the ability to fabricate at the wafer scale make PSL a potential method for production of nanopatterned sapphire substrates.

  17. Structure-property correlation in epitaxial (2 0 0) rutile films on sapphire substrates

    SciTech Connect

    Bayati, M.R.; Joshi, Sh.; Molaei, R.; Narayan, R.J.; Narayan, J.

    2012-03-15

    We have investigated the influence of the deposition variables on photocatalytic properties of epitaxial rutile films. Despite a large lattice misfit of rutile with sapphire substrate, (2 0 0) epitaxial layers were grown on (0 0 0 1)sapphire by domain matching epitaxy paradigm. Using {phi}-scan XRD and cross section TEM, the epitaxial relationship was determined to be rutile(1 0 0)||sapphire(0 0 0 1), rutile(0 0 1)||sapphire(1 0 -1 0), and rutile(0 1 0)||sapphire(1 -2 1 0). Based on the XRD patterns, increasing the repetition rate introduced tensile stress along the film normal direction, which may arise as a result of trapped defects. Formation of such defects was studied by UV-VIS, PL, and XPS techniques. AFM studies showed that the film roughness increases with the repetition rate. Finally, photocatalytic performance of the layers was investigated through measuring decomposition rate of 4-chlorophenol on the films surface. The films grown at higher frequencies revealed higher photocatalytic efficiency. This behavior was mainly related to formation of point defects which enhance the charge separation. - Graphical abstract: In this report, epitaxial rutile TiO{sub 2} thin films were deposited by PLD process under various deposition rates (frequencies) and their physical and chemical properties, especially photocatalytic performance, were investigated. It was found that photocatalytic efficiency improves when frequency increases. This behavior was mainly related to formation of point defects which enhance the charge separation. Highlights: Black-Right-Pointing-Pointer Rutile epitaxial thin films were deposited via PLD process under different frequencies. Black-Right-Pointing-Pointer Defect characteristic was studied. Black-Right-Pointing-Pointer Photocatalytic performance of the layers was investigated.

  18. High Mobility SiGe/Si n-MODFET Structures and Devices on Sapphire Substrates

    NASA Technical Reports Server (NTRS)

    Mueller, Carl; Alterovitz, Samuel; Croke, Edward; Ponchak, George

    2004-01-01

    Si/Ge/Si n-type modulation doped field effect structures and transistors (n-MODFET's) have been fabricated on r-plane sapphire substrates. Mobilities as high as 1380 cm(exp 2)/Vs were measured at room temperature. Excellent carrier confinement was shown by Shubnikov-de Haas measurements. Atomic force microscopy indicated smooth surfaces, with rm's roughness less than 4 nm, similar to the quality of SiGe/Si n-MODFET structures made on Si substrates. Transistors with 2 micron gate lengths and 200 micron gate widths were fabricated and tested.

  19. On the generation of charge-carrier recombination centers in the sapphire substrates of silicon-on-sapphire structures

    SciTech Connect

    Aleksandrov, P. A. Belova, N. E.; Demakov, K. D.; Shemardov, S. G.

    2015-08-15

    A method for the production of high-quality radiation-resistant silicon-on-sapphire structures through the fabrication of a layer of nanopores in sapphire by helium ion implantation, i.e., by creating charge-carrier recombination centers, is proposed. In this case, the quality of the silicon layer is simultaneously improved. The problem of the thermal stability of the pores is discussed with the aim of analyzing the possibility of producing a microcircuit on the resultant modified silicon-on-sapphire sample. The layer of pores possesses a large total surface area and, hence, decreases the lifetime of charge carriers generated during irradiation of the operating microcircuit. This effect reduces the charge at the silicon-sapphire interface and improves radiation resistance.

  20. Substrate-induced disorder in V2O3 thin films grown on annealed c-plane sapphire substrates

    NASA Astrophysics Data System (ADS)

    Brockman, J.; Samant, M. G.; Roche, K. P.; Parkin, S. S. P.

    2012-07-01

    We investigate the structural and electronic properties of V2O3 thin films deposited by oxygen plasma-assisted molecular beam epitaxy onto annealed and unannealed c-plane sapphire substrates. Annealing the substrates before growth to produce ultra-smooth surfaces improved initial epitaxy, according to in situ reflection high-energy electron diffraction. Surprisingly, films deposited on annealed substrates had a more island-like surface, broader x-ray diffraction peaks, and an increased resistivity of V2O3's normally metallic high-temperature phase. We attribute these results to enhanced strain coupling at the interface between the substrate and film, highlighting the vulnerability of V2O3's strongly correlated metallic phase to crystalline defects and structural disorder.

  1. Measurement and thermal modeling of sapphire substrate temperature at III-Nitride MOVPE conditions

    SciTech Connect

    Creighton, J. Randall; Coltrin, Michael E.; Figiel, Jeffrey J.

    2016-11-17

    Here, growth rates and alloy composition of AlGaN grown by MOVPE is often very temperature dependent due to the presence of gas-phase parasitic chemical processes. These processes make wafer temperature measurement highly important, but in fact such measurements are very difficult because of substrate transparency in the near- IR (~900 nm) where conventional pyrometers detect radiation. The transparency problem can be solved by using a mid-IR pyrometer operating at a wavelength (~7500 nm) where sapphire is opaque. We employ a mid- IR pyrometer to measure the sapphire wafer temperature and simultaneously a near-IR pyrometer to measure wafer pocket temperature, while varying reactor pressure in both a N2 and H2 ambient. Near 1300 °C, as the reactor pressure is lowered from 300 Torr to 10 Torr the wafer temperature drops dramatically, and the ΔT between the pocket and wafer increases from ~20 °C to ~250 °C. Without the mid-IR pyrometer the large wafer temperature change with pressure would not have been noted. In order to explain this behavior we have developed a quasi-2D thermal model that includes a proper accounting of the pressure-dependent thermal contact resistance, and also accounts for sapphire optical transmission. The model and experimental results demonstrate that at most growth conditions the majority of the heat is transported from the wafer pocket to the wafer via gas conduction, in the free molecular flow limit. In this limit gas conductivity is independent of gap size but first order in pressure, and can quantitatively explain results from 20 to 300 Torr. Further analysis yields a measure of the thermal accommodation coefficients; α(H2) =0.23, α(N2) =0.50, which are in the range typically measured.

  2. Measurement and thermal modeling of sapphire substrate temperature at III-Nitride MOVPE conditions

    NASA Astrophysics Data System (ADS)

    Creighton, J. Randall; Coltrin, Michael E.; Figiel, Jeffrey J.

    2017-04-01

    Growth rates and alloy composition of AlGaN grown by MOVPE is often very temperature dependent due to the presence of gas-phase parasitic chemical processes. These processes make wafer temperature measurement highly important, but in fact such measurements are very difficult because of substrate transparency in the near-IR ( 900 nm) where conventional pyrometers detect radiation. The transparency problem can be solved by using a mid-IR pyrometer operating at a wavelength ( 7500 nm) where sapphire is opaque. We employ a mid-IR pyrometer to measure the sapphire wafer temperature and simultaneously a near-IR pyrometer to measure wafer pocket temperature, while varying reactor pressure in both a N2 and H2 ambient. Near 1300 °C, as the reactor pressure is lowered from 300 Torr to 10 Torr the wafer temperature drops dramatically, and the ∆T between the pocket and wafer increases from 20 °C to 250 °C. Without the mid-IR pyrometer the large wafer temperature change with pressure would not have been noted. In order to explain this behavior we have developed a quasi-2D thermal model that includes a proper accounting of the pressure-dependent thermal contact resistance, and also accounts for sapphire optical transmission. The model and experimental results demonstrate that at most growth conditions the majority of the heat is transported from the wafer pocket to the wafer via gas conduction, in the free molecular flow limit. In this limit gas conductivity is independent of gap size but first order in pressure, and can quantitatively explain results from 20 to 300 Torr. Further analysis yields a measure of the thermal accommodation coefficients; α(H2) =0.23, α(N2) =0.50, which are in the range typically measured.

  3. Measurement and thermal modeling of sapphire substrate temperature at III-Nitride MOVPE conditions

    DOE PAGES

    Creighton, J. Randall; Coltrin, Michael E.; Figiel, Jeffrey J.

    2017-04-01

    Here, growth rates and alloy composition of AlGaN grown by MOVPE is often very temperature dependent due to the presence of gas-phase parasitic chemical processes. These processes make wafer temperature measurement highly important, but in fact such measurements are very difficult because of substrate transparency in the near- IR (~900 nm) where conventional pyrometers detect radiation. The transparency problem can be solved by using a mid-IR pyrometer operating at a wavelength (~7500 nm) where sapphire is opaque. We employ a mid- IR pyrometer to measure the sapphire wafer temperature and simultaneously a near-IR pyrometer to measure wafer pocket temperature, whilemore » varying reactor pressure in both a N2 and H2 ambient. Near 1300 °C, as the reactor pressure is lowered from 300 Torr to 10 Torr the wafer temperature drops dramatically, and the ΔT between the pocket and wafer increases from ~20 °C to ~250 °C. Without the mid-IR pyrometer the large wafer temperature change with pressure would not have been noted. In order to explain this behavior we have developed a quasi-2D thermal model that includes a proper accounting of the pressure-dependent thermal contact resistance, and also accounts for sapphire optical transmission. The model and experimental results demonstrate that at most growth conditions the majority of the heat is transported from the wafer pocket to the wafer via gas conduction, in the free molecular flow limit. In this limit gas conductivity is independent of gap size but first order in pressure, and can quantitatively explain results from 20 to 300 Torr. Further analysis yields a measure of the thermal accommodation coefficients; α(H2) =0.23, α(N2) =0.50, which are in the range typically measured.« less

  4. YBCO High-Temperature Superconducting Filters on M-Plane Sapphire Substrates

    NASA Technical Reports Server (NTRS)

    Sabataitis, J. C.; Mueller, C. H.; Miranda, F. A.; Warner, J.; Bhasin, K. B.

    1996-01-01

    Since the discovery of High Temperature Superconductors (HTS) in 1986, microwave circuits have been demonstrated using HTS films on various substrates. These HTS-based circuits have proven to operate with less power loss than their metallic film counterparts at 77 K. This translates into smaller and lighter microwave circuits for space communication systems such as multiplexer filter banks. High quality HTS films have conventionally been deposited on lanthanum aluminate (LaAlO3) substrates. However, LaAlO3 has a relative dielectric constant (epsilon(sub r)) of 24. With a epsilon(sub r) approx. 9.4-11.6, sapphire (Al2O3) would be a preferable substrate for the fabrication of HTS-based components since the lower dielectric constant would permit wider microstrip lines to be used in filter design, since the lower dielectric constant would permit wider microstrip lines to be used for a given characteristic impedance (Z(sub 0)), thus lowering the insertion losses and increasing the power handling capabilities of the devices. We report on the fabrication and characterization of YBa2Cu3O(7-delta) (YBCO) on M-plane sapphire bandpass filters at 4.0 GHz. For a YBCO 'hairpin' filter, a minimum insertion loss of 0.5 dB was measured at 77 K as compared with 1.4 dB for its gold counterpart. In an 'edge-coupled' configuration, the insertion loss went down from 0.9 dB for the gold film to 0.8 dB for the YBCO film at the same temperature.

  5. Electrical and optical properties of VO2 thin films grown on various sapphire substrates by using RF sputtering deposition

    NASA Astrophysics Data System (ADS)

    Jung, Dae Ho; So, Hyeon Seob; Ko, Kun Hee; Park, Jun Woo; Lee, Hosun; Nguyen, Trang Thi Thu; Yoon, Seokhyun

    2016-12-01

    VO2 thin films were grown on a-, c-, m-, and r-plane sapphire and SiO2/Si substrates under identical conditions by using RF sputtering deposition from a VO2 target. The structural and the morphological properties of all VO2 films were investigated. The grain sizes of the VO2 films varied between 268 nm and 355 nm depending on the substrate's orientation. The electrical and the optical properties of all VO2 thin films were examined in detail. The metal-insulator transition temperature (TMI) varied with the substrate's orientation. The (200)/(bar 211 )-oriented VO2 films on the a-plane sapphire showed the lowest TMI of about 329.3 K (56.3 °C) while the (020)/(002)-VO2 films on the c-plane sapphire displayed the highest TMI of about 339.6 K (66.6 °C). The VO2 films showed reversible changes in the resistivity as large as 1.19 × 105 and a hysteresis of 2 K upon traversing the transition temperature. The variations observed in the TMI with respect to the substrate's orientation were due to changes in the lattice strain and the grain size distribution. Raman spectroscopy showed that metal (rutile) - insulator (monoclinic) transitions occurred via the M2 phase for VO2 films on the c-plane substrate rather than the direct M1 to rutile transition. The shifts in the phonon frequencies of the VO2 film grown on various sapphire substrates were explained in terms of the strain along the V-V atomic bond direction (cR). Our work shows a possible correlation between the transition parameters ( e.g., TMI, sharpness, and hysteresis width) and the width ( σ) of the grain size distribution. It also shows a possible correlation between the TMI and the resistivities at the insulating and the metallic phases for VO2 films grown on various sapphire substrates.

  6. Transmission Electron Microscopy (TEM) Sample Preparation of Si(1-x)Gex in c-Plane Sapphire Substrate

    NASA Technical Reports Server (NTRS)

    Kim, Hyun Jung; Choi, Sang H.; Bae, Hyung-Bin; Lee, Tae Woo

    2012-01-01

    The National Aeronautics and Space Administration-invented X-ray diffraction (XRD) methods, including the total defect density measurement method and the spatial wafer mapping method, have confirmed super hetero epitaxy growth for rhombohedral single crystalline silicon germanium (Si1-xGex) on a c-plane sapphire substrate. However, the XRD method cannot observe the surface morphology or roughness because of the method s limited resolution. Therefore the authors used transmission electron microscopy (TEM) with samples prepared in two ways, the focused ion beam (FIB) method and the tripod method to study the structure between Si1-xGex and sapphire substrate and Si1?xGex itself. The sample preparation for TEM should be as fast as possible so that the sample should contain few or no artifacts induced by the preparation. The standard sample preparation method of mechanical polishing often requires a relatively long ion milling time (several hours), which increases the probability of inducing defects into the sample. The TEM sampling of the Si1-xGex on sapphire is also difficult because of the sapphire s high hardness and mechanical instability. The FIB method and the tripod method eliminate both problems when performing a cross-section TEM sampling of Si1-xGex on c-plane sapphire, which shows the surface morphology, the interface between film and substrate, and the crystal structure of the film. This paper explains the FIB sampling method and the tripod sampling method, and why sampling Si1-xGex, on a sapphire substrate with TEM, is necessary.

  7. Growth of thick GaN layers on laser-processed sapphire substrate by hydride vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Koyama, Koji; Aida, Hideo; Kim, Seong-Woo; Ikejiri, Kenjiro; Doi, Toshiro; Yamazaki, Tsutomu

    2014-10-01

    A 600 μm thick GaN layer was successfully grown by hydride vapor phase epitaxy by replacing the standard sapphire substrate with that processed by a focused laser beam within the substrate. The effects of the laser processing on the curvature and cracking of the GaN layer were investigated. Microscopic observations of the interior of the thick GaN layer revealed that the laser-processed substrate suppressed the generation of microcracks in the GaN layer. In addition, the laser processing was also found to reduce the change in the curvature during the GaN layer growth in comparison to that on the standard substrate. It is shown that the overlapping microcracks observed in the GaN layer on the standard sapphire substrate lead to serious cracking after thick GaN layer growth.

  8. Growth and characterization of AlGaN films on patterned sapphire substrates

    NASA Astrophysics Data System (ADS)

    Kwak, Y. S.; Lee, D. S.; Kim, K. H.; Kim, W. H.; Moon, S. W.

    2011-12-01

    A GaN film and two AlGaN films with Al compositions of 5% and 10% have been grown on the patterned sapphire substrates (PSSs) by metal organic chemical vapor deposition (MOCVD). Optical properties and crystalline qualities of the films have been investigated. The GaN film and the Al0.05Ga0.95N film are almost entirely coalesced except for some point defects. However, the Al0.1Ga0.9N film contains large pits encircled by small pits adjacent to them. The large pits are distributed in the same manner with the PSS arrangement. Dislocations and inversion domain boundaries were also observed in the Al0.1Ga0.9N film.

  9. High Electron Mobility in SiGe/Si n-MODFET Structures on Sapphire Substrates

    NASA Technical Reports Server (NTRS)

    Mueller, Carl H.; Croke, Edward T.; Alterovitz, Samuel A.

    2003-01-01

    For the first time, SiGe/Si n-Modulation Doped Field Effect Transistors (n-MODFET) structures have been grown on sapphire substrates. Room temperature electron mobility value of 1271 square centimeters N-sec at an electron carrier density (n(sub e) = 1.33x10(exp 12) per square centimeter)) of 1.6 x 10(exp 12) per square centimeter was obtained. At 250 mK, the mobility increases to 13,313 square centimeters/V-sec (n(sub e)=1.33x10(exp 12) per square centimeter)) and Shubnikov-de Haas oscillations appear, showing excellent confinement of the two-dimensional electron gas.

  10. High-T(sub c) Edge-geometry SNS Weak Links on Silicon-on-sapphire Substrates

    NASA Technical Reports Server (NTRS)

    Hunt, B.; Foote, M.; Pike, W.; Barner, J.; Vasquez, R.

    1994-01-01

    High-quality superconductor/normal-metal/superconductor(SNS) edge-geometry weak links have been produced on silicon-on-sapphire (SOS) substrates using a new SrTiO(sub 3)/'seed layer'/cubic-zirconia (YS2) buffer system.

  11. (110)-oriented indium tin oxide films grown on m- and r-plane sapphire substrates

    NASA Astrophysics Data System (ADS)

    Chern, Ming-Yau; Lu, Tso-Wen; Xu, Wei-Lun

    2015-04-01

    Indium tin oxide (ITO) thin films have been deposited by pulsed laser deposition on m-plane (100) and r-plane (012) sapphire substrates. For both substrates, the films were grown with their [110] direction perpendicular to the substrate planes under the conditions of high growth temperature and high oxygen pressure. Their in-plane epitaxial relations with the substrates were identified to be ITO[001] ∥ Al2O3[020] and \\text{ITO}[1\\bar{1}0]\\parallel \\text{Al}2\\text{O}3[001] for the m-plane substrate. For the r-plane substrate, two types of lattice matching were observed: one being \\text{ITO}[001]\\parallel \\text{Al}2\\text{O}3[2,1, - 1/2] and \\text{ITO}[1\\bar{1}0]\\parallel \\text{Al}2\\text{O}3[4/3, - 4/3,2/3], the other being \\text{ITO}[001]\\parallel \\text{Al}2\\text{O}3[1, - 1,1/2] and \\text{ITO}[1\\bar{1}0]/\\text{Al}2\\text{O}3[8/3,4/3, - 2/3]. The electrical properties were measured by the Hall effect and van der Pauw methods at room temperature. All of the samples have low electrical resistivity on the order of 3.0 × 10-4 Ω cm, high carrier concentration of about 2.5 × 1020 cm-3, and mobility ranging from 70 to 90 cm2 V-1 s-1.

  12. High Electron Mobility Transistor Structures on Sapphire Substrates Using CMOS Compatible Processing Techniques

    NASA Technical Reports Server (NTRS)

    Mueller, Carl; Alterovitz, Samuel; Croke, Edward; Ponchak, George

    2004-01-01

    System-on-a-chip (SOC) processes are under intense development for high-speed, high frequency transceiver circuitry. As frequencies, data rates, and circuit complexity increases, the need for substrates that enable high-speed analog operation, low-power digital circuitry, and excellent isolation between devices becomes increasingly critical. SiGe/Si modulation doped field effect transistors (MODFETs) with high carrier mobilities are currently under development to meet the active RF device needs. However, as the substrate normally used is Si, the low-to-modest substrate resistivity causes large losses in the passive elements required for a complete high frequency circuit. These losses are projected to become increasingly troublesome as device frequencies progress to the Ku-band (12 - 18 GHz) and beyond. Sapphire is an excellent substrate for high frequency SOC designs because it supports excellent both active and passive RF device performance, as well as low-power digital operations. We are developing high electron mobility SiGe/Si transistor structures on r-plane sapphire, using either in-situ grown n-MODFET structures or ion-implanted high electron mobility transistor (HEMT) structures. Advantages of the MODFET structures include high electron mobilities at all temperatures (relative to ion-implanted HEMT structures), with mobility continuously improving to cryogenic temperatures. We have measured electron mobilities over 1,200 and 13,000 sq cm/V-sec at room temperature and 0.25 K, respectively in MODFET structures. The electron carrier densities were 1.6 and 1.33 x 10(exp 12)/sq cm at room and liquid helium temperature, respectively, denoting excellent carrier confinement. Using this technique, we have observed electron mobilities as high as 900 sq cm/V-sec at room temperature at a carrier density of 1.3 x 10(exp 12)/sq cm. The temperature dependence of mobility for both the MODFET and HEMT structures provides insights into the mechanisms that allow for enhanced

  13. Evaluation of Piezoelectric Ta2O5 Thin Films Deposited on Sapphire Substrates

    NASA Astrophysics Data System (ADS)

    Iwamoto, Shunsuke; Saigusa, Ryosuke; Kakio, Shoji

    2013-07-01

    X-axis-oriented tantalum pentoxide (Ta2O5) piezoelectric thin films were deposited on sapphire (Al2O3) substrates, from which single crystallization due to epitaxial growth can be expected, using an RF magnetron sputtering system. The crystallinity and Rayleigh-type surface acoustic wave (R-SAW) propagation properties of the thin films were evaluated. From the measured diffraction (X-ray diffraction) patterns and the spotted pattern in the measured pole figures, in which poles were arranged to form the vertices of a hexagon, the possibility of the crystallization of hexagonal Ta2O5 with a (203)-plane oriented in the c-Al2O3 substrate plane due to epitaxial growth was shown. For the first mode of the R-SAW on the Ta2O5/R-plane Al2O3 sample, a coupling factor of 1.65% and a phase velocity of 5,120 m/s were obtained for a normalized thickness of 0.175. Unfortunately, no increase in coupling factor and no major improvement in propagation loss were observed upon the crystallization of hexagonal Ta2O5.

  14. High Mobility SiGe/Si Transistor Structures on Sapphire Substrates Using Ion Implantation

    NASA Technical Reports Server (NTRS)

    Alterovitz, S. A.; Mueller, C. H.; Croke, E. T.

    2003-01-01

    High mobility n-type SiGe/Si transistor structures have been fabricated on sapphire substrates by ion implanting phosphorus ions into strained 100 Angstrom thick silicon channels for the first time. The strained Si channels were sandwiched between Si(sub 0.7)Ge(sub 0.3) layers, which, in turn, were deposited on Si(sub 0.7)Ge(sub 0.3) virtual substrates and graded SiGe buffer layers. After the molecular beam epitaxy (MBE) film growth process was completed, ion thick silicon channels implantation and post-annealing were used to introduce donors. The phosphorous ions were preferentially located in the Si channel at a peak concentration of approximately 1x10(exp 18)/cu cm. Room temperature electron mobilities exceeding 750 sq cm/V-sec at carrier densities of 1x10(exp 12)/sq cm were measured. Electron concentration appears to be the key factor that determines mobility, with the highest mobility observed for electron densities in the 1 - 2x10(exp 12)/sq cm range.

  15. Surface Texture and Crystallinity Variation of ZnTe Epilayers Grown on the Step-Terrace Structure of the Sapphire Substrate

    NASA Astrophysics Data System (ADS)

    Nakasu, Taizo; Kizu, Takeru; Yamashita, Sotaro; Aiba, Takayuki; Hattori, Shota; Sun, Wei-Che; Taguri, Kosuke; Kazami, Fukino; Hashimoto, Yuki; Ozaki, Shun; Kobayashi, Masakazu; Asahi, Toshiaki

    2016-04-01

    ZnTe/sapphire heterostructures were focused, and ZnTe thin films were prepared on highly mismatched sapphire substrates by molecular beam epitaxy. A sapphire substrate possessing an atomically-smooth step-terrace structure was used to improve the crystallinity and morphology of the produced ZnTe film. The growth mode of the ZnTe thin film on a sapphire substrate with an atomically-smooth step-terrace structure was found to shift to a two-dimensional growth mode, and a ZnTe thin film possessing a flat surface was obtained. The crystallographic properties of the ZnTe film suggested that the resulting layer consisted of a single (111)-oriented domain. The photoluminescence property was also improved, and the interface lattice alignment between the ZnTe and sapphire was also affected by the atomically-smooth step-terrace structure.

  16. Effects of the ultrasonic flexural vibration on the interaction between the abrasive particles; pad and sapphire substrate during chemical mechanical polishing (CMP)

    NASA Astrophysics Data System (ADS)

    Xu, Wenhu; Lu, Xinchun; Pan, Guoshun; Lei, Yuanzhong; Luo, Jianbin

    2011-01-01

    In this paper, the technique of ultrasonic flexural vibration assisted chemical mechanical polishing (UFV-CMP) was used for sapphire substrate CMP. The functions of the polishing pad, the silica abrasive particles, and the chemical additives of the slurry such as pH value regulator and dispersant during the sapphire's UFV-CMP were investigated. The results showed that the actions of the ultrasonic and silica abrasive particles were the main factors in the sapphire material removal rate (MMR) and the chemical additives were helpful to decrease the roughness of sapphire. Then the effects of the flexural vibration on the interaction between the silica abrasive particles, pad and sapphire substrate from the kinematics and dynamics were investigated to explain why the MRR of UFV-CMP was bigger than that of the traditional CMP. It indicated that such functions improved the sapphire's MRR: the increasing of the contact silica particles' motion path lengths on the sapphire's surface, the enhancement of the contact force between the contact silica particles and the sapphire's surface, and the impaction of the suspending silica particles to the sapphire's surface.

  17. Fabrication of volcano-shaped nano-patterned sapphire substrates using colloidal self-assembly and wet chemical etching.

    PubMed

    Geng, Chong; Zheng, Lu; Fang, Huajing; Yan, Qingfeng; Wei, Tongbo; Hao, Zhibiao; Wang, Xiaoqing; Shen, Dezhong

    2013-08-23

    Patterned sapphire substrates (PSS) have been widely used to enhance the light output power in GaN-based light emitting diodes. The shape and feature size of the pattern in a PSS affect its enhancement efficiency to a great degree. In this work we demonstrate the nanoscale fabrication of volcano-shaped PSS using a wet chemical etching approach in combination with a colloidal monolayer templating strategy. Detailed analysis by scanning electron microscopy reveals that the unique pattern shape is a result of the different corrosion-resistant abilities of silica masks of different effective heights during wet chemical etching. The formation of silica etching masks of different effective heights has been ascribed to the silica precursor solution in the interstice of the colloidal monolayer template being distributed unevenly after infiltration. In the subsequent wet chemical etching process, the active reaction sites altered as etching duration was prolonged, resulting in the formation of volcano-shaped nano-patterned sapphire substrates.

  18. Design of patterned sapphire substrates for GaN-based light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Wang, Hai-Yan; Lin, Zhi-Ting; Han, Jing-Lei; Zhong, Li-Yi; Li, Guo-Qiang

    2015-06-01

    A new method for patterned sapphire substrate (PSS) design is developed and proven to be reliable and cost-effective. As progress is made with LEDs’ luminous efficiency, the pattern units of PSS become more complicated, and the effect of complicated geometrical features is almost impossible to study systematically by experiments only. By employing our new method, the influence of pattern parameters can be systematically studied, and various novel patterns are designed and optimized within a reasonable time span, with great improvement in LEDs’ light extraction efficiency (LEE). Clearly, PSS pattern design with such a method deserves particular attention. We foresee that GaN-based LEDs on these newly designed PSSs will achieve more progress in the coming years. Project supported by the National Natural Science Fundation for Excellent Young Scholars of China (Grant No. 51422203), the National Natural Science Foundation of China (Grant No. 51372001), the Outstanding Youth Foundation of Guangdong Scientific Committee (Grant No. S2013050013882), and the Strategic Special Funds for LEDs of Guangdong Province, China (Grant Nos. 2011A081301010, 2011A081301012, 2012A080302002, and 2012A080302004).

  19. Reduction of batwing effect in white light interferometry for measurement of patterned sapphire substrates (PSS) wafer

    NASA Astrophysics Data System (ADS)

    Tapilouw, Abraham Mario; Chang, Yi-Wei; Yu, Long-Yo; Wang, Hau-Wei

    2016-08-01

    Patterned sapphire substrates (PSS) wafers are used in LED manufacturing to enhance the luminous conversion of LED chips. The most critical characteristics in PSS wafers are height, width, pitch and shape of the pattern. The common way to measure these characteristics is by using surface electron microscope (SEM). White light interferometry is capable to measure dimension with nanometer accuracy and it is suitable for measuring the characteristics of PSS wafers. One of the difficulties in measuring PSS wafers is the aspect ratio and density of the features. The high aspect ratio combined with dense pattern spacing diffracts incoming lights and reduces the accuracy of the white light interferometry measurement. In this paper, a method to improve the capability of white light interferometry for measuring PSS wafers by choosing the appropriate wavelength and microscope objective with high numerical aperture. The technique is proven to be effective for reducing the batwing effect in edges of the feature and improves measurement accuracy for PSS wafers with circular features of 1.95 um in height and diameters, and 700 nm spacing between the features. Repeatability of the measurement is up to 5 nm for height measurement and 20 nm for pitch measurement.

  20. Comparison of ultraviolet APDs grown on free-standing GaN and sapphire substrates

    NASA Astrophysics Data System (ADS)

    Cicek, Erdem; Vashaei, Zahra; Bayram, Can; McClintock, Ryan; Razeghi, Manijeh; Ulmer, Melville P.

    2010-08-01

    There is a need for semiconductor-based ultraviolet photodetectors to support avalanche gain in order to realize better performance andmore effective compete with existing technologies. Wide bandgap III-Nitride semiconductors are the promising material system for the development of avalanche photodiodes (APDs) that could be a viable alternative to current bulky UV detectors such as photomultiplier tubes. In this paper, we review the current state-of-the-art in IIINitride visible-blind APDs, and present our latest results on GaN APDs grown on both conventional sapphire and low dislocation density free-standing c- and m-plane GaN substrates. Leakage current, gain, and single photon detection efficiency (SPDE) of these APDs were compared. The spectral response and Geiger-mode photon counting performance of UV APDs are studied under low photon fluxes, with single photon detection capabilities as much as 30% being demonstrated in smaller devices. Geiger-mode operation conditions are optimized for enhanced SPDE.

  1. AlN/GaN high electron mobility transistors on sapphire substrates for Ka band applications

    NASA Astrophysics Data System (ADS)

    Xubo, Song; Yuanjie, Lü; Guodong, Gu; Yuangang, Wang; Xin, Tan; Xingye, Zhou; Shaobo, Dun; Peng, Xu; Jiayun, Yin; Bihua, Wei; Zhihong, Feng; Shujun, Cai

    2016-04-01

    We report the DC and RF characteristics of AlN/GaN high electron mobility transistors (HEMTs) with the gate length of 100 nm on sapphire substrates. The device exhibits a maximum drain current density of 1.29 A/mm and a peak transconductance of 440 mS/mm. A current gain cutoff frequency and a maximum oscillation frequency of 119 GHz and 155 GHz have been obtained, respectively. Furthermore, the large signal load pull characteristics of the AlN/GaN HEMTs were measured at 29 GHz. An output power density of 429 mW/mm has been demonstrated at a drain bias of 10 V. To the authors' best knowledge, this is the earliest demonstration of power density at the Ka band for AlN/GaN HEMTs in the domestic, and also a high frequency of load-pull measurements for AlN/GaN HEMTs. Project supported by the National Natural Science Foundation of China (No. 61306113).

  2. High Electron Mobility SiGe/Si Transistor Structures on Sapphire Substrates

    NASA Technical Reports Server (NTRS)

    Alterovitz, Samuel A.; Mueller, Carl H.; Croke, Edward T.; Ponchak, George E.

    2003-01-01

    SiGe/Si n-type modulation doped field effect structures and transistors (n-MODFETs) have been fabricated on r-plane sapphire substrates. The structures were deposited using molecular beam epitaxy, and antimony dopants were incorporated via a delta doping process. Secondary ion mass spectroscopy (SIMS) indicates that the peak antimony, concentration was approximately 4 x 10(exp19) per cubic cm. The electron mobility was over 1,200 and 13,000 sq cm/V-sec at room temperature and 0.25 K, respectively. At these two temperatures, the electron carrier densities were 1.6 and 1.33 x 10(exp 12) per sq cm, thus demonstrating that carrier confinement was excellent. Shubnikov-de Haas oscillations were observed at 0.25 K, thus confirming the two-dimensional nature of the carriers. Transistors, with gate lengths varying from 1 micron to 5 microns, were fabricated using these structures and dc characterization was performed at room temperature. The saturated drain current region extended over a wide source-to-drain voltage (V(sub DS)) range, with (V(sub DS)) knee voltages of approximately 0.5 V and increased leakage starting at voltages slightly higher than 4 V.

  3. High Electron Mobility SiGe/Si Transistor Structures on Sapphire Substrates

    NASA Technical Reports Server (NTRS)

    Alterovitz, Samuel A.; Mueller, Carl H.; Croke, Edward T.; Ponchak, George E.

    2004-01-01

    SiGe/Si n-type modulation doped field effect structures and transistors (n-MODFETs) have been fabricated on r-plane sapphire substrates. The structures were deposited using molecular beam epitaxy, and antimony dopants were incorporated via a delta doping process. Secondary ion mass spectroscopy (SIMS) indicates that the peak antimony concentration was approximately 4 x 10(exp 19) per cubic centimeter. At these two temperatures, the electron carrier densities were 1.6 and 1.33 x 10(exp 12) per square centimeter, thus demonstrating that carrier confinement was excellent. Shubnikov-de Haas oscillations were observed at 0.25 K, thus confirming the two-dimensional nature of the carriers. Transistors, with gate lengths varying from 1 micron to 5 microns, were fabricated using these structures and dc characterization was performed at room temperature. The saturated drain current region extended over a wide source-to-drain voltage (V (sub DS)) range, with V (sub DS) knee voltages of approximately 0.5 V and increased leakage starting at voltages slightly higher than 4 V.

  4. Heteroepitaxial growth of Cu{sub 2}ZnSnS{sub 4} thin film on sapphire substrate by radio frequency magnetron sputtering

    SciTech Connect

    Song, Ning E-mail: n.song@student.unsw.edu.au; Huang, Yidan; Li, Wei; Huang, Shujuan; Hao, Xiaojing E-mail: n.song@student.unsw.edu.au; Wang, Yu; Hu, Yicong

    2014-03-03

    The heteroepitaxy of tetragonal Cu2ZnSnS4 (CZTS) thin films on hexagonal sapphire (0001) single crystal substrates is successfully obtained by radio frequency magnetron sputtering. The sputtered CZTS film has a mirror-like smooth surface with a root mean square roughness of about 5.44 nm. X-ray θ-2θ scans confirm that CZTS film is (112) oriented on sapphire with an out of plane arrangement of CZTS (112) ‖ sapphire (0001). X-ray Phi scan further illustrates an in plane ordering of CZTS [201{sup ¯}] ‖ sapphire [21{sup ¯}1{sup ¯}0]. The high resolution transmission electron microscopy image of the interface region clearly shows that the CZTS thin film epitaxially grows on the sapphire (0001) substrate. The band gap of the film is found to be approximately 1.51 eV.

  5. Dependence of adhesion strength between GaN LEDs and sapphire substrate on power density of UV laser irradiation

    NASA Astrophysics Data System (ADS)

    Park, Junsu; Sin, Young-Gwan; Kim, Jae-Hyun; Kim, Jaegu

    2016-10-01

    Selective laser lift-off (SLLO) is an innovative technology used to manufacture and repair micro-light-emitting diode (LED) displays. In SLLO, laser is irradiated to selectively separate micro-LED devices from a transparent sapphire substrate. The light source used is an ultraviolet (UV) laser with a wavelength of 266 nm, pulse duration of 20 ns, and repetition rate of 30 kHz. Controlled adhesion between a LED and the substrate is key for a SLLO process with high yield and reliability. This study examined the fundamental relationship between adhesion and laser irradiation. Two competing mechanisms affect adhesion at the irradiated interface between the GaN LED and sapphire substrate: Ga precipitation caused by the thermal decomposition of GaN and roughened interface caused by thermal damage on the sapphire. The competition between these two mechanisms leads to a non-trivial SLLO condition that needs optimization. This study helps understand the SLLO process, and accelerate the development of a process for manufacturing micro-LED displays via SLLO for future applications.

  6. High-quality AlN epitaxy on nano-patterned sapphire substrates prepared by nano-imprint lithography

    NASA Astrophysics Data System (ADS)

    Zhang, Lisheng; Xu, Fujun; Wang, Jiaming; He, Chenguang; Guo, Weiwei; Wang, Mingxing; Sheng, Bowen; Lu, Lin; Qin, Zhixin; Wang, Xinqiang; Shen, Bo

    2016-11-01

    We report epitaxial growth of AlN films with atomically flat surface on nano-patterned sapphire substrates (NPSS) prepared by nano-imprint lithography. The crystalline quality can be greatly improved by using the optimized 1-μm-period NPSS. The X-ray diffraction ω-scan full width at half maximum values for (0002) and (102) reflections are 171 and 205 arcsec, respectively. The optimized NPSS contribute to eliminating almost entirely the threading dislocations (TDs) originating from the AlN/sapphire interface via bending the dislocations by image force from the void sidewalls before coalescence. In addition, reducing the misorientations of the adjacent regions during coalescence adopting the low lateral growth rate is also essential for decreasing TDs in the upper AlN epilayer.

  7. High-quality AlN epitaxy on nano-patterned sapphire substrates prepared by nano-imprint lithography

    PubMed Central

    Zhang, Lisheng; Xu, Fujun; Wang, Jiaming; He, Chenguang; Guo, Weiwei; Wang, Mingxing; Sheng, Bowen; Lu, Lin; Qin, Zhixin; Wang, Xinqiang; Shen, Bo

    2016-01-01

    We report epitaxial growth of AlN films with atomically flat surface on nano-patterned sapphire substrates (NPSS) prepared by nano-imprint lithography. The crystalline quality can be greatly improved by using the optimized 1-μm-period NPSS. The X-ray diffraction ω-scan full width at half maximum values for (0002) and (102) reflections are 171 and 205 arcsec, respectively. The optimized NPSS contribute to eliminating almost entirely the threading dislocations (TDs) originating from the AlN/sapphire interface via bending the dislocations by image force from the void sidewalls before coalescence. In addition, reducing the misorientations of the adjacent regions during coalescence adopting the low lateral growth rate is also essential for decreasing TDs in the upper AlN epilayer. PMID:27812006

  8. Surface modification of a-plane sapphire substrates and its effect on crystal orientation of ZnTe layer

    NASA Astrophysics Data System (ADS)

    Nakasu, Taizo; Sun, Wei-Che; Kobayashi, Masakazu

    2017-01-01

    Domain structures of ZnTe layers grown on a-plane sapphire substrates were investigated by changing the crystallographic properties of the surface and interface. Pole figure images were obtained and we investigated the domain structure in the grown film and the orientation relationships between films and substrates. It was confirmed that two kinds of {111} domains were oriented by annealing the buffer layer at 350 °C, while the (100) domain was obtained by annealing the buffer layer at 300 °C. From the results of the rocking curve measurement, the introduction of a step-terrace surface through the high-temperature treatment of the substrate resulted in an improved crystallographic quality. However, it did not affect the domain structure in the layer. The introduction of an off-angle on the substrate surface resulted in the formation of a single (111) domain layer. These crystallographic features were mainly affected by the surface atom arrangement of the sapphire substrate and its chemical nature.

  9. Semipolar (202{sup ¯}1) GaN and InGaN quantum wells on sapphire substrates

    SciTech Connect

    Leung, Benjamin; Wang, Dili; Kuo, Yu-Sheng; Xiong, Kanglin; Song, Jie; Chen, Danti; Park, Sung Hyun; Han, Jung; Hong, Su Yeon; Choi, Joo Won

    2014-06-30

    Here, we demonstrate a process to produce planar semipolar (202{sup ¯}1) GaN templates on sapphire substrates. We obtain (202{sup ¯}1) oriented GaN by inclined c-plane sidewall growth from etched sapphire, resulting in single crystal material with on-axis x-ray diffraction linewidth below 200 arc sec. The surface, composed of (101{sup ¯}1) and (101{sup ¯}0) facets, is planarized by the chemical-mechanical polishing of full 2 in. wafers, with a final surface root mean square roughness of <0.5 nm. We then analyze facet formation and roughening mechanisms on the (202{sup ¯}1) surface and establish a growth condition in N{sub 2} carrier gas to maintain a planar surface for further device layer growth. Finally, the capability of these semipolar (202{sup ¯}1) GaN templates to produce high quality device structures is verified by the growth and characterization of InGaN/GaN multiple quantum well structures. It is expected that the methods shown here can enable the benefits of using semipolar orientations in a scalable and practical process and can be readily extended to achieve devices on surfaces using any orientation of semipolar GaN on sapphire.

  10. Neutron reflectivity study of substrate surface chemistry effects on supported phospholipid bilayer formation on (1120) sapphire.

    SciTech Connect

    Oleson, Timothy A.; Sahai, Nita; Wesolowski, David J; Dura, Joseph A; Majkrzak, Charles F; Giuffre, Anthony J.

    2012-01-01

    Oxide-supported phospholipid bilayers (SPBs) used as biomimetric membranes are significant for a broad range of applications including improvement of biomedical devices and biosensors, and in understanding biomineralization processes and the possible role of mineral surfaces in the evolution of pre-biotic membranes. Continuous-coverage and/or stacjed SPBs retain properties (e.,g. fluidity) more similar to native biological membranes, which is desirable for most applications. Using neutron reflectivity, we examined face coverage and potential stacking of dipalmitoylphosphatidylcholine (DPPC) bilayers on the (1120) face of sapphire (a-Al2O3). Nearly full bilayers were formed at low to neutral pH, when the sapphire surface is positively charged, and at low ionic strength (l=15 mM NaCl). Coverage decreased at higher pH, close to the isoelectric point of sapphire, and also at high I>210mM, or with addition of 2mM Ca2+. The latter two effects are additive, suggesting that Ca2+ mitigates the effect of higher I. These trends agree with previous results for phospholipid adsorption on a-Al2O3 particles determined by adsorption isotherms and on single-crystal (1010) sapphire by atomic force microscopy, suggesting consistency of oxide surface chemistry-dependent effects across experimental techniques.

  11. Development and Industrialization of InGaN/GaN LEDs on Patterned Sapphire Substrates for Low Cost Emitter Architecture

    SciTech Connect

    Flemish, Joseph; Soer, Wouter

    2015-11-30

    Patterned sapphire substrate (PSS) technology has proven to be an effective approach to improve efficacy and reduce cost of light-emitting diodes (LEDs). The volume emission from the transparent substrate leads to high package efficiency, while the simple and robust architecture of PSS-based LEDs enables low cost. PSS substrates have gained wide use in mid-power LEDs over the past years. In this project, Lumileds has developed and industrialized PSS and epitaxy technology for high- power flip-chip LEDs to bring these benefits to a broader range of applications and accelerate the adoption of energy-efficient solid-state lighting (SSL). PSS geometries were designed for highly efficient light extraction in a flip-chip architecture and high-volume manufacturability, and corresponding sapphire patterning and epitaxy manufacturing processes were integrally developed. Concurrently, device and package architectures were developed to take advantage of the PSS flip-chip die in different types of products that meet application needs. The developed PSS and epitaxy technology has been fully implemented in manufacturing at Lumileds’ San Jose, CA location, and incorporated in illumination-grade LED products that have been successfully introduced to the market, including LUXEON Q and LUXEON FlipChip White.

  12. Nanomechanical probing of the layer/substrate interface of an exfoliated InSe sheet on sapphire

    PubMed Central

    Beardsley, Ryan; Akimov, Andrey V.; Greener, Jake D. G.; Mudd, Garry W.; Sandeep, Sathyan; Kudrynskyi, Zakhar R.; Kovalyuk, Zakhar D.; Patanè, Amalia; Kent, Anthony J.

    2016-01-01

    Van der Waals (vdW) layered crystals and heterostructures have attracted substantial interest for potential applications in a wide range of emerging technologies. An important, but often overlooked, consideration in the development of implementable devices is phonon transport through the structure interfaces. Here we report on the interface properties of exfoliated InSe on a sapphire substrate. We use a picosecond acoustic technique to probe the phonon resonances in the InSe vdW layered crystal. Analysis of the nanomechanics indicates that the InSe is mechanically decoupled from the substrate and thus presents an elastically imperfect interface. A high degree of phonon isolation at the interface points toward applications in thermoelectric devices, or the inclusion of an acoustic transition layer in device design. These findings demonstrate basic properties of layered structures and so illustrate the usefulness of nanomechanical probing in nanolayer/nanolayer or nanolayer/substrate interface tuning in vdW heterostructures. PMID:27256805

  13. Air-void embedded GaN-based light-emitting diodes grown on laser drilling patterned sapphire substrates

    NASA Astrophysics Data System (ADS)

    Liu, Hao; Li, Yufeng; Wang, Shuai; Feng, Lungang; Xiong, Han; Su, Xilin; Yun, Feng

    2016-07-01

    Air-void structure was introduced in GaN-based blue light-emitting diodes (LED) with one-step growth on periodic laser drilling patterned sapphire substrate, which free of any photolithography or wet/dry etching process. The influence of filling factors (FF) of air-void on crystal quality and optical performance were investigate. Transmission electron microscopy images and micro-Raman spectroscopy indicated that the dislocation was bended and the partially compressed strain was released. When FF was 55.43%, compared with the LED structure grown on flat sapphire substrate, the incorporation of air-void was observed to reduce the compressed stress of ˜20% and the luminance intensity has improved by 128%. Together with the simulated reflection intensity enhancement by finite difference time-domain (FDTD) method, we attribute the enhanced optical performance to the combined contribution of strong back-side light reflection of air-void and better GaN epitaxial quality. This approach provides a simple replacement to the conventional air-void embedded LED process.

  14. The improvement of GaN-based light-emitting diodes using nanopatterned sapphire substrate with small pattern spacing

    SciTech Connect

    Zhang, Yonghui; Wei, Tongbo Wang, Junxi; Chen, Yu; Hu, Qiang; Lu, Hongxi; Li, Jinmin; Lan, Ding

    2014-02-15

    Self-assembly SiO{sub 2} nanosphere monolayer template is utilized to fabricate nanopatterned sapphire substrates (NPSSs) with 0-nm, 50-nm, and 120-nm spacing, receptively. The GaN growth on top of NPSS with 0-nm spacing has the best crystal quality because of laterally epitaxial overgrowth. However, GaN growth from pattern top is more difficult to get smooth surface than from pattern bottom. The rougher surface may result in a higher work voltage. The stimulation results of finite-difference time-domain (FDTD) display that too large or too small spacing lead to the reduced light extracted efficiency (LEE) of LEDs. Under a driving current 350 mA, the external quantum efficiencies (EQE) of GaN-based LEDs grown on NPSSs with 0-nm, 50-nm, and 120-nm spacing increase by 43.3%, 50.6%, and 39.1%, respectively, compared to that on flat sapphire substrate (FSS). The optimized pattern spacing is 50 nm for the NPSS with 600-nm pattern period.

  15. The effect of substrate on high-temperature annealing of GaN epilayers: Si versus sapphire

    SciTech Connect

    Pastor, D.; Cusco, R.; Artus, L.; Gonzalez-Diaz, G.; Iborra, E.; Jimenez, J.; Peiro, F.; Calleja, E.

    2006-08-15

    We have studied the effects of rapid thermal annealing at 1300 deg.C on GaN epilayers grown on AlN buffered Si(111) and on sapphire substrates. After annealing, the epilayers grown on Si display visible alterations with craterlike morphology scattered over the surface. The annealed GaN/Si layers were characterized by a range of experimental techniques: scanning electron microscopy, optical confocal imaging, energy dispersive x-ray microanalysis, Raman scattering, and cathodoluminescence. A substantial Si migration to the GaN epilayer was observed in the crater regions, where decomposition of GaN and formation of Si{sub 3}N{sub 4} crystallites as well as metallic Ga droplets and Si nanocrystals have occurred. The average diameter of the Si nanocrystals was estimated from Raman scattering to be around 3 nm. Such annealing effects, which are not observed in GaN grown on sapphire, are a significant issue for applications of GaN grown on Si(111) substrates when subsequent high-temperature processing is required.

  16. Structural, Optical, and Electrical Characterization of Monoclinic β-Ga2O3 Grown by MOVPE on Sapphire Substrates

    NASA Astrophysics Data System (ADS)

    Tadjer, Marko J.; Mastro, Michael A.; Mahadik, Nadeemullah A.; Currie, Marc; Wheeler, Virginia D.; Freitas, Jaime A.; Greenlee, Jordan D.; Hite, Jennifer K.; Hobart, Karl D.; Eddy, Charles R.; Kub, Fritz J.

    2016-04-01

    Epitaxial growth of monoclinic β-Ga2O3 on a-plane and c-plane sapphire substrates by metalorganic vapor-phase epitaxy (MOVPE) is reported. Crystalline phase, growth rate (˜150 nm/h), and energy gap (˜4.7 eV) were determined by x-ray diffraction and optical reflectance measurements. Film density of ˜5.6 g/cm3 measured by x-ray reflectivity suggests the presence of vacancies, and the O-rich growth regime implies the presence of Ga vacancies in the films. O/Ga ratio of 1.13, as measured by XPS for Ga2O3 grown on c-plane Al2O3, suggests that, near the surface, the film is O-deficient. Atomic force microscopy revealed smoother, smaller grain size when films were grown on c-plane Al2O3. Raman spectroscopy suggested inclusions of α-Ga2O3, likely present at the sapphire interface due to growth on nonnative substrate. Samples of β-Ga2O3 were selectively implanted with Si in the source/drain regions and subsequently annealed at 1000°C for 10 min. Normally-off transistors (V T ≅ 4.7 V) with 20-nm-thick Al2O3 gate oxide were fabricated, and a maximum drain-source current of 4.8 nA was measured.

  17. High-phase-purity zinc-blende InN on r-plane sapphire substrate with controlled nitridation pretreatment

    NASA Astrophysics Data System (ADS)

    Hsiao, Ching-Lien; Liu, Ting-Wei; Wu, Chien-Ting; Hsu, Hsu-Cheng; Hsu, Geng-Ming; Chen, Li-Chyong; Shiao, Wen-Yu; Yang, C. C.; Gällström, Andreas; Holtz, Per-Olof; Chen, Chia-Chun; Chen, Kuei-Hsien

    2008-03-01

    High-phase-purity zinc-blende (zb) InN thin film has been grown by plasma-assisted molecular-beam epitaxy on r-plane sapphire substrate pretreated with nitridation. X-ray diffraction analysis shows that the phase of the InN films changes from wurtzite (w) InN to a mixture of w-InN and zb-InN, to zb-InN with increasing nitridation time. High-resolution transmission electron microscopy reveals an ultrathin crystallized interlayer produced by substrate nitridation, which plays an important role in controlling the InN phase. Photoluminescence emission of zb-InN measured at 20K shows a peak at a very low energy, 0.636eV, and an absorption edge at ˜0.62eV is observed at 2K, which is the lowest bandgap reported to date among the III-nitride semiconductors.

  18. InGaN-Based Light-Emitting Diodes Fabricated on Nano Patterned Sapphire Substrates with Pillar Height of More than 600 nm by Nanoimprint Lithography

    NASA Astrophysics Data System (ADS)

    Okada, Narihito; Egami, Takuya; Miyoshi, Seita; Inomoto, Ryo; Yamane, Keisuke; Tadatomo, Kazuyuki; Nishimiya, Tomoyasu; Hiramoto, Michihiro; Motoyama, Shin-ichi

    2013-11-01

    GaN-based light-emitting diodes (LEDs) were fabricated on nano patterned sapphire substrates (nano-PSSs) by nanoimprint (NIP) lithography. A nano-PSS with a pillar height of more than 600 nm was achieved. The surface emission of the LEDs was strongly affected by pillar height, and the surface emission intensity was highest at a pillar height of 250 nm. In contrast, the external quantum efficiency of the LEDs on the nano-PSSs with diameters of 100 and 450 nm was approximately 30% higher than that on a flat sapphire substrate, which is similar to that on a conventional PSS.

  19. Crack-free thick (∼5 µm) α-Ga2O3 films on sapphire substrates with α-(Al,Ga)2O3 buffer layers

    NASA Astrophysics Data System (ADS)

    Oda, Masaya; Kaneko, Kentaro; Fujita, Shizuo; Hitora, Toshimi

    2016-12-01

    To obtain crack-free thick α-Ga2O3 films on sapphire substrates, effects and behaviors of buffer layers have been investigated. With the growth of an α-Ga2O3 layer, there appeared an unintentionally formed layer in the sample, which was associated with stress accumulation and could be the seed for crack generation. We obtained a thick (∼5 µm) α-Ga2O3 layer on a sapphire substrate with the insertion of α-(Al0.12Ga0.88)2O3/α-(Al0.02Ga0.98)2O3 buffer layers, and for this sample, we did not observe the intermediate layer, suggesting that the buffer layers were effective for eliminating the stress accumulation at the α-Ga2O3/sapphire interface region.

  20. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: The effects of vicinal sapphire substrates on the properties of AlGaN/GaN heterostructures

    NASA Astrophysics Data System (ADS)

    Xu, Zhi-Hao; Zhang, Jin-Cheng; Zhang, Zhong-Fen; Zhu, Qing-Wei; Duan, Huan-Tao; Hao, Yue

    2009-12-01

    AlGaN/GaN heterostructures on vicinal sapphire substrates and just-oriented sapphire substrates (0001) are grown by the metalorganic chemical vapor deposition method. Samples are studied by high-resolution x-ray diffraction, atomic force microscopy, capacitance-voltage measurement and the Van der Pauw Hall-effect technique. The investigation reveals that better crystal quality and surface morphology of the sample are obtained on the vicinal substrate. Furthermore, the electrical properties are also improved when the sample is grown on the vicinal substrate. This is due to the fact that the use of vicinal substrate can promote the step-flow mode of crystal growth, so many macro-steps are formed during crystal growth, which causes a reduction of threading dislocations in the crystal and an improvement in the electrical properties of the AlGaN/GaN heterostructure.

  1. Growth kinetics of AlN and GaN films grown by molecular beam epitaxy on R-plane sapphire substrates

    SciTech Connect

    Chandrasekaran, R.; Moustakas, T. D.; Ozcan, A. S.; Ludwig, K. F.; Zhou, L.; Smith, David J.

    2010-08-15

    This paper reports the growth by molecular beam epitaxy of AlN and GaN thin films on R-plane sapphire substrates. Contrary to previous findings that GaN grows with its (1120) A-plane parallel to the (1102) R-plane of sapphire, our results indicate that the crystallographic orientation of the III-nitride films is strongly dependent on the kinetic conditions of growth for the GaN or AlN buffer layers. Thus, group III-rich conditions for growth of either GaN or AlN buffers result in nitride films having (1120) planes parallel to the sapphire surface, and basal-plane stacking faults parallel to the growth direction. The growth of these buffers under N-rich conditions instead leads to nitride films with (1126) planes parallel to the sapphire surface, with inclined c-plane stacking faults that often terminate threading dislocations. Moreover, electron microscope observations indicate that slight miscut ({approx}0.5 deg. ) of the R-plane sapphire substrate almost completely suppresses the formation of twinning defects in the (1126) GaN films.

  2. Influence of patterned sapphire substrates with different symmetry on the light output power of InGaN-based LEDs

    PubMed Central

    2014-01-01

    This paper aims to investigate the light output power (LOP) of InGaN-based light-emitting diodes (LEDs) grown on patterned sapphire substrates (PSSs) with different symmetry. The GaN epitaxial layers grown on the hexagonal lattice arrangement PSS (HLAPSS) have a lower compressive strain than the ones grown on the square lattice arrangement PSS (SLAPSS). The quantum-confined Stark effect (QCSE) is also affected by the residual compressive strain. Based on the experimentally measured data and the ray tracing simulation results, the InGaN-based LED with the HLAPSS has a higher LOP than the one with the SLAPSS due to the weaker QCSE within multiple-quantum wells (MQWs). PMID:25392706

  3. In-situ mapping of electroluminescent enhancement of light-emitting diodes grown on patterned sapphire substrates

    NASA Astrophysics Data System (ADS)

    Su, Jung-Chieh; Lee, Chung-Hao; Huang, Yi-Hsuan; Yang, Henglong

    2017-02-01

    The mechanism for enhancing extraction efficiency of light emitting diodes (LEDs) grown on patterned sapphire substrates (PSSs) was observed by the in-situ lateral electroluminescence (EL) mapping using optical microscopy equipped with a laser energy profiler. The observed spatial intensity distribution of epilayers, varying from epilayer to epilayer on the lateral surface of the PSS LED chip, revealed that the perimeter scattering on the convex facets of PSSs converges the propagation of emitted light with random directionality into a spot near the top surface of the buffer layer. Moreover, this in-situ sidewall mapping implied that the enhancement of light extraction of the PSS LED is due to reducing the total internal reflection effect, resulting from the spot located closer to the LED/air interface. Simulated results and EL images of convex patterns on the PSS surface were consistent with sidewall surface-based observations.

  4. High Mobility SiGe/Si n-Type Structures and Field Effect Transistors on Sapphire Substrates

    NASA Technical Reports Server (NTRS)

    Alterovitz, Samuel A.; Ponchak, George E.; Mueller, Carl H.; Croke, Edward T.

    2004-01-01

    SiGe/Si n-type modulation doped field effect transistors (MODFETs) fabricated on sapphire substrates have been characterized at microwave frequencies for the first time. The highest measured room temperature electron mobility is 1380 sq cm/V-sec at a carrier density of 1.8 x 10(exp 12)/sq cm for a MODFET structure, and 900 sq cm/V-sec at a carrier density of 1.3 x 10/sq cm for a phosphorus ion implanted sample. A two finger, 2 x 200 micron gate n-MODFET has a peak transconductance of 37 mS/mm at a drain to source voltage of 2.5 V and a transducer gain of 6.4 dB at 1 GHz.

  5. Direct Growth of a-Plane GaN on r-Plane Sapphire Substrate by Metalorganic Vapor Phase Epitaxy

    NASA Astrophysics Data System (ADS)

    Araki, Masahiro; Mochimizo, Noriaki; Hoshino, Katsuyuki; Tadatomo, Kazuyuki

    2007-02-01

    We have investigated the direct growth of nonpolar a-plane GaN layers on an r-plane sapphire substrate by metalorganic vapor-phase epitaxy (MOVPE). A high-density nucleation of GaN islands was obtained on the r-plane sapphire substrate at the initial stage of the high-temperature growth without a buffer layer, which resulted in a two-dimensional (2D) growth mode. We studied the effects of V/III ratio growth conditions on the surface morphology and growth features of an a-plane GaN layer. The results showed that a high density of pits with an inverse-pyramidal shape were formed at a high V/III ratio, whereas a relatively low density of pits were formed at a low V/III ratio due to the increase in the rate of lateral growth along the c-axis direction. We successfully grew a-plane GaN layers with a flat and pit-free surface using the “two-step growth method”. The method consisted of growing a first layer at a high V/III ratio and growing a second layer at a low V/III ratio. We found that the first layer plays an important role in GaN layer growth. The formation of a void-free GaN layer with sidewall facets in the first step leads to a flat and pit-free layer grown at a high rate of lateral growth along the c-axis direction in the second step.

  6. Investigation of void formation beneath thin AlN layers by decomposition of sapphire substrates for self-separation of thick AlN layers grown by HVPE

    NASA Astrophysics Data System (ADS)

    Kumagai, Yoshinao; Enatsu, Yuuki; Ishizuki, Masanari; Kubota, Yuki; Tajima, Jumpei; Nagashima, Toru; Murakami, Hisashi; Takada, Kazuya; Koukitu, Akinori

    2010-09-01

    Void formation at the interface between thick AlN layers and (0 0 0 1) sapphire substrates was investigated to form a predefined separation point of the thick AlN layers for the preparation of freestanding AlN substrates by hydride vapor phase epitaxy (HVPE). By heating 50-200 nm thick intermediate AlN layers above 1400 °C in a gas flow containing H 2 and NH 3, voids were formed beneath the AlN layers by the decomposition reaction of sapphire with hydrogen diffusing to the interface. The volume of the sapphire decomposed at the interface increased as the temperature and time of the heat treatment was increased and as the thickness of the AlN layer decreased. Thick AlN layers subsequently grown at 1450 °C after the formation of voids beneath the intermediate AlN layer with a thickness of 100 nm or above self-separated from the sapphire substrates during post-growth cooling with the aid of voids. The 79 μm thick freestanding AlN substrate obtained using a 200 nm thick intermediate AlN layer had a flat surface with no pits, high optical transparency at wavelengths above 208.1 nm, and a dislocation density of 1.5×10 8 cm -2.

  7. Effect of surface pretreatment of r-plane sapphire substrates on the crystal quality of a-plane AlN

    NASA Astrophysics Data System (ADS)

    Lin, Chia-Hung; Yasui, Daiki; Tamaki, Shinya; Miyake, Hideto; Hiramatsu, Kazumasa

    2016-05-01

    Single-crystal a-plane AlN(11\\bar{2}0) films were grown on r-plane sapphire (1\\bar{1}02) substrates by hydride vapor phase epitaxy (HVPE). We performed the optimization of thermal cleaning and nitridation conditions for r-plane sapphire substrates, and investigated the effect of ammonia (NH3) preflow on the crystallinity of a-plane AlN. An r-plane sapphire substrate with uniformly straight atomic steps was formed at 1000 °C, and NH3 preflow was subsequently supplied. The growth mode of a-plane AlN was promoted to be three-dimensional (3D) growth by the nitridation of r-plane sapphire substrates, and sizes of 3D islands were modified by changing the NH3 preflow time. The crystallinity of a-plane AlN films was improved by varying the NH3 preflow time from 30 to 90 s. The optimum crystal quality of a-plane AlN films was obtained with NH3 preflow for 30 s.

  8. Influence of vicinal sapphire substrate on the properties of N-polar GaN films grown by metal-organic chemical vapor deposition

    SciTech Connect

    Lin, Zhiyu; Zhang, Jincheng Xu, Shengrui; Chen, Zhibin; Yang, Shuangyong; Tian, Kun; Hao, Yue; Su, Xujun; Shi, Xuefang

    2014-08-25

    The influence of vicinal sapphire substrates on the growth of N-polar GaN films by metal-organic chemical vapor deposition is investigated. Smooth GaN films without hexagonal surface feature are obtained on vicinal substrate. Transmission electron microscope results reveal that basal-plane stacking faults are formed in GaN on vicinal substrate, leading to a reduction in threading dislocation density. Furthermore, it has been found that there is a weaker yellow luminescence in GaN on vicinal substrate than that on (0001) substrate, which might be explained by the different trends of the carbon impurity incorporation.

  9. Optical and electrical properties of high-quality Ti2O3 epitaxial film grown on sapphire substrate

    NASA Astrophysics Data System (ADS)

    Fan, Haibo; Wang, Mingzi; Yang, Zhou; Ren, Xianpei; Yin, Mingli; Liu, Shengzhong

    2016-11-01

    Epitaxial film of Ti2O3 with high crystalline quality was grown on Al2O3 substrate by pulsed laser deposition process using a powder-pressed TiO2 target in active O2 flow. X-ray diffraction clearly reveals the (0006) crystalline Ti2O3 orientation and its (10overline{1} 0)_{{{{Ti}}_{ 2} {{O}}_{ 3} }} ||(10overline{1} 0)_{{sapphire}} in-plane epitaxial relationship with the substrate. Scanning electron microscopy images show that the film grew uniformly on the substrate with a Volmer-Weber mode. High-resolution transmission electron microscopy and selected area electron diffraction further confirm the high crystalline quality of the film. Transmittance spectrum shows that the Ti2O3 film is highly transparent in 400-800 nm with the optical band gap estimated to be 3.53 eV by Tauc plot. The temperature-dependent Hall effect measurement indicates that the Ti2O3 film appears to be n-type semiconductor with carrier concentration, mobility, and resistivity showing typical temperature-dependent behavior. The donor ionization energy was estimated to be 83.6 meV by linear relationship of conductivity versus temperature.

  10. Substrate Effects on Growth of MoS2 Film by Laser Physical Vapor Deposition on Sapphire, Si and Graphene (on Cu)

    NASA Astrophysics Data System (ADS)

    Jagannadham, K.; Cui, J.; Zhu, Y.

    2017-02-01

    Molybdenum disulfide (MoS2) films were deposited on sapphire (0001), Si (001) and graphene on Cu by laser physical vapor deposition at 600°C for different time periods to achieve control of thickness. MoS2 film was found to grow on all the substrates in the (0002) orientation. Films are found to be S-deficient and a free Mo peak was observed in the x-ray diffraction. Raman spectroscopy showed the characteristic peaks of MoS2 film with decreasing separation between the A1g and E 2g 1 peaks for a shorter time of deposition or smaller thickness of the film. MoS2 films on sapphire substrate showed additional peaks due to MoO3 and Mo4O11 phases. Films on Si substrate and graphene on Cu contained only the characteristic peaks. MoS2 films on graphene suppressed the graphene peak as a result of large fluorescence background in the Raman spectrum. Interfacial effects and the presence of an oxygen impurity are considered responsible for the large fluorescence background in the Raman spectrum. X-ray photoelectron spectroscopy indicated substrate interaction with the films on sapphire and Si. Coverage of the film on the substrates is uniform with uniform distribution of the Mo and S as evidenced from the x-ray maps. Atomic force microscopy image revealed the surface of the film on sapphire to be very smooth. Electrical conductance measurements showed the MoS2 film on sapphire is semiconducting but with much lower activation energy compared to the bandgap. The presence of excess Mo in the film is considered responsible for the lower activation energy.

  11. Three dimensional material removal model of laser-induced backside wet etching of sapphire substrate with CuSO4 solutions

    NASA Astrophysics Data System (ADS)

    Xie, Xiaozhu; Huang, Xiandong; Jiang, Wei; Wei, Xin; Hu, Wei; Ren, Qinglei

    2017-03-01

    The mechanism of laser-induced backside wet etching (LIBWE) of sapphire substrate with CuSO4 solution is considered as a two-step process. First, it deposits the layer from copper sulfate solution on the backside of sapphire substrate by 1064 nm laser irradiation. Then it is followed by the absorption of deposited layer to laser irradiation, resulting in the etching of the sapphire. Therefore, the material removal of LIBWE is based on laser interaction with multilayer materials (sapphire substrate-deposition layer-liquid solution). A three-dimensional thermal model is established to simulate the material removal during the LIBWE process by considering the material data variations of temperature, enthalpy change and latent heat fusion. The model can predict the groove shape influenced by the laser processing parameters (laser fluence, scanning velocity and scanning pass). The simulation results indicate that the groove depth increases with the decreasing of scanning velocity, the increasing of laser fluence and the scanning pass. The groove width is comparable with the focal beam diameter. Some peaks and valleys occur at the bottom of the groove. A comparison between the modeling and experiment indicates that the groove shape in simulation agrees well with the experiment data at laser pulse energy of 4.3 mJ/pulse, scanning velocity of 15 mm/s and the scanning pass of 4. i.e, the present physical model is effective and feasible.

  12. Temperature dependence of the crystalline quality of AlN layer grown on sapphire substrates by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Li, Xiao-Hang; Wei, Yong O.; Wang, Shuo; Xie, Hongen; Kao, Tsung-Ting; Satter, Md. Mahbub; Shen, Shyh-Chiang; Douglas Yoder, P.; Detchprohm, Theeradetch; Dupuis, Russell D.; Fischer, Alec M.; Ponce, Fernando A.

    2015-03-01

    We studied temperature dependence of crystalline quality of AlN layers at 1050-1250 °C with a fine increment step of around 18 °C. The AlN layers were grown on c-plane sapphire substrates by metalorganic chemical vapor deposition (MOCVD) and characterized by X-ray diffraction (XRD) ω-scans and atomic force microscopy (AFM). At 1050-1068 °C, the templates exhibited poor quality with surface pits and higher XRD (002) and (102) full-width at half-maximum (FWHM) because of insufficient Al atom mobility. At 1086 °C, the surface became smooth suggesting sufficient Al atom mobility. Above 1086 °C, the (102) FWHM and thus edge dislocation density increased with temperatures which may be attributed to the shorter growth mode transition from three-dimension (3D) to two-dimension (2D). Above 1212 °C, surface macro-steps were formed due to the longer diffusion length of Al atoms than the expected step terrace width. The edge dislocation density increased rapidly above 1212 °C, indicating this temperature may be a threshold above which the impact of the transition from 3D to 2D is more significant. The (002) FWHM and thus screw dislocation density were insensitive to the temperature change. This study suggests that high-quality AlN/sapphire templates may be potentially achieved at temperatures as low as 1086 °C which is accessible by most of the III-nitride MOCVD systems.

  13. Epitaxial chemical vapour deposition growth of monolayer hexagonal boron nitride on a Cu(111)/sapphire substrate.

    PubMed

    Uchida, Yuki; Iwaizako, Tasuku; Mizuno, Seigi; Tsuji, Masaharu; Ago, Hiroki

    2017-03-22

    Hexagonal boron nitride (h-BN), an atomically thin insulating material, shows a large band gap, mechanical flexibility, and optical transparency. It can be stacked with other two-dimensional (2D) materials through van der Waals interactions to form layered heterostructures. These properties promise its application as an insulating layer of novel 2D electronic devices due to its atomically smooth surface with a large band gap. Herein, we demonstrated the ambient-pressure chemical vapour deposition (CVD) growth of high-quality, large-area monolayer h-BN on a Cu(111) thin film deposited on a c-plane sapphire using ammonia borane (BH3NH3) as the feedstock. Highly oriented triangular h-BN grains grow on Cu(111), which finally coalescence to cover the entire Cu surface. Low-energy electron diffraction (LEED) measurements indicated that the hexagonal lattice of the monolayer h-BN is well-oriented along the underlying Cu(111) lattice, thus implying the epitaxial growth of h-BN, which can be applied in various 2D electronic devices.

  14. Twin symmetry texture of energetically condensed niobium thin films on sapphire substrate (a-plane Al2O3)

    NASA Astrophysics Data System (ADS)

    Zhao, X.; Phillips, L.; Reece, C. E.; Seo, Kang; Krishnan, M.; Valderrama, E.

    2011-08-01

    An energetic condensation technique, cathodic arc discharge deposition, is used to grow epitaxial Niobium (Nb) thin films on a-plane sapphire (hexagonal-closed-packed Al2O3) at moderate substrate heating temperature (<400 °C). The epitaxial Nb(110)/Al2O3(1,1,-2,0) thin films reached a maximum residual resistance ratio (RRR) value 214, despite using a reactor-grade Nb cathode source whose RRR was only 30. The measurements suggest that the film's density of impurities and structural defects are lower when compared to Nb films produced by other techniques, such as magnetron sputtering, e-beam evaporation or molecular-beam-epitaxy. At lower substrate temperature, textured polycrystalline Nb thin films were created, and the films might have twin symmetry grains with {110} orientations in-plane. The texture was revealed by x-ray diffraction pole figures. The twin symmetry might be caused by a combination effect of the Nb/Al2O3 three-dimensional epitaxial relationship ("3D-Registry" Claassen's nomenclature) and the "Volmer-Weber" (Island) growth model. However, pole figures obtained by electron backscattering diffraction (EBSD) found no twin symmetry on the thin films' topmost surface (˜50 nm in depth). The EBSD pole figures showed only one Nb{110} crystal plane orientation. A possible mechanism is suggested to explain the differences between the bulk (XRD) and surface (EBSD) pole figures.

  15. Vapor phase epitaxy of CdTe on sapphire substrates in dependence on the vapor-flow orientation

    NASA Astrophysics Data System (ADS)

    Muslimov, A. E.; Butashin, A. V.; Vlasov, V. P.; Kanevsky, V. M.

    2016-11-01

    The growth of cadmium telluride films on a structured (0001) sapphire surface oriented at an angle of 44° to the vapor-flow direction and normal to the steps formed along the 11overline 2 0 direction is studied. It is found that this geometry of the vapor source and a substrate (heated to a temperature of 300°C) provides the growth of single-crystal CdTe films if a step height on the substrate surface is more than 1 nm. The results are explained by the occurrence of a longitudinal component of the diffusion flux of CdTe molecules and atoms toward the steps from the inner side and their high density at the step edge from the outer side due to the presence of the Ehrlich-Schwoebel barrier, which ensures the efficient supply of material and minimum supersaturation necessary for the nucleation at the step edge and growth of oriented CdTe islands. The cadmium telluride films that are grown have the ( {110} )[ {1overline 1 0} ]CdTe| {( {0001} )} .[ {11overline 2 0} ]A{l_2}{O_3} orientation and a composition similar to stoichiometric CdTe.

  16. A comparative study of efficiency droop and internal electric field for InGaN blue lighting-emitting diodes on silicon and sapphire substrates.

    PubMed

    Ryu, H Y; Jeon, K S; Kang, M G; Yuh, H K; Choi, Y H; Lee, J S

    2017-04-12

    We investigated the efficiency droop and polarization-induced internal electric field of InGaN blue light-emitting diodes (LEDs) grown on silicon(111) and c-plane sapphire substrates. The efficiency droop of the LED sample grown on silicon substrates was considerably lower than that of the identically fabricated LED sample grown on sapphire substrates. Consequently, the LED on silicon showed higher efficiency at a sufficiently high injection current despite the lower peak efficiency caused by the poorer crystal quality. The reduced efficiency droop for the LED on silicon was attributed to its lower internal electric field, which was confirmed by reverse-bias electro-reflectance measurements and numerical simulations. The internal electric field of the multiple quantum wells (MQWs) on silicon was found to be reduced by more than 40% compared to that of the MQWs on sapphire, which resulted in a more homogenous carrier distribution in InGaN MQWs, lower Auger recombination rates, and consequently reduced efficiency droop for the LEDs grown on the silicon substrates. Owing to its greatly reduced efficiency droop, the InGaN blue LED on silicon substrates is expected to be a good cost effective solution for future lighting technology.

  17. Structural and optical properties of AgAlTe{sub 2} layers grown on sapphire substrates by closed space sublimation method

    SciTech Connect

    Uruno, A. Usui, A.; Kobayashi, M.

    2014-11-14

    AgAlTe{sub 2} layers were grown on a- and c-plane sapphire substrates using a closed space sublimation method. Grown layers were confirmed to be single phase layers of AgAlTe{sub 2} by X-ray diffraction. AgAlTe{sub 2} layers were grown to have a strong preference for the (112) orientation on both kinds of substrates. The variation in the orientation of grown layers was analyzed in detail using the X-ray diffraction pole figure measurement, which revealed that the AgAlTe{sub 2} had a preferential epitaxial relationship with the c-plane sapphire substrate. The atomic arrangement between the (112) AgAlTe{sub 2} layer and sapphire substrates was compared. It was considered that the high order of the lattice arrangement symmetry probably effectively accommodated the lattice mismatch. The optical properties of the grown layer were also evaluated by transmittance measurements. The bandgap energy was found to be around 2.3 eV, which was in agreement with the theoretical bandgap energy of AgAlTe{sub 2}.

  18. High quality Al0.99Ga0.01N layers on sapphire substrates grown at 1150 °C by metalorganic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Katsuno, Shota; Yasuda, Toshiki; Hagiwara, Koudai; Koide, Norikatsu; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu; Amano, Hiroshi

    2017-01-01

    We systematically investigated metalorganic vapor phase epitaxy (MOVPE) growths of AlN layers with trimethylgallium (TMGa) supply on sapphire substrates at 1100-1250 °C. We found that Ga incorporations into the AlN layers contributed to smooth surfaces covered with step terraces at the early stage of the Al(Ga)N growth. In addition, a GaN mole fraction leading to the smooth surfaces was found to be around 2-3% at the beginning of growth. The Ga supply during the AlN layer growth at 1150 °C provided very smooth Al0.99Ga0.01N layers on sapphire substrates.

  19. Tl 2Ba 2CaCu 2O 8 thin film high frequency filters on 3 inch sapphire substrates

    NASA Astrophysics Data System (ADS)

    Schneidewind, H.; Manzel, M.; Stelzner, T.

    2002-08-01

    Modern communication systems require densely packed frequency channels in the expensive frequency bands. Therefore high temperature superconducting (HTS) high frequency filters are of increasing importance, taking advantage of their outstanding properties namely steep filter skirts, low insertion loss, and furthermore reduced mass and volume compared to conventional cavity or dielectric resonator systems. Within the framework of a German BMBF pilot project a HTS equiped satellite repeater will be developed to demonstrate the performance advantage of HTS. For that purpose we prepare filters on double-sided Tl 2Ba 2CaCu 2O 8 thin films on CeO 2 buffered 3 inch sapphire substrates. The HTS films are prepared in the two-step process by sputtering an amorphous thallium free precursor and following oxythallination. The critical temperature and spatial distribution of critical current density at 77 K, both measured by inductive techniques, show values above 100 K or 1 MA/cm 2, respectively. We use a dielectric resonator technique at 3.9 GHz and power levels up to some mT to determine the films surface resistance. We present measurements of input filters made from our double-sided 3 inch films.

  20. The determining factor of a preferred orientation of GaN domains grown on m-plane sapphire substrates

    NASA Astrophysics Data System (ADS)

    Jue, Miyeon; Kim, Cheol-Woon; Kang, Seoung-Hun; Yoon, Hansub; Jang, Dongsoo; Kwon, Young-Kyun; Kim, Chinkyo

    2015-11-01

    Epitaxial lateral overgrowth in tandem with the first-principles calculation was employed to investigate the determining factor of a preferred orientation of GaN on SiO2-patterned m-plane sapphire substrates. We found that the (100)-orientation is favored over the (10)-orientation in the region with a small filling factor of SiO2, while the latter orientation becomes preferred in the region with a large filling factor. This result suggests that the effective concentration determines the preferred orientation of GaN: the (100)- and (10)-orientations preferred at their low and high concentrations, respectively. Our computational study revealed that at a low coverage of Ga and N atoms, the local atomic arrangement resembles that on the (10) surface, although the (100) surface is more stable at their full coverage. Such a (10)-like atomic configuration crosses over to the local structure resembling that on the (100) surface as the coverage increases. Based on results, we determined that high effective concentration of Ga and N sources expedites the growth of the (10)-orientation while keeping from transition to the (100)-orientation. At low effective concentration, on the other hand, there is a sufficient time for the added Ga and N sources to rearrange the initial (10)-like orientation to form the (100)-orientation.

  1. Continuous Tuning of Phase Transition Temperature in VO2 Thin Films on c-Cut Sapphire Substrates via Strain Variation.

    PubMed

    Jian, Jie; Wang, Xuejing; Li, Leigang; Fan, Meng; Zhang, Wenrui; Huang, Jijie; Qi, Zhimin; Wang, Haiyan

    2017-02-15

    Vanadium dioxide (VO2) thin films with controlled thicknesses are deposited on c-cut sapphire substrates with Al-doped ZnO (AZO) buffer layers by pulsed laser deposition. The surface roughness of AZO buffer layers is varied by controlling oxygen pressure during growth. The strain in the VO2 lattice is found to be dependent on the VO2 thickness and the VO2/AZO interface roughness. The semiconductor-to-metal transition (SMT) properties of VO2 thin films are characterized and the transition temperature (Tc) is successfully tuned by the VO2 thickness as well as the VO2/AZO interface roughness. It shows that the Tc of VO2 decreases with the decrease of film thickness or VO2/AZO interface roughness. Other SMT properties of the VO2 films are maintained during the Tc tuning. The results suggest that the strain tuning induced by AZO buffer provides an effective approach for tuning Tc of VO2 continuously.

  2. Preparation and modification of VO2 thin film on R-sapphire substrate by rapid thermal process

    NASA Astrophysics Data System (ADS)

    Zhu, Nai-Wei; Hu, Ming; Xia, Xiao-Xu; Wei, Xiao-Ying; Liang, Ji-Ran

    2014-04-01

    The VO2 thin film with high performance of metal-insulator transition (MIT) is prepared on R-sapphire substrate for the first time by magnetron sputtering with rapid thermal process (RTP). The electrical characteristic and THz transmittance of MIT in VO2 film are studied by four-point probe method and THz time domain spectrum (THz-TDS). X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and search engine marketing (SEM) are employed to analyze the crystalline structure, valence state, surface morphology of the film. Results indicate that the properties of VO2 film which is oxidized from the metal vanadium film in oxygen atmosphere are improved with a follow-up RTP modification in nitrogen atmosphere. The crystallization and components of VO2 film are improved and the film becomes compact and uniform. A better phase transition performance is shown that the resistance changes nearly 3 orders of magnitude with a 2-°C hysteresis width and the THz transmittances are reduced by 64% and 60% in thermal and optical excitation respectively.

  3. Metalorganic chemical vapor deposition of hexagonal boron nitride on (001) sapphire substrates for thermal neutron detector applications

    NASA Astrophysics Data System (ADS)

    Ahmed, K.; Dahal, R.; Weltz, A.; Lu, James J.-Q.; Danon, Y.; Bhat, I. B.

    2017-03-01

    This paper reports on the growth and characterization of hexagonal boron nitride (hBN) and its use for solid-state thermal neutron detection. The hBN epilayers were grown by metalorganic chemical vapor deposition on sapphire substrates at a temperature of 1350 C. X-ray diffraction peak from the (002) hBN plane at a 2theta angle of 26.7 deg exhibited the c-lattice constant of 6.66 {\\AA} for these films. A strong peak corresponding to the high frequency Raman active mode of hBN was found for the films at 1370.5/cm. hBN-based solid-state neutron detectors were fabricated and tested with a metal-semiconductor-metal configuration with an electrode spacing of 1 mm and hBN thickness of 2.5 micron. Fabricated detectors showed strong response to deep UV light as well. An intrinsic thermal neutron detection efficiency of 0.86% was measured, which is close to the theoretically expected efficiency of 0.87%. These results demonstrate that epitaxial hBN films are promising for thermal neutron detection applications.

  4. Growth and characterization of periodically polarity-inverted ZnO structures on sapphire substrates

    SciTech Connect

    Park, Jinsub; Yao, Takafumi

    2012-10-15

    We report on the fabrication and characterization of periodically polarity inverted (PPI) ZnO heterostructures on (0 0 0 1) Al{sub 2}O{sub 3} substrates. For the periodically inverted array of ZnO polarity, CrN and Cr{sub 2}O{sub 3} polarity selection buffer layers are used for the Zn- and O-polar ZnO films, respectively. The change of polarity and period in fabricated ZnO structures is evaluated by diffraction patterns and polarity sensitive piezo-response microscopy. Finally, PPI ZnO structures with subnanometer scale period are demonstrated by using holographic lithography and regrowth techniques.

  5. Growing oriented AlN films on sapphire substrates by plasma-enhanced atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Tarala, V. A.; Altakhov, A. S.; Ambartsumov, M. G.; Martens, V. Ya.

    2017-01-01

    The possibility of growing oriented AlN films on Al2O3 substrates at temperatures below 300°C by plasma-enhanced atomic layer deposition was examined. The samples were subjected to X-ray phase analysis and ellipsometry. It was demonstrated that the refraction index of films deposited with plasma exposures longer than 20 s was 2.03 ± 0.03. The (0002) and (0004) reflections at 2Θ angles of 35.7° and 75.9° were present in the X-ray diffraction patterns of these samples. These reflections are typical of the hexagonal AlN polytype. The full width at half maximum of the rocking curve of reflection (0002) in the best sample was 162 ± 11 arcsec.

  6. Pulsed modification of germanium films on silicon, sapphire, and quartz substrates: Structure and optical properties

    SciTech Connect

    Novikov, H. A.; Batalov, R. I. Bayazitov, R. M.; Faizrakhmanov, I. A.; Lyadov, N. M.; Shustov, V. A.; Galkin, K. N.; Galkin, N. G.; Chernev, I. M.; Ivlev, G. D.; Prokop’ev, S. L.; Gaiduk, P. I.

    2015-06-15

    The structural and optical properties of thin Ge films deposited onto semiconducting and insulating substrates and modified by pulsed laser radiation are studied. The films are deposited by the sputtering of a Ge target with a low-energy Xe{sup +} ion beam. Crystallization of the films is conducted by their exposure to nanosecond ruby laser radiation pulses (λ = 0.694 μm) with the energy density W = 0.2−1.4 J cm{sup −2}. During pulsed laser treatment, the irradiated area is probed with quasi-cw (quasi-continuous-wave) laser radiation (λ = 0.532 and 1.064 μm), with the reflectance recorded R(t). Experimental data on the lifetime of the Ge melt are compared with the results of calculation, and good agreement between them is demonstrated. Through the use of a number of techniques, the dependences of the composition of the films, their crystal structure, the level of strains, and the reflectance and transmittance on the conditions of deposition and annealing are established.

  7. Demonstration of transverse-magnetic deep-ultraviolet stimulated emission from AlGaN multiple-quantum-well lasers grown on a sapphire substrate

    SciTech Connect

    Li, Xiao-Hang E-mail: dupuis@gatech.edu; Kao, Tsung-Ting; Satter, Md. Mahbub; Shen, Shyh-Chiang; Yoder, P. Douglas; Detchprohm, Theeradetch; Dupuis, Russell D. E-mail: dupuis@gatech.edu; Wei, Yong O.; Wang, Shuo; Xie, Hongen; Fischer, Alec M.; Ponce, Fernando A.

    2015-01-26

    We demonstrate transverse-magnetic (TM) dominant deep-ultraviolet (DUV) stimulated emission from photo-pumped AlGaN multiple-quantum-well lasers grown pseudomorphically on an AlN/sapphire template by means of photoluminescence at room temperature. The TM-dominant stimulated emission was observed at wavelengths of 239, 242, and 243 nm with low thresholds of 280, 250, and 290 kW/cm{sup 2}, respectively. In particular, the lasing wavelength of 239 nm is shorter compared to other reports for AlGaN lasers grown on foreign substrates including sapphire and SiC. The peak wavelength difference between the transverse-electric (TE)-polarized emission and TM-polarized emission was approximately zero for the lasers in this study, indicating the crossover of crystal-field split-off hole and heavy-hole valence bands. The rapid variation of polarization between TE- and TM-dominance versus the change in lasing wavelength from 243 to 249 nm can be attributed to a dramatic change in the TE-to-TM gain coefficient ratio for the sapphire-based DUV lasers in the vicinity of TE-TM switch.

  8. Response to Comment on '#28;Twin Symmetry Texture of Energetically Condensed 2 Niobium Thin Films on Sapphire Substrate' #29; [J. Appl. Phys. 110, 033523(2011)

    SciTech Connect

    Xin Zhao, Charles Reece, Phillips Larry, Mahadevan Krishnan, Kang Seo

    2012-07-01

    Welander commented that in our article [J. Appl. Phys. 110, 033523(2011)] , Zhao et al claim to have found a new three-dimensional (3D) relationship for niobium-on-sapphire epitaxy”. Welander might have misunderstood the purpose of our article, which was to show that energetic condensation of Nb on sapphire drives crystal growth that is quite distinct from the type of epitaxy encountered in lower energy deposition. Welander is correct about the misidentified crystal-directions in the top-view sapphire lattice (Fig.4[ref.1]). He is also correct about the misorientation of the pole figures in Fig4[ref.1]. In Fig.1 of this response, we have corrected these errors. Perhaps because of these errors, Welander misconstrued our discussion of the Nb crystal growth as claiming a new 3D registry. That was not our intention. Rather, we wished to highlight the role of energetic condensation that drives low-defect crystal growth by a combination of non-equilibrium sub-plantation that disturbs the substrate lattice and thermal annealing that annihilates defects and promotes large-grain crystal growth.

  9. Electron scattering mechanisms in GZO films grown on a-sapphire substrates by plasma-enhanced molecular beam epitaxy

    SciTech Connect

    Liu, H. Y.; Avrutin, V.; Izyumskaya, N.; Oezguer, Ue.; Morkoc, H.; Yankovich, A. B.; Kvit, A. V.; Voyles, P. M.

    2012-05-15

    We report on the mechanisms governing electron transport using a comprehensive set of ZnO layers heavily doped with Ga (GZO) grown by plasma-enhanced molecular-beam epitaxy on a-plane sapphire substrates with varying oxygen-to-metal ratios and Ga fluxes. The analyses were conducted by temperature dependent Hall measurements which were supported by microstructural investigations as well. Highly degenerate GZO layers with n > 5 x 10{sup 20} cm{sup -3} grown under metal-rich conditions (reactive oxygen-to-metal ratio <1) show relatively larger grains ({approx}20-25 nm by x-ray diffraction) with low-angle boundaries parallel to the polar c-direction. For highly conductive GZO layers, ionized-impurity scattering with almost no compensation is the dominant mechanism limiting the mobility in the temperature range from 15 to 330 K and the grain-boundary scattering governed by quantum-mechanical tunnelling is negligible. However, due to the polar nature of ZnO having high crystalline quality, polar optical phonon scattering cannot be neglected for temperatures above 150 K, because it further reduces mobility although its effect is still substantially weaker than the ionized impurity scattering even at room temperature (RT). Analysis of transport measurements and sample microstructures by x-ray diffraction and transmission electron microscopy led to a correlation between the grain sizes in these layers and mobility even for samples with a carrier concentration in the upper 10{sup 20} cm{sup -3} range. In contrast, electron transport in GZO layers grown under oxygen-rich conditions (reactive oxygen-to-metal ratio >1), which have inclined grain boundaries and relatively smaller grain sizes of 10-20 nm by x-ray diffraction, is mainly limited by compensation caused by acceptor-type point-defect complexes, presumably (Ga{sub Zn}-V{sub Zn}), and scattering on grain boundaries. The GZO layers with n <10{sup 20} cm{sup -3} grown under metal-rich conditions with reduced Ga fluxes

  10. Sapphire substrate-induced effects in VO{sub 2} thin films grown by oxygen plasma-assisted pulsed laser deposition

    SciTech Connect

    Skuza, J. R. E-mail: apradhan@nsu.edu; Scott, D. W.; Pradhan, A. K. E-mail: apradhan@nsu.edu

    2015-11-21

    We investigate the structural and electronic properties of VO{sub 2} thin films on c-plane sapphire substrates with three different surface morphologies to control the strain at the substrate-film interface. Only non-annealed substrates with no discernible surface features (terraces) provided a suitable template for VO{sub 2} film growth with a semiconductor-metal transition (SMT), which was much lower than the bulk transition temperature. In addition to strain, oxygen vacancy concentration also affects the properties of VO{sub 2}, which can be controlled through deposition conditions. Oxygen plasma-assisted pulsed laser deposition allows favorable conditions for VO{sub 2} film growth with SMTs that can be easily tailored for device applications.

  11. Demonstration of Y1Ba2Cu3O(7-delta) and complementary metal-oxide-semiconductor device fabrication on the same sapphire substrate

    NASA Technical Reports Server (NTRS)

    Burns, M. J.; De La Houssaye, P. R.; Russell, S. D.; Garcia, G. A.; Clayton, S. R.; Ruby, W. S.; Lee, L. P.

    1993-01-01

    We report the first fabrication of active semiconductor and high-temperature superconducting devices on the same substrate. Test structures of complementary MOS transistors were fabricated on the same sapphire substrate as test structures of Y1Ba2Cu3O(7-delta) flux-flow transistors, and separately, Y1Ba2Cu3O(7-delta) superconducting quantum interference devices utilizing both biepitaxial and step-edge Josephson junctions. Both semiconductor and superconductor devices were operated at 77 K. The cofabrication of devices using these disparate yet complementary electronic technologies on the same substrate opens the door for the fabrication of true semiconductive/superconductive hybrid integrated circuits capable of exploiting the best features of each of these technologies.

  12. Heteroepitaxy of N-type β-Ga2O3 thin films on sapphire substrate by low pressure chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Rafique, Subrina; Han, Lu; Neal, Adam T.; Mou, Shin; Tadjer, Marko J.; French, Roger H.; Zhao, Hongping

    2016-09-01

    This paper presents the heteroepitaxial growth of ultrawide bandgap β-Ga2O3 thin films on c-plane sapphire substrates by low pressure chemical vapor deposition. N-type conductivity in silicon (Si)-doped β-Ga2O3 films grown on sapphire substrate is demonstrated. The thin films were synthesized using high purity metallic gallium (Ga) and oxygen (O2) as precursors. The morphology, crystal quality, and properties of the as-grown thin films were characterized and analyzed by field emission scanning electron microscopy, X-ray diffraction, electron backscatter diffraction, photoluminescence and optical, photoluminescence excitation spectroscopy, and temperature dependent van der Pauw/Hall measurement. The optical bandgap is ˜4.76 eV, and room temperature electron mobility of 42.35 cm2/V s was measured for a Si-doped heteroepitaxial β-Ga2O3 film with a doping concentration of 1.32 × 1018 cm-3.

  13. Structural studies in the epitaxial-growth of indium nitride crystals with flower-like structure on a sapphire (112¯0) substrate

    NASA Astrophysics Data System (ADS)

    Wakasugi, Satoshi; Sugiura, Haruka; Shimomura, Masaru; Nakamura, Takato; Takahashi, Naoyuki

    2007-11-01

    Indium nitride crystals with flower-like structure are grown on a-plane sapphire substrate by means of chemical vapor deposition using InCl 3 and NH 3 as starting materials under atmospheric pressure. They have similar shape and size. It was found that a style and petals which constitute flower-like structure were grown homoepitaxially. This was deduced by the results of the reciprocal space mappings. Also, it was suggested that there are the following relationships between the style and petals: the directions [//[ and [//[//[ are parallel and perpendicular to the substrate, respectively. Selective growth of the flower-like InN crystals is explained in terms of the homoepitaxy.

  14. On the polarity of GaN micro- and nanowires epitaxially grown on sapphire (0001) and Si(111) substrates by metal organic vapor phase epitaxy and ammonia-molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Alloing, B.; Vézian, S.; Tottereau, O.; Vennéguès, P.; Beraudo, E.; Zuniga-Pérez, J.

    2011-01-01

    The polarity of GaN micro- and nanowires grown epitaxially by metal organic vapor phase epitaxy on sapphire substrates and by molecular-beam epitaxy, using ammonia as a nitrogen source, on sapphire and silicon substrates has been investigated. On Al2O3(0001), whatever the growth technique employed, the GaN wires show a mixture of Ga and N polarities. On Si(111), the wires grown by ammonia-molecular beam epitaxy are almost entirely Ga-polar (around 90%) and do not show inversion domains. These results can be understood in terms of the growth conditions employed during the nucleation stage.

  15. On the polarity of GaN micro- and nanowires epitaxially grown on sapphire (0001) and Si(111) substrates by metal organic vapor phase epitaxy and ammonia-molecular beam epitaxy

    SciTech Connect

    Alloing, B.; Vezian, S.; Tottereau, O.; Vennegues, P.; Beraudo, E.; Zuniga-Perez, J.

    2011-01-03

    The polarity of GaN micro- and nanowires grown epitaxially by metal organic vapor phase epitaxy on sapphire substrates and by molecular-beam epitaxy, using ammonia as a nitrogen source, on sapphire and silicon substrates has been investigated. On Al{sub 2}O{sub 3}(0001), whatever the growth technique employed, the GaN wires show a mixture of Ga and N polarities. On Si(111), the wires grown by ammonia-molecular beam epitaxy are almost entirely Ga-polar (around 90%) and do not show inversion domains. These results can be understood in terms of the growth conditions employed during the nucleation stage.

  16. Growth and characterization of well-aligned densely-packed rutile TiO(2) nanocrystals on sapphire substrates via metal-organic chemical vapor deposition.

    PubMed

    Chen, C A; Chen, Y M; Korotcov, A; Huang, Y S; Tsai, D S; Tiong, K K

    2008-02-20

    Well-aligned densely-packed rutile TiO(2) nanocrystals (NCs) have been grown on sapphire (SA) (100) and (012) substrates via metal-organic chemical vapor deposition (MOCVD), using titanium-tetraisopropoxide (TTIP, Ti(OC(3)H(7))(4)) as a source reagent. The surface morphology as well as structural and spectroscopic properties of the as-deposited NCs were characterized using field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected-area electron diffractometry (SAED), x-ray diffraction (XRD) and micro-Raman spectroscopy. FESEM micrographs reveal that vertically aligned NCs were grown on SA(100), whereas the NCs on the SA(012) were grown with a tilt angle of ∼33° from the normal to substrates. TEM and SAED measurements showed that the TiO(2) NCs on SA(100) with square cross section have their long axis directed along the [001] direction. The XRD results reveal TiO(2) NCs with either (002) orientation on SA(100) substrate or (101) orientation on SA(012) substrate. A strong substrate effect on the alignment of the growth of TiO(2) NCs has been demonstrated and the probable mechanism for the formation of these NCs has been discussed.

  17. Growth and characterization of well-aligned densely-packed rutile TiO2 nanocrystals on sapphire substrates via metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Chen, C. A.; Chen, Y. M.; Korotcov, A.; Huang, Y. S.; Tsai, D. S.; Tiong, K. K.

    2008-02-01

    Well-aligned densely-packed rutile TiO2 nanocrystals (NCs) have been grown on sapphire (SA) (100) and (012) substrates via metal-organic chemical vapor deposition (MOCVD), using titanium-tetraisopropoxide (TTIP, Ti(OC3H7)4) as a source reagent. The surface morphology as well as structural and spectroscopic properties of the as-deposited NCs were characterized using field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected-area electron diffractometry (SAED), x-ray diffraction (XRD) and micro-Raman spectroscopy. FESEM micrographs reveal that vertically aligned NCs were grown on SA(100), whereas the NCs on the SA(012) were grown with a tilt angle of ~33° from the normal to substrates. TEM and SAED measurements showed that the TiO2 NCs on SA(100) with square cross section have their long axis directed along the [001] direction. The XRD results reveal TiO2 NCs with either (002) orientation on SA(100) substrate or (101) orientation on SA(012) substrate. A strong substrate effect on the alignment of the growth of TiO2 NCs has been demonstrated and the probable mechanism for the formation of these NCs has been discussed.

  18. Residual and intentional n-type doping of ZnO thin films grown by metal-organic vapor phase epitaxy on sapphire and ZnO substrates

    NASA Astrophysics Data System (ADS)

    Brochen, Stéphane; Lafossas, Matthieu; Robin, Ivan-Christophe; Ferret, Pierre; Gemain, Frédérique; Pernot, Julien; Feuillet, Guy

    2014-03-01

    ZnO epilayers usually exhibit high n-type residual doping which is one of the reasons behind the difficulties to dope this material p-type. In this work, we aimed at determining the nature of the involved impurities and their potential role as dopant in ZnO thin films grown by metalorganic vapor phase epitaxy (MOVPE) on sapphire and ZnO substrates. In both cases, secondary ion mass spectroscopy (SIMS) measurements give evidence for a strong diffusion of impurities from the substrate to the epilayer, especially for silicon and aluminum. In the case of samples grown on sapphire substrates, aluminum follows Fick's diffusion law on a wide growth temperature range (800-1000°C). Thus, the saturation solubility and the diffusion coefficient of aluminum in ZnO single crystals have been determined. Furthermore, the comparison between SIMS impurity and effective dopant concentrations determined by capacitance-voltage measurements highlights, on one hand a substitutional mechanism for aluminum diffusion, and on the other hand that silicon acts as a donor in ZnO and not as an amphoteric impurity. In addition, photoluminescence spectra exhibit excitonic recombinations at the same energy for aluminum and silicon, indicating that silicon behaves as an hydrogenic donor in ZnO. Based on these experimental observations, ZnO thin films with a controlled n-type doping in the 1016-1019cm-3 range have been carried out. These results show that MOVPE growth is fully compatible with the achievement of highly Al-doped n-type thin films, but also with the growth of materials with low residual doping, which is a crucial parameter to address ZnO p-type doping issues.

  19. Influence of different aspect ratios on the structural and electrical properties of GaN thin films grown on nanoscale-patterned sapphire substrates

    NASA Astrophysics Data System (ADS)

    Lee, Fang-Wei; Ke, Wen-Cheng; Cheng, Chun-Hong; Liao, Bo-Wei; Chen, Wei-Kuo

    2016-07-01

    This study presents GaN thin films grown on nanoscale-patterned sapphire substrates (NPSSs) with different aspect ratios (ARs) using a homemade metal-organic chemical vapor deposition system. The anodic aluminum oxide (AAO) technique is used to prepare the dry etching mask. The cross-sectional view of the scanning electron microscope image shows that voids exist between the interface of the GaN thin film and the high-AR (i.e. ∼2) NPSS. In contrast, patterns on the low-AR (∼0.7) NPSS are filled full of GaN. The formation of voids on the high-AR NPSS is believed to be due to the enhancement of the lateral growth in the initial growth stage, and the quick-merging GaN thin film blocks the precursors from continuing to supply the bottom of the pattern. The atomic force microscopy images of GaN on bare sapphire show a layer-by-layer surface morphology, which becomes a step-flow surface morphology for GaN on a high-AR NPSS. The edge-type threading dislocation density can be reduced from 7.1 × 108 cm-2 for GaN on bare sapphire to 4.9 × 108 cm-2 for GaN on a high-AR NPSS. In addition, the carrier mobility increases from 85 cm2/Vs for GaN on bare sapphire to 199 cm2/Vs for GaN on a high-AR NPSS. However, the increased screw-type threading dislocation density for GaN on a low-AR NPSS is due to the competition of lateral growth on the flat-top patterns and vertical growth on the bottom of the patterns that causes the material quality of the GaN thin film to degenerate. Thus, the experimental results indicate that the AR of the particular patterning of a NPSS plays a crucial role in achieving GaN thin film with a high crystalline quality.

  20. Influence of strain relaxation on the relative orientation of ZnO and ZnMnO wurtzite lattice with respect to sapphire substrates

    NASA Astrophysics Data System (ADS)

    Avramenko, K. A.; Bryksa, V. P.; Petrenko, T. L.; Kladko, V. P.; Stanchu, H. V.; Belyaev, A. E.; Deparis, C.; Zuñiga-Pérez, J.; Morhain, C.

    2016-09-01

    ZnO and Zn1-x Mn x O (0≤slant x≤slant 0.07) films with 2 μm thickness were grown on (0001) sapphire substrate by molecular beam epitaxy. X-ray, electronic and optical studies show that films have a single crystalline columnar structure with unevenly distributed impurities and defects at the interfaces and boundaries of columns. ZnO and Zn1-x Mn x O films shows a high-quality hexagonal crystal structure with ZnO cells rotated by 30° relative to the sapphire substrate. We establish that the lateral coherence length obtained from x-ray analysis of Zn1-x Mn x O films is decreased from 900 nm to 400 nm at Mn variation from x = 0 to 0.07, which corresponds to variation of an average column diameter in these films. We find that in Zn1-x Mn x O films the area sizes of coherent phonon decaying are determined by the coherent areas of concentration homogeneity of Mn distributions which are much smaller then the dimensions of the columns. Modeling of ZnO/Al2O3 interface structure and properties was performed by means of first-principle density functional theory calculations. We employ an approach based on the use of large supercells (up to 460 atoms) which makes the simulation of interfaces with very large lattice mismatch possible. In this case amorphization of crystal structure in the vicinity of the interface is appears as a natural result of calculations leading to reduction of internal strains that that originate from the ZnO/Al2O3 lattice mismatch. In all cases the double ZnO layer next closest to the to interface (as well as the upper layers) maintains a nearly perfect wurtzite crystal structure. Based on calculations we propose a new model of interface microstructure which includes Zn- or O-monolayers located between conventional ZnO and Al2O3 surfaces. Adhesion energies of ZnO films to sapphire substrate were calculated for unrotated as well as for 30° rotated domains in the cases of Zn- and O-faced ZnO surfaces both with and without additional Zn- or O

  1. Homogeneity improvement of N-polar (000\\bar{1}) InGaN/GaN multiple quantum wells by using c-plane sapphire substrate with off-cut-angle toward a-sapphire plane

    NASA Astrophysics Data System (ADS)

    Shojiki, Kanako; Hanada, Takashi; Tanikawa, Tomoyuki; Imai, Yasuhiko; Kimura, Shigeru; Nonoda, Ryohei; Kuboya, Shigeyuki; Katayama, Ryuji; Matsuoka, Takashi

    2016-05-01

    To improve the homogeneity of the N-polar (000\\bar{1}) (-c-plane) InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic vapor phase epitaxy (MOVPE), the growth of GaN and MQW on two c-plane sapphire substrates with an off-cut angle of 0.8° toward the a-plane (sub-A) and the m-plane (sub-M) was performed. The effects of the off-cut direction on the structural properties and surface morphologies of -c-plane GaN films were elucidated. It was found that the step bunching and meandering of -c-plane GaN were significantly suppressed on sub-A. The spatial homogeneity of the -c-plane InGaN/GaN MQWs along the off-cut direction was observed in the submicrometer scale using microbeam X-ray diffraction. By inhibiting the step bunching of the GaN template using sub-A, the thickness homogeneity of the MQWs on sub-A has been significantly improved in comparison with that on sub-M.

  2. Epitaxial yttria-stabilized zirconia on (1 -1 0 2) sapphire for YBa2Cu3O(7-delta) thin films

    NASA Technical Reports Server (NTRS)

    Wu, X. D.; Muenchausen, R. E.; Nogar, N. S.; Pique, A.; Edwards, R.

    1991-01-01

    Epitaxial yttria-stabilized zirconia (YSZ) films were deposited on (1 -1 0 2) sapphire by pulsed laser deposition. The films are formed in a cubic phase with the a axis normal to the substrate surface. Ion beam channeling measurements show that the YSZ films are highly crystalline with a channeling minimum yield of 8 percent. The epitaxial relationship between the film and substrate is further confirmed by a cross-section TEM study. Epitaxial YBa2Cu3O(7-delta) thin films deposited on YSZ/sapphire have Tc and Jc of up to 89 K and 10 to the 6th A/sq cm at 77 K, respectively.

  3. Dispersive growth and laser-induced rippling of large-area singlelayer MoS2 nanosheets by CVD on c-plane sapphire substrate

    NASA Astrophysics Data System (ADS)

    Liu, Hongfei; Chi, Dongzhi

    2015-06-01

    Vapor-phase growth of large-area two-dimensional (2D) MoS2 nanosheets via reactions of sulfur with MoO3 precursors vaporized and transferred from powder sources onto a target substrate has been rapidly progressing. Recent studies revealed that the growth yield of high quality singlelayer (SL) MoS2 is essentially controlled by quite a few parameters including the temperature, the pressure, the amount/weight of loaded source precursors, and the cleanup of old precursors. Here, we report a dispersive growth method where a shadow mask is encapsulated on the substrate to ‘indirectly’ supply the source precursors onto the laterally advancing growth front at elevated temperatures. With this method, we have grown large-area (up to millimeters) SL-MoS2 nanosheets with a collective in-plane orientation on c-plane sapphire substrates. Regular ripples (~1 nm in height and ~50 nm in period) have been induced by laser scanning into the SL-MoS2 nanosheets. The MoS2 ripples easily initiate at the grain boundaries and extend along the atomic steps of the substrate. Such laser-induced ripple structures can be fundamental materials for studying their effects, which have been predicted to be significant but hitherto not evidenced, on the electronic, mechanical, and transport properties of SL-MoS2.

  4. Characterization of the InGaN/GaN Multi-Quantum-Wells Light-Emitting Diode Grown on Patterned Sapphire Substrate with Wide Electroluminescence Spectrum

    NASA Astrophysics Data System (ADS)

    Lee, Ah Reum; Jeon, Hunsoo; Lee, Gang-Seok; Ok, Jin-Eun; Jo, Dong-Wan; Kim, Kyoung Hwa; Yi, Sam Nyung; Yang, Min; Ahn, Hyung Soo; Cho, Chae-Ryong; Kim, Suok-Whan; Lee, Jae-Hak; Ha, Hong-Ju

    2011-01-01

    We report the characterization of the InGaN/GaN multi-quantum-well (MQW) light-emitting diode (LED) grown on a patterned sapphire substrate by metal organic chemical vapor deposition (MOCVD) using the selective area growth (SAG) method. The SAG patterns were designed to be circular and their diameters were 700 and 200 μm. After the growth, the InGaN/GaN MQW LED of 200 μm diameter had various crystal facets and a shape similar to volcanic craters, which were not observed in the 700-μm-diameter sample. We obtained an active layer with compositional nonuniformity and superior optical properties. We found wide electroluminescence (EL) spectral peaks near 470, 570, and 600 nm. The distribution of the EL spectrum of the sample was similar to that of a conventional phosphor-converted white LED.

  5. Characterization of the InGaN/GaN Multi-Quantum-Wells Light-Emitting Diode Grown on Patterned Sapphire Substrate with Wide Electroluminescence Spectrum

    NASA Astrophysics Data System (ADS)

    Reum Lee, Ah; Jeon, Hunsoo; Lee, Gang-Seok; Ok, Jin-Eun; Jo, Dong-Wan; Kim, Kyoung Hwa; Yi, Sam Nyung; Yang, Min; Ahn, Hyung Soo; Cho, Chae-Ryong; Kim, Suok-Whan; Lee, Jae-Hak; Ha, Hong-Ju

    2011-01-01

    We report the characterization of the InGaN/GaN multi-quantum-well (MQW) light-emitting diode (LED) grown on a patterned sapphire substrate by metal organic chemical vapor deposition (MOCVD) using the selective area growth (SAG) method. The SAG patterns were designed to be circular and their diameters were 700 and 200 µm. After the growth, the InGaN/GaN MQW LED of 200 µm diameter had various crystal facets and a shape similar to volcanic craters, which were not observed in the 700-µm-diameter sample. We obtained an active layer with compositional nonuniformity and superior optical properties. We found wide electroluminescence (EL) spectral peaks near 470, 570, and 600 nm. The distribution of the EL spectrum of the sample was similar to that of a conventional phosphor-converted white LED.

  6. Second and third order nonlinear optical properties of microrod ZnO films deposited on sapphire substrates by thermal oxidation of metallic zinc

    NASA Astrophysics Data System (ADS)

    Kulyk, B.; Essaidi, Z.; Luc, J.; Sofiani, Z.; Boudebs, G.; Sahraoui, B.; Kapustianyk, V.; Turko, B.

    2007-12-01

    We report the preparation of microcrystalline ZnO thin films on sapphire substrates using a simple method based on the thermal evaporation of metallic Zn in vacuum with further annealing process. The aim of annealing in the oxygen atmosphere in the range of 800-850°C was to obtain the high quality ZnO films. The surface morphology was studied by scanning electron microscopy and atomic force microscopy. The polycrystalline films with ZnO microrods at different stages of their growth were investigated. Second and third harmonic generation measurements were performed by means of the rotational Maker fringe technique using Nd:YAG laser at 1064nm in picosecond regime. The obtained values of second and third order nonlinear susceptibilities were found to be high enough for the potential applications of the investigated materials in the optical switching devices based on refractive index changes.

  7. Defects reduction in a-plane AlGaN epi-layers grown on r-plane sapphire substrates by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Zhao, Jianguo; Zhang, Xiong; Dai, Qian; Wang, Nan; Wu, Zili; Wang, Shuchang; Cui, Yiping

    2017-01-01

    Nonpolar a-plane AlGaN epi-layers were grown on a semi-polar r-plane sapphire substrate with an innovative two-way pulsed-flows metal organic chemical vapor deposition growth technology. A root-mean-square value of 1.79 nm was achieved, and the relative light transmittance of the a-plane AlGaN epi-layer was enhanced by 36.9%. These results reveal that the innovative growth method is able to improve the surface morphology and reduce the defect density in nonpolar a-plane Al x Ga1- x N epi-layers, particularly those with an Al composition greater than 0.5, which are key materials for the fabrication of nonpolar AlGaN-based high light emission efficiency deep-ultraviolet light-emitting diodes.

  8. Low-threshold stimulated emission at 249 nm and 256 nm from AlGaN-based multiple-quantum-well lasers grown on sapphire substrates

    SciTech Connect

    Li, Xiao-Hang; Detchprohm, Theeradetch; Kao, Tsung-Ting; Satter, Md. Mahbub; Shen, Shyh-Chiang; Douglas Yoder, P.; Dupuis, Russell D.; Wang, Shuo; Wei, Yong O.; Xie, Hongen; Fischer, Alec M.; Ponce, Fernando A.; Wernicke, Tim; Reich, Christoph; Martens, Martin; Kneissl, Michael

    2014-10-06

    Optically pumped deep-ultraviolet (DUV) lasing with low threshold was demonstrated from AlGaN-based multiple-quantum-well (MQW) heterostructures grown on sapphire substrates. The epitaxial layers were grown pseudomorphically by metalorganic chemical vapor deposition on (0001) sapphire substrates. Stimulated emission was observed at wavelengths of 256 nm and 249 nm with thresholds of 61 kW/cm{sup 2} and 95 kW/cm{sup 2} at room temperature, respectively. The thresholds are comparable to the reported state-of-the-art AlGaN-based MQW DUV lasers grown on bulk AlN substrates emitting at 266 nm. These low thresholds are attributed to the optimization of active region and waveguide layer as well as the use of high-quality AlN/sapphire templates. The stimulated emission above threshold was dominated by transverse-electric polarization. This work demonstrates the potential candidacy of sapphire substrates for DUV diode lasers.

  9. A Microstructural Comparison of the Initial Growth of AIN and GaN Layers on Basal Plane Sapphire and SiC Substrates by Low Pressure Metalorganic Chemical Vapor Depositon

    NASA Technical Reports Server (NTRS)

    George, T.; Pike, W. T.; Khan, M. A.; Kuznia, J. N.; Chang-Chien, P.

    1994-01-01

    The initial growth by low pressure metalorganic chemical vapor deposition and subsequent thermal annealing of AIN and GaN epitaxial layers on SiC and sapphire substrates is examined using high resolution transmission electron microscopy and atomic force microscopy.

  10. Quasi-heteroepitaxial growth of β-Ga2O3 on off-angled sapphire (0 0 0 1) substrates by halide vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Oshima, Yuichi; Vίllora, Encarnaciόn G.; Shimamura, Kiyoshi

    2015-01-01

    We demonstrate the high-speed growth of β-Ga2O3 quasi-heteroepilayers on off-angled sapphire (0 0 0 1) substrates by halide vapor phase epitaxy (HVPE). (2 bar 0 1) oriented β-Ga2O3 layers were successfully grown using GaCl and O2 as source gases. The growth rate monotonically increased with increasing the partial pressures of the source gases, reaching over 250 μm/h. This rate is over two orders of magnitude larger than those of conventional vapor phase epitaxial growth techniques such as molecular beam epitaxy or metalorganic vapor phase epitaxy. X-ray pole figure measurements indicated the presence of six in-plane rotational domains, in accordance with the substrate symmetry, plus some minor (3 1 0) domains. By the use of off-angled substrates and thick layer overgrowth, one of the in-plane orientations was strongly favored and the (3 1 0) residuals effectively suppressed, so that quasi-heteroepitaxial growth was achieved. Therefore, these results indicate the high-potential of the HVPE technique for the growth of thick and thin β-Ga2O3 layers for the cost-effective production of β-Ga2O3 based devices.

  11. Strain-dependence Of The Structure And Ferroic Properties Of Epitaxial Ni-1 (-) Ti-x(1) (-) O-y(3) Thin Films Grown On Sapphire Substrates

    SciTech Connect

    Varga, Tamas; Droubay, Timothy C.; Bowden, Mark E.; Stephens, Sean A.; Manandhar, Sandeep; Shutthanandan, V.; Colby, Robert J.; Hu, Dehong; Shelton, William A.; Chambers, Scott A.

    2015-03-01

    Polarization-induced weak ferromagnetism has been predicted a few years back in perovskite MTiO3 (M = Fe, Mn, Ni) [Fennie, Phys. Rev. Lett. 100, 167203 (2008)]. We set out to stabilize this metastable perovskite structure by growing NiTiO3 epitaxially on sapphire Al2O3 (001) substrate, and to control the polar and magnetic properties via strain. Epitaxial Ni1-xTi1-yO3 films of different Ni/Ti ratios and thicknesses were deposited on Al2O3 substrates by pulsed laser deposition at different temperatures, and characterized using several techniques. The effect of film thickness, deposition temperature, and film stoichiometry on lattice strain, film structure, and physical properties was investigated. Our structural data from x-ray diffraction, electron microscopy, and x-ray absorption spectroscopy shows that substrate-induced strain has a marked effect on the structure and crystalline quality of the films. Physical property measurements reveal a dependence of the Néel transition and lattice polarization on strain, and highlight our ability to control the ferroic properties in NiTiO3 thin films by film stoichiometry and thickness.

  12. Fast epitaxial growth of a-axis- and c-axis-oriented YBa 2Cu 3O 7- δ films on (1 0 0) LaAlO 3 substrate by laser chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Zhao, Pei; Ito, Akihiko; Tu, Rong; Goto, Takashi

    2011-02-01

    a-axis- and c-axis-oriented YBa2Cu3O7-δ (YBCO) films were epitaxially grown on (1 0 0) LaAlO3 substrates by laser chemical vapor deposition. The preferred orientation in the YBCO film changed from the a-axis to the c-axis with increasing laser powers from 77 to 158 W (the deposition temperatures from 951 to 1087 K). The a-axis-oriented YBCO film showed in-plane epitaxial growth of YBCO [0 0 1]//LAO [0 0 1], and the c-axis-oriented YBCO film showed that of YBCO [0 1 0]//LAO [0 0 1]. A c-axis-oriented YBCO film with a high critical temperature of 90 K was prepared at a deposition rate of 90 μm h-1, about 2-1000 times higher than that of metalorganic chemical vapor deposition.

  13. Eutectic bonding of sapphire to sapphire

    NASA Technical Reports Server (NTRS)

    Deluca, J. J.

    1973-01-01

    Eutectic mixture of aluminum oxide and zirconium oxide provides new bonding technique for sapphires and rubies. Technique effectively reduces possibility of contamination. Bonding material is aluminum oxide and zirconium oxide mixture that matches coefficient of thermal expansion of sapphire.

  14. Three dimensional characterization of GaN-based light emitting diode grown on patterned sapphire substrate by confocal Raman and photoluminescence spectromicroscopy

    PubMed Central

    Li, Heng; Cheng, Hui-Yu; Chen, Wei-Liang; Huang, Yi-Hsin; Li, Chi-Kang; Chang, Chiao-Yun; Wu, Yuh-Renn; Lu, Tien-Chang; Chang, Yu-Ming

    2017-01-01

    We performed depth-resolved PL and Raman spectral mappings of a GaN-based LED structure grown on a patterned sapphire substrate (PSS). Our results showed that the Raman mapping in the PSS-GaN heterointerface and the PL mapping in the InxGa1−xN/GaN MQWs active layer are spatially correlated. Based on the 3D construction of E2(high) Raman peak intensity and frequency shift, V-shaped pits in the MQWs can be traced down to the dislocations originated in the cone tip area of PSS. Detail analysis of the PL peak distribution further revealed that the indium composition in the MQWs is related to the residual strain propagating from the PSS-GaN heterointerface toward the LED surface. Numerical simulation based on the indium composition distribution also led to a radiative recombination rate distribution that shows agreement with the experimental PL intensity distribution in the InxGa1−xN/GaN MQWs active layer. PMID:28358119

  15. Growth and crystallographic characterization of molecular beam epitaxial WO3 and MoO3/WO3 thin films on sapphire substrates

    NASA Astrophysics Data System (ADS)

    Yano, Mitsuaki; Koike, Kazuto; Matsuo, Masayuki; Murayama, Takayuki; Harada, Yoshiyuki; Inaba, Katsuhiko

    2016-09-01

    Molecular beam epitaxy of tungsten trioxide (WO3) on (01 1 bar 2)-oriented (r-plane) sapphire substrates and molybdenum trioxide (MoO3) on the WO3 was studied by focusing on their crystallogrhaphic properties. Although polycrystalline monoclinic (γ-phase) WO3 films were grown at 500 °C and they became single-crystalline (0 0 1)-oriented γ-phase at 700 °C, the latter films were oxygen-deficient from stoichiometry and contained dense and deep thermal etchpits. By using a two-step growth method where only the initial 15 nm was grown at 700 °C and the rest part was grown at 500 °C, (0 0 1)-oriented γ-phase single-crystalline WO3 films with stoichiometric composition and smooth surface were obtained. On top of the 15-nm-thick WO3 initiation layer, (1 1 0)-oriented orthorhombic (α-phase) MoO3 films with smooth surface were obtained.

  16. Dispersion properties and low infrared optical losses in epitaxial AlN on sapphire substrate in the visible and infrared range

    SciTech Connect

    Soltani, A. Stolz, A.; Gerbedoen, J.-C.; Rousseau, M.; Bourzgui, N.; De Jaeger, J.-C.; Charrier, J.; Mattalah, M.; Barkad, H. A.; Mortet, V.

    2014-04-28

    Optical waveguiding properties of a thick wurtzite aluminum nitride highly [002]-textured hetero-epitaxial film on (001) basal plane of sapphire substrate are studied. The physical properties of the film are determined by X-ray diffraction, atomic force microscopy, microRaman, and photocurrent spectroscopy. The refractive index and the thermo-optic coefficients are determined by m-lines spectroscopy using the classical prism coupling technique. The optical losses of this planar waveguide are also measured in the spectral range of 450–1553 nm. The lower value of optical losses is equal to 0.7 dB/cm at 1553 nm. The optical losses due to the surface scattering are simulated showing that the contribution is the most significant at near infrared wavelength range, whereas the optical losses are due to volume scattering and material absorption in the visible range. The good physical properties and the low optical losses obtained from this planar waveguide are encouraging to achieve a wide bandgap optical guiding platform from these aluminum nitride thin films.

  17. Three dimensional characterization of GaN-based light emitting diode grown on patterned sapphire substrate by confocal Raman and photoluminescence spectromicroscopy.

    PubMed

    Li, Heng; Cheng, Hui-Yu; Chen, Wei-Liang; Huang, Yi-Hsin; Li, Chi-Kang; Chang, Chiao-Yun; Wu, Yuh-Renn; Lu, Tien-Chang; Chang, Yu-Ming

    2017-03-30

    We performed depth-resolved PL and Raman spectral mappings of a GaN-based LED structure grown on a patterned sapphire substrate (PSS). Our results showed that the Raman mapping in the PSS-GaN heterointerface and the PL mapping in the InxGa1-xN/GaN MQWs active layer are spatially correlated. Based on the 3D construction of E2(high) Raman peak intensity and frequency shift, V-shaped pits in the MQWs can be traced down to the dislocations originated in the cone tip area of PSS. Detail analysis of the PL peak distribution further revealed that the indium composition in the MQWs is related to the residual strain propagating from the PSS-GaN heterointerface toward the LED surface. Numerical simulation based on the indium composition distribution also led to a radiative recombination rate distribution that shows agreement with the experimental PL intensity distribution in the InxGa1-xN/GaN MQWs active layer.

  18. Evaluation of AlGaN/GaN high electron mobility transistors grown on ZrTi buffer layers with sapphire substrates

    DOE PAGES

    Ren, Fan; Pearton, Stephen J.; Ahn, Shihyun; ...

    2016-09-21

    Here, AlGaN/GaN high electron mobility transistors (HEMTs) have been grown on sapphire substrates, using ZrTi buffer layers to provide in-plane lattice-matching to hexagonal GaN. X-ray diffraction (XRD) as well as cross-section transmission electron microscopy (TEM) were used to assess the quality of the HEMT structure. The XRD 2θ scans showed full-width-at-half-maximum values of 0.16°, 0.07°, and 0.08° for ZrTi alloy, GaN buffer layer, and the entire HEMT structure, respectively. TEM studies of the GaN buffer layer and the AlN/ZrTi/AlN stack showed the importance of growing thin AlN buffer layers on the ZrTi layer prior to growth of the GaN buffermore » layer. The density of threading dislocations in the GaN channel layer of the HEMT structure was estimated to be in the 108 cm–2 range. The HEMT device exhibited a saturation drain current density of 820 mA/mm, and the channel of the fabricated HEMTs could be well modulated. A cutoff frequency (fT) of 8.9 GHz and a maximum frequency of oscillation (fmax) of 17.3 GHz were achieved for HEMTs with gate dimensions of 1 × 200 μm.« less

  19. Evaluation of AlGaN/GaN high electron mobility transistors grown on ZrTi buffer layers with sapphire substrates

    SciTech Connect

    Ren, Fan; Pearton, Stephen J.; Ahn, Shihyun; Lin, Yi -Hsuan; Machuca, Francisco; Weiss, Robert; Welsh, Alex; McCartney, Martha R.; Smith, David J.; Kravchenko, Ivan I.

    2016-09-21

    Here, AlGaN/GaN high electron mobility transistors (HEMTs) have been grown on sapphire substrates, using ZrTi buffer layers to provide in-plane lattice-matching to hexagonal GaN. X-ray diffraction (XRD) as well as cross-section transmission electron microscopy (TEM) were used to assess the quality of the HEMT structure. The XRD 2θ scans showed full-width-at-half-maximum values of 0.16°, 0.07°, and 0.08° for ZrTi alloy, GaN buffer layer, and the entire HEMT structure, respectively. TEM studies of the GaN buffer layer and the AlN/ZrTi/AlN stack showed the importance of growing thin AlN buffer layers on the ZrTi layer prior to growth of the GaN buffer layer. The density of threading dislocations in the GaN channel layer of the HEMT structure was estimated to be in the 108 cm–2 range. The HEMT device exhibited a saturation drain current density of 820 mA/mm, and the channel of the fabricated HEMTs could be well modulated. A cutoff frequency (fT) of 8.9 GHz and a maximum frequency of oscillation (fmax) of 17.3 GHz were achieved for HEMTs with gate dimensions of 1 × 200 μm.

  20. Efficiency improvement of GaN-based ultraviolet light-emitting diodes with reactive plasma deposited AlN nucleation layer on patterned sapphire substrate

    NASA Astrophysics Data System (ADS)

    Lee, Chia-Yu; Tzou, An-Jye; Lin, Bing-Cheng; Lan, Yu-Pin; Chiu, Ching-Hsueh; Chi, Gou-Chung; Chen, Chi-Hsiang; Kuo, Hao-Chung; Lin, Ray-Ming; Chang, Chun-Yen

    2014-09-01

    The flip chip ultraviolet light-emitting diodes (FC UV-LEDs) with a wavelength of 365 nm are developed with the ex situ reactive plasma deposited (RPD) AlN nucleation layer on patterned sapphire substrate (PSS) by an atmospheric pressure metal-organic chemical vapor deposition (AP MOCVD). The ex situ RPD AlN nucleation layer can significantly reduce dislocation density and thus improve the crystal quality of the GaN epitaxial layers. Utilizing high-resolution X-ray diffraction, the full width at half maximum of the rocking curve shows that the crystalline quality of the epitaxial layer with the (RPD) AlN nucleation layer is better than that with the low-temperature GaN (LT-GaN) nucleation layer. The threading dislocation density (TDD) is estimated by transmission electron microscopy (TEM), which shows the reduction from 6.8 × 107 cm-2 to 2.6 × 107 cm-2. Furthermore, the light output power (LOP) of the LEDs with the RPD AlN nucleation layer has been improved up to 30 % at a forward current of 350 mA compared to that of the LEDs grown on PSS with conventional LT-GaN nucleation layer.

  1. Twin symmetry texture of energetically condensed niobium thin films on sapphire substrate (a-plane Al2O3)

    SciTech Connect

    Zhao, X.; Phillips, L.; Reece, C. E.; Seo, Kang; Krishnan, M.; Valderrama, E.

    2011-01-01

    An energetic condensation technique, cathodic arc discharge deposition, is used to growepitaxialNiobium(Nb)thin films on a-plane sapphire (hexagonal-closed-packed Al2O3) at moderate substrate heating temperature (<400 °C). The epitaxial Nb(110)/Al2O3(1,1,-2,0) thin films reached a maximum residual resistance ratio (RRR) value 214, despite using a reactor-grade Nbcathode source whose RRR was only 30. The measurements suggest that the film’s density of impurities and structural defects are lower when compared to Nb films produced by other techniques, such as magnetron sputtering, e-beam evaporation or molecular-beam-epitaxy. At lower substrate temperature, textured polycrystalline Nbthin films were created, and the films might have twin symmetry grains with {110} orientations in-plane. The texture was revealed by x-ray diffraction pole figures. The twin symmetry might be caused by a combination effect of the Nb/Al2O3 three-dimensional epitaxial relationship (“3D-Registry” Claassen’s nomenclature) and the “Volmer-Weber” (Island) growth model. However, pole figures obtained by electron backscattering diffraction (EBSD) found no twin symmetry on the thin films’ topmost surface (~50 nm in depth). The EBSD pole figures showed only one Nb{110} crystal plane orientation. Finally, a possible mechanism is suggested to explain the differences between the bulk (XRD) and surface (EBSD) pole figures.

  2. Optical properties of a-plane InGaN/GaN multiple quantum wells on r-plane sapphire substrates with different indium compositions

    NASA Astrophysics Data System (ADS)

    Chiu, C. H.; Kuo, S. Y.; Lo, M. H.; Ke, C. C.; Wang, T. C.; Lee, Y. T.; Kuo, H. C.; Lu, T. C.; Wang, S. C.

    2009-03-01

    A-plane InxGa1-xN/GaN (x =0.09, 0.14, 0.24, and 0.3) multiple-quantum-wells (MQWs) samples, with a well width of about 4.5 nm, were achieved by utilizing r-plane sapphire substrates. Optical quality was investigated by means of photoluminescence (PL), cathodoluminescence, and time resolved PL measurements (TRPL). Two distinguishable emission peaks were examined from the low temperature PL spectra, where the high- and low-energy peaks were ascribed to quantum wells and localized states, respectively. Due to an increase in the localized energy states and absence of quantum confined Stark effect, the quantum efficiency was increased with increasing indium composition up to 24%. As the indium composition reached 30%, however, pronounced deterioration in luminescence efficiency was observed. The phenomenon could be attributed to the high defect densities in the MQWs resulted from the increased accumulation of strain between the InGaN well and GaN barrier. This argument was verified from the much shorter carrier lifetime at 15 K and smaller activation energy for In0.3Ga0.7N/GaN MQWs. In addition, the polarization-dependent PL revealed that the degree of polarization decreased with increasing indium compositions because of the enhancement of zero-dimensional nature of the localizing centers. Our detailed investigations indicate that the indium content in a-plane InGaN/GaN MQWs not only has an influence on optical performance, but is also important for further application of nitride semiconductors.

  3. Vapor-phase growth and characterization of Mo1-xWxS2 (0 <= x <= 1) atomic layers on 2-inch sapphire substrates

    NASA Astrophysics Data System (ADS)

    Liu, Hongfei; Antwi, K. K. Ansah; Chua, Soojin; Chi, Dongzhi

    2013-12-01

    Atomically thin Mo1-xWxS2 (0 <= x <= 1) ternary compounds have been grown on 2-inch c-plane sapphire substrates with high uniformity by sulfurizing thin Mo1-xWx layers that were deposited at room temperature using a co-sputtering technique. Atomic force microscopy (AFM), Raman scattering, and optical absorbance spectroscopy (OAS) studies reveal that the Mo1-xWxS2 films consist of crystallites of two-to-four monolayers in thickness. X-ray photoelectron spectroscopy (XPS) shows that the core levels of Mo3d and W4f shift to lower binding energies while that of S2p shifts to higher ones with the increase in W compositions, which can be related to the larger electron affinity of W (0.8163 eV) than that of Mo (0.7473 eV). OAS has also shown that the direct bandgap of Mo1-xWxS2 is tuned from 1.85 to 1.99 eV by increasing x from 0 to 1. Both E12g and A1g phonon modes of the Mo1-xWxS2 films exhibit a two-mode behavior. The bandgap tuning and the two-mode phonon behaviors are typically the same as those recently observed in monolayer Mo1-xWxS2 obtained by mechanical exfoliation, thus shedding light on the bottom-up growth of large-scale two-dimensional Mo1-xWxS2 ternary alloys.

  4. Latest developments of large-diameter c-axis sapphire grown by CHES method

    NASA Astrophysics Data System (ADS)

    Richard Schwerdtfeger, C.; Ullal, Saurabh; Shetty, Raj; Filgate, Joshua; Dhanaraj, Govindhan

    2014-05-01

    Large diameter c-axis crystal growth of sapphire boules up to 50 kg is in production at many sites world-wide. It has long been known that c-axis growth of sapphire could be the most cost-effective way to produce large diameter substrates for LED applications compared to a-axis growth with orthogonal coring due to the extremely large size boule required to core large diameter cores from the side of the boule. This paper will discuss the latest improvements, characterization, material utilizations, and crystal quality of boules designed specifically for 6-in., 8-in., and 10-in. wafer production. Improvements and continued R&D in slicing, polishing, and MOCVD of 6-in. and 8-in. sapphire has poised the industry for a rapid shift to larger diameter substrates, if the cores can be cost-effective. ARC Energy's CHES technology can produce 170 mm diameter boules optimized for 6-in. (150 mm) diameter wafer production. Additionally it can produce 8-in. or 10-in. diameter cores directly from 220 mm or 260 mm diameter boules, respectively. The latest developments, both equipment and process, will be discussed along with the resulting boule and core quality. Cost reductions for these large diameter cores will be shown to provide much more cost-effective 6-in. and 8-in. substrates. This low-cost enabling technology is poised to spur stable and long-term LED industry growth.

  5. Thermal Conductance through Sapphire-Sapphire Bonding

    NASA Astrophysics Data System (ADS)

    Suzuki, T.; Tomaru, T.; Haruyama, T.; Shintomi, T.; Uchinyama, T.; Miyoki, S.; Ohashi, M.; Kuroda, K.

    2003-07-01

    Thermal conductance on sapphire-sapphire bonded interface has been investigated. Two pieces of single crystal sapphire bar with square cross section were bonded together by adhesion free bonding. In two sections of the bar, thermal conductivity was measured between 5 K to 300K. One section contains a bonded interface and the other section measured a thermal conductivity of the sapphire as a reference. No significant thermal resistance due to bonded interface was found from this measurement. Obtained thermal conductivity reaches κ 1 × 104 [W/m·K] in temperature range of T = 20 ˜ 30 K which is a planned operating temperature of a cryogenic mirror of the Large scale Cryogenic Gravitational wave telescope. It looks promising for sapphire bonding technique to improve a heat transfer from a large cryogenic mirror to susp ension wires.

  6. Lattice spacings and domain sizes of room-temperature epitaxial LixNi1-xO (0 ≤ x ≤ 0.48) thin films grown on ultra-smooth sapphire substrates

    NASA Astrophysics Data System (ADS)

    Yang, Anli; Sakata, Osami; Yamauchi, Ryosuke; Katsuya, Yoshio; Kumara, L. S. R.; Shimada, Yoshitomo; Matsuda, Akifumi; Yoshimoto, Mamoru

    2014-11-01

    The effects of heavy Li doping on lattice spacings, out-of-plane, and in-plane domain sizes of room-temperature epitaxial LixNi1-xO (0 ≤ x ≤ 0.48) thin films on ultra-smooth sapphire (0 0 0 1) substrates were investigated. The pseudocubic-on-hexagonal epitaxial relationship between the LixNi1-xO epitaxial thin films and the sapphire substrates was verified. The (1 1 1) lattice spacing of the film was larger than the (1 1 bar 1) lattice spacing of the film regardless of the Li content. It indicated that all the crystal structures deviated from the ideal cubic structure and elongated along the [1 1 1] out-of-plane growth direction. The crystal domain sizes of LixNi1-xO thin films in the in-plane direction were found to be very similar, while the out-of-plane domain size increased with a Li content up to 48 mol%. It suggested that the out-of-plane growth can be improved by heavy Li doping. Moreover, the crystal quality of the films was compared with that grown by high temperature pulse laser deposition in view of the domain size information.

  7. Temperature-modulated annealing of c-plane sapphire for long-range-ordered atomic steps

    NASA Astrophysics Data System (ADS)

    Yatsui, Takashi; Kuribara, Kazunori; Sekitani, Tsuyoshi; Someya, Takao; Yoshimoto, Mamoru

    2016-03-01

    High-quality single-crystalline sapphire is used to prepare various semiconductors because of its thermal stability. Here, we applied the tempering technique, which is well known in the production of chocolate, to prepare a sapphire substrate. Surprisingly, we successfully realised millimetre-range ordering of the atomic step of the sapphire substrate. We also obtained a sapphire atomic step with nanometre-scale uniformity in the terrace width and atomic-step height. Such sapphire substrates will find applications in the preparation of various semiconductors and devices.

  8. DOE SAPPHIRE PROJECT

    SciTech Connect

    Dr. Gary R. Pickrell

    2000-03-01

    Since this is the first report for this project an extensive background section follows on the theory of operation of the single crystal sapphire sensor technology which will be developed and field tested at the Wabash River Coal Gasification Facility. Requirements for the temperature sensors for implementation in the coal gasifiers has been established in conjunction with the industrial partner, Dynegy. Coal slag immersion tests indicate good corrosion resistance of the single crystal sapphire. However, a more sophisticated corrosion apparatus has been constructed in order to test the optical attenuation of a single crystal sapphire fiber immersed in the coal slag at high temperature. These results will be reported in the next period. The data to date for sapphire sensor development is promising. More extensive data on the sapphire fiber sensor development will be reported for the next period.

  9. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Comparative studies on Zn0.95Co0.05O thin films on C- and R-sapphire substrates

    NASA Astrophysics Data System (ADS)

    Peng, Ying-Zi; Thomas, Liew; Song, Wen-Dong; Chong, Chong Tow

    2009-12-01

    Zn0.95Co0.05O precipitate-free single crystal thin films were synthesized by a dual beam pulsed laser deposition method. The films form a wurtzite structure whose hexagonal axis is perpendicular or parallel to the plane of the surface depending on the C-plane (0001) or R-plane (11bar 20) sapphire substrate. Based on the results of high-resolution transmission electron microscopy and x-ray diffraction, C-plane films show larger lattice mismatch. The films exhibit magnetic and semiconductor properties at room temperature. The coercivity of the film is about 8000 A/m at room temperature. They are soft magnetic materials with small remanent squareness S for both crystal orientations. There is no evidence to show that the anisotropy is fixed to the hexagonal axis (C-axis) for the wurtzite structure.

  10. Self-regulated in-plane polarity of [11¯00]-oriented GaN domains coalesced from twins grown on a SiO2-patterned m-plane sapphire substrate

    NASA Astrophysics Data System (ADS)

    Lee, Hyemi; Jue, Miyeon; Yoon, Hansub; Lee, Sanghwa; Kim, Chinkyo

    2014-05-01

    In-plane polarity of [11¯00]-oriented GaN domains coalesced from twins grown on a SiO2-patterned m-plane sapphire substrate was observed to be self-regulated in such a way that basal faces of coalesced domains were mainly found to have the (0001¯) polarity only. This self-regulation behavior of in-plane polarity was explained by a computational simulation of plan-view surface morphology evolution during coalescence of twins. Based on a computational simulation, asymmetrically suppressed growth rates of twins near a SiO2 pattern were proposed to be responsible for the survival of the slower growing (0001¯) basal faces instead of the faster growing (0001) basal faces during coalescence of twins.

  11. The effect of nucleation layer thickness on the structural evolution and crystal quality of bulk GaN grown by a two-step process on cone-patterned sapphire substrate

    NASA Astrophysics Data System (ADS)

    Shang, Lin; Zhai, Guangmei; Mei, Fuhong; Jia, Wei; Yu, Chunyan; Liu, Xuguang; Xu, Bingshe

    2016-05-01

    The role of nucleation layer thickness on the GaN crystal quality grown on cone-patterned sapphire substrate (PSS) was explored. The morphologies of epitaxial GaN at different growth stages were investigated by a series of growth interruption in detail. After 10- and 15-min three-dimensional growth, the nucleation sites are very important for the bulk GaN crystal quality. They have a close relationship with the nucleation layer thickness, as confirmed through the scanning electron microscope (SEM) analysis. Nucleation sites formed mainly on patterns are bad for bulk GaN crystal quality and nucleation sites formed mainly in the trenches of PSS mounds are good for bulk GaN crystal quality, as proved by X-ray diffraction analysis. Nucleation layer thickness can effectively control the nucleation sites and thus determine the crystal quality of bulk GaN.

  12. MOCVD growth of N-polar GaN on on-axis sapphire substrate: Impact of AlN nucleation layer on GaN surface hillock density

    NASA Astrophysics Data System (ADS)

    Marini, Jonathan; Leathersich, Jeffrey; Mahaboob, Isra; Bulmer, John; Newman, Neil; (Shadi) Shahedipour-Sandvik, F.

    2016-05-01

    We report on the impact of growth conditions on surface hillock density of N-polar GaN grown on nominally on-axis (0001) sapphire substrate by metal organic chemical vapor deposition (MOCVD). Large reduction in hillock density was achieved by implementation of an optimized high temperature AlN nucleation layer and use of indium surfactant in GaN overgrowth. A reduction by more than a factor of five in hillock density from 1000 to 170 hillocks/cm-2 was achieved as a result. Crystal quality and surface morphology of the resultant GaN films were characterized by high resolution x-ray diffraction and atomic force microscopy and found to be relatively unaffected by the buffer conditions. It is also shown that the density of smaller surface features is unaffected by AlN buffer conditions.

  13. Enhanced Performance of GaN-Based Light-Emitting Diodes by Using Al Mirror and Atomic Layer Deposition-TiO2/Al2O3 Distributed Bragg Reflector Backside Reflector with Patterned Sapphire Substrate

    NASA Astrophysics Data System (ADS)

    Chen, Hongjun; Guo, Hao; Zhang, Peiyuan; Zhang, Xiong; Liu, Honggang; Wang, Shengkai; Cui, Yiping

    2013-02-01

    GaN-based light-emitting diodes (LEDs) coated with an Al mirror and a three-pair TiO2/Al2O3 distributed Bragg reflector (DBR) by atomic layer deposition (ALD) grown on a patterned sapphire substrate (PSS) were proposed and realized for the first time. A 43.1% enhancement in light output power (LOP) was realized at 60 mA with the LED coated with an Al mirror and a three-pair ALD-grown TiO2/Al2O3 DBR compared with the LED without a backside reflector, as well as a 10.7% enhancement compared with the LED with a conventional Al mirror and a three-pair TiO2/SiO2 DBR reflector.

  14. High performance sapphire windows

    NASA Technical Reports Server (NTRS)

    Bates, Stephen C.; Liou, Larry

    1993-01-01

    High-quality, wide-aperture optical access is usually required for the advanced laser diagnostics that can now make a wide variety of non-intrusive measurements of combustion processes. Specially processed and mounted sapphire windows are proposed to provide this optical access to extreme environment. Through surface treatments and proper thermal stress design, single crystal sapphire can be a mechanically equivalent replacement for high strength steel. A prototype sapphire window and mounting system have been developed in a successful NASA SBIR Phase 1 project. A large and reliable increase in sapphire design strength (as much as 10x) has been achieved, and the initial specifications necessary for these gains have been defined. Failure testing of small windows has conclusively demonstrated the increased sapphire strength, indicating that a nearly flawless surface polish is the primary cause of strengthening, while an unusual mounting arrangement also significantly contributes to a larger effective strength. Phase 2 work will complete specification and demonstration of these windows, and will fabricate a set for use at NASA. The enhanced capabilities of these high performance sapphire windows will lead to many diagnostic capabilities not previously possible, as well as new applications for sapphire.

  15. Sapphire tube pressure vessel

    SciTech Connect

    Outwater, J.O.

    2000-05-23

    A pressure vessel is provided for observing corrosive fluids at high temperatures and pressures. A transparent Teflon bag contains the corrosive fluid and provides an inert barrier. The Teflon bag is placed within a sapphire tube, which forms a pressure boundary. The tube is received within a pipe including a viewing window. The combination of the Teflon bag, sapphire tube and pipe provides a strong and inert pressure vessel. In an alternative embodiment, tie rods connect together compression fittings at opposite ends of the sapphire tube.

  16. Sapphire tube pressure vessel

    DOEpatents

    Outwater, John O.

    2000-01-01

    A pressure vessel is provided for observing corrosive fluids at high temperatures and pressures. A transparent Teflon bag contains the corrosive fluid and provides an inert barrier. The Teflon bag is placed within a sapphire tube, which forms a pressure boundary. The tube is received within a pipe including a viewing window. The combination of the Teflon bag, sapphire tube and pipe provides a strong and inert pressure vessel. In an alternative embodiment, tie rods connect together compression fittings at opposite ends of the sapphire tube.

  17. Reduced cost and improved figure of sapphire optical components

    NASA Astrophysics Data System (ADS)

    Walters, Mark; Bartlett, Kevin; Brophy, Matthew R.; DeGroote Nelson, Jessica; Medicus, Kate

    2015-10-01

    Sapphire presents many challenges to optical manufacturers due to its high hardness and anisotropic properties. Long lead times and high prices are the typical result of such challenges. The cost of even a simple 'grind and shine' process can be prohibitive. The high precision surfaces required by optical sensor applications further exacerbate the challenge of processing sapphire thereby increasing cost further. Optimax has demonstrated a production process for such windows that delivers over 50% time reduction as compared to traditional manufacturing processes for sapphire, while producing windows with less than 1/5 wave rms figure error. Optimax's sapphire production process achieves significant improvement in cost by implementation of a controlled grinding process to present the best possible surface to the polishing equipment. Following the grinding process is a polishing process taking advantage of chemical interactions between slurry and substrate to deliver excellent removal rates and surface finish. Through experiments, the mechanics of the polishing process were also optimized to produce excellent optical figure. In addition to reducing the cost of producing large sapphire sensor windows, the grinding and polishing technology Optimax has developed aids in producing spherical sapphire components to better figure quality. In addition to reducing the cost of producing large sapphire sensor windows, the grinding and polishing technology Optimax has developed aids in producing spherical sapphire components to better figure quality. Through specially developed polishing slurries, the peak-to-valley figure error of spherical sapphire parts is reduced by over 80%.

  18. Atomic-scale investigation of structural defects in GaN layer on c-plane sapphire substrate during initial growth stage

    NASA Astrophysics Data System (ADS)

    Matsubara, Tohoru; Sugimoto, Kohei; Okada, Narihito; Tadatomo, Kazuyuki

    2016-04-01

    Structural defects in the initial growth stages of GaN on sapphire, including stacking faults (SFs), threading dislocations (TDs), and mosaic structure containing grain boundaries, are investigated at the atomic scale. Individual grains in the as-deposited low temperature-GaN buffer layer are found to have twists correlated with those of the adjacent grains. These grains have little similarity on the stacking sequences, and the atomic arrangement on each side of the grain boundaries may be rearranged by annealing to achieve higher similarity in the stacking sequence. The TD identified as a-type at the top of the SFs-rich interfacial region is thought to originate from Frank partial dislocations. The Frank partial dislocation produces a distorted wurtzite-type structure. At the intermediate region of the basal-plane stacking fault between Frank and Shockley partial dislocations, the TD relieves the distortion in the wurtzite-type structure. In the TD, the wurtzite structure slips relative to the surrounding wurtzite.

  19. Damage testing of sapphire and Ti: sapphire laser materials

    NASA Technical Reports Server (NTRS)

    1999-01-01

    Diffusion bonded sapphire and Ti (Titanium). Sapphire laser materials that will be damage tested to determine if there is an increase in damage threshold. Photographed in building 1145, photographic studio.

  20. Blocks and residual stresses in shaped sapphire single crystals

    NASA Astrophysics Data System (ADS)

    Krymov, V. M.; Nosov, Yu. G.; Bakholdin, S. I.; Maslov, V. N.; Shul‧pina, I. L.; Nikolaev, V. I.

    2017-01-01

    The formation of blocks and residual stresses in shaped sapphire crystals grown from the melt by the Stepanov method (EFG) has been studied. The probability of block formation is higher for the growth along the c axis compared to that grown in the a-axis direction. The distribution of residual stress in sapphire crystals of tubular, rectangular and round cross section was measured by the conoscopy method. It was found that the magnitude of the residual stress increases from the center to the periphery of the crystal and reaches up to about 20 MPa. Residual stress tensor components for solid round rod and tubular single crystals were determined by numerical integration.

  1. Change in equilibrium position of misfit dislocations at the GaN/sapphire interface by Si-ion implantation into sapphire. II. Electron energy loss spectroscopic study

    SciTech Connect

    Lee, Sung Bo Han, Heung Nam; Kim, Young-Min

    2015-07-15

    In Part I, we have shown that the addition of Si into sapphire by ion implantationmakes the sapphire substrate elastically softer than for the undoped sapphire. The more compliant layer of the Si-implanted sapphire substrate can absorb the misfit stress at the GaN/sapphire interface, which produces a lower threading-dislocation density in the GaN overlayer. Here in Part II, based on experimental results by electron energy loss spectroscopy and a first-principle molecular orbital calculation in the literature, we suggest that the softening effect of Si results from a reduction of ionic bonding strength in sapphire (α-Al{sub 2}O{sub 3}) with the substitution of Si for Al.

  2. Influences of group-III source preflow on the polarity, optical, and structural properties of GaN grown on nitridated sapphire substrates by metal-organic chemical vapor deposition

    SciTech Connect

    Li, Chengguo; Liu, Hongfei; Chua, Soo Jin

    2015-03-28

    We report the influences of group-III source preflow, which were introduced prior to the growth of the low temperature GaN on the polarity, photoluminescence (PL), and crystallographic properties of GaN epilayers grown on nitridated c-plane sapphire substrates by metal-organic chemical vapor deposition. By studying the surface morphology evolutions under chemical etching in KOH, we found that with increasing the trimethyl-gallium (TMGa) preflow duration (t), the polarity of the GaN film can be changed from a complete N-polarity to a mixture of N- and Ga-polarity and further to a complete Ga-polarity. PL and high-resolution X-ray diffraction studies revealed that the impurity incorporation and the edge- and screw-type threading dislocations are strongly polarity dependent. A further study at the optimized t (i.e., 30 s for TMGa) shows that the polarity inversion of GaN can be realized not only by TMGa preflow but also by trimethyl-aluminium preflow and by trimethyl-indium preflow. A two-monolayer model was employed to explain the polarity inversion mechanism.

  3. Tuning the effective band gap and finding the optimal growth condition of InN thin films on GaN/sapphire substrates by plasma assisted molecular beam epitaxy technique

    NASA Astrophysics Data System (ADS)

    Ghosh, Kankat; Rathore, Jaswant Singh; Laha, Apurba

    2017-01-01

    InN thin films are grown on GaN/sapphire substrates with varying the nitrogen plasma power in plasma assisted molecular beam epitaxy (PA-MBE) system. In order to evaluate the effect of nitrogen plasma power on the different properties of the InN films, several characterization viz. x-ray diffraction, atomic force microscopy, photoluminescence measurement, infra-red spectroscopy and Hall measurement were performed. Two interesting phenomena observed from the measurements are described in this paper. Firstly, it is found from both the photoluminescence and infrared spectroscopy that only by varying the nitrogen plasma power (thus the III/V ratio), one can fine tune the optical absorption edge, i.e., the effective band gap of InN from ∼0.72 eV to ∼ 0.77 eV. Secondly, it is inferred that the film grown with stoichiometric condition (III/V ∼ 1) exhibits the best structural and electrical properties.

  4. Ion Milling of Sapphire

    NASA Technical Reports Server (NTRS)

    Gregory, Don A.

    2002-01-01

    The ion figuring system at the Marshall Space Flight Center has been successfully used for at least three previous investigations into the ion milling of metals. The research was directed toward improving the surface quality of X-ray directing optics. These studies were performed on surfaces that were already hand polished to an excellent surface quality and were intended to remove the residual unwanted figure left by those techniques. The ion milling was typically carried out on test surfaces or mandrels that were several centimeters in width and length. The good thermal conductivity of the metal samples allowed the ion beam to be directed onto the sample for an indefinite period of time. This is not true of sapphire or most electrical insulators and problems have arisen in recent attempts to ion mill thin samples of sapphire. The failure and fracture of the material was likely due to thermal stresses and the relatively low thermal conductivity of sapphire (compared to most metals), These assumed stresses actually provided the key as to how they might be monitored. A thermal gradient in the sapphire sample will induce an effective index of refraction change and because of the shape constraint and the crystal structure and simple thermal expansion, this index change will be nonuniform across the sample. In all but simple cubic crystal structures, this leads to a spatially nonuniform optical retardance induced on any polarized optical beam traversing the sample, and it is this retardance that can be monitored using standard polarimetric procedures.

  5. Mechanism of Growth of Cr2O3 Thin Films on (1bar 102), (11bar 20), and (0001) Surfaces of Sapphire Substrates by Direct Current-Radio Frequency Magnetron Sputtering

    NASA Astrophysics Data System (ADS)

    Iwata, Nobuyuki; Kuroda, Takuji; Yamamoto, Hiroshi

    2012-11-01

    With the aim of directly controlling the magnetization in a ferromagnetic (FM) metal/Cr2O3 multilayer by means of an electric field without field cooling, the mechanism of growth of magnetoelectric (ME) Cr2O3 thin films on r-, a-, and c-cut sapphire substrates is investigated. In all the films, epitaxial growth is observed with a unit step on the film surface. The growth difference, which appears during the initial growth stage (at about 1 nm film thickness), is observed in the oriented films on each substrate surface. This growth difference arises from the different surface energies and the presence of twin grains due to the dislocation of Cr atoms. The twin-free r-oriented film contains coalesced grains with deep trenches at the grain boundaries, which release film stress and maintain flat grain surfaces because of the lowest surface energy. The a-oriented film shows anisotropic grains with the unit step and no trenches because the film starts to grow in a three-dimensional mode. The c-oriented film contains twin grains with the lowest full width at half-maximum of the rocking curve for the Bragg diffraction and a surface roughness of 0.17 nm. The twin grains in the c-oriented film contain a mixture of Cr atoms with up and down spins, which would simultaneously induce both an increase and a decrease in the exchange bias magnetic field (HEB) under an applied electric field through the ME effect. Therefore, the magnetization depends on the ratio of the twin grains. The Cr spins of the twin-free r-oriented film are expected to show FM ordering, indicating that HEB can be increased or decreased by an applied electric field. This r-oriented film is thus a promising surface for direct magnetization control using an electric field.

  6. Recrystallization of silicon-on-sapphire structures at various amorphization-ion-beam energies

    SciTech Connect

    Alexandrov, P. A. Demakov, K. D.; Shemardov, S. G.; Kuznetsov, Yu. Yu.

    2013-02-15

    Silicon films on sapphire substrates are grown via recrystallization from the silicon-sapphire interface. An amorphous layer is formed using ion implantation with silicon ion energies of 90-150 keV. An X-ray rocking curve is used to estimate the crystalline perfection of the silicon films. After recrystallization, the silicon layer consists of two parts with different crystalline quality. The recrystallized silicon-on-sapphire structures have a highly perfect upper layer (for fabricating microelectronic devices) and a lower layer adjacent to the sapphire substrate containing a large number of defects.

  7. Orientation of FePt nanoparticles on top of a-SiO2/Si(001), MgO(001) and sapphire(0001): effect of thermal treatments and influence of substrate and particle size

    PubMed Central

    Schilling, Martin; Ziemann, Paul; Zhang, Zaoli; Biskupek, Johannes; Kaiser, Ute

    2016-01-01

    Summary Texture formation and epitaxy of thin metal films and oriented growth of nanoparticles (NPs) on single crystal supports are of general interest for improved physical and chemical properties especially of anisotropic materials. In the case of FePt, the main focus lies on its highly anisotropic magnetic behavior and its catalytic activity, both due to the chemically ordered face-centered tetragonal (fct) L10 phase. If the c-axis of the tetragonal system can be aligned normal to the substrate plane, perpendicular magnetic recording could be achieved. Here, we study the orientation of FePt NPs and films on a-SiO2/Si(001), i.e., Si(001) with an amorphous (a-) native oxide layer on top, on MgO(001), and on sapphire(0001) substrates. For the NPs of an approximately equiatomic composition, two different sizes were chosen: “small” NPs with diameters in the range of 2–3 nm and “large” ones in the range of 5–8 nm. The 3 nm thick FePt films, deposited by pulsed laser deposition (PLD), served as reference samples. The structural properties were probed in situ, particularly texture formation and epitaxy of the specimens by reflection high-energy electron diffraction (RHEED) and, in case of 3 nm nanoparticles, additionally by high-resolution transmission electron microscopy (HRTEM) after different annealing steps between 200 and 650 °C. The L10 phase is obtained at annealing temperatures above 550 °C for films and 600 °C for nanoparticles in accordance with previous reports. On the amorphous surface of a-SiO2/Si substrates we find no preferential orientation neither for FePt films nor nanoparticles even after annealing at 630 °C. On sapphire(0001) supports, however, FePt nanoparticles exhibit a clearly preferred (111) orientation even in the as-prepared state, which can be slightly improved by annealing at 600–650 °C. This improvement depends on the size of NPs: Only the smaller NPs approach a fully developed (111) orientation. On top of MgO(001) the

  8. Ion Milling of Sapphire

    NASA Technical Reports Server (NTRS)

    Gregory, Don A.; Herren, Kenneth A.

    2004-01-01

    The ion milling of sapphire is a complicated operation due to several characteristics of the material itself. It is a relatively hard transparent nonconductive crystalline material that does not transfer heat nearly as well as metals that have been successfully ion milled in the past. This investigation involved designing an experimental arrangement, using existing ion milling equipment, as the precursor to figuring the surface of sapphire and other insulating optical materials. The experimental arrangement employs a laser probe beam to constantly monitor the stresses being induced in the material, as it is being ion milled. The goal is to determine if the technique proposed would indeed indicate the stress being induced in the material so that these stresses can be managed to prevent failure of the optic.

  9. (abstract) Transmission Electron Microscopy of Al(sub x)Ga(sub 1-x)N/SiC Multilayer Structures Grown on Sapphire Substrates

    NASA Technical Reports Server (NTRS)

    Pike, W. T.; George, T.; Khan, M. A.; Kuznia, J. N.

    1994-01-01

    The potential of wide-band-gap III-V nitrides as ultraviolet sensors and light emitters has prompted an increasing amount of work recently, including the fabrication of the first UV sensors from as-deposited single crystal GaN. We have used high resolution transmission electron microscopy (TEM) to study the microstructure of two novel developments of wide-band-gap III-V nitrides: the growth of ultra-short period GaN/AlN superlattices; and the incorporation of SiC layers into Al(sub x)Ga(sub 1-x)N structures. By varying the relative periods in a GaN/AlN superlattice, the band gap of the composite can be tailored to lie between the elemental values of 365 nm for GaN and 200 nm for AlN. The group IV semiconductor, SiC, has a wide band-gap and has a close lattice match (less than 3 %) to Al(sub x)Ga(sub 1-x)N for growth on the basal plane. Demonstration of epitaxial growth for Al(sub x)Ga(sub 1-x)N/SiC multilayers would introduce a wide band-gap analog to the already existing family of III-V and Si(sub 1-x)Ge(sub x) heteroepitaxial growth systems. Although good quality growth of GaN on SiC substrates has been demonstrated, Al(sub x)Ga(sub 1-x)N/SiC multilayer structures have never been grown and the interfacial structure is unknown.

  10. Growth of crystalline ZnO films on the nitridated (0001) sapphire surface

    SciTech Connect

    Butashin, A. V.; Kanevsky, V. M.; Muslimov, A. E. Prosekov, P. A.; Kondratev, O. A.; Blagov, A. E.; Vasil’ev, A. L.; Rakova, E. V.; Babaev, V. A.; Ismailov, A. M.; Vovk, E. A.; Nizhankovsky, S. V.

    2015-07-15

    The surface morphology and structure of (0001) sapphire substrates subjected to thermochemical nitridation in a mixture of N{sub 2}, CO, and H{sub 2} gases are investigated by electron and probe microscopy and X-ray and electron diffraction. It is shown that an aluminum nitride layer is formed on the substrate surface and heteroepitaxial ZnO films deposited onto such substrates by magnetron sputtering have a higher quality when compared with films grown on sapphire.

  11. Sapphire shaped crystals for medicine

    NASA Astrophysics Data System (ADS)

    Shikunova, A.; Kurlov, V. N.

    2016-01-01

    The favorable combination of excellent optical and mechanical properties of sapphire makes it an attractive structural material for medicine. We have developed a new kind of medical instruments and devices for laser photodynamic and thermal therapy, laser surgery, fluorescent diagnostics, and cryosurgery based on sapphire crystals of various shapes with capillary channels in their volume.

  12. High T(sub c) Superconducting Bolometer on Chemically Etched 7 Micrometer Thick Sapphire

    NASA Technical Reports Server (NTRS)

    Lakew, B.; Brasunas, J. C.; Pique, A.; Fettig, R.; Mott, B.; Babu, S.; Cushman, G. M.

    1997-01-01

    A transition-edge IR detector, using a YBa2Cu3O(7-x) (YBCO) thin film deposited on a chemically etched, 7 micrometer thick sapphire substrate has been built. To our knowledge it is the first such high T(sub c) superconducting (HTS) bolometer on chemically thinned sapphire. The peak optical detectivity obtained is l.2 x 10(exp 10) cmHz(sup 1/2)/W near 4Hz. Result shows that it is possible to obtain high detectivity with thin films on etched sapphire with no processing after the deposition of the YBCO film. We discuss the etching process and its potential for micro-machining sapphire and fabricating 2-dimensional detector arrays with suspended sapphire membranes. A 30 micrometer thick layer of gold black provided IR absorption. Comparison is made with the current state of the art on silicon substrates.

  13. World's largest sapphire for many applications

    NASA Astrophysics Data System (ADS)

    Khattak, Chandra P.; Shetty, Raj; Schwerdtfeger, C. Richard; Ullal, Saurabh

    2016-10-01

    Sapphire has been used for many high technology applications because of its excellent optical, mechanical, high temperature, abrasion resistance and dielectric properties. However, it is expensive and the volume of sapphire used has been limited. The potential sapphire requirements for LED and consumer electronic applications are very high. Emphasis has been on producing larger sapphire boules to achieve significant cost reductions so these applications are realized. World's largest sapphire boules, 500 mm diameter 300+kg, have been grown to address these markets.

  14. Microstructure of spinel islands on the sapphire surface grown by ion implantation and annealing.

    PubMed

    Wang, Y; Liu, X P; Qin, G W

    2014-09-01

    Fe ions were implanted into α-Al2O3 single crystals (sapphire) at energy of 50 keV and annealed in an oxidizing environment. Transmission electron microscopy (TEM) investigation indicated that Fe ions in the near surface region precipitated as α-Fe2O3 islands and spinel islands on the specimen surface, at the same time, Fe ions in the region away from the surface precipitated as α-Fe particles in the interior region of specimen. Two orientation relationships (ORs) between the spinel islands and sapphire substrate were discovered as follows: (111)spinel∥(0001)sapphire, [1 1 2¯]spinel∥[1 1 2¯ 0]sapphire and (1 1 2¯)spinel∥(0 0 0 1)sapphire, [1 1 1]spinel∥[1 1 2¯ 0]sapphire. The first OR was frequently observed in the spinel/sapphire system, however, the second OR has never been reported before. The interfaces between the spinel islands and sapphire substrate are a type-3 incoherent interface (i.e. low-index OR in at least one direction with an ill-matched low-index habit planes). The formation of spinel islands on the specimen surface can be attributed to the oxidizing atmosphere and the low accelerating voltage for ion implantation.

  15. Homogeneity of material and optical properties in HEM grown sapphire

    NASA Astrophysics Data System (ADS)

    Stout, M.; Hibbard, D.

    2015-09-01

    Sapphire crystal boules, approximately 34 cm in diameter and 22 cm tall, grown by the Heat Exchanger Method (HEM) are currently being sliced, ground and polished for use as window substrates in a variety of aerospace applications. As the need for larger volumes of higher quality material increases, it is necessary to evaluate and understand the homogeneity of optical and material properties within sapphire boules to ensure the needs of the industry can be met. The optical homogeneity throughout the full useable thickness of a representative sapphire boule was evaluated by measuring the transmitted wavefront error of multiple thin slices. This approach allowed the creation of a full-volume three-dimensional homogeneity map. Additionally, the uniformity of other critical characteristics of the material was evaluated at multiple locations within a boule. Specific properties investigated were equibiaxial flexural strength, index of refraction, Knoop hardness, coefficient of thermal expansion and modulus of elasticity. The results of those evaluations will be reported.

  16. Miniature Sapphire Acoustic Resonator - MSAR

    NASA Technical Reports Server (NTRS)

    Wang, Rabi T.; Tjoelker, Robert L.

    2011-01-01

    A room temperature sapphire acoustics resonator incorporated into an oscillator represents a possible opportunity to improve on quartz ultrastable oscillator (USO) performance, which has been a staple for NASA missions since the inception of spaceflight. Where quartz technology is very mature and shows a performance improvement of perhaps 1 dB/decade, these sapphire acoustic resonators when integrated with matured quartz electronics could achieve a frequency stability improvement of 10 dB or more. As quartz oscillators are an essential element of nearly all types of frequency standards and reference systems, the success of MSAR would advance the development of frequency standards and systems for both groundbased and flight-based projects. Current quartz oscillator technology is limited by quartz mechanical Q. With a possible improvement of more than x 10 Q with sapphire acoustic modes, the stability limit of current quartz oscillators may be improved tenfold, to 10(exp -14) at 1 second. The electromagnetic modes of sapphire that were previously developed at JPL require cryogenic temperatures to achieve the high Q levels needed to achieve this stability level. However sapphire fs acoustic modes, which have not been used before in a high-stability oscillator, indicate the required Q values (as high as Q = 10(exp 8)) may be achieved at room temperature in the kHz range. Even though sapphire is not piezoelectric, such a high Q should allow electrostatic excitation of the acoustic modes with a combination of DC and AC voltages across a small sapphire disk (approximately equal to l mm thick). The first evaluations under this task will test predictions of an estimated input impedance of 10 kilohms at Q = 10(exp 8), and explore the Q values that can be realized in a smaller resonator, which has not been previously tested for acoustic modes. This initial Q measurement and excitation demonstration can be viewed similar to a transducer converting electrical energy to

  17. Evolution of the sapphire industry: Rubicon Technology and Gavish

    NASA Astrophysics Data System (ADS)

    Harris, Daniel C.

    2009-05-01

    A. Verneuil developed flame fusion to grow sapphire and ruby on a commercial scale around 1890. Flame fusion was further perfected by Popov in the Soviet Union in the 1930s and by Linde Air Products Co. in the U.S. during World War II. Union Carbide Corp., the successor to Linde, developed Czochralski crystal growth for sapphire laser materials in the 1960s. Stepanov in the Soviet Union published his sapphire growth method in 1959. Edge-Defined Film-Fed Growth (EFG), which is similar to the Stepanov method, was developed by H. Labelle in the U. S. in the 1960s and 1970s. The Heat Exchanger Method (HEM), invented by F. Schmid and D. Viechnicki in 1967 was commercialized in the 1970s. Gradient solidification was invented in Israel in the 1970s by J. Makovsky. The Horizontal Directional Solidification Method (HDSM) proposed by Kh. S. Bagdasorov in the Soviet Union in the 1960s was further developed at the Institute for Single Crystals in Ukraine. Kyropoulos growth of sapphire, known as GOI crystal growth in the Soviet Union, was developed by M. Musatov at the State Optical Institute in St. Petersburg in the 1970s and 1980s. At the Institute for Single Crystals in Ukraine, E. Dobrovinskaya characterized Verneuil, Czochralsky, Bagdasarov, and GOI sapphire. In 1995, she emigrated to the United States and joined S&R Rubicon, founded near Chicago by R. Mogilevsky initially to import sapphire and ruby. Mogilevsky began producing sapphire by the Kyropoulos method in 1999. In 2000 the company name was changed to Rubicon Technology. Today, Dobrovinskaya is Chief Scientist and Rubicon produces high quality Kyropoulos sapphire substrates for solid-state lighting. In 1995, H. Branover of Ben Gurion University and a sole investor founded Gavish, which is Hebrew for "crystal." They invited another veteran of the Ukrainian Institute for Single Crystals, V. Pishchik, to become Chief Scientist. Under Pishchik's technical leadership and J. Sragowicz's business leadership, Gavish now

  18. LASE Ti: Sapphire Laser

    NASA Technical Reports Server (NTRS)

    1995-01-01

    In the photo, Messrs. Leroy F. Matthews (left) and Frank J. Novak (Lockheed Engineering & Sciences Co.) are preparing the Lidar Atmospheric Sensing Experiment (LASE) Instrument for integration into a NASA/ER-2 aircraft for a field mission. LASE is the first fully- engineered, autonomous differential Absorption Lidar (DIAL) System for the measurement of water vapor, aerosol and cloud in the troposphere. LASE uses a double-pulsed Ti:Sapphire laser for the transmitter with a 30 ns pulse length and 150 mJ/pulse. The laser beam is seeded to operate on a selected water vapor absorption line in the 815-nm region using a laser diode and an onboard absorption reference cell. A 40 cm diameter telescope collects the backscattered signals and directs them onto two detectors. LASE collects DIAL data at 5 Hz while flying at altitudes from 16-21 km. LASE was designed to operate autonomously within the environment and physical constraints of the ER-2 aircraft and to make water vapor profile measurements across the troposphere with accuracy having less than 6% of error. No other instrument can provide the spatial coverage and accuracy of LASE. Water vapor is the most radiative active gas in the troposphere, and the lack of understanding about its distribution provides one of the largest uncertainties in modeling climate change. LASE has demonstrated the necessary potential in providing high resolution water vapor measurements that can advance the studies of tropospheric water vapor distributions. LASE has flown 19 times during the development of the instrument and the validation of the science data. A joint international field mission was completed in the summer of 1996; adding 9 more successful flights. The LASE Instrument is being adapted to other aircraft platforms to support planned missions and to increase its utility.

  19. LASE Ti: Sapphire Laser

    NASA Technical Reports Server (NTRS)

    1995-01-01

    In the photo, Mr. Leroy F. Matthews (Lockheed Engineering & Sciences Co.) is connecting the Thermal Control Unit cables in preparing the Lidar Atmospheric Sensing Experiment (LASE) Instrument for integration into a NASA/ER-2 aircraft for a field mission. LASE is the first fully-engineered, autonomous differential Absorption Lidar (DIAL) System for the measurement of water vapor, aerosol and cloud in the troposphere. LASE uses a double-pulsed Ti:Sapphire laser for the transmitter with a 30 ns pulse length and 150 mJ/pulse. The laser beam is seeded to operate on a selected water vapor absorption line in the 815-nm region using a laser diode and an onboard absorption reference cell. A 40 cm diameter telescope collects the backscattered signals and directs them onto two detectors. LASE collects DIAL data at 5 Hz while flying at altitudes from 16-21 km. LASE was designed to operate autonomously within the environment and physical constraints of the ER-2 aircraft and to make water vapor profile measurements across the troposphere with accuracy having less than 6% of error. No other instrument can provide the spatial coverage and accuracy of LASE. Water vapor is the most radiative active gas in the troposphere, and the lack of understanding about its distribution provides one of the largest uncertainties in modeling climate change. LASE has demonstrated the necessary potential in providing high resolution water vapor measurements that can advance the studies of tropospheric water vapor distributions. LASE has flown 19 times during the development of the instrument and the validation of the science data. A joint international field mission was completed in the summer of 1996; adding 9 more successful flights. The LASE Instument is being adapted to other aircraft platforms to support planned missions and to increase its utility.

  20. Supersmooth and modified surface of sapphire crystals: Formation, characterization, and applications in nanotechnologies

    NASA Astrophysics Data System (ADS)

    Muslimov, A. E.; Asadchikov, V. E.; Butashin, A. V.; Vlasov, V. P.; Deryabin, A. N.; Roshchin, B. S.; Sulyanov, S. N.; Kanevsky, V. M.

    2016-09-01

    The results of studying the state of the surface of sapphire crystals by a complex of methods in different stages of crystal treatment are considered by an example of preparing sapphire substrates with a supersmooth surface. The possibility of purposefully forming regular micro- and nanoreliefs and thin transition layers using thermal and thermochemical impacts are considered. The advantages of sapphire substrates with a modified surface for forming heteroepitaxial CdTe and ZnO semiconductor films and ordered ensembles of gold nanoparticles are described. The results of the experiments on the application of crystalline sapphire as a material for X-ray optical elements are reported. These elements include total external reflection mirrors and substrates for multilayer mirrors, output windows for synchrotron radiation, and monochromators working in the reflection geometry in X-ray spectrometers. In the latter case, the problems of the defect structure of bulk crystals sapphire and the choice of a method for growing sapphire crystals of the highest structural quality are considered.

  1. Growth and Crystal Orientation of ZnTe on m-Plane Sapphire with Nanofaceted Structure

    NASA Astrophysics Data System (ADS)

    Nakasu, Taizo; Sun, Wei-Che; Kobayashi, Masakazu; Asahi, Toshiaki

    2017-04-01

    ZnTe thin films on sapphire substrate with nanofaceted structure have been studied. The nanofaceted structure of the m-plane (10-10) sapphire was obtained by heating the substrate at above 1100°C in air, and the r-plane (10-12) and S-plane (1-101) were confirmed. ZnTe layers were prepared on the nanofaceted m-plane sapphire substrates by molecular beam epitaxy (MBE). The effect of the nanofaceted structure on the orientation of the thin films was examined based on x-ray diffraction (XRD) pole figures. Transmission electron microscopy (TEM) was also employed to characterize the interface structures. The ZnTe layer on the nanofaceted m-plane sapphire substrate exhibited (331)-plane orientation, compared with (211)-plane without the nanofaceted structure. After thermal treatment, the m-plane surface vanished and (211) layer could not be formed because of the lack of surface lattice matching. On the other hand, (331)-plane thin film was formed on the nanofaceted m-plane sapphire substrate, since the (111) ZnTe domains were oriented on the S-facet. The orientation of the ZnTe epilayer depended on the atomic ordering on the surface and the influence of the S-plane.

  2. Chemical etching mechanism and properties of microstructures in sapphire modified by femtosecond laser

    NASA Astrophysics Data System (ADS)

    Liu, Manyu; Hu, Youwang; Sun, Xiaoyan; Wang, Cong; Zhou, Jianying; Dong, Xinran; Yin, Kai; Chu, Dongkai; Duan, Ji'an

    2017-01-01

    Sapphire, with extremely high hardness, high-temperature stability and wear resistance, often corroded in molten KOH at 300 °C after processing. The fabrication of microstructures on sapphire substrate performed by femtosecond laser irradiation combined with KOH solution chemical etching at room temperature is presented. It is found that this method reduces the harsh requirements of sapphire corrosion. After femtosecond irradiation, the sapphire has a high corrosion speed at room temperature. Through the analysis of Raman spectrum and XRD spectrum, a novel insight of femtosecond laser interaction with sapphire (α-Al2O3) is proposed. Results indicated that grooves on sapphire surface were formed by the lasers ablation removal, and the groove surface was modified in a certain depth. The modified area of the groove surface was changed from α-Al2O3 to γ-Al2O3. In addition, the impacts of three experimental parameters, laser power, scanning velocities and etching time, on the width and depth of microstructures are investigated, respectively. The modified area dimension is about 2 μm within limits power and speed. This work could fabricate high-quality arbitrary microstructures and enhance the performance of sapphire processing.

  3. Sapphire decomposition and inversion domains in N-polar aluminum nitride

    SciTech Connect

    Hussey, Lindsay White, Ryan M.; Kirste, Ronny; Bryan, Isaac; Guo, Wei; Osterman, Katherine; Haidet, Brian; Bryan, Zachary; Bobea, Milena; Collazo, Ramón; Sitar, Zlatko; Mita, Seiji

    2014-01-20

    Transmission electron microscopy (TEM) techniques and potassium hydroxide (KOH) etching confirmed that inversion domains in the N-polar AlN grown on c-plane sapphire were due to the decomposition of sapphire in the presence of hydrogen. The inversion domains were found to correspond to voids at the AlN and sapphire interface, and transmission electron microscopy results showed a V-shaped, columnar inversion domain with staggered domain boundary sidewalls. Voids were also observed in the simultaneously grown Al-polar AlN, however no inversion domains were present. The polarity of AlN grown above the decomposed regions of the sapphire substrate was confirmed to be Al-polar by KOH etching and TEM.

  4. Single crystalline AlN film formed by direct nitridation of sapphire using aluminum oxynitride buffer

    NASA Astrophysics Data System (ADS)

    Nakao, Wataru; Fukuyama, Hiroyuki

    2003-12-01

    A noble method forming single crystalline AlN films has been developed as a new substrate for blue/UV light emitters. Sapphire substrates have been nitrided by appropriate CO-N 2 gas mixtures saturated with graphite based on the chemical potential diagram of the Al-N-O-C system. The nitrided surface of sapphire consists of consecutive layers of AlN and γ-aluminum oxynitride (γ-ALON) with low-level dislocation density, where the γ-ALON layer spontaneously forms as an equilibrium phase and acts as a buffer. The lattice mismatch between sapphire substrate and AlN layer has been effectively reduced by using the γ-ALON buffer, which significantly attributes to the growth of single crystalline AlN.

  5. Hydrogen effect on the properties of sapphire

    NASA Astrophysics Data System (ADS)

    Mogilevsky, Radion N.; Sharafutdinova, Liudmila G.; Nedilko, Sergiy; Gavrilov, Valeriy; Verbilo, Dmitriy; Mittl, Scott D.

    2009-05-01

    Sapphire is a widely used material for optical, electronic and semiconductor applications due to its excellent optical properties and very high durability. Optical and mechanical properties of sapphire depend on many factors such as the starting materials that are used to grow crystals, methods to grow sapphire crystals, etc. Demand for highest purity and quality of sapphire crystals increased ten fold for the last several years due to new applications for this material. In this work we studied the effect of starting materials and crystal growth methods on the optical and mechanical properties of sapphire, especially concentrating on the effect of hydrogen on the properties of sapphire. It was found that the infrared (IR) absorption which is traditionally used to measure the hydrogen content in sapphire crystals cannot be reliably used and the data obtained by this method provides a much lower hydrogen concentration than actual. We have shown for the first time that Nuclear Magnetic Resonance techniques can be successfully used to determine hydrogen concentration in sapphire crystals. We have shown that hydrogen concentration in sapphire can reach thousands of ppm if these crystals are grown from Verneuil starting material or aluminum oxide powder. Alternatively, the hydrogen concentration is very low if sapphire crystals are grown from High Purity Densified Alumina (HPDA®) as a starting material. HPDA® is produced by EMT, Inc through their proprietary patented technology. It was found that optical and mechanical properties of sapphire crystals grown using EMT HPDA® starting material are much better than those sapphire crystals grown using a starting material of Verneuil crystals or aluminum oxide powder.

  6. Large-area YBa2Cu3O(7-delta) thin films on sapphire for microwave applications

    NASA Technical Reports Server (NTRS)

    Cole, B. F.; Liang, G.-C.; Newman, N.; Char, K.; Zaharchuk, G.; Martens, J. S.

    1992-01-01

    We have deposited YBa2Cu3O(7-delta) (YBCO) films with low microwave surface resistance (Rs) on 5-cm-diam, oxide-buffered sapphire substrates by planar magnetron sputtering. MgO buffer layers are used on M-plane (1 0 -1 0) sapphire, and R-plane (1 -1 0 2) sapphire is buffered by CeO2. Rs values of 450-620 microhms at 77 K and 10 GHz were measured across an entire 5-cm diam YBCO film on M-plane sapphire. For YBCO on R-plane sapphire, Rs values at 77 K and 10 GHz were 950 microohms for a 5-cm-diam wafer and 700 microohms for 1 x 1 sq cm samples.

  7. Microwave Frequency Discriminator With Sapphire Resonator

    NASA Technical Reports Server (NTRS)

    Santiago, David G.; Dick, G. John

    1994-01-01

    Cooled sapphire resonator provides ultralow phase noise. Apparatus comprises microwave oscillator operating at nominal frequency of about 8.1 GHz, plus frequency-discriminator circuit measuring phase fluctuations of oscillator output. One outstanding feature of frequency discriminator is sapphire resonator serving as phase reference. Sapphire resonator is dielectric ring resonator operating in "whispering-gallery" mode. Functions at room temperature, but for better performance, typically cooled to operating temperature of about 80 K. Similar resonator described in "Sapphire Ring Resonator for Microwave Oscillator" (NPO-18082).

  8. Improvement of luminous intensity of InGaN light emitting diodes grown on hemispherical patterned sapphire

    NASA Astrophysics Data System (ADS)

    Lee, Jae-Hoon; Oh, Jeong-Tak; Park, Jin-Sub; Kim, Je-Won; Kim, Yong-Chun; Lee, Jeong-Wook; Cho, Hyung-Koun

    2006-06-01

    To improve the external quantum efficiency, high quality GaN film was grown on hemispherical patterned sapphire by controlling the V/III ratio during the initial growth stage. The luminous intensity of white flash light emitting diode (LED) grown on hemispherical patterned sapphire (HPS) was estinated to be 5.8 cd at a forward current of 150 mA, which is improved by 20% more than that of LED grown on conventional sapphire substrate. The improvement of luminous intensity was explained by considering not only an increase of the extraction efficiency via the suppressed total internal reflection at the corrugated interface but also a decrease of dislocation density.

  9. Effects of sapphire nitridation and growth temperature on the epitaxial growth of hexagonal boron nitride on sapphire

    NASA Astrophysics Data System (ADS)

    Ahmed, Kawser; Dahal, Rajendra; Weltz, Adam; J-Q Lu, James; Danon, Yaron; Bhat, Ishwara B.

    2017-01-01

    This paper reports on the epitaxial growth of hexagonal boron nitride (hBN) films on sapphire substrates in a cold wall chemical vapor deposition (CVD) system where different sapphire nitridation and hBN growth temperatures were employed. A thin and amorphous nitridated layer was formed at a low temperature (850 °C), which enabled subsequent epitaxial hBN growth at 1350 °C. The influences of the sapphire nitridation temperature and the growth temperature on the film quality were analyzed by x-ray diffraction (XRD) measurements. Higher than optimum nitridation and growth temperatures improve the crystalline quality of the nitridated layer, but does not favor the epitaxial growth of hBN. hBN films grown at the optimum conditions exhibit the c-lattice constant of 6.66 Å from the XRD θ–2θ scan and the characteristic in plane stretching vibration at 1370.5 cm‑1 from Raman spectroscopy. X-ray photoelectron spectroscopy analysis confirmed the formation of stoichiometric hBN films with excellent uniformity.

  10. High-temperature strength of sapphire

    NASA Astrophysics Data System (ADS)

    Harris, Daniel C.

    2000-10-01

    The Sapphire Statistical Characterization and Risk Reduction Program tested approximately 1500 4-point flexure bars with different crystal orientations at different temperatures to establish a mechanical strength database for engineering design. Sapphire coupons were selected to represent surfaces on two different missile windows and a missile dome. Sapphire was obtained from the same suppliers used for the windows or dome and, as much as possible, coupons were fabricated in the same manner as the corresponding part of the window or dome. Perhaps the most interesting result was that sapphire from one fabricator was 50% stronger than sapphire made to the same specifications from the same blanks by another fabricator. In laser heating tests, sapphire performed better than predicted from flexure tests. When a compliant layer of graphite was used as a pad between the test specimens and the load fixture, sapphire in which the principal axis of tension and compression was parallel to the c-axis increased in apparent strength by a factor of 2 - 3. Strengths of other crystal orientations were not significantly affected by the graphite pads, but the incidence of twinning at 883 K was reduced by graphite.

  11. Advances in sapphire optical fiber sensors

    NASA Technical Reports Server (NTRS)

    Wang, Anbo; Wang, George Z.; Gollapudi, Sridhar; May, Russell G.; Murphy, Kent A.; Claus, Richard O.

    1993-01-01

    We describe the development and testing of two sapphire fiber sensor designs intended for use in high temperature environments. The first is a birefringence-balanced polarimetric sapphire fiber sensor. In this sensor, two single crystal sapphire rods, acting as the birefringence sensing element, are connected to each other in such a way that the slow axis of the first rod is aligned along with the fast axis of the second rod, and the fast axis of the first rod is along the slow axis of the second rod. This sensor has been demonstrated for measurement of temperature up to 1500 C. The second is a sapphire-fiber-based intrinsic interferometric sensor. In this sensor, a length of uncoated, unclad, structural-graded multimode sapphire fiber is fusion spliced to a singlemode silica fiber to form a Fabry-Perot cavity. The reflections from the silica-to-sapphire fiber splice and the free endface of the sapphire fiber give rise to the interfering fringe output. This sensor has been demonstrated for the measurement of temperature above 1510 C, and a resolution of 0.1 C has been obtained.

  12. Change in equilibrium position of misfit dislocations at the GaN/sapphire interface by Si-ion implantation into sapphire—I. Microstructural characterization

    SciTech Connect

    Lee, Sung Bo Han, Heung Nam Lee, Dong Nyung; Ju, Jin-Woo; Kim, Young-Min; Yoo, Seung Jo; Kim, Jin-Gyu

    2015-07-15

    Much research has been done to reduce dislocation densities for the growth of GaN on sapphire, but has paid little attention to the elastic behavior at the GaN/sapphire interface. In this study, we have examined effects of the addition of Si to a sapphire substrate on its elastic property and on the growth of GaN deposit. Si atoms are added to a c-plane sapphire substrate by ion implantation. The ion implantation results in scratches on the surface, and concomitantly, inhomogeneous distribution of Si. The scratch regions contain a higher concentration of Si than other regions of the sapphire substrate surface, high-temperature GaN being poorly grown there. However, high-temperature GaN is normally grown in the other regions. The GaN overlayer in the normally-grown regions is observed to have a lower TD density than the deposit on the bare sapphire substrate (with no Si accommodated). As compared with the film on an untreated, bare sapphire, the cathodoluminescence defect density decreases by 60 % for the GaN layer normally deposited on the Si-ion implanted sapphire. As confirmed by a strain mapping technique by transmission electron microscopy (geometric phase analysis), the addition of Si in the normally deposited regions forms a surface layer in the sapphire elastically more compliant than the GaN overlayer. The results suggest that the layer can largely absorb the misfit strain at the interface, which produces the overlayer with a lower defect density. Our results highlight a direct correlation between threading-dislocation density in GaN deposits and the elastic behavior at the GaN/sapphire interface, opening up a new pathway to reduce threading-dislocation density in GaN deposits.

  13. Sapphire reinforced alumina matrix composites

    NASA Technical Reports Server (NTRS)

    Jaskowiak, Martha H.; Setlock, John A.

    1994-01-01

    Unidirectionally reinforced A1203 matrix composites have been fabricated by hot pressing. Approximately 30 volume % of either coated or uncoated sapphire fiber was used as reinforcement. Unstabilized ZrO2 was applied as the fiber coating. Composite mechanical behavior was analyzed both after fabrication and after additional heat treatment. The results of composite tensile tests were correlated with fiber-matrix interfacial shear strengths determined from fiber push-out tests. Substantially higher strength and greater fiber pull-out were observed for the coated fiber composites for all processing conditions studied. The coated fiber composites retained up to 95% and 87% of their as-fabricated strength when heat treated at 14000C for 8 or 24 hours, respectively. Electron microscopy analysis of the fracture surfaces revealed extensive fiber pull-out both before and after heat treatment.

  14. LASE Ti:Sapphire Laser

    NASA Technical Reports Server (NTRS)

    1995-01-01

    In the photo, Dr. Larry B. Petway (Science Applications International Corp.) is making final adjustments to the Ti:Sapphire Laser in preparing the Lidar Atmospheric Sensing Experiment (LASE) Instrument for intergration into a NASA/ER-2 aircraft. LASE is the first fully- engineered, autonomous differential Absorption Lidar (DIAL) System for the measurement of water vapor, aerosol and cloud in the troposphere. LASE uses a double-pulsed Ti:Sapphire laser for the transmitter with a 30 ns pulse length and 150mJ/pulse. The laser beam is seeded to operate on a selected water vapor absorption line in the 815-nm region using a laser diode and an onboard absorption reference cell. A 40 cm diameter telescope collects the backscattered signals and directs them onto two detectors. LASE collects DIAL data at 5 Hz while flying at altitudes from 16-21 km. LASE was designed to operate autonomously within the environment and physical constraints of the ER-2 aircraft and to make water vapor profile measurements across the troposphere with accuracy having less than 6% of error. No other instrument can provide the spatial coverage and accuracy of LASE.Water vapor is the most radiative active gas in the troposphere, and the lack of understanding about its distribution provides one of the largest uncertainties in modeling climate change. LASE has demonstrated the necessary potential in providing high resolution water vapor measurements that can advance the studies of tropospheric water vapor distributions. LASE has flown 19 times during the development of the instrument and the validation of the science data. A joint international field mission was completed in the summer of 1996; adding 9 more successful flights. The LASE Instument is being adapted to other aircraft platforms to support planned missions and to increase its utility.

  15. Temperature dependence of sapphire fiber Raman scattering

    SciTech Connect

    Liu, Bo; Yu, Zhihao; Tian, Zhipeng; Homa, Daniel; Hill, Cary; Wang, Anbo; Pickrell, Gary

    2015-04-27

    Anti-Stokes Raman scattering in sapphire fiber has been observed for the first time. Temperature dependence of Raman peaks’ intensity, frequency shift, and linewidth were also measured. Three anti-Stokes Raman peaks were observed at temperatures higher than 300°C in a 0.72-m-long sapphire fiber excited by a second-harmonic Nd YAG laser. The intensity of anti-Stokes peaks are comparable to that of Stokes peaks when the temperature increases to 1033°C. We foresee the combination of sapphire fiber Stokes and anti-Stokes measurement in use as a mechanism for ultrahigh temperature sensing.

  16. Rayleigh scattering in sapphire test mass for laser interferometric gravitational-wave detectors:. II: Rayleigh scattering induced noise in a laser interferometric-wave detector

    NASA Astrophysics Data System (ADS)

    Benabid, F.; Notcutt, M.; Ju, L.; Blair, D. G.

    1999-10-01

    We present the level of noise induced by Rayleigh-scattered light from sapphire test mass, the limit of scattering loss on build-up power inside the interferometer and finally the tolerable absorption loss in order to meet the specification of the interferometer sensitivity. The results show that the Rayleigh scattering induced noise remains below h˜10 -25 Hz -1/2 and a higher tolerance on the absorption level in sapphire substrate compared with silica substrate.

  17. Thermal debracketing of single crystal sapphire brackets.

    PubMed

    Rueggeberg, F A; Lockwood, P E

    1992-01-01

    Because of their optical clarity, single crystal sapphire brackets provide an esthetic advantage over many other types of orthodontic brackets. However, debonding of these brackets has caused iatrogenic damage to enamel. Thermal debonding has been proposed for use in removing sapphire brackets without causing damage to teeth. This study determined the temperature required at the enamel/resin interface to thermally debond sapphire brackets from etched bovine enamel using 23 different commercially available orthodontic resins and one experimental product. The results indicate a wide range of debonding temperatures for the various resins. As a group, the powder-liquid materials had a statistically lower debonding temperature than the two-paste, the no-mix products, or the light-cured materials, for which the temperatures were all similar. This paper presents relative information a clinician can use in selecting an orthodontic bonding resin to minimize thermal damage to the teeth while debonding sapphire brackets.

  18. Anisotropic strain relaxation and the resulting degree of polarization by one- and two-step growth in nonpolar a-plane GaN grown on r-sapphire substrate

    SciTech Connect

    Feng, Shih-Wei Chen, Yu-Yu; Lai, Chih-Ming; Tu, Li-Wei; Han, Jung

    2013-12-21

    Anisotropic strain relaxation and the resulting degree of polarization of the electronic transition in nonpolar a-plane GaN using one- and two-step growth are studied. By using two-step growth, a slower coalescence and a longer roughening-recovery process lead to larger anisotropic strain relaxation, a less striated surface, and lower densities of basal stacking fault (BSF) and prismatic stacking fault (PSF). It is suggested that anisotropic in-plane strains, surface striation, and BSF and PSF densities in nonpolar a-GaN are consequences of the rate of coalescence, the period of roughening-recovery process, and the degree of anisotropic strain relaxation. In addition, the two-step growth mode can enhance the degree of polarization of the electronic transition. The simulation results of the k⋅p perturbation approach show that the oscillator strength and degree of polarization of the electronic transition strongly depend on the in-plane strains upon anisotropic in-plane strain relaxation. The research results provide important information for optimized growth of nonpolar III-nitrides. By using two-step growth and by fabricating the devices on the high-quality nonpolar free-standing GaN substrates, high-efficiency nonpolar a-plane InGaN LEDs can be realized. Nonpolar a-plane InGaN/GaN LEDs can exhibit a strongly polarized light to improve the contrast, glare, eye discomfort and eye strain, and efficiency in display application.

  19. High Q Miniature Sapphire Acoustic Resonator

    NASA Technical Reports Server (NTRS)

    Wang, Rabi T.; Tjoelker, R. L.

    2010-01-01

    We have demonstrated high Q measurements in a room temperature Miniature Sapphire Acoustic Resonator (MSAR). Initial measurements of bulk acoustic modes in room temperature sapphire at 39 MHz have demonstrated a Q of 8.8 x 10(exp 6). The long term goal of this work is to integrate such a high Q resonator with small, low noise quartz oscillator electronics, providing a fractional frequency stability better than 1 x 10(exp -14) @ 1s.

  20. Modeling the curvature and interface shear stress of GaN-sapphire system

    NASA Astrophysics Data System (ADS)

    Li, Jia; Shi, Junjie; Wu, Jiejun; Liu, Huizhao

    2016-03-01

    The curvature and interface shear stress of GaN-sapphire system are studied by establishing the mechanical equations based on two main assumptions: (a) the thickness of GaN film can be compared to the thickness of sapphire substrate, and (b) the thickness of GaN film is non-uniform. Our results show that the curvature of GaN-sapphire system is a variable within the whole circular system. The interface shear stress changes direction around at the middle of radius for the circular system, and the curvature have an important effect on the interface shear stress due to the consideration of non-uniform thickness for GaN film.

  1. Secondary particle emission from sapphire single crystal

    NASA Astrophysics Data System (ADS)

    Minnebaev, K. F.; Khvostov, V. V.; Zykova, E. Yu.; Tolpin, K. A.; Colligon, J. S.; Yurasova, V. E.

    2015-07-01

    Secondary ion emission from sapphire single crystal has been studied experimentally and by means of computer simulation. The particular oscillations of secondary ion energy spectra and two specific maxima of O+ and Al+ ions were observed under irradiation of (0001) sapphire face by 1 and 10 keV Ar+ ions. We have explained this by the interplay of the charge exchange processes between moving particles and solids. The existence of two maxima in energy spectra of O+ and Al+ secondary ions can be also connected with special features of single-crystal sputtering: the low-energy peak can be formed by random sputtering and the high-energy peak from focusing collisions. In addition some similarity was found between the positions of low-energy maximum in energy spectra of Al+ ions emitted from sapphire and the principal maxima of Al+ ions ejected from the aluminum single crystal. This indicates a possibility to explain the presence of low-energy maximum in energy spectra of secondary ions ejecting from sapphire by emission of Al+ ions from aluminum islands appearing in a number of cases on the sapphire surface due to preferential sputtering of oxygen. These different mechanisms of creating the energy spectra of ions emitted from sapphire should be taken in account.

  2. Carbon nanotube assisted Lift off of GaN layers on sapphire

    NASA Astrophysics Data System (ADS)

    Long, Hao; Feng, Xiaohui; Wei, Yang; Yu, Tongjun; Fan, Shoushan; Ying, Leiying; Zhang, Baoping

    2017-02-01

    Laser lift off (LLO) was one of the most essential processes in fabrication of vertical GaN-based LEDs. However, traditional laser lift off of GaN on sapphire substrates needed high laser energy threshold, which deteriorated the GaN crystal. In this paper, it was found that inserting carbon nanotube between GaN and sapphire could effectively reduce the laser energy threshold in GaN LLO, from 1.5 J /cm2 of conventional GaN/sapphire to 1.3 J /cm2 of CNT inserted GaN/sapphire. The temperature distributions at the GaN/sapphire interfaces with and without CNTs were simulated by the finite elements calculation under laser irradiation. It was found that, due to the higher laser absorption coefficient of CNT, the CNT played as a powerful heating wire, sending out the thermal outside to elevate the GaN's temperature, and thus reduce the laser threshold for LLO. Raman and photoluminescence measurements indicated that residual stress of GaN membranes was as small as 0.3 GPa by the carbon nanotube assisted LLO. This work not only opens new application of CNTs, but also demonstrates the potential of high performance blue and green LEDs.

  3. ZrO2 thin-film-based sapphire fiber temperature sensor.

    PubMed

    Wang, Jiajun; Lally, Evan M; Wang, Xiaoping; Gong, Jianmin; Pickrell, Gary; Wang, Anbo

    2012-04-20

    A submicrometer-thick zirconium dioxide film was deposited on the tip of a polished C-plane sapphire fiber to fabricate a temperature sensor that can work to an extended temperature range. Zirconium dioxide was selected as the thin film material to fabricate the temperature sensor because it has relatively close thermal expansion to that of sapphire, but more importantly it does not react appreciably with sapphire up to 1800 °C. In order to study the properties of the deposited thin film, ZrO2 was also deposited on C-plane sapphire substrates and characterized by x-ray diffraction for phase analysis as well as by atomic force microscopy for analysis of surface morphology. Using low-coherence optical interferometry, the fabricated thin-film-based sapphire fiber sensor was tested in the lab up to 1200 °C and calibrated from 200° to 1000 °C. The temperature resolution is determined to be 5.8 °C when using an Ocean Optics USB4000 spectrometer to detect the reflection spectra from the ZrO2 thin-film temperature sensor.

  4. Highly transparent sapphire micro-grating structures with large diffuse light scattering.

    PubMed

    Ko, Yeong Hwan; Yu, Jae Su

    2011-08-01

    The highly transparent micro-grating structures (MGSs) of sapphire substrate with large diffuse light scattering were theoretically and experimentally studied. From the finite difference time domain simulation, it was found that the degree of diffuse light scattering is strongly dependent on the size of grating structures. For a highly transparent property, the sapphire MGSs were optimally designed by the theoretical calculations using the rigorous coupled wave analysis method. The order of taper, geometry (i.e., width and height), and pitch length of MGSs were optimized to maximize their average total transmittance over a wide wavelength range of 300-1800 nm. Additionally, the influence of the deposition of low-refractive index material such as SiO2 onto sapphire MGSs on the transmittance characteristics was investigated. To verify experimentally the feasibility, the sapphire MGSs were fabricated by the conventional lithography and dry etching processes. The SiO2 deposited sapphire MGS exhibited a further increase in the total transmittance due to its relatively more graded refractive index profile while maintaining a significantly enhanced diffuse light scattering. The experimental data were in a reasonable agreement with the theoretical results.

  5. A lead-on-sapphire superconducting cavity of superior quality

    NASA Technical Reports Server (NTRS)

    Thakoor, S.; Strayer, D. M.; Dick, G. J.; Mercereau, J. E.

    1986-01-01

    A cavity consisting of a superconducting lead film on a sapphire substrate has been fabricated to obtain the enhanced frequency stability possible with this configuration. The cavity exhibits a quality value Q exceeding 2 x 10 to the 9th in its TE011 mode with a resonant frequency of 2.689 GHz. Methods of fabrication and testing of the cavity are presented. Since the interface between the film and substrate is exposed ot the full value of the resonant magnetic field, the present experiment is the most sensitive test to date for enhanced losses at the interface itself. No evidence of such losses is used. In fact, the measured values of the surface resistance match very well predictions for RF losses based on the BCS theory.

  6. Nitridation of an unreconstructed and reconstructed (√31 ×√31)R ± 9° (0001) sapphire surface in an ammonia flow

    SciTech Connect

    Milakhina, D. S. Malin, T. V.; Mansurov, V. G.; Galitsin, Yu. G.; Zhuravlev, K. S.

    2015-07-15

    This paper is devoted to the study of the nitridation of unreconstructed and reconstructed (√31 ×√31)R ± 9° (0001) sapphire surfaces in an ammonia flow by reflection high-energy electron diffraction (RHEED). The experimental results show that sapphire nitridation occurs on the unreconstructed (1 × 1) surface, which results in AlN phase formation on the substrate surface. However, if sapphire nitridation is preceded by high-temperature annealing (1150°C) resulting in sapphire surface reconstruction with formation of the (√31 ×√31)R ± 9° surface, the crystalline AlN phase on the sapphire surface is not formed during surface exposure to an ammonia flow.

  7. Investigation on orientation, epitaxial growth and microstructure of a-axis-, c-axis-, (103)/(110)- and (113)-oriented YBa2Cu3O7-δ films prepared on (001), (110) and (111) SrTiO3 single crystal substrates by spray atomizing and coprecipitating laser chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Zhao, Pei; Wang, Ying; Huang, Zhi liang; Mao, Yangwu; Xu, Yuan Lai

    2015-04-01

    a-axis-, c-axis-, (103)/(110)- and (113)-oriented YBa2Cu3O7-δ (YBCO) films were pareared by spray atomizing and coprecipitating laser chemical vapor deposition. The surface of the a-axis-oriented YBCO film consisted of rectangular needle-like grains whose in-plane epitaxial growth relationship was YBCO [100] // STO [001] (YBCO [001] // STO [100]), and that of the c-axis-oriented YBCO film consisted of dense flat surface with epitaxial growth relationship of YBCO [001] // STO [001] (YBCO [100] //STO [100]). For the (103)/(110)-oriented and (113)-oriented YBCO film, they showed wedge-shaped and triangle-shaped grains, with corresponding in-plane epitaxial growth relationship of YBCO [110] // STO [110] (YBCO [010] // STO [010]) and YBCO [100] // STO [100] (YBCO [113] // STO [111], respectively.

  8. Submicron diameter single crystal sapphire optical fiber

    DOE PAGES

    Hill, Cary; Homa, Daniel; Liu, Bo; ...

    2014-10-02

    In this work, a submicron-diameter single crystal sapphire optical fiber was demonstrated via wet acid etching at elevated temperatures. Etch rates on the order 2.3 µm/hr were achievable with a 3:1 molar ratio sulfuric-phosphoric acid solution maintained at a temperature of 343°C. A sapphire fiber with an approximate diameter of 800 nm was successfully fabricated from a commercially available fiber with an original diameter of 50 µm. The simple and controllable etching technique provides a feasible approach to the fabrication of unique waveguide structures via traditional silica masking techniques. The ability to tailor the geometry of sapphire optical fibers ismore » the first step in achieving optical and sensing performance on par with its fused silica counterpart.« less

  9. Submicron diameter single crystal sapphire optical fiber

    SciTech Connect

    Hill, Cary; Homa, Daniel; Liu, Bo; Yu, Zhihao; Wang, Anbo; Pickrell, Gary

    2014-10-02

    In this work, a submicron-diameter single crystal sapphire optical fiber was demonstrated via wet acid etching at elevated temperatures. Etch rates on the order 2.3 µm/hr were achievable with a 3:1 molar ratio sulfuric-phosphoric acid solution maintained at a temperature of 343°C. A sapphire fiber with an approximate diameter of 800 nm was successfully fabricated from a commercially available fiber with an original diameter of 50 µm. The simple and controllable etching technique provides a feasible approach to the fabrication of unique waveguide structures via traditional silica masking techniques. The ability to tailor the geometry of sapphire optical fibers is the first step in achieving optical and sensing performance on par with its fused silica counterpart.

  10. Sapphire Energy - Integrated Algal Biorefinery

    SciTech Connect

    White, Rebecca L.; Tyler, Mike

    2015-07-22

    Sapphire Energy, Inc. (SEI) is a leader in large-scale photosynthetic algal biomass production, with a strongly cohesive research, development, and operations program. SEI takes a multidiscipline approach to integrate lab-based strain selection, cultivation and harvest and production scale, and extraction for the production of Green Crude oil, a drop in replacement for traditional crude oil.. SEI’s technical accomplishments since 2007 have produced a multifunctional platform that can address needs for fuel, feed, and other higher value products. Figure 1 outlines SEI’s commercialization process, including Green Crude production and refinement to drop in fuel replacements. The large scale algal biomass production facility, the SEI Integrated Algal Biorefinery (IABR), was built in Luna County near Columbus, New Mexico (see fig 2). The extraction unit was located at the existing SEI facility in Las Cruces, New Mexico, approximately 95 miles from the IABR. The IABR facility was constructed on time and on budget, and the extraction unit expansion to accommodate the biomass output from the IABR was completed in October 2012. The IABR facility uses open pond cultivation with a proprietary harvesting method to produce algal biomass; this biomass is then shipped to the extraction facility for conversion to Green Crude. The operation of the IABR and the extraction facilities has demonstrated the critical integration of traditional agricultural techniques with algae cultivation knowledge for algal biomass production, and the successful conversion of the biomass to Green Crude. All primary unit operations are de-risked, and at a scale suitable for process demonstration. The results are stable, reliable, and long-term cultivation of strains for year round algal biomass production. From June 2012 to November 2014, the IABR and extraction facilities produced 524 metric tons (MT) of biomass (on a dry weight basis), and 2,587 gallons of Green Crude. Additionally, the IABR

  11. Bonding of sapphire to sapphire by eutectic mixture of aluminum oxide and zirconium oxide

    NASA Technical Reports Server (NTRS)

    Deluca, J. J. (Inventor)

    1975-01-01

    Bonding of an element comprising sapphire, ruby or blue sapphire to another element of such material with a eutectic mixture of aluminum oxide and zirconium oxide is discussed. The bonding mixture may be applied in the form of a distilled water slurry or by electron beam vapor deposition. In one embodiment the eutectic is formed in situ by applying a layer of zirconium oxide and then heating the assembly to a temperature above the eutectic temperature and below the melting point of the material from which the elements are formed. The formation of a sapphire rubidium maser cell utilizing eutectic bonding is shown.

  12. Bonding of sapphire to sapphire by eutectic mixture of aluminum oxide and zirconium oxide

    NASA Technical Reports Server (NTRS)

    Deluca, J. J. (Inventor)

    1979-01-01

    An element comprising sapphire, ruby or blue sapphire can be bonded to another element of such material with a eutectic mixture of aluminum oxide and zirconium oxide. The bonding mixture may be applied in the form of a distilled water slurry or by electron beam vapor deposition. In one embodiment the eutectic is formed in situ by applying a layer of zirconium oxide and then heating the assembly to a temperature above the eutectic temperature and below the melting point of the material from which the elements are formed. The formation of a sapphire rubidium maser cell utilizing eutectic bonding is shown.

  13. Silver doping: A potential means to grow high quality YBa{sub 2}Cu{sub 3}O{sub 7-x} thin films on bare sapphire

    SciTech Connect

    Kumar, D.; Satyalakshmi, K.M.; Manoharan, S.S.

    1995-10-01

    High quality Ag-doped YBa{sub 2}Cu{sub 3}O{sub 7-x} (YBCO) thin films have been grown by laser ablation on < {bar 1}012 > bare sapphire. This work demonstrates that Ag-doping can be used as very convenient means to realize good quality YBCO films on highly coveted sapphire substrates for microwave applications of high T{sub c} thin films.

  14. Shear Strength and Interfacial Toughness Characterization of Sapphire-Epoxy Interfaces for Nacre-Inspired Composites.

    PubMed

    Behr, Sebastian; Jungblut, Laura; Swain, Michael V; Schneider, Gerold A

    2016-10-12

    The common tensile lap-shear test for adhesive joints is inappropriate for brittle substrates such as glasses or ceramics where stress intensifications due to clamping and additional bending moments invalidate results. Nevertheless, bonding of glasses and ceramics is still important in display applications for electronics, in safety glass and ballistic armor, for dental braces and restoratives, or in recently developed bioinspired composites. To mechanically characterize adhesive bondings in these fields nonetheless, a novel approach based on the so-called Schwickerath test for dental sintered joints is used. This new method not only matches data from conventional analysis but also uniquely combines the accurate determination of interfacial shear strength and toughness in one simple test. The approach is verified for sapphire-epoxy joints that are of interest for bioinspired composites. For these, the procedure not only provides quantitative interfacial properties for the first time, it also exemplarily suggests annealing of sapphire at 1000 °C for 10 h for mechanically and economically effective improvements of the interfacial bond strength and toughness. With increases of strength and toughness from approximately 8 to 29 MPa and from 2.6 to 35 J/m(2), respectively, this thermal modification drastically enhances the properties of unmodified sapphire-epoxy interfaces. At the same time, it is much more convenient than wet-chemical approaches such as silanization. Hence, besides the introduction of a new testing procedure for adhesive joints of brittle or expensive substrates, a new and facile annealing process for improvements of the adhesive properties of sapphire is suggested and quantitative data for the mechanical properties of sapphire-epoxy interfaces that are common in synthetic nacre-inspired composites are provided for the first time.

  15. Pseudorotational epitaxy of self-assembled octadecyltrichlorosilane monolayers on sapphire (0001)

    SciTech Connect

    Steinrück, H. -G.; Magerl, A.; Deutsch, M.; Ocko, B. M.

    2014-10-06

    The structure of octadecyltrichlorosilane self-assembled monolayers (SAMs) on sapphire (0001) was studied by Å-resolution surface-specific x-ray scattering methods. The monolayer was found to consist of three sublayers where the outermost layer corresponds to vertically oriented, closely packed alkyl tails. Laterally, the monolayer is hexagonally packed and exhibits pseudorotational epitaxy to the sapphire, manifested by a broad scattering peak at zero relative azimuthal rotation, with long powderlike tails. The lattice mismatch of ~1% – 3% to the sapphire’s and the different length scale introduced by the lateral Si-O-Si bonding prohibit positional epitaxy. However, the substrate induces an intriguing increase in the crystalline coherence length of the SAM’s powderlike crystallites when rotationally aligned with the sapphire’s lattice. As a result, the increase correlates well with the rotational dependence of the separation of corresponding substrate-monolayer lattice sites.

  16. Pseudorotational epitaxy of self-assembled octadecyltrichlorosilane monolayers on sapphire (0001)

    DOE PAGES

    Steinrück, H. -G.; Magerl, A.; Deutsch, M.; ...

    2014-10-06

    The structure of octadecyltrichlorosilane self-assembled monolayers (SAMs) on sapphire (0001) was studied by Å-resolution surface-specific x-ray scattering methods. The monolayer was found to consist of three sublayers where the outermost layer corresponds to vertically oriented, closely packed alkyl tails. Laterally, the monolayer is hexagonally packed and exhibits pseudorotational epitaxy to the sapphire, manifested by a broad scattering peak at zero relative azimuthal rotation, with long powderlike tails. The lattice mismatch of ~1% – 3% to the sapphire’s and the different length scale introduced by the lateral Si-O-Si bonding prohibit positional epitaxy. However, the substrate induces an intriguing increase in themore » crystalline coherence length of the SAM’s powderlike crystallites when rotationally aligned with the sapphire’s lattice. As a result, the increase correlates well with the rotational dependence of the separation of corresponding substrate-monolayer lattice sites.« less

  17. Si nanowire growth on sapphire: Classical incubation, reverse reaction, and steady state supersaturation

    SciTech Connect

    Shakthivel, Dhayalan; Rathkanthiwar, Shashwat; Raghavan, Srinivasan

    2015-04-28

    Si nanowire growth on sapphire substrates by the vapor-liquid-solid (VLS) method using Au catalyst particles has been studied. Sapphire was chosen as the substrate to ensure that the vapor phase is the only source of Si. Three hitherto unreported observations are described. First, an incubation period of 120–480 s, which is shown to be the incubation period as defined in classical nucleation theory, is reported. This incubation period permits the determination of a desolvation energy of Si from Au-Si alloys of 15 kT. Two, transmission electron microscopy studies of incubation, point to Si loss by reverse reaction as an important part of the mechanism of Si nanowire growth by VLS. Three, calculations using these physico-chemical parameters determined from incubation and measured steady state growth rates of Si nanowires show that wire growth happens from a supersaturated catalyst droplet.

  18. Silicon on sapphire for ion implantation studies

    NASA Technical Reports Server (NTRS)

    Pisciotta, B. P.

    1974-01-01

    Van der Pauw or bridge samples are ultrasonically cut from silicon on sapphire wafers. Contact pad regions are implanted with moderately heavy dose of ions. Ion of interest is implanted into sample; and, before being annealed in vacuum, sample is sealed with sputtered layer of silicon dioxide. Nickel or aluminum is sputtered onto contact pad areas and is sintered in nitrogen atmosphere.

  19. Temperature-Compensated Sapphire Microwave Resonator

    NASA Technical Reports Server (NTRS)

    Dick, G. John; Santiago, David G.

    1996-01-01

    Sapphire-dielectric-ring microwave resonator operating in "whispering-gallery" electromagnetic mode features differential-thermal-expansion design providing temperature compensation for ultrahigh frequency stability. Designed to minimize frequency fluctuations caused by temperature fluctuations at normal temperature equal to or even somewhat greater than temperature of liquid nitrogen. Ancillary equipment needed for operation smaller and less expensive, and liquid nitrogen used as coolant.

  20. Low temperature rhombohedral single crystal SiGe epitaxy on c-plane sapphire

    NASA Astrophysics Data System (ADS)

    Duzik, Adam J.; Choi, Sang H.

    2016-04-01

    Current best practice in epitaxial growth of rhombohedral SiGe onto (0001) sapphire (Al2O3) substrate surfaces requires extreme conditions to grow a single crystal SiGe film. Previous models described the sapphire surface reconstruction as the overriding factor in rhombohedral epitaxy, requiring a high temperature Al-terminated surface for high quality films. Temperatures in the 850-1100°C range were thought to be necessary to get SiGe to form coherent atomic matching between the (111) SiGe plane and the (0001) sapphire surface. Such fabrication conditions are difficult and uneconomical, hindering widespread application. This work proposes an alternative model that considers the bulk sapphire structure and determines how the SiGe film nucleates and grows. Accounting for thermal expansion effects, calculations using this new model show that both pure Ge and SiGe can form single crystal films in the 450-550°C temperature range. Experimental results confirm these predictions, where x-ray diffraction and atomic force microscopy show the films fabricated at low temperature rival the high temperature films in crystallographic and surface quality. Finally, an explanation is provided for why films of comparable high quality can be produced in either temperature range.

  1. Low Temperature Rhombohedral Single Crystal SiGe Epitaxy on c-plane Sapphire

    NASA Technical Reports Server (NTRS)

    Duzik, Adam J.; Choi, Sang H.

    2016-01-01

    Current best practice in epitaxial growth of rhombohedral SiGe onto (0001) sapphire (Al2O3) substrate surfaces requires extreme conditions to grow a single crystal SiGe film. Previous models described the sapphire surface reconstruction as the overriding factor in rhombohedral epitaxy, requiring a high temperature Al-terminated surface for high quality films. Temperatures in the 850-1100 C range were thought to be necessary to get SiGe to form coherent atomic matching between the (111) SiGe plane and the (0001) sapphire surface. Such fabrication conditions are difficult and uneconomical, hindering widespread application. This work proposes an alternative model that considers the bulk sapphire structure and determines how the SiGe film nucleates and grows. Accounting for thermal expansion effects, calculations using this new model show that both pure Ge and SiGe can form single crystal films in the 450-550 C temperature range. Experimental results confirm these predictions, where x-ray diffraction and atomic force microscopy show the films fabricated at low temperature rival the high temperature films in crystallographic and surface quality. Finally, an explanation is provided for why films of comparable high quality can be produced in either temperature range.

  2. Transfer-free graphene synthesis on sapphire by catalyst metal agglomeration technique and demonstration of top-gate field-effect transistors

    SciTech Connect

    Miyoshi, Makoto Arima, Yukinori; Kubo, Toshiharu; Egawa, Takashi; Mizuno, Masaya; Soga, Tetsuo

    2015-08-17

    Transfer-free graphene synthesis was performed on sapphire substrates by using the catalyst metal agglomeration technique, and the graphene film quality was compared to that synthesized on sputtered SiO{sub 2}/Si substrates. Raman scattering measurements indicated that the graphene film on sapphire has better structural qualities than that on sputtered SiO{sub 2}/Si substrates. The cross-sectional transmission microscopic study also revealed that the film flatness was drastically improved by using sapphire substrates instead of sputtered SiO{sub 2}/Si substrates. These quality improvements seemed to be due the chemical and thermal stabilities of sapphire. Top-gate field-effect transistors were fabricated using the graphene films on sapphire, and it was confirmed that their drain current can be modulated with applied gate voltages. The maximum field-effect mobilities were estimated to be 720 cm{sup 2}/V s for electrons and 880 cm{sup 2}/V s for holes, respectively.

  3. Luminescence of CdSe quantum dots near a layer of silver nanoparticles ion-synthesized in sapphire

    NASA Astrophysics Data System (ADS)

    Galyametdinov, Yu. G.; Shamilov, R. R.; Nuzhdin, V. I.; Valeev, V. F.; Stepanov, A. L.

    2016-11-01

    We study the characteristics of the luminescence of composite films based on polymethyl methacrylate with CdSe quantum dots deposited from solution onto the surface of a sapphire substrate containing a preliminarily formed layer with ion-synthesized silver nanoparticles. The sapphire layer with silver nanoparticles exhibits selective plasmon absorption in the visible spectral range with a peak at 463 nm. Enhancement in the exciton luminescence intensity of quantum dots with a peak at 590 nm is observed upon excitation at wavelengths lying in the region of plasmon resonance of metal nanoparticles, as well as luminescence quenching for quantum dots located in the vicinity of silver nanoparticles.

  4. The depth-profiled carrier concentration and scattering mechanism in undoped GaN film grown on sapphire

    NASA Astrophysics Data System (ADS)

    Huang, Y.; Chen, X. D.; Fung, S.; Beling, C. D.; Ling, C. C.; Wei, Z. F.; Xu, S. J.; Zhi, C. Y.

    2004-07-01

    Temperature-dependent Hall (TDH) measurements and confocal micro-Raman spectroscopy have been used to study the free carrier spatial distribution and scattering mechanism in unintentionally doped GaN film grown on the sapphire substrate with the method of metalorganic chemical vapor deposition. Both the TDH data and the depth-profiled Raman spectra agreed with the existence of a nonuniform spatial distribution of free carriers in the GaN film with a highly conductive layer of ˜1 μm thickness near the GaN sapphire boundary. With the consideration of this parallel conduction channel adjacent to GaN sapphire boundary, detailed analysis of the TDH mobility data suggests that a relatively high concentration of nitrogen vacancies exists and nitrogen vacancy scattering has an important influence on limiting the electron mobility in the bulk film of the present GaN sample.

  5. Surface modification of sapphire by ion implantation

    SciTech Connect

    McHargue, C.J.

    1998-11-01

    The range of microstructures and properties of sapphire (single crystalline Al{sub 2}O{sub 3}) that are produced by ion implantation are discussed with respect to the implantation parameters of ion species, fluence, irradiation temperature and the orientation of the ion beam relative to crystallographic axes. The microstructure of implanted sapphire may be crystalline with varying concentrations of defects or it may be amorphous perhaps with short-range order. At moderate to high fluences, implanted metallic ions often coalesce into pure metallic colloids and gas ions form bubbles. Many of the implanted microstructural features have been identified from studies using transmission electron microscopy (TEM), optical spectroscopy, Moessbauer spectroscopy, and Rutherford backscattering-channeling. The chemical, mechanical, and physical properties reflect the microstructures.

  6. Sapphire Viewports for a Venus Probe

    NASA Technical Reports Server (NTRS)

    Bates, Stephen

    2012-01-01

    A document discusses the creation of a viewport suitable for use on the surface of Venus. These viewports are rated for 500 C and 100 atm pressure with appropriate safety factors and reliability required for incorporation into a Venus Lander. Sapphire windows should easily withstand the chemical, pressure, and temperatures of the Venus surface. Novel fixture designs and seals appropriate to the environment are incorporated, as are materials compatible with exploration vessels. A test cell was fabricated, tested, and leak rate measured. The window features polish specification of the sides and corners, soft metal padding of the sapphire, and a metal C-ring seal. The system safety factor is greater than 2, and standard mechanical design theory was used to size the window, flange, and attachment bolts using available material property data. Maintenance involves simple cleaning of the window aperture surfaces. The only weakness of the system is its moderate rather than low leak rate for vacuum applications.

  7. Compared growth mechanisms of Zn-polar ZnO nanowires on O-polar ZnO and on sapphire.

    PubMed

    Perillat-Merceroz, G; Thierry, R; Jouneau, P H; Ferret, P; Feuillet, G

    2012-03-30

    Controlling the growth of zinc oxide nanowires is necessary to optimize the performance of nanowire-based devices such as photovoltaic solar cells, nano-generators, or light-emitting diodes. With this in mind, we investigate the nucleation and growth mechanisms of ZnO nanowires grown by metalorganic vapor phase epitaxy either on O-polar ZnO or on sapphire substrates. Whatever the substrate, ZnO nanowires are Zn-polar, as demonstrated by convergent beam electron diffraction. For growth on O-polar ZnO substrate, the nanowires are found to sit on O-polar pyramids. As growth proceeds, the inversion domain boundary moves up in order to remain at the top of the O-polar pyramids. For growth on sapphire substrates, the nanowires may also originate from the sapphire/ZnO interface. The presence of atomic steps and the non-polar character of sapphire could be the cause of the Zn-polar crystal nucleation on sapphire, whereas it is proposed that the segregation of aluminum impurities could account for the nucleation of inverted domains for growth on O-polar ZnO.

  8. Anisotropy of sapphire single crystal sputtering

    SciTech Connect

    Minnebaev, K. F.; Tolpin, K. A.; Yurasova, V. E.

    2015-08-15

    We have studied the spatial distribution of particles sputtered from the base (0001) plane of a sapphire single crystal with trigonal crystalline lattice (α-Al{sub 2}O{sub 3}) that can be considered a superposition of two hexagonal close packed (hcp) structures–the ideal sublattice of oxygen and a somewhat deformed sublattice of aluminum. It is established that the particles sputtered from the base plane of sapphire are predominantly deposited along the sides of an irregular hexagon with spots at its vertices. The patterns of spots have been also studied for sputtering of particles from the (0001) face of a zinc single crystal with the hcp lattice. The spots of sputtered Zn atoms are arranged at the vertices of concentric equilateral hexagons. In both cases, the observed anisotropy of sputtering is related to focused collisions (direct and assisted focusing) and the channeling process. The chemical composition of spots has been determined in various regions of sputtered sapphire deposition. The results are discussed in comparison to analogous earlier data for secondary ion emission from an α-Al{sub 2}O{sub 3} single crystal.

  9. Failure Analysis of Sapphire Refractive Secondary Concentrators

    NASA Technical Reports Server (NTRS)

    Salem, Jonathan A.; Quinn, George D.

    2009-01-01

    Failure analysis was performed on two sapphire, refractive secondary concentrators (RSC) that failed during elevated temperature testing. Both concentrators failed from machining/handling damage on the lens face. The first concentrator, which failed during testing to 1300 C, exhibited a large r-plane twin extending from the lens through much of the cone. The second concentrator, which was an attempt to reduce temperature gradients and failed during testing to 649 C, exhibited a few small twins on the lens face. The twins were not located at the origin, but represent another mode of failure that needs to be considered in the design of sapphire components. In order to estimate the fracture stress from fractographic evidence, branching constants were measured on sapphire strength specimens. The fractographic analysis indicated radial tensile stresses of 44 to 65 MPa on the lens faces near the origins. Finite element analysis indicated similar stresses for the first RSC, but lower stresses for the second RSC. Better machining and handling might have prevented the fractures, however, temperature gradients and resultant thermal stresses need to be reduced to prevent twinning.

  10. Gate-controlled-diodes in silicon-on-sapphire: A computer simulation

    NASA Technical Reports Server (NTRS)

    Gassaway, J. D.

    1974-01-01

    The computer simulation of the electrical behavior of a Gate-Controlled Diode (GCD) fabricated in Silicon-On-Sapphire (SOS) was described. A procedure for determining lifetime profiles from capacitance and reverse current measurements on the GCD was established. Chapter 1 discusses the SOS structure and points out the need of lifetime profiles to assist in device design for GCD's and bipolar transistors. Chapter 2 presents the one-dimensional analytical formula for electrostatic analysis of the SOS-GCD which are useful for data interpretation and setting boundary conditions on a simplified two-dimensional analysis. Chapter 3 gives the results of a two-dimensional analysis which treats the field as one-dimensional until the silicon film is depleted and the field penetrates the sapphire substrate. Chapter 4 describes a more complete two-dimensional model and gives results of programs implementing the model.

  11. Structural, transport and microwave properties of 123/sapphire films: Thickness effect

    SciTech Connect

    Predtechensky, MR.; Smal, A.N.; Varlamov, Y.D.

    1994-12-31

    The effect of thickness and growth conditions on the structure and microwave properties has been investigated for the 123/sapphire films. It has been shown that in the conditions of epitaxial growth and Al atoms do not diffuse from substrate into the film and the films with thickness up to 100nm exhibit the excellent DC properties. The increase of thickness of GdBaCuO films causes the formation of extended line-mesh defects and the increase of the surface resistance (R{sub S}). The low value of surface resistance R{sub S}(75GHz,77K)=20 mOhm has been obtained for the two layer YBaCuO/CdBaCuO/sapphire films.

  12. Structural, transport and microwave properties of 123/sapphire films: Thickness effect

    NASA Technical Reports Server (NTRS)

    Predtechensky, M. R.; Smal, A. N.; Varlamov, Yu. D.; Vatnik, S. M.; Tukhto, O. M.; Vasileva, I. G.

    1995-01-01

    The effect of thickness and growth conditions on the structure and microwave properties has been investigated for the 123/sapphire films. It has been shown that in the conditions of epitaxial growth the Al atoms do not diffuse from substrate into the film and the films with thickness up to 100 nm exhibit the excellent direct current (DC) properties. The increase of thickness of GdBaCuO films causes the formation of extended line-mesh defects and the increase of the surface resistance (R(sub S)). The low value of surface resistance R(sub S)(75 GHz, 77K) = 20 mOhm has been obtained for the two layer YBaCuO/CdBaCuO/sapphire films.

  13. Study of the crystal structure of silicon nanoislands on sapphire

    SciTech Connect

    Krivulin, N. O. Pirogov, A. V.; Pavlov, D. A.; Bobrov, A. I.

    2015-02-15

    The results of studies of the crystal structure of silicon nanoislands on sapphire are reported. It is shown that the principal defects in silicon nanoislands on sapphire are twinning defects. As a result of the formation of such defects, different crystallographic orientations are formed in silicon nanoislands on sapphire. In the initial stages of the molecular-beam epitaxy of silicon on sapphire, there are two basic orientations: the (001) orientation parallel to the surface and the (001) orientation at an angle of 70° to the surface.

  14. Sapphire-fiber-based intrinsic Fabry-Perot interferometer

    NASA Technical Reports Server (NTRS)

    Wang, Anbo; Gollapudi, Sridhar; Murphy, Kent A.; May, Russell G.; Claus, Richard O.

    1992-01-01

    A sapphire optical fiber intrinsic Fabry-Perot interferometric sensor is demonstrated. A length of multimode sapphire fiber that functions as a Fabry-Perot cavity is spliced to a silica single-mode fiber. The interferometric signals of this sensor are produced by the interference between the reflection from the silica-sapphire fiber splice and the reflection from the free end face of the sapphire fiber. This sensor has been demonstrated for temperature measurement. A resolution of 0.2 C has been obtained over a measurement range of 310 C to 976 C.

  15. Leveraging Python Interoperability Tools to Improve Sapphire's Usability

    SciTech Connect

    Gezahegne, A; Love, N S

    2007-12-10

    The Sapphire project at the Center for Applied Scientific Computing (CASC) develops and applies an extensive set of data mining algorithms for the analysis of large data sets. Sapphire's algorithms are currently available as a set of C++ libraries. However many users prefer higher level scripting languages such as Python for their ease of use and flexibility. In this report, we evaluate four interoperability tools for the purpose of wrapping Sapphire's core functionality with Python. Exposing Sapphire's functionality through a Python interface would increase its usability and connect its algorithms to existing Python tools.

  16. Spontaneous formation of GaN/AlN core-shell nanowires on sapphire by hydride vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Trassoudaine, Agnès; Roche, Elissa; Bougerol, Catherine; André, Yamina; Avit, Geoffrey; Monier, Guillaume; Ramdani, Mohammed Réda; Gil, Evelyne; Castelluci, Dominique; Dubrovskii, Vladimir G.

    2016-11-01

    Spontaneous GaN/AlN core-shell nanowires with high crystal quality were synthesized on sapphire substrates by vapor-liquid-solid hydride vapor phase epitaxy (VLS-HVPE) without any voluntary aluminum source. Deposition of aluminum is difficult to achieve in this growth technique which uses metal-chloride gaseous precursors: the strong interaction between the AlCl gaseous molecules and the quartz reactor yields a huge parasitic nucleation on the walls of the reactor upstream the substrate. We open up an innovative method to produce GaN/AlN structures by HVPE, thanks to aluminum etching from the sapphire substrate followed by redeposition onto the sidewalls of the GaN core. The paper presents the structural characterization of GaN/AlN core-shell nanowires, speculates on the growth mechanism and discusses a model which describes this unexpected behavior.

  17. Fabrication of GaN Microporous Structure at a GaN/Sapphire Interface as the Template for Thick-Film GaN Separation Grown by HVPE

    NASA Astrophysics Data System (ADS)

    Chen, Jianli; Cheng, Hongjuan; Zhang, Song; Lan, Feifei; Qi, Chengjun; Xu, Yongkuan; Wang, Zaien; Li, Jing; Lai, Zhanping

    2016-10-01

    In this paper, a microporous structure at the GaN/sapphire interface has been obtained by an electrochemical etching method via a selective etching progress using an as-grown GaN/sapphire wafer grown by metal organic chemical vapor deposition. The as-prepared GaN interfacial microporous structure has been used as a template for the following growth of thick-film GaN crystal by hydride vapor phase epitaxy (HVPE), facilitating the fabrication of a free-standing GaN substrate detached from a sapphire substrate. The evolution of the interfacial microporous structure has been investigated by varying the etching voltages and time, and the formation mechanism of interfacial microporous structure has been discussed in detail as well. Appropriate interfacial microporous structure is beneficial for separating the thick GaN crystal grown by HVPE from sapphire during the cooling down process. The separation that occurred at the place of interfacial microporous can be attributed to the large thermal strain between GaN and sapphire. This work realized the fabrication of a free-standing GaN substrate with high crystal quality and nearly no residual strain.

  18. Mode Orientation Control For Sapphire Dielectric Ring Resonator

    NASA Technical Reports Server (NTRS)

    Santiago, David G.; Dick, G. John; Prata, Aluizio

    1996-01-01

    Small sapphire tuning wedge used in technique for solving mode-purity problem associated with sapphire dielectric-ring resonator part of cryogenic microwave frequency discriminator. Breaks quasi-degeneracy of two modes and allows selective coupling to just one mode. Wedge mounted on axle entering resonator cavity and rotated while resonator cryogenically operating in vacuum. Furthermore, axle moved vertically to tune resonant frequency.

  19. On-Orbit Results for Canada's Sapphire Optical Payload

    NASA Astrophysics Data System (ADS)

    Scott, A.; Hackett, J.

    2013-09-01

    Sapphire is the first Space Situational Awareness (SSA) satellite mission flown by Canada's Department of National Defence (DND). On February 25, 2013 Sapphire was successfully launched into a sun synchronous orbit at ~786 km altitude. The commissioning phase was a success and the Sapphire system is entering its operational phase. Canada and the United States signed an SSA Memorandum of Understanding on May 4, 2012. Under the agreement, data from DND's Sapphire satellite will be contributed to the U.S. Space Surveillance Network (SSN), enhancing the ability of both countries to detect and avoid the collision of critical space platforms with orbital debris. The Sapphire system is now collecting SSA data that will be shared with the SSN. This SSA partnership will strengthen the long standing defence relationship between the US and Canada and provide diversity in space based sensors at a time of fiscal constraint. The Sapphire satellite optical imaging payload was designed and built by COM DEV based around a small (13.25 cm) Three Mirror Anastigmat (TMA) telescope similar in design to the Space Based Visible sensor on the US Mid-Course Space Experiment satellite. The paper provides an overview of the design and operational performance of the Sapphire instrument, comparing the actual performance to the requirements. Based on lessons learned on this program we discuss potential improvements that would be feasible in a second generation Sapphire payload including the potential for using this sensor as a hosted payload in other applications.

  20. Study on sapphire microstructure processing technology based on wet etching

    NASA Astrophysics Data System (ADS)

    Shang, Ying-Qi; Qi, Hong; Ma, Yun-Long; Wu, Ya-Lin; Zhang, Yan; Chen, Jing

    2017-03-01

    Aiming at the problem that sapphire surface roughness is quite large after wet etching in sapphire microstructure processing technology, we optimize the wet etching process parameters, study on the influences of concentration and temperature of etching solution and etching time on the sapphire surface roughness and etching rate, choose different process parameters for the experiment and test and analyze the sapphire results after wet etching. Aiming at test results, we also optimize the process parameters and do experiment. Experimental results show that, after optimizing the parameters of etching solution, surface roughness of etched sapphire is 0.39 nm, effectively with reduced surface roughness, improved light extraction efficiency and meeting the production requirements of high-precision optical pressure sensor.

  1. Proton and neutron irradiation effect of Ti: Sapphires

    SciTech Connect

    Wang, G.; Zhang, J.; Yang, J.

    1999-07-01

    Various effects of proton and neutron irradiated Ti: sapphires were studied. Proton irradiation induced F, F{sup +} and V center in Ti: sapphires and 3310 cm{sup -1} infrared absorption, and made ultraviolet absorption edge shift to short wave. Neutron irradiation produced a number of F, F{sup +} and F{sub 2} centers and larger defects in Ti: sapphires, and changed Ti{sup 4+}into Ti{sup 3+} ions. Such valence state variation enhanced characteristic luminescence of Ti: sapphires, and no singular variances of intrinsic fluorescence spectra of Ti: sapphires took place with neutron flux of 1 x 10{sup 17}n/cm{sup 2}, but the fluorescence vanished with neutron flux of 1 x 10{sup 18}n/cm{sup 2} which means the threshold for the concentration of improving Ti{sup 3+} ions by neutron irradiation.

  2. Double Sided Si(Ge)/Sapphire/III-Nitride Hybrid Structure

    NASA Technical Reports Server (NTRS)

    Park, Yeonjoon (Inventor); Choi, Sang Hyouk (Inventor)

    2016-01-01

    One aspect of the present invention is a double sided hybrid crystal structure including a trigonal Sapphire wafer containing a (0001) C-plane and having front and rear sides. The Sapphire wafer is substantially transparent to light in the visible and infrared spectra, and also provides insulation with respect to electromagnetic radio frequency noise. A layer of crystalline Si material having a cubic diamond structure aligned with the cubic <111> direction on the (0001) C-plane and strained as rhombohedron to thereby enable continuous integration of a selected (SiGe) device onto the rear side of the Sapphire wafer. The double sided hybrid crystal structure further includes an integrated III-Nitride crystalline layer on the front side of the Sapphire wafer that enables continuous integration of a selected III-Nitride device on the front side of the Sapphire wafer.

  3. Ion beam mixing of Fe with sapphire and silica

    SciTech Connect

    Sinha, S. K.; Vigen, K. M.; Kothari, D. C.; Som, T.; Kulkarni, V. N.; Nair, K. G. M.

    1999-06-10

    We have studied ion beam mixing of Fe with sapphire, silica, Al and Si using different mass of the ions (Ne{sup +},Ar{sup +}), different doses (5x10{sup 15} to 2x10{sup 17} ions/cm{sup 2}) and different temperatures (273 deg. K, 423 deg. K and 573 deg. K). Thin film of Fe was deposited by thermal evaporation method. Ion energy was chosen from 30 to 110 keV so that F{sub d} is maximum at the interface. All the specimens were analyzed by RBS. It is found that the square of the diffusion length Dt is proportional to the ion dose for both types of the substrates (Al{sub 2}O{sub 3} and SiO{sub 2}) implying that mixing is due to the ballistic effect (i.e. cascade mixing). Also mixing is more when irradiated by Ar{sup +} ions than Ne{sup +} ions. Comparison of Dt's shows that mixing is less in ceramics than in pure-elements Al and Si. In Fe-Al{sub 2}O{sub 3} samples, mixing decreases with increase in irradiation temperatures implying de-mixing in crystalline ionic bonded oxide whereas mixing increases in the covalently bonded oxide SiO{sub 2}. Irradiated annealed samples of Fe/Al{sub 2}O{sub 3} and Fe/SiO{sub 2} show de-mixing and mixing respectively.

  4. Nanomechanical and optical properties of highly a-axis oriented AlN films

    NASA Astrophysics Data System (ADS)

    Jose, Feby; Ramaseshan, R.; Tripura Sundari, S.; Dash, S.; Tyagi, A. K.; Kiran, M. S. R. N.; Ramamurty, U.

    2012-12-01

    This paper reports optical and nanomechanical properties of predominantly a-axis oriented AlN thin films. These films were deposited by reactive DC magnetron sputtering technique at an optimal target to substrate distance of 180 mm. X-ray rocking curve (FWHM = 52 arcsec) studies confirmed the preferred orientation. Spectroscopic ellipsometry revealed a refractive index of 1.93 at a wavelength of 546 nm. The hardness and elastic modulus of these films were 17 and 190 GPa, respectively, which are much higher than those reported earlier can be useful for piezoelectric films in bulk acoustic wave resonators.

  5. Characteristics of Coplanar Waveguide on Sapphire for High Temperature Applications (25 to 400 degrees C)

    NASA Technical Reports Server (NTRS)

    Ponchak, George E.; Jordan, Jennifer L.; Scardelletti, Maximilian; Stalker, Amy R.

    2007-01-01

    This paper presents the characteristics of coplanar waveguide transmission lines fabricated on R-plane sapphire substrates as a function of temperature across the temperature range of 25 to 400 C. Effective permittivity and attenuation are measured on a high temperature probe station. Two techniques are used to obtain the transmission line characteristics, a Thru-Reflect-Line calibration technique that yields the propagation coefficient and resonant stubs. To a first order fit of the data, the effective permittivity and the attenuation increase linearly with temperature.

  6. Characteristics of Coplanar Waveguide on Sapphire for High Temperature Applications (25 to 400 C)

    NASA Technical Reports Server (NTRS)

    Ponchak, George E.; Jordan, Jennifer L.; Scardelletti, Maximillian; Stalker, Amy R.

    2007-01-01

    This paper presents the characteristics of coplanar waveguide transmission lines fabricated on R-plane sapphire substrates as a function of temperature across the temperature range of 25 to 400 C. Effective permittivity and attenuation are measured on a high temperature probe station. Two techniques are used to obtain the transmission line characteristics, a Thru-Reflect-Line calibration technique that yields the propagation coefficient and resonant stubs. To a first order fit of the data, the effective permittivity and the attenuation increase linearly with temperature

  7. High Temperature Characteristics of Coplanar Waveguide on R-Plane Sapphire and Alumina

    NASA Technical Reports Server (NTRS)

    Ponchak, George E.; Jordan, Jennifer L.; Scardelletti, Maximilian C.

    2007-01-01

    This paper presents the characteristics of coplanar waveguide transmission lines on R-plane sapphire and alumina over the temperature range of 25 to 400 C and the frequency range of 45 MHz to 50 GHz. A Thru-Reflect-Line calibration technique and open circuited terminated stubs are used to extract the attenuation and effective permittivity. It is shown that the effective permittivity of the transmission lines and, therefore, the relative dielectric constant of the two substrates increase linearly with temperature. The attenuation of the coplanar waveguide varies linearly with temperature through 200 C, and increases at a greater rate above 200 C.

  8. Electron Beam Welder Used to Braze Sapphire to Platinum

    NASA Technical Reports Server (NTRS)

    Forsgren, Roger C.; Vannuyen, Thomas

    1998-01-01

    A new use for electron beam brazing was recently developed by NASA Lewis Research Center's Manufacturing Engineering Division. This work was done to fabricate a fiberoptic probe (developed by Sentec Corporation) that could measure high temperatures less than 600 deg C of vibrating machinery, such as in jet engine combustion research. Under normal circumstances, a sapphire fiber would be attached to platinum by a ceramic epoxy. However, no epoxies can adhere ceramic fibers to platinum under such high temperatures and vibration. Also, since sapphire and platinum have different thermal properties, the epoxy bond is subjected to creep over time. Therefore, a new method had to be developed that would permanently and reliably attach a sapphire fiber to platinum. Brazing a sapphire fiber to a platinum shell. The fiber-optic probe assembly consists of a 0.015-in.-diameter sapphire fiber attached to a 0.25-in.-long, 0.059-in.-diameter platinum shell. Because of the small size of this assembly, electron beam brazing was chosen instead of conventional vacuum brazing. The advantage of the electron beam is that it can generate a localized heat source in a vacuum. Gold reactive braze was used to join the sapphire fiber and the platinum. Consequently, the sapphire fiber was not affected by the total heat needed to braze the components together.

  9. Impact of high-temperature annealing of AlN layer on sapphire and its thermodynamic principle

    NASA Astrophysics Data System (ADS)

    Fukuyama, Hiroyuki; Miyake, Hideto; Nishio, Gou; Suzuki, Shuhei; Hiramatsu, Kazumasa

    2016-05-01

    The N2-CO gas annealing technique was demonstrated to improve the crystalline quality of the AlN layer on sapphire. 300-nm-thick AlN layers were fabricated on sapphire substrates by a metal-organic vapor phase epitaxy method. The AlN layers were annealed in N2 and/or N2-CO gas atmosphere at 1923-1973 K for 0.5-4 h. Many pits and voids were observed on the AlN surface annealed in N2 atmosphere at 1973 K for 2 h. The rough surface was, however, much improved for the AlN annealed in N2-CO gas atmosphere. The thermodynamic principle of the N2-CO gas annealing technique is explained in this paper on the basis of the phase stability diagram of the Al2O3-AlN-C-N2-CO system. Voids and γ-aluminum oxynitride (γ-AlON) at the AlN/sapphire interface formed during the annealing, which is also explained on the basis of the phase stability diagram. The in-plane epitaxial relationships among AlN, γ-AlON, and sapphire are presented, and misfits among them are discussed.

  10. The study on the nanomachining property and cutting model of single-crystal sapphire by atomic force microscopy.

    PubMed

    Huang, Jen-Ching; Weng, Yung-Jin

    2014-01-01

    This study focused on the nanomachining property and cutting model of single-crystal sapphire during nanomachining. The coated diamond probe is used to as a tool, and the atomic force microscopy (AFM) is as an experimental platform for nanomachining. To understand the effect of normal force on single-crystal sapphire machining, this study tested nano-line machining and nano-rectangular pattern machining at different normal force. In nano-line machining test, the experimental results showed that the normal force increased, the groove depth from nano-line machining also increased. And the trend is logarithmic type. In nano-rectangular pattern machining test, it is found when the normal force increases, the groove depth also increased, but rather the accumulation of small chips. This paper combined the blew by air blower, the cleaning by ultrasonic cleaning machine and using contact mode probe to scan the surface topology after nanomaching, and proposed the "criterion of nanomachining cutting model," in order to determine the cutting model of single-crystal sapphire in the nanomachining is ductile regime cutting model or brittle regime cutting model. After analysis, the single-crystal sapphire substrate is processed in small normal force during nano-linear machining; its cutting modes are ductile regime cutting model. In the nano-rectangular pattern machining, due to the impact of machined zones overlap, the cutting mode is converted into a brittle regime cutting model.

  11. Fe-sapphire and C-Fe-sapphire interactions and their effect on the growth of single-walled carbon nanotubes by chemical vapor deposition.

    PubMed

    Yudasaka, M; Kasuya, Y; Jing, F; Zhang, M; Iijima, S

    2004-04-01

    We previously reported that the quantity of single-walled carbon nanotubes grown on Fe-coated sapphire by chemical vapor deposition depended on the crystallographic faces of sapphires. In this report, we show that the interaction of Fe, sapphire, and carbon depended on the sapphire faces. We deduce that the quantity of Fe available to catalyze the growth of single-walled carbon nanotubes was suppressed by the formation of Fe-Al alloys and whether the Fe-Al alloys were formed on Fe-coated sapphire or not depended on the sapphire-surface structure.

  12. Ruby and sapphire from Jegdalek, Afghanistan

    USGS Publications Warehouse

    Bowersox, G.W.; Foord, E.E.; Laurs, B.M.; Shigley, J.E.; Smith, C.P.

    2000-01-01

    This study provides detailed mining and gemological information on the Jegdalek deposit, in east-central Afghanistan, which is hosted by elongate beds of corundum-bearing marble. Some facet-grade ruby has been recovered, but most of the material consists of semitransparent pink sapphire of cabochon or carving quality. The most common internal features are dense concentrations of healed and nonhealed fracture planes and lamellar twin planes. Color zoning is common, and calcite, apatite, zircon, mica, iron sulfide minerals, graphite, rutile, aluminum hydroxide, and other minerals are also present in some samples. Although the reserves appear to be large, future potential will depend on the establishment of a stable government and the introduction of modern mining and exploration techniques. ?? 2000 Gemological Institute of America.

  13. Sapphire fiber interferometer for microdisplacement measurements at high temperatures

    NASA Technical Reports Server (NTRS)

    Murphy, Kent A.; Fogg, Brian R.; Wang, George Z.; Vengsarkar, Ashish M.; Claus, Richard O.

    1991-01-01

    We report the use of a short-length, multimode sapphire rod as an extension to a Michelson configuration, but operated as a low-finesse Fabry-Perot cavity. We demonstrate the performance of such a device as an interferometric sensor, where the interference between the reflections from the sapphire-air interface and an air-metallic surface is observed for microdisplacement of the metallic surface which is placed close to the sapphire endface. We describe in detail the fabrication procedure and present results obtained from the detection of temperature changes, applied strain, and surface acoustic waves.

  14. Temperature Compensated Sapphire Resonator for Ultra-Stable Oscillator Capability

    NASA Technical Reports Server (NTRS)

    Dick, G. J.; Santiago, D. G.; Wang, R. T.

    1994-01-01

    We report on the design and test of a whispering gallery sapphire resonator for which the dominant microwave mode family shows frequency-stable, compensated operation for temperatures above 77 kelvin.

  15. A high sensitivity sapphire transducer for vibration measurements

    SciTech Connect

    Peng, H.; Blair, D.G.; Ivanov, E.

    1994-12-31

    In this report we describe an interferometric Sapphire Dielectric Resonator (SDR) transducer which avoids the need for an ultra low noise oscillator. An initial performance of the transducer is presented.

  16. Buffer layers for high-Tc thin films on sapphire

    NASA Technical Reports Server (NTRS)

    Wu, X. D.; Foltyn, S. R.; Muenchausen, R. E.; Cooke, D. W.; Pique, A.; Kalokitis, D.; Pendrick, V.; Belohoubek, E.

    1992-01-01

    Buffer layers of various oxides including CeO2 and yttrium-stabilized zirconia (YSZ) have been deposited on R-plane sapphire. The orientation and crystallinity of the layers were optimized to promote epitaxial growth of YBa2Cu3O(7-delta) (YBCO) thin films. An ion beam channeling minimum yield of about 3 percent was obtained in the CeO2 layer on sapphire, indicating excellent crystallinity of the buffer layer. Among the buffer materials used, CeO2 was found to be the best one for YBCO thin films on R-plane sapphire. High Tc and Jc were obtained in YBCO thin films on sapphire with buffer layers. Surface resistances of the YBCO films were about 4 mOmega at 77 K and 25 GHz.

  17. Ti:sapphire - A theoretical assessment for its spectroscopy

    NASA Astrophysics Data System (ADS)

    Da Silva, A.; Boschetto, D.; Rax, J. M.; Chériaux, G.

    2017-03-01

    This article tries to theoretically compute the stimulated emission cross-sections when we know the oscillator strength of a broad material class (dielectric crystals hosting metal-transition impurity atoms). We apply the present approach to Ti:sapphire and check it by computing some emission cross-section curves for both π and σ polarizations. We also set a relationship between oscillator strength and radiative lifetime. Such an approach will allow future parametric studies for Ti:sapphire spectroscopic properties.

  18. Progress on 10 Kelvin cryo-cooled sapphire oscillator

    NASA Technical Reports Server (NTRS)

    Wang, Rabi T.; Dick, G. John; Diener, William A.

    2004-01-01

    We present recent progress on the 10 Kelvin Cryocooled Sapphire Oscillator (10K CSO). Included are incorporation of a new pulse tube cryocooler, cryocooler vibration comparisons between G-M and pulse-tube types, phase noise, and frequency stability tests. For the advantage of a single stage pulse tube cryocooler, we also present results for a 40K Compensated Sapphire Oscillator (40K CSO).

  19. Gold coated zinc oxide nanonecklaces as a SERS substrate.

    PubMed

    He, Lili; Shi, Jian; Sun, Xin; Lin, Mengshi; Yu, Ping; Li, Hao

    2011-04-01

    Faceted zinc oxide nanonecklace (ZnO NN) arrays were grown on r-plane sapphires along one direction (ZnO [0001] II sapphire [10-11] and ZnO (-12-10) II sapphire (01-12)) using chemical vapor deposition. After coated with 45 nm gold films and annealed at 250 degrees C for 30 seconds, the coated ZnO NNs exhibit satisfactory and stable surface enhanced Raman scattering (SERS) effects when tested with melamine and other chemicals. The limit of detection of melamine is 10(-5) mol/L and the analytical enhancement factor is 10(4), which is competitive to a commercial substrate. This study indicates that gold coated ZnO NN substrates have a great potential as SERS-active substrates in rapid detection of trace amount food contaminants such as melamine and other chemicals.

  20. Ti : sapphire laser synchronised with femtosecond Yb pump laser via nonlinear pulse coupling in Ti : sapphire active medium

    NASA Astrophysics Data System (ADS)

    Didenko, N. V.; Konyashchenko, A. V.; Konyashchenko, D. A.; Kostryukov, P. V.; Kuritsyn, I. I.; Lutsenko, A. P.; Mavritskiy, A. O.

    2017-02-01

    A laser system utilising the method of synchronous pumping of a Ti : sapphire laser by a high-power femtosecond Yb3+-doped laser is described. The pulse repetition rate of the Ti : sapphire laser is successfully locked to the repetition rate of the Yb laser for more than 6 hours without the use of any additional electronics. The measured timing jitter is shown to be less than 1 fs. A simple qualitative model addressing the synchronisation mechanism utilising the cross-phase modulation of oscillation and pump pulses within a Ti : sapphire active medium is proposed. Output parameters of the Ti : sapphire laser as functions of its cavity length are discussed in terms of this model.

  1. Cryogenic Pound Circuits for Cryogenic Sapphire Oscillators

    NASA Technical Reports Server (NTRS)

    Dick, G. John; Wang, Rabi

    2006-01-01

    Two modern cryogenic variants of the Pound circuit have been devised to increase the frequency stability of microwave oscillators that include cryogenic sapphire-filled cavity resonators. The original Pound circuit is a microwave frequency discriminator that provides feedback to stabilize a voltage-controlled microwave oscillator with respect to an associated cavity resonator. In the present cryogenic Pound circuits, the active microwave devices are implemented by use of state-of-the-art commercially available tunnel diodes that exhibit low flicker noise (required for high frequency stability) and function well at low temperatures and at frequencies up to several tens of gigahertz. While tunnel diodes are inherently operable as amplitude detectors and amplitude modulators, they cannot, by themselves, induce significant phase modulation. Therefore, each of the present cryogenic Pound circuits includes passive circuitry that transforms the AM into the required PM. Each circuit also contains an AM detector that is used to sample the microwave signal at the input terminal of the high-Q resonator for the purpose of verifying the desired AM null at this point. Finally, each circuit contains a Pound signal detector that puts out a signal, at the modulation frequency, having an amplitude proportional to the frequency error in the input signal. High frequency stability is obtained by processing this output signal into feedback to a voltage-controlled oscillator to continuously correct the frequency error in the input signal.

  2. Nanostructured sapphire vicinal surfaces as templates for the growth of self-organized oxide nanostructures

    NASA Astrophysics Data System (ADS)

    Thune, E.; Boulle, A.; Babonneau, D.; Pailloux, F.; Hamd, W.; Guinebretière, R.

    2009-11-01

    Vicinal substrates of sapphire with miscut angle of 10° from the (0 0 1) planes towards the [1 1 0] direction have been annealed in air in the range from 1000 to 1500 °C. The behaviour of these surfaces has been characterized as a function of the temperature and the thermal treatment time by Atomic Force Microscopy observations. A thermal treatment at 1250 °C allows to stabilize a surface made of periodically spaced nanosized step-bunches. Such stepped surfaces were used as template to grow self-patterned epitaxial oxide nanoparticles by thermal annealing of yttria-stabilized zirconia thin films produced by sol-gel dip-coating. Grazing Incidence Small Angle X-ray Scattering and High-Resolution Transmission Electron Microscopy were used to study the morphology of the nanoparticles and their epitaxial relationships with the substrate.

  3. Spatial distribution of carrier concentration in un-doped GaN film grown on sapphire

    NASA Astrophysics Data System (ADS)

    Huang, Y.; Chen, X. D.; Beling, C. D.; Fung, S.; Ling, C. C.

    2004-03-01

    The depth and lateral dependent carrier concentration of un-intentionally doped GaN film grown on sapphire substrate have been studied by temperature-dependent Hall effect measurement, confocal micro-Raman spectroscopy and capacitance-voltage (C-V) measurements. The depth-dependent free carrier concentration extracted from the depth-profiled Raman spectra confirms a non-uniform spatial distribution of free carriers in the GaN film with a highly conductive layer of 1 m thickness near the GaN/sapphire boundary. The temperature dependent Hall data have been analyzed using two-layer model to extract the carrier concentration in the GaN bulk film and in the parallel conduction channel adjacent to the GaN/sapphire boundary. The carrier concentrations of the two layers derived from the Raman technique and the Hall measurements agree with each other. The lateral-dependent carrier concentration of the 2-inch GaN epitaxial wafer has also been studied by micro-Raman spectroscopy and C-V measurements. The line-shape fitting of the Raman A1(LO) coupled modes taken from horizontal lateral-different positions on the wafer yielded a rudimentary spatial map of the carrier concentration. These data are compared well with a lateral-dependent carrier concentration map of the wafer revealed by C-V measurements. The study in the article indicates that Raman spectroscopy of the LO phonon-plasmon mode can be used as a nondestructive and reliable, in situ diagnostic for GaN wafer production.

  4. A peek into the history of sapphire crystal growth

    NASA Astrophysics Data System (ADS)

    Harris, Daniel C.

    2003-09-01

    After the chemical compositions of sapphire and ruby were unraveled in the middle of the 19th century, chemists set out to grow artificial crystals of these valuable gemstones. In 1885 a dealer in Geneva began to sell ruby that is now believed to have been created by flame fusion. Gemnologists rapidly concluded that the stones were artificial, but the Geneva ruby stimulated A. V. L. Verneuil in Paris to develop a flame fusion process to produce higher quality ruby and sapphire. By 1900 there was brisk demand for ruby manufactured by Verneuil's method, even though Verneuil did not publicly announce his work until 1902 and did not publish details until 1904. The Verneuil process was used with little alteration for the next 50 years. From 1932-1953, S. K. Popov in the Soviet Union established a capability for manufacturing high quality sapphire by the Verneuil process. In the U.S., under government contract, Linde Air Products Co. implemented the Verneuil process for ruby and sapphire when European sources were cut off during World War II. These materials were essential to the war effort for jewel bearings in precision instruments. In the 1960s and 1970s, the Czochralski process was implemented by Linde and its successor, Union Carbide, to make higher crystal quality material for ruby lasers. Stimulated by a government contract for structural fibers in 1966, H. LaBelle invented edge-defined film-fed growth (EFG). The Saphikon company, which is currently owned by Saint-Gobain, evolved from this effort. Independently and simultaneously, Stepanov developed edge-defined film-fed growth in the Soviet Union. In 1967 F. Schmid and D. Viechnicki at the Army Materials Research Lab grew sapphire by the heat exchanger method (HEM). Schmid went on to establish Crystal Systems, Inc. around this technology. Rotem Industries, founded in Israel in 1969, perfected the growth of sapphire hemispheres and near-net-shape domes by gradient solidification. In the U.S., growth of near

  5. Scaling STI's sapphire cryocooler for applications requiring higher heat loads

    NASA Astrophysics Data System (ADS)

    Karandikar, Abhijit; Fiedler, Andreas

    2012-06-01

    Superconductor Technologies Inc. (STI) developed the Sapphire cryocooler specifically for the SuperLink® product; a high performance superconducting Radio Frequency (RF) front-end receiver used by wireless carriers such as Verizon Wireless and AT&T to improve network cell coverage and data speeds. STI has built and deployed over 6,000 systems operating 24 hours a day (24/7), 7 days a week in the field since 1999. Sapphire is an integrated free piston Stirling cycle cryocooler with a cooling capacity of 5 Watts at 77 Kelvin (K) with less than 100 Watts (W) input power. It has a field-proven Mean Time Between Failure (MTBF) of well over 1 million hours, requires zero maintenance and has logged over 250 million cumulative runtime hours. The Sapphire cooler is built on a scalable technology platform, enabling the design of machines with cooling capacities greater than 1 kilowatt (kW). This scalable platform also extends the same outstanding attributes as the Sapphire cooler, namely high reliability, zero maintenance, and compact size - all at a competitive cost. This paper will discuss emerging applications requiring higher heat loads and these attributes, describe Sapphire, and show a preliminary concept of a scaled machine with a 100 W cooling capacity.

  6. Size and shape dependence of CO adsorption sites on sapphire supported Fe microcrystals

    NASA Technical Reports Server (NTRS)

    Papageorgopoulos, C.; Heinemann, K.

    1985-01-01

    The surface structure and stoichiometry of alumina substrates, as well as the size, growth characteristics, and shape of Fe deposits on sapphire substrates have been investigated by low energy electron diffraction (LEED), Auger electron spectroscopy, electron energy loss spectroscopy, and X-ray photoemission spectroscopy (XPS), as well as work function measurements, in conjunction with transition electron microscopy observations. The substrates used in this work were the following: (1) new, clean Al2O3; (2) same surface amorphized by Ar ion bombardment; (3) same surface regenerated by 650 C annealing; (4) amorphous alumina films on Ta slab; and (5) polycrystal alumina films, obtained by heating amorphous films to 600 C. Substrate cleaning was found to be most effective in producing a reproducible surface upon oxygen RF plasma treatment. The Fe nucleation and growth process was found to depend strongly on the type of substrate surface and deposition conditions. Ar ion bombardment under beam flooding, and subsequent annealing at 650 C was found an effective means to restore the original Al2O3 (1102) surface for renewed Fe deposition.

  7. Sapphire Fiber Optics Sensors for Engine Test Instrumentation

    SciTech Connect

    Janney, MA

    2003-09-19

    This document is the final report for the Cooperative Research and Development Agreement (CRADA) between UT-Battelle and Prime Photonics, Inc. The purpose of this CRADA was to improve the properties of single crystal sapphire optical fibers for sensor applications. A reactive coating process was developed to form a magnesium aluminate spinel cladding on sapphire optical fibers. The resulting clad fiber had a numerical aperture, NA, of 0.09 as compared with 0.83 for the unclad fiber, dramatically enhancing its usefulness for sensor applications. Because the process allows one to control the diameter of the sapphire core within the fiber, it may be possible using this technology to develop waveguides that approach single-mode transmission character.

  8. A microfabricated sun sensor using GaN-on-sapphire ultraviolet photodetector arrays

    NASA Astrophysics Data System (ADS)

    Miller, Ruth A.; So, Hongyun; Chiamori, Heather C.; Suria, Ateeq J.; Chapin, Caitlin A.; Senesky, Debbie G.

    2016-09-01

    A miniature sensor for detecting the orientation of incident ultraviolet light was microfabricated using gallium nitride (GaN)-on-sapphire substrates and semi-transparent interdigitated gold electrodes for sun sensing applications. The individual metal-semiconductor-metal photodetector elements were shown to have a stable and repeatable response with a high sensitivity (photocurrent-to-dark current ratio (PDCR) = 2.4 at -1 V bias) and a high responsivity (3200 A/W at -1 V bias) under ultraviolet (365 nm) illumination. The 3 × 3 GaN-on-sapphire ultraviolet photodetector array was integrated with a gold aperture to realize a miniature sun sensor (1.35 mm × 1.35 mm) capable of determining incident light angles with a ±45° field of view. Using a simple comparative figure of merit algorithm, measurement of incident light angles of 0° and 45° was quantitatively and qualitatively (visually) demonstrated by the sun sensor, supporting the use of GaN-based sun sensors for orientation, navigation, and tracking of the sun within the harsh environment of space.

  9. Reaction layers and mechanisms for a Ti-activated braze on sapphire

    NASA Astrophysics Data System (ADS)

    Stephens, J. J.; Hosking, F. M.; Headley, T. J.; Hlava, P. F.; Yost, F. G.

    2003-12-01

    A study was conducted to understand the wetting phenomena observed in brazing of a Ti-containing active filler metal on sapphire substrates. The goal of the study was to understand the interfacial reactions that permit wetting of commercial Ag-Cu-Ti active filler metal to pure alumina, despite the lower thermodynamic stability of TiO2 relative to Al2O3. Based upon transmission electron microscope, electron microprobe, and Auger analyses, it is proposed that two coupled reactions and diffusion of reactants take place. The oxides TiO, Ti2O, and Cu3Ti3O were observed at the braze/ceramic interface. It is suggested that the complex oxide Cu3Ti3O grows at its interface with TiO, and the oxide TiO is produced by reaction of Ti and sapphire and is subsequently consumed at its interface with Cu3Ti3O. It is also suggested that Ti2O forms from Ti and TiO while cooling from the brazing cycle.

  10. Wavelength Tunability of Ion-bombardment Induced Surface Ripples on Sapphire

    NASA Astrophysics Data System (ADS)

    Zhou, Hua; Zhou, Lan; Wang, Yi-Ping; Headrick, Randall L.; Ozcan, Ahmet S.; Wang, Yi-Yi; Ozaydin, Gozde; Ludwig, Karl F., Jr.; Siddons, David P.

    2006-03-01

    Energetic particle bombardment on surfaces is known to produce well ordered 2-D (ripples or wires) and 1-D (dots) structures at submicron/nanoscale by a self-organization process. Recently, significant experimental and theoretical effort has been expended to develop methods to produce self-organized nanostructures on diverse substrates from semiconductors to metals. These studies have shown potential in tailoring surface morphology in order to exploit novel physical properties, and contributed much to reveal the mechanisms of the instability-driven self-organization process. In this work, a study of ripple formation on sapphire surfaces by ion sputtering is presented. Surface characterization by in-situ synchrotron grazing incidence small angle x-ray scattering (GISAXS) and ex-situ atomic force microscopy (AFM) for the wavelength, shape and amplitude of sapphire ripples is performed. The wavelength can be varied over two orders of magnitude by changing the ion incidence angle. The linear Bradley-Harper (B-H) theory with ion induced viscous flow (IVF) relaxation fits the general trends of the data. However, anomalous smoothing not predicted by current models is observed near normal incidence.

  11. Sapphire fiber interferometer for microdisplacement measurements at high temperature

    NASA Technical Reports Server (NTRS)

    Murphy, Kent A.; Feth, Shari; Vengsarkar, Ashish M.; Claus, Richard O.

    1992-01-01

    Attention is given to the use of a short-length multimode sapphire rod as an extension to a conventional Michelson interferometric configuration, but with operation of Fabry-Perot cavity-based sensor element type. The performance of such a device as an interferometric sensor is demonstrated for a case where the interference between the reflections from the sapphire-air interface and an air-metallic surface is inspected for microdisplacements of the metallic surface. A detailed account is given of the sensor's fabrication procedure; results are presented for the detection of surface-acoustic waves.

  12. Molecular-orbital model for metal-sapphire interfacial strength

    NASA Technical Reports Server (NTRS)

    Johnson, K. H.; Pepper, S. V.

    1982-01-01

    Self-consistent-field X-Alpha scattered-wave cluster molecular-orbital models have been constructed for transition and noble metals (Fe, Ni, Cu, and Ag) in contact with a sapphire (Al2O3) surface. It is found that a chemical bond is established between the metal d-orbital electrons and the nonbonding 2p-orbital electrons of the oxygen anions on the Al2O3 surface. An increasing number of occupied metal-sapphire antibonding molecular orbitals explains qualitatively the observed decrease of contact shear strength through the series Fe, Ni, Cu, and Ag.

  13. SERS Raman Sensor Based on Diameter-Modulated Sapphire Fiber

    SciTech Connect

    Shimoji, Yutaka

    2010-08-09

    Surface enhanced Raman scattering (SERS) has been observed using a sapphire fiber coated with gold nano-islands for the first time. The effect was found to be much weaker than what was observed with a similar fiber coated with silver nanoparticles. Diameter-modulated sapphire fibers have been successfully fabricated on a laser heated pedestal growth system. Such fibers have been found to give a modest increase in the collection efficiency of induced emission. However, the slow response of the SERS effect makes it unsuitable for process control applications.

  14. Silicon-on-Sapphire Waveguides: Mode-converting Couplers and Four-wave Mixing

    DTIC Science & Technology

    2014-09-01

    TECHNICAL DOCUMENT 3283 September 2014 Silicon-on-Sapphire Waveguides: Mode-converting Couplers and Four-Wave Mixing Sanja...fabrication and performance of mode-converting couplers and silicon-on-sapphire waveguides  Measurements of four-wave mixing in silicon-on-sapphire...2  2.2.  WAVEGUIDE COUPLERS

  15. Step-induced misorientation of GaN grown on r-plane sapphire

    SciTech Connect

    Smalc-Koziorowska, J.; Dimitrakopulos, G. P.; Sahonta, S.-L.; Komninou, Ph.; Tsiakatouras, G.; Georgakilas, A.

    2008-07-14

    In the growth of nonpolar (1120) a-plane GaN on r-plane (1102) sapphire by plasma-assisted molecular beam epitaxy, misoriented crystallites are observed close to the substrate. They have average diameter {approx}10 nm and are oriented with the (0001){sub GaN} plane approximately parallel to the (2113){sub sapph.} plane and [0110]{sub GaN} parallel [1101]{sub sapph.}. This semipolar orientation is promoted by a low misfit (2.4%) between (1011){sub GaN} and (1210){sub sapph.} planes. Its introduction, after nitridation treatment, is due to GaN nucleation on (2113){sub sapph.} step facets inclined at 26 deg. relative to the r-plane. Two variants are observed, leading to twinning when they abut inside the epilayer.

  16. Formation of superwetting surface with line-patterned nanostructure on sapphire induced by femtosecond laser

    NASA Astrophysics Data System (ADS)

    Yin, Kai; Duan, Ji'an; Sun, Xiaoyan; Wang, Cong; Luo, Zhi

    2015-04-01

    In this study, an effective approach is presented for the fabrication of line-patterned superwetting surface on sapphire by using a femtosecond laser. The fabricated surface shows a powerful capillary action by which water could be rapidly sucked into the as-prepared surface structures and spread even on the vertical surface against gravitation. In addition, the effects of the period and the dimensions of the microgrooves on surface wettability are investigated. It is demonstrated that the wettability can be significantly enhanced in the case when the sizable line-patterned nanostructures exist. This work could provide a facile and promising strategy for enhancing the performance of heat dissipation in the electronic devices substrate.

  17. Growth of single-crystalline zirconium diboride thin film on sapphire

    NASA Astrophysics Data System (ADS)

    Bera, Sambhunath; Sumiyoshi, Yuichiro; Yamada-Takamura, Yukiko

    2009-09-01

    Conducting and reflecting thin film of ZrB2, which has lattice mismatch of only 0.6% to GaN, was grown epitaxially on sapphire substrate [α-Al2O3(0001)] via thermal decomposition of Zr(BH4)4. In situ reflection high energy electron diffraction and ex situ x-ray diffraction analyses indicate that the epitaxial relationship is singular, i.e., ZrB2[0001]∥Al2O3[0001] and ZrB2[112¯0]∥Al2O3[101¯0]. X-ray photoelectron spectroscopy and scanning tunneling microscopy revealed that the oxide-free surface could be recovered by heating the film at approximately 750 °C under ultrahigh vacuum, which demonstrates its suitability as a template for the growth of nitride semiconductors.

  18. Silicon-Germanium Films Grown on Sapphire for Ka-Band Communications Applications

    NASA Technical Reports Server (NTRS)

    Alterovitz, Samuel A.; Mueller, Carl H.; Croke, Edward T.

    2004-01-01

    NASA's vision in the space communications area is to develop a broadband data network in which there is a high degree of interconnectivity among the various satellite systems, ground stations, and wired systems. To accomplish this goal, we will need complex electronic circuits integrating analog and digital data handling at the Ka-band (26 to 40 GHz). The purpose of this project is to show the feasibility of a new technology for Ka-band communications applications, namely silicon germanium (SiGe) on sapphire. This new technology will have several advantages in comparison to the existing silicon-substrate- based circuits. The main advantages are extremely low parasitic reactances that enable much higher quality active and passive components, better device isolation, higher radiation tolerance, and the integration of digital and analog circuitry on a single chip.

  19. Neurosurgery contact handheld probe based on sapphire shaped crystal

    NASA Astrophysics Data System (ADS)

    Shikunova, I. A.; Stryukov, D. O.; Rossolenko, S. N.; Kiselev, A. M.; Kurlov, V. N.

    2017-01-01

    A handheld contact probe based on sapphire shaped crystal is developed for intraoperative spectrally-resolved optical diagnostics, laser coagulation and aspiration of malignant brain tissue. The technology was integrated into the neurosurgical workflow for intraoperative real-time identification and removing of invasive brain cancer.

  20. Modal reduction in single crystal sapphire optical fiber

    SciTech Connect

    Cheng, Yujie; Hill, Cary; Liu, Bo; Yu, Zhihao; Xuan, Haifeng; Homa, Daniel; Wang, Anbo; Pickrell, Gary

    2015-10-12

    A new type of single crystal sapphire optical fiber (SCSF) design is proposed to reduce the number of guided modes via a highly dispersive cladding with a periodic array of high and low index regions in the azimuthal direction. The structure retains a “core” region of pure single crystal (SC) sapphire in the center of the fiber and a “cladding” region of alternating layers of air and SC sapphire in the azimuthal direction that is uniform in the radial direction. The modal characteristics and confinement losses of the fundamental mode were analyzed via the finite element method by varying the effective core diameter and the dimensions of the “windmill” shaped cladding. The simulation results showed that the number of guided modes were significantly reduced in the “windmill” fiber design, as the radial dimension of the air and SC sapphire cladding regions increase with corresponding decrease in the azimuthal dimension. It is anticipated that the “windmill” SCSF will readily improve the performance of current fiber optic sensors in the harsh environment and potentially enable those that were limited by the extremely large modal volume of unclad SCSF.

  1. High power continuous-wave titanium:sapphire laser

    DOEpatents

    Erbert, G.V.; Bass, I.L.; Hackel, R.P.; Jenkins, S.L.; Kanz, V.K.; Paisner, J.A.

    1993-09-21

    A high-power continuous-wave laser resonator is provided, wherein first, second, third, fourth, fifth and sixth mirrors form a double-Z optical cavity. A first Ti:sapphire rod is disposed between the second and third mirrors and at the mid-point of the length of the optical cavity, and a second Ti:sapphire rod is disposed between the fourth and fifth mirrors at a quarter-length point in the optical cavity. Each Ti:sapphire rod is pumped by two counter-propagating pump beams from a pair of argon-ion lasers. For narrow band operation, a 3-plate birefringent filter and an etalon are disposed in the optical cavity so that the spectral output of the laser consists of 5 adjacent cavity modes. For increased power, seventy and eighth mirrors are disposed between the first and second mirrors to form a triple-Z optical cavity. A third Ti:sapphire rod is disposed between the seventh and eighth mirrors at the other quarter-length point in the optical cavity, and is pumped by two counter-propagating pump beams from a third pair of argon-ion lasers. 5 figures.

  2. High power continuous-wave titanium:sapphire laser

    DOEpatents

    Erbert, Gaylen V.; Bass, Isaac L.; Hackel, Richard P.; Jenkins, Sherman L.; Kanz, Vernon K.; Paisner, Jeffrey A.

    1993-01-01

    A high-power continuous-wave laser resonator (10) is provided, wherein first, second, third, fourth, fifth and sixth mirrors (11-16) form a double-Z optical cavity. A first Ti:Sapphire rod (17) is disposed between the second and third mirrors (12,13) and at the mid-point of the length of the optical cavity, and a second Ti:Sapphire rod (18) is disposed between the fourth and fifth mirrors (14,15) at a quarter-length point in the optical cavity. Each Ti:Sapphire rod (17,18) is pumped by two counter-propagating pump beams from a pair of argon-ion lasers (21-22, 23-24). For narrow band operation, a 3-plate birefringent filter (36) and an etalon (37) are disposed in the optical cavity so that the spectral output of the laser consists of 5 adjacent cavity modes. For increased power, seventy and eighth mirrors (101, 192) are disposed between the first and second mirrors (11, 12) to form a triple-Z optical cavity. A third Ti:Sapphire rod (103) is disposed between the seventh and eighth mirrors (101, 102) at the other quarter-length point in the optical cavity, and is pumped by two counter-propagating pump beams from a third pair of argon-ion lasers (104, 105).

  3. Modal reduction in single crystal sapphire optical fiber

    DOE PAGES

    Cheng, Yujie; Hill, Cary; Liu, Bo; ...

    2015-10-12

    A new type of single crystal sapphire optical fiber (SCSF) design is proposed to reduce the number of guided modes via a highly dispersive cladding with a periodic array of high and low index regions in the azimuthal direction. The structure retains a “core” region of pure single crystal (SC) sapphire in the center of the fiber and a “cladding” region of alternating layers of air and SC sapphire in the azimuthal direction that is uniform in the radial direction. The modal characteristics and confinement losses of the fundamental mode were analyzed via the finite element method by varying themore » effective core diameter and the dimensions of the “windmill” shaped cladding. The simulation results showed that the number of guided modes were significantly reduced in the “windmill” fiber design, as the radial dimension of the air and SC sapphire cladding regions increase with corresponding decrease in the azimuthal dimension. It is anticipated that the “windmill” SCSF will readily improve the performance of current fiber optic sensors in the harsh environment and potentially enable those that were limited by the extremely large modal volume of unclad SCSF.« less

  4. Superconducting, surface and interface properties of Ho(123) and Bi(2212) films on sapphire with cerium oxide buffer layers

    NASA Astrophysics Data System (ADS)

    Castro, L. F.; Suryanarayanan, R.; Das, A.; Bacca, E.; Gómez, M. E.; Lopera, W.; Prieto, P.; Kreisler, A.; Martin, J. C.

    1995-09-01

    We report on the X-ray diffraction, secondary ion mass spectrometry, and atomic force microscopy on Ho(123) and Bi(2212) films dc sputtered in pure oxygen atmosphere onto heated sapphire substrates with CeO 2 buffer layers. The films were c-axis oriented. The Ho(123) films had a T c of 88 K but had a relatively high room temperature resistivity of 400 μΩcm. The Bi(2212) films showed a broad transition and a low T c of 46 K. The data may be explained by a certain amount of Al diffusion and inhomogenous grain growth.

  5. HVPE-GaN growth on GaN-based Advanced Substrates by Smart Cut™

    NASA Astrophysics Data System (ADS)

    Iwinska, M.; Amilusik, M.; Fijalkowski, M.; Sochacki, T.; Lucznik, B.; Grzanka, E.; Litwin-Staszewska, E.; Weyher, J. L.; Nowakowska-Siwinska, A.; Muziol, G.; Skierbiszewski, C.; Grzegory, I.; Guiot, E.; Caulmilone, R.; Bockowski, M.

    2016-12-01

    Advanced Substrates consist of a thin GaN layer bonded to a carrier wafer. The layer is separated from starting material by Smart Cut™ technology. GaN on sapphire Advanced Substrates were successfully used as seeds for HVPE-GaN growth. Unintentionally doped and silicon-doped thick GaN layers were crystallized. The results were compared to HVPE-GaN grown on standard MOCVD-GaN/sapphire templates. Free-standing HVPE-GaN with high free carrier concentration was obtained. A laser diode was built on the n-type doped HVPE-GaN grown on an Advanced Substrate.

  6. Direct spontaneous growth and interfacial structural properties of inclined GaN nanopillars on r-plane sapphire

    SciTech Connect

    Adikimenakis, A.; Aretouli, K. E.; Tsagaraki, K.; Androulidaki, M.; Georgakilas, A.; Lotsari, A.; Dimitrakopulos, G. P. Kehagias, Th.; Komninou, Ph.

    2015-06-28

    The spontaneous growth of GaN nanopillars (NPs) by direct plasma-assisted molecular beam epitaxy on nitridated r-plane sapphire substrates has been studied. The emanation of metal-polarity NPs from inside an a-plane nonpolar GaN film was found to depend on both the substrate nitridation and the growth conditions. The density of NPs increased with increasing the duration of the nitridation process and the power applied on the radio-frequency plasma source, as well as the III/V flux ratio, while variation of the first two parameters enhanced the roughness of the substrate's surface. Transmission electron microscopy (TEM) techniques were employed to reveal the structural characteristics of the NPs and their nucleation mechanism from steps on the sapphire surface and/or interfacial semipolar GaN nanocrystals. Lattice strain measurements showed a possible Al enrichment of the first 5–6 monolayers of the NPs. By combining cross-sectional and plan-view TEM observations, the three-dimensional model of the NPs was constructed. The orientation relationship and interfacial accommodation between the NPs and the nonpolar a-plane GaN film were also elucidated. The NPs exhibited strong and narrow excitonic emission, suggesting an excellent structural quality.

  7. Optical Properties of Single-Crystal Sapphire Fibers

    NASA Astrophysics Data System (ADS)

    Merberg, Glenn N.

    1992-01-01

    The optical properties of edge-defined, film-fed growth (EFG) and laser heated pedestal growth (LHPG) sapphire fibers were characterized, and the utility of these fibers for medical and industrial applications assessed. While EFG fibers are not yet produced with good optical quality, they offer enormous potential for mass production of sapphire fibers. The LHPG process has been successfully employed to produce good optical quality sapphire. This dissertation focussed on the optical attenuation mechanisms which limit the transmission properties of both EFG and LHPG sapphire fibers. The EFG fibers obtained for this research were found to contain bubbles along the fiber axes. As a result of the bubble inclusions, the measured optical scattering coefficients of the fibers were quite high. At a wavelength of 2.94 mum, a typical 280 μm diameter EFG fiber had a total attenuation coefficient of 18 dB/m. The contribution of scattering to this loss was measured as 17 dB/m, and the absorptive component as measured by laser calorimetry was 1 dB/m. The wavelength dependence of the scattering in EFG fibers was found to be lambda^{-1.5}, which is consistent with a Mie scattering model for scattering of light by bubbles on the dimensional order of the wavelength. Some of the LHPG fibers grown at Rutgers had measured attenuation coefficients of less than 2 dB/m at 2.94 μm wavelength. The absorptive component of this loss was measured by laser calorimetry as 0.7 dB/m, while the scattering loss was 1 dB/m. Optical scattering in Rutgers LHPG fibers had a lambda^ {-4} wavelength dependence, although the scattering coefficients were considerably higher than predicted for intrinsic scattering. Although visible absorbing color -centers were discovered in Rutgers LHPG fibers, excessive optical scattering dominated the attenuation in this spectral region. Melt extruded Teflon-FEP claddings were applied to LHPG fibers. The claddings were very effective in reducing evanescent coupling of Er

  8. Sub-surface oxide features at the aluminum-sapphire interface after low temperature annealing

    NASA Astrophysics Data System (ADS)

    Dutta, Sreya

    This work focuses on the formation of sub-surface oxide features that form at the aluminum-sapphire interface during a low temperature heat-treatment. The features consist of two parts, stable alpha-alumina ridges on the substrate, and faceted pyramidal structures composed of thin, low-temperature oxide shells that are bounded by the ridges. It is surprising to observe the formation of thermodynamically stable alpha-alumina at a low temperature. The ridges are epitaxial with the (0001) sapphire substrate and the overlying metal. The pyramidal features resemble closely the Wulff shape in aluminum. Experiments show that these features are underlying the annealing hillocks. This work is a detailed study of such oxide interfacial features associated with hollow hillocks. At the annealing temperatures (below the melting point of aluminum), the aluminum thin film is subjected to compressive stresses arising from the thermal expansion coefficient mismatch and this is aided by dewetting at the aluminum-sapphire interface. Creep cavitation and grain boundary sliding are postulated to help in the cavity formation. Annealing holes are also observed in the thin films. Two different types of holes are seen: dendritic branched holes and hexagonal faceted holes (drums). At lower temperature and thickness, dendritic holes are seen to be formed at the grain boundaries. The drums form within the grains at higher temperatures and in thicker films. The drums have a surface oxide layer suspended on the top. It is postulated that clustering of vacancies due to the presence of irregularities, defects, and dislocations at the interface as well as dewetting causes the nucleation of the drums at the interface. Numerous hillock-hole couples were seen. Thinning of the metal in areas near the hillocks could possibly aid in the hole formation process. It is speculated that the hole growth occurred during the cooling stage when the film was subjected to tensile stresses. Another interesting

  9. Single-Crystal Sapphire Optical Fiber Sensor Instrumentation

    SciTech Connect

    Pickrell, Gary; Scott, Brian; Wang, Anbo; Yu, Zhihao

    2013-12-31

    This report summarizes technical progress on the program “Single-Crystal Sapphire Optical Fiber Sensor Instrumentation,” funded by the National Energy Technology Laboratory of the U.S. Department of Energy, and performed by the Center for Photonics Technology of the Bradley Department of Electrical and Computer Engineering at Virginia Tech. This project was completed in three phases, each with a separate focus. Phase I of the program, from October 1999 to April 2002, was devoted to development of sensing schema for use in high temperature, harsh environments. Different sensing designs were proposed and tested in the laboratory. Phase II of the program, from April 2002 to April 2009, focused on bringing the sensor technologies, which had already been successfully demonstrated in the laboratory, to a level where the sensors could be deployed in harsh industrial environments and eventually become commercially viable through a series of field tests. Also, a new sensing scheme was developed and tested with numerous advantages over all previous ones in Phase II. Phase III of the program, September 2009 to December 2013, focused on development of the new sensing scheme for field testing in conjunction with materials engineering of the improved sensor packaging lifetimes. In Phase I, three different sensing principles were studied: sapphire air-gap extrinsic Fabry-Perot sensors; intensity-based polarimetric sensors; and broadband polarimetric sensors. Black body radiation tests and corrosion tests were also performed in this phase. The outcome of the first phase of this program was the selection of broadband polarimetric differential interferometry (BPDI) for further prototype instrumentation development. This approach is based on the measurement of the optical path difference (OPD) between two orthogonally polarized light beams in a single-crystal sapphire disk. At the beginning of Phase II, in June 2004, the BPDI sensor was tested at the Wabash River coal gasifier

  10. Blue inorganic light emitting diode on flexible polyimide substrate using laser lift-off process.

    PubMed

    Barange, Nilesh; Kim, Young Dong; Ko, Hyungduk; Park, Joon-Suh; Park, Byoungnam; Ko, Doo-Hyun; Han, Ii Ki

    2014-11-01

    The fabrication process for the blue GaN inorganic light emitting diode (ILED) on flexible polyimide (PI) substrate by laser lift off (LLO) method was demonstrated. The GaN epi-structure was grown on patterned sapphire wafer. GaN samples were temporary bonded with polyimide substrate by flexible silver epoxy. Separation of the whole GaN LED film from GaN/sapphire wafer was accomplished using a single KrF excimer (248 nm) laser pulse directed through the transparent sapphire wafer. Device fabrication was carried out on both rigid silicon and flexible polyimide substrate, and I-V performance for both devices was measured. The optimized LLO process for the whole GaN LED film transfer would be applicable in flexible LED applications without compromising electrical properties.

  11. Measurements of prompt radiation induced conductivity of alumina and sapphire

    SciTech Connect

    Hartman, E. Frederick; Zarick, Thomas Andrew; Sheridan, Timothy J.; Preston, Eric F.

    2011-04-01

    We performed measurements of the prompt radiation induced conductivity in thin samples of Alumina and Sapphire at the Little Mountain Medusa LINAC facility in Ogden, UT. Five mil thick samples were irradiated with pulses of 20 MeV electrons, yielding dose rates of 1E7 to 1E9 rad/s. We applied variable potentials up to 1 kV across the samples and measured the prompt conduction current. Analysis rendered prompt conductivity coefficients between 1E10 and 1E9 mho/m/(rad/s), depending on the dose rate and the pulse width for Alumina and 1E7 to 6E7 mho/m/(rad/s) for Sapphire.

  12. A neutron method for NDA analysis in the SAPPHIRE Project

    SciTech Connect

    Lewis, K.D.

    1995-01-09

    The implementation of Project SAPPHIRE, the top secret mission to the Republic of Kazakhstan to recover weapons grade nuclear materials, consisted of four major elements: (1) the re-packing of fissile material from Kazakh containers into suitable US containers; (2) nondestructive analyses (NDA) to quantify the U-235 content of each container for Nuclear Criticality Safety and compliance purposes; (3) the packaging of the fissile material containers into 6M/2R drums, which are internationally approved for shipping fissile material; and (4) the shipping or transport of the recovered fissile material to the United States. This paper discusses the development and application of a passive neutron counting technique used in the NDA phase of SAPPHIRE operations to analyze uranium/beryllium (U/Be) alloys and compounds for U-235 content.

  13. Wavelength Tunability of Ion-Bombardment-Induced Ripples on Sapphire

    SciTech Connect

    Zhou,H.; Wang, Y.; Zhou, L.; Headrick, R.; Ozcan, A.; Wang, Y.; Ozaydin, G.; Ludwig, Jr., K.; Siddons, D.

    2007-01-01

    A study of ripple formation on sapphire surfaces by 300-2000 eV Ar{sup +} ion bombardment is presented. Surface characterization by in-situ synchrotron grazing incidence small angle x-ray scattering and ex-situ atomic force microscopy is performed in order to study the wavelength of ripples formed on sapphire (0001) surfaces. We find that the wavelength can be varied over a remarkably wide range -- nearly two orders of magnitude -- by changing the ion incidence angle. Within the linear theory regime, the ion induced viscous flow smoothing mechanism explains the general trends of the ripple wavelength at low temperature and incidence angles larger than 30{sup o}. In this model, relaxation is confined to a few nm thick damaged surface layer. The behavior at high temperature suggests relaxation by surface diffusion. However, strong smoothing is inferred from the observed ripple wavelength near normal incidence, which is not consistent with either surface diffusion or viscous flow relaxation.

  14. SAPPHIRE WILDERNESS STUDY AREA AND CONTIGUOUS ROADLESS AREAS, MONTANA.

    USGS Publications Warehouse

    Wallace, C.A.; Bannister, D'Arcy P.

    1984-01-01

    Geologic and mineral studies located sulfide-bearing quartz veins with demonstrated metallic mineral resources in granitic and metasedimentary rocks in several parts of the Sapphire Wilderness Study Area and contiguous roadless areas, Montana. Mines and prospects contain demonstrated resources of gold, silver, lead, copper, and zinc. Gold-bearing placers occur downstream from each of these vein occurrences; most of the gold placers have a probable mineral-resource potential. A replacement body of sulfide minerals is present at the Senate mine adjacent to the Sapphire Wilderness Study Area. Around the Senate mine is an area of probable mineral-resource potential that extends into the study area. There is little promise for the occurrence of energy resources in the study area.

  15. Progress Report for a New Cryogenic Sapphire Oscillator

    NASA Technical Reports Server (NTRS)

    Wang, Rabi T.; Dick, G. J.; Tjoelker, R. L.

    2006-01-01

    We present design progress and subsystem test results for a new short-term frequency standard, the Voltage Controlled Sapphire Oscillator (VCSO). Included are sapphire resonator and coupling design, cryocooler environmental sensitivity tests, Q measurement results, and turnover temperature results. A previous report presented history of the design related to resonator frequency and frequency compensation [1]. Performance goals are a frequency stability of 1x10(exp -14) (1 second less than or equal to (tau) less than or equal to 100 seconds) and two years or more continuous operation. Long-term operation and small size are facilitated by use of a small Stirling cryo-cooler (160W wall power) with an expected 5 year life.

  16. Strong Geometrical Effects in Submillimeter Selective Area Growth and Light Extraction of GaN Light Emitting Diodes on Sapphire

    PubMed Central

    Tanaka, Atsunori; Chen, Renjie; Jungjohann, Katherine L.; Dayeh, Shadi A.

    2015-01-01

    Advanced semiconductor devices often utilize structural and geometrical effects to tailor their characteristics and improve their performance. We report here detailed understanding of such geometrical effects in the epitaxial selective area growth of GaN on sapphire substrates and utilize them to enhance light extraction from GaN light emitting diodes. Systematic size and spacing effects were performed side-by-side on a single 2” sapphire substrate to minimize experimental sampling errors for a set of 144 pattern arrays with circular mask opening windows in SiO2. We show that the mask opening diameter leads to as much as 4 times increase in the thickness of the grown layers for 20 μm spacings and that spacing effects can lead to as much as 3 times increase in thickness for a 350 μm dot diameter. We observed that the facet evolution in comparison with extracted Ga adatom diffusion lengths directly influences the vertical and lateral overgrowth rates and can be controlled with pattern geometry. Such control over the facet development led to 2.5 times stronger electroluminescence characteristics from well-faceted GaN/InGaN multiple quantum well LEDs compared to non-faceted structures. PMID:26611405

  17. Strong geometrical effects in submillimeter selective area growth and light extraction of GaN light emitting diodes on sapphire

    DOE PAGES

    Tanaka, Atsunori; Chen, Renjie; Jungjohann, Katherine L.; ...

    2015-11-27

    Advanced semiconductor devices often utilize structural and geometrical effects to tailor their characteristics and improve their performance. Our detailed understanding of such geometrical effects in the epitaxial selective area growth of GaN on sapphire substrates is reported here, and we utilize them to enhance light extraction from GaN light emitting diodes. Systematic size and spacing effects were performed side-by-side on a single 2” sapphire substrate to minimize experimental sampling errors for a set of 144 pattern arrays with circular mask opening windows in SiO2. We show that the mask opening diameter leads to as much as 4 times increase inmore » the thickness of the grown layers for 20 μm spacings and that spacing effects can lead to as much as 3 times increase in thickness for a 350 μm dot diameter. We also observed that the facet evolution in comparison with extracted Ga adatom diffusion lengths directly influences the vertical and lateral overgrowth rates and can be controlled with pattern geometry. Lastly, such control over the facet development led to 2.5 times stronger electroluminescence characteristics from well-faceted GaN/InGaN multiple quantum well LEDs compared to non-faceted structures.« less

  18. Strong geometrical effects in submillimeter selective area growth and light extraction of GaN light emitting diodes on sapphire

    SciTech Connect

    Tanaka, Atsunori; Chen, Renjie; Jungjohann, Katherine L.; Dayeh, Shadi A.

    2015-11-27

    Advanced semiconductor devices often utilize structural and geometrical effects to tailor their characteristics and improve their performance. Our detailed understanding of such geometrical effects in the epitaxial selective area growth of GaN on sapphire substrates is reported here, and we utilize them to enhance light extraction from GaN light emitting diodes. Systematic size and spacing effects were performed side-by-side on a single 2” sapphire substrate to minimize experimental sampling errors for a set of 144 pattern arrays with circular mask opening windows in SiO2. We show that the mask opening diameter leads to as much as 4 times increase in the thickness of the grown layers for 20 μm spacings and that spacing effects can lead to as much as 3 times increase in thickness for a 350 μm dot diameter. We also observed that the facet evolution in comparison with extracted Ga adatom diffusion lengths directly influences the vertical and lateral overgrowth rates and can be controlled with pattern geometry. Lastly, such control over the facet development led to 2.5 times stronger electroluminescence characteristics from well-faceted GaN/InGaN multiple quantum well LEDs compared to non-faceted structures.

  19. Strong Geometrical Effects in Submillimeter Selective Area Growth and Light Extraction of GaN Light Emitting Diodes on Sapphire.

    PubMed

    Tanaka, Atsunori; Chen, Renjie; Jungjohann, Katherine L; Dayeh, Shadi A

    2015-11-27

    Advanced semiconductor devices often utilize structural and geometrical effects to tailor their characteristics and improve their performance. We report here detailed understanding of such geometrical effects in the epitaxial selective area growth of GaN on sapphire substrates and utilize them to enhance light extraction from GaN light emitting diodes. Systematic size and spacing effects were performed side-by-side on a single 2" sapphire substrate to minimize experimental sampling errors for a set of 144 pattern arrays with circular mask opening windows in SiO2. We show that the mask opening diameter leads to as much as 4 times increase in the thickness of the grown layers for 20 μm spacings and that spacing effects can lead to as much as 3 times increase in thickness for a 350 μm dot diameter. We observed that the facet evolution in comparison with extracted Ga adatom diffusion lengths directly influences the vertical and lateral overgrowth rates and can be controlled with pattern geometry. Such control over the facet development led to 2.5 times stronger electroluminescence characteristics from well-faceted GaN/InGaN multiple quantum well LEDs compared to non-faceted structures.

  20. Dark matter search with a low temperature sapphire bolometer

    NASA Astrophysics Data System (ADS)

    de Bellefon, A.; Berkes, I.; Bobin, C.; Broszkiewicz, D.; Chambon, B.; Chapellier, M.; Chardin, G.; Charvin, P.; Chazal, V.; Coron, N.; De Jésus, M.; Drain, D.; Dumoulin, L.; Giraud-Héraud, Y.; Goldbach, C.; Guerier, G.; Hadjout, J. P.; Leblanc, J.; Marchand, D.; Massaq, M.; Messous, Y.; Navick, X.; Nollez, G.; Pari, P.; Pastor, C.; Perillo-Isaac, M. C.; Prostakov, I.; Yvon, D.

    1996-12-01

    A dark matter detection experiment using a low temperature 24 g sapphire bolometer is presented. The low radioactive background cryogenic facility, installed in a deep underground site, is described, as well as the low-noise read-out electronics and the data analysis. From the energy spectrum, measured down to 4 keV, exclusion plots are derived for WIMPs having coherent vector coupling or axial coupling to ordinary matter.

  1. New compressed Ti:sapphire femtosecond amplifier layout

    NASA Astrophysics Data System (ADS)

    Carson, Andrew J.; Barnes, Charles C.; Tenyakov, Sergey

    2006-02-01

    A novel new design for an 8-pass multipass Titanium doped sapphire femtosecond amplifier (MPA) is studied. Ultrafast amplifiers based on the chirped pulse amplification (CPA) technique have been widely used to amplify the output pulses of Kerr lens mode locked (KLM) Ti:sapphire lasers from the nanojoule to the microjoule level. The system presented here also takes advantage of CPA to reduce the peak power and thus the potential damage to optical components from self-focusing. The amplifier scheme is based on a single curved mirror and a Brewster cut Ti:sapphire laser rod. Optical excitation of the Ti:sapphire gain medium is achieved by pumping with a Q-switched and frequency doubled Nd:YLF laser at 527 nm. The rear face of the gain crystal is coated to form a high reflector for both the pumping wavelength (490-550 nm) and the amplified seed pulse (740-860 nm). In this configuration the gain crystal itself acts as a second mirror, reducing the size of the amplifier and allowing for the most effective use of the pumping energy. By employing a Brewster cut lasing crystal the amount of active gain material can be adjusted for maximum gain. The advantages of this approach, compared to traditional two curved mirror MPA designs, are the reduced foot print and the ability to easily adjust the amount of gain material. At the same time the system retains the low amplified spontaneous emission (ASE) and temporally clean output pulse characteristic of MPA systems.

  2. Epitaxial growth of hexagonal silicon polytypes on sapphire

    SciTech Connect

    Pavlov, D. A.; Pirogov, A. V. Krivulin, N. O.; Bobrov, A. I.

    2015-01-15

    The formation of a single-crystal silicon polytype is observed in silicon-on-sapphire structures by high-resolution transmission electron microscopy. The appearance of inclusions with a structure different from that of diamond is attributed to the formation of strong-twinning regions and the aggregation of stacking faults, which form their own crystal structure in the crystal lattice of silicon. It is demonstrated that the given modification belongs to the 9R silicon polytype.

  3. Visualization and Analysis of Impact Damage in Sapphire

    DTIC Science & Technology

    2011-11-01

    Analysis of Impact Damage in Sapphire Elmar Strassburger Fraunhofer-Institut für Kurzzeitdynamik, Ernst - Mach -Institut (EMI) Parimal Patel and...Miami, FL, 12–16 September 2011. *Fraunhofer-Institut für Kurzzeitdynamik, Ernst - Mach -Institut (EMI), Am Christianswuhr 2, 79400 Kandern, Germany 14...ABSTRACT This report reviews work carried out with the fully instrumented Edge-on Impact (EOI) facility at the Ernst - Mach -Institute (EMI), using a

  4. Titanium-doped sapphire laser research and design study

    NASA Technical Reports Server (NTRS)

    Moulton, Peter F.

    1987-01-01

    Three main topics were considered in this study: the fundamental laser parameters of titanium-doped sapphire, characterization of commercially grown material, and design of a tunable, narrow-linewidth laser. Fundamental parameters investigated included the gain cross section, upper-state lifetime as a function of temperature and the surface-damage threshold. Commercial material was found to vary widely in the level of absorption of the laser wavelength with the highest absorption in Czochralski-grown crystals. Several Yi:sapphire lasers were constructed, including a multimode laser with greater than 50mJ of output energy and a single-transverse-mode ring laser, whose spectral and temporal characteristics were completely characterized. A design for a narrow-linewidth (single-frequency) Ti:sapphire laser was developed, based on the results of the experimental work. The design involves the use of a single-frequency, quasi-cw master oscillator, employed as an injection source for a pulsed ring laser.

  5. Multilayer pinning in a-axis-oriented EuBa2Cu3O7/PrBa2Cu3O7 superconducting superlattices

    NASA Astrophysics Data System (ADS)

    Martin, J. I.; Velez, M.; Vicent, J. L.

    1995-08-01

    a-axis EuBa2Cu3O7/PrBa2Cu3O7 superlattices and a-axis films have been grown by dc sputtering to study the interplay between the natural material anisotropy (Cu-O planes) and the artificial layered structure (PrBa2Cu3O7 layers). These a-axis-oriented superlattices are unique because, in comparison with c-axis superlattices, they allow one to separate both effects: in c-axis multilayers Cu-O planes and the artificial layers are parallel whereas in a-axis multilayers the intrinsic and the artificial layers are perpendicular to each other. When B is parallel to the substrate plane, the superlattices show an enhancement of the pinning force in comparison with the behavior of the films that is controlled by the EuBa2Cu3O7 layer thickness. If B is perpendicular to the substrate plane, the flux motion presents a log B dependence of the activation energy up to at least, 40-unit-cell-thick layers.

  6. Polar and Nonpolar Gallium Nitride and Zinc Oxide based thin film heterostructures Integrated with Sapphire and Silicon

    NASA Astrophysics Data System (ADS)

    Gupta, Pranav

    This dissertation work explores the understanding of the relaxation and integration of polar and non-polar of GaN and ZnO thin films with Sapphire and silicon substrates. Strain management and epitaxial analysis has been performed on wurtzitic GaN(0001) thin films grown on c-Sapphire and wurtzitic non-polar a-plane GaN(11-20) thin films grown on r-plane Sapphire (10-12) by remote plasma atomic nitrogen source assisted UHV Pulsed Laser Deposition process. It has been established that high-quality 2-dimensional c-axis GaN(0001) nucleation layers can be grown on c-Sapphire by PLD process at growth temperatures as low as ˜650°C. Whereas the c-axis GaN on c-sapphire has biaxially negative misfit, the crystalline anisotropy of the a-plane GaN films on r-Sapphire results in compressive and tensile misfits in the two major orthogonal directions. The measured strains have been analyzed in detail by X-ray, Raman spectroscopy and TEM. Strain relaxation in GaN(0001)/Sapphire thin film heterostructure has been explained by the principle of domain matched epitaxial growth in large planar misfit system and has been demonstrated by TEM study. An attempt has been made to qualitatively understand the minimization of free energy of the system from the strain perspective. Analysis has been presented to quantify the strain components responsible for the compressive strain observed in the GaN(0001) thin films on c-axis Sapphire substrates. It was also observed that gallium rich deposition conditions in PLD process lead to smoother nucleation layers because of higher ad-atom mobility of gallium. We demonstrate near strain relaxed epitaxial (0001) GaN thin films grown on (111) Si substrates using TiN as intermediate buffer layer by remote nitrogen plasma assisted UHV pulsed laser deposition (PLD). Because of large misfits between the TiN/GaN and TiN/Si systems the TIN buffer layer growth occurs via nucleation of interfacial dislocations under domain matching epitaxy paradigm. X-ray and

  7. [Gemology characterization and identification of beryllium diffused, heated and untreated bicolor sapphires from Changle City, China].

    PubMed

    Chen, Tao; Yang, Ming-xing

    2012-03-01

    Be-diffused, heated and untreated bicolor sapphires (blue and yellow) from Changle City, Shandong Province, China were studied by using standard gemological methods, ultraviolet-visible (UV-Vis) spectroscopy, infrared (IR) spectroscopy, electron microprobe, and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to obtain the spectra characterization, and to suggest identification methods for them. Only Fe(3+)-Fe3+ absorption bands formed in ultraviolet region appear in Be-diffused bicolor sapphire, which is especially strong at 377 nm. In IR absorption spectra, absorption peak at 3 310 cm(-1) appears in heated and untreated bicolor sapphires, while it disappears in Be-diffused bicolor sapphire. Therefore, UV-Vis and IR absorption spectra can be used to identify Be-diffused, heated and untreated bicolor sapphires. On the other hand, methylene iodide immersion observation also can be used to identify Be-diffused bicolor sapphire.

  8. Semipolar InGaN/GaN nanostructure light-emitting diodes on c-plane sapphire

    NASA Astrophysics Data System (ADS)

    Rishinaramangalam, Ashwin K.; Nami, Mohsen; Fairchild, Michael N.; Shima, Darryl M.; Balakrishnan, Ganesh; Brueck, S. R. J.; Feezell, Daniel F.

    2016-03-01

    The fabrication of electrically injected triangular-nanostripe core-shell semipolar III-nitride LEDs (TLEDs) is demonstrated using interferometric lithography and catalyst-free bottom-up selective-area metal-organic chemical vapor deposition (MOCVD). This alternative approach enables semipolar orientations on inexpensive, c-plane sapphire substrates, in comparison with planar growth on free-standing GaN substrates. Transmission electron microscopy and energy dispersive X-ray spectroscopy reveal nonuniform quantum well thickness and composition, respectively, as a function of location on the triangular stripes. The broad electroluminescence spectra, wavelength shift with increasing current density, and nonlinear light vs current characteristics are well correlated with the observed quantum-well nonuniformities.

  9. Growth modes in metal-organic molecular beam epitaxy of TiO{sub 2} on r-plane sapphire

    SciTech Connect

    Jalan, Bharat; Engel-Herbert, Roman; Cagnon, Joeel; Stemmer, Susanne

    2009-03-15

    Phase pure, epitaxial (101) rutile TiO{sub 2} films were grown on (012) sapphire substrates at temperatures between 485 and 725 deg. C using metal-organic molecular beam epitaxy with titanium tetraisopropoxide as the Ti source. Growth modes and rates were investigated as a function of substrate temperature using reflection high-energy electron diffraction, x-ray reflectivity, atomic force microscopy, and transmission electron microscopy. Growth rates were as high as 125 nm/h. The influence of additional oxygen supplied from a rf plasma source was investigated. Without oxygen plasma, the growth rate exhibited reaction and flux-limited regimes and layer-by-layer growth was observed in the initial stages of film growth. With oxygen plasma the growth rate became independent of temperature; films grew initially in step-flow mode and were insulating. The mechanisms for the different growth modes as a function of film thickness, temperature, and presence of oxygen are discussed.

  10. Optical diagnostics of the laser-induced phase transformations in thin germanium films on silicon, sapphire, and fused silica

    NASA Astrophysics Data System (ADS)

    Novikov, H. A.; Batalov, R. I.; Bayazitov, R. M.; Faizrakhmanov, I. A.; Ivlev, G. D.; Prokop'ev, S. L.

    2015-03-01

    The in-situ procedure is used to study the modification of thin (200-600 nm) germanium films induced by nanosecond pulses of a ruby laser. The films are produced using the ion-beam or magnetron sputtering on single-crystalline silicon (Si), sapphire (Al2O3), and fused silica (α-SiO2) substrates. The results on the dynamics of the laser-induced processes are obtained using the optical probing of the irradiated region at wavelengths of λ = 0.53 and 1.06 μm. The results of probing make it possible to determine the threshold laser energy densities that correspond to the Ge and Si melting and the generation of the Ge ablation plasma versus the amount of deposited Ge and thermophysical parameters of the substrate. The reflection oscillograms are used to obtain the dependences of the melt lifetime on the laser-pulse energy density.

  11. SINGLE-CRYSTAL SAPPHIRE OPTICAL FIBER SENSOR INSTRUMENTATION

    SciTech Connect

    A. Wang; G. Pickrell; R. May

    2002-09-10

    Accurate measurement of temperature is essential for the safe and efficient operation and control of a wide range of industrial processes. Appropriate techniques and instrumentation are needed depending on the temperature measurement requirements in different industrial processes and working environments. Harsh environments are common in many industrial applications. These harsh environments may involve extreme physical conditions, such as high-temperature, high-pressure, corrosive agents, toxicity, strong electromagnetic interference, and high-energy radiation exposure. Due to these severe environmental conditions, conventional temperature sensors are often difficult to apply. This situation has opened a new but challenging opportunity for the sensor society to provide robust, high-performance, and cost-effective temperature sensors capable of operating in those harsh environments. The focus of this research program has been to develop a temperature measurement system for temperature measurements in the primary and secondary stages of slagging gasifiers. For this application the temperature measurement system must be able to withstand the extremely harsh environment posed by the high temperatures and corrosive agents present in these systems. Real-time, accurate and reliable monitoring of temperature for the coal gasification process is important to realize the full economic potential of these gasification systems. Long life and stability of operation in the high temperature environment is essential for the temperature measurement system to ensure the continuous running of the coal gasification system over the long term. In this high temperature and chemically corrosive environment, rather limited high temperature measurement techniques such as high temperature thermocouples and optical/acoustic pyrometers are available, each with their own limitations. In this research program, five different temperature sensing schemes based on the single crystal sapphire

  12. Homoepitaxial growth of catalyst-free GaN wires on N-polar substrates

    NASA Astrophysics Data System (ADS)

    Chen, X. J.; Perillat-Merceroz, G.; Sam-Giao, D.; Durand, C.; Eymery, J.

    2010-10-01

    The shape of c-oriented GaN nanostructures is found to be directly related to the crystal polarity. As evidenced by convergent beam electron diffraction applied to GaN nanostructures grown by metal-organic vapor phase epitaxy on c-sapphire substrates: wires grown on nitridated sapphire have the N-polarity ([0001¯]) whereas pyramidal crystals have Ga-polarity ([0001]). In the case of homoepitaxy, the GaN wires can be directly selected using N-polar GaN freestanding substrates and exhibit good optical properties. A schematic representation of the kinetic Wulff's plot points out the effect of surface polarity.

  13. Electronic Properties of Large-scale Graphene Chemical Vapor Synthesized on Nickel and on Sapphire

    NASA Astrophysics Data System (ADS)

    Cao, Helin; Zhang, Liyuan; Chen, Yong; Yu, Qingkai; Li, Hao

    2009-03-01

    We have studied the electronic transport properties of large area few-layer graphene/graphitic films grown by two different chemical vapor based methods. The first type of samples (metal-transfer graphene) is synthesized by carbon segregation from Ni, then transferred to SiO2/Si substrates. The second type of samples is synthesized by direct chemical vapor deposition (CVD) on sapphire. We measured these samples under variable temperatures (from 2K to 300 K) and transverse magnet fields (from 0 to 7 T). For both types of samples, we found a negative magnetoresistance at low field, and carrier mobilities on the order of several hundreds of cm^2/V-s. For metal-transfer graphene in particular, we were able to measure a moderate field effect response, using the highly doped Si substrate as back gate. The observed magnetoresistance shows characteristic features of weak localization, from which we extract various carrier scattering lengths in the metal-transfer graphene samples. Comparison with those measured in mechanically exfoliated graphene suggests possibly different carrier scattering mechanisms for graphene materials prepared with different methods.

  14. Thermal resistance of indium coated sapphire-copper contacts below 0.1 K

    NASA Astrophysics Data System (ADS)

    Eisel, T.; Bremer, J.; Koettig, T.

    2014-11-01

    High thermal resistances exist at ultra-low temperatures for solid-solid interfaces. This is especially true for pressed metal-sapphire joints, where the heat is transferred by phonons only. For such pressed joints it is difficult to achieve good physical, i.e. thermal contacts due to surface irregularities in the microscopic or larger scale. Applying ductile indium as an intermediate layer reduces the thermal resistance of such contacts. This could be proven by measurements of several researchers. However, the majority of the measurements were performed at temperatures higher than 1 K. Consequently, it is difficult to predict the thermal resistance of pressed metal-sapphire joints at temperatures below 1 K. In this paper the thermal resistances across four different copper-sapphire-copper sandwiches are presented in a temperature range between 30 mK and 100 mK. The investigated sandwiches feature either rough or polished sapphire discs (Ø 20 mm × 1.5 mm) to investigate the phonon scattering at the boundaries. All sandwiches apply indium foils as intermediate layers on both sides of the sapphire. Additionally to the indium foils, thin indium films are vapour deposited onto both sides of one rough and one polished sapphire in order to improve the contact to the sapphire. Significantly different thermal resistances have been found amongst the investigated sandwiches. The lowest total thermal resistivity (roughly 26 cm2 K4/W at 30 mK helium temperature) is achieved across a sandwich consisting of a polished sapphire with indium vapour deposition. The thermal boundary resistance between indium and sapphire is estimated from the total thermal resistivity by assuming the scattering at only one boundary, which is the warm sapphire boundary where phonons impinge, and taking the scattering in the sapphire bulk into account. The so derived thermal boundary resistance agrees at low temperatures very well with the acoustic mismatch theory.

  15. Detection of beryllium treatment of natural sapphires by NRA

    NASA Astrophysics Data System (ADS)

    Gutiérrez, P. C.; Ynsa, M.-D.; Climent-Font, A.; Calligaro, T.

    2010-06-01

    Since the 1990's, artificial treatment of natural sapphires (Al 2O 3 crystals coloured by impurities) by diffusion of beryllium at high temperature has become a growing practice. This process permits to enhance the colour of these gemstones, and thus to increase their value. Detection of such a treatment - diffusion of tens of μg/g of beryllium in Al 2O 3 crystals - is usually achieved using high sensitivity techniques like laser-ablation inductively coupled plasma mass spectrometry (LA-ICP/MS) or laser-induced breakdown spectrometry (LIBS) which are unfortunately micro-destructive (leaving 50-100-μm diameter craters on the gems). The simple and non-destructive alternative method proposed in this work is based on the nuclear reaction 9Be(α, nγ) 12C with an external helium ion beam impinging on the gem directly placed in air. The 4439 keV prompt γ-ray tagging Be atoms are detected with a high efficiency bismuth germanate scintillator. Beam dose is monitored using the 2235 keV prompt γ-ray produced during irradiation by the aluminium of the sapphire matrix through the 27Al(α, pγ) 30Si nuclear reaction. The method is tested on a series of Be-treated sapphires previously analyzed by LA-ICP/MS to determine the optimal conditions to obtain a peak to background appropriate to reach the required μg/g sensitivity. Using a 2.8-MeV external He beam and a beam dose of 200 μC, beryllium concentrations from 5 to 16 μg/g have been measured in the samples, with a detection limit of 1 μg/g.

  16. Injection mode-locking Ti-sapphire laser system

    DOEpatents

    Hovater, James Curtis; Poelker, Bernard Matthew

    2002-01-01

    According to the present invention there is provided an injection modelocking Ti-sapphire laser system that produces a unidirectional laser oscillation through the application of a ring cavity laser that incorporates no intracavity devices to achieve unidirectional oscillation. An argon-ion or doubled Nd:YVO.sub.4 laser preferably serves as the pump laser and a gain-switched diode laser serves as the seed laser. A method for operating such a laser system to produce a unidirectional oscillating is also described.

  17. Sapphire fiber evanescent wave absorption in turbid media.

    PubMed

    Zhang, Jian; Xiong, Feibing; Djeu, Nicholas

    2009-08-01

    The influence of particulates on sapphire fiber evanescent wave absorption by water has been studied. Suspensions containing micro-sized graphite flakes and glassy carbon powder were used. Conventional free-space transmittance measurements of these samples showed strong absorption and scattering, which severely screened the absorption by water. However, the absorption on the water band determined from the evanescent wave interaction was unaffected by the presence of the graphite flakes. These results indicate that fiber-optic evanescent wave chemical sensors may be suitable for process control applications involving turbid reactor streams.

  18. Electroform replication of smooth mirrors from sapphire masters

    NASA Technical Reports Server (NTRS)

    Altkorn, R.; Chang, J.; Haidle, R.; Takacs, P. Z.; Ulmer, M. P.

    1992-01-01

    A sapphire master was used to produce mirrors that exhibit mid-to-high-frequency roughness as low as 3 A. The fabrication procedure and potential applications in X-ray astronomy are discussed. It is shown that foils replicated from flat smooth mandrels should offer at least equivalent HF roughness and significantly lower mid-frequency ripple than those coated with lacquer. A ceramic-surface mandrel could also be expected to last far longer without the need for repolishing than electroless nickel-coated mandrels.

  19. Orientation relationship between α-Fe precipitate and α-Al2O3 matrix in iron-implanted sapphire.

    PubMed

    Wang, Y; Liu, X P; Qin, G W

    2014-07-01

    Fe ions were implanted into α-Al2O3 single crystals (sapphire) at room temperature and annealed in a reducing atmosphere. The orientation relationships (ORs) between α-Fe particles and sapphire matrix were investigated using transmission electron microscopy (TEM). All the α-Fe particles have the orientation relationship (OR) of (111)α-Fe||(0001)sapphire and [11¯0]α-Fe||[112¯0]sapphire with sapphire. This OR is predicted precisely by the coincidence of reciprocal lattice points (CRLP) method. The other OR of (110)α-Fe||(0001)sapphire and [111]α-Fe||[51¯4¯0]sapphire reported before is confirmed by the same method to be one of the secondary preferred orientation relationships in the α-Fe/sapphire system.

  20. Frequency Stability of 1X10(sup -13) in a Compensated Sapphire Oscillator Operating Above 77 K

    NASA Technical Reports Server (NTRS)

    Santiago, D. G.; Dick, G. J.; Wang, R. T.

    1996-01-01

    We report on a frequency-stable temperature compensated sapphire oscillator (CSO) at temperatures above 77 K. Previously, high stability in sapphire oscillators had only been obtained with liquid helium cooling.

  1. Effect of Charging Electron Exposure on 1064nm Transmission through Bare Sapphire Optics and SiO2 over HfO2 AR-coated Sapphire Optics

    NASA Technical Reports Server (NTRS)

    Ottens, Brian P.; Connelly, Joseph; Brown, Stephen; Roeder, james; Kauder, Lonny; Cavanaugh, John

    2008-01-01

    Experiments measuring the effect of electron exposure on 1064nm transmission for optical sapphire were conducted. Detailed before and after inspections did not identify any resulting Litchenburg patterns. Pre- and post-exposure 1064nm transmission measurements are compared.

  2. Effect of Charging Electron Exposure on 1064nm Transmission Through Bare Sapphire Optics and SiO2 over HfO2 AR-Coated Sapphire Optics

    NASA Technical Reports Server (NTRS)

    Ottens, Brian P.; Connelly, Joseph; Brown, Stephen; Roeder, James; Kauder, Lonny; Cavanaugh, John

    2010-01-01

    Experiments measuring the effect of electron exposure on 1064nm transmission for optical sapphire were conducted. Detailed before and after inspections did not identify any resulting Litchenburg patterns. Pre- and post-exposure 1064nm transmission measurements are compared.

  3. Analysis and modification of blue sapphires from Rwanda by ion beam techniques

    NASA Astrophysics Data System (ADS)

    Bootkul, D.; Chaiwai, C.; Tippawan, U.; Wanthanachaisaeng, B.; Intarasiri, S.

    2015-12-01

    Blue sapphire is categorised in a corundum (Al2O3) group. The gems of this group are always amazed by their beauties and thus having high value. In this study, blue sapphires from Rwanda, recently came to Thai gemstone industry, are chosen for investigations. On one hand, we have applied Particle Induced X-ray Emission (PIXE), which is a highly sensitive and precise analytical technique that can be used to identify and quantify trace elements, for chemical analysis of the sapphires. Here we have found that the major element of blue sapphires from Rwanda is Al with trace elements such as Fe, Ti, Cr, Ga and Mg as are commonly found in normal blue sapphire. On the other hand, we have applied low and medium ion implantations for color improvement of the sapphire. It seems that a high amount of energy transferring during cascade collisions have altered the gems properties. We have clearly seen that the blue color of the sapphires have been intensified after nitrogen ion bombardment. In addition, the gems were also having more transparent and luster. The UV-Vis-NIR measurement detected the modification of their absorption properties, implying of the blue color increasing. Here the mechanism of these modifications is postulated and reported. In any point of view, the bombardment by using nitrogen ion beam is a promising technique for quality improvement of the blue sapphire from Rwanda.

  4. Growth of Sapphire Single Crystals Transparent Armor by a Modified Verneuil Technique.

    DTIC Science & Technology

    modified Verneuil technique for transparent armor applications. Seeded single crystals of sapphire were grown with widths in excess of 2 1/2 inches, lengths...single crystals by the ’strip’ Verneuil technique is feasible. An engineering cost analysis indicated that 8 inch by 1/4 inch sapphire windows could

  5. Growth of self-standing GaN substrates

    NASA Astrophysics Data System (ADS)

    Lee, Hyun-Jae; Fujii, Katsushi; Goto, Takenari; Kim, Chinkyo; Chang, Jiho; Hong, Soon-Ku; Cho, Meoungwhan; Yao, Takafumi

    2010-03-01

    Large-sized and high-quality free standing GaN are required with the development of GaN-based devices. We have developed new techniques to reduce the price of GaN substrates. In this paper, we introduce a simple fabrication way of freestanding GaN substrate using hydride vapor phase epitaxy (HVPE). An evaporable buffer layer was applied for the fabrication of 2inch freestanding GaN to separate from a sapphire substrate, in other words, a freestanding GaN was fabricated only by HVPE (one-stop process) without any process.

  6. Epitaxial growth of In{sub x}Ga{sub 1-x}N alloy films on sapphire and silicon by reactive co-sputtering of GaAs and indium

    SciTech Connect

    Mohan, Shyam Major, S. S.; Srinivasa, R. S.

    2015-06-24

    In{sub x}Ga{sub 1-x}N alloy films (0.2sapphire and Si (100) substrates by reactive co-sputtering of GaAs and indium with 100% nitrogen at a substrate temperature of 600 °C. X-ray diffraction studies show the formation of completely c-axis oriented, single phase alloy films over the studied range of composition. The crystallite size along the growth direction and surface morphology of alloy films, particularly those with higher indium fraction exhibit substantial improvement on Si (100) substrate, compared to the c-cut sapphire substrate. The electrical resistivity decreases monotonously with increase in indium fraction and the alloy films on Si (100) show substantially higher mobility, compared to those on sapphire. These features are attributed to superior crystallinity of alloy films on Si (100), which possibly arise from the formation of interfacial hexagonal α-Si{sub 3}N{sub 4}, owing to the interaction of nitrogen plasma with Si surface.

  7. Effect of the substrate on the insulator-metal transition of vanadium dioxide films

    NASA Astrophysics Data System (ADS)

    Kovács, György J.; Bürger, Danilo; Skorupa, Ilona; Reuther, Helfried; Heller, René; Schmidt, Heidemarie

    2011-03-01

    Single-phase vanadium dioxide films grown on (0001) sapphire and (001) silicon substrates show a very different insulator-metal electronic transition. A detailed description of the growth mechanisms and the substrate-film interaction is given, and the characteristics of the electronic transition are described by the morphology and grain boundary structure. (Tri-)epitaxy-stabilized columnar growth of VO2 takes place on the sapphire substrate, whereas on silicon the expected Zone II growth is identified. We have found that in the case of the Si substrate the reasons for the broader hysteresis and the lower switching amplitude are the formation of an amorphous insulating VOx (x > 2.6) phase coexisting with VO2 and the high vanadium vacancy concentration of the VO2. These phenomena are the result of the excess oxygen during the growth and the interaction between the silicon substrate and the growing film.

  8. (abstract) Epitaxial High-T(sub c) SNS Weak Links on Silicon-on-Sapphire Substrates

    NASA Technical Reports Server (NTRS)

    Hunt, B. D.; Barner, J. B.; Foote, M. C.; Vasquez, R. P.; Schoelkopf, R. J.; Phillips, T. G.; Zmuidzinas, J.

    1994-01-01

    High-T(sub c) SNS weak links are expected to prove useful as high frequency sources and detectors. Recent studies with low-T(sub c) Josephson mixers using shunted tunnel junctions at 100 GHz show good initial performance, and modeling suggests that these results should extrapolate to higher frequencies if larger I(sub c)R(sub n) products can be achieved. Progress on this work will be reported.

  9. AlN/GaN Metal Insulator Semiconductor Field Effect Transistor on Sapphire Substrate

    NASA Astrophysics Data System (ADS)

    Seo, Sanghyun; Ghose, Kaustav; Zhao, Guang Yuan; Pavlidis, Dimitris

    AlN/GaN Metal Insulator Semiconductor Field Effect Transistors (MISFETs) were designed, simulated and fabricated. DC, S-parameter and power measurements were also performed. Drift-diffusion simulations using DESSIS compared AlN/GaN MISFETs and Al32Ga68N/GaN Heterostructure FETs (HFETs) with the same geometries. The simulation results show the advantages of AlN/GaN MISFETs in terms of higher saturation current, lower gate leakage and higher transconductance than AlGaN/GaN HFETs. First results from fabricated AlN/GaN devices with 1μm gate length and 200μm gate width showed a maximum drain current density of ˜380mA/mm and a peak extrinsic transconductance of 85mS/mm. S-parameter measurements showed that currentgain cutoff frequency (fT) and maximum oscillation frequency (fmax) were 5.85GHz and 10.57GHz, respectively. Power characteristics were measured at 2GHz and showed output power density of 850mW/mm with 23.8% PAE at VDS=15V. To the authors knowledge this is the first report of a systematic study of AlN/GaN MISFETs addressing their physical modeling and experimental high-frequency characteristics including the power performance.

  10. The effect of crystal orientation on the cryogenic strength of hydroxide catalysis bonded sapphire

    NASA Astrophysics Data System (ADS)

    Haughian, K.; Douglas, R.; van Veggel, A. A.; Hough, J.; Khalaidovski, A.; Rowan, S.; Suzuki, T.; Yamamoto, K.

    2015-04-01

    Hydroxide catalysis bonding has been used in gravitational wave detectors to precisely and securely join components of quasi-monolithic silica suspensions. Plans to operate future detectors at cryogenic temperatures has created the need for a change in the test mass and suspension material. Mono-crystalline sapphire is one candidate material for use at cryogenic temperatures and is being investigated for use in the KAGRA detector. The crystalline structure of sapphire may influence the properties of the hydroxide catalysis bond formed. Here, results are presented of studies of the potential influence of the crystal orientation of sapphire on the shear strength of the hydroxide catalysis bonds formed between sapphire samples. The strength was tested at approximately 8 K; this is the first measurement of the strength of such bonds between sapphire at such reduced temperatures. Our results suggest that all orientation combinations investigated produce bonds of sufficient strength for use in typical mirror suspension designs, with average strengths >23 MPa.

  11. Broadband dielectric characterization of sapphire/TiOx/Ba₀.₃Sr₀.₇TiO₃ (111)-oriented thin films for the realization of a tunable interdigitated capacitor.

    PubMed

    Ghalem, Areski; Ponchel, Freddy; Remiens, Denis; Legier, Jean-Francois; Lasri, Tuami

    2013-05-01

    A complete microwave characterization up to 67 GHz using specific coplanar waveguides was performed to determine the dielectric properties (permittivity, losses, and tunability) of sapphire/TiOx/Ba0.3Sr0.7TiO3 (BST) (111)-oriented thin films. To that end, BaxSr1-xTiO3 thin films were deposited by RF magnetron sputtering on sapphire (0001) substrate. To control the preferred (111) orientation, a TiOx buffer layer was deposited on sapphire. According to the detailed knowledge of the material properties, it has been possible to conceive, fabricate, and test interdigitated capacitors, the basic element for future microwave tunable applications. Retention of capacitive behavior up to 67 GHz and a tunability of 32% at 67 GHz at an applied voltage of 30 V (150 kV/cm) were observed. The Q-factor remains greater than 30 over the entire frequency band. The possibility of a complete characterization of the material for the realization of high-performance interdigitated capacitors opens the door to microwave device fabrication.

  12. Anisotropic Transverse Stress in Calcite and Sapphire Measured Using Birefringence

    NASA Astrophysics Data System (ADS)

    Tear, Gareth R.; Chapman, David J.; Eakins, Daniel E.; Proud, William G.

    2015-06-01

    Many significant geological minerals have anisotropic crystal structures leading to material properties that are anisotropic, including compressive elastic behaviour. A non-invasive approach to investigate the directional dependence of transverse stress in these materials during shock compression would supplement current understanding. As many geological minerals are transparent and hence optically anisotropic, measuring the change in birefringence induced by transverse stress in the material offers the possibility of a fast, non-invasive approach to probe transverse behaviour. Shock compression experiments have been performed on a-cut calcite and a-cut sapphire for strain rates of order 105 s-1 and up to longitudinal stresses of 2 GPa for calcite and 12 GPa for sapphire. We present measured changes in birefringence for these materials under shock compression, comparing with current and past literature as well as an in house optical model. The authors would like to thank Mr Steve Johnson and Mr David Pittman for technical support. The Institute of Shock Physics acknowledges the continued support of AWE and Imperial College London.

  13. Valence state of Ti in conductive nanowires in sapphire

    SciTech Connect

    Mizoguchi, Teruyasu; Nakamura, Atsutomo; Matsunaga, Katsuyuki; Ikuhara, Yuichi; Sakurai, Masaki; Tanaka, Isao; Yamamoto, Takahisa

    2004-10-15

    In order to reveal the valence state of Ti in conductive nanowires in sapphire, near-edge x-ray-absorption fine structures (NEXAFS) were observed. From experimental and theoretical studies on NEXAFS of reference compounds including rutile, anatase, and Ti{sub 2}O{sub 3}, it was found that the valence state of Ti can be identified by regarding the positions of the spectral onset and the shoulder in the main peak of Ti-K NEXAFS. The valence states of Ti doped Al{sub 2}O{sub 3} polycrystalline specimens which were annealed at oxidized and reduced atmospheres were determined to be +4 and +3, respectively. The solubility limit of Ti in Al{sub 2}O{sub 3} polycrystal was found to be between 1000 ppm to 1.0% at the both atmospheres. The spectrum from Ti nanowires in sapphire has a lot of similarities to the reduced specimen, the valence state was therefore concluded to be +3.

  14. Holographic fabrication of gratings in metal substrates

    NASA Technical Reports Server (NTRS)

    Fletcher, R. M.; Wagner, D. K.; Ballantyne, J. M.

    1982-01-01

    A program for investigating the grain enlargement resulting from the laser recrystallization of a thin gallium arsenide film on a patterned substrate, a technique known as graphoepitaxy was evaluated. More specifically, the effects of recrystallizing an uncapped gallium arsenide film using a continuous wave neodymium YAG laser operating at 1.06 microns were studied. In an effort to minimize arsenic loss from the film, the specimens were held in an arsine atmosphere during recrystallization. Two methods for fabricating patterned substrates were developed, one using reactive ion etching of a molybdenum film on both sapphire and silicon substates and another by preferential wet etching of a silicon substrate onto which a film of molybdenum was subsequently deposited.

  15. Surface-Energy-Anisotropy-Induced Orientation Effects on RayleighInstabilities in Sapphire

    SciTech Connect

    Santala, Melissa; Glaeser, Andreas M.

    2006-01-01

    Arrays of controlled-geometry, semi-infinite pore channels of systematically varied crystallographic orientation were introduced into undoped m-plane (10{bar 1}0) sapphire substrates using microfabrication techniques and ion-beam etching and subsequently internalized by solid-state diffusion bonding. A series of anneals at 1700 C caused the breakup of these channels into discrete pores via Rayleigh instabilities. In all cases, channels broke up with a characteristic wavelength larger than that expected for a material with isotropic surface energy, reflecting stabilization effects due to surface-energy anisotropy. The breakup wavelength and the time required for complete breakup varied significantly with channel orientation. For most orientations, the instability wavelength for channels of radius R was in the range of 13.2R-25R, and complete breakup occurred within 2-10 h. To first order, the anneal times for complete breakup scale with the square of the breakup wavelength. Channels oriented along a <11{bar 2}0> direction had a wavelength of {approx} 139R, and required 468 h for complete breakup. Cross-sectional analysis of channels oriented along a <11{bar 2}0> direction showed the channel to be completely bounded by stable c(0001), r{l_brace}{bar 1}012{r_brace}, and s{l_brace}10{bar 1}1{r_brace} facets.

  16. Atomic Step Formation on Sapphire Surface in Ultra-precision Manufacturing

    PubMed Central

    Wang, Rongrong; Guo, Dan; Xie, Guoxin; Pan, Guoshun

    2016-01-01

    Surfaces with controlled atomic step structures as substrates are highly relevant to desirable performances of materials grown on them, such as light emitting diode (LED) epitaxial layers, nanotubes and nanoribbons. However, very limited attention has been paid to the step formation in manufacturing process. In the present work, investigations have been conducted into this step formation mechanism on the sapphire c (0001) surface by using both experiments and simulations. The step evolutions at different stages in the polishing process were investigated with atomic force microscopy (AFM) and high resolution transmission electron microscopy (HRTEM). The simulation of idealized steps was constructed theoretically on the basis of experimental results. It was found that (1) the subtle atomic structures (e.g., steps with different sawteeth, as well as steps with straight and zigzag edges), (2) the periodicity and (3) the degree of order of the steps were all dependent on surface composition and miscut direction (step edge direction). A comparison between experimental results and idealized step models of different surface compositions has been made. It has been found that the structure on the polished surface was in accordance with some surface compositions (the model of single-atom steps: Al steps or O steps). PMID:27444267

  17. Atomic Step Formation on Sapphire Surface in Ultra-precision Manufacturing.

    PubMed

    Wang, Rongrong; Guo, Dan; Xie, Guoxin; Pan, Guoshun

    2016-07-22

    Surfaces with controlled atomic step structures as substrates are highly relevant to desirable performances of materials grown on them, such as light emitting diode (LED) epitaxial layers, nanotubes and nanoribbons. However, very limited attention has been paid to the step formation in manufacturing process. In the present work, investigations have been conducted into this step formation mechanism on the sapphire c (0001) surface by using both experiments and simulations. The step evolutions at different stages in the polishing process were investigated with atomic force microscopy (AFM) and high resolution transmission electron microscopy (HRTEM). The simulation of idealized steps was constructed theoretically on the basis of experimental results. It was found that (1) the subtle atomic structures (e.g., steps with different sawteeth, as well as steps with straight and zigzag edges), (2) the periodicity and (3) the degree of order of the steps were all dependent on surface composition and miscut direction (step edge direction). A comparison between experimental results and idealized step models of different surface compositions has been made. It has been found that the structure on the polished surface was in accordance with some surface compositions (the model of single-atom steps: Al steps or O steps).

  18. Raman mapping of hexagonal hillocks in N-polar GaN grown on c-plane sapphire

    NASA Astrophysics Data System (ADS)

    Jiang, Teng; Lin, Zhiyu; Zhang, Jincheng; Xu, Shengrui; Huang, Jun; Niu, Mutong; Gao, Xiaodong; Guo, Lixin; Hao, Yue

    2017-04-01

    A large amount of huge hexagonal hillocks were observed on the surface of N-polar GaN film grown on c-plane sapphire substrate by MOCVD. The distribution of residual stress and dislocation density in a typical hexagonal hillock was investigated by the mapping measurement of Micro-Raman and Cathodoluminescence (CL) spectroscopy. It is found that the residual stress at the top region of the hillock is much smaller than that of the sidewall region and the region around the hillock. Meanwhile, the CL images confirmed that the dislocation density around the hexagonal hillock is higher than the top region of the hillock. The bending and annihilation of the dislocations during the growth of the hexagonal hillock result in the relaxation of residual stress which should be responsible for the spatial variation of dislocation density and residual stress.

  19. Electroluminescence from nonpolar n-ZnO/p-AlGaN heterojunction light-emitting diode on r-sapphire

    NASA Astrophysics Data System (ADS)

    Chen, Jingwen; Zhang, Jun; Dai, Jiangnan; Wu, Feng; Wang, Shuai; Chen, Cheng; Long, Hanling; Liang, Renli; Zhao, Chong; Chen, Changqing; Tang, Zhiwu; Cheng, Hailing; He, Yunbin; Li, Mingkai

    2017-03-01

    Nonpolar a-plane n-ZnO/p-AlGaN heterojunction light-emitting diodes (LEDs) have been prepared on r-sapphire substrate using metal organic chemical vapor deposition and a pulsed laser deposition method. The dominant electroluminescence emission at 390 nm from the interband transition in n-ZnO layer under a forward bias was observed. Interestingly, electroluminescence with emission at 385 nm based on an avalanche mechanism was also achieved under reverse bias. The mechanisms of both the electroluminescence and I–V characteristics are discussed in detail by considering the avalanche effect. It is demonstrated that the crystalline quality of n-ZnO, not the p-AlGaN, is what affects the performance of the nonpolar ZnO based avalanche LED.

  20. Improved structural quality of AlN grown on sapphire by 3D/2D alternation growth

    NASA Astrophysics Data System (ADS)

    Guo, Yanmin; Fang, Yulong; Yin, Jiayun; Zhang, Zhirong; Wang, Bo; Li, Jia; Lu, Weili; Feng, Zhihong

    2017-04-01

    Three dimensional (3D) and two dimensional (2D) alternation growth was used to grow AlN epitaxial layers on sapphire substrates. AlN samples grown using this technique have higher crystalline quality and lower dislocation density than samples grown using only 3D or 2D growth modes as witnessed by the high-resolution X-ray diffraction. Smooth atomic terraces with root mean square roughness of 0.107 nm were observed using atomic force microscopy (AFM) when the 3D and 2D AlN were 75 nm and 425 nm, respectively. This sample possesses single crystallographic orientation along the c-axis identified by Raman spectroscopy. Furthermore, the 3D/2D alternating growth mode modulates internal stress in AlN epitaxial layer by adjusting 2D AlN thickness, and the mechanism was studied in detail.

  1. Deep-UV sensors based on SAW oscillators using low-temperature-grown AlN films on sapphires.

    PubMed

    Laksana, Chipta; Chen, Meei-Ru; Liang, Yen; Tzou, An-Jyeg; Kao, Hui-Ling; Jeng, Erik; Chen, Jyh; Chen, Hou-Guang; Jian, Sheng-Rui

    2011-08-01

    High-quality epitaxial AlN films were deposited on sapphire substrates at low growth temperature using a helicon sputtering system. SAW filters fabricated on the AlN films exhibited excellent characteristics, with center frequency of 354.2 MHz, which corresponds to a phase velocity of 5667 m/s. An oscillator fabricated using AlN-based SAW devices is presented and applied to deep-UV light detection. A frequency downshift of about 43 KHz was observed when the surface of SAW device was illuminated by a UV source with dominant wavelength of around 200 nm. The results indicate the feasibility of developing remote sensors for deep-UV measurement using AlN-based SAW oscillators.

  2. Improved crystal quality and performance of GaN-based light-emitting diodes by decreasing the slanted angle of patterned sapphire

    NASA Astrophysics Data System (ADS)

    Cheng, Ji-Hao; Wu, YewChung Sermon; Liao, Wei-Chih; Lin, Bo-Wen

    2010-02-01

    Periodic triangle pyramidal array patterned sapphire substrates (PSSs) with various slanted angles were fabricated by wet etching. It was found beside normal wurtzite GaN, zinc blende GaN was found on the sidewall surfaces of PSS. The crystal quality and performance of PSS-LEDs improved with decrease in slanted angle from 57.4° to 31.6°. This is because most of the growth of GaN was initiated from c-planes. As the growth time increased, GaN epilayers on the bottom c-plane covered these pyramids by lateral growth causing the threading dislocation to bend toward the pyramids.

  3. A visualization of threading dislocations formation and dynamics in mosaic growth of GaN-based light emitting diode epitaxial layers on (0001) sapphire

    NASA Astrophysics Data System (ADS)

    Ravadgar, P.; Horng, R. H.; Ou, S. L.

    2012-12-01

    A clear visualization of the origin and characteristics of threading dislocations (TDs) of GaN-based light emitting diode epitaxial layers on (0001) sapphire substrates have been carried out. Special experimental set up and chemical etchant along with field emission scanning electron microscopy are employed to study the dynamics of GaN TDs at different growth stages. Cross-sectional transmission electron microscopy analysis visualized the formation of edge TDs is arising from extension of coalescences at boundaries of different tilting-twining nucleation grains "mosaic growth." Etch pits as representatives of edge TDs are in agreement with previous theoretical models and analyses of TDs core position and characteristics.

  4. Epitaxial Nd-doped α-(Al(1-x)Ga(x))2O3 films on sapphire for solid-state waveguide lasers.

    PubMed

    Kumaran, Raveen; Tiedje, Thomas; Webster, Scott E; Penson, Shawn; Li, Wei

    2010-11-15

    Single-crystal aluminum-gallium oxide films have been grown by molecular beam epitaxy in the corundum phase. Films of the (Al(1-x)Ga(x))(2)O(3) alloys doped with neodymium have favorable properties for solid-state waveguide lasers, including a high-thermal-conductivity sapphire substrate and a dominant emission peak in the 1090-1096 nm wavelength range. The peak position is linearly correlated to the unit cell volume, which is dependent on film composition and stress. Varying the Ga-Al alloy composition during growth will enable the fabrication of graded-index layers for tunable lasing wavelengths and low scattering losses at the interfaces.

  5. Melting of linear alkanes between swollen elastomers and solid substrates.

    PubMed

    Nanjundiah, Kumar; Dhinojwala, Ali

    2013-10-01

    We have measured the melting and freezing behavior of linear alkanes confined between cross-linked poly(dimethylsiloxane) (PDMS) elastomers and solid sapphire substrates. Small molecules are often used as lubricants to reduce friction or as plasticizers, but very little is directly known about the migration or changes in physical properties of these small molecules at interfaces, particularly the changes in transition temperatures upon confinement. Our previous studies highlighted striking differences between the crystal structure of confined and unconfined pentadecane crystals in contact with sapphire substrates. Here, we have used surface-sensitive infrared-visible sum-frequency-generation spectroscopy (SFG) to study the melting temperatures (Tm) of alkanes in nanometer thick interfacial regions between swollen PDMS elastomers in contact with sapphire substrate. We find that confined alkanes show depression in Tm compared to the melting temperature of unconfined bulk alkanes. The depression in Tm is a function of chain length, and these differences were smallest for shorter alkanes and largest for 19 unit long alkanes. In comparison, the DSC results for swollen PDMS elastomer show a broad distribution of melting points corresponding to different sizes of crystals formed within the network. The Tm for confined alkanes has been modeled using the combination of Flory-Rehner and Gibbs-Thomson models, and the depression in Tm is related to the thickness of the confined alkanes. These findings have important implications in understanding friction and adhesion of soft elastomeric materials and also the effects of confinement between two solid materials.

  6. High-temperature sapphire optical sensor fiber coatings

    NASA Astrophysics Data System (ADS)

    Desu, Seshu B.; Claus, Richard O.; Raheem, Ruby; Murphy, Kent A.

    1990-10-01

    the filter. These modes may be attributed to a number of material degradation mechanisms, such as thermal shock, oxidation corrosion of the material, mechanical loads, or phase changes in the filter material. Development of high temperature optical fiber (sapphire) sensors embedded in the CXF filters would be very valuable for both monitoring the integrity of the filter during its use and understanding the mechanisms of degradation such that durable filter development will be facilitated. Since the filter operating environment is very harsh, the high temperature sapphire optical fibers need to be protected and for some sensing techniques the fiber must also be coated with low refractive index film (cladding). The objective of the present study is to identify materials and develop process technologies for the application of claddings and protective coatings that are stable and compatible with sapphire fibers at both high temperatures and pressures.

  7. Final EDP Ti: sapphire amplifiers for ELI project

    NASA Astrophysics Data System (ADS)

    Chvykov, Vladimir; Kalashnikov, Mikhail; Osvay, Károly

    2015-05-01

    Recently several ultrahigh intensity Chirped Pulse Amplification (CPA) laser systems have reached petawatt output powers [1, 2] setting the next milestone at tens or even hundreds petawatts for the next three to ten years [3, 4]. These remarkable results were reached when laser amplifiers (opposite to Optical Parametric Amplification (OPA) [5]) were used as final ones and from them Ti:Sapphire crystals supposed to be the working horses as well in the future design of these laser systems. Nevertheless, the main limitation that arises on the path toward ultrahigh output power and intensity is the restriction on the pumping and extraction energy imposed by Transverse Amplified Spontaneous Emission (TASE) [6] and/or transverse parasitic generation (TPG) [7] within the large aperture of the disc-shape amplifier volume.

  8. Large-scale inhomogeneity in sapphire test masses revealed by Rayleigh scattering imaging

    NASA Astrophysics Data System (ADS)

    Yan, Zewu; Ju, Li; Eon, François; Gras, Slawomir; Zhao, Chunnong; Jacob, John; Blair, David G.

    2004-03-01

    Rayleigh scattering in test masses can introduce noise and reduce the sensitivity of laser interferometric gravitational wave detectors. In this paper, we present laser Rayleigh scattering imaging as a technique to investigate sapphire test masses. The system provides three-dimensional Rayleigh scattering mapping of entire test masses and quantitative evaluation of the Rayleigh scattering coefficient. Rayleigh scattering mapping of two sapphire samples reveals point defects as well as inhomogeneous structures in the samples. We present results showing significant non-uniform scattering within two 4.5 kg sapphire test masses manufactured by the heat exchanger method.

  9. Temperature Compensated Sapphire Resonator for Ultra-Stable Oscillator Capability at Temperatures Above 77 Kelvin

    NASA Technical Reports Server (NTRS)

    Dick, G.; Santiago, D.; Wang, R.

    1994-01-01

    We report on the design and test of a whispering gallery sapphire resonator for which the dominant (WGH xxxsubn11) microwave mode family shows frequency-stable, compensated operation for temperatures above 77 Kelvin. The resonator makes possible a new ultra-stable oscillator (USO) capability that promises performance improvements over the best available crystal quartz oscillators in a compact cryogenic package. A mechanical compensation mechanism, enabled by the difference between copper and sapphire expansion coefficients, tunes the resonator to cancel the temperature variation of sapphire's dielectric constant.

  10. Influence of the electron spin resonance saturation on the power sensitivity of cryogenic sapphire resonators

    SciTech Connect

    Giordano, Vincent Grop, Serge; Bourgeois, Pierre-Yves; Kersalé, Yann; Rubiola, Enrico

    2014-08-07

    Here, we study the paramagnetic ions behavior in presence of a strong microwave electromagnetic field sustained inside a cryogenic sapphire whispering gallery mode resonator. The high frequency measurement resolution that can be now achieved by comparing two Cryogenic Sapphire Oscillators (CSOs) permit to observe clearly the non-linearity of the resonator power sensitivity. These observations that, in turn, allow us to optimize the CSO operation are well explained by the electron spin resonance saturation of the paramagnetic impurities contained in the sapphire crystal.

  11. [The design of all solid-state tunable pulsed Ti:sapphire laser system].

    PubMed

    Chen, Zhe; Ku, Geng; Wan, Junchao; Wang, Wei; Zhou, Chuanqing

    2013-05-01

    This paper presented a design of broadly all solid-state tunable pulsed Ti:sapphire laser with high power and stable performance. The laser was pumped by custom-made Nd:YAG laser which had water cooling system and amplified by two stage amplifier. The method accomplished tunable output of all solid-state tunable pulsed Ti:sapphire laser by modifying the reflection angle of the back mirror. We investigated the relationship between the power of the pumping laser and the all solid-state tunable pulsed Ti: sapphire laser by changing the power of the pumping source.

  12. Sharp semiconductor-to-metal transition of VO{sub 2} thin films on glass substrates

    SciTech Connect

    Jian, Jie; Chen, Aiping; Zhang, Wenrui; Wang, Haiyan

    2013-12-28

    Outstanding phase transition properties of vanadium dioxide (VO{sub 2}) thin films on amorphous glass were achieved and compared with the ones grown on c-cut sapphire and Si (111) substrates, all by pulsed laser deposition. The films on glass substrate exhibit a sharp semiconductor-to-metal transition (∼4.3 °C) at a near bulk transition temperature of ∼68.4 °C with an electrical resistance change as high as 3.2 × 10{sup 3} times. The excellent phase transition properties of the films on glass substrate are correlated with the large grain size and low defects density achieved. The phase transition properties of VO{sub 2} films on c-cut sapphire and Si (111) substrates were found to be limited by the high defect density.

  13. The Impact of GaN/Substrate Thermal Boundary Resistance on a HEMT Device

    DTIC Science & Technology

    2011-11-01

    stack between the GaN and Substrate layers. The University of Bristol recently reported that this TBR in commercial devices on Silicon Carbide ( SiC ...Circuit RF Radio Frequency PA Power Amplifier SiC Silicon Carbide FEA Finite Element Analysis heff Effective Heat transfer Coefficient (W/m 2 K...substrate material switched from sapphire to silicon , and by another factor of two from silicon to SiC . TABLE 1: SAMPLE RESULTS FROM DOUGLAS ET AL. FOR

  14. Infrared reflection spectroscopy and optical constants of LiNbO3 films on crystal substrates

    NASA Astrophysics Data System (ADS)

    Novikova, N. N.; Yakovlev, V. A.; Medaglia, P. G.

    2016-12-01

    We have measured infrared reflectivity spectra of thin lithium niobate films of nanometer thickness, grown by a pulsed laser deposition technique using KrF-excimer laser (λ=248 nm) on the single crystalline substrates (sapphire, MgO, NdGaO3 and SrTiO3). Using the dispersion analysis technique, we have calculated thicknesses and optical constants of the films. The phonon parameters of the substrates and films are obtained.

  15. Fabrication of an anti-reflective microstructure on sapphire by femtosecond laser direct writing.

    PubMed

    Li, Qian-Kun; Cao, Jia-Ji; Yu, Yan-Hao; Wang, Lei; Sun, Yun-Lu; Chen, Qi-Dai; Sun, Hong-Bo

    2017-02-01

    Herein, we report a facile approach for the maskless production of subwavelength-structured antireflective surfaces on sapphire with high and broadband transmittance in the mid-IR: femtosecond laser direct writing assist with wet etching. With this method, inverted pyramid and cone arrays with a pitch of about 2 μm and a total height of near 900 nm on the sapphire were produced. The resulting subwavelength structures greatly suppress specular reflection at normal incidence. The transmission measurements between 3 and 5 μm are in agreement with the simulations performed using VirtualLab, and the transmittance reached a maximum value of 92.5% at 4 μm. The sapphire with subwavelength structures also exhibits angle-independent transmittance characteristics up to a high θ=60°. Therefore, these subwavelength structures on sapphire are of great technological importance in mid-IR optics, especially for the harsh-condition-applicable windows of military mid-IR devices.

  16. The MSFC silicon gate silicon-on-sapphire standard cell library

    NASA Technical Reports Server (NTRS)

    1978-01-01

    A pictorial representation of the MSFC silicon-on-sapphire standard cell library is presented. The cells are intended to be used with the PR2D (Place, Route in 2 Dimensions) automatic layout computer program.

  17. Terahertz characteristics of graphene deposited on different substrates

    NASA Astrophysics Data System (ADS)

    Gong, Chen; Mu, Kaijun; Zuo, Jian; Zhang, Cunlin

    2016-11-01

    Graphene is a promising candidate material for ultra-broadband photodetectors, as it interacts with light strongly from microwave to ultraviolet. We have characterized terahertz response from monolayer graphene samples deposited on sapphire, poly(methyl methacrylate) (PMMA), and high-resistivity silicon (HRS) substrates. The transmittance and sheet conductivity, and attenuation of graphene samples were obtained from transmission terahertz time-domain spectroscopy (THz-TDS). The mechanisms that contribute to the optical response of graphene were quite diverse among the different substrate media used. The results are promising for the development of modulators and switchable photoelectric devices.

  18. Thermal characteristics of sapphire contact probe delivery systems for laser angioplasty.

    PubMed

    Ashley, S; Brooks, S G; Gehani, A A; Kester, R C; Rees, M R

    1990-01-01

    Contact probes made from synthetic sapphire crystal, designed for general laser surgery, are currently being evaluated for use in laser angioplasty. Their mode of action and safety in the context of arterial recanalisation is unknown, particularly with respect to the degree of probe and catheter heating. Infrared thermal imaging was used to investigate the surface temperature rise of various rounded sapphire probes during emission of continuous wave Nd-YAG (1,064 nm) laser energy. Catheter safety was addressed by analyzing the temperature of the metal interface between the optical fiber and sapphire, as well as the catheter proximal to this junction. Transmission of Nd-YAG energy through each probe was also measured. Five rounded probes of 1.8-3.0 mm diameter (three supplied by Surgical Laser Technologies [SLT], two by Living Technology [LT]), along with their respective optical catheters, were compared. There was a large temperature gradient between the front and rim of the probes. The maximum surface temperature rise of the sapphire (at 20 W, 5-second exposure) was 314-339 degrees C (SLT) and 90-108 degrees C (LT) [P less than 0.001, 3-way ANOVA]. The reason for this difference may be related to "crazing" of the front surface of the SLT sapphires. At all energy levels sapphire temperatures were considerably lower than attained by metal laser thermal angioplasty probes. Forward transmission was slightly higher in the SLT probes (75-85%) than the LT sapphires (54-69%). With fiber perfusion at 2 ml/minute, a minor degree of heating of the metal sapphire holders was recorded (maximum rise 35 degrees C), but heating of the catheter proximal to this was negligible. Therefore, it would appear that the risk of tip detachment or arterial injury due to heating of the connecting metal interface is extremely low. Without perfusion, however, there was a greater degree of interface heating in the LT delivery system suggestive of more laser backscattering by these sapphires

  19. Determining residual impurities in sapphire by means of electron paramagnetic resonance and nuclear activation analysis

    NASA Astrophysics Data System (ADS)

    Bletskan, D. I.; Bratus', V. Ya.; Luk'yanchuk, A. R.; Maslyuk, V. T.; Parlag, O. A.

    2008-07-01

    Sapphire (α-Al2O3) single crystals grown using the Verneuil and Kyropoulos methods have been analyzed using electron paramagnetic resonance and γ-ray spectroscopy with 12-MeV bremsstrahlung excitation. It is established that uncontrolled impurities in the final sapphire single crystals grown by the Kyropoulos method in molybdenum-tungsten crucibles are supplied both from the initial materials and from the furnace and crucible materials

  20. Epitaxial (100) GaAs Thin Films on Sapphire for Surface Acoustic Wave/Electronic Devices.

    DTIC Science & Technology

    1985-12-01

    demonstrated that undoped -,111> single crystal a’ gallium arsenide could be grown on 򒠰> sapphire using the metalorganic chemical vapor deposition...chip. Metalorganic chemical vapor deposition (MO-CVD) was used for all depositions during this work. Sapphire with an orientation of (01 T2 > was...as quartz. d& I SECTION 2 MO-CVD GROWTH SYSTEMS All GaAs depositions were performed in our second MO-CVD system which is also being used in a

  1. Experimental analysis of sapphire contact probes for Nd-YAG laser angioplasty.

    PubMed

    Ashley, S; Brooks, S G; Gehani, A A; Kester, R C; Rees, M R

    1990-06-01

    Laser angioplasty may offer percutaneous recanalization of occluded vessels where conventional guidewire and balloon techniques fail. Metal laser thermal angioplasty probes may, however, cause excessive thermal damage due to high tip temperatures (greater than 400.C). Therefore, contact probes made from artificial sapphire crystal designed for general laser surgery are currently being evaluated for use in laser angioplasty with continuous wave Nd-YAG energy. The sapphire modifies the laser energy in various ways, and this paper examines the physical characteristics of five types of rounded sapphire probe (SMTR, MTR, MTRL, OS, LT) and how these properties are affected by clinical usage. The laser beam profile emitted by these probes demonstrates a focal spot 1-2 mm in front of the tip. However, the forward transmission of Nd-YAG energy through the sapphires varied (SMTR, 85%; MTR, 83%; MTRL, 75%; OS, 54%; LT, 69%). Probe heating occurs owing to energy absorption within the sapphire. The surface temperature of the sapphires was measured in air by infrared thermography and the hottest region within the probes localized by an isothermographic technique. At energy settings used clinically (20 J, 10 watts for 2 s) the SMTR, MTR, and MTRL probes exhibited higher temperature rises (94-112.C) than the OS and LT probes (30.C), and heating was localized to the front surface of the former probes. Peak sapphire temperatures remained lower than those of metal probes even at higher energies. After clinical use, the MTR probe demonstrated reduced transmission, beam defocusing, and increased heating, due to surface pitting. Thus, recanalization with sapphire probes occurs by a combination of photothermal and contact thermal effects that are localized to the probe tip and may reduce the degree of thermal injury associated with metal probes. Understanding these basic properties is important to the application and development of contact probes for laser recanalization.

  2. Quality-enhanced AlN epitaxial films grown on c-sapphire using ZnO buffer layer for SAW applications

    NASA Astrophysics Data System (ADS)

    Fu, Sulei; Li, Qi; Gao, Shuang; Wang, Guangyue; Zeng, Fei; Pan, Feng

    2017-04-01

    AlN epitaxial films with a thin ZnO buffer layer were successfully deposited on c-sapphire by DC magnetron sputtering for surface acoustic wave (SAW) applications. The effect of ZnO buffer layer thickness on structural properties of AlN epitaxial films and the related SAW properties were investigated systematically. The results revealed that a thin ZnO buffer layer can significantly enhance the crystalline quality of AlN films and release the strain in AlN films. The AlN films were epitaxially grown on ZnO buffered-substrate with orientation relationship of (0001) [ 10 1 bar 0 ] AlN//(0001) [ 10 1 bar 0 ] ZnO//(0001) [2 bar 110 ] Al2O3. High frequency SAW devices with a center frequency of 1.4 GHz, a phase velocity of 5600 m/s were achieved on the obtained AlN films. The optimum ZnO buffer layer thickness was found to be 10 nm, resulting in high-quality epitaxial AlN films with a FWHM value of the rocking curve of 0.84°, nearly zero stress and low insertion loss of SAW devices. This work offers an effective approach to achieve high-quality AlN epitaxial films on sapphire substrates for the applications of AlN-based SAW devices.

  3. Growth of self-aligned Ga2O3 nanostructures deposited on r-plane sapphire by using metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Lee, Seoyoung; Lee, Seunghyun; Jo, Hyunjin; Bae, Sangki; Kim, Kimin; Song, Jiho; Cho, Younghwan; Kim, Jinsung; Ahn, Hyungsoo; Yang, Min

    2016-11-01

    The growth temperature dependence of self-aligned β-Ga2O3 nanostructures grown on an r-plane sapphire substrate by using metal-organic chemical vapor deposition is reported. Periodic self-alignment of the β-Ga2O3 grains was observed for certain growth temperature windows and the grain size of the β-Ga2O3 structure varied in response to the growth temperature. At temperatures under 800 °C, self-alignment of the β-Ga2O3 structures was not observed. The self-alignment tendency began to appear at 900 °C, and obvious self-alignment characteristics in a certain direction were observed at approximately 950 °C. However, as the growth temperature was increased to more than 900 °C the growth mode of the β-Ga2O3 structure gradually deviated from the self-alignment mode, finally exhibiting a two-dimensional thin film mode at 1100 °C. We surmise that the driving force of β-Ga2O3 grain self-alignment is the surface-potential difference between the planar and the step regions of the substrate on an atomic scale, which originates from misorientation occurring during the r-plane sapphire cutting process.

  4. Cellular and Humoral Antibody Responses of Normal Pastel and Sapphire Mink to Goat Erythrocytes

    PubMed Central

    Lodmell, D. L.; Bergman, R. K.; Hadlow, W. J.; Munoz, J. J.

    1971-01-01

    This study was undertaken to determine whether normal sapphire and royal pastel mink differ immunologically at the cellular and humoral levels. Two days after primary intraperitoneal (ip) inoculation of goat erythrocytes (GE), essentially no 19 or 7S plaque-forming cells (PFC) per 106 cells were detected in spleen or in abdominal and peripheral lymph nodes of either color phase. On the 4th day, more 19S PFC were detected in pastel than in sapphire tissues; pastel tissues also contained 7S PFC, whereas essentially none was present in sapphires until the 6th day. After an ip booster inoculation, the number of PFC was markedly different between the two color phases. These differences were most apparent in spleen and peripheral lymph nodes. In parallel with differences observed in PFC responses between the color phases, total hemolysin and 2-mercaptoethanol-resistant hemolysin titers of pastels exceeded those of sapphires in all but one interval after the primary, and at every interval after the booster, inoculation. These data indicate that sapphire mink are not immunological cripples, nor are they immunologically hyperactive, but that differences do exist between sapphire and royal pastel mink, especially in the response to booster injections of GE. PMID:16557957

  5. Feasibility for non-destructive discrimination of natural and beryllium-diffused sapphires using Raman spectroscopy.

    PubMed

    Chang, Kyeol; Lee, Sanguk; Park, Jimin; Chung, Hoeil

    2016-03-01

    Raman spectroscopy based non-destructive discrimination between natural and beryllium-diffused (Be-diffused) sapphires has been attempted. The initial examination of Raman image acquired on a sapphire revealed that microscopic structural and compositional heterogeneity was apparent in the sample, so acquisition of spectra able to represent a whole body of sapphire rather than a localized area was necessary for a reliable discrimination. For this purpose, a wide area illumination (WAI) scheme (illumination area: 28.3mm(2)) providing a large sampling volume was employed to collect representative Raman spectra of sapphires. Upon the diffusion of Be into a sapphire, the band shift originated from varied lattice structure by substitution of Be at cation sites was observed and utilized as a valuable spectral signature for the discrimination. In the domain of principal component (PC) scores, the groups of natural and Be-diffused sapphires were identifiable with minor overlapping and the cross-validated discrimination error was 7.3% when k-Nearest Neighbor (k-NN) was used as a classifier.

  6. Wafer-scale highly-transparent and superhydrophilic sapphires for high-performance optics.

    PubMed

    Leem, Jung Woo; Yu, Jae Su

    2012-11-19

    We reported the wafer-scale highly-transparent and superhydrophilic sapphires with antireflective subwavelength structures (SWSs) which were fabricated by dry etching using thermally dewetted gold (Au) nanomasks. Their optical transmittance properties were experimentally and theoretically investigated. The density, size, and period of the thermally dewetted Au nanopatterns can be controlled by the Au film thickness. For the sapphire with both-side SWSs at 5 nm of Au film, the average total transmittance (T(avg)) of ~96.5% at 350-800 nm was obtained, indicating a higher value than those of the flat sapphire (T(avg)~85.6%) and the sapphire with one-side SWSs (T(avg)~91%), and the less angle-dependent transmittance property was observed. The calculated transmittance results also showed a similar tendency to the measured data. The SWSs enhanced significantly the surface hydrophilicity of sapphires, exhibiting a water contact angle (θ(c)) of < 5° for Au film of 5 nm compared to θ(c)~37° of the flat sapphire.

  7. Cellular and humoral antibody responses of normal pastel and sapphire mink to goat erythrocytes.

    PubMed

    Lodmell, D L; Bergman, R K; Hadlow, W J; Munoz, J J

    1971-02-01

    This study was undertaken to determine whether normal sapphire and royal pastel mink differ immunologically at the cellular and humoral levels. Two days after primary intraperitoneal (ip) inoculation of goat erythrocytes (GE), essentially no 19 or 7S plaque-forming cells (PFC) per 10(6) cells were detected in spleen or in abdominal and peripheral lymph nodes of either color phase. On the 4th day, more 19S PFC were detected in pastel than in sapphire tissues; pastel tissues also contained 7S PFC, whereas essentially none was present in sapphires until the 6th day. After an ip booster inoculation, the number of PFC was markedly different between the two color phases. These differences were most apparent in spleen and peripheral lymph nodes. In parallel with differences observed in PFC responses between the color phases, total hemolysin and 2-mercaptoethanol-resistant hemolysin titers of pastels exceeded those of sapphires in all but one interval after the primary, and at every interval after the booster, inoculation. These data indicate that sapphire mink are not immunological cripples, nor are they immunologically hyperactive, but that differences do exist between sapphire and royal pastel mink, especially in the response to booster injections of GE.

  8. Local dielectric permittivity profiles of sapphire/polypropylene interfaces

    NASA Astrophysics Data System (ADS)

    Yu, Liping; Ranjan, V.; Buongiorno Nardelli, M.; Bernholc, J.

    2009-03-01

    Recently, the need for high-power-density capacitors has stimulated research to develop composite dielectric materials with high-k nanoparticles embedded in a polymer matrix. In these materials, surfaces and interfaces may play an important role in determining the overall dielectric properties. We present first-principles investigations of the dielectric permittivity profiles across slabs and interfaces of sapphire(α-Al2O3)/isotactic-polypropylene(iPP). Our results indicate that the permittivity profile at interface strongly depends on the nanoscale averaging procedure. We propose an averaging model that ensures near-locality of the dielectric function. We find that: (i) the dielectric permittivity approaches the corresponding bulk value just a few atomic layers away from the interface or surface; (ii) the dielectric constant is enhanced at the surfaces of the isolated α-Al2O3 slabs, while no enhancement is observed at the iPP slab surfaces; and (iii) the dielectric transition at the αAl2O3/iPP is mainly confined in the αAl2O3 side.

  9. Epitaxial Growth of Mo Single Crystal on Sapphire by H2 Reduction of MoO3 and Characterization by Reflection High-Energy Electron Diffraction

    NASA Astrophysics Data System (ADS)

    Igarashi, Osamu

    1995-05-01

    Mo depositions on sapphire ( Al2O3) were effected by H2 reduction of MoO3, and the crystallinity of the films was characterized by reflection high-energy electron diffraction (RHEED). In the case of growth on the (1\\=102) Al2O3 substrates, single-crystal epitaxial growth of (001) Mo was realized. On (0001) Al2O3, single-crystal Mo was not obtained; Mo deposited on (0001) Al2O3 was composed of three sets of (110)-oriented crystallites. To obtain Debye-Scherrer ring-free Mo films whose RHEED patterns did not include arcs, growth temperatures of 890 and 920° C were required in growths on (1\\=102) and (0001) Al2O3 substrates, respectively.

  10. Sub-nanoscale nanoimprint fabrication of atomically stepped glassy substrates of silicate glass and acryl polymer

    NASA Astrophysics Data System (ADS)

    Yoshimoto, Mamoru

    2015-11-01

    In the nanoimprint process, the resolution limit of patterning has attracted much attention from both scientific and industrial aspects. In this article, we briefly review the main achievements of our research group on sub-nanoscale nanoimprint fabrication of atomically patterned glassy substrates of oxide glass and polymer. By applying the sapphire (α-Al2O3 single crystal) wafers with self-organized nanopatterns of atomic steps as thermal nanoimprinting molds, we successfully transferred their nanoscale patterns onto the surfaces of glassy substrates such as soda-lime silicate glasses and poly(methyl methacrylate) polymers. The surfaces of nanoimprinted glassy materials exhibited regularly arrayed atomic stairs with 0.2-0.3 nm step height, which were in good agreement with the sub-nanopatterns of sapphire molds. These atomically stepped morphologies on the glassy substrates were found to be stable for about 1 year.

  11. Accurate determination of optical bandgap and lattice parameters of Zn{sub 1-x}Mg{sub x}O epitaxial films (0{<=}x{<=}0.3) grown by plasma-assisted molecular beam epitaxy on a-plane sapphire

    SciTech Connect

    Laumer, Bernhard; Schuster, Fabian; Stutzmann, Martin; Bergmaier, Andreas; Dollinger, Guenther; Eickhoff, Martin

    2013-06-21

    Zn{sub 1-x}Mg{sub x}O epitaxial films with Mg concentrations 0{<=}x{<=}0.3 were grown by plasma-assisted molecular beam epitaxy on a-plane sapphire substrates. Precise determination of the Mg concentration x was performed by elastic recoil detection analysis. The bandgap energy was extracted from absorption measurements with high accuracy taking electron-hole interaction and exciton-phonon complexes into account. From these results a linear relationship between bandgap energy and Mg concentration is established for x{<=}0.3. Due to alloy disorder, the increase of the photoluminescence emission energy with Mg concentration is less pronounced. An analysis of the lattice parameters reveals that the epitaxial films grow biaxially strained on a-plane sapphire.

  12. Optimization of the structural quality of sapphire rods grown by the Stepanov method in a reducing atmosphere

    SciTech Connect

    Kryvonosov, Ye. V.; Konevskiy, P. V. Lytvynov, L. A.; Tkachenko, V. F.

    2015-03-15

    Historically, the Stepanov method has been used for growing long shaped sapphire crystals (rods, tubes, and ribbons) for practical design. The recent intense development of this technique was stimulated by sapphire applications in optics and electronics; thus, the optical and structural quality of these crystals is of great importance. The results of studying the structural quality of sapphire rods up to 18 mm in diameter grown under optimized conditions are reported.

  13. Study of high-temperature Smart Cut™: Application to silicon-on-sapphire films and to thin foils of single crystal silicon

    NASA Astrophysics Data System (ADS)

    Meyer, Raphaël; Kononchuck, Oleg; Moriceau, Hubert; Lemiti, Mustapha; Bruel, Michel

    2016-01-01

    Two novel processes of elaboration of silicon thin films and silicon foils are proposed, based on the knowledge brought from the Smart Cut™. The first relies on the laser-beam annealing of an implanted silicon wafer in order to induce a separation layer within the implanted wafer and a transfer upon a transparent wafer. The second consists in depositing a layer of liquid silicon upon an implanted silicon wafer and to form a silicon foil by liquid phase epitaxial growth that can be separated from the substrate by Smart Cut™. The separation kinetics of an implanted silicon wafer is characterized for temperature between 450 °C and 700 °C, considering doses of implantation from 3.5 ∗ 1016 H cm-2 to 1.0 ∗ 1017 H cm-2. The out-diffusion of hydrogen is studied by Energy Recoil Detection Analysis and a model of diffusion of hydrogen in implanted silicon is proposed. Based on this analysis, a model for the kinetics of splitting at high temperature is established. Smart Cut™ separation is demonstrated for temperature up to 1250 °C, considering an implanted silicon wafer bonded with a sapphire wafer, through which a laser beam anneals the structure. The kinetics of separation by laser beam annealing is characterized and compared to the kinetics established between 450 °C and 700 °C. The roughness of the silicon on sapphire film is characterized by Atomic Force Microscopy and a transfer is realized considering an implanted silicon bonded with a glass wafer of 200 mm of diameter. Finally, this article presents results of liquid silicon deposition onto an implanted silicon substrate. These results demonstrate the possibility to detach the film grown by liquid phase epitaxy and the upper part of the implanted substrate by Smart Cut™. Electron Backscattering Diffraction Pattern analysis is considered in order to demonstrate the occurrence of epitaxy of the deposited liquid onto the implanted substrate.

  14. Study of the environmental and optical durability of AR microstructures in sapphire, ALON, and diamond

    NASA Astrophysics Data System (ADS)

    Hobbs, Douglas S.

    2009-05-01

    Data is presented for the erosion resistance and pulsed laser damage threshold of anti-reflecting (AR) microstructures built in the surface of the infrared light transmitting window materials sapphire, ALON, and diamond. It was found that the erosion resistance of AR microstructures (ARMs) in sapphire is comparable to the resistance of sapphire with no AR treatment. Such environmental durability, combined with the enhanced light transmission of windows incorporating ARMs, provides system designers with an effective solution for applications requiring high transmission over long mission times operating in abrasive environments. In addition, the optical power handling capacity of sapphire and ALON windows was investigated through pulsed laser damage threshold measurements with a laser source operating in the near infrared at a wavelength of 1573nm. As with prior results reported for ARMs in fused silica and borosilicate glass, the measured damage threshold of 19 J/cm2 for ARMs treated sapphire windows is comparable to the damage level measured for untreated sapphire windows, and this level is at least two times higher than that found with the most durable thin-film AR coatings designed for fused silica. The damage thresholds measured for untreated and ARMs treated ALON windows was also comparable, but at a level more than four times less than the sapphire windows. Lastly, the long-wave infrared light transmission of high performance ARMs fabricated in clear diamond windows is presented. The Air Force Research Laboratoy's Laser Hardened Materials Evaluation Laboratory at WPAFB tested the damage threshold of the ARMs treated diamond windows along with untreated diamond windows using their pulsed CO2 laser setup operating at 9.56μm. Although the results of the tests using two different laser settings were quite variable and inconsistent due to the nature of the diamond material, the damage thresholds measured were in the 50 to 100 J/cm2 range, a level much higher than

  15. Uncarboxylated Osteocalcin and Gprc6a Axis Produce Intratumoral Androgens in Castration-Resistant Prostate Cancer

    DTIC Science & Technology

    2015-03-01

    at metastatic sites by the activity of androgen biosynthetic enzymes . Recent study shows that Gprc6a/Osteocalcin axis regulates physiological... enzymes . This data suggest that prostate cancer bone tumors hijack Osteocalcin/Gprc6a axis for the production of intratumoral androgens via...overexpression of certain androgen biosynthetic enzyme expression. Bone tumor expressed androgens promote disease progression via tumoral androgen production

  16. Inverted vertical algan deep ultraviolet leds grown on p-SiC substrates by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Nothern, Denis Maurice

    Deep ultraviolet light emitting diodes (UV LEDs) are an important emerging technology for a number of applications such as water/air/surface disinfection, communications, and epoxy curing. However, as of yet, deep UV LEDs grown on sapphire substrates are neither efficient enough nor powerful enough to fully serve these and other potential applications. The majority of UV LEDs reported so far in the literature are grown on sapphire substrates and their design consists of AlGaN quantum wells (QWs) embedded in an AlGaN p-i-n junction with the n-type layer on the sapphire. These devices suffer from a high concentration of threading defects originating from the large lattice mismatch between the sapphire substrate and AlGaN alloys. Other issues include the poor doping efficiency of the n- and particularly the p-AlGaN alloys, the extraction of light through the sapphire substrate, and the heat dissipation through the thermally insulating sapphire substrate. These problems have historically limited the internal quantum efficiency (IQE), injection efficiency (IE), and light extraction efficiency (EE) of devices. As a means of addressing these efficiency and power challenges, I have contributed to the development of a novel inverted vertical deep UV LED design based on AlGaN grown on p-SiC substrates. Starting with a p-SiC substrate that serves as the p-type side of the p-i-n junction largely eliminates the necessity for the notoriously difficult p-type doping of AlGaN alloys, and allows for efficient heat dissipation through the highly thermally conductive SiC substrate. UV light absorption in the SiC substrate can be addressed by first growing p-type doped distributed Bragg reflectors (DBRs) on top of the substrate prior to the deposition of the active region of the device. A number of n-AlGaN films, AlGaN/AlGaN multiple quantum wells, and p-type doped AlGaN DBRs were grown by molecular beam epitaxy (MBE). These were characterized in situ by reflected high energy electron

  17. Influence of annealing temperature on the dielectric properties of BaSrTiO3 thin films deposited on various substrates

    NASA Astrophysics Data System (ADS)

    Lee, Chil-Hyoung; Oh, Young-Jei; Lee, Deuk Yong; Choi, Doo-Jin

    2016-11-01

    (Ba0.5Sr0.5)TiO3 (BST) thin films were deposited on various substrates, such as LaAlO3(100), MgO(100), R-plane sapphire[1012], and polycrystalline sapphire, by using RF magnetron sputtering to investigate the influence of annealing temperature on the dielectric properties and the tunability of the films. The BST thin films deposited on LaAlO3(100) exhibited a high tunability of 42 % and a low dielectric loss of 0.004 due to the small differences in the lattice parameters and the thermal expansion coefficients between the BST films and the substrates. In contrast, the BST films deposited on a polycrystalline sapphire, exhibiting a relatively high mismatch factor, showed the tunability of 24 % and a dielectric loss of 0.007. The BST thin films on LaAlO3(100), MgO(100), R-plane sapphire[1012], and polycrystalline sapphire were annealed. The optimized annealing temperatures were found to be 950 °C, 1050 °C, 1100 °C, and 1150 °C, respectively. The difference in annealing temperature is likely due to the differences in the lattice parameters and the thermal expansion coefficients between the films and the substrates.

  18. GaN-based light-emitting diodes on various substrates: a critical review

    NASA Astrophysics Data System (ADS)

    Li, Guoqiang; Wang, Wenliang; Yang, Weijia; Lin, Yunhao; Wang, Haiyan; Lin, Zhiting; Zhou, Shizhong

    2016-05-01

    GaN and related III-nitrides have attracted considerable attention as promising materials for application in optoelectronic devices, in particular, light-emitting diodes (LEDs). At present, sapphire is still the most popular commercial substrate for epitaxial growth of GaN-based LEDs. However, due to its relatively large lattice mismatch with GaN and low thermal conductivity, sapphire is not the most ideal substrate for GaN-based LEDs. Therefore, in order to obtain high-performance and high-power LEDs with relatively low cost, unconventional substrates, which are of low lattice mismatch with GaN, high thermal conductivity and low cost, have been tried as substitutes for sapphire. As a matter of fact, it is not easy to obtain high-quality III-nitride films on those substrates for various reasons. However, by developing a variety of techniques, distincts progress has been made during the past decade, with high-performance LEDs being successfully achieved on these unconventional substrates. This review focuses on state-of-the-art high-performance GaN-based LED materials and devices on unconventional substrates. The issues involved in the growth of GaN-based LED structures on each type of unconventional substrate are outlined, and the fundamental physics behind these issues is detailed. The corresponding solutions for III-nitride growth, defect control, and chip processing for each type of unconventional substrate are discussed in depth, together with a brief introduction to some newly developed techniques in order to realize LED structures on unconventional substrates. This is very useful for understanding the progress in this field of physics. In this review, we also speculate on the prospects for LEDs on unconventional substrates.

  19. Highly c-axis oriented growth of GaN film on sapphire (0001) by laser molecular beam epitaxy using HVPE grown GaN bulk target

    SciTech Connect

    Kushvaha, S. S.; Kumar, M. Senthil; Maurya, K. K.; Dalai, M. K.; Sharma, Nita D.

    2013-09-15

    Growth temperature dependant surface morphology and crystalline properties of the epitaxial GaN layers grown on pre-nitridated sapphire (0001) substrates by laser molecular beam epitaxy (LMBE) were investigated in the range of 500–750 °C. The grown GaN films were characterized using high resolution x-ray diffraction, atomic force microscopy (AFM), micro-Raman spectroscopy, and secondary ion mass spectroscopy (SIMS). The x-ray rocking curve full width at a half maximum (FWHM) value for (0002) reflection dramatically decreased from 1582 arc sec to 153 arc sec when the growth temperature was increased from 500 °C to 600 °C and the value further decreased with increase of growth temperature up to 720 °C. A highly c-axis oriented GaN epitaxial film was obtained at 720 °C with a (0002) plane rocking curve FWHM value as low as 102 arc sec. From AFM studies, it is observed that the GaN grain size also increased with increasing growth temperature and flat, large lateral grains of size 200-300 nm was obtained for the film grown at 720 °C. The micro-Raman spectroscopy studies also exhibited the high-quality wurtzite nature of GaN film grown on sapphire at 720 °C. The SIMS measurements revealed a non-traceable amount of background oxygen impurity in the grown GaN films. The results show that the growth temperature strongly influences the surface morphology and crystalline quality of the epitaxial GaN films on sapphire grown by LMBE.

  20. Highly c-axis oriented growth of GaN film on sapphire (0001) by laser molecular beam epitaxy using HVPE grown GaN bulk target

    NASA Astrophysics Data System (ADS)

    Kushvaha, S. S.; Kumar, M. Senthil; Maurya, K. K.; Dalai, M. K.; Sharma, Nita D.

    2013-09-01

    Growth temperature dependant surface morphology and crystalline properties of the epitaxial GaN layers grown on pre-nitridated sapphire (0001) substrates by laser molecular beam epitaxy (LMBE) were investigated in the range of 500-750 °C. The grown GaN films were characterized using high resolution x-ray diffraction, atomic force microscopy (AFM), micro-Raman spectroscopy, and secondary ion mass spectroscopy (SIMS). The x-ray rocking curve full width at a half maximum (FWHM) value for (0002) reflection dramatically decreased from 1582 arc sec to 153 arc sec when the growth temperature was increased from 500 °C to 600 °C and the value further decreased with increase of growth temperature up to 720 °C. A highly c-axis oriented GaN epitaxial film was obtained at 720 °C with a (0002) plane rocking curve FWHM value as low as 102 arc sec. From AFM studies, it is observed that the GaN grain size also increased with increasing growth temperature and flat, large lateral grains of size 200-300 nm was obtained for the film grown at 720 °C. The micro-Raman spectroscopy studies also exhibited the high-quality wurtzite nature of GaN film grown on sapphire at 720 °C. The SIMS measurements revealed a non-traceable amount of background oxygen impurity in the grown GaN films. The results show that the growth temperature strongly influences the surface morphology and crystalline quality of the epitaxial GaN films on sapphire grown by LMBE.

  1. Properties Data for Adhesion and Surface Chemistry of Aluminum: Sapphire-Aluminum, Single-Crystal Couple

    NASA Technical Reports Server (NTRS)

    Miyoshi, Kazuhisa; Pohlchuck, Bobby; Whitle, Neville C.; Hector, Louis G., Jr.; Adams, Jim

    1998-01-01

    An investigation was conducted to examine the adhesion and surface chemistry of single-crystal aluminum in contact with single-crystal sapphire (alumina). Pull-off force (adhesion) measurements were conducted under loads of 0. I to I mN in a vacuum of 10(exp -1) to 10(exp -9) Pa (approx. 10(exp -10) to 10(exp -11) torr) at room temperature. An Auger electron spectroscopy analyzer incorporated directly into an adhesion-measuring vacuum system was primarily used to define the chemical nature of the surfaces before and after adhesion measurements. The surfaces were cleaned by argon ion sputtering. With a clean aluminum-clean -sapphire couple the mean value and standard deviation of pull-off forces required to separate the surfaces were 3015 and 298 micro-N, respectively. With a contaminated aluminum-clean sapphire couple these values were 231 and 241 micro-N. The presence of a contaminant film on the aluminum surface reduced adhesion by a factor of 13. Therefore, surfaces cleanliness, particularly aluminum cleanliness, played an important role in the adhesion of the aluminum-sapphire couples. Pressures on the order of 10(exp -8) to 10(exp -9) Pa (approx. 10(exp -10) to 10(exp -11) torr) maintained a clean aluminum surface for only a short time (less then 1 hr) but maintained a clean sapphire surface, once it was achieved, for a much longer time.

  2. Enhancing the Thermal Conductance of Polymer and Sapphire Interface via Self-Assembled Monolayer.

    PubMed

    Zheng, Kun; Sun, Fangyuan; Zhu, Jie; Ma, Yongmei; Li, Xiaobo; Tang, Dawei; Wang, Fosong; Wang, Xiaojia

    2016-08-23

    Interfacial thermal conductance (ITC) receives enormous consideration because of its significance in determining thermal performance of hybrid materials, such as polymer based nanocomposites. In this study, the ITC between sapphire and polystyrene (PS) was systematically investigated by time domain thermoreflectance (TDTR) method. Silane based self-assembled monolayers (SAMs) with varying end groups, -NH2, -Cl, -SH and -H, were introduced into sapphire/PS interface, and their effects on ITC were investigated. The ITC was found to be enhanced up by a factor of 7 through functionalizing the sapphire surface with SAM, which ends with a chloride group (-Cl). The results show that the enhancement of the thermal transport across the SAM-functionalized interface comes from both strong covalent bonding between sapphire and silane-based SAM, and the high compatibility between the SAM and PS. Among the SAMs studied in this work, we found that the ITC almost linearly depends on solubility parameters, which could be the dominant factor influencing on the ITC compared with wettability and adhesion. The SAMs serve as an intermediate layer that bridges the sapphire and PS. Such a feature can be applied to ceramic-polymer immiscible interfaces by functionalizing the ceramic surface with molecules that are miscible with the polymer materials. This research provides guidance on the design of critical-heat transfer materials such as composites and nanofluids for thermal management.

  3. Absorption and fluorescence of alexandrite and of titanium in sapphire and glass

    NASA Technical Reports Server (NTRS)

    Byvik, C. E.; Hess, R. V.; Buoncristiani, A. M.

    1985-01-01

    The fluorescence and absorption data for titanium in crystalline sapphire and titanium doped into two silicate and one phosphate glass structures are analyzed. It is observed that the Ti-doped silicate glass sample exhibits no absorption related to the Ti(III) ion, the Ti-doped phosphate glass is deep blue, the absorption line width of the glass samples are a factor of two larger than that of sapphire, and the absorption peak for the Ti in the glass shifted about 100 nm to the red from the Ti:sapphire absorption peak. This shift reveals that the Ti(III) ion is sensitive to the crystalline environment and not to the glass environment. The photoluminescence spectra for Ti-doped sapphire and alexandrite are compared. It is detected that the Ti:sapphire exhibits a broader spectrum than that for alexandrite with a peak at 750 nm. The three zero phonon transitions of Ti:Al2O3 at liquid nitrogen temperatures are studied.

  4. Temperature Compensated Sapphire Resonator for Ultrastable Oscillator Operating at Temperatures Near 77 Deg Kelvin

    NASA Technical Reports Server (NTRS)

    Dick, G. John (Inventor); Santiago, David G. (Inventor)

    1999-01-01

    A sapphire resonator for an ultrastable oscillator capable of substantial performance improvements over the best available crystal quartz oscillators in a compact cryogenic package is based on a compensation mechanism enabled by the difference between copper and sapphire thermal expansion coefficients for so tuning the resonator as to cancel the temperature variation of the sapphire's dielectric constant. The sapphire resonator consists of a sapphire ring separated into two parts with webs on the outer end of each to form two re-entrant parts which are separated by a copper post. The re-entrant parts are bonded to the post by indium solder for good thermal conductivity between parts of that subassembly which is supported on the base plate of a closed copper cylinder (rf shielding casing) by a thin stainless steel cylinder. A unit for temperature control is placed in the stainless steel cylinder and is connected to the subassembly of re-entrant parts and copper post by a layer of indium for good thermal conduction. In normal use, the rf shielding casing is placed in a vacuum tank which is in turn placed in a thermos flask of liquid nitrogen. The temperature regulator is controlled from outside the thermos flask to a temperature in a range of about 40K to 150K, such as 87K for the WGH-811, mode of resonance in response to microwave energy inserted into the rf shielding casing through a port from an outside source.

  5. High quality AlN epilayers grown on nitrided sapphire by metal organic chemical vapor deposition.

    PubMed

    Wang, Jiaming; Xu, Fujun; He, Chenguang; Zhang, Lisheng; Lu, Lin; Wang, Xinqiang; Qin, Zhixin; Shen, Bo

    2017-02-21

    Influence of sapphire pretreatment conditions on crystalline quality of AlN epilayers has been investigated by metal organic chemical vapor deposition (MOCVD). Compared to alumination treatment, it is found that appropriate sapphire nitridation significantly straightens the surface atomic terraces and decreases the X-ray diffraction (0002) full width at half maximum (FWHM) to a minimum of 55 arcsec, indicating a great improvement of the tilting feature of the grain structures in the AlN epilayer. More importantly, there is no inversion domains (IDs) found in the AlN epilayers, which clarifies that optimal sapphire nitridation is promising in the growth of high quality AlN. It is deduced that the different interfacial atomic structures caused by various pretreatment conditions influence the orientation of the AlN nucleation layer grains, which eventually determines the tilting features of the AlN epilayers.

  6. Oxygen isotope composition as a tracer for the origins of rubies and sapphires

    NASA Astrophysics Data System (ADS)

    Giuliani, Gaston; Fallick, Anthony E.; Garnier, Virginie; France-Lanord, Christian; Ohnenstetter, Daniel; Schwarz, Dietmar

    2005-04-01

    Oxygen isotopic compositions of rubies and sapphires from 106 deposits worldwide, as well as heated natural corundum, have been measured in this study. Artificially heated corundums have the same oxygen isotopic composition as unheated material. The 18O/16O ratio of natural corundum is a good indicator of its geological environment of formation. The consistently restricted δ18O range found for each type of deposit is explained by host-rock buffering during fluid-rock interaction. The δ18O constrains the geological source of the major type of gem-quality rubies sold on the market and brings new insight to gems found in placers. High-quality blue sapphires from Kashmir, Andranondambo, and Sri Lanka have specific oxygen isotopic ranges, but they overlap those of Mogok in Myanmar. Combined with traditional gemology techniques, oxygen isotope analysis will contribute toward defining the origin of some commercial high-value blue sapphires, especially from Kashmir.

  7. Synthesis and characterization of large optical grade sapphire windows produced from a horizontal growth process

    NASA Astrophysics Data System (ADS)

    Levine, Jonathan B.; Burks, Timothy; Ciraldo, John; Montgomery, Matthew; Novoselov, Andrey; Podlozhenov, Sergey

    2013-06-01

    As sensor technology and applications have advanced over the years, the size of sensor windows has grown substantially to satisfy current and future demands. Rubicon Technology, with their strong history in scaling sapphire crystal growth and large scale production processes, has successfully produced large sapphire blanks using a highly modified horizontal directional solidification process. Several prototypes have been synthesized up to 1.75 inches thick, 14 inches wide and 20 inches long. Crystal properties and optical characteristics such as transmission and refractive index homogeneity will be presented on several polished bubble-free windows with excellent results. This research sets the standard for high quality monolithic sapphire sheets large enough for use as seamless integrated optical windows in both military and civilian applications.

  8. Interfacial Shear Strength of Cast and Directionally Solidified Nial-Sapphire Fiber Composites

    NASA Technical Reports Server (NTRS)

    Tewari, S. N.; Asthana, R.; Noebe, R. D.

    1993-01-01

    The feasibility of fabricating intermetallic NiAl-sapphire fiber composites by casting and zone directional solidification has been examined. The fiber-matrix interfacial shear strengths measured using a fiber push-out technique in both cast and directionally solidified composites are greater than the strengths reported for composites fabricated by powder cloth process using organic binders. Microscopic examination of fibers extracted from cast, directionally solidified (DS), and thermally cycled composites, and the high values of interfacial shear strengths suggest that the fiber-matrix interface does not degrade due to casting and directional solidification. Sapphire fibers do not pin grain boundaries during directional solidification, suggesting that this technique can be used to fabricate sapphire fiber reinforced NiAl composites with single crystal matrices.

  9. Surface characterization of diamond film tool grinding on the monocrystal sapphire under different liquid environments

    NASA Astrophysics Data System (ADS)

    Feng, Wei; Lu, Wenzhuang; Zhou, Hai; Yang, Bin; Zuo, Dunwen

    2016-11-01

    Surface characterization of diamond film tool on the monocrystal sapphire under H2O, 3% ethylene glycol and 3% ethylenediamine was investigated. The typical components and chemical changes of the surface of diamond thick film were studied by means of Raman and XPS. Results showed that tribological properties of diamond film tool were associated with the liquid environment located the grinding. Diamond film tool under 3% ethylenediamine solution exhibited the minimum value of friction coefficient, while that under H2O exhibited maximum value of friction coefficient. As the ethylenediamine and ethylene glycol were added during the grinding process, the reaction between diamond film and the sapphire pieces occurred, and the chemical composition change of the surface was also studied. Under the same process parameters, a better surface quality of sapphire under the grinding fluid of ethylenediamine can be obtained.

  10. Morphology and formation mechanism of metallic inclusions in VB-grown sapphire crystals

    NASA Astrophysics Data System (ADS)

    Taishi, T.; Kobayashi, T.; Shinozuka, M.; Ohba, E.; Miyagawa, C.; Hoshikawa, K.

    2014-09-01

    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 μm 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.

  11. Stability of trapped charges in sapphires and alumina ceramics: Evaluation by secondary electron emission

    NASA Astrophysics Data System (ADS)

    Zarbout, K.; Si Ahmed, A.; Moya, G.; Bernardini, J.; Goeuriot, D.; Kallel, A.

    2008-03-01

    The stability of trapped charges in sapphires and alumina ceramics is characterized via an experimental parameter expressing the variation of the secondary electron emission yield between two electron injections performed in a scanning electron microscope. Two types of sapphires and polycrystalline alumina, which differ mainly by their impurity content, are investigated in the temperature range 300-663K. The stable trapping behavior in sapphires is attributed to trapping in different defects, whose nature depends on the purity level. In alumina ceramics, the ability to trap charges in a stable way is stronger in samples of high impurity content. In the low impurity samples, stable trapping is promoted when the grain diameter decreases, whereas the reverse is observed in high impurity materials. These behaviors can stem from a gettering effect occurring during sintering. The strong dependence of the variation of the secondary electron emission yield on the grain diameter and impurities enables a scaling of the stable trapping ability of alumina materials.

  12. High Temperature Testing with Sapphire Fiber White-Light Michelson Interferometers

    NASA Technical Reports Server (NTRS)

    Barnes, A.; Pedrazzani, J.; May, R.; Murphy, K.; Tran, T.; Coate, J.

    1996-01-01

    In the design of new aerospace materials, developmental testing is conducted to characterize the behavior of the material under severe environmental conditions of high stress, temperature, and vibration. But to test these materials under extreme conditions requires sensors that can perform in harsh environments. Current sensors can only monitor high temperature test samples using long throw instrumentation, but this is inherently less accurate than a surface mounted sensor, and provides no means for fabrication process monitoring. A promising alternative is the use of sapphire optical fiber sensors. Sapphire is an incredibly rugged material, being extremely hard (9 mhos), chemically inert, and having a melting temperature (over 2000 C). Additionally, there is a extensive background of optical fiber sensors upon which to draw for sapphire sensor configurations.

  13. Photoelastic lensing effect in Ti:sapphire crystal pumped by high-energy pulses.

    PubMed

    Zheng, Wei; Lüpke, Gunter

    2012-04-20

    We have built a setup with high temporal resolution to measure the very fast photoelastic lensing effect, which is on the scale of microseconds in a Ti:sapphire crystal pumped by very strong laser pulses (up to 5 J/cm2). The experimental results measured by this method and the real multimode beam profile taken by a CCD camera are applied to a three-dimensional crystal model to calculate one of the photoelastic constants of Ti:sapphire crystal, which is found to be p31=-0.03±0.01. This value is helpful to evaluate the photoelastic lensing effect in Ti:sapphire crystal for a laser beam polarized along the c axis, commonly used for laser amplification.

  14. Single-crystal sapphire tubes as economical probes for optical pyrometry in harsh environments

    SciTech Connect

    Ruzicka, Jakub; Houzvicka, Jindrich; Bok, Jiri; Praus, Petr; Mojzes, Peter

    2011-12-20

    One-end-sealed single-crystal sapphire tubes are presented as a simple, robust, and economical alternative for bulky lightpipe probes. Thermal radiation from a blackbody cavity created at the inner surface of the sealed end is gathered by a simple lens-based collecting system and transmitted via optical fiber to the remote detection unit. Simplicity and applicability of the concept are demonstrated by the combination of commercially available sapphire tubes with a common optical pyrometer. Radiation thermometers with sapphire tubes as invasive probes can be useful for applications requiring immunity to electromagnetic interference, resistance to harsh environments, simple replacement in the case of failure, and enhanced mechanical firmness, enabling wider range probe positioning inside the medium of interest.

  15. High quality AlN epilayers grown on nitrided sapphire by metal organic chemical vapor deposition

    PubMed Central

    Wang, Jiaming; Xu, Fujun; He, Chenguang; Zhang, Lisheng; Lu, Lin; Wang, Xinqiang; Qin, Zhixin; Shen, Bo

    2017-01-01

    Influence of sapphire pretreatment conditions on crystalline quality of AlN epilayers has been investigated by metal organic chemical vapor deposition (MOCVD). Compared to alumination treatment, it is found that appropriate sapphire nitridation significantly straightens the surface atomic terraces and decreases the X-ray diffraction (0002) full width at half maximum (FWHM) to a minimum of 55 arcsec, indicating a great improvement of the tilting feature of the grain structures in the AlN epilayer. More importantly, there is no inversion domains (IDs) found in the AlN epilayers, which clarifies that optimal sapphire nitridation is promising in the growth of high quality AlN. It is deduced that the different interfacial atomic structures caused by various pretreatment conditions influence the orientation of the AlN nucleation layer grains, which eventually determines the tilting features of the AlN epilayers. PMID:28220829

  16. Fabrication of Monolithic Sapphire Membranes for High Tc Bolometer Array Development

    NASA Technical Reports Server (NTRS)

    Pugel, D. E.; Lakew, B.; Aslam, S.; Wang, L.

    2003-01-01

    This paper examines the effectiveness of Pt/Cr thin film masks for the architecture of monolithic membrane structures in r-plane sapphire. The development of a pinhole-free Pt/Cr composite mask that is resistant to hot H2SO4:H3PO4 etchant, will lead to the fabrication of smooth sapphire membranes whose surfaces are well-suited for the growth of low-noise high Tc films. In particular, the relationship of thermal annealing conditions on the Pt/Cr composite mask system to: (1) changes in the surface morphology and elemental concentration of the Pt/Cr thin film layers and (2) etch pit formation on the sapphire surface will be presented.

  17. Fabrication of Monolithic Sapphire Membranes for High T(sub c) Bolometer Array Development

    NASA Technical Reports Server (NTRS)

    Pugel, D. E.; Lakew, B.; Aslam, S.; Wang, L.

    2004-01-01

    This paper examines the effectiveness of Pt/Cr thin film masks for the architecture of monolithic membrane structures in r-plane single crystal sapphire. The development of a pinhole-free Pt/Cr composite mask that is resistant to boiling H2SO4:H3PO4 etchant will lead to the fabrication of smooth sapphire membranes whose surfaces are well-suited for the growth of low-noise high Tc films. In particular, the relationship of thermal annealing conditions on the Pt/Cr composite mask system to: (1) changes in the surface morphology (2) elemental concentration of the Pt/Cr thin film layers and (3) etch pit formation on the sapphire surface will be presented.

  18. High quality AlN epilayers grown on nitrided sapphire by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Wang, Jiaming; Xu, Fujun; He, Chenguang; Zhang, Lisheng; Lu, Lin; Wang, Xinqiang; Qin, Zhixin; Shen, Bo

    2017-02-01

    Influence of sapphire pretreatment conditions on crystalline quality of AlN epilayers has been investigated by metal organic chemical vapor deposition (MOCVD). Compared to alumination treatment, it is found that appropriate sapphire nitridation significantly straightens the surface atomic terraces and decreases the X-ray diffraction (0002) full width at half maximum (FWHM) to a minimum of 55 arcsec, indicating a great improvement of the tilting feature of the grain structures in the AlN epilayer. More importantly, there is no inversion domains (IDs) found in the AlN epilayers, which clarifies that optimal sapphire nitridation is promising in the growth of high quality AlN. It is deduced that the different interfacial atomic structures caused by various pretreatment conditions influence the orientation of the AlN nucleation layer grains, which eventually determines the tilting features of the AlN epilayers.

  19. Anisotropic structural and optical properties of semi-polar (11–22) GaN grown on m-plane sapphire using double AlN buffer layers

    PubMed Central

    Zhao, Guijuan; Wang, Lianshan; Yang, Shaoyan; Li, Huijie; Wei, Hongyuan; Han, Dongyue; Wang, Zhanguo

    2016-01-01

    We report the anisotropic structural and optical properties of semi-polar (11–22) GaN grown on m-plane sapphire using a three-step growth method which consisted of a low temperature AlN buffer layer, followed by a high temperature AlN buffer layer and GaN growth. By introducing double AlN buffer layers, we substantially improve the crystal and optical qualities of semi-polar (11–22) GaN, and significantly reduce the density of stacking faults and dislocations. The high resolution x-ray diffraction measurement revealed that the in-plane anisotropic structural characteristics of GaN layer are azimuthal dependent. Transmission electron microscopy analysis showed that the majority of dislocations in the GaN epitaxial layer grown on m-sapphire are the mixed-type and the orientation of GaN layer was rotated 58.4° against the substrate. The room temperature photoluminescence (PL) spectra showed the PL intensity and wavelength have polarization dependence along parallel and perpendicular to the [1–100] axis (polarization degrees ~ 0.63). The realization of a high polarization semi-polar GaN would be useful to achieve III-nitride based lighting emission device for displays and backlighting. PMID:26861595

  20. The experimentation research of IR imaging system capability affected by sapphire window's pneumatic calefaction

    NASA Astrophysics Data System (ADS)

    Liu, Yang-peng; Pan, Guo-qing; Zhang, Yun-qiang

    2009-07-01

    In the inclement pneumatic calefaction condition, the window of IR imaging system will be calefied and emit infrared radiation, so that the Signal-to-Noise and quality of target IR image are felled off that are from the imaging system. At this rate the physical characteristic of IR window direct affect capability of imaging system controlled and guided homing by IR tracker and measure precision of target IR characteristics. The properties of sapphire make it an ideal choice for the high speed missile applications compared to other existing or emerging materials. But the research has not been reported about the infrared radiation characteristic of sapphire as the IR window. In this paper, based on an IR imaging system using the sapphire window, the experimentation and conclusions of IR thermal image measurement affected by IR window's pneumatic calefaction have been accomplished. Firstly, the temperatures of sapphire window at supersonic flight extended over 1 km and 15 km from the ground have been estimated by calculating the flow and state variables and the aerodynamic heating into the window. On the base of the results calculated the window static state calefaction experimentation and electric arc wind tunnel experimentation had been designed and completed to validate the effect degree of pneumatic calefaction to the imaging system. With the temperatures of the sapphire window rising, in the image coming from the imaging system, the peak luminance of target image detected is increased, the background average luminance of the image is also increased, and the margin of above two varies in a little range. The data obtained from the different temperature experimentation have demonstrated that the IR flux due to the sapphire window becomes heated by friction with the air and heat transfer to the dome can obscure the target image created by the onboard IR sensor, depress Signal-to-Noise and resolving power of the imaging system, but can not overload the detector.

  1. High-pressure Sapphire Cell for Phase Equilibria Measurements of CO2/Organic/Water Systems

    PubMed Central

    Pollet, Pamela; Ethier, Amy L.; Senter, James C.; Eckert, Charles A.; Liotta, Charles L.

    2014-01-01

    The high pressure sapphire cell apparatus was constructed to visually determine the composition of multiphase systems without physical sampling. Specifically, the sapphire cell enables visual data collection from multiple loadings to solve a set of material balances to precisely determine phase composition. Ternary phase diagrams can then be established to determine the proportion of each component in each phase at a given condition. In principle, any ternary system can be studied although ternary systems (gas-liquid-liquid) are the specific examples discussed herein. For instance, the ternary THF-Water-CO2 system was studied at 25 and 40 °C and is described herein. Of key importance, this technique does not require sampling. Circumventing the possible disturbance of the system equilibrium upon sampling, inherent measurement errors, and technical difficulties of physically sampling under pressure is a significant benefit of this technique. Perhaps as important, the sapphire cell also enables the direct visual observation of the phase behavior. In fact, as the CO2 pressure is increased, the homogeneous THF-Water solution phase splits at about 2 MPa. With this technique, it was possible to easily and clearly observe the cloud point and determine the composition of the newly formed phases as a function of pressure. The data acquired with the sapphire cell technique can be used for many applications. In our case, we measured swelling and composition for tunable solvents, like gas-expanded liquids, gas-expanded ionic liquids and Organic Aqueous Tunable Systems (OATS)1-4. For the latest system, OATS, the high-pressure sapphire cell enabled the study of (1) phase behavior as a function of pressure and temperature, (2) composition of each phase (gas-liquid-liquid) as a function of pressure and temperature and (3) catalyst partitioning in the two liquid phases as a function of pressure and composition. Finally, the sapphire cell is an especially effective tool to gather

  2. High-pressure sapphire cell for phase equilibria measurements of CO2/organic/water systems.

    PubMed

    Pollet, Pamela; Ethier, Amy L; Senter, James C; Eckert, Charles A; Liotta, Charles L

    2014-01-24

    The high pressure sapphire cell apparatus was constructed to visually determine the composition of multiphase systems without physical sampling. Specifically, the sapphire cell enables visual data collection from multiple loadings to solve a set of material balances to precisely determine phase composition. Ternary phase diagrams can then be established to determine the proportion of each component in each phase at a given condition. In principle, any ternary system can be studied although ternary systems (gas-liquid-liquid) are the specific examples discussed herein. For instance, the ternary THF-Water-CO2 system was studied at 25 and 40 °C and is described herein. Of key importance, this technique does not require sampling. Circumventing the possible disturbance of the system equilibrium upon sampling, inherent measurement errors, and technical difficulties of physically sampling under pressure is a significant benefit of this technique. Perhaps as important, the sapphire cell also enables the direct visual observation of the phase behavior. In fact, as the CO2 pressure is increased, the homogeneous THF-Water solution phase splits at about 2 MPa. With this technique, it was possible to easily and clearly observe the cloud point and determine the composition of the newly formed phases as a function of pressure. The data acquired with the sapphire cell technique can be used for many applications. In our case, we measured swelling and composition for tunable solvents, like gas-expanded liquids, gas-expanded ionic liquids and Organic Aqueous Tunable Systems (OATS)(1-4). For the latest system, OATS, the high-pressure sapphire cell enabled the study of (1) phase behavior as a function of pressure and temperature, (2) composition of each phase (gas-liquid-liquid) as a function of pressure and temperature and (3) catalyst partitioning in the two liquid phases as a function of pressure and composition. Finally, the sapphire cell is an especially effective tool to gather

  3. 78 FR 56691 - Sapphire Power Marketing LLC; Supplemental Notice That Initial Market-Based Rate Filing Includes...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-09-13

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF ENERGY Federal Energy Regulatory Commission Sapphire Power Marketing LLC; Supplemental Notice That Initial Market-Based... above-referenced proceeding, of Sapphire Power Marketing LLC's application for market-based...

  4. Investigation of optical properties of nickel oxide thin films deposited on different substrates

    NASA Astrophysics Data System (ADS)

    Nama Manjunatha, Krishna; Paul, Shashi

    2015-10-01

    Nickel oxide has been investigated for several potential applications, namely, ultraviolet detectors, electro chromic devices, displays, diodes for light emitting, transparent conductive electrode, and optoelectronic devices. These applications require an in depth analysis of nickel oxide prior to its exploration in aforementioned devices. Optical properties of materials were investigated by depositing thin film of nickel oxide on different substrates in order to understand if the choice of substrate can have effect on deducing various optical parameters and can lead to wrong conclusions. In view of this, we have investigated optical properties of nickel oxide deposited on different substrates (glass, transparent plastic, sapphire, potassium bromide, and calcium fluoride).

  5. Wear residue from polishing sapphire with silica aquasol on a tin lap

    NASA Astrophysics Data System (ADS)

    Werner, Joachim; Weis, Olaf

    1994-08-01

    Sapphire can be superpolished with a tin lap and aqueous colloidal silica as a polishing liquid. We present investigations of the polishing residue that was enriched in a special wearing mill. Elemental analysis, X-ray analysis by diffraction and MAS-NMR studies were performed to obtain an understanding of the microscopic polishing mechanism. We conclude that sapphire is abraded atom by atom in this polishing procedure and that the abraded aluminum atoms are finally chemically bonded in the colloidal silica clusters, in contrast to models proposed earlier.

  6. High-power Ti:sapphire lasers for spectroscopy of antiprotonic atoms and radioactive ions

    NASA Astrophysics Data System (ADS)

    Hori, M.; Dax, A.; Soter, A.

    2012-12-01

    The ASACUSA collaboration has developed injection-seeded Ti:sapphire lasers of linewidth Γpl ˜ 6 MHz, pulse energy 50-100 mJ, and output wavelength λ = 726-941 nm. They are being used in two-photon spectroscopy experiments of antiprotonic helium atoms at the Antiproton Decelerator (AD) of CERN. Ti:sapphire lasers of larger linewidth Γpl ˜ 100 MHz but more robust design will also be used in collinear resonance ionization spectroscopy (CRIS) experiments of neutron-deficient francium ions at the ISOLDE facility.

  7. High-power Ti:sapphire lasers for spectroscopy of antiprotonic atoms and radioactive ions

    NASA Astrophysics Data System (ADS)

    Hori, M.; Dax, A.; Soter, A.

    The ASACUSA collaboration has developed injection-seeded Ti:sapphire lasers of linewidth Γpl ˜ 6 MHz, pulse energy 50-100 mJ, and output wavelength λ = 726-941 nm. They are being used in two-photon spectroscopy experiments of antiprotonic helium atoms at the Antiproton Decelerator (AD) of CERN. Ti:sapphire lasers of larger linewidth Γpl ˜ 100 MHz but more robust design will also be used in collinear resonance ionization spectroscopy (CRIS) experiments of neutron-deficient francium ions at the ISOLDE facility.

  8. Sapphire: Relation between luminescence of starting materials and luminescence of single crystals

    NASA Astrophysics Data System (ADS)

    Mogilevsky, R.; Nedilko, S.; Sharafutdinova, L.; Burlay, S.; Sherbatskii, V.; Boyko, V.; Mittl, S.

    2009-10-01

    A relation between photoluminescence (PL) characteristics of different starting materials used for crystal growth and un-doped sapphire single crystals manufactured using various methods of crystal growth (Kyropolus, HEM, Czochralski, and EFG) was found. The crystals grown using the Verneuil starting material exhibited significant PL when any method of crystal growth was used. On the contrary, sapphire samples grown by the same technologies wherein the starting material was EMT HPDA R revealed very low PL. (HPDA R is produced by EMT, Inc., with proprietary and patented technology.)

  9. Multiphoton imaging with a novel compact diode-pumped Ti:sapphire oscillator.

    PubMed

    König, Karsten; Andersen, Peter; Le, Tuan; Breunig, Hans Georg

    2015-12-01

    Multiphoton laser scanning microscopy commonly relies on bulky and expensive femtosecond lasers. We integrated a novel minimal-footprint Ti:sapphire oscillator, pumped by a frequency-doubled distributed Bragg reflector tapered diode laser, into a clinical multiphoton tomograph and evaluated its imaging capability using different biological samples, i.e. cell monolayers, corneal tissue, and human skin. With the novel laser, the realization of very compact Ti:sapphire-based systems for high-quality multiphoton imaging at a significantly size and weight compared to current systems will become possible.

  10. Ti:Sapphire micro-structures by femtosecond laser inscription: Guiding and luminescence properties

    NASA Astrophysics Data System (ADS)

    Ren, Yingying; Jiao, Yang; Vázquez de Aldana, Javier R.; Chen, Feng

    2016-08-01

    We report on the fabrication of buried cladding waveguides with different diameters in a Ti:Sapphire crystal by femtosecond laser inscription. The propagation properties are studied, showing that the cladding waveguides could support near- to mid-infrared waveguiding at both TE and TM polarizations. Confocal micro-photoluminescence experiments reveal that the original fluorescence properties in the waveguide region are very well preserved, while it suffers from a strong quenching at the centers of laser induced filaments. Broadband waveguide fluorescence emissions with high efficiency are realized, indicating the application of the cladding waveguides in Ti:Sapphire as compact broadband luminescence sources in biomedical fields.

  11. Fabry-Perot cavity based on sapphire-derived fiber for high temperature sensor

    NASA Astrophysics Data System (ADS)

    Chen, Pengfei; Pang, Fufei; Zhao, Ziwen; Hong, Lin; Chen, Na; Chen, Zhenyi; Wang, Tingyun

    2015-09-01

    An optical fiber high temperature sensor is demonstrated by using a special sapphire-derived fiber. An air cavity is easily created through splicing the sapphire-derived fiber with standard single mode fiber (SMF). Utilizing the air cavity as one reflecting face, a Fabry-Perot (F-P) interferometer is fabricated in the special fiber. Attributed to the high ratio alumina component, the F-P interferometer exhibits high sensitivity response to temperature variation within the range up to 1000 °C. The sensitivity is 15.7 pm/°C.

  12. Blocks and residual stresses in sapphire rods of different crystallographic orientations grown by the Stepanov method

    SciTech Connect

    Krymov, V. M. Nosov, Yu. G.; Bakholdin, S. I.; Maslov, V. N.; Shul’pina, I. L.

    2015-05-15

    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.

  13. Analysis of the growth dependences of silicon-on-sapphire heteroepitaxy

    SciTech Connect

    Pavlov, D. A.; Shilyaev, P. A.; Pirogov, A. V. Krivulin, N. O. Bobrov, A. I.; Pegasina, M. D.

    2013-06-15

    The formation of nanoislands of two forms (dome-shaped and a truncated dome) is experimentally found during the initial stage of silicon-on-sapphire heteroepitaxy. Atomic-resolution images of the silicon islands on sapphire are obtained by transmission electron microscopy. A model is proposed to explain the instability of the shape of islands and its transition from isotropic to anisotropic and to describe the evolution of average island sizes during growth. It is shown that the height dependence of the island diameter is approximately linear; however, for large island sizes there is a significant discrepancy with the experimental data due to island coalescence, which is disregarded in the model.

  14. High-efficiency cluster laser vaporization sources based on Ti: sapphire lasers

    NASA Astrophysics Data System (ADS)

    Pellarin, M.; Cottancin, E.; Lerme, J.; Vialle, J.L.; Wolf, J.P.; Broyer, M.; Paillard, V.; Dupuis, V.; Perez, A.; Perez, J.P.; Tuaillon, J.; Melinon, P.

    1994-07-01

    A new laser vaporization source based on a flashlamp-pumped Ti:sapphire laser has been used to produce cluster beams. The performance is compared to the standard cluster sources based on neodyme YAG lasers. We show that the Ti:sapphire source is much more efficient: the clusters deposition rate are about 30 times higher, and larger clusters are produced. Finally the quality of nanostructured films is comparable to those obtained by the standard source, but the time deposition is 30 times shorter. This opens new possibilites for film growth by cluster deposition.

  15. The Influence of Surface Anisotropy Crystalline Structure on Wetting of Sapphire by Molten Aluminum

    NASA Astrophysics Data System (ADS)

    Aguilar-Santillan, Joaquin

    2013-05-01

    The wetting of sapphire by molten aluminum was investigated by the sessile drop technique from 1073 K to 1473 K (800 °C to 1200 °C) at PO2 <10-15 Pa under Ar atmosphere. This study focuses on sapphire crystalline structure and its principle to the interface. The planes " a" and " b" are oxygen terminated structures and wet more by Al, whereas the " c" plane is an aluminum terminated structure. A wetting transition at 1273 K (1000 °C) was obtained and a solid surface tension proves the capillarity trends of the couple.

  16. Substrate temperature and oxygen pressure dependence of pulsed laser-deposited Sr ferrite films

    NASA Astrophysics Data System (ADS)

    Papakonstantinou, P.; O'Neill, M.; Atkinson, R.; Salter, I. W.; Gerber, R.

    1996-01-01

    The effect of substrate temperature and oxygen pressure on the microstructure, magnetic and magneto-optical properties of Sr ferrite (SrM) films grown on (001) single-crystal sapphire substrates by pulsed laser deposition has been investigated. Polycrystalline SrM films with perpendicular magnetic anisotropy could be prepared under a wide range of oxygen pressures and relatively high temperatures, sufficient to crystallise the material. However, an almost exclusive c-axis orientation normal to the film plane could be attained only at a narrow operational window centered at 0.1 mbar and 840°C. The magneto-optical properties of the films were comparable to those of the bulk barium hexaferrite single-crystal material. In addition, results obtained by atomic force microscopy provide convincing evidence that the growth of Sr ferrite on sapphire takes place by a spiral growth mechanism.

  17. Epitaxial growth, electrical and optical properties of a-plane InN on r-plane sapphire

    SciTech Connect

    Ajagunna, A. O.; Iliopoulos, E.; Tsiakatouras, G.; Tsagaraki, K.; Androulidaki, M.; Georgakilas, A.

    2010-01-15

    The heteroepitaxy of a-plane (1120) InN films on r-plane (1102) sapphire substrates, by nitrogen radio frequency plasma-assisted molecular beam epitaxy, has been investigated and compared to that of c-plane (0001) InN. The epitaxial growth of a-plane InN proceeded through the nucleation, growth, and coalescence of three-dimensional islands, resulting in surface roughness that increased monotonically with epilayer thickness. The full width at half maximum of (1120) x-ray diffraction rocking curves decreased significantly with increasing InN thickness, characteristic of structural improvement, and it reached the value of 24 arcmin for a 1 {mu}m thick film. Hall-effect measurements exhibited a similar dependence of electron concentration and mobility on thickness for both the a- and c-plane InN films. The analysis of the Hall-effect measurements, by considering the contribution of two conducting layers, indicates a similar accumulation of low mobility electrons with N{sub s}>10{sup 14} cm{sup -2} at the films' surface/interfacial region for both the a- and c-plane InN films. From optical transmittance measurements, the absorption edge of 0.768 eV was determined for the 1 {mu}m a-plane film, consistent with the expected Burstein-Moss effect. Photoluminescence spectra exhibited a lower energy peak at 0.631 eV, suggesting defect-related transitions.

  18. Ultraviolet-visible absorption spectra of N-doped TiO2 film deposited on sapphire

    NASA Astrophysics Data System (ADS)

    Park, Jaewon; Lee, Jung-Yup; Cho, Jun-Hyung

    2006-12-01

    The optical-response properties of nitrogen(N)-doped titanium dioxide (TiO2) films are investigated by means of a combination of ultraviolet-visible absorption spectroscopy and first-principles density-functional calculations. The TiO2 films were epitaxially grown on the sapphire substrate by the pulsed laser deposition method. The doping of N atoms was achieved by 70keV of N+ ion implantation, followed by postirradiation heat treatment at 550°C for 2h in air. We find that when 5×1016 (1×1017)Nions/cm2 were implanted into the epitaxially grown TiO2 film, the absorption edge is reproducibly shifted to lower energy by about 0.06 (0.12)eV together with a significant optical absorption extending into the visible-light region. These experimental data can be explained by our calculated band structure of N-doped TiO2, where the bands originating from N 2p states locate above the valence band edge, while the band gap narrowing due to the mixing of N with O 2p states is 0.04eV.

  19. Growth mechanism and electronic properties of epitaxial In{sub 2}O{sub 3} films on sapphire

    SciTech Connect

    Wang, Ch. Y.; Kirste, L.; Roehlig, C. C.; Koehler, K.; Cimalla, V.; Ambacher, O.; Morales, F. M.; Manuel, J. M.; Garcia, R.

    2011-11-01

    In this work, we report on the epitaxial growth of high-quality cubic indium oxide thick films on c-plane sapphire substrates using a two-step growth process. The epitaxial relationship of In{sub 2}O{sub 3} on (0001) Al{sub 2}O{sub 3} has been investigated. The (222) plane spacing and lattice parameter of a most strain-relaxed high-quality In{sub 2}O{sub 3} film have been determined to be 292.58 pm and 1013.53 pm, respectively. The electronic properties in dependence of the film thickness are interpreted using a three-region model. The density at the surface and interface totals (3.3{+-}1.5)x10{sup 13}cm{sup -2}, while the background electron density in the bulk was determined to be (2.4{+-}0.5)x10{sup 18}cm{sup -3}. Furthermore, post treatments such as irradiation via ultraviolet light and ozone oxidation have been found to influence only the surface layer, while the bulk electronic properties remain unchanged.

  20. UV laser with an acousto-optic intra-cavity control for GaN-sapphire cut

    NASA Astrophysics Data System (ADS)

    Gradoboev, Yury G.; Kazaryan, Mishik A.; Mokrushin, Yury M.; Shakin, Oleg V.

    2012-09-01

    A copper vapor laser is proposed as the basic component of the installation for processing of sapphire substrates with a GaN-coating. Laser radiation is transformed to UV range by optical frequency doubling. Powerful UV lasers are prospective tools for crystal cutting, photolithography and recording of the fiber Bragg gratings. The proposed approach is more promising in comparison with the use of excimer radiation because of instabilities of excimer laser generation and low coherence of its radiation, which makes difficult precise focusing and using interference pattern of UV radiation for exposing materials. UV laser based on second harmonic radiation of copper vapors laser has been designed. The UV laser system of high operation stability has been developed with output power 1 W at wavelengths 255.5 nm, 271.1 nm, 289.1 nm and coherence length radiation about 4 cm. The original intra-cavity acousto-optic control of output radiation is developed. It is allows adjusting frequency and on-off time ratio of output laser pulses with high accuracy. The stable heat regime was achieved for an active element of copper vapor laser̤ The laser system allows to select an optimum mode of ultra-violet radiation exposition for production of different optical elements. Intra-cavity acousto-optic cell was used for controlling of single pulse amplitude and number of pulses without any power supply tuning providing the stable operation of the laser system.

  1. Ti:sapphire-pumped deep-infrared femtosecond optical parametric oscillator based on CdSiP2.

    PubMed

    Ramaiah-Badarla, V; Chaitanya Kumar, S; Esteban-Martin, A; Devi, K; Zawilski, K T; Schunemann, P G; Ebrahim-Zadeh, M

    2016-04-15

    We report on a femtosecond optical parametric oscillator (OPO) for the deep-infrared (deep-IR) based on the Kerr-lens-mode-locked Ti:sapphire laser as the pump source. By deploying a novel cascaded intracavity arrangement, comprising a femtosecond OPO based on the nonlinear crystal, CdSiP2, synchronously pumped internal to a MgO:PPLN femtosecond OPO, we have generated broadly tunable radiation across 5958-8117 nm using rapid static cavity delay tuning, with a maximum power of 64 μW at 6791 nm, limited by the absorption in mirror substrates as well as polarization-dependent intracavity losses. The deep-IR idler power exhibits excellent passive stability of better than 1.1% rms over 2 h, with a spectral bandwidth as large as ∼650 nm at ∼6800 nm. The demonstrated concept is generic and can be similarly deployed in other operating time scales and wavelength regions, also using different laser pump sources and nonlinear materials.

  2. Channel Temperature Determination for AlGaN/GaN HEMTs on SiC and Sapphire

    NASA Technical Reports Server (NTRS)

    Freeman, Jon C.; Mueller, Wolfgang

    2008-01-01

    Numerical simulation results (with emphasis on channel temperature) for a single gate AlGaN/GaN High Electron Mobility Transistor (HEMT) with either a sapphire or SiC substrate are presented. The static I-V characteristics, with concomitant channel temperatures (T(sub ch)) are calculated using the software package ATLAS, from Silvaco, Inc. An in-depth study of analytical (and previous numerical) methods for the determination of T(sub ch) in both single and multiple gate devices is also included. We develop a method for calculating T(sub ch) for the single gate device with the temperature dependence of the thermal conductivity of all material layers included. We also present a new method for determining the temperature on each gate in a multi-gate array. These models are compared with experimental results, and show good agreement. We demonstrate that one may obtain the channel temperature within an accuracy of +/-10 C in some cases. Comparisons between different approaches are given to show the limits, sensitivities, and needed approximations, for reasonable agreement with measurements.

  3. Surface tension of liquid Al-Cu and wetting at the Cu/Sapphire solid-liquid interface

    NASA Astrophysics Data System (ADS)

    Schmitz, J.; Brillo, J.; Egry, I.

    2014-02-01

    For the study of the interaction of a liquid alloy with differently oriented single crystalline sapphire surfaces precise surface tension data of the liquid are fundamental. We measured the surface tension of liquid Al-Cu contactlessly on electromagnetically levitated samples using the oscillating drop technique. Data were obtained for samples covering the entire range of composition and in a broad temperature range. The surface tensions can be described as linear functions of temperature with negative slopes. Moreover, they decrease monotonically with an increase of aluminium concentration. The observed behaviour with respect to both temperature and concentration is in agreement with a thermodynamic model calculation using the regular solution approximation. Surface tensions were used to calculate interfacial energies from the contact angles of liquid Cu droplets, deposited on the C(0001), A(11-20), R(1-102) surfaces of an α-Al2O3 substrate. The contact angles were measured by means of the sessile drop method at 1380 K. In the Cu/α-Al2O3 system, no anisotropy is evident neither for the contact angles nor for the interfacial energies of different surfaces. The work of adhesion of this system is isotropic, too.

  4. Preparation of AlGaN/GaN Heterostructures on Sapphire Using Light Radiation Heating Metal-Organic Chemical Vapor Deposition at Low Pressure

    NASA Astrophysics Data System (ADS)

    Zhou, Yu-Gang; Shen, Bo; Zhang, Rong; Li, Wei-Ping; Chen, Peng; Chen, Zhi-Zhong; Gu, Shu-Lin; Shi, Yi; Z, Huang C.; Zheng, You-Dou

    2000-08-01

    AlGaN/GaN heterostructures on sapphire substrate were fabricated by using light radiation heating metalorganic chemical vapor deposition. Photoluminescence excitation spectra show that there are two abrupt slopes corresponding to the absorption edges of AlGaN and GaN, respectively. X-ray diffraction spectra clearly exhibit the GaN (0002), (0004), and AlGaN (0002), (0004) diffraction peaks, and no diffraction peak other than those from the GaN {0001} and AlGaN {0001} planes is found. Reciprocal space mapping indicates that there is no tilt between the AlGaN layer and the GaN layer. All results also indicate that the sample is of sound quality and the Al composition in the AlGaN layer is of high uniformity.

  5. Single crystalline Er{sub 2}O{sub 3}:sapphire films as potentially high-gain amplifiers at telecommunication wavelength

    SciTech Connect

    Kuznetsov, A. S.; Sadofev, S.; Schäfer, P.; Kalusniak, S.; Henneberger, F.

    2014-11-10

    Single crystalline thin films of Er{sub 2}O{sub 3}, demonstrating efficient 1.5 μm luminescence of Er{sup 3+} at room temperature were grown on Al{sub 2}O{sub 3} substrate by molecular beam epitaxy. The absorption coefficient at 1.536 μm was found to reach 270 cm{sup −1} translating in a maximal possible gain of 1390 dBcm{sup −1}. In conjunction with the 10% higher refractive index as compared to Al{sub 2}O{sub 3}, this opens the possibility to use Er{sub 2}O{sub 3}:sapphire films as short-length waveguide amplifiers in telecommunication.

  6. Response to “Comment on ‘Twin symmetry texture of energetically condensed niobium thin films on sapphire substrate’ ” [J. Appl. Phys. 112, 016101 (2012)

    DOE PAGES

    Zhao, X.; Philips, L.; Reece, C. E.; ...

    2012-07-01

    Welander is correct about the misidentified crystal-directions in the top-view sapphire lattice (Fig. 4 [Zhao et al., J. Appl. Phys. 110, 033523 (2011)]). He is also correct about the misorientation of the pole figures in Fig. 4. In Fig. 1 of this response, we have corrected these errors. Perhaps because of these errors, Welander misconstrued our discussion of the Nbcrystal growth as claiming a new 3D registry. That was not our intention. Rather, we wished to highlight the role of energetic condensation that drives low-defect crystal growth by a combination of non-equilibrium sub-plantation that disturbs the substrate lattice and thermalmore » annealing that annihilates defects and promotes large-grain crystal growth.« less

  7. X-ray and transmission electron microscopy characterization of twinned CdO thin films grown on a-plane sapphire by metalorganic vapour phase epitaxy

    NASA Astrophysics Data System (ADS)

    Martínez-Tomás, M. C.; Zúñiga-Pérez, J.; Vennéguès, P.; Tottereau, O.; Muñoz-Sanjosé, V.

    2007-07-01

    In the frame of studying II VI oxides of interest in optoelectronic technologies, the structural properties of CdO films grown by metalorganic vapour phase epitaxy on a-plane sapphire substrates have been analysed. The study has been performed by means of X-ray diffraction and cross-sectional transmission electron microscopy measurements. CdO films have been found to grow along [111] with the presence of twinned domains. Asymmetrical reflections have been used to study the crystalline quality of the twinned domains, independent of each other, as well as to determine their relative population. The analysis has been made as a function of growth conditions: VI/II precursors molar ratio and growth temperature.

  8. Effects of Nano- and Microscale SiO2 Masks on the Growth of a-Plane GaN Layers on r-Plane Sapphire

    NASA Astrophysics Data System (ADS)

    Son, Ji-Su; Miao, Cao; Honda, Yoshio; Yamaguchi, Masahito; Amano, Hiroshi; Seo, Yong Gon; Hwang, Sung-Min; Baik, Kwang Hyeon

    2013-08-01

    We report on the combined effects of a-plane GaN layers on a nanoscale patterned insulator on an r-plane sapphire substrate and epitaxial lateral overgrowth (ELOG) techniques. The fully coalescent a-plane GaN layer using nano- and microscale SiO2 masks showed the formation of nano- and microscale voids on the masks, respectively. Atomic force microscopy (AFM) measurements revealed a surface roughness of 0.63 nm and a submicron pit density of ˜7.8 ×107 cm-2. Photoluminescence (PL) intensity was enhanced by a factor of 9.0 in comparison with that of a planar sample. Omega full-width at half-maximum (FWHM) values of the (11bar 20) X-ray rocking curve along the c- and m-axes were 553 and 788 arcsec, respectively. A plan-view cathodoluminescence (CL) mapping image showed high luminescence intensity on the SiO2 masks.

  9. Low-Temperature Heteroepitaxial Growth of Single-Domain V-Doped ZnO Films on c-Face Sapphire

    NASA Astrophysics Data System (ADS)

    Chiba, Hiroshi; Mori, Tatsuya; Kawashima, Tomoyuki; Washio, Katsuyoshi

    2015-05-01

    High-quality single-domain (ZnO[11-20]//Al2O3[10-10]) ZnO heteroepitaxial growth on c-face sapphire [Al2O3(0001)] substrate at low temperature was investigated by vanadium (V) doping at growth temperatures between 150°C and 450°C using radiofrequency (RF) magnetron sputtering. In low-temperature growth at 150°C and 200°C, 30° twisted domains (ZnO[10-10]//Al2O3[10-10]) were eliminated and good in-plane crystal orientation was obtained for V doping of about 2 at.% to 3 at.%. Single domains were grown from the early stage. From the changes of surface morphology and growth rate, it was considered that migration during the growth was enhanced due to the increase of the diffusion energy of adatoms, while random nucleation was suppressed.

  10. Neutron irradiation and post annealing effect on sapphire by positron annihilation.

    PubMed

    Han, Jie-cai; Zhang, Hai-liang; Zhang, Ming-fu; Wang, Bao-yi; Li, Zhuo-xin; Xu, Cheng-hai; Guo, Huai-xin

    2010-09-01

    Sapphire single crystals grown by an improved Kyropoulos-like method are irradiated by fast neutron flux. The irradiated doses of neutron are 10(18) and 10(19)n/cm(2). The infrared transmission spectra of sapphire were studied before and after irradiation. The irradiated samples were annealed at 200, 400, 600, 800 and 1000 degrees C for 10min in ambient atmosphere. Positron annihilation studies have been carried out before and after neutron irradiation. The experimentally measured positron lifetime in the pristine specimen is 143ps. There were aluminum vacancies produced in sapphire crystals after neutron irradiation. The positron lifetime increased with the dose of neutron flux. A longer value tau(2) was found after annealing at 600 degrees C, which indicated vacancies were aggregated with each other. The second long-time component tau(2) has been found to increase with the annealing temperature. There was almost no change in peak position of the CDB spectra after neutron irradiation and isothermal annealing. The chemical environment of core in sapphire did not change greatly after neutron irradiation.

  11. Vanadium-rich ruby and sapphire within Mogok Gemfield, Myanmar: implications for gem color and genesis

    NASA Astrophysics Data System (ADS)

    Zaw, Khin; Sutherland, Lin; Yui, Tzen-Fu; Meffre, Sebastien; Thu, Kyaw

    2015-01-01

    Rubies and sapphires are of both scientific and commercial interest. These gemstones are corundum colored by transition elements within the alumina crystal lattice: Cr3+ yields red in ruby and Fe2+, Fe3+, and Ti4+ ionic interactions color sapphires. A minor ion, V3+ induces slate to purple colors and color change in some sapphires, but its role in coloring rubies remains enigmatic. Trace element and oxygen isotope composition provide genetic signatures for natural corundum and assist geographic typing. Here, we show that V can dominate chromophore contents in Mogok ruby suites. This raises implications for their color quality, enhancement treatments, geographic origin, exploration and exploitation and their comparison with rubies elsewhere. Precise LA-ICP-MS analysis of ruby and sapphire from Mogok placer and in situ deposits reveal that V can exceed 5,000 ppm, giving V/Cr, V/Fe and V/Ti ratios up to 26, 78, and 97 respectively. Such values significantly exceed those found elsewhere suggesting a localized geological control on V-rich ruby distribution. Our results demonstrate that detailed geochemical studies of ruby suites reveal that V is a potential ruby tracer, encourage comparisons of V/Cr-variation between ruby suites and widen the scope for geographic typing and genesis of ruby. This will allow more precise comparison of Asian and other ruby fields and assist confirmation of Mogok sources for rubies in historical and contemporary gems and jewelry.

  12. A century of sapphire crystal growth: origin of the EFG method

    NASA Astrophysics Data System (ADS)

    Harris, Daniel C.

    2009-08-01

    A. Verneuil developed flame fusion to grow sapphire and ruby on a commercial scale around 1890. Flame fusion was further perfected by Popov in the Soviet Union in the 1930s and by Linde Air Products Co. in the U.S. during World War II. Union Carbide Corp., the successor to Linde, developed Czochralski crystal growth for sapphire laser materials in the 1960s. Edge-Defined Film-Fed Growth (EFG) was invented by H. Labelle in the 1960s and the Heat Exchanger Method (HEM) was invented by F. Schmid and D. Viechnicki in 1967. Both methods were commercialized in the 1970s. Gradient solidification was invented in Israel in the 1970s by J. Makovsky. The Horizontal Directional Solidification Method (HDSM) was invented by Kh. S. Bagdasorov in the Soviet Union in the 1960s. Kyropoulos growth of sapphire, known as GOI crystal growth in the Soviet Union, was developed by M. Musatov at the State Optical Institute in St. Petersburg in the 1970s. Today, half of the world's sapphire is produced by the GOI method.

  13. Vacuum-ultraviolet characterization of sapphire, ALON, and spinel near the band gap

    NASA Astrophysics Data System (ADS)

    Thomas, Michael E.; Tropf, William J.; Gilbert, Summer L.

    1993-06-01

    UV properties are presently investigated immediately above and below the bandgap of polycrystalline Al23O27N5 (ALON), single-crystal sapphire, and spinel. Room-temperature transmission and reflection measurements are conducted on these materials from 2500 to 1150 A; the corresponding absorption coefficient at the band gap is represented by Urbach's rule.

  14. Fully-depleted silicon-on-sapphire and its application to advanced VLSI design

    NASA Technical Reports Server (NTRS)

    Offord, Bruce W.

    1992-01-01

    In addition to the widely recognized advantages of full dielectric isolation, e.g., reduced parasitic capacitance, transient radiation hardness, and processing simplicity, fully-depleted silicon-on-sapphire offers reduced floating body effects and improved thermal characteristics when compared to other silicon-on-insulator technologies. The properties of this technology and its potential impact on advanced VLSI circuitry will be discussed.

  15. Light refraction in sapphire plates with a variable angle of crystal optical axis to the surface

    SciTech Connect

    Vetrov, V. N. Ignatenkov, B. A.

    2013-05-15

    The modification of sapphire by inhomogeneous plastic deformation makes it possible to obtain plates with a variable angle of inclination of the crystal optical axis to the plate surface. The refraction of light in this plate at perpendicular and oblique incidence of a parallel beam of rays is considered. The algorithm of calculating the refractive index of extraordinary ray and the birefringence is proposed.

  16. New sapphire and ruby components and their manufacture using diamond abrasives

    NASA Astrophysics Data System (ADS)

    Sauser, D.

    The properties of synthetic aluminum oxides (sapphire and ruby) and their applications in watchmaking (watch bearings and watchglasses) and as hard-wearing components such as centering devices for optical fibres and water jet nozzles for material cutting are discussed. Examples are given of the use of diamonds tools for machining such components, including sawing, drilling, grinding and polishing operations.

  17. High-power solid-state sapphire whispering gallery mode maser.

    PubMed

    Creedon, Daniel L; Benmessaï, Karim; Tobar, Michael E; Hartnett, John G; Bourgeois, Pierre-Yves; Kersale, Yann; Le Floch, Jean-Michel; Giordano, Vincent

    2010-03-01

    We present new results on a cryogenic solid-state maser frequency standard, which relies on the excitation of whispering gallery (WG) modes within a doped monocrystalline sapphire resonator (alpha-Al2O3). Included substitutively within the highest purity HEMEX-grade sapphire crystal lattice are Fe2+ impurities at a concentration of parts per million, an unavoidable result of the manufacturing process. Mass conversion of Fe2+ to Fe3+ ions was achieved by thermally annealing the sapphire in air. Above-threshold maser oscillation was then excited in the resonator at zero applied DC magnetic field by pumping high-Q WG modes coincident in frequency with the electron spin resonance (ESR) energy levels of the Fe3+ spin population. A 2 stage annealing process was undertaken for a sapphire resonator with exceptionally low Fe3+ concentration, resulting in an improvement of 6 orders of magnitude in output power for this particular crystal, and exceeding the previous best implementation of our scheme in another crystal by nearly 20 dB. This represents an output signal 7 orders of magnitude more powerful than a typical commercial hydrogen maser. At this power level, we estimate a limit on the frequency stability of order 1 x 10(-17)/square root(tau) due to the Schawlow-Townes fundamental thermal noise limit.

  18. Transmittance enhancement of sapphires with antireflective subwavelength grating patterned UV polymer surface structures by soft lithography.

    PubMed

    Lee, Soo Hyun; Leem, Jung Woo; Yu, Jae Su

    2013-12-02

    We report the total and diffuse transmission enhancement of sapphires with the ultraviolet curable SU8 polymer surface structures consisting of conical subwavelength gratings (SWGs) at one- and both-side surfaces for different periods. The SWGs patterns on the silicon templates were transferred into the SU8 polymer film surface on sapphires by a simple and cost-effective soft lithography technique. For the fabricated samples, the surface morphologies, wetting behaviors, and optical characteristics were investigated. For theoretical optical analysis, a rigorous coupled-wave analysis method was used. At a period of 350 nm, the sample with SWGs on SU8 film/sapphire exhibited a hydrophobic surface and higher total transmittance compared to the bare sapphire over a wide wavelength of 450-1000 nm. As the period of SWGs was increased, the low total transmittance region of < 85% was shifted towards the longer wavelengths and became broader while the diffuse transmittance was increased (i.e., larger haze ratio). For the samples with SWGs at both-side surfaces, the total and diffuse transmittance spectra were further enhanced compared to the samples with SWGs at one-side surface. The theoretical optical calculation results showed a similar trend to the experimentally measured data.

  19. A mechanically compensated sapphire oscillator optimized for operation at 40 Kelvin

    NASA Technical Reports Server (NTRS)

    Dick, G. J.; Wang, R. T.

    2000-01-01

    We present features for a second-generation thermomechanically compensated sapphire resonator. The new design shares the short thermal time constants characteristic of previously developed 10K and 77K CSO resonators. This, together with a thermal ballast methodology, allows effective compensation of temperature fluctuations over a wide range of time scales.

  20. "You Hafta Push": Using Sapphire's Novel to Teach Introduction to American Government

    ERIC Educational Resources Information Center

    Pappas, Christine

    2007-01-01

    Using fiction in the classroom can dramatize public policy issues and political science concepts, therefore, making them more real and relevant to students. Sapphire's 1996 novel "Push" puts a face on welfare, rape, incest, child abuse, educational inequalities, homophobia, and AIDS. I also use this novel to discuss the public policy process,…

  1. Nobel Lecture: Growth of GaN on sapphire via low-temperature deposited buffer layer and realization of p -type GaN by Mg doping followed by low-energy electron beam irradiation*

    NASA Astrophysics Data System (ADS)

    Amano, Hiroshi

    2015-10-01

    This is a personal history of one of the Japanese researchers engaged in developing a method for growing GaN on a sapphire substrate, paving the way for the realization of smart television and display systems using blue LEDs. The most important work was done in the mid to late 1980s. The background to the author's work and the process by which the technology enabling the growth of GaN and the realization of p -type GaN was established are reviewed.

  2. Growth of GaN on Sapphire via Low-Temperature Deposited Buffer Layer and Realization of p-Type GaN by Mg Doping Followed by Low-Energy Electron Beam Irradiation

    NASA Astrophysics Data System (ADS)

    Amano, Hiroshi

    2015-12-01

    This is a personal history of one of the Japanese researchers engaged in developing a method for growing GaN on a sapphire substrate, paving the way for the realization of smart television and display systems using blue LEDs. The most important work was done in the mid- to late 80s. The background to the author's work and the process by which the technology enabling the growth of GaN and the realization of p-type GaN was established are reviewed.

  3. Quasi ?non-destructive? laser ablation-inductively coupled plasma-mass spectrometry fingerprinting of sapphires

    NASA Astrophysics Data System (ADS)

    Guillong, M.; Günther, D.

    2001-07-01

    A homogenized 193 nm excimer laser with a flat-top beam profile was used to study the capabilities of LA-ICP-MS for 'quasi' non-destructive fingerprinting and sourcing of sapphires from different locations. Sapphires contain 97-99% of Al 2O 3 (corundum), with the remainder composed of several trace elements, which can be used to distinguish the origin of these gemstones. The ablation behavior of sapphires, as well as the minimum quantity of sample removal that is required to determine these trace elements, was investigated. The optimum ablation conditions were a fluency of 6 J cm -2, a crater diameter of 120 μm, and a laser repetition rate of 10 Hz. The optimum time for the ablation was determined to be 2 s, equivalent to 20 laser pulses. The mean sample removal was 60 nm per pulse (approx. 3 ng per pulse). This allowed satisfactory trace element determination, and was found to cause the minimum amount of damage, while allowing for the fingerprinting of sapphires. More than 40 isotopes were measured using different spatial resolutions (20-120 μm) and eight elements were reproducibly detected in 25 sapphire samples from five different locations. The reproducibility of the trace element distribution is limited by the heterogeneity of the sample. The mean of five or more replicate analyses per sample was used. Calibration was carried out using NIST 612 glass reference material as external standard. The linear dynamic range of the ICP-MS (nine orders of magnitude) allowed the use of Al, the major element in sapphire, as an internal standard. The limits of detection for most of the light elements were in the μg g -1 range and were better for heavier elements (mass >85), being in the 0.1 μg g -1 range. The accuracy of the determinations was demonstrated by comparison with XRF analyses of the same set of samples. Using the quantitative analyses obtained using LA-ICP-MS, natural sapphires from five different origins were statistically classified using ternary plots and

  4. Growth of Low Defect Density Gallium Nitride (GaN) Films on Novel Tantalum Carbide (TaC) Substrates for Improved Device Performance

    DTIC Science & Technology

    2009-05-01

    on SiC substrates by pulse laser deposition (PLD) (10) and on magnesium oxide ( MgO ) substrates by electron beam evaporation (11), using TaC films...matched to GaN than currently used substrates. We created the TaC substrate, using pulse laser deposition (PLD) of TaC onto (0001) SiC substrates at...films grown on SiC or sapphire, and they contained more than an order of magnitude fewer dislocations compared to a typical value of 4 x 109 cm–2

  5. Crystalline polarity of ZnO thin films deposited under dc external bias on various substrates

    NASA Astrophysics Data System (ADS)

    Ohsawa, Takeo; Tsunoda, Kei; Dierre, Benjamin; Zellhofer, Caroline; Grachev, Sergey; Montigaud, Hervé; Ishigaki, Takamasa; Ohashi, Naoki

    2017-04-01

    Effects of the nature of substrates, either crystalline or non-crystalline, on the structure and properties of ZnO films deposited by sputtering were investigated. This study focuses mainly on the role of the external electric bias applied to substrates during magnetron sputtering deposition in controlling crystalline polarity, i.e., Zn-face or O-face, and the resulting film properties. It was found that polarity control was achieved on silica and silicon substrates but not on sapphire substrates. The substrate bias did influence the lattice parameters in the structural formation; however, the selection of the substrate type had a significant influence on the defect structures and the film properties.

  6. Substrate Preparations in Epitaxial ZnO Film Growth

    NASA Technical Reports Server (NTRS)

    Zhu, Shen; Su, C.-H.; Lehoczky, S. L.; Harris, M. T.; Callahan, M. J.; George, M. A.

    2000-01-01

    Epitaxial ZnO films were grown on the two polar surfaces (O-face and Zn-face) of (0001) ZnO single crystal substrates using off-axis magnetron sputtering deposition. Annealing-temperature dependence of ZnO substrates was studied. ZnO films grown on sapphire substrates have also been investigated for comparison purposes and the annealing temperature of A1203 substrates is 1000 C. Substrates and films were characterized using photoluminescence (PL) spectrum, x-ray diffraction, atomic force microscope, energy dispersive spectrum, and electric transport measurements. It has been found that the ZnO film properties were different when films were grown on the two polarity surfaces of ZnO substrates and the A1203 substrates. An interesting result shows that high temperature annealing of ZnO single crystals will improve the surface structure on the O-face surface rather than the opposite surface. The measurements of homoepitaxial ZnO films indicate that the O-terminated surface is better for ZnO epitaxial film growth.

  7. Growth modes and epitaxy of FeAl thin films on a-cut sapphire prepared by pulsed laser and ion beam assisted deposition

    SciTech Connect

    Yao, Xiang; Trautvetter, Moritz; Ziemann, Paul; Wiedwald, Ulf

    2014-01-14

    FeAl films around equiatomic composition are grown on a-cut (112{sup ¯}0) sapphire substrates by ion beam assisted deposition (IBAD) and pulsed laser deposition (PLD) at ambient temperature. Subsequent successive annealing is used to establish chemical order and crystallographic orientation of the films with respect to the substrate. We find a strongly [110]-textured growth for both deposition techniques. Pole figures prove the successful preparation of high quality epitaxial films by PLD with a single in-plane orientation. IBAD-grown films, however, exhibit three in-plane orientations, all of them with broad angular distributions. The difference of the two growth modes is attributed to the existence of a metastable intermediate crystalline orientation as concluded from nonassisted sputter depositions at different substrate temperatures. The formation of the chemically ordered crystalline B2 phase is accompanied by the expected transition from ferromagnetic to paramagnetic behavior of the films. In accordance with the different thermally induced structural recovery, we find a step-like magnetic transition to paramagnetic behavior after annealing for 1 h at T{sub A} = 300 °C for IBAD deposition, while PLD-grown films show a gradual decrease of ferromagnetic signals with rising annealing temperatures.

  8. In-rich Al x In1-x N grown by RF-sputtering on sapphire: from closely-packed columnar to high-surface quality compact layers

    NASA Astrophysics Data System (ADS)

    Núñez-Cascajero, A.; Valdueza-Felip, S.; Monteagudo-Lerma, L.; Monroy, E.; Taylor-Shaw, E.; Martin, R. W.; González-Herráez, M.; Naranjo, F. B.

    2017-02-01

    The structural, morphological, electrical and optical properties of In-rich Al x In1-x N (0  <  x  <  0.39) layers grown by reactive radio-frequency (RF) sputtering on sapphire are investigated as a function of the deposition parameters. The RF power applied to the aluminum target (0 W-150 W) and substrate temperature (300 °C-550 °C) are varied. X-ray diffraction measurements reveal that all samples have a wurtzite crystallographic structure oriented with the c-axis along the growth direction. The aluminum composition is tuned by changing the power applied to the aluminum target while keeping the power applied to the indium target fixed at 40 W. When increasing the Al content from 0 to 0.39, the room-temperature optical band gap is observed to blue-shift from 1.76 eV to 2.0  eV, strongly influenced by the Burstein-Moss effect. Increasing the substrate temperature, results in an evolution of the morphology from closely-packed columnar to compact. For a substrate temperature of 500 °C and RF power for Al of 150 W, compact Al0.39In0.61N films with a smooth surface (root-mean-square surface roughness below 1 nm) are produced.

  9. Promising new wavelengths for multi-photon microscopy: thinking outside the Ti:Sapphire box

    NASA Astrophysics Data System (ADS)

    Norris, Greg; Amor, Rumelo; Dempster, John; Amos, William B.; McConnell, Gail

    2013-02-01

    Multi-photon excitation (MPE) imaging is dominated by the Ti:Sapphire laser as the source for excitation. However, it is limited when considering 3PE of common fluorophores and efficient 2PE of UV dyes which require wavelengths beyond the range of the Ti:Sapphire. Two ultra-short pulsed sources are presented as alternatives: a novel optical parametric oscillator (OPO) geometry (1400-1600nm) and the sum-frequency mixing of an OPO and Yb-doped fibre laser, providing a tunable output (626-635nm). For long wavelengths, we report three-photon laser scanning microscopy (3PLSM) using a bi-directional pumped optical parametric oscillator (OPO) with signal wavelength output at 1500 nm. This novel laser was used to overcome the high optical loss in the infrared spectral region observed in laser scanning microscopes and objective lenses that renders them otherwise difficult to use for imaging. To test our system, we performed 3PLSM auto-fluorescence imaging of live plant cells at 1500 nm, specifically Spirogyra, and compared performance with two-photon excitation (2PLSM) imaging using a femtosecond pulsed Ti:Sapphire laser at 780 nm. Analysis of cell viability based on cytoplasmic organelle streaming and structural changes of cells revealed that at similar peak powers, 2PLSM caused gross cell damage after 5 minutes but 3PLSM showed little or no interference with cell function after 15 minutes. The 1500 nm OPO was thus shown to be a practical laser source for live cell imaging. For short wavelengths, we report the use of an all-solid-state ultra-short pulsed source specifically for two-photon microscopy at wavelengths shorter than those of the conventional Ti:Sapphire laser. Our approach involved sumfrequency mixing of the output from the long-wavelength OPO described above with residual pump radiation to generate fs-pulsed output in the red spectral region. We demonstrated the performance of our ultra-short pulsed system using fluorescently labelled and autofluorescent tissue

  10. GaN-Ready Aluminum Nitride Substrates for Cost-Effective, Very Low Dislocation Density III-Nitride LED's

    SciTech Connect

    Sandra Schujman; Leo Schowalter

    2010-10-15

    The objective of this project was to develop and then demonstrate the efficacy of a costeffective approach for a low defect density substrate on which AlInGaN LEDs can be fabricated. The efficacy of this “GaN-ready” substrate would then be tested by growing high efficiency, long lifetime InxGa1-xN blue LEDs. The approach used to meet the project objectives was to start with low dislocation density AlN single-crystal substrates and grow graded AlxGa1-xN layers on top. Pseudomorphic AlxGa1-xN epitaxial layers grown on bulk AlN substrates were used to fabricate light emitting diodes and demonstrate better device performance as a result of the low defect density in these layers when benched marked against state-of-the-art LEDs fabricated on sapphire substrates. The pseudomorphic LEDs showed excellent output powers compared to similar wavelength devices grown on sapphire substrates, with lifetimes exceeding 10,000 hours (which was the longest time that could reliably be estimated). In addition, high internal quantum efficiencies were demonstrated at high driving current densities even though the external quantum efficiencies were low due to poor photon extraction. Unfortunately, these pseudomorphic LEDs require high Al content so they emit in the ultraviolet. Sapphire based LEDs typically have threading dislocation densities (TDD) > 108 cm-2 while the pseudomorphic LEDs have TDD ≤ 105 cm-2. The resulting TDD, when grading the AlxGa1-xN layer all the way to pure GaN to produce a “GaN-ready” substrate, has varied between the mid 108 down to the 106 cm-2. These inconsistencies are not well understood. Finally, an approach to improve the LED structures on AlN substrates for light extraction efficiency was developed by thinning and roughening the substrate.

  11. Evaluation of the Quality of Sapphire Using X-Ray Rocking Curves and Double-Crystal X-Ray Topography

    DTIC Science & Technology

    1994-05-01

    hard, high-strength, chemically resistant optical windows; and sub- srates for the growth of epitaxial films. The quality of a sapphire crystal can... crystal diffractometer. Single- crystal sapphire may be grown by a variety of different methods, of which the more common are Verneuil (flame fusion...Linear features (L), which may represent slight variations in lattice parameter along the crystal growth front, or dislocation networks, ad small

  12. Experimental investigation about influences of longitudinal-mode structure of pumping source on a Ti:sapphire laser.

    PubMed

    Lu, Huadong; Su, Jing; Xie, Changde; Peng, Kunchi

    2011-01-17

    Using a multi-longitudinal-mode (MLM) and a single-longitudinal-mode (SLM) all-solid-state green lasers to be the pumping sources of a continuous-wave Ti:sapphire laser, respectively, the intensity-noise dependence of the Ti:sapphire laser on the longitudinal-mode structure of pumping sources is experimentally studied. The comparison between the theoretical prediction based on the quantum-mechanical model and the experimental measurement for the intensity-noise spectra is presented.

  13. Diamond LED substrate and novel quantum dots.

    PubMed

    Sung, James C; Sung, Michael

    2009-02-01

    Nitride LED (e.g., GaN) has become the mainstream of blue light source. The blue light can be converted to white light by exciting a phosphor (e.g., Nichia's YAG or Osram's TAG) with the complementary yellow emission. However, GaN is typically deposited on sapphire (Al2O3) substrates formed by crystal pulling or hexagonal (e.g., 4 H or 6 H) SiC wafers condensed from SiC vapor. In either case, the nitride lattice is ridden (e.g., 10(9)/cm2) with dislocations. The high dislocation density with sapphire is due to the large (>13%) lattice mismatch; and with hexagonal SiC, because of intrinsic defects. Cubic (beta) SiC may be deposited epitaxially using a CVD reactor onto silicon wafer by diffusing the interface and by chemical gradation. A reactive echant (e.g., hydrogen or fluorine) can be introduced periodically to gasify mis-aligned atoms. In this case, large single crystal wafers would be available for the manufacture of high bright LED with superb electro-optical efficiency. The SiC wafer may be coated with diamond film that can eliminate heat in real time. As a result of lower temperature, the nitride LED can be brighter and it will last longer. The blue light of GaN LED formed on SiC on Diamond (SiCON) LED may also be scattered by using novel quantum dots (e.g., 33 atom pairs of CdSe) to form a broad yellow light that blend in with the original blue light to form sunlight-like white light. This would be the ideal source for general illumination (e.g., for indoor) or backlighting (e.g., for LCD).

  14. Structure of a monoclinic polymorph of human carbonic anhydrase II with a doubled a axis

    SciTech Connect

    Robbins, Arthur H.; Domsic, John F.; Agbandje-McKenna, Mavis; McKenna, Robert

    2010-05-01

    The crystal structure of human carbonic anhydrase II with a doubled a axis from that of the usually observed monoclinic cell has been determined and refined to 1.4 Å resolution. The two molecules comprising the asymmetric unit are related by a noncrystallographic translation of ½ along a, but one of the molecules has two alternate orientations related by a rotation of approximately 2°. The crystal structure of human carbonic anhydrase II with a doubled a axis from that of the usually observed monoclinic unit cell has been determined and refined to 1.4 Å resolution. The diffraction data with h = 2n + 1 were systematically weaker than those with h = 2n. Consequently, the scaling of the data, structure solution and refinement were challenging. The two molecules comprising the asymmetric unit are related by a noncrystallographic translation of ½ along a, but one of the molecules has two alternate positions related by a rotation of approximately 2°. This rotation axis is located near the edge of the central β-sheet, causing a maximum distance disparity of 1.7 Å between equivalent atoms on the diametrically opposite side of the molecule. The crystal-packing contacts are similar to two sequential combined unit cells along a of the previously determined monoclinic unit cell. Abnormally high final R{sub cryst} and R{sub free} values (20.2% and 23.7%, respectively) are not unusual for structures containing pseudo-translational symmetry and probably result from poor signal to noise in the weak h-odd data.

  15. Formation of silicon nanocrystals in sapphire by ion implantation and the origin of visible photoluminescence

    SciTech Connect

    Yerci, S.; Serincan, U.; Dogan, I.; Tokay, S.; Genisel, M.; Aydinli, A.; Turan, R.

    2006-10-01

    Silicon nanocrystals, average sizes ranging between 3 and 7 nm, were formed in sapphire matrix by ion implantation and subsequent annealing. Evolution of the nanocrystals was detected by Raman spectroscopy and x-ray diffraction (XRD). Raman spectra display that clusters in the matrix start to form nanocrystalline structures at annealing temperatures as low as 800 deg. C in samples with high dose Si implantation. The onset temperature of crystallization increases with decreasing dose. Raman spectroscopy and XRD reveal gradual transformation of Si clusters into crystalline form. Visible photoluminescence band appears following implantation and its intensity increases with subsequent annealing process. While the center of the peak does not shift, the intensity of the peak decreases with increasing dose. The origin of the observed photoluminescence is discussed in terms of radiation induced defects in the sapphire matrix.

  16. Degradation of picosecond temporal contrast of Ti:sapphire lasers with coherent pedestals.

    PubMed

    Khodakovskiy, Nikita; Kalashnikov, Mikhail; Gontier, Emilien; Falcoz, Franck; Paul, Pierre-Mary

    2016-10-01

    Recompressed pulses from Ti:sapphire chirped-pulse lasers are accompanied by a slowly decaying post-pulse pedestal that is coherent with the main pulse. The pedestal typically consists of numerous pulses with temporal separation in the picosecond range. The source of this artifact lies in the Ti:sapphire active medium itself, both in the Kerr-lens mode-locked oscillator and in subsequent amplifiers. In the presence of substantial self-phase modulation, after recompression the post-pedestal generates a mirror-symmetric pre-pulse pedestal. This pedestal severely degrades the leading edge of the output pulse. This degradation is far more limiting than the original post-pedestal and severely lowers the achievable temporal contrast.

  17. Simple, picojoule-sensitive ultraviolet autocorrelator based on two-photon conductivity in sapphire.

    PubMed

    Leedle, Kenneth J; Urbanek, Karel E; Byer, Robert L

    2017-03-10

    We present a simple autocorrelator for ultraviolet pulses based on two-photon conductivity in a bench-top fabricatable sapphire sensor. We perform measurements on femtosecond 226-278 nm ultraviolet pulses from the third and fourth harmonics of a standard 76 MHz titanium sapphire oscillator and picosecond 266 nm pulses from the fourth harmonic of a 1064 nm 50 MHz neodymium vanadate oscillator. Our device is sensitive to 2.6 pJ ultraviolet pulses with peak powers below 20 W. These results represent the lowest measured autocorrelation peak powers by over one order of magnitude for a system with no reference pulse in the deep ultraviolet (<300  nm). The autocorrelator can potentially support UV pulse lengths from 50 fs-10s of picoseconds.

  18. Bend Properties of Sapphire Fibers at Elevated Temperatures. 1; Bend Survivability

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Sayir, Haluk

    1995-01-01

    The effect of temperature on the bend radius that a c-axis-oriented sapphire fiber can withstand was determined for fibers of various diameter. Bend stress rupture tests were performed for times of 1-100 h and temperatures of 300-1700 C. Fibers would survive the bend test undeformed, would fracture or would deform. The bend survival radius was determined to be the radius above which no fibers fractured or deformed for a given time-temperature treatment. It was found that the ability of fibers to withstand curvature decreases substantially with time and increasing temperature and that fibers of smaller diameter (46-83 micron) withstood smaller bend radii than would be expected from just a difference in fiber diameter when compared with the bend results of the fibers of large diameter (144 micron). This was probably due to different flaw populations, causing high temperature bend failure for the tested sapphire fibers of different diameters.

  19. Process for the Φ130 sapphire window element with long distance and high resolution

    NASA Astrophysics Data System (ADS)

    Xu, Zengqi; Su, Ying; Lei, Jianli; Guo, Rui; Zhang, Feng; Guo, Xinlong; Liu, Xuanmin; Sun, Taohui

    2016-10-01

    With the process test for the choice of materials, the test materials and the molds, the abrasives, the temperature and the different machining process monitoring parameters of the polishing machine, the process method and the quality control technology were figured out for the Φ130 sapphire window element with long distance and high resolution (hereinafter referred to as window element), meantime, the optimum process condition was determined to machine the element. The results were that the high resolution imaging window was processed with the surface roughness Ra of 0.639nm, the transmission distortion of λ/10 (λ=632.8nm), the parallel error of 5″, the resolution of 1.47″ and the focal length of 5 km, which can satisfy the imaging requirements better for the military photoelectric device for sapphire window with long distance and high resolution.

  20. High-Temperature Mechanical Properties of Cr(3+) Doped Sapphire Fibers

    NASA Technical Reports Server (NTRS)

    Sayir, A.; QuispeCancapa, J. J.; deArellanoLopez, A. R.; Gray, Hugh R. (Technical Monitor)

    2002-01-01

    High-temperature slow-crack growth of single crystal 10 wt% Cr2O3 - Al2O3 (nominal composition) fibers has been studied by tensile rupture experiments at 1400 C, under different stressing rates (0.5 to 41.5 MPa/s). Slow-crack growth (SCG) is less pronounced with increasing Cr2O3. Rupture stresses increased with the stressing rate from 397 MPa to 515 MPa, resulting in a SCG exponent, N=19. The Cr2O3 composition was analyzed by Energy Dispersed X-Ray Spectra (EDS) and fracture surfaces were studied by scanning electron microscopy (SEM). Results are compared with previous studies on 100-300 ppm Cr3(+) doped sapphire fibers and on commercial sapphire fibers.

  1. Two-photon imaging with 80 MHz and 1-GHz repetition rate Ti:sapphire oscillators

    NASA Astrophysics Data System (ADS)

    Studier, Hauke; Breunig, Hans Georg; König, Karsten

    2010-02-01

    We report on multiphoton optical imaging with a laser scanning microscope (TauMapTM, Jenlab GmbH) in combination with two different excitation fs-lasers: a 80 MHz Ti:sapphire oscillator generating spectrally tunable 100 fs pulses and a 1 GHz Ti:sapphire oscillator producing ultra broadband 6 fs pulses. While the ultra-broadband pulses enable simultaneous excitation of several different types of fluorophores due their large spectral width, the 100 fs pulses are spectrally more selective and require tuning the center wavelength to cover the same excitation range. The wavelength selectivity was confirmed in measurements with microspheres with absorption maxima in the green and blue spectral region. Furthermore, the potential of both lasers for imaging of human skin is evaluated.

  2. System design and relaxation oscillations of a titanium-sapphire laser. Master thesis

    SciTech Connect

    Erikson, W.L.

    1992-08-01

    A general method for designing a laser system is presented. Using the Ti:sapphire laser as an example, the requirements of stability, astigmatic compensation, and matching of the pump and cavity modes are addressed. Investigations into the relaxation oscillations of a Ti-sapphire laser are reported. Using four level laser rate equation theory, a technique is developed for analyzing relaxation oscillations exhibited by a laser. This technique presents a new and simple method for measuring the upper state lifetime and intrinsic cavity losses of a laser system. Beam-like vector solutions to Maxwell's equations are also presented. These solutions present a more detailed description of the polarization properties of laser beams. Experimental evidence of these properties is shown using an Argon laser.

  3. Simple, picojoule-sensitive ultraviolet autocorrelator based on two-photon conductivity in sapphire

    NASA Astrophysics Data System (ADS)

    Leedle, Kenneth J.; Urbanek, Karel E.; Byer, Robert L.

    2017-03-01

    We present a simple autocorrelator for ultraviolet pulses based on two-photon conductivity in a bench-top fabricatable sapphire sensor. We perform measurements on femtosecond 226 - 278 nm ultraviolet pulses from the third and fourth harmonics of a standard 76 MHz titanium sapphire oscillator and picosecond 266 nm pulses from the fourth harmonic of a 1064 nm 50 MHz neodymium vanadate oscillator. Our device is sensitive to 2.6 pJ ultraviolet pulses with peak powers below 20 W. These results represent the lowest measured autocorrelation peak powers by over one order of magnitude for a system with no reference pulse in the deep ultraviolet ( < 300 nm). The autocorrelator can potentially support UV pulse lengths from 50 fs - 10's of picoseconds.

  4. Design and analysis of large-core single-mode windmill single crystal sapphire optical fiber

    SciTech Connect

    Cheng, Yujie; Hill, Cary; Liu, Bo; Yu, Zhihao; Xuan, Haifeng; Homa, Daniel; Wang, Anbo; Pickrell, Gary

    2016-06-01

    We present a large-core single-mode “windmill” single crystal sapphire optical fiber (SCSF) design, which exhibits single-mode operation by stripping off the higher-order modes (HOMs) while maintaining the fundamental mode. The “windmill” SCSF design was analyzed using the finite element analysis method, in which all the HOMs are leaky. The numerical simulation results show single-mode operation in the spectral range from 0.4 to 2 μm in the windmill SCSF, with an effective core diameter as large as 14 μm. Such fiber is expected to improve the performance of many of the current sapphire fiber optic sensor structures.

  5. Formation of silicon nanocrystals in sapphire by ion implantation and the origin of visible photoluminescence

    NASA Astrophysics Data System (ADS)

    Yerci, S.; Serincan, U.; Dogan, I.; Tokay, S.; Genisel, M.; Aydinli, A.; Turan, R.

    2006-10-01

    Silicon nanocrystals, average sizes ranging between 3 and 7nm, were formed in sapphire matrix by ion implantation and subsequent annealing. Evolution of the nanocrystals was detected by Raman spectroscopy and x-ray diffraction (XRD). Raman spectra display that clusters in the matrix start to form nanocrystalline structures at annealing temperatures as low as 800°C in samples with high dose Si implantation. The onset temperature of crystallization increases with decreasing dose. Raman spectroscopy and XRD reveal gradual transformation of Si clusters into crystalline form. Visible photoluminescence band appears following implantation and its intensity increases with subsequent annealing process. While the center of the peak does not shift, the intensity of the peak decreases with increasing dose. The origin of the observed photoluminescence is discussed in terms of radiation induced defects in the sapphire matrix.

  6. Suppression of thermal lens effect in high-pulse-energy Ti:sapphire amplifiers

    NASA Astrophysics Data System (ADS)

    Wu, Fenxiang; Yu, Linpeng; Lu, Jun; Li, Wenkai; Xu, Yi; Leng, Yuxin

    2017-01-01

    In high-pulse-energy Ti:sapphire amplifiers with moderate repetition rate, the thermal lens effect can significantly decrease the energy extraction efficiency and increase the risk of optical damage. A new method, without introducing any additional components, is proposed to suppress the thermal lens effect in such amplifiers. By utilizing a particularly designed beam expander before the amplifier, specific expanding ratio and beam divergence can be introduced to the injected seed pulses, which can improve the spatial matching between the seed pulses and the pump pulses, and thus enhance the energy extraction efficiency. The enhancement of the energy extraction efficiency has reached approximately 10% in our experimental four-pass Ti:sapphire amplifier, and the good agreement between theoretical and experimental results also demonstrates the validity and feasibility of this method.

  7. Chemical reactivity imprint lithography on graphene: Controlling the substrate influence on electron transfer reactions

    NASA Astrophysics Data System (ADS)

    Wang, Qing Hua; Jin, Zhong; Kim, Ki Kang; Hilmer, Andrew; Paulus, Geraldine; Shih, Chih-Jen; Ham, Moon-Ho; Sanchez-Yamagishi, Javier; Watanabe, Kenji; Taniguchi, Takashi; Kong, Jing; Jarillo-Herrero, Pablo; Strano, Michael

    2012-02-01

    The chemical functionalization of graphene enables control over electronic properties and interactions with other materials. Graphene's chemical reactivity is strongly influenced by the underlying substrate. In this paper, we show a stark difference in the rate of electron transfer chemistry with aryl diazonium salts on monolayer graphene supported on a broad range of substrates. Reactions proceed rapidly when graphene is on SiO2 and Al2O3 (sapphire), but negligibly on alkyl-terminated and hexagonal boron nitride (hBN) surfaces. The effect cannot be explained by the overall graphene doping levels alone, and can instead be described using a reactivity model accounting for substrate-induced electron-hole puddles in graphene. Raman spectroscopic mapping is used to characterize the effect of the substrates on graphene. Reactivity imprint lithography (RIL) is demonstrated as a technique for spatially patterning chemical groups on graphene by patterning the underlying substrate, and is applied to the covalent tethering of proteins on graphene.

  8. Substrate compliance effects on buckle driven delamination in thin gold film systems.

    SciTech Connect

    Yeager, John.; Cordill, Megan J.; Adams, David Price; Moody, Neville Reid; Corona, Edmundo; Kennedy, Marian S.; Bahr, David F.; Reedy, Earl David, Jr.

    2010-10-01

    Film durability is a primary factor governing the use of emerging thin film flexible substrate devices where compressive stresses can lead to delamination and buckling. It is of particular concern in gold film systems found in many submicron and nanoscale applications. We are therefore studying these effects in gold on PMMA systems using compressively stressed tungsten overlayers to force interfacial failure and simulations employing cohesive zone elements to model the fracture process. Delamination and buckling occurred spontaneously following deposition with buckle morphologies that differed significantly from existing model predictions. Moreover, use of thin adhesive interlayers had no discernable effect on performance. In this presentation we will use observations and simulations to show how substrate compliance and yielding affects the susceptibility to buckling of gold films on compliant substrates. We will also compare the fracture energies and buckle morphologies of this study with those of gold films on sapphire substrates to show how changing substrate compliance affects buckle formation.

  9. INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Laser deposition of ZnO films on silicon and sapphire substrates

    NASA Astrophysics Data System (ADS)

    Zherikhin, A. N.; Khudobenko, A. I.; Williams, R. T.; Wilkinson, J.; User, K. B.; Xiong, Gang; Voronov, Valerii V.

    2003-11-01

    Laser deposition of zinc oxide films is studied. An intermediate screen is used to prevent microparticles formed during laser ablation of the target from falling on the film. The effect of deposition conditions on the morphology of the film, its electrical properties and crystal structure is studied. It is shown that the laser deposition technique can be used to obtain films of both types. The resistivity of the films was 0.07 Ω cm for films with the n-type conduction and 0.08 Ω cm for films with the p-type conduction. The photoluminescence studies of the films have shown that stimulated radiation is generated in the films under pump intensity exceeding 6 MW cm-2.

  10. Conductivity control of Sn-doped α-Ga2O3 thin films grown on sapphire substrates

    NASA Astrophysics Data System (ADS)

    Akaiwa, Kazuaki; Kaneko, Kentaro; Ichino, Kunio; Fujita, Shizuo

    2016-12-01

    We achieved the successful fabrication of Sn-doped α-Ga2O3 thin films with higher electron mobility and wider conductivity controls by improving the crystal quality. α-Ga2O3 films showed n-type conductivity with a maximum electron mobility of 24 cm2 V-1 s-1. The carrier concentration was successfully controlled in the range of 1017-1019 cm-3. Crystal defects such as dislocations severely compensate the free carriers in α-Ga2O3 films and restrict the mobility at low carrier concentrations. Therefore, to achieve further conductivity control and higher mobility, improving the crystallinity of α-Ga2O3 films is necessary.

  11. Elastic properties of indium nitrides grown on sapphire substrates determined by nano-indentation: In comparison with other nitrides

    NASA Astrophysics Data System (ADS)

    Yonenaga, Ichiro; Ohkubo, Yasushi; Deura, Momoko; Kutsukake, Kentaro; Tokumoto, Yuki; Ohno, Yutaka; Yoshikawa, Akihiko; Wang, Xin Qiang

    2015-07-01

    The hardness of wurtzite indium nitride (α-InN) films of 0.5 to 4 μm in thickness was measured by the nano-indentation method at room temperature. After investigation of crystalline quality by x-ray diffraction, the hardness and Young's modulus were determined to be 8.8 ± 0.4 and 184 ± 5 GPa, respectively, for the In (0001)- and N ( 000 1 ¯ ) -growth faces of InN films. The bulk and shear moduli were then derived to be 99 ± 3 and 77 ± 2 GPa, respectively. The Poisson's ratio was evaluated to be 0.17 ± 0.03. The results were examined comprehensively in comparison with previously reported data of InN as well as those of other nitrides of aluminum nitride and gallium nitride. The underlying physical process determining the moduli and hardness was examined in terms of atomic bonding and dislocation energy of the nitrides and wurtzite zinc oxide.

  12. Crystallographic Wet Chemical Etching of Semipolar GaN (11-22) Grown on m-Plane Sapphire Substrates.

    PubMed

    Kim, Jae-Kwan; Lee, Sung Nam; Song, Keun-Man; Yoon, Jae-Sik; Lee, Ji-Myon

    2015-07-01

    This paper reports the etch rates and etched surface morphology of semipolar GaN using a potassium hydroxide (KOH) solution. Semipolar (11-22) GaN could be etched easily using a KOH solution and the etch rate was higher than that of Ga-polar c-plane GaN (0001). The etch rate was anisotropic and the highest etch rate was measured to be approximately 116 nm/min for the (1011) plane and 62 nm/min for the (11-20) plane GaN using a 4 M KOH solution at 100 °C, resulting in specific surface features, such as inclined trigonal cells.

  13. Effects of time reversal symmetry on phonons in sapphire substrate for ZnO and GaN

    NASA Astrophysics Data System (ADS)

    Kunert, H. W.; Hoffmann, A.; Machatine, A. G. J.; Malherbe, J.; Barnas, J.; Kaczmarczyk, G.; Haboeck, U.; Seguin, R.

    2007-07-01

    Vibrational states in a crystal are classified according to the irreducible representations (irreps) of the corresponding factor group G0k/T. The wave vector k runs over the entire Brillouin zone (BZ). For trigonal BZs, the factor groups are determined by the symmetry points Γ, F, L, T, and the symmetry lines Λ, Σ, Y. When the irreps are complex, the time reversal symmetry has to be taken into account. Using the Frobenuis-Schur criterion adapted to space groups with real and complex irreps, we have investigated high symmetry points and lines of the phonons in trigonal crystals: Cr 2O 3,Fe 2O 3,Ti 2O 3,V 2O 3,FeCO 3,CaCO 3,CdCO 3,MgCO 3,MnCO 3,NaCO 3 and ZnCO 3, with the common space group D3d6( R3¯c). We have found several phonons which are influenced by the time reversal symmetry. Therefore, an extra degeneracy of phonons arises. The theoretical results are also compared with available experimental data.

  14. Use of Be(p,{alpha}) and Be(p,d) Reactions to Determine Be Content in Sapphire

    SciTech Connect

    Franklyn, C. B.

    2011-12-13

    Since natural coloured sapphire ({alpha}-Al{sub 2}O{sub 3}) commands a high gem stone market price there is a need for a reliable method of identifying artificially coloured sapphire that has an inherently lower value. Diffusing beryllium into sapphire at high temperatures results in a coloured stone virtually indistinguishable from a natural one. Beryllium can occur naturally in sapphire but at levels of <1 ppma. Beryllium diffused sapphire typically contains >10 ppma, which is difficult to determine in a non destructive way. It is possible to utilize nuclear reaction analysis techniques to determine the beryllium content in a macroscopically non destructive way. Kinematically ideal reactions are Be(p,{alpha}) and Be(p,d) which, for Ep = 0.5 to 0.9 MeV, exhibit distinct reaction product signatures well separated from other proton induced reactions in aluminium or oxygen. Due to the lack of comprehensive cross section data for the Be(p,{alpha}) and Be(p,d) reactions in the energy range of interest, a series of measurements were made at the Van de Graaff accelerator facility at Necsa to create a new data base. A further outcome of these measurements was a deviation in reported values for the non-Rutherfordian proton back-scatter cross section. These new data bases, which extend to Ep = 2.6MeV, can now facilitate a procedure for determining beryllium content in sapphire.

  15. Silicon-on-Sapphire Waveguides for Widely Tunable Coherent Mid-IR Sources

    DTIC Science & Technology

    2013-09-01

    Navy need to extend the range of spectrum dominance. Previous investigations have shown that this spectral range is of interest for applications that...mixing in silicon-on-sapphire waveguides. This project will address the Navy need to extend the range of spectrum dominance. Previous investigations...have shown that this spectral range is of interest for applications that include free- space communications, laser radar, optical countermeasures, and

  16. Sub-100 fs high average power directly blue-diode-laser-pumped Ti:sapphire oscillator

    NASA Astrophysics Data System (ADS)

    Rohrbacher, Andreas; Markovic, Vesna; Pallmann, Wolfgang; Resan, Bojan

    2016-03-01

    Ti:sapphire oscillators are a proven technology to generate sub-100 fs (even sub-10 fs) pulses in the near infrared and are widely used in many high impact scientific fields. However, the need for a bulky, expensive and complex pump source, typically a frequency-doubled multi-watt neodymium or optically pumped semiconductor laser, represents the main obstacle to more widespread use. The recent development of blue diodes emitting over 1 W has opened up the possibility of directly diode-laser-pumped Ti:sapphire oscillators. Beside the lower cost and footprint, a direct diode pumping provides better reliability, higher efficiency and better pointing stability to name a few. The challenges that it poses are lower absorption of Ti:sapphire at available diode wavelengths and lower brightness compared to typical green pump lasers. For practical applications such as bio-medicine and nano-structuring, output powers in excess of 100 mW and sub-100 fs pulses are required. In this paper, we demonstrate a high average power directly blue-diode-laser-pumped Ti:sapphire oscillator without active cooling. The SESAM modelocking ensures reliable self-starting and robust operation. We will present two configurations emitting 460 mW in 82 fs pulses and 350 mW in 65 fs pulses, both operating at 92 MHz. The maximum obtained pulse energy reaches 5 nJ. A double-sided pumping scheme with two high power blue diode lasers was used for the output power scaling. The cavity design and the experimental results will be discussed in more details.

  17. Self-seeding of a pulsed double-grating Ti:sapphire laser oscillator

    SciTech Connect

    Tamura, Koji

    2008-04-01

    A self-seeded pulsed double-grating Ti:sapphire laser oscillator consisting of a grazing incidence cavity geometry with a pair of gratings and a standing-wave cavity pumped by a frequency-doubled Nd:YAG laser was developed and characterized. With self-seeding, narrow-linewidth single-longitudinal-mode (SLM) operation and SLM scanning were possible with a reduced lasing threshold, which was desirable for the intended applications.

  18. A microwave exciter for Cs frequency standards based on a sapphire-loaded cavity oscillator.

    PubMed

    Koga, Y; McNeilage, C; Searls, J H; Ohshima, S

    2001-01-01

    A low noise and highly stable microwave exciter system has been built for Cs atomic frequency standards using a tunable sapphire-loaded cavity oscillator (SLCO), which works at room temperature. This paper discusses the successful implementation of a control system for locking the SLCO to a long-term reference signal and reports an upper limit of the achieved frequency tracking error 6 x 10(-15) at tau = 1 s.

  19. A Ti:Sapphire laser for the new polarized electron source

    SciTech Connect

    Frisch, J.; Woods, M.B.; Zolotorev, M.

    1992-10-01

    The SLAC polarized electron source uses a laser driven photo cathode gun. We have developed a Titanium Sapphire laser at SLAC to replace the dye laser currently used for the source. The new laser is designed to operate at wavelengths between 750 and 850 nm while producing 400mJ of energy in 1.6 ns pulses at 120 Hz. Installation on the accelerator is expected in January of 1993.

  20. Surface-induced anisotropic orientations of interfacial ethanol molecules at air/sapphire (1-102) and ethanol/sapphire (1-102) interfaces

    SciTech Connect

    Sung, J.; Waychunas, G. A.; Shen, Y. R.

    2011-06-01

    Sum frequency vibrational spectroscopy was used to study the interfacial arrangement of ethanol molecules at the vapor/α-Al{sub 2}O{sub 3} (1{bar 1}02 ) and α-Al{sub 2}O{sub 3} (1{bar 1}02 )/ethanol liquid interfaces. The spectra in the C-H range show that ethanol molecules adsorbed from vapor onto α-Al{sub 2}O{sub 3} (1{bar 1}02 ) surface have a welldefined anisotropic arrangement following the structure of the α-Al{sub 2}O{sub 3} (1{bar 1}02 ) surface. The arrangement can be explained by the formation of two specific hydrogen bonds between the adsorbed ethanol molecule and hydroxyls on the sapphire surface. At the α-Al{sub 2}O{sub 3} (1{bar 1}02 )/ethanol liquid interface, the first ethanol monolayer assumes a similar anisotropic arrangement as in the case of an ethanol monolayer on the dry sapphire surface. The second monolayer has a rather broad orientation distribution that is azimuthally nearly isotropic, but with molecules flipped 180 degrees with respect to those in the first monolayer.

  1. Orientation of Vanadium Dioxide Grains on Various Substrates

    NASA Astrophysics Data System (ADS)

    Rivera, Felipe; Davis, Robert; Vanfleet, Richard

    2010-10-01

    Crystalline vanadium dioxide VO2 experiences a fast and reversible semiconductor-to-metal structural phase transition near 68^oC. The changes exhibited during this phase transition comprise a well known change in resistivity of several orders of magnitude, as well as a significant drop in optical transmittance in the infrared. Due to the changes in these optical and electronic properties, vanadium dioxide shows promise as a material to be used in many applications ranging from thermochromic window coatings to optoelectronic devices. However, since there is a structural component to the phase transition of VO2, it is of interest to study the orientation of the crystalline grains deposited. Substrates such as glass, SiO2, Sapphire, and TiO2 have been used for the deposition of this material. We used orientation imaging microscopy to study and characterize the orientation of the grains deposited on several of these substrates. Here we present results on this study.

  2. Large-aperture broadband sapphire windows for common aperture, target acquisition, tracking, and surveillance systems

    NASA Astrophysics Data System (ADS)

    Askinazi, Joel

    1997-06-01

    State of the art optical sensing systems performing target acquisition/tracking and surveillance functions are being designed to incorporate a number of sensors into one package. These include visual and MWIR cameras, FLIRs, and laser range finders. These combined systems are being configured to view through a common aperture window. Typical window diameters are to eleven inches, but some surveillance applications have windows approaching twenty inches in diameter. These sensor windows typically operate in hostile environments including very high pressure differentials, large thermal gradients, and severe rain and sand abrasion. EMI/EMC protection and de-icing capabilities are also commonly required. For airborne applications and to minimize thermal gradients, thinner, lightweight, high strength windows are also necessary. Sapphire is an ideal window material to satisfy these requirements due to its high strength, UV-MWIR bandpass, minimal optical scatter, excellent index of refraction homogeneity and very high scratch/impact resistance. Associated optical fabrication, grid lithography and optical coating processes have been developed at Hughes Danbury for sapphire windows. This paper addresses the development of a family of large aperture, broadband sapphire windows which also provide EMI/EMC protection and de-icing capabilities. The resulting design configuration and performance characteristics are also addressed. Future technology development requirements are also discussed.

  3. Refractive index and phase transformation of sapphire under shock pressures up to 210 GPa

    NASA Astrophysics Data System (ADS)

    Cao, Xiuxia; Wang, Yuan; Li, Xuhai; Xu, Liang; Liu, Lixin; Yu, Yin; Qin, Rui; Zhu, Wenjun; Tang, Shihui; He, Lin; Meng, Chuanmin; Zhang, Botao; Peng, Xusheng

    2017-03-01

    Under shock pressures up to 210 GPa, we measured the refractive index of sapphire at a wavelength of 1550 nm by performing plate impact experiments in order to investigate its refractive-index change behaviors and phase transitions along the Hugoniot state. There were two discontinuities in the refractive index at ˜65 to 92 GPa and ˜144 to 163 GPa, respectively. Moreover, above the Hugoniot elastic limit, the pressure dependence of the refractive index was divided into three segments, and there were large differences in their pressure-change trends: the refractive index decreased evidently with pressure in the first segment (˜20 to 65 GPa), remained nearly constant from ˜92 to ˜144 GPa in the second segment, and obviously increased with pressure in the last segment (˜163 to 210 GPa). Our first-principles calculations suggest that the observed discontinuities were closely related to the corundum-Rh2O3(II) and Rh2O3(II)-CaIrO3 structural transitions, and the shock-induced vacancy point defects could be one factor causing these great discrepancies in pressure-change trends. This work provides sapphire refractive-index information in a megabar-pressure range and clear evidence of its shock structural transitions. This not only has a great significance for the velocity correction of laser interferometer experiments and the analysis of sapphire high-pressure properties but also indicates a possible approach to explore the shock transitions of transparent materials.

  4. A reliable low-maintenance flashlamp-pumped Ti:sapphire laser operating at 120 PPS

    SciTech Connect

    Witte, K.H.

    1994-03-01

    Flashlamp-pumped Ti:sapphire lasers have been reported to produce high-energy pulses with broad tunability. However, with the flashlamps operated close to their explosion energy, and thermal loading effects in the laser rod, these lasers were restricted to low repetition rates (typically around 10 PPS). Higher repetition rates at constant laser pulse energy reduce the flashlamp lifetime drastically. The author reports on a reliable flashlamp-pumped Ti:sapphire laser that has been operating at 120 PPS for over 10{sup 9} shots with the only cavity or pump chamber maintenance being flashlamp changes less than every 2{times}10{sup 8} pulses -- the lowest maintenance reported. A specular dual-lamp pump chamber was used to pump a 4 mm {times} 6 inches, 0.1% doped Ti:sapphire rod. This resulted in a very low lasing threshold, which ensured a stable output at low pump levels. The criterion for pump power was to obtain a highly stable output at the edge of the selected tuning range, from 790 to 860 nm. The combination of flashlamp walls, flashlamp flow tubes, and rod solarization.

  5. Bonding Lexan and sapphire to form high-pressure, flame-resistant window

    NASA Technical Reports Server (NTRS)

    Richardson, William R.; Walker, Ernie D.

    1987-01-01

    Flammable materials have been studied in normal gravity and microgravity for many years. Photography plays a major role in the study of the combustion process giving a permanent visual record that can be analyzed. When these studies are extended to manned spacecraft, safety becomes a primary concern. The need for a high-pressure, flame-resistant, shatter-resistant window permitting photographic recording of combustion experiments in manned spacecraft prompted the development of a method for bonding Lexan and sapphire. Materials that resist shattering (e.g., Lexan) are not compatible with combustion experiments; the material loses strength at combustion temperatures. Sapphire is compatible with combustion temperatures in oxygen-enriched atmospheres but is subject to shattering. Combining the two materials results in a shatter-resistant, flame-resistant window. Combustion in microgravity produces a low-visibility flame; however, flame propagation and flame characteristics are readily visible as long as there is no deterioration of the image. Since an air gap between the Lexan and the sapphire would reduce transmission, a method was developed for bonding these unlike materials to minimize light loss.

  6. Milli-electronvolt monochromatization of hard X-rays with a sapphire backscattering monochromator

    PubMed Central

    Sergueev, I.; Wille, H.-C.; Hermann, R. P.; Bessas, D.; Shvyd’ko, Yu. V.; Zając, M.; Rüffer, R.

    2011-01-01

    A sapphire backscattering monochromator with 1.1 (1) meV bandwidth for hard X-rays (20–40 keV) is reported. The optical quality of several sapphire crystals has been studied and the best crystal was chosen to work as the monochromator. The small energy bandwidth has been obtained by decreasing the crystal volume impinged upon by the beam and by choosing the crystal part with the best quality. The monochromator was tested at the energies of the nuclear resonances of 121Sb at 37.13 keV, 125Te at 35.49 keV, 119Sn at 23.88 keV, 149Sm at 22.50 keV and 151Eu at 21.54 keV. For each energy, specific reflections with sapphire temperatures in the 150–300 K region were chosen. Applications to nuclear inelastic scattering with these isotopes are demonstrated. PMID:21862862

  7. Increased signals from short-wavelength-excited fluorescent molecules using sub-Ti:Sapphire wavelengths.

    PubMed

    Norris, G; Amor, R; Dempster, J; Amos, W B; McConnell, G

    2012-11-01

    We report the use of an all-solid-state ultrashort pulsed source specifically for two-photon microscopy at wavelengths shorter than those of the conventional Ti:Sapphire laser. Our approach involves sum-frequency mixing of the output from an optical parametric oscillator (λ= 1400-1640 nm) synchronously pumped by a Yb-doped fibre laser (λ= 1064 nm), with the residual pump radiation. This generated an fs-pulsed output tunable in the red spectral region (λ= 620-636 nm, ~150 mW, 405 fs, 80 MHz, M(2) ~ 1.3). We demonstrate the performance of our ultrashort pulsed system using fluorescently labelled and autofluorescent tissue, and compare with conventional Ti:Sapphire excitation. We observe a more than 3-fold increase in fluorescence signal intensity using our visible laser source in comparison with the Ti:Sapphire laser for two-photon excitation at equal illumination peak powers of 1.16 kW or less.

  8. High-harmonic generation by field enhanced femtosecond pulses in metal-sapphire nanostructure

    PubMed Central

    Han, Seunghwoi; Kim, Hyunwoong; Kim, Yong Woo; Kim, Young-Jin; Kim, Seungchul; Park, In-Yong; Kim, Seung-Woo

    2016-01-01

    Plasmonic high-harmonic generation (HHG) drew attention as a means of producing coherent extreme ultraviolet (EUV) radiation by taking advantage of field enhancement occurring in metallic nanostructures. Here a metal-sapphire nanostructure is devised to provide a solid tip as the HHG emitter, replacing commonly used gaseous atoms. The fabricated solid tip is made of monocrystalline sapphire surrounded by a gold thin-film layer, and intended to produce EUV harmonics by the inter- and intra-band oscillations of electrons driven by the incident laser. The metal-sapphire nanostructure enhances the incident laser field by means of surface plasmon polaritons, triggering HHG directly from moderate femtosecond pulses of ∼0.1 TW cm−2 intensities. The measured EUV spectra exhibit odd-order harmonics up to ∼60 nm wavelengths without the plasma atomic lines typically seen when using gaseous atoms as the HHG emitter. This experimental outcome confirms that the plasmonic HHG approach is a promising way to realize coherent EUV sources for nano-scale near-field applications in spectroscopy, microscopy, lithography and atto-second physics. PMID:27721374

  9. Tuning the Interfacial Thermal Conductance between Polystyrene and Sapphire by Controlling the Interfacial Adhesion.

    PubMed

    Zheng, Kun; Sun, Fangyuan; Tian, Xia; Zhu, Jie; Ma, Yongmei; Tang, Dawei; Wang, Fosong

    2015-10-28

    In polymer-based electric microdevices, thermal transport across polymer/ceramic interface is essential for heat dissipation, which limits the improvement of the device performance and lifetime. In this work, four sets of polystyrene (PS) thin films/sapphire samples were prepared with different interface adhesion values, which was achieved by changing the rotation speeds in the spin-coating process. The interfacial thermal conductance (ITC) between the PS films and the sapphire were measured by time domain thermoreflectance method, and the interfacial adhesion between the PS films and the sapphire, as measured by a scratch tester, was found to increase with the rotation speed from 2000 to 8000 rpm. The ITC shows a similar dependence on the rotation speed, increasing up to a 3-fold from 7.0 ± 1.4 to 21.0 ± 4.2 MW/(m(2) K). This study demonstrates the role of spin-coating rotation speed in thermal transport across the polymer/ceramic interfaces, evoking a much simpler mechanical method for tuning this type of ITC. The findings of enhancement of the ITC of polymer/ceramic interface can shed some light on the thermal management and reliability of macro- and microelectronics, where polymeric and hybrid organic-inorganic nano films are employed.

  10. Study of discharge after electron irradiation in sapphires and polycrystalline alumina

    SciTech Connect

    Zarbout, K.; Moya, G.; Ahmed, A. Si; Damamme, G.; Kallel, A.

    2010-11-15

    The fraction R of charges undergoing discharge during the time separating two electron pulses is derived from the induced current method developed in a scanning electron microscope. Irradiation is performed via a 10 keV defocused electron beam and low current density. The evolution of R with temperature (in the range 300-663 K) obeys to an Arrhenius type relation. Activation energies connected with the processes involved are deduced. In sapphire, no discernible discharge is observed due to the dominance of deep traps. In silver doped sapphire, R increases sharply from 10% to 70% as the temperature rises from 360 to 420 K, with a corresponding activation energy of 0.51 eV. In contrast, in polycrystalline alumina processed by solid state sintering (grain diameters of 1.7, 2.7, and 4.5 {mu}m) the degree of discharge increases continuously with temperature and grain size. The enhancement with grain size indicates that the sintering conditions influence strongly the efficiency of a gettering effect. The activation energy below 573 K is about 0.12 eV independently of grain size. Above 573 K, a second activation energy of 0.26 eV appears for the smallest grain size sample. The results suggest that discharge may stem from a density of trapping states, associated to grain boundaries in sintered samples, rather than from a single trapping level linked to the doping element as Ag in sapphire.

  11. A Voltage Controlled Oscillator for a Phase-Locked Loop Frequency Synthesizer in a Silicon-on-Sapphire Process

    SciTech Connect

    Garrison, Sean

    2009-05-21

    Engineers from a government-owned engineering and manufacturing facility were contracted by government-owned research laboratory to design and build an S-band telemetry transmitter using Radio Frequency Integrated Circuit (RFIC) technology packaged in a Low-Temperature Co-fired Ceramic (LTCC) Multi-Chip Module. The integrated circuit technology chosen for the Phase-Locked Loop Frequency Synthesizer portion of the telemetry transmitter was a 0.25 um CMOS process that utilizes a sapphire substrate and is fabricated by Peregrine Semiconductor corporation. This thesis work details the design of the Voltage Controlled Oscillator (VCO) portion of the PLL frequency synthesizer and constitutes an fully integrated VCO core circuit and a high-isolation buffer amplifier. The high-isolation buffer amplifier was designed to provide 16 dB of gain for 2200-3495 MHz as well as 60 dB of isolation for the oscillator core to provide immunity to frequency pulling due to RF load mismatch. Actual measurements of the amplifier gain and isolation showed the gain was approximately 5 dB lower than the simulated gain when all bond-wire and test substrate parasitics were taken into account. The isolation measurements were shown to be 28 dB at the high end of the frequency band but the measurement was more than likely compromised due to the aforementioned bond-wire and test substrate parasitics. The S-band oscillator discussed in this work was designed to operate over a frequency range of 2200 to 2300 MHz with a minimum output power of 0 dBm with a phase-noise of -92 dBc/Hz at a 100 kHz offset from the carrier. The tuning range was measured to be from 2215 MHz to 2330 MHz with a minimum output power of -7 dBm over the measured frequency range. A phase-noise of -90 dBc was measured at a 100 kHz offset from the carrier.

  12. RF Magnetron Sputtering Grown Cu2O Film Structural, Morphological, and Electrical Property Dependencies on Substrate Type.

    PubMed

    Ahn, Heejin; Um, Youngho

    2015-03-01

    We investigated the structural, morphological, and electrical properties of cuprous oxide (Cu2O) film dependency on substrate type. Thin films grown using RF magnetron sputtering were characterized by scanning electron microscopy, X-ray diffraction (XRD), and Hall effect measurements. Cu2O thin films were deposited onto sapphire (0001), Si (100), and MgO (110) substrates, and showed Cu2O single phase only, which was confirmed by XRD measurement. Relatively larger compressive strain existed in Cu2O film grown on sapphire and Si, while a smaller tensile strain appeared in Cu2O film grown on MgO. Cu2O thin film crystallite sizes showed a linear dependence on strain. Moreover, film carrier concentration and mobility increased with increasing strain, while resistivity decreased with decreasing strain. Cu2O film strain due to induced strain opens the possibility of controlling structural and electrical properties in device applications.

  13. Very strong photoluminescence emission from GaN grown on amorphous silica substrate by gas source MBE

    NASA Astrophysics Data System (ADS)

    Asahi, H.; Iwata, K.; Tampo, H.; Kuroiwa, R.; Hiroki, M.; Asami, K.; Nakamura, S.; Gonda, S.

    1999-05-01

    Polycrystalline GaN layers showing very strong photoluminescence (PL) intensities are successfully grown on amorphous fused silica (SiO 2) substrates by gas source molecular beam epitaxy (MBE) using an ion removed electron cyclotron resonance radical cell. The PL intensity is larger than that of undoped single crystalline GaN grown on sapphire by gas source MBE and is comparable to that of Si-doped single crystalline GaN grown on sapphire by metalorganic vapor-phase epitaxy at Nichia Chemical. The PL peak emission is considered to be excitonic. Undoped GaN layers grown on silica substrates exhibit n-type conduction and both n- and p-type conductions are achieved by impurity doping. These results open up the area of "Polycrystalline Semiconductor Photonics".

  14. Au-assisted fabrication of nano-holes on c-plane sapphire via thermal treatment guided by Au nanoparticles as catalysts

    NASA Astrophysics Data System (ADS)

    Sui, Mao; Pandey, Puran; Li, Ming-Yu; Zhang, Quanzhen; Kunwar, Sundar; Lee, Jihoon

    2017-01-01

    Nanoscale patterning of sapphires is a challenging task due to the high mechanical strength, chemical stability as well as thermal durability. In this paper, we demonstrate a gold droplet assisted approach of nano-hole fabrication on c-plane sapphire via a thermal treatment. Uniformly distributed nano-holes are fabricated on the sapphire surface guided by dome shaped Au nanoparticles (NPs) as catalysts and the patterning process is discussed based on the disequilibrium of vapor, liquid, solid interface energies at the Au NP/sapphire interface induced by the Au evaporation at high temperature. Followed by the re-equilibration of interface energy, transport of alumina from the beneath of NPs to the sapphire surface can occur along the NP/sapphire interface resulting in the formation of nano-holes. The fabrication of nano-holes using Au NPs as catalysts is a flexible, economical and convenient approach and can find applications in various optoelectronics.

  15. Laser damage resistant anti-reflection microstructures in Raytheon ceramic YAG, sapphire, ALON, and quartz

    NASA Astrophysics Data System (ADS)

    Hobbs, Douglas S.; MacLeod, Bruce D.; Sabatino, Ernest, III; Hartnett, Thomas M.; Gentilman, Richard L.

    2011-06-01

    A study of the laser induced damage threshold (LiDT) of anti-reflection (AR) microstructures (ARMs) built in the end facets of metal ion doped yttrium aluminum garnet (YAG) laser gain material, has been conducted. Test samples of undoped and ytterbium-doped polycrystalline YAG produced by Raytheon Company were processed with ARMs in one surface and subjected to standardized pulsed LiDT testing at the near-infrared (NIR) wavelength of 1064nm. As received YAG samples with a simple commercial polish were also submitted to the damage tests for comparison, along with YAG samples that were treated with a single layer thin-film AR coating designed for maximum transmission at 1064nm. Additional samples of single crystal sapphire and quartz, and polycrystalline ALONTM windows were prepared with thin-film AR coatings and ARMs textures to expand the 1064nm laser damage testing to other important NIR transmitting materials. It was found that the pulsed laser damage resistance of ARMs textured ceramic YAG windows is 11 J/cm2, a value that is 43% higher than untreated ceramic YAG windows, suggesting that ARMs fabrication removed residual sub-surface damage, a factor that has been shown to be important for increasing the damage resistance of an optic. This conclusion is also supported by the high damage threshold values found with the single layer AR coatings on ceramic YAG where the coatings may have shielded the sub-surface polishing damage. Testing results for the highly polished sapphire windows also support the notion that better surface preparation produces higher damage resistance. The damage threshold for untreated sapphire windows exceeded 32 J/cm2 for one sample with an average of 27.5 J/cm2 for the two samples tested. The ARMs-treated sapphire windows had similar damage thresholds as the untreated material, averaging 24.9 J/cm2, a value 1.5 to 2 times higher than the damage threshold of the thin film AR coated sapphire windows.

  16. NpN-GaN/InxGa1-xN/GaN heterojunction bipolar transistor on free-standing GaN substrate

    NASA Astrophysics Data System (ADS)

    Lochner, Zachary; Jin Kim, Hee; Lee, Yi-Che; Zhang, Yun; Choi, Suk; Shen, Shyh-Chiang; Doug Yoder, P.; Ryou, Jae-Hyun; Dupuis, Russell D.

    2011-11-01

    Data and analysis are presented for NpN-GaN/InGaN/GaN double-heterojunction bipolar transistors (HBTs) grown and fabricated on a free-standing GaN (FS-GaN) substrate in comparison to that on a sapphire substrate to investigate the effect of dislocations in III-nitride HBT epitaxial structures. The performance characteristics of HBTs on FS-GaN exhibit a maximum collector current density of ˜12.3 kA/cm2, dc current gain of ˜90, and maximum differential gain of ˜120 without surface passivation, representing a substantial improvement over similar devices grown on sapphire. This is attributed to the reduction in threading dislocation density afforded by using a homoepitaxial growth on a high-crystalline-quality substrate. The minority carrier diffusion length increases significantly owing to not only a mitigated carrier trap effect via fewer dislocations, but also possibly reduced microscopic localized states.

  17. Impact of thermal stress on the piezoelectric and dielectric properties of PbTiO{sub 3} thick films on various substrates

    SciTech Connect

    Bai, Gang; Liu, Zhiguo; Yan, Xiaobing; Zhang, Changchun

    2014-08-07

    The impact of thermal stress on the polarization, as well as dielectric and piezoelectric properties of (001) oriented PbTiO{sub 3} (PTO) thick films deposited on various substrates was investigated based on Landau-Devonshire thermodynamic model. The results showed that dielectric and piezoelectric properties of PTO films depend strongly on the thermal stress in PTO films decided by the deposition temperature T{sub G} and the thermal expansion coefficients' difference between PTO films and substrates. For IC-compatible substrates such as Si, c-sapphire, and a-sapphire that induce tensile in-plane thermal stresses, the dielectric and piezoelectric responses and tunabilities of PTO films were enhanced. Whereas for PTO films on MgO, compressive thermal in-plane stresses can degraded the dielectric and piezoelectric responses and tunabilities of the films.

  18. Power electronics substrate for direct substrate cooling

    DOEpatents

    Le, Khiet [Mission Viejo, CA; Ward, Terence G [Redondo Beach, CA; Mann, Brooks S [Redondo Beach, CA; Yankoski, Edward P [Corona, CA; Smith, Gregory S [Woodland Hills, CA

    2012-05-01

    Systems and apparatus are provided for power electronics substrates adapted for direct substrate cooling. A power electronics substrate comprises a first surface configured to have electrical circuitry disposed thereon, a second surface, and a plurality of physical features on the second surface. The physical features are configured to promote a turbulent boundary layer in a coolant impinged upon the second surface.

  19. Characterization of the Performance of Sapphire Optical Fiber in Intense Radiation Fields, when Subjected to Very High Temperatures

    NASA Astrophysics Data System (ADS)

    Petrie, Christian M.

    The U.S. Department of Energy is interested in extending optically-based instrumentation from non-extreme environments to extremely high temperature radiation environments for the purposes of developing in-pile instrumentation. The development of in-pile instrumentation would help support the ultimate goal of understanding the behavior and predicting the performance of nuclear fuel systems at a microstructural level. Single crystal sapphire optical fibers are a promising candidate for in-pile instrumentation due to the high melting temperature and radiation hardness of sapphire. In order to extend sapphire fiber-based optical instrumentation to high temperature radiation environments, the ability of sapphire fibers to adequately transmit light in such an environment must first be demonstrated. Broadband optical transmission measurements of sapphire optical fibers were made in-situ as the sapphire fibers were heated and/or irradiated. The damage processes in sapphire fibers were also modeled from the primary knock-on event from energetic neutrons to the resulting damage cascade in order to predict the formation of stable defects that ultimately determine the resulting change in optical properties. Sapphire optical fibers were shown to withstand temperatures as high as 1300 °C with minimal increases in optical attenuation. A broad absorption band was observed to grow over time without reaching a dynamic equilibrium when the sapphire fiber was heated at temperatures of 1400 °C and above. The growth of this absorption band limits the use of sapphire optical fibers, at least in air, to temperatures of 1300 °C and below. Irradiation of sapphire fibers with gamma rays caused saturation of a defect center located below 500 nm, and extending as far as ~1000 nm, with little effect on the transmission at 1300 and 1550 nm. Increasing temperature during gamma irradiation generally reduced the added attenuation. Reactor irradiation of sapphire fibers caused an initial rapid

  20. Electron beam evaporation induced discoloration of reflective film on InGaN/sapphire in III-V LED TFFC device manufacturing

    NASA Astrophysics Data System (ADS)

    Neelakandan, Sivanantham; Chai, Chun Hoo; Chaw, Kam Hoe; Sae Tae, Veera

    2015-07-01

    In this paper, the discoloration of indium-gallium-nitride (InGaN) on sapphire (Al2O3) substrate after processing in electron beam vacuum evaporation for mirror metal evaporation has been investigated. Discoloration can be detrimental to light output of a light emitting diode (LED) as the light extraction through discolored gallium nitride (GaN) epitaxy is impacted. The investigation shows that the discoloration caused by an interaction between few factors such as the level of organic contamination present at the edges of the substrate, contact area with holding dome of the evaporator, thickness of the film deposited and radiation intensity from the evaporation source. Reflection Spectroscopy was used to quantify reflectivity of discolored mirror metal while X-ray fluorescence spectrometry (XRF) was used to measure film thickness and time of flight - secondary ion mass spectrometry (TOF-SIMS) was employed to measure organic contamination amounts. A residual gas analyzing (RGA) technique was established to detect potential discoloration to eliminate disruptions to manufacturing.

  1. Alteration of architecture of MoO₃ nanostructures on arbitrary substrates: growth kinetics, spectroscopic and gas sensing properties.

    PubMed

    Illyaskutty, Navas; Sreedhar, Sreeja; Sanal Kumar, G; Kohler, Heinz; Schwotzer, Matthias; Natzeck, Carsten; Pillai, V P Mahadevan

    2014-11-21

    MoO3 nanostructures have been grown in thin film form on five different substrates by RF magnetron sputtering and subsequent annealing; non-aligned nanorods, aligned nanorods, bundled nanowires, vertical nanorods and nanoslabs are formed respectively on the glass, quartz, wafer, alumina and sapphire substrates. The nanostructures formed on these substrates are characterized by AFM, SEM, GIXRD, XPS, micro-Raman, diffuse reflectance and photoluminescence spectroscopy. A detailed growth model for morphology alteration with respect to substrates has been discussed by considering various aspects such as surface roughness, lattice parameters and the thermal expansion coefficient, of both substrates and MoO3. The present study developed a strategy for the choice of substrates to materialize different types MoO3 nanostructures for future thin film applications. The gas sensing tests point towards using these MoO3 nanostructures as principal detection elements in gas sensors.

  2. High quality (In)GaN films on homoepitaxial substrates

    NASA Astrophysics Data System (ADS)

    Liu, Li; Zhang, Yong; Yin, Yian

    2017-02-01

    High quality GaN and InGaN epitaxial thin films were deposited by metal organic chemical vapor deposition (MOCVD). Two sets of thin film samples were prepared by varying the substrates and temperatures under a proper condition for achieving better optical properties. The morphological, crystalline quality and optical property of epitaxial layers were characterized by atomic force microscope (AFM), X-ray diffraction (XRD), photoluminescence (PL) and Raman spectra, respectively. It was found that the epitaxial layers grown on GaN homoepitaxial substrate have higher quality than those grown on sapphire substrate. The root mean square (RMS) of GaN film and InGaN film in AFM morphological were 0.5 nm, 2.7 nm respectively. The full width at half maximum (FWHM) of (102) in GaN film on GaN substrate was 33arcsec and the FWHM of (002) in InGaN film on GaN substrate was 50.58arcsec by XRD. The PL peaks of GaN film and InGaN film were 361 nm, 458 nm respectively. The E2 (high) of GaN film and InGaN film in Raman were both 567.08 cm-1.

  3. In situ reactor radiation-induced attenuation in sapphire optical fibers heated up to 1000 °C

    NASA Astrophysics Data System (ADS)

    Petrie, Christian M.; Blue, Thomas E.

    2015-01-01

    The purpose of this work was to determine the suitability of using instrumentation utilizing sapphire optical fibers in a high temperature nuclear reactor environment. For this, the broadband (500-2200 nm, or 0.56-2.48 eV) optical transmission in commercially available sapphire optical fibers was monitored in situ prior to, during, and after reactor irradiation. Portions of the sapphire fibers were heated to temperatures up to 1000 °C during irradiation. The sapphire fibers were irradiated, mostly at a neutron flux of 5.0 × 1011 n/cm2/s and a gamma dose rate of 28 kGy/h (dose in sapphire), to a total neutron fluence of 6.4 × 1016 n/cm2 and total gamma dose on the order of 1 MGy. Results were generally consistent with the results of previous in situ measurements of the transmission in unheated sapphire fibers during reactor irradiation. Added attenuation at 850, 1300, and 1550 nm, appears to be limited by the growth of radiation-induced defect centers that are located in the ultra violet to the visible range and is therefore less at 1300 and 1550 nm than at 850 nm. A linear increase in attenuation, due to displacement damage effects, was observed with increased irradiation time at constant reactor power. However, the rate of increase of the added attenuation during constant power reactor irradiation monotonically decreased with increasing temperature up to 1000 °C, with the most significant decrease occurring between 300 and 600 °C. Additional calculations predicted that the majority of (if not all of) the observed increases in attenuation during irradiation at 600 and 1000 °C were due to effects in the unheated sections of the irradiated sapphire fibers. These results suggest that, for a reactor radiation environment similar to that tested in this work, heating sapphire fibers to temperatures of 600 °C or greater during irradiation would significantly reduce (or possibly eliminate entirely) the rate of growth of the added attenuation in the sapphire fibers.

  4. Gain-switched 311-nm Ti:Sapphire laser might be a potential treatment modality for atopic dermatitis.

    PubMed

    Choi, Sun Young; Oh, Chang Taek; Kwon, Tae-Rin; Kwon, Hyun Jung; Choi, Eun Ja; Jang, Yu-Jin; Kim, Hye Sung; Chu, Hong; Mun, Seog Kyun; Kim, Myeung Nam; Kim, Beom Joon

    2016-09-01

    Phototherapy with 311-nm narrowband-UVB (NBUVB) is an effective adjuvant treatment modality for atopic dermatitis (AD). In this study, we evaluated the therapeutic effect of the newly developed gain-switched 311-nm Ti:Sapphire laser device using a NC/Nga mouse AD model. A total number of 50 mice were used in this study. Atopic dermatitis (AD) was induced in mice by exposure to Dermatophagoides farina. These, NC/Nga mice were then treated with conventional 311-nm NBUVB or the newly developed gain-switched 311-nm Ti:Sapphire laser. The clinical features, dermatitis severity scores, and scratching behavior were assessed. In addition, serologic analyses including inflammatory cytokines and histological analyses were performed. Gain-switched 311-nm Ti:Sapphire laser improved the AD-like skin lesions, severity, and symptoms of AD in the NC/Nga mouse model. This new laser also modulated the immune response found in the AD model, including hyper-IgE, upregulated Th2 cytokines, and the Th2-mediated allergic inflammatory reaction. Gain-switched 311-nm Ti:Sapphire laser shows therapeutic promise via an immune-modulation mechanism in an AD mouse model. These data suggest that gain-switched 311-nm Ti:Sapphire laser may be useful as a targeted phototherapy modality for AD.

  5. Molecular beam epitaxy of 2D-layered gallium selenide on GaN substrates

    NASA Astrophysics Data System (ADS)

    Lee, Choong Hee; Krishnamoorthy, Sriram; O'Hara, Dante J.; Brenner, Mark R.; Johnson, Jared M.; Jamison, John S.; Myers, Roberto C.; Kawakami, Roland K.; Hwang, Jinwoo; Rajan, Siddharth

    2017-03-01

    Large area epitaxy of two-dimensional (2D) layered materials with high material quality is a crucial step in realizing novel device applications based on 2D materials. In this work, we report high-quality, crystalline, large-area gallium selenide (GaSe) films grown on bulk substrates such as c-plane sapphire and gallium nitride (GaN) using a valved cracker source for Se. (002)-Oriented GaSe with random in-plane orientation of domains was grown on sapphire and GaN substrates at a substrate temperature of 350-450 °C with complete surface coverage. Higher growth temperature (575 °C) resulted in the formation of single-crystalline ɛ-GaSe triangular domains with six-fold symmetry confirmed by in-situ reflection high electron energy diffraction and off-axis x-ray diffraction. A two-step growth method involving high temperature nucleation of single crystalline domains and low temperature growth to enhance coalescence was adopted to obtain continuous (002)-oriented GaSe with an epitaxial relationship with the substrate. While six-fold symmetry was maintained in the two step growth, β-GaSe phase was observed in addition to the dominant ɛ-GaSe in cross-sectional scanning transmission electron microscopy images. This work demonstrates the potential of growing high quality 2D-layered materials using molecular beam epitaxy and can be extended to the growth of other transition metal chalcogenides.

  6. A modified pump laser system to pump the titanium sapphire laser

    NASA Technical Reports Server (NTRS)

    Petway, Larry B.

    1990-01-01

    As a result of the wide tunability of the titanium sapphire laser NASA has sited it to be used to perform differential absorption lidar (DIAL) measurements of H2O vapor in the upper and lower troposphere. The titanium sapphire laser can provide a spectrally narrow (0.3 to 1.0 pm), high energy (0.5 to 1.0 J) output at 727, 762, and 940 nm which are needed in the DIAL experiments. This laser performance can be obtained by addressing the line-narrowing issues in a master oscillator and the high energy requirement in a fundamental mode oscillator. By injection seeding, the single frequency property of the master oscillator can produce a line narrow high energy power oscillator. A breadboard model of the titanium sapphire laser that will ultimately be used in NASA lidar atmospheric sensing experiment is being designed. The task was to identify and solve any problem that would arise in the actual laser system. One such problem was encountered in the pump laser system. The pump laser that is designed to pump both the master oscillator and power oscillator is a Nd:YLF laser. Nd:YLF exhibits a number of properties which renders this material an attractive option to be used in the laser system. The Nd:YLF crystal is effectively athermal; it produces essentially no thermal lensing and thermally induced birefringence is generally insignificant in comparison to the material birefringence resulting from the uniaxial crystal structure. However, in application repeated fracturing of these laser rods was experience. Because Nd:YLF rods are not commercially available at the sizes needed for this application a modified pump laser system to replace the Nd:YLF laser rod was designed to include the more durable Nd:YAG laser rods. In this design, compensation for the thermal lensing effect that is introduced because of the Nd:YAG laser rods is included.

  7. Mutant presenilin2 promotes apoptosis through the p53/miR-34a axis in neuronal cells.

    PubMed

    Li, Liu-Hong; Tu, Qiu-Yun; Deng, Xiao-Hua; Xia, Jian; Hou, De-Ren; Guo, Ke; Zi, Xiao-Hong

    2017-05-01

    Neurodegenerative disorders have attracted attention in last decades due to their high incidence in the world. The p53/miR-34a axis triggers apoptosis and suppresses viability in multiple types of cells, but little is known about its role in neurodegenerative diseases. In this study, we showed that presenilin (PS)-2, a major gene associated with familial Alzheimer's disease (AD) could trigger the apoptosis through the p53/miR-34a axis in PC12 cells. First we found that PC12 cell viability was downregulated by PS-2 and mutant PS-2 overexpression, especially by mutant PS-2 overexpression. Then, we established a mutant PS-2-overexpressing PC12 cell line and confirmed that mutant PS-2 induced not only p53 but also miR-34a expression. The transfection of miR-34a inhibitor reversed PS-2-induced effects on cellular viability and apoptosis. Mutant PS-2 overexpression promoted caspase-3 expression, reduced Sirt1 and Bcl-2 expression, all of which were miR-34a downstream genes related with cell apoptosis. Moreover, mutant PS-2 also activated the p53/miR-34a axis and induced apoptosis in AD transgenic mice brain. These results implied that mutant PS-2 might promote the apoptosis of neuronal cells through triggering the p53/miR-34a axis. Altogether our results provide a novel insight into neurodegenerative disease and deepen our understandings of AD pathogenic processes.

  8. Thermal resistance optimization of GaN/substrate stacks considering thermal boundary resistance and temperature-dependent thermal conductivity

    NASA Astrophysics Data System (ADS)

    Park, K.; Bayram, C.

    2016-10-01

    Here, we investigate the effects of thermal boundary resistance (TBR) and temperature-dependent thermal conductivity on the thermal resistance of GaN/substrate stacks. A combination of parameters such as substrates {diamond, silicon carbide, silicon, and sapphire}, thermal boundary resistance {10-60 m2K/GW}, heat source lengths {10 nm-20 μm}, and power dissipation levels {1-8 W} are studied by using technology computer-aided design (TCAD) software Synopsys. Among diamond, silicon carbide, silicon, and sapphire substrates, the diamond provides the lowest thermal resistance due to its superior thermal conductivity. We report that due to non-zero thermal boundary resistance and localized heating in GaN-based high electron mobility transistors, an optimum separation between the heat source and substrate exists. For high power (i.e., 8 W) heat dissipation on high thermal conductive substrates (i.e., diamond), the optimum separation between the heat source and substrate becomes submicron thick (i.e., 500 nm), which reduces the hotspot temperature as much as 50 °C compared to conventional multi-micron thick case (i.e., 4 μm). This is attributed to the thermal conductivity drop in GaN near the heat source. Improving the TBR between GaN and diamond increases temperature reduction by our further approach. Overall, we provide thermal management design guidelines for GaN-based devices.

  9. Sub-surface channels in sapphire made by ultraviolet picosecond laser irradiation and selective etching.

    PubMed

    Moser, Rüdiger; Ojha, Nirdesh; Kunzer, Michael; Schwarz, Ulrich T

    2011-11-21

    We demonstrate the realization of sub-surface channels in sapphire prepared by ultraviolet picosecond laser irradiation and subsequent selective wet etching. By optimizing the pulse energy and the separation between individual laser pulses, an optimization of channel length can be achieved with an aspect ratio as high as 3200. Due to strong variation in channel length, further investigation was done to improve the reproducibility. By multiple irradiations the standard deviation of the channel length could be reduced to 2.2%. The achieved channel length together with the high reproducibility and the use of a commercial picosecond laser system makes the process attractive for industrial application.

  10. High efficiency light emitting diode with anisotropically etched GaN-sapphire interface

    NASA Astrophysics Data System (ADS)

    Lo, M. H.; Tu, P. M.; Wang, C. H.; Hung, C. W.; Hsu, S. C.; Cheng, Y. J.; Kuo, H. C.; Zan, H. W.; Wang, S. C.; Chang, C. Y.; Huang, S. C.

    2009-07-01

    We report the fabrication and study of high efficiency ultraviolet light emitting diodes with inverted micropyramid structures at GaN-sapphire interface. The micropyramid structures were created by anisotropic chemical wet etching. The pyramid structures have significantly enhanced the light output efficiency and at the same time also improved the crystal quality by partially relieving the strain and reducing the dislocation defects in GaN. The electroluminescent output power at normal direction was enhanced by 120% at 20 mA injection current and the output power integrated over all directions was enhanced by 85% compared to a reference sample.

  11. Parametric sensitivity and temporal dynamics of sapphire crystal growth via the micro-pulling-down method

    NASA Astrophysics Data System (ADS)

    Samanta, Gaurab; Yeckel, Andrew; Bourret-Courchesne, Edith D.; Derby, Jeffrey J.

    2012-11-01

    The micro-pulling-down (μ-PD) crystal growth of sapphire fibers, whose steady-state limits were the focus of our prior study [Samanta et al., Journal of Crystal Growth 335 (2011) 148-159], is further examined using a parametric sensitivity computation derived by linearizing the nonlinear model around a quasi-steady-state (QSS). In addition, transient analyses are performed to assess inherent stability and dynamic responses in this μ-PD system. Information from these two approaches enlarges our understanding of this particular process, and the approaches themselves are put forth as valuable complements to classical QSS analysis.

  12. Mechanical Behavior of Sapphire Reinforced Alumina Matrix Composites at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Jaskowiak, Martha H.; Eldridge, Jeffrey I.; Setlock, John A.; Gyekenyesi, John Z.

    1997-01-01

    Zirconia coated sapphire reinforced alumina matrix composites have been tested both after heat treatment to 1400 C and at temperatures ranging from 800 C to 1200 C in. air. Interfacial shear stress has also been measured with fiber pushout tests performed in air at room temperature, 800 C and 1OOO C. Matrix crack spacing was measured for the tensile tested composites and used to estimate interfacial shear stress up to 1200 C. Electron microscopy was used to determine the source of fiber fracture and to study interfacial failure within the composite.

  13. Hidden instabilities in the Ti:sapphire Kerr lens mode-locked laser.

    PubMed

    Kovalsky, M G; Hnilo, A A; González Inchauspe, C M

    1999-11-15

    It is experimentally shown that pulse-to-pulse instabilities in the output of Kerr lens mode-locked Ti:sapphire lasers are usual and that they can affect some of the pulse variables (e.g., the spot size) and not others (e.g., pulse duration and energy). These instabilities are not detectable in the averaged signals (such as the autocorrelation of the pulse) that are customarily used for controlling the laser. But, if they are present but are disregarded, these instabilities have undesirable consequences in almost any application. A simple way to detect and eliminate the instabilities is described.

  14. Autonomous cryogenic sapphire oscillators employing low vibration pulse-tube cryocoolers at NMIJ

    NASA Astrophysics Data System (ADS)

    Ikegami, Takeshi; Watabe, Ken-ichi; Yanagimachi, Shinya; Takamizawa, Akifumi; Hartnett, John G.

    2016-06-01

    Two liquid-helium-cooled cryogenic sapphire-resonator oscillators (CSOs), have been modified to operate using cryo-refrigerators and low-vibration cryostats. The Allan deviation of the first CSO was evaluated to be better than 2 x 10-15 for averaging times of 1 s to 30 000 s, which is better than that of the original liquid helium cooled CSO. The Allan deviation of the second CSO is better than 4 x 10-15 from 1 s to 6 000 s averaging time.

  15. 0.1-Hz 1-PW Ti:Sapphire Laser Facility

    NASA Astrophysics Data System (ADS)

    Lee, Seong Ku; Yu, Tae Jun; Sung, Jae Hee; Jeong, Tae Moon; Choi, Il Woo; Lee, Jongmin

    2010-04-01

    Ultrashort quantum beam facility (UQBF) project in Advanced Photonics Research Institute (APRI), GIST aims to develop a 0.1-Hz petawatt Ti:sapphire laser system based on chirped pulse amplification. Currently, the average output energy of 46.3 J has been reached at 0.1-Hz repetition rate. The output energy of 46.3 J corresponds to 1.1 PW, considering the pulse duration of 30 fs and the grating efficiency of 69.3%, which have been measured with a single-shot SPIDER and a preliminary pulse compressor. UQBF construction is on schedule for the first petawatt experiments in 2010.

  16. A Completely Solid-State Tunable Ti:Sapphire Laser System

    NASA Technical Reports Server (NTRS)

    Guerra, David V.; Coyle, D. Barry; Krebs, Danny J.

    1994-01-01

    Compact, completely solid-state tunable pulsed laser system passively cooled developed for potential employment in aircraft and sounding-rocket lidar experiments. Ti:sapphire based laser system pumped with frequency-doubled diode-pumped Nd:YAG. Rugged, self-contained system extremely flexible and provides pulsed output at specific frequencies with low input-power requirements. In-situ measurements enables scientists to study upper-atmosphere dynamics. Tuning range easily extended to bands between 650-950 nm in order to study other atmospheric constituents.

  17. Improved Performance of a Temperature Compensated LN2 Cooled Sapphire Oscillator

    NASA Technical Reports Server (NTRS)

    Santiago, David G.; Wang, Rabi T.; Dick, G. John

    1995-01-01

    We report on improved stability in a whispering gallery sapphire resonator for which the dominant WGHn11 microwave mode family shows frequency-stable, compensated operation for temperatures above 77K. Several modifications during the past year have led to significant improvements in performance. Current tests with improved thermal stability provide Allan Deviation of frequency of 2.6 - 4 ? 10-13 for measurement times of 1#t#100 seconds. We project a frequency stability of 1014 for this resonator with stabilized housing temperature and with a mode Q of 107.!.

  18. Operation of a Ti:Sapphire laser for the SLAC polarized electron source

    SciTech Connect

    Frisch, J.; Alley, R.; Browne, M.; Woods, M.

    1993-04-01

    A new laser system has been developed as the light source for the SLAC polarized electron source for the 1993 SLD physics run. A Q-switched and cavity-dumped Ti:Sapphire laser, pumped by a doubled YAG laser is used. This laser delivers typically 5O{mu}J to the photocathode with the required 2 nanosecond, double pulse, 12OHz time structure. The laser operates at wavelengths between 760nm and 870nm. The laser was installed on the SLAC linac in January 1993, and is currently in use.

  19. 2PE-STED microscopy with a single Ti:sapphire laser for reduced illumination.

    PubMed

    Li, Qifeng; Wang, Yang; Chen, Da; Wu, Sherry S H

    2014-01-01

    We reported a new effective approach to carry out two-photon excitation stimulated emission depletion (2PE-STED) microscopy using a single Ti:sapphire laser system. With an acoustic-optic Bragg cell, the modulated-CW 2PE STED microscope had the benefits of both CW and pulse approaches: lower input power, simple optical scheme and no complicated synchronization. Additionally, it also took advantages of fluorescence yield increasing. The sub-diffraction-limit resolution was demonstrated using ATTO 425-tagged clathrin-coated vesicles.

  20. Flashlamp-pumped Ti:Sapphire laser with different rods grown by Czochralski and Verneuil methods

    NASA Astrophysics Data System (ADS)

    Boquillon, J. P.; Said, J.

    1992-04-01

    The design and the development of a flashlamp-pumped Ti:Sapphire laser is described. Design criteria are discussed and performance improvements using different types of fluorescent UV converters or filters, such as organic dyes or doped glass are presented. We have tested different laser rods at various Ti-concentrations obtained by Verneuil or Czochralski growth techniques. The maximum laser output energy of 540 mJ with a differential efficiency up to 1% was achieved by using only a pyrex filter surrounding the laser rod.