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Sample records for multi-nanolayer structures grown

  1. 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.

  2. Structure and growth process of vapor-grown carbon fibers

    NASA Technical Reports Server (NTRS)

    Koyama, T.; Endo, M.

    1983-01-01

    The structure, effect of heat, and growth process of vapor-grown carbon fibers are investigated. The growth process of the carbon fibers could be divided into three stages; nucleation, elongation, and thickening processes. Also, a multi-layered structure can be produced as well as graphitization.

  3. Superlattice structures grown by metalorganic MBE

    NASA Astrophysics Data System (ADS)

    Tokumitsu, E.; Katoh, T.; Sung, C. P.; Sandhu, A.; Kimura, R.; Konagai, M.; Takahashi, K.

    1986-08-01

    The metalorganic molecular beam epitaxial (MOMBE) growth of GaAs and (GaAl)As using triethylgallium (TEG) and triethylaluminum (TEA) has been studied. GaAs/GaAlAs multi quantum well (MQW) heterostructures were fabricated and it was found that the photoluminescence peak energy at room temperature agreed with calculated values. Furthermore, a new technique to grow a nipi superlattice structure was proposed and as a trial growth a n-GaAs/n +-GaAs multilayer was prepared by applying an alternating ionization voltage to hydrogen.

  4. Structure property relationships of carbonaceous films grown under ion enhancement

    SciTech Connect

    Weissmantel, C.; Ackermann, E.; Bewilogua, K.; Hecht, G.; Kupfer, H.; Rau, B.

    1986-11-01

    Based on our own results and in comparison with data published by other groups the structure property relationships of carbon and carbon/metal films prepared by sputtering and deposition of partially ionized species are discussed. Films grown by ion beam sputtering are dark brownish and amorphous with a small fraction of microcrystals. However, a transition to transparent and insulating layers can be effected by ion bombardment. C/Me coatings, where Me stands for Ti or Sn, were obtained by magnetron sputtering of composite targets. The films proved to be amorphous up to metal concentrations of more than 10 at. %, but metal and carbide crystals grow upon annealing. Measurements of the hardness, the electrical conductivity, and the contact behavior in dependence on the composition provided interesting information. For carbon films prepared by deposition of partially ionized benzene species it has been found that the properties depend characteristically on the ion energy; typical ''diamondlike'' i-C films are obtained by applying a bias voltage from 1--3 keV. The thermal stability of the amorphous coatings is discussed in conjunction with their electrical conductivity. Summarizing extensive structure investigations, a structure model based on tetrahedrally interlinked carbon rings is proposed. Composites of the type i-C/Me (Me: Al, Ti, Cr), which were prepared by simultaneous metal evaporation, exhibit a wide range of structure property relations.

  5. Structure of droplet-epitaxy-grown InAs/GaAs quantum dots

    NASA Astrophysics Data System (ADS)

    Cohen, Eyal; Yochelis, Shira; Westreich, Ohad; Shusterman, Sergey; Kumah, Divine P.; Clarke, Roy; Yacoby, Yizhak; Paltiel, Yossi

    2011-06-01

    We have used a direct x-ray phasing method, coherent Bragg rod analysis, to obtain sub-angstrom resolution electron density maps of the InAs/GaAs dot system. The dots were grown by the droplet heteroepitaxy (DHE) technique and their structural and compositional properties are compared with those of dots grown by the strain-driven Stranski-Krastanov method. Our results show that the Ga diffusion into the DHE-grown dots is somewhat larger; however, other characteristics such as the composition of the dots' uppermost layers, the interlayer spacing, and the bowing of the atomic layers are similar.

  6. Crystal structure of thin oxide films grown on Zr-Nb alloys studied by RHEED

    NASA Astrophysics Data System (ADS)

    Khatamian, D.; Lalonde, S. D.

    1997-05-01

    The highly surface sensitive reflection high energy electron diffraction (RHEED) technique was used to determine thecrystal structure of oxide films grown on Zr-Nb alloys in air up to 673 K. The results show that the oxide films grown on Zr-2.5 wt% Nb(α-Zr + β-Zr) have a mixture of nearly-cubic-tetragona and monoclinic structures for films of 200 nm thick or less and that the outer layers of films thicker than 800 nm only have the monoclinic crystal structure. However, oxide films grown on Zr-20 wt% Nb (β-Zr) have a stabilized nearly-cubic-tetragonal structure for all film thicknesses, studied here, up to 2100 nm.

  7. Structure of a randomly grown 2-d network.

    PubMed

    Ajazi, Fioralba; Napolitano, George M; Turova, Tatyana; Zaurbek, Izbassar

    2015-10-01

    We introduce a growing random network on a plane as a model of a growing neuronal network. The properties of the structure of the induced graph are derived. We compare our results with available data. In particular, it is shown that depending on the parameters of the model the system undergoes in time different phases of the structure. We conclude with a possible explanation of some empirical data on the connections between neurons. PMID:26375356

  8. Hierarchical tubular structures grown from the gel/liquid interface.

    PubMed

    Steenbjerg Ibsen, Casper Jon; Mikladal, Bjørn Fridur; Bjørnholt Jensen, Uffe; Birkedal, Henrik

    2014-12-01

    Three dimensional hierarchical materials are widespread in nature but are difficult to synthesize by using self-assembly/organization. Here, we employ a gel-liquid interface to obtain centimeter-long ∼100 μm diameter tubes with complex mineral wall structures that grow from the interface into solution. The gel, made from gelatin, is loaded with metal chloride salt, whereas the solution is a high pH anion source. Tubes were obtained with a range of cations (Ca(2+) , Sr(2+) , Ba(2+) , Cu(2+) , and Zn(2+) ) and anions (CO3 (2-) and PO4 (3-) ). The crystalline phases found in the tube walls corresponded to expectations from solution chemistries and phase solubilities. The growth mechanism is found to be akin to that of chemical gardens. The divalent cations modify the strength of the gelatin gel in a manner that involves not only simple electrostatic screening, but also ion-specific effects. Thus, tubes were not obtained for those ions and/or concentrations that significantly changed the gel's mechanical structure. At high Cu(2+) loading, for example, vertical convection bands, not Liesegang bands, were observed in the gels. PMID:25336024

  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. PMID:26625884

  10. Epitaxial Structure of (001)- and (111)-Oriented Perovskite Ferrate Films Grown by Pulsed-Laser Deposition.

    PubMed

    Chakraverty, Suvankar; Ohtomo, Akira; Okude, Masaki; Ueno, Kazunori; Kawasaki, Masashi

    2010-04-01

    The epitaxial structures of SrFeO(2.5) films grown on SrTiO(3) (001) and (111) substrates by PLD are reported. A layer-by-layer growth mode was achieved in the initial stage on both substrates. The films were stabilized with a monoclinic structure, where we identified the in-plane domain structures and orientation relationship. Our study presents a guide to control the heteroepitaxy of (111)-oriented noncubic perovskites. PMID:20383295

  11. Temperature threshold for nanorod structuring of metal and oxide films grown by glancing angle deposition

    SciTech Connect

    Deniz, Derya; Lad, Robert J.

    2011-01-15

    Thin films of tin (Sn), aluminum (Al), gold (Au), ruthenium (Ru), tungsten (W), ruthenium dioxide (RuO{sub 2}), tin dioxide (SnO{sub 2}), and tungsten trioxide (WO{sub 3}) were grown by glancing angle deposition (GLAD) to determine the nanostructuring temperature threshold, {Theta}{sub T}, above which adatom surface diffusion becomes large enough such that nanorod morphology is no longer formed during growth. The threshold was found to be lower in metals compared to oxides. Films were grown using both dc and pulsed dc magnetron sputtering with continuous substrate rotation over the temperature range from 291 to 866 K. Film morphologies, structures, and compositions were characterized by high resolution scanning electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy. Films were also grown in a conventional configuration for comparison. For elemental metals, nanorod structuring occurs for films with melting points higher than that of Al (933 K) when grown at room temperature with a rotation rate of {approx}5 rpm, corresponding to a value of {Theta}{sub T}{approx_equal}0.33{+-}0.01. For the oxide films, a value of {Theta}{sub T}{approx_equal}0.5 was found, above which GLAD nanorod structuring does not occur. The existence of a nanostructuring temperature threshold in both metal and oxide GLAD films can be attributed to greater adatom mobilities as temperature is increased resulting in nonkinetically limited film nucleation and growth processes.

  12. Optically addressed spatial light modulators by MBE-grown nipi MQW structures

    NASA Technical Reports Server (NTRS)

    Maserjian, Joseph; Andersson, P. O.; Hancock, B. R.; Iannelli, J. M.; Eng, S. T.; Grunthaner, F. J.

    1989-01-01

    Promising approaches for achieving optically addressed spatial light modulators (O-SLMs) are investigated based on combining nipi and multiple quantum well structures. Theoretical aspects of photooptic effects achievable in such structures are treated. Test structures are grown by molecular beam epitaxy using two material systems. (In,Ga)As/GaAs and (Al,Ga)As/GaAs. Experiments show large optically controlled modulation of the absorption coefficient in the quantum well layers, a log power dependence on the control signal, millisecond and shorter time response, and generally predictable behavior. The results are encouraging for several different O-SLM device structures proposed.

  13. 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.

  14. Enhanced terahertz emission from a multilayered low temperature grown GaAs structure

    NASA Astrophysics Data System (ADS)

    Rihani, Samir; Faulks, Richard; Beere, Harvey E.; Farrer, Ian; Evans, Michael; Ritchie, David A.; Pepper, Michael

    2010-03-01

    We report the use of a multilayered structure comprising of alternating layers of low temperature grown GaAs and high temperature grown AlAs, as a terahertz (THz) photoconductive antenna emitter and receiver. Devices based on 10×10 μm2 mesa defined photoconductive gaps were fabricated on the multilayered structure, and a comparison made to conventional planar devices. The mesa defined photoconductive antennas allowed successive contact through the multilayered structure, which resulted in an increase in THz emission power and detection responsivity with increasing number of layers in contact with the antenna electrodes. A comparison with a conventional single layered device, processed in an identical mesa geometry, confirmed that the enhancement in THz emission is solely due to the multilayered nature of the device, whereas the improved receiver performance can be partially attributed to the mesa geometry.

  15. Defect structure of a free standing GaN wafer grown by the ammonothermal method

    NASA Astrophysics Data System (ADS)

    Sintonen, Sakari; Suihkonen, Sami; Jussila, Henri; Lipsanen, Harri; Tuomi, Turkka O.; Letts, Edward; Hoff, Sierra; Hashimoto, Tadao

    2014-11-01

    White beam synchrotron radiation X-ray topography (SR-XRT) and X-ray diffraction (XRD) measurements were used to non-destructively study the defect structure of a bulk GaN wafer, grown by the ammonothermal method. SR-XRT topographs revealed high crystal quality with threading dislocation density 8.8×104 cm-2 and granular structure consisting of large, slightly misaligned grains. The threading dislocations within grains were identified as mixed and screw type, while no pure threading edge dislocations were observed.

  16. 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.

  17. Structural analysis of infinite layer superlattices grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Del Vecchio, A.; Tapfer, L.; Aruta, C.; Balestrino, G.; Petrocelli, G.

    1996-07-01

    In this work we investigate the structural properties of SrCuO2/CaCuO2 infinite layer superlattices by high-resolution x-ray diffraction and x-ray specular reflectivity measurements. The infinite layer superlattices are grown by pulsed laser deposition on slightly misoriented (001) SrTiO3 substrates. We demonstrate that good quality superlattices with few monolayers thick constituent SrCuO2 and CaCuO2 layers can be grown having an interface roughness of less than 3-4 Å. A strain analysis of the epitaxial film shows that the SrCuO2 layers are completely relaxed with respect to the substrate. However, the CaCuO2 layers are elastically strained with respect to the SrCuO2 layer. The Poisson ratio of the CaCuO2 is estimated to be 0.40±0.08.

  18. 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

  19. 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.

  20. 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.

  1. Synthesis, crystal growth, structural, thermal, optical and mechanical properties of solution grown 4-methylpyridinium 4-hydroxybenzoate single crystal.

    PubMed

    Sudhahar, S; Krishna Kumar, M; Sornamurthy, B M; Mohan Kumar, R

    2014-01-24

    Organic nonlinear optical material, 4-methylpyridinium 4-hydroxybenzoate (4MPHB) was synthesized and single crystal was grown by slow evaporation solution growth method. Single crystal and powder X-ray diffraction analyses confirm the structure and crystalline perfection of 4MPHB crystal. Infrared, Raman and NMR spectroscopy techniques were used to elucidate the functional groups present in the compound. TG-DTA analysis was carried out in nitrogen atmosphere to study the decomposition stages, endothermic and exothermic reactions. UV-visible and Photoluminescence spectra were recorded for the grown crystal to estimate the transmittance and band gap energy respectively. Linear refractive index, birefringence, and SHG efficiency of the grown crystal were studied. Laser induced surface damage threshold and mechanical properties of grown crystal were studied to assess the suitability of the grown crystals for device applications. PMID:24184578

  2. MBE grown GaAsBi/GaAs multiple quantum well structures: Structural and optical characterization

    NASA Astrophysics Data System (ADS)

    Richards, Robert D.; Bastiman, Faebian; Roberts, John S.; Beanland, Richard; Walker, David; David, John P. R.

    2015-09-01

    A series of GaAsBi/GaAs multiple quantum well p-i-n diodes were grown by molecular beam epitaxy. Nomarski images showed evidence of sub-surface damage in each diode, with an increase in the cross-hatching associated with strain relaxation for the diodes containing more than 40 quantum wells. X-ray diffraction ω-2θ scans of the (004) reflections showed that multiple quantum well regions with clearly defined well periodicities were grown. The superlattice peaks of the diodes containing more than 40 wells were much broader than those of the other diodes. The photoluminescence spectra showed a redshift of 56 meV and an attenuation of nearly two orders of magnitude for the 54 and 63 well diodes. Calculations of the quantum confinement and strain induced band gap modifications suggest that the wells in all diodes are thinner than their intended widths and that both loss of quantum confinement and strain probably contributed to the observed redshift and attenuation in the 54 and 63 well diodes. Comparison of this data with that gathered for InGaAs/GaAs multiple quantum wells, suggests that the onset of relaxation occurs at a similar average strain-thickness product for both systems. Given the rapid band gap reduction of GaAsBi with Bi incorporation, this data suggests that GaAsBi is a promising photovoltaic material candidate.

  3. 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

  4. Structure and transport properties of the interface between CVD-grown graphene domains.

    PubMed

    Ogawa, Yui; Komatsu, Katsuyoshi; Kawahara, Kenji; Tsuji, Masaharu; Tsukagoshi, Kazuhito; Ago, Hiroki

    2014-07-01

    During the chemical vapor deposition (CVD) growth of graphene, graphene domains grown on a Cu surface merge together and form a uniform graphene sheet. For high-performance electronics and other applications, it is important to understand the interfacial structure of the merged domains, as well as their influence on the physical properties of graphene. We synthesized large hexagonal graphene domains with controlled orientations on a heteroepitaxial Cu film and studied the structure and properties of the interfaces between the domains mainly merged with the same angle. Although the merged domains have various interfaces with/without wrinkles and/or increased defect-related Raman D-band intensity, the intra-domain transport showed higher carrier mobility reaching 20,000 cm(2) V(-1) s(-1) on SiO2 at 280 K (the mean value was 7200 cm(2) V(-1) s(-1)) than that measured for inter-domain areas, 6400 cm(2) V(-1) s(-1) (mean value 2000 cm(2) V(-1) s(-1)). The temperature dependence of the mobility suggests that impurity scattering dominates at the interface even for the merged domains with the same orientation. This study highlights the importance of domain interfaces, especially on the carrier transport properties, in CVD-grown graphene. PMID:24847777

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

    PubMed

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

    2016-04-01

    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

  6. Structural and Magnetic Characterization of EuTe/SnTe Superlattices Grown by Molecular Beam Epitaxy

    SciTech Connect

    Diaz, B.; Abramof, E.; Rappl, P. H. O.; Granado, E.; Chitta, V. A.; Henriques, A. B.; Oliveira, N. F. Jr.

    2010-01-04

    Here we investigate the structural and magnetic properties of 24 repetitions EuTe/SnTe superlattices (SLs), with 3 monolayers (ML) EuTe films and SnTe thicknesses between 13 and 36 ML. The SLs were grown by molecular beam epitaxy on 3 {mu}m SnTe buffer layers, grown on top of (111)BaF{sub 2} substrates. High resolution x-ray diffraction measurements indicated that the SLs with thicker SnTe layers have higher structural quality. This is due to the SnTe growth mode on EuTe, which starts in islands and evolves to layer-by-layer. The magnetic diffraction peak observed for the higher quality SLs proved the existence of antiferromagnetic order within the individual EuTe layers. Decreasing the width of the non-magnetic SnTe layers resulted in rougher interfaces, and the fading of the magnetic peak signal. The magnetization versus applied field curves indicated that the magnetic moments of SLs with thinner SnTe layers were also harder to align along the field direction. We interpret our results considering the loss of Eu neighbors, related with the increasing roughness of the SL interfaces.

  7. Structural and optical characterization of MOCVD-grown ZnO thin films

    NASA Astrophysics Data System (ADS)

    Pagni, O.; James, G. R.; Leitch, A. W. R.

    2004-03-01

    We report on the characterization of ZnO thin films grown by metal organic chemical vapor deposition (MOCVD) using diethyl zinc (DEZ) and tert-butanol (TBOH) as precursors. Substrate temperature proved to be a crucial factor in the crystallization process, as it vastly impacted the structural properties of the samples studied. Highly c-axis oriented films with large grain size (52 nm), low tensile strain (0.6%), uniform substrate coverage and a columnar structure devoid of hexagonal needles were successfully deposited on n-Si (100) substrates. The temperature-dependent luminescence spectra recorded confirmed the excellent quality of the material obtained in this work. Our results so far set TBOH apart as an outstanding oxygen source for the MOCVD growth of ZnO.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Structural, optical and electrochromic properties of nickel oxide thin films grown from electrodeposited nickel sulphide

    NASA Astrophysics Data System (ADS)

    Uplane, M. M.; Mujawar, S. H.; Inamdar, A. I.; Shinde, P. S.; Sonavane, A. C.; Patil, P. S.

    2007-10-01

    Nickel oxide thin films were grown onto FTO-coated glass substrates by a two-step process: electrodeposition of nickel sulphide and their thermal oxidation at 425, 475 and 525 °C. The influence of thermal oxidation temperature on structural, optical, morphological and electrochromic properties was studied. The structural properties undoubtedly revealed NiO formation. The electrochromic properties were studied by means of cyclic voltammetry. The films exhibited anodic electrochromism, changing from a transparent state to a coloured state at +0.75 V versus SCE, i.e. by simultaneous ion and electron ejection. The transmittance in the coloured and bleached states was recorded to access electrochromic quality of the films. Colouration efficiency and electrochromic reversibility were found to be maximum (21 mC/cm 2 and 89%, respectively) for the films oxidized at 425 °C. The optical band gap energy of nickel oxide slightly varies with increase in annealing temperature.

  13. Structural characterization of nanostructures grown by Ni metal induced lateral crystallization of amorphous-Si

    NASA Astrophysics Data System (ADS)

    Radnóczi, G. Z.; Dodony, E.; Battistig, G.; Vouroutzis, N.; Kavouras, P.; Stoemenos, J.; Frangis, N.; Kovács, A.; Pécz, B.

    2016-02-01

    The nickel metal induced lateral crystallization of amorphous silicon is studied by transmission electron microscopy in the range of temperatures from 413 to 521 °C. The structural characteristics of the whiskers grown at 413 °C are compared to the grains grown at 600 °C, where both Metal Induced Lateral Crystallization (MILC) and Solid Phase Crystallization (SPC) are involved. At 413 °C, long whiskers are formed at any crystallographic direction almost free of defects. In contrary, whiskers grown by MILC around 600 °C are crystallized along the ⟨111⟩ directions. These differences are attributed to the low crystallization rate and suppression of the SPC process. The activation energy of the pure MILC was measured in the order of 2 eV. The effect of Ni on the crystallization rate is studied by in-situ heating experiments inside the microscope. The role of contamination that can inhibit MILC is discussed. The cases of MILC process under limited Ni and unlimited Ni source were studied and compared to in-situ annealing experiments. The crystallization rate is strongly influenced by the neighbouring Ni sources; this long-range interaction is attributed to the requirement of a critical Ni concentration in amorphous silicon before the initiation of the MILC process. The long-range interaction can enhance crystallization along a certain direction. The transition from MILC to SPC and the change of the crystallization mode due to the lack of Ni are discussed. The beneficial effect of long annealing at 413 °C is also discussed.

  14. CdTe-Cd1 - xMnxTe multiple quantum well structures grown by pulsed laser evaporation and epitaxy

    NASA Astrophysics Data System (ADS)

    Dubowski, J. J.; Roth, A. P.; Wasilewski, Z. R.; Rolfe, S. J.

    1991-09-01

    Structural and optical properties of (001) CdTe-Cd1-xMnxTe (x=0.10) multiple quantum well structures grown by pulsed laser evaporation and epitaxy (PLEE) are investigated. The layers are grown on (001) CdZnTe wafers held at a temperature in the range of 210-230 °C. Secondary-ion mass spectroscopy in-depth profiles reveal that highly uniform structures are grown. Numerical analysis of double crystal x-ray diffraction results demonstrates high structural quality of the layers and indicates partial relaxation of the strain in these structures. Low-temperature photoluminescence exhibits excitonic recombinations in the CdTe wells whereas photoluminescence from the Cd1-xMnxTe barriers is not observed. The chemical composition of the barriers deduced from photoluminescence is in excellent agreement with the intended chemical composition set during growth.

  15. Plant growth and soil microbial community structure of legumes and grasses grown in monoculture or mixture.

    PubMed

    Chen, Meimei; Chen, Baodong; Marschner, Petra

    2008-01-01

    A greenhouse pot experiment was conducted to investigate the influence of soil moisture content on plant growth and the rhizosphere microbial community structure of four plant species (white clover, alfalfa, sudan grass, tall fescue), grown individually or in a mixture. The soil moisture content was adjusted to 55% or 80% water holding capacity (WHC). The results indicated that the total plant biomass of one pot was lower at 55% WHC. At a given soil moisture, the total plant biomass of white clover and tall fescue in the mixture was lower than that in a monoculture, indicating their poor competitiveness. For leguminous plants, the decrease in soil moisture reduced the total microbial biomass, bacterial biomass, fungal biomass, and fungal/bacterial ratio in soil as assessed by the phospholipid fatty acid analysis, whereas, lower soil moisture increased those parameters in the tall fescue. The microbial biomass in the soil with legumes was higher than that in the soil with grasses and the two plant groups differed in soil microbial community composition. At high soil moisture content, microbial communities of the plant mixture were similar to those of the legume monoculture, and the existence of legumes in the mixture enhanced the bacterial and fungal biomass in the soil compared to the grasses grown in the monoculture, indicating that legumes played a dominant role in the soil microbial community changes in the plant mixture. PMID:19143348

  16. Photoluminescence, electrical and structural properties of ZnO films, grown by ALD at low temperature

    NASA Astrophysics Data System (ADS)

    Przeździecka, E.; Wachnicki, Ł.; Paszkowicz, W.; Łusakowska, E.; Krajewski, T.; Łuka, G.; Guziewicz, E.; Godlewski, M.

    2009-10-01

    We report the first results of the low-temperature photoluminescence study on polycrystal zinc oxide (ZnO) films obtained by atomic layer deposition at 100 °C, 130 °C and 200 °C. These ZnO films, when studied 'as-grown', show a strong excitonic emission even at room temperature. Low-temperature (T = 9 K) photoluminescence reveals lack of defect-related bands and a sharp photoluminescence peak at 3.36 eV with full width at half maximum of 6 meV which is comparable with the value reported for good quality bulk ZnO crystals. The energy position of the excitonic peak scales with temperature according to standard formulas and give the Debye temperature of 963 ± 26 K. We show that optical properties of low-temperature 'as-grown' ZnO films are correlated with structural and electrical ones and that optical study can be a valuable tool for evaluation of quality of ZnO films for novel electronic applications.

  17. Structure and transport properties of the interface between CVD-grown graphene domains

    NASA Astrophysics Data System (ADS)

    Ogawa, Yui; Komatsu, Katsuyoshi; Kawahara, Kenji; Tsuji, Masaharu; Tsukagoshi, Kazuhito; Ago, Hiroki

    2014-06-01

    During the chemical vapor deposition (CVD) growth of graphene, graphene domains grown on a Cu surface merge together and form a uniform graphene sheet. For high-performance electronics and other applications, it is important to understand the interfacial structure of the merged domains, as well as their influence on the physical properties of graphene. We synthesized large hexagonal graphene domains with controlled orientations on a heteroepitaxial Cu film and studied the structure and properties of the interfaces between the domains mainly merged with the same angle. Although the merged domains have various interfaces with/without wrinkles and/or increased defect-related Raman D-band intensity, the intra-domain transport showed higher carrier mobility reaching 20 000 cm2 V-1 s-1 on SiO2 at 280 K (the mean value was 7200 cm2 V-1 s-1) than that measured for inter-domain areas, 6400 cm2 V-1 s-1 (mean value 2000 cm2 V-1 s-1). The temperature dependence of the mobility suggests that impurity scattering dominates at the interface even for the merged domains with the same orientation. This study highlights the importance of domain interfaces, especially on the carrier transport properties, in CVD-grown graphene.During the chemical vapor deposition (CVD) growth of graphene, graphene domains grown on a Cu surface merge together and form a uniform graphene sheet. For high-performance electronics and other applications, it is important to understand the interfacial structure of the merged domains, as well as their influence on the physical properties of graphene. We synthesized large hexagonal graphene domains with controlled orientations on a heteroepitaxial Cu film and studied the structure and properties of the interfaces between the domains mainly merged with the same angle. Although the merged domains have various interfaces with/without wrinkles and/or increased defect-related Raman D-band intensity, the intra-domain transport showed higher carrier mobility reaching 20

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Structural evolution of platinum thin films grown by atomic layer deposition

    SciTech Connect

    Geyer, Scott M.; Methaapanon, Rungthiwa; Bent, Stacey; Johnson, Richard; Clemens, Bruce; Brennan, Sean; Toney, Mike F.

    2014-08-14

    The structural properties of Pt films grown by atomic layer deposition (ALD) are investigated with synchrotron based x-ray scattering and x-ray diffraction techniques. Using grazing incidence small angle scattering, we measure the lateral growth rate of the Pt islands to be 1.0 Å/cycle. High resolution x-ray diffraction reveals that the in-plane strain of the Pt lattice undergoes a transition from compressive strain to tensile strain when the individual islands coalescence into a continuous film. This transition to tensile strain is attributed to the lateral expansion that occurs when neighboring islands merge to reduce their surface energy. Using 2D grazing incidence x-ray diffraction, we show that the lattice orientation becomes more (111) oriented during deposition, with a sharp transition occurring during coalescence. Pt ALD performed at a lower deposition temperature (250 °C) is shown to result in significantly more randomly oriented grains.

  3. Raman spectroscopic investigation of polycrystalline structures of CVD-grown graphene by isotope labeling

    NASA Astrophysics Data System (ADS)

    Wang, Shengnan; Suzuki, Satoru; Hibino, Hiroki

    2014-10-01

    Topological defects, such as point defects, dislocations and grain boundaries, have a dramatic influence on the chemical and physical properties of large-scale graphene grown by chemical vapor deposition (CVD) method. Here we demonstrate the Raman visualization of polycrystalline structures in an isotopically modified CVD graphene. By means of the reversible reaction of methane on a copper catalyst, the etching of 12C-lattice and surface deposition of 13C-atoms occur in CVD graphene by sequentially introducing hydrogen and isotopic methane after standard growth of graphene with full monolayer coverage. Spatial Raman spectroscopic mapping on labeled graphene reveals pronounced network-like 13C-rich regions, which are further identified to exist along the grain boundaries of graphene by low-energy electron microscopy. The structural defects inside the graphene grains are also targeted in the isotope labeling process. Our work opens a new way to investigate multiple grain structures in CVD graphene with a simple spectroscopic technique.Topological defects, such as point defects, dislocations and grain boundaries, have a dramatic influence on the chemical and physical properties of large-scale graphene grown by chemical vapor deposition (CVD) method. Here we demonstrate the Raman visualization of polycrystalline structures in an isotopically modified CVD graphene. By means of the reversible reaction of methane on a copper catalyst, the etching of 12C-lattice and surface deposition of 13C-atoms occur in CVD graphene by sequentially introducing hydrogen and isotopic methane after standard growth of graphene with full monolayer coverage. Spatial Raman spectroscopic mapping on labeled graphene reveals pronounced network-like 13C-rich regions, which are further identified to exist along the grain boundaries of graphene by low-energy electron microscopy. The structural defects inside the graphene grains are also targeted in the isotope labeling process. Our work opens a new

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    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 6.42×10-5 A to 7.31×10-7 A after annealing. The value of series resistance (Rs) was extracted from Cheung method and the value of Rs 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.

  5. 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.

  6. 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.

  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. Influence of Subsurface Hydrogen on the Structural Properties of Graphene Templates Grown on Ru(0001)

    NASA Astrophysics Data System (ADS)

    Grady, Maxwell; Diaconescu, Bogdan; Valovcin, Darren; Hagelberg, Frank; Pohl, Karsten

    2014-03-01

    Graphene has aroused tremendous interest due to its remarkable electronic and mechanical properties. Graphene's optical properties and conductance make it an ideal candidate for use in nanoelectronic devices and organic photoelectric devices. We will present a STM/LEED/DFT study of the single layer graphene on Ru(0001) system grown via a novel growth mechanism that co-adsorbs atomic hydrogen and carbon vapor to the ruthenium surface while simultaneously segregating carbon from the crystal bulk to the surface. Structural studies show a wide array of moire superlattices sizes ranging from 0.9 to 3.0 nm. DFT calculations help explain the appearance of these graphene reconstructions driven by the H presence at the Ru interface. A LEED I(V) study guided by DFT calculations will accompany the STM investigation to provide insight into the graphene layer thickness. The structural polymorphism displayed by this system is of interest for the study of directed self-assembly. Control over moire superstructure size can aid in future work using graphene as a nanotemplate for self-assembled growth of nanoelectronic and organic photovoltaic devices based on pentacenes and fullerenes. Finally the impact of the structural changes on the electronic properties of the system will be studied. Supported by NSF NSEC-425826 and DMR-1006863.

  9. Raman spectroscopic investigation of polycrystalline structures of CVD-grown graphene by isotope labeling.

    PubMed

    Wang, Shengnan; Suzuki, Satoru; Hibino, Hiroki

    2014-11-21

    Topological defects, such as point defects, dislocations and grain boundaries, have a dramatic influence on the chemical and physical properties of large-scale graphene grown by chemical vapor deposition (CVD) method. Here we demonstrate the Raman visualization of polycrystalline structures in an isotopically modified CVD graphene. By means of the reversible reaction of methane on a copper catalyst, the etching of (12)C-lattice and surface deposition of (13)C-atoms occur in CVD graphene by sequentially introducing hydrogen and isotopic methane after standard growth of graphene with full monolayer coverage. Spatial Raman spectroscopic mapping on labeled graphene reveals pronounced network-like (13)C-rich regions, which are further identified to exist along the grain boundaries of graphene by low-energy electron microscopy. The structural defects inside the graphene grains are also targeted in the isotope labeling process. Our work opens a new way to investigate multiple grain structures in CVD graphene with a simple spectroscopic technique. PMID:25303722

  10. Effect of substrate growth temperatures on H diffusion in hydrogenated Si/Si homoepitaxial structures grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Shao, Lin; Lee, J. K.; Wang, Y. Q.; Nastasi, M.; Thompson, Phillip E.; David Theodore, N.; Alford, T. L.; Mayer, J. W.; Chen, Peng; Lau, S. S.

    2006-06-01

    We have investigated hydrogen diffusion in hydrogenated <100> Si/Si homoepitaxial structures, which were grown by molecular beam epitaxy at various temperatures. The substrate growth temperature can significantly affect the H diffusion behavior, with higher growth temperatures resulting in deeper H diffusion. For the Si/Si structure grown at the highest temperature of 800 °C, H trapping occurs at the epitaxial Si/Si substrate interface, which results in the formation of (100) oriented microcracks at the interface. The mechanism of H trapping and the potential application of these findings for the development of a method of transferring ultrathin Si layers are discussed.

  11. Structure and collapse of a surface-grown strong polyelectrolyte brush on sapphire.

    PubMed

    Dunlop, Iain E; Thomas, Robert K; Titmus, Simon; Osborne, Victoria; Edmondson, Steve; Huck, Wilhelm T S; Klein, Jacob

    2012-02-14

    We have used neutron reflectometry to investigate the behavior of a strong polyelectrolyte brush on a sapphire substrate, grown by atom-transfer radical polymerization (ATRP) from a silane-anchored initiator layer. The initiator layer was deposited from vapor, following treatment of the substrate with an Ar/H(2)O plasma to improve surface reactivity. The deposition process was characterized using X-ray reflectometry, indicating the formation of a complete, cross-linked layer. The brush was grown from the monomer [2-(methacryloyloxy)ethyl]trimethylammonium chloride (METAC), which carries a strong positive charge. The neutron reflectivity profile of the swollen brush in pure water (D(2)O) showed that it adopted a two-region structure, consisting of a dense surface region ∼100 Å thick, in combination with a diffuse brush region extending to around 1000 Å from the surface. The existence of the diffuse brush region may be attributed to electrostatic repulsion from the positively charged surface region, while the surface region itself most probably forms due to polyelectrolyte adsorption to the hydrophobic initiator layer. The importance of electrostatic interactions in maintaining the brush region is confirmed by measurements at high (1 M) added 1:1 electrolyte, which show a substantial transfer of polymer from the brush to the surface region, together with a strong reduction in brush height. On addition of 10(-4) M oppositely charged surfactant (sodium dodecyl sulfate), the brush undergoes a dramatic collapse, forming a single dense layer about 200 Å in thickness, which may be attributed to the neutralization of the monomers by adsorbed dodecyl sulfate ions in combination with hydrophobic interactions between these dodecyl chains. Subsequent increases in surfactant concentration result in slow increases in brush height, which may be caused by stiffening of the polyelectrolyte chains due to further dodecyl sulfate adsorption. PMID:22292571

  12. 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.

  13. 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. PMID:25857977

  14. 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.

  15. 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.

  16. 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. PMID:19348427

  17. Ultrafast structural dynamics of LaVO3 thin films grown by hybrid molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Brahlek, Matthew; Lapano, Jason; Stoica, Vladimir; Zhang, Lei; Zhang, Hai-Tian; Akamatsu, Hirofumi; Eaton, Craig; Gopalan, Venkatraman; Freeland, John; Wen, Haidan; Engel-Herbert, Roman

    LaVO3, with a partially full d-shell is expected to be metallic, but due to electron-electron interactions a gap emerges and the ground state is a Mott insulator. Such effects are a strong function of the bonding geometry, and particularly the V-O-V bond angle. Controlling these structural effects on the ultrafast time scale can lead to control over the underlying electronic ground state. Here we report the ultrafast structural dynamics of 25 and 50 nm thick LaVO3 thin films grown by the hybrid molecular beam epitaxy technique on SrTiO3 when excited across the bandgap by 800 nm light. Using time-resolved x-ray diffraction on the 100 ps time scale at Sector 7 of the Advanced Photon Source, we directly measured the structural changes with atomic accuracy by monitoring integer Bragg diffraction peaks and find a large out-of-plane strain of 0.18% upon optical excitation; the recovery time is ~1 ns for the 25 nm film and ~2 ns for the 50 nm film, consistent with the thermal transport from the film to the substrate. Further, we will discuss the response of the oxygen octahedral rotation patterns indicated by changes of the half-order diffraction peaks. Understanding such ultrafast structural deformation is important for optimizing optical excitations to create new metastable phases starting from a Mott insulator. This work was supported by the Department of Energy under Grant DE-SC0012375, and DE-AC02-06CH11357.

  18. Structural and optical properties of dilute InAsN grown by molecular beam epitaxy

    SciTech Connect

    Ibanez, J.; Oliva, R.; De la Mare, M.; Zhuang, Q.; Godenir, A.; Krier, A.; Schmidbauer, M.; Hernandez, S.; Pellegrino, P.; Scurr, D. J.; Cusco, R.; Artus, L.; Shafi, M.; Mari, R. H.; Henini, M.

    2010-11-15

    We perform a structural and optical characterization of InAs{sub 1-x}N{sub x} epilayers grown by molecular beam epitaxy on InAs substrates (x < or approx. 2.2%). High-resolution x-ray diffraction (HRXRD) is used to obtain information about the crystal quality and the strain state of the samples and to determine the N content of the films. The composition of two of the samples investigated is also obtained with time-of-flight secondary ion mass spectroscopy (ToF-SIMS) measurements. The combined analysis of the HRXRD and ToF-SIMS data suggests that the lattice parameter of InAsN might significantly deviate from Vegard's law. Raman scattering and far-infrared reflectivity measurements have been carried out to investigate the incorporation of N into the InAsN alloy. N-related local vibrational modes are detected in the samples with higher N content. The origin of the observed features is discussed. We study the compositional dependence of the room-temperature band gap energy of the InAsN alloy. For this purpose, photoluminescence and optical absorption measurements are presented. The results are analyzed in terms of the band-anticrossing (BAC) model. We find that the room-temperature coupling parameter for InAsN within the BAC model is C{sub NM}=2.0{+-}0.1 eV.

  19. Structural and optical properties of dilute InAsN grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Ibáñez, J.; Oliva, R.; De la Mare, M.; Schmidbauer, M.; Hernández, S.; Pellegrino, P.; Scurr, D. J.; Cuscó, R.; Artús, L.; Shafi, M.; Mari, R. H.; Henini, M.; Zhuang, Q.; Godenir, A.; Krier, A.

    2010-11-01

    We perform a structural and optical characterization of InAs1-xNx epilayers grown by molecular beam epitaxy on InAs substrates (x ≲2.2%). High-resolution x-ray diffraction (HRXRD) is used to obtain information about the crystal quality and the strain state of the samples and to determine the N content of the films. The composition of two of the samples investigated is also obtained with time-of-flight secondary ion mass spectroscopy (ToF-SIMS) measurements. The combined analysis of the HRXRD and ToF-SIMS data suggests that the lattice parameter of InAsN might significantly deviate from Vegard's law. Raman scattering and far-infrared reflectivity measurements have been carried out to investigate the incorporation of N into the InAsN alloy. N-related local vibrational modes are detected in the samples with higher N content. The origin of the observed features is discussed. We study the compositional dependence of the room-temperature band gap energy of the InAsN alloy. For this purpose, photoluminescence and optical absorption measurements are presented. The results are analyzed in terms of the band-anticrossing (BAC) model. We find that the room-temperature coupling parameter for InAsN within the BAC model is CNM=2.0±0.1 eV.

  20. 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.

  1. Effects of Complex Structured Anodic Oxide Dielectric Layer Grown in Pore Matrix for Aluminum Capacitor.

    PubMed

    Shin, Jin-Ha; Yun, Sook Young; Lee, Chang Hyoung; Park, Hwa-Sun; Suh, Su-Jeong

    2015-11-01

    Anodization of aluminum is generally divided up into two types of anodic aluminum oxide structures depending on electrolyte type. In this study, an anodization process was carried out in two steps to obtain high dielectric strength and break down voltage. In the first step, evaporated high purity Al on Si wafer was anodized in oxalic acidic aqueous solution at various times at a constant temperature of 5 degrees C. In the second step, citric acidic aqueous solution was used to obtain a thickly grown sub-barrier layer. During the second anodization process, the anodizing potential of various ranges was applied at room temperature. An increased thickness of the sub-barrier layer in the porous matrix was obtained according to the increment of the applied anodizing potential. The microstructures and the growth of the sub-barrier layer were then observed with an increasing anodizing potential of 40 to 300 V by using a scanning electron microscope (SEM). An impedance analyzer was used to observe the change of electrical properties, including the capacitance, dissipation factor, impedance, and equivalent series resistance (ESR) depending on the thickness increase of the sub-barrier layer. In addition, the breakdown voltage was measured. The results revealed that dielectric strength was improved with the increase of sub-barrier layer thickness. PMID:26726615

  2. 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.

  3. 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.

  4. 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. PMID:23987395

  5. Structure, morphologies and dye removal efficiency of ZnO nanorods grown on polycrystalline Zn substrate

    NASA Astrophysics Data System (ADS)

    Yin, Tiantian; Chen, Nan; Zhang, Yingying; Cai, Xiaoyan; Wang, Yude

    2014-10-01

    Rod-like ZnO with the different morphologies were grown on polycrystalline Zn substrate by a simple hydrothermal process in a NaOH or NH4OH solution at the hydrothermal temperature range from 80 to 150 °C for different reaction time. Variations preparation in the different alkali solution concentration, hydrothermal temperature, and reaction times were explored to shed light on the morphology of the rod-like nanostructures. The thorough structural characterization including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron diffraction, and X-ray photoelectron spectrum (XPS) were employed to examine the morphology and the microstructure of the final products. It was found that alkali solution concentration, hydrothermal temperature and time have important influence on the morphology of the rod-like nanostructures. The dye removal efficiency of ZnO nanorods was explored by the decoloration of azo dye Congo red (CR). In order to obtain the optimum removal conditions of Congo red, the performance of removing CR with various initial concentrations by ZnO nanorods on Zn substrates with different morphologies was tested under various ambient conditions (visible light illumination and darkness). All prepared samples showed an excellent dye removal efficiency for organic pollutants CR from wastewater, making them promising candidates for the wastewater treatment.

  6. 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.

  7. 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.

  8. Structural and Magnetic Phase Transitions in Manganese Arsenide Thin-Films Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Jaeckel, Felix Till

    Phase transitions play an important role in many fields of physics and engineering, and their study in bulk materials has a long tradition. Many of the experimental techniques involve measurements of thermodynamically extensive parameters. With the increasing technological importance of thin-film technology there is a pressing need to find new ways to study phase transitions at smaller length-scales, where the traditional methods are insufficient. In this regard, the phase transitions observed in thin-films of MnAs present interesting challenges. As a ferromagnetic material that can be grown epitaxially on a variety of technologically important substrates, MnAs is an interesting material for spintronics applications. In the bulk, the first order transition from the low temperature ferromagnetic alpha-phase to the beta-phase occurs at 313 K. The magnetic state of the beta-phase has remained controversial. A second order transition to the paramagnetic gamma-phase takes place at 398 K. In thin-films, the anisotropic strain imposed by the substrate leads to the interesting phenomenon of coexistence of alpha- and beta-phases in a regular array of stripes over an extended temperature range. In this dissertation these phase transitions are studied in films grown by molecular beam epitaxy on GaAs (001). The films are confirmed to be of high structural quality and almost purely in the A0 orientation. A diverse set of experimental techniques, germane to thin-film technology, is used to probe the properties of the film: Temperature-dependent X-ray diffraction and atomic-force microscopy (AFM), as well as magnetotransport give insights into the structural properties, while the anomalous Hall effect is used as a probe of magnetization during the phase transition. In addition, reflectance difference spectroscopy (RDS) is used as a sensitive probe of electronic structure. Inductively coupled plasma etching with BCl3 is demonstrated to be effective for patterning MnAs. We show

  9. 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.

  10. Structural and magnetic properties of epitaxial CrO2 thin films grown on TiO2 (001) substrates

    NASA Astrophysics Data System (ADS)

    Zhang, Xueyu; Zhong, Xing; Visscher, P. B.; LeClair, Patrick R.; Gupta, Arunava

    2013-04-01

    The structural and magnetic properties of epitaxial CrO2 thin films grown on (001)-oriented TiO2 substrates by atmospheric pressure chemical vapor deposition are investigated. Due to the competition between demagnetization and a relatively weak perpendicular magnetocrystalline anisotropy, the deposited CrO2 (001) films exhibit magnetic properties that are significantly different from CrO2 (100) and CrO2 (110) films grown on TiO2 substrates. Based on the thickness dependence of M-H curves, a surface anisotropy is confirmed to exist, likely originating from strain in the film. The out-of-plane hysteresis curves can be well described by a distribution of effective anisotropy that may be due to a varying local demagnetizing field and a distribution of strain across the film. For the in-plane magnetization, the hysteresis curves are consistent with stripe or vortex domain structures of an almost closed flux configuration at remanence.

  11. Mosaic Structure Evolution in GaN Films with Annealing Time Grown by Metalorganic Chemical Vapour Deposition

    NASA Astrophysics Data System (ADS)

    Chen, Zhi-Tao; Xu, Ke; Guo, Li-Ping; Yang, Zhi-Jian; Pan, Yao-Bo; Su, Yue-Yong; Zhang, Han; Shen, Bo; Zhang, Guo-Yi

    2006-05-01

    We investigate mosaic structure evolution of GaN films annealed for a long time at 800°C grown on sapphire substrates by metalorganic chemical vapour deposition by high-resolution x-ray diffraction. The result show that residual stress in GaN films is relaxed by generating edge-type threading dislocations (TDs) instead of screw-type TDs. Compared to as-grown GaN films, the annealed ones have larger mean twist angles corresponding to higher density of edge-type TDs but smaller mean tilt angles corresponding to lower density of screw-type TDs films. Due to the increased edge-type TD density, the lateral coherence lengths of the annealed GaN films also decrease. The results obtained from chemical etching experiment and grazing-incidence x-ray diffraction (GIXRD) also support the proposed structure evolution.

  12. Fe films grown on GaAs(110) in a two-step process: Improved structural and magnetic properties

    SciTech Connect

    Winking, L.; Wenderoth, M.; Homoth, J.; Siewers, S.; Ulbrich, R. G.

    2008-05-12

    Fe films of up to 10 ML thickness were grown on cleaved GaAs(110) in a two-step process that associates low-temperature deposition at 130 K with a subsequent annealing to room temperature. Low-energy electron diffraction, scanning tunneling microscopy, and in situ magneto-optical Kerr effect were combined to study these films. The observed magnetic and structural properties are distinctly different from the characteristics of conventionally grown Fe films on GaAs. We found no indication of interface compound formation. The applied two-step growth process is a promising technique to further increase spin-injection and detection efficiencies of Fe/GaAs hybrid structures.

  13. 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.

  14. Structural and optical characterization of Mg-doped GaAs nanowires grown on GaAs and Si substrates

    SciTech Connect

    Falcão, B. P. Leitão, J. P.; Correia, M. R.; Soares, M. R.; Morales, F. M.; Mánuel, J. M.; Garcia, R.; Gustafsson, A.; Moreira, M. V. B.; Oliveira, A. G. de; González, J. C.

    2013-11-14

    We report an investigation on the morphological, structural, and optical properties of large size wurtzite GaAs nanowires, low doped with Mg, grown on GaAs(111)B and Si(111) substrates. A higher density of vertical nanowires was observed when grown upon GaAs(111)B. Very thin zinc-blende segments are observed along the axis of the nanowires with a slightly higher linear density being found on the nanowires grown on Si(111). Low temperature cathodoluminescence and photoluminescence measurements reveal an emission in the range 1.40–1.52 eV related with the spatial localization of the charge carriers at the interfaces of the two crystalline phases. Mg related emission is evidenced by cathodoluminescence performed on the GaAs epilayer. However, no direct evidence for a Mg related emission is found for the nanowires. The excitation power dependency on both peak energy and intensity of the photoluminescence gives a clear evidence for the type II nature of the radiative transitions. From the temperature dependence on the photoluminescence intensity, non-radiative de-excitation channels with different activation energies were found. The fact that the estimated energies for the escape of the electron are higher in the nanowires grown on Si(111) suggests the presence of wider zinc-blende segments.

  15. Surface structure analysis of BaSi2(100) epitaxial film grown on Si(111) using CAICISS

    NASA Astrophysics Data System (ADS)

    Okasaka, Shouta; Kubo, Osamu; Tamba, Daiki; Ohashi, Tomohiro; Tabata, Hiroshi; Katayama, Mitsuhiro

    2015-05-01

    Geometry and surface structure of a BaSi2(100) film on Si(111) formed by reactive deposition epitaxy (RDE) have been investigated using coaxial impact-collision ion scattering spectroscopy and atomic force microscopy. BaSi2(100) film can be grown only when the Ba deposition rate is sufficiently fast. It is revealed that a BaSi2(100) film grown at 600 °C has better crystallinity than a film grown at 750 °C owing to the mixture of planes other than (100) in the RDE process at higher temperatures. The azimuth angle dependence of the scattering intensity from Ba shows sixfold symmetry, indicating that the minimum height of surface steps on BaSi2(100) is half of the length of unit cell. By comparing the simulated azimuth angle dependences for more than ten surface models with experimental one, it is strongly indicated that the surface of a BaSi2(100) film grown on Si(111) is terminated by Si tetrahedra.

  16. 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.

  17. Led InGaN/GaN Structures with Short-Period Superlattice Grown on Flat and Patterned Sapphire Substrates

    NASA Astrophysics Data System (ADS)

    Romanov, I. S.; Prudaev, I. A.; Brudnyi, V. N.; Kop'ev, V. V.; Novikov, Vad. A.; Marmalyuk, A. A.; Kureshov, V. A.; Sabitov, D. R.; Mazalov, A. V.

    2015-03-01

    The results of studies of blue LED InGaN/GaN heterostructures with a short-period InGaN/GaN superlattice in front of an active region of the structure grown on flat and patterned Al2O3 substrates are presented. In these structures, an increase of the internal quantum efficiency is observed. The high-resolution X-ray diffraction spectra and the integrated PL intensity are measured for two temperatures - 10 and 300 K - at different levels of optical YAG-laser pumping.

  18. Structural transitions in different monolayers of cobalt phthalocyanine film grown on Bi(1 1 1)

    NASA Astrophysics Data System (ADS)

    Tao, Min-Long; Tu, Yu-Bing; Sun, Kai; Zhang, Yao; Zhang, Xin; Li, Zhao-Bing; Hao, Shao-Jie; Xiao, Hua-Fang; Ye, Juan; Wang, Jun-Zhong

    2016-01-01

    The structural evolution of cobalt phthalocyanine (CoPc) thin films grown on a Bi(1 1 1) surface from the sub-monolayer to the third layer has been investigated with low-temperature scanning tunneling microscopy (STM). Two crucial transitions have been identified during the film epitaxial growth: one is the structural transition from zigzag chains to linear dimerized chains in the monolayer regime; the other is the molecular orientational transition from a flat-lying to a standing-up configuration in the multilayer regime. These results are helpful in understanding the growth mechanism of transition-metal phthalocyanine films on semi-metallic surfaces.

  19. 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.

  20. Analysis of HgTe/CdTe MOCVD grown superlattice epitaxial structures on GaAs by ion beam techniques

    NASA Astrophysics Data System (ADS)

    Wielunski, L. S.; Kenny, M. J.; Pain, G. N.

    1992-02-01

    Heteroepitaxial MOCVD grown HgTe/CdTe superlattice structures have been examined by Rutherford backscattering spectrometry (RBS) to monitor Hg, Cd and Te concentrations as a function of depth. Individual sublayers thicknesses have been measured at the same time. Crystal quality has been assessed using ion channeling. In addition the nuclear reaction 12C(d,p) 13C was used to detect carbon impurities and proton induced X-ray emision (PIXE) analysis used to detect In and Sb introduced during growth. The results show that the as-grown HgTe/CdTe superlattice has good crystal quality and reasonable lateral uniformity. Mercury concentration is difficult to control during growth and variation between sub-layers is observed. Hg-Cd interdiffusion is observed in heat treated samples. Carbon concentration varies; in a good quality samples ⩽ 20 ppm is present.

  1. Differences and similarities between structural properties of GaN grown by different growth methods

    SciTech Connect

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

    2002-08-01

    In this paper defects formed in GaN grown by different methods are reviewed. The crystal growth direction and growth rate play important roles. For bulk crystals grown under high pressure the highest growth rates are for planes perpendicular to the c-axis. Only planar defects formed on c-planes are observed in these crystals. There are no threading dislocations or nanotubes in the c-direction. However, polarity of the growth direction plays a role in the surface roughness and the distribution of planar defects. For growth of homo-epitaxial and hetero-epitaxial layers the growth is forced to take place in the much slower c-direction. As a result defects related to the purity of constituents used for growth are formed such as nanotubes and pinholes. In addition threading dislocations and dislocations that accommodate lattice and thermal expansion mismatch are formed.

  2. 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.

  3. Structural transformations in low-temperature grown GaAs:Sb

    NASA Astrophysics Data System (ADS)

    Vasyukov, D. A.; Baidakova, M. V.; Chaldyshev, V. V.; Suvorova, A. A.; Preobrazhenskii, V. V.; Putyato, M. A.; Semyagin, B. R.

    2001-05-01

    Sb-doped and Sb-free GaAs films were grown by molecular beam epitaxy (MBE) at low temperature (LT) and were annealed in the MBE set-up at various temperatures within the range of 500-900 °C. The concentrations of arsenic antisites in as-grown samples obtained using near-infra-red optical absorption were found to be as high as 6×1019 and 7×1019 cm-3 in Sb-doped and Sb-free samples, respectively. Samples were studied by high-resolution x-ray diffractometry (HRXRD) and transmission electron microscopy (TEM). Despite the high concentration of intrinsic point defects, x-ray rocking curves demonstrated perfect crystalline quality in as-grown samples. After annealing at temperatures of 500-700 °C, the lattice mismatch decreased in both Sb-doped and Sb-free samples, but in Sb-doped samples the reduction was much higher than would be expected for the antisite defect concentration determined from optical measurements. The segregation of isovalent Sb impurity into the As clusters was suggested. Upon annealing at temperatures higher than 700 °C, Sb-doped samples manifested a strong broadening of the diffraction maximum related to the LT GaAs:Sb layer. The TEM and HRXRD studies revealed that high-temperature annealing resulted in formation of dislocation loops attached to the large As clusters.

  4. Electrical and structural characterization of as-grown and annealed hydrothermal bulk ZnO

    SciTech Connect

    Kassier, G. H.; Hayes, M.; Auret, F. D.; Mamor, M.; Bouziane, K.

    2007-07-01

    Hall effect measurements in the range 20-370 K on as-grown and annealed hydrothermal bulk ZnO have been performed. The bulk conductivity in the highly resistive as-grown sample was found to decrease and then increase after annealing at 550 deg. C and 930 deg. C, respectively. The conduction in the as-grown material is attributed to a deep donor which is replaced by a much shallower donor after annealing at 930 deg. C. Annealing at both temperatures also produced strong surface conduction effects. Nondegenerate low-mobility surface conduction dominated the electrical properties of the sample annealed at 550 deg. C, while a degenerate surface channel was formed after annealing at 930 deg. C. In addition, Rutherford backscattering and channeling spectrometry (RBS/C) was used to assess the effect of annealing on the crystalline quality of the samples. RBS/C measurements reveal that annealing at 930 deg. C leads to significant improvement of the crystalline quality of the material, while annealing at 550 deg. C results in the segregation of a nonchanneling impurity at the surface.

  5. Enhancement of minority carrier lifetime of GaInP with lateral composition modulation structure grown by molecular beam epitaxy

    SciTech Connect

    Park, K. W.; Ravindran, Sooraj; Kang, S. J.; Hwang, H. Y.; Jho, Y. D.; Park, C. Y.; Jo, Y. R.; Kim, B. J.; Lee, Y. T.

    2014-07-28

    We report the enhancement of the minority carrier lifetime of GaInP with a lateral composition modulated (LCM) structure grown using molecular beam epitaxy (MBE). The structural and optical properties of the grown samples are studied by transmission electron microscopy and photoluminescence, which reveal the formation of vertically aligned bright and dark slabs corresponding to Ga-rich and In-rich GaInP regions, respectively, with good crystal quality. With the decrease of V/III ratio during LCM GaInP growth, it is seen that the band gap of LCM GaInP is reduced, while the PL intensity remains high and is comparable to that of bulk GaInP. We also investigate the minority carrier lifetime of LCM structures made with different flux ratios. It is found that the minority carrier lifetime of LCM GaInP is ∼37 times larger than that of bulk GaInP material, due to the spatial separation of electrons and holes by In-rich and Ga-rich regions of the LCM GaInP, respectively. We further demonstrate that the minority carrier lifetime of the grown LCM GaInP structures can easily be tuned by simply adjusting the V/III flux ratio during MBE growth, providing a simple yet powerful technique to tailor the electrical and optical properties at will. The exceptionally high carrier lifetime and the reduced band gap of LCM GaInP make them a highly attractive candidate for forming the top cell of multi-junction solar cells and can enhance their efficiency, and also make them suitable for other optoelectronics devices, such as photodetectors, where longer carrier lifetime is beneficial.

  6. 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.

  7. 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.

  8. Laser MBE-grown yttrium iron garnet films on GaN: characterization of the crystal structure and magnetic properties

    NASA Astrophysics Data System (ADS)

    Kaveev, A. K.; Bursian, V. E.; Gastev, S. V.; Krichevtsov, B. B.; Suturin, S. M.; Volkov, M. P.; Sokolov, N. S.

    2016-07-01

    Yttrium iron garnet (YIG) films were grown on GaN substrates using the laser molecular beam epitaxy method. X-ray diffraction data showed polycrystalline YIG layers without additional structural modifications. The magnetic properties of the YIG films were studied at room temperature with the aid of a vibration sample magnetometer, the magneto-optical Kerr effect and ferromagnetic resonance methods. ‘Easy-plane’-type magnetic anisotropy was found in the films. The gyromagnetic ratio and 4 πMS value were calculated.

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

    SciTech Connect

    Roberts, J.G.

    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.

  10. Large anomalous Hall resistance of pair {delta}-doped GaAs structures grown by molecular-beam epitaxy

    SciTech Connect

    Jung, D. W.; Noh, J. P.; Touhidul Islam, A. Z. M.; Otsuka, N.

    2008-02-15

    Beryllium/silicon pair {delta}-doped GaAs structures grown by molecular-beam epitaxy exhibit a Hall resistance which has a nonlinear dependence on the applied magnetic field and which is strongly correlated to the negative magnetoresistance observed under the applied magnetic field parallel to the {delta}-doped layers. Dependence of the occurrence of the nonlinear Hall resistance on the growth condition is investigated. A significantly large increase in both the magnitude and the nonlinearity of the Hall resistance is observed from samples whose GaAs buffer layers are grown under the condition of a low As/Ga flux ratio. Reflection high energy electron diffraction and electron microscope observations show that a faceted surface develops with the growth and postgrowth annealing of a GaAs buffer layer under the condition of a low As flux. From samples which have only Si {delta}-doped layers and exhibit the n-type conduction, such nonlinear Hall resistance is not observed. The nonlinearity of the Hall resistance of Be/Si pair {delta}-doped structures depends on the single parameter B/T, where B and T are the applied magnetic field and the temperature, respectively. Based on these results, it is suggested that the nonlinear Hall resistance of Be/Si pair {delta}-doped structures is the anomalous Hall effect caused by localized spins in {delta}-doped layers.

  11. 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.

  12. Structural and electronic characterization of graphene grown by chemical vapor deposition and transferred onto sapphire

    NASA Astrophysics Data System (ADS)

    Joucken, Frédéric; Colomer, Jean-François; Sporken, Robert; Reckinger, Nicolas

    2016-08-01

    We present a combination of magnetotransport and local probe measurements on graphene grown by chemical vapor deposition on copper foil and subsequently transferred onto a sapphire substrate. A rather strong p-doping is observed (∼9 × 1012 cm-2) together with quite low carrier mobility (∼1350 cm2/V s). Atomic force and tunneling imaging performed on the transport devices reveals the presence of contaminants between sapphire and graphene, explaining the limited performance of our devices. The transferred graphene displays ridges similar to those observed whilst graphene is still on the copper foil. We show that, on sapphire, these ridges are made of different thicknesses of the contamination layer and that, contrary to what was reported for hBN or certain transition metal dichalcogenides, no self-cleansing process of the sapphire substrate is observed.

  13. 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

  14. Concentration and structure inhomogeneities in GaSb(Si) single crystals grown at different heat and mass transfer conditions

    NASA Astrophysics Data System (ADS)

    Serebryakov, Yu. A.; Prokhorov, I. A.; Vlasov, V. N.; Korobeynikova, E. N.; Zakharov, B. G.; Shul'pina, I. L.; Marchenko, M. P.; Fryazinov, I. V.

    2007-06-01

    Results of ground-based experiments on crystallization of gallium antimonide on the POLIZON facility carried out within the framework of space experiment preparation aboard FOTON satellite are submitted. Technical and technological opportunities of suppression of disturbing factors for improvement of quality of grown crystals in space are substantiated. Features of formation of concentration and structure inhomogeneities in GaSb:Si crystals grown under non-stationary and stationary convection conditions are investigated. Experimental data about structure and dopant distribution inhomogeneities are discussed taking into account results of numerical researches of GaSb:Si crystallization. Also earlier received results of modeling of GaSb:Te crystallization under close temperature conditions are used. Correlation between computational and experimental data is shown. The data on intensity of flows close to crystallization front are received at which non-stationary or stationary conditions of crystallization are realized. The forecast for space conditions is made. The influence of a rotating magnetic field on convection in melt for application in space experiment projected is investigated.

  15. 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.

  16. Effects of thermally-induced changes of Cu grains on domain structure and electrical performance of CVD-grown graphene

    NASA Astrophysics Data System (ADS)

    Wu, Yaping; Hao, Yufeng; Fu, Mingming; Jiang, Wei; Wu, Qingzhi; Thrower, Peter A.; Piner, Richard D.; Ke, Congming; Wu, Zhiming; Kang, Junyong; Ruoff, Rodney S.

    2015-12-01

    During the chemical vapor deposition (CVD) growth of graphene on Cu foils, evaporation of Cu and changes in the dimensions of Cu grains in directions both parallel and perpendicular to the foils are induced by thermal effects. Such changes in the Cu foil could subsequently change the shape and distribution of individual graphene domains grown on the foil surface, and thus influence the domain structure and electrical properties of the resulting graphene films. Here, a slower cooling rate is used after the CVD process, and the graphene films are found to have an improved electrical performance, which is considered to be associated with the Cu surface evaporation and grain structure changes in the Cu substrate.

  17. 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.

  18. 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.

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

    NASA Astrophysics Data System (ADS)

    Das, Jayanta; Menon, Krishnakumar S. R.

    2015-06-01

    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.

  20. 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.

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

    DOE PAGESBeta

    Liu, Zheng; Amani, Matin; Najmaei, Sina; Xu, Quan; Zou, Xiaolong; Zhou, Wu; Yu, Ting; Qiu, Caiyu; Birdwell, A. Glen; Crowne, Frank J.; et al

    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

  2. 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. PMID:21942189

  3. Structural and magnetic characterization of Sm-doped GaN grown by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Dehara, Kentaro; Miyazaki, Yuta; Hasegawa, Shigehiko

    2016-05-01

    We have investigated structural, optical and magnetic properties of Sm-doped GaN thin films grown by plasma-assisted molecular beam epitaxy. Reflection high-energy electron diffraction and X-ray diffraction reveal that Ga1- x Sm x N films with a SmN mole fraction of ˜8% or below are grown on GaN templates without segregation of any secondary phases. With increasing SmN mole fraction, the c-axis lattice parameter of the GaSmN films linearly increases. GaSmN films with low Sm concentrations exhibit inner-4f transitions of Sm3+ in photoluminescence spectra. The present findings show that Sm atoms are substituted for some Ga atoms as trivalent ions (Sm3+). The Ga1- x Sm x N films display hysteresis loops in magnetization versus external magnetic field (M-H) curves even at 300 K. We will discuss the origin of these features together with the corresponding temperature dependences of magnetization.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    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 ZnOnanorods. 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.

  5. Structure of Stoichiometric and Oxygen-Rich Ultrathin FeO(111) Films Grown on Pd(111)

    SciTech Connect

    Zeuthen, Helene; Kudernatsch, Wilhelmine; Peng, Guowen; Merte, Lindsay R.; Ono, Luis K.; Lammich, Lutz; Bai, Yunhai; Grabow, Lars C.; Mavrikakis, Manos; Wendt, Stefan; Besenbacher, Flemming

    2013-07-25

    Monolayer thin FeO(111) films were grown on Pd(111) and oxidized by atomic oxygen (O). The stoichiometric and oxidized films were studied in detail by scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. Compared to the previously studied FeO(111)/Pt(111) system, small structural differences were observed for stoichiometric FeO monolayer films. Upon O exposure, the stoichiometric FeO film reconstructs, leading to the formation of new O-rich structures incorporating increasing amounts of additional O atoms. At low O exposures, the STM images exhibit bright features of regularly sized triangular structures assigned to O-adatom dislocation loops. A model of this O-rich structure composed of four-fold O-coordinated Fe atoms is proposed and confirmed by DFT calculations. Furthermore, these O dislocation loops induce the inversion of the FeO film and enclose portions of the film in which the order of the high-symmetry domains is inverted. For higher O exposures, the formation of FeO2–x islands coexisting with O-adatom dislocations and stoichiometric FeO patches was observed. Finally, these FeO2–x islands are reminiscent of the O-rich structures previously reported for FeO supported on Pt(111) and are catalytically active toward CO oxidation.

  6. Structural Properties and Electrochemical Performance of ZnO Nanosheets Grown Directly on Al substrate by Chemical Bath Deposition Techniques

    NASA Astrophysics Data System (ADS)

    Al-Asadi, Ahmed; Ferrera, Roberto; Henley, Luke; Lopez, Nestor; Carozo, Victor; Lin, Zhong; Terrones, Mauricio; Talapatra, Saikat

    We will report on the synthesis & electrochemical characterization of 2-dimentional zinc oxide grown directly on Al substrate by a simple chemical bath deposition method at low temperature (below 1000C). Detail structural characterizations of the synthesized ZnO sheets will be presented and discussed. The electrochemical performances of electrochemical double layer capacitors (EDLC) on electrodes fabricated using these materials were evaluated using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy using various electrolytes. We found that high specific capacitance values (greater than 300 F/g) could be achieved using an aqueous electrolyte. The aforementioned results indicates the possibly for using 2-D ZnO architectures fabricated by this simple and cost efficient technique for future electrochemical energy storage devices.

  7. 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. PMID:22962824

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

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

    PubMed

    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

  14. 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

    2015-09-01

    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. PMID:26280305

  15. Minimalist Approach to Complexity: Templating the Assembly of DNA Tile Structures with Sequentially Grown Input Strands.

    PubMed

    Lau, Kai Lin; Sleiman, Hanadi F

    2016-07-26

    Given its highly predictable self-assembly properties, DNA has proven to be an excellent template toward the design of functional materials. Prominent examples include the remarkable complexity provided by DNA origami and single-stranded tile (SST) assemblies, which require hundreds of unique component strands. However, in many cases, the majority of the DNA assembly is purely structural, and only a small "working area" needs to be aperiodic. On the other hand, extended lattices formed by DNA tile motifs require only a few strands; but they suffer from lack of size control and limited periodic patterning. To overcome these limitations, we adopt a templation strategy, where an input strand of DNA dictates the size and patterning of resultant DNA tile structures. To prepare these templating input strands, a sequential growth technique developed in our lab is used, whereby extended DNA strands of defined sequence and length may be generated simply by controlling their order of addition. With these, we demonstrate the periodic patterning of size-controlled double-crossover (DX) and triple-crossover (TX) tile structures, as well as intentionally designed aperiodicity of a DX tile structure. As such, we are able to prepare size-controlled DNA structures featuring aperiodicity only where necessary with exceptional economy and efficiency. PMID:27303951

  16. Structural characterization of low temperature Epi-silicon grown on {100} and {111} Si substrates using ultrahigh resolution cross-sectional TEM

    NASA Astrophysics Data System (ADS)

    Ye, Zhizhen; Liu, Yaping; Zhou, Zhen-Hong; Reif, Rafael

    1993-02-01

    Low defect-density epitaxial silicon was grown at 550°C, but it became polysilicon or amorphous silicon when the substrate was submitted to bombardment of ECR argon plasma prior to growth. Through carefully characterizing the interface and structure of low temperature epitaxial silicon films using ultrahigh resolution cross-sectional transmission electron microscopy (UHRXTEM), defects were found to have different features in silicon epitaxial layers grown on {100} and {111} silicon substrates. Twinning was more likely to generate in the epitaxial layer grown on the {111} silicon substrate while stacking faults had priority in forming in the epitaxial layer grown on the {100} substrate. The probable causes of different defect formation mechanisms were analyzed and discussed with the help of UHRXTEM lattice images. The atom model of the twin boundary in the epitaxial silicon film was analyzed in detail.

  17. Structural Properties and Resistance-Switching Behavior of Thermally Grown NiO Thin Films

    NASA Astrophysics Data System (ADS)

    Kim, Dong-Wook; Jung, Ranju; Park, Bae Ho; Li, Xiang-Shu; Park, Chanwoo; Shin, Seongmo; Kim, Dong-Chirl; Lee, Chang Won; Seo, Sunae

    2008-03-01

    We investigated the structural and electrical properties of polycrystalline NiO thin films on Pt electrodes formed by thermal oxidation. A Ni-Pt alloy phase was found at the interface, which could be explained by the oxidation kinetics and reactions of Ni, NiO, and Pt. An increase in the oxidation temperature decreased the volume of the alloy layer and improved the crystalline quality of the NiO thin films. Pt/NiO/Pt structures were fabricated, and they showed reversible resistance switching from a high-resistance state (HRS) to a low-resistance state (LRS) and vice versa during unipolar current-voltage measurements. The oxidation temperature affected (did not affect) the HRS (LRS) resistance of the Pt/NiO/Pt structures. This indicated that the transport characteristics of HRS and LRS should be different.

  18. Simulating nitrate leaching under winter wheat grown on a structured clay soil considering bypass flow

    NASA Astrophysics Data System (ADS)

    Ragab, R.; Coopers, D. M.; Harris, G. L.; Catt, J. A.

    1996-07-01

    Nitrate leaching from drained plots of structured clay soil under winter wheat is simulated for one growing season using the SOILN model. Results are compared with field measurements from two replicate plots. Soil water movement is simulated both with and without a bypass flow component using the SOIL model. Flow to field drains and soil water content in the root zone are simulated better when bypass flow is included. The results emphasise the importance of considering bypass flow in modelling leaching from structured clay soils. Simulations of nitrate leaching using the SOILN model show that the model captures the main features of the cumulative loss of nitrate over the year.

  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. 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.

  1. INSTRUMENTS AND METHODS OF INVESTIGATION: Atomic structures on a GaAs(001) surface grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Bakhtizin, Raouf Z.; Hashizume, T.; Xue, Qi-Kun; Sakurai, Toshio

    1997-11-01

    A unique apparatus for in-situ atomic-resolution study of solid state structures grown by molecular beam epitaxy (MBE) is developed, in which a scanning tunneling microscope (STM) is combined with an MBE chamber within the same vacuum system. The utility of the apparatus is demonstrated by examining atomic structures on a molecular-beam-epitaxial GaAs(001) surface over a wide range of [As]/[Ga] ratios. By varying the As surface coverage, the 2×4 - α, β, γ and c(4×4) phases are examined in detail. High-resolution STM images indicate that 2×4 - α, β, and γ phases in the outermost surface layer have essentially the same unit cell consisting of two As dimers and two As dimer vacancies. Using the STM images, reflection high-energy electron diffraction (RHEED) patterns and dynamical RHEED calculations, the existing structural models for the 2×4 phases are analysed and a new model of the As-rich GaAs(001) surface is proposed, found to be consistent with most of the previous observations.

  2. Structural, electrical, and optical properties of CoxNi1-xO films grown by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Roffi, Teuku Muhammad; Uchida, Kazuo; Nozaki, Shinji

    2015-03-01

    Thin films of cobalt-nickel oxide (CoxNi1-xO, x=0.01, 0.02, 0.08, 0.17, 0.22, 0.35, 0.56, 0.72) were grown on Al2O3 substrate by atmospheric pressure metalorganic chemical vapor deposition (APMOCVD). The effect of the cobalt composition on the structural, morphological, optical, and electrical properties of the films was investigated. X-ray diffraction (XRD) analysis revealed that all of the films grew with a preferred orientation towards [1 1 1]NiO and a twinned structure. Cobalt was well dispersed in the NiO structure up to x=0.08. CoxNi1-xO alloys were formed from x=0.17 to x=0.22, while phase-separated NiO and CoxNi1-xO formed when x≥0.35. The bandgap of the CoxNi1-xO film was found to decrease with increasing cobalt composition. Four-point probe measurements showed that the resistivity of the film also decreased with increasing cobalt composition, reaching a minimum of 0.006 Ωcm. Hall measurements of the films revealed n-type conductivity. The correlation between the presence of cobalt in different ionization states and the observed decrease in resistivity as well as the type of conductivity in CoxNi1-xO is discussed.

  3. 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. PMID:20413840

  4. Structural, optical and magnetic properties of Fe-doped barium stannate thin films grown by PLD

    NASA Astrophysics Data System (ADS)

    James, K. K.; Aravind, Arun; Jayaraj, M. K.

    2013-10-01

    Barium stannate is a wide band gap semiconductor with cubic perovskite structure. Polycrystalline bulk samples of BaSn1-xFexO3d (BFS), with x = 0.00, 0.02, 0.03, 0.05 and 0.10 were prepared by solid-state reaction. In this paper, we report the growth of undoped and Fe doped barium stannate thin films on fused silica substrate using pulsed laser deposition (PLD) technique at a relatively high substrate temperature and low oxygen pressure. The deposited films have wide bandgap and are transparent in the visible region. The X-ray diffraction analysis of the films confirmed the cubic structure. Microstructural studies were carried out using micro-Raman spectroscopy and AFM analysis. Defect induced Raman shifts were observed in the samples. Magnetic studies revealed an increase in magnetic properties for films doped with 10 at% Fe doped samples.

  5. 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. PMID:27437115

  6. 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

  7. Structural and magnetic properties of SmCo-based magnetic films grown by electron-beam evaporation

    NASA Astrophysics Data System (ADS)

    Saravanan, P.; Vinod, V. T. P.; Černík, Miroslav; Vishnuraj, R.; Arout Chelvane, J.; Kamat, S. V.; Hsu, Jen-Hwa

    2015-07-01

    Sub-micron thick Sm-Co films (200 and 300 nm) with selective phase composition are grown on Si (100) substrates by electron-beam evaporation using Sm-lean alloy targets such as Sm4Co96 and Sm8Co92. The structural and magnetic properties of Sm-Co films are characterized by x-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and super-conducting quantum interference device (SQUID) magnetometer. The Sm-Co films obtained with the Sm4Co96 target exhibit Sm2Co17 as a prominent phase; while the films produced with the Sm8Co92 target show Sm2Co7 as a major phase. Both the Sm-Co films reveal granular morphology; however, the estimated grain size values are slightly lower in the case of Sm2Co7 films, irrespective of their thicknesses. Coercivity (Hc) values of 1.48 and 0.9 kOe are achieved for the as-grown 200-nm thick Sm2Co17 and Sm2Co7-films. Temperature-dependent magnetization studies confirm that the demagnetization behaviors of these films are consistent with respect to the identified phase composition. Upon rapid thermal annealing, maximum Hc value of 8.4 kOe is achieved for the 200 nm thick Sm2Co17-films. As far as e-beam evaporated Sm-Co films are concerned, this Hc value is one of the best values reported so far.

  8. 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. PMID:27454873

  9. 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

  10. Polycrystalline domain structure of pentacene thin films epitaxially grown on a hydrogen-terminated Si(111) surface

    SciTech Connect

    Nishikata, S.; Sadowski, J. T.; Al-Mahboob, A.; Nishihara, T.; Fujikawa, Y.; Sakurai, T.; Nakajima, K.; Sazaki, G.; Suto, S.

    2007-10-15

    Single-monolayer high pentacene (Pn) dendrites grown on a hydrogen-terminated Si(111) surface [H-Si(111)] under ultrahigh vacuum were observed by low-energy electron microscopy and microbeam low-energy electron diffraction analyses. We determined the epitaxial structure (type I) inside a unique polycrystalline domain structure of such dendrites, each of which has six equivalent epitaxial orientations of Pn two-dimensional (2D) unit cells. There are three sets of these cells, which are rotated {+-}120 deg. relative to each other. Domain boundaries inside each dendrite were successfully observed by scanning tunneling microscopy. In addition, we found another epitaxial relation (type II): the polycrystalline domain structure and lattice parameters are similar to those of the type-I dendrite; however, the 2D unit cells of the type-II dendrite are rotated approximately 90 deg. relative to those of the type-I dendrite. These results suggest that the crystal structure of the dendrites on H-Si(111) is determined mainly by the interaction between Pn molecules. Each dendrite is composed of domains that are exclusively of type I or II. The so-called point-on-line coincidences are found between the Pn 2D lattices of types I and II, and H-Si(111). The higher commensurability of the type-I dendrites than the type-II dendrites results in a higher probability of type-I dendrite formation. Moreover, for both the type-I and type-II dendrites, we found supercell structures. We estimated the minimum interface energy between the dendrite and H-Si(111) from an island's free energy, which is necessary to reproduce the growth of a single-monolayer high dendrite.

  11. 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.

  12. Comparison between structural properties of bulk GaN grown in liquid Ga under high N pressure and GaN grown by other methods

    NASA Astrophysics Data System (ADS)

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

    2002-12-01

    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 the formation of defects characteristic for a specific dopant. This type of defects tends to be growth method independent but can depend on growth polarity.

  13. 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.

  14. 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.

  15. 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

    2014-04-01

    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. PMID:26274451

  16. Photonic bandgap amorphous chalcogenide thin films with multilayered structure grown by pulsed laser deposition method

    NASA Astrophysics Data System (ADS)

    Zhang, Shao-qian; Němec, Petre; Nazabal, Virginie; Jin, Yu-qi

    2016-05-01

    Amorphous chalcogenide thin films were fabricated by the pulsed laser deposition technique. Thereafter, the stacks of multilayered thin films for reflectors and microcavity were designed for telecommunication wavelength. The prepared multilayered thin films for reflectors show good compatibility. The microcavity structure consists of Ge25Ga5Sb10S65 (doped with Er3+) spacer layer surrounded by two 5-layer As40Se60/Ge25Sb5S70 reflectors. Scanning/transmission electron microscopy results show good periodicity, great adherence and smooth interfaces between the alternating dielectric layers, which confirms a suitable compatibility between different materials. The results demonstrate that the chalcogenides can be used for preparing vertical Bragg reflectors and microcavity with high quality.

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    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.

  18. 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.

  19. Synthesis, optical and structural properties of quantum-wells crystals grown into porous alumina

    NASA Astrophysics Data System (ADS)

    Zaghdoudi, W.; Dammak, T.; ElHouichet, H.; Chtourou, R.

    2014-07-01

    In this work, we present the confinement effect of the incorporation of perovskite compounds (C12H25-NH3)2PbI4 quantum wells into different porous anodic aluminum oxide (PAA) matrix via a chemical route. The detailed structure and optical property of the quantum wells in PAA were characterized by FT-IR, UV-Vis absorption and photoluminescence (PL) spectroscopy. The surface topography for the two used PAA matrix has been studied using atomic force microscopy (AFM). The pores diameters (pores spacing) for the two matrix are 15 (35 nm) and 45 (82 nm). UV-visible and photoluminescence spectroscopy of (C12H25-NH3)2PbI4/PAA exhibits a clear blue shift of the fundamental excitonic transition. This effect is attributed to the confinement of the exciton mode in the pore of the PAA matrix.

  20. Thermoelectric energy conversion in layered structures with strained Ge quantum dots grown on Si surfaces

    NASA Astrophysics Data System (ADS)

    Korotchenkov, Oleg; Nadtochiy, Andriy; Kuryliuk, Vasyl; Wang, Chin-Chi; Li, Pei-Wen; Cantarero, Andres

    2014-03-01

    The efficiency of the energy conversion devices depends in many ways on the materials used and various emerging cost-effective nanomaterials have promised huge potentials in highly efficient energy conversion. Here we show that thermoelectric voltage can be enhanced by a factor of 3 using layer-cake growth of Ge quantum dots through thermal oxidation of SiGe layers stacked in SiO2/Si3N4 multilayer structure. The key to achieving this behavior has been to strain the Ge/Si interface by Ge dots migrating to Si substrate. Calculations taking into account the carrier trapping in the dot with a quantum transmission into the neighboring dot show satisfactory agreement with experiments above ≈200 K. The results may be of interest for improving the functionality of thermoelectric devices based on Ge/Si.

  1. 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.

  2. 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.

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

    PubMed

    Saxena, Nupur; Kumar, Pragati; Kabiraj, Debulal; Kanjilal, Dinakar

    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

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

    NASA Astrophysics Data System (ADS)

    Saxena, Nupur; Kumar, Pragati; Kabiraj, Debulal; Kanjilal, Dinakar

    2012-10-01

    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.

  6. 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.

  7. 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. PMID:26965558

  8. Structural, optical and ferroelectric behavior of hydrothermally grown ZnO nanostructures

    NASA Astrophysics Data System (ADS)

    Chand, Prakash; Gaur, Anurag; Kumar, Ashavani

    2013-12-01

    In the present study, zinc oxide (ZnO) nanostructures have been synthesized at 100 °C for different aging periods, 1, 24, 48 and 96 h by hydrothermal method. Structural, optical and ferroelectric properties were investigated using X-ray diffractometer, field emission scanning electron microscope, Transmission electron microscope, photoluminescence, UV-visible, Raman spectroscopy and P-E loop tracer. The X-ray diffractometer pattern indicates the pure phase formation of ZnO without any impurity for the samples synthesized from 1 to 96 h aging periods, respectively. Field emission scanning electron microscope and transmission electron microscope analysis also shows that the average diameter and length of these nanorods increases with increasing the aging periods. Moreover Raman and Photoluminescence spectrum also confirm the wurtzite phase formation of ZnO. The optical band gaps calculated through UV-visible spectroscopy are found to decrease from 3.81 to 3.45 eV with increase in aging periods, 1-96 h, respectively. Further, improved ferroelectric behavior has been observed for 48 and 96 h aged samples.

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

    PubMed

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

    2012-01-01

    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

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    We prepared the b-axis-oriented polycrystalline Na0.85Ti0.51Ga4.37O8 (NTGO) embedded in Ga2O3-doped Na2Ti4O9 matrix using the reactive diffusion technique. When the sandwich-type Ga2TiO5/NaGaO2/Ga2TiO5 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 1.3×10-4 to 7.3×10-3 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+ 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.

  12. Variation of strain in single and multilayer (In xGa 1-xAs) structures grown on Si(100), and Si(111), by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Sobiesierski, Z.; Woolf, D. A.; Westwood, D. I.; Williams, R. H.

    The difference in thermal expansion coefficients between GaAs and Si is known to induce a biaxial tensile strain, below room temperature, for GaAs epilayers grown on Si(100). We have performed photoluminescence (PL) measurements for GaAs layers grown on both Si(111) and misorientated Si(100) substrates by molecular beam epitaxy. These measurements indicate that the thermally-induced strain is greater for the (111) growth direction. Strained In xGa 1-xAs-GaAs multiple quantum well structures grown on Si(100), (MQW/Si), exhibit systematic decreases in low temperature PL transition energies when compared with similar structures grown on GaAs(100), (MQW/GaAs). The MQW structures incorporating greater strain (18.7% In content) show decreases in PL transition energies of 3-9 meV between MQW/Si and MQW/GaAs, while MQW structures containing less-strained layers (11% In content) exhibit 12-13 meV shifts to lower transition energies. It seems, therefore, that the effect of thermal strain becomes more pronounced at lower levels of coherency strain.

  13. 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.

    2001-01-01

    It was found that atomically flat Co(110) films 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, low-energy electron diffraction, surface magneto-optic Kerr effect (SMOKE), and scanning tunneling microscopy. 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 {approx}5 ML Co. Above 5 ML Co, layer-by-layer growth resumes. No significant Cu segregation is observed. SMOKE studies at room temperature show that the Co film is magnetic above {approx}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.

  14. 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.

  15. Bi surfactant control of ordering and surface structure in GaInP grown by organometallic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Jun, S. W.; Lee, R. T.; Fetzer, C. M.; Shurtleff, J. K.; Stringfellow, G. B.; Choi, C. J.; Seong, T.-Y.

    2000-10-01

    The surfactant Bi has been added during organometallic vapor phase epitaxial growth (OMVPE) of GaInP using the precursor trimethylbismuth. The addition of a small amount of Bi during growth results in disordered material using conditions that would otherwise produce highly ordered GaInP. Significant changes in the surface structure are observed to accompany the disordering. Atomic force microscopy measurements show that Bi causes an order of magnitude increase in step velocity, leading to the complete elimination of three-dimensional islands for growth on singular (001) GaAs substrates, and a significant reduction in surface roughness. Surface photoabsorption measurements indicate that Bi reduces the number of [1¯10] P dimers on the surface. Secondary ion mass spectroscopy measurements reveal that the Bi is rejected from the bulk, even though it changes the surface reconstruction. Clearly, Bi acts as a surfactant during OMVPE growth of GaInP. The difference in band gap energy caused by the reduction in order parameter during growth is measured using photoluminescence to be about 110 meV for layers grown on singular substrates. Disorder/order/disorder heterostructures were successfully produced in GaInP with a constant solid composition by modulating the TMBi flow rate during growth.

  16. Structural study and ferroelectricity of epitaxial BaTiO3 films on silicon grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Mazet, L.; Bachelet, R.; Louahadj, L.; Albertini, D.; Gautier, B.; Cours, R.; Schamm-Chardon, S.; Saint-Girons, G.; Dubourdieu, C.

    2014-12-01

    Integration of epitaxial complex ferroelectric oxides such as BaTiO3 on semiconductor substrates depends on the ability to finely control their structure and properties, which are strongly correlated. The epitaxial growth of thin BaTiO3 films with high interfacial quality still remains scarcely investigated on semiconductors; a systematic investigation of processing conditions is missing although they determine the cationic composition, the oxygen content, and the microstructure, which, in turn, play a major role on the ferroelectric properties. We report here the study of various relevant deposition parameters in molecular beam epitaxy for the growth of epitaxial tetragonal BaTiO3 thin films on silicon substrates. The films were grown using a 4 nm-thick epitaxial SrTiO3 buffer layer. We show that the tetragonality of the BaTiO3 films, the crystalline domain orientations, and SiO2 interfacial layer regrowth strongly depend on the oxygen partial pressure and temperature during the growth and on the post-deposition anneal. The ferroelectricity of the films, probed using piezoresponse force microscopy, is obtained in controlled temperature and oxygen pressure conditions with a polarization perpendicular to the surface.

  17. 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.

  18. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    Pulsed laser deposition has been used to grow thin (10-84 nm) epitaxial layers of Yttrium Iron Garnet Y3Fe5O12 (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.

  20. 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.

  1. 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.

  2. Structure of KTiOPO{sub 4} single crystals grown by the top-seeded solution and spontaneous flux crystallization methods

    SciTech Connect

    Novikova, N. E. Verin, I. A.; Sorokina, N. I.; Alekseeva, O. A.; Voronkova, V. I.; Tseitlin, M.; Roth, M.

    2008-11-15

    This paper reports on the results of precision X-ray structural investigations of KTiOPO{sub 4} single crystals grown by one method (crystallization from a solution in the melt) in two variants (the spontaneous formation of crystallization centers or top-seeded solution growth during slow cooling of saturated solution melts). It is shown that spontaneous flux crystallization leads to the formation of a larger number of defects. Potassium atoms are found to be disordered. The splitting of the K1 and K2 potassium positions is equal to 0.347(4) and 0.279(3) A, respectively, for the crystals grown by the top-seeded solution method and 0.308(5) and 0.321(4) A, respectively, for the crystals grown through the spontaneous flux crystallization.

  3. Morphological dependent Indium incorporation in InGaN/GaN multiple quantum wells structure grown on 4° misoriented sapphire substrate

    NASA Astrophysics Data System (ADS)

    Jiang, Teng; Xu, Shengrui; Zhang, Jincheng; Li, Peixian; Huang, Jun; Ren, Zeyang; Zhu, Jiaduo; Chen, Zhibin; Zhao, Ying; Hao, Yue

    2016-03-01

    The epitaxial layers of InGaN/GaN MQWs structure were grown on both planar and vicinal sapphire substrates by metal organic chemical vapor deposition. By comparing the epitaxial layers grown on planar substrate, the sample grown on 4° misoriented from c-plane toward < 10 1 ¯ 0 > m-plane substrate exhibited many variations both on surface morphology and optical properties according to the scanning electronic microscopy and cathodoluminescence (CL) spectroscopy results. Many huge steps were observed in the misoriented sample and a large amount of V-shape defects located around the boundary of the steps. Atoms force microscopy images show that the steps were inclined and deep grooves were formed at the boundary of the adjacent steps. Phase separation was observed in the CL spectra. CL mapping results also indicated that the deep grooves could effectively influence the localization of Indium atoms and form an In-rich region.

  4. Investigation on the structural properties of GaN films grown on La0.3Sr1.7AlTaO6 substrates

    NASA Astrophysics Data System (ADS)

    Wang, Wenliang; Zhou, Shizhong; Liu, Zuolian; Yang, Weijia; Lin, Yunhao; Qian, Huirong; Gao, Fangliang; Li, Guoqiang

    2014-04-01

    Gallium nitride (GaN) films with excellent structural, electrical and optical properties have been epitaxially grown on La0.3Sr1.7AlTaO6 (LSAT) (111) substrates by radio-frequency molecular beam epitaxy at low temperature. The GaN films grown at 500 °C exhibits high crystalline quality with the (0002) and (10-12) full width at half maximum of 0.056° and 0.071°. There is a maximum of 1.1-nm-thick interfacial layer existing between the as-grown GaN and LSAT (111) substrate, and the as-grown about 300-nm-thick GaN films are almost fully relaxed only with a 0.0094% in-plane tensile strain. Hall and photoluminescence (PL) measurements also reveal outstanding electrical and optical properties of the as-grown GaN films on LSAT. This achievement brings the prospect for achieving highly-efficient GaN-based optoelectronic devices on LSAT (111) substrates.

  5. Highly doped p-ZnTe films and quantum well structures grown by nonequilibrium pulsed laser ablation

    SciTech Connect

    Lowndes, D.H.; Rouleau, C.M.; Budai, J.D.; Geohegan, D.B.; McCamy, J.W.

    1995-06-01

    Highly p-doped ZnTe films have been grown on semi-insulating GaAs (001) and unintentionally doped (p-type) GaSb (001) substrates by pulsed KrF (248 nm) excimer laser ablation of a ZnTe target through an N{sub 2} ambient, without the use of any assisting (DC or AC) plasma source. Free hole concentrations in the mid-10{sup 19} cm{sup {minus}3} to > 10{sup 20} cm{sup {minus}3} range have been obtained. This appears to be the first time that any wide band gap (E{sub g} {ge} 2 eV) II-VI compound (or other) semiconductor has been impurity-doped from the gas phase by pulsed-laser ablation (PLA). The maximum carrier concentrations also may be the highest obtained for ZnTe by any method thus far. Because pulsed laser deposition is inherently digital, attractive deposition rates can be combined with precise control of layer thickness in epitaxial multilayered structures. Typical deposition conditions are < 0.5 {angstrom} per laser pulse, with crystalline quality governed by tradeoffs between substrate temperature, pulse repetition rate, and the focused pulsed laser energy density. PLA`s capability for growth of very thin epitaxial layers is being exploited and studied through growth of doped heteroepitaxial quantum well structures in the nearly lattice-matched ZnTe/CdSe//GaSb(substrate) system. Results obtained from growth and characterization of heterostructures in this system will be presented.

  6. Study of GaAs/AlGaAs quantum-well structures grown by MOVPE using tertiarybutylarsine

    NASA Astrophysics Data System (ADS)

    Lee, Hyung G.; Kim, HyungJun; Park, S. H.; Langer, Dietrich W.

    1991-03-01

    Tertiarybutylarsine (TBAs) was utilized in the fabrication of GaAs A1GaAs and GaAs/A1GaAs structures in a Low Pressure - Metal Organic Vapor Phase Epitaxy (LP-MOVPE) system. Good quality epitaxial layers were achieved at 700 C with V/LI! ratio of 50. Undoped GaAs and AI (x 3-0. 6) layers were p-type with typical background carrier concentrations of mid 1014 cm3 and 1016 cm3 range respectively. Carbon could be used as p-type dopant in A1GaAS layers by controlling the TBAs mole fraction. Double-heterostructure lasers were fabricated and showed a threshold current density of 500 A/cm2. GaAs/AlGaAs multiple quantum well structures produced photoluminescence spectra with very narrow FWHM comparable to arsine-grown samples. Electro-absorptive waveguide modulator with MQW active layer demonstrated more than 2: 1 modulation ratio at the energy far below the QW exciton absorption peak. The deposition of 111-V compound semiconductors by metalorganic vapor phase epitaxy (MOVPE) is normally accomplished with gaseous group V precursors. These sources arsine (AsH3) and phosphine (PH3) are highly toxic and are stored in high pressure cylinders. Thus careful handlings are required to avoid accidental leakage. Lately a number of less hazardous arsenic compounds have been investigated as alternative As sources Methyl ethyl and butyl groups are substituted for one or more of the hydrogen atoms in arsine. In particular Tertiarybutylarsine (TBAs) has been most successful in growing high quality GaAs and A1GaAS films and useful electronic devices have

  7. 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

  8. 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. PMID:24552130

  9. InP/InGaAs/InP DHBT structures with graded composition base grown by gas source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Teng, Teng; Ai, Likun; Xu, Anhuai; Sun, Hao; Zhu, Fuying; Qi, Ming

    2011-05-01

    A new InP/InGaAs/InP DHBT structure with graded composition base was optimized and grown successfully in this work. The gallium (Ga) composition increased gradually from 47% on the collector side to 55% on the emitter side. The InP/InGaAs/InP DHBT structures were grown by gas source molecular beam epitaxy (GSMBE). Characteristics of InP, InGaAs and InGaAsP materials were investigated. High quality InP/InGaAs/InP DHBT structural materials were obtained. The InP/InGaAs/InP DHBT device with emitter area of 100×100 μm2 was fabricated. The offset voltage of 0.2 V, BVCEO>1.2 V, current gain of ß=550 at VCE of 1.0 V were achieved. The reasons for the low breakdown voltage were analyzed.

  10. Structure of CdTe-Cd1 - xMnxTe multiple quantum wells grown on (001) InSb substrates by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Williams, G. M.; Cullis, A. G.; Whitehouse, C. R.; Ashenford, D. E.; Lunn, B.

    1989-09-01

    Molecular beam epitaxy has been used to prepare multiple quantum well structures of CdTe/Cd1-xMnxTe on (001) InSb substrates. The growth of such a system on InSb allows the use of particularly low growth temperatures, hence minimizing interdiffusion effects. This study presents the first transmission electron microscope investigation of this multilayer system grown on InSb. The work clearly demonstrates that multiple quantum wells of high structural quality can be grown reproducibly over a wide range of layer thicknesses. The importance of efficient substrate surface cleaning prior to growth is demonstrated. In order to grow high structural quality multilayers, the choice of buffer layer is also important and a possible explanation for this observation is given.

  11. 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

    2016-06-01

    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.

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

    DOE PAGESBeta

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

    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

  13. 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}.

  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. 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.

  16. 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

  17. 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.

  18. 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.

  19. 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.

  20. Lithiated cobaltates for lithium-ion batteries. Structure, morphology and electrochemistry of oxides grown by solid-state reaction, wet chemistry and film deposition

    NASA Astrophysics Data System (ADS)

    Julien, C.; Gastro-Garcia, S.

    We present the structural (XRD and Raman) and electrochemical properties of various oxides of the cobaltate family (with the α-NaFeO 2-type structure) grown by solid-state reaction, wet chemistry and film deposition techniques. It is shown that synthesis greatly affects the electrochemistry and cycle life characteristics of these layer structured cathode materials. HT-LiCoO 2, LT-LiCoO 2, doped LiCo 1- yAl yO 2 and LiCoO 2 films are investigated.

  1. The influence of aluminum content on the surface morphology of heavily doped (Al)GaN mesastrip structures grown by selective metalorganic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Lundin, W. V.; Zavarin, E. E.; Popov, M. G.; Troshkov, S. I.; Sakharov, A. V.; Smirnova, I. P.; Kulagina, M. M.; Davydov, V. Yu.; Smirnov, A. N.; Tsatsulnikov, A. F.

    2015-10-01

    Heavily Si-doped Al x Ga1- x N mesastrip structures were grown by selective MOVPE technology. Al x Ga1- x N:Si mesastructures with x ~ 0.01-0.07 possess a smoother top and more even side surfaces as compared to those in analogous GaN:Si structures. During the growth of mesastructures with x ~ 0.03-0.07, a thin nanocrystalline AlN deposit appears on the Si3N4 mask. This deposit is not formed during the growth of structures with sufficiently low aluminum content.

  2. 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.

  3. Surface photo-voltage characterization of GaAs/AlGaAs single quantum well laser structures grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Muralidharan, R.; Ramesh, V.; Mishra, Puspashree; Srinivasan, T.

    2014-03-01

    We present surface photo-voltage (SPV) measurements on molecular beam epitaxy (MBE) grown single quantum well (SQW) laser structures. Each layer in the hetero-structure has been identified by measurement of the SPV signal after a controlled sequential chemical etching process. These results have been correlated with high resolution x-ray diffraction and photoluminescence (PL) measurements. Quantum confined Stark effect and the carrier screening of electric field have been taken into consideration both theoretically and experimentally to account for the differences observed in SPV and PL results. It is shown that SPV can be used as a very effective tool for evaluation of hetero-structures involving multiple layers.

  4. 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.

  5. Structural and optical properties of Cd 0.7Hg 0.3Te-CdTe heterostructures grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Lentz, G.; Magnea, N.; Mariette, H.; Tuffigo, H.; Feuillet, G.; Fontenille, J.; Ligeon, E.; Saminadayar, K.

    1990-04-01

    Layers and single quantum wells of Cd xHg 1- xTe with x ⋍ 0.7 have been grown by molecular beam epitaxy. Structural analysis shows that growth free of defects (twins, dislocations) can be achieved on (111)Te Cd 0.96Zn 0.04Te substrates. The Photoluminescence analysis of the layers and the wells reveal that they are efficient light emittors in the 1.3-1.5 μm range.

  6. Effects of N and F passivation on the reliability and interface structure of 700 °C grown ultrathin silicon oxide/Si(100) gate films

    NASA Astrophysics Data System (ADS)

    Yamada, Hiroshi

    2008-01-01

    Correlations between reliability and interfacial structure changes of ultrathin silicon oxide gate films grown at 700 °C with in situ pyrolytic-gas passivation (PGP) were investigated. PGP uses a little pyrolytic N2O and NF3 during ultradry oxidation with pure O2 at less than 1 ppb humidity and has a potential for application to future low-temperature device fabrication processes due to the reliability retention of the films. It was found that the reliability for the 700 °C grown PGP films is much like that of the 800-900 °C grown ones, with an interface state density of less than 1-3×1010/eV cm2 maintained. Quantitative analyses of N, F, and O indicated that this is probably due to microscopic, interfacial structure changes, that is, N and F passivation effectively contributes to compensate inconsistent-state bonding sites and to generate a high-density structure with few dangling bonds.

  7. 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.

  8. Correlation of growth temperature with stress, defect states and electronic structure in an epitaxial GaN film grown on c-sapphire via plasma MBE.

    PubMed

    Krishna, Shibin; Aggarwal, Neha; Mishra, Monu; Maurya, K K; Singh, Sandeep; Dilawar, Nita; Nagarajan, Subramaniyam; Gupta, Govind

    2016-03-21

    The relationship of the growth temperature with stress, defect states, and electronic structure of molecular beam epitaxy grown GaN films on c-plane (0001) sapphire substrates is demonstrated. A minimum compressively stressed GaN film is grown by tuning the growth temperature. The correlation of dislocations/defects with the stress relaxation is scrutinized by high-resolution X-ray diffraction and photoluminescence measurements which show a high crystalline quality with significant reduction in the threading dislocation density and defect related bands. A substantial reduction in yellow band related defect states is correlated with the stress relaxation in the grown film. Temperature dependent Raman analysis shows the thermal stability of the stress relaxed GaN film which further reveals a downshift in the E2 (high) phonon frequency owing to the thermal expansion of the lattice at elevated temperatures. Electronic structure analysis reveals that the Fermi level of the films is pinned at the respective defect states; however, for the stress relaxed film it is located at the charge neutrality level possessing the lowest electron affinity. The analysis demonstrates that the generated stress not only affects the defect states, but also the crystal quality, surface morphology and electronic structure/properties. PMID:26916430

  9. Structural and optical characterization of nonpolar (10-10) m-InN/m-GaN epilayers grown by PAMBE

    NASA Astrophysics Data System (ADS)

    Mukundan, Shruti; Chandan, Greeshma; Mohan, Lokesh; Roul, Basanta; Krupanidhi, S. B.

    2016-01-01

    Plasma-assisted molecular beam epitaxy growth of (10-10) m-InN/(10-10) m-GaN was carried out on bare (10-10) m-sapphire substrate. The high resolution X-ray diffraction studies confirmed the orientation of the as-grown films. Nonpolar InN layer was grown at different growth temperatures ranging from 390 °C to 440 °C and the FWHM of rocking curve revealed good quality film at low temperatures. An in-plane relationship was established for the hetrostructures using phi-scan and a perfect alignment was found for the epilayers. Change of morphology of the films grown at different temperatures was observed using an atomic force microscopy technique showing the smoothest film grown at 400 °C. InN optical band gap was found to be vary from 0.79-0.83 eV from absorption spectra. The blue-shift of absorption edge was found to be induced by excess background electron concentration.

  10. 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

  11. 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.

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

    DOE PAGESBeta

    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.; et al

    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

  13. 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.

  14. 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. PMID:27483897

  15. Structural characterization of Hg 0.78Cd 0.22Te/CdTe LPE heterostructures grown from Te solutions

    NASA Astrophysics Data System (ADS)

    Bernardi, S.; Bocchi, C.; Ferrari, C.; Franzosi, P.; Lazzarini, L.

    1991-08-01

    Hg 0.78Cd 0.22Te epilayers have been grown on CdTe substrates by slider liquid phase epitaxy. The crystal quality of the epitaxial material has been studied in as-grown structures and chemically or mechano-chemically prepared bevels using X-ray topography, double crystal diffractometry and transmission electron microscopy. It has been found that the bulk epilayers exhibit a very high crystal quality, as evidenced by the relatively low density of dislocations and the very narrow Bragg peaks. In contrast, a high dislocation and precipitate density and a broadening of the Bragg peak have been detected in the epilayer near the interface. Finally, a Hg decrease in the layer and a corresponding Hg increase in the substrate close to the interface have been observed.

  16. 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.

  17. The effect of AlN buffer growth parameters on the defect structure of GaN grown on sapphire by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Wong, Yuen-Yee; Chang, Edward Yi; Yang, Tsung-Hsi; Chang, Jet-Rung; Chen, Yi-Cheng; Ku, Jui-Tai; Lee, Ching-Ting; Chang, Chun-Wei

    2009-03-01

    The defect structure of GaN film grown on sapphire by plasma-assisted molecular beam epitaxy (PAMBE) depends on the growth temperature and thickness of the aluminum nitride (AlN) buffer layer. High-resolution X-ray diffraction was used to measure symmetric (0 0 0 2) and asymmetric (1 0 1¯ 2) rocking curve (ω-scans) broadening, which allowed the estimation of screw threading dislocation (TD) and edge TD densities, respectively. For GaN grown on lower-temperature buffer, the density of screw TD was increased while the density of edge TD was decreased. Further examinations revealed that the edge TD was closely related to stress in GaN film and the screw TD was controlled by AlN surface roughness. Since the GaN defect was dominated by edge TD, the total TD was also effectively suppressed with the use of lower-temperature buffer with appropriate thickness.

  18. Structural and optical properties of InAs/InAsSb superlattices grown by metal organic chemical vapor deposition for mid-wavelength infrared photodetectors

    NASA Astrophysics Data System (ADS)

    Ning, Zhen-Dong; Liu, Shu-Man; Luo, Shuai; Ren, Fei; Wang, Feng-Jiao; Yang, Tao; Liu, Feng-Qi; Wang, Zhan-Guo; Zhao, Lian-Cheng

    2016-04-01

    InAs/InAsSb superlattices were grown on (0 0 1) GaSb substrates by metal organic chemical vapor deposition for potential applications as mid-infrared optoelectronic devices. X-ray diffraction, transmission electron microscopy, photoluminescence emission and spectral photoconductivity were used to characterize the grown structures. Generally, photoluminescence emission measurements of InAs/InAsSb superlattices were performed over the temperature range from 11 K to 300 K. The Varshni and Bose-Einstein parameters were determined. Low-temperature photoluminescence measurements showed peaks at 3-5 μm, while photoconductance results showed strong spectral response up to room temperature, when the photoresponse onset was extended to 5.5 μm. The photoluminescence emission band covers the CO2 absorption peak making it suitable for application in CO2 detection.

  19. Effects of Uniaxial and Biaxial Strain on Few-Layered Terrace Structures of MoS₂ Grown by Vapor Transport.

    PubMed

    McCreary, Amber; Ghosh, Rudresh; Amani, Matin; Wang, Jin; Duerloo, Karel-Alexander N; Sharma, Ankit; Jarvis, Karalee; Reed, Evan J; Dongare, Avinash M; Banerjee, Sanjay K; Terrones, Mauricio; Namburu, Raju R; Dubey, Madan

    2016-03-22

    One of the most fascinating properties of molybdenum disulfide (MoS2) is its ability to be subjected to large amounts of strain without experiencing degradation. The potential of MoS2 mono- and few-layers in electronics, optoelectronics, and flexible devices requires the fundamental understanding of their properties as a function of strain. While previous reports have studied mechanically exfoliated flakes, tensile strain experiments on chemical vapor deposition (CVD)-grown few-layered MoS2 have not been examined hitherto, although CVD is a state of the art synthesis technique with clear potential for scale-up processes. In this report, we used CVD-grown terrace MoS2 layers to study how the number and size of the layers affected the physical properties under uniaxial and biaxial tensile strain. Interestingly, we observed significant shifts in both the Raman in-plane mode (as high as -5.2 cm(-1)) and photoluminescence (PL) energy (as high as -88 meV) for the few-layered MoS2 under ∼1.5% applied uniaxial tensile strain when compared to monolayers and few-layers of MoS2 studied previously. We also observed slippage between the layers which resulted in a hysteresis of the Raman and PL spectra during further applications of strain. Through DFT calculations, we contended that this random layer slippage was due to defects present in CVD-grown materials. This work demonstrates that CVD-grown few-layered MoS2 is a realistic, exciting material for tuning its properties under tensile strain. PMID:26881920

  20. Electronic structure of Ga1- x Al x As nanostructures grown on the GaAs surface by ion implantation

    NASA Astrophysics Data System (ADS)

    Donaev, S. B.; Umirzakov, B. E.; Tashmukhamedova, D. A.

    2015-10-01

    The surface morphology and electronic properties of nanocrystalline phases and 2-7-nm-thick Ga1- x Al x As films grown on the GaAs(111) surface by Al+ ion implantation with subsequent (laser + thermal) annealing are studied. It is found that bandgap E g of the Ga0.5Al0.5As nanocrystalline surface phase 25-30 nm in size equals 2.8-2.9 eV.

  1. Structural and Morphological Difference Between Ti/TiN/TiCN Coatings Grown in Multilayer and Graded Form

    SciTech Connect

    Restrepo, E.; Baena, A.; Agudelo, C.; Castillo, H.; Devia, A.; Marino, A.

    2006-12-04

    Thin films can be grown in super-lattice, multilayers and graded form, having each one advantages and disadvantages. The difference between multilayer and graded coatings is the interface. In multilayers the interface is abrupt and in graded coatings it is diffuse. The interface influences many chemical and physical properties of the materials, and its choice depends on the application. Graded coatings have the advantage of having gradual properties such as thermal expansion coefficient and lattice parameter, avoiding adherence problems due to good match between their component materials. In this work the comparison between some properties of coatings grown as multilayer and graded is performed. The materials are produced using the sputtering DC technique because of its facility to control the deposition parameters and generate a slow growth. The target is a disc of titanium and the samples are made of stainless steel 304. The working gases are argon, nitrogen and methane, which are mixed according to the material to be produced, i.e. Ti layer is grown with argon, the TiN film is produced with a mixture of argon and nitrogen, and the TiCN material is obtained mixing argon, nitrogen and methane. These materials are characterized with AFM in order to determine grain size and with XPS studying the chemical composition and performing depth profiles.

  2. Effects of Strain on CVD-Grown Few-Layered Terrace Structures of MoS2

    NASA Astrophysics Data System (ADS)

    McCreary, Amber; Ghosh, R.; Amani, M.; Wang, J.; Duerloo, K.-A.; Sharma, A.; Jarvis, K.; Reed, E.; Dongare, A.; Banerjee, S. K.; Terrones, M.; Namburu, R.; Dubey, M.

    In this report, we used CVD-grown terrace MoS2 layers to study how the number and size of the layers affected the physical properties under uniaxial and biaxial tensile strain. Interestingly, we observed significant shifts in both the Raman in-plane mode (as high as -5.2 cm-1) and photoluminescence (PL) energy (as high as -88 meV) for the few-layered MoS2 under approximately 1.5% applied uniaxial tensile strain. The observed results were compared to monolayers and few-layers of MoS2 previously reported. We also observed slippage between the layers which resulted in a hysteresis of the Raman and PL spectra during further applications of strain. Through DFT calculations, we contended that this random layer slippage was due to defects present in CVD-grown materials. This work demonstrates that the properties of CVD-grown few-layered MoS2 studied here can be tuned under strain as well as, if not better than, it's exfoliated monolayered counterpart. Funded by ARL DSI on stacked 2D atomic layered materials, ARO MURI Grant W911NF-11-1-0362, ARO STTR Award W911NF-14-P-0030, and ARL Cooperative Agreement Number W911NF-14-2-0059.

  3. Chemical lift-off and direct wafer bonding of GaN/InGaN P-I-N structures grown on ZnO

    NASA Astrophysics Data System (ADS)

    Pantzas, K.; Rogers, D. J.; Bove, P.; Sandana, V. E.; Teherani, F. H.; El Gmili, Y.; Molinari, M.; Patriarche, G.; Largeau, L.; Mauguin, O.; Suresh, S.; Voss, P. L.; Razeghi, M.; Ougazzaden, A.

    2016-02-01

    p-GaN/i-InGaN/n-GaN (PIN) structures were grown epitaxially on ZnO-buffered c-sapphire substrates by metal organic vapor phase epitaxy using the industry standard ammonia precursor for nitrogen. Scanning electron microscopy revealed continuous layers with a smooth interface between GaN and ZnO and no evidence of ZnO back-etching. Energy Dispersive X-ray Spectroscopy revealed a peak indium content of just under 5 at% in the active layers. The PIN structure was lifted off the sapphire by selectively etching away the ZnO buffer in an acid and then direct bonded onto a glass substrate. Detailed high resolution transmission electron microscoy and grazing incidence X-ray diffraction studies revealed that the structural quality of the PIN structures was preserved during the transfer process.

  4. Computational Analysis of the Optical and Charge Transport Properties of Ultrasonic Spray Pyrolysis-Grown Zinc Oxide/Graphene Hybrid Structures.

    PubMed

    Ali, Amgad Ahmed; Hashim, Abdul Manaf

    2016-12-01

    We demonstrate a systematic computational analysis of the measured optical and charge transport properties of the spray pyrolysis-grown ZnO nanostructures, i.e. nanosphere clusters (NSCs), nanorods (NRs) and nanowires (NWs) for the first time. The calculated absorbance spectra based on the time-dependent density functional theory (TD-DFT) shows very close similarity with the measured behaviours under UV light. The atomic models and energy level diagrams for the grown nanostructures were developed and discussed to explain the structural defects and band gap. The induced stresses in the lattices of ZnO NSCs that formed during the pyrolysis process seem to cause the narrowing of the gap between the energy levels. ZnO NWs and NRs show homogeneous distribution of the LUMO and HOMO orbitals all over the entire heterostructure. Such distribution contributes to the reduction of the band gap down to 2.8 eV, which has been confirmed to be in a good agreement with the experimental results. ZnO NWs and NRs exhibited better emission behaviours under the UV excitation as compared to ZnO NSCs and thin film as their visible range emissions are strongly quenched. Based on the electrochemical impedance measurement, the electrical models and electrostatic potential maps were developed to calculate the electron lifetime and to explain the mobility or diffusion behaviours in the grown nanostructure, respectively. PMID:27173675

  5. Computational Analysis of the Optical and Charge Transport Properties of Ultrasonic Spray Pyrolysis-Grown Zinc Oxide/Graphene Hybrid Structures

    NASA Astrophysics Data System (ADS)

    Ali, Amgad Ahmed; Hashim, Abdul Manaf

    2016-05-01

    We demonstrate a systematic computational analysis of the measured optical and charge transport properties of the spray pyrolysis-grown ZnO nanostructures, i.e. nanosphere clusters (NSCs), nanorods (NRs) and nanowires (NWs) for the first time. The calculated absorbance spectra based on the time-dependent density functional theory (TD-DFT) shows very close similarity with the measured behaviours under UV light. The atomic models and energy level diagrams for the grown nanostructures were developed and discussed to explain the structural defects and band gap. The induced stresses in the lattices of ZnO NSCs that formed during the pyrolysis process seem to cause the narrowing of the gap between the energy levels. ZnO NWs and NRs show homogeneous distribution of the LUMO and HOMO orbitals all over the entire heterostructure. Such distribution contributes to the reduction of the band gap down to 2.8 eV, which has been confirmed to be in a good agreement with the experimental results. ZnO NWs and NRs exhibited better emission behaviours under the UV excitation as compared to ZnO NSCs and thin film as their visible range emissions are strongly quenched. Based on the electrochemical impedance measurement, the electrical models and electrostatic potential maps were developed to calculate the electron lifetime and to explain the mobility or diffusion behaviours in the grown nanostructure, respectively.

  6. 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.

  7. 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.

  8. 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.

  9. FAST TRACK COMMUNICATION: Electronic structure of a graphene/hexagonal-BN heterostructure grown on Ru(0001) by chemical vapor deposition and atomic layer deposition: extrinsically doped graphene

    NASA Astrophysics Data System (ADS)

    Bjelkevig, Cameron; Mi, Zhou; Xiao, Jie; Dowben, P. A.; Wang, Lu; Mei, Wai-Ning; Kelber, Jeffry A.

    2010-08-01

    A significant BN-to-graphene charge donation is evident in the electronic structure of a graphene/h-BN(0001) heterojunction grown by chemical vapor deposition and atomic layer deposition directly on Ru(0001), consistent with density functional theory. This filling of the lowest unoccupied state near the Brillouin zone center has been characterized by combined photoemission/k vector resolved inverse photoemission spectroscopies, and Raman and scanning tunneling microscopy/spectroscopy. The unoccupied σ*(Γ1 +) band dispersion yields an effective mass of 0.05 me for graphene in the graphene/h-BN(0001) heterostructure, in spite of strong perturbations to the graphene conduction band edge placement.

  10. Structural and magnetic properties of GaMnAs layers with high Mn-content grown by migration-enhanced epitaxy on GaAs(100) substrates

    NASA Astrophysics Data System (ADS)

    Sadowski, J.; Mathieu, R.; Svedlindh, P.; Domagała, J. Z.; Bak-Misiuk, J.; Światek, K.; Karlsteen, M.; Kanski, J.; Ilver, L.; Åsklund, H.; Södervall, U.

    2001-05-01

    Ferromagnetic GaMnAs containing up to 10% Mn has been grown by migration-enhanced epitaxy at a substrate temperature of 150 °C. The lattice constant of hypothetical zinc-blende structure MnAs is determined to be 5.90 Å, which deviates somewhat from previously reported values. This deviation is ascribed to growth-condition-dependent density of point defects. Magnetization measurements showed an onset of ferromagnetic ordering around 75 K for the GaMnAs layer with 10% Mn. This means that the trend of falling Curie temperatures with increasing Mn concentrations above 5.3% is broken.

  11. Prediction of the structure of a novel amylopectin-based Cd-associated molecule in the stem of common reed grown in the presence of Cd.

    PubMed

    Higuchi, Kyoko; Ito, Naho; Nukada, Tomoo

    2016-10-01

    We previously found a novel Cd-associated molecule with an apparent molecular weight of 10-50 kDa in common reeds grown in the presence of Cd. The partial structure of this molecule was predicted by enzymatic digestion to release Cd from a trace amount that had been partially purified from the cell sap. The major component was branched α-glucan, whereas a peptide, β-1,4 glucan, and mannose were found as minor components. Uronic acids appeared to provide functional groups that bind Cd. PMID:27296512

  12. A TEM investigation of the nucleation, growth and structure of HWE grown lead-tin telluride films

    NASA Astrophysics Data System (ADS)

    Snyman, H. C.; Gouws, G. J.; Muller, R. J.

    1984-12-01

    The epitaxial growth of thin films is usually explained in terms of the interfacial energy of the critical nucleus. In a systematic TEM study of the nucleation and growth of (PbSn)Te on (111) BaF 2 substrates strong evidence is found that the post nucleation stage of recrystallisation and reorientation, rather than nucleation, is dominant in determining the degree of epitaxy. Thin films of various thicknesses were grown, in a hot wall epitaxial (HWE) system, onto (111) BaF 2 substrates at 250°C. Using dark field techniques and microdiffraction the recrystallisation processes and degree of epitaxy were studied as a function of overgrowth thickness. It was found that the degree of epitaxy was critically dependent on the film thickness. Films grown on pre-baked substrates changed from completely polycrystalline at an average thickness of 10 nm to a good epitaxially oriented overgrowth at 150 nm. The driving force for this recrystallisation process is explained in terms of the relative stability of (001) and (111) islands. Electron microscopy and microdiffraction provides direct confirmation of the proposed mechanism and its direction.

  13. 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.

  14. 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.

  15. 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

  16. 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

  17. Structural and Electrical Properties of EOT HfO2 (<1 nm) Grown on InAs by Atomic Layer Deposition and Its Thermal Stability.

    PubMed

    Kang, Yu-Seon; Kang, Hang-Kyu; Kim, Dae-Kyoung; Jeong, Kwang-Sik; Baik, Min; An, Youngseo; Kim, Hyoungsub; Song, Jin-Dong; Cho, Mann-Ho

    2016-03-23

    We report on changes in the structural, interfacial, and electrical characteristics of sub-1 nm equivalent oxide thickness (EOT) HfO2 grown on InAs by atomic layer deposition. When the HfO2 film was deposited on an InAs substrate at a temperature of 300 °C, the HfO2 was in an amorphous phase with an sharp interface, an EOT of 0.9 nm, and low preexisting interfacial defect states. During post deposition annealing (PDA) at 600 °C, the HfO2 was transformed from an amorphous to a single crystalline orthorhombic phase, which minimizes the interfacial lattice mismatch below 0.8%. Accordingly, the HfO2 dielectric after the PDA had a dielectric constant of ∼24 because of the permittivity of the well-ordered orthorhombic HfO2 structure. Moreover, border traps were reduced by half than the as-grown sample due to a reduction in bulk defects in HfO2 dielectric during the PDA. However, in terms of other electrical properties, the characteristics of the PDA-treated sample were degraded compared to the as-grown sample, with EOT values of 1.0 nm and larger interfacial defect states (Dit) above 1 × 10(14) cm(-2) eV(-1). X-ray photoelectron spectroscopy data indicated that the diffusion of In atoms from the InAs substrate into the HfO2 dielectric during the PDA at 600 °C resulted in the development of substantial midgap states. PMID:26928131

  18. Correlation of Crystalline and Structural Properties of C60 Thin Films Grown at Various Temperature with Charge Carrier Mobility

    SciTech Connect

    Singh,T.; Sarciftci, N.; Yang, H.; Yang, L.; Plochberger, B.; Sitter, H.

    2007-01-01

    Transistors fabricated from C{sub 60} films grown by hot wall epitaxy at higher substrate temperature, showed an order of magnitude increased charge carrier mobility up to 6 cm{sup 2}/V s. In this letter, the authors present an extensive study of morphology and crystallinity of the fullerene films using atomic force microscopy and grazing-incidence x-ray diffraction. A clear correlation of crystalline quality of the C{sub 60} film and charge carrier mobility was found. A higher substrate temperature leads to a single crystal-like faceted fullerene crystals. The high crystalline quality solely brings a drastic improvement in the charge carrier mobility. A gate voltage independent mobility is also observed in these devices which can be attributed to the highly conjugated nature of the C{sub 60} thin film.

  19. Interfacial mixing and internal structure of Pt-containing nanocomposites grown by room temperature electron beam induced deposition

    SciTech Connect

    Li Juntao; Dunn, Kathleen A.; Thiel, Bradley L.; Toth, Milos

    2010-05-15

    Material grown by room temperature electron beam induced deposition (EBID) using (CH{sub 3}){sub 3}CH{sub 3}C{sub 5}H{sub 4}Pt precursor consists of platinum nanocrystals embedded in an amorphous matrix. The crystallites are shown to intermix with the amorphous oxide on a Si substrate. The extent of intermixing scales with the electron energy density delivered to the material during growth. Dependencies on electron flux, fluence, and exposure time indicate that the intermixing process is athermal, electron-activated, and rate limited by mass transport inside the solid. Furthermore, the degree of deposit crystallinity is shown to scale with the electron flux and fluence used for EBID. We discuss mechanisms behind the observed changes in nanostructure and implications for the growth of functional materials by EBID.

  20. Probing the chemical structure of monolayer covalent-organic frameworks grown via Schiff-base condensation reactions.

    PubMed

    Hu, Ya; Goodeal, Niall; Chen, Ying; Ganose, Alex M; Palgrave, Robert G; Bronstein, Hugo; Blunt, Matthew O

    2016-08-01

    Two-dimensional covalent-organic frameworks (2D-COFs) on surfaces offer a facile route to new 2D materials. Schiff-base condensation reactions have proven to be an effective fabrication route for such materials. We present scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) studies of porphyrin 2D-COFs grown at a solid-vapour interface. XPS shows that covalent links between porphyrins consist of a mixture of imines and hemiaminals, a non-conjugated intermediate in the Schiff-base condensation reaction. These results demonstrate that environmental conditions during growth can have an important impact on the chemical composition of Schiff-base 2D-COFs. PMID:27436064

  1. 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}.

  2. Anisotropic structural and optical properties of semi-polar (11-22) GaN grown on m-plane sapphire using double AlN buffer layers

    NASA Astrophysics Data System (ADS)

    Zhao, Guijuan; Wang, Lianshan; Yang, Shaoyan; Li, Huijie; Wei, Hongyuan; Han, Dongyue; Wang, Zhanguo

    2016-02-01

    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.

  3. Anisotropic structural and optical properties of semi-polar (11-22) GaN grown on m-plane sapphire using double AlN buffer layers.

    PubMed

    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

  4. 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

  5. The management of stress in MOCVD-grown InGaN/GaN LED multilayer structures on Si(1 1 1) substrates

    NASA Astrophysics Data System (ADS)

    Jiang, Quanzhong; Allsopp, Duncan W. E.; Bowen, Chris R.; Wang, Wang N.

    2013-09-01

    The tensile stress in light-emitting diode (LED)-on-Si(1 1 1) multilayer structures must be reduced so that it does not compromise the multiple quantum well emission wavelength uniformity and structural stability. In this paper it is shown for non-optimized LED structures grown on Si(1 1 1) substrates that both emission wavelength uniformity and structural stability can be achieved within the same growth process. In order to gain a deeper understanding of the stress distribution within such a structure, cross-sectional Raman and photo-luminescence spectroscopy techniques were developed. It is observed that for a Si:GaN layer grown on a low-temperature (LT) AlN intermediate layer there is a decrease in compressive stress with increasing Si:GaN layer thickness during MOCVD growth which leads to a high level of tensile stress in the upper part of the layer. This may lead to the development of cracks during cooling to room temperature. Such a phenomenon may be associated with annihilation of defects such as dislocations. Therefore, a reduction of dislocation intensity should take place at the early stage of GaN growth on an AlN or AlGaN layer in order to reduce a build up of tensile stress with thickness. Furthermore, it is also shown that a prolonged three dimensional GaN island growth on a LT AlN interlayer for the reduction of dislocations may result in a reduction in the compressive stress in the resulting GaN layer.

  6. 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.

  7. InP/InGaAs/InP DHBT structures with high carbon-doped base grown by gas source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Teng, Teng; Xu, Anhuai; Ai, Likun; Sun, Hao; Qi, Ming

    2013-09-01

    A new InP/InGaAs/InP DHBT structure with high carbon (C)-doped base was optimized and grown successfully by gas source molecular beam epitaxy (GSMBE) in this work. The C-doping concentration is 3×1019 cm-3 with carrier mobility of 66.3 cm2/V s. Characteristics of C-doped InGaAs materials were investigated. High quality InP/InGaAs/InP DHBT structural materials were obtained. The InP/InGaAs/InP DHBT device with emitter area of 100×100 μm2 was fabricated. The open base breakdown voltage (VBCEO) of 4.2 V and current gain of 60 at VCE of 3.0 V were achieved. All these results prove the material is suitable for DHBT device fabrication.

  8. Study of the optical properties and structure of ZnSe/ZnO thin films grown by MOCVD with varying thicknesses

    NASA Astrophysics Data System (ADS)

    Jabri, S.; Amiri, G.; Sallet, V.; Souissi, A.; Meftah, A.; Galtier, P.; Oueslati, M.

    2016-05-01

    ZnSe layers were grown on ZnO substrates by the metal organic chemical vapor deposition technique. A new structure appeared at lower thicknesses films. The structural properties of the thin films were studied by the X-ray diffraction (XRD) and Raman spectroscopy methods. First, Raman selection rules are explicitly put forward from a theoretical viewpoint. Second, experimentally-retrieved-intensities of the Raman signal as a function of polarization angle of incident light are fitted to the obtained theoretical dependencies in order to confirm the crystallographic planes of zinc blend ZnSe thin film, and correlate with DRX measurements. Raman spectroscopy has been used to characterize the interfacial disorder that affects energy transport phenomena at ZnSe/ZnO interfaces and the Photoluminescence (PL) near the band edge of ZnSe thin films.

  9. Effects of decreased pH on membrane structural organization of Escherichia coli grown in different fatty acid-supplemented media: a 31P NMR study.

    PubMed

    Ianzini, F; Guidoni, L; Simone, G; Viti, V; Yatvin, M B

    1990-04-01

    Total membranes from Escherichia coli cells grown in different fatty acid-supplemented media have been examined by 31P NMR at different pH values. The isolated inner and outer membranes were also studied and compared to the liposomes formed with the corresponding extracted lipids. While the liposomes show structures that are correlated with lipid composition, degree of fatty acid unsaturation, and pH, the membrane structure is mainly bilayer. The presence of two bilayer phases characterized by different chemical shift anisotropy values (delta nu csa) is detectable at neutral pH; a perturbation of the bilayer phase characterized by the smallest delta nu csa is produced by low pH. Moreover, an isotropic peak is always present in the membrane NMR spectra: its attribution to cardiolipin molecules is discussed on the basis of digestion experiments with phospholipase C. PMID:2181934

  10. 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.

  11. Temperature dependent surface photovoltage spectroscopy characterization of highly strained InGaAs/GaAs double quantum well structures grown by metal organic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Chan, C. H.; Wu, J. D.; Huang, Y. S.; Su, Y. K.; Tiong, K. K.

    2009-08-01

    Highly strained InxGa1-xAs/GaAs double quantum well (DQW) structures grown by metal organic vapor phase epitaxy with different In compositions are investigated by surface photovoltage spectroscopy (SPS) in the temperature range 20-300 K. A lineshape fit of spectral features in the differential surface photovoltage (SPV) spectra determines the transition energies accurately. A comprehensive analysis of the anomalous phenomena appearing in lower temperature SPV spectra enable us to evaluate directly the band lineup of DQW and to remove the ambiguity in the identification of spectral features. The process of separation of carriers within the QW with possible capture by the interface defect traps plays an important role for phase change in SPV signal in the vicinity of light-hole related feature at low temperature. The results demonstrate the considerable diagnostic values of the SPS technique for characterizing these highly strained DQW structures.

  12. Optical properties of CdTe- Cd0.90Mn0.10Te multiple quantum well structures grown by pulsed laser evaporation and epitaxy

    NASA Astrophysics Data System (ADS)

    Dubowski, J. J.; Roth, A. P.; Deleporte, E.; Peter, G.; Feng, Z. C.; Perkowitz, S.

    1992-02-01

    Low-temperature photoluminescence, photoluminescence excitation and Raman spectroscopy measurements of CdTeCd 0.90Mn 0.10Te multiple quantum well (MQW) structures grown by pulsed laser evaporation and epitaxy (PLEE) on (001) Cd 1- xZn xTe substrates are carried out. The samples are grown from fluxes of Cd-Te and Cd-Mn-Te provided by ablation of solid CdTe and Cd 0.93Mn 0.07Te targets with Nd:YAG and excimer XeCl lasers, respectively. The excitonic lines corresponding to the quantum well E 1-HH 1 transition are investigated. Comparison between the observed PL excitonic emissions and calculated energy levels using a Kronig-Penney model with the well width as a fitting parameter allowed us to determine the "optical" well widths of the samples and to compare them with those determined from secondary ion mass spectroscopy in-depth profiles. Raman spectra for non-resonance excitation at 501.7 nm are dominated by the CdTe-like longitudinal optical (LO) modes at 166 cm -1 and MnTe-like LO modes at 194 cm -1 from the Cd 0.90Mn 0.10Te barriers. Under resonance conditions, with excitation at 476.5 nm the CdTe LO, 2LO and 3LO modes from the wells near 170,340 and 510 cm -1 dominate the spectra. The results clearly indicate that the PLEE-grown MQWs have the characteristics of the best currently available material.

  13. The electrical, optical, and structural properties of GaN epitaxial layers grown on Si(111) substrate with SiN interlayers

    NASA Astrophysics Data System (ADS)

    Arslan, Engin; Duygulu, Özgür; Kaya, Ali Arslan; Teke, Ali; Özçelik, Süleyman; Ozbay, Ekmel

    2009-12-01

    The effect of the in situ substrate nitridation time on the electrical, structural and optical properties of GaN films grown on Si(111) substrates by metal organic chemical vapor deposition (MOCVD) was investigated. A thin buffer layer of silicon nitride (SiN x) with various thicknesses was achieved through the nitridation of the substrate at different nitridation times ranging from 0 to 660 s. The surface roughness of the GaN film, which was grown on the Si substrate 10 s, exhibited a root mean square (RMS) value of 1.12 nm for the surface roughness. However, further increments in the nitridation times in turn cause increments in the surface roughness in the GaN layers. The number of threading dislocation (TD) was counted from plan-view TEM (Transmission Electron Microscopy) images. The determined density of these threading dislocations was of the order of 9×10 9 cm -2. The sheet resistances of the GaN layers were measured. The average sheet resistance significantly increases from 2867 Ω sq -1 for sample A (without nitridation) to 8124 Ω sq -1 for sample F (with 660 s nitridation). The photoluminescence (PL) measurements of the samples nitridated at various nitridation times were done at a temperature range of 10-300 K. A strong band edge PL emission line, which was centered at approx. 3.453 eV along with its phonon replicas which was separated by approx. 92 meV in successive orders, was observed at 10 K. The full width at half maximum (FWHM) of this peak is approx. 14 meV, which indicates the reasonable optical quality of the GaN epilayers grown on Si substrate. At room temperature, the peak position and FWHM of this emission became 3.396 eV and 58 meV, respectively.

  14. Morphology and structure of photosensitive dye J-aggregates adsorbed on AgBr microcrystals grown in gelatin.

    PubMed

    Saijo, H; Shiojiri, M

    1998-07-15

    Though the cyanine dye J-aggregates carry the role to sense the exposing light in the silver halide photographic system, little research on the morphology of the aggregates in adsorption has been made with modern surface analytical methods. In this paper, we describe the size, epitaxy, multi-layered array formation, nucleation and preferential adsorption, and irregular distribution of population between particles and the segregation on a particle, of J-aggregates adsorbed on AgBr grown in gelatin. We employed cathodoluminescence microscopy, low energy high resolution scanning electron microscopy, and atomic force microscopy. Dye molecules aggregate together near the surface of AgBr and adsorb on the surface. The growth of adsorbed aggregates is controlled by the diffusion of dye molecules from the surrounding solution. The population of J-aggregates adsorbed on an AgBr particle varies from almost none to full coverage. Each aggregate is about (20-30) x (30-50) nm in size and is 2.1 nm thick for thiacarbocyanine with sodium ion, 1.04 nm for thiacarbocyanine with tosyl ion, and 0.5 nm for an oxacarbocyanine. The aggregates connect their longer edges to each other to form arrays, and the arrays build up multi-layered stacks. The arrays align parallel and segregate to form terraces. The longer edges of J-aggregates align along [210] on AgBr (100) or [632] on AgBr (111). PMID:9728883

  15. 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.

  16. Electrical and structural properties of buried CoSi2 layers in Si(100) grown by molecular beam allotaxy

    NASA Astrophysics Data System (ADS)

    Dolle, M.; Gassig, U.; Bay, H. L.; Schueppen, A.; Mantl, S.

    1994-12-01

    Buried, single-crystal CoSi2 layers in Si(100) were fabricated by molecular beam allotaxy, a new two-step method to fabricate buried epitaxial layers. At first CoSi2 precipitates embedded in Si(100) were grown in a molecular beam system. In a second step a continuous, buried silicide layer was formed by rapid thermal annealing. Buried layers with thicknesses ranging from 27 to 224 nm were fabricated and investigated by transmission electron microscopy, Rutherford backscattering, He ion channelling and various electrical methods. Electrical resistivity measurements between 4.2 and 300 K revealed a specific resistivity of 14 micro-Ohm cm at room temperature and 1 micro-Ohm cm at 4.2 K. The temperature dependence follows the Bloch-Grueneisen relation. The resistivity increases with decreasing layer thickness. Schottky diodes were fabricated and characterized using I-V and I-T methods. Excellent diodes were produced with barrier heights of 0.64+/-0.03 eV and idealities of 1.08.

  17. 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.

  18. Hole trapping in thermal oxides grown under various oxidation conditions using avalanche injection in poly-silicon gate structures

    NASA Astrophysics Data System (ADS)

    Anand, K. V.; Cairns, B. R.; Strain, R. J.

    1985-03-01

    I/v data (where I is the dc current and v is the maximum value of the ac applied voltage across the device) was analyzed with respect to the theory and it was shown that the hole temperature not only depends on the substrate doping density and the electric field as measured by the Delta V subscript FB is not only a characteristic of the way that an oxide is grown and annealed, but it also depends on the quality of the substrate and its detailed thermal history. This substrate effect shows itself in the I/v characteristic of a particular device. If the dc current Idc was kept constant at a particular level (as was the case for our experiments), then the v value would represent the temperature of the hot carriers. Since the evidence suggests that the hot carriers generate trap levels, then any change in carrier temperature would reflect in Delta V subscript FB. These substrate related effects were found to be significant.

  19. Structure and polymer form of poly-3-hydroxyalkanoates produced by Pseudomonas oleovorans grown with mixture of sodium octanoate/undecylenic acid and sodium octanoate/5-phenylvaleric acid.

    PubMed

    Ho, I-Ching; Yang, Sheng-Pin; Chiu, Wen-Yen; Huang, Shih-Yow

    2007-01-30

    PHAs (poly-3-hydroxyalkanoates) obtained by Pseudomonas oleovorans grown with mixed carbon sources were investigated. Mixed carbon sources were sodium octanoate/undecylenic acid and sodium octanoate/5-phenylvaleric acid. Effect of carbon source in pre-culture on PHAs structure was investigated. Main fermentation was conducted with mixture of sodium octanoate/undecylenic acid, and PHA contained both saturated and unsaturated units. When more undecylenic acid was used in the medium, the ratio of unsaturated unit increased and the T(g) of the products also changed. The PHA grown with mixture of sodium octanoate and undecylenic acid was a random copolymer, which was determined by DSC analysis. Using mixed carbon sources of sodium octanoate and 5-phenylvaleric acid, highest dry cell weight and PHA concentration were obtained when 0.02g or 0.04g of 5-phenylvaleric acid were added in 50mL medium. Cultured with sodium octanoate and 5-phenylvaleric acid, PHA containing HO (3-hydroxyoctanoate) unit and HPV (3-hydroxy-5-phenylvalerate) unit was produced. T(g) of the products fell between those of pure PHO and pure PHPV. By means of DSC analysis and fractionation method, the PHA obtained was regarded as a random copolymer. PMID:16919325

  20. Structural and Magnetotransport Studies of MBE-grown Pn(Sn)Te films and PbTe:Bi/CdTe Quantum Wells

    NASA Astrophysics Data System (ADS)

    Li, Xiang; Liu, Xinyu; Furdyna, Jacek; Dobrowolska, Malgorzata; Wojtowicz, Tomasz

    2014-03-01

    Recent studies confirmed the existence of topological crystalline insulators (TCIs), in which crystalline symmetry replaces the role of time-reversal symmetry in ensuring topological protection. In the narrow-gap semiconductor TCIs, chemical potential can be tuned by modifications of crystal growth and/or annealing to yield n-type or p-type conductivity, which makes them especially well-suited for magnetotransport measurements. In this work, we have grown a series of Pb1-xSnxTe films and PbTe:Bi/CdTe QWs on CdTe/GaAs(100) substrates using MBE. Structural studies of these thin films were carried out using XRD and SEM techniques. XRD results shows satisfactory crystal quality of Pb(Sn)Te films grown on CdTe. SEM studies show the presence of inclusions in the films, indicating that the crystal quality still requires improvement. Magnetostransport studies of PbTe:Bi/CdTe QWs suggests that Bi acts as a donor in PbTe, and the electron mobility in the 2D electron gas in the QW depends on the growth conditions, such as substrate temperature. The study of Pb1-xSnxTe QWs is currently underway, and will also be discussed in this talk.

  1. Structural and magnetoelectric properties of Ga2-xFexO3 single crystals grown by a floating-zone method

    NASA Astrophysics Data System (ADS)

    Arima, T.; Higashiyama, D.; Kaneko, Y.; He, J. P.; Goto, T.; Miyasaka, S.; Kimura, T.; Oikawa, K.; Kamiyama, T.; Kumai, R.; Tokura, Y.

    2004-08-01

    Lattice-structural, magnetic, and magnetoelectric (ME) properties have been investigated for single crystals of prototypical polar ferrimagnet Ga2-xFexO3 (0.8⩽x⩽1.4) as melt-grown by a floating-zone (FZ) method. Magnetization measurements show that the saturated magnetization as well as the ferrimagnetic phase transition temperature (TC) increases with as increase of Fe content x , while the coercive force decreases. A neutron powder diffraction study indicates fairly low ordering of Ga and Fe arrangement at cation sites, which is likely related to the lower TC in the FZ crystals than in the corresponding flux-grown crystals. Coefficients of linear and quadratic ME effects have been obtained with measurements of change in electric polarization induced by sweeping a magnetic field. Electric polarization was largely modulated in a magnetic field applied parallel to the direction of spontaneous magnetization, but not in a field parallel to that of the spontaneous polarization. A simple model to explain the sharp contrast is presented.

  2. Effect of post-annealing temperature on structural and optical properties of ZnO thin films grown on mica substrates using sol-gel spin-coating

    NASA Astrophysics Data System (ADS)

    Kim, Younggyu; Leem, Jae-Young

    2015-09-01

    ZnO thin films were grown on flexible muscovite mica substrates using sol-gel spin-coating. The structural and optical properties of the sol-gel-derived ZnO thin films annealed at temperatures between 300 - 600 °C were investigated. The surface morphology of the ZnO thin films was found to depend slightly on the annealing temperature. In the photoluminescence spectra, the position of the near-band-edge (NBE) peak was shifted towards a lower energy by the post-annealing process, and the full width at half maximum (FWHM) values of the NBE peaks for the annealed ZnO thin films were significantly lower than those for the as-grown film. Defect-related deep-level peaks exhibiting green and red emissions were observed only for the annealed ZnO thin films. The Urbach energy and optical band gap of the films decreased with an increase in annealing temperatures up to 500 °C.

  3. Effect of multilayer barriers on the optical properties of GaInNAs single quantum-well structures grown by metalorganic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Sun, H. D.; Clark, A. H.; Calvez, S.; Dawson, M. D.; Kim, K. S.; Kim, T.; Park, Y. J.

    2005-07-01

    We report on the effects of combined strain-compensating and strain-mediating layers of various widths on the optical properties of 1.3 μm GaInNAs/GaAs single quantum well structures grown by metalorganic vapor phase epitaxy (MOVPE). While the emission wavelength of GaInNAs/GaAs quantum wells can be redshifted by the adoption of strain-compensated GaNAs layers, the material quality is degraded by the increased stress at the well/barrier interface. This detrimental effect can be cured by inserting a strain-mediating InGaAs layer between them. Contrary to what is expected, however, the emission wavelength is blueshifted by the insertion of the InGaAs layer, which is attributed to the reduced N incorporation due to the improved interface quality. Our results indicate that the optical properties of MOVPE-grown GaInNAs/GaAs quantum wells can be optimized in quantum efficiency and emission wavelength by combination of strain-compensating and strain-mediating layers with suitable characteristics.

  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. Comparison of luminescent efficiency of InGaAs quantum well structures grown on Si, GaAs, Ge, and SiGe virtual substrate

    NASA Astrophysics Data System (ADS)

    Yang, V. K.; Ting, S. M.; Groenert, M. E.; Bulsara, M. T.; Currie, M. T.; Leitz, C. W.; Fitzgerald, E. A.

    2003-05-01

    In order to study the luminescent efficiency of InGaAs quantum wells on Si via SiGe interlayers, identical In0.2Ga0.8As quantum well structures with GaAs and Al0.25Ga0.75As cladding layers were grown on several substrates by an atmospheric metalorganic vapor deposition system. The substrates used include GaAs, Si, Ge, and SiGe virtual substrates. The SiGe virtual substrates were graded from Si substrates to 100% Ge content. Because of the small lattice mismatch between GaAs and Ge (0.07%), high-quality GaAs-based thin films with threading dislocation densities <3×106 cm-2 were realized on these SiGe substrates. Quantitative cathodoluminescence was used to compare the luminescent efficiency of the quantum well structure on the different substrates and cross-sectional transmission electron microscopy was used to characterize dislocation densities. Our results show that the InGaAs quantum wells grown on the GaAs substrates have the highest luminescent efficiencies due to the lowest dislocation densities. Interestingly, InGaAs quantum wells grown on the SiGe virtual substrates outperform those on Ge substrates, both in terms of luminescent efficiency and dislocation density. This difference is attributed to the variation in thermal expansion coefficient (α) and its impact on defect structure during the process cycle. The SiGe virtual substrate has a smaller α compared to a Ge substrate because of the smaller α of the Si substrate, which helps minimize compressive strain in the quantum well layer during the temperature decrease from the growth temperature. Consequently, fewer misfit dislocations are created between the quantum well and cladding interfaces. These misfits can greatly affect the luminescent efficiency since they can act as recombination sites. In general, the efficiencies of the quantum wells on the SiGe and Ge substrates were affected only by higher misfit dislocation densities, whereas the quantum wells on the Si substrate had low efficiency due to

  6. A comparative study of blue, green and yellow light emitting diode structures grown by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Ramaiah, Kodigala Subba; Su, Y. K.; Chang, S. J.; Chen, C. H.

    2006-02-01

    The blue, green and yellow light emitting diode (LED) structures have been fabricated by metal organic chemical vapor deposition (MOCVD), and characterized by using different techniques, in order to understand the mechanism between these LEDs. Atomic force microscopy (AFM) analysis revealed that the surface roughness value and density of etch pits were different in the blue, green and yellow LEDs. The threading, misfit dislocations, interfacial dislocations, nano-pipe-like structures and quantum dot-like structures, which determine quality of the structures, were observed by transmission electron microscope (TEM) in the LED structures. The reasons for their formation in the layers are now elucidated. The indium composition, period width such as well and barrier widths were determined by simulating experimental high resolution X-ray diffraction (HRXRD) spectra. The In composition obtained by HRXRD and photoluminescence (PL) measurements for the same LED structure was not one and the same due to several reasons. In fact, the InGaN quantum well emission peaks at 2.667 and 2.544 eV of the blue and green LEDs, respectively showed S-shaped character shift, whereas the quantum well peak at 2.219 eV of yellow LEDs did not show any shift in the PL spectra with decreasing temperature. The blue, green and yellow LEDs showed different activation energies.

  7. The relationship between electrical and structural characteristics of CdTe and CdMnTe layers grown on InSb

    NASA Astrophysics Data System (ADS)

    Ashenford, D.; Hogg, J. H. C.; Lunn, B.; Scott, C. G.

    1991-06-01

    CdTe and CdMnTe layers with thickness in the range 1-2 μm have been grown by MBE on (001) InSb substrates. Measurements of the free-carrier concentration as a function of depth through these layers have revealed non-unformities attributed to the presence of extended defects arising from the relief of lattice strain resulting from the epilayer-substrate lattice mismatch. Evidence for the existence of such structural non-uniformity has been provided by DCXRD rocking curve measurements. Detailed analysis of these curves also indicates the presence of a thin interfacial layer of a different phase. The use of an excess Cd flux during growth has been found to lead to increased and more uniform carrier densities in both undoped and In doped layers.

  8. 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.

  9. Structural and electrical transport properties of MOVPE-grown pseudomorphic AlAs/InGaAs/InAs resonant tunneling diodes on InP substrates

    NASA Astrophysics Data System (ADS)

    Sugiyama, Hiroki; Teranishi, Atsushi; Suzuki, Safumi; Asada, Masahiro

    2014-03-01

    We report metal-organic vapor-phase epitaxy (MOVPE) growth of pseudomorphic AlAs/InGaAs/InAs resonant tunneling diodes (RTDs) on InP substrates for the first time. X-ray diffraction (XRD) measurements and transmission electron microscopy (TEM) observations reveal that a uniform strained InAs subwell is coherently grown in the double-barrier (DB) structure. The AlAs/InGaAs/InAs RTDs exhibit excellent current-voltage characteristics with a high peak current density (JP) of around 2 × 105 A/cm2 and peak-to-valley ratio (PVR) of around 6. A comparison with control RTDs consisting of AlAs/In0.8Ga0.2As DB confirms the effectiveness of InAs subwell insertion for the improvement of PVR.

  10. Temporal changes in population genetic diversity and structure in red and white clover grown in three contrasting environments in northern Europe

    PubMed Central

    Collins, Rosemary P.; Helgadóttir, Áslaug; Frankow-Lindberg, Bodil E.; Skøt, Leif; Jones, Charlotte; Skøt, Kirsten P.

    2012-01-01

    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. Methods 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. Key Results 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. Conclusions 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. PMID:22437665