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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. PMID:21267000

  2. 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

  3. 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.

  4. 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

    2015-01-01

    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

  5. 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. PMID:27026281

  6. 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. PMID:15631421

  7. Resistance switching in a single-crystalline NiO thin film grown on a Pt0.8Ir0.2 electrode

    NASA Astrophysics Data System (ADS)

    Kawai, Masanori; Ito, Kimihiko; Shimakawa, Yuichi

    2009-07-01

    A single-crystalline NiO thin film was grown epitaxially on an atomically flat Pt0.8Ir0.2 bottom electrode layer grown epitaxially on a SrTiO3(100) substrate. The memory cells of the single-crystalline NiO thin film with Pt top electrodes showed unipolar resistance switching behaviors. The result demonstrates that a unipolar resistance switching is not a characteristic phenomenon in the polycrystalline NiO but it can also occur in the single-crystalline NiO.

  8. 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.

  9. 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.

  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. Controlling wave-vector of propagating surface plasmon polaritons on single-crystalline gold nanoplates

    PubMed Central

    Luo, Si; Yang, Hangbo; Yang, Yuanqing; Zhao, Ding; Chen, Xingxing; Qiu, Min; Li, Qiang

    2015-01-01

    Surface plasmon polaritons (SPPs) propagating at metal nanostructures play an important role in breaking the diffraction limit. Chemically synthesized single-crystalline metal nanoplates with atomically flat surfaces provide favorable features compared with traditional polycrystalline metal films. The excitation and propagation of leaky SPPs on micrometer sized (10–20 μm) and thin (30 nm) gold nanoplates are investigated utilizing leakage radiation microscopy. By varying polarization and excitation positions of incident light on apexes of nanoplates, wave-vector (including propagation constant and propagation direction) distributions of leaky SPPs in Fourier planes can be controlled, indicating tunable SPP propagation. These results hold promise for potential development of chemically synthesized single-crystalline metal nanoplates as plasmonic platforms in future applications. PMID:26302955

  12. A Single-Crystalline Mesoporous Quartz Superlattice.

    PubMed

    Matsuno, Takamichi; Kuroda, Yoshiyuki; Kitahara, Masaki; Shimojima, Atsushi; Wada, Hiroaki; Kuroda, Kazuyuki

    2016-05-10

    There has been significant interest in the crystallization of nanostructured silica into α-quartz because of its physicochemical properties. We demonstrate a single-crystalline mesoporous quartz superlattice, a silica polymorph with unprecedentedly ordered hierarchical structures on both the several tens of nanometers scale and the atomic one. The mesoporous quartz superlattice consists of periodically arranged α-quartz nanospheres whose crystalline axes are mostly oriented in an assembly. The superlattice is prepared by thermal crystallization of amorphous silica nanospheres constituting a colloidal crystal. We found that the deposition of a strong flux of Li(+) only on the surface of silica nanospheres is effective for crystallization. PMID:27060365

  13. 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. PMID:26306027

  14. 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.

  15. Self-assembly of gold nanoparticles on a single crystalline sapphire substrate

    NASA Astrophysics Data System (ADS)

    Takahashi, Hiroyuki; Shirahata, Naoto; Narushima, Takashi; Yonezawa, Tetsu

    2012-12-01

    Single crystalline sapphire is an atomically flat substrate with a high transparency in a wide wavelength region. However, its surface is chemically stable so that the modification by a self-assembled monolayer is somewhat difficult. We have used a H2O2 treatment at 70 °C to activate the surface and modified with a silan coupling reagent. The modification of the surface is discussed with the water contact angle. Immobilization of citrate-stabilized anionic gold nanoparticles on a cationically modified sapphire surface was carried out.

  16. 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.

  17. 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.

  18. Single-crystalline aluminum film for ultraviolet plasmonic nanolasers.

    PubMed

    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

  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. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. Plasma-assisted self-sharpening of platelet-structured single-crystalline carbon nanocones

    SciTech Connect

    Levchenko, I.; Ostrikov, K.; Long, J. D.; Xu, S.

    2007-09-10

    A mechanism and model for the vertical growth of platelet-structured vertically aligned single-crystalline carbon nanostructures by the formation of graphene layers on a flat top surface are proposed and verified experimentally. It is demonstrated that plasma-related effects lead to self-sharpening of tapered nanocones to form needlelike nanostructures, in a good agreement with the predicted dependence of the radius of a nanocone's flat top on the incoming ion flux and surface temperature. The growth mechanism is relevant to a broad class of nanostructures including nanotips, nanoneedles, and nanowires and can be used to improve the predictability of nanofabrication processes.

  7. Growth Of Single Crystalline Copper Nanowhiskers

    SciTech Connect

    Kolb, Matthias; Richter, Gunther

    2010-11-24

    Nanowhiskers are defect free single crystals with high aspect ratios and as result exhibit superior physical, e.g. mechanical properties. This paper sheds light on the kinetics of copper nanowhisker growth and thickening. Whisker growth was provoked by covering silicon wafers with a thin carbon film and subsequently coating them with copper by molecular beam epitaxy. The whiskers grown were examined by scanning electron microscopy and the length and diameter were measured as a function of the amount of copper deposited. The experiments show that nanowhisker growth follows Ruth and Hirth's growth model. A fit of the model parameters to the acquired data shows that adsorption of atoms on the substrate and on the whisker surface, with subsequent surface diffusion to the whisker tip, delivers by far the greatest portion of material for whisker growth. Additionally, the experiments demonstrate that the crystallographic orientation of the substrate surface greatly influences the growth rate in the early stage of whisker growth.

  8. 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.

  9. 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.

  10. 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.

  11. Nonvolatile resistive switching in single crystalline ZnO nanowires.

    PubMed

    Yang, Yuchao; Zhang, Xiaoxian; Gao, Min; Zeng, Fei; Zhou, Weiya; Xie, Sishen; Pan, Feng

    2011-04-01

    We demonstrate nonvolatile resistive switching in single crystalline ZnO nanowires with high ON/OFF ratios and low threshold voltages. Unlike the mechanism of continuous metal filament formation along grain boundaries in polycrystalline films, the resistive switching in single crystalline ZnO nanowires is speculated to be induced by the formation of a metal island chain on the nanowire surface. Resistive memories based on bottom-up semiconductor nanowires hold potential for next generation ultra-dense nonvolatile memories. PMID:21394361

  12. Preparation of C 60 single crystalline thin film by ionized cluster beam deposition and ion implantation into single crystalline C 60 thin film

    NASA Astrophysics Data System (ADS)

    Isoda, Satoru; Kawakubo, Hiroaki; Nishikawa, Satoshi; Wada, Osamu

    1996-05-01

    We have succeeded in preparing single crystalline C 60 thin film of a lateral extension in the order of several millimeters on mica by ionized cluster beam (ICB) deposition. During the growth process, planar dendrite-like single crystalline islands were observed by an atomic force microscope (AFM). It was concluded from reflection high-energy electron diffraction (RHEED) and transmission electron diffraction (TED) analyses that these islands grow hetero-epitaxially on mica. As the deposition process continues, the single crystalline islands coalesce and finally form a giant single crystal without grain boundaries between the former islands. This layered dendrite-like crystal growth is considered to be due to the ICB process, namely, ionizing molecules and accelerating them. Furthermore, the effect of ion (P +, B +, Ar +) implantation into C 60 thin films on the molecular structure and the conductivity has been studied under various implantation conditions. It was found from the analyses of FT-IR and Raman spectroscopies that the soccer-ball-like structure of C 60 changes into a diamond-like carbon (DLC) structure with an implantation energy higher than 40 keV, whereas the structure undergoes virtually no change with 10 keV implantation. As for conductivity changes under the lower implantation energy condition, the minimum dose of P + ions required to increase the conductivity from the non-doped value (10 12 cm -2) is 10 times lower than in the case of Ar + implantation. The conductivity change for the P + implantation could be explained satisfactorily not only by the effect of chemically-modified C 60 but also by the effect of a charge-transfer state between C 60 and implanted ions. It was concluded from these results that the conductivity of the C 60 film can be controlled over a wide range based on the carrier generation mechanism, which depends on the implantation conditions.

  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. PMID:21138038

  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. Single-crystalline nanoporous Nb2O5 nanotubes.

    PubMed

    Liu, Jun; Xue, Dongfeng; Li, Keyan

    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

  16. 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.

  17. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    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.

  19. 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.

  20. Growth of one-dimensional single-crystalline hydroxyapatite nanorods

    NASA Astrophysics Data System (ADS)

    Ren, Fuzeng; Ding, Yonghui; Ge, Xiang; Lu, Xiong; Wang, Kefeng; Leng, Yang

    2012-06-01

    A facile, effective and template/surfactant-free hydrothermal route in the presence of sodium bicarbonate was developed to synthesize highly uniform single-crystalline hydroxyapatite (HA) nanorods with the lengths of several hundred nanometers and aspect ratio up to ˜20. One dimensional (1-D) growth and aspect ratio could be controlled by hydrothermal reaction time and temperature. The longitudinal axis, also the growth direction of the nanorods, is parallel to the [001] direction of HA hexagonal crystal structure.

  1. 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.

  2. Oxygen recoil implant from SiO{sub 2} layers into single-crystalline silicon

    SciTech Connect

    Wang, G.; Chen, Y.; Li, D.; Oak, S.; Srivastav, G.; Banerjee, S.; Tasch, A.; Merrill, P.; Bleiler, R.

    2001-06-01

    It is important to understand the distribution of recoil-implanted atoms and the impact on device performance when ion implantation is performed at a high dose through surface materials into single crystalline silicon. For example, in ultralarge scale integration impurity ions are often implanted through a thin layer of screen oxide and some of the oxygen atoms are inevitably recoil implanted into single-crystalline silicon. Theoretical and experimental studies have been performed to investigate this phenomenon. We have modified the Monte Carlo ion implant simulator, UT-Marlowe (B. Obradovic, G. Wang, Y. Chen, D. Li, C. Snell, and A. F. Tasch, UT-MARLOWE Manual, 1999), which is based on the binary collision approximation, to follow the full cascade and to dynamically modify the stoichiometry of the Si layer as oxygen atoms are knocked into it. CPU reduction techniques are used to relieve the demand on computational power when such a full cascade simulation is involved. Secondary ion mass spectrometry (SIMS) profiles of oxygen have been carefully obtained for high dose As and BF{sub 2} implants at different energies through oxide layers of various thicknesses, and the simulated oxygen profiles are found to agree very well with the SIMS data. {copyright} 2001 American Institute of Physics.

  3. 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

  4. 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.

  5. Single crystalline nature of para-sexiphenyl crystallites grown on KCl(100).

    PubMed

    Haber, T; Oehzelt, M; Resel, R; Andreev, A; Thierry, A; Sitter, H; Smilgies, D M; Schaffer, B; Grogger, W; Resel, R

    2006-03-01

    This work focuses on studies of the single crystal nature of para-sexiphenyl structures grown on freshly cleaved KCl(100) surfaces. Two different kinds of morphologies, namely terrace like structures and needle like structures, are found by atomic force microscopy as well as by electron microscopy. Regardless of the morphology the individual crystallites show highly regular shapes. The crystalline alignment and the degree of order of the crystallites on the surface are determined by X-ray diffraction. Several epitaxial alignments of para-sexiphenyl on KCl(100) are observed and all of them are perfectly aligned on the surface. The rocking curve widths of the organic crystallites do not exceed 800" which is approximately only the four fold of the substrates' ones. The single crystalline nature of para-sexiphenyl crystallites is proven by transmission electron microscopy, diffraction patterns, dark field imaging and high resolution techniques. Single crystalline terraced mounds reach diameters of several microns and heights of 50 nm. Single crystal needles show heights and breadths of more than 100 nm and lengths of several microns. PMID:16573123

  6. Atomically flat reconstructed rutile TiO2(001) surfaces for oxide film growth

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Lee, S.; Vilmercati, P.; Lee, H. N.; Weitering, H. H.; Snijders, P. C.

    2016-02-01

    The availability of low-index rutile TiO2 single crystal substrates with atomically flat surfaces is essential for enabling epitaxial growth 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 reconstructed surface 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 homoepitaxial growth 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.

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

    DOE PAGESBeta

    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 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

  8. Periodic magnetic domains in single-crystalline cobalt filament arrays

    NASA Astrophysics Data System (ADS)

    Chen, Fei; Wang, Fan; Jia, Fei; Li, Jingning; Liu, Kai; Huang, Sunxiang; Luan, Zhongzhi; Wu, Di; Chen, Yanbin; Zhu, Jianmin; Peng, Ru-Wen; Wang, Mu

    2016-02-01

    Magnetic structures with controlled domain wall pattern may be applied as potential building blocks for three-dimensional magnetic memory and logic devices. Using a unique electrochemical self-assembly method, we achieve regular single-crystalline cobalt filament arrays with specific geometric profile and crystallographic orientation, and the magnetic domain configuration can be conveniently tailored. We report the transition of periodic antiparallel magnetic domains to compressed vortex magnetic domains depending on the ratio of height to width of the wires. A "phase diagram" is obtained to describe the dependence of the type of magnetic domain and the geometrical profiles of the wires. Magnetoresistance of the filaments demonstrates that the contribution of a series of 180∘ domain walls is over 0.15 % of the zero-field resistance ρ (H =0 ) . These self-assembled magnetic nanofilaments, with controlled periodic domain patterns, offer an interesting platform to explore domain-wall-based memory and logic devices.

  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. 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.

  11. Optical and electrical properties of single-crystalline zirconium carbide

    SciTech Connect

    Modine, F.A.; Haywood, T.W.; Allison, C.Y.

    1985-12-15

    Optical and electrical properties are reported for single-crystalline ZrC/sub 0.89/. The specular reflectance was measured between 0.025 and 6.5 eV, and ellipsometry measurements were made between 1.2 and 4.5 eV. The combination of ellipsometry with reflectance allows optical functions to be computed reliably between 0 and 6.5 eV and also provides a check on the consistency of the measurements. The van der Pauw technique was used to measure the electrical resistivity of the samples at temperatures between 4.2 and 300 K and the Hall coefficient at room temperature. Drude parameters obtained from the electrical measurements are in good agreement with those obtained from the optical data. Both the optical and electrical results are compared to other experimental results and to theory.

  12. Dynamic crack propagation in single-crystalline silicon

    SciTech Connect

    Cramer, T.; Gumbsch, P.; Wanner, A.

    1999-08-01

    Tensile tests on notched plates of single-crystalline silicon were carried out at high overloads. Cracks were forced to propagate on {l_brace}110{r_brace} planes in a {l_angle}1{bar 1}0{r_angle} direction. The dynamics of the fracture process was measured using the potential drop technique and correlated with the fracture surface morphology. Crack propagation velocity did not exceed a terminal velocity of v{sub c} = 3,800 m/s, which corresponds to 83% of the Rayleigh wave velocity v{sub R}. Specimens fractured at low stresses exhibited crystallographic cleavage whereas a transition from mirror-like smooth regions to rougher hackle zones was observed in case of the specimens fractured at high stresses. Inspection of the mirror zone at high magnification revealed a deviation of the {l_brace}110{r_brace} plane onto {l_brace}111{r_brace}crystallographic facets.

  13. 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.

  14. Deformation mechanisms in nanoscale single crystalline electroplated copper pillars

    NASA Astrophysics Data System (ADS)

    Jennings, Andrew T.

    Scientific research in nanotechnology has enabled advances in a diverse range of applications, such as: electronics, chemical sensing, and cancer treatment. In order to transition these nanotechnology-driven innovations out of the laboratory and into real-world applications, the resilience and mechanical reliability of nanoscale structures must be well understood in order to preserve functionality under real-world operating environments. Understanding the mechanical properties of nanoscale materials is especially important because several authors have shown that single crystalline metal pillars produced through focused-ion-beam milling have unique properties when the pillar diameter, D, approaches nanotechnology-relevant dimensions. The strength, sigma, of these pillars is size-dependent and is well described through a power-law relation showing that smaller is stronger: sigma∝D-n , where n is the exponent and is found to be 0.5≤n≤1.0 in face-centered-cubic metals. In this work, the fundamental deformation mechanisms governing the size-dependent mechanical properties are investigated through uniaxial compression and tension tests of electroplated single crystalline copper pillars with diameters between 75 nm and 1000 nm. At larger pillar diameters, D >125 nm, these copper pillars are shown to obey a similar size-dependent regime, demonstrating that the "smaller is stronger" phenomenon is a function of the pillar microstructure, as opposed to the fabrication route. Furthermore, the dominant dislocation mechanism in this size-dependent regime is shown to be the result of single-arm, or spiral, sources. At smaller pillar diameters, D≤125 nm, a strain-rate-dependent mechanism transition is observed through both the size-strength relation and also quantitative, experimental measures of the activation volume. This new deformation regime is characterized by a size-independent strength and is governed by surface dislocation nucleation, a thermally activated

  15. 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.

  16. 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.

  17. "Liquid Knife" to Fabricate Patterning Single-Crystalline Perovskite Microplates toward High-Performance Laser Arrays.

    PubMed

    Feng, Jiangang; Yan, Xiaoxu; Zhang, Yifan; Wang, Xuedong; Wu, Yuchen; Su, Bin; Fu, Hongbin; Jiang, Lei

    2016-05-01

    A facile and effective "liquid knife" is created by controlling the dewetting process of the liquid precursor, yielding patterning single-crystalline perovskite microplates with uniform size, precise positioning, high quality, and low lasing thresholds. The sizes and location of single-crystalline perovskite are controllable, leading to mode-tunable lasing emission and patterned lasers. PMID:27000628

  18. Initial growth on microcrystalline silicon on atomically flat hetero-substrate

    SciTech Connect

    Saitoh, K.; Kondo, M.; Matsuda, A.

    1997-07-01

    Initial growth of microcrystalline silicon ({micro}c-Si:H) deposited on an atomically flat GaAs (001) wafer using a RF glow-discharge decomposition of hydrogen diluted monosilane gas mixture has been studied by means of atomic force microscope (AFM), Auger electron spectroscopy (AES), and cross-sectional transmission electron microscopy (XTEM). It is shown that the initial growth of {micro}c-Si:H deposited at a substrate temperature of 50--250 C consists of four successive stages, i.e., (1) a layer-by-layer growth of a-Si:H up to d {approximately}5 {angstrom}, (2) island formation of a-Si:H, (3) the coalescence of the islands and the nucleation of microcrystalline at d{approximately}10{approximately}40 {angstrom} depending on the growth temperature, and (4) a rapid roughening with microcrystalline growth.

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

    PubMed

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

    2016-09-16

    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. PMID:27505713

  20. 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.

  1. 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.

  2. 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

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

    PubMed

    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 cm(2) 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

  4. Gallium Arsenide Layers Grown by Molecular Beam Epitaxy on Single Crystalline Germanium Islands on Insulator

    NASA Astrophysics Data System (ADS)

    Takai, Mikio; Tanigawa, Takaho; Minamisono, Tadanori; Gamo, Kenji; Namba, Susumu

    1984-05-01

    Gallium arsenide (GaAs) layers have successfully been grown by molecular beam epitaxy on single crystalline germanium (Ge) islands, recrystallized by zone melting with SiO2 capping layers, on thermally-oxidized Si-wafers. The GaAs layers, grown on the single crystalline Ge islands, show smooth surfaces without any grain-boundaries, while those, grown on the Ge islands with grain-boundaries and on the SiO2, have grain-boundaries. The GaAs layers on the single crystalline Ge islands emit photoluminescence, the intensity of which is almost comparable to that of GaAs layers on bulk Ge crystals.

  5. A route to fabricate single crystalline bismuth nanowire arrays with different diameters

    NASA Astrophysics Data System (ADS)

    Li, Liang; Zhang, Yong; Li, Guanghai; Zhang, Lide

    2003-09-01

    Single crystalline bismuth nanowire arrays in anodic alumina membrane have been fabricated by pulsed electrodeposition. The nanowires of different diameters were obtained by changing the electrical parameter of the pulsed electrodeposition using anodic alumina membrane as template with the same pore size. X-ray diffraction and TEM analysis show that the bismuth nanowires are single crystalline with highly preferential orientation, and the diameter of nanowires increases with increasing the relaxation time of pulse. The growth mechanism of nanowires was discussed.

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

    PubMed

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

    2015-01-01

    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. PMID:26563901

  7. Synthesis and characterization of single-crystalline zinc tin oxide nanowires.

    PubMed

    Shi, Jen-Bin; Wu, Po-Feng; Lin, Hsien-Sheng; Lin, Ya-Ting; Lee, Hsuan-Wei; Kao, Chia-Tze; Liao, Wei-Hsiang; Young, San-Lin

    2014-01-01

    Crystalline zinc tin oxide (ZTO; zinc oxide with heavy tin doping of 33 at.%) nanowires were first synthesized using the electrodeposition and heat treatment method based on an anodic aluminum oxide (AAO) membrane, which has an average diameter of about 60 nm. According to the field emission scanning electron microscopy (FE-SEM) results, the synthesized ZTO nanowires are highly ordered and have high wire packing densities. The length of ZTO nanowires is about 4 μm, and the aspect ratio is around 67. ZTO nanowires with a Zn/(Zn + Sn) atomic ratio of 0.67 (approximately 2/3) were observed from an energy dispersive spectrometer (EDS). X-ray diffraction (XRD) and corresponding selected area electron diffraction (SAED) patterns demonstrated that the ZTO nanowire is hexagonal single-crystalline. The study of ultraviolet/visible/near-infrared (UV/Vis/NIR) absorption showed that the ZTO nanowire is a wide-band semiconductor with a band gap energy of 3.7 eV. PMID:24872800

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

    PubMed Central

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

    2015-01-01

    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. PMID:26563901

  9. Single-Crystalline Ultrathin Nickel Nanosheets Array from In Situ Topotactic Reduction for Active and Stable Electrocatalysis

    PubMed Central

    Kuang, Yun; Feng, Guang; Li, Pengsong; Bi, Yongmin; Li, Yaping; Sun, Xiaoming

    2016-01-01

    Simultaneously synthesizing and structuring atomically thick or ultrathin 2D non-precious metal nanocrystal may offer a new class of materials to replace the state-of-art noble-metal electrocatalysts; however, the synthetic strategy is the bottleneck which should be urgently solved. Here we report the synthesis of an ultrathin nickel nanosheet array (Ni-NSA) through in situ topotactic reduction from Ni(OH)2 array precursors. The Ni nanosheets showed a single-crystalline lamellar structure with only ten atomic layers in thickness and an exposed (111) facet. Combined with a superaerophobic (low bubble adhesive) arrayed structure the Ni-NSAs exhibited a dramatic enhancement on both activity and stability towards the hydrazine-oxidation reaction (HzOR) relative to platinum. Furthermore, the partial oxidization of Ni-NSAs in ambient atmosphere resulted in effective water-splitting electrocatalysts for the hydrogen-evolution reaction (HER). PMID:26582545

  10. Single-Crystalline Ultrathin Nickel Nanosheets Array from In Situ Topotactic Reduction for Active and Stable Electrocatalysis.

    PubMed

    Kuang, Yun; Feng, Guang; Li, Pengsong; Bi, Yongmin; Li, Yaping; Sun, Xiaoming

    2016-01-11

    Simultaneously synthesizing and structuring atomically thick or ultrathin 2D non-precious metal nanocrystal may offer a new class of materials to replace the state-of-art noble-metal electrocatalysts; however, the synthetic strategy is the bottleneck which should be urgently solved. Here we report the synthesis of an ultrathin nickel nanosheet array (Ni-NSA) through in situ topotactic reduction from Ni(OH)2 array precursors. The Ni nanosheets showed a single-crystalline lamellar structure with only ten atomic layers in thickness and an exposed (111) facet. Combined with a superaerophobic (low bubble adhesive) arrayed structure the Ni-NSAs exhibited a dramatic enhancement on both activity and stability towards the hydrazine-oxidation reaction (HzOR) relative to platinum. Furthermore, the partial oxidization of Ni-NSAs in ambient atmosphere resulted in effective water-splitting electrocatalysts for the hydrogen-evolution reaction (HER). PMID:26582545

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    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.

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

    PubMed

    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 cm(2) V(-1) s(-1) in intrinsic portion and ~2,500 cm(2) 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

  13. 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.

  14. 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.

  15. Preparation of atomically flat TiO2(001) surfaces

    NASA Astrophysics Data System (ADS)

    Wang, Yang; Weitering, Hanno H.; Snijders, Paul C.

    2015-03-01

    Transition metal oxides with the rutile structure (MO2, M = e.g. Ti, V, or Nb) have highly directional partially occupied t2g orbitals. Some of these orbitals form quasi-1D electronic bands along the rutile c-axis, and Peierls-like ordering phenomena have been observed in VO2 and NbO2. Tailoring the electronic properties of these materials via quantum confinement requires epitaxial growth on suitable substrates such as low index TiO2 surfaces. Because of the high surface energy of rutile TiO2(001), the standard approach of sputtering and annealing usually introduces faceting. Here we demonstrate a facile method to create atomically flat, non-faceted TiO2(001) surfaces. Using scanning tunneling microscopy we observe terraces with a width of approximately 150 nm. Step heights of approximately 0.3 nm are observed, consistent with the c lattice parameter of rutile TiO2. Low energy electron diffraction patterns reveal sharp diffraction spots with an in-plane lattice constant of 0.358 nm which is consistent with a (1x1) ordering of the (001) plane. These TiO2(001) single crystal surfaces can serve as an ideal substrate for further growth of rutile heterostructures. Research sponsored by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.

  16. 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

  17. 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.

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

    PubMed

    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

  19. 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

  20. 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.

  1. Wurtzite-type faceted single-crystalline GaN nanotubes

    NASA Astrophysics Data System (ADS)

    Liu, Baodan; Bando, Yoshio; Tang, Chengchun; Shen, Guozhen; Golberg, Dmitri; Xu, Fangfang

    2006-02-01

    We report on the direct fabrication of single-crystalline wurtzite-type hexagonal GaN nanotubes via a newly designed, controllable, and reproducible chemical thermal-evaporation process. The nanotubes are single crystalline, have one end closed, an average outer diameter of ˜300nm, an inner diameter of ˜100nm, and a wall thickness of ˜100nm. The structure and morphology of the tubes are characterized using a scanning electron microscope and a transmission electron microscope. The cathodoluminescence of individual nanotubes is also investigated. The growth mechanism, formation kinetics, and crystallography of GaN nanotubes are finally discussed.

  2. Controlled spatial switching and routing of surface plasmons in designed single-crystalline gold nanostructures

    NASA Astrophysics Data System (ADS)

    Könenkamp, R.; Word, R. C.; Fitzgerald, J. P. S.; Nadarajah, Athavan; Saliba, S. D.

    2012-10-01

    Electron emission microscopy is used to visualize plasmonic routing in gold nano-structures. We show that in single-crystalline gold structures reliable routing can be achieved with polarization switching. The routing is due to the polarization dependence of the photon-to-plasmon coupling, which controls the mode distribution in the plasmonic gold film. We use specifically designed, single-crystalline planar structures. In these structures, the plasmon propagation length is sufficiently large such that significant plasmon power can be delivered to the near-field region around the end tips of the router. Solid state devices based on internal electron excitation and emission processes appear feasible.

  3. Micro-organic single crystalline phototransistors of 7,7,8,8-tetracyanoquinodimethane and tetrathiafulvalene

    NASA Astrophysics Data System (ADS)

    Jiang, Hui; Yang, Xianjin; Cui, Zhenduo; Liu, Yongchang; Li, Hongxiang; Hu, Wenping

    2009-03-01

    Classical p-type and n-type organic single crystals, tetrathiafulvalene (TTF) and 7,7,8,8-tetracyanoquinodimethane (TCNQ), are introduced to investigate photoswitch and phototransistor. High photoresponsivity, low persistent conductivity, and response reversibility can be found in single crystalline TCNQ, while TTF has large persistent conductivity when the light is switched on and off. It is probably attributed to different band gaps and the compactness of molecular packing. Single crystalline TCNQ combines light detection, switching, signal amplification in a single device and realization of multiple functions which exhibit a very promising potential for the fabrication of organic photoelectric devices.

  4. 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. PMID:26143863

  5. 3D Dewetting for Crystal Patterning: Toward Regular Single-Crystalline Belt Arrays and Their Functionality.

    PubMed

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

    2016-03-01

    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. PMID:26823061

  6. 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.

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

    PubMed

    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. PMID:27454488

  8. 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

  9. Single-crystalline Ni(OH)2 and NiO nanoplatelet arrays as supercapacitor electrodes

    NASA Astrophysics Data System (ADS)

    Li, Jiangtian; Zhao, Wei; Huang, Fuqiang; Manivannan, Ayyakkannu; Wu, Nianqiang

    2011-12-01

    Vertically aligned Ni(OH)2 and NiO single-crystalline nanoplatelet arrays were directly grown on the fluorine-doped tin oxide (FTO) substrate by a simple hydrothermal method. The effects of the hydrothermal parameters on the morphology and crystal structure of the nanoarray film were investigated. Controlling the ammonia and persulfate concentrations was the key to controlling the morphology of the nanoarray film. The experimental results showed that the single-crystalline NiO nanoplatelet array was a promising candidate for the supercapacitor electrode. It exhibited a high specific capacitance, prompt charge/discharge rate, and good stability of cycling performance. It is believed that the vertically oriented aligned single-crystalline NiO nanoplatelet array is beneficial to the charge transfer in the electrode and to the ion transport in the solution during redox reaction.Vertically aligned Ni(OH)2 and NiO single-crystalline nanoplatelet arrays were directly grown on the fluorine-doped tin oxide (FTO) substrate by a simple hydrothermal method. The effects of the hydrothermal parameters on the morphology and crystal structure of the nanoarray film were investigated. Controlling the ammonia and persulfate concentrations was the key to controlling the morphology of the nanoarray film. The experimental results showed that the single-crystalline NiO nanoplatelet array was a promising candidate for the supercapacitor electrode. It exhibited a high specific capacitance, prompt charge/discharge rate, and good stability of cycling performance. It is believed that the vertically oriented aligned single-crystalline NiO nanoplatelet array is beneficial to the charge transfer in the electrode and to the ion transport in the solution during redox reaction. Electronic supplementary information (ESI) available: XRD patterns of Ni(OH)2 and NiO powders; SEM and TEM images of Ni(OH)2 and NiO nanoplatelet arrays; and electrochemical performances for NiO nanoarrays and powders. See

  10. Atomically flat La-silicate/Si interface using tungsten carbide gate electrode with nano-sized grain

    SciTech Connect

    Tuokedaerhan, K.; Natori, K.; Iwai, H.; Kakushima, K. Kataoka, Y.; Nishiyama, A.; Sugii, N.; Wakabayashi, H.; Tsutsui, K.

    2014-01-13

    Interface properties of La-silicate gate dielectrics on Si substrates with W or nano-sized grain W{sub 2}C gate electrodes have been investigated. A low interface state density of 2.5 × 10{sup 11} cm{sup −2}/eV has been achieved with W{sub 2}C gate electrodes, which is one third of those with W gate electrode. An interface roughness of 0.33 nm with spatial frequency comparable to the grain size of W gate electrode has been observed. Besides, an atomically flat interface of 0.12 nm has been obtained with W{sub 2}C gate electrode. The origin of flat interface may be attributed to the elimination of inhomogeneous stress by grains in metal electrode.

  11. 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.

  12. 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.

  13. 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⁾

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

    DOE PAGESBeta

    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.; et al

    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

  15. 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. PMID:26855204

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

    SciTech Connect

    Fong, Dillon D.; Paskiewicz, Deborah M.; Sichel-Tissot, Rebecca; Stan, Liliana; Karapetrova, Evguenia

    2016-01-01

    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. The synthesis technique described here represents a significant advancement in materials integration and provides a new platform for the development of flexible oxide electronics.

  17. Single-crystalline polytetrafluoroethylene-like nanotubes prepared from atmospheric plasma discharge

    SciTech Connect

    Zhang, J.; Guo, Y.; Xu, J.Z.; Fang, X.S.; Xie, H.K.; Shi, D.L.; He, P.; Ooij, W.J. van

    2005-03-28

    Atmospheric plasma polymerization of perfluorohexane was investigated in this letter. A large quantity of single-crystalline polytetrafluoroethylene (PTFE)-like nanotubes were formed on a simultaneously deposited film at room temperature without any catalysts or templates. The outer diameter of the nanotubes varied from 60 to 1200 nm with a maximum aspect ratio up to 100:1. Transmission electron microscopy and x-ray diffraction results indicated a single crystal close-packed hexagonal (cph) structure in the nanotubes. Polarization optical micrographs of the nanotubes showed their thermal stability comparable to PTFE. It is suggested that the plasma filament played a key role in the rapid formation of the nanotubes. This atmospheric plasma discharge synthesis can serve as a common method for nanofabrication of many other single-crystalline polymer systems.

  18. Single crystalline graphene synthesized by thermal annealing of humic acid over copper foils

    NASA Astrophysics Data System (ADS)

    Beall, Gary W.; Duraia, El-Shazly M.; Yu, Q.; Liu, Z.

    2014-02-01

    Production of graphene by thermal annealing on copper foil substrates has been studied with different sources of carbon. The three carbon sources include humic acid derived from leonardite, graphenol, and activated charcoal. Hexagonal single crystalline graphene has been synthesized over the copper foil substrates by thermal annealing of humic acid, derived from leonardite, in argon and hydrogen atmosphere (Ar/H2=20). The annealing temperature was varied between 1050 °C and 1100 °C at atmospheric pressure. Samples have been investigated using scanning electron microscope (SEM) and Raman spectroscopy. At lower temperatures the thermal annealing of the three carbon sources used in this study produces pristine graphene nanosheets which cover almost the whole substrate. However when the annealing temperature has been increased up to 1100 °C, hexagonal single crystalline graphene have been observed only in the case of the humic acid. Raman analysis showed the existence of 2D band around 2690 cm-1.

  19. Highly Polarized and Self-Waveguided Emission from Single-Crystalline Organic Nanobelts

    SciTech Connect

    Che, Yanke; Yang, Xiaomei; Balakrishnan, Kaushik; Zuo, Jianmin; Zang, Ling

    2009-09-15

    Well-defined single-crystalline nanobelts with strong fluorescence were fabricated from a perylene tetracarboxylic diimide molecule modified with specific side-chains that afford flip-flap stacking, rather than the common translated stacking, between the molecules along the long axis of the nanobelt. The nanobelts thus fabricated possess highly polarized, self-waveguided emission, making them ideal candidates for application in nanolasers and other angle-dependent optical nanodevices.

  20. 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. PMID:24740465

  1. 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

  2. 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.

  3. Three-dimensional bicomponent supramolecular nanoporous self-assembly on a hybrid all-carbon atomically flat and transparent platform.

    PubMed

    Li, Juan; Wieghold, Sarah; Öner, Murat Anil; Simon, Patrick; Hauf, Moritz V; Margapoti, Emanuela; Garrido, Jose A; Esch, Friedrich; Palma, Carlos-Andres; Barth, Johannes V

    2014-08-13

    Molecular self-assembly is a versatile nanofabrication technique with atomic precision en route to molecule-based electronic components and devices. Here, we demonstrate a three-dimensional, bicomponent supramolecular network architecture on an all-carbon sp(2)-sp(3) transparent platform. The substrate consists of hydrogenated diamond decorated with a monolayer graphene sheet. The pertaining bilayer assembly of a melamine-naphthalenetetracarboxylic diimide supramolecular network exhibiting a nanoporous honeycomb structure is explored via scanning tunneling microscopy initially at the solution-highly oriented pyrolytic graphite interface. On both graphene-terminated copper and an atomically flat graphene/diamond hybrid substrate, an assembly protocol is demonstrated yielding similar supramolecular networks with long-range order. Our results suggest that hybrid platforms, (supramolecular) chemistry and thermodynamic growth protocols can be merged for in situ molecular device fabrication. PMID:25115337

  4. Broken particle-hole symmetry at atomically flat a-axis YBa2Cu3O7-delta interfaces.

    PubMed

    Davidson, Bruce A; Ramazashvili, Revaz; Kos, Simon; Eckstein, James N

    2004-09-01

    We have studied quasiparticle tunneling into atomically flat a-axis films of YBa(2)Cu(3)O(7-delta) and DyBa(2)Cu(3)O(7-delta) through epitaxial CaTiO3 barriers. The junction heterostructures were grown by oxide molecular beam epitaxy and were carefully optimized using in situ monitoring techniques, resulting in unprecedented crystalline perfection of the superconductor-insulator interface. Below T(c), the tunneling conductance shows the evolution of a large unexpected asymmetrical feature near zero-bias. This is evidence that superconducting YBCO crystals, atomically truncated along the lobe direction with a titanate layer, have intrinsically broken particle-hole symmetry over macroscopically large areas. PMID:15447441

  5. Room-temperature single-electron memory made by pulse-mode atomic force microscopy nano oxidation process on atomically flat α-alumina substrate

    NASA Astrophysics Data System (ADS)

    Matsumoto, Kazuhiko; Gotoh, Yoshitaka; Maeda, Tatsuro; Dagata, John A.; Harris, James S.

    2000-01-01

    A single-electron memory was fabricated using the improved pulse-mode atomic force microscopy nano oxidation process which oxidized the surface of the thin titanium (Ti) metal on the atomically flat α-alumina (α-Al2O3) substrate and formed the narrow oxidized titanium (TiOx) line that works as a tunnel junction for the device. This single-electron memory consists of the multitunnel junction and a memory capacitance. The single-electron transistor, which works as an electrometer, was connected to the memory node of the single-electron memory to detect the potential change of the memory node by the injection of the individual electrons. The fabricated single-electron memory showed the hysteresis loop even at room temperature by the return trip of the memory bias when starting from 0 to 10 V and again coming back to 0 V. About 25 electrons were stored at the memory node.

  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. PMID:26018943

  7. Investigation of the nonlinear refractive index of single-crystalline thin gold films and plasmonic nanostructures

    NASA Astrophysics Data System (ADS)

    Goetz, Sebastian; Razinskas, Gary; Krauss, Enno; Dreher, Christian; Wurdack, Matthias; Geisler, Peter; Pawłowska, Monika; Hecht, Bert; Brixner, Tobias

    2016-04-01

    The nonlinear refractive index of plasmonic materials may be used to obtain nonlinear functionality, e.g., power-dependent switching. Here, we investigate the nonlinear refractive index of single-crystalline gold in thin layers and nanostructures on dielectric substrates. In a first step, we implement a z-scan setup to investigate ~100-µm-sized thin-film samples. We determine the nonlinear refractive index of fused silica, n 2(SiO2) = 2.9 × 10-20 m2/W, in agreement with literature values. Subsequent z-scan measurements of single-crystalline gold films reveal a damage threshold of 0.22 TW/cm2 and approximate upper limits of the real and imaginary parts of the nonlinear refractive index, | n 2'(Au)| < 1.2 × 10-16 m2/W and | n 2″(Au)| < 0.6 × 10-16 m2/W, respectively. To further determine possible effects of a nonlinear refractive index in plasmonic circuitry, interferometry is proposed as a phase-sensitive probe. In corresponding nanostructures, relative phase changes between two propagating near-field modes are converted to amplitude changes by mode interference. Power-dependent experiments using sub-10-fs near-infrared pulses and diffraction-limited resolution (NA = 1.4) reveal linear behavior up to the damage threshold (0.23 times relative to that of a solid single-crystalline gold film). An upper limit for the nonlinear power-dependent phase change between two propagating near-field modes is determined to Δ φ < 0.07 rad.

  8. 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.

  9. 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.

  10. Synthesis of single-crystalline anisotropic gold nano-crystals via chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Manna, Sohini; Kim, Jong Woo; Takahashi, Yukiko; Shpyrko, Oleg G.; Fullerton, Eric E.

    2016-05-01

    We report on a novel one-step catalyst-free, thermal chemical vapor deposition procedure to synthesize gold nanocrystals on silicon substrates. This approach yields single-crystal nanocrystals with various morphologies, such as prisms, icosahedrons, and five-fold twinned decahedrons. Our approach demonstrates that high-quality anisotropic crystals composed of fcc metals can be produced without the need for surfactants or templates. Compared with the traditional wet chemical synthesis processes, our method enables direct formation of highly pure and single crystalline nanocrystals on solid substrates which have applications in catalysis. We investigated the evolution of gold nanocrystals and established their formation mechanism.

  11. Multiple charge-density-wave transitions in single-crystalline Lu2Ir3Si5

    NASA Astrophysics Data System (ADS)

    Sangeetha, N. S.; Thamizhavel, A.; Tomy, C. V.; Basu, Saurabh; Awasthi, A. M.; Rajak, Piu; Bhattacharyya, Somnath; Ramakrishnan, S.; Pal, D.

    2015-05-01

    The physical properties of the single-crystalline samples of Lu2Ir3Si5 have been investigated by magnetic susceptibility, resistivity, and heat capacity studies. We observed multiple charge-density-wave (CDW) transitions in all the measurements. A strong thermal hysteresis at these transitions suggests a possible first order CDW ordering. In addition, the first order nature is ascertained by a very narrow and a huge cusp (62 J/mol K) in the zero field specific heat data which also suggests strong electron-phonon interchain coupling.

  12. Synthesis and ethanol sensing characteristics of single crystalline SnO2 nanorods

    NASA Astrophysics Data System (ADS)

    Chen, Y. J.; Xue, X. Y.; Wang, Y. G.; Wang, T. H.

    2005-12-01

    In a basic water-alcohol mixing solution without any other toxically organic solvents, the single crystalline SnO2 nanorods with diameters of 4-15 nm and lengths of 100-200 nm were synthesized using SnCl4 as a precursor. The sensors fabricated from the nanorods exhibited the sensitivity of 31.4 for 300 ppm of ethanol. Both the response and recovery time are short, around 1 s. Moreover, a linear dependence of the sensitivity on the ethanol concentration was observed. These behaviors were well explained by considering the high surface-to-volume ratio of the nanorods.

  13. Versatile method for template-free synthesis of single crystalline metal and metal alloy nanowires

    NASA Astrophysics Data System (ADS)

    Scott, John A.; Totonjian, Daniel; Martin, Aiden A.; Tran, Toan Trong; Fang, Jinghua; Toth, Milos; McDonagh, Andrew M.; Aharonovich, Igor; Lobo, Charlene J.

    2016-01-01

    Metal and metal alloy nanowires have applications ranging from spintronics to drug delivery, but high quality, high density single crystalline materials have been surprisingly difficult to fabricate. Here we report a versatile, template-free, self-assembly method for fabrication of single crystalline metal and metal alloy nanowires (Co, Ni, NiCo, CoFe, and NiFe) by reduction of metal nitride precursors formed in situ by reaction of metal salts with a nitrogen source. Thiol reduction of the metal nitrides to the metallic phase at 550-600 °C results in nanowire growth. In this process, sulfur acts as a uniaxial structure-directing agent, passivating the surface of the growing nanowires and preventing radial growth. The versatility of the method is demonstrated by achieving nanowire growth from gas-phase, solution-phase or a combination of gas- and solution-phase precursors. The fabrication method is suited to large-area CVD on a wide range of solid substrates.Metal and metal alloy nanowires have applications ranging from spintronics to drug delivery, but high quality, high density single crystalline materials have been surprisingly difficult to fabricate. Here we report a versatile, template-free, self-assembly method for fabrication of single crystalline metal and metal alloy nanowires (Co, Ni, NiCo, CoFe, and NiFe) by reduction of metal nitride precursors formed in situ by reaction of metal salts with a nitrogen source. Thiol reduction of the metal nitrides to the metallic phase at 550-600 °C results in nanowire growth. In this process, sulfur acts as a uniaxial structure-directing agent, passivating the surface of the growing nanowires and preventing radial growth. The versatility of the method is demonstrated by achieving nanowire growth from gas-phase, solution-phase or a combination of gas- and solution-phase precursors. The fabrication method is suited to large-area CVD on a wide range of solid substrates. Electronic supplementary information (ESI) available

  14. Thin-film transistor fabricated in single-crystalline transparent oxide semiconductor.

    PubMed

    Nomura, Kenji; Ohta, Hiromichi; Ueda, Kazushige; Kamiya, Toshio; Hirano, Masahiro; Hosono, Hideo

    2003-05-23

    We report the fabrication of transparent field-effect transistors using a single-crystalline thin-film transparent oxide semiconductor, InGaO3(ZnO)5, as an electron channel and amorphous hafnium oxide as a gate insulator. The device exhibits an on-to-off current ratio of approximately 106 and a field-effect mobility of approximately 80 square centimeters per volt per second at room temperature, with operation insensitive to visible light irradiation. The result provides a step toward the realization of transparent electronics for next-generation optoelectronics. PMID:12764192

  15. 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

  16. 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.

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

    NASA Astrophysics Data System (ADS)

    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, Joel W., III; 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.

  18. 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.

  19. A simple method to synthesize single-crystalline lanthanide orthovanadate nanorods

    NASA Astrophysics Data System (ADS)

    Fan, Weiliu; Zhao, Wei; You, Liping; Song, Xinyu; Zhang, Weimin; Yu, Haiyun; Sun, Sixiu

    2004-12-01

    Single-crystalline tetragonal LnVO 4 ( Ln=La, Nd, Sm, Eu, Dy) nanorods were prepared via a simple hydrothermal method, in the absence of any surfactant or template using cheap and simple inorganic salts as raw materials. The products were characterized by XRD, TEM, HRTEM, and PL. It has been shown that after the hydrothermal process, LaVO 4 transformed its crystal structure from monoclinic to tetragonal phase, but LnVO 4 ( Ln=Nd, Sm, Eu, Dy) have not exhibited the structural change. This could be associated with the change of lanthanide ion radius. TEM and HRTEM results show that the nanorods are pure, structurally uniform, single crystalline, and most of them are free from dislocations. Further study reveals the nanorods grow along the [001] direction. A possible growth mechanism of lanthanide orthovanadate nanorods was also proposed. The advantages of our method for the nanorods synthesis lie in the high yield and the low temperature and mild reaction conditions, which permit large scale production at low cost.

  20. Free-Standing Two-Dimensional Single-Crystalline InSb Nanosheets.

    PubMed

    Pan, D; Fan, D X; Kang, N; Zhi, J H; Yu, X Z; Xu, H Q; Zhao, J H

    2016-02-10

    Growth of high-quality single-crystalline InSb layers remains challenging in material science. Such layered InSb materials are highly desired for searching for and manipulation of Majorana Fermions in solid state, a fundamental research task in physics today, and for development of novel high-speed nanoelectronic and infrared optoelectronic devices. Here, we report on a new route toward growth of single-crystalline, layered InSb materials. We demonstrate the successful growth of free-standing, two-dimensional InSb nanosheets on one-dimensional InAs nanowires by molecular-beam epitaxy. The grown InSb nanosheets are pure zinc-blende single crystals. The length and width of the InSb nanosheets are up to several micrometers and the thickness is down to ∼10 nm. The InSb nanosheets show a clear ambipolar behavior and a high electron mobility. Our work will open up new technology routes toward the development of InSb-based devices for applications in nanoelectronics, optoelectronics, and quantum electronics and for the study of fundamental physical phenomena. PMID:26788662

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

    DOE PAGESBeta

    Chen, Kevin; Kapadia, Rehan; Harker, Audrey; Desai, Sujay; Seuk Kang, Jeong; Chuang, Steven; Tosun, Mahmut; Sutter-Fella, Carolin M.; Tsang, Michael; Zeng, Yuping; et al

    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

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

    SciTech Connect

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

    2014-03-21

    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.

  3. 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

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

    PubMed

    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

  5. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    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.

  7. 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. PMID:19504862

  8. 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.

  9. Versatile method for template-free synthesis of single crystalline metal and metal alloy nanowires.

    PubMed

    Scott, John A; Totonjian, Daniel; Martin, Aiden A; Tran, Toan Trong; Fang, Jinghua; Toth, Milos; McDonagh, Andrew M; Aharonovich, Igor; Lobo, Charlene J

    2016-02-01

    Metal and metal alloy nanowires have applications ranging from spintronics to drug delivery, but high quality, high density single crystalline materials have been surprisingly difficult to fabricate. Here we report a versatile, template-free, self-assembly method for fabrication of single crystalline metal and metal alloy nanowires (Co, Ni, NiCo, CoFe, and NiFe) by reduction of metal nitride precursors formed in situ by reaction of metal salts with a nitrogen source. Thiol reduction of the metal nitrides to the metallic phase at 550-600 °C results in nanowire growth. In this process, sulfur acts as a uniaxial structure-directing agent, passivating the surface of the growing nanowires and preventing radial growth. The versatility of the method is demonstrated by achieving nanowire growth from gas-phase, solution-phase or a combination of gas- and solution-phase precursors. The fabrication method is suited to large-area CVD on a wide range of solid substrates. PMID:26763153

  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. PMID:23054205

  11. Photochemical Modification of Single Crystalline GaN Film Using n-Alkene with Different Carbon Chain Lengths as Biolinker.

    PubMed

    Wang, Chun; Zhuang, Hao; Huang, Nan; Heuser, Steffen; Schlemper, Christoph; Zhai, Zhaofeng; Liu, Baodan; Staedler, Thorsten; Jiang, Xin

    2016-06-14

    As a potential material for biosensing applications, gallium nitride (GaN) films have attracted remarkable attention. In order to construct GaN biosensors, a corresponding immobilization of biolinkers is of great importance in order to render a surface bioactive. In this work, two kinds of n-alkenes with different carbon chain lengths, namely allylamine protected with trifluoroacetamide (TFAAA) and 10-aminodec-1-ene protected with trifluoroacetamide (TFAAD), were used to photochemically functionalize single crystalline GaN films. The successful linkage of both TFAAA and TFAAD to the GaN films is confirmed by time-of-flight secondary ion mass spectrometry (ToF-SIMS) measurement. With increased UV illumination time, the intensity of the secondary ions corresponding to the linker molecules initially increases and subsequently decreases in both cases. Based on the SIMS measurements, the maximum coverage of TFAAA is achieved after 14 h of UV illumination, while only 2 h is required in the case of TFAAD to reach the situation of a fully covered GaN surface. This finding leads to the conclusion that the reaction rate of TFAAD is significantly higher compared to TFAAA. Measurements by atomic force microscopy (AFM) indicate that the coverage of GaN films by a TFAAA layer leads to an increased surface roughness. The atomic terraces, which are clearly observable for the pristine GaN films, disappear once the surface is fully covered by a TFAAA layer. Such TFAAA layers will feature a homogeneous surface topography even for reaction times of 24 h. In contrast to this, TFAAD shows strong cross-polymerization on the surface, this is confirmed by optical microscopy. These results demonstrate that TFAAA is a more suitable candidate as biolinker in context of the GaN surfaces due to its improved controllability. PMID:27217218

  12. Robust ferromagnetism of single crystalline CoxZn1-xO (0.3 ≤ x ≤ 0.45) epitaxial films with high Co concentration

    NASA Astrophysics Data System (ADS)

    Cao, Qiang; Zhu, Dapeng; Fu, Maoxiang; Cai, Li; Yang, Ping; Li, Shuang; Zhu, Yinlian; Ma, Xiuliang; Liu, Guolei; Chen, Yanxue; Yan, Shishen; Mei, Liangmo; Wang, Xiaolin

    2016-08-01

    In contrast to conventional dilute magnetic semiconductors with concentrations of magnetic ions of just a few percent, here, we report the fabrication of epitaxial CoxZn1-xO single crystalline films with Co concentrations from x = 0.3 up to 0.45 by radio-frequency oxygen-plasma-assisted molecular beam epitaxy. The films retain their single crystalline wurtzite structure without any other crystallographic phase from precipitates, based on reflection high energy electron diffraction, X-ray diffraction, transmission electron microscopy, and Raman scattering. The results of X-ray diffraction, optical transmission spectroscopy, and in-situ X-ray photoelectron spectroscopy confirm the incorporation of Co2+ cations into the wurtzite lattice. The films exhibit robust ferromagnetism and the magneto-optical Kerr effect at room temperature. The saturation magnetization reaches 265 emu/cm3 at x = 0.45, which corresponds to the average magnetic moment of 1.5 μ B per Co atom.

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    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.

  14. Strain Anisotropies and Self-limiting Capacities in Single-crystalline 3D Silicon Microstructures: Models for High Energy Denisty Lithium-Ion Battery Anodes

    SciTech Connect

    Goldman, Jason L.; Long, Brandon R.; Gewirth, Andrew A.; Nuzzo, Ralph G

    2011-01-01

    This study examines the crystallographic anisotropy of strain evolution in model, single-crystalline silicon anode microstructures on electrochemical intercalation of lithium atoms. The 3D hierarchically patterned single- crystalline silicon microstructures used as model anodes were prepared using combined methods of photolithography and anisotropic dry and wet chemical etching. Silicon anodes, which possesses theoretically ten times the energy density by weight compared to conventional carbon anodes, reveal highly anisotropic but more importantly, variably recoverable crystallographic strains during cycling. Model strain-limiting silicon anode architectures that mitigate these impacts are highlighted. By selecting a specific design for the silicon anode microstructure, and exploiting the crystallographic anisotropy of strain evolution upon lithium intercalation to control the direction of volumetric expansion, the volume available for expansion and thus the charging capacity of these structures can be broadly varied. We highlight exemplary design rules for this self-strain-limited charging in which an anode can be variably optimized between capacity and stability. Strain-limited capacities ranging from 677 mAhg-1 to 2833 mAhg-1 were achieved by constraining the area available for volumetric expansion via the design rules of the microstructures.

  15. 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. PMID:27389929

  16. 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.

  17. Atomically flat areas on silicon (001) and (111): Fabrication by evaporation or growth and defect characterization

    NASA Astrophysics Data System (ADS)

    Lee, Doohan

    As the dimensions of devices such as field effect transistors, optical devices and layered quantum well structures are decreased, it may be critical to have surfaces and interfaces that are extremely smooth and have no atomic steps at those locations on a wafer where devices will be fabricated and to understand the characteristics of those surfaces. For this work, we have eliminated the atomic steps on Si(111) and Si(001) vicinal surfaces by high temperature annealing and epitaxial growth in the step flow regime on patterned Si substrates with ridges and mesas respectively. In both the annealing and growth cases, the characteristics of the step clearing process as well as the stability of the step free areas are different for Si(111) and Si(001). It is more difficult to make step free regions on Si(001) than on Si(111) mainly due to the smaller adatom diffusivity on Si(001). Excessive annealing (or growth) on large step free areas leads to the formation of circular vacancy pits (or adatom islands). Anisotropic surface diffusion and stress on Si(001) due to the (1 x 2) and (2 x 1) reconstructions lead to interesting step distributions on quenched and slowly cooled Si(001) surfaces which are initially step free. Quenching experiments can give information about the nature and concentrations of point defects on the step free terraces. The result of the quenching experiments are very dependent on quenching conditions such as quenching rate, applied stress, and temperature from which the samples are quenched. The quenched Si(111) surfaces may exhibit some degree of disorder in the reconstructed regions or island formation. A series of experiments have been performed to try to relate the room temperature observations to the defect characteristics at high temperature.

  18. Improvement of electron mobility in La:BaSnO3 thin films by insertion of an atomically flat insulating (Sr,Ba)SnO3 buffer layer

    NASA Astrophysics Data System (ADS)

    Shiogai, Junichi; Nishihara, Kazuki; Sato, Kazuhisa; Tsukazaki, Atsushi

    2016-06-01

    One perovskite oxide, ASnO3 (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 SrTiO3 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 BaSnO3 / (Sr,Ba)SnO3 for buffering this large lattice mismatch between La:BaSnO3 and SrTiO3 substrate. The insertion of 200-nm-thick BaSnO3 on (Sr,Ba)SnO3 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 BaSnO3 buffer layer thickness dependence on Hall mobility of the electron transport in La:BaSnO3 shows that the highest obtained value of mobility is 78 cm2V-1s-1 because of its fewer dislocations. High electron mobility films based on perovskite BaSnO3 can provide a good platform for transparent-conducting-oxide electronic devices and for creation of fascinating perovskite heterostructures.

  19. Weak antilocalization and conductance fluctuation in a single crystalline Bi nanowire

    SciTech Connect

    Kim, Jeongmin; Lee, Seunghyun; Kim, MinGin; Lee, Wooyoung E-mail: pk2015@columbia.edu; Brovman, Yuri M.; Kim, Philip E-mail: pk2015@columbia.edu

    2014-01-27

    We present the low temperature transport properties of an individual single-crystalline Bi nanowire grown by the on-film formation of nanowire method. The temperature dependent resistance and magnetoresistance of Bi nanowires were investigated. The phase coherence length was obtained from the fluctuation pattern of the magnetoresistance below 40 K using universal conductance fluctuation theory. The obtained temperature dependence of phase coherence length and the fluctuation amplitude indicates that the transport of electrons shows 2-dimensional characteristics originating from the surface states. The temperature dependence of the coherence length derived from the weak antilocalization effect using the Hikami–Larkin–Nagaoka model is consistent with that from the universal conductance fluctuations theory.

  20. Mask-free fabrication of inverted-pyramid texture on single-crystalline Si wafer

    NASA Astrophysics Data System (ADS)

    Yang, Bogeum; Lee, Myeongkyu

    2014-11-01

    We here show that inverted-pyramid (IP) textures can be fabricated on single-crystalline Si wafer by simply irradiating the surface with a nanosecond pulsed laser at 532 nm, followed by alkali etching. This process is fundamentally based on the laser-induced melting of material. When exposed to three interfering laser beams, the surface was locally melted in a periodic fashion in accordance with the interference pattern. This generated concave holes on the surface because the melted material overflowed and condensed at the periphery. When subsequently etched by KOH, the internal morphology of the concave holes changed into an IP shape as a result of the position-dependent different etching rates. Uniform IP structures could be obtained with a minimum reflectance of 15.8%.

  1. Synthesis and size-dependent magnetic properties of single-crystalline hematite nanodiscs

    NASA Astrophysics Data System (ADS)

    Bao, Liu; Yang, Heqing; Wang, Xuewen; Zhang, Fenghua; Shi, Ruyu; Liu, Bin; Wang, Lin; Zhao, Hua

    2011-08-01

    Single-crystalline α-Fe 2O 3 nanodiscs with diameters of 132-150 nm were synthesized by a facile and efficient hydrothermal reaction of FeCl 3 with NaH 2PO 4 and H 2O at 200 °C for 12 h. The diameters of the nanodiscs can be decreased to 91-112 and 78-92 nm by adding ethanol glycol into the hydrothermal system. The α-Fe 2O 3 nanodiscs are formed by the cooperative action of selective adsorption and etching of the phosphate ions. The as-synthesized α-Fe 2O 3 nanodiscs exhibit weak ferromagnetic behaviours. The remanent magnetization and coercivity of the nanodiscs with the diameters of 132-150 nm are 0.01743 emu g -1 and 214.8 Oe, respectively, and the remanent magnetization and coercivity decrease with deceasing the nanodisc size.

  2. Finite-size scaling law in single-crystalline Fe3O4 hollow nanostructures

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoping; Wang, Jun; Gao, Miao

    2016-07-01

    Single-crystalline Fe3O4 hollow nanostructures (nanoring and nanotube) have been successfully synthesized by a hydrothermal method along with a heat treatment process. The temperature dependences of the magnetization of the hollow nanostructures were measured under a high vacuum ( < 9.5 × 10‑6 Torr) from 300K to 900K. The Curie temperatures of the nanoring and nanotube samples were found to decrease with decreasing the mean wall thickness. The Curie temperatures of the hollow magnetite nanostructures follow a finite-size scaling relation with the scaling exponent ν = 1.04 ± 0.03. By comparison with those of the zero-dimensional Fe3O4 particles and two-dimensional Fe3O4 films, we show that the scaling relation for our hollow nanostructures is in better agreement with the quasi-two-dimensional finite-size scaling law.

  3. Catalytic Growth of Graphene: Toward Large-Area Single-Crystalline Graphene.

    PubMed

    Ago, Hiroki; Ogawa, Yui; Tsuji, Masaharu; Mizuno, Seigi; Hibino, Hiroki

    2012-08-16

    For electronic applications, synthesis of large-area, single-layer graphene with high crystallinity is required. One of the most promising and widely employed methods is chemical vapor deposition (CVD) using Cu foil/film as the catalyst. However, the CVD graphene is generally polycrystalline and contains a significant amount of domain boundaries that limit intrinsic physical properties of graphene. In this Perspective, we discuss the growth mechanism of graphene on a Cu catalyst and review recent development in the observation and control of the domain structure of graphene. We emphasize the importance of the growth condition and crystallinity of the Cu catalyst for the realization of large-area, single-crystalline graphene. PMID:26295775

  4. Formation of carbon nanostructures containing single-crystalline cobalt carbides by ion irradiation method

    NASA Astrophysics Data System (ADS)

    Wang, Zhipeng; Yusop, Zamri; Ghosh, Pradip; Hayashi, Yasuhiko; Tanemura, Masaki

    2011-02-01

    Carbon nanofibers (CNFs) with a diameter of 17 nm, and carbon nanoneedles (CNNs) with sharp tips have been synthesized on graphite substrates by ion irradiation of argon ions with the Co supplies rate of 1 and 3.4 nm/min, respectively. Energy dispersive X-ray spectrometry, combined with selected area electron diffraction patterns has been used to identify the chemical composition and crystallinity of these carbon nanostructures. The CNFs were found to be amorphous in nature, while the structures of the CNNs consisted of cubic CoCx, orthorhombic Co2C and Co3C depending on the cobalt content in the CNNs. The diameter of the carbide crystals was almost as large as the diameter of the CNN. Compared to the ion-induced nickel carbides and iron carbides, the formation of single-crystalline cobalt carbides might be due to the high temperature produced by the irradiation.

  5. Electrochemical preparation of single-crystalline Cr 2O 3 from molten salts

    NASA Astrophysics Data System (ADS)

    Abe, Hideki; Nishida, Kenji; Imai, Motoharu; Kitazawa, Hideaki

    2004-06-01

    Single crystals of Cr 2O 3 have been grown by means of electrolysis on a 1:100 stoichiometric mixture of CrO 3 and cesium molybdate, Cs 2MoO 4, fused at 1000°C in an ambient atmosphere. Potentiometric measurements on the molten salts have shown the existence of a critical voltage of -320 mV below which hexagonal platelets-shaped single-crystalline Cr 2O 3 is grown on the surface of the working electrode. Coulometry measurements have revealed that the Cr ions are at their highest oxidation state of Cr +6 in the molten electrolyte, which suggests that the electric reduction of Cr +6 to Cr +3 drives the single-crystal growth of Cr 2O 3.

  6. 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

  7. 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.

  8. 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. PMID:24139943

  9. Unusual angular dependent magnetoresistance in single-crystalline Co/Pt bilayers

    NASA Astrophysics Data System (ADS)

    Xiao, X.; Li, J. X.; Ding, Z.; Liang, J. H.; Sun, L.; Wu, Y. Z.

    2016-05-01

    The magnetoresistance (MR) of the single-crystalline Co/Pt(111) bilayers was studied systematically as a function of Co or Pt thickness at room temperature. For Co thickness dCo < 6 nm, the resistances with in-plane magnetization M parallel ( R∥ ) and transverse ( R⊥ ) to current and with a perpendicular M normal ( RP ) to film show the unconventional behavior of RP>R∥>R⊥ . This MR behavior can be attributed to the combination effect of spin Hall MR with RP≈R∥>R⊥ and the geometrical size effect. In addition, the angular dependent magnetoresistance behavior of the (111)-oriented Co/Pt bilayer shows striking difference with that of the (001)-oriented Co/Pt bilayer.

  10. 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.

  11. 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.

  12. 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.

  13. Synthesis and nonlinear optical properties of single-crystalline KNb3O8 nanowires

    NASA Astrophysics Data System (ADS)

    Yu, Bin; Cao, Bo; Cao, Huiqun; Zhang, Xinpeng; Chen, Danni; Qu, Junle; Niu, Hanben

    2013-03-01

    Single-crystalline KNb3O8 nanowires with widths of 100-300 nm and lengths up to tens of microns were synthesized by calcining Nb2O5 powders in molten KCl and K2SO4. The phase of the products was determined by means of x-ray diffraction, and the morphology and structure were characterized by using scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy and selected area electron diffraction techniques. The growth direction of the KNb3O8 obtained was determined to be the [001] crystallographic direction. Meanwhile, the polarization response of the second-harmonic generation (SHG) response was investigated. The as-synthesized nanowires clearly exhibited a SHG response, which means that the nanowires were an efficient nanoscale second-harmonic light source. The excellent nonlinear optical property of KNb3O8 shows potential for application in nano-optical devices.

  14. Synthesis and nonlinear optical properties of single-crystalline KNb3O8 nanowires.

    PubMed

    Yu, Bin; Cao, Bo; Cao, Huiqun; Zhang, Xinpeng; Chen, Danni; Qu, Junle; Niu, Hanben

    2013-03-01

    Single-crystalline KNb(3)O(8) nanowires with widths of 100-300 nm and lengths up to tens of microns were synthesized by calcining Nb(2)O(5) powders in molten KCl and K(2)SO(4). The phase of the products was determined by means of x-ray diffraction, and the morphology and structure were characterized by using scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy and selected area electron diffraction techniques. The growth direction of the KNb(3)O(8) obtained was determined to be the [001] crystallographic direction. Meanwhile, the polarization response of the second-harmonic generation (SHG) response was investigated. The as-synthesized nanowires clearly exhibited a SHG response, which means that the nanowires were an efficient nanoscale second-harmonic light source. The excellent nonlinear optical property of KNb(3)O(8) shows potential for application in nano-optical devices. PMID:23377103

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

    PubMed

    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

    2013-01-01

    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

  16. 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

  17. Carrier Transport Mechanism in Single Crystalline Organic Semiconductor Thin Film Elucidated by Visualized Carrier Motion.

    PubMed

    Matsubara, Kohei; Abe, Kentaro; Manaka, Takaaki; Iwamoto, Mitsumasa

    2016-04-01

    Time-resolved microscopic second harmonic generation (TRM-SHG) measurement was conducted to evaluate temperature dependence of the anisotropic carrier transport process in 6,13-Bis(triisopropylsilylethynyl) (TIPS) pentacene single crystalline domains for two orthogonal directions. Enhancement of the electric field induced SHG (EFI-SHG) signal at the electrode edge at low temperature suggests the presence of potential drop in the injection process. We directly evaluated temperature dependence of the carrier mobility by taking into account the potential drop, and concluded that the Marcus theory is appropriate to interpret the carrier transport in anisotropic TIPS pentacene thin film. TRM-SHG method is a facile and effective way to directly visualize transport process in anisotropic materials and to evaluate injection and transport processes simultaneously. PMID:27451638

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Rational Concept for Designing Vapor-Liquid-Solid Growth of Single Crystalline Metal Oxide Nanowires.

    PubMed

    Klamchuen, Annop; Suzuki, Masaru; Nagashima, Kazuki; Yoshida, Hideto; Kanai, Masaki; Zhuge, Fuwei; He, Yong; Meng, Gang; Kai, Shoichi; Takeda, Seiji; Kawai, Tomoji; Yanagida, Takeshi

    2015-10-14

    Metal oxide nanowires hold great promise for various device applications due to their unique and robust physical properties in air and/or water and also due to their abundance on Earth. Vapor-liquid-solid (VLS) growth of metal oxide nanowires offers the high controllability of their diameters and spatial positions. In addition, VLS growth has applicability to axial and/or radial heterostructures, which are not attainable by other nanowire growth methods. However, material species available for the VLS growth of metal oxide nanowires are substantially limited even though the variety of material species, which has fascinating physical properties, is the most interesting feature of metal oxides. Here we demonstrate a rational design for the VLS growth of various metal oxide nanowires, based on the "material flux window". This material flux window describes the concept of VLS nanowire growth within a limited material flux range, where nucleation preferentially occurs only at a liquid-solid interface. Although the material flux was previously thought to affect primarily the growth rate, we experimentally and theoretically demonstrate that the material flux is the important experimental variable for the VLS growth of metal oxide nanowires. On the basis of the material flux window concept, we discover novel metal oxide nanowires, composed of MnO, CaO, Sm2O3, NiO, and Eu2O3, which were previously impossible to form via the VLS route. The newly grown NiO nanowires exhibited stable memristive properties superior to conventional polycrystalline devices due to the single crystallinity. Thus, this VLS design route offers a useful guideline for the discovery of single crystalline nanowires that are composed of functional metal oxide materials. PMID:26372675

  5. Macroscopic Quantum Tunneling in a Bi2Sr2CaCu2O8+δ Single Crystalline Whisker

    NASA Astrophysics Data System (ADS)

    Kubo, Yuimaru; Takahide, Yamaguchi; Ueda, Shinya; Takano, Yoshihiko; Ootuka, Youiti

    2010-06-01

    Macroscopic quantum tunneling (MQT) has been observed in an intrinsic Josephson junction (IJJ) stack of a Bi2Sr2CaCu2O8+δ (BSCCO) single crystalline whisker with high precision using a home made setup. The cross-over temperature between thermal activation and MQT was about 260 mK, and the Josephson plasma frequency was estimated to be 86 GHz. Both the thermal escape theory and the MQT theory are consistent with the experiments. These facts strongly suggest that single crystalline BSCCO whiskers are high enough quality to be used as intrinsic Josephson quantum devices such as intrinsic Josephson phase qubits. This is the first demonstration of MQT in BSCCO single crystalline whiskers.

  6. 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. PMID:26202730

  7. 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.

  8. Fast growth of inch-sized single-crystalline graphene from a controlled single nucleus on Cu-Ni alloys

    NASA Astrophysics Data System (ADS)

    Wu, Tianru; Zhang, Xuefu; Yuan, Qinghong; Xue, Jiachen; Lu, Guangyuan; Liu, Zhihong; Wang, Huishan; Wang, Haomin; Ding, Feng; Yu, Qingkai; Xie, Xiaoming; Jiang, Mianheng

    2016-01-01

    Wafer-scale single-crystalline graphene monolayers are highly sought after as an ideal platform for electronic and other applications. At present, state-of-the-art growth methods based on chemical vapour deposition allow the synthesis of one-centimetre-sized single-crystalline graphene domains in ~12 h, by suppressing nucleation events on the growth substrate. Here we demonstrate an efficient strategy for achieving large-area single-crystalline graphene by letting a single nucleus evolve into a monolayer at a fast rate. By locally feeding carbon precursors to a desired position of a substrate composed of an optimized Cu-Ni alloy, we synthesized an ~1.5-inch-large graphene monolayer in 2.5 h. Localized feeding induces the formation of a single nucleus on the entire substrate, and the optimized alloy activates an isothermal segregation mechanism that greatly expedites the growth rate. This approach may also prove effective for the synthesis of wafer-scale single-crystalline monolayers of other two-dimensional materials.

  9. Fast growth of inch-sized single-crystalline graphene from a controlled single nucleus on Cu-Ni alloys.

    PubMed

    Wu, Tianru; Zhang, Xuefu; Yuan, Qinghong; Xue, Jiachen; Lu, Guangyuan; Liu, Zhihong; Wang, Huishan; Wang, Haomin; Ding, Feng; Yu, Qingkai; Xie, Xiaoming; Jiang, Mianheng

    2016-01-01

    Wafer-scale single-crystalline graphene monolayers are highly sought after as an ideal platform for electronic and other applications. At present, state-of-the-art growth methods based on chemical vapour deposition allow the synthesis of one-centimetre-sized single-crystalline graphene domains in ∼12 h, by suppressing nucleation events on the growth substrate. Here we demonstrate an efficient strategy for achieving large-area single-crystalline graphene by letting a single nucleus evolve into a monolayer at a fast rate. By locally feeding carbon precursors to a desired position of a substrate composed of an optimized Cu-Ni alloy, we synthesized an ∼1.5-inch-large graphene monolayer in 2.5 h. Localized feeding induces the formation of a single nucleus on the entire substrate, and the optimized alloy activates an isothermal segregation mechanism that greatly expedites the growth rate. This approach may also prove effective for the synthesis of wafer-scale single-crystalline monolayers of other two-dimensional materials. PMID:26595118

  10. 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.

  11. 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

  12. 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. PMID:26832229

  13. 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

    2016-01-01

    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 (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. PMID:26757945

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    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.

  15. Magnetic and Transport properties of single crystalline FeSi1-xGex

    NASA Astrophysics Data System (ADS)

    Yeo, Sunmog; Nakatsuji, Satoru; Bianchi, Andrea; Drymiotis, Fivos; Fisk, Zachary

    2002-03-01

    Title : Magnetic and Transport properties of single crystalline FeSi1-xGex Author : S. Yeo, S. Nakatsuji, A. D. Bianchi*, F. R. Drymiotis, Z. Fisk National High Magnetic Field Laboratory, Florida State University, 1800 East Paul Dirac Drive, Tallahassee, Florida 32306 The isomorphic iron intermetallic compounds FeSi and FeGe have significantly distinct ground states: Kondo insulator and ferromagnetic metal, respectively. We have recently succeeded in growing single crystals of the whole range of the solution system FeSi1-xGex and performed the susceptibility, resistivity and specific heat measurements throughout the composition range. In the Kondo insulating phase near FeSi, we find that the temperature dependence of the susceptibility is well described by a thermally activated Curie law. Starting from 622 K in the case of FeSi, the activation gap systematically decreases below 190 K for Ge concentration near xc ? 0.25. Above xc, we find the sudden appearance of a ferromagnetic phase with Curie temperature of 125 K, comparable to the gap of the neighboring Kondo insulating phase. Both resistivity and specific measurements suggest that the insulator to metal transition occurs around xc. We will show the phase diagram constructed on the basis of these results, and discuss the origin of the interesting evolution of the ground state. This works were supported by NSF-DMR-9971348 * Present address : Los Alamos National Laboratory, Los Alamos, New Mexico 87545

  16. Fabrication of 3D fractal structures using nanoscale anisotropic etching of single crystalline silicon

    NASA Astrophysics Data System (ADS)

    Berenschot, Erwin J. W.; Jansen, Henri V.; Tas, Niels R.

    2013-05-01

    When it comes to high-performance filtration, separation, sunlight collection, surface charge storage or catalysis, the effective surface area is what counts. Highly regular fractal structures seem to be the perfect candidates, but manufacturing can be quite cumbersome. Here it is shown--for the first time—that complex 3D fractals can be engineered using a recursive operation in conventional micromachining of single crystalline silicon. The procedure uses the built-in capability of the crystal lattice to form self-similar octahedral structures with minimal interference of the constructor. The silicon fractal can be used directly or as a mold to transfer the shape into another material. Moreover, they can be dense, porous, or like a wireframe. We demonstrate, after four levels of processing, that the initial number of octahedral structures is increased by a factor of 625. Meanwhile the size decreases 16 times down to 300 nm. At any level, pores of less than 100 nm can be fabricated at the octahedral vertices of the fractal. The presented technique supports the design of fractals with Hausdorff dimension D free of choice and up to D = 2.322.

  17. 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.

  18. 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.

  19. High-Operation-Temperature Plasmonic Nanolasers on Single-Crystalline Aluminum.

    PubMed

    Chou, Yu-Hsun; Wu, Yen-Mo; Hong, Kuo-Bin; Chou, Bo-Tsun; Shih, Jheng-Hong; Chung, Yi-Cheng; Chen, Peng-Yu; Lin, Tzy-Rong; Lin, Chien-Chung; Lin, Sheng-Di; Lu, Tien-Chang

    2016-05-11

    The recent development of plasmonics has overcome the optical diffraction limit and fostered the development of several important components including nanolasers, low-operation-power modulators, and high-speed detectors. In particular, the advent of surface-plasmon-polariton (SPP) nanolasers has enabled the development of coherent emitters approaching the nanoscale. SPP nanolasers widely adopted metal-insulator-semiconductor structures because the presence of an insulator can prevent large metal loss. However, the insulator is not necessary if permittivity combination of laser structures is properly designed. Here, we experimentally demonstrate a SPP nanolaser with a ZnO nanowire on the as-grown single-crystalline aluminum. The average lasing threshold of this simple structure is 20 MW/cm(2), which is four-times lower than that of structures with additional insulator layers. Furthermore, single-mode laser operation can be sustained at temperatures up to 353 K. Our study represents a major step toward the practical realization of SPP nanolasers. PMID:27089144

  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. PMID:24175637

  1. 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

  2. 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

    2015-01-01

    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

  3. 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.

  4. Single-crystalline ZnO sheet Source-Gated Transistors

    NASA Astrophysics Data System (ADS)

    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.

  5. 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.

  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. 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.

  8. 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

  9. 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%.

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

    NASA Astrophysics Data System (ADS)

    Moon, Junghwan; Cho, Maenghyo; Zhou, Min

    2015-06-01

    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. 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

  12. Single-crystalline ceramic whisker-reinforced carboxylic acid-resin composites with fluoride release.

    PubMed

    Xu, H H; Eichmiller, F C; Antonucci, J M; Flaim, G M

    2000-01-01

    Currently available glass-ionomer, resin-modified glass-ionomer, and compomer materials have relatively low strength and toughness and, therefore, are inadequate for use in large stress-bearing posterior restorations. In the present study, ceramic single-crystalline whiskers were mixed with fluorosilicate glass particles and used as fillers to reinforce experimental carboxylic acid-resin composites. The carboxylic acid was a monofunctional methacryloxyethyl phthalate (MEP). Five mass fractions of whisker/(whisker + fluorosilicate glass), and corresponding resin (resin + MEP), were evaluated. Four control materials were also tested for comparison: a glass ionomer, a resin-modified glass ionomer, a compomer, and a hybrid composite resin. Flexural specimens were fabricated to measure the flexural strength, elastic modulus, and work-of-fracture (an indication of toughness). Fluoride release was measured by using a fluoride ion selective electrode. The properties of whisker composites depended on the whisker/(whisker + fluorosilicate glass) mass fraction. At a mass fraction of 0.8, the whisker composite had a flexural strength in MPa (mean +/- sd; n = 6) of 150 +/- 16, significantly higher than that of a glass ionomer (15 +/- 7) or a compomer control (89 +/- 18) (Tukey's multiple comparison test; family confidence coefficient = 0.95). Depending on the ratio of whisker:fluorosilicate glass, the whisker composites had a cumulative fluoride release up to 60% of that of a traditional glass ionomer. To conclude, combining ceramic whiskers and fluorosilicate glass in a carboxylic acid-resin matrix can result in fluoride-releasing composites with significantly improved mechanical properties. PMID:11203805

  13. 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. PMID:27438189

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

    NASA Astrophysics Data System (ADS)

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

    2011-02-01

    We present the magnetic and transport properties of single crystalline U2PdSi3 measured with the magnetic field (H) (or measuring current, I) applied along two typical crystallographic directions, i.e. H\\perp c -axis and H\\parallel c -axis (or I\\perp c -axis and I\\parallel c -axis). For both directions, a spin-glass state is confirmed to form at low temperature with the same spin freezing temperature Tf (= 11.5 K), initial frequency shift δTf (= 0.023) and activation energy Ea/kB (= 90.15 K) in zero dc field. Strong anisotropy in magnetic and transport behavior is found to be a significant feature of U2PdSi3. The unusual ferromagnetic-like anomaly in ac susceptibility and dc magnetization curves around Tm = 71 K is observed in the case of H\\parallel c -axis but not in the cases of H \\perp c -axis. The characteristic temperature Tir, below which evident irreversible magnetism originated from random spin freezing can be observed, shows much stronger field dependence for H \\perp c -axis than for H\\parallel 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 \\perp c -axis, while the coherent-Kondo-effect-like behavior is obvious for I\\parallel 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 U2PdSi3 and other 2:1:3 intermetallic compounds.

  15. 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.

  16. 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.

  17. 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.

  18. 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).

  19. 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.

  20. Dynamic response of single crystalline copper subjected to quasi-isentropic laser and gas-gun driven loading

    NASA Astrophysics Data System (ADS)

    Meyers, M.; Jarmakani, H.; McNaney, J. M.; Schneider, M.; Nguyen, J. H.; Kad, B.

    2006-08-01

    Single crystalline copper was subjected to quasi-isentropic compression via gas-gun and laser loading at pressures between 18 GPa and 59 GPa. The deformation substructure was analyzed via transmission electron microscopy (TEM). Twins and laths were evident at the highest pressures, and stacking faults and dislocation cells in the intermediate and lowest pressures, respectively. The Preston-Tonks-Wallace (PTW) constitutive description was used to model the slip-twinning process in both cases.

  1. 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. PMID:25848830

  2. Aligned Single-Crystalline Perovskite Microwire Arrays for High-Performance Flexible Image Sensors with Long-Term Stability.

    PubMed

    Deng, Wei; Zhang, Xiujuan; Huang, Liming; Xu, Xiuzhen; Wang, Liang; Wang, Jincheng; Shang, Qixun; Lee, Shuit-Tong; Jie, Jiansheng

    2016-03-16

    A simple, low-cost blade-coating method is developed for the large-area fabrication of single-crystalline aligned CH3NH3PbI3 microwire (MW) arrays. The solution-coating method is applicable to flexible substrates, enabling the fabrication of MW-array-based photodetectors with excellent long-term stability, flexibility, and bending durability. Integrated devices from such photodetectors demonstrate high performance for high-resolution, flexible image sensors. PMID:26780594

  3. Dynamic response of single crystalline copper subjected to quasi-isentropic laser and gas-gun driven loading

    SciTech Connect

    Meyers, M; Jarmakani, H; McNaney, J; Schneider, M; Nguyen, J; Kad, B

    2006-05-22

    Single crystalline copper was subjected to quasi-isentropic compression via gas-gun and laser loading at pressures between 18 GPa and 59 GPa. The deformation substructure was analyzed via transmission electron microscopy (TEM). Twins and laths were evident at the highest pressures, and stacking faults and dislocation cells in the intermediate and lowest pressures, respectively. The Preston-Tonks-Wallace (PTW) constitutive description was used to model the slip-twinning process in both cases.

  4. 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.

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

    PubMed

    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

  6. 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

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    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.

  8. Ripple formation on atomically flat cleaved Si surface with roughness of 0.038 nm rms by low-energy Ar{sup 1+} ion bombardment

    SciTech Connect

    Pahlovy, Shahjada A.; Mahmud, S. F.; Yanagimoto, K.; Miyamoto, I.

    2011-03-15

    The authors have conducted research regarding ripple formation on an atomically flat cleaved Si surface by low-energy Ar{sup +} ion bombardment. The cleaved atomically flat and smooth plane of a Si wafer was obtained by cutting vertically against the orientation of a Si (100) wafer. Next, the cleaved surface was sputtered by a 1 keV Ar{sup +} ion beam at ion-incidence angles of 0 deg., 60 deg., 70 deg., and 80 deg. The results confirm the successful ripple formation at ion-incidence angles of 60 deg. - 80 deg. and that the wavelength of the ripples increases with the increase of the ion-incidence angle, as well as the inverse of ion doses. The direction of the ripple also changes from perpendicular to parallel to the projection of the ion-beam direction along the surface with the increasing ion-incidence angle. The authors have also observed the dose effects on surface roughness of cleaved Si surface at the ion-incidence angle of 60 deg., where the surface roughness increases with the increased ion dose. Finally, to understand the roughening mechanism, the authors studied the scaling behavior, measured the roughness exponent {alpha}, and compared the evolution of scaling regimes with Cuerno's one-dimensional simulation results.

  9. Bioreactive self-assembled monolayers on hydrogen-passivated Si(111) as a new class of atomically flat substrates for biological scanning probe microscopy.

    PubMed

    Wagner, P; Nock, S; Spudich, J A; Volkmuth, W D; Chu, S; Cicero, R L; Wade, C P; Linford, M R; Chidsey, C E

    1997-07-01

    This is the first report of bioreactive self-assembled monolayers, covalently bound to atomically flat silicon surfaces and capable of binding biomolecules for investigation by scanning probe microscopy and other surface-related assays and sensing devices. These monolayers are stable under a wide range of conditions and allow tailor-made functionalization for many purposes. We describe the substrate preparation and present an STM and SFM characterization, partly performed with multiwalled carbon nanotubes as tapping-mode supertips. Furthermore, we present two strategies of introducing in situ reactive headgroup functionalities. One method entails a free radical chlorosulfonation process with subsequent sulfonamide formation. A second method employs singlet carbenemediated hydrogen-carbon insertion of a heterobifunctional, amino-reactive trifluoromethyl-diazirinyl crosslinker. We believe that this new substrate is advantageous to others, because it (i) is atomically flat over large areas and can be prepared in a few hours with standard equipment, (ii) is stable under most conditions, (iii) can be modified to adjust a certain degree of reactivity and hydrophobicity, which allows physical adsorption or covalent crosslinking of the biological specimen, (iv) builds the bridge between semiconductor microfabrication and organic/biological molecular systems, and (v) is accessible to nanopatterning and applications requiring conductive substrates. PMID:9245759

  10. Current-direction dependence of the transport properties in single-crystalline face-centered-cubic cobalt films

    NASA Astrophysics Data System (ADS)

    Xiao, X.; Liang, J. H.; Chen, B. L.; Li, J. X.; Ma, D. H.; Ding, Z.; Wu, Y. Z.

    2015-07-01

    Face-centered-cubic cobalt films are epitaxially grown on insulating LaAlO3(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.

  11. 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.

  12. Self-Assembled Organic Single Crystalline Nanosheet for Solution Processed High-Performance n-Channel Field-Effect Transistors.

    PubMed

    Kim, Jin Hong; Park, Sang Kyu; Kim, Jong H; Whang, Dong Ryeol; Yoon, Won Sik; Park, Soo Young

    2016-07-01

    Submillimeter sized n-channel organic single crystalline nanosheet based on dicyanodistyrylbenzene derivative, (2E,2'E)-3,3'-(2,5-dimethoxy-1,4-pheny-lene)bis(2-(5-(4-(trifluoromethyl)phenyl)thiophen-2-yl)acrylonitrile) (Me-4-TFPTA), is developed. Strong π-π interaction, hydrogen bonding interactions derived from cyano group (CN) as well as solvent inclusion along the lateral direction play a key role in forming nanosheet morphology. Me-4-TFPTA nanosheets exhibit excellent field-effect electron mobility of up to 7.81 cm(2) v(-1) s(-1) . PMID:27165653

  13. Dynamic instabilities during the continuous electro-oxidation of CO on poly- and single crystalline Pt electrodes

    NASA Astrophysics Data System (ADS)

    Malkhandi, Sauradip; Bonnefont, Antoine; Krischer, Katharina

    2009-06-01

    Dynamic instabilities during bulk CO electro-oxidation on poly- and single crystalline rotating Pt electrodes in different electrolytes were investigated experimentally. In sulphuric and perchloric electrolytic media, only bistability is observed. The dependence of the width of the bistable regime on some parameters is discussed. The addition of small amounts of chloride ions induces current oscillations under potentiostatic conditions on polycrystalline Pt, Pt(1 1 0) and Pt(1 0 0) electrodes. Existence range, shape and mean frequency of the mainly irregular kinetic oscillations vary significantly with the crystallographic structure of the electrode surface.

  14. Investigation of electrically-active deep levels in single-crystalline diamond by particle-induced charge transient spectroscopy

    NASA Astrophysics Data System (ADS)

    Kada, W.; Kambayashi, Y.; Ando, Y.; Onoda, S.; Umezawa, H.; Mokuno, Y.; Shikata, S.; Makino, T.; Koka, M.; Hanaizumi, O.; Kamiya, T.; Ohshima, T.

    2016-04-01

    To investigate electrically-active deep levels in high-resistivity single-crystalline diamond, particle-induced charge transient spectroscopy (QTS) techniques were performed using 5.5 MeV alpha particles and 9 MeV carbon focused microprobes. For unintentionally-doped (UID) chemical vapor deposition (CVD) diamond, deep levels with activation energies of 0.35 eV and 0.43 eV were detected which correspond to the activation energy of boron acceptors in diamond. The results suggested that alpha particle and heavy ion induced QTS techniques are the promising candidate for in-situ investigation of deep levels in high-resistivity semiconductors.

  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. 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

  17. 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.

  18. 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.

  19. High quality single atomic layer deposition of hexagonal boron nitride on single crystalline Rh(111) four-inch wafers.

    PubMed

    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. PMID:24689614

  20. 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.

  1. 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. PMID:24028676

  2. Towards intrinsic graphene biosensor: A label-free, suspended single crystalline graphene sensor for multiplex lung cancer tumor markers detection.

    PubMed

    Li, Peng; Zhang, Bo; Cui, Tianhong

    2015-10-15

    Graphene biosensors reported so far are based on polycrystalline graphene flakes which are anchored on supporting substrates. The influence of grain boundary and the scattering from substrate drastically degrade the properties of graphene and conceal the performance of intrinsic graphene as a sensor. Here we report a label-free biosensor based on suspended single crystalline graphene (SCG), which can get rid of grain boundary and substrate scattering, revealing the biosensing mechanism of intrinsic graphene for the first time. Monolayer SCG flakes were derived from low pressure chemical vapor deposition (LPCVD) method. Multiplex detection of three different lung cancer tumor markers was realized. The suspended structure can largely improve the sensitivity and detection limit (0.1 pg/ml) of the sensor, and the single crystalline nature of SCG enable the biosensor to have superior uniformity compared to polycrystalline ones. The SCG sensors exhibit superb specificity and large linear detection range from 1 pg/ml to 1 μg/ml, showing the prominent advantages of graphene as a sensing material. PMID:25982724

  3. Oriented single crystalline TiO 2 nano-pillar arrays directly grown on titanium substrate in tetramethylammonium hydroxide solution

    NASA Astrophysics Data System (ADS)

    Dong, Xiang; Tao, Jie; Li, Yingying; Zhu, Hong

    2010-02-01

    Oriented single crystalline titanium dioxide (TiO 2) nano-pillar arrays were directly synthesized on the Ti plate in tetramethylammonium hydroxide (TMAOH) solution by one-pot hydrothermal method. The samples were characterized respectively by means of field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD). Results showed that the TiO 2 nano-pillar with a tetrahydral bipyramidal tip grew vertically on the titanium substrate. HRTEM and Raman results confirmed that the TiO 2 nano-pillar arrays were single crystalline anatase. The controls of morphology, size, and orientation of the nano-pillar could be achieved by varying the solution concentration and hydrothermal temperature. Furthermore, the special morphology of the TiO 2 nano-pillar arrays was caused by the selectively absorption of the tetramethylammonium (TMA) through hydrogen bonds on the lattice planes parallel to (0 0 1) of anatase TiO 2. Less grain boundaries and direct electrical pathway for electron transferring were crucial for the superior photoelectrochemical properties of the single anatase TiO 2 nano-pillar arrays. This approach provides a facile in situ method to synthesize TiO 2 nano-pillar arrays with a special morphology on titanium substrate.

  4. Synthesis and electrochromic property of single-crystalline V2O5 nanorod arrays by template-based deposition

    NASA Astrophysics Data System (ADS)

    Takahashi, Katsunori; Limmer, Steven J.; Wang, Ying; Cao, Guozhong

    2004-10-01

    Growth and electrochemical and optical properties of single crystalline vanadium pentoxide (V2O5) nanorod arrays were investigated. Vanadium pentoxide nanorod arrays were grown by electrochemical deposition, surface condensation induced by a pH change and sol electrophoretic deposition. Uniformly sized vanadium oxide nanorods with a length of about 10μm and diameters of 100 or 200nm were grown over a large area with near unidirectional alignment. TEM micrographs and electron diffraction patterns of V2O5 nanorods clearly show the single-crystalline nature of nanorods from all three growth routes with a growth direction of [010]. The growth mechanisms of single crystal vanadium pentoxide nanorods have been discussed. The transmittance of nanorod arrays decrease more quickly under applied electric field than sol-gel derived film, which suggests nanorod array electrodes possess significantly improved charge/discharge rate. Electrochemical analysis is proves that nanorod arrays have higher efficiency than sol-gel derived film. The relationships between electrochemical and optical properties, nano and microstructures, and growth mechanisms have been discussed.

  5. 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.

  6. Highly mesoporous single-crystalline zeolite beta synthesized using a nonsurfactant cationic polymer as a dual-function template.

    PubMed

    Zhu, Jie; Zhu, Yihan; Zhu, Liangkui; Rigutto, Marcello; van der Made, Alexander; Yang, Chengguang; Pan, Shuxiang; Wang, Liang; Zhu, Longfeng; Jin, Yinying; Sun, Qi; Wu, Qinming; Meng, Xiangju; Zhang, Daliang; Han, Yu; Li, Jixue; Chu, Yueying; Zheng, Anmin; Qiu, Shilun; Zheng, Xiaoming; Xiao, Feng-Shou

    2014-02-12

    Mesoporous zeolites are useful solid catalysts for conversion of bulky molecules because they offer fast mass transfer along with size and shape selectivity. We report here the successful synthesis of mesoporous aluminosilicate zeolite Beta from a commercial cationic polymer that acts as a dual-function template to generate zeolitic micropores and mesopores simultaneously. This is the first demonstration of a single nonsurfactant polymer acting as such a template. Using high-resolution electron microscopy and tomography, we discovered that the resulting material (Beta-MS) has abundant and highly interconnected mesopores. More importantly, we demonstrated using a three-dimensional electron diffraction technique that each Beta-MS particle is a single crystal, whereas most previously reported mesoporous zeolites are comprised of nanosized zeolitic grains with random orientations. The use of nonsurfactant templates is essential to gaining single-crystalline mesoporous zeolites. The single-crystalline nature endows Beta-MS with better hydrothermal stability compared with surfactant-derived mesoporous zeolite Beta. Beta-MS also exhibited remarkably higher catalytic activity than did conventional zeolite Beta in acid-catalyzed reactions involving large molecules. PMID:24450997

  7. 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. PMID:19711908

  8. Single Crystalline Co3O4 Nanocrystals Exposed with Different Crystal Planes for Li-O2 Batteries

    NASA Astrophysics Data System (ADS)

    Su, Dawei; Dou, Shixue; Wang, Guoxiu

    2014-08-01

    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}.

  9. Effect of nitridation surface treatment on silicon (1 1 1) substrate for the growth of high quality single-crystalline GaN hetero-epitaxy layer by MOCVD

    NASA Astrophysics Data System (ADS)

    Rahman, Mohd Nazri Abd.; Yusuf, Yusnizam; Mansor, Mazwan; Shuhaimi, Ahmad

    2016-01-01

    A single-crystalline with high quality of gallium nitride epilayers was grown on silicon (1 1 1) substrate by metal organic chemical vapor deposition. The process of nitridation surface treatment was accomplished on silicon (1 1 1) substrate by flowing the ammonia gaseous. Then, it was followed by a thin aluminum nitride nucleation layer, aluminum nitride/gallium nitride multi-layer and a thick gallium nitride epilayer. The influence of in situ nitridation surface treatment on the crystallinity quality of gallium nitride epilayers was studied by varying the nitridation times at 40, 220 and 400 s, respectively. It was shown that the nitridation times greatly affect the structural properties of the grown top gallium nitride epilayer on silicon (1 1 1) substrate. In the (0 0 0 2) and (1 0 1 bar 2) X-ray rocking curve analysis, a narrower value of full width at half-maximum has been obtained as the nitridation time increased. This is signifying the reduction of dislocation density in the gallium nitride epilayer. This result was supported by the value of bowing and root mean square roughness measured by surface profilometer and atomic force microscopy. Furthermore, a crack-free gallium nitride surface with an abrupt cross-sectional structure that observed using field effect scanning electron microscopy was also been obtained. The phi-scan curve of asymmetric gallium nitride proved the top gallium nitride epilayer exhibited a single-crystalline structure.

  10. Oxygen-Driven Porous Film Formation of Single-Crystalline Ru Deposited on Au(111).

    PubMed

    Herd, Benjamin; Langsdorf, Daniel; Sack, Christian; He, Yunbin; Over, Herbert

    2016-05-31

    We examined the interaction of oxygen with ultrathin Ru layers deposited on a Au(111) substrate using scanning tunneling microscopy, X-ray photoelectron spectroscopy, and low-energy electron diffraction. The deposition of pure Ru below one monolayer (ML) at room temperature leads to the formation of clusters on the Au(111) surface, preferentially located at the elbow sites of the herringbone reconstruction. Subsequent exposure of molecular oxygen to such a Ru-covered Au(111) surface at 680 K results in the growth of two-layer-thick Ru islands that are embedded in the top Au(111) layer. This structural reorganization of Ru is driven by the minimization of surface energy and mediated by a mobile RuOx species. Deposition of an increasing amount of Ru at 620 K (0.5-10 ML, ML = monolayer) leads to a rough Ru film on Au(111). Subsequent oxygen treatment (10(-5) mbar) at 680 K creates either a porous Ru film (<4 ML) or a flat RuO2(110) film (>6 ML) depending on the thickness of the Ru film. PMID:27173402

  11. 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

  12. 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).

  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. PMID:27483844

  14. 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.

  15. 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

  16. 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.

  17. 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

  18. Mechanical properties of bulk single crystalline nanoporous gold investigated by millimetre-scale tension and compression testing

    NASA Astrophysics Data System (ADS)

    Briot, Nicolas J.; Kennerknecht, Tobias; Eberl, Christoph; Balk, T. John

    2014-03-01

    In this work, the mechanical behaviour of millimetre-scale, bulk single crystalline, nanoporous gold at room temperature is reported for the first time. Tension and compression tests were performed with a custom-designed test system that accommodates small-scale samples. The absence of grain boundaries in the specimens allowed measurement of the inherent strength of millimetre-scale nanoporous gold in tension. The elastic modulus and strength values in tension and compression were found to be significantly lower than values measured with nanoindentation-based techniques and previously reported in the literature, but close to those reported for millimetre-scale polycrystalline samples tested using traditional compression techniques. Fracture toughness was found to be very low, in agreement with the macroscopic brittleness of nanoporous gold, but this is due to the localization of deformation to a narrow zone of ligaments, which individually exhibit significant plasticity and necking.

  19. 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.

  20. 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.

  1. 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.

  2. Influence of crystal orientation and ion bombardment on the nitrogen diffusivity in single-crystalline austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Martinavičius, A.; Abrasonis, G.; Möller, 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-2), ion energy (0.5-1.2 keV), and temperature (370-430 °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.

  3. 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.

  4. 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

  5. Quantum size effect on Shubnikov-de Haas oscillations in 100 nm diameter single-crystalline bismuth nanowire

    NASA Astrophysics Data System (ADS)

    Kim, Jeongmin; Kim, Dohun; Chang, Taehoo; Lee, Wooyoung

    2014-09-01

    Quantum size effect (QSE) in Bi nanowire is theoretically predicted to decrease band overlap energy resulting in semimetal-to-semiconductor transition. However, this effect has been rarely demonstrated on transport properties because of carrier-surface scattering and charge carriers induced from surface states of Bi. We report QSE on Shubnikov-de Haas (SdH) oscillations in a single-crystalline Bi nanowire with a diameter of 100 nm. The variation of intrinsic properties estimated using SdH oscillations indicates that the subband energy shift due to QSE. The enhanced effective mass of the electrons is consistent with the theoretical prediction pertaining to strong electron-hole coupling of Bi.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Single-Crystalline B12As2 on m-plane (1100) 15R-SiC

    SciTech Connect

    Chen,H.; Wang, G.; Dudley, M.; Xu, Z.; Edgar, J.; Batten, T.; Kuball, M.; Zhang, L.; Zhu, Y.

    2008-01-01

    Single crystal, heteroepitaxial growth of icosahedral B12As2 (IBA, a boride semiconductor) on m-plane 15R-SiC is demonstrated. Previous studies of IBA on other substrates, i.e., (111)Si and (0001)6H-SiC, produced polycrystalline and twinned epilayers. In contrast, single-crystalline and untwinned IBA was achieved on m-plane 15R-SiC. Synchrotron white beam x-ray topography, Raman spectroscopy, and high resolution transmission electron microscopy confirm the high quality of the films. High quality growth is shown to be mediated by ordered nucleation of IBA on (474) substrate facets. This work demonstrates that m-plane 15R-SiC is a good substrate choice to grow high-quality untwinned IBA epilayers for future device applications.