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Sample records for multi-nanolayer structures grown

  1. Quantum spin polarization effect in multi-nanolayer structures

    NASA Astrophysics Data System (ADS)

    Makarov, Vladimir I.; Khmelinskii, Igor

    2017-08-01

    We studied the spin-polarized state transport in Fe-SnO2-Ag and Fe-BeO-Ag three-nanolayer sandwich structures. The exchange-resonance spectra of these sandwich structures are quite specific and different from those observed earlier in other three-nanolayer structures. The presently recorded spectra comprise a set of discrete lines, their width increasing with the sample temperature and also with the Ag layer thickness, for both samples. The linewidth dependences on temperature and Ag layer thickness were studied in detail. The effect of thickness of the intermediate nanolayers of SnO2 and BeO on the linewidth was also explored. To explain the observed line broadening effects, we proposed and developed the spin-orbit (SO) coupling mechanism of the electron spin relaxation. In the frameworks of this mechanism, we assumed that the electron spin of a bonding electron in one of the layers of the sandwich system is coupled by SO interaction with the other layers. We found that the change in phonon densities affects the linewidths of the exchange resonance spectra. We estimated the values of the model parameters from the analysis of the experimental data. To that end, we continue further development of our earlier theoretical model, using it to interpret the current experimental results, including ab initio calculations of the electronic structure. The exchange resonance spectra were simulated using phenomenological model, where the anisotropy of the g-factor was introduced. We performed ab initio simulations of the exchange resonance spectra and their linewidths, using Gaussian-2000 and a homemade FORTRAN code.

  2. Flyweight, Superelastic, Electrically Conductive, and Flame-Retardant 3D Multi-Nanolayer Graphene/Ceramic Metamaterial.

    PubMed

    Zhang, Qiangqiang; Lin, Dong; Deng, Biwei; Xu, Xiang; Nian, Qiong; Jin, Shengyu; Leedy, Kevin D; Li, Hui; Cheng, Gary J

    2017-07-01

    A ceramic/graphene metamaterial (GCM) with microstructure-derived superelasticity and structural robustness is achieved by designing hierarchical honeycomb microstructures, which are composited with two brittle constituents (graphene and ceramic) assembled in multi-nanolayer cellular walls. Attributed to the designed microstructure, well-interconnected scaffolds, chemically bonded interface, and coupled strengthening effect between the graphene framework and the nanolayers of the Al2 O3 ceramic (NAC), the GCM demonstrates a sequence of multifunctional properties simultaneously that have not been reported for ceramics and ceramics-matrix-composite structures, such as flyweight density, 80% reversible compressibility, high fatigue resistance, high electrical conductivity, and excellent thermal-insulation/flame-retardant performance simultaneously. The 3D well-ordered graphene aerogel templates are strongly coupled with the NAC by the chemically bonded interface, exhibiting mutual strengthening, compatible deformability, and a linearly dependent relationship between the density and Young's modulus. Considerable size effects of the ceramic nanolayers on the mechanical properties are revealed in these ceramic-based metamaterials. The designed hierarchical honeycomb graphene with a fourth dimensional control of the ceramic nanolayers on new ways to scalable fabrication of advanced multifunctional ceramic composites with controllable design suggest a great potential in applications of flexible conductors, shock/vibration absorbers, thermal shock barriers, thermal insulation/flame-retardant skins, and porous microwave-absorbing coatings. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Spin polarized state filter based on semiconductor–dielectric–iron–semiconductor multi-nanolayer device

    SciTech Connect

    Makarov, Vladimir I.; Khmelinskii, Igor

    2015-04-15

    Highlights: • Development of a new spintronics device. • Development of quantum spin polarized filters. • Development of theory of quantum spin polarized filter. - Abstract: Presently we report spin-polarized state transport in semiconductor–dielectric–iron–semiconductor (SDIS) four-nanolayer sandwich devices. The exchange-resonance spectra in such devices are quite specific, differing also from spectra observed earlier in other three-nanolayer devices. The theoretical model developed earlier is extended and used to interpret the available experimental results. A detailed ab initio analysis of the magnetic-field dependence of the output magnetic moment is also performed. The model predicts an exchange spectrum comprising a series of peaks, with the spectral structure determined by several factors, discussed in the paper.

  4. Functional Multi-Nanolayer Coatings of Amorphous Carbon/Tungsten Carbide with Exceptional Mechanical Durability and Corrosion Resistance.

    PubMed

    Nemati, Narguess; Bozorg, Mansoor; Penkov, Oleksiy V; Shin, Dong-Gap; Sadighzadeh, Asghar; Kim, Dae-Eun

    2017-09-06

    A novel functional multilayer coating with periodically stacked nanolayers of amorphous carbon (a:C)/tungsten carbide (WC) and an adhesion layer of chromium (Cr) was deposited on 304 stainless steel using a dual magnetron sputtering technique. Through process optimization, highly densified coatings with high elasticity and shear modulus, excellent wear resistance, and minimal susceptibility to corrosive and caustic media could be acquired. The structural and mechanical properties of the optimized coatings were studied in detail using a variety of analytical techniques. Furthermore, finite element method simulations indicated that the stress generated due to contact against a steel ball was distributed well within the coating, which allowed the stresses to be lower than the yield threshold of the coating. Thus, an ultralow wear rate of ∼10(-12)mm(3)/N mm could be achieved in dry sliding conditions under relatively high Hertzian contact pressures of ∼0.4-0.9 GPa. The amorphous and pinhole-free structure of the individual layers, sufficient number of pairs, and the relatively dense stacked layers resulted in significant polarization resistance (Z″ = 5.5 × 10(6) Ω cm(2)) and increased the corrosion resistance of the coating by 10-fold compared to that of recently reported corrosion-resistant coatings.

  5. Structural properties of opals grown with vertical controlled drying.

    PubMed

    Hartsuiker, Alex; Vos, Willem L

    2008-05-06

    We have grown thin opals of self-assembled silica colloids by the well-known vertically controlled drying method. The volume fraction at the start of the growth and the temperature were systematically varied. We have quantitatively characterized the lateral domain sizes by scanning electron microscopy. The sample thickness as a function of position was obtained from Fabry-Pérot fringes measured in optical reflectivity. We observe that the sample thickness strongly increases from top to bottom, independent of temperature, in agreement with a model that we propose. The inhomogeneity in thickness contrasts with earlier reports. The lateral domain shapes of the single-crystal domains are found to vary from irregular near the top to rectangular near the bottom. A surprising observation is that, grosso modo, the lateral domain extents increase linearly with thickness (i.e., thin crystals are small, and thick crystals are large). This behavior agrees qualitatively with results on completely different colloids such as disordered slurries. The consequence of our results for optical applications, including photonic crystals, is that unwanted scattering due to grain boundaries is reduced for large domains that are thick. Conversely, thin crystals will scatter relatively strongly from grain boundaries.

  6. Fine structure of Cryptococcus neoformans grown in vivo as observed by freeze-etching.

    PubMed

    Takeo, K; Uesaka, I; Uehira, K; Nishiura, M

    1973-03-01

    Cryptococcus neoformans grown in the parasitic state was observed by the freeze-etching technique and was compared with that grown on culture media. Unlike other yeasts, this organism grown in vivo is very often devoid of the "ordinary" invaginations. The membrane of the cell grown in vivo was almost free from concavity and convexity except for many round depressions which represent the surface view of paramural bodies. Some of the paramural bodies were found to be multivesicular systems. Most were spherical invaginations containing a single vesicle or its ghost remaining after secretion of the vesicles. In clear contrast to the cell grown in vitro, the in vivo cell contained a great number of vesicles in the cytoplasm. These seemed to show high-secretion activity in C. neoformans grown in the parasitic state. On transfer from in vitro to in vivo, this organism enlarged the cell wall, capsule, and cell body. The appearance of a large vacuole, accumulation of storage organelles, and the existence of rodlike structures, seemingly lipid deposits, were also noted in the cytoplasm of the cell grown in vivo. the meaning of these results as well as the mode of capsular production are discussed.

  7. Multilayer porous structures of HVPE and MOCVD grown GaN for photonic applications

    NASA Astrophysics Data System (ADS)

    Braniste, T.; Ciers, Joachim; Monaico, Ed.; Martin, D.; Carlin, J.-F.; Ursaki, V. V.; Sergentu, V. V.; Tiginyanu, I. M.; Grandjean, N.

    2017-02-01

    In this paper we report on a comparative study of electrochemical processes for the preparation of multilayer porous structures in hydride vapor phase epitaxy (HVPE) and metal organic chemical vapor phase deposition (MOCVD) grown GaN. It was found that in HVPE-grown GaN, multilayer porous structures are obtained due to self-organization processes leading to a fine modulation of doping during the crystal growth. However, these processes are not totally under control. Multilayer porous structures with a controlled design have been produced by optimizing the technological process of electrochemical etching in MOCVD-grown samples, consisting of five pairs of thin layers with alternating-doping profiles. The samples have been characterized by SEM imaging, photoluminescence spectroscopy, and micro-reflectivity measurements, accompanied by transfer matrix analysis and simulations by a method developed for the calculation of optical reflection spectra. We demonstrate the applicability of the produced structures for the design of Bragg reflectors.

  8. Crystalline and electronic energy structure of OMVPE-grown AlGaInP/GaAs

    NASA Astrophysics Data System (ADS)

    Kondow, M.; Kakibayashi, H.; Minagawa, S.; Inoue, Y.; Nishino, T.; Hamakawa, Y.

    1988-12-01

    The crystalline and electronic energy structure of AlGaInP/GaAs grown by organometallic vapor phase epitaxy (OMVPE) is investigated using transmission electron microscopy (TEM) and electroreflectance (ER), as well as photoluminescence (PL) and Raman scattering measurements. In TEM observation, sharp superstructure spots at the h+ {1}/{2}, k- {1}/{2}, l± {1}/{2} position, corresponding to CuPt type structure, are present in the (110) diffraction pattern. Based on this observation, the relationship between the bond and the ordered structure configuration on 9001) growth surface is discussed. It is also found by photoluminescence and Raman scattering measurements that the GaInP grown on (111)B is in a disordered state. Photoluminescence measurement for AlGaInP grown under various conditions shows that an ordered structure exists not only in GaInP but throughout the entire compositional range of the AlGaInP/GaAs. The electroreflectance spectrum shows anomalous structures specific to OMVPE-grown GaInP. The structures around 2.2 and 2.4 eV suggest that there exist additional interband transition edges caused possibly by zone-folding from the L point to the Γ point.

  9. AlN Nanowall Structures Grown on Si (111) Substrate by Molecular Beam Epitaxy.

    PubMed

    Tamura, Yosuke; Hane, Kazuhiro

    2015-12-01

    AlN nanowall structures were grown on Si (111) substrate using molecular beam epitaxy at substrate temperature of 700 °C with N/Al flux ratios ranging from 50 to 660. A few types of other AlN nanostructures were also grown under the nitrogen-rich conditions. The AlN nanowalls were ranged typically 60-120 nm in width and from 190 to 470 nm in length by changing N/Al flux ratio. The AlN nanowall structures grown along the c-plane consisted of AlN (0002) crystal with full-width at half maximum of the rocking curve about 5000 arcsec.

  10. Step structure of GaInAsSb grown by OMVPE (Organometallic Vapor Phase Epitaxy)

    SciTech Connect

    Charache, G.W.; Wang, C.A.

    1999-05-23

    The microscopic surface morphology of GaInAsSb grown by organometallic vapor phase epitaxy (OMVPE)on GaSb substrates has been studied by atomic force microscopy. The effects of growth temperature, alloy composition, and substrate misorientation on the step structure were investigated. The competition between thermodynamically driven phase separation and kinetically limited surface diffusion is discussed.

  11. Structure of carbon nanotubes grown by microwave-plasma-enhanced chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Okai, M.; Muneyoshi, T.; Yaguchi, T.; Sasaki, S.

    2000-11-01

    Carbon nanotubes grown on a Ni substrate and an Fe-Ni-Cr alloy substrate by plasma-enhanced chemical vapor deposition were investigated by transmission electron microscope (TEM) and energy dispersive x-ray (EDX) analysis. TEM showed that the nanotubes on both substrates have a piled-cone structure with metal particles on top which determine the diameter of the nanotubes. Their diameter ranges from 60 to 80 nm. Moreover, EDX showed that the metal particles are composed of Ni when the nanotubes are grown on Ni substrate and of Fe and Ni in the case of the Fe-Ni-Cr alloy substrate.

  12. Growth Mechanisms and Structural Properties of Lead Chalcogenide Films Grown by Pulsed Laser Deposition

    NASA Astrophysics Data System (ADS)

    Virt, I. S.; Rudyi, I. O.; Lopatynskyi, I. Ye.; Dubov, Yu.; Tur, Y.; Lusakowska, E.; Luka, G.

    2017-01-01

    Three lead chalcogenide films, PbTe, PbSe, and PbS, with a high structural quality were grown by pulsed lased deposition (PLD). The films were grown on single crystal substrates (Si, KCl, Al2O3) and on Si covered with a Si3N4 buffer layer. The Si3N4 layer latter facilitated the lead chalcogenide layer nucleation during the first growth stages and resulted in a more homogeneous surface morphology and a lower surface roughness. The surface geometry (roughness) of the films grown on Si3N4 was studied by means of the power spectral density analysis. Different growth modes, ranging from plasma plume condensation to bulk diffusion, resulting in observed film morphologies were identified. The investigations were complemented by electrical characterization of the chalcogenide films.

  13. Space-grown protein crystals are more useful for structure determination.

    PubMed

    Ng, Joseph D

    2002-10-01

    The usefulness of X-ray data derived from space-grown protein crystals for calculating a more accurate structure is reviewed here for three model proteins. These include the plant sweetening protein, thaumatin, from Thaumatococcus daniellii; the aspartyl-tRNA synthetase from Thermus thermophilus; and pea lectin from Pisum sativum. In all three cases, X-ray diffraction data collected from protein crystals obtained under reduced gravity lead to better defined initial electron density maps, facilitating model building and improved crystallographic statistics. With thaumatin, the phasing power of the anomalous scattering atom, sulfur, is used to determine protein crystal quality in terms of its usefulness for ab initio structure determination. Thaumatin crystals grown under microgravity provided improved phasing statistics compared to those of Earth-grown crystals. Consequently, generating a de novo protein model of higher quality was facilitated using X-ray diffraction data from space-grown crystals. This lends evidence to the possibility that a microgravity environment can favor protein crystal growth and, subsequently, be more useful for structure determination.

  14. Structure Dependence of Magnetic Properties for Annealed GaMnN Films Grown by MOCVD

    NASA Astrophysics Data System (ADS)

    Jiang, Xian-Zhe; Yang, Xue-Lin; Ji, Cheng; Xing, Hai-Ying; Yang, Zhi-Jian; Wang, Cun-Da; Yu, Tong-Jun; Zhang, Guo-Yi

    2014-06-01

    GaMnN/GaN multilayers and conventional GaMnN single layers are grown by metal-organic chemical vapor deposition. Both kinds of samples show room-temperature ferromagnetism. After thermal annealing, the sample with GaMnN/GaN multilayer structure displays a larger coercivity and better thermal stability compared to the GaMnN single layer. The annealing effects on VGa related defects are observed from photoluminescence measurements. Moreover, a different magnetic behavior is also found in the annealed GaMnN films grown on different (n-type GaN and p-type GaN) templates. These kinds of structure-dependent magnetic behaviors indicate that defects or carriers transformation introduced during annealing may have important effects on the electronic structure of Mn ions and on the ferromagnetism. Our work may be helpful for further understanding the origin of ferromagnetism in GaN-based diluted magnetic semiconductors.

  15. Investigations about series resistance of MOVPE grown GaN laser structures

    NASA Astrophysics Data System (ADS)

    Scholz, F.; Moutchnik, G.; Dumitru, V.; Härle, R.; Schweizer, H.

    2003-02-01

    In order to reduce the total series resistance of an AlGaInN laser structure, we have exchanged the GaN:Mg contact layer normally covering a laser structure by GaInN:Mg and have investigated the influence of several growth conditions on its electrical properties. We found a significant decrease of the series resistance for a GaInN layer grown at 800°C with hydrogen as carrier gas which results, at lower current densities, in a voltage drop of at least 2 V compared to GaN contact layers. Our studies show that not only the changed growth conditions, but indeed the In content plays a major role for these improvements, although it is only about 2%. Laser structures grown on SiC wafers show minimum total differential resistivities below 1.5×10 -4 Ω cm 2.

  16. Atomic structure of "multilayer silicene" grown on Ag(111): Dynamical low energy electron diffraction analysis

    NASA Astrophysics Data System (ADS)

    Kawahara, Kazuaki; Shirasawa, Tetsuroh; Lin, Chun-Liang; Nagao, Ryo; Tsukahara, Noriyuki; Takahashi, Toshio; Arafune, Ryuichi; Kawai, Maki; Takagi, Noriaki

    2016-09-01

    We have investigated the atomic structure of the "multilayer silicene" grown on the Ag(111) single crystal surface by using low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). We measured the intensity of the LEED spot as a function of the incident electron energy (I-V curve) and analyzed the I-V curve using a dynamical LEED theory. We have found that the Si(111)(√{ 3} ×√{ 3})-Ag model well reproduces the I-V curve whereas the models consisting of the honeycomb structure of Si do not. The bias dependence of the STM image of multilayer silicene agrees with that of the Si(111)(√{ 3} ×√{ 3})-Ag reconstructed surface. Consequently, we have concluded that the multilayer silicene grown on Ag(111) is identical to the Si(111)(√{ 3} ×√{ 3})-Ag reconstructed structure.

  17. Correlation between bioactivity and structural properties of titanium dioxide coatings grown by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Grigal, I. P.; Markeev, A. M.; Gudkova, S. A.; Chernikova, A. G.; Mityaev, A. S.; Alekhin, A. P.

    2012-02-01

    TiO2 coatings were grown on Ti and Si by Atomic Layer Deposition (ALD) from titanium ethoxide and water at 300 °C in a wide range of the reaction cycles number N = 100-2000. TiO2 coatings were found to be amorphous at low value of N < 300 while the coatings grown at N ≥ 300 revealed anatase polycrystalline structure. The TiO2 coatings bioactivity was evaluated by hydroxyapatite forming ability by the technique of soaking in Simulated Body Fluid (SBF). Correlation between bioactivity and structural properties of TiO2 was determined. X-ray diffraction and scanning electron microscopy with electron probe microanalysis showed that amorphous TiO2 coating did not induce the hydroxyapatite growth whereas anatase resulted in the hydroxyapatite forming on the samples surfaces which confirmed TiO2 anatase bioactivity.

  18. Possible spin excitation structure in monolayer FeSe grown on SrTiO3

    NASA Astrophysics Data System (ADS)

    Gao, Yi; Yu, Yan; Zhou, Tao; Huang, Huaixiang; Wang, Qiang-Hua

    2017-07-01

    Based on recent high-resolution angle-resolved photoemission spectroscopy measurement in monolayer FeSe grown on SrTiO3, we constructed a tight-binding model and proposed a superconducting (SC) pairing function which can well fit the observed band structure and SC gap anisotropy. Then we investigated the spin excitation spectra in order to determine the possible sign structure of the SC order parameter. We found that a resonancelike spin excitation may occur if the SC order parameter changes sign along the Fermi surfaces. However, this resonance is located at different locations in momentum space compared to other FeSe-based superconductors, suggesting that the Fermi surface shape and pairing symmetry in monolayer FeSe grown on SrTiO3 may be different from other FeSe-based superconductors.

  19. Local structure and magnetic properties of ultrathin Mn films grown on Si(001)

    NASA Astrophysics Data System (ADS)

    Kahwaji, Samer; Monchesky, Theodore; Crozier, Daryl; Gordon, Robert

    2012-02-01

    We report on the structural and magnetic properties of ultrathin Mn layers deposited onto Si(001) by molecular beam epitaxy (MBE) at low temperature. X-ray absorption fine structure (XAFS) studies reveal that the structure of the silicide layer that forms depends on the growth temperature of the capping layer. A capping layer grown at 200 ^oC on 0.35 monolayer (ML) Mn results in a metastable MnSi phase with a B2-like (CsCl) structure, whereas a cap grown at room temperature on 0.5 ML followed by annealing at 200 ^oC produces a lower coordinated MnSi phase with a B20-like structure. Increasing the Mn thickness from 0.5 to 4 monolayers does not trigger a structural transformation but drives the structure closer to MnSi-B20. Using SQUID magnetometry, we show that the sample with B2-like structure has the largest Mn magnetic moment of 0.33μB/Mn at T=2 K, and a Curie temperature TC above 250 K. MnSi-B20 layers showed lower moments and much lower TC's, in-line with those reported for MnSi-B20 thin films.

  20. Detailed Structural and Quantitative Analysis Reveals the Spatial Organization of the Cell Walls of in Vivo Grown Mycobacterium leprae and in Vitro Grown Mycobacterium tuberculosis*

    PubMed Central

    Bhamidi, Suresh; Scherman, Michael S.; Jones, Victoria; Crick, Dean C.; Belisle, John T.; Brennan, Patrick J.; McNeil, Michael R.

    2011-01-01

    The cell wall of mycobacteria consists of an outer membrane, analogous to that of Gram-negative bacteria, attached to the peptidoglycan (PG) via a connecting polysaccharide arabinogalactan (AG). Although the primary structure of these components is fairly well deciphered, issues such as the coverage of the PG layer by covalently attached mycolates in the outer membrane and the spatial details of the mycolic acid attachment to the arabinan have remained unknown. It is also not understood how these components work together to lead to the classical acid-fast staining of mycobacteria. Because the majority of Mycobacterium tuberculosis bacteria in established experimental animal infections are acid-fast negative, clearly cell wall changes are occurring. To address both the spatial properties of mycobacterial cell walls and to begin to study the differences between bacteria grown in animals and cultures, the cell walls of Mycobacterium leprae grown in armadillos was characterized and compared with that of M. tuberculosis grown in culture. Most fundamentally, it was determined that the cell wall of M. leprae contained significantly more mycolic acids attached to PG than that of in vitro grown M. tuberculosis (mycolate:PG ratios of 21:10 versus 16:10, respectively). In keeping with this difference, more arabinogalactan (AG) molecules, linking the mycolic acids to PG, were found. Differences in the structures of the AG were also found; the AG of M. leprae is smaller than that of M. tuberculosis, although the same basic structural motifs are retained. PMID:21555513

  1. Detailed structural and quantitative analysis reveals the spatial organization of the cell walls of in vivo grown Mycobacterium leprae and in vitro grown Mycobacterium tuberculosis.

    PubMed

    Bhamidi, Suresh; Scherman, Michael S; Jones, Victoria; Crick, Dean C; Belisle, John T; Brennan, Patrick J; McNeil, Michael R

    2011-07-01

    The cell wall of mycobacteria consists of an outer membrane, analogous to that of gram-negative bacteria, attached to the peptidoglycan (PG) via a connecting polysaccharide arabinogalactan (AG). Although the primary structure of these components is fairly well deciphered, issues such as the coverage of the PG layer by covalently attached mycolates in the outer membrane and the spatial details of the mycolic acid attachment to the arabinan have remained unknown. It is also not understood how these components work together to lead to the classical acid-fast staining of mycobacteria. Because the majority of Mycobacterium tuberculosis bacteria in established experimental animal infections are acid-fast negative, clearly cell wall changes are occurring. To address both the spatial properties of mycobacterial cell walls and to begin to study the differences between bacteria grown in animals and cultures, the cell walls of Mycobacterium leprae grown in armadillos was characterized and compared with that of M. tuberculosis grown in culture. Most fundamentally, it was determined that the cell wall of M. leprae contained significantly more mycolic acids attached to PG than that of in vitro grown M. tuberculosis (mycolate:PG ratios of 21:10 versus 16:10, respectively). In keeping with this difference, more arabinogalactan (AG) molecules, linking the mycolic acids to PG, were found. Differences in the structures of the AG were also found; the AG of M. leprae is smaller than that of M. tuberculosis, although the same basic structural motifs are retained.

  2. Atomic and electronic structure of Fe films grown on Pd l brace 001 r brace

    SciTech Connect

    Quinn, J.; Li, Y.S.; Li, H.; Tian, D.; Jona, F. ); Marcus, P.M. )

    1991-02-15

    The atomic and electronic structure of Fe films grown on Pd{l brace}001{r brace} is investigated by means of low-energy electron diffraction and angle-resolved photoemission spectroscopy (ARPES). The films grow pseudomorphically, probably by way of nucleation and growth of flat islands, which ultimately coalesce to form continuous Fe{l brace}001{r brace} films. The structure of these continuous films, if grown at slow rates (of the order of 0.1 A/min), is body-centered tetragonal and is shown to be a distortion from the stable bcc structure of Fe: the in-plane lattice constant is 2.75 A, as dictated by the Pd{l brace}001{r brace} substrate, and the bulk interlayer spacing is 1.50--1.53 A. In 10--12-layer films the first interlayer spacing is expanded by 3.6% above bulk, but with increasing thickness that spacing contracts progressively to about 6.3% below the bulk value in 40--50-layer films. Films as thick as 60--70 layers can be grown pseudomorphically at slow rates despite the large misfit (4.2%) between bcc Fe{l brace}001{r brace} and fcc Pd{l brace}001{r brace}. ARPES data indicate that these films are electronically indistinguishable from bulk bcc Fe. Thick (about 200-layer) films grown at fast rates are essentially bcc, with in-plane lattice constants of 2.87 A, but with slightly expanded (3%) interlayer spacing, attributed to the presence of carbon impurities.

  3. Columnar structured FePt films epitaxially grown on large lattice mismatched intermediate layer

    NASA Astrophysics Data System (ADS)

    Dong, K. F.; Deng, J. Y.; Peng, Y. G.; Ju, G.; Chow, G. M.; Chen, J. S.

    2016-09-01

    The microstructure and magnetic properties of the FePt films grown on large mismatched ZrN (15.7%) intermediate layer were investigated. With using ZrN intermediate layer, FePt 10 nm films exhibited (001) texture except for some weaker FePt (110) texture. Good epitaxial relationships of FePt (001) <100>//ZrN (001) <100>//TiN (001) <100> among FePt and ZrN/TiN were revealed from the transmission electron microscopy (TEM) results. As compared with TiN intermediate layer, although FePt-SiO2-C films grown on ZrN/TiN intermediate layer showed isotropic magnetic properties, the large interfacial energy and lattice mismatch between FePt and ZrN would lead to form columnar structural FePt films with smaller grain size and improved isolation. By doping ZrN into the TiN layer, solid solution of ZrTiN was formed and the lattice constant is increased comparing with TiN and decreased comparing with ZrN. Moreover, FePt-SiO2-C films grown on TiN 2 nm-20 vol.% ZrN/TiN 3 nm intermediate layer showed an improved perpendicular magnetic anisotropy. Simultaneously, columnar structure with smaller grain size retained.

  4. Columnar structured FePt films epitaxially grown on large lattice mismatched intermediate layer

    PubMed Central

    Dong, K. F.; Deng, J. Y.; Peng, Y. G.; Ju, G.; Chow, G. M.; Chen, J. S.

    2016-01-01

    The microstructure and magnetic properties of the FePt films grown on large mismatched ZrN (15.7%) intermediate layer were investigated. With using ZrN intermediate layer, FePt 10 nm films exhibited (001) texture except for some weaker FePt (110) texture. Good epitaxial relationships of FePt (001) <100>//ZrN (001) <100>//TiN (001) <100> among FePt and ZrN/TiN were revealed from the transmission electron microscopy (TEM) results. As compared with TiN intermediate layer, although FePt-SiO2-C films grown on ZrN/TiN intermediate layer showed isotropic magnetic properties, the large interfacial energy and lattice mismatch between FePt and ZrN would lead to form columnar structural FePt films with smaller grain size and improved isolation. By doping ZrN into the TiN layer, solid solution of ZrTiN was formed and the lattice constant is increased comparing with TiN and decreased comparing with ZrN. Moreover, FePt-SiO2-C films grown on TiN 2 nm-20 vol.% ZrN/TiN 3 nm intermediate layer showed an improved perpendicular magnetic anisotropy. Simultaneously, columnar structure with smaller grain size retained. PMID:27686046

  5. Columnar structured FePt films epitaxially grown on large lattice mismatched intermediate layer.

    PubMed

    Dong, K F; Deng, J Y; Peng, Y G; Ju, G; Chow, G M; Chen, J S

    2016-09-30

    The microstructure and magnetic properties of the FePt films grown on large mismatched ZrN (15.7%) intermediate layer were investigated. With using ZrN intermediate layer, FePt 10 nm films exhibited (001) texture except for some weaker FePt (110) texture. Good epitaxial relationships of FePt (001) <100>//ZrN (001) <100>//TiN (001) <100> among FePt and ZrN/TiN were revealed from the transmission electron microscopy (TEM) results. As compared with TiN intermediate layer, although FePt-SiO2-C films grown on ZrN/TiN intermediate layer showed isotropic magnetic properties, the large interfacial energy and lattice mismatch between FePt and ZrN would lead to form columnar structural FePt films with smaller grain size and improved isolation. By doping ZrN into the TiN layer, solid solution of ZrTiN was formed and the lattice constant is increased comparing with TiN and decreased comparing with ZrN. Moreover, FePt-SiO2-C films grown on TiN 2 nm-20 vol.% ZrN/TiN 3 nm intermediate layer showed an improved perpendicular magnetic anisotropy. Simultaneously, columnar structure with smaller grain size retained.

  6. Ga/1-x/Al/x/As LED structures grown on GaP substrates.

    NASA Technical Reports Server (NTRS)

    Woodall, J. M.; Potemski, R. M.; Blum, S. E.; Lynch, R.

    1972-01-01

    Ga(1-x)Al(x)As light-emitting diode structures have been grown on GaP substrates by the liquid-phase-epitaxial method. In spite of the large differences in lattice constants and thermal-expansion coefficients, room-temperature efficiencies up to 5.5% in air have been observed for a peak emission of 8500 A. Using undoped GaP substrates, which are transparent to the infrared and red portions of the spectrum, thin structures of Ga(1-x)Al(x)As with large external efficiencies can now be made.

  7. Ga/1-x/Al/x/As LED structures grown on GaP substrates.

    NASA Technical Reports Server (NTRS)

    Woodall, J. M.; Potemski, R. M.; Blum, S. E.; Lynch, R.

    1972-01-01

    Ga(1-x)Al(x)As light-emitting diode structures have been grown on GaP substrates by the liquid-phase-epitaxial method. In spite of the large differences in lattice constants and thermal-expansion coefficients, room-temperature efficiencies up to 5.5% in air have been observed for a peak emission of 8500 A. Using undoped GaP substrates, which are transparent to the infrared and red portions of the spectrum, thin structures of Ga(1-x)Al(x)As with large external efficiencies can now be made.

  8. The magnetic and chemical structural property of the epitaxially-grown multilayered thin film

    NASA Astrophysics Data System (ADS)

    Lee, Hwachol

    L10 FePt- and Fe-related alloys such as FePtRh, FeRh and FeRhPd have been studied for the high magnetocrystalline anisotropy and magnetic phase transition property for the future application. In this work, the thin film structural and magnetic property is investigated for the selected FePtRh and FeRhPd alloys. The compositionally-modulated L10 FePtRh multilayered structure is grown epitaxially on a-plane Al2O3 with Cr and Pt buffer layer at 600degC growth temperature by DC sputtering technique and examined for the structural, interfacial and magnetic property. For the epitaxially grown L10 [Fe50Pt45Rh5 (FM) (10nm) / Fe50Pt25Rh25 (AFM) (20nm)]x8 superlattice, the magnetically and chemically sharp interface formation between layers was observed in X-ray diffraction, transmission electron microscopy and polarized neutron reflectivity measurements with the negligible exchange bias at room and a slight coupling effect at lower temperature regime. For FeRhPd, the magnetic phase transition of epitaxially-grown 111-oriented Fe46Rh48Pd6 thin film is studied. The applied Rhodium buffer layer on a-plane Al2O3 (11 20) at 600degC shows the extraordinarily high quality of epitaxial film in (111) orientation, where two broad and coherent peak in rocking curve, and Laue oscillations are observed. The epitaxially-grown Pd-doped FeRh on Pt (111) grown at 600degC, 700degC exhibits the co-existing stable L10 (111) and B2 (110) structures and magnetic phase transition around 300degC. On the other hand, the partially-ordered FeRhPd structure grown at 400degC, 500degC shows background high ferromagnetic state over 5K˜350K temperature. For the reduced thickness of Fe46Rh48Pd 6, the ferromagnetic state becomes dominant with a reduced portion of the film undergoing a magnetic phase transition. For some epitaxial FeRhPd film, the spin-glass-like disordered state is also observed in field dependent SQUID measurement. For the tri-layered FeRhPd with thin Pt spacer, the background

  9. Structural characterization of InSb thin films grown by electrodeposition

    SciTech Connect

    Singh, Joginder Rajaram, P.

    2015-06-24

    In the present work we have grown InSb thin films on brass substrates, using the electrodeposition technique. The electrochemical baths used in the growth were made up of aqueous solutions of InCl{sub 3} and SbCl{sub 3} mixed together in various proportions. The films grown were characterized by X-Ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive Analysis of X-rays (EDAX). Compositional studies show that stoichiometric InSb films can be prepared from a bath containing 0.05M InCl{sub 3} and 0.04M SbCl{sub 3}. XRD studies reveal that the films grown are polycrystalline having the zinc blende structure with (111) orientation. Crystallite size, dislocation density and strain were calculated using the XRD results. Optical transmission spectra were recorded using an FTIR spectrophotometer. The value of direct band gap was found to be around 0.20 eV for the thin films having the best stoichiometry.

  10. Structural evolution of dilute magnetic (Sn,Mn)Se films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Kanzyuba, Vasily; Dong, Sining; Liu, Xinyu; Li, Xiang; Rouvimov, Sergei; Okuno, Hanako; Mariette, Henri; Zhang, Xueqiang; Ptasinska, Sylwia; Tracy, Brian D.; Smith, David J.; Dobrowolska, Margaret; Furdyna, Jacek K.

    2017-02-01

    We describe the structural evolution of dilute magnetic (Sn,Mn)Se films grown by molecular beam epitaxy on GaAs (111) substrates, as revealed by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. When the Mn concentration is increased, the lattice of the ternary (Sn,Mn)Se films evolves quasi-coherently from a SnSe2 two-dimensional (2D) crystal structure into a more complex quasi-2D lattice rearrangement, ultimately transforming into the magnetically concentrated antiferromagnetic MnSe 3D rock-salt structure as Mn approaches 50 at. % of this material. These structural transformations are expected to underlie the evolution of magnetic properties of this ternary system reported earlier in the literature.

  11. Atom probe tomography characterisation of a laser diode structure grown by molecular beam epitaxy

    SciTech Connect

    Bennett, Samantha E.; Humphreys, Colin J.; Oliver, Rachel A.; Smeeton, Tim M.; Hooper, Stewart E.; Heffernan, Jonathan; Saxey, David W.; Smith, George D. W.

    2012-03-01

    Atom probe tomography (APT) has been used to achieve three-dimensional characterization of a III-nitride laser diode (LD) structure grown by molecular beam epitaxy (MBE). Four APT data sets have been obtained, with fields of view up to 400 nm in depth and 120 nm in diameter. These data sets contain material from the InGaN quantum well (QW) active region, as well as the surrounding p- and n-doped waveguide and cladding layers, enabling comprehensive study of the structure and composition of the LD structure. Two regions of the same sample, with different average indium contents (18% and 16%) in the QW region, were studied. The APT data are shown to provide easy access to the p-type dopant levels, and the composition of a thin AlGaN barrier layer. Next, the distribution of indium within the InGaN QW was analyzed, to assess any possible inhomogeneity of the distribution of indium (''indium clustering''). No evidence for a statistically significant deviation from a random distribution was found, indicating that these MBE-grown InGaN QWs do not require indium clusters for carrier localization. However, the APT data show steps in the QW interfaces, leading to well-width fluctuations, which may act to localize carriers. Additionally, the unexpected presence of a small amount (x = 0.005) of indium in a layer grown intentionally as GaN was revealed. Finally, the same statistical method applied to the QW was used to show that the indium distribution within a thick InGaN waveguide layer in the n-doped region did not show any deviation from randomness.

  12. Growth and atomic structure of tellurium thin films grown on Bi2Te3

    NASA Astrophysics Data System (ADS)

    Okuyama, Yuma; Sugiyama, Yuya; Ideta, Shin-ichiro; Tanaka, Kiyohisa; Hirahara, Toru

    2017-03-01

    We have grown tellurium (Te) thin films on Bi2Te3 and investigated the atomic structure. From low-energy electron diffraction (LEED) measurements, we found that the Te films are [10 1 bar0]-oriented with six domains. A detailed analysis of the reflection high-energy electron diffraction (RHEED) pattern revealed that the films are strained with the in-plane lattice constant compressed by ∼1.5% compared to the bulk value due to the epitaxy between Te and Bi2Te3. These films will be interesting systems to investigate the predicted topological phases that occur in strained Te.

  13. Structural and optoelectronic properties of germanium-rich islands grown on silicon using molecular beam epitaxy

    SciTech Connect

    Nataraj, L.; Sustersic, N.; Coppinger, M.; Gerlein, L. F.; Kolodzey, J.; Cloutier, S. G.

    2010-03-22

    We report on the structural and optoelectronic properties of self-assembled germanium-rich islands grown on silicon using molecular beam epitaxy. Raman, photocurrent, photoluminescence, and transient optical spectroscopy measurements suggest significant built-in strains and a well-defined interface with little intermixing between the islands and the silicon. The shape of these islands depends on the growth conditions and includes pyramid, dome, barn-shaped, and superdome islands. Most importantly, we demonstrate that these germanium-rich islands provide efficient light emission at telecommunication wavelengths on a complementary metal-oxide semiconductor-compatible platform.

  14. Rhizobacterial Community Structures Associated with Native Plants Grown in Chilean Extreme Environments.

    PubMed

    Jorquera, Milko A; Maruyama, Fumito; Ogram, Andrew V; Navarrete, Oscar U; Lagos, Lorena M; Inostroza, Nitza G; Acuña, Jacquelinne J; Rilling, Joaquín I; de La Luz Mora, María

    2016-10-01

    Chile is topographically and climatically diverse, with a wide array of diverse undisturbed ecosystems that include native plants that are highly adapted to local conditions. However, our understanding of the diversity, activity, and role of rhizobacteria associated with natural vegetation in undisturbed Chilean extreme ecosystems is very poor. In the present study, the combination of denaturing gradient gel electrophoresis and 454-pyrosequencing approaches was used to describe the rhizobacterial community structures of native plants grown in three representative Chilean extreme environments: Atacama Desert (ATA), Andes Mountains (AND), and Antarctic (ANT). Both molecular approaches revealed the presence of Proteobacteria, Bacteroidetes, and Actinobacteria as the dominant phyla in the rhizospheres of native plants. Lower numbers of operational taxonomic units (OTUs) were observed in rhizosphere soils from ATA compared with AND and ANT. Both approaches also showed differences in rhizobacterial community structures between extreme environments and between plant species. The differences among plant species grown in the same environment were attributed to the higher relative abundance of classes Gammaproteobacteria and Alphaproteobacteria. However, further studies are needed to determine which environmental factors regulate the structures of rhizobacterial communities, and how (or if) specific bacterial groups may contribute to the growth and survival of native plants in each Chilean extreme environments.

  15. Co3O4(100) films grown on Ag(100): Structure and chemical properties

    NASA Astrophysics Data System (ADS)

    Arman, Mohammad A.; Merte, Lindsay R.; Lundgren, Edvin; Knudsen, Jan

    2017-03-01

    Spinel type Co3O4(100) is successfully grown on Ag(100) at ultrahigh vacuum conditions and its structure, electronic and chemical properties are compared with those of Co3O4(111) grown on Ir(100). We find that the Co3O4(100) is unreconstructed. In contrast to the defect free Co3O4(111) surface the Co3O4(100) surface contains a high concentration of defects that we assign to subsurface cation vacancies analogous to those observed for Fe3O4(100). Our photoemission and absorption spectroscopy experiments reveal a very similar electronic structure of the Co3O4(111) and Co3O4(100) surfaces. The similar electronic structure of the two surfaces is reflected in the CO adsorption properties at low temperatures, as we observe adsorption of molecular CO as well as the formation of carbonate (CO3) species on both surfaces upon CO exposure at 85 K.

  16. Observation and understanding of anisotropic strain relaxation in selectively grown SiGe fin structures

    NASA Astrophysics Data System (ADS)

    Schulze, A.; Loo, R.; Ryan, P.; Wormington, M.; Favia, P.; Witters, L.; Collaert, N.; Bender, H.; Vandervorst, W.; Caymax, M.

    2017-04-01

    The performance of heterogeneous 3D transistor structures critically depends on the composition and strain state of the buffer, channel and source/drain regions. In this paper we used an in-line high resolution x-ray diffraction (HRXRD) tool to study in detail the composition and strain in selectively grown SiGe/Ge fin structures with widths down to 20 nm. For this purpose we arranged fins of identical dimensions into larger arrays which were then analyzed using an x-ray beam several tens of micrometers in size. Asymmetric reciprocal space maps measured both parallel and perpendicular to the fins allowed us to extract the lattice parameters in all three spatial directions. Our results demonstrate an anisotropic in-plane strain state of the selectively grown SiGe buffer in case of narrower fins with significantly reduced relaxation in the direction along the fin. This observation was verified using nano-beam electron diffraction, and is explained based on the reduced probability for dislocation half-loops to evolve in trenches narrower than a few times the critical radius. Moreover, we introduce and discuss in detail a methodology for the determination of the composition in case of an anisotropic in-plane strain state which differs from the procedure commonly used for blanket layers. Our findings verify the importance of in-line HRXRD measurements for process development and monitoring as well as the fundamental study of relaxation and defect formation in confined volumes.

  17. Observation and understanding of anisotropic strain relaxation in selectively grown SiGe fin structures.

    PubMed

    Schulze, A; Loo, R; Ryan, P; Wormington, M; Favia, P; Witters, L; Collaert, N; Bender, H; Vandervorst, W; Caymax, M

    2017-04-07

    The performance of heterogeneous 3D transistor structures critically depends on the composition and strain state of the buffer, channel and source/drain regions. In this paper we used an in-line high resolution x-ray diffraction (HRXRD) tool to study in detail the composition and strain in selectively grown SiGe/Ge fin structures with widths down to 20 nm. For this purpose we arranged fins of identical dimensions into larger arrays which were then analyzed using an x-ray beam several tens of micrometers in size. Asymmetric reciprocal space maps measured both parallel and perpendicular to the fins allowed us to extract the lattice parameters in all three spatial directions. Our results demonstrate an anisotropic in-plane strain state of the selectively grown SiGe buffer in case of narrower fins with significantly reduced relaxation in the direction along the fin. This observation was verified using nano-beam electron diffraction, and is explained based on the reduced probability for dislocation half-loops to evolve in trenches narrower than a few times the critical radius. Moreover, we introduce and discuss in detail a methodology for the determination of the composition in case of an anisotropic in-plane strain state which differs from the procedure commonly used for blanket layers. Our findings verify the importance of in-line HRXRD measurements for process development and monitoring as well as the fundamental study of relaxation and defect formation in confined volumes.

  18. Woody plant diversity and structure of shade-grown-coffee plantations in northern Chiapas, Mexico.

    PubMed

    Soto-Pinto, L; Romero-Alvarado, Y; Caballero-Nieto, J; Segura Warnholtz, G

    2001-01-01

    Shade-grown coffee is an agricultural system that contains some forest-like characteristics. However, structure and diversity are poorly known in shade coffee systems. In 61 coffee-growers' plots of Chiapas, Mexico, structural variables of shade vegetation and coffee yields were measured, recording species and their use. Coffee stands had five vegetation strata. Seventy seven woody species mostly used as wood were found (mean density 371.4 trees per hectare). Ninety percent were native species (40% of the local flora), the remaining were introduced species, mainly fruit trees/shrubs. Diametric distribution resembles that of a secondary forest. Principal Coordinates Analysis grouped plots in four classes by the presence of Inga, however the majority of plots are diverse. There was no difference in equitability among groups or coffee yields. Coffee yield was 835 g clean coffee per shrub, or ca. 1,668 kg ha-1. There is a significant role of shade-grown coffee as diversity refuge for woody plants and presumably associated fauna as well as an opportunity for shade-coffee growers to participate in the new biodiversity-friendly-coffee market.

  19. A pipeline for structure determination of in vivo-grown crystals using in cellulo diffraction

    PubMed Central

    Boudes, Marion; Garriga, Damià; Fryga, Andrew; Caradoc-Davies, Tom; Coulibaly, Fasséli

    2016-01-01

    While structure determination from micrometre-sized crystals used to represent a challenge, serial X-ray crystallography on microfocus beamlines at synchrotron and free-electron laser facilities greatly facilitates this process today for microcrystals and nanocrystals. In addition to typical microcrystals of purified recombinant protein, these advances have enabled the analysis of microcrystals produced inside living cells. Here, a pipeline where crystals are grown in insect cells, sorted by flow cytometry and directly analysed by X-ray diffraction is presented and applied to in vivo-grown crystals of the recombinant CPV1 polyhedrin. When compared with the analysis of purified crystals, in cellulo diffraction produces data of better quality and a gain of ∼0.35 Å in resolution for comparable beamtime usage. Importantly, crystals within cells are readily derivatized with gold and iodine compounds through the cellular membrane. Using the multiple isomorphous replacement method, a near-complete model was autobuilt from 2.7 Å resolution data. Thus, in favourable cases, an in cellulo pipeline can replace the complete workflow of structure determination without compromising the quality of the resulting model. In addition to its efficiency, this approach maintains the protein in a cellular context throughout the analysis, which reduces the risk of disrupting transient or labile interactions in protein–protein or protein–ligand complexes. PMID:27050136

  20. Electrical and structural studies of AlGaAs/GaAs wires grown on patterned substrates

    NASA Astrophysics Data System (ADS)

    Schäpers, Th.; Hartmann, A.; Schwarz, A.; Hardtdegen, H.; Bongartz, M.; Dieker, Ch.; Lüth, H.

    1998-01-01

    The electrical and structural properties of U- and V-shaped Al0.3Ga0.7As/GaAs wire structures grown by low-pressure metal-organic vapor phase epitaxy were investigated. By using dimethylethylamine alane (DMEAA) and triethylgallium (TEGa) for the growth of the bottom Al0.3Ga0.7As buffer layer, a non-conductive, polycrystalline layer is formed on top of the SiO2 masked areas, leading to an effective electrical isolation between adjacent wire structures. The characterization of the morphology by TEM confirmed the formation of a wire structure at the bottom of the V-groove. Additionally, it was observed that if DMEAA/TEGa is used as a source for the growth of the lower Al0.3Ga0.7As barrier layer, the radius of curvature of the crescent-shaped quantum wires at bottom of the V-shaped groove is larger than in structures where this barrier layer is based on trimethylaluminum and trimethylgallium sources. From magneto-transport measurements under different orientations of the magnetic field it could be concluded that in U-shaped structures, the main conductive channel is located at the (100) bottom layer, while for the V-shaped structures the side-wall quantum well and the quantum wire contribute to the conductance.

  1. Surface Structure of Kio (3) Grown By Heterogeneous Reaction of Ozone With Ki (001)

    SciTech Connect

    Brown, M.A.; Liu, Z.; Ashby, P.D.; Mehta, A.; Grimm, R.L.; Hemminger, J.C.

    2009-05-12

    The crystal structure of KIO{sub 3} grown by heterogeneous surface oxidation of KI (001) with ozone is reported. Under ambient reaction conditions (RH {approx}35%, room temperature) a thick layer of KIO{sub 3} grows at the gas-solid interface. Two doublets are present in the I(4d) X-ray photoelectron spectroscopy structure measurements, characteristic of unreacted KI (I{sup -}) from the substrate and the oxidized KIO{sub 3} (I{sup 5+}) reaction product. X-ray diffraction measurements confirm the presence at the interface of randomly oriented polycrystalline-triclinic KIO{sub 3} with an average particle diameter of 15 nm. KIO{sub 3} particle diameters determined from the X-ray diffraction peak widths are consistent with the results of atomic force microscopy. There is no X-ray powder diffraction evidence to suggest that the underlying KI substrate is altered in any manner during this heterogeneous interfacial reaction.

  2. Structural properties and gas sensing behavior of sol-gel grown nanostructured zinc oxide

    NASA Astrophysics Data System (ADS)

    Rajyaguru, Bhargav; Gadani, Keval; Rathod, K. N.; Solanki, Sapana; Kansara, S. B.; Pandya, D. D.; Shah, N. A.; Solanki, P. S.

    2016-05-01

    In this communication, we report the results of the studies on structural properties and gas sensing behavior of nanostructured ZnO grown using acetone precursor based modified sol-gel technique. Final product of ZnO was sintered at different temperatures to vary the crystallite size while their structural properties have been studied using X-ray diffraction (XRD) measurement performed at room temperature. XRD results suggest the single phasic nature of all the samples and crystallite size increases from 11.53 to 20.96nm with increase in sintering temperature. Gas sensing behavior has been studied for acetone gas which indicates that lower sintered samples are more capable to sense the acetone gas and related mechanism has been discussed in the light of crystallite size, crystal boundary density, defect mechanism and possible chemical reaction between gas traces and various oxygen species.

  3. Structural Control in Porous/Compact Multilayer Systems Grown by Magnetron Sputtering.

    PubMed

    Garcia-Valenzuela, Aurelio; Lopez-Santos, Carmen; Alvarez, Rafael; Rico, Victor J; Cotrino, Jose; Gonzalez-Elipe, Agustin Rodriguez; Palmero, Alberto

    2017-09-15

    In this work we analyze a phenomenon that takes place when growing magnetron sputtered porous/compact multilayer systems by alternating the oblique angle and the classical configuration geometries. We show that the compact layers develop numerous fissures rooted in the porous structures of the film below, in a phenomenon that amplifies when increasing the number of stacked layers. We demonstrate that these fissures emerge during growth due to the high roughness of the porous layers and the coarsening of a discontinuous interfacial region. To minimize this phenomenon, we have grown thin interlayers between porous and compact films under the impingement of energetic plasma ions, responsible for smoothing out the interfaces and inhibiting the formation of structural fissures. This method has been tested in practical situations for compact TiO2/porous SiO2 multilayer systems, although it can be extrapolated to other materials and conditions. © 2017 IOP Publishing Ltd.

  4. Structural and optical characterizations of InPBi thin films grown by molecular beam epitaxy.

    PubMed

    Gu, Yi; Wang, Kai; Zhou, Haifei; Li, Yaoyao; Cao, Chunfang; Zhang, Liyao; Zhang, Yonggang; Gong, Qian; Wang, Shumin

    2014-01-13

    InPBi thin films have been grown on InP by gas source molecular beam epitaxy. A maximum Bi composition of 2.4% is determined by Rutherford backscattering spectrometry. X-ray diffraction measurements show good structural quality for Bi composition up to 1.4% and a partially relaxed structure for higher Bi contents. The bandgap was measured by optical absorption, and the bandgap reduction caused by the Bi incorporation was estimated to be about 56 meV/Bi%. Strong and broad photoluminescence signals were observed at room temperature for samples with xBi < 2.4%. The PL peak position varies from 1.4 to 1.9 μm, far below the measured InPBi bandgap.

  5. Structural and optical properties of PbS thin films grown by chemical bath deposition

    SciTech Connect

    Seghaier, S.; Kamoun, N.; Guasch, C.; Zellama, K.

    2007-09-19

    Lead sulphide thin films are grown on glass substrates at various deposition times tD, in the range of 40-60 min per step of 2 min, using the chemical bath deposition technique. X-ray diffraction and atomic force microscopy are used to characterize the film structure. The surface composition is analysed by Auger electron spectroscopy. It appears that the as-prepared thin films are polycrystalline with cubic structure. Nanometric scale crystallites are uniformly distributed on the surface. They exhibit almost a stoechiometric composition with a [Pb]/[S] ratio equal to 1.10. Optical properties are studied in the range of 300-3300 nm by spectrophotometric measurements. Analysis of the optical absorption data of lead sulphide thin layers reveals a narrow optical direct band gap equal to 0.46 eV for the layer corresponding to a deposition time equal to 60 min.

  6. Electronic and magnetic structure of ultra-thin Ni films grown on W(110)

    NASA Astrophysics Data System (ADS)

    Calloni, A.; Bussetti, G.; Berti, G.; Yivlialin, R.; Camera, A.; Finazzi, M.; Duò, L.; Ciccacci, F.

    2016-12-01

    We studied the electronic structure of thin Ni films grown on a W(110) single crystal, as a function of the Ni thickness, by means of angle-resolved photoemission and inverse photoemission spectroscopy, also with spin resolution. The results are discussed in the light of the different stages characterizing the transition from the pseudomorphic bcc to the fully relaxed fcc phase. A clear spin polarization is detected as soon as a bulk-like electronic structure is observed. In these conditions, we characterized the exchange splitting of the occupied bands at the Γbar and Mbar points of the surface Brillouin zone, providing further experimental support to previous interpretations of photoemission spectra from bulk Ni.

  7. Structural and optical characterization and scintillator application of hydrothermal-grown ZnO microrods

    NASA Astrophysics Data System (ADS)

    Empizo, Melvin John F.; Santos-Putungan, Alexandra B.; Yamanoi, Kohei; Salazar, Hernanie T.; Anguluan, Eloise P.; Mori, Kazuyuki; Arita, Ren; Minami, Yuki; Luong, Mui Viet; Shimizu, Toshihiko; Estacio, Elmer S.; Somintac, Armando S.; Salvador, Arnel A.; Sarmago, Roland V.; Fukuda, Tsuguo; Sarukura, Nobuhiko

    2017-03-01

    ZnO microrods are fabricated by a simple hydrothermal growth route using zinc acetate dihydrate [Zn(CH3COO)2·2H2O] and hexamethylenetetramine [(CH2)6N4] aqueous solutions. The as-prepared microrods exhibit uniform dimensions, well-faceted surfaces, and hexagonal crystal structure. The microrods also have an intense ultraviolet (UV) emission at 392 nm with an average lifetime of 80 ps. No peaks are observed at the visible wavelengths that can be attributed to defect-related emissions. With excellent structural and optical properties and with loose adhesion to their substrates, the ZnO microrods can be isolated, harvested, and manipulated and can be integrated as building blocks of a microstructured scintillator screen. The proposed scintillator screen possibly offers efficient and precise detection with high resolution. Hydrothermal-grown ZnO microrods then hold a promise towards radiation detector innovation and integrated optoelectronic microsystems.

  8. Structural features of Ge(Ga) single crystals grown by the floating zone method in microgravity

    NASA Astrophysics Data System (ADS)

    Prokhorov, I. A.; Zakharov, B. G.; Senchenkov, A. S.; Egorov, A. V.; Camel, D.; Tison, P.

    2008-11-01

    Structural features of the Ge(Ga) single crystal grown by the floating zone (FZ) method in microgravity environment aboard the FOTON-9 spacecraft are investigated by methods of X-ray topography, double-crystal diffractometry, selective chemical etching and spreading resistance measurements. It is established that the crystal structure is characterized by the presence of an incompletely melted region and defects caused by its formation. Growth striations revealed in regrown part of the crystal, testify to development of non-stationary capillary Marangoni convection in melt at the realized parameters of FZ remelting under space conditions. Periodicity of the growth striations is compared to frequency characteristics of heat flux pulsations through the crystallization front, found as a result of numerical simulation of melt hydrodynamics.

  9. Structural properties and gas sensing behavior of sol-gel grown nanostructured zinc oxide

    SciTech Connect

    Rajyaguru, Bhargav; Gadani, Keval; Kansara, S. B.; Pandya, D. D.; Shah, N. A.; Solanki, P. S.; Rathod, K. N.; Solanki, Sapana

    2016-05-06

    In this communication, we report the results of the studies on structural properties and gas sensing behavior of nanostructured ZnO grown using acetone precursor based modified sol-gel technique. Final product of ZnO was sintered at different temperatures to vary the crystallite size while their structural properties have been studied using X-ray diffraction (XRD) measurement performed at room temperature. XRD results suggest the single phasic nature of all the samples and crystallite size increases from 11.53 to 20.96 nm with increase in sintering temperature. Gas sensing behavior has been studied for acetone gas which indicates that lower sintered samples are more capable to sense the acetone gas and related mechanism has been discussed in the light of crystallite size, crystal boundary density, defect mechanism and possible chemical reaction between gas traces and various oxygen species.

  10. Correlation between structure and electrical transport in ion-irradiated graphene grown on Cu foils

    SciTech Connect

    Buchowicz, G.; Stone, P.R.; Robinson, J.T.; Cress, C.D.; Beeman, J.W.; Dubon, O.D.

    2010-11-04

    Graphene grown by chemical vapor deposition and supported on SiO2 and sapphire substrates was studied following controlled introduction of defects induced by 35 keV carbon ion irradiation. Changes in Raman spectra following fluences ranging from 1012 cm-2 to 1015 cm-2 indicate that the structure of graphene evolves from a highly-ordered layer, to a patchwork of disordered domains, to an essentially amorphous film. These structural changes result in a dramatic decrease in the Hall mobility by orders of magnitude while, remarkably, the Hall concentration remains almost unchanged, suggesting that the Fermi level is pinned at a hole concentration near 1x1013 cm-2. A model for scattering by resonant scatterers is in good agreement with mobility measurements up to an ion fluence of 1x1014 cm-2.

  11. Highly ordered Ga(As)Sb quantum dots grown on pre-structured GaAs

    NASA Astrophysics Data System (ADS)

    Loeber, Thomas Henning; Strassner, Johannes; Wolff, Sandra; Laegel, Bert; Foukhardt, Henning

    2017-02-01

    Ga(Sb)As quantum dots (QDs) are usually grown on plane GaAs substrates by self-organization in the StranskiKrastanov mode. Here we report on Ga(As)Sb QD growth on a pre-structured GaAs substrate to achieve highly ordered QDs. The structure consists of a two-dimensional array of holes/troughs milled into the substrate (wafer with initial epitaxial buffer layer) with a gallium focused ion beam (Ga-FIB). Thus, the area density of the QDs can be controled. For exact positioning of the QDs in the milled holes it is important that the diameter of the dots equals the diameter of the milled holes. In a previous publication we have shown that we are able to change the diameter as well as the height of the QDs by controlled variation of growth temperature, Ga/Sb ratio, and nominal coverage. The diameter and depth of the milled holes as well as their separation are varied. Also, different milling techniques are examined to optimize milling time and procedure. The pre-structured GaAs substrate is overgrown in a second molecular-beam-epitaxial (MBE) step, first with another thin GaAs buffer layer, then with a QD layer. With the optimum of the milling and growth parameter sets the diameter of the QDs equals the size of the milled holes and the QDs can be grown highly ordered in the given pre-structured array. To the best of our knowledge this is the first report about exact positioning of Ga(As)Sb QDs on GaAs.

  12. Optical and structural characterisation of epitaxial nanoporous GaN grown by CVD.

    PubMed

    Mena, Josué; Carvajal, Joan J; Martínez, Oscar; Jiménez, Juan; Zubialevich, Vitaly Z; Parbrook, Peter J; Diaz, Francesc; Aguiló, Magdalena

    2017-09-15

    In this paper we study the optical properties of nanoporous gallium nitride (GaN) epitaxial layers grown by chemical vapour deposition on non-porous GaN substrates, using photoluminescence, cathodoluminescence, and resonant Raman scattering, and correlate them with the structural characteristic of these films. We pay special attention to the analysis of the residual strain of the layers and the influence of the porosity in the light extraction. The nanoporous GaN epitaxial layers are under tensile strain, although the strain is progressively reduced as the deposition time and the thickness of the porous layer increases, becoming nearly strain free for a thickness of 1.7 μm. The analysis of the experimental data point to the existence of vacancy complexes as the main source of the tensile strain.

  13. Solidification structures grown under induced flow and continuous casting of steel

    NASA Technical Reports Server (NTRS)

    Tsavaras, A. A.

    1984-01-01

    The use of induced flow as a means to control solidification structures in strand cast steel is investigated. The quality problems in strand cast steel stemming from columnar growth can be partially controlled, by Electro Magnetic Stirring (EMS). Induced flow changes the normal morphology of dendrites. Solids grown under intense stirring conditions show both negative and positive segregation which is considered unacceptable by some steel producers. The inclusion size and population is strongly affected by induced flow (EMS). Laboratory and industrial data show substantial reduction in inclusion size and content, but the overall effect of flow on inclusions is affected by the particular type of flow patterns utilized in each case. Productivity and quality are raised substantially in steel strand casting by utilizing EMS.

  14. Dislocation structure of Ge crystals grown by low thermal gradient Czochralski technique

    NASA Astrophysics Data System (ADS)

    Trukhanov, E. M.; Fritzler, K. B.; Vasilenko, A. P.; Kolesnikov, A. V.; Kasimkin, P. V.; Moskovskih, V. A.

    2017-06-01

    Dislocation structure of the Ge single crystals grown by Czochralski method with low thermal gradient has been studied. The selective etching technique and the X-Ray transmission and reflection topography were used. Clearly defined non-uniform dislocation distribution over the crystal cross - section is revealed. Helical dislocations and sets of prismatic dislocation loops are registered. Helical dislocations perpendicular to the ingot axis are situated near the boundary between the regions with low and high dislocation densities (102 and 103 cm-2, respectively). Their length can be as much as several millimeters. Dislocation formations lying at a 35.3° to the crystal axis along <110> directions are also observed. These formations have the shape of prism confined by {111} planes.

  15. Structural Defects in Laterally Overgrown GaN Layers Grown onNon-polar Substrates

    SciTech Connect

    Liliental-Weber, Z.; Ni, X.; Morkoc, H.

    2007-02-14

    Transmission electron microscopy was used to study defects in lateral epitaxial layers of GaN which were overgrown on a template of a-plane (11{und 2}0) GaN grown on (1{und 1}02) r-plane Al2O3. A high density of basal stacking faults is formed in these layers because the c-planes of wurtzite structure are arranged along the growth direction. Density of these faults is decreasing at least by two orders of magnitude lower in the wings compared to the seed areas. Prismatic stacking faults and threading dislocations are also observed, but their densities drastically decrease in the wings. The wings grow with opposite polarities and the Ga-wing width is at least 6 times larger than N-wing and coalescence is rather difficult. Some tilt and twist was detected using Large Angle Convergent Beam Electron Diffraction.

  16. Interface structure of epitaxial graphene grown on 4H-SiC(0001)

    SciTech Connect

    Hass, J.; Millán-Otoya, J.E.; First, P.N.; Conrad, E.H.

    2009-06-12

    We present a structural analysis of the graphene-4HSiC(0001) interface using surface x-ray reflectivity. We find that the interface is composed of an extended reconstruction of two SiC bilayers. The interface directly below the first graphene sheet is an extended layer that is more than twice the thickness of a bulk SiC bilayer ({approx}1.7 {angstrom} compared to 0.63 {angstrom}). The distance from this interface layer to the first graphene sheet is much smaller than the graphite interlayer spacing but larger than the same distance measured for graphene grown on the (000{bar 1}) surface, as predicted previously by ab initio calculations.

  17. Optical and structural characterisation of epitaxial nanoporous GaN grown by CVD

    NASA Astrophysics Data System (ADS)

    Mena, Josué; Carvajal, Joan J.; Martínez, Oscar; Jiménez, Juan; Zubialevich, Vitaly Z.; Parbrook, Peter J.; Diaz, Francesc; Aguiló, Magdalena

    2017-09-01

    In this paper we study the optical properties of nanoporous gallium nitride (GaN) epitaxial layers grown by chemical vapour deposition on non-porous GaN substrates, using photoluminescence, cathodoluminescence, and resonant Raman scattering, and correlate them with the structural characteristic of these films. We pay special attention to the analysis of the residual strain of the layers and the influence of the porosity in the light extraction. The nanoporous GaN epitaxial layers are under tensile strain, although the strain is progressively reduced as the deposition time and the thickness of the porous layer increases, becoming nearly strain free for a thickness of 1.7 μm. The analysis of the experimental data point to the existence of vacancy complexes as the main source of the tensile strain.

  18. Structural investigations of hydrogenated epitaxial graphene grown on 4H-SiC (0001)

    SciTech Connect

    Tokarczyk, M.; Kowalski, G. Stępniewski, R.; Możdżonek, M.; Strupiński, W.; Ciepielewski, P.; Borysiuk, J.

    2013-12-09

    Structural investigations of hydrogenated epitaxial graphene grown on SiC(0001) are presented. It is shown that hydrogen plays a dual role. In addition to contributing to the well-known removal of the buffer layer, it goes between the graphene planes, resulting in an increase of the interlayer spacing to 3.6 Å–3.8 Å. It is explained by the intercalation of molecular hydrogen between carbon planes, which is followed by H{sub 2} dissociation, resulting in negatively charged hydrogen atoms trapped between the graphene layers, with some addition of covalent bonding to carbon atoms. Negatively charged hydrogen may be responsible for p-doping observed in hydrogenated multilayer graphene.

  19. Graphene originated 3D structures grown on the assembled nickel particles

    NASA Astrophysics Data System (ADS)

    Paronyan, Tereza; Harutyunyan, Avetik; Honda Research Institute USA Inc. Team

    2013-03-01

    Recently, the fabrication of various morphologies of graphene originated structures became very important due to the perspective of wide range of new applications. Particularly, free standing 3D structured graphene foams could be imperative in energy related areas . Here, we present the new approach of the CVD growth of 3D graphene network by using primarily sintered Ni particle's (~40 μm size) assembles as a template-catalyst via decomposition of low rate of CH4 at 1100° C based on synthesis method described earlier. SEM and Raman spectra analysis revealed the formation of graphene structure containing a single up to few layers grown on the sintered metal particles served as a catalyst-template. After etching the metal frame without using any support polymer, 3D free-standing graphene microporous structure was formed demonstrating high BET surface area. Two probe measurements of frame resistance were ~2-8 Ω. Our approach allows controllable tune the pore size and thereby the surface area of 3D graphene network through the variation of the template-catalyst particles size.

  20. Micromechanical and structural study of ambient grown Au nanostructures on P doped Si(100)

    NASA Astrophysics Data System (ADS)

    Senevirathne, Indrajith; Tatham, Joshua

    2012-02-01

    Au nanostructure have wide application potential due to their noble nature, plasmonic, catalytic and specific conductive properties. Such nanostructures grown on substrate support under ambient conditions are complex but provides unique opportunities in dirty systems. In this model system Au was self assembled on solvent cleaned P doped Si(100) surface giving rise to near spherical geometry. Self assembly was initiated by magnetron sputter deposited Au at RT (300K) under high vacuum, on Si(100) which subsequently exposed to atmosphere. The micromechanical properties of the structures were measured by contact mode force curves in Atomic Force Microscopy (AFM). Both the stiffness and young modulus was measured for the nanostructures assembled and annealed at different temperatures. Initial plasticity of the nano structures was observed to reduce at annealing. Au nano structures were likely Stranski - Krastanov growth mode. Observed structure and their variations when annealed at successively higher temperatures will also be discussed. All measurements were taken by the AFM in contact intermittent contact and non-contact modes.

  1. Electrical and structural properties of (Pd/Au) Schottky contact to as grown and rapid thermally annealed GaN grown by MBE

    SciTech Connect

    Nirwal, Varun Singh Singh, Joginder; Gautam, Khyati; Peta, Koteswara Rao

    2016-05-06

    We studied effect of thermally annealed GaN surface on the electrical and structural properties of (Pd/Au) Schottky contact to Ga-polar GaN grown by molecular beam epitaxy on Si substrate. Current voltage (I-V) measurement was used to study electrical properties while X-ray diffraction (XRD) measurement was used to study structural properties. The Schottky barrier height calculated using I-V characteristics was 0.59 eV for (Pd/Au) Schottky contact on as grown GaN, which increased to 0.73 eV for the Schottky contact fabricated on 700 °C annealed GaN film. The reverse bias leakage current at -1 V was also significantly reduced from 6.42×10{sup −5} A to 7.31×10{sup −7} A after annealing. The value of series resistance (Rs) was extracted from Cheung method and the value of R{sub s} decreased from 373 Ω to 172 Ω after annealing. XRD results revealed the formation of gallide phases at the interface of (Pd/Au) and GaN for annealed sample, which could be the reason for improvement in the electrical properties of Schottky contact after annealing.

  2. Electronic excitation induced structural and optical modifications in InGaN/GaN quantum well structures grown by MOCVD

    NASA Astrophysics Data System (ADS)

    Prabakaran, K.; Ramesh, R.; Jayasakthi, M.; Surender, S.; Pradeep, S.; Balaji, M.; Asokan, K.; Baskar, K.

    2017-03-01

    The present study focuses on the electronic excitation induced structural and optical properties of InGaN/GaN quantum well (QW) structures grown by metal organic chemical vapor deposition technique. These excitations were produced using Au7+ ion irradiation with 100 MeV energy. The X-ray rocking curves intensity and full width at half-maximum values corresponding to the planes of (0 0 0 2) and (1 0 -1 5) of the irradiated QW structures show the modifications in the screw and edge-type dislocation densities vary with the ion fluences. The structural characteristics using the reciprocal space mapping indicate the intermixing effects in InGaN/GaN QW structures. Atomic force microscopy images confirmed the presence of nanostructures and the surface modification due to heavy ion irradiation. The irradiated QW structures exhibited degraded photoluminescence intensity and a subsequent decrease in the yellow luminescence band intensity with the fluences of 1 × 1011 and 5 × 1012 ions/cm2 compared to the pristine QW structures.

  3. Structural modulation of nanowire interfaces grown over selectively disrupted single crystal surfaces

    NASA Astrophysics Data System (ADS)

    Garratt, E.; Nikoobakht, B.

    2015-08-01

    Recent breakthroughs in deterministic approaches to the fabrication of nanowire arrays have demonstrated the possibility of fabricating such networks using low-cost scalable methods. In this regard, we have developed a scalable growth platform for lateral fabrication of nanocrystals with high precision utilizing lattice match and symmetry. Using this planar architecture, a number of homo- and heterostructures have been demonstrated including ZnO nanowires grown over GaN. The latter combination produces horizontal, epitaxially formed crystals aligned in the plane of the substrate containing a very low number of intrinsic defects. We use such ordered structures as model systems in the interests of gauging the interfacial structural dynamics in relation to external stimuli. Nanosecond pulses of focused ion beams are used to slightly modify the substrate surface and selectively form lattice disorders in the path of nanowire growth to examine the nanocrystal, namely: its directionality and lattice defects. High resolution electron microscopies are used to reveal some interesting structural effects; for instance, a minimum threshold of surface defects that can divert nanowires. We also discuss data indicating formation of surface strains and show their mitigation during the growth process.

  4. Structural properties of highly conductive ultra-nanocrystalline diamond films grown by hot-filament CVD

    NASA Astrophysics Data System (ADS)

    Mertens, M.; Lin, I.-N.; Manoharan, D.; Moeinian, A.; Brühne, K.; Fecht, H. J.

    2017-01-01

    In this work we show the correlation of the electrical conductivity of ultra-nanocrystalline (UNCD) diamond films grown by hot filament chemical vapor deposition (HFCVD) with their structural properties. The substrate temperature, the methane to hydrogen ratio and the pressure are the main factor influencing the growth of conductive UNCD films, which extends from electrical resistive diamond films (<10-4 S/cm) to highly conductive diamond films with a specific conductivity of 300 S/cm. High-resolution-transmission-electron-microscopy (HRTEM) and electron-energy-loss-spectroscopy (EELS) have been done on the highly conductive diamond films, to show the origin of the high electrical conductivity. The HRTEM results show random oriented diamond grains and a large amount of nano-graphite between the diamond crystals. EELS investigations are confirming these results. Raman measurements are correlated with the specific conductivity, which shows structural changes of sp2 carbons bonds as function of conductivity. Hall experiments complete the results, which lead to a model of an electron mobility based conductivity, which is influenced by the structural properties of the grain boundary regions in the ultra-nanocrystalline diamond films.

  5. Superheating suppresses structural disorder in layered BiI3 semiconductors grown by the Bridgman method

    NASA Astrophysics Data System (ADS)

    Johns, Paul M.; Sulekar, Soumitra; Yeo, Shinyoung; Baciak, J. E.; Bliss, Mary; Nino, Juan C.

    2016-01-01

    The susceptibility of layered structures to stacking faults is a problem in some of the more attractive semiconductor materials for ambient-temperature radiation detectors. In this work, Bridgman-grown BiI3 layered single crystals are investigated to understand and eliminate structural disorder, which reduces radiation detector performance. The use of superheating gradients has been shown by others to improve crystal quality in non-layered semiconductor crystals (Rudolph et al., 1996) [26]; thus the technique was explored to improve the growth of BiI3. When investigating the homogeneity of non-superheated crystals, highly geometric void defects were found to populate the bulk of the crystals. Applying a superheating gradient to the melt prior to crystal growth improved structural quality and decreased defect density from the order of 4600 voids per cm3 to 300 voids per cm3. Corresponding moderate improvements to electronic properties also resulted from the superheat gradient method of crystal growth. Comparative measurements through infrared microscopy, etch-pit density, X-ray rocking curves, and sheet resistivity readings show that superheat gradients in BiI3 growth led to higher quality crystals.

  6. Superheating Suppresses Structural Disorder in Layered BiI3 Semiconductors Grown by the Bridgman Method

    SciTech Connect

    Johns, Paul M.; Sulekar, Soumitra; Yeo, Shinyoung; Baciak, James E.; Bliss, Mary; Nino, Juan C.

    2016-01-01

    The susceptibility of layered structures to stacking faults is a problem in some of the more attractive semiconductor materials for ambient-temperature radiation detectors. In the work presented here, Bridgman-grown BiI3 layered single crystals are investigated to understand and eliminate this structural disorder, which reduces radiation detector performance. The use of superheating gradients has been shown to improve crystal quality in non-layered semiconductor crystals; thus the technique was here explored to improve the growth of BiI3. When investigating the homogeneity of non-superheated crystals, highly geometric void defects were found to populate the bulk of the crystals. Applying a superheating gradient to the melt prior to crystal growth improved structural quality and decreased defect density from the order of 4600 voids per cm3 to 300 voids per cm3. Corresponding moderate improvements to electronic properties also resulted from the superheat gradient method of crystal growth. Comparative measurements through infrared microscopy, etch-pit density, x-ray rocking curves, and sheet resistivity readings show that superheat gradients in BiI3 growth led to higher quality crystals.

  7. Structure and Morphology of Phthalocyanine Films Grown in Electrical Fields by Vapor Deposition

    NASA Technical Reports Server (NTRS)

    Zhu, Shen; Banks, Curtis E.; Frazier, Donald O.; Penn, Benjamin; Abdeldayem, Hossin; Hicks, Roslin

    1999-01-01

    Phthalocyanine is a very stable organic material in the atmosphere and has been used in numerous applications, such as optical switching and optical storage devices. Although this material has already been discovered for several decades and has had extensive studies conducted on it, many properties still need to be better understood, for example, the mechanisms of forming different solid phases and of changing film morphology by external forces. Phthalocyanine has two preferred solid phases (alpha and beta phases) for which the crystal structures, surface morphology and optical properties are different. In order to investigate these phenomena and the relationship among them, phthalocyanine films have been synthesized by vapor deposition on quartz substrates with and without an external electrical field. Some substrates were coated with a very thin gold film for the electrical field. These films have been characterized using x-ray diffraction, scanning electron microscopy, Fourier transfer infrared spectroscopy, and Z-scan technique. The films have excellent chemical and thermal stability. However, the surface of these films grown without the electrical field shows flower-like morphology. When films are deposited under an electrical field (approximately 3000 V/cm), an aligned structure is revealed on the surface. A comparison of the structure, morphology, optical properties, and the growth mechanism for these films with and without an electrical field will be discussed.

  8. Optical waveguide loss minimized into gallium nitride based structures grown by metal organic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Stolz, A.; Cho, E.; Dogheche, E.; Androussi, Y.; Troadec, D.; Pavlidis, D.; Decoster, D.

    2011-04-01

    The waveguide properties are reported for wide bandgap gallium nitride (GaN) structures grown by metal organic vapor phase epitaxy on sapphire using a AlN/GaN short period-superlattice (SPS) buffer layer system. A detailed optical characterization of GaN structures has been performed using the prism coupling technique in order to evaluate its properties and, in particular, the refractive index dispersion and the propagation loss. In order to identify the structural defects in the samples, we performed transmission electron microscopy analysis. The results suggest that AlN/GaN SPS plays a role in acting as a barrier to the propagation of threading dislocations in the active GaN epilayer; above this defective region, the dislocations density is remarkably reduced. The waveguide losses were reduced to a value around 0.65dB/cm at 1.55 μm, corresponding to the best value reported so far for a GaN-based waveguide.

  9. Optoelectronic and structural properties of InGaN nanostructures grown by plasma-assisted MOCVD

    NASA Astrophysics Data System (ADS)

    Seidlitz, Daniel; Senevirathna, M. K. I.; Abate, Y.; Hoffmann, A.; Dietz, N.

    2015-09-01

    This paper presents optoelectronic and structural layer properties of InN and InGaN epilayers grown on sapphire templates by Migration-Enhanced Plasma Assisted Metal Organic Chemical Vapor Deposition (MEPA-MOCVD). Real-time characterization techniques have been applied during the growth process to gain insight of the plasma-assisted decomposition of the nitrogen precursor and associated growth surface processes. Analyzed Plasma Emission Spectroscopy (PES) and UV Absorption Spectroscopy (UVAS) provide detection and concentrations of plasma generated active species (N*/NH*/NHx*). Various precursors have been used to assess the nitrogen-active fragments that are directed from the hollow cathode plasma tube to the growth surface. The in-situ diagnostics results are supplemented with ex-situ materials structures investigation results of nanoscale structures using Scanning Near-field Optical Microscopy (SNOM). The structural properties have been analyzed by Raman spectroscopy and Fourier transform infrared (FTIR) reflectance. The Optoelectronic and optical properties were extracted by modeling the FTIR reflectance (e.g. free carrier concentration, high frequency dielectric constant, mobility) and optical absorption spectroscopy. The correlation and comparison between the in-situ metrology results with the ex-situ nano-structural and optoelectronic layer properties provides insides into the growth mechanism on how plasma-activated nitrogen-fragments can be utilized as nitrogen precursor for group III-nitride growth. The here assessed growth process parameter focus on the temporal precursor exposure of the growth surface, the reactor pressure, substrate temperature and their effects of the properties of the InN and InGaN epilayers.

  10. Chloroplasts of salt-grown Arabidopsis seedlings are impaired in structure, genome copy number and transcript levels.

    PubMed

    Peharec Štefanić, Petra; Koffler, Tal; Adler, Guy; Bar-Zvi, Dudy

    2013-01-01

    The chloroplast is the most prominent and metabolically active plastid in photosynthetic plants. Chloroplasts differentiate from proplastids in the plant meristem. Plant plastids contain multiple copies of a small circular genome. The numbers of chloroplasts per mesophyll cell and of plastid genome copies are affected by developmental stage and environmental signals. We compared chloroplast structure, gene expression and genome copy number in Arabidopsis seedlings germinated and grown under optimal conditions to those in seedlings germinated and grown in the presence of NaCl. Chloroplasts of the NaCl-grown seedlings were impaired, with less developed thylakoid and granum membranes than control seedlings. In addition, chloroplasts of salt-grown Arabidopsis seedlings accumulated more starch grains than those in the respective control plants. Steady-state transcript levels of chloroplast-encoded genes and of nuclear genes encoding chloroplast proteins were reduced in salt-grown seedlings. This reduction did not result from a global decrease in gene expression, since the expression of other nuclear genes was induced or not affected. Average cellular chloroplast genome copy number was reduced in salt-grown seedlings, suggesting that the reduction in steady-state transcript levels of chloroplast-encoded genes might result from a decrease in template DNA.

  11. RF Magnetron Sputtering Grown Cu2O Film Structural, Morphological, and Electrical Property Dependencies on Substrate Type.

    PubMed

    Ahn, Heejin; Um, Youngho

    2015-03-01

    We investigated the structural, morphological, and electrical properties of cuprous oxide (Cu2O) film dependency on substrate type. Thin films grown using RF magnetron sputtering were characterized by scanning electron microscopy, X-ray diffraction (XRD), and Hall effect measurements. Cu2O thin films were deposited onto sapphire (0001), Si (100), and MgO (110) substrates, and showed Cu2O single phase only, which was confirmed by XRD measurement. Relatively larger compressive strain existed in Cu2O film grown on sapphire and Si, while a smaller tensile strain appeared in Cu2O film grown on MgO. Cu2O thin film crystallite sizes showed a linear dependence on strain. Moreover, film carrier concentration and mobility increased with increasing strain, while resistivity decreased with decreasing strain. Cu2O film strain due to induced strain opens the possibility of controlling structural and electrical properties in device applications.

  12. Thermodynamic and structural properties of tuber starches from transgenic potato plants grown in vitro and in vivo.

    PubMed

    Wasserman, Luybov A; Sergeev, Andrey I; Vasil'ev, Viktor G; Plashchina, Irina G; Aksenova, Nina P; Konstantinova, Tatyana N; Golyanovskaya, Svetlana A; Sergeeva, Lidiya I; Romanov, Georgy A

    2015-07-10

    Potato plants harboring Phytochrome B (PHYB) gene from Arabidopsis thaliana or rol genes from Agrobacterium rhizogenes were used to study the effect of transgene expression on structure and properties of starch in tubers. Thermodynamic characteristics of starch (melting temperature, enthalpy of melting, thickness of crystalline lamellae) were shown to be variable depending on the transgene expression and plant culturing mode: in vitro or in soil. The expression of rolB or rolC genes in in vitro cultured plants evoked opposite effects on starch melting temperature and crystalline lamellae thickness. AtPHYB or rolB expression in the soil-grown potato led to the formation of more defective or more ordered starch structures, respectively, in comparison with starches of the same lines grown in vitro. On the whole, our study revealed genotype-dependent differences between starches extracted from tubers of in vitro or in vivo grown plants.

  13. Structural and morphological evolution of gallium nitride nanorods grown by chemical beam epitaxy

    SciTech Connect

    Kuo, Shou-Yi; Lai, Fang-I; Chen, Wei-Chun; Hsiao, Chien-Nan; Lin, Woei-Tyng

    2009-07-15

    The morphological and structural evolution is presented for GaN nanorods grown by chemical beam epitaxy on (0001) Al{sub 2}O{sub 3} substrates. Their structural and optical properties are investigated by x-ray diffraction, scanning and transmission electron microscopy, and temperature-dependent photoluminescence measurements. While increasing the growth temperature and the flow rate of radio-frequency nitrogen radical, the three-dimensional growth mode will be enhanced to form one-dimensional nanostructures. The high density of well-aligned nanorods with a diameter of 30-50 nm formed uniformly over the entire sapphire substrate. The x-ray diffraction patterns and transmission electron microscopic images indicate that the self-assembled GaN nanorods are a pure single crystal and preferentially oriented in the c-axis direction. Particularly, the ''S-shape'' behavior with localization of {approx}10 meV observed in the temperature-dependent photoluminescence might be ascribed to the fluctuation in crystallographic defects and composition.

  14. Structural and electrical properties of large area epitaxial VO2 films grown by electron beam evaporation

    NASA Astrophysics Data System (ADS)

    Théry, V.; Boulle, A.; Crunteanu, A.; Orlianges, J. C.; Beaumont, A.; Mayet, R.; Mennai, A.; Cosset, F.; Bessaudou, A.; Fabert, M.

    2017-02-01

    Large area (up to 4 squared inches) epitaxial VO2 films, with a uniform thickness and exhibiting an abrupt metal-insulator transition with a resistivity ratio as high as 2.85 × 10 4 , have been grown on (001)-oriented sapphire substrates by electron beam evaporation. The lattice distortions (mosaicity) and the level of strain in the films have been assessed by X-ray diffraction. It is demonstrated that the films grow in a domain-matching mode where the distortions are confined close to the interface which allows growth of high-quality materials despite the high film-substrate lattice mismatch. It is further shown that a post-deposition high-temperature oxygen annealing step is crucial to ensure the correct film stoichiometry and provide the best structural and electrical properties. Alternatively, it is possible to obtain high quality films with a RF discharge during deposition, which hence do not require the additional annealing step. Such films exhibit similar electrical properties and only slightly degraded structural properties.

  15. Structure of GaSb layers grown on (111) GaAs surfaces

    NASA Astrophysics Data System (ADS)

    Babkevich, A. Yu.; Cowley, R. A.; Mason, N. J.; Shields, P. A.; Stadelman, T.; Brown, S.; Mannix, D.; Paul, D.

    2004-09-01

    The structure of GaSb layers with thicknesses of 70Å, 160Å, and 1260Å grown on GaAs (111) substrates by metal-organic vapor phase epitaxy has been studied by high-resolution x-ray diffraction. The lattice mismatch between the layer and the substrate is large and most of the misfit strain is taken up by a regular network of dislocations localized at the interface between the GaSb and the GaAs. The spacing between the dislocations is about 49Å along the [1¯1¯2] direction. We observe that the layers have both the ABC … and ACB … face-centered-cubic (fcc) domains with a domain size of about 1500Å. The presence of approximately the same volume of both the domains in the overall layer suggests that the particular domain is chosen largely randomly and independent of the orientation of the substrate. In contrast, the results show that the structure of the GaAs substrate was a single fcc domain. The widths of the off-axis Bragg reflections along the [111] direction for the thinnest sample was within error the same as those for the (hhh ) Bragg reflections showing that each fcc domain penetrated through the entire layer.

  16. THz pulse emission from InAs-based epitaxial structures grown on InP substrates

    NASA Astrophysics Data System (ADS)

    Nevinskas, I.; Butkutė, R.; Stanionytė, S.; Bičiūnas, A.; Geižutis, A.; Krotkus, A.

    2016-11-01

    Undoped InAs and InAs p-n junction epitaxial layers were grown on (100)-cut InP substrates with molecular beam epitaxy. The lattice difference between the substrate and the InAs layers was matched with a graded AlInAs buffer layer. The alloy composition, structural characteristics and carrier mobility of the structures were determined from the high-resolution x-ray diffraction, atomic force microscopy and Hall-effect measurements, respectively. The optical parameters of the layers were characterized by the emission of terahertz (THz) pulses when the samples were illuminated with femtosecond laser pulses. It has been found that the built-in electric field in the p-n junction enhances the THz emission. Registering THz signals in the quasi-reflection direction, the p-n junction emits more intense radiation in comparison to an undoped bulk InAs. At excitation wavelengths >1.8 μm the InAs p-n junction provides stronger THz pulses than those from (111)-cut p-InAs, the best surface THz emitter known to date. The epitaxial layers were also exposed to a constant magnetic field from neodymium permanent magnets, which further enhances THz emission and allows registering THz radiation in the line-of-sight terahertz time-domain-spectroscopy geometry.

  17. Electrochromism and photocatalysis in dendrite structured Ti:WO3 thin films grown by sputtering

    NASA Astrophysics Data System (ADS)

    Karuppasamy, A.

    2015-12-01

    Titanium doped tungsten oxide (Ti:WO3) thin films with dendrite surface structures were grown by co-sputtering titanium and tungsten in Ar + O2 atmosphere. Ti:WO3 thin films were deposited at oxygen flow rates corresponding to pressures in the range 1.0 × 10-3-5.0 × 10-3 mbar. Argon flow rate and sputtering power densities for titanium (2 W/cm2) and tungsten (3 W/cm2) were kept constant. Ti:WO3 films deposited at an oxygen pressure of 5 × 10-3 mbar are found to be better electrochromic and photocatalytic. They have high optical modulation (80% at λ = 550 nm), coloration efficiency (60 cm2/C at λ = 550 nm), electron/ion storage and removal capacity (Qc: -22.01 mC/cm2, Qa: 17.72 mC/cm2), reversibility (80%) and methylene blue decomposition rate (-1.38 μmol/l d). The combined effects of titanium doping, dendrite surface structures and porosity leads to significant enhancement in the electrochromic and photocatalytic properties of Ti:WO3 films.

  18. Electronic structures of GeSi nanoislands grown on pit-patterned Si(001) substrate

    SciTech Connect

    Ye, Han Yu, Zhongyuan

    2014-11-15

    Patterning pit on Si(001) substrate prior to Ge deposition is an important approach to achieve GeSi nanoislands with high ordering and size uniformity. In present work, the electronic structures of realistic uncapped pyramid, dome, barn and cupola nanoislands grown in (105) pits are systematically investigated by solving Schrödinger equation for heavy-hole, which resorts to inhomogeneous strain distribution and nonlinear composition-dependent band parameters. Uniform, partitioned and equilibrium composition profile (CP) in nanoisland and inverted pyramid structure are simulated separately. We demonstrate the huge impact of composition profile on localization of heavy-hole: wave function of ground state is confined near pit facets for uniform CP, at bottom of nanoisland for partitioned CP and at top of nanoisland for equilibrium CP. Moreover, such localization is gradually compromised by the size effect as pit filling ratio or pit size decreases. The results pave the fundamental guideline of designing nanoislands on pit-patterned substrates for desired applications.

  19. Structural analysis of fructans from Agave americana grown in South Africa for spirit production.

    PubMed

    Ravenscroft, Neil; Cescutti, Paola; Hearshaw, Meredith A; Ramsout, Ronica; Rizzo, Roberto; Timme, Elizabeth M

    2009-05-27

    Fructans isolated from Agave americana grown in South Africa are currently used for spirit production. Structural studies on water-soluble fructans were performed to facilitate the development of other applications including its use as a prebiotic. Acid hydrolysis followed by HPAEC-PAD analysis confirmed that the fructan was composed of glucose and fructose, and size analysis by HPAEC-PAD and size exclusion chromatography indicated that the saccharides have a DP range from 6 to 50. An average DP of 14 was estimated by (1)H NMR analysis. Linkage analysis and ESI-MS studies suggest that A. americana has a neofructan structure consisting of a central sucrose to which (2 → 1)- and (2 → 6)-linked β-D-Fruf chains are attached. The (2 → 1)-linked units extend from C-1 of Fru and C-6 of glucose, whereas the (2 → 6)-linked β-D-Fruf units are attached to C-6 of the central Fru. This structure accounts for the presence of equimolar amounts of 1,6-linked Glu and 1,2,6-linked Fru found in linkage analysis and the multiplicity of the NMR signals observed. Detailed ESI-MS studies were performed on fructan fractions: native, periodate oxidized/reduced, and permethylated oligomers. These derivatizations introduced mass differences between Glc and Fru following oxidation and between 1,2-, 1,6-, 2,6-, and 1,2,6-linked units after methylation. Thus, ESI-MS showed the presence of a single Glc per fructan chain and that it is predominantly internal, rather than terminal as found in inulin. These structural features were confirmed by the use of 1D and 2D NMR experiments.

  20. Impact of Nutrient Restriction on the Structure of Listeria monocytogenes Biofilm Grown in a Microfluidic System

    PubMed Central

    Cherifi, Tamazight; Jacques, Mario; Quessy, Sylvain; Fravalo, Philippe

    2017-01-01

    Biofilm formation by the pathogen Listeria monocytogenes is a major concern in food industries. The aim of this work was to elucidate the effect of nutrient limitation on both biofilm architecture and on the viability of the bacteria in microfluidic growth conditions. Biofilm formation by two L. monocytogenes strains was performed in a rich medium (BHI) and in a 10-fold diluted BHI (BHI/10) at 30°C for 24 h by using both static conditions and the microfluidic system Bioflux. In dynamic conditions, biofilms grown in rich and poor medium showed significant differences as well in structure and in the resulting biovolume. In BHI/10, biofilm was organized in a knitted network where cells formed long chains, whereas in the rich medium, the observed structure was homogeneous cellular multilayers. Biofilm biovolume production in BHI/10 was significantly higher than in BHI in these dynamic conditions. Interestingly, biovolume of dead cells in biofilms formed under limited nutrient conditions (BHI/10) was significantly higher than in biofilms formed in the BHI medium. In the other hand, in static conditions, biofilm is organized in a multilayer cells and dispersed cells in a rich medium BHI and poor medium BHI/10 respectively. There was significantly more biomass in the rich medium compared to BHI/10 but no difference was noted in the dead/damaged subpopulation showing how L. monocytogenes biofilm could be affected by the growth conditions. This work demonstrated that nutrient concentration affects biofilm structure and the proportion of dead cells in biofilms under microfluidic condition. Our study also showed that limited nutrients play an important role in the structural stability of L. monocytogenes biofilm by enhancing cell death and liberating extracellular DNA. PMID:28567031

  1. Impact of Nutrient Restriction on the Structure of Listeria monocytogenes Biofilm Grown in a Microfluidic System.

    PubMed

    Cherifi, Tamazight; Jacques, Mario; Quessy, Sylvain; Fravalo, Philippe

    2017-01-01

    Biofilm formation by the pathogen Listeria monocytogenes is a major concern in food industries. The aim of this work was to elucidate the effect of nutrient limitation on both biofilm architecture and on the viability of the bacteria in microfluidic growth conditions. Biofilm formation by two L. monocytogenes strains was performed in a rich medium (BHI) and in a 10-fold diluted BHI (BHI/10) at 30°C for 24 h by using both static conditions and the microfluidic system Bioflux. In dynamic conditions, biofilms grown in rich and poor medium showed significant differences as well in structure and in the resulting biovolume. In BHI/10, biofilm was organized in a knitted network where cells formed long chains, whereas in the rich medium, the observed structure was homogeneous cellular multilayers. Biofilm biovolume production in BHI/10 was significantly higher than in BHI in these dynamic conditions. Interestingly, biovolume of dead cells in biofilms formed under limited nutrient conditions (BHI/10) was significantly higher than in biofilms formed in the BHI medium. In the other hand, in static conditions, biofilm is organized in a multilayer cells and dispersed cells in a rich medium BHI and poor medium BHI/10 respectively. There was significantly more biomass in the rich medium compared to BHI/10 but no difference was noted in the dead/damaged subpopulation showing how L. monocytogenes biofilm could be affected by the growth conditions. This work demonstrated that nutrient concentration affects biofilm structure and the proportion of dead cells in biofilms under microfluidic condition. Our study also showed that limited nutrients play an important role in the structural stability of L. monocytogenes biofilm by enhancing cell death and liberating extracellular DNA.

  2. 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.

  3. Interfacial Coupling and Electronic Structure of Two-Dimensional Silicon Grown on the Ag(111) Surface at High Temperature

    PubMed Central

    Feng, Jiagui; Wagner, Sean R.; Zhang, Pengpeng

    2015-01-01

    Freestanding silicene, a monolayer of Si arranged in a honeycomb structure, has been predicted to give rise to massless Dirac fermions, akin to graphene. However, Si structures grown on a supporting substrate can show properties that strongly deviate from the freestanding case. Here, combining scanning tunneling microscopy/spectroscopy and differential conductance mapping, we show that the electrical properties of the phase of few-layer Si grown on Ag(111) strongly depend on film thickness, where the electron phase coherence length decreases and the free-electron-like surface state gradually diminishes when approaching the interface. These features are presumably attributable to the inelastic inter-band electron-electron scattering originating from the overlap between the surface state, interface state and the bulk state of the substrate. We further demonstrate that the intrinsic electronic structure of the as grown phase is identical to that of the R30° reconstructed Ag on Si(111), both of which exhibit the parabolic energy-momentum dispersion relation with comparable electron effective masses. These findings highlight the essential role of interfacial coupling on the properties of two-dimensional Si structures grown on supporting substrates, which should be thoroughly scrutinized in pursuit of silicene. PMID:26084916

  4. Surface and edge electroluminescence study of as-grown VCSEL structures

    NASA Astrophysics Data System (ADS)

    Zhao, Yongming; Sun, Yurun; He, Yang; Yu, Shuzhen; Song, Yan; Dong, Jianrong

    2016-12-01

    We present a simple quick evaluation method on vertical-cavity-surface-emitting laser (VCSEL) structures, which is designed for atomic clock working at high temperature (>350 K), to determine the temperature at which the wavelength of the VCSEL cavity mode (CM) aligns with that of the quantum well (QW) gain peak. The surface and edge electroluminescence (EL) measurements were performed non-destructively on pieces of as-grown VCSEL structures by employing soldered indium (In) contacts. The surface EL spectra determine the CM position, while the edge EL spectra are used to identify the wavelength of ground-state emission from the QW in the active region (QW gain peak). The room temperature EL measurements from a cleaved edge of the VCSEL structures indicate that the QW gain peak is at ∼780.5 nm, while the CM measured in the VCSEL surface emission EL peak (sample B) is at ∼793 nm. When the sample is heated up, the amount of CM shift with temperature can be fitted with ΔλCM =T × 0.068 nm /K, also corroborated by temperature dependence surface reflectivity measurement, and the gain peak can be fitted withλQWpeak = 780.5nm + T × 0.26 nm /K. The CM and QW gain peak of sample B will be brought into alignment at ∼365 K by fitting curve and this was confirmed by measurement. In summary, the surface and edge EL measurements using soldered In as electrodes can be very useful for post growth non-destructive characterization of VCSELs at different temperature.

  5. Atomic structure of defects in GaN:Mg grown with Ga polarity

    SciTech Connect

    Liliental-Weber, Z.; Tomaszewicz, T.; Zakharov, D.; Jasinski, J.; O'Keef e, M.A.

    2004-04-15

    The atomic structure of characteristic defects (Mg-rich hexagonal pyramids and truncated pyramids) in GaN:Mg thin films grown with Ga polarity was determined at atomic resolution by direct reconstruction of the scattered electron wave in a transmission electron microscope. Small cavities were present inside the defects. The inside walls of the cavities were covered by GaN which grew with reverse polarity compared to the matrix. It was proposed that lateral overgrowth of the cavities restores matrix polarity on the defect base. Exchange of Ga and N sublattices within the defect compared to the matrix lead to a 0.6 +- 0.2 Angstrom displacement between the Ga sublattices of these two areas. A [1100]/3 shift with change from AB stacking in the matrix to BC within the entire pyramid is observed. Changes in the shape of the NKa edge and oxygen presence on the defect walls were detected using electron energy loss spectroscopy. These observations explain the Mg compensation and decrease of acceptor concentration in heavily doped GaN:Mg.

  6. Interfacial stability of CoSi2/Si structures grown by molecular beam epitaxy

    NASA Technical Reports Server (NTRS)

    George, T.; Fathauer, R. W.

    1992-01-01

    The stability of CoSi2/Si interfaces was examined in this study using columnar silicide structures grown on (111) Si substrates. In the first set of experiments, Co and Si were codeposited using MBE at 800 C and the resulting columnar silicide layer was capped by epitaxial Si. Deposition of Co on the surface of the Si capping layer at 800 C results in the growth of the buried silicide columns. The buried columns grow by subsurface diffusion of the deposited Co, suppressing the formation of surface islands of CoSi2. The column sidewalls appear to be less stable than the top and bottom interfaces, resulting in preferential lateral growth and ultimately in the coalescence of the columns to form a continuous buried CoSi2 layer. In the second set of experiments, annealing of a 250 nm-thick buried columnar layer at 1000 C under a 100 nm-thick Si capping layer results in the formation of a surface layer of CoSi2 with a reduction in the sizes of the CoSi2 columns. For a sample having a thicker Si capping layer the annealing leads to Ostwald ripening producing buried equiaxed columns. The high CoSi2/Si interfacial strain could provide the driving force for the observed behavior of the buried columns under high-temperature annealing.

  7. Interfacial stability of CoSi2/Si structures grown by molecular beam epitaxy

    NASA Technical Reports Server (NTRS)

    George, T.; Fathauer, R. W.

    1992-01-01

    The stability of CoSi2/Si interfaces was examined in this study using columnar silicide structures grown on (111) Si substrates. In the first set of experiments, Co and Si were codeposited using MBE at 800 C and the resulting columnar silicide layer was capped by epitaxial Si. Deposition of Co on the surface of the Si capping layer at 800 C results in the growth of the buried silicide columns. The buried columns grow by subsurface diffusion of the deposited Co, suppressing the formation of surface islands of CoSi2. The column sidewalls appear to be less stable than the top and bottom interfaces, resulting in preferential lateral growth and ultimately in the coalescence of the columns to form a continuous buried CoSi2 layer. In the second set of experiments, annealing of a 250 nm-thick buried columnar layer at 1000 C under a 100 nm-thick Si capping layer results in the formation of a surface layer of CoSi2 with a reduction in the sizes of the CoSi2 columns. For a sample having a thicker Si capping layer the annealing leads to Ostwald ripening producing buried equiaxed columns. The high CoSi2/Si interfacial strain could provide the driving force for the observed behavior of the buried columns under high-temperature annealing.

  8. Structural and optical properties of GaAsSb QW heterostructures grown by laser deposition

    SciTech Connect

    Zvonkov, B. N.; Vikhrova, O. V. Dorokhin, M. V.; Kalentyeva, I. L.; Morozov, S. V.; Kryzhkov, D. I.; Yunin, P. A.

    2015-01-15

    The possibility of using the laser deposition method to grow crystalline light-emitting structures with GaAsSb/GaAs quantum wells (QWs) is experimentally demonstrated for the first time. The growth temperature of the GaAs{sub 1−x}Sb{sub x} layers is varied within the range 450–550°C; according to X-ray diffraction analyses, the content of antimony reaches x{sub Sb} ≈ 0.37 at a growth temperature of 450°C. Low-temperature (4 K) photoluminescence spectroscopy demonstrates the presence of a peak associated with the GaAsSb/GaAs QW at around 1.3 μm at the minimum laser-light pumping level. The optimal growth temperature T{sub g} = 500°C and arsine flow rate P{sub A} = 2.2 × 10{sup −8} mol/s at which the best emission properties of QWs with x{sub Sb} ∼ 0.17–0.25 are observed at temperatures of 77 and 300 K are determined. It is shown that GaAsSb/GaAs QWs with similar parameters (width and composition) grown by laser deposition at 500°C and metal-organic vapor-phase epitaxy at 580°C have comparable optical quality.

  9. Magnetic and structural properties of Co2FeAl thin films grown on Si substrate

    NASA Astrophysics Data System (ADS)

    Belmeguenai, Mohamed; Tuzcuoglu, Hanife; Gabor, Mihai; Petrisor, Traian; Tiusan, Coriolan; Berling, Dominique; Zighem, Fatih; Mourad Chérif, Salim

    2015-01-01

    The correlation between magnetic and structural properties of Co2FeAl (CFA) thin films of different thicknesses (10 nmgrown at room temperature on MgO-buffered Si/SiO2 substrates and annealed at 600 °C has been studied. x-ray diffraction (XRD) measurements revealed an (011) out-of-plane textured growth of the films. The deduced lattice parameter increases with the film thickness. Moreover, pole figures showed no in-plane preferential growth orientation. The magneto-optical Kerr effect hysteresis loops showed the presence of a weak in-plane uniaxial anisotropy with a random easy axis direction. The coercive field, measured with the applied field along the easy axis direction, and the uniaxial anisotropy field increase linearly with the inverse of the CFA thickness. The microstrip line ferromagnetic resonance measurements for in-plane and perpendicular applied magnetic fields revealed that the effective magnetization and the uniaxial in-plane anisotropy field follow a linear variation versus the inverse CFA thickness. This allows deriving a perpendicular surface anisotropy coefficient of -1.86 erg/cm2.

  10. Isolated starches from yams (Dioscorea sp) grown at the Venezuelan Amazons: structure and functional properties.

    PubMed

    Pérez, Elevina; Rolland-Sabaté, Agnès; Dufour, Dominique; Guzmán, Romel; Tapia, María; Raymundez, Marìa; Ricci, Julien; Guilois, Sophie; Pontoire, Bruno; Reynes, Max; Gibert, Olivier

    2013-10-15

    This work aimed to characterize the molecular structure and functional properties of starches isolated from wild Dioscorea yams grown at the Amazons, using conventional and up-to-date methodologies. Among the high purity starches isolated (≥99%), the chain lengths were similar, whereas variations in gelatinization profile were observed. Starches have shown varied-shaped granules with monomodal distribution, and B-type crystallinity. Variations in amylose contents found by three analyses were hypothesized being related to intermediate material. Linear chain lengths were similar, and their amylopectins showed a dense, spherical conformation and similar molecular characteristics. The average molar mass and the radius of gyration of the chromatograms of the yam amylopectin, M¯W and R¯G were ranging between 174×10(6) g mol(-1) and 237×10(6) g mol(-1), and 201 nm and 233 nm, respectively. The white yams starches were more sensible to enzymes than the other two. All starches have shown a wide range of functional and nutritional properties.

  11. Epitaxially grown zinc-blende structured Mn doped ZnO nanoshell on ZnS nanoparticles

    SciTech Connect

    Limaye, Mukta V.; Singh, Shashi B.; Date, Sadgopal K.; Gholap, R.S.; Kulkarni, Sulabha K.

    2009-02-04

    Zinc oxide in the bulk as well as in the nanocrystalline form is thermodynamically stable in the wurtzite structure. However, zinc oxide in the zinc-blende structure is more useful than that in the wurtzite structure due to its superior electronic properties as well as possibility of efficient doping. Therefore, zinc oxide shell is grown epitaxially on zinc sulphide core nanoparticles having zinc-blende structure. It is shown that doping of manganese could be achieved in zinc oxide nanoshell with zinc-blende structure.

  12. Flame Temperature Effect on the Structure of SiC Nanoparticles Grown by Laser Pyrolysis

    NASA Astrophysics Data System (ADS)

    Herlin-Boime, N.; Vicens, J.; Dufour, C.; Ténégal, F.; Reynaud, C.; Rizk, R.

    2004-02-01

    Small SiC nanoparticles (10 nm diameter) have been grown in a flow reactor by CO2 laser pyrolysis from a C2H2 and SiH4 mixture. The laser radiation is strongly absorbed by SiH4 vibration. The energy is transferred to the reactive medium and leads to the dissociation of molecules and the subsequent growth of the nanoparticles. The reaction happens with a flame. The purpose of the experiments reported in this paper is to limit the size of the growing particles to the nanometric scale for which specific properties are expected to appear. Therefore the effects of experimental parameters on the structure and chemical composition of nanoparticles have been investigated. For a given reactive mixture and gas velocity, the flame temperature is governed by the laser power. In this study, the temperature was varied from 875°C to 1100°C. The chemical analysis of the products indicate that their composition is a function of the temperature. For the same C/Si atomic ratio in the gaseous phase, the C/Si ratio in the powder increases from 0.7 at 875°C up to 1.02 at 1100°C, indicating a growth mechanism limited by C2H2 dissociation. As expected, X-ray diffraction has shown an improved crystallisation with increasing temperature. Transmission electron microscopy observations have revealed the formation of 10 nm grains for all values of laser power (or flame temperature). These grains appear amorphous at low temperature, whereas they contain an increasing number of nanocrystals (2 nm diameter) when the temperature increases. These results pave the way to a better control of the structure and chemical composition of laser synthesised SiC nanoparticles in the 10 nm range.

  13. Growth and structure of MBE grown TiO2 anatase films with rutile nano-crystallites

    SciTech Connect

    Shao, Rui; Wang, Chong M.; McCready, David E.; Droubay, Timothy C.; Chambers, Scott A.

    2007-03-15

    We have grown TiO2 anatase films with rutile nanocrystalline inclusions using molecular beam epitaxy under different growth conditions. This model system is important for investigating the role of rutile/anatase interfaces in heterogeneous photocatalysis. To control the film structure, we grew a pure anatase (001) layer at a slow rate and then increased the growth rate to drive the nucleation of rutile particles. Structure analysis indicates that the rutile phase has four preferred orientations in the anatase film.

  14. Optimization of the structural quality of sapphire rods grown by the Stepanov method in a reducing atmosphere

    SciTech Connect

    Kryvonosov, Ye. V.; Konevskiy, P. V. Lytvynov, L. A.; Tkachenko, V. F.

    2015-03-15

    Historically, the Stepanov method has been used for growing long shaped sapphire crystals (rods, tubes, and ribbons) for practical design. The recent intense development of this technique was stimulated by sapphire applications in optics and electronics; thus, the optical and structural quality of these crystals is of great importance. The results of studying the structural quality of sapphire rods up to 18 mm in diameter grown under optimized conditions are reported.

  15. Interface Structures in AlGaAs/GaAs Quantum Wells Grown by Metalorganic Chemical Vapor Deposition (MOCVD)

    NASA Astrophysics Data System (ADS)

    Ikuta, Kenji; Shinohara, Masanori; Inoue, Naohisa

    1995-02-01

    AlGaAs/GaAs quantum wells (QWs) were grown by metalorganic chemical vapor deposition (MOCVD) with controlled growth modes: step propagation, and mixtures of step propagation and two-dimensional nucleation. Surface structure on the multilayers was characterized by atomic force microscopy. Photoluminescence (PL) spectra from the QWs with such well-controlled and well-characterized interfaces were obtained for the first time, and PL linewidths were explained by the observed surface structures and growth modes.

  16. Ruthenium intermetallics grown from La-Ni flux: synthesis, structure, and physical properties.

    PubMed

    Zaikina, Julia V; Jo, Young-Jung; Latturner, Susan E

    2010-03-15

    Crystals of three new intermetallic compounds were grown from reactions of ruthenium with other elements in La(0.8)Ni(0.2) eutectic flux. The new boride LaRu(2)Al(2)B crystallizes in a filled CeMg(2)Si(2) structure type (P4/mmm, a = 4.2105(5) A, c = 5.6613(8); Z = 1, R(1) = 0.014), with Ru atoms forming a planar square net; B atoms center alternating Ru squares, which is an unusual coordination of boron by transition metals. Al atoms connect the Ru(2)B layers, forming large voids where La ions reside. The chemical bonding analysis using the electron localization function (ELF) reveals two-center covalent bonding between Al atoms, an absence of direct Ru-Ru interactions, and three-centered bonds between Ru and B or Al atoms. The band structure calculation shows LaRu(2)Al(2)B to be metallic, which is in agreement with the observed temperature independent paramagnetism and heat capacity data. The crystal structure of La(2)Ni(2-x)Ru(x)Al (HT-Pr(2)Co(2)Al-type; x = 0.21(1) and x = 0.76(1); C2/c; a = 9.9001(3) A, b = 5.7353(1) A, c = 7.8452(2) A, beta = 104.275(1); Z = 4, R(1) = 0.016 for x = 0.76(1)) features infinite [Ni(2-x)Ru(x)Al] spiral-twisted chains composed of Al(2)M(2)-rhombic units (M = Ni/Ru) seen in many La-Ni-Al intermetallics. The structure of La(6)SnNi(3.67)Ru(0.76)Al(3.6) (Nd(6)Co(5)Ge(2.2)-type; P6m2, a = 9.620(1) A, c = 4.2767(9) A; Z = 1, R(1) = 0.015) is composed of a three-dimensional [Ni(3.67)Ru(0.76)Al(3.6)](3)(infinity) network with large hexagonal channels accommodating interconnected tin-centered lanthanum clusters Sn@La(9).

  17. Structural and chemical characterization of terbia thin films grown on hexagonally close packed metal substrates

    NASA Astrophysics Data System (ADS)

    Cartas, William

    Rare earth oxides (REOs) exhibit favorable catalytic performance for a diverse set of chemical transformations, including both partial and complete oxidation reactions. I will discuss our efforts to develop thin film systems of terbia for model surface science investigations of a REO that is effectively reducible, and which is thus expected to promote complete oxidation chemistry of adsorbed species. The growth of terbia on Cu(111) is shown to produce a complex surface that exhibits multiple phases of the oxide as well as exposed substrate. Growing the film on Pt(111) results in more uniform, single phase, and closed film. We used low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) to characterize the structural properties of terbia thin films grown on Pt(111) in ultrahigh vacuum (UHV) using physical vapor deposition. We find that the REO grows as a high quality Tb2O 3(111) film, and adopts oxygen-deficient fluorite structures wherein the metal cations form a hexagonal lattice in registry with the Pt(111) substrate, while oxygen vacancies are randomly distributed within the film. The Tb 2O3(111) films are thermally stable when heated to 1000 K in UHV. LEED and STM show that a fraction of the Tb2O3 forms hexagonal islands when first deposited, and further depositions typically result in three dimensional growth of the film. The Tb2O3 (111) / Pt(111) system produces a coincidence structure, seen very clearly in LEED images. We have also found that Tb2O3(111) films can be oxidized in UHV by exposure to plasma-generated atomic oxygen beams. The oxidized films have an estimated TbO2 stoichiometry and decompose to Tb2O3 during heating, with O2 desorption starting at about 500 K. Terbia films oxidized at 90 K show a weakly bound state of oxygen that is likely chemisorbed. Temperature programmed reaction spectroscopy (TPRS) studies using methanol show that increased oxygen in the film does not modify the chemical selectivity of the film; however

  18. Optical, structural and microhardness properties of KDP crystals grown from urea-doped solutions

    SciTech Connect

    Pritula, I. Kosinova, A.; Kolybayeva, M.; Puzikov, V.; Bondarenko, S.; Tkachenko, V.; Tsurikov, V.; Fesenko, O.

    2008-10-02

    Potassium dihydrophosphate single crystals were grown from aqueous solutions onto a point seed using temperature reduction method by doping with different molar values of urea. The characterization of the grown crystals was made by visible and Fourier transform infrared spectroscopy, Vicker's hardness studies, X-ray powder diffraction, non-linear optical and laser damage threshold measurements. By comparing these crystals with the ones grown from the pure solution, it is shown that 0.2-2.0 M of the urea additive enhances the laser damage threshold and the second harmonic efficiency more than by 25 and 20%, respectively. By means of the Bond method using a multipurpose three-crystal X-ray diffractometer it is shown that the presence of urea additive increases the crystal lattice parameter c of the grown crystals, whereas the lattice parameter a is by an order less sensitive to the changing urea concentration in the solution. The Vicker's hardness studies at room temperature carried out on (1 0 0) and (0 0 1) crystallographic planes show an increased hardness of the doped crystals (grown in the presence of urea additive) on the plane (0 0 1) in comparison with that of pure potassium dihydrophosphate crystal.

  19. Local structure and magnetic properties of B2- and B20-like ultrathin Mn films grown on Si(001)

    NASA Astrophysics Data System (ADS)

    Kahwaji, S.; Gordon, R. A.; Crozier, E. D.; Monchesky, T. L.

    2012-01-01

    The structural and magnetic properties of ultrathin Mn layers deposited onto Si(001) by molecular beam epitaxy at low temperature are reported. X-ray absorption fine structure studies reveal that the structure of the silicide layer that forms depends on the growth temperature of the capping layer. A capping layer grown at 200 °C on 0.35-monolayer (ML) Mn results in a metastable MnSi phase with a B2-like (CsCl) structure, whereas a cap grown at room temperature on 0.5 ML followed by annealing at 200 °C produces a lower coordinated MnSi phase with a B20-like structure. Increasing the Mn thickness from 0.5 to 4 monolayers does not trigger a structural transformation but drives the structure closer to MnSi-B20. The sample with B2-like structure has the largest Mn magnetic moment of 0.33 μB/Mn at T = 2 K, and a Curie temperature TC above 250 K. MnSi-B20 layers showed lower moments and much lower TC's, in line with those reported for MnSi-B20 thin films.

  20. Optical polarization characteristics of m-plane GaN/AlGaN quantum well structures grown on m-plane SiC substrate

    NASA Astrophysics Data System (ADS)

    Park, Seoung-Hwan; Ahn, Doyeol

    2015-12-01

    Optical polarization characteristics of m-plane GaN/AlGaN QW structures grown on m-plane SiC substrate were theoretically investigated using the multiband effective-mass theory. The QW structure grown on SiC substrate shows much larger in-plane optical polarization than that grown on GaN substrate. This is attributed to the fact that the QW structure grown on SiC substrate has larger y‧-polarized optical emission and smaller x‧-polarized optical emission than the QW structure grown on GaN substrate. Also, the magnitude of the optical polarization is found to depend on the carrier density and decrease gradually with increasing carrier density. This can be explained by the fact that, with increasing k∥, the x‧-polarized matrix element increases while the y‧-polarized matrix element rapidly decreases.

  1. Hole Trapping in Thermal Oxides Grown under Various Oxidation Conditions Using Avalanche Injection in Poly-Silicon Gate Structures

    DTIC Science & Technology

    2014-05-01

    Hole Trapping in Thermal Oxides Grown under Vaious Oxidation Conditions Using Avalanche Injection in Poly-Silicon Gate Structures Contractor... Avalanche In ection in Poly-Silicon Gate Structureac 12. PERSONAL AUTHOR(S) K.V. Anand, B.R. Cairns, R.J. Strain 13a. TYPE OF REPORT 13b. TIME...Trapping, Oxidation Conditions, Avalanche Injection, Poly-Silicon Gates, Oxide Traps 19. ABSTRACT (Continue on reverse If necenry W Identify by block

  2. Robust optical properties of sandwiched lateral composition modulation GaInP structure grown by molecular beam epitaxy

    DOE PAGES

    Park, Kwangwook; Kang, Seokjin; Ravindran, Sooraj; ...

    2016-12-26

    Double-hetero structure lateral composition modulated (LCM) GaInP and sandwiched LCM GaInP having the same active layer thickness were grown and their optical properties were compared. Sandwiched LCM GaInP showed robust optical properties due to periodic potential nature of the LCM structure, and the periodicity was undistorted even for thickness far beyond the critical layer thickness. A thick LCM GaInP structure with undistorted potential that could preserve the properties of native LCM structure was possible by stacking thin LCM GaInP structures interspaced with strain compensating GaInP layers. Furthermore, the sandwiched structure could be beneficial in realizing the LCM structure embedded highmore » efficiency solar cells.« less

  3. Robust optical properties of sandwiched lateral composition modulation GaInP structure grown by molecular beam epitaxy

    SciTech Connect

    Park, Kwangwook; Kang, Seokjin; Ravindran, Sooraj; Min, Jung-Wook; Hwang, Hyeong-Yong; Jho, Young-Dahl; Lee, Yong Tak

    2016-12-26

    Double-hetero structure lateral composition modulated (LCM) GaInP and sandwiched LCM GaInP having the same active layer thickness were grown and their optical properties were compared. Sandwiched LCM GaInP showed robust optical properties due to periodic potential nature of the LCM structure, and the periodicity was undistorted even for thickness far beyond the critical layer thickness. A thick LCM GaInP structure with undistorted potential that could preserve the properties of native LCM structure was possible by stacking thin LCM GaInP structures interspaced with strain compensating GaInP layers. The sandwiched structure could be beneficial in realizing the LCM structure embedded high efficiency solar cells.

  4. Enhanced photocatalytic properties of hierarchical three-dimensional TiO2 grown on femtosecond laser structured titanium substrate

    NASA Astrophysics Data System (ADS)

    Huang, Ting; Lu, Jinlong; Xiao, Rongshi; Wu, Qiang; Yang, Wuxiong

    2017-05-01

    Three-dimensional micro-/nanostructured TiO2 (3D-TiO2) fabricated on titanium substrate effectively improves its performance in photocatalysis, dye-sensitized solar cell and lithium-ion battery applications. In this study, the hierarchical 3D-TiO2 with anatase phase directly grown on femtosecond laser structured titanium substrate is reported. First, the primary columnar arrays were fabricated on the surface of titanium substrate by femtosecond laser structuring. Next, the secondary nano-sheet substructures were grown on the primary columnar arrays by NaOH hydrothermal treatment. Followed by ion-exchange process in HCl and annealing in the air, the hierarchical anatase 3D-TiO2 was achieved. The hierarchical anatase 3D-TiO2 exhibited enhanced performances in light harvesting and absorption ability compared to that of nano-sheet TiO2 grown on flat titanium surface without femtosecond laser structuring. The photocatalytic degradation of methyl orange reveals that photocatalytic efficiency of the hierarchical anatase 3D-TiO2 was improved by a maximum of 57% compared to that of nano-sheet TiO2 (55% vs 35%). Meanwhile, the hierarchical anatase 3D-TiO2 remained mechanically stable and constant in consecutive degradation cycles, which promises significance in practical application.

  5. GaN based LEDs with semipolar QWs employing embedded sub-micrometer sized selectively grown 3D structures

    NASA Astrophysics Data System (ADS)

    Leute, R. A. R.; Heinz, D.; Wang, J.; Lipski, F.; Meisch, T.; Thonke, K.; Thalmair, J.; Zweck, J.; Scholz, F.

    2013-05-01

    We present LED structures with embedded semipolar {101¯1} quantum wells based on 2-inch c-plane GaN templates grown on c-plane sapphire substrates. Using selective area epitaxy, we achieved periodic GaN stripe structures with triangular cross-section with dimensions of a few 100 nm on continuous areas of several cm2. These structures exhibit semipolar side facets on which GaInN quantum wells with reduced piezoelectric fields have been deposited. The small dimensions of these structures allow complete embedding by GaN cladding layers eventually resulting in a flat c-plane surface. Consequently, our approach allows conventional device processing to be applied. Structural, optical, and electrical characterization is presented and the influence of mask material and pattern on the performances of LED structures is investigated.

  6. X-Ray Characterization of Structural Defects in Seeded and Self-Seeded ZnSe Crystal Grown by PVT in Horizontal and Vertical Configurations

    NASA Technical Reports Server (NTRS)

    Raghothamachar, B.; Dudley, M.; Su, C.-H.; Volz, H. M.; Matyi, R.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    As part of a pre-flight ground based investigation of crystal growth of II-VI compound semiconductors, a number of ZnSe boules have been grown by physical vapor transport (PVT) at Marshall Space Flight Center. Boules were grown in both horizontal and vertical configurations and seeded and self-seeded growth techniques were employed. As-grown and/or cleaved boules were examined by a combination of synchrotron white beam x-ray topography (SWBXT) and high resolution triple axis diffraction (HRTXD) to characterized the structural defects and correlate them with the growth conditions. Horizontal grown boules tend to grow away from the ampoule wall (contactless growth) and generally exhibit large (110) facets parallel to the gravity vector. Vertical grown boules grew to the full diameter of the ampoule and exhibited no faceting. X-ray topography combined with back reflection x-ray diffraction revealed the presence of lamellar twins (180 deg type about the [111] axis) in horizontal grown boules while vertically grown boules contain a few large grains, some of which are twinned. X-ray topographs and reciprocal space maps recorded from the boules show the better crystal quality of horizontal grown boules. The relationship between crystal quality and gravity vector is investigated. Further, an attempt is made to extend the Hurle theory of twin nucleation in Czochralski grown crystals to explain the twinning mechanisms in horizontal grown boules.

  7. Electrical and Optical Studies of Defect Structure of HgCdTe Films Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Świątek, Z.; Ozga, P.; Izhnin, I. I.; Fitsych, E. I.; Voitsekhovskii, A. V.; Korotaev, A. G.; Mynbaev, K. D.; Varavin, V. S.; Dvoretsky, S. A.; Mikhailov, N. N.; Yakushev, M. V.; Bonchyk, A. Yu.; Savytsky, H. V.

    2016-07-01

    Electrical and optical studies of defect structure of HgCdTe films grown by molecular beam epitaxy (MBE) are performed. It is shown that the peculiarity of these films is the presence of neutral defects formed at the growth stage and inherent to the material grown by MBE. It is assumed that these neutral defects are the Te nanocomplexes. Under ion milling, they are activated by mercury interstitials and form the donor centers with the concentration of 1017 cm-3, which makes it possible to detect such defects by measurements of electrical parameters of the material. Under doping of HgCdTe with arsenic using high temperature cracking, the As2 dimers are present in the arsenic flow and block the neutral Te nanocomplexes to form donor As2Te3 complexes. The results of electrical studies are compared with the results of studies carried out by micro-Raman spectroscopy.

  8. Structural, FTIR, thermal and dielectric studies of gel grown manganese-copper mixed levo tartrate crystals

    NASA Astrophysics Data System (ADS)

    Joshi, Sudhir J.; Tank, Kashmira P.; Vyas, Poorvesh M.; Joshi, Mihirkumar J.

    2014-09-01

    Pure manganese tartrate and copper tartrate compounds find various applications. In the present study, manganese-copper mixed levo tartrate crystals of different compositions have been grown by single diffusion gel growth technique in silica hydro gel. Purple blue colored mainly dendrite type crystals with orthorhombic system were grown. From EDAX analysis, the estimation of the presence of copper and manganese was made in the crystal. The coloration of the crystals as well their unit cell dimensions changed with the contents of copper and manganese. The presence of various functional groups was confirmed from FTIR spectra and the effect of composition of the crystals on the spectra was identified. The crystals were found to be hydrated and thermally unstable. Results are discussed.

  9. Multilayer epitaxial graphene grown on the SiC (000- 1) surface; structure and electronic properties

    SciTech Connect

    Sprinkle, M.; Hicks, J.; Tejeda, A.; Taleb-Ibrahimi, A.; Le Fevre, P.; Bertran, F.; Tinkey, H.; Clark, M.C.; Soukiassian, P.; Martinotti, D.; Hass, J.; Conrad, E.H.

    2010-10-22

    We review the progress towards developing epitaxial graphene as a material for carbon electronics. In particular, we discuss improvements in epitaxial graphene growth, interface control and the understanding of multilayer epitaxial graphene's (MEG's) electronic properties. Although graphene grown on both polar faces of SiC will be discussed, our discussions will focus on graphene grown on the (000{bar 1}) C-face of SiC. The unique properties of C-face MEG have become apparent. These films behave electronically like a stack of nearly independent graphene sheets rather than a thin Bernal stacked graphite sample. The origins of multilayer graphene's electronic behaviour are its unique highly ordered stacking of non-Bernal rotated graphene planes. While these rotations do not significantly affect the inter-layer interactions, they do break the stacking symmetry of graphite. It is this broken symmetry that leads to each sheet behaving like isolated graphene planes.

  10. Effect of RF power density on micro- and macro-structural properties of PECVD grown hydrogenated nanocrystalline silicon thin films

    SciTech Connect

    Gokdogan, Gozde Kahriman; Anutgan, Tamila

    2016-03-25

    This contribution provides the comparison between micro- and macro-structure of hydrogenated nanocrystalline silicon (nc-Si:H) thin films grown by plasma enhanced chemical vapor deposition (PECVD) technique under different RF power densities (P{sub RF}: 100−444 mW/cm{sup 2}). Micro-structure is assessed through grazing angle X-ray diffraction (GAXRD), while macro-structure is followed by surface and cross-sectional morphology via field emission scanning electron microscopy (FE-SEM). The nanocrystallite size (∼5 nm) and FE-SEM surface conglomerate size (∼40 nm) decreases with increasing P{sub RF}, crystalline volume fraction reaches maximum at 162 mW/cm{sup 2}, FE-SEM cross-sectional structure is columnar except for the film grown at 162 mW/cm{sup 2}. The dependence of previously determined ‘oxygen content–refractive index’ correlation on obtained macro-structure is investigated. Also, the effect of P{sub RF} is discussed in the light of plasma parameters during film deposition process and nc-Si:H film growth models.

  11. Effects of post-deposition annealing on the structure and magnetization of PLD grown yttrium iron garnet films

    NASA Astrophysics Data System (ADS)

    Kumar, Ravinder; Hossain, Z.; Budhani, R. C.

    2017-03-01

    We report on the recrystallization of 200 nm thick as-grown Yttrium Iron Garnet ( Y 3.4 Fe 4.6 O 12 ) films on the (111) face of gadolinium gallium garnet single crystals by post-deposition annealing. Epitaxial conversion of the as-grown microcrystalline yttrium iron garnet films was seen after annealing at 800 °C for more than 30 min both in ambient oxygen and in air. The as-grown oxygen annealed samples at 800 °C for 60 min crystallize epitaxially and show excellent figure-of-merit for saturation magnetization (MS = 3.3 μB/f.u., comparable to the bulk value) and coercivity (HC ˜ 1.1 Oe). The ambient air annealing at 800 °C with a very slow rate of cooling (2 °C/min) results in a double layer structure with a thicker unstrained epitaxial top layer having the MS and HC of 2.9 μB/f.u. and 0.12 Oe, respectively. The symmetric and asymmetric reciprocal space maps of both the samples reveal a locking of the in-plane lattice of the film to the in-plane lattice of the substrate, indicating a pseudomorphic growth. The residual stress calculated by the sin 2 ψ technique is compressive in nature. The lower layer in the air annealed sample is highly strained, whereas the top layer has negligible compressive stress.

  12. Atomic structure of defects in GaN:Mg grown with Ga polarity

    SciTech Connect

    Liliental-Weber, Z.; Tomaszewicz, T.; Zakharov, D.; Jasinski, J.; O'Keefe, M.A.; Hautakangas, S.; Laakso, A.; Saarinen, K.

    2003-11-25

    Electron microscope phase images, produced by direct reconstruction of the scattered electron wave from a focal series of high-resolution images, were used to determine the nature of defects formed in GaN:Mg crystals. We studied bulk crystals grown from dilute solutions of atomic nitrogen in liquid gallium at high pressure and thin films grown by the MOCVD method. All the crystals were grown with Ga-polarity. In both types of samples the majority of defects were three dimensional Mg-rich hexagonal pyramids with bases on the (0001) plane and six walls on {l_brace}11{und 2}3{r_brace} planes seen in cross-section as triangulars. Some other defects appear in cross-section as trapezoidal (rectangular) defects as a result of presence of truncated pyramids. Both type of defects have hollow centers. They are decorated by Mg on all six side walls and a base. The GaN which grows inside on the defect walls shows polarity inversion. It is shown that change of polarity starts from the defect tip and propagates to the base, and that the stacking sequence changes from ab in the matrix to bc inside the defect. Exchange of the Ga sublattice with the N sublattice within the defect leads to 0.6 {+-} 0.2{angstrom} displacement between Ga sublattices outside and inside the defects. It is proposed that lateral overgrowth of the cavities formed within the defect takes place to restore matrix polarity on the defect base.

  13. Structure and Morphology of Phthalocyanine Films Grown in Electrical Fields by Vapor Deposition

    NASA Technical Reports Server (NTRS)

    Zhu, Shen; Banks, C. E.; Frazier, D. O.; Penn, B.; Abdeldayem, H.; Hicks, R.; Burns, H. D.; Thompson, G. W.

    1999-01-01

    Phthalocyanine (Pc) films have been synthesized by vapor deposition on quartz substrates, some of which were coated with a very thin gold film before depositing Pc films. Electrical fields up to 6200 V/cm between a mech electrode and the substrate are introduced during film growth. These films have been characterized by x-ray diffraction and scanning electron microscopy. The molecular orientations and surface morphology of Pc films were changed under the electrical fields. The surface of these films grown without electrical field shows whisk-like morphology. When films are deposited under an electrical field, a dense film with flat surface is obtained.

  14. Experimental phasing for structure determination using membrane-protein crystals grown by the lipid cubic phase method

    SciTech Connect

    Li, Dianfan; Pye, Valerie E.; Caffrey, Martin

    2015-01-01

    Very little information is available in the literature concerning the experimental heavy-atom phasing of membrane-protein structures where the crystals have been grown using the lipid cubic phase (in meso) method. In this paper, pre-labelling, co-crystallization, soaking, site-specific mercury binding to genetically engineered single-cysteine mutants and selenomethionine labelling as applied to an integral membrane kinase crystallized in meso are described. An assay to assess cysteine accessibility for mercury labelling of membrane proteins is introduced. Despite the marked increase in the number of membrane-protein structures solved using crystals grown by the lipid cubic phase or in meso method, only ten have been determined by SAD/MAD. This is likely to be a consequence of the technical difficulties associated with handling proteins and crystals in the sticky and viscous hosting mesophase that is usually incubated in glass sandwich plates for the purposes of crystallization. Here, a four-year campaign aimed at phasing the in meso structure of the integral membrane diacylglycerol kinase (DgkA) from Escherichia coli is reported. Heavy-atom labelling of this small hydrophobic enzyme was attempted by pre-labelling, co-crystallization, soaking, site-specific mercury binding to genetically engineered single-cysteine mutants and selenomethionine incorporation. Strategies and techniques for special handling are reported, as well as the typical results and the lessons learned for each of these approaches. In addition, an assay to assess the accessibility of cysteine residues in membrane proteins for mercury labelling is introduced. The various techniques and strategies described will provide a valuable reference for future experimental phasing of membrane proteins where crystals are grown by the lipid cubic phase method.

  15. Cathodoluminescence evaluation of defect structure in hydrothermally grown ZnO:Sb nanorods.

    PubMed

    González, A; Herrera, M; Valenzuela, J; Escobedo, A; Pal, U

    2011-06-01

    Cathodoluminescence emission of hydrothermally grown antimony doped ZnO nanostructures with different antimony doping (2.5, 4.8, and 11.8 at%) was studied in a scanning electron microscope (CL-SEM). Incorporation of antimony results in formation of mostly nanorods with low aspect ratio together with some Sb-rich nanoparticles. Transmissibn electron microscopy (TEM) of the Sb-doped samples revealed delaminated {10-10} planes produced by antimony surface segregation. CL spectra of the as-grown samples revealed well defined emission bands centered at 3.2, 2.74 and 2.0 eV, attributed to excitonic recombination, and the so-called blue and yellow emissions, respectively. It was observed that the intensity of the blue emission depends strongly on antimony content, suggesting the formation of point defects on Sb doping. While the yellow emission red-shifted after thermal annealing, either in argon or oxygen atmosphere, the intensity of the blue band decreases considerably; such behavior is explained through the reduction of the population of Zn(i) defects.

  16. Surface structure determinations of crystalline ionic thin films grown on transition metal single crystal surfaces by low energy electron diffraction

    SciTech Connect

    Roberts, Joel Glenn

    2000-05-01

    The surface structures of NaCl(100), LiF(100) and alpha-MgCl2(0001) adsorbed on various metal single crystals have been determined by low energy electron diffraction (LEED). Thin films of these salts were grown on metal substrates by exposing the heated metal surface to a molecular flux of salt emitted from a Knudsen cell. This method of investigating thin films of insulators (ionic salts) on a conducting substrate (metal) circumvents surface charging problems that plagued bulk studies, thereby allowing the use of electron-based techniques to characterize the surface.

  17. The structural state of epitaxial GaP films of different polarities grown on misoriented Si(001) substrates

    NASA Astrophysics Data System (ADS)

    Loshkarev, I. D.; Vasilenko, A. P.; Trukhanov, E. M.; Kolesnikov, A. V.; Putyato, M. A.; Esin, M. Yu.; Petrushkov, M. O.

    2017-02-01

    The structure of GaP films grown by molecular-beam epitaxy on vicinal Si(1113) substrates has been studied by X-ray diffraction. It is established that the crystalline lattice of a pseudomorphic film rotates about the <110> axis toward increasing deviation from the singular orientation, while the subsequent relaxation leads to rotation in the opposite direction. This is valid for the films of both (001) and (001¯) polarities. Differences between the surface morphologies of relaxed and pseudomorphic GaP films are revealed.

  18. Correlation of electrical and structural properties of single as-grown GaAs nanowires on Si (111) substrates.

    PubMed

    Bussone, Genziana; Schäfer-Eberwein, Heiko; Dimakis, Emmanouil; Biermanns, Andreas; Carbone, Dina; Tahraoui, Abbes; Geelhaar, Lutz; Bolívar, Peter Haring; Schülli, Tobias U; Pietsch, Ullrich

    2015-02-11

    We present the results of the study of the correlation between the electrical and structural properties of individual GaAs nanowires measured in their as-grown geometry. The resistance and the effective charge carrier mobility were extracted for several nanowires, and subsequently, the same nano-objects were investigated using X-ray nanodiffraction. This revealed a number of perfectly stacked zincblende and twinned zincblende units separated by axial interfaces. Our results suggest a correlation between the electrical parameters and the number of intrinsic interfaces.

  19. Evidence of rhombohedral structure within BiFeO3 thin film grown on SrTiO3

    NASA Astrophysics Data System (ADS)

    Bae, In-Tae; Naganuma, Hiroshi

    2015-03-01

    Comprehensive crystal structure analysis was performed for a BiFeO3 thin layer (∼30 nm) grown on a SrTiO3 substrate using cross-sectional transmission electron microscopy along three different zone axes. Nano-beam electron diffraction patterns combined with structure factor calculations and high-resolution transmission electron microscopy images unambiguously revealed that the BiFeO3 thin layer grew with a rhombohedral structure identical to its bulk form. No evidence of monoclinic and/or tetragonal distortion was found. The rhombohedral BiFeO3 thin layer was found to grow onto SrTiO3 by maintaining an epitaxial relationship in a manner minimizing the lattice mismatch at the BiFeO3/SrTiO3 interface.

  20. Optical Properties of ZnO Soccer-Ball Structures Grown by Vapor Phase Transport

    NASA Astrophysics Data System (ADS)

    Nam, Giwoong; Lee, Sang-heon; Kim, Soaram; Kim, Min Su; Kim, Do Yeob; Gug Yim, Kwang; Lee, Dong-Yul; Kim, Jin Soo; Kim, Jong Su; Son, Jeong-Sik; Kim, Sung-O.; Jung, Jae Hak; Leem, Jae-Young

    2012-02-01

    ZnO soccer balls were grown on an Au-catalyzed Si(100) substrate by vapor phase transport (VPT) with a mixture of zinc oxide and graphite powders. Temperature-dependent PL was carried out to investigate the mechanism governing the quenching behavior of the PL spectra. From the PL spectra of the ZnO soccer balls at 10 K, several PL peaks were observed at 3.365, 3.318, 3.249, and 3.183 eV corresponding to excitons bound to neutral donors (DoX), a donor-acceptor pair (DAP), first-order longitudinal optical phonon replica of donor-acceptor pair (DAP-1LO), and DAP-2LO, respectively. The mixed system composed of the free exciton (FX) and DoX and the DAP radiative lifetimes were estimated with a theoretical relation between the lifetime and the spectral width. The exciton radiative lifetimes were observed to increase linearly with temperature.

  1. Structural and magnetic properties of MBE grown GeMnN2 thin films

    SciTech Connect

    Liu, Y; Lazarov, V. K.; Cheung, S.H.; Keavney, D.J.; Gai, Zheng; Gajdardziska-Josifovska, M; Weinert, M; Li, Lian

    2012-01-01

    Epitaxial GeMnN{sub 2} thin films are synthesized by plasma-assisted molecular beam epitaxy. Transmission electron microscopy and x-ray diffraction measurements confirm that it is the orthorhombic variant, consistent with the predictions of first-principles calculations. The magnetic properties of the films are related to defects, with samples grown under Ge-rich conditions exhibiting a net magnetic moment above room temperature. These results are explained by first-principles calculations, indicating that the preferential substitution of one magnetic sublattice of GeMnN{sub 2} by impurities and/or intrinsic defects such as Ge antisites produces a net magnetic moment in an antiferromagnetic background, and also introduces spin-polarized carriers near the Fermi level.

  2. Micro structural and dielectric property analysis on hydrothermally grown gadolinium doped SnO2 crystals

    NASA Astrophysics Data System (ADS)

    Pilakavil, Jaya T.; Pradyumnan, P. P.

    2016-09-01

    A series of SnO2-Gd2O3 mixed oxides were grown in aqueous medium by varying the thermodynamic parameters by hydrothermal method. X ray diffraction data identified tetragonal phases corresponding to tin oxide. The average crystallite size of the samples were between 21 and 31 nm. The morphological studies were conducted using scanning electron microscopy and compositional purity confirmed using energy dispersive spectroscopy. Detailed dielectric studies on the samples were performed in the frequency range 100 Hz-5 MHz, which showed that dielectric constant decreases with frequency in the low frequency range, whereas remains constant at higher frequencies. Impedance analysis is used to explain the effects of grain and grain boundary on transport mechanism of Gd:SnO2 particles synthesised at various pH.

  3. Structural and morphological properties of ITO thin films grown by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Ghorannevis, Z.; Akbarnejad, E.; Ghoranneviss, M.

    2015-10-01

    Physical properties of transparent and conducting indium tin oxide (ITO) thin films grown by radiofrequency (RF) magnetron sputtering are studied systematically by changing deposition time. The X-ray diffraction (XRD) data indicate polycrystalline thin films with grain orientations predominantly along the (2 2 2) and (4 0 0) directions. From atomic force microscopy (AFM) it is found that by increasing the deposition time, the roughness of the film increases. Scanning electron microscopy (SEM) images show a network of a high-porosity interconnected nanoparticles, which approximately have a pore size ranging between 20 and 30 nm. Optical measurements suggest an average transmission of 80 % for the ITO films. Sheet resistances are investigated using four-point probes, which imply that by increasing the film thickness the resistivities of the films decrease to 2.43 × 10-5 Ω cm.

  4. Structural and magnetic properties of epitaxially grown MnAs films on GaAs(110)

    NASA Astrophysics Data System (ADS)

    Kolovos-Vellianitis, D.; Herrmann, C.; Däweritz, L.; Ploog, K. H.

    2005-08-01

    MnAs films were grown by molecular beam epitaxy (MBE) on GaAs(110) substrates, since this orientation was recently identified as promising for the increase of spin lifetimes in semiconductor heterojunctions, which is of interest in spin injection experiments. A single epitaxial orientation was revealed for the MnAs films which consist of both the ferromagnetic, hexagonal α-MnAs and the paramagnetic, orthorhombic β-MnAs phase at room temperature. This phase coexistence could be imaged as a well ordered stripe pattern, whose periodicity depends on the film thickness. The study of the ferromagnetic properties shows a strong influence of the film thickness on the measured coercive fields and saturation magnetizations.

  5. Structural and magnetic properties of epitaxially grown MnAs films on GaAs(110)

    SciTech Connect

    Kolovos-Vellianitis, D.; Herrmann, C.; Daeweritz, L.; Ploog, K.H.

    2005-08-29

    MnAs films were grown by molecular beam epitaxy (MBE) on GaAs(110) substrates, since this orientation was recently identified as promising for the increase of spin lifetimes in semiconductor heterojunctions, which is of interest in spin injection experiments. A single epitaxial orientation was revealed for the MnAs films which consist of both the ferromagnetic, hexagonal {alpha}-MnAs and the paramagnetic, orthorhombic {beta}-MnAs phase at room temperature. This phase coexistence could be imaged as a well ordered stripe pattern, whose periodicity depends on the film thickness. The study of the ferromagnetic properties shows a strong influence of the film thickness on the measured coercive fields and saturation magnetizations.

  6. Investigations on the interface abruptness in CBE-grown InGaAs/InP QW structures

    NASA Astrophysics Data System (ADS)

    Antolini, A.; Bradley, P. J.; Cacciatore, C.; Campi, D.; Gastaldi, L.; Genova, F.; Iori, M.; Lamberti, C.; Papuzza, C.; Rigo, C.

    1992-02-01

    In this work we present a detailed analysis of chemical beam epitaxy-grown (CBE) InGaAs/InP multi quantum well (MQW) interfaces to explain experimental data from high quality single and multi-QWs. Our results compare well with the best published data we have obtained some outstanding results. For example, the very intense absorption peak and the high number of satellite peaks in the diffraction rocking curve, were obtained even on samples grown in non-optimized conditions. A careful use of growth interruption at the interfaces allows us to obtain monolayer (ml) interfaces. Nevertheless, the switching of the group V element at each interface leads to strain formation. This effect could become dramatic in superlattice structures with periods smaller than about 5 nm and barriers of less than 3 4 nm. More generally, the conditions for the growth of high quality single and multiple QWs is discussed in this work and these will be correlated with fourier transform photoluminesence (FTPL), high resolution x-ray diffraction (HRXRD), absorption, photo-absorption and photo-current (in PIN structures) measurements.

  7. Study of the morphological, optical, structural and photoelectrochemical properties of TiO2 nanorods grown with various precursor concentrations

    NASA Astrophysics Data System (ADS)

    Choi, Hayoung; Ryu, Hyukhyun; Lee, Won-Jae

    2017-06-01

    Vertically aligned TiO2 nanorods were grown on a fluorine-doped tin oxide (FTO) substrate covered with a TiO2 buffer layer by using the hydrothermal method with various titanium precursor concentrations. In this study, the effects of the precursor concentration on the morphological, structural, optical and photoelectrochemical properties of TiO2 nanorods were investigated. We observed that photoelectrochemical properties were mainly dependent on the nanorod length, surface area, transmittance and (002) XRD peak intensity, which indicates the oriented growth of the TiO2 nanorods perpendicular to the substrate. As a result, the sample grown from a 0.09 M precursor solution, which grew vertically and had the highest surface area, showed the highest photocurrent density, 0.733 mA/cm2 (at 1.0 V vs. SCE). Field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) were used to characterize the morphology of the nanorods, X-ray diffraction (XRD) was used to detect the structural properties of the nanorods, UV-visual spectroscopy was used to measure the optical properties, and analysis with a three-electrode potentiostat was used to measure the photoelectrochemical properties. [Figure not available: see fulltext.

  8. Experimental phasing for structure determination using membrane-protein crystals grown by the lipid cubic phase method

    PubMed Central

    Li, Dianfan; Pye, Valerie E.; Caffrey, Martin

    2015-01-01

    Despite the marked increase in the number of membrane-protein structures solved using crystals grown by the lipid cubic phase or in meso method, only ten have been determined by SAD/MAD. This is likely to be a consequence of the technical difficulties associated with handling proteins and crystals in the sticky and viscous hosting mesophase that is usually incubated in glass sandwich plates for the purposes of crystallization. Here, a four-year campaign aimed at phasing the in meso structure of the integral membrane diacylglycerol kinase (DgkA) from Escherichia coli is reported. Heavy-atom labelling of this small hydrophobic enzyme was attempted by pre-labelling, co-crystallization, soaking, site-specific mercury binding to genetically engineered single-cysteine mutants and selenomethionine incorporation. Strategies and techniques for special handling are reported, as well as the typical results and the lessons learned for each of these approaches. In addition, an assay to assess the accessibility of cysteine residues in membrane proteins for mercury labelling is introduced. The various techniques and strategies described will provide a valuable reference for future experimental phasing of membrane proteins where crystals are grown by the lipid cubic phase method. PMID:25615865

  9. Possibilities for LWIR detectors using MBE-grown Si(/Si(1-x)Ge(x) structures

    NASA Technical Reports Server (NTRS)

    Hauenstein, Robert J.; Miles, Richard H.; Young, Mary H.

    1990-01-01

    Traditionally, long wavelength infrared (LWIR) detection in Si-based structures has involved either extrinsic Si or Si/metal Schottky barrier devices. Molecular beam epitaxially (MBE) grown Si and Si/Si(1-x)Ge(x) heterostructures offer new possibilities for LWIR detection, including sensors based on intersubband transitions as well as improved conventional devices. The improvement in doping profile control of MBE in comparison with conventional chemical vapor deposited (CVD) Si films has resulted in the successful growth of extrinsic Si:Ga, blocked impurity-band conduction detectors. These structures exhibit a highly abrupt step change in dopant profile between detecting and blocking layers which is extremely difficult or impossible to achieve through conventional epitaxial growth techniques. Through alloying Si with Ge, Schottky barrier infrared detectors are possible, with barrier height values between those involving pure Si or Ge semiconducting materials alone. For both n-type and p-type structures, strain effects can split the band edges, thereby splitting the Schottky threshold and altering the spectral response. Measurements of photoresponse of n-type Au/Si(1-x)Ge(x) Schottky barriers demonstrate this effect. For intersubband multiquntum well (MQW) LWIR detection, Si(1-x)Ge(x)/Si detectors grown on Si substrates promise comparable absorption coefficients to that of the Ga(Al)As system while in addition offering the fundamental advantage of response to normally incident light as well as the practical advantage of Si-compatibility. Researchers grew Si(1-x)Ge(x)/Si MQW structures aimed at sensitivity to IR in the 8 to 12 micron region and longer, guided by recent theoretical work. Preliminary measurements of n- and p-type Si(1-x)Ge(x)/Si MQW structures are given.

  10. Ferromagnetism and electronic structures of nonstoichiometric Heusler-alloy Fe3-xMnxSi Epilayers grown on Ge(111).

    PubMed

    Hamaya, K; Itoh, H; Nakatsuka, O; Ueda, K; Yamamoto, K; Itakura, M; Taniyama, T; Ono, T; Miyao, M

    2009-04-03

    For the study of ferromagnetic materials which are compatible with group-IV semiconductor spintronics, we demonstrate control of the ferromagnetic properties of Heusler-alloy Fe3-xMnxSi epitaxially grown on Ge(111) by tuning the Mn composition x. Interestingly, we obtain L2(1)-ordered structures even for nonstoichiometric atomic compositions. The Curie temperature of the epilayers with x approximately 0.6 exceeds 300 K. Theoretical calculations indicate that the electronic structures of the nonstoichiometric Fe3-xMnxSi alloys become half-metallic for 0.75 < or = x < or = 1.5. We discuss the possibility of room-temperature ferromagnetic Fe(3-x)Mn(x)Si/Ge epilayers with high spin polarization.

  11. Structural and magnetic properties of {eta}-phase manganese nitride films grown by molecular-beam epitaxy

    SciTech Connect

    Yang, Haiqiang; Al-Brithen, Hamad; Smith, Arthur R.; Borchers, J. A.; Cappelletti, R. L.; Vaudin, M. D.

    2001-06-11

    Face-centered tetragonal (fct) {eta}-phase manganese nitride films have been grown on magnesium oxide (001) substrates by molecular-beam epitaxy. For growth conditions described here, reflection high energy electron diffraction and neutron scattering show primarily two types of domains rotated by 90{degree} to each other with their c axes in the surface plane. Scanning tunneling microscopy images reveal surface domains consisting of row structures which correspond directly to the bulk domains. Neutron diffraction data confirm that the Mn moments are aligned in a layered antiferromagnetic structure. The data are consistent with the fct model of G. Kreiner and H. Jacobs for bulk Mn{sub 3}N{sub 2} [J. Alloys Compd. 183, 345 (1992)]. {copyright} 2001 American Institute of Physics.

  12. Effects of Mn dope on morphological, structural and optical properties of ZnO nanorods grown by a hydrothermal method

    NASA Astrophysics Data System (ADS)

    Putri, N. A.; Febrianti, Y.; Sugihartono, I.; Fauzia, V.; Handoko, D.

    2017-07-01

    ZnO nanorods were grown on glass substrate has been systematically investigated by varying Mn doping concentrations. The nanorods have been developed by a simple hydrothermal method on the ZnO seed layers which were deposited by ultrasonic spray pyrolysis method. The influences of Mn on the morphological, structural and optical behavior were observed by measuring Scanning Electron Microscope, X-Ray Diffraction, and UV-Vis spectrophotometer, respectively. It is found that the nanorods growth without any orientation. Interestingly, all the nanorods under investigated exhibit a polycrystalline hexagonal wurtzite structure with strong absorption in UV region and a high transparency in the visible region suggesting that optical properties of ZnO nanorods have been modified by Mn doping.

  13. Study of optical and structural properties of CZTS thin films grown by co-evaporation and spray pyrolysis

    NASA Astrophysics Data System (ADS)

    Moreno, R.; Ramirez, E. A.; Gordillo Guzmán, G.

    2016-02-01

    Results regarding optical and structural properties of Cu2ZnSnS4 (CZTS) thin films prepared by co-evaporation using a novel procedure are compared with those obtained with CZTS films grown using a solution based route. The lattice strain ε and crystallite size D of CZTS films prepared by co-evaporation and by spray pyrolysis were estimated through X-ray diffraction (XRD) measurements using Williamson-Hall-isotropic strain model. The results of estimated average crystallite size of CZTS films by Scherrer and Williamson-Hall plot methods were compared with AFM (atomic force microscopy) measurements. It was found that the average crystallite size measured by Williamson-Hall plot methods agree quite well with AFM results. Further, information regarding the influence of preparation method on both, crystalline phases and the formation of structural defects was achieved through Raman and Urbach energy measurements.

  14. Structural and optical characterization of ZrO2 thin films grown on silicon and quartz substrates

    NASA Astrophysics Data System (ADS)

    Hojabri, Alireza

    2016-09-01

    Zirconium oxide thin films were grown successfully by thermal annealing of zirconium thin films deposited on quartz and silicon substrates by direct current magnetron sputtering technique. The structural and optical properties in relation to thermal annealing times were investigated. The X-ray diffraction patterns revealed that structure of films changes from amorphous to crystalline by increase of annealing times in range 60-240 min. The composition of films was determined by Rutherford back scattering spectroscopy. Atomic force microscopy results exhibited that surface morphology and roughness of films depend on the annealing time. The refractive index of the films was calculated using Swanepoel's method. The optical band gap energy of annealed films decreased from 5.50 to 5.34 eV with increasing thermal annealing time.

  15. Surface electronic structure of polar NiO thin film grown on Ag(111)

    SciTech Connect

    Das, Jayanta; Menon, Krishnakumar S. R.

    2015-06-24

    The growth and structure of NiO thin films on top of Ag(111) substrate were studied where the formation of faceted surface was confirmed by Low Energy Electron Diffraction. The electronic structure of polar NiO(111) surface has been probed using photoemission techniques. The core energy levels and the valence band electronic structure were excited by x-ray and ultraviolet photons respectively. The modifications in physical structure and valence band electronic structure of the film under vacuum annealing have also been enlightened.

  16. Human norovirus infection of caco-2 cells grown as a three-dimensional tissue structure.

    PubMed

    Straub, Timothy M; Bartholomew, Rachel A; Valdez, Catherine O; Valentine, Nancy B; Dohnalkova, Alice; Ozanich, Richard M; Bruckner-Lea, Cynthia J; Call, Douglas R

    2011-06-01

    Human norovirus (hNoV) infectivity was studied using a three-dimensional model of large intestinal epithelium. Large intestine Caco-2 cells were grown in rotating wall vessel bioreactors for 18-21 days at 37 degrees C and then transferred to 24-well tissue culture plates where they were infected with GI.1 and GII.4 human noroviruses collected from human challenge trials and various outbreak settings, respectively. Compared with uninfected cells, transmission micrographs of norovirus-infected cells displayed evidence of shortening or total loss of apical microvilli, and vacuolization. Quantitative reverse transcription real-time PCR (qRT-PCR) indicated an approximate 2-3 log10 increase in viral RNA copies for the infected cells. A passage experiment examined both the ability for continued viral RNA and viral antigen detection. In the passaged samples 1.01x10(6) copies ml(-1) were detected by qRT-PCR. Immune electron microscopy using primary antibody to hNoV GI.1 capsids in conjunction with 6 nm gold-labelled secondary antibodies was performed on crude cellular lysates. Localization of antibody was observed in infected but not for uninfected cells. Our present findings, coupled with earlier work with the three-dimensional small intestinal INT407 model, demonstrate the utility of 3-D cell culture methods to develop infectivity assays for enteric viruses that do not readily infect mammalian cell cultures.

  17. Structural, thermal and dielectric properties of cobaltous malonate single crystals grown in limited diffusion media

    NASA Astrophysics Data System (ADS)

    Lincy, A.; Mahalakshmi, V.; Tinto, A. J.; Thomas, J.; Saban, K. V.

    2010-11-01

    Well-faceted crystals of cobaltous malonate (C 6 H 12 Co 2 O 12) have been grown by the controlled diffusion of ionic species in hydrosilica gel. Single crystal X-ray diffraction studies show that the crystal belongs to the monoclinic system with space group C2/m. The unit cell dimensions are a=12.6301(9) Å, b=7.3857(9) Å, c=7.2945(7) Å, α= γ=90°, β=120.193(9)°. The functional groups, elucidated from the FT-IR spectrum, are in conformity with the information derived from the X-ray diffraction studies. The thermal behaviour of the material has been investigated using TG-DTA in the temperature range 30-1050 °C. The optical band gap of the sample is estimated using diffuse reflectance spectroscopy (DRS). The dielectric constant and dielectric loss of the crystal have been studied over wide temperature and frequency ranges. AC conductivity measurements reveal a thermally activated process and the mechanism behind the conduction process has been discussed.

  18. Strain and structure heterogeneity in MoS2 atomic layers grown by chemical vapour deposition

    DOE PAGES

    Liu, Zheng; Amani, Matin; Najmaei, Sina; ...

    2014-11-18

    Monolayer molybdenum disulfide (MoS2) has attracted tremendous attention due to its promising applications in high-performance field-effect transistors, phototransistors, spintronic devices, and nonlinear optics. The enhanced photoluminescence effect in monolayer MoS2 was discovered and, as a strong tool, was employed for strain and defect analysis in MoS2. Recently, large-size monolayer MoS2 has been produced by chemical vapor deposition but has not yet been fully explored. Here we systematically characterize chemical vapor deposition grown MoS2 by PL spectroscopy and mapping, and demonstrate non-uniform strain in single-crystalline monolayer MoS2 and strain-induced band gap engineering. We also evaluate the effective strain transferred from polymermore » substrates to MoS2 by three-dimensional finite element analysis. In addition, our work demonstrates that PL mapping can be used as a non-contact approach for quick identification of grain boundaries in MoS2.« less

  19. Toward epitaxially grown two-dimensional crystal hetero-structures: Single and double MoS2/graphene hetero-structures by chemical vapor depositions

    NASA Astrophysics Data System (ADS)

    Lin, Meng-Yu; Chang, Chung-En; Wang, Cheng-Hung; Su, Chen-Fung; Chen, Chi; Lee, Si-Chen; Lin, Shih-Yen

    2014-08-01

    Uniform large-size MoS2/graphene hetero-structures fabricated directly on sapphire substrates are demonstrated with layer-number controllability by chemical vapor deposition (CVD). The cross-sectional high-resolution transmission electron microscopy (HRTEM) images provide the direct evidences of layer numbers of MoS2/graphene hetero-structures. Photo-excited electron induced Fermi level shift of the graphene channel are observed on the single MoS2/graphene hetero-structure transistors. Furthermore, double hetero-structures of graphene/MoS2/graphene are achieved by CVD fabrication of graphene layers on top of the MoS2, as confirmed by the cross-sectional HRTEM. These results have paved the possibility of epitaxially grown multi-hetero-structures for practical applications.

  20. Effect of lattice strain on structural and optical properties of ZnO nanorods grown by hydrothermal method

    SciTech Connect

    Gautam, Khyati Nirwal, Varun Singh; Singh, Joginder; Peta, Koteswara Rao; Bhatnagar, P. K.; Singh, Inderpreet

    2016-05-06

    In this work, we have synthesized ZnO nanorods over ZnO seeds/ITO/glass substrate by the facile hydrothermal method. ZnO seeds are grown at different temperatures ranging from 150°C to 550°C in steps of 100°C. We have studied the effect of strain on the structural and optical properties of ZnO nanorods. It was observed that the growth temperature of seed layer has an influence over the lattice strain present in the nanorods. The as synthesized nanorods were characterized by scanning electron microscope (SEM), x-ray diffraction (XRD) and photoluminescence (PL). SEM images confirm the formation of dense arrays of vertically aligned nanorods on seeds which are grown at 350°C. In addition to this, XRD patterns reveal that these ZnO nanorods are preferentially oriented along (002) direction. The strain analysis based on the XRD results reveals that the minimum value of strain is obtained at 350°C which is attributed to the improved crystalline quality of the interface of seed layer and nanorods leading to their c-axis alignment and enhancement of ultraviolet emission as observed in the PL spectra.

  1. Annealing Effect on the Structural and Optical Properties of Sputter-Grown Bismuth Titanium Oxide Thin Films

    PubMed Central

    Alfonso, José E.; Olaya, Jhon J.; Bedoya-Hincapié, Claudia M.; Toudert, Johann; Serna, Rosalia

    2014-01-01

    The aim of this work is to assess the evolution of the structural and optical properties of BixTiyOz films grown by rf magnetron sputtering upon post-deposition annealing treatments in order to obtain good quality films with large grain size, low defect density and high refractive index similar to that of single crystals. Films with thickness in the range of 220–250 nm have been successfully grown. After annealing treatment at 600 °C the films show excellent transparency and full crystallization. It is shown that to achieve larger crystallite sizes, up to 17 nm, it is better to carry the annealing under dry air than under oxygen atmosphere, probably because the nucleation rate is reduced. The refractive index of the films is similar under both atmospheres and it is very high (n =2.5 at 589 nm). However it is still slightly lower than that of the single crystal value due to the polycrystalline morphology of the thin films. PMID:28788626

  2. Structural, morphological and mechanical properties of niobium nitride thin films grown by ion and electron beams emanated from plasma

    NASA Astrophysics Data System (ADS)

    Siddiqui, Jamil; Hussain, Tousif; Ahmad, Riaz; Umar, Zeeshan A.; Abdus Samad, Ubair

    2016-05-01

    The influence of variation in plasma deposition parameters on the structural, morphological and mechanical characteristics of the niobium nitride films grown by plasma-emanated ion and electron beams are investigated. Crystallographic investigation made by X-ray diffractometer shows that the film synthesized at 10 cm axial distance with 15 plasma focus shots (PFS) exhibits better crystallinity when compared to the other deposition conditions. Morphological analysis made by scanning electron microscope reveals a definite granular pattern composed of homogeneously distributed nano-spheroids grown as clustered particles for the film synthesized at 10 cm axial distance for 15 PFS. Roughness analysis demonstrates higher rms roughness for the films synthesized at shorter axial distance and by greater number of PFS. Maximum niobium atomic percentage (35.8) and maximum average hardness (19.4 ± 0.4 GPa) characterized by energy-dispersive spectroscopy and nano-hardness analyzer respectively are observed for film synthesized at 10 cm axial distance with 15 PFS.

  3. Structural variability and niche differentiation in the rhizosphere and endosphere bacterial microbiome of field-grown poplar trees.

    PubMed

    Beckers, Bram; Op De Beeck, Michiel; Weyens, Nele; Boerjan, Wout; Vangronsveld, Jaco

    2017-02-23

    The plant microbiome represents one of the key determinants of plant health and productivity by providing a plethora of functional capacities such as access to low-abundance nutrients, suppression of phytopathogens, and resistance to biotic and/or abiotic stressors. However, a robust understanding of the structural composition of the bacterial microbiome present in different plant microenvironments and especially the relationship between below-ground and above-ground communities has remained elusive. In this work, we addressed hypotheses regarding microbiome niche differentiation and structural stability of the bacterial communities within different ecological plant niches. We sampled the rhizosphere soil, root, stem, and leaf endosphere of field-grown poplar trees (Populus tremula × Populus alba) and applied 16S rRNA amplicon pyrosequencing to unravel the bacterial communities associated with the different plant habitats. We found that the structural variability of rhizosphere microbiomes in field-grown poplar trees (P. tremula × P. alba) is much lower than that of the endosphere microbiomes. Furthermore, our data not only confirm microbiome niche differentiation reports at the rhizosphere soil-root interface but also clearly show additional fine-tuning and adaptation of the endosphere microbiome in the stem and leaf compartment. Each plant compartment represents an unique ecological niche for the bacterial communities. Finally, we identified the core bacterial microbiome associated with the different ecological niches of Populus. Understanding the complex host-microbe interactions of Populus could provide the basis for the exploitation of the eukaryote-prokaryote associations in phytoremediation applications, sustainable crop production (bio-energy efficiency), and/or the production of secondary metabolites.

  4. Structural, morphological and optical characterizations of ZnO:Al thin films grown on silicon substrates by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Alyamani, A.; Sayari, A.; Albadri, A.; Albrithen, H.; El Mir, L.

    2016-09-01

    The pulsed laser deposition (PLD) technique is used to grow Al-doped ZnO (AZO) thin films at 500 ° C on silicon substrates under vacuum or oxygen gas background from ablating AZO nanoparticle targets synthesized via the sol-gel process. The structural, morphological and optical properties were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and spectroscopic ellipsometry (SE) techniques. XRD and TEM images show that AZO powder has a wurtzite-type structure and is composed of small prismatic-like shape nanoparticles with an average size of 30nm. The structural properties of the AZO films grown under oxygen show no significant changes compared to those of the film grown under vacuum. However, the optical properties show a dependence on the growth conditions of the AZO films. Highly c -axis-oriented AZO thin films were obtained with grain size ˜ 15 nm. The stress in the AZO films is tensile as measured from the c -parameter. The dielectric function, the refractive index and the extinction coefficient as a function of the photon energy for the AZO films were determined by using spectroscopic ellipsometry measurements in the photon energy region from 1 to 6eV. The band gap energy was observed to slightly decrease in the presence of the O2 gas background and this may be attributed to the stress. The surface and volume energy loss functions are calculated and exhibit different behaviors in the energy range 1-6eV. Refractive indices of 1.9-2.1 in the visible region were obtained for the AZO films. Also, the electronic carrier concentration appears to be related to the presence of O2 during the growth process.

  5. Zinc deficiency in field-grown pecan trees: changes in leaf nutrient concentrations and structure.

    PubMed

    Ojeda-Barrios, Dámaris; Abadía, Javier; Lombardini, Leonardo; Abadía, Anunciación; Vázquez, Saúl

    2012-06-01

    Zinc (Zn) deficiency is a typical nutritional disorder in pecan trees [Carya illinoinensis (Wangenh.) C. Koch] grown under field conditions in calcareous soils in North America, including northern Mexico and south-western United States. The aim of this study was to assess the morphological and nutritional changes in pecan leaves affected by Zn deficiency as well as the Zn distribution within leaves. Zinc deficiency led to decreases in leaf chlorophyll concentrations, leaf area and trunk cross-sectional area. Zinc deficiency increased significantly the leaf concentrations of K and Ca, and decreased the leaf concentrations of Zn, Fe, Mn and Cu. All nutrient values found in Zn-deficient leaves were within the sufficiency ranges, with the only exception of Zn, which was approximately 44, 11 and 9 µg g(-1) dry weight in Zn-sufficient, moderately and markedly Zn-deficient leaves, respectively. Zinc deficiency led to decreases in leaf thickness, mainly due to a reduction in the thickness of the palisade parenchyma, as well as to increases in stomatal density and size. The localisation of Zn was determined using the fluorophore Zinpyr-1 and ratio-imaging technique. Zinc was mainly localised in the palisade mesophyll area in Zn-sufficient leaves, whereas no signal could be obtained in Zn-deficient leaves. The effects of Zn deficiency on the leaf characteristics of pecan trees include not only decreases in leaf chlorophyll and Zn concentrations, but also a reduction in the thickness of the palisade parenchyma, an increase in stomatal density and pore size and the practical disappearance of Zn leaf pools. These characteristics must be taken into account to design strategies to correct Zn deficiency in pecan tree in the field. Copyright © 2012 Society of Chemical Industry.

  6. Microstructural Evolution and Domain Structures of Flux-grown Ferroelectric Thin Films

    NASA Astrophysics Data System (ADS)

    Burch, Matthew James

    Barium titanate is one of the most commonly utilized dielectric materials for commercial applications. As devices continue to scale smaller, it is necessary to find processing routes that allow for the integration of high-permittivity barium titanate into the thin film geometry. In the bulk, high permittivity barium titanate can be produced at high processing temperatures (>1250°C). This is several hundred degrees higher than many low temperature substrates are able to withstand, which makes integration of high-permittivity barium titanate onto these substrates a challenge.One method to lower the processing temperature and maintain bulk-like permittivity of barium titanate thin films is through the addition of a liquid forming flux. The fluxing agent increases the kinetics of the system while encouraging densification. This increase in kinetics results in large-grained, dense samples, with high dielectric properties at relatively low processing temperatures. In this dissertation, the underlying mechanisms of how the flux system actually impacts the microstructural evolution of physically vapor deposited barium titanate thin films on sapphire substrates is explored. The flux-system utilized is the barium-borate system (BaOB2O3). It will be shown that the flux system results in large-grained, dense barium titanate thin films grown on sapphire. However, the evolution of the microstructure depends on a complex interaction between the liquid forming flux, a reaction between the sapphire substrate and barium titanate, the resulting reactionary phase of BaAl2O4, and {111}-barium titanate twins. (Abstract shortened by ProQuest.).

  7. Effects of growth temperature and device structure on GaP solar cells grown by molecular beam epitaxy

    SciTech Connect

    Vaisman, M.; Tomasulo, S.; Masuda, T.; Lang, J. R.; Faucher, J.; Lee, M. L.

    2015-02-09

    Gallium phosphide (GaP) is an attractive candidate for wide-bandgap solar cell applications, possessing the largest bandgap of the III-arsenide/phosphides without aluminum. However, GaP cells to date have exhibited poor internal quantum efficiency (IQE), even for photons absorbed by direct transitions, motivating improvements in material quality and device structure. In this work, we investigated GaP solar cells grown by molecular beam epitaxy over a range of substrate temperatures, employing a much thinner emitter than in prior work. Higher growth temperatures yielded the best solar cell characteristics, indicative of increased diffusion lengths. Furthermore, the inclusion of an AlGaP window layer improved both open-circuit voltage and short wavelength IQE.

  8. Structural and electronic properties of InN nanowire network grown by vapor-liquid-solid method

    SciTech Connect

    Barick, B. K. E-mail: subho-dh@yahoo.co.in; Dhar, S. E-mail: subho-dh@yahoo.co.in; Rodríguez-Fernández, Carlos; Cantarero, Andres

    2015-05-15

    Growth of InN nanowires have been carried out on quartz substrates at different temperatures by vapor-liquid-solid (VLS) technique using different thicknesses of Au catalyst layer. It has been found that a narrow window of Au layer thickness and growth temperature leads to multi-nucleation, in which each site acts as the origin of several nanowires. In this multi-nucleation regime, several tens of micrometer long wires with diameter as small as 20 nm are found to grow along [112{sup -}0] direction (a-plane) to form a dense network. Structural and electronic properties of these wires are studied. As grown nanowires show degenerate n-type behavior. Furthermore, x-ray photoemission study reveals an accumulation of electrons on the surface of these nanowires. Interestingly, the wire network shows persistence of photoconductivity for several hours after switching off the photoexcitation.

  9. Synthesis and characterization of ZnO nano and micro structures grown by low temperature spray pyrolysis and vapor transport.

    PubMed

    Agouram, S; Bushiri, M J; Montenegro, D N; Reig, C; Martínez-Tomás, M C; Muñoz-Sanjosé, V

    2012-08-01

    In this work we present a systematic study of ZnO micro and nanostructures grown by spray pyrolysis (SP) and by physical vapour transport (PVT) on glass and c-sapphire substrates at low temperatures. Optimised growth conditions have allowed to obtain homogeneous ZnO nanolayers composed of quasi-spherical nanoparticles in the range 2 to 8 nm by spray pyrolysis, while by PVT the selected growth conditions allow to produce a wide variety of morphologies (tripods, grains, arrows and wires) of nano and microsize dimension. Grazing incidence X-ray diffraction, field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDX) were used as characterization techniques in the investigation of structural, morphological and compositional nature of these nanostructures in relation with the growth method.

  10. InGaAsP-based uni-travelling carrier photodiode structure grown by solid source molecular beam epitaxy.

    PubMed

    Natrella, Michele; Rouvalis, Efthymios; Liu, Chin-Pang; Liu, Huiyun; Renaud, Cyril C; Seeds, Alwyn J

    2012-08-13

    We report the first InGaAsP-based uni-travelling carrier photodiode structure grown by Solid Source Molecular Beam Epitaxy; the material contains layers of InGaAsP as thick as 300 nm and a 120 nm thick InGaAs absorber. Large area vertically illuminated test devices have been fabricated and characterised; the devices exhibited 0.1 A/W responsivity at 1550 nm, 12.5 GHz -3 dB bandwidth and -5.8 dBm output power at 10 GHz for a photocurrent of 4.8 mA. The use of Solid Source Molecular Beam Epitaxy enables the major issue associated with the unintentional diffusion of zinc in Metal Organic Vapour Phase Epitaxy to be overcome and gives the benefit of the superior control provided by MBE growth techniques without the costs and the risks of handling toxic gases of Gas Source Molecular Beam Epitaxy.

  11. Effects of growth temperature and device structure on GaP solar cells grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Vaisman, M.; Tomasulo, S.; Masuda, T.; Lang, J. R.; Faucher, J.; Lee, M. L.

    2015-02-01

    Gallium phosphide (GaP) is an attractive candidate for wide-bandgap solar cell applications, possessing the largest bandgap of the III-arsenide/phosphides without aluminum. However, GaP cells to date have exhibited poor internal quantum efficiency (IQE), even for photons absorbed by direct transitions, motivating improvements in material quality and device structure. In this work, we investigated GaP solar cells grown by molecular beam epitaxy over a range of substrate temperatures, employing a much thinner emitter than in prior work. Higher growth temperatures yielded the best solar cell characteristics, indicative of increased diffusion lengths. Furthermore, the inclusion of an AlGaP window layer improved both open-circuit voltage and short wavelength IQE.

  12. Low threshold laser operation at room temperature in GaAs/(Al,Ga)As structures grown directly on (100)Si

    SciTech Connect

    Fischer, R.; Kopp, W.; Morkoc, H.; Pion, M.; Specht, A.; Burkhart, G.; Appelman, H.; McGougan, D.; Rice, R.

    1986-05-19

    We report the room-temperature pulsed operation of GaAs/(Al,Ga)As double heterojunction laser structures grown directly on (100)Si. Current thresholds of as low as 170 mA in 10-..mu..m-wide stripe lasers have been achieved at 280 K. Power output as high as 44 mW per facet was also obtained. Assuming no current spreading, the corresponding current threshold density is 6.9 kA/cm/sup 2/. Slope efficiencies and T/sub 0/ values of 0.18 W/A and 165 K, respectively, have also been obtained. These results are directly attributable to the reduction of dislocations by choosing growth conditions and step density on the surface.

  13. Structural and magnetic phase transitions in chromium nitride thin films grown by rf nitrogen plasma molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Alam, Khan; Disseler, Steven M.; Ratcliff, William D.; Borchers, Julie A.; Ponce-Pérez, Rodrigo; Cocoletzi, Gregorio H.; Takeuchi, Noboru; Foley, Andrew; Richard, Andrea; Ingram, David C.; Smith, Arthur R.

    2017-09-01

    A magnetostructural phase transition is investigated in single-crystal chromium nitride (CrN) thin films grown by rf plasma molecular beam epitaxy on MgO(001) substrates. While still within the vacuum environment following molecular beam epitaxy growth, in situ low-temperature scanning tunneling microscopy, and in situ variable low-temperature reflection high-energy electron diffraction are applied, revealing an atomically smooth and metallic CrN(001) surface, and an in-plane structural transition from 1 ×1 (primitive CrN unit cell) to √{2 }×√{2 }-R 45∘ with a transition temperature of (278 ±3 ) K, respectively. Ex situ temperature-dependent measurements using neutron diffraction are also performed, looking at the structural peaks and likewise revealing a first-order structural transition along the [111] out-of-plane direction, with transition temperatures of (268 ± 3) K. Turning to the magnetic peaks, neutron diffraction confirms a clear magnetic transition from paramagnetic at room temperature to antiferromagnetic at low temperatures with a sharp, first-order phase transition and a Néel temperature of (270 ±2 ) K or (280 ±2 ) K for two different films. In addition to the experimental measurements of structural and magnetic ordering, we also discuss results from first-principles theoretical calculations which explore various possible magnetostructural models.

  14. Structural and magnetic properties of MnPd/Fe grown on MgO(100) substrate: Ab initio studies

    NASA Astrophysics Data System (ADS)

    Malonda-Boungou, B. R.; Magnoungou, J. H. J.; M'Passi-Mabiala, B.; Demangeat, C.

    2016-07-01

    Structural and magnetic properties of ultrathin films MnPd/Fe grown on MgO(001) are investigated using a self-consistent pseudopotential plane waves method based on density functional theory in the Perdew-Burke-Ernzerhof generalized gradient approximation. The results obtained reveal the presence of an antiferromagnetic coupling between successive Mn [100] rows, combined with a ripple where Mn outward atoms exhibit a positive magnetic moment, in the case of Mn overlayer on Fe/MgO(001). In the case of MnPd monolayer ordered alloy, the c(2 × 2) structure formation is more favorable than the p(1 × 2) one, exhibiting a ferromagnetic coupling between Mn neighbor atoms with a positive induced ferromagnetic moment on Pd atoms. Pd atoms are pushed outward. For 1-ML MnxPd1 - x on Fe/MgO, the Mn absolute mean magnetization per atom increases as x coverage increases, whereas the Pd mean induced magnetic moment decreases. For systems alternating Mn and Pd monolayers on Fe/MgO(001), a complex magnetic structure is shown on Mn monolayers: changing from Mn neighboring antiferromagnetic coupling to Mn [010] rows antiferromagnetic behavior. The correlation is made between the electronic structure and the magnetic properties, by comparing filled with partially filled components (Pd, Mn and Fe) d-bands. The magnetization easy-axis changes between the in-plane and the out-of-plane orientations from Fe/MgO to MnPd/Fe/MgO systems.

  15. Self-assembled strained GeSiSn nanoscale structures grown by MBE on Si(100)

    NASA Astrophysics Data System (ADS)

    Nikiforov, A. I.; Timofeev, V. A.; Tuktamyshev, A. R.; Yakimov, A. I.; Mashanov, V. I.; Gutakovskii, A. K.

    2017-01-01

    Gradual relaxation of elastic deformations in a silicon layer at the growth of a covering layer on strained layers was established. The dependence of the thickness of a silicon film, where full elastic strain relaxation occurs, on the germanium layer thickness was determined. The dependence of the critical thickness of 2D-3D transition of temperature and composition of the GeSiSn film on Si(100) was studied. Regularities of the formation of multilayer structures on quantum wells comprising pseudomorphous GeSiSn layers without relaxed buffer layers but creating the structures directly on Si. A possibility of synthesizing multilayer structures by molecular beam epitaxy was shown, and the crystal lattice constants using the high-resolution transmission electron microscopy were determined. Based on multilayer GeSiSn/Si structures the p-i-n-diodes, which demonstrated the photoresponse increasing by several orders of magnitude compared to the Sn-free structures at an increase in the Sn content, were created.

  16. Broadband High-Performance Infrared Antireflection Nanowires Facilely Grown on Ultrafast Laser Structured Cu Surface.

    PubMed

    Fan, Peixun; Bai, Benfeng; Long, Jiangyou; Jiang, Dafa; Jin, Guofan; Zhang, Hongjun; Zhong, Minlin

    2015-09-09

    Infrared antireflection is an essential issue in many fields such as thermal imaging, sensors, thermoelectrics, and stealth. However, a limited antireflection capability, narrow effective band, and complexity as well as high cost in implementation represent the main unconquered problems, especially on metal surfaces. By introducing precursor micro/nano structures via ultrafast laser beforehand, we present a novel approach for facile and uniform growth of high-quality oxide semiconductor nanowires on a Cu surface via thermal oxidation. Through the enhanced optical phonon dissipation of the nanowires, assisted by light trapping in the micro structures, ultralow total reflectance of 0.6% is achieved at the infrared wavelength around 17 μm and keeps steadily below 3% over a broad band of 14-18 μm. The precursor structures and the nanowires can be flexibly tuned by controlling the laser processing procedure to achieve desired antireflection performance. The presented approach possesses the advantages of material simplicity, structure reconfigurability, and cost-effectiveness for mass production. It opens a new path to realize unique functions by integrating semiconductor nanowires onto metal surface structures.

  17. Crystal structure and properties of tetragonal EuAg{sub 4}In{sub 8} grown by metal flux technique

    SciTech Connect

    Subbarao, Udumula; Sarkar, Sumanta; Peter, Sebastian C.

    2015-03-15

    The compound EuAg{sub 4}In{sub 8} has been obtained as single crystals in high yield from reactions run in liquid indium. X-ray diffraction on single crystals suggests that EuAg{sub 4}In{sub 8} crystallizes in the CeMn{sub 4}Al{sub 8} structure type, tetragonal space group I4/mmm with lattice constants a=b=9.7937(2) Å and c=5.7492(2) Å. Crystal structure of EuAg{sub 4}In{sub 8} is composed of pseudo Frank–Kasper cages occupied by one europium atom in each ring, which are shared through the corner along the ab plane resulting in a three dimensional network. The magnetic susceptibility of EuAg{sub 4}In{sub 8} was measured in the temperature range 2–300 K, which obeyed Curie–Weiss law above 50 K. Magnetic moment value calculated from the fitting indicates the presence of divalent europium, which was confirmed by X-ray absorption near edge spectroscopy. Electrical resistivity measurements suggest that EuAg{sub 4}In{sub 8} is metallic in nature with a probable Fermi liquid behavior at low temperature. - Graphical abstract: The tetragonal EuAg{sub 4}In{sub 8} has been grown as single crystals from reactions run in liquid indium. Magnetic and XANES measurements suggest divalent nature of Eu and resistivity measurements suggest metallic nature. - Highlights: • EuAg{sub 4}In{sub 8} phase having tetragonal phase is grown by metal flux technique. • Magnetic and XANES measurements exhibit divalent nature of Eu in EuAg{sub 4}In{sub 8}. • Resistivity measurement suggests metallic nature and probable Fermi liquid behavior.

  18. Structural and electronic properties of polar MnO ultrathin film grown on Ag(111)

    SciTech Connect

    Kundu, Asish K. Menon, Krishnakumar S. R.

    2016-05-23

    Surface electronic structure of ultrathin polar MnO film was studied by Low-energy Electron Diffraction (LEED) and Photoemission Spectroscopic (PES) techniques. Epitaxial monolayer to facet formation with increasing film thickness has been observed by LEED. Our LEED result shows p(2x2) surface reconstruction along with facet formation, stabilize the polar MnO(111) surface. The core levels and the valence band electronic structure of MnO films have been studied as a function of film thickness using X-ray and ultraviolet photoelectron spectroscopy techniques.

  19. Structural and electronic properties of polar MnO ultrathin film grown on Ag(111)

    NASA Astrophysics Data System (ADS)

    Kundu, Asish K.; Menon, Krishnakumar S. R.

    2016-05-01

    Surface electronic structure of ultrathin polar MnO film was studied by Low-energy Electron Diffraction (LEED) and Photoemission Spectroscopic (PES) techniques. Epitaxial monolayer to facet formation with increasing film thickness has been observed by LEED. Our LEED result shows p(2x2) surface reconstruction along with facet formation, stabilize the polar MnO(111) surface. The core levels and the valence band electronic structure of MnO films have been studied as a function of film thickness using X-ray and ultraviolet photoelectron spectroscopy techniques.

  20. Structural and electronic properties of molecular beam epitaxially grown Ni1+xTiSn films

    NASA Astrophysics Data System (ADS)

    Rice, A. D.; Kawasaki, J. K.; Verma, N.; Pennachio, D. J.; Schultz, B. D.; Palmstrøm, C. J.

    2017-06-01

    This paper demonstrates the molecular beam epitaxial growth of metallic full-Heusler Ni2TiSn precipitates within semiconducting NiTiSn host matrix, and discusses the structural and chemical stability of this biphasic epitaxial composite and its influence on the electronic properties. Structural properties of the epitaxial films were characterized by in-situ reflection high-energy electron diffraction and ex-situ by X-ray diffraction and transmission electron microscopy. The results indicate the presence of a secondary phase with full Heusler ordering within half-Heusler host matrix. Both the parent half-Heusler and the secondary full-Heusler phases in the epitaxial films are strained from their bulk lattice parameters. Electronic properties show an increase in resistivity at low Ni excess.

  1. Electronic, chemical and structural characterization of CNTs grown by SiC surface decomposition

    NASA Astrophysics Data System (ADS)

    Policicchio, A.; Caruso, T.; Agostino, R. G.; Maccallini, E.; Chiarello, G.; Colavita, E.; Formoso, V.; Castriota, M.; Cazzanelli, E.

    2008-03-01

    The electronic, chemical and structural properties of Carbon NanoTubes (CNTs) synthesized by Silicon Carbide surface decomposition were analyzed by Scanning Electron Microscopy (SEM), Scanning Tunnelling Microscopy/Spectroscopy (STM/STS), Electron Energy Loss (EEL) and Raman spectroscopy. A clear relationship between the bonding features and the growth condition (temperature and growth time) is obtained. The morphology of the sample investigated by SEM reveals a well-packed and aligned structure of the CNTs. Different lengths of the CNTs are observed depending on the local temperature of the sample surface. The longest observed CNTs were 500/600 nm. The STS measurements show I-V diode-like characteristic curve which can be used, for instance, as an electron collector in solar cells applications. As a perspective metallic electrode, gold, will be deposited on top of the CNTs in the future, to collect the electron current and investigated by the same techniques.

  2. Preparation, Structural and Dielectric Properties of Solution Grown Polyvinyl Alcohol(PVA) Film

    NASA Astrophysics Data System (ADS)

    Nangia, Rakhi; Shukla, Neeraj K.; Sharma, Ambika

    2017-08-01

    Flexible dielectrics with high permittivity have been investigated extensively due to their applications in electronic industry. In this work, structural and electrical characteristics of polymer based film have been analysed. Poly vinyl alcohol (PVA) film was prepared by solution casting method. X-ray diffraction (XRD) characterization technique is used to investigate the structural properties. The semi-crystalline nature has been determined by the analysis of the obtained XRD pattern. Electrical properties of the synthesized film have been analysed from the C-V and I-V curves obtained at various frequencies and temperatures. Low conductivity values confirm the insulating behaviour of the film. However, it is found that conductivity increases with temperature. Also, the dielectric permittivity is found to be higher at lower frequencies and higher temperatures, that proves PVA to be an excellent dielectric material which can be used in interface electronics. Dielectric behaviour of the film has been explained based on dipole orientations to slow and fast varying electric field. However further engineering can be done to modulate the structural, electrical properties of the film.

  3. Structural and optical characteristics of the hexagonal ZnO films grown on cubic MgO (001) substrates.

    PubMed

    Shen, Xiangqian; Zhou, Hua; Li, Yaping; Kang, Junyong; Zheng, Jin-Cheng; Ke, Shanming; Wang, Qingkang; Wang, Hui-Qiong

    2016-11-01

    In this Letter, we report on the structural and optical characteristics of ZnO films with a wurtzite structure grown on MgO (001) substrates with cubic structures. The ZnO films were prepared through the molecular beam epitaxy method, and growth orientation transformation from [0001] to [10-10] direction was observed with the change of growth temperature and thickness. The x-ray diffraction pole figures and in situ RHEED patterns demonstrated that the rotational relationship among grains within the ZnO films appeared in a typical two-fold rotation of about 30° for the [0001] growth orientation and four-fold rotation of about 30° or 60° for the [10-10] growth orientation, respectively. Last, we investigated their optical properties through measuring the transmission and photoluminescence spectra of the ZnO films, which showed the bulk-like bandgap feature of the ZnO films in spite of the existing growth orientation transformation.

  4. Stoichiometric structures of defects in high-purity GaAs grown by the liquid encapsulated Czochralski method

    SciTech Connect

    Morrow, R.A.

    1988-06-15

    We analyze some existing data obtained on a GaAs sample grown by the liquid encapsulated Czochralski (LEC) method from a near-stoichiometric melt after the sample was cycled through various thermal processes. By using the constraint of constant deviation from stoichiometry we are led to suggest that the defects observed or inferred to exist in the sample have the following properties: (1) the acceptor associated with the 1.45-eV photoluminescence signal has the stoichiometric structure of Ga/sub As/ if doubly charged or of V/sub Ga/Ga/sub As/ if singly charged; (2) the (presumed) donor at E/sub c/-0.134 eV has the stoichiometric structure of V/sub As/; (3) another (inferred) acceptor has the stoichiometric structure of V/sub Ga/; and (4) the very shallow donor at E/sub c/-0.003 eV is the precursor of EL2 and becomes EL2 upon reaction with V/sub Ga/ or its stoichiometric equivalent

  5. An investigation of near-infrared photoluminescence from AP-MOVPE grown InSb/GaSb quantum dot structures

    NASA Astrophysics Data System (ADS)

    Ahia, C. C.; Tile, N.; Urgessa, Z. N.; Botha, J. R.; Neethling, J. H.

    2017-01-01

    In this work, the near-infrared photoluminescence (PL) of InSb/GaSb QD structures grown on GaSb substrate (2° off (100)) using atmospheric pressure Metalorganic Vapor Phase Epitaxy is investigated. The structures are analyzed before capping and after capping using scanning probe microscopy and high resolution transmission electron microscopy (HRTEM), respectively. At 10 K, with an excitation power of 2 mW, a PL peak at ∼ 732 meV is observed. Upon an increase in laser power to 120 mW, a blue shift of ∼ 8 meV is noticed. This emission typically persists up to 60-70 K, after which it becomes weak. An SPM analysis of the size distribution of uncapped dots reveals a mono-modal distribution with an average density of ∼ 5×1010 cm-2. However, a HRTEM investigation of the capped dots reveals the formation of an InGaSb quantum well-like structure, ∼ 10 nm thick, which gives rise to the PL signal mentioned above.

  6. The electrical and structural properties of n-type InAs nanowires grown from metal-organic precursors.

    PubMed

    Thelander, C; Dick, K A; Borgström, M T; Fröberg, L E; Caroff, P; Nilsson, H A; Samuelson, L

    2010-05-21

    The electrical and structural properties of 111B-oriented InAs nanowires grown using metal-organic precursors have been studied. On the basis of electrical measurements it was found that the trends in carbon incorporation are similar to those observed in the layer growth, where an increased As/In precursor ratio and growth temperature result in a decrease in carbon-related impurities. Our results also show that the effect of non-intentional carbon doping is weaker in InAs nanowires compared to bulk, which may be explained by lower carbon incorporation in the nanowire core. We determine that differences in crystal quality, here quantified as the stacking fault density, are not the primary cause for variations in resistivity of the material studied. The effects of some n-dopant precursors (S, Se, Si, Sn) on InAs nanowire morphology, crystal structure and resistivity were also investigated. All precursors result in n-doped nanowires, but high precursor flows of Si and Sn also lead to enhanced radial overgrowth. Use of the Se precursor increases the stacking fault density in wurtzite nanowires, ultimately at high flows leading to a zinc blende crystal structure with strong overgrowth and very low resistivity.

  7. Surface termination structure of α-Ga2O3 film grown by mist chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Tamba, Daiki; Kubo, Osamu; Oda, Masaya; Osaka, Shun; Takahashi, Kazuki; Tabata, Hiroshi; Kaneko, Kentaro; Fujita, Shizuo; Katayama, Mitsuhiro

    2016-06-01

    The surface structure of α-Ga2O3(0001) grown on an α-Al2O3(0001) substrate by mist chemical vapor deposition was studied by coaxial impact-collision ion scattering spectroscopy (CAICISS) and atomic force microscopy (AFM). The minimum step height observed in the AFM image was 0.21 ± 0.01 nm, coinciding with the height of three atomic layers of α-Ga2O3(0001). It was revealed by CAICISS analysis that the surface of α-Ga2O3(0001) is terminated by a Ga layer followed by an O layer, which is consistent with the surface termination of α-Al2O3(0001). A structural model taking surface relaxation into account was also constructed by fitting the simulated curve for the azimuth angle dependence of the Ga intensity to the experimental dependence. The resultant structural model is similar to the model of an α-Al2O3(0001) surface, which indicates analogous behavior in corundum crystals.

  8. Structure and magnetic properties of electrodeposited, ferromagnetic, group 3-d element films grown onto GaAs (011) substrate

    NASA Astrophysics Data System (ADS)

    Scheck, C.; Evans, P.; Schad, R.; Zangari, G.

    2003-05-01

    Ni, Co, and iron-rich FeNi films were grown onto n-GaAs (011) substrates using electrodeposition from metal sulfate solutions, at room temperature, with a current density of 3.5 mA/cm2 at a pH of 2.5. The structure of Ni film is found to be fcc with a (111) preferred orientation, whereas Co films show a mixed fcc and hcp structure that is confirmed by x-ray diffraction and transmission electron microscopy data. The structure of iron-rich (>90%) FeNi films remains unclear at the moment. The films show a well-defined, in-plane, uniaxial anisotropy with the easy axis along the [011] GaAs direction for Ni, and [011¯] GaAs direction for Co and FeNi films (i.e., anisotropy rotated by 90° compared to Ni). Co films maintain their anisotropy even for large thicknesses (>250 nm) and so does Ni (up to 90 nm). Surprisingly, thin Ni films exhibit a larger HK value (950 Oe) than what would be expected from a purely crystalline anisotropy. This effect is ascribed to internal stresses in the as-deposited films.

  9. Surface termination structure of α-Ga{sub 2}O{sub 3} film grown by mist chemical vapor deposition

    SciTech Connect

    Tamba, Daiki; Kubo, Osamu Osaka, Shun; Takahashi, Kazuki; Tabata, Hiroshi; Katayama, Mitsuhiro; Oda, Masaya; Kaneko, Kentaro; Fujita, Shizuo

    2016-06-20

    The surface structure of α-Ga{sub 2}O{sub 3}(0001) grown on an α-Al{sub 2}O{sub 3}(0001) substrate by mist chemical vapor deposition was studied by coaxial impact-collision ion scattering spectroscopy (CAICISS) and atomic force microscopy (AFM). The minimum step height observed in the AFM image was 0.21 ± 0.01 nm, coinciding with the height of three atomic layers of α-Ga{sub 2}O{sub 3}(0001). It was revealed by CAICISS analysis that the surface of α-Ga{sub 2}O{sub 3}(0001) is terminated by a Ga layer followed by an O layer, which is consistent with the surface termination of α-Al{sub 2}O{sub 3}(0001). A structural model taking surface relaxation into account was also constructed by fitting the simulated curve for the azimuth angle dependence of the Ga intensity to the experimental dependence. The resultant structural model is similar to the model of an α-Al{sub 2}O{sub 3}(0001) surface, which indicates analogous behavior in corundum crystals.

  10. Structural and optical properties of 70-keV carbon ion beam synthesized carbon nanoclusters in thermally grown silicon dioxide

    NASA Astrophysics Data System (ADS)

    Poudel, P. R.; Poudel, P. P.; Paramo, J. A.; Strzhemechny, Y. M.; Rout, B.; McDaniel, F. D.

    2014-09-01

    The structural and optical properties of carbon nanoclusters formed in thermally grown silicon dioxide film via the ion beam synthesis process have been investigated. A low-energy (70 keV) carbon ion beam (C-) at a fluence of 3 × 1017 atoms/cm2 was used for implantation into a thermally grown silicon dioxide layer (500 nm thick) on a Si (100) wafer. Several parts of the implanted samples were subsequently annealed in a gas mixture (4 % H2 + 96 % Ar) at 900 °C for different time periods. The as-implanted and annealed samples were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM), and photoluminescence spectroscopy (PL). The carbon ion implantation depth profile was simulated using a widely used Monte Carlo-based simulation code SRIM-2012. Additionally, the elemental depth profile of the implanted carbon along with host elements of silicon and oxygen were simulated using a dynamic ion-solid interaction code T-DYN, which incorporates the effects of the surface sputtering and gradual change in the elemental composition in the implanted layers due to high-fluence ion implantation. The elemental depth profile obtained from the XPS measurements matches closely to the T-DYN predictions. Raman measurements indicate the formation of graphitic phases in the annealed samples. The graphitic peak (G-peak) was found to be increased with the annealing time duration. In the sample annealed for 10 min, the sizes of the carbon nanoclusters were found to be 1-4 nm in diameter using TEM. The PL measurements at room temperature using a 325-nm laser show broad-band emissions in the ultraviolet to visible range in the as-implanted sample. Intense narrow bands along with the broad bands were observed in the annealed samples. The defects present in the as-grown samples along with carbon ion-induced defect centers in the as-implanted samples are the main contributors to the observed

  11. Structural and optical properties of 70-keV carbon ion beam synthesized carbon nanoclusters in thermally grown silicon dioxide

    NASA Astrophysics Data System (ADS)

    Poudel, P. R.; Poudel, P. P.; Paramo, J. A.; Strzhemechny, Y. M.; Rout, B.; McDaniel, F. D.

    2015-02-01

    The structural and optical properties of carbon nanoclusters formed in thermally grown silicon dioxide film via the ion beam synthesis process have been investigated. A low-energy (70 keV) carbon ion beam (C-) at a fluence of 3 × 1017 atoms/cm2 was used for implantation into a thermally grown silicon dioxide layer (500 nm thick) on a Si (100) wafer. Several parts of the implanted samples were subsequently annealed in a gas mixture (4 % H2 + 96 % Ar) at 900 °C for different time periods. The as-implanted and annealed samples were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM), and photoluminescence spectroscopy (PL). The carbon ion implantation depth profile was simulated using a widely used Monte Carlo-based simulation code SRIM-2012. Additionally, the elemental depth profile of the implanted carbon along with host elements of silicon and oxygen were simulated using a dynamic ion-solid interaction code T-DYN, which incorporates the effects of the surface sputtering and gradual change in the elemental composition in the implanted layers due to high-fluence ion implantation. The elemental depth profile obtained from the XPS measurements matches closely to the T-DYN predictions. Raman measurements indicate the formation of graphitic phases in the annealed samples. The graphitic peak (G-peak) was found to be increased with the annealing time duration. In the sample annealed for 10 min, the sizes of the carbon nanoclusters were found to be 1-4 nm in diameter using TEM. The PL measurements at room temperature using a 325-nm laser show broad-band emissions in the ultraviolet to visible range in the as-implanted sample. Intense narrow bands along with the broad bands were observed in the annealed samples. The defects present in the as-grown samples along with carbon ion-induced defect centers in the as-implanted samples are the main contributors to the observed

  12. Structural and optical properties of AlGaN/GaN quantum well structures grown by MOCVD on sapphire

    SciTech Connect

    Niebuhr, R.; Bachem, K.H.; Behr, D.

    1997-12-31

    AlGaN/GaN single quantum wells (QW) have been grown on 2 in. sapphire substrates (c-plane) by metal-organic chemical vapor deposition (MOCVD). The well width was varied between 20 and 40 {angstrom} for barriers containing 4% and 16% of aluminum. Cathodoluminescence (CL) and Photoluminescence (PL) spectra of the samples show, as expected, a shift of the quantum well emission to higher energies with decreasing well width, whereas the barrier luminescence stays at constant energy. Examination of the QWs by resonant Raman spectroscopy tuned to the gap of the well, clearly shows the GaN A{sub 1}(LO) phonon besides the AlGaN A{sub 1}(LO) phonon from the barrier. For a well width of 20 {angstrom} the authors observe a shift of the A{sub 1}(LO) GaN phonon indicating a certain degree of intermixing at the GaN/AlGaN interface. Atomic Force Microscopy (AFM) reveals that the layers are growing in a 2-dimensional step flow growth mode with step heights of 3 and 6 {angstrom} corresponding to mono- and biatomic steps. High Resolution Transmission Electron Microscopy (HRTEM) micrographs of the 40 {angstrom} well show a very low interface roughness of 1--2 atomic layers.

  13. Comparison between structural properties of bulk GaN grown under high N pressure and GaN grown by other methods

    SciTech Connect

    Liliental-Weber, Z.; Jasinski, J.; Washburn, J.

    2002-07-31

    In this paper defects formed in GaN grown by different methods are reviewed. Formation of particular defects are often related to the crystallographic direction in which the crystals grow. For bulk crystals the highest growth rates are observed for directions perpendicular to the c-axis. Threading dislocations and nanopipes along the c-axis are not formed in these crystals, but polarity of the growth direction plays a role concerning defects that are formed and surface roughness. For growth of homoepitaxial layers, where growth is forced to take place in the c-direction threading dislocations are formed and their density is related to the purity of constituents used for growth and to substrate surface inhomogeneities. In heteroepitaxial layers two other factors: lattice mismatch and thermal expansion mismatch are related to the formation of dislocations. Doping of crystals can also lead to formation of defects characteristic for a specific dopant. This type of defects tends to be growth method independent but can depend on growth polarity.

  14. Structural Modifications of Fructans in Aloe barbadensis Miller (Aloe Vera) Grown under Water Stress

    PubMed Central

    Salinas, Carlos; Cardemil, Liliana

    2016-01-01

    Aloe barbadensis Miller (Aloe vera) has a Crassulaceae acid metabolism which grants the plant great tolerance to water restrictions. Carbohydrates such as acemannans and fructans are among the molecules responsible for tolerating water deficit in other plant species. Nevertheless, fructans, which are prebiotic compounds, have not been described nor studied in Aloe vera, whose leaf gel is known to possess beneficial pharmaceutical, nutritional and cosmetic properties. As Aloe vera is frequently cultivated in semi-arid conditions, like those found in northern Chile, we investigated the effect of water deficit on fructan composition and structure. For this, plants were subjected to different irrigation regimes of 100%, 75%, 50% and 25% field capacity (FC). There was a significant increase in the total sugars, soluble sugars and oligo and polyfructans in plants subjected to water deficit, compared to the control condition (100% FC) in both leaf tips and bases. The amounts of fructans were also greater in the bases compared to the leaf tips in all water treatments. Fructans also increase in degree of polymerization with increasing water deficit. Glycosidic linkage analyses by GC-MS, led to the conclusion that there are structural differences between the fructans present in the leaves of control plants with respect to plants irrigated with 50% and 25% FC. Therefore, in non-stressed plants, the inulin, neo-inulin and neo-levan type of fructans predominate, while in the most stressful conditions for the plant, Aloe vera also synthesizes fructans with a more branched structure, the neofructans. To our knowledge, the synthesis and the protective role of neo-fructans under extreme water deficit has not been previously reported. PMID:27454873

  15. Structural Modifications of Fructans in Aloe barbadensis Miller (Aloe Vera) Grown under Water Stress.

    PubMed

    Salinas, Carlos; Handford, Michael; Pauly, Markus; Dupree, Paul; Cardemil, Liliana

    2016-01-01

    Aloe barbadensis Miller (Aloe vera) has a Crassulaceae acid metabolism which grants the plant great tolerance to water restrictions. Carbohydrates such as acemannans and fructans are among the molecules responsible for tolerating water deficit in other plant species. Nevertheless, fructans, which are prebiotic compounds, have not been described nor studied in Aloe vera, whose leaf gel is known to possess beneficial pharmaceutical, nutritional and cosmetic properties. As Aloe vera is frequently cultivated in semi-arid conditions, like those found in northern Chile, we investigated the effect of water deficit on fructan composition and structure. For this, plants were subjected to different irrigation regimes of 100%, 75%, 50% and 25% field capacity (FC). There was a significant increase in the total sugars, soluble sugars and oligo and polyfructans in plants subjected to water deficit, compared to the control condition (100% FC) in both leaf tips and bases. The amounts of fructans were also greater in the bases compared to the leaf tips in all water treatments. Fructans also increase in degree of polymerization with increasing water deficit. Glycosidic linkage analyses by GC-MS, led to the conclusion that there are structural differences between the fructans present in the leaves of control plants with respect to plants irrigated with 50% and 25% FC. Therefore, in non-stressed plants, the inulin, neo-inulin and neo-levan type of fructans predominate, while in the most stressful conditions for the plant, Aloe vera also synthesizes fructans with a more branched structure, the neofructans. To our knowledge, the synthesis and the protective role of neo-fructans under extreme water deficit has not been previously reported.

  16. Study of structural property of Co ferrite thin film grown by pulsed laser deposition technique

    NASA Astrophysics Data System (ADS)

    Nongjai, Razia; Khan, Shakeel; Ahmad, Hilal; Khan, Imran; Asokan, K.

    2012-06-01

    Thin film of Cobalt Ferrite was deposited on Si (1 0 0) substrate using Pulsed Laser Deposition (PLD) technique. The deposited film was characterized by X-ray Diffraction (XRD), X-ray reflectivity (XRR), Rutherford Backscattering Spectroscopy (RBS) and Raman Spectroscopy and was found to be single phase, textured along (1 1 1) directions and approximately matching the stoichoimetry of the target with negligible strain. The film had a very uniform and flat surface. Raman spectroscopy measurement further confirmed the formation of single phase cubic spinel structure. T2g Raman mode was missing from the spectra which may be due to cation redistribution and crystallite size effect.

  17. Structure of a heterogeneous, glycosylated, lipid-bound, in vivo-grown protein crystal at atomic resolution from the viviparous cockroach Diploptera punctata

    PubMed Central

    Banerjee, Sanchari; Coussens, Nathan P.; Gallat, François-Xavier; Sathyanarayanan, Nitish; Srikanth, Jandhyam; Yagi, Koichiro J.; Gray, James S. S.; Tobe, Stephen S.; Stay, Barbara; Chavas, Leonard M. G.; Ramaswamy, Subramanian

    2016-01-01

    Macromolecular crystals for X-ray diffraction studies are typically grown in vitro from pure and homogeneous samples; however, there are examples of protein crystals that have been identified in vivo. Recent developments in micro-crystallography techniques and the advent of X-ray free-electron lasers have allowed the determination of several protein structures from crystals grown in cellulo. Here, an atomic resolution (1.2 Å) crystal structure is reported of heterogeneous milk proteins grown inside a living organism in their functional niche. These in vivo-grown crystals were isolated from the midgut of an embryo within the only known viviparous cockroach, Diploptera punctata. The milk proteins crystallized in space group P1, and a structure was determined by anomalous dispersion from the native S atoms. The data revealed glycosylated proteins that adopt a lipocalin fold, bind lipids and organize to form a tightly packed crystalline lattice. A single crystal is estimated to contain more than three times the energy of an equivalent mass of dairy milk. This unique storage form of nourishment for developing embryos allows access to a constant supply of complete nutrients. Notably, the crystalline cockroach-milk proteins are highly heterogeneous with respect to amino-acid sequence, glycosylation and bound fatty-acid composition. These data present a unique example of protein heterogeneity within a single in vivo-grown crystal of a natural protein in its native environment at atomic resolution. PMID:27437115

  18. Structure of a heterogeneous, glycosylated, lipid-bound, in vivo-grown protein crystal at atomic resolution from the viviparous cockroach Diploptera punctata.

    PubMed

    Banerjee, Sanchari; Coussens, Nathan P; Gallat, François-Xavier; Sathyanarayanan, Nitish; Srikanth, Jandhyam; Yagi, Koichiro J; Gray, James S S; Tobe, Stephen S; Stay, Barbara; Chavas, Leonard M G; Ramaswamy, Subramanian

    2016-07-01

    Macromolecular crystals for X-ray diffraction studies are typically grown in vitro from pure and homogeneous samples; however, there are examples of protein crystals that have been identified in vivo. Recent developments in micro-crystallography techniques and the advent of X-ray free-electron lasers have allowed the determination of several protein structures from crystals grown in cellulo. Here, an atomic resolution (1.2 Å) crystal structure is reported of heterogeneous milk proteins grown inside a living organism in their functional niche. These in vivo-grown crystals were isolated from the midgut of an embryo within the only known viviparous cockroach, Diploptera punctata. The milk proteins crystallized in space group P1, and a structure was determined by anomalous dispersion from the native S atoms. The data revealed glycosylated proteins that adopt a lipocalin fold, bind lipids and organize to form a tightly packed crystalline lattice. A single crystal is estimated to contain more than three times the energy of an equivalent mass of dairy milk. This unique storage form of nourishment for developing embryos allows access to a constant supply of complete nutrients. Notably, the crystalline cockroach-milk proteins are highly heterogeneous with respect to amino-acid sequence, glycosylation and bound fatty-acid composition. These data present a unique example of protein heterogeneity within a single in vivo-grown crystal of a natural protein in its native environment at atomic resolution.

  19. High mobility GaAs/AlAs/(211)Si structures grown by MBE

    NASA Astrophysics Data System (ADS)

    Christou, A.; Varmazis, K.; Hatzopoulos, Z.

    1987-02-01

    The growth on the preferred (211) silicon surface has been accomplished utilizing an interfacial layer of 100 Å of AlAs. We report on the (i) surface preparation, (ii) arsenic rich growth and (iii) mobility measurements of the resultant GaAs/AlAs(211) Si structure. An arsenic rich initial growth was utilized, which resulted in a sharp 2×2 reconstructed GaAs surface. In comparison, a gallium rich surface resulted in antiphase domains and in worst case Ga rich modules. Surface oxides were desorbed at 800°C prior to deposition at a final substrate temperature of 600-610°C for GaAs and 700°C for AlAs. The deposition in both cases was initiated at 250°C. Undoped GaAs/AlAs/(211) Si structures resulted in room temperature mobility values of 5275-8000 cm 2/V·s. The mobility values were optimizing by varying the thickness of the AlAs. A thickness of 100-120 Å was found to be necessary to prevent compensation due to outdiffusion from the silicon substrate. The GaAs films were shown to be smooth without evidence of antiphase domains.

  20. Structural and optical properties of silicon nanocrystals grown by plasma-enhanced chemical vapor deposition.

    PubMed

    Prakash, G V; Daldosso, N; Degoli, E; Iacona, F; Cazzanelli, M; Gaburro, Z; Pucker, G; Dalba, P; Rocca, F; Ceretta Moreira, E; Franzò, G; Pacifici, D; Priolo, F; Arcangeli, C; Filonov, A B; Ossicini, S; Pavesi, L

    2001-06-01

    Silicon nanocrystals (Si-nc) embedded in SiO2 matrix have been prepared by high temperature thermal annealing (1000-1250 degrees C) of substoichiometric SiOx films deposited by plasma-enhanced chemical vapor deposition (PECVD). Different techniques have been used to examine the optical and structural properties of Si-nc. Transmission electron microscopy analysis shows the formation of nanocrystals whose sizes are dependent on annealing conditions and deposition parameters. The spectral positions of room temperature photoluminescence are systematically blue shifted with reduction in the size of Si-nc obtained by decreasing the annealing temperature or the Si content during the PECVD deposition. A similar trend has been found in optical absorption measurements. X-ray absorption fine structure measurements indicate the presence of an intermediate region between the Si-nc and the SiO2 matrix that participates in the light emission process. Theoretical observations reported here support these findings. All these efforts allow us to study the link between dimensionality, optical properties, and the local environment of Si-nc and the surrounding SiO2 matrix.

  1. Some of structural and morphological optimization of GaN thin film on Si(100) substrate grown by RF sputter

    NASA Astrophysics Data System (ADS)

    Mantarcı, Asim; Kundakçı, Mutlu

    2017-04-01

    One of important material of III-nitrides can be said to be GaN with direct-wide band gap ( 3.4 eV) and many industrial devices such as solar cell, LED has been based on GaN thin film. In this research, we elaborately investigated growth of GaN thin film on Si(100) substrate by RF sputter technique and characterization of the film. We have successfully grown GaN thin film on Si substrate with hexagonal structure which has been confirmed by analysis of X-ray measurements. Also, we obtained structural properties of GaN film by (XRD) X-ray Diffraction measurements depending on different Argon, nitrogen and RF power values. During experiment, the value from 25sccm to 100sccm Argon gas value, the value from 0sccm to 4sccm Nitrogen gas value and from 50 watt to 125 watt RF power value has been applied. Among these values, we determined the best film in terms of crystalline structure of film. From AFM results, we attained and analyzed average roughness (Ra), maximum peak height (Rp), and maximum depth (Rv), average absolute slope of the profile (Δa)(°) of the fılms successfully. The film having the lowest roughness (Ra) has been achieved depending on different Argon, nitrogen and RF power values. Atomic Force Microscopy results confirmed that some of the films have homogeneous and uniform structure without any holes and crack; but others has voids referring impurities coming from growth process. To sum up, not only growing GaN thin film on Si substrate has been investigated, but also some of structural and morphological parameters' optimization has been studied, analyzed and the best film was determined in view of varied Argon, nitrogen and RF power values. For future direction, optimization of GaN thin film in detail can enable us to fabricate high quality film; therefore it will helps to improving device technology.

  2. Structural change upon annealing of amorphous GeSbTe grown on Si(111)

    SciTech Connect

    Bragaglia, V. Jenichen, B.; Giussani, A.; Perumal, K.; Riechert, H.; Calarco, R.

    2014-08-07

    The structural change upon annealing of an amorphous GeSbTe (GST) film deposited by molecular beam epitaxy on a Si(111) substrate is studied by means of X-ray diffraction (XRD), X-ray reflectivity (XRR), and atomic force microscopy (AFM). XRD profiles reveal that both metastable cubic and stable hexagonal phases are obtained with a single out-of-plane orientation. XRR study shows a density increase and consequent thickness decrease upon annealing, in accordance with literature. From both, the XRD and the AFM study, it emerges that the crystalline substrate acts as a template for the film, favoring the crystallization of the amorphous GST into the [111] oriented metastable cubic phase, and the latter turns into the [0001] stable hexagonal phase for higher annealing temperature.

  3. Superconductivity in artificial cuprate structures grown by laser molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Tebano, A.; Aruta, C.; Boggio, N. G.; Medaglia, P. G.; Balestrino, G.

    2006-03-01

    Pulsed laser deposition in a molecular beam epitaxy environment has been used to deposit high quality thin films of BaCuO2+x,CaCuO2, and superconducting (BaCuO2+x)2/(CaCuO2)2 artificial superlattices. In situ reflection high energy electron diffraction (RHEED) has shown that the growth mechanism is two dimensional, and ex situ x-ray diffraction spectra confirmed the growth rate deduced from RHEED oscillations. The BaCuO2+x,CaCuO2 films alone are not superconducting; however, in infinite layer based heterostructures the occurrence of charge transfer amongst layers containing different alkaline earth ions can give rise to superconductivity. Structural features of these heterostructures can be engineered over a wide range and, consequently, their superconducting properties studied.

  4. Structural and morphological properties of metallic thin films grown by pulsed laser deposition for photocathode application

    NASA Astrophysics Data System (ADS)

    Lorusso, A.; Gontad, F.; Caricato, A. P.; Chiadroni, E.; Broitman, E.; Perrone, A.

    2016-03-01

    In this work yttrium and lead thin films have been deposited by pulsed laser deposition technique and characterized by ex situ different diagnostic methods. All the films were adherent to the substrates and revealed a polycrystalline structure. Y films were uniform with a very low roughness and droplet density, while Pb thin films were characterized by a grain morphology with a relatively high roughness and droplet density. Such metallic materials are studied because they are proposed as a good alternative to copper and niobium photocathodes which are generally used in radiofrequency and superconducting radiofrequency guns, respectively. The photoemission performances of the photocathodes based on Y and Pb thin films have been also studied and discussed.

  5. Properties of Inconel 625 Mesh Structures Grown by Electron Beam Additive Manufacturing

    SciTech Connect

    List III, Frederick Alyious; Dehoff, Ryan R; Lowe, Larry E; Sames, William J

    2014-01-01

    Relationships between electron beam parameters (beam current, beam speed, and beam focus) and physical properties (mass, diameter, elastic modulus, and yield strength) have been investigated for Inconel 625 mesh cubes fabricated using an additive manufacturing technology based on electron beam melting. The elastic modulus and yield strength of the mesh cubes have been systematically varied by approximately a factor of ten by changing the electron beam parameters. Simple models have been used to understand better these relationships. Structural anisotropies of the mesh associated with the layered build architecture have been observed and may contribute, along with microstructural anisotropies, to the anisotropic mechanical properties of the mesh. Knowledge of this kind is likely applicable to other metal and alloy systems and is essential to rapidly realize the full potential of this burgeoning technology.

  6. Structure and Properties of Platinum, Gold and Mercury Nanowires Grown in Superfluid Helium.

    PubMed

    Gordon, Eugene B; Karabulin, Alexander V; Morozov, Andrey A; Matyushenko, Vladimir I; Sizov, Vyacheslav D; Khodos, Igor I

    2014-04-03

    Webs consisting of nanowires made of gold, platinum and mercury were produced by the technique based on laser ablation of metals inside superfluid helium. Their morphology and structure as well as their electrical conductivity have been studied. Diameters of gold and platinum nanowires are 4.5 and 3 nm, respectively. Fortunately, they are close to diameters of nanospheres made of these metals, which, as known from the literature, possess anomalous catalytic activity. Web resistivities for all metals up to room temperature are controlled by conductive electron scattering on a wire surface, thus they are almost independent of T. Nanowires in the webs are electrically interconnected, and therefore the web can be used as a catalyst without any support. Possible advantages of this type of nanocatalyst are outlined.

  7. Magnetostrictive iron gallium thin films grown onto antiferromagnetic manganese nitride: Structure and magnetism

    NASA Astrophysics Data System (ADS)

    Mandru, Andrada-Oana; Corbett, Joseph P.; Richard, Andrea L.; Gallagher, James; Meng, Keng-Yuan; Ingram, David C.; Yang, Fengyuan; Smith, Arthur R.

    2016-10-01

    We report structural and magnetic properties of magnetostrictive Fe100 -xGax (x ≈ 15) alloys when deposited onto antiferromagnetic manganese nitride and non-magnetic magnesium oxide substrates. From X-ray diffraction measurements, we find that the FeGa films are single crystalline. Scanning tunneling microscopy imaging reveals that the surface morphologies are dictated by the growth temperature, composition, and substrate. The magnetic properties can be tailored by the substrate, as found by magnetic force microscopy imaging and vibrating sample magnetometry measurements. In addition to pronounced tetragonal deformations, depositing FeGa onto manganese nitride leads to the formation of stripe-like magnetic domain patterns and to the appearance of perpendicular magnetic anisotropy.

  8. Structural changes induced spin-reorientation of ultrathin Mn films grown on Ag(001)

    NASA Astrophysics Data System (ADS)

    Ouarab, N.; Haroun, A.; Baadji, N.

    2016-12-01

    The strained body centered tetragonal (bct) Mn ultrathin film from lattice parameter a=2.89 Å to lattice value of 2.73 Å induces anti-ferromagnetic behavior between Mn layers. The magnetic easy axis of Mn film was demonstrated theoretically to switch from the in-plane to out-of-plane by magneto-optical Kerr effect investigation. By including spin-orbit coupling in full potential linearized augmented plane waves and linearized muffin-tin orbitals methods, manganese ultrathin film displays different magnetic behaviors and the spin-reorientation transition is shown to be correlated to these structural changes. The calculated magnetic moment of manganese planes are enhanced and reach a value of ~4.02 μB. The polar magneto-optical Kerr effect is calculated for a photon energy range extended to 15 eV. It shows a pronounced peak in visible light.

  9. Visualizing the 3D internal structure of calcite single crystals grown in agarose hydrogels.

    PubMed

    Li, Hanying; Xin, Huolin L; Muller, David A; Estroff, Lara A

    2009-11-27

    Single crystals are usually faceted solids with homogeneous chemical compositions. Biogenic and synthetic calcite single crystals, however, have been found to incorporate macromolecules, spurring investigations of how large molecules are distributed within the crystals without substantially disrupting the crystalline lattice. Here, electron tomography reveals how random, three-dimensional networks of agarose nanofibers are incorporated into single crystals of synthetic calcite by allowing both high- and low-energy fiber/crystal interface facets to satisfy network curvatures. These results suggest that physical entrapment of polymer aggregates is a viable mechanism by which macromolecules can become incorporated inside inorganic single crystals. As such, this work has implications for understanding the structure and formation of biominerals as well as toward the development of new high-surface area, single-crystal composite materials.

  10. Effects of field-grown genetically modified Zoysia grass on bacterial community structure.

    PubMed

    Lee, Yong-Eok; Yang, Sang-Hwan; Bae, Tae-Woong; Kang, Hong-Gyu; Lim, Pyung-Ok; Lee, Hyo-Yeon

    2011-04-01

    Herbicide-tolerant Zoysia grass has been previously developed through Agrobacterium-mediated transformation. We investigated the effects of genetically modified (GM) Zoysia grass and the associated herbicide application on bacterial community structure by using culture-independent approaches. To assess the possible horizontal gene transfer (HGT) of transgenic DNA to soil microorganisms, total soil DNAs were amplified by PCR with two primer sets for the bar and hpt genes, which were introduced into the GM Zoysia grass by a callus-type transformation. The transgenic genes were not detected from the total genomic DNAs extracted from 1.5 g of each rhizosphere soils of GM and non-GM Zoysia grasses. The structures and diversities of the bacterial communities in rhizosphere soils of GM and non-GM Zoysia grasses were investigated by constructing 16S rDNA clone libraries. Classifier, provided in the RDP II, assigned 100 clones in the 16S rRNA gene sequences library into 11 bacterial phyla. The most abundant phyla in both clone libraries were Acidobacteria and Proteobacteria. The bacterial diversity of the GM clone library was lower than that of the non- GM library. The former contained four phyla, whereas the latter had seven phyla. Phylogenetic trees were constructed to confirm these results. Phylogenetic analyses of the two clone libraries revealed considerable difference from each other. The significance of difference between clone libraries was examined with LIBSHUFF statistics. LIBSHUFF analysis revealed that the two clone libraries differed significantly (P〈0.025), suggesting alterations in the composition of the microbial community associated with GM Zoysia grass.

  11. Characterization of as-grown and annealed GaAs: Structural defects and electrical properties

    SciTech Connect

    Lee, B.T.

    1988-07-01

    Structural defects in GaAs related to excess As were characterized and their behavior upon heat treatments studied. The observed defects included precipitates and dislocations. Results showed most of the precipitates in As-rich GaAs to the rhombohedral arsenic. Two exceptions were observed in an In-doped LEC (liguid encapsulated Czochralski) GaAs, which were As-rich but could not be further identified. Some of the observed As precipitates showed a simple orientation relationship with the matrix which yields structural coherence between As precipitates and GaAs matrix. Other As precipitates showed less coherent orientation. The dislocation loops in As-rich GaAs consisted a faulted loop with Shockley type Burgers vector and a perfect loop associated with an extra /l brace/111/r brace/ plane. It was proposed that these loops were formed as a result of dual condensation of both excess As interstitials and Ga vacancies, followed by generation and movement of Shockley partial dislocations. These precipitates and dislocation loops disappear after annealing, indicating a solvus temperature between 600--700/degree/C. The EL2 concentration increased as the defects dissolved, showing the defects to be the source of the excess As required to form EL2. The implication is that the As interstitial and Ga vacancies coexist in GaAs at high temperatures, which indicates that these point defects are responsible for the formation of arsenic antisites by direct combination. During the cooling period, they freeze into the matrix as point defects during a rapid cooling and condense as dislocation loops and precipitates during very slow cooling, in the dislocation-free region of the crystals. Around dislocations, the excess As precipitates heterogeneously even during rapid cooling. 217 refs.

  12. Atomic structure and stoichiometry of In(Ga)As/GaAs quantum dots grown on an exact-oriented GaP/Si(001) substrate

    SciTech Connect

    Schulze, C. S.; Prohl, C.; Füllert, V.; Rybank, S.; Huang, X.; Lee, M. L.; Maddox, S. J.; March, S. D.; Bank, S. R.; Lenz, A.

    2016-04-04

    The atomic structure and stoichiometry of InAs/InGaAs quantum-dot-in-a-well structures grown on exactly oriented GaP/Si(001) are revealed by cross-sectional scanning tunneling microscopy. An averaged lateral size of 20 nm, heights up to 8 nm, and an In concentration of up to 100% are determined, being quite similar compared with the well-known quantum dots grown on GaAs substrates. Photoluminescence spectra taken from nanostructures of side-by-side grown samples on GaP/Si(001) and GaAs(001) show slightly blue shifted ground-state emission wavelength for growth on GaP/Si(001) with an even higher peak intensity compared with those on GaAs(001). This demonstrates the high potential of GaP/Si(001) templates for integration of III-V optoelectronic components into silicon-based technology.

  13. Structural and optical investigations on seed layer assisted hydrothermally grown ZnO nanorods on flat and textured substrates

    NASA Astrophysics Data System (ADS)

    Rayerfrancis, Arokiyadoss; Balaji Bhargav, P.; Ahmed, Nafis; Balaji, C.; Dhara, Sandip

    2016-12-01

    In this article we report the synthesis of vertically aligned ZnO nanorods on plain as well as textured fluorine doped tin oxide (FTO) coated glass substrate using hydrothermal method. Prior to hydrothermal method, AZO seed layer of thickness 5, 10 and 15 nm were deposited on the chosen substrates by DC magnetron sputtering. The as-grown nanorods were annealed at 450 °C for 3 h to improve the crystallinity. Morphology and structure of the nanorods was observed by field emission scanning electron microscopy. The formation of wurtzite structure was confirmed through x-ray diffraction studies. The optical mode of ZnO, E2 (high) at 434 cm-1 present in the samples was confirmed by Raman spectroscopy. The seed layer assisted growth of ZnO nanorods were defect free, which is confirmed from the photoluminescence spectra, and the intensity of band to band emission is much greater than the emission from the defects at the deep level.

  14. Influence of low-energy plasma annealing on structural and optical properties of silver nanoclusters grown by magnetron sputtering deposition

    NASA Astrophysics Data System (ADS)

    Antad, V.; Simonot, L.; Babonneau, D.

    2014-03-01

    Structural and optical modifications induced by low-energy (≤80 eV) bias-plasma annealing of silver nanoclusters (2-25 nm) grown by magnetron sputtering deposition are reported. By combining postmortem structural characterizations and real-time optical measurements, we show that etching effects associated with enhanced Ag mobility result in progressive and irreversible changes of both the morphology and organization of the nanoclusters (i.e., decrease of the cluster size and intercluster distance as well as increase of their out-of-plane aspect ratio). Surface plasmon resonance bands of the nanoclusters are also modified by plasma treatment, which causes a blue-shift together with an amplitude decrease and a narrowing of the band. In addition, the kinetics of plasma-induced modifications can be easily controlled by varying the applied bias voltage. Therefore, plasma annealing could emerge as an efficient alternative to more traditional thermal annealing treatments for tuning the plasmonic properties of noble metal nanoclusters with great flexibility.

  15. Structure and magnetic properties of flux grown single crystals of Co3-xFexSn2S2 shandites

    NASA Astrophysics Data System (ADS)

    Kassem, Mohamed A.; Tabata, Yoshikazu; Waki, Takeshi; Nakamura, Hiroyuki

    2016-01-01

    We report a successful single crystal growth of the shandite-type half-metallic ferromagnet Co3Sn2S2, and its Fe-substituted compounds, Co3-xFexSn2S2, by employing the flux method. Although Fe3Sn2S2 is unstable phase, we found that using the self Sn flux enables us to obtain single phase crystals up to x=0.53. The chemical composition of the grown plate-shaped single crystals was examined using wavelength-dispersive X-ray spectroscopy. The shandite structure with R 3 ̅m symmetry was confirmed by powder X-ray diffraction and the crystal structure parameters were refined using the Rietveld method. Magnetization measurements show suppression of the ferromagnetic order upon Fe-substitution , as well as in other substituted systems such as In- and Ni-substituted Co3Sn2S2. The almost identical magnetic phase diagrams of the Fe- and In-substituted compounds indicate that the electron number is dominantly significant to the magnetism in the Co-based shandite.

  16. Structural, electrical, and optical characterization of coalescent p-n GaN nanowires grown by molecular beam epitaxy

    SciTech Connect

    Kolkovsky, Vl.; Zytkiewicz, Z. R.; Sobanska, M.; Klosek, K.; Korona, K. P.

    2015-12-14

    The electrical, structural, and optical properties of coalescent p-n GaN nanowires (NWs) grown by molecular beam epitaxy on Si (111) substrate are investigated. From photoluminescence measurements the full width at half maximum of bound exciton peaks AX and DA is found as 1.3 and 1.2 meV, respectively. These values are lower than those reported previously in the literature. The current-voltage characteristics show the rectification ratio of about 10{sup 2} and the leakage current of about 10{sup −4} A/cm{sup 2} at room temperature. We demonstrate that the thermionic mechanism is not dominant in these samples and spatial inhomogeneties and tunneling processes through a ∼2 nm thick SiN{sub x} layer between GaN and Si could be responsible for deviation from the ideal diode behavior. The free carrier concentration in GaN NWs determined by capacitance-voltage measurements is about 4 × 10{sup 15 }cm{sup −3}. Two deep levels (H190 and E250) are found in the structures. We attribute H190 to an extended defect located at the interface between the substrate and the SiN{sub x} interlayer or near the sidewalls at the bottom of the NWs, whereas E250 is tentatively assigned to a gallium-vacancy- or nitrogen interstitials-related defect.

  17. Inhibition of a structural phase transition in one-dimensional organometal halide perovskite nanorods grown inside porous silicon nanotube templates

    NASA Astrophysics Data System (ADS)

    Arad-Vosk, N.; Rozenfeld, N.; Gonzalez-Rodriguez, R.; Coffer, J. L.; Sa'ar, A.

    2017-02-01

    One-dimensional organo-metal halide perovskite (C H3N H3Pb I3 ) nanorods whose diameter and length are dictated by the inner size of porous silicon nanotube templates have been grown, characterized, and compared to bulk perovskites in the form of microwires. We have observed a structural phase transition for bulk perovskites, where the crystal structure changes from tetragonal to orthorhombic at about 160 K, as opposed to small diameter one-dimensional perovskite nanorods, of the order of 30-70 nm in diameter, where the phase transition is inhibited and the dominant phase remains tetragonal. Two major experimental techniques, infrared absorption spectroscopy and photoluminescence, were utilized to probe the temperature dependence of the perovskite phases over the 4-300 K temperature range. Yet, different characteristics of the phase transition were measured by the two spectroscopic methods and explained by the presence of small, tetragonal inclusions embedded in the orthorhombic phase. The inhibition of the phase transition is attributed to the large surface area of these one-dimensional perovskite nanorods, which gives rise to a large stress that, in turn, prevents the formation of the orthorhombic phase. The absence of phase transition enables the measurement of the tetragonal bandgap energy down to low temperatures.

  18. Effect of substrate temperature on the structure of amorphous oxygenated hydrocarbon films grown with a pulsed supersonic methane plasma flow

    NASA Astrophysics Data System (ADS)

    Fedoseeva, Yu. V.; Pozdnyakov, G. A.; Okotrub, A. V.; Kanygin, M. A.; Nastaushev, Yu. V.; Vilkov, O. Y.; Bulusheva, L. G.

    2016-11-01

    Since amorphous oxygenated hydrocarbon (COxHy) films are promising engineering materials a study of the structure and composition of the films depending on the conditions of synthesis is important for controlling of their physicochemical properties. Here, we used the methods of scanning and transmission electron microscopy, X-ray photoelectron, near-edge X-ray absorption fine structure, Fourier transform infrared and Raman spectroscopy to reveal changes in the chemical connectivity of COxHy films grown on silicon substrates heated to 300, 500, and 700 °C using a supersonic flow of methane plasma. It was found that the COxHy films, deposited at 300 and 500 °C, were mainly composed of the sp2-hybridized carbon areas with various oxygen species. A rise of the substrate temperature caused an increase of the portion of tetrahedral carbon atoms as well as carboxyl and hydroxyl groups. With growth of the substrate temperature, the film thickness reduced monotonically from 400 to 180 nm, while the film adhesion improved substantially. The films, deposited at lower temperatures, showed high hydrophilicity due to porosity and presence of oxygenated groups both at the surface and in the bulk.

  19. Selectively grown photonic crystal structures for high efficiency InGaN emitting diodes using nanospherical-lens lithography

    NASA Astrophysics Data System (ADS)

    Wei, Tongbo; Wu, Kui; Lan, Ding; Yan, Qingfeng; Chen, Yu; Du, Chengxiao; Wang, Junxi; Zeng, Yiping; Li, Jinmin

    2012-11-01

    We report a low-cost and high-throughput process for the fabrication of two-dimensional SiO2 photonic crystal (PhC) by nanospherical-lens photolithography method to improve the light extraction of GaN-based light-emitting diodes (LEDs). The PhC structures were realized by the selective area growth of p-GaN using SiO2 nanodisks, which were patterned utilizing a self-assembled nanosphere as an optical lens. Without prejudice to the electrical properties of LEDs, the light output power (at 350 mA) of LEDs with the SiO2 and corresponding air-hole PhC was enhanced by 71.3% and 49.3%, respectively, compared to that without PhC. The LEDs with selectively grown PhC structures were found to exhibit partial compression strain release and reduced emission divergence. The finite-difference time-domain simulation was also performed to further reveal the emission characteristics of PhC LEDs.

  20. Substrate dependent structural, optical and electrical properties of ZnS thin films grown by RF sputtering

    NASA Astrophysics Data System (ADS)

    Pathak, Trilok K.; Kumar, Vinod; Purohit, L. P.; Swart, H. C.; Kroon, R. E.

    2016-10-01

    Zinc sulphide (ZnS) films are of great importance for applications in various optoelectronic devices. ZnS thin films were grown on glass, indium tin oxide (ITO) and Corning glass substrates by radio-frequency magnetron sputtering at a temperature of 373 K and a comparative study of the structural, optical and electrical properties was performed using X-ray diffraction (XRD), scanning electron microscopy, optical and current-voltage (I-V) measurements. The XRD patterns showed that the sputtered thin films exhibited good crystallinity with the (111) peak around 2θ=28.3° indicating preferential orientation of the cubic structure. The maximum strain and most densely packed grains were obtained for the Corning glass substrate. The transmittance spectra of the films were measured in the wavelength range from 200 to 800 nm, showing that the films are about 77% transparent in the visible region. A slight change of 3.50 eV to 3.54 eV was found for the bandgap of the films deposited on different substrates. The ZnS thin films deposited on Corning glass show better crystallinity, morphology and I-V characteristics than that deposited on ordinary glass and ITO substrates.

  1. Opto-structural studies of well-dispersed silicon nano-crystals grown by atom beam sputtering

    PubMed Central

    2012-01-01

    Synthesis and characterization of nano-crystalline silicon grown by atom beam sputtering technique are reported. Rapid thermal annealing of the deposited films is carried out in Ar + 5% H2 atmosphere for 5 min at different temperatures for precipitation of silicon nano-crystals. The samples are characterized for their optical and structural properties using various techniques. Structural studies are carried out by micro-Raman spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy (TEM), high resolution transmission electron microscopy, and selected area electron diffraction. The optical properties are studied by photoluminescence and UV-vis absorption spectroscopy, and bandgaps are evaluated. The bandgaps are found to decrease after rapid thermal treatment. The micro-Raman studies show the formation of nano-crystalline silicon in as-deposited as well as annealed films. The shifting and broadening in Raman peak suggest formation of nano-phase in the samples. Results of micro-Raman, photoluminescence, and TEM studies suggest the presence of a bimodal crystallite size distribution for the films annealed at higher temperatures. The results show that atom beam sputtering is a suitable technique to synthesize nearly mono-dispersed silicon nano-crystals. The size of the nano-crystals may be controlled by varying annealing parameters. PMID:23031449

  2. Structural and optical characterization of MOVPE grown InGaP/GaAs MQWs for advanced photovoltaic devices

    NASA Astrophysics Data System (ADS)

    Longo, M.; Parisini, A.; Tarricone, L.; Vantaggio, S.; Bocchi, C.; Germini, F.; Lazzarini, L.

    2009-09-01

    The optimization of the electronic properties of InGaP/GaAs MQWs, to be inserted in multilayers heterostructure for novel photovoltaic devices, was performed by structural, optical and photoelectrical measurements. Different sequences of nominally undoped InGaP and GaAs alternated layers were grown by low-pressure metalorganic vapour phase epitaxy, employing tertiarybutylarsine and tertiarybutylphosphine as metalorganic precursors for the V-group elements. In order to minimize the As/P exchange effect, the interface In segregation, and to control the whole lattice matching, single and multi-quantum wells (MQWs) with different: (i) periods, (ii) well widths, (iii) growth temperatures, (iv) gas-switching sequences at the interfaces and (v) indium concentrations in the InGaP alloy, were prepared and investigated. The interface sharpness and the compositional fluctuation of thick MQW region containing up to 40 well-barrier sequences were investigated for the modelling, realization and evaluation of test structures based on low-dimensional systems for third generation solar cells.

  3. Structural, electrical, and optical characterization of coalescent p-n GaN nanowires grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Kolkovsky, Vl.; Zytkiewicz, Z. R.; Korona, K. P.; Sobanska, M.; Klosek, K.

    2015-12-01

    The electrical, structural, and optical properties of coalescent p-n GaN nanowires (NWs) grown by molecular beam epitaxy on Si (111) substrate are investigated. From photoluminescence measurements the full width at half maximum of bound exciton peaks AX and DA is found as 1.3 and 1.2 meV, respectively. These values are lower than those reported previously in the literature. The current-voltage characteristics show the rectification ratio of about 102 and the leakage current of about 10-4 A/cm2 at room temperature. We demonstrate that the thermionic mechanism is not dominant in these samples and spatial inhomogeneties and tunneling processes through a ˜2 nm thick SiNx layer between GaN and Si could be responsible for deviation from the ideal diode behavior. The free carrier concentration in GaN NWs determined by capacitance-voltage measurements is about 4 × 1015 cm-3. Two deep levels (H190 and E250) are found in the structures. We attribute H190 to an extended defect located at the interface between the substrate and the SiNx interlayer or near the sidewalls at the bottom of the NWs, whereas E250 is tentatively assigned to a gallium-vacancy- or nitrogen interstitials-related defect.

  4. {CdTe(111) B}/{Si(100) } structure grown by metalorganic vapor phase epitaxy with Te adsorption and annealing

    NASA Astrophysics Data System (ADS)

    Nishino, Hironori; Nishijima, Yoshito

    1996-10-01

    We studied the crystal structure of CdTe(111)B layers directly grown on Si(100) by MOVPE using a new pre-growth process, which includes a metalorganic Te adsorption and an annealing process. In this paper, we discussed the CdTe structure from the three aspects of antiphase, twinning and tilt. We investigated the dependence of the antiphase content in CdTe(111)B on the anneal temperature and the Si misorientation angle. From the results, we assume that the origin of the antiphase formation is the difference in the arrangement of adsorbed Te atoms. Te arrangement leading to antiphase formation occurs on Si terraces away from steps at relatively low temperatures. We reduced most of the twinning in epilayers by optimizing the {VI}/{II} ratio. We think the remaining twinning was confined to near the interface and it nucleated from the Te arrangement on terraces. We found that the Si(100)-CdTe(111) tilt was much smaller than that expected from the well-known Nagai model. We propose that a negative tilt is induced to reduce the lateral mismatch. To adjust the lateral distance of unit cells, 30 CdTe lattices match to 31 Si lattices. CdTe(111)B planes are inclined to reduce the remaining mismatch between two lattices. This initial tilt also causes wider CdTe terraces. We modified Nagai's tilting model for this reconstructed CdTe surface. The total tilt angle is defined by these two tilting mechanisms.

  5. Structural and electrical properties of ultrathin niobium nitride films grown by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Linzen, S.; Ziegler, M.; Astafiev, O. V.; Schmelz, M.; Hübner, U.; Diegel, M.; Il’ichev, E.; Meyer, H.-G.

    2017-03-01

    We studied and optimised the properties of ultrathin superconducting niobium nitride films fabricated with a plasma-enhanced atomic layer deposition (PEALD) process. By adjusting process parameters, the chemical embedding of undesired oxygen into the films was minimised and a film structure consisting of mainly polycrystalline niobium nitride with a small fraction of amorphous niobium oxide and niobium oxo-nitrides were formed. For this composition a critical temperature of 13.8 K and critical current densities of 7 × 106 A cm–2 at 4.2 K were measured on 40 nm thick films. A fundamental correlation between these superconducting properties and the crystal lattice size of the cubic δ-niobium-nitride grains were found. Moreover, the film thickness variation between 40 and 2 nm exhibits a pronounced change of the electrical conductivity at room temperature and reveals a superconductor–insulator-transition in the vicinity of 3 nm film thickness at low temperatures. The thicker films with resistances up to 5 kΩ per square in the normal state turn to the superconducting one at low temperatures. The perfect thickness control and film homogeneity of the PEALD growth make such films extremely promising candidates for developing novel devices on the coherent quantum phase slip effect.

  6. Structural analysis of Gossypium hirsutum fibers grown under greenhouse and hydroponic conditions.

    PubMed

    Natalio, Filipe; Tahir, Muhammad Nawaz; Friedrich, Norman; Köck, Margret; Fritz-Popovski, Gerhard; Paris, Oskar; Paschke, Reinhard

    2016-06-01

    Cotton is the one of the world's most important crops. Like any other crop, cotton growth/development and fiber quality is highly dependent on environmental factors. Increasing global weather instability has been negatively impacting its economy. Cotton is a crop that exerts an intensive pressure over natural resources (land and water) and demands an overuse of pesticides. Thus, the search for alternative cotton culture methods that are pesticide-free (biocotton) and enable customized standard fiber quality should be encouraged. Here we describe a culture of Gossypium hirsutum ("Upland" Cotton) utilizing a greenhouse and hydroponics in which the fibers are morphological similar to conventional cultures and structurally fit into the classical two-phase cellulose I model with 4.19nm crystalline domains surrounded by amorphous regions. These fibers exhibit a single crystalline form of cellulose I-Iß, monoclinic unit cell. Fiber quality bulk analysis shows an improved length, strength, whiteness when compared with soil-based cultures. Finally, we show that our fibers can be spun, used for production of non-woven fabrics and indigo-vat stained demonstrating its potential in industrial and commercial applications. Copyright © 2016 Elsevier Inc. All rights reserved.

  7. Structural, electronic and photovoltaic characterization of multiwalled carbon nanotubes grown directly on stainless steel

    PubMed Central

    Scarselli, Manuela; Gobbo, Silvano Del; Castrucci, Paola; Gautron, Eric; De Crescenzi, Maurizio

    2012-01-01

    Summary We have taken advantage of the native surface roughness and the iron content of AISI-316 stainless steel to grow multiwalled carbon nanotubes (MWCNTs) by chemical vapour deposition without the addition of an external catalyst. The structural and electronic properties of the synthesized carbon nanostructures have been investigated by a range of electron microscopy and spectroscopy techniques. The results show the good quality and the high graphitization degree of the synthesized MWCNTs. Through energy-loss spectroscopy we found that the electronic properties of these nanostructures are markedly different from those of highly oriented pyrolytic graphite (HOPG). Notably, a broadening of the π-plasmon peak in the case of MWCNTs is evident. In addition, a photocurrent was measured when MWCNTs were airbrushed onto a silicon substrate. External quantum efficiency (EQE) and photocurrent values were reported both in planar and in top-down geometry of the device. Marked differences in the line shapes and intensities were found for the two configurations, suggesting that two different mechanisms of photocurrent generation and charge collection are in operation. From this comparison, we are able to conclude that the silicon substrate plays an important role in the production of electron–hole pairs. PMID:23016140

  8. Structural, compositional, and photoluminescence characterization of thermal chemical vapor deposition-grown Zn₃N₂ microtips

    SciTech Connect

    Wei, Pai-Chun E-mail: tsengcm@phys.sinica.edu.tw; Chang, Chung-Chieh; Hsu, Chia-Hao; Tong, Shih-Chang; Shen, Ji-Lin; Tseng, Chuan-Ming E-mail: tsengcm@phys.sinica.edu.tw

    2014-10-14

    The catalytic growth of Zn₃N₂ using guided-stream thermal chemical vapor deposition has been investigated within the parameter range of acicular growth to obtain uniform microtips with a high crystalline quality. The cubic anti-bixbyite crystal structure of Zn₃N₂ microtips and its related phonon mode are revealed by X-ray diffraction and Raman spectroscopy, respectively. The surface morphologies of pure and surface-oxidized Zn₃N₂ microtips are depicted by scanning electron microscopy and show the crack formation on the surface-oxidized Zn₃N₂ microtips. The spatial element distribution map confirms the VLS growth mechanism for Zn₃N₂ microtips and reveals the depth profile of zinc, nitrogen, oxygen, and nickel elements. Photoluminescence (PL) spectra of Zn₃N₂ microtips show a sharp infrared band-to-band emission peak at 1.34 eV with a full width at half maximum of ~100 meV and a very broad oxygen-related defect band emission peak centered at ~0.85 eV.

  9. Structural Characteristics of La2O3 Thin Film Grown on LaB6

    NASA Astrophysics Data System (ADS)

    Kafadaryan, Y. A.; Petrosyan, S. I.; Badalyan, G. R.; Lazaryan, V. G.; Shirinyan, G. H.; Aghamalyan, N. R.; Hovsepyan, R. K.; Semerjian, H. S.; Igityan, A. S.; Kuzanyan, A. M.

    Within the framework of hexagonal lanthanum oxide (h-La2O3) formation, lanthanum hexaboride film on sapphire substrate (LaB6/Al2O3) was oxidized at different temperatures (700-1000 °C) under reduced atmospheric pressure (1·10-2,1.5·10-1Torr) during 30 min. The composition evolution of La2O3/LaB6 structure versus annealing temperature has been studied using XRD, FIR reflectivity spectroscopy, SEM and electron probe X-ray microanalysis (EDS). The annealing of the LaB6 film at T=700 °C under air pressure of 1·10-2 Torr generates thin La2O3 layer which exhibits as inferred from XRD the hexagonal phase. The hydratation of La2O3/LaB6/Al2O3 in distilled water for 30 min and postannealing at 900 °C under air pressure of 1.5·10-1 Torr transform h-La2O3 into hexagonal La(OH)3 phase accompanied monoclinic LaO(OH) and lanthanum oxide carbonate hydrate species.

  10. Structure and ionic conductivity of well-aligned polycrystalline sodium titanogallate grown by reactive diffusion

    SciTech Connect

    Hasegawa, Ryo; Okabe, Momoko; Asaka, Toru; Ishizawa, Nobuo; Fukuda, Koichiro

    2015-09-15

    We prepared the b-axis-oriented polycrystalline Na{sub 0.85}Ti{sub 0.51}Ga{sub 4.37}O{sub 8} (NTGO) embedded in Ga{sub 2}O{sub 3}-doped Na{sub 2}Ti{sub 4}O{sub 9} matrix using the reactive diffusion technique. When the sandwich-type Ga{sub 2}TiO{sub 5}/NaGaO{sub 2}/Ga{sub 2}TiO{sub 5} diffusion couple was heated at 1323 K for 24 h, the NTGO polycrystal was readily formed in the presence of a liquid phase. The resulting polycrystalline material was characterized by X-ray diffractometry, electron microscopy and impedance spectroscopy. We mechanically processed the annealed diffusion couple and obtained the thin-plate electrolyte consisting mostly of the grain-aligned NTGO polycrystal. The ionic conductivity (σ) of the electrolyte along the common b-axis direction steadily increased from 1.3×10{sup −4} to 7.3×10{sup −3} S/cm as the temperature increased from 573 to 1073 K. There was a slope change at ca. 792 K for the Arrhenius plot of σ; the activation energies were 0.39 eV above this temperature and 0.57 eV below it. The NTGO showed the crystal structure (space group C2/m) with substantial positional disordering of one of the two Ga sites. The Na{sup +} ions occupied ca. 43% of the Wyckoff position 4i site, the deficiency of which would contribute to the relatively high ionic conductivity along the b-axis. The reactive diffusion could be widely applicable as the novel technique to the preparation of grain-aligned ceramics of multi-component systems. - Graphical abstract: We have prepared the b-axis-oriented Na{sub 0.85}Ti{sub 0.51}Ga{sub 4.37}O{sub 8} polycrystal embedded in Ga{sub 2}O{sub 3}-doped Na{sub 2}Ti{sub 4}O{sub 9} matrix by the heat treatment of sandwich-type diffusion couple of Ga{sub 2}TiO{sub 5}/NaGaO{sub 2}/Ga{sub 2}TiO{sub 5}. The resulting Na{sub 0.85}Ti{sub 0.51}Ga{sub 4.37}O{sub 8} electrolyte showed the ionic conductivity ranging from 1.3×10{sup −4} S/cm at 573 K to 7.3×10{sup −3} S/cm at 1073 K. - Highlights: • The b

  11. Measuring the electronic structure of atomically uniform silver films grown on silicon using angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Speer, Nathan James

    Electronic structures derived from Valence electrons in thin films and at surfaces are often much different from those of their bulk counter parts. When the film thickness is less than the electron-coherence length, the boundary conditions at the surface and interface can give rise to standing-wave-like quantum-well states. Electrons in these states are often described as particles in a box. Confinement in the perpendicular direction gives rise to a quantized band structure along the same direction, where the energy spacing is determined by the film thickness. Changing the film by a single atomic layer can cause properties derived from the band structure to vary like ˜ 1/N , where N is the number of monolayers. Recent advances in thin film techniques have made it possible to fabricate films with atomically uniform thickness. Because the electronic structure is a function of film thickness, such techniques are crucial to efforts for a comprehensive understanding of thin films. In this thesis, the electronic properties of atomically uniform Ag films grown on Si(111) substrates are studied using angle-resolved photoemission spectroscopy (ARPES). Using molecular beam epitaxy (MBE) deposition at low temperatures, we are able to fabricate atomically uniform, ultra-thin Ag films on Si substrates for the first time, and the electronic structures are measured using ARPES. The electrons in these uniform film systems have very long coherence lengths and occupy standing-wave-like quantum-well states that propagate through the film and, surprisingly, can reach deep into the substrate despite a lattice mismatched, incommensurate interface. This interaction with the substrate is so strong that it can produce an electronic interference pattern in the photoemission spectra. As the film thickness increases, the electronic structure evolves to form the bulk band continuum plus separates surfaces states. A careful analysis of this evolution allows us to separate surface from bulk

  12. Structural, morphological, and optoelectrical characterization of Bi2S3 thin films grown by co-evaporation

    NASA Astrophysics Data System (ADS)

    Mesa, F.; Arredondo, C. A.; Vallejo, W.

    2016-03-01

    This work presents the results of synthesis and characterization of polycrystalline n-type Bi2S3 thin films. The films were grown through a chemical reaction from co-evaporation of their precursor elements in a soda-lime glass substrate. The effect of the experimental conditions on the optical, morphological structural properties, the growth rate, and the electrical conductivity (σ) was studied through spectral transmittance, X-ray diffraction (XRD), atomic force microscopy (AFM) and σ versus T measurements, respectively. The results showed that the films grow only in the orthorhombic Bi2S3 bismuthinite phase. It was also found that the Bi2S3 films present an energy band gap (Eg) of about 1.38 eV. In addition to these results, the electrical conductivity of the Bi2S3 films was affected by both the transport of free carriers in extended states of the conduction band and for variable range hopping transport mechanisms, each one predominating in a different temperature range.

  13. Structural and optical characterization of GaAs nano-crystals selectively grown on Si nano-tips by MOVPE.

    PubMed

    Skibitzki, Oliver; Prieto, Ivan; Kozak, Roksolana; Capellini, Giovanni; Zaumseil, Peter; Arroyo Rojas Dasilva, Yadira; Rossell, Marta D; Erni, Rolf; von Känel, Hans; Schroeder, Thomas

    2017-03-01

    We present the nanoheteroepitaxial growth of gallium arsenide (GaAs) on nano-patterned silicon (Si) (001) substrates fabricated using a CMOS technology compatible process. The selective growth of GaAs nano-crystals (NCs) was achieved at 570 °C by MOVPE. A detailed structure and defect characterization study of the grown nano-heterostructures was performed using scanning transmission electron microscopy, x-ray diffraction, micro-Raman, and micro-photoluminescence (μ-PL) spectroscopy. The results show single-crystalline, nearly relaxed GaAs NCs on top of slightly, by the SiO2-mask compressively strained Si nano-tips (NTs). Given the limited contact area, GaAs/Si nanostructures benefit from limited intermixing in contrast to planar GaAs films on Si. Even though a few growth defects (e.g. stacking faults, micro/nano-twins, etc) especially located at the GaAs/Si interface region were detected, the nanoheterostructures show intensive light emission, as investigated by μ-PL spectroscopy. Achieving well-ordered high quality GaAs NCs on Si NTs may provide opportunities for superior electronic, photonic, or photovoltaic device performances integrated on the silicon technology platform.

  14. Structural and optical characterization of GaAs nano-crystals selectively grown on Si nano-tips by MOVPE

    NASA Astrophysics Data System (ADS)

    Skibitzki, Oliver; Prieto, Ivan; Kozak, Roksolana; Capellini, Giovanni; Zaumseil, Peter; Arroyo Rojas Dasilva, Yadira; Rossell, Marta D.; Erni, Rolf; von Känel, Hans; Schroeder, Thomas

    2017-03-01

    We present the nanoheteroepitaxial growth of gallium arsenide (GaAs) on nano-patterned silicon (Si) (001) substrates fabricated using a CMOS technology compatible process. The selective growth of GaAs nano-crystals (NCs) was achieved at 570 °C by MOVPE. A detailed structure and defect characterization study of the grown nano-heterostructures was performed using scanning transmission electron microscopy, x-ray diffraction, micro-Raman, and micro-photoluminescence (μ-PL) spectroscopy. The results show single-crystalline, nearly relaxed GaAs NCs on top of slightly, by the SiO2-mask compressively strained Si nano-tips (NTs). Given the limited contact area, GaAs/Si nanostructures benefit from limited intermixing in contrast to planar GaAs films on Si. Even though a few growth defects (e.g. stacking faults, micro/nano-twins, etc) especially located at the GaAs/Si interface region were detected, the nanoheterostructures show intensive light emission, as investigated by μ-PL spectroscopy. Achieving well-ordered high quality GaAs NCs on Si NTs may provide opportunities for superior electronic, photonic, or photovoltaic device performances integrated on the silicon technology platform.

  15. Structural and Magnetotransport Study of SrTiO3-δ/Si Films Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Currie, Alex; Cottier, Ryan; Villarreal, Oscar; Cantu, Jesus; Ponce, Arturo; Theodoropoulou, Nikoleta; Texas State University, San Marcos Collaboration; University of Texas, San Antonio Collaboration

    2014-03-01

    SrTiO3 (STO) films were grown on p-Si (001) substrates using molecular beam epitaxy (MBE). Oxygen vacancies were introduced by controlling the Oxygen resulting in SrTiO3-δ with δ ~ 0.02% for the lowest pressure. The single phase STO/Si films were of high crystalline quality as verified by x-ray diffraction, transmission electron microscopy, and had an rms roughness of less than 0.5nm measured by atomic force microscopy. Transport measurements were performed on the STO/Si structures in a Van der Pauw configuration. We measured resistance as a function of temperature, T = 3K-300K and as a function of an applied magnetic field , H =0 to +/- 9T. The resistivity decreased from 1 Ohm cm to 3x10-2 Ohm cm as the film thickness increased (3nm-60nm) for all temperatures. The magnetoresistance (MR) shows a reproducible trend for all films, the MR is positive at 300K, becomes negative between 200K and 100K and at low temperatures T =3-20K the MR is positive at low H =0 to +/- 2T but at high fields, it starts decreasing again. The MR behavior combined with the Hall effect data indicates the presence of localized electrons that delocalize with H and T. This research was supported by NSF Carrer Award DMR-1255629.

  16. Effect of gas flow rate on structural properties of zinc oxide nanowires grown by vapor-solid mechanism

    NASA Astrophysics Data System (ADS)

    Sakrani, S.; Jamaludin, N.; Muhammad, R.; Wahab, Y.; Ismail, A. K.; Suhaimi, S.; Mohammed, Y. H.

    2016-07-01

    ZnO nanowires have been grown on pre-coated (ZnO thin film) silicon (100) substrates with special attention on the effect of gas flow rate. The samples were fabricated using a simple thermal evaporation method within a horizontal quartz tube under controlled supply of Ar and O2 gas where ZnO powder source were previously weighed and heated at 960 °C for 2 h, allowing the reactant vapors to deposit onto substrate to form the nanowires. FESEM images revealed the randomly-oriented nanowires in which the shapes varied with increasing gas flow rates from varied from 90 to 130 sccm. According, both diameter and aspect ratio of the nanowires was observed to shift at 110 sccm where optimum growth condition was expected at this gas flow rate. From EDX spectrum analysis, ZnO nanowires appeared to have uniform composition and purity and confirming the hexagonal wurtzite crystal structure. These measured parameters in combination with unique properties made the possibility of ZnO nanowires potentially useful for functional nanodevices.

  17. Investigation on structural, optical and electrical properties of Cp2Mg flow varied p-GaN grown by MOCVD

    NASA Astrophysics Data System (ADS)

    Surender, S.; Pradeep, S.; Ramesh, R.; Baskar, K.

    2016-05-01

    In this work the effect of different concentration of Magnesium doped GaN (p-GaN) were systematically studied. The p-GaN epilayers were grown on c-plane sapphire substrate by horizontal flow Metal Organic Chemical Vapor Deposition (MOCVD) with various flow rates of 100 sccm to 300 sccm using bis-(cyclopentadienyl) - magnesium (Cp2Mg) precursor. The samples were subjected to structural, optical, morphological and electrical studies using High Resolution X-ray diffraction (HRXRD), room temperature photoluminescence (PL), Atomic Force Microscopy (AFM) and Hall measurement respectively. Results indicated that the Mg doped GaN of 200 sccm Cp2Mg has the root mean square (rms) roughness of about 0.3 nm for a scan area of 5×5 µm2 which has good two dimensional growth. Moreover, Hall measurements results shows that (200 sccm Cp2Mg) Mg-doped GaN possess the highest hole concentration of 5.4×1017cm-3 and resistivity of 1.7 Ωcm at room temperature.

  18. Effect of oxygen surfactant on the magnetic and structural properties of Co films grown on Cu(110)

    SciTech Connect

    Ling, W.L.; Qiu, Z.Q.; Takeuchi, O.; Ogletree, D.F.; Salmeron, M.

    2000-04-13

    It was found that atomically flat Co(110) film could be grown on Cu(110) using O as a surfactant. To obtain detailed knowledge on the effect of O on the growth, as well as on the magnetic properties of Co overlayer, we carried out an investigation on this system using Auger Electron Spectroscopy (AES), Low Energy Electron Diffraction (LEED), Surface Magneto-Optic Kerr Effect (SMOKE), and Scanning Tunneling Microscopy (STM). With O as a surfactant, the initial growth of Co (< 1 ML) results in a flat monolayer structure. When the Co is thicker than 1 ML, three-dimensional clusters begin to form. These clusters become ordered islands at 3 ML Co and coalesce at about 5 ML Co. Above 5 ML Co, layer-by-layer growth resumes. No Cu segregation is observed. SMOKE studies at room temperature show that the Co film is magnetic above about 5 ML Co, with the magnetization easy axis along the [001] direction. On the other hand, without using oxygen as a surfactant, Co grows three-dimensionally on Cu(110). The Co overlayer has its easy magnetization axis along the [001] direction, but the onset of the magnetization was observed at 11 ML Co at room temperature.

  19. Investigation on structural, optical and electrical properties of Cp2Mg flow varied p-GaN grown by MOCVD

    SciTech Connect

    Surender, S.; Pradeep, S.; Ramesh, R.; Baskar, K.

    2016-05-23

    In this work the effect of different concentration of Magnesium doped GaN (p-GaN) were systematically studied. The p-GaN epilayers were grown on c-plane sapphire substrate by horizontal flow Metal Organic Chemical Vapor Deposition (MOCVD) with various flow rates of 100 sccm to 300 sccm using bis-(cyclopentadienyl) - magnesium (Cp2Mg) precursor. The samples were subjected to structural, optical, morphological and electrical studies using High Resolution X-ray diffraction (HRXRD), room temperature photoluminescence (PL), Atomic Force Microscopy (AFM) and Hall measurement respectively. Results indicated that the Mg doped GaN of 200 sccm Cp2Mg has the root mean square (rms) roughness of about 0.3 nm for a scan area of 5×5 µm{sup 2} which has good two dimensional growth. Moreover, Hall measurements results shows that (200 sccm Cp2Mg) Mg-doped GaN possess the highest hole concentration of 5.4×10{sup 17}cm{sup −3} and resistivity of 1.7 Ωcm at room temperature.

  20. Thin yttrium iron garnet films grown by pulsed laser deposition: Crystal structure, static, and dynamic magnetic properties

    SciTech Connect

    Sokolov, N. S. Fedorov, V. V.; Korovin, A. M.; Suturin, S. M.; Baranov, D. A.; Gastev, S. V.; Krichevtsov, B. B.; Bursian, V. E.; Lutsev, L. V.; Maksimova, K. Yu.; Grunin, A. I.; Tabuchi, M.

    2016-01-14

    Pulsed laser deposition has been used to grow thin (10–84 nm) epitaxial layers of Yttrium Iron Garnet Y{sub 3}Fe{sub 5}O{sub 12} (YIG) on (111)–oriented Gadolinium Gallium Garnet substrates at different growth conditions. Atomic force microscopy showed flat surface morphology both on micrometer and nanometer scales. X-ray diffraction measurements revealed that the films are coherent with the substrate in the interface plane. The interplane distance in the [111] direction was found to be by 1.2% larger than expected for YIG stoichiometric pseudomorphic film indicating presence of rhombohedral distortion in this direction. Polar Kerr effect and ferromagnetic resonance measurements showed existence of additional magnetic anisotropy, which adds to the demagnetizing field to keep magnetization vector in the film plane. The origin of the magnetic anisotropy is related to the strain in YIG films observed by XRD. Magneto-optical Kerr effect measurements revealed important role of magnetization rotation during magnetization reversal. An unusual fine structure of microwave magnetic resonance spectra has been observed in the film grown at reduced (0.5 mTorr) oxygen pressure. Surface spin wave propagation has been demonstrated in the in-plane magnetized films.

  1. Piezoelectric InAs (211)B quantum dots grown by molecular beam epitaxy: Structural and optical properties

    SciTech Connect

    Dialynas, G. E.; Kalliakos, S.; Xenogianni, C.; Androulidaki, M.; Kehagias, T.; Komninou, P.; Savvidis, P. G.; Pelekanos, N. T.; Hatzopoulos, Z.

    2010-11-15

    The structural and optical properties of piezoelectric (211)B InAs nanostructures grown by molecular beam epitaxy are systematically investigated as a function of the various growth parameters. Depending on the specific growth conditions, we show that the InAs nanostructures take the form of a quantum dot (QD) or a quantum dash, their height ranges between 2 and 20 nm, and their density varies from a few times 10{sup 8} cm{sup -2} all the way up to a few times 10{sup 10} cm{sup -2}. The (211)B QDs are characterized by large aspect ratios, which are compatible with a truncated pyramid morphology. By analyzing the QD emission spectrum, we conclude that only small size QDs, with heights less than 3 nm, are optically active. This is consistent with high resolution transmission electron microscopy observations showing that large QDs contain misfit dislocations, whereas small QDs are dislocation-free. The formation of a two-dimensional wetting layer is observed optically, and its thickness is determined to be between 0.30 and 0.39 nm. Finally, the large blueshift in the QD emission observed with increasing excitation power represents a clear evidence of the strong built-in piezoelectric field present in these dots.

  2. Electronic structure, morphology and emission polarization of enhanced symmetry InAs quantum-dot-like structures grown on InP substrates by molecular beam epitaxy

    SciTech Connect

    Maryński, A.; Sĕk, G.; Musiał, A.; Andrzejewski, J.; Misiewicz, J.; Gilfert, C.; Reithmaier, J. P.; Capua, A.; Karni, O.; Gready, D.; Eisenstein, G.; Atiya, G.; Kaplan, W. D.; Kölling, S.

    2013-09-07

    The optical and structural properties of a new kind of InAs/InGaAlAs/InP quantum dot (QD)-like objects grown by molecular beam epitaxy have been investigated. These nanostructures were found to have significantly more symmetrical shapes compared to the commonly obtained dash-like geometries typical of this material system. The enhanced symmetry has been achieved due to the use of an As{sub 2} source and the consequent shorter migration length of the indium atoms. Structural studies based on a combination of scanning transmission electron microscopy (STEM) and atom probe tomography (APT) provided detailed information on both the structure and composition distribution within an individual nanostructure. However, it was not possible to determine the lateral aspect ratio from STEM or APT. To verify the in-plane geometry, electronic structure calculations, including the energy levels and transition oscillator strength for the QDs have been performed using an eight-band k·p model and realistic system parameters. The results of calculations were compared to measured polarization-resolved photoluminescence data. On the basis of measured degree of linear polarization of the surface emission, the in-plane shape of the QDs has been assessed proving a substantial increase in lateral symmetry. This results in quantum-dot rather than quantum-dash like properties, consistent with expectations based on the growth conditions and the structural data.

  3. Optical, electrical, and X-ray-structural studies on Verneuil-grown SrTiO 3 single crystal: Annealing study

    NASA Astrophysics Data System (ADS)

    Mochizuki, S.; Fujishiro, F.; Shibata, K.; Ogi, A.; Konya, T.; Inaba, K.

    2007-12-01

    In order to clarify crystal defect effects on the physical phenomena observed for a SrTiO 3 single crystal grown by Verneuil method, the optical density and photoluminescence spectra, complex impedance spectra, and crystal structure were fully studied for the as-grown crystal boule. The as-grown crystal boule consists of a shell (which is colorless transparent and electrically good insulator) and a core (which is dark blue and has a high electrical conductivity (>10 -3 Ω -1cm -1), and a colossal static dielectric constant (>10 6) at room temperature). The as-grown single crystal was then annealed at 973 K in an Ar-H 2 gas stream. With the progressing of annealing, the as-grown single crystal becomes colorless-transparent insulator and the static dielectric constant decreases down to approximately 300 at room temperature. The X-ray crystallographic studies indicate that the crystallinity is almost independent of the annealing, while the dielectric property is considerably affected by the annealing. A model on the basis of a (Ti 3+-oxygen vacancy) complex defect is proposed for explaining the observed properties of SrTiO 3.

  4. Optical properties and structure of HfO2 thin films grown by high pressure reactive sputtering

    NASA Astrophysics Data System (ADS)

    Martínez, F. L.; Toledano-Luque, M.; Gandía, J. J.; Cárabe, J.; Bohne, W.; Röhrich, J.; Strub, E.; Mártil, I.

    2007-09-01

    Thin films of hafnium oxide (HfO2) have been grown by high pressure reactive sputtering on transparent quartz substrates (UV-grade silica) and silicon wafers. Deposition conditions were adjusted to obtain polycrystalline as well as amorphous films. Optical properties of the films deposited on the silica substrates were investigated by transmittance and reflectance spectroscopy in the ultraviolet, visible and near infrared range. A numerical analysis method that takes into account the different surface roughness of the polycrystalline and amorphous films was applied to calculate the optical constants (refractive index and absorption coefficient). Amorphous films were found to have a higher refractive index and a lower transparency than polycrystalline films. This is attributed to a higher density of the amorphous samples, which was confirmed by atomic density measurements performed by heavy-ion elastic recoil detection analysis. The absorption coefficient gave an excellent fit to the Tauc law (indirect gap), which allowed a band gap value of 5.54 eV to be obtained. The structure of the films (amorphous or polycrystalline) was found to have no significant influence on the nature of the band gap. The Tauc plots also give information about the structure of the films, because the slope of the plot (the Tauc parameter) is related to the degree of order in the bond network. The amorphous samples had a larger value of the Tauc parameter, i.e. more order than the polycrystalline samples. This is indicative of a uniform bond network with percolation of the bond chains, in contrast to the randomly oriented polycrystalline grains separated by grain boundaries.

  5. Microstructures and growth mechanisms of GaN films epitaxially grown on AlN/Si hetero-structures by pulsed laser deposition at different temperatures

    PubMed Central

    Wang, Wenliang; Yang, Weijia; Lin, Yunhao; Zhou, Shizhong; Li, Guoqiang

    2015-01-01

    2 inch-diameter GaN films with homogeneous thickness distribution have been grown on AlN/Si(111) hetero-structures by pulsed laser deposition (PLD) with laser rastering technique. The surface morphology, crystalline quality, and interfacial property of as-grown GaN films are characterized in detail. By optimizing the laser rastering program, the ~300 nm-thick GaN films grown at 750 °C show a root-mean-square (RMS) thickness inhomogeneity of 3.0%, very smooth surface with a RMS surface roughness of 3.0 nm, full-width at half-maximums (FWHMs) for GaN(0002) and GaN(102) X-ray rocking curves of 0.7° and 0.8°, respectively, and sharp and abrupt AlN/GaN hetero-interfaces. With the increase in the growth temperature from 550 to 850 °C, the surface morphology, crystalline quality, and interfacial property of as-grown ~300 nm-thick GaN films are gradually improved at first and then decreased. Based on the characterizations, the corresponding growth mechanisms of GaN films grown on AlN/Si hetero-structures by PLD with various growth temperatures are hence proposed. This work would be beneficial to understanding the further insight of the GaN films grown on Si(111) substrates by PLD for the application of GaN-based devices. PMID:26563573

  6. The Application of Iii-V Semiconductor Heterojunction Structures Grown by Molecular Beam Epitaxy to Microwave Devices

    NASA Astrophysics Data System (ADS)

    Schaff, William Joseph

    Semiconductor devices capable of higher speeds and higher frequency operation have been a subject of great interest for many years. New fabrication techniques have provided the tools for pushing conventional device performance to new limits. These new techniques have also made possible entirely new clases of devices such as inverted High Electron Mobility Transistors and AlGaAs buffered GaAs MESFETs. The production of such state of the art devices invariably leads to a discovery of materials and process limitations that need to be eliminated. The requirement for achieving changes in composition in semiconductor materials within a single atomic layer is central to the above devices as well as many proposed devices. Molecular Beam Epitaxy has already produced materials with atomic monolayer abruptness in some structures. There are however, some desirable structures that have not been successfully produced by this technique. The fundamental problem is that good quality AlGaAs/GaAs interfaces for GaAs on AlGaAs have not been obtained when the thickness of the AlGaAs is comparable to that needed for inverted High Electron Mobility Transistors or AlGaAs buffered power Field Effect Transistors. It has been found that impurity contamination of GaAs grown on top of AlGaAs can be a severe problem. The purpose of this work is to understand the difficulties which occur and demonstrate the successful application of some techniques which minimize, or eliminate, some of the limitations on current and anticipated device performance. The concept of impurity gettering by an interface and a form of strained layer superlattice effected lattice matching are explored for GaAs and AlGaAs structures. A GaAs MESFET has been fabricated on a superlattice buffer for the first time. It has superior performance to devices with simpler structures. The improved material properties obtained by substitution of a superlattice buffer for the homogeneous GaAs buffer are measured, as a final test, by

  7. Shifts in microbial community structure and function in light- and dark-grown biofilms driven by warming.

    PubMed

    Romaní, Anna M; Borrego, Carles M; Díaz-Villanueva, Verónica; Freixa, Anna; Gich, Frederic; Ylla, Irene

    2014-08-01

    Biofilms are dynamic players in biogeochemical cycling in running waters and are subjected to environmental stressors like those provoked by climate change. We investigated whether a 2°C increase in flowing water would affect prokaryotic community composition and heterotrophic metabolic activities of biofilms grown under light or dark conditions. Neither light nor temperature treatments were relevant for selecting a specific bacterial community at initial phases (7-day-old biofilms), but both variables affected the composition and function of mature biofilms (28-day-old). In dark-grown biofilms, changes in the prokaryotic community composition due to warming were mainly related to rotifer grazing, but no significant changes were observed in functional fingerprints. In light-grown biofilms, warming also affected protozoan densities, but its effect on prokaryotic density and composition was less evident. In contrast, heterotrophic metabolic activities in light-grown biofilms under warming showed a decrease in the functional diversity towards a specialized use of several carbohydrates. Results suggest that prokaryotes are functionally redundant in dark biofilms but functionally plastic in light biofilms. The more complex and self-serving light-grown biofilm determines a more buffered response to temperature than dark-grown biofilms. Despite the moderate increase in temperature of only 2°C, warming conditions drive significant changes in freshwater biofilms, which responded by finely tuning a complex network of interactions among microbial populations within the biofilm matrix.

  8. Growth parameter dependence of structural, electrical and magnetic properties in GaGdN layers grown on GaN(0001)

    NASA Astrophysics Data System (ADS)

    Sano, S.; Hasegawa, S.; Mitsuno, Y.; Higashi, K.; Ishimaru, M.; Sakurai, T.; Ohta, H.; Asahi, H.

    2013-09-01

    The growth parameter dependence of structural, electrical and magnetic properties in Gd-doped GaN layers grown by plasma-assisted molecular beam epitaxy has been investigated. The structural and magnetic properties of Gd-doped GaN films grown on GaN templates strongly depend on the MBE growth condition. While Gd-doped GaN grown under relatively high Ga fluxes consist of wurtzite GaGdN layers without Gd-related precipitates, Gd-incorporated GaN films grown under low Ga fluxes contain a lot of nanoparticles ranging from several nm to several tens nm in size. The samples with Gd-related nanoparticles exhibit hysteresis in the magnetization-magnetic field curves at 10 K. The separation between the field-cooled and zero-field-cooled magnetization-temperature curves is observed at around 30 K. This behavior is understood in terms of super-paramagnetism originating from the ferromagnetic nanoparticles observed in the cross-sectional transmission electron microscopy images.

  9. 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.

  10. Structural and optical properties of InGaN-GaN nanowire heterostructures grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Limbach, F.; Gotschke, T.; Stoica, T.; Calarco, R.; Sutter, E.; Ciston, J.; Cusco, R.; Artus, L.; Kremling, S.; Höfling, S.; Worschech, L.; Grützmacher, D.

    2011-01-01

    InGaN/GaN nanowire (NW) heterostructures grown by plasma assisted molecular beam epitaxy were studied in comparison to their GaN and InGaN counterparts. The InGaN/GaN heterostructure NWs are composed of a GaN NW, a thin InGaN shell, and a multifaceted InGaN cap wrapping the top part of the GaN NW. High-resolution transmission electron microscopy (HRTEM) images taken from different parts of a InGaN/GaN NW show a wurtzite structure of the GaN core and the epitaxial InGaN shell around it, while additional crystallographic domains are observed whithin the InGaN cap region. Large changes in the lattice parameter along the wire, from pure GaN to higher In concentration demonstrate the successful growth of a complex InGaN/GaN NW heterostructure. Photoluminescence (PL) spectra of these heterostructure NW ensembles show rather broad and intense emission peak at 2.1 eV. However, μ-PL spectra measured on single NWs reveal a reduced broadening of the visible luminescence. The analysis of the longitudinal optical phonon Raman peak position and its shape reveal a variation in the In content between 20% and 30%, in agreement with the values estimated by PL and HRTEM investigations. The reported studies are important for understanding of the growth and properties of NW heterostructures suitable for applications in optoelectronics and photovoltaics.

  11. Characterization of structural defects in MLEK grown InP single crystals using synchrotron white beam X-ray topography

    NASA Astrophysics Data System (ADS)

    Chung, H.; Si, W.; Dudley, M.; Anselmo, A.; Bliss, D. F.; Maniatty, A.; Zhang, H.; Prasad, V.

    1997-04-01

    Structural defects in MLEK grown InP single crystals have been studied using synchrotron white beam X-ray topography. Results here are presented for both a S-doped boule which was wafered longitudinally (i.e., parallel to the growth axis) and an Fe-doped boule which was wafered laterally (i.e., perpendicular to the growth axis). For longitudinal wafers from the S-doped boule, slip bands were observed to have nucleated from high-stress concentration located at the peripheral regions of the boule and to have propagated into the interior of the samples. In the same crystals, the growth interface morphology at different stages of crystal growth was determined. The interface is revealed as contours of equal lattice parameter, visible via strain contrast, as the concentration of the dopant changed periodically during growth. The interface shape was observed to be slightly convex to the melt, once the growth conditions were stabilized. For the laterally sliced wafers from the Fe-doped boule, systematic studies revealed that the density of dislocations changed during growth. A high density of uniformly distributed dislocations were observed in wafers taken from the early and later stages of growth. On the other hand, dislocations in well-defined four-fold symmetric distributions were observed in wafers sliced from the intermediate growth stages. The origins of this four-fold distribution were investigated using a thermal stress model which consisted of imposing a compressive radial stress, uniformly distributed around the boule circumference. The calculated stress distributions also showed four-fold symmetry in agreement with the observed dislocation distributions.

  12. Local Structures and Interface Morphology of InGaAsN Thin Films Grown on GaAs

    SciTech Connect

    Allerman, A.A.; Chen, J.G.; Geisz, J.F.; Huang, S.; Hulbert, S.L.; Jones, E.D.; Kao, Y.H.; Kurtz, S.; Kurtz, S.R.; Olson, J.M.; Soo, Y.L.

    1999-02-23

    The compound semiconductor system InGaAsN exhibits many intriguing properties which are particularly useful for the development of innovative high efficiency thin film solar cells and long wavelength lasers. The bandgap in these semiconductors can be varied by controlling the content of N and In and the thin films can yet be lattice-matched to GaAs. In the present work, x-ray absorption fine structure (XAFS) and grazing incidence x-ray scattering (GIXS) techniques have been employed to probe the local environment surrounding both N and In atoms as well as the interface morphology of InGaAsN thin films epitaxially grown on GaAs. The soft x-ray XAFS results around nitrogen K-edge reveal that N is in the sp{sup 3} hybridized bonding configuration in InGaAsN and GaAsN, suggesting that N impurities most likely substitute for As sites in these two compounds. The results of In K-edge XAFS suggest a possible trend of a slightly larger coordination number of As nearest neighbors around In atoms in InGaAsN samples with a narrower bandgap whereas the In-As interatomic distance remains practically the same as in InAs within the experimental uncertainties. These results combined suggest that N-substitution of the As sites plays an important role of bandgap-narrowing while in the meantime counteracting the compressive strain caused by In-doping. Grazing incidence x-ray scattering (GIXS) experiments verify that InGaAsN thin films can indeed form very smooth interfaces with GaAs yielding an average interfacial roughness of 5-20{angstrom}.

  13. Structural and optical properties of InGaN--GaN nanowire heterostructures grown by molecular beam epitaxy

    DOE PAGES

    Limbach, F.; Gotschke, T.; Stoica, T.; ...

    2011-01-01

    InGaN/GaN nanowire (NW) heterostructures grown by plasma assisted molecular beam epitaxy were studied in comparison to their GaN and InGaN counterparts. The InGaN/GaN heterostructure NWs are composed of a GaN NW, a thin InGaN shell, and a multifaceted InGaN cap wrapping the top part of the GaN NW. High-resolution transmission electron microscopy (HRTEM) images taken from different parts of a InGaN/GaN NW show a wurtzite structure of the GaN core and the epitaxial InGaN shell around it, while additional crystallographic domains are observed whithin the InGaN cap region. Large changes in the lattice parameter along the wire, from pure GaNmore » to higher In concentration demonstrate the successful growth of a complex InGaN/GaN NW heterostructure. Photoluminescence (PL) spectra of these heterostructure NW ensembles show rather broad and intense emission peak at 2.1 eV. However, μ-PL spectra measured on single NWs reveal a reduced broadening of the visible luminescence. The analysis of the longitudinal optical phonon Raman peak position and its shape reveal a variation in the In content between 20% and 30%, in agreement with the values estimated by PL and HRTEM investigations. The reported studies are important for understanding of the growth and properties of NW heterostructures suitable for applications in optoelectronics and photovoltaics.« less

  14. Structural and optical properties of InGaN--GaN nanowire heterostructures grown by molecular beam epitaxy

    SciTech Connect

    Limbach, F.; Gotschke, T.; Stoica, T.; Calarco, R.; Sutter, E.; Ciston, J.; Cusco, R.; Artus, L.; Kremling, S.; Hofling, S.; Worschech, L.; Grutzmacher, D.

    2011-01-01

    InGaN/GaN nanowire (NW) heterostructures grown by plasma assisted molecular beam epitaxy were studied in comparison to their GaN and InGaN counterparts. The InGaN/GaN heterostructure NWs are composed of a GaN NW, a thin InGaN shell, and a multifaceted InGaN cap wrapping the top part of the GaN NW. High-resolution transmission electron microscopy (HRTEM) images taken from different parts of a InGaN/GaN NW show a wurtzite structure of the GaN core and the epitaxial InGaN shell around it, while additional crystallographic domains are observed whithin the InGaN cap region. Large changes in the lattice parameter along the wire, from pure GaN to higher In concentration demonstrate the successful growth of a complex InGaN/GaN NW heterostructure. Photoluminescence (PL) spectra of these heterostructure NW ensembles show rather broad and intense emission peak at 2.1 eV. However, μ-PL spectra measured on single NWs reveal a reduced broadening of the visible luminescence. The analysis of the longitudinal optical phonon Raman peak position and its shape reveal a variation in the In content between 20% and 30%, in agreement with the values estimated by PL and HRTEM investigations. The reported studies are important for understanding of the growth and properties of NW heterostructures suitable for applications in optoelectronics and photovoltaics.

  15. Structural and magnetic properties of epitaxial L2{sub 1}-structured Co{sub 2}(Cr,Fe)Al films grown on GaAs(001) substrates

    SciTech Connect

    Hirohata, A.; Kurebayashi, H.; Okamura, S.; Kikuchi, M.; Masaki, T.; Nozaki, T.; Tezuka, N.; Inomata, K.

    2005-05-15

    We have successfully grown both L2{sub 1} polycrystalline Co{sub 2}CrAl and epitaxial L2{sub 1}-structured Co{sub 2}FeAl films onto GaAs(001) substrates under an optimized condition. Both structural and magnetic analyses reveal the detailed growth mechanism of the alloys, and suggest that the Co{sub 2}CrAl film contains atomically disordered phases, which decreases the magnetic moment per f.u., while the Co{sub 2}FeAl film satisfies the generalized Slater-Pauling behavior. By using these films, magnetic tunnel junctions (MTJs) have been fabricated, showing 2% tunnel magnetoresistance (TMR) for the Co{sub 2}CrAl MTJ at 5 K and 9% for the Co{sub 2}FeAl MTJ at room temperature (RT). Even though the TMR ratio still needs to be improved for future device applications, these results explicitly include that the Co{sub 2}(Cr,Fe)Al full Heusler alloy is a promising compound to achieve half-metallicity at RT by controlling both disorder and surface structures in the atomic level by manipulating the Fe concentration.

  16. Stress engineering in GaN structures grown on Si(111) substrates by SiN masking layer application

    SciTech Connect

    Szymański, Tomasz Wośko, Mateusz; Paszkiewicz, Bogdan; Paszkiewicz, Regina

    2015-07-15

    GaN layers without and with an in-situ SiN mask were grown by using metal organic vapor phase epitaxy for three different approaches used in GaN on silicon(111) growth, and the physical and optical properties of the GaN layers were studied. For each approach applied, GaN layers of 1.4 μm total thickness were grown, using silan SiH{sub 4} as Si source in order to grow Si{sub x}N{sub x} masking layer. The optical micrographs, scanning electron microscope images, and atomic force microscope images of the grown samples revealed cracks for samples without SiN mask, and micropits, which were characteristic for the samples grown with SiN mask. In situ reflectance signal traces were studied showing a decrease of layer coalescence time and higher degree of 3D growth mode for samples with SiN masking layer. Stress measurements were conducted by two methods—by recording micro-Raman spectra and ex-situ curvature radius measurement—additionally PLs spectra were obtained revealing blueshift of PL peak positions with increasing stress. The authors have shown that a SiN mask significantly improves physical and optical properties of GaN multilayer systems reducing stress in comparison to samples grown applying the same approaches but without SiN masking layer.

  17. Structural characterization of niobium oxide thin films grown on SrTiO3 (111) and (La,Sr)(Al,Ta)O3 (111) substrates

    NASA Astrophysics Data System (ADS)

    Dhamdhere, Ajit R.; Hadamek, Tobias; Posadas, Agham B.; Demkov, Alexander A.; Smith, David J.

    2016-12-01

    Niobium oxide thin films have been grown by molecular beam epitaxy on SrTiO3 (STO) (111) and (La0.18Sr0.82)(Al0.59Ta0.41)O3 (LSAT) (111) substrates. Transmission electron microscopy (TEM) confirmed the formation of high quality films with coherent interfaces. Films grown with higher oxygen pressure on STO (111) resulted in a (110)-oriented NbO2 phase with a distorted rutile structure, which can be described as body-centered tetragonal. The a lattice parameter of NbO2 was determined to be ˜13.8 Å in good agreement with neutron diffraction results published in the literature. Films grown on LSAT (111) at lower oxygen pressure produced the NbO phase with a defective rock salt cubic structure. The NbO lattice parameter was determined to be a ≈ 4.26 Å. The film phase/structure identification from TEM was in good agreement with in situ x-ray photoelectron spectroscopy measurements that confirmed the dioxide and monoxide phases, respectively. The atomic structure of the NbO2/STO and NbO/LSAT interfaces was determined based on comparisons between high-resolution electron micrographs and image simulations.

  18. Structural Characterization and Antimicrobial Activity of a Biosurfactant Obtained From Bacillus pumilus DSVP18 Grown on Potato Peels

    PubMed Central

    Sharma, Deepak; Ansari, Mohammad Javed; Gupta, Sonam; Al Ghamdi, Ahmad; Pruthi, Parul; Pruthi, Vikas

    2015-01-01

    Background: Biosurfactants constitute a structurally diverse group of surface-active compounds derived from microorganisms. They are widely used industrially in various industrial applications such as pharmaceutical and environmental sectors. Major limiting factor in biosurfactant production is their production cost. Objectives: The aim of this study was to investigate biosurfactant production under laboratory conditions with potato peels as the sole source of carbon source. Materials and Methods: A biosurfactant-producing bacterial strain (Bacillus pumilus DSVP18, NCBI GenBank accession no. GQ865643) was isolated from motor oil contaminated soil samples. Biochemical characteristics of the purified biosurfactant were determined and its chemical structure was analyzed. Stability studies were performed and biological activity of the biosurfactant was also evaluated. Results: The strain, when grown on modified minimal salt media supplemented with 2% potato peels as the sole carbon source, showed the ability to reduce Surface Tension (ST) value of the medium from 72 to 28.7 mN/m. The isolated biosurfactant (3.2 ± 0.32 g/L) was stable over a wide range of temperatures (20 - 120 ºC), pH (2-12) and salt concentrations (2 - 12%). When characterized using high-performance liquid chromatography (HPLC) and Fourier transform infrared spectroscopy, it was found to be a lipopeptide in nature, which was further confirmed by Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (mass peak 1044.60) and nuclear magnetic resonance (NMR) studies. Data showed that the isolated biosurfactant at the concentration range of 30 - 35 µg/ml had strong antimicrobial activity when tested against standard strains of Bacillus cereus, Escherichia coli, Salmonella enteritidis, Staphylococcus aureus and Paenibacillus larvae. Conclusions: Potato peels were proved to be potentially useful substrates for biosurfactant production by B. pumilus DSVP18. The strain possessed a

  19. Effects of sapphire annealing on the structural properties of AIN thin films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Liu, Yun; Zhang, Jia

    2010-03-01

    The effects of sapphire annealing on high-quality AlN growth by molecular beam epitaxy have been studied. AlN thin films grown on annealed sapphire (1200 °C, 12 h) were hole-free. The full width at half maximum of the (0 0 0 2) and (1 0 1bar 5)ω-rocking curves for 260 nm-thick AlN thin films grown on annealed sapphires were 200 and 900 arcsec, respectively. The substantial improvement of AlN quality is ascribed to reduction of dislocation density by sapphire annealing.

  20. Cathodoluminescence study of radiative interface defects in thermally grown SiO{sub 2}/4H-SiC(0001) structures

    SciTech Connect

    Fukushima, Yuta; Chanthaphan, Atthawut; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

    2015-06-29

    Radiative defects in thermally grown SiO{sub 2}/4H-SiC(0001) structures and their location in depth were investigated by means of cathodoluminescence spectroscopy. It was found that while luminescence peaks ascribed to oxygen vacancy and nonbridging oxygen hole centers were observed both from thermal oxides grown on (0001) Si-face and C-face surfaces as with thermal oxides on Si, intense yellow luminescence at a wavelength of around 600 nm was identified only from the oxide interface on the Si-face substrate regardless of the oxide thickness and dopant type. Possible physical origins of the radiative centers localized near an oxide interface of a few nm thick are discussed on the basis of visible light emission from Si backbone structures.

  1. Structure and morphology characters of GaN grown by ECR-MBE using hydrogen-nitrogen mixed gas plasma[Electron Cyclotron Resonance-Molecular Beam Epitaxy

    SciTech Connect

    Araki, Tsutomu; Chiba, Yasuo; Nanishi, Yasushi

    2000-07-01

    GaN growth by electron-cyclotron-resonance plasma-excited molecular beam epitaxy using hydrogen-nitrogen mixed gas plasma were carried out on GaN templates with a different polar-surface. Structure and surface morphology of the GaN layers were characterized using transmission electron microscopy. The GaN layer grown with hydrogen on N-polar template showed a relatively flat morphology including hillocks. Columnar domain existed in the center of the hillock, which might be attributed to the existence of tiny inversion domain with Ga-polarity. On the other hand, columnar structure was formed in the GaN layer grown with hydrogen on Ga-polar template.

  2. TEM study of defect structure of GaN epitaxial films grown on GaN/Al2O3 substrates with buried column pattern

    NASA Astrophysics Data System (ADS)

    Mynbaeva, M. G.; Kremleva, A. V.; Kirilenko, D. A.; Sitnikova, A. A.; Pechnikov, A. I.; Mynbaev, K. D.; Nikolaev, V. I.; Bougrov, V. E.; Lipsanen, H.; Romanov, A. E.

    2016-07-01

    A TEM study of defect structure of GaN films grown by chloride vapor-phase epitaxy (HVPE) on GaN/Al2O3 substrates was performed. The substrates were fabricated by metal-organic chemical vapor deposition overgrowth of templates with buried column pattern. The results of TEM study showed that the character of the defect structure of HVPE-grown films was determined by the configuration of the column pattern in the substrate. By choosing the proper pattern, the reduction in the density of threading dislocations in the films by two orders of magnitude (in respect to the substrate material), down to the value of 107 cm-2, was achieved.

  3. A systematic study of the relationship among the morphological, structural and photoelectrochemical properties of ZnO nanorods grown using the microwave chemical bath deposition method

    NASA Astrophysics Data System (ADS)

    Oh, Sungjin; Ryu, Hyukhyun; Lee, Won-Jae

    2017-08-01

    In this study, zinc oxide (ZnO) nanostructures were grown on a ZnO seed layer/fluorine-doped tin oxide (FTO) substrate for different growth durations ranging from 5 to 40 min using the microwave chemical bath deposition method. We studied the effect of growth duration on the morphological, structural, optical and photoelectrochemical properties of the ZnO nanostructures. From this study, we found that the photoelectrochemical properties of the ZnO nanostructures were largely affected by their morphological and structural properties. As a result, we obtained the highest photocurrent density of 0.46 mA/cm2 (at 1.5 V vs. SCE) from the sample grown for 30 min.

  4. Band gap tunability of molecular beam epitaxy grown lateral composition modulated GaInP structures by controlling V/III flux ratio

    SciTech Connect

    Park, K. W.; Park, C. Y.; Lee, Y. T.

    2012-07-30

    Lateral composition modulated (LCM) GaInP structures were grown on (001) GaAs substrate by molecular beam epitaxy with different V/III flux ratios. Band gap of LCM structures could be tuned from 1.93 eV to 1.83 eV by decreasing flux ratio while maintaining the same photoluminescence intensity, enhanced light absorption, and widened absorption spectrum. It is shown that for band gap tuning of LCM structures, flux ratio adjustment is a more viable method compared to growth temperature adjustment.

  5. ELECTROABSORPTION OF UNSTRAINED InGaAs/InAlGaAs MULTIPLE QUANTUM WELL STRUCTURE GROWN ON GaAs SUBSTRATES

    NASA Astrophysics Data System (ADS)

    Lee, Ching-Ting; Nee, Tzer-En

    Large electroabsorption was observed in InGaAs/InAlGaAs multiple quantum well structures grown on GaAs substrates operating near 1.3 μm. The molecular beam epitaxy (MBE) growth of these structures was incorporation of a carefully designed InAlAs multistage strain-relaxed buffer. The optical absorption spectra as a function of the reverse bias at room temperature are shown. The good characteristics of the optical modulators fabricated on this structure have indicated its potential for practical applications of high-speed modulation.

  6. Structure and sublimation of water ice films grown in vacuo at 120-190 K studied by positron and positronium annihilation.

    PubMed

    Townrow, S; Coleman, P G

    2014-03-26

    The crystalline structure of ∼ 5-20 μm water ice films grown at 165 and 172 K has been probed by measuring the fraction of positrons forming ortho-positronium (ortho-Ps) and decaying into three gamma photons. It has been established that films grown at slower rates (water vapour pressure ≥ 1 mPa) have lower concentrations of lattice defects and closed pores, which act as Ps traps, than those grown at higher rates (vapour pressure ∼ 100 mPa), evidenced by ortho-Ps diffusion lengths being approximately four times greater in the former. By varying the growth temperature between 162 and 182 K it was found that films become less disordered at temperatures above ∼ 172 K, with the ortho-Ps diffusion length rising by ∼ 60%, in this range. The sublimation energy for water ice films grown on copper has been measured to be 0.462(5) eV using the time dependence of positron annihilation parameters from 165 to 195 K, in agreement with earlier studies and with no measurable dependence on growth rate and thermal history.

  7. Structural properties and metallic conductivity of Ti1-x Nb x O2 films grown by atomic layer deposition on crystalline substrates

    NASA Astrophysics Data System (ADS)

    Luka, Grzegorz; Wachnicki, Lukasz; Jakiela, Rafal; Lusakowska, Elzbieta

    2015-12-01

    Niobium-doped titanium dioxide (Ti1-x Nb x O2, x  ≈  0.04, TNO) films were grown by atomic layer deposition (ALD) at a low growth temperature (220 °C) on LaAlO3(1 0 0) (LAO) and Al2O3(0 0 0 1) (c-sapphire) substrates. The films were without any post-deposition annealing. The films grown on both kinds of substrates have anatase structure. However, the films grown on LAO substrates have (0 0 1) predominant orientation compared to a higher content of (1 1 2) orientation in the films grown on sapphire. TNO/LAO films showed low resistivities (~10-3 Ω cm at room temperature) and a metallic-type electrical conductivity as opposed to higher resistivities (~10-2 Ω cm) and a thermally activated conductivity of TNO/sapphire layers. ALD growth mechanisms of TNO films on crystalline substrates were described.

  8. Origins of Ripples in CVD-Grown Few-layered MoS2 Structures under Applied Strain at Atomic Scales

    PubMed Central

    Wang, Jin; Namburu, Raju R.; Dubey, Madan; Dongare, Avinash M.

    2017-01-01

    The potential of the applicability of two-dimensional molybdenum disulfide (MoS2) structures, in various electronics, optoelectronics, and flexible devices requires a fundamental understanding of the effects of strain on the electronic, magnetic and optical properties. Particularly important is the recent capability to grow large flakes of few-layered structures using chemical vapor deposition (CVD) wherein the top layers are relatively smaller in size than the bottom layers, resulting in the presence of edges/steps across adjacent layers. This paper investigates the strain response of such suspended few-layered structures at the atomic scales using classic molecular dynamics (MD) simulations. MD simulations suggest that the suspended CVD-grown structures are able to relax the applied in-plane strain through the nucleation of ripples under both tensile and compressive loading conditions. The presence of terraced edges in these structures is the cause for the nucleation of ripples at the edges that grow towards the center of the structure under applied in-plane strains. The peak amplitudes of ripples observed are in excellent agreement with the experimental observations. The study provides critical insights into the mechanisms of strain relaxation of suspended few-layered MoS2 structures that determine the interplay between the mechanical response and the electronic properties of CVD-grown structures. PMID:28102351

  9. Origins of Ripples in CVD-Grown Few-layered MoS2 Structures under Applied Strain at Atomic Scales

    NASA Astrophysics Data System (ADS)

    Wang, Jin; Namburu, Raju R.; Dubey, Madan; Dongare, Avinash M.

    2017-01-01

    The potential of the applicability of two-dimensional molybdenum disulfide (MoS2) structures, in various electronics, optoelectronics, and flexible devices requires a fundamental understanding of the effects of strain on the electronic, magnetic and optical properties. Particularly important is the recent capability to grow large flakes of few-layered structures using chemical vapor deposition (CVD) wherein the top layers are relatively smaller in size than the bottom layers, resulting in the presence of edges/steps across adjacent layers. This paper investigates the strain response of such suspended few-layered structures at the atomic scales using classic molecular dynamics (MD) simulations. MD simulations suggest that the suspended CVD-grown structures are able to relax the applied in-plane strain through the nucleation of ripples under both tensile and compressive loading conditions. The presence of terraced edges in these structures is the cause for the nucleation of ripples at the edges that grow towards the center of the structure under applied in-plane strains. The peak amplitudes of ripples observed are in excellent agreement with the experimental observations. The study provides critical insights into the mechanisms of strain relaxation of suspended few-layered MoS2 structures that determine the interplay between the mechanical response and the electronic properties of CVD-grown structures.

  10. Influence of edge-grown HVPE GaN on the structural quality of c-plane oriented HVPE-GaN grown on ammonothermal GaN substrates

    NASA Astrophysics Data System (ADS)

    Domagala, J. Z.; Smalc-Koziorowska, J.; Iwinska, M.; Sochacki, T.; Amilusik, M.; Lucznik, B.; Fijalkowski, M.; Kamler, G.; Grzegory, I.; Kucharski, R.; Zajac, M.; Bockowski, M.

    2016-12-01

    Study on the sources of stress in HVPE-GaN layer crystallized on 1-in. ammonothermally grown GaN seed is presented in this paper. Characterization by means of X-ray diffraction and transmission electron microscopy is performed. HVPE-GaN samples of high quality and those with visible quality deterioration are investigated on c-plane and m-plane cross-sections. Special attention is paid to HVPE material growing in semi-polar and non-polar directions on the edges of the seed and the growing layer. It is shown that this material generates significant stress leading to a structural deterioration of HVPE-GaN growing in the c-direction.

  11. Reduction of structural defects in thick 4H-SiC epitaxial layers grown on 4° off-axis substrates

    NASA Astrophysics Data System (ADS)

    Yazdanfar, M.; Ivanov, I. G.; Pedersen, H.; Kordina, O.; Janzén, E.

    2013-06-01

    By carefully controlling the surface chemistry of the chemical vapor deposition process for silicon carbide (SiC), 100 μm thick epitaxial layers with excellent morphology were grown on 4° off-axis SiC substrates at growth rates exceeding 100 μm/h. In order to reduce the formation of step bunching and structural defects, mainly triangular defects, the effect of varying parameters such as growth temperature, C/Si ratio, Cl/Si ratio, Si/H2 ratio, and in situ pre-growth surface etching time are studied. It was found that an in-situ pre growth etch at growth temperature and pressure using 0.6% HCl in hydrogen for 12 min reduced the structural defects by etching preferentially on surface damages of the substrate surface. By then applying a slightly lower growth temperature of 1575 °C, a C/Si ratio of 0.8, and a Cl/Si ratio of 5, 100 μm thick, step-bunch free epitaxial layer with a minimum triangular defect density and excellent morphology could be grown, thus enabling SiC power device structures to be grown on 4° off axis SiC substrates.

  12. Effects of annealing on the polymorphic structure of starches from sweet potatoes (Ayamurasaki and Sunnyred cultivars) grown at various soil temperatures.

    PubMed

    Genkina, Natalia K; Wasserman, Lyubov A; Noda, Takahiro; Tester, Richard F; Yuryev, Vladimir P

    2004-04-28

    Starches extracted from the sweet potato cultivars Sunnyred and Ayamurasaki grown at 15 or 33 degrees C (soil temperature) were annealed in excess water (3 mg starch/mL water) for different times (1, 4, 8 or 10h) at the temperatures 2-3 degrees K below the onset melting temperature. The structures of annealed starches, as well as their gelatinisation (melting) properties, were studied using high-sensitivity differential scanning calorimetry (HSDSC). In excess water, the single endothermic peak shifted to higher temperatures, while the melting (gelatinisation) enthalpy changed only very slightly, if any. The elevation of gelatinisation temperature was associated with increasing order/thickness of the crystalline lamellae. The only DSC endotherm identified in 0.6 M KCl for Sunnyred starch grown at 33 degrees C was attributed to A-type polymorphic structure. The multiple endothermic forms observed by DSC performed in 0.6M KCl for annealed starches from both cultivars grown at 15 degrees C provided evidence of a complex C-type (A- plus B-type) polymorphic structure of crystalline lamellae. The A:B-ratio of two polymorphic forms increased upon annealing due to partial transformation of B- to A-polymorph, which was time dependent. Long heating periods facilitated the maximal transformation of B- to A-polymorph associated with limited A:B ratio.

  13. Stability and structure of nanowires grown from silver, copper and their alloys by laser ablation into superfluid helium.

    PubMed

    Gordon, Eugene; Karabulin, Alexander; Matyushenko, Vladimir; Sizov, Vyacheslav; Khodos, Igor

    2014-12-14

    Nanowires with 5 nm diameter made of silver, copper, and their alloys were grown in superfluid helium. The silver nanowires being heated to 300 K disintegrated into individual clusters. In contrast, copper nanowires were stable at room temperature, and nanowires made of alloys were also stable despite their low melting temperature.

  14. Characterization of dislocation structures and deformation mechanisms in as-grown and deformed directionally solidified NiAl–Mo composites

    DOE PAGES

    Kwon, J.; Bowers, M. L.; Brandes, M. C.; ...

    2015-02-26

    In this paper, directionally solidified (DS) NiAl–Mo eutectic composites were strained to plastic strain values ranging from 0% to 12% to investigate the origin of the previously observed stochastic versus deterministic mechanical behaviors of Mo-alloy micropillars in terms of the development of dislocation structures at different pre-strain levels. The DS composites consist of long, [1 0 0] single-crystal Mo-alloy fibers with approximately square cross-sections embedded in a [1 0 0] single-crystal NiAl matrix. Scanning transmission electron microscopy (STEM) and computational stress state analysis were conducted for the current study. STEM of the as-grown samples (without pre-straining) reveal no dislocations inmore » the investigated Mo-alloy fibers. In the NiAl matrix, on the other hand, a(1 0 0)-type dislocations exist in two orthogonal orientations: along the [1 0 0] Mo fiber axis, and wrapped around the fiber axis. They presumably form to accommodate the different thermal contractions of the two phases during cool down after eutectic solidification. At intermediate pre-strain levels (4–8%), a/2(1 1 1)-type dislocations are present in the Mo-alloy fibers and the pre-existing dislocations in the NiAl matrix seem to be swept toward the interphase boundary. Some of the dislocations in the Mo-alloy fibers appear to be transformed from a(1 0 0)-type dislocations present in the NiAl matrix. Subsequently, the transformed dislocations in the fibers propagate through the NiAl matrix as a(1 1 1) dislocations and aid in initiating additional slip bands in adjacent fibers. Thereafter, co-deformation presumably occurs by (1 1 1) slip in both phases. With a further increase in the pre-strain level (>10%), multiple a/2(1 1 1)-type dislocations are observed in many locations in the Mo-alloy fibers. Interactions between these systems upon subsequent deformation could lead to stable junctions and persistent dislocation sources. Finally, the transition from stochastic to

  15. Characterization of dislocation structures and deformation mechanisms in as-grown and deformed directionally solidified NiAl–Mo composites

    SciTech Connect

    Kwon, J.; Bowers, M. L.; Brandes, M. C.; McCreary, V.; Robertson, Ian M.; Phani, P. Sudaharshan; Bei, H.; Gao, Y. F.; Pharr, George M.; George, Easo P.; Mills, M. J.

    2015-02-26

    In this paper, directionally solidified (DS) NiAl–Mo eutectic composites were strained to plastic strain values ranging from 0% to 12% to investigate the origin of the previously observed stochastic versus deterministic mechanical behaviors of Mo-alloy micropillars in terms of the development of dislocation structures at different pre-strain levels. The DS composites consist of long, [1 0 0] single-crystal Mo-alloy fibers with approximately square cross-sections embedded in a [1 0 0] single-crystal NiAl matrix. Scanning transmission electron microscopy (STEM) and computational stress state analysis were conducted for the current study. STEM of the as-grown samples (without pre-straining) reveal no dislocations in the investigated Mo-alloy fibers. In the NiAl matrix, on the other hand, a(1 0 0)-type dislocations exist in two orthogonal orientations: along the [1 0 0] Mo fiber axis, and wrapped around the fiber axis. They presumably form to accommodate the different thermal contractions of the two phases during cool down after eutectic solidification. At intermediate pre-strain levels (4–8%), a/2(1 1 1)-type dislocations are present in the Mo-alloy fibers and the pre-existing dislocations in the NiAl matrix seem to be swept toward the interphase boundary. Some of the dislocations in the Mo-alloy fibers appear to be transformed from a(1 0 0)-type dislocations present in the NiAl matrix. Subsequently, the transformed dislocations in the fibers propagate through the NiAl matrix as a(1 1 1) dislocations and aid in initiating additional slip bands in adjacent fibers. Thereafter, co-deformation presumably occurs by (1 1 1) slip in both phases. With a further increase in the pre-strain level (>10%), multiple a/2(1 1 1)-type dislocations are observed in many locations in the Mo-alloy fibers. Interactions between these systems upon subsequent deformation could lead to stable junctions and persistent dislocation sources. Finally, the transition from stochastic to

  16. Interface-structure of the Si/SiC heterojunction grown on 6H-SiC

    SciTech Connect

    Li, L. B.; Chen, Z. M.; Zang, Y.

    2015-01-07

    The Si/SiC heterojunctions were prepared on 6H-SiC (0001) C-face by low-pressure chemical vapour deposition at 850 ∼ 1050 °C. Transmission electron microscopy and selected area electron diffraction were employed to investigate the interface-structure of Si/SiC heterojunctions. The Si/6H-SiC heterostructure of large lattice-mismatch follows domain matching epitaxy mode, which releases most of the lattice-mismatch strain, and the coherent Si epilayers can be grown on 6H-SiC. Si(1-11)/6H-SiC(0001) heterostructure is obtained at 900 °C, and the in-plane orientation relationship of Si/6H-SiC heterostructure is (1–11)[1-1-2]{sub Si}//(0001)[-2110]{sub 6H-SiC}. The Si(1-11)/6H-SiC(0001) interface has the same 4:5 Si-to-SiC matching mode with a residual lattice-mismatch of 0.26% along both the Si[1-1-2] and Si[110] orientations. When the growth temperature increases up to 1000 °C, the 〈220〉 preferential orientation of the Si film appears. SAED patterns at the Si/6H-SiC interface show that the in-plane orientation relationship is (-220)[001]{sub Si}//(0001)[2-1-10]{sub 6H-SiC}. Along Si[110] orientation, the Si-to-SiC matching mode is still 4:5; along the vertical orientation Si[001], the Si-to-SiC mode change to approximate 1:2 and the residual mismatch is 1.84% correspondingly. The number of the atoms in one matching-period decreases with increasing residual lattice-mismatch in domain matching epitaxy and vice versa. The Si film grows epitaxially but with misfit dislocations at the interface between the Si film and the 6H-SiC substrate. And the misfit dislocation density of the Si(1-11)/6H-SiC(0001) and Si(-220)/6H-SiC(0001) obtained by experimental observations is as low as 0.487 × 10{sup 14 }cm{sup −2} and 1.217 × 10{sup 14 }cm{sup −2}, respectively, which is much smaller than the theoretical calculation results.

  17. Peculiarities of photoluminescence of vertical n +/ n-GaAs/Al0.25Ga0.75As MBE- and MOCVD-grown structures designed for microwave detectors

    NASA Astrophysics Data System (ADS)

    Čerškus, Aurimas; Kundrotas, Jurgis; Sužiedėlis, Algirdas; Gradauskas, Jonas; Ašmontas, Steponas; Johannessen, Eric; Johannessen, Agne

    2015-09-01

    Vertical MBE- and MOCVD-grown structures used for microwave electronics have been studied with continuous wave and time-correlated single photon counting dynamic photoluminescence technique. The photoluminescence spectra and light emission lifetimes are used to explain the recombination mechanisms of the excited carriers. This paper presents results showing the differences in recombination characteristics of layers grown using MBE process compared with MOCVD process. One of these differences is that the PL spectrum of the MOCVD-grown layer is shifted towards the forbidden energy gap region, as well as the characteristic recombination time is longer than for the MBE-grown sample. This peculiarity can be attributed to the formation of the localised band tails in the MOCVD-grown sample. The proposed analytical model explains the differences in microwave detection properties of the samples grown by MBE and MOCVD processes.

  18. Impact of low temperature annealing on structural, optical, electrical and morphological properties of ZnO thin films grown by RF sputtering for photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Purohit, Anuradha; Chander, S.; Sharma, Anshu; Nehra, S. P.; Dhaka, M. S.

    2015-11-01

    This paper presents effect of low temperature annealing on the physical properties of ZnO thin films for photovoltaic applications. The thin films of thickness 50 nm were grown on glass and indium tin oxide (ITO) coated glass substrates employing radio frequency magnetron sputtering technique followed by thermal annealing within low temperature range 150-450 °C. These as-grown and annealed films were subjected to the X-ray diffraction (XRD), UV-Vis spectrophotometer, source meter and scanning electron microscopy (SEM) for structural, optical, electrical and surface morphological analysis respectively. The compositional analysis of the as-grown ZnO film was also carried out using energy dispersive spectroscopy (EDS). The XRD patterns reveal that the films have wurtzite structure of hexagonal phase with preferred orientation (1 0 0) and polycrystalline in nature. The crystallographic and optical parameters are calculated and discussed in detail. The optical band gap was found in the range 3.30-3.52 eV and observed to decrease with annealing temperature except 150 °C. The current-voltage characteristics show that the films exhibit approximately ohmic behavior. The SEM studies show that the films are uniform, homogeneous and free from crystal defects and voids. The experimental results reveal that ZnO thin films may be used as alternative materials for eco-friendly buffer layer to the thin film solar cell applications.

  19. Atomic scale structure and chemistry of Bi2Te3/GaAs interfaces grown by metallorganic van der Waals epitaxy

    NASA Astrophysics Data System (ADS)

    Houston Dycus, J.; White, Ryan M.; Pierce, Jonathan M.; Venkatasubramanian, Rama; LeBeau, James M.

    2013-02-01

    Here, we report the atomic scale structure and chemistry of epitaxial Bi2Te3 thin films grown via metallorganic chemical vapor deposition on (001) GaAs substrates. Using aberration corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM), we report an atomically abrupt interface spanned by a second phase. Further, we demonstrate that interpretation of HAADF STEM image intensities does not provide an unambiguous interface structure. Combining atomic resolution imaging and spectroscopy, we determine the identity of the interfacial species is found to be consistent with that of a bilayer of Ga-Te that terminates GaAs dangling bonds.

  20. Effects of Precursor Concentration on Structural and Optical Properties of ZnO Thin Films Grown on Muscovite Mica Substrates by Sol-Gel Spin-Coating.

    PubMed

    Kim, Younggyu; Leem, Jae-Young

    2016-05-01

    The structural and optical properties of the ZnO thin films grown on mica substrates for different precursor concentrations were investigated. The surface morphologies of all the samples indicated that they consisted of granular structures with spherical nano-sized crystallites. The thickness of the ZnO thin films increased significantly and the optical band gap exhibited a blue shift with an increase in the precursor concentration. It is remarkable that the highest I(NBE)/I(DLE) ratio was observed for the ZnO thin film with 0.8 M precursor concentration, even though cracks formed on the surface of this film.

  1. Structural, Optical and Electrical Properties of n-type GaN on Si (111) Grown by RF-plasma assisted Molecular Beam Epitaxy

    SciTech Connect

    Chin, C. W.; Hassan, Z.; Yam, F. K.

    2008-05-20

    In this paper, we present the study of the structural, optical and electrical of n-type GaN grown on silicon (111) by RF plasma-assisted molecular beam epitaxy (RF-MBE). X-ray diffraction (XRD) measurement reveals that the GaN was epitaxially grown on silicon. For the photoluminescence (PL) measurement, a sharp and intense peak at 364.5 nm indicates that the sample is of high optical quality. Hall effect measurement shows that the film has a carrier concentration of 3.28x10{sup 19} cm{sup -3}. The surface of the n-type GaN was smooth and no any cracks and pits.

  2. Structural, optical, thermal, mechanical and dielectrical characterizations of γ-glycine crystals grown in strontium chloride solution

    NASA Astrophysics Data System (ADS)

    Helina, B.; Selvarajan, P.; Rose, A. S. J. Lucia

    2012-05-01

    γ-glycine (GG) was synthesized from α-glycine in an aqueous solution of strontium chloride. A solubility study of the synthesized GG sample was conducted at various temperatures ranging from 30 to 55 °C. The saturated solution of GG was prepared using solubility data, and single crystals of GG were grown over a period of three weeks by the slow evaporation method at room temperature. The grown GG crystals were characterized by single-crystal x-ray diffraction analysis, UV-visible transmittance studies, thermogravimetric/differential thermal analysis studies, dielectric studies and Fourier transform infrared studies. The mechanical behavior of the crystals was assessed by Vickers microhardness measurements. The second-harmonic generation efficiency of the sample was measured using a Nd:YAG laser and the value was observed to be larger than that of potassium dihydrogen orthophosphate (KDP).

  3. Structural and electrical characterization of Bi₂Se₃ nanostructures grown by metal-organic chemical vapor deposition.

    PubMed

    Alegria, L D; Schroer, M D; Chatterjee, A; Poirier, G R; Pretko, M; Patel, S K; Petta, J R

    2012-09-12

    We characterize nanostructures of Bi(2)Se(3) that are grown via metal-organic chemical vapor deposition using the precursors diethyl selenium and trimethyl bismuth. By adjusting growth parameters, we obtain either single-crystalline ribbons up to 10 μm long or thin micrometer-sized platelets. Four-terminal resistance measurements yield a sample resistivity of 4 mΩ·cm. We observe weak antilocalization and extract a phase coherence length l(ϕ) = 178 nm and spin-orbit length l(so) = 93 nm at T = 0.29 K. Our results are consistent with previous measurements on exfoliated samples and samples grown via physical vapor deposition.

  4. 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.

  5. Characterization of leakage current related to a selectively grown collector in SiGeC heterojunction bipolar transistor structure

    NASA Astrophysics Data System (ADS)

    Suvar, E.; Haralson, E.; Radamson, H. H.; Wang, Y.-B.; Grahn, J. V.; Malm, B. G.; Östling, M.

    2004-03-01

    Sources of base-collector and base-emitter leakage current in a SiGeC-based heterojunction bipolar transistor (HBT) with a selectively grown and chemical-mechanical polished (CMP) collector are discussed. Transmission electron microscopy and electrical measurement have been applied to investigate the leakage current. It has been demonstrated that the edge-located defects generated by selective epitaxy process are the origin of the junction leakage.

  6. Study of structural defects and crystalline perfection of near stoichiometric LiNbO3 crystals grown from flux and prepared by VTE technique

    NASA Astrophysics Data System (ADS)

    Bhatt, R.; Bhaumik, Indranil; Ganesamoorthy, S.; Karnal, A. K.; Gupta, P. K.; Swami, M. K.; Patel, H. S.; Sinha, A. K.; Upadhyay, A.

    2014-10-01

    Near-stoichiometric LiNbO3 (SLN) single crystals were grown/prepared by top seeded solution growth/vapor transport equilibration (VTE) technique, and investigated for stoichiometry, disorder and structural defects. The optical absorption and Raman line-width studies revealed higher stoichiometry (i.e., higher Li/Nb) for SLN prepared by vapor transport equilibration (SLN_V) technique in comparison to SLN grown from K2O flux (SLN_K) and Li-rich melt (SLN_L). The nearly symmetric single diffraction curve (DC), though broad, as observed for SLN_L specimen in high resolution X-rays diffraction (HRXRD) analysis depicted lesser low angle grain boundaries. On the other hand, relatively sharp DC with lowest full-width at half-maximum (FWHM ∼45 arc-sec) in HRXRD and lesser Urbach energy (∼80 meV) in the absorption spectra for SLN_V crystal revealed less structural defects with respect to other SLN crystals. The higher FWHM of DCs in HRXRD for SLN_L and SLN_K is attributed to growth related imperfections usually observed in solution growth. Though, VTE process results in SLN crystals with better stoichiometry and lesser structural defects but the limitation being that samples up to ∼1 mm thickness can be prepared with this technique. For bulk SLN, growth from K2O flux resulted in better stoichiometry whereas Li-rich flux resulted in better structural quality. The absorption spectra of the grown SLN crystals depicted oxygen vacancy induced electronic defects (Nb4+, polarons), which was further authenticated by X-ray absorption near-edge structure (XANES) analysis at Nb K edge revealing lesser Nb4+ defects in SLN with respect to congruent lithium niobate (CLN) crystal.

  7. Bound-solvent structures for microgravity-, ground control-, gel- and microbatch-grown hen egg-white lysozyme crystals at 1.8 A resolution.

    PubMed

    Dong, J; Boggon, T J; Chayen, N E; Raftery, J; Bi, R C; Helliwell, J R

    1999-04-01

    A number of methods can be used to improve the stability of the protein crystal-growth environment, including growth in microgravity without an air-liquid phase boundary, growth in gels and growth under oil ('microbatch'). In this study, X-ray data has been collected from and structures refined for crystals of hen egg-white lysozyme (HEWL) grown using four different methods, liquid-liquid dialysis on Earth and in microgravity using the European Space Agency's (ESA) Advanced Protein Crystallization Facility (APCF) on board the NASA Space Shuttle Life and Microgravity Spacelab (LMS) mission (STS-78), crystallization in agarose gel using a tube liquid-gel diffusion method and crystallization in microbatch under oil. A comparison of the overall quality of the X-ray data, the protein structures and especially the bound-water structures has been carried out at 1.8 A. The lysozyme protein structures corresponding to these four different crystallization methods remain similar. A small improvement in the bound-solvent structure is seen in lysozyme crystals grown in microgravity by liquid-liquid dialysis, which has a more stable fluid physics state in microgravity, and is consistent with a better formed protein crystal in microgravity.

  8. Electronic structure and nematic phase transition in superconducting multiple-layer FeSe films grown by pulsed laser deposition method

    NASA Astrophysics Data System (ADS)

    Shen, Bing; Feng, Zhong-Pei; Huang, Jian-Wei; Hu, Yong; Gao, Qiang; Li, Cong; Xu, Yu; Liu, Guo-Dong; Yu, Li; Zhao, Lin; Jin, Kui; Zhou, X. J.

    2017-06-01

    We report comprehensive angle-resolved photoemission investigations on the electronic structure of single crystal multiple-layer FeSe films grown on CaF2 substrate by pulsed laser deposition (PLD) method. Measurements on FeSe/CaF2 samples with different superconducting transition temperatures Tc of 4 K, 9 K and 14 K reveal electronic difference in their Fermi surface and band structure. Indication of the nematic phase transition is observed from temperature-dependent measurements of these samples; the nematic transition temperature is 140-160 K, much higher than 90 K for the bulk FeSe. Potassium deposition is applied onto the surface of these samples; the nematic phase is suppressed by potassium deposition which introduces electrons to these FeSe films and causes a pronounced electronic structure change. We compared and discussed the electronic structure and superconductivity of the FeSe/CaF2 films by PLD method with the FeSe/SrTiO3 films by molecular beam epitaxy (MBE) method and bulk FeSe. The PLD-grown multilayer FeSe/CaF2 is more hole-doped than that in MBE-grown multiple-layer FeSe films. Our results on FeSe/CaF2 films by PLD method establish a link between bulk FeSe single crystal and FeSe/SrTiO3 films by MBE method, and provide important information to understand superconductivity in FeSe-related systems.

  9. Investigation of deep-level defects in InGaAsN/GaAs 3xQWs structures grown by AP-MOVPE

    NASA Astrophysics Data System (ADS)

    Gelczuk, Ł.; Dabrowska-Szata, M.; Kamyczek, P.; Płaczek-Popko, E.; Kopalko, K.; Ściana, B.; Pucicki, D.; Radziewicz, D.; Tłaczała, M.

    2013-07-01

    We have investigated deep-level defects in InGaAsN/GaAs 3xQW structures by means of conventional as well as high-resolution deep level transient spectroscopy (DLTS). The three samples were grown by atmospheric pressure metalorganic vapour phase epitaxy (AP-MOVPE) in different growth temperatures (566°C, 575°C and 585°C). The DLTS measurements revealed four electron traps E1 (0.17-0.24 eV), E2 (0.36-0.38 eV), E3 (0.46-0.49 eV) and E4 (0.81-0.84 eV) and one hole trap H1(0.8 eV) in our structures. The electron trap E1 was associated with N-related complexes while the other electron traps with native defects, usually observed in GaAs-based structures EL6, EL3 and EL2, respectively. Finally, the trap E2 and H1, observed in the structure grown at lowest temperature, were associated with the same trap, which can act as both an electron and hole trap. It was thus concluded that E2/H1 may be a generation-recombination center.

  10. Structural and magnetic properties of Ni 2MnIn Heusler thin films grown on modulation-doped InAs heterostructures with metamorphic buffer

    NASA Astrophysics Data System (ADS)

    Bohse, S.; Zolotaryov, A.; Volland, A.; Landgraf, B.; Albrecht, O.; Bastjan, M.; Vossmeyer, T.; Görlitz, D.; Heyn, Ch.; Hansen, W.

    2012-01-01

    This paper reports on the morphological, structural, magnetic, and magneto-optic properties of Ni 2MnIn Heusler films grown on InAs-high electron-mobility transistor structures (HEMT) with metamorphic buffers for spintronic applications. Similar to our previous results on the Ni 2MnIn/InAs (001) system, the Heusler layer is found to have a (110) orientation relative to the (001) InAs-HEMT surface. We observe almost equal spin-polarizations for Heusler films on (001) InAs-HEMT as well as on (001) InAs. In addition, we find further support for interfacial intermixing previously reported for the Ni 2MnIn/InAs (001) system. On the other hand, the Heusler/InAs-HEMT system shows distinct morphologic, structural, and magnetic properties as compared to the Ni 2MnIn/InAs (001) system. In particular, more rapid and complex plastic deformation effects resulting in a high surface density of pin-holes in the Heusler films are found. We report on complex mutual deformation effects between the Heusler films and the underlying InAs-HEMT structure. Furthermore, a hysteresis loop squareness close to 1 for a 50 nm Heusler film on InAs-HEMT is observed. We tentatively associate these phenomena with the higher mismatch strain of the Ni 2MnIn/InAs-HEMT system compared to Ni 2MnIn films grown on (001) InAs.

  11. Raman tensor and domain structure study of single-crystal-like epitaxial films of CaCu3Ti4O12 grown by pulsed laser deposition.

    PubMed

    Ahlawat, Anju; Mishra, Dileep K; Sathe, V G; Kumar, Ravi; Sharma, T K

    2013-01-16

    The local domain structure of a strain free, 150 nm thick, epitaxially grown single crystalline thin film of CaCu(3)Ti(4)O(12) is probed by polarized Raman spectroscopy. The polarization dependence of the Raman intensities of the observed bands as a function of varying angle between the domain axes and the polarization vector of the scattered laser photon is measured. Theoretical formulations involving the Raman tensor are presented, which enable determination of the domain structure from the observed polarized Raman spectra, and a single-crystal-like domain structure is found. The Raman tensor elements and domain orientation direction were determined by fitting the observed Raman intensities with theoretical calculations and by carrying out Raman mapping of the film. Our data show an absence of twin domain structure and twin domain boundaries in the single-crystal-like epitaxial thin films of CaCu(3)Ti(4)O(12).

  12. Effect of growth interrupt and growth rate on MOVPE-grown InGaN/GaN MQW structures

    NASA Astrophysics Data System (ADS)

    Jacobs, K.; Van Daele, B.; Leys, M. R.; Moerman, I.; Van Tendeloo, G.

    2003-02-01

    InGaN/GaN multiple quantum wells (MQWs) were grown by metalorganic vapor phase epitaxy to quantify the influence of various growth parameters on the optical properties and on the In incorporation. Decreasing the group III flux results in improved room temperature photoluminescence intensity. Introduction of 5 and 10 s interrupts at the MQW interfaces gives rise to loss of In. High temperature capping of MQWs with GaN:Mg produces blackening of the layers for an In content exceeding 12%, due to formation of In platelets.

  13. Structural, morphological and electrical studies of lithium ion irradiated sodium potassium niobate single crystal grown by flux method

    NASA Astrophysics Data System (ADS)

    Saravanan, R.; Rajesh, D.; Rajasekaran, S. V.; Perumal, R.; Chitra, M.; Jayavel, R.

    2013-02-01

    Single crystals of sodium potassium niobate (K0.5Na0.5)NbO3 (KNN) were grown by flux method and crystals were irradiated with 45 MeV Li ions to modify the electrical properties. Energy of the irradiated heavy ion was lower than the threshold energy to produce columnar defect and only clusters of defect was observed. The surface morphology of the irradiated single crystals was studied using scanning electron microscope (SEM) and atomic force microscope (AFM). The results show that the surface roughness value was found to increase with increasing fluence.

  14. Structural, morphological and electrical studies of lithium ion irradiated sodium potassium niobate single crystal grown by flux method

    SciTech Connect

    Saravanan, R.; Rajesh, D.; Rajasekaran, S. V.; Perumal, R.; Chitra, M.; Jayavel, R.

    2013-02-05

    Single crystals of sodium potassium niobate (K{sub 0.5}Na{sub 0.5})NbO{sub 3} (KNN) were grown by flux method and crystals were irradiated with 45 MeV Li ions to modify the electrical properties. Energy of the irradiated heavy ion was lower than the threshold energy to produce columnar defect and only clusters of defect was observed. The surface morphology of the irradiated single crystals was studied using scanning electron microscope (SEM) and atomic force microscope (AFM). The results show that the surface roughness value was found to increase with increasing fluence.

  15. Structure and defects of a linear chain polymer film; GeO phthalocyanine epitaxially grown on KC1

    NASA Astrophysics Data System (ADS)

    Kobayashi, Takashi; Uyeda, Natsu

    1987-10-01

    Epitaxial film of GeO phthalocyanine polymer grown on KC1 has been investigated by direct observation of molecular images and electron diffraction. The film is composed of many crystallites oriented in two directions. The mechanism of the epitaxial growth of an organic crystal has been related to the determination of a staggering angle of the molecules stacked in polymer chains. Prominent diffuse scatterings have been observed and their origin has been revealed to be the existence of stacking faults in the crystal. The molecular orientation at the fault is discussed.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  17. Optical, structural, and transport properties of indium nitride, indium gallium nitride alloys grown by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Khan, Neelam

    InGaN based, blue and green light emitting diodes (LEDs) have been successfully produced over the past decade. But the progress of these LEDs is often limited by the fundamental problems of InGaN such as differences in lattice constants, thermal expansion coefficients and physical properties between InN and GaN. This difficulty could be addressed by studying pure InN and InxGa 1-xN alloys. In this context Ga-rich InxGa1-xN (x ≤ 0.4) epilayers were grown by metal organic chemical vapor deposition (MOCVD). X-ray diffraction (XRD) measurements showed InxGa1-xN films with x= 0.37 had single phase. Phase separation occurred for x ˜ 0.4. To understand the issue of phase separation in Ga-rich InxGa 1-xN, studies on growth of pure InN and In-rich InxGa 1-xN alloys were carried out. InN and In-rich InxGa1-xN (x ˜ 0.97-0.40) epilayers were grown on AlN/Al2O3 templates. A Hall mobility of 1400 cm2/Vs with a carrier concentration of 7x1018cm -3 was observed for InN epilayers grown on AlN templates. Photoluminescence (PL) emission spectra revealed a band to band emission peak at ˜0.75 eV for InN. This peak shifted to 1.15 eV when In content was varied from 1.0 to 0.63 in In-rich InxGa1-xN epilayers. After growth parameter optimization of In-rich InxGa1-xN alloys with (x = 0.97-0.40) were successfully grown without phase separation. Effects of Mg doping on the PL properties of InN epilayers grown on GaN/Al 2O3 templates were investigated. An emission line at ˜ 0.76 eV, which was absent in undoped InN epilayers and was about 60 meV below the band edge emission peak at ˜ 0.82 eV, was observed to be the dominant emission in Mg-doped InN epilayers. PL peak position and the temperature dependent emission intensity corroborated each other and suggested that Mg acceptor level in InN is about 60 meV above the valance band maximum. Strain effects on the emission properties of InGaN/GaN multiple quantum wells (MQWs) were studied using a single blue LED wafer possessing a continuous

  18. A multiple p-n junction structure obtained from as-grown Czochralski silicon crystals by heat treatment - Application to solar cells

    NASA Technical Reports Server (NTRS)

    Chi, J. Y.; Gatos, H. C.; Mao, B. Y.

    1980-01-01

    Multiple p-n junctions have been prepared in as-grown Czochralski p-type silicon through overcompensation near the oxygen periodic concentration maxima by oxygen thermal donors generated during heat treatment at 450 C. Application of the multiple p-n-junction configuration to photovoltaic energy conversion has been investigated. A new solar-cell structure based on multiple p-n-junctions was developed. Theoretical analysis showed that a significant increase in collection efficiency over the conventional solar cells can be achieved.

  19. A multiple p-n junction structure obtained from as-grown Czochralski silicon crystals by heat treatment - Application to solar cells

    NASA Technical Reports Server (NTRS)

    Chi, J. Y.; Gatos, H. C.; Mao, B. Y.

    1980-01-01

    Multiple p-n junctions have been prepared in as-grown Czochralski p-type silicon through overcompensation near the oxygen periodic concentration maxima by oxygen thermal donors generated during heat treatment at 450 C. Application of the multiple p-n-junction configuration to photovoltaic energy conversion has been investigated. A new solar-cell structure based on multiple p-n-junctions was developed. Theoretical analysis showed that a significant increase in collection efficiency over the conventional solar cells can be achieved.

  20. Structural properties of Bi2Te3 topological insulator thin films grown by molecular beam epitaxy on (111) BaF2 substrates

    NASA Astrophysics Data System (ADS)

    Fornari, Celso I.; Rappl, Paulo H. O.; Morelhão, Sérgio L.; Abramof, Eduardo

    2016-04-01

    Structural properties of topological insulator bismuth telluride films grown epitaxially on (111) BaF2 with a fixed Bi2Te3 beam flux were systematically investigated as a function of substrate temperature and additional Te flux. A layer-by-layer growth mode is observed since the early stages of epitaxy and remains throughout the whole deposition. Composition of the epitaxial films produced here stays between Bi2Te3 and Bi4Te5, as determined from the comparison of the measured x-ray diffraction curves with calculations. The substrate temperature region, where the growth rate remains constant, is found to be the most appropriate to obtain ordered Bi2Te3 films. Line width of the L = 18 Bi2Te3 diffraction peaks as low as 140 arcsec was obtained, indicating high crystalline quality. Twinning domains density rises with increasing growth temperature and reducing Te extra flux. X-ray reflectivity curves of pure Bi2Te3 films with thickness from 165 to 8 nm exhibited well defined interference fringes, evidencing homogeneous layers with smooth surface. Our results demonstrate that Bi2Te3 films with very well controlled structural parameters can be obtained. High structural quality Bi2Te3 films as thin as only eight quintuple layers grown here are promising candidates for intrinsic topological insulator.

  1. Influence of GaN column diameter on structural properties for InGaN nanocolumns grown on top of GaN nanocolumns

    NASA Astrophysics Data System (ADS)

    Oto, Takao; Mizuno, Yutaro; Yanagihara, Ai; Miyagawa, Rin; Kano, Tatsuya; Yoshida, Jun; Sakakibara, Naoki; Kishino, Katsumi

    2016-11-01

    The influence of GaN column diameter DGaN on structural properties was systematically investigated for InGaN nanocolumns (NCs) grown on top of GaN NCs. We demonstrated a large critical layer thickness of above 400 nm for In0.3Ga0.7N/GaN NCs. The structural properties were changed at the boundary of DGaN=D0 (˜120 nm). Homogeneous InGaN NCs grew axially on the GaN NCs with DGaN≤D0, while InGaN-InGaN core-shell structures were spontaneously formed on the GaN NCs with DGaN>D0. These results can be explained by a growth system that minimizes the total strain energy of the NCs.

  2. InGaAsP/InAlAs type I/type II multiple quantum well structures grown by gas source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Kawamura, Yuichi; Iwamura, Hidetoshi

    1995-05-01

    In 1- xGa xAs 1- yP y/In 0.52Al 0.48As multiple quantum well (MQW) structures have been grown on InP substrates by gas source molecular beam epitaxy and the compositional dependence of the optical properties are studied by photoluminescence and optical absorption measurements. It is found that the type I/type II transition occurs at a P composition of 0.60. From the compositional dependence of the effective bandgap of the InGaAsP/InAlAs MQW structure, the valence band discontinuity ( ΔEv) of the InP/InAlAs hetero-interface is estimated to be 0.20 eV, which is consistent with the result for the conduction band discontinuity ( ΔEc) of In 1- w-zGa wAl zAs/InP MQW structures.

  3. Effect of AlN buffer layers on the structural and optoelectronic properties of InN/AlN/Sapphire heterostructures grown by MEPA-MOCVD

    NASA Astrophysics Data System (ADS)

    Indika, S. M. K.; Seidlitz, Daniel; Fali, Alireza; Cross, Brendan; Abate, Yohannes; Dietz, Nikolaus

    2016-09-01

    This contribution presents results on the structural and optoelectronic properties of InN layers grown on AlN/sapphire (0001) templates by Migration-Enhanced Plasma Assisted Metal Organic Chemical Vapor Deposition (MEPAMOCVD). The AlN nucleation layer (NL) was varied to assess the physical properties of the InN layers. For ex-situ analysis of the deposited structures, Raman spectroscopy, Atomic Force Microscopy (AFM), and Fourier Transform Infrared (FTIR) reflectance spectroscopy have been utilized. The structural and optoelectronic properties are assessed by Raman-E2 high FWHM values, surface roughness, free carrier concentrations, mobility of the free carriers, and high frequency dielectric function. This study focus on optimizing the AlN nucleation layer (e.g. temporal precursor exposure, nitrogen plasma exposure, plasma power and AlN buffer growth temperature) and its effect on the InN layer properties.

  4. Effect of Arbuscular Mycorrhizal Fungi on Plant Biomass and the Rhizosphere Microbial Community Structure of Mesquite Grown in Acidic Lead/Zinc Mine Tailings

    PubMed Central

    Solís-Domínguez, Fernando A.; Valentín-Vargas, Alexis; Chorover, Jon; Maier, Raina M.

    2011-01-01

    Mine tailings in arid and semi-arid environments are barren of vegetation and subject to eolian dispersion and water erosion. Revegetation is a cost-effective strategy to reduce erosion processes and has wide public acceptance. A major cost of revegetation is the addition of amendments, such as compost, to allow plant establishment. In this paper we explore whether arbuscular mycorrhizal fungi (AMF) can help support plant growth in tailings at a reduced compost concentration. A greenhouse experiment was performed to determine the effects of three AMF inocula on biomass, shoot accumulation of heavy metals, and changes in the rhizosphere microbial community structure of the native plant Prosopis juliflora (mesquite). Plants were grown in an acidic lead/zinc mine tailings amended with 10% (w/w) compost amendment, which is slightly sub-optimal for plant growth in these tailings. After two months, AMF-inoculated plants showed increased dry biomass and root length (p < 0.05) and effective AMF colonization compared to controls grown in uninoculated compost-amended tailings. Mesquite shoot tissue lead and zinc concentrations did not exceed domestic animal toxicity limits regardless of whether AMF inoculation was used. The rhizosphere microbial community structure was assessed using denaturing gradient gel electrophoresis (DGGE) profiles of the small subunit RNA gene for bacteria and fungi. Canonical correspondence analysis (CCA) of DGGE profiles showed that the rhizosphere fungal community structure at the end of the experiment was significantly different from the community structure in the tailings, compost, and AMF inocula prior to planting. Further, CCA showed that AMF inoculation significantly influenced the development of both the fungal and bacterial rhizosphere community structures after two months. The changes observed in the rhizosphere microbial community structure may be either a direct effect of the AMF inocula, caused by changes in plant physiology induced by

  5. Effect of arbuscular mycorrhizal fungi on plant biomass and the rhizosphere microbial community structure of mesquite grown in acidic lead/zinc mine tailings.

    PubMed

    Solís-Domínguez, Fernando A; Valentín-Vargas, Alexis; Chorover, Jon; Maier, Raina M

    2011-02-15

    Mine tailings in arid and semi-arid environments are barren of vegetation and subject to eolian dispersion and water erosion. Revegetation is a cost-effective strategy to reduce erosion processes and has wide public acceptance. A major cost of revegetation is the addition of amendments, such as compost, to allow plant establishment. In this paper we explore whether arbuscular mycorrhizal fungi (AMF) can help support plant growth in tailings at a reduced compost concentration. A greenhouse experiment was performed to determine the effects of three AMF inocula on biomass, shoot accumulation of heavy metals, and changes in the rhizosphere microbial community structure of the native plant Prosopis juliflora (mesquite). Plants were grown in an acidic lead/zinc mine tailings amended with 10% (w/w) compost amendment, which is slightly sub-optimal for plant growth in these tailings. After two months, AMF-inoculated plants showed increased dry biomass and root length (p<0.05) and effective AMF colonization compared to controls grown in uninoculated compost-amended tailings. Mesquite shoot tissue lead and zinc concentrations did not exceed domestic animal toxicity limits regardless of whether AMF inoculation was used. The rhizosphere microbial community structure was assessed using denaturing gradient gel electrophoresis (DGGE) profiles of the small subunit RNA gene for bacteria and fungi. Canonical correspondence analysis (CCA) of DGGE profiles showed that the rhizosphere fungal community structure at the end of the experiment was significantly different from the community structure in the tailings, compost, and AMF inocula prior to planting. Further, CCA showed that AMF inoculation significantly influenced the development of both the fungal and bacterial rhizosphere community structures after two months. The changes observed in the rhizosphere microbial community structure may be either a direct effect of the AMF inocula, caused by changes in plant physiology induced by

  6. Structural and compositional characterization of Bi1-xSbx nanowire arrays grown by pulsed deposition to improve growth uniformity

    NASA Astrophysics Data System (ADS)

    Cassinelli, M.; Müller, S.; Aabdin, Z.; Peranio, N.; Eibl, O.; Trautmann, C.; Toimil-Molares, M. E.

    2015-12-01

    Arrays of Bi1-xSbx nanowire with various compositions (0 ⩽ x ⩽ 1) are grown in etched ion-track membranes by pulsed electrochemical deposition. Nanowires of diameter from 130 nm down to 18 nm are characterized by means of X-ray diffraction and high-resolution electron microscopy combined with electron diffraction and energy dispersive X-ray analysis. Compared to potentiostatic deposition, the pulsed synthesis method leads to a more uniform growth and higher filling rate of the wires across the entire template. By tuning the deposition parameters, we demonstrate excellent control over the wire composition and crystallographic orientation. The deposition process presented facilitates the development of future nanowire-based thermoelectric sensors, which are expected to exhibit a higher sensitivity and a faster response compared to thin film sensors.

  7. Electrical property and structural analysis of amphoteric impurity Ge doped GaSe crystal grown by liquid phase growth

    NASA Astrophysics Data System (ADS)

    Sato, Y.; Zhao, S.; Maeda, K.; Tanabe, T.; Oyama, Y.

    2017-06-01

    In order to improve conversion efficiency of THz wave generation, Germanium (Ge)-doped gallium selenide (GaSe) single crystals have been grown by Temperature Difference Method under Controlled Vapor Pressure (TDM-CVP). In this article, electrical property and lattice constant of Ge doped GaSe (GaSe:Ge) crystal are compared with that of not-intentionally doped GaSe crystal. Compared with non-doped GaSe crystal, carrier concentration p was decreased by Ge-doping (not-intentionally doped GaSe p = 3.2 ×1015 cm-3 at 255 K, GaSe:Ge p = 4.9 ×1014 cm-3 at 255 K). In addition, it has been confirmed that lattice constant of GaSe crystal increased with doping Ge concentration increased.

  8. Surface structure and surface kinetics of InN grown by plasma-assisted atomic layer epitaxy: A HREELS study

    SciTech Connect

    Acharya, Ananta R. E-mail: anantaach@gmail.com; Thoms, Brian D.; Nepal, Neeraj; Eddy, Charles R.

    2015-03-15

    The surface bonding configuration and kinetics of hydrogen desorption from InN grown by plasma-assisted atomic layer epitaxy have been investigated. High resolution electron energy loss spectra exhibited loss peaks assigned to a Fuchs–Kliewer surface phonon, N-N and N-H surface species. The surface N-N vibrations are attributed to surface defects. The observation of N-H but no In-H surface species suggested N-terminated InN. Isothermal desorption data were best fit by the first-order desorption kinetics with an activation energy of (0.88 ± 0.06) eV and pre-exponential factor of (1.5 ± 0.5) × 10{sup 5 }s{sup −1}.

  9. Relation between growth rate and structure of graphene grown in a 4″ showerhead chemical vapor deposition reactor.

    PubMed

    Bekdüz, B; Beckmann, Y; Meier, J; Rest, J; Mertin, W; Bacher, G

    2017-04-07

    The chemical vapor deposition (CVD) growth of graphene on copper is controlled by a complex interplay of substrate preparation, substrate temperature, pressure and flow of reactive gases. A large variety of recipes have been suggested in literature, often quite specific to the reactor, which is being used. Here, we report on a relation between growth rate and quality of graphene grown in a scalable 4″ CVD reactor. The growth rate is varied by substrate pre-treatment, chamber pressure, and methane to hydrogen (CH4:H2) ratio, respectively. We found that at lower growth rates graphene grains become hexagonal rather than randomly shaped, which leads to a reduced defect density and a sheet resistance down to 268 Ω/sq.

  10. Structure and optical band gaps of (Ba,Sr)SnO{sub 3} films grown by molecular beam epitaxy

    SciTech Connect

    Schumann, Timo; Raghavan, Santosh; Ahadi, Kaveh; Kim, Honggyu; Stemmer, Susanne

    2016-09-15

    Epitaxial growth of (Ba{sub x}Sr{sub 1−x})SnO{sub 3} films with 0 ≤ x ≤ 1 using molecular beam epitaxy is reported. It is shown that SrSnO{sub 3} films can be grown coherently strained on closely lattice and symmetry matched PrScO{sub 3} substrates. The evolution of the optical band gap as a function of composition is determined by spectroscopic ellipsometry. The direct band gap monotonously decreases with x from to 4.46 eV (x = 0) to 3.36 eV (x = 1). A large Burnstein-Moss shift is observed with La-doping of BaSnO{sub 3} films. The shift corresponds approximately to the increase in Fermi level and is consistent with the low conduction band mass.

  11. Anisotropic structural and optical properties of semi-polar (11–22) GaN grown on m-plane sapphire using double AlN buffer layers

    PubMed Central

    Zhao, Guijuan; Wang, Lianshan; Yang, Shaoyan; Li, Huijie; Wei, Hongyuan; Han, Dongyue; Wang, Zhanguo

    2016-01-01

    We report the anisotropic structural and optical properties of semi-polar (11–22) GaN grown on m-plane sapphire using a three-step growth method which consisted of a low temperature AlN buffer layer, followed by a high temperature AlN buffer layer and GaN growth. By introducing double AlN buffer layers, we substantially improve the crystal and optical qualities of semi-polar (11–22) GaN, and significantly reduce the density of stacking faults and dislocations. The high resolution x-ray diffraction measurement revealed that the in-plane anisotropic structural characteristics of GaN layer are azimuthal dependent. Transmission electron microscopy analysis showed that the majority of dislocations in the GaN epitaxial layer grown on m-sapphire are the mixed-type and the orientation of GaN layer was rotated 58.4° against the substrate. The room temperature photoluminescence (PL) spectra showed the PL intensity and wavelength have polarization dependence along parallel and perpendicular to the [1–100] axis (polarization degrees ~ 0.63). The realization of a high polarization semi-polar GaN would be useful to achieve III-nitride based lighting emission device for displays and backlighting. PMID:26861595

  12. Structural properties of InN films grown on O-face ZnO(0001) by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Cho, Yong Jin; Brandt, Oliver; Kaganer, Vladimir M.; Ramsteiner, Manfred; Riechert, Henning; Korytov, Maxim; Albrecht, Martin

    2012-04-09

    We study the impact of substrate temperature and layer thickness on the morphological and structural properties of InN films directly grown on O-face ZnO(0001) substrates by plasma-assisted molecular beam epitaxy. With increasing substrate temperature, an interfacial reaction between InN and ZnO takes place that eventually results in the formation of cubic In{sub 2}O{sub 3} and voids. The properties of the InN films, however, are found to be unaffected by this reaction for substrate temperatures less than 550 deg. C. In fact, both the morphological and the structural quality of InN improve with increasing substrate temperature in the range from 350 to 500 deg. C. High quality films with low threading dislocation densities are demonstrated.

  13. Structural and optical properties of the In(x)Ga(1-x)As nanowires grown on SiO2 via vapor-liquid-solid method.

    PubMed

    Shin, Hyun Wook; Shin, Jae Cheol; Kim, Do Yang; Choi, Won Jun; Choe, Jeong-Woo

    2014-08-01

    We report the crystal growth of the In(x)Ga(1-x)As nanowires (NWs) on SiO2 substrate using metal organic chemical vapor deposition. Au nanoparticles which are disintegrated from thin Au film have been used as a catalyst for the vapor-liquid-solid growth. Electron microscopy characterization is performed to investigate the structural properties of the In(x)Ga(1-x)As NW. The In(x)Ga(1-x)As NW grown under an optimal condition has a single-crystal wurtzite structure without any misfit dislocation or stacking fault. Strong room temperature photoluminescence peaks are observed from In(x)Ga(1-x)As NWs passivated by GaAs. Very low light reflectance is measured at the NW surface in the wavelength range from 250 to 1200 nm. The single crystal In(x)Ga(1-x)As NWs are applicable to the various electrical and optical devices.

  14. Spatially correlated structural and optical characterization of a single InGaAs quantum well fin selectively grown on Si by microscopy and cathodoluminescence techniques

    NASA Astrophysics Data System (ADS)

    David, S.; Roque, J.; Rochat, N.; Bernier, N.; Piot, L.; Alcotte, R.; Cerba, T.; Martin, M.; Moeyaert, J.; Bogumilowizc, Y.; Arnaud, S.; Bertin, F.; Bassani, F.; Baron, T.

    2016-05-01

    Structural and optical properties of InGaAs quantum well fins (QWFs) selectively grown on Si using the aspect ratio trapping (ART) method in 200 nm deep SiO2 trenches are studied. A new method combining cathodoluminescence, transmission electron microscopy, and precession electron diffraction techniques is developed to spatially correlate the presence of defects and/or strain with the light emission properties of a single InGaAs QWF. Luminescence losses and energy shifts observed at the nanoscale along InGaAs QWF are correlated with structural defects. We show that strain distortions measured around threading dislocations delimit both high and low luminescent areas. We also show that trapped dislocations on SiO2 sidewalls can also result in additional distortions. Both behaviors affect optical properties of QWF at the nanoscale. Our study highlights the need to improve the ART growth method to allow integration of new efficient III-V optoelectronic components on Si.

  15. Structural and molecular regulation of lung maturation by intratracheal vascular endothelial growth factor administration in the normally grown and placentally restricted fetus.

    PubMed

    McGillick, Erin V; Orgeig, Sandra; Morrison, Janna L

    2016-03-01

    Inhibition of hypoxia signalling leads to respiratory distress syndrome (RDS), whereas administration of vascular endothelial growth factor (VEGF), the most widely characterized hypoxia responsive factor, protects from RDS. In the lung of the chronically hypoxaemic placentally restricted (PR) fetus, there is altered regulation of hypoxia signalling. This leads to reduced surfactant maturation in late gestation and provides evidence for the increased risk of RDS in growth restricted neonates at birth. We evaluated the effect of recombinant human VEGF administration with respect to bypassing the endogenous regulation of hypoxia signalling in the lung of the normally grown and PR sheep fetus. There was no effect of VEGF administration on fetal blood pressure or fetal breathing movements. We examined the effect on the expression of genes regulating VEGF signalling (FLT1 and KDR), angiogenesis (ANGPT1, AQP1, ADM), alveolarization (MMP2, MMP9, TIMP1, COL1A1, ELN), proliferation (IGF1, IGF2, IGF1R, MKI67, PCNA), inflammation (CCL2, CCL4, IL1B, TNFA, TGFB1, IL10) and surfactant maturation (SFTP-A, SFTP-B, SFTP-C, SFTP-D, PCYT1A, LPCAT, LAMP3, ABCA3). Despite the effects of PR on the expression of genes regulating airway remodelling, inflammatory signalling and surfactant maturation, there were very few effects of VEGF administration on gene expression in the lung of both the normally grown and PR fetus. There were, however, positive effects of VEGF administration on percentage tissue, air space and numerical density of SFTP-B positive alveolar epithelial cells in fetal lung tissue. These results provide evidence for the stimulatory effects of VEGF administration on structural maturation in the lung of both the normally grown and PR fetus. © 2015 The Authors. The Journal of Physiology © 2015 The Physiological Society.

  16. Optical properties and structural characteristics of ZnMgO grown by plasma assisted molecular beam epitaxy

    SciTech Connect

    Wassner, Thomas A.; Laumer, Bernhard; Maier, Stefan; Stutzmann, Martin; Laufer, Andreas; Meyer, Bruno K.; Eickhoff, Martin

    2009-01-15

    Wurtzite Zn{sub 1-x}Mg{sub x}O thin films with Mg contents between x=0 and x=0.37 were grown on c-plane sapphire substrates by plasma assisted molecular beam epitaxy using a MgO/ZnMgO buffer layer. The a-lattice parameter is independent from the Mg concentration, whereas the c-lattice parameter decreases from 5.20 A for x=0 to 5.17 A for x=0.37, indicating pseudomorphic growth. The near band edge photoluminescence shows a blueshift with increasing Mg concentration to an emission energy of 4.11 eV for x=0.37. Simultaneously, the energetic position of the deep defect luminescence shows a linear shift from 2.2 to 2.8 eV. Low temperature transmission measurements reveal strong excitonic features for the investigated composition range and alloy broadening effects for higher Mg contents. The Stokes shift as well as the Urbach energy is increased to values of up to 125 and 54 meV for x=0.37, respectively, indicating exciton localization due to alloy fluctuations.

  17. Infrared study of the absorption edge of {beta}-InN films grown on GaN/MgO structures

    SciTech Connect

    Perez-Caro, M.; Rodriguez, A. G.; Vidal, M. A.; Navarro-Contreras, H.

    2010-07-15

    Infrared optical studies were carried out in a group of cubic InN samples grown by gas source molecular beam epitaxy on MgO (001) substrates. Room temperature (RT) reflectance and low-temperature (LT) transmittance measurements were performed by using fast Fourier transform infrared spectrometry. Reflectance fittings allowed to establish that {beta}-InN films have large free-carrier concentrations present (>10{sup 19} cm{sup -3}), a result that is corroborated by Hall effect measurements. Each sample explored exhibited a different optical absorption edge. The Varshni parameters that describe adequately the optical absorption edge responses with temperature are obtained for the set of samples studied. The observed temperatures changes, from LT to RT, are the lowest reported for III-V semiconductor binary compounds. The temperature coefficient of the conduction band depends on the strength of the electron-phonon interaction (e-ph-i), as well as on the thermal expansion. It has been predicted that cubic InN has one of the smallest e-ph-i of all III-V compounds, which is corroborated by these results. The variation in values of absorption edges is clearly consistent with the Burstein-Moss and band renormalization effects, produced by high free electron concentrations. It is shown that the conduction band in {beta}-InN, analogous to wurtzite InN, follows a nonparabolic behavior.

  18. Photoluminescence quenching, structures, and photovoltaic properties of ZnO nanostructures decorated plasma grown single walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Aïssa, Brahim; Nedil, Mourad; Belaidi, Abdelhak; Isaifan, Rima J.; Bentouaf, Ali; Fauteux, Christian; Therriault, Daniel

    2017-05-01

    Zinc oxide (ZnO) nanostructures were successfully grown directly on single walled carbon nanotubes (SWCNT) template through the CO2 laser-induced chemical liquid deposition (LCLD) process. Photoluminescence (PL) of the deposited ZnO/SWCNT hybrid composites exhibits, at room temperature, a narrow near UV band located at 390 nm with no emission bands in the visible region, indicating a high degree of crystalline quality of the ZnO nanostructures. Moreover, when the relative SWCNT loads are varied within the composites, the PL intensity and the diffused optical reflectance diminish in comparison with those of ZnO alone, owing to the transfer of photo-excited electrons from ZnO to the SWCNT, and the enhancement of the optical absorbance, respectively. Finally, these ZnO/SWCNT hybrid composites are integrated into a heterojunction photovoltaic-based device, using PEDOT:PSS on ITO/glass substrate. The devices show an evident p-n junction behavior in the dark, and a clear I- V curve shift downward when illuminated with an open-circuit voltage of 1.1 V, a short circuit current density of 14.05 μA cm-2, and a fill factor of ˜35%. These results indicate that these composites fabricated via LCLD process could be promising for optoelectronic and energy-harvesting devices.

  19. Surface segregation and structure of Sb-doped Si(100) films grown at low temperature by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Hobart, K. D.; Godbey, D. J.; Twigg, M. E.; Fatemi, M.; Thompson, P. E.; Simons, D. S.

    1995-07-01

    Sb surface segregation and doping during Si(100) molecular beam epitaxy were studied for growth temperatures of 320-500°C. Surface segregation was analyzed by depth profiling with secondary ion mass spectrometry and the results indicate the existence of several distinct dopant concentration- and temperature-dependent surface segregation regimes: (1) For dilute Sb surface concentrations the measurements reveal a region where bulk and surface concentrations are linearly related, and the surface segregation is described by a constant. However, the experimentally determined temperature dependence of the segregation does not follow simple kinetics theory, and appreciable surface segregation is observed at temperatures ≤ 400°C. (2) At temperatures ≥ 350°C, the surface segregation reaches a maximum for Sb surface concentrations of 0.5 monolayers. (3) For surface concentrations near 1 monolayer, the surface segregation decreases with increasing surface Sb coverage due to dopant interaction within surface and subsurface layers. In cases where films were grown under very high dopant fluxes, we have identified cone-like defects and stacking faults that are the result of the apparent surface concentration exceeding 1 monolayer.

  20. Effect of substrate temperature on structural and optical properties of ZnO nanostructures grown by thermal evaporation method

    NASA Astrophysics Data System (ADS)

    Tu, Nguyen; Trung, Do Quang; Kien, N. D. T.; Huy, P. T.; Nguyen, D. H.

    2017-01-01

    In this study, ZnO nanostructures were synthesized on SiO2/Si substrate by thermal evaporation method. The dependence of the crystalline phase, morphologies and chemical composition of the samples grown at different substrate temperatures were systematically studied. The XRD, Raman spectra, FTIR spectra and XPS results reveal the existence of Zn2SiO4 phase, beside the ZnO phase. The Zn2SiO4 phase dominates at high substrate temperature and vise versa. Under UV excitation at room temperature, the samples show three distinct emission bands namely UV ( 380 nm), green ( 525 nm), and NIR (730 nm). The increase of the PL intensity of the NIR emission with increasing substrate temperature, indicates the relation between this emission and the higher Zn2SiO4 phase content in the samples. Origin of the rarely observed NIR emission band is attributed to the energy transition from non-bridging oxygen hole centers of SiO2 to the Zni and Vo states of Zn2SiO4.

  1. Strain and structure heterogeneity in MoS2 atomic layers grown by chemical vapour deposition

    SciTech Connect

    Liu, Zheng; Amani, Matin; Najmaei, Sina; Xu, Quan; Zou, Xiaolong; Zhou, Wu; Yu, Ting; Qiu, Caiyu; Birdwell, A. Glen; Crowne, Frank J.; Vajtai, Robert; Yakobson, Boris I.; Xia, Zhenhai; Dubey, Madan; Ajayan, Pulickel M.; Lou, Jun

    2014-11-18

    Monolayer molybdenum disulfide (MoS2) has attracted tremendous attention due to its promising applications in high-performance field-effect transistors, phototransistors, spintronic devices, and nonlinear optics. The enhanced photoluminescence effect in monolayer MoS2 was discovered and, as a strong tool, was employed for strain and defect analysis in MoS2. Recently, large-size monolayer MoS2 has been produced by chemical vapor deposition but has not yet been fully explored. Here we systematically characterize chemical vapor deposition grown MoS2 by PL spectroscopy and mapping, and demonstrate non-uniform strain in single-crystalline monolayer MoS2 and strain-induced band gap engineering. We also evaluate the effective strain transferred from polymer substrates to MoS2 by three-dimensional finite element analysis. In addition, our work demonstrates that PL mapping can be used as a non-contact approach for quick identification of grain boundaries in MoS2.

  2. Temperature Dependences of the Product of the Differential Resistance by the Area in MIS-Structures Based on Cd x Hg1- x Te Grown by Molecularbeam Epitaxy on Alternative Si and GaAs Substrates

    NASA Astrophysics Data System (ADS)

    Voitsekhovskii, A. V.; Nesmelov, S. N.; Dzyadukh, S. M.; Varavin, V. S.; Vasil'ev, V. V.; Dvoretskii, S. A.; Mikhailov, N. N.; Yakushev, M. V.; Sidorov, G. Yu.

    2017-06-01

    In a temperature range of 9-200 K, temperature dependences of the differential resistance of space-charge region in the strong inversion mode are experimentally studied for MIS structures based on CdxHg1-xTe (x = 0.22-0.40) grown by molecular-beam epitaxy. The effect of various parameters of structures: the working layer composition, the type of a substrate, the type of insulator coating, and the presence of a near-surface graded-gap layer on the value of the product of differential resistance by the area is studied. It is shown that the values of the product RSCRA for MIS structures based on n-CdHgTe grown on a Si(013) substrate are smaller than those for structures based on the material grown on a GaAs(013) substrate. The values of the product RSCRA for MIS structures based on p-CdHgTe grown on a Si(013) substrate are comparable with the value of the analogous parameter for MIS structures based on p-CdHgTe grown on a GaAs(013) substrate.

  3. Structure, magnetic, and microwave properties of thick Ba-hexaferrite films epitaxially grown on GaN/Al2O3 substrates

    NASA Astrophysics Data System (ADS)

    Chen, Z.; Yang, A.; Mahalingam, K.; Averett, K. L.; Gao, J.; Brown, G. J.; Vittoria, C.; Harris, V. G.

    2010-06-01

    Thick barium hexaferrite [BaOṡ(Fe2O3)6] films, having the magnetoplumbite structure (i.e., Ba M), were epitaxially grown on c-axis oriented GaN/Al2O3 substrates by pulsed laser deposition followed by liquid phase epitaxy. X-ray diffraction showed (0,0,2n) crystallographic alignment with pole figure analyses confirming epitaxial growth. High resolution transmission electron microscopy images revealed magnetoplumbite unit cells stacked with limited interfacial mixing. Saturation magnetization, 4πMs, was measured for as-grown films to be 4.1±0.3 kG with a perpendicular magnetic anisotropy field of 16±0.3 kOe. Ferromagnetic resonance linewidth, the peak-to-peak power absorption derivative at 53 GHz, was 86 Oe. These properties will prove enabling for the integration of low loss Ba M ferrite microwave passive devices with active semiconductor circuit elements in systems-on-a-wafer architecture.

  4. Growth temperature effect on the structural and magnetic properties of Fe{sub 3}O{sub 4} films grown by the self-template method

    SciTech Connect

    Takahashi, R. Misumi, H.; Lippmaa, M.

    2014-07-21

    We have investigated the effect of growth temperature on the structure, surface morphology, and magnetic properties of Fe{sub 3}O{sub 4} thin films grown on SrTiO{sub 3}(001) substrates by a self-template method. To eliminate the intermixing of (001) and (111) orientations that usually occurs in spinel films grown on perovskite substrates, a thin self-template layer of (001)-oriented Fe{sub 3}O{sub 4} was deposited on a SrTiO{sub 3}(001) substrate at 400 °C prior to the main film growth at temperatures of up to 1100 °C. Increasing the growth temperature from 400 °C to 1100 °C resulted in greatly improved crystallinity of the Fe{sub 3}O{sub 4} thin films, with the rocking curve width dropping from 1.41° to 0.28°. Surface analysis by atomic force microscopy showed that raising the growth temperature increased the grain size and the surface roughness, ultimately leading to the formation of regular nanopyramid arrays at 1100 °C. The surface roughening and pyramid formation are caused by the dominance of the lowest surface energy spinel (111) crystal facet. The nanopyramids were fully relaxed but still perfectly (001)-oriented in the out-of-plane direction. The largest pyramids had the lowest coercivity due to a reduction of the demagnetization effect.

  5. Strain-balanced InAs/GaSb type-II superlattice structures and photodiodes grown on InAs substrates by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Huang, Yong; Ryou, Jae-Hyun; Dupuis, Russell D.; Zuo, Daniel; Kesler, Benjamin; Chuang, Shun-Lien; Hu, Hefei; Kim, Kyou-Hyun; Ting Lu, Yen; Hsieh, K. C.; Zuo, Jian-Min

    2011-07-01

    We propose and demonstrate strain-balanced InAs/GaSb type-II superlattices (T2SLs) grown on InAs substrates employing GaAs-like interfacial (IF) layers by metalorganic chemical vapor deposition (MOCVD) for effective strain management, simplified growth scheme, improved materials crystalline quality, and reduced substrate absorption. The in-plane compressive strain from the GaSb layers in the T2SLs on the InAs was completely balanced by the GaAs-like IF layers formed by controlled precursor carry-over and anion exchange effects, avoiding the use of complicated IF layers and precursor switching schemes that were used for the MOCVD growth of T2SLs on GaSb. An infrared (IR) p-i-n photodiode structure with 320-period InAs/GaSb T2SLs on InAs was grown and the fabricated devices show improved performance characteristics with a peak responsivity of ˜1.9 A/W and a detectivity of ˜6.78 × 109 Jones at 8 μm at 78 K. In addition, the InAs buffer layer and substrate show a lower IR absorption coefficient than GaSb substrates in most of the mid- and long-IR spectral range.

  6. Structural, compositional, optical, and electrical properties of solution-grown Zn{sub x}Cd{sub 1{minus}x}S films

    SciTech Connect

    Al Kuhaimi, S.A.; Tulbah, Z.

    2000-01-01

    Thin films of zinc cadmium sulfide (Zn{sub x}Cd{sub 1{minus}x}S) have been prepared in the entire range from ZnS to CdS by using a chemical solution growth technique. Structural, compositional, optical, and electrical properties of thin films of Zn{sub x}Cd{sub 1{minus}x}S have been studied as a function of x. X-ray studies show that as-grown films are composed of a hexagonal phase in the range 0 {le} x < 0.5 and a cubic sphalerite phase for x {ge} 0.5. Film optical parameters (n,k,{alpha},E{sub g}) were evaluated and correlated with the composition ratio, x. These studies show that Zn{sub x}Cd{sub 1{minus}x}S films of different compositions have two direct transitions with corresponding energy gaps E{sub g} and E{sub g} + {Delta}S{sub 0}. The variations in E{sub g} and E{sub g}+ {Delta}S{sub 0} with x indicate that Zn{sub x}Cd{sub 1{minus}x}S is an amalgamation type following quadratic equations with bowing parameters 0.3 and 0.5, respectively. The resistivity of solution-grown Zn{sub x}Cd{sub 1{minus}x}S films was found to increase with increasing x. The effect of boron doping on electrical properties was also investigated.

  7. Study of post annealing effects on structural and optical properties of sol-gel derived ZnO thin films grown on n-Si substrate

    NASA Astrophysics Data System (ADS)

    Bahadur Yadav, Aniruddh; Periasamy, C.; Jit, S.

    2015-02-01

    Zinc oxide (ZnO) thin films were grown on n-type silicon (100) substrates by sol- gel spin coating technique. The prepared thin films were annealed in the presence of Ar at three different temperatures (at 450°C, 550°C and 650°C) to study the impact of annealing temperature on the structural and optical properties of the ZnO thin films. The structural, surface morphology and optical properties of the thin film were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) measurements respectively. The grown ZnO thin films are polycrystalline in nature with wurtzite hexagonal structure as evident from the XRD and SEM analyses. It further indicates that the crystalline size increases with increasing annealing temperature. The post annealing is also found to influence the optical properties in the terms of band gap energy of the ZnO thin films. The optical energy band gap was found to be decreased from 3.205 to 3.13eV as the annealing temperature is increased from 450°C to 650°C. However, our results concerning the growth of ZnO thin films on Si substrates suggest that there is an intermediate growth temperature allowing for the optimization of the ZnO film growth. The results of the study can be used as a guideline for growing ZnO thin films on n-Si substrates with a homogenous surface morphology, high surface to volume ratio and desired particle size, which are suited for optoelectronic/ gas sensing applications.

  8. Structural properties of Bi{sub 2}Te{sub 3} topological insulator thin films grown by molecular beam epitaxy on (111) BaF{sub 2} substrates

    SciTech Connect

    Fornari, Celso I. Rappl, Paulo H. O.; Abramof, Eduardo; Morelhão, Sérgio L.

    2016-04-28

    Structural properties of topological insulator bismuth telluride films grown epitaxially on (111) BaF{sub 2} with a fixed Bi{sub 2}Te{sub 3} beam flux were systematically investigated as a function of substrate temperature and additional Te flux. A layer-by-layer growth mode is observed since the early stages of epitaxy and remains throughout the whole deposition. Composition of the epitaxial films produced here stays between Bi{sub 2}Te{sub 3} and Bi{sub 4}Te{sub 5}, as determined from the comparison of the measured x-ray diffraction curves with calculations. The substrate temperature region, where the growth rate remains constant, is found to be the most appropriate to obtain ordered Bi{sub 2}Te{sub 3} films. Line width of the L = 18 Bi{sub 2}Te{sub 3} diffraction peaks as low as 140 arcsec was obtained, indicating high crystalline quality. Twinning domains density rises with increasing growth temperature and reducing Te extra flux. X-ray reflectivity curves of pure Bi{sub 2}Te{sub 3} films with thickness from 165 to 8 nm exhibited well defined interference fringes, evidencing homogeneous layers with smooth surface. Our results demonstrate that Bi{sub 2}Te{sub 3} films with very well controlled structural parameters can be obtained. High structural quality Bi{sub 2}Te{sub 3} films as thin as only eight quintuple layers grown here are promising candidates for intrinsic topological insulator.

  9. Role of surface energy on the morphology and optical properties of GaP micro & nano structures grown on polar and non-polar substrates

    NASA Astrophysics Data System (ADS)

    Roychowdhury, R.; Kumar, Shailendra; Wadikar, A.; Mukherjee, C.; Rajiv, K.; Sharma, T. K.; Dixit, V. K.

    2017-10-01

    Role of surface energy on the morphology, crystalline quality, electronic structure and optical properties of GaP layer grown on Si (001), Si (111), Ge (111) and GaAs (001) is investigated. GaP layers are grown on four different substrates under identical growth kinetics by metal organic vapour phase epitaxy. The atomic force microscopy images show that GaP layer completely covers the surface of GaAs substrate. On the other hand, the surfaces of Si (001), Si (111), Ge (111) substrates are partially covered with crystallographically morphed GaP island type micro and nano-structures. Origin of these crystallographically morphed GaP island is explained by the theoretical calculation of surface energy of the layer and corresponding substrates respectively. The nature of GaP island type micro and nano-structures and layers are single crystalline with existence of rotational twins on Si and Ge (111) substrates which is confirmed by the phi, omega and omega/2theta scans of high resolution x-ray diffraction. The electronic valence band offsets between the GaP and substrates have been determined from the valence band spectra of ultraviolet photoelectron spectroscopy. The valence electron plasmon of GaP are investigated by studying the energy values of Ga (3d) core level along with loss peaks in the energy dependent photoelectron spectra. The peak observed within the range of 3-6 eV from the Ga (3d) core level in the photoelectron spectra are associated to inter band transitions as their energy values are estimated from the pseudo dielectric function by the spectroscopic ellipsometry.

  10. Effect of vanadium substitution on structural and electrical properties of sol-gel grown nanostructured zinc oxide

    NASA Astrophysics Data System (ADS)

    Boricha, Hetal; Rajyaguru, Bhargav; Gadani, Keval; Rathod, K. N.; Shrimali, V. G.; Udeshi, Bhagyashree; Keshvani, M. J.; Joshi, A. D.; Pandya, D. D.; Solanki, P. S.; Shah, N. A.

    2017-05-01

    In the present communication, we report the results on the structural and electrical studies on nanostructured pure (ZnO) and Vanadium (V) doped Zn0.95V0.05O samples synthesized using low cost Sol-Gel technique. To understand the structural properties and their dependence on V substitution, X-Ray diffraction (XRD) measurement was carried out for both the samples understudy. XRD results reveal the single phasic wurtzite nature of both the samples showing hexagonal unit cell structure. A minor phase of ZnV2O6 is observed in V doped ZnO sample. Improved dielectric permittivity, enhanced ac conductivity (σac) and suppression in impedance have been discussed on the basis of structural modifications by the substitution of V in ZnO, enhanced charge carrier concentration, charge carrier polarization and correlated barrier hopping due to the localized state.

  11. Optical Properties of Novel GaN 3D Structures Grown by Metal-Organic Chemical Vapor Deposition (MOCVD)

    NASA Astrophysics Data System (ADS)

    Sacilotti, Marco; Imhoff, Luc; Dumas, Colette; Viste, Pierre; Vial, Jean-Claude; Baldeck, Patrice; Colombier, Isabelle; Donatini, Fabrice

    2004-06-01

    Optical properties of novel micrometer-size Ga and GaN three-dimensional structures obtained by the metal-organic chemical vapour deposition (MOCVD) technique are presented in this letter. These structures are obtained as metallic three dimensions (3D) micrometer-size objects on an appropriate substrate by metalorganic (TMGa) pyrolisis and then GaN transformed on annealing under NH3 atmosphere at 650-750°C. These 3D GaN structures are analysed by optical means, using two-photon excitation (800 nm) and by UV Hg lamp fluorescent spectroscopy techniques, adapted to two-optical-microscopes apparatus. Very intense and blue/yellow light emission is observed from these 3D structures under 800 nm two-photon laser excitation and under UV Hg lamp excitation.

  12. Multienergy gold ion implantation for enhancing the field electron emission characteristics of heterogranular structured diamond films grown on Au-coated Si substrates

    NASA Astrophysics Data System (ADS)

    Sankaran, K. J.; Manoharan, D.; Sundaravel, B.; Lin, I. N.

    2016-09-01

    Multienergy Au-ion implantation enhanced the electrical conductivity of heterogranular structured diamond films grown on Au-coated Si substrates to a high level of 5076.0 (Ω cm)-1 and improved the field electron emission (FEE) characteristics of the films to low turn-on field of 1.6 V/μm, high current density of 5.4 mA/cm2 (@ 2.65 V/μm), and high lifetime stability of 1825 min. The catalytic induction of nanographitic phases in the films due to Au-ion implantation and the formation of diamond-to-Si eutectic interface layer due to Au-coating on Si together encouraged the efficient conducting channels for electron transport, thereby improved the FEE characteristics of the films.

  13. Optical quality and structural perfection in La/sub 3/Ga/sub 5/SiO/sub 14/ single crystals grown by Czochralski's method

    SciTech Connect

    Dubovik, M.F.; Ivanova, G.M.; Lebedev, S.A.; Nazarenko, B.P.; Tkachenko, V.F.

    1988-08-01

    Single crystals of La/sub 3/Ga/sub 5/SiO/sub 14/ (LGS, langasite) can act as laser media and are also highly effective piezoelectrics having zero temperature coefficient of frequency. We have grown large langasite single crystals, diameter up to 50 mm and mass up to 600 g, by a modified form of Czochralski's method with automatic control, where we found that the main inhomogeneities are bulk defects, which are localized in the axial section no matter what the orientation for the seed, and inclusions, which include bubbles and microcracks, transverse growth banding, and block structure. These inhomogeneities are related to the growth conditions and make themselves felt in different ways. The optical quality was evaluated from the anomalous birefringence.

  14. The effect of sputtering gas pressure on the structure and optical properties of MgNiO films grown by radio frequency magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Xie, Wuze; Jiao, Shujie; Wang, Dongbo; Gao, Shiyong; Wang, Jinzhong; Yu, Qingjiang; Li, Hongtao

    2017-05-01

    In this study, MgNiO thin films were grown on quartz substrates by radio frequency (RF) magnetron sputtering. The influence of different sputtering pressures on the crystalline and optical properties of MgNiO thin films has been studied. X-ray diffraction measurement indicates that the MgNiO films are cubic structure with (200) preferred orientation. UV-vis transmission spectra show that all the MgNiO thin films show more than 75% transmission at visible region, and the absorption edges of all thin films locate at solar-blind region (220 nm-280 nm). The lattice constant and Mg content of MgNiO samples were calculated using X-ray diffraction and transmission spectra data. The phase separation is observed both in the X-ray diffraction patterns and transmission spectra, and the phase separation is studied in detail based on the crystal growth theory and sputtering process.

  15. Structural properties of free-standing 50 mm diameter GaN waferswith (101_0) orientation grown on LiAlO2

    SciTech Connect

    Jasinski, Jacek; Liliental-Weber, Zuzanna; Maruska, Herbert-Paul; Chai, Bruce H.; Hill, David W.; Chou, Mitch M.C.; Gallagher, John J.; Brown, Stephen

    2005-09-27

    (10{und 1}0) GaN wafers grown on (100) face of {gamma}-LiAlO{sub 2} were studied using transmission electron microscopy. Despite good lattice matching in this heteroepitaxial system, high densities of planar structural defects in the form of stacking faults on the basal plane and networks of boundaries located on prism planes inclined to the layer/substrate interface were present in these GaN layers. In addition, significant numbers of threading dislocations were observed. High-resolution electron microscopy indicates that stacking faults present on the basal plane in these layers are of low-energy intrinsic I1type. This is consistent with diffraction contrast experiments.

  16. 1-eV InGaAsN/GaAs quantum well structure for high efficiency solar application grown by MOVPE

    NASA Astrophysics Data System (ADS)

    Wu, T. H.; Su, Y. K.; Chuang, R. W.; Huang, C. Y.; Wu, H. J.; Lin, Y. C.

    2013-05-01

    In this article, we have demonstrated 1-eV energy band gap In0.22GaAsNy/GaAs multi-quantum well (MQW) solar cells grown by a metal organic vapor phase epitaxy (MOVPE) system. With nitrogen incorporation, the equivalent band gap energy of quantum well structure will decrease and reach near 1 eV. The structures of In0.22GaAsNy/GaAs MQWs were inserted into an intrinsic absorption layer for absorbing the incident light in the longer wavelength region. From the measurement results, the absorption band edge of In0.22GaAsNy/GaAs MQW solar cells is extended over 1300 nm. On the other hand, in order to improve the device performance pre-deteriorated by nitrogen incorporation, a hybrid structure which consists of In0.22GaAs/GaAs and In0.22GaAsN0.043/GaAs quantum wells is adopted; with this hybrid quantum well structure as the absorption layer, consequently the short circuit current is enhanced from 10.85 to 15.29 mA/cm2.

  17. Influence of arsenic flow on the crystal structure of epitaxial GaAs grown at low temperatures on GaAs (100) and (111) A substrates

    NASA Astrophysics Data System (ADS)

    Galiev, G. B.; Klimov, E. A.; Vasiliev, A. L.; Imamov, R. M.; Pushkarev, S. S.; Trunkin, I. N.; Maltsev, P. P.

    2017-01-01

    The influence of arsenic flow in a growth chamber on the crystal structure of GaAs grown by molecular-beam epitaxy at a temperature of 240°C on GaAs (100) and (111) A substrates has been investigated. The flow ratio γ of arsenic As4 and gallium was varied in the range from 16 to 50. GaAs films were either undoped, or homogeneously doped with silicon, or contained three equidistantly spaced silicon δ-layers. The structural quality of the annealed samples has been investigated by transmission electron microscopy. It is established for the first time that silicon δ-layers in "low-temperature" GaAs serve as formation centers of arsenic precipitates. Their average size, concentration, and spatial distribution are estimated. The dependence of the film structural quality on γ is analyzed. Regions 100-150 nm in size have been revealed in some samples and identified (by X-ray microanalysis) as pores. It is found that, in the entire range of γ under consideration, GaAs films on (111) A substrates have a poorer structural quality and become polycrystalline beginning with a thickness of 150-200 nm.

  18. The influence of In composition on properties of InxGa1-xAs/GaAs structures grown by MOVPE and in situ monitored by spectral reflectance

    NASA Astrophysics Data System (ADS)

    Bedoui, M.; Habchi, M. M.; Moussa, I.; Rebey, A.

    2017-01-01

    Series of InxGa1-xAs/GaAs structures with indium vapor composition ranging from 13 to 100%, denoted samples A, B, C and D, were grown by metalorganic vapor phase epitaxy (MOVPE) at 450 °C and in situ monitored by spectral reflectance (SR). In order to contribute to the enhancement of crystal quality and to understand growth kinetic of InxGa1-xAs/GaAs structures, the dependence of structural and morphological properties on indium composition x was studied. Basing on high resolution x-ray diffraction (HRXRD) measurements, solid indium compositions x of samples A, B, C and D were determined. Also, the evolution of structural quality (dislocations density, grain size, etc.) as a function of indium composition x was quantified. Besides, morphological properties (hatching and islands formations, densities, sizes and uniformities, RMS surface roughness, etc.) and growth process (growth anisotropy, etc.) versus indium composition x were examined using atomic force microscopy (AFM) analysis. Also, reflectance three-dimensional plot as function of time and wavelength was recorded to quantify the evolution of reflectivity in the wavelength range from 400 to 1000 nm and to determine some growth parameters such as growth rates and thicknesses of InxGa1-xAs samples. A good correlation between experimental results issued from different characterizations tools was obtained.

  19. Self-assembling iron oxyhydroxide/oxide tubular structures: laboratory-grown and field examples from Rio Tinto.

    PubMed

    Barge, Laura M; Cardoso, Silvana S S; Cartwright, Julyan H E; Doloboff, Ivria J; Flores, Erika; Macías-Sánchez, Elena; Sainz-Díaz, C Ignacio; Sobrón, Pablo

    2016-11-01

    Rio Tinto in southern Spain has become of increasing astrobiological significance, in particular for its similarity to environments on early Mars. We present evidence of tubular structures from sampled terraces in the stream bed at the source of the river, as well as ancient, now dry, terraces. This is the first reported finding of tubular structures in this particular environment. We propose that some of these structures could be formed through self-assembly via an abiotic mechanism involving templated precipitation around a fluid jet, a similar mechanism to that commonly found in so-called chemical gardens. Laboratory experiments simulating the formation of self-assembling iron oxyhydroxide tubes via chemical garden/chemobrionic processes form similar structures. Fluid-mechanical scaling analysis demonstrates that the proposed mechanism is plausible. Although the formation of tube structures is not itself a biosignature, the iron mineral oxidation gradients across the tube walls in laboratory and field examples may yield information about energy gradients and potentially habitable environments.

  20. Self-assembling iron oxyhydroxide/oxide tubular structures: laboratory-grown and field examples from Rio Tinto

    NASA Astrophysics Data System (ADS)

    Barge, Laura M.; Cardoso, Silvana S. S.; Cartwright, Julyan H. E.; Doloboff, Ivria J.; Flores, Erika; Macías-Sánchez, Elena; Sainz-Díaz, C. Ignacio; Sobrón, Pablo

    2016-11-01

    Rio Tinto in southern Spain has become of increasing astrobiological significance, in particular for its similarity to environments on early Mars. We present evidence of tubular structures from sampled terraces in the stream bed at the source of the river, as well as ancient, now dry, terraces. This is the first reported finding of tubular structures in this particular environment. We propose that some of these structures could be formed through self-assembly via an abiotic mechanism involving templated precipitation around a fluid jet, a similar mechanism to that commonly found in so-called chemical gardens. Laboratory experiments simulating the formation of self-assembling iron oxyhydroxide tubes via chemical garden/chemobrionic processes form similar structures. Fluid-mechanical scaling analysis demonstrates that the proposed mechanism is plausible. Although the formation of tube structures is not itself a biosignature, the iron mineral oxidation gradients across the tube walls in laboratory and field examples may yield information about energy gradients and potentially habitable environments.

  1. Design of Electrically Conductive Structural Composites by Modulating Aligned CVD-Grown Carbon Nanotube Length on Glass Fibers.

    PubMed

    He, Delong; Fan, Benhui; Zhao, Hang; Lu, Xiaoxin; Yang, Minhao; Liu, Yu; Bai, Jinbo

    2017-01-25

    Function-integration in glass fiber (GF) reinforced polymer composites is highly desired for developing lightweight structures and devices with improved performance and structural health monitoring. In this study, homogeneously aligned carbon nanotube (CNT) shell was in situ grafted on GF by chemical vapor deposition (CVD). It was demonstrated that the CNT shell thickness and weight fraction can be modulated by controlling the CVD conditions. The obtained hierarchical CNTs-GF/epoxy composites show highly improved electrical conductivity and thermo-mechanical and flexural properties. The composite through-plane and in-plane electrical conductivities increase from a quasi-isolator value to ∼3.5 and 100 S/m, respectively, when the weight fraction of CNTs grafted on GF fabric varies from 0% to 7%, respectively. Meanwhile, the composite storage modulus and flexural modulus and strength improve as high as 12%, 21%, and 26%, respectively, with 100% retention of the glass transition temperature. The reinforcing mechanisms are investigated by analyzing the composite microstructure and the interfacial adhesion and wetting properties of CNTs-GF hybrids. Moreover, the specific damage-related resistance variation characteristics could be employed to in situ monitor the structural health state of the composites. The outstanding electrical and structural properties of the CNTs-GF composites were due to the specific interfacial and interphase structures created by homogeneously grafting aligned CNTs on each GF of the fabric.

  2. Temporal changes in population genetic diversity and structure in red and white clover grown in three contrasting environments in northern Europe.

    PubMed

    Collins, Rosemary P; Helgadóttir, Áslaug; Frankow-Lindberg, Bodil E; Skøt, Leif; Jones, Charlotte; Skøt, Kirsten P

    2012-11-01

    BACKGOUND AND AIMS: Extending the cultivation of forage legume species into regions where they are close to the margin of their natural distribution requires knowledge of population responses to environmental stresses. This study was conducted at three north European sites (Iceland, Sweden and the UK) using AFLP markers to analyse changes in genetic structure over time in two population types of red and white clover (Trifolium pratense and T. repens, respectively): (1) standard commercial varieties; (2) wide genetic base (WGB) composite populations constructed from many commercial varieties plus unselected material obtained from germplasm collections. At each site populations were grown in field plots, then randomly sampled after 3-5 years to obtain survivor populations. AFLP markers were used to calculate genetic differentiation within and between original and survivor populations. No consistent changes in average genetic diversity were observed between original and survivor populations. In both species the original varieties were always genetically distinct from each other. Significant genetic shift was observed in the white clover 'Ramona' grown in Sweden. The WGB original populations were more genetically similar. However, genetic differentiation occurred between original and survivor WGB germplasm in both species, particularly in Sweden. Regression of climatic data with genetic differentiation showed that low autumn temperature was the best predictor. Within the set of cold sites the highest level of genetic shift in populations was observed in Sweden. The results suggest that changes in population structure can occur within a short time span in forage legumes, resulting in the rapid formation of distinct survivor populations in environmentally challenging sites.

  3. Magnetic and structural properties of BiFeO3 thin films grown epitaxially on SrTiO3/Si substrates

    NASA Astrophysics Data System (ADS)

    Laughlin, Ryan P.; Currie, Daniel A.; Contreras-Guererro, Rocio; Dedigama, Aruna; Priyantha, Weerasinghe; Droopad, Ravindranath; Theodoropoulou, Nikoleta; Gao, Peng; Pan, Xiaoqing

    2013-05-01

    The integration of oxides with semiconductors is important for the technological advancement of the next generation electronics. Concomitant ferroelectric and antiferromagnetic (AF) behavior is demonstrated in single crystal BiFeO3 (BFO) films grown on 20 nm SrTiO3 (STO) virtual substrates on Si(100) using molecular beam epitaxy (MBE). STO thin films are grown in an oxide MBE chamber by co-deposition of Sr, Ti, and molecular O2. Careful control of the O2 during nucleation produced commensurate growth of STO on Si. The sequence of the steps allows for the suppression of an amorphous SiO2 layer. This STO(20 nm)/Si structure was used as a virtual substrate for MBE deposition of BFO on Si without breaking vacuum. BFO was deposited using Fe and O2 plasma with an overpressure of Bi flux, the growth rate was controlled by the incoming Fe flux. The reflection high energy electron diffraction image shows a 2-D growth front with a 6-fold surface reconstruction under optimized O2 pressure of 5 × 10-8 mbar. Cross-sectional transmission electron microscopy (TEM) confirms the high crystallinity of the films and shows sharp, atomically flat interfaces. The selected area diffraction pattern (SADP) reveals that BFO grows in a distorted rhombohedral crystal structure. X-ray diffraction does not show formation of second phases and is consistent with the TEM and SADP results. The BFO films show AF behavior with a Neel temperature that exceeds 350 K, as expected (TN = 673 K) and with a residual ferromagnetic behavior that decreases with film thickness and is consistent with the G-type AF due to the canted spins. The saturation magnetization per unit volume for a 40 nm thick film was 180 emu/cm3 at an in-plane magnetic field of 8 kOe. The ferroelectric behavior of the films was verified using piezoresponse force microscopy.

  4. Structural, electrical and magnetic measurements on oxide layers grown on 316L exposed to liquid lead-bismuth eutectic

    NASA Astrophysics Data System (ADS)

    Hosemann, Peter; Hofer, Christian; Hlawacek, Gregor; Li, Ning; Maloy, Stuart A.; Teichert, Christian

    2012-02-01

    Fast reactors and spallation neutron sources may use lead-bismuth eutectic (LBE) as a coolant. Its physical, chemical, and irradiation properties make it a safe coolant compared to Na cooled designs. However, LBE is a corrosive medium for most steels and container materials. The present study was performed to evaluate the corrosion behavior of the austenitic steel 316L (in two different delivery states). Detailed atomic force microscopy, magnetic force microscopy, conductive atomic force microscopy, and scanning transmission electron microscopy analyses have been performed on the oxide layers to get a better understanding of the corrosion and oxidation mechanisms of austenitic and ferritic/martensitic stainless steel exposed to LBE. The oxide scale formed on the annealed 316L material consisted of multiple layers with different compositions, structures, and properties. The innermost oxide layer maintained the grain structure of what used to be the bulk steel material and shows two phases, while the outermost oxide layer possessed a columnar grain structure.

  5. Colony structure in Ce-doped Al2O3/YAG eutectic systems grown by vertical Bridgman technique

    NASA Astrophysics Data System (ADS)

    Yamada, Seiya; Yoshimura, Masafumi; Sakata, Shin-ichi; Taishi, Toshinori; Hoshikawa, Keigo

    2016-08-01

    We investigated the influence of growth rate and Ce concentration on colony structure variation in Al2O3/YAG:Ce eutectic systems. The distance between boundary zones in the colony structure decreased with increases in either growth rate or Ce concentration. The eutectic spacing in the coarse microstructure in the boundary zone decreased with increasing growth rate but increased with increasing Ce concentration. We conclude that the colony structure is formed by cellular growth driven by constitutional supercooling with an interface instability due to Ce atom accumulation, so that the distance between boundary zones depends on both the growth rate and Ce concentration, and the coarse microstructure in the boundary zone depends on the solidification rate perpendicular to the growth interface at the cell bottom of the microscopic growth interface shape in the cellular growth.

  6. Grain boundary effects on the structural, microstructural and transport behavior of sol - gel grown PrMnO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Keshvani, M. J.; Katba, Savan; Jethva, Sadaf; Udeshi, Malay; Pandya, D. D.; Shah, N. A.; Ravalia, Ashish; Kataria, Bharat; Kuberkar, D. G.

    2017-05-01

    In this communication, we report the results of the studies on the grain boundary (GB) effect on the structural, microstructural and transport properties of nanostructured PrMnO3 (PMO) manganites synthesized by acetate precursor based sol - gel method. As synthesized PMO samples were sintered at various temperatures to understand the role of sintering temperature in modifying the structure - property correlations in the context of GB effects. Structural analysis using X-ray diffraction studies reveal the single phasic nature of all the PMO samples while TEM analysis reveals uniform particle size distribution with agglomeration effect observed in samples sintered at higher temperatures. SEM micrographs depict the increase in grain size with sharp grain boundaries in the samples sintered at a higher temperature. Size-dependent resistivity behavior of the PMO samples have been understood in the light of grain size modification and GB effect.

  7. Structural differences between capped GaSb nanostructures grown by Stranski-Krastanov and droplet epitaxy growth modes

    NASA Astrophysics Data System (ADS)

    DeJarld, Matt; Yan, Lifan; Luengo-Kovac, Marta; Sih, Vanessa; Millunchick, Joanna

    2017-01-01

    Droplet epitaxy (DE) has emerged as an alternative to Stranski-Krastanov (SK) as a method for epitaxial nanostructure formation. We find significant structural differences of similar sized nanostructures embedded in GaAs between the two methods. Atomic force microscopy and atom probe tomography measurements reveal that uncapped and capped SK structures resemble each other. However, the DE nanostructures appear as rings topographically but are quantum dots compositionally. A GaSb wetting layer is present regardless of the growth method and shares a nearly identical Sb concentration profile. DE nanostructures are shown to have a lower Sb concentration, and transmission electron microscopy measurements reveal that they produce less strain on the capping layer. Despite significant structural differences, SK and DE nanostructures exhibit the same photoluminescence response, suggesting that the emission is from a shared feature such as the wetting layer, rather than the nanostructures.

  8. Cellular porous anodic alumina grown in neutral organic electrolyte. 1. Structure, composition, and properties of the films

    SciTech Connect

    Liu, Y.; Alwitt, R.S.; Shimizu, K.

    2000-04-01

    Anodic alumina films with cellular porous structure grow in neutral organic electrolytes with low water content and containing ethylene glycol and a large dicarboxylic acid. An Al carboxylate precipitates in the pore and is extruded from the coating. The porous structure develops even though the current efficiency for film formation is near 95%. The coating matrix contains substantial organic material, 15 wt % by thermal analysis. It is an oxide/organic composite with higher field strength and lower dielectric constant than pure anodic alumina.

  9. Structure of cadmium selen-telluride alloy films grown by the thermal-screen method under highly nonequilibrium conditions

    SciTech Connect

    Belyaev, A. P. Rubets, V. P.; Antipov, V. V.; Toshkhodzhaev, Kh. A.

    2009-06-15

    The results of technological experiments and structural investigations of films of CdSe{sub x}Te{sub 1-x} alloys synthesized by the thermal-screen method on heated and cooled substrates (under highly nonequilibrium conditions) are presented. It is shown that the synthesis of the entire range of compositions of alloy films with the structure from epitaxial to amorphous is possible from the mechanical mixture of CdSe and CdTe powders of the same composition under highly nonequilibrium conditions. The electron diffraction patterns and the microphotographs of film surfaces are reported.

  10. Structural characterization of metastable hcp-Ni thin films epitaxially grown on Au(100) single-crystal underlayers

    SciTech Connect

    Ohtake, Mitsuru; Tanaka, Takahiro; Futamoto, Masaaki; Kirino, Fumiyoshi

    2010-05-15

    Ni(1120) epitaxial thin films with hcp structure were prepared on Au(100) single-crystal underlayers at 100 deg. C by ultra high vacuum molecular beam epitaxy. The detailed film structure is studied by in situ reflection high energy electron diffraction, x-ray diffraction, and transmission electron microscopy. The hcp-Ni film consists of two types of variants whose c-axes are rotated around the film normal by 90 deg. each other. An atomically sharp boundary is recognized between the film and the underlayer, where misfit dislocations are introduced. Presence of such dislocations seems to relieve the strain caused by the lattice mismatch between the film and the underlayer.

  11. Evolution of morphology and structure of Pb thin films grown by pulsed laser deposition at different substrate temperatures

    SciTech Connect

    Lorusso, Antonella Maiolo, Berlinda; Perrone, Alessio; Gontad, Francisco; Maruccio, Giuseppe; Tasco, Vittorianna

    2014-03-15

    Pb thin films were prepared by pulsed laser deposition on a Si (100) substrate at different growth temperatures to investigate their morphology and structure. The morphological analysis of the thin metal films showed the formation of spherical submicrometer grains whose average size decreased with temperature. X-ray diffraction measurements confirmed that growth temperature influences the Pb polycrystalline film structure. A preferred orientation of Pb (111) normal to the substrate was achieved at 30 °C and became increasingly pronounced along the Pb (200) plane as the substrate temperature increased. These thin films could be used to synthesize innovative materials, such as metallic photocathodes, with improved photoemission performances.

  12. The Optical Emission and Absorption Properties of Silicon-Germanium Superlattice Structures Grown on Non-Conventional Silicon Substrate Orientation

    DTIC Science & Technology

    1994-08-01

    26 6. A resonant tunneling quantum well ...a quantum well structure ...................... 35 9. Illustration of free-carrier absorption transitions within the conduction and valence bands...to the quantum well plane in r-space with respect to incident polarized light

  13. Structural and electrical properties of AlN layers grown on silicon by reactive RF magnetron sputtering

    SciTech Connect

    Bazlov, N. Pilipenko, N. Vyvenko, O.; Petrov, Yu.; Mikhailovskii, V.; Ubyivovk, E.; Kotina, I.; Zharinov, V.

    2016-06-17

    AlN films of different thicknesses were deposited on n-Si (100) substrates by reactive radio frequency (rf) magnetron sputtering. Dependences of structure and electrical properties on thickness of deposited films were researched. The structures of the films were analyzed with scanning electron microscopy (SEM) and with transmitting electron microscopy (TEM). Electrical properties of the films were investigated on Au-AlN-(n-Si) structures by means of current-voltage (I-V), capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) techniques. Electron microscopy investigations had shown that structure and chemical composition of the films were thickness stratified. Near silicon surface layer was amorphous aluminum oxide one contained traps of positive charges with concentration of about 4 × 10{sup 18} cm{sup −3}. Upper layers were nanocrystalline ones consisted of both wurzite AlN and cubic AlON nanocrystals. They contained traps both positive and negative charges which were situated within 30 nm distance from silicon surface. Surface densities of these traps were about 10{sup 12} cm{sup −2}. Electron traps with activation energies of (0.2 ÷ 0.4) eV and densities of about 10{sup 10} cm{sup −2} were revealed on interface between aluminum oxide layer and silicon substrate. Their densities varied weakly with the film thickness.

  14. Structural and Electrical Properties of MoTe2 and MoSe2 Grown by Molecular Beam Epitaxy.

    PubMed

    Roy, Anupam; Movva, Hema C P; Satpati, Biswarup; Kim, Kyounghwan; Dey, Rik; Rai, Amritesh; Pramanik, Tanmoy; Guchhait, Samaresh; Tutuc, Emanuel; Banerjee, Sanjay K

    2016-03-23

    We demonstrate the growth of thin films of molybdenum ditelluride and molybdenum diselenide on sapphire substrates by molecular beam epitaxy. In situ structural and chemical analyses reveal stoichiometric layered film growth with atomically smooth surface morphologies. Film growth along the (001) direction is confirmed by X-ray diffraction, and the crystalline nature of growth in the 2H phase is evident from Raman spectroscopy. Transmission electron microscopy is used to confirm the layered film structure and hexagonal arrangement of surface atoms. Temperature-dependent electrical measurements show an insulating behavior that agrees well with a two-dimensional variable-range hopping model, suggesting that transport in these films is dominated by localized charge-carrier states.

  15. 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%.

  16. Structural, optical, and conducting properties of crystalline ZnO:Co thin films grown by reactive electron beam deposition

    NASA Astrophysics Data System (ADS)

    Gürbüz, Osman; Güner, Sadık; Büyükbakkal, Ömer; Çalışkan, Serkan

    2015-01-01

    We deposited an undoped ZnO and 6 different Co doped ZnO (ZnO:Co) thin films on fused silica (SiO2) substrates with ~100 nm thickness at substrate temperature of 125 °C using a Reactive Electron Beam Deposition technique. Energy-Dispersive X-ray Spectroscopy (EDS) was used to analyze the elemental composition rates of films. Elemental Co concentration varies from 4.62 to 28.77 at. %. The surface morphologies and grain sizes of thin films were investigated by Scanning Electron Microscope (SEM). The crystal and phase structures of the ZnO:Co thin films were characterized using X-ray diffraction (XRD). The films have single crystal and polycrystalline structures due to Co concentrations. Theoretical crystallite size and strain calculations were performed by applying the Scherrer and Williamson-Hall (W-H) methods. The grain sizes are 2-4 times greater than the crystalline sizes for ZnO:Co films. Optical properties of the films were studied by absorbance measurements using a UV-vis spectrophotometer. The analysis of the optical absorption spectra indicated that the energy band gap of the bulk ZnO film increased from 3.22 eV to maximum 4.17 eV upon Co deposition. Co2+ ion replaces Zn2+ ion in the structure without causing any remarkable defect for its hexagonal Wurtzite structure. Electrical conducting properties were investigated by using a Four Point Probe (FPP) technique. The conductivity depends on crystalline quality and Co concentration.

  17. SEM and Raman spectroscopy analyses of laser-induced periodic surface structures grown by ethanol-assisted femtosecond laser ablation of chromium

    NASA Astrophysics Data System (ADS)

    Bashir, Shazia; Shahid Rafique, M.; Nathala, Chandra S. R.; Ajami, Ali; Husinsky, Wolfgang

    2015-05-01

    The effect of fluence and pulse duration on the growth of nanostructures on chromium (Cr) surfaces has been investigated upon irradiation of femtosecond (fs) laser pulses in a liquid confined environment of ethanol. In order to explore the effect of fluence, targets were exposed to 1000 pulses at various peak fluences ranging from 4.7 to 11.8 J cm-2 for pulse duration of ∼25 fs. In order to explore the effect of pulse duration, targets were exposed to fs laser pulses of various pulse durations ranging from 25 to 100 fs, for a constant fluence of 11.8 J cm-2. Surface morphology and structural transformations have been analyzed by scanning electron microscopy and Raman spectroscopy, respectively. After laser irradiation, disordered sputtered surface with intense melting and cracking is obtained at the central ablated areas, which are augmented with increasing laser fluence due to enhanced thermal effects. At the peripheral ablated areas, where local fluence is approximately in the range of 1.4-4 mJ cm-2, very well-defined laser-induced periodic surface structures (LIPSS) with periodicity ranging from 270 to 370 nm along with dot-like structures are formed. As far as the pulse duration is concerned, a significant effect on the surface modification of Cr has been revealed. In the central ablated areas, for the shortest pulse duration (25 fs), only melting has been observed. However, LIPSS with dot-like structures and droplets have been grown for longer pulse durations. The periodicity of LIPSS increases and density of dot-like structures decreases with increasing pulse duration. The chemical and structural modifications of irradiated Cr have been revealed by Raman spectroscopy. It confirms the formation of new bands of chromium oxides and enol complexes or Cr-carbonyl compounds. The peak intensities of identified bands are dependent upon laser fluence and pulse duration.

  18. Magnitude differences in agronomic, chemical, nutritional, and structural features among different varieties of forage corn grown on dry land and irrigated land.

    PubMed

    Xin, Hangshu; Abeysekara, Samen; Zhang, Xuewei; Yu, Peiqiang

    2015-03-11

    In this study, eight varieties of corn forage grown in semiarid western Canada (including Pioneer P2501, Pioneer P39m26, Pioneer P7443, Hyland HL3085, Hyland HLBaxxos, Hyland HLR219, Hyland HLSR22, and Pickseed Silex BT) were selected to explore the effect of irrigation implementation in comparison with nonirrigation on (1) agronomic characteristics, (2) basic chemical profiles explored by using a near-infrared reflectance (NIR) system, and (3) protein and carbohydrate internal structural parameters revealed by using an attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) system. Also, principal component analysis (PCA) was performed on spectroscopic data for clarification of differences in molecular structural makeup among the varieties. The results showed that irrigation treatment significantly increased (P < 0.05) contents of dry matter (DM) and organic matter (OM) but decreased crude protein (CP) of corn forages. Significant interactions of irrigation treatment and corn variety were observed on most agronomic characteristics (DM yield, T/ha, days to tasseling, days to silking) and crude fiber (CF) and ether extract (EE) contents as well as some spectral data such as cellulosic compounds (CELC) peak intensity, peak ratios of CHO third peak to CELC, α-helix to β-sheet, and CHO third peak to amide I. Additionally, the spectral ratios of chemical functional groups that related to structural and nonstructural carbohydrates and protein polymers in forages did not remain constant over corn varieties cultivated with and without water treatment. Moreover, different cultivars had different growth, structure, and nutrition performances in this study. Although significant differences could be found in peak intensities, PCA results indicated some structural similarities existed between two treated corn forages with the exception of HL3085 and HLBaxxos. In conclusion, irrigation and corn variety had interaction effects on agronomic, chemical

  19. Atomic structures of silicene layers grown on Ag(111): scanning tunneling microscopy and noncontact atomic force microscopy observations.

    PubMed

    Resta, Andrea; Leoni, Thomas; Barth, Clemens; Ranguis, Alain; Becker, Conrad; Bruhn, Thomas; Vogt, Patrick; Le Lay, Guy

    2013-01-01

    Silicene, the considered equivalent of graphene for silicon, has been recently synthesized on Ag(111) surfaces. Following the tremendous success of graphene, silicene might further widen the horizon of two-dimensional materials with new allotropes artificially created. Due to stronger spin-orbit coupling, lower group symmetry and different chemistry compared to graphene, silicene presents many new interesting features. Here, we focus on very important aspects of silicene layers on Ag(111): First, we present scanning tunneling microscopy (STM) and non-contact Atomic Force Microscopy (nc-AFM) observations of the major structures of single layer and bi-layer silicene in epitaxy with Ag(111). For the (3 × 3) reconstructed first silicene layer nc-AFM represents the same lateral arrangement of silicene atoms as STM and therefore provides a timely experimental confirmation of the current picture of the atomic silicene structure. Furthermore, both nc-AFM and STM give a unifying interpretation of the second layer (√3 × √3)R ± 30° structure. Finally, we give support to the conjectured possible existence of less stable, ~2% stressed, (√7 × √7)R ± 19.1° rotated silicene domains in the first layer.

  20. Atomic Structures of Silicene Layers Grown on Ag(111): Scanning Tunneling Microscopy and Noncontact Atomic Force Microscopy Observations

    PubMed Central

    Resta, Andrea; Leoni, Thomas; Barth, Clemens; Ranguis, Alain; Becker, Conrad; Bruhn, Thomas; Vogt, Patrick; Le Lay, Guy

    2013-01-01

    Silicene, the considered equivalent of graphene for silicon, has been recently synthesized on Ag(111) surfaces. Following the tremendous success of graphene, silicene might further widen the horizon of two-dimensional materials with new allotropes artificially created. Due to stronger spin-orbit coupling, lower group symmetry and different chemistry compared to graphene, silicene presents many new interesting features. Here, we focus on very important aspects of silicene layers on Ag(111): First, we present scanning tunneling microscopy (STM) and non-contact Atomic Force Microscopy (nc-AFM) observations of the major structures of single layer and bi-layer silicene in epitaxy with Ag(111). For the (3 × 3) reconstructed first silicene layer nc-AFM represents the same lateral arrangement of silicene atoms as STM and therefore provides a timely experimental confirmation of the current picture of the atomic silicene structure. Furthermore, both nc-AFM and STM give a unifying interpretation of the second layer (√3 × √3)R ± 30° structure. Finally, we give support to the conjectured possible existence of less stable, ~2% stressed, (√7 × √7)R ± 19.1° rotated silicene domains in the first layer. PMID:23928998

  1. Control of Phase, Structural and Optical Properties of Tin Sulfide Nanostructured Thin Films Grown via Chemical Bath Deposition

    NASA Astrophysics Data System (ADS)

    Mahdi, Mohamed S.; Ibrahim, K.; Hmood, Arshad; Ahmed, Naser M.; Mustafa, Falah I.

    2017-02-01

    In this study, nanostructured tin sulfide (SnS) thin films were synthesized on glass substrates by means of low-cost chemical bath deposition using non-toxic trisodium citrate (TSC) as complexing agent. The influence of varying molar concentration of TSC (0.15-0.21 M) on the tin sulfide phases was investigated. The structural, morphological and optical properties of the films were studied using x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Raman spectroscopy and optical absorption spectroscopy. The XRD patterns confirmed an orthorhombic polycrystalline structure of the as-prepared SnS thin films. The values of average crystalline size and texture coefficient of the major XRD peak increased with increasing TSC concentration. The FESEM micrographs revealed that the synthesized thin films are characterized by a flake-stack structure. The Raman spectra of the films showed the presence of a Sn2S3 peak, which gradually declined in intensity until almost disappearing as the TSC concentration increased from 0.15 M to 0.21 M. The direct energy band gaps estimated from ultraviolet-visible-near-infrared absorption spectra also varied between 1.64 eV to 1.1 eV with increasing TSC concentration from 0.15 M to 0.21 M. The results indicate the crucial role of TSC in the synthesis of SnS nanostructured thin films.

  2. Correlating the Morphological Properties and Structural Organization of Monodisperse Spherical Silica Nanoparticles Grown on a Commercial Silica Surface.

    PubMed

    Moreno, Yolice P; Cardoso, Mateus B; Moncada, Edwin A; dos Santos, João H Z

    2015-10-05

    A variety of nanosilicas have been widely used to fabricate rough surfaces with superhydrophobic and superhydrophilic properties. In this context, we prepared mixed silica and mixed nanosilica that were generated by the growth and self-assembly of synthesized monodisperse silica nanospheres (11-30 nm, 363 m(2)  g(-1) ) on the surface of Sylopol-948 and Dispercoll S3030 by using a base-catalyzed sol-gel route. Using this process, the interactions and hierarchical structure between the nano- and microsized synthesized silica particles were studied by changing the amount of tetraethoxysilane. The resulting materials were characterized by BET analysis, small-angle X-ray scattering (SAXS), dynamic light scattering, FTIR spectroscopy, and SEM. The mixed silica presented a higher specific surface area (326 m(2)  g(-1) ), a six-fold higher percentage of (SiO)6 (44-68 %), and a higher amount of silanol groups (14.0-30.7 %) than Sylopol-948 (271 m(2)  g(-1), 42.6 %, and 12.5 %, respectively). The morphological and hierarchical structural differences in the silica nanoparticles synthesized on the surface of commercial silica (micrometric or nanometric) were identified by SAXS. Mixed micrometric silica exhibited a higher degree of structural organization between particles than mixed nanosilica. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Control of Phase, Structural and Optical Properties of Tin Sulfide Nanostructured Thin Films Grown via Chemical Bath Deposition

    NASA Astrophysics Data System (ADS)

    Mahdi, Mohamed S.; Ibrahim, K.; Hmood, Arshad; Ahmed, Naser M.; Mustafa, Falah I.

    2017-07-01

    In this study, nanostructured tin sulfide (SnS) thin films were synthesized on glass substrates by means of low-cost chemical bath deposition using non-toxic trisodium citrate (TSC) as complexing agent. The influence of varying molar concentration of TSC (0.15-0.21 M) on the tin sulfide phases was investigated. The structural, morphological and optical properties of the films were studied using x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Raman spectroscopy and optical absorption spectroscopy. The XRD patterns confirmed an orthorhombic polycrystalline structure of the as-prepared SnS thin films. The values of average crystalline size and texture coefficient of the major XRD peak increased with increasing TSC concentration. The FESEM micrographs revealed that the synthesized thin films are characterized by a flake-stack structure. The Raman spectra of the films showed the presence of a Sn2S3 peak, which gradually declined in intensity until almost disappearing as the TSC concentration increased from 0.15 M to 0.21 M. The direct energy band gaps estimated from ultraviolet-visible-near-infrared absorption spectra also varied between 1.64 eV to 1.1 eV with increasing TSC concentration from 0.15 M to 0.21 M. The results indicate the crucial role of TSC in the synthesis of SnS nanostructured thin films.

  4. Atomic structure of an ultrathin Fe-silicate film grown on a metal: a monolayer of clay?

    PubMed

    Włodarczyk, Radosław; Sauer, Joachim; Yu, Xin; Boscoboinik, Jorge Anibal; Yang, Bing; Shaikhutdinov, Shamil; Freund, Hans-Joachim

    2013-12-26

    Ultrathin Fe-doped silicate films were prepared on a Ru(0001) surface and, as a function of the Fe/Si ratio, structurally characterized by low-energy electron diffraction, X-ray photoelectron spectroscopy, infrared reflection-absorption spectroscopy, and scanning tunneling microscopy. Density functional theory (DFT) was used to identify the atomic structure. The results show that uniform substitution of Si by Fe in the silicate bilayer frame is thermodynamically unfavorable: the film segregates into a pure silicate and an Fe-silicate phase. The DFT calculations reveal that the Fe-silicate film with an Fe/Si = 1:1 ratio consists of a monolayer of [SiO4] tetrahedra on top of an iron oxide monolayer. As such, it closely resembles the structure of the clay mineral nontronite, a representative of the Fe-rich smectites. Furthermore, the DFT calculations predict formation of bridging Fe-O-Ru bonds between the Fe-silicate film and the Ru substrate accompanied by charge transfer from the metal substrate to the film, so that iron is in the oxidation state +III as in nontronite.

  5. Broad range tuning of structural and optical properties of Zn x Mg1-x O nanostructures grown by vapor transport method

    NASA Astrophysics Data System (ADS)

    Vanjaria, Jignesh V.; Azhar, Ebraheem Ali; Yu, Hongbin

    2016-11-01

    One-dimensional (1D) Zn x Mg1-x O nanomaterials have drawn global attention due to their remarkable chemical and physical properties, and their diverse current and future technological applications. In this work, 1D ZnMgO nanostructures with different magnesium concentrations and different morphologies were grown directly on zinc oxide-coated silicon substrates by thermal evaporation of zinc oxide, magnesium boride and graphite powders. Highly well-defined Mg-rich ZnMgO nanorods with a rock salt structure and Zn-rich ZnMgO nanostructures with a wurtzite structure have been deposited individually by careful optimization of the source mixture and process parameters. Structural and optical properties of the deposited products were studied by scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, and Raman spectroscopy. Cathodoluminescence measurements demonstrate strong dominant peaks at 3.3 eV in Mg poor ZnMgO nanostructures and 4.8 eV in Mg rich nanostructures implying that the ZnMgO nanostructures can be used for the fabrication of deep UV optoelectronic devices. A mechanism for the formation and achieved diverse morphology of the ZnMgO nanostructures was proposed based on the characterization results.

  6. Critical thickness of high structural quality SrTiO3 films grown on orthorhombic (101) DyScO3

    SciTech Connect

    Hawley, Marilyn E; Biegalski, Michael D; Schlom, Darrell G

    2008-01-01

    Strained epitaxial SrTiO{sub 3} films were grown on orthorhombic (101) DyScO{sub 3} substrates by reactive molecular-beam epitaxy. The epitaxy of this substrate/film combination is cube on cube with a pseudocubic out-of-plane (001) orientation. The strain state and structural perfection of films with thicknesses ranging from 50 to 1000 {angstrom} were examined using x-ray scattering. The critical thickness at which misfit dislocations was introduced was between 350 and 500 {angstrom}. These films have the narrowest rocking curves (full width at half maximum) ever reported for any heteroepitaxial oxide film (0.0018{sup o}). Only a modest amount of relaxation is seen in films exceeding the critical thicknesses even after postdeposition annealing at 700{sup o}C in 1 atm of oxygen. The dependence of strain relaxation on crystallographic direction is attributed to the anisotropy of the substrate. These SrTiO{sub 3} films show structural quality more typical of semiconductors such as GaAs and silicon than perovskite materials; their structural relaxation behavior also shows similarity to that of compound semiconductor films.

  7. Non-destructive mapping of doping and structural composition of MOVPE-grown high current density resonant tunnelling diodes through photoluminescence spectroscopy

    NASA Astrophysics Data System (ADS)

    Jacobs, K. J. P.; Stevens, B. J.; Mukai, T.; Ohnishi, D.; Hogg, R. A.

    2015-05-01

    We report on photoluminescence (PL) characterisation of metal-organic vapour phase epitaxy (MOVPE) grown high current density (~700 kA/cm2) InGaAs/AlAs/InP based resonant tunnelling diodes (RTDs) for terahertz emission. The PL mapping we describe allows important information about doping level and uniformity, ternary alloy composition and uniformity, and uniformity of quantum well thickness to be deduced. PL as a function of doping concentration is studied for InGaAs test layers at low temperatures and correlated to secondary-ion mass spectroscopy (SIMS) and electrochemical capacitance-voltage (eCV) profiling to provide non-destructive mapping of doping over the wafer. For the RTD structures, we utilise eCV as a selective etch tool to identify the origin of low temperature PL emission from the quantum well (QW) and the highly doped contact layers. PL mapping of the RTD wafer at low temperatures is shown to allow the assessment of variations in InGaAs alloy composition and QW thickness. Details of the growth process are discussed and confirmed using high resolution X-ray diffraction (HRXRD) crystallography. The rapid non-destructive characterisation and wafer mapping of these structures promises a route to future growth optimisation of such structures.

  8. Structural properties of Bi{sub 2−x}Mn{sub x}Se{sub 3} thin films grown via molecular beam epitaxy

    SciTech Connect

    Babakiray, Sercan; Johnson, Trent A.; Borisov, Pavel; Holcomb, Mikel B.; Lederman, David; Marcus, Matthew A.; Tarafder, Kartick

    2015-07-28

    The effects of Mn doping on the structural properties of the topological insulator Bi{sub 2}Se{sub 3} in thin film form were studied in samples grown via molecular beam epitaxy. Extended x-ray absorption fine structure measurements, supported by density functional theory calculations, indicate that preferential incorporation occurs substitutionally in Bi sites across the entire film volume. This finding is consistent with x-ray diffraction measurements which show that the out of plane lattice constant expands while the in plane lattice constant contracts as the Mn concentration is increased. X-ray photoelectron spectroscopy indicates that the Mn valency is 2+ and that the Mn bonding is similar to that in MnSe. The expansion along the out of plane direction is most likely due to weakening of the Van der Waals interactions between adjacent Se planes. Transport measurements are consistent with this Mn{sup 2+} substitution of Bi sites if additional structural defects induced by this substitution are taken into account.

  9. X-ray absorption near-edge structure of GaN with high Mn concentration grown on SiC

    NASA Astrophysics Data System (ADS)

    Sancho-Juan, O.; Cantarero, A.; Garro, N.; Cros, A.; Martínez-Criado, G.; Salomé, M.; Susini, J.; Olguín, D.; Dhar, S.

    2009-07-01

    By means of x-ray absorption near-edge structure (XANES) several Ga1-xMnxN (0.03grown by molecular beam epitaxy on [0001] SiC substrates. The low mismatch between GaN and SiC allows for a good quality and homogeneity of the material. The measurements were performed in fluorescence mode around both the Ga and Mn K edges. All samples studied present a similar Mn ionization state, very close to 2+, and tetrahedral coordination. In order to interpret the near-edge structure, we have performed ab initio calculations using the full potential linear augmented plane wave method as implemented in the Wien2k code. The calculations show the appearance of a Mn bonding \\mathrm {t_{2}}\\uparrow band localized in the gap region, and the corresponding anti-bonding state \\mathrm {t_{2}}\\downarrow , which seem to be responsible for the double structure which appears at the pre-edge absorption region. The shoulders and main absorption peak of the XANES spectra are attributed to transitions from the Mn(1s) band to the conduction bands, which are partially dipole allowed because of the Mn(4p) contribution to these bands.

  10. Structural differences between light and heavy rare earth element binding chlorophylls in naturally grown fern: Dicranopteris linearis.

    PubMed

    Wei, Zhenggui; Hong, Fashui; Yin, Ming; Li, Huixin; Hu, Feng; Zhao, Guiwen; Wong, Jonathan Woonchung

    2005-09-01

    Chloroplasts and chlorophylls were isolated from the leaves of Dicranopteris linearis, a natural perennial fern sampled at rare earth element (REE) mining areas in the South-Jiangxi region (southern China). The inductively coupled plasma-mass spectrometry (ICP-MS) results indicated that REEs were present in the chloroplasts and chlorophylls of D. linearis. The in vivo coordination environment of light REE (lanthanum) or heavy REE (yttrium) ions in D. linearis chlorophyll-a was determined by the extended X-ray absorption fine structure (EXAFS). Results revealed that there were eight nitrogen atoms in the first coordination shell of the lanthanum atom, whereas there were four nitrogen atoms in the first coordination shell of yttrium. It was postulated that the lanthanum-chlorophyll-a complex might have a double-layer sandwich-like structure, but yttrium-binding chlorophyll-a might be in a single-layer form. Because the content of REE-binding chlorophylls in D. linearis chlorophylls was very low, it is impossible to obtain structural characteristics of REE-binding chlorophylls by direct analysis of the Fourier transform infrared (FTIR) and ultraviolet (UV)-visible spectra of D. linearis chlorophylls. In order to acquire more structural information of REE-binding chlorophyll-a in D. linearis, lanthanum - and yttrium-chlorophyll-a complexes were in vitro synthesized in acetone solution. Element analyses and EXAFS results indicated that REE ions (lanthanum or yttrium) of REE-chlorophyll-a possessed the same coordination environment whether in vivo or in vitro. The FTIR spectra of the REE-chlorophyll-a complexes indicated that REEs were bound to the porphyrin rings of chlorophylls. UV-visible results showed that the intensity ratios of Soret to the Q-band of REE-chlorophyll-a complexes were higher than those of standard chlorophyll-a and pheophytin-a, indicating that REE-chlorophyll-a might have a much stronger ability to absorb the ultraviolet light. The MCD spectrum in

  11. Altered physiological function, not structure, drives increased radiation-use efficiency of soybean grown at elevated CO2.

    PubMed

    Rascher, Uwe; Biskup, Bernhard; Leakey, Andrew D B; McGrath, Justin M; Ainsworth, Elizabeth A

    2010-07-01

    Previous studies of elevated carbon dioxide concentration ([CO(2)]) on crop canopies have found that radiation-use efficiency is increased more than radiation-interception efficiency. It is assumed that increased radiation-use efficiency is due to changes in leaf-level physiology; however, canopy structure can affect radiation-use efficiency if leaves are displayed in a manner that optimizes their physiological capacity, even though the canopy intercepts the same amount of light. In order to determine the contributions of physiology and canopy structure to radiation-use and radiation-interception efficiency, this study relates leaf-level physiology and leaf display to photosynthetic rate of the outer canopy. We used a new imaging approach that delivers three-dimensional maps of the outer canopy during the growing season. The 3D data were used to model leaf orientation and mean photosynthetic electron transport of the outer canopy to show that leaf orientation changes did not contribute to increased radiation-use; i.e. leaves of the outer canopy showed similar diurnal leaf movements and leaf orientation in both treatments. Elevated [CO(2)] resulted in an increased maximum electron transport rate (ETR(max)) of light reactions of photosynthesis. Modeling of canopy light interception showed that stimulated leaf-level electron transport at elevated [CO(2)], and not alterations in leaf orientation, was associated with stimulated radiation-use efficiency and biomass production in elevated [CO(2)]. This study provides proof of concept of methodology to quantify structure-function relationships in combination, allowing a quantitative estimate of the contribution of both effects to canopy energy conversion under elevated [CO(2)].

  12. Optical and structural study of GaN nanowires grown by catalyst-free molecular beam epitaxy. II. Sub-band-gap luminescence and electron irradiation effects

    SciTech Connect

    Robins, Lawrence H.; Bertness, Kris A.; Barker, Joy M.; Sanford, Norman A.; Schlager, John B.

    2007-06-01

    GaN nanowires with diameters of 50-250 nm, grown by catalyst-free molecular beam epitaxy, were characterized by photoluminescence (PL) and cathodoluminescence (CL) spectroscopy at temperatures from 3 to 297 K. Both as-grown samples and dispersions of the nanowires onto other substrates were examined. The properties of the near-band-edge PL and CL spectra were discussed in Part I of this study by [Robins et al. [L. H. Robins, K. A. Bertness, J. M. Barker, N. A. Sanford, and J. B. Schlager, J. Appl. Phys. 101,113505 (2007)]. Spectral features below the band gap, and the effect of extended electron irradiation on the CL, are discussed in Part II. The observed sub-band-gap PL and CL peaks are identified as phonon replicas of the free-exciton transitions, or excitons bound to structural defects or surface states. The defect-related peaks in the nanowires are correlated with luminescence lines previously reported in GaN films, denoted the Y lines [M. A. Reshchikov and H. Morkoc, J. Appl. Phys. 97, 061301 (2005)]. The CL was partially quenched by electron beam irradiation for an extended time; the quenching was stronger for the free and shallow-donor-bound exciton peaks than for the defect-related peaks. The quenching appeared to saturate at high irradiation dose (with final intensity {approx_equal}30% of initial intensity) and was reversible on thermal cycling to room temperature. The electron irradiation-induced quenching of the CL is ascribed to charge injection and trapping phenomena.

  13. Optical and structural study of GaN nanowires grown by catalyst-free molecular beam epitaxy. II. Sub-band-gap luminescence and electron irradiation effects

    NASA Astrophysics Data System (ADS)

    Robins, Lawrence H.; Bertness, Kris A.; Barker, Joy M.; Sanford, Norman A.; Schlager, John B.

    2007-06-01

    GaN nanowires with diameters of 50-250 nm, grown by catalyst-free molecular beam epitaxy, were characterized by photoluminescence (PL) and cathodoluminescence (CL) spectroscopy at temperatures from 3 to 297 K. Both as-grown samples and dispersions of the nanowires onto other substrates were examined. The properties of the near-band-edge PL and CL spectra were discussed in Part I of this study by [Robins et al. [L. H. Robins, K. A. Bertness, J. M. Barker, N. A. Sanford, and J. B. Schlager, J. Appl. Phys. 101,113505 (2007)]. Spectral features below the band gap, and the effect of extended electron irradiation on the CL, are discussed in Part II. The observed sub-band-gap PL and CL peaks are identified as phonon replicas of the free-exciton transitions, or excitons bound to structural defects or surface states. The defect-related peaks in the nanowires are correlated with luminescence lines previously reported in GaN films, denoted the Y lines [M. A. Reshchikov and H. Morkoc, J. Appl. Phys. 97, 061301 (2005)]. The CL was partially quenched by electron beam irradiation for an extended time; the quenching was stronger for the free and shallow-donor-bound exciton peaks than for the defect-related peaks. The quenching appeared to saturate at high irradiation dose (with final intensity ≈30% of initial intensity) and was reversible on thermal cycling to room temperature. The electron irradiation-induced quenching of the CL is ascribed to charge injection and trapping phenomena.

  14. Structural and magnetic properties of Co-doped ZnO thin films grown by ultrasonic spray pyrolysis method

    NASA Astrophysics Data System (ADS)

    Baghdad, R.; Lemée, N.; Lamura, G.; Zeinert, A.; Hadj-Zoubir, N.; Bousmaha, M.; Bezzerrouk, M. A.; Bouyanfif, H.; Allouche, B.; Zellama, K.

    2017-04-01

    Cobalt-doped ZnO thin films with several different percentage of Co from 0 up to 15 at% were synthesized via a cheap, simple and versatile method i.e. ultrasonic spray pyrolysis at atmospheric pressure and a substrate temperature of 350 °C. The structure of the as-prepared samples was characterized by X-ray diffraction (XRD), Raman spectroscopy and FTIR. The Co-doping effect is revealed by the presence of three additional peaks around 235, 470 and 538 cm-1 respect to the Raman spectra of the unsubstituted film. Fourier transform infrared spectroscopy (FTIR) put in evidence the decrease of the bond force constant f with increasing Co-doping. By ultra-violet visible near infrared (UV-Vis-NIR) spectroscopy on Co-doped samples it was possible to show the presence of additional absorption bands at approximately 570, 620 and 660 nm suggesting that Co2+ ions do not change their oxidation when substituted to zinc and the ZnO lattice does not change its wurtzite structure as well. Finally, all our samples exhibit a paramagnetic behavior without any trace of intrinsic room temperature ferromagnetism.

  15. Al2O3 passivation effect in HfO2·Al2O3 laminate structures grown on InP substrates.

    PubMed

    Kang, Hang-Kyu; Kang, Yu-Seon; Kim, Dae-Kyoung; Baik, Min; Song, Jin Dong; An, Youngseo; Kim, Hyoungsub; Cho, Mann-Ho

    2017-04-07

    The passivation effect of an Al2O3 layer on electrical properties were investigated in HfO2--Al2O3 laminate structures grown on InP substrate by atomic layer deposition (ALD). The chemical state using HR-XPS showed that interfacial reactions were dependent on the presence of the Al2O3 passivation layer and its sequence in the HfO2--Al2O3 laminate structures. The Al2O3/HfO2/Al2O3 structure showed the best electrical characteristics, due to the interfacial reaction, compared with those of different stacking structures. The top Al2O3 layer suppressed the interdiffusion of oxidizing species into the HfO2 films, while the bottom Al2O3 layer blocked the outdiffusion of In and P atoms. As a result, the formation of In-O bonds was effectively suppressed in the Al2O3/HfO2/Al2O3/InP structure than that of HfO2-on-InP system. Moreover, conductance data revealed that the Al2O3/ layer on InP reduces the midgap traps to 2.6 × 10(12) eV(-1)cm(-2) (compared with that of HfO2/InP = 5.4 × 10(12) eV(-1)cm(-2)). The suppression of gap states caused by the outdiffusion of In atoms significantly controls the degradation of capacitors caused by leakage current through the stacked oxide layers.

  16. Electronic structures and magnetic moments of Co{sub 3}FeN thin films grown by molecular beam epitaxy

    SciTech Connect

    Ito, Keita; Sanai, Tatsunori; Yasutomi, Yoko; Toko, Kaoru; Honda, Syuta; Suemasu, Takashi; Zhu, Siyuan; Kimura, Akio; Ueda, Shigenori; Takeda, Yukiharu; Saitoh, Yuji; Imai, Yoji

    2013-12-02

    We evaluated electronic structures and magnetic moments in Co{sub 3}FeN epitaxial films on SrTiO{sub 3}(001). The experimentally obtained hard x-ray photoemission spectra of the Co{sub 3}FeN film have a good agreement with those calculated. Site averaged spin magnetic moments deduced by x-ray magnetic circular dichroism were 1.52 μ{sub B} per Co atom and 2.08 μ{sub B} per Fe atom at 100 K. They are close to those of Co{sub 4}N and Fe{sub 4}N, respectively, implying that the Co and Fe atoms randomly occupy the corner and face-centered sites in the Co{sub 3}FeN unit cell.

  17. Genetic Diversity and Population Structure of the Major Peanut (Arachis hypogaea L.) Cultivars Grown in China by SSR Markers

    PubMed Central

    Ren, Xiaoping; Jiang, Huifang; Yan, Zhongyuan; Chen, Yuning; Zhou, Xiaojing; Huang, Li; Lei, Yong; Huang, Jiaquan; Yan, Liying; Qi, Yue; Wei, Wenhui; Liao, Boshou

    2014-01-01

    One hundred and forty-six highly polymorphic simple sequence repeat (SSR) markers were used to assess the genetic diversity and population structure of 196 peanut (Arachis Hypogaea L.) cultivars which had been extensively planted in different regions in China. These SSR markers amplified 440 polymorphic bands with an average of 2.99, and the average gene diversity index was 0.11. Eighty-six rare alleles with a frequency of less than 1% were identified in these cultivars. The largest Fst or genetic distance was found between the cultivars that adapted to the south regions and those to the north regions in China. A neighbor-joining tree of cultivars adapted to different ecological regions was constructed based on pairwise Nei’s genetic distances, which showed a significant difference between cultivars from the south and the north regions. A model-based population structure analysis divided these peanut cultivars into five subpopulations (P1a, P1b, P2, P3a and P3b). P1a and P1b included most the cultivars from the southern provinces including Guangdong, Guangxi and Fujian. P2 population consisted of the cultivars from Hubei province and parts from Shandong and Henan. P3a and P3b had cultivars from the northern provinces including Shandong, Anhui, Henan, Hebei, Jiangsu and the Yangtze River region including Sichuan province. The cluster analysis, PCoA and PCA based on the marker genotypes, revealed five distinct clusters for the entire population that were related to their germplasm regions. The results indicated that there were obvious genetic variations between cultivars from the south and the north, and there were distinct genetic differentiation among individual cultivars from the south and the north. Taken together, these results provided a molecular basis for understanding genetic diversity of Chinese peanut cultivars. PMID:24520347

  18. Genetic diversity and population structure of the major peanut (Arachis hypogaea L.) cultivars grown in China by SSR markers.

    PubMed

    Ren, Xiaoping; Jiang, Huifang; Yan, Zhongyuan; Chen, Yuning; Zhou, Xiaojing; Huang, Li; Lei, Yong; Huang, Jiaquan; Yan, Liying; Qi, Yue; Wei, Wenhui; Liao, Boshou

    2014-01-01

    One hundred and forty-six highly polymorphic simple sequence repeat (SSR) markers were used to assess the genetic diversity and population structure of 196 peanut (Arachis Hypogaea L.) cultivars which had been extensively planted in different regions in China. These SSR markers amplified 440 polymorphic bands with an average of 2.99, and the average gene diversity index was 0.11. Eighty-six rare alleles with a frequency of less than 1% were identified in these cultivars. The largest Fst or genetic distance was found between the cultivars that adapted to the south regions and those to the north regions in China. A neighbor-joining tree of cultivars adapted to different ecological regions was constructed based on pairwise Nei's genetic distances, which showed a significant difference between cultivars from the south and the north regions. A model-based population structure analysis divided these peanut cultivars into five subpopulations (P1a, P1b, P2, P3a and P3b). P1a and P1b included most the cultivars from the southern provinces including Guangdong, Guangxi and Fujian. P2 population consisted of the cultivars from Hubei province and parts from Shandong and Henan. P3a and P3b had cultivars from the northern provinces including Shandong, Anhui, Henan, Hebei, Jiangsu and the Yangtze River region including Sichuan province. The cluster analysis, PCoA and PCA based on the marker genotypes, revealed five distinct clusters for the entire population that were related to their germplasm regions. The results indicated that there were obvious genetic variations between cultivars from the south and the north, and there were distinct genetic differentiation among individual cultivars from the south and the north. Taken together, these results provided a molecular basis for understanding genetic diversity of Chinese peanut cultivars.

  19. Emissions of volatile organic compounds and leaf structural characteristics of European aspen (Populus tremula) grown under elevated ozone and temperature.

    PubMed

    Hartikainen, Kaisa; Nerg, Anne-Marja; Kivimäenpää, Minna; Kontunen-Soppela, Sari; Mäenpää, Maarit; Oksanen, Elina; Rousi, Matti; Holopainen, Toini

    2009-09-01

    Northern forest trees are challenged to adapt to changing climate, including global warming and increasing tropospheric ozone (O(3)) concentrations. Both elevated O(3) and temperature can cause significant changes in volatile organic compound (VOC) emissions as well as in leaf anatomy that can be related to adaptation or increased stress tolerance, or are signs of damage. Impacts of moderately elevated O(3) (1.3x ambient) and temperature (ambient + 1 degrees C), alone and in combination, on VOC emissions and leaf structure of two genotypes (2.2 and 5.2) of European aspen (Populus tremula L.) were studied in an open-field experiment in summer 2007. The impact of O(3) on measured variables was minor, but elevated temperature significantly increased emissions of total monoterpenes and green leaf volatiles. Genotypic differences in the responses to warming treatment were also observed. alpha-Pinene emission, which has been suggested to protect plants from elevated temperature, increased from genotype 5.2 only. Isoprene emission from genotype 2.2 decreased, whereas genotype 5.2 was able to retain high isoprene emission level also under elevated temperature. Elevated temperature also caused formation of thinner leaves, which was related to thinning of epidermis, palisade and spongy layers as well as reduced area of palisade cells. We consider aspen genotype 5.2 to have better potential for adaptation to increasing temperature because of thicker photosynthetic active palisade layer and higher isoprene and alpha-pinene emission levels compared to genotype 2.2. Our results show that even a moderate elevation in temperature is efficient enough to cause notable changes in VOC emissions and leaf structure of these aspen genotypes, possibly indicating the effort of the saplings to adapt to changing climate.

  20. Thickness modulation and strain relaxation in strain-compensated InGaP/InGaP multiple-quantum-well structure grown by metalorganic molecular beam epitaxy on GaAs (100) substrate

    NASA Astrophysics Data System (ADS)

    Mitsuhara, M.; Watanabe, N.; Yokoyama, H.; Iga, R.; Shigekawa, N.

    2016-09-01

    We have investigated the structural features of a strain-compensated InGaP/InGaP multiple-quantum-well (MQW) structure on GaAs (100) substrate with a band-gap energy of around 1.7 eV for solar cell applications. In transmission electron microscopy images, noticeable thickness modulation was observed in the barrier layers for a sample grown at the substrate temperature of 530 °C. Meanwhile, the X-ray diffraction patterns indicated that strain relaxation predominantly occurred in the well layers. Decreasing the substrate temperature from 530 to 510 °C was effective in suppressing both the thickness modulation and strain relaxation. Additionally, increasing the growth rate of the well layer further suppressed the thickness modulation. In room-temperature photoluminescence (PL) emission spectra, the sample grown at 510 °C showed approximately 50 times higher PL peak intensity than the one grown at 530 °C.

  1. Characterization of structural defects in SnSe2 thin films grown by molecular beam epitaxy on GaAs (111)B substrates

    NASA Astrophysics Data System (ADS)

    Tracy, Brian D.; Li, Xiang; Liu, Xinyu; Furdyna, Jacek; Dobrowolska, Margaret; Smith, David J.

    2016-11-01

    Tin selenide thin films have been grown by molecular beam epitaxy on GaAs (111)B substrates at a growth temperature of 150 °C, and a microstructural study has been carried out, primarily using the technique of transmission electron microscopy. The Se:Sn flux ratio during growth was systematically varied and found to have a strong impact on the resultant crystal structure and quality. Low flux ratios (Se:Sn=3:1) led to defective films consisting primarily of SnSe, whereas high flux ratios (Se:Sn>10:1) gave higher quality, single-phase SnSe2. The structure of the monoselenide films was found to be consistent with the Space Group Pnma with the epitaxial growth relationship of [011]SnSe// [ 1 1 bar 0 ] GaAs, while the diselenide films were consistent with the Space Group P 3 bar m1 , and had the epitaxial growth relationship [ 2 1 bar 1 bar 0 ]SnSe2// [ 1 1 bar 0 ] GaAs.

  2. Structural Mapping of Functional Ge Layers Grown on Graded SiGe Buffers for sub-10 nm CMOS Applications Using Advanced X-ray Nanodiffraction.

    PubMed

    Richard, Marie-Ingrid; Zoellner, Marvin H; Chahine, Gilbert A; Zaumseil, Peter; Capellini, Giovanni; Häberlen, Maik; Storck, Peter; Schülli, Tobias U; Schroeder, Thomas

    2015-12-09

    We report a detailed advanced materials characterization study on 40 nm thick strained germanium (Ge) layers integrated on 300 mm Si(001) wafers via strain-relaxed silicon-germanium (SiGe) buffer layers. Fast-scanning X-ray microscopy is used to directly image structural inhomogeneities, lattice tilt, thickness, and strain of a functional Ge layer down to the sub-micrometer scale with a real space step size of 750 μm. The structural study shows that the metastable Ge layer, pseudomorphically grown on Si(0.3)Ge(0.7), exhibits an average compressive biaxial strain of -1.27%. By applying a scan area of 100 × 100 μm(2), we observe microfluctuations of strain, lattice tilt, and thickness of ca. ±0.03%, ±0.05°, and ±0.8 nm, respectively. This study confirms the high materials homogeneity of the compressively strained Ge layer realized by the step-graded SiGe buffer approach on 300 mm Si wafers. This presents thus a promising materials science approach for advanced sub-10 nm complementary metal oxide-semiconductor applications based on strain-engineered Ge transistors to outperform current Si channel technologies.

  3. Extended x-ray absorption fine structure and micro-Raman spectra of Bridgman grown Cd1-xZnxTe ternary alloys

    NASA Astrophysics Data System (ADS)

    Talwar, Devki N.; Feng, Zhe Chuan; Lee, Jyh-Fu; Becla, P.

    2014-03-01

    We have performed low-temperature micro-Raman scattering and extended x-ray absorption fine-structure (EXAFS) measurements on the Bridgman-grown bulk zinc-blende Cd1-x Zn x Te (1.0 ≧̸ x ≧̸ 0.03) ternary alloys to comprehend their structural and lattice dynamical properties. The micro-Raman results are carefully appraised to authenticate the classical two-phonon mode behavior insinuated by far-infrared (FIR) reflectivity study. The composition-dependent EXAFS experiments have revealed a bimodal distribution of the nearest-neighbor bond lengths—its analysis by first-principles bond-orbital model enabled us to estimate the lattice relaxations around Zn/Cd atoms in CdTe/ZnTe to help evaluate the necessary force constant variations for constructing the impurity-perturbation matrices. The simulated results of impurity vibrational modes by average-t-matrix Green’s function (ATM-GF) theory has put our experimental findings of the gap mode ˜153 cm-1 near x ≈ 1 on a much firmer ground.

  4. Ca10Li(VO4)7:Nd3+, a promising laser material: growth, structure and spectral characteristics of a Czochralski-grown single crystal

    NASA Astrophysics Data System (ADS)

    Kosmyna, M. B.; Nazarenko, B. P.; Puzikov, V. M.; Shekhovtsov, A. N.; Paszkowicz, W.; Behrooz, A.; Romanowski, P.; Yasukevich, A. S.; Kuleshov, N. V.; Demesh, M. P.; Wierzchowski, W.; Wieteska, K.; Paulmann, C.

    2016-07-01

    Pure and Nd-doped Ca10Li(VO4)7 single crystals were grown by the Czochralski method. The structure of Ca10Li(VO4)7 single crystal was refined starting from a model of Ca10K(VO4)7 using the powder diffraction data collected at a laboratory high-resolution diffractometer. The defect structure of the single crystal was studied with the use of both, high-resolution diffraction using a laboratory instrument and X-ray topographic techniques employing synchrotron radiation at the Hasylab laboratory (Hamburg). Polarized absorption and luminescence spectra of Nd-doped Ca10Li(VO4)7 crystal were investigated in details. The laser oscillation was obtained under flash lamp pumping and the slope efficiency of 0.87% was achieved in the free-running mode. Preliminary examination of lasing properties points that Ca10Li(VO4)7:Nd crystal can be a highly efficient solid state laser medium. Crystals of this kind are expected to be suitable for application as efficient non-linear optics materials.

  5. Structure and magnetism in strained Ge1-x-ySnxMny films grown on Ge(001) by low temperature molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Prestat, E.; Barski, A.; Bellet-Amalric, E.; Jacquot, J.-F.; Morel, R.; Tainoff, D.; Jain, A.; Porret, C.; Bayle-Guillemaud, P.; Jamet, M.

    2013-07-01

    In this letter, we study the structural and magnetic properties of Ge1-x-ySnxMny films grown on Ge(001) by low temperature molecular beam epitaxy using X-ray diffraction, high resolution transmission electron microscopy, and superconducting quantum interference device. Like in Mn doped Ge films, Mn atoms diffuse during the growth and aggregate into vertically aligned Mn-rich nanocolumns of a few nanometers in diameter. Transmission electron microscopy observations in plane view clearly indicate that the Sn incorporation is not uniform with concentration in Mn rich vertical nanocolumns lower than the detection limit of electron energy loss spectroscopy. The matrix exhibits a GeSn solid solution while there is a Sn-rich GeSn shell around GeMn nanocolumns. The magnetization in Ge1-x-ySnxMny layers is higher than in Ge1-xMnx films. This magnetic moment enhancement in Ge1-x-ySnxMny is probably related to the modification of the electronic structure of Mn atoms in the nanocolumns by the Sn-rich shell, which is formed around the nanocolumns.

  6. Resistance Switching Memory Characteristics of Si/CaF2/CdF2 Quantum-Well Structures Grown on Metal (CoSi2) Layer

    NASA Astrophysics Data System (ADS)

    Denda, Junya; Uryu, Kazuya; Watanabe, Masahiro

    2013-04-01

    A novel scheme of resistance switching random access memory (ReRAM) devices fabricated using Si/CaF2/CdF2/CaF2/Si quantum-well structures grown on metal CoSi2 layer formed on a Si substrate has been proposed, and embryonic write/erase memory operation has been demonstrated at room temperature. It has been found that the oxide-mediated epitaxy (OME) technique for forming the CoSi2 layer on Si dramatically improves the stability and reproducibility of the current-voltage (I-V) curve. This technology involves 10-nm-thick Co layer deposition on a protective oxide prepared by boiling in a peroxide-based solution followed by annealing at 550 °C for 30 min for silicidation in ultrahigh vacuum. A switching voltage of lower than 1 V, a peak current density of 32 kA/cm2, and an ON/OFF ratio of 10 have been observed for the sample with the thickness sequence of 0.9/0.9/2.5/0.9/5.0 nm for the respective layers in the Si/CaF2/CdF2/CaF2/Si structure. Results of surface morphology analysis suggest that the grain size of crystal islands with flat surfaces strongly affects the quality of device characteristics.

  7. Electron transport in unipolar InGaN/GaN multiple quantum well structures grown by NH3 molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Browne, David A.; Mazumder, Baishakhi; Wu, Yuh-Renn; Speck, James S.

    2015-05-01

    Unipolar-light emitting diode like structures were grown by NH3 molecular beam epitaxy on c plane (0001) GaN on sapphire templates. Studies were performed to experimentally examine the effect of random alloy fluctuations on electron transport through quantum well active regions. These unipolar structures served as a test vehicle to test our 2D model of the effect of compositional fluctuations on polarization-induced barriers. Variables that were systematically studied included varying quantum well number from 0 to 5, well thickness of 1.5 nm, 3 nm, and 4.5 nm, and well compositions of In0.14Ga0.86N and In0.19Ga0.81N. Diode-like current voltage behavior was clearly observed due to the polarization-induced conduction band barrier in the quantum well region. Increasing quantum well width and number were shown to have a significant impact on increasing the turn-on voltage of each device. Temperature dependent IV measurements clearly revealed the dominant effect of thermionic behavior for temperatures from room temperature and above. Atom probe tomography was used to directly analyze parameters of the alloy fluctuations in the quantum wells including amplitude and length scale of compositional variation. A drift diffusion Schrödinger Poisson method accounting for two dimensional indium fluctuations (both in the growth direction and within the wells) was used to correctly model the turn-on voltages of the devices as compared to traditional 1D simulation models.

  8. Structural and dynamical properties of Bridgman-grown CdSexTe1-x (0

    NASA Astrophysics Data System (ADS)

    Talwar, Devki N.; Feng, Zhe Chuan; Lee, Jyh-Fu; Becla, P.

    2013-04-01

    Measurements of the Raman scattering and extended x-ray-absorption fine-structure (EXAFS) spectroscopy are reported on a series of Bridgman-grown zinc-blende CdTe1-xSex (0.35 ≥ x > 0.05) ternary alloys to empathize their lattice dynamical and structural properties. Low-temperature Raman spectra have revealed the classic CdTe-like (TO1, LO1) and CdSe-like (TO2, LO2) pairs of optical phonons. The composition-dependent peak positions of the LO2 modes exhibited shifts towards the higher-energy side, while those of the LO1 phonon frequencies have unveiled the slight redshifts. Detailed analyses of EXAFS data by using the first-principles bond orbital model have enabled us to estimate both the lattice relaxations and nearest-neighbor radial force constants around the Se/Te atoms in the CdTe/CdSe matrix. These results are methodically integrated in the “average t-matrix” formalism within the Green's-function theory for defining the impurity perturbations to comprehend the composition-dependent optical phonons in CdTe1-xSex alloys. Based on our comprehensive calculations of impurity modes in the low-composition regime x→ 0, we have assigned the weak phonon feature observed near ˜175 cm-1 in the low-temperature infrared reflectivity spectroscopy study to a SeTe localized vibrational mode.

  9. 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.

  10. Suppression of interfacial intermixing between MBE-grown Heusler alloy Ni2MnIn and (0 0 1)InAs or InAs-HEMT structures

    NASA Astrophysics Data System (ADS)

    Bohse, S.; Zolotaryov, A.; Kreuzpaintner, W.; Lott, D.; Kornowski, A.; Stemmann, A.; Heyn, Ch.; Hansen, W.

    2011-05-01

    This paper reports on the application of a thin MgO interlayer as a diffusion barrier between a Ni2MnIn Heusler film and the substrate consisting of either (0 0 1)InAs or a high electron mobility transistor structure with an InAs channel layer. The functionality of the MgO interlayers is studied in dependence of their layer thicknesses. Our studies reveal that MgO interlayers are effective diffusion barriers, which in conjunction with post-growth annealing significantly improve the structural and magnetic properties of the Heusler films. For all as-grown samples, a Curie temperature of 170 K was found indicating that the Ni2MnIn films are crystallized in the B2 phase. Post-growth annealing for 15 h at 350 °C of samples with MgO layer thicknesses smaller than 3 nm leads to a strong decrease in magnetisation. This film degradation may be attributed to the intermixing of the Heusler films with substrate material through not-completely closed MgO films. For samples with a MgO interlayer thickness of 3 nm, the Curie temperature increases up to 300 K. This Curie temperature is close to the value reported for bulk Ni2MnIn films in the desired L21 phase. Furthermore, an increase in saturation magnetisation by a factor of 2.4 was observed.

  11. The structural and optical properties of GaSb/InGaAs type-II quantum dots grown on InP (100) substrate

    PubMed Central

    2012-01-01

    We have investigated the structural and optical properties of type-II GaSb/InGaAs quantum dots [QDs] grown on InP (100) substrate by molecular beam epitaxy. Rectangular-shaped GaSb QDs were well developed and no nanodash-like structures which could be easily found in the InAs/InP QD system were formed. Low-temperature photoluminescence spectra show there are two peaks centered at 0.75eV and 0.76ev. The low-energy peak blueshifted with increasing excitation power is identified as the indirect transition from the InGaAs conduction band to the GaSb hole level (type-II), and the high-energy peak is identified as the direct transition (type-I) of GaSb QDs. This material system shows a promising application on quantum-dot infrared detectors and quantum-dot field-effect transistor. PMID:22277096

  12. 1550-nm InGaAsP multi-quantum-well structures selectively grown on v-groove-patterned SOI substrates

    NASA Astrophysics Data System (ADS)

    Megalini, Ludovico; Bonef, Bastien; Cabinian, Brian C.; Zhao, Hongwei; Taylor, Aidan; Speck, James S.; Bowers, John E.; Klamkin, Jonathan

    2017-07-01

    We report direct growth of 1550-nm InGaAsP multi-quantum-well (MQW) structures in densely packed, smooth, highly crystalline, and millimeter-long InP nanoridges grown by metalorganic chemical vapor deposition on silicon-on-insulator (SOI) substrates. Aspect-ratio-trapping and selective area growth techniques were combined with a two-step growth process to obtain good material quality as revealed by photoluminescence, scanning electronic microscopy, and high-resolution X-ray diffraction characterization. Transmission electron microscopy images revealed sharp MQW/InP interfaces as well as thickness variation of the MQW layer. This was confirmed by atom probe tomography analysis, which also suggests homogenous incorporation of the various III-V elements of the MQW structure. This approach is suitable for the integration of InP-based nanoridges in the SOI platform for new classes of ultra-compact, low-power, nano-electronic, and photonic devices for future tele- and data-communications applications.

  13. Harvesting and cryo-cooling crystals of membrane proteins grown in lipidic mesophases for structure determination by macromolecular crystallography.

    PubMed

    Li, Dianfan; Boland, Coilín; Aragao, David; Walsh, Kilian; Caffrey, Martin

    2012-09-02

    An important route to understanding how proteins function at a mechanistic level is to have the structure of the target protein available, ideally at atomic resolution. Presently, there is only one way to capture such information as applied to integral membrane proteins (Figure 1), and the complexes they form, and that method is macromolecular X-ray crystallography (MX). To do MX diffraction quality crystals are needed which, in the case of membrane proteins, do not form readily. A method for crystallizing membrane proteins that involves the use of lipidic mesophases, specifically the cubic and sponge phases(1-5), has gained considerable attention of late due to the successes it has had in the G protein-coupled receptor field(6-21) (www.mpdb.tcd.ie). However, the method, henceforth referred to as the in meso or lipidic cubic phase method, comes with its own technical challenges. These arise, in part, due to the generally viscous and sticky nature of the lipidic mesophase in which the crystals, which are often micro-crystals, grow. Manipulating crystals becomes difficult as a result and particularly so during harvesting(22,23). Problems arise too at the step that precedes harvesting which requires that the glass sandwich plates in which the crystals grow (Figure 2)(24,25) are opened to expose the mesophase bolus, and the crystals therein, for harvesting, cryo-cooling and eventual X-ray diffraction data collection. The cubic and sponge mesophase variants (Figure 3) from which crystals must be harvested have profoundly different rheologies(4,26). The cubic phase is viscous and sticky akin to a thick toothpaste. By contrast, the sponge phase is more fluid with a distinct tendency to flow. Accordingly, different approaches for opening crystallization wells containing crystals growing in the cubic and the sponge phase are called for as indeed different methods are required for harvesting crystals from the two mesophase types. Protocols for doing just that have been

  14. Genetic Structure and Molecular Variability Analysis of Citrus sudden death-associated virus Isolates from Infected Plants Grown in Brazil.

    PubMed

    Matsumura, Emilyn Emy; Coletta Filho, Helvécio Della; de Oliveira Dorta, Silvia; Nouri, Shahideh; Machado, Marcos Antonio

    2016-12-16

    Citrus sudden death-associated virus (CSDaV) is a monopartite positive-sense single-stranded RNA virus that was suggested to be associated with citrus sudden death (CSD) disease in Brazil. Here, we report the first study of the genetic structure and molecular variability among 31 CSDaV isolates collected from both symptomatic and asymptomatic trees in CSD-affected areas. Analyses of partial nucleotide sequences of five domains of the CSDaV genomic RNA, including those encoding for the methyltransferase, the multi-domain region (MDR), the helicase, the RNA-dependent RNA polymerase and the coat protein, showed that the MDR coding region was the most diverse region assessed here, and a possible association between this region and virus adaption to different host or plant tissues is considered. Overall, the nucleotide diversity (π) was low for CSDaV isolates, but the phylogenetic analyses revealed the predominance of two main groups, one of which showed a higher association with CSD-symptomatic plants. Isolates obtained from CSD-symptomatic plants, compared to those obtained from asymptomatic plants, showed higher nucleotide diversity, nonsynonymous and synonymous substitution rates and number of amino acid changes on the coding regions located closer to the 5' end region of the genomic RNA. This work provides new insights into the genetic diversity of the CSDaV, giving support for further epidemiological studies.

  15. Community structures and antagonistic activities of the bacteria associated with surface-sterilized pepper plants grown in different field soils.

    PubMed

    Kang, Sin Ae; Han, Jae Woo; Kim, Beom Seok

    2016-12-01

    Endophytic bacteria may act individually or in consortia in controlling certain plant diseases. In this study, pepper plants (Capsicum annuum L. cv. Nokkwang) were cultivated in glasshouse conditions using field soils collected from two different geographic locations, Deokso (DS) and Gwangyang (GY) in Korea. Community structure and antifungal activity of pepper endophytic bacteria were analyzed using culture-independent (PCR-DGGE) and culture-dependent (plating) methods, respectively. Dissimilarities were observed between DGGE profiles of DS and GY samples at all plant tissues. However, sequencing of the major DGGE bands revealed an enrichment of Firmicutes in the leaves of plants propagated in either soil. Similar results were observed with the culturable assays. Firmicutes dominated the isolates from both leaf samples, DS leaf (100 %) and GY leaf (83.3 %), although the genus compositions of DS leaf and GY leaf isolates were different. We assessed the antifungal activity of each isolate recovered to better understand the potential role that these endophytic bacteria may play. Of the 27 representative isolates from DS plant samples, 17 isolates (63.0 %) had antagonistic activity against at least one of the fungi tested. Seventeen isolates from GY plant samples (58.6 %) displayed antagonistic properties. The results show that the endophytic communities differ in the same plant species when propagated in different soils. Exploring the internal tissues of plants growing in diverse soil environments could be a way to find potential candidates for biocontrol agents.

  16. Structural and optical properties of La-doped BaSnO3 thin films grown by PLD

    NASA Astrophysics Data System (ADS)

    James, K. K.; Krishnaprasad, P. S.; Hasna, K.; Jayaraj, M. K.

    2015-01-01

    In this study the structural and optical properties of lanthanum-doped BaSnO3 powder samples and thin films deposited on fused silica were investigaed using laser ablation. Under an oxygen pressure of 5×10-4 mbar, phase pure BaSnO3 films with a lattice constant of 0.417 nm and grain size of 21 nm were prepared at 630 °C. The band gap of BaSnO3 powder sample and thin films was calculated to be 3.36 eV and 3.67 eV, respectively. There was a progressive increase in conductivity for thin films of BaSnO3 doped with 0~7 at% of La. The highest conductivity, 9 Scm-1, was obtained for 7 at% La-doped BaSnO3. Carrier concentration, obtained from Burstein-Moss (B-M) shift, nearly matches the measured values except for 3 at% and 10 at% La-doped BaSnO3 thin films.

  17. 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.

  18. Genetic Structure and Molecular Variability Analysis of Citrus sudden death-associated virus Isolates from Infected Plants Grown in Brazil

    PubMed Central

    Matsumura, Emilyn Emy; Coletta Filho, Helvécio Della; de Oliveira Dorta, Silvia; Nouri, Shahideh; Machado, Marcos Antonio

    2016-01-01

    Citrus sudden death-associated virus (CSDaV) is a monopartite positive-sense single-stranded RNA virus that was suggested to be associated with citrus sudden death (CSD) disease in Brazil. Here, we report the first study of the genetic structure and molecular variability among 31 CSDaV isolates collected from both symptomatic and asymptomatic trees in CSD-affected areas. Analyses of partial nucleotide sequences of five domains of the CSDaV genomic RNA, including those encoding for the methyltransferase, the multi-domain region (MDR), the helicase, the RNA-dependent RNA polymerase and the coat protein, showed that the MDR coding region was the most diverse region assessed here, and a possible association between this region and virus adaption to different host or plant tissues is considered. Overall, the nucleotide diversity (π) was low for CSDaV isolates, but the phylogenetic analyses revealed the predominance of two main groups, one of which showed a higher association with CSD-symptomatic plants. Isolates obtained from CSD-symptomatic plants, compared to those obtained from asymptomatic plants, showed higher nucleotide diversity, nonsynonymous and synonymous substitution rates and number of amino acid changes on the coding regions located closer to the 5’ end region of the genomic RNA. This work provides new insights into the genetic diversity of the CSDaV, giving support for further epidemiological studies. PMID:27999249

  19. Effect of substrate temperature on structure and luminescence properties of YVO4:Eu3+ thin films grown by PLD

    NASA Astrophysics Data System (ADS)

    Foka, K. E.; Dejene, B. F.; Swart, H. C.

    2016-03-01

    YVO4:Eu3+ thin films were deposited by pulse laser deposition at substrate temperatures of 200, 300 and 400 °C. The oxygen deposition background pressure was also changed from 20 to 85 mTorr at a substrate temperature of 400 °C. The films deposited at the higher temperatures showed a tetragonal phase in consistent with the standard JCPDS card 17-0341. The X-ray diffraction patterns obtained from the 200 °C sample showed only a very small peak at the (200) orientation. The other phosphor thin film showed an improved crystalline structure when the temperature was increased. Scanning electron microscope images indicated larger particles on the surface at the higher temperatures. Atomic force microscopy results showed smooth surfaces with small particles at lower temperatures and an increase in surface roughness at higher temperatures due to the improvement in crystallinity. The photoluminescence showed the typical emission peaks of Eu3+ in the red region at 594 and 618 nm attributed to the 5D0-7F1 and 5D0-7F2 transitions. The peaks at 652 and 699 nm corresponding to the 5D0-7F3 and 5D0-7F4 transitions were also observed. The spectra showed an increase in PL intensity when the deposition temperature and oxygen pressure were increased.

  20. Determination of the Solid Electrolyte Interphase Structure Grown on a Silicon Electrode Using a Fluoroethylene Carbonate Additive.

    PubMed

    Veith, Gabriel M; Doucet, Mathieu; Sacci, Robert L; Vacaliuc, Bogdan; Baldwin, J Kevin; Browning, James F

    2017-07-24

    In this work we explore how an electrolyte additive (fluorinated ethylene carbonate - FEC) mediates the thickness and composition of the solid electrolyte interphase formed over a silicon anode in situ as a function of state-of-charge and cycle. We show the FEC condenses on the surface at open circuit voltage then is reduced to C-O containing polymeric species around 0.9 V (vs. Li/Li(+)). The resulting film is about 50 Å thick. Upon lithiation the SEI thickens to 70 Å and becomes more organic-like. With delithiation the SEI thins by 13 Å and becomes more inorganic in nature, consistent with the formation of LiF. This thickening/thinning is reversible with cycling and shows the SEI is a dynamic structure. We compare the SEI chemistry and thickness to 280 Å thick SEI layers produced without FEC and provide a mechanism for SEI formation using FEC additives.

  1. Structural Complexity of Non-acid Glycosphingolipids in Human Embryonic Stem Cells Grown under Feeder-free Conditions*

    PubMed Central

    Barone, Angela; Benktander, John; Ångström, Jonas; Aspegren, Anders; Björquist, Petter; Teneberg, Susann; Breimer, Michael. E.

    2013-01-01

    Due to their pluripotency and growth capability, there are great expectations for human embryonic stem cells, both as a resource for functional studies of early human development and as a renewable source of cells for use in regenerative medicine and transplantation. However, to bring human embryonic stem cells into clinical applications, their cell surface antigen expression and its chemical structural complexity have to be defined. In the present study, total non-acid glycosphingolipid fractions were isolated from two human embryonic stem cell lines (SA121 and SA181) originating from leftover in vitro fertilized human embryos, using large amounts of starting material (1 × 109 cells/cell line). The total non-acid glycosphingolipid fractions were characterized by antibody and lectin binding, mass spectrometry, and proton NMR. In addition to the globo-series and type 1 core chain glycosphingolipids previously described in human embryonic stem cells, a number of type 2 core chain glycosphingolipids (neo-lactotetraosylceramide, the H type 2 pentaosylceramide, the Lex pentaosylceramide, and the Ley hexaosylceramide) were identified as well as the blood group A type 1 hexaosylceramide. Finally, the mono-, di-, and triglycosylceramides were characterized as galactosylceramide, glucosylceramide, lactosylceramide, galabiaosylceramide, globotriaosylceramide, and lactotriaosylceramide. Thus, the glycan diversity of human embryonic stem cells, including cell surface immune determinants, is more complex than previously appreciated. PMID:23404501

  2. The compositional, structural, and magnetic properties of a Fe3O4/Ga2O3/GaN spin injecting hetero-structure grown by metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Xu, Zhonghua; Huang, Shimin; Tang, Kun; Gu, Shulin; Zhu, Shunming; Ye, Jiandong; Xu, Mingxiang; Wang, Wei; Zheng, Youdou

    2016-12-01

    In this article, the authors have designed and fabricated a Fe3O4/Ga2O3/GaN spin injecting hetero-structure by metal-organic chemical vapor deposition. The compositional, structural, and magnetic properties of the hetero-structure have been characterized and discussed. From the characterizations, the hetero-structure has been successfully grown generally. However, due to the unintentional diffusion of Ga ions from Ga2O3/GaN layers, the most part of the nominal Fe3O4 layer is actually in the form of GaxFe3-xO4 with gradually decreased x values from the Fe3O4/Ga2O3 interface to the Fe3O4 surface. Post-annealing process can further aggravate the diffusion. Due to the similar ionic radius of Ga and Fe, the structural configuration of the GaxFe3-xO4 does not differ from that of pure Fe3O4. However, the ferromagnetism has been reduced with the incorporation of Ga into Fe3O4, which has been explained by the increased Yafet-Kittel angles in presence of considerable amount of Ga incorporation. A different behavior of the magnetoresistance has been found on the as-grown and annealed samples, which could be modelled and explained by the competition between the spin-dependent and spin-independent conduction channels. This work has provided detailed information on the interfacial properties of the Fe3O4/Ga2O3/GaN spin injecting hetero-structure, which is the solid basis for further improvement and application of the structure.

  3. Structural and magnetic ordering of CrNb3S6 single crystals grown by gas transport method

    NASA Astrophysics Data System (ADS)

    Borisenko, E. B.; Berezin, V. A.; Kolesnikov, N. N.; Gartman, V. K.; Matveev, D. V.; Shakhlevich, O. F.

    2017-07-01

    Paramagnetic layered semiconductor NbS2 doped with some transition metals can transform into ferromagnetic material. That is why such materials are promising candidates for spintronic devices. It is found that only at certain concentrations of a doping metal T crystallographic ordering is possible, which is essential for magnetic ordering of ternary compounds TNbS2. In particular, CrNb3S6 crystals are studied, which form almost completely ordered superstructure with intercalated Cr between NbS2 layers. The main difficulty in crystal growth is reaching stoichiometry of the compound. This problem is solved in the developed method of two-staged gas transport chemical reaction. This new approach provides growth of CrNb3S6 single crystals of several millimeters in diameter and 0.3-0.5 mm thickness. X-ray phase analysis (XRD) of powders is performed to identify all phases involved in synthesis and growth of the crystals. High frequency absorption in external periodic magnetic field as a function of temperature and intensity of magnetic field is used to estimate the temperature of ferromagnetic transition in CrNb3S6 single crystals. The Curie temperature is estimated as 115 K. Growth of CrNb3S6 crystals from vapor phase is studied in detail and full analysis of phase transitions during growth is given. It has been shown that using of high frequency absorption in the crystal provides reliable estimation of the point of ferromagnetic transition in this semiconductor. The authors are grateful to the Physical Science Department of Russian Academy of Sciences for financial support of the studies in the frameworks of the program "Physics of new materials and structures" (project no. 00-12-10).

  4. Si-rich Al2O3 films grown by RF magnetron sputtering: structural and photoluminescence properties versus annealing treatment

    PubMed Central

    2013-01-01

    Silicon-rich Al2O3 films (Six(Al2O3)1−x) were co-sputtered from two separate silicon and alumina targets onto a long silicon oxide substrate. The effects of different annealing treatments on the structure and light emission of the films versus x were investigated by means of spectroscopic ellipsometry, X-ray diffraction, micro-Raman scattering, and micro-photoluminescence (PL) methods. The formation of amorphous Si clusters upon the deposition process was found for the films with x ≥ 0.38. The annealing treatment of the films at 1,050°C to 1,150°C results in formation of Si nanocrystallites (Si-ncs). It was observed that their size depends on the type of this treatment. The conventional annealing at 1,150°C for 30 min of the samples with x = 0.5 to 0.68 leads to the formation of Si-ncs with the mean size of about 14 nm, whereas rapid thermal annealing of similar samples at 1,050°C for 1 min showed the presence of Si-ncs with sizes of about 5 nm. Two main broad PL bands were observed in the 500- to 900-nm spectral range with peak positions at 575 to 600 nm and 700 to 750 nm accompanied by near-infrared tail. The low-temperature measurement revealed that the intensity of the main PL band did not change with cooling contrary to the behavior expected for quantum confined Si-ncs. Based on the analysis of PL spectrum, it is supposed that the near-infrared PL component originates from the exciton recombination in the Si-ncs. However, the most intense emission in the visible spectral range is due to either defects in matrix or electron states at the Si-nc/matrix interface. PMID:23758885

  5. Scandium effect on the luminescence of Er-Sc silicates prepared from multi-nanolayer films

    PubMed Central

    2014-01-01

    Polycrystalline Er-Sc silicates (Er x Sc2-x Si2O7 and Er x Sc2-x SiO5) were fabricated using multilayer nanostructured films of Er2O3/SiO2/Sc2O3 deposited on SiO2/Si substrates by RF sputtering and thermal annealing at high temperature. The films were characterized by synchrotron radiation grazing incidence X-ray diffraction, cross-sectional transmission electron microscopy, energy-dispersive X-ray spectroscopy, and micro-photoluminescence measurements. The Er-Sc silicate phase Er x Sc2-x Si2O7 is the dominant film, and Er and Sc are homogeneously distributed after thermal treatment because of the excess of oxygen from SiO2 interlayers. The Er concentration of 6.7 × 1021 atoms/cm3 was achieved due to the presence of Sc that dilutes the Er concentration and generates concentration quenching. During silicate formation, the erbium diffusion coefficient in the silicate phase is estimated to be 1 × 10-15 cm2/s at 1,250°C. The dominant Er x Sc2 - x Si2O7 layer shows a room-temperature photoluminescence peak at 1,537 nm with the full width at half maximum (FWHM) of 1.6 nm. The peak emission shift compared to that of the Y-Er silicate (where Y and Er have almost the same ionic radii) and the narrow FWHM are due to the small ionic radii of Sc3+ which enhance the crystal field strength affecting the optical properties of Er3+ ions located at the well-defined lattice sites of the Sc silicate. The Er-Sc silicate with narrow FWHM opens a promising way to prepare photonic crystal light-emitting devices. PMID:25114648

  6. Magnetic and structural properties of BiFeO{sub 3} thin films grown epitaxially on SrTiO{sub 3}/Si substrates

    SciTech Connect

    Laughlin, Ryan P.; Currie, Daniel A.; Contreras-Guererro, Rocio; Dedigama, Aruna; Priyantha, Weerasinghe; Droopad, Ravindranath; Theodoropoulou, Nikoleta; Gao Peng; Pan Xiaoqing

    2013-05-07

    The integration of oxides with semiconductors is important for the technological advancement of the next generation electronics. Concomitant ferroelectric and antiferromagnetic (AF) behavior is demonstrated in single crystal BiFeO{sub 3} (BFO) films grown on 20 nm SrTiO{sub 3} (STO) virtual substrates on Si(100) using molecular beam epitaxy (MBE). STO thin films are grown in an oxide MBE chamber by co-deposition of Sr, Ti, and molecular O{sub 2}. Careful control of the O{sub 2} during nucleation produced commensurate growth of STO on Si. The sequence of the steps allows for the suppression of an amorphous SiO{sub 2} layer. This STO(20 nm)/Si structure was used as a virtual substrate for MBE deposition of BFO on Si without breaking vacuum. BFO was deposited using Fe and O{sub 2} plasma with an overpressure of Bi flux, the growth rate was controlled by the incoming Fe flux. The reflection high energy electron diffraction image shows a 2-D growth front with a 6-fold surface reconstruction under optimized O{sub 2} pressure of 5 Multiplication-Sign 10{sup -8} mbar. Cross-sectional transmission electron microscopy (TEM) confirms the high crystallinity of the films and shows sharp, atomically flat interfaces. The selected area diffraction pattern (SADP) reveals that BFO grows in a distorted rhombohedral crystal structure. X-ray diffraction does not show formation of second phases and is consistent with the TEM and SADP results. The BFO films show AF behavior with a Neel temperature that exceeds 350 K, as expected (T{sub N} = 673 K) and with a residual ferromagnetic behavior that decreases with film thickness and is consistent with the G-type AF due to the canted spins. The saturation magnetization per unit volume for a 40 nm thick film was 180 emu/cm{sup 3} at an in-plane magnetic field of 8 kOe. The ferroelectric behavior of the films was verified using piezoresponse force microscopy.

  7. Effects of Concentration and Substrate Type on Structure and Conductivity of p-Type CuS Thin Films Grown by Spray Pyrolysis Deposition

    NASA Astrophysics Data System (ADS)

    Sabah, Fayroz A.; Ahmed, Naser M.; Hassan, Z.

    2017-01-01

    Copper sulphide (CuS) thin films were grown upon Ti, indium tin oxide (ITO), and glass substrates by using spray pyrolysis deposition at 200°C. The films exhibited good adhesion compared to chemical bath deposition. CuCl2·2H2O and Na2S2O3·5H2O precursors were used as Cu2+ and S2- sources, respectively. Two concentrations (i.e., 0.2 M and 0.4 M) were selected in this study. X-ray diffraction analysis reveals that the films with 0.2 M showed only the formation of a covellite CuS phase having a hexagonal crystal structure with diffraction peaks of low intensity. For 0.4 M concentration, in addition to the covellite CuS phase, chalcocite Cu2S phase having a hexagonal crystal structure also appeared with relatively higher intensity peaks for all thin films. Field-emission scanning electron microscopy observations showed the formation of small grains for 0.2 M, whereas a mixture of grains with square-like shape and nanoplates were formed for 0.4 M. Depending on the 0.2 M and 0.4 M thin films thicknesses (3.2 μm and 4 μm, respectively), the band gap energy was obtained from optical measurements to be approximately 2.64 eV for 0.2 M (pure CuS phase), which slightly decreased up to 2.56 eV for 0.4 M concentration. Hall effect measurements showed that all grown films are p-type. The 0.2 M film exhibited much lower sheet resistance ( R sh = 33.96 Ω/Sq-55.70 Ω/Sq) compared to 0.4 M film ( R sh = 104.33 Ω/Sq-466.6 Ω/Sq). Moreover, for both concentrations, the films deposited onto ITO substrate showed the lowest sheet resistance ( R sh = 33.96 Ω/Sq-104.33 Ω/Sq).

  8. CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: Structural and Electrical Properties of Single Crystalline Ga-Doped ZnO Thin Films Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Lu, Zhong-Lin; Zou, Wen-Qin; Xu, Ming-Xiang; Zhang, Feng-Ming; Du, You-Wei

    2009-11-01

    High-quality Ga-doped ZnO (ZnO:Ga) single crystalline films with various Ga concentrations are grown on a-plane sapphire substrates using molecular-beam epitaxy. The site configuration of doped Ga atoms is studied by means of x-ray absorption spectroscopy. It is found that nearly all Ga can substitute into ZnO lattice as electrically active donors, a generating high density of free carriers with about one electron per Ga dopant when the Ga concentration is no more than 2%. However, further increasing the Ga doping concentration leads to a decrease of the conductivity due to partial segregation of Ga atoms to the minor phase of the spinel ZnGa2O4 or other intermediate phase. It seems that the maximum solubility of Ga in the ZnO single crystalline film is about 2 at.% and the lowest resistivity can reach 1.92 × 10-4 Ω·cm at room temperature, close to the best value reported. In contrast to ZnO:Ga thin film with 1% or 2% Ga doping, the film with 4% Ga doping exhibits a metal semiconductor transition at 80 K. The scattering mechanism of conducting electrons in single crystalline ZnO:Ga thin film is discussed.

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  10. (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.

  11. Electronic properties and structure of vanadia ultra-thin films grown on TiO 2( 1 1 0 ) in a water vapour ambient

    NASA Astrophysics Data System (ADS)

    Della Negra, Michela; Sambi, Mauro; Granozzi, Gaetano

    2001-12-01

    This paper reports on the deposition of a vanadium oxide ultra-thin film on TiO 2(1 1 0) by means of e-beam evaporation in an atmosphere of water vapour at room temperature. Photoelectron, X-ray excited Auger and valence band spectra have shown features very similar to those reported in the literature for vanadia ultra-thin films on TiO 2(1 1 0) identified as V 2O 3. An X-ray photoelectron diffraction analysis has been performed as a function of the overlayer thickness and after annealing treatments. It demonstrates that the overlayer grows ordered on the short range, pseudomorphic to the substrate, with a defective rutile crystal structure. The epitaxial relationship is maintained, with an approximately linear decrease in anisotropy, up to at least a coverage of 16 monolayers (ML); short annealing treatments are sufficient to restore the ordered structure, even on 20 ML thick films. Although in the bulk phase V 2O 3 is characterised by the corundum structure, which is also found when depositing vanadium oxide under similar experimental conditions on other substrates, such as Al 2O 3(0 0 0 1) and Pd(1 1 1), it appears that TiO 2(1 1 0) stabilises the isomorphic rutile lattice, which pertains to bulk VO 2 in its metallic phase, as well as to Magnéli phases of general formula V nO 2 n-1 . This particular behaviour of vanadia ultra-thin films grown on TiO 2 could be a key to understanding the catalytic activity and selectivity of the vanadia/titania systems in several chemical reactions.

  12. Ultraviolet InGaN and GaN Single-Quantum-Well-Structure Light-Emitting Diodes Grown on Epitaxially Laterally Overgrown GaN Substrates

    NASA Astrophysics Data System (ADS)

    Mukai, Takashi; Nakamura, Shuji

    1999-10-01

    Ultraviolet (UV) InGaN and GaN single-quantum-well-structure light-emitting diodes (LEDs) were grown on epitaxially laterally overgrown GaN (ELOG) and sapphire substrates. When the emission wavelength of UV InGaN LEDs was shorter than 380 nm, the external quantum efficiency (EQE) of the LED on ELOG was much higher than that on sapphire only under high-current operation. At low-current operation, both LEDs had the same EQE. When the active layer was GaN, EQE of the LED on sapphire was much lower than that on ELOG even under low-and high-current operations, due to the lack of localized energy states formed by alloy composition fluctuations. When the emission wavelengths were in the blue and green regions, EQE was almost the same between LEDs on both ELOG and sapphire due to a large number of deep localized energy states formed by large alloy composition fluctuations. The localized energy states are responsible for the high efficiency of InGaN-based LEDs in spite of a large number of dislocations.

  13. Deletion of FtsH11 protease has impact on chloroplast structure and function in Arabidopsis thaliana when grown under continuous light.

    PubMed

    Wagner, Raik; von Sydow, Lotta; Aigner, Harald; Netotea, Sergiu; Brugière, Sabine; Sjögren, Lars; Ferro, Myriam; Clarke, Adrian; Funk, Christiane

    2016-11-01

    The membrane-integrated metalloprotease FtsH11 of Arabidopsis thaliana is proposed to be dual-targeted to mitochondria and chloroplasts. A bleached phenotype was observed in ftsh11 grown at long days or continuous light, pointing to disturbances in the chloroplast. Within the chloroplast, FtsH11 was found to be located exclusively in the envelope. Two chloroplast-located proteins of unknown function (Tic22-like protein and YGGT-A) showed significantly higher abundance in envelope membranes and intact chloroplasts of ftsh11 and therefore qualify as potential substrates for the FtsH11 protease. No proteomic changes were observed in the mitochondria of 6-week-old ftsh11 compared with wild type, and FtsH11 was not immunodetected in these organelles. The abundance of plastidic proteins, especially of photosynthetic proteins, was altered even during standard growth conditions in total leaves of ftsh11. At continuous light, the amount of photosystem I decreased relative to photosystem II, accompanied by a drastic change of the chloroplast morphology and a drop of non-photochemical quenching. FtsH11 is crucial for chloroplast structure and function during growth in prolonged photoperiod.

  14. InGaAs quantum dot structures grown in GaAs barrier by metal-organic chemical vapor deposition for high-efficient long-wavelength emission

    NASA Astrophysics Data System (ADS)

    Passaseo, Adriana; Tasco, Vittorianna; De Giorgi, Milena; Todaro, Maria T.; Tarantini, Iolena; Cingolani, Roberto; De Vittorio, Massimo

    2004-06-01

    In this work we present a method to obtain room temperature ground state emission beyond 1.3 μm from InGaAs QDs, grown by MOCVD, embedded directly into a binary GaAs matrix. The wavelength is tuned from 1.26 μm up to 1.33 μm by varying the V/III ratio during the growth of the GaAs cap layer, without using seeding layer or InGaAs wells. A line-shape narrowing (from 36 meV to 24 meV) and a strong reduction of the temperature dependent quenching of the emission (down to a factor 3 from 10K to 300K) are observed, that represent the best value reported for QD structures emitting at 1.3 μm. The results are explained in term different morphological evolution and surface reconstruction undergone by the InGaAs islands during the GaAs overgrowth that result in larger QD size and in lower In-Ga intermixing. Indeed, cross sectional TEM images show an increase in the QD size of more than 30% with decreasing the AsH3 flow. The overall strain reduction due to the use of the GaAs matrix allows the fabrication of highly efficient staked QD layers. The single and multiple QDs samples show a systematic increase of the emission intensity and similar spectral shape.

  15. Effects of Rapid Thermal Annealing on the Structural, Electrical, and Optical Properties of Zr-Doped ZnO Thin Films Grown by Atomic Layer Deposition.

    PubMed

    Wu, Jingjin; Zhao, Yinchao; Zhao, Ce Zhou; Yang, Li; Lu, Qifeng; Zhang, Qian; Smith, Jeremy; Zhao, Yongming

    2016-08-13

    The 4 at. % zirconium-doped zinc oxide (ZnO:Zr) films grown by atomic layer deposition (ALD) were annealed at various temperatures ranging from 350 to 950 °C. The structural, electrical, and optical properties of rapid thermal annealing (RTA) treated ZnO:Zr films have been evaluated to find out the stability limit. It was found that the grain size increased at 350 °C and decreased between 350 and 850 °C, while creeping up again at 850 °C. UV-vis characterization shows that the optical band gap shifts towards larger wavelengths. The Hall measurement shows that the resistivity almost keeps constant at low annealing temperatures, and increases rapidly after treatment at 750 °C due to the effect of both the carrier concentration and the Hall mobility. The best annealing temperature is found in the range of 350-550 °C. The ZnO:Zr film-coated glass substrates show good optical and electrical performance up to 550 °C during superstrate thin film solar cell deposition.

  16. Effects of Rapid Thermal Annealing on the Structural, Electrical, and Optical Properties of Zr-Doped ZnO Thin Films Grown by Atomic Layer Deposition

    PubMed Central

    Wu, Jingjin; Zhao, Yinchao; Zhao, Ce Zhou; Yang, Li; Lu, Qifeng; Zhang, Qian; Smith, Jeremy; Zhao, Yongming

    2016-01-01

    The 4 at. % zirconium-doped zinc oxide (ZnO:Zr) films grown by atomic layer deposition (ALD) were annealed at various temperatures ranging from 350 to 950 °C. The structural, electrical, and optical properties of rapid thermal annealing (RTA) treated ZnO:Zr films have been evaluated to find out the stability limit. It was found that the grain size increased at 350 °C and decreased between 350 and 850 °C, while creeping up again at 850 °C. UV–vis characterization shows that the optical band gap shifts towards larger wavelengths. The Hall measurement shows that the resistivity almost keeps constant at low annealing temperatures, and increases rapidly after treatment at 750 °C due to the effect of both the carrier concentration and the Hall mobility. The best annealing temperature is found in the range of 350–550 °C. The ZnO:Zr film-coated glass substrates show good optical and electrical performance up to 550 °C during superstrate thin film solar cell deposition. PMID:28773816

  17. XPS analysis and structural and morphological characterization of Cu2ZnSnS4 thin films grown by sequential evaporation

    NASA Astrophysics Data System (ADS)

    Gordillo, G.; Calderón, C.; Bartolo-Pérez, P.

    2014-06-01

    This work describes a procedure to grow single phase Cu2ZnSnS4 (CZTS) thin films with tetragonal-kesterite type structure, through sequential evaporation of the elemental metallic precursors under sulphur vapor supplied from an effusion cell. X-ray diffraction analysis (XRD) is mostly used for phase identification but cannot clearly distinguish the formation of secondary phases such as Cu2SnS3 (CTS) because both compounds have the same diffraction pattern; therefore the use of a complementary technique is needed. Raman scattering analysis was used to distinguish these phases. The influence of the preparation conditions on the morphology and phases present in CZTS thin films were investigated through measurements of scanning electron microscopy (SEM) and XRD, respectively. From transmittance measurements, the energy band gap of the CZTS films was estimated to be around 1.45 eV. The limitation of XRD to identify some of the remaining phases after the growth process are investigated and the results of Raman analysis on the phases formed in samples grown by this method are presented. Further, the influence of the preparation conditions on the homogeneity of the chemical composition in the volume was studied by X-ray photoelectron spectroscopy (XPS) analysis.

  18. Structure and electronic properties of Zn-tetra-phenyl-porphyrin single- and multi-layers films grown on Fe(001)-p(1 × 1)O

    NASA Astrophysics Data System (ADS)

    Bussetti, Gianlorenzo; Calloni, Alberto; Celeri, Matteo; Yivlialin, Rossella; Finazzi, Marco; Bottegoni, Federico; Duò, Lamberto; Ciccacci, Franco

    2016-12-01

    The structure and the electronic properties of thin (1 molecular layer) and thick (20 molecular layers) Zn-tetra-phenyl-porphyrin (ZnTPP) films grown on a single metal oxide (MO) layer, namely Fe(001)-p(1 × 1)O, are shown and discussed. During the first stages of deposition, the ultra-thin MO layer reduces the molecule-substrate interaction enhancing the molecular diffusivity with the respect to other investigated substrates [namely, Si(111), Au(001) and oxygen-free Fe(001)]. On Fe(001)-p(1 × 1)O, ZnTPP molecules form an ordered and stable square-lattice array. The photoemission analysis of the valence bands reveals that all the characteristic features of the molecule are already visible in the 1 monolayer-thick sample spectrum. Similarly, the core level investigation suggests a weak molecule perturbation. The ZnTPP/Fe(001)-p(1 × 1)O interface represents a prototypical system to investigate the organic film adhesion on ultra-thin MO layers and the processes involved during the film growth.

  19. Electronic structure of antimonene grown on Sb{sub 2}Te{sub 3} (111) and Bi{sub 2}Te{sub 3} substrates

    SciTech Connect

    Lei, Tao; Liu, Chen; Zhao, Jia-Li; Li, Jin-Mei; Wang, Jia-Ou; Wu, Rui; Qian, Hai-Jie; Ibrahim, Kurash; Li, Ya-Ping; Wang, Hui-Qiong

    2016-01-07

    We explore the formation of single bilayer Sb(111) ultrathin film (Antimonene) on Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} substrates for the first time, which is theoretically predicated to be a robust trivial semiconductor but can be tuned to a 2D TI by reducing the buckling height. From angle-resolved photoemission spectroscopy measurements, the antimonene can be well grown on the two surfaces and shows clear band dispersion. The electronic structure of the antimonene shows similar character on the two surfaces, but due to the interfacial strain effect, the bands of antimonene on Bi{sub 2}Te{sub 3} are flatter than on Sb{sub 2}Te{sub 3}, which attributes to Bi{sub 2}Te{sub 3} substrate lattice constants lager than Sb{sub 2}Te{sub 3}. At the same time, the charge transfer effect is also observed through core level shift, which influences the band dispersion simultaneously.

  20. Effects of ultrathin AlAs interfacial layer on the structure and optical properties of GaInP epilayer grown on germanium

    NASA Astrophysics Data System (ADS)

    Jia, S. P.; Chen, G. F.; He, W.; Dai, P.; Chen, J. X.; Lu, S. L.; Yang, H.

    2014-10-01

    Structure and optical properties of GaInP epilayer with the ultrathin interfacial layers grown on germanium by metal-organic vapor-phase epitaxy (MOVPE) were characterized by high resolution transmission electron microscopy (HRTEM), photoluminescence (PL), Raman as well as surface morphology measurement. A five angstroms (5 Å) AlAs interfacial layer results in the decrease of PL intensity arising from the emission of [Ge(Ga,In) - V(Ga,In)] complex. With the incorporation of AlAs interfacial layer, an increased ordered degree of GaInP epilayer is observed. On the basis of the combination of step-terrace-reconstruction (STR) mode with the dimer-induced-stress model, a CuPt-B type ordering of GaInP which is related to AlAs reconstruction with 2× periodicity process is proposed to explain this effect. Long range order occurs as a consequence of the minimization of the strain energy with increased interfacial layer thickness from 5 Å to 5 nm.

  1. Influences of annealing on structural and compositional properties of Al2O3 thin films grown on 4H-SiC by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Tian, Li-Xin; Zhang, Feng; Shen, Zhan-Wei; Yan, Guo-Guo; Liu, Xing-Fang; Zhao, Wan-Shun; Wang, Lei; Sun, Guo-Sheng; Zeng, Yi-Ping

    2016-12-01

    Annealing effects on structural and compositional performances of Al2O3 thin films on 4H-SiC substrates are studied comprehensively. The Al2O3 films are grown by atomic layer deposition through using trimethylaluminum and H2O as precursors at 300 °C, and annealed at various temperatures in ambient N2 for 1 min. The Al2O3 film transits from amorphous phase to crystalline phase as annealing temperature increases from 750 °C to 768 °C. The refractive index increases with annealing temperature rising, which indicates that densification occurs during annealing. The densification and grain formation of the film upon annealing are due to crystallization which is relative with second-nearest-neighbor coordination variation according to the x-ray photoelectron spectroscopy (XPS). Although the binding energies of Al 2p and O 1s increase together during crystallization, separations between Al 2p and O 1s are identical between as-deposited and annealed sample, which suggests that the nearest-neighbour coordination is similar. Project supported by the National Basic Research Program of China (Grant No. 2015CB759600), the National Natural Science Foundation of China (Grant Nos. 61474113, 61574140, and 61274007), and the Beijing Nova Program, China (Grant No. xx2016071), and the CAEP Microsystem and THz Science and Technology Foundation (Grant No. CAEPMT201502).

  2. Magnetism and Nanoscale Structural and Compositional Irregularities in MBE-grown La2MnNiO6 on SrTiO3(001)

    NASA Astrophysics Data System (ADS)

    Chambers, Scott; Du, Yingge; Droubay, Timothy; Sushko, Peter; Spurgeon, Steven; Devaraj, Arun; Bowden, Mark; Shutthanandan, V.; Gustafsson, Torgny

    Double perovskites (A2BB'O6) are a fascinating class of oxides with considerable potential for applications requiring ferromagnetic and semiconducting properties. We have investigated MBE-grown La2MnNiO6 and have found that despite the fact that Mn and Ni are present as 4 + (d 3 : t2g 3eg0) and 2 + (d 8 : t2g 6eg2) respectively, and exhibit suitable XMCD signatures, the volume-averaged moment per formula unit is considerably less than 5 Bohr magnetons. Our electron energy loss spectroscopy (STEM-EELS) and atom probe tomography (APT) results to date reveal that there is considerable disorder in the B-site sublattice for as-deposited films, despite excellent volume-averaged stoichiometry. While air annealing results in substantial ordering, the moment remains low due to the nucleation of NiO inclusions with needle-like shapes revealed only by APT. First principles modeling suggests that even though the double perovskite is quite stable if nucleated in excess O, the presence of O vacancies facilitates structural disorder. In this talk, we will present our latest results on this fascinating material.

  3. Structural properties and dielectric function of graphene grown by high-temperature sublimation on 4H-SiC(000-1)

    SciTech Connect

    Bouhafs, C. Darakchieva, V.; Persson, I. L.; Persson, P. O. Å.; Yakimova, R.; Tiberj, A.; Paillet, M.; Zahab, A.-A.; Landois, P.; Juillaguet, S.; Schöche, S.; Schubert, M.

    2015-02-28

    Understanding and controlling growth of graphene on the carbon face (C-face) of SiC presents a significant challenge. In this work, we study the structural, vibrational, and dielectric function properties of graphene grown on the C-face of 4H-SiC by high-temperature sublimation in an argon atmosphere. The effect of growth temperature on the graphene number of layers and crystallite size is investigated and discussed in relation to graphene coverage and thickness homogeneity. An amorphous carbon layer at the interface between SiC and the graphene is identified, and its evolution with growth temperature is established. Atomic force microscopy, micro-Raman scattering spectroscopy, spectroscopic ellipsometry, and high-resolution cross-sectional transmission electron microscopy are combined to determine and correlate thickness, stacking order, dielectric function, and interface properties of graphene. The role of surface defects and growth temperature on the graphene growth mechanism and stacking is discussed, and a conclusion about the critical factors to achieve decoupled graphene layers is drawn.

  4. Defect structures and growth mechanisms of boron arsenide epilayers grown on 6H-silicon carbide and 15R-silicon carbide substrates

    NASA Astrophysics Data System (ADS)

    Chen, Hui

    B12As2 possesses the extraordinary properties, such as wide bandgap of 3.47eV and unique 'self heal' ability from electron irradiation damage, which make it attractive for the applications in space electronics, high temperature semiconductors and in particular, beta cells, devices capable of producing electrical energy by coupling a radioactive beta emitter to a semiconductor junction. Due to the absence of native substrates, B12As2 has been grown on substrates with compatible structural parameters via chemical vapor deposition. To date, growth on Si with (100), (110) and (111) orientation and (0001) 6H-SiC has been attempted. However, structural variants, including rotational and translational variants, have been observed in the epilayers and are expected to have a detrimental effect on device performance which has severely hindered progress of this material to date. In addition, none of the earlier reports provide a detailed atomic level study of defect structures in the films and growth mechanisms remain obscure. The focus of this thesis is to study defect structures in B12As2 films grown on different SiC substrates using synchrotron x-ray topography, high resolution transmission microscopy as well as other characterization techniques. The goals of the studies are to understand the generations of the defects present in B12As 2 films and their growth mechanisms so as to develop strategies to reduce defect densities and obtain better film quality for future device fabrication. The following detailed studies have been carried out: (1) The microstructures in B12As2 epitaxial layers grown on on-axis c-plane (0001) 6H-SiC substrates were analyzed in detail. Synchrotron white beam X-ray topography (SWBXT) and scanning electron microscopy (SEM) revealed a mosaic structure consisting of a solid solution of twin and matrix epilayer domains. The epitaxial relationship was determined to be (0001)B12As2<112¯0> B12As2||(0001)6H-SiC<112¯0>6H-SiC. B 12As2 twinned domains were

  5. The influence of Er3+ doping on the structural and optical properties of CeO2 thin films grown by PED

    NASA Astrophysics Data System (ADS)

    Tatar, B.; Gökdemir, F. P.; Pehlivan, E.; Urgen, M.

    2013-11-01

    Erbium doped CeO2 thin films were deposited on both Corning glass substrates and indium doped tin oxide (ITO) coated glass substrates by pulsed e-beam deposition (PED) method at room temperature. Structural features of Er doped CeO2 thin films were studied with X-ray diffraction (XRD) and micro-Raman spectra. The XRD patterns of all films showed polycrystalline nature and cubic crystalline structure. Raman active peaks for both undoped CeO2 and Er doped CeO2 films were determined at ˜465 cm-1. The Raman shift observed in this study can also be assigned to Raman active modes of CeO2 that are shifted from the original position due to different doping concentration. The optical properties of CeO2 films and Er doped CeO2 films, which were determined from transmittance and reflectance measurements at room temperature, were very similar in character. The refractive indices and extinction coefficients, which were calculated from 3.5 to 1.25 eV (300-1000 nm), were between 1.5-3 and 0.05-0.2, respectively. The optical band gaps were deduced from the absorption coefficient according to solid band theory. The electrochromic measurements revealed that 2% Er doped CeO2 films grown on ITO + WO3 substrates had highest charge density compared to the other samples. Long-time cyclic voltammetry (CV) and chronoamperometry (CA) measurements were carried out to investigate the stability of this film.

  6. Structural and dielectric properties of thin ZrO2 films on silicon grown by atomic layer deposition from cyclopentadienyl precursor

    NASA Astrophysics Data System (ADS)

    Niinistö, J.; Putkonen, M.; Niinistö, L.; Kukli, K.; Ritala, M.; Leskelä, M.

    2004-01-01

    ZrO2 thin films with thicknesses below 20 nm were deposited by the atomic layer deposition process on Si(100) substrates at 350 °C. An organometallic precursor, Cp2Zr(CH3)2 (Cp=cyclopentadienyl, C5H5) was used as the zirconium source and water or ozone as oxygen source. The influence of oxygen source and substrate pretreatment on the dielectric properties of ZrO2 films was investigated. Structural characterization with high-resolution transmission electron microscopy was performed to films grown onto HF-etched or native oxide covered silicon. Strong inhibition of ZrO2 film growth was observed with the water process on HF-etched Si. Ozone process on HF-etched Si resulted in interfacial SiO2 formation between the dense and uniform film and the substrate while water process produced interfacial layer with intermixing of SiO2 and ZrO2. The effective permittivity of ZrO2 in Al/ZrO2/Si/Al capacitor structures was dependent on the ZrO2 layer thickness and oxygen source used. The interfacial layer formation increased the capacitance equivalent oxide thickness (CET). CET of 2.0 nm was achieved with 5.9 nm ZrO2 film deposited with the H2O process on HF-stripped Si. The ozone-processed films showed good dielectric properties such as low hysteresis and nearly ideal flatband voltage. The leakage current density was lower and breakdown field higher for the ozone-processed ZrO2 films.

  7. Study of defect structures in 6H-SiC a/m-plane pseudofiber crystals grown by hot-wall CVD epitaxy

    SciTech Connect

    Goue, Ouloide Y.; Raghothamachar, Balaji; Yang, Yu; Guo, Jianqiu; Dudley, Michael; Kisslinger, Kim; Trunek, Andrew J.; Neudeck, Philip G.; Spry, David J.; Woodworth, Andrew A.

    2015-11-25

    Structural perfection of silicon carbide (SiC) single crystals is essential to achieve high-performance power devices. A new bulk growth process for SiC proposed by researchers at NASA Glenn Research Center, called large tapered crystal (LTC) growth, based on axial fiber growth followed by lateral expansion, could produce SiC boules with potentially as few as one threading screw dislocation per wafer. In this study, the lateral expansion aspect of LTC growth is addressed through analysis of lateral growth of 6H-SiC a/m-plane seed crystals by hot-wall chemical vapor deposition. Preliminary synchrotron white-beam x-ray topography (SWBXT) indicates that the as-grown boules match the polytype structure of the underlying seed and have a faceted hexagonal morphology with a strain-free surface marked by steps. SWBXT Laue diffraction patterns of transverse and axial slices of the boules reveal streaks suggesting the existence of stacking faults/polytypes, and this is confirmed by micro-Raman spectroscopy. Transmission x-ray topography of both transverse and axial slices reveals inhomogeneous strains at the seed–epilayer interface and linear features propagating from the seed along the growth direction. Micro-Raman mapping of an axial slice reveals that the seed contains high stacking disorder, while contrast extinction analysis (g·b and g·b×l) of the linear features reveals that these are mostly edge-type basal plane dislocations. Further high-resolution transmission electron microscopy investigation of the seed–homoepilayer interface also reveals nanobands of different SiC polytypes. A model for their formation mechanism is proposed. Lastly, the implication of these results for improving the LTC growth process is addressed.

  8. Electron transport in unipolar InGaN/GaN multiple quantum well structures grown by NH{sub 3} molecular beam epitaxy

    SciTech Connect

    Browne, David A.; Speck, James S.; Mazumder, Baishakhi; Wu, Yuh-Renn

    2015-05-14

    Unipolar-light emitting diode like structures were grown by NH{sub 3} molecular beam epitaxy on c plane (0001) GaN on sapphire templates. Studies were performed to experimentally examine the effect of random alloy fluctuations on electron transport through quantum well active regions. These unipolar structures served as a test vehicle to test our 2D model of the effect of compositional fluctuations on polarization-induced barriers. Variables that were systematically studied included varying quantum well number from 0 to 5, well thickness of 1.5 nm, 3 nm, and 4.5 nm, and well compositions of In{sub 0.14}Ga{sub 0.86}N and In{sub 0.19}Ga{sub 0.81}N. Diode-like current voltage behavior was clearly observed due to the polarization-induced conduction band barrier in the quantum well region. Increasing quantum well width and number were shown to have a significant impact on increasing the turn-on voltage of each device. Temperature dependent IV measurements clearly revealed the dominant effect of thermionic behavior for temperatures from room temperature and above. Atom probe tomography was used to directly analyze parameters of the alloy fluctuations in the quantum wells including amplitude and length scale of compositional variation. A drift diffusion Schrödinger Poisson method accounting for two dimensional indium fluctuations (both in the growth direction and within the wells) was used to correctly model the turn-on voltages of the devices as compared to traditional 1D simulation models.

  9. Effect of Au nanosandwiching on the structural, optical and dielectric properties of the as grown and annealed InSe thin films

    NASA Astrophysics Data System (ADS)

    Omareya, Olfat A.; Qasrawi, A. F.; Al Garni, S. E.

    2017-09-01

    In the current work, the structural, optical and dielectric properties of the InSe/Au/InSe nanosandwiched structures are investigated by means of X-ray diffraction and UV-visible light spectrophotometry techniques. The insertion of a 20 and 100 nm thick Au metal slabs between two InSe layers did not alter the amorphous nature of the as grown InSe films but decreased the energy band gap and the free carrier density. It also increased; the absorption ratio and the values of dielectric constant by 3 times. The insertion of 100 nm Au layers as a nanosandwich enhanced the drift mobility (31.3 cm2/V s) and plasmon frequency (1.53 GHz) of the InSe films. On the other hand, upon annealing, a metal induced crystallization process is observed for the InSe/Au (100 nm)/InSe sandwiches. Particularly, while the samples sandwiched with a layer of 20 nm thickness hardly revealed hexagonal γ - In2Se3 when annealed at 300 °C, those sandwiched with 100 nm Au slab, displayed well crystalline phase of hexagonal γ - In2Se3 at annealing temperature of 200 °C. The further annealing at 300 °C, forced the appearing of the orthorhombic In4Se3 phase. Optically, the annealing of the InSe/Au(100 nm)/InSe at 200 °C improved the absorption ratio by 9 times and decreased the energy band gap. The nanosandwiching technique of InSe seems to be promising for the engineering of the optical properties of the InSe photovoltaic material.

  10. Study of defect structures in 6H-SiC a/m-plane pseudofiber crystals grown by hot-wall CVD epitaxy

    DOE PAGES

    Goue, Ouloide Y.; Raghothamachar, Balaji; Yang, Yu; ...

    2015-11-25

    Structural perfection of silicon carbide (SiC) single crystals is essential to achieve high-performance power devices. A new bulk growth process for SiC proposed by researchers at NASA Glenn Research Center, called large tapered crystal (LTC) growth, based on axial fiber growth followed by lateral expansion, could produce SiC boules with potentially as few as one threading screw dislocation per wafer. In this study, the lateral expansion aspect of LTC growth is addressed through analysis of lateral growth of 6H-SiC a/m-plane seed crystals by hot-wall chemical vapor deposition. Preliminary synchrotron white-beam x-ray topography (SWBXT) indicates that the as-grown boules match themore » polytype structure of the underlying seed and have a faceted hexagonal morphology with a strain-free surface marked by steps. SWBXT Laue diffraction patterns of transverse and axial slices of the boules reveal streaks suggesting the existence of stacking faults/polytypes, and this is confirmed by micro-Raman spectroscopy. Transmission x-ray topography of both transverse and axial slices reveals inhomogeneous strains at the seed–epilayer interface and linear features propagating from the seed along the growth direction. Micro-Raman mapping of an axial slice reveals that the seed contains high stacking disorder, while contrast extinction analysis (g·b and g·b×l) of the linear features reveals that these are mostly edge-type basal plane dislocations. Further high-resolution transmission electron microscopy investigation of the seed–homoepilayer interface also reveals nanobands of different SiC polytypes. A model for their formation mechanism is proposed. Lastly, the implication of these results for improving the LTC growth process is addressed.« less

  11. Fully ALD-grown TiN/Hf0.5Zr0.5O2/TiN stacks: Ferroelectric and structural properties

    NASA Astrophysics Data System (ADS)

    Zarubin, Sergei; Suvorova, Elena; Spiridonov, Maksim; Negrov, Dmitrii; Chernikova, Anna; Markeev, Andrey; Zenkevich, Andrei

    2016-11-01

    Since the discovery of ferroelectricity (FE) in HfO2-based thin films, they are gaining increasing attention as a viable alternative to conventional FE in the next generation of non-volatile memory devices. In order to further increase the density of elements in the integrated circuits, it is essential to adopt a three-dimensional design. Since atomic layer deposition (ALD) processes are extremely conformal, ALD is the favored approach in the production of 3D ferroelectric random access memory. Here, we report the fabrication of fully ALD-grown capacitors comprising a 10-nm-thick FE Hf0.5Zr0.5O2 layer sandwiched between TiN electrodes, which are subjected to a detailed investigation of the structural and functional properties. The robust FE properties of Hf0.5Zr0.5O2 films in capacitors are established by several alternative techniques. We demonstrate a good scalability of TiN/Hf0.5Zr0.5O2/TiN FE capacitors down to 100-nm size and the polarization retention in the test "one transistor-one capacitor" (1T-1C) cells after 1010 writing cycles. The presence of a non-centrosymmetric orthorhombic phase responsible for FE properties in the alloyed polycrystalline Hf0.5Zr0.5O2 films is established by transmission electron microscopy. Given the ability of the ALD technique to grow highly conformal films and multilayered structures, the obtained results indicate the route for the design of FE non-volatile memory devices in 3D integrated circuits.

  12. Structure-Processing-Property Interrelationships of Vapor Grown Carbon Nanofiber, Single-Walled Carbon Nanotube and Functionalized Single-Walled Carbon Nanotube - Polypropylene Nanocomposites

    NASA Astrophysics Data System (ADS)

    Radhakrishnan, Vinod Karumathil

    This dissertation describes the first use of a design of experiments approach to investigate the interrelationships between structure, processing, and properties of melt extruded polypropylene (PP) carbon nanomaterial composites. The effect of nanomaterial structure was evaluated by exploring the incorporation of vapor grown carbon nanofibers (VGCFs), or pristine or functionalized single-walled carbon nanotubes (SWNTs or C12SWNTs) in polypropylene, while the effect of processing was investigated by studying the influence of melt extrusion temperature, speed, and time. The nanomaterials and PP were combined by an initial mixing method prior to melt extrusion. The nanocomposite properties were characterized by a combination of morphological, rheological, and thermal methods. Preliminary investigations into the effects of the initial mixing method revealed that the distribution of nanomaterials obtained after the mixing had a considerable influence on the properties of the final melt extruded nanocomposite. Dry mixing (DM) resulted in minimal adhesion between nanomaterials and PP during initial mixing; the majority of nanomaterials descended to the bottom. Hot coagulation (HC) mixing resulted in extremely high degrees of interaction between the nanomaterials and PP chains. Rotary evaporation (RE) mixing resulted in nanomaterial distribution uniformity between that obtained from DM and HC. Employing design of experiments to investigate the effects of structure and processing conditions on melt extruded PP nanocomposite properties revealed several interesting effects. The effect of processing conditions varied depending on the degree of nanomaterial distribution in PP attained prior to melt processing. Increasing melt extrusion temperature increased the decomposition temperature (Td) of PP/C12SWNT obtained from HC mixing but decreased T d of PP/C12SWNT obtained from RE mixing. Higher melt extrusion screw speed, on the other hand, significantly improved the nanocomposite

  13. Study on growth, structural, optical, thermal and mechanical properties of organic single crystal ethyl p-amino benzoate (EPAB) grown using vertical Bridgman technique

    NASA Astrophysics Data System (ADS)

    Muthuraja, A.; Kalainathan, S.

    2017-02-01

    Ethyl p-aminobenzoate (EPAB) single crystal was grown using vertical Bridgman technique (VBT). The crystal system of grown crystal was identified, and lattice parameters have been measured from the powder X-ray diffraction (PXRD). The optical transparency of EPAB single crystal was 55%, and the cut-off wavelength was found to be 337 nm. The thermal stability of EPAB single crystal was analyzed by thermogravimetric analysis. Etching studie were carried out for the grown crystal using different solvents, and etch pit density (EPD) was calculated and compared. Vickers microhardness (Hv) measurements revealed that EPAB belongs to the category of soft material. The dielectric studies reveal that the dielectric constant and dielectric loss of grown crystal decreases with increasing frequency for various temperatures. The third-order nonlinear optical property of EPAB was investigated and compared with other organic crystals. The evaluation of third-order optical properties such as nonlinear refractive index (n2), nonlinear absorption (β) and third-order nonlinear susceptibility (χ3) have found to be in the range of 10-11 m2/W, 10-4 m/W and 10-5 esu respectively. The Laser damage threshold energy of EPAB was measured using Nd: YAG laser. The blue emission of the grown crystal was identified by photoluminescence (PL) spectra measurements. The second harmonic generation (SHG) for the grown EPAB crystal was confirmed by Kurtz powder technique.

  14. Synthesis, growth, structural, optical, luminescence, surface and HOMO LUMO analysis of 2-[2-(4-cholro-phenyl)-vinyl]-1-methylquinolinium naphthalene-2-sulfonate organic single crystals grown by a slow evaporation technique

    NASA Astrophysics Data System (ADS)

    Karthigha, S.; Kalainathan, S.; Maheswara Rao, Kunda Uma; Hamada, Fumio; Yamada, Manabu; Kondo, Yoshihiko

    2016-02-01

    Single crystals of 2-[2-(4-cholro-phenyl)-vinyl]-1-methylquinolinium naphthalene-2-sulfonate (4CLNS) were grown by a slow evaporation technique. The formation of molecule was confirmed from 1H NMR and FTIR analysis. The confirmation of crystal structure was done by single crystal XRD and atomic packing of grown crystal was identified. The grown single crystal crystallized in triclinic structure with centrosymmetric space group P-1. The crystalline nature of the synthesised material was recorded by powder XRD. The optical absorption properties of the grown crystals were analyzed by UV-vis spectral studies. The thermal behaviour of the title material has been studied by TG/DTA analysis which revealed the stability of the compound till its melting point 276.7 °C. The third order nonlinear optical property of 4CLNS was investigated in detail by Z scan technique and it confirms that the title crystal is suitable for photonic devices and NLO optical applications. Emissions at 519 nm in green region of the EM spectrum were found by photoluminescence studies. The charge transfer occurring within the molecule is explained by the calculated HOMO and LUMO energies.

  15. Molecule diagram from space-grown crystals

    NASA Technical Reports Server (NTRS)

    2004-01-01

    Researchers' at Hauptman-Woodward Medical Research Institute, in Buffalo, N.Y. have analyzed the molecular structures of insulin crystals grown during Space Shuttle experiments and are unlocking the mystery of how insulin works.

  16. Molecule diagram from space-grown crystals

    NASA Technical Reports Server (NTRS)

    2004-01-01

    Researchers' at Hauptman-Woodward Medical Research Institute, in Buffalo, N.Y. have analyzed the molecular structures of insulin crystals grown during Space Shuttle experiments and are unlocking the mystery of how insulin works.

  17. Electronic band structure and material gain of III-V-Bi quantum wells grown on GaSb substrate and dedicated for mid-infrared spectral range

    NASA Astrophysics Data System (ADS)

    Gladysiewicz, M.; Kudrawiec, R.; Wartak, M. S.

    2016-02-01

    The 8-band kp Hamiltonian is applied to calculate electronic band structure and material gain in III-V-Bi quantum wells (QWs) grown on GaSb substrates. We analyzed three Bi-containing QWs (GaSbBi, GaInSbBi, and GaInAsSbBi) and different Bi-free barriers (GaSb and AlGaInAsSb), lattice matched to GaSb. Bi-related changes in the electronic band structure of III-V host incorporated into our formalism are based on recent ab-initio calculations for ternary alloys (III-Ga-Bi and III-In-Bi) [Polak et al., Semicond. Sci. Technol. 30, 094001 (2015)]. When compared to Bi-free QWs, the analyzed Bi-containing structures show much better quantum confinement in the valence band and also larger redshift of material gain peak per percent of compressive strain. For 8 nm thick GaInSb/GaSb QWs, material gain of the transverse electric (TE) mode is predicted at 2.1 μm for the compressive strain of ɛ = 2% (32% In). The gain peak of the TE mode in 8 nm thick GaSbBi/GaSb QW reaches this wavelength for compressive strain of 0.15% that corresponds to about 5% Bi. It has also been shown that replacing In atoms by Bi atoms in GaInSbBi/GaSb QWs while keeping the same compressive strain (ɛ = 2%) in QW region enhances and shifts gain peak significantly to the longer wavelengths. For 8 nm wide GaInSbBi/GaSb QW with 5% Bi, the gain peak is predicted at around 2.6 μm, i.e., is redshifted by about 400 nm compared to Bi-free QW. For 8 nm wide GaInAsSbSb QWs (80% In, 5% Bi, and ɛ = 2%) with proper AlGaInAsSb barriers, it is possible to achieve large material gain even at 4.0 μm.

  18. Composition dependences of crystal structure and electrical properties of epitaxial Pb(Zr,Ti)O3 films grown on Si and SrTiO3 substrates

    NASA Astrophysics Data System (ADS)

    Okamoto, Shoji; Okamoto, Satoshi; Yokoyama, Shintaro; Akiyama, Kensuke; Funakubo, Hiroshi

    2016-10-01

    {100}-oriented Pb(Zr x ,Ti1- x )O3 (PZT) thin films of approximately 2 µm thickness and Zr/(Zr + Ti) ratios of 0.39-0.65 were epitaxially grown on (100)cSrRuO3//(100)SrTiO3 (STO) and (100)cSrRuO3//(100)cLaNiO3//(100)CeO2//(100)YSZ//(100)Si (Si) substrates having different thermal expansion coefficients by pulsed metal-organic chemical vapor deposition (MOCVD). The effects of Zr/(Zr + Ti) ratio and type of substrate on the crystal structure and dielectric, ferroelectric and piezoelectric properties of the films were systematically investigated. The X-ray diffraction measurement showed that both films changed from having a tetragonal symmetry to rhombohedral symmetry through the coexisting region with increasing Zr/(Zr + Ti) ratio. This region showed the Zr/(Zr + Ti) ratios of 0.45-0.59 for the films on the STO substrates that were wider than the films on the Si substrates. Saturation polarization values were minimum at approximately Zr/(Zr + Ti) = 0.50 for the films on the STO substrates, and no obvious Zr/(Zr + Ti) ratio dependence was detected in the films on the Si substrates. On the other hand, the maximum field-induced strain values measured by scanning force microscopy at approximately Zr/(Zr + Ti) = 0.50 at 100 kV/cm were about 0.5 and 0.1% in the films on the Si and STO, respectively.

  19. 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}.

  20. Studies on the growth aspects, structural, thermal, dielectric and third order nonlinear optical properties of solution grown 4-methylpyridinium p-nitrophenolate single crystal

    NASA Astrophysics Data System (ADS)

    Devi, S. Reena; Kalaiyarasi, S.; Zahid, I. MD.; Kumar, R. Mohan

    2016-11-01

    An ionic organic optical crystal of 4-methylpyridinium p-nitrophenolate was grown from methanol by slow evaporation method at ambient temperature. Powder and single crystal X-ray diffraction studies revealed the crystal system and its crystalline perfection. The rocking curve recorded from HRXRD study confirmed the crystal quality. FTIR spectral analysis confirmed the functional groups present in the title compound. UV-visible spectral study revealed the optical window and band gap of grown crystal. The thermal, electrical and surface laser damage threshold properties of harvested crystal were examined by using TGA/DTA, LCR/Impedance Analyzer and Nd:YAG laser system respectively. The third order nonlinear optical property of grown crystal was elucidated by Z-scan technique.

  1. Structural Study of SiC Nanoparticles Grown by Inductively Coupled Plasma and Laser Pyrolysis for Nano-structured Ceramics Elaboration

    SciTech Connect

    Leconte, Yann; Portier, Xavier; Herlin-Boime, Nathalie; Reynaud, Cecile

    2008-07-01

    Refractory carbide nano-structured ceramics as SiC constitute interesting materials for high temperature applications and particularly for fourth generation nuclear plants. To elaborate such nano-materials, weighable amounts of SiC nano-powders have to be synthesized first with an accurate control of the grain size and stoichiometry. The inductively coupled plasma and the laser pyrolysis techniques, respectively developed at EMPA Thun and CEA Saclay, allow meeting these requirements. Both techniques are able to produce dozens of grams per hour of silicon carbide nano-powders. The particle size can be adjusted down to around 20 nm for the plasma synthesis and even down to 5-10 nm for the laser pyrolysis. The stoichiometry Si/C can be tuned by the addition of methane into the plasma and acetylene for the laser process. (authors)

  2. Combined impact of strain and stoichiometry on the structural and ferroelectric properties of epitaxially grown N a1 +xNb O3 +δ films on (110) NdGa O3

    NASA Astrophysics Data System (ADS)

    Cai, Biya; Schwarzkopf, J.; Feldt, C.; Sellmann, J.; Markurt, T.; Wördenweber, R.

    2017-05-01

    We demonstrate that the strain of an epitaxially grown film, which is induced by the lattice mismatch between the crystalline substrate and film and relaxes with increasing film thickness, can be conserved beyond the critical thickness of plastic relaxation of the respective film/substrate heterostructure system by adding epitaxially embedded nanoprecipitates and/or nanopillars of a secondary phase. By doing so we modify the ferroelectric properties of the film in a very controlled way. For this purpose, strained N a1 +xNb O3 +δ films are epitaxially grown on (110 ) NdGa O3 and their structural and electronic properties are investigated. X-ray diffraction and transmission electron microscopy analysis indicate that in addition to the epitaxially grown majority phase NaNb O3 , a second phase N ayNb O3 +δ is present in the films and forms crystalline precipitates and vertically aligned pillars a few nanometers in diameter. For large enough concentrations, this secondary phase appears to be able to suppress the plastic relaxation of the NaNb O3 matrix. In contrast to stoichiometric films and films with small Na excess, which demonstrate strain relaxation for film thickness exceeding a few nanometers and relaxor-type ferroelectric behavior, the N a1 +xNb O3 +δ film with the largest off-stoichiometry (grown from a target with x =17 % ) exhibits the "classic" ferroelectric behavior of unstrained NaNb O3 with a hysteretic structural and ferroelectric transition. However, the temperature of this hysteretic transition is shifted from 616 K to 655 K for unstrained material to room temperature for the strained N a1 +xNb O3 +δ film grown from the off-stoichiometric target.

  3. Structural properties of phase-change InSbTe thin films grown at a low temperature by metalorganic chemical vapor deposition.

    PubMed

    Ahn, Jun-Ku; Park, Kyoung-Woo; Hur, Sung-Gi; Kim, Chung-Soo; Lee, Jeong-Yong; Yoon, Soon-Gil

    2011-01-01

    The feasibility of new InSbTe (IST) chalcogenide materials at the deposition temperatures of 225 and 250 degrees C using metalorganic chemical vapor deposition (MOCVD) for phase-change random access memory (PRAM) applications was investigated. Samples grown at 225 degrees C consisted of the main InTe phase, including a small amount of Sb. On the other hand, samples grown at 250 degrees C included the crystalline phases of InSb and InSbTe. MOCVD-IST materials are powerful candidates for highly-integrated PRAM applications.

  4. Electrical and structural characterization of GaAs on InP grown by OMCVD; application to GaAs MESFETs

    NASA Astrophysics Data System (ADS)

    Azoulay, R.; Clei, A.; Dugrand, L.; Draïdia, auN.; Leroux, G.; Biblemont, S.

    1991-01-01

    The growth of GaAs on InP has attracted considerable interest recently because of the possibility of integration of GaAs electronic devices and 1.3 μm optical devices on the same wafer. In this work, we have investigated the growth of GaAs MESFETs and doped channel MIS-like FETs on InP by atmospheric pressure OMCVD. Because of the difference between the thermal expansion coefficient of GaAs and InP, the layers are under biaxial strain. The lowest FWHM of the (004) reflection curve of the double crystal X-ray diffraction spectra is 110 arc sec for a 12 μm thick layer. We have investigated the influence of the substrate temperature and of the arsine molar fraction on the residual carrier concentration of layers grown side by side on GaAs and on InP. The GaAs layers grown on InP are much more compensated than the layers grown on GaAs, indicating a higher incorporation of impurities. On MESFETs grown on InP, gm = 200mS/mm with Fmax higher than 30 GHz. On doped-channel MIS-like FETs on InP, we have measured gm = 145mS/mm.

  5. Temperature-induced changes in optical properties of thin film TiO2-Al2O3 bi-layer structures grown by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Ali, Rizwan; Saleem, Muhammad Rizwan; Honkanen, Seppo

    2016-02-01

    We investigate the optical properties and corresponding temperature-induced changes in highly uniform thin amorphous films and their bi-layer stacks grown by Atomic Layer Deposition (ALD). The environmentally driven conditions such as temperature, humidity and pressure have a significant influence on optical properties of homogeneous and heterogeneous bi-layer stacked structures of TiO2-Al2O3 and subsequently affect the specific sensitive nature of optical signals from nano-optical devices. Owing to the super hydrophilic behavior and inhibited surface defects in the form of hydrogenated species, the thermo-optic coefficient (TOC) of ~ 100 nm thick ALD-TiO2 films vary significantly with temperature, which can be used for sensing applications. On the other hand, the TOC of ~ 100 nm thick ALD-Al2O3 amorphous films show a differing behavior with temperature. In this work, we report on reduction of surface defects in ALD-TiO2 films by depositing a number of ultra-thin ALD-Al2O3 films to act as impermeable barrier layers. The designed and fabricated heterostructures of ALD-TiO2/Al2O3 films with varying ALD-Al2O3 thicknesses are exploited to stabilize the central resonance peak of Resonant Waveguide Gratings (RWGs) in thermal environments. The temperature-dependent optical constants of ALD-TiO2/Al2O3 bi-layer films are measured by a variable angle spectroscopic ellipsometer (VASE), covering a wide spectral range 380 <= λ <= 1800 nm at a temperature range from 25 to 105 °C. The Cauchy model is used to design and retrieve refractive indices at these temperatures, measured with three angles of incidence (59°, 67°, and 75°). The optical constants of 100 nm thick ALD-TiO2 and various combinational thicknesses of ALD-Al2O3 films are used to predict TOCs using a polynomial fitting algorithm.

  6. In Situ Oxidation of GaN Layer and Its Effect on Structural Properties of Ga2O3 Films Grown by Plasma-Assisted Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Ngo, Trong Si; Le, Duc Duy; Tran, Duy Khanh; Song, Jung-Hoon; Hong, Soon-Ku

    2017-06-01

    Plasma-assisted molecular beam epitaxy (PAMBE) was used to grow Ga2O3 films on oxidized GaN layers on nitrided sapphire substrates. The GaN layer was grown by PAMBE, and the in situ oxidation of the GaN layer was achieved through exposure to oxygen plasma, which resulted in the formation of monoclinic β-Ga2O3. Crystalline monoclinic β-Ga2O3 films were grown on the GaN layers, with and without oxidation. The orientation relationships were [11\\overline{2} 0] Al2O3//[1\\overline{1} 00] AlN//[1\\overline{1} 00] GaN//[102] β-Ga2O3 and [1\\overline{1} 00] Al2O3//[11\\overline{2} 0] AlN//[11\\overline{2} 0] GaN//[010] β-Ga2O3. The grown β-Ga2O3 films were not single-crystalline but showed rotational domains along the growth direction with three variations, which resulted in six-fold rotational symmetry instead of two-fold rotational symmetry. The surface roughness of the grown β-Ga2O3 film was closely reflected to that of as-grown GaN and oxidized GaN. By analyzing the x-ray omega rocking curves for the on-axis (\\overline{2} 01) and off-axis (002) reflections, it was concluded that rotational domains dominantly affected the crystal quality of the β-Ga2O3 films.

  7. In Situ Oxidation of GaN Layer and Its Effect on Structural Properties of Ga2O3 Films Grown by Plasma-Assisted Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Ngo, Trong Si; Le, Duc Duy; Tran, Duy Khanh; Song, Jung-Hoon; Hong, Soon-Ku

    2017-01-01

    Plasma-assisted molecular beam epitaxy (PAMBE) was used to grow Ga2O3 films on oxidized GaN layers on nitrided sapphire substrates. The GaN layer was grown by PAMBE, and the in situ oxidation of the GaN layer was achieved through exposure to oxygen plasma, which resulted in the formation of monoclinic β-Ga2O3. Crystalline monoclinic β-Ga2O3 films were grown on the GaN layers, with and without oxidation. The orientation relationships were [11overline{2} 0 ] Al2O3//[1overline{1} 00 ] AlN//[1overline{1} 00 ] GaN//[102] β-Ga2O3 and [1overline{1} 00 ] Al2O3//[11overline{2} 0 ] AlN//[11overline{2} 0 ] GaN//[010] β-Ga2O3. The grown β-Ga2O3 films were not single-crystalline but showed rotational domains along the growth direction with three variations, which resulted in six-fold rotational symmetry instead of two-fold rotational symmetry. The surface roughness of the grown β-Ga2O3 film was closely reflected to that of as-grown GaN and oxidized GaN. By analyzing the x-ray omega rocking curves for the on-axis (overline{2} 01 ) and off-axis (002) reflections, it was concluded that rotational domains dominantly affected the crystal quality of the β-Ga2O3 films.

  8. Uniaxial pressure effect on structural and magnetic phase transitions in NaFeAs and its comparison with as-grown and annealed BaFe2As2

    SciTech Connect

    Song, Yu; Carr, Scott Victor; Lu, Xingye; Zhang, Chenglin; Luttrell, N.F.; Zhao, Yang; Lynn, J. W.; Dai, Pengcheng; Sims, Zachary; Chi, Songxue

    2013-01-01

    We use neutron scattering to study the effect of uniaxial pressure on the tetragonal-toorthorhombic structural (Ts) and paramagnetic-to-antiferromagnetic (TN) phase transitions in NaFeAs and compare the outcome with similar measurements on as-grown and annealed BaFe2As2. In previous work on as-grown BaFe2As2, uniaxial pressure necessary to detwin the sample was found to induce a significant increase in zero pressure TN and Ts. However, we find that similar uniaxial pressure used to detwin NaFeAs and annealed BaFe2As2 has a very small effect on their TN and Ts. Since transport measurements on these samples still reveal resistivity anisotropy above TN and Ts, we conclude that such anisotropy cannot be due to uniaxial strain induced TN and Ts shifts, but must arise from intrinsic electronic anisotropy in these materials.

  9. Structural and optical properties of ZrB 2 and Hf xZr 1-xB 2 films grown by vicinal surface epitaxy on Si(1 1 1) substrates

    NASA Astrophysics Data System (ADS)

    Roucka, R.; An, Y.-J.; Chizmeshya, A. V. G.; D'Costa, V. R.; Tolle, J.; Menéndez, J.; Kouvetakis, J.

    2008-11-01

    ZrB2 and HfxZr1-xB2 films were grown on 4° miscut Si(1 1 1) substrates by chemical vapor deposition of gaseous Hf(BH4)4 and Zr(BH4)4. The films display superior structural and optical properties when compared with ZrB2 films grown on on-axis Si(1 1 1). The observed improvements include an optically featureless surface with rms roughness of ∼2.5-3.5 nm, a ∼50% reduction in the amount of residual strain, and a ∼50% lower resistivity. These properties should promote the use of diboride films as buffer layers for nitride semiconductor epitaxy on large-area Si substrates.

  10. Optical properties and structural investigations of (11-22)-oriented GaN/Al{sub 0.5}Ga{sub 0.5}N quantum wells grown by molecular beam epitaxy

    SciTech Connect

    Rosales, Daniel; Gil, Bernard; Bretagnon, Thierry; Brault, Julien; Vennéguès, Philippe; Nemoz, Maud; Mierry, Philippe de; Damilano, Benjamin; Massies, Jean; Bigenwald, Pierre

    2015-07-14

    We have grown (11-22)-oriented GaN/Al{sub 0.5}Ga{sub 0.5}N quantum wells (QWs) using molecular beam epitaxy on GaN (11-22)-oriented templates grown by metal-organic vapor phase epitaxy on m-plane oriented sapphire substrates. The performance of epitaxial growth of GaN/Al{sub 0.5}Ga{sub 0.5}N heterostructures on the semi-polar orientation (11-22) in terms of surface roughness and structural properties, i.e., strain relaxation mechanisms is discussed. In addition, high resolution transmission electron microscopy reveals very smooth QW interfaces. The photoluminescence of such samples are strictly originating from radiative recombination of free excitons for temperatures above 100 K. At high temperature, the population of localized excitons, moderately trapped (5 meV) at low temperature, is negligible.

  11. Comparison of the In distribution in InGaN/GaN quantum well structures grown by molecular beam epitaxy and metalorganic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Potin, V.; Hahn, E.; Rosenauer, A.; Gerthsen, D.; Kuhn, B.; Scholz, F.; Dussaigne, A.; Damilano, B.; Grandjean, N.

    2004-02-01

    We have compared the In distribution in InGaN quantum wells grown by molecular beam epitaxy (MBE) and metalorganic vapor phase epitaxy (MOVPE). The samples were studied by conventional and high-resolution transmission electron microscopy (HRTEM). The local and average In concentrations and the In distribution in the quantum wells were determined using the digital analysis of lattice images (DALI) method based on the evaluation of HRTEM lattice-fringe images. Similar lateral fluctuations of the In concentration were observed in MBE- and MOVPE-grown samples. The In concentration varies on a small scale (In-rich clusters with lateral extensions below 4 nm) and on a larger scale of a few 10 nm, which is attributed to phase separation. In contrast, the In distribution in growth direction differs significantly in the MBE and MOVPE samples which is explained by different In-segregation efficiencies and In desorption before the GaN cap layer deposition during MBE.

  12. Structural and photoluminescence studies on europium-doped lithium tetraborate (Eu:Li2B4O7) single crystal grown by microtube Czochralski (μT-Cz) technique

    NASA Astrophysics Data System (ADS)

    A, Kumaresh; R, Arun Kumar; N, Ravikumar; U, Madhusoodanan; B, S. Panigrahi; K, Marimuthu; M, Anuradha

    2016-05-01

    Rare earth europium (Eu3+)-doped lithium tetraborate (Eu:Li2B4O7) crystal is grown from its stoichiometric melt by microtube Czochralski pulling technique (μT-Cz) for the first time. The grown crystals are subjected to powder x-ray diffraction (PXRD) analysis which reveals the tetragonal crystal structure of the crystals. UV-vis-NIR spectral analysis is carried out to study the optical characteristics of the grown crystals. The crystal is transparent in the entire visible region, and the lower cutoff is observed to be at 304 nm. The existence of BO3 and BO4 bonding structure and the molecular associations are analyzed by Fourier transform infrared (FTIR) spectroscopy. The results of excitation and emission-photoluminescence spectra of europium ion incorporated in lithium tetraborate (LTB) single crystal reveal that the observations of peaks at 258, 297, and 318 nm in the excitation spectra and peaks at 579, 591, 597, 613, and 651 nm are observed in the emission spectra. The chromaticity coordinates are calculated from the emission spectra, and the emission intensity of the grown crystal is characterized through a CIE 1931 (Commission International d’Eclairage) color chromaticity diagram. Project supported by the Department of Science and Technology-Science and Engineering Research Board (Grant No. SR/S2/LOP-0012/2011), the Government of India for Awarding Major Research Project, the University Grants Commission-Department of Atomic Research-Consortium for Scientific Research (Grant No. CSR-KN/CSR-63/2014-2015/503), and the Kalpakkam and Indore, India.

  13. Growth mechanism and structure characterizations of GaSb islands grown on Si (1 0 0) substrates by LP-MOCVD

    NASA Astrophysics Data System (ADS)

    Lv, You; Liu, Ren-Jun; Wang, Lian-Kai; Li, Guo-Xing; Zhang, Yuan-Tao; Dong, Xin; Zhang, Bao-Lin

    2015-07-01

    In this paper, the growth mechanism and the morphologies of GaSb islands grown on Si (1 0 0) by low-pressure metal-organic chemical vapor deposition have been studied. It was observed the GaSb growth mode transited from SK to VW mode with time, while the islands migrated in VW mode on the surface. As growth time prolonging, the islands were coarsening consistent with the considerations of Ostwald ripening substituting for migration. And it was the similar coalescence process in the various interruption time. The formation of giant islands reduced the surface energy with the island-induced strain fields which drive the islands distribution evenly.

  14. Dielectric response and structure of in-plane tensile strained BaTiO3 thin films grown on the LaNiO3 buffered Si substrate

    NASA Astrophysics Data System (ADS)

    Qiao, Liang; Bi, Xiaofang

    2008-02-01

    Highly (001)-textured BaTiO3 films were grown epitaxially on the LaNiO3 buffered Si substrate. A strong in-plane tensile strain has been revealed by using x-ray diffraction and high resolution transmission electron microscopy. The BaTiO3 film has exhibited a small remnant polarization, indicating the presence of ca1/ca2/ca1/ca2 polydomain state in the film. Temperature dependent dielectric permittivity has demonstrated that two phase transitions occurred at respective temperatures of 170 and 30°C. The result was discussed in detail based on the misfit strain-temperature phase diagrams theory.

  15. Real-time monitoring of structure and stress evolution of boron films grown on Si(100) by ultrahigh vacuum chemical vapor deposition

    SciTech Connect

    Nesting, D.C.; Kouvetakis, J.; Hearne, S.; Chason, E.; Tsong, I.S.

    1999-05-01

    The morphology and biaxial stress of amorphous boron films grown on silicon at 630 {degree}C have been determined {ital in situ} and in real time using energy dispersive x-ray reflectivity and multiple-beam optical stress sensor techniques. The capability to determine the morphology and stress of light-element thin films {ital in situ} and in real time provides a unique opportunity to optimize the parameters of thin film deposition under chemical vapor deposition conditions. {copyright} {ital 1999 American Vacuum Society.}

  16. Structural and electrical characterization of NbO2 vertical devices grown on TiN coated SiO2/Si substrate

    NASA Astrophysics Data System (ADS)

    Joshi, Toyanath; Borisov, Pavel; Lederman, David

    Due to its relatively high MIT temperature (1081 K) and current-controlled negative differential resistance, NbO2 is a robust candidate for memory devices and electrical switching applications. In this work, we present in-depth analysis of NbO2 thin film vertical devices grown on TiN coated SiO2/Si substrates using pulsed laser deposition (PLD). Two of the films grown in 1 mTorr and 10 mTorr O2/Ar (~7% O2) mixed growth pressures were studied. The formation of NbO2 phase was confirmed by Grazing Incidence X-ray Diffractometry (GIXRD), X-ray Photoelectron Spectroscopy (XPS) and current vs. voltage measurements. A probe station tip (tip size ~2 μm) or conductive AFM tip was used as a top and TiN bottom layer was used as a bottom contact. Device conductivity showed film thickness and contact size dependence. Current pulse measurements, performed in response to applied triangular voltage pulses, showed a non-linear threshold switching behavior for voltage pulse durations of ~100 ns and above. Self-sustained current oscillations were analyzed in terms of defect density presented in the film. Supported by FAME (sponsored by MARCO and DARPA, Contract 2013-MA-2382), WV Higher Education Policy Commission Grant (HEPC.dsr.12.29), and WVU SRF. We also thank S. Kramer from Micron for providing the TiN-coated Si substrates.

  17. Early silicification of leaves and roots of seedlings of a panicoid grass grown under different conditions: anatomical relations and structural role.

    PubMed

    Fernández Honaine, M; Benvenuto, M L; Borrelli, N L; Osterrieth, M

    2016-11-01

    Grasses accumulate high amounts of silica deposits in tissues of all their organs, especially at mature stage. However, when and under which conditions do grass seedlings begin to produce these silica deposits and their relation with anatomy and development is little known. Here we investigated the silicification process in the first leaves and roots of seedlings of Bothriochloa laguroides grown in different substrate and Si treatments. The distribution and content of silica deposits in the organs of the seedlings grown under different conditions were analyzed through staining techniques and SEM-EDAX analyses. Leaf silica deposits were accumulated 3-4 days after the first leaf emergence, also under low silica solution (0.17-0.2 mM). Their location was mainly restricted to short costal cells from basal sectors, and scarcely in trichomes and xylem at tips. Silica content in leaves increased with the age of the seedlings. Roots presented dome-shaped silica aggregates, between 4-12 μm of diameter, located in the inner tangential wall of endodermal cells and similar to those produced at maturity. Silicification begins early in the first photosynthetic leaf, and silica distribution is opposite to that found in mature plants, mainly restricted to basal sectors, probably acting as a reinforcing element. The fast incorporation of solid amorphous silica in leaves and roots, may be useful for farm applications in species that are Si-fertilized. © 2016 German Botanical Society and The Royal Botanical Society of the Netherlands.

  18. Structure and photoluminescence of the TiO2 films grown by atomic layer deposition using tetrakis-dimethylamino titanium and ozone.

    PubMed

    Jin, Chunyan; Liu, Ben; Lei, Zhongxiang; Sun, Jiaming

    2015-01-01

    TiO2 films were grown on silicon substrates by atomic layer deposition (ALD) using tetrakis-dimethylamino titanium and ozone. Amorphous TiO2 film was deposited at a low substrate temperature of 165°C, and anatase TiO2 film was grown at 250°C. The amorphous TiO2 film crystallizes to anatase TiO2 phase with annealing temperature ranged from 300°C to 1,100°C in N2 atmosphere, while the anatase TiO2 film transforms into rutile phase at a temperature of 1,000°C. Photoluminescence from anatase TiO2 films contains a red band at 600 nm and a green band at around 515 nm. The red band exhibits a strong correlation with defects of the under-coordinated Ti(3+) ions, and the green band shows a close relationship with the oxygen vacancies on (101) oriented anatase crystal surface. A blue shift of the photoluminescence spectra reveals that the defects of under-coordinated Ti(3+) ions transform to surface oxygen vacancies in the anatase TiO2 film annealing at temperature from 800°C to 900°C in N2 atmosphere.

  19. Structural and interfacial characteristics of thin (<10 nm) SiO{sub 2} films grown by electron cyclotron resonance plasma oxidation on [100] Si substrates

    SciTech Connect

    Nguyen, T.D.; Carl, D.A.; Hess, D.W.; Lieberman, M.A.; Gronsky, R.

    1991-04-01

    The feasibility of fabricating ultra-thin SiO{sub 2} films on the order of a few nanometer thickness has been demonstrated. SiO{sub 2} thin films of approximately 7 nm thickness have been produced by ion flux-controlled Electron Cyclotron Resonance plasma oxidation at low temperature on [100] Si substrates, in reproducible fashion. Electrical measurements of these films indicate that they have characteristics comparable to those of thermally grown oxides. The thickness of the films was determined by ellipsometry, and further confirmed by cross-sectional High-Resolution Transmission Electron Microscopy. Comparison between the ECR and the thermal oxide films shows that the ECR films are uniform and continuous over at least a few microns in lateral direction, similar to the thermal oxide films grown at comparable thickness. In addition, HRTEM images reveal a thin (1--1.5 nm) crystalline interfacial layer between the ECR film and the [100] substrate. Thinner oxide films of approximately 5 nm thickness have also been attempted, but so far have resulted in nonuniform coverage. Reproducibility at this thickness is difficult to achieve.

  20. Structural and interfacial characteristics of thin (<10 nm) SiO sub 2 films grown by electron cyclotron resonance plasma oxidation on (100) Si substrates

    SciTech Connect

    Nguyen, T.D.; Carl, D.A.; Hess, D.W.; Lieberman, M.A.; Gronsky, R.

    1991-04-01

    The feasibility of fabricating ultra-thin SiO{sub 2} films on the order of a few nanometer thickness has been demonstrated. SiO{sub 2} thin films of approximately 7 nm thickness have been produced by ion flux-controlled Electron Cyclotron Resonance plasma oxidation at low temperature on (100) Si substrates, in reproducible fashion. Electrical measurements of these films indicate that they have characteristics comparable to those of thermally grown oxides. The thickness of the films was determined by ellipsometry, and further confirmed by cross-sectional High-Resolution Transmission Electron Microscopy. Comparison between the ECR and the thermal oxide films shows that the ECR films are uniform and continuous over at least a few microns in lateral direction, similar to the thermal oxide films grown at comparable thickness. In addition, HRTEM images reveal a thin (1--1.5 nm) crystalline interfacial layer between the ECR film and the (100) substrate. Thinner oxide films of approximately 5 nm thickness have also been attempted, but so far have resulted in nonuniform coverage. Reproducibility at this thickness is difficult to achieve.

  1. Structural and optical properties of dense vertically aligned ZnO nanorods grown onto silver and gold thin films by galvanic effect with iron contamination

    SciTech Connect

    Scarpellini, D.; Paoloni, S.; Medaglia, P.G.; Pizzoferrato, R.; Orsini, A.; Falconi, C.

    2015-05-15

    Highlights: • ZnO nanorods were grown on Au and Ag films in aqueous solution by galvanic effect. • The method is prone to metal contamination which can influence the ZnO properties. • Iron doping improves the lattice matching between ZnO and the substrate. • Energy levels of point defects are lowered and the light emission is red-shifted. • Galvanic-induced nucleation starts and proceeds continuously during the growth. - Abstract: Dense arrays of vertically aligned ZnO nanorods have been grown onto either silver or gold seedless substrates trough a simple hydrothermal method by exploiting the galvanic effect between the substrate and metallic parts. The nanorods exhibit larger bases and more defined hexagonal shapes, in comparison with standard non-galvanic wet-chemistry synthesis. X-ray diffraction (XRD) shows that the iron contamination, associated with the galvanic contact, significantly improves the in-plane compatibility of ZnO with the Au and Ag cubic lattice. Photoluminescence (PL) measurements indicate that the contamination does not affect the number density of localized defects, but lowers their energy levels uniformly; differently, the band-edge emission is not altered appreciably. Finally, we have found that the ZnO hetero-nucleation by galvanic effect initiates at different times in different sites of the substrate area. Our results can be useful for the fabrication of high performance piezonanodevices comprising high-density metal-to-ZnO nanoscaled junctions without intermediate polycrystalline layers.

  2. Structural Characterization of Lateral-grown 6H-SiC am-plane Seed Crystals by Hot Wall CVD Epitaxy

    NASA Technical Reports Server (NTRS)

    Goue, Ouloide Yannick; Raghothamachar, Balaji; Dudley, Michael; Trunek, Andrew J.; Neudeck, Philip G.; Woodworth, Andrew A.; Spry, David J.

    2014-01-01

    The performance of commercially available silicon carbide (SiC) power devices is limited due to inherently high density of screw dislocations (SD), which are necessary for maintaining polytype during boule growth and commercially viable growth rates. The NASA Glenn Research Center (GRC) has recently proposed a new bulk growth process based on axial fiber growth (parallel to the c-axis) followed by lateral expansion (perpendicular to the c-axis) for producing multi-faceted m-plane SiC boules that can potentially produce wafers with as few as one SD per wafer. In order to implement this novel growth technique, the lateral homoepitaxial growth expansion of a SiC fiber without introducing a significant number of additional defects is critical. Lateral expansion is being investigated by hot wall chemical vapor deposition (HWCVD) growth of 6H-SiC am-plane seed crystals (0.8mm x 0.5mm x 15mm) designed to replicate axially grown SiC single crystal fibers. The post-growth crystals exhibit hexagonal morphology with approximately 1500 m (1.5 mm) of total lateral expansion. Preliminary analysis by synchrotron white beam x-ray topography (SWBXT) confirms that the growth was homoepitaxial, matching the polytype of the respective underlying region of the seed crystal. Axial and transverse sections from the as grown crystal samples were characterized in detail by a combination of SWBXT, transmission electron microscopy (TEM) and Raman spectroscopy to map defect types and distribution. X-ray diffraction analysis indicates the seed crystal contained stacking disorders and this appears to have been reproduced in the lateral growth sections. Analysis of the relative intensity for folded transverse acoustic (FTA) and optical (FTO) modes on the Raman spectra indicate the existence of stacking faults. Further, the density of stacking faults is higher in the seed than in the grown crystal. Bundles of dislocations are observed propagating from the seed in m-axis lateral directions

  3. Wafer-scale controlled exfoliation of metal organic vapor phase epitaxy grown InGaN/GaN multi quantum well structures using low-tack two-dimensional layered h-BN

    NASA Astrophysics Data System (ADS)

    Ayari, Taha; Sundaram, Suresh; Li, Xin; El Gmili, Youssef; Voss, Paul L.; Salvestrini, Jean Paul; Ougazzaden, Abdallah

    2016-04-01

    Recent advances in epitaxial growth have led to the growth of III-nitride devices on 2D layered h-BN. This advance has the potential for wafer-scale transfer to arbitrary substrates, which could improve the thermal management and would allow III-N devices to be used more flexibly in a broader range of applications. We report wafer scale exfoliation of a metal organic vapor phase epitaxy grown InGaN/GaN Multi Quantum Well (MQW) structure from a 5 nm thick h-BN layer that was grown on a 2-inch sapphire substrate. The weak van der Waals bonds between h-BN atomic layers break easily, allowing the MQW structure to be mechanically lifted off from the sapphire substrate using a commercial adhesive tape. This results in the surface roughness of only 1.14 nm on the separated surface. Structural characterizations performed before and after the lift-off confirm the conservation of structural properties after lift-off. Cathodoluminescence at 454 nm was present before lift-off and 458 nm was present after. Electroluminescence near 450 nm from the lifted-off structure has also been observed. These results show that the high crystalline quality ultrathin h-BN serves as an effective sacrificial layer—it maintains performance, while also reducing the GaN buffer thickness and temperature ramps as compared to a conventional two-step growth method. These results support the use of h-BN as a low-tack sacrificial underlying layer for GaN-based device structures and demonstrate the feasibility of large area lift-off and transfer to any template, which is important for industrial scale production.

  4. Wafer-scale controlled exfoliation of metal organic vapor phase epitaxy grown InGaN/GaN multi quantum well structures using low-tack two-dimensional layered h-BN

    SciTech Connect

    Ayari, Taha; Li, Xin; Voss, Paul L.; Ougazzaden, Abdallah; Sundaram, Suresh; El Gmili, Youssef; Salvestrini, Jean Paul

    2016-04-25

    Recent advances in epitaxial growth have led to the growth of III-nitride devices on 2D layered h-BN. This advance has the potential for wafer-scale transfer to arbitrary substrates, which could improve the thermal management and would allow III-N devices to be used more flexibly in a broader range of applications. We report wafer scale exfoliation of a metal organic vapor phase epitaxy grown InGaN/GaN Multi Quantum Well (MQW) structure from a 5 nm thick h-BN layer that was grown on a 2-inch sapphire substrate. The weak van der Waals bonds between h-BN atomic layers break easily, allowing the MQW structure to be mechanically lifted off from the sapphire substrate using a commercial adhesive tape. This results in the surface roughness of only 1.14 nm on the separated surface. Structural characterizations performed before and after the lift-off confirm the conservation of structural properties after lift-off. Cathodoluminescence at 454 nm was present before lift-off and 458 nm was present after. Electroluminescence near 450 nm from the lifted-off structure has also been observed. These results show that the high crystalline quality ultrathin h-BN serves as an effective sacrificial layer—it maintains performance, while also reducing the GaN buffer thickness and temperature ramps as compared to a conventional two-step growth method. These results support the use of h-BN as a low-tack sacrificial underlying layer for GaN-based device structures and demonstrate the feasibility of large area lift-off and transfer to any template, which is important for industrial scale production.

  5. Structural characterization of zincblende Ga{sub 1-x}Mn{sub x}N epilayers grown by molecular beam epitaxy on (001) GaAs substrates

    SciTech Connect

    Fay, M.W.; Han, Y.; Brown, P.D.; Novikov, S.V.; Edmonds, K.W.; Campion, R.P.; Gallagher, B.L.; Foxon, C.T.

    2005-07-18

    Zincblende p-type Ga{sub 1-x}Mn{sub x}N epilayers, grown with and without AlN/GaN buffer layers using plasma-assisted molecular beam epitaxy on (001) oriented GaAs substrates, have been investigated using a variety of complementary transmission electron microscopy techniques. The epilayers were found to contain a high anisotropic density of stacking faults and microtwins. MnAs inclusions were identified at the Ga{sub 1-x}Mn{sub x}N/(001)GaAs interface extending into the substrate. The use of AlN/GaN buffer layers was found to inhibit the formation of these inclusions.

  6. The Structural Quality of AlxGa1-xN Epitaxial Layers Grown by Digitally-AlloyedModulated Precursor Epitaxy Determined by Transmission Electron Microscopy

    SciTech Connect

    Hawkridge, Michael E; Liliental-Weber, Zuzanna; Kim, Hee Jin; Choi, Suk; Yoo, Dongwon; Ryou, Jae-Hyun; Dupuis, Russell

    2008-10-13

    Al(x)Ga(1-x)N layers of varying composition (0.5grown in the digitally-alloyed modulated precursor epitaxial regime employing AlN and GaN binary sub-layers by metalorganic chemical vapor deposition on AlN templates were characterized by transmission electron microscopy techniques. Fine lamellae were observed in bright field images that indicate a possible variation in composition due to the modulated nature of growth. In higher Ga content samples (x(Al)<0.75), a compositional inhomogeniety associated with thicker island regions was observed, which is determined to be due to large Ga-rich areas formed at the base of the layer. Possible causes for the separation of Ga-rich material are discussed in the context of the growth regime used.

  7. A comparative study of the structural and electrical properties of n-type InGaN epilayer grown by MBE and commercially

    NASA Astrophysics Data System (ADS)

    Abud, Saleh H.; Ramiy, Asmiet; Hussein, A. S.; Hassan, Z.; Yam, F. K.

    2013-08-01

    This work reports the growth of n-In0.27Ga0.73N/GaN/AlN epitaxial layer on Si(1 1 1) substrate by using plasma-assisted molecular beam epitaxy (MBE) and commercially obtained n-In0.08Ga0.92N/AlN. As-grown and commercial thin films were characterized by using field emission scanning electron microscopy, atomic force microscopy, and high-resolution X-ray diffraction. A high work function metal (Pt) was deposited as metal contact on the thin films, and the electrical characteristics of the films pre- and post-annealed at 500 °C were studied under 3 V. Results show that the electrical characteristics of post-annealed thin films are better than those of pre-annealed thin films.

  8. Memory characteristics of metal-oxide-semiconductor structures based on Ge nanoclusters-embedded GeO(x) films grown at low temperature.

    PubMed

    Lin, Tzu-Shun; Lou, Li-Ren; Lee, Ching-Ting; Tsai, Tai-Cheng

    2012-03-01

    The memory devices constructed from the Ge-nanoclusters embedded GeO(x) layer deposited by the laser-assisted chemical vapor deposition (LACVD) system were fabricated. The Ge nanoclusters were observed by a high-resolution transmission electron microscopy. Using the capacitance versus voltage (C-V) and the conductance versus voltage (G-V) characteristics measured under various frequencies, the memory effect observed in the C-V curves was dominantly attributed to the charge storage in the Ge nanoclusters. Furthermore, the defects existed in the deposited film and the interface states were insignificant to the memory performances. Capacitance versus time (C-t) measurement was also executed to evaluate the charge retention characteristics. The charge storage and retention behaviors of the devices demonstrated that the Ge nanoclusters grown by the LACVD system at low temperature are promising for memory device applications.

  9. 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.

  10. Capacitance-voltage characterization of AlN/GaN metal-insulator-semiconductor structures grown on sapphire substrate by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Hashizume, Tamotsu; Alekseev, Egor; Pavlidis, Dimitris; Boutros, Karim S.; Redwing, Joan

    2000-08-01

    Electrical characterization of AlN/GaN interfaces was carried out by the capacitance-voltage (C-V) technique in materials grown by metalorganic chemical vapor deposition. The high-frequency C-V characteristics showed clear deep-depletion behavior at room temperature, and the doping density derived from the slope of 1/C2 plots under the deep depletion condition agreed well with the growth design parameters. A low value of interface state density Dit of 1×1011cm-2 eV-1 or less around the energy position of Ec-0.8 eV was demonstrated, in agreement with an average Dit value estimated from photoassisted C-V characteristics.

  11. Dual-polarity GaN micropillars grown by metalorganic vapour phase epitaxy: Cross-correlation between structural and optical properties

    SciTech Connect

    Coulon, P. M.; Mexis, M.; Teisseire, M.; Vennéguès, P.; Leroux, M.; Zuniga-Perez, J.; Jublot, M.

    2014-04-21

    Self-assembled catalyst-free GaN micropillars grown on (0001) sapphire substrates by metal organic vapor phase epitaxy are investigated. Transmission electron microscopy, as well as KOH etching, shows the systematic presence of two domains of opposite polarity within each single micropillar. The analysis of the initial growth stages indicates that such double polarity originates at the micropillar/substrate interface, i.e., during the micropillar nucleation, and it propagates along the micropillar. Furthermore, dislocations are also generated at the wire/substrate interface, but bend after several hundreds of nanometers. This leads to micropillars several tens of micrometers in length that are dislocation-free. Spatially resolved cathodoluminescence and microphotoluminescence show large differences in the optical properties of each polarity domain, suggesting unequal impurity/dopant/vacancy incorporation depending on the polarity.

  12. Structural Properties Characterized by the Film Thickness and Annealing Temperature for La2O3 Films Grown by Atomic Layer Deposition.

    PubMed

    Wang, Xing; Liu, Hongxia; Zhao, Lu; Fei, Chenxi; Feng, Xingyao; Chen, Shupeng; Wang, Yongte

    2017-12-01

    La2O3 films were grown on Si substrates by atomic layer deposition technique with different thickness. Crystallization characteristics of the La2O3 films were analyzed by grazing incidence X-ray diffraction after post-deposition rapid thermal annealing treatments at several annealing temperatures. It was found that the crystallization behaviors of the La2O3 films are affected by the film thickness and annealing temperatures as a relationship with the diffusion of Si substrate. Compared with the amorphous La2O3 films, the crystallized films were observed to be more unstable due to the hygroscopicity of La2O3. Besides, the impacts of crystallization characteristics on the bandgap and refractive index of the La2O3 films were also investigated by X-ray photoelectron spectroscopy and spectroscopic ellipsometry, respectively.

  13. Comparative study of semipolar (2 0 2 bar 1) , nonpolar (1 0 1 bar 0) and polar (0 0 0 1) InGaN multi-quantum well structures grown under N- and In-excess by plasma assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Sawicka, M.; Wolny, P.; Kryśko, M.; Turski, H.; Szkudlarek, K.; Grzanka, S.; Skierbiszewski, C.

    2017-05-01

    InGaN multi-quantum well (MQW) structures were grown by plasma-assisted molecular beam epitaxy (PAMBE) on semipolar (2 0 2 bar 1) , nonpolar m-plane (1 0 1 bar 0) and polar c-plane (0 0 0 1) GaN substrates. The impact of In- and N-rich growth conditions on surface morphology, luminescence properties and structural quality was studied. Semipolar MQWs grown under N-excess have a smooth surface and narrow photoluminescence (PL) at room temperature at 420 nm. Semipolar MQWs grown under In-rich conditions emitted at 414 nm with slightly broader emission and higher surface roughness. Nonpolar m-plane MQWs grown under N-excess emitted at 411 nm and its surface was very rough. When grown under In-rich conditions, nonpolar MQWs also emitted at 411 nm but significant peak broadening was observed due to hillock formation resulting in surface roughening and inhomogeneous In incorporation. The c-plane reference MQW structures grown in the same growth run did not show PL at room temperature due to poor structural quality related to three-dimensional growth mode and structure relaxation.

  14. Graphic Grown Up

    ERIC Educational Resources Information Center

    Kim, Ann

    2009-01-01

    It's no secret that children and YAs are clued in to graphic novels (GNs) and that comics-loving adults are positively giddy that this format is getting the recognition it deserves. Still, there is a whole swath of library card-carrying grown-up readers out there with no idea where to start. Splashy movies such as "300" and "Spider-Man" and their…

  15. Graphic Grown Up

    ERIC Educational Resources Information Center

    Kim, Ann

    2009-01-01

    It's no secret that children and YAs are clued in to graphic novels (GNs) and that comics-loving adults are positively giddy that this format is getting the recognition it deserves. Still, there is a whole swath of library card-carrying grown-up readers out there with no idea where to start. Splashy movies such as "300" and "Spider-Man" and their…

  16. Mechanisms of the micro-crack generation in an ultra-thin AlN/GaN superlattice structure grown on Si(110) substrates by metalorganic chemical vapor deposition

    SciTech Connect

    Shen, X. Q. Takahashi, T.; Ide, T.; Shimizu, M.

    2015-09-28

    We investigate the generation mechanisms of micro-cracks (MCs) in an ultra-thin AlN/GaN superlattice (SL) structure grown on Si(110) substrates by metalorganic chemical vapor deposition. The SL is intended to be used as an interlayer (IL) for relaxing tensile stress and obtaining high-quality crack-free GaN grown on Si substrates. It is found that the MCs can be generated by two different mechanisms, where large mismatches of the lattice constant (LC) and the coefficient of thermal expansion (CTE) play key roles in the issue. Different MC configurations (low-density and high-density MCs) are observed, which are considered to be formed during the different growth stages (SL growth and cooling down processes) due to the LC and the CTE effects. In-situ and ex-situ experimental results support the mechanism interpretations of the MCs generation. The mechanism understanding makes it possible to optimize the SL IL structure for growing high-quality crack-free GaN films on Si substrates for optical and electronic device applications.

  17. Effects of substrate misorientation and background impurities on electron transport in molecular-beam-epitaxial grown GaAs/AlGaAs modulation-doped quantum-well structures

    NASA Technical Reports Server (NTRS)

    Radulescu, D. C.; Wicks, G. W.; Schaff, W. J.; Calawa, A. R.; Eastman, L. F.

    1987-01-01

    The effects of substrate misorientation off the (001) plane and of background impurities on electron transport in MBE-grown GaAs/AlGaAs modulation-doped superlattice-buffered quantum-well structures were investigated. Low-field transport data were obtained on GaAs/AlGaAs structures grown on substrates oriented 0, 2, 4, and 6.5 deg off the (001) plane towards either (111)A or (111)B. It is shown that the low-field two-dimensional electron gas (2DEG) mobility is a function of the angle and direction of the substrate orientation, and that the 2DEG mobility is a function of the direction of the applied electric field in the GaAs quantum well. The anisotropy in the 2DEG mobility is also a function of the tilt angle and tilt azimuth direction of the substrate from the (001) plane. In addition, it is shown that the amount of interface scattering from the inverted interface is a sensitive function of the amount of background impurities in the MBE machine.

  18. Structural, thermal, laser damage, photoconductivity, NLO and mechanical properties of modified vertical Bridgman method grown AgGa0.5In0.5Se2 single crystal

    NASA Astrophysics Data System (ADS)

    Vijayakumar, P.; Ramasamy, P.

    2016-08-01

    AgGa0.5In0.5Se2 single crystal was grown using modified vertical Bridgman method. The structural perfection of the AgGa0.5In0.5Se2 single crystal has been analyzed by high-resolution X-ray diffraction rocking curve measurements. The structural and compositional uniformities of AgGa0.5In0.5Se2 were studied using Raman scattering spectroscopy at room temperature. The FWHM of the Γ1 (W1) and Γ5L (Γ15) measured at different regions of the crystal confirms that the composition throughout its length is fairly uniform. Thermal properties of the as-grown crystal, including specific heat, thermal diffusivity and thermal conductivity have been investigated. The multiple shot surface laser damage threshold value was measured using Nd:YAG laser. Photoconductivity measurements with different temperatures have confirmed the positive photoconducting behavior. Second harmonic generation (SHG) on powder samples has been measured using the Kurtz and Perry technique and the results display that AgGa0.5In0.5Se2 is a phase-matchable NLO material. The hardness behavior has been measured using Vickers micro hardness measurement and the indentation size effect has been observed. The classical Meyer's law, propositional resistance model and modified propositional resistance model have been used to analyse the micro hardness behavior.

  19. Structure and properties of Bi(Zn0.5Ti0.5)O3- Pb(Zr(1-x)Ti(x))O3 ferroelectric single crystals grown by a top-seeded solution growth technique.

    PubMed

    Wang, Bixia; Wu, Xiaoqing; Ren, Wei; Ye, Zuo-Guang

    2015-06-01

    Bi(Zn0.5Ti0.5)O3 (BZT)-modified Pb(Zr(1-x)Ti(x))O3 (PZT) single crystals have been grown using a top-seeded solution growth technique and characterized by various methods. The crystal structure is found to be rhombohedral by means of X-ray powder diffraction. The composition and homogeneity of the as-grown single crystals are studied by laser ablation inductively coupled plasma mass spectrometry and X-ray photoelectron spectroscopy. The domain structure of a (001)(cub) platelet is investigated by polarized light microscopy (PLM), which confirms the rhombohedral symmetry. The paraelectric-to-ferroelectric phase transition temperature T(C) is found to be 313°C with the absence of rhombohedral-tetragonal phase transition. The ferroelectric properties of the ternary crystals are enhanced by the BZT substitution with a remanent polarization of 28 μC/cm(2) and a coercive field E(C) of 22.1 kV/cm.

  20. Growth and coalescence control of inclined c-axis polar and semipolar GaN multilayer structures grown on Si(111), Si(112), and Si(115) by metalorganic vapor phase epitaxy

    SciTech Connect

    Szymański, Tomasz Wośko, Mateusz; Paszkiewicz, Bartłomiej; Paszkiewicz, Bogdan; Paszkiewicz, Regina

    2016-09-15

    Herein, silicon substrates in alternative orientations from the commonly used Si(111) were used to enable the growth of polar and semipolar GaN-based structures by the metalorganic vapor phase epitaxy method. Specifically, Si(112) and Si(115) substrates were used for the epitaxial growth of nitride multilayer structures, while the same layer schemes were also deposited on Si(111) for comparison purposes. Multiple approaches were studied to examine the influence of the seed layers and the growth process conditions upon the final properties of the GaN/Si(11x) templates. Scanning electron microscope images were acquired to examine the topography of the deposited samples. It was observed that the substrate orientation and the process conditions allow control to produce an isolated GaN block growth or a coalesced layer growth, resulting in inclined c-axis GaN structures under various forms. The angles of the GaN c-axis inclination were determined by x-ray diffraction measurements and compared with the results obtained from the analysis of the atomic force microscope (AFM) images. The AFM image analysis method to determine the structure tilt was found to be a viable method to estimate the c-axis inclination angles of the isolated blocks and the not-fully coalesced layers. The quality of the grown samples was characterized by the photoluminescence method conducted at a wide range of temperatures from 77 to 297 K, and was correlated with the sample degree of coalescence. Using the free-excitation peak positions plotted as a function of temperature, analytical Bose-Einstein model parameters were fitted to obtain further information about the grown structures.

  1. Characterization of graded interface In(x)Ga(1-x)As/In(0.52)Al(0.48)As (x between 0.53 and 0.70) structures grown by molecular-beam epitaxy

    NASA Technical Reports Server (NTRS)

    Peng, C. K.; Sinha, S.; Morkoc, H.

    1987-01-01

    Modulation-doped In(x)Ga(1-x)As/In(0.52)Al(0.48)As/InP structures were grown by molecular-beam epitaxy with x values between 53 and 70 percent. For pseudomorphic cases, graded instead of abrupt interfaces were used. Hall mobility and persistent photoconductivity measurements as a function of temperature were used to characterize samples with different structural parameters. Consistent trends in the variation of mobilities and two-dimensional carrier concentration, n(2D), under light and dark conditions have been observed and discussed in terms of applicable scattering mechanisms. The Hall mobilities are comparable to the best results obtained to date but with significantly higher n(2D) concentration.

  2. Molecule diagram from earth-grown crystals

    NASA Technical Reports Server (NTRS)

    2004-01-01

    Like many chemicals in the body, the three-dimensional structure of insulin is extremely complex. When grown on the ground, insulin crystals do not grow as large or as ordered as researchers desire--obscuring the blueprint of the insulin molecules.

  3. Molecule diagram from earth-grown crystals

    NASA Technical Reports Server (NTRS)

    2004-01-01

    Like many chemicals in the body, the three-dimensional structure of insulin is extremely complex. When grown on the ground, insulin crystals do not grow as large or as ordered as researchers desire--obscuring the blueprint of the insulin molecules.

  4. Structure and low-temperature tribology of lubricious nanocrystalline zinc oxide/aluminium oxide nanolaminates and zirconium dioxide monofilms grown by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Romanes, Maia Castillo

    Currently available solid lubricants only perform well under a limited range of environmental conditions. Unlike them, oxides are thermodynamically stable and relatively inert over a broad range of temperatures and environments. However, conventional oxides are brittle at normal temperatures; exhibiting significant plasticity only at high temperatures (>0.5Tmelting). This prevents oxides' use in tribological applications at low temperatures. If oxides can be made lubricious at low temperatures, they would be excellent solid lubricants for a wide range of conditions. Atomic layer deposition (ALD) is a growth technique capable of depositing highly uniform and conformal films in challenging applications that have buried surfaces and high-aspect-ratio features such as microelectromechanical (MEMS) devices where the need for robust solid lubricants is sometimes necessary. This dissertation investigates the surface and subsurface characteristics of ALD-grown ZnO/Al2O 3 nanolaminates and ZrO2 monofilms before and after sliding at room temperature. Significant enhancement in friction and wear performance was observed for some films. HRSEM/FIB, HRTEM and ancillary techniques (i.e. SAED, EELS) were used to determine the mechanisms responsible for this enhancement. Contributory characteristics and energy dissipation modes were identified that promote low-temperature lubricity in both material systems.

  5. Structural and optical properties of self-catalytic GaAs:Mn nanowires grown by molecular beam epitaxy on silicon substrates.

    PubMed

    Gas, Katarzyna; Sadowski, Janusz; Kasama, Takeshi; Siusys, Aloyzas; Zaleszczyk, Wojciech; Wojciechowski, Tomasz; Morhange, Jean-François; Altintaş, Abdulmenaf; Xu, H Q; Szuszkiewicz, Wojciech

    2013-08-21

    Mn-doped GaAs nanowires were grown in the self-catalytic growth mode on the oxidized Si(100) surface by molecular beam epitaxy and characterized by scanning and transmission electron microscopy, Raman scattering, photoluminescence, cathodoluminescence, and electron transport measurements. The transmission electron microscopy studies evidenced the substantial accumulation of Mn inside the catalyzing Ga droplets on the top of the nanowires. Optical and transport measurements revealed that the limit of the Mn content for self-catalysed growth of GaAs nanowires corresponds to the doping level, i.e., it is much lower than the Mn/Ga flux ratio (about 3%) used during the MBE growth. The resistivity measurements of individual nanowires confirmed that they are conductive, in accordance with the photoluminescence measurements which showed the presence of Mn(2+) acceptors located at Ga sites of the GaAs host lattice of the nanowires. An anomalous temperature dependence of the photoluminescence related to excitons was demonstrated for Mn-doped GaAs nanowires.

  6. Structural and waveguiding characteristics of Er3+:Yb3Al5-yGayO12 films grown by the liquid phase epitaxy

    NASA Astrophysics Data System (ADS)

    Hlásek, T.; Rubešová, K.; Jakeš, V.; Nekvindová, P.; Kučera, M.; Daniš, S.; Veis, M.; Havránek, V.

    2015-11-01

    Erbium (Er3+) doped ytterbium garnet (Er:Yb3Al5-yGayO12; y = 0, 0.55 and 1.1) single crystalline thick films have been grown by the low-temperature liquid phase epitaxy method (LPE). The composition of the films was determined using the high resolution XRD, the particle-induced X-ray emission spectroscopy (PIXE) and the particle-induced gamma-ray emission spectroscopy (PIGE). The lattice mismatch between films and substrates was investigated by the high-resolution X-ray diffraction. The surface analysis was carried out by the atomic force microscopy (AFM). Pure infrared emission of Er3+ ions was observed in all films containing gallium. The characteristics such as refractive index, thickness and light propagation were studied by the m-line spectroscopy (MLS) using several wavelengths (633, 964, 1311 and 1552 nm). All samples, where y = 1.1, were multimode waveguides. For these reasons, the Er:Yb3Al3.9Ga1.1O12 seems to be a promising material for light amplifiers in the IR region.

  7. Ion implanted epitaxially grown ZnSe

    NASA Technical Reports Server (NTRS)

    1974-01-01

    The epitaxial growth of ZnSe on (100) Ge using the close-spaced transport process is described. Substrate temperature of 575 C and source temperatures of 675 C yield 10 micron, single crystal layers in 10 hours. The Ge substrates provides a nonreplenishable chemical transport agent and the epitaxial layer thickness is limited to approximately 10 microns. Grown epitaxial layers show excellent photoluminescence structure at 77 K. Grown layers exhibit high resistivity, and annealing in Zn vapor at 575 C reduces the resistivity to 10-100 ohms-cm. Zinc vapor annealing quenches the visible photoluminescence.

  8. The single crystal X-ray structure of β-hematin DMSO solvate grown in the presence of chloroquine, a β-hematin growth-rate inhibitor

    PubMed Central

    Gildenhuys, Johandie; le Roex, Tanya; Egan, Timothy J.; de Villiers, Katherine A.

    2012-01-01

    Single crystals of solvated β-hematin were grown from a DMSO solution containing the antimalarial drug chloroquine, a known inhibitor of β-hematin formation. In addition, a kinetics study employing biomimetic lipid-water emulsion conditions was undertaken to further investigate the effect of chloroquine and quinidine on the formation of β-hematin. Scanning electron microscopy shows that the external morphology of the β-hematin DMSO solvate crystals is almost indistinguishable from that of malaria pigment (hemozoin) and single crystal X-ray diffraction confirms the presence of μ-propionato coordination dimers of iron(III) protoporphyrin IX. The free propionic acid functional groups of adjacent dimers hydrogen bond to included DMSO molecules, rather than forming carboxylic acid dimers. The observed exponential kinetics were modeled using the Avrami equation, with an Avrami constant equal to 1. The decreased rate of β-hematin formation observed at low concentrations of both drugs could be accounted for by assuming a mechanism of drug adsorption to sites on the fastest growing face of β-hematin. This behavior was modeled using the Langmuir isotherm. Higher concentrations of drug resulted in decreased final yields of β-hematin, and an irreversible drug-induced precipitation of iron(III) protoporphyrin IX was postulated to account for this. The model permits determination of the equilibrium adsorption constant (Kads). The values for chloroquine (log Kads = 5.55 ± 0.03) and quinidine (log Kads = 4.92 ± 0.01) suggest that the approach may be useful as a relative probe of the mechanism of action of novel antimalarial compounds. PMID:23253048

  9. The mechanism of twinning in zincblende structure crystals: New insights on polarity effects from a study of magnetic liquid encapsulated Czochralski grown InP single crystals

    SciTech Connect

    Dudley, M.; Raghothamachar, B.; Guo, Y.

    1998-12-31

    Synchrotron White Beam X-ray Topography (SWBXT) and synchrotron X-ray anomalous scattering have been employed to determine the polarity of {l_brace}111{r_brace} edge facets, anchored to the three phase boundary (TPB) on which twinning is observed to nucleate in Magnetic Liquid Encapsulated Czochralski (MLEC) grown sulfur doped, <001> InP single crystals. Analysis of the results indicates that both the formation of edge facets and the nucleation of twins occur preferentially on {l_brace}{bar 1}{bar 1}{bar 1}{r_brace}{sub P} faces. Of the four possible sets of edge facets, belonging to the {l_brace}{bar 1}{bar 1}{bar 1}{r_brace}{sub P} form, which are oriented so as to be thermodynamically favored to be anchored to the TPB, two can give rise to a {l_brace}115{r_brace} to {l_brace}{bar 1}{bar 1}{bar 1}{r_brace}{sub P} external should facet conversion upon twinning, while the other two can give rise to a {l_brace}114{r_brace} to {l_brace}110{r_brace} conversion. For these cases, twinning is only observed when the {l_brace}{bar 1}{bar 1}{bar 1}{r_brace}{sub P} edge facets are anchored to the TPB in a region where the shoulder angle is close to 74.21{degree} or 70.53{degree}, facilitating the production of the {l_brace}115{r_brace} and {l_brace}114{r_brace} external should facets, respectively, prior to twinning. These observations are discussed in light of calculated surface energies of the various internal and external facets.

  10. Anomalous Hall effect in epitaxially grown ferromagnetic FeGa/Fe3Ga hybrid structure: Evidence of spin carrier polarized by clusters

    NASA Astrophysics Data System (ADS)

    Duc Dung, Dang; Cho, Sunglae

    2013-05-01

    The anomalous Hall resistance relative with magnetic anisotropy of clusters Fe3Ga in Fe3Ga/Fe-Ga hybrid structural epitaxial was reported. The out-of-plane magnetic anisotropy was obtained for Fe3Ga/Fe-Ga hybrid structure, while in-plane magnetic anisotropy is shown in the single Fe-Ga phase epitaxial on GaAs(001). The observation of trend of saturation Hall resistance in Fe3Ga/Fe-Ga hybrid structural is compared with the Fe-Ga single crystal, which is solid evidence for spin polarization by local magnetic clusters.

  11. The structure of the glucuronoxylomannan produced by culinary-medicinal yellow brain mushroom (Tremella mesenterica Ritz.:Fr., Heterobasidiomycetes) grown as one cell biomass in submerged culture.

    PubMed

    Vinogradov, Evgeny; Petersen, Bent O; Duus, Jens Ø; Wasser, Solomon

    2004-06-01

    The yellow brain mushroom Tremella mesenterica possesses a wide spectrum of medicinal properties, including immunostimulating, protecting against radiation, antidiabetic, anti-inflammatory, hypocholesterolemic, hepatoprotective, and antiallergic effects. A unique feature of T. mesenterica is that most of the above mentioned medicinal properties depend on glucuronoxylomannan (GXM) contained in fruiting bodies or produced in pure culture conditions. We developed a new strain of T. mesenterica CBS 101939, which grows in submerged culture and offers superior yields of one-cell biomass rich in exocellular heteropolysaccharide GXM. The structure of the GXM was analyzed by NMR spectroscopy and chemical methods. The polysaccharide has a defined repeating unit structure, which is O-acetylated at several points: [structure: see text]. These results differ from previously published structure of Tremella extracellular polysaccharides, where mannan backbone was believed to be randomly glycosylated with xylan chains of different length.

  12. Photoluminescence Mapping and Angle-Resolved Photoluminescence of MBE-Grown InGaAs/GaAs RC LED and VCSEL Structures

    DTIC Science & Technology

    2002-06-03

    structures. The first method is spatially resolved photoluminescence, i.e. mapping of the spontaneous emission and the cavity resonance wavelength over the...the physical processes underlying light generation in microcavity devices. The information provided by both methods is crucial for designing optimum...challenge among optical devices, properties of InGaAs/GaAs RC LEDs, although the The high degree of complexity of the epitaxial structure methods used are

  13. 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.

  14. Strain-relaxed structure in (001)/(100)-oriented epitaxial PbTiO3 films grown on (100) SrTiO3 substrates by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Nakaki, Hiroshi; Kim, Yong Kwan; Yokoyama, Shintaro; Ikariyama, Rikyu; Funakubo, Hiroshi; Nishida, Ken; Saito, Keisuke

    2007-09-01

    The authors grew (001)- and (001)/(100)-oriented epitaxial PbTiO3 films with various thicknesses on (100)SrTiO3 substrates. They used x-ray diffraction to measure the angles between surface normal [001] of (001)-oriented domains and [100] of (100)-oriented domains. The angles were found to be approximately 3.6° when the film thickness exceeded 1100nm. This value is consistent with the value obtained by a geometric calculation for strain-free PbTiO3. This result suggests that thick epitaxial PbTiO3 films grown on (100)SrTiO3 substrates have a fully strain-relaxed structure.

  15. Growth conditions, structure, Raman characterization and optical properties of Sm-doped (LuxGd1-x)2SiO5 single crystals grown by the Czochralski method

    NASA Astrophysics Data System (ADS)

    GŁowacki, MichaŁ; Dominiak-Dzik, Grażyna; Ryba-Romanowski, Witold; Lisiecki, RadosŁaw; Strzęp, Adam; Runka, Tomasz; Drozdowski, MirosŁaw; Domukhovski, Viktor; Diduszko, Ryszard; Berkowski, Marek

    2012-02-01

    The (LuxGd0.995-xSm0.005)2SiO5 single crystals with x=0.095, 0.11, 0.15, 0.17, 0.19 0.35 and 0.5 were grown by the Czochralski method. Structural properties were investigated by X-ray diffraction measurements. Unit cell parameters and cell volume were determined by the Rietveld refinement of the collected X-ray powder spectra. The segregation features between Gd and Lu were estimated and analyzed. Vibrational properties of the solid solutions were analyzed on the basis of polarized Raman spectra acquired at 300-875 K temperature range. Absorption and emission spectra of Sm3+ ion in the crystals with different composition were analyzed in the terms of dopant energy levels, oscillator strengths of transitions and spectral features of luminescence bands in the visible range. Both structural and optical investigations revealed that change of Lu3+ content in (LuxGd0.995-xSm0.005)2SiO5 solid solution crystals induces the phase transition from C2/c (Lu2SiO5) to P21/c (Gd2SiO5) structure. It was found that the break of LSO to GSO-type structure occurs at 0.15

  16. 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.

  17. Structural optical and electronic properties of Fe and Ga doped ZnO thin films grown using pulsed laser deposition technique

    NASA Astrophysics Data System (ADS)

    Singh, Karmvir; Shukla, D. K.; Majid, S.; Dhar, R.; Choudhary, R. J.; Phase, D. M.

    2016-10-01

    Band gap engineering in ZnO thin films have been subject of intensive studies. The thin films of 2 wt % Fe and 2 wt % Ga doped ZnO and undoped ZnO were deposited on glass substrate by pulse laser deposition technique. Structural, optical and electronic structure properties of these thin films were investigated by X- Ray diffraction (XRD), UV-Vis spectroscopy and X-ray absorption spectroscopy (XAS), respectively. XRD studies show that all the thin films are highly oriented along the c-axis and maintain the wurtzite structure. Out of plane lattice parameter in Ga doped is smaller while in Fe doped is larger, compared to undoped ZnO. The band gaps of doped films have been found to increase due to doping of the Ga and Fe ions. XAS studies across O K edges of doped thin films show that the conduction band edge structure probed via oxygen 1s to 2p transitions have modified significantly in Ga doped sample.

  18. 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.

  19. Strain-Dependence of the Structure and Ferroic Properties of Epitaxial NiTiO 3 Thin Films Grown on Different Substrates

    DOE PAGES

    Varga, Tamas; Droubay, Timothy C.; Bowden, Mark E.; ...

    2015-01-01

    Polarization-induced weak ferromagnetism has been predicted a few years back in perovskite MTiO 3 (M = Fe, Mn, and Ni). We set out to stabilize this metastable perovskite structure by growing NiTiO 3 epitaxially on different substrates and to investigate the dependence of polar and magnetic properties on strain. Epitaxial NiTiO 3 films were deposited on Al 2 O 3 , Fe 2 O 3 , and LiNbO 3 substrates by pulsed laser deposition and characterized using several techniques. The effect of substrate choice on lattice strain, film structure, and physical properties was investigated. Our structural data from X-raymore » diffraction and electron microscopy 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 weak ferromagnetism and lattice polarization on strain and highlight our ability to control the ferroic properties in NiTiO 3 thin films by the choice of substrate. Our results are also consistent with the theoretical prediction that the ferromagnetism in acentric NiTiO 3 is polarization induced. From the substrates studied here, the perovskite substrate LiNbO 3 proved to be the most promising one for strong multiferroism.« less

  20. Strain-dependence Of The Structure And Ferroic Properties Of Epitaxial NiTiO3 Thin Films Grown On Different Substrates

    SciTech Connect

    Varga, Tamas; Droubay, Timothy C.; Bowden, Mark E.; Kovarik, Libor; Hu, Dehong; Chambers, Scott A.

    2015-08-14

    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 different substrates, and to investigate the dependence of polar and magnetic properties on strain. Epitaxial NiTiO3 films were deposited on Al2O3, Fe2O3, and LiNbO3 substrates by pulsed laser deposition, and characterized using several techniques. The effect of substrate choice on lattice strain, film structure, and physical properties was investigated. Our structural data from x-ray diffraction and electron microscopy 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 weak ferromagnetism and lattice polarization on strain, and highlight our ability to control the ferroic properties in NiTiO3 thin films by the choice of substrate. Our results are also consistent with the theoretical prediction that the ferromagnetism in acentric NiTiO3 is polarization-induced. From the substrates studied here, the perovskite substrate LiNbO3 proved to be the most promising one for strong multiferroism.

  1. Structure, morphology and Raman and optical spectroscopic analysis of In1-xCuxP thin films grown by MOCVD technique for solar cell applications

    NASA Astrophysics Data System (ADS)

    Alshahrie, Ahmed; Juodkazis, S.; Al-Ghamdi, A. A.; Hafez, M.; Bronstein, L. M.

    2017-10-01

    Nanocrystalline In1-xCuxP thin films (0 ≤ x ≤ 0.5) have been deposited on quartz substrates by a Metal-Organic Chemical Vapor Deposition (MOCVD) technique. The effect of the copper ion content on the structural crystal lattice, morphology and optical behavior of the InP thin films was assessed using X-ray diffraction, scanning electron microscopy, atomic force microscopy, Raman spectroscopy and spectrophotometry. All films exhibited a crystalline cubic zinc blende structure, inferring the solubility of the Cu atoms in the InP crystal structure. The XRD patterns demonstrated that the inclusion of Cu atoms into the InP films forced the nanoparticles in the films to grow along the (1 1 1) direction. The AFM topography showed that the Cu ions reduce the surface roughness of deposited films. The Raman spectra of the deposited films contain the first and second order anti-stoke ΓTO, ΓLO, ΧLO + ΧTO, 2ΓTO, and ΓLO + ΓTO bands which are characteristic of the InP crystalline structure. The intensities of these bands decreased with increasing the content of the Cu atoms in the InP crystals implying the creation of a stacking fault density in the InP crystal structure. The In1-xCuxP thin films have shown high optical transparency of 90%. An increase of the optical band gap from 1.38 eV to 1.6 eV was assigned to the increase of the amount of Cu ions in the InP films. The In0.5Cu0.5P thin film exhibited remarkable optical conductivity with very low dissipation factor which makes it a promising buffer window for solar energy applications.

  2. Thickness dependences of the structural optical, and electrical properties of Cu2 Se thin films grown by using DC magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Ahn, Heejin; Um, Youngho

    2014-05-01

    The thickness dependences of the structural, optical, and electrical properties of p-type Cu2Se films have been investigated in the thickness range of 200-600 nm. X-ray diffraction analysis confirmed that a stoichiometric Cu2Se phase with a cubic structure was formed. From the Hall effect measurements, the electrical resistivity of the Cu2Se film showed a low resistivity of 4.21 × 10-5 Ω·cm. The optical band gap energy estimated from the optical transmittance measurements varied in the range from 2.01 to 2.41 eV at room temperature Moreover, the surface roughness of the film increased with increasing film thickness.

  3. Effect of the annealing temperature on the low-temperature photoluminescence in Si:Er light-emitting structures grown by molecular-beam epitaxy

    SciTech Connect

    Andreev, B. A.; Sobolev, N. A. Denisov, D. V.; Shek, E. I.

    2013-10-15

    The photoluminescence spectra of light-emitting structures based on silicon doped with erbium during the course of molecular-beam epitaxy at a temperature of 500 Degree-Sign C are studied at 4.2 K on being annealed at 800-900 Degree-Sign C. Three sets of lines belonging to the emitting centers of erbium in silicon with a low oxygen-impurity concentration are revealed.

  4. Electronic structure, optical and magnetic studies of PLD-grown (Mn, P)-doped ZnO nanocolumns at room temperature

    NASA Astrophysics Data System (ADS)

    Phan, The-Long; Ho, T. A.; Dang, N. T.; Nguyen, Manh Cuong; Dao, Van-Duong

    2017-07-01

    We prepared well-aligned Zn1-x Mn x O:yP nanocolumns (x  =  0-0.02, and y  =  0 and 1 mol%) on SiO2/Si(0 0 1) substrates by using pulsed laser deposition (PLD) and then investigated their electronic structure and optical and magnetic properties at room temperature. The analyses of x-ray photoelectron and x-ray absorption fine structure spectra revealed Mn2+ and/or P ions existing in nanocolumns, where Mn2+ ions are situated in the Zn2+ site of the ZnO-wurtzite structure. Although the incorporation of Mn2+ and/or P ions did not form secondary phases, as confirmed by x-ray and electron diffraction patterns, more lattice defects were created, and consequently changed the band-gap energy as well as the electron-phonon interactions in the nanocolumns. Magnetization versus magnetic-field measurements revealed that all the samples exhibited FM order. In particular, the (Mn, P) co-doping with x  =  0.02 and y  =  1 remarkably enhanced the magnetic moment up to 2.92 µ B/Mn. Based on the results obtained from analyzing the electronic structures, UV-Vis absorption and resonant Raman scattering spectra, and theoretical calculations, we believe that the enhancement of the FM order in (Mn, P)-doped ZnO nanocolumns is due to exchange interactions taking place between vacancy-mediated Mn2+ ions.

  5. Eshelby Twist as a Possible Source of Lattice Rotation in a Perfectly Ordered Protein/Silica Structure Grown by a Simple Organism.

    PubMed

    Zlotnikov, Igor; Werner, Peter; Fratzl, Peter; Zolotoyabko, Emil

    2015-11-11

    The formation mechanism of a perfectly ordered protein/silica structure in the axial filament of the anchor spicule of the silica sponge Monorhaphis chuni is suggested. Experimental evidence shows that the growth of this architecture is realized by a thermodynamically driven dislocation-mediated spiral growth mechanism, resulting in a specific rotation of the mesoscopic crystal lattice (Eshelby twist). © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Electrolysis as a controllable method for establishing p-n junctions in multi-nanolayer films of amorphous selenium

    NASA Astrophysics Data System (ADS)

    John, Joshua D.; Saito, Ichitaro; Ochiai, Jun; Toyama, Ryo; Masuzawa, Tomoaki; Yamada, Takatoshi; Chua, Daniel H. C.; Okano, Ken

    2017-08-01

    We present a controllable way of establishing a p-n junction in amorphous selenium (a-Se) using electrolysis. Amorphous selenium is used as an anode in the electrolysis of NaCl solution. By varying the duration of the electrolysis, we can make the contact to a-Se either Ohmic or rectifying and control the built-in potential and full depletion voltage of the contacts and junctions formed in the a-Se. I-V and C-V measurements show that after electrolysis rectification occurs and that as the duration of electrolysis increases, the direction of rectification changes, with the magnitudes of the built-in potential and the full depletion becoming higher. From the results, we present a model for the electrochemical process of forming the p-n junction and highlight the dependence on the duration of the electrolysis.

  7. Different continuous cropping spans significantly affect microbial community membership and structure in a vanilla-grown soil as revealed by deep pyrosequencing.

    PubMed

    Xiong, Wu; Zhao, Qingyun; Zhao, Jun; Xun, Weibing; Li, Rong; Zhang, Ruifu; Wu, Huasong; Shen, Qirong

    2015-07-01

    In the present study, soil bacterial and fungal communities across vanilla continuous cropping time-series fields were assessed through deep pyrosequencing of 16S ribosomal RNA (rRNA) genes and internal transcribed spacer (ITS) regions. The results demonstrated that the long-term monoculture of vanilla significantly altered soil microbial communities. Soil fungal diversity index increased with consecutive cropping years, whereas soil bacterial diversity was relatively stable. Bray-Curtis dissimilarity cluster and UniFrac-weighted principal coordinate analysis (PCoA) revealed that monoculture time was the major determinant for fungal community structure, but not for bacterial community structure. The relative abundances (RAs) of the Firmicutes, Actinobacteria, Bacteroidetes, and Basidiomycota phyla were depleted along the years of vanilla monoculture. Pearson correlations at the phyla level demonstrated that Actinobacteria, Armatimonadetes, Bacteroidetes, Verrucomicrobia, and Firmicutes had significant negative correlations with vanilla disease index (DI), while no significant correlation for fungal phyla was observed. In addition, the amount of the pathogen Fusarium oxysporum accumulated with increasing years and was significantly positively correlated with vanilla DI. By contrast, the abundance of beneficial bacteria, including Bradyrhizobium and Bacillus, significantly decreased over time. In sum, soil weakness and vanilla stem wilt disease after long-term continuous cropping can be attributed to the alteration of the soil microbial community membership and structure, i.e., the reduction of the beneficial microbes and the accumulation of the fungal pathogen.

  8. Nanotransfer and nanoreplication using deterministically grown sacrificial nanotemplates

    DOEpatents

    Melechko, Anatoli V [Oak Ridge, TN; McKnight, Timothy E [Greenback, TN; Guillorn, Michael A [Ithaca, NY; Ilic, Bojan [Ithaca, NY; Merkulov, Vladimir I [Knoxville, TN; Doktycz, Mitchel J [Knoxville, TN; Lowndes, Douglas H [Knoxville, TN; Simpson, Michael L [Knoxville, TN

    2011-08-23

    Methods, manufactures, machines and compositions are described for nanotransfer and nanoreplication using deterministically grown sacrificial nanotemplates. An apparatus, includes a substrate and a nanoreplicant structure coupled to a surface of the substrate.

  9. Process modeling and analysis of structure and stoichiometry of magnesium oxide nano thin films grown by molecular beam epitaxy on 6 hydrogen-silicon carbide substrates

    NASA Astrophysics Data System (ADS)

    Uddin, Ghulam Moeen

    In recent years there has been an increasing interest in effective integration of nano scale functional oxides with semiconductors for third and fourth generation nano devices including high-K dielectrics based electronic devices and paradigm-shifting spintronics-based circuits. In this research we investigate the growth of MgO nano thin films on 6H-SiC substrate in a molecular beam epitaxy process. Here MgO serves as a template layer to minimize the mismatch with both substrate and a functional oxide films such as BTO and BaM. In this research we constructed neural network based process models using historical experimental data. Based on these process models we performed structural and stoichiometric analyses through both design of experiments and Monte Carlo simulation. We found that the percentage starting oxygen on the substrate is the most critical variable that promotes the undesired bonding states, i.e., Mg-OH and excessive strain in film crystalline structure. In addition the impact of percentage of starting oxygen on structure and stoichiometry is affected by the film thickness. The interaction between substrate temperature and oxygen on the starting substrate surface is the critical pair that affects the dynamics of Mg-OH bonding state. This study helped us analyze the process behavior and gain process knowledge to conduct systematic experimentation. After conducting the systematic experiments we quantitatively studied the causal relationship the undesired bonding states and the percentage starting oxygen at 3 levels of film thickness. Moreover, the cleaning of silicon carbide (6H-SiC) substrate surface is an essential and important step to grow MgO films with minimum undesired bonding states. We investigated high temperature hydrogen etching process to clean the substrate surface. In this research we studied the impact of cleaning time and cleaning temperature by analyzing the reflection high energy electron diffraction (RHEED) structural performance

  10. The effect of cation doping on the morphology, optical and structural properties of highly oriented wurtzite ZnO-nanorod arrays grown by a hydrothermal method.

    PubMed

    Hassanpour, A; Guo, P; Shen, S; Bianucci, P

    2017-10-27

    Undoped and C-doped (C: Mg(2+), Ni(2+), Mn(2+), Co(2+), Cu(2+), Cr(3+)) ZnO nanorods were synthesized by a hydrothermal method at temperatures as low as 60 °C. The effect of doping on the morphology of the ZnO nanorods was visualized by taking their cross section and top SEM images. The results show that the size of nanorods was increased in both height and diameter by cation doping. The crystallinity change of the ZnO nanorods due to each doping element was thoroughly investigated by an x-ray diffraction (XRD). The XRD patterns show that the wurtzite crystal structure of ZnO nanorods was maintained after cation addition. The optical Raman-active modes of undoped and cation-doped nanorods were measured with a micro-Raman setup at room temperature. The surface chemistry of samples was investigated by x-ray photoelectron spectroscopy and energy-dispersive x-ray spectroscopy. Finally, the effect of each cation dopant on band-gap shift of the ZnO nanorods was investigated by a photoluminescence setup at room temperature. Although the amount of dopants (Mg(2+), Ni(2+), and Co(2+)) was smaller than the amount of Mn(2+), Cu(2+), and Cr(3+) in the nanorods, their effect on the band structure of the ZnO nanorods was profound. The highest band-gap shift was achieved for a Co-doped sample, and the best crystal orientation was for Mn-doped ZnO nanorods. Our results can be used as a comprehensive reference for engineering of the morphological, structural and optical properties of cation-doped ZnO nanorods by using a low-temperature synthesis as an economical mass-production approach.

  11. Effects of hydrogen on the structural and optical properties of MoSe2 grown by hot filament chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Wang, B. B.; Zhu, M. K.; Levchenko, I.; Zheng, K.; Gao, B.; Xu, S.; Ostrikov, K.

    2017-10-01

    The role of reactive environment and hydrogen specifically in growth and structure of molybdenum selenide (MoSe2) nanomaterials is presently debated, and it is not clear whether hydrogen can promote the growth of MoSe2 sheets and alter their electronic properties. To find efficient, convenient methods for controlling the nucleation, growth and resultant properties of MoSe2 nanomaterials, MoSe2 nanoflakes were synthesized on silicon substrates by hot filament chemical vapor deposition using molybdenum trioxide and selenium powders in pure hydrogen, nitrogen gases and hydrogen-nitrogen mixtures. The structures and composition of synthesized MoSe2 nanoflakes were studied using the advanced characterization instruments including field emission scanning electron microscopy, micro-Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy and energy dispersive X-ray spectrometry. The analysis of the growth process indicates that hydrogen can improve the formation of MoSe2 nanoflakes and significantly alter their properties due to the high reduction capacity of hydrogen and the creation of more nucleation centers of MoSe2 nanoflakes on the silicon surface. The study of photoluminescent (PL) properties reveals that the MoSe2 nanoflakes can generate a strong PL band at about 631 nm, differently from the plain MoSe2 nanoflakes. The major difference in the PL properties may be related to the edges of MoSe2 nanoflakes. These results can be used to control the growth and structure of MoSe2-based nanomaterials and contribute to the development of advanced MoSe2-based optoelectronic devices.

  12. Atomically-Resolved In-Situ Studies of Surface Structure Evolution of PLD-Grown La5/8Ca3/8MnO3 Thin Films

    NASA Astrophysics Data System (ADS)

    Tselev, Alexander; Vasudevan, Rama; Qiao, Liang; Biegalski, Michael; Baddorf, Arthur; Kalinin, Sergei

    2014-03-01

    Here, we report atomically resolved in-situ Scanning Tunneling Microscopy (STM) studies of La5/8Ca3/8MnO3 (LCMO) thin films grown by RHEED-assisted PLD. Films were grown on TiO2-terminated (001) SrTiO3 substrates at a substrate temperature of 750 °C and O2 pressure of 50 mTorr. In-situ UHV STM was performed at room temperature. LCMO is known to grow in layer-by layer (LBL) mode. We find that the initial growth does not follow the best physically possible LBL growth (with only three u.c. layers exposed). RHEED oscillations decay during deposition of the first 10-15th unit cells. Subsequently, the RHEED intensity oscillations grow and remain persistent. STM images of 16 u.c.-thick films revealed surfaces with up to five u.c. layers being exposed in a stepped island-like morphology with 1/2 u.c. step heights. Such morphology allowed studies of atomic surface structure of both terminations. 25 u.c.-thick samples were found to be almost single-terminated. The minor termination is ordered and exhibits (1x1) reconstructions; RHEED suggests that this termination is the La/Ca-O termination. A 250 u.c.-thick film was found to be single-terminated with only three u.c. layers exposed. This research was sponsored by DMSE (AT, RV, SVK) and by SUFD (LQ, MDB, APB) of BES, DOE. Research was conducted at the CNMS, which is sponsored at ORNL by SUFD, BES, DOE.

  13. In-plane orientation and composition dependences of crystal structure and electrical properties of {100}-oriented Pb(Zr,Ti)O3 films grown on (100) Si substrates by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Okamoto, Shoji; Sankara Rama Krishnan, P. S.; Okamoto, Satoshi; Yokoyama, Shintaro; Akiyama, Kensuke; Funakubo, Hiroshi

    2017-10-01

    In-plane orientation-controlled Pb(Zr x ,Ti1‑ x )O3 (PZT) films with a thickness of approximately 2 µm and a Zr/(Zr + Ti) ratio of 0.39–0.65 were grown on (100) Si substrates by pulsed metal–organic chemical vapor deposition (MOCVD). In-plane-oriented epitaxial PZT films and in-plane random fiber-textured PZT films with {100} out-of-plane orientation were grown on (100)c SrRuO3//(100)c LaNiO3//(100) CeO2//(100) YSZ//(100) Si and (100)c SrRuO3/(100)c LaNiO3/(111) Pt/TiO2/SiO2/(100) Si substrates, respectively. The effects of Zr/(Zr + Ti) ratio and in-plane orientation on the crystal structure, dielectric, ferroelectric, and piezoelectric properties of the films were systematically investigated. The X-ray diffraction measurement showed that the epitaxial PZT films had a higher volume fraction of (100) orientation than the fiber-textured PZT films in the tetragonal Zr/(Zr + Ti) ratio region. A large difference was not detected between the epitaxial films and the fiber-textured films for Zr/(Zr + Ti) ratio dependence of the dielectric constant, and remanent polarization. However, in the rhombohedral phase region [Zr/(Zr + Ti) = 0.65], coercive field was found to be 1.5-fold different between the epitaxial and fiber-textured PZT films. The maximum field-induced strains measured at 0–100 kV/cm by scanning atomic force microscopy were obtained at approximately Zr/(Zr + Ti) = 0.50 and were about 0.5 and 0.3% for the epitaxial and fiber-textured PZT films, respectively.

  14. Isolation and structure determination of a benzofuran and a bis-nor-isoprenoid from Aspergillus niger grown on the water soluble fraction of Morinda citrifolia Linn. leaves.

    PubMed

    Siddiqui, Bina S; Ismail, Fouzia A Sattar; Gulzar, Tahsin; Begum, Sabira

    2003-10-01

    The leaves of Morinda citrifolia, Linn. afforded a new benzofuran and a bis-nor-isoprenoid, blumenol C, hitherto unreported from this source. The structures of these have been elucidated as 5-benzofuran carboxylic acid-6-formyl methyl ester (1) and 4-(3'(R)-hydroxybutyl)-3,5,5, trimethyl-cyclohex-2-en-1-one (2) respectively through spectroscopic studies. The NMR data (including 1D, 2D techniques) and stereochemistry at C-3' of Compound 2 is also being reported for the first time.

  15. Structural properties of Al-rich AlInN grown on c-plane GaN substrate by metal-organic chemical vapor deposition

    PubMed Central

    2014-01-01

    The attractive prospect for AlInN/GaN-based devices for high electron mobility transistors with advanced structure relies on high-quality AlInN epilayer. In this work, we demonstrate the growth of high-quality Al-rich AlInN films deposited on c-plane GaN substrate by metal-organic chemical vapor deposition. X-ray diffraction, scanning electron microscopy, and scanning transmission electron microscopy show that the films lattice-matched with GaN can have a very smooth surface with good crystallinity and uniform distribution of Al and In in AlInN. PMID:25489282

  16. Structural, microstructural, and optical properties of Zn1- x Mg x O thin films grown onto glass substrate by ultrasonic spray pyrolysis

    NASA Astrophysics Data System (ADS)

    Hoggas, K.; Nouveau, Corinne; Djelloul, A.; Bououdina, M.

    2015-08-01

    Pure and doped Zn1- x Mg x O films were deposited onto glass substrate by ultrasonic spray pyrolysis technique. The variation of lattice constant and the blue shift of near-band-edge emission indicate that Zn2+ ions are successfully substituted by Mg2+ ions within ZnO lattice. At higher Mg content ( x ≥ 0.21), a drastic change appears in the morphology, as a result of structural changes from wurtzite (ZnO) structure into a mixture of wurtzite and cubic (MgO) phases. FTIR study indicated the existence of distinct characteristic absorption peaks at ~442 cm-1 for Zn-O stretching mode that shifted toward the red region with the increase in Mg content. In addition to the host phonons of ZnO, one additional band was observed around 523 cm-1, presumably attributed to the Mg-related vibrational mode. The optical constants and thickness of thin films have been determined using experimental transmittance data. The luminescence intensity at 2.63 eV of Zn0.85Mg0.15O thin films was found to be approximately 13 times higher than that of pure ZnO film measured under the same excitation conditions.

  17. Diversity and structure of landraces of Agave grown for spirits under traditional agriculture: A comparison with wild populations of A. angustifolia (Agavaceae) and commercial plantations of A. tequilana.

    PubMed

    Vargas-Ponce, Ofelia; Zizumbo-Villarreal, Daniel; Martínez-Castillo, Jaime; Coello-Coello, Julián; Colunga-Garcíamarín, Patricia

    2009-02-01

    Traditional farming communities frequently maintain high levels of agrobiodiversity, so understanding their agricultural practices is a priority for biodiversity conservation. The cultural origin of agave spirits (mezcals) from west-central Mexico is in the southern part of the state of Jalisco where traditional farmers cultivate more than 20 landraces of Agave angustifolia Haw. in agroecosystems that include in situ management of wild populations. These systems, rooted in a 9000-year-old tradition of using agaves as food in Mesoamerica, are endangered by the expansion of commercial monoculture plantations of the blue agave variety (A. tequilana Weber var. Azul), the only agave certified for sale as tequila, the best-known mezcal. Using intersimple sequence repeats and Bayesian estimators of diversity and structure, we found that A. angustifolia traditional landraces had a genetic diversity (H(BT) = 0.442) similar to its wild populations (H(BT) = 0.428) and a higher genetic structure ((B) = 0.405; (B) =0. 212). In contrast, the genetic diversity in the blue agave commercial system (H(B) = 0.118) was 73% lower. Changes to agave spirits certification laws to allow the conservation of current genetic, ecological and cultural diversity can play a key role in the preservation of the traditional agroecosystems.

  18. Hierarchical core/shell structure of MnO2@polyaniline composites grown on carbon fiber paper for application in pseudocapacitors.

    PubMed

    Yang, MinHo; Hong, Seok Bok; Choi, Bong Gill

    2015-11-28

    Hierarchical core/shell structured arrays of MnO2@polyaniline (PANI) nanosheets are successfully deposited on the surface of carbon fiber paper (CFP) by a two-step method of a redox reaction-assisted deposition of MnO2 and post electrodeposition of PANI. The CFP is used as a three-dimensional (3D) current collector to ensure 3D transport of ions and electrons with a large surface area. In addition, the electrodeposition technique enables conformal and thin coating of a layer of PANI across the entire MnO2 nanosheet. The MnO2@PANI on the CFP shows a unique architecture for efficient ion diffusion pathways in hierarchical porous structures and rapid electron transfer through PANI coated layers. The MnO2@PANI/CFP can be applied as a binder- and carbon-free electrode for supercapacitors. Evaluation of the electrochemical performance revealed that the as-prepared electrodes have a high value of specific capacitance (437 F g(-1) at 1 A g(-1)), high rate capability (62.4% retention at 15 A g(-1)), and good cycle life (∼100% at sequential current densities of 1 and 5 A g(-1) over 3000 cycles).

  19. Widely tunable alloy composition and crystal structure in catalyst-free InGaAs nanowire arrays grown by selective area molecular beam epitaxy

    SciTech Connect

    Treu, J. E-mail: Gregor.Koblmueller@wsi.tum.de; Speckbacher, M.; Saller, K.; Morkötter, S.; Xu, X.; Riedl, H.; Abstreiter, G.; Finley, J. J.; Koblmüller, G. E-mail: Gregor.Koblmueller@wsi.tum.de; Döblinger, M.

    2016-02-01

    We delineate the optimized growth parameter space for high-uniformity catalyst-free InGaAs nanowire (NW) arrays on Si over nearly the entire alloy compositional range using selective area molecular beam epitaxy. Under the required high group-V fluxes and V/III ratios, the respective growth windows shift to higher growth temperatures as the Ga-content x(Ga) is tuned from In-rich to Ga-rich InGaAs NWs. Using correlated x-ray diffraction, transmission electron microscopy, and micro-photoluminescence spectroscopy, we identify structural defects to govern luminescence linewidths in In-rich (x(Ga) < 0.4) and Ga-rich (x(Ga) > 0.6) NWs, whereas limitations at intermediate Ga-content (0.4 < x(Ga) < 0.6) are mainly due to compositional inhomogeneities. Most remarkably, the catalyst-free InGaAs NWs exhibit a characteristic transition in crystal structure from wurtzite to zincblende (ZB) dominated phase near x(Ga) ∼ 0.4 that is further reflected in a cross-over from blue-shifted to red-shifted photoluminescence emission relative to the band edge emission of the bulk ZB InGaAs phase.

  20. Preparation of regularly structured nanotubular TiO2 thin films on ITO and their modification with thin ALD-grown layers

    NASA Astrophysics Data System (ADS)

    Tupala, Jere; Kemell, Marianna; Härkönen, Emma; Ritala, Mikko; Leskelä, Markku

    2012-03-01

    Nanotubular titanium dioxide thin films were prepared by anodization of titanium metal films evaporated on indium tin oxide (ITO) coated glass. A facile method to enhance the adhesion of the titanium film to the ITO glass was developed. An optimum thickness of 550 nm for the evaporated titanium was found to keep the film adhered to ITO during the anodization. The films were further modified by growing amorphous titania, alumina and tantala thin films conformally in the nanotubes by atomic layer deposition (ALD). The optical, electrical and physical properties of the different structures were compared. It was shown that even 5 nm thin layers can modify the properties of the nanotubular titanium dioxide films.