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Sample records for atomically flat single-crystalline

  1. Atomically flat single-crystalline gold nanostructures for plasmonic nanocircuitry.

    PubMed

    Huang, Jer-Shing; Callegari, Victor; Geisler, Peter; Brüning, Christoph; Kern, Johannes; Prangsma, Jord C; Wu, Xiaofei; Feichtner, Thorsten; Ziegler, Johannes; Weinmann, Pia; Kamp, Martin; Forchel, Alfred; Biagioni, Paolo; Sennhauser, Urs; Hecht, Bert

    2010-01-01

    Deep subwavelength integration of high-definition plasmonic nanostructures is of key importance in the development of future optical nanocircuitry for high-speed communication, quantum computation and lab-on-a-chip applications. To date, the experimental realization of proposed extended plasmonic networks consisting of multiple functional elements remains challenging, mainly because of the multi-crystallinity of commonly used thermally evaporated gold layers. This can produce structural imperfections in individual circuit elements that drastically reduce the yield of functional integrated nanocircuits. In this paper we demonstrate the use of large (>100 μm(2)) but thin (<80 nm) chemically grown single-crystalline gold flakes that, after immobilization, serve as an ideal basis for focused ion beam milling and other top-down nanofabrication techniques on any desired substrate. Using this methodology we obtain high-definition ultrasmooth gold nanostructures with superior optical properties and reproducible nano-sized features over micrometre-length scales. Our approach provides a possible solution to overcome the current fabrication bottleneck and realize high-definition plasmonic nanocircuitry.

  2. Short-range surface plasmonics: Localized electron emission dynamics from a 60-nm spot on an atomically flat single-crystalline gold surface.

    PubMed

    Frank, Bettina; Kahl, Philip; Podbiel, Daniel; Spektor, Grisha; Orenstein, Meir; Fu, Liwei; Weiss, Thomas; Horn-von Hoegen, Michael; Davis, Timothy J; Meyer Zu Heringdorf, Frank-J; Giessen, Harald

    2017-07-01

    We experimentally and theoretically visualize the propagation of short-range surface plasmon polaritons using atomically flat single-crystalline gold platelets on silicon substrates. We study their excitation and subfemtosecond dynamics via normal-incidence two-photon photoemission electron microscopy. By milling a plasmonic disk and grating structure into a single-crystalline gold platelet, we observe nanofocusing of the short-range surface plasmon polariton. Localized two-photon ultrafast electron emission from a spot with a smallest dimension of 60 nm is observed. Our novel approach opens the door toward reproducible plasmonic nanofocusing devices, which do not degrade upon high light intensity or heating due to the atomically flat surface without any tips, protrusions, or holes. Our nanofoci could also be used as local emitters for ultrafast electron bunches in time-resolved electron microscopes.

  3. Single Crystalline Film of Hexagonal Boron Nitride Atomic Monolayer by Controlling Nucleation Seeds and Domains.

    PubMed

    Wu, Qinke; Park, Ji-Hoon; Park, Sangwoo; Jung, Seong Jun; Suh, Hwansoo; Park, Noejung; Wongwiriyapan, Winadda; Lee, Sungjoo; Lee, Young Hee; Song, Young Jae

    2015-11-05

    A monolayer hexagonal boron nitride (h-BN) film with controllable domain morphology and domain size (varying from less than 1 μm to more than 100 μm) with uniform crystalline orientation was successfully synthesized by chemical vapor deposition (CVD). The key for this extremely large single crystalline domain size of a h-BN monolayer is a decrease in the density of nucleation seeds by increasing the hydrogen gas flow during the h-BN growth. Moreover, the well-defined shape of h-BN flakes can be selectively grown by controlling Cu-annealing time under argon atmosphere prior to h-BN growth, which provides the h-BN shape varies in triangular, trapezoidal, hexagonal and complex shapes. The uniform crystalline orientation of h-BN from different nucleation seeds can be easily confirmed by polarized optical microscopy (POM) with a liquid crystal coating. Furthermore, seamlessly merged h-BN flakes without structural domain boundaries were evidence by a selective hydrogen etching after a full coverage of a h-BN film was achieved. This seamless large-area and atomic monolayer of single crystalline h-BN film can offer as an ideal and practical template of graphene-based devices or alternative two-dimensional materials for industrial applications with scalability.

  4. Single Crystalline Film of Hexagonal Boron Nitride Atomic Monolayer by Controlling Nucleation Seeds and Domains

    NASA Astrophysics Data System (ADS)

    Wu, Qinke; Park, Ji-Hoon; Park, Sangwoo; Jung, Seong Jun; Suh, Hwansoo; Park, Noejung; Wongwiriyapan, Winadda; Lee, Sungjoo; Lee, Young Hee; Song, Young Jae

    2015-11-01

    A monolayer hexagonal boron nitride (h-BN) film with controllable domain morphology and domain size (varying from less than 1 μm to more than 100 μm) with uniform crystalline orientation was successfully synthesized by chemical vapor deposition (CVD). The key for this extremely large single crystalline domain size of a h-BN monolayer is a decrease in the density of nucleation seeds by increasing the hydrogen gas flow during the h-BN growth. Moreover, the well-defined shape of h-BN flakes can be selectively grown by controlling Cu-annealing time under argon atmosphere prior to h-BN growth, which provides the h-BN shape varies in triangular, trapezoidal, hexagonal and complex shapes. The uniform crystalline orientation of h-BN from different nucleation seeds can be easily confirmed by polarized optical microscopy (POM) with a liquid crystal coating. Furthermore, seamlessly merged h-BN flakes without structural domain boundaries were evidence by a selective hydrogen etching after a full coverage of a h-BN film was achieved. This seamless large-area and atomic monolayer of single crystalline h-BN film can offer as an ideal and practical template of graphene-based devices or alternative two-dimensional materials for industrial applications with scalability.

  5. Single Crystalline Film of Hexagonal Boron Nitride Atomic Monolayer by Controlling Nucleation Seeds and Domains

    PubMed Central

    Wu, Qinke; Park, Ji-Hoon; Park, Sangwoo; Jung, Seong Jun; Suh, Hwansoo; Park, Noejung; Wongwiriyapan, Winadda; Lee, Sungjoo; Lee, Young Hee; Song, Young Jae

    2015-01-01

    A monolayer hexagonal boron nitride (h-BN) film with controllable domain morphology and domain size (varying from less than 1 μm to more than 100 μm) with uniform crystalline orientation was successfully synthesized by chemical vapor deposition (CVD). The key for this extremely large single crystalline domain size of a h-BN monolayer is a decrease in the density of nucleation seeds by increasing the hydrogen gas flow during the h-BN growth. Moreover, the well-defined shape of h-BN flakes can be selectively grown by controlling Cu-annealing time under argon atmosphere prior to h-BN growth, which provides the h-BN shape varies in triangular, trapezoidal, hexagonal and complex shapes. The uniform crystalline orientation of h-BN from different nucleation seeds can be easily confirmed by polarized optical microscopy (POM) with a liquid crystal coating. Furthermore, seamlessly merged h-BN flakes without structural domain boundaries were evidence by a selective hydrogen etching after a full coverage of a h-BN film was achieved. This seamless large-area and atomic monolayer of single crystalline h-BN film can offer as an ideal and practical template of graphene-based devices or alternative two-dimensional materials for industrial applications with scalability. PMID:26537788

  6. Electrochemical Stripping of Atomic Oxygen on Single-Crystalline Platinum: Bridging Gas-Phase and Electrochemical Oxidation

    PubMed Central

    2017-01-01

    To understand the interaction between Pt and surface oxygenated species in electrocatalysis, this paper correlates the electrochemistry of atomic oxygen on Pt formed in the gas phase with electrochemically generated oxygen species on a variety of single-crystal platinum surfaces. The atomic oxygen adsorbed on single-crystalline Pt electrodes, made by thermal dissociation of molecular oxygen, is used for voltammetry measurements in acidic electrolytes (HClO4 and H2SO4). The essential knowledge of coverage, binding energy, and surface construction of atomic oxygen is correlated with the charge, potential, and shape of voltammograms, respectively. The differences of the voltammograms between the oxide made by thermal dissociation of molecular oxygen and electrochemical oxidation imply that atomic oxygen is not an intermediate of the electrochemical oxidation of Pt(111). The reconstruction of (100) terrace and step and the low-potential stripping of atomic oxygen on (111) step site provide insight into the first stages of degradation of Pt-based electrocatalysts. PMID:28225278

  7. Preparation and Loading Process of Single Crystalline Samples into a Gas Environmental Cell Holder for In Situ Atomic Resolution Scanning Transmission Electron Microscopic Observation.

    PubMed

    Straubinger, Rainer; Beyer, Andreas; Volz, Kerstin

    2016-06-01

    A reproducible way to transfer a single crystalline sample into a gas environmental cell holder for in situ transmission electron microscopic (TEM) analysis is shown in this study. As in situ holders have only single-tilt capability, it is necessary to prepare the sample precisely along a specific zone axis. This can be achieved by a very accurate focused ion beam lift-out preparation. We show a step-by-step procedure to prepare the sample and transfer it into the gas environmental cell. The sample material is a GaP/Ga(NAsP)/GaP multi-quantum well structure on Si. Scanning TEM observations prove that it is possible to achieve atomic resolution at very high temperatures in a nitrogen environment of 100,000 Pa.

  8. Modifying single-crystalline silicon by femtosecond laser pulses: an analysis by micro Raman spectroscopy, scanning laser microscopy and atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Bonse, J.; Brzezinka, K.-W.; Meixner, A. J.

    2004-01-01

    The surface modification of single-crystalline silicon induced by single 130 femtosecond (fs) Ti:sapphire laser pulses (wavelength 800 nm) in air is investigated by means of micro Raman spectroscopy (μ-RS), atomic force microscopy and scanning laser microscopy. Depending on the laser fluence, in some regions the studies indicate a thin amorphous top-layer as well as ablated and recrystallized zones. The single-pulse threshold fluences for melting, ablation and polycrystalline recrystallization are determined quantitatively. Several different topographical surface structures (rims and protrusions) are found. Their formation is discussed in the context of recent studies of the laser irradiation of silicon. In combination with a thin-film optical model, the thickness of the amorphous layer is determined by two independent and nondestructive optical methods to be in the order of several 10 nm.

  9. Single crystalline magnetite nanotubes.

    PubMed

    Liu, Zuqin; Zhang, Daihua; Han, Song; Li, Chao; Lei, Bo; Lu, Weigang; Fang, Jiye; Zhou, Chongwu

    2005-01-12

    We descried a method to synthesize single crystalline Fe3O4 nanotubes by wet-etching the MgO inner cores of MgO/Fe3O4 core-shell nanowires. Homogeneous Fe3O4 nanotubes with controllable length, diameter, and wall thickness have been obtained. Resistivity of the Fe3O4 nanotubes was estimated to be approximately 4 x 10-2 Omega cm at room temperature. Magnetoresistance of approximately 1% was observed at T = 77 K when a magnetic field of B = 0.7 T was applied. The synthetic strategy presented here may be extended to a variety of materials such as YBCO, PZT, and LCMO which should provide ideal candidates for fundamental studies of superconductivity, piezoelectricity, and ferromagnetism in nanoscale structures.

  10. Surface properties of atomically flat poly-crystalline SrTiO3

    PubMed Central

    Woo, Sungmin; Jeong, Hoidong; Lee, Sang A.; Seo, Hosung; Lacotte, Morgane; David, Adrian; Kim, Hyun You; Prellier, Wilfrid; Kim, Yunseok; Choi, Woo Seok

    2015-01-01

    Comparison between single- and the poly-crystalline structures provides essential information on the role of long-range translational symmetry and grain boundaries. In particular, by comparing single- and poly-crystalline transition metal oxides (TMOs), one can study intriguing physical phenomena such as electronic and ionic conduction at the grain boundaries, phonon propagation, and various domain properties. In order to make an accurate comparison, however, both single- and poly-crystalline samples should have the same quality, e.g., stoichiometry, crystallinity, thickness, etc. Here, by studying the surface properties of atomically flat poly-crystalline SrTiO3 (STO), we propose an approach to simultaneously fabricate both single- and poly-crystalline epitaxial TMO thin films on STO substrates. In order to grow TMOs epitaxially with atomic precision, an atomically flat, single-terminated surface of the substrate is a prerequisite. We first examined (100), (110), and (111) oriented single-crystalline STO surfaces, which required different annealing conditions to achieve atomically flat surfaces, depending on the surface energy. A poly-crystalline STO surface was then prepared at the optimum condition for which all the domains with different crystallographic orientations could be successfully flattened. Based on our atomically flat poly-crystalline STO substrates, we envision expansion of the studies regarding the TMO domains and grain boundaries. PMID:25744275

  11. Epitaxial growth of homogeneous single-crystalline AlN films on single-crystalline Cu (1 1 1) substrates

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    The homogeneous and crack free single-crystalline AlN thin films have been epitaxially grown on single-crystalline Cu (1 1 1) substrates with an in-plane alignment of AlN [11-20]//Cu [1-10] by pulsed laser deposition (PLD) technology with an integrated laser rastering program. The as-grown AlN films are studied by spectroscopic ellipsometry, field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), polarized light microscopy, high-resolution X-ray diffraction, and high-resolution transmission electron microscopy (HRTEM). The spectroscopic ellipsometry reveals the excellent thickness uniformity of as-grown AlN films on the Cu (1 1 1) substrates with a root-mean-square (RMS) thickness inhomogeneity less than 2.6%. AFM and FESEM measurements indicate that very smooth and flat surface AlN films are obtained with a surface RMS roughness of 2.3 nm. The X-ray reflectivity image illustrates that there is a maximum of 1.2 nm thick interfacial layer existing between the as-grown AlN and Cu (1 1 1) substrates and is confirmed by HRTEM measurement, and reciprocal space mapping shows that almost fully relaxed AlN films are achieved only with a compressive strain of 0.48% within ∼321 nm thick films. This work demonstrates a possibility to obtain homogeneous and crack free single-crystalline AlN films on metallic substrates by PLD with optimized laser rastering program, and brings up a broad prospect for the application of acoustic filters that require abrupt hetero-interfaces between the AlN films and the metallic electrodes.

  12. Atomically flat single terminated oxide substrate surfaces

    NASA Astrophysics Data System (ADS)

    Biswas, Abhijit; Yang, Chan-Ho; Ramesh, Ramamoorthy; Jeong, Yoon H.

    2017-05-01

    Scientific interest in atomically controlled layer-by-layer fabrication of transition metal oxide thin films and heterostructures has increased intensely in recent decades for basic physics reasons as well as for technological applications. This trend has to do, in part, with the coming post-Moore era, and functional oxide electronics could be regarded as a viable alternative for the current semiconductor electronics. Furthermore, the interface of transition metal oxides is exposing many new emergent phenomena and is increasingly becoming a playground for testing new ideas in condensed matter physics. To achieve high quality epitaxial thin films and heterostructures of transition metal oxides with atomically controlled interfaces, one critical requirement is the use of atomically flat single terminated oxide substrates since the atomic arrangements and the reaction chemistry of the topmost surface layer of substrates determine the growth and consequent properties of the overlying films. Achieving the atomically flat and chemically single terminated surface state of commercially available substrates, however, requires judicious efforts because the surface of as-received substrates is of chemically mixed nature and also often polar. In this review, we summarize the surface treatment procedures to accomplish atomically flat surfaces with single terminating layer for various metal oxide substrates. We particularly focus on the substrates with lattice constant ranging from 4.00 Å to 3.70 Å, as the lattice constant of most perovskite materials falls into this range. For materials outside the range, one can utilize the substrates to induce compressive or tensile strain on the films and explore new states not available in bulk. The substrates covered in this review, which have been chosen with commercial availability and, most importantly, experimental practicality as a criterion, are KTaO3, REScO3 (RE = Rare-earth elements), SrTiO3, La0.18Sr0.82Al0.59Ta0.41O3 (LSAT), Nd

  13. Single crystalline mesoporous silicon nanowires

    SciTech Connect

    Hochbaum, A.I.; Gargas, Daniel; Jeong Hwang, Yun; Yang, Peidong

    2009-08-04

    Herein we demonstrate a novel electroless etching synthesis of monolithic, single-crystalline, mesoporous silicon nanowire arrays with a high surface area and luminescent properties consistent with conventional porous silicon materials. These porous nanowires also retain the crystallographic orientation of the wafer from which they are etched. Electron microscopy and diffraction confirm their single-crystallinity and reveal the silicon surrounding the pores is as thin as several nanometers. Confocal fluorescence microscopy showed that the photoluminescence (PL) of these arrays emanate from the nanowires themselves, and their PL spectrum suggests that these arrays may be useful as photocatalytic substrates or active components of nanoscale optoelectronic devices.

  14. Single crystalline mesoporous silicon nanowires.

    PubMed

    Hochbaum, Allon I; Gargas, Daniel; Hwang, Yun Jeong; Yang, Peidong

    2009-10-01

    Herein we demonstrate a novel electroless etching synthesis of monolithic, single-crystalline, mesoporous silicon nanowire arrays with a high surface area and luminescent properties consistent with conventional porous silicon materials. These porous nanowires also retain the crystallographic orientation of the wafer from which they are etched. Electron microscopy and diffraction confirm their single-crystallinity and reveal the silicon surrounding the pores is as thin as several nanometers. Confocal fluorescence microscopy showed that the photoluminescence (PL) of these arrays emanate from the nanowires themselves, and their PL spectrum suggests that these arrays may be useful as photocatalytic substrates or active components of nanoscale optoelectronic devices.

  15. Atomically flat ultrathin cobalt ferrite islands.

    PubMed

    Martín-García, Laura; Quesada, Adrián; Munuera, Carmen; Fernández, Jose F; García-Hernández, Mar; Foerster, Michael; Aballe, Lucía; de la Figuera, Juan

    2015-10-21

    A route for fabricating structurally perfect cobalt ferrite magnetic nanostructures is demonstrated. Ultrathin islands of up to 100 μm(2) with atomically flat surfaces and free from antiphase boundaries are developed. The extremely low defect concentration leads to a robust magnetic order, even for thicknesses below 1 nm, and exceptionally large magnetic domains. This approach allows the evaluation of the influence of specific extrinsic effects on domain wall pinning. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Single crystalline mesoporous silicon nanowires

    SciTech Connect

    Hochbaum, Allon; Dargas, Daniel; Hwang, Yun Jeong; Yang, Peidong

    2009-08-18

    Herein we demonstrate a novel electroless etching synthesis of monolithic, single-crystalline, mesoporous silicon nanowire arrays with a high surface area and luminescent properties consistent with conventional porous silicon materials. The photoluminescence of these nanowires suggest they are composed of crystalline silicon with small enough dimensions such that these arrays may be useful as photocatalytic substrates or active components of nanoscale optoelectronic devices. A better understanding of this electroless route to mesoporous silicon could lead to facile and general syntheses of different narrow bandgap semiconductor nanostructures for various applications.

  17. Liquid crystal deposition on poled, single crystalline lithium niobate

    NASA Astrophysics Data System (ADS)

    Bharath, S. C.; Pimputkar, K. R.; Pronschinske, A. M.; Pearl, T. P.

    2008-01-01

    For the purpose of elucidating the mechanisms for molecular organization at poled ferroelectric surfaces, single crystalline lithium niobate (LN), 'Z-cut' along the (0 0 0 1) plane, has been prepared and characterized and subsequently exposed to liquid crystal molecules. As a model system we chose to study the anchoring of 4- n-octyl-4'-cyanobiphenyl (8CB) to LN. Liquid crystalline films are of interest because of their useful electronic and optical properties as well as chemical sensing attributes. Low-energy electron diffraction (LEED), atomic force microscopy (AFM), surface contact angle measurements (CA), and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface of lithium niobate as well as the nature of 8CB films grown on the surface. Atomically flat LN surfaces were prepared as a support for monolayer thick, 8CB molecular domains. 8CB liquid crystal molecules were deposited by an ambient vaporization technique and the films were analyzed using XPS and CA. Understanding electrostatic anchoring mechanisms and thin film organization for this molecule on uniformly poled surfaces allows for a fuller appreciation of how molecular deposition of other polarizable molecules on periodically poled and patterned poled lithium niobate surfaces would occur.

  18. Single-crystalline monolayer and multilayer graphene nano switches

    SciTech Connect

    Li, Peng; Cui, Tianhong; Jing, Gaoshan; Zhang, Bo; Sando, Shota

    2014-03-17

    Growth of monolayer, bi-layer, and tri-layer single-crystalline graphene (SCG) using chemical vapor deposition method is reported. SCG's mechanical properties and single-crystalline nature were characterized and verified by atomic force microscope and Raman spectroscopy. Electro-mechanical switches based on mono- and bi-layer SCG were fabricated, and the superb properties of SCG enable the switches to operate at pull-in voltage as low as 1 V, and high switching speed about 100 ns. These devices exhibit lifetime without a breakdown of over 5000 cycles, far more durable than any other graphene nanoelectromechanical system switches reported.

  19. Single-crystalline aluminum film for ultraviolet plasmonic nanolasers

    PubMed Central

    Chou, Bo-Tsun; Chou, Yu-Hsun; Wu, Yen-Mo; Chung, Yi-Cheng; Hsueh, Wei-Jen; Lin, Shih-Wei; Lu, Tien-Chang; Lin, Tzy-Rong; Lin, Sheng-Di

    2016-01-01

    Significant advances have been made in the development of plasmonic devices in the past decade. Plasmonic nanolasers, which display interesting properties, have come to play an important role in biomedicine, chemical sensors, information technology, and optical integrated circuits. However, nanoscale plasmonic devices, particularly those operating in the ultraviolet regime, are extremely sensitive to the metal and interface quality. Thus, these factors have a significant bearing on the development of ultraviolet plasmonic devices. Here, by addressing these material-related issues, we demonstrate a low-threshold, high-characteristic-temperature metal-oxide-semiconductor ZnO nanolaser that operates at room temperature. The template for the ZnO nanowires consists of a flat single-crystalline Al film grown by molecular beam epitaxy and an ultrasmooth Al2O3 spacer layer synthesized by atomic layer deposition. By effectively reducing the surface plasmon scattering and metal intrinsic absorption losses, the high-quality metal film and the sharp interfaces formed between the layers boost the device performance. This work should pave the way for the use of ultraviolet plasmonic nanolasers and related devices in a wider range of applications. PMID:26814581

  20. Single-crystalline aluminum film for ultraviolet plasmonic nanolasers

    NASA Astrophysics Data System (ADS)

    Chou, Bo-Tsun; Chou, Yu-Hsun; Wu, Yen-Mo; Chung, Yi-Cheng; Hsueh, Wei-Jen; Lin, Shih-Wei; Lu, Tien-Chang; Lin, Tzy-Rong; Lin, Sheng-Di

    2016-01-01

    Significant advances have been made in the development of plasmonic devices in the past decade. Plasmonic nanolasers, which display interesting properties, have come to play an important role in biomedicine, chemical sensors, information technology, and optical integrated circuits. However, nanoscale plasmonic devices, particularly those operating in the ultraviolet regime, are extremely sensitive to the metal and interface quality. Thus, these factors have a significant bearing on the development of ultraviolet plasmonic devices. Here, by addressing these material-related issues, we demonstrate a low-threshold, high-characteristic-temperature metal-oxide-semiconductor ZnO nanolaser that operates at room temperature. The template for the ZnO nanowires consists of a flat single-crystalline Al film grown by molecular beam epitaxy and an ultrasmooth Al2O3 spacer layer synthesized by atomic layer deposition. By effectively reducing the surface plasmon scattering and metal intrinsic absorption losses, the high-quality metal film and the sharp interfaces formed between the layers boost the device performance. This work should pave the way for the use of ultraviolet plasmonic nanolasers and related devices in a wider range of applications.

  1. Atomically flat nickel film grown on synthetic mica

    NASA Astrophysics Data System (ADS)

    Tanaka, Hiroyuki; Taniguchi, Masateru

    2016-07-01

    We have grown nickel heteroepitaxially on muscovite and synthetic mica in vacuo for use as substrates for scanning probe microscopy (SPM) and graphene formation. We have determined annealing conditions that could generate atomically flat surfaces (with rms surface roughness of less than 1 nm). Owing to accelerated degradation at temperatures above 600 °C, muscovite mica was unsuitable as a substrate at high growth temperatures. Thermally stable synthetic fluorophlogopite mica [KMg3(AlSi3O10)F2], on the other hand, was found to be stable at 800 °C and successfully employed for the formation of atomically flat films.

  2. Atomically flat superconducting nanofilms: multiband properties and mean-field theory

    NASA Astrophysics Data System (ADS)

    Shanenko, A. A.; Aguiar, J. Albino; Vagov, A.; Croitoru, M. D.; Milošević, M. V.

    2015-05-01

    Recent progress in materials synthesis enabled fabrication of superconducting atomically flat single-crystalline metallic nanofilms with thicknesses down to a few monolayers. Interest in such nano-thin systems is attracted by the dimensional 3D-2D crossover in their coherent properties which occurs with decreasing the film thickness. The first fundamental aspect of this crossover is dictated by the Mermin-Wagner-Hohenberg theorem and concerns frustration of the long-range order due to superconductive fluctuations and the possibility to track its impact with an unprecedented level of control. The second important aspect is related to the Fabri-Pérot modes of the electronic motion strongly bound in the direction perpendicular to the nanofilm. The formation of such modes results in a pronounced multiband structure that changes with the nanofilm thickness and affects both the mean-field behavior and superconductive fluctuations. Though the subject is very rich in physics, it is scarcely investigated to date. The main obstacle is that there are no manageable models to study a complex magnetic response in this case. Full microscopic consideration is rather time consuming, if practicable at all, while the standard Ginzburg-Landau theory is not applicable. In the present work we review the main achievements in the subject to date, and construct and justify an efficient multiband mean-field formalism which allows for numerical and even analytical treatment of nano-thin superconductors in applied magnetic fields.

  3. Effective Propagation of Surface Plasmon Polaritons on Graphene-Protected Single-Crystalline Silver Films.

    PubMed

    Hong, Hyun Young; Ha, Jeong Sook; Lee, Sang-Soo; Park, Jong Hyuk

    2017-02-08

    Silver (Ag) is a promising material for manipulation of surface plasmon polaritons (SPPs), due to its optical and electrical properties; however, the intrinsic properties are easily degraded by surface corrosion under atmospheric conditions, restricting its applications in plasmonics. Here, we address this issue via single-crystalline Ag films protected with graphene layers and demonstrate effective propagation of SPPs on the graphene-protected Ag films. Single-crystalline Ag films with atomically flat surfaces are prepared by epitaxial growth; graphene layers are then transferred onto the Ag films. The propagation lengths of SPPs on the graphene-protected Ag films are measured, and their variations under corrosive conditions are investigated. The initial SPP propagation lengths for the bare Ag films are very long (about 50 μm in the wavelength range 550-700 nm). However, the values decrease significantly (11-13 μm) under corrosive conditions. On the contrary, the double-layer-graphene-protected Ag films exhibit SPP propagation lengths of about 23 μm and retain over 90% (21-23 μm) of the propagation lengths even after exposure to corrosive conditions, guaranteeing the reliability of Ag plasmonic devices. This approach can encourage extending the application of the graphene-metal hybrid structure and thus developing Ag plasmonic devices.

  4. A pseudo-single-crystalline germanium film for flexible electronics

    NASA Astrophysics Data System (ADS)

    Higashi, H.; Kasahara, K.; Kudo, K.; Okamoto, H.; Moto, K.; Park, J.-H.; Yamada, S.; Kanashima, T.; Miyao, M.; Tsunoda, I.; Hamaya, K.

    2015-01-01

    We demonstrate large-area (˜600 μm), (111)-oriented, and high-crystallinity, i.e., pseudo-single-crystalline, germanium (Ge) films at 275 °C, where the temperature is lower than the softening temperature of a flexible substrate. A modulated gold-induced layer exchange crystallization method with an atomic-layer deposited Al2O3 barrier and amorphous-Ge/Au multilayers is established. From the Raman measurements, we can judge that the crystallinity of the obtained Ge films is higher than those grown by aluminum-induced-crystallization methods. Even on a flexible substrate, the pseudo-single-crystalline Ge films for the circuit with thin-film transistor arrays can be achieved, leading to high-performance flexible electronics based on an inorganic-semiconductor channel.

  5. A pseudo-single-crystalline germanium film for flexible electronics

    SciTech Connect

    Higashi, H.; Yamada, S.; Kanashima, T.; Hamaya, K.; Kasahara, K.; Park, J.-H.; Miyao, M.; Kudo, K.; Okamoto, H.; Moto, K.; Tsunoda, I.

    2015-01-26

    We demonstrate large-area (∼600 μm), (111)-oriented, and high-crystallinity, i.e., pseudo-single-crystalline, germanium (Ge) films at 275 °C, where the temperature is lower than the softening temperature of a flexible substrate. A modulated gold-induced layer exchange crystallization method with an atomic-layer deposited Al{sub 2}O{sub 3} barrier and amorphous-Ge/Au multilayers is established. From the Raman measurements, we can judge that the crystallinity of the obtained Ge films is higher than those grown by aluminum-induced-crystallization methods. Even on a flexible substrate, the pseudo-single-crystalline Ge films for the circuit with thin-film transistor arrays can be achieved, leading to high-performance flexible electronics based on an inorganic-semiconductor channel.

  6. Atomically Flat Surfaces Developed for Improved Semiconductor Devices

    NASA Technical Reports Server (NTRS)

    Powell, J. Anthony

    2001-01-01

    New wide bandgap semiconductor materials are being developed to meet the diverse high temperature, -power, and -frequency demands of the aerospace industry. Two of the most promising emerging materials are silicon carbide (SiC) for high-temperature and high power applications and gallium nitride (GaN) for high-frequency and optical (blue-light-emitting diodes and lasers) applications. This past year Glenn scientists implemented a NASA-patented crystal growth process for producing arrays of device-size mesas whose tops are atomically flat (i.e., step-free). It is expected that these mesas can be used for fabricating SiC and GaN devices with major improvements in performance and lifetime. The promising new SiC and GaN devices are fabricated in thin-crystal films (known as epi films) that are grown on commercial single-crystal SiC wafers. At this time, no commercial GaN wafers exist. Crystal defects, known as screw defects and micropipes, that are present in the commercial SiC wafers propagate into the epi films and degrade the performance and lifetime of subsequently fabricated devices. The new technology isolates the screw defects in a small percentage of small device-size mesas on the surface of commercial SiC wafers. This enables atomically flat surfaces to be grown on the remaining defect-free mesas. We believe that the atomically flat mesas can also be used to grow GaN epi films with a much lower defect density than in the GaN epi films currently being grown. Much improved devices are expected from these improved low-defect epi films. Surface-sensitive SiC devices such as Schottky diodes and field effect transistors should benefit from atomically flat substrates. Also, we believe that the atomically flat SiC surface will be an ideal surface on which to fabricate nanoscale sensors and devices. The process for achieving atomically flat surfaces is illustrated. The surface steps present on the "as-received" commercial SiC wafer is also illustrated. because of the

  7. Surface electronic structure of single-crystalline zirconium diboride thin films

    NASA Astrophysics Data System (ADS)

    Yamada-Takamura, Y.; Bussolotti, F.; Fleurence, A.; Bera, S.; Friedlein, R.

    2010-03-01

    Single-crystalline thin films of zirconium diboride (ZrB2) with a simple crystal structure consisting of alternating hexagonal close-packed Zr and honeycomb B layers have been epitaxially grown on Si(111) by chemical vapor epitaxy. Oxide layers formed upon exposure to air can be removed by heating in ultra-high vacuum resulting in oxide-free and atomically-flat surfaces making the ZrB2 films ideal for the epitaxial growth of heterostructures in other setups. The electronic structure of the as obtained ZrB2(0001)-(2x2) surface has been studied using angle-resolved ultraviolet photoelectron spectroscopy. Along the γM direction two parabolic features in the vicinity of the Fermi level are clearly resolved. While the dispersion of these Zr-derived surface states is similar to those observed at (1x1) single crystal surfaces and calculated dispersion curves for a Zr-terminated slab model, a pronounced intensity change at the zone boundary is a strong indication of a back-folding of electronic bands into the reduced Brillouin zone. The origin of the (2x2) reconstruction is likely the presence of Si atoms on the surface. A flat band at 0.25 eV is accordingly assigned to localized Si-derived states

  8. Improved Silicon Carbide Crystals Grown From Atomically Flat Surfaces

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.

    2003-01-01

    The NASA Glenn Research Center is demonstrating that atomically flat (i.e., step-free) silicon carbide (SiC) surfaces are ideal for realizing greatly improved wide bandgap semiconductor films with lower crystal defect densities. Further development of these improved films could eventually enable harsh-environment electronics beneficial to jet engine and other aerospace and automotive applications, as well as much more efficient and compact power distribution and control. The technique demonstrated could also improve blue-light lasers and light-emitting-diode displays.

  9. Controlled synthesis of single-crystalline graphene

    SciTech Connect

    Xueshen, Wang Jinjin, Li Qing, Zhong; Yuan, Zhong; Mengke, Zhao; Yonggang, Liu

    2014-03-15

    This paper reports the controlled synthesis of single-crystalline graphene on the back side of copper foil using CH{sub 4} as the precursor. The influence of growth time and the pressure ratio of CH{sub 4}/H{sub 2} on the structure of graphene are examined. An optimized polymer-assisted method is used to transfer the synthesized graphene onto a SiO{sub 2}/Si substrate. Scanning electron microscopy and Raman spectroscopy are used to characterize the graphene.

  10. Co nanoparticle hybridization with single-crystalline Bi nanowires

    NASA Astrophysics Data System (ADS)

    Noh, Jin-Seo; Lee, Min-Kyung; Ham, Jinhee; Lee, Wooyoung

    2011-11-01

    Crystalline Co nanoparticles were hybridized with single-crystalline Bi nanowires simply by annealing Co-coated Bi nanowires at elevated temperatures. An initially near-amorphous Co film of 2-7 nm in thickness began to disrupt its morphology and to be locally transformed into crystallites in the early stage of annealing. The Co film became discontinuous after prolonged annealing, finally leading to isolated, crystalline Co nanoparticles of 8-27 nm in size. This process spontaneously proceeds to reduce the high surface tension and total energy of Co film. The annealing time required for Co nanoparticle formation decreased as annealing temperature increased, reflecting that this transformation occurs by the diffusional flow of Co atoms. The Co nanoparticle formation process was explained by a hole agglomeration and growth mechanism, which is similar to the model suggested by Brandon and Bradshaw, followed by the nanoparticle refinement.

  11. Growth of Atomically Flat DBCO Films Using Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Andrus, Aaron E.; Oh, Seongshik; Davidson, Bruce A.; O'Donnell, Jim; Eckstein, James N.

    2000-03-01

    We have grown atomically flat a-axis dysprosium barium copper oxide (DBCO) films by molecular beam epitaxy (MBE) using a pure ozone source. Such films can be used, for example, to exploit the inherent anisotropy of DBCO in spin injection devices using ferromagnetic polarized electron sources or all-superconducting Josephson junctions. The a-axis films are grown on a strontium titanate (STO) substrate using a low temperature DBCO template to achieve a-axis orientation. During growth, we use reflection high energy electron diffraction (RHEED) to observe the emergence of one-third order streaks in the diffraction pattern and a reduction in the surface roughness as we increase the growth temperature. Subsequent x-ray diffraction shows complete a-axis normal orientation with pseudomorphic growth (in-plane lattice constants identical to the substrate) and a slightly larger out of plane lattice constant than bulk crystals. Atomic force microscopy (AFM) shows an RMS roughness of 4 Å over several millimeters of the film surface, sufficient to construct tunnel junction devices.

  12. Microscale material testing of single crystalline silicon

    NASA Astrophysics Data System (ADS)

    Yi, Taechung

    The mechanical properties of single crystalline silicon (SCS) in microscale are characterized using a uniaxial tension test. The samples are prepared using, various micromachining techniques. The dimensions of the tension specimen at the maximum stress region are 5 to 10 mum in thickness and 20 to 100 mum in width. The sample has two illumination marks on the top surface for strain measurement. The uniaxial tension test setup has been built to accommodate requirements such as sample handling, sample alignment, and friction elimination. Stress is measured using a commercial load cell. Strain is measured by laser interferometry. All the components are connected to a data acquisition board and controlled by a personal computer. Measured Young's moduli in three directions agree well with the reference values and verify the reliability of the setup and measurement procedure. The measured fracture strength is 0.6 GPa to 1.2 GPa, depending on sample preparation methods and loading directions. Preliminary work for fracture toughness measurements using a sharp initial crack is also presented. Future works include further investigation of fracture surfaces, fracture toughness measurement using crack opening criteria, and improvement of the testing apparatus.

  13. Liquid-gated interface superconductivity on an atomically flat film.

    PubMed

    Ye, J T; Inoue, S; Kobayashi, K; Kasahara, Y; Yuan, H T; Shimotani, H; Iwasa, Y

    2010-02-01

    Liquid/solid interfaces are attracting growing interest not only for applications in catalytic activities and energy storage, but also for their new electronic functions in electric double-layer transistors (EDLTs) exemplified by high-performance organic electronics, field-induced electronic phase transitions, as well as superconductivity in SrTiO(3) (ref. 12). Broadening EDLTs to induce superconductivity within other materials is highly demanded for enriching the materials science of superconductors. However, it is severely hampered by inadequate choice of materials and processing techniques. Here we introduce an easy method using ionic liquids as gate dielectrics, mechanical micro-cleavage techniques for surface preparation, and report the observation of field-induced superconductivity showing a transition temperature T(c)=15.2 K on an atomically flat film of layered nitride compound, ZrNCl. The present result reveals that the EDLT is an extremely versatile tool to induce electronic phase transitions by electrostatic charge accumulation and provides new routes in the search for superconductors beyond those synthesized by traditional chemical methods.

  14. Single crystalline Ge(1-x)Mn(x) nanowires as building blocks for nanoelectronics.

    PubMed

    van der Meulen, Machteld I; Petkov, Nikolay; Morris, Michael A; Kazakova, Olga; Han, Xinhai; Wang, Kang L; Jacob, Ajey P; Holmes, Justin D

    2009-01-01

    Magnetically doped Si and Ge nanowires have potential application in future nanowire spin-based devices. Here, we report a supercritical fluid method for producing single crystalline Mn-doped Ge nanowires with a Mn-doping concentration of between 0.5-1.0 atomic % that display ferromagnetism above 300 K and a superior performance with respect to the hole mobility of around 340 cm(2)/Vs, demonstrating the potential of using these nanowires as building blocks for electronic devices.

  15. Flat bands, Dirac cones, and atom dynamics in an optical lattice

    SciTech Connect

    Apaja, V.; Hyrkaes, M.; Manninen, M.

    2010-10-15

    We study atoms trapped with a harmonic confinement in an optical lattice characterized by a flat band and Dirac cones. We show that such an optical lattice can be constructed which can be accurately described with the tight-binding or Hubbard models. In the case of fermions the release of the harmonic confinement removes fast atoms occupying the Dirac cones while those occupying the flat band remain immobile. Using exact diagonalization and dynamics we demonstrate that a similar strong occupation of the flat band does not happen in the bosonic case and furthermore that the mean-field model is not capable of describing the dynamics of the boson cloud.

  16. Atomically Flat Zigzag Edges in Monolayer MoS2 by Thermal Annealing.

    PubMed

    Chen, Qu; Li, Huashan; Xu, Wenshuo; Wang, Shanshan; Sawada, Hidetaka; Allen, Christopher S; Kirkland, Angus I; Grossman, Jeffrey C; Warner, Jamie H

    2017-09-13

    The edges of 2D materials show novel electronic, magnetic, and optical properties, especially when reduced to nanoribbon widths. Therefore, methods to create atomically flat edges in 2D materials are essential for future exploitation. Atomically flat edges in 2D materials are found after brittle fracture or when electrically biasing, but a simple scalable approach for creating atomically flat periodic edges in monolayer 2D transition metal dichalcogenides has yet to be realized. Here, we show how heating monolayer MoS2 to 800 °C in vacuum produces atomically flat Mo terminated zigzag edges in nanoribbons. We study this at the atomic level using an ultrastable in situ heating holder in an aberration-corrected transmission electron microscope and discriminating Mo from S at the edge, revealing unique Mo terminations for all zigzag orientations that remain stable and atomically flat when cooling back to room temperature. Highly faceted MoS2 nanoribbon constrictions are produced with Mo rich edge structures that have theoretically predicted spin separated transport channels, which are promising for spin logic applications.

  17. Epitaxial layers of 2122 BCSCO superconductor thin films having single crystalline structure

    NASA Technical Reports Server (NTRS)

    Pandey, Raghvendra K. (Inventor); Raina, Kanwal K. (Inventor); Solayappan, Narayanan (Inventor)

    1995-01-01

    A substantially single phase, single crystalline, highly epitaxial film of Bi.sub.2 CaSr.sub.2 Cu.sub.2 O.sub.8 superconductor which has a T.sub.c (zero resistance) of 83K is provided on a lattice-matched substrate with no intergrowth. This film is produced by a Liquid Phase Epitaxy method which includes the steps of forming a dilute supercooled molten solution of a single phase superconducting mixture of oxides of Bi, Ca, Sr, and Cu having an atomic ratio of about 2:1:2:2 in a nonreactive flux such as KCl, introducing the substrate, e.g., NdGaO.sub.3, into the molten solution at 850.degree. C., cooling the solution from 850.degree. C. to 830.degree. C. to grow the film and rapidly cooling the substrate to room temperature to maintain the desired single phase, single crystalline film structure.

  18. Method for forming single phase, single crystalline 2122 BCSCO superconductor thin films by liquid phase epitaxy

    NASA Technical Reports Server (NTRS)

    Pandey, Raghvendra K. (Inventor); Raina, Kanwal (Inventor); Solayappan, Narayanan (Inventor)

    1994-01-01

    A substantially single phase, single crystalline, highly epitaxial film of Bi.sub.2 CaSr.sub.2 Cu.sub.2 O.sub.8 superconductor which has a T.sub.c (zero resistance) of 83 K is provided on a lattice-matched substrate with no intergrowth. This film is produced by a Liquid Phase Epitaxy method which includes the steps of forming a dilute supercooled molten solution of a single phase superconducting mixture of oxides of Bi, Ca, Sr, and Cu having an atomic ratio of about 2:1:2:2 in a nonreactive flux such as KCl, introducing the substrate, e.g., NdGaO.sub.3, into the molten solution at 850.degree. C., cooling the solution from 850.degree. C. to 830.degree. C. to grow the film and rapidly cooling the substrate to room temperature to maintain the desired single phase, single crystalline film structure.

  19. Transfer of single-crystalline silicon nanolayer onto alien substrate

    NASA Astrophysics Data System (ADS)

    Usenko, Alexander Y.; Carr, William N.; Chen, Bo

    2003-04-01

    Starting from 60 nanometer node, next generations of mainstream semiconductor devices (i.e.,CMOS) will be mostly manufactured from silicon-on-insulator (SOI) initial substrates with the top silicon layer having a thickness 50 nm or less. We describe a process that is capable for transfer of nanoscale thick layers. The layer is delaminated from a single crystalline silicon substrate and laminated onto another substrate thus resulting in SOI. The process includes: (1) forming a trap layer for hydrogen in an initial substrate (2) delivery of hydrogen to the traps by diffusion of monatomic hydrogen (3) evolving the trapped hydrogen into a layer of hydrogen platelets (4) stiffening of the surface of the initial substrate by laminating to another substrate (5) delaminating a layer from the initial substrate along the hydrogen platelet layer. Details of the new layer transfer process is described. A depth where the buried trap layer locates is critical for the process. An implantation of heavy ions is used to form the trap layer. A trap capacity for hydrogen is evaluated as a function of implantation conditions. Plasma hydrogenation is used to deliver an atomic hydrogen to the traps. ECR, microwave, rf, and DC plasma are compared as the hydrogenation sources. Dependence of a thickness of a transferred layer as a function of the mass of implanted ions and implantation energy is described. Types of layer transfer faults are described. Mechanisms of the layer transfer faults are suggested. We discuss limits of scaling down of thickness of the layer that is transferred from one substrate to another one. Scaling limit of our process is compared to the limits of other (SIMOX, Smart-cut, and ELTRAN) processes.

  20. A single crystalline InP nanowire photodetector

    NASA Astrophysics Data System (ADS)

    Yan, Xin; Li, Bang; Wu, Yao; Zhang, Xia; Ren, Xiaomin

    2016-08-01

    Single crystalline nanowires are critical for achieving high-responsivity, high-speed, and low-noise nanoscale photodetectors. Here, we report a metal-semiconductor-metal photodetector based on a single crystalline InP nanowire. The nanowires are grown by a self-catalyzed method and exhibit stacking-fault-free zinc blende crystal structure. The nanowire exhibits a typical n-type semiconductor property and shows a low room temperature dark current of several hundred pA at moderate biases. A photoresponsivity of 6.8 A/W is obtained at a laser power density of 0.2 mW/cm2. This work demonstrates that single crystalline InP nanowires are good candidates for future optoelectronic device applications.

  1. Synthesis of single-crystalline -Ga2O3 nanoribbons

    NASA Astrophysics Data System (ADS)

    Yang, Z. X.; Wu, Y. J.; Zhu, F.; Zhang, Y. F.

    2004-11-01

    Quasi-one-dimensional thin single-crystalline -Ga2O3 nanoribbons have been successfully synthesized via thermal evaporation of a Ga droplet at temperatures as low as 900 °C without the presence of a catalyst. Unlike the commonly used thermal evaporation method, the liquid phase was employed to synthesize the nanoribbons. The as-synthesized -Ga2O3 nanoribbons are pure, structurally uniform, single crystalline, and most of them are free from defects. Other interesting -Ga2O3 microstructures have also been found and can be helpful in understanding the growth mechanisms of β-Ga2O3 nanoribbons.

  2. Plasmon confinement in atomically thin and flat metallic films

    NASA Astrophysics Data System (ADS)

    Nagao, T.; Yaginuma, S.; Liu, C.; Inaoka, T.; Nazarov, V. U.; Nakayama, T.; Aono, M.

    2007-09-01

    We report on the direct measurement of dispersion relations of plasmons confined in atomically thin metal films and wires by electron energy loss spectroscopy in wide energy-momentum range. Ultrathin Ag films are prepared on single crystal Si surfaces by molecular beam epitaxy, and its crystallinity is checked by electron diffraction. For the case of multi-atomic-layer Ag films, two plasmon modes are observed at around 3.9 eV and 1.8 eV which are localized at the top and the bottom surfaces of the films, respectively. For the case of Ag monoatomic layer, a single mode is observed that steeply disperses in the mid-infrared range. Nonlocal and quantum effects are found to be essential in understanding its full plasmon dispersion curve up to the critical wave number of Landau damping. For the case of Au atom chains, an anisotropic sound-wave-like plasmon dispersion is found that clearly shows 1D plasmon confinement in each atom chain.

  3. Patterned Aqueous Growth of Single Crystalline Zinc Oxide for Photonic Applications

    NASA Astrophysics Data System (ADS)

    Pooley, Kathryn Jessica

    Typically a top-down approach is used in the fabrication of functional nanodevices beginning with the bulk material and imposing a two or three-dimensional structure on the material through a combination of lithography and etching. Pre-patterning of a substrate, resulting in the selective growth of a material, has potential for forming three-dimensional device structures in ways that can be more efficient and which can avoid process complexity and process induced damage. In this thesis, the low temperature (90°C) aqueous growth of complex, single crystalline zinc oxide (ZnO) three-dimensional devices through pre-patterned micron and nanometer sized molds is presented. This work focuses on the quality of the single crystalline ZnO material, the constrained growth of ZnO through various sizes and shapes of molds, and the fabrication of several device structures including pillars, rings, and photonic crystals. Due to their single crystalline nature and crystallographically smooth sidewalls, photonic devices created using this growth method have the potential to outperform traditionally fabricated structures in a range of optoelectronic applications. In addition, metal-oxide interfaces are the critical components of many electrical and optical devices, and it is rare to find epitaxial metal-oxide structures. In this work, the first demonstration of low temperature, epitaxial growth of ZnO on single crystalline gold plates is presented. The quality and structure of the ZnO on the gold plates is investigated using scanning electron microscopy, atomic force microscopy, and photoluminescence spectroscopy. The epitaxial growth is confirmed using electron backscatter diffraction and transmission electron microscopy. The metal-oxide interfaces fabricated have the potential to be used in a number of technologically important applications. Possible examples include creating high quality electrical contacts on high bandgap materials and improving light extraction from planar

  4. Growth of single-crystalline particles of metallic copper

    NASA Astrophysics Data System (ADS)

    Guo, Jinlei; Shen, Shaobo; Zhao, Yingshi; Wang, Fuming

    2016-10-01

    Most of ultrafine particles of metallic copper reported so far were of polycrystalline structures. Here, some ultrafine particles of metallic copper of single-crystalline structure were synthesized in gas phase. Some mixtures of a raw copper powder (about 79 μm) and sodium chloride powder were used as the precursor materials. The materials were chlorinated by dry chlorine at 400 °C. Some anhydrous eutectics composed of copper chlorides and sodium chloride were thus obtained. The eutectics were first heated in situ up to 900 °C and then carried to a gas space by evaporation using a flowing Argon, where they met H2 and were reduced to metallic copper particles. It was found that all these copper particles prepared were of single-crystalline structure irrespective of the molar ratio of raw copper and sodium chloride. When the molar ratio of NaCl to Cu in the precursor materials was 1 to 3, some dispersed octahedral particles of single-crystalline copper with an average size of 776 nm were prepared. However, when the ratio was increased to 4 to 1, some dispersed spherical particles of single-crystalline copper with a size of 92 nm were obtained. No impurities from the two shapes of copper particles were detected. The mechanisms involved in controlling the shape and size of copper particles were proposed.

  5. Nonequilibrium synthesis of highly porous single-crystalline oxide nanostructures

    DOE PAGES

    Lee, Dongkyu; Gao, Xiang; Fan, Lisha; ...

    2017-01-20

    A novel synthesis route to the formation of vertically aligned single-crystalline oxide nanostructures is found by precisely controlling the nonequilibrium pulsed laser deposition process. Here, the columnar nanostructures with deep crevices offering a large surface area are generated owing to the diffusion limited geometric shadowing effect.

  6. Synthesis of single crystalline layered lithium manganese oxide nanorods

    NASA Astrophysics Data System (ADS)

    Wang, Xiong; Song, Jimei; Gao, Lisheng; Zheng, Huagui; Ji, Mingrong; Zhang, Zude

    2004-12-01

    Single-crystalline layered lithium manganese oxide nanorods were prepared via a low-temperature molten salt synthesis method. The material was investigated by a variety of techniques, including X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectrum (XPS).

  7. Electroanalytical performance of carbon films with near-atomic flatness.

    PubMed

    Ranganathan, S; McCreery, R L

    2001-03-01

    Physicochemical and electrochemical characterization of carbon films obtained by pyrolyzing a commercially available photoresist has been performed. Photoresist spin-coated on to a silicon wafer was pyrolyzed at 1,000 degrees C in a reducing atmosphere (95% nitrogen and 5% hydrogen) to produce conducting carbon films. The pyrolyzed photoresist films (PPF) show unusual surface properties compared to other carbon electrodes. The surfaces are nearly atomically smooth with a root-mean-square roughness of <0.5 nm. PPF have a very low background current and oxygen/carbon atomic ratio compared to conventional glassy carbon and show relatively weak adsorption of methylene blue and anthraquinone-2,6-disulfonate. The low oxygen/carbon ratio and the relative stability of PPF indicate that surfaces may be partially hydrogen terminated. The pyrolyzed films were compared to glassy carbon (GC) heat treated under the same conditions as pyrolysis to evaluate the electroanalytical utility of PPF. Heterogeneous electron-transfer kinetics of various redox systems were evaluated. For Ru(NH3)6(3+/2+), Fe(CN)6(3-/4-), and chlorpromazine, fresh PPF surfaces show electron-transfer rates similar to those on GC, but for redox systems such as Fe3+/2+, ascorbic acid, dopamine, and oxygen, the kinetics on PPF are slower. Very weak interactions between the PPF surface and these redox systems lead to their slow electron-transfer kinetics. Electrochemical anodization results in a simultaneous increase in background current, adsorption, and electron-transfer kinetics. The PPF surfaces can be chemically modified via diazonium ion reduction to yield a covalently attached monolayer. Such a modification could help in the preparation of low-cost, high-volume analyte-specific electrodes for diverse electroanalytical applications. Overall, pyrolysis of the photoresist yields an electrode surface with properties similar to a very smooth version of glassy carbon, with some important differences in surface

  8. Electric dipolar interaction assisted growth of single crystalline organic thin films

    SciTech Connect

    Jin-ming, Cai; Yu-Yang, Zhang; Hao, Hu; Li-Hong, Bao; Li-Da, Pan; Wei, Tang; Guo, Li; Shi-Xuan, Du; Jian, Shen; Hong-Jun, Gao

    2010-01-01

    We report on a forest-like-to-desert-like pattern evolution in the growth of an organic thin film observed by using an atomic force microscope. We use a modified diffusion limited aggregation model to simulate the growth process and are able to reproduce the experimental patterns. The energy of electric dipole interaction is calculated and determined to be the driving force for the pattern formation and evolution. Based on these results, single crystalline films are obtained by enhancing the electric dipole interaction while limiting effects of other growth parameters.

  9. Proton irradiation effects on the thermoelectric properties in single-crystalline Bi nanowires

    SciTech Connect

    Chang, Taehoo; Kim, Jeongmin; Song, Min-Jung; Lee, Wooyoung

    2015-05-15

    The effects of proton irradiation on the thermoelectric properties of Bi nanowires (Bi-NWs) were investigated. Single crystalline Bi-NWs were grown by the on-film formation of nanowires method. The devices based on individual Bi-NWs were irradiated with protons at different energies. The total number of displaced atoms was estimated using the Kinchin-Pease displacement model. The electric conductivity and Seebeck coefficient in the Bi-NW devices were investigated before and after proton irradiation at different temperatures. Although the Seebeck coefficient remained stable at various irradiation energies, the electrical conductivity significantly declined with increasing proton energy up to 40 MeV.

  10. Single crystalline thin films as a novel class of electrocatalysts

    DOE PAGES

    Snyder, Joshua; Markovic, Nenad; Stamenkovic, Vojislav

    2013-01-01

    The ubiquitous use of single crystal metal electrodes has garnered invaluable insight into the relationship between surface atomic structure and functional electrochemical properties. But, the sensitivity of their electrochemical response to surface orientation and the amount of precious metal required can limit their use. We present here a generally applicable procedure for producing thin metal films with a large proportion of atomically flat (111) terraces without the use of an epitaxial template. Thermal annealing in a controlled atmosphere induces long-range ordering of magnetron sputtered thin metal films deposited on an amorphous substrate. The ordering transition in these thin metal filmsmore » yields characteristic (111) electrochemical signatures with minimal amount of material and provides an adequate replacement for oriented bulk single crystals. Our procedure can be generalized towards a novel class of practical multimetallic thin film based electrocatalysts with tunable near-surface compositional profile and morphology. Annealing of atomically corrugated sputtered thin film Pt-alloy catalysts yields an atomically smooth structure with highly crystalline, (111)-like ordered and Pt segregated surface that displays superior functional properties, bridging the gap between extended/bulk surfaces and nanoscale systems.« less

  11. Single crystalline thin films as a novel class of electrocatalysts

    SciTech Connect

    Snyder, Joshua; Markovic, Nenad; Stamenkovic, Vojislav

    2013-01-01

    The ubiquitous use of single crystal metal electrodes has garnered invaluable insight into the relationship between surface atomic structure and functional electrochemical properties. But, the sensitivity of their electrochemical response to surface orientation and the amount of precious metal required can limit their use. We present here a generally applicable procedure for producing thin metal films with a large proportion of atomically flat (111) terraces without the use of an epitaxial template. Thermal annealing in a controlled atmosphere induces long-range ordering of magnetron sputtered thin metal films deposited on an amorphous substrate. The ordering transition in these thin metal films yields characteristic (111) electrochemical signatures with minimal amount of material and provides an adequate replacement for oriented bulk single crystals. Our procedure can be generalized towards a novel class of practical multimetallic thin film based electrocatalysts with tunable near-surface compositional profile and morphology. Annealing of atomically corrugated sputtered thin film Pt-alloy catalysts yields an atomically smooth structure with highly crystalline, (111)-like ordered and Pt segregated surface that displays superior functional properties, bridging the gap between extended/bulk surfaces and nanoscale systems.

  12. Imparting amphiphobicity on single-crystalline porous materials.

    PubMed

    Sun, Qi; He, Hongming; Gao, Wen-Yang; Aguila, Briana; Wojtas, Lukasz; Dai, Zhifeng; Li, Jixue; Chen, Yu-Sheng; Xiao, Feng-Shou; Ma, Shengqian

    2016-10-31

    The sophisticated control of surface wettability for target-specific applications has attracted widespread interest for use in a plethora of applications. Despite the recent advances in modification of non-porous materials, surface wettability control of porous materials, particularly single crystalline, remains undeveloped. Here we contribute a general method to impart amphiphobicity on single-crystalline porous materials as demonstrated by chemically coating the exterior of metal-organic framework (MOF) crystals with an amphiphobic surface. As amphiphobic porous materials, the resultant MOF crystals exhibit both superhydrophobicity and oleophobicity in addition to retaining high crystallinity and intact porosity. The chemical shielding effect resulting from the amphiphobicity of the MOFs is illustrated by their performances in water/organic vapour adsorption, as well as long-term ultrastability under highly humidified CO2 environments and exceptional chemical stability in acid/base aqueous solutions. Our work thereby pioneers a perspective to protect crystalline porous materials under various chemical environments for numerous applications.

  13. Subsurface damage of single crystalline silicon carbide in nanoindentation tests.

    PubMed

    Yan, Jiwang; Gai, Xiaohui; Harada, Hirofumi

    2010-11-01

    The response of single crystalline silicon carbide (SiC) to a Berkovich nanoindenter was investigated by examining the indents using a transmission electron microscope and the selected area electron diffraction technique. It was found that the depth of indentation-induced subsurface damage was far larger than the indentation depth, and the damaging mechanism of SiC was distinctly different from that of single crystalline silicon. For silicon, a broad amorphous region is formed underneath the indenter after unloading; for SiC, however, no amorphous phase was detected. Instead, a polycrystalline structure with a grain size of ten nanometer level was identified directly under the indenter tip. Micro cracks, basal plane dislocations and possible cross slips were also found around the indent. These finding provide useful information for ultraprecision manufacturing of SiC wafers.

  14. Single-crystalline nanoporous Nb2O5 nanotubes

    PubMed Central

    2011-01-01

    Single-crystalline nanoporous Nb2O5 nanotubes were fabricated by a two-step solution route, the growth of uniform single-crystalline Nb2O5 nanorods and the following ion-assisted selective dissolution along the [001] direction. Nb2O5 tubular structure was created by preferentially etching (001) crystallographic planes, which has a nearly homogeneous diameter and length. Dense nanopores with the diameters of several nanometers were created on the shell of Nb2O5 tubular structures, which can also retain the crystallographic orientation of Nb2O5 precursor nanorods. The present chemical etching strategy is versatile and can be extended to different-sized nanorod precursors. Furthermore, these as-obtained nanorod precursors and nanotube products can also be used as template for the fabrication of 1 D nanostructured niobates, such as LiNbO3, NaNbO3, and KNbO3. PMID:21711650

  15. Imparting amphiphobicity on single-crystalline porous materials

    NASA Astrophysics Data System (ADS)

    Sun, Qi; He, Hongming; Gao, Wen-Yang; Aguila, Briana; Wojtas, Lukasz; Dai, Zhifeng; Li, Jixue; Chen, Yu-Sheng; Xiao, Feng-Shou; Ma, Shengqian

    2016-10-01

    The sophisticated control of surface wettability for target-specific applications has attracted widespread interest for use in a plethora of applications. Despite the recent advances in modification of non-porous materials, surface wettability control of porous materials, particularly single crystalline, remains undeveloped. Here we contribute a general method to impart amphiphobicity on single-crystalline porous materials as demonstrated by chemically coating the exterior of metal-organic framework (MOF) crystals with an amphiphobic surface. As amphiphobic porous materials, the resultant MOF crystals exhibit both superhydrophobicity and oleophobicity in addition to retaining high crystallinity and intact porosity. The chemical shielding effect resulting from the amphiphobicity of the MOFs is illustrated by their performances in water/organic vapour adsorption, as well as long-term ultrastability under highly humidified CO2 environments and exceptional chemical stability in acid/base aqueous solutions. Our work thereby pioneers a perspective to protect crystalline porous materials under various chemical environments for numerous applications.

  16. Freestanding single-crystalline magnetic structures fabricated by ion bombardment

    SciTech Connect

    Schoenherr, P.; Bischof, A.; Boehm, B.; Eib, P.; Grimm, S.; Gross, L.; Allenspach, R.; Alvarado, S. F.

    2015-01-19

    Starting from an ultrathin Fe film grown epitaxially on top of a GaAs(001) substrate, we show that freestanding structures can be created by ion-beam treatment. These structures are single-crystalline blisters and only a few nanometers thick. Anisotropic stress in the rim of a blister induces magnetic domain states magnetized in the direction normal to the blister edge. Experimental evidence is provided that the lateral size can be confined by starting from a nanostructured template.

  17. Synthesis and characterization of single crystalline selenium nanowire arrays

    SciTech Connect

    Zhang, X.Y. . E-mail: apzhxy@polyu.edu.hk; Xu, L.H.; Dai, J.Y.; Cai, Y.; Wang, N.

    2006-09-14

    Ordered selenium nanowire arrays with diameters about 40 nm have been fabricated by electrodeposition using anodic porous alumina templates. As determined by X-ray diffraction, Raman spectra, electron diffraction and high-resolution transmission electron microscopy, selenium nanowires have uniform diameters, which are fully controllable. Single crystalline trigonal selenium nanowires have been obtained after postannealing at 180 deg. C. These nanowires are perfect with a c-axis growth orientation. The optical absorption spectra reveal two types of electron transition activity.

  18. Single-crystalline germanium nanomembrane photodetectors on foreign nanocavities

    DOE PAGES

    Xia, Zhenyang; Song, Haomin; Kim, Munho; ...

    2017-07-07

    Miniaturization of optoelectronic devices offers tremendous performance gain. As the volume of photoactive material decreases, optoelectronic performance improves, including the operation speed, the signal-to-noise ratio, and the internal quantum efficiency. Over the past decades, researchers have managed to reduce the volume of photoactive materials in solar cells and photodetectors by orders of magnitude. However, two issues arise when one continues to thin down the photoactive layers to the nanometer scale (for example, <50 nm). First, light-matter interaction becomes weak, resulting in incomplete photon absorption and low quantum efficiency. Second, it is difficult to obtain ultrathin materials with single-crystalline quality. Wemore » introduce a method to overcome these two challenges simultaneously. It uses conventional bulk semiconductor wafers, such as Si, Ge, and GaAs, to realize single-crystalline films on foreign substrates that are designed for enhanced light-matter interaction. We use a high-yield and high-throughput method to demonstrate nanometer-thin photodetectors with significantly enhanced light absorption based on nanocavity interference mechanism. As a result, these single-crystalline nanomembrane photodetectors also exhibit unique optoelectronic properties, such as the strong field effect and spectral selectivity.« less

  19. Single-crystalline germanium nanomembrane photodetectors on foreign nanocavities

    PubMed Central

    Xia, Zhenyang; Song, Haomin; Kim, Munho; Zhou, Ming; Chang, Tzu-Hsuan; Liu, Dong; Yin, Xin; Xiong, Kanglin; Mi, Hongyi; Wang, Xudong; Xia, Fengnian; Yu, Zongfu; Ma, Zhenqiang (Jack); Gan, Qiaoqiang

    2017-01-01

    Miniaturization of optoelectronic devices offers tremendous performance gain. As the volume of photoactive material decreases, optoelectronic performance improves, including the operation speed, the signal-to-noise ratio, and the internal quantum efficiency. Over the past decades, researchers have managed to reduce the volume of photoactive materials in solar cells and photodetectors by orders of magnitude. However, two issues arise when one continues to thin down the photoactive layers to the nanometer scale (for example, <50 nm). First, light-matter interaction becomes weak, resulting in incomplete photon absorption and low quantum efficiency. Second, it is difficult to obtain ultrathin materials with single-crystalline quality. We introduce a method to overcome these two challenges simultaneously. It uses conventional bulk semiconductor wafers, such as Si, Ge, and GaAs, to realize single-crystalline films on foreign substrates that are designed for enhanced light-matter interaction. We use a high-yield and high-throughput method to demonstrate nanometer-thin photodetectors with significantly enhanced light absorption based on nanocavity interference mechanism. These single-crystalline nanomembrane photodetectors also exhibit unique optoelectronic properties, such as the strong field effect and spectral selectivity. PMID:28695202

  20. Ab initio study of single-crystalline and polycrystalline elastic properties of Mg-substituted calcite crystals.

    PubMed

    Zhu, L-F; Friák, M; Lymperakis, L; Titrian, H; Aydin, U; Janus, A M; Fabritius, H-O; Ziegler, A; Nikolov, S; Hemzalová, P; Raabe, D; Neugebauer, J

    2013-04-01

    We employ ab initio calculations and investigate the single-crystalline elastic properties of (Ca,Mg)CO3 crystals covering the whole range of concentrations from pure calcite CaCO3 to pure magnesite MgCO3. Studying different distributions of Ca and Mg atoms within 30-atom supercells, our theoretical results show that the energetically most favorable configurations are characterized by elastic constants that nearly monotonously increase with the Mg content. Based on the first principles-derived single-crystalline elastic anisotropy, the integral elastic response of (Ca,Mg)CO3 polycrystals is determined employing a mean-field self-consistent homogenization method. As in case of single-crystalline elastic properties, the computed polycrystalline elastic parameters sensitively depend on the chemical composition and show a significant stiffening impact of Mg atoms on calcite crystals in agreement with the experimental findings. Our analysis also shows that it is not advantageous to use a higher-scale two-phase mix of stoichiometric calcite and magnesite instead of substituting Ca atoms by Mg ones on the atomic scale. Such two-phase composites are not significantly thermodynamically favorable and do not provide any strong additional stiffening effect.

  1. Preparation of atomically flat rutile TiO2(001) surfaces for oxide film growth

    DOE PAGES

    Wang, Yang; Lee, Shinbuhm; Vilmercati, P.; ...

    2016-01-01

    The availability of low-index rutile TiO2 single crystal substrates with atomically flat surfaces is essential for enabling epitaxialgrowth of rutile transition metal oxide films. The high surface energy of the rutile (001) surface often leads to surface faceting, which precludes the sputter and annealing treatment commonly used for the preparation of clean and atomically flat TiO2(110) substrate surfaces. In this work, we reveal that stable and atomically flat rutile TiO2(001) surfaces can be prepared with an atomically ordered reconstructedsurface already during a furnace annealing treatment in air. We tentatively ascribe this result to the decrease in surface energy associated withmore » the surface reconstruction, which removes the driving force for faceting. Despite the narrow temperature window where this morphology can initially be formed, we demonstrate that it persists in homoepitaxialgrowth of TiO2(001) thin films. The stabilization of surface reconstructions that prevent faceting of high-surface-energy crystal faces may offer a promising avenue towards the realization of a wider range of high quality epitaxial transition metal oxide heterostructures.« less

  2. Flat-response spin-exchange relaxation free atomic magnetometer under negative feedback.

    PubMed

    Lee, Hyun Joon; Shim, Jeong Hyun; Moon, Han Seb; Kim, Kiwoong

    2014-08-25

    We demonstrate that the use of negative feedback extends the detection bandwidth of an atomic magnetometer in a spin-exchange relaxation free (SERF) regime. A flat-frequency response from zero to 190 Hz was achieved, which is nearly a three-fold enhancement while maintaining sensitivity, 3 fT/Hz1/2 at 100 Hz. With the extension of the bandwidth, the linear correlation between measured signals and a magne-tocardiographic field synthesized for comparison was increased from 0.21 to 0.74. This result supports the feasibility of measuring weak biomagnetic signals containing multiple frequency components using a SERF atomic magnetometer under negative feedback.

  3. Imparting amphiphobicity on single-crystalline porous materials

    PubMed Central

    Sun, Qi; He, Hongming; Gao, Wen-Yang; Aguila, Briana; Wojtas, Lukasz; Dai, Zhifeng; Li, Jixue; Chen, Yu-Sheng; Xiao, Feng-Shou; Ma, Shengqian

    2016-01-01

    The sophisticated control of surface wettability for target-specific applications has attracted widespread interest for use in a plethora of applications. Despite the recent advances in modification of non-porous materials, surface wettability control of porous materials, particularly single crystalline, remains undeveloped. Here we contribute a general method to impart amphiphobicity on single-crystalline porous materials as demonstrated by chemically coating the exterior of metal-organic framework (MOF) crystals with an amphiphobic surface. As amphiphobic porous materials, the resultant MOF crystals exhibit both superhydrophobicity and oleophobicity in addition to retaining high crystallinity and intact porosity. The chemical shielding effect resulting from the amphiphobicity of the MOFs is illustrated by their performances in water/organic vapour adsorption, as well as long-term ultrastability under highly humidified CO2 environments and exceptional chemical stability in acid/base aqueous solutions. Our work thereby pioneers a perspective to protect crystalline porous materials under various chemical environments for numerous applications. PMID:27796363

  4. A novel method for formation of single crystalline tungsten nanotip

    NASA Astrophysics Data System (ADS)

    Hayashi, Shigeki; Ono, Masashi; Tomonaga, Shinya; Nakanishi, Haruka

    2016-12-01

    A point electron source is desired to improve performance of high brightness electron beam instruments. It is valuable to create nano-sized tungsten (W) tip from sharp ordinary polycrystalline W needle. The sharp W needle, which is manufactured by electrochemical etching, has been practically utilized as a cold field emission electron source. A novel method for formation of single crystalline W nanotip on the top of h-BN coated conventional polycrystalline tungsten, by supplying high voltage, has been found. The W nanotip with an apex radius as small as a few times 10 nm would be grown on the top of the polycrystalline W needle. Field emission characteristics of obtained W nanotip are measured, and the field emission microscopic (FEM) and transmission emission microscopic (TEM) images are observed. The emission current from the W nanotip is measured to exceed 0.1 mA. The FEM image shows significant electron emission from the crystallographic facets of the W single crystal. From these results, the present method for formation of the single crystalline W nanotip would be expected as a key technology to realize a point electron source with a nano-sized apex which makes it possible to improve the performance of high brightness electron beam instruments, especially tiny X-ray tubes for medical use, as well as a cantilever of scanning probe microscope.

  5. Epitaxial single crystalline ferrite films for high frequency applications

    SciTech Connect

    Suzuki, Y.; Dover, R.B. van; Korenivski, V.; Werder, D.; Chen, C.H.; Felder, R.J.; Phillips, J.M.

    1996-11-01

    The successful growth of single crystal ferrites in thin film form is an important step towards their future incorporation into integrated circuits operating at microwave frequencies. The authors have successfully grown high quality single crystalline spinel ferrite thin films of (Mn,Zn)Fe{sub 2}O{sub 4} and CoFe{sub 2}O{sub 4} on (100) and (110) SrTiO{sub 3} and MgAl{sub 2}O{sub 4} at low temperature. These ferrite films are buffered with spinel structure layers that are paramagnetic at room temperature. In contrast to ferrite films grown directly on the substrates, ferrite films grown on buffered substrates exhibit excellent crystallinity and bulk saturation magnetization values, thus indicating the importance of lattice match and structural similarity between the film and the immediately underlying layer. X-ray, RBS, AFM and TEM analysis provide a consistent picture of the structural properties of these ferrite films. The authors then use this technique to grow exchange-coupled bilayers of single crystalline CoFe{sub 2}O{sub 4} and (Mn,Zn)Fe{sub 2}O{sub 4}. In these bilayers, they observe strong exchange coupling across the interface that is similar in strength to the exchange coupling in the individual layers.

  6. Half-flat vs. atomically flat: Alkyl monolayers on morphologically controlled Si(100) and Si(111) have very similar structure, density, and chemical stability

    NASA Astrophysics Data System (ADS)

    DeBenedetti, William J. I.; Li, Thomas L.; Hines, Melissa A.

    2017-02-01

    Chemists have long preferred the Si(111) surface for chemical functionalization, as a simple aqueous etch can be used to produce ideal, atomically flat H/Si(111) surfaces for subsequent reactions. In contrast, industry-standard etches produce rough H/Si(100) surfaces terminated by nanohillocks. The recent discovery of an aqueous etch that produces morphologically controlled H/Si(100) surfaces with a near atomically flat or "half-flat" morphology challenges the assumption that Si(111) is an inherently preferable starting point for chemical functionalization. This study shows that alkyl functionalization of morphologically controlled, "half-flat" Si(100) surfaces by terminal alkenes produces dense, tightly packed monolayers that are essentially identical to those on atomically flat Si(111). The striking similarity between the infrared spectra on these two surfaces — in terms of absolute absorbance, line shape and position, and polarization dependence — strongly suggests that alkyl monolayers on morphologically controlled Si(111) and Si(100) have essentially identical structures. The principle difference between the two surfaces is the amount of residual H at the Si/organic interface, a difference that is dictated by the structure of the Si(100) surface. Alkyl monolayers on morphologically controlled Si(111) and Si(100) surfaces were shown to be equally resistant to harsh oxidants. As a result, there appears to be no chemical reason to prefer one surface over the other, at least for functionalization with terminal alkenes.

  7. Half-flat vs. atomically flat: Alkyl monolayers on morphologically controlled Si(100) and Si(111) have very similar structure, density, and chemical stability.

    PubMed

    DeBenedetti, William J I; Li, Thomas L; Hines, Melissa A

    2017-02-07

    Chemists have long preferred the Si(111) surface for chemical functionalization, as a simple aqueous etch can be used to produce ideal, atomically flat H/Si(111) surfaces for subsequent reactions. In contrast, industry-standard etches produce rough H/Si(100) surfaces terminated by nanohillocks. The recent discovery of an aqueous etch that produces morphologically controlled H/Si(100) surfaces with a near atomically flat or "half-flat" morphology challenges the assumption that Si(111) is an inherently preferable starting point for chemical functionalization. This study shows that alkyl functionalization of morphologically controlled, "half-flat" Si(100) surfaces by terminal alkenes produces dense, tightly packed monolayers that are essentially identical to those on atomically flat Si(111). The striking similarity between the infrared spectra on these two surfaces - in terms of absolute absorbance, line shape and position, and polarization dependence - strongly suggests that alkyl monolayers on morphologically controlled Si(111) and Si(100) have essentially identical structures. The principle difference between the two surfaces is the amount of residual H at the Si/organic interface, a difference that is dictated by the structure of the Si(100) surface. Alkyl monolayers on morphologically controlled Si(111) and Si(100) surfaces were shown to be equally resistant to harsh oxidants. As a result, there appears to be no chemical reason to prefer one surface over the other, at least for functionalization with terminal alkenes.

  8. Accelerating atomic-level protein simulations by flat-histogram techniques

    NASA Astrophysics Data System (ADS)

    Jónsson, Sigurður Ć.; Mohanty, Sandipan; Irbäck, Anders

    2011-09-01

    Flat-histogram techniques provide a powerful approach to the simulation of first-order-like phase transitions and are potentially very useful for protein studies. Here, we test this approach by implicit solvent all-atom Monte Carlo (MC) simulations of peptide aggregation, for a 7-residue fragment (GIIFNEQ) of the Cu/Zn superoxide dismutase 1 protein (SOD1). In simulations with 8 chains, we observe two distinct aggregated/non-aggregated phases. At the midpoint temperature, these phases coexist, separated by a free-energy barrier of height 2.7 kBT. We show that this system can be successfully studied by carefully implemented flat-histogram techniques. The frequency of barrier crossing, which is low in conventional canonical simulations, can be increased by turning to a two-step procedure based on the Wang-Landau and multicanonical algorithms.

  9. Fatigue crack propagation behavior of a single crystalline superalloy

    NASA Technical Reports Server (NTRS)

    Lerch, B. A.; Antolovich, Stephen D.

    1990-01-01

    Crack propagation mechanisms occurring at various temperatures in a single crystalline Ni-base alloy, Rene N4, were investigated. The rates of crack growth at 21, 704, 927, 1038, and 1093 C were measured in specimens with 001-line and 110-line directions parallel to the load axis and the machined notch, respectively, using a pulsed dc potential drop apparatus, and the fracture surfaces at each temperature were examined using SEM. Crack growth rates (CGRs) for specimens tested at or below 927 C were similar, while at two higher temperatures, the CGRs were about an order of magnitude higher than at the lower temperatures. Results of SEM observations showed that surface morphologies depended on temperature.

  10. Fatigue crack propagation behavior of a single crystalline superalloy

    NASA Technical Reports Server (NTRS)

    Lerch, B. A.; Antolovich, Stephen D.

    1990-01-01

    Crack propagation mechanisms occurring at various temperatures in a single crystalline Ni-base alloy, Rene N4, were investigated. The rates of crack growth at 21, 704, 927, 1038, and 1093 C were measured in specimens with 001-line and 110-line directions parallel to the load axis and the machined notch, respectively, using a pulsed dc potential drop apparatus, and the fracture surfaces at each temperature were examined using SEM. Crack growth rates (CGRs) for specimens tested at or below 927 C were similar, while at two higher temperatures, the CGRs were about an order of magnitude higher than at the lower temperatures. Results of SEM observations showed that surface morphologies depended on temperature.

  11. Performance of single crystalline silicon solar cell with irradiance

    NASA Astrophysics Data System (ADS)

    Chander, Subhash; Purohit, A.; Nehra, Anshu; Nehra, S. P.; Dhaka, M. S.

    2015-06-01

    In this paper, the effect of irradiance on the performance parameters of single crystalline silicon solar cell is undertaken. The experiment was carried out employing solar cell simulator with varying irradiance in the range 115-550W/m2 at constant cell temperature 25°C. The results show that the short circuit current is found to be increased linearly with irradiance and the open circuit voltage is increased slightly. The fill factor, maximum power and cell efficiency are also found to be increased with irradiance. The efficiency is increased linearly at lower irradiance while slightly increased at higher. The results revealed that the irradiance has a dominant effect on the performance parameters. The results are in good agreement with the available literature.

  12. Size dependent mechanical properties of single crystalline nickel nanowires

    NASA Astrophysics Data System (ADS)

    Peng, Cheng; Ganesan, Yogeeswaran; Lu, Yang; Lou, Jun

    2012-03-01

    Using a simple micromechanical device, in situ tensile testing of single crystalline nickel (Ni) nanowires (NWs) with different diameters (100 to 300 nm) and crystalline orientations was performed inside a scanning electron microscope. With the aid of a quantitative nanoindenter and corresponding theoretical analysis, the load applied to the sample and the sample displacement were ascertained from nanoindenter load versus displacement curves so as to obtain engineering stress-strain curves. Limited plasticity and brittle-like fracture modes were evident in the Ni NWs investigated, and the breaking strength values were found to be much higher than that of the bulk material. More important, the critical resolved shear stress was found to increase as the NW diameter decreased, showing strong size dependence. The quantitative experimental results from this work could offer important insights into the origin of the size dependent mechanical behaviors of metals at the nano-scale.

  13. Physical properties of single crystalline BaSn{sub 5}

    SciTech Connect

    Lin, Xiao; Budko, Sergey; Canfield, Paul

    2012-01-30

    We present a comprehensive study of the binary intermetallic superconductor, BaSn{sub 5}. High-quality single crystalline BaSn{sub 5} was grown out of a Sn flux. Detailed thermodynamic and transport measurements were performed to study BaSn{sub 5}'s normal and superconducting state properties. This material appears to be a strongly coupled, multiband superconductor. H{sub c2}(T) is almost isotropic. De Haas–van Alphen oscillations were observed and two effective masses were estimated from the FFT spectra. Hydrostatic pressure causes a decrease in the superconducting transition temperature at the rate of ≈−0.053 ± 0.001 K/kbar.

  14. Hydrogen Gas Sensors Fabricated on Atomically Flat 4H-SiC Webbed Cantilevers

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Spry, David J.; Trunek, Andrew J.; Evans, Laura J.; Chen, Liang-Yu; Hunter, Gary W.; Androjna, Drago

    2007-01-01

    This paper reports on initial results from the first device tested of a "second generation" Pt-SiC Schottky diode hydrogen gas sensor that: 1) resides on the top of atomically flat 4H-SiC webbed cantilevers, 2) has integrated heater resistor, and 3) is bonded and packaged. With proper selection of heater resistor and sensor diode biases, rapid detection of H2 down to concentrations of 20 ppm was achieved. A stable sensor current gain of 125 +/- 11 standard deviation was demonstrated during 250 hours of cyclic test exposures to 0.5% H2 and N2/air.

  15. Synthesis of Single Crystalline ZnO Nanoparticles by Salt-Assisted Spray Pyrolysis

    NASA Astrophysics Data System (ADS)

    Panatarani, Camellia; Lenggoro, I. Wuled; Okuyama, Kikuo

    2003-04-01

    LiNO3 was used as a shield in the preparation of single crystalline ZnO particles by a spray pyrolysis process in order to prevent agglomeration and enhance the crystallinity of the ZnO. LiNO3 was added to a precursor solution of zinc acetate dihydrate prior to its atomization by means of an ultrasonic transducer. Agglomerate-free particles having a mean particle size of 26 nm were successfully obtained after washing the product. X-ray diffractometry, field-emission scanning electron micrograph and transmission electron micrograph data indicate that the size and morphology of ZnO were strongly influenced by the operating temperature used and the residence time of the particle in the reactor.

  16. Controllable fabrication and electromechanical characterization of single crystalline Sb-doped ZnO nanobelts

    NASA Astrophysics Data System (ADS)

    Yang, Ya; Qi, Junjie; Zhang, Yue; Liao, Qingliang; Tang, Lidan; Qin, Zi

    2008-05-01

    We report the fabrication of the high-quality Sb-doped ZnO nanobelts by using a simple chemical vapor deposition method. The nanobelts consist of single-crystalline wurtzite ZnO crystal and grow along [011¯2] direction. An electromechanical system is constructed to explore the transverse electrical properties of a single nanobelt under the different applied loading forces. The I-V results indicate that a little barrier exists in between the nanobelt and the atomic force microscopy tip. An almost linear relationship between the force and the resistance was found at small deformation regions, which demonstrates that the nanobelts have potential applications as force/pressure sensor for measuring the nano-Newton forces.

  17. Cold welding of copper nanowires with single-crystalline and twinned structures: A comparison study

    NASA Astrophysics Data System (ADS)

    Huang, Rao; Shao, Gui-Fang; Wen, Yu-Hua

    2016-09-01

    In this article, molecular simulations were adopted to explore the cold welding processes of copper nanowires with both single-crystalline and fivefold twinned structures. It was verified that the twinned nanowires exhibited enhanced strength but lowered elastic limit and ductility. Both nanowires could be successfully welded through rather small loadings, although their stress-strain responses toward compression were different. Meanwhile, more stress was accumulated in the twinned nanowire due to repulsive force of the twin boundaries against the nucleation and motions of dislocations. Moreover, by characterizing the structure evolutions in the welding process, it can be ascertained that perfect atomic order was finally built at the weld region in both nanowires. This comparison study will be of great importance to future mechanical processing of metallic nanowires.

  18. Flat metallic surface gratings with sub-10 nm gaps controlled by atomic-layer deposition

    NASA Astrophysics Data System (ADS)

    Chen, Borui; Ji, Dengxin; Cheney, Alec; Zhang, Nan; Song, Haomin; Zeng, Xie; Thomay, Tim; Gan, Qiaoqiang; Cartwright, Alexander

    2016-09-01

    Atomic layer lithography is a recently reported new technology to fabricate deep-subwavelength features down to 1-2 nm, based on combinations of electron beam lithography (EBL) and atomic layer deposition (ALD). However, the patterning area is relatively small as limited by EBL, and the fabrication yield is not very high due to technical challenges. Here we report an improved procedure to fabricate flat metallic surfaces with sub-10 nm features based on ALD processes. To demonstrate the scalability of the new manufacturing method, we combine the ALD process with large area optical interference patterning, which is particularly promising for the development of practical applications for nanoelectronics and nanophotonics with extremely strong confinement of electromagnetic fields.

  19. Molecular dynamics simulations of atomically flat and nanoporous electrodes with a molten salt electrolyte.

    PubMed

    Vatamanu, Jenel; Borodin, Oleg; Smith, Grant D

    2010-01-07

    The electric double layer (EDL) structure and capacitance have been studied for atomically flat and nanoporous conductive electrodes with a molten LiCl electrolyte using an electroactive interface molecular dynamics simulation methodology. For the atomically flat electrodes the electrolyte was observed to form a multilayer structure near the electrode described by exponentially decaying sinusoidal oscillations in ion and charge densities perpendicular to the electrode/electrolyte interface. The differential EDL capacitance vs. electrode potential was found to exhibit "U-shaped" behavior while the EDL capacitance exhibited complex dependence on electrode potential including regions of negative capacitance near zero electrode potential. Increased capacitance and an enhanced degree of electrode-electrolyte interface structure were observed with decreasing temperature. For nanoporous electrodes with both slit and cylindrical pore geometries, the electrolyte was observed to form highly structured alternating charged layers within the electrode nanopores. A maximum in the normalized (per unit electrode area) EDL capacitance was found for pore widths that accommodate several charged layers inside the pores. The observed dependence of capacitance on pore size appears to be a compromise between increasing structure/charge imbalance and decreasing ion density with decreasing pore width/diameter.

  20. Unveiling the Formation Pathway of Single Crystalline Porous Silicon Nanowires

    PubMed Central

    Zhong, Xing; Qu, Yongquan; Lin, Yung-Chen; Liao, Lei; Duan, Xiangfeng

    2011-01-01

    Porous silicon nanowire is emerging as an interesting material system due to its unique combination of structural, chemical, electronic, and optical properties. To fully understand their formation mechanism is of great importance for controlling the fundamental physical properties and enabling potential applications. Here we present a systematic study to elucidate the mechanism responsible for the formation of porous silicon nanowires in a two-step silver-assisted electroless chemical etching method. It is shown that silicon nanowire arrays with various porosities can be prepared by varying multiple experimental parameters such as the resistivity of the starting silicon wafer, the concentration of oxidant (H2O2) and the amount of silver catalyst. Our study shows a consistent trend that the porosity increases with the increasing wafer conductivity (dopant concentration) and oxidant (H2O2) concentration. We further demonstrate that silver ions, formed by the oxidation of silver, can diffuse upwards and re-nucleate on the sidewalls of nanowires to initiate new etching pathways to produce porous structure. The elucidation of this fundamental formation mechanism opens a rational pathway to the production of wafer-scale single crystalline porous silicon nanowires with tunable surface areas ranging from 370 m2·g−1 to 30 m2·g−1, and can enable exciting opportunities in catalysis, energy harvesting, conversion, storage, as well as biomedical imaging and therapy. PMID:21244020

  1. Facile morphological control of single-crystalline silicon nanowires

    NASA Astrophysics Data System (ADS)

    Wu, Shao-long; Zhang, Ting; Zheng, Rui-ting; Cheng, Guo-an

    2012-10-01

    To realize wider potentials of silicon nanowires (SiNWs), the morphological controllability is desirable. In this paper, we synthesized well vertically- and slantingly-aligned SiNWs with ultra-high aspect ratio in metal-assisted chemical etching method, and wafer-scale zigzag SiNWs with three types of turning angle were also obtained. The formation of the curved SiNWs is a result of the alternation of moving direction of Ag nanoparticles between the preferred <1 0 0> and other directions in Si substrates. The as-prepared SiNWs are single-crystalline and their orientations are mostly along the <1 0 0> or <1 1 1> directions. The surface of the resulting SiNWs can be controlled to be smooth or rough, with or without mesopores, by adjusting the etching conditions and using various Si substrates with different crystal orientations and doping levels. Moreover, the effects of the etching conditions (etching time, oxidant concentration, deposition time of Ag nanoparticles and etching temperature) and substrate properties (crystal orientation and doping level) on the as-prepared SiNWs have been discussed.

  2. Unveiling the formation pathway of single crystalline porous silicon nanowires.

    PubMed

    Zhong, Xing; Qu, Yongquan; Lin, Yung-Chen; Liao, Lei; Duan, Xiangfeng

    2011-02-01

    Porous silicon nanowire is emerging as an interesting material system due to its unique combination of structural, chemical, electronic, and optical properties. To fully understand their formation mechanism is of great importance for controlling the fundamental physical properties and enabling potential applications. Here we present a systematic study to elucidate the mechanism responsible for the formation of porous silicon nanowires in a two-step silver-assisted electroless chemical etching method. It is shown that silicon nanowire arrays with various porosities can be prepared by varying multiple experimental parameters such as the resistivity of the starting silicon wafer, the concentration of oxidant (H(2)O(2)) and the amount of silver catalyst. Our study shows a consistent trend that the porosity increases with the increasing wafer conductivity (dopant concentration) and oxidant (H(2)O(2)) concentration. We further demonstrate that silver ions, formed by the oxidation of silver, can diffuse upwards and renucleate on the sidewalls of nanowires to initiate new etching pathways to produce a porous structure. The elucidation of this fundamental formation mechanism opens a rational pathway to the production of wafer-scale single crystalline porous silicon nanowires with tunable surface areas ranging from 370 to 30 m(2) g(-1) and can enable exciting opportunities in catalysis, energy harvesting, conversion, storage, as well as biomedical imaging and therapy.

  3. Single crystalline film on glass for thin film solar cells.

    PubMed

    Lin, C H; Yang, Y J; Encinas, E; Chen, W Y; Tsai, J J; Liu, C W

    2009-06-01

    A simple Ge-on-glass metal-oxide-semiconductor solar cell has been demonstrated by wafer bonding and smart-cut. Since single crystalline Ge is directly bonded on glass, the crystalline substrate is not necessary. The metal-oxide-semiconductor structure can be easily fabricated without n and p dopant diffusion or implantation. The reason for low efficiency is discussed, and then the optimized structures are designed by simulation. An outstanding enhancement on efficiency can be achieved with the Si/Ge/Si structure. The best performance can be achieved by optimization of the position of the Ge layer, the thickness of the Ge layer, and the number of the Ge layers. The efficiency of the thin film Si/Ge/Si solar cell with single layer of 30-nm-thick Ge outside the depletion region reaches 15.9%, as compared to the control Si sample of 11.8%. Based on the simulation and technologies, high efficiency thin film solar cells can be demonstrated in the future.

  4. Development of novel UV emitting single crystalline film scintillators

    NASA Astrophysics Data System (ADS)

    Zorenko, Yu; Gorbenko, V.; Savchyn, V.; Voznyak, T.; Nikl, M.; Mares, J. A.; Martin, T.; Douissard, P.-A.

    2011-04-01

    The work is dedicated to development of new types of UV -emitting scintillators based on single crystalline films (SCF) of aluminimum perovskites and garnets grown by the liquid phase epitaxy (LPE) method. The development of the following three types of UV SCF scintillators is considered in this work: i) Ce-doped SCF of Y-Lu-Al-perovskites with Ce3+ emission in the 360-370 nm range with a decay time of 16-17 ns; ii) Pr-doped SCF of Y-Lu-Al garnets with Pr3+ emission in the 300-400 nm range with a decay time of 13-17 ns; iii) La3+ and Sc3+ doped SCF of Y-Lu-Al-garnets, emitting in the 290-400 nm range due to formation of the LaY,Lu, ScY,Lu and ScAl centers with decay time of 250-575 ns. The results of testing the several novel UV-emitting SCFs scintillators for visualization of X-ray images at ESFR are presented. It is shown that the UV emission of the LuAG:Sc, LuAG:La and LuAG:Pr SCFs is efficient enough for conversion of X-ray to the UV light and that these scintillators can be used for improvement of the resolution of imaging detectors in synchrotron radiation applications.

  5. Ultrathin and Atomically Flat Transition-Metal Oxide: Promising Building Blocks for Metal-Insulator Electronics.

    PubMed

    Cui, Qingsong; Sakhdari, Maryam; Chamlagain, Bhim; Chuang, Hsun-Jen; Liu, Yi; Cheng, Mark Ming-Cheng; Zhou, Zhixian; Chen, Pai-Yen

    2016-12-21

    We present a new and viable template-assisted thermal synthesis method for preparing amorphous ultrathin transition-metal oxides (TMOs) such as TiO2 and Ta2O5, which are converted from crystalline two-dimensional (2D) transition-metal dichalcogenides (TMDs) down to a few atomic layers. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning transmission electron microscopy (STEM) were used to characterize the chemical composition and bonding, surface morphology, and atomic structure of these ultrathin amorphous materials to validate the effectiveness of our synthesis approach. Furthermore, we have fabricated metal-insulator-metal (MIM) diodes using the TiO2 and Ta2O5 as ultrathin insulating layers with low potential barrier heights. Our MIM diodes show a clear transition from direct tunneling to Fowler-Nordheim tunneling, which was not observed in previously reported MIM diodes with TiO2 or Ta2O5 as the insulating layer. We attribute the improved performance of our MIM diodes to the excellent flatness and low pinhole/defect densities in our TMO insulting layers converted from 2D TMDs, which enable the low-threshold and controllable electron tunneling transport. We envision that it is possible to use the ultrathin TMOs converted from 2D TMDs as the insulating layer of a wide variety of metal-insulator and field-effect electronic devices for various applications ranging from microwave mixing, parametric conversion, infrared photodetection, emissive energy harvesting, to ultrafast electronic switching.

  6. Combined single-crystalline and polycrystalline CVD diamond substrates for diamond electronics

    SciTech Connect

    Vikharev, A. L. Gorbachev, A. M.; Dukhnovsky, M. P.; Muchnikov, A. B.; Ratnikova, A. K.; Fedorov, Yu. Yu.

    2012-02-15

    The fabrication of diamond substrates in which single-crystalline and polycrystalline CVD diamond form a single wafer, and the epitaxial growth of diamond films on such combined substrates containing polycrystalline and (100) single-crystalline CVD diamond regions are studied.

  7. Silane-catalysed fast growth of large single-crystalline graphene on hexagonal boron nitride

    PubMed Central

    Tang, Shujie; Wang, Haomin; Wang, Hui Shan; Sun, Qiujuan; Zhang, Xiuyun; Cong, Chunxiao; Xie, Hong; Liu, Xiaoyu; Zhou, Xiaohao; Huang, Fuqiang; Chen, Xiaoshuang; Yu, Ting; Ding, Feng; Xie, Xiaoming; Jiang, Mianheng

    2015-01-01

    The direct growth of high-quality, large single-crystalline domains of graphene on a dielectric substrate is of vital importance for applications in electronics and optoelectronics. Traditionally, graphene domains grown on dielectrics are typically only ~1 μm with a growth rate of ~1 nm min−1 or less, the main reason is the lack of a catalyst. Here we show that silane, serving as a gaseous catalyst, is able to boost the graphene growth rate to ~1 μm min−1, thereby promoting graphene domains up to 20 μm in size to be synthesized via chemical vapour deposition (CVD) on hexagonal boron nitride (h-BN). Hall measurements show that the mobility of the sample reaches 20,000 cm2 V−1 s−1 at room temperature, which is among the best for CVD-grown graphene. Combining the advantages of both catalytic CVD and the ultra-flat dielectric substrate, gaseous catalyst-assisted CVD paves the way for synthesizing high-quality graphene for device applications while avoiding the transfer process. PMID:25757864

  8. Reaction of Ta thin film with single crystalline (001) beta-SiC

    NASA Technical Reports Server (NTRS)

    Chen, J. S.; Kolawa, E.; Nicolet, M.-A.; Ruiz, R. P.; Baud, L.; Jaussaud, C.; Madar, R.

    1994-01-01

    The reaction between a sputtered-deposited Ta film (320 nm thick) and a single crystalline (001) beta-SiC substrate induced by vacuum annealing at temperatures of 600-1200 C for 1 h (30 min at 1100 C) is investigated by 3 MeV He(+2) backscattering spectrometry, x-ray diffraction, secondary ion mass spectrometry, and transmission and scanning electron microscopies. No significant reaction is observed at 800 C or at lower tempertures. At 900 C, the main product phases are Ta2C and carbon-stabilized Ta5Si3. A minor amount of unreacted Ta is also present. After annealing at 1000 C, all the tantalum has reacted; the reaction zone possesses a multilayered structure of beta-SiC/TaC/carbon-stabilized Ta5Si3/alpha-Ta5Si3/Ta2C. The diffusion path at 1000 C is plotted on the isothermal section of the Ta-Si-C phase diagram. At 1100 C, the reacted layer has an interface with the SiC substrate that is still quite flat but has a rough surface due to the formation of macroscopic voids within the reacted layer. The equilibrium products predicted by the phase diagram are TaC and TaSi2. This final state is reached by annealing at 1200 C for 1 h. At that point, the reacted layer has a latterally very uneven structure and morphology.

  9. Reaction of Ta thin film with single crystalline (001) beta-SiC

    NASA Technical Reports Server (NTRS)

    Chen, J. S.; Kolawa, E.; Nicolet, M.-A.; Ruiz, R. P.; Baud, L.; Jaussaud, C.; Madar, R.

    1994-01-01

    The reaction between a sputtered-deposited Ta film (320 nm thick) and a single crystalline (001) beta-SiC substrate induced by vacuum annealing at temperatures of 600-1200 C for 1 h (30 min at 1100 C) is investigated by 3 MeV He(+2) backscattering spectrometry, x-ray diffraction, secondary ion mass spectrometry, and transmission and scanning electron microscopies. No significant reaction is observed at 800 C or at lower tempertures. At 900 C, the main product phases are Ta2C and carbon-stabilized Ta5Si3. A minor amount of unreacted Ta is also present. After annealing at 1000 C, all the tantalum has reacted; the reaction zone possesses a multilayered structure of beta-SiC/TaC/carbon-stabilized Ta5Si3/alpha-Ta5Si3/Ta2C. The diffusion path at 1000 C is plotted on the isothermal section of the Ta-Si-C phase diagram. At 1100 C, the reacted layer has an interface with the SiC substrate that is still quite flat but has a rough surface due to the formation of macroscopic voids within the reacted layer. The equilibrium products predicted by the phase diagram are TaC and TaSi2. This final state is reached by annealing at 1200 C for 1 h. At that point, the reacted layer has a latterally very uneven structure and morphology.

  10. Single-crystalline titanium dioxide hollow tetragonal nanocones with large exposed (101) facets for excellent photocatalysis.

    PubMed

    Wu, Zhengcui; Xue, Yejing; Zou, Zexian; Wang, Xia; Gao, Feng

    2017-03-15

    Crystal facet engineering and surface modification of semiconductor have become important strategies to improve photocatalytic activity by optimizing surface charge carrier separation/transfer and extending solar spectrum utilization. In this work, we report anatase single-crystalline TiO2 hollow tetragonal nanocones with large exposed (101) facets by a facile liquid-phase interfacial synthetic strategy, using the hydrolysis of tetrabutyltitanate with adscititious water in the organic solvent of cyclohexane and a capping agent of 1, 6-hexanediamine. The specific surface area of these TiO2 hollow tetragonal nanocones is as high as 331.3m(2)/g. Thanks to large exposed (101) facets and high surface area, these TiO2 hollow tetragonal nanocones exhibited excellent full-arc photocatalytic activities for the degradation of organic pollutants. Remarkably, the butoxy group could be modified onto TiO2 hollow tetragonal nanocones through post-synthesis treatment in tetrabutyltitanate glycol solution, which brought about eximious visible light photocatalytic activities for the degradation of colored dyes of RhB and MO, especially for RhB, by virtue of much improved electron trapping ability of the Ti-O group from the excited dye due to the strong electronegativity of the oxygen atom in the butoxy group. This work advances us to rationally tailor the atomic and electronic structure of the photocatalyst for outstanding photocatalytic properties in various environmental and energy-related applications. Copyright © 2016 Elsevier Inc. All rights reserved.

  11. Control growth of single crystalline ZnO nanorod arrays and nanoflowers with enhanced photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Feng, Jiu-Ju; Wang, Zhen-Zhen; Li, Yong-Fang; Chen, Jian-Rong; Wang, Ai-Jun

    2013-04-01

    Single crystalline vertical nanorod arrays and nanoflowers of ZnO have been grown in situ on cheap zinc foils under hydrothermal conditions, by means of hexamethylenetetramine and ethanolamine, respectively. Their morphologies and crystal structures are characterized by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. The nanorods and flowers of ZnO grew along the { 10bar{1}1} and { 0001} planes, respectively. Both types of ZnO display high photocatalytic ability toward the degradation of methylene orange under UV irradiation. The ZnO nanorods show better performance than that of the ZnO nanoflowers, and the { 10bar{1}1} facets of the ZnO nanorods have higher photoactivity than that of the { 000bar{1}} or { 10bar{1}0} crystal planes. This is because the weaker coordinated O atoms on the surface are more likely to be saturated by H atoms in aqueous solution, thereby releasing more free OH radicals.

  12. Atomistic migration mechanisms of atomically flat, stepped, and kinked grain boundaries

    NASA Astrophysics Data System (ADS)

    Hadian, R.; Grabowski, B.; Race, C. P.; Neugebauer, J.

    2016-10-01

    We studied the migration behavior of mixed tilt and twist grain boundaries in the vicinity of a symmetric tilt <111 > Σ 7 grain boundary in aluminum. We show that these grain boundaries fall into two main categories of stepped and kinked grain boundaries around the atomically flat symmetric tilt boundary. Using these structures together with size converged molecular dynamics simulations and investigating snapshots of the boundaries during migration, we obtain an intuitive and quantitative description of the kinetic and atomistic mechanisms of the migration of general mixed grain boundaries. This description is closely related to well-known concepts in surface growth such as step and kink-flow mechanisms and allows us to derive analytical kinetic models that explain the dependence of the migration barrier on the driving force. Using this insight we are able to extract energy barrier data for the experimentally relevant case of vanishing driving forces that are not accessible from direct molecular dynamics simulations and to classify arbitrary boundaries based on their mesoscopic structures.

  13. Variations in Crystalline Structures and Electrical Properties of Single Crystalline Boron Nitride Nanosheets.

    PubMed

    Aldalbahi, Ali; Zhou, Andrew Feng; Feng, Peter

    2015-11-13

    We report the studies of (1) the basic mechanism underlying the formation of defect-free, single crystalline boron nitride nanosheets (BNNSs) synthesized using pulsed laser plasma deposition (PLPD) technique, (2) the variation in the crystalline structure at the edges of the hexagonal boron nitride (h-BN) nanosheets, and (3) the basic electrical properties related to the BNNSs tunneling effect and electrical breakdown voltage. The nanoscale morphologies of BNNSs are characterized using scanning electron microscope (SEM) and high-resolution transmission electron microscope (HRTEM). The results show that each sample consisted of a number of transparent BNNSs that partially overlapped one another. Varying the deposition duration yielded different thicknesses of sample but did not affect the morphology, structure, and thickness of individual BNNSs pieces. Analysis of the SEM and HRTEM data revealed changes in the spatial period of the B3-N3 hexagonal structures and the interlayer distance at the edge of the BNNSs, which occurred due to the limited number of atomic layers and was confirmed further by x-ray diffraction (XRD) study. The experimental results clearly indicate that the values of the electrical conductivities of the super-thin BNNSs and the effect of temperature relied strongly on the direction of observation.

  14. Variations in Crystalline Structures and Electrical Properties of Single Crystalline Boron Nitride Nanosheets

    NASA Astrophysics Data System (ADS)

    Aldalbahi, Ali; Zhou, Andrew Feng; Feng, Peter

    2015-11-01

    We report the studies of (1) the basic mechanism underlying the formation of defect-free, single crystalline boron nitride nanosheets (BNNSs) synthesized using pulsed laser plasma deposition (PLPD) technique, (2) the variation in the crystalline structure at the edges of the hexagonal boron nitride (h-BN) nanosheets, and (3) the basic electrical properties related to the BNNSs tunneling effect and electrical breakdown voltage. The nanoscale morphologies of BNNSs are characterized using scanning electron microscope (SEM) and high-resolution transmission electron microscope (HRTEM). The results show that each sample consisted of a number of transparent BNNSs that partially overlapped one another. Varying the deposition duration yielded different thicknesses of sample but did not affect the morphology, structure, and thickness of individual BNNSs pieces. Analysis of the SEM and HRTEM data revealed changes in the spatial period of the B3-N3 hexagonal structures and the interlayer distance at the edge of the BNNSs, which occurred due to the limited number of atomic layers and was confirmed further by x-ray diffraction (XRD) study. The experimental results clearly indicate that the values of the electrical conductivities of the super-thin BNNSs and the effect of temperature relied strongly on the direction of observation.

  15. Equilibrium segregation of sulfur to the free surface of single crystalline titanium

    NASA Astrophysics Data System (ADS)

    Cao, Z. X.

    2001-09-01

    Equilibrium segregation of sulfur to the free surface of single crystalline titanium from 560{°}C to 800{°}C was investigated using Auger electron spectroscopy (AES) measurements. To describe the concentration evolution in the sulfur overlayer, Fick's first law was modified by adding a local function df(x)/dx, to the concentration gradient to drive the segregation starting from an initially homogeneous distribution. The diffusion equation thus derived was solved for the case f(x) = asexp (-x/ds). It was found that the solution leads to an AES intensity evolution for segregants, IS(t) = IS∞(1- eαerfc((α)1/2)), α = Dt/ds2, which fits the experimental results extremely well. An exponentially decaying distribution of sulfur beneath the titanium surface at equilibrium was revealed by sputter depth profiling, which in turn justifies our modification to Fick's first law. Without referring to the detailed kinetics, an activation energy Ea = 718 meV/atom was determined by comparing the sulfur concentration evolution at different temperatures.

  16. Large-Area Dry Transfer of Single-Crystalline Epitaxial Bismuth Thin Films.

    PubMed

    Walker, Emily S; Na, Seung Ryul; Jung, Daehwan; March, Stephen D; Kim, Joon-Seok; Trivedi, Tanuj; Li, Wei; Tao, Li; Lee, Minjoo L; Liechti, Kenneth M; Akinwande, Deji; Bank, Seth R

    2016-11-09

    We report the first direct dry transfer of a single-crystalline thin film grown by molecular beam epitaxy. A double cantilever beam fracture technique was used to transfer epitaxial bismuth thin films grown on silicon (111) to silicon strips coated with epoxy. The transferred bismuth films retained electrical, optical, and structural properties comparable to the as-grown epitaxial films. Additionally, we isolated the bismuth thin films on freestanding flexible cured-epoxy post-transfer. The adhesion energy at the bismuth/silicon interface was measured to be ∼1 J/m(2), comparable to that of exfoliated and wet transferred graphene. This low adhesion energy and ease of transfer is unexpected for an epitaxially grown film and may enable the study of bismuth's unique electronic and spintronic properties on arbitrary substrates. Moreover, this method suggests a route to integrate other group-V epitaxial films (i.e., phosphorus) with arbitrary substrates, as well as potentially to isolate bismuthene, the atomic thin-film limit of bismuth.

  17. Electrodeposition of single-crystalline molybdenum layers from tungstate-molybdate melts

    SciTech Connect

    Esina, N.O.; Tarasova, K.P.; Baraboshkin, A.N.

    1987-07-01

    The structure and growth rates of single-crystalline molybdenum layers produced by electrolysis of tungstate-molybdate melts on single-crystalline substrates with the orientations (110), (112), (100), and (111) were investigated. Growth pyramids having a symmetry coincident with that of the substrate plane were revealed as the characteristic feature of surface structure of these layers. The change from single- to polycrystalline molybdenum structure occurs via the development of twinning defects.

  18. Preparation of atomically flat rutile TiO2(001) surfaces for oxide film growth

    SciTech Connect

    Wang, Yang; Lee, Shinbuhm; Vilmercati, P.; Lee, Ho Nyung; Weitering, Hanno; Snijders, Paul C.

    2016-01-01

    The availability of low-index rutile TiO2 single crystal substrates with atomically flat surfaces is essential for enabling epitaxialgrowth of rutile transition metal oxide films. The high surface energy of the rutile (001) surface often leads to surface faceting, which precludes the sputter and annealing treatment commonly used for the preparation of clean and atomically flat TiO2(110) substrate surfaces. In this work, we reveal that stable and atomically flat rutile TiO2(001) surfaces can be prepared with an atomically ordered reconstructedsurface already during a furnace annealing treatment in air. We tentatively ascribe this result to the decrease in surface energy associated with the surface reconstruction, which removes the driving force for faceting. Despite the narrow temperature window where this morphology can initially be formed, we demonstrate that it persists in homoepitaxialgrowth of TiO2(001) thin films. The stabilization of surface reconstructions that prevent faceting of high-surface-energy crystal faces may offer a promising avenue towards the realization of a wider range of high quality epitaxial transition metal oxide heterostructures.

  19. Modulation-doped growth of mosaic graphene with single-crystalline p–n junctions for efficient photocurrent generation

    PubMed Central

    Yan, Kai; Wu, Di; Peng, Hailin; Jin, Li; Fu, Qiang; Bao, Xinhe; Liu, Zhongfan

    2012-01-01

    Device applications of graphene such as ultrafast transistors and photodetectors benefit from the combination of both high-quality p- and n-doped components prepared in a large-scale manner with spatial control and seamless connection. Here we develop a well-controlled chemical vapour deposition process for direct growth of mosaic graphene. Mosaic graphene is produced in large-area monolayers with spatially modulated, stable and uniform doping, and shows considerably high room temperature carrier mobility of ~5,000 cm2 V−1 s−1 in intrinsic portion and ~2,500 cm2 V−1 s−1 in nitrogen-doped portion. The unchanged crystalline registry during modulation doping indicates the single-crystalline nature of p–n junctions. Efficient hot carrier-assisted photocurrent was generated by laser excitation at the junction under ambient conditions. This study provides a facile avenue for large-scale synthesis of single-crystalline graphene p–n junctions, allowing for batch fabrication and integration of high-efficiency optoelectronic and electronic devices within the atomically thin film. PMID:23232410

  20. Wave-function vortex attachment via matrix products: Application to atomic Fermi gases in flat spin-orbit bands

    NASA Astrophysics Data System (ADS)

    Scarola, V. W.

    2014-03-01

    Variational wave functions that introduce zeros (vortices) to screen repulsive interactions are typically difficult to verify in unbiased microscopic calculations. An approach is constructed to insert vortices into ansatz wave functions using a matrix-product representation. This approach opens the door to validation of a broad class of Jastrow-based wave functions. The formalism is applied to a model motivated by experiments on ultracold atomic gases in the presence of synthetic spin-orbit coupling. Validated wave functions show that vortices in atomic Fermi gases with flat Rashba spin-orbit bands cluster near the system center and should therefore be directly visible in time-of-flight imaging.

  1. Magnetic properties of single-crystalline UCu3Al2

    NASA Astrophysics Data System (ADS)

    Nakotte, H.; Brueck, E.; Brabers, J. H. V. J.; Prokes, K.; Deboer, F. R.; Sechovsky, V.; Buschow, K. H. J.; Andreev, A. V.; Robinson, R. A.; Puranto, A.

    UCu3Al2 crystallizes in an ordered variant of the hexagonal CaCu5 structure. By neutron powder-diffraction, the U atoms were found to occupy the 1a sites, while the 2c sites are occupied by Cu atoms only and a random occupation of the 3g sites by the remaining Cu and Al is found. The magnetic susceptibility, measured on a single crystal grown by the Czochralski tri-arc technique, is found to be maximal within the hexagonal basal plane with a maximum at about 10 K. For fields applied within the basal plane, the magnetization at 4.2 K exhibits a slight S-shape starting slightly below 15 T. No such anomalies are found for fields applied along the c-axis where the magnetic response is found to be much lower. No additional magnetic peaks, which could be related with long-range antiferromagnetic ordering, were detected in the neutron powder-patterns at low temperatures.

  2. Field emission from single-crystalline HfC nanowires

    SciTech Connect

    Yuan, Jinshi; Tang, Jie; Zhang Han; Shinya, Norio; Nakajima, Kiyomi; Qin, Lu-Chang

    2012-03-12

    Single HfC nanowire field emitter/electrode structures have been fabricated using nano-assembling and electron beam induced deposition. Field ion microscopy has been applied to study the atomic arrangement of facets formed on a field evaporation-modified HfC nanowire tip. Field evaporation and crystal form studies suggest that the {l_brace}111{r_brace} and {l_brace}110{r_brace} crystal planes have lower work functions, while the {l_brace}100{r_brace}, {l_brace}210{r_brace}, and {l_brace}311{r_brace} planes have higher work functions. Field emission measurement permits us to obtain that the work function of the {l_brace}111{r_brace} crystal plane is about 3.4 eV.

  3. Healing of graphene on single crystalline Ni(111) films

    SciTech Connect

    Zeller, Patrick; Wintterlin, Joost; Speck, Florian; Ostler, Markus; Weinl, Michael; Schreck, Matthias; Seyller, Thomas

    2014-11-10

    The annealing of graphene layers grown on 150 nm thick single crystal Ni(111) films was investigated in situ by low energy electron microscopy and photoemission electron microscopy. After growth, by means of chemical vapor deposition of ethylene, the graphene layers consist of several domains showing different orientations with respect to the underlying Ni surface and also of small bilayer areas. It is shown that, in a controlled process, the rotated domains can be transformed into lattice-aligned graphene, and the bilayer areas can be selectively dissolved, so that exclusively the aligned monolayer graphene is obtained. The ordering mechanism involves transport of C atoms across the surface and solution in the bulk.

  4. CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: Structural and Electrical Properties of Single Crystalline Ga-Doped ZnO Thin Films Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Lu, Zhong-Lin; Zou, Wen-Qin; Xu, Ming-Xiang; Zhang, Feng-Ming; Du, You-Wei

    2009-11-01

    High-quality Ga-doped ZnO (ZnO:Ga) single crystalline films with various Ga concentrations are grown on a-plane sapphire substrates using molecular-beam epitaxy. The site configuration of doped Ga atoms is studied by means of x-ray absorption spectroscopy. It is found that nearly all Ga can substitute into ZnO lattice as electrically active donors, a generating high density of free carriers with about one electron per Ga dopant when the Ga concentration is no more than 2%. However, further increasing the Ga doping concentration leads to a decrease of the conductivity due to partial segregation of Ga atoms to the minor phase of the spinel ZnGa2O4 or other intermediate phase. It seems that the maximum solubility of Ga in the ZnO single crystalline film is about 2 at.% and the lowest resistivity can reach 1.92 × 10-4 Ω·cm at room temperature, close to the best value reported. In contrast to ZnO:Ga thin film with 1% or 2% Ga doping, the film with 4% Ga doping exhibits a metal semiconductor transition at 80 K. The scattering mechanism of conducting electrons in single crystalline ZnO:Ga thin film is discussed.

  5. Advanced fabrication of single-crystalline silver nanopillar on SiO{sub 2} substrate

    SciTech Connect

    Mori, Tomohiro E-mail: kenzo@eng.kagawa-u.ac.jp; Tanaka, Yasuhiro; Suzaki, Yoshifumi; Yamaguchi, Kenzo E-mail: kenzo@eng.kagawa-u.ac.jp

    2016-01-25

    Nanoscale crystallographic textures have received very little attention in research on surface plasmons using metallic nanostructures. A single-crystalline metallic nanostructure with a controlled crystallographic texture is expected to reduce optical losses. We elucidated the grain growth mechanism in silver thin films deposited on a highly transparent SiO{sub 2} substrate by electron backscatter diffraction methods with nanoscale resolution. At higher substrate temperatures, the grain growth was facilitated but the preferred orientation was not achieved. Moreover, we fabricated a single-crystalline silver nanopillar in a (111)-oriented large growing grain, which was controlled by varying the substrate temperature during film deposition by focused ion-beam milling. Furthermore, the light intensity of the scattering spectrum was measured for a single-crystalline silver nanopillar (undersurface diameter: 200 nm) for which surface plasmon resonance was observed. The single-crystalline silver nanopillar exhibits a stronger and sharper spectrum than the polycrystalline silver nanopillar. These results can be applied to the direct fabrication of a single-crystalline silver nanopillar using only physical processing.

  6. Generation and the role of dislocations in single-crystalline phase-change In 2 Se 3 nanowires under electrical pulses

    SciTech Connect

    Mafi, Elham; Tao, Xin; Zhu, Wenguang; Gao, Yanfei; Wang, Chongmin; Gu, Yi

    2016-07-08

    Using single crystalline In2Se3 nanowires as a platform, we have studied the RESET switching (from low to high electrical resistance) in this phase-change material under electric pulses. Particularly, we correlated the atomic-scale structural evolutions with local electrical resistance variations, by performing transmission electron microscopy and scanning Kelvin probe microscopy on the same nanowires. By coupling the experimental results with density functional theory calculations, we show that the immobile dislocations generated via vacancy condensations are responsible for the RESET switching and that the material maintains the single crystallinity during the process. This new mechanism is fundamentally different from the crystalline-amorphous transition, which is commonly understood as the underlying process for the RESET switching in similar phase-change materials.

  7. Controllable growth of ultrathin BiFeO3 from finger-like nanostripes to atomically flat films

    NASA Astrophysics Data System (ADS)

    Feng, Yu; Wang, Can; Tian, Shilu; Zhou, Yong; Ge, Chen; Guo, Haizhong; He, Meng; Jin, Kuijuan; Yang, Guozhen

    2016-09-01

    BiFeO3 (BFO) ultrathin films with nominal thicknesses from 2 to 12 nm were grown with a SrRuO3 (SRO) buffer layer on TiO2-terminated (001) SrTiO3 (STO) substrates using pulsed laser deposition. The surface morphologies and domain configurations of the thin films were investigated using atomic force microscopy and piezoelectric force microscopy. Periodical one-dimensional finger-like nanostripes of BFO on the SRO covered STO substrates were observed. With increasing thickness, the BFO ultrathin films develop from the finger-like nanostripes to an atomically flat surface. The formation of the finger-like nanostructures of BFO is related to the atomic step or terrace structure of the substrate. The BFO nanostripes and the atomically flat thin films both show good ferroelectricity. The as-grown domain orientations of the BFO ultrathin films are ascribed to the chemical terminations at the surface of the SRO layer. These results indicate that the surface morphologies and the domain configurations of BFO ultrathin films can be artificially designed by using substrates with optimized terrace structures and chemical termination, and these films are potentially useful in multifunctional nanoelectronic devices.

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

    NASA Technical Reports Server (NTRS)

    Choi, Sang; King, Glen; Park, Yeonjoon

    2009-01-01

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

  9. Advacancy-mediated atomic steps kinetics and two-dimensional negative island nucleation on ultra-flat Si(111) surface

    NASA Astrophysics Data System (ADS)

    Sitnikov, S. V.; Latyshev, A. V.; Kosolobov, S. S.

    2017-01-01

    We have investigated Si(111) surface morphology transformations during high-temperature sublimation and oxygen treatments by means of in situ ultrahigh vacuum reflection electron microscopy. By analyzing atomic steps kinetics and two-dimensional negative (vacancy) islands nucleation on ultra-flat Si(111) surface with extremely wide (up to 120 μm in size) terraces we have estimated the activation energy associated with the surface-bulk vacancy exchange processes. We show that atomic steps motion and negative islands nucleation kinetics at temperatures above 1180 °C can be described by the step-flow model of Burton, Cabrera and Frank taking into account advacancies formation. By comparing experimental results with predictions of model we conclude that the surface mass transport at temperatures above 1180 °C is governed by surface vacancies nucleation and interaction with atomic steps rather than via adatoms surface diffusion.

  10. Experimental and Theoretical Investigation of Crystallographic Orientation Dependence of Nanoscratching of Single Crystalline Copper

    PubMed Central

    Geng, Yanquan; Zhang, Junjie; Yan, Yongda; Yu, Bowen; Geng, Lin; Sun, Tao

    2015-01-01

    In the present work, we perform experiments and molecular dynamics simulations to elucidate the underlying deformation mechanisms of single crystalline copper under the load-controlled multi-passes nanoscratching using a triangular pyramidal probe. The correlation of microscopic deformation behavior of the material with macroscopically-observed machining results is revealed. Moreover, the influence of crystallographic orientation on the nanoscratching of single crystalline copper is examined. Our simulation results indicate that the plastic deformation of single crystalline Cu under the nanoscratching is exclusively governed by dislocation mechanisms. However, there is no glissile dislocation structure formed due to the probe oscillation under the load-controlled mode. Both experiments and MD simulations demonstrate that the machined surface morphologies in terms of groove depth and surface pile-up exhibit strong crystallographic orientation dependence, because of different geometries of activated slip planes cutting with free surfaces and strain hardening abilities associated with different crystallographic orientations. PMID:26147506

  11. Adsorption and thin-film adhesion on single-crystalline surfaces: Enthalpies, entropies, and kinetic prefactors for surface reactions

    NASA Astrophysics Data System (ADS)

    Sellers, Jason R. V.

    Chemical bonding at solid surfaces and interfaces is influential in a wide range of important technological applications including catalysis, fuel cells, batteries, chemical sensors, and device fabrication for microelectronics, computers, solar cells, and all variety of coatings. Adsorption and adhesion energetics are key elements in understanding interfacial properties, and these properties can be used to develop functional industrial materials. First, the properties of single-crystalline oxide surfaces are reviewed in detail, particularly in regards to the adsorption energetics of these surfaces. This includes the largest collection of experimental adsorption data on single-crystalline oxide surfaces ever presented, from which trends in the thermodynamic properties of adsorbates are revealed which greatly expand our understanding of the physical processes occurring on these surfaces. Among these trends is the discovery that the entropy of adsorbed molecules tracks their gas-phase entropy, retaining ~2/3 of that entropy upon adsorption. This allows for a method of predicting not only entropies of adsorption, but also the kinetic prefactors associated with many classes of elementary surface reactions. These estimations of desorption prefactors are then used to improve calculations of adsorption energies from temperature programmed desorption (TPD) measurements for many systems. Metal adsorption on oxide surfaces and the strength of the binding at metal / oxide interfaces are then discussed. The motivation here is to understand oxide-supported transition metal nanoparticles such as those used in industrial heterogeneous catalysis. For metal atom adsorption, adsorption energetics and adhesion energies are directly related to the energy of the adsorbed atoms, which define their stability, sintering rates, and reactivity, and which are found to vary with both the size of the nanoparticle and the nature of the oxide support. The experimental techniques necessary for

  12. Synthesis and Characterization of Bowl-Like Single-Crystalline BaTiO3 Nanoparticles

    PubMed Central

    2010-01-01

    Novel bowl-like single-crystalline BaTiO3 nanoparticles were synthesized by a simple hydrothermal method using Ba(OH)2·8H2O and TiO2 as precursors. The as-prepared products were characterized by XRD, Raman spectroscopy, SEM and TEM. The results show that the bowl-like BaTiO3 nanoparticles are single-crystalline and have a size about 100–200 nm in diameter. Local piezoresponse force measurements indicate that the BaTiO3 nanoparticles have switchable polarization at room temperature. The local effective piezoelectric coefficient is approximately 28 pm/V. PMID:20596350

  13. Initial Growth of Single-Crystalline Nanowires: From 3D Nucleation to 2D Growth

    NASA Astrophysics Data System (ADS)

    Huang, X. H.; Li, G. H.; Sun, G. Z.; Dou, X. C.; Li, L.; Zheng, L. X.

    2010-06-01

    The initial growth stage of the single-crystalline Sb and Co nanowires with preferential orientation was studied, which were synthesized in porous anodic alumina membranes by the pulsed electrodeposition technique. It was revealed that the initial growth of the nanowires is a three-dimensional nucleation process, and then gradually transforms to two-dimensional growth via progressive nucleation mechanism, which resulting in a structure transition from polycrystalline to single crystalline. The competition among the nuclei inside the nanoscaled-confined channel and the growth kinetics is responsible for the structure transition of the initial grown nanowires.

  14. Atomically flat Ge buffer layers and alternating shutter growth of CaGe2 for large area germanane

    NASA Astrophysics Data System (ADS)

    Xu, Jinsong; Katoch, Jyoti; Ahmed, Adam; Pinchuk, Igor; Williams, Robert; McComb, David; Kawakami, Roland

    Germanane (GeH), which is converted from CaGe2 by soaking in HCl acid, has recently attracted interest because of its novel properties, such as large band gap (1.56eV), spin orbit coupling and predictions of high mobility (18000 cm2/Vs). Previously CaGe2 was successfully grown on Ge(111) substrates by molecular beam epitaxy (MBE) growth. But there were cracks between µm-sized islands, which is not desirable for scientific study and application, and limits the material quality. By growing atomically flat Ge buffer layers and using alternating shutter MBE growth, we are able to grow crack-free, large area films of CaGe2 films. Reflection high energy electron diffraction (RHEED) patterns of Ge buffer layer and CaGe2 indicates high quality two dimensional surfaces, which is further confirmed by atomic force microscopy (AFM), showing atomically flat and uniform Ge buffer layer and CaGe2. The appearance of Laue oscillation in X-ray diffraction (XRD) and Kiessig fringes in X-ray reflectivity (XRR) proves the uniformity of CaGe2 film and the smoothness of the interface. The high quality of CaGe2 film makes it promising to explore novel properties of GeH. Funded by NSF MRSEC DMR-1420451.

  15. Atomic Scale Flatness of Chemically Cleaned Silicon Surfaces Studied by Infrared Attenuated-Total-Reflection Spectroscopy

    NASA Astrophysics Data System (ADS)

    Sawara, Kenichi; Yasaka, Tatsuhiro; Miyazaki, Seiichi; Hirose, Masataka

    1992-07-01

    Hydrogen-terminated Si(111) and Si(100) surfaces obtained by aqueous HF or pH-modified (pH{=}5.3) buffered-HF (BHF) treatments have been characterized by a Fourier transform infrared (FT-IR) attenuated-total-reflection (ATR) technique. The BHF treatment provides better surface flatness than the HF treatment. Pure water rinse is effective for improving the Si(111) surface flatness, while this is not the case for Si(100) because the pure water acts as an alkaline etchant and promotes the formation of (111) microfacets or microdefects on the (100) surface.

  16. 3D Dewetting for Crystal Patterning: Toward Regular Single-Crystalline Belt Arrays and Their Functionality.

    PubMed

    Wu, Yuchen; Feng, Jiangang; Su, Bin; Jiang, Lei

    2016-03-16

    Arrays of unidirectional dewetting behaviors can be generated by using 3D-wettability-difference micropillars, yielding highly ordered organic single-crystalline belt arrays. These patterned organic belts show an improved mobility record and can be used as flexible pressure sensors with high sensitivity.

  17. Single crystalline tantalum oxychloride microcubes: controllable synthesis, formation mechanism and enhanced photocatalytic hydrogen production activity.

    PubMed

    Tu, Hao; Xu, Leilei; Mou, Fangzhi; Guan, Jianguo

    2015-08-11

    Single crystalline microcubes of a new tantalum compound, tantalum oxychloride (TaO2.18Cl0.64), have been fabricated hydrothermally in a concentrated aqueous solution of hydrochloric acid and acetic acid. They contain a superstructure and exhibit remarkably enhanced photocatalytic activities for hydrogen production due to the improved light harvest and facilitated charge transport.

  18. Formation of quasi-single crystalline porous ZnO nanostructures with a single large cavity

    NASA Astrophysics Data System (ADS)

    Cho, Seungho; Kim, Semi; Jung, Dae-Won; Lee, Kun-Hong

    2011-09-01

    We report a method for synthesizing quasi-single crystalline porous ZnO nanostructures containing a single large cavity. The microwave-assisted route consists of a short (about 2 min) temperature ramping stage (from room temperature to 120 °C) and a stage in which the temperature is maintained at 120 °C for 2 h. The structures produced by this route were 200-480 nm in diameter. The morphological yields of this method were very high. The temperature- and time-dependent evolution of the synthesized powders and the effects of an additive, vitamin C, were studied. Spherical amorphous/polycrystalline structures (70-170 nm in diameter), which appeared transitorily, may play a key role in the formation of the single crystalline porous hollow ZnO nanostructures. Studies and characterization of the nanostructures suggested a possible mechanism for formation of the quasi-single crystalline porous ZnO nanostructures with an interior space.We report a method for synthesizing quasi-single crystalline porous ZnO nanostructures containing a single large cavity. The microwave-assisted route consists of a short (about 2 min) temperature ramping stage (from room temperature to 120 °C) and a stage in which the temperature is maintained at 120 °C for 2 h. The structures produced by this route were 200-480 nm in diameter. The morphological yields of this method were very high. The temperature- and time-dependent evolution of the synthesized powders and the effects of an additive, vitamin C, were studied. Spherical amorphous/polycrystalline structures (70-170 nm in diameter), which appeared transitorily, may play a key role in the formation of the single crystalline porous hollow ZnO nanostructures. Studies and characterization of the nanostructures suggested a possible mechanism for formation of the quasi-single crystalline porous ZnO nanostructures with an interior space. Electronic supplementary information (ESI) available: TEM images and the corresponding SAED image of a Zn

  19. The difference of energies of Si atoms with single-crystalline, amorphous, free and nanoparticle configurations

    NASA Astrophysics Data System (ADS)

    Wang, Y. L.; Deng, Z. C.; Chu, L. Z.; Fu, G. S.; Peng, Y. C.

    2009-04-01

    Nanocrystalline silicon (nc-Si) films were systematically prepared via three ways: a) laser anneal or b) thermal anneal of the amorphous silicon (α-Si) films deposited by pulsed-laser ablation (PLA) in base vacuum, c) direct PLA in high-purity Ar gas with pressure of 10 Pa. The anneal-laser fluence, thermal-anneal temperature and ablation-laser fluence thresholds corresponding to the beginning of nanoparticles formation were respectively determined by using scanning electron microscopy (SEM), Raman and X-ray diffraction (XRD) techniques. Incorporated with crystallization mechanism, energies compensated for the formation of one Si nanoparticle in the three ways were calculated approximately. The result shows that for different crystallization ways, the potential barriers during the formation of one ~16 nm nanoparticle are on the order of 10-9 mJ.

  20. Graphene-silicon layered structures on single-crystalline Ir(111) thin films

    SciTech Connect

    Que, Yande D.; Tao, Jing; Zhang, Yong; Wang, Yeliang L.; Wu, Lijun J.; Zhu, Yimei M.; Kim, Kisslinger; Weinl, Michael; Schreck, Matthias; Shen, Chengmin M.; Du, Shixuan X.; Liu, Yunqi Q.; Gao, H. -J.; Huang, Li; Xu, Wenyan Y.

    2015-01-20

    Epitaxial growth of graphene on transition metal crystals, such as Ru,⁽¹⁻³⁾ Ir,⁽⁴⁻⁶⁾ and Ni,⁽⁷⁾ provides large-area, uniform graphene layers with controllable defect density, which is crucial for practical applications in future devices. To decrease the high cost of single-crystalline metal bulks, single-crystalline metal films are strongly suggested as the substrates for epitaxial growth large-scale high-quality graphene.⁽⁸⁻¹⁰⁾ Moreover, in order to weaken the interactions of graphene with its metal host, which may result in a suppression of the intrinsic properties of graphene,⁽¹¹ ¹²⁾ the method of element intercalation of semiconductors at the interface between an epitaxial graphene layer and a transition metal substrate has been successfully realized.⁽¹³⁻¹⁶⁾

  1. Fabrication of single-crystalline plasmonic nanostructures on transparent and flexible amorphous substrates

    NASA Astrophysics Data System (ADS)

    Mori, Tomohiro; Mori, Takeshi; Tanaka, Yasuhiro; Suzaki, Yoshifumi; Yamaguchi, Kenzo

    2017-02-01

    A new experimental technique is developed for producing a high-performance single-crystalline Ag nanostructure on transparent and flexible amorphous substrates for use in plasmonic sensors and circuit components. This technique is based on the epitaxial growth of Ag on a (001)-oriented single-crystalline NaCl substrate, which is subsequently dissolved in ultrapure water to allow the Ag film to be transferred onto a wide range of different substrates. Focused ion beam milling is then used to create an Ag nanoarray structure consisting of 200 cuboid nanoparticles with a side length of 160 nm and sharp, precise edges. This array exhibits a strong signal and a sharp peak in plasmonic properties and Raman intensity when compared with a polycrystalline Ag nanoarray.

  2. GAGG:ce single crystalline films: New perspective scintillators for electron detection in SEM.

    PubMed

    Bok, Jan; Lalinský, Ondřej; Hanuš, Martin; Onderišinová, Zuzana; Kelar, Jakub; Kučera, Miroslav

    2016-04-01

    Single crystal scintillators are frequently used for electron detection in scanning electron microscopy (SEM). We report gadolinium aluminum gallium garnet (GAGG:Ce) single crystalline films as a new perspective scintillators for the SEM. For the first time, the epitaxial garnet films were used in a practical application: the GAGG:Ce scintillator was incorporated into a SEM scintillation electron detector and it showed improved image quality. In order to prove the GAGG:Ce quality accurately, the scintillation properties were examined using electron beam excitation and compared with frequently used scintillators in the SEM. The results demonstrate excellent emission efficiency of the GAGG:Ce single crystalline films together with their very fast scintillation decay useful for demanding SEM applications. Copyright © 2016 Elsevier B.V. All rights reserved.

  3. Specific Heat Capacity Measurement of Single-Crystalline Silicon as New Reference Material

    NASA Astrophysics Data System (ADS)

    Abe, Haruka; Kato, Hideyuki; Baba, Tetsuya

    2011-11-01

    We started to develop a new certified reference material for specific heat capacity measurement using a new type of cryogenic adiabatic calorimeter, applying a pulse-tube cryocooler in the temperature range from 50 to 350 K. A candidate certified reference material is single-crystalline silicon. To check the performance of the equipment, we measured the specific heat capacity of NIST SRM720, a type of synthetic sapphire. The relative expanded uncertainty of the measurement was estimated to be 0.65% at 350 K and 8.2% at 50 K, and the certified value of SRM720 was within the limits of uncertainty. In the next step, we measured the temperature dependence of the specific heat capacity of single-crystalline silicon. The result was compared with some reference data, and good agreement within 0.6% residual was found.

  4. Laser writing of single-crystalline gold substrates for surface enhanced Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Singh, Astha; Sharma, Geeta; Ranjan, Neeraj; Mittholiya, Kshitij; Bhatnagar, Anuj; Singh, B. P.; Mathur, Deepak; Vasa, Parinda

    2017-07-01

    Surface enhanced Raman scattering (SERS) spectroscopy, a powerful contemporary tool for studying low-concentration analytes via surface plasmon induced enhancement of local electric field, is of utility in biochemistry, material science, threat detection, and environmental studies. We have developed a simple, fast, scalable, and relatively low-cost optical method of fabricating and characterizing large-area, reusable and broadband SERS substrates with long storage lifetime. We use tightly focused, intense infra-red laser pulses to write gratings on single-crystalline, Au (1 1 1) gold films on mica which act as SERS substrates. Our single-crystalline SERS substrates compare favourably, in terms of surface quality and roughness, to those fabricated in poly-crystalline Au films. Tests show that our SERS substrates have the potential of detecting urea and 1,10-phenantroline adulterants in milk and water, respectively, at 0.01 ppm (or lower) concentrations.

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

    NASA Astrophysics Data System (ADS)

    Nakao, Wataru; Fukuyama, Hiroyuki

    2003-12-01

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

  6. Single-crystalline zinc oxide nanowires as photoanode material for dye-sensitized solar cells.

    PubMed

    Ho, Shu-Te; Hsiao, Ching-Lun; Lin, Hsin-Yu; Chen, Hsiang-An; Wang, Chiu-Yen; Lin, Heh-Nan

    2010-10-01

    This study reports the use of single-crystalline and well-aligned ZnO nanowires as photoanode material for dye-sensitized solar cells. The ZnO nanowires are grown on fluorine-doped tin oxide coated glass substrates without catalysts by thermal evaporation. In spite of low roughness factors of around 25 for the nanowire photoanodes, the fabricated solar cells yield power conversion efficiencies of around 1.3% under AM 1.5G (100 mW cm-2) illumination. Moreover, fill factors of around 0.5 have been achieved and are relatively high when compared with reported values from ZnO nanowire photoanodes. The results reveal the advantage of using single-crystalline nanowires as photoanode material and provide clues for the advancement of nanowire based dye-sensitized solar cells.

  7. Fabrication of single-crystalline plasmonic nanostructures on transparent and flexible amorphous substrates

    PubMed Central

    Mori, Tomohiro; Mori, Takeshi; Tanaka, Yasuhiro; Suzaki, Yoshifumi; Yamaguchi, Kenzo

    2017-01-01

    A new experimental technique is developed for producing a high-performance single-crystalline Ag nanostructure on transparent and flexible amorphous substrates for use in plasmonic sensors and circuit components. This technique is based on the epitaxial growth of Ag on a (001)-oriented single-crystalline NaCl substrate, which is subsequently dissolved in ultrapure water to allow the Ag film to be transferred onto a wide range of different substrates. Focused ion beam milling is then used to create an Ag nanoarray structure consisting of 200 cuboid nanoparticles with a side length of 160 nm and sharp, precise edges. This array exhibits a strong signal and a sharp peak in plasmonic properties and Raman intensity when compared with a polycrystalline Ag nanoarray. PMID:28216626

  8. Growth of single crystalline germanium thin film on (100) silicon substrate

    NASA Astrophysics Data System (ADS)

    Kim, Sung Wook; Lee, Jaejun; Park, Youn Ho; Park, Jeong Min; Park, Sangwon; Kim, Yeon Joo; Choi, Heon-Jin

    2017-03-01

    Epitaxial growth of germanium thin films (GeTFs) on Si (111) and Si (100) substrates was investigated, and the prepared films were compared with the films grown on SiO2 substrates. Ge films were prepared in three steps. Initially, a Ge interlayer film with thickness of ˜ 10 nm was deposited on the substrate followed by annealing and recrystallization of the film. A Ge film with a thickness of 500 nm was then deposited. A single crystalline Ge film was grown on Si (100) whereas polycrystalline films were grown on the other substrates. The growth rate of the films depends on the type of the substrates used, which in turn determines the crystallinity of the films. Highly crystalline films were obtained with slow growth rates. The single crystalline epitaxial layer of GeTFs formed on Si (100) exhibited a lower threading dislocation density as compared with those grown on Si (111) and SiO2.

  9. Large scale synthesis of highly pure single crystalline tellurium nanowires by thermal evaporation method.

    PubMed

    Mohanty, Paritosh; Park, Jeunghee; Kim, Bongsoo

    2006-11-01

    Single crystalline tellurium nanowires were successfully synthesized in large scale by a facile approach of vaporizing tellurium metal and condensing the vapor in an inert atmosphere onto a Si substrate. Tellurium was evaporated by heating at 300 degrees C at 1 torr and condensed on the Si substrate at 100-150 degrees C, in the downstream of argon (Ar) gas at a flow rate of 25 sccm for 30 min. The as-synthesized nanowires have diameters between 100-300 nm and lengths up to several micrometers. The single crystalline nanowires grew in a preferred [0001] direction. The obtained nanowires were highly pure as only tellurium metal was used in the vaporization process, and no other reagent, surfactant, or template were used for the growth. This low temperature and high-yield approach to the tellurium nanowires synthesis may facilitate its industrial production for various applications.

  10. Graphene-silicon layered structures on single-crystalline Ir(111) thin films

    DOE PAGES

    Que, Yande D.; Tao, Jing; Zhang, Yong; ...

    2015-01-20

    Epitaxial growth of graphene on transition metal crystals, such as Ru,⁽¹⁻³⁾ Ir,⁽⁴⁻⁶⁾ and Ni,⁽⁷⁾ provides large-area, uniform graphene layers with controllable defect density, which is crucial for practical applications in future devices. To decrease the high cost of single-crystalline metal bulks, single-crystalline metal films are strongly suggested as the substrates for epitaxial growth large-scale high-quality graphene.⁽⁸⁻¹⁰⁾ Moreover, in order to weaken the interactions of graphene with its metal host, which may result in a suppression of the intrinsic properties of graphene,⁽¹¹ ¹²⁾ the method of element intercalation of semiconductors at the interface between an epitaxial graphene layer and a transitionmore » metal substrate has been successfully realized.⁽¹³⁻¹⁶⁾« less

  11. Nonvolatile MoS2 field effect transistors directly gated by single crystalline epitaxial ferroelectric

    NASA Astrophysics Data System (ADS)

    Lu, Zhongyuan; Serrao, Claudy; Khan, Asif Islam; You, Long; Wong, Justin C.; Ye, Yu; Zhu, Hanyu; Zhang, Xiang; Salahuddin, Sayeef

    2017-07-01

    We demonstrate non-volatile, n-type, back-gated, MoS2 transistors, placed directly on an epitaxial grown, single crystalline, PbZr0.2Ti0.8O3 (PZT) ferroelectric. The transistors show decent ON current (19 μA/μm), high on-off ratio (107), and a subthreshold swing of (SS ˜ 92 mV/dec) with a 100 nm thick PZT layer as the back gate oxide. Importantly, the ferroelectric polarization can directly control the channel charge, showing a clear anti-clockwise hysteresis. We have self-consistently confirmed the switching of the ferroelectric and corresponding change in channel current from a direct time-dependent measurement. Our results demonstrate that it is possible to obtain transistor operation directly on polar surfaces, and therefore, it should be possible to integrate 2D electronics with single crystalline functional oxides.

  12. The development steps towards the single-crystalline solidification of shaped components in space

    NASA Astrophysics Data System (ADS)

    Amende, W.; Harmathy, P.; Holl, S.; Preu, P.

    This paper gives a survey on the activities leading to the production of single crystalline ODS components under microgravity. The starting material is alloyed powder which is densified to a compact component. The sample is covered with a ceramic mold skin prior to being remelted and solidified with a single crystal matrix which contains finely distributed oxide particle dispersion. The proces is developped in ground tests and by means of a computer assisted simulation.

  13. Liquid/Liquid interfacial polymerization to grow single crystalline nanoneedles of various conducting polymers.

    PubMed

    Nuraje, Nurxat; Su, Kai; Yang, Nan-Loh; Matsui, Hiroshi

    2008-03-01

    Single crystalline nanoneedles of polyaniline (PANI) and polypyrrole (PPY) were synthesized using an interfacial polymerization for the first time. The interfacial crystallization of conductive polymers at the liquid/liquid interface allowed PANI and PPY polymers to form single crystalline nanocrystals in a rice-like shape in the dimensions of 63 nm x 12 nm for PANI and 70 nm x 20 nm for PPY. Those crystalline nanoneedles displayed a fast conductance switching in the time scale of milliseconds. An important growth condition necessary to yield highly crystalline conductive polymers was the extended crystallization time at the liquid/liquid interfaces to increase the degree of crystallization. As compared to other interfacial polymerization methods, lower concentrations of monomer and oxidant solutions were employed to further extend the crystallization time. While other interfacial growth of conducting polymers yielded noncrystalline polymer fibers, our interfacial method produced single crystalline nanocrystals of conductive polymers. We recently reported the liquid/liquid interfacial synthesis of conducting PEDOT nanocrystals; however, this liquid/liquid interfacial method needs to be extended to other conductive polymer nanocrystal syntheses in order to demonstrate that our technique could be applied as the general fabrication procedure for the single crystalline conducting polymer growth. In this report, we showed that the liquid/liquid interfacial crystallization could yield PANI nanocrystals and PPY nanocrystals, other important conductive polymers, in addition to PEDOT nanocrystals. The resulting crystalline polymers have a fast conductance switching time between the insulating and conducting states on the order of milliseconds. This technique will be useful to synthesize conducting polymers via oxidative coupling processes in a single crystal state, which is extremely difficult to achieve by other synthetic methods.

  14. Self-powered cardiac pacemaker enabled by flexible single crystalline PMN-PT piezoelectric energy harvester.

    PubMed

    Hwang, Geon-Tae; Park, Hyewon; Lee, Jeong-Ho; Oh, SeKwon; Park, Kwi-Il; Byun, Myunghwan; Park, Hyelim; Ahn, Gun; Jeong, Chang Kyu; No, Kwangsoo; Kwon, HyukSang; Lee, Sang-Goo; Joung, Boyoung; Lee, Keon Jae

    2014-07-23

    A flexible single-crystalline PMN-PT piezoelectric energy harvester is demonstrated to achieve a self-powered artificial cardiac pacemaker. The energy-harvesting device generates a short-circuit current of 0.223 mA and an open-circuit voltage of 8.2 V, which are enough not only to meet the standard for charging commercial batteries but also for stimulating the heart without an external power source.

  15. Aerosol-assisted synthesis of monodisperse single-crystalline α-cristobalite nanospheres.

    PubMed

    Jiang, Xingmao; Bao, Lihong; Cheng, Yung-Sung; Dunphy, Darren R; Li, Xiaodong; Brinker, C Jeffrey

    2012-01-30

    Monodisperse single-crystalline α-cristobalite nanospheres have been synthesized by hydrocarbon-pyrolysis-induced carbon deposition on amorphous silica aerosol nanoparticles, devitrification of the coated silica at high temperature, and subsequent carbon removal by oxidation. The nanosphere size can be well controlled by tuning the size of the colloidal silica precursor. Uniform, high-purity nanocrystalline α-cristobalite is important for catalysis, nanocomposites, advanced polishing, and understanding silica nanotoxicology.

  16. Controlled Vapor Phase Growth of Single Crystalline, Two-Dimensional GaSe Crystals with High Photoresponse

    PubMed Central

    Li, Xufan; Lin, Ming-Wei; Puretzky, Alexander A.; Idrobo, Juan C.; Ma, Cheng; Chi, Miaofang; Yoon, Mina; Rouleau, Christopher M.; Kravchenko, Ivan I.; Geohegan, David B.; Xiao, Kai

    2014-01-01

    Compared with their bulk counterparts, atomically thin two-dimensional (2D) crystals exhibit new physical properties, and have the potential to enable next-generation electronic and optoelectronic devices. However, controlled synthesis of large uniform monolayer and multi-layer 2D crystals is still challenging. Here, we report the controlled synthesis of 2D GaSe crystals on SiO2/Si substrates using a vapor phase deposition method. For the first time, uniform, large (up to ~60 μm in lateral size), single-crystalline, triangular monolayer GaSe crystals were obtained and their structure and orientation were characterized from atomic scale to micrometer scale. The size, density, shape, thickness, and uniformity of the 2D GaSe crystals were shown to be controllable by growth duration, growth region, growth temperature, and argon carrier gas flow rate. The theoretical modeling of the electronic structure and Raman spectroscopy demonstrate a direct-to-indirect bandgap transition and progressive confinement-induced bandgap shifts for 2D GaSe crystals. The 2D GaSe crystals show p-type semiconductor characteristics and high photoresponsivity (~1.7 A/W under white light illumination) comparable to exfoliated GaSe nanosheets. These 2D GaSe crystals are potentially useful for next-generation electronic and optoelectronic devices such as photodetectors and field-effect transistors. PMID:24975226

  17. Controlled vapor phase growth of single crystalline, two-dimensional GaSe crystals with high photoresponse.

    PubMed

    Li, Xufan; Lin, Ming-Wei; Puretzky, Alexander A; Idrobo, Juan C; Ma, Cheng; Chi, Miaofang; Yoon, Mina; Rouleau, Christopher M; Kravchenko, Ivan I; Geohegan, David B; Xiao, Kai

    2014-06-30

    Compared with their bulk counterparts, atomically thin two-dimensional (2D) crystals exhibit new physical properties, and have the potential to enable next-generation electronic and optoelectronic devices. However, controlled synthesis of large uniform monolayer and multi-layer 2D crystals is still challenging. Here, we report the controlled synthesis of 2D GaSe crystals on SiO2/Si substrates using a vapor phase deposition method. For the first time, uniform, large (up to ~60 μm in lateral size), single-crystalline, triangular monolayer GaSe crystals were obtained and their structure and orientation were characterized from atomic scale to micrometer scale. The size, density, shape, thickness, and uniformity of the 2D GaSe crystals were shown to be controllable by growth duration, growth region, growth temperature, and argon carrier gas flow rate. The theoretical modeling of the electronic structure and Raman spectroscopy demonstrate a direct-to-indirect bandgap transition and progressive confinement-induced bandgap shifts for 2D GaSe crystals. The 2D GaSe crystals show p-type semiconductor characteristics and high photoresponsivity (~1.7 A/W under white light illumination) comparable to exfoliated GaSe nanosheets. These 2D GaSe crystals are potentially useful for next-generation electronic and optoelectronic devices such as photodetectors and field-effect transistors.

  18. Controlled Vapor Phase Growth of Single Crystalline, Two-Dimensional GaSe Crystals with High Photoresponse

    SciTech Connect

    Li, Xufan; Lin, Ming-Wei; Zhang, Huidong; Puretzky, Alexander A; Idrobo Tapia, Juan C; Ma, Cheng; Chi, Miaofang; Yoon, Mina; Rouleau, Christopher M; Kravchenko, Ivan I; Geohegan, David B; Xiao, Kai

    2014-01-01

    Abstract Compared with their bulk counterparts, atomically thin two-dimensional (2D) crystals exhibit new physical properties, and have the potential to enable next-generation electronic and optoelectronic devices. However, controlled synthesis of large uniform monolayer and multi-layer 2D crystals is still challenging. Here, we report the controlled synthesis of 2D GaSe crystals on SiO2/Si substrates using a vapor phase deposition method. For the first time, uniform, large (up to ~60 m in lateral size), single-crystalline, triangular monolayer GaSe crystals were obtained and their atomic resolution structure were characterized. The size, density, shape, thickness, and uniformity of the 2D GaSe crystals were shown to be controllable by growth duration, growth region, growth temperature, and argon carrier gas flow rate. The theoretical modeling of the electronic structure and Raman spectroscopy demonstrate a direct-to-indirect bandgap transition and progressive confinement-induced bandgap shifts for 2D GaSe crystals. The 2D GaSe crystals show p-type semiconductor characteristics and high photoresponsivity (~1.7 A/W under white light illumination) comparable to exfoliated GaSe nanosheets. These 2D GaSe crystals are potentially useful for next-generation electronic and optoelectronic devices such as photodetectors and field-effect transistors.

  19. Solution coating of large-area organic semiconductor thin films with aligned single-crystalline domains.

    PubMed

    Diao, Ying; Tee, Benjamin C-K; Giri, Gaurav; Xu, Jie; Kim, Do Hwan; Becerril, Hector A; Stoltenberg, Randall M; Lee, Tae Hoon; Xue, Gi; Mannsfeld, Stefan C B; Bao, Zhenan

    2013-07-01

    Solution coating of organic semiconductors offers great potential for achieving low-cost manufacturing of large-area and flexible electronics. However, the rapid coating speed needed for industrial-scale production poses challenges to the control of thin-film morphology. Here, we report an approach--termed fluid-enhanced crystal engineering (FLUENCE)--that allows for a high degree of morphological control of solution-printed thin films. We designed a micropillar-patterned printing blade to induce recirculation in the ink for enhancing crystal growth, and engineered the curvature of the ink meniscus to control crystal nucleation. Using FLUENCE, we demonstrate the fast coating and patterning of millimetre-wide, centimetre-long, highly aligned single-crystalline organic semiconductor thin films. In particular, we fabricated thin films of 6,13-bis(triisopropylsilylethynyl) pentacene having non-equilibrium single-crystalline domains and an unprecedented average and maximum mobilities of 8.1±1.2 cm(2) V(-1) s(-1) and 11 cm(2) V(-1) s(-1). FLUENCE of organic semiconductors with non-equilibrium single-crystalline domains may find use in the fabrication of high-performance, large-area printed electronics.

  20. Solution coating of large-area organic semiconductor thin films with aligned single-crystalline domains

    NASA Astrophysics Data System (ADS)

    Diao, Ying; Tee, Benjamin C.-K.; Giri, Gaurav; Xu, Jie; Kim, Do Hwan; Becerril, Hector A.; Stoltenberg, Randall M.; Lee, Tae Hoon; Xue, Gi; Mannsfeld, Stefan C. B.; Bao, Zhenan

    2013-07-01

    Solution coating of organic semiconductors offers great potential for achieving low-cost manufacturing of large-area and flexible electronics. However, the rapid coating speed needed for industrial-scale production poses challenges to the control of thin-film morphology. Here, we report an approach—termed fluid-enhanced crystal engineering (FLUENCE)—that allows for a high degree of morphological control of solution-printed thin films. We designed a micropillar-patterned printing blade to induce recirculation in the ink for enhancing crystal growth, and engineered the curvature of the ink meniscus to control crystal nucleation. Using FLUENCE, we demonstrate the fast coating and patterning of millimetre-wide, centimetre-long, highly aligned single-crystalline organic semiconductor thin films. In particular, we fabricated thin films of 6,13-bis(triisopropylsilylethynyl) pentacene having non-equilibrium single-crystalline domains and an unprecedented average and maximum mobilities of 8.1±1.2 cm2 V-1 s-1 and 11 cm2 V-1 s-1. FLUENCE of organic semiconductors with non-equilibrium single-crystalline domains may find use in the fabrication of high-performance, large-area printed electronics.

  1. Effect of strontium ions on the early formation of biomimetic apatite on single crystalline rutile

    NASA Astrophysics Data System (ADS)

    Lindahl, Carl; Engqvist, Håkan; Xia, Wei

    2013-02-01

    Single crystalline rutile is a good model to investigate the growth mechanism of hydroxyapatite on bioactive Ti surfaces. Previous studies have shown the difference on different crystalline rutile faces in the early stage and during the growth of HAp crystals from simulated body fluids. It is known that the biological apatite crystal is an ion-substituted apatite. Ion substitution will influence the HAp crystal growth and morphology. In the present study, the effect of strontium ions on the adsorption of Ca and phosphate ions on three different faces of single crystalline rutile substrates has been investigated. The ion adsorption is the crucial step in the nucleation of HAp crystals on specific surfaces. Single crystalline rutile surfaces ((1 1 0), (1 0 0) and (0 0 1)) were soaked in phosphate buffer solutions containing calcium and strontium ions for different time periods. The results showed that the adsorption of Sr, Ca and P is faster on the (1 1 0) surface than on the (1 0 0) and (0 0 1) surfaces. Almost same amount of Sr ion was adsorbed on the surfaces compared to the adsorption of Ca ion. Strontium ion influenced the biological apatite formation in the early stage in this study.

  2. Single-layer MoS{sub 2} roughness and sliding friction quenching by interaction with atomically flat substrates

    SciTech Connect

    Quereda, J.; Castellanos-Gomez, A.; Agraït, N.; Rubio-Bollinger, G.

    2014-08-04

    We experimentally study the surface roughness and the lateral friction force in single-layer MoS{sub 2} crystals deposited on different substrates: SiO{sub 2}, mica, and hexagonal boron nitride (h-BN). Roughness and sliding friction measurements are performed by atomic force microscopy. We find a strong dependence of the MoS{sub 2} roughness on the underlying substrate material, being h-BN the substrate which better preserves the flatness of the MoS{sub 2} crystal. The lateral friction also lowers as the roughness decreases, and attains its lowest value for MoS{sub 2} flakes on h-BN substrates. However, it is still higher than for the surface of a bulk MoS{sub 2} crystal, which we attribute to the deformation of the flake due to competing tip-to-flake and flake-to-substrate interactions.

  3. Effects of Formulated Glyphosate and Adjuvant Tank Mixes on Atomization from Aerial Application Flat Fan Nozzles

    DTIC Science & Technology

    2012-01-01

    and Siddiqui, H. A., “Measurement of Drop Spectra from Rotary Cage Aerial Atomizers,” Crop Protect., Vol. 9, No. 1, 1990, pp. 33–38. [9] Teske , M. E...piled from Wind Tunnel Tests,” Report No. FPM 90-9, USDA Forest Service, Washington, D.C., 1991. [20] Teske , M. E., Skyler, P. J., and Barry, J. W., “A...International Conference, NIST Special Publication 813, National Institute of Standard and Tech- nology, Gaithersburg, MD, 1991, pp. 325–332. [21] Teske , M. E

  4. The Nanostructuring of Atomically Flat Ru(0001) upon Oxidation and Reduction

    NASA Astrophysics Data System (ADS)

    Goriachko, A.; Over, H.

    2016-12-01

    The O/Ru(0001) system is widely studied due to its rich phase variety of various stoichiometry and atomic arrangements, including the formation of a RuO2/Ru(0001) oxide layer. Apart from homogeneous ruthenium surfaces in certain oxidation states, also strongly heterogeneous surfaces can exist due to oxidation state's variation at the nanoscale. We report on a scanning tunneling microscopy (STM) study of the nanostructuring of the oxidized Ru(0001) surface as a result of its interaction with molecular oxygen at elevated temperatures and subsequent reduction of a resulting RuO2 film by CO or HCl molecules from the gas phase in high-vacuum environment.

  5. Atomically flat surface of (0 0 1) textured FePt thin films by residual stress control

    NASA Astrophysics Data System (ADS)

    Liu, S. H.; Hsiao, S. N.; Chou, C. L.; Chen, S. K.; Lee, H. Y.

    2015-11-01

    Single-layered Fe52Pt48 films with thickness of 10 nm were sputter-deposited on glass substrates. Rapid thermal annealing with different heating rates (10-110 K/s) was applied to transform as-deposited fcc phase into L10 phase and meanwhile to align [0 0 1]-axis of L10 crystal along plane normal direction. Based on X-ray diffractometry using synchrotron radiation source, the texture coefficient of (0 0 1)-plane increases with increasing heating rate from 10 to 40 K/s, which is correlated with perpendicular magnetic anisotropy and in-plane tensile stress analyzed by asymmetric sin2 ψ method. Furthermore, it was revealed by atomic force microscopy that the dewetting process occurred as heating rate was raised up to 80 K/s and higher. The change in the microstructure due to stress relaxation leads to the degradation of (0 0 1) orientation and magnetic properties. Surface roughness is closely related to the in-plane tensile stress. Enhanced perpendicular magnetic anisotropy and atomically flat surface were achieved for the samples annealed at 40 K/s, which may be suitable for further practical applications. This work also suggests a feasible way for surface engineering by controlling internal stress of the FePt without introducing cap layer.

  6. Synthesis and magnetic properties of the chromium-doped iron sulfide Fe1-xCrxS single crystalline nanoplates with a NiAs crystal structure.

    PubMed

    Starchikov, S S; Lyubutin, I S; Lin, Chun-Rong; Tseng, Yaw-Teng; Funtov, K O; Ogarkova, Yu L; Dmitrieva, T V; Ivanova, A G

    2015-06-28

    Single crystalline iron sulfide nanoparticles doped with chromium Fe1-xCrxS (0 ≤x≤ 0.15) have been successfully prepared by a thermal decomposition method. The particles are self-organized into the single crystalline plates with the accurate hexagonal shape and dimensions up to 1 μ in plane and about 30-40 nm in thickness. The samples have the NiAs-type crystal structure (P63/mmc) at all Cr concentrations up to x = 0.15. Fe(57)-Mössbauer spectroscopy data reveal four nonequivalent iron sites in these nanocrystals related to the different number of cation vacancies in neighboring of the iron atoms. A 2C-type superstructure or a mixture of 2C and 3C superstructures of vacancy ordering can appear in these samples. It was established that in the Fe1-xCrxS series chromium prefers to replace iron in the cation layers containing vacancies at 0.00 < x < 0.10 and Cr atoms occupy both iron and vacant sites at x > 0.10. The specific magnetic properties, which can be tuned by chromium doping, enable potential applications of these nanoparticles in technical devices using the material with thermally activated magnetic memory, for example, switches or storages.

  7. Deposition of an Ultraflat Graphene Oxide Nanosheet on Atomically Flat Substrates

    NASA Astrophysics Data System (ADS)

    Khan, M. Z. H.; Shahed, S. M. F.; Yuta, N.; Komeda, T.

    2017-02-01

    In this study, graphene oxide (GO) sheets produced in the form of stable aqueous dispersions were deposited on Au (111), freshly cleaved mica, and highly oriented pyrolytic graphite (HOPG) substrates. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to study the presence and distinct contact of GO sheets on the substrates. It was revealed from the topography images that high-quality ultraflat GO monolayer sheets formed on the substrates without distinct cracking/wrinkling or folding. GO sheets with apparent height variation observed by microscopy also indicate ultraflat deposition with clear underlying steps. It was observed that ultrasonication and centrifuge steps prior to deposition were very effective for getting oxidation debris (OD)-free ultraflat single monolayer GO nanosheets onto substrates and that the process depends on the concentration of supplied GO solutions.

  8. Deposition of an Ultraflat Graphene Oxide Nanosheet on Atomically Flat Substrates

    NASA Astrophysics Data System (ADS)

    Khan, M. Z. H.; Shahed, S. M. F.; Yuta, N.; Komeda, T.

    2017-07-01

    In this study, graphene oxide (GO) sheets produced in the form of stable aqueous dispersions were deposited on Au (111), freshly cleaved mica, and highly oriented pyrolytic graphite (HOPG) substrates. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to study the presence and distinct contact of GO sheets on the substrates. It was revealed from the topography images that high-quality ultraflat GO monolayer sheets formed on the substrates without distinct cracking/wrinkling or folding. GO sheets with apparent height variation observed by microscopy also indicate ultraflat deposition with clear underlying steps. It was observed that ultrasonication and centrifuge steps prior to deposition were very effective for getting oxidation debris (OD)-free ultraflat single monolayer GO nanosheets onto substrates and that the process depends on the concentration of supplied GO solutions.

  9. The facile synthesis of single crystalline palladium arrow-headed tripods and their application in formic acid electro-oxidation.

    PubMed

    Su, Na; Chen, Xueying; Ren, Yuanhang; Yue, Bin; Wang, Han; Cai, Wenbin; He, Heyong

    2015-04-28

    Single crystalline palladium arrow-headed tripods prepared via a simple one-pot strategy exhibit high electro-activity in formic acid oxidation, which could be a promising anodic catalyst for direct formic acid fuel cells.

  10. Enhanced photocatalytic efficiency in zirconia buffered n-NiO/p-NiO single crystalline heterostructures by nanosecond laser treatment

    SciTech Connect

    Molaei, R.; Bayati, M. R.; Alipour, H. M.; Nori, S.; Narayan, J.

    2013-06-21

    We report the formation of NiO based single crystalline p-n junctions with enhanced photocatalytic activity induced by pulsed laser irradiation. The NiO epilayers were grown on Si(001) substrates buffered with cubic yttria-stabilized zirconia (c-YSZ) by using pulsed laser deposition. The NiO/c-YSZ/Si heterostructures were subsequently laser treated by 5 pulses of KrF excimer laser (pulse duration = 25 Multiplication-Sign 10{sup -9} s) at lower energies. Microstructural studies, conducted by X-ray diffraction ({theta}-2{theta} and {phi} techniques) and high resolution transmission electron microscope, showed a cube-on-cube epitaxial relationship at the c-YSZ/Si interface; the epitaxial relationship across the NiO/c-YSZ interface was established as NiO<111 > Double-Vertical-Line Double-Vertical-Line c-YSZ<001> and in-plane NiO<110> Double-Vertical-Line Double-Vertical-Line c-YSZ<100>. Electron microscopy studies showed that the interface between the laser annealed and the pristine region as well as the NiO/c-YSZ interface was atomically sharp and crystallographically continuous. The formation of point defects, namely oxygen vacancies and NiO, due to the coupling of the laser photons with the NiO epilayers was confirmed by XPS. The p-type electrical characteristics of the pristine NiO epilayers turned to an n-type behavior and the electrical conductivity was increased by one order of magnitude after laser treatment. Photocatalytic activity of the pristine (p-NiO/c-YSZ/Si) and the laser-annealed (n-NiO/p-NiO/c-YSZ/Si) heterostructures were assessed by measuring the decomposition rate of 4-chlorophenol under UV light. The photocatalytic reaction rate constants were determined to be 0.0059 and 0.0092 min{sup -1} for the as-deposited and the laser-treated samples, respectively. The enhanced photocatalytic efficiency was attributed to the suppressed charge carrier recombination in the NiO based p-n junctions and higher electrical conductivity. Besides, the oxygen vacancies

  11. Large-scale growth of millimeter-long single-crystalline ZnS nanobelts

    SciTech Connect

    Li Jianye Zhang Qi; An Lei; Qin Luchang; Liu Jie

    2008-11-15

    Millimeter-long single-crystalline hexagonal ZnS nanobelts were grown on specific locations on a wafer scale. This is the first time that the millimeter-scale ZnS nanobelt has been synthesized. The longest nanobelts are about 3 mm. The as-grown nanobelts were characterized by means of field emission scanning electron microscopy, X-ray powder diffraction, high-resolution transmission electron microscopy, and selected area electron diffraction. The results indicate that the ultra-long nanobelts are pure single-crystalline hexagonal ZnS. There are two kinds of ZnS nanobelts existing in the products. One is the nanobelts that have two smooth sides and grow along the [0 0 1] longitudinal direction, and the other is the nanobelts that have one smooth side and one saw-teeth-like side, namely nanosaws, and grow along the [2 1 0] longitudinal direction. A vapor-liquid-solid mechanism is suggested for the lengthwise growth of the ZnS nanobelts (nanosaws) and a vapor-solid mechanism for the side direction growth of the saw-teeth of the nanosaws. - Graphical Abstract: Millimeter-long single-crystalline ZnS nanobelts were grown on specific locations on a large scale. There are two kinds of nanobelts in the products-one has two smooth sides, and the other has one smooth side and one saw-teeth-like side, namely nanosaws. Mechanisms for the longitudinal direction growth of the nanobelts/nanosaws and the side saw-teeth direction growth of the nanosaws are discussed.

  12. Dependence of Fracture Toughness on Crystallographic Orientation in Single-Crystalline Cubic (β) Silicon Carbide

    SciTech Connect

    Pharr, M.; Katoh, Y.; Bei, H.

    2006-01-01

    Along with other desirable properties, the ability of silicon carbide (SiC) to retain high strength after elevated temperature exposures to neutron irradiation renders it potentially applicable in fusion and advanced fission reactors. However, properties of the material such as room temperature fracture toughness must be thoroughly characterized prior to such practical applications. The objective of this work is to investigate the dependence of fracture toughness on crystallographic orientation for single-crystalline β-SiC. X-ray diffraction was first performed on the samples to determine the orientation of the crystal. Nanoindentation was used to determine a hardness of 39.1 and 35.2 GPa and elastic modulus of 474 and 446 GPa for the single-crystalline and polycrystalline samples, respectively. Additionally, crack lengths and indentation diagonals were measured via a Vickers micro-hardness indenter under a load of 100 gf for different crystallographic orientations with indentation diagonals aligned along fundamental cleavage planes. Upon examination of propagation direction of cracks, the cracks usually did not initiate and propagate from the corners of the indentation where the stresses are concentrated but instead from the indentation sides. Such cracks clearly moved along the {1 1 0} family of planes (previously determined to be preferred cleavage plane), demonstrating that the fracture toughness of SiC is comparatively so much lower along this set of planes that the lower energy required to cleave along this plane overpowers the stress-concentration at indentation corners. Additionally, fracture toughness in the <1 1 0> direction was 1.84 MPa·m1/2, lower than the 3.46 MPa·m1/2 measured for polycrystalline SiC (which can serve as an average of a spectrum of orientations), further demonstrating that single-crystalline β-SiC has a strong fracture toughness anisotropy.

  13. Freestanding mesoporous quasi-single-crystalline CO3O4 nanowire arrays.

    PubMed

    Li, Yanguang; Tan, Bing; Wu, Yiying

    2006-11-08

    We report a facile template-free method for the large-area growth of freestanding hollow Co3O4 nanowire arrays on a variety of substrates including transparent conducting glass, Si wafer, and copper foil, et al. These nanowires have the interesting combined properties of mesoporosity and quasi-single-crystallinity. With their high surface area and crystallinity, and their direct growth on conductive substrate, these Co3O4 nanowire arrays will have promising applications in lithium-ion batteries, chemical sensing, and field-emission and electrochromic devices. Using the prepared nanowire arrays as electrode, an electrochemical sensor for hydrogen peroxide sensing has been demonstrated.

  14. Explanation of relatively high values of the magnetic entropy change in single crystalline terbium

    NASA Astrophysics Data System (ADS)

    Zverev, V. I.; Gimaev, R. R.

    2016-12-01

    Heat capacity and magnetization data from 5 to 300 K at applied magnetic fields of up to 100 kOe were used to determine the entropy change of single crystalline terbium. This was found to be relatively high in comparison with other heavy rare-earths possessing comparable magnetic moments. In addition, the refined magnetic phase diagram of Tb was used to estimate the main contributions to the entropy change and compared to that of the giant magnetocaloric effect in Gd5(Ge2Si2) .

  15. Superconducting and charge density wave transition in single crystalline LaPt2Si2

    NASA Astrophysics Data System (ADS)

    Gupta, Ritu; Dhar, S. K.; Thamizhavel, A.; Rajeev, K. P.; Hossain, Z.

    2017-06-01

    We present results of our comprehensive studies on single crystalline LaPt2Si2. Pronounced anomaly in electrical resistivity and heat capacity confirms the bulk nature of superconductivity (SC) and charge density wave (CDW) transition in the single crystals. While the charge density wave transition temperature is lower, the superconducting transition temperature is higher in single crystal compared to the polycrystalline sample. This result confirms the competing nature of CDW and SC. Another important finding is the anomalous temperature dependence of upper critical field H C2(T). We also report the anisotropy in the transport and magnetic measurements of the single crystal.

  16. Morphology and magnetic flux distribution in superparamagnetic, single-crystalline Fe3O4 nanoparticle rings

    NASA Astrophysics Data System (ADS)

    Takeno, Yumu; Murakami, Yasukazu; Sato, Takeshi; Tanigaki, Toshiaki; Park, Hyun Soon; Shindo, Daisuke; Ferguson, R. Matthew; Krishnan, Kannan M.

    2014-11-01

    This study reports on the correlation between crystal orientation and magnetic flux distribution of Fe3O4 nanoparticles in the form of self-assembled rings. High-resolution transmission electron microscopy demonstrated that the nanoparticles were single-crystalline, highly monodispersed, (25 nm average diameter), and showed no appreciable lattice imperfections such as twins or stacking faults. Electron holography studies of these superparamagnetic nanoparticle rings indicated significant fluctuations in the magnetic flux lines, consistent with variations in the magnetocrystalline anisotropy of the nanoparticles. The observations provide useful information for a deeper understanding of the micromagnetics of ultrasmall nanoparticles, where the magnetic dipolar interaction competes with the magnetic anisotropy.

  17. Observation of the D'yakonov-Perel' Spin Relaxation in Single-Crystalline Pt Thin Films

    NASA Astrophysics Data System (ADS)

    Ryu, Jeongchun; Kohda, Makoto; Nitta, Junsaku

    2016-06-01

    The spin relaxation mechanism in single-crystalline and polycrystalline platinum (Pt) thin films is revealed by a quantum interference effect. Examining the relationship between the spin relaxation rate and momentum scattering rate by changing Pt thickness, we find that the spin relaxation rate of Pt strongly depends on both crystal structure and thickness even though the quality of material (Pt) is unchanged. In particular, the D'yakonov-Perel' mechanism is considered as a dominant mechanism under cases where scattering events are suppressed or the interface effect is not negligible.

  18. Femtosecond-pulse laser ablation of dental hydroxyapatite and single-crystalline fluoroapatite

    NASA Astrophysics Data System (ADS)

    Krüger, J.; Kautek, W.; Newesely, H.

    Laser microdrilling of healthy human enamel and dentine using 300 fs pulses at a wavelength of 615 nm and 3 Hz repetition rate leads to an enhanced structuring quality in comparison with nanosecond-laser results. Microcracking and damage to neighboring tissue can be reduced. Ablation threshold fluences for 100 laser pulses of 0.3 Jcm-2 (human dentine), 0.6 Jcm-2 (human enamel) and 0.8 Jcm-2 (single crystalline fluoroapatite) could be determined. Ablation depths per pulse below 1 μm were observed.

  19. Single-crystalline δ-Ni2Si nanowires with excellent physical properties

    NASA Astrophysics Data System (ADS)

    Chiu, Wen-Li; Chiu, Chung-Hua; Chen, Jui-Yuan; Huang, Chun-Wei; Huang, Yu-Ting; Lu, Kuo-Chang; Hsin, Cheng-Lun; Yeh, Ping-Hung; Wu, Wen-Wei

    2013-06-01

    In this article, we report the synthesis of single-crystalline nickel silicide nanowires (NWs) via chemical vapor deposition method using NiCl2·6H2O as a single-source precursor. Various morphologies of δ-Ni2Si NWs were successfully acquired by controlling the growth conditions. The growth mechanism of the δ-Ni2Si NWs was thoroughly discussed and identified with microscopy studies. Field emission measurements show a low turn-on field (4.12 V/μm), and magnetic property measurements show a classic ferromagnetic characteristic, which demonstrates promising potential applications for field emitters, magnetic storage, and biological cell separation.

  20. Magnetic properties of single crystalline Co nanowire arrays with different diameters and orientations

    NASA Astrophysics Data System (ADS)

    Huang, X. H.; Li, G. H.; Dou, X. C.; Li, L.

    2009-04-01

    Single crystalline Co nanowire arrays with different diameters and orientations were grown within porous anodic alumina membranes by a pulsed electrodeposition technique and the magnetic properties of the nanowire were systematically studied. It was found that the magnetization behavior of the Co nanowire arrays is anisotropic and their magnetic properties can be effectively modulated through tuning either the diameter or the orientation of the nanowires. The magnetic properties of the Co nanowires were discussed qualitatively by using the classical magnetization theory and single domain model.

  1. Dissolution chemistry and biocompatibility of single-crystalline silicon nanomembranes and associated materials for transient electronics.

    PubMed

    Hwang, Suk-Won; Park, Gayoung; Edwards, Chris; Corbin, Elise A; Kang, Seung-Kyun; Cheng, Huanyu; Song, Jun-Kyul; Kim, Jae-Hwan; Yu, Sooyoun; Ng, Joanne; Lee, Jung Eun; Kim, Jiyoung; Yee, Cassian; Bhaduri, Basanta; Su, Yewang; Omennetto, Fiorenzo G; Huang, Yonggang; Bashir, Rashid; Goddard, Lynford; Popescu, Gabriel; Lee, Kyung-Mi; Rogers, John A

    2014-06-24

    Single-crystalline silicon nanomembranes (Si NMs) represent a critically important class of material for high-performance forms of electronics that are capable of complete, controlled dissolution when immersed in water and/or biofluids, sometimes referred to as a type of "transient" electronics. The results reported here include the kinetics of hydrolysis of Si NMs in biofluids and various aqueous solutions through a range of relevant pH values, ionic concentrations and temperatures, and dependence on dopant types and concentrations. In vitro and in vivo investigations of Si NMs and other transient electronic materials demonstrate biocompatibility and bioresorption, thereby suggesting potential for envisioned applications in active, biodegradable electronic implants.

  2. Luminescent and scintillation properties of YAG:Tm and YAG:Ce,Tm single crystalline films

    NASA Astrophysics Data System (ADS)

    Zorenko, Yu.; Gorbenko, V.; Savchyn, V.; Suchocki, A.; Wrzesinski, H.; Walczyk, K.; Fabisiak, K.; Bilski, P.; Twardak, A.

    2014-08-01

    The paper is dedicated to studying the luminescent and scintillation properties of the single crystalline films (SCF) of Tm and Tm-Ce doped Y3Al5O12 garnets grown by the liquid phase epitaxy method. We have found that the effective Tm → Ce energy transfer is observed in YAG:Ce,Tm SCF. As a result of such transfer, the scintillation light yield of YAG:Ce,Tm SCF under α-particles excitation can be large in comparison with YAG:Ce SCF counterpart.

  3. Single crystalline molybdenum nanowires, nanowire arrays and nanopore arrays in nickel-aluminium.

    PubMed

    Milenkovic, Srdjan; Smith, Andrew Jonathan; Hassel, Achim Walter

    2009-06-01

    This work describes a novel fabrication method of single crystalline Mo nanowires and nanowire arrays. The method utilizes directional solidification (ds) of a NiAl-Mo eutectic alloy and its subsequent electrochemical processing. In the first step, a self-organized array of Mo nanowires embedded in a NiAl matrix is obtained. By combining the Pourbaix diagrams of the three elements involved, a strategy for selective removal of either of the two phases is derived. An oxidizing acidic solution of pH 0.2 dissolved the matrix and released an array of long and uniform Mo wires. Even a complete extraction of the wires is possible through entire dissolution of the matrix. On the other hand, electrodissolution of the Mo with a simultaneous passivation of the NiAl matrix at the pH 6 and the potential of 200 mV SHE yielded nanopore arrays with rectangular pores. This method has several advantages. First of all, it is one of the few top-down methods that allow the production of large amounts of nanostructures. In addition, both the wires and the matrix are single crystalline which makes them favorable for various applications. Further, the obtained nanostructures exhibit extremely high aspect ratios (> 1000), unreachable by most other techniques. This technique has the potential for the production of nanowire arrays either for employment in sensors or in field emission.

  4. Single-Crystalline Ultrathin Co3O4 Nanosheets with Massive Vacancy Defects for Enhanced Electrocatalysis

    DOE PAGES

    Cai, Zhao; Bi, Yongmin; Hu, Enyuan; ...

    2017-09-18

    The role of vacancy defects is demonstrated to be positive in various energy-related processes. However, introducing vacancy defects into single-crystalline nanostructures with given facets and studying their defect effect on electrocatalytic properties remains a great challenge. Here this paper deliberately introduces oxygen defects into single-crystalline ultrathin Co3O4 nanosheets with O-terminated {111} facets by mild solvothermal reduction using ethylene glycol under alkaline condition. As-prepared defect-rich Co3O4 nanosheets show a low overpotential of 220 mV with a small Tafel slope of 49.1 mV dec-1 for the oxygen evolution reaction (OER), which is among the best Co-based OER catalysts to date and evenmore » more active than the state-of-the-art IrO2 catalyst. Such vacancy defects are formed by balancing with reducing environments under solvothermal conditions, but are surprisingly stable even after 1000 cycles of scanning under OER working conditions. Density functional theory plus U calculation attributes the enhanced performance to the oxygen vacancies and consequently exposed second-layered Co metal sites, which leads to the lowered OER activation energy of 2.26 eV and improved electrical conductivity. Finally, this mild solvothermal reduction concept opens a new door for the understanding and future designing of advanced defect-based electrocatalysts.« less

  5. Solution-grown organic single-crystalline donor-acceptor heterojunctions for photovoltaics.

    PubMed

    Li, Hanying; Fan, Congcheng; Fu, Weifei; Xin, Huolin L; Chen, Hongzheng

    2015-01-12

    Organic single crystals are ideal candidates for high-performance photovoltaics due to their high charge mobility and long exciton diffusion length; however, they have not been largely considered for photovoltaics due to the practical difficulty in making a heterojunction between donor and acceptor single crystals. Here, we demonstrate that extended single-crystalline heterojunctions with a consistent donor-top and acceptor-bottom structure throughout the substrate can be simply obtained from a mixed solution of C60 (acceptor) and 3,6-bis(5-(4-n-butylphenyl)thiophene-2-yl)-2,5-bis(2-ethylhexyl)pyrrolo[3,4-c]pyrrole-1,4-dione (donor). 46 photovoltaic devices were studied with the power conversion efficiency of (0.255±0.095)% under 1 sun, which is significantly higher than the previously reported value for a vapor-grown organic single-crystalline donor-acceptor heterojunction (0.007%). As such, this work opens a practical avenue for the study of organic photovoltaics based on single crystals.

  6. Bifunctional single-crystalline rutile nanorod decorated heterostructural photoanodes for efficient dye-sensitized solar cells.

    PubMed

    Hao, Feng; Lin, Hong; Zhou, Chen; Liu, Yizhu; Li, Jianbao

    2011-09-21

    A novel heterostructural TiO(2) nanocomposite, which consists of single-crystalline rutile TiO(2) nanorod decorated Degussa P25 nanoparticles, has been fabricated through a facile acidic hydrothermal method and successfully applied as the photoanodes for efficient dye-sensitized solar cells. The morphology, crystal structure, specific surface area and pore size distribution of the obtained nanocomposite were systematically investigated by X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HRTEM), selected-area electron diffraction patterns (SAED) and nitrogen adsorption-desorption measurements. Under standard illumination conditions (AM 1.5, 100 mW cm(-2)), devices with these hybrid anodes exhibited considerably enhanced photocurrent density and overall conversion efficiency in comparison with that of the commercial Degussa P25 electrodes, which can be partially attributed to the light scattering effect in the long-wavelength region as evidenced from the incident photon-to-current conversion efficiency (IPCE) response and the diffuse reflectance spectroscopy. More importantly, devices employing these hybrid anodes have demonstrated extended electron lifetimes and larger electron diffusion coefficient as validated by the intensity-modulated photocurrent/photovoltage spectroscopy measurements, which can be mainly ascribed to the fast electron transport and collection superiority of the single-crystalline nanorods.

  7. PbO networks composed of single crystalline nanosheets synthesized by a facile chemical precipitation method

    SciTech Connect

    Samberg, Joshua P.; Kajbafvala, Amir; Koolivand, Amir

    2014-03-01

    Graphical abstract: - Highlights: • Synthesis of PbO networks through a simple chemical precipitation route. • The synthesis method is rapid and low-cost. • Each network is composed of single crystalline PbO nanosheets. • A possible growth mechanism is proposed for synthesized PbO networks. - Abstract: For the field of energy storage, nanostructured lead oxide (PbO) shows immense potential for increased specific energy and deep discharge for lead acid battery technologies. In this work, PbO networks composed of single crystalline nanosheets were synthesized utilizing a simple, low cost and rapid chemical precipitation method. The PbO networks were prepared in a single reaction vessel from starting reagents of lead acetate dehydrate, ammonium hydroxide and deionized water. Lead acetate dehydrate was chosen as a reagent, as opposed to lead nitrate, to eliminate the possibility of nitrate contamination of the final product. X-ray diffraction (XRD) analysis, high resolution scanning electron microscopy (HRSEM) and high resolution transmission electron microscopy (HRTEM) analysis were used to characterize the synthesized PbO networks. The reproducible method described herein synthesized pure β-PbO (massicot) powders, with no byproducts. A possible formation mechanism for these PbO networks is proposed. The growth is found to proceed predominately in the 〈1 1 1〉 and 〈2 0 0〉 directions while being limited in the 〈0 1 1〉 direction.

  8. Single-Crystalline SrRuO3 Nanomembranes: A Platform for Flexible Oxide Electronics

    DOE PAGES

    Paskiewicz, Deborah M.; Sichel-Tissot, Rebecca; Karapetrova, Evguenia; ...

    2016-12-11

    The field of oxide electronics has benefited from the wide spectrum of functionalities available to the ABO3 perovskites, and researchers are now employing defect engineering in single crystalline heterostructures to tailor properties. However, bulk oxide single crystals are not conducive to many types of applications, particularly those requiring mechanical flexibility. Here, we demonstrate the realization of an all-oxide, single-crystalline nanomembrane heterostructure. With a surface-to-volume ratio of 2 × 107 , the nanomembranes are fully flexible and can be readily transferred to other materials for handling purposes or for new materials integration schemes. Using in situ synchrotron X-ray scattering, we findmore » that the nanomembranes can bond to other host substrates near room temperature and demonstrate coupling between surface reactivity and electromechanical properties in ferroelectric nanomembrane systems. Finally, the synthesis technique described here represents a significant advancement in materials integration and provides a new platform for the development of flexible oxide electronics.« less

  9. Probing the low thermal conductivity of single-crystalline porous Si nanowires

    NASA Astrophysics Data System (ADS)

    Zhao, Yunshan; Lina Yang Collaboration; Lingyu Kong Collaboration; Baowen Li Collaboration; John T L Thong Collaboration; Kedar Hippalgaonkar Collaboration

    Pore-like structures provide a novel way to reduce the thermal conductivity of silicon nanowires, compared to both smooth-surface VLS nanowires and rough EE nanowires. Because of enhanced phonon scattering with interface and decrease in phonon transport path, the porous nanostructures show reduction in thermal conductance by few orders of magnitude. It proves to be extremely challenging to evaluate porosity accurately in an experimental manner and further understand its effect on thermal transport. In this study, we use the newly developed electron-beam based micro-electrothermal device technique to study the porosity dependent thermal conductivity of mesoporous silicon nanowires that have single-crystalline scaffolding. Based on the Casino simulation, the power absorbed by the nanowire, coming from the loss of travelling electron energy, has a linear relationship with it cross section. The relationship has been verified experimentally as well. Monte Carlo simulation is carried out to theoretically predict the thermal conductivity of silicon nanowires with a specific value of porosity. These single-crystalline porous silicon nanowires show extremely low thermal conductivity, even below the amorphous limit. These structures together with our experimental techniques provide a particularly intriguing platform to understand the phonon transport in nanoscale and aid the performance improvement in future nanowires-based devices.

  10. Single-crystalline nanogap electrodes: enhancing the nanowire-breakdown process with a gaseous environment.

    PubMed

    Suga, Hiroshi; Sumiya, Touru; Furuta, Shigeo; Ueki, Ryuichi; Miyazawa, Yosuke; Nishijima, Takuya; Fujita, Jun-ichi; Tsukagoshi, Kazuhito; Shimizu, Tetsuo; Naitoh, Yasuhisa

    2012-10-24

    A method for fabricating single-crystalline nanogaps on Si substrates was developed. Polycrystalline Pt nanowires on Si substrates were broken down by current flow under various gaseous environments. The crystal structure of the nanogap electrode was evaluated using scanning electron microscopy and transmission electron microscopy. Nanogap electrodes sandwiched between Pt-large-crystal-grains were obtained by the breakdown of the wire in an O(2) or H(2) atmosphere. These nanogap electrodes show intense spots in the electron diffraction pattern. The diffraction pattern corresponds to Pt (111), indicating that single-crystal grains are grown by the electrical wire breakdown process in an O(2) or H(2) atmosphere. The Pt wires that have (111)-texture and coherent boundaries can be considered ideal as interconnectors for single molecular electronics. The simple method for fabrication of a single-crystalline nanogap is one of the first steps toward standard nanogap electrodes for single molecular instruments and opens the door to future research on physical phenomena in nanospaces.

  11. Interdiffusion and stress development in single-crystalline Pd/Ag bilayers

    SciTech Connect

    Noah, Martin A. Flötotto, David; Wang, Zumin; Mittemeijer, Eric J.

    2016-04-14

    Interdiffusion and stress evolution in single-crystalline Pd/single-crystalline Ag thin films were investigated by Auger electron spectroscopy sputter-depth profiling and in-situ X-ray diffraction, respectively. The concentration-dependent chemical diffusion coefficient, as well as the impurity diffusion coefficient of Ag in Pd could be determined in the low temperature range of 356 °C–455 °C. As a consequence of the similarity of the strong concentration-dependences of the intrinsic diffusion coefficients, the chemical diffusion coefficient varies only over three orders of magnitude over the whole composition range, despite the large difference of six orders of magnitude of the self-diffusion coefficients of Ag in Ag and Pd in Pd. It is shown that the Darken-Manning treatment should be adopted for interpretation of the experimental data; the Nernst-Planck treatment yielded physically unreasonable results. Apart from the development of compressive thermal stress, the development of stress in both sublayers separately could be ascribed to compositional stress (tensile in the Ag sublayer and compressive in the Pd sublayer) and dominant relaxation processes, especially in the Ag sublayer. The effect of these internal stresses on the values determined for the diffusion coefficients is shown to be negligible.

  12. Direct growth of single-crystalline III–V semiconductors on amorphous substrates

    PubMed Central

    Chen, Kevin; Kapadia, Rehan; Harker, Audrey; Desai, Sujay; Seuk Kang, Jeong; Chuang, Steven; Tosun, Mahmut; Sutter-Fella, Carolin M.; Tsang, Michael; Zeng, Yuping; Kiriya, Daisuke; Hazra, Jubin; Madhvapathy, Surabhi Rao; Hettick, Mark; Chen, Yu-Ze; Mastandrea, James; Amani, Matin; Cabrini, Stefano; Chueh, Yu-Lun; Ager III, Joel W.; Chrzan, Daryl C.; Javey, Ali

    2016-01-01

    The III–V compound semiconductors exhibit superb electronic and optoelectronic properties. Traditionally, closely lattice-matched epitaxial substrates have been required for the growth of high-quality single-crystal III–V thin films and patterned microstructures. To remove this materials constraint, here we introduce a growth mode that enables direct writing of single-crystalline III–V's on amorphous substrates, thus further expanding their utility for various applications. The process utilizes templated liquid-phase crystal growth that results in user-tunable, patterned micro and nanostructures of single-crystalline III–V's of up to tens of micrometres in lateral dimensions. InP is chosen as a model material system owing to its technological importance. The patterned InP single crystals are configured as high-performance transistors and photodetectors directly on amorphous SiO2 growth substrates, with performance matching state-of-the-art epitaxially grown devices. The work presents an important advance towards universal integration of III–V's on application-specific substrates by direct growth. PMID:26813257

  13. Preparation and oxidation resistance of single crystalline β-Zn4Sb3

    NASA Astrophysics Data System (ADS)

    Liu, Hong-xia; Deng, Shu-ping; Li, De-cong; Shen, Lan-xian; Cheng, Feng; Wang, Jin-song; Deng, Shu-kang

    2016-11-01

    This study prepared a Zn-rich single crystal β-Zn4Sb3 using a Sn flux method based on the stoichiometric ratios of Zn4.4Sb3Sn3. The oxidation resistance of the sample was determined by exploring the effects of heat treatment in air on electrical transport properties and thermal stability, which is of practical importance in the application of the material at high temperatures. Results showed that the prepared sample possessed high electrical transport properties, with a high power factor of 1.67×10-3 W m-1 K-2 at 563 K. The heat treatment in air weakened the electrical conductivity of the single crystalline β-Zn4Sb3, whereas the Seebeck coefficients were rarely independent of the annealing condition. Eventually, the power factor obtained after the first heating at 523 K for 4 h became comparable to that of the as-prepared sample, although it decreased after the second heating at 573 K for 5 h. Nevertheless, the single crystalline β-Zn4Sb3 still possessed a good thermal stability after the heat treatment process.

  14. True Vapor-Liquid-Solid Process Suppresses Unintentional Carrier Doping of Single Crystalline Metal Oxide Nanowires.

    PubMed

    Anzai, Hiroshi; Suzuki, Masaru; Nagashima, Kazuki; Kanai, Masaki; Zhu, Zetao; He, Yong; Boudot, Mickaël; Zhang, Guozhu; Takahashi, Tsunaki; Kanemoto, Katsuichi; Seki, Takehito; Shibata, Naoya; Yanagida, Takeshi

    2017-08-09

    Single crystalline nanowires composed of semiconducting metal oxides formed via a vapor-liquid-solid (VLS) process exhibit an electrical conductivity even without an intentional carrier doping, although these stoichiometric metal oxides are ideally insulators. Suppressing this unintentional doping effect has been a challenging issue not only for metal oxide nanowires but also for various nanostructured metal oxides toward their semiconductor applications. Here we demonstrate that a pure VLS crystal growth, which occurs only at liquid-solid (LS) interface, substantially suppresses an unintentional doping of single crystalline SnO2 nanowires. By strictly tailoring the crystal growth interface of VLS process, we found the gigantic difference of electrical conduction (up to 7 orders of magnitude) between nanowires formed only at LS interface and those formed at both LS and vapor-solid (VS) interfaces. On the basis of investigations with spatially resolved single nanowire electrical measurements, plane-view electron energy-loss spectroscopy, and molecular dynamics simulations, we reveal the gigantic suppression of unintentional carrier doping only for the crystal grown at LS interface due to the higher annealing effect at LS interface compared with that grown at VS interface. These implications will be a foundation to design the semiconducting properties of various nanostructured metal oxides.

  15. Fabrication of single crystalline, uniaxial single domain Co nanowire arrays with high coercivity

    NASA Astrophysics Data System (ADS)

    Ramazani, A.; Almasi Kashi, M.; Montazer, A. H.

    2014-03-01

    Whilst Co nanorods with high coercivity were synthesized during recent years, they did not achieve the same results as for Co nanowires embedded in solid templates. In the present work, Co nanowire arrays (NWAs) with high coercivity were successfully fabricated in porous aluminum oxide template under optimum conditions by using pulsed ac electrodeposition technique. Magnetic properties and crystalline characteristics of the nanowires were investigated by hysteresis loop measurements, first-order reversal curve (FORC) analysis, X-ray diffraction (XRD), and selected area electron diffraction (SAED) patterns. Hysteresis loop measurements showed high coercivity of about 4.8 kOe at room temperature together with optimum squareness of 1, resulting in an increase of the previous maximum coercivity for Co NWAs up to 45%. XRD and SAED patterns revealed a single crystalline texture along the [0002] direction, indicating the large magnetocrystalline anisotropy. On the other hand, FORC analysis confirmed a single domain structure for the Co NWAs. In addition, the reversal mechanism of the single crystalline, single domain Co NWAs was studied which resulted in the fixed easy axis with a coherent rotation. Accordingly, these nanowires might offer promising applications in high density bit patterned media and low power logic devices.

  16. Direct growth of single-crystalline III–V semiconductors on amorphous substrates

    SciTech Connect

    Chen, Kevin; Kapadia, Rehan; Harker, Audrey; Desai, Sujay; Seuk Kang, Jeong; Chuang, Steven; Tosun, Mahmut; Sutter-Fella, Carolin M.; Tsang, Michael; Zeng, Yuping; Kiriya, Daisuke; Hazra, Jubin; Madhvapathy, Surabhi Rao; Hettick, Mark; Chen, Yu-Ze; Mastandrea, James; Amani, Matin; Cabrini, Stefano; Chueh, Yu-Lun; Ager III, Joel W.; Chrzan, Daryl C.; Javey, Ali

    2016-01-27

    The III–V compound semiconductors exhibit superb electronic and optoelectronic properties. Traditionally, closely lattice-matched epitaxial substrates have been required for the growth of high-quality single-crystal III–V thin films and patterned microstructures. To remove this materials constraint, here we introduce a growth mode that enables direct writing of single-crystalline III–V’s on amorphous substrates, thus further expanding their utility for various applications. The process utilizes templated liquid-phase crystal growth that results in user-tunable, patterned micro and nanostructures of single-crystalline III–V’s of up to tens of micrometres in lateral dimensions. InP is chosen as a model material system owing to its technological importance. The patterned InP single crystals are configured as high-performance transistors and photodetectors directly on amorphous SiO2 growth substrates, with performance matching state-of-the-art epitaxially grown devices. In conclusion, the work presents an important advance towards universal integration of III–V’s on application-specific substrates by direct growth.

  17. Direct growth of single-crystalline III–V semiconductors on amorphous substrates

    DOE PAGES

    Chen, Kevin; Kapadia, Rehan; Harker, Audrey; ...

    2016-01-27

    The III–V compound semiconductors exhibit superb electronic and optoelectronic properties. Traditionally, closely lattice-matched epitaxial substrates have been required for the growth of high-quality single-crystal III–V thin films and patterned microstructures. To remove this materials constraint, here we introduce a growth mode that enables direct writing of single-crystalline III–V’s on amorphous substrates, thus further expanding their utility for various applications. The process utilizes templated liquid-phase crystal growth that results in user-tunable, patterned micro and nanostructures of single-crystalline III–V’s of up to tens of micrometres in lateral dimensions. InP is chosen as a model material system owing to its technological importance. Themore » patterned InP single crystals are configured as high-performance transistors and photodetectors directly on amorphous SiO2 growth substrates, with performance matching state-of-the-art epitaxially grown devices. In conclusion, the work presents an important advance towards universal integration of III–V’s on application-specific substrates by direct growth.« less

  18. Tunneling into the d-wave lobe on atomically-flat a-axis DyBaCuO films

    NASA Astrophysics Data System (ADS)

    Davidson, B. A.; Andrus, A.; Diluccio, T.; O'Donnell, J.; Oh, S.; Ramazashvili, R.; Kos, S.; Eckstein, J. N.

    2001-03-01

    To study the density of states (DOS) in high-Tc cuprates in the lobe direction of the d-wave order parameter, we have exploited the capability of molecular-beam epitaxy to grow atomically-flat films of a-axis DBCO capped with uniform dielectric barriers. Normal-state tunneling between DBCO and gold (T>90 K) exhibits a parabolic dependence of conductance on voltage. The tunneling conductance below Tc for CaTiO3 barriers shows an unusual dependence on the polarity of the applied voltage. When tunneling into empty states in the gold, a 25 mV gap feature is present, in which all states that disappear as the gap opens up are shifted to higher energies. For tunneling into empty states in the DBCO, an increase in conductance is observed between zero and 25 mV where the gap-shoulder structure is expected, and spectral weight is not conserved. If interpreted as a signature of the DOS, this implies a discontinuity of the DOS at the Fermi level that develops logarithmically in T. This type of tunneling behavior has not been published previously, and we will discuss possible intrinsic and extrinsic explanations.

  19. Generation and the role of dislocations in single-crystalline phase-change In2Se3 nanowires under electrical pulses.

    PubMed

    Mafi, Elham; Tao, Xin; Zhu, Wenguang; Gao, Yanfei; Wang, Chongmin; Gu, Yi

    2016-08-19

    We report the observation of the generation of dislocations in single-crystal phase-change In2Se3 nanowires under electrical pulses and the impact of these dislocations on electrical properties. Particularly, we correlated the atomic-scale structural characteristics with local electrical resistance variations, by performing transmission electron microscopy and scanning Kelvin probe microscopy on the same nanowires. By coupling the experimental results with first-principles density functional theory calculations, we show that the immobile dislocations are generated via vacancy condensations. Importantly, these dislocations lead to several orders of magnitude increase in the electrical resistance, while maintaining the single crystallinity of the lattice. These results significantly advance the fundamental understanding of the structure-property relation in this phase-change material under transient electrical excitations. From a practical perspective, the significant increase in the electrical resistance, driven by the formation of dislocations, can be exploited as a new electronic state in the single-crystalline phase in this phase-change material.

  20. Exploring metamagnetism of single crystalline EuNiGe3 by neutron scattering

    NASA Astrophysics Data System (ADS)

    Fabrèges, X.; Gukasov, A.; Bonville, P.; Maurya, A.; Thamizhavel, A.; Dhar, S. K.

    2016-06-01

    We present here a neutron diffraction study, both in zero field and as a function of magnetic field, of the magnetic structure of the tetragonal intermetallic EuNiGe3 on a single crystalline sample. This material is known to undergo a cascade of transitions, first at 13.2 K towards an incommensurate modulated magnetic structure, then at 10.5 K to an antiferromagnetic structure. We show here that the low-temperature phase presents a spiral moment arrangement with wave vector k =(1/4 ,δ ,0 ) . For a magnetic field applied along the tetragonal c axis, the square root of the scattering intensity of the (1 0 1) reflection matches very well the complex metamagnetic behavior of the magnetization along c measured previously. For the magnetic field applied along the b axis, two magnetic transitions are observed below the transition to a fully polarized state.

  1. Investigation of charge multiplication in single crystalline CVD diamond particle detectors

    NASA Astrophysics Data System (ADS)

    Muškinja, M.; Cindro, V.; Gorišek, A.; Kagan, H.; Kramberger, G.; Mandić, I.; Mikuž, M.; Phan, S.; Smith, D. S.; Zavrtanik, M.

    2017-01-01

    A special metallization pattern was created on a single crystalline diamond detector aimed at creating high enough electric field for impact ionization in the detector material. Electric field line focusing through electrode design and very high bias voltages were used to obtain high electric fields. Previous measurements and theoretical calculations indicated that drifting charge multiplication by impact ionization could take place. A large increase of induced charge was observed for the smallest dot electrode which points to charge multiplication while for the large dot and pad detector structure no such effect was observed. The evolution of induced currents was also monitored with the transient current technique. Induced current pulses with duration of order 1 μs were measured. The multiplication gain was found to depend on the particle rate.

  2. Molecular beam epitaxy of single crystalline GaN nanowires on a flexible Ti foil

    NASA Astrophysics Data System (ADS)

    Calabrese, Gabriele; Corfdir, Pierre; Gao, Guanhui; Pfüller, Carsten; Trampert, Achim; Brandt, Oliver; Geelhaar, Lutz; Fernández-Garrido, Sergio

    2016-05-01

    We demonstrate the self-assembled growth of vertically aligned GaN nanowire ensembles on a flexible Ti foil by plasma-assisted molecular beam epitaxy. The analysis of single nanowires by transmission electron microscopy reveals that they are single crystalline. Low-temperature photoluminescence spectroscopy demonstrates that in comparison to standard GaN nanowires grown on Si, the nanowires prepared on the Ti foil exhibit an equivalent crystalline perfection, a higher density of basal-plane stacking faults, but a reduced density of inversion domain boundaries. The room-temperature photoluminescence spectrum of the nanowire ensemble is not influenced or degraded by the bending of the substrate. The present results pave the way for the fabrication of flexible optoelectronic devices based on GaN nanowires on metal foils.

  3. Orientation dependent size effects in single crystalline anisotropic nanoplates with regard to surface energy

    NASA Astrophysics Data System (ADS)

    Assadi, Abbas; Salehi, Manouchehr; Akhlaghi, Mehdi

    2015-07-01

    In this work, size dependent behavior of single crystalline normal and auxetic anisotropic nanoplates is discussed with consideration of material surface stresses via a generalized model. Bending of pressurized nanoplates and their fundamental resonant frequency are discussed for different crystallographic directions and anisotropy degrees. It is explained that the orientation effects are considerable when the nanoplates' edges are pinned but for clamped nanoplates, the anisotropy effect may be ignored. The size effects are the highest when the simply supported nanoplates are parallel to [110] direction but as the anisotropy gets higher, the size effects are reduced. The orientation effect is also discussed for possibility of self-instability occurrence in nanoplates. The results in simpler cases are compared with previous experiments for nanowires but with a correction factor. There are still some open questions for future studies.

  4. Electrical resistivity measurements of single crystalline α-Mn under high pressure

    NASA Astrophysics Data System (ADS)

    Miyake, A.; Kanemasa, T.; Yagi, R.; Kagayama, T.; Shimizu, K.; Haga, Y.; Ōnuki, Y.

    We have measured electrical resistivity of single crystalline α-manganese ( α-Mn) under high pressure. α-Mn shows an antiferromagnetic ordering at TN=95 K and has four inequivalent crystal sites with different magnetic moments. With increasing pressure, TN shifts toward lower temperature. At higher pressure, the shape of anomaly at TN changes to a kink-like one, which may indicate different magnetic ordering from that at lower pressure. Such a difference between lower and higher pressure regions is considered to be caused by the four inequivalent magnetic moments in α-Mn. At ˜1.9 GPa, the boundary of the ordered phases, we observe a sudden decrease of the residual resistivity and a peak of the A-coefficient of T2-term of the resistivity.

  5. Antibacterial activity of single crystalline silver-doped anatase TiO2 nanowire arrays

    NASA Astrophysics Data System (ADS)

    Zhang, Xiangyu; Li, Meng; He, Xiaojing; Hang, Ruiqiang; Huang, Xiaobo; Wang, Yueyue; Yao, Xiaohong; Tang, Bin

    2016-05-01

    Well-ordered, one-dimensional silver-doped anatase TiO2 nanowire (AgNW) arrays have been prepared through a hydrothermal growth process on the sputtering-deposited AgTi layers. Electron microscope analyses reveal that the as-synthesized AgNW arrays exhibit a single crystalline phase with highly uniform morphologies, diameters ranging from 85 to 95 nm, and lengths of about 11 μm. Silver is found to be doped into TiO2 nanowire evenly and mainly exists in the zerovalent state. The AgNW arrays show excellent efficient antibacterial activity against Escherichia coli (E. coli), and all of the bacteria can be killed within 1 h. Additionally, the AgNW arrays can still kill E. coli after immersion for 60 days, suggesting the long-term antibacterial property. The technique reported here is environmental friendly for formation of silver-containing nanostructure without using any toxic organic solvents.

  6. Single-crystalline self-branched anatase titania nanowires for dye-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Li, Zhenquan; Yang, Huang; Wu, Fei; Fu, Jianxun; Wang, Linjun; Yang, Weiguang

    2017-03-01

    The morphology of the anatase titania plays an important role in improving the photovoltaic performance in dye-sensitized solar cells. In this work, single-crystalline self-branched anatase TiO2 nanowires have been synthesized by hydrothermal method using TBAH and CTAB as morphology controlling agents. The obtained self-branched TiO2 nanowires dominated by a large percentage of (010) facets. The photovoltaic conversion efficiency (6.37%) of dye-sensitized solar cell (DSSC) based on the self-branched TiO2 nanowires shows a significant improvement (26.6%) compared to that of P25 TiO2 (5.03%). The enhanced performance of the self-branched TiO2 nanowires-based DSSC is due to heir large percent of exposed (010) facets which have strong dye adsorption capacity and effective charge transport of the self-branched 1D nanostructures.

  7. Integration of single-crystalline nanocolumns into highly ordered nanopore arrays

    NASA Astrophysics Data System (ADS)

    Ding, G. Q.; Shen, W. Z.; Zheng, M. J.; Zhou, Z. B.

    2006-05-01

    The arrangement of nanostructures into desired well-ordered architectures is crucial for the realization of functional nanodevices and has been the focus of current nanotechnology. Existing physical and chemical approaches have the ability to assemble nanostructures, but it is still a challenge to arrange basic nanostructures into a highly ordered designed pattern. Here, we report a novel method to integrate tin-doped indium oxide single-crystalline nanocolumns into highly ordered two-dimensional nanopore patterns through radio-frequency magnetron sputtering by the aid of porous alumina membranes (PAMs). We have further demonstrated that the morphology of the assembled nanopore arrays is controllable by adjusting either the PAM configurations or sputtering conditions. Our present method provides the possibility of a general approach for nanounit integration, and these assembled regular nanopore arrays pave the way for the application of novel filters and sensors.

  8. Laser ablation of single-crystalline silicon by radiation of pulsed frequency-selective fiber laser

    NASA Astrophysics Data System (ADS)

    Veiko, V. P.; Skvortsov, A. M.; Huynh, C. T.; Petrov, A. A.

    2015-07-01

    We have studied the process of destruction of the surface of a single-crystalline silicon wafer scanned by the beam of a pulsed ytterbium-doped fiber laser radiation with a wavelength of λ = 1062 nm. It is established that the laser ablation can proceed without melting of silicon and the formation of a plasma plume. Under certain parameters of the process (radiation power, beam scan velocity, and beam overlap density), pronounced oxidation of silicon microparticles with the formation of a characteristic loose layer of fine powdered silicon dioxide has been observed for the first time. The range of lasing and beam scanning regimes in which the growth of SiO2 layer takes place is determined.

  9. Formation and Stabilization of Single-Crystalline Metastable AuGe Phases in Ge Nanowires

    SciTech Connect

    Sutter, E.; Sutter, P.

    2011-07-22

    We use in situ observations by variable temperature transmission electron microscopy on AuGe alloy drops at the tips of Ge nanowires (NWs) with systematically varying composition to demonstrate the controlled formation of metastable solid phases integrated in NWs. The process, which operates in the regime of vapor-liquid-solid growth, involves a size-dependent depression of the alloy liquidus at the nanoscale that leads to extremely Ge-rich AuGe melts at low temperatures. During slow cooling, these liquid AuGe alloy drops show pronounced departures from equilibrium, i.e., a frustrated phase separation of Ge into the adjacent solid NW, and ultimately crystallize as single-crystalline segments of metastable {gamma}-AuGe. Our findings demonstrate a general avenue for synthesizing NW heterostructures containing stable and metastable solid phases, applicable to a wide range of materials of which NWs form by the vapor-liquid-solid method.

  10. Single-crystalline δ-Ni2Si nanowires with excellent physical properties

    PubMed Central

    2013-01-01

    In this article, we report the synthesis of single-crystalline nickel silicide nanowires (NWs) via chemical vapor deposition method using NiCl2·6H2O as a single-source precursor. Various morphologies of δ-Ni2Si NWs were successfully acquired by controlling the growth conditions. The growth mechanism of the δ-Ni2Si NWs was thoroughly discussed and identified with microscopy studies. Field emission measurements show a low turn-on field (4.12 V/μm), and magnetic property measurements show a classic ferromagnetic characteristic, which demonstrates promising potential applications for field emitters, magnetic storage, and biological cell separation. PMID:23782805

  11. Interfacial electronic transport phenomena in single crystalline Fe-MgO-Fe thin barrier junctions

    SciTech Connect

    Gangineni, R. B.; Negulescu, B.; Baraduc, C.; Gaudin, G.

    2014-05-05

    Spin filtering effects in nano-pillars of Fe-MgO-Fe single crystalline magnetic tunnel junctions are explored with two different sample architectures and thin MgO barriers (thickness: 3–8 monolayers). The two architectures, with different growth and annealing conditions of the bottom electrode, allow tuning the quality of the bottom Fe/MgO interface. As a result, an interfacial resonance states (IRS) is observed or not depending on this interface quality. The IRS contribution, observed by spin polarized tunnel spectroscopy, is analyzed as a function of the MgO barrier thickness. Our experimental findings agree with theoretical predictions concerning the symmetry of the low energy (0.2 eV) interfacial resonance states: a mixture of Δ{sub 1}-like and Δ{sub 5}-like symmetries.

  12. Valence state of Sm in single-crystalline EuO thin films

    NASA Astrophysics Data System (ADS)

    Reisner, A.; Kasinathan, D.; Wirth, S.; Tjeng, L. H.; Altendorf, S. G.

    2017-02-01

    Samarium has two stable valence states, 2+ and 3+, which coexist in many compounds forming spatially homogeneous intermediate valence states. We study the valence state of samarium when incorporated in a single crystalline EuO thin film which crystallizes in a fcc structure similar to that of the intermediate valence SmO, but with a larger lattice constant. Due to the increased lattice spacing, a stabilization of the larger Sm2+ ion is expected. Surprisingly, the samarium incorporated in Sm x Eu1-x O thin films shows a predominantly trivalent character, as determined by x-ray photoelectron spectroscopy and magnetometry measurements. We infer that the O2- ions in the EuO lattice have enough room to move locally, so as to reduce the Sm-O distance and stabilize the Sm3+ valence.

  13. Dislocation Nucleation and Interaction under Nanoindentation in Single Crystalline Al and Cu: Molecular Dynamics Simulations

    NASA Astrophysics Data System (ADS)

    Tsuru, Tomohito; Shibutani, Yoji

    Recent advances in miniaturization and highly-accurate measurement techniques have allowed mechanical properties to be measured at the nanometer scale. Nanoindentation has been widely used because of its applicability in ambient conditions. Unstable displacement burst or the abrupt growth of indent displacement after homogeneous elastic deformation observed in crystalline materials is a unique plastic deformation characteristic (nanoplasticity). In the present paper, a series of atomistic simulations of nanoindentation in single crystalline aluminum and copper are performed in analyzing the critical state for dislocation nucleation and interaction between dislocations beneath the indenter. With reference to the Hertzian solution based on isotropic linear elastic theory, both the anisotropic effect and nonlinear behavior of nanoindentation are discussed in detail. The discovery was made that the incipient yield process is strongly related to the triaxial stress state created beneath the indenter, and that energetically unfavorable interactions accompanied with cross slip induce the formation of prismatic dislocations.

  14. Reentrant spin glass behavior in antiferromagnetic single crystalline Ba 6Mn 24O 48 nanoribbons

    NASA Astrophysics Data System (ADS)

    Zhang, Xianke; Tang, Shaolong; Li, Yulong; Du, Youwei

    2010-04-01

    Single crystalline Ba 6Mn 24O 48 nanoribbons with diameters ranging from one hundred nanometers to a few hundred nanometers and length up to tens of microns are synthesized via a facile molten salt method. These nanoribbons are characterized by a range of methods including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). The magnetic properties of Ba 6Mn 24O 48 nanoribbons are investigated by the zero-field-cooled (ZFC), field-cooled (FC) magnetization, and ac susceptibility. Upon cooling, we find the reentrant spin glass (RSG) behavior in these nanoribbons, i.e., paramagnetic (PM), antiferromagnetic (AFM), and spin glass (SG). The RSG behavior might be due to the surface spin disorder, geometrical frustration and Mn 3+/Mn 4+ mixture in Ba 6Mn 24O 48 nanoribbons.

  15. Growth of platelike and branched single-crystalline Si 3N 4 whiskers

    NASA Astrophysics Data System (ADS)

    Yang, Weiyou; Xie, Zhipeng; Li, Jingjing; Miao, Hezhuo; Zhang, Ligong; An, Linan

    2004-10-01

    In this communication, we report for the first time the growth of platelike and branched Si 3N 4 whiskers via catalyst-assisted pyrolysis of polymeric precursors. The as-prepared whiskers are single crystalline with a uniform thickness and width. The thickness and width of the Si 3N 4 whiskers range from 200 to 300 nm and 800 to 1200 nm, respectively. The platelike α-Si 3N 4 whiskers grew along [010] direction, while the branches grew along [001] direction. A growth mechanism based on solid-liquid-gas-solid reaction/crystallization is proposed. The formation of platelike whiskers instead of cylindrical whiskers is attributed to an anisotropic growth at an early nucleation/growth stage.

  16. Graphene Enhances Li Storage Capacity of Porous Single-crystalline Silicon Nanowires

    SciTech Connect

    Wang, X.; Han, W.

    2010-12-01

    We demonstrated that graphene significantly enhances the reversible capacity of porous silicon nanowires used as the anode in Li-ion batteries. We prepared our experimental nanomaterials, viz., graphene and porous single-crystalline silicon nanowires, respectively, using a liquid-phase graphite exfoliation method and an electroless HF/AgNO{sub 3} etching process. The Si porous nanowire/graphene electrode realized a charge capacity of 2470 mAh g{sup -1} that is much higher than the 1256 mAh g{sup -1} of porous Si nanowire/C-black electrode and 6.6 times the theoretical capacity of commercial graphite. This relatively high capacity could originate from the favorable charge-transportation characteristics of the combination of graphene with the porous Si 1D nanostructure.

  17. Transport properties in single-crystalline rutile TiO2 nanorods

    NASA Astrophysics Data System (ADS)

    Chen, R. S.; Chen, C. A.; Wang, W. C.; Tsai, H. Y.; Huang, Y. S.

    2011-11-01

    Electronic transport properties of the single-crystalline titanium dioxide (TiO2) nanorods (NRs) with single rutile phase have been investigated. The conductivity values for the individual TiO2 NRs grown by metal-organic chemical vapor deposition are in the range of 1-10 Ω-1 cm-1. The temperature-dependent measurement shows the presence of two shallow donor levels/bands with activation energies at 8 and 28 meV, respectively. On the photoconductivity (PC), the TiO2 NRs exhibit the much higher normalized PC gain and sensitive excitation-power dependence than the polycrystalline nanotubes. The results demonstrate the superior photoconduction efficiency and distinct mechanism in the monocrystalline one-dimensional TiO2 nanostructures in comparison to the polycrystalline or nanoporous counterparts.

  18. Graphene enhances Li storage capacity of porous single-crystalline silicon nanowires.

    PubMed

    Wang, Xiao-Liang; Han, Wei-Qiang

    2010-12-01

    We demonstrated that graphene significantly enhances the reversible capacity of porous silicon nanowires used as the anode in Li-ion batteries. We prepared our experimental nanomaterials, viz., graphene and porous single-crystalline silicon nanowires, respectively, using a liquid-phase graphite exfoliation method and an electroless HF/AgNO3 etching process. The Si porous nanowire/graphene electrode realized a charge capacity of 2470 mAh g(-1) that is much higher than the 1256 mAh g(-1) of porous Si nanowire/C-black electrode and 6.6 times the theoretical capacity of commercial graphite. This relatively high capacity could originate from the favorable charge-transportation characteristics of the combination of graphene with the porous Si 1D nanostructure.

  19. Morphology and magnetic flux distribution in superparamagnetic, single-crystalline Fe3O4 nanoparticle rings

    PubMed Central

    Takeno, Yumu; Murakami, Yasukazu; Sato, Takeshi; Tanigaki, Toshiaki; Park, Hyun Soon; Shindo, Daisuke; Ferguson, R. Matthew

    2014-01-01

    This study reports on the correlation between crystal orientation and magnetic flux distribution of Fe3O4 nanoparticles in the form of self-assembled rings. High-resolution transmission electron microscopy demonstrated that the nanoparticles were single-crystalline, highly monodispersed, (25 nm average diameter), and showed no appreciable lattice imperfections such as twins or stacking faults. Electron holography studies of these superparamagnetic nanoparticle rings indicated significant fluctuations in the magnetic flux lines, consistent with variations in the magnetocrystalline anisotropy of the nanoparticles. The observations provide useful information for a deeper understanding of the micromagnetics of ultrasmall nanoparticles, where the magnetic dipolar interaction competes with the magnetic anisotropy. PMID:25422526

  20. Revealing crystalline domains in a mollusc shell single-crystalline prism

    NASA Astrophysics Data System (ADS)

    Mastropietro, F.; Godard, P.; Burghammer, M.; Chevallard, C.; Daillant, J.; Duboisset, J.; Allain, M.; Guenoun, P.; Nouet, J.; Chamard, V.

    2017-09-01

    Biomineralization integrates complex processes leading to an extraordinary diversity of calcareous biomineral crystalline architectures, in intriguing contrast with the consistent presence of a sub-micrometric granular structure. Hence, gaining access to the crystalline architecture at the mesoscale, that is, over a few granules, is key to building realistic biomineralization scenarios. Here we provide the nanoscale spatial arrangement of the crystalline structure within the `single-crystalline' prisms of the prismatic layer of a Pinctada margaritifera shell, exploiting three-dimensional X-ray Bragg ptychography microscopy. We reveal the details of the mesocrystalline organization, evidencing a crystalline coherence extending over a few granules. We additionally prove the existence of larger iso-oriented crystalline domains, slightly misoriented with respect to each other, around one unique rotation axis, and whose shapes are correlated with iso-strain domains. The highlighted mesocrystalline properties support recent biomineralization models involving partial fusion of oriented nanoparticle assembly and/or liquid droplet precursors.

  1. Reusability of contaminated seed crystal for cast quasi-single crystalline silicon ingots

    NASA Astrophysics Data System (ADS)

    Li, Zaoyang; Liu, Lijun; Zhou, Genshu

    2015-04-01

    Reusing seed crystal is beneficial for reducing the production costs for cast quasi-single crystalline (QSC) silicon ingots. We numerically investigate the reusability of seed crystal in the casting processes with quartz crucible and silicon feedstock of different purities. The reused seed crystal is recycled from the standard QSC ingot and has been highly contaminated by iron impurity. Transient simulations of iron transport are carried out and special attention is paid to the diffusion and distribution characteristics of iron impurity at the ingot bottom. The heights of the bottom iron contaminated region are compared for silicon ingots grown from normal and recycled seed crystals. The results show that the purity of quartz crucible can influence the reusability of seed crystal more significantly than that of the feedstock. The recycled seed crystal with high iron concentration can be reused for casting processes with standard crucible, whereas it is not recommended for reusing for processes with pure crucible.

  2. Revealing crystalline domains in a mollusc shell single-crystalline prism.

    PubMed

    Mastropietro, F; Godard, P; Burghammer, M; Chevallard, C; Daillant, J; Duboisset, J; Allain, M; Guenoun, P; Nouet, J; Chamard, V

    2017-09-01

    Biomineralization integrates complex processes leading to an extraordinary diversity of calcareous biomineral crystalline architectures, in intriguing contrast with the consistent presence of a sub-micrometric granular structure. Hence, gaining access to the crystalline architecture at the mesoscale, that is, over a few granules, is key to building realistic biomineralization scenarios. Here we provide the nanoscale spatial arrangement of the crystalline structure within the 'single-crystalline' prisms of the prismatic layer of a Pinctada margaritifera shell, exploiting three-dimensional X-ray Bragg ptychography microscopy. We reveal the details of the mesocrystalline organization, evidencing a crystalline coherence extending over a few granules. We additionally prove the existence of larger iso-oriented crystalline domains, slightly misoriented with respect to each other, around one unique rotation axis, and whose shapes are correlated with iso-strain domains. The highlighted mesocrystalline properties support recent biomineralization models involving partial fusion of oriented nanoparticle assembly and/or liquid droplet precursors.

  3. A simple route to the synthesis of single crystalline copper metagermanate nanowires

    SciTech Connect

    Pei, L.Z.; Zhao, H.S.; Tan, W.; Yu, H.Y.; Chen, Y.W.; Zhang Qianfeng; Fan, C.G.

    2009-12-15

    Single crystalline copper metagermanate (CuGeO{sub 3}) nanowires with the diameter of 30-300 nm and length of longer than 100 {mu}m have been prepared by a simple hydrothermal deposition route. X-ray diffraction (XRD), selected area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM) and Raman analyses confirm that the nanowires are orthorhombic single crystals with a main growth direction along <101>. Room temperature photoluminescence (PL) measurement shows a strong blue emission peak at 442 nm with a broad emission band. The blue emission may be ascribed to radiative recombination of oxygen vacancies and oxygen-germanium vacancies. The formation process of CuGeO{sub 3} nanowires is also discussed.

  4. Single crystalline ZnO nanorods grown by a simple hydrothermal process

    SciTech Connect

    Pei, L.Z.; Zhao, H.S.; Tan, W.; Yu, H.Y.; Chen, Y.W.; Zhang Qianfeng

    2009-09-15

    Single crystalline ZnO nanorods with wurtzite structure have been prepared by a simple hydrothermal process. The microstructure and composition of the products were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM, energy dispersive X-ray spectrum (EDS) and Raman spectrum. The nanorods have diameters ranging from 100 nm to 800 nm and length of longer than 10 {mu}m. Raman peak at 437.8 cm{sup -1} displays the characteristic peak of wurtzite ZnO. Photoluminescence (PL) spectrum shows a blue light emission at 441 nm, which is related to radiative recombination of photo-generated holes with singularly ionized oxygen vacancies.

  5. Single-crystalline self-branched anatase titania nanowires for dye-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Li, Zhenquan; Yang, Huang; Wu, Fei; Fu, Jianxun; Wang, Linjun; Yang, Weiguang

    2016-12-01

    The morphology of the anatase titania plays an important role in improving the photovoltaic performance in dye-sensitized solar cells. In this work, single-crystalline self-branched anatase TiO2 nanowires have been synthesized by hydrothermal method using TBAH and CTAB as morphology controlling agents. The obtained self-branched TiO2 nanowires dominated by a large percentage of (010) facets. The photovoltaic conversion efficiency (6.37%) of dye-sensitized solar cell (DSSC) based on the self-branched TiO2 nanowires shows a significant improvement (26.6%) compared to that of P25 TiO2 (5.03%). The enhanced performance of the self-branched TiO2 nanowires-based DSSC is due to heir large percent of exposed (010) facets which have strong dye adsorption capacity and effective charge transport of the self-branched 1D nanostructures.

  6. Characterization of single crystalline CdS nanowires synthesized by solvothermal method.

    PubMed

    Hadia, N M A; García-Granda, Santiago; García, José R

    2014-07-01

    Cadmium sulfide (CdS) nanowires with uniform diameter were prepared by the solvothermal method using ethylenediamine (en) as solvent. The products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scan electron microscopy (SEM), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). It was found that the products are hexagonal crystals of CdS nanowires with diameter of 28 nm and length up to several micrometres. Selected area electron diffraction (SAED) and high resolution TEM (HRTEM) studies indicate the single-crystalline nature of CdS nanowires with an oriented growth along the c-axis direction. The absorption spectrum of the as-prepared CdS nanowires shows an absorption peak of around 485 nm. These CdS nanowires exhibit bright photoluminescence (PL) with two distinct emission bands at 502 nm and 696 nm.

  7. Spin Pumping and Thermal Effects in Single-Crystalline Fe /Pt Bilayers at the Nonresonant Condition

    NASA Astrophysics Data System (ADS)

    Huo, Y.; Zeng, F. L.; Zhou, C.; Wu, Y. Z.

    2017-07-01

    The voltage signal driven by a microwave at the nonresonant condition has been systematically studied in well-designed single-crystalline Fe and Fe /Pt bilayers. The voltage signals at the nonresonant condition in Fe and Fe /Pt show different angular dependence on the magnetization orientation. Through theoretical simulation and experiments of varying sample structures and field strength, it can be concluded that the voltage signal at the nonresonant condition consists of the thermal effects including the anomalous Nernst effect and the spin Seebeck effect, and the inverse spin Hall effect induced by spin pumping. Our results indicate that the microwave-induced signal at the nonresonant conditions may enable the device operation in the absence of any external magnetic field, which is beneficial for practical applications.

  8. Nanomechanical Behavior of Single Crystalline SiC Nanotubes Revealed by Molecular Dynamics Simulations

    SciTech Connect

    Wang, Zhiguo; Zu, Xiaotao T.; Gao, Fei; Weber, William J.

    2008-11-01

    Molecular dynamics simulations with Tersoff potentials were used to study the response of single crystalline SiC nanotubes under tensile, compressive, torsional, combined tension-torsional and combined compression-torsional strains. The simulation results reveal that the nanotubes deform through bond-stretching and breaking and exhibit brittle properties under uniaxial tensile strain, except for the thinnest nanotube at high temperatures, which fails in a ductile manner. Under uniaxial compressive strain, the SiC nanotubes buckle with two modes, i.e. shell buckling and column buckling, depending on the length of the nanotubes. Under torsional strain, the nanotubes buckle either collapse in the middle region into a dumbbell-like structure for thinner wall thicknesses or fail by bond breakage for the largest wall thickness. Both the tensile failure stress and buckling stress decrease under combined tension-torsional and combined compression-torsional strain, and they decrease with increasing torsional rate under combined loading.

  9. Conically shaped single-crystalline diamond backing plates for a diamond anvil cell

    NASA Astrophysics Data System (ADS)

    Krauss, G.; Reifler, H.; Steurer, W.

    2005-10-01

    Based on computer-aided design (CAD) and finite-element calculations (FEM), single-crystalline diamond backing plates were tailored as a replacement of beryllium for high-pressure diamond anvil cells with a focus on in-house single-crystal experiments. Although the modified cell has an opening angle of 90°, a very homogeneous stress distribution all over the backing plate was realized to avoid failure. The conically shaped backing plates work well in the targeted pressure range up to Mg2Co3Sn10.15 up to 9.69 GPa. The influence of simultaneous diffraction phenomena in the diamonds (diamond dips) is illustrated by single-counter and area-detector measurements using standard laboratory equipment.

  10. Bendable Photodetector on Fibers Wrapped with Flexible Ultra-Thin Single Crystalline Silicon Nanomembranes.

    PubMed

    Song, Enming; Guo, Qinglei; Huang, Gaoshan; Jia, Bo; Mei, Yongfeng

    2017-03-29

    Silicon (Si) nanomembranes (NMs) enable conformal covering on complicated surfaces for novel applications. We adopt classical fibers as flexible/curved substrates and wrap them with freestanding ultra-thin Si-NMs with a thickness of ~20 nm. Intrinsic defects in single-crystalline Si-NMs provide a flow path for hydrofluoric acid (HF) to release the NM with a consecutive area of ~0.25 cm2. Such Si-NMs with ultra-low flexural rigidities are transferred onto a single-mode fiber (SMF) and functionalized into bendable photodetectors, which detects the leaked light when the fiber is bent. Our demonstration exemplifies optoelectronic applications in flexible photodetector for Si-NMs in a three-dimensional (3D) geometry.

  11. Surface modification via wet chemical etching of single-crystalline silicon for photovoltaic application.

    PubMed

    Reshak, A H; Shahimin, M M; Shaari, S; Johan, N

    2013-11-01

    The potential of solar cells have not been fully tapped due to the lack of energy conversion efficiency. There are three important mechanisms in producing high efficiency cells to harvest solar energy; reduction of light reflectance, enhancement of light trapping in the cell and increment of light absorption. The current work represent studies conducted in surface modification of single-crystalline silicon solar cells using wet chemical etching techniques. Two etching types are applied; alkaline etching (KOH:IPA:DI) and acidic etching (HF:HNO3:DI). The alkaline solution resulted in anisotropic profile that leads to the formation of inverted pyramids. While acidic solution formed circular craters along the front surface of silicon wafer. This surface modification will leads to the reduction of light reflectance via texturizing the surface and thereby increases the short circuit current and conversion rate of the solar cells.

  12. Evidence of density waves in single-crystalline nanowires of pyrochlore iridates

    NASA Astrophysics Data System (ADS)

    Juyal, Abhishek; Agarwal, Amit; Mukhopadhyay, Soumik

    2017-03-01

    We present experimental evidence of emergent density-wave instability in single-crystalline low-dimensional wires of yttrium-based pyrochlore iridates. We demonstrate electric-field-induced nonlinear hysteretic switching of the density wave at low temperature, followed by smooth nonlinear conduction at higher temperature (T >40 K) in Y2 -xBixIr2O7 , with x =0 and 0.3. The ac transport measurements reveal the presence of four different collective relaxation processes which dominate at different temperature scales. There is a strong coupling of the normal charge carriers with the density-wave condensate, which is reflected in the linear scaling of the dc conductivity with the collective relaxation rate across a wide range of frequencies and temperatures. The evidence of the density wave in low-dimensional single crystals of pyrochlore iridate could be a precursor to the possible experimental confirmation of the Weyl semimetallic ground state with broken chiral symmetry.

  13. Luminescent properties of Tm3-xLuxAl5O12:Ce single crystalline films

    NASA Astrophysics Data System (ADS)

    Zorenko, Yu.; Gorbenko, V.; Zorenko, T.; Suchocki, A.; Zhydachevskyy, Ya.; Fabisiak, K.; Paprocki, K.; Bilski, P.; Twardak, A.; Fedorov, A.

    2017-07-01

    The work devoted to the investigation of a new luminescent and scintillation material based on the single crystalline films (SCFs) of Tm3-xLuxAG:Ce garnet; x = 0-1.5, grown by LPE method from PbO based flux. The best scintillation properties are achieved for SCFs of Tm1.5Lu1.5Al5O12:Ce composition. We have found that direct Tm → Ce and backside Ce → Tm energy transfer processes are observed in Tm1.5Lu1.5Al5O12:Ce. Due to elimination of traps in the 300-450 °C range, the relatively fast scintillation decay is realized in highly doped Tm1.5Lu1.5Al5O12:Ce SCFs. For this reason, Tm doping can be considered as a suitable way for improvement of the scintillation efficiency in other Ce3+ doped garnet compounds.

  14. Luminescent properties of Al2O3:Ce single crystalline films under synchrotron radiation excitation

    NASA Astrophysics Data System (ADS)

    Zorenko, Yu.; Zorenko, T.; Gorbenko, V.; Savchyn, V.; Voznyak, T.; Fabisiak, K.; Zhusupkalieva, G.; Fedorov, A.

    2016-09-01

    The paper is dedicated to study the luminescent and scintillation properties of the Al2O3:Ce single crystalline films (SCF) grown by LPE method onto saphire substrates from PbO based flux. The structural quality of SCF samples was investigated by XRD method. For characterization of luminescent properties of Al2O3:Ce SCFs the cathodoluminescence spectra, scintillation light yield (LY) and decay kinetics under excitation by α-particles of Pu239 source were used. We have found that the scintillation LY of Al2O3:Ce SCF samples is relatively large and can reach up to 50% of the value realized in the reference YAG:Ce SCF. Using the synchrotron radiation excitation in the 3.7-25 eV range at 10 K we have also determined the basic parameters of the Ce3+ luminescence in Al2O3 host.

  15. Luminescent properties of Mn-doped Y3Al5O12 single crystalline films

    NASA Astrophysics Data System (ADS)

    Zorenko, Yu.; Gorbenko, V.; Zorenko, T.; Kuklinski, B.; Grinberg, M.; Wiśniewski, K.; Bilski, P.

    2014-08-01

    The absorption, cathodoluminescence and photoluminescence (PL) spectra as well as PL decay kinetics of Mn doped Y3Al5O12 (YAG:Mn) single crystalline films (SCF) with manganese concentration in the 0.002-0.2 at.% range, grown by the LPE method from PbO to B2O3 based flux onto YAG substrates, were analyzed in this work. The special goal was spectroscopic determination of valence states of manganese ions which are realized in these SCF depending on Mn content. In SCF with Mn content (0.002-0.02 at.%), the incorporation of Mn4+ and Mn2+ ions was found. The absorption and emission spectra of YAG:Mn SCF at higher (0.02-0.2 at.%) content confirmed that the main valence state of manganese ions is Mn3+ state.

  16. Single-crystalline gold nanoplates from a commercial gold plating solution.

    PubMed

    Li, Zhonghao; Lapeyre, Véronique; Ravaine, Valérie; Ravaine, Serge; Kuhn, Alexander

    2009-03-01

    A novel route was proposed to synthesize gold nanoplates using a commercial gold plating solution as the reactant. Single-crystalline gold nanoplates can be successfully synthesized by reacting gold plating solution with HCl. The as-prepared nanoplates are from several micrometers to tens of micrometers in size. The effects of reactant concentration and temperature on the morphology of the gold products were investigated. The size of the gold nanoplate increases with the decrease of the amount of gold plating solution, while irregular gold nanoparticles are formed as the HCl concentration becomes low. When the reaction temperature is as low as room temperature, nanoplates with a concavity form. Specifically, it is found that the Cl- plays an important role for the formation of these gold nanoplates. The formation mechanism of the gold nanoplates is studied in detail.

  17. Four-fold symmetric anisotropic magnetoresistance of single-crystalline Ni(001) film

    SciTech Connect

    Xiao, X.; Li, J. X.; Ding, Z.; Wu, Y. Z.

    2015-11-28

    Temperature, current-direction, and film-thickness dependent anisotropic magnetoresistance measurements were performed on single-crystalline face-centered-cubic nickel films. An additional four-fold symmetry was confirmed besides the typical two-fold term even at room temperature. The angular-dependent longitudinal resistivity resolves into a two-fold term, which varies as a function of current direction, and a four-fold term, which is isotropically independent of current direction. The experimental results are interpreted well using an expression based on the phenomenological model. Both the two- and four-fold terms vary inversely proportional to film thickness, indicating that interfacial scattering can significantly influence the spin-dependent transport properties.

  18. Direct monolithic integration of vertical single crystalline octahedral molecular sieve nanowires on silicon

    SciTech Connect

    Carretero-Genevrier, Adrian; Oro-Sole, Judith; Gazquez, Jaume; Magen, Cesar; Miranda, Laura; Puig, Teresa; Obradors, Xavier; Ferain, Etienne; Sanchez, Clement; Rodriguez-Carvajal, Juan; Mestres, Narcis

    2013-12-13

    We developed an original strategy to produce vertical epitaxial single crystalline manganese oxide octahedral molecular sieve (OMS) nanowires with tunable pore sizes and compositions on silicon substrates by using a chemical solution deposition approach. The nanowire growth mechanism involves the use of track-etched nanoporous polymer templates combined with the controlled growth of quartz thin films at the silicon surface, which allowed OMS nanowires to stabilize and crystallize. α-quartz thin films were obtained after thermal activated crystallization of the native amorphous silica surface layer assisted by Sr2+- or Ba2+-mediated heterogeneous catalysis in the air at 800 °C. These α-quartz thin films work as a selective template for the epitaxial growth of randomly oriented vertical OMS nanowires. Furthermore, the combination of soft chemistry and epitaxial growth opens new opportunities for the effective integration of novel technological functional tunneled complex oxides nanomaterials on Si substrates.

  19. Laser Cladding for Crack Repair of CMSX-4 Single-Crystalline Turbine Parts

    NASA Astrophysics Data System (ADS)

    Rottwinkel, Boris; Nölke, Christian; Kaierle, Stefan; Wesling, Volker

    2016-12-01

    The increase of the lifetime of modern single crystalline (SX) turbine blades is of high economic priority. The currently available repair methods using polycrystalline cladding of the damaged area do not address the issue of monocrystallinity and are restricted to few areas of the blade. The tip area of the blade is most prone to damage and undergoes the most wear, erosion and cracking during its lifetime. To repair such defects, the common procedure is to remove the whole tip with the damaged area and rebuild it by applying a polycrystalline solidification of the material. The repair of small cracks is conducted in the same way. To reduce repair cost, the investigation of a manufacturing process to repair these cracked areas while maintaining single-crystal solidification is of high interest as this does not diminish material properties and thereby its lifetime. To establish this single-crystal solidification, the realization of a directed temperature gradient is needed. The initial scope of this work is the computational prediction of the temperature field that arises and its verification during the process. The laser cladding process of CMSX-4 substrates was simulated and the necessary parameters calculated. These parameters were then applied to notched substrates and their microstructures analyzed. Starting with a simulation of the temperature field using ANSYS®, a process to repair parts of single crystalline nickel-based alloys was developed. It could be shown that damages to the tip area and cracks can be repaired by establishing a specific temperature gradient during the repair process in order to control the solidification process.

  20. Laser Cladding for Crack Repair of CMSX-4 Single-Crystalline Turbine Parts

    NASA Astrophysics Data System (ADS)

    Rottwinkel, Boris; Nölke, Christian; Kaierle, Stefan; Wesling, Volker

    2017-03-01

    The increase of the lifetime of modern single crystalline (SX) turbine blades is of high economic priority. The currently available repair methods using polycrystalline cladding of the damaged area do not address the issue of monocrystallinity and are restricted to few areas of the blade. The tip area of the blade is most prone to damage and undergoes the most wear, erosion and cracking during its lifetime. To repair such defects, the common procedure is to remove the whole tip with the damaged area and rebuild it by applying a polycrystalline solidification of the material. The repair of small cracks is conducted in the same way. To reduce repair cost, the investigation of a manufacturing process to repair these cracked areas while maintaining single-crystal solidification is of high interest as this does not diminish material properties and thereby its lifetime. To establish this single-crystal solidification, the realization of a directed temperature gradient is needed. The initial scope of this work is the computational prediction of the temperature field that arises and its verification during the process. The laser cladding process of CMSX-4 substrates was simulated and the necessary parameters calculated. These parameters were then applied to notched substrates and their microstructures analyzed. Starting with a simulation of the temperature field using ANSYS®, a process to repair parts of single crystalline nickel-based alloys was developed. It could be shown that damages to the tip area and cracks can be repaired by establishing a specific temperature gradient during the repair process in order to control the solidification process.

  1. Van der Waals Epitaxial Growth of Two-Dimensional Single-Crystalline GaSe Domains on Graphene.

    PubMed

    Li, Xufan; Basile, Leonardo; Huang, Bing; Ma, Cheng; Lee, Jaekwang; Vlassiouk, Ivan V; Puretzky, Alexander A; Lin, Ming-Wei; Yoon, Mina; Chi, Miaofang; Idrobo, Juan C; Rouleau, Christopher M; Sumpter, Bobby G; Geohegan, David B; Xiao, Kai

    2015-08-25

    Two-dimensional (2D) van der Waals (vdW) heterostructures are a family of artificially structured materials that promise tunable optoelectronic properties for devices with enhanced functionalities. Compared to transferring, direct epitaxy of vdW heterostructures is ideal for clean interlayer interfaces and scalable device fabrication. Here we report the synthesis and preferred orientations of 2D GaSe atomic layers on graphene (Gr) by vdW epitaxy. GaSe crystals are found to nucleate predominantly on random wrinkles or grain boundaries of graphene, share a preferred lattice orientation with underlying graphene, and grow into large (tens of micrometers) irregularly shaped, single-crystalline domains. The domains are found to propagate with triangular edges that merge into the large single crystals during growth. Electron diffraction reveals that approximately 50% of the GaSe domains are oriented with a 10.5 ± 0.3° interlayer rotation with respect to the underlying graphene. Theoretical investigations of interlayer energetics reveal that a 10.9° interlayer rotation is the most energetically preferred vdW heterostructure. In addition, strong charge transfer in these GaSe/Gr vdW heterostructures is predicted, which agrees with the observed enhancement in the Raman E(2)1g band of monolayer GaSe and highly quenched photoluminescence compared to GaSe/SiO2. Despite the very large lattice mismatch of GaSe/Gr through vdW epitaxy, the predominant orientation control and convergent formation of large single-crystal flakes demonstrated here is promising for the scalable synthesis of large-area vdW heterostructures for the development of new optical and optoelectronic devices.

  2. Mössbauer study of the magnetic phase composition of single-crystalline rutile (TiO2) implanted with iron ions

    NASA Astrophysics Data System (ADS)

    Dulov, E. N.; Ivoilov, N. G.; Khripunov, D. M.; Tagirov, L. R.; Khaibullin, R. I.; Valeev, V. F.; Nuzhdin, V. I.

    2009-06-01

    Depth-resolved Mössbauer measurements have been performed for four ferromagnetic samples obtained by the implantation of iron ions (enriched to ˜ 50% with 57Fe isotope) into single-crystalline rutile (TiO2) substrates with two crystallographic orientations [(100) and (001)] at different temperatures (300 and 900 K). It is established that the ferromagnetic properties of iron-implanted rutile samples at room temperature are determined by the presence of α-Fe and Fe3O4 phases. The phase composition of samples obtained by iron implantation into substrates heated to 900 K depends on the crystallographic orientation of the substrate, which is explained by a significant anisotropy of the diffusion of iron atoms in rutile.

  3. Magnetic property and microstructure of single crystalline Nd2Fe14B ultrafine particles ball milled from HDDR powders

    SciTech Connect

    Li, WF; Hu, XC; Cui, BZ; Yang, JB; Han, JZ; Hadjipanayis, GC

    2013-08-01

    In this work we report the microstructure and magnetic property of single crystalline Nd2Fe14B ultrafine particles ball milled from HDDR Nd-Fe-B alloys. The average size of the particles is 283 nm, and TEM observation reveals that these particles are single crystalline. The coercivity of these particles is 6.0 kOe, which is much higher than that of the particles ball milled from sintered and hot pressed Nd-Fe-B magnets. Micromagnetic analysis shows that the coercivity degradation is caused by surface damage during ball milling. (C) 2013 Elsevier B.V. All rights reserved.

  4. Single-crystalline ZnTe nanowires for application as high-performance green/ultraviolet photodetector.

    PubMed

    Cao, Y L; Liu, Z T; Chen, L M; Tang, Y B; Luo, L B; Jie, J S; Zhang, W J; Lee, S T; Lee, C S

    2011-03-28

    Single-crystalline ZnTe nanowires were prepared by a simple vapor transport and deposition method. Photodetectors of individual ZnTe nanowires were fabricated to study photoconductivity of the nanowires. It was observed the nanowire photodetectors show the highest visible-light photoconductive gains among all reported photodetectors based on 1D nanostructure semiconductors, including CdS, CdSe, ZnSe, etc. The high photosensitivity and relatively fast response speed are attributable to the high crystal quality of the ZnTe nanowires. These results reveal that such single-crystalline ZnTe nanowires are excellent candidates for optoelectronic applications.

  5. Microwave synthesis of single-crystalline perovskite BiFeO3 nanocubes for photoelectrode and photocatalytic applications

    NASA Astrophysics Data System (ADS)

    Joshi, Upendra A.; Jang, Jum Suk; Borse, Pramod H.; Lee, Jae Sung

    2008-06-01

    A simple microwave synthesis procedure has been developed for the single-crystalline perovskite nanocubes composed of bismuth ferrite (BiFeO3). Typical nanocubes had sizes ranging from 50to200nm. The single-crystalline nature of nanocubes was confirmed by high resolution transmission electron microscopy and selected area electron diffraction pattern. X-ray diffraction pattern showed the rhombohedral phase with R3c space group. The material showed photoinduced water oxidation activity in both photoelectrochemical and photocatalytic modes. It could become a useful material for photoelectrode and photocatalytic applications.

  6. Microwave synthesis of single-crystalline perovskite BiFeO{sub 3} nanocubes for photoelectrode and photocatalytic applications

    SciTech Connect

    Joshi, Upendra A.; Jang, Jum Suk; Borse, Pramod H.; Lee, Jae Sung

    2008-06-16

    A simple microwave synthesis procedure has been developed for the single-crystalline perovskite nanocubes composed of bismuth ferrite (BiFeO{sub 3}). Typical nanocubes had sizes ranging from 50 to 200 nm. The single-crystalline nature of nanocubes was confirmed by high resolution transmission electron microscopy and selected area electron diffraction pattern. X-ray diffraction pattern showed the rhombohedral phase with R3c space group. The material showed photoinduced water oxidation activity in both photoelectrochemical and photocatalytic modes. It could become a useful material for photoelectrode and photocatalytic applications.

  7. Conductive Polymer Synthesis with Single-Crystallinity via a Novel Plasma Polymerization Technique for Gas Sensor Applications

    PubMed Central

    Park, Choon-Sang; Kim, Dong Ha; Shin, Bhum Jae; Kim, Do Yeob; Lee, Hyung-Kun; Tae, Heung-Sik

    2016-01-01

    This study proposes a new nanostructured conductive polymer synthesis method that can grow the single-crystalline high-density plasma-polymerized nanoparticle structures by enhancing the sufficient nucleation and fragmentation of the pyrrole monomer using a novel atmospheric pressure plasma jet (APPJ) technique. Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FE-SEM) results show that the plasma-polymerized pyrrole (pPPy) nanoparticles have a fast deposition rate of 0.93 µm·min−1 under a room-temperature process and have single-crystalline characteristics with porous properties. In addition, the single-crystalline high-density pPPy nanoparticle structures were successfully synthesized on the glass, plastic, and interdigitated gas sensor electrode substrates using a novel plasma polymerization technique at room temperature. To check the suitability of the active layer for the fabrication of electrochemical toxic gas sensors, the resistance variations of the pPPy nanoparticles grown on the interdigitated gas sensor electrodes were examined by doping with iodine. As a result, the proposed APPJ device could obtain the high-density and ultra-fast single-crystalline pPPy thin films for various gas sensor applications. This work will contribute to the design of highly sensitive gas sensors adopting the novel plasma-polymerized conductive polymer as new active layer. PMID:28773932

  8. Single-crystalline Pd square nanoplates enclosed by {100} facets on reduced graphene oxide for formic acid electro-oxidation.

    PubMed

    Jiang, Yi; Yan, Yucong; Chen, Wenlong; Khan, Yousaf; Wu, Jianbo; Zhang, Hui; Yang, Deren

    2016-12-06

    Single-crystalline Pd square nanoplates enclosed by {100} facets were generated on reduced graphene oxide and exhibited the substantially enhanced properties for the formic acid oxidation reaction. The combination of carbonyl groups formed on the surface of annealed graphene oxide and Br(-) ions played important roles in this synthesis.

  9. One-pot synthesis of single-crystalline PtPb nanodendrites with enhanced activity for electrooxidation of formic acid.

    PubMed

    Qu, Ximing; Cao, Zhenming; Zhang, Binwei; Tian, XiaoChun; Zhu, Fuchun; Zhang, Zongcheng; Jiang, Yanxia; Sun, Shigang

    2016-03-25

    Bimetallic PtPb nanodendrites with a single-crystalline structure were obtained by a facile one-pot strategy. The as-synthesized dendritic structure was well characterized and the growth mechanism was investigated. PtPb nanodendrites exhibited superior activity (5.1 times higher than commercial Pd black) and strong anti-poisoning ability for electrooxidation of formic acid.

  10. Conductive Polymer Synthesis with Single-Crystallinity via a Novel Plasma Polymerization Technique for Gas Sensor Applications.

    PubMed

    Park, Choon-Sang; Kim, Dong Ha; Shin, Bhum Jae; Kim, Do Yeob; Lee, Hyung-Kun; Tae, Heung-Sik

    2016-09-30

    This study proposes a new nanostructured conductive polymer synthesis method that can grow the single-crystalline high-density plasma-polymerized nanoparticle structures by enhancing the sufficient nucleation and fragmentation of the pyrrole monomer using a novel atmospheric pressure plasma jet (APPJ) technique. Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FE-SEM) results show that the plasma-polymerized pyrrole (pPPy) nanoparticles have a fast deposition rate of 0.93 µm·min(-1) under a room-temperature process and have single-crystalline characteristics with porous properties. In addition, the single-crystalline high-density pPPy nanoparticle structures were successfully synthesized on the glass, plastic, and interdigitated gas sensor electrode substrates using a novel plasma polymerization technique at room temperature. To check the suitability of the active layer for the fabrication of electrochemical toxic gas sensors, the resistance variations of the pPPy nanoparticles grown on the interdigitated gas sensor electrodes were examined by doping with iodine. As a result, the proposed APPJ device could obtain the high-density and ultra-fast single-crystalline pPPy thin films for various gas sensor applications. This work will contribute to the design of highly sensitive gas sensors adopting the novel plasma-polymerized conductive polymer as new active layer.

  11. Single crystalline hollow metal-organic frameworks: a metal-organic polyhedron single crystal as a sacrificial template.

    PubMed

    Kim, Hyehyun; Oh, Minhak; Kim, Dongwook; Park, Jeongin; Seong, Junmo; Kwak, Sang Kyu; Lah, Myoung Soo

    2015-02-28

    Single crystalline hollow metal-organic frameworks (MOFs) with cavity dimensions on the order of several micrometers and hundreds of micrometers were prepared using a metal-organic polyhedron single crystal as a sacrificial hard template. The hollow nature of the MOF crystal was confirmed by scanning electron microscopy of the crystal sliced using a focused ion beam.

  12. Single-crystalline, wormlike hematite photoanodes for efficient solar water splitting

    PubMed Central

    Kim, Jae Young; Magesh, Ganesan; Youn, Duck Hyun; Jang, Ji-Wook; Kubota, Jun; Domen, Kazunari; Lee, Jae Sung

    2013-01-01

    A hematite photoanode showing a stable, record-breaking performance of 4.32 mA/cm2 photoelectrochemical water oxidation current at 1.23 V vs. RHE under simulated 1-sun (100 mW/cm2) irradiation is reported. This photocurrent corresponds to ca. 34% of the maximum theoretical limit expected for hematite with a band gap of 2.1 V. The photoanode produced stoichiometric hydrogen and oxygen gases in amounts close to the expected values from the photocurrent. The hematitle has a unique single-crystalline “wormlike” morphology produced by in-situ two-step annealing at 550°C and 800°C of β-FeOOH nanorods grown directly on a transparent conducting oxide glass via an all-solution method. In addition, it is modified by platinum doping to improve the charge transfer characteristics of hematite and an oxygen-evolving co-catalyst on the surface. PMID:24045290

  13. Composition engineering of single crystalline films based on the multicomponent garnet compounds

    NASA Astrophysics Data System (ADS)

    Zorenko, Yuriy; Gorbenko, Vitalii; Zorenko, Tetiana; Paprocki, Kazimierz; Bilski, Paweł; Twardak, Anna; Voznyak, Taras; Sidletskiy, Oleg; Gerasimov, Yaroslav; Gryniov, Boris; Fedorov, Alexandr

    2016-11-01

    The paper demonstrates our last achievement in development of the novel scintillating screens based on single crystalline films (SCF) of Ce doped multicomponent garnets using the Liquid Phase Epitaxy (LPE) method. We report in this work the optimized content and excellent scintillation properties of SCF of Lu3-xGdxAl5-yGayO12, Lu3-xTbxAl5-yGayO12 and TbxGdxAl5-yGayO12 garnet compounds grown by the LPE method from PbOsbnd B2O3 based melt-solution onto Gd3Al2.5Ga2.5O12 and YAG substrates. We also show that the Tb1.5Gd1.5Al2.5Ga2.5O12:Ce SCF possess the highest light yield (LY) in comparison with all ever grown garnet SCF scintillators. Namely, the LY of these SCF exceeds by 3.8 and 1.85 times the LY values of the best samples of YAG:Ce and LuAG:Ce SCF scintillators, respectively. The SCF samples of the mentioned compounds show low thermoluminescence in the above room temperature range and relatively fast scintillation decay time t1/e in the 180-200 ns range.

  14. Reversible Sodium Ion Insertion in Single Crystalline Manganese Oxide Nanowires with Long Cycle Life

    SciTech Connect

    Cao, Yuliang; Xiao, Lifen; Wang, Wei; Choi, Daiwon; Nie, Zimin; Yu, Jianguo; Saraf, Laxmikant V.; Yang, Zhenguo; Liu, Jun

    2011-07-26

    Single crystalline Na4Mn9O18 nanowires were synthesized via pyrolysis of polyacrylate salt precursors prepared by in-situ polymerization of the metal salts and acrylate acid, followed by calcinations at an appropriate temperature to achieve good crystalline structure and uniform nanowire morphology with an average diameter of 50 nm. The Na4Mn9O18 nanowires have shown a high, reversible, and near theoretical sodium ion insertion capacity (128 mA h g-1 at 0.1C), excellent long cyclability (77% capacity retention for 1000 cycles at 0.5 C), along with good rate capability. Good capacity and charge-discharge stability are also observed for full cell experiments using a pyrolyzed carbon as the anode, therefore demonstrating the potential of these materials for sodium-ion batteries for large scale energy storage. Furthermore, this research shows that a good crystallinity and small particles are required to enhance the Na-ion diffusion and increase the stability of the electrode materials for long charge-discharge cycles.

  15. Fabrications and application of single crystalline GaN for high-performance deep UV photodetectors

    SciTech Connect

    Velazquez, R.; Rivera, M.; Feng, P.

    2016-08-15

    High-quality single crystalline Gallium Nitride (GaN) semiconductor has been synthesized using molecule beam epitaxy (MBE) technique for development of high-performance deep ultraviolet (UV) photodetectors. Thickness of the films was estimated by using surface profile meter and scanning electron microscope. Electronic states and elemental composition of the films were obtained using Raman scattering spectroscopy. The orientation, crystal structure and phase purity of the films were examined using a Siemens x-ray diffractometer radiation. The surface microstructure was studied using high resolution scanning electron microscopy (SEM). Two types of metal pairs: Al-Al, Al-Cu or Cu-Cu were used for interdigital electrodes on GaN film in order to examine the Schottky properties of the GaN based photodetector. The characterizations of the fabricated prototype include the stability, responsivity, response and recovery times. Typical time dependent photoresponsivity by switching different UV light source on and off five times for each 240 seconds at a bias of 2V, respectively, have been obtained. The detector appears to be highly sensitive to various UV wavelengths of light with very stable baseline and repeatability. The obtained photoresponsivity was up to 354 mA/W at the bias 2V. Higher photoresponsivity could be obtained if higher bias was applied but it would unavoidably result in a higher dark current. Thermal effect on the fabricated GaN based prototype was discussed.

  16. Structurally nanocrystalline-electrically single crystalline ZnO-reduced graphene oxide composites.

    PubMed

    Nam, Woo Hyun; Kim, Bo Bae; Seo, Seul Gi; Lim, Young Soo; Kim, Jong-Young; Seo, Won-Seon; Choi, Won Kook; Park, Hyung-Ho; Lee, Jeong Yong

    2014-09-10

    ZnO, a wide bandgap semiconductor, has attracted much attention due to its multifunctionality, such as transparent conducting oxide, light-emitting diode, photocatalyst, and so on. To improve its performances in the versatile applications, numerous hybrid strategies of ZnO with graphene have been attempted, and various synergistic effects have been achieved in the ZnO-graphene hybrid nanostructures. Here we report extraordinary charge transport behavior in Al-doped ZnO (AZO)-reduced graphene oxide (RGO) nanocomposites. Although the most challenging issue in semiconductor nanocomposites is their low mobilities, the AZO-RGO nanocomposites exhibit single crystal-like Hall mobility despite the large quantity of nanograin boundaries, which hinder the electron transport by the scattering with trapped charges. Because of the significantly weakened grain boundary barrier and the proper band alignment between the AZO and RGO, freely conducting electrons across the nanograin boundaries can be realized in the nanocomposites. This discovery of the structurally nanocrystalline-electrically single crystalline composite demonstrates a new route for enhancing the electrical properties in nanocomposites based on the hybrid strategy.

  17. Weak localization and the approach to metal-insulator transition in single crystalline germanium nanowires

    NASA Astrophysics Data System (ADS)

    Sett, Shaili; Das, K.; Raychaudhuri, A. K.

    2017-03-01

    We study the low-temperature electronic transport properties of single germanium nanowires (NWs) with diameters down to 45 nm to investigate the weak localization (WL) behavior and approach to metal-insulator transition (MIT) within them. The NWs (single crystalline) we investigate lie on the metallic side of the MIT with an extrapolated zero temperature conductivity {σ0} in the range 23 to 1790 (Ω cm)-1 and show a temperature-dependent conductivity which below 30 K can be described by a 3D WL behavior with Thouless length {{L}\\text{Th}}˜ {{T}-\\frac{p{2}}} and p˜ 4 . From the observed value of {σ0} and the value of the critical carrier concentration n c, it is observed that the approach to MIT can be described by the scaling equation {σ0}˜ {{≤ft(n-{{n}\\text{c}}\\right)}ν} with ν ≈ 0.6 , which is a value expected for an uncompensated system. The investigation establishes a NW size limit for the applicability of 3D scaling theories.

  18. Enhanced piezoelectric properties of vertically aligned single-crystalline NKN nano-rod arrays

    PubMed Central

    Kang, Min-Gyu; Oh, Seung-Min; Jung, Woo-Suk; Gyu Moon, Hi; Baek, Seung-Hyub; Nahm, Sahn; Yoon, Seok-Jin; Kang, Chong-Yun

    2015-01-01

    Piezoelectric materials capable of converting between mechanical and electrical energy have a great range of potential applications in micro- and nano-scale smart devices; however, their performance tends to be greatly degraded when reduced to a thin film due to the large clamping force by the substrate and surrounding materials. Herein, we report an effective method for synthesizing isolated piezoelectric nano-materials as means to relax the clamping force and recover original piezoelectric properties of the materials. Using this, environmentally friendly single-crystalline NaxK1-xNbO3 (NKN) piezoelectric nano-rod arrays were successfully synthesized by conventional pulsed-laser deposition and demonstrated to have a remarkably enhanced piezoelectric performance. The shape of the nano-structure was also found to be easily manipulated by varying the energy conditions of the physical vapor. We anticipate that this work will provide a way to produce piezoelectric micro- and nano-devices suitable for practical application, and in doing so, open a new path for the development of complex metal-oxide nano-structures. PMID:25955763

  19. The Nature of Metastable AA' Graphite: Low Dimensional Nano- and Single-Crystalline Forms.

    PubMed

    Lee, Jae-Kap; Kim, Jin-Gyu; Hembram, K P S S; Kim, Yong-Il; Min, Bong-Ki; Park, Yeseul; Lee, Jeon-Kook; Moon, Dong Ju; Lee, Wooyoung; Lee, Sang-Gil; John, Phillip

    2016-12-21

    Over the history of carbon, it is generally acknowledged that Bernal AB stacking of the sp(2) carbon layers is the unique crystalline form of graphite. The universal graphite structure is synthesized at 2,600~3,000 °C and exhibits a micro-polycrystalline feature. In this paper, we provide evidence for a metastable form of graphite with an AA' structure. The non-Bernal AA' allotrope of graphite is synthesized by the thermal- and plasma-treatment of graphene nanopowders at ~1,500 °C. The formation of AA' bilayer graphene nuclei facilitates the preferred texture growth and results in single-crystal AA' graphite in the form of nanoribbons (1D) or microplates (2D) of a few nm in thickness. Kinetically controlled AA' graphite exhibits unique nano- and single-crystalline feature and shows quasi-linear behavior near the K-point of the electronic band structure resulting in anomalous optical and acoustic phonon behavior.

  20. Phase Transitions of SrFeO3 Studied Using a Single-Crystalline Film

    NASA Astrophysics Data System (ADS)

    Hayashi, Naoaki; Muranaka, Shigetoshi; Terashima, Takahito; Takano, Mikio

    2006-03-01

    To study the electronic nature of SrFeO3 (SFO), which is a cubic perovskite containing Fe^4+ equipped with deep d levels and is, therefore, dominated by p-hole character, a single crystalline film was grown and the resistivity (ρ), Hall effect, magnetoresistance (MR) and susceptibility were measured. It is known that this oxide in bulk form becomes antiferromagnetically ordered in a screw spin structure. The TN of the film has been found to be at 120˜125 K from the susceptibility measurement, while the transport properties showed well-defined anomalies at 105 K, rather than at the TN. The metallic film (ρ = 9x10-4 φcm at 300 K) exhibited a hysteretic, inflectional drop in the ρ -T curve at 105 K after showing a very small anomaly at 125 K; the Hall coefficient was positive and temperature-independent above 110 K but increased quickly below ˜100 K; the MR changed its sign from negative to positive quite steeply at 105 K. Considering these results together with what is known about bulk samples, we conclude that SFO undergoes its antiferromagnetic transition in two stages, passing an incompletely coherent stage before entering the final coherent state.

  1. Phase-controlled solvothermal synthesis and characterization of nickel sulfides with good single crystalline nature

    NASA Astrophysics Data System (ADS)

    Chen, Shuguang; Zeng, Kai; Li, Haibin; Li, Fujin

    2011-08-01

    Dispersed rhombohedral NiS rods with high aspect ratios and rhombic dodecahedron-like cubic NiS 2 crystals were prepared by solvothermal routes using NiCl 2·6H 2O and Na 2S 2O 3·5H 2O as reagents and ethylenediamine as a solvent, and 3D blossoming flower-like rhombohedral NiS microstructures were synthesized using different sulfur sources of thiourea. The products were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy dispersion spectrometry and selected area electronic diffraction. All the products were pure and had good single crystalline nature. The synthesis parameters were of great importance on the purity and morphology of the products. The possible growth mechanisms have been discussed based on the analyses of the effects of sulfur sources and solvent on the crystal structures and detailed configurations of the products. The present work is likely to help the phase-controlled synthesis of other metal chalcogenides.

  2. Single crystalline β-SiAlON nanowhiskers: preparation and enhanced properties at high temperature.

    PubMed

    Hou, Xinmei; Yu, Ziyou; Chen, Zhiyuan; Zhao, Baojun; Chou, Kuo-Chih

    2012-06-21

    Single crystalline β-SiAlON (z = 1.0) nanowhiskers with uniform morphology were prepared using a reaction sintering method at 1773 K for 6 h under flowing nitrogen atmosphere. The as-synthesized whiskers were well-crystallized with about 100-200 nm in diameter and a few hundred microns in length. According to the thermodynamic calculation, Al(g) and SiO(g) are important intermediate reactants to synthesize β-SiAlON whiskers. In the experiment, the two phases was controlled by changing the flow rate of nitrogen to make β-SiAlON whiskers grow in a stable way. The formation of β-SiAlON whiskers occurred through a vapor-solid (VS) mechanism. SiAlON was found to grow as a single crystal whisker from the (10 ̅10) plane of the granule. Furthermore, an enhanced oxidation resistance for β-SiAlON whiskers at high temperature was also observed using the thermogravimetry method (TG), demonstrating that β-SiAlON whiskers with uniform morphology is a promising candidate as a reinforcing agent in composite.

  3. Optical phased array using single crystalline silicon high-contrast-gratings for beamsteering

    NASA Astrophysics Data System (ADS)

    Yoo, Byung-Wook; Chan, Trevor; Megens, Mischa; Sun, Tianbo; Yang, Weijian; Rao, Yi; Horsley, David A.; Chang-Hasnain, Connie J.; Wu, Ming C.

    2013-03-01

    We present a single crystalline silicon optical phased array using high-contrast-gratings (HCG) for fast two dimensional beamforming and beamsteering at 0.5 MHz. Since there are various applications for beamforming and beamsteering such as 3D imaging, optical communications, and light detection and ranging (LIDAR), it is great interest to develop ultrafast optical phased arrays. However, the beamsteering speed of optical phased arrays using liquid crystal and electro-wetting are typically limited to tens of milliseconds. Optical phased arrays using micro-electro-mechanical systems (MEMS) technologies can operate in the submegahertz range, but generally require metal coatings. The metal coating unfortunately cause bending of mirrors due to thermally induced stress. The novel MEMS-based optical phased array presented here consists of electrostatically driven 8 × 8 HCG pixels fabricated on a silicon-on-insulator (SOI) wafer. The HCG mirror is designed to have 99.9% reflectivity at 1550 nm wavelength without any reflective coating. The size of the HCG mirror is 20 × 20 μm2 and the mass is only 140 pg, much lighter than traditional MEMS mirrors. Our 8 × 8 optical phased array has a total field of view of +/-10° × 10° and a beam width of 2°. The maximum phase shift regarding the actuation gap defined by a 2 μm buried oxide layer of a SOI wafer is 1.7π at 20 V.

  4. Nanometre-thick single-crystalline nanosheets grown at the water-air interface.

    PubMed

    Wang, Fei; Seo, Jung-Hun; Luo, Guangfu; Starr, Matthew B; Li, Zhaodong; Geng, Dalong; Yin, Xin; Wang, Shaoyang; Fraser, Douglas G; Morgan, Dane; Ma, Zhenqiang; Wang, Xudong

    2016-01-20

    To date, the preparation of free-standing 2D nanomaterials has been largely limited to the exfoliation of van der Waals solids. The lack of a robust mechanism for the bottom-up synthesis of 2D nanomaterials from non-layered materials has become an obstacle to further explore the physical properties and advanced applications of 2D nanomaterials. Here we demonstrate that surfactant monolayers can serve as soft templates guiding the nucleation and growth of 2D nanomaterials in large area beyond the limitation of van der Waals solids. One- to 2-nm-thick, single-crystalline free-standing ZnO nanosheets with sizes up to tens of micrometres are synthesized at the water-air interface. In this process, the packing density of surfactant monolayers adapts to the sub-phase metal ions and guides the epitaxial growth of nanosheets. It is thus named adaptive ionic layer epitaxy (AILE). The electronic properties of ZnO nanosheets and AILE of other materials are also investigated.

  5. Temperature dependent van der Pauw-Hall measurements on sodium doped single crystalline cadmium telluride

    NASA Astrophysics Data System (ADS)

    Ahmad, Faisal R.

    2015-03-01

    In this report, results of the temperature dependent electrical conductivity measurements conducted on single crystalline cadmium telluride (CdTe), containing sodium (Na) impurities are presented and discussed. The electrical conductivity measurements were conducted using an apparatus that allowed the implementation of a standard van der Pauw-Hall effect technique through which the electrical resistivity, concentration of majority carriers, as well as the carrier mobility were determined for temperatures ranging between 24 K and 350 K. Over this temperature range, the electrical resistivity was observed to change by 7 orders of magnitude. Hall measurements showed that the hole concentration at 300 K was ˜3 × 1015 cm-3 and the hole mobility at the same temperature was ˜80 cm2/V s. Measuring the concentration of holes as a function of the sample temperature enabled the estimation of the acceptor energy level with respect to the valence band maximum to be ˜60 meV. The same data also revealed the potential presence of a compensating donor level. Furthermore, the hole mobility was also analyzed over the entire temperature range and the data revealed that above 100 K, the carrier mobility was dominated by the scattering of holes from lattice vibrations.

  6. Magnetotransport properties of single-crystalline LaFeAsO

    NASA Astrophysics Data System (ADS)

    McElroy, C. A.; Hamlin, J. J.; White, B. D.; McGuire, M. A.; Sales, B. C.; Maple, M. B.

    2013-10-01

    Measurements of magnetization, specific heat, electrical resistivity, Hall effect, and magnetoresistance on single crystalline samples of LaFeAsO grown in a NaAs flux are reported. While this material is known to be a semimetal, the temperature dependence of the electrical resistivity data presented herein is reminiscent of semiconducting behavior and exhibits distinct features associated with a structural transition and spin density wave (SDW) order. Low-temperature x-ray diffraction measurements have confirmed that the structural transition in these samples occurs near 140 K, compared to a transition temperature of 156 K observed in polycrystalline samples. Magnetoresistance and Hall coefficient measurements were performed in magnetic fields up to 9 T applied perpendicular to the basal plane using a van der Pauw configuration. The charge carrier density and mobility indicate that electrons are the majority charge carriers and exhibit features indicative of the structural transition and SDW formation. Isotherms of magnetoresistivity measured as a function of magnetic field can be scaled onto a single curve.

  7. Surface Engineering of Copper Foils for Growing Centimeter-Sized Single-Crystalline Graphene.

    PubMed

    Lin, Li; Li, Jiayu; Ren, Huaying; Koh, Ai Leen; Kang, Ning; Peng, Hailin; Xu, H Q; Liu, Zhongfan

    2016-02-23

    The controlled growth of high-quality graphene on a large scale is of central importance for applications in electronics and optoelectronics. To minimize the adverse impacts of grain boundaries in large-area polycrystalline graphene, the synthesis of large single crystals of monolayer graphene is one of the key challenges for graphene production. Here, we develop a facile surface-engineering method to grow large single-crystalline monolayer graphene by the passivation of the active sites and the control of graphene nucleation on copper surface using the melamine pretreatment. Centimeter-sized hexagonal single-crystal graphene domains were successfully grown, which exhibit ultrahigh carrier mobilities exceeding 25,000 cm(2) V(-1) s(-1) and quantum Hall effects on SiO2 substrates. The underlying mechanism of melamine pretreatments were systematically investigated through elemental analyses of copper surface in the growth process of large single-crystals. This present work provides a surface design of a catalytic substrate for the controlled growth of large-area graphene single crystals.

  8. Electrical properties of pseudo-single-crystalline germanium thin-film-transistors fabricated on glass substrates

    NASA Astrophysics Data System (ADS)

    Kasahara, K.; Nagatomi, Y.; Yamamoto, K.; Higashi, H.; Nakano, M.; Yamada, S.; Wang, D.; Nakashima, H.; Hamaya, K.

    2015-10-01

    By developing a low-temperature (≤300 °C) fabrication process for the gate-stack structure on Ge(111), we study electrical properties of thin film transistors (TFTs) consisting of (111)-oriented pseudo-single-crystalline-germanium (PSC-Ge) channels on glass. Although the Hall mobility ( μ Hall ) of p-type PSC-Ge layers reaches 210 cm2/V s and the gate-stack/Ge interface has low trap density, we observe field-effect-mobility (μFE) fluctuation in the p-channel TFTs from 8.2 to 71 cm2/V s, depending on the thickness of the PSC-Ge layer. Considering the μFE fluctuation and low I on / I off ratio in the p-TFTs, we infer the presence of defective Ge layers near the surface of the glass substrate. This study reveals that it is quite important for the high-performance p-Ge TFTs to improve the quality of the Ge layer near the surface of the glass substrate or to choose other materials with better Ge/substrate interface qualities.

  9. Reinvestigation of the thermal properties of single-crystalline SnSe

    NASA Astrophysics Data System (ADS)

    Ibrahim, D.; Vaney, J.-B.; Sassi, S.; Candolfi, C.; Ohorodniichuk, V.; Levinsky, P.; Semprimoschnig, C.; Dauscher, A.; Lenoir, B.

    2017-01-01

    The simple binary SnSe has been recently proposed as a prospective candidate for thermoelectric applications due to its exceptionally low lattice thermal conductivity. However, the thermal transport in single crystals was found to be significantly lower than in polycrystalline samples despite the presence of grain boundary scattering in the latter. In order to better understand the origin of this issue, we report here on a detailed characterization of the thermoelectric properties of a vertical-Bridgman-grown single-crystal of SnSe along the a, b, and c crystallographic axes in a wide range of temperatures (5-700 K). We find that the thermal conductivity features a pronounced Umklapp peak near 12 K whose magnitude depends on the crystal orientation. Unlike prior reports, our results evidence a significant anisotropy between the a, b, and c directions with lattice thermal conductivity values reaching 1.2, 2.3, and 1.7 W m-1 K-1 at 300 K, respectively. While the fundamental reasons behind these differences remain unclear, our results indicate that the intrinsic lattice thermal conductivity of single-crystalline SnSe is likely significantly higher than previously thought.

  10. Fabrications and application of single crystalline GaN for high-performance deep UV photodetectors

    NASA Astrophysics Data System (ADS)

    Velazquez, R.; Aldalbahi, A.; Rivera, M.; Feng, P.

    2016-08-01

    High-quality single crystalline Gallium Nitride (GaN) semiconductor has been synthesized using molecule beam epitaxy (MBE) technique for development of high-performance deep ultraviolet (UV) photodetectors. Thickness of the films was estimated by using surface profile meter and scanning electron microscope. Electronic states and elemental composition of the films were obtained using Raman scattering spectroscopy. The orientation, crystal structure and phase purity of the films were examined using a Siemens x-ray diffractometer radiation. The surface microstructure was studied using high resolution scanning electron microscopy (SEM). Two types of metal pairs: Al-Al, Al-Cu or Cu-Cu were used for interdigital electrodes on GaN film in order to examine the Schottky properties of the GaN based photodetector. The characterizations of the fabricated prototype include the stability, responsivity, response and recovery times. Typical time dependent photoresponsivity by switching different UV light source on and off five times for each 240 seconds at a bias of 2V, respectively, have been obtained. The detector appears to be highly sensitive to various UV wavelengths of light with very stable baseline and repeatability. The obtained photoresponsivity was up to 354 mA/W at the bias 2V. Higher photoresponsivity could be obtained if higher bias was applied but it would unavoidably result in a higher dark current. Thermal effect on the fabricated GaN based prototype was discussed.

  11. Facile fabrication of electrolyte-gated single-crystalline cuprous oxide nanowire field-effect transistors

    NASA Astrophysics Data System (ADS)

    Stoesser, Anna; von Seggern, Falk; Purohit, Suneeti; Nasr, Babak; Kruk, Robert; Dehm, Simone; Wang, Di; Hahn, Horst; Dasgupta, Subho

    2016-10-01

    Oxide semiconductors are considered to be one of the forefront candidates for the new generation, high-performance electronics. However, one of the major limitations for oxide electronics is the scarcity of an equally good hole-conducting semiconductor, which can provide identical performance for the p-type metal oxide semiconductor field-effect transistors as compared to their electron conducting counterparts. In this quest, here we present a bulk synthesis method for single crystalline cuprous oxide (Cu2O) nanowires, their chemical and morphological characterization and suitability as active channel material in electrolyte-gated, low-power, field-effect transistors (FETs) for portable and flexible logic circuits. The bulk synthesis method used in the present study includes two steps: namely hydrothermal synthesis of the nanowires and the removal of the surface organic contaminants. The surface treated nanowires are then dispersed on a receiver substrate where the passive electrodes are structured, followed by printing of a composite solid polymer electrolyte (CSPE), chosen as the gate insulator. The characteristic electrical properties of individual nanowire FETs are found to be quite interesting including accumulation-mode operation and field-effect mobility of 0.15 cm2 V-1 s-1.

  12. Nb-doped single crystalline MoS{sub 2} field effect transistor

    SciTech Connect

    Das, Saptarshi E-mail: das@anl.gov; Demarteau, Marcellinus; Roelofs, Andreas

    2015-04-27

    We report on the demonstration of a p-type, single crystalline, few layer MoS{sub 2} field effect transistor (FET) using Niobium (Nb) as the dopant. The doping concentration was extracted and determined to be ∼3 × 10{sup 19}/cm{sup 3}. We also report on bilayer Nb-doped MoS{sub 2} FETs with ambipolar conduction. We found that the current ON-OFF ratio of the Nb-doped MoS{sub 2} FETs changes significantly as a function of the flake thickness. We attribute this experimental observation to bulk-type electrostatic effect in ultra-thin MoS{sub 2} crystals. We provide detailed analytical modeling in support of our claims. Finally, we show that in the presence of heavy doping, even ultra-thin 2D-semiconductors cannot be fully depleted and may behave as a 3D material when used in transistor geometry. Our findings provide important insights into the doping constraints of 2D materials, in general.

  13. Ultrahigh efficient single-crystalline TiO2 nanorod photoconductors

    NASA Astrophysics Data System (ADS)

    Chen, R. S.; Chen, C. A.; Tsai, H. Y.; Wang, W. C.; Huang, Y. S.

    2012-03-01

    Photoconductive gain and normalized gain, which determine the device and material properties on photoconduction, respectively, have been defined for single-crystalline titanium dioxide (TiO2) nanorods (NRs) with various diameter sizes. The gain values of the NR photodetectors can reach 105 easily at a low bias of 0.1 V. By excluding the contributions of experimental parameters, the optimal normalized gain of the indirect-bandgap TiO2 NRs at 5.4 × 10-5 m2V-1 is comparable with that estimated from the direct-bandgap ZnO nanowires. The average normalized gain value at 3.3 ± 2.2 × 10-5 m2V-1 obtained from eight individual TiO2 NRs with diameters ranging from 120 to 1250 nm is also over three orders of magnitude higher than the polycrystalline nanotube counterpart. The results demonstrate the superior photoconductivity efficiency in boundary-free titania one-dimensional nanostructure, which is crucial for ultraviolet photodetector, dye-sensitized solar cell, and photochemical device applications.

  14. The Electrochemical Response of Single Crystalline Copper Nanowires to Atmospheric Air and Aqueous Solution.

    PubMed

    Zhang, Bowei; Chen, Bensong; Wu, Junsheng; Hao, Shiji; Yang, Guang; Cao, Xun; Jing, Lin; Zhu, Minmin; Tsang, Siu Hon; Teo, Edwin Hang Tong; Huang, Yizhong

    2017-03-01

    In this paper, single crystalline copper nanowires (CuNWs) have been electrochemically grown through anodic aluminum oxide template. The environmental stability of the as-obtained CuNWs in both 40% relative humidity (RH) atmosphere and 0.1 m NaOH aqueous solution has been subsequently studied. In 40% RH atmosphere, a uniform compact Cu2 O layer is formed as a function of exposure time following the logarithmic law and epitaxially covers the CuNW surfaces. It is also found that the oxide layers on CuNWs are sequentially grown when subjected to the cyclic voltammetry measurement in 0.1 m NaOH solution. An epitaxially homogeneous Cu2 O layer is initially formed over the surface of the CuNW substrates by solid-state reaction (SSR). Subsequently, the conversion of Cu2 O into epitaxial CuO based on the SSR takes place with the increase of applied potential. This CuO layer is partially dissolved in the solution forming Cu(OH)2 , which then redeposited on the CuNW surfaces (i.e., dissolution-redeposition (DR) process) giving rise to a mixed polycrystalline CuO/Cu(OH)2 layer. The further increase of applied potential allows the complete oxidation of Cu2 O into CuO to form a dual-layer structure (i.e., CuO inner layer and Cu(OH)2 outer layer) with random orientations through an enhanced DR process.

  15. The Nature of Metastable AA’ Graphite: Low Dimensional Nano- and Single-Crystalline Forms

    NASA Astrophysics Data System (ADS)

    Lee, Jae-Kap; Kim, Jin-Gyu; Hembram, K. P. S. S.; Kim, Yong-Il; Min, Bong-Ki; Park, Yeseul; Lee, Jeon-Kook; Moon, Dong Ju; Lee, Wooyoung; Lee, Sang-Gil; John, Phillip

    2016-12-01

    Over the history of carbon, it is generally acknowledged that Bernal AB stacking of the sp2 carbon layers is the unique crystalline form of graphite. The universal graphite structure is synthesized at 2,600~3,000 °C and exhibits a micro-polycrystalline feature. In this paper, we provide evidence for a metastable form of graphite with an AA’ structure. The non-Bernal AA’ allotrope of graphite is synthesized by the thermal- and plasma-treatment of graphene nanopowders at ~1,500 °C. The formation of AA’ bilayer graphene nuclei facilitates the preferred texture growth and results in single-crystal AA’ graphite in the form of nanoribbons (1D) or microplates (2D) of a few nm in thickness. Kinetically controlled AA’ graphite exhibits unique nano- and single-crystalline feature and shows quasi-linear behavior near the K-point of the electronic band structure resulting in anomalous optical and acoustic phonon behavior.

  16. Nb-doped Single Crystalline MoS2 Field Effect Transistor

    SciTech Connect

    Das, Saptarshi; Demarteau, Marcel; Roelofs, Andreas

    2015-04-27

    We report on the demonstration of a p-type, single crystalline, few layer MoS2 field effect transistor (FET) using Niobium (Nb) as the dopant. The doping concentration was extracted and determined to be similar to 3 x 10(19)/cm(3). We also report on bilayer Nb-doped MoS2 FETs with ambipolar conduction. We found that the current ON-OFF ratio of the Nb-doped MoS2 FETs changes significantly as a function of the flake thickness. We attribute this experimental observation to bulk-type electrostatic effect in ultra-thin MoS2 crystals. We provide detailed analytical modeling in support of our claims. Finally, we show that in the presence of heavy doping, even ultra-thin 2D-semiconductors cannot be fully depleted and may behave as a 3D material when used in transistor geometry. Our findings provide important insights into the doping constraints of 2D materials, in general. (C) 2015 AIP Publishing LLC.

  17. Weak localization and the approach to metal-insulator transition in single crystalline germanium nanowires.

    PubMed

    Sett, Shaili; Das, K; Raychaudhuri, A K

    2017-03-22

    We study the low-temperature electronic transport properties of single germanium nanowires (NWs) with diameters down to 45 nm to investigate the weak localization (WL) behavior and approach to metal-insulator transition (MIT) within them. The NWs (single crystalline) we investigate lie on the metallic side of the MIT with an extrapolated zero temperature conductivity [Formula: see text] in the range 23 to 1790 [Formula: see text] cm)(-1) and show a temperature-dependent conductivity which below 30 K can be described by a 3D WL behavior with Thouless length [Formula: see text] and [Formula: see text]. From the observed value of [Formula: see text] and the value of the critical carrier concentration n c, it is observed that the approach to MIT can be described by the scaling equation [Formula: see text] with [Formula: see text], which is a value expected for an uncompensated system. The investigation establishes a NW size limit for the applicability of 3D scaling theories.

  18. XPS characterization of single crystalline SrLaGa3O7:Nd

    NASA Astrophysics Data System (ADS)

    Iwanowski, R. J.; Heinonen, M. H.; Pracka, I.; Kachniarz, J.

    2013-10-01

    Core-level XPS studies of single crystalline SrLaGa3O7 (SLGO) doped with Nd have been performed for the first time. The detailed analysis of the main XPS core lines of SLGO:Nd included the comparative literature data for the selected oxide compounds containing La and/or Sr, Nd or Ga cations. In particular, the binding energies (BEs) of the Ln 3d5/2 core levels (Ln = La, Nd) in SLGO:Nd were found consistent with the relevant ones for the La- and Nd-based oxides considered, thus indicating that they represent the ground final states of La3+ and Nd3+ ions (respectively) in the crystal lattice after photoexcitation. Analogous consistency has been found for the XPS-derived BEs of the Sr 3d5/2 and Ga 2p3/2 core levels related to the Sr2+ and Ga3+ cationic states in SLGO and the corresponding oxide compounds. Generally, the binding energies of the deep core levels of cations in SLGO:Nd and the other oxides considered are mainly determined by their common oxygen ligand, irrespectively of the crystalline structure.

  19. Growth and mechanisms of enamel-like hierarchical nanostructures on single crystalline hydroxyapatite micro-ribbons.

    PubMed

    Ma, Guobin; Liu, Xiang Yang; Wang, Mu

    2011-06-01

    In vitro growth of enamel-like microstructured hydroxyapatite (HAP) crystals is highly expected for developing novel biomaterials/scaffolds. It is also essential for a clearer understanding of in vivo biomineralization process. In this paper, hierarchical HAP structures are controllably fabricated by growth of nanocrystals on single crystalline micro-ribbon substrates in vitro at biophysical conditions. HAP crystals grown on the substrate change from disordered aggregations of nano-flakes to well-oriented nano-needles, branched bundles of nano-needles, and finally highly porous aggregates, with increase of F- concentrations. The flexibility of the size, morphology, and microstructure control highlights a method to produce hierarchical HAP structures for potential applications in dental restoration or bone implant. We demonstrate that the mutual effects of F- on the crystallinity of HAP and on the supersaturation of the solutions control the morphology and assembly properties of the products. Moreover, the products excellently mimic real tooth enamel structures formed with different F- intakes. The work represents an appropriate simplified model system for an in-depth understanding of the microscopic mechanisms of the effects of F- on enamel growth, and the relationship of enamel microstructures and dental diseases.

  20. Topological surface transport properties of single-crystalline SnTe nanowire.

    PubMed

    Safdar, Muhammad; Wang, Qisheng; Mirza, Misbah; Wang, Zhenxing; Xu, Kai; He, Jun

    2013-01-01

    SnTe has attracted worldwide interest since its theoretical predication as topological crystalline insulator. Because of promising applications of one-dimensional topological insulator in nanoscale electronics and spintronics device, it is very important to realize the observation of topological surface states in one-dimensional SnTe. In this work, for the first time we successfully synthesized high-quality single crystalline SnTe nanowire via gold-catalyst chemical vapor deposition method. Systematical investigation of Aharonov-Bohm and Shubnikov-de Haas oscillations in single SnTe nanowire prove the existence of Dirac electrons. Further analysis of temperature-dependent Shubnikov-de Haas oscillations gives valuable information of cyclotron mass, mean-free path, and mobility of Dirac electrons in SnTe nanowire. Our study provides the experimental groundwork for research in low-dimensional topological crystalline insulator materials and paves the way for the application of SnTe nanowire in nanoelectronics and spintronics device.

  1. Enhanced piezoelectric properties of vertically aligned single-crystalline NKN nano-rod arrays.

    PubMed

    Kang, Min-Gyu; Oh, Seung-Min; Jung, Woo-Suk; Moon, Hi Gyu; Baek, Seung-Hyub; Nahm, Sahn; Yoon, Seok-Jin; Kang, Chong-Yun

    2015-05-08

    Piezoelectric materials capable of converting between mechanical and electrical energy have a great range of potential applications in micro- and nano-scale smart devices; however, their performance tends to be greatly degraded when reduced to a thin film due to the large clamping force by the substrate and surrounding materials. Herein, we report an effective method for synthesizing isolated piezoelectric nano-materials as means to relax the clamping force and recover original piezoelectric properties of the materials. Using this, environmentally friendly single-crystalline NaxK1-xNbO3 (NKN) piezoelectric nano-rod arrays were successfully synthesized by conventional pulsed-laser deposition and demonstrated to have a remarkably enhanced piezoelectric performance. The shape of the nano-structure was also found to be easily manipulated by varying the energy conditions of the physical vapor. We anticipate that this work will provide a way to produce piezoelectric micro- and nano-devices suitable for practical application, and in doing so, open a new path for the development of complex metal-oxide nano-structures.

  2. Epitaxial growth of AlN films on single-crystalline Ta substrates

    SciTech Connect

    Hirata, S.; Okamoto, K.; Inoue, S. Kim, T-W.; Ohta, J.; Fujioka, H.; Oshima, M.

    2007-08-15

    We have demonstrated the first epitaxial growth of AlN films on single-crystalline Ta substrates by the use of a low-temperature growth technique based on pulsed laser deposition (PLD). Although previous AlN films grown on Ta(100) and (111) substrates have exhibited quite poor crystallinity, an epitaxial AlN(0001) film with an in-plane epitaxial relationship of AlN[112-bar 0]//Ta[001] has been obtained on a Ta(110) substrate at a growth temperature of 450 deg. C. We found that the full-width at half-maximum values for the crystal orientation distribution in the tilt and twist directions of the AlN film were 0.37{sup o} and 0.41{sup o}, respectively. Grazing-incidence X-ray reflection (GIXR) and X-ray photoelectron spectroscopy (XPS) measurements have revealed that the AlN/Ta heterointerface is quite abrupt, and that its abruptness remains unchanged even after annealing at 1000 deg. C. - Graphical abstract: An epitaxial AlN(0001) film with an in-plane epitaxial relationship of AlN[112-bar 0]//Ta[001] has been obtained for the first time on a Ta(110) substrate by the use of a PLD low-temperature growth technique.

  3. The Nature of Metastable AA’ Graphite: Low Dimensional Nano- and Single-Crystalline Forms

    PubMed Central

    Lee, Jae-Kap; Kim, Jin-Gyu; Hembram, K. P. S. S.; Kim, Yong-Il; Min, Bong-Ki; Park, Yeseul; Lee, Jeon-Kook; Moon, Dong Ju; Lee, Wooyoung; Lee, Sang-Gil; John, Phillip

    2016-01-01

    Over the history of carbon, it is generally acknowledged that Bernal AB stacking of the sp2 carbon layers is the unique crystalline form of graphite. The universal graphite structure is synthesized at 2,600~3,000 °C and exhibits a micro-polycrystalline feature. In this paper, we provide evidence for a metastable form of graphite with an AA’ structure. The non-Bernal AA’ allotrope of graphite is synthesized by the thermal- and plasma-treatment of graphene nanopowders at ~1,500 °C. The formation of AA’ bilayer graphene nuclei facilitates the preferred texture growth and results in single-crystal AA’ graphite in the form of nanoribbons (1D) or microplates (2D) of a few nm in thickness. Kinetically controlled AA’ graphite exhibits unique nano- and single-crystalline feature and shows quasi-linear behavior near the K-point of the electronic band structure resulting in anomalous optical and acoustic phonon behavior. PMID:28000780

  4. Nanometre-thick single-crystalline nanosheets grown at the water–air interface

    PubMed Central

    Wang, Fei; Seo, Jung-Hun; Luo, Guangfu; Starr, Matthew B.; Li, Zhaodong; Geng, Dalong; Yin, Xin; Wang, Shaoyang; Fraser, Douglas G.; Morgan, Dane; Ma, Zhenqiang; Wang, Xudong

    2016-01-01

    To date, the preparation of free-standing 2D nanomaterials has been largely limited to the exfoliation of van der Waals solids. The lack of a robust mechanism for the bottom-up synthesis of 2D nanomaterials from non-layered materials has become an obstacle to further explore the physical properties and advanced applications of 2D nanomaterials. Here we demonstrate that surfactant monolayers can serve as soft templates guiding the nucleation and growth of 2D nanomaterials in large area beyond the limitation of van der Waals solids. One- to 2-nm-thick, single-crystalline free-standing ZnO nanosheets with sizes up to tens of micrometres are synthesized at the water–air interface. In this process, the packing density of surfactant monolayers adapts to the sub-phase metal ions and guides the epitaxial growth of nanosheets. It is thus named adaptive ionic layer epitaxy (AILE). The electronic properties of ZnO nanosheets and AILE of other materials are also investigated. PMID:26786708

  5. Temperature dependent van der Pauw-Hall measurements on sodium doped single crystalline cadmium telluride

    SciTech Connect

    Ahmad, Faisal R.

    2015-03-21

    In this report, results of the temperature dependent electrical conductivity measurements conducted on single crystalline cadmium telluride (CdTe), containing sodium (Na) impurities are presented and discussed. The electrical conductivity measurements were conducted using an apparatus that allowed the implementation of a standard van der Pauw-Hall effect technique through which the electrical resistivity, concentration of majority carriers, as well as the carrier mobility were determined for temperatures ranging between 24 K and 350 K. Over this temperature range, the electrical resistivity was observed to change by 7 orders of magnitude. Hall measurements showed that the hole concentration at 300 K was ∼3 × 10{sup 15 }cm{sup –3} and the hole mobility at the same temperature was ∼80 cm{sup 2}/V s. Measuring the concentration of holes as a function of the sample temperature enabled the estimation of the acceptor energy level with respect to the valence band maximum to be ∼60 meV. The same data also revealed the potential presence of a compensating donor level. Furthermore, the hole mobility was also analyzed over the entire temperature range and the data revealed that above 100 K, the carrier mobility was dominated by the scattering of holes from lattice vibrations.

  6. Luminescent properties of YAlO3:Mn single crystalline films

    NASA Astrophysics Data System (ADS)

    Zorenko, Yu; Gorbenko, V.; Savchyn, V.; Kuklinski, B.; Grinberg, M.; Bilski, P.; Gieszczyk, W.; Twardak, A.; Mandowski, A.; Mandowska, E.; Fedorov, A.

    2012-10-01

    The YAP:Mn single crystalline films (SCF) have been crystallized by liquid phase epitaxy (LPE) method onto YAP substrates. The cathode- (CL) and photo-luminescence (PL) spectra of the YAP:Mn SCF were analyzed for determination of the preferable valence states of manganese ions which are realized in these SCF depending on Mn content in the 0.01-0.81 at.% range. The thermoluminescence (TL) properties of YAP:Mn SCF with the different Mn content above the RT range were also examined in comparison with the properties of YAP:Mn single crystal counterpart. We show that YAP:Mn (0.01 at.%) SCF possesses effective TL properties both under α-particle and γ-quanta excitation with main TSL peaks at 130 and 195 °C. We assume that the different valence states of Mn ions are responsible for their TL properties, e.g. both emission and trapping centers in YAP:Mn are formed mainly by the different valence states of Mn ions.

  7. Single-crystalline ZnO sheet Source-Gated Transistors.

    PubMed

    Dahiya, A S; Opoku, C; Sporea, R A; Sarvankumar, B; Poulin-Vittrant, G; Cayrel, F; Camara, N; Alquier, D

    2016-01-13

    Due to their fabrication simplicity, fully compatible with low-cost large-area device assembly strategies, source-gated transistors (SGTs) have received significant research attention in the area of high-performance electronics over large area low-cost substrates. While usually based on either amorphous or polycrystalline silicon (α-Si and poly-Si, respectively) thin-film technologies, the present work demonstrate the assembly of SGTs based on single-crystalline ZnO sheet (ZS) with asymmetric ohmic drain and Schottky source contacts. Electrical transport studies of the fabricated devices show excellent field-effect transport behaviour with abrupt drain current saturation (IDS(SAT)) at low drain voltages well below 2 V, even at very large gate voltages. The performance of a ZS based SGT is compared with a similar device with ohmic source contacts. The ZS SGT is found to exhibit much higher intrinsic gain, comparable on/off ratio and low off currents in the sub-picoamp range. This approach of device assembly may form the technological basis for highly efficient low-power analog and digital electronics using ZnO and/or other semiconducting nanomaterial.

  8. Single-crystalline ZnO sheet Source-Gated Transistors

    PubMed Central

    Dahiya, A. S.; Opoku, C.; Sporea, R. A.; Sarvankumar, B.; Poulin-Vittrant, G.; Cayrel, F.; Camara, N.; Alquier, D.

    2016-01-01

    Due to their fabrication simplicity, fully compatible with low-cost large-area device assembly strategies, source-gated transistors (SGTs) have received significant research attention in the area of high-performance electronics over large area low-cost substrates. While usually based on either amorphous or polycrystalline silicon (α-Si and poly-Si, respectively) thin-film technologies, the present work demonstrate the assembly of SGTs based on single-crystalline ZnO sheet (ZS) with asymmetric ohmic drain and Schottky source contacts. Electrical transport studies of the fabricated devices show excellent field-effect transport behaviour with abrupt drain current saturation (IDSSAT) at low drain voltages well below 2 V, even at very large gate voltages. The performance of a ZS based SGT is compared with a similar device with ohmic source contacts. The ZS SGT is found to exhibit much higher intrinsic gain, comparable on/off ratio and low off currents in the sub-picoamp range. This approach of device assembly may form the technological basis for highly efficient low-power analog and digital electronics using ZnO and/or other semiconducting nanomaterial. PMID:26757945

  9. Enzyme-modified field effect transistors based on surface-conductive single-crystalline diamond.

    PubMed

    Härtl, Andreas; Baur, Barbara; Stutzmann, Martin; Garrido, Jose A

    2008-09-02

    Enzyme-modified field effect transistors (ENFETs) were realized using surface-conductive single-crystalline diamond films. The enzymes penicillinase and acetylcholinesterase were immobilized onto the active area of diamond-based electrolytic solution gated FETs, using different organic linker molecules and cross-linking chemistries. The active area of the devices was patterned to generate enzyme-modified regions next to surface-conductive regions. Penicillinase was chosen as a robust model system, but the main focus of the present paper is on acetylcholinesterase, an enzyme essential for many neuronal signal transduction processes. All the different ENFETs show a clear and specific response to the corresponding substrate, penicillin and acetylcholine. The device response is based on the pH sensitivity of the surface-conductive active area and is enabled by the local pH change induced during the enzymatic reaction. The devices demonstrate promising stability and characteristic variations of the enzymatic activity with measurement conditions. Furthermore, the results from the ENFET measurements were compared with the results of spectrophotometric experiments, carried out with enzymes immobilized on diamond substrates and also with free enzymes in solution. This allows an analysis of the enzyme kinetics, as well as qualitative comparison of the different functionalization methods employed in this study.

  10. Size- and structure-dependence of thermal and mechanical behaviors of single-crystalline and polytypic superlattice ZnS nanowires

    SciTech Connect

    Moon, Junghwan; Cho, Maenghyo; Zhou, Min

    2015-06-07

    Molecular dynamics (MD) simulations are carried out to study the thermal and mechanical behaviors of single-crystalline wurtzite (WZ), zinc-blende (ZB), and polytypic superlattice ZnS nanowires containing alternating WZ and ZB regions with thicknesses between 1.85 nm and 29.62 nm under tensile loading. The wires analyzed have diameters between 1.77 nm and 5.05 nm. The Green-Kubo method is used to calculate the thermal conductivity of the wires at different deformed states. A non-equilibrium MD approach is used to analyze the thermal transport behavior at the interfaces between different structural regions in the superlattice nanowires (SLNWs). The Young's modulus and thermal conductivity of ZB nanowires are approximately 2%–12% and 23%–35% lower than those of WZ nanowires, respectively. The lower initial residual compressive stress due to higher irregularity of surface atoms causes the Young's modulus of ZB nanowires to be lower. The dependence of the thermal conductivity on structure comes from differences in phonon group velocities associated with the different wires. The thermal conductivity of polytypic superlattice nanowires is up to 55% lower than that of single-crystalline nanowires, primarily because of phonon scattering at the interfaces and the resulting lower effective phonon mean free paths for each structural region. As the periodic lengths (1.85–29.62 nm) and specimen lengths (14.81–59.24 nm) of SLNWs decrease, these effects become more pronounced, causing the thermal conductivity to further decrease by up to 30%.

  11. Channeling analysis of intrinsic and radiation-induced disorder in single crystalline high- Tc YBa 2Cu 3O 7 thin films

    NASA Astrophysics Data System (ADS)

    Meyer, O.; Weschenfelder, F.; XI, X. X.; Xiong, G. C.; Linker, G.; Geerk, J.

    1988-12-01

    He ion channeling and backscattering spectroscopy was applied to analyze the crystalline quality and the surface preparation of SrTiO 3 single crystals which were used as substrates for the growth of large area single crystalline YBa 2Cu 3O 7 thin films. The analysis supported by Monte Carlo simulation calculations revealed a strain-free growth with the c-axis perpendicular to the substrate surface. The films reveal a mosaic structure with a standard deviation of 0.2° for the misoriented crystallites. The best minimum yield values of 0.12 are obtained for 1 MeV He ions. Energy dependent yield measurements indicate the existence of dislocations. He ion channeling and the resonant scattering at 3.04 MeV was used to determine the oxygen content and to study the damage production and annealing. After irradiation at 300 K the dechanneling yield of the metal atoms and the oxygen increases by about the same amount indicating that the same number of atoms are displaced in different sublattices. The displaced atom fraction is equal to the amorphous fraction as determined by X-ray diffraction.

  12. Recovery Act : Near-Single-Crystalline Photovoltaic Thin Films on Polycrystalline, Flexible Substrates

    SciTech Connect

    Venkat Selvamanickam; Alex Freundlich

    2010-11-29

    III-V photovoltaics have exhibited efficiencies above 40%, but have found only a limited use because of the high cost of single crystal substrates. At the other end of the spectrum, polycrystalline and amorphous thin film solar cells offer the advantage of low-cost fabrication, but have not yielded high efficiencies. Our program is based on single-crystalline-like thin film photovoltaics on polycrystalline substrates using biaxially-textured templates made by Ion Beam-Assisted Deposition (IBAD). MgO templates made by IBAD on flexible metal substrate have been successfully used for epitaxial growth of germanium films. In spite of a 4.5% lattice mismatch, heteroepitaxial growth of Ge was achieved on CeO2 that was grown on IBAD MgO template. Room temperature optical bandgap of the Ge films was identified at 0.67 eV indicating minimal residual strain. Refraction index and extinction coefficient values of the Ge films were found to match well with that measured from a reference Ge single crystal. GaAs has been successfully grown epitaxially on Ge on metal substrate by molecular beam epitaxy. RHEED patterns indicate self annihilation of antiphase boundaries and the growth of a single domain GaAs. The GaAs is found to exhibit strong photoluminescence signal and, an existence of a relatively narrow (FWHM~20 meV) band-edge excitons measured in this film indicates a good optoelectronic quality of deposited GaAs. While excellent epitaxial growth has been achieved in GaAs on flexible metal substrates, the defect density of the films as measured by High Resolution X-ray Diffraction and etch pit experiments showed a high value of 5 * 10^8 per cm^2. Cross sectional transmission electron microscopy of the multilayer architecture showed concentration of threading dislocations near the germanium-ceria interface. The defect density was found decrease as the Ge films were made thicker. The defects appear to originate from the MgO layer presumably because of large lattice mismatches

  13. Unusual non saturating Giant Magneto-resistance in single crystalline Bi2Te3 topological insulator

    NASA Astrophysics Data System (ADS)

    Sultana, Rabia; Neha, P.; Goyal, R.; Patnaik, S.; Awana, V. P. S.

    2017-04-01

    We report synthesis, structural details and electrical transport properties of topological insulator Bi2Te3. The single crystalline specimens of Bi2Te3 are obtained from high temperature (950 °C) melt and slow cooling (2 °C/hour). The resultant crystals were shiny, one piece (few cm) and of bright silver color. The Bi2Te3 crystal is found to be perfect with clear [00l] alignment. The powder XRD pattern being carried out on crushed crystals showed that Bi2Te3 crystallized in R3̅m symmetry with a=b=4.3866(2) Å, c=30.4978(13) Å and γ=120°. The Bi position is refined to (0, 0, 0.4038 (9)) at Wyckoff position 6c and of Te are (0, 0, 0) at Wyckoff position 3a and at (0, 0, 0.2039(8)) at 6c. Ambient pressure and low temperature (down to 2 K) electrical transport measurements revealed metallic behavior. Magneto transport measurements under magnetic field showed huge non saturating magneto resistance (MR) reaching up to 250% at 2.5 K and under 50 kOe field. Summarily, the short communication clearly demonstrates that Bi2Te3 topological insulator exhibit non-saturating large positive MR at low temperature of say below 10 K. The non saturating MR is seen right up to room temperature albeit with much decreased magnitude. Worth mentioning is the fact that these crystals are bulk in nature and hence the anomalous MR is clearly an intrinsic property and not due to the size effect as reported for nano-wires or thin films of the same.

  14. Phase-controlled solvothermal synthesis and characterization of nickel sulfides with good single crystalline nature

    SciTech Connect

    Chen Shuguang; Zeng Kai; Li Haibin; Li Fujin

    2011-08-15

    Dispersed rhombohedral NiS rods with high aspect ratios and rhombic dodecahedron-like cubic NiS{sub 2} crystals were prepared by solvothermal routes using NiCl{sub 2}.6H{sub 2}O and Na{sub 2}S{sub 2}O{sub 3}.5H{sub 2}O as reagents and ethylenediamine as a solvent, and 3D blossoming flower-like rhombohedral NiS microstructures were synthesized using different sulfur sources of thiourea. The products were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy dispersion spectrometry and selected area electronic diffraction. All the products were pure and had good single crystalline nature. The synthesis parameters were of great importance on the purity and morphology of the products. The possible growth mechanisms have been discussed based on the analyses of the effects of sulfur sources and solvent on the crystal structures and detailed configurations of the products. The present work is likely to help the phase-controlled synthesis of other metal chalcogenides. - Graphical abstract: Rhombohedral NiS dispersed rods and 3D flower-like microstructures are evolved from dispersed nucleus and aggregate of nucleus, respectively, and the cross-sections of such rods are in equilateral triangle-like shape. Highlights: > 3D blossoming flower-like r-NiS microstructures are obtained. > Equilateral triangle-like cross-sections of r-NiS rods are observed. > Approach based on XRD analysis to phase-controlled synthesis is presented.

  15. Vertical Single-Crystalline Organic Nanowires on Graphene: Solution-Phase Epitaxy and Optical Microcavities.

    PubMed

    Zheng, Jian-Yao; Xu, Hongjun; Wang, Jing Jing; Winters, Sinéad; Motta, Carlo; Karademir, Ertuğrul; Zhu, Weigang; Varrla, Eswaraiah; Duesberg, Georg S; Sanvito, Stefano; Hu, Wenping; Donegan, John F

    2016-08-10

    Vertically aligned nanowires (NWs) of single crystal semiconductors have attracted a great deal of interest in the past few years. They have strong potential to be used in device structures with high density and with intriguing optoelectronic properties. However, fabricating such nanowire structures using organic semiconducting materials remains technically challenging. Here we report a simple procedure for the synthesis of crystalline 9,10-bis(phenylethynyl) anthracene (BPEA) NWs on a graphene surface utilizing a solution-phase van der Waals (vdW) epitaxial strategy. The wires are found to grow preferentially in a vertical direction on the surface of graphene. Structural characterization and first-principles ab initio simulations were performed to investigate the epitaxial growth and the molecular orientation of the BPEA molecules on graphene was studied, revealing the role of interactions at the graphene-BPEA interface in determining the molecular orientation. These free-standing NWs showed not only efficient optical waveguiding with low loss along the NW but also confinement of light between the two end facets of the NW forming a microcavity Fabry-Pérot resonator. From an analysis of the optical dispersion within such NW microcavities, we observed strong slowing of the waveguided light with a group velocity reduced to one-tenth the speed of light. Applications of the vertical single-crystalline organic NWs grown on graphene will benefit from a combination of the unique electronic properties and flexibility of graphene and the tunable optical and electronic properties of organic NWs. Therefore, these vertical organic NW arrays on graphene offer the potential for realizing future on-chip light sources.

  16. Specific heat and magnetic properties of single-crystalline ZnxDyyCrzSe4 spinels

    NASA Astrophysics Data System (ADS)

    Jendrzejewska, Izabela; Groń, Tadeusz; Maciążek, Ewa; Duda, Henryk; Kubisztal, Marian; Ślebarski, Andrzej; Pietrasik, Ewa; Fijałkowski, Marcin

    2016-06-01

    The crystal structure, magnetic isotherm, magnetic susceptibility, electrical conductivity and specific heat measurements for single-crystalline ZnxDyyCrzSe4 (where x+y+z≈3) spinels are presented. A semiconducting behavior with the activation energy of 0.53 eV, an antiferromagnetic order with a Néel temperature TN=22 K and a strong ferromagnetic exchange evidenced by a positive Curie-Weiss temperature θ=79, 71 and 70 K with increasing Dy-content in the sequence 0.05, 0.13 and 0.19 were established. Below TN the magnetic field dependence of magnetization, M(H), shows two peaks at critical fields Hc1 and Hc2. The values of Hc1 decrease slightly with temperature, especially for the larger Dy-content, while the values of Hc2 drop rapidly with temperature. The magnetic contribution to the specific heat displays a sharp peak at TN, which is strongly shifted to much lower temperatures in the applied magnetic fields. Similar behavior was found for the temperature dependence of the specific heat C(T) plotted as C(T)/T vs. T. The value of the magnetic and phonon contribution to the entropy at TN and at H=0 is only ∼4.8, ∼4.4 and ∼4.2 J mol-1 K-1/Cr3+ for y=0.05, 0.13 and 0.19, respectively, much lower than the average magnetic contribution Sm=(z/2)Rln(2S+1)=12.33 J mol-1 K-1/Cr3+ calculated for Cr3+ ion with S=3/2, as the dysprosium one is paramagnetic.

  17. Construction of cuprous oxide electrodes composed of 2D single-crystalline dendritic nanosheets.

    PubMed

    Jang, Ho Seong; Kim, Suk Jun; Choi, Kyoung-Shin

    2010-10-04

    An unusual anisotropic growth of Cu(2)O is stabilized via the electrochemical synthesis of Cu(2)O in the presence of Ag(+) ions, which results in the formation of Cu(2)O electrodes composed of 2D sheetlike crystals containing complex dendritic patterns. It is quite unusual for Cu(2)O to form a 2D morphology since it has a 3D isotropic cubic crystal structure where the a, b, and c axes are equivalent. Each Cu(2)O sheet is single-crystalline in nature and is grown parallel to the {110} plane, which is rarely observed in Cu(2)O crystal shapes. A various set of experiments are performed to understand the role of Ag(+) ions on the 2D growth of Cu(2)O. The results show that Ag(+) ions are deposited as silver islands on already growing Cu(2)O crystals and serve as nucleation sites for the new growth of Cu(2)O crystals. As a result, the growth direction of the newly forming Cu(2)O crystals is governed by the diffusion layer structure created by the pre-existing Cu(2)O crystals, which results in the formation of 2D dendritic patterns. The thin 2D crystal morphology can significantly increase the surface-to-volume ratio of Cu(2)O crystals, which is beneficial for enhancing various electrochemical and photoelectrochemical properties of the electrodes. The photoelectrochemical properties of the Cu(2)O electrodes composed of 2D dendritic crystals are investigated and compared to those of 3D dendritic crystals. This study provides a unique and effective route to maximize the {110} area per unit volume of Cu(2)O, which will be beneficial for any catalytic/sensing abilities that can be anisotropically enhanced by the {110} planes of Cu(2)O.

  18. Magnetic anisotropy and spin-glass behavior in single crystalline U2PdSi3.

    PubMed

    Li, D X; Kimura, A; Haga, Y; Nimori, S; Shikama, T

    2011-02-23

    We present the magnetic and transport properties of single crystalline U(2)PdSi(3) measured with the magnetic field (H) (or measuring current, I) applied along two typical crystallographic directions, i.e. H ⊥ c-axis and H c-axis (or I ⊥ c-axis and I c-axis). For both directions, a spin-glass state is confirmed to form at low temperature with the same spin freezing temperature T(f) (=11.5 K), initial frequency shift δT(f) (=0.023) and activation energy E(a)/k(B) (=90.15 K) in zero dc field. Strong anisotropy in magnetic and transport behavior is found to be a significant feature of U(2)PdSi(3). The unusual ferromagnetic-like anomaly in ac susceptibility and dc magnetization curves around T(m)=71 K is observed in the case of H c-axis but not in the cases of H ⊥ c-axis. The characteristic temperature T(ir), below which evident irreversible magnetism originated from random spin freezing can be observed, shows much stronger field dependence for H ⊥ c-axis than for H c-axis. Moreover, an unusual finding is that the electrical resistivity measurements indicate the formation of magnetic Brillouin-zone boundary gaps and much larger magnetic scattering for I ⊥ c-axis, while the coherent-Kondo-effect-like behavior is obvious for I c-axis. We also emphasize that no resistivity minimum can be detected down to 2.5 K for either direction. The observed magnetic and transport behaviors are compared with those in polycrystalline U(2)PdSi(3) and other 2:1:3 intermetallic compounds.

  19. Dental composite resins containing silica-fused ceramic single-crystalline whiskers with various filler levels.

    PubMed

    Xu, H H

    1999-07-01

    Currently available direct-filling composite resins are susceptible to fracture and hence are not recommended for use in large stress-bearing posterior restorations involving cusps. The glass fillers in composites provide only limited reinforcement because of the brittleness and low strength of glass. The aim of the present study was to use ceramic single-crystalline whiskers as fillers to reinforce composites, and to investigate the effect of whisker filler level on composite properties. Silica particles were fused onto the whiskers to facilitate silanization and to roughen the whiskers, thereby improving retention in the matrix. The composite flexural strength, elastic modulus, hardness, and degree of polymerization conversion were measured as a function of whisker filler mass fraction, which ranged from 0% to 70%. Selected composites were polished simulating clinical procedures, and the surface roughness was measured with profilometry. The whisker composite with a filler mass fraction of 55% had a flexural strength (mean +/- SD; n = 6) of 196+/-10 MPa, significantly higher than 83+/-14 MPa of a microfill and 120+/-16 MPa of a hybrid composite control (family confidence coefficient = 0.95; Tukey's multiple comparison). The composite modulus and hardness increased monotonically with filler level. The flexural strength first increased, then plateaued with increasing filler level. The degree of conversion decreased with increasing filler level. The whisker composite had a polished surface roughness similar to that of a conventional hybrid composite (p>0.1; Student's t). To conclude, ceramic whisker reinforcement can significantly improve the mechanical properties of composite resins; the whisker filler level plays a key role in determining composite properties; and the reinforcement mechanisms appear to be crack pinning by whiskers and friction from whisker pullout resisting crack propagation.

  20. Development of silicon carbide substrates by carbonization and ion implantation of single-crystalline substrates

    NASA Astrophysics Data System (ADS)

    Morales Sanchez, Francisco Miguel

    Mechanisms of formation involved in both thin films and crystalline precipitates of silicon carbide (SiC) are studied in this Ph. D. thesis. SiC is fabricated starting from single-crystalline silicon (Si) substrates by carbonization or by ion implantation. The characterization of these structures allows to gather data and better physical and chemical understanding of these systems. The main objectives are (i) the fabrication and characterization of SiC and other interesting crystalline phases obtained from Si wafers and (ii) to demonstrate that these products are a viable way for using them as templates, compliant, seed or buffer layers in SiC or III-N overgrowth by epitaxial growth techniques. These approaches let the consecution of a crystalline quality enough to the development of devices. Indeed, their use allow a significant reduction of the high defect density present in III-N or SiC alloys compared to their quality when directly grown on Si. Therefore, long life are foreseen for electronic devices that could use these substrates. This is the limit needed for the beginning of their industrial production and commercialization. Samples studied in this work are framed inside three groups: (1) Silicon Carbide and other phases (Silicon Nitride (Si3N4) and carbon nitride (C3N4)) synthesized by Silicon ion implantation, (2) Silicon Carbide synthesized by Si carbonisation and (3) Silicon Carbide and Gallium Nitride heteroepitaxial growth on carbonized Si. All these structures are fabricated by techniques derived from classic (i) Ion Beam Induced Crystallization (IBIC), (ii) Chemical Vapour Deposition (CVD) or (iii) Molecular Beam Epitaxy (MBE). Structural characterizations are carried out mainly by (i) Scanning Electron Microscopy (SEM), (ii) Transmission Electron Microscopy (TEM), (iii) Fourier Transform Infra Red Spectrometry (FTIR) and other techniques.

  1. Single-crystalline M-type Sr Hexaferrites studied by 57Fe Mössbauer spectroscopy

    NASA Astrophysics Data System (ADS)

    Nagasawa, Nobumoto; Ikeda, Shugo; Shimoda, Aiko; Waki, Takeshi; Tabata, Yoshikazu; Nakamura, Hiroyuki; Kobayashi, Hisao

    2016-12-01

    The 57Fe Mössbauer spectra of the single crystalline and the finely ground Sr1- x La x Fe12- y Co y O19 ( x = 0 : y = 0, x = 0.192 : y = 0.152 and x = 0.456 : y = 0.225) samples have been measured to investigate the La-Co substitution effects. All observed spectra at 150 K were well fitted using the five subspectra which correspond to the five crystallographical nonequivalent Fe sites in the M-type hexaferrite, indicating that the valence changes to Fe2+ ions in the Fe3+ ions were not observed in our Sr1- x La x Fe12- y Co y O19 samples. In SrFe12O19, the relative absorption intensities in the five subspectra show the large anisotropies in the recoilless fractions at the five Fe sites whereas these anisotropies were not observed in Sr0.544La0.456Fe11.775Co0.225O19. These results indicate the chemical compositional dependence on the anisotropies of the recoilless fractions at the five Fe sites. The substitution of a Co2+ ion for the Fe3+ ion changes the center shifts of the Fe3+ ions near the Co2+ ion by the perturbation of the Fe-O-Co hybridizations. Therefore, the Co2+ ions occupy the 4 f 1 and the 4 f 2 sites due to the chemical compositional dependences of the refined magnetic hyperfine field and center shifts of the Fe3+ ions.

  2. Conducting LaAlO3/SrTiO3 heterointerfaces on atomically-flat substrates prepared by deionized-water

    PubMed Central

    Connell, J. G.; Nichols, J.; Gruenewald, J. H.; Kim, D.-W.; Seo, S. S. A.

    2016-01-01

    We have investigated how the recently-developed water-leaching method for atomically-flat SrTiO3 (STO) substrates affects the transport properties of LaAlO3 (LAO) and STO heterointerfaces. Using pulsed laser deposition at identical growth conditions, we have synthesized epitaxial LAO thin-films on two different STO substrates, which are prepared by water-leaching and buffered hydrofluoric acid (BHF) etching methods. The structural, transport, and optical properties of LAO/STO heterostructures grown on water-leached substrates show the same high-quality as the samples grown on BHF-etched substrates. These results indicate that the water-leaching method can be used to grow complex oxide heterostructures with atomically well-defined heterointerfaces without safety concerns. PMID:27033248

  3. Formation of single crystalline tellurium supersaturated silicon pn junctions by ion implantation followed by pulsed laser melting

    NASA Astrophysics Data System (ADS)

    Xiyuan, Wang; Yongguang, Huang; Dewei, Liu; Xiaoning, Zhu; Xiao, Cui; Hongliang, Zhu

    2013-06-01

    Pn junctions based on single crystalline tellurium supersaturated silicon were formed by ion implantation followed by pulsed laser melting (PLM). P type silicon wafers were implanted with 245 keV 126Te+ to a dose of 2 × 1015 ions/cm2, after a PLM process (248 nm, laser fluence of 0.30 and 0.35 J/cm2, 1-5 pulses, duration 30 ns), an n+ type single crystalline tellurium supersaturated silicon layer with high carrier density (highest concentration 4.10 × 1019 cm-3, three orders of magnitude larger than the solid solution limit) was formed, it shows high broadband optical absorption from 400 to 2500 nm. Current—voltage measurements were performed on these diodes under dark and one standard sun (AM 1.5), and good rectification characteristics were observed. For present results, the samples with 4-5 pulses PLM are best.

  4. The fabrication and characterization of flexible single-crystalline silicon and germanium p-intrinsic-n photodetectors on plastic substrates

    NASA Astrophysics Data System (ADS)

    Dang, Mengjiao; Yuan, Hao-Chih; Ma, Zhenqiang; Ma, Jianguo; Qin, Guoxuan

    2017-06-01

    The flexible photodetector is the essential device for many of the optoelectronic applications and its performance can be influenced by a number of factors, including semiconductor materials, illumination conditions, device structures, etc. Therefore, in order to better design and use the flexible photodetectors, it is necessary to understand how these factors affect their performance. In this study, we fabricated flexible lateral p-intrinsic-n photodetectors formed with single-crystalline silicon and germanium nanomembranes on polyethylene terephthalate substrates. The performance of the flexible photodetectors with various dimensions is presented under different illumination conditions. The influences of different semiconductor materials, illumination conditions (wavelength and power of the incident light), and dimensions of the intrinsic region (length and width) on the photocurrent and efficiency are investigated, and the underlying mechanisms are studied based on experimental, simulation, and theoretical analysis. The results provide guidelines for the design and fabrication of flexible single-crystalline semiconductor photodetectors on the plastic substrates.

  5. Fluorescence signals of core-shell quantum dots enhanced by single crystalline gold caps on silicon nanowires

    NASA Astrophysics Data System (ADS)

    Christiansen, S. H.; Chou, J. W.; Becker, M.; Sivakov, V.; Ehrhold, K.; Berger, A.; Chou, W. C.; Chuu, D. S.; Gösele, U.

    2009-04-01

    We use nanoscale (20-300 nm in diameter) single crystalline gold (Au)-caps on silicon nanowires (NWs) grown by the vapor-liquid-solid (VLS) growth mechanism to enhance the fluorescence photoluminescence (PL) signals of highly dilute core/shell CdSeTe/ZnS quantum dots (QDs) in aqueous solution (10-5 M). For NWs without Au-caps, as they appear, for example, after Au etching in aqua regia or buffered KI/I2-solution, essentially no fluorescence signal of the same diluted QDs could be observed. Fluorescence PL signals were measured using excitation with a laser wavelength of 633 nm. The signal enhancement by single crystalline, nanoscale Au-caps is discussed and interpreted based on finite element modeling (FEM).

  6. A simple approach to controllably grow network-like branched single-crystalline Si 3N 4 nanostructures

    NASA Astrophysics Data System (ADS)

    Zhu, Na; Peng, Zhijian; Fu, Xiuli; Wang, Chengbiao; Fu, Zhiqiang; Qi, Longhao; Miao, Hezhuo

    2010-07-01

    We reported a simple, large-scale, and controllable growth method for network-like branched single-crystalline Si 3N 4 nanostructures by catalyst-assisted pyrolysis of a polysilazane. The templates were a silicon wafer deposited with a 5 nm Fe film. The processes simply involved in thermal cross-linking of the polymer precursor, crushing of the solidified preceramic polymer chunks into fine powder, and thermal pyrolysis of the powder under the protection of ultra-high purity nitrogen. The collected white network-like branched nanostructures were formed through "metal-absorption on the surface of nanostructures" model by vapor-liquid-solid mechanism. Microstructure characterizations indicate that the nanostructures are single-crystalline hexagonal α-Si 3N 4. The reaction mechanism of Si 3N 4 nanonetworks was also proposed.

  7. Enhanced non-volatile resistive switching in suspended single-crystalline ZnO nanowire with controllable multiple states

    NASA Astrophysics Data System (ADS)

    Zhang, Rui; Pang, Wei; Zhang, Qing; Chen, Yan; Chen, Xuejiao; Feng, Zhihong; Yang, Jianhua; Zhang, Daihua

    2016-08-01

    Resistive switching nanostructures are a promising candidate for next-generation non-volatile memories. In this report, we investigate the switching behaviors of single-crystalline ZnO nanowires suspended in air. They exhibit significantly higher current density, lower switching voltage, and more pronounced multiple conductance states compared to nanowires in direct contact with substrate. We attribute the effect to enhanced Joule heating efficiency, reduced surface scattering, and more significantly, the positive feedback established between the current density and local temperature in the suspended nanowires. The proposed mechanism has been quantitatively examined by finite element simulations. We have also demonstrated an innovative approach to initiating the current-temperature mutual enhancement through illumination by ultraviolet light, which further confirmed our hypothesis and enabled even greater enhancement. Our work provides further insight into the resistive switching mechanism of single-crystalline one-dimensional nanostructures, and suggests an effective means of performance enhancement and device optimization.

  8. Enhanced non-volatile resistive switching in suspended single-crystalline ZnO nanowire with controllable multiple states.

    PubMed

    Zhang, Rui; Pang, Wei; Zhang, Qing; Chen, Yan; Chen, Xuejiao; Feng, Zhihong; Yang, Jianhua; Zhang, Daihua

    2016-06-27

    Resistive switching nanostructures are a promising candidate for next-generation non-volatile memories. In this report, we investigate the switching behaviors of single-crystalline ZnO nanowires suspended in air. They exhibit significantly higher current density, lower switching voltage, and more pronounced multiple conductance states compared to nanowires in direct contact with substrate. We attribute the effect to enhanced Joule heating efficiency, reduced surface scattering, and more significantly, the positive feedback established between the current density and local temperature in the suspended nanowires. The proposed mechanism has been quantitatively examined by finite element simulations. We have also demonstrated an innovative approach to initiating the current-temperature mutual enhancement through illumination by ultraviolet light, which further confirmed our hypothesis and enabled even greater enhancement. Our work provides further insight into the resistive switching mechanism of single-crystalline one-dimensional nanostructures, and suggests an effective means of performance enhancement and device optimization.

  9. Generation of single-crystalline domain in nano-scale silicon pillars by near-field short pulsed laser

    NASA Astrophysics Data System (ADS)

    In, Jung Bin; Xiang, Bin; Hwang, David J.; Ryu, Sang-Gil; Kim, Eunpa; Yoo, Jae-Hyuck; Dubon, Oscar; Minor, Andrew M.; Grigoropoulos, Costas P.

    2014-01-01

    We observe laser-induced grain morphology change in silicon nanopillars under a transmission electron microscopy (TEM) environment. We couple the TEM with a near-field scanning optical microscopy pulsed laser processing system. This novel combination enables immediate scrutiny on the grain morphologies that the pulsed laser irradiation produces. We find unusual transformation of the tip of the amorphous or polycrystalline silicon pillar into a single crystalline domain via melt-mediated crystallization. On the basis of the three-dimensional finite difference simulation result and the dark field TEM data, we propose that the creation of the distinct single crystalline tip originates from the dominant grain growth initiated at the apex of the non-planar liquid-solid interface. Our microscopic observation provides a fundamental basis for laser-induced conversion of amorphous nanostructures into coarse-grained crystals.

  10. π-π interaction of aromatic groups in amphiphilic molecules directing for single-crystalline mesostructured zeolite nanosheets.

    PubMed

    Xu, Dongdong; Ma, Yanhang; Jing, Zhifeng; Han, Lu; Singh, Bhupendra; Feng, Ji; Shen, Xuefeng; Cao, Fenglei; Oleynikov, Peter; Sun, Huai; Terasaki, Osamu; Che, Shunai

    2014-06-24

    One of the challenges in material science has been to prepare macro- or mesoporous zeolite. Although examples of their synthesis exist, there is a need for a facile yet versatile approach to such hierarchical structures. Here we report a concept for designing a single quaternary ammonium head amphiphilic template with strong ordered self-assembling ability through π-π stacking in hydrophobic side, which stabilizes the mesostructure to form single-crystalline mesostructured zeolite nanosheets. The concept is demonstrated for the formation of a new type of MFI (zeolite framework code by International Zeolite Association) nanosheets joined with a 90° rotational boundary, which results in a mesoporous zeolite with highly specific surface area even after calcination. Low binding energies for this self-assembling system are supported by a theoretical analysis. A geometrical matching between the arrangement of aromatic groups and the zeolitic framework is speculated for the formation of single-crystalline MFI nanosheets.

  11. Heteroepitaxial growth of GaN on atomically flat LiTaO 3 (0 0 0 1) using low-temperature AIN buffer layers

    NASA Astrophysics Data System (ADS)

    Tsuchiya, Y.; Kobayashi, A.; Ohta, J.; Fujioka, H.; Oshima, M.

    2006-07-01

    We have grown GaN films on atomically-flat LiTaO 3 substrates by using pulsed laser deposition (PLD), and we then investigated the effect of the use of low-temperature AlN (LT-AlN) buffer layers on the structural properties of GaN. The full-width at half-maximum (FWHM) values for the crystal orientation distribution of the GaN films in the tilt directions were reduced from 0.48° to 0.17°, and those in the twist directions were reduced from 0.40° to 0.17° by the incorporation of AlN buffer layers grown at 580 °C. The surface morphology of GaN has also been improved by the insertion of LT-AlN buffer layers. X-ray reflectivity measurements have revealed that the interfacial layer thickness between LT-AlN and LiTaO 3 is as thin as 1.7 nm, and that the increase in the interfacial layer thickness caused by annealing at up to 700 °C is quite small. These results indicate that the PLD growth of GaN on atomically flat substrates using LT-AlN buffer layers is quite promising for achieving GaN on LiTaO 3.

  12. Single-Crystalline Aluminum Nanostructures on a Semiconducting GaAs Substrate for Ultraviolet to Near-Infrared Plasmonics.

    PubMed

    Liu, Hsuan-Wei; Lin, Fan-Cheng; Lin, Shi-Wei; Wu, Jau-Yang; Chou, Bo-Tsun; Lai, Kuang-Jen; Lin, Sheng-Di; Huang, Jer-Shing

    2015-04-28

    Aluminum, as a metallic material for plasmonics, is of great interest because it extends the applications of surface plasmon resonance into the ultraviolet (UV) region and is superior to noble metals in natural abundance, cost, and compatibility with modern semiconductor fabrication processes. Ultrasmooth single-crystalline metallic films are beneficial for the fabrication of high-definition plasmonic nanostructures, especially complex integrated nanocircuits. The absence of surface corrugation and crystal boundaries also guarantees superior optical properties and applications in nanolasers. Here, we present UV to near-infrared plasmonic resonance of single-crystalline aluminum nanoslits and nanoholes. The high-definition nanostructures are fabricated with focused ion-beam milling into an ultrasmooth single-crystalline aluminum film grown on a semiconducting GaAs substrate with a molecular beam epitaxy method. The single-crystalline aluminum film shows improved reflectivity and reduced two-photon photoluminescence (TPPL) due to the ultrasmooth surface. Both linear scattering and nonlinear TPPL are studied in detail. The nanoslit arrays show clear Fano-like resonance, and the nanoholes are found to support both photonic modes and localized surface plasmon resonance. We also found that TPPL generation is more efficient when the excitation polarization is parallel rather than perpendicular to the edge of the aluminum film. Such a counterintuitive phenomenon is attributed to the high refractive index of the GaAs substrate. We show that the polarization of TPPL from aluminum preserves the excitation polarization and is independent of the crystal orientation of the film or substrate. Our study gains insight into the optical property of aluminum nanostructures on a high-index semiconducting GaAs substrate and illustrates a practical route to implement plasmonic devices onto semiconductors for future hybrid nanodevices.

  13. Nanoscale magneto-structural coupling in as-deposited and freestanding single-crystalline Fe7Pd3 ferromagnetic shape memory alloy thin films.

    PubMed

    Landgraf, Anja; Jakob, Alexander M; Ma, Yanhong; Mayr, Stefan G

    2013-08-01

    Ferromagnetic shape memory alloys are characterized by strong magneto-mechanical coupling occurring at the atomic scale causing large magnetically inducible strains at the macroscopic level. Employing combined atomic and magnetic force microscopy studies at variable temperature, we systematically explore the relation between the magnetic domain pattern and the underlying structure for as-deposited and freestanding single-crystalline Fe7Pd3 thin films across the martensite-austenite transition. We find experimental evidence that magnetic domain appearance is strongly affected by the presence and absence of nanotwinning. While the martensite-austenite transition upon temperature variation of as-deposited films is clearly reflected in topography by the presence and absence of a characteristic surface corrugation pattern, the magnetic domain pattern is hardly affected. These findings are discussed considering the impact of significant thermal stresses arising in the austenite phase. Freestanding martensitic films reveal a hierarchical structure of micro- and nanotwinning. The associated domain organization appears more complex, since the dominance of magnetic energy contributors alters within this length scale regime.

  14. Nanoscale magneto-structural coupling in as-deposited and freestanding single-crystalline Fe7Pd3 ferromagnetic shape memory alloy thin films

    NASA Astrophysics Data System (ADS)

    Landgraf, Anja; Jakob, Alexander M.; Ma, Yanhong; Mayr, Stefan G.

    2013-08-01

    Ferromagnetic shape memory alloys are characterized by strong magneto-mechanical coupling occurring at the atomic scale causing large magnetically inducible strains at the macroscopic level. Employing combined atomic and magnetic force microscopy studies at variable temperature, we systematically explore the relation between the magnetic domain pattern and the underlying structure for as-deposited and freestanding single-crystalline Fe7Pd3 thin films across the martensite-austenite transition. We find experimental evidence that magnetic domain appearance is strongly affected by the presence and absence of nanotwinning. While the martensite-austenite transition upon temperature variation of as-deposited films is clearly reflected in topography by the presence and absence of a characteristic surface corrugation pattern, the magnetic domain pattern is hardly affected. These findings are discussed considering the impact of significant thermal stresses arising in the austenite phase. Freestanding martensitic films reveal a hierarchical structure of micro- and nanotwinning. The associated domain organization appears more complex, since the dominance of magnetic energy contributors alters within this length scale regime.

  15. Braze Alloy Development for Fast Epitaxial High-Temperature Brazing of Single-Crystalline Nickel-Based Superalloys

    NASA Astrophysics Data System (ADS)

    Laux, B.; Piegert, S.; Rösler, J.

    2009-01-01

    For the repair of single-crystalline turbine components, fabricated from nickel-based superalloys, a new high-temperature brazing technology has been developed. Cracks in single-crystalline parts can be repaired by reproducing the single-crystalline microstructure over the complete gap width within very short brazing times. Nickel-manganese-based alloys were identified as systems that provide very high, epitaxial solidification rates. In contrast to commonly used braze alloys, such as nickel-boron or nickel-silicon systems, the process is not completely diffusion controlled but works with consolute systems. For brazing experiments 300- μm-wide parallel gaps as well as V-shaped gaps with a maximum width of 250 μm were used. A complete epitaxial solidification, that is, the absence of large-angle grain boundaries, could be achieved within brazing times, being up to 100 times shorter compared to commonly used transient-liquid-phase bonding technologies. To quantify the misorientation relative to the base material and the composition within and near the filled gaps, the results of the brazing experiments were visualized by means of light microscopy and scanning electron microscopy (SEM). Furthermore, electron backscatter diffraction (EBSD) analyses and energy dispersive X-ray (EDX) analyses were conducted.

  16. In situ transmission electron microscope formation of a single-crystalline Bi film on an amorphous substrate

    NASA Astrophysics Data System (ADS)

    Neklyudova, M.; Sabater, C.; Erdamar, A. K.; van Ruitenbeek, J. M.; Zandbergen, H. W.

    2017-03-01

    We have performed a range of in situ heating experiments of polycrystalline Bi films of 22-25 nm-thickness in a transmission electron microscope (TEM). This shows that it is possible to locally transform a polycrystalline thin film into a [111]-oriented single-crystalline film, whereby the unique feature is that the original thickness of the film is maintained, and the substrate used in our experiments is amorphous. The single-crystalline areas have been created by heating the Bi film to temperatures close to the melting temperature with additional heating by focusing of the electron beam (e-beam), which results in local melting of the film. The film does not collapse by dewetting, and upon subsequent cooling, the film transforms into a single-crystalline [111] oriented area. The observed phenomenon is attributed to the presence of a thin Bi-oxide layer on top of Bi film. We show that removal of the Bi-oxide layer by heating the film in a H2 gas atmosphere results in changes in the Bi film thickness and dewetting upon in situ heating in the TEM.

  17. Anisotropic thermodynamic and transport properties of single-crystalline CaKFe4As4

    NASA Astrophysics Data System (ADS)

    Meier, W. R.; Kong, T.; Kaluarachchi, U. S.; Taufour, V.; Jo, N. H.; Drachuck, G.; Böhmer, A. E.; Saunders, S. M.; Sapkota, A.; Kreyssig, A.; Tanatar, M. A.; Prozorov, R.; Goldman, A. I.; Balakirev, Fedor F.; Gurevich, Alex; Bud'ko, S. L.; Canfield, P. C.

    2016-08-01

    Single-crystalline, single-phase CaKFe4As4 has been grown out of a high-temperature, quaternary melt. Temperature-dependent measurements of x-ray diffraction, anisotropic electrical resistivity, elastoresistivity, thermoelectric power, Hall effect, magnetization, and specific heat, combined with field-dependent measurements of electrical resistivity and field and pressure-dependent measurements of magnetization indicate that CaKFe4As4 is an ordered, stoichiometric, Fe-based superconductor with a superconducting critical temperature, Tc=35.0 ±0.2 K. Other than superconductivity, there is no indication of any other phase transition for 1.8 K≤T ≤300 K. All of these thermodynamic and transport data reveal striking similarities to those found for optimally or slightly overdoped (Ba1 -xKx )Fe2As2 , suggesting that stoichiometric CaKFe4As4 is intrinsically close to what is referred to as "optimal-doped" on a generalized, Fe-based superconductor, phase diagram. The anisotropic superconducting upper critical field, Hc 2(T ) , of CaKFe4As4 was determined up to 630 kOe. The anisotropy parameter γ (T ) =Hc2 ⊥/Hc2 ∥ , for H applied perpendicular and parallel to the c axis, decreases from ≃2.5 at Tc to ≃1.5 at 25 K, which can be explained by interplay of paramagnetic pair breaking and orbital effects. The slopes of d Hc2 ∥/d T ≃-44 kOe/K and d Hc2 ⊥/d T ≃-109 kOe/K at Tc yield an electron mass anisotropy of m⊥/m∥≃1 /6 and short Ginzburg-Landau coherence lengths ξ∥(0 ) ≃5.8 Å and ξ⊥(0 ) ≃14.3 Å . The value of Hc2 ⊥(0 ) can be extrapolated to ≃920 kOe, well above the BCS paramagnetic limit.

  18. Anisotropic thermodynamic and transport properties of single-crystalline CaKFe4As4

    DOE PAGES

    Meier, W. R.; Kong, T.; Kaluarachchi, U. S.; ...

    2016-08-01

    We grew single-crystalline, single-phase CaKFe4As4 out of a high-temperature, quaternary melt. Temperature-dependent measurements of x-ray diffraction, anisotropic electrical resistivity, elastoresistivity, thermoelectric power, Hall effect, magnetization, and specific heat, combined with field-dependent measurements of electrical resistivity and field and pressure-dependent measurements of magnetization indicate that CaKFe4As4 is an ordered, stoichiometric, Fe-based superconductor with a superconducting critical temperature, Tc=35.0±0.2 K. Other than superconductivity, there is no indication of any other phase transition for 1.8K≤T≤300 K. All of these thermodynamic and transport data reveal striking similarities to those found for optimally or slightly overdoped (Ba1-xKx)Fe2As2, suggesting that stoichiometric CaKFe4As4 is intrinsically close to what is referred to as “optimal-doped” on a generalized, Fe-based superconductor, phase diagram. Furthermore, the anisotropic superconducting upper critical field, Hc2(T), of CaKFe4As4 was determined up to 630 kOe. The anisotropy parameter γ(T)=Hmore » $$⊥\\atop{c2}$$/H$$∥\\atop{c2}$$, for H applied perpendicular and parallel to the c axis, decreases from ≃2.5 at Tc to ≃1.5 at 25 K, which can be explained by interplay of paramagnetic pair breaking and orbital effects. The slopes of dH$$∥\\atop{c2}$$/dT≃-44 kOe/K and dH$$⊥\\atop{c2}$$/dT≃-109 kOe/K at Tc yield an electron mass anisotropy of m⊥/m∥≃1/6 and short Ginzburg-Landau coherence lengths ξ∥(0)≃5.8Å and ξ⊥(0)≃14.3Å. Finally, the value of H$$⊥\\atop{c2}$$(0) can be extrapolated to ≃920 kOe, well above the BCS paramagnetic limit.« less

  19. Atom and Amine Adsorption on Flat and Stepped Gold Surfaces & Structure, Stability and Spin Ordering in Manganese Sulfide Clusters

    NASA Astrophysics Data System (ADS)

    Lewoczko, April D.

    In part I, we investigate gold catalysis in the chemistry of organonitrogen compounds. We examine the adsorption of oxygen, nitrogen and sulfur atoms on the gold (111), (100) and (211) surfaces using density functional theory (DFT). Sulfur atoms bind most strongly, followed by oxygen and nitrogen atoms with stronger adsorption for greater coordination to the surface. We see a trend of stronger adsorption to undercoordinated gold, but find it is non-universal with the adsorption strength trend: (111) > (211) > (100). We consider the diffusion of oxygen, nitrogen and sulfur adatoms and find facile long-range diffusion of oxygen atoms on the (100) surface. Lastly, we compare the adsorption of methylamine on gold to that of a selection of alkylamines, methanol and methanethiol. In each case, the ontop site is preferred with stronger adsorption at low coordinated gold. At oxygen atom coverages of 0.125 -- 0.25 ML on Au (111), we find cooperative adsorption of methylamine and oxygen atoms. Energetic costs for adsorbate tilt from the surface normal and rotation about the gold-nitrogen bond are calculated. While methylamine rotation is barrierless on the (111) and (211) surfaces, it has a low energetic barrier for the 0.125 ML and 0.25 ML O atom pre-covered Au (111) surfaces. In part II, we interpret the experimental mass spectrum of small gas phase manganese sulfide clusters using DFT and elucidate the role of ionicity and spin ordering in sizes with special stability, i.e. magic clusters. We first consider nine low lying minima (MnS)6 structures and reveal antiferromagnetic (AFM) spin ordering with a ˜0.1 eV/pair AFM energy benefit and a ˜0.1 A shrinkage of average Mn-Mn distances over clusters with ferromagnetic (FM) spin ordering. We calculate energetic barriers for interconversion between the two lowest lying (MnS)6 isomers and predict an elevated cluster melting temperature due to increased configurational entropy in a pre-melted state. Second, we demonstrate the

  20. Structure, morphology, and magnetic properties of Fe nanoparticles deposited onto single-crystalline surfaces

    PubMed Central

    Kleibert, Armin; Rosellen, Wolfgang; Getzlaff, Mathias

    2011-01-01

    Summary Background: Magnetic nanostructures and nanoparticles often show novel magnetic phenomena not known from the respective bulk materials. In the past, several methods to prepare such structures have been developed – ranging from wet chemistry-based to physical-based methods such as self-organization or cluster growth. The preparation method has a significant influence on the resulting properties of the generated nanostructures. Taking chemical approaches, this influence may arise from the chemical environment, reaction kinetics and the preparation route. Taking physical approaches, the thermodynamics and the kinetics of the growth mode or – when depositing preformed clusters/nanoparticles on a surface – the landing kinetics and subsequent relaxation processes have a strong impact and thus need to be considered when attempting to control magnetic and structural properties of supported clusters or nanoparticles. Results: In this contribution we focus on mass-filtered Fe nanoparticles in a size range from 4 nm to 10 nm that are generated in a cluster source and subsequently deposited onto two single crystalline substrates: fcc Ni(111)/W(110) and bcc W(110). We use a combined approach of X-ray magnetic circular dichroism (XMCD), reflection high energy electron diffraction (RHEED) and scanning tunneling microscopy (STM) to shed light on the complex and size-dependent relation between magnetic properties, crystallographic structure, orientation and morphology. In particular XMCD reveals that Fe particles on Ni(111)/W(110) have a significantly lower (higher) magnetic spin (orbital) moment compared to bulk iron. The reduced spin moments are attributed to the random particle orientation being confirmed by RHEED together with a competition of magnetic exchange energy at the interface and magnetic anisotropy energy in the particles. The RHEED data also show that the Fe particles on W(110) – despite of the large lattice mismatch between iron and tungsten – are

  1. Synthesis, characterization and phase transitions of single-crystalline vanadium(IV) oxide nanostructures

    NASA Astrophysics Data System (ADS)

    Whittaker, Luisa

    The influence of finite size in altering the phase stabilities of strongly correlated materials gives rise to the interesting prospect of achieving additional tunability of solid-solid phase transitions such as those involved in metal-insulator switching, ferroelectricity, and superconductivity. The peculiarities in the electronic structure of the seemingly simple binary vanadium oxide VO 2, as manifested in a pronounced metal-insulator phase transition in proximity to room temperature, have made it the subject of extensive theoretical and experimental investigations over the last several decades. VO2 exhibits a first-order metal-insulator phase transition near room temperature at 68 °C in the bulk. Associated with the phase transition are dramatic changes in the electrical conductivity, optical properties of VO2 at all wavelengths, and a structural transition from an insulating, low-temperature monoclinic phase to a metallic, high-temperature tetragonal phase. Such properties make VO2 a suitable material for Mott field-effect transistors, optical switching devices, thermochromic coatings, and electronic devices exhibiting sharp thresholdlike variation of electrical and optical properties in response to external stimuli such as temperature and voltage. Scaling VO2 to nanoscale dimensions has recently been possible and has allowed well-defined VO2 nanostructures to serve as model systems for measurements of intrinsic properties without obscuration from grain boundary connectivities and domain dynamics. Geometric confinement, substrate interactions, and varying defect densities of VO2 nanostructures gives rise to an electronic and structural phase diagram that is substantially altered from the bulk. In my talk, I will outline two distinct hydrothermal approaches for the synthesis of 1D single-crystalline VO2 nanostructures exhibiting a substantial diminution in the metal-insulator phase transition temperature based on (a) the hydrothermal hydration, exfoliation, and

  2. High quality single atomic layer deposition of hexagonal boron nitride on single crystalline Rh(111) four-inch wafers

    NASA Astrophysics Data System (ADS)

    Hemmi, A.; Bernard, C.; Cun, H.; Roth, S.; Klöckner, M.; Kälin, T.; Weinl, M.; Gsell, S.; Schreck, M.; Osterwalder, J.; Greber, T.

    2014-03-01

    The setup of an apparatus for chemical vapor deposition (CVD) of hexagonal boron nitride (h-BN) and its characterization on four-inch wafers in ultra high vacuum (UHV) environment is reported. It provides well-controlled preparation conditions, such as oxygen and argon plasma assisted cleaning and high temperature annealing. In situ characterization of a wafer is accomplished with target current spectroscopy. A piezo motor driven x-y stage allows measurements with a step size of 1 nm on the complete wafer. To benchmark the system performance, we investigated the growth of single layer h-BN on epitaxial Rh(111) thin films. A thorough analysis of the wafer was performed after cutting in atmosphere by low energy electron diffraction, scanning tunneling microscopy, and ultraviolet and X-ray photoelectron spectroscopies. The apparatus is located in a clean room environment and delivers high quality single layers of h-BN and thus grants access to large area UHV processed surfaces, which had been hitherto restricted to expensive, small area single crystal substrates. The facility is versatile enough for customization to other UHV-CVD processes, e.g., graphene on four-inch wafers.

  3. High quality single atomic layer deposition of hexagonal boron nitride on single crystalline Rh(111) four-inch wafers

    SciTech Connect

    Hemmi, A.; Bernard, C.; Cun, H.; Roth, S.; Klöckner, M.; Kälin, T.; Osterwalder, J.; Greber, T.; Weinl, M.; Gsell, S.; Schreck, M.

    2014-03-15

    The setup of an apparatus for chemical vapor deposition (CVD) of hexagonal boron nitride (h-BN) and its characterization on four-inch wafers in ultra high vacuum (UHV) environment is reported. It provides well-controlled preparation conditions, such as oxygen and argon plasma assisted cleaning and high temperature annealing. In situ characterization of a wafer is accomplished with target current spectroscopy. A piezo motor driven x-y stage allows measurements with a step size of 1 nm on the complete wafer. To benchmark the system performance, we investigated the growth of single layer h-BN on epitaxial Rh(111) thin films. A thorough analysis of the wafer was performed after cutting in atmosphere by low energy electron diffraction, scanning tunneling microscopy, and ultraviolet and X-ray photoelectron spectroscopies. The apparatus is located in a clean room environment and delivers high quality single layers of h-BN and thus grants access to large area UHV processed surfaces, which had been hitherto restricted to expensive, small area single crystal substrates. The facility is versatile enough for customization to other UHV-CVD processes, e.g., graphene on four-inch wafers.

  4. Survival of hydrogen anions near atomically flat metal surfaces: Band gap confinement and image state recapture effects

    NASA Astrophysics Data System (ADS)

    Schmitz, Andrew; Shaw, John; Chakraborty, Himadri; Thumm, Uwe

    2010-03-01

    Resonant charge transfer (RCT) between ions and surfaces is a key intermediate step in surface-chemical processes as well as in micro- and nano-fabrications on the surface. The RCT process in the collision of hydrogen anions with metal surfaces is described within a wave packet propagation methodology using Crank-Nicholson algorithm [1]. The ion-survival probability is found to strongly enhance at two different ion velocities perpendicular to the surface. The low velocity enhancement is induced from a dynamical confinement of the ion level inside the band gap, while the high velocity enhancement emerges owing to the recapture from transiently populated image states [2]. These structures are found to be somewhat sensitive to the ion's distance of closest approach to the surface and the choice of inter-atomic potentials between the ion and the surface atoms. [1] Chakraborty et al., Phys. Rev. A 70, 052903 (2004); [2] Schmitz et al., Phys. Rev. A (submitted).

  5. Dissociative adsorption of molecular deuterium and thermal stability onto hydrogenated, bare and ion beam damaged poly- and single crystalline diamond surfaces

    NASA Astrophysics Data System (ADS)

    Michaelson, Sh.; Chandran, M.; Zalkind, S.; Shamir, N.; Akhvlediani, R.; Hoffman, A.

    2015-12-01

    In this work we report on dissociative adsorption of deuterium (D2) on bare, hydrogenated and ion beam bombarded polycrystalline and single crystalline diamond surfaces. Polycrystalline diamond films with an average grain size of 300 nm were deposited on silicon substrates by hot filament chemical vapor deposition technique from methane/hydrogen gas mixture. Deposited films were characterized using Raman spectroscopy, atomic force microscopy and scanning electron microscopy to estimate the phase composition and microstructure. High resolution electron energy loss spectroscopy and direct recoil spectrometry were used to study hydrogen (deuterium) bonding configuration of the upper surface region. Near surface amorphization was achieved by 1 keV Ar+ implantation at 1 × 1015 ions/cm2 at room temperature (RT). As deposited and Ar+ bombarded films are annealed to 500-1000 °C in ultra-high vacuum conditions and also under D2 partial pressure of 5 × 10- 6 Torr. For comparison, key experiments were repeated on the single crystal (100) diamond. Our results clearly show the preferential dissociative adsorption of D2 on low hybridized carbon (sp/sp2) states with activation temperature as low as RT, but with a lower thermal stability compared to pure diamond Csbnd D bonds.

  6. Ion-irradiation-assisted tuning of phase transformations and physical properties in single crystalline Fe7Pd3 ferromagnetic shape memory alloy thin films

    NASA Astrophysics Data System (ADS)

    Arabi-Hashemi, A.; Witte, R.; Lotnyk, A.; Brand, R. A.; Setzer, A.; Esquinazi, P.; Hahn, H.; Averback, R. S.; Mayr, S. G.

    2015-05-01

    Control of multi-martensite phase transformations and physical properties constitute greatly unresolved challenges in Fe7Pd3-based ferromagnetic shape memory alloys. Single crystalline Fe7Pd3 thin films reveal an austenite to martensite phase transformation, continuously ranging from the face-centered cubic (fcc) to the face-centered tetragonal (fct) and body-centered cubic (bcc) phases upon irradiation with 1.8 MeV Kr+ ions. Within the present contribution, we explore this scenario within a comprehensive experimental study: employing atomic force microscopy (AFM) and high resolution transmission electron microscopy (HR-TEM), we first clarify the crystallography of the ion-irradiation-induced austenite \\Rightarrow martensite and inter-martensite transitions, explore the multi-variant martensite structures with c-a twinning and unravel a very gradual transition between variants at twin boundaries. Accompanying magnetic properties, addressed locally and globally, are characterized by an increasing saturation magnetization from fcc to bcc, while coercivity and remanence are demonstrated to be governed by magnetocrystalline anisotropy and ion-irradiation-induced defect density, respectively. Based on reversibility of ion-irradiation-induced materials changes due to annealing treatment and a conversion electron Mößbauer spectroscopy (CEMS) study to address changes in order, a quantitative defect-based physical picture of ion-irradiation-induced austenite ⇔ martensite transformation in Fe7Pd3 is developed. The presented concepts thus pave the way for ion-irradiation-assisted optimization strategies for tailored functional alloys.

  7. Experimental investigation of off-stoichiometry and 3d transition metal (Mn, Ni, Cu)-substitution in single-crystalline FePt thin films

    NASA Astrophysics Data System (ADS)

    Ono, Takuya; Nakata, Hitoshi; Moriya, Tomohiro; Kikuchi, Nobuaki; Okamoto, Satoshi; Kitakami, Osamu; Shimatsu, Takehito

    2016-05-01

    In L10 (fct)-FePt thin films, both tuning Fe and Pt concentrations and substitution with third-metal were studied for magnetic characteristic optimization. We investigated single-crystalline FePt-X (X = Mn, Ni, Cu) thin films grown epitaxially on MgO(001) substrates at a substrate temperature of 350 °C by changing Fe, Pt, and X contents, and explored the effects of off-stoichiometry and 3d-metal-substitution. The magnetic moment per atom (m) of FePt-X films as a function of the effective number of valence electrons (neff) in 3d metal sites follows the Slater-Pauling-type trend, by which m decreases by the neff deviation from neff = 8, independently of the X metal and the Pt concentration. The magnetic anisotropy (Ku) exhibits neff dependence similar to m. This trend was almost independent of the Pt concentration after compensation using the theoretical prediction on the relation between Ku and Fe/Pt concentrations. Such a trend has been proved for stoichiometric FePt-X films, but it was clarified as robust against off-stoichiometry. The compensated Ku ( Ku comp ) of FePt-Mn and FePt-Cu followed a similar trend to that predicted by the rigid-band model, although the Ku comp of the FePt-Mn thin films dropped more rapidly than the rigid band calculation. However, it followed the recent first-principles calculation.

  8. Surface-Electronic-State-Modulated, Single-Crystalline (001) TiO2 Nanosheets for Sensitive Electrochemical Sensing of Heavy-Metal Ions.

    PubMed

    Zhou, Wen-Yi; Liu, Jin-Yun; Song, Jie-Yao; Li, Jin-Jin; Liu, Jin-Huai; Huang, Xing-Jiu

    2017-03-21

    Intrinsically low conductivity and poor reactivity restrict many semiconductors from electrochemical detection. Usually, metal- and carbon-based modifications of semiconductors are necessary, making them complex, expensive, and unstable. Here, for the first time, we present a surface-electronic-state-modulation-based concept applied to semiconductors. This concept enables pure semiconductors to be directly available for ultrasensitive electrochemical detection of heavy-metal ions without any modifications. As an example, a defective single-crystalline (001) TiO2 nanosheet exhibits high electrochemical performance toward Hg(II), including a sensitivity of 270.83 μA μM(-1) cm(-2) and a detection limit of 0.017 μM, which is lower than the safety standard (0.03 μM) of drinking water established by the World Health Organization (WHO). It has been confirmed that the surface oxygen vacancy adsorbs an O2 molecule while the Ti(3+) donates an electron, forming the O2(•-) species that facilitate adsorption of Hg(II) and serve as active sites for electron transfer. These findings not only extend the electrochemical sensing applications of pure semiconductors but also stimulate new opportunities for investigating atom-level electrochemical behaviors of semiconductors by surface electronic-state modulation.

  9. Preparation and characterization of clean, single-crystalline YH{sub x} films (0{<=}x{<=}2.9) on W(110)

    SciTech Connect

    Hayoz, J.; Pillo, Th.; Bovet, M.; Zuettel, A.; Guthrie, St.; Pastore, G.; Schlapbach, L.; Aebi, P.

    2000-09-01

    Yttrium can be loaded with hydrogen up to high concentrations causing dramatic structural and electronic changes of the host lattice. We report on the preparation of clean, single-crystalline YH{sub x} films (0{<=}x{<=}2.9). The films have been characterized in situ combining angle-resolved photoelectron spectroscopy (ARPES) and low energy electron diffraction. Direct Y dihydride growth, i.e., Y evaporation under a H{sub 2} partial pressures of {approx_equal}5x10{sup -6} mbar at 500 K on W(110), is the most convenient starting point for the preparation of clean single-crystalline Y hydride films covering H concentrations from the ''clean metal'' (x{approx_equal}0) up to the lower boundary of the pure trihydride phase (x{approx_equal}2.9). Upon annealing Y dihydride films the desired H concentration can be adjusted within the {alpha}-phase or the ({alpha}+{beta}) two-phase regime. On the other hand, the extension of our photoelectron spectrometer with an homemade ultrahigh vacuum (UHV) compatible hydrogenation system allows to induce the transition from Y dihydride to Y trihydride within a few minutes. The hydrogenation system combines a high-pressure reaction cell with hydrogen permeation through a Pd-24%Ag tube. The overall design is such that the sample never gets in contact with non-UHV compartments. For direct Y dihydride growth on W(110) two equally populated face-centered- cubic(111) domains rotated by 180 degree sign with respect to each other are observed. In the {alpha}- and {gamma}-phase the Y atoms form a hexagonal-close-packed(0001) oriented lattice. Furthermore, the previously established model for in situ H concentration estimation in Y [J. Hayoz et al., Phys. Rev. B 58, R4270 (1998)] is extended successfully from the {alpha} to {beta} to the {beta} to {gamma}-phase transition. Ultraviolet photoemission spectroscopy data unequivocally reveal the opening of a gap extending as far as 1 eV below E{sub F} for normal electron emission upon the phase

  10. Constructing MnO{sub 2}/single crystalline ZnO nanorod hybrids with enhanced photocatalytic and antibacterial activity

    SciTech Connect

    Yu, Weiwei; Liu, Tiangui; Cao, Shiyi; Wang, Chen; Chen, Chuansheng

    2016-07-15

    In order to improve the photocatalytic and antibacterial activity of ZnO nanorods, ZnO nanorods decorated with MnO{sub 2} nanoparticles (MnO{sub 2}/ZnO nanorod hybrids) were prepared by using microwave assisted coprecipitation method under the influence of hydrogen peroxide, and the structure, photocatalytic activity and antibacterial property of the products were studied. Experimental results indicated that MnO{sub 2} nanoparticles are decorated on the surface of single crystalline ZnO nanorods. Moreover, the resultant MnO{sub 2}/ZnO nanorod hybrids have been proven to possess good photocatalytic and antibacterial activity, which their degradated efficiency for Rhodamin B (RhB) is twice as the pure ZnO nanorods. Enhancement for photocatalytic and antibacterial activity is mainly attributed to the low band gap energy and excellent electrochemical properties of MnO{sub 2} nanoparticles. - Graphical abstract: The MnO{sub 2}/single crystalline ZnO nanorods hybrids, which MnO{sub 2} nanoparticles are loaded on the surface of ZnO nanorods, were prepared by the step-by-step precipitation method under the assistance of ammonia and hydrogen peroxide. Display Omitted - Highlights: • MnO{sub 2}/ZnO nanorod hybrids were prepared by the step-by-step assembly method. • Single crystalline ZnO nanorods can be decorated by MnO{sub 2} nanoparticles. • MnO{sub 2}/ZnO nanorod hybrids possess good photocatalytic and antibacterial activity. • MnO{sub 2} can improve the photocatalytic activity of ZnO nanorods under visible light.

  11. Synthesis and magnetic properties of single-crystalline Na2-xMn8O16 nanorods

    PubMed Central

    2011-01-01

    The synthesis of single-crystalline hollandite-type manganese oxides Na2-xMn8O16 nanorods by a simple molten salt method is reported for the first time. The nanorods were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and a superconducting quantum interference device magnetometer. The magnetic measurements indicated that the nanorods showed spin glass behavior and exchange bias effect at low temperatures. The low-temperature magnetic behaviors can be explained by the uncompensated spins on the surface of the nanorods. PMID:21711626

  12. Direct writing of large-area micro/nano-structural arrays on single crystalline germanium substrates using femtosecond lasers

    NASA Astrophysics Data System (ADS)

    Li, Lin; Wang, Jun

    2017-06-01

    A direct writing technique for fabricating micro/nano-structural arrays without using a multi-scanning process, multi-beam interference, or any assisted microlens arrays is reported. Various sub-wavelength micro/nano-structural arrays have been directly written on single crystalline germanium substrate surfaces using femtosecond laser pulses. The evolution of the multiscale surface morphology from periodic micro/nano-structures to V-shaped microgrooves has been achieved, and the relationship between array characteristics and laser polarization directions has been discussed. The self-organization model agrees well with the experimental results in this study.

  13. Intrinsic and Ce 3+-related luminescence of YAG and YAG:Ce single crystals, single crystalline films and nanopowders

    NASA Astrophysics Data System (ADS)

    Zorenko, Yu.; Zych, E.; Voloshinovskii, A.

    2009-10-01

    A comparative analysis of the luminescent properties of YAG and YAG:Ce nanopowders (NP) in comparison with single crystalline film (SCF) and single crystal (SC) analogues was performed under excitation by a pulsed synchrotron and X-ray radiation. It was shown that the natural defects concentration in NP was between the SC with a large (˜0.18-0.19 at.%) concentration of Y Al antisite defects (AD) and SCF of these garnets where Y Al AD were completely absent. At the same time, Ce 3+ doped YAG NP showed luminescent properties close to those of YAG:Ce SCF.

  14. Facile synthesis of single crystalline rhenium (VI) trioxide nanocubes with high catalytic efficiency for photodegradation of methyl orange.

    PubMed

    Chong, Yuan Yi; Fan, Wai Yip

    2013-05-01

    Single-crystalline rhenium trioxide (ReO3) nanocubes have been prepared for the first time without the need of surfactants via controlled reduction of rhenium (VII) oxide (Re2O7), sandwiched between silicon wafers at 250°C. The metallic ReO3 nanocubes are magnetic and possess surface plasmon resonance (SPR) bands down to the NIR region. The nanocubes also show very high catalytic activity toward the photodegradation of methyl orange (MO) under ambient conditions. A mechanism has been proposed to account for the photodegradation process.

  15. Facile synthesis of single-crystalline microwires based on anthracene derivative and their efficient optical waveguides and linearly polarized emission

    NASA Astrophysics Data System (ADS)

    Peng, Hong-Dan; Wang, Juan-Ye; Liu, Zheng-Hui; Pan, Ge-Bo

    2016-05-01

    The well-defined single-crystalline microwires of a solid-emissive organic functional molecule, 2-(anthracen-9-yl)-4, 5-diphenyl-1H-imidozole (ADPI) were successfully prepared by a facile solution process without the use of surfactant or additional templates. In addition, the optical loss coefficient is as low as 0.1 dB μm-1 for the as-prepared ADPI microwires, which is lower than most previous reported organic optical waveguides. Meanwhile, these microwires also show optically uniaxial properties as demonstrated by the linearly polarized emission, providing potentially orientation-sensitive applications as optical waveguides with low optical loss.

  16. Single-crystalline C60 nanostructures by sonophysical preparation: tuning hollow nanobowls as catalyst supports for methanol oxidation.

    PubMed

    Zhang, Yang; Jiang, Lang; Li, Hui; Fan, Louzhen; Hu, Wenping; Wang, Chunru; Li, Yongfang; Yang, Shihe

    2011-04-18

    Large-scale single-crystalline hollow nanobowls of pure C(60) were prepared by applying a sonophysical strategy in a binary organic solution. Through the simple adjustment of the concentration of the C(60) /m-xylene solution and the volume ratio of m-xylene to acetonitrile, C(60) nanorings, nanoplates, nanorods, and nanowires were also selectively synthesized. The promise of the C(60) hollow structures as Pt catalyst supports is heightened by the significantly enhanced catalytic activity toward methanol oxidation for a given amount of C(60) used, which demonstrates their potential application in fuel cells.

  17. Growth of single crystalline delafossite LaCuO2 by the travelling-solvent floating zone method

    NASA Astrophysics Data System (ADS)

    Mohan, A.; Büchner, B.; Wurmehl, S.; Hess, C.

    2014-09-01

    Single crystals of LaCuO2 have been grown for the first time using the travelling-solvent floating zone method. The crystal was grown in an Ar-atmosphere by reduction of La2Cu2O5, which was used as the feed rod composition for the growth. The grown crystal has been characterized with regard to phase purity and single crystallinity using powder X-ray diffraction, energy dispersive X-ray analysis, Laue diffraction and scanning electron microscopy.

  18. Current-direction dependence of the transport properties in single-crystalline face-centered-cubic cobalt films

    SciTech Connect

    Xiao, X.; Liang, J. H.; Chen, B. L.; Li, J. X.; Ding, Z.; Wu, Y. Z.; Ma, D. H.

    2015-07-28

    Face-centered-cubic cobalt films are epitaxially grown on insulating LaAlO{sub 3}(001) substrates by molecular beam epitaxy. Transport measurements are conducted in different current directions relative to the crystal axes. We find that the temperature dependent anisotropic magnetoresistance ratio strongly depends on the current direction. However, the anomalous Hall effect shows isotropic behavior independent of the current direction. Our results demonstrate the interplay between the current direction and the crystalline lattice in single-crystalline ferromagnetic films. A phenomenological analysis is presented to interpret the experimental data.

  19. MPACVD growth of single crystalline diamond substrates with PCD rimless and expanding surfaces

    NASA Astrophysics Data System (ADS)

    Nad, Shreya; Charris, Amanda; Asmussen, Jes

    2016-10-01

    Single crystal diamond (SCD) growth was performed in optimized pocket substrate holders at a high pressure (240 Torr) and a high power density (˜1000 W/cm3). In an effort to overcome the challenges of growing large area SCD substrates without a corresponding polycrystalline diamond (PCD) rim, a growth recipe using these pocket holders was developed. This growth recipe controls the substrate temperature (Ts) and the incident microwave power (Pinc) in a prescribed function of growth time. Through this process, the feasibility to enlarge the SCD substrate in situ, i.e., during the growth itself is shown. By allowing the temperature to increase from ˜980 °C to 1040 °C, then reducing the temperature, and then allowing it to drift up again, the deposition process alternates between the fast growth of the different crystal directions (i.e., <110>, <111>, and <100>) and a slow growth to smoothen the top surface. This leads to an increased lateral SCD growth. The slow growth of the crystal faces in turn leads to a smooth and enlarged top surface. Certain strategies such as the termination of the growth process at the appropriate time are critical in obtaining flat and smooth SCD surfaces without the formation of any PCD rim. The SCD substrates grown via this method have been analyzed by optical and scanning electron microscopies. The lateral SCD surface area increased between 1.7 and 2 times greater than the initial seed surface area during one continuous run. The deposited SCDs have high growth rates of ˜30 μm/h resulting in smooth, flat and rimless substrates, hence indicating the improvement in the quality and morphology of the deposited substrates.

  20. Single-crystalline MFe(2)O(4) nanotubes/nanorings synthesized by thermal transformation process for biological applications.

    PubMed

    Fan, Hai-Ming; Yi, Jia-Bao; Yang, Yi; Kho, Kiang-Wei; Tan, Hui-Ru; Shen, Ze-Xiang; Ding, Jun; Sun, Xiao-Wei; Olivo, Malini Carolene; Feng, Yuan-Ping

    2009-09-22

    We report a general thermal transformation approach to synthesize single-crystalline magnetic transition metal oxides nanotubes/nanorings including magnetite Fe(3)O(4), maghematite gamma-Fe(2)O(3), and ferrites MFe(2)O(4) (M = Co, Mn, Ni, Cu) using hematite alpha-Fe(2)O(3) nanotubes/nanorings template. While the straightforward reduction or reduction-oxides process was employed to produce Fe(3)O(4) and gamma-Fe(2)O(3), the alpha-Fe(2)O(3)/M(OH)(2) core/shell nanostructure was used as precursor to prepare MFe(2)O(4) nanotubes via MFe(2)O(4-x) (0 < x < 1) intermediate. The transformed ferrites nanocrystals retain the hollow structure and single-crystalline nature of the original templates. However, the crystallographic orientation-relationships of cubic spinel ferrites and trigonal hematite show strong correlation with their morpologies. The hollow-structured MFe(2)O(4) nanocrystals with tunable size, shape, and composition have exhibited unique magnetic properties. Moreover, they have been demonstrated as a highly effective peroxidase mimic catalysts for laboratory immunoassays or as a universal nanocapsules hybridized with luminescent QDs for magnetic separation and optical probe of lung cancer cells, suggesting that these biocompatible magnetic nanotubes/nanorings have great potential in biomedicine and biomagnetic applications.

  1. Single Crystalline Co3O4 Nanocrystals Exposed with Different Crystal Planes for Li-O2 Batteries

    PubMed Central

    Su, Dawei; Dou, Shixue; Wang, Guoxiu

    2014-01-01

    Single crystalline Co3O4 nanocrystals exposed with different crystal planes were synthesised, including cubic Co3O4 nanocrystals enclosed by {100} crystal planes, pseudo octahedral Co3O4 enclosed by {100} and {110} crystal planes, Co3O4 nanosheets exposed by {110} crystal planes, hexagonal Co3O4 nanoplatelets exposed with {111} crystal planes, and Co3O4 nanolaminar exposed with {112} crystal planes. Well single crystalline features of these Co3O4 nanocrystals were confirmed by FESEM and HRTEM analyses. The electrochemical performance for Li-O2 batteries shows that Co3O4 nanocrystals can significantly reduce the discharge-charge over-potential via the effect on the oxygen evolution reaction (OER). From the comparison on their catalytic performances, we found that the essential factor to promote the oxygen evolution reactions is the surface crystal planes of Co3O4 nanocrystals, namely, crystal planes-dependent process. The correlation between different Co3O4 crystal planes and their effect on reducing charge-discharge over-potential was established: {100} < {110} < {112} < {111}. PMID:25169737

  2. Morphology evolution of single-crystalline hematite nanocrystals: magnetically recoverable nanocatalysts for enhanced facet-driven photoredox activity.

    PubMed

    Patra, Astam K; Kundu, Sudipta K; Bhaumik, Asim; Kim, Dukjoon

    2016-01-07

    We have developed a new green chemical approach for the shape-controlled synthesis of single-crystalline hematite nanocrystals in aqueous medium. FESEM, HRTEM and SAED techniques were used to determine the morphology and crystallographic orientations of each nanocrystal and its exposed facets. PXRD and HRTEM techniques revealed that the nanocrystals are single crystalline in nature; twins and stacking faults were not detected in these nanocrystals. The structural, vibrational, and electronic spectra of these nanocrystals were highly dependent on their shape. Different shaped hematite nanocrystals with distinct crystallographic planes have been synthesized under similar reaction conditions, which can be desired as a model for the purpose of properties comparison with the nanocrystals prepared under different reaction conditions. Here we investigated the photocatalytic performance of these different shaped-nanocrystals for methyl orange degradation in the presence of white light (λ > 420 nm). In this study, we found that the density of surface Fe(3+) ions in particular facets was the key factor for the photocatalytic activity and was higher on the bitruncated-dodecahedron shape nanocrystals by coexposed {104}, {100} and {001} facets, attributing to higher catalytic activity. The catalytic activity of different exposed facet nanocrystals were as follows: {104} + {100} + {001} (bitruncated-dodecahedron) > {101} + {001} (bitruncated-octahedron) > {001} + {110} (nanorods) > {012} (nanocuboid) which provided the direct evidence of exposed facet-driven photocatalytic activity. The nanocrystals were easily recoverable using an external magnet and reused at least six times without significant loss of its catalytic activity.

  3. Magnetic entropy change and accurate determination of Curie temperature in single-crystalline helimagnet FeGe

    NASA Astrophysics Data System (ADS)

    Xu, Lisha; Han, Hui; Fan, Jiyu; Shi, Daning; Hu, Dazhi; Du, Haifeng; Zhang, Lei; Zhang, Yuheng; Yang, Hao

    2017-02-01

    Cubic helimagnet FeGe has emerged as a class of skyrmion materials near room temperature that may impact future information technology. Experimentally identifying the detailed properties of skyrmion materials enables their practical application acceleratedly. Here we study the magnetic entropy change (MEC) of single-crystalline FeGe in its precursor region and clarify its close relation to the critical exponents of a second-order phase transition in this area. The maximum MEC is found to be 2.86 J/kg · K for a 7.0 T magnetic-field change smaller than that of common magnetocaloric materials indicating the multiplicity and complexity of the magnetic structure phases in the precursor region. This result also implies that the competition among the multimagnetic phases can partly counteract the magnetic-field-driven force and establishes a stable balance. Based on the obtained MEC and the critical exponents, the exact Curie temperature of single-crystalline FeGe under zero magnetic field is confirmed to be 279.1 K, higher than the previously reported 278.2 K. This finding paves the way for reconstruction of the FeGe phase diagram in the precursor region.

  4. Large-scale synthesis and electrical transport properties of single-crystalline SmB6 nanowires

    NASA Astrophysics Data System (ADS)

    Zhou, Yong; Peng, Yuehua; Yin, Yanling; Zhou, Weichang; Zhou, Fang; Liu, Chang; Liu, Guangtong; Sun, Lianfeng; Tang, Dongsheng

    2016-07-01

    Topological Kondo insulator samarium hexaboride (SmB6) nanowires, with diameters of 60-150 nm and lengths up to 1-5 μm, were successfully synthesized in large scale by chemical vapor deposition using BCl3 and SmCl3 as precursors at 1070 °C. Transmission electron microscopy observation and selected area electron diffraction analysis indicate that SmB6 nanowires are single-crystalline and grow in a preferred direction of [1 0 0]. It also indicates that the growth of SmB6 nanowires might be governed by a vapor-solid mechanism. Conventional four-terminal resistance measurements show that the resistance of an SmB6 nanowire increases with decreasing temperature, but saturates at temperatures less than 10 K, which might be attributed to a true topological insulator with a metallic surface and fully insulating bulk states. Resistance measurements also indicate that the contribution of surface states to conductance in the SmB6 nanowire is enhanced remarkably; therefore the high-quality single-crystalline SmB6 nanowires with large surface-to-bulk ratio might be the best candidate for investigating the topological properties of this material.

  5. Magnetic properties of single crystalline expanded austenite obtained by plasma nitriding of austenitic stainless steel single crystals.

    PubMed

    Menéndez, Enric; Templier, Claude; Garcia-Ramirez, Pablo; Santiso, José; Vantomme, André; Temst, Kristiaan; Nogués, Josep

    2013-10-23

    Ferromagnetic single crystalline [100], [110], and [111]-oriented expanded austenite is obtained by plasma nitriding of paramagnetic 316L austenitic stainless steel single crystals at either 300 or 400 °C. After nitriding at 400 °C, the [100] direction appears to constitute the magnetic easy axis due to the interplay between a large lattice expansion and the expected decomposition of the expanded austenite, which results in Fe- and Ni-enriched areas. However, a complex combination of uniaxial (i.e., twofold) and biaxial (i.e., fourfold) in-plane magnetic anisotropies is encountered. It is suggested that the former is related to residual stress-induced effects while the latter is associated to the in-plane projections of the cubic lattice symmetry. Increasing the processing temperature strengthens the biaxial in-plane anisotropy in detriment of the uniaxial contribution, in agreement with a more homogeneous structure of expanded austenite with lower residual stresses. In contrast to polycrystalline expanded austenite, single crystalline expanded austenite exhibits its magnetic easy axes along basic directions.

  6. Effect of Mg co-doping on cathodoluminescence properties of LuGAGG:Ce single crystalline garnet films

    NASA Astrophysics Data System (ADS)

    Schauer, P.; Lalinský, O.; Kučera, M.; Lučeničová, Z.; Hanuš, M.

    2017-10-01

    Mg2+ co-doped (LuGd)3(GaAl)5O12:Ce (LuGAGG:Ce,Mg) multicomponent single crystalline epitaxial garnet films were prepared and their cathodoluminescence (CL) and thermoluminescence (TSL) properties were studied in this paper. The films were prepared using the liquid phase epitaxy from lead-free BaO-B2O3-BaF2 flux and their scintillation properties were characterized using the 10 keV collimated e-beam. More specifically, temperature dependent CL intensity, CL emission spectra, CL decay characteristics as well as TSL emission characteristics of the mentioned films were measured. At the highest content of Mg (700 ppm), the CL decay time was as low as 28 ns and the CL afterglow was as low as 0.01% at 1 μs after the e-beam excitation cut-off, which are important parameters for electron detectors in e-beam devices. The CL temperature quenching of the studied films began above room temperature. An increase of Mg concentration to or above 280 ppm quenched the characteristic CL emission of LuGAGG:Ce,Mg. The TSL measurements show that the trap population in studied garnet samples is considerably suppressed. The LuGAGG:Ce,Mg multicomponent single crystalline epitaxial films were evaluated as the perspective fast scintillators for the electron detectors in the e-beam devices.

  7. Single-Crystalline SrRuO3 Nanomembranes: A Platform for Flexible Oxide Electronics

    SciTech Connect

    Paskiewicz, Deborah M.; Sichel-Tissot, Rebecca; Karapetrova, Evguenia; Stan, Liliana; Fong, Dillon D.

    2016-12-11

    The field of oxide electronics has benefited from the wide spectrum of functionalities available to the ABO3 perovskites, and researchers are now employing defect engineering in single crystalline heterostructures to tailor properties. However, bulk oxide single crystals are not conducive to many types of applications, particularly those requiring mechanical flexibility. Here, we demonstrate the realization of an all-oxide, single-crystalline nanomembrane heterostructure. With a surface-to-volume ratio of 2 × 107 , the nanomembranes are fully flexible and can be readily transferred to other materials for handling purposes or for new materials integration schemes. Using in situ synchrotron X-ray scattering, we find that the nanomembranes can bond to other host substrates near room temperature and demonstrate coupling between surface reactivity and electromechanical properties in ferroelectric nanomembrane systems. Finally, the synthesis technique described here represents a significant advancement in materials integration and provides a new platform for the development of flexible oxide electronics.

  8. Structural study of nanometer-sized iron crystallites in single crystalline iron-MgO composite films.

    PubMed

    Tanaka, N; Nagao, M; Yoshizaki, F; Mihama, K

    1989-07-01

    Single crystalline composite films of iron and MgO are prepared by a simultaneous vacuum deposition technique. The structures of the composite films, especially of the iron crystallites embedded, are studied by high-resolution electron microscopy and nanometer-area electron diffraction. The alpha-iron (b.c.c.) crystallites of 1 nm in size are epitaxially embedded in single crystalline MgO films, the orientation being (011)[100]Fe parallel (001)[100]MgO and (001)[110]Fe parallel (001)[100]MgO. A heat treatment of the as-grown films at 500-1,000 degrees C brings about a phase transformation of the crystallites from alpha-iron to gamma-iron (f.c.c.), followed by a grain growth of alpha-iron and finally the growth of the spinel, MgFe2O4. The gamma-iron crystallites transformed are circular plates and have strains at the periphery to accommodate the surrounding MgO-matrix. The magnetic property of the composite films is also reported.

  9. Experimental exploration of the origin of magnetostriction in single crystalline iron.

    SciTech Connect

    Xing, Q.; Lograsso, T. A.; Ruffoni, M. P.; Azimonte, C.; Pascarelli, S.; Miller, D. J.; Materials Science Division; Ames Lab.; European Synchrotron Radiation Facility

    2010-01-01

    The magnetostrictive atomic strain in a pure Fe single crystal was measured by differential x-ray absorption spectroscopy. The obtained tetragonal magnetostriction constant, (3/2){lambda}{sub 100}, was determined to be 45 ppm, consistent with the previously reported theoretical value calculated from a spin-orbit coupling theory. These results provide a foundation for understanding the origin of magnetostriction in pure Fe as well as Fe-based binary alloys.

  10. Improvement of electron mobility in La:BaSnO{sub 3} thin films by insertion of an atomically flat insulating (Sr,Ba)SnO{sub 3} buffer layer

    SciTech Connect

    Shiogai, Junichi Nishihara, Kazuki; Sato, Kazuhisa; Tsukazaki, Atsushi

    2016-06-15

    One perovskite oxide, ASnO{sub 3} (A = Sr, Ba), is a candidate for use as a transparent conductive oxide with high electron mobility in single crystalline form. However, the electron mobility of films grown on SrTiO{sub 3} substrates does not reach the bulk value, probably because of dislocation scattering that originates from the large lattice mismatch. This study investigates the effect of insertion of bilayer BaSnO{sub 3} / (Sr,Ba)SnO{sub 3} for buffering this large lattice mismatch between La:BaSnO{sub 3} and SrTiO{sub 3} substrate. The insertion of 200-nm-thick BaSnO{sub 3} on (Sr,Ba)SnO{sub 3} bilayer buffer structures reduces the number of dislocations and improves surface smoothness of the films after annealing as proved respectively by scanning transmission electron microscopy and atomic force microscopy. A systematic investigation of BaSnO{sub 3} buffer layer thickness dependence on Hall mobility of the electron transport in La:BaSnO{sub 3} shows that the highest obtained value of mobility is 78 cm{sup 2}V{sup −1}s{sup −1} because of its fewer dislocations. High electron mobility films based on perovskite BaSnO{sub 3} can provide a good platform for transparent-conducting-oxide electronic devices and for creation of fascinating perovskite heterostructures.

  11. Some Like It Flat: Decoupled h-BN Monolayer Substrates for Aligned Graphene Growth.

    PubMed

    Roth, Silvan; Greber, Thomas; Osterwalder, Jürg

    2016-12-27

    On the path to functional graphene electronics, suitable templates for chemical vapor deposition (CVD) growth of high-mobility graphene are of great interest. Among various substrates, hexagonal boron nitride (h-BN) has established itself as one of the most promising candidates. The nanomesh, a h-BN monolayer grown on the Rh(111) surface where the lattice mismatch of h-BN and rhodium leads to a characteristic corrugation of h-BN, offers an interesting graphene/h-BN interface, different from flat graphene/h-BN systems hitherto studied. In this report, we describe a two-step CVD process for graphene formation on h-BN/Rh(111) at millibar pressures and describe the influence of the surface texture on the CVD process. During a first exposure to the 3-pentanone precursor, carbon atoms are incorporated in the rhodium subsurface, which leads to decoupling of the h-BN layer from the Rh(111) surface. This is reflected in the electronic band structure, where the corrugation-induced splitting of the h-BN bands vanishes. In a second 3-pentanone exposure, a graphene layer is formed on the flat h-BN layer, evidenced by the appearance of the characteristic linear dispersion of its π band. The graphene layer grows incommensurate and highly oriented. The formation of graphene/h-BN on rhodium opens the door to scalable production of well-aligned heterostacks since single-crystalline thin-film Rh substrates are available in large dimensions.

  12. Single crystalline monoclinic La0.7Sr0.3MnO3 nanowires with high temperature ferromagnetism

    SciTech Connect

    Carretero-Genevrier, Adrian; Gazquez Alabart, Jaume; Idrobo Tapia, Juan C; Oro, Judith; Arbiol, Jordi; Varela del Arco, Maria; Ferain, Etienne; Rodriguez-Carvajal, Juan; Puig, Teresa; Mestres, Narcis; Obradors, Xavier

    2011-01-01

    Porous mixed-valent manganese oxides are a group of multifunctional materials that can be used as molecular sieves, catalysts, battery materials, and gas sensors. However, material properties and thus activity can vary significantly with different synthesis methods or process conditions, such as temperature and time. Here, we report on a new synthesis route for MnO{sub 2} and LaSr-doped molecular sieve single crystalline nanowires based on a solution chemistry methodology combined with the use of nanoporous polymer templates supported on top of single crystalline substrates. Because of the confined nucleation in high aspect ratio nanopores and of the high temperatures attained, new structures with novel physical properties have been produced. During the calcination process, the nucleation and crystallization of {var_epsilon}-MnO{sub 2} nanoparticles with a new hexagonal structure is promoted. These nanoparticles generated up to 30 {mu}m long and flexible hexagonal nanowires at mild growth temperatures (T{sub g} = 700 C) as a consequence of the large crystallographic anisotropy of {var_epsilon}-MnO{sub 2}. The nanocrystallites of MnO{sub 2} formed at low temperatures serve as seeds for the growth of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} nanowires at growth temperatures above 800 C, through the diffusion of La and Sr into the empty 1D-channels of {var_epsilon}-MnO{sub 2}. Our particular growth method has allowed the synthesis of single crystalline molecular sieve (LaSr-2 x 4) monoclinic nanowires with composition La{sub 0.7}Sr{sub 0.3}MnO{sub 3} and with ordered arrangement of La{sup 3+} and Sr{sup 2+} cations inside the 1D-channels. These nanowires exhibit ferromagnetic ordering with strongly enhanced Curie temperature (T{sub c} > 500 K) that probably results from the new crystallographic order and from the mixed valence of manganese.

  13. Interfacial Layer Control by Dry Cleaning Technology for Polycrystalline and Single Crystalline Silicon Growth.

    PubMed

    Im, Dong-Hyun; Kong-Soo Lee; Kang, Yoongoo; Jeong, Myoungho; Park, Kwang Wuk; Lee, Soon-Gun; Ma, Jin-Won; Kim, Youngseok; Kim, Bonghyun; Im, Ki-Vin; Lim, Hanjin; Lee, Jeong Yong

    2016-05-01

    Native oxide removal prior to poly-Si contact and epitaxial growth of Si is the most critical technology to ensure process and device performances of poly-Si plugs and selective epitaxial growth (SEG) layers for DRAM, flash memory, and logic device. Recently, dry cleaning process for interfacial oxide removal has attracted a world-wide attention due to its superior passivation properties to conventional wet cleaning processes. In this study, we investigated the surface states of Si substrate during and after dry cleaning process, and the role of atomic elements including fluorine and hydrogen on the properties of subsequent deposited silicon layer using SIMS, XPS, and TEM analysis. The controlling of residual fluorine on the Si surface after dry cleaning is a key factor for clean interface. The mechanism of native oxide re-growth caused by residual fluorine after dry cleaning is proposed based on analytical results.

  14. Luminescence and scintillation properties of liquid phase epitaxy grown Y2SiO5:Ce single crystalline films

    NASA Astrophysics Data System (ADS)

    Wantong, Kriangkrai; Yawai, Nattasuda; Chewpraditkul, Weerapong; Kucera, Miroslav; Hanus, Martin; Nikl, Martin

    2017-06-01

    Luminescence and scintillation properties of Y2SiO5:Ce single crystalline film (YSO:Ce-LPE) grown by the liquid phase epitaxy technique are investigated and compared to the bulk Czochralski-grown YSO:Ce single crystal (YSO:Ce-SC). The light yield (LY) and energy resolution are measured using an R6231 photomultiplier under excitation with α - and γ- rays. At 662 keV γ- rays, the LY value of 12,410 ph/MeV obtained for YSO:Ce -LPE is lower than that of 20,150 ph/MeV for YSO:Ce -SC whereas the comparable LY value and energy resolution are obtained under excitation with 5.5 MeV α- rays. The ratio of LY under excitation with α- and γ- rays (α/γ ratio) is determined. Dependence of LY on an amplifier shaping time (0.5-12 μs) is also measured.

  15. Constructing MnO2/single crystalline ZnO nanorod hybrids with enhanced photocatalytic and antibacterial activity

    NASA Astrophysics Data System (ADS)

    Yu, Weiwei; Liu, Tiangui; Cao, Shiyi; Wang, Chen; Chen, Chuansheng

    2016-07-01

    In order to improve the photocatalytic and antibacterial activity of ZnO nanorods, ZnO nanorods decorated with MnO2 nanoparticles (MnO2/ZnO nanorod hybrids) were prepared by using microwave assisted coprecipitation method under the influence of hydrogen peroxide, and the structure, photocatalytic activity and antibacterial property of the products were studied. Experimental results indicated that MnO2 nanoparticles are decorated on the surface of single crystalline ZnO nanorods. Moreover, the resultant MnO2/ZnO nanorod hybrids have been proven to possess good photocatalytic and antibacterial activity, which their degradated efficiency for Rhodamin B (RhB) is twice as the pure ZnO nanorods. Enhancement for photocatalytic and antibacterial activity is mainly attributed to the low band gap energy and excellent electrochemical properties of MnO2 nanoparticles.

  16. Morphology evolution of single-crystalline hematite nanocrystals: magnetically recoverable nanocatalysts for enhanced facet-driven photoredox activity

    NASA Astrophysics Data System (ADS)

    Patra, Astam K.; Kundu, Sudipta K.; Bhaumik, Asim; Kim, Dukjoon

    2015-12-01

    We have developed a new green chemical approach for the shape-controlled synthesis of single-crystalline hematite nanocrystals in aqueous medium. FESEM, HRTEM and SAED techniques were used to determine the morphology and crystallographic orientations of each nanocrystal and its exposed facets. PXRD and HRTEM techniques revealed that the nanocrystals are single crystalline in nature; twins and stacking faults were not detected in these nanocrystals. The structural, vibrational, and electronic spectra of these nanocrystals were highly dependent on their shape. Different shaped hematite nanocrystals with distinct crystallographic planes have been synthesized under similar reaction conditions, which can be desired as a model for the purpose of properties comparison with the nanocrystals prepared under different reaction conditions. Here we investigated the photocatalytic performance of these different shaped-nanocrystals for methyl orange degradation in the presence of white light (λ > 420 nm). In this study, we found that the density of surface Fe3+ ions in particular facets was the key factor for the photocatalytic activity and was higher on the bitruncated-dodecahedron shape nanocrystals by coexposed {104}, {100} and {001} facets, attributing to higher catalytic activity. The catalytic activity of different exposed facet nanocrystals were as follows: {104} + {100} + {001} (bitruncated-dodecahedron) > {101} + {001} (bitruncated-octahedron) > {001} + {110} (nanorods) > {012} (nanocuboid) which provided the direct evidence of exposed facet-driven photocatalytic activity. The nanocrystals were easily recoverable using an external magnet and reused at least six times without significant loss of its catalytic activity.We have developed a new green chemical approach for the shape-controlled synthesis of single-crystalline hematite nanocrystals in aqueous medium. FESEM, HRTEM and SAED techniques were used to determine the morphology and crystallographic orientations of

  17. The unusually high Tc in rare-earth-doped single crystalline CaFe2As2

    NASA Astrophysics Data System (ADS)

    Wei, Fengyan; Lv, Bing; Deng, Liangzi; Meen, James K.; Xue, Yu-Yi; Chu, Ching-Wu

    2014-08-01

    In rare-earth-doped single crystalline CaFe2As2, the mysterious small volume fraction which superconducts up to 49 K, much higher than the bulk Tc ~ 30 s K, has prompted a long search for a hidden variable that could enhance the Tc by more than 30% in iron-based superconductors of the same structure. Here we report a chemical, structural and magnetic study of CaFe2As2 systematically doped with La, Ce, Pr and Nd. Coincident with the high Tc phase, we find extreme magnetic anisotropy, accompanied by an unexpected doping-independent Tc and equally unexpected superparamagnetic clusters associated with As vacancies. These observations lead us to conjecture that the tantalizing Tc enhancement may be associated with naturally occurring chemical interfaces and may thus provide a new paradigm in the search for superconductors with higher Tc.

  18. Morphology and magnetic flux distribution in superparamagnetic, single-crystalline Fe{sub 3}O{sub 4} nanoparticle rings

    SciTech Connect

    Takeno, Yumu; Murakami, Yasukazu E-mail: kannanmk@uw.edu; Shindo, Daisuke; Sato, Takeshi; Tanigaki, Toshiaki; Park, Hyun Soon; Ferguson, R. Matthew; Krishnan, Kannan M. E-mail: kannanmk@uw.edu

    2014-11-03

    This study reports on the correlation between crystal orientation and magnetic flux distribution of Fe{sub 3}O{sub 4} nanoparticles in the form of self-assembled rings. High-resolution transmission electron microscopy demonstrated that the nanoparticles were single-crystalline, highly monodispersed, (25 nm average diameter), and showed no appreciable lattice imperfections such as twins or stacking faults. Electron holography studies of these superparamagnetic nanoparticle rings indicated significant fluctuations in the magnetic flux lines, consistent with variations in the magnetocrystalline anisotropy of the nanoparticles. The observations provide useful information for a deeper understanding of the micromagnetics of ultrasmall nanoparticles, where the magnetic dipolar interaction competes with the magnetic anisotropy.

  19. Synthesis, Structural Characterization, and Electronic Structure of Single-Crystalline CuxV2O5 Nanowires

    SciTech Connect

    Patridge, C.; Jaye, C; Zhang, H; Marschilok, A; Fischer, D; Takeuchi, E; Banerjee, S

    2009-01-01

    Single-crystalline copper vanadium oxide nanowires ??-CuxV2O5 (x 0.60) have been synthesized by the hydrothermal reduction of bulk CuV2O6 using small-molecule aliphatic alcohols as reducing agents. The prepared copper vanadium bronze nanowires are metallic in nature and exhibit aspect ratios as high as 300. The recent discovery of superconductivity and charge disproportionation in bulk ??-CuxV2O5 has led to renewed interest in these one-dimensional metallic systems. Scaling these systems to nanoscale dimensions offers the potential for further tunability of electronic transport and Li-ion intercalation kinetics. A combination of spectroscopic and electrical measurement methods has been used to provide evidence for the metallic nature and the presence of room-temperature charge disproportionation in these nanowires.

  20. Single crystalline silicon-based surface micromachining for high-precision inertial sensors: technology and design for reliability

    NASA Astrophysics Data System (ADS)

    Knechtel, Roy

    2009-05-01

    In this paper, a foundry process for surface micromachined inertial sensors such as accelerometers or gyroscopes is introduced, with special attention on reliability aspects. Reliability was a major focus during the development phase, leading to the choice of the single crystalline silicon layer of an SOI device wafer as the mechanically active material. Glass frit wafer bonding is used for capping and hermetic sealing, but in addition to these fundamental reliability aspects, many influences on reliability must be considered, such as the risk of sticking, local stress concentration, electrical effects or the defined limitations of the mechanical movement in the interaction of design and technology. Reliability test results, as well as measures for improving the reliability and performance, are discussed in this paper.

  1. Single crystalline 3C-SiC nanowires grown on the diamond surface with the assistance of graphene

    NASA Astrophysics Data System (ADS)

    Dai, W.; Yu, J. H.; Wang, Y.; Song, Y. Z.; Bai, H.; Jiang, N.

    2015-06-01

    Single crystalline 3C-SiC nanowires were grown directly on the surface of bulk diamond in a catalyst-participated heating treatment process at 1300 °C. The iron powder was used as catalyst and graphene was served as the second carbon source during the reaction. The sample was characterized by Raman spectroscopy, scanning electron microscope (SEM), transmission electron microscope (TEM) and energy-dispersed X-ray (EDX). The results showed that the nanowires consisted of a crystalline 3C-SiC core that had a diameter of 40-60 nm and wrapped with about 10 nm amorphous SiO2 shell. Their lengths were up to several micrometers. The axes of nanowires lay along the [111] direction with a high density of stacking fault. Accordingly, we proposed graphene-assisted growth model to interpret the growth process of SiC nanowires on the diamond surface.

  2. Positive temperature variation of the bandgap energy in the single-crystalline chalcopyrite semiconductor AgInS{sub 2}

    SciTech Connect

    Ozaki, Shunji Horikoshi, Yoshimichi

    2014-02-07

    Optical absorption spectra have been measured on the single-crystalline chalcopyrite semiconductor AgInS{sub 2} using polarized light at T = 10–300 K. The bandgap energy E{sub g} of AgInS{sub 2} shows unusual temperature dependence at low temperatures. The resultant temperature coefficient ∂E{sub g}/∂T is found to be positive at T < 130 K and negative above 130 K. This result has been successfully explained by considering the effects of thermal expansion and electron–phonon interaction. The free-exciton emission of photoluminescence spectra also indicates positive temperature dependence of the peak energies at low temperatures. The exciton binding energy of AgInS{sub 2} is determined to be 26.4 meV.

  3. TiO2 single-crystalline nanorod electrode for quasi-solid-state dye-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Song, Mi Yeon; Ahn, Young Rack; Jo, Seong Mu; Kim, Dong Young; Ahn, Jae-Pyoung

    2005-09-01

    TiO2 single-crystalline nanorods are prepared from electrospun fibers which are composed of nanofibrils with an islands-in-a-sea morphology. The mechanical pressure produces each fibril into nanorods which are converted to anatase single crystals after calcination. High-resolution transmission electron microscopy shows that the (001) plane is growing along the longitudinal direction of the rod. In this work, the nanorod electrode provides the efficient photocurrent generation in a quasi-solid-state dye-sensitized solar cell using highly viscous poly(vinylidenefluoride-co-hexafluoropropylene)-based gel electrolytes. The overall conversion efficiency of the TiO2 nanorods shows 6.2% under 100mW /cm2 (AM 1.5G) illumination.

  4. Single-crystalline LiFePO4 nanosheets for high-rate Li-ion batteries.

    PubMed

    Zhao, Yu; Peng, Lele; Liu, Borui; Yu, Guihua

    2014-05-14

    The lithiation/delithiation in LiFePO4 is highly anisotropic with lithium-ion diffusion being mainly confined to channels along the b-axis. Controlling the orientation of LiFePO4 crystals therefore plays an important role for efficient mass transport within this material. We report here the preparation of single crystalline LiFePO4 nanosheets with a large percentage of highly oriented {010} facets, which provide the highest pore density for lithium-ion insertion/extraction. The LiFePO4 nanosheets show a high specific capacity at low charge/discharge rates and retain significant capacities at high C-rates, which may benefit the development of lithium batteries with both favorable energy and power density.

  5. CdS/CdSe cosensitized oriented single-crystalline TiO2 nanowire array for solar cell application

    NASA Astrophysics Data System (ADS)

    Li, Ming; Liu, Yong; Wang, Hai; Shen, Hui; Zhao, Wenxia; Huang, Hong; Liang, Chaolun

    2010-11-01

    Vertically oriented single-crystalline TiO2 nanowires array was grown on transparent conductive oxide glass substrate, and then CdS and CdSe quantum dots (QDs) were deposited on nanowires to form a TiO2/CdS/CdSe core-shell structure films. The optical properties of films with different layers of QDs were compared. The QD sensitized solar cells (QD-SSCs) were assembled and the effect of coating cycles of QDs on the photovoltaic performance was investigated. Under optimum parameters, QD-SSCs assembled with 5 μm thick TiO2 nanowires film exhibited a short-circuit current density of 7.92 mA cm-2, an open-circuit voltage of 0.40 V, and a power conversion efficiency of 1.14%.

  6. Vapor-phase hydrothermal transformation of HTiOF3 intermediates into {001} faceted anatase single-crystalline nanosheets.

    PubMed

    Liu, Porun; Wang, Yun; Zhang, Haimin; An, Taicheng; Yang, Huagui; Tang, Zhiyong; Cai, Weiping; Zhao, Huijun

    2012-12-07

    For the first time, a facile, one-pot hydrofluoric acid vapor-phase hydrothermal (HF-VPH) method is demonstrated to directly grow single-crystalline anatase TiO(2) nanosheets with 98.2% of exposed {001} faceted surfaces on the Ti substrate via a distinctive two-stage formation mechanism. The first stage produces a new intermediate crystal (orthorhombic HTiOF(3) ) that is transformed into anatase TiO(2) nanosheets during the second stage. The findings reveal that the HF-VPH reaction environment is unique and differs remarkably from that of liquid-phase hydrothermal processes. The uniqueness of the HF-VPH conditions can be readily used to effectively control the nanostructure growth.

  7. Simple and rapid green synthesis of micrometer scale single crystalline gold nanoplates using chitosan as the reducing agent

    NASA Astrophysics Data System (ADS)

    Alex, Saji; Tian, Kun; Teng, Shiang; Siegel, Gene; Tiwari, Ashutosh

    2014-11-01

    A simple, rapid and green chemical method for the synthesis of single crystalline gold nanoplates of several micrometeres in size has been demonstrated. The synthesis involved the reduction of HAuCl4 in aqueous solution using low molecular weight chitosan at boiling temperature for 25 min. The [Au3+]:[chitosan] molar ratio plays an important role in the formation of gold nanoplates and found that an optimized molar ratio in the range of 80 to 125 was suitable for the formation of nanoplates. The size and morphology of the nanoplates can be tuned by adjusting the molar ratio. In this process, the chitosan functions both as a reducing as well as a stabilizing agent and no other special agents were added to induce the nanoplate formation. The obtained nanoplates were single crystals with (1 1 1) planes as the basal planes with shapes of hexagonal, triangular, or truncated triangular plates.

  8. Observation of Low-Energy Einstein Phonon and Superconductivity in Single-Crystalline LaBe13

    NASA Astrophysics Data System (ADS)

    Hidaka, Hiroyuki; Shimizu, Yusei; Yamazaki, Seigo; Miura, Naoyuki; Nagata, Ryoma; Tabata, Chihiro; Mombetsu, Shota; Yanagisawa, Tatsuya; Amitsuka, Hiroshi

    2017-02-01

    The thermal and electrical transport properties of single-crystalline LaBe13 have been investigated by specific-heat (C) and electrical-resistivity (ρ) measurements. The specific-heat measurements in a wide temperature range revealed the presence of a hump anomaly near 40 K in the C(T)/T curve, indicating that LaBe13 has a low-energy Einstein-like-phonon mode with a characteristic temperature of ˜177 K. In addition, a superconducting transition was observed in the ρ measurements at the transition temperature of 0.53 K, which is higher than the value of 0.27 K reported previously by Bonville et al. Furthermore, an unusual T3 dependence was found in ρ(T) below ˜50 K, in contrast to the behavior expected from the electron-electron scattering or the electron-Debye phonon scattering.

  9. Influence of crystal orientation and ion bombardment on the nitrogen diffusivity in single-crystalline austenitic stainless steel

    SciTech Connect

    Martinavicius, A.; Abrasonis, G.; Moeller, W.

    2011-10-01

    The nitrogen diffusivity in single-crystalline AISI 316L austenitic stainless steel (ASS) during ion nitriding has been investigated at different crystal orientations ((001), (110), (111)) under variations of ion flux (0.3-0.7 mA cm{sup -2}), ion energy (0.5-1.2 keV), and temperature (370-430 deg. C). The nitrogen depth profiles obtained from nuclear reaction analysis are in excellent agreement with fits using the model of diffusion under the influence of traps, from which diffusion coefficients were extracted. At fixed ion energy and flux, the diffusivity varies by a factor up to 2.5 at different crystal orientations. At (100) orientation, it increases linearly with increasing ion flux or energy. The findings are discussed on the basis of atomistic mechanisms of interstitial diffusion, potential lattice distortions, local decomposition, and ion-induced lattice vibrational excitations.

  10. The modulation of surface texture for single-crystalline Si solar cells using calibrated silver nanoparticles as a catalyst

    NASA Astrophysics Data System (ADS)

    Gu, Xin; Yu, Xuegong; Liu, Tao; Li, Dongsheng; Yang, Deren

    2011-01-01

    We have employed Ag nanoparticles with calibrated size as catalysts to modulate the surface texture of single-crystalline Si surfaces for reducing sunlight reflectivity. Both experiments and theoretical analysis have proved that a well-organized microporous structure on the pyramids can be obtained by optimizing the size of Ag nanoparticles and the texturing time, and the Si wafer with such structures can effectively reduce the reflectivity of sunlight. However, based on the conventional cell fabrication process, the performance of silicon solar cells with such microporous structures gets degraded. It is closely associated with the strong surface recombination and the high phosphorus diffusion barrier induced by the microporous textures. These results are interesting for us to understand the application of nanotechnology on the silicon solar cell.

  11. Synthesis of one-molecule-thick single-crystalline nanosheets of energetic material for high-sensitive force sensor

    PubMed Central

    Yang, Guangcheng; Hu, Hailong; Zhou, Yong; Hu, Yingjie; Huang, Hui; Nie, Fude; Shi, Weimei

    2012-01-01

    Energetic material is a reactive substance that contains a great amount of potential energy, which is extremely sensitive to external stimuli like force. In this work, one-molecule-thick single-crystalline nanosheets of energetic material were synthesized. Very small force applied on the nanosheet proves to lead to the rotation of the tilted nitro groups, and subsequently change of current of the nanosheet. We apply this principle to design high-sensitive force sensor. A theoretical model of force-current dependence was established based on the nanosheets' molecular packing structure model that was well supported with the high resolution XPS, AFM analysis results. An ultra-low-force with range of several picoNewton to several nanoNewton can be measured by determination of corresponding current value. PMID:23019519

  12. Superconducting single crystalline YBa2Cu3O7- δ on SrTiO3 buffered Si (100)

    NASA Astrophysics Data System (ADS)

    Jahangir Moghadam, Mohammadreza; Ahmadi Majlan, Kamyar; Zhang, Hao; Shen, Xuan; Chrysler, Matthew; Conlin, Patrick; Hensley, Ricky; Su, Dong; Wei, John; Ngai, Joseph

    2015-03-01

    The growth of crystalline oxides on semiconductors enables new functionalities to be integrated with semiconducting technologies. Here, thin films of optimally-doped (001)-oriented YBa2Cu3O7- δ are epitaxially integrated on silicon (001) through growth on a SrTiO3 buffer. The former is grown using pulsed-laser deposition and the latter is grown on Si using oxide molecular beam epitaxy. The single crystal nature of the SrTiO3 buffer enables very high transition temperatures to be achieved. For a 30 nm thick SrTiO3 buffer, YBa2Cu3O7- δ films exhibiting a transition temperature of ~ 95 K, and a narrow transition width (<5 K) are achieved. The integration of single crystalline YBa2Cu3O7- δ on Si (001) paves the way for the potential exploration of cuprate materials in a variety of applications.

  13. Formation of titanium monoxide (001) single-crystalline thin film induced by ion bombardment of titanium dioxide (110)

    NASA Astrophysics Data System (ADS)

    Pabón, B. M.; Beltrán, J. I.; Sánchez-Santolino, G.; Palacio, I.; López-Sánchez, J.; Rubio-Zuazo, J.; Rojo, J. M.; Ferrer, P.; Mascaraque, A.; Muñoz, M. C.; Varela, M.; Castro, G. R.; de La Fuente, O. Rodríguez

    2015-02-01

    A plethora of technological applications justify why titanium dioxide is probably the most studied oxide, and an optimal exploitation of its properties quite frequently requires a controlled modification of the surface. Low-energy ion bombardment is one of the most extended techniques for this purpose and has been recently used in titanium oxides, among other applications, to favour resistive switching mechanisms or to form transparent conductive layers. Surfaces modified in this way are frequently described as reduced and defective, with a high density of oxygen vacancies. Here we show, at variance with this view, that high ion doses on rutile titanium dioxide (110) induce its transformation into a nanometric and single-crystalline titanium monoxide (001) thin film with rocksalt structure. The discovery of this ability may pave the way to new technical applications of ion bombardment not previously reported, which can be used to fabricate heterostructures and interfaces.

  14. Controllable Synthesis of Single-Crystalline CdO and Cd(OH)2Nanowires by a Simple Hydrothermal Approach

    PubMed Central

    2010-01-01

    Single-crystalline Cd(OH)2 or CdO nanowires can be selectively synthesized at 150 °C by a simple hydrothermal method using aqueous Cd(NO3)2 as precursor. The method is biosafe, and compared to the conventional oil-water surfactant approach, more environmental-benign. As revealed by the XRD results, CdO or Cd(OH)2 nanowires can be generated in high purity by varying the time of synthesis. The results of FESEM and HRTEM analysis show that the CdO nanowires are formed in bundles. Over the CdO-nanowire bundles, photoluminescence at ~517 nm attributable to near band-edge emission of CdO was recorded. Based on the experimental results, a possible growth mechanism of the products is proposed. PMID:20672033

  15. Thermal conductivity of a single Bi0.5Sb1.5Te3 single-crystalline nanowire

    NASA Astrophysics Data System (ADS)

    Li, Liang; Jin, Chiming; Xu, Sichao; Yang, Jiyong; Du, Haifeng; Li, Guanghai

    2014-10-01

    Single-crystalline Bi0.5Sb1.5Te3 nanowires were fabricated by a template-assisted pulsed electrodeposition technique; the thermal conductivity of a single Bi0.5Sb1.5Te3 nanowire of different diameters was characterized through a self-heating 3 ω method. The temperature-dependent resistance measurements prove the semiconductor behavior of the nanowires. The extremely low thermal conductivity of the nanowires was found compared with the corresponding bulk, and the Umklapp peaks shift to a higher temperature as the decreasing nanowire’s diameter decreases, which qualitatively agrees with the theoretical calculations based on the Callaway model. The boundary scattering plays an important role in the reduction of the thermal conductivity and in the shift of the Umklapp peak of the Bi0.5Sb1.5Te3 nanowires.

  16. Single-Crystalline, Nanoporous Gallium Nitride Films With Fine Tuning of Pore Size for Stem Cell Engineering.

    PubMed

    Han, Lin; Zhou, Jing; Sun, Yubing; Zhang, Yu; Han, Jung; Fu, Jianping; Fan, Rong

    2014-11-01

    Single-crystalline nanoporous gallium nitride (GaN) thin films were fabricated with the pore size readily tunable in 20-100 nm. Uniform adhesion and spreading of human mesenchymal stem cells (hMSCs) seeded on these thin films peak on the surface with pore size of 30 nm. Substantial cell elongation emerges as pore size increases to ∼80 nm. The osteogenic differentiation of hMSCs occurs preferentially on the films with 30 nm sized nanopores, which is correlated with the optimum condition for cell spreading, which suggests that adhesion, spreading, and stem cell differentiation are interlinked and might be coregulated by nanotopography.

  17. One step solution synthesis towards ultra-thin and uniform single-crystalline ZnO nanowires

    NASA Astrophysics Data System (ADS)

    Ho, G. W.; Wong, A. S. W.

    2007-03-01

    Bundles of high-aspect-ratio single-crystalline ZnO nanowires were fabricated by a single-step mild hydrothermal condition without the use of a seeding layer, thus eliminating an annealing step. The growth yields nanowires of high aspect ratio (>200). No significant lateral growth takes place with prolonged reaction time. The morphology and aspect ratio of the final products depend on the concentration of the precursors; a highly water-soluble tetradentate cyclic tertiary amine and zinc nitrate system. The nanowires grow along the [0001] direction and have an average width of <10 nm and a narrow distribution of ±5 nm. Photoluminescence measurements of the ultra-thin nanowires exhibit a strong band-edge emission at room temperature. The highly crystalline sub tens of nanometer scale diameter nanowires can, in combination, be a good one-dimensional candidate to study optical and electronic properties.

  18. Direct writing of continuous and discontinuous sub-wavelength periodic surface structures on single-crystalline silicon using femtosecond laser

    SciTech Connect

    Kuladeep, Rajamudili; Sahoo, Chakradhar; Narayana Rao, Desai E-mail: dnr-laserlab@yahoo.com

    2014-06-02

    Laser-induced ripples or uniform arrays of continuous near sub-wavelength or discontinuous deep sub-wavelength structures are formed on single-crystalline silicon (Si) by femtosecond (fs) laser direct writing technique. Laser irradiation was performed on Si wafers at normal incidence in air and by immersing them in dimethyl sulfoxide using linearly polarized Ti:sapphire fs laser pulses of ∼110 fs pulse duration and ∼800 nm wavelength. Morphology studies of laser written surfaces reveal that sub-wavelength features are oriented perpendicular to laser polarization, while their morphology and spatial periodicity depend on the surrounding dielectric medium. The formation mechanism of the sub-wavelength features is explained by interference of incident laser with surface plasmon polaritons. This work proves the feasibility of fs laser direct writing technique for the fabrication of sub-wavelength features, which could help in fabrication of advanced electro-optic devices.

  19. Thin single-crystalline Bi2(Te1-xSex)3 ternary nanosheets synthesized by a solvothermal technique

    NASA Astrophysics Data System (ADS)

    Guo, Jing; Jian, Jikang; Zhang, Zhihua; Wu, Rong; Li, Jin; Sun, Yanfei

    2016-01-01

    Bi2(Te1-xSex)3 ternary nanosheets have been successfully synthesized through a facile solvothermal technique using diethylenetriamine as solvent, where x can vary from 0 to 1. X-ray diffraction (XRD) and Scanning electron microscopy (SEM) indicate that the as-synthesized Bi2(Te1-xSex)3 samples are nanosheets with rhombohedral structure, and the thickness of the nanosheets can be as thin as several nanometers. High resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) reveal that the nanosheets are single crystalline with a rhombohedral structure. Energy disperse spectroscopy (EDS) and XRD analysis by Vegard's law confirm that the ternary Bi2(Te1-xSex)3 nanosheets have been obtained here. The growth of the nanosheets is discussed based on an amine-based molecular template mechanism that has been employed to synthesize some other metal chalcogenides.

  20. Electrical probing of magnetic phase transition and domain wall motion in single-crystalline Mn₅Ge₃ nanowire.

    PubMed

    Tang, Jianshi; Wang, Chiu-Yen; Jiang, Wanjun; Chang, Li-Te; Fan, Yabin; Chan, Michael; Wu, Can; Hung, Min-Hsiu; Liu, Pei-Hsuan; Yang, Hong-Jie; Tuan, Hsing-Yu; Chen, Lih-Juann; Wang, Kang L

    2012-12-12

    In this Letter, the magnetic phase transition and domain wall motion in a single-crystalline Mn(5)Ge(3) nanowire were investigated by temperature-dependent magneto-transport measurements. The ferromagnetic Mn(5)Ge(3) nanowire was fabricated by fully germaniding a single-crystalline Ge nanowire through the solid-state reaction with Mn contacts upon thermal annealing at 450 °C. Temperature-dependent four-probe resistance measurements on the Mn(5)Ge(3) nanowire showed a clear slope change near 300 K accompanied by a magnetic phase transition from ferromagnetism to paramagnetism. The transition temperature was able to be controlled by both axial and radial magnetic fields as the external magnetic field helped maintain the magnetization aligned in the Mn(5)Ge(3) nanowire. Near the magnetic phase transition, the critical behavior in the 1D system was characterized by a power-law relation with a critical exponent of α = 0.07 ± 0.01. Besides, another interesting feature was revealed as a cusp at about 67 K in the first-order derivative of the nanowire resistance, which was attributed to a possible magnetic transition between two noncollinear and collinear ferromagnetic states in the Mn(5)Ge(3) lattice. Furthermore, temperature-dependent magneto-transport measurements demonstrated a hysteretic, symmetric, and stepwise axial magnetoresistance of the Mn(5)Ge(3) nanowire. The interesting features of abrupt jumps indicated the presence of multiple domain walls in the Mn(5)Ge(3) nanowire and the annihilation of domain walls driven by the magnetic field. The Kurkijärvi model was used to describe the domain wall depinning as thermally assisted escape from a single energy barrier, and the fitting on the temperature-dependent depinning magnetic fields yielded an energy barrier of 0.166 eV.

  1. Real-time observation of the swelling and hydrolysis of a single crystalline cellulose fiber catalyzed by cellulase 7B from Trichoderma reesei.

    PubMed

    Wang, Jingpeng; Quirk, Amanda; Lipkowski, Jacek; Dutcher, John R; Hill, Christopher; Mark, Adam; Clarke, Anthony J

    2012-06-26

    The biodegradation of cellulose involves the enzymatic action of cellulases (endoglucanases), cellobiohydrolases (exoglucanases), and β-glucosidases that act synergistically. The rate and efficiency of enzymatic hydrolysis of crystalline cellulose in vitro decline markedly with time, limiting the large-scale, cost-effective production of cellulosic biofuels. Several factors have been suggested to contribute to this phenomenon, but there is considerable disagreement regarding the relative importance of each. These earlier investigations were hampered by the inability to observe the disruption of crystalline cellulose and its subsequent hydrolysis directly. Here, we show the application of high-resolution atomic force microscopy to observe the swelling of a single crystalline cellulose fiber and its-hydrolysis in real time directly as catalyzed by a single cellulase, the industrially important cellulase 7B from Trichoderma reesei. Volume changes, the root-mean-square roughness, and rates of hydrolysis of the surfaces of single fibers were determined directly from the images acquired over time. Hydrolysis dominated the early stage of the experiment, and swelling dominated the later stage. The high-resolution images revealed that the combined action of initial hydrolysis followed by swelling exposed individual microfibrils and bundles of microfibrils, resulting in the loosening of the fiber structure and the exposure of microfibrils at the fiber surface. Both the hydrolysis and swelling were catalyzed by the native cellulase; under the same conditions, its isolated carbohydrate-binding module did not cause changes to crystalline cellulose. We anticipate that the application of our AFM-based analysis on other cellulolytic enzymes, alone and in combination, will provide significant insight into the process of cellulose biodegradation and greatly facilitate its application for the efficient and economical production of cellulosic ethanol.

  2. Phase transformation between Cu(In,Sn){sub 2} and Cu{sub 2}(In,Sn) compounds formed on single crystalline Cu substrate during solid state aging

    SciTech Connect

    Tian, Feifei; Liu, Zhi-Quan Guo, Jingdong

    2014-01-28

    Interfacial reactions between eutectic SnIn and single crystalline Cu during solid-state aging at low temperature were investigated systematically. Three types of phase transformations between Cu(In,Sn){sub 2} layer and Cu{sub 2}(In,Sn) layer were observed, which are Cu(In,Sn){sub 2} grows and Cu{sub 2}(In,Sn) consumes at 40 °C, Cu(In,Sn){sub 2} and Cu{sub 2}(In,Sn) grow simultaneously at 60 °C, as well as Cu(In,Sn){sub 2} consumes and Cu{sub 2}(In,Sn) grows at 80 and 100 °C. According to physicochemical approach, the chemical reactions at Cu/Cu{sub 2}(In,Sn)/Cu(In,Sn){sub 2}/SnIn interfaces were discussed in detail. It was concluded that the diffusion ability of Cu and In atoms dominated different phase transformations. When diffusion constants k{sub 1In2} > 8/3k{sub 1Cu2} Cu(In,Sn){sub 2} will grow, and if k{sub 1Cu2} ≫ k{sub 1In2} Cu{sub 2}(In,Sn) will grow. Both Cu(In,Sn){sub 2} and Cu{sub 2}(In,Sn) can grow in the condition of k{sub 1In2} ≈ k{sub 1Cu2}. The values of k{sub 1Cu2} and k{sub 1In2} at different temperatures on (100)Cu and (111)Cu substrate were also calculated or estimated by analyzing the growth kinetics of the compound layers.

  3. Preparation of Single-Crystalline AgIn5S8 Octahedrons with Exposed {111} Facets and Its Visible-Light-Responsive Photocatalytic H2 Production Activity.

    PubMed

    Song, Shuaishuai; Liang, Zechen; Fu, Wenli; Peng, Tianyou

    2017-05-24

    Although AgIn5S8 as one kind of ternary chalcogenides has been extensively investigated due to its band-edge positions meeting the thermodynamic requirement for water photosplitting, very little attention has been focused on the crystallinity and facet effects of AgIn5S8 on its photocatalytic activity. Herein, a facile hydrothermal route was developed to fabricate regular single-crystalline AgIn5S8 octahedrons with only {111} facets exposed. Also, the effects of the hydrothermal reaction conditions on the composition, crystal phase, crystallinity, and morphology of the obtained AgxInyS(x+3y/2) products (hereafter denoted as AIS-x, where x represents the pH value of the reaction solution) were investigated, and it was found that the accurately released S(2-) ions from the thermal decomposition of thioacetamide (TAA) is the central factor for the nucleation and growth of the AgIn5S8 octahedrons. The experimental results indicate that the resultant regular AgIn5S8 octahedrons (AIS-10.6) exhibit the best photocatalytic activity for H2 production among those AgxInyS(x+3y/2) products, and the higher crystallinity and fewer defects of the AgIn5S8 octahedrons compared to the other AgxInyS(x+3y/2) products can retard the photogenerated charge recombination, while those indium atoms with higher density in the exposed {111} facets might be beneficial for the photocatalytic H2 production reaction by acting as active sites to promote the charge separation and transfer processes. The results presented here provide new insights into the significance of crystallinity and exposed facets in the visible-light-responsive activity of AgIn5S8, thus paving new ways into the design and synthesis of high-performance, cost-effective AgIn5S8 photocatalysts for H2 production.

  4. Construction of single-crystalline supramolecular networks of perchlorinated hexa-peri-hexabenzocoronene on Au(111)

    SciTech Connect

    Zhang, Yi; Zhang, Yanfang; Li, Geng; Lu, Jianchen; Du, Shixuan E-mail: hjgao@iphy.ac.cn; Gao, Hong-Jun E-mail: hjgao@iphy.ac.cn; Lin, Xiao; Tan, Yuanzhi; Feng, Xinliang; Müllen, Klaus

    2015-03-14

    The self-assembly of the perchlorinated hexa-peri-hexabenzocoronene (PCHBC) molecules on Au(111) has been studied by a low temperature scanning tunneling microscopy (STM) combining with density functional theory based first principle calculations. Highly ordered supramolecular networks with single domains limited by the terraces are formed on Au(111) substrate. High resolution images of the PCHBC molecules, confirmed by first principle simulations, are obtained. It reveals the close-packed arrangement of the PCHBC molecules on Au(111). The calculated charge distribution of PCHBC molecules shows the existence of attractive halogen–halogen interaction between neighboring molecules. Compared with the disordered adsorption of hexa-peri-hexabenzocoronene on Au(111), we conclude that the formation of attractive ClCl interactions between neighbors is the key factor to form the highly ordered, close-packed networks. Due to the steric hindrance resulted from the peripheral chlorine atoms, the PCHBC molecule is contorted and forms the doubly concave conformation, which is different from the hexa-peri-hexabenzocoronene with a planar structure. By using this supramolecular network as a template, we deposited C{sub 60} molecules on it at room temperature with low coverage. The STM images taken at low temperature show that the C{sub 60} molecules are mono-dispersed on the networks and adsorb on top of the PCHBC molecules, forming a typical concave-convex host-guest system.

  5. Magnetically induced ferroelectricity in single crystalline ferrimagnet, Mn2Mo3O8

    NASA Astrophysics Data System (ADS)

    Chikara, Shalinee; Singleton, John; Gao, Bin; Wang, Yazhong; Cheong, Sang-Wook; Zapf, Vivien

    We present magnetization and electric polarization results on multiferroic ferrimagnet molybdate system, Mn2Mo3O8 in pulsed magnetic fields. Mn2Mo3O8, also known as the mineral isiemite crystallizes in a hexagonal P63 mc space group. The magnetism is attributed to the Mn ions whereas the Mo is diamagnetic. The Mo and Mn atoms are stacked alternately along c-axis. The Mn ions form a hexagonal lattice and occur in octahedral and tetragonal coordination. The spins on two different Mn sites give rise to ferrimagnetism. The system orders at about 42 K accompanied by a lambda like anomaly in heat capacity. Mn2Mo3O8 shows anisotropic magnetization with a change in slope at 40 K signaling possibly an AFM to ferrimagnet ordering. We observe magnetic field induced electric polarization in our preliminary results and an anomaly at 40 K corresponding to TN. A portion of this work was performed at the NHMFL, which is supported by National Science Foundation Cooperative Agreement No. DMR-1157490, the State of Florida, and the U.S. Department of Energy.

  6. Construction of single-crystalline supramolecular networks of perchlorinated hexa-peri-hexabenzocoronene on Au(111).

    PubMed

    Zhang, Yi; Zhang, Yanfang; Li, Geng; Lu, Jianchen; Lin, Xiao; Tan, Yuanzhi; Feng, Xinliang; Du, Shixuan; Müllen, Klaus; Gao, Hong-Jun

    2015-03-14

    The self-assembly of the perchlorinated hexa-peri-hexabenzocoronene (PCHBC) molecules on Au(111) has been studied by a low temperature scanning tunneling microscopy (STM) combining with density functional theory based first principle calculations. Highly ordered supramolecular networks with single domains limited by the terraces are formed on Au(111) substrate. High resolution images of the PCHBC molecules, confirmed by first principle simulations, are obtained. It reveals the close-packed arrangement of the PCHBC molecules on Au(111). The calculated charge distribution of PCHBC molecules shows the existence of attractive halogen-halogen interaction between neighboring molecules. Compared with the disordered adsorption of hexa-peri-hexabenzocoronene on Au(111), we conclude that the formation of attractive Cl∙∙∙Cl interactions between neighbors is the key factor to form the highly ordered, close-packed networks. Due to the steric hindrance resulted from the peripheral chlorine atoms, the PCHBC molecule is contorted and forms the doubly concave conformation, which is different from the hexa-peri-hexabenzocoronene with a planar structure. By using this supramolecular network as a template, we deposited C60 molecules on it at room temperature with low coverage. The STM images taken at low temperature show that the C60 molecules are mono-dispersed on the networks and adsorb on top of the PCHBC molecules, forming a typical concave-convex host-guest system.

  7. Fabrication of tensile-strained single-crystalline GeSn on transparent substrate by nucleation-controlled liquid-phase crystallization

    NASA Astrophysics Data System (ADS)

    Oka, Hiroshi; Amamoto, Takashi; Koyama, Masahiro; Imai, Yasuhiko; Kimura, Shigeru; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

    2017-01-01

    We developed a method of forming single-crystalline germanium-tin (GeSn) alloy on transparent substrates that is based on liquid-phase crystallization. By controlling and designing nucleation during the melting growth process, a highly tensile-strained single-crystalline GeSn layer was grown on a quartz substrate without using any crystal-seeds or catalysts. The peak field-effect hole mobility of 423 cm2/V s was obtained for a top-gate single-crystalline GeSn MOSFET on a quartz substrate with a Sn content of 2.6%, indicating excellent crystal quality and mobility enhancement due to Sn incorporation and tensile strain.

  8. HNO₃-assisted polyol synthesis of ultralarge single-crystalline Ag microplates and their far propagation length of surface plasmon polariton.

    PubMed

    Chang, Cheng-Wei; Lin, Fan-Cheng; Chiu, Chun-Ya; Su, Chung-Yi; Huang, Jer-Shing; Perng, Tsong-Pyng; Yen, Ta-Jen

    2014-07-23

    We developed a HNO3-assisted polyol reduction method to synthesize ultralarge single-crystalline Ag microplates routinely. The edge length of the synthesized Ag microplates reaches 50 μm, and their top facets are (111). The mechanism for dramatically enlarging single-crystalline Ag structure stems from a series of competitive anisotropic growths, primarily governed by carefully tuning the adsorption of Ag(0) by ethylene glycol and the desorption of Ag(0) by a cyanide ion on Ag(100). Finally, we measured the propagation length of surface plasmon polaritons along the air/Ag interface under 534 nm laser excitation. Our single-crystalline Ag microplate exhibited a propagation length (11.22 μm) considerably greater than that of the conventional E-gun deposited Ag thin film (5.27 μm).

  9. Defect evolution in single crystalline tungsten following low temperature and low dose neutron irradiation

    SciTech Connect

    Hu, Xunxiang; Koyanagi, Takaaki; Fukuda, Makoto; Katoh, Yutai; Wirth, Brian D; Snead, Lance Lewis

    2016-01-01

    The tungsten plasma-facing components of fusion reactors will experience an extreme environment including high temperature, intense particle fluxes of gas atoms, high-energy neutron irradiation, and significant cyclic stress loading. Irradiation-induced defect accumulation resulting in severe thermo-mechanical property degradation is expected. For this reason, and because of the lack of relevant fusion neutron sources, the fundamentals of tungsten radiation damage must be understood through coordinated mixed-spectrum fission reactor irradiation experiments and modeling. In this study, high-purity (110) single-crystal tungsten was examined by positron annihilation spectroscopy and transmission electron microscopy following low-temperature (~90 °C) and low-dose (0.006 and 0.03 dpa) mixed-spectrum neutron irradiation and subsequent isochronal annealing at 400, 500, 650, 800, 1000, 1150, and 1300 °C. The results provide insights into microstructural and defect evolution, thus identifying the mechanisms of different annealing behavior. Following 1 h annealing, ex situ characterization of vacancy defects using positron lifetime spectroscopy and coincidence Doppler broadening was performed. The vacancy cluster size distributions indicated intense vacancy clustering at 400 °C with significant damage recovery around 1000 °C. Coincidence Doppler broadening measurements confirm the trend of the vacancy defect evolution, and the S–W plots indicate that only a single type of vacancy cluster is present. Furthermore, transmission electron microscopy observations at selected annealing conditions provide supplemental information on dislocation loop populations and visible void formation. This microstructural information is consistent with the measured irradiation-induced hardening at each annealing stage. This provides insight into tungsten hardening and embrittlement due to irradiation-induced matrix defects.

  10. Defect evolution in single crystalline tungsten following low temperature and low dose neutron irradiation

    DOE PAGES

    Hu, Xunxiang; Koyanagi, Takaaki; Fukuda, Makoto; ...

    2016-01-01

    The tungsten plasma-facing components of fusion reactors will experience an extreme environment including high temperature, intense particle fluxes of gas atoms, high-energy neutron irradiation, and significant cyclic stress loading. Irradiation-induced defect accumulation resulting in severe thermo-mechanical property degradation is expected. For this reason, and because of the lack of relevant fusion neutron sources, the fundamentals of tungsten radiation damage must be understood through coordinated mixed-spectrum fission reactor irradiation experiments and modeling. In this study, high-purity (110) single-crystal tungsten was examined by positron annihilation spectroscopy and transmission electron microscopy following low-temperature (~90 °C) and low-dose (0.006 and 0.03 dpa) mixed-spectrum neutronmore » irradiation and subsequent isochronal annealing at 400, 500, 650, 800, 1000, 1150, and 1300 °C. The results provide insights into microstructural and defect evolution, thus identifying the mechanisms of different annealing behavior. Following 1 h annealing, ex situ characterization of vacancy defects using positron lifetime spectroscopy and coincidence Doppler broadening was performed. The vacancy cluster size distributions indicated intense vacancy clustering at 400 °C with significant damage recovery around 1000 °C. Coincidence Doppler broadening measurements confirm the trend of the vacancy defect evolution, and the S–W plots indicate that only a single type of vacancy cluster is present. Furthermore, transmission electron microscopy observations at selected annealing conditions provide supplemental information on dislocation loop populations and visible void formation. This microstructural information is consistent with the measured irradiation-induced hardening at each annealing stage. This provides insight into tungsten hardening and embrittlement due to irradiation-induced matrix defects.« less

  11. Defect evolution in single crystalline tungsten following low temperature and low dose neutron irradiation

    NASA Astrophysics Data System (ADS)

    Hu, Xunxiang; Koyanagi, Takaaki; Fukuda, Makoto; Katoh, Yutai; Snead, Lance L.; Wirth, Brian D.

    2016-03-01

    The tungsten plasma-facing components of fusion reactors will experience an extreme environment including high temperature, intense particle fluxes of gas atoms, high-energy neutron irradiation, and significant cyclic stress loading. Irradiation-induced defect accumulation resulting in severe thermo-mechanical property degradation is expected. For this reason, and because of the lack of relevant fusion neutron sources, the fundamentals of tungsten radiation damage must be understood through coordinated mixed-spectrum fission reactor irradiation experiments and modeling. In this study, high-purity (110) single-crystal tungsten was examined by positron annihilation spectroscopy and transmission electron microscopy following low-temperature (∼90 °C) and low-dose (0.006 and 0.03 dpa) mixed-spectrum neutron irradiation and subsequent isochronal annealing at 400, 500, 650, 800, 1000, 1150, and 1300 °C. The results provide insights into microstructural and defect evolution, thus identifying the mechanisms of different annealing behavior. Following 1 h annealing, ex situ characterization of vacancy defects using positron lifetime spectroscopy and coincidence Doppler broadening was performed. The vacancy cluster size distributions indicated intense vacancy clustering at 400 °C with significant damage recovery around 1000 °C. Coincidence Doppler broadening measurements confirm the trend of the vacancy defect evolution, and the S-W plots indicate that only a single type of vacancy cluster is present. Furthermore, transmission electron microscopy observations at selected annealing conditions provide supplemental information on dislocation loop populations and visible void formation. This microstructural information is consistent with the measured irradiation-induced hardening at each annealing stage, providing insight into tungsten hardening and embrittlement due to irradiation-induced matrix defects.

  12. Spin-related thermoelectric conversion in lateral spin-valve devices with single-crystalline Co2FeSi electrodes

    NASA Astrophysics Data System (ADS)

    Yamasaki, Kento; Oki, Soichiro; Yamada, Shinya; Kanashima, Takeshi; Hamaya, Kohei

    2015-04-01

    We demonstrate the conversion between a heat current and a spin current in Cu-based lateral spin valves (LSVs) with single-crystalline Co2FeSi (CFS) electrodes. We can observe the thermally induced spin injection from CFS into Cu resulting from the spin-dependent Seebeck effect, and the heat current generated by the spin-dependent Peltier effect can be detected even in the LSV structures. This study is an important step toward understanding heat-spin conversion in single-crystalline materials with various electronic band structures.

  13. Predicting the optimal process window for the coating of single-crystalline organic films with mobilities exceeding 7 cm2/Vs.

    NASA Astrophysics Data System (ADS)

    Janneck, Robby; Vercesi, Federico; Heremans, Paul; Genoe, Jan; Rolin, Cedric

    2016-09-01

    Organic thin film transistors (OTFTs) based on single crystalline thin films of organic semiconductors have seen considerable development in the recent years. The most successful method for the fabrication of single crystalline films are solution-based meniscus guided coating techniques such as dip-coating, solution shearing or zone casting. These upscalable methods enable rapid and efficient film formation without additional processing steps. The single-crystalline film quality is strongly dependent on solvent choice, substrate temperature and coating speed. So far, however, process optimization has been conducted by trial and error methods, involving, for example, the variation of coating speeds over several orders of magnitude. Through a systematic study of solvent phase change dynamics in the meniscus region, we develop a theoretical framework that links the optimal coating speed to the solvent choice and the substrate temperature. In this way, we can accurately predict an optimal processing window, enabling fast process optimization. Our approach is verified through systematic OTFT fabrication based on films grown with different semiconductors, solvents and substrate temperatures. The use of best predicted coating speeds delivers state of the art devices. In the case of C8BTBT, OTFTs show well-behaved characteristics with mobilities up to 7 cm2/Vs and onset voltages close to 0 V. Our approach also explains well optimal recipes published in the literature. This route considerably accelerates parameter screening for all meniscus guided coating techniques and unveils the physics of single crystalline film formation.

  14. Synthesis of single-crystalline spinel LiMn2 O4 Nanorods for lithium-ion batteries with high rate capability and long cycle life.

    PubMed

    Xie, Xiuqiang; Su, Dawei; Sun, Bing; Zhang, Jinqiang; Wang, Chengyin; Wang, Guoxiu

    2014-12-15

    The long-standing challenge associated with capacity fading of spinel LiMn2 O4 cathode material for lithium-ion batteries is investigated. Single-crystalline spinel LiMn2 O4 nanorods were successfully synthesized by a template-engaged method. Porous Mn3 O4 nanorods were used as self-sacrificial templates, into which LiOH was infiltrated by a vacuum-assisted impregnation route. When used as cathode materials for lithium-ion batteries, the spinel LiMn2 O4 nanorods exhibited superior long cycle life owing to the one-dimensional nanorod structure, single-crystallinity, and Li-rich effect. LiMn2 O4 nanorods retained 95.6 % of the initial capacity after 1000 cycles at 3C rate. In particular, the nanorod morphology of the spinel LiMn2 O4 was well-preserved after a long-term cycling, suggesting the ultrahigh structural stability of the single crystalline spinel LiMn2 O4 nanorods. This result shows the promising applications of single-crystalline spinel LiMn2 O4 nanorods as cathode materials for lithium-ion batteries with high rate capability and long cycle life.

  15. Ti3+-self doped brookite TiO2 single-crystalline nanosheets with high solar absorption and excellent photocatalytic CO2 reduction

    NASA Astrophysics Data System (ADS)

    Xin, Xiaoye; Xu, Tao; Wang, Lan; Wang, Chuanyi

    2016-03-01

    Black brookite TiO2 single-crystalline nanosheets with outstanding photocatalytic activity toward CO2 reduction is prepared by a facile oxidation-based hydrothermal reaction method combined with post-annealing treatment. Large amount of Ti3+ defects are introduced into the bulk of brookite nanoparticles, which increases the solar energy absorption and enhances the photocatalytic activity.

  16. Ti3+-self doped brookite TiO2 single-crystalline nanosheets with high solar absorption and excellent photocatalytic CO2 reduction

    PubMed Central

    Xin, Xiaoye; Xu, Tao; Wang, Lan; Wang, Chuanyi

    2016-01-01

    Black brookite TiO2 single-crystalline nanosheets with outstanding photocatalytic activity toward CO2 reduction is prepared by a facile oxidation-based hydrothermal reaction method combined with post-annealing treatment. Large amount of Ti3+ defects are introduced into the bulk of brookite nanoparticles, which increases the solar energy absorption and enhances the photocatalytic activity. PMID:27021203

  17. Ion-induced synthesis of uniform single-crystalline sulphide-based quaternary-alloy hexagonal nanorings for highly efficient photocatalytic hydrogen evolution.

    PubMed

    Hu, Peng; Pramana, Stevin Snellius; Cao, Shaowen; Ngaw, Chee Keong; Lin, Jingdong; Loo, Say Chye Joachim; Tan, Timothy Thatt Yang

    2013-05-14

    Uniform single-crystalline quaternary sulphide nanoring photocatalysts are synthesized via the copper-ion-induced Kirkendall effect and is followed by a cation exchange reaction. The obtained Cu(2+)-doped ZnIn(2)S(4) nanorings show highly preserved morphology, and demonstrate high visible-light-driven photocatalytic activity for H(2) evolution in water splitting.

  18. Development of scintillating screens based on the single crystalline films of Ce doped (Gd,Y)3(Al,Ga,Sc)5O12 multi-component garnets

    NASA Astrophysics Data System (ADS)

    Zorenko, Yuriy; Gorbenko, Vitaliy; Savchyn, Volodymyr; Zorenko, Tanya; Fedorov, Alexander; Sidletskiy, Oleg

    2014-09-01

    The paper is dedicated to development of scintillators based on single crystalline films of Ce doped (Gd,Y)3(Al,Ga,Sc)5O12 multi-component garnets onto Gd3Ga5O12 substrates using the liquid phase epitaxy method.

  19. Luminescent properties of the Sc3+ doped single crystalline films of (Y,Lu,La)3(Al,Ga)5O12 multi-component garnets

    NASA Astrophysics Data System (ADS)

    Zorenko, Yu.; Gorbenko, V.; Zorenko, T.; Vasylkiv, Ya.

    2014-08-01

    The paper is dedicated to studying the luminescent and scintillation properties of the single crystalline films of Sc doped multi-component (Y,Lu,La)3(Al,Ga)5O12 garnets grown by the liquid phase epitaxy method.

  20. Growth and luminescent properties of Ce and Ce-Tb doped (Y,Lu,Gd)2SiO5:Ce single crystalline films

    NASA Astrophysics Data System (ADS)

    Zorenko, Yuriy; Gorbenko, Vitaliy; Savchyn, Volodymyr; Zorenko, Tetyana; Grinyov, Boris; Sidletskiy, Oleg; Fedorov, Alexander

    2014-09-01

    The paper presents the results of systematic research directed on the development of scintillating screens based on single crystalline films of Ce and Ce-Tb doped (Y,Lu,Gd)2SiO5 orthosilicates using the liquid phase epitaxy method.

  1. 3D spin-flop transition in enhanced 2D layered structure single crystalline TlCo2Se2

    NASA Astrophysics Data System (ADS)

    Jin, Z.; Xia, Z.-C.; Wei, M.; Yang, J.-H.; Chen, B.; Huang, S.; Shang, C.; Wu, H.; Zhang, X.-X.; Huang, J.-W.; Ouyang, Z.-W.

    2016-10-01

    The enhanced 2D layered structure single crystalline TlCo2Se2 has been successfully fabricated, which exhibits field-induced 3D spin-flop phase transitions. In the case of the magnetic field parallel to the c-axis (B//c), the applied magnetic field induces the evolution of the noncollinear helical magnetic coupling into a ferromagnetic (FM) state with all the magnetization of the Co ion parallel to the c-axis. A striking variation of the field-induced strain within the ab-plane is noticed in the magnetic field region of 20-30 T. In the case of the magnetic field perpendicular to the c-axis (B  ⊥  c), the inter-layer helical antiferromagnetic (AFM) coupling may transform to an initial canted AFM coupling, and then part of it transforms to an intermediate metamagnetic phase with the alignment of two-up-one-down Co magnetic moments and finally to an ultimate FM coupling in higher magnetic fields. The robust noncollinear AFM magnetic coupling is completely destroyed above 30 T. In combination with the measurements of magnetization, magnetoresistance and field-induced strain, a complete magnetic phase diagram of the TlCo2Se2 single crystal has been depicted, demonstrating complex magnetic structures even though the crystal geometry itself gives no indication of the magnetic frustration.

  2. Perovskite Solar Cells with Near 100% Internal Quantum Efficiency Based on Large Single Crystalline Grains and Vertical Bulk Heterojunctions

    SciTech Connect

    Yang, Bin; Dyck, Ondrej; Poplawsky, Jonathan; Keum, Jong; Puretzky, Alexander; Das, Sanjib; Ivanov, Ilia; Rouleau, Christopher; Duscher, Gerd; Geohegan, David; Xiao, Kai

    2015-07-09

    Grain boundaries (GBs) as defects in the crystal lattice detrimentally impact the power conversion efficiency (PCE) of polycrystalline solar cells, particularly in recently emerging hybrid perovskites where non-radiative recombination processes lead to significant carrier losses. Here, the beneficial effects of activated vertical GBs are demonstrated by first growing large, vertically-oriented methylammonium lead tri-iodide (CH3NH3PbI3) single-crystalline grains. We show that infiltration of p-type doped 2 -7,7 -tetrakis(N,Ndi-p-methoxyphenylamine)-9,9-spirobifluorene (Spiro-OMeTAD) into CH3NH3PbI3 films along the GBs creates space charge regions to suppress non-radiative recombination and enhance carrier collection efficiency. Solar cells with such activated GBs yielded average PCE of 16.3 ± 0.9%, which are among the best solution-processed perovskite devices. As an important alternative to growing ideal CH3NH3PbI3 single crystal films, which is difficult to achieve for such fast-crystallizing perovskites, activating GBs paves a way to design a new type of bulk heterojunction hybrid perovskite photovoltaics toward theoretical maximum PCE.

  3. Single crystalline InGaAs nanopillar grown on polysilicon with dimensions beyond the substrate grain size limit.

    PubMed

    Ng, Kar Wei; Tran, Thai-Truong D; Ko, Wai Son; Chen, Roger; Lu, Fanglu; Chang-Hasnain, Connie J

    2013-01-01

    Monolithic integration of III-V optoelectronic devices with materials for various functionalities inexpensively is always desirable. Polysilicon (poly-Si) is an ideal platform because it is dopable and semiconducting, and can be deposited and patterned easily on a wide range of low cost substrates. However, the lack of crystalline coherency in poly-Si poses an immense challenge for high-quality epitaxial growth. In this work, we demonstrate, for the first time, direct growth of micrometer-sized InGaAs/GaAs nanopillars on polysilicon. Transmission electron microscopy shows that the micrometer-sized pillars are single-crystalline with pure wurzite-phase, far exceeding the substrate crystal grain size ~100 nm. The high quality growth is enabled by the unique tapering geometry at the base of the nanostructure, which reduces the effective InGaAs/Si contact area to <40 nm in diameter. The small footprint not only reduces stress due to lattice mismatch but also prevents the nanopillar from nucleating on multiple Si crystal grains. This relaxes the grain size requirement for poly-Si, potentially reducing the cost for poly-Si deposition. Lasing is achieved in the as-grown pillars under optical pumping, attesting their excellent crystalline and optical quality. These promising results open up a pathway for low-cost synergy of optoelectronics with other technologies such as CMOS integrated circuits, sensing, nanofluidics, thin film transistor display, photovoltaics, and so forth.

  4. Cryogenic mechanical loss of a single-crystalline GaP coating layer for precision measurement applications

    NASA Astrophysics Data System (ADS)

    Murray, Peter G.; Martin, Iain W.; Craig, Kieran; Hough, James; Rowan, Sheila; Bassiri, Riccardo; Fejer, Martin M.; Harris, James S.; Lantz, Brian T.; Lin, Angie C.; Markosyan, Ashot S.; Route, Roger K.

    2017-02-01

    The first direct observations of gravitational waves have been made by the Advanced LIGO detectors. However, the quest to improve the sensitivities of these detectors remains, and epitaxially grown single-crystal coatings show considerable promise as alternatives to the ion-beam sputtered amorphous mirror coatings typically used in these detectors and other such precision optical measurements. The mechanical loss of a 1 μ m thick single-crystalline gallium phosphide (GaP) coating, incorporating a buffer layer region necessary for the growth of high quality epitaxial coatings, has been investigated over a broad range of frequencies and with fine temperature resolution. It is shown that at 20 K the mechanical loss of GaP is a factor of 40 less than an undoped tantala film heat-treated to 600 °C and is comparable to the loss of a multilayer GaP/AlGaP coating. This is shown to translate into possible reductions in coating thermal noise of a factor of 2 at 120 K and 5 at 20 K over the current best IBS coatings (alternating stacks of silica and titania-doped tantala). There is also evidence of a thermally activated dissipation process between 50 and 70 K.

  5. Radiative recombination mechanisms in individual wurtzite ZnSe nanowires with a defect-free single-crystalline microstructure.

    PubMed

    Saxena, Ankur; Pan, Qi; Ruda, Harry E

    2013-04-07

    Photoluminescence (PL) spectroscopy performed on arrays of semiconductor nanowires (NWs) suffers from ensemble broadening of PL lines, and fails to separate the PL from NWs of different crystal structures in the ensemble. Even the results on PL from single NWs are not devoid of ambiguity. This is because the influence of structural defects in NWs, such as stacking faults, twin boundaries and dislocations, on their optical spectra cannot be accounted for since the structural characteristics of the same NW remain largely unknown. We performed low-temperature PL spectroscopy on individual wurtzite (WZ) ZnSe NWs, and confirmed a homogeneous single-crystalline microstructure without any extended defects in these NWs, thus excluding any role of structural imperfections in their optical spectra. The luminescence is shown to be dominated solely by native point defects, while no role of extrinsic impurities was found. The radiative recombination is shown to originate from excitons bound to vacancies of Zn (VZn), VZn-complexes, and their phonon replicas. The binding energies of the acceptor-bound excitons, ionization energies of the acceptors, and average number of phonons emitted for shallow donor-VZn acceptor pair related transition were determined. Distinct from previous studies on PL from arrays of ZnSe NWs, this work provides an unambiguous interpretation of the PL spectra and assignment of PL peaks to WZ ZnSe. Narrow excitonic emission of linewidths 2.9 meV indicate excellent optical quality of WZ ZnSe NWs.

  6. Giant Peak Voltage of Thermopower Waves Driven by the Chemical Potential Gradient of Single-Crystalline Bi2 Te3.

    PubMed

    Singh, Swati; Mun, Hyeona; Lee, Sanghoon; Kim, Sung Wng; Baik, Seunghyun

    2017-09-01

    The self-propagating exothermic chemical reaction with transient thermovoltage, known as the thermopower wave, has received considerable attention recently. A greater peak voltage and specific power are still demanded, and materials with greater Seebeck coefficients have been previously investigated. However, this study employs an alternative mechanism of transient chemical potential gradient providing an unprecedentedly high peak voltage (maximum: 8 V; average: 2.3 V) and volume-specific power (maximum: 0.11 W mm(-3) ; average: 0.04 W mm(-3) ) using n-type single-crystalline Bi2 Te3 substrates. A mixture of nitrocellulose and sodium azide is used as a fuel, and ultraviolet photoelectron spectroscopy reveals a significant downshift in Fermi energy (≈5.09 eV) of the substrate by p-doping of the fuel. The induced electrical potential by thermopower waves has two distinct sources: the Seebeck effect and the transient chemical potential gradient. Surprisingly, the Seebeck effect contribution is less than 2.5% (≈201 mV) of the maximum peak voltage. The right combination of substrate, fuel doping, and anisotropic substrate geometry results in an order of magnitude greater transient chemical potential gradient (≈5.09 eV) upon rapid removal of fuel by exothermic chemical reaction propagation. The role of fuel doping and chemical potential gradient can be viewed as a key mechanism for enhanced heat to electric conversion performance. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Intrinsic spin and momentum relaxation in organic single-crystalline semiconductors probed by ESR and Hall measurements

    NASA Astrophysics Data System (ADS)

    Tsurumi, Junto; Häusermann, Roger; Watanabe, Shun; Mitsui, Chikahiko; Okamoto, Toshihiro; Matsui, Hiroyuki; Takeya, Jun

    Spin and charge momentum relaxation mechanism has been argued among organic semiconductors with various methods, devices, and materials. However, little is known in organic single-crystalline semiconductors because it has been hard to obtain an ideal organic crystal with an excellent crystallinity and controllability required for accurate measurements. By using more than 1-inch sized single crystals which are fabricated via contentious edge-casting method developed by our group, we have successfully demonstrated a simultaneous determination of spin and momentum relaxation time for gate-induced charges of 3,11-didecyldinaphtho[2,3- d:2',3'- d']benzo[1,2- b:4,5- b']dithiophene, by combining electron spin resonance (ESR) and Hall effect measurements. The obtained temperature dependences of spin and momentum relaxation times are in good agreement in terms of power law with a factor of approximately -2. It is concluded that Elliott-Yafet spin relaxation mechanism can be dominant at room temperature regime (200 - 300 K). Probing characteristic time scales such as spin-lattice, spin-spin, and momentum relaxation times, demonstrated in the present work, would be a powerful tool to elucidate fundamental spin and charge transport mechanisms. We acknowledge the New Energy and Industrial Technology Developing Organization (NEDO) for financial support.

  8. Fabrication, characterization, and kinetic study of vertical single-crystalline CuO nanowires on Si substrates

    PubMed Central

    2012-01-01

    We report here on the first study of the growth kinetics of high-yield, vertical CuO nanowires on silicon substrates produced by the process of thermal oxidation. The length of the CuO nanowires could be tuned from several to tens of micrometers by adjusting the oxidation temperature and time. The grown CuO nanowires were determined to be single-crystalline with different axial crystallographic orientations. After a series of scanning electron microscopy examinations, the average length of CuO nanowires produced at each temperature was found to follow a parabolic relationship with the oxidation time. The parabolic growth rate at different oxidation temperatures was measured. The activation energy for the growth of CuO nanowires calculated from an Arrhenius plot was found to be about 174.2 kJ/mole. In addition, the current-voltage characterization indicated that the sample with high-density CuO nanowires exhibited ohmic behavior, and its resistance was found to significantly decrease with increasing environmental temperature. The result can be attributed to an increase in the number of carriers at higher temperatures. PMID:22330902

  9. Application of single-crystalline PMN-PT and PIN-PMN-PT in high-performance pyroelectric detectors.

    PubMed

    Yu, Ping; Ji, Yadong; Neumann, Norbert; Lee, Sang-Goo; Luo, Hasou; Es-Souni, Mohammed

    2012-09-01

    The suitability for use in pyroelectric detectors of single-crystalline doped and undoped lead indium niobate-lead magnesium niobate-lead titanate was tested and compared with high-quality Mn-doped lead magnesium niobate-lead titanate and standard lithium tantalate. Pyroelectric and dielectric measurements confirmed an increased processing and operating temperature range because of the higher phase transitions of lead indium niobate-lead magnesium niobate-lead titanate. Pyroelectric coefficients of 705 to 770 μC/m(2)K were obtained with doped and undoped lead indium niobate-lead magnesium niobate-lead titanate, which are about 70% to 80% of the pyroelectric coefficient of lead magnesium niobate-lead titanate but 4 times higher than standard lithium tantalate. Manganese doping has been proved as a solution to decrease the dielectric loss of lead magnesium niobate-lead titanate and it also works well for lead indium niobate-lead magnesium niobate-lead titanate. An outstanding specific detectivity D* of about 1.1 · 10(9) cm·Hz(1/2)/W was achieved at a frequency of 2 Hz for Mn-doped lead magnesium niobate-based detectors.

  10. Perovskite Solar Cells with Near 100% Internal Quantum Efficiency Based on Large Single Crystalline Grains and Vertical Bulk Heterojunctions

    DOE PAGES

    Yang, Bin; Dyck, Ondrej; Poplawsky, Jonathan; ...

    2015-07-09

    Grain boundaries (GBs) as defects in the crystal lattice detrimentally impact the power conversion efficiency (PCE) of polycrystalline solar cells, particularly in recently emerging hybrid perovskites where non-radiative recombination processes lead to significant carrier losses. Here, the beneficial effects of activated vertical GBs are demonstrated by first growing large, vertically-oriented methylammonium lead tri-iodide (CH3NH3PbI3) single-crystalline grains. We show that infiltration of p-type doped 2 -7,7 -tetrakis(N,Ndi-p-methoxyphenylamine)-9,9-spirobifluorene (Spiro-OMeTAD) into CH3NH3PbI3 films along the GBs creates space charge regions to suppress non-radiative recombination and enhance carrier collection efficiency. Solar cells with such activated GBs yielded average PCE of 16.3 ± 0.9%, whichmore » are among the best solution-processed perovskite devices. As an important alternative to growing ideal CH3NH3PbI3 single crystal films, which is difficult to achieve for such fast-crystallizing perovskites, activating GBs paves a way to design a new type of bulk heterojunction hybrid perovskite photovoltaics toward theoretical maximum PCE.« less

  11. Behavior of crystal defects in synthetic type-IIa single-crystalline diamond at high temperatures under normal pressure

    NASA Astrophysics Data System (ADS)

    Tatsumi, Natsuo; Tamasaku, Kenji; Ito, Toshimichi; Sumiya, Hitoshi

    2017-01-01

    The behavior of dislocation lines (DLs) and stacking faults (SFs) in synthetic type-IIa single-crystalline diamond at high temperatures under normal pressure has been investigated. After annealing the diamond at 1500 °C for 60 min in pure N2 atmosphere, straight DLs were bent to converge to fewer curved dislocation bundles, so that some of the stacking faults were extinct while new DLs appeared at the edges of the removed SFs. These results indicate that SFs in the diamond examined belong to the Shockley type, and that the Shockley partials changed to a perfect dislocation. From this result, the following generation mechanism has been proposed for SFs in diamond. On one hand, because [112] dislocations in the (111) growth sector are contained in the slip plane labelled as (1 ̅ 1 ̅ 1), one perfect dislocation tends to be split into two Shockley partials and a SF when an appropriate stress is applied. On the other hand, the angle between the {111} slip plane and the direction of bundled dislocations in the (001) growth sector is as high as 54.7°, so that a perfect dislocation can hardly slip into partial dislocations. Thus, SFs exist only in the (111) growth sector of type IIa diamond.

  12. Magnetization and magnetoacoustics of single-crystalline ErFe5Al7 in high magnetic fields

    NASA Astrophysics Data System (ADS)

    Gorbunov, D. I.; Yasin, S.; Andreev, A. V.; Skourski, Y.; Zherlitsyn, S.; Wosnitza, J.

    2014-05-01

    The magnetization and sound propagation in single-crystalline ErFe5Al7 (tetragonal crystal structure) have been studied in steady (up to 18 T) and pulsed magnetic fields (up to 60 T). The compound orders ferrimagnetically at a Curie temperature TC=201 K and has a compensation point at Tcomp=34 K. ErFe5Al7 displays a strong magnetic easy-plane anisotropy. A strong magnetic anisotropy is present as well within the basal plane; the [100] axis is the easy magnetization direction with a spontaneous magnetic moment Ms=1.3 µB/f.u. at 2 K. Field-induced magnetic transitions, two along the [100] axis and two along the [110] axis, have been found in the vicinity of T=Tcomp. Changes in the magnetic state at the transitions result in significant alterations of the spin-phonon coupling, which is manifested by sharp anomalies in the sound velocity and sound attenuation. Along the easy [100] axis the forced ferromagnetic state is reached in a field of about 50 T at 2 K, whereas along the [110] direction saturation is expected only above 60 T. A magnetic field-temperature phase diagram has been extracted up to 60 T. From the experimental data a value of nErFe=3.3 T/µB for the inter-sublattice Er-Fe exchange interaction has been obtained.

  13. Direct Observation of Defect Range and Evolution in Ion-Irradiated Single Crystalline Ni and Ni Binary Alloys

    DOE PAGES

    Lu, Chenyang; Jin, Ke; Béland, Laurent K.; ...

    2016-02-01

    We report that energetic ions have been widely used to evaluate the irradiation tolerance of structural materials for nuclear power applications and to modify material properties. It is important to understand the defect production, annihilation and migration mechanisms during and after collision cascades. In this study, single crystalline pure nickel metal and single-phase concentrated solid solution alloys of 50%Ni50%Co (NiCo) and 50%Ni50%Fe (NiFe) without apparent preexisting defect sinks were employed to study defect dynamics under ion irradiation. Both cross-sectional transmission electron microscopy characterization (TEM) and Rutherford backscattering spectrometry channeling (RBS-C) spectra show that the range of radiation-induced defect clusters farmore » exceed the theoretically predicted depth in all materials after high-dose irradiation. Defects in nickel migrate faster than in NiCo and NiFe. Both vacancy-type stacking fault tetrahedra (SFT) and interstitial loops coexist in the same region, which is consistent with molecular dynamics simulations. Kinetic activation relaxation technique (k-ART) simulations for nickel showed that small vacancy clusters, such as di-vacancies and tri-vacancies, created by collision cascades are highly mobile, even at room temperature. The slower migration of defects in the alloy along with more localized energy dissipation of the displacement cascade may lead to enhanced radiation tolerance.« less

  14. Direct Observation of Defect Range and Evolution in Ion-Irradiated Single Crystalline Ni and Ni Binary Alloys

    SciTech Connect

    Lu, Chenyang; Jin, Ke; Béland, Laurent K.; Zhang, Feifei; Yang, Taini; Qiao, Liang; Zhang, Yanwen; Bei, Hongbin; Christen, Hans M.; Stoller, Roger E.; Wang, Lumin

    2016-02-01

    We report that energetic ions have been widely used to evaluate the irradiation tolerance of structural materials for nuclear power applications and to modify material properties. It is important to understand the defect production, annihilation and migration mechanisms during and after collision cascades. In this study, single crystalline pure nickel metal and single-phase concentrated solid solution alloys of 50%Ni50%Co (NiCo) and 50%Ni50%Fe (NiFe) without apparent preexisting defect sinks were employed to study defect dynamics under ion irradiation. Both cross-sectional transmission electron microscopy characterization (TEM) and Rutherford backscattering spectrometry channeling (RBS-C) spectra show that the range of radiation-induced defect clusters far exceed the theoretically predicted depth in all materials after high-dose irradiation. Defects in nickel migrate faster than in NiCo and NiFe. Both vacancy-type stacking fault tetrahedra (SFT) and interstitial loops coexist in the same region, which is consistent with molecular dynamics simulations. Kinetic activation relaxation technique (k-ART) simulations for nickel showed that small vacancy clusters, such as di-vacancies and tri-vacancies, created by collision cascades are highly mobile, even at room temperature. The slower migration of defects in the alloy along with more localized energy dissipation of the displacement cascade may lead to enhanced radiation tolerance.

  15. Direct Observation of Defect Range and Evolution in Ion-Irradiated Single Crystalline Ni and Ni Binary Alloys

    PubMed Central

    Lu, Chenyang; Jin, Ke; Béland, Laurent K.; Zhang, Feifei; Yang, Taini; Qiao, Liang; Zhang, Yanwen; Bei, Hongbin; Christen, Hans M.; Stoller, Roger E.; Wang, Lumin

    2016-01-01

    Energetic ions have been widely used to evaluate the irradiation tolerance of structural materials for nuclear power applications and to modify material properties. It is important to understand the defect production, annihilation and migration mechanisms during and after collision cascades. In this study, single crystalline pure nickel metal and single-phase concentrated solid solution alloys of 50%Ni50%Co (NiCo) and 50%Ni50%Fe (NiFe) without apparent preexisting defect sinks were employed to study defect dynamics under ion irradiation. Both cross-sectional transmission electron microscopy characterization (TEM) and Rutherford backscattering spectrometry channeling (RBS-C) spectra show that the range of radiation-induced defect clusters far exceed the theoretically predicted depth in all materials after high-dose irradiation. Defects in nickel migrate faster than in NiCo and NiFe. Both vacancy-type stacking fault tetrahedra (SFT) and interstitial loops coexist in the same region, which is consistent with molecular dynamics simulations. Kinetic activation relaxation technique (k-ART) simulations for nickel showed that small vacancy clusters, such as di-vacancies and tri-vacancies, created by collision cascades are highly mobile, even at room temperature. The slower migration of defects in the alloy along with more localized energy dissipation of the displacement cascade may lead to enhanced radiation tolerance. PMID:26829570

  16. Behavior and role of superficial oxygen in Cu for the growth of large single-crystalline graphene

    NASA Astrophysics Data System (ADS)

    Ding, Dong; Solís-Fernández, Pablo; Yunus, Rozan Mohamad; Hibino, Hiroki; Ago, Hiroki

    2017-06-01

    Decreasing the nucleation density of graphene grown on copper (Cu) foil by chemical vapor deposition (CVD) is essential for the synthesis of large-area single-crystalline graphene. Here, the behavior of the copper oxide layer and its impact on the graphene growth have been investigated. We found that a small amount of oxygen dissolves into the Cu when the oxide layer decomposes during the heating up in a non-reducing Ar environment. The remaining oxygen in the Cu foil can play an important role in decreasing the graphene nucleation density. The dissolved oxygen can withstand at high temperatures even in reducing H2 environments without completely losing its effectiveness for maintaining a low graphene nucleation density. However, heating up in a H2 environment significantly reduces the copper oxide layer during the very first moments of the process at low temperatures, preventing the oxygen to dissolve into the Cu and significantly increasing the nucleation density. These findings will help to improve the graphene growth on Cu catalyst by increasing the grain size while decreasing the grain density.

  17. Ambient surfactantless synthesis, growth mechanism, and size-dependent electrocatalytic behavior of high-quality, single crystalline palladium nanowires.

    PubMed

    Koenigsmann, Christopher; Santulli, Alexander C; Sutter, Eli; Wong, Stanislaus S

    2011-09-27

    In this report, we utilize the U-tube double diffusion device as a reliable, environmentally friendly method for the size-controlled synthesis of high-quality, single crystalline Pd nanowires. The nanowires grown in 200 and 15 nm polycarbonate template pores maintain diameters of 270 ± 45 nm and 45 ± 9 nm, respectively, and could be isolated either as individual nanowires or as ordered free-standing arrays. The growth mechanism of these nanowires has been extensively explored, and we have carried out characterization of the isolated nanowires, free-standing nanowire arrays, and cross sections of the filled template in order to determine that a unique two-step growth process predominates within the template pores. Moreover, as-prepared submicrometer and nanosized wires were studied by comparison with ultrathin 2 nm Pd nanowires in order to elucidate the size-dependent trend in oxygen reduction reaction (ORR) electrocatalysis. Subsequently, the desired platinum monolayer overcoating was reliably deposited onto the surface of the Pd nanowires by Cu underpotential deposition (UPD) followed by galvanic displacement of the Cu adatoms. The specific and platinum mass activity of the core-shell catalysts was found to increase from 0.40 mA/cm(2) and 1.01 A/mg to 0.74 mA/cm(2) and 1.74 A/mg as the diameter was decreased from the submicrometer size regime to the ultrathin nanometer range.

  18. Unit Cell Level Thickness Control of Single-Crystalline Zinc Oxide Nanosheets Enabled by Electrical Double-Layer Confinement.

    PubMed

    Yin, Xin; Shi, Yeqi; Wei, Yanbing; Joo, Yongho; Gopalan, Padma; Szlufarska, Izabela; Wang, Xudong

    2017-08-08

    Ionic layer epitaxy (ILE) has recently been developed as an effective strategy to synthesize nanometer thick 2D materials with a nonlayered crystal structure, such as ZnO. The packing density of the amphiphilic monolayer is believed to be a key parameter that controls the nanosheet nucleation and growth. In this work, we systematically investigated the growth behavior of single-crystalline ZnO nanosheets templated at the water-air interface by an anionic oleylsulfate monolayer with different packing densities. The thicknesses of ZnO nanosheets were tuned from one unit cell to four unit cells and exhibited good correlation with the width of Zn(2+) ion concentration zone (the Stern layer) underneath the ionized surfactant monolayer. Further analysis of the nanosheet sizes and density revealed that the nanosheet growth was dominated by the steric hindrance from the surfactant monolayer at lower surface pressure, while the nucleation density became the dominating factor at higher surface pressure. The ZnO nanosheets exhibited a decreasing work function as the thickness reduced to a few unit cells. This research validated a critical hypothesis that the nanosheet growth is self-limited by the formation of a double layer of ionic precursors. This work will open up a new way toward controlled synthesis of novel 2D nanosheets from nonlayered materials with a thickness down to one unit cell.

  19. Intermolecular band dispersion of quasi-single crystalline organic semiconductor monolayer measured by angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Ohtomo, Manabu; Shimada, Toshihiro; Hasegawa, Tetsuya

    2010-03-01

    Band structure of organic semiconductors is important knowledge to improve the molecular design. Angle-Resolved Photoemission Spectroscopy (ARPES) studies using highly conductive single domain samples grown in-situ is the most direct technique. In this study, we developed a novel method to grow quasi-single crystalline monolayer on conductive substrate and electronic structure was investigated. As a template for orientation control, we used a step-bunched Si(111) substrate with dangling bond termination. In case of pentacene, it was confirmed that the crystal is quasi-single crystal with 2.2^o rotated twins. The band dispersion was identical to that of thin-film phase. The effective mass and transfer integrals are evaluated using two-dimensional tight binding fit and compared with band calculations [1]. We also report the growth of 2,7-Dipheny[1]benzothieno[3,2-b]benzothiophene (DPh-BTBT) [2] on Bi-Si substrate and compare discuss its band structure. [4pt] [1] M.Ohtomo et al., APL 95, 123308 (2009).[0pt] [2] K.Takimiya, JACS 128, 3044 (2006).

  20. Growth mechanism of single-crystalline NiO thin films grown by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

    Nickel oxide (NiO) thin films were grown by atmospheric-pressure metal organic chemical vapor deposition (APMOCVD). Growth was carried out using various growth parameters, including the growth temperature, the input precursor (O2/Ni) ratio, and the type of substrate material. Effects of the growth parameters on the structural and electrical properties of the films were investigated. X-ray diffraction analysis revealed that the crystal structure and quality were strongly affected by the growth temperature and the type of substrate material. At an optimized growth temperature, single-crystalline NiO films were grown on MgO(100) and MgO(111) substrates in a cube-on-cube orientation relationship, while on an Al2O3(001) substrate, the film was grown in the NiO[111] direction. The use of MgO substrates successfully suppressed the formation of twin defects, which have been frequently reported in the growth of NiO. The difference in the formation of the twin defects on MgO and Al2O3 substrates was discussed. It was observed that the resistivity dependence on crystal quality was affected by the choice of substrate material. The effects of the precursor ratio on the transmittance and resistivity of the films were also investigated. Improved transparency in the visible wavelength region and higher conductivity were found in films grown with higher O2/Ni ratios.

  1. Direct Observation of Defect Range and Evolution in Ion-Irradiated Single Crystalline Ni and Ni Binary Alloys

    NASA Astrophysics Data System (ADS)

    Lu, Chenyang; Jin, Ke; Béland, Laurent K.; Zhang, Feifei; Yang, Taini; Qiao, Liang; Zhang, Yanwen; Bei, Hongbin; Christen, Hans M.; Stoller, Roger E.; Wang, Lumin

    2016-02-01

    Energetic ions have been widely used to evaluate the irradiation tolerance of structural materials for nuclear power applications and to modify material properties. It is important to understand the defect production, annihilation and migration mechanisms during and after collision cascades. In this study, single crystalline pure nickel metal and single-phase concentrated solid solution alloys of 50%Ni50%Co (NiCo) and 50%Ni50%Fe (NiFe) without apparent preexisting defect sinks were employed to study defect dynamics under ion irradiation. Both cross-sectional transmission electron microscopy characterization (TEM) and Rutherford backscattering spectrometry channeling (RBS-C) spectra show that the range of radiation-induced defect clusters far exceed the theoretically predicted depth in all materials after high-dose irradiation. Defects in nickel migrate faster than in NiCo and NiFe. Both vacancy-type stacking fault tetrahedra (SFT) and interstitial loops coexist in the same region, which is consistent with molecular dynamics simulations. Kinetic activation relaxation technique (k-ART) simulations for nickel showed that small vacancy clusters, such as di-vacancies and tri-vacancies, created by collision cascades are highly mobile, even at room temperature. The slower migration of defects in the alloy along with more localized energy dissipation of the displacement cascade may lead to enhanced radiation tolerance.

  2. 3D spin-flop transition in enhanced 2D layered structure single crystalline TlCo2Se2.

    PubMed

    Jin, Z; Xia, Z-C; Wei, M; Yang, J-H; Chen, B; Huang, S; Shang, C; Wu, H; Zhang, X-X; Huang, J-W; Ouyang, Z-W

    2016-10-05

    The enhanced 2D layered structure single crystalline TlCo2Se2 has been successfully fabricated, which exhibits field-induced 3D spin-flop phase transitions. In the case of the magnetic field parallel to the c-axis (B//c), the applied magnetic field induces the evolution of the noncollinear helical magnetic coupling into a ferromagnetic (FM) state with all the magnetization of the Co ion parallel to the c-axis. A striking variation of the field-induced strain within the ab-plane is noticed in the magnetic field region of 20-30 T. In the case of the magnetic field perpendicular to the c-axis (B  ⊥  c), the inter-layer helical antiferromagnetic (AFM) coupling may transform to an initial canted AFM coupling, and then part of it transforms to an intermediate metamagnetic phase with the alignment of two-up-one-down Co magnetic moments and finally to an ultimate FM coupling in higher magnetic fields. The robust noncollinear AFM magnetic coupling is completely destroyed above 30 T. In combination with the measurements of magnetization, magnetoresistance and field-induced strain, a complete magnetic phase diagram of the TlCo2Se2 single crystal has been depicted, demonstrating complex magnetic structures even though the crystal geometry itself gives no indication of the magnetic frustration.

  3. Perovskite Solar Cells with Near 100% Internal Quantum Efficiency Based on Large Single Crystalline Grains and Vertical Bulk Heterojunctions

    DOE PAGES

    Yang, Bin; Dyck, Ondrej; Poplawsky, Jonathan D; ...

    2015-01-01

    Grain boundaries (GBs) as defects in the crystal lattice detrimentally impact the power conversion efficiency (PCE) of polycrystalline solar cells, particularly in recently emerging hybrid perovskites where non-radiative recombination processes lead to significant carrier losses. Here, the beneficial effects of activated vertical GBs are demonstrated by first growing large, vertically-oriented methylammonium lead tri-iodide (CH3NH3PbI3) single-crystalline grains. We show that infiltration of p-type doped 2 -7,7 -tetrakis(N,Ndi-p-methoxyphenylamine)-9,9-spirobifluorene (Spiro-OMeTAD) into CH3NH3PbI3 films along the GBs creates space charge regions to suppress non-radiative recombination and enhance carrier collection efficiency. Solar cells with such activated GBs yielded average PCE of 16.3 0.9%, which aremore » among the best solution-processed perovskite devices. As an important alternative to growing ideal CH3NH3PbI3 single crystal films, which is difficult to achieve for such fast-crystallizing perovskites, activating GBs paves a way to design a new type of bulk heterojunction hybrid perovskite photovoltaics toward theoretical maximum PCE.« less

  4. Luminescent and scintillation properties of Lu3Al5O12:Sc single crystal and single crystalline films

    NASA Astrophysics Data System (ADS)

    Zorenko, Y.; Gorbenko, V.; Voznyak, T.; Savchyn, V.; Nizhankovskiy, S.; Dan'ko, A.; Puzikov, V.; Laguta, V.; Mares, J. A.; Nikl, M.; Nejezchleb, K.; Batentschuk, M.; Winnacker, A.

    2012-10-01

    The work is dedicated to growth by the liquid phase epitaxy method and study of the luminescence and scintillation properties of Sc3+ doped single crystalline films (SCF) of Lu3Al5O12 (LuAG) garnet. The scintillation properties of SCF are compared with single crystal (SC) analogues grown by the Horizontal Direct Crystallization and Czochralski methods. We consider the dependence of intensity of the Sc3+ emission in LuAG host on the activator concentration and influence of flux contamination on the light yield (LY) of the Sc3+ luminescence in LuAG:Sc SCF with respect to their SC counterparts and the reference YAP:Ce scintillator. From the NMR investigations of LuAG:Sc SCF we confirm the substitution by Sc3+ ions both the octahedral and dodecahedral positions of LuAG host and formation of the ScAl and ScLu related emission centers, respectively. We also show that the luminescence spectrum in the UV range and decay kinetics of LuAG:Sc SCF can be effectively tuned by changing the scandium content.

  5. Luminescence of lead-related centres in single crystalline films of Lu2SiO5

    NASA Astrophysics Data System (ADS)

    Gorbenko, V.; Krasnikov, A.; Mihokova, E.; Nikl, M.; Zazubovich, S.; Zorenko, Yu

    2012-09-01

    The steady-state and time-resolved emission and excitation spectra and luminescence decay kinetics of nominally undoped Lu2SiO5 single crystalline films (SCFs) grown by the liquid phase epitaxy method from the PbO-based flux are studied in the range 4.2-300 K. Due to the preparation method, the films contain lead ions. Luminescence characteristics of Pb-related centres of different types are identified. A weak 3.65 eV emission is ascribed to the radiative decay of the triplet relaxed excited state (RES) of Pb2+ ions substituting for Lu3+ ions in the Lu1 lattice sites of the X2 structure. Possible origins of the intense complex lead-related ≈2.8 eV emission are discussed. We propose phenomenological models describing the excited-state dynamics of the studied luminescence centres. We also determine the characteristic parameters of the corresponding RESs, in particular, the energy separations between the excited states and the rates of the radiative and non-radiative transitions from these states.

  6. Electrical Transport Properties of Single Crystalline β-Zn4Sb3 Prepared by α-Sn Flux Method

    NASA Astrophysics Data System (ADS)

    Liu, Hong-xia; Deng, Shu-ping; Shen, Lan-xian; Wang, Jin-song; Cheng, Feng; Deng, Shu-kang

    2017-05-01

    In this study, p-type single crystalline β-Zn4Sb3 thermoelectric materials with space group R {\\bar{3}} c were successfully prepared using the α-Sn flux method based on the stoichiometric ratios of Zn4+ x Sb3Sn3 ( x = 0, 0.2, 0.4, 0.6). All the crystal sizes were more than 5 mm. The prepared samples had high density and no microcracks. The powder x-ray diffraction patterns showed that all the samples were single phase. All single-crystal samples possessed good electrical transport performance. Compared with polycrystalline β-Zn4Sb3, the carrier mobility of the single crystals were significantly improved. Moreover, excess Zn improved the Seebeck coefficient of the material. The electrical conductivities of the samples were comparable with those obtained by the β-Sn flux method, whereas the Seebeck coefficient declined on the whole and the intrinsic conduction temperature decreased. The power factor of the sample with x = 0.2 is 0.82 × 10-3 W m-1 K-2 at 635 K, which exhibited the best electrical transport performance.

  7. Temperature dependent exchange bias training effect in single-crystalline BiFeO{sub 3}/Co bilayers

    SciTech Connect

    He, M. C.; You, B.; Tu, H. Q.; Rui, W. B.; Gao, Y.; Zhang, Y. Q.; Sheng, Y.; Xu, Q. Y. E-mail: jdu@nju.edu.cn; Xu, Y. B.; Du, J. E-mail: jdu@nju.edu.cn

    2015-05-07

    Single-crystalline BiFeO{sub 3} (BFO)/Co bilayers were prepared by combined pulsed laser deposition and magnetron sputtering on (001) SrTiO{sub 3} substrates. Exchange bias (EB) and accompanying training effect have been studied as a function of temperature (T) between 5 K and 300 K. A non-monotonic exchange field variation with sharp increase below 100 K has been observed. In the meanwhile, strong training effect was recorded when T < 100 K and it weakens monotonically with increasing T up to 300 K. These temperature dependent EB and training effect may be caused by the uncompensated spins in both the interfacial spin-glass (SG) phase at low temperature and the antiferromagnetic BFO layer at higher temperature. The low temperature EB training results can be well fitted by a modified Binek's model considering asymmetric changes of the pinning SG spins at the descending and the ascending branches.

  8. Effects of specimen size and yttria concentration on mechanical properties of single crystalline yttria-stabilized tetragonal zirconia nanopillars

    NASA Astrophysics Data System (ADS)

    Zhang, Ning; Asle Zaeem, Mohsen

    2017-07-01

    The nanoscale plastic deformation of yttria-stabilized tetragonal zirconia (YSTZ) is highly dependent on the crystallographic orientations, i.e., dislocation is induced when the loading direction is 45° tilted to {111} and {101} slip planes, while tetragonal to monoclinic phase transformation dominates the plastic deformation when loading direction is perpendicular to the slip planes. This study investigates the effects of specimen size and yttria concentration on the mechanical response of single crystalline YSTZ nanopillars. Through uniaxial compression test, the smaller-is-stronger phenomenon is revealed in nanopillars deformed through a dislocation motion mechanism. Serrated stacking faults are observed in the smallest nanopillar, while neat primary slip plane forms in the largest nanopillar. In contrast, the larger-is-stronger relation is observed in nanopillars in which deformation is mediated by tetragonal to monoclinic phase transformation. It is noted that the ratio of transformed monoclinic phase to the remaining tetragonal phase is the highest in the smallest nanopillar. The strength of nanopillars is identified to decrease by increasing the amount of yttria due to the creation of more oxygen vacancies that act as weak points to facilitate dislocation motion and accelerate phase transformation.

  9. Detachment of CVD-grown graphene from single crystalline Ni films by a pure gas phase reaction

    NASA Astrophysics Data System (ADS)

    Zeller, Patrick; Henß, Ann-Kathrin; Weinl, Michael; Diehl, Leo; Keefer, Daniel; Lippmann, Judith; Schulz, Anne; Kraus, Jürgen; Schreck, Matthias; Wintterlin, Joost

    2016-11-01

    Despite great previous efforts there is still a high need for a simple, clean, and upscalable method for detaching epitaxial graphene from the metal support on which it was grown. We present a method based on a pure gas phase reaction that is free of solvents and polymer supports and avoids mechanical transfer steps. The graphene was grown on 150 nm thick, single crystalline Ni(111) films on Si(111) wafers with YSZ buffer layers. Its quality was monitored by using low energy electron diffraction and scanning tunneling microscopy. The gas phase etching uses a chemical transport reaction, the so-called Mond process, based on the formation of gaseous nickel tetracarbonyl in ~ 1 bar of CO at ~ 75 °C and by adding small amounts of sulfide catalysts. X-ray photoelectron spectroscopy, Raman spectroscopy and scanning electron microscopy were used to characterize the detached graphene. It was found that the method successfully removes the nickel from underneath the graphene layer, so that the graphene lies on the insulating oxide buffer layer. Small residual particles of nickel sulfide and cracks in the obtained graphene layer were identified. The defect concentrations were comparable to graphene samples obtained by wet chemical etching and by the bubbling transfer.

  10. Single-Crystalline, Metallic TiC Nanowires for Highly Robust and Wide-Temperature Electrochemical Energy Storage.

    PubMed

    Xia, Xinhui; Zhan, Jiye; Zhong, Yu; Wang, Xiuli; Tu, Jiangping; Fan, Hong Jin

    2017-02-01

    Customized electrode materials with good temperature adaptability and high-rate capability are critical to the development of wide-temperature power sources. Herein, high-quality TiC nanowires are uniformly grown on flexible carbon cloth as free-standing electric-double-layer supercapacitor electrode. The TiC nanowires, 20-40 nm wide and 3-6 µm long, are single-crystalline and highly conductive that is close to typical metal. Symmetric supercapacitors are constructed with ionic liquid electrolyte and TiC nanowires electrodes as wide-temperature and long-cycle stable power source. Ultrastable high-rate cycling life of TiC nanowire arrays electrodes is demonstrated with capacitance retention of 96.8% at 60 °C (≈440 F g(-1) ), 99% at 25 °C (≈400 F g(-1) ), and 98% at -25 °C (≈240 F g(-1) ) after 50 000 cycles at 10 A g(-1) . Moreover, due to high electrical conductivity, the TiC nanowire arrays show ultrafast energy release with a fast response time constant of ≈0.7 ms. The results demonstrate the viability of metal carbide nanostructures as wide-temperature, robust electrode materials for high-rate and ultrastable supercapacitors.

  11. Reviews Opera: Doctor Atomic DVD: Doctor Atomic Equipment: Digital stopclock with external trigger Book: I Cyborg Book: Flat Earth: The History of an Infamous Idea Book: Mere Thermodynamics Book: CGP revision guides Book: Hiding the Elephant: How Magicians Invented the Impossible Book: Back of the Envelope Physics Web Watch

    NASA Astrophysics Data System (ADS)

    2009-07-01

    WE RECOMMEND Doctor Atomic The new Doctor Atomic opera provkes discussion on ethics I Cyborg The world's first human cyborg shares his life story in I Cyborg Flat Earth: The History of an Infamous Idea Flat Earth gives us a different perspective on creationism Mere Thermodynamics An introductory text on the three laws CGP revision guides This revision guide suits all courses and every pocket Hiding the Elephant: How Magicians Invented the Impossible The mystery of many illusions are solved in this book Back of the Envelope Physics This reference deserves a place on your bookshelf WORTH A LOOK Doctor Atomic The DVD doesn't do justice to the live performance Digital stopclock with external trigger Use these stopclocks when you need an external trigger WEB WATCH Webcasts reach out to an online audience

  12. Hierarchically plasmonic photocatalysts of Ag/AgCl nanocrystals coupled with single-crystalline WO3 nanoplates

    NASA Astrophysics Data System (ADS)

    Chen, Deliang; Li, Tao; Chen, Qianqian; Gao, Jiabing; Fan, Bingbing; Li, Jian; Li, Xinjian; Zhang, Rui; Sun, Jing; Gao, Lian

    2012-08-01

    The hierarchical photocatalysts of Ag/AgCl@plate-WO3 have been synthesized by anchoring Ag/AgCl nanocrystals on the surfaces of single-crystalline WO3 nanoplates that were obtained via an intercalation and topochemical approach. The heterogeneous precipitation process of the PVP-Ag+-WO3 suspensions with a Cl- solution added drop-wise was developed to synthesize AgCl@WO3 composites, which were then photoreduced to form Ag/AgCl@WO3 nanostructures in situ. WO3 nanocrystals with various shapes (i.e., nanoplates, nanorods, and nanoparticles) were used as the substrates to synthesize Ag/AgCl@WO3 photocatalysts, and the effects of the WO3 contents and photoreduction times on their visible-light-driven photocatalytic performance were investigated. The techniques of TEM, SEM, XPS, EDS, XRD, N2 adsorption-desorption and UV-vis DR spectra were used to characterize the compositions, phases and microstructures of the samples. The RhB aqueous solutions were used as the model system to estimate the photocatalytic performance of the as-obtained Ag/AgCl@WO3 nanostructures under visible light (λ >= 420 nm) and sunlight. The results indicated that the hierarchical Ag/AgCl@plate-WO3 photocatalyst has a higher photodegradation rate than Ag/AgCl, AgCl, AgCl@WO3 and TiO2 (P25). The contents and morphologies of the WO3 substrates in the Ag/AgCl@plate-WO3 photocatalysts have important effects on their photocatalytic performance. The related mechanisms for the enhancement in visible-light-driven photodegradation of RhB molecules were analyzed.The hierarchical photocatalysts of Ag/AgCl@plate-WO3 have been synthesized by anchoring Ag/AgCl nanocrystals on the surfaces of single-crystalline WO3 nanoplates that were obtained via an intercalation and topochemical approach. The heterogeneous precipitation process of the PVP-Ag+-WO3 suspensions with a Cl- solution added drop-wise was developed to synthesize AgCl@WO3 composites, which were then photoreduced to form Ag/AgCl@WO3 nanostructures in

  13. A facile strategy to fabricate high-quality single crystalline brookite TiO2 nanoarrays and their photoelectrochemical properties

    NASA Astrophysics Data System (ADS)

    Choi, Mingi; Yong, Kijung

    2014-10-01

    Vertically aligned high-quality single crystalline brookite TiO2 nanoarrays were synthesized for the first time using an environmentally benign one-step hydrothermal reaction. They have a unique bullet-shaped structure which has a length of 700-1000 nm and a width of 150-250 nm with a sharpened tip structure. By adjusting the concentration of NaOH in hydrothermal reaction, we could also synthesize other types of TiO2 nanostructures including anatase TiO2 nanotubes/nanowires. The morphologies and crystal structures of the products were confirmed by scanning electron microscopy, transmission electron microscopy and X-ray diffraction analysis. Their vertically aligned structures facilitate their application as photoanodes in photoelectrochemical cells, and the photoelectrochemical properties such as photocurrent density and open circuit voltage were measured in a three-electrode electrochemical cell with TiO2 nanoarrays, Ag/AgCl and a Pt flag as the working, reference and counter electrodes, respectively, incorporating a 0.1 M NaOH electrolyte solution. The fabricated brookite TiO2 nanoarrays exhibited a highly enhanced photocurrent density and a longer electron lifetime compared with anatase TiO2 nanoarrays with similar lengths.Vertically aligned high-quality single crystalline brookite TiO2 nanoarrays were synthesized for the first time using an environmentally benign one-step hydrothermal reaction. They have a unique bullet-shaped structure which has a length of 700-1000 nm and a width of 150-250 nm with a sharpened tip structure. By adjusting the concentration of NaOH in hydrothermal reaction, we could also synthesize other types of TiO2 nanostructures including anatase TiO2 nanotubes/nanowires. The morphologies and crystal structures of the products were confirmed by scanning electron microscopy, transmission electron microscopy and X-ray diffraction analysis. Their vertically aligned structures facilitate their application as photoanodes in photoelectrochemical

  14. Well-Defined Nanostructured, Single-Crystalline TiO2 Electron Transport Layer for Efficient Planar Perovskite Solar Cells.

    PubMed

    Choi, Jongmin; Song, Seulki; Hörantner, Maximilian T; Snaith, Henry J; Park, Taiho

    2016-06-28

    An electron transporting layer (ETL) plays an important role in extracting electrons from a perovskite layer and blocking recombination between electrons in the fluorine-doped tin oxide (FTO) and holes in the perovskite layers, especially in planar perovskite solar cells. Dense TiO2 ETLs prepared by a solution-processed spin-coating method (S-TiO2) are mainly used in devices due to their ease of fabrication. Herein, we found that fatal morphological defects at the S-TiO2 interface due to a rough FTO surface, including an irregular film thickness, discontinuous areas, and poor physical contact between the S-TiO2 and the FTO layers, were inevitable and lowered the charge transport properties through the planar perovskite solar cells. The effects of the morphological defects were mitigated in this work using a TiO2 ETL produced from sputtering and anodization. This method produced a well-defined nanostructured TiO2 ETL with an excellent transmittance, single-crystalline properties, a uniform film thickness, a large effective area, and defect-free physical contact with a rough substrate that provided outstanding electron extraction and hole blocking in a planar perovskite solar cell. In planar perovskite devices, anodized TiO2 ETL (A-TiO2) increased the power conversion efficiency by 22% (from 12.5 to 15.2%), and the stabilized maximum power output efficiency increased by 44% (from 8.9 to 12.8%) compared with S-TiO2. This work highlights the importance of the ETL geometry for maximizing device performance and provides insights into achieving ideal ETL morphologies that remedy the drawbacks observed in conventional spin-coated ETLs.

  15. Facile synthesis and enhanced photocatalytic activity of single-crystalline nanohybrids for the removal of organic pollutants.

    PubMed

    Pervaiz, Erum; Liu, Honghong; Yang, Minghui

    2017-03-10

    This study focused on the synthesis of α-MoO3/rGO (rGO, reduced graphene oxide). One-dimensional nanohybrids under mild conditions and a low temperature wet chemical route produced highly pure single-crystalline orthorhombic α-MoO3 on GO sheets. Four nanohybrids, labeled as GMO-0, GMO-1, GMO-2 and GMO-3, were synthesized with different mass chargings of GO (0 mg, 40 mg, 60 mg and 100 mg, respectively). The photocatalytic performance for reduction of organic pollutants was analyzed. The presence of different amounts of GO in the prepared metal oxide hybrids altered the performance of the material as elaborated by the Brunauer-Emmett-Teller surface area, UV-visible diffuse reflectance spectra and the resulting reduction of organic dyes depicted by photocatalytic experiments. GO as a support material and active co-catalyst decreased the band gap of α-MoO3 (2.82 eV) to lower values (2.51 eV), rendering the prepared hybrids usable for visible-light-induced photocatalysis. The large specific surface area (72 m(2) g(-1)) of the mesoporous α-MoO3/rGO nanohybrid made it an efficient photocatalyst for the elimination of azo dyes. Very fast reduction (100%) of Rhodamine B was observed in a few minutes, while Congo Red was degraded by 76% in 10 min, leading to the formation of stable intermediates that were completely neutralized in 12-14 h under light irradiation. The amount of GO loaded in the samples was limited to a point to achieve better results. After that, increasing the amount of GO decreased the extent of degradation due to the presence of a higher electron acceptor. Photocatalytic experiments revealed the synergistic effect, high selectivity of the prepared nanohybrids and degradation of azo dyes. The kinetics of the degradation reaction were studied and found to follow a pseudo first-order reaction.

  16. Scintillating screens based on the LPE grown Tb3Al5O12:Ce single crystalline films

    NASA Astrophysics Data System (ADS)

    Zorenko, Yuriy; Douissard, Paul-Antoine; Martin, Thierry; Riva, Federica; Gorbenko, Vitaliy; Zorenko, Tetiana; Paprocki, Kazimierz; Iskalieva, Aizhan; Witkiewicz, Sandra; Fedorov, Alexander; Bilski, Paweł; Twardak, Anna

    2017-03-01

    We report in this work the creation of new heavy and efficient Tb3Al5O12:Ce (TbAG:Ce) single crystalline film (SCF) scintillators, grown by LPE method from PbO-B2O3 based flux onto Y3Al5O12 (YAG) and Gd3Ga2.5Al2.5O12 (GAGG) substrates, for different optoelectronic applications. The luminescent and scintillation properties of the TbAG:Ce SCF screens, grown onto different types of substrates, are studied and compared with the properties of the Lu3Al5O12:Ce (LuAG:Ce) and YAG:Ce SCF counterparts. TbAG:Ce SCFs show very high scintillation light yield (LY) under α-particles excitation, which overcomes by 30% the LY of high-quality LuAG:Ce SCF samples. In comparison with YAG:Ce and LuAG:Ce SCFs, TbAG:Ce SCF screens show also significantly lower afterglow (up to 10-4 level at X-ray burst duration of 0.1 s), which is comparable with the afterglow level of the best samples of LSO:Ce, Tb SCFs typically being used now for microimaging. Together with a high light output of X-ray excited luminescence, such extremely low afterglow of TbAG:Ce SCF is a very good reason for future development of scintillating screens based on the mentioned garnet. We also introduce the possibility to create new types of ;film-substrate; hybrid scintillators using the LPE method for simultaneous registration of different components of ionizing radiation and microimaging based on the TbAG:Ce SCF and GAGG:Ce substrates.

  17. Facile synthesis and enhanced photocatalytic activity of single-crystalline nanohybrids for the removal of organic pollutants

    NASA Astrophysics Data System (ADS)

    Pervaiz, Erum; Liu, Honghong; Yang, Minghui

    2017-03-01

    This study focused on the synthesis of α-MoO3/rGO (rGO, reduced graphene oxide). One-dimensional nanohybrids under mild conditions and a low temperature wet chemical route produced highly pure single-crystalline orthorhombic α-MoO3 on GO sheets. Four nanohybrids, labeled as GMO-0, GMO-1, GMO-2 and GMO-3, were synthesized with different mass chargings of GO (0 mg, 40 mg, 60 mg and 100 mg, respectively). The photocatalytic performance for reduction of organic pollutants was analyzed. The presence of different amounts of GO in the prepared metal oxide hybrids altered the performance of the material as elaborated by the Brunauer-Emmett-Teller surface area, UV-visible diffuse reflectance spectra and the resulting reduction of organic dyes depicted by photocatalytic experiments. GO as a support material and active co-catalyst decreased the band gap of α-MoO3 (2.82 eV) to lower values (2.51 eV), rendering the prepared hybrids usable for visible-light-induced photocatalysis. The large specific surface area (72 m2 g-1) of the mesoporous α-MoO3/rGO nanohybrid made it an efficient photocatalyst for the elimination of azo dyes. Very fast reduction (100%) of Rhodamine B was observed in a few minutes, while Congo Red was degraded by 76% in 10 min, leading to the formation of stable intermediates that were completely neutralized in 12-14 h under light irradiation. The amount of GO loaded in the samples was limited to a point to achieve better results. After that, increasing the amount of GO decreased the extent of degradation due to the presence of a higher electron acceptor. Photocatalytic experiments revealed the synergistic effect, high selectivity of the prepared nanohybrids and degradation of azo dyes. The kinetics of the degradation reaction were studied and found to follow a pseudo first-order reaction.

  18. The effect of exceptionally high fluorine doping on the anisotropy of single crystalline SmFeAsO1-xFx

    NASA Astrophysics Data System (ADS)

    Fujioka, Masaya; Denholme, Saleem J.; Tanaka, Masashi; Takeya, Hiroyuki; Yamaguchi, Takahide; Takano, Yoshihiko

    2014-09-01

    We prepared single crystalline SmFeAsO1-xFx with an exceptionally high fluorine concentration by using a CsCl flux method. Comparing to conventional flux methods, this method can introduce about double the amount of fluorine into the oxygen site. The obtained single crystal shows the highest superconducting transition temperature (Tc = 57.5 K) in single crystalline iron pnictides. In addition, the residual resistivity ratio is almost three times as large as that of previously reported single crystals. This suggests that our single crystals are suitable for investigation of the intrinsic superconducting properties, since they have few defects and impurities. Using both the Werthamer-Helfand-Hohenberg model and the effective mass model, we demonstrated that a higher fluorine concentration suppresses the anisotropic superconductivity of SmFeAsO1-xFx.

  19. Facile and fast synthesis of single-crystalline fractal zinc structures through a solution phase reaction and their conversion to zinc oxide.

    PubMed

    Cho, Seungho; Kim, Semi; Kim, Hye-Jin; Lee, Bo Ram; Lee, Kun-Hong

    2009-09-01

    We report a novel method for the synthesis of fractal Zn structures through a solution phase reaction. An Al-film-deposited substrate was immersed in an aqueous ammonia solution containing Zn ions and maintained at 95 degrees C for 5 min. After the reaction, the Al-deposited side of the substrate was found to be covered with fractal Zn structures. These Zn structures are highly oriented, and the Zn(002) planes are parallel to the substrate. They are single-crystalline and the average thickness of the plates is approximately 50 nm. On the basis of our results, we propose a mechanism for the spontaneous growth of such fractal Zn structures. Single-crystalline fractal ZnO structures can also be obtained by calcination of the as-synthesized fractal Zn crystals at 500 degrees C for 5 h in air. These fractal ZnO structures are highly oriented and inherit their morphologies from the Zn structures.

  20. Improvement of electroluminescence performance by integration of ZnO nanowires and single-crystalline films on ZnO/GaN heterojunction

    SciTech Connect

    Shi, Zhifeng; Zhang, Yuantao Cui, Xijun; Wu, Bin; Zhuang, Shiwei; Yang, Fan; Zhang, Baolin; Du, Guotong; Yang, Xiaotian

    2014-03-31

    Heterojunction light-emitting diodes based on n-ZnO nanowires/ZnO single-crystalline films/p-GaN structure have been demonstrated for an improved electroluminescence performance. A highly efficient ultraviolet emission was observed under forward bias. Compared with conventional n-ZnO/p-GaN structure, high internal quantum efficiency and light extraction efficiency were simultaneously considered in the proposed diode. In addition, the diode can work continuously for ∼10 h with only a slight degradation in harsh environments, indicating its good reliability and application prospect in the future. This route opens possibilities for the development of advanced nanoscale devices in which the advantages of ZnO single-crystalline films and nanostructures can be integrated together.

  1. Nonaqueous sol-gel synthesis and growth mechanism of single crystalline TiO{sub 2} nanorods with high photocatalytic activity

    SciTech Connect

    Jia Huimin; Zheng Zhi; Zhao Hongxiao; Zhang Lizhi; Zou Zhigang

    2009-06-03

    In this paper, we report on a nonaqueous synthesis of single crystalline anatase TiO{sub 2} nanorods by reaction between TiCl{sub 4} and benzyl alcohol at a low temperature of 80 deg. C. The resulting samples were characterized with X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy, nitrogen adsorption, X-ray photoelectron spectrometry and UV-vis diffuse reflectance spectroscopy. We proposed that the TiO{sub 2} nanorods were formed through an oriented attachment mechanism. More importantly, these single crystalline anatase TiO{sub 2} nanorods exhibited significantly higher photocatalytic activities than commercial photocatalyst P25. This study provides an environmentally friendly and economic approach to produce highly active TiO{sub 2} photocatalyst.

  2. Ti(3+) Self-Doped Blue TiO2(B) Single-Crystalline Nanorods for Efficient Solar-Driven Photocatalytic Performance.

    PubMed

    Zhang, Yan; Xing, Zipeng; Liu, Xuefeng; Li, Zhenzi; Wu, Xiaoyan; Jiang, Jiaojiao; Li, Meng; Zhu, Qi; Zhou, Wei

    2016-10-12

    Ti(3+) self-doped blue TiO2(B) single-crystalline nanorods (b-TR) are fabricated via a simple sol-gelation method, cooperated with hydro-thermal treatment and subsequent in situ treatment method, and afterward annealed at 350 °C in Ar. The structures are characterized by X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (UV-vis), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The prepared b-TR with narrow band gap possesses single-crystalline TiO2(B) phase, Ti(3+) self-doping, and one-dimensional (1D) rodlike nanostructure. In addition, the improved photocatalytic performance is studied by decomposition of Rhodamine B (RhB) and hydrogen evolution. The degradation rate of RhB by Ti(3+) self-doped blue TiO2(B) single-crystalline nanorods is ∼6.9- and 2.1-times higher compared with the rates of titanium dioxide nanoparticles and pristine TiO2(B) nanorods under visible light illumination, respectively. The hydrogen evolution rate of b-TR is 26.6 times higher compared with that of titanium dioxide nanoparticles under AM 1.5 irradiation. The enhanced photocatalytic performances arise from the synergetic action of the special TiO2(B) phase, Ti(3+) self-doping, and the 1D rod-shaped single-crystalline nanostructure, favoring the visible light utilization and the separation and transportation of photogenerated charge carriers.

  3. Formation of hollow and mesoporous structures in single-crystalline microcrystals of metal-organic frameworks via double-solvent mediated overgrowth

    NASA Astrophysics Data System (ADS)

    Chou, Lien-Yang; Hu, Pan; Zhuang, Jia; Morabito, Joseph V.; Ng, Ka Chon; Kao, Ya-Chuan; Wang, Shao-Chun; Shieh, Fa-Kuen; Kuo, Chun-Hong; Tsung, Chia-Kuang

    2015-11-01

    The creation of hierarchical porosity in metal-organic frameworks (MOFs) could benefit various applications of MOFs such as gas storage and separation. Having single-crystalline microcrystals instead of poly-crystalline composites is critical for these potential applications of MOFs with hierarchical porosity. We developed a room temperature synthetic method to generate uniform hollow and mesoporous zeolitic imidazolate framework-8 (ZIF-8) microcrystals with a single-crystalline structure via overgrowing a ZIF-8 shell in methanol solution on a ZIF-8 core with water adsorbed in the pores. The cavities formed as a result of the different solvent micro-environment. This double-solvent mediated overgrowth method could be applied to prepare other MOFs with hierarchical porosity.The creation of hierarchical porosity in metal-organic frameworks (MOFs) could benefit various applications of MOFs such as gas storage and separation. Having single-crystalline microcrystals instead of poly-crystalline composites is critical for these potential applications of MOFs with hierarchical porosity. We developed a room temperature synthetic method to generate uniform hollow and mesoporous zeolitic imidazolate framework-8 (ZIF-8) microcrystals with a single-crystalline structure via overgrowing a ZIF-8 shell in methanol solution on a ZIF-8 core with water adsorbed in the pores. The cavities formed as a result of the different solvent micro-environment. This double-solvent mediated overgrowth method could be applied to prepare other MOFs with hierarchical porosity. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06532a

  4. Porous and single-crystalline ZnO nanobelts: fabrication with annealing precursor nanobelts, and gas-sensing and optoelectronic performance.

    PubMed

    Jin, Xiao-Bo; Li, Yi-Xiang; Su, Yao; Guo, Zheng; Gu, Cui-Ping; Huang, Jia-Rui; Meng, Fan-Li; Huang, Xing-Jiu; Li, Min-Qiang; Liu, Jin-Huai

    2016-09-02

    Porous and single-crystalline ZnO nanobelts have been prepared through annealing precursors of ZnSe · 0.5N2H4 well-defined and smooth nanobelts, which have been synthesized via a simple hydrothermal method. The composition and morphology evolutions with the calcination temperatures have been investigated in detail for as-prepared precursor nanobelts, suggesting that they can be easily transformed into ZnO nanobelts by preserving their initial morphology via calcination in air. In contrast, the obtained ZnO nanobelts are densely porous, owing to the thermal decomposition and oxidization of the precursor nanobelts. More importantly, the achieved porous ZnO nanobelts are single-crystalline, different from previously reported ones. Motivated by the intrinsic properties of the porous structure and good electronic transporting ability of single crystals, their gas-sensing performance has been further explored. It is demonstrated that porous ZnO single-crystalline nanobelts exhibit high response and repeatability toward volatile organic compounds, such as ethanol and acetone, with a short response/recovery time. Furthermore, their optoelectronic behaviors indicate that they can be promisingly employed to fabricate photoelectrochemical sensors.

  5. Evolution of CuO poly-crystalline layers to coherent single-crystalline dots on ZnO nanorods upon annealing

    NASA Astrophysics Data System (ADS)

    Wang, Ruey-Chi; Hou, Yuan-Ru; Chen, Yi-Wen

    2017-02-01

    ZnO/CuO p-n heterojunctions have attracted much attention for device applications, but coherent junctions, which are crucial for controlling electrical properties, still remain a challenge due to different crystal structure. In this work, CuO single-crystalline dots are coherently synthesized on ZnO nanorods by using a proposed two-step process. Transmission electron microscopy images confirm the formation of CuO coherent dots on single-crystalline ZnO nanorods upon annealing the nanorods covered with a poly-crystalline CuxO layer. The coherent dots exhibit two types of epitaxial orientations: CuO [002] ǀǀ ZnO [ 10 1 bar 1 ], CuO [111] ǀǀ ZnO [0002], and CuO [002] ǀǀ ZnO [ 10 1 bar 1 bar ], CuO [111] ǀǀ ZnO [ 000 2 bar ]. As the thickness of the as-deposited CuxO layer increases from 10 to 30 nm, the aspect ratio of the resulting CuO dots decreases from 0.43 to 0.21, approaching a film-like morphology. This work provides a route to prepare CuO coherent single-crystalline structures on ZnO, which is one step further toward fabricating excellent CuO/ZnO nanodevices.

  6. Porous and single-crystalline ZnO nanobelts: fabrication with annealing precursor nanobelts, and gas-sensing and optoelectronic performance

    NASA Astrophysics Data System (ADS)

    Jin, Xiao-Bo; Li, Yi-Xiang; Su, Yao; Guo, Zheng; Gu, Cui-Ping; Huang, Jia-Rui; Meng, Fan-Li; Huang, Xing-Jiu; Li, Min-Qiang; Liu, Jin-Huai

    2016-09-01

    Porous and single-crystalline ZnO nanobelts have been prepared through annealing precursors of ZnSe · 0.5N2H4 well-defined and smooth nanobelts, which have been synthesized via a simple hydrothermal method. The composition and morphology evolutions with the calcination temperatures have been investigated in detail for as-prepared precursor nanobelts, suggesting that they can be easily transformed into ZnO nanobelts by preserving their initial morphology via calcination in air. In contrast, the obtained ZnO nanobelts are densely porous, owing to the thermal decomposition and oxidization of the precursor nanobelts. More importantly, the achieved porous ZnO nanobelts are single-crystalline, different from previously reported ones. Motivated by the intrinsic properties of the porous structure and good electronic transporting ability of single crystals, their gas-sensing performance has been further explored. It is demonstrated that porous ZnO single-crystalline nanobelts exhibit high response and repeatability toward volatile organic compounds, such as ethanol and acetone, with a short response/recovery time. Furthermore, their optoelectronic behaviors indicate that they can be promisingly employed to fabricate photoelectrochemical sensors.

  7. γ-Irradiation assisted synthesis of graphene oxide sheets supported Ag nanoparticles with single crystalline structure and parabolic distribution from interlamellar limitation

    NASA Astrophysics Data System (ADS)

    Yue, Yunhao; Zhou, Baoming; Shi, Jie; Chen, Cheng; Li, Nan; Xu, Zhiwei; Liu, Liangsen; Kuang, Liyun; Ma, Meijun; Fu, Hongjun

    2017-05-01

    This paper reported a method to fabricate graphene oxide sheets supported Ag nanoparticles (AgNPs/GOS) with single crystalline structure and parabolic distribution without surfactant or functional agent. We used imidazole silver nitrate as intercalation precursor into the layers of graphite oxide, and subsequently reduction and growth of interlamellar AgNPs were induced via γ-irradiation. The results illustrated that the synergism of interlamellar limitation of graphite oxide and fragmentation ability of γ-irradiation could prevent coalescent reaction of AgNPs with other oligomeric clusters, and the single crystalline and small-sized (below 13.9 nm) AgNPs were prepared. Moreover, the content and size of AgNPs exhibited parabolic distribution on GOS surface because the graphite oxide exfoliated to GOS from the edge to the central area of layers. In addition, complete exfoliation degree of GOS and large-sized AgNPs were obtained simultaneously under suitable silver ions concentration. Optimized composites exhibited outstanding surface-enhanced Raman scattering properties for crystal violet with enhancement factor of 1.3 × 106 and detection limit of 1.0 × 10-7 M, indicating that the AgNPs/GOS composites could be applied to trace detection of organic dyes molecules. Therefore, this study presented a strategy for developing GOS supported nanometal with single crystalline structure and parabolic distribution based on γ-irradiation.

  8. High mobility single-crystalline-like GaAs thin films on inexpensive flexible metal substrates by metal-organic chemical vapor deposition

    SciTech Connect

    Dutta, P. Rathi, M.; Gao, Y.; Yao, Y.; Selvamanickam, V.; Zheng, N.; Ahrenkiel, P.; Martinez, J.

    2014-09-01

    We demonstrate heteroepitaxial growth of single-crystalline-like n and p-type doped GaAs thin films on inexpensive, flexible, and light-weight metal foils by metal-organic chemical vapor deposition. Single-crystalline-like Ge thin film on biaxially textured templates made by ion beam assisted deposition on metal foil served as the epitaxy enabling substrate for GaAs growth. The GaAs films exhibited strong (004) preferred orientation, sharp in-plane texture, low grain misorientation, strong photoluminescence, and a defect density of ∼10{sup 7 }cm{sup −2}. Furthermore, the GaAs films exhibited hole and electron mobilities as high as 66 and 300 cm{sup 2}/V-s, respectively. High mobility single-crystalline-like GaAs thin films on inexpensive metal substrates can pave the path for roll-to-roll manufacturing of flexible III-V solar cells for the mainstream photovoltaics market.

  9. Intrinsic electrical, magnetic, and thermal properties of single-crystalline Al64Cu23Fe13 icosahedral quasicrystal: Experiment and modeling

    NASA Astrophysics Data System (ADS)

    Dolinšek, J.; Vrtnik, S.; Klanjšek, M.; Jagličić, Z.; Smontara, A.; Smiljanić, I.; Bilušić, A.; Yokoyama, Y.; Inoue, A.; Landauro, C. V.

    2007-08-01

    In order to test for the true intrinsic properties of icosahedral i-Al-Cu-Fe quasicrystals, we performed investigations of magnetism, electrical resistivity, thermoelectric power, and thermal conductivity on a single-crystalline Al64Cu23Fe13 quasicrystal grown by the Czochralski technique. This sample shows superior quasicrystallinity, an almost phason-free structure, and excellent thermal stability. Magnetic measurements revealed that the sample is best classified as a weak paramagnet. Electrical resistivity exhibits a negative temperature coefficient with ρ4K=3950μΩcm and R=ρ4K/ρ300K=1.8 , whereas the thermopower exhibits a sign reversal at T=278K . Simultaneous analysis of the resistivity and thermopower using spectral-conductivity model showed that the Fermi energy is located at the minimum of the pseudogap in the spectral conductivity σ(ɛ) . Thermal conductivity is anomalously low for an alloy of metallic elements. Comparing the physical properties of the investigated single-crystalline Al64Cu23Fe13 quasicrystal to literature reports on polycrystalline i-Al-Cu-Fe material, we conclude that there are no systematic differences between the high-quality single-crystalline and polycrystalline i-Al-Cu-Fe quasicrystals, except for the hindering of long-range transport by grain boundaries in the polycrystalline material. The so far reported physical properties of i-Al-Cu-Fe appear to be intrinsic to this family of icosahedral quasicrystals, regardless of the form of the material.

  10. Pulsed laser deposition of single-crystalline Cu7In3/CuIn0.8Ga0.2Se2 core/shell nanowires.

    PubMed

    Zhao, Yu; Li, Hui; Zhu, Yan-Yan; Guan, Lei-Lei; Li, Yan-Li; Sun, Jian; Ying, Zhi-Feng; Wu, Jia-Da; Xu, Ning

    2014-01-01

    Single-crystalline Cu7In3/CuIn0.8Ga0.2Se2 (CI/CIGS) core/shell nanowires are fabricated by pulsed laser deposition with Ni nanoparticles as catalyst. The CI/CIGS core/shell nanowires are made up of single-crystalline CI cores surrounded by single-crystalline CIGS shells. The CI/CIGS nanowires are grown at a considerably low temperature (350°C ~ 450°C) by vapor-liquid-solid mode combined with vapor-solid mode. The distribution density of the nanowires increases with the increasing of the deposition duration, and the substrate temperature determines the lengths of the nanowires. The U-V absorption spectra of the CIGS thin films with and without the CI/CIGS core/shell nanowires demonstrate that the CI/CIGS nanowires can remarkably enhance the absorption of CIGS thin films in the spectrum range of 300 to 900 nm. 61.46. + w; 61.41.e; 81.15.Fg; 81.07.b.

  11. Pulsed laser deposition of single-crystalline Cu7In3/CuIn0.8Ga0.2Se2 core/shell nanowires

    PubMed Central

    2014-01-01

    Single-crystalline Cu7In3/CuIn0.8Ga0.2Se2 (CI/CIGS) core/shell nanowires are fabricated by pulsed laser deposition with Ni nanoparticles as catalyst. The CI/CIGS core/shell nanowires are made up of single-crystalline CI cores surrounded by single-crystalline CIGS shells. The CI/CIGS nanowires are grown at a considerably low temperature (350°C ~ 450°C) by vapor-liquid-solid mode combined with vapor-solid mode. The distribution density of the nanowires increases with the increasing of the deposition duration, and the substrate temperature determines the lengths of the nanowires. The U-V absorption spectra of the CIGS thin films with and without the CI/CIGS core/shell nanowires demonstrate that the CI/CIGS nanowires can remarkably enhance the absorption of CIGS thin films in the spectrum range of 300 to 900 nm. PACS 61.46. + w; 61.41.e; 81.15.Fg; 81.07.b PMID:25520597

  12. Vapor-solid synthesis of monolithic single-crystalline CoP nanowire electrodes for efficient and robust water electrolysis.

    PubMed

    Li, Wei; Gao, Xuefei; Xiong, Dehua; Xia, Fang; Liu, Jian; Song, Wei-Guo; Xu, Junyuan; Thalluri, Sitaramanjaneya Mouli; Cerqueira, M F; Fu, Xiuli; Liu, Lifeng

    2017-04-01

    Electrochemical water splitting into hydrogen and oxygen is a promising technology for sustainable energy storage. The development of earth-abundant transition metal phosphides (TMPs) to catalyze the hydrogen evolution reaction (HER) and TMP-derived oxy-hydroxides to catalyze the oxygen evolution reaction (OER) has recently drawn considerable attention. However, most monolithically integrated metal phosphide electrodes are prepared by laborious multi-step methods and their operational stability at high current densities has been rarely studied. Herein, we report a novel vapor-solid synthesis of single-crystalline cobalt phosphide nanowires (CoP NWs) on a porous Co foam and demonstrate their use in overall water splitting. The CoP NWs grown on the entire surface of the porous Co foam ligaments have a large aspect ratio, and hence are able to provide a large catalytically accessible surface over a given geometrical area. Comprehensive investigation shows that under the OER conditions CoP NWs are progressively and conformally converted to CoOOH through electrochemical in situ oxidation/dephosphorization; the latter serving as an active species to catalyze the OER. The in situ oxidized electrode shows exceptional electrocatalytic performance for the OER in 1.0 M KOH, delivering 100 mA cm(-2) at an overpotential (η) of merely 300 mV and a small Tafel slope of 78 mV dec(-1) as well as excellent stability at various current densities. Meanwhile, the CoP NW electrode exhibits superior catalytic activity for the HER in the same electrolyte, affording -100 mA cm(-2) at η = 244 mV and showing outstanding stability. An alkaline electrolyzer composed of two symmetrical CoP NW electrodes can deliver 10 and 100 mA cm(-2) at low cell voltages of 1.56 and 1.78 V, respectively. The CoP NW electrolyzer demonstrates exceptional long-term stability for overall water splitting, capable of working at 20 and 100 mA cm(-2) for 1000 h without obvious degradation.

  13. Single-crystalline organic-inorganic layered cobalt hydroxide nanofibers: facile synthesis, characterization, and reversible water-induced structural conversion.

    PubMed

    Guo, Xiaodi; Wang, Lianying; Yue, Shuang; Wang, Dongyang; Lu, Yanluo; Song, Yufei; He, Jing

    2014-12-15

    New pink organic-inorganic layered cobalt hydroxide nanofibers intercalated with benzoate ions [Co(OH)(C6H5COO)·H2O] have been synthesized by using cobalt nitrate and sodium benzoate as reactants in water with no addition of organic solvent or surfactant. The high-purity nanofibers are single-crystalline in nature and very uniform in size with a diameter of about 100 nm and variable lengths over a wide range from 200 μm down to 2 μm by simply adjusting reactant concentrations. The as-synthesized products are well-characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), fast Fourier transforms (FFT), X-ray diffraction (XRD), energy dispersive X-ray spectra (EDX), X-ray photoelectron spectra (XPS), elemental analysis (EA), Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), and UV-vis diffuse reflectance spectra (UV-vis). Our results demonstrate that the structure consists of octahedral cobalt layers and the benzoate anions, which are arranged in a bilayer due to the π-π stacking of small aromatics. The carboxylate groups of benzoate anions are coordinated to Co(II) ions in a strong bridging mode, which is the driving force for the anisotropic growth of nanofibers. When NaOH is added during the synthesis, green irregular shaped platelets are obtained, in which the carboxylate groups of benzoate anions are coordinated to the Co(II) ions in a unidentate fashion. Interestingly, the nanofibers exhibit a reversible transformation of the coordination geometry of the Co(II) ions between octahedral and pseudotetrahedral with a concomitant color change between pink and blue, which involves the loss and reuptake of unusual weakly coordinated water molecules without destroying the structure. This work offers a facile, cost-effective, and green strategy to rationally design and synthesize functional nanomaterials for future applications in catalysis, magnetism

  14. Charlie Flats

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This image from the Mars Exploration Rover Opportunity's panoramic camera shows a region of the rock outcrop at Meridiani Planum, Mars, dubbed 'Charlie Flats.' This region is a rich science target for Opportunity because it contains a diverse assortment of small grains, pebbles and spherules, as well as both dark and light soil deposits. The area seen here measures approximately 0.6 meters (2 feet) across. The smallest grains visible in this image are only a few millimeters in size. The approximate true color image was acquired on Sol 20 of Opportunity's mission with panoramic camera filters red, green and blue. [figure removed for brevity, see original site] Click on image for larger view Charlie Flats Spectra The chart above shows examples of spectra, or light wave patterns, extracted from the region of the Meridiani Planum rock outcrop dubbed 'Charlie Flats,' a rich science target for the Mars Exploration Rover Opportunity. The spectra were extracted from the similarly colored regions in the image on the left, taken by the rover's panoramic camera. The green circle identifies a bright, dust-like soil deposit. The red circle identifies a dark soil region. The yellow identifies a small, angular rock chip with a strong near-infrared band. The pink identifies a sphere-shaped pebble with a different strong near-infrared band. The cyan circle shows a dark, grayish pebble.

  15. Charlie Flats

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This image from the Mars Exploration Rover Opportunity's panoramic camera shows a region of the rock outcrop at Meridiani Planum, Mars, dubbed 'Charlie Flats.' This region is a rich science target for Opportunity because it contains a diverse assortment of small grains, pebbles and spherules, as well as both dark and light soil deposits. The area seen here measures approximately 0.6 meters (2 feet) across. The smallest grains visible in this image are only a few millimeters in size. The approximate true color image was acquired on Sol 20 of Opportunity's mission with panoramic camera filters red, green and blue. [figure removed for brevity, see original site] Click on image for larger view Charlie Flats Spectra The chart above shows examples of spectra, or light wave patterns, extracted from the region of the Meridiani Planum rock outcrop dubbed 'Charlie Flats,' a rich science target for the Mars Exploration Rover Opportunity. The spectra were extracted from the similarly colored regions in the image on the left, taken by the rover's panoramic camera. The green circle identifies a bright, dust-like soil deposit. The red circle identifies a dark soil region. The yellow identifies a small, angular rock chip with a strong near-infrared band. The pink identifies a sphere-shaped pebble with a different strong near-infrared band. The cyan circle shows a dark, grayish pebble.

  16. "Roadrunner Flats"

    NASA Image and Video Library

    1997-10-14

    This enhanced color image of the Pathfinder landing site shows the eastern horizon. The elongated, reddish, low contrast region in the distance is "Roadrunner Flats." This image was taken by the Imager for Mars Pathfinder (IMP). Sojourner spent 83 days of a planned seven-day mission exploring the Martian terrain, acquiring images, and taking chemical, atmospheric and other measurements. The final data transmission received from Pathfinder was at 10:23 UTC on September 27, 1997. Although mission managers tried to restore full communications during the following five months, the successful mission was terminated on March 10, 1998. http://photojournal.jpl.nasa.gov/catalog/PIA00979

  17. Growth of ultrathin layers of Au on LiNbO 3(0 0 0 1) measured with atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Bharath, Satyaveda C.; Pearl, Thomas P.

    2010-04-01

    Atomic force microscopy (AFM) has been used to characterize the growth of Au deposited via evaporation onto the positive face of single crystalline, lithium niobate, LiNbO 3(0 0 0 1) surface. In order to study the mechanisms for the ordering and aggregation of a noble metal on this ferroelectric surface, topographic and phase contrast imaging of the fractional surface coverage of Au were performed. Atomically flat, uniformly poled LiNbO 3 surfaces were prepared via an ambient high temperature anneal and served as a support for the thin gold films. These gold atomic layers were grown using electron bombardment evaporation sources under ultra-high vacuum (UHV) conditions and subsequently characterized under both vacuum and ambient environments. Using AFM it was found that gold preferentially nucleates at the top of LiNbO 3 substrate step edges. With increased coverage, island formation proceeds due to local aggregation of adsorbed gold on each substrate terrace. Based on local imaging of the growth morphology, the data is discussed in terms of thin film growth mechanisms as well as the influence of native surface features such as defects and charge distribution. Understanding growth mechanisms for gold layers on ferroelectric surfaces allows for a fuller appreciation of how atomic deposition of metal atoms on patterned poled LiNbO 3 surfaces would occur as well as yielding greater insight on the atomic characteristics of metals on ferroelectric interfaces.

  18. Single crystalline La0.7Sr0.3MnO3 molecular sieve nanowires with high temperature ferromagnetism.

    PubMed

    Carretero-Genevrier, Adrián; Gázquez, Jaume; Idrobo, Juan Carlos; Oró, Judith; Arbiol, Jordi; Varela, María; Ferain, Etienne; Rodríguez-Carvajal, Juan; Puig, Teresa; Mestres, Narcís; Obradors, Xavier

    2011-03-23

    Porous mixed-valent manganese oxides are a group of multifunctional materials that can be used as molecular sieves, catalysts, battery materials, and gas sensors. However, material properties and thus activity can vary significantly with different synthesis methods or process conditions, such as temperature and time. Here, we report on a new synthesis route for MnO(2) and LaSr-doped molecular sieve single crystalline nanowires based on a solution chemistry methodology combined with the use of nanoporous polymer templates supported on top of single crystalline substrates. Because of the confined nucleation in high aspect ratio nanopores and of the high temperatures attained, new structures with novel physical properties have been produced. During the calcination process, the nucleation and crystallization of ε-MnO(2) nanoparticles with a new hexagonal structure is promoted. These nanoparticles generated up to 30 μm long and flexible hexagonal nanowires at mild growth temperatures (T(g) = 700 °C) as a consequence of the large crystallographic anisotropy of ε-MnO(2). The nanocrystallites of MnO(2) formed at low temperatures serve as seeds for the growth of La(0.7)Sr(0.3)MnO(3) nanowires at growth temperatures above 800 °C, through the diffusion of La and Sr into the empty 1D-channels of ε-MnO(2). Our particular growth method has allowed the synthesis of single crystalline molecular sieve (LaSr-2 × 4) monoclinic nanowires with composition La(0.7)Sr(0.3)MnO(3) and with ordered arrangement of La(3+) and Sr(2+) cations inside the 1D-channels. These nanowires exhibit ferromagnetic ordering with strongly enhanced Curie temperature (T(c) > 500 K) that probably results from the new crystallographic order and from the mixed valence of manganese.

  19. Self-Assembly of "Chalcone" Type Push-Pull Dye Molecules into Organic Single Crystalline Microribbons and Rigid Microrods for Vis/NIR Range Photonic Cavity Applications.

    PubMed

    Vattikunta, Radhika; Venkatakrishnarao, Dasari; Mohiddon, Mahamad Ahamad; Chandrasekar, Rajadurai

    2016-11-04

    A novel supramolecular fluorescent donor-acceptor type dye molecule, (2E,4E)-1-(2-hydroxyphenyl)-5-(pyren-1-yl)penta-2,4-dien-1-one (HPPD) self-assembles in a mixture of ethanol/chloroform through intermolecular π-π stacking (distance ca. 3.384 Å) to form J-aggregated single-crystalline microribbons displaying Fabry-Pèrot (F-P) type visible-range optical resonance. The corresponding borondifluoride dye (HPPD-BF), with a reduced HOMO-LUMO gap, self-assembles into crystalline microrods acting as an F-P type resonator in the near-infrared (NIR) range.

  20. Electronic and structural instabilities of single-crystalline La 2- x- yNd ySr xCuO 4 near 1/8 doping

    NASA Astrophysics Data System (ADS)

    Sakita, S.; Nakamura, F.; Takase, J.; Suzuki, T.; Fujita, T.

    1997-08-01

    We have performed ultrasonic measurements, X-ray diffraction, resistivity and susceptibility measurements in order to investigate the correlation between the structural instability and the electronic states in the normal state of single-crystalline La 2- x- yNd ySr xCuO 4 with x=1/8 and y=0.4. There exist two structural phase transitions at low temperatures, one of which is of the 2nd order (OMT-OLT) and the other is of the 1st order (OLT-TLT). The phase transition to the TLT phase appears to couple to the electronic instability leading to the local suppression of superconductivity.

  1. Cobalt-modified porous single-crystalline LaTiO2N for highly efficient water oxidation under visible light.

    PubMed

    Zhang, Fuxiang; Yamakata, Akira; Maeda, Kazuhiko; Moriya, Yosuke; Takata, Tsuyoshi; Kubota, Jun; Teshima, Katsuya; Oishi, Shuji; Domen, Kazunari

    2012-05-23

    Highly efficient water oxidation utilizing visible photons of up to 600 nm is a crucial step in artificial photosynthesis. Here we present a highly active photocatalyst for visible-light-driven water oxidation, consisting of single-crystalline meso- and macroporous LaTiO(2)N (LTON) with a band gap of 2.1 eV, and earth-abundasnt cobalt oxide (CoO(x)) as a cocatalyst. The optimized CoO(x)/LTON had a high quantum efficiency of 27.1 ± 2.6% at 440 nm, which substantially exceeds the values reported for previous particulate photocatalysts with a 600-nm absorption edge.

  2. Ambient Large-Scale Template-Mediated Synthesis of High-Aspect Ratio Single-Crystalline, Chemically Doped Rare-Earth Phosphate Nanowires for Bioimaging

    SciTech Connect

    Zhang, F.; Wong, S.

    2009-12-30

    A simple and effective template-mediated protocol has been developed for the large-scale, room-temperature preparation of high-aspect-ratio, single-crystalline Tb-doped CePO{sub 4} nanowires, measuring {approx}12 nm in diameter and over 10 {mu}m in length. Moreover, we also isolated sheaf-like bundles of nanostructures. The synthesis mechanism likely involved a crystal splitting step. The resulting nanowires demonstrated an intense redox-sensitive green photoluminescence, which was exploited, in addition to their inherently high biocompatibility and low toxicity, for potential applications in biological imaging and labeling of cells.

  3. Single crystalline YAG:Ce phosphor for powerful solid-state sources of white light. The influence of production conditions on luminescence properties and lighting characteristics

    NASA Astrophysics Data System (ADS)

    Nizhankovskyi, S. V.; Tan'ko, A. V.; Savvin, Yu. N.; Krivonogov, S. I.; Budnikov, A. T.; Voloshin, A. V.

    2016-06-01

    It is shown that the spectral properties and spatial distribution of LED radiation with a YAG:Ce single crystalline luminescent converter significantly depend on the morphology of the converter surface. The variation of surface roughness enables one to obtain a light source with a wide range of color characteristics. As a result of optimization of converter parameters we demonstrate a possibility of creating a white light LED with correlated color temperature TCC ~ 5000-6500 K and color rendering index CRI ≈ 60-70.

  4. Isotropic plasticity of β-type Ti-29Nb-13Ta-4.6Zr alloy single crystals for the development of single crystalline β-Ti implants

    PubMed Central

    Hagihara, Koji; Nakano, Takayoshi; Maki, Hideaki; Umakoshi, Yukichi; Niinomi, Mitsuo

    2016-01-01

    β-type Ti-29Nb-13Ta-4.6Zr alloy is a promising novel material for biomedical applications. We have proposed a ‘single crystalline β-Ti implant’ as new hard tissue replacements for suppressing the stress shielding by achieving a drastic reduction in the Young’s modulus. To develop this, the orientation dependence of the plastic deformation behavior of the Ti-29Nb-13Ta-4.6Zr single crystal was first clarified. Dislocation slip with a Burgers vector parallel to <111> was the predominant deformation mode in the wide loading orientation. The orientation dependence of the yield stress due to <111> dislocations was small, in contrast to other β-Ti alloys. In addition, {332} twin was found to be operative at the loading orientation around [001]. The asymmetric features of the {332} twin formation depending on the loading orientation could be roughly anticipated by their Schmid factors. However, the critical resolved shear stress for the {332} twins appeared to show orientation dependence. The simultaneous operation of <111> slip and {332} twin were found to be the origin of the good mechanical properties with excellent strength and ductility. It was clarified that the Ti-29Nb-13Ta-4.6Zr alloy single crystal shows the “plastically almost-isotropic and elastically highly-anisotropic” nature, that is desirable for the development of ‘single crystalline β-Ti implant’. PMID:27417073

  5. Controlled Growth of Large-Area Aligned Single-Crystalline Organic Nanoribbon Arrays for Transistors and Light-Emitting Diodes Driving

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Wang, Liang; Dai, Gaole; Deng, Wei; Zhang, Xiujuan; Jie, Jiansheng; Zhang, Xiaohong

    2017-10-01

    Organic field-effect transistors (OFETs) based on organic micro-/nanocrystals have been widely reported with charge carrier mobility exceeding 1.0 cm2 V-1 s-1, demonstrating great potential for high-performance, low-cost organic electronic applications. However, fabrication of large-area organic micro-/nanocrystal arrays with consistent crystal growth direction has posed a significant technical challenge. Here, we describe a solution-processed dip-coating technique to grow large-area, aligned 9,10-bis(phenylethynyl) anthracene (BPEA) and 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-PEN) single-crystalline nanoribbon arrays. The method is scalable to a 5 × 10 cm2 wafer substrate, with around 60% of the wafer surface covered by aligned crystals. The quality of crystals can be easily controlled by tuning the dip-coating speed. Furthermore, OFETs based on well-aligned BPEA and TIPS-PEN single-crystalline nanoribbons were constructed. By optimizing channel lengths and using appropriate metallic electrodes, the BPEA and TIPS-PEN-based OFETs showed hole mobility exceeding 2.0 cm2 V-1 s-1 (average mobility 1.2 cm2 V-1 s-1) and 3.0 cm2 V-1 s-1 (average mobility 2.0 cm2 V-1 s-1), respectively. They both have a high on/off ratio ( I on/ I off) > 109. The performance can well satisfy the requirements for light-emitting diodes driving.

  6. Enhanced Solar Water Splitting by Swift Charge Separation in Au/FeOOH Sandwiched Single-Crystalline Fe2 O3 Nanoflake Photoelectrodes.

    PubMed

    Wang, Lei; Nguyen, Nhat Truong; Zhang, Yajun; Bi, Yingpu; Schmuki, Patrik

    2017-07-10

    In this work, single crystalline α-Fe2 O3 nanoflakes (NFs) are formed in a highly dense array by Au seeding of a Fe substrate by a thermal oxidation technique. The NFs are conformally decorated with a thin FeOOH cocatalyst layer. Photoelectrochemical (PEC) measurements show that this photoanode, incorporating α-Fe2 O3 /FeOOH NFs rooted on the Au/Fe structure, exhibits significantly enhanced PEC water oxidation performance compared to the plain α-Fe2 O3 nanostructure on the Fe substrate. The α-Fe2 O3 /FeOOH NFs on Au/Fe photoanode yields a photocurrent density of 3.1 mA cm(-2) at 1.5 VRHE , and a remarkably low onset potential of 0.5-0.6 VRHE in 1 m KOH under AM 1.5G (100 mW cm(-2) ) simulated sunlight illumination. The enhancement in PEC performance can be attributed to a synergistic effect of the FeOOH top decoration and the Au underlayer, whereby FeOOH facilitates hole transfer at the interface of electrode/electrolyte and the Au layer provides a sink for the electron transport to the back contact. This results in a drastically improved charge-separation efficiency in the single crystalline α-Fe2 O3 NF photoanode. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Isotropic plasticity of β-type Ti-29Nb-13Ta-4.6Zr alloy single crystals for the development of single crystalline β-Ti implants.

    PubMed

    Hagihara, Koji; Nakano, Takayoshi; Maki, Hideaki; Umakoshi, Yukichi; Niinomi, Mitsuo

    2016-07-15

    β-type Ti-29Nb-13Ta-4.6Zr alloy is a promising novel material for biomedical applications. We have proposed a 'single crystalline β-Ti implant' as new hard tissue replacements for suppressing the stress shielding by achieving a drastic reduction in the Young's modulus. To develop this, the orientation dependence of the plastic deformation behavior of the Ti-29Nb-13Ta-4.6Zr single crystal was first clarified. Dislocation slip with a Burgers vector parallel to <111> was the predominant deformation mode in the wide loading orientation. The orientation dependence of the yield stress due to <111> dislocations was small, in contrast to other β-Ti alloys. In addition, {332} twin was found to be operative at the loading orientation around [001]. The asymmetric features of the {332} twin formation depending on the loading orientation could be roughly anticipated by their Schmid factors. However, the critical resolved shear stress for the {332} twins appeared to show orientation dependence. The simultaneous operation of <111> slip and {332} twin were found to be the origin of the good mechanical properties with excellent strength and ductility. It was clarified that the Ti-29Nb-13Ta-4.6Zr alloy single crystal shows the "plastically almost-isotropic and elastically highly-anisotropic" nature, that is desirable for the development of 'single crystalline β-Ti implant'.

  8. The impact of ZnO nanoparticle interlayer on the growth and morphology of broom-like single crystalline gallium nitride.

    PubMed

    Uthirakumar, Periyayya; Suh, Eun-Kyung; Hong, Chang-Hee

    2008-10-01

    Broom-like single crystalline gallium nitride (GaN) nanomaterials have been successfully grown on Si (100) substrates through ammoniating the new type of complex precursor hexafluoroammonium gallate [(NH4)3GaF6], under a constant flow of ammonia at 900 degrees C in a quartz tube. This research mainly deals with the effect of zinc oxide (ZnO) interlayer on the growth and morphological changes of GaN nanoparticles. Broom-like GaN nanomaterials were obtained upon the influence of very fine ZnO nanoparticle interlayer in between the silicon substrate and the Ga source complex materials. On the other hand, well organized micron size hexagonal GaN particles were resulted in absence of ZnO interlayer. The transformation of hexagonal to broom-like GaN nanomaterials was predominant due to improved surface compatibility between the Si substrate and Ga source complex by the ZnO interlayer. The starting point for the transformation was indentified by controlling the process time. The structure and morphology changes of the GaN product were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM images demonstrate the difference in their morphological changes of single crystalline GaN upon the ZnO nanoparticles layer deposition.

  9. Isotropic plasticity of β-type Ti-29Nb-13Ta-4.6Zr alloy single crystals for the development of single crystalline β-Ti implants

    NASA Astrophysics Data System (ADS)

    Hagihara, Koji; Nakano, Takayoshi; Maki, Hideaki; Umakoshi, Yukichi; Niinomi, Mitsuo

    2016-07-01

    β-type Ti-29Nb-13Ta-4.6Zr alloy is a promising novel material for biomedical applications. We have proposed a ‘single crystalline β-Ti implant’ as new hard tissue replacements for suppressing the stress shielding by achieving a drastic reduction in the Young’s modulus. To develop this, the orientation dependence of the plastic deformation behavior of the Ti-29Nb-13Ta-4.6Zr single crystal was first clarified. Dislocation slip with a Burgers vector parallel to <111> was the predominant deformation mode in the wide loading orientation. The orientation dependence of the yield stress due to <111> dislocations was small, in contrast to other β-Ti alloys. In addition, {332} twin was found to be operative at the loading orientation around [001]. The asymmetric features of the {332} twin formation depending on the loading orientation could be roughly anticipated by their Schmid factors. However, the critical resolved shear stress for the {332} twins appeared to show orientation dependence. The simultaneous operation of <111> slip and {332} twin were found to be the origin of the good mechanical properties with excellent strength and ductility. It was clarified that the Ti-29Nb-13Ta-4.6Zr alloy single crystal shows the “plastically almost-isotropic and elastically highly-anisotropic” nature, that is desirable for the development of ‘single crystalline β-Ti implant’.

  10. Hydrothermal transformation of titanate nanotubes into single-crystalline TiO{sub 2} nanomaterials with controlled phase composition and morphology

    SciTech Connect

    Xu, Yuanmei; Fang, Xiaoming; Xiong, Jian; Zhang, Zhengguo

    2010-07-15

    Single-crystalline TiO{sub 2} nanomaterials were synthesized by hydrothermally treating suspensions of H-titanate nanotubes and characterized by XRD, TEM, and HRTEM. The effects of the pH values of the suspensions and the hydrothermal temperatures on the phase composition and morphology of the obtained TiO{sub 2} nanomaterials were systematically investigated. The H-titanate nanotubes were predominately transformed into anatase nanoparticle with rhombic shape when the pH value was greater than or equal to 1.0, whereas primarily turned into rutile nanorod with two pyramidal ends at the pH value less than or equal to 0.5. We propose a possible mechanism for hydrothermal transformation of H-titanate nanotubes into single-crystalline TiO{sub 2} nanomaterials. While the H-titanate nanotubes transform into tiny anatase nanocrystallites of ca. 3 nm in size, the formed nanocrystallites as an intermediate grow into the TiO{sub 2} nanomaterials with controlled phase composition and morphology. This growth process involves the steps of protonation, oriented attachment, and Ostwald ripening.

  11. Enhancing s, p-d exchange interactions at room temperature by carrier doping in single crystalline Co0.4Zn0.6O epitaxial films

    NASA Astrophysics Data System (ADS)

    Cao, Qiang; Fu, Maoxiang; Zhu, Dapeng; Cai, Li; Zhang, Kun; Liu, Guolei; Chen, Yanxue; Kang, Shishou; Yan, Shishen; Mei, Liangmo; Wang, Xiaolin

    2017-02-01

    Magnetic doping of semiconductors has been actively pursued because of their potential applications in the spintronic devices. Central to these efforts is a drive to control the mutual interactions between their magnetic properties (supported by d electrons of the magnetic ions) and their semiconductor properties (supported by s and/or p electrons) at room temperature (RT). Despite the long, intensive efforts, the experimental evidence of thermally robust s, p-d coupling in a semiconductor remains scarce and controversial. Here, we report the enhancement of RT ferromagnetic s, p-d exchange interaction by means of carrier doping in single crystalline Co0.4Zn0.6O epitaxial films with a high Co concentration. Magneto-transport measurements reveal that spin-polarized conducting carriers are produced at RT and are increased with the carrier density through Ga3+ doping, owing to the s, p-d coupling between Ga (4s), O (2p), and Co (3d) orbitals. With the ability to individually control carrier density and magnetic doping, single crystalline Ga(Co, Zn)O films can lay a solid foundation for the development of practical semiconductor spintronic devices operable at RT.

  12. Layer-by-layer growth of SrFeO 3- δ thin films on atomically flat single-terminated SrRuO 3/SrTiO 3 (111) surfaces

    NASA Astrophysics Data System (ADS)

    Chang, Jaewan; Lee, Jong-Woo; Kim, Sang-Koog

    2010-02-01

    We successfully grew SrFeO 3- δ thin films in a layer-by-layer manner by pulsed laser deposition (PLD). When the SrFeO 3- δ films were directly grown on atomically flat Ti 4+-terminated SrTiO 3 (1 1 1) substrates, the oscillatory reflection-high-energy-electron-diffraction intensity was completely damped after its third oscillation. By contrast, the introduction of SrRuO 3 buffer layers onto the SrTiO 3 substrates allowed the SFO thin films to grow in a layer-by-layer manner over a far-extended thickness range. The probable mechanism of that growth is electronic reconstruction-reduced electrostatic potential divergence. With that result, the present study provides a means of growing pseudocubic (1 1 1)-oriented SrFeO 3- δ heterointerfaces, making possible the fabrication of high-functionality oxide heterostructures.

  13. Epitaxial silicene formed on single-crystalline ZrB2 thin films: structure and electronic properties

    NASA Astrophysics Data System (ADS)

    Fleurence, Antoine; Friedlein, Rainer; Wang, Ying; Yamada-Takamura, Yukiko

    2011-03-01

    The experimental realization of extended, two-dimensional sheets of silicene, the silicon counterpart of graphene, has been elusive so far. Here, we demonstrate that such a two-dimensional, epitaxial honeycomb Si layer forms through surface segregation on a metallic zirconium diboride (Zr B2) film grown itself epitaxially on Si(111). The honeycomb Si layer uniformly covers the Zr B2 (0001) surface forming a (2 × 2) reconstruction. Surface-sensitive core-level photoelectron spectroscopy performed using a photon energy of 130 eV identifies Si atoms in different chemical states that are either in contact with Zr atoms or not, confirming details of the slightly-buckled honeycomb structure obtained through scanning tunneling microscopy. Angle-resolved ultraviolet photoelectron spectra reflect surface electronic states related to the predicted band structure of slightly-buckled, free standing silicene together with those of the uppermost Zr layer. Supported by Special Coordination Funds for Promoting Science and Technology, MEXT, and also by KAKENHI (22015008).

  14. Smoothing single-crystalline SiC surfaces by reactive ion etching using pure NF{sub 3} and NF{sub 3}/Ar mixture gas plasmas

    SciTech Connect

    Tasaka, Akimasa; Kotaka, Yuki; Oda, Atsushi; Saito, Morihiro; Tojo, Tetsuro; Inaba, Minoru

    2014-09-01

    In pure NF{sub 3} plasma, the etching rates of four kinds of single-crystalline SiC wafer etched at NF{sub 3} pressure of 2 Pa were the highest and it decreased with an increase in NF{sub 3} pressure. On the other hand, they increased with an increase in radio frequency (RF) power and were the highest at RF power of 200 W. A smooth surface was obtained on the single-crystalline 4H-SiC after reactive ion etching at NF{sub 3}/Ar gas pressure of 2 Pa and addition of Ar to NF{sub 3} plasma increased the smoothness of SiC surface. Scanning electron microscopy observation revealed that the number of pillars decreased with an increase in the Ar-concentration in the NF{sub 3}/Ar mixture gas. The roughness factor (R{sub a}) values were decreased from 51.5 nm to 25.5 nm for the As-cut SiC, from 0.25 nm to 0.20 nm for the Epi-SiC, from 5.0 nm to 0.7 nm for the Si-face mirror-polished SiC, and from 0.20 nm to 0.16 nm for the C-face mirror-polished SiC by adding 60% Ar to the NF{sub 3} gas. Both the R{sub a} values of the Epi- and the C-face mirror-polished wafer surfaces etched using the NF{sub 3}/Ar (40:60) plasma were similar to that treated with mirror polishing, so-called the Catalyst-Referred Etching (CARE) method, with which the lowest roughness of surface was obtained among the chemical mirror polishing methods. Etching duration for smoothing the single-crystalline SiC surface using its treatment was one third of that with the CARE method.

  15. Simultaneous presence of two different magnetic structures in a single-crystalline solid? Hydrogen-distribution-dependent magnetism.

    PubMed

    Koo, Hyun-Joo; Whangbo, Myung-Hwan

    2014-10-20

    In terms of density functional theory calculations, we explored the reason why the neutron diffraction patterns of a crystalline solid, NaFe2(H3O2)(MoO4)2, are explained by invoking the simultaneous presence of two widely different magnetic structures. The partitioning into OH and H2O groups of the "H3O2" units, which interconnect FeO4 chains in each [Fe2(H3O2)(MoO4)2](-) layer, leads to various layers different only in their H-atom positions. The crystal structure containing only symmetric FeO2(HO)(H2O) chains and that containing only asymmetric FeO4 chains are found to be responsible for the two observed magnetic structures.

  16. Van der Waals epitaxial growth of two-dimensional single-crystalline GaSe domains on graphene

    DOE PAGES

    Li, Xufan; Basile, Leonardo; Huang, Bing; ...

    2015-07-22

    Two-dimensional (2D) van der Waals (vdW) heterostructures are a family of artificially-structured materials that promise tunable optoelectronic properties for devices with enhanced functionalities. Compared to stamping, direct epitaxy of vdW heterostructures is ideal for clean interlayer interfaces and scalable device fabrication. Here, we explore the synthesis and preferred orientations of 2D GaSe atomic layers on graphene (Gr) by vdW epitaxy. Guided by the wrinkles on graphene, GaSe nuclei form that share a predominant lattice orientation. Due to vdW epitaxial growth many nuclei grow as perfectly aligned crystals and coalesce to form large (tens of microns), single-crystal flakes. Through theoretical investigationsmore » of interlayer energetics, and measurements of preferred orientations by atomic-resolution STEM and electron diffraction, a 10.9 interlayer rotation of the GaSe lattice with respect to the underlying graphene is found to be the most energetically preferred vdW heterostructure with the largest binding energy and the longest-range ordering. These GaSe/Gr vdW heterostructures exhibit an enhanced Raman E21g band of monolayer GaSe along with highly-quenched photoluminescence due to strong charge transfer. Despite the very large lattice mismatch of GaSe/Gr through vdW epitaxy, the predominant orientation control and convergent formation of large single-crystal flakes demonstrated here is promising for the scalable synthesis of large-area vdW heterostructures for the development of new optical and optoelectronic devices.« less

  17. Van der Waals epitaxial growth of two-dimensional single-crystalline GaSe domains on graphene

    SciTech Connect

    Li, Xufan; Basile, Leonardo; Huang, Bing; Ma, Cheng; Lee, Jaekwang; Vlassiouk, Ivan V.; Puretzky, Alexander A.; Lin, Ming -Wei; Chi, Miaofang; Idrobo Tapia, Juan Carlos; Rouleau, Christopher M.; Sumpter, Bobby G.; Yoon, Mina; Geohegan, David B.; Xiao, Kai

    2015-07-22

    Two-dimensional (2D) van der Waals (vdW) heterostructures are a family of artificially-structured materials that promise tunable optoelectronic properties for devices with enhanced functionalities. Compared to stamping, direct epitaxy of vdW heterostructures is ideal for clean interlayer interfaces and scalable device fabrication. Here, we explore the synthesis and preferred orientations of 2D GaSe atomic layers on graphene (Gr) by vdW epitaxy. Guided by the wrinkles on graphene, GaSe nuclei form that share a predominant lattice orientation. Due to vdW epitaxial growth many nuclei grow as perfectly aligned crystals and coalesce to form large (tens of microns), single-crystal flakes. Through theoretical investigations of interlayer energetics, and measurements of preferred orientations by atomic-resolution STEM and electron diffraction, a 10.9 interlayer rotation of the GaSe lattice with respect to the underlying graphene is found to be the most energetically preferred vdW heterostructure with the largest binding energy and the longest-range ordering. These GaSe/Gr vdW heterostructures exhibit an enhanced Raman E21g band of monolayer GaSe along with highly-quenched photoluminescence due to strong charge transfer. Despite the very large lattice mismatch of GaSe/Gr through vdW epitaxy, the predominant orientation control and convergent formation of large single-crystal flakes demonstrated here is promising for the scalable synthesis of large-area vdW heterostructures for the development of new optical and optoelectronic devices.

  18. A Single Step Lapping and Polishing Process for Achieving Surfaces of Compound Semiconductors with Atomic Flatness using a Sub-micron Agglomerate-free Alumina Slurry

    SciTech Connect

    P.S. Dutta; G. Rajagopalan; J.J. Gutmann; D. Keller; L. Sweet

    2002-08-29

    A novel approach for a single step lapping and final polishing of III-V and II-VI compounds using agglomerate-free alumina slurries has been developed. The agglomerate-free nature of the sub-micron slurry leads to removal rates comparable to conventional slurries (with larger particles of tens of microns) used for semiconductor lapping. Surfaces with minimal surface damage and extremely low surface roughness have been obtained using the sub-micron slurries and a soft pad. Strategies for post polishing surface cleaning have been discussed. The new methodology has been experimented on GaSb, InAs, GaAs, InP, InSb, CdTe, GaInSb, GaInAs, AlGaAsSb, GaInAsSb and HgCdTe. Selected results of surface analyses of GaSb and GaInSb using atomic force microscopy will be presented.

  19. Large magnetoresistance in single-crystalline Ni50Mn50-xInx alloys (x=14-16) upon martensitic transformation

    NASA Astrophysics Data System (ADS)

    Yu, S. Y.; Liu, Z. H.; Liu, G. D.; Chen, J. L.; Cao, Z. X.; Wu, G. H.; Zhang, B.; Zhang, X. X.

    2006-10-01

    Variation of electrical resistance in single-crystalline Ni50Mn50-xInx alloys (x=14-16) upon martensitic transformation was investigated. In Ni50Mn35In15 with Tm˜295K, a negative magnetoresistance (MR) over 60% is attainable at moderate field strengths; in Ni50Mn34In16 with Tm˜190K, the MR can exceed 70% over a temperature of approximately 100K. The significant change in electric resistance upon martensitic transformation originates primarily from the altered electronic structure, while the large effect of a magnetic field follows its ability to manipulate the transformation in materials of low Tm and large ΔM /ΔS. The extremely large MR promises more innovative applications for these important alloys.

  20. Single-crystalline α-Fe2O3 oblique nanoparallelepipeds: high-yield synthesis, growth mechanism and structure enhanced gas-sensing properties.

    PubMed

    Li, Xuelian; Wei, Wenjing; Wang, Shaozhen; Kuai, Long; Geng, Baoyou

    2011-02-01

    In this paper, single-crystalline α-Fe2O3 oblique nanoparallelepipeds are fabricated in high yield via a facile surfactant-free hydrothermal method, which involves oriented aggregation and Ostwald ripening. The obtained nanocrystals have exposed facets of {012}, {01-4} and {-210} with a rhombohedral α-Fe2O3 structure. The gas sensors based on the as-synthesized α-Fe2O3 nanostructures exhibit high sensitivity, short recovery time, and good reproducibility in ethanol and acetone. The superiority of the gas-sensing properties of the obtained nanostructures should be attributed to the surface structure of the nanocrystals. The as-prepared α-Fe2O3 nanocrystals are significant for exploiting their other applications in the future.

  1. Kinetics aspects of initial stage thin γ-Al2O3 film formation on single crystalline β-NiAl (110)

    NASA Astrophysics Data System (ADS)

    Zhang, Zhongfan; Jung, Keeyoung; Li, Long; Yang, Judith C.

    2012-02-01

    The growth kinetics and mechanisms of thermally-grown thin γ-Al2O3 film at 650 °C in air on single-crystalline β-NiAl (110) was characterized via transmission electron microscopy, X-ray diffractometry, and thermo-gravimetric analyses. The oxidation kinetics as a function of thickness was gradually changing from an inverse-logarithmic to parabolic behavior across the "intermediate thickness regime" as the oxide thickness increases. To define the boundaries of the three thickness regimes, the high field approximation (x1) and Debye-Hückel length (LD) were determined using the existing theoretical kinetics models combined with experimentally measured data. All the relevant constants for each rate law at the three thickness regimes were also experimentally determined to quantitatively describe the initial stage growth kinetics.

  2. Magnetic and Mössbauer characterization of the magnetic properties of single-crystalline sub-micron sized Bi₂Fe₄O₉ cubes

    SciTech Connect

    Papaefthymiou, Georgia C.; Wong, Stanislaus S.; Viescas, Arthur J.; Le Breton, Jean-Marie; Chiron, Hubert; Juraszek, Jean; Park, Tae-Jin

    2014-11-25

    Magnetic and Mössbauer characterization of single crystalline, sub-micron sized Bi₂Fe₄O₉ cubes has been performed using SQUID magnetometry and transmission Mössbauer spectroscopy in the temperature range of 4.2 K ≤ T ≤ 300 K. A broad magnetic phase transition from the paramagnetic to the anti-ferromagnetic state is observed below 250 K, with the Mössbauer spectra exhibiting a superposition of magnetic, collapsed and quadrupolar spectra in the transition region of 200 K < T < 245 K. Room temperature Mössbauer spectra obtained in transmission geometry are identical to those recorded in back-scattering geometry via conversion electron Mössbauer spectroscopy, indicating the absence of strain at the surface. A small hysteresis loop is observed in SQUID measurements at 5 K, attributable to the presence of weak-ferromagnetism arising from the canting of Fe³⁺ ion sublattices in the antiferromagnetic matrix.

  3. One-step fabrication of single-crystalline ZnS nanotubes with a novel hollow structure and large surface area for photodetector devices

    NASA Astrophysics Data System (ADS)

    An, Qinwei; Meng, Xianquan; Xiong, Ke; Qiu, Yunlei; Lin, Weihua

    2017-03-01

    ZnS nanotubes (NTs) were successfully prepared via a one-step thermal evaporation process without using any templates. The resulting NTs were single crystalline and structurally uniform. Based on experimental analysis, a tube-growth vapor-liquid-solid process was proposed as the growth mechanism of ZnS NTs. A metal-semiconductor-metal full-nanostructured ultraviolet (UV) photodetector with ZnS NTs as the active layer, and Ag nanowires of low resistivity and high transmissivity as electrodes, was fabricated and characterized. The ZnS NT-based device displayed a high I on/I off ratio of up to ˜1.56 × 105 with a high response to UV incident light at low operation voltage. This work is a meaningful exploration for preparing other one-dimensional semiconductor NTs, and developing a high-performance and power-saving UV sensor.

  4. Single crystalline Er{sub 2}O{sub 3}:sapphire films as potentially high-gain amplifiers at telecommunication wavelength

    SciTech Connect

    Kuznetsov, A. S.; Sadofev, S.; Schäfer, P.; Kalusniak, S.; Henneberger, F.

    2014-11-10

    Single crystalline thin films of Er{sub 2}O{sub 3}, demonstrating efficient 1.5 μm luminescence of Er{sup 3+} at room temperature were grown on Al{sub 2}O{sub 3} substrate by molecular beam epitaxy. The absorption coefficient at 1.536 μm was found to reach 270 cm{sup −1} translating in a maximal possible gain of 1390 dBcm{sup −1}. In conjunction with the 10% higher refractive index as compared to Al{sub 2}O{sub 3}, this opens the possibility to use Er{sub 2}O{sub 3}:sapphire films as short-length waveguide amplifiers in telecommunication.

  5. Template-directed synthesis of ordered single-crystalline nanowires arrays of Cu2ZnSnS4 and Cu2ZnSnSe4.

    PubMed

    Shi, Liang; Pei, Congjian; Xu, Yeming; Li, Quan

    2011-07-13

    Highly ordered quaternary semiconductor Cu(2)ZnSnS(4) nanowires array have been prepared via a facile solvothermal approach using anodic aluminum oxide (AAO) as a hard template. The as-prepared nanowires are uniform and single crystalline. They grow along either the crystalline [110] or [111] direction. The structure, morphology, composition, and optical absorption properties of the as-prepared Cu(2)ZnSnS(4) samples were characterized using X-ray powder diffraction, transmission electron microscopy, energy dispersive X-ray spectrometry, scanning electron microscopy, and UV-vis spectrometry. A possible formation mechanism of the nanowire arrays is proposed. Governed by similar mechanism, we show that Cu(2)ZnSnSe(4) nanowire array with similar structural characteristics can also be obtained.

  6. Fabrication of N-channel single crystalline silicon (100) thin-film transistors on glass substrate by meniscus force-mediated layer transfer technique

    NASA Astrophysics Data System (ADS)

    Akazawa, Muneki; Sakaike, Kohei; Nakamura, Shogo; Higashi, Seiichiro

    2014-10-01

    We propose a novel low-temperature layer transfer of single crystalline silicon (100) to glass substrate using meniscus force and midair cavity structure. Local transfer of thermally-oxidized silicon-on-insulator (SOI) layer to glass was successfully carried out at 80 °C. N-channel thin-film transistor (TFT) fabricated on glass at 300 °C showed a field-effect mobility of 1097 cm2 V-1 s-1, a threshold voltage of 1.1 V and a subthreshold swing value of 78 mV/dec. Raman scattering analysis suggests such a high mobility of TFT is originated from tensile strain introduced after gate SiO2 film deposition.

  7. Single crystalline Pr{sub 2-x}Y{sub x}O{sub 3} (x=0-2) dielectrics on Si with tailored electronic and crystallographic structure

    SciTech Connect

    Seifarth, O.; Schubert, M. A.; Giussani, A.; Schroeder, T.; Klenov, D. O.; Schmeisser, D.

    2010-11-15

    Crystalline oxides on Si with tailored electronic and crystallographic properties are of importance for the integration of functional oxides or alternative semiconductors to enable novel device concepts in Si microelectronics. We present an electronic band gap study of single crystalline Pr{sub 2-x}Y{sub x}O{sub 3} (0{<=}x{<=}2) heterostructures on Si(111). The perfect solubility of the isomorphic bixbyites Pr{sub 2}O{sub 3} and Y{sub 2}O{sub 3} during molecular beam epitaxy thin film growth on Si enables a linear band gap tuning. Special focus is devoted to the determination of the electronic band offsets across the dielectric/Si interface. In addition, the composition x allows to control the crystallographic lattice parameter where, for example, Pr{sub 0.8}Y{sub 1.2}O{sub 3} enables the growth of fully lattice matched oxide heterostructures on Si.

  8. Energy band structure of the single crystalline MgO/n-Ge(001) heterojunction determined by x-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Jeon, Kun-Rok; Lee, Sang-Jun; Park, Chang-Yup; Lee, Hun-Sung; Shin, Sung-Chul

    2010-09-01

    We report the energy band structure of the single crystalline MgO/n-Ge(001) heterojunction characterized by x-ray photoelectron spectroscopy. The valence band offset of ΔEV=3.64±0.07 eV with a 1.49±0.02 eV band bending was obtained. Given the experimental band gap of MgO (7.83 eV), a type-I band alignment with a conduction band offset of ΔEC=3.52±0.07 eV is found. The band alignment of the MgO/n-Ge heterojunction including the large band bending was analyzed by a theoretical model taking into account the formation of the interface dipole.

  9. Single-crystalline In2S3 nanowire-based flexible visible-light photodetectors with an ultra-high photoresponse.

    PubMed

    Xie, Xuming; Shen, Guozhen

    2015-03-21

    With a band gap of 2.28 eV, In2S3 is an excellent candidate for visible-light sensitive photodetectors. By growing single-crystalline In2S3 nanowires via a simple CVD method, we report the fabrication of high-performance single-crystal In2S3 nanowire-based flexible photodetectors. The as-fabricated flexible photodetectors exhibited an ultra-high Ion/Ioff ratio up to 10(6) and a high sensitivity to visible incident light with responsivity and quantum efficiency as high as 7.35 × 10(4) A W(-1) and 2.28 × 10(7)%, respectively. Besides, the flexible photodetectors were demonstrated to possess a robust flexibility and excellent stability. With these favorable merits, In2S3 nanowires are believed to have a promising future in the application of high performance and flexible integrated optoelectronic devices.

  10. Zero lattice mismatch and twin-free single crystalline ScN buffer layers for GaN growth on silicon

    SciTech Connect

    Lupina, L.; Zoellner, M. H.; Dietrich, B.; Capellini, G.; Niermann, T.; Lehmann, M.; Thapa, S. B.; Haeberlen, M.; Storck, P.; Schroeder, T.

    2015-11-16

    We report the growth of thin ScN layers deposited by plasma-assisted molecular beam epitaxy on Sc{sub 2}O{sub 3}/Y{sub 2}O{sub 3}/Si(111) substrates. Using x-ray diffraction, Raman spectroscopy, and transmission electron microscopy, we find that ScN films grown at 600 °C are single crystalline, twin-free with rock-salt crystal structure, and exhibit a direct optical band gap of 2.2 eV. A high degree of crystalline perfection and a very good lattice matching between ScN and GaN (misfit < 0.1%) makes the ScN/Sc{sub 2}O{sub 3}/Y{sub 2}O{sub 3} buffer system a very promising template for the growth of high quality GaN layers on silicon.

  11. Single-crystalline hyperbranched nanostructure of iron hydroxyl phosphate Fe5(PO4)4(OH)3·2H2O for highly selective capture of phosphopeptides.

    PubMed

    Chen, Qun; Wei, Chengzhen; Zhang, Yizhou; Pang, Huan; Lu, Qingyi; Gao, Feng

    2014-01-17

    Single-crystalline hyperbranched nanostructures of iron hydroxyl phosphate Fe5(PO4)4(OH)3·2H2O (giniite) with orthorhombic phase were synthesized through a simple route. They have a well-defined dendrite fractal structure with a pronounced trunk and highly ordered branches. The toxicity test shows that the hyperbranched nanostructures have good biocompatibility and low toxicity level, which makes them have application potentials in life science. The study herein demonstrated that the obtained hyperbranched giniite nanostructures show highly selective capture of phosphopeptides and could be used as a kind of promising nanomaterial for the specific capture of phosphopeptides from complex tryptic digests with the detection of MALDI-TOF mass spectrometry.

  12. Single-Crystalline Hyperbranched Nanostructure of Iron Hydroxyl Phosphate Fe5(PO4)4(OH)3·2H2O for Highly Selective Capture of Phosphopeptides

    PubMed Central

    Chen, Qun; Wei, Chengzhen; Zhang, Yizhou; Pang, Huan; Lu, Qingyi; Gao, Feng

    2014-01-01

    Single-crystalline hyperbranched nanostructures of iron hydroxyl phosphate Fe5(PO4)4(OH)3·2H2O (giniite) with orthorhombic phase were synthesized through a simple route. They have a well-defined dendrite fractal structure with a pronounced trunk and highly ordered branches. The toxicity test shows that the hyperbranched nanostructures have good biocompatibility and low toxicity level, which makes them have application potentials in life science. The study herein demonstrated that the obtained hyperbranched giniite nanostructures show highly selective capture of phosphopeptides and could be used as a kind of promising nanomaterial for the specific capture of phosphopeptides from complex tryptic digests with the detection of MALDI-TOF mass spectrometry. PMID:24435094

  13. Detection and imaging of the oxygen deficiency in single crystalline YBa2Cu3O7-δ thin films using a scanning positron beam

    NASA Astrophysics Data System (ADS)

    Reiner, M.; Gigl, T.; Jany, R.; Hammerl, G.; Hugenschmidt, C.

    2015-03-01

    Single crystalline YBa2Cu3O7-δ (YBCO) thin films were grown by pulsed laser deposition in order to probe the oxygen deficiency δ using a mono-energetic positron beam. The sample set covered a large range of δ (0.191 < δ < 0.791) yielding a variation of the critical temperature Tc between 25 and 90 K. We found a linear correlation between the Doppler broadening of the positron electron annihilation line and δ determined by X-ray diffraction. Ab-initio calculations have been performed in order to exclude the presence of Y vacancies and to ensure the negligible influence of potentially present Ba or Cu vacancies to the found correlation. Moreover, scanning with the positron beam allowed us to analyze the spatial variation of δ, which was found to fluctuate with a standard deviation of up to 0.079(5) within a single YBCO film.

  14. Synthesis and characterization of structural and optical properties of single crystalline a-TiO2 films on MgAl2O4(111) substrate

    NASA Astrophysics Data System (ADS)

    Xu, Haisheng; Feng, Xianjin; Luan, Caina; Ma, Jin

    2017-01-01

    Anatase phase TiO2 (a-TiO2) films have been deposited on MgAl2O4(111) substrates by the metal organic chemical vapor deposition (MOCVD) method at the substrate temperatures of 500-650°C. The structural analyses showed that the films were highly (004) oriented with tetragonal anatase structure and the epitaxial relationship was given as a-TiO2(004)||MgAl2O4 (111). The sample prepared at 600°C exhibited the best crystallization with a single-crystalline epitaxial film. The average transmittance of every TiO2 film in the visible range exceeded 90% excluding the influence of the substrate. The morphology and composition of the TiO2 films have also been studied in detail.

  15. Growth and luminescent properties of Lu 2SiO 5 and Lu 2SiO 5:Ce single crystalline films

    NASA Astrophysics Data System (ADS)

    Zorenko, Yu.; Nikl, M.; Gorbenko, V.; Savchyn, V.; Voznyak, T.; Kucerkova, R.; Sidletskiy, O.; Grynyov, B.; Fedorov, A.

    2011-04-01

    Single crystalline films (SCF) of Lu 2SiO 5 (LSO) and Lu 2SiO 5:Ce (LSO:Ce) silicates with thickness of 2.5-15 μm were crystallized by liquid phase epitaxy method onto undoped LSO substrates from melt-solution based on PbO-B 2O 3 flux. The scintillation and luminescence properties of LSO:Ce SCF were compared with the properties of LSO:Ce single crystal. The peculiarities of luminescence properties of LSO:Ce SCF in comparison with crystal analog can be due to different distribution of Ce 3+ over the Lu1 and Lu2 positions of LSO host and are further influenced by Pb 2+ flux-originated contamination.

  16. Hetero-epitaxial growth of the cubic single crystalline HfO 2 film as high k materials by pulsed laser ablation

    NASA Astrophysics Data System (ADS)

    Zhang, Xinqiang; Tu, Hailing; Wang, Xiaona; Xiong, Yuhua; Yang, Mengmeng; Wang, Lei; Du, Jun

    2010-10-01

    We report a hetero-epitaxial growth of cubic single crystalline HfO 2 film on Si substrates as high k materials by pulse laser ablation (PLA) at 820 °C. To eliminate the interfacial defects, the HfO 2 film has then been annealed at 900 °C for 5 min in N 2. Reflection high-energy electron diffraction (RHEED) results indicate orientation of the HfO 2 film on Si substrates corresponding to (∥( and [∥[. An interface layer has been revealed by high-resolution transmission electron microscope (HRTEM). Through capacitance-voltage ( C- V) and current-voltage ( I- V), it has been obtained that the leakage current of the HfO 2 gate insulator with dielectric constant of 26 is 5×10 -6 A/cm 2 at -1 V.

  17. Local and long-range order and the influence of applied magnetic field on single-crystalline NiSb2O6

    NASA Astrophysics Data System (ADS)

    Christian, A. B.; Hunt, C. D.; Neumeier, J. J.

    2017-07-01

    The magnetic and thermal properties of single-crystalline NiSb2O6 are reported. The Ni2 + ions exhibit local magnetic order below ˜50 K followed by long-range antiferromagnetic order below TN=6.7 K. Analysis of the magnetic susceptibility data using the one-dimensional Heisenberg model with spin S =1 results in a magnetic exchange coupling J||/kB˜26.0 (1 ) K. TN is observed to either increase or decrease depending on whether field is applied perpendicular or parallel to the magnetic moment axis. A two-sublattice magnetic structure, with the axis of alignment alternating by 90 ∘ between neighboring layers along the crystallographic c axis, is argued to result in two magnetic transition temperatures for certain magnetic field directions, which agrees well with theory. This leads to a highly anisotropic magnetocaloric effect.

  18. A simple self-assembly route to single crystalline SnO2 nanorod growth by oriented attachment for dye sensitized solar cells.

    PubMed

    Song, Hui; Lee, Kwang-Ho; Jeong, Huisu; Um, Soong Ho; Han, Gil-Sang; Jung, Hyun Suk; Jung, Gun Young

    2013-02-07

    One-dimensional (1-D) SnO(2) nanorods (NRs) with a rutile structure are grown on various substrates regardless of the lattice-mismatch by using a new nutrient solution based on tin oxalate, which generated supersaturated Sn(2+) sources. These affluent sources are appropriate for producing a large number of SnO(2) nanoparticles, sufficient for stacking on a substrate surface by gravity, which then acts as a seed layer for subsequent nanorod growth. Single crystalline nanorods are grown along the [001] direction by the oriented attachment phenomenon in which the attached nanoparticles were rearranged to reduce the overall surface energy through sharing thermodynamically unstable crystal (001) planes. Furthermore, the grown SnO(2) NRs are covered with a TiO(2) particulate film and utilized as a photoanode in DSSCs. The power conversion efficiency is 8.61%, enhanced by 14.2% compared to the photoanode with only a TiO(2) particulate film.

  19. Stabilization and acidic dissolution mechanism of single-crystalline ZnO(0001) surfaces in electrolytes studied by in-situ AFM imaging and ex-situ LEED.

    PubMed

    Valtiner, Markus; Borodin, Sergiy; Grundmeier, Guido

    2008-05-20

    A combined approach of pH-dependent in-situ AFM topography and ex-situ LEED studies of the stability and dissolution of single-crystalline ZnO(0001)-Zn surfaces in aqueous media is presented. Hydroxide-stabilized and single-crystalline ZnO(0001)-Zn surfaces turned out to be stable within a wide pH range between 11 and 4 around the point of zero charge of pH PZC = 8.7 +/- 0.2. Hydroxide stabilization turned out to be a very effective stabilization mechanism for polar oxide surfaces in electrolyte solutions. The dissolution of the oxide surface started at an acidic pH level of 5.5 and occurred selectively at the pre-existing step edges, which consist of nonpolar surfaces. In comparison, the oxide dissolution along the ZnO(0001) direction proved to be effectively inhibited above a pH value of 3.8. On the basis of these microscopic observations, the mechanistic understanding of the acidic dissolution process of ZnO could be supported. Moreover, both the in-situ AFM and the ex-situ LEED studies showed that the stabilization mechanism of the ZnO(0001) surfaces changes in acidic electrolytes. At pH values below 3.8, the hydroxide-stabilized surface is destabilized by dissolution of the well-ordered radical3. radical3. R30 hydroxide ad-layer as proven by LEED. Restabilization occurs and leads to the formation of triangular nanoterraces with a specific edge termination. However, below pH 4 the surface structure of the crystal itself is ill-defined on the macroscopic scale because preferable etching along crystal defects as dislocations into the bulk oxide results in very deep hexagonal etching pits.

  20. Sub-micron free-standing metal slabs with dielectric nano-voids of arbitrary shapes embedded beneath atomically-flat surface.

    PubMed

    Kho, Kiang Wei; Shen, Zexiang; Olivo, Malini

    2011-05-23

    Thin metal slabs with plasmonic nano-voids buried within the skin depth (< 25 nm) of surface plasmon polaritons have been of theoretical as well as technical interests for many years due to its unique optical properties such as sharp absorbance dips and anti-crossing plasmonic dispersion characteristics. Unfortunately, such interesting plasmonic properties have not been experimentally reproduced, especially in the UV-Vis regime, owing to the involuntary surface roughness occurred in systems fabricated using conventional techniques. Here, we describe a versatile cryogenic-stripping approach for encapsulating a monolayer of nano-voids of virtually any arbitrary shapes underneath an atomically-smooth (δ < 0.55 nm) surface of a free-standing metal slab. By artificially varying the topography of the capping metal surface from ultra-smooth to moderately-rough, we show structural symmetricity in a nano-void-metal system can render the overall plasmonic responses becoming profoundly influenced by the surface smoothness. The current fabrication technique is thus of primary importance to the preparation of any kind of smooth nano-void-passivated metal slabs.

  1. One-pot high-yield synthesis of single-crystalline gold nanorods using glycerol as a low-cost and eco-friendly reducing agent

    NASA Astrophysics Data System (ADS)

    Parveen, Rashida; Gomes, Janaina F.; Ullah, Sajjad; Acuña, José J. S.; Tremiliosi-Filho, Germano

    2015-10-01

    The formation of gold nanorods (AuNRs) has recently attracted great attention due to their shape-dependent optical properties that are important for many applications. The development of simpler and safer methods for the high-yield synthesis of AuNRs employing low-cost and easily handled reagents is thus of great importance. Here, we introduce, for the first time, a one-pot seedless method for the preparation of single-crystalline AuNRs in almost 100 % yield based on the use of glycerol in alkaline medium as an eco-friendly, low-cost and pH-tunable reducing agent. The synthesized AuNRs were characterized by UV-Vis-NIR spectroscopy, FEG-SEM and HRTEM. The effect of the presence of capping agent (CTAB) and the concentration of reactants (glycerol, NaOH and AgNO3) on the yield and aspect ratio (AR) of AuNRs is discussed. The AR and yield of AuNRs showed a clear dependence on the pH and temperature of the reaction mixture as well as on the concentration of AgNO3 added as an auxiliary reagent. The longitudinal plasmon resonance band of the resulting AuNRs can be tuned between 620 and 1200 nm by varying the reaction conditions. AuNRs with an aspect ratio (AR) of around 4 were obtained in almost 100 % yield at room temperature and under mild reducing environment. The formation of AuNRs is faster at higher pH (>11) and higher temperature (>30 °C), but the AuNR yield is smaller (<70 %). Variation in the pH of the reaction mixture in the range 12-13.5 results in the formation of AuNRs with different ARs and in different yields (27-99 %). Detailed study of the AuNRs crystallography by HRTEM showed that the AuNRs grow in [001] direction and have a perfect single-crystalline fcc structure, free from structural faults or dislocations. The present green method, which introduces glycerol as a tunable reducing agent with a pH-dependent reducing power, can provide a more general strategy for the preparation of a wide range of metallic nanoparticles.

  2. Single-crystalline In2S3 nanowire-based flexible visible-light photodetectors with an ultra-high photoresponse

    NASA Astrophysics Data System (ADS)

    Xie, Xuming; Shen, Guozhen

    2015-03-01

    With a band gap of 2.28 eV, In2S3 is an excellent candidate for visible-light sensitive photodetectors. By growing single-crystalline In2S3 nanowires via a simple CVD method, we report the fabrication of high-performance single-crystal In2S3 nanowire-based flexible photodetectors. The as-fabricated flexible photodetectors exhibited an ultra-high Ion/Ioff ratio up to 106 and a high sensitivity to visible incident light with responsivity and quantum efficiency as high as 7.35 × 104 A W-1 and 2.28 × 107%, respectively. Besides, the flexible photodetectors were demonstrated to possess a robust flexibility and excellent stability. With these favorable merits, In2S3 nanowires are believed to have a promising future in the application of high performance and flexible integrated optoelectronic devices.With a band gap of 2.28 eV, In2S3 is an excellent candidate for visible-light sensitive photodetectors. By growing single-crystalline In2S3 nanowires via a simple CVD method, we report the fabrication of high-performance single-crystal In2S3 nanowire-based flexible photodetectors. The as-fabricated flexible photodetectors exhibited an ultra-high Ion/Ioff ratio up to 106 and a high sensitivity to visible incident light with responsivity and quantum efficiency as high as 7.35 × 104 A W-1 and 2.28 × 107%, respectively. Besides, the flexible photodetectors were demonstrated to possess a robust flexibility and excellent stability. With these favorable merits, In2S3 nanowires are believed to have a promising future in the application of high performance and flexible integrated optoelectronic devices. Electronic supplementary information (ESI) available: XRD pattern, SEM image of the back gate FETs, Electronic transport properties, and I-V curves of the device in dark. See DOI: 10.1039/c5nr00410a

  3. Single-Crystalline Gold Nanowires Synthesized from Light-Driven Oriented Attachment and Plasmon-Mediated Self-Assembly of Gold Nanorods or Nanoparticles.

    PubMed

    Yu, Shang-Yang; Gunawan, Hariyanto; Tsai, Shiao-Wen; Chen, Yun-Ju; Yen, Tzu-Chen; Liaw, Jiunn-Woei

    2017-03-16

    Through the light-driven geometrically oriented attachment (OA) and self-assembly of Au nanorods (NRs) or nanoparticles (NPs), single-crystalline Au nanowires (NWs) were synthesized by the irradiation of a linearly-polarized (LP) laser. The process was conducted in a droplet of Au colloid on a glass irradiated by LP near-infrared (e.g. 1064 nm and 785 nm) laser beam of low power at room temperature and atmospheric pressure, without any additive. The FE-SEM images show that the cross sections of NWs are various: tetragonal, pentagonal or hexagonal. The EDS spectrum verifies the composition is Au, and the pattern of X-ray diffraction identifies the crystallinity of NWs with the facets of {111}, {200}, {220} and {311}. We proposed a hypothesis for the mechanism that the primary building units are aligned and coalesced by the plasmon-mediated optical torque and force to form the secondary building units. Subsequently, the secondary building units undergo the next self-assembly, and so forth the tertiary ones. The LP light guides the translational and rotational motions of these building units to perform geometrically OA in the side-by-side, end-to-end and T-shaped manners. Consequently, micron-sized ordered mesocrystals are produced. Additionally, the concomitant plasmonic heating causes the annealing for recrystallizing the mesocrystals in water.

  4. Growth of aligned single-crystalline rutile TiO2 nanowires on arbitrary substrates and their application in dye-sensitized solar cells

    SciTech Connect

    Kumar, Akshay; Madaria, Anuj R.; Zhou, Chongwu

    2010-05-06

    TiO{sub 2} is a wide band gap semiconductor with important applications in photovoltaic cells and photocatalysis. In this paper, we report synthesis of single-crystalline rutile phase TiO{sub 2} nanowires on arbitrary substrates, including fluorine-doped tin oxide (FTO), glass slides, tin-doped indium oxide (ITO), Si/SiO{sub 2}, Si(100), Si(111), and glass rods. By controlling the growth parameters such as growth temperature, precursor concentrations, and so forth, we demonstrate that anisotropic growth of TiO{sub 2} is possible leading to various morphologies of nanowires. Optimization of the growth recipe leads to well-aligned vertical array of TiO{sub 2} nanowires on both FTO and glass substrates. Effects of various titanium precursors on the growth kinetics, especially on the growth rate of nanowires, are also studied. Finally, application of vertical array of TiO{sub 2} nanowires on FTO as the photoanode is demonstrated in dye-sensitized solar cell with an efficiency of 2.9 ± 0.2%.

  5. One-pot synthesis of uniform hollow cuprous oxide spheres fabricated by single-crystalline particles via a simple solvothermal route

    NASA Astrophysics Data System (ADS)

    Li, Shi-Kuo; Li, Chuan-Hao; Huang, Fang-Zhi; Wang, Yang; Shen, Yu-Hua; Xie, An-Jian; Wu, Qiong

    2011-07-01

    Uniform Cu2O hollow spheres fabricated by single-crystalline particles (smaller than 20 nm) are facile synthesized in ethylene glycol (EG) solution by a simple solvothermal route without using pre-fabricated templates and reductive agents. EG in this protocol is not only used as a solvent, complexing agent, and reducing agent, but also served as a structure-directing agent for the formation of hollow structure. By control of reaction conditions, such as reaction time, temperature, and the anions, the morphology and structure of the hollow spheres can be tuned. A coordination adsorption and oriented attachment and Ostwald ripening mechanism is proposed for explaining the formation process of hollow Cu2O spheres in EG solution; and importantly, the hollow Cu2O spheres exhibit an excellent property for the electro-catalytic oxidization of ascorbic acid in acetic acid buffer solution. Moreover, the hollow spherical Cu2O particles could be potentially applied in catalysis, sensor, and as model for fundamental research.

  6. Progress on First-Principles Calculations and Experimental Results of Single-crystalline Magnetic Tunnel Junctions with MgO barriers

    SciTech Connect

    Wang, Y.; Zhang, J.; Zhang, Xiaoguang; Wang, Shouguo; Han, Xiufeng

    2009-01-01

    Since the theoretical prediction and experimental observation of giant tunneling magnetoresistance (TMR) effect at room temperature in magnetic tunnel junctions (MTJs) with single-crystalline MgO(001) barrier, MgO-based MTJs have been extensively studied due to their broad potential applications in spintronic devices. In this paper, progress on theoretical calculations and experimental results in MgO-based MTJs is reported. Spin-dependent electronic structure and transport properties of MgO-based MTJs, including structures of Fe(001)/MgO/Fe, Fe(001)/FeO/MgO/Fe, Fe(001)/Mg/MgO/Fe, Fe(001)/Co/MgO/Co/Fe, and Fe(001)/MgO/Fe/MgO/Fe, have been studied using the Layer-KKR first-principles method. The quantitative result not only provide a better way to understand the electronic structures and spin-dependent transport properties of MgO-based MTJs, but also shows a direction to exploit new kinds of spintronic materials with high room-temperature TMR ratio.

  7. Hydrothermal fabrication of quasi-one-dimensional single-crystalline anatase TiO2 nanostructures on FTO glass and their applications in dye-sensitized solar cells.

    PubMed

    Liao, Jin-Yun; Lei, Bing-Xin; Wang, Yu-Fen; Liu, Jun-Min; Su, Cheng-Yong; Kuang, Dai-Bin

    2011-01-24

    One-dimensional and quasi-one-dimensional semiconductor nanostructures are desirable for dye-sensitized solar cells (DSSCs), since they can provide direct pathways for the rapid collection of photogenerated electrons, which could improve the photovoltaic performance of the device. Quasi-1D single-crystalline anatase TiO(2) nanostructures have been successfully prepared on transparent, conductive fluorine-doped tin oxide (FTO) glass with a growth direction of [101] through a facile hydrothermal approach. The influences of the initial titanium n-butoxide (TBT) concentration, hydrothermal reaction temperature, and time on the length of quasi-1D anatase TiO(2) nanostructures and on the photovoltaic performance of DSSCs have been investigated in detail. A power conversion efficiency of 5.81% has been obtained based on the prepared TiO(2) nanostructure photoelectrode 6.7 μm thick and commercial N719 dye, with a short-circuit current density of 13.3 mA cm(-2) , an open-circuit voltage of 810 mV, and a fill factor of 0.54. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Highly Ordered Single Crystalline Nanowire Array Assembled Three-Dimensional Nb3O7(OH) and Nb2O5 Superstructures for Energy Storage and Conversion Applications.

    PubMed

    Zhang, Haimin; Wang, Yun; Liu, Porun; Chou, Shu Lei; Wang, Jia Zhao; Liu, Hongwei; Wang, Guozhong; Zhao, Huijun

    2016-01-26

    Three-dimensional (3D) metal oxide superstructures have demonstrated great potentials for structure-dependent energy storage and conversion applications. Here, we reported a facile hydrothermal method for direct growth of highly ordered single crystalline nanowire array assembled 3D orthorhombic Nb3O7(OH) superstructures and their subsequent thermal transformation into monoclinic Nb2O5 with well preserved 3D nanowire superstructures. The performance of resultant 3D Nb3O7(OH) and Nb2O5 superstructures differed remarkably when used for energy conversion and storage applications. The thermally converted Nb2O5 superstructures as anode material of lithium-ion batteries (LiBs) showed higher capacity and excellent cycling stability compared to the Nb3O7(OH) superstructures, while directly hydrothermal grown Nb3O7(OH) nanowire superstructure film on FTO substrate as photoanode of dye-sensitized solar cells (DSSCs) without the need for further calcination exhibited an overall light conversion efficiency of 6.38%, higher than that (5.87%) of DSSCs made from the thermally converted Nb2O5 film. The high energy application performance of the niobium-based nanowire superstructures with different chemical compositions can be attributed to their large surface area, superior electron transport property, and high light utilization efficiency resulting from a 3D superstructure, high crystallinity, and large sizes. The formation process of 3D nanowire superstructures before and after thermal treatment was investigated and discussed based on our theoretical and experimental results.

  9. Meniscus-force-mediated layer transfer technique using single-crystalline silicon films with midair cavity: Application to fabrication of CMOS transistors on plastic substrates

    NASA Astrophysics Data System (ADS)

    Sakaike, Kohei; Akazawa, Muneki; Nakagawa, Akitoshi; Higashi, Seiichiro

    2015-04-01

    A novel low-temperature technique for transferring a silicon-on-insulator (SOI) layer with a midair cavity (supported by narrow SiO2 columns) by meniscus force has been proposed, and a single-crystalline Si (c-Si) film with a midair cavity formed in dog-bone shape was successfully transferred to a poly(ethylene terephthalate) (PET) substrate at its heatproof temperature or lower. By applying this proposed transfer technique, high-performance c-Si-based complementary metal-oxide-semiconductor (CMOS) transistors were successfully fabricated on the PET substrate. The key processes are the thermal oxidation and subsequent hydrogen annealing of the SOI layer on the midair cavity. These processes ensure a good MOS interface, and the SiO2 layer works as a “blocking” layer that blocks contamination from PET. The fabricated n- and p-channel c-Si thin-film transistors (TFTs) on the PET substrate showed field-effect mobilities of 568 and 103 cm2 V-1 s-1, respectively.

  10. Influences of guide-tube and bluff-body on advanced atmospheric pressure plasma source for single-crystalline polymer nanoparticle synthesis at low temperature

    NASA Astrophysics Data System (ADS)

    Kim, Dong Ha; Park, Choon-Sang; Kim, Won Hyun; Shin, Bhum Jae; Hong, Jung Goo; Park, Tae Seon; Seo, Jeong Hyun; Tae, Heung-Sik

    2017-02-01

    The use of a guide-tube and bluff-body with an advanced atmospheric pressure plasma source is investigated for the low-temperature synthesis of single-crystalline high-density plasma polymerized pyrrole (pPPy) nano-materials on glass and flexible substrates. Three process parameters, including the position of the bluff-body, Ar gas flow rate, and remoteness of the substrate from the intense and broadened plasma, are varied and examined in detail. Plus, for an in-depth understanding of the flow structure development with the guide-tube and bluff-body, various numerical simulations are also conducted using the same geometric conditions as the experiments. As a result, depending on both the position of the bluff-body and the Ar gas flow rate, an intense and broadened plasma as a glow-like discharge was produced in a large area. The production of the glow-like discharge played a significant role in increasing the plasma energy required for full cracking of the monomers in the nucleation region. Furthermore, a remote growth condition was another critical process parameter for minimizing the etching and thermal damage during the plasma polymerization, resulting in single- and poly-crystalline pPPy nanoparticles at a low temperature with the proposed atmospheric pressure plasma jet device.

  11. Growth and shape control of orthorhombic Fe 5(PO 4) 4(OH) 3·2H 2O single crystalline dendrites

    NASA Astrophysics Data System (ADS)

    Li, Guicun; Zhang, Shuai; Peng, Hongrui; Chen, Kezheng

    2010-10-01

    Orthorhombic Fe 5(PO 4) 4(OH) 3·2H 2O single crystalline dendritic nanostructures have been synthesized by a facile and reproducible hydrothermal method without the aid of any surfactants. The influences of synthetic parameters, such as reaction time, temperature, the amount of H 2O 2 solution, pH values, and types of iron precursors, on the crystal structures and morphologies of the resulting products have been investigated. The formation process of Fe 5(PO 4) 4(OH) 3·2H 2O dendritic nanostructures is time dependent: amorphous FePO 4· nH 2O nanoparticles are formed firstly, and then Fe 5(PO 4) 4(OH) 3·2H 2O dendrites are assembled via a crystallization-orientation attachment process, accompanying a color change from yellow to green. The shapes and sizes of Fe 5(PO 4) 4(OH) 3·2H 2O products can be controlled by adjusting the amount of H 2O 2 solution, pH values, and types of iron precursors in the reaction system.

  12. Single-Crystalline Gold Nanowires Synthesized from Light-Driven Oriented Attachment and Plasmon-Mediated Self-Assembly of Gold Nanorods or Nanoparticles

    NASA Astrophysics Data System (ADS)

    Yu, Shang-Yang; Gunawan, Hariyanto; Tsai, Shiao-Wen; Chen, Yun-Ju; Yen, Tzu-Chen; Liaw, Jiunn-Woei

    2017-03-01

    Through the light-driven geometrically oriented attachment (OA) and self-assembly of Au nanorods (NRs) or nanoparticles (NPs), single-crystalline Au nanowires (NWs) were synthesized by the irradiation of a linearly-polarized (LP) laser. The process was conducted in a droplet of Au colloid on a glass irradiated by LP near-infrared (e.g. 1064 nm and 785 nm) laser beam of low power at room temperature and atmospheric pressure, without any additive. The FE-SEM images show that the cross sections of NWs are various: tetragonal, pentagonal or hexagonal. The EDS spectrum verifies the composition is Au, and the pattern of X-ray diffraction identifies the crystallinity of NWs with the facets of {111}, {200}, {220} and {311}. We proposed a hypothesis for the mechanism that the primary building units are aligned and coalesced by the plasmon-mediated optical torque and force to form the secondary building units. Subsequently, the secondary building units undergo the next self-assembly, and so forth the tertiary ones. The LP light guides the translational and rotational motions of these building units to perform geometrically OA in the side-by-side, end-to-end and T-shaped manners. Consequently, micron-sized ordered mesocrystals are produced. Additionally, the concomitant plasmonic heating causes the annealing for recrystallizing the mesocrystals in water.

  13. Front Side Metallization of n- and p-Type, High-Efficiency, Single-Crystalline Si Solar Cells: Assessing the Temperature-Dependent Series Resistance

    NASA Astrophysics Data System (ADS)

    Willsch, Benjamin; Kumar, Praveen; Eibl, Oliver

    2016-06-01

    The series resistance of high-quality, single crystalline p-type and n-type solar cells was measured in a temperature range between 80 K and room temperature. Among one cell type ( n or p), cells were processed identically. Only the processing of the front side metallization was varied by using different processing conditions and screen printing pastes. High-efficiency n- ( η = 20.0%) and p-type ( η = 18.0%) cells yielded similar contact and series resistance and common features of the microstructure of the front side contact, i.e. a glass layer containing Ag colloids with typical diameters of 5-200 nm. Temperature-dependent current voltage curves ( I- V curves) were acquired and evaluated with respect to the series resistance by using two different methods yielding different results. On average the series resistance follows the trends of the contact resistance of the front side metallization determined at room temperature. Optimally processed cells yielded series resistances of less than 25 mΩ cm2 (method #1) both for n- and p-type cells. It could be shown that the series resistance reflected the processing conditions and paste properties and yielded similar temperature dependence for p- and n-type cells with small contact resistance. Therefore, the relevant current paths of high-efficiency n- and p-type cells appear to be similar in the front side metallization and include the glass layer which contains a high density of Ag colloids.

  14. Single-crystalline Bi2Sr2CaCu2O8+x detectors for direct detection of microwave radiation

    NASA Astrophysics Data System (ADS)

    Li, M.; Winkler, D.; Yurgens, A.

    2015-04-01

    We test radiation detectors made from single-crystalline Bi2Sr2CaCu2O8+x flakes put on oxidized Si substrates. The 100-nm-thick flakes are lithographically patterned into 4 ×12 μm2 large rectangles embedded in thin-film log-spiral antennas. The SiO2 layer weakens the thermal link between the flakes and the bath. Two modes of radiation detection have been observed. For a bolometric type of sensors a responsivity of ˜300 V/W and a noise equivalent power of 30 nW/ √{Hz } has been deduced at 70 K. Much more sensitive is the non-bolometric device showing characteristics similar to a Golay-type detector while being at least a thousand times faster. Making smaller (sub-μm) structures is expected to significantly improve the performance of these devices and makes them very competitive among other microwave and terahertz detectors.

  15. Low-temperature growth and characterization of single crystalline ZnO nanorod arrays using a catalyst-free inductively coupled plasma-metal organic chemical vapor deposition.

    PubMed

    Jeong, Sang-Hun; Lee, Chang-Bae; Moon, Won-Jin; Song, Ho-Jun

    2008-10-01

    Vertically aligned ZnO nanorod arrays have been synthesized on c-plane sapphires at a low temperature of 400 degrees C using catalyst-free inductively coupled plasma (ICP) metal organic chemical vapor deposition (MOCVD) technique by varying the ICP powers. Diameters of the ZnO nanorods changed from 200 nm to 400 nm as the ICP power increased from 200 to 400 Watt. TEM and XRD investigations indicated that the ZnO nanorod arrays grown at ICP powers above 200 Watt had a homogeneous in-plane alignment and single crystalline nature. PL study at room temperature (RT) and 6 K confirmed that the ZnO nanorod arrays in the present study are of high optical quality as well as good crystalline quality, showing only exciton-related emission peaks without any trace of defect-related deep level emissions in visible range. The blueshift of exciton emission peak in RTPL spectra was also found as rod diameter decreased and it is deduced that this shift in emission energy may be due to the surface resonance effect resulted from the increased surface-to-volume ratio, based on the observation and behavior of the surface exciton (SX) emission in the high-resolution 6 K PL spectra.

  16. Single-crystalline Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x} detectors for direct detection of microwave radiation

    SciTech Connect

    Li, M. Winkler, D.; Yurgens, A.

    2015-04-13

    We test radiation detectors made from single-crystalline Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x} flakes put on oxidized Si substrates. The 100-nm-thick flakes are lithographically patterned into 4×12 μm{sup 2} large rectangles embedded in thin-film log-spiral antennas. The SiO{sub 2} layer weakens the thermal link between the flakes and the bath. Two modes of radiation detection have been observed. For a bolometric type of sensors a responsivity of ∼300 V/W and a noise equivalent power of 30 nW/√(Hz) has been deduced at 70 K. Much more sensitive is the non-bolometric device showing characteristics similar to a Golay-type detector while being at least a thousand times faster. Making smaller (sub-μm) structures is expected to significantly improve the performance of these devices and makes them very competitive among other microwave and terahertz detectors.

  17. Single-Crystalline Gold Nanowires Synthesized from Light-Driven Oriented Attachment and Plasmon-Mediated Self-Assembly of Gold Nanorods or Nanoparticles

    PubMed Central

    Yu, Shang-Yang; Gunawan, Hariyanto; Tsai, Shiao-Wen; Chen, Yun-Ju; Yen, Tzu-Chen; Liaw, Jiunn-Woei

    2017-01-01

    Through the light-driven geometrically oriented attachment (OA) and self-assembly of Au nanorods (NRs) or nanoparticles (NPs), single-crystalline Au nanowires (NWs) were synthesized by the irradiation of a linearly-polarized (LP) laser. The process was conducted in a droplet of Au colloid on a glass irradiated by LP near-infrared (e.g. 1064 nm and 785 nm) laser beam of low power at room temperature and atmospheric pressure, without any additive. The FE-SEM images show that the cross sections of NWs are various: tetragonal, pentagonal or hexagonal. The EDS spectrum verifies the composition is Au, and the pattern of X-ray diffraction identifies the crystallinity of NWs with the facets of {111}, {200}, {220} and {311}. We proposed a hypothesis for the mechanism that the primary building units are aligned and coalesced by the plasmon-mediated optical torque and force to form the secondary building units. Subsequently, the secondary building units undergo the next self-assembly, and so forth the tertiary ones. The LP light guides the translational and rotational motions of these building units to perform geometrically OA in the side-by-side, end-to-end and T-shaped manners. Consequently, micron-sized ordered mesocrystals are produced. Additionally, the concomitant plasmonic heating causes the annealing for recrystallizing the mesocrystals in water. PMID:28300218

  18. One-step fabrication of single-crystalline ZnS nanotubes with a novel hollow structure and large surface area for photodetector devices.

    PubMed

    An, Qinwei; Meng, Xianquan; Xiong, Ke; Qiu, Yunlei; Lin, Weihua

    2017-03-10

    ZnS nanotubes (NTs) were successfully prepared via a one-step thermal evaporation process without using any templates. The resulting NTs were single crystalline and structurally uniform. Based on experimental analysis, a tube-growth vapor-liquid-solid process was proposed as the growth mechanism of ZnS NTs. A metal-semiconductor-metal full-nanostructured ultraviolet (UV) photodetector with ZnS NTs as the active layer, and Ag nanowires of low resistivity and high transmissivity as electrodes, was fabricated and characterized. The ZnS NT-based device displayed a high I on/I off ratio of up to ∼1.56 × 10(5) with a high response to UV incident light at low operation voltage. This work is a meaningful exploration for preparing other one-dimensional semiconductor NTs, and developing a high-performance and power-saving UV sensor.

  19. Magnetic and Superconducting Properties in Single Crystalline Fe1+δTe1-xSex (x<0.50) System

    NASA Astrophysics Data System (ADS)

    Jinhu Yang,; Mami Matsui,; Masatomo Kawa,; Hiroto Ohta,; Chishiro Michioka,; Chiheng Dong,; Hangdong Wang,; Huiqiu Yuan,; Minghu Fang,; Kazuyoshi Yoshimura,

    2010-07-01

    The spin-fluctuation effect in the Se-substituted single crystalline Fe1+δTe1-xSex (x = 0, 0.05, 0.12, 0.20, 0.30, 0.33, 0.45, and 0.48; 0≤δ≤ 0.12) and the polycrystalline Fe1.11Se has been studied by the measurements of the X-ray diffraction, the magnetic susceptibility under high magnetic fields and the electrical resistivity under magnetic fields up to 14 T. The samples with x = 0.05, 0.12, 0.20, 0.30, 0.33, 0.45, and 0.48 show superconducting transition temperatures in the ranger of 10-14 K. We obtained their intrinsic susceptibilities by the Honda-Owen method. A nearly linear-in-T behavior in magnetic susceptibility of Se-rich superconducting samples was observed, indicating the antiferromagnetic spin fluctuations have a strong link with the superconductivity in this series. The upper critical field μ0Hc2orb for T\\to 0 was estimated to exceed the Pauli paramagnetic limit. The Kadowaki-Woods and Wilson ratios indicate that electrons are strongly correlated in this system. Furthermore, the superconducting coherence length and the electron mean free path were also discussed. These superconducting parameters indicate that the superconductivity in the Fe1+δTe1-xSex system is unconventional.

  20. Magnetotransport properties of the single-crystalline nodal-line semimetal candidates Ca T X (T =Ag,Cd;X =As,Ge)

    NASA Astrophysics Data System (ADS)

    Emmanouilidou, Eve; Shen, Bing; Deng, Xiaoyu; Chang, Tay-Rong; Shi, Aoshuang; Kotliar, Gabriel; Xu, Su-Yang; Ni, Ni

    2017-06-01

    Topological semimetals are characterized by protected crossings between conduction and valence bands. These materials have recently attracted significant interest because of the deep connections to high-energy physics, the novel topological surface states, and the unusual transport phenomena. While Dirac and Weyl semimetals have been extensively studied, the nodal-line semimetal remains largely unexplored due to the lack of an ideal material platform. In this paper, we report the magnetotransport properties of the two nodal-line semimetal candidates CaAgAs and CaCdGe. First, the transport properties of our single crystalline CaAgAs agree with those of CaAgAs polycrystals. They can be explained by the single-band model, consistent with the theoretical proposal that only nontrivial Fermi pockets linked by the topological nodal-line are present at the Fermi level. Second, our CaCdGe sample provides an ideal platform to perform comparative studies because the theoretical calculation shows that it features the same topological nodal line but has a more complicated Fermiology with irrelevant Fermi pockets. As a result, the magnetoresistance of our CaCdGe sample is more than 100 times larger than that of CaAgAs. Through our systematic magnetotransport and first-principles band structure calculations, we show that our CaTX compounds can be used to study, isolate, and control the novel topological nodal-line physics in real materials.