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Sample records for a-plane sapphire substrate

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Effects of AlN buffer layer thickness on the crystallinity and surface morphology of 10-µm-thick a-plane AlN films grown on r-plane sapphire substrates

    NASA Astrophysics Data System (ADS)

    Lin, Chia-Hung; Tamaki, Shinya; Yamashita, Yasuhiro; Miyake, Hideto; Hiramatsu, Kazumasa

    2016-08-01

    10-µm-thick a-plane AlN(11\\bar{2}0) films containing a low-temperature AlN (LT-AlN) buffer layer and a high-temperature AlN (HT-AlN) film were prepared on r-plane sapphire (1\\bar{1}02) substrates. The crystallinity of all the samples with different LT-AlN buffer layer thicknesses was improved after thermal annealing and HT-AlN growth, mainly owing to the elimination of domain boundaries and the concurrent suppression of facet formation. The optimum crystallinity of HT-AlN films was obtained with full widths at half maximum of the X-ray rocking curves of 660 arcsec for AlN(11\\bar{2}0)\\parallel [1\\bar{1}00]AlN and 840 arcsec for (0002) using a 200-nm-thick LT-AlN buffer layer.

  10. Fabrication of high-crystallinity a-plane AlN films grown on r-plane sapphire substrates by modulating buffer-layer growth temperature and thermal annealing conditions

    NASA Astrophysics Data System (ADS)

    Lin, Chia-Hung; Yamashita, Yasuhiro; Miyake, Hideto; Hiramatsu, Kazumasa

    2017-06-01

    High-crystallinity a-plane AlN(11 2 ̅0) films containing a low-temperature AlN (LT-AlN) buffer layer and a high-temperature AlN (HT-AlN) film were grown on r-plane sapphire(1 1 ̅02) substrates. We investigated the effect of the growth temperature and thermal annealing conditions for the LT-AlN buffer layers on the crystallinity and surface morphology. The surface roughness of the buffer layers became smooth with the decrease in growth temperature to 900 °C, and the crystallinity of the buffer layers was improved by thermal annealing at temperatures over 1600 °C. HT-AlN films were then grown on the annealed LT-AlN buffer layers at 1500 °C. The optimum crystallinity of HT-AlN films without any facet formation at the surfaces was obtained with full width at half maximum values of the X-ray rocking curves for AlN(11 2 ̅0)//[1 1 ̅00]AlN at 770 and (0002) at 640″.

  11. Zeta potential orientation dependence of sapphire substrates.

    PubMed

    Kershner, Ryan J; Bullard, Joseph W; Cima, Michael J

    2004-05-11

    The zeta potential of planar sapphire substrates for three different crystallographic orientations was measured by a streaming potential technique in the presence of KCl and (CH3)4NCl electrolytes. The streaming potential was measured for large single crystalline C-plane (0001), A-plane (1120), and R-plane (1102) wafers over a full pH range at three or more ionic strengths ranging from 1 to 100 mM. The roughness of the epi-polished wafers was verified using atomic force microscopy to be on the order of atomic scale, and X-ray photoelectron spectroscopy (XPS) was used to ensure that the samples were free of silica and other contaminants. The results reveal a shift in the isoelectric point (iep) of the three samples by as much as two pH units, with the R-plane surface exhibiting the most acidic behavior and the C-plane samples having the highest iep. The iep at all ionic strengths was tightly centered around a single pH for each wafer. These values of iep are substantially different from the range of pH 8-10 consistently reported in the literature for alpha-Al2O3 particles. Particle zeta potential measurements were performed on a model powder using phase analysis light scattering, and the iep was confirmed to occur at pH 8. Modified Auger parameters (MAP) were calculated from XPS spectra of a monolayer of iridium metal deposited on the sapphire by electron beam deposition. A shift in MAP consistent with the observed differences in iep of the surfaces confirms the effect of surface structure on the transfer of charge between the Ir and sapphire, hence accounting for the changes in acidity as a function of crystallographic orientation.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. Electronic Devices Grown on Off-Axis Sapphire Substrate

    DTIC Science & Technology

    1999-07-15

    growth of high quality semiconducting films of III/V elements of the Periodic Table on a sapphire substrate has been a topic of major interest in recent...PATENT APPLICATION Inventors’ Name: Fatemi et al. elements of Group III of the Periodic Table and one or more elements of Group V of the Periodic ... Table . A preferred film is a nitride of Group III elements of barium, aluminum, gallium, indium and titanium. Although gallium nitride is a specific and

  18. The frequency-dependent AC photoresistance behavior of ZnO thin films grown on different sapphire substrates.

    PubMed

    Cholula-Díaz, Jorge L; Barzola-Quiquia, José; Videa, Marcelo; Yin, Chunhai; Esquinazi, Pablo

    2017-09-13

    Zinc oxide (ZnO) thin films were grown by pulsed layer deposition under an N2 atmosphere at low pressures on a- and r-plane sapphire substrates. Structural studies using X-ray diffraction confirmed that all films had a wurtzite phase. ZnO thin films on a- and r-plane sapphire have grown with orientations along the [0002] and [112[combining macron]0] directions, respectively. Room temperature photoluminescence measurements indicate that the presence of native point defects (interstitial zinc, oxygen vacancies, oxygen antisites and zinc vacancies) is more preponderant for ZnO thin films grown on the r-plane sapphire substrate than the sample grown on the a-plane sapphire substrate. Room temperature impedance spectroscopy measurements were performed in an alternating current frequency range from 40 to 10(5) Hz in the dark and under normal light. An unusual positive photoresistance effect is observed at frequencies above 100 kHz, which we suggest to be due to intrinsic defects present in the ZnO thin films. Furthermore, an analysis of the optical time response revealed that the film grown on the r-plane sapphire substrate responds faster (characteristic relaxation times for τ1, τ2 and τ3 of 0.05, 0.26 and 6.00 min, respectively) than the film grown on the a-plane sapphire substrate (characteristic relaxation times for τ1, τ2 and τ3 of 0.10, 0.73 and 4.02 min, respectively).

  19. AlN growth on sapphire substrate by ammonia MBE

    NASA Astrophysics Data System (ADS)

    Mansurov, V. G.; Nikitin, A. Yu.; Galitsyn, Yu. G.; Svitasheva, S. N.; Zhuravlev, K. S.; Osvath, Z.; Dobos, L.; Horvath, Z. E.; Pecz, B.

    2007-03-01

    Kinetics of (0 0 0 1) Al 2O 3 surface nitridation and subsequent growth of AlN films on the sapphire substrate by ammonia molecular beam epitaxy (MBE) are investigated. Surface morphology evolution during AlN growth is studied in situ by reflection high energy electron diffraction and ex situ by atomic force microscopy. It is found that the surfaces of AlN layers thicker than 100 nm have two major features: a quite smooth background and noticeable amount of hillocks. The influence of growth conditions on the AlN surface morphology is studied in order to find a way for reducing of the hillocks density. A modification of nitridated sapphire surface by small amount of Al (1-2 monolayers) with subsequent treatment of the surface under ammonia flux is proposed. An improvement of AlN surface morphology of the layers grown on the modified surfaces is demonstrated.

  20. Direct Growth of a-Plane GaN on r-Plane Sapphire by Metal Organic Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Hsu, Hsiao-Chiu; Su, Yan-Kuin; Huang, Shyh-Jer; Wang, Yu-Jen; Wu, Chun-Ying; Chou, Ming-Chieh

    2010-04-01

    In this study, we had demonstrated the direct growth of nonpolar a-plane GaN on an r-plane sapphire by metal organic chemical vapor deposition (MOCVD) without any buffer layer. First, in this experiment, we had determined the optimum temperature for two-step growth, including obtaining three-dimensional (3D) GaN islands in the nucleation layer and coalescing with a further two-dimensional (2D) growth mode. The result shows that the nucleation layer grown under high temperature (1150 °C) leads to large islands with few grain boundaries. Under the same temperature, the effect of the V/III ratio on the growth of the overlaying GaN layer to obtain a flat and void free a-plane GaN layer is also studied. The result indicates one can directly grow a smooth epitaxial layer on an r-plane sapphire by changing the V/III ratio. The rms roughness decreases from 13.61 to 2.02 nm. The GaN crystal quality is verified using a mixed acid to etch the film surface. The etch pit density (EPD) is 3.16 ×107 cm-2.

  1. 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.

  2. 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

  3. 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.

  4. 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.

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

    DTIC Science & Technology

    2005-08-24

    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...goals of the program from the original proposal: Part 1 1. Deposition of GaN/ InGaN heterostructures and quantum Wells on Ti and Cr- doped sapphire...substrates by MOCVD. 2. Characterization of doped sapphire/ InGaN structures byPL to simulate electrical injection by laser or LED device structures Part 2 1

  6. Structural anisotropic properties of a-plane GaN epilayers grown on r-plane sapphire by molecular beam epitaxy

    SciTech Connect

    Lotsari, A.; Kehagias, Th.; Katsikini, M.; Arvanitidis, J.; Ves, S.; Komninou, Ph.; Dimitrakopulos, G. P.; Tsiakatouras, G.; Tsagaraki, K.; Georgakilas, A.; Christofilos, D.

    2014-06-07

    Heteroepitaxial non-polar III-Nitride layers may exhibit extensive anisotropy in the surface morphology and the epilayer microstructure along distinct in-plane directions. The structural anisotropy, evidenced by the “M”-shape dependence of the (112{sup ¯}0) x-ray rocking curve widths on the beam azimuth angle, was studied by combining transmission electron microscopy observations, Raman spectroscopy, high resolution x-ray diffraction, and atomic force microscopy in a-plane GaN epilayers grown on r-plane sapphire substrates by plasma-assisted molecular beam epitaxy (PAMBE). The structural anisotropic behavior was attributed quantitatively to the high dislocation densities, particularly the Frank-Shockley partial dislocations that delimit the I{sub 1} intrinsic basal stacking faults, and to the concomitant plastic strain relaxation. On the other hand, isotropic samples exhibited lower dislocation densities and a biaxial residual stress state. For PAMBE growth, the anisotropy was correlated to N-rich (or Ga-poor) conditions on the surface during growth, that result in formation of asymmetric a-plane GaN grains elongated along the c-axis. Such conditions enhance the anisotropy of gallium diffusion on the surface and reduce the GaN nucleation rate.

  7. 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).

  8. 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

  9. 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.

  10. Epitaxy of CdTe on sapphire substrates with titanium buffer layers

    NASA Astrophysics Data System (ADS)

    Muslimov, A. E.; Butashin, A. V.; Kanevsky, V. M.; Babaev, V. A.; Alikhanov, N. M.-R.

    2017-05-01

    The formation of a developed electrical relief on the sapphire substrate surface is investigated. A technique is proposed for introducing Ti4+ impurity atoms into the sapphire crystal lattice by depositing titanium layers with a thickness of about 5 nm and their annealing in air (oxidizing atmosphere) to a temperature of 1400°C. It is shown that this preliminary treatment of the sapphire substrate surface results in epitaxial growth of (111) CdTe films parallel to the sapphire (0001) plane at a temperature of 350°C.

  11. 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.

  12. 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.

  13. 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.

  14. Effect of sapphire substrate on the localized surface plasmon resonance of aluminum triangular nanoparticles

    NASA Astrophysics Data System (ADS)

    Ye, Wei; Zhang, Wei; Wang, Shuai; Qi, Zhiqiang; Luo, Zhongwei; Chen, Changqing; Dai, Jiangnan

    2017-07-01

    In this paper, we explore the effect of the sapphire substrate on the localized surface plasmon resonance of Al triangular nanoparticles fabricated by nanosphere lithography. We find an obvious shoulder peak which is rarely noticed before as well as a main peak in the the ultraviolet range of the extinction spectrum. Then the electric field distributions surrounding the single Al triangular nanoparticle have been further investigated by numerical simulation using the finite-difference time-domain method. By analyzing the simulation results, we demonstrate that the two peaks in the extinction spectrum are originated from the hybridization of dipolar and quadrupolar modes when the sapphire substrate exists. And this work may provide a better understanding of the effect of sapphire substrate on the localized surface plasmon resonance properties of aluminum triangular nanoparticles.

  15. 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.

  16. Orientational control of CeO2 films on sapphire substrates grown by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Yamamoto, S.; Sugimoto, M.; Koshikawa, H.; Hakoda, T.; Yamaki, T.

    2017-06-01

    The effect of deposition temperature and post-annealing on the crystallographic orientation of cerium dioxide (CeO2) films on sapphire (α-Al2O3) substrates were investigated. CeO2 films, with thickness of 17 nm, were grown on c-plane and r-plane sapphire substrates by radiofrequency (rf) magnetron sputtering. Deposition temperatures between 150 and 500 °C were used with a sintered CeO2 target in an Ar-O2 gas mixture. The post-annealing treatment was performed in air at various temperatures ranging from 400 to 1000 °C. The films were characterized by X-ray diffraction, atomic force microscopy, and Rutherford backscattering spectroscopy. X-ray diffraction studies revealed that the orientation of the CeO2 films changed from (001) to mixed (001)/(111) and then to (111), with increasing deposition temperatures on both the c-plane and r-plane sapphire substrates. Post-annealing at 1000 °C improved the degree of crystallinity of the films, and formed rectangular grains. The results suggest that control of the deposition and post-annealing temperatures provides orientation-controlled CeO2 films on c- and r-plane sapphire substrates.

  17. 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

  18. Scribing of thin sapphire substrates with a 266-nm Q-switched solid state laser

    NASA Astrophysics Data System (ADS)

    Rea, Edward C., Jr.

    2004-07-01

    Thin sections of single-crystal sapphire are favored as substrates for the epitaxial deposition of gallium nitride and other III-V and II-VI thin films used in the fabrication of electro-optic devices such as blue-green LEDs and laser diodes. Due to difficulties commonly encountered in cutting this hard material, alternatives to traditional mechanical processing techniques are of particular interest. This paper reviews a recent study characterizing the scribing of sapphire using the tightly focused output of an ultraviolet wavelength pulsed solid-state laser.

  19. Fabrication of three-dimensional autocloned photonic crystal on sapphire substrate.

    PubMed

    Ku, Hao Ming; Huang, Chen Yang; Chao, Shiuh

    2011-03-20

    We applied the laser interference lithography method to form a patterned sapphire substrate (PSS). A three-dimensional photonic crystal was formed by autocloning the PSS with alternate Ta2O5/SiO2 coatings. A high total integrated reflectance (TIR) band was obtained around the 410 to 470 nm wavelength range that matched the emission spectrum of the gallium nitride (GaN) light-emitting diode (LED) for application in manipulating the light extraction of the sapphire-based GaN LED.

  20. 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.

  1. 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

  2. Pulsed Laser Deposition of VO2 Single Crystal Thin Films on Sapphire Substrates

    NASA Astrophysics Data System (ADS)

    Zhu, Pei-ran; S, Yamamoto; A, Miyashita; H, Naramoto

    1998-12-01

    Thin films of VO2 single-crystalline on (0001) sapphire substrates have been prepared by visible pulsed laser ablation technique. The crystal quality and properties of the films are evaluated through electrical resistance measurement, x-ray diffraction (XRD), and Rutherford-backscattering spectroscopy/channeling (RBS/C) analysis. The dependence of the surface electrical resistance of the films on the temperature shows semiconductor-to-metal transitions with the resistance change of 7 × 103-2 × 104. The hysteresis widths are from less than 1 to 3 K. XRD and RBS/C data reveal that the films prepared in particular conditions are single-crystalline VO2 with the (010) planes parallel to the surface of the sapphire substrate.

  3. High-quality AlN epitaxy on sapphire substrates with sputtered buffer layers

    NASA Astrophysics Data System (ADS)

    Zhang, Lisheng; Xu, Fujun; Wang, Mingxing; Sun, Yuanhao; Xie, Nan; Wang, Tao; Dong, Boyu; Qin, Zhixin; Wang, Xinqiang; Shen, Bo

    2017-05-01

    In this work, a novel strategy for high-quality AlN templates epitaxy on sapphire substrates with sputtered buffer layers combined with a low- and high-temperature alteration technique is proposed. The best full width at half maximum values for (0002) and (1 1 bar 02) reflections are 207 and 377 arcsec, respectively. Investigations indicate the joint effect of growth mode control and sputtered buffer layer results in the improvement of AlN crystalline quality. Firstly, threading dislocations density can be significantly decreased due to the alteration from three-dimensional to two-dimensional growth mode. Moreover, the graded composition of AlON layer in the sputtered buffer layer is believed to alleviate lattice mismatch between sapphire substrates and AlN, which also contributes to low dislocations density in AlN templates.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Crystallographic tilt and in-plane anisotropies of an a-plane InGaN/GaN layered structure grown by MOCVD on r-plane sapphire using a ZnO buffer

    NASA Astrophysics Data System (ADS)

    Liu, H. F.; Liu, W.; Guo, S.; Chi, D. Z.

    2016-03-01

    High-resolution x-ray diffraction (HRXRD) was used to investigate the crystallographic tilts and structural anisotropies in epitaxial nonpolar a-plane InGaN/GaN grown by metal-organic chemical vapor deposition on r-plane sapphire using a ZnO buffer. The substrate had an unintentional miscut of 0.14° towards its [-4 2 2 3] axis. However, HRXRD revealed a tilt of 0.26° (0.20°) between the ZnO (GaN) (11-20) and the Al2O3 (1-102) atomic planes, with the (11-20) axis of ZnO (GaN) tilted towards its c-axis, which has a difference of 163° in azimuth from that of the substrate’s miscut. Excess broadenings in the GaN/ZnO (11-20) rocking curves (RCs) were observed along its c-axis. Specific analyses revealed that partial dislocations and anisotropic in-plane strains, rather than surface-related effects, wafer curvature or stacking faults, are the dominant factors for the structural anisotropy. The orientation of the partial dislocations is most likely affected by the miscut of the substrate, e.g. via tilting of the misfit dislocation gliding planes created during island coalescences. Their Burgers vector components in the growth direction, in turn, gave rise to crystallographic tilts in the same direction as that of the excess RC-broadenings.

  9. 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.

  10. Epitaxial growth of aluminium-doped zinc oxide films by magnetron sputtering on (001), (110), and (012) oriented sapphire substrates

    NASA Astrophysics Data System (ADS)

    Kuppusami, P.; Vollweiler, G.; Rafaja, D.; Ellmer, K.

    2005-01-01

    Highly aluminium-doped zinc oxide (ZnO) films have been grown on differently oriented sapphire substrates by magnetron sputtering from an oxidic target. Rocking curve measurements, Rutherford backscattering analysis and transmission electron microscopy show that the films exhibit a disturbed film growth. However, despite the large nominal lattice mismatch between ZnO and sapphire (-31%), the films grow epitaxially on every sapphire orientation, even at room temperature. This was proven by pole figure analysis. The reason that epitaxial growth can be observed is an incommensurate lattice fitting between ZnO and sapphire by a mutual rotational alignment of their lattices. Films of the best crystallographic quality have been grown on (110)-oriented sapphire, which is also reflected by the highest Hall mobility in these layers.

  11. Polarized photoluminescence excitation spectroscopy of a-plane InGaN/GaN multiple quantum wells grown on r-plane sapphire

    NASA Astrophysics Data System (ADS)

    Kundys, D.; Schulz, S.; Oehler, F.; Sutherland, D.; Badcock, T. J.; Dawson, P.; Kappers, M. J.; Oliver, R. A.; Humphreys, C. J.

    2014-03-01

    We have performed a detailed study of the impact of basal plane stacking faults (BSFs) on the optical properties of both a-plane InGaN/GaN quantum wells (QWs) and GaN template samples grown on r-sapphire. In particular, we have used polarised photoluminescence excitation spectroscopy (P-PLE) to investigate the nature of the low temperature recombination as well as extracting information on the valence band (VB) polarisation anisotropy. Our low temperature P-PLE results revealed not only excitons associated with intersubband quantum well transitions and the GaN barrier material but also a transition associated with creation of excitons in BSFs. The strength of this BSF transition varied with detection energy across the quantum well emission suggesting that there is a significant contribution to the emission line width from changes in the local electronic environment of the QWs due to interactions with BSFs. Furthermore, we observed a corresponding progressive increase in the VB splitting of the QWs as the detection energy was varied across the quantum well emission spectrum.

  12. 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.

  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. In situ technique for measuring the orthogonality of a plane wave to a substrate.

    PubMed

    Châteauneuf, Marc; Ayliffe, Michael H; Kirk, Andrew G

    2003-05-01

    A new compact in situ method of measuring the perpendicularity of a plane wave to a substrate is proposed. Off-axis cylindrical Fresnel lenses are used to focus a portion of the incident plane wave onto target lines. The displacement of the focal line from the targets is determined by the degree of angular misalignment. The proposed design has been incorporated into a 10-mm-thick fused-silica module, which enables us to obtain an alignment precision of better than 0.0083 degrees. This method is designed for use in optical assembly procedures that require an incident collimated beam that is normal to the alignment features. Experimental results are presented.

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. (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.

  5. 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

  6. 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.

  7. 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.

  8. Coplanar microwave filters with YBa 2Cu 3O 7- δ thin films on sapphire substrates

    NASA Astrophysics Data System (ADS)

    Wünsch, S.; Crocoll, E.; Neuhaus, M.; Scherer, T. A.; Stassen, A.; Wermund, H.-J.; Jutzi, W.; Geerk, J.; Ratzel, F.; Lochner, O.

    2002-08-01

    A bandpass filter for a 1 dB relative bandwidth of 2.5% at 1.417 GHz is implemented with five end coupled resonators of meander coplanar lines with air bridges for ground connections on a 4.0×2.6 cm 2 substrate. A single sided sputtered YBa 2Cu 3O 7- δ film with a CeO 2 buffer layer on a sapphire substrate is patterned with an Ar ion beam. The wanted bandwidth of 35 MHz near 1.4 GHz is measured with a minimum insertion loss smaller than 0.1 dB at 15 K. Filters for a two channel receiver with almost identical characteristics have been fabricated without manual tuning screws. In the passband an insertion loss difference of less than 0.2 dB has been achieved. Their characteristics are not affected by mechanical vibrations on a cold finger. To attenuate higher order pass bands the design of a superconducting low pass filter is discussed.

  9. 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.

  10. Structural properties, crystal quality and growth modes of MOCVD-grown AlN with TMAl pretreatment of sapphire substrate

    NASA Astrophysics Data System (ADS)

    Sun, Haiding; Wu, Feng; tahtamouni, T. M. Al; Alfaraj, Nasir; Li, Kuang-Hui; Detchprohm, Theeradetch; Dupuis, Russell D.; Li, Xiaohang

    2017-10-01

    The growth of high quality AlN epitaxial films relies on precise control of the initial growth stages. In this work, we examined the influence of the trimethylaluminum (TMAl) pretreatment of sapphire substrates on the structural properties, crystal quality and growth modes of heteroepitaxial AlN films on (0 0 0 1) sapphire substrates. Without the pretreatment, the AlN films nucleated on the smooth surface but exhibited mixed crystallographic Al- (N-) polarity, resulting in rough AlN film surfaces. With increasing the pretreatment time from 1 to 5 s, the N-polarity started to be impeded. However, small islands were formed on sapphire surface due to the decompostion of TMAl. As a result, small voids became noticeable at the nucleation layer (NL) because the growth started as quasi three-dimensional (3D) but transformed to 2D mode as the film grew thicker and got coalesced, leading to smoother and Al-polar films. On the other hand, longer pretreatment time of 40 s formed large 3D islands on sapphire, and thus initiated a 3D-growth mode of the AlN film, generating Al-polar AlN nanocolumns with different facets, which resulted into rougher film surfaces. The epitaxial growth modes and their correlation with the AlN film crystal quality under different TMAl pretreatments are also discussed.

  11. 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.

  12. 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).

  13. Synthesis of monoclinic structure gallium oxide film on sapphire substrate by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Sun, Jian-xu; Mi, Wei; Zhang, De-shuang; Yang, Zheng-chun; Zhang, Kai-liang; Han, Ye-mei; Yuan, Yu-jie; Zhao, Jin-shi; Li, Bo

    2017-07-01

    Gallium oxide (Ga2O3) films were deposited on singlecrystalline sapphire (0001) substrate by radio frequency (RF) magnetron sputtering technique in the temperature range of 300—500 °C. The microstructure of the β-Ga2O3 films were investigated in detail using X-ray diffractometer (XRD) and scanning electron microscope (SEM). The results show that the film prepared at 500 °C exhibits the best crystallinity with a monoclinic structure ( β-Ga2O3). Structure analysis reveals a clear out-of-plane orientation of β-Ga2O3 (2̅01) ǁ Al2O3 (0001). The average transmittance of these films in the visible wavelength range exceeds 90%, and the optical band gap of the films varies from 4.68 eV to 4.94 eV which were measured by an ultraviolet-visible-near infrared (UV-vis-NIR) spectrophotometer. Therefore, it is hopeful that the β-Ga2O3 film can be used in the UV optoelectronic devices.

  14. 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.

  15. 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.

  16. 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.

  17. GaN-based Schottky barrier ultraviolet photodetectors with graded doping on patterned sapphire substrates

    NASA Astrophysics Data System (ADS)

    Mou, Wenjie; Zhao, Linna; Chen, Leilei; Yan, Dawei; Ma, Huarong; Yang, Guofeng; Gu, Xiaofeng

    2017-07-01

    In this paper, we demonstrate high performance GaN-based Schottky-barrier ultraviolet (UV) photodetectors with graded doping prepared on patterned sapphire substrates. The fabricated devices exhibit an extremely low dark current density of ∼1.3 × 10-8 A/cm2 under -5 V bias, a large UV-to-visible light rejection ratio of ∼4.2 × 103, and a peak external quantum efficiency of ∼50.7% at zero bias. Even in the deeper 250-360 nm range, the average external quantum efficiency still remains ∼40%. From the transient response characteristics, the average rising and falling time constants are estimated ∼115 μs and 120 μs, respectively, showing a good electrical and thermal reliability. The specific detectivities D∗, limited by the thermal equilibrium noise and the low-frequency 1/f noise, are derived ∼5.5 × 1013 cm Hz1/2/W (at 0 V) and ∼2.68 × 1010 cm Hz1/2 W-1 (at -5 V), respectively.

  18. 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).

  19. 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.

  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. 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.

  2. 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.

  3. 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.

  4. Structural and optical properties of near-UV LEDs grown on V-grooved sapphire substrates fabricated by wet etching

    NASA Astrophysics Data System (ADS)

    Cheong, H. S.; Na, M. G.; Choi, Y. J.; Cuong, T. V.; Hong, C.-H.; Suh, E.-K.; Kong, B. H.; Cho, H. K.

    2007-01-01

    V-grooved sapphire substrates (VGSS) were fabricated by a simple wet etching process with SiO 2 stripe masks along < 1 1¯ 2 0> orientation of the sapphire substrate and a mixed solution of H 2SO 4 and H 3PO 4. The growth of low-defect GaN template was optimized by two-step growth technique of metalorganic vapor deposition (MOCVD), resulting in the threading dislocation (TD) density of 2-4×10 7 cm -2 in the entire region of the GaN template. The epitaxial structure of near-UV light emitting diode (LED) was grown on the GaN templates on both the VGSS and the flat sapphire substrate (FSS) in order to compare the characteristics of their structural and optical properties. The internal quantum efficiency and the extraction efficiency of the LED structure grown on the VGSS were remarkably increased when compared to the conventional LED structure grown on the FSS. It seems to be attributed to the reduction in the TD density of the GaN template on the VGSS and the decrease in the number of times of total internal reflections of the light flux due to the V-grooved pattern, respectively. The increase in optical output power of the LED grown on the VGSS agreed well with the expected value based on the simulation of the commercial Light Tool program and temperature-dependent photoluminescence (PL) intensities.

  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. Influence of the microstructure geometry of patterned sapphire substrates on the light extraction efficiency of GaN LEDs.

    PubMed

    Kuo, Chien-Ting; Hsu, Lung-Hsing; Huang, Bo-Hsin; Kuo, Hao-Chung; Lin, Chien-Chung; Cheng, Yuh-Jen

    2016-09-10

    The influence of the microstructure geometry of patterned sapphire substrates (PSS) on the light extraction efficiency (LEE) of GaN light-emitting diodes (LEDs) is numerically analyzed. Cone structures of various dimensions are studied, along with dome and mixed microstructures. LEE is found to mainly depend on the microstructure surface slope. LEE rises quickly with slope and flattens out when the slope exceeds 0.6. Scaling down the microstructure has little effect on LEE. Light rays are found to travel longer distances in PSS LEDs, as compared with LEDs grown on a flat substrate. Keeping GaN absorption loss low is important for LEE optimization.

  7. 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

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. Crystal Quality and Light Output Power of GaN-Based LEDs Grown on Concave Patterned Sapphire Substrate.

    PubMed

    Wu, YewChung Sermon; Isabel, A Panimaya Selvi; Zheng, Jian-Hsuan; Lin, Bo-Wen; Li, Jhen-Hong; Lin, Chia-Chen

    2015-04-22

    The crystal quality and light output power of GaN-based light-emitting diodes (LEDs) grown on concave patterned sapphire substrate (CPSS) were investigated. It was found that the crystal quality of GaN-based LEDs grown on CPSS improved with the decrease of the pattern space (percentage of c-plane). However, when the pattern space decreased to 0.41 μm (S0.41-GaN), the GaN crystallinity dropped. On the other hand, the light output power of GaN-based LEDs was increased with the decrease of the pattern space due to the change of the light extraction efficiency.

  13. 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.

  14. Sapphire substrate-induced effects in VO2 thin films grown by oxygen plasma-assisted pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Skuza, J. R.; Scott, D. W.; Pradhan, A. K.

    2015-11-01

    We investigate the structural and electronic properties of VO2 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 VO2 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 VO2, which can be controlled through deposition conditions. Oxygen plasma-assisted pulsed laser deposition allows favorable conditions for VO2 film growth with SMTs that can be easily tailored for device applications.

  15. 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

  16. The effect of inductively-coupled-plasma reactive ion etching power on the etching rate and the surface roughness of a sapphire substrate.

    PubMed

    Chang, Chun-Ming; Shiao, Ming-Hua; Yang, Chin-Tien; Cheng, Chung-Ta; Hsueh, Wen-Jeng

    2014-10-01

    In this study, patterned sapphire substrates are fabricated using nanosphere lithography (NSL) and inductively-coupled-plasma reactive ion etching (ICP-RIE). Polystyrene nanospheres of approximately 600 nm diameter are self-assembled on c-plane sapphire substrates by spin-coating. The diameter of the polystyrene nanospheres is modified to adjust the etching mask pitch cycle using oxygen plasma in the ICP-RIE system. A nickel thin film mask of 100 nm thickness is deposited by electron-beam evaporation on a substrate covered with treated nanospheres. The sapphire substrate is then etched in an inductively coupled plasma system using BCl3/Ar gas, to fabricate a structure with a periodic sub-micron hole array with different sidewall intervals. The DC bias voltage, the sapphire etching rate, the surface roughness, are studied as a function of the ICP and the RF power. Different sub-micron hole arrays with spacing cycles of 89 nm, 139 nm and 167 nm are successfully fabricated on the sapphire substrate, using suitable etching parameters.

  17. Spatially resolved and orientation dependent Raman mapping of epitaxial lateral overgrowth nonpolar a-plane GaN on r-plane sapphire

    PubMed Central

    Jiang, Teng; Xu, Sheng-rui; Zhang, Jin-cheng; Xie, Yong; Hao, Yue

    2016-01-01

    Uncoalesced a-plane GaN epitaxial lateral overgrowth (ELO) structures have been synthesized along two mask stripe orientations on a-plane GaN template by MOCVD. The morphology of two ELO GaN structures is performed by Scanning electronic microscopy. The anisotropy of crystalline quality and stress are investigated by micro-Raman spectroscopy. According to the Raman mapping spectra, the variations on the intensity, peak shift and the full width at half maximum (FWHM) of GaN E2 (high) peak indicate that the crystalline quality improvement occurs in the window region of the GaN stripes along [0001], which is caused by the dislocations bending towards the sidewalls. Conversely, the wing regions have better quality with less stress as the dislocations propagated upwards when the GaN stripes are along []. Spatial cathodoluminescence mapping results further support the explanation for the different dislocation growth mechanisms in the ELO processes with two different mask stripe orientations. PMID:26821824

  18. Substrate-induced disorder in V{sub 2}O{sub 3} thin films grown on annealed c-plane sapphire substrates

    SciTech Connect

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

    2012-07-30

    We investigate the structural and electronic properties of V{sub 2}O{sub 3} 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 V{sub 2}O{sub 3}'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 V{sub 2}O{sub 3}'s strongly correlated metallic phase to crystalline defects and structural disorder.

  19. 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.

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

    SciTech Connect

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

    2016-07-15

    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.

  1. 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.

  2. 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.

  3. Performance enhancement of GaN-based light emitting diodes by transfer from sapphire to silicon substrate using double-transfer technique

    PubMed Central

    2012-01-01

    GaN-based light emitting diodes (LEDs) fabricated on sapphire substrates were successfully transferred onto silicon substrates using a double-transfer technique. Compared with the conventional LEDs on sapphire, the transferred LEDs showed a significant improvement in the light extraction and thermal dissipation, which should be mainly attributed to the removal of sapphire and the good thermal conductivity of silicon substrate. Benefited from the optimized wafer bonding process, the transfer processes had a negligible influence on electrical characteristics of the transferred LEDs. Thus, the transferred LEDs showed a similar current–voltage characteristic with the conventional LEDs, which is of crucial importance for practical applications. It is believed that the double-transfer technique offers an alternative way to fabricate high performance GaN-based thin-film LEDs. PMID:22559228

  4. 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.

  5. 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.

  6. Morphological and microstructural evolution in the two-step growth of nonpolar a-plane GaN on r-plane sapphire

    NASA Astrophysics Data System (ADS)

    Sun, Qian; Kong, Bo Hyun; Yerino, Christopher D.; Ko, Tsung-Shine; Leung, Benjamin; Cho, Hyung Koun; Han, Jung

    2009-12-01

    In this paper, we report a detailed study on the evolution of surface morphology and microstructure of nonpolar a-plane GaN (a-GaN) through controlled growth interruptions. Microscopy imaging shows that the two-step a-GaN growth went through a roughening-recovery process. The first-step growth (under high V/III and high pressure) produced a rough surface with tall mesas separated by voids. The second-step growth (under low V/III and low pressure) promoted the lateral growth and filled up the voids. Striations that formed during the island coalescence persisted throughout the second-step growth, but could be relieved by an additional third-step growth. The morphological evolution was explained according to the kinetic Wulff plots. The microstructure of the a-GaN films was investigated by transmission electron microscopy (TEM) and x-ray rocking curve analysis. Most of the extended defects observed in the plan-view TEM images were I1 type basal-plane stacking faults (BSFs) and their associated partial dislocations (PDs). It is found that the bending of PDs (at the inclined/vertical growth fronts) within the basal plane toward the m-axes was responsible for the substantial reduction in threading PDs and the increase in BSF dimension. Based on a careful correlation between the morphological evolution and the microstructure development, we proposed a model explaining the possible mechanisms for the great reduction in defect density during the two-step growth process.

  7. 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.

  8. 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.

  9. Effect of Different Substrate Temperature on Sb-Doped ZnO Thin Films Prepared by Pulsed Laser Deposition on Sapphire Substrates

    NASA Astrophysics Data System (ADS)

    Zhao, Zi-Wen; Hu, Li-Zhong; Zhang, He-Qiu; Sun, Jing-Chang; Bian, Ji-Ming; Sun, Kai-Tong; Chen, Xi; Zhao, Jian-Ze; Li, Xue; Zhu, Jin-Xia

    2010-01-01

    Sb-doped ZnO thin films are deposited on c-plane sapphire substrates by pulsed laser deposition. Hall results indicate that the conductivity of the Sb-doped ZnO thin films is strongly dependent on the substrate temperature. The sample deposited at the temperature of 550°C exhibits p-type conductivity. It gives a resistivity of 15.25 Ω · cm, with a Hall mobility of 1.79cm2V-1s-1 and a carrier concentration of 2.290 × 1017 cm-3 at room temperature. The x-ray diffraction indicates that the Sb-doped ZnO thin films deposited in the range of 450-650°C are high c-axis oriented. Low-temperature photoluminescence spectra indicate that the sample deposited at 550°C shows the strong acceptor-bound exciton (A0X) emission.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

    You, Yao-Hong; Su, Vin-Cent; Ho, Ti-En; Lin, Bo-Wen; Lee, Ming-Lun; Das, Atanu; Hsu, Wen-Ching; Kuan, Chieh-Hsiung; Lin, Ray-Ming

    2014-11-01

    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).

  12. 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

  13. 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.

  14. InGaN-Based Light-Emitting Diodes Grown on a Micro/Nanoscale Hybrid Patterned Sapphire Substrate.

    PubMed

    Ke, Wen-Cheng; Lee, Fang-Wei; Chiang, Chih-Yung; Liang, Zhong-Yi; Chen, Wei-Kuo; Seong, Tae-Yeon

    2016-12-21

    A hybrid patterned sapphire substrate (hybrid-PSS) was prepared using an anodic aluminum oxide etching mask to transfer nanopatterns onto a conventional patterned sapphire substrate with microscale patterns (bare-PSS). The threading dislocation (TD) suppression of light-emitting diodes (LEDs) grown on a hybrid-PSS (HP-LED) exhibits a smaller reverse leakage current compared with that of LEDs grown on a bare-PSS (BP-LED). The strain-free GaN buffer layer and fully strained InGaN active layer were evidenced by cross-sectional Raman spectra and reciprocal space mapping of the X-ray diffraction intensity for both samples. The calculated piezoelectric fields for both samples are close, implying that the quantum-confined Stark effect was not a dominant mechanism influencing the electroluminescence (EL) peak wavelength under a high injection current. The bandgap shrinkage effect of the InGaN well layer was considered to explain the large red-shifted EL peak wavelength under high injection currents. The estimated LED chip temperatures rise from room temperature to 150 °C and 75 °C for BP-LED and HP-LED, respectively, at a 600-mA injection current. This smaller temperature rise of the LED chip is attributed to the increased contact area between the sapphire and the LED structural layer because of the embedded nanopattern. Although the chip generates more heat at high injection currents, the accumulated heat can be removed to outside the chip effectively. The high diffuse reflection (DR) rate of hybrid-PSS increases the escape probability of photons, resulting in an increase in the viewing angle of the LEDs from 130° to 145°. The efficiency droop was reduced from 46% to 35%, effects which can be attributed to the elimination of TDs and strain relaxation by embedded nanopatterns. In addition, the light output power of HP-LED at 360-mA injection currents exhibits a ∼ 22.3% enhancement, demonstrating that hybrid-PSSs are beneficial to apply in high-power LEDs.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Effect of Sapphire Substrate Thickness on the Characteristics of 450 nm InGaN/GaN Multi-Quantum Well Light-Emitting Diodes.

    PubMed

    Tawfik, Wael Z; Bea, Seo-Jung; Yang, Seung Bea; Ryu, Sang-Wan; Lee, June Key

    2015-07-01

    450 nm InGaN/GaN multi-quantum well (MQW) ligth-emitting diodes (LEDs) prepared on sapphire substrate with different thicknesses were fabricated and characterized. By thinning the sapphire substrate to 50 µm, it was found that the LED exhibited the highest light output power of ~48 mW under high injection current of 50 mA, improved by about 35% compared to that with 200 µm-thick sapphire without increasing the operating voltage. The electroluminescence intensity was increased and the spectral peak wavelength was blue-shifted, because the wafer bowing-induced mechanical stress alters the piezoelectric field in the InGaN/GaN MQW active region of the LED. The internal quantum efficiency was also improved by about 10% at an injection current of 50 mA. Moreover, the external quantum efficiency and light extraction efficiency were optimized because of enhanced light output intensity. The results confirmed that sapphire substrate thinning effectively alters the piezoelectric field in the InGaN/GaN active region, and hence increases both of the effective band gap and the probability of radiative recombination.

  1. Improved light extraction of nitride-based flip-chip light-emitting diodes by forming air voids on Ar-implanted sapphire substrate

    NASA Astrophysics Data System (ADS)

    Yeh, Yu-Hsiang; Sheu, Jinn-Kong; Lee, Ming-Lun; Chen, Po-Cheng; Yang, Yu-Chen; Yen, Cheng-Hsiung; Lai, Wei-Chih

    2014-09-01

    GaN-based flip-chip light emitting diodes (FC-LEDs) with embedded air voids grown on a selective-area Arimplanted AlN/sapphire (AIAS) substrate was demonstrated in this study. The proposed FC LED with an embedded light scattering layer can destroy the light interference and thereby increase the LEE of GaN-based flip-chip LEDs. The epitaxial layers grown on Ar-implanted regions exhibited lower growth rates compared with those grown on implantation-free regions. Accordingly, air voids formed over the implanted regions after merging laterally grown GaN facet fronts. The light-output power of LEDs grown on AIAS was greater than that of LEDs grown on implantation free sapphire substrates. At an injection current of 700 mA, the output power of LEDs grown on AIAS was enhanced by 20% compared with those of LEDs without embedded air voids. The increase in output power was mainly attributed to the scattering of light around the air voids, which increased the probability of photons escaping from the LEDs. This study on FC LEDs with embedded light-scattering layer highlights the potential application of these LEDs as an alternative to conventional patterned sapphire substrates for improving the LEE of GaN/sapphire-based LEDs. Based on ray tracing simulation, if the height and the width of bottom of gaps were increased to 3 μm, the Lop could be enhanced over 60%.

  2. 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.

  3. 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.

  4. 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.

  5. Density functional calculations of graphene-based humidity and carbon dioxide sensors: effect of silica and sapphire substrates

    NASA Astrophysics Data System (ADS)

    Elgammal, Karim; Hugosson, Håkan W.; Smith, Anderson D.; Råsander, Mikael; Bergqvist, Lars; Delin, Anna

    2017-09-01

    We present dispersion-corrected density functional calculations of water and carbon dioxide molecules adsorption on graphene residing on silica and sapphire substrates. The equilibrium positions and bonding distances for the molecules are determined. Water is found to prefer the hollow site in the center of the graphene hexagon, whereas carbon dioxide prefers sites bridging carbon-carbon bonds as well as sites directly on top of carbon atoms. The energy differences between different sites are however minute - typically just a few tenths of a millielectronvolt. Overall, the molecule-graphene bonding distances are found to be in the range 3.1-3.3 Å. The carbon dioxide binding energy to graphene is found to be almost twice that of the water binding energy (around 0.17 eV compared to around 0.09 eV). The present results compare well with previous calculations, where available. Using charge density differences, we also qualitatively illustrate the effect of the different substrates and molecules on the electronic structure of the graphene sheet.

  6. Hg-based cuprate superconducting thin films prepared on CeO2 buffered R-plane sapphire substrate

    NASA Astrophysics Data System (ADS)

    Chromik, S.; Sin, A.; Strbík, V.; Plesch, G.; Odier, P.; Weiss, F.

    2001-10-01

    Hg-Ba-Ca-Cu-O films have been grown on CeO2/R-plane sapphire substrates using a two-step process. First, a 200 nm thick Ba-Ca-Cu-(O, F) precursor film was prepared by sequential evaporation, then Hg-Re-Ba-Ca-Cu-O pellets as a source of Hg-vapour were applied using heat treatment. The prepared films were continuous with sufficient adhesion to the substrate and a maximum zero-resistance critical temperature of TC0 = 118 K. The x-ray diffraction measurements of all the prepared films confirmed the Hg-1212 phase as well as the minor Hg-1223 phase in some cases. We found that the best results were obtained at the mercuration temperature of 775 °C and an optimal annealing time within the range 0.5-5 h. The superconducting properties of the films prepared under unsuitable conditions were mostly improved after annealing in oxygen atmosphere. Darker parts of the film exhibited a different surface morphology and the presence of the Hg-1223 phase in plate-like grains.

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

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

    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.

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

    PubMed Central

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

    2017-01-01

    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. PMID:28401941

  9. 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.

  10. InGaN/GaN multi-quantum well and LED growth on wafer-bonded sapphire-on-polycrystalline AlN substrates by metalorganic chemical vapor deposition.

    SciTech Connect

    Crawford, Mary Hagerott; Olson, S. M.; Banas, M.; Park, Y. -B.; Ladous, C.; Russell, Michael J.; Thaler, Gerald; Zahler, J. M.; Pinnington, T.; Koleske, Daniel David; Atwater, Harry A.

    2008-06-01

    We report growth of InGaN/GaN multi-quantum well (MQW) and LED structures on a novel composite substrate designed to eliminate the coefficient of thermal expansion (CTE) mismatch problems which impact GaN growth on bulk sapphire. To form the composite substrate, a thin sapphire layer is wafer-bonded to a polycrystalline aluminum nitride (P-AlN) support substrate. The sapphire layer provides the epitaxial template for the growth; however, the thermo-mechanical properties of the composite substrate are determined by the P-AlN. Using these substrates, thermal stresses associated with temperature changes during growth should be reduced an order of magnitude compared to films grown on bulk sapphire, based on published CTE data. In order to test the suitability of the substrates for GaN LED growth, test structures were grown by metalorganic chemical vapor deposition (MOCVD) using standard process conditions for GaN growth on sapphire. Bulk sapphire substrates were included as control samples in all growth runs. In situ reflectance monitoring was used to compare the growth dynamics for the different substrates. The material quality of the films as judged by X-ray diffraction (XRD), photoluminescence and transmission electron microscopy (TEM) was similar for the composite substrate and the sapphire control samples. Electroluminescence was obtained from the LED structure grown on a P-AlN composite substrate, with a similar peak wavelength and peak width to the control samples. XRD and Raman spectroscopy results confirm that the residual strain in GaN films grown on the composite substrates is dramatically reduced compared to growth on bulk sapphire substrates.

  11. 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}.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. GaN-based light emitting diodes on nano-hole patterned sapphire substrate prepared by three-beam laser interference lithography

    NASA Astrophysics Data System (ADS)

    Sang, Wei-hua; Lin, Lu; Wang, Long; Min, Jia-hua; Zhu, Jian-jun; Wang, Min-rui

    2016-05-01

    Nano-hole patterned sapphire substrates (NHPSSs) were successfully prepared using a low-cost and high-efficiency approach, which is the laser interference lithography (LIL) combined with reactive ion etching (RIE) and inductively coupled plasma (ICP) techniques. Gallium nitride (GaN)-based light emitting diode (LED) structure was grown on NHPSS by metal organic chemical vapor deposition (MOCVD). Photoluminescence (PL) measurement was conducted to compare the luminescence efficiency of the GaN-based LED structure grown on NHPSS (NHPSS-LED) and that on unpatterned sapphire substrates (UPSS-LED). Electroluminescence (EL) measurement shows that the output power of NHPSS-LED is 2.3 times as high as that of UPSS-LED with an injection current of 150 mA. Both PL and EL results imply that NHPSS has an advantage in improving the crystalline quality of GaN epilayer and light extraction efficiency of LEDs at the same time.

  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. 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.

  20. 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.

  1. Influence of sapphire substrate thickness on the characteristics of AlGaN/AlN/GaN heterostructure field-effect transistors

    NASA Astrophysics Data System (ADS)

    Yang, Ming; Lin, Zhaojun; Zhao, Jingtao; Wang, Yutang; Li, Zhiyuan; Lv, Yuanjie; Feng, Zhihong

    2015-09-01

    A standard AlGaN/AlN/GaN heterostructure field-effect transistor (HFET) on a 420 μm thick sapphire substrate was fabricated, and then the sapphire substrate was thinned to several different thicknesses by grinding. When the remaining substrate thickness is more than 170 μm, the characteristics of the substrate thinned AlGaN/AlN/GaN HFET are almost the same as the original device. However, when the substrate thickness is less than 170 μm, the drain-to-source current, the threshold voltage, and the electron mobility of the two-dimensional electron gas (2DEG) in the channel are varied compared to the original one. It is attributed to the shrinkage of the GaN layer with the reduction of substrate thickness, which induces the decrease of both the 2DEG sheet density and the polarization charge sheet density, and a possible increase of dislocation scattering and the reduction of polarization Coulomb field scattering.

  2. 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.

  3. Impact of layer and substrate properties on the surface acoustic wave velocity in scandium doped aluminum nitride based SAW devices on sapphire

    SciTech Connect

    Gillinger, M. Knobloch, T.; Schneider, M.; Schmid, U.; Shaposhnikov, K.; Kaltenbacher, M.

    2016-06-06

    This paper investigates the performance of surface acoustic wave (SAW) devices consisting of reactively sputter deposited scandium doped aluminum nitride (Sc{sub x}Al{sub 1-x}N) thin films as piezoelectric layers on sapphire substrates for wireless sensor or for RF-MEMS applications. To investigate the influence of piezoelectric film thickness on the device properties, samples with thickness ranging from 500 nm up to 3000 nm are fabricated. S{sub 21} measurements and simulations demonstrate that the phase velocity is predominantly influenced by the mass density of the electrode material rather than by the thickness of the piezoelectric film. Additionally, the wave propagation direction is varied by rotating the interdigital transducer structures with respect to the crystal orientation of the substrate. The phase velocity is about 2.5% higher for a-direction compared to m-direction of the sapphire substrate, which is in excellent agreement with the difference in the anisotropic Young's modulus of the substrate corresponding to these directions.

  4. 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.

  5. 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.

  6. Improvement of crystal quality and optical property in (11-22) semipolar InGaN/GaN LEDs grown on patterned m-plane sapphire substrate

    NASA Astrophysics Data System (ADS)

    Jang, Jongjin; Lee, Kwanhyun; Hwang, Junghwan; Jung, Joocheol; Lee, Seunga; Lee, Kyuho; Kong, Bohyun; Cho, Hyunghoun; Nam, Okhyun

    2012-12-01

    Semipolar GaN layers were grown on the m-plane hemispherical patterned sapphire substrates (HPSS) using metal organic chemical vapor deposition in order to reduce the defect density and enhance the extraction efficiency of light. The roughness values of the GaN surface grown on the planar sapphire and the HPSS were 30 and 23 nm root-mean-square roughness for a 20×20-μm2 area, respectively. The reduction of basal stacking fault density was demonstrated by x-ray rocking curve of off-axis planes and cross-sectional transmission electron microscopy. The low-temperature photoluminescence measurement showed that the near band-edge emission from HPSS semipolar GaN was approximately one order of magnitude stronger than that from planar semipolar GaN layer. The InGaN light emitting diode grown on the HPSS showed an output power approximately 1.5 times that on the planar m-sapphire.

  7. A-plane GaN growth on (11-20) 4H-SiC substrate with an ultrathin interlayer

    NASA Astrophysics Data System (ADS)

    Sun, Zheng; Song, Peifeng; Nitta, Shugo; Honda, Yoshio; Amano, Hiroshi

    2017-06-01

    A-plane GaN was attempted to be grown on (11-20) 4H-SiC bulk substrate without using a traditional thick buffer layer. By inducing TMAl treatment before the GaN growth step and using both a low pressure and V/III ratio, the interlayer thickness of the a-plane GaN/SiC was reduced to 1.7+0.5 nm. The ultrathin interlayer was observed to be either AlN or AlGaN with a low Ga composition. This study is aimed to contribute to the understanding of GaN growth on the sidewalls of c-plane trench structure SiC. The ultrathin growth technique is also hoped to be applied to the fabrication of GaN-based vertical structure nonpolar optical or electrical devices.

  8. Patterning of light-extraction nanostructures on sapphire substrates using nanoimprint and ICP etching with different masking materials.

    PubMed

    Chen, Hao; Zhang, Qi; Chou, Stephen Y

    2015-02-27

    Sapphire nanopatterning is the key solution to GaN light emitting diode (LED) light extraction. One challenge is to etch deep nanostructures with a vertical sidewall in sapphire. Here, we report a study of the effects of two masking materials (SiO2 and Cr) and different etching recipes (the reaction gas ratio, the reaction pressure and the inductive power) in a chlorine-based (BCl3 and Cl2) inductively coupled plasma (ICP) etching of deep nanopillars in sapphire, and the etching process optimization. The masking materials were patterned by nanoimprinting. We have achieved high aspect ratio sapphire nanopillar arrays with a much steeper sidewall than the previous etching methods. We discover that the SiO2 mask has much slower erosion rate than the Cr mask under the same etching condition, leading to the deep cylinder-shaped nanopillars (122 nm diameter, 200 nm pitch, 170 nm high, flat top, and a vertical sidewall of 80° angle), rather than the pyramid-shaped shallow pillars (200 nm based diameter, 52 nm height, and 42° sidewall) resulted by using Cr mask. The processes developed are scalable to large volume LED manufacturing.

  9. Neutron reflectivity study of substrate surface chemistry effects on supported phospholipid bilayer formation on (11 ̅20) sapphire.

    PubMed

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

    2012-03-15

    Oxide-supported phospholipid bilayers (SPBs) used as biomimetic 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 stacked SPBs retain properties (e.g., fluidity) more similar to native biological membranes, which is desirable for most applications. Using neutron reflectivity, we examined the role of oxide surface charge (by varying pH and ionic strength) and of divalent Ca(2+) in controlling surface coverage and potential stacking of dipalmitoylphosphatidylcholine (DPPC) bilayers on the (11 ̅20) face of sapphire (α-Al(2)O(3)). Nearly full bilayers were formed at low to neutral pH, when the sapphire surface is positively charged, and at low ionic strength (I=15 mM NaCl). Coverage decreased at higher pH, close to the isoelectric point of sapphire, and also at high I≥210 mM, or with addition of 2mM Ca(2+). The latter two effects are not additive, suggesting that Ca(2+) mitigates the effect of higher I. These trends agree with previous results for phospholipid adsorption on α-Al(2)O(3) particles determined by adsorption isotherms and on single-crystal (10 ̅10) sapphire by atomic force microscopy, suggesting consistency of oxide surface chemistry-dependent effects across experimental techniques. Copyright © 2011 Elsevier Inc. All rights reserved.

  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. 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.

  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

    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.

  15. 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.

  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. 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.

  18. 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.

  19. 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

  20. Effect of sapphire substrate orientations on the microstructural, optical and NO2 gas sensing properties of Zn(1-x)CdxO thin films synthesized by sol gel spin-coating method

    NASA Astrophysics Data System (ADS)

    Boukadhaba, M. A.; Chebil, W.; Fouzri, A.; Sallet, V.; Lusson, A.; Amiri, G.; Vilar, C.; Oumezzine, M.

    2016-06-01

    A simple and cost-effective sol-gel technique was employed to elaborate ZnO and Zn(1-x)CdxO thin films deposit by spin coating onto the c- and r-plane sapphire substrates. The deposited films were characterized for their structural, morphological and optical properties using high resolution X ray diffraction (HRXRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM) as function of Cd incorporation and employed substrate. Higher Cd incorporation (4.5%) is obtained for ZnCdO layer deposited on r-plane sapphire, which is confirmed by the greatest energy shift (110 meV) to lower energy measured by low temperature photoluminescence. X-ray diffraction study revealed that all films are polycrystalline with a hexagonal wurtzite structure. A preferred orientation along [001] and [110] direction is obtained respectively for layer deposited on c- and r-plane sapphire. However, the (002) and (110) XRD layers peak were shifted towards the lower 2θ values after Cd incorporation showing a slight variation of cell parameters. SEM and AFM image show no very significant variation in the morphology of the layers depending on the substrate orientation and Cd content incorporated. A mixture of large and small hexagonal grains are obtained which are more pronounced for ZnCdO deposited on r-plane sapphire and their agglomeration leaves more empty space in films. The gas sensing performances were tested in NO2 containing air for different operating temperatures as function of Cd incorporation and sapphire substrate orientation. The experimental result exhibited that ZnCdO sensors deposited on r-plane sapphire shows a more better gas response with fast response and recovery time at moderate operating temperatures as Cd contend increase.

  1. 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.

  2. 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.

  3. 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.

  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)

    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.

  5. Improved performance of AlGaN-based deep ultraviolet light-emitting diodes with nano-patterned AlN/sapphire substrates

    NASA Astrophysics Data System (ADS)

    Lee, Donghyun; Lee, Jong Won; Jang, Jeonghwan; Shin, In-Su; Jin, Lu; Park, Jun Hyuk; Kim, Jungsub; Lee, Jinsub; Noh, Hye-Seok; Kim, Yong-Il; Park, Youngsoo; Lee, Gun-Do; Park, Yongjo; Kim, Jong Kyu; Yoon, Euijoon

    2017-05-01

    We demonstrated AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) with periodic air-voids-incorporated nanoscale patterns enabled by nanosphere lithography and epitaxial lateral overgrowth (ELO) on a 4-in. sapphire substrate. The nanoscale ELO improved the crystal quality of overgrown epitaxial layers at a relatively low growth temperature of 1050 °C and at small coalescence thickness less than 2 μm. The light output power of the DUV LED was enhanced significantly by 67% at an injection current of 20 mA. We attribute such a remarkable enhancement to the formation of embedded periodic air voids which cause simultaneous improvements in the crystal quality of epitaxial layers by ELO and light extraction efficiency enabled by breaking the predominant in-plane guided propagation of DUV photons.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  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. Monocrystalline germanium film on sapphire

    NASA Astrophysics Data System (ADS)

    Godbey, David J.; Qadri, Syed B.

    1993-04-01

    A monocrystalline germanium film is grown on a sapphire substrate with a (I 102) orientation. The substrate is first pretreated to restructure the (1102) surface plane. Typically, restructuring is accomplished by either an anneal at high temperature or ion bombardment. A monocrystalline germanium layer is grown on the pretreated surface by a vapor deposition process such as molecular beam epitaxy or chemical vapor deposition.

  12. A study into the impact of sapphire substrate orientation on the properties of nominally-undoped β-Ga2O3 thin films grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Teherani, F. H.; Rogers, D. J.; Sandana, V. E.; Bove, P.; Ton-That, C.; Lem, L. L. C.; Chikoidze, E.; Neumann-Spallart, M.; Dumont, Y.; Huynh, T.; Phillips, M. R.; Chapon, P.; McClintock, R.; Razeghi, M.

    2017-03-01

    Nominally-undoped Ga2O3 layers were deposited on a-, c- and r-plane sapphire substrates using pulsed laser deposition. Conventional x-ray diffraction analysis for films grown on a- and c-plane sapphire showed the layers to be in the β-Ga2O3 phase with preferential orientation of the (-201) axis along the growth direction. Pole figures revealed the film grown on r-plane sapphire to also be in the β-Ga2O3 phase but with epitaxial offsets of 29.5°, 38.5° and 64° from the growth direction for the (-201) axis. Optical transmission spectroscopy indicated that the bandgap was 5.2eV, for all the layers and that the transparency was > 80% in the visible wavelength range. Four point collinear resistivity and Van der Pauw based Hall measurements revealed the β-Ga2O3 layer on r-plane sapphire to be 4 orders of magnitude more conducting than layers grown on a- and c-plane sapphire under similar conditions. The absolute values of conductivity, carrier mobility and carrier concentration for the β-Ga2O3 layer on r-sapphire (at 20Ω-1.cm-1, 6 cm2/Vs and 1.7 x 1019 cm-3, respectively) all exceeded values found in the literature for nominally-undoped β-Ga2O3 thin films by at least an order of magnitude. Gas discharge optical emission spectroscopy compositional depth profiling for common shallow donor impurities (Cl, F, Si and Sn) did not indicate any discernable increase in their concentrations compared to background levels in the sapphire substrate. It is proposed that the fundamentally anisotropic conductivity in β-Ga2O3 combined with the epitaxial offset of the (-201) axis observed for the layer grown on r-plane sapphire may explain the much larger carrier concentration, electrical conductivity and mobility compared with layers having the (-201) axis aligned along the growth direction.

  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. 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.

  15. 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.

  16. 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

  17. 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

  18. Super-aligned carbon nanotubes patterned sapphire substrate to improve quantum efficiency of InGaN/GaN light-emitting diodes.

    PubMed

    Shan, Liang; Wei, Tongbo; Sun, Yuanping; Zhang, Yonghui; Zhen, Aigong; Xiong, Zhuo; Wei, Yang; Yuan, Guodong; Wang, Junxi; Li, Jinmin

    2015-07-27

    In this paper, the high performance GaN-based light-emitting diodes (LEDs) on carbon-nanotube-patterned sapphire substrate (CNPSS) by metal-organic chemical vapor deposition (MOCVD) are demonstrated. By studying the mechanism of nucleation, we analyze the reasons of the crystal quality improvement induced by carbon nanotubes (CNTs) in different growth process. Combining with low temperatures photoluminescence (PL) measurements and two-dimensional (2D) finite difference time-domain (FDTD) simulation results, we conclude that the improvement of optical properties and electrical properties of CNPSS mainly originates from the improvement of the internal quantum efficiency (IQE) due to decreased dislocation density during nano-epitaxial growth on CNPSS. Additionally, in order to reduce the light absorption characteristics of CNTs, different time annealing under the oxygen environment is carried out to remove part of CNTs. Under 350 mA current injections, the light output power (LOP) of CNPSS-LED annealed 2 h and 10 h exhibit 11% and 6% enhancement, respectively, compared to that of the CNPSS-LED without annealing. Therefore, high temperature annealing can effectively remove parts of CNTs and further increase the LOP, while overlong annealing time has caused degradation of the quantum well resulting in the attenuation of optical power.

  19. 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.

  20. 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.

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

    PubMed Central

    2014-01-01

    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. PMID:25258616

  2. 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.

  3. 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.

  4. Growth, characterization, and application of well-defined separated GaN-based pyramid array on micropatterned sapphire substrate

    NASA Astrophysics Data System (ADS)

    Tian, Zhenhuan; Li, Yufeng; Su, Xilin; Feng, Lungang; Wang, Shuai; Zhang, Minyan; Ding, Wen; Li, Qiang; Zhang, Ye; Guo, Maofeng; Yun, Feng; Lee, S. W. Ricky

    2017-09-01

    We tried to obtain microstructures on a three-dimensional (3D) micropatterned substrate by laser drilling. The influences of the dimensions of the drilling holes on the morphology and the material quality of the grown structures were studied. Uniform micropyramid arrays with relatively low dislocation density can be achieved by adjusting the laser drilling parameters. The internal quantum efficiency was estimated to be improved by a factor of 3 for a pyramid structure compared with that of planar LEDs. We fabricated 5 × 7 mm2 flexible LEDs employing the pyramid structure and the devices exhibited good flexibility without performance reduction after bending.

  5. MOVPE deposition of Sb2Te3 and other phases of Sb-Te system on sapphire substrate

    NASA Astrophysics Data System (ADS)

    Kuznetsov, P. I.; Shchamkhalova, B. S.; Yapaskurt, V. O.; Shcherbakov, V. D.; Luzanov, V. A.; Yakushcheva, G. G.; Jitov, V. A.; Sizov, V. E.

    2017-08-01

    The films of Sb-Te system have been deposited by MOVPE on (0 0 0 1) Al2O3 substrates with thin ZnTe buffer layers at different temperatures and Te/Sb ratios in the vapor phase. X-ray diffractometry, SEM microscopy, Raman and EDX spectroscopy were used to study as-grown films. The surface morphology and stoichiometry of Sb-Te films strongly depend on Te/Sb ratio in vapor phase. We have deposited the phases of homologous series nSb2·mSb2Te3 with following stoichiometries: Sb2Te3, Sb4Te5, Sb8Te9, Sb10Te9, Sb4Te3, Sb2Te, Sb8Te3, Sb10Te3, Sb16Te3, Sb18Te3 and Sb. Transport properties of Sb2Te3, Sb4Te5, Sb8Te9, Sb4Te3, Sb2Te were evaluated using Van der Pauw technique at 300 K.

  6. 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.

  7. 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.

  8. 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.

  9. A study of the optical and polarisation properties of InGaN/GaN multiple quantum wells grown on a-plane and m-plane GaN substrates

    PubMed Central

    Kundys, Dmytro; Sutherland, Danny; Davies, Matthew J.; Oehler, Fabrice; Griffiths, James; Dawson, Philip; Kappers, Menno J.; Humphreys, Colin J.; Schulz, Stefan; Tang, Fengzai; Oliver, Rachel A.

    2016-01-01

    Abstract We report on a comparative study of the low temperature emission and polarisation properties of InGaN/GaN quantum wells grown on nonpolar (112¯0) a-plane and (101¯0) m-plane free-standing bulk GaN substrates where the In content varied from 0.14 to 0.28 in the m-plane series and 0.08 to 0.21 for the a-plane series. The low temperature photoluminescence spectra from both sets of samples are broad with full width at half maximum height increasing from 81 to 330 meV as the In fraction increases. Photoluminescence excitation spectroscopy indicates that the recombination mainly involves strongly localised carriers. At 10 K the degree of linear polarisation of the a-plane samples is much smaller than of the m-plane counterparts and also varies across the spectrum. From polarisation-resolved photoluminescence excitation spectroscopy we measured the energy splitting between the lowest valence sub-bands to lie in the range of 23–54 meV for the a- and m-plane samples in which we could observe distinct exciton features. Thus the thermal occupation of a higher valence sub-band cannot be responsible for the reduction of the degree of linear polarisation at 10 K. Time-resolved spectroscopy indicates that in a-plane samples there is an extra emission component which is at least partly responsible for the reduction in the degree of linear polarisation. PMID:27933113

  10. 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.

  11. High responsivity A-plane GaN-based metal-semiconductor-metal photodetectors for polarization-sensitive applications

    SciTech Connect

    Navarro, A.; Rivera, C.; Pereiro, J.; Munoz, E.; Imer, B.; DenBaars, S. P.; Speck, J. S.

    2009-05-25

    The fabrication and characterization of metal-semiconductor-metal polarization-sensitive photodetectors based on A-plane GaN grown on R-plane sapphire substrates is reported. These photodetectors take advantage of the in-plane crystal anisotropy, which results in linear dichroism near the band gap energy. The high resistivity of the A-plane GaN material leads to extremely low dark currents. For an optimized finger spacing of 1 {mu}m, dark current density and responsivity at 30 V are 0.3 nA/mm{sup 2} and 2 A/W, respectively. A maximum polarization sensitivity ratio of 1.8 was determined. In a differential configuration, the full width at half maximum of the polarization-sensitive region is 8.5 nm.

  12. Analysis of the AlGaN/GaN vertical bulk current on Si, sapphire, and free-standing GaN substrates

    SciTech Connect

    Perez-Tomas, A.; Fontsere, A.; Llobet, J.; Placidi, M.; Rennesson, S.; Chenot, S.; Moreno, J. C.; Cordier, Y.; Baron, N.

    2013-05-07

    The vertical bulk (drain-bulk) current (I{sub db}) properties of analogous AlGaN/GaN hetero-structures molecular beam epitaxially grown on silicon, sapphire, and free-standing GaN (FS-GaN) have been evaluated in this paper. The experimental I{sub db} (25-300 Degree-Sign C) have been well reproduced with physical models based on a combination of Poole-Frenkel (trap assisted) and hopping (resistive) conduction mechanisms. The thermal activation energies (E{sub a}), the (soft or destructive) vertical breakdown voltage (V{sub B}), and the effect of inverting the drain-bulk polarity have also been comparatively investigated. GaN-on-FS-GaN appears to adhere to the resistive mechanism (E{sub a} = 0.35 eV at T = 25-300 Degree-Sign C; V{sub B} = 840 V), GaN-on-sapphire follows the trap assisted mechanism (E{sub a} = 2.5 eV at T > 265 Degree-Sign C; V{sub B} > 1100 V), and the GaN-on-Si is well reproduced with a combination of the two mechanisms (E{sub a} = 0.35 eV at T > 150 Degree-Sign C; V{sub B} = 420 V). Finally, the relationship between the vertical bulk current and the lateral AlGaN/GaN transistor leakage current is explored.

  13. 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.

  14. 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.

  15. Low Al-composition p-GaN/Mg-doped Al0.25Ga0.75N/n+-GaN polarization-induced backward tunneling junction grown by metal-organic chemical vapor deposition on sapphire substrate

    PubMed Central

    Zhang, Kexiong; Liang, Hongwei; Liu, Yang; Shen, Rensheng; Guo, Wenping; Wang, Dongsheng; Xia, Xiaochuan; Tao, Pengcheng; Yang, Chao; Luo, Yingmin; Du, Guotong

    2014-01-01

    Low Al-composition p-GaN/Mg-doped Al0.25Ga0.75N/n+-GaN polarization-induced backward tunneling junction (PIBTJ) was grown by metal-organic chemical vapor deposition on sapphire substrate. A self-consistent solution of Poisson-Schrödinger equations combined with polarization-induced theory was used to model PIBTJ structure, energy band diagrams and free carrier concentrations distribution. The PIBTJ displays reliable and reproducible backward tunneling with a current density of 3 A/cm2 at the reverse bias of −1 V. The absence of negative differential resistance behavior of PIBTJ at forward bias can mainly be attributed to the hole compensation centers, including C, H and O impurities, accumulated at the p-GaN/Mg-doped AlGaN heterointerface. PMID:25205042

  16. 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.

  17. High-Performance GaN-Based Light-Emitting Diodes on Patterned Sapphire Substrate with a Novel Patterned SiO2/Al2O3 Passivation Layer

    NASA Astrophysics Data System (ADS)

    Guo, Hao; Zhang, Xiong; Chen, Hongjun; Liu, Honggang; Zhang, Peiyuan; Liao, Qinghua; Hu, Shujuan; Chang, Hudong; Sun, Bing; Wang, Shengkai; Cui, Yiping

    2013-07-01

    GaN-based light-emitting diodes (LEDs) on patterned sapphire substrate (PSS) with a novel patterned SiO2/Al2O3 passivation layer have been proposed and fabricated. Due to the excellent uniformity and compactness of atomic layer deposition (ALD) for the first Al2O3 layer, a high passivation effect has been achieved. The second SiO2 layer with patterned hemisphere arrays decreases the total internal reflection (TIR) and, hence, increases the light output power (LOP). With a 60 mA injection current, an enhancement of 21.6% in LOP was realized for the LED with an appropriately patterned SiO2/Al2O3 passivation layer as compared with the conventional LED with a SiO2 passivation layer.

  18. 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.

  19. 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.

  20. 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.

  1. High-performance GaN-based light-emitting diodes on patterned sapphire substrate with a novel hybrid Ag mirror and atomic layer deposition-TiO2/Al2O3 distributed Bragg reflector backside reflector

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

    GaN-based light-emitting diodes (LED) on a patterned sapphire substrate with a novel hybrid atomic layer deposition (ALD)-TiO2Al2O3 distributed Bragg reflector (DBR) and Ag mirror have been proposed and fabricated. Due to the excellent thickness uniformity of ALD for the proposed reflector, high reflectivity over 99.3% at an incident angle of 5 deg has been achieved. It was also found that the reflectivity of a backside reflector with an Ag mirror slightly depends on incident light wavelength and incident angle. Moreover, because of the good adhesion between TiO2/Al2O3 DBR and the Ag mirror, the fabrication process was simplified and reliable. With a 60 mA current injection, an enhancement of 5.2%, 8.9%, and 47.1% in light output power (LOP) at the 460 nm wavelength was realized for the proposed LED with Ag mirror and 3-pair ALD-TiO2Al2O3 DBR as compared with a LED with a traditional Ag mirror and 3-pair TiO2/SiO2 DBR, with Al mirror and 3-pair ALD-TiO2Al2O3 DBR, and without backside reflector, respectively. This result shows that the ALD-TiO/O3 DBR can be used to enhance the LOP greatly and improve adhesion between the sapphire substrate and the metallic mirror, and thus is very promising for fabricating high performance GaN-based LEDs.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    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. 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%.

  8. 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.

  9. 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

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

    2016-01-01

    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 effect of annealing on

  10. Single-crystal germanium grown on (1-1 0 2) sapphire by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Godbey, D. J.; Qadri, S. B.; Twigg, M. E.; Richmond, E. D.

    1989-06-01

    Crystalline germanium films have been successfully grown on the (1-1 0 2) sapphire surface using molecular beam epitaxy. Growth at temperatures above 700 C and after preannealing the sapphire substrates above 1100 C resulted in germanium films with a (110) orientation. A 500 nm germanium film grown at 800 C after preannealing the sapphire substrate at 1400 C gave an X-ray rocking curve width that measured 317 arcsec at half maximum for the (220) reflection.

  11. 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.

  12. 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.

  13. Positional dependence of defect distribution in semipolar (20\\bar{2}1) hydride vapor phase epitaxy-GaN films grown on (22\\bar{4}3) patterned sapphire substrates

    NASA Astrophysics Data System (ADS)

    Uchiyama, Toshiro; Takeuchi, Shotaro; Kamada, Shohei; Arauchi, Takuji; Hashimoto, Yasuhiro; Yamane, Keisuke; Okada, Narihito; Imai, Yasuhiko; Kimura, Shigeru; Tadatomo, Kazuyuki; Sakai, Akira

    2016-05-01

    We have investigated the position dependence of crystalline quality and defect distribution in a semipolar (20\\bar{2}1) hydride vapor phase epitaxy (HVPE)-GaN film grown on a (22\\bar{4}3) patterned sapphire substrate (PSS). Position-dependent X-ray microdiffraction (XRMD) measurement clearly revealed the periodic fluctuation of the 20\\bar{2}1 lattice plane tilting in HVPE-GaN films. This correlated with the periodic distribution of (a + c)-type dislocations owing to the patterning pitch of the PSS as confirmed by transmission electron microscopy (TEM). In the three-dimensional reciprocal lattice space map, the diffuse streak exactly along the c-axis can be clearly detected, indicating the presence of basal plane stacking faults in HVPE-GaN films. Furthermore, we have quantitatively estimated the defect densities from the results of XRMD and TEM measurements. From the obtained results of XRMD and TEM measurements, the fluctuation of the lattice plane tilting and the defect distribution in (20\\bar{2}1) HVPE-GaN films grown on two types of metalorganic vapor phase epitaxy-GaN templates will be discussed in detail.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. Current mapping of nonpolar a-plane and polar c-plane GaN films by conductive atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Xu, Shengrui; Jiang, Teng; Lin, Zhiyu; Zhao, Ying; Yang, Linan; Zhang, Jincheng; Li, Peixian; Hao, Yue

    2016-10-01

    Nonpolar (11-20) a-plane GaN and polar (0001) c-plane GaN films have been grown by metal organic chemical vapor deposition on r-plane (1-102) and c-plane (0001) sapphire substrates, respectively. Conductive atomic force microscopy (C-AFM) has been used to investigate the local conductivity of the films. C-AFM shows enhanced current conduction within the etch pits of c-plane GaN and triangular pits of a-plane GaN. The results indicate that the off-axis planes are more electrically active than c-plane and a-plane. Surprisingly, the C-AFM values in triangular pit of the a-plane GaN are much smaller than that in etch pits of the c-plane GaN. The dislocations type related current leakage mechanism is revealed for polar c-plane and nonpolar a-plane GaN films.

  20. 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.

  1. 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.

  2. Stealth dicing of sapphire wafers with near infra-red femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Yadav, Amit; Kbashi, Hani; Kolpakov, Stanislav; Gordon, Neil; Zhou, Kaiming; Rafailov, Edik U.

    2017-05-01

    The quality of the reflecting faces after dicing is critical for the fabrication of efficient and stable laser diodes emitting in the green-violet region. However, high-quality faces can be difficult to achieve for devices grown on a sapphire substrate as this material is difficult to cleave cleanly. We have therefore investigated a technology known as "stealth dicing". The technology uses a pulsed laser to damage a plane of material inside of the wafer due to multi-photon absorption instead of cutting through the wafer surface. If the damage is induced in a line of stress points, the sample can then be cleaved easily along the damaged plane to leave a high-quality surface. The use of this technique also reduces thermal damage and debris.

  3. 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

  4. 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.

  5. 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.

  6. (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.

  7. (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.

  8. 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.

  9. Thermal Modeling of GaN HEMTs on Sapphire and Diamond

    DTIC Science & Technology

    2005-12-01

    substrate material of an existing GaN HEMT from sapphire to diamond through the use of commercially available Silvaco software for modeling and simulation...from sapphire to diamond through the use of commercially available Silvaco software for modeling and simulation. The unparalleled thermal...11 A. SILVACO

  10. Study on the relationships between Raman shifts and temperature range for a-plane GaN using temperature-dependent Raman scattering

    NASA Astrophysics Data System (ADS)

    Wang, Dang-Hui; Xu, Sheng-Rui; Hao, Yue; Zhang, Jin-Cheng; Xu, Tian-Han; Lin, Zhi-Yu; Zhou, Hao; Xue, Xiao-Yong

    2013-02-01

    In this paper, Raman shifts of a-plane GaN layers grown on r-plane sapphire substrates by low-pressure metal—organic chemical vapor deposition (LPMOCVD) are investigated. We compare the crystal qualities and study the relationships between Raman shift and temperature for conventional a-plane GaN epilayer and insertion AlN/AlGaN superlattice layers for a-plane GaN epilayer using temperature-dependent Raman scattering in a temperature range from 83 K to 503 K. The temperature-dependences of GaN phonon modes (A1 (TO), E2 (high), and E1 (TO)) and the linewidths of E2 (high) phonon peak are studied. The results indicate that there exist two mechanisms between phonon peaks in the whole temperature range, and the relationship can be fitted to the pseudo-Voigt function. From analytic results we find a critical temperature existing in the relationship, which can characterize the anharmonic effects of a-plane GaN in different temperature ranges. In the range of higher temperature, the relationship exhibits an approximately linear behavior, which is consistent with the analyzed results theoretically.

  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. Computer-controlled fabrication of sapphire windows

    NASA Astrophysics Data System (ADS)

    Askinazi, Joel; Hasan, Wasim; Dunn, Daniel E.; La Fleur, L. David

    1997-11-01

    Sapphire optical materials have limited index of refraction homogeneity. This homogeneity can limit the degree of transmitted wavefront error achievable with current, conventional optical finishing practices. Current practices can not typically compensate well for the localized inhomogeneities in the sapphire substrates resulting in limited transmitted wavefront values. Emerging transmitted wavefront requirements exceed those achievable with current practices. Hughes Danbury Optical Systems recently completed a successful demonstration program in which computer controlled polishing was applied to the fabrication of very low transmitted wavefront error sapphire window. This technique involves measuring the windows in transmission and then polishing them in localized areas to remove the wavefront errors arising from the material index inhomogeneity. The net effect of each localized correction is a high fidelity transmitted wavefront over each subaperture. In the demonstration completed, we stated with windows fabricated to the limit of current, conventional practices. Applying computer controlled polishing, the transmitted wavefront quality was rapidly improved by a factor of up to five over the starting value. These results not only satisfied emerging requirements, but the process also resulted in satisfying parallel requirements of extreme surface smoothness and scatter as defined by the bi- directional transmittance distribution function. This paper addresses the process developed, its results, benefits and applications.

  13. 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.

  14. 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.

  15. 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.

  16. Critical parameters for grinding large sapphire window panels

    NASA Astrophysics Data System (ADS)

    Bashe, Joseph R.; Dempsey, Gene; Akwani, Ikerionwu A.; Jacoby, Keith T.; Hibbard, Douglas L.

    2007-04-01

    Advances in optical manufacturing and testing technologies for sapphire material are required to support the increasing use of large-aperture sapphire panels as windscreens for various electro-optical system applications. Single surface grinding is a crucial process step in both the figuring and finishing of optical components. Improper grinding can make subsequent polishing operations more difficult and time consuming. Poor grinding can also lead to the introduction of surface stress and sub-surface damage which can affect critical opto-mechanical performance characteristics such as strength and durability. Initial efforts have been completed at Exotic Electro-Optics under the funding of the Office of Naval Research and the Air Force Research Laboratory to investigate a number of process enhancements in the grinding of a-plane sapphire panels. The information gained from this study will ultimately provide a better understanding of the overall manufacturing process leading to optimized process time and cost. EEO has completed two sets of twelve-run Plackett-Burman designs of experiment (DOE) to study the effects of fundamental grinding parameters on sapphire panel surfaces. The relative importance of specific process parameters on window characteristics including surface roughness, stress, sub-surface damage are reported.

  17. 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.

  18. Sapphire surface preparation and gallium nitride nucleation by hydride vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Dwikusuma, Fransiska

    The nucleation and initial growth of gallium nitride (GaN) films on sapphire substrates using hydride vapor phase epitaxy (HVPE) technique depends on many factors including the chemical treatment of sapphire surface, nitridation, and the specific growth conditions. Liquid and gas phase treatments of the sapphire surface were systematically studied as a function of temperature and time. Phosphoric acid (H3PO4) etches sapphire preferentially at defect sites and resulted in pits formation on the surface, while etching in sulfuric acid (H2SO4) can produce a smooth, pit-free surface. Air-annealing the sapphire at 1400°C produces an atomically smooth surface consisting of a terrace-and-step structure. The mechanism of sapphire nitridation within the HVPE environment was elucidated. During nitridation, nitrogen is incorporated into the sapphire surface. The sapphire nitridation mechanism can be modeled as a diffusion couple of aluminum nitride (AlN) and aluminum oxide (Al2O 3), where N3- and O2- inter-diffuse in the 'rigid' Al3+ framework. Nitrogen diffuses into sapphire and substitutes for oxygen to bond with aluminum. The replaced oxygen diffuses out to the surface. The overall nitridation rate is controlled by the diffusion of oxygen. Sapphire surface treatments of air-annealing and liquid-based etchings have different effects on nitridation and HVPE GaN nucleation. Upon nitridation, the air-annealed sapphire has ˜1.5 times higher nitrogen content compared to liquid-based etchings. Nevertheless, the air-annealed sapphire yields the lowest density of GaN islands. Sapphire nitridation, which yields a thin AlN layer, results in the growth of higher GaN island densities with a smaller mosaic spread. Sapphire surface, which is etched in H2SO4 and then nitridated, produces a high density GaN islands resulting in improved-quality of thick GaN films. The nucleation and initial growth kinetics of GaN on sapphire grown by HVPE were investigated. As the growth temperature

  19. 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

  20. 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

  1. 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.

  2. 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.

  3. Ultraviolet Photoconductive Detectors Based on A-Plane ZnO Film Grow by Hydrothermal Method

    NASA Astrophysics Data System (ADS)

    Yu, Naisen; Dong, Dapeng; Qi, Yan; Wu, Yunfeng; Chen, Lu

    2016-02-01

    A-plane ZnO film was grown on a-plane GaN/r-sapphire template by using the hydrothermal growth method. The film was characterized for the structural and morphological properties by means of x-ray diffraction, scanning electron microscopy, and atomic force microscopy. The results show the a-plane ZnO film with a very uniform striated morphology was achieved. Meanwhile, an ultraviolet (UV) photoconductive detector based on the as-grown a-plane film was fabricated, and the detector current was increased by more than 17 times under 5 V bias upon UV illumination. Moreover, it also showed good reproducibility and stability, which confirms the film as a good potential material for UV optoelectronic devices.

  4. 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

  5. Unintentional doping of a-plane GaN by insertion of in situ SiN masks

    NASA Astrophysics Data System (ADS)

    Witte, H.; Wieneke, M.; Rohrbeck, A.; Guenther, K.-M.; Dadgar, A.; Krost, A.

    2011-03-01

    Undoped a-plane GaN layers grown by metal-organic vapour phase epitaxy on sapphire (1 0 - 1 2) substrates using low temperature (LT) GaN seed layers and in situ SiN masks were characterized by Hall-effect measurements, CV-characteristics and photovoltage spectroscopy. With increasing deposition time of the SiN masks the electron concentrations of the GaN layers are enhanced. The dominant activation energy between 14 and 22 meV determined by temperature-dependent Hall effect is very similar to the donor silicon on gallium site. Two other activation energies at 30 meV and between 50 and 70 meV were found corresponding well with OGa and VN defects, respectively. The depth profiles of the net donor densities show a strong increase towards the substrate/LT-GaN/high temperature(HT)-GaN interface indicating diffusion of silicon from the SiN mask towards the surface. Therefore, the Si doping is attributed to the dissolution of the SiN masks during the following HT GaN layer growth. The Si doping from the SiN masks also explains the deterioration of the band bending within the LT-GaN/HT-GaN junction found by photovoltage spectroscopy.

  6. Vertical InGaN light-emitting diode with a retained patterned sapphire layer.

    PubMed

    Yang, Y C; Sheu, Jinn-Kong; Lee, Ming-Lun; Yen, C H; Lai, Wei-Chih; Hon, Schang Jing; Ko, Tsun Kai

    2012-11-05

    We present an efficient vertical InGaN light-emitting diode (LED) in which the proposed vertical LEDs were fabricated with patterned sapphire substrates (PSS) using thinning techniques. After the thinning of sapphire substrate, selective dry etching process was performed on the remainder sapphire layer to expose the n-GaN contact layer instead of removing the sapphire substrate using the laser lift-off technique. These processes feature the LEDs with a sapphire-face-up structure and vertical conduction property. The PSS was adopted as a growth substrate to mitigate the light-guided effect, and thereby increase the light-extraction efficiency. Compared with conventional lateral GaN LEDs grown on PSS, the proposed vertical LEDs exhibit a higher light output power and less power degradation at a high driving current. This could be attributed to the fact that the vertical LEDs behave in a manner similar to flip-chip GaN/sapphire LEDs with excellent heat conduction.

  7. Molecular spiders on a plane

    NASA Astrophysics Data System (ADS)

    Antal, Tibor; Krapivsky, P. L.

    2012-06-01

    Synthetic biomolecular spiders with “legs” made of single-stranded segments of DNA can move on a surface covered by single-stranded segments of DNA called substrates when the substrate DNA is complementary to the leg DNA. If the motion of a spider does not affect the substrates, the spider behaves asymptotically as a random walk. We study the diffusion coefficient and the number of visited sites for spiders moving on the square lattice with a substrate in each lattice site. The spider's legs hop to nearest-neighbor sites with the constraint that the distance between any two legs cannot exceed a maximal span. We establish analytic results for bipedal spiders, and investigate multileg spiders numerically. In experimental realizations legs usually convert substrates into products (visited sites). The binding of legs to products is weaker, so the hopping rate from the substrates is smaller. This makes the problem non-Markovian and we investigate it numerically. We demonstrate the emergence of a counterintuitive behavior—the more spiders are slowed down on unvisited sites, the more motile they become.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Sapphire Surface Polymorphs and The Growth of Pb Overlayers

    NASA Astrophysics Data System (ADS)

    Hong, Hawoong; Gray, Aaron; Chiang, T.-C.

    2008-03-01

    The surface structure of sapphire (α-alumina) is an issue of long-standing interest, both scientifically and technologically. Molecular dynamics simulations showed the γ-alumina structure to have a lower energy than that of α-alumina [1], thus suggesting a possibly modified surface structure when sapphire is treated at high temperatures. We have performed x-ray reflectivity measurements at the Advanced Photon Source to address this issue. Standard sapphire substrates were prepared by furnace annealing at 1600^o C in air. The resulting surfaces showed large terraces with straight step edges. The substrates were then annealed in a UHV chamber at increasingly higher temperatures. Many new features emerged in the reflectivity curves, which could be attributed to various transition alumina structures, including the θ'-, δ-, and θ- polymorphs [2]. Pb films were grown on these surfaces. The resulting structure and morphology was characterized. This talk will summarize our findings. [1] S. Blonski and S. H. Garofalini, Surf. Sci. 295, 263 (1993). [2] I. Levin and D. Brandon, J. Am. Ceram. Soc. 81, 1995 (1998).

  14. Fabrication and surface profile simulation of sapphire microlens array

    NASA Astrophysics Data System (ADS)

    Liu, Xiangyang; Liu, Shijia; Qiao, Hui; Zhu, Longyuan; Li, Xiangyang

    2015-04-01

    In this paper, photoresist reflow method was used to fabricate microlens array on the sapphire substrate which possesses high mechanical strength and transmittance in broad spectrum. High etch selectivity of sapphire over photoresist was obtained through adjusting ICP etching parameters. To test the fabrication process, a geometric model of square aperture microlens was built by finite element method. The validation of this model was done by comparing the surface profiles of three samples reflowed under different condition with the geometric model. In all three cases the simulation results were close to the experiment results. So the model was justified. On the other hand, the fabrication process was found to be repeatable because the surface profile of fabricated microlens was close to the theoretical surface profile of reflowed photoresist. The geometric model can be used to check the repeatability of photoresist reflow process and to predict the surface profile of microlens with irregular aperture.

  15. 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.

  16. Growth and characterizations of various GaN nanostructures on C-plane sapphire using laser MBE

    NASA Astrophysics Data System (ADS)

    Ch., Ramesh; Tyagi, P.; Maurya, K. K.; Kumar, M. Senthil; Kushvaha, S. S.

    2017-05-01

    We have grown various GaN nanostructures such as three-dimensional islands, nanowalls and nanocolumns on c-plane sapphire substrates using laser assisted molecular beam epitaxy (LMBE) system. The shape of the GaN nanostructures was controlled by using different nucleation surfaces such as bare and nitridated sapphire with GaN or AlN buffer layers. The structural and surface morphological properties of grown GaN nanostructures were characterized by ex-situ high resolution x-ray diffraction, Raman spectroscopy and field emission scanning electron microscopy. The symmetric x-ray rocking curve along GaN (0002) plane shows that the GaN grown on pre-nitridated sapphire with GaN or AlN buffer layer possesses good crystalline quality compared to sapphire without nitridation. The Raman spectroscopy measurements revealed the wurtzite phase for all the GaN nanostructures grown on c-sapphire.

  17. 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.

  18. 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).

  19. Patterned growth of aligned ZnO nanowire arrays on sapphire and GaN layers

    NASA Astrophysics Data System (ADS)

    Fan, H. J.; Fleischer, F.; Lee, W.; Nielsch, K.; Scholz, R.; Zacharias, M.; Gösele, U.; Dadgar, A.; Krost, A.

    2004-07-01

    Patterned growth of vertically aligned ZnO nanowire arrays on the micrometer and nanometer scale on sapphire and GaN epilayers is reported. In order to control the position and distribution density of the ZnO nanowires, Au seeding nanodots are defined, as regular arrays, with the assistance of deposition shadow masks. Electron micrographs reveal that the wires are single crystals having wire axes along the hexagonal c-axes. The epitaxial growth of ZnO nanowires on sapphire and GaN films on Si substrates was further verified by cross sectional electron microscopy investigations. Compared to the sapphire case, the perfect epitaxial growth on a GaN film on a Si substrate is believed to be more suitable for potential electronic device applications of ZnO nanowire arrays.

  20. 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.

  1. 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.

  2. Growth of b-axis rare earths on sapphire by molecular beam epitaxy

    SciTech Connect

    Ritley, K.A.; Flynn, C.P.

    1998-01-01

    A process is described whereby hcp rare-earth metals can be grown heteroepitaxially as high-quality single-crystal films with the b axis normal to the growth plane. The growth employs molecular beam epitaxy, starting from available sapphire substrates. The results of characterization by several techniques are described. {copyright} {ital 1998 American Institute of Physics.}

  3. Rhombohedral Super Heteero Epitaxy of Cubic SiGe on Trigonal c-plane Sapphire

    NASA Technical Reports Server (NTRS)

    Choi, Sang H.; Duzik, Adam J.

    2017-01-01

    New rhombohedral super-hetero-epitaxy technology was developed at NASA. This epitaxy technology enables the growth of unprecedented cubic-trigonal hybrid single crystal structures with lattice match on sapphire (Al2O3) substrates, hence with little strain and very few defects at the interface.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. Role of sapphire nitridation temperature on GaN growth by plasma assisted molecular beam epitaxy: Part II. Interplay between chemistry and structure of layers

    NASA Astrophysics Data System (ADS)

    Losurdo, Maria; Capezzuto, Pio; Bruno, Giovanni; Namkoong, Gon; Doolittle, W. Alan; Brown, April S.

    2002-02-01

    The effect of sapphire nitridation temperature on the chemistry and microstructure of the sapphire substrate/GaN interface, nucleation layer, and of the GaN epilayers grown by rf plasma assisted molecular beam epitaxy is investigated. It is found that a sapphire nitridation temperature as low as 200 °C improves the structural and optical quality of GaN epilayers. This result can be explained by the chemistry of the sapphire nitridation process, which is discussed in the framework of a model considering the competitive formation of AlN and oxynitride (NO). In particular, at 200 °C, NO desorbs from the sapphire surface, yielding an homogeneous 6 Å AlN layer upon N2 plasma nitridation. This low temperature AlN template favors the nucleation of hexagonal GaN nuclei which coalesce completely resulting in a hexagonal GaN buffer layer that homogeneously covers the sapphire substrate. This condition promotes the growth of a high quality GaN epilayer. In contrast, high nitridation temperatures result in a mixed AlN/NO nitrided sapphire surface which induce a perturbed and more defected interface with the occurrence of cubic crystallites in the GaN buffer. A sapphire surface with random GaN islands is found upon annealing of the GaN buffer and this condition results in a low-quality GaN epilayer.

  12. 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.

  13. A Century of Sapphire Crystal Growth

    DTIC Science & Technology

    2004-05-17

    process • 1904: Full publication: A. Verneuil, “Memoire sur la reproduction du rubis par fusion,” Annales de Chimie et de Physique Ser. 8, 3: 20-48...quality 54 Sapphire from Atlas Russian Research and Production Company Kyropoulos growth method, also called GOI in Russia 55 Verneuil Sapphire from... Atlas Russian Research and Production Company 56 Acknowledgements: • Kurt Nassau, Gems Made by Man Bell Labs • Fred Schmid and Chandra Khattak Crystal

  14. 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.

  15. Theoretical studies on lattice-oriented growth of single-walled carbon nanotubes on sapphire

    NASA Astrophysics Data System (ADS)

    Li, Zhengwei; Meng, Xianhong; Xiao, Jianliang

    2017-09-01

    Due to their excellent mechanical and electrical properties, single-walled carbon nanotubes (SWNTs) can find broad applications in many areas, such as field-effect transistors, logic circuits, sensors and flexible electronics. High-density, horizontally aligned arrays of SWNTs are essential for high performance electronics. Many experimental studies have demonstrated that chemical vapor deposition growth of nanotubes on crystalline substrates such as sapphire offers a promising route to achieve such dense, perfectly aligned arrays. In this work, a theoretical study is performed to quantitatively understand the van der Waals interactions between SWNTs and sapphire substrates. The energetically preferred alignment directions of SWNTs on A-, R- and M-planes and the random alignment on the C-plane predicted by this study are all in good agreement with experiments. It is also shown that smaller SWNTs have better alignment than larger SWNTs due to their stronger interaction with sapphire substrate. The strong vdW interactions along preferred alignment directions can be intuitively explained by the nanoscale ‘grooves’ formed by atomic lattice structures on the surface of sapphire. This study provides important insights to the controlled growth of nanotubes and potentially other nanomaterials.

  16. Theoretical studies on lattice-oriented growth of single-walled carbon nanotubes on sapphire.

    PubMed

    Li, Zhengwei; Meng, Xianhong; Xiao, Jianliang

    2017-09-20

    Due to their excellent mechanical and electrical properties, single-walled carbon nanotubes (SWNTs) can find broad applications in many areas, such as field-effect transistors, logic circuits, sensors and flexible electronics. High-density, horizontally aligned arrays of SWNTs are essential for high performance electronics. Many experimental studies have demonstrated that chemical vapor deposition growth of nanotubes on crystalline substrates such as sapphire offers a promising route to achieve such dense, perfectly aligned arrays. In this work, a theoretical study is performed to quantitatively understand the van der Waals interactions between SWNTs and sapphire substrates. The energetically preferred alignment directions of SWNTs on A-, R- and M-planes and the random alignment on the C-plane predicted by this study are all in good agreement with experiments. It is also shown that smaller SWNTs have better alignment than larger SWNTs due to their stronger interaction with sapphire substrate. The strong vdW interactions along preferred alignment directions can be intuitively explained by the nanoscale 'grooves' formed by atomic lattice structures on the surface of sapphire. This study provides important insights to the controlled growth of nanotubes and potentially other nanomaterials.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. Fabrication of geometric sapphire shaped InGaN/Al2O3 (S) LED scribed by using wet chemical etching

    NASA Astrophysics Data System (ADS)

    Kawan, Anil; Yu, S. J.; Park, Hwa Jin; Seo, Ju-Ok; Yoon, Seok-Beom

    2014-02-01

    The wet chemical etching method for etching V-grooves into sapphire substrates is used as scribing technique, and a geometric sapphire shaped InGaN/Al2O3 (S) light-emitting diode (LED) chip is fabricated. The V-groove is formed on the backside of a 150-µ-thick sapphire substrate by wet etching in a 3H2SO4:1H3PO4 chemical solution. The fabricated wet scribed geometric sapphire shaped LED exhibits a 15.86% enhancement in the light output power at 60-mA compared to the laser-stealth-scribed conventional rectangular LED. In addition, a ray-tracing simulation using "Light Tools" is performed on shaped geometric sapphire samples to investigate the enhancement of the light extracted from the substrate. The enhancement of the light output power for the wetscribed geometric sapphire shaped LED is thought to be due to the elimination of thermal damage and to an increase in light extraction from geometric sapphire shaped structure.

  4. Characterization of nonpolar a-plane InGaN/GaN multiple quantum well using double nanopillar SiO2 mask

    NASA Astrophysics Data System (ADS)

    Son, Ji-Su; Honda, Yoshio; Yamaguchi, Masahito; Amano, Hiroshi

    2014-01-01

    The characteristics of nonpolar a-plane (11\\bar{2}0) GaN (a-GaN) grown using single and double nanopillar SiO2 masks were investigated. The two nanopillar SiO2 masks were directly fabricated on an r-plane sapphire substrate and a-GaN by the epitaxial lateral overgrowth (ELOG) technique. Through the use of the single and double nanopillar SiO2 masks, the crystalline quality and optical properties of a-GaN were markedly improved because of the nanoscale ELOG effect and a number of voids in the single and double nanopillar SiO2 mask areas in comparison with the planar sample. The submicron pit densities of the planar, single, and double nanopillar mask samples were ˜2 × 109, ˜7 × 108, and ˜4 × 108 cm-2, respectively. The internal quantum efficiency (IQE) values at room temperature of three-period InGaN/GaN multiple quantum wells (MQWs) grown using the planar, single, and double nanopillar masks were 45, 60, and 68% at a carrier concentration of 1.0 × 1018 cm-3, respectively.

  5. 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.

  6. Slow Crack Growth and Fracture Toughness of Sapphire for the International Space Station Fluids and Combustion Facility

    NASA Technical Reports Server (NTRS)

    Salem, Jonathan A.

    2006-01-01

    The fracture toughness, inert flexural strength, and slow crack growth parameters of the r- and a-planes of sapphire grown by the Heat Exchange Method were measured to qualify sapphire for structural use in the International Space Station. The fracture toughness in dry nitrogen, K(sub Ipb), was 2.31 +/- 0.12 MPa(square root of)m and 2.47 +/- 0.15 MPa(squre root of)m for the a- and r-planes, respectively. Fracture toughness measured in water via the operational procedure in ASTM C1421 was significantly lower, K(sub Ivb) = 1.95+/- 0.03 MPa(square root of)m, 1.94 +/- 0.07 and 1.77 +/- 0.13 MPa(square root of)m for the a- , m- and r-planes, respectively. The mean inert flexural strength in dry nitrogen was 1085 +/- 127 MPa for the r-plane and 1255 +/- 547 MPa for the a-plane. The power law slow crack growth exponent for testing in water was n = 21 +/- 4 for the r-plane and n (greater than or equal to) 31 for the a-plane. The power law slow crack growth coefficient was A = 2.81 x 10(exp -14) m/s x (MPa(squre root of)m)/n for the r-plane and A (approx. equals)2.06 x 10(exp -15) m/s x (MPa(square root of)m)/n for the a-plane. The r- and a-planes of sapphire are relatively susceptible to stress corrosion induced slow crack growth in water. However, failure occurs by competing modes of slow crack growth at long failure times and twinning for short failure time and inert environments. Slow crack growth testing needs to be performed at low failure stress levels and long failure times so that twinning does not affect the results. Some difficulty was encountered in measuring the slow crack growth parameters for the a-plane due to a short finish (i.e., insufficient material removal for elimination of the damage generated in the early grinding stages). A consistent preparation method that increases the Weibull modulus of sapphire test specimens and components is needed. This would impart higher component reliability, even if higher Weibull modulus is gained at the sacrifice of

  7. How edge finish effects the strength of sapphire

    NASA Astrophysics Data System (ADS)

    Jacoby, Keith T.; Goodrich, Steven M.

    2005-05-01

    Exotic Electro-Optics (EEO) has completed a study of how the edge finish of an A-plane sapphire sample affects its flexural strength when tested using the 4-point bend test method. Flexural bar samples were fabricated out of a sapphire panel that was polished to production quality using EEO's standard production methods. All samples were configured to meet the requirements for a C-size sample as defined by ASTM C-1161. The only difference between the three sample groups was the edge finish applied to the sample - conventionally ground, fine ground or a commercial polish edge finish. The edge finish on each sample was quantitatively characterized prior to strength testing. All samples were visually inspected prior to testing to identify any potential fracture initiation points. The samples were then tested using an Instron Universal tester per ASTM C-1161 in the UDRI Ceramics and Glasses Laboratory. After testing, a visual inspection was performed to identify the fracture initiation surface and location. Observations confirmed that all sample data was valid (all fractures initiated inside the two inner load dowels), no fractures were initiated on the edges, and no fractures initiated at any of the suspect sites noted in the pre-test visual inspection. The data was post processed using standard statistical and Weibull analysis methodologies. The results showed no significant difference when comparing the flexural strength of the three edge finish groups. The data suggest that the surface quality of the planar surfaces and the bevels is more critical than the finish of the full edge.

  8. 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.

  9. 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

  10. Nanostructuring of sapphire using time-modulated nanosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Lorenz, P.; Zagoranskiy, I.; Ehrhardt, M.; Bayer, L.; Zimmer, K.

    2017-02-01

    The nanostructuring of dielectric surfaces using laser radiation is still a challenge. The IPSM-LIFE (laser-induced front side etching using in-situ pre-structured metal layer) method allows the easy, large area and fast laser nanostructuring of dielectrics. At IPSM-LIFE a metal covered dielectric is irradiated where the structuring is assisted by a self-organized molten metal layer deformation process. The IPSM-LIFE can be divided into two steps: STEP 1: The irradiation of thin metal layers on dielectric surfaces results in a melting and nanostructuring process of the metal layer and partially of the dielectric surface. STEP 2: A subsequent high laser fluence treatment of the metal nanostructures result in a structuring of the dielectric surface. At this study a sapphire substrate Al2O3(1-102) was covered with a 10 nm thin molybdenum layer and irradiated by an infrared laser with an adjustable time-dependent pulse form with a time resolution of 1 ns (wavelength λ = 1064 nm, pulse duration Δtp = 1 - 600 ns, Gaussian beam profile). The laser treatment allows the fabrication of different surface structures into the sapphire surface due to a pattern transfer process. The resultant structures were investigated by scanning electron microscopy (SEM). The process was simulated and the simulation results were compared with experimental results.

  11. Surface Functionalized Graphene Biosensor on Sapphire for Cancer Cell Detection.

    PubMed

    Joe, Daniel J; Hwang, Jeonghyun; Johnson, Christelle; Cha, Ho-Young; Lee, Jo-Won; Shen, Xiling; Spencer, Michael G; Tiwari, Sandip; Kim, Moonkyung

    2016-01-01

    Graphene has several unique physical, optical and electrical properties such as a two-dimensional (2D) planar structure, high optical transparency and high carrier mobility at room temperature. These make graphene interesting for electrical biosensing. Using a catalyst-free chemical vapor deposition (CVD) method, graphene film is grown on a sapphire substrate. There is a single or a few sheets as confirmed by Raman spectroscopy and atomic force microscopy (AFM). Electrical graphene biosensors are fabricated to detect large-sized biological analytes such as cancer cells. Human colorectal carcinoma cells are sensed by the resistance change of an active bio-functionalized graphene device as the cells are captured by the immobilized antibody surface. The functionalized sensors show an increase in resistance as large as ~20% of the baseline with a small number of adhered cells. This study suggests that the bio-functionalized electrical graphene sensors on sapphire, which is a highly transparent material, can potentially detect circulating tumor cells (CTCs) and monitor cellular electrical behavior while being compatible with fluorescence-based optical-detection bioassays.

  12. 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

  13. 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.

  14. 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.

  15. Semipolar (202̅1̅) GaN and InGaN Light-Emitting Diodes Grown on Sapphire.

    PubMed

    Song, Jie; Choi, Joowon; Xiong, Kanglin; Xie, Yujun; Cha, Judy J; Han, Jung

    2017-04-26

    We have demonstrated growing uniform and purely nitrogen polar semipolar (202̅1̅) GaN epilayers on 2 in. patterned sapphire substrates. The as-grown surface of (202̅1̅) GaN is composed of two stable facets: (101̅0) and (101̅1̅). A chemical mechanical polishing process was further used to planarize the surface with a final surface root-mean-square roughness of less than 1.5 nm over an area of 10 × 10 μm(2). InGaN light-emitting diodes were grown on a polished (202̅1̅) GaN/sapphire template with an electroluminescence emission at around 490 nm. Our work exhibits the potential to produce high-quality nitrogen-polar semipolar GaN templates and optoelectronic devices on large-area sapphire substrates with economical feasibility.

  16. 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.

  17. 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

  18. 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.

  19. 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.

  20. Peripheral laser angioplasty with sapphire tip.

    PubMed

    Fourrier, J L; Van Franchen, B; Henri, M; Lefebvre, J M; Brunetaud, J M; Bertrand, M E

    1991-01-01

    To improve the result of peripheral laser recanalization (less perforation with wider tunnels of vaporization), we used the technique of sapphire laser angioplasty. A Nd:YAG laser with continuous emission was connected to a catheter with a 600 mum fiber and a sapphire probe to its extremity (1.8-3 mm in diameter). Treatment was performed on 127 patients with severe stenosis or occlusion of peripheral arteries (iliac, femoral, or popliteal arteries). Recanalization was obtained in 102 cases (80%) and was further embellished by balloon dilatation. The rate of success decreased proportionally with the length of occlusions (93% for 3 cm, 33% for 15 cm and more). Most failures were due to wall perforation or wall entry of the probe; passage of the sapphire tip was rarely blocked by the occlusion. At follow-up, 26.4% of arteries were reoccluded after 2 months. laser angioplasty with a sapphire tip can totally recanalize occluded arteries with low rate of failure and complications.

  1. 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.

  2. 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.

  3. Epitaxial growth of HfS2 on sapphire by chemical vapor deposition and application for photodetectors

    NASA Astrophysics Data System (ADS)

    Wang, Denggui; Zhang, Xingwang; Liu, Heng; Meng, Junhua; Xia, Jing; Yin, Zhigang; Wang, Ye; You, Jingbi; Meng, Xiang-Min

    2017-09-01

    Group IVB transition metal (Zr and Hf) dichalcogenides (TMDs) have been attracting intensive attention as promising candidates in the modern electronic and/or optoelectronic fields. However, the controllable growth of HfS2 monolayers or few layers still remains a great challenge, thus hindering their further applications so far. Here, for the first time we demonstrate the epitaxial growth of high-quality HfS2 with a controlled number of layers on c-plane sapphire substrates by chemical vapor deposition (CVD). The HfS2 layers exhibit an atomically sharp interface with the sapphire substrate, followed by flat, 2D layers with octahedral coordination. The epitaxial relationship between HfS2 and substrate was determined by x-ray diffraction and transmission electron microscopy measurements to be: HfS2 (0 0 0 1) [10-10]||sapphire (0 0 0 1)[1-100]. Moreover, a high-performance photodetector with a high on/off ratio of more than 103 and an ultrafast response rate of 130 µs for the rise and 155 µs for the decay times were fabricated based on the CVD-grown HfS2 layers on sapphire substrates. This simple and controllable approach opens up a new way to produce highly crystalline HfS2 atomic layers, which are promising materials for nanoelectronics.

  4. 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.

  5. 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.

  6. 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.

  7. Molecular beam epitaxy of InN dots on nitrided sapphire

    SciTech Connect

    Romanyuk, Yaroslav E.; Dengel, Radu-Gabriel; Stebounova, LarissaV.; Leone, Stephen R.

    2007-04-20

    A series of self-assembled InN dots are grown by radio frequency (RF) plasma-assisted molecular beam epitaxy (MBE) directly on nitrided sapphire. Initial nitridation of the sapphire substrates at 900 C results in the formation of a rough AlN surface layer, which acts as a very thin buffer layer and facilitates the nucleation of the InN dots according to the Stranski-Krastanow growth mode, with a wetting layer of {approx}0.9 nm. Atomic force microscopy (AFM) reveals that well-confined InN nanoislands with the greatest height/width at half-height ratio of 0.64 can be grown at 460 C. Lower substrate temperatures result in a reduced aspect ratio due to a lower diffusion rate of the In adatoms, whereas the thermal decomposition of InN truncates the growth at T>500 C. The densities of separated dots vary between 1.0 x 10{sup 10} cm{sup -2} and 2.5 x 10{sup 10} cm{sup -2} depending on the growth time. Optical response of the InN dots under laser excitation is studied with apertureless near-field scanning optical microscopy and photoluminescence spectroscopy, although no photoluminescence is observed from these samples. In view of the desirable implementation of InN nanostructures into photonic devices, the results indicate that nitrided sapphire is a suitable substrate for growing self-assembled InN nanodots.

  8. 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.

  9. 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.

  10. Symmetric faceting of a sapphire vicinal surface revealed by grazing incidence small-angle X-ray scattering 3D mapping

    NASA Astrophysics Data System (ADS)

    Matringe, C.; Fakih, A.; Thune, E.; Babonneau, D.; Arnaud, S.; Blanc, N.; Boudet, N.; Guinebretière, R.

    2017-07-01

    A one dimensional periodic vicinal surface of sapphire was obtained through a self-ordering process after high-temperature thermal treatment. The morphology of the surface is described as an assembly of prisms exhibiting a rectangular base and a triangular profile orthogonal to the mean surface. Careful measurements of the whole 3D reciprocal map around the origin of the reciprocal space were performed through grazing incidence small-angle X-ray scattering experiments combined with a strict orientation procedure with respect to specific crystallographic directions of the sapphire crystal. We were thus able to determine accurately the actual shape of the prisms, which exhibit an isosceles triangular profile. Such a profile symmetric with respect to a plane normal to the mean sapphire vicinal surface has never been reported.

  11. 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.

  12. 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.

  13. Crystal front shape control by use of an additional heater in a Czochralski sapphire single crystal growth system

    NASA Astrophysics Data System (ADS)

    Hur, Min-Jae; Han, Xue-Feng; Choi, Ho-Gil; Yi, Kyung-Woo

    2017-09-01

    The quality of sapphire single crystals used as substrates for LED production is largely influenced by two defects: dislocation density and bubbles trapped in the crystal. In particular, the dislocation density has a higher value in sapphire grown by the Czochralski (CZ) method than by other methods. In the present study, we predict a decreased value for the convexity and thermal gradient at the crystal front (CF) through the use of an additional heater in an induction-heated CZ system. In addition, we develop a solute concentration model by which the location of bubble formation in CZ growth is calculated, and the results are compared with experimental results. We further calculate the location of bubble entrapment corresponding with the use of an additional heater. We find that sapphire crystal growth with an additional heater yields a decreased thermal gradient at the CF, together with decreased CF convexity, improved energy efficiency, and improvements in terms of bubble formation location.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Growth and characterization of VO2/p-GaN/sapphire heterostructure with phase transition properties

    NASA Astrophysics Data System (ADS)

    Bian, Jiming; Wang, Minhuan; Miao, Lihua; Li, Xiaoxuan; Luo, Yingmin; Zhang, Dong; Zhang, Yuzhi

    2015-12-01

    High quality pure phase VO2 films were deposited on p-GaN/sapphire substrates by pulsed laser deposition (PLD). A well-defined interface with dense and uniform morphology was observed in the as-grown VO2/p-GaN/sapphire heterostructure. The X-ray photoelectron spectroscopy (XPS) analyses confirmed the valence state of vanadium (V) in VO2 films was principally composed of V4+ with trace amount of V5+, no other valence state of V was detected. Meanwhile, a distinct reversible semiconductor-to-metal (SMT) phase transition with resistance change up to nearly three orders of magnitude was observed in the temperature dependent electrical resistance measurement, which was comparable to the high quality VO2 film grown directly on sapphire substrates. Our present findings will give a deeper insight into the physical mechanism behind the exotic characteristics of VO2/p-GaN heterostructure, and further motivate research in novel devices with combined functional properties of both correlated oxide and wide bandgap nitride semiconductors.

  19. Highly ordered catalyst-free and mask-free GaN nanorods on r-plane sapphire.

    PubMed

    Aschenbrenner, T; Kruse, C; Kunert, G; Figge, S; Sebald, K; Kalden, J; Voss, T; Gutowski, J; Hommel, D

    2009-02-18

    Self-organized and highly ordered GaN nanorods were grown without catalyst on r-plane sapphire using a combination of molecular beam epitaxy and metal-organic vapor-phase epitaxy. AlN nucleation centers for the nanorods were prepared by nitridation of the sapphire in a metal-organic vapor-phase epitaxy reactor, while the nanorods were grown by molecular beam epitaxy. A coalesced two-dimensional GaN layer was observed between the nanorods. The nanorods are inclined by 62 degrees towards the [Formula: see text]-directions of the a-plane GaN layer. The high degree of ordering and the structural perfection were confirmed by micro-photoluminescence measurements.

  20. 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.

  1. 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.

  2. The nucleation and growth of germanium on (11¯02) sapphire deposited by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Godbey, D. J.; Twigg, M. E.

    1991-04-01

    Single-crystal germanium on (11¯02) sapphire films are grown after a substrate preanneal of 1400 °C and at growth temperatures above 700 °C. At a growth temperature of 800 °C, the nucleation site density was ˜1011 cm-2. For thin germanium films, the isolated islands were singly oriented, with single-crystal films obtained for thicker grown films. A 400 °C growth temperature on sapphire was insufficiently high to get epitaxial growth and produced polycrystallites. Growth at 400 °C on an 800 °C grown germanium template did result in epitaxy. However, a high fraction of the twinned orientation was produced, resulting in a bicrystalline film.

  3. 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.

  4. Quantum dynamics of a plane pendulum

    SciTech Connect

    Leibscher, Monika; Schmidt, Burkhard

    2009-07-15

    A semianalytical approach to the quantum dynamics of a plane pendulum is developed, based on Mathieu functions which appear as stationary wave functions. The time-dependent Schroedinger equation is solved for pendular analogs of coherent and squeezed states of a harmonic oscillator, induced by instantaneous changes of the periodic potential energy function. Coherent pendular states are discussed between the harmonic limit for small displacements and the inverted pendulum limit, while squeezed pendular states are shown to interpolate between vibrational and free rotational motion. In the latter case, full and fractional revivals as well as spatiotemporal structures in the time evolution of the probability densities (quantum carpets) are quantitatively analyzed. Corresponding expressions for the mean orientation are derived in terms of Mathieu functions in time. For periodic double well potentials, different revival schemes, and different quantum carpets are found for the even and odd initial states forming the ground tunneling doublet. Time evolution of the mean alignment allows the separation of states with different parity. Implications for external (rotational) and internal (torsional) motion of molecules induced by intense laser fields are discussed.

  5. 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.

  6. 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.

  7. 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.

  8. ZnO:Sb/ZnO:Ga Light Emitting Diode on c-Plane Sapphire by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Yang, Zheng; Chu, Sheng; Chen, Winnie V.; Li, Lin; Kong, Jieying; Ren, Jingjian; Yu, Paul K. L.; Liu, Jianlin

    2010-03-01

    p-type Sb-doped ZnO (ZnO:Sb)/n-type Ga-doped ZnO (ZnO:Ga) junctions were grown on c-plane sapphire substrates using plasma-assisted molecular-beam epitaxy. Mesa geometry light emitting diodes (LEDs) were fabricated using standard photolithography and lift-off process, with ohmic contacts achieved using Au/Ni and Au/Ti for top ZnO:Sb and bottom ZnO:Ga layers, respectively. Rectifying current-voltage characteristics were achieved. Ultraviolet emission dominates in the electroluminescence spectra of the ZnO LED. An output power of ˜32 nW at an applied current of 60 mA was demonstrated. The enhanced output power, as compared to those made on silicon substrates, is attributed to the improved ZnO film quality on sapphire substrates, which is confirmed by X-ray diffraction rocking curve studies.

  9. 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.

  10. 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.

  11. The sub-micron hole array in sapphire produced by inductively-coupled plasma reactive ion etching.

    PubMed

    Shiao, Ming-Hua; Chang, Chun-Ming; Huang, Su-Wei; Lee, Chao-Te; Wu, Tzung-Chen; Hsueh, Wen-Jeng; Ma, Kung-Jeng; Chiang, Donyau

    2012-02-01

    The sub-micron hole array in a sapphire substrate was fabricated by using nanosphere lithography (NSL) combined with inductively-coupled-plasma reactive ion etching (ICP-RIE) technique. Polystyrene nanospheres of about 600 nm diameter were self-assembled on c-plane sapphire substrates by the spin-coating method. The diameter of polystyrene nanosphere was modified by using oxygen plasma in ICP-RIE system. The size of nanosphere modified by oxygen plasma was varied from 550 to 450 nm with different etching times from 15 to 35 s. The chromium thin film of 100 nm thick was then deposited on the shrunk nanospheres on the substrate by electron-beam evaporation system. The honeycomb type chromium mask can be obtained on the sapphire substrate after the polystyrene nanospheres were removed. The substrate was further etched in two sets of chlorine/Argon and boron trichloride/Argon mixture gases at constant pressure of 50 mTorr in ICP-RIE processes. The 400 nm hole array in diameter can be successfully produced under suitable boron trichloride/Argon gas flow ratio.

  12. 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.

  13. Heteroepitaxy of tetragonal BiFeO(3) on hexagonal sapphire(0001).

    PubMed

    Zhao, Y J; Yin, Z G; Zhang, X W; Fu, Z; Sun, B J; Wang, J X; Wu, J L

    2014-02-26

    Highly elongated BiFeO3 is epitaxially grown on hexagonal sapphire(0001) substrate within a rather narrow synthesis window. Both X-ray reciprocal space maps and Raman characterizations reveal that it is of true tetragonal symmetry but not the commonly observed MC type monoclinic structure. The tetragonal BiFeO3 film exhibits an island growth mode, with the island edges oriented parallel to the ⟨10-10⟩ and ⟨12-30⟩ directions of the sapphire substrate. With increasing deposition time, a transition from square island to elongated island and then to a continuous film is observed. The metastable tetragonal phase can remain on the substrate without relaxation to the thermally stable rhombohedral phase up to a critical thickness of 450 nm, providing an exciting opportunity for practicable lead-free ferroelectrics. These results facilitate a better understanding of the phase stability of BiFeO3 polymorphs and enrich the knowledge about the heteroepitaxial growth mechanism of functional oxides on symmetry-mismatched substrates.

  14. Melt inclusions in alluvial sapphires from Montana, USA: Formation of sapphires as a restitic component of lower crustal melting?

    NASA Astrophysics Data System (ADS)

    Palke, Aaron C.; Renfro, Nathan D.; Berg, Richard B.

    2017-05-01

    We report here compositions of glassy melt inclusions hosted in sapphires (gem quality corundum) from three alluvial deposits in Montana, USA including the Rock Creek, Dry Cottonwood Creek, and Missouri River deposits. While it is likely that sapphires in these deposits were transported to the surface by Eocene age volcanic events, their ultimate origin is still controversial with many models suggesting the sapphires are xenocrysts with a metamorphic or metasomatic genesis. Melt inclusions are trachytic, dacitic, and rhyolitic in composition. Microscopic observations allow separation between primary and secondary melt inclusions. The primary melt inclusions represent the silicate liquid that was present at the time of sapphire formation and are enriched in volatile components (8-14 wt.%). Secondary melt inclusions analyzed here for Dry Cottonwood Creek and Rock Creek sapphires are relatively volatile depleted and represent the magma that carried the sapphires to the surface. We propose that alluvial Montana sapphires from these deposits formed through a peritectic melting reaction during partial melting of a hydrated plagioclase-rich protolith (e.g. an anorthosite). The heat needed to drive this reaction was likely derived from the intrusion of mantle-derived mafic magmas near the base of the continental lithosphere during rollback of the Farallon slab around 50 Ma. These mafic magmas may have ended up as the ultimate carrier of the sapphires to the surface as evidenced by the French Bar trachybasalt near the Missouri River deposit. Alternatively, the trachytic, rhyolitic, and dacitic secondary melt inclusions at Rock Creek and Dry Cottonwood Creek suggests that the same magmas produced during the partial melting event that generated the sapphires may have also transported them to the surface. Determining the genesis of these deposits will further our understanding of sapphire deposits around the world and may help guide future sapphire prospecting techniques. This

  15. 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.

  16. 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.

  17. Study on effect of the surface variation of colloidal silica abrasive during chemical mechanical polishing of sapphire

    NASA Astrophysics Data System (ADS)

    Bun-Athuek, Natthaphon; Yoshimoto, Yutaka; Sakai, Koya; Khajornrungruang, Panart; Suzuki, Keisuke

    2017-07-01

    The surface and diameter size variations of colloidal silica particles during the chemical mechanical polishing (CMP) of sapphire substrates were investigated using different particle diameters of 20 and 55 nm. Dynamic light scattering (DLS) results show that the silica particles became larger after CMP under both conditions. The increase in particle size in the slurry was proportional to the material removal amount (MRA) as a function of the removed volume of sapphire substrates by CMP and affected the material removal rate (MRR). Transmission electron microscopy (TEM) images revealed an increase in the size of the fine particles and a change in their surface shape in the slurry. The colloidal silica was coated with the material removed from the substrate during CMP. In this case, the increase in the size of 55 nm diameter particles is larger than that of 20 nm diameter particles. X-ray fluorescence spectrometry (XRF) results indicate that the aluminum element from polished sapphire substrates adhered to the surfaces of silica particles. Therefore, MRR decreases with increasing of polishing time owing to the degradation of particles in the slurry.

  18. 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.

  19. 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.

  20. 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.

  1. Influence of TMAl preflow on AlN epitaxy on sapphire

    NASA Astrophysics Data System (ADS)

    Sun, Haiding; Wu, Feng; Park, Young Jae; Al tahtamouni, T. M.; Li, Kuang-Hui; Alfaraj, Nasir; Detchprohm, Theeradetch; Dupuis, Russell D.; Li, Xiaohang

    2017-05-01

    The trimethylaluminum (TMAl) preflow process has been widely applied on sapphire substrates prior to growing Al-polar AlN films by metalorganic chemical vapor deposition. However, it has been unclear how the TMAl preflow process really works. In this letter, we reported on carbon's significance in the polarity and growth mode of AlN films due to the TMAl preflow. Without the preflow, no trace of carbon was found at the AlN/sapphire interface and the films possessed mixed Al- and N-polarity. With the 5 s preflow, carbon started to precipitate due to the decomposition of TMAl, forming scattered carbon-rich clusters which were graphitic carbon. It was discovered that the carbon attracted surrounding oxygen impurity atoms and consequently suppressed the formation of AlxOyNz and thus N-polarity. With the 40 s preflow, the significant presence of carbon clusters at the AlN/sapphire interface was observed. While still attracting oxygen and preventing the N-polarity, the carbon clusters served as randomly distributed masks to further induce a 3D growth mode for the AlN growth. The corresponding epitaxial growth mode change is discussed.

  2. 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.

  3. 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.

  4. 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

  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. Nanodroplets deposited in microarrays by femtosecond Ti:sapphire laser-induced forward transfer

    SciTech Connect

    Banks, David P.; Grivas, Christos; Mills, John D.; Eason, Robert W.; Zergioti, Ioanna

    2006-11-06

    The authors present the deposition of nanoscale droplets of Cr using femtosecond Ti:sapphire laser-induced forward transfer. Deposits around 300 nm in diameter, significantly smaller than any previously reported, are obtained from a 30 nm thick source film. Deposit size, morphology, and adhesion to a receiver substrate as functions of applied laser fluence are investigated. The authors show that deposits can be obtained from previously irradiated areas of the source material film with negligible loss of deposition quality, allowing subspot size period microarrays to be produced without the need to move the source film.

  7. Surface acoustic wave devices based on AlN/sapphire structure for high temperature applications

    NASA Astrophysics Data System (ADS)

    Aubert, Thierry; Elmazria, Omar; Assouar, Badreddine; Bouvot, Laurent; Oudich, Mourad

    2010-05-01

    AlN/sapphire layered structure has been investigated as a potential substrate for surface acoustic wave (SAW) devices operating at high temperatures up to 950 °C under air atmosphere. Frequency characterizations of the SAW delay lines based on this structure indicate a slight increase of 2 dB in the insertion losses after annealing for 30 min at 900 °C. Scanning electron and atomic force microscopy as well as x-ray diffraction measurements suggest that theses losses are due to the deterioration of the Pt/Ta electrodes and to a slight oxidation of the AlN film.

  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. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. Nanostructured sapphire optical fiber for sensing in harsh environments

    NASA Astrophysics Data System (ADS)

    Chen, Hui; Liu, Kai; Ma, Yiwei; Tian, Fei; Du, Henry

    2017-05-01

    We describe an innovative and scalable strategy of transforming a commercial unclad sapphire optical fiber to an allalumina nanostructured sapphire optical fiber (NSOF) that overcomes decades-long challenges faced in the field of sapphire fiber optics. The strategy entails fiber coating with metal Al followed by subsequent anodization to form anodized alumina oxide (AAO) cladding of highly organized pore channel structure. We show that Ag nanoparticles entrapped in AAO show excellent structural and morphological stability and less susceptibility to oxidation for potential high-temperature surface-enhanced Raman Scattering (SERS). We reveal, with aid of numerical simulations, that the AAO cladding greatly increases the evanescent-field overlap both in power and extent and that lower porosity of AAO results in higher evanescent-field overlap. This work has opened the door to new sapphire fiber-based sensor design and sensor architecture.

  18. 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.

  19. 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.

  20. 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).

  1. Numerical Study of Damage Propagation and Dynamic Fracture in Sapphire

    DTIC Science & Technology

    2016-08-30

    ARL-RP-0570 ● JUNE 2016 US Army Research Laboratory Numerical Study of Damage Propagation and Dynamic Fracture in Sapphire by...Research Laboratory Numerical Study of Damage Propagation and Dynamic Fracture in Sapphire by Costas G Fountzoulas Weapons and Materials Research...with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 1

  2. 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.

  3. 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).

  4. SINGLE-CRYSTAL SAPPHIRE OPTICAL FIBER SENSOR INSTRUMENTATION

    SciTech Connect

    A. Wang; G. Pickrell; R. May

    2002-09-10

    In this research program, several optical instruments for high temperature measurement based on single crystal sapphire material are introduced and tested for real-time, reliable, long-term monitoring of temperatures for coal gasifier. These are sapphire fiber extrinsic Fabry-Perot interferometric (EFPI) sensor; intensity-measurement based polarimetric sapphire sensor and broadband polarimetric differential interferometric (BPDI) sapphire sensor. Based on current evaluation and analysis of the experimental results, the broadband polarimetric differential interferometric (BPDI) sensor system was chosen for further prototype instrumentation development. This approach is based on the self-calibrating measurement of optical path differences (OPD) in a single-crystal sapphire disk, which is a function of both the temperature dependent birefringence and the temperature dependent dimensional changes. The BPDI sensor system extracts absolute temperature information by absolute measurement of phase delays. By encoding temperature information in optical spectrum instead of optical intensity, this sensor guarantees its relative immunity to optical source power fluctuations and fiber losses, thus providing a high degree of long-term measurement stability which is highly desired in industrial applications. The entire prototype for BPDI system including the single crystal sapphire probe, zirconia prism, alumina extension tube, optical components and signal processing hardware and software have shown excellent performance in the laboratory experiments shown in this report.

  5. 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.

  6. 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.

  7. Lattice strains and polarized luminescence in homoepitaxial growth of a-plane ZnO

    NASA Astrophysics Data System (ADS)

    Matsui, Hiroaki; Tabata, Hitoshi

    2012-12-01

    In-plane lattice strains in a-plane zinc oxide (ZnO) homoepitaxial layers were selectively introduced by changing substrate type and growth conditions. Strain-free layers were observed when using a Crystec ZnO substrate, which resulted in atomically flat surfaces with nano-facets consisting of the m-plane (10-10) at atomic scale. In contrast, ZnO layers on Goodwill ZnO substrates possessed in-plane lattice strains due to generation of basal-plane stacking faults. The degree of lattice strains was systematically changed by the oxygen pressure, which clarified the close correlation between photoluminescence (PL) polarization and lattice strains. The polarization ratio of PL enhanced with the lattice strains.

  8. 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.

  9. 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.

  10. Crystal Structure and Ferroelectric Properties of ε-Ga2O3 Films Grown on (0001)-Sapphire.

    PubMed

    Mezzadri, Francesco; Calestani, Gianluca; Boschi, Francesco; Delmonte, Davide; Bosi, Matteo; Fornari, Roberto

    2016-11-21

    The crystal structure and ferroelectric properties of ε-Ga2O3 deposited by low-temperature MOCVD on (0001)-sapphire were investigated by single-crystal X-ray diffraction and the dynamic hysteresis measurement technique. A thorough investigation of this relatively unknown polymorph of Ga2O3 showed that it is composed of layers of both octahedrally and tetrahedrally coordinated Ga(3+) sites, which appear to be occupied with a 66% probability. The refinement of the crystal structure in the noncentrosymmetric space group P63mc pointed out the presence of uncompensated electrical dipoles suggesting ferroelectric properties, which were finally demonstrated by independent measurements of the ferroelectric hysteresis. A clear epitaxial relation is observed with respect to the c-oriented sapphire substrate, with the Ga2O3 [10-10] direction being parallel to the Al2O3 direction [11-20], yielding a lattice mismatch of about 4.1%.

  11. 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.

  12. 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

  13. 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.

  14. 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.

  15. Epitaxial growth of WO3 films on SrTiO3 and sapphire

    NASA Astrophysics Data System (ADS)

    Garg, A.; Leake, J. A.; Barber, Z. H.

    2000-05-01

    Tungsten trioxide films were deposited on (100) SrTiO3 and R-plane (10icons/Journals/Common/1bar" ALT="bar" ALIGN="TOP"/> 2) cut sapphire substrates by dc magnetron sputtering, using a tungsten target in an Ar/O2 sputtering gas mixture at substrate temperatures ranging from 500 to 850 °C. Deposited films were characterized by x-ray diffraction using icons/Journals/Common/theta" ALT="theta" ALIGN="TOP"/> -2icons/Journals/Common/theta" ALT="theta" ALIGN="TOP"/> scans and pole figure analysis. X-ray results showed that films deposited on both types of substrate were epitaxial. The equilibrium phase was monoclinic icons/Journals/Common/gamma" ALT="gamma" ALIGN="TOP"/> -WO3 , confirmed by Raman spectroscopy. Films on both substrates were (001) oriented. This preferred orientation improved as the deposition temperature was reduced. The in-plane orientation relationship of the films with the substrate was obtained from the pole figures.

  16. Direct diode pumped Ti:sapphire ultrafast regenerative amplifier system

    DOE PAGES

    Backus, Sterling; Durfee, Charles; Lemons, Randy; ...

    2017-02-10

    Here, we report on a direct diode-pumped Ti:sapphire ultrafast regenerative amplifier laser system producing multi-uJ energies with repetition rate from 50 to 250 kHz. By combining cryogenic cooling of Ti:sapphire with high brightness fiber-coupled 450nm laser diodes, we for the first time demonstrate a power-scalable CW-pumped architecture that can be directly applied to demanding ultrafast applications such as coherent high-harmonic EUV generation without any complex post-amplification pulse compression. Initial results promise a new era for Ti:sapphire amplifiers not only for ultrafast laser applications, but also for tunable CW sources. We discuss the unique challenges to implementation, as well as themore » solutions to these challenges.« less

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Silicon-on-Sapphire Waveguides for Widely Tunable Coherent Mid-IR Sources

    DTIC Science & Technology

    2013-09-01

    dioxide (a) and sapphire (b). ............................ 2 Figure 3. Mode profile of the silicon waveguide with air cladding above and sapphire... cladding below. ................................................................................................................ 3 Figure 4. Effective...contact mask. ......................................................... 8 Figure 10. Process sequence for nitride cladding of waveguides

  2. Inversion domains in AlN grown on (0001) sapphire

    SciTech Connect

    Jasinski, J.; Liliental-Weber, Z.; Paduano, Q.S.; Weyburne, D.W.

    2003-08-25

    Al-polarity inversion domains formed during AlN layer growth on (0001) sapphire were identified using transmission electron microscopy (TEM). They resemble columnar inversion domains reported for GaN films grown on (0001) sapphire. However, for AlN, these columns have a V-like shape with boundaries that deviate by 2 {+-} 0.5{sup o} from the c-axis. TEM identification of these defects agrees with the post-growth surface morphology as well as with the microstructure revealed by etching in hot aqueous KOH.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Modelling the landing of a plane in a calculus lab

    NASA Astrophysics Data System (ADS)

    Morante, Antonio; Vallejo, José A.

    2012-10-01

    We exhibit a simple model of a plane landing that involves only basic concepts of differential calculus, so it is suitable for a first-year calculus lab. We use the computer algebra system Maxima and the interactive geometry software GeoGebra to do the computations and graphics.

  8. A Simple Chaotic Flow with a Plane of Equilibria

    NASA Astrophysics Data System (ADS)

    Jafari, Sajad; Sprott, J. C.; Molaie, Malihe

    2016-06-01

    Using a systematic computer search, a simple four-dimensional chaotic flow was found that has the unusual feature of having a plane of equilibria. Such a system belongs to a newly introduced category of chaotic systems with hidden attractors that are important and potentially problematic in engineering applications.

  9. Modelling the Landing of a Plane in a Calculus Lab

    ERIC Educational Resources Information Center

    Morante, Antonio; Vallejo, Jose A.

    2012-01-01

    We exhibit a simple model of a plane landing that involves only basic concepts of differential calculus, so it is suitable for a first-year calculus lab. We use the computer algebra system Maxima and the interactive geometry software GeoGebra to do the computations and graphics. (Contains 5 figures and 1 note.)

  10. Modelling the Landing of a Plane in a Calculus Lab

    ERIC Educational Resources Information Center

    Morante, Antonio; Vallejo, Jose A.

    2012-01-01

    We exhibit a simple model of a plane landing that involves only basic concepts of differential calculus, so it is suitable for a first-year calculus lab. We use the computer algebra system Maxima and the interactive geometry software GeoGebra to do the computations and graphics. (Contains 5 figures and 1 note.)

  11. Petrogenesis of alkaline basalt-hosted sapphire megacrysts. Petrological and geochemical investigations of in situ sapphire occurrences from the Siebengebirge Volcanic Field, Germany

    NASA Astrophysics Data System (ADS)

    Baldwin, L. C.; Tomaschek, F.; Ballhaus, C.; Gerdes, A.; Fonseca, R. O. C.; Wirth, R.; Geisler, T.; Nagel, T.

    2017-06-01

    Megacrystic sapphires are frequently associated with alkaline basalts, most notably in Asia and Australia, although basalt is not generally normative in corundum. Most of these sapphire occurrences are located in alluvial or eluvial deposits, making it difficult to study the enigmatic relationship between the sapphires and their host rocks. Here, we present detailed petrological and geochemical investigations of in situ megacrystic sapphires within alkaline basalts from the Cenozoic Siebengebirge Volcanic Field (SVF) in Germany. Markedly, the sapphires show several micrometer thick spinel coronas at the contact with the host basalt, indicating chemical disequilibrium between the sapphire and the basaltic melt, supporting a xenogenetic relationship. However, in situ U-Pb dating of a Columbite Group inclusion within one Siebengebirge sapphire using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) indicates a close genetic relationship between sapphire crystallization and alkaline mafic volcanism in the SVF. The syngenetic mineral inclusion suite including carbonates, members of the Pyrochlore, Betafite and Columbite Groupe minerals, as well as a high abundance of HFSE and of gaseous low-density CO2 inclusions support a parentage of a highly evolved, MgO and FeO deficient carbonatitic melt. We identified CO2 to be the link between alkaline basaltic volcanism and the xenocrystic sapphires. Only alkaline volcanic suites can build up enough CO2 in this magma chamber upon fractionation so that at high degrees of fractionation a carbonatitic melt exsolves which in turn can crystallize sapphires.

  12. Structural and electronic properties of InN epitaxial layer grown on c-plane sapphire by chemical vapor deposition technique

    SciTech Connect

    Barick, Barun Kumar Prasad, Nivedita; Saroj, Rajendra Kumar; Dhar, Subhabrata

    2016-09-15

    Growth of InN epilayers on c-plane sapphire substrate by chemical vapor deposition technique using pure indium metal and ammonia as precursors has been systematically explored. It has been found that [0001] oriented indium nitride epitaxial layers with smooth surface morphology can be grown on c-plane sapphire substrates by optimizing the growth conditions. Bandgap of the film is observed to be Burstein–Moss shifted likely to be due to high background electron concentration. It has been found that the concentration of this unintentional doping decreases with the increase in the growth temperature and the ammonia flux. Epitaxial quality on the other hand deteriorates as the growth temperature increases. Moreover, the morphology of the deposited layer has been found to change from flat top islands to faceted mounds as the flow rate of ammonia increases. This phenomenon is expected to be related to the difference in surface termination character at low and high ammonia flow rates.

  13. 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.

  14. 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.

  15. 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.

  16. Antireflection coatings for intraocular lenses of sapphire and fianite

    SciTech Connect

    Babin, A.A.; Konoplev, Yu.N.; Mamaev, Yu.A.

    1995-10-01

    Broadband antireflection coatings for intraocular lenses of sapphire and fianite are calculated and implemented practically. Their residual reflectance in the liquid with a refracting index of 1.336 is below 0.2% from each face virtually over the entire visible region. 7 refs., 2 figs., 2 tabs.

  17. 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).

  18. 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.

  19. 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

  20. 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.

  1. Oxidation states of Fe and Ti in blue sapphire

    NASA Astrophysics Data System (ADS)

    Wongrawang, P.; Monarumit, N.; Thammajak, N.; Wathanakul, P.; Wongkokua, W.

    2016-02-01

    X-ray absorption near-edge spectroscopy (XANES) can be used to study the oxidation state of a dilute system such as transition metal defects in solid-state samples. In blue sapphire, Fe and Ti are defects that cause the blue color. Inter-valence charge transfer (IVCT) between Fe2+ and Ti4+ has been proposed to describe the optical color’s origin. However, the existence of divalent iron cations has not been thoroughly investigated. Fluorescent XANES is therefore employed to study K-edge absorptions of Fe and Ti cations in various blue sapphire samples including natural, synthetic, diffused and heat-treated sapphires. All the samples showed an Fe absorption edge at 7124 eV, corresponding to the Fe3+ state; and Ti at 4984 eV, corresponding to Ti4+. From these results, we propose Fe3+-Ti4+ mixed acceptor states located at 1.75 eV and 2.14 eV above the valence band of corundum, that correspond to 710 nm and 580 nm bands of UV-vis absorption spectra, to describe the cause of the color of blue sapphire.

  2. Broadband IR supercontinuum generation using single crystal sapphire fibers.

    PubMed

    Kim, Jae Hun; Chen, Meng-Ku; Yang, Chia-En; Lee, Jon; Yin, Stuart Shizhuo; Ruffin, Paul; Edwards, Eugene; Brantley, Christina; Luo, Claire

    2008-03-17

    In this paper, an investigation on broadband IR supercontinuum generation in single crystal sapphire fibers is presented. It is experimentally demonstrated that broadband IR supercontinuum spectrum (up to 3.2microm) can be achieved by launching ultra-short femtosecond laser pulses into single crystal sapphire fiber with a dimension 115microm in diameter and 5cm in length, which covers both the near IR spectral region and the lower end of the mid-IR spectral range. Furthermore, the mechanism of supercontinuum generation in single crystal sapphire fibers is briefly addressed. When the fiber length is shorter than the dispersion length, the self-phase modulation dominates the broadening effect. In this case, the broad supercontinuum spectrum with a smooth profile can be obtained. However, when the fiber length is longer than the dispersion length, the soliton-related dynamics accompanied by the self-phase modulation dominates the broadening effect. There are discrete spikes in the spectrum (corresponding to different order solitons). The above assumption of supercontinuum generation mechanism is quantitatively modeled by the computer simulation program and verified by the experimental results. Thus, one can adjust the spectral profile by properly choosing the length of the sapphire fibers. The broad IR spectral nature of this supercontinuum source can be very useful in a variety of applications such as broadband LADAR, remote sensing, and multi-spectrum free space communications.

  3. 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.

  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. A first-principles study on Al-doped ZnO growth polarity on sapphire (0001) surface

    NASA Astrophysics Data System (ADS)

    Yang, Ping; Gao, Qian; Hu, Zhen-Peng; Zhang, Li-Xin

    2016-06-01

    Based on the first-principles method, the polarity inversion mechanism of Al-doped ZnO grown on sapphire (0001) substrate was investigated. This study revealed that the Al dopant tends to float on the surface of the buffer layer and leads to form ZnO nucleation islands of Zn-polarity without changing in-plane orientation. Finally, these islands evolve to wall-like nanostructure with Zn-termination. The results can explain the reason of the polarity inversion phenomenon in the experiment and supply more information for controlling the ZnO growth polarity.

  6. 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

  7. 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

  8. 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.

  9. High quality, transferrable graphene grown on single crystal Cu(111) thin films on basal-plane sapphire

    NASA Astrophysics Data System (ADS)

    Reddy, Kongara M.; Gledhill, Andrew D.; Chen, Chun-Hu; Drexler, Julie M.; Padture, Nitin P.

    2011-03-01

    The current method of growing large-area graphene on polycrystalline Cu surfaces (foils or thin films) and its transfer to arbitrary substrates is technologically attractive. However, the quality of graphene can be improved significantly by growing it on single-crystal Cu surfaces. Here we show that high quality, large-area graphene can be grown on epitaxial single-crystal Cu(111) thin films on reusable basal-plane sapphire [α-Al2O3(0001)] substrates for transfer to another substrate. While enabling graphene growth on Cu single-crystal surfaces, this method has the potential to avoid the high cost and extensive damage to graphene associated with sacrificing bulk single-crystal Cu during graphene transfer.

  10. Stretching of a plane with a lattice of cuts

    NASA Astrophysics Data System (ADS)

    Dahl, Yu. M.

    2016-06-01

    An exact analytical solution of the problem in elasticity theory about stretching of a plane with an infinite lattice of rectilinear cuts has been obtained. The analysis is based on G.V. Kolosov's formulas associating the stress components with two regular functions of a complex variable. The obtained solution revealed the original effects of stretching stress screening and localization of compressive stresses between cuts.

  11. Self-assembled growth and structural analysis of inclined GaN nanorods on nanoimprinted m-sapphire using catalyst-free metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Lee, Kyuseung; Chae, Sooryong; Jang, Jongjin; Min, Daehong; Kim, Jaehwan; Nam, Okhyun

    2016-04-01

    In this study, self-assembled inclined (1-10-3)-oriented GaN nanorods (NRs) were grown on nanoimprinted (10-10) m-sapphire substrates using catalyst-free metal-organic chemical vapor deposition. According to X-ray phi-scans, the inclined GaN NRs were tilted at an angle of ˜57.5° to the [10-10]sapp direction. Specifically, the GaN NRs grew in a single inclined direction to the [11-20]sapp. Uni-directionally inclined NRs were formed through the one-sided (10-11)-faceted growth of the interfacial a-GaN plane layer. It was confirmed that a thin layer of a-GaN was formed on r-facet nanogrooves of the m-sapphire substrate by nitridation. The interfacial a-GaN nucleation affected both the inclined angle and the growth direction of the inclined GaN NRs. Using X-ray diffraction and selective area electron diffraction, the epitaxial relationship between the inclined (1-10-3) GaN NRs and interfacial a-GaN layer on m-sapphire substrates was systematically investigated. Moreover, the inclined GaN NRs were observed to be mostly free of stacking fault-related defects using high-resolution transmission electron microscopy.

  12. Self-assembled growth and structural analysis of inclined GaN nanorods on nanoimprinted m-sapphire using catalyst-free metal-organic chemical vapor deposition

    SciTech Connect

    Lee, Kyuseung; Chae, Sooryong; Jang, Jongjin; Min, Daehong; Kim, Jaehwan; Nam, Okhyun

    2016-04-15

    In this study, self-assembled inclined (1-10-3)-oriented GaN nanorods (NRs) were grown on nanoimprinted (10-10) m-sapphire substrates using catalyst-free metal-organic chemical vapor deposition. According to X-ray phi-scans, the inclined GaN NRs were tilted at an angle of ∼57.5° to the [10-10]{sub sapp} direction. Specifically, the GaN NRs grew in a single inclined direction to the [11-20]{sub sapp}. Uni-directionally inclined NRs were formed through the one-sided (10-11)-faceted growth of the interfacial a-GaN plane layer. It was confirmed that a thin layer of a-GaN was formed on r-facet nanogrooves of the m-sapphire substrate by nitridation. The interfacial a-GaN nucleation affected both the inclined angle and the growth direction of the inclined GaN NRs. Using X-ray diffraction and selective area electron diffraction, the epitaxial relationship between the inclined (1-10-3) GaN NRs and interfacial a-GaN layer on m-sapphire substrates was systematically investigated. Moreover, the inclined GaN NRs were observed to be mostly free of stacking fault-related defects using high-resolution transmission electron microscopy.

  13. 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

  14. Optical study of a-plane InGaN/GaN multiple quantum wells with different well widths grown by metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Ko, T. S.; Lu, T. C.; Wang, T. C.; Chen, J. R.; Gao, R. C.; Lo, M. H.; Kuo, H. C.; Wang, S. C.; Shen, J. L.

    2008-11-01

    a-plane InGaN/GaN multiple quantum wells of different widths ranging from 3 to 12 nm grown on r-plane sapphire by metal-organic chemical vapor deposition were investigated. The peak emission intensity of the photoluminescence (PL) reveals a decreasing trend as the well width increases from 3 to 12 nm. Low temperature (9 K) time-resolved PL (TRPL) study shows that the sample with 3-nm-thick wells has the best optical property with a fastest exciton decay time of 0.57 ns. The results of cathodoluminescence and micro-PL scanning images for samples of different well widths further verify that the more uniform and stronger luminescence intensity distribution are observed for the samples of thinner quantum wells. In addition, more effective capturing of excitons due to larger localization energy Eloc and shorter radiative lifetime of localized excitons are observed in thinner well width samples in the temperature dependent TRPL.

  15. Generation of a crowned pinion tooth surface by a plane

    NASA Technical Reports Server (NTRS)

    Litvin, F. L.; Zhang, J.; Handschuh, R. F.

    1988-01-01

    The topology of a crowned spur pinion tooth surface that reduces the level of transmission errors due to misalignment is described. The geometry of the modified pinion tooth surface and of the regular involute gear tooth surface is discussed. The tooth contact analysis between the meshing surfaces is also described. Generating a modified pinion tooth surface by a plane whose motion is controlled by a 5-degree-of-freedom system is investigated. The numerical results included indicate that the transmission error remains low as the gears are misaligned.

  16. Stability of Alfven oscillations in a plane plasma slab

    SciTech Connect

    Patudin, V.M.; Sagalakov, A.M.

    1983-05-01

    The stability of the natural Alfven oscillations of a plane slab of a collisional, slightly nonequilibrium plasma in a uniform magnetic field is studied. An effective numerical method, a special version of the differential sweepout method, is proposed. A calculation procedure has been developed. The small-oscillation spectrum is analyzed for parabolic plasma density profiles, and neutral curves are plotted. The growth rates and critical parameters are determined. At a high plasma conductivity, both strongly and weakly localized perturbations near the axis can go unstable. For a density profile with an inflection point, weakly damped oscillations are observed near the inflection point. These oscillations can also be excited by an ion beam.

  17. A plane mirror experiment inspired by a comic strip

    NASA Astrophysics Data System (ADS)

    Lúcio Prados Ribeiro, Jair

    2016-01-01

    A comic strip about a plane mirror was used in a high school optics test, and it was perceived that a large portion of the students believed that the mirror should be larger than the object so the virtual image could be entirely visible. Inspired on the comic strip, an experimental demonstration with flat mirrors was developed, in order to readdress this topic learning. Students were encouraged to create their own investigation of the phenomenon with a simple instrumental apparatus and also suggest different experimental approaches.

  18. Reflection of a plane shock wave from a slit

    NASA Astrophysics Data System (ADS)

    Serov, A. O.; Shtemenko, L. S.; Shugaev, F. V.

    Laser shadow photography was used in a shock-tube visualization study of a plane shock wave reflected from a slit. The working gases were air and Freon 14, and the Mach number of the incident shock wave was in the 2-3 range. An intense interaction between the reflected wave and the walls of the slit was observed. This interaction could lead to the disappearance of the rectilinear part of this wave, thus reducing the load experienced by the body during this type of reflection.

  19. Dispersal of motile bacteria from a plane layer.

    PubMed Central

    Cridland, J V; Thonemann, P C

    1984-01-01

    The dispersal of an initially well-defined concentration of the motile bacterium Escherichia coli was measured under nonchemotactic conditions. The distribution of bacteria along a glass observation cell was measured by recording the intensity of light scattered by the organisms. For comparison, the diffusion of fluorescein was also measured by determining the distribution of fluorescence throughout the observation cell. The dispersal of bacteria from a plane layer, under nonchemotactic conditions, can be adequately described by the Gaussian solution of the diffusion equation. PMID:6440604

  20. 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.

  1. 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.

  2. SINGLE-CRYSTAL SAPPHIRE OPTICAL FIBER SENSOR INSTRUMENTATION

    SciTech Connect

    A. Wang; G. Pickrell; R. May

    2001-10-31

    Testing results of a Broadband Polarized-Light Interferometric (BPLI) high temperature sensor is presented in this report. The state of polarization of the broadband incident light is modulated by the high birefringence of the sapphire disk used as the sensing element and becomes a wavelength-encoded signal, which is detected by an Optical Spectrum Analyzer (OSA) and then is processed by a computer, an internally developed algorithm is employed to directly calculate gap changes between two optical path between two orthogonal linear polarizations of light in a sapphire phase retarder, its phase retardation changes with temperature. The great advantages of this sensor are its simplicity and long-term stability in harsh environment. The system has been laboratory successfully tested up to 1600 C.

  3. Inversion domains in GaN grown on sapphire

    SciTech Connect

    Romano, L.T.; Northrup, J.E.; OKeefe, M.A.

    1996-10-01

    Planar defects observed in GaN films grown on (0001) sapphire have been identified as inversion domain boundaries (IDBs) by a combination of high resolution transmission electron microscopy, multiple dark field imaging, and convergent beam electron diffraction techniques. Films grown by molecular beam epitaxy (MBE), metalorganic vapor deposition (MOCVD), and hydride vapor phase epitaxy (HVPE) were investigated and all were found to contain IDBs. The IDBs in the MBE and HVPE films extended from the interface to the film surface and formed columnar domains that ranged in width from 3 to 20 nm in the MBE films and up to 100 nm in the HVPE films. For the films investigated, the MBE films had the highest density, and the MOCVD films had the lowest density of IDBs. The nucleation of inversion domains (IDs) may result from step-related inhomogeneities of the GaN/sapphire interface. {copyright} {ital 1996 American Institute of Physics.}

  4. 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.

  5. 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.

  6. 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.

  7. Investigating Multi-Dimensional Effects in Single-Crystal Sapphire

    NASA Astrophysics Data System (ADS)

    Reinhart, W. D.; Chhabildas, L. C.; Trott, W. M.; Dandekar, D. P.

    2002-07-01

    Most studies in the past have focused on obtaining uni-axial strain states in shocked materials. In this study, however, results of symmetric impact gas gun experiments on single-crystal C-cut sapphire are described to observe edge relief waves as they propagate toward the center of the sapphire target shocked to high pressures. This is made possible by the recent development of a LINE ORVIS, which measures both spatial and time-resolved particle-velocity variations in materials. A series of experiments have been conducted over the impact velocity from approx0.25 to 0.8 km/s, and in the elastic regime (except the 0.8km/s experiment). In these experiments, a new line imaging optically recording velocity interferometer system is used over a line segment of 13mm. Edge relief waves are unmistakably visible with local variations following the edge relief wave. Heterogeneous effects following dynamic yielding is also observed.

  8. 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

  9. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    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.

  11. 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

  12. Highly textured growth of AlN films on sapphire by magnetron sputtering for high temperature surface acoustic wave applications

    SciTech Connect

    Aubert, T.; Assouar, M. B.; Legrani, O.; Elmazria, O.; Tiusan, C.; Robert, S.

    2011-03-15

    Piezoelectric aluminum nitride films were deposited onto 3 in. [0001] sapphire substrates by reactive magnetron sputtering to explore the possibility of making highly (002)-textured AlN films to be used in surface acoustic wave (SAW) devices for high temperature applications. The synthesized films, typically 1 {mu}m thick, exhibited a columnar microstructure and a high c-axis texture. The relationship between the microstructures and process conditions was examined by x-ray diffraction (XRD), transmission electron microscopy, and atomic force microscopy analyses. The authors found that highly (002)-textured AlN films with a full width at half maximum of the rocking curve of less than 0.3 deg. can be achieved under high nitrogen concentration and moderate growth temperature, i.e., 250 deg. C. The phi-scan XRD reveals the high in-plane texture of deposited AlN films. The SAW devices, based on the optimized AlN films on sapphire substrate, were characterized before and after an air annealing process at 800 deg. C for 90 min. The frequency response, recorded after the annealing process, confirmed that the thin films were still strong in a high temperature environment and that they had retained their piezoelectric properties.

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. Indium clustering in a-plane InGaN quantum wells as evidenced by atom probe tomography

    SciTech Connect

    Tang, Fengzai; Zhu, Tongtong; Oehler, Fabrice; Fu, Wai Yuen; Griffiths, James T.; Massabuau, Fabien C.-P.; Kappers, Menno J.; Oliver, Rachel A.; Martin, Tomas L.; Bagot, Paul A. J.; Moody, Michael P.

    2015-02-16

    Atom probe tomography (APT) has been used to characterize the distribution of In atoms within non-polar a-plane InGaN quantum wells (QWs) grown on a GaN pseudo-substrate produced using epitaxial lateral overgrowth. Application of the focused ion beam microscope enabled APT needles to be prepared from the low defect density regions of the grown sample. A complementary analysis was also undertaken on QWs having comparable In contents grown on polar c-plane sample pseudo-substrates. Both frequency distribution and modified nearest neighbor analyses indicate a statistically non-randomized In distribution in the a-plane QWs, but a random distribution in the c-plane QWs. This work not only provides insights into the structure of non-polar a-plane QWs but also shows that APT is capable of detecting as-grown nanoscale clustering in InGaN and thus validates the reliability of earlier APT analyses of the In distribution in c-plane InGaN QWs which show no such clustering.

  20. Growth of M- and A-plane GaN on LiGaO{sub 2} by plasma-assisted MBE

    SciTech Connect

    Schuber, R.; Schaadt, D. M.; Chou, M. M. C.; Vincze, P.; Schimmel, Th.

    2011-12-23

    We have performed non-polar M- and A-plane GaN growth on LiGaO{sub 2}(LGO) by plasma-assisted molecular beam expitaxy (MBE). We demonstrate that non-polar GaN growth on LGO yields high phase purity and flat surfaces. We find that annealing of the substrates prior to growth is a suitable method for avoiding a peeling off of the film from the substrate after growth.

  1. Pressure Stagnation Line on a Planing Hull in Calm Water

    NASA Astrophysics Data System (ADS)

    Ikeda, Christine; Judge, Carolyn

    2014-11-01

    High-speed planing boats are subjected to repeat impacts due to slamming, which can cause structural damage and discomfort or injury to passengers. An experimental study aimed at understanding and predicting the physics of a planing craft re-entering the water after becoming partially airborne was conducted. A subset of this experiment includes calm water analysis to gain an understanding of the pressure stagnation line and its correlation with the wetted surface on the planning craft in calm water conditions. A planing hull model was towed in a 116-m long, 8-m wide tow-tank with a water depth of 5 m. Hull models at 1/10 and 1/4 of full-scale were examined. These models, only free to move in heave and pitch, were instrumented to measure dynamic pressures with point-pressure sensors at 12 locations near the LCG (longitudinal center of gravity) and transom as well as a highly spatially resolved pressure mapping system. These pressure measurements were sampled at rates up to 20 kHz. Using these pressure measurements along with underwater photos of the wetted surface allowed for the v-shaped wetted line and stagnation line to be measured. Preliminary results show that the peak pressures occur before the wetted line and that atmospheric pressure is reached at the transom. Supported by the Office of Naval Research.

  2. 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.

  3. Defect analysis by transmission electron microscopy of epitaxial Al-doped ZnO films grown on (0001) ZnO and a-sapphire by RF magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Rengachari, Mythili; Bikowski, André; Ellmer, Klaus

    2016-07-01

    Microstructural investigations by cross section Transmission Electron Microscopy have been carried out on Al-doped ZnO films epitaxially grown on (0001) ZnO and a-sapphire by RF magnetron sputtering, since it is known that crystallographic defects influence the physical properties of ZnO films. Threading dislocations and basal stacking faults were the predominant defects observed in these films, which were dependent on the type of the substrate and its orientation. The orientational relationship between the ZnO:Al film and the a-sapphire was determined to be ( 11 2 ¯ 0 )sapphire||(0001)ZnO:Al and [0001]sapphire||[ 11 2 ¯ 0 ]ZnO:Al. The density of dislocations in the heteroepitaxial film of ZnO:Al on a-sapphire was higher than that of the homoepitaxial film of ZnO:Al on undoped ZnO, due to the difference in the lattice mismatch, which also affected the crystallinity of the film.

  4. [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.

  5. 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

  6. SINGLE-CRYSTAL SAPPHIRE OPTICAL FIBER SENSOR INSTRUMENTATION

    SciTech Connect

    A. Wang; G. Pickrell; R. May

    2002-10-18

    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

  7. 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.

  8. 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.

  9. 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.

  10. The structure of sheared turbulence near a plane boundary

    NASA Technical Reports Server (NTRS)

    Lee, Moon J.; Hunt, J. C. R.

    1988-01-01

    An analysis is presented of how a plane boundary affects the structure of turbulence in a sheared free stream. A uniform-shear boundary layer (USBL) is formulated with slip velocity condition at the surface, and inhomogeneous rapid distortion theory is applied. The effects of blocking by the surface on the turbulence structure in USBL is compared with those in the shear-free boundary layer (SFBL). Shear produces highly anisotropic eddies elongated in the flow direction. The vertical velocity variance is reduced with shear at all heights, roughly in proportion to the reduction in the homogeneous value, but the shape of the profile remains unchanged only near the surface. The streamwise integral scales increase with shear, indicating elongation of the streamwise extent of eddies.

  11. On the direct initiation of a plane detonation wave

    NASA Astrophysics Data System (ADS)

    Clarke, J. F.; Kassoy, D. R.; Riley, N.

    1986-11-01

    It is assumed that energy is transferred at a rapid rate through a plane wall into a spatially uniform and initially stagnant combustible gas mixture. This action generates a shock wave, just as it does in an inert mixture, and also switches on a significant rate of chemical reaction. The Navier-Stokes equations for plane unsteady flow are integrated numerically in order to reveal the subsequent history of events. Four principal time domains are identified, namely 'early', 'transitional', 'formation', and 'ZND'. The first contains a conduction-dominated explosion and formation of a shock wave; in the second interval the shock wave is responsible for the acceleration of chemical activity, which becomes intense during the 'formation' period. Finally a wave whose structure is in essence that of a ZND detonation wave emerges.

  12. Simultaneous measurements and flow visualization in a plane mixing layer

    NASA Astrophysics Data System (ADS)

    Sherikar, S. V.; Chevray, R.

    Wind tunnel experiments performed to determine the flow characteristics of a plane mixing layer are described. Two parallel streams of air moving at different velocities were separated by a splitter plate prior to their mixing in the test section. Gaseous NH3 and gaseous HCI were introduced near the splitter plate to produce an ammonium chloride aerosol which made flow visualization possible. Flow visualization records (movies) and velocity measurements, using laser-doppler-velocimeters tracking silicone oil particles in the flow, were made simultaneously and synchronized using a chopped beam of a He-Ne laser which left a signature on the move film and provided a signal for flow rate data acquisition. Analysis of these synchronized data verified the existence of large, essentially two-dimensional coherent structures in the plane mixing layer.

  13. 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.

  14. Ultrathin Films of VO2 on r-Cut Sapphire Achieved by Postdeposition Etching.

    PubMed

    Yamin, Tony; Wissberg, Shai; Cohen, Hagai; Cohen-Taguri, Gili; Sharoni, Amos

    2016-06-15

    The metal-insulator transition (MIT) properties of correlated oxides thin films, such as VO2, are dramatically affected by strain induced at the interface with the substrate, which usually changes with deposition thickness. For VO2 grown on r-cut sapphire, there is a minimum deposition thickness required for a significant MIT to appear, around 60 nm. We show that in these thicker films an interface layer develops, which accompanies the relaxation of film strain and enhanced electronic transition. If these interface dislocations are stable at room temperature, we conjectured, a new route opens to control thickness of VO2 films by postdeposition thinning of relaxed films, overcoming the need for thickness-dependent strain-engineered substrates. This is possible only if thinning does not alter the films' electronic properties. We find that wet etching in a dilute NaOH solution can effectively thin the VO2 films, which continue to show a significant MIT, even when etched to 10 nm, for which directly deposited films show nearly no transition. The structural and chemical composition were not modified by the etching, but the grain size and film roughness were, which modified the hysteresis width and magnitude of the MIT resistance change.

  15. 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.

  16. Surface nitridation induced AlN nano-columnar growth on c-sapphire

    NASA Astrophysics Data System (ADS)

    Shetty, Satish; Ghatak, Jay; Shivaprasad, S. M.

    2014-02-01

    We probe the parametric dependence of the nitridation mechanism of Al2O3 surface by radio frequency nitrogen plasma in a molecular beam epitaxy system. Our quantitative analysis by XPS and RHEED shows that the chemical composition varies with exposure time and is independent of nitrogen plasma fluence and substrate temperature. Here we show that nitrogen incorporation into the host material is diffusion limited process and involves the conversion of Al2O3 into AlN, which has a higher rate initially and then saturates at 6 h of nitrogen plasma exposure. We deposit a thin AlN layer on this saturated nitrided sapphire substrate, which was found to consist of nanorods with a bimodal diameter distribution and apex morphology. By RHEED, XRD and TEM studies we attribute that the faceted nanocolumns are formed at misfit-induced dislocations with the dislocations propagating axially in the nanorods, while the oval apexed features are diffusion mediated. We find that nanorods of both the morphologies are c-oriented, single crystalline and strain relaxed, but possess different in-plane orientation.

  17. Laser welding of fused silica glass with sapphire using a non- stoichiometric, fresnoitic Ba2TiSi2O8·3 SiO2 thin film as an absorber

    NASA Astrophysics Data System (ADS)

    de Pablos-Martín, A.; Lorenz, M.; Grundmann, M.; Höche, Th.

    2017-07-01

    Laser welding of dissimilar materials is challenging, due to their difference in coefficients of thermal expansion (CTE). In this work, fused silica-to-sapphire joints were achieved by employment of a ns laser focused in the intermediate Si-enriched fresnoitic glass thin film sealant. The microstructure of the bonded interphase was analyzed down to the nanometer scale and related to the laser parameters used. The crystallization of fresnoite in the glass sealant upon laser process leads to an intense blue emission intensity under UV excitation. This crystallization is favored in the interphase with the silica glass substrate, rather than in the border with the sapphire. The formation of SiO2 particles was confirmed, as well. The bond quality was evaluated by scanning acoustic microscopy (SAM). The substrates remain bonded even after heat treatment at 100 °C for 30 min, despite the large CTE difference between both substrates.

  18. 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.

  19. Methodology of growing gigantic sapphire for GSLW project

    NASA Astrophysics Data System (ADS)

    Abgaryan, Artoush A.; Hartounian, Gomidas

    2005-09-01

    In our present world the Crystal Growth Technology does not have the necessary and sufficient conditions to manufacture large sizes; especially in the Sapphire Crystal world. We have a theoretical and methodological development for growing gigantic Sapphire Crystal Lenses. Our gigantic Sapphire Crystal Lenses have a unique optical characteristic which will be used in the Global System of Laser Weapons (GSLW); hence solving one of the crucial problems in the Relay Mirror System; where it captures the Laser beam from the earth surface, cleaning the beam in the Satellite and redirecting the laser energy to the precise desired target. Developed and solution for the temperature and heat-elasticity fields in growth systems are considered theoretical, in order to assess their effects on the optical symmetry of the growing crystal. The process is modeled using three-dimensional curvilinear coordinates to describe a closed, low-strain heat-elasticity system, with allowance made for the temperature variations of the thermal properties of the multilayer growth system, and nonlinear and unsteady-state process with arbitrary boundary conditions. The results presented as plots of the strain, stress, displacement, and temperature fields; demonstrate the potential of the method for designing new growth units and improving the existing ones and suggesting that crystals, in general, without frustration of optical symmetry can, in principle, be grown. In order to solve generalized problem for large optics. It is required to have super and correct mathematical computing calculations, and using basic fundamental laws of nature regarding optical symmetry in the crystal, and discovering the radical "new wave method" for crystal growth technology.

  20. 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.

  1. 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.

  2. 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.

  3. Electroform replication of smooth mirrors from sapphire masters

    NASA Astrophysics Data System (ADS)

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

    1992-09-01

    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.

  4. 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.

  5. 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.

  6. Vortex motion around a circular cylinder above a plane

    NASA Astrophysics Data System (ADS)

    Vasconcelos, G. L.; Moura, M.

    2017-08-01

    The study of vortex flows around solid obstacles is of considerable interest from both a theoretical and practical perspective. One geometry that has attracted renewed attention recently is that of vortex flows past a circular cylinder placed above a plane wall, where a stationary recirculating eddy can form in front of the cylinder, in contradistinction to the usual case (without the plane boundary) for which a vortex pair appears behind the cylinder. Here we analyze the problem of vortex flows past a cylinder near a wall through the lenses of the point-vortex model. By conformally mapping the fluid domain onto an annular region in an auxiliary complex plane, we compute the vortex Hamiltonian analytically in terms of certain special functions related to elliptic theta functions. A detailed analysis of the equilibria of the model is then presented. The location of the equilibrium in front of the cylinder is shown to be in qualitative agreement with recent experimental findings. We also show that a topological transition occurs in phase space as the parameters of the systems are varied.

  7. Energy Spectrum of Nonthermal Electrons Accelerated at a Plane Shock

    NASA Astrophysics Data System (ADS)

    Kang, Hyesung

    2011-04-01

    We calculate the energy spectra of cosmic ray (CR) protons and electrons at a plane shock with quasi-parallel magnetic fields,using time-dependent, diffusive shock acceleration (DSA) simulations,including energy losses via synchrotron emission and Inverse Compton (IC) scattering. A thermal leakage injection model and a Bohm type diffusion coefficient are adopted. The electron spectrum at the shock becomes steady after the DSA energy gains balance the synchrotron/IC losses, and it cuts off at the equilibrium momentum p_{eq}.In the postshock region the cutoff momentum of the electron spectrum decreases with the distance from the shock due to the energy losses and the thickness of the spatial distribution of electrons scales as p^{-1}. Thus the slope of the downstream integrated spectrum steepens by one power of p for p_{br}

  8. 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.

  9. 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. Copyright © 2014 Elsevier Ltd. All rights reserved.

  10. Improved emission efficiency of a-plane GaN light emitting diodes with silica nano-spheres integrated into a-plane GaN buffer layer

    NASA Astrophysics Data System (ADS)

    Park, S. H.; Park, J.; You, D.-J.; Joo, K.; Moon, D.; Jang, J.; Kim, D.-U.; Chang, H.; Moon, S.; Song, Y.-K.; Lee, G.-D.; Jeon, H.; Xu, J.; Nanishi, Y.; Yoon, E.

    2012-05-01

    A simple and inexpensive technique to improve the emission efficiency of nonpolar a-plane light emitting diodes (LEDs) is proposed. The 3-dimensional growth nature of a-plane GaN was utilized to form the regrowth template of a-plane GaN. Subsequently, the controlled integration of silica nano-spheres (CIS) into the regrowth template is performed to improve the crystal quality of a-plane GaN by epitaxial lateral overgrowth method. In addition, the CIS improves light extraction by the scattering process. The light output power from the CIS a-plane GaN LEDs showed 130%-150% increase compared to that of LED without silica nano-spheres.

  11. 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.

  12. 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.

  13. 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.

  14. 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

  15. 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.

  16. 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.

  17. 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.

  18. (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.

  19. Electron induced surface chemistry at the Cs/sapphire interface

    SciTech Connect

    Zavadil, K.R.; Ing, J.L.

    1996-03-01

    Electron induced etching of sapphire in the presence of Cs has been studied using a variety of surface analytical techniques. We find that this process occurs on both the (0001) and (1{bar 1}02) orientations of sapphire. Monolayer amounts of Al and sub-oxides of Al are thermally desorbed from the surface at temperatures as low as 1000 K when the surface is irradiated with electrons in the presence of Cs. Etching is highly dependent on Cs coverage with the (0001) and (1{bar 1}02) surfaces requiring 2.0{times}10{sup 14} and 3.4{times}10{sup 14} atoms/cm{sup 2} to support etching, respectively. Adsorption profiles demonstrate that these coverages correspond to initial saturation of the surface with Cs. Electron damage of the surface in the absence of Cs also produces desorption of Al and sub-oxides of Al, indicating a possible mechanism for etching. The impact of etching on the surface is to increase the adsorption capacity on the (0001) surface while decreasing both initial adsorption probability and capacity on the (1{bar 1}02) surface. {copyright} {ital 1996 American Institute of Physics.}

  20. 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.

  1. 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.

  2. Investigating Effects of Edge Release in Single-Crystal Sapphire

    NASA Astrophysics Data System (ADS)

    Reinhart, W. D.; Chhabildas, L. C.; Trott, W. M.; Dandekar, D. P.

    2001-06-01

    Most studies in the past have focussed on obtaining uni-axial strain states in shocked materials. In this study, however, we describe the results of symmetric impact gas gun experiments on single crystal sapphire to observe edge relief waves as they propagate toward the center of the sapphire target shocked to high pressures. This is made possible by the recent development of a LINE ORVIS, which measures both spatial and time-resolved particle-velocity variations in materials. A series of experiments have been conducted over the impact velocity from 0.25 to 0.6 km/s, and in the elastic regime. In these experiments, a new line-imaging ORVIS is used over a line segment of 13mm. Edge relief waves are unmistakably visible with local variations following the edge relief wave. Results of these experiments will be discussed in detail. * This work was supported by the U.S. DOE under contract DE-AC04-94AL85000. Sandia is a multi-program laboratory operated by Sandia Corporation a Lockheed Martin Company, for the U.S. DOE.

  3. 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.

  4. Interface Characteristics of Sapphire Direct Bonding for High-Temperature Applications.

    PubMed

    Li, Wangwang; Liang, Ting; Chen, Yulei; Jia, Pinggang; Xiong, Jijun; Hong, Yingping; Lei, Cheng; Yao, Zong; Qi, Lei; Liu, Wenyi

    2017-09-11

    In this letter, we present a sapphire direct bonding method using plasma surface activation, hydrophilic pre-bonding, and high temperature annealing. Through the combination of sapphire inductively coupled plasma etching and the direct bonding process, a vacuum-sealed cavity employable for high temperature applications is achieved. Cross-sectional scanning electron microscopy (SEM) research of the bonding interface indicates that the two sapphire pieces are well bonded and the cavity structure stays intact. Moreover, the tensile testing shows that the bonding strength of the bonding interface is in excess of 7.2 MPa. The advantage of sapphire direct bonding is that it is free from the various problems caused by the mismatch in the coefficients of thermal expansion between different materials. Therefore, the bonded vacuum-sealed cavity can be potentially further developed into an all-sapphire pressure sensor for high temperature applications.

  5. 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.

  6. 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.

  7. Nd3+-doped colloidal SiO2 composite abrasives: Synthesis and the effects on chemical mechanical polishing (CMP) performances of sapphire wafers

    NASA Astrophysics Data System (ADS)

    Liu, Tingting; Lei, Hong

    2017-08-01

    Abrasive is one of the most important factors in chemical mechanical polishing (CMP). In order to improve the polishing qualities of sapphire substrates, the novel Nd3+-doped colloidal SiO2 composite abrasives were prepared by seed-induced growth method. In this work, there were a series of condensation reactions during the synthesis process of Nd3+-doped colloidal SiO2 composite abrasives and the silica cores were coated by shells (which contains SiO2, Nd2Si2O7 and Nd(OH)3) via chemical bonds and hydrogen bonds in the Nd3+-doped colloidal SiO2 composite abrasives, which made the composite abrasives' core-shell structure more sTable Scanning electron microscopy (SEM) showed that Nd3+-doped colloidal SiO2 composite abrasives were spherical and uniform in size. And the acting mechanisms of Nd3+-doped colloidal SiO2 composite abrasives on sapphire in CMP were investigated. Time-of-flight secondary ion mass spectroscopy (TOF-SIMS) analysis and X-ray photoelectron spectroscopy (XPS) analysis demonstrated that the solid-state chemical reactions between the shells (which contained SiO2, Nd2Si2O7 and Nd(OH)3) of Nd3+-doped colloidal SiO2 composite abrasives and the sapphire occurred during the CMP process. Furthermore, Nd3+-doped colloidal SiO2 composite abrasives exhibited lower surface roughness and higher material removal rate (MRR) than the pure colloidal SiO2 abrasives in the same polishing conditions, which was attributed to the solid-state chemical reactions between shells of Nd3+-doped colloidal SiO2 composite abrasives and sapphire.

  8. 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

  9. Infrared Reflectance Analysis of Epitaxial n-Type Doped GaN Layers Grown on Sapphire

    NASA Astrophysics Data System (ADS)

    Tsykaniuk, Bogdan I.; Nikolenko, Andrii S.; Strelchuk, Viktor V.; Naseka, Viktor M.; Mazur, Yuriy I.; Ware, Morgan E.; DeCuir, Eric A.; Sadovyi, Bogdan; Weyher, Jan L.; Jakiela, Rafal; Salamo, Gregory J.; Belyaev, Alexander E.

    2017-06-01

    Infrared (IR) reflectance spectroscopy is applied to study Si-doped multilayer n+/n0/n+-GaN structure grown on GaN buffer with GaN-template/sapphire substrate. Analysis of the investigated structure by photo-etching, SEM, and SIMS methods showed the existence of the additional layer with the drastic difference in Si and O doping levels and located between the epitaxial GaN buffer and template. Simulation of the experimental reflectivity spectra was performed in a wide frequency range. It is shown that the modeling of IR reflectance spectrum using 2 × 2 transfer matrix method and including into analysis the additional layer make it possible to obtain the best fitting of the experimental spectrum, which follows in the evaluation of GaN layer thicknesses which are in good agreement with the SEM and SIMS data. Spectral dependence of plasmon-LO-phonon coupled modes for each GaN layer is obtained from the spectral dependence of dielectric of Si doping impurity, which is attributed to compensation effects by the acceptor states.

  10. 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).

  11. 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.

  12. 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.

  13. Monte Carlo simulations of supercoiled DNAs confined to a plane.

    PubMed Central

    Fujimoto, Bryant S; Schurr, J Michael

    2002-01-01

    Recent advances in atomic force microscopy (AFM) have enabled researchers to obtain images of supercoiled DNAs deposited on mica surfaces in buffered aqueous milieux. Confining a supercoiled DNA to a plane greatly restricts its configurational freedom, and could conceivably alter certain structural properties, such as its twist and writhe. A program that was originally written to perform Monte Carlo simulations of supercoiled DNAs in solution was modified to include a surface potential. This potential flattens the DNAs to simulate the effect of deposition on a surface. We have simulated transfers of a 3760-basepair supercoiled DNA from solution to a surface in both 161 and 10 mM ionic strength. In both cases, the geometric and thermodynamic properties of the supercoiled DNAs on the surface differ significantly from the corresponding quantities in solution. At 161 mM ionic strength, the writhe/twist ratio is 1.20-1.33 times larger for DNAs on the surface than for DNAs in solution and significant differences in the radii of gyration are also observed. Simulated surface structures in 161 mM ionic strength closely resemble those observed by AFM. Simulated surface structures in 10 mM ionic strength are similar to a minority of the structures observed by AFM, but differ from the majority of such structures for unknown reasons. In 161 mM ionic strength, the internal energy (excluding the surface potential) decreases substantially as the DNA is confined to the surface. Evidently, supercoiled DNAs in solution are typically deformed farther from the minimum energy configuration than are the corresponding surface-confined DNAs. Nevertheless, the work (Delta A(int)) done on the internal coordinates, which include uniform rotations at constant configuration, during the transfer is positive and 2.6-fold larger than the decrease in internal energy. The corresponding entropy change is negative, and its contribution to Delta A(int) is positive and exceeds the decrease in internal

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.