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Sample records for scanning tunneling spectra

  1. Scanning tunneling microscope light emission spectra of polycrystalline GeSbTe and SbTe

    Science.gov (United States)

    Uehara, Y.; Kuwahara, M.; Katano, S.; Ushioda, S.

    2009-11-01

    We have observed scanning tunneling microscope light emission (STM-LE) spectra of Ge 2Sb 2Te 5 and Sb 2Te 3. Although these chalcogenide alloys exhibit band gaps less than 0.5 eV, the STM-LE was observed with a narrow spectral width at a photon energy of 1.5 eV for both materials. By analyzing its bias voltage, polarity, and temperature dependencies combined with recently reported theoretical electronic structures, we concluded that the STM-LE is excited by electronic transitions taking place in the local electronic structure having a direct gap-like shape with a band gap of 1.5 eV, commonly found in the electronic structures of both materials.

  2. Ultrafast scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Botkin, D.A. [California Univ., Berkeley, CA (United States). Dept. of Physics]|[Lawrence Berkeley Lab., CA (United States)

    1995-09-01

    I have developed an ultrafast scanning tunneling microscope (USTM) based on uniting stroboscopic methods of ultrafast optics and scanned probe microscopy to obtain nanometer spatial resolution and sub-picosecond temporal resolution. USTM increases the achievable time resolution of a STM by more than 6 orders of magnitude; this should enable exploration of mesoscopic and nanometer size systems on time scales corresponding to the period or decay of fundamental excitations. USTM consists of a photoconductive switch with subpicosecond response time in series with the tip of a STM. An optical pulse from a modelocked laser activates the switch to create a gate for the tunneling current, while a second laser pulse on the sample initiates a dynamic process which affects the tunneling current. By sending a large sequence of identical pulse pairs and measuring the average tunnel current as a function of the relative time delay between the pulses in each pair, one can map the time evolution of the surface process. USTM was used to measure the broadband response of the STM`s atomic size tunnel barrier in frequencies from tens to hundreds of GHz. The USTM signal amplitude decays linearly with the tunnel junction conductance, so the spatial resolution of the time-resolved signal is comparable to that of a conventional STM. Geometrical capacitance of the junction does not appear to play an important role in the measurement, but a capacitive effect intimately related to tunneling contributes to the measured signals and may limit the ultimate resolution of the USTM.

  3. Femtosecond scanning tunneling microscope

    Energy Technology Data Exchange (ETDEWEB)

    Taylor, A.J.; Donati, G.P.; Rodriguez, G.; Gosnell, T.R.; Trugman, S.A.; Some, D.I.

    1998-11-01

    This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). By combining scanning tunneling microscopy with ultrafast optical techniques we have developed a novel tool to probe phenomena on atomic time and length scales. We have built and characterized an ultrafast scanning tunneling microscope in terms of temporal resolution, sensitivity and dynamic range. Using a novel photoconductive low-temperature-grown GaAs tip, we have achieved a temporal resolution of 1.5 picoseconds and a spatial resolution of 10 nanometers. This scanning tunneling microscope has both cryogenic and ultra-high vacuum capabilities, enabling the study of a wide range of important scientific problems.

  4. Identifying the Assembly Configuration and Fluorescence Spectra of Nanoscale Zinc-Tetraphenylporphyrin Aggregates with Scanning Tunneling Microscopy

    Science.gov (United States)

    Zhang, Xiao-Lei; Jiang, Jian-Wei; Liu, Yi-Ting; Lou, Shi-Tao; Gao, Chun-Lei; Jin, Qing-Yuan

    2016-03-01

    ZnTPP (Zinc-Tetraphenylporphyrin) is one of the most common nanostructured materials, having high stability and excellent optoelectronic properties. In this paper, the fluorescence features of self-assembled ZnTPP monomers and aggregates on Au(111) surface are investigated in detail on the nanometer scale with scanning tunneling microscopy (STM). The formation of ZnTPP dimers is found in thick layers of a layer-by-layer molecular assembly on Au substrate with its specific molecular arrangement well characterized. Tip-induced luminescence shows a red shift from tilted dimers comparing with the behavior from monomers, which can be attributed to the change of vibrational states due to the intermolecular interaction and the increasing dielectric effect. The nanoscale configuration dependence of electroluminescence is demonstrated to provide a powerful tool aiding the design of functional molecular photoelectric devices.

  5. Introduction to scanning tunneling microscopy

    CERN Document Server

    Chen, C Julian

    2008-01-01

    The scanning tunneling and the atomic force microscope, both capable of imaging individual atoms, were crowned with the Physics Nobel Prize in 1986, and are the cornerstones of nanotechnology today. This is a thoroughly updated version of this 'bible' in the field.

  6. Tunneling spectra of graphene on copper unraveled.

    Science.gov (United States)

    Zhang, Xin; Stradi, Daniele; Liu, Lei; Luo, Hong; Brandbyge, Mads; Gu, Gong

    2016-06-22

    Scanning tunneling spectroscopy is often employed to study two-dimensional (2D) materials on conductive growth substrates, in order to gain information on the electronic structures of the 2D material-substrate systems, which can lead to insight into 2D material-substrate interactions, growth mechanisms, etc. The interpretation of the spectra can be complicated, however. Specifically for graphene grown on copper, there have been conflicting reports of tunneling spectra. A clear understanding of the mechanisms behind the variability is desired. In this work, we have revealed that the root cause of the variability in tunneling spectra is the variation in graphene-substrate coupling under various experimental conditions, providing a salutary perspective on the important role of 2D material-substrate interactions. The conclusions are drawn from measured data and theoretical calculations for monolayer, AB-stacked bilayer, and twisted bilayer graphene coexisting on the same substrates in areas with and without intercalated oxygen, demonstrating a high degree of consistency. The Van Hove singularities of the twisted graphene unambiguously indicate the Dirac energy between them, lending strong evidence to our assignment of the spectral features. In addition, we have discovered an O-Cu superstructure that has never been observed before.

  7. Seismic scanning tunneling macroscope - Theory

    KAUST Repository

    Schuster, Gerard T.

    2012-09-01

    We propose a seismic scanning tunneling macroscope (SSTM) that can detect the presence of sub-wavelength scatterers in the near-field of either the source or the receivers. Analytic formulas for the time reverse mirror (TRM) profile associated with a single scatterer model show that the spatial resolution limit to be, unlike the Abbe limit of λ/2, independent of wavelength and linearly proportional to the source-scatterer separation as long as the point scatterer is in the near-field region; if the sub-wavelength scatterer is a spherical impedance discontinuity then the resolution will also be limited by the radius of the sphere. Therefore, superresolution imaging can be achieved as the scatterer approaches the source. This is analogous to an optical scanning tunneling microscope that has sub-wavelength resolution. Scaled to seismic frequencies, it is theoretically possible to extract 100 Hz information from 20 Hz data by imaging of near-field seismic energy.

  8. Fiber coupled ultrafast scanning tunneling microscope

    DEFF Research Database (Denmark)

    Keil, Ulrich Dieter Felix; Jensen, Jacob Riis; Hvam, Jørn Märcher

    1997-01-01

    We report on a scanning tunneling microscope with a photoconductive gate in the tunneling current circuit. The tunneling tip is attached to a coplanar transmission line with an integrated photoconductive switch. The switch is illuminated through a fiber which is rigidly attached to the switch...

  9. Colloquium: Time-resolved scanning tunneling microscopy

    NARCIS (Netherlands)

    Houselt, van Arie; Zandvliet, Harold J.W.

    2010-01-01

    Scanning tunneling microscopy has revolutionized our ability to image, study, and manipulate solid surfaces on the size scale of atoms. One important limitation of the scanning tunneling microscope (STM) is, however, its poor time resolution. Recording a standard image with a STM typically takes abo

  10. Investigation into scanning tunnelling luminescence microscopy

    CERN Document Server

    Manson-Smith, S K

    2001-01-01

    This work reports on the development of a scanning tunnelling luminescence (STL) microscope and its application to the study of Ill-nitride semiconductor materials used in the production of light emitting devices. STL microscopy is a technique which uses the high resolution topographic imaging capabilities of the scanning tunnelling microscope (STM) to generate high resolution luminescence images. The STM tunnelling current acts as a highly localised source of electrons (or holes) which generates luminescence in certain materials. Light generated at the STM tunnelling junction is collected concurrently with the height variation of the tunnelling probe as it is scanned across a sample surface, producing simultaneous topographic and luminescence images. Due to the very localised excitation source, high resolution luminescence images can be obtained. Spectroscopic resolution can be obtained by using filters. Additionally, the variation of luminescence intensity with tunnel current and with bias voltage can provi...

  11. Tunneling spectra of graphene on copper unraveled

    DEFF Research Database (Denmark)

    Zhang, Xin; Stradi, Daniele; Liu, Lei

    2016-01-01

    mechanisms, etc. The interpretation of the spectra can be complicated, however. Specifically for graphene grown on copper, there have been conflicting reports of tunneling spectra. A clear understanding of the mechanisms behind the variability is desired. In this work, we have revealed that the root cause...

  12. Scanning tunneling spectroscopy of Pb thin films

    Energy Technology Data Exchange (ETDEWEB)

    Becker, Michael

    2010-12-13

    The present thesis deals with the electronic structure, work function and single-atom contact conductance of Pb thin films, investigated with a low-temperature scanning tunneling microscope. The electronic structure of Pb(111) thin films on Ag(111) surfaces is investigated using scanning tunneling spectroscopy (STS). Quantum size effects, in particular, quantum well states (QWSs), play a crucial role in the electronic and physical properties of these films. Quantitative analysis of the spectra yields the QWS energies as a function of film thickness, the Pb bulk-band dispersion in {gamma}-L direction, scattering phase shifts at the Pb/Ag interface and vacuum barrier as well as the lifetime broadening at anti {gamma}. The work function {phi} is an important property of surfaces, which influences catalytic reactivity and charge injection at interfaces. It controls the availability of charge carriers in front of a surface. Modifying {phi} has been achieved by deposition of metals and molecules. For investigating {phi} at the atomic scale, scanning tunneling microscopy (STM) has become a widely used technique. STM measures an apparent barrier height {phi}{sub a}, which is commonly related to the sample work function {phi}{sub s} by: {phi}{sub a}=({phi}{sub s}+{phi}{sub t}- vertical stroke eV vertical stroke)/2, with {phi}{sub t} the work function of the tunneling tip, V the applied tunneling bias voltage, and -e the electron charge. Hence, the effect of the finite voltage in STM on {phi}{sub a} is assumed to be linear and the comparison of {phi}{sub a} measured at different surface sites is assumed to yield quantitative information about work function differences. Here, the dependence of {phi}{sub a} on the Pb film thickness and applied bias voltage V is investigated. {phi}{sub a} is found to vary significantly with V. This bias dependence leads to drastic changes and even inversion of contrast in spatial maps of {phi}{sub a}, which are related to the QWSs in the Pb

  13. A Student-Built Scanning Tunneling Microscope

    Science.gov (United States)

    Ekkens, Tom

    2015-01-01

    Many introductory and nanotechnology textbooks discuss the operation of various microscopes including atomic force (AFM), scanning tunneling (STM), and scanning electron microscopes (SEM). In a nanotechnology laboratory class, students frequently utilize microscopes to obtain data without a thought about the detailed operation of the tool itself.…

  14. Towards high-speed scanning tunneling microscopy

    NARCIS (Netherlands)

    Tabak, Femke Chantal

    2013-01-01

    In this thesis, two routes towards high-speed scanning tunneling microscopy (STM) are described. The first possibility for high-speed scanning that is discussed is the use of MEMS (Micro-Electro Mechanical Systems) devices as high-speed add-ons in STM microscopes. The functionality of these devices

  15. Scanning tunneling microscope assembly, reactor, and system

    Science.gov (United States)

    Tao, Feng; Salmeron, Miquel; Somorjai, Gabor A

    2014-11-18

    An embodiment of a scanning tunneling microscope (STM) reactor includes a pressure vessel, an STM assembly, and three spring coupling objects. The pressure vessel includes a sealable port, an interior, and an exterior. An embodiment of an STM system includes a vacuum chamber, an STM reactor, and three springs. The three springs couple the STM reactor to the vacuum chamber and are operable to suspend the scanning tunneling microscope reactor within the interior of the vacuum chamber during operation of the STM reactor. An embodiment of an STM assembly includes a coarse displacement arrangement, a piezoelectric fine displacement scanning tube coupled to the coarse displacement arrangement, and a receiver. The piezoelectric fine displacement scanning tube is coupled to the coarse displacement arrangement. The receiver is coupled to the piezoelectric scanning tube and is operable to receive a tip holder, and the tip holder is operable to receive a tip.

  16. SCANNING TUNNELING MICROSCOPY STUDIES ON OPTICAL DISC

    Institute of Scientific and Technical Information of China (English)

    徐磊; 顾冬红; 等

    1994-01-01

    Scanning tunneling microscope(STM) is used to investigate the optical dise.The areas with and without data stampers are all observedcarefully.Three-dimensional images of the disc surface clearly demonstrate the period.depth of the grooves and the shape of data stampers.Some phenomena of STM imaging are also discussed.

  17. Traceable long range scanning tunneling microscopy

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Dimensionally correct and directly traceable measurement is not feasible with conventional scanning tunneling microscopy (STMs) due to severe hysteresis and non-linearity of the commonly applied piezo tube scanners and the very short range.By integrating a custom made probing system based on tunneling current measurement into a commercially available and laser-interferometrically position controlled positioning system, an STM with a principal measuring range of 25 mm×25 mm×5 mm and traceable position measurement has been set-up and tested.

  18. Vibration Compensation for Scanning Tunneling Microscope

    Institute of Scientific and Technical Information of China (English)

    LI Meng-chao; FU Xing; WEI Xiao-lei; HU Xiao-tang

    2003-01-01

    The influence of vibration is already one of main obstacles for improving the nano measuring accuracy.The techniques of anti-vibration,vibration isolation and vibration compensation become an important branch in nano measuring field.Starting with the research of sensitivity to vibration of scanning tunneling microscope(STM),the theory,techniques and realization methods of nano vibration sensor based on tunnel effect are initially investigated,followed by developing the experimental devices.The experiments of the vibration detection and vibration compensation are carried out.The experimental results show that vibration sensor based on tunnel effect is characterized by high sensitivity,good frequency characteristic and the same vibratory response characteristic consistent with STM.

  19. Scanning tunneling microscopy II further applications and related scanning techniques

    CERN Document Server

    Güntherodt, Hans-Joachim

    1992-01-01

    Scanning Tunneling Microscopy II, like its predecessor, presents detailed and comprehensive accounts of the basic principles and broad range of applications of STM and related scanning probe techniques. The applications discussed in this volume come predominantly from the fields of electrochemistry and biology. In contrast to those described in Vol. I, these sudies may be performed in air and in liquids. The extensions of the basic technique to map other interactions are described inchapters on scanning force microscopy, magnetic force microscopy, scanning near-field optical microscopy, together with a survey of other related techniques. Also described here is the use of a scanning proximal probe for surface modification. Togehter, the two volumes give a comprehensive account of experimental aspcets of STM. They provide essentialreading and reference material for all students and researchers involvedin this field.

  20. Scanning tunneling microscopy II further applications and related scanning techniques

    CERN Document Server

    Güntherodt, Hans-Joachim

    1995-01-01

    Scanning Tunneling Microscopy II, like its predecessor, presents detailed and comprehensive accounts of the basic principles and broad range of applications of STM and related scanning probe techniques. The applications discussed in this volume come predominantly from the fields of electrochemistry and biology. In contrast to those described in STM I, these studies may be performed in air and in liquids. The extensions of the basic technique to map other interactions are described in chapters on scanning force microscopy, magnetic force microscopy, and scanning near-field optical microscopy, together with a survey of other related techniques. Also described here is the use of a scanning proximal probe for surface modification. Together, the two volumes give a comprehensive account of experimental aspects of STM. They provide essential reading and reference material for all students and researchers involved in this field. In this second edition the text has been updated and new methods are discussed.

  1. Topography Structure and Scanning Tunneling Spectrum of Nickel(Ⅱ)-tetraphenylporphyrin Molecules on Au(111)

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) were performed on monolayer film of NiTPP supported on Au(111) under ultrahigh vacuum (UHV) conditions. The constant current STM images show remarkable bias dependence. High resolution STM data clearly show the individual NiTPP molecules and allow easy differentiation between NiTPP and CoTPP reported before. Scanning tunneling spectra, as a function of molecule-tip separation, were acquired over a range of tip motion of 0.42 nm. Spectra do not show the variation in band splitting with tip distance. It appears for molecules such as NiTPP that the average potential at the molecule is essentially the same at the same metal substrate. For molecules of the height of NiTPP, the scanning tunneling spectra should give reliable occupied and unoccupied orbital energies over a wide range of tip-molecule distances.

  2. Conductivity map from scanning tunneling potentiometry.

    Science.gov (United States)

    Zhang, Hao; Li, Xianqi; Chen, Yunmei; Durand, Corentin; Li, An-Ping; Zhang, X-G

    2016-08-01

    We present a novel method for extracting two-dimensional (2D) conductivity profiles from large electrochemical potential datasets acquired by scanning tunneling potentiometry of a 2D conductor. The method consists of a data preprocessing procedure to reduce/eliminate noise and a numerical conductivity reconstruction. The preprocessing procedure employs an inverse consistent image registration method to align the forward and backward scans of the same line for each image line followed by a total variation (TV) based image restoration method to obtain a (nearly) noise-free potential from the aligned scans. The preprocessed potential is then used for numerical conductivity reconstruction, based on a TV model solved by accelerated alternating direction method of multiplier. The method is demonstrated on a measurement of the grain boundary of a monolayer graphene, yielding a nearly 10:1 ratio for the grain boundary resistivity over bulk resistivity.

  3. Conductivity map from scanning tunneling potentiometry

    Science.gov (United States)

    Zhang, Hao; Li, Xianqi; Chen, Yunmei; Durand, Corentin; Li, An-Ping; Zhang, X.-G.

    2016-08-01

    We present a novel method for extracting two-dimensional (2D) conductivity profiles from large electrochemical potential datasets acquired by scanning tunneling potentiometry of a 2D conductor. The method consists of a data preprocessing procedure to reduce/eliminate noise and a numerical conductivity reconstruction. The preprocessing procedure employs an inverse consistent image registration method to align the forward and backward scans of the same line for each image line followed by a total variation (TV) based image restoration method to obtain a (nearly) noise-free potential from the aligned scans. The preprocessed potential is then used for numerical conductivity reconstruction, based on a TV model solved by accelerated alternating direction method of multiplier. The method is demonstrated on a measurement of the grain boundary of a monolayer graphene, yielding a nearly 10:1 ratio for the grain boundary resistivity over bulk resistivity.

  4. Scanning tunneling spectroscopy in MgB2.

    Science.gov (United States)

    Karapetrov, G; Iavarone, M; Kwok, W K; Crabtree, G W; Hinks, D G

    2001-05-01

    We present scanning tunneling microscopy measurements of the surface of superconducting MgB2 with a critical temperature of 39 K. In zero magnetic field the conductance spectra can be analyzed in terms of the standard BCS theory with a smearing parameter gamma. The value of the superconducting gap is 5 meV at 4.2 K, with no experimentally significant variation across the surface of the sample. The temperature dependence of the gap follows the BCS form, fully consistent with phonon-mediated superconductivity in this novel superconductor. The application of a magnetic field induces strong pair breaking as seen in the conductance spectra in fields up to 6 T.

  5. Measuring voltage transients with an ultrafast scanning tunneling microscope

    DEFF Research Database (Denmark)

    Keil, Ulrich Dieter Felix; Jensen, Jacob Riis; Hvam, Jørn Märcher

    1997-01-01

    We use an ultrafast scanning tunneling microscope to resolve propagating voltage transients in space and time. We demonstrate that the previously observed dependence of the transient signal amplitude on the tunneling resistance was only caused by the electrical sampling circuit. With a modified...... circuit, where the tunneling tip is directly connected to the current amplifier of the scanning tunneling microscope, this dependence is eliminated. Ail results can be explained with coupling through the geometrical capacitance of the tip-electrode junction. By illuminating the current...

  6. Investigation of local tunneling current noise spectra on the silicon crystal surfaces by means of STM/STS

    Energy Technology Data Exchange (ETDEWEB)

    Mantsevich, V. N., E-mail: vmantsev@spmlab.phys.msu.su; Maslova, N. S. [Moscow State University, Department of Physics (Russian Federation); Cao, G. Y. [Chinese Academy of Sciences, Wuhan Institute of Physics and Mathematics (China)

    2015-08-15

    We report on a careful analysis of the local tunneling conductivity by means of ultra-high vacuum scanning tunneling microscopy/spectroscopy (STM/STS) technique in the vicinity of low-dimensional structures on the Si(111)–(7 × 7) and Si(110)–(16 × 2) surfaces. The power-law exponent α of low-frequency tunneling current noise spectra is investigated for different values of the tunneling contact parameters: relaxation rates, the localized state coupling, and the tunneling barrier width and height.

  7. Spectral Measurement of Photon Emission from Individual Gold Nanoparticles Using Scanning Tunneling Microscopy

    Directory of Open Access Journals (Sweden)

    S.A. Nepijko

    2016-06-01

    Full Text Available The light emission spectra of individual Au nanoparticles induced by a scanning tunneling microscope (STM have been investigated. Two-dimensional ensembles of tunnel-coupled Au particles were prepared by thermal evaporation onto a native oxide silicon wafer in ultrahigh vacuum (10 – 9 mbar. Our STM measurements show a single peak at photon energy 1.6 eV in the tunneling mode and two peaks at 2.2 eV (connected with the Mie plasmon and 1.45 eV (a new peak which was not discussed in literature before in the field emission mode.

  8. A versatile high resolution scanning tunneling potentiometry implementation.

    Science.gov (United States)

    Druga, T; Wenderoth, M; Homoth, J; Schneider, M A; Ulbrich, R G

    2010-08-01

    We have developed a new scanning tunneling potentiometry technique which can-with only minor changes of the electronic setup-be easily added to any standard scanning tunneling microscope (STM). This extension can be combined with common STM techniques such as constant current imaging or scanning tunneling spectroscopy. It is capable of performing measurements of the electrochemical potential with microvolt resolution. Two examples demonstrate the versatile application. First of all, we have determined local variations of the electrochemical potential due to charge transport of biased samples down to angstrom length scales. Second, with tip and sample at different temperatures we investigated the locally varying thermovoltage occurring at the tunneling junction. Aside from its use in determining the chemical identity of substances at the sample surface our method provides a controlled way to eliminate the influence of laterally varying thermovoltages on low-bias constant current topographies.

  9. Development of the tunneling junction simulation environment for scanning tunneling microscope evaluation

    Science.gov (United States)

    Gajewski, Krzysztof; Piasecki, Tomasz; Kopiec, Daniel; Gotszalk, Teodor

    2017-03-01

    Proper configuration of scanning tunneling microscope electronics plays an important role in the atomic scale resolution surface imaging. Device evaluation in the tunneling contact between scanning tip and sample may be prone to the surface quality or mechanical disturbances. Thus the use of tunneling junction simulator makes electronics testing more reliable and increases its repeatability. Here, we present the theoretical background enabling the proper selection of electronic components circuitry used as a tunneling junction simulator. We also show how to simulate mechanics related to the piezoelectric scanner, which is applied in real experiments. Practical use of the proposed simulator and its application in metrological characterization of the developed scanning tunneling microscope is also shown.

  10. Optical characterication of probes for photon scanning tunnelling microscopy

    DEFF Research Database (Denmark)

    Vohnsen, Brian; Bozhevolnyi, Sergey I.

    1999-01-01

    The photon scanning tunnelling microscope is a well-established member of the family of scanning near-field optical microscopes used for optical imaging at the sub-wavelength scale. The quality of the probes, typically pointed uncoated optical fibres, used is however difficult to evaluate...

  11. Structural monitoring of tunnels using terrestrial laser scanning

    NARCIS (Netherlands)

    Lindenbergh, R.C.; Uchanski, L.; Bucksch, A.; Van Gosliga, R.

    2009-01-01

    In recent years terrestrial laser scanning is rapidly evolving as a surveying technique for the monitoring of engineering objects like roof constructions, mines, dams, viaducts and tunnels. The advantage of laser scanning above traditional surveying methods is that it allows for the rapid acquisitio

  12. A cryogen-free low temperature scanning tunneling microscope capable of inelastic electron tunneling spectroscopy.

    Science.gov (United States)

    Zhang, Shuai; Huang, Di; Wu, Shiwei

    2016-06-01

    The design and performance of a cryogen-free low temperature scanning tunneling microscope (STM) housed in ultrahigh vacuum (UHV) are reported. The cryogen-free design was done by directly integrating a Gifford-McMahon cycle cryocooler to a Besocke-type STM, and the vibration isolation was achieved by using a two-stage rubber bellow between the cryocooler and a UHV-STM interface with helium exchange gas cooling. A base temperature of 15 K at the STM was achieved, with a possibility to further decrease by using a cryocooler with higher cooling power and adding additional low temperature stage under the exchange gas interface. Atomically sharp STM images and high resolution dI/dV spectra on various samples were demonstrated. Furthermore, we reported the inelastic tunneling spectroscopy on a single carbon monoxide molecule adsorbed on Ag(110) surface with a cryogen-free STM for the first time. Being totally cryogen-free, the system not only saves the running cost significantly but also enables uninterrupted data acquisitions and variable temperature measurements with much ease. In addition, the system is capable of coupling light to the STM junction by a pair of lens inside the UHV chamber. We expect that these enhanced capabilities could further broaden our views to the atomic-scale world.

  13. A cryogen-free variable temperature scanning tunneling microscope capable for inelastic electron tunneling spectroscopy

    Science.gov (United States)

    Zhang, Shuai; Huang, Di; Wu, Shiwei

    While low temperature scanning tunneling microscope (STM) has become an indispensable research tool in surface science, its versatility is yet limited by the shortage or high cost of liquid helium. The makeshifts include the use of alternative cryogen (such as liquid nitrogen) at higher temperature or the development of helium liquefier system usually at departmental or campus wide. The ultimate solution would be the direct integration of a cryogen-free cryocooler based on GM or pulse tube closed cycle in the STM itself. However, the nasty mechanical vibration at low frequency intrinsic to cryocoolers has set the biggest obstacle because of the known challenges in vibration isolation required to high performance of STM. In this talk, we will present the design and performance of our home-built cryogen-free variable temperature STM at Fudan University. This system can obtain atomically sharp STM images and high resolution dI/dV spectra comparable to state-of-the-art low temperature STMs, but with no limitation on running hours. Moreover, we demonstrated the inelastic tunneling spectroscopy (STM-IETS) on a single CO molecule with a cryogen-free STM for the first time.

  14. Scanning tunneling spectroscopy on electron-boson interactions in superconductors

    CERN Document Server

    Schackert, Michael Peter

    2015-01-01

    This work describes the experimental study of electron-boson interactions in superconductors by means of inelastic electron tunneling spectroscopy performed with a scanning tunneling microscope (STM) at temperatures below 1 K. This new approach allows the direct measurement of the Eliashberg function of conventional superconductors as demonstrated on lead (Pb) and niobium (Nb). Preparative experiments on unconventional iron-pnictides are presented in the end.

  15. Design of a scanning tunneling microscope for electrochemical applications

    OpenAIRE

    Dovek, Moris M.; Heben, Michael J.; Lang, Christop A.; Lewis, Nathan S.; Quate, Calvin F.

    1988-01-01

    A design for a scanning tunneling microscope that is well suited for electrochemical investigations is presented. The construction of the microscope ensures that only the tunneling tip and the sample participate in electrochemical reactions. The design also allows rapid replacement of the tip or sample, and enables facile introduction of auxiliary electrodes for use in electrochemical experiments. The microscope utilizes stepper motor driven approach mechanics in order to achieve fully remote...

  16. Measurement of turbulence spectra using scanning pulsed wind lidars

    NARCIS (Netherlands)

    Sathe, A.; Mann, J.

    2012-01-01

    Turbulent velocity spectra, as measured by a scanning pulsed wind lidar (WindCube), are analyzed. The relationship between ordinary velocity spectra and lidar derived spectra is mathematically very complex, and deployment of the three-dimensional spectral velocity tensor is necessary. The resulting

  17. A nanoscale gigahertz source realized with Josephson scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Jäck, Berthold, E-mail: b.jaeck@fkf.mpg.de; Eltschka, Matthias; Assig, Maximilian; Etzkorn, Markus; Ast, Christian R. [Max-Planck-Institut für Festkörperforschung, 70569 Stuttgart (Germany); Hardock, Andreas [Institut für Theoretische Elektrotechnik, Technische Universität Hamburg-Harburg, 21079 Hamburg (Germany); Kern, Klaus [Max-Planck-Institut für Festkörperforschung, 70569 Stuttgart (Germany); Institut de Physique de la Matière Condensée, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne (Switzerland)

    2015-01-05

    Using the AC Josephson effect in the superconductor-vacuum-superconductor tunnel junction of a scanning tunneling microscope (STM), we demonstrate the generation of GHz radiation. With the macroscopic STM tip acting as a λ/4-monopole antenna, we first show that the atomic scale Josephson junction in the STM is sensitive to its frequency-dependent environmental impedance in the GHz regime. Further, enhancing Cooper pair tunneling via excitations of the tip eigenmodes, we are able to generate high-frequency radiation. We find that for vanadium junctions, the enhanced photon emission can be tuned from about 25 GHz to 200 GHz and that large photon flux in excess of 10{sup 20 }cm{sup −2} s{sup −1} is reached in the tunnel junction. These findings demonstrate that the atomic scale Josephson junction in an STM can be employed as a full spectroscopic tool for GHz frequencies on the atomic scale.

  18. Atomic and molecular manipulation with the scanning tunneling microscope.

    Science.gov (United States)

    Stroscio, J A; Eigler, D M

    1991-11-29

    The prospect of manipulating matter on the atomic scale has fascinated scientists for decades. This fascination may be motivated by scientific and technological opportunities, or from a curiosity about the consequences of being able to place atoms in a particular location. Advances in scanning tunneling microscopy have made this prospect a reality; single atoms can be placed at selected positions and structures can be built to a particular design atom-by-atom. Atoms and molecules may be manipulated in a variety of ways by using the interactions present in the tunnel junction of a scanning tunneling microscope. Some of these recent developments and some of the possible uses of atomic and molecular manipulation as a tool for science are discussed.

  19. Electric field effects in scanning tunneling microscope imaging

    DEFF Research Database (Denmark)

    Stokbro, Kurt; Quaade, Ulrich; Grey, Francois

    1998-01-01

    We present a high-voltage extension of the Tersoff-Hamann theory of scanning tunneling microscope (STM) images, which includes the effect of the electric field between the tip and the sample. The theoretical model is based on first-principles electronic structure calculations and has no adjustable...

  20. Apparent Barrier Height in Scanning Tunneling Microscopy Revisited

    DEFF Research Database (Denmark)

    Olesen, L.; Brandbyge, Mads; Sørensen, Mads Reinholdt;

    1996-01-01

    The apparent barrier height phi(ap), that is, the rate of change of the logarithm of the conductance with tip-sample separation in a scanning tunneling microscope (STM), has been measured for Ni, Pt, and Au single crystal surfaces. The results show that phi(ap) is constant until point contact...

  1. Scanning tunneling microscopy III theory of STM and related scanning probe methods

    CERN Document Server

    Güntherodt, Hans-Joachim

    1996-01-01

    Scanning Tunneling Microscopy III provides a unique introduction to the theoretical foundations of scanning tunneling microscopy and related scanning probe methods. The different theoretical concepts developed in the past are outlined, and the implications of the theoretical results for the interpretation of experimental data are discussed in detail. Therefore, this book serves as a most useful guide for experimentalists as well as for theoreticians working in the filed of local probe methods. In this second edition the text has been updated and new methods are discussed.

  2. Electron-beam-assisted Scanning Tunneling Microscopy Of Insulating Surfaces

    CERN Document Server

    Bullock, E T

    2000-01-01

    Insulating materials are widely used in electronic devices. Bulk insulators and insulating films pose unique challenges for high resolution study since most commonly used charged particle surface analysis techniques are incompatible with insulating surfaces and materials. A, method of performing scanning tunneling microscopy (STM) on insulating surfaces has been investigated. The method is referred to as electron-beam assisted scanning tunneling microscopy (e-BASTM). It is proposed that by coupling the STM and the scanning electron microscopy (SEM) as one integrated device, that insulating materials may be studied, obtaining both high spatial resolution, and topographic and electronic resolution. The premise of the technique is based on two physical consequences of the interaction of an energetic electron beam (PE) with a material. First, when an electron beam is incident upon a material, low level material electrons are excited into conduction band states. For insulators, with very high secondary electron yi...

  3. Holders for in situ treatments of scanning tunneling microscopy tips.

    Science.gov (United States)

    Ishida, Nobuyuki; Subagyo, Agus; Ikeuchi, Akira; Sueoka, Kazuhisa

    2009-09-01

    We have developed holders for scanning tunneling microscopy tips that can be used for in situ treatments of the tips, such as electron bombardment (EB) heating, ion sputtering, and the coating of magnetic materials. The holders can be readily installed into the transfer paths and do not require any special type of base stages. Scanning electron microscopy is used to characterize the tip apex after EB heating. Also, spin-polarized scanning tunneling spectroscopy using an Fe coated W tip on the Cr(001) single crystal surface is performed in order to confirm both the capability of heating a tip up to about 2200 K and the spin sensitivity of the magnetically coated tip.

  4. Measurement of turbulence spectra using scanning pulsed wind lidars

    DEFF Research Database (Denmark)

    Sathe, Ameya; Mann, Jakob

    2012-01-01

    Turbulent velocity spectra, as measured by a scanning pulsed wind lidar (WindCube), are analyzed. The relationship between ordinary velocity spectra and lidar derived spectra is mathematically very complex, and deployment of the three-dimensional spectral velocity tensor is necessary. The resulting...... scanning lidar spectra depend on beam angles, line-of-sight averaging, sampling rate, and the full three-dimensional structure of the turbulence being measured, in a convoluted way. The model captures the attenuation and redistribution of the spectral energy at high and low wave numbers very well...

  5. Seismic scanning tunneling macroscope - Elastic simulations and Arizona mine test

    KAUST Repository

    Hanafy, Sherif M.

    2012-01-01

    Elastic seismic simulations and field data tests are used to validate the theory of a seismic scanning tunneling macroscope (SSTM). For nearfield elastic simulation, the SSTM results show superresolution to be better than λ/8 if the only scattered data are used as input data. If the direct P and S waves are muted then the resolution of the scatterer locations are within about λ/5. Seismic data collected in an Arizona tunnel showed a superresolution limit of at least λ/19. These test results are consistent with the theory of the SSTM and suggest that the SSTM can be a tool used by geophysicists as a probe for near-field scatterers.

  6. Scanning tunneling microscope-laser fabrication of nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Yau, S.T.; Saltz, D.; Nayfeh, M.H. (Univ. of Illinois, Urbana (United States))

    The authors report on a technique to write nanometer-scale features on surfaces. The technique combines two of the most advanced technologies: the laser and the scanning tunneling microscope (STM). Laser radiation is used to break the chemical bonds of trimethylaluminum to free aluminum atoms in the region of the tunneling gap of the STM. The atoms are subsequently selectively excited and ionized. The ions are then driven softly toward the surface where they are deposited by the field in the tunneling gap of the microscope. Since the field of the tip can be confined to a few nanometers, the writing can be controlled with high resolution. The technique is also capable of filling holes and addressable nondestructive erasing.

  7. Scanning tunneling microscopy and spectroscopy studies of graphite edges

    CERN Document Server

    Niimi, Y; Kambara, H; Tagami, K; Tsukada, M; Fukuyama, H; Fukuyama, Hiroshi

    2004-01-01

    We studied experimentally and theoretically the electronic local density of states (LDOS) near single step edges at the surface of exfoliated graphite. In scanning tunneling microscopy measurements, we observed the $(\\sqrt{3} \\times \\sqrt{3}) R 30^{\\circ}$ and honeycomb superstructures both extending over 3$-$4 nm either from the zigzag or armchair edge. Calculations based on a density-functional derived non-orthogonal tight-binding model show that these superstructures can coexist if the two types of edge admix each other in real graphite step edges. Scanning tunneling spectroscopy measurements near the zigzag edge reveal a clear peak in the LDOS at an energy below the Fermi energy by 20 meV. No such a peak was observed near the armchair edge. We concluded that this peak corresponds to the "edge state" theoretically predicted for graphene ribbons, since a similar prominent LDOS peak due to the edge state is obtained by the first principles calculations.

  8. Active nanocharacterization of nanofunctional materials by scanning tunneling microscopy

    OpenAIRE

    FUJITA, Daisuke; Sagisaka, Keisuke

    2008-01-01

    Recent developments in the application of scanning tunneling microscopy (STM) to nanofabrication and nanocharacterization are reviewed. The main focus of this paper is to outline techniques for depositing and manipulating nanometer-scale structures using STM tips. Firstly, the transfer of STM tip material through the application of voltage pulses is introduced. The highly reproducible fabrication of metallic silver nanodots and nanowires is discussed. The mechanism is thought to be spontaneou...

  9. Surfaces of III-V semiconductors studied by scanning tunneling microscopy and scanning luminescence

    Science.gov (United States)

    Chizhov, Ilya Yu

    The investigation of semiconductor surfaces on an atomic scale is of key importance for research areas such as the growth of thin films and low-dimensional objects by epitaxial techniques. Surfaces of III-V semiconductors, especially GaAs(001) surface, hold a central position in semiconductor surface science due to their extremely wide use in the growth of heterostructure-based electronic and optoelectronic devices. This work describes the results of experimental studies of (001) surfaces of two III-V semiconductors, GaAs and InAs, using scanning tunneling microscopy (STM) and scanning tunneling luminescence (STL). For STL studies an optical detection system consisting of an optical spectrometer (replacable by a photomultiplier tube), electronics, an IBM PC computer and acquisition software has been added to an existing STM (Omicron). The system is capable of recording luminescence images of surfaces and the acquisition of optical spectra of STM-induced luminescence. Application of STL to GaAs(001) surfaces has revealed that atomic-scale features, such as steps, domain boundaries etc., do not give any contrast in luminescence images, while larger objects, such as arsenic islands, do produce a pronounced contrast. The work in STL has helped to identify several key problems that have to be solved in order to make STL a valuable analytical technique. The STM studies of reconstructions on the GaAs(001) surface, which has a fairly complicated phase diagram, have concentrated on two major phase transitions, from As-rich c(4× 4) to As-rich (2× 4) phase and from As-rich (2× 4) to Ga-rich (4× 2) phase. The first transition has been found to proceed through an intermediate (4× 3)/c(4× 6) phase which has been previously identified as having (2× 3) symmetry. The second transition has been found to involve the formation of (3× 6) and (4× 6) multi-domain phases. The local structure and composition of these phases have been analyzed in detail and a comprehensive dynamic

  10. Scanning tunneling microscopy/spectroscopy of vortices in LiFeAs

    Science.gov (United States)

    Hanaguri, T.; Kitagawa, K.; Matsubayashi, K.; Mazaki, Y.; Uwatoko, Y.; Takagi, H.

    2012-06-01

    We investigate vortices in LiFeAs using scanning tunneling microscopy/spectroscopy. Zero-field tunneling spectra show two superconducting gaps without detectable spectral weight near the Fermi energy, evidencing fully gapped multiband superconductivity. We image vortices in a wide field range from 0.1 T to 11 T by mapping the tunneling conductance at the Fermi energy. A quasihexagonal vortex lattice at low field contains domain boundaries which consist of alternating vortices with unusual coordination numbers of 5 and 7. With increasing field, the domain boundaries become ill defined, resulting in a uniformly disordered vortex matter. Tunneling spectra taken at the vortex center are characterized by a sharp peak just below the Fermi energy, apparently violating particle-hole symmetry. The image of each vortex shows energy-dependent 4-fold anisotropy which may be associated with the anisotropy of the Fermi surface. The vortex radius shrinks with decreasing temperature and becomes smaller than the coherence length estimated from the upper critical field. This is direct evidence of the Kramer-Pesch effect expected in a clean superconductor.

  11. Bases for time-resolved probing of transient carrier dynamics by optical pump-probe scanning tunneling microscopy.

    Science.gov (United States)

    Yokota, Munenori; Yoshida, Shoji; Mera, Yutaka; Takeuchi, Osamu; Oigawa, Haruhiro; Shigekawa, Hidemi

    2013-10-07

    The tangled mechanism that produces optical pump-probe scanning tunneling microscopy spectra from semiconductors was analyzed by comparing model simulation data with experimental data. The nonlinearities reflected in the spectra, namely, the excitations generated by paired laser pulses with a delay time, the logarithmic relationship between carrier density and surface photovoltage (SPV), and the effect of the change in tunneling barrier height depending on SPV, were examined along with the delay-time-dependent integration process used in measurement. The optimum conditions required to realize reliable measurement, as well as the validity of the microscopy technique, were demonstrated for the first time.

  12. Theory and feasibility tests for a seismic scanning tunnelling macroscope

    KAUST Repository

    Schuster, Gerard T.

    2012-09-01

    We propose a seismic scanning tunnelling macroscope (SSTM) that can detect subwavelength scatterers in the near-field of either the source or the receivers. Analytic formulas for the time reverse mirror (TRM) profile associated with a single scatterer model show that the spatial resolution limit to be, unlike the Abbe limit of λ/2, independent of wavelength and linearly proportional to the source-scatterer separation as long as the scatterer is in the near-field region. This means that, as the scatterer approaches the source, imaging of the scatterer with super-resolution can be achieved. Acoustic and elastic simulations support this concept, and a seismic experiment in an Arizona tunnel shows a TRM profile with super-resolution adjacent to the fault location. The SSTM is analogous to the optical scanning tunnelling microscopes having subwavelength resolution. Scaled to seismic frequencies, it is theoretically possible to extract 100 Hz information from 20 Hz data by the imaging of near-field seismic energy.

  13. SPATIAL REPARTITION OF CURRENT FLUCTUATIONS IN A SCANNING TUNNELING MICROSCOPE

    Directory of Open Access Journals (Sweden)

    Jerome Lagoute

    2011-05-01

    Full Text Available Scanning Tunneling Microscopy (STM is a technique where the surface topography of a conducting sample is probed by a scanning metallic tip. The tip-to-surface distance is controlled by monitoring the electronic tunneling current between the two metals. The aim of this work is to extend the temporal range of this instrument by characterising the time fluctuations of this current on different surfaces. The current noise power spectral density is dominated by a characteristic 1/f component, the physical origin of which is not yet clearly identified, despite a number of investigations. A new I-V preamplifier was developed in order to characterise these fluctuations of the tunnelling current and to obtain images of their spatial repartition. It is observed that their intensity is correlated with some topographical features. This information can be used to get insights on the physical phenomena involved that are not accessible by the usual STM set-up, which is limited to low frequencies.

  14. Oxygen-free in situ scanning tunnelling microscopy

    DEFF Research Database (Denmark)

    Zhang, Jingdong; Ulstrup, Jens

    2007-01-01

    Scanning tunneling microscopy under full electrochemical potential control (in situ STM) has been used extensively as an efficient method to characterize microstructures at solid/liquid interfaces at the atomic and molecular levels. However, under ambient conditions oxygen may interfere in open......, the STM image quality of the monolayer structures has improved significantly in the absence of oxygen. Reasons for the drastic effects of dioxygen based on both chemical surface reactivity and electron scattering effects are discussed. These observations are important in general for STM of oxygen...

  15. Observation of diamond turned OFHC copper using Scanning Tunneling Microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Grigg, D.A.; Russell, P.E.; Dow, T.A.

    1988-12-01

    Diamond turned OFHC copper samples have been observed within the past few months using the Scanning Tunneling Microscope. Initial results have shown evidence of artifacts which may be used to better understand the diamond turning process. The STM`s high resolution capability and three dimensional data representation allows observation and study of surface features unobtainable with conventional profilometry systems. Also, the STM offers a better quantitative means by which to analyze surface structures than the SEM. This paper discusses findings on several diamond turned OFHC copper samples having different cutting conditions. Each sample has been cross referenced using STM and SEM.

  16. Scanning tunneling microscope data acquisition and control in visual basic

    Science.gov (United States)

    Porter, T. L.

    1993-12-01

    A general purpose data acquisition and control system for scanning tunneling microscopy (STM) using Visual Basic is presented. This Windows hosted Visual Basic environment is highly desirable for use in STM image manipulation, storage, and printing, but in its standard form is not suitable for most data acquisition and display applications. Many of the inherent limitations in the Visual Basic language have been overcome by the use of direct calls to the Windows Application Program Interface. In this paper, we describe a general Visual Basic STM user interface and control system, and the extensions to the language using the Windows API needed to implement this system.

  17. Scanning Tunnelling Spectroscopy of Vortices with Normal and Superconducting tips

    Science.gov (United States)

    Rodrigo, J. G.; Suderow, H.; Vieira, S.

    Scanning tunnelling microscopy and spectroscopy (STM/S) has proved to be a powerful tool to study superconductivity down to atomic level. Vortex lattice studies require characterizing areas of enough size to contain a large number of vortices. On the other hand, it is necessary to combine this capability with high spectroscopic and microscopic resolution. This is a fundamental aspect to measure and detect the subtle changes appearing inside and around a single vortex. We report in this chapter our approach to the use of STM/S, using normal and superconducting tips, to observe the lattice of vortices in several compounds, and the information acquired inside these fascinating entities. The combination of superconducting tips and scanning tunneling spectroscopy, (ST)2S, presents advantages for the study of superconducting samples. It allows to distinguish relevant features of the sample density of states, which manifest itself as small changes in the Josephson coupling between sample and tip condensates, and it has also shown to be very efficient in the study of the ferromagnetic-superconductor transition in the re-entrant superconductor ErRh4B4.

  18. Scanning Tunneling Microscopy of SILICON(100) 2 X 1

    Science.gov (United States)

    Hubacek, Jerome S.

    1992-01-01

    The Si(100) 2 x 1 surface, a technologically important surface in microelectronics and silicon molecular beam epitaxy (MBE), has been studied with the scanning tunneling microscope (STM) to attempt to clear up the controversy that surrounds previous studies of this surface. To this end, an ultra-high vacuum (UHV) STM/surface science system has been designed and constructed to study semiconductor surfaces. Clean Si(100) 2 x 1 surfaces have been prepared and imaged with the STM. Atomic resolution images probing both the filled states and empty states indicate that the surface consists of statically buckled dimer rows. With electronic device dimensions shrinking to smaller and smaller sizes, the Si-SiO_2 interface is becoming increasingly important and, although it is the most popular interface used in the microelectronics industry, little is known about the initial stages of oxidation of the Si(100) surface. Scanning tunneling microscopy has been employed to examine Si(100) 2 x 1 surfaces exposed to molecular oxygen in UHV. Ordered rows of bright and dark spots, rotated 45^circ from the silicon dimer rows, appear in the STM images, suggesting that the Si(100)-SiO_2 interface may be explained with a beta -cristobalite(100) structure rotated by 45^ circ on the Si(100) surface.

  19. Nanoscale assembly of superconducting vortices with scanning tunnelling microscope tip

    Science.gov (United States)

    Ge, Jun-Yi; Gladilin, Vladimir N.; Tempere, Jacques; Xue, Cun; Devreese, Jozef T.; van de Vondel, Joris; Zhou, Youhe; Moshchalkov, Victor V.

    2016-12-01

    Vortices play a crucial role in determining the properties of superconductors as well as their applications. Therefore, characterization and manipulation of vortices, especially at the single-vortex level, is of great importance. Among many techniques to study single vortices, scanning tunnelling microscopy (STM) stands out as a powerful tool, due to its ability to detect the local electronic states and high spatial resolution. However, local control of superconductivity as well as the manipulation of individual vortices with the STM tip is still lacking. Here we report a new function of the STM, namely to control the local pinning in a superconductor through the heating effect. Such effect allows us to quench the superconducting state at nanoscale, and leads to the growth of vortex clusters whose size can be controlled by the bias voltage. We also demonstrate the use of an STM tip to assemble single-quantum vortices into desired nanoscale configurations.

  20. Fault detection by surface seismic scanning tunneling macroscope: Field test

    KAUST Repository

    Hanafy, Sherif M.

    2014-08-05

    The seismic scanning tunneling macroscope (SSTM) is proposed for detecting the presence of near-surface impedance anomalies and faults. Results with synthetic data are consistent with theory in that scatterers closer to the surface provide brighter SSTM profiles than those that are deeper. The SSTM profiles show superresolution detection if the scatterers are in the near-field region of the recording line. The field data tests near Gulf of Aqaba, Haql, KSA clearly show the presence of the observable fault scarp, and identify the subsurface presence of the hidden faults indicated in the tomograms. Superresolution detection of the fault is achieved, even when the 35 Hz data are lowpass filtered to the 5-10 Hz band.

  1. A high stability and repeatability electrochemical scanning tunneling microscope

    Energy Technology Data Exchange (ETDEWEB)

    Xia, Zhigang; Wang, Jihao; Lu, Qingyou, E-mail: qxl@ustc.edu.cn [High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026 (China); Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China); Hou, Yubin [High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026 (China)

    2014-12-15

    We present a home built electrochemical scanning tunneling microscope (ECSTM) with very high stability and repeatability. Its coarse approach is driven by a closely stacked piezo motor of GeckoDrive type with four rigid clamping points, which enhances the rigidity, compactness, and stability greatly. It can give high clarity atomic resolution images without sound and vibration isolations. Its drifting rates in XY and Z directions in solution are as low as 84 pm/min and 59 pm/min, respectively. In addition, repeatable coarse approaches in solution within 2 mm travel distance show a lateral deviation less than 50 nm. The gas environment can be well controlled to lower the evaporation rate of the cell, thus reducing the contamination and elongating the measurement time. Atomically resolved SO{sub 4}{sup 2−} image on Au (111) work electrode is demonstrated to show the performance of the ECSTM.

  2. Direct control and characterization of a Schottky barrier by scanning tunneling microscopy

    Science.gov (United States)

    Bell, L. D.; Kaiser, W. J.; Hecht, M. H.; Grunthaner, F. J.

    1988-01-01

    Scanning tunneling microscopy (STM) methods are used to directly control the barrier height of a metal tunnel tip-semiconductor tunnel junction. Barrier behavior is measured by tunnel current-voltage spectroscopy and compared to theory. A unique surface preparation method is used to prepare a low surface state density Si surface. Control of band bending with this method enables STM investigation of semiconductor subsurface properties.

  3. A scanning tunneling microscopy tip with a stable atomic structure

    Science.gov (United States)

    Kim, Yeong-Cheol; Seidman, David N.

    2004-02-01

    A single stable adatom on a {110}-type plane of a tungsten tip is created via field-evaporation in a field-ion microscope (FIM) operating at room temperature. This single adatom has sufficient surface mobility at room temperature and migrates, in one-dimension, along a -type direction toward an edge of a {110}-type plane, due to the existence of an electric field gradient. The plane edge has a higher local electric field than its center, since it has a higher local geometric curvature. This result implies that the stable position of a single adatom during a scan of a scanning tunneling microscope (STM) tip on a surface is at the edge and not at the center of a {110}-type plane at room temperature. Therefore, the electron wave function of a tip is not symmetric and this fact should be taken into account in a careful analysis of STM images. Also a tip with a dislocation emerging at a {110}-type plane is suggested as an improved STM tip configuration, as the step at the surface, created by the intersection of the dislocation with it, is a perpetual source of single adatoms.

  4. Inelastic scanning tunneling microscopy in conventional and unconventional superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Hlobil, Patrik; Schmalian, Joerg; Wulfhekel, Wulf; Jandke, Jasmin [Karlsruhe Institute of Technologie (Germany)

    2015-07-01

    Electron tunneling spectroscopy has been used extremely successful in order to verify the microscopic phonon pairing mechanism in conventional BCS superconductors using the Eliashberg theory. Nevertheless, earlier theories and experiments focused mainly on elastic tunneling processes. We present, motivated by recent experiments, a theoretical description of inelastic tunneling in STM in which an electrons tunnels from the tip into a BCS superconductor and coherently excites a phonon during the tunneling process. This additional channel enhances the measured conductivity and we show that if the superconductor is in the normal state, within some limitations, the derivative dσ/dV will be proportional to the Eliashberg function α2F. Additionally, the influence of the inelastic contributions on the tunneling spectrum in the superconducting state will be discussed. Finally, we generalize the theory to other bosonic excitations and focus on the question if inelastic tunneling could be used to unveil the electronic pairing mechanism in the iron pnictides.

  5. Local potentiometry using a multiprobe scanning tunneling microscope.

    Science.gov (United States)

    Bannani, A; Bobisch, C A; Möller, R

    2008-08-01

    Scanning tunneling potentiometry (STP) is a powerful tool to analyze the conductance through thin conducting layers with lateral resolution in the nanometer range. In this work, we show how a commercial ultrahigh vacuum multiprobe system, equipped with four independent tips, can be used to perform STP experiments. Two tips are gently pushed into the surface applying a lateral current through the layer of interest. Simultaneously, the topography and the potential distribution across the metal film are measured with a third tip. The signal-to-noise ratio of the potentiometry signal may be enhanced by using a fourth tip, providing a reference potential in close vicinity of the studied area. Two different examples are presented. For epitaxial (111) oriented Bi films, grown on a Si(100)-(2 x 1) surface, an almost constant gradient of the potential as well as potential drops at individual Bi-domain boundaries were observed. On the surface of the Si(111)(3 x 3)-Ag superstructure the potential variation at individual monoatomic steps could be precisely resolved.

  6. Interpretation of scanning tunneling quasiparticle interference and impurity states

    Science.gov (United States)

    Kreisel, Andreas; Choubey, P.; Berlijn, T.; Andersen, B. M.; Hirschfeld, P. J.

    2015-03-01

    We use a simple method of calculating inhomogeneous, atomic-scale phenomena in superconductors to obtain real-space conductance maps as measured in scanning tunneling spectroscopy (STM). Our approach makes use of first principles Wannier functions in conjunction with self-consistent solutions of the Bogoliubov-de Gennes equations on a lattice to image superconducting phenomena. This method is a powerful tool since it captures correctly local symmetries on the surface that can be lower than the global lattice symmetry; it improves the spatial resolution from one pixel per lattice point to the sub-atomic scale; and simplifies the interpretation of STM data. As an example, we show how the pattern observed around a Zn impurity in BSCCO-2212, can be understood by accounting for the tails of the Cu Wannier functions, and thus compare perfectly to experimental findings. Further applications of this method include the investigation of impurity states in multiorbital systems as well as the study of quasi particle interference phenomena to enable a better understanding of novel phenomena in high temperature superconductors. P.C., A.K., and P.J.H. were supported by DOE DE-FG02-05ER46236, T.B. as a Wigner Fellow at the Oak Ridge National Laboratory, and B.M.A. and A.K. by Lundbeckfond fellowship (Grant A9318).

  7. Electronic Single Molecule Measurements with the Scanning Tunneling Microscope

    Science.gov (United States)

    Im, Jong One

    Richard Feynman said "There's plenty of room at the bottom". This inspired the techniques to improve the single molecule measurements. Since the first single molecule study was in 1961, it has been developed in various field and evolved into powerful tools to understand chemical and biological property of molecules. This thesis demonstrates electronic single molecule measurement with Scanning Tunneling Microscopy (STM) and two of applications of STM; Break Junction (BJ) and Recognition Tunneling (RT). First, the two series of carotenoid molecules with four different substituents were investigated to show how substituents relate to the conductance and molecular structure. The measured conductance by STM-BJ shows that Nitrogen induces molecular twist of phenyl distal substituents and conductivity increasing rather than Carbon. Also, the conductivity is adjustable by replacing the sort of residues at phenyl substituents. Next, amino acids and peptides were identified through STM-RT. The distribution of the intuitive features (such as amplitude or width) are mostly overlapped and gives only a little bit higher separation probability than random separation. By generating some features in frequency and cepstrum domain, the classification accuracy was dramatically increased. Because of large data size and many features, supporting vector machine (machine learning algorithm for big data) was used to identify the analyte from a data pool of all analytes RT data. The STM-RT opens a possibility of molecular sequencing in single molecule level. Similarly, carbohydrates were studied by STM-RT. Carbohydrates are difficult to read the sequence, due to their huge number of possible isomeric configurations. This study shows that STM-RT can identify not only isomers of mono-saccharides and disaccharides, but also various mono-saccharides from a data pool of eleven analytes. In addition, the binding affinity between recognition molecule and analyte was investigated by comparing with

  8. 3D LASER SCANNING TECHNIQUE FOR THE INSPECTION AND MONITORING OF RAILWAY TUNNELS

    Directory of Open Access Journals (Sweden)

    Han-Mei CHEN

    2015-12-01

    Full Text Available Railway tunnel inspection and monitoring has predominantly been a visual and manual procedure, which is time-consuming and subjective, giving rise to variance in standards and quality. Thus, alternative, novel, automated techniques need to be developed, for more efficient and reliable tunnel examination. The reported research aimed to investigate the application of a laser scanning technique for the inspection of tunnel degradation and structural integrity. The proposed method may either substitute or supplement traditional survey techniques, being more efficient, and contributing thus to the standardisation of tunnel inspections. For the purpose of investigating the applicability and accuracy of laser scanning in tunnels, a set of tunnel lining models was constructed for laboratory tests, with the objective of determining the quality of the imaging. Initial tests were carried out using a performant laser scanner and demonstrated the feasibility of the concept. As a result, refined laboratory models were built, and experiments conducted, to establish the quality and precision of laser scanning imaging, for condition monitoring of tunnels. The experimental results indicate that the laser scanning technique used in this research has high potential for detecting the tunnel condition, monitoring the depth of weathered mortar, spalling bricks etc. with high accuracy in static scanning mode.

  9. The study of transition metal surfaces and thin films with inverse photoemission and scanning tunnelling microscopy

    CERN Document Server

    Wilson, L K

    1997-01-01

    clean Cr(001) and the thick films. This suggests that hybridisation between the substrate bands and the film bands and interface induced states are significant. The spectra taken from sub-monolayer coverages of Fe show marked intensity increase at the Fermi energy, this is a feature of LDOS calculations on Fe atoms at the Fe/Cr interface. Fe growth on surfaces of Cu(100) precovered with c(2x2)N has been studied with scanning tunnelling microscopy. The images show that the Fe does not grow on areas covered with nitrogen. Two different c(2x2)N templates have been used and the shape and size of the Fe islands is seen to be altered. The unoccupied electronic states at the surface of Cr(001) have been observed using k-resolved inverse photoemission. Normal incidence IPE spectra have been taken over a range of incident electron energies (14-24 eV). The spectra show only small variation with incident energy, this is attributed to densities of states effects due to the absence of symmetry allowed initial states at th...

  10. 3D LASER SCANNING TECHNIQUE FOR THE INSPECTION AND MONITORING OF RAILWAY TUNNELS

    OpenAIRE

    2015-01-01

    Railway tunnel inspection and monitoring has predominantly been a visual and manual procedure, which is time-consuming and subjective, giving rise to variance in standards and quality. Thus, alternative, novel, automated techniques need to be developed, for more efficient and reliable tunnel examination. The reported research aimed to investigate the application of a laser scanning technique for the inspection of tunnel degradation and structural integrity. The proposed method may either subs...

  11. Scanning Tunnelling Spectroscopic Studies of Dirac Fermions in Graphene and Topological Insulators

    Directory of Open Access Journals (Sweden)

    wang K.-L.

    2012-03-01

    Full Text Available We report novel properties derived from scanning tunnelling spectroscopic (STS studies of Dirac fermions in graphene and the surface state (SS of a strong topological insulator (STI, Bi2Se3. For mono-layer graphene grown on Cu by chemical vapour deposition (CVD, strain-induced scalar and gauge potentials are manifested by the charging effects and the tunnelling conductance peaks at quantized energies, respectively. Additionally, spontaneous time-reversal symmetry breaking is evidenced by the alternating anti-localization and localization spectra associated with the zero-mode of two sublattices while global time-reversal symmetry is preserved under the presence of pseudo-magnetic fields. For Bi2Se3 epitaxial films grown on Si(111 by molecular beam epitaxy (MBE, spatially localized unitary impurity resonances with sensitive dependence on the energy difference between the Fermi level and the Dirac point are observed for samples thicker than 6 quintuple layers (QL. These findings are characteristic of the SS of a STI and are direct manifestation of strong topological protection against impurities. For samples thinner than 6-QL, STS studies reveal the openup of an energy gap in the SS due to overlaps of wave functions between the surface and interface layers. Additionally, spin-preserving quasiparticle interference wave-vectors are observed, which are consistent with the Rashba-like spin-orbit splitting.

  12. Scanning tunneling microscopy III theory of STM and related scanning probe methods

    CERN Document Server

    Güntherodt, Hans-Joachim

    1993-01-01

    While the first two volumes on Scanning Tunneling Microscopy (STM) and its related scanning probe (SXM) methods have mainly concentrated on intro­ ducing the experimental techniques, as well as their various applications in different research fields, this third volume is exclusively devoted to the theory of STM and related SXM methods. As the experimental techniques including the reproducibility of the experimental results have advanced, more and more theorists have become attracted to focus on issues related to STM and SXM. The increasing effort in the development of theoretical concepts for STM/SXM has led to considerable improvements in understanding the contrast mechanism as well as the experimental conditions necessary to obtain reliable data. Therefore, this third volume on STM/SXM is not written by theorists for theorists, but rather for every scientist who is not satisfied by just obtaining real­ space images of surface structures by STM/SXM. After a brief introduction (Chap. 1), N. D. Lang first co...

  13. Relationship between the electric performance and the photoluminescence spectra of resonant tunnelling diodes

    Institute of Scientific and Technical Information of China (English)

    Zhang Xiao-Xin; Zeng Yi-Ping; Wang Xiao-Guang; Wang Bao-Qiang; Zhu Zhan-Ping

    2004-01-01

    Resonant tunnelling diodes with different structures were grown. Their photoluminescence spectra were investigated. By contrast, the luminescence in the quantum well is separated from that of other epilayers. The result is obtained that the exciton of the luminescence in the quantum well is partly come from the cap layer in the experiment.So the photoluminescence spectrum is closely related to the electron transport in the resonant tunnelling diode structure.This offers a method by which the important performance of resonant tunnelling diode could be forecast by analysing the integrated photoluminescence intensities.

  14. New approach towards imaging -DNA using scanning tunneling microscopy/spectroscopy (STM/STS)

    Indian Academy of Sciences (India)

    Shirshendu Dey; Sushama Pethkar; Suguna D Adyanthaya; Murali Sastry; C V Dharmadhikari

    2008-06-01

    A new methodology to anchor -DNA to silanized -Si(111) surface using Langmuir Blodget trough was developed. The -Si (111) was silanized by treating it with low molecular weight octyltrichlorosilane in toluene. Scanning tunneling microscopy (STM) image of -DNA on octyltrichlorosilane deposited Si substrate shows areas exhibiting arrayed structures of 700 nm length and 40 nm spacing. Scanning tunneling spectroscopy (STS) at different stages depict a broad distribution of defect states in the bandgap region of -Si(111) which presumably facilitates tunneling through otherwise insulating DNA layer.

  15. Making Mn substitutional impurities in InAs using a scanning tunneling microscope.

    Science.gov (United States)

    Song, Young Jae; Erwin, Steven C; Rutter, Gregory M; First, Phillip N; Zhitenev, Nikolai B; Stroscio, Joseph A

    2009-12-01

    We describe in detail an atom-by-atom exchange manipulation technique using a scanning tunneling microscope probe. As-deposited Mn adatoms (Mn(ad)) are exchanged one-by-one with surface In atoms (In(su)) to create a Mn surface-substitutional (Mn(In)) and an exchanged In adatom (In(ad)) by an electron tunneling induced reaction Mn(ad) + In(su) --> Mn(In) + In(ad) on the InAs(110) surface. In combination with density-functional theory and high resolution scanning tunneling microscopy imaging, we have identified the reaction pathway for the Mn and In atom exchange.

  16. Effects of intermolecular interaction on inelastic electron tunneling spectra

    Science.gov (United States)

    Kula, Mathias; Luo, Yi

    2008-02-01

    We have examined the effects of intermolecular interactions on the inelastic electron tunneling spectroscopy (IETS) of model systems: a pair of benzenethiol or a pair of benzenedithiol sandwiched between gold electrodes. The dependence of the IETS on the mutual position of and distance between the paired molecules has been predicted and discussed in detailed. It is shown that, although in most cases, there are clear spectral fingerprints present which allow identification of the actual structures of the molecules inside the junction. Caution must be exercised since some characteristic lines can disappear at certain symmetries. The importance of theoretical simulation is emphasized.

  17. Quantitative analysis of scanning tunneling microscopy images of mixed-ligand-functionalized nanoparticles.

    Science.gov (United States)

    Biscarini, Fabio; Ong, Quy Khac; Albonetti, Cristiano; Liscio, Fabiola; Longobardi, Maria; Mali, Kunal S; Ciesielski, Artur; Reguera, Javier; Renner, Christoph; De Feyter, Steven; Samorì, Paolo; Stellacci, Francesco

    2013-11-12

    Ligand-protected gold nanoparticles exhibit large local curvatures, features rapidly varying over small scales, and chemical heterogeneity. Their imaging by scanning tunneling microscopy (STM) can, in principle, provide direct information on the architecture of their ligand shell, yet STM images require laborious analysis and are challenging to interpret. Here, we report a straightforward, robust, and rigorous method for the quantitative analysis of the multiscale features contained in STM images of samples consisting of functionalized Au nanoparticles deposited onto Au/mica. The method relies on the analysis of the topographical power spectral density (PSD) and allows us to extract the characteristic length scales of the features exhibited by nanoparticles in STM images. For the mixed-ligand-protected Au nanoparticles analyzed here, the characteristic length scale is 1.2 ± 0.1 nm, whereas for the homoligand Au NPs this scale is 0.75 ± 0.05 nm. These length scales represent spatial correlations independent of scanning parameters, and hence the features in the PSD can be ascribed to a fingerprint of the STM contrast of ligand-protected nanoparticles. PSD spectra from images recorded at different laboratories using different microscopes and operators can be overlapped across most of the frequency range, proving that the features in the STM images of nanoparticles can be compared and reproduced.

  18. Transient measurements with an ultrafast scanning tunneling microscope

    DEFF Research Database (Denmark)

    Keil, Ulrich Dieter Felix; Jensen, Jacob Riis; Hvam, Jørn Märcher

    1998-01-01

    the transmission line while the change in delay time between pump beam (on the sample) and probe beam (on the probe) provides the temporal information. The investigated photoconductor sample is a low-temperature-grown GaAs layer placed on a sapphire substrate with a thin, semitransparent gold layer. In tunneling...

  19. Development of micro-four-point probe in a scanning tunneling microscope for in situ electrical transport measurement.

    Science.gov (United States)

    Ge, Jian-Feng; Liu, Zhi-Long; Gao, Chun-Lei; Qian, Dong; Liu, Canhua; Jia, Jin-Feng

    2015-05-01

    Electrons at surface may behave differently from those in bulk of a material. Multi-functional tools are essential in comprehensive studies on a crystal surface. Here, we developed an in situ microscopic four-point probe (4PP) transport measurement system on the basis of a scanning tunneling microscope (STM). In particular, convenient replacement between STM tips and micro-4PPs enables systematic investigations of surface morphology, electronic structure, and electrical transport property of a same sample surface. Performances of the instrument are demonstrated with high-quality STM images, tunneling spectra, and low-noise electrical I-V characteristic curves of a single-layer FeSe film grown on a conductive SrTiO3 surface.

  20. Development of micro-four-point probe in a scanning tunneling microscope for in situ electrical transport measurement

    Energy Technology Data Exchange (ETDEWEB)

    Ge, Jian-Feng; Liu, Zhi-Long; Gao, Chun-Lei; Qian, Dong; Liu, Canhua, E-mail: canhualiu@sjtu.edu.cn, E-mail: jfjia@sjtu.edu.cn; Jia, Jin-Feng, E-mail: canhualiu@sjtu.edu.cn, E-mail: jfjia@sjtu.edu.cn [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240 (China)

    2015-05-15

    Electrons at surface may behave differently from those in bulk of a material. Multi-functional tools are essential in comprehensive studies on a crystal surface. Here, we developed an in situ microscopic four-point probe (4PP) transport measurement system on the basis of a scanning tunneling microscope (STM). In particular, convenient replacement between STM tips and micro-4PPs enables systematic investigations of surface morphology, electronic structure, and electrical transport property of a same sample surface. Performances of the instrument are demonstrated with high-quality STM images, tunneling spectra, and low-noise electrical I-V characteristic curves of a single-layer FeSe film grown on a conductive SrTiO{sub 3} surface.

  1. In Situ Scanning-Tunneling-Microscope Observation on Dissolution of a Cu-20Zr Film

    Institute of Scientific and Technical Information of China (English)

    Haibo LU; Guoze MENG; Ying LI; Fuhui WANG

    2005-01-01

    A nanocrystalline coating of Cu-20Zr (in wt pct) was obtained on glass by magnetron sputtering. The corrosion behavior of the Cu-20Zr film in 0.001 mol/L HCl solution was investigated using potentiodynamic polarization and in situ electrochemical scanning-tunneling-microscopy (ECSTM). Results demonstrated that the film exhibits active behavior. Microscopic pitting corrosion and tunneling are caused by localized electrodissolution of Zr atoms and the diffusion of Cu atoms at surface defects.

  2. Design and performance of a practical variable-temperature scanning tunneling potentiometry system.

    Science.gov (United States)

    Rozler, M; Beasley, M R

    2008-07-01

    We have constructed a scanning tunneling potentiometry system capable of simultaneously mapping the transport-related electrochemical potential of a biased sample along with its surface topography. Combining a novel sample biasing technique with a continuous current-nulling feedback scheme pushes the noise performance of the measurement to its fundamental limit--the Johnson noise of the scanning tunneling microscope (STM) tunnel junction. The resulting 130 nV voltage sensitivity allows us to spatially resolve local potentials at scales down to 2 nm, while maintaining angstrom scale STM imaging, all at scan sizes of up to 15 microm. A millimeter-range two-dimensional coarse positioning stage and the ability to operate from liquid helium to room temperature with a fast turn-around time greatly expand the versatility of the instrument. By performing studies of several model systems, we discuss the implications of various types of surface morphology for potentiometric measurements.

  3. Imaging by Electrochemical Scanning Tunneling Microscopy and Deconvolution Resolving More Details of Surfaces Nanomorphology

    DEFF Research Database (Denmark)

    Andersen, Jens Enevold Thaulov

    to crystallographic-surface structures. Within the wide range of new technologies, those images surface features, the electrochemical scanning tunneling microscope (ESTM) provides means of atomic resolution where the tip participates actively in the process of imaging. Two metallic surfaces influence ions trapped...... observed in high-resolution images of metallic nanocrystallites may be effectively deconvoluted, as to resolve more details of the crystalline morphology (see figure). Images of surface-crystalline metals indicate that more than a single atomic layer is involved in mediating the tunneling current......Upon imaging, electrochemical scanning tunneling microscopy (ESTM), scanning electrochemical micro-scopy (SECM) and in situ STM resolve information on electronic structures and on surface topography. At very high resolution, imaging processing is required, as to obtain information that relates...

  4. Electronic, vibrational, Raman, and scanning tunneling microscopy signatures of two-dimensional boron nanomaterials

    Science.gov (United States)

    Massote, Daniel V. P.; Liang, Liangbo; Kharche, Neerav; Meunier, Vincent

    2016-11-01

    Compared to graphene, the synthesis of large area atomically thin boron materials is particularly challenging, owing to the electronic shell structure of B, which does not lend itself to the straightforward assembly of pure B materials. This difficulty is evidenced by the fact that the first synthesis of a pure two-dimensional boron was only very recently reported, using silver as a growing substrate. In addition to experimentally observed 2D boron allotropes, a number of other stable and metastable 2D boron materials are predicted to exist, depending on growth conditions and the use of a substrate during growth. This first-principles study based on density functional theory aims at providing guidelines for the identification of these materials. To this end, this report presents a comparative description of a number of possible 2D B allotropes. Electronic band structures, phonon dispersion curves, Raman scattering spectra, and scanning tunneling microscopy images are simulated to highlight the differences between five distinct realizations of these B systems. The study demonstrates the existence of clear experimental signatures that constitute a solid basis for the unambiguous experimental identification of layered B materials.

  5. Scanning tunneling spectroscopy of CdSe nanocrystals covalently bound to GaAs

    DEFF Research Database (Denmark)

    Walzer, K.; Marx, E.; Greenham, N.C.;

    2003-01-01

    We present scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) measurements of CdSe nanocrystals covalently attached to doped GaAs substrates using monolayers of 1,6-hexanedithiol. STM measurements showed the formation of stable, densely packed, homogeneous monolayers of...... Elsevier Science B.V. All rights reserved....... and the bands in the substrate which are bent under the influence of the strong electric field between the closely separated semiconductor substrate and STM tip. The polarity of the forward bias direction is determined by the alignment of the CdSe electronic states with the semiconductor bands. (C) 2003...

  6. Scanning tunneling microscopy I general principles and applications to clean and adsorbate-covered surfaces

    CERN Document Server

    Wiesendanger, Roland

    1992-01-01

    Scanning Tunneling Microscopy I provides a unique introduction to a novel and fascinating technique that produces beautiful images of nature on an atomic scale. It is the first of three volumes that together offer a comprehensive treatment of scanning tunneling microscopy, its diverse applications, and its theoretical treatment. In this volume the reader will find a detailed description of the technique itself and of its applications to metals, semiconductors, layered materials, adsorbed molecules and superconductors. In addition to the many representative results reviewed, extensive references to original work will help to make accessible the vast body of knowledge already accumulated in this field.

  7. Scanning tunneling microscopy of initial nitridation processes on oxidized Si(100) surface with radical nitrogen

    CERN Document Server

    Takahashi, R; Ikeda, H; Sakashita, M; Sakai, A; Yasuda, Y; Nakatsuka, O; Zaima, S

    2003-01-01

    We have investigated the initial nitridation processes on oxidized Si(100) with radical nitrogen at a substrate temperature of 850degC using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). It is found that the thin oxide layer suppresses the changes of original Si step structures during nitridation, and this effect critically depends on the growth conditions of the oxide layer. Comparison of the nitride island morphology to the case of the clean surface suggests that the migration of the precursor during nitridation is suppressed by the oxygen in the layer. (author)

  8. Four-probe scanning tunnelling microscope with atomic resolution for electrical and electro-optical property measurements of nanosystems

    Institute of Scientific and Technical Information of China (English)

    Lin Xiao; He Xiao-Bo; Lu Jun-Ling; Gao Li; Huan Qing; Shi Dong-Xia; Gao Hong-Jun

    2005-01-01

    We demonstrate a special four-probe scanning tunnelling microscope (STM) system in ultrahigh vacuum (UHV),which can provide coarse positioning for every probe independently with the help of scanning electron microscope (SEM)and fine positioning down to nanometre using the STM technology. The system allows conductivity measurement by means of a four-point probe method, which can draw out more accurate electron transport characteristics in nanostructures, and provides easy manipulation of low dimension materials. All measurements can be performed in variable temperature (from 30K to 500K), magnetic field (from 0 to 0.1T), and different gas environments. Simultaneously, the cathodoluminescence (CL) spectrum can be achieved through an optical subsystem. Test measurements using some nanowire samples show that this system is a powerful tool in exploring electron transport characteristics and spectra in nanoscale physics.

  9. Three-dimensional laser scanning for geometry documentation and construction management of highway tunnels during excavation.

    Science.gov (United States)

    Gikas, Vassilis

    2012-01-01

    Driven by progress in sensor technology, computer software and data processing capabilities, terrestrial laser scanning has recently proved a revolutionary technique for high accuracy, 3D mapping and documentation of physical scenarios and man-made structures. Particularly, this is of great importance in the underground space and tunnel construction environment as surveying engineering operations have a great impact on both technical and economic aspects of a project. This paper discusses the use and explores the potential of laser scanning technology to accurately track excavation and construction activities of highway tunnels. It provides a detailed overview of the static laser scanning method, its principles of operation and applications for tunnel construction operations. Also, it discusses the planning, execution, data processing and analysis phases of laser scanning activities, with emphasis given on geo-referencing, mesh model generation and cross-section extraction. Specific case studies are considered based on two construction sites in Greece. Particularly, the potential of the method is examined for checking the tunnel profile, producing volume computations and validating the smoothness/thickness of shotcrete layers at an excavation stage and during the completion of excavation support and primary lining. An additional example of the use of the method in the geometric documentation of the concrete lining formwork is examined and comparisons against dimensional tolerances are examined. Experimental comparisons and analyses of the laser scanning method against conventional surveying techniques are also considered.

  10. Three-Dimensional Laser Scanning for Geometry Documentation and Construction Management of Highway Tunnels during Excavation

    Directory of Open Access Journals (Sweden)

    Vassilis Gikas

    2012-08-01

    Full Text Available Driven by progress in sensor technology, computer software and data processing capabilities, terrestrial laser scanning has recently proved a revolutionary technique for high accuracy, 3D mapping and documentation of physical scenarios and man-made structures. Particularly, this is of great importance in the underground space and tunnel construction environment as surveying engineering operations have a great impact on both technical and economic aspects of a project. This paper discusses the use and explores the potential of laser scanning technology to accurately track excavation and construction activities of highway tunnels. It provides a detailed overview of the static laser scanning method, its principles of operation and applications for tunnel construction operations. Also, it discusses the planning, execution, data processing and analysis phases of laser scanning activities, with emphasis given on geo-referencing, mesh model generation and cross-section extraction. Specific case studies are considered based on two construction sites in Greece. Particularly, the potential of the method is examined for checking the tunnel profile, producing volume computations and validating the smoothness/thickness of shotcrete layers at an excavation stage and during the completion of excavation support and primary lining. An additional example of the use of the method in the geometric documentation of the concrete lining formwork is examined and comparisons against dimensional tolerances are examined. Experimental comparisons and analyses of the laser scanning method against conventional surveying techniques are also considered.

  11. Zeeman effects on the tunneling spectra of a ferromagnetic d-wave superconductor in contact with a quantum wire

    Energy Technology Data Exchange (ETDEWEB)

    Emamipour, Hamidreza, E-mail: h_emamipour@yahoo.com [Department of Physics, Ilam University, Ilam (Iran, Islamic Republic of); Mehrabzad, Narges [Islamic Azad University, Central Tehran Branch, Tehran (Iran, Islamic Republic of)

    2016-07-15

    We study tunneling conductance in a quantum wire–insulator–ferromagnetic d-wave superconductor junction. The results show that exchange field of superconductor has a strong impact on tunneling spectra depending on the junction parameters. We have found a gap like structure in the tunneling limit when we have an interface normal to the (100) axis of superconductor. In the case of (110) axis of superconductor, there is not any zero- bias conductance peaks in tunneling spectra. For a metallic junction the dips disappear.

  12. Scanning Tunneling Microscopic Characterization of an Engineered Organic Molecule

    Science.gov (United States)

    2011-08-01

    attachment and wide -band MCT detector, was used. Figure 3 shows the spectra obtained for SAM of PMNBT (top), which was compared to raw crystal PMNBT...Graphite Covered with Phthalocyanine Molecules. Science , 1992, 255, 1115– 1118. 10. Stabel, A.; Herwig, P.; Mullen, K.; Rabe, J. P. Diode Like...J. J.; Dunbar, T. D.; Allara, D. L.; Weiss, P. S. Electron Transfer through Organic Molecules. J. Phys. Chem. B 1999, 103, 8122–8127. 16. Wold , D

  13. Light amplification by stimulated emission from an optically pumped molecular junction in a scanning tunneling microscope

    CERN Document Server

    Braun, K; Wang, X; Adler, H; Peisert, H; Chasse, T; Zhang, D; Meixner, A J

    2013-01-01

    Here, we introduce and experimentally demonstrate optical amplification and stimulated emission from a single optically pumped molecular tunneling junction of a scanning tunneling microscope. The gap between a sharp gold tip and a flat gold substrate covered with a self-assembled monolayer of 5-chloro-2-mercaptobenzothiazole molecules forms an extremely small optical gain medium. When electrons tunnel from the molecules highest occupied molecular orbital to the tip, holes are left behind. These can be repopulated by hot electrons induced by the laser-driven plasmon oscillation on the metal surfaces enclosing the cavity. Solving the laser-rate equations for this system shows that the repopulation process can be efficiently stimulated by the gap modes near field, TERS scattering from neighboring molecules acting as an optical seed. Our results demonstrate how optical enhancement inside the plasmonic cavity can be further increased by a stronger localization via tunneling through molecules. We anticipate that st...

  14. Scanning tunneling microscopy of copper electrodeposited in the presence of benzotriazole

    Energy Technology Data Exchange (ETDEWEB)

    Armstrong, M.J.; Muller, R.H.

    1988-12-01

    In the present work, the effects of benzotriazole (BTA) on the topography of Cu deposited on a Pt <111> single crystal surface under potential control was investigated with STM. The surfaces of the Cu deposits were continuously scanned with the tunneling probe during deposition. In the presence of BTA the initial monolayer of Cu was detected. 4 refs., 2 figs.

  15. Simultaneous topographic and elemental chemical and magnetic contrast in scanning tunneling microscopy

    Science.gov (United States)

    Rose, Volker; Preissner, Curt A; Hla, Saw-Wai; Wang, Kangkang; Rosenmann, Daniel

    2014-09-30

    A method and system for performing simultaneous topographic and elemental chemical and magnetic contrast analysis in a scanning, tunneling microscope. The method and system also includes nanofabricated coaxial multilayer tips with a nanoscale conducting apex and a programmable in-situ nanomanipulator to fabricate these tips and also to rotate tips controllably.

  16. Preparation of Chemically Etched Tips for Ambient Instructional Scanning Tunneling Microscopy

    Science.gov (United States)

    Zaccardi, Margot J.; Winkelmann, Kurt; Olson, Joel A.

    2010-01-01

    A first-year laboratory experiment that utilizes concepts of electrochemical tip etching for scanning tunneling microscopy (STM) is described. This experiment can be used in conjunction with any STM experiment. Students electrochemically etch gold STM tips using a time-efficient method, which can then be used in an instructional grade STM that…

  17. Integration of a gate electrode into carbon nanotube devices for scanning tunneling microscopy

    NARCIS (Netherlands)

    Kong, J.; LeRoy, B.J.; Lemay, S.G.; Dekker, C.

    2005-01-01

    We have developed a fabrication process for incorporating a gate electrode into suspended single-walled carbon nanotube structures for scanning tunneling spectroscopy studies. The nanotubes are synthesized by chemical vapor deposition directly on a metal surface. The high temperature (800 °C) involv

  18. First-principles modelling of scanning tunneling microscopy using non-equilibrium Green's functions

    DEFF Research Database (Denmark)

    Lin, H.P.; Rauba, J.M.C.; Thygesen, Kristian Sommer

    2010-01-01

    The investigation of electron transport processes in nano-scale architectures plays a crucial role in the development of surface chemistry and nano-technology. Experimentally, an important driving force within this research area has been the concurrent refinements of scanning tunneling microscopy...

  19. Ionic channels in Langmuir-Blodgett films imaged by a scanning tunneling microscope.

    Science.gov (United States)

    Kolomytkin, O V; Golubok, A O; Davydov, D N; Timofeev, V A; Vinogradova, S A; Tipisev SYa

    1991-01-01

    The molecular structure of channels formed by gramicidin A in a lipid membrane was imaged by a scanning tunneling microscope operating in air. The mono- and bimolecular films of lipid with gramicidin A were deposited onto a highly oriented pyrolitic graphite substrate by the Langmuir-Blodgett technique. It has been shown that under high concentration gramicidin A molecules can form in lipid films a quasi-regular, densely packed structure. Single gramicidin A molecules were imaged for the first time as well. The cavity of 0.4 +/- 0.05 nm in halfwidth was found on the scanning tunneling microscopy image of the gramicidin A molecule. The results of direct observation obtained by means of scanning tunneling microscope are in good agreement with the known molecular model of gramicidin A. It was shown that gramicidin A molecules can exist in a lipid monolayer as individual molecules or combined into clusters. The results demonstrate that scanning tunneling microscope can be used for high spatial resolution study of ionic channel structure. Images FIGURE 1 FIGURE 2 FIGURE 4 FIGURE 5 PMID:1712239

  20. Theoretical analysis of a dual-probe scanning tunneling microscope setup on graphene

    DEFF Research Database (Denmark)

    Settnes, Mikkel; Power, Stephen R.; Petersen, Dirch Hjorth;

    2014-01-01

    Experimental advances allow for the inclusion of multiple probes to measure the transport properties of a sample surface. We develop a theory of dual-probe scanning tunneling microscopy using a Green's function formalism, and apply it to graphene. Sampling the local conduction properties at finit...

  1. New design of a variable-temperature ultrahigh vacuum scanning tunneling microscope

    NARCIS (Netherlands)

    Mugele, F.; Rettenberger, A.; Boneberg, J.; Leiderer, P.

    1998-01-01

    We present the design of a variable-temperature ultrahigh vacuum (UHV) scanning tunneling microscope which can be operated between 20 and 400 K. The microscope is mounted directly onto the heat exchanger of a He continuous flow cryostat without vibration isolation inside the UHV chamber. The coarse

  2. Single-molecule conductance of redox molecules in electrochemical scanning tunneling microscopy

    DEFF Research Database (Denmark)

    Haiss, W.; Albrecht, Tim; van Zalinge, H.;

    2007-01-01

    Experimental data and theoretical notions are presented for 6-[1'-(6-mercapto-hexyl)-[4,4']bipyridinium]-hexane-1-thiol iodide (6V6) "wired" between a gold electrode surface and tip in an in situ scanning tunneling microscopy configuration. The viologen group can be used to "gate" charge transpor...

  3. Scanning Tunneling Microscopy Studies of Topological Insulators Grown by Molecular Beam Epitaxy

    Directory of Open Access Journals (Sweden)

    Xue Qikun

    2012-03-01

    Full Text Available We summarize our recent scanning tunneling microscopy (STM study of topological insulator thin films grown by molecular beam epitaxy (MBE, which includes the observation of electron standing waves on topological insulator surface and the Landau quantization of topological surface states. The work has provided valuable information to the understanding of intriguing properties of topological insulators, as predicted by theory.

  4. Covalently Immobilised Cytochrome C Imaged by In Situ Scanning Tunnelling Microscopy

    DEFF Research Database (Denmark)

    Andersen, Jens Enevold Thaulov; Olesen, Klaus G.; Danilov, Alexey I.;

    1997-01-01

    In situ scanning tunnelling microscopy (STM) imaging of cytochrome c (cyt c) on polycrystalline Pt surfaces and on Au(lll) was achieved first by covalent immobilisation of 3-aminopropyltriethoxysilane (3-APTS) brought to react with oxide present on the Pt surfaces. Covalently bound 3-APTS forms...

  5. A development in the preparation of sharp scanning tunneling microscopy tips

    DEFF Research Database (Denmark)

    Song, J. P.; Pryds, N. H.; Glejbøl, K.;

    1993-01-01

    An improved and reliable method for making sharp scanning tunneling microscopy (STM) tips is described. It is based on the widely used drop-off electrochemical etching procedure, here modified to improve the control of the tip shape. A second etching is applied not only to remove the oxide layer...

  6. Transient measurements with an ultrafast scanning tunneling microscope on semiconductor surfaces

    DEFF Research Database (Denmark)

    Keil, Ulrich Dieter Felix; Jensen, Jacob Riis; Hvam, Jørn Märcher

    1998-01-01

    We demonstrate: the use of an ultrafast scanning tunneling microscope on a semiconductor surface. Laser-induced transient signals with 1.8 ps rise time are detected, The investigated sample is a low-temperature grown GaAs layer plated on a sapphire substrate with a thin gold layer that serves as st...

  7. First-Principle Calculation for Scanning-Tunneling-Microscopic Images of a Monolayer Graphite Surface

    Institute of Scientific and Technical Information of China (English)

    陈向荣; 押山淳; 岡田晋; 芶清泉

    2003-01-01

    We have applied first-principle total-energy electronic structure calculations in the local density approximation to calculate the scanning tunnelling microscopy images of a monolayer graphite surface near the Fermi level. The results obtained agree well with the observation, which has not been interpreted before.

  8. Stochastic and photochromic switching of diarylethenes studied by scanning tunnelling microscopy

    NARCIS (Netherlands)

    Molen, S.J. van der; Vegte, H. van der; Kudernac, T.; Amin, I.; Feringa, B.L.; Wees, B.J. van

    2006-01-01

    We investigate switching of photochromic, thiophene-substituted diarylethene switches on gold. For this, the conjugated isomer is inserted in a dodecanethiol self-assembled monolayer. This layer is subsequently scanned by tunnelling microscopy. First, we study the statistics of stochastic switching

  9. Adsorption of Cu phthalocyanine on Pt modified Ge(001): A scanning tunneling microscopy study

    NARCIS (Netherlands)

    Saedi, Amirmehdi; Berkelaar, Robin P.; Kumar, Avijit; Poelsema, Bene; Zandvliet, Harold J.W.

    2010-01-01

    The adsorption configurations of copper phthalocyanine (CuPc) molecules on platinum-modified Ge(001) have been studied using scanning tunneling microscopy. After deposition at room temperature and cooling down to 77 K the CuPc molecules are still dynamic. However, after annealing at 550±50 K, the ad

  10. Observation of a Ag protrusion on a Ag2S island using a scanning tunneling microscope

    Directory of Open Access Journals (Sweden)

    Takeo Ohno

    2015-01-01

    Full Text Available A silver sulfide (Ag2S island as an ionic conductor in resistive switching memories was formed and a protrusion of silver from the Ag2S formed by an electrochemical reaction was observed using a scanning tunneling microscope.

  11. Probing Nanoscale Electronic and Magnetic Interaction with Scanning Tunneling Spectroscopy

    DEFF Research Database (Denmark)

    Bork, Jakob

    This thesis is concerned with fundamental research into electronic and magnetic interaction on the nanoscale. From small metallic and magnetic islands and layers to single atoms. The research revolves around magnetic interaction probed through the spectroscopic capabilities of the scanning....... This is related to research in correlated electron materials such as studies of phase transitions in heavy fermion compounds and magnetic interaction in spintronic research. The capping of cobalt islands on Cu(111) with silver is investigated with STM and photoemission spectroscopy. It is shown that at low...... coverage the silver preferably nucleates on top of the bilayer high cobalt islands compared to directly on the Cu(111) substrate. Furthermore, the silver forms a combination of a reconstruction and a Moire pattern which is investigated with low-energy electron diraction and spectroscopic STM mapping at 6...

  12. Apparent rippling with honeycomb symmetry and tunable periodicity observed by scanning tunneling microscopy on suspended graphene

    Science.gov (United States)

    Georgi, A.; Nemes-Incze, P.; Szafranek, B.; Neumaier, D.; Geringer, V.; Liebmann, M.; Morgenstern, M.

    2016-11-01

    Suspended graphene is difficult to image by scanning probe microscopy due to the inherent van der Waals and dielectric forces exerted by the tip, which are not counteracted by a substrate. Here, we report scanning tunneling microscopy data of suspended monolayer graphene in constant-current mode, revealing a surprising honeycomb structure with amplitude of 50-200 pm and lattice constant of 10-40 nm. The apparent lattice constant is reduced by increasing the tunneling current I , but does not depend systematically on tunneling voltage V or scan speed vscan. The honeycomb lattice of the rippling is aligned with the atomic structure observed on supported areas, while no atomic corrugation is found on suspended areas down to the resolution of about 3 -4 pm. We rule out that the honeycomb structure is induced by the feedback loop using a changing vscan, that it is a simple enlargement effect of the atomic lattice, as well as models predicting frozen phonons or standing phonon waves induced by the tunneling current. Although we currently do not have a convincing explanation for the observed effect, we expect that our intriguing results will inspire further research related to suspended graphene.

  13. Field-Induced Deformation as a Mechanism for Scanning Tunneling Microscopy Based Nanofabrication

    DEFF Research Database (Denmark)

    Hansen, Ole; Ravnkilde, Jan Tue; Quaade, Ulrich;

    1998-01-01

    The voltage between tip and sample in a scanning tunneling microscope (STM) results in a large electric field localized near the tip apex. The mechanical stress due to this field can cause appreciable deformation of both tip and sample on the scale of the tunnel gap. We derive an approximate...... analytical expression for this deformation and confirm the validity of the result by comparison with a finite element analysis. We derive the condition for a field-induced jump to contact of tip and sample and show that this agrees well with experimental results for material transfer between tip and sample...

  14. Field emission current-voltage curves as a diagnostic for scanning tunneling microscope tips

    Science.gov (United States)

    Meyer, J. A.; Stranick, S. J.; Wang, J. B.; Weiss, P. S.

    1991-12-01

    The current-voltage (I-V) characteristics of a low temperature ultrahigh vacuum scanning tunneling microscope (STM) tip positioned greater than 100 A from a planar surface have been recorded. We find curvature in the Fowler-Nordheim plots (log 10 I/V(sup 2) vs. I/V) due to the tip-plane geometry as has been predicted theoretically. Additionally, oscillations and sharp breaks in these I-V curves are observed over a wide voltage range, 50-1000 V. These I-V curves are used to characterize the STM tips prior to tunneling.

  15. Combined frequency modulated atomic force microscopy and scanning tunneling microscopy detection for multi-tip scanning probe microscopy applications

    Science.gov (United States)

    Morawski, Ireneusz; Spiegelberg, Richard; Korte, Stefan; Voigtländer, Bert

    2015-12-01

    A method which allows scanning tunneling microscopy (STM) tip biasing independent of the sample bias during frequency modulated atomic force microscopy (AFM) operation is presented. The AFM sensor is supplied by an electronic circuit combining both a frequency shift signal and a tunneling current signal by means of an inductive coupling. This solution enables a control of the tip potential independent of the sample potential. Individual tip biasing is specifically important in order to implement multi-tip STM/AFM applications. An extensional quartz sensor (needle sensor) with a conductive tip is applied to record simultaneously topography and conductivity of the sample. The high resonance frequency of the needle sensor (1 MHz) allows scanning of a large area of the surface being investigated in a reasonably short time. A recipe for the amplitude calibration which is based only on the frequency shift signal and does not require the tip being in contact is presented. Additionally, we show spectral measurements of the mechanical vibration noise of the scanning system used in the investigations.

  16. EDITORIAL: Three decades of scanning tunnelling microscopy that changed the course of surface science Three decades of scanning tunnelling microscopy that changed the course of surface science

    Science.gov (United States)

    Ramachandra Rao, M. S.; Margaritondo, Giorgio

    2011-11-01

    Three decades ago, with a tiny tip of platinum, the scientific world saw the real space imaging of single atoms with unprecedented spatial resolution. This signalled the birth of one of the most versatile surface probes, based on the physics of quantum mechanical tunnelling: the scanning tunnelling microscope (STM). Invented in 1981 by Gerd Binnig and Heinrich Rohrer of IBM, Zurich, it led to their award of the 1986 Nobel Prize. Atoms, once speculated to be abstract entities used by theoreticians for mere calculations, can be seen to exist for real with the nano-eye of an STM tip that also gives real-space images of molecules and adsorbed complexes on surfaces. From a very fundamental perspective, the STM changed the course of surface science and engineering. STM also emerged as a powerful tool to study various fundamental phenomena relevant to the properties of surfaces in technological applications such as tribology, medical implants, catalysis, sensors and biology—besides elucidating the importance of local bonding geometries and defects, non-periodic structures and the co-existence of nano-scale phases. Atom-level probing, once considered a dream, has seen the light with the evolution of STM. An important off-shoot of STM was the atomic force microscope (AFM) for surface mapping of insulating samples. Then followed the development of a flurry of techniques under the general name of scanning probe microscopy (SPM). These techniques (STM, AFM, MFM, PFM etc) designed for atomic-scale-resolution imaging and spectroscopy, have led to brand new developments in surface analysis. All of these novel methods enabled researchers in recent years to image and analyse complex surfaces on microscopic and nanoscopic scales. All of them utilize a small probe for sensing the surface. The invention of AFM by Gerd Binnig, Calvin Quate and Christopher Gerber opened up new opportunities for characterization of a variety of materials, and various industrial applications could be

  17. Theoretical study of carbon-based tips for scanning tunnelling microscopy.

    Science.gov (United States)

    González, C; Abad, E; Dappe, Y J; Cuevas, J C

    2016-03-11

    Motivated by recent experiments, we present here a detailed theoretical analysis of the use of carbon-based conductive tips in scanning tunnelling microscopy. In particular, we employ ab initio methods based on density functional theory to explore a graphitic, an amorphous carbon and two diamond-like tips for imaging with a scanning tunnelling microscope (STM), and we compare them with standard metallic tips made of gold and tungsten. We investigate the performance of these tips in terms of the corrugation of the STM images acquired when scanning a single graphene sheet. Moreover, we analyse the impact of the tip-sample distance and show that it plays a fundamental role in the resolution and symmetry of the STM images. We also explore in depth how the adsorption of single atoms and molecules in the tip apexes modifies the STM images and demonstrate that, in general, it leads to an improved image resolution. The ensemble of our results provides strong evidence that carbon-based tips can significantly improve the resolution of STM images, as compared to more standard metallic tips, which may open a new line of research in scanning tunnelling microscopy.

  18. Theoretical study of carbon-based tips for scanning tunnelling microscopy

    Science.gov (United States)

    González, C.; Abad, E.; Dappe, Y. J.; Cuevas, J. C.

    2016-03-01

    Motivated by recent experiments, we present here a detailed theoretical analysis of the use of carbon-based conductive tips in scanning tunnelling microscopy. In particular, we employ ab initio methods based on density functional theory to explore a graphitic, an amorphous carbon and two diamond-like tips for imaging with a scanning tunnelling microscope (STM), and we compare them with standard metallic tips made of gold and tungsten. We investigate the performance of these tips in terms of the corrugation of the STM images acquired when scanning a single graphene sheet. Moreover, we analyse the impact of the tip-sample distance and show that it plays a fundamental role in the resolution and symmetry of the STM images. We also explore in depth how the adsorption of single atoms and molecules in the tip apexes modifies the STM images and demonstrate that, in general, it leads to an improved image resolution. The ensemble of our results provides strong evidence that carbon-based tips can significantly improve the resolution of STM images, as compared to more standard metallic tips, which may open a new line of research in scanning tunnelling microscopy.

  19. Method and apparatus for differential spectroscopic atomic-imaging using scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kazmerski, L.L.

    1990-07-17

    This patent describes a spectroscopic scanning tunneling microscope (SSTM) apparatus for differential atomic imaging the surface of a material sample. It comprises: a mounting stage for mounting the sample; a fine-point electrode probe positioned adjacent the mounting stage and being positionable very closely adjacent a sample that is mounted on the stage to accommodate a tunneling current between the sample and the probe; tunable electronic surface bias means connected to the surface of the sample and to the probe for electronically biasing the surface of the sample in relation to the probe with a surface voltage bias; photon bias means adjacent the stage for providing photon biasing of selected wavelengths and frequencies on the surface of the sample adjacent the probe; instrumentation means for measuring tunneling current through the probe and electronic voltage bias; data processing means; and display means.

  20. Fabrication and Characterization of Low-Dimensional Nanostructures using Scanning Tunneling Microscopy

    Science.gov (United States)

    Fujita, Daisuke; Sagisaka, Keisuke; Onishi, Keiko; Ohgi, Taizo

    Recent developments of fabrication, manipulation and characterization techniques at nanometer scale for low-dimensional nanostructures using scanning tunneling microscopy (STM) are reviewed. Firstly two reliable methods for metallic nanostructure formation using tip material transfer are introduced. Secondly STM-manipulation of Au nanoclusters grown on self-assembled monolayers is introduced, where single electron tunneling effect is clearly observable using tunneling spectroscopy. As a new type of STM manipulation, a reversible control method of surface periodic structures (phases) on Si(100) at low temperatures is introduced. Finally using a single atom deposition technique using a controlled point contact, fabrication of one-dimensional quantum well on a single dimer row of Si(100) surface is explained. Combining the fabrication and characterization capabilities of STM in various environments, STM can be a powerful tool for the exploration of nanotechnology and nanoscience.

  1. Automatic Extraction of Tunnel Lining Cross-Sections from Terrestrial Laser Scanning Point Clouds.

    Science.gov (United States)

    Cheng, Yun-Jian; Qiu, Wenge; Lei, Jin

    2016-10-06

    Tunnel lining (bare-lining) cross-sections play an important role in analyzing deformations of tunnel linings. The goal of this paper is to develop an automatic method for extracting bare-lining cross-sections from terrestrial laser scanning (TLS) point clouds. First, the combination of a 2D projection strategy and angle criterion is used for tunnel boundary point detection, from which we estimate the two boundary lines in the X-Y plane. The initial direction of the cross-sectional plane is defined to be orthogonal to one of the two boundary lines. In order to compute the final cross-sectional plane, the direction is adjusted twice with the total least squares method and Rodrigues' rotation formula, respectively. The projection of nearby points is made onto the adjusted plane to generate tunnel cross-sections. Finally, we present a filtering algorithm (similar to the idea of the morphological erosion) to remove the non-lining points in the cross-section. The proposed method was implemented on railway tunnel data collected in Sichuan, China. Compared with an existing method of cross-sectional extraction, the proposed method can offer high accuracy and more reliable cross-sectional modeling. We also evaluated Type I and Type II errors of the proposed filter, at the same time, which gave suggestions on the parameter selection of the filter.

  2. Automatic Extraction of Tunnel Lining Cross-Sections from Terrestrial Laser Scanning Point Clouds

    Directory of Open Access Journals (Sweden)

    Yun-Jian Cheng

    2016-10-01

    Full Text Available Tunnel lining (bare-lining cross-sections play an important role in analyzing deformations of tunnel linings. The goal of this paper is to develop an automatic method for extracting bare-lining cross-sections from terrestrial laser scanning (TLS point clouds. First, the combination of a 2D projection strategy and angle criterion is used for tunnel boundary point detection, from which we estimate the two boundary lines in the X-Y plane. The initial direction of the cross-sectional plane is defined to be orthogonal to one of the two boundary lines. In order to compute the final cross-sectional plane, the direction is adjusted twice with the total least squares method and Rodrigues' rotation formula, respectively. The projection of nearby points is made onto the adjusted plane to generate tunnel cross-sections. Finally, we present a filtering algorithm (similar to the idea of the morphological erosion to remove the non-lining points in the cross-section. The proposed method was implemented on railway tunnel data collected in Sichuan, China. Compared with an existing method of cross-sectional extraction, the proposed method can offer high accuracy and more reliable cross-sectional modeling. We also evaluated Type I and Type II errors of the proposed filter, at the same time, which gave suggestions on the parameter selection of the filter.

  3. Scanning tunneling potentiometry implemented into a multi-tip setup by software

    Science.gov (United States)

    Lüpke, F.; Korte, S.; Cherepanov, V.; Voigtländer, B.

    2015-12-01

    We present a multi-tip scanning tunneling potentiometry technique that can be implemented into existing multi-tip scanning tunneling microscopes without installation of additional hardware. The resulting setup allows flexible in situ contacting of samples under UHV conditions and subsequent measurement of the sample topography and local electric potential with resolution down to Å and μV, respectively. The performance of the potentiometry feedback is demonstrated by thermovoltage measurements on the Ag / Si ( 111 ) - ( √{ 3 } × √{ 3 } ) R 3 0 ∘ surface by resolving a standing wave pattern. Subsequently, the ability to map the local transport field as a result of a lateral current through the sample surface is shown on Ag / Si ( 111 ) - ( √{ 3 } × √{ 3 } ) R 3 0 ∘ and Si(111) - (7 × 7) surfaces.

  4. Adsorption of L-Alanine on Cu(111) Studied by Scanning Tunnelling Microscopy

    Institute of Scientific and Technical Information of China (English)

    GE Si-Ping; L(U) Chao; ZHAO Ru-Guang

    2006-01-01

    The adsorption of L-alanine on Cu(111)surface is studied by means of scanning tunnelling microscopy under ultra-high Vacuum conditions.The results show that the adsorbates are chemisorbed on the surface,and can form a two-dimensional gas phase,chain phase and solid phase,depending on deposition rate and amount.The adsorbed molecules can be imaged as individual protrusions and parallel chains in gas and chain phases respectively.It is also found that alanine can form(2×2)superstructure on Cu(111)and copper step facet to directions in solid phase.On the basis of our scanning tunnelling microscopic images,a model js proposed for the Cu(111)(2×2)-alanine superstructure.In the model,we point out the close link between -direction hydrogen bond chains with the same direction copper step faceting.

  5. Observation and manipulation of hexa-adamantyl-hexa-benzocoronene molecules by low temperature scanning tunneling microscopy.

    Science.gov (United States)

    Calmettes, Bastien; Vernisse, Loranne; Guillermet, Olivier; Benjalal, Youness; Bouju, Xavier; Coudret, Christophe; Coratger, Roland

    2014-11-07

    Large molecules made of a central hexa-adamantyl-hexa-benzocoronene plateau surrounded by six adamantyl groups have been investigated by low temperature scanning tunneling microscopy and scanning tunneling spectroscopy coupled with image calculations and molecular mechanics. The structure of large self-assembled domains reveals that the intermolecular interactions between adamantyl peripheral groups dominate film growth. At very low coverage, the molecules can exhibit a certain instability for negative bias voltages which induces a partial rotation. Manipulations of single objects using the STM tip are used to create small clusters of two or three molecules. The formed structures can be obtained and manipulated provided that the flexible adamantyl moieties of neighbouring molecules are brought in close contact promoting a robust mechanical anchoring.

  6. Scanning tunneling potentiometry implemented into a multi-tip setup by software.

    Science.gov (United States)

    Lüpke, F; Korte, S; Cherepanov, V; Voigtländer, B

    2015-12-01

    We present a multi-tip scanning tunneling potentiometry technique that can be implemented into existing multi-tip scanning tunneling microscopes without installation of additional hardware. The resulting setup allows flexible in situ contacting of samples under UHV conditions and subsequent measurement of the sample topography and local electric potential with resolution down to Å and μV, respectively. The performance of the potentiometry feedback is demonstrated by thermovoltage measurements on the Ag/Si(111)-(√3×√3)R30° surface by resolving a standing wave pattern. Subsequently, the ability to map the local transport field as a result of a lateral current through the sample surface is shown on Ag/Si(111)-(√3×√3)R30° and Si(111) - (7 × 7) surfaces.

  7. Scanning Tunneling Spectroscopy of Metal Phthalocyanines on a Au(111) Surface with a Ni Tip

    Institute of Scientific and Technical Information of China (English)

    JIA Zhi-Chun; HU Zhen-Peng; ZHAO Ai-Di; LI Zhen-Yu; LI Bin

    2011-01-01

    Scanning tunneling spectroscopy of metal phthalocyanines (MPc) adsorbed on a A u(111) surface with a Ni(111) scanning tunneling microscopy tip is simulated on the basis of first-principles calculations and a modified Bardeen approximation.Local d orbital symmetry matching between the molecule and the Ni tip brings obvious negative differential resistance (NDR) phenomena,of which,bias voltage and resonant orbitals can be tuned sensitively by the central ion of the molecule.Different dependences of the NDR peak on the tip-molecule distance at two bias polarities and rectifying phenomena are also interpreted in terms of specific structures of 3d orbitals of the adsorbed MPc and Ni tip.

  8. Mono-Cycle Photonics and Optical Scanning Tunneling Microscopy Route to Femtosecond Ångstrom Technology

    CERN Document Server

    Yamashita, Mikio; Morita, Ryuji

    2005-01-01

    "Mono-Cycle Photonics and Optical Scanning Tunneling Microscopy" deals with both the ultrashort laser-pulse technology in the few- to mono-cycle region and the laser-surface-controlled scanning-tunneling microscopy (STM) extending into the spatiotemporal extreme technology. The former covers the theory of nonlinear pulse propagation beyond the slowly-varing-envelope approximation, the generation and active chirp compensation of ultrabroadband optical pulses, the amplitude and phase characterization of few- to mono-cycle pulses, and the feedback field control for the mono-cycle-like pulse generation. In addition, the wavelength-multiplex shaping of ultrabroadband pulse is described. The latter covers the CW-laser-excitation STM, the femtosecond-time-resolved STM and atomic-level surface phenomena controlled by femtosecond pulses.

  9. Three-Dimensional Laser Scanning for Geometry Documentation and Construction Management of Highway Tunnels during Excavation

    OpenAIRE

    Gikas, Vassilis

    2012-01-01

    Driven by progress in sensor technology, computer software and data processing capabilities, terrestrial laser scanning has recently proved a revolutionary technique for high accuracy, 3D mapping and documentation of physical scenarios and man-made structures. Particularly, this is of great importance in the underground space and tunnel construction environment as surveying engineering operations have a great impact on both technical and economic aspects of a project. This paper discusses the...

  10. Scanning tunneling spectroscopy on heavy-fermion systems; Rastertunnelspektroskopie an Schwere-Fermionen-Systemen

    Energy Technology Data Exchange (ETDEWEB)

    Ernst, Stefan

    2011-06-24

    in the framework of this thesis different heavy-fermion systems were studied by means of scanning tunneling microscopy and spectroscopy. In the experiment two main topics existed. On the one hand the heavy-fermion superconductivity in the compounds CeCu{sub 2}Si{sub 2}, CeCoIn{sub 5}, and on the other hand the Kondo effect in the Kondo-lattice system YbRh{sub 2}Si{sub 2}.

  11. Pulse Plating on Gold Surfaces Studied by In Situ Scanning Tunneling Microscopy

    DEFF Research Database (Denmark)

    Andersen, Jens Enevold Thaulov; Bech-Nielsen, Gregers; Møller, Per

    1994-01-01

    Deposition of bulk copper on thin film gold surfaces is carried out by computer-aided pulse plating. It is demonstrated that the morphology of the copper deposit can be studied by in situ scanning tunnelling microscopy both in potentiostatic experiments and in galvanostatic experiments. Optimized...... procedures for obtaining smooth deposits by pulse plating are explained in terms of a levelling effect. Possible non-faradaic processes observed in measurements with high frequency pulse plating are discussed....

  12. TOPICAL REVIEW: Active nanocharacterization of nanofunctional materials by scanning tunneling microscopy

    OpenAIRE

    Daisuke Fujita and Keisuke Sagisaka

    2008-01-01

    Recent developments in the application of scanning tunneling microscopy (STM) to nanofabrication and nanocharacterization are reviewed. The main focus of this paper is to outline techniques for depositing and manipulating nanometer-scale structures using STM tips. Firstly, the transfer of STM tip material through the application of voltage pulses is introduced. The highly reproducible fabrication of metallic silver nanodots and nanowires is discussed. The mechanism is thought to be spontaneou...

  13. Characterization of thin film semiconductors by scanning probe microscopy and tunneling spectroscopy

    Science.gov (United States)

    Gichuhi, Anthony

    We have used scanning tunneling microscopy, atomic force microscopy, tunneling spectroscopy, resonance Raman spectroscopy and electrochemistry to study the electrosynthesis of II-VI compound semiconductors with special emphasis on ZnS, CdS, and HgS. This dissertation will focus mainly on the electrochemical and scanning probe (STM and AFM) applications to these compounds, in addition to novel materials such as CoSb. We hope to understand the structural, as well optical properties of these materials. Finally, we hope to develop a recipe for the electrosynthesis of high quality semiconductor films. In Chapter 2, we report an electrochemical, scanning probe microscopic and Raman spectroscopic investigation of thin US films grown by electrochemical atomic layer epitaxy (EC-ALE) aimed at understanding the role played by the order of deposition on film quality. In Chapter 3, we report a study of electrosynthesized CdS-HgS heterojunctions using scanning tunneling microscopy (STM), photoluminescence spectroscopy (PL), and electrochemistry. US thin films were grown by electrochemical atomic layer epitaxy onto Au(111) substrates and were terminated with a single HgS monolayer. In Chapter 4, the structure and chemical composition of electrosynthesized ZnS thin films on Au(111) substrates grown by alternating underpotential deposition and oxidative adsorption cycles of S and Zn from solution precursors was studied by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). In Chapter 5, conditions for the growth of. stable mercury sulfide (HgS) monolayers on Au(111) surfaces using electrochemical atomic layer epitaxy have been investigated. HgS thin films were characterized by X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). Chapter 6: This chapter describes the use of resonance Raman spectroscopy to characterize thin films of the II-VI compound semiconductors electrosynthesized on metal surfaces. We describe how resonance

  14. Origin of Symmetric Dimer Images of Si(001) Observed by Low-Temperature Scanning Tunneling Microscopy

    Science.gov (United States)

    Ren, Xiao-Yan; Kim, Hyun-Jung; Niu, Chun-Yao; Jia, Yu; Cho, Jun-Hyung

    2016-06-01

    It has been a long-standing puzzle why buckled dimers of the Si(001) surface appeared symmetric below ~20 K in scanning tunneling microscopy (STM) experiments. Although such symmetric dimer images were concluded to be due to an artifact induced by STM measurements, its underlying mechanism is still veiled. Here, we demonstrate, based on a first-principles density-functional theory calculation, that the symmetric dimer images are originated from the flip-flop motion of buckled dimers, driven by quantum tunneling (QT). It is revealed that at low temperature the tunneling-induced surface charging with holes reduces the energy barrier for the flipping of buckled dimers, thereby giving rise to a sizable QT-driven frequency of the flip-flop motion. However, such a QT phenomenon becomes marginal in the tunneling-induced surface charging with electrons. Our findings provide an explanation for low-temperature STM data that exhibits apparent symmetric (buckled) dimer structure in the filled-state (empty-state) images.

  15. Combining mobile terrestrial laser scanning geometric and radiometric data to eliminate accessories in circular metro tunnels

    Science.gov (United States)

    Tan, Kai; Cheng, Xiaojun; Ju, Qiaoqiao

    2016-07-01

    Terrestrial laser scanning (TLS) is a noninvasive technique to monitor surface conditions and morphological characteristics of structures and has been successfully introduced to the regular inspection and maintenance of metro tunnels. To accurately analyze the deformation and structural conditions of a metro tunnel, nonliner points (e.g., outliers and accessories) should be detected and eliminated. Nevertheless, the accessories are attached very closely to the liner and cannot be thoroughly eliminated by three-dimensional (3D) geometric information. This study proposes to separate the liner and accessories by combining TLS geometric and radiometric information. A refitted mobile Faro Focus3D X330 system is used for data collection of a new-built metro tunnel in Hangzhou, China. The results show that the corrected intensity data are an effective physical criterion and a complementary data source to remove accessories that cannot be eliminated by geometric data. After the removal of accessories by geometric and radiometric data, the remaining liner points can accurately reflect the actual structural and deformation conditions of metro tunnels.

  16. Scanning tunneling microscope light emission: Effect of the strong dc field on junction plasmons

    Science.gov (United States)

    Kalathingal, Vijith; Dawson, Paul; Mitra, J.

    2016-07-01

    The observed energies of the localized surface plasmons (LSPs) excited at the tip-sample junction of a scanning tunneling microscope, as identified by spectral peaks in the light output, are very significantly redshifted with respect to calculations that use standard optical data for the tip and sample material, gold in this case. We argue that this anomaly depends on the extreme field in the sub-nm tunneling proximity of the tip and the sample, across which a dc bias (1-2 V) is applied. Finite element modeling analysis is presented of a gold nanosphere-plane (NS-P) combination in tunneling proximity and, crucially, in the presence of a high static electric field (˜109V /m ). It is argued that the strong dc field induces nonlinear corrections to the dielectric function of the gold via the effect of a large background polarizability through the nonlinear, χ(3 ) susceptibility contribution. When fed into the model system the modified optical data alters the LSP cavity modes of the NS-P system to indeed reveal a large redshift in energy compared to those of the virgin gold NS-P system. The net outcome may be regarded as equivalent to lowering the bulk plasmon energy, the physical interpretation being that the intense field of the tunneling environment leads to surface charge screening, effectively reducing the density of free electrons available to participate in the plasmon oscillations.

  17. Theory of scanning tunneling spectroscopy: from Kondo impurities to heavy fermion materials

    Science.gov (United States)

    Morr, Dirk K.

    2017-01-01

    Kondo systems ranging from the single Kondo impurity to heavy fermion materials present us with a plethora of unconventional properties whose theoretical understanding is still one of the major open problems in condensed matter physics. Over the last few years, groundbreaking scanning tunneling spectroscopy (STS) experiments have provided unprecedented new insight into the electronic structure of Kondo systems. Interpreting the results of these experiments—the differential conductance and the quasi-particle interference spectrum—however, has been complicated by the fact that electrons tunneling from the STS tip into the system can tunnel either into the heavy magnetic moment or the light conduction band states. In this article, we briefly review the theoretical progress made in understanding how quantum interference between these two tunneling paths affects the experimental STS results. We show how this theoretical insight has allowed us to interpret the results of STS experiments on a series of heavy fermion materials providing detailed knowledge of their complex electronic structure. It is this knowledge that is a conditio sine qua non for developing a deeper understanding of the fascinating properties exhibited by heavy fermion materials, ranging from unconventional superconductivity to non-Fermi-liquid behavior in the vicinity of quantum critical points.

  18. Theory of spin dynamics of magnetic adatoms traced by time-resolved scanning tunneling spectroscopy

    CERN Document Server

    Schüler, Michael; Berakdar, Jamal

    2012-01-01

    The inelastic scanning tunneling microscopy (STM) has been shown recently (Loth et al. Science 329, 1628 (2010)) to be extendable as to access the nanosecond, spin-resolved dynamics of magnetic adatoms and molecules. Here we analyze theoretically this novel tool by considering the time-resolved spin dynamics of a single adsorbed Fe atom excited by a tunneling current pulse from a spin-polarized STM tip. The adatom spin-configuration can be controlled and probed by applying voltage pulses between the substrate and the spin-polarized STM tip. We demonstrate how, in a pump-probe manner, the relaxation dynamics of the sample spin is manifested in the spin-dependent tunneling current. Our model calculations are based on the scattering theory in a wave-packet formulation. The scheme is nonpertubative and hence, is valid for all voltages. The numerical results for the tunneling probability and the conductance are contrasted with the prediction of simple analytical models and compared with experiments.

  19. Scanning tunneling microscopy study of organic molecules and self-assembled monolayers

    Science.gov (United States)

    Park, Hayn

    In this dissertation I present my findings on alkanethiol self-assembled monolayers (SAM) on Au(111), as well as investigations of the self-assembly and electron transport properties of a custom-synthesized organic molecule (bis-phenyloxazole: BPO) chosen for its interesting physical and electronic structure. Utilizing scanning tunneling microscopy (STM) techniques, we observed unique molecular structures at the boundaries of single-species alkanethiol SAM domains, and propose packing arrangements for the observed structures. We also found evidence for island formation in alkanethiol SAMs; these islands were dynamic and exhibited ordered packing of the adsorbed molecules. For codeposited two-species (dodecanethiol, octanethiol) SAMs, we observed preferential insertion of the longer molecules at domain boundaries, edges, and defect sites, and found that they tended to segregate into separate domains. Scanning tunneling spectroscopy (STS) of the inserted dodecanethiol molecules revealed evidence of conduction resonances within the HOMO-LUMO gap. We explored the charge transport and self-assembly properties of the BPO molecules on a Au(111) surface. The molecules self-assembled into a novel columnar structure after annealing in vacuum. We compare tunneling spectroscopy results to ab initio computations of the molecular orbitals.

  20. Effects of pairing potential scattering on Fourier-transformed inelastic tunneling spectra of high-Tc cuprate superconductors with bosonic modes.

    Science.gov (United States)

    Zhu, Jian-Xin; McElroy, K; Lee, J; Devereaux, T P; Si, Qimiao; Davis, J C; Balatsky, A V

    2006-10-27

    Recent scanning tunneling microscopy (STM) experimentally observed strong gap inhomogeneity in Bi2Sr2CaCu2O(8+delta) (BSCCO). We argue that disorder in the pair potential underlies the gap inhomogeneity, and investigate its role in the Fourier-transformed inelastic tunneling spectra as revealed in the STM. We find that the random pair potential induces unique q-space patterns in the local density of states (LDOS) of a d-wave superconductor. We consider the effects of electron coupling to various bosonic modes and find the pattern of LDOS modulation due to coupling to the B(1g) phonon mode to be consistent with the one observed in the inelastic electron tunnneling STM experiment in BSCCO. These results suggest strong electron-lattice coupling as an essential part of the superconducting state in high-Tc materials.

  1. Spatially resolved quasiparticle tunneling spectra in the vortex state of optimally hole-doped YBa2Cu3Ox (Y-123)

    Science.gov (United States)

    Grinolds, M. S.; Beyer, A. D.; Teague, M. L.; Yeh, N.-C.

    2008-03-01

    We report cryogenic scanning tunneling spectroscopic (STS) studies of superconducting single crystalline Y-123 (Tc = 93 K) as a function of magnetic field. We study and model the influence of competing orders (COs), which coexist with superconductivity (SC), on the quasiparticle (QP) excitation spectra. The spatial dependence of the QP tunneling spectra is probed via STS to quantify the presence and spatial extent of SC and CO. Zero-field spatial maps of the QP spectra (100x100 nm^2) in Y-123 exhibit long-range spatial homogeneity of SC (δSC = 23±1 meV) associated with the spectral coherence peaks and the presence of CO (VCO = 33±2 meV) that gives rise to the spectral satellite features at δeff = [(δSC)^2+(VCO)^2]^1/2. Conductance maps of the Y-123 in finite fields demonstrate spatially varying spectra consistent with the periodicity a0 of the vortex lattice, with pseudogap (PG) like features at ˜VCO inside the vortex core and SC gap features remaining at ˜δSC outside the vortex core. Moreover, conductance histograms of the vortex state reveal that the ratio of the areas associated with δSC and VCO is comparable to (a0/ξab)^2, (ξab: in-plane SC coherence length). These results therefore suggest the important role of COs in the cuprate QP excitations. This work is supported by NSF Grant DMR-0405088.

  2. Self-assembled gold nanoparticles on functionalized gold(111) studied by scanning tunneling microscopy

    Institute of Scientific and Technical Information of China (English)

    PENG, Zhang-Quan; WANG, Er-Kang

    2000-01-01

    Nanogold colloidal solutions are prepared by the reduction of HAuClO4 with sodium citrate and sodium borohydride. 4- Aminothiophenol (ATP) self-assembled monolayers (SAMs) are formed on gold(111) surface, on which gold nanoparticles are immobilized and a sub-monolayer of the particles appears. This sub-monolayer of gold nanoparticles is characterized with scanning tunneling microscopy (STM), and a dual energy barrier tunneling model is proposed to explain the imgeability of the gold nanoparticles by STM. This model can also be used to construct multiple energy barrier structure on solid/ liquid interface and to evaluate the electron transport ability of some organic monolayers with the aid of electrochemical method.

  3. Scanning tunneling microscopy characterization of the geometric and electronic structure of hydrogen-terminated silicon surfaces

    Science.gov (United States)

    Kaiser, W. J.; Bell, L. D.; Hecht, M. H.; Grunthaner, F. J.

    1988-01-01

    Scanning tunneling microscopy (STM) methods are used to characterize hydrogen-terminated Si surfaces prepared by a novel method. The surface preparation method is used to expose the Si-SiO2 interface. STM images directly reveal the topographic structure of the Si-SiO2 interface. The dependence of interface topography on oxide preparation conditions observed by STM is compared to the results of conventional surface characterization methods. Also, the electronic structure of the hydrogen-terminated surface is studied by STM spectroscopy. The near-ideal electronic structure of this surface enables direct tunnel spectroscopy measurements of Schottky barrier phenomena. In addition, this method enables probing of semiconductor subsurface properties by STM.

  4. Scanning Tunneling Microscopy and Spectroscopy of Air Exposure Effects on Molecular Beam Epitaxy Grown WSe2 Monolayers and Bilayers.

    Science.gov (United States)

    Park, Jun Hong; Vishwanath, Suresh; Liu, Xinyu; Zhou, Huawei; Eichfeld, Sarah M; Fullerton-Shirey, Susan K; Robinson, Joshua A; Feenstra, Randall M; Furdyna, Jacek; Jena, Debdeep; Xing, Huili Grace; Kummel, Andrew C

    2016-04-26

    The effect of air exposure on 2H-WSe2/HOPG is determined via scanning tunneling microscopy (STM). WSe2 was grown by molecular beam epitaxy on highly oriented pyrolytic graphite (HOPG), and afterward, a Se adlayer was deposited in situ on WSe2/HOPG to prevent unintentional oxidation during transferring from the growth chamber to the STM chamber. After annealing at 773 K to remove the Se adlayer, STM images show that WSe2 layers nucleate at both step edges and terraces of the HOPG. Exposure to air for 1 week and 9 weeks caused air-induced adsorbates to be deposited on the WSe2 surface; however, the band gap of the terraces remained unaffected and nearly identical to those on decapped WSe2. The air-induced adsorbates can be removed by annealing at 523 K. In contrast to WSe2 terraces, air exposure caused the edges of the WSe2 to oxidize and form protrusions, resulting in a larger band gap in the scanning tunneling spectra compared to the terraces of air-exposed WSe2 monolayers. The preferential oxidation at the WSe2 edges compared to the terraces is likely the result of dangling edge bonds. In the absence of air exposure, the dangling edge bonds had a smaller band gap compared to the terraces and a shift of about 0.73 eV in the Fermi level toward the valence band. However, after air exposure, the band gap of the oxidized WSe2 edges became about 1.08 eV larger than that of the WSe2 terraces, resulting in the electronic passivation of the WSe2.

  5. BTA inhibition mechanism on clean Cu(110) surface by ultraviolet photoemission spectroscopy (UPS) and scanning tunneling microscope (STM)

    Energy Technology Data Exchange (ETDEWEB)

    Cho, K. [Yeungnam Univ., Kyungsan (Korea, Republic of); Park, Y.J.; Kuk, Y. [Seoul National Univ. (Korea, Republic of); Sakurai, T. [Tohoku Univ., Sendai (Japan). Inst. for Materials Research

    1998-12-31

    Adsorption and film growth of the Benzotriazole (BTA) on a copper (110) surface were investigated by the angle-resolved ultra-violet photoemission (UPS), and scanning tunneling microscope (STM). Coverage dependence of the BTA adsorbed structure on the Cu (110) surface exhibited well-ordered c(4 x 2)structure by STM image and sharp low-energy electron diffraction (LEED) pattern. Further deposition of BTA on monolayer film, polymerized BTA images were observed while a sharp LEED pattern changed to a c(4 x 2). In a good agreement with STM results, UPS spectra of BTA film by coverage dependence showed that BTA adsorbed flat up to 1 monolayer (ML), followed by stand-up polymerization above 1 monolayer. It is also suggested that 3-dimensional polymerization exhibited at least 2 BTA layers on Cu surface. The proposed orientation of the first adsorbed BTA layer on Cu (110) surface is the flat adsorption position based on the atomic scale resolution of STM and thickness dependence of UPS spectra. This adsorption structure and polymerized multilayer film of the BTA blocks the surface completely. Adsorption sites on the copper surface for attacking media are unavailable for oxidation reaction.

  6. Scanning tunneling microscopy and spectroscopy measurements of superconductor/ferromagnet hybrids

    Science.gov (United States)

    Moore, Steven A.

    The focus of this thesis work is the study of the nanoscale electronic properties of magnetically coupled superconductor/ferromagnet hybrid structures using low-temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) under ultra-high vacuum conditions. There are a number of novel effects that can occur due to the non-homogenous magnetic field from the ferromagnet, which directly influence the global and local superconducting properties. These effects include the generation of vortices/anti-vortices by the non-uniform magnetic stray field, local modulations in the critical temperature, filamentary superconductivity close to the transition temperature, and superconducting channels that can be controlled by external magnetic fields. Prior to this dissertation the subject of superconductor/ferromagnet hybrid structures has been mainly studied using global measurements (such as transport and magnetization) or scanning probe techniques that are sensitive to the magnetic field. Scanning tunneling microscopy probes the local electronic density of states with atomic resolution, and therefore is the only technique that can study the emergence of superconductivity on the length scale of the coherence length. The novel results presented in this dissertation show that magnetically coupled superconductor/ferromagnet heterostructures offer the possibility to control and tune the strength and location of superconductivity and superconducting vortices, which has potential for promising technological breakthroughs in computing and power applications.

  7. Controlled manipulation of gadolinium-coordinated supramolecules by low-temperature scanning tunneling microscopy.

    Science.gov (United States)

    Urgel, José I; Ecija, David; Auwärter, Willi; Barth, Johannes V

    2014-03-12

    Coordination bonding between para-quarterphenyl-dicarbonitrile linkers and gadolinium on Ag(111) has been exploited to construct pentameric mononuclear supramolecules, consisting of a rare-earth center surrounded by five molecular linkers. By employing a scanning tunneling microscope tip, a manipulation protocol was developed to position individual pentamers on the surface. In addition, the tip was used to extract and replace individual linkers yielding tetrameric, pentameric, nonameric, and dodecameric metallosupramolecular arrangements. These results open new avenues toward advanced nanofabrication methods and rare-earth nanochemistry by combining the versatility of metal-ligand interactions and atomistic manipulation capabilities.

  8. Investigation on the Morphology of Adsorbed Benzotriazole Film on Copper Surface by Scanning Tunneling Microcopy

    Institute of Scientific and Technical Information of China (English)

    XUChunchun; Win-yanNG; 等

    2002-01-01

    It is observed by scanning tunneling microscopy (STM) that the adsorbed Benzotriazole (BTA) on copper is long in shape and has an irregular rectangle.The growth of BTA on copper is in the from of polymeric chain and mainly in one dimension rather than two dimensions.The copper surface covered by BTA becomes flatter,smoother and the roughness was smaller than that of bare copper,so the corrosion is largely decreased.However,many grooves can be seen between BTA polymeric chains in which corrosion may exist to a degrees.

  9. Identification of nitrogen dopants in single-walled carbon nanotubes by scanning tunneling microscopy.

    Science.gov (United States)

    Tison, Yann; Lin, Hong; Lagoute, Jérôme; Repain, Vincent; Chacon, Cyril; Girard, Yann; Rousset, Sylvie; Henrard, Luc; Zheng, Bing; Susi, Toma; Kauppinen, Esko I; Ducastelle, François; Loiseau, Annick

    2013-08-27

    Using scanning tunnelling microscopy and spectroscopy, we investigated the atomic and electronic structure of nitrogen-doped single walled carbon nanotubes synthesized by chemical vapor deposition. The insertion of nitrogen in the carbon lattice induces several types of point defects involving different atomic configurations. Spectroscopic measurements on semiconducting nanotubes reveal that these local structures can induce either extended shallow levels or more localized deep levels. In a metallic tube, a single doping site associated with a donor state was observed in the gap at an energy close to that of the first van Hove singularity. Density functional theory calculations reveal that this feature corresponds to a substitutional nitrogen atom in the carbon network.

  10. Adsorbate-induced quantum Hall system probed by scanning tunneling spectroscopy combined with transport measurements

    Energy Technology Data Exchange (ETDEWEB)

    Masutomi, Ryuichi, E-mail: masutomi@phys.s.u-tokyo.ac.jp; Okamoto, Tohru [Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)

    2015-06-22

    An adsorbate-induced quantum Hall system at the cleaved InSb surfaces is investigated in magnetic fields up to 14 T using low-temperature scanning tunneling microscopy and spectroscopy combined with transport measurements. We show that an enhanced Zeeman splitting in the Shubnikov-de Haas oscillations is explained by an exchange enhancement of spin splitting and potential disorder, both of which are obtained from the spatially averaged density of states (DOS). Moreover, the Altshuler–Aronov correlation gap is observed in the spatially averaged DOS at 0 T.

  11. In situ scanning tunnelling microscopy of redox molecules. Coherent electron transfer at large bias voltages

    DEFF Research Database (Denmark)

    Zhang, Jingdong; Kuznetsov, A.M.; Ulstrup, Jens

    2003-01-01

    Theories of in situ scanning tunnelling microscopy (STM) of molecules with redox levels near the substrate and tip Fermi levels point to 'spectroscopic' current-overpotential features. Prominent features require a narrow 'probing tip', i.e. a small bias voltage, eV(bias), compared...... and tip Fermi levels. STM here involves coherent two-step interfacial electron transfer between the redox level and the enclosing substrate and tip. We have also extended previous experimental in situ STM studies of the blue copper protein Pseudomonas aeruginosa azurin, adsorbed on Au(111), to cover...

  12. Photochemical Reactions in Self-Assembled Organic Monolayers Characterized by using Scanning Tunneling Microscopy.

    Science.gov (United States)

    Guo, Chao; Li, Min; Kang, ShiZhao

    2016-03-16

    Research on the supramolecular self-assembly behavior at interfaces is of great importance to improving the performance of nanodevices that are based on optical functional materials. In this Minireview, several photoinduced isomerization and polymerization reactions in self-assembled organic monolayers on surfaces are discussed. Typical organic molecules contain azobenzene, alkynyl, or olefins groups. The feature surface base is a highly oriented pyrolytic graphite (HOPG) surface or a gold surface. Scanning tunneling microscopy (STM) is used as a strong tool to characterize new species' structures before and after illumination.

  13. Structure and Reactions of Carbon and Hydrogen on Ru(0001): A Scanning Tunneling Microscopy Study

    Energy Technology Data Exchange (ETDEWEB)

    Shimizu, Tomoko K.; Mugarza, Aitor; Cerda, Jorge; Salmeron, Miquel

    2008-09-09

    The interaction between carbon and hydrogen atoms on a Ru(0001) surface was studied using scanning tunneling microscopy (STM), Density Functional Theory (DFT) and STM image calculations. Formation of CH species by reaction between adsorbed H and C was observed to occur readily at 100 K. When the coverage of H increased new complexes of the form CH+nH (n = 1, 2 and 3) were observed. These complexes, never observed before, might be precursors for further hydrogenation reactions. DFT analysis reveals that a considerable energy barrier exists for the CH+H {yields} CH{sub 2} reaction.

  14. Halogen bonded two-dimensional supramolecul arassemblies studied by high resolution scanning tunneling microscopy

    Institute of Scientific and Technical Information of China (English)

    YANG XunYu; WANG Fang; CHEN QiuXia; WANG LiYan; WANG ZhiQiang

    2007-01-01

    We described the formation of self-organized two-dimensional (2D) assemblies of N-(2,3,5,6-tetrafluoro- 4-iodophenyl)hexadecylamine and 1-dodecyl-imidazole at the liquid/HOPG interface. The two-dimen- sional assemblies showed a fishbone-like pattern structure as revealed by high-resolution scanning tunneling microscopy. Although different interactions can drive the formation of 2D assemblies,as far as we know,this is the first report on halogen bond-driven 2D assemblies.

  15. Atomic-scale structure of dislocations revealed by scanning tunneling microscopy and molecular dynamics

    DEFF Research Database (Denmark)

    Christiansen, Jesper; Morgenstern, K.; Schiøtz, Jakob;

    2002-01-01

    , the simulations can be used to determine dislocation structure and orientation in the near-surface region. In a similar way, the subsurface structure of other extended defects can be studied. The simulations show dislocations to reorient the partials in the surface region leading to an increased splitting width......The intersection between dislocations and a Ag(111) surface has been studied using an interplay of scanning tunneling microscopy (STM) and molecular dynamics. Whereas the STM provides atomically resolved information about the surface structure and Burgers vectors of the dislocations...

  16. Scanning Tunnelling Microscopy Observation on 10,12-Tricosadiynoic Acid Monolayers Deposited by Schaefer's Method

    Institute of Scientific and Technical Information of China (English)

    张耿民

    2001-01-01

    The Langmuir-Blodgett monolayers of 10, 12-tricosadiynoic acid molecules were deposited onto the basal plane of highly oriented pyrolytic graphite (HOPG) by Schaefer's method and then observed with the scanning tunnelling microscope (STM). With a view to achieving a parallel molecular arrangement on the graphite surface, the deposition was deliberately conducted at a relatively low surface pressure. As exhibited by the STM images, by this approach the 10,12-tricosadiynoic acid molecules could constitute an ordered structure with their molecular chains lying parallel to the substrate. The model of molecular dimer is put forward for the interpretation of the observed phenomena.

  17. Probing large area surface plasmon interference in thin metal films using photon scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Passian, A.; Wig, A.; Lereu, A.L.; Evans, P.G.; Meriaudeau, F.; Thundat, T.; Ferrell, T.L

    2004-08-15

    The interference of surface plasmons can provide important information regarding the surface features of the hosting thin metal film. We present an investigation of the interference of optically excited surface plasmons in the Kretschmann configuration in the visible spectrum. Large area surface plasmon interference regions are generated at several wavelengths and imaged with the photon scanning tunneling microscope. Furthermore, we discuss the non-retarded dispersion relations for the surface plasmons in the probe-metal system modeled as confocal hyperboloids of revolution in the spheroidal coordinate systems.

  18. Optical characterization of individual semiconductor nanostructures using a scanning tunneling microscope.

    Science.gov (United States)

    Tsuruoka, Tohru; Ushioda, Sukekatsu

    2004-01-01

    By injecting low-energy minority carriers from the tip of a scanning tunneling microscope (STM) and analyzing the light emitted from the tip-sample gap of the STM, it is possible to study the optical and electronic properties of individual semiconductor nanostructures with an extremely high spatial resolution close to the atomic scale. This technique has been applied to investigate the transport properties of hot electrons injected into AlGaAs/GaAs quantum well structures and the optical properties of single self-assembled InAs/AlGaAs quantum dots. The physical principles, usefulness and future expectations of this novel technique are discussed.

  19. Scanning tunneling microscopy of monoatomic gold chains on vicinal Si(335) surface: experimental and theoretical study

    Energy Technology Data Exchange (ETDEWEB)

    Krawiec, M.; Kwapinski, T.; Jalochowski, M. [Institute of Physics and Nanotechnology Center, M. Curie-Sklodowska University, pl. M. Curie-Sklodowskiej 1, 20-031 Lublin (Poland)

    2005-02-01

    We study electronic and topographic properties of the Si(335) surface, containing Au wires parallel to the steps. We use scanning tunneling microscopy (STM) supplemented by reflection of high energy electron diffraction (RHEED) technique. The STM data show the space and voltage dependent oscillations of the distance between STM tip and the surface which can be explained within one band tight binding Hubbard model. We calculate the STM current using nonequilibrium Keldysh Green function formalism. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. In situ electrochemical scanning tunneling microscopy investigation of renewing graphite surface accompanied by electrochemical reaction

    Science.gov (United States)

    Zhang, Jingdong; Zhu, Guoyi; Wang, Erkang

    1996-08-01

    In situ electrochemical scanning tunneling microscopy (ECSTM) has been employed to follow the renewal process of a graphite electrode accompanied by flavin adenine dinucleotide (FAD) electrochemical reaction which involves adsorption of the reduced form (FADH 2) and desorption of the oxidized form (FAD). The renewal process initiates from steps or kinks on the electrode surface, which provide high active sites for adsorption. This renewal depends on the working electrode potential, especially in the range near the FAD redox potential. Our experiment suggests that delamination of the graphite surface is caused by interaction between the substrate and adsorbed molecules. A simple model is proposed to explain this phenomenon.

  1. A functional renormalization group application to the scanning tunneling microscopy experiment

    Directory of Open Access Journals (Sweden)

    José Juan Ramos Cárdenas

    2015-12-01

    Full Text Available We present a study of a system composed of a scanning tunneling microscope (STM tip coupled to an absorbed impurity on a host surface using the functional renormalization group (FRG. We include the effect of the STM tip as a correction to the self-energy in addition to the usual contribution of the host surface in the wide band limit. We calculate the differential conductance curves at two different lateral distances from the quantum impurity and find good qualitative agreement with STM experiments where the differential conductance curves evolve from an antiresonance to a Lorentzian shape.

  2. Bistability in Scanning Tunneling Spectroscopy of Ga-terminated Si(111)

    Science.gov (United States)

    Chen, Dongmin; Altfeder, Igor

    2000-03-01

    The bistable transport characteristics have been the basis of modern power and high speed switching devices. All these devices share a common and essential double barrier structure. Here we report on a surprising observation of the bistable tunneling characteristics in an apparent single barrier tunnel junction consisted of a Ga-terminated Si(111) surface and a W-tip of a scanning tunneling microscope (STM) operating at 77K. Under a negative tip bias condition, a switching from an initially high-impedance, low-current OFF state to a low-impedance, high-current ON state occurs at a bias higher than that for the subsequent reversal transition, giving rise to a large hysteresis loops. The turn-on bias varies from 3.1V to 4.0V,showing a large inverse dependence on the tip-sample distances, indicating strong field effect. On contrary, the turn-off bias is essentially pined at 2.7V, suggesting the existence of a conductance threshold. This opens the possioblity to engineer a new type of swithching device using only single layer atomic dopping in place of a more complex double barrier structure.

  3. Variable-temperature independently driven four-tip scanning tunneling microscope.

    Science.gov (United States)

    Hobara, Rei; Nagamura, Naoka; Hasegawa, Shuji; Matsuda, Iwao; Yamamoto, Yuko; Miyatake, Yutaka; Nagamura, Toshihiko

    2007-05-01

    The authors have developed an ultrahigh vacuum (UHV) variable-temperature four-tip scanning tunneling microscope (STM), operating from room temperature down to 7 K, combined with a scanning electron microscope (SEM). Four STM tips are mechanically and electrically independent and capable of positioning in arbitrary configurations in nanometer precision. An integrated controller system for both of the multitip STM and SEM with a single computer has also been developed, which enables the four tips to operate either for STM imaging independently and for four-point probe (4PP) conductivity measurements cooperatively. Atomic-resolution STM images of graphite were obtained simultaneously by the four tips. Conductivity measurements by 4PP method were also performed at various temperatures with the four tips in square arrangement with direct contact to the sample surface.

  4. Renormalization of the graphene dispersion velocity determined from scanning tunneling spectroscopy.

    Science.gov (United States)

    Chae, Jungseok; Jung, Suyong; Young, Andrea F; Dean, Cory R; Wang, Lei; Gao, Yuanda; Watanabe, Kenji; Taniguchi, Takashi; Hone, James; Shepard, Kenneth L; Kim, Phillip; Zhitenev, Nikolai B; Stroscio, Joseph A

    2012-09-14

    In graphene, as in most metals, electron-electron interactions renormalize the properties of electrons but leave them behaving like noninteracting quasiparticles. Many measurements probe the renormalized properties of electrons right at the Fermi energy. Uniquely for graphene, the accessibility of the electrons at the surface offers the opportunity to use scanned probe techniques to examine the effect of interactions at energies away from the Fermi energy, over a broad range of densities, and on a local scale. Using scanning tunneling spectroscopy, we show that electron interactions leave the graphene energy dispersion linear as a function of excitation energy for energies within ±200  meV of the Fermi energy. However, the measured dispersion velocity depends on density and increases strongly as the density approaches zero near the charge neutrality point, revealing a squeezing of the Dirac cone due to interactions.

  5. Method and apparatus for differential spectroscopic atomic-imaging using scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kazmerski, Lawrence L. (Lakewood, CO)

    1990-01-01

    A Method and apparatus for differential spectroscopic atomic-imaging is disclosed for spatial resolution and imaging for display not only individual atoms on a sample surface, but also bonding and the specific atomic species in such bond. The apparatus includes a scanning tunneling microscope (STM) that is modified to include photon biasing, preferably a tuneable laser, modulating electronic surface biasing for the sample, and temperature biasing, preferably a vibration-free refrigerated sample mounting stage. Computer control and data processing and visual display components are also included. The method includes modulating the electronic bias voltage with and without selected photon wavelengths and frequency biasing under a stabilizing (usually cold) bias temperature to detect bonding and specific atomic species in the bonds as the STM rasters the sample. This data is processed along with atomic spatial topography data obtained from the STM raster scan to create a real-time visual image of the atoms on the sample surface.

  6. Submolecular Electronic Mapping of Single Cysteine Molecules by in Situ Scanning Tunneling Imaging

    DEFF Research Database (Denmark)

    Zhang, Jingdong; Chi, Qijin; Nazmutdinov, R. R.;

    2009-01-01

    We have used L-Cysteine (Cys) as a model system to study the surface electronic structures of single molecules at the submolecular level in aqueous buffer solution by a combination of electrochemical scanning tunneling microscopy (in situ STM), electrochemistry including voltammetry and chronocou......We have used L-Cysteine (Cys) as a model system to study the surface electronic structures of single molecules at the submolecular level in aqueous buffer solution by a combination of electrochemical scanning tunneling microscopy (in situ STM), electrochemistry including voltammetry...... and tip. The computational images recast as constant-current-height profiles show that the most favorable molecular orientation is the adsorption of cysteine as a radical in zwitterionic form located on the bridge between the Au(I 10) atomic rows and with the amine and carboxyl group toward the solution...... bulk. The correlation between physical location and electronic contrast of the adsorbed molecules was also revealed by the computational data. The present study shows that cysteine packing in the adlayer on Au(110) from the liquid environment is in contrast to that from the ultrahigh-vacuum environment...

  7. Tip-Dependent Scanning Tunneling Microscopy Imaging of Ultrathin FeO Films on Pt(111)

    DEFF Research Database (Denmark)

    Merte, Lindsay Richard; Grabow, Lars C.; Peng, Guowen;

    2011-01-01

    High-resolution scanning tunneling microscope (STM) images of moiré-structured FeO films on Pt(111) were obtained in a number of different tip-dependent imaging modes. For the first time, the STM images are distinguished and interpreted unambiguously with the help of distinct oxygen-vacancy dislo......High-resolution scanning tunneling microscope (STM) images of moiré-structured FeO films on Pt(111) were obtained in a number of different tip-dependent imaging modes. For the first time, the STM images are distinguished and interpreted unambiguously with the help of distinct oxygen......-vacancy dislocation loops in the FeO moiré structure. The experimental STM results are compared with the results of electronic structure calculations within the DFT+U scheme for a realistic (sqrt(91)xsqrt(91)R5.2 moiré unit cell supported on Pt(111) as well as with the results from previous studies. We find that one...... on the specific tip apex state and likely result from specific tip-sample chemical interactions. From the present STM results we show that several of the previously published conclusions for the FeO system have to be revisited....

  8. Spatially resolved scanning tunneling spectroscopy of single-layer steps on Si(100) surfaces

    Science.gov (United States)

    Wang, Xiqiao; Namboodiri, Pradeep; Li, Kai; Deng, Xiao; Silver, Richard

    2016-09-01

    Single-layer steps at Si(100) surfaces/interfaces present significant challenges to the quantitative characterization of buried dopant devices as well as the accurate imaging and relocation of fabricated quantum structures. We demonstrate the detailed spatially resolved scanning tunneling spectroscopy study across monolayer step edges on Si(100) surfaces and quantitative determination of the local density of state distributions and behavior of the band gap at step edges. The influence on the local electrostatic environment due to step edge states has been quantified while accounting for the effects of scanning tunneling measurement conditions. The dangling bond states on Si(100) surfaces are utilized as a fingerprint to quantify the local band bending landscape and to make corrections to the experimentally observed surface state energy levels and band gap values at the step edge regions. We observe a significant band gap narrowing behavior along a rebonded single-layer type B step edge on a degenerately boron-doped p -type Si substrate.

  9. Fabrication of Gate-tunable Graphene Devices for Scanning Tunneling Microscopy Studies with Coulomb Impurities.

    Science.gov (United States)

    Jung, Han Sae; Tsai, Hsin-Zon; Wong, Dillon; Germany, Chad; Kahn, Salman; Kim, Youngkyou; Aikawa, Andrew S; Desai, Dhruv K; Rodgers, Griffin F; Bradley, Aaron J; Velasco, Jairo; Watanabe, Kenji; Taniguchi, Takashi; Wang, Feng; Zettl, Alex; Crommie, Michael F

    2015-07-24

    Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees of freedom to control electronic devices. In particular, the behavior of graphene's charge carriers in response to potentials from charged Coulomb impurities is predicted to differ significantly from that of most materials. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) can provide detailed information on both the spatial and energy dependence of graphene's electronic structure in the presence of a charged impurity. The design of a hybrid impurity-graphene device, fabricated using controlled deposition of impurities onto a back-gated graphene surface, has enabled several novel methods for controllably tuning graphene's electronic properties. Electrostatic gating enables control of the charge carrier density in graphene and the ability to reversibly tune the charge and/or molecular states of an impurity. This paper outlines the process of fabricating a gate-tunable graphene device decorated with individual Coulomb impurities for combined STM/STS studies. These studies provide valuable insights into the underlying physics, as well as signposts for designing hybrid graphene devices.

  10. Control of donor charge states with the tip of a scanning tunnelling microscope

    Energy Technology Data Exchange (ETDEWEB)

    Teichmann, K.; Wenderoth, M.; Loth, S.; Ulbrich, R.G. [IV. Physikalisches Institut, Georg-August-Universitaet Goettingen (Germany); Garlef, J.K.; Wijnheijmer, A.P.; Koenraad, P.M. [PSN, Eindhoven University of Technology (Netherlands)

    2009-07-01

    The functionality of nanoscale semiconductor devices crucially depends on details of the electrostatic potential landscape on the atomic scale and its microscopic response to external electric fields. We report here an investigation of charge state switching of buried single Si donors in 6.10{sup 18} cm{sup -3} n-doped GaAs with scanning tunnelling microscopy (STM) under UHV conditions at 5 K. The effect of tip induced band bending (TIBB) through the freshly cleaved (110)-surface was used to change the charge state of individual donors from neutral to positively charged and reverse. Scanning tunnelling spectroscopy (STS) revealed a ring like feature around each donor center. The ring radius depends on tip bias voltage. The charge state of each donor in the random arrangement of dopants was in most cases unambiguously fixed by the extension of the tip-induced space charge cloud, which was located under the tip and controlled by the applied voltage. For certain geometric configurations the system showed bi- (or multi-) stable behaviour, this lead to dynamic flickering of the ionization sequence.

  11. Structural changes in a Schiff base molecular assembly initiated by scanning tunneling microscopy tip

    Science.gov (United States)

    Tomak, A.; Bacaksiz, C.; Mendirek, G.; Sahin, H.; Hur, D.; Görgün, K.; Senger, R. T.; Birer, Ö.; Peeters, F. M.; Zareie, H. M.

    2016-08-01

    We report the controlled self-organization and switching of newly designed Schiff base (E)-4-((4-(phenylethynyl) benzylidene) amino) benzenethiol (EPBB) molecules on a Au (111) surface at room temperature. Scanning tunneling microscopy and spectroscopy (STM/STS) were used to image and analyze the conformational changes of the EPBB molecules. The conformational change of the molecules was induced by using the STM tip while increasing the tunneling current. The switching of a domain or island of molecules was shown to be induced by the STM tip during scanning. Unambiguous fingerprints of the switching mechanism were observed via STM/STS measurements. Surface-enhanced Raman scattering was employed, to control and identify quantitatively the switching mechanism of molecules in a monolayer. Density functional theory calculations were also performed in order to understand the microscopic details of the switching mechanism. These calculations revealed that the molecular switching behavior stemmed from the strong interaction of the EPBB molecules with the STM tip. Our approach to controlling intermolecular mechanics provides a path towards the bottom-up assembly of more sophisticated molecular machines.

  12. Understanding the inelastic electron-tunneling spectra of alkanedithiols on gold.

    Science.gov (United States)

    Solomon, Gemma C; Gagliardi, Alessio; Pecchia, Alessandro; Frauenheim, Thomas; Di Carlo, Aldo; Reimers, Jeffrey R; Hush, Noel S

    2006-03-01

    We present results for a simulated inelastic electron-tunneling spectra (IETS) from calculations using the "gDFTB" code. The geometric and electronic structure is obtained from calculations using a local-basis density-functional scheme, and a nonequilibrium Green's function formalism is employed to deal with the transport aspects of the problem. The calculated spectrum of octanedithiol on gold(111) shows good agreement with experimental results and suggests further details in the assignment of such spectra. We show that some low-energy peaks, unassigned in the experimental spectrum, occur in a region where a number of molecular modes are predicted to be active, suggesting that these modes are the cause of the peaks rather than a matrix signal, as previously postulated. The simulations also reveal the qualitative nature of the processes dominating IETS. It is highly sensitive only to the vibrational motions that occur in the regions of the molecule where there is electron density in the low-voltage conduction channel. This result is illustrated with an examination of the predicted variation of IETS with binding site and alkane chain length.

  13. A first principles scanning tunneling potentiometry study of an opaque graphene grain boundary in the ballistic transport regime.

    Science.gov (United States)

    Bevan, Kirk H

    2014-10-17

    We report on a theoretical interpretation of scanning tunneling potentiometry (STP), formulated within the Keldysh non-equilibrium Green's function description of quantum transport. By treating the probe tip as an electron point source/sink, it is shown that this approach provides an intuitive bridge between existing theoretical interpretations of scanning tunneling microscopy and STP. We illustrate this through ballistic transport simulations of the potential drop across an opaque graphene grain boundary, where atomistic features are predicted that might be imaged through high resolution STP measurements. The relationship between the electrochemical potential profile measured and the electrostatic potential drop across such a nanoscale defect is also explored in this model system.

  14. Atomic-scale electrochemistry on the surface of a manganite by scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Vasudevan, Rama K., E-mail: rvv@ornl.gov; Tselev, Alexander; Baddorf, Arthur P. [Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); ORNL Institute for Functional Imaging of Materials, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Gianfrancesco, Anthony G. [UT/ORNL Bredesen Center, University of Tennessee, Knoxville, Tennessee 37996 (United States); Kalinin, Sergei V. [Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); ORNL Institute for Functional Imaging of Materials, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); UT/ORNL Bredesen Center, University of Tennessee, Knoxville, Tennessee 37996 (United States)

    2015-04-06

    The doped manganese oxides (manganites) have been widely studied for their colossal magnetoresistive effects, for potential applications in oxide spintronics, electroforming in resistive switching devices, and are materials of choice as cathodes in modern solid oxide fuel cells. However, little experimental knowledge of the dynamics of the surfaces of perovskite manganites at the atomic scale exists. Here, through in-situ scanning tunneling microscopy (STM), we demonstrate atomic resolution on samples of La{sub 0.625}Ca{sub 0.375}MnO{sub 3} grown on (001) SrTiO{sub 3} by pulsed laser deposition. Furthermore, by applying triangular DC waveforms of increasing amplitude to the STM tip, and measuring the tunneling current, we demonstrate the ability to both perform and monitor surface electrochemical processes at the atomic level, including formation of oxygen vacancies and removal and deposition of individual atomic units or clusters. Our work paves the way for better understanding of surface oxygen reactions in these systems.

  15. Temperature dependence of the superconducting proximity effect quantified by scanning tunneling spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Stępniak, A.; Caminale, M.; Leon Vanegas, A. A.; Oka, H.; Sander, D., E-mail: sander@mpi-halle.mpg.de [Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle (Saale) (Germany); Kirschner, J. [Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle (Saale) (Germany); Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, 06120 Halle (Saale) (Germany)

    2015-01-15

    Here, we present the first systematic study on the temperature dependence of the extension of the superconducting proximity effect in a 1–2 atomic layer thin metallic film, surrounding a superconducting Pb island. Scanning tunneling microscopy/spectroscopy (STM/STS) measurements reveal the spatial variation of the local density of state on the film from 0.38 up to 1.8 K. In this temperature range the superconductivity of the island is almost unaffected and shows a constant gap of a 1.20 ± 0.03 meV. Using a superconducting Nb-tip a constant value of the proximity length of 17 ± 3 nm at 0.38 and 1.8 K is found. In contrast, experiments with a normal conductive W-tip indicate an apparent decrease of the proximity length with increasing temperature. This result is ascribed to the thermal broadening of the occupation of states of the tip, and it does not reflect an intrinsic temperature dependence of the proximity length. Our tunneling spectroscopy experiments shed fresh light on the fundamental issue of the temperature dependence of the proximity effect for atomic monolayers, where the intrinsic temperature dependence of the proximity effect is comparably weak.

  16. Temperature dependence of the superconducting proximity effect quantified by scanning tunneling spectroscopy

    Directory of Open Access Journals (Sweden)

    A. Stępniak

    2015-01-01

    Full Text Available Here, we present the first systematic study on the temperature dependence of the extension of the superconducting proximity effect in a 1–2 atomic layer thin metallic film, surrounding a superconducting Pb island. Scanning tunneling microscopy/spectroscopy (STM/STS measurements reveal the spatial variation of the local density of state on the film from 0.38 up to 1.8 K. In this temperature range the superconductivity of the island is almost unaffected and shows a constant gap of a 1.20 ± 0.03 meV. Using a superconducting Nb-tip a constant value of the proximity length of 17 ± 3 nm at 0.38 and 1.8 K is found. In contrast, experiments with a normal conductive W-tip indicate an apparent decrease of the proximity length with increasing temperature. This result is ascribed to the thermal broadening of the occupation of states of the tip, and it does not reflect an intrinsic temperature dependence of the proximity length. Our tunneling spectroscopy experiments shed fresh light on the fundamental issue of the temperature dependence of the proximity effect for atomic monolayers, where the intrinsic temperature dependence of the proximity effect is comparably weak.

  17. In situ scanning tunneling microscope tip treatment device for spin polarization imaging

    Science.gov (United States)

    Li, An-Ping [Oak Ridge, TN; Jianxing, Ma [Oak Ridge, TN; Shen, Jian [Knoxville, TN

    2008-04-22

    A tip treatment device for use in an ultrahigh vacuum in situ scanning tunneling microscope (STM). The device provides spin polarization functionality to new or existing variable temperature STM systems. The tip treatment device readily converts a conventional STM to a spin-polarized tip, and thereby converts a standard STM system into a spin-polarized STM system. The tip treatment device also has functions of tip cleaning and tip flashing a STM tip to high temperature (>2000.degree. C.) in an extremely localized fashion. Tip coating functions can also be carried out, providing the tip sharp end with monolayers of coating materials including magnetic films. The device is also fully compatible with ultrahigh vacuum sample transfer setups.

  18. Magnetic fingerprint of individual Fe4 molecular magnets under compression by a scanning tunnelling microscope

    Science.gov (United States)

    Burgess, Jacob A.J.; Malavolti, Luigi; Lanzilotto, Valeria; Mannini, Matteo; Yan, Shichao; Ninova, Silviya; Totti, Federico; Rolf-Pissarczyk, Steffen; Cornia, Andrea; Sessoli, Roberta; Loth, Sebastian

    2015-01-01

    Single-molecule magnets (SMMs) present a promising avenue to develop spintronic technologies. Addressing individual molecules with electrical leads in SMM-based spintronic devices remains a ubiquitous challenge: interactions with metallic electrodes can drastically modify the SMM's properties by charge transfer or through changes in the molecular structure. Here, we probe electrical transport through individual Fe4 SMMs using a scanning tunnelling microscope at 0.5 K. Correlation of topographic and spectroscopic information permits identification of the spin excitation fingerprint of intact Fe4 molecules. Building from this, we find that the exchange coupling strength within the molecule's magnetic core is significantly enhanced. First-principles calculations support the conclusion that this is the result of confinement of the molecule in the two-contact junction formed by the microscope tip and the sample surface. PMID:26359203

  19. Restoration of Scanning Tunneling Microscope Images by means of Two-Dimensional Maximum Entropy Method

    Science.gov (United States)

    Matsumoto, Hisanori; Tokiwano, Kazuo; Hosoi, Hirotaka; Sueoka, Kazuhisa; Mukasa, Koichi

    2002-05-01

    We present a new technique for the restoration of scanning tunneling microscopy (STM) images, which is a two-dimensional extension of a recently developed statistical approach based on the one-dimensional least-squares method (LSM). An STM image is regarded as a realization of a stochastic process and assumed to be a composition of an underlying image and noise. We express the underlying image in terms of a two-dimensional generalized trigonometric polynomial suitable for representing the atomic protrusions in STM images. The optimization of the polynomial is performed by the two-dimensional LSM combined with the power spectral density function estimated by means of the maximum entropy method (MEM) iterative algorithm for two-dimensional signals. The restored images are obtained as the optimum least-squares fitting polynomial which is a continuous surface. We apply this technique to modeled and actual STM data. Results show that the present method yields a reasonable restoration of STM images.

  20. Growth of 4-aminothiophenol on iodine modified Au(100) studied by scanning tunneling microscopy

    Science.gov (United States)

    Huerta, Tizoc F.; Valenzuela, José

    2017-01-01

    The adsorption and growth mechanism of 4-aminothiophenol (4-ATP) molecules on iodine modified Au(100) has been investigated by electrochemical scanning tunneling microscopy (ECSTM) and cyclic voltammetry in perchloric acid solution. The first stage of ATP adsorption is characterized by one dimensional molecular growth along the [001] of the Au(100) substrate, together with long and thin trenches between molecular lines that are present even after several layers of growth. At more positive potentials complete surface coverage and 3D growth is observed on the surface. Potential-induced molecular desorption forms randomly distributed pits or vacancies on the surface. This markedly different desorption mechanism from the adsorption process is explained in terms of the different molecular bonds during the oxidation of the ATP molecule. The role of the iodine layer on the growth of 4-ATP on Au(100) is discussed.

  1. How the vortex lattice of a superconductor becomes disordered: a study by scanning tunneling spectroscopy.

    Science.gov (United States)

    Zehetmayer, M

    2015-01-01

    Order-disorder transitions take place in many physical systems, but observing them in detail in real materials is difficult. In two- or quasi-two-dimensional systems, the transition has been studied by computer simulations and experimentally in electron sheets, dusty plasmas, colloidal and other systems. Here I show the different stages of defect formation in the vortex lattice of a superconductor while it undergoes an order-disorder transition by presenting real-space images of the lattice from scanning tunneling spectroscopy. When the system evolves from the ordered to the disordered state, the predominant kind of defect changes from dislocation pairs to single dislocations, and finally to defect clusters forming grain boundaries. Correlation functions indicate a hexatic-like state preceding the disordered state. The transition in the microscopic vortex distribution is mirrored by the well-known spectacular second peak effect observed in the macroscopic current density of the superconductor.

  2. High-Resolution Scanning Tunneling Microscopy Studies of Molecular Nanostructures on Surfaces

    DEFF Research Database (Denmark)

    Song, Xin

    of nanostructures requires deeper insight into the adsorption sites, adsorption configurations, diffusion behaviour and driving forces for self-assembly of different molecules or atoms on different substrates. To study these fundamental issues, scanning tunneling microscopy (STM) has proven to be an ideal choice....... First, to study the role of hydrogen bonding in self-assembly, we investigate the monomolecular self-assembled system of pyrene-4,5,9,10-tetrone and phenanthrene- 9,10-dione molecules on Au(111) and HOPG surface respectively and the binary molecular self-assembled system of stearic acid and guanine...... molecules co-adsorbed on HOPG surface. Hydrogen bonding plays a key role in these self-assembled nanostructures and the substrate could also give an effect in the self-assembly. Second, to study the self-assembly across the terrace steps as a defect on surface, the chiral self-assembled supramolecular...

  3. Local transport measurements at mesoscopic length scales using scanning tunneling potentiometry.

    Science.gov (United States)

    Wang, Weigang; Munakata, Ko; Rozler, Michael; Beasley, Malcolm R

    2013-06-07

    Under mesoscopic conditions, the transport potential on a thin film carrying a current is theoretically expected to bear spatial variation due to quantum interference. Scanning tunneling potentiometry is the ideal tool to investigate such variation, by virtue of its high spatial resolution. We report in this Letter the first detailed measurement of transport potential under mesoscopic conditions. Epitaxial graphene at a temperature of 17 K was chosen as the initial system for study because the characteristic transport length scales in this material are relatively large. Tip jumping artifacts are a major possible contribution to systematic errors; and we mitigate such problems by using custom-made slender and sharp tips manufactured by focused ion beam. In our data, we observe residual resistivity dipoles associated with topographical defects, and local peaks and dips in the potential that are not associated with topographical defects.

  4. Magnetotransport in Graphene on the Nano Scale measured by Scanning Tunneling Potentiometry

    Science.gov (United States)

    Willke, Philip; Druga, Thomas; Kotzott, Thomas; Ulbrich, Rainer; Schneider, Alexander; Wenderoth, Martin

    The method of scanning tunneling potentiometry (STP) has been introduced by Muralt and Pohl as a technique for mapping the electrochemical potential locally. Here we present a new home-built low-temperature STP setup with applicable magnetic field of up to 6T to study the spatial evolution of the voltage drop at extended defects in graphene with high-resolution. We show that the voltage drop at a monolayer-bilayer boundary in graphene clearly extends spatially up to a few nanometers into the bilayer and hence is not located strictly at the structural defect. Moreover, different scattering mechanisms can be disentangled. Besides, we perform magnetotransport STP measurements mapping the local electrochemical potential as a function of the applied magnetic field. This allows us to identify localized and delocalized contributions to the magnetoresistance in epitaxial-grown graphene and to reveal the contribution of defects. This work was supported by the priority program 1459 ``Graphene'' of the German Science Foundation.

  5. Study on the Structure of C-Phycocyanin in Spirulina platensis with Scanning Tunneling Microscope.

    Science.gov (United States)

    Zhang, Yu-Zhong; Shi, Dong-Xia; Zhou, Bai-Cheng; Zeng, Cheng-Kui; Pang, Shi-Jin

    1997-01-01

    The C-phycocyanin (C-PC) trimmer was isolated from the blue-green alga Spirulina platensis, and scanning tunneling microscope (STM) was used to investigate its structure. High resolution STM images of C-PC were obtained. From the STM images, it could be observed that the C-PC molecules were disk-like in shape and the subunits of C-PC arranged in ring-like pattern with a channel in the center. After filter treatment, the folding of the polypeptide chains could be seen clearly. This is the first time to observe directly the topography of phycobiliprotein, and the results showed STM to be a powerful tool for the structural study of phycobiliproteins.

  6. Calculation of scanning tunnelling microscopy images for Kr/graphite system

    Institute of Scientific and Technical Information of China (English)

    周晓林; 陈向荣; 杨向东; 芶清泉

    2003-01-01

    The scanning-tunnelling-microscopy(STM)images of Kr atoms adsorbed on a monolayer graphite sheet(Kr/graphite system)are calculated using the first-principle total-energy electronic structure calculations within the density functional theory in the local density approximation.The results obtained agree well with the observations.It is found that the optimal site of the adsorbed Kr atom is at the top of the centre of the carbon hexagon,and its equilibrium distance from monolayer graphite surface is about 0.335nm.It is shown that the hybridization of C 2p electronic states(π-electronic states)and Kr 4p and 5s electronic states is the main origin of the Fermi-level local density of state.

  7. PTCDA growth on Ge(111)-c(2\\times 8) surfaces: a scanning tunneling microscopy study

    Science.gov (United States)

    Martínez-Galera, A. J.; Wei, Z.; Nicoara, N.; Brihuega, I.; Gómez-Rodríguez, J. M.

    2017-03-01

    The initial stages of growth of PTCDA (3,4,9,10 perylene tetracarboxylic dianhydride) at room temperature (RT) on Ge(111)-c(2× 8) surfaces have been studied by means of scanning tunneling microscopy (STM) under ultrahigh vacuum conditions. The results show that PTCDA molecules have a high mobility at RT on the well ordered areas of the semiconductor substrate, since nucleation is only observed in domain walls, steps and surface defects. However, no molecular ordering has been detected at submonolayer coverage. For higher coverages, the formation of three-dimensional (3D) molecular islands has been observed. These 3D islands present a crystalline nature as demostrated by molecularly resolved STM images. According to these STM measurements, PTCDA molecules are ordered in a herringbone structure, similar to the one observed in PTCDA bulk crystals. Moreover, the 3D crystallites are grown on top of a disordered molecular layer, which acts as a passivating layer.

  8. Friedel oscillations in graphene-based systems probed by Scanning Tunneling Microscopy

    Science.gov (United States)

    Mallet, Pierre; Brihuega, Iván; Cherkez, Vladimir; Gómez-Rodríguez, Jose Marìa; Veuillen, Jean-Yves

    2016-03-01

    For the last 25 years, scientists have demonstrated the capabilities of Scanning Tunneling Microscopy (STM) to visualize in real space the response of a two-dimensional electron gas to atomic-scale impurities. The analysis of the Friedel oscillations surrounding the impurities yields valuable information regarding the elastic scattering properties, the band structure, the doping level and the symmetry of the electronic states in the two-dimensional host system. We will address in this article the use of this technique for probing the electronic properties of graphene, the star two-dimensional compound of the last decade. In particular, we will emphasize how this technique can be pushed up to unravel the electronic pseudospin, a distinctive degree of freedom of graphene's Dirac fermions.

  9. Scanning tunneling microscopy studies of niobium carbide (100) and (110) surfaces

    Science.gov (United States)

    Tsong, R. M.; Schmid, M.; Nagl, C.; Varga, P.; Davis, R. F.; Tsong, I. S. T.

    1996-10-01

    Scanning tunneling microscopy (STM) studies were conducted on the surfaces of NbC 0.75(100) and NbC 0.865(110) single crystals after in situ cleaning treatments of sputtering and annealing cycles. STM images show atom-resolved structures of both surfaces. On NbC 0.75(100), localized areas of a square (1 × 1) structure were observed, together with regions of hexagonal structure, indicative of a coexisting surface phase, possibly that of Nb 4C 3- x. On the NbC 0.865(110) surface, a ridge-and-valley grating structure consisting of both (4 × 1) and (5 × 1) geometries was observed over large areas. The nanometer-scale faceting phenomenon may be common to the (110) surfaces of most transition-metal carbides.

  10. Design and Implementation of a 4K Cryocooler-Based Scanning Tunneling Microscope

    Science.gov (United States)

    Vishnubhotla, Ramya; Harrington, Neal; Dusch, Bill; Geng, Carrie; Bannerjee, Riju; Pabbi, Lavish; Hudson, Eric W.

    2013-03-01

    Low temperature, ultra-high vacuum scanning tunneling microscopes (STMs) have proved to be excellent tools for the study of electronic properties of complex materials. Unfortunately, with the continuing increase in liquid helium prices, already a dominant cost for operating these systems, their use is becoming exceedingly expensive. Here we describe the design and implementation of a STM cooled by a Cryomech PT407 Remote Motor Cryorefrigerator, allowing us to reach helium temperatures using a closed thermodynamic cycle with zero cryogen waste. Unfortunately, this refrigeration technique is not ultra-high vacuum (UHV) compatible and introduces vibrations. To tackle these problems, we separately house the cryocooler in a high-vacuum (HV) chamber. This provides both a UHV environment for the STM and mechanical isolation to minimize vibrations reaching the instrument. However, it makes for more challenging thermal connections. This last difficulty we solve by introducing a novel coaxial thermal feedthrough between the HV and UHV chambers. Supported by NSF DMR-0904400

  11. Imaging and modification of polymers by scanning tunneling and atomic force microscopy

    Science.gov (United States)

    Albrecht, T. R.; Dovek, M. M.; Lang, C. A.; Grütter, P.; Quate, C. F.; Kuan, S. W. J.; Frank, C. W.; Pease, R. F. W.

    1988-08-01

    Direct imaging of ultrathin organic films on solid surfaces is important for a variety of reasons; in particular, the use of such films as ultrathin resists for nanometer scale fabrication and information recording requires that we understand their microstrucure. We have used the Langmuir-Blodgett technique to prepare monolayer and submonolayer films of poly(octadecylacrylate) (PODA) and poly(methylmethacrylate) (PMMA) on graphite substrates. Atomic scale images obtained with the scanning tunneling microscope (STM) and the atomic force microscope of the PODA films showed a variety of structures, including isolated narrow fibrils, parallel groups of fibrils, and an ordered structure consistent with the side chain crystallization expected with that material. The fibrils observed are interpreted as individual polymer chains or small bundles of parallel chains. Images of the PMMA samples show no ordered regions. By applying voltage pulses on the STM tip, we were able to locally modify and apparently cut through the PODA fibrils.

  12. Possible formation of one-dimensional chains of C20 fullerenes observed by scanning tunneling microscopy

    Science.gov (United States)

    Kurokawa, Shu; Yamamoto, Daisuke; Hirashige, Kenji; Sakai, Akira

    2016-04-01

    We found one-dimensional chains of carbon particles on Ag(111) and Au(111) surfaces after the deposition of carbon using an arc-plasma gun (APG). The observed periodicity of the chains on Ag(111) was 0.58-0.6 nm. Ex situ Fourier transform infrared (FT-IR) spectroscopy indicated two peaks at 1343 and 1406 cm-1. The simulation of the infrared spectrum for a tetramer of C20 fullerenes showed good agreement with the experimental result. From these findings, we propose the formation of chains of C20 fullerenes as the most probable explanation of the results of both scanning tunneling microscopy (STM) and FT-IR spectroscopy.

  13. Single atomic manipulation and writing with scanning tunnelling microscopy at low temperatures

    Institute of Scientific and Technical Information of China (English)

    Gu Chang-Zhi(顾长志); K F Braun; K H Rieder

    2002-01-01

    In the work reported in this paper, we have used a low-temperature scanning tunnelling microscope (LT-STM)system to manipulate accurately single atoms. We show how we can use a LT-STM to image and modify a bulk Ag(111) surface and manipulate Ag atoms from substrate and evaporated adsorbates on Ag(111) substrates. We present a synergistic combination of STM-induced modification and ordered arrays of nanometre-scale structures. In particular, we demonstrate the ability to modify Ag atomic nanometre structures on the Ag(111) substrate, and some English letters and a Chinese character can be written by single Ag atoms coming from the substrate and evaporated adsorbates on Ag(111). In this way, we supply an effective basis to explore the fundamental physical properties of a nanometre structure and to develop nanotechnology with a ‘bottom-up' approach.

  14. Growth mechanisms and defects in boronated CVD diamond as identified by scanning tunneling microscopy

    Science.gov (United States)

    Kreutz, T. J.; Clausing, R. E.; Heatherly, L., Jr.; Warmack, R. J.; Thundat, T.; Feigerle, C. S.; Wandelt, K.

    1995-05-01

    Boron-doped CVD-diamond films were grown in a simple hot filament reactor. A set of samples grown using various methane-in-hydrogen concentrations has been examined by scanning tunneling microscopy in air. On the diamond (111) crystal faces monoatomic steps could be observed giving evidence for layer growth. At low CH4 concentrations the layers form triangular growth spirals. Screw dislocations in the middle of the spirals serve as continuous sources of steps for the layer growth producing (111) faces of high crystal perfection. At higher methane concentrations the crystal perfection declines and the (111) crystal faces exhibit a mosaic structure. The size of the subgrains in the mosaic pattern decreases with increasing CH4 concentration. Nucleation of new layers takes place at the subgrain boundaries. The topography of (001) crystal faces did not significantly change with the methane-in-hydrogen concentration and did not allow the determination of the underlying growth mechanism.

  15. A density-functional theory study of tip electronic structures in scanning tunneling microscopy.

    Science.gov (United States)

    Choi, Heesung; Longo, Roberto C; Huang, Min; Randall, John N; Wallace, Robert M; Cho, Kyeongjae

    2013-03-15

    In this work, we report a detailed analysis of the atomic and electronic structures of transition metal scanning tunneling microscopy tips: Rh, Pd, W, Ir, and Pt pyramidal models, and transition metal (TM) atom tips supported on the W surface, by means of ab initio density-functional theory methods. The d electrons of the apex atoms of the TM tips (Rh, Pd, W, Ir, and Pt tetrahedral structures) show different behaviors near the Fermi level and, especially for the W tip, dz(2) states are shown to be predominant near the Fermi level. The electronic structures of larger pyramidal TM tip structures with a single apex atom are also reported. Their obtained density of states are thoroughly discussed in terms of the different d-electron occupations of the TM tips.

  16. Scanning tunneling microscopy studies of organic monolayers adsorbed on the rhodium(111) crystal surface

    Energy Technology Data Exchange (ETDEWEB)

    Cernota, Paul Davis [Univ. of California, Berkeley, CA (United States)

    1999-08-01

    Scanning Tunneling Microscopy studies were carried out on ordered overlayers on the (111) surface of rhodium. These adsorbates include carbon monoxide (CO), cyclohexane, cyclohexene, 1,4-cyclohexadiene, para-xylene, and meta-xylene. Coadsorbate systems included: CO with ethylidyne, CO with para- and meta-xylene, and para-xylene with meta-xylene. In the case of CO, the structure of the low coverage (2x2) overlayer has been observed. The symmetry of the unit cell in this layer suggests that the CO is adsorbed in the 3-fold hollow sites. There were also two higher coverage surface structures with (√7x√7) unit cells. One of these is composed of trimers of CO and has three CO molecules in each unit cell. The other structure has an additional CO molecule, making a total of four. This extra CO sits on a top site.

  17. Invited Article: Autonomous assembly of atomically perfect nanostructures using a scanning tunneling microscope

    Energy Technology Data Exchange (ETDEWEB)

    Celotta, Robert J., E-mail: robert.celotta@nist.gov, E-mail: joseph.stroscio@nist.gov; Hess, Frank M.; Rutter, Gregory M.; Stroscio, Joseph A., E-mail: robert.celotta@nist.gov, E-mail: joseph.stroscio@nist.gov [Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Balakirsky, Stephen B. [Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Georgia Tech Research Institute, Atlanta, Georgia 30332 (United States); Fein, Aaron P. [Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)

    2014-12-15

    A major goal of nanotechnology is to develop the capability to arrange matter at will by placing individual atoms at desired locations in a predetermined configuration to build a nanostructure with specific properties or function. The scanning tunneling microscope has demonstrated the ability to arrange the basic building blocks of matter, single atoms, in two-dimensional configurations. An array of various nanostructures has been assembled, which display the quantum mechanics of quantum confined geometries. The level of human interaction needed to physically locate the atom and bring it to the desired location limits this atom assembly technology. Here we report the use of autonomous atom assembly via path planning technology; this allows atomically perfect nanostructures to be assembled without the need for human intervention, resulting in precise constructions in shorter times. We demonstrate autonomous assembly by assembling various quantum confinement geometries using atoms and molecules and describe the benefits of this approach.

  18. Scanning tunneling microscopy studies of organic monolayers adsorbed on the rhodium(111) crystal surface

    Energy Technology Data Exchange (ETDEWEB)

    Cernota, Paul D.

    1999-08-01

    Scanning Tunneling Microscopy studies were carried out on ordered overlayers on the (111) surface of rhodium. These adsorbates include carbon monoxide (CO), cyclohexane, cyclohexene, 1,4-cyclohexadiene, para-xylene, and meta-xylene. Coadsorbate systems included: CO with ethylidyne, CO with para- and meta-xylene, and para-xylene with meta-xylene. In the case of CO, the structure of the low coverage (2x2) overlayer has been observed. The symmetry of the unit cell in this layer suggests that the CO is adsorbed in the 3-fold hollow sites. There were also two higher coverage surface structures with ({radical}7x{radical}7) unit cells. One of these is composed of trimers of CO and has three CO molecules in each unit cell. The other structure has an additional CO molecule, making a total of four. This extra CO sits on a top site.

  19. Invited Article: Autonomous assembly of atomically perfect nanostructures using a scanning tunneling microscope.

    Science.gov (United States)

    Celotta, Robert J; Balakirsky, Stephen B; Fein, Aaron P; Hess, Frank M; Rutter, Gregory M; Stroscio, Joseph A

    2014-12-01

    A major goal of nanotechnology is to develop the capability to arrange matter at will by placing individual atoms at desired locations in a predetermined configuration to build a nanostructure with specific properties or function. The scanning tunneling microscope has demonstrated the ability to arrange the basic building blocks of matter, single atoms, in two-dimensional configurations. An array of various nanostructures has been assembled, which display the quantum mechanics of quantum confined geometries. The level of human interaction needed to physically locate the atom and bring it to the desired location limits this atom assembly technology. Here we report the use of autonomous atom assembly via path planning technology; this allows atomically perfect nanostructures to be assembled without the need for human intervention, resulting in precise constructions in shorter times. We demonstrate autonomous assembly by assembling various quantum confinement geometries using atoms and molecules and describe the benefits of this approach.

  20. Magnetic fingerprint of individual Fe4 molecular magnets under compression by a scanning tunnelling microscope.

    Science.gov (United States)

    Burgess, Jacob A J; Malavolti, Luigi; Lanzilotto, Valeria; Mannini, Matteo; Yan, Shichao; Ninova, Silviya; Totti, Federico; Rolf-Pissarczyk, Steffen; Cornia, Andrea; Sessoli, Roberta; Loth, Sebastian

    2015-01-01

    Single-molecule magnets (SMMs) present a promising avenue to develop spintronic technologies. Addressing individual molecules with electrical leads in SMM-based spintronic devices remains a ubiquitous challenge: interactions with metallic electrodes can drastically modify the SMM's properties by charge transfer or through changes in the molecular structure. Here, we probe electrical transport through individual Fe4 SMMs using a scanning tunnelling microscope at 0.5 K. Correlation of topographic and spectroscopic information permits identification of the spin excitation fingerprint of intact Fe4 molecules. Building from this, we find that the exchange coupling strength within the molecule's magnetic core is significantly enhanced. First-principles calculations support the conclusion that this is the result of confinement of the molecule in the two-contact junction formed by the microscope tip and the sample surface.

  1. Scanning tunneling microscopy studies of thin foil x-ray mirrors

    DEFF Research Database (Denmark)

    Christensen, Finn Erland; Besenbacher, Flemming; Garnaes, Jorgen;

    1990-01-01

    In this paper scanning tunneling microscopy (STM) measurements of x-ray mirrors are presented. The x-ray mirrors are 0.3 mm thick dip-lacquered aluminum foils coated with gold by evaporation, as well as state-of-the-art polished surfaces coated with gold, platinum, or iridium. The measurements....... The results can be used as a guide when selecting the best coating process in the production of x-ray mirrors....... that the microroughness depends on the thickness of the gold layer. The roughness is smallest (~7 to 9 Å) for gold layers between ~100 and ~250Å, and it becomes significantly greater (~10 to 15Å) for gold layers thicker than ~350 Å. With a few exceptions the STM measurements agree well with recent x-ray studies...

  2. Low-temperature-compatible tunneling-current-assisted scanning microwave microscope utilizing a rigid coaxial resonator

    Science.gov (United States)

    Takahashi, Hideyuki; Imai, Yoshinori; Maeda, Atsutaka

    2016-06-01

    We present a design for a tunneling-current-assisted scanning near-field microwave microscope. For stable operation at cryogenic temperatures, making a small and rigid microwave probe is important. Our coaxial resonator probe has a length of approximately 30 mm and can fit inside the 2-in. bore of a superconducting magnet. The probe design includes an insulating joint, which separates DC and microwave signals without degrading the quality factor. By applying the SMM to the imaging of an electrically inhomogeneous superconductor, we obtain the spatial distribution of the microwave response with a spatial resolution of approximately 200 nm. Furthermore, we present an analysis of our SMM probe based on a simple lumped-element circuit model along with the near-field microwave measurements of silicon wafers having different conductivities.

  3. Compressed Sensing in Scanning Tunneling Microscopy/Spectroscopy for Observation of Quasi-Particle Interference

    Science.gov (United States)

    Nakanishi-Ohno, Yoshinori; Haze, Masahiro; Yoshida, Yasuo; Hukushima, Koji; Hasegawa, Yukio; Okada, Masato

    2016-09-01

    We applied a method of compressed sensing to the observation of quasi-particle interference (QPI) by scanning tunneling microscopy/spectroscopy to improve efficiency and save measurement time. To solve an ill-posed problem owing to the scarcity of data, the compressed sensing utilizes the sparseness of QPI patterns in momentum space. We examined the performance of a sparsity-inducing algorithm called least absolute shrinkage and selection operator (LASSO), and demonstrated that LASSO enables us to recover a double-circle QPI pattern of the Ag(111) surface from a dataset whose size is less than that necessary for the conventional Fourier transformation method. In addition, the smallest number of data required for the recovery is discussed on the basis of cross validation.

  4. Gap Measurement of Na2IrO3 with a Scanning Tunneling Microscope

    Science.gov (United States)

    Ansary, Armin; Nichols, John; Cao, Gang; Ng, Kwok-Wai

    2015-03-01

    5d transition metal oxides such as iridates have recently stimulated substantial interest. Many exciting new phases can be found in this class of materials because of the comparable strength between spin-orbit coupling and the Coulomb interaction. In particular, we have studied high quality single crystal Na2IrO3 with a scanning tunneling microscope (STM). Na2IrO3 has a layered structure with a honeycomb lattice. The gap is measured to be about 400 meV according to the dI/dV curve, which is consistent with optical measurements. We will show topographic images and discuss the evolution of the density of states and the behavior of the gap from room temperature down to 100 K. This work was supported by the National Science Foundation under Grant DMR-1265162.

  5. Structure investigation of Cellobiohydrolase I from Trichoderma pseudokoningii S38 with a scanning tunneling microscope

    Science.gov (United States)

    Zhang, Y. Z.; Liu, J.; Gao, P. J.; Ma, L. P.; Shi, D. X.; Pang, S. J.

    Cellobiohydrolase I (CBH I) was isolated from a cellulolytic fungal strain Trichoderma pseudokoningii S38, and its ultrastructure was investigated with a scanning tunneling microscope (STM). The STM images showed that the shape of intact CBH I was tadpole-like, consisting of a big head and a long tail. It could be deduced that the head domain was the core protein for the catalytic function, and the long tail was the cellulose binding domain for substrate binding. Thus, for this enzyme molecule, functional differentiation is reflected in the structure peculiarities. This is the first direct observation of the three-dimensional structure of intact CBH I from real space at nanometer scale. The functional mechanism is also discussed.

  6. Modification of a Scanning Tunneling Microscope for Measurement of Ballistic Electron Emission Microscopy

    Science.gov (United States)

    Hsieh, Satcher; Hong, Jeongmin; Bokor, Jeffrey

    2014-03-01

    Magnetic memory and logic devices show great promise for integration with, and even replacement of, conventional complementary metal-oxide-semiconductor (CMOS) architectures. In order to characterize materials and deposition techniques for these devices, ballistic electron emission microscopy (BEEM) is used. BEEM is a spatially resolved metrological tool most commonly used for subsurface interface structures at the nanometer scale. We modify a scanning tunneling microscope (STM) to perform BEEM measurement via design and fabrication of a novel sample stage. Furthermore, we design and fabricate an external magnetic field source that encapsulates the sample stage, setting the foundation for future measurement of ballistic electron magnetic microscopy (BEMM). Instrumentation of the device and characterization of a sample with an ohmic interface, Ni-Si, are implemented and discussed. With support from National Science Foundation Award ECCS-0939514.

  7. Interfacial scanning tunneling spectroscopy (STS) of chalcogenide/metal hybrid nanostructure

    Energy Technology Data Exchange (ETDEWEB)

    Saad, Mahmoud M.; Abdallah, Tamer [Physics Department, Faculty of Science, Ain Shams University, Abbassia, Cairo (Egypt); Easawi, Khalid; Negm, Sohair [Department of Physics and Mathematics, Faculty of Engineering (Shoubra), Benha University (Egypt); Talaat, Hassan, E-mail: hassantalaat@hotmail.com [Physics Department, Faculty of Science, Ain Shams University, Abbassia, Cairo (Egypt)

    2015-05-15

    Graphical abstract: - Highlights: • Comparing band gaps values obtained optically with STS. • Comparing direct imaging with calculated dimensions. • STS determination of the interfacial band bending of metal/chalcogenide. - Abstract: The electronic structure at the interface of chalcogenide/metal hybrid nanostructure (CdSe–Au tipped) had been studied by UHV scanning tunneling spectroscopy (STS) technique at room temperature. This nanostructure was synthesized by a phase transfer chemical method. The optical absorption of this hybrid nanostructure was recorded, and the application of the effective mass approximation (EMA) model gave dimensions that were confirmed by the direct measurements using the scanning tunneling microscopy (STM) as well as the high-resolution transmission electron microscope (HRTEM). The energy band gap obtained by STS agrees with the values obtained from the optical absorption. Moreover, the STS at the interface of CdSe–Au tipped hybrid nanostructure between CdSe of size about 4.1 ± 0.19 nm and Au tip of size about 3.5 ± 0.29 nm shows a band bending about 0.18 ± 0.03 eV in CdSe down in the direction of the interface. Such a result gives a direct observation of the electron accumulation at the interface of CdSe–Au tipped hybrid nanostructure, consistent with its energy band diagram. The presence of the electron accumulation at the interface of chalcogenides with metals has an important implication for hybrid nanoelectronic devices and the newly developed plasmon/chalcogenide photovoltaic solar energy conversion.

  8. Preparation of scanning tunneling microscopy tips using pulsed alternating current etching

    Energy Technology Data Exchange (ETDEWEB)

    Valencia, Victor A.; Thaker, Avesh A.; Derouin, Jonathan; Valencia, Damian N.; Farber, Rachael G.; Gebel, Dana A.; Killelea, Daniel R., E-mail: dkillelea@luc.edu [Department of Chemistry and Biochemistry, Loyola University Chicago, 1068 W. Sheridan Rd., Chicago, Illinois 60660 (United States)

    2015-03-15

    An electrochemical method using pulsed alternating current etching (PACE) to produce atomically sharp scanning tunneling microscopy (STM) tips is presented. An Arduino Uno microcontroller was used to control the number and duration of the alternating current (AC) pulses, allowing for ready optimization of the procedures for both Pt:Ir and W tips using a single apparatus. W tips prepared using constant and pulsed AC power were compared. Tips fashioned using PACE were sharper than those etched with continuous AC power alone. Pt:Ir tips were prepared with an initial coarse etching stage using continuous AC power followed by fine etching using PACE. The number and potential of the finishing AC pulses was varied and scanning electron microscope imaging was used to compare the results. Finally, tip quality using the optimized procedures was verified by UHV-STM imaging. With PACE, at least 70% of the W tips and 80% of the Pt:Ir tips were of sufficiently high quality to obtain atomically resolved images of HOPG or Ni(111)

  9. Scanning tunneling microscopy I general principles and applications to clean and absorbate-covered surfaces

    CERN Document Server

    Wiesendanger, Roland

    1994-01-01

    Since the first edition of "Scanning 'funneling Microscopy I" has been pub­ lished, considerable progress has been made in the application of STM to the various classes of materials treated in this volume, most notably in the field of adsorbates and molecular systems. An update of the most recent develop­ ments will be given in an additional Chapter 9. The editors would like to thank all the contributors who have supplied up­ dating material, and those who have provided us with suggestions for further improvements. We also thank Springer-Verlag for the decision to publish this second edition in paperback, thereby making this book affordable for an even wider circle of readers. Hamburg, July 1994 R. Wiesendanger Preface to the First Edition Since its invention in 1981 by G. Binnig, H. Rohrer and coworkers at the IBM Zurich Research Laboratory, scanning tunneling microscopy (STM) has devel­ oped into an invaluable surface analytical technique allowing the investigation of real-space surface structures at th...

  10. Coating of tips for electrochemical scanning tunneling microscopy by means of silicon, magnesium, and tungsten oxides.

    Science.gov (United States)

    Salerno, Marco

    2010-09-01

    Different combinations of metal tips and oxide coatings have been tested for possible operation in electrochemical scanning tunneling microscopy. Silicon and magnesium oxides have been thermally evaporated onto gold and platinum-iridium tips, respectively. Two different thickness values have been explored for both materials, namely, 40 and 120 nm for silicon oxide and 20 and 60 nm for magnesium oxide. Alternatively, tungsten oxide has been grown on tungsten tips via electrochemical anodization. In the latter case, to seek optimal results we have varied the pH of the anodizing electrolyte between one and four. The oxide coated tips have been first inspected by means of scanning electron microscopy equipped with microanalysis to determine the morphological results of the coating. Second, the coated tips have been electrically characterized ex situ for stability in time by means of cyclic voltammetry in 1 M aqueous KCl supporting electrolyte, both bare and supplemented with K(3)[Fe(CN)(6)] complex at 10 mM concentration in milliQ water as an analyte. Only the tungsten oxide coated tungsten tips have shown stable electrical behavior in the electrolyte. For these tips, the uncoated metal area has been estimated from the electrical current levels, and they have been successfully tested by imaging a gold grating in situ, which provided stable results for several hours. The successful tungsten oxide coating obtained at pH=4 has been assigned to the WO(3) form.

  11. Adsorption of human insulin on single-crystal gold surfaces investigated by in situ scanning tunnelling microscopy and electrochemistry

    DEFF Research Database (Denmark)

    Welinder, Anna Christina; Zhang, Jingdong; Steensgaard, D.B.;

    2010-01-01

    We have explored the adsorption of zinc-free human insulin on the three low-index single-crystalline Au(111)-, Au(100)- and Au(110)-surfaces in aqueous buffer (KH2PO4, pH 5) by a combination of electrochemical scanning tunnelling microscopy (in situ STM) at single-molecule resolution and linear s...

  12. Atomic structure of screw dislocations intersecting the Au(111) surface: A combined scanning tunneling microscopy and molecular dynamics study

    DEFF Research Database (Denmark)

    Engbæk, Jakob; Schiøtz, Jakob; Dahl-Madsen, Bjarke;

    2006-01-01

    The atomic-scale structure of naturally occurring screw dislocations intersecting a Au(111) surface has been investigated both experimentally by scanning tunneling microscopy (STM) and theoretically using molecular dynamics (MD) simulations. The step profiles of 166 dislocations were measured usi...

  13. Scanning Tunneling Microscopic Observation of Adatom-Mediated Motifs on Gold-Thiol Self-assembled Monolayers at High Coverage

    DEFF Research Database (Denmark)

    Wang, Yun; Chi, Qijin; Hush, Noel S.;

    2009-01-01

    Self-assembled monolayers (SAMs) formed by chemisorption of a branched-chain alkanethiol, 2-methyl-1-propanethiol, on Au(111) surfaces were studied by in situ scanning tunneling microscopy (STM) under electrochemical potential control and analyzed using extensive density functional theory (DFT) c...

  14. Vectorial mapping of noncollinear antiferromagnetic structure of semiconducting FeSe surface with spin-polarized scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, K. F.; Yang, Fang; Song, Y. R. [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Zhang, Xiaole [Institute of Natural Sciences, Shanghai Jiao Tong University, Shanghai 200240 (China); The State Key Laboratory of Advanced Optical Communication Systems and Networks, Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Chen, Xianfeng [The State Key Laboratory of Advanced Optical Communication Systems and Networks, Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Liu, Canhua; Qian, Dong; Gao, C. L., E-mail: clgao@sjtu.edu.cn; Jia, Jin-Feng [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing (China); Luo, Weidong, E-mail: wdluo@sjtu.edu.cn [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Institute of Natural Sciences, Shanghai Jiao Tong University, Shanghai 200240 (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing (China)

    2016-02-08

    Antiferromagnetic semiconductors gain increasing interest due to their possible application in spintronics. Using spin polarized scanning tunneling microscopy operating in a vector field, we mapped the noncollinear antiferromagnetic spin structure of a semiconducting hexagonal FeSe surface on the atomic scale. The surface possesses an in-plane compensated Néel structure which is further confirmed by first-principles calculations.

  15. Towards automated discrimination of lipids versus peptides from full scan mass spectra

    Directory of Open Access Journals (Sweden)

    Piotr Dittwald

    2014-09-01

    Full Text Available Although physicochemical fractionation techniques play a crucial role in the analysis of complex mixtures, they are not necessarily the best solution to separate specific molecular classes, such as lipids and peptides. Any physical fractionation step such as, for example, those based on liquid chromatography, will introduce its own variation and noise. In this paper we investigate to what extent the high sensitivity and resolution of contemporary mass spectrometers offers viable opportunities for computational separation of signals in full scan spectra. We introduce an automatic method that can discriminate peptide from lipid peaks in full scan mass spectra, based on their isotopic properties. We systematically evaluate which features maximally contribute to a peptide versus lipid classification. The selected features are subsequently used to build a random forest classifier that enables almost perfect separation between lipid and peptide signals without requiring ion fragmentation and classical tandem MS-based identification approaches. The classifier is trained on in silico data, but is also capable of discriminating signals in real world experiments. We evaluate the influence of typical data inaccuracies of common classes of mass spectrometry instruments on the optimal set of discriminant features. Finally, the method is successfully extended towards the classification of individual lipid classes from full scan mass spectral features, based on input data defined by the Lipid Maps Consortium.

  16. Properties of Single Molecules: Manipulation, Dissociation and Synthesis with the Scanning Tunneling Microscope

    Science.gov (United States)

    Braun, Kai-Felix; Hla, Saw-Wai

    The fascinating advances in the manipulation of single atoms and molecules with the scanning tunneling microscope tip allow scientists to build atomic scale structures and to probe chemical and physical properties of matters at an atomic level. Due to these advances, the basic steps of a catalyzed chemical reaction such as dissociation, diffusion, adsorption, re-adsorption and bond formation processes can be performed by using the STM-tip. Here a short review of these steps and the techniques involved is presented. The lateral manipulation is used for the controlled positioning of atoms/molecules whereby only the tip- atom/molecule forces are employed. By measuring the tip-height signal during the manipulation, different modes of motion of the adparticle can be distinguished. Lower corrugated surfaces exhibit more complex motions than higher corrugated surfaces where the adparticle movement is confined to one dimension. Molecules have more degrees of freedom which allow a rotational motion or change in configuration. Even internal degrees of freedom can be detected and manipulated. The vertical manipulation not only allows the pick-up of adparticles and the subsequent transfer back to the surface, but also the manipulation of fragments of larger molecules. Effects due to the tunneling curent can be used for a controlled dissociation of chemical bonds as well as for the formation of new bonds. The combination of these manipulation techniques can induce chemical reactions at a single molecule level and construct new molecules. These achievements in STM manipulation of molecules open up new opportunities in nanochemistry and nanochemical technology. In this article, various STM manipulation techniques used for the single molecule reaction process are reviewed, and their impact on the future of nanoscience and nanotechnology is discussed.

  17. Scanning tunnelling spectroscopy as a probe of multi-Q magnetic states of itinerant magnets

    Science.gov (United States)

    Gastiasoro, Maria N.; Eremin, Ilya; Fernandes, Rafael M.; Andersen, Brian M.

    2017-02-01

    The combination of electronic correlations and Fermi surfaces with multiple nesting vectors can lead to the appearance of complex multi-Q magnetic ground states, hosting unusual states such as chiral density waves and quantum Hall insulators. Distinguishing single-Q and multi-Q magnetic phases is however a notoriously difficult experimental problem. Here we propose theoretically that the local density of states (LDOS) near a magnetic impurity, whose orientation may be controlled by an external magnetic field, can be used to map out the detailed magnetic configuration of an itinerant system and distinguish unambiguously between single-Q and multi-Q phases. We demonstrate this concept by computing and contrasting the LDOS near a magnetic impurity embedded in three different magnetic ground states relevant to iron-based superconductors--one single-Q and two double-Q phases. Our results open a promising avenue to investigate the complex magnetic configurations in itinerant systems via standard scanning tunnelling spectroscopy, without requiring spin-resolved capability.

  18. Defects in oxide surfaces studied by atomic force and scanning tunneling microscopy

    Directory of Open Access Journals (Sweden)

    Thomas König

    2011-01-01

    Full Text Available Surfaces of thin oxide films were investigated by means of a dual mode NC-AFM/STM. Apart from imaging the surface termination by NC-AFM with atomic resolution, point defects in magnesium oxide on Ag(001 and line defects in aluminum oxide on NiAl(110, respectively, were thoroughly studied. The contact potential was determined by Kelvin probe force microscopy (KPFM and the electronic structure by scanning tunneling spectroscopy (STS. On magnesium oxide, different color centers, i.e., F0, F+, F2+ and divacancies, have different effects on the contact potential. These differences enabled classification and unambiguous differentiation by KPFM. True atomic resolution shows the topography at line defects in aluminum oxide. At these domain boundaries, STS and KPFM verify F2+-like centers, which have been predicted by density functional theory calculations. Thus, by determining the contact potential and the electronic structure with a spatial resolution in the nanometer range, NC-AFM and STM can be successfully applied on thin oxide films beyond imaging the topography of the surface atoms.

  19. Magnetoelectric coupling in supercoducting Sr2 VO3 FeAs revealed by scanning tunneling microscopy

    Science.gov (United States)

    Choi, Seokhwan; Choi, Hyunwoo; Lee, Hyun-Jung; Jung, Jin-Oh; Son, Donghyun; Kim, Jun Sung; Ok, Jong Mok; Lee, Jhinhwan

    2015-03-01

    Sr2VO3FeAs is known to exhibit high Tc (~ 37K) superconductivity with no magnetic ordering in the FeAs layer but weak magnetic moment in the V sublattice. An angle resolved photo emission spectroscopy also shows the non-trivial Fermi surface due to the V 3d orbitals. We have studied on Sr2VO3FeAs single crystal using spectroscopic imaging scanning tunneling microscopy (SI-STM) with variable temperature from 4.6K to 100K, and magnetic field up to 7T. Our results show that Sr2VO3FeAs has charge density wave (CDW) modulation in the V sublattice with the same wave vector observed in the neutron scattering experiment. The modulation strength is reduced with applying magnetic field. An electronic Fermi surface with largest V 3d character shows suppressed superconductivity possibly due to strong V-site correlation. However the multi-orbital nature of FeAs allows overall unsuppressed superconductivity at high Tc.

  20. Scanning tunneling microscopy of cleaved AlPdMn icosahedral quasicrystals

    Science.gov (United States)

    Urban, K.

    1997-03-01

    Quasicrystal surfaces produced by in-situ cleavage in ultra-high vacuum have been investigated by scanning tunneling microscopy. Twofold and fivefold surfaces of icosahedral AlPdMn single-quasicrystals have been studied. The surfaces were found to be rough. Their structure is determined by cluster aggregates of various sizes formed on the basis of an elementary cluster whose contrast behavior and diameter of about 1 nm point to the Mackay-type cluster [1]. The surface of these elementary clusters exhibits a smooth density of electronic states. These observations agree with the predictions of recent models on the quasicrystal structure and electronic properties in which the Mackay-type clusters play a dominant role [2]. In particular, these clusters are believed to act as deep potential wells leading to electron states primarily bound to these. Crack propagation during cleavage occurs along zones of lower strength between the clusters indicating that these act as rigid entities. This corroborates the assumption made in modern treatments of quasicrystal plasticity that the Mackay-type clusters control the mechanical properties [3,4]. [1] Ph. Ebert, M. Feuerbacher, N. Tamura, M. Wollgarten, and K. Urban, Phys. Rev. Lett. 77, 3827 (1996). [2] C. Janot, Phys. Rev. B 53, 181 (1996). [3] M. Feuerbacher, B. Baufeld, R. Rosenfeld, M. Bartsch, G. Hanke, M. Beyss, M. Wollgarten, and K. Urban, Philos. Mag. Lett. 71, 91 (1995). [4] F. Krul, R. Mikulla, P. Gumbsch, and H.-R. Trebin (to be published).

  1. Compact low temperature scanning tunneling microscope with in-situ sample preparation capability

    Science.gov (United States)

    Kim, Jungdae; Nam, Hyoungdo; Qin, Shengyong; Kim, Sang-ui; Schroeder, Allan; Eom, Daejin; Shih, Chih-Kang

    2015-09-01

    We report on the design of a compact low temperature scanning tunneling microscope (STM) having in-situ sample preparation capability. The in-situ sample preparation chamber was designed to be compact allowing quick transfer of samples to the STM stage, which is ideal for preparing temperature sensitive samples such as ultra-thin metal films on semiconductor substrates. Conventional spring suspensions on the STM head often cause mechanical issues. To address this problem, we developed a simple vibration damper consisting of welded metal bellows and rubber pads. In addition, we developed a novel technique to ensure an ultra-high-vacuum (UHV) seal between the copper and stainless steel, which provides excellent reliability for cryostats operating in UHV. The performance of the STM was tested from 2 K to 77 K by using epitaxial thin Pb films on Si. Very high mechanical stability was achieved with clear atomic resolution even when using cryostats operating at 77 K. At 2 K, a clean superconducting gap was observed, and the spectrum was easily fit using the BCS density of states with negligible broadening.

  2. Scanning tunnelling spectroscopy as a probe of multi-Q magnetic states of itinerant magnets

    Science.gov (United States)

    Gastiasoro, Maria N.; Eremin, Ilya; Fernandes, Rafael M.; Andersen, Brian M.

    2017-01-01

    The combination of electronic correlations and Fermi surfaces with multiple nesting vectors can lead to the appearance of complex multi-Q magnetic ground states, hosting unusual states such as chiral density waves and quantum Hall insulators. Distinguishing single-Q and multi-Q magnetic phases is however a notoriously difficult experimental problem. Here we propose theoretically that the local density of states (LDOS) near a magnetic impurity, whose orientation may be controlled by an external magnetic field, can be used to map out the detailed magnetic configuration of an itinerant system and distinguish unambiguously between single-Q and multi-Q phases. We demonstrate this concept by computing and contrasting the LDOS near a magnetic impurity embedded in three different magnetic ground states relevant to iron-based superconductors—one single-Q and two double-Q phases. Our results open a promising avenue to investigate the complex magnetic configurations in itinerant systems via standard scanning tunnelling spectroscopy, without requiring spin-resolved capability. PMID:28176779

  3. Scanning Tunneling Microscopy of the π Magnetism of a Single Carbon Vacancy in Graphene.

    Science.gov (United States)

    Zhang, Yu; Li, Si-Yu; Huang, Huaqing; Li, Wen-Tian; Qiao, Jia-Bin; Wang, Wen-Xiao; Yin, Long-Jing; Bai, Ke-Ke; Duan, Wenhui; He, Lin

    2016-10-14

    Pristine graphene is strongly diamagnetic. However, graphene with single carbon atom defects could exhibit paramagnetism. Theoretically, the π magnetism induced by the monovacancy in graphene is characteristic of two spin-split density-of-states (DOS) peaks close to the Dirac point. Since its prediction, many experiments have attempted to study this π magnetism in graphene, whereas only a notable resonance peak has been observed around the atomic defects, leaving the π magnetism experimentally elusive. Here, we report direct experimental evidence of π magnetism by using a scanning tunneling microscope. We demonstrate that the localized state of the atomic defects is split into two DOS peaks with energy separations of several tens of meV. Strong magnetic fields further increase the energy separations of the two spin-polarized peaks and lead to a Zeeman-like splitting. Unexpectedly, the effective g factor around the atomic defect is measured to be about 40, which is about 20 times larger than the g factor for electron spins.

  4. Unveiling Stability Criteria of DNA-Carbon Nanotubes Constructs by Scanning Tunneling Microscopy and Computational Modeling

    Directory of Open Access Journals (Sweden)

    Svetlana Kilina

    2011-01-01

    Full Text Available We present a combined approach that relies on computational simulations and scanning tunneling microscopy (STM measurements to reveal morphological properties and stability criteria of carbon nanotube-DNA (CNT-DNA constructs. Application of STM allows direct observation of very stable CNT-DNA hybrid structures with the well-defined DNA wrapping angle of 63.4° and a coiling period of 3.3 nm. Using force field simulations, we determine how the DNA-CNT binding energy depends on the sequence and binding geometry of a single strand DNA. This dependence allows us to quantitatively characterize the stability of a hybrid structure with an optimal π-stacking between DNA nucleotides and the tube surface and better interpret STM data. Our simulations clearly demonstrate the existence of a very stable DNA binding geometry for (6,5 CNT as evidenced by the presence of a well-defined minimum in the binding energy as a function of an angle between DNA strand and the nanotube chiral vector. This novel approach demonstrates the feasibility of CNT-DNA geometry studies with subnanometer resolution and paves the way towards complete characterization of the structural and electronic properties of drug-delivering systems based on DNA-CNT hybrids as a function of DNA sequence and a nanotube chirality.

  5. Investigation of Two-Dimensional Transition Metal Dichalcogenides by Optical and Scanning Tunneling Spectroscopy

    Science.gov (United States)

    Rigosi, Albert F.

    The goal of this dissertation is not only to present works completed and projects initiated and accomplished, but to also attempt to teach some of the material to readers who have limited exposure to condensed matter. I will offer an introduction to two-dimensional transition metal dichalcogenide materials (2D TMDCs) and the mathematics required to understand the research conducted. Some effort will be given on explaining the experimental setups and preparations. Projects that required elaborate sample fabrication and the yielded results will be summarized. These results have heavy implications for the science behind bound electron-hole pairs, the effects of magnetic fields on such pairs, and extracting the useful optical properties from the material systems in which these pairs reside. Specialized fabrication techniques of samples for longer term projects that I led will also be presented, namely those of constructing heterostructures by stacking various 2D TMDCs for exploring the modulated properties of these novel arrangements. The latter portion of this dissertation will cover the nanoscopic dynamics of TMDC heterostructures. The Kramers-Kronig relations will be derived and discussed in detail. Data and results regarding the electronic structure of these materials, their heterostructures, and their custom alloys measured via scanning tunneling microscopy will be presented. Coupled with the measured optical properties, significant numerical quantities that characterize these materials are extracted. There will be several appendices that offer some supplementary information and basic summaries about all the projects that were initiated.

  6. Nanometer-Scale Compositional Structure in III-V Semiconductor Heterostructures Characterized by Scanning Tunneling Microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Allerman, A.A.; Bi, W.G.; Biefeld, R.M.; Tu, C.W.; Yu, E.T.; Zuo, S.L.

    1998-11-10

    Nanometer-scale compositional structure in InAsxP1.InNYAsxPl.x-Y/InP, grown by gas-source molecular-beam epitaxy and in InAsl-xPJkAsl$b#InAs heterostructures heterostructures grown by metal-organic chemical vapor deposition has been characterized using cross-sectional scanning tunneling microscopy. InAsxP1-x alloy layers are found to contain As-rich and P-rich clusters with boundaries formed preferentially within (T 11) and (111) crystal planes. Similar compositional structure is observed within InNYAsxP1-x-Y alloy layers. Imaging of InAsl-xp@Asl#bY superlattices reveals nanometer-scale clustering within both the hAsI-.p and InAsl$bY alloy layers, with preferential alignment of compositional features in the direction. Instances are observed of compositional structure correlated across a heterojunction interface, with regions whose composition corresponds to a smaller unstrained lattice, constant relative to the surrounding alloy material appearing to propagate across the interface.

  7. Current-induced magnetization switching with a spin-polarized scanning tunneling microscope

    Science.gov (United States)

    Krause, Stefan

    2008-03-01

    In present data storage applications magnetic nanostructures are switched by external magnetic fields. Due to their non-local character, however, cross-talk between adjacent nanomagnets may occur. An elegant method to circumvent this problem is magnetization switching by spin-polarized currents, as observed in GMR,1] as well as in TMR,2] studies. However, the layered structures of these devices do not provide any insight to the details of the spatial distribution of the switching processes. Spin-polarized scanning tunneling microscopy (SP-STM) is a well-established tool to reveal the magnetic structure of surfaces at spatial resolution down to the atomic scale. Besides, SP-STM takes advantage of a perfect TMR junction consisting of an isolating vacuum barrier separating two magnetic electrodes, which are represented by the foremost tip atom and the sample. Our experiments demonstrate that SP-STM serves as a tool to manipulate the switching behavior of uniaxial superparamagnetic nanoislands,3]. Furthermore, we show how SP-STM can be used to switch the magnetization of quasistable magnetic nanoislands at low temperature (T=31,). Besides its scientific relevance to investigate the details of current-induced magnetization switching (CIMS), this technique opens perspectives for future data storage technologies based on SP-STM. [1] J. A. Katine et al., Phys. Rev. Lett. 84, 3149 (2000). [2] Y. Liu et al., Appl. Phys. Lett. 82, 2871 (2003). [3] S. Krause et al., Science 317, 1537 (2007).

  8. Dynamic covalent chemistry of bisimines at the solid/liquid interface monitored by scanning tunnelling microscopy

    Science.gov (United States)

    Ciesielski, Artur; El Garah, Mohamed; Haar, Sébastien; Kovaříček, Petr; Lehn, Jean-Marie; Samorì, Paolo

    2014-11-01

    Dynamic covalent chemistry relies on the formation of reversible covalent bonds under thermodynamic control to generate dynamic combinatorial libraries. It provides access to numerous types of complex functional architectures, and thereby targets several technologically relevant applications, such as in drug discovery, (bio)sensing and dynamic materials. In liquid media it was proved that by taking advantage of the reversible nature of the bond formation it is possible to combine the error-correction capacity of supramolecular chemistry with the robustness of covalent bonding to generate adaptive systems. Here we show that double imine formation between 4-(hexadecyloxy)benzaldehyde and different α,ω-diamines as well as reversible bistransimination reactions can be achieved at the solid/liquid interface, as monitored on the submolecular scale by in situ scanning tunnelling microscopy imaging. Our modular approach enables the structurally controlled reversible incorporation of various molecular components to form sophisticated covalent architectures, which opens up perspectives towards responsive multicomponent two-dimensional materials and devices.

  9. Manipulation of charge on a single donor atom by scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Teichmann, K.; Wenderoth, M.; Loth, S.; Ulbrich, R.G. [IV. Phys. Inst., Georg-August-Universitaet Goettingen (Germany); Garleff, J.K.; Wijnheijmer, A.P.; Koenraad, P.M. [PSN, Eindhoven University of Technology (Netherlands)

    2008-07-01

    We investigated silicon donors in highly doped GaAs by spatially resolved scanning tunneling spectroscopy at 6 K. Recently it was shown by Feenstra, that the shape of the tip has a strong influence of the extension of the tip induced band bending (TIBB) in the semiconductor. Sharp tips produce a lateral extension of TIBB in the semiconductor within the range of nanometers. The charge of an individual impurity can be manipulated by the TIBB in the following way: Donors, away from the tip, will be neutral, as the thermal energy at 6K is much smaller than the ionisation energy of the donor. The bands and the donor energy levels are lifted for positive sample voltage. At a certain amount of TIBB the donor ground state is lifted above the onset of the conduction band and the donor will be ionised. In the measurement the ionisation of the donor is seen as a peak in the dI/dV signal. In spatially resolved dI/dV maps the signal has a ring like structure. For higher applied voltages the diameter of the ring increases. By comparing the calculated TIBB and the voltage dependence of the lateral displacement of the measured peak a value of about 150 meV for the donor level can be extracted.

  10. Observation of removal of an Fmoc protecting group by scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kudo, H.; Okamoto, Y.; Kwak, K.J.; Fujihira, M

    2004-08-15

    We demonstrate here by imaging successive surface reactions in self-assembled monolayers (SAMs) on Au(1 1 1) at molecular scale with a scanning tunneling microscope (STM): (i) SAM matrices formation with 1-octanethiol on Au(1 1 1) in ethanol, (ii) insertion of N-Fmoc-aminooctanethiol into the SAM matrices in ethanol, and (iii) removal of the Fmoc protecting group with tris(2-aminoethyl)amine (TAEA). The total reaction is formation of SAMs containing a small amount of NH{sub 2} terminated molecules in the CH{sub 3} terminated SAM matrices. After the reaction of the protecting group with TAEA, STM imaging revealed the decrease in heights of the inserted molecules on average. We attributed this observation to removal of the protecting group by taking account of a convolution of electronic and topographic contributions to observed STM heights. Apparent areas of the terminal groups, however, became larger on removal. The increase in the areas was attributed to water adsorption to the NH{sub 2} terminal group under air.

  11. Scanning tunneling microscopy study of molecular growth structures of Gd@C82 on Cu(111)

    Institute of Scientific and Technical Information of China (English)

    Chen Jian; Qin Zhi-Hui; Pan Jin-Bo; Lu Shuang-Zan; Du Shi-Xuan; Gao Hong-Jun; Cao Geng-Yu

    2013-01-01

    The coverage and temperature-dependent nucleation behaviors of the Gd@C82 metallofullerenes on Cu(111) have been studied by low-temperature scanning tunneling microscopy (LT-STM) in detail.Upon molecular deposition at low temperature,Gd@C82 molecules preferentially decorate the steps and nucleate into single layer islands with increasing coverage.Further annealing treatment leads some of the Gd@C82 molecules to assemble into bright and dim patches,which are correlated to the adsorption induced substrate reconstruction.Upon sufficient thermal activation,Gd@C82 molecules sink into the Cu(111) surface one-copper-layer-deep,forming hexagonal close-packed molecular islands with intra-molecular details observed as striped patterns.By considering the commensurability between the Gd@C82 nearest-neighbor distance and the lattice of the underlying Cu(111),we clearly identified two kinds of in-plane molecular arrangements as ((√)19 × (√)19)R23.4° and ((√)19 × (√)19)R36.6° with respect to Cu(111).Within the assembled Gd@C82 molecular,island molecules with dim-bright contrast are spatially distributed,which may be modulated by the preexisted species on Cu(111).

  12. Scanning Tunneling Microscopy of the π Magnetism of a Single Carbon Vacancy in Graphene

    Science.gov (United States)

    Zhang, Yu; Li, Si-Yu; Huang, Huaqing; Li, Wen-Tian; Qiao, Jia-Bin; Wang, Wen-Xiao; Yin, Long-Jing; Bai, Ke-Ke; Duan, Wenhui; He, Lin

    2016-10-01

    Pristine graphene is strongly diamagnetic. However, graphene with single carbon atom defects could exhibit paramagnetism. Theoretically, the π magnetism induced by the monovacancy in graphene is characteristic of two spin-split density-of-states (DOS) peaks close to the Dirac point. Since its prediction, many experiments have attempted to study this π magnetism in graphene, whereas only a notable resonance peak has been observed around the atomic defects, leaving the π magnetism experimentally elusive. Here, we report direct experimental evidence of π magnetism by using a scanning tunneling microscope. We demonstrate that the localized state of the atomic defects is split into two DOS peaks with energy separations of several tens of meV. Strong magnetic fields further increase the energy separations of the two spin-polarized peaks and lead to a Zeeman-like splitting. Unexpectedly, the effective g factor around the atomic defect is measured to be about 40, which is about 20 times larger than the g factor for electron spins.

  13. Adsorption stages of O on Ru(0001) studied by means of scanning tunnelling microscopy

    CERN Document Server

    Meinel, K; Ammer, C; Beckmann, A; Neddermeyer, H

    1997-01-01

    The adsorption of O on Ru(0001) at a temperature of 400 K is studied in detail by means of scanning tunnelling microscopy (STM). With increasing O coverage, an ordered p(2x2) structure develops, followed by a p(2x1) structure. While the p(2x2) structure grows via island formation, the p(2x1) structure is abruptly formed by a disorder - order phase transition. After completion of the p(2x2) structure at a coverage of 0.25 ML, the surface develops a rough structure where the (2x2) units remain visible but appear with different heights. As the origin of this phenomenon, we propose additional O-O interactions and/or subsurface O due to the increase in O coverage. At coverages between 0.3 monolayer (ML) and 0.35 ML, different preformations of the p(2x1) structure are observed. First, small fragments of p(2x1) rows develop, which are randomly distributed over the surface and rotated by 120 deg. with respect to each other. They grow in one dimension and induce a criss-cross arrangement of linear chains of O atoms. T...

  14. Odd-Even Sequence Effect of Surface-Mediated Peptide Assemblies Observed by Scanning Tunneling Microscopy

    Institute of Scientific and Technical Information of China (English)

    郭元元; 王晨轩; 侯静菲; 杨爱华; 张雪梅; 王宜冰; 张敏; 杨延莲; 王琛

    2012-01-01

    The peptide assembly structures of polyglutamine (PolyQ) have been studied by using scanning tunneling microscopy (STM) with high spatial resolution in ambient conditions. 4,4'-Bipyridyl (4Bpy) was introduced into the PolyQ7 and PolyQ8 peptide assemblies for labeling the C-termini of the peptides. The fine structures of the 4Bpy-PolyQ7 and 4Bpy-PolyQ8 co-assemblies are observed, and the statistics of the apparent peptide strand length reveal different length distributions for PolyQ7 and PolyQs. One predominant apparent peptide strand length is ob- served for PolyQ7 reflecting one predominant peptide conformation in assembly structures, while three major ap- parent strand lengths can be identified with PolyQ8 reflecting three co-existing peptide conformations in peptide as- semblies. Such drastic difference in assembling characteristics can be considered as a reflection of asymmetric ad- sorption effect ofpeptides relating to odd-even residue numbers of PolyQ7 and PolyQ8,

  15. Theoretical Scanning Tunnelling Microscopy Images of Metal (Fe, Co, Ni and Cu) Phthalocyanines

    Institute of Scientific and Technical Information of China (English)

    李群祥; 朱清时; 袁岚峰; 杨金龙; 侯建国

    2001-01-01

    The scanning tunnelling microscopy (STM) images of isolated iron phthalocyanine (FePc), cobalt phthalocyanine (CoPc), nickel phthalocyanine (NiPc) and copper phthalocyanine (CuPc) are simulated theoretically. All the simulated STM images show submolecular structures and reproduce well the features of the experimental images. The results show that there is a strong dependence of the STM images on the ion valence configuration of the metal ion. At the small tip bias voltages of less than 0.5 V, the central metal ions in NiPc and CuPc appear as holes in the molecular images, while they are the highlighted bumps in FePc and CoPc. The simulated images are interpreted by the fact that both FePc and CoPc systems have a significant dz2 character near the Fermi level while the NiPc and CuPc systems do not. Moreover, we predict that the central nickel ion for NiPc appears as a highlighted point when the tip bias voltage is larger than 0.7 V.

  16. Scanning Tunneling Spectroscopy Study of Single Layer Step Edges on Si (100) Surfaces

    Science.gov (United States)

    Wang, Xiqiao; Namboodiri, Pradeep; Li, Kai; Deng, Xiao; Silver, Richard

    Advanced Hydrogen lithography enables the fabrication of atomically precise donor-based quantum devices on Si(100) surfaces. Understanding the defect and step edge interaction with local electronic and geometric structures is needed to properly interpret device measurement results. Low temperature Si epitaxy, used to encapsulate devices, introduces island growth and step edges near/above buried donor nanostructures, presenting a real challenge in relocating and characterizing buried donor devices using Scanning Tunneling Microscopy/Spectroscopy (STM/STS). We present spatially resolved STS results across single layer steps on Si(100) surfaces. While the electronic properties across SA steps were found to be very similar to that on flat terraces, we observed an edge induced gap state on rebonded SB step edges, which was assigned to the unpaired dangling bond state at the lower edge atom of the rebonded SB steps. In addition, we used computational simulation within Bardeen's formalism to probe the influence of subsurface doping density profiles on the observed STS features over step edges and other defects. This study will help to elucidate the role played by surface step edges and subsurface doping densities in characterizing surface and subsurface nanostructures using STS/STM.

  17. Shape control of QDs studied by cross-sectional scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Keizer, J. G.; Bozkurt, M.; Bocquel, J.; Koenraad, P. M. [Eindhoven University of Technology, Eindhoven (Netherlands)

    2011-05-15

    In this cross-sectional scanning tunneling microscopy study we investigated various techniques to control the shape of self-assembled quantum dots (QDs) and wetting layers (WLs). The result shows that application of an indium flush during the growth of strained InGaAs/GaAs QD layers results in flattened QDs and a reduced WL. The height of the QDs and WLs could be controlled by varying the thickness of the first capping layer. Concerning the technique of antimony capping we show that the surfactant properties of Sb result in the preservation of the shape of strained InAs/InP QDs during overgrowth. This could be achieved by both a growth interrupt under Sb flux and capping with a thin GaAsSb layer prior to overgrowth of the uncapped QDs. The technique of droplet epitaxy was investigated by a structural analysis of strain free GaAs/AlGaAs QDs. We show that the QDs have a Gaussian shape, that the WL is less than 1 bilayer thick, and that minor intermixing of Al with the QDs takes place.

  18. TOPICAL REVIEW: Active nanocharacterization of nanofunctional materials by scanning tunneling microscopy

    Directory of Open Access Journals (Sweden)

    Daisuke Fujita and Keisuke Sagisaka

    2008-01-01

    Full Text Available Recent developments in the application of scanning tunneling microscopy (STM to nanofabrication and nanocharacterization are reviewed. The main focus of this paper is to outline techniques for depositing and manipulating nanometer-scale structures using STM tips. Firstly, the transfer of STM tip material through the application of voltage pulses is introduced. The highly reproducible fabrication of metallic silver nanodots and nanowires is discussed. The mechanism is thought to be spontaneous point-contact formation caused by field-enhanced diffusion to the apex of the tip. Transfer through the application of z-direction pulses is also introduced. Sub-nanometer displacement pulses along the z-direction form point contacts that can be used for reproducible nanodot deposition. Next, the discovery of the STM structural manipulation of surface phases is discussed. It has been demonstrated that superstructures on Si(001 surfaces can be reverse-manipulated by controlling the injected carriers. Finally, the fabrication of an atomic-scale one-dimensional quantum confinement system by single-atom deposition using a controlled point contact is presented. Because of its combined nanofabrication and nanocharacterization capabilities, STM is a powerful tool for exploring the nanotechnology and nanoscience fields.

  19. Strong tip-sample coupling in thermal radiation scanning tunneling microscopy

    CERN Document Server

    Joulain, Karl; Chapuis, Pierre-Olivier; De Wilde, Yannick; Babuty, Arthur; Henkel, Carsten

    2014-01-01

    We analyze how a probing particle modifies the infrared electromagnetic near field of a sample. The particle, described by electric and magnetic polarizabilities, represents the tip of an apertureless scanning optical near-field microscope (SNOM). We show that the interaction with the sample can be accounted for by ascribing to the particle dressed polarizabilities that combine the effects of image dipoles with retardation. When calculated from these polarizabilities, the SNOM signal depends only on the fields without the perturbing tip. If the studied surface is not illuminated by an external source but heated instead, the signal is closely related to the projected electromagnetic local density of states (EM-LDOS). Our calculations provide the link between the measured far-field spectra and the sample's optical properties.We also analyze the case where the probing particle is hotter than the sample and evaluate the impact of the dressed polarizabilities on near-field radiative heat transfer. We show that suc...

  20. Demonstration of synchronised scanning Lidar measurements of 2D velocity fields in a boundary-layer wind tunnel

    Science.gov (United States)

    van Dooren, M. F.; Kühn, M.; PetroviĆ, V.; Bottasso, C. L.; Campagnolo, F.; Sjöholm, M.; Angelou, N.; Mikkelsen, T.; Croce, A.; Zasso, A.

    2016-09-01

    This paper combines the currently relevant research methodologies of scaled wind turbine model experiments in wind tunnels with remote-sensing short-range WindScanner Lidar measurement technology. The wind tunnel of the Politecnico di Milano was equipped with three wind turbine models and two short-range WindScanner Lidars to demonstrate the benefits of synchronised scanning Lidars in such experimental surroundings for the first time. The dual- Lidar system can provide fully synchronised trajectory scans with sampling time scales ranging from seconds to minutes. First, staring mode measurements were compared to hot wire probe measurements commonly used in wind tunnels. This yielded goodness of fit coefficients of 0.969 and 0.902 for the 1 Hz averaged u- and v-components of the wind speed, respectively, validating the 2D measurement capability of the Lidar scanners. Subsequently, the measurement of wake profiles on a line as well as wake area scans were executed to illustrate the applicability of Lidar scanning to measuring small scale wind flow effects. The downsides of Lidar with respect to the hot wire probes are the larger measurement probe volume and the loss of some measurements due to moving blades. In contrast, the benefits are the high flexibility in conducting both point measurements and area scanning, and the fact that remote sensing techniques do not disturb the flow while measuring. The research campaign revealed a high potential for using short-range WindScanner Lidar for accurately measuring small scale flow structures in a wind tunnel.

  1. High Pressure Scanning Tunneling Microscopy Studies of AdsorbateStructure and Mobility during Catalytic Reactions: Novel Design of anUltra High Pressure, High Temperature Scanning Tunneling MicroscopeSystem for Probing Catalytic Conversions

    Energy Technology Data Exchange (ETDEWEB)

    Tang, David Chi-Wai [Univ. of California, Berkeley, CA (United States)

    2005-05-16

    The aim of the work presented therein is to take advantage of scanning tunneling microscope’s (STM) capability for operation under a variety of environments under real time and at atomic resolution to monitor adsorbate structures and mobility under high pressures, as well as to design a new generation of STM systems that allow imaging in situ at both higher pressures (35 atm) and temperatures (350 °C).

  2. New Applications of Scanning Tunneling Microscopy in Air, Liquids, and Ultra-High Vacuum

    Science.gov (United States)

    Dovek, Moris Musa

    Scanning tunneling microscopy (STM) offers a wide range of applications besides being a high resolution tool for atomic scale surface structure determination. We present three applications that are of particular relevance to integrated circuit fabrication: molecular imaging of ultrathin resists, nanometer scale lithography, and epitaxial growth characterization on an atomically flat substrate. The use of thin organic films as ultrathin resists for nanometer scale fabrication and information recording requires an understanding of their microstructure. We have used the Langmuir-Blodgett technique to prepare and the STM to study monolayer and submonolayer films of poly(octadecylacrylate) (PODA) and poly(methylmethacrylate) (PMMA) on graphite. One striking feature was the degree of order observed; a second was the morphological differences between films of submonolayer thickness and those of at least one monolayer. We were also able to locally modify and apparently cut through the polymer fibrils by pulsing the gap voltage in excess of 4 V. Nanometer-scale surface modification has important potential applications in areas such as high resolution lithography for solid-state devices or high density data storage. The STM can be used for surface modification by either mechanical indentation of the surface with the very sharp tip or by applying short voltage or current pulses across the tunnel junction. We review some of the mechanical writing techniques on Au(111), which render depressions of approximately 100 A in diameter. We also introduce a technique for writing permanent features on graphite of 40 A average and 20 A minimum diameter with an average resolvable spacing of 60 A. We found the reliability of the writing process on graphite to depend strongly on the presence of water vapor. STM can also be used to analyze epitaxial growth on an atomic scale, a resolution range not available to SEM, HRTEM, and REM, which have so far been the only tools used to verify

  3. First-principles theory of inelastic currents in a scanning tunneling microscope

    DEFF Research Database (Denmark)

    Stokbro, Kurt; Hu, Ben Yu-Kuang; Thirstrup, C.;

    1998-01-01

    A first-principles theory of inelastic tunneling between a model probe tip and an atom adsorbed on a surface is presented, extending the elastic tunneling theory of Tersoff and Hamann. The inelastic current is proportional to the change in the local density of states at the center of the tip due ...

  4. High-yield synthesis of conductive carbon nanotube tips for multiprobe scanning tunneling microscope.

    Science.gov (United States)

    Konishi, H; Murata, Y; Wongwiriyapan, W; Kishida, M; Tomita, K; Motoyoshi, K; Honda, S; Katayama, M; Yoshimoto, S; Kubo, K; Hobara, R; Matsuda, I; Hasegawa, S; Yoshimura, M; Lee, J-G; Mori, H

    2007-01-01

    We have established a fabrication process for conductive carbon nanotube (CNT) tips for multiprobe scanning tunneling microscope (STM) with high yield. This was achieved, first, by attaching a CNT at the apex of a supporting W tip by a dielectrophoresis method, second, by reinforcing the adhesion between the CNT and the W tip by electron beam deposition of hydrocarbon and subsequent heating, and finally by wholly coating it with a thin metal layer by pulsed laser deposition. More than 90% of the CNT tips survived after long-distance transportation in air, indicating the practical durability of the CNT tips. The shape of the CNT tip did not change even after making contact with another metal tip more than 100 times repeatedly, which evidenced its mechanical robustness. We exploited the CNT tips for the electronic transport measurement by a four-terminal method in a multiprobe STM, in which the PtIr-coated CNT portion of the tip exhibited diffusive transport with a low resistivity of 1.8 kOmega/microm. The contact resistance at the junction between the CNT and the supporting W tip was estimated to be less than 0.7 kOmega. We confirmed that the PtIr thin layer remained at the CNT-W junction portion after excess current passed through, although the PtIr layer was peeled off on the CNT to aggregate into particles, which was likely due to electromigration or a thermally activated diffusion process. These results indicate that the CNT tips fabricated by our recipe possess high reliability and reproducibility sufficient for multiprobe STM measurements.

  5. Cross-Sectional Scanning Tunneling Microscopy of InAsSb/InAsP Superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Allerman, A.A.; Biefeld, R.M.; Yu, E.T.; Zuo, S.L.

    1999-02-10

    Cross-sectional scanning tunneling microscopy has been used to characterize compositional structure in InAs{sub 0.87}Sb{sub 0.13}/InAs{sub 0.73}P{sub 0.27} and InAs{sub 0.83}Sb{sub 0.17}/InAs{sub 0.60}P{sub 0.40} strained-layer superlattice structures grown by metal-organic chemical vapor deposition. High-resolution STM images of the (110) cross section reveal compositional features within both the InAs{sub x}Sb{sub 1{minus}x} and InAs{sub y}P{sub 1{minus}y} alloy layers oriented along the [{bar 1}12] and [1{bar 1}2] directions--the same as those in which features would be observed for CuPt-B type ordered alloys. Typically one variant dominates in a given area, although occasionally the coexistence of both variants is observed. Furthermore, such features in the alloy layers appear to be correlated across heterojunction interfaces in a manner that provides support for III-V alloy ordering models which suggest that compositional order can arise from strain-induced order near the surface of an epitaxially growing crystal. Finally, atomically resolved (1{bar 1}0) images obtained from the InAs{sub 0.87}Sb{sub 0.13}/InAs{sub 0.73}P{sub 0.27} sample reveal compositional features in the [112] and [{bar 1}{bar 1}2] directions, i.e., those in which features would be observed for CuPt-A type ordering.

  6. Self-assembly of tetraalkoxydinaphthophenazines in monolayers on HOPG by scanning tunneling microscopy

    Science.gov (United States)

    Jaroch, Tomasz; Maranda-Niedbala, Agnieszka; Kotwica, Kamil; Wamil, Damian; Bujak, Piotr; Pron, Adam; Nowakowski, Robert

    2015-11-01

    2D supramolecular organization in monolayers of tetraalkoxydinaphthophenazines, a new group of solution processable organic semiconductors obtained by simple functionalization of indanthrone (6,15-dihydrodinaphtho[2,3-a:2‧,3‧-h]phenazine-5,9,14,18-tetraone), an old intractable dye, was investigated by scanning tunneling microscopy (STM). Five derivatives with increasing substituent length from butoxy (P-C4) to dodecyloxy (P-C12) were tested. All derivatives show a strong tendency to form ordered monolayers on HOPG graphite via self-assembly which constitute of rows of molecules oriented in one direction. However, local arrangement in this 2D supramolecular organization is strongly dependent on the substituent length. Two tendencies in the structural evolution are observed. For butoxy (P-C4), hexyloxy (P-C6) and octyloxy (P-C8) derivatives increasing substituent length results in the transformation of the structure governed by the conjugated core interactions to the one in which mutual interactions of the alkoxy groups dominate. As a consequence, for P-C8 a very stable 2D structure is obtained with a nearly rectangular 2D unit cell, as a consequence of the alkoxy group interdigitation in two perpendicular directions. With further increase of the substituent length to decyloxy (P-C10) and dodecyloxy (P-C12) a different effect is observed-a directional expansion of the unit cell along the longitudinal axis of the molecules. This is a consequence of structural nonequivalence of the alkoxy groups attached to the same aromatic ring.

  7. A high-stability scanning tunneling microscope achieved by an isolated tiny scanner with low voltage imaging capability

    Science.gov (United States)

    Wang, Qi; Hou, Yubin; Wang, Junting; Lu, Qingyou

    2013-11-01

    We present a novel homebuilt scanning tunneling microscope (STM) with high quality atomic resolution. It is equipped with a small but powerful GeckoDrive piezoelectric motor which drives a miniature and detachable scanning part to implement coarse approach. The scanning part is a tiny piezoelectric tube scanner (industry type: PZT-8, whose d31 coefficient is one of the lowest) housed in a slightly bigger polished sapphire tube, which is riding on and spring clamped against the knife edges of a tungsten slot. The STM so constructed shows low back-lashing and drifting and high repeatability and immunity to external vibrations. These are confirmed by its low imaging voltages, low distortions in the spiral scanned images, and high atomic resolution quality even when the STM is placed on the ground of the fifth floor without any external or internal vibration isolation devices.

  8. Visualization of postoperative anterior cruciate ligament reconstruction bone tunnels: Reliability of standard radiographs, CT scans, and 3D virtual reality images

    NARCIS (Netherlands)

    D.E. Meuffels (Duncan); J.W. Potters (Jan Willem); A.H.J. Koning (Anton); C.H. Brown Jr Jr. (Charles); J.A.N. Verhaar (Jan); M. Reijman (Max)

    2011-01-01

    textabstractBackground and purpose: Non-anatomic bone tunnel placement is the most common cause of a failed ACL reconstruction. Accurate and reproducible methods to visualize and document bone tunnel placement are therefore important. We evaluated the reliability of standard radiographs, CT scans, a

  9. Features in Quasi-particle Excitations and Tunnelling Spectra due to Coupling to Spin Fluctuations in High-Tc Cuprates

    Institute of Scientific and Technical Information of China (English)

    赵力; 李建新; 龚昌德; 赵柏儒

    2002-01-01

    In a self-consistent mean-field treatment of the two-dimensional t - t' - J model, we theoretically examine thecoupling of in-plane quasi-particles to the antiferromagnetic spin fluctuations in high-Tc superconductors, whichrenormalizes the fermionic self-energy. We reproduce the characteristic peak,lip-hump structure observed notonly in angle-resolved photoemission spectroscopy, but also in superconductor-insulator-normal metal junctionsand scanning tunnelling microscopy experiments. We consider the evolution of this structure with doping. Itis shown that this kind of coupling can account for many anomalous properties of high-Tc superconductors insuperconducting states.

  10. Co on Pt(111) studied by spin-polarized scanning tunneling microscopy and spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Meier, F.K.

    2006-07-01

    In this thesis the electronic properties of the bare Pt(111) surface, the structural, electronic, and magnetic properties of monolayer and double-layer high Co nanostructures as well as the spin-averaged electronic structure of single Co atoms on Pt(111) were studied by low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS). The experiments on the bare Pt(111) surface and on single Co atoms have been performed in an STM facility operating at temperatures of down to 0.3 K and at magnetic fields of up to 14 T under ultra-high vacuum conditions. The facility has been taken into operation within the time period of this thesis and its specifications were tested by STS measurements. These characterization measurements show a very high stability of the tunneling junction and an energy resolution of about 100 {mu}eV, which is close to the thermal limit. The investigation of the electronic structure of the bare Pt(111) surface reveals the existence of an unoccupied surface state. By a comparison of the measured dispersion to first-principles electronic structure calculations the state is assigned to an sp-derived surface band at the lower boundary of the projected bulk band gap. The surface state exhibits a strong spin-orbit coupling induced spin splitting. The close vicinity to the bulk bands leads to a strong linear contribution to the dispersion and thus to a deviant appearance in the density of states in comparison to the surface states of the (111) surfaces of noble metals. A detailed study of Co monolayer and double-layer nanostructures on the Pt(111) surface shows that both kinds of nanostructures exhibit a highly inhomogeneous electronic structure which changes at the scale of only a few Aa due to a strong stacking dependence with respect to the Pt(111) substrate. With the help of first principles calculations the different spectroscopic appearance for Co atoms within the Co monolayer is assigned to a stacking dependent hybridization of Co states

  11. An Approach to Long-Range Electron Transfer Mechanisms in Metalloproteins: In situ Scanning Tunneling Microscopy with Submolecular Resolution

    Science.gov (United States)

    Friis, Esben P.; Andersen, Jens E. T.; Kharkats, Yu. I.; Kuznetsov, A. M.; Nichols, R. J.; Zhang, J.-D.; Ulstrup, Jens

    1999-02-01

    In situ scanning tunneling microscopy (STM) of redox molecules, in aqueous solution, shows interesting analogies and differences compared with interfacial electrochemical electron transfer (ET) and ET in homogeneous solution. This is because the redox level represents a deep indentation in the tunnel barrier, with possible temporary electronic population. Particular perspectives are that both the bias voltage and the overvoltage relative to a reference electrode can be controlled, reflected in spectroscopic features when the potential variation brings the redox level to cross the Fermi levels of the substrate and tip. The blue copper protein azurin adsorbs on gold(111) via a surface disulfide group. Well resolved in situ STM images show arrays of molecules on the triangular gold(111) terraces. This points to the feasibility of in situ STM of redox metalloproteins directly in their natural aqueous medium. Each structure also shows a central brighter contrast in the constant current mode, indicative of 2- to 4-fold current enhancement compared with the peripheral parts. This supports the notion of tunneling via the redox level of the copper atom and of in situ STM as a new approach to long-range electron tunneling in metalloproteins.

  12. A theoretical analysis of the spin dynamics of magnetic adatoms traced by time-resolved scanning tunneling spectroscopy

    Science.gov (United States)

    Schüler, M.; Pavlyukh, Y.; Berakdar, J.

    2012-04-01

    Inelastic scanning tunneling microscopy (STM) has recently been shown (Loth et al 2010 Science 329 1628) to be extendable to access the nanosecond, spin-resolved dynamics of magnetic adatoms and molecules. Here we analyze this novel tool theoretically by considering the time-resolved spin dynamics of a single adsorbed Fe atom excited by a tunneling current pulse from a spin-polarized STM tip. The adatom spin configuration can be controlled and probed by applying voltage pulses between the substrate and the spin-polarized STM tip. We demonstrate how, in a pump-probe manner, the relaxation dynamics of the sample spin is manifested in the spin-dependent tunneling current. Our model calculations are based on the scattering theory in a wave-packet formulation. The scheme is non-perturbative and, hence, is valid for all voltages. The numerical results for the tunneling probability and the conductance are contrasted with the predictions of simple analytical models and compared with experiments.

  13. The Nanomanipulator: a Virtual-Reality Interface to a Scanning Tunneling Microscope.

    Science.gov (United States)

    Taylor, Russell Morton, II

    We have developed a virtual-reality interface to a scanning tunneling microscope (STM); the resulting system is called the Nanomanipulator. The user interface comprises a stereoscopic color head-mounted display, a force-feedback remote manipulator master station, and a high-performance graphics computer. It provides the illusion of a surface floating in space in front of the user. The user's hand gestures are translated into commands that are sent to the STM in real time; the returned video and haptic signals allow the user to see and feel the surface topography and to control the timing and location of voltage pulses applied between the tip of the STM probe and the sample under study. My thesis is that a virtual-reality interface is a powerful and effective user interface to an STM--allowing qualitatively different types of experiments to be performed. The success of our investigations using this system demonstrates the validity of the thesis. We have used the Nanomanipulator to examine various surfaces and to perform surface modification experiments. This investigation has led to new insight into the meaning of certain surface features and into the mechanisms by which voltage pulses change the tip and sample. These insights were the direct results of the real-time visualization and the more interactive nature of our system compared to standard methods. The key to the success of the Nanomanipulator system is that it provides an intuitive two-way interface to the instrument. Raw data from an STM is not in a format easily understood by a scientist, and the Etch-a-Sketch type of controls required for positioning an STM tip are neither natural nor familiar to a user. The Nanomanipulator system acts as a translator between the instrument and the scientist, allowing the scientist to concentrate on interacting with the surface under study rather than on the computer interface or the STM itself. This system seeks to put the scientists on the surface, in control, while the

  14. Bimetallic Catalysts and Platinum Surfaces Studied by X-ray Absorption Spectroscopy and Scanning Tunnelling Microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Roenning, Magnus

    2000-07-01

    Bimetallic catalyst systems used in Fischer-Tropsch synthesis (Co-Re/Al{sub 2}O{sub 3}) and in the naphtha reforming process (Pt-Re/Al{sub 2}O{sub 3}) have been studied in situ using X-ray absorption spectroscopy (EXAFS). Additionally, the adsorption of ethene on platinum single crystal surfaces has been investigated using scanning tunnelling microscopy. In situ EXAFS at the cobalt K absorption edge have been carried out at 450{sup o}C on the hydrogen reduction of a rhenium-promoted Co{sub 3}O{sub 4}/Al{sub 2}O{sub 3} catalyst. Reductions carried out using 100% hydrogen and 5% hydrogen in helium gave different results. Whereas the reduction using dilute hydrogen leads to bulk-like metallic cobalt particles (hcp or fcc), reaction with pure hydrogen yields a more dispersed system with smaller cobalt metal particles (< 40 A). The results are rationalised in terms of different degrees of reoxidation of cobalt by the higher and lower concentrations of water generated during the reduction of cobalt oxide by 100% and 5% hydrogen, respectively. Additionally, in both reduction protocols a small fraction (3 -4 wt%) of the cobalt content is randomly dispersed over the tetrahedral vacancies of the alumina support. This dispersion occurs during reduction and not calcination. The cobalt in these sites cannot be reduced at 450 {sup o}C. The local environments about the rhenium atoms in Co-Re/{gamma}-A1{sub 2}O{sub 3} catalyst after different reduction periods have been studied by X-ray absorption spectroscopy. A bimetallic catalyst containing 4.6 wt% cobalt and 2 wt% rhenium has been compared with a corresponding monometallic sample with 2 wt% rhenium on the same support. The rhenium L{sub III} EXAFS analysis shows that bimetallic particles are formed after reduction at 450{sup o}C with the average particle size being 10-15 A. Rhenium is shown to be reduced at a later stage than cobalt. The fraction of cobalt atoms entering the support obstructs the access to the support for the

  15. Bimetallic Catalysts and Platinum Surfaces Studied by X-ray Absorption Spectroscopy and Scanning Tunnelling Microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Roenning, Magnus

    2000-07-01

    Bimetallic catalyst systems used in Fischer-Tropsch synthesis (Co-Re/Al{sub 2}O{sub 3}) and in the naphtha reforming process (Pt-Re/Al{sub 2}O{sub 3}) have been studied in situ using X-ray absorption spectroscopy (EXAFS). Additionally, the adsorption of ethene on platinum single crystal surfaces has been investigated using scanning tunnelling microscopy. In situ EXAFS at the cobalt K absorption edge have been carried out at 450{sup o}C on the hydrogen reduction of a rhenium-promoted Co{sub 3}O{sub 4}/Al{sub 2}O{sub 3} catalyst. Reductions carried out using 100% hydrogen and 5% hydrogen in helium gave different results. Whereas the reduction using dilute hydrogen leads to bulk-like metallic cobalt particles (hcp or fcc), reaction with pure hydrogen yields a more dispersed system with smaller cobalt metal particles (< 40 A). The results are rationalised in terms of different degrees of reoxidation of cobalt by the higher and lower concentrations of water generated during the reduction of cobalt oxide by 100% and 5% hydrogen, respectively. Additionally, in both reduction protocols a small fraction (3 -4 wt%) of the cobalt content is randomly dispersed over the tetrahedral vacancies of the alumina support. This dispersion occurs during reduction and not calcination. The cobalt in these sites cannot be reduced at 450 {sup o}C. The local environments about the rhenium atoms in Co-Re/{gamma}-A1{sub 2}O{sub 3} catalyst after different reduction periods have been studied by X-ray absorption spectroscopy. A bimetallic catalyst containing 4.6 wt% cobalt and 2 wt% rhenium has been compared with a corresponding monometallic sample with 2 wt% rhenium on the same support. The rhenium L{sub III} EXAFS analysis shows that bimetallic particles are formed after reduction at 450{sup o}C with the average particle size being 10-15 A. Rhenium is shown to be reduced at a later stage than cobalt. The fraction of cobalt atoms entering the support obstructs the access to the support for the

  16. Discretization of Electronic States in Large InAsP/InP Multilevel Quantum Dots Probed by Scanning Tunneling Spectroscopy

    Science.gov (United States)

    Fain, B.; Robert-Philip, I.; Beveratos, A.; David, C.; Wang, Z. Z.; Sagnes, I.; Girard, J. C.

    2012-03-01

    The topography and the electronic structure of InAsP/InP quantum dots are probed by cross-sectional scanning tunneling microscopy and spectroscopy. The study of the local density of states in such large quantum dots confirms the discrete nature of the electronic levels whose wave functions are measured by differential conductivity mapping. Because of their large dimensions, the energy separation between the discrete electronic levels is low, allowing for quantization in both the lateral and growth directions as well as the observation of the harmonicity of the dot lateral potential.

  17. First-Principles Calculations of Scanning-Tunnelling-Microscopy Images of Ar Atoms Adsorbed on a Graphite Sheet

    Institute of Scientific and Technical Information of China (English)

    白玉林; 周晓林; 陈向荣; 芶清泉

    2003-01-01

    Local density approximation within the framework of the density functional theory is applied to calculate the scanning tunnelling microscopy(STM)images of Ar atoms adsorbed on a graphite sheet(Ar/graphite system).It is found that the optimal site of adsorbed Ar atom is at the top of the centre of the carbon hexagon and its equilibrium distance from the graphite surface is about 3.20A.We demonstrate that it is the hybridization of the C 2 p electronic states with the Ar 3 p and 4 s electronic states,which renders Ar atoms visible in the STM experiment.

  18. Characterization of Si3N4/SiO2 optical channel waveguides by photon scanning tunneling microscopy

    Science.gov (United States)

    Wang, Yan; Chudgar, Mona H.; Jackson, Howard E.; Miller, Jeffrey S.; De Brabander, Gregory N.; Boyd, Joseph T.

    1993-01-01

    Photon scanning tunneling microscopy (PSTM) is used to characterize Si3N4/Si02 optical channel waveguides being used for integrated optical-micromechanical sensors. PSTM utilizes an optical fiber tapered to a fine point which is piezoelectrically positioned to measure the decay of the evanescent field intensity associated with the waveguide propagating mode. Evanescent field decays are recorded for both ridge channel waveguides and planar waveguide regions. Values for the local effective refractive index are calculated from the data for both polarizations and compared to model calculations.

  19. Electronic structures of one-dimensional metal-molecule hybrid chains studied using scanning tunneling microscopy and density functional theory.

    Science.gov (United States)

    Chung, Kyung-Hoon; Koo, Bon-Gil; Kim, Howon; Yoon, Jong Keon; Kim, Ji-Hoon; Kwon, Young-Kyun; Kahng, Se-Jong

    2012-05-28

    The electronic structures of self-assembled hybrid chains comprising Ag atoms and organic molecules were studied using scanning tunneling microscopy (STM) and spectroscopy (STS) in parallel with density functional theory (DFT). Hybrid chains were prepared by catalytic breaking of Br-C bonds in 4,4″-dibromo-p-terphenyl molecules, followed by spontaneous formation of Ag-C bonds on Ag(111). An atomic model was proposed for the observed hybrid chain structures. Four electronic states were resolved using STS measurements, and strong energy dependence was observed in STM images. These results were explained using first-principles calculations based on DFT.

  20. A variable-temperature nanostencil compatible with a low-temperature scanning tunneling microscope/atomic force microscope

    Energy Technology Data Exchange (ETDEWEB)

    Steurer, Wolfram, E-mail: wst@zurich.ibm.com; Gross, Leo; Schlittler, Reto R.; Meyer, Gerhard [IBM Research-Zurich, 8803 Rüschlikon (Switzerland)

    2014-02-15

    We describe a nanostencil lithography tool capable of operating at variable temperatures down to 30 K. The setup is compatible with a combined low-temperature scanning tunneling microscope/atomic force microscope located within the same ultra-high-vacuum apparatus. The lateral movement capability of the mask allows the patterning of complex structures. To demonstrate operational functionality of the tool and estimate temperature drift and blurring, we fabricated LiF and NaCl nanostructures on Cu(111) at 77 K.

  1. Demonstration of synchronised scanning Lidar measurements of 2D velocity fields in a boundary-layer wind tunnel

    DEFF Research Database (Denmark)

    van Dooren, M F; Kühn, M.; Petrovic, V.;

    2016-01-01

    compared to hot wire probe measurements commonly used in wind tunnels. This yielded goodness of fit coefficients of 0.969 and 0.902 for the 1 Hz averaged u- and v-components of the wind speed, respectively, validating the 2D measurement capability of the Lidar scanners. Subsequently, the measurement...... to moving blades. In contrast, the benefits are the high flexibility in conducting both point measurements and area scanning, and the fact that remote sensing techniques do not disturb the flow while measuring. The research campaign revealed a high potential for using short-range WindScanner Lidar...

  2. Scanning tunneling microscopy and spectroscopy of ion-bombarded Si(111) and Si(100) surfaces

    NARCIS (Netherlands)

    Zandvliet, H.J.W.; Elswijk, H.B.; Loenen, van E.J.; Tsong, I.S.T.

    1992-01-01

    Surfaces of Si(111)-(7×7) and Si(100)-(2×1) were bombarded by 3-keV Ar+ ions at doses of ≤1012 ions cm-2 to study the effect of individual ion impacts on the atomic structure of surfaces. Atom-resolved images show damaged regions of missing and displaced atoms. Current-imaging tunneling spectroscop

  3. Surface damage through grazing incidence ions investigated by scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Redinger, Alex

    2009-07-10

    Surface damage, caused by grazing incidence ions, is investigated with variable temperature scanning tunneling microscopy. The experiments are carried out on a Pt(111) crystal. The kinetic energy of noble gas ions is varied between 1-15 keV and the angle of incidence can be adjusted between {theta} = 78.5 and {theta} = 90 measured with respect to the surface normal. The damage patterns of single ion impacts, on flat terraces and at step edges of monoatomic height, are investigated at low surface temperatures. Ions hitting a flat terrace are usually specular reflected. The energy transfer from the ion to the crystal atoms is small and only little damage is produced. In contrast, at ascending step edges, which are illuminated by the ion beam, large angle scattering events occur. Sputtering, adatom and vacancy production is induced. However, a significant fraction of the ions, which hit step edges, enter the crystal and are guided in between two atomic layers parallel to the surface via small angle binary collisions. This steering process is denoted as subsurface channeling. The energy loss per length scale of the channeled particles is low, which results in long ion trajectories (up to 1000A). During the steering process, the ions produce surface damage. Depending on the ion species and the ion energy, adatom and vacancies or surface vacancy trenches of monoatomic width are observed. The surface damage can be used to track the path of the ion. This makes the whole trajectory of single ions with keV energy visible. The number of sputtered atoms per incident ion at ascending step edges, i.e. the step edge sputtering yield, is measured experimentally for different irradiation conditions. For {theta} = 86 , the sputtering yield is determined from the fluence dependent retraction of pre-existing illuminated step edges. An alternative method for the step edge sputtering yield determination, is the analysis of the concentration of ascending steps and of the removed amount

  4. Development and set-up of a new low temperature scanning tunneling microscope Applications on microscopy and spectroscopy of lanthanid metals

    CERN Document Server

    Mühlig, A

    2000-01-01

    Scanning tunneling microscopy and spectroscopy are suitable methods to study the physical properties of thin magnetic metal films with a thickness of a few monolayers. These systems are of current interest because they give insight into solids states physics of metals. This thesis deals with following subjects: Introduction to scanning tunneling microscopy. Set-up of a low temperatur scanning tunneling microscope. Growth of thin Co and lanthanid metal films on W(110). Interplay of morphologie and magnetism on the example of Co/W(110). Making of Gd wires which are only a few nanometers thin. Diskussion of the studied exchange splitting of a d-like surface state in a local moment magnet. Measurement of the lifetime of hot holes and hot electrons near the fermi edge.

  5. Local analysis of semiconductor nanoobjects by scanning tunneling atomic force microscopy

    Directory of Open Access Journals (Sweden)

    Natalia A. Lashkova

    2015-03-01

    Full Text Available The features of the current–voltage (I–V measurements in local regions of semiconductor nanostructures by conductive atomic force microscopy (AFM are discussed. The standard procedure of I–V measurements in conductive AFM leads not infrequently to the thermomechanical stresses in the sample and, as a consequence, nonreproducibility and unreliability of measurements. The technique of obtaining reproducible current–voltage characteristics is proposed. According to the technique, a series of measurements of the selected scanning area in the mode of conducting AFM should be taken, each at the certain value of the potential. According to a series of scans I–V curve at a particular point (for any point of the scan was plotted. The program is realized in the LabVIEW software. The proposed method extends the capabilities of scanning probe microscopy in the diagnosis of nanostructured semiconductor materials.

  6. Observation of Atomic Steps on Vicinal Si(111) Annealed in Hydrogen Gas Flow by Scanning Tunneling Microscopy

    Science.gov (United States)

    Kitahara, Kuninori; Ueda, Osamu

    1993-12-01

    The surface of vicinal Si(111) annealed in H2 flow was observed by equipping the chemical vapor deposition chamber with the scanning tunneling microscope. Samples were annealed at 1000°C for 10 min by passing an electric current under the H2 pressure of 7 Torr. Their surface morphology was compared with those annealed in ultrahigh vacuum (UHV) and in N2 flow at the same temperature. We found that the step motion during annealing in H2 was obviously smaller than that for annealing in UHV and N2. The multisteps formed during the annealing in UHV and N2 were not observed for H2 annealing except in the case of heating by direct current in the direction of lower to higher terraces. The mechanism of the interruption of the step motion is discussed from the viewpoint of the interaction between the surface and hydrogen.

  7. INTER-LAYER INTERACTION IN DOUBLE-WALLED CARBON NANOTUBES EVIDENCED BY SCANNING TUNNELING MICROSCOPY AND SPECTROSCOPY

    DEFF Research Database (Denmark)

    Giusca, Cristina E; Tison, Yann; Silva, S. Ravi P.

    2008-01-01

    Scanning Tunneling Microscopy and Spectroscopy have been used in an attempt to elucidate the electronic structure of nanotube systems containing two constituent shells. Evidence for modified electronic structure due to the inter-layer interaction in double-walled carbon nanotubes is provided...... and the overall electronic structure for double-walled carbon nanotubes, is demonstrated by our experiments, showing that the effect the inner tube has on the overall electronic structure of double-walled nanotubes cannot be neglected, and is key to the opto-electronic properties of the system. We postulate...... that previous analysis of the opto-electronic properties on multiple-walled carbon nanotubes based purely on the outer layer chirality of the tube needs significant modification based on new understanding brought forth with our analysis....

  8. Strongly compressed Bi (111) bilayer films on Bi{sub 2}Se{sub 3} studied by scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, K. F.; Yang, Fang; Song, Y. R. [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Liu, Canhua; Qian, Dong; Gao, C. L.; Jia, Jin-Feng [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093 (China)

    2015-09-21

    Ultra-thin Bi films show exotic electronic structure and novel quantum effects, especially the widely studied Bi (111) film. Using reflection high-energy electron diffraction and scanning tunneling microscopy, we studied the structure and morphology evolution of Bi (111) thin films grown on Bi{sub 2}Se{sub 3}. A strongly compressed, but quickly released in-plane lattice of Bi (111) is found in the first three bilayers. The first bilayer of Bi shows a fractal growth mode with flat surface, while the second and third bilayer show a periodic buckling due to the strong compression of the in-plane lattice. The lattice slowly changes to its bulk value with further deposition of Bi.

  9. Two-Dimensional Cysteine and Cystine Cluster Networks on Au(111) Disclosed by Voltammetry and in Situ Scanning Tunneling Microscopy

    DEFF Research Database (Denmark)

    Zhang, Jingdong; Chi, Qijin; Nielsen, Jens Ulrik;

    2000-01-01

    Microscopic structures for molecular monolayers of L-cysteine and L-cystine assembled on Au(111) have been disclosed by employing electrochemistry and in situ scanning tunneling microscopy (STM). HighresolutionSTMimages show that the adlayers of both cyteine and cystine exhibit highly......-ordered networklike clusters with (3x3 6)R30° structure. By combining the surface coverage estimated from voltammetric data, each cluster is demonstrated to include six individual cysteine molecules or three cystine molecules. As a comparison, no cluster structure is observed for the 1-butanethiol adlayer prepared...... and examined under the same conditions as those for cysteine and cystine. This suggests that intermolecular and intramolecular hydrogen bonds among adsorbed cysteine or cystine molecules could be responsible for the origin of the cluster-network structures for the adlayers. Several models are proposed and used...

  10. Superconducting scanning tunneling microscopy tips in a magnetic field: Geometry-controlled order of the phase transition

    Energy Technology Data Exchange (ETDEWEB)

    Eltschka, Matthias, E-mail: m.eltschka@fkf.mpg.de; Jäck, Berthold; Assig, Maximilian; Etzkorn, Markus; Ast, Christian R. [Max-Planck-Institut für Festkörperforschung, 70569 Stuttgart (Germany); Kondrashov, Oleg V. [Moscow Institute of Physics and Technology, 141700 Moscow (Russian Federation); Skvortsov, Mikhail A. [Moscow Institute of Physics and Technology, 141700 Moscow (Russian Federation); Skolkovo Institute of Science and Technology, 143026 Moscow (Russian Federation); L. D. Landau Institute for Theoretical Physics, 142432 Chernogolovka (Russian Federation); Kern, Klaus [Max-Planck-Institut für Festkörperforschung, 70569 Stuttgart (Germany); Institut de Physique de la Matière Condensée, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne (Switzerland)

    2015-09-21

    The properties of geometrically confined superconductors significantly differ from their bulk counterparts. Here, we demonstrate the geometrical impact for superconducting scanning tunneling microscopy (STM) tips, where the confinement ranges from the atomic to the mesoscopic scale. To this end, we compare the experimentally determined magnetic field dependence for several vanadium tips to microscopic calculations based on the Usadel equation. For our theoretical model of a superconducting cone, we find a direct correlation between the geometry and the order of the superconducting phase transition. Increasing the opening angle of the cone changes the phase transition from first to second order. Comparing our experimental findings to the theory reveals first and second order quantum phase transitions in the vanadium STM tips. In addition, the theory also explains experimentally observed broadening effects by the specific tip geometry.

  11. Mn doped InSb studied at the atomic scale by cross-sectional scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Mauger, S. J. C.; Bocquel, J.; Koenraad, P. M., E-mail: p.m.koenraad@tue.nl [Department of Applied Physics, Eindhoven University of Technology, Den Dolech 2, 5612 AZ Eindhoven (Netherlands); Feeser, C. E.; Parashar, N. D.; Wessels, B. W. [Department of Materials Science and Engineering and Materials Research Center, Northwestern University, Evanston, Illinois 60208 (United States)

    2015-11-30

    We present an atomically resolved study of metal-organic vapor epitaxy grown Mn doped InSb. Both topographic and spectroscopic measurements have been performed by cross-sectional scanning tunneling microscopy (STM). The measurements on the Mn doped InSb samples show a perfect crystal structure without any precipitates and reveal that Mn acts as a shallow acceptor. The Mn concentration of the order of ∼10{sup 20 }cm{sup −3} obtained from the cross-sectional STM data compare well with the intended doping concentration. While the pair correlation function of the Mn atoms showed that their local distribution is uncorrelated beyond the STM resolution for observing individual dopants, disorder in the Mn ion location giving rise to percolation pathways is clearly noted. The amount of clustering that we see is thus as expected for a fully randomly disordered distribution of the Mn atoms and no enhanced clustering or second phase material was observed.

  12. Interface-induced chiral domain walls, spin spirals and skyrmions revealed by spin-polarized scanning tunneling microscopy.

    Science.gov (United States)

    von Bergmann, Kirsten; Kubetzka, André; Pietzsch, Oswald; Wiesendanger, Roland

    2014-10-01

    The spin textures of ultra-thin magnetic layers exhibit surprising variety. The loss of inversion symmetry at the interface of the magnetic layer and substrate gives rise to the so-called Dzyaloshinskii-Moriya interaction which favors non-collinear spin arrangements with unique rotational sense. Here we review the application of spin-polarized scanning tunneling microscopy to such systems, which has led to the discovery of interface-induced chiral domain walls and spin spirals. Recently, different interface-driven skyrmion lattices have been found, and the writing as well as the deleting of individual skyrmions based on local spin-polarized current injection has been demonstrated. These interface-induced non-collinear magnetic states offer new exciting possibilities to study fundamental magnetic interactions and to tailor material properties for spintronic applications.

  13. Manipulation of adsorbed atoms and creation of new structures on room-temperature surfaces with a scanning tunneling microscope.

    Science.gov (United States)

    Whitman, L J; Stroscio, J A; Dragoset, R A; Celotta, R J

    1991-03-01

    A general method of manipulating adsorbed atoms and molecules on room-temperature surfaces with the use of a scanning tunneling microscope is described. By applying an appropriate voltage pulse between the sample and probe tip, adsorbed atoms can be induced to diffuse into the region beneath the tip. The field-induced diffusion occurs preferentially toward the tip during the voltage pulse because of the local potential energy gradient arising from the interaction of the adsorbate dipole moment with the electric field gradient at the surface. Depending upon the surface and pulse parameters, cesium (Cs) structures from one nanometer to a few tens of nanometers across have been created in this way on the (110) surfaces of gallium arsenide (GaAs) and indium antimonide (InSb), including structures that do not naturally occur.

  14. Scanning tunneling spectroscopy of Si donors in GaAs {l_brace}110{r_brace}

    Energy Technology Data Exchange (ETDEWEB)

    Teichmann, K.; Wenderoth, M.; Loth, S.; Ulbrich, R.G. [Universitaet Goettingen, IV. Physikalisches Institut (Germany)

    2007-07-01

    Silicon donors in highly n-doped GaAs(6.5 x 10{sup 18} cm{sup -3}) are investigated by Cross-Sectional Scanning Tunneling Microscopy in UHV at 8K. Donors near the surface of the {l_brace}110{r_brace} cleavage planes are studied by spatially resolved I(V)-spectroscopy. The dopant atoms are identified by their bias dependent topographic and spectroscopic properties. In addition to the known features at negative and small positive voltages, our measurements on single donors show an additional transport channel for larger positive bias voltages. The current distribution has a circular symmetric structure. The diameter is bias dependent, and can extend up to several nanometers around the donor. The minimal bias voltage of the current onset is localized above the donors. We discuss different scenarios - including tip induced band bending - that can lead to the observed ring-like shapes.

  15. Scanning tunnelling microscope studies of growth of RuO2(110) thin layer on Ru(0001)

    Institute of Scientific and Technical Information of China (English)

    Zhang Han-Jie; Lü Bin; Lu Yun-Hao; Huang Han; Li Hai-Yang; Bao Shi-Ning; He Pei-Mo

    2006-01-01

    This paper reports that the growth of RuO2(110) thin layer growth on Ru(0001) has been investigated by means of scanning tunnelling microscope (STM). The STM images showed a domain structure with three rotational domains of RuO2(110) rotated by an angle of 120°. The as-grown RuO2(110) thin layer is expanded from the bulk-truncated RuCO2(110) due to the large mismatch between RuCO2(110) and the Ru(0001) substrate. The results also indicate that growth of RuO2(110) thin layer on the Ru(0001) substrate by oxidation tends first to formation of the Ru-O (oxygen) chains in the [001] direction of RuO2(110).

  16. Adsorption of ethylene on Sn and In terminated Si(001) surface studied by photoelectron spectroscopy and scanning tunneling microscopy

    Science.gov (United States)

    Zimmermann, Petr; Sobotík, Pavel; Kocán, Pavel; Ošt'ádal, Ivan; Vorokhta, Mykhailo; Acres, Robert George; Matolín, Vladimír

    2016-09-01

    Interaction of ethylene (C2H4) with Si(001)-Sn-2 × 2 and Si(001)-In-2 × 2 at room temperature has been studied using core level (C 1s) X-ray photoelectron spectroscopy with synchrotron radiation and scanning tunneling microscopy. Sn and In form similar dimer chains on Si(001)2 × 1, but exhibit different interaction with ethylene. While ethylene adsorbs on top of Sn dimers of the Si(001)-Sn-2 × 2 surface, the Si(001)-In-2 × 2 surface turned out to be inert. Furthermore, the reactivity of the Sn terminated surface is found to be considerably decreased in comparison with Si(001)2 × 1. According to the proposed adsorption model ethylene bonds to Sn dimers via [2 + 2] cycloaddition by interacting with their π dimer bonds. In contrast, indium dimers do not contain π bonds, which renders the In terminated Si(001) surface inert for ethylene adsorption.

  17. Growth of Cu Films on Si(111)-7 × 7 Surfaces at Low Temperature: A Scanning Tunnelling Microscopy Study

    Institute of Scientific and Technical Information of China (English)

    SHEN Quan-Tong; SUN Guo-Feng; LI Wen-Juan; DONG Guo-Cai; HAN Tie-Zhu; MA Da-Yan; SUN Yu-Jie; JIA Jin-Feng; XUE Qi-Kun

    2007-01-01

    Morphologies of Cu(111) Rims on Si(111)-7×7 surfaces prepared at low temperature are investigated by scanning tunnelling microscopy (STM) and reflection high-energy electron diffraction (RHEED). At the initial growth stage, Cu 61ms are Bat due to the formation of silicide at the interface that decreases the mismatch between Cu films and the Si substrate. Different from the usual multilayer growth of Cu/Cu(111), on the silicide layer a layer-by-layer growth is observed. The two dimensional (2D) growth is explained by the enhanced high island density at low deposition temperature. Increasing deposition rate produces films with different morphologies, which is the result of Ostwald ripening.

  18. Adsorption of ethylene on Sn and In terminated Si(001) surface studied by photoelectron spectroscopy and scanning tunneling microscopy.

    Science.gov (United States)

    Zimmermann, Petr; Sobotík, Pavel; Kocán, Pavel; Ošt'ádal, Ivan; Vorokhta, Mykhailo; Acres, Robert George; Matolín, Vladimír

    2016-09-07

    Interaction of ethylene (C2H4) with Si(001)-Sn-2 × 2 and Si(001)-In-2 × 2 at room temperature has been studied using core level (C 1s) X-ray photoelectron spectroscopy with synchrotron radiation and scanning tunneling microscopy. Sn and In form similar dimer chains on Si(001)2 × 1, but exhibit different interaction with ethylene. While ethylene adsorbs on top of Sn dimers of the Si(001)-Sn-2 × 2 surface, the Si(001)-In-2 × 2 surface turned out to be inert. Furthermore, the reactivity of the Sn terminated surface is found to be considerably decreased in comparison with Si(001)2 × 1. According to the proposed adsorption model ethylene bonds to Sn dimers via [2 + 2] cycloaddition by interacting with their π dimer bonds. In contrast, indium dimers do not contain π bonds, which renders the In terminated Si(001) surface inert for ethylene adsorption.

  19. Real-space post-processing correction of thermal drift and piezoelectric actuator nonlinearities in scanning tunneling microscope images

    CERN Document Server

    Yothers, Mitchell P; Bumm, Lloyd A

    2016-01-01

    We have developed a real-space method to correct distortion due to thermal drift and piezoelectric actuator nonlinearities on scanning tunneling microscope images using Matlab. The method uses the known structures typically present in high-resolution atomic and molecularly-resolved images as an internal standard. Each image feature (atom or molecule) is first identified in the image. The locations of each feature's nearest neighbors (NNs) are used to measure the local distortion at that location. The local distortion map across the image is simultaneously fit to our distortion model, which includes thermal drift in addition to piezoelectric actuator hysteresis and creep. The image coordinates of the features and image pixels are corrected using an inverse transform from the distortion model. We call this technique the thermal-drift, hysteresis, and creep transform (DHCT). Performing the correction in real space allows defects, domain boundaries, and step edges to be excluded with a spatial mask. Additional re...

  20. A novel cryogenic scanning laser microscope tested on Josephson tunnel junctions

    DEFF Research Database (Denmark)

    Holm, Jesper; Mygind, Jesper

    1995-01-01

    A novel cryogenic scanning laser microscope with a spatial resolution of less than 5 µm has been designed for on-chip in situ investigations of the working properties of normal and superconducting circuits and devices. The instrument relies on the detection of the electrical response of the circuit...... to a very localized heating induced by irradiation with 675 nm wavelength light from a semiconductor laser. The hot spot is moved by a specially designed piezoelectric scanner sweeping the tip of a single-mode optical fiber a few µm above the circuit. Depending on the scanner design the scanning area can...

  1. iSpectra: An Open Source Toolbox For The Analysis of Spectral Images Recorded on Scanning Electron Microscopes.

    Science.gov (United States)

    Liebske, Christian

    2015-08-01

    iSpectra is an open source and system-independent toolbox for the analysis of spectral images (SIs) recorded on energy-dispersive spectroscopy (EDS) systems attached to scanning electron microscopes (SEMs). The aim of iSpectra is to assign pixels with similar spectral content to phases, accompanied by cumulative phase spectra with superior counting statistics for quantification. Pixel-to-phase assignment starts with a threshold-based pre-sorting of spectra to create groups of pixels with identical elemental budgets, similar to a method described by van Hoek (2014). Subsequent merging of groups and re-assignments of pixels using elemental or principle component histogram plots enables the user to generate chemically and texturally plausible phase maps. A variety of standard image processing algorithms can be applied to groups of pixels to optimize pixel-to-phase assignments, such as morphology operations to account for overlapping excitation volumes over pixels located at phase boundaries. iSpectra supports batch processing and allows pixel-to-phase assignments to be applied to an unlimited amount of SIs, thus enabling phase mapping of large area samples like petrographic thin sections.

  2. A novel technique for nano-scale lithography of cadmium selenide via a scanning tunneling microscope tip-induced reaction

    Science.gov (United States)

    Olson, Joel Andrew

    In the introductory chapter the physical and interfacial properties of cadmium selenide are presented, as well as a discussion of select surface properties of CdSe. Also, a brief review of scanning probe lithographic techniques currently under investigation is presented. As a portion of the project presented herein, a research-grade scanning tunneling microscope was constructed. The second chapter includes information specific to this instrument. Included are descriptions of the electrical components, descriptions of the mechanical components, and a description of the noise reduction and calibration of the instrument. When cleaved-in-air (112¯0) CdSe is imaged repeatedly under humidified conditions, small (˜20 nm wide and between 6 A and 12 A in height) features are observed to form. The features are similar in shape to one another, suggesting tip imaging. Under an atmosphere of dried nitrogen feature growth is not observed. The growth of the features shows a strong dependence on both the tunneling current and the bias voltage. The initial rate of feature growth increases with tunneling current. Feature growth as a function of bias voltage displays an onset at a sample bias of -1. 2 V to -1. 3 V and is no longer observed at sample biases more negative than -2.5 V. Two possible models are presented for feature growth. The smallest feature observed is ˜6 nm in width. The fourth chapter describes simple and inexpensive classroom demonstrations of nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI). The demonstrations comprise common orienteering compasses, whose needles represent magnetic dipoles, along with three collinear permanent magnets, and a magnetic stir plate or pulseable electromagnets. The trio of permanent magnets provides a laterally uniform magnetic field, whose strength decreases with distance from the magnets. Resonance can be observed by adjusting the frequency of the magnetic stirrer when it is in close proximity to the compasses

  3. Design and calibration of a scanning tunneling microscope for large machined surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Grigg, D.A.; Russell, P.E.; Dow, T.A.

    1988-12-01

    During the last year the large sample STM has been designed, built and used for the observation of several different samples. Calibration of the scanner for prope dimensional interpretation of surface features has been a chief concern, as well as corrections for non-linear effects such as hysteresis during scans. Several procedures used in calibration and correction of piezoelectric scanners used in the laboratorys STMs are described.

  4. Cadmium underpotential deposition on Cu(111) in situ scanning tunneling microscopy.

    Science.gov (United States)

    Hommrich, J; Hümann, S; Wandelt, K

    2002-01-01

    Atomically resolved in situ STM images are presented for an underpotentially deposited (upd) cadmium layer on a Cu(111) electrode from a 10(-4) M CdCl2/10(-2) M HCl solution. The observed moiré-like structure seen in the images is analysed by means of an algebraic model for this long-range superstructure. A structure model for the upd layer is developed which reflects all features of the observed moiré pattern. Furthermore the height modulation was simulated by a hard-sphere model for the Cd overlayer and shows remarkable agreement with the detailed tunneling current density distribution of the measured STM images. The existence of translational and rotational domains is demonstrated. The results are also compared and shown to be fully consistent with previous (ex situ) low-energy electron diffraction (LEED) observations of this system. The mechanism of Cd upd involves a dynamic site exchange between preadsorbed Cl- anions and adsorbing Cd2+ cations as previously concluded from ex situ X-ray photoelectron (XPS) and low-energy ion scattering (LEIS) measurements.

  5. Electronic properties of conductive pili of the metal-reducing bacterium Geobacter sulfurreducens probed by scanning tunneling microscopy

    Science.gov (United States)

    Veazey, Joshua P.; Reguera, Gemma; Tessmer, Stuart H.

    2011-12-01

    The metal-reducing bacterium Geobacter sulfurreducens produces conductive protein appendages known as “pilus nanowires” to transfer electrons to metal oxides and to other cells. These processes can be harnessed for the bioremediation of toxic metals and the generation of electricity in bioelectrochemical cells. Key to these applications is a detailed understanding of how these nanostructures conduct electrons. However, to the best of our knowledge, their mechanism of electron transport is not known. We used the capability of scanning tunneling microscopy (STM) to probe conductive materials with higher spatial resolution than other scanning probe methods to gain insights into the transversal electronic behavior of native, cell-anchored pili. Despite the presence of insulating cellular components, the STM topography resolved electronic molecular substructures with periodicities similar to those reported for the pilus shaft. STM spectroscopy revealed electronic states near the Fermi level, consistent with a conducting material, but did not reveal electronic states expected for cytochromes. Furthermore, the transversal conductance was asymmetric, as previously reported for assemblies of helical peptides. Our results thus indicate that the Geobacter pilus shaft has an intrinsic electronic structure that could play a role in charge transport.

  6. Combined low-temperature scanning tunneling/atomic force microscope for atomic resolution imaging and site-specific force spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Schwarz, Udo; Albers, Boris J.; Liebmann, Marcus; Schwendemann, Todd C.; Baykara, Mehmet Z.; Heyde, Markus; Salmeron, Miquel; Altman, Eric I.; Schwarz, Udo D.

    2008-02-27

    The authors present the design and first results of a low-temperature, ultrahigh vacuum scanning probe microscope enabling atomic resolution imaging in both scanning tunneling microscopy (STM) and noncontact atomic force microscopy (NC-AFM) modes. A tuning-fork-based sensor provides flexibility in selecting probe tip materials, which can be either metallic or nonmetallic. When choosing a conducting tip and sample, simultaneous STM/NC-AFM data acquisition is possible. Noticeable characteristics that distinguish this setup from similar systems providing simultaneous STM/NC-AFM capabilities are its combination of relative compactness (on-top bath cryostat needs no pit), in situ exchange of tip and sample at low temperatures, short turnaround times, modest helium consumption, and unrestricted access from dedicated flanges. The latter permits not only the optical surveillance of the tip during approach but also the direct deposition of molecules or atoms on either tip or sample while they remain cold. Atomic corrugations as low as 1 pm could successfully be resolved. In addition, lateral drifts rates of below 15 pm/h allow long-term data acquisition series and the recording of site-specific spectroscopy maps. Results obtained on Cu(111) and graphite illustrate the microscope's performance.

  7. Non-collinear exchange coupling in Fe/Mn/Fe(0 0 1): insight from scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Pierce, D.T. E-mail: daniel.pierce@nist.gov; Davies, A.D.; Stroscio, J.A.; Tulchinsky, D.A.; Unguris, J.; Celotta, R.J

    2000-12-01

    The film growth and morphology of epitaxial Mn films grown on Fe(0 0 1) single-crystal whiskers measured with scanning tunneling microscopy (STM) provides insight into the mechanism of interlayer exchange coupling in Fe/Mn/Fe(0 0 1) trilayers. The proximity model of Slonczewski for exchange coupling through an antiferromagnet predicts that the coupling angle between the ferromagnetic layers will oscillate around a mean value of 90 deg. with an amplitude that is very sensitive to the width of the thickness distribution of the spacer layer. We measure the thickness distribution with the STM and find that the coupling angle variation predicted by the proximity model is qualitatively consistent with the actual coupling angle variations in Fe/Mn/Fe(0 0 1) measured with scanning electron microscopy with polarization analysis (SEMPA). Going beyond the proximity model and allowing for a non-uniform magnetization of the thin Fe overlayer provides an improved explanation of the results. We contrast the behavior of Fe/Mn/Fe(0 0 1), where the proximity model appears applicable, to coupling through antiferro-magnetic Cr in Fe/Cr/Fe(0 0 1), where it is not, and discuss possible reasons for the difference.

  8. Combined low-temperature scanning tunneling/atomic force microscope for atomic resolution imaging and site-specific force spectroscopy

    Science.gov (United States)

    Albers, Boris J.; Liebmann, Marcus; Schwendemann, Todd C.; Baykara, Mehmet Z.; Heyde, Markus; Salmeron, Miquel; Altman, Eric I.; Schwarz, Udo D.

    2008-03-01

    We present the design and first results of a low-temperature, ultrahigh vacuum scanning probe microscope enabling atomic resolution imaging in both scanning tunneling microscopy (STM) and noncontact atomic force microscopy (NC-AFM) modes. A tuning-fork-based sensor provides flexibility in selecting probe tip materials, which can be either metallic or nonmetallic. When choosing a conducting tip and sample, simultaneous STM/NC-AFM data acquisition is possible. Noticeable characteristics that distinguish this setup from similar systems providing simultaneous STM/NC-AFM capabilities are its combination of relative compactness (on-top bath cryostat needs no pit), in situ exchange of tip and sample at low temperatures, short turnaround times, modest helium consumption, and unrestricted access from dedicated flanges. The latter permits not only the optical surveillance of the tip during approach but also the direct deposition of molecules or atoms on either tip or sample while they remain cold. Atomic corrugations as low as 1pm could successfully be resolved. In addition, lateral drifts rates of below 15pm/h allow long-term data acquisition series and the recording of site-specific spectroscopy maps. Results obtained on Cu(111) and graphite illustrate the microscope's performance.

  9. Topographic and electronic contrast of the graphene moir´e on Ir(111) probed by scanning tunneling microscopy and noncontact atomic force microscopy

    NARCIS (Netherlands)

    Sun, Z.; Hämäläinen, K.; Sainio, K.; Lahtinen, J.; Vanmaekelbergh, D.A.M.; Liljeroth, P.

    2011-01-01

    Epitaxial graphene grown on transition-metal surfaces typically exhibits a moir´e pattern due to the lattice mismatch between graphene and the underlying metal surface. We use both scanning tunneling microscopy (STM) and atomic force microscopy (AFM) to probe the electronic and topographic contrast

  10. Cysteine adsorption on the Au(111) surface and the electron transfer in configuration of a scanning tunneling microscope: A quantum-chemical approach

    DEFF Research Database (Denmark)

    Nazmutdinov, R.R.; Manyurov, I.R.; Zinkicheva, T.T.

    2007-01-01

    to the size of a fragment observed experimentally. Adsorption calculations are used to build three-dimensional isosurfaces (STM images), where the tungsten needle of the scanning tunneling microscope is simulated by a tungsten atom or by small clusters. The calculated images are sensitive to both the Cys...

  11. Acquisition of a Scanning Tunneling Microscope to Enhance Research and Education in Stress-Controlled Catalysis

    Science.gov (United States)

    2015-01-14

    experiments. MFP- 3D Scanner : The MFP- 3D features closed-loop sample scanning with a low-noise piezo driven flexure stage. Closed-loop operation...educational objectives of the ARO-MURI program currently funded at Brown University on “stress-controlled catalysis.” We have acquired an Asylum MFP- 3D -SA...program currently funded at Brown University on “stress-controlled catalysis.” We have acquired an Asylum MFP- 3D -SA instrument to, which has been

  12. Note: Automated electrochemical etching and polishing of silver scanning tunneling microscope tips.

    Science.gov (United States)

    Sasaki, Stephen S; Perdue, Shawn M; Rodriguez Perez, Alejandro; Tallarida, Nicholas; Majors, Julia H; Apkarian, V Ara; Lee, Joonhee

    2013-09-01

    Fabrication of sharp and smooth Ag tips is crucial in optical scanning probe microscope experiments. To ensure reproducible tip profiles, the polishing process is fully automated using a closed-loop laminar flow system to deliver the electrolytic solution to moving electrodes mounted on a motorized translational stage. The repetitive translational motion is controlled precisely on the μm scale with a stepper motor and screw-thread mechanism. The automated setup allows reproducible control over the tip profile and improves smoothness and sharpness of tips (radius 27 ± 18 nm), as measured by ultrafast field emission.

  13. Note: Automated electrochemical etching and polishing of silver scanning tunneling microscope tips

    Science.gov (United States)

    Sasaki, Stephen S.; Perdue, Shawn M.; Perez, Alejandro Rodriguez; Tallarida, Nicholas; Majors, Julia H.; Apkarian, V. Ara; Lee, Joonhee

    2013-09-01

    Fabrication of sharp and smooth Ag tips is crucial in optical scanning probe microscope experiments. To ensure reproducible tip profiles, the polishing process is fully automated using a closed-loop laminar flow system to deliver the electrolytic solution to moving electrodes mounted on a motorized translational stage. The repetitive translational motion is controlled precisely on the μm scale with a stepper motor and screw-thread mechanism. The automated setup allows reproducible control over the tip profile and improves smoothness and sharpness of tips (radius 27 ± 18 nm), as measured by ultrafast field emission.

  14. SpectraFox: A free open-source data management and analysis tool for scanning probe microscopy and spectroscopy

    Science.gov (United States)

    Ruby, Michael

    In the last decades scanning probe microscopy and spectroscopy have become well-established tools in nanotechnology and surface science. This opened the market for many commercial manufacturers, each with different hardware and software standards. Besides the advantage of a wide variety of available hardware, the diversity may software-wise complicate the data exchange between scientists, and the data analysis for groups working with hardware developed by different manufacturers. Not only the file format differs between manufacturers, but also the data often requires further numerical treatment before publication. SpectraFox is an open-source and independent tool which manages, processes, and evaluates scanning probe spectroscopy and microscopy data. It aims at simplifying the documentation in parallel to measurement, and it provides solid evaluation tools for a large number of data.

  15. SpectraFox: A free open-source data management and analysis tool for scanning probe microscopy and spectroscopy

    Directory of Open Access Journals (Sweden)

    Michael Ruby

    2016-01-01

    Full Text Available In the last decades scanning probe microscopy and spectroscopy have become well-established tools in nanotechnology and surface science. This opened the market for many commercial manufacturers, each with different hardware and software standards. Besides the advantage of a wide variety of available hardware, the diversity may software-wise complicate the data exchange between scientists, and the data analysis for groups working with hardware developed by different manufacturers. Not only the file format differs between manufacturers, but also the data often requires further numerical treatment before publication. SpectraFox is an open-source and independent tool which manages, processes, and evaluates scanning probe spectroscopy and microscopy data. It aims at simplifying the documentation in parallel to measurement, and it provides solid evaluation tools for a large number of data.

  16. Compact device for cleaning scanner-mounted scanning tunneling microscope tips using electron bombardment

    Science.gov (United States)

    Hellmann, D.; Worbes, L.; Kittel, A.

    2011-08-01

    Most scanning probe techniques rely on the assumption that both sample and tip are free from adsorbates, residues, and oxide not deposited intentionally. Getting a clean sample surface can be readily accomplished by applying ion sputtering and subsequent annealing, whereas finding an adequate treatment for tips is much more complicated. The method of choice would effectively desorb undesired compounds without reducing the sharpness or the general geometry of the tip. Several devices which employ accelerated electrons to achieve this are described in the literature. To minimize both the effort to implement this technique in a UHV chamber and the overall duration of the cleaning procedure, we constructed a compact electron source fitted into a sample holder, which can be operated in a standard Omicron variable-temperature (VT)-STM while the tip stays in place. This way a maximum of compatibility with existing systems is achieved and short turnaround times are possible for tip cleaning.

  17. In situ scanning tunneling microscopy investigation of sulfur oxidative underpotential deposition on Ag(100) and Ag(110).

    Science.gov (United States)

    Lastraioli, E; Loglio, F; Cavallini, M; Simeone, F C; Innocenti, M; Carlà, F; Foresti, M L

    2010-11-16

    Underpotential (UPD) deposition of sulfur from Na(2)S solution in 0.1 M NaOH was studied on Ag(100) and Ag(110) using in situ scanning tunneling microscopy (STM). The cyclic voltammogram on Ag(100) presents two broad peaks, whereas three partial overlapping peaks and a sharper one are observed on Ag(110). STM measurements carried out during the whole UPD process show that progressively more compact structures are formed as the applied potential is scanned toward more positive potentials. More precisely, p(2×2), c(2×6), and c(2×2) were found on Ag(100) at E = -1.25, -1.0, and -0.9 V, respectively. Less definite conclusions can be drawn for the structures of S overlayers on Ag(110). However, the experimental findings are consistent with an incomplete p(2×1) at potentials preceding the sharp peak, and with a c(2×2) structure at E = -0.9 V vs Ag/AgCl, KCl(sat). The coverage values calculated on the basis of the hypothesized structures have been compared with the values obtained from chronocoulometric measurements at the most positive potentials investigated. Thus, the experimental coverage θ = 0.5 coincides with the coverage calculated for the c(2×2) structure found on Ag(110) at E = -0.9 V by STM, whereas the experimental coverage θ = 0.42 suggests that a mixture of structures c(2×6) and c(2×2) is formed on Ag(100).

  18. Multiband superconductivity in 2 H -NbSe2 probed by Doppler-modulated scanning tunneling spectroscopy

    Science.gov (United States)

    Fridman, I.; Kloc, C.; Petrovic, C.; Wei, J. Y. T.

    Cooper pairing in multiband superconductors can involve carriers from bands having different dimensionalities, and the interband coupling can provide for novel pairing interactions. In addition to MgB2, recent experiments on 2 H -NbSe2 have studied the Fermi surface topology using angle- and temperature-dependent scanning tunneling spectroscopy. We present another novel method for probing multiband pairing: using a field-induced diamagnetic supercurrent, applied along different crystal axes, to perturb the quasiparticle density-of-states spectrum. By measuring the evolution of the quasiparticle spectrum under finite superfluid momentum, we characterize the pairing gaps and gap anisotropies. This approach is demonstrated on 2 H -NbSe2 at 300 mK with a magnetic field of up to 9 T applied in the ab -plane. The STM measurements revealed unambiguous evidence for multiband pairing, and evidence for a novel transition of the in-plane vortex lattice. We discuss the characteristics of this transition in light of data from other probes Work supported by NSERC, CFI/OIT, CIFAR, U.S. DOE and Brookhaven Science Associates (No. DE-AC02-98CH10886).

  19. Adsorption and growth morphology of rare-earth metals on graphene studied by ab initio calculations and scanning tunneling microscopy

    Science.gov (United States)

    Liu, Xiaojie; Wang, C. Z.; Hupalo, M.; Yao, Y. X.; Tringides, M. C.; Lu, W. C.; Ho, K. M.

    2010-12-01

    Adsorption of rare-earth (RE) adatoms (Nd, Gd, Eu, and Yb) on graphene was studied by first-principles calculations based on the density-functional theory. The calculations show that the hollow site of graphene is the energetically favorable adsorption site for all the RE adatoms studied. The adsorption energies and diffusion barriers of Nd and Gd on graphene are found to be larger than those of Eu and Yb. Comparison with scanning tunneling microscopy experiments for Gd and Eu epitaxially grown on graphene confirms these calculated adsorption and barrier differences, since fractal-like islands are observed for Gd and flat-topped crystalline islands for Eu. The formation of flat Eu islands on graphene can be attributed to its low diffusion barrier and relatively larger ratio of adsorption energy to its bulk cohesive energy. The interactions between the Nd and Gd adatoms and graphene cause noticeable in-plane lattice distortions in the graphene layer. Adsorption of the RE adatoms on graphene also induces significant electric dipole and magnetic moments.

  20. In situ scanning tunneling microscopy study of Ca-modified rutile TiO2(110 in bulk water

    Directory of Open Access Journals (Sweden)

    Giulia Serrano

    2015-02-01

    Full Text Available Despite the rising technological interest in the use of calcium-modified TiO2 surfaces in biomedical implants, the Ca/TiO2 interface has not been studied in an aqueous environment. This investigation is the first report on the use of in situ scanning tunneling microscopy (STM to study calcium-modified rutile TiO2(110 surfaces immersed in high purity water. The TiO2 surface was prepared under ultrahigh vacuum (UHV with repeated sputtering/annealing cycles. Low energy electron diffraction (LEED analysis shows a pattern typical for the surface segregation of calcium, which is present as an impurity on the TiO2 bulk. In situ STM images of the surface in bulk water exhibit one-dimensional rows of segregated calcium regularly aligned with the [001] crystal direction. The in situ-characterized morphology and structure of this Ca-modified TiO2 surface are discussed and compared with UHV-STM results from the literature. Prolonged immersion (two days in the liquid leads to degradation of the overlayer, resulting in a disordered surface. X-ray photoelectron spectroscopy, performed after immersion in water, confirms the presence of calcium.

  1. Scanning tunneling microscopy observation of ultrathin epitaxial CoSi2(111) films grown at a high temperature

    Science.gov (United States)

    Alekseev, A. A.; Olyanich, D. A.; Utas, T. V.; Kotlyar, V. G.; Zotov, A. V.; Saranin, A. A.

    2015-10-01

    Scanning tunneling microscopy (STM) is used to study the basic laws of growth of ultrathin epitaxial CoSi2(111) films with Co coverages up to 4 ML formed upon sequential deposition of Co and Si atoms taken in a stoichiometric ratio onto the Co-Si(111) surface at room temperature and subsequent annealing at 600-700°C. When the coverage of Co atoms is lower than ~2.7 ML, flat CoSi2 islands up to ~3 nm high with surface structure 2 × 2 or 1 × 1 grow. It is shown that continuous epitaxial CoSi2 films containing 3-4 triple Si-Co-Si layers grow provided precise control of deposition. CoSi2 films can contain inclusions of the local regions with (2 × 1)Si reconstruction. At a temperature above 700°C, a multilevel CoSi2 film with pinholes grows because of vertical growth caused by the difference between the free energies of the CoSi2(111) and Si(111) surfaces. According to theoretical calculations, structures of A or B type with a coordination number of 8 of Co atoms are most favorable for the CoSi2(111)2 × 2 interface.

  2. Surface morphologies of MOCVD-grown GaN films on sapphire studied by scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, J.; Reddic, J.E.; Sinha, M.; Ricker, W.S.; Karlinsey, J.; Yang, J.-W.; Khan, M.A.; Chen, D.A

    2002-12-30

    The surface morphologies of MOCVD GaN films grown on sapphire substrates have been investigated by scanning tunneling microscopy (STM). High quality STM images could not be obtained prior to cleaning the les in HF, hot HCl or 2 M NaOH. STM images of the GaN films showed that the surfaces consisted of curved step edges and interlocking terraces, which were roughly 224 nm wide. Surface pits approximately 2-5 nm deep and 50-80 nm wide were observed on the GaN films, and these pits were preferentially located at a juncture between two step edges. Previous studies in the literature involving MOCVD-grown GaN on sapphire have demonstrated that the surface pits are associated with screw-component threading dislocations. Therefore, the number of screw-component threading dislocations in these GaN films is estimated as 6.3x10{sup 8} cm{sup -2} from the number surface pits observed in the STM images. X-ray photoelectron studies indicated that the major surface contaminants before cleaning were carbon and oxygen. Treatment in HF or HCl removed oxygen from the surface while treatment in NaOH was more effective at removing surface carbon.

  3. Scanning tunneling microscopy investigation of self-assembled CuPc/F16CuPc binary superstructures on graphite.

    Science.gov (United States)

    Huang, Yu Li; Li, Hui; Ma, Jing; Huang, Han; Chen, Wei; Wee, Andrew T S

    2010-03-01

    The self-assembly of the binary molecular system comprising copper(II) phthalocyanine (CuPc) and copper-hexadecafluoro-phthalocyanine (F(16)CuPc) on graphite has been investigated by in situ low-temperature scanning tunneling microscopy (LT-STM). The adsorption of this binary molecular system on graphite results in the formation of a well-ordered chessboardlike nanopattern. The in-plane molecular orientation of the guest CuPc molecules can be tuned by varying the coverage. At low coverage, the sparse CuPc molecules are randomly embedded in the host F(16)CuPc monolayer, possessing two different in-plane orientations; as the CuPc coverage increases, the in-plane molecular orientations of CuPc and F(16)CuPc become unidirectional and a highly ordered chessboardlike pattern forms. Molecular dynamic (MD) simulation results suggest that the selective and directional intermolecular hydrogen bonding determines the in-plane molecular orientation as well as the supramolecular packing arrangement.

  4. Growth of ordered molecular layers of PTCDA on Pb/Si(111) surfaces: a scanning tunneling microscopy study

    Science.gov (United States)

    Nicoara, N.; Méndez, J.; Gómez-Rodríguez, J. M.

    2016-09-01

    The growth of well-ordered layers of PTCDA (3,4,9,10-perylene-tetracarboxylic-dianhydride) molecules on Pb/Si(111) surfaces has been investigated by scanning tunneling microscopy (STM) under ultra-high vacuum conditions. These Pb/Si(111) substrates, which present several distinct phases with different reconstructions, have allowed the exploration of new passivation schemes for the growth of ordered organic layers on Si(111) surfaces. According to our STM measurements, the higher Pb coverage phases (namely the so-called hexagonal incommensurate and (1× 1) reconstructions) present rather inert surfaces that allow easy diffusion of PTCDA molecules at room temperature and the formation of a well ordered first molecular layer which displays a herringbone reconstruction. For multilayer PTCDA coverage on these Pb/Si(111) phases, the formation of three-dimensional crystallites, with structure similar to that of the bulk PTCDA crystal, has been observed, indicating that a Stranski-Krastanov growth mode is dominant. On lower Pb coverage substrates (presenting the defective β -(\\sqrt{3}× \\sqrt{3})R30^\\circ and mosaic γ -(\\sqrt{3}× \\sqrt{3})R30^\\circ reconstructions) no long range PTCDA order has been obtained. The systematic variation of the substrate reconstruction has allowed in the present work the relation of the surface reactivity of each reconstruction to the formation of ordered layers of PTCDA on Pb/Si(111) substrates.

  5. Adsorption geometry of glycine on Cu(001) determined with low—energy electron diffraction and scanning tunnelling microscopy

    Institute of Scientific and Technical Information of China (English)

    葛四平; 赵学应; 等

    2002-01-01

    Using low-energy electron diffraction(LEED)and scanning tunnelling microscopy (STM) it has been found that glycine molecules adsorbed on Cu(001) can form but only the (2×4) superstructures.On the basis of the missing LEED spots of the surface,it has been concluded that.each(2×4) unit cell consists of two molecules,one being the mirror image of the other,the C-C axis of both molecules lies in the mirror plane of the Cu substrate without a significant shift and twish from the plane;and the two O atoms of the carboxylate group of both molecules locate at the same height level without significant buckling.According to these conclusions,a structural model has been propsed for the (2×4) superstructure (a model for the c(2×4) supersturcture already exists).We argue that the (2×4) and c(2×4) superstructures must have similar specific surface free energy,that their hydrogen bonds must be of N-H-OII type,and that their local adsorption geometry must be similar or even the same.The advantage of combining STM with LEED to determine surface sturctures is clearly demonstrated.

  6. Adsorption geometry of glycine on Cu(001) determined with low-energy electron diffraction and scanning tunnelling microscopy

    Institute of Scientific and Technical Information of China (English)

    葛四平; 赵学应; 盖峥; 赵汝光; 杨威生

    2002-01-01

    Using low-energy electron diffraction (LEED) and scanning tunnelling microscopy (STM) it has been found thatglycine molecules adsorbed on Cu(001) can form but only the (2×4) and c(2×4) superstructures. On the basis of themissing LEED spots of the surface, it has been concluded that: each (2 ×4) unit cell consists of two molecules, one beingthe mirror image of the other; the C-C axis of both molecules lies in the mirror plane of the Cu substrate without asignificant shift and twist from the plane; and the two O atoms of the carboxylate group of both molecules locate at thesame height level without significant buckling. According to these conclusions, a structural model has been proposed forthe (2×4) superstructure (a model for the c(2×4) superstructure already exists). We argue that the (2×4) and c(2×4)superstructures must have similar specific surface free energy, that their hydrogen bonds must be of N-H-OⅡ type, andthat their local adsorption geometry must be similar or even the same. The advantage of combining STM with LEEDto determine surface structures is clearly demonstrated.

  7. Influence of the atmospheric humidity on the behaviour of silicon AFM probes in photon scanning tunneling microscopy

    Science.gov (United States)

    Benfedda, M.; Lahimer, S.; Bonnafe, J.

    1998-11-01

    The photon scanning tunneling microscopy (PSTM) allows to characterize the surface topography with high resolution. This microscopy exploits the exponential decay of the evanescent field achieved by the total internal reflection under the surface sample. When the distance between the sensor and the surface becomes small (sim 100 nm), the non propagating photons of the evanescent field can be converted into guided propagating mode of polaritons. A bulk Silicon probe is used in the AFM experiment as a sensor of van der Waals forces. The aim of this paper is to discuss the influence of the atmospheric humidity on the PSTM measurements. We have showed that the theoretical predictions of the dielectrical capture model (DCM) are very different from the experimental results when the humidity level is higher than a threshold value (30%). We present the results obtained with TE polarization, but the same behaviour is found with TM polarization. Although, in this paper we do not propose a theoretical model explaining the deviations between DCM values and experimental, however we found a validity threshold for our experimental results and we have emited the assumption that under high humidity level the pollution film presents on the sample surface slide during the displacement of the probe. La microscopie optique à effet tunnel (PSTM) est un outil de caractérisation de surface à haute résolution. Ce microscope exploite la décroissance du champ évanescent créé sur la surface de l'échantillon. Quand la distance entre le capteur et la surface est de quelques dizaines de nanomètres, les ondes évanescentes créées sur la surface sont converties en ondes propagatives et détectées en champ lointain. Le capteur est une sonde en silicium utilisée en microscopie à force atomique. Cet article montre l'influence des conditions atmosphériques sur les mesures PSTM. Il montre qu'au-delà d'un certain taux d'humidité (30%), les mesures ne sont plus valables et ne suivent

  8. Refined tip preparation by electrochemical etching and ultrahigh vacuum treatment to obtain atomically sharp tips for scanning tunneling microscope and atomic force microscope.

    Science.gov (United States)

    Hagedorn, Till; El Ouali, Mehdi; Paul, William; Oliver, David; Miyahara, Yoichi; Grütter, Peter

    2011-11-01

    A modification of the common electrochemical etching setup is presented. The described method reproducibly yields sharp tungsten tips for usage in the scanning tunneling microscope and tuning fork atomic force microscope. In situ treatment under ultrahigh vacuum (p ≤10(-10) mbar) conditions for cleaning and fine sharpening with minimal blunting is described. The structure of the microscopic apex of these tips is atomically resolved with field ion microscopy and cross checked with field emission.

  9. Research and Application of Scanning Tunneling Microscopy%扫描隧道显微术研究及其应用

    Institute of Scientific and Technical Information of China (English)

    冯异; 赵军武; 高芬

    2006-01-01

    介绍了扫描隧道显微术(Scanning Tunneling Microscopy,STM)的工作原理及特点,并阐述了STM在表面结构的观测、表面化学反应、表面微细加工、单原子操作、电双稳材料等领域的应用.

  10. Construction of a four tip scanning tunneling microscope/scanning electron microscope combination and conductivity measurements of silicide nanowires; Aufbau einer Vierspitzen-Rastertunnelmikroskop/Rasterelektronenmikroskop-Kombination und Leitfaehigkeitsmessungen an Silizid Nanodraehten

    Energy Technology Data Exchange (ETDEWEB)

    Zubkov, Evgeniy

    2013-09-01

    In this work the combination of a four-tip scanning tunneling microscope with a scanning electron microscope is presented. By means of this apparatus it is possible to perform the conductivity measurements on the in-situ prepared nanostructures in ultra-high vacuum. With the aid of a scanning electron microscope (SEM), it becomes possible to position the tunneling tips of the four-tip scanning tunneling microscope (STM), so that an arrangement for a four-point probe measurement on nanostructures can be obtained. The STM head was built according to the novel coaxial Beetle concept. This concept allows on the one hand, a very compact arrangement of the components of the STM and on the other hand, the new-built STM head has a good mechanical stability, in order to achieve atomic resolution with all four STM units. The atomic resolution of the STM units was confirmed by scanning a Si(111)-7 x 7 surface. The thermal drift during the STM operation, as well as the resonant frequencies of the mechanical structure of the STM head, were determined. The scanning electron microscope allows the precise and safe navigation of the tunneling tips on the sample surface. Multi tip spectroscopy with up to four STM units can be performed synchronously. To demonstrate the capabilities of the new-built apparatus the conductivity measurements were carried out on metallic yttrium silicide nanowires. The nanowires were prepared by the in-situ deposition of yttrium on a heated Si(110) sample surface. Current-voltage curves were recorded on the nanowires and on the wetting layer in-between. The curves indicate an existence of the Schottky barrier between the yttrium silicide nanowires and the silicon bulk. By means of the two-tip measurements with a gate, the insulating property of the Schottky barrier has been confirmed. Using this Schottky barrier, it is possible to limit the current to the nanowire and to prevent it from flowing through the silicon bulk. A four-tip resistance measurement

  11. Nanoscale probing of electronic band gap and topography of VO2 thin film surfaces by scanning tunneling microscopy

    Science.gov (United States)

    Yin, W.; Wolf, S.; Ko, C.; Ramanathan, S.; Reinke, P.

    2011-01-01

    The metal-insulator transition (MIT) in vanadium dioxide in the vicinity of room temperature makes it one of the most interesting materials for novel switching device applications. It is therefore essential to have a fundamental understanding of the VO2 surface when it is incorporated into multilayer structures or nanodevices. This study focuses on the surface modification of VO2 in response to the thermal treatment during phase transition. Vacuum annealing at temperatures in the vicinity of the MIT triggers a partial reduction in the surface, and thus initiates a chemical phase transition. Scanning tunneling microscopy and spectroscopy are used to investigate the electronic properties and surface structure of the VO2 thin film on (0001) sapphire substrates. Band gap maps with a high spatial resolution and single point spectroscopy I-V curves are measured as the sample is cycled through the MIT, and thus provide a direct observation of the surface phase transition at the nanoscale. The VO2 surface exhibits a homogeneous insulating behavior with a typical band gap of ˜0.5 eV at room temperature, and the surface becomes more metallic and spatially inhomogeneous in conductivity during MIT, and wide range of surface oxides can be identified. The surface still remains partially metallic after cooling down from a long period anneal, and such irreversible surface electrical change is attributed to the loss of oxygen. The location of metallic islands after thermal cycling is strongly coupled to the topography of the film, and relaxation processes and continued modification of the spatial distribution of the metallic regions are recognized on a longer timescale. The impact of film morphology, strain, surface chemistry, and structural phase transition on the electronic characteristics of VO2 surfaces are discussed.

  12. Investigating the Self-Assembly and Nanopatterning Characteristics of Organic Molecular Adlayers on Silicon and Graphene via Scanning Tunneling Microscopy

    Science.gov (United States)

    Karmel, Hunter Jason

    The controlled nanostructuring of matter on the atomic and molecular scale requires deep insight into the complex physical and chemical interactions that occur between adsorbates and surfaces. This dissertation examines the self assembly of molecularly thin organic adlayers on technologically significant nanoelectronic substrates using ultra high vacuum (UHV) scanning tunneling microscopy (STM). The three material systems considered in this work are cyclopentene monolayers on silicon, perylenetetracarboxylic diimide (PTCDI) adlayers on epitaxial graphene, and PTCDI melamine nanoporous molecular arrays on epitaxial graphene. The nanolithographic properties of each of these organic inorganic hybrid interfaces are extensively characterized at the molecular level. First, the molecularly precise desorption of individual cyclopentene molecules from a saturated organic passivation layer is demonstrated using feedback controlled lithography (FCL), thus achieving sub nanometer patterning resolution and the possibility of generating molecularly abrupt nanostructures on the silicon (100) surface. Second, the exceptional structural and thermal stability of PTCDI adlayers on epitaxial graphene is established using a combination of STM and X ray reflectivity (XRR) measurements. The enhanced stability of the PTCDI adlayer allows it to accommodate sub 5 nanometer voids with molecularly defined boundaries in addition to isolated molecular vacancies at room temperature. Third, a hydrogen bonded molecularly thin organic heteromolecular nanoporous network is generated on epitaxial graphene, formed by the intermixing of PTCDI and melamine. This molecular array exhibits a sub 5 nanometer two dimensional periodicity with hexagonal symmetry and is in atomic registry with the underlying graphene lattice. Overall this thesis explores the richly diverse physical and chemical interactions that promote molecularly precise lithography on nanoelectronic surfaces. In conclusion, the key insights

  13. Resistivity of thin gold films on mica induced by electron-surface scattering: Application of quantitative scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Robles, Marcelo E. [Departamento de Ciencias de la Construccion, FCCyOT, Universidad Tecnologica Metropolitana, Dieciocho 390, Santiago 8330526 (Chile); Gonzalez-Fuentes, Claudio A.; Henriquez, Ricardo [Departamento de Fisica, Facultad de Ciencias Fisicas y Matematicas, Universidad de Chile, Blanco Encalada 2008, Casilla 487-3, Santiago 8370449 (Chile); Kremer, German [Departamento de Fisica, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Santiago 7800024 (Chile); Moraga, Luis; Oyarzun, Simon; Suarez, Marco Antonio; Flores, Marcos [Departamento de Fisica, Facultad de Ciencias Fisicas y Matematicas, Universidad de Chile, Blanco Encalada 2008, Casilla 487-3, Santiago 8370449 (Chile); Munoz, Raul C., E-mail: ramunoz@ing.uchile.cl [Departamento de Fisica, Facultad de Ciencias Fisicas y Matematicas, Universidad de Chile, Blanco Encalada 2008, Casilla 487-3, Santiago 8370449 (Chile)

    2012-02-01

    We report a comparison between the resistivity measured on thin gold films deposited on mica, with predictions based upon classical theories of size effects (Drude's, Sondheimer's and Calecki's), as well as predictions based upon quantum theories of electron-surface scattering (the modified theory of Sheng, Xing and Wang, the theory of Tesanovic, Jaric and Maekawa, and that of Trivedi and Aschroft). From topographic images of the surface recorded with a Scanning Tunneling Microscope, we determined the rms roughness amplitude, {delta} and the lateral correlation length, {xi} corresponding to a Gaussian representation of the average height-height autocorrelation function, describing the roughness of each sample in the scale of length set by the Fermi wave length. Using ({delta}, {xi}) as input data, we present a rigorous comparison between resistivity data and predictions based upon the theory of Calecki as well as quantum theoretical predictions without adjustable parameters. The resistivity was measured on gold films of different thickness evaporated onto mica substrates, between 4 K and 300 K. The resistivity data covers the range 0.1 < x(T) < 6.8, for 4 K < T < 300 K, where x(T) is the ratio between film thickness and electron mean free path in the bulk at temperature T. We experimentally identify electron-surface and electron-phonon scattering as the microscopic electron scattering mechanisms giving rise to the macroscopic resistivity. The different theories are all capable of estimating the thin film resistivity to an accuracy better than 10%; however the mean free path and the resistivity characterizing the bulk turn out to depend on film thickness. Surprisingly, only the Sondheimer theory and its quantum version, the modified theory of Sheng, Xing and Wang, predict and increase in resistivity induced by size effects that seems consistent with published galvanomagnetic phenomena also arising from electron-surface scattering measured at low

  14. Electronic phase diagram of NaFe1-xCoxAs investigated by scanning tunneling microscopy

    Institute of Scientific and Technical Information of China (English)

    Zhou Xiao-Dong; Cai Peng; Wang Ya-Yu

    2013-01-01

    Our recent scanning tunneling microscopy (STM) studies of the NaFe1-xCoxAs phase diagram over a wide range of dopings and temperatures are reviewed.Similar to the high-Tc cuprates,the iron-based superconductors lie in close proximity to a magnetically ordered phase.Therefore,it is widely believed that magnetic interactions or fluctuations play an important role in triggering their Cooper pairings.Among the key issues regarding the electronic phase diagram are the properties of the parent spin density wave (SDW) phase and the superconducting (SC) phase,as well as the interplay between them.The NaFe1-xCoxAs is an ideal system for resolving these issues due to its rich electronic phases and the charge-neutral cleaved surface.In our recent work,we directly observed the SDW gap in the parent state,and it exhibits unconventional features that are incompatible with the simple Fermi surface nesting picture.The optimally doped sample has a single SC gap,but in the underdoped regime we directly viewed the microscopic coexistence of the SDW and SC orders,which compete with each other.In the overdoped regime we observed a novel pseudogap-like feature that coexists with superconductivity in the ground state,persists well into the normal state,and shows great spatial variations.The rich electronic structures across the phase diagram of NaFel-xCoxAs revealed here shed important new light for defining microscopic models of the iron-based superconductors.In particular,we argue that both the itinerant electrons and local moments should be considered on an equal footing in a realistic model.

  15. Electron tunnel sensor technology

    Science.gov (United States)

    Waltman, S. B.; Kaiser, W. J.

    1989-01-01

    The recent development of Scanning Tunneling Microscopy technology allows the application of electron tunneling to position detectors for the first time. The vacuum tunnel junction is one of the most sensitive position detection mechanisms available. It is also compact, simple, and requires little power. A prototype accelerometer based on electron tunneling, and other sensor applications of this promising new technology are described.

  16. Scanning Tunneling Microscopy

    Science.gov (United States)

    1992-03-17

    1l1P lw:<t hands (<< deep resonances>>). ’l:he;r may aJ;.:o li<· rei’Ollallt; with tlw Ynh·JH’e bantls (hin<ling cm~rgi(·S grNtt<’r than tl1t• haml ...e1ierg~· band stru(·- ture C’omputNl using tllif’ mcul<’l yields a llir<•c·t haml gap E .. (.~·) 1’.𔃻. nll(ly (’Olll· JlOi>ition ,r (fig. 16) a11d <’X

  17. Characterization of Artifacts Introduced by the Empirical Volcano-Scan Atmospheric Correction Commonly Applied to CRISM and OMEGA Near-Infrared Spectra

    Science.gov (United States)

    Wiseman, S.M.; Arvidson, R.E.; Wolff, M. J.; Smith, M. D.; Seelos, F. P.; Morgan, F.; Murchie, S. L.; Mustard, J. F.; Morris, R. V.; Humm, D.; McGuire, P. C.

    2014-01-01

    The empirical volcano-scan atmospheric correction is widely applied to Martian near infrared CRISM and OMEGA spectra between 1000 and 2600 nanometers to remove prominent atmospheric gas absorptions with minimal computational investment. This correction method employs division by a scaled empirically-derived atmospheric transmission spectrum that is generated from observations of the Martian surface in which different path lengths through the atmosphere were measured and transmission calculated using the Beer-Lambert Law. Identifying and characterizing both artifacts and residual atmospheric features left by the volcano-scan correction is important for robust interpretation of CRISM and OMEGA volcano scan corrected spectra. In order to identify and determine the cause of spectral artifacts introduced by the volcano-scan correction, we simulated this correction using a multiple scattering radiative transfer algorithm (DISORT). Simulated transmission spectra that are similar to actual CRISM- and OMEGA-derived transmission spectra were generated from modeled Olympus Mons base and summit spectra. Results from the simulations were used to investigate the validity of assumptions inherent in the volcano-scan correction and to identify artifacts introduced by this method of atmospheric correction. We found that the most prominent artifact, a bowl-shaped feature centered near 2000 nanometers, is caused by the inaccurate assumption that absorption coefficients of CO2 in the Martian atmosphere are independent of column density. In addition, spectral albedo and slope are modified by atmospheric aerosols. Residual atmospheric contributions that are caused by variable amounts of dust aerosols, ice aerosols, and water vapor are characterized by the analysis of CRISM volcano-scan corrected spectra from the same location acquired at different times under variable atmospheric conditions.

  18. Two-dimensional functional molecular nanoarchitectures - Complementary investigations with scanning tunneling microscopy and X-ray spectroscopy

    Science.gov (United States)

    Klappenberger, Florian

    2014-02-01

    Functional molecular nanoarchitectures (FMNs) are highly relevant for the development of future nanotechnology devices. Profound knowledge about the atomically controlled construction of such nanoscale assemblies is an indispensable requirement to render the implementation of such components into a real product successful. For exploiting their full potential the architectures’ functionalities have to be characterized in detail including the ways to tailor them. In recent years a plethora of sophisticated constructs were fabricated touching a wide range of research topics. The present review summarizes important achievements of bottom-up fabricated, molecular nanostructures created on single crystal metal surfaces under ultra-high vacuum conditions. This selection focuses on examples where self-assembly mechanisms played a central role for their construction. Such systems, though typically quite complex, can be comprehensively understood by the STM+XS approach combining scanning tunneling microscopy (STM) with X-ray spectroscopy (XS) and being aided in the atomic interpretation by the appropriate theoretic analysis, often from density functional theory. The symbiosis of the techniques is especially fruitful because of the complementary character of the information accessed by the local microscopy and the space-averaging spectroscopy tools. STM delivers sub-molecular spatial-resolution, but suffers from limited sensitivity for the chemical and conformational states of the building-blocks. XS compensates these weaknesses with element- and moiety-specific data, which in turn would be hard to interpret with respect to structure formation without the topographic details revealed by STM. The united merit of this methodology allows detailed geometric information to be obtained and addresses both the electronic and chemical state of the complex organic species constituting such architectures. Thus, possible changes induced by the various processes such as surface

  19. 电子自旋共振扫描隧道显微镜%Electron spin resonance scanning tunneling microscope

    Institute of Scientific and Technical Information of China (English)

    郭阳; 李健梅; 陆兴华

    2015-01-01

    It is highly expected that the future informatics will be based on the spins of in-dividual electrons. The development of elementary information unit will eventually leads to novel single-molecule or single-atom devices based on electron spins;the quantum computer in the fu-ture can be constructed with single electron spins as the basic quantum bits. However, it is still a great challenge in detection and manipulation of a single electron spin, as well as its coherence and entanglement. As an ideal experimental tool for such tasks, the development of electron spin resonance scanning tunneling microscope (ESR-STM) has attracted great attention for decades. This paper briefly introduces the basic concept of ESR-STM. The development history of this in-strument and recent progresses are reviewed. The underlying mechanism is explored and summa-rized. The challenges and possible solutions are discussed. Finally, the prospect of future direction and applications are presented.%单电子自旋极有可能发展成为未来信息学的基础。以电子自旋为核心的新型单分子或单原子器件将最终成为基本信息单元,基于单电子的自旋态将有可能构筑未来量子计算机的量子比特。但是,如何实现对单个电子自旋及其相干态和纠缠态的测量和控制,目前仍然是一个很大的挑战。作为调控单个电子自旋的重要实验手段,电子自旋共振扫描隧道显微镜的发展一直备受关注。文章简要介绍了电子自旋共振扫描隧道显微镜的基本概念,阐述了其发展历史和最新进展,归纳了机理探索的研究成果,论述了该设备研发面临的挑战与对策,并对未来的发展和应用做了展望。

  20. Scanning tunneling microscopic and spectroscopic studies on a crystalline silica monolayer epitaxially formed on hexagonal SiC(0001¯) surfaces

    Science.gov (United States)

    Tochihara, Hiroshi; Shirasawa, Tetsuroh; Suzuki, Takayuki; Miyamachi, Toshio; Kajiwara, Takashi; Yagyu, Kazuma; Yoshizawa, Shunsuke; Takahashi, Toshio; Tanaka, Satoru; Komori, Fumio

    2014-02-01

    An epitaxial silicon-oxide monolayer of chemical composition of Si2O3 (the Si2O3 layer) formed on hexagonal SiC(0001¯) surfaces has been observed by scanning tunneling microscopy (STM). Filled- and empty-state STM images with atomic resolution support the previously reported model. Typical structural defects in the Si2O3 layer are found to be missing SiOn (n = 1, 2, 3) molecules. The band gap of the Si2O3 layer obtained by point tunneling spectroscopy is 5.5±0.5 eV, exhibiting considerable narrowing from that of bulk SiO2, 8.9 eV. It is proposed that the Si2O3 layer is suitable as a relevant interface material for formation of SiC-based metal-oxide-semiconductor devices.

  1. 铁基超导体FeSe Te 表面隧道谱的研究∗%Investigation of scanning tunneling sp ectra on iron-based superconductor FeSe0.5Te0.5

    Institute of Scientific and Technical Information of China (English)

    杜增义; 方德龙; 王震宇; 杜冠; 杨雄; 杨欢; 顾根大; 闻海虎

    2015-01-01

    用扫描隧道显微镜/谱仪仔细研究了铁基超导单晶FeSe0.5 Te0.5样品的表面形貌和隧道谱,测量到了清晰的表面原子形貌和在空间比较稳定的隧道谱结构.在样品中测量的隧道谱零能态密度比较高,说明样品里面有比较强的非弹性准粒子散射.在正能5mV附近有个较大的背景鼓包,这一背景在很高温度也未消失.空间中Se和Te集中的位置会带来高能背景的变化,超导能隙附近谱的形状大致相同.较强的非弹性准粒子散射破坏了超导的准粒子散射,因此没有在二维微分电导图中发现超导准粒子相干散射的特征亮斑.%FeSe0.5Te0.5 single crystals with superconducting critical temperature of 13.5 K are investigated by scanning tun-neling microscopy/spectroscopy (STM/STS) measurements in detail. STM image on the top surface shows an atomically resolved square lattice consisted by white and dark spots with a constant of about 3.73±0.03 Å which is consistent with the lattice constant 3.78 Å. The Se and Te atoms with a height difference of about 0.35 Å are successfully identified since the sizes of the two kinds of atoms are different. The tunneling spectra show very large zero-bias conductance value and asymmetric coherent peaks in the superconducting state. According to the positions of coherence peaks, we determine the superconducting gap 2∆=5.5 meV, and the reduced gap 2∆/kBTc =4.9 is larger than the value predicted by the weak-coupling BCS theory. The zero-bias conductance at 1.7 K only have a decrease of about 40% compared with the normal state conductance, which may originate from some scattering and broadening mechanism in the material. This broadening effect will also make the superconducting gap determined by the distance between the coherence peaks larger than the exact gap value. The asymmetric structure of the tunneling spectra near the superconducting gap is induced by the hump on the background. This hump

  2. Scanning tunneling microscopy and spectroscopy on GaN and InGaN surfaces; Rastertunnelmikroskopie und -spektroskopie an GaN- und InGaN-Oberflaechen

    Energy Technology Data Exchange (ETDEWEB)

    Krueger, David

    2009-12-02

    Optelectronic devices based on gallium nitride (GaN) and indium gallium nitride (InGaN) are in the focus of research since more than 20 years and still have great potential for optical applications. In the first part of this work non-polar surfaces of GaN are investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and scanning tunneling microscopy (STM). In SEM and AFM, the (1 anti 100)- and especially the (anti 2110)-plane are quite corrugated. For the first time, the (anti 2110)-plane of GaN is atomically resolved in STM. In the second part InGaN quantum dot layers are investigated by X-ray photoelectron spectroscopy (XPS), scanning tunneling spectroscopy (STS) and STM. The STMmeasurements show the dependency of surface morphology on growth conditions in the metalorganic vapour phase epitaxy (MOVPE). Nucleation, a new MOVPE-strategy, is based on phase separations on surfaces. It is shown that locally varying density of states and bandgaps can be detected by STS, that means bandgap histograms and 2D-bandgap-mapping. (orig.)

  3. c(4 × 2) and related structural units on the SrTiO3(001) surface: scanning tunneling microscopy, density functional theory, and atomic structure.

    Science.gov (United States)

    Becerra-Toledo, A E; Marshall, M S J; Castell, M R; Marks, L D

    2012-06-07

    Density functional theory is used to simulate high-bias, constant-current scanning tunneling micrographs for direct comparison with experimental images. Coupled to previous spectroscopic data, these simulations are used to determine the atomic structure of Ti-rich nanostructures on strontium titanate (001) surfaces. These nanostructures have three consecutive TiO(x) surface layers and exploit the distinctive structural motif of the c(4 × 2) reconstruction as their main building block. A structural model of a characteristic triline defect is also proposed.

  4. Polymer adsorption on reconstructed Au(001): a statistical description of P3HT by scanning tunneling microscopy and coarse-grained Monte Carlo simulations.

    Science.gov (United States)

    Förster, S; Kohl, E; Ivanov, M; Gross, J; Widdra, W; Janke, W

    2014-10-28

    We report on a combined theoretical and experimental characterization of isolated Poly(3-hexylthiophene) (P3HT) chains weakly adsorbed on a reconstructed Au(001) surface. The local chain conformations of in situ deposited P3HT molecules were investigated by means of scanning tunneling microscopy. For comparison, Monte Carlo simulations of the system were performed up to a maximum chain length of 60 monomer units. The dependence of the end-to-end distance and the radius of gyration on the polymer chain length shows a good agreement between experiment and Monte Carlo simulations using simple updates for short chains.

  5. Nano-localized desorption and time-of-flight mass analysis using solely optical enhancement in the proximity of a scanning tunneling microscope tip

    Science.gov (United States)

    Ding, Yu; Micheletto, Ruggero; Okazaki, Satoshi; Otsuka, Koji

    2003-04-01

    The combination of scanning tunneling microscopy (STM) with time-of-flight mass system (TOF-MS) adds new information to STM imaging. In this study, an STM system has been combined with laser excitation and was used for desorption and ionization of surface molecules, without the use of any other external stimulus. Desorbed ions from confined areas were accelerated and detected by a TOF chamber. We demonstrate in this paper that the technique proposed enables desorption of superficial structures within a small area of approximately 5 nm diameter and simultaneous mass spectroscopy of the desorbed atoms.

  6. Structure determination of the indium induced Si(001)-(4X3) reconstruction by surface x-ray diffraction and scanning tunneling microscopy

    DEFF Research Database (Denmark)

    Bunk, O.; Falkenberg, G.; Seehofer, L.;

    1998-01-01

    The indium-induced Si(001)-(4 X 3) reconstruction has been investigated by surface X-ray diffraction (SXRD) measurements with synchrotron radiation and scanning tunneling microscopy (STM). The Patterson function analysis enables us to exclude In dimers as a structural element in this reconstruction....... We present a new structural model which includes 6 In atoms threefold coordinated to Si atoms and 5 displaced Si atoms per unit cell. Relaxations down to the sixth layer were determined. 'Trimers' made up of In-Si-In atoms are a key structural element. (C) 1998 Elsevier Science B.V....

  7. Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy.

    Science.gov (United States)

    Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R

    2014-04-01

    Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without

  8. Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R., E-mail: smitha2@ohio.edu [Department of Physics and Astronomy, Nanoscale and Quantum Phenomena Institute, Ohio University, Athens, Ohio 45701 (United States)

    2014-04-15

    Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without

  9. Scanning tunneling microscopy study of the c(4x4) structure formation in the sub-monolayer Sb/Si(100) system

    Energy Technology Data Exchange (ETDEWEB)

    Saranin, A.A.; Zotov, A.V. [Osaka Univ., Suita (Japan). Faculty of Engineering; Kotlyar, V.G. [Institute of Automation and Control Processes, Vladivostok (RU)] (and others)

    2001-10-01

    Upon Sb desorption from a Sb-saturated Si(100) surface, the c(4x4) structure formed at about 0.25 monolayer Sb coverage. The c(4x4) reconstruction has been found to develop best when the surface is slightly contaminated, plausibly, by carbon. The Si(100)-c(4x4)-Sb surface shows up in the high-resolution filled state scanning tunneling microscopy images as being very similar to that of the recently reported c(4x4)-Si reconstruction. Here the main features of the Si(100)-c(4x4)-Sb structure are identified and the possible atomic arrangement is discussed. (author)

  10. Binding structures of propylene glycol stereoisomers on the Si(001)-2×1 surface: a combined scanning tunneling microscopy and theoretical study.

    Science.gov (United States)

    Hahn, Jae Ryang; Bharath, Satyaveda C; Jeong, Sukmin; Pearl, Thomas P

    2011-01-28

    The binding configuration of propylene glycol stereoisomer molecules adsorbed on the Si(001)-2×1 surface was investigated using a combination of scanning tunneling microscopy (STM) and density functional theory calculations. Propylene glycol was found to adsorb dissociatively via two hydroxyl groups exclusively as a bridge between the ends of two adjacent dimers along the dimer row. The chirality was preserved during bonding to Si atoms and was identifiable with STM imaging. The large number of propylene glycol conformers in the gas phase was reduced to a single configuration adsorbed on the surface at low molecular coverage.

  11. Investigation of inelastic electron tunneling spectra of metal-molecule-metal junctions fabricated using direct metal transfer method

    Energy Technology Data Exchange (ETDEWEB)

    Jeong, Hyunhak; Hwang, Wang-Taek; Kim, Pilkwang; Kim, Dongku; Jang, Yeonsik; Min, Misook; Park, Yun Daniel; Lee, Takhee, E-mail: tlee@snu.ac.kr [Department of Physics and Astronomy, Institute of Applied Physics, Seoul National University, Seoul 151-747 (Korea, Republic of); Xiang, Dong [Institute of Modern Optics, Nankai University, Tianjin 300071 (China); Song, Hyunwook [Department of Applied Physics, Kyung Hee University, Yongin-si, Gyeonggi-do 446–701 (Korea, Republic of); Jeong, Heejun, E-mail: hjeong@hanyang.ac.kr [Department of Applied Physics, Hanyang University, Ansan 426-791 (Korea, Republic of)

    2015-02-09

    We measured the inelastic electron tunneling spectroscopy (IETS) characteristics of metal-molecule-metal junctions made with alkanethiolate self-assembled monolayers. The molecular junctions were fabricated using a direct metal transfer method, which we previously reported for high-yield metal-molecule-metal junctions. The measured IETS data could be assigned to molecular vibration modes that were determined by the chemical structure of the molecules. We also observed discrepancies and device-to-device variations in the IETS data that possibly originate from defects in the molecular junctions and insulating walls introduced during the fabrication process and from the junction structure.

  12. A combined frequency modulation dynamic force microscopy (FM-DFM) and scanning tunneling microscopy (STM) study of a SiO{sub 2}/Ru(0001) model system

    Energy Technology Data Exchange (ETDEWEB)

    Buechner, Christin; Lichtenstein, Leonid; Heinke, Lars; Heyde, Markus; Freund, Hans-Joachim [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin (Germany)

    2011-07-01

    Silica based support materials play an important role in catalysis. A stable and well characterized crystalline silica film can act as a model system for bulk silica and help us to understand silica's properties in detail. In order to examine catalytically relevant processes on such model surfaces, a thorough investigation of defect sites of any form is eminent. Recently, a double-layer silica film could be prepared on Ru(0001). Here we used a combined frequency modulation dynamic force microscope (FM-DFM) and scanning tunneling microscope (STM) under low temperature and ultra-high vacuum conditions to unveil the thin film's structural and electronic surface properties. Atomically resolved images of the crystalline silica film grown on Ru(0001) are presented. Structural elements of the pristine film, as well as its defects, are highlighted. Based on atomic resolution FM-DFM and STM images a direct comparison with density functional theory calculation can be made. Theory as well as experiment favor a hexagonal honeycomb structure of the film. Spectroscopy measurements, i.e. scanning tunneling spectroscopy (STS) and Kelvin probe force microscopy (KPFM), provide first insights into electronic properties of the system.

  13. Scanning tunneling spectroscopy of SrFe{sub 2}(As{sub 1-x}P{sub x}){sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Jandke, Jasmin; Wild, Petra; Schackert, Michael; Wulfhekel, Wulf [Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Str. 1, 76131 Karlsruhe (Germany)

    2015-07-01

    The antiferromagnetic parent compound SrFe{sub 2}As{sub 2} shows a supression of the spin density wave and a subsequent superconducting state upon partial substitution of As by P. We investigated single crystals for four different P-concentrations x in the superconducting (x=0.35,0.46) as well as in the spin density wave phase (x=0,0.2). The superconducting samples display a v-shaped superconducting gap, which suggests nodal superconductivity in this system. Furthermore, we were able to determine the superconducting coherence length by measuring the spatial resolved superconducting density of states. From inelastic tunneling spectra it is possible to determine the Eliashberg function from the normal state. We thus investigated bosonic excitations for the four different P-concentrations. Indeed, evidence suggests peaks which can be related to bosonic modes. The phonon an non-phonon mechanism for the origin of these peaks will be discussed.

  14. Computer-aided screening system for cervical precancerous cells based on field emission scanning electron microscopy and energy dispersive x-ray images and spectra

    Science.gov (United States)

    Jusman, Yessi; Ng, Siew-Cheok; Hasikin, Khairunnisa; Kurnia, Rahmadi; Osman, Noor Azuan Bin Abu; Teoh, Kean Hooi

    2016-10-01

    The capability of field emission scanning electron microscopy and energy dispersive x-ray spectroscopy (FE-SEM/EDX) to scan material structures at the microlevel and characterize the material with its elemental properties has inspired this research, which has developed an FE-SEM/EDX-based cervical cancer screening system. The developed computer-aided screening system consisted of two parts, which were the automatic features of extraction and classification. For the automatic features extraction algorithm, the image and spectra of cervical cells features extraction algorithm for extracting the discriminant features of FE-SEM/EDX data was introduced. The system automatically extracted two types of features based on FE-SEM/EDX images and FE-SEM/EDX spectra. Textural features were extracted from the FE-SEM/EDX image using a gray level co-occurrence matrix technique, while the FE-SEM/EDX spectra features were calculated based on peak heights and corrected area under the peaks using an algorithm. A discriminant analysis technique was employed to predict the cervical precancerous stage into three classes: normal, low-grade intraepithelial squamous lesion (LSIL), and high-grade intraepithelial squamous lesion (HSIL). The capability of the developed screening system was tested using 700 FE-SEM/EDX spectra (300 normal, 200 LSIL, and 200 HSIL cases). The accuracy, sensitivity, and specificity performances were 98.2%, 99.0%, and 98.0%, respectively.

  15. Design and performance of an ultra-high vacuum scanning tunneling microscope operating at dilution refrigerator temperatures and high magnetic fields

    CERN Document Server

    Misra, Shashank; Drozdov, Ilya K; Seo, Jungpil; Gyenis, Andras; Kingsley, Simon C J; Jones, Howard; Yazdani, Ali

    2013-01-01

    We describe the construction and performance of a scanning tunneling microscope (STM) capable of taking maps of the tunneling density of states with sub-atomic spatial resolution at dilution refrigerator temperatures and high (14 T) magnetic fields. The fully ultra-high vacuum system features visual access to a two-sample microscope stage at the end of a bottom-loading dilution refrigerator, which facilitates the transfer of in situ prepared tips and samples. The two-sample stage enables location of the best area of the sample under study and extends the experiment lifetime. The successful thermal anchoring of the microscope, described in detail, is confirmed through a base temperature reading of 20 mK, along with a measured electron temperature of 250 mK. Atomically-resolved images, along with complementary vibration measurements, are presented to confirm the effectiveness of the vibration isolation scheme in this instrument. Finally, we demonstrate that the microscope is capable of the same level of perform...

  16. Experimental evidence for s-wave pairing symmetry in superconducting Cu(x)Bi2Se3 single crystals using a scanning tunneling microscope.

    Science.gov (United States)

    Levy, Niv; Zhang, Tong; Ha, Jeonghoon; Sharifi, Fred; Talin, A Alec; Kuk, Young; Stroscio, Joseph A

    2013-03-15

    Topological superconductors represent a newly predicted phase of matter that is topologically distinct from conventional superconducting condensates of Cooper pairs. As a manifestation of their topological character, topological superconductors support solid-state realizations of Majorana fermions at their boundaries. The recently discovered superconductor Cu(x)Bi(2)Se(3) has been theoretically proposed as an odd-parity superconductor in the time-reversal-invariant topological superconductor class, and point-contact spectroscopy measurements have reported the observation of zero-bias conductance peaks corresponding to Majorana states in this material. Here we report scanning tunneling microscopy measurements of the superconducting energy gap in Cu(x)Bi(2)Se(3) as a function of spatial position and applied magnetic field. The tunneling spectrum shows that the density of states at the Fermi level is fully gapped without any in-gap states. The spectrum is well described by the Bardeen-Cooper-Schrieffer theory with a momentum independent order parameter, which suggests that Cu(x)Bi(2)Se(3) is a classical s-wave superconductor contrary to previous expectations and measurements.

  17. Scanning tunneling microscopic and spectroscopic studies on a crystalline silica monolayer epitaxially formed on hexagonal SiC(0001{sup ¯}) surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Tochihara, Hiroshi, E-mail: tochihara@fukuoka-u.ac.jp, E-mail: tochihara.hiroshi.146@m.kyushu-u.ac.jp; Suzuki, Takayuki; Yagyu, Kazuma [Department of Electronics Engineering and Computer Science, Fukuoka University, Fukuoka 814-0180 (Japan); Shirasawa, Tetsuroh; Takahashi, Toshio [Laser and Synchrotron Research Center, Institute for Solid State Physics, University of Tokyo, Chiba 277-8581 (Japan); Miyamachi, Toshio; Yoshizawa, Shunsuke; Komori, Fumio [Nanoscale Science Division, Institute for Solid State Physics, University of Tokyo, Chiba 277-8581 (Japan); Kajiwara, Takashi; Tanaka, Satoru [Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Fukuoka 819-0395 (Japan)

    2014-02-03

    An epitaxial silicon-oxide monolayer of chemical composition of Si{sub 2}O{sub 3} (the Si{sub 2}O{sub 3} layer) formed on hexagonal SiC(0001{sup ¯}) surfaces has been observed by scanning tunneling microscopy (STM). Filled- and empty-state STM images with atomic resolution support the previously reported model. Typical structural defects in the Si{sub 2}O{sub 3} layer are found to be missing SiO{sub n} (n = 1, 2, 3) molecules. The band gap of the Si{sub 2}O{sub 3} layer obtained by point tunneling spectroscopy is 5.5±0.5 eV, exhibiting considerable narrowing from that of bulk SiO{sub 2}, 8.9 eV. It is proposed that the Si{sub 2}O{sub 3} layer is suitable as a relevant interface material for formation of SiC-based metal-oxide-semiconductor devices.

  18. Iron on GaN(0001) pseudo-1 × 1 (1+1/(12) ) investigated by scanning tunneling microscopy and first-principles theory

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Wenzhi; Mandru, Andrada-Oana; Smith, Arthur R., E-mail: smitha2@ohio.edu [Department of Physics and Astronomy, Nanoscale and Quantum Phenomena Institute, Ohio University, Athens, Ohio 45701 (United States); Takeuchi, Noboru [Centro de Nanociencias y Nanotecnologia, Universidad Nacional Autonoma de Mexico Apartado Postal 14, Ensenada Baja California, Codigo Postal 22800 (Mexico); Al-Brithen, Hamad A. H. [Physics and Astronomy Department, King Abdulah Institute for Nanotechnology, King Saud University, Riyadh, Saudi Arabia, and National Center for Nano Technology, KACST, Riyadh (Saudi Arabia)

    2014-04-28

    We have investigated sub-monolayer iron deposition on atomically smooth GaN(0001) pseudo-1 × 1 (1+1/(12) ). The iron is deposited at a substrate temperature of 360 °C, upon which reflection high energy electron diffraction shows a transformation to a √(3)×√(3)-R30° pattern. After cooling to room temperature, the pattern transforms to a 6 × 6, and scanning tunneling microscopy reveals 6 × 6 reconstructed regions decorating the GaN step edges. First-principles theoretical calculations have been carried out for a range of possible structural models, one of the best being a Ga dimer model consisting of 2/9 monolayer of Fe incorporated into 7/3 monolayer of Ga in a relaxed but distorted structure.

  19. An Observation of Benzotriazole (BTA) Adsorption on Cu(110) by the Ultra High Vacuum (UHV)-Scanning Tunneling Microscope (STM) and Low Energy Electron Difiraction (LEED)

    Science.gov (United States)

    Cho, Kyehyun; Kishimoto, Jiro; Hashizume, Tomihiro; Sakurai, Toshio

    1994-01-01

    We have investigated Benzotriazole (BTA) adsorption structures and kinetics on the clean Cu(110) and oxygen reconstructed Cu(110)-2×1 surfaces. The first atomicaly resolved scanning tunneling microscope (STM) images showed that BTA adsorbed on the clean Cu(110)-1×1 surface to form the c(4×2) commensurate structure, agreeing the c(4×2) LEED pattern. On the other hand, STM images of BTA adsorbed on the oxygen induced Cu(110)-2×1 surface were a fully disordered structure. In kinetic point of view, BTA molecules should adsorb preferentially on the oxygen induced Cu(110)-2×1 missing row compared to the clean Cu(110) surface.

  20. Thermal stress in the scanning tunneling microscopy of the metallic heterostructure lead on copper(111); Thermospannung bei der Rastertunnelmikroskopie der metallischen Heterostruktur Blei auf Kupfer(111)

    Energy Technology Data Exchange (ETDEWEB)

    Langenkamp, Winfried

    2008-02-22

    The thermal stress, which arises, when tip and sample of a scanning tunneling microscope have different temperatures, was studied in the system lead on copper(111). Thereby atomic resolution on the 4 x 4 superstructure of the lead atoms of the first layer was reached. The thermal stress of lead island was studied because the electronic density of states here is in the greatest part determined by quantum pot states. The density of states as function of the energy can by approached as step function und is by this available for a mathematical modelling. As sum of the influence of the substrates and the influence by the quantum pot states it bas possible to develop a model. in which the thermal stress for lead islands on copper(111) can be described also quantitatively.

  1. Structure, Mobility, and Composition of Transition Metal Catalyst Surfaces. High-Pressure Scanning Tunneling Microscopy and Ambient-Pressure X-ray Photoelectron Spectroscopy Studies

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Zhongwei [Univ. of California, Berkeley, CA (United States)

    2013-12-06

    Surface structure, mobility, and composition of transition metal catalysts were studied by high-pressure scanning tunneling microscopy (HP-STM) and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) at high gas pressures. HP-STM makes it possible to determine the atomic or molecular rearrangement at catalyst surfaces, particularly at the low-coordinated active surface sites. AP-XPS monitors changes in elemental composition and chemical states of catalysts in response to variations in gas environments. Stepped Pt and Cu single crystals, the hexagonally reconstructed Pt(100) single crystal, and Pt-based bimetallic nanoparticles with controlled size, shape and composition, were employed as the model catalysts for experiments in this thesis.

  2. DESORPTION OF Te CAPPING LAYER FROM ZnTe (100: AUGER SPECTROSCOPY, LOW-ENERGY ELECTRON DIFFRACTION AND SCANNING TUNNELING MICROSCOPY

    Directory of Open Access Journals (Sweden)

    K. K. Sossoe

    2016-01-01

    Full Text Available The influence of the annealing temperature to desorb a protective Te capping layer of the zinc telluride (ZnTe (100 surface was investigated. The surface reconstruction of the ZnTe (100 upon the removal of a Te capping layer grown by the molecular beam epitaxy was characterized by different methods. Auger spectroscopy brought out the chemical composition of the surface before and after annealing; the Low-energy electron diffraction (LEED gave information about the crystallographic structure. The surface crystallographic configurations of tellurium Te (c (2x2 and Te (c (2x1 are confirmed by scanning tunneling microscopy (STM. Such a study reveals a phase transition from a rich-Te to a poor-Te surface as the annealing temperature increases. 

  3. In situ scanning tunneling microscopy study of selective dissolution of Au{sub 3}Cu and Cu{sub 3}Au (0 0 1)

    Energy Technology Data Exchange (ETDEWEB)

    Renner, Frank Uwe [Max-Planck-Institut fuer Eisenforschung, Max-Planck-Str.1, Duesseldorf 40237 (Germany); Eckstein, Gerald Andreas [Universitaet Erlangen-Nuernberg, Martensstrasse 7, D-91058 Erlangen (Germany); Lymperakis, Liverios [Max-Planck-Institut fuer Eisenforschung, Max-Planck-Str.1, Duesseldorf 40237 (Germany); Dakkouri-Baldauf, Andrea [Universitaet Erlangen-Nuernberg, Martensstrasse 7, D-91058 Erlangen (Germany); Rohwerder, Michael, E-mail: m.rohwerder@mpie.d [Max-Planck-Institut fuer Eisenforschung, Max-Planck-Str.1, Duesseldorf 40237 (Germany); Neugebauer, Joerg; Stratmann, Martin [Max-Planck-Institut fuer Eisenforschung, Max-Planck-Str.1, Duesseldorf 40237 (Germany)

    2011-01-15

    We present an electrochemical study of Au{sub 3}Cu (0 0 1) single crystal surfaces in 0.1 mol dm{sup -3} H{sub 2}SO{sub 4} and 0.1 mol dm{sup -3} H{sub 2}SO{sub 4} + 0.1 mmol dm{sup -3} HCl, and of Cu{sub 3}Au (0 0 1) in 0.1 mol dm{sup -3} H{sub 2}SO{sub 4}. The focus is on in situ scanning tunneling microscopy experiments. The changes of the surface morphology, which are time- and potential-dependent, have been observed, clearly resolving single atomic steps and mono-atomic islands and pits. Chloride additives enhance the surface diffusion and respective morphologies are observed earlier. All surfaces have shown considerable roughening already in the passive region far below the critical potential.

  4. Low-temperature scanning tunneling microscopy/ultraviolet photoelectron spectroscopy investigation of two-dimensional crystallization of C60: pentacence binary system on Ag(111)

    Science.gov (United States)

    Lin Zhang, Jia; Hong Liang Zhang, Kelvin; Qiang Zhong, Jian; Chao Niu, Tian; Chen, Wei

    2012-02-01

    Atomic scale investigation of temperature-dependent two-dimensional (2 D) crystallization processes of fullerene-C60 on pentacene-covered Ag(111) surface has been carried out by in situ low-temperature scanning tunneling microscopy (LT-STM) experiments. To evaluate the effect of molecule-substrate interfacial interactions on the 2 D crystallization of C60: pentacene binary system, we also carried out the same self-assembly experiments of C60 on monolayer pentacene covered graphite substrate. It is revealed that temperature-dependent structural transition of various ordered C60 nanoassemblies is strongly influenced by the molecule-Ag(111) interfacial interactions, and further mediated by the weak C60-pentacene intermolecular interactions. In situ ultraviolet photoelectron spectroscopy (UPS) has been used to evaluate the nature of the intermolecular interactions between C60 and pentacene films.

  5. Molecular beam epitaxy growth and post-growth annealing of FeSe films on SrTiO3: a scanning tunneling microscopy study.

    Science.gov (United States)

    Li, Zhi; Peng, Jun-Ping; Zhang, Hui-Min; Zhang, Wen-Hao; Ding, Hao; Deng, Peng; Chang, Kai; Song, Can-Li; Ji, Shuai-Hua; Wang, Lili; He, Ke; Chen, Xi; Xue, Qi-Kun; Ma, Xu-Cun

    2014-07-02

    Low temperature scanning tunneling microscopy and spectroscopy are used to investigate the atomic and electronic structure evolution of FeSe films grown on SrTiO3 as a function of post-growth annealing. Single unit cell FeSe films are found to bond strongly with the underlying substrate, and become superconductive with diminishing chemical bond disorders at the interface via post-annealing. For thicker FeSe films, post-annealing removes excess Se in the films and leads to a transition from semiconductor into metallic behaviors. In double and multilayer films, strain-induced complex textures are observed and suggested to be the main cause for the absent superconductivity.

  6. September 1981: Invention of the scanning tunneling microscope%1981年9月:扫描隧道显微镜的发明

    Institute of Scientific and Technical Information of China (English)

    萧如珀; 杨信男

    2010-01-01

    @@ 科学仪器在20世纪80年代初由于扫描隧道式显微术(scanning tunneling microscopy, STM)--一个根据被称为隧道效应这个量子力学现象的解析性技术--的发展,而向前跨进了极大的一步.虽然探针尖端和物体表面并未实际接触,但它们之间的电压却会让电流在两者之间流通,此仪器因此得名.

  7. Toward quantitative STM: Scanning tunneling microscopy study of structure and dynamics of adsorbates on transition metal surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Dunphy, J.C.

    1995-05-01

    STM was applied to chemisorbed S layers on Re(000l) and Mo(100) surfaces. As function of coverage on both these surfaces, S orders into several different overlayer structures, which have been studied by dynamic LEED. STM images of all these structures were obtained. Approximate location of S atoms in the structures was determined by inspecting the images, especially the regions containing defects. Results are in agreement with LEED except for the p(2{times}l) overlayer of sulfur on Mo(100). The STM images were compared to calculations made with Electron Scattering Quantum Chemistry (ESQC) theory. Variation of contrast in experimental images is explained as a result of changes in STM tip termination structure. STM image contrast is a result of changes in the interference between different paths for the tunneling electrons. The simplest structure on the Mo(100) surface was used as a model for developing and testing a method of quantitative structure determination with the STM. Experimental STM images acquired under a range of tunneling conditions were compared to theoretical calculations of the images as a function of surface structure to determine the structure which best fit. Results matched within approximately 0.1 Angstroms a LEED structural determination. At lower S coverage, diffusion of S atoms over the Re(0001) surface and the lateral interaction between these atoms were investigated by application of a new image analysis technique. The interaction between the S and a coadsorbed CO layer was also studied, and CO was found to induce compression of the S overlayer. A similar result was found for Au deposited on the sulfur covered Mo(100) surface. The interaction between steps on the Mo surface was found to be influenced by S adsorption and this observation was interpreted with the theory of equilibrium crystal shape. Design of an STM instrument which operates at cryogenic and variable sample temperatures, and its future applications, are described.

  8. Ultrasonic lateral modulation imaging, speckle reduction, and displacement vector measurements using simple single-beam scanning or plural crossed-beam scanning with new spectra frequency division processing methods

    Directory of Open Access Journals (Sweden)

    Sumi C

    2012-10-01

    spectra frequency division method (SFDM. However, the lateral carrier frequency and the measurement accuracy acquired by using such a single-beam scanning method are lower than those achieved with the original LM scanning methods and should be increased (ie, by using a quasi-LM method. In this report, the effectiveness of the use of the new SFDMs is verified with experiments on agar phantoms, in which conventional non-steered, focused single-beam transmission/reception scanning is performed together with high-speed non-steered single plane-wave transmission and non-steered, focused single-beam reception scanning using a linear array-type transducer. For comparison, the original LMs, with their respective transmissions of crossed, steered focused beams and plane waves are also performed. Because the use of rectangular apodization functions (ie, no apodization yields a larger bandwidth in a lateral direction than the effective use of parabolic functions with the original LM method, it is shown that disregarding the lateral low-frequency spectra yields useful quasi-LM echo imaging with a high lateral frequency, and further significantly increases the measurement accuracy of a displacement vector. In addition, when no apodization is used with the original version of LM, disregarding the low-frequency lateral spectra is effective. In addition, the interchangeability of cosine and sine modulations performed after completing beamforming can also be used for single-beam scanning as well as for the original LM scanning method. Specifically, the cosine and sine modulations, respectively, are used for LM and quasi-LM imaging and displacement vector measurements. It is concluded that the appropriate use of the new SFDMs with simple single-beam scanning or with simple plural crossed-beam scanning with no apodization can achieve almost the same accuracy as the original LM scanning method using plural crossed beams with the effective apodization. Another new application of SFDM is also

  9. Studies of the intrinsic inhomogeneity and pseudogap phenomena of La0.7Ca0.3MnO3 epitaxial films using spin-polarized (SP) scanning tunneling microscopy (STM)

    Science.gov (United States)

    Hughes, C. R.; Shi, J.; Beyer, A. D.; Yeh, N.-C.

    2010-03-01

    Spatially resolved tunneling spectra of La0.7Ca0.3MnO3 (Tc = 260K) epitaxial films are studied using STM under varying temperature, magnetic field, and the degree of spin polarization in the tunneling currents. With both regular and magnetic STM tips, conductance inhomogeneity related to the phase separation nature of manganites is observed below the Curie temperature and in zero fields, and the inhomogeneity decreases with magnetic field and above the Curie temperature. On the other hand, with magnetic tips the field-dependent tunneling spectra may be quantitatively explained by SP tunneling in a spin-valve configuration. In addition, a nearly temperature independent psuedogap (˜ 0.4 eV) and a larger energy gap (˜ 0.6 eV) at low temperatures are found; the former disappears upon the application of magnetic field, and the latter may be attributed to a surface ferromagnetic insulator phase because of the manifestation of spin filtering effect under SP tunneling in opposite field orientations.

  10. Local X-ray magnetic circular dichroism study of Fe/Cu(111) using a tunneling smart tip

    Energy Technology Data Exchange (ETDEWEB)

    DiLullo, Andrew; Shirato, Nozomi; Cummings, Marvin [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Kersell, Heath; Chang, Hao [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Ohio University, Athens, OH 45701 (United States); Rosenmann, Daniel; Miller, Dean; Freeland, John W. [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Hla, Saw-Wai [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Ohio University, Athens, OH 45701 (United States); Rose, Volker, E-mail: vrose@anl.gov [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States)

    2016-01-28

    A tunneling smart tip of a synchrotron X-ray scanning tunneling microscope provides simultaneously localized topographic, elemental and magnetic information. Localized spectroscopy with simultaneous topographic, elemental and magnetic information is presented. A synchrotron X-ray scanning tunneling microscope has been employed for the local study of the X-ray magnetic circular dichroism at the Fe L{sub 2,3}-edges of a thin iron film grown on Cu(111). Polarization-dependent X-ray absorption spectra have been obtained through a tunneling smart tip that serves as a photoelectron detector. In contrast to conventional spin-polarized scanning tunneling microscopy, X-ray excitations provide magnetic contrast even with a non-magnetic tip. Intensity variations in the photoexcited tip current point to chemical variations within a single magnetic Fe domain.

  11. Heterodimers formed through a partial anionic exchange process: scanning tunneling spectroscopy to monitor bands across the junction vis-à-vis photoinduced charge separation

    Science.gov (United States)

    Bera, Abhijit; Saha, Sudip K.; Pal, Amlan J.

    2015-10-01

    We report controlled formation of heterodimers and their charge separation properties. CdS|CdTe heterodimers were formed through an anionic exchange process of CdS nanostructures. With control over the duration of the anionic exchange process, bulk|dot, bulk|bulk, and then dot|bulk phases of the semiconductors could be observed to have formed. A mapping of density of states as derived from scanning tunneling spectroscopy (STS) brought out conduction and valence band-edges along the nanostructures and heterodimers. The CdS|CdTe heterodimers evidenced a type-II band-alignment between the semiconductors along with the formation of a depletion region at the interface. The width (of the depletion region) and the energy-offset at the interface depended on the size of the semiconductors. We report that the width that is instrumental for photoinduced charge separation in the heterodimers has a direct correlation with the performance of hybrid bulk-heterojunction solar cells based on the nanostructures in a polymer matrix.We report controlled formation of heterodimers and their charge separation properties. CdS|CdTe heterodimers were formed through an anionic exchange process of CdS nanostructures. With control over the duration of the anionic exchange process, bulk|dot, bulk|bulk, and then dot|bulk phases of the semiconductors could be observed to have formed. A mapping of density of states as derived from scanning tunneling spectroscopy (STS) brought out conduction and valence band-edges along the nanostructures and heterodimers. The CdS|CdTe heterodimers evidenced a type-II band-alignment between the semiconductors along with the formation of a depletion region at the interface. The width (of the depletion region) and the energy-offset at the interface depended on the size of the semiconductors. We report that the width that is instrumental for photoinduced charge separation in the heterodimers has a direct correlation with the performance of hybrid bulk

  12. Electron paramagnetic resonance-based pH mapping using spectral-spatial imaging of sequentially scanned spectra

    OpenAIRE

    Koda, Shunichi; Goodwin, Jonathan; Khramtsov, Valery V.; Fujii, Hirotada; Hirata, Hiroshi

    2012-01-01

    The development of electron paramagnetic resonance (EPR)-based mapping of pH is an important advancement for the field of diagnostic imaging. The ability to accurately quantify pH change in vivo and monitor spatial distribution is desirable for the assessment of a number of pathological conditions in the human body as well as the monitoring of treatment response. In this work we introduce a method for EPR-based pH mapping, utilizing a method of spectral-spatial imaging of sequentially scanned...

  13. Solvent-controlled 2D host-guest (2,7,12-trihexyloxytruxene/coronene) molecular nanostructures at organic liquid/solid interface investigated by scanning tunneling microscopy.

    Science.gov (United States)

    Liu, Jia; Zhang, Xu; Yan, Hui-Juan; Wang, Dong; Wang, Jie-Yu; Pei, Jian; Wan, Li-Jun

    2010-06-01

    The two-dimensional (2D) self-assembled networks of 2,7,12-trihexyloxytruxene (Tr) are shown to accommodate coronene guest molecules on highly oriented pyrolytic graphite (HOPG) surfaces. The host-guest structures are revealed by scanning tunneling microscopy (STM) at liquid/solid interfaces. The effect of solvents on the host-guest structures is intensively investigated in different solvents such as 1,2,4-trichlorobenzene (TCB), 1-phenyloctane, 1-octanol, and tetradecane. In contrast to the similar 2D hexagonal self-assembly of Tr host template on HOPG in different solvents, the formation of host-guest nanostructures of coronene in Tr 2D network strongly depend on the polarity of the solvents. The thermodynamic equilibrium during the host-guest assembly process is discussed, and the solvent-guest interaction is proposed as a main contributor for the observed solvent effect in the 2D host-guest self-assembly process. The results are significant to surface host-guest chemistry and nanopatterning.

  14. All-In Laser Scanning Methods for Surveying, Representing and Sharing Information on Archaeology. Via Flaminia and the Furlo Tunnel Complex

    Science.gov (United States)

    Clini, P.; Nespeca, R.; Bernetti, A.

    2013-07-01

    The aim of this paper is to describe the results of the laser scanner survey of an archaeological complex, aimed at knowledge, documentation and diagnostic operations to make premises secure. Archaeology has always been the most complex subject where the discipline of surveying is continually being put to the test and experimented with. The development in laser scanner technologies has led to an extremely important turning point in this field. Complex geometrical shapes or irregular surfaces, such as those in archaeology, are defined through surfaces that can be directly extrapolated from the point cloud with extremely high precision, allowing even the finest details to be mapped. The precision of this surveying technique together with the wide range of data that can be acquired and represented provide several opportunities for communication and investigation. This experimental work has concentrated on the Furlo tunnel complex, located along one of the most important infrastructural arteries from Roman antiquity, the Via Flaminia. The need in this case was to be able to acquire the entire rocky complex, extending the scan area as far as possible so as to assess the whole system in its entirety. The results of our metric and morphological survey provide an excellent basis for record the situation as it is today, so as to establish the initial temporal step to be used in future monitoring programmes. The accuracy of the survey allows static assessments and effective planning for future safety-oriented projects.

  15. Structural investigation of 1,1'-biphenyl-4-thiol self-assembled monolayers on Au(111) by scanning tunneling microscopy and low-energy electron diffraction.

    Science.gov (United States)

    Matei, D G; Muzik, H; Gölzhäuser, A; Turchanin, A

    2012-10-02

    Self-assembled monolayers (SAMs) of 1,1'-biphenyl-4-thiol (H-(C(6)H(4))(2)-SH) on Au(111) were prepared from solution or via vapor deposition in ultrahigh vacuum and characterized by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and X-ray photoelectron spectroscopy (XPS). In contrast to the typically observed for densely packed alkane-thiol SAMs on Au(111) (√3 × √3)R30° structure, the densely packed aromatic biphenylthiol SAMs prepared by both methods exhibit an unusual hexagonal (2 × 2) structure. Upon annealing at 100 °C, this structure evolves into the (2 × 7√3) structure resulting in the formation of highly ordered pinstripes oriented along the [1 -1 0] directions. Lower density SAMs, prepared by vapor deposition in vacuum, show mixed structures comprising the hexagonal (2 × 2) structure and two rectangular arrangements with the unit cells of (3√3 × 9) and (2√3 × 8). An extinction of the (3√3 × 9) structure in the favor of the (2√3 × 8) structure is observed upon annealing at temperatures of ~100 °C.

  16. Electronic and geometric properties of Au nanoparticles on Highly Ordered Pyrolytic Graphite (HOPG) studied using X-ray Photoelectron Spectroscopy (XPS) and Scanning Tunneling Microscopy (STM).

    Science.gov (United States)

    Lopez-Salido, Ignacio; Lim, Dong Chan; Dietsche, Rainer; Bertram, Nils; Kim, Young Dok

    2006-01-26

    Au nanoparticles grown on mildly sputtered Highly Ordered Pyrolytic Graphite (HOPG) surfaces were studied using Scanning Tunneling Microscopy (STM) and X-ray Photoelectron Spectroscopy (XPS). The results were compared with those of Ag nanoparticles on the same substrate. By varying the defect densities of HOPG and the Au coverages, one can create Au nanoparticles in various sizes. At high Au coverages, the structures of the Au films significantly deviate from the ideal truncated octahedral form: the existence of many steps between different Au atomic layers can be observed, most likely due to a high activation barrier of the diffusion of Au atoms across the step edges. This implies that the particle growth at room temperature is strongly limited by kinetic factors. Hexagonal shapes of Au structures could be identified, indicating preferential growth of Au nanostructures along the (111) direction normal to the surface. In the case of Au, XPS studies reveal a weaker core level shift with decreasing particle size compared to the 3d level in similarly sized Ag particles. Also taking into account the Auger analysis of the Ag particles, the core level shifts of the metal nanoparticles on HOPG can be understood in terms of the metal/substrate charge transfer. Ag is (partially) positively charged, whereas Au negatively charged on HOPG. It is demonstrated that XPS can be a useful tool to study metal-support interactions, which plays an important role for heterogeneous catalysis, for example.

  17. Spatially Resolved Imaging on Photocarrier Generations and Band Alignments at Perovskite/PbI2 Heterointerfaces of Perovskite Solar Cells by Light-Modulated Scanning Tunneling Microscopy.

    Science.gov (United States)

    Shih, Min-Chuan; Li, Shao-Sian; Hsieh, Cheng-Hua; Wang, Ying-Chiao; Yang, Hung-Duen; Chiu, Ya-Ping; Chang, Chia-Seng; Chen, Chun-Wei

    2017-02-08

    The presence of the PbI2 passivation layers at perovskite crystal grains has been found to considerably affect the charge carrier transport behaviors and device performance of perovskite solar cells. This work demonstrates the application of a novel light-modulated scanning tunneling microscopy (LM-STM) technique to reveal the interfacial electronic structures at the heterointerfaces between CH3NH3PbI3 perovskite crystals and PbI2 passivation layers of individual perovskite grains under light illumination. Most importantly, this technique enabled the first observation of spatially resolved mapping images of photoinduced interfacial band bending of valence bands and conduction bands and the photogenerated electron and hole carriers at the heterointerfaces of perovskite crystal grains. By systematically exploring the interfacial electronic structures of individual perovskite grains, enhanced charge separation and reduced back recombination were observed when an optimal design of interfacial PbI2 passivation layers consisting of a thickness less than 20 nm at perovskite crystal grains was applied.

  18. Dopant Diffusion and Activation in Silicon Nanowires Fabricated by ex Situ Doping: A Correlative Study via Atom-Probe Tomography and Scanning Tunneling Spectroscopy.

    Science.gov (United States)

    Sun, Zhiyuan; Hazut, Ori; Huang, Bo-Chao; Chiu, Ya-Ping; Chang, Chia-Seng; Yerushalmi, Roie; Lauhon, Lincoln J; Seidman, David N

    2016-07-13

    Dopants play a critical role in modulating the electric properties of semiconducting materials, ranging from bulk to nanoscale semiconductors, nanowires, and quantum dots. The application of traditional doping methods developed for bulk materials involves additional considerations for nanoscale semiconductors because of the influence of surfaces and stochastic fluctuations, which may become significant at the nanometer-scale level. Monolayer doping is an ex situ doping method that permits the post growth doping of nanowires. Herein, using atom-probe tomography (APT) with subnanometer spatial resolution and atomic-ppm detection limit, we study the distributions of boron and phosphorus in ex situ doped silicon nanowires with accurate control. A highly phosphorus doped outer region and a uniformly boron doped interior are observed, which are not predicted by criteria based on bulk silicon. These phenomena are explained by fast interfacial diffusion of phosphorus and enhanced bulk diffusion of boron, respectively. The APT results are compared with scanning tunneling spectroscopy data, which yields information concerning the electrically active dopants. Overall, comparing the information obtained by the two methods permits us to evaluate the diffusivities of each different dopant type at the nanowire oxide, interface, and core regions. The combined data sets permit us to evaluate the electrical activation and compensation of the dopants in different regions of the nanowires and understand the details that lead to the sharp p-i-n junctions formed across the nanowire for the ex situ doping process.

  19. Lateral ordering of PTCDA on the clean and the oxygen pre-covered Cu(100) surface investigated by scanning tunneling microscopy and low energy electron diffraction.

    Science.gov (United States)

    Gärtner, Stefan; Fiedler, Benjamin; Bauer, Oliver; Marele, Antonela; Sokolowski, Moritz M

    2014-01-01

    We have investigated the adsorption of perylene-3,4,9,10-tetracarboxylic acid dianhydride (PTCDA) on the clean and on the oxygen pre-covered Cu(100) surface [referred to as (√2 × 2√2)R45° - 2O/Cu(100)] by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). Our results confirm the (4√2 × 5√2)R45° superstructure of PTCDA/Cu(100) reported by A. Schmidt et al. [J. Phys. Chem. 1995, 99,11770-11779]. However, contrary to Schmidt et al., we have no indication for a dissociation of the PTCDA upon adsorption, and we propose a detailed structure model with two intact PTCDA molecules within the unit cell. Domains of high lateral order are obtained, if the deposition is performed at 400 K. For deposition at room temperature, a significant density of nucleation defects is found pointing to a strong interaction of PTCDA with Cu(100). Quite differently, after preadsorption of oxygen and formation of the (√2 × 2√2)R45° - 2O/Cu(100) superstructure on Cu(100), PTCDA forms an incommensurate monolayer with a structure that corresponds well to that of PTCDA bulk lattice planes.

  20. Lateral ordering of PTCDA on the clean and the oxygen pre-covered Cu(100 surface investigated by scanning tunneling microscopy and low energy electron diffraction

    Directory of Open Access Journals (Sweden)

    Stefan Gärtner

    2014-09-01

    Full Text Available We have investigated the adsorption of perylene-3,4,9,10-tetracarboxylic acid dianhydride (PTCDA on the clean and on the oxygen pre-covered Cu(100 surface [referred to as (√2 × 2√2R45° – 2O/Cu(100] by scanning tunneling microscopy (STM and low energy electron diffraction (LEED. Our results confirm the (4√2 × 5√2R45° superstructure of PTCDA/Cu(100 reported by A. Schmidt et al. [J. Phys. Chem. 1995, 99,11770–11779]. However, contrary to Schmidt et al., we have no indication for a dissociation of the PTCDA upon adsorption, and we propose a detailed structure model with two intact PTCDA molecules within the unit cell. Domains of high lateral order are obtained, if the deposition is performed at 400 K. For deposition at room temperature, a significant density of nucleation defects is found pointing to a strong interaction of PTCDA with Cu(100. Quite differently, after preadsorption of oxygen and formation of the (√2 × 2√2R45° – 2O/Cu(100 superstructure on Cu(100, PTCDA forms an incommensurate monolayer with a structure that corresponds well to that of PTCDA bulk lattice planes.

  1. Termination-specific study of oxygen vacancy transition levels on SrTiO3(001) surfaces by scanning tunneling spectroscopy

    Science.gov (United States)

    Sitaputra, Wattaka; Sivadas, Nikhil; Skowronski, Marek; Xiao, Di; Feenstra, Randall

    2015-03-01

    We have studied the surface electronic structure of oxygen vacancies on SrTiO3(001) surfaces using scanning tunneling spectroscopy and DFT calculations with local spin density approximation (LSDA +U). With high dynamic range measurements, a mid-gap level associated with the surface oxygen vacancies was observed for SrO-terminated surfaces. TiO2-terminated surfaces, on the other hand, did not exhibit observable mid-gap states (this lack of signal is believed to be due to the nature of defect wavefunction involved, as well as possibly involving transport limitations in the STS measurements). Both vacuum-cleaved and MBE-grown surface have been studied. For the former, the Fermi level is pinned near mid-gap owing to disorder-induced surface states. The amount of surface disorder can be controlled in the case of epitaxially grown surfaces. Rougher MBE-grown surfaces were found to exhibit similar spectral characteristics to the cleaved surfaces, while a shift of the Fermi level toward the conduction band was observed for flatter grown surfaces. Notably, with a decreasing number of disorder-induced surface states, the Fermi level is found to be pinned within the observed band of oxygen vacancy levels. This research was supported by AFOSR Grant No. FA9550-12-1-0479, and it used resources of the National Energy Research Scientific Computing Center, supported by the Office of Science, US Department of Energy under Contract No. DEAC02-05CH11231.

  2. The structures and dynamics of atomic and molecular adsorbates on metal surfaces by scanning tunneling microscopy and low energy electron diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Yoon, Hyungsuk Alexander [Univ. of California, Berkeley, CA (United States)

    1996-12-01

    Studies of surface structure and dynamics of atoms and molecules on metal surfaces are presented. My research has focused on understanding the nature of adsorbate-adsorbate and adsorbate-substrate interactions through surface studies of coverage dependency and coadsorption using both scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). The effect of adsorbate coverage on the surface structures of sulfur on Pt(111) and Rh(111) was examined. On Pt(111), sulfur forms p(2x2) at 0.25 ML of sulfur, which transforms into a more compressed (√3x√3)R30° at 0.33 ML. On both structures, it was found that sulfur adsorbs only in fcc sites. When the coverage of sulfur exceeds 0.33 ML, it formed more complex c(√3x7)rect structure with 3 sulfur atoms per unit cell. In this structure, two different adsorption sites for sulfur atoms were observed - two on fcc sites and one on hcp site within the unit cell.

  3. Mn Doping Effects on the Electronic Band Structure of PbS Quantum Dot Thin Films: A Scanning Tunneling Microscopy Analysis

    Science.gov (United States)

    Yost, Andrew J.; Rimal, Gaurab; Tang, Jinke; Chien, Teyu

    A thorough understanding of the phenomena associated with doping of transition metals in semiconductors is important for the development of semiconducting electronic technologies such as semiconducting quantum dot sensitized solar cells (QDSSC). Manganese doping is of particular interest in a PbS QD as it is potentially capable of increasing overall QDSSC performance. Here we present scanning tunneling microscopy and spectroscopy studies about the effects of Manganese doping on the energy band structures of PbS semiconducting QD thin films, grown using pulsed laser deposition. As a result of Manganese doping in the PbS QD thin films, a widening of the electronic band gap was observed, which is responsible for the observed increase in resistivity. Furthermore, a loss of long range periodicity observed by XRD, upon incorporation of Manganese, indicates that the Manganese dopants also induce a large amount of grain boundaries. This work was supported by the following: U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering, DEFG02-10ER46728 and the National Science Foundation Grant #0948027.

  4. Comparative electrochemical scanning tunneling microscopy study of nonionic fluorosurfactant zonyl FSN self-assembled monolayers on Au(111) and Au(100): a potential-induced structural transition.

    Science.gov (United States)

    Tang, Yongan; Yan, Jiawei; Zhu, Feng; Sun, Chunfeng; Mao, Bingwei

    2011-02-01

    We investigate the structure of nonionic fluorosurfactant zonyl FSN self-assembled monolayers on Au(111) and Au(100) in 0.05 M H(2)SO(4) as a function of the electrode potential by electrochemical scanning tunneling microscopy (ECSTM). On Au(111), a (3(1/2) × 3(1/2))R30° arrangement of the FSN SAMs is observed, which remains unchanged in the potential range where the redox reaction of FSN molecules does not occur. On Au(100), some parallel corrugations of the FSN SAMs are observed, which originate from the smaller distance and the repulsive interaction between FSN molecules to make the FSN molecules deviate from the bridging sites, and ECSTM reveals a potential-induced structural transition of the FSN SAMs. The experimental observations are rationalized by the effect of the intermolecular interaction. The smaller distance between molecules on Au(100) results in the repulsive force, which increases the probability of structural change induced by external factors (i.e., the electrode potential). The appropriate distance and interactions of FSN molecules account for the stable structure of FSN SAMs on Au(111). Surface crystallography may influence the intermolecular interaction through changing the molecular arrangements of the SAMs. The results benefit the molecular-scale understanding of the behavior of the FSN SAMs under electrochemical potential control.

  5. Si(111)-sq root 21 x sq root 21 -(Ag+Cs) surface studied by scanning tunneling microscopy and angle-resolved photoemission spectroscopy

    CERN Document Server

    Liu, C; Morikawa, H; Okino, H; Hasegawa, S; Okuda, T; Kinoshita, T

    2003-01-01

    Scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES) were used to study the atomic and electronic structures of the Si(111)-sq root 21 x sq root 21-(Ag + Cs) surface (sq root 21-Cs in short), which was induced by depositing caesium atoms on the Si(111)-sq root 3 x sq root 3-Ag surface at room temperature (RT). Compared with previously reported STM images of noble-metal induced sq root 21 x sq root 21 phases including the Si(111)-sq root 21 x sq root 21-(Ag+Ag) and Si(111)-sq root 21 x sq root 21-(Ag+Au) surfaces (sq root 21-Ag and sq root 21-Au, respectively), the sq root 21-Cs surface displayed quite different features in STM images. The ARPES data of the sq root 21-Cs surface revealed an intrinsic dispersive surface-state band, together with a non-dispersive one near the Fermi level, which was also different from those of the sq root 21-Ag and sq root 21-Au surfaces. These results strongly suggest different atomic arrangements between Cs- and noble-metal induced sq root ...

  6. A study of the O/Ag(111) system with scanning tunneling microscopy and x-ray photoelectron spectroscopy at ambient pressures

    Science.gov (United States)

    Heine, Christian; Eren, Baran; Lechner, Barbara A. J.; Salmeron, Miquel

    2016-10-01

    The interaction of O2 with the Ag(111) surface was studied with scanning tunneling microscopy (STM) in the pressure range from 10- 9 Torr to 1 atm at room temperature and with X-ray photoelectron spectroscopy (XPS) up to 0.3 Torr O2 in the temperature range from RT to 413 K. STM images show that the Ag(111) surface topography is little affected in regions with large flat terraces, except for the appearance of mobile features due to oxygen atoms at pressures above 0.01 Torr. In regions where the step density is high, the surface became rough under 0.01 Torr of O2, due to the local oxidation of Ag. Various chemical states of oxygen due to chemisorbed, oxide and subsurface species were identified by XPS as a function of pressure and temperature. The findings from the STM images and XPS measurements indicate that formation of an oxide phase, the thermodynamically stable form at room temperature under ambient O2 pressure, is kinetically hindered in the flat terrace areas but proceeds readily in regions with high-step density.

  7. Adjusting island density and morphology of the SrTiO3(110)-(4 × 1) surface: Pulsed laser deposition combined with scanning tunneling microscopy

    Science.gov (United States)

    Gerhold, Stefan; Riva, Michele; Yildiz, Bilge; Schmid, Michael; Diebold, Ulrike

    2016-09-01

    The first stages of homoepitaxial growth of the (4 × 1) reconstructed surface of SrTiO3(110) are probed by a combination of pulsed laser deposition (PLD) with in-situ reflection high energy electron diffraction (RHEED) and scanning tunneling microscopy (STM). Considerations of interfacing high-pressure PLD growth with ultra-high-vacuum surface characterization methods are discussed, and the experimental setup and procedures are described in detail. The relation between RHEED intensity oscillations and ideal layer-by-layer growth is confirmed by analysis of STM images acquired after deposition of sub-monolayer amounts of SrTiO3. For a quantitative agreement between RHEED and STM results one has to take into account two interfaces: the steps at the circumference of islands, as well as the borders between two different reconstruction phases on the islands themselves. Analysis of STM images acquired after one single laser shot reveals an exponential decrease of the island density with increasing substrate temperature. This behavior is also directly visible from the temperature dependence of the relaxation times of the RHEED intensity. Moreover, the aspect ratio of islands changes considerably with temperature. The growth mode depends on the laser pulse repetition rate, and can be tuned from predominantly layer-by-layer to the step-flow growth regime.

  8. Visualizing the gap closure by Rh dopant in SOC induced Mott insulator Sr2IrO4 with Scanning Tunneling Microscopy

    Science.gov (United States)

    Dai, Jixia; Calleja, Eduardo; McElroy, Kyle; Qi, Tongfei; Cao, Gang

    2013-03-01

    Sr2IrO4 is a novel Jeff = 1/2 Mott insulator with characteristics of 5d electrons. The strong spin orbit coupling (SOC) in the 5d orbitals of iridium plays an important role in the insulating nature of the parent compound, while replacing Ir4+ with the isoelectronic Rh4+ is able to drive the system to a metallic regime. We use variable temperature Scanning Tunneling Microscope to study both the insulating parent compound and the Rh doped Sr2Ir1-xRhxO4, with x =0.04, 0.11. By doing differential conductance measurement, we were able to observe an insulating gap both in the parent compound and the low doping areas of the x =0.04 and 0.11 samples. We also observed that in the doped samples, local gaps varies largely at the atomic length scale. By correlating the locations of Rh dopant and the size of local gaps, we found that Rh doping will decrease the insulating gap size which is in accordance with the metallic behavior observed by transport measurements.

  9. Analyzing topological defects in disordered charge density waves in transition-metal dichalcogenides TaSe2 and TaS2 using scanning tunneling microscopy

    Science.gov (United States)

    Schaper, Danielle; McElroy, Kyle; Calleja, Eduardo; Dai, Jixia; Li, Lijun; Lu, Wenjian; Sun, Yuping; Zhu, Xiangde

    2014-03-01

    Charged ordered states are becoming a common feature in the phase diagrams of correlated materials. In many cased there are indications that doping controlled quantum critical points between the CO state and others are related to interesting properties including superconductivity. An interesting test case is the ordered 2D CDW found in the transition metal dichalcogenides. We performed an analytical study on the dichalcogenides tantalum disulfide (TaS2) and tantalum diselenide (TaSe2) to observe how CDWs present in the material can be melted as disorder is introduced into the system via copper doping. Data was taken using a scanning tunneling microscope (STM) below the transition to the CDW state, both with and without copper dopants added. The resulting topographs were then analyzed to investigate the relationship between the phase and the amplitude of the disordered CDW. We found that the copper doping caused disorder in the CDW state characterized by phase wanderings and 2 π phase winding ``point defects'' in the CDW not present in the undoped parent compound. The locations of these point defects and windings were, in turn, found to have the characteristics of topological defects. Implications for studies of other disordered CO states seen in STM will be discussed.

  10. In Situ Observation of Water Dissociation with Lattice Incorporation at FeO Particle Edges Using Scanning Tunneling Microscopy and X-ray Photoelectron Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Deng, Xingyi [National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States); Lee, Junseok [National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States); Wang, Congjun [National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States); Matranga, Christopher [National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States); Aksoy, Funda [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Nigde University, Nigde (Turkey). Dept. of Physics; Liu, Zhi [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

    2011-03-15

    The dissociation of H2O and formation of adsorbed hydroxyl groups, on FeO particles grown on Au(111) were identified with in situ,: X:ray photoelectron spectroscopy (XPS) at water pressures ranging from 3 x 10-8 to 0.1 Torr. The facile dissociation of H2O takes place at FeO particle edges, and it was successfully observed in situ With atomically resolved scanning tunneling microscopy (STM). The in situ STM studies show that adsorbed hydroxyl groups were formed exclusively along the edges of the FeO particles with the 0 atom becoming directly incorporated into the oxide crystalline lattice The STM results are consistent with coordinatively unsaturated ferrous (CUF) sites along the FeO particle edge causing the observed reactivity with H2O. Our results also directly illustrate how structural defects and under.-coordinated sites participate in chemical reactions.

  11. Final Report – Study of Shortwave Spectra in Fully 3D Environment. Synergy Between Scanning Radars and Spectral Radiation Measurements

    Energy Technology Data Exchange (ETDEWEB)

    Chiu, Jui-Yuan [University of Reading (United Kingdom)

    2015-09-14

    ARM set out 20 years ago to “close” the radiation problem, that is, to improve radiation models to the point where they could routinely predict the observed spectral radiation fluxes knowing the optical properties of the surface and of gases, clouds and aerosols in the atmosphere. Only then could such radiation models form a proper springboard for global climate model (GCM) parameterizations of spectral radiation. Sustained efforts have more or less achieved that goal with regard to longwave radiation; ASR models now routinely predict ARM spectral longwave radiances to 1–2%. Similar efforts in the shortwave have achieved far less; the successes are mainly for carefully selected 1D stratiform cloud cases. Such cases amount, even with the most optimistic interpretation, to no more than 30% of all cases at SGP. The problem has not been lack of effort but lack of appropriate instruments.The new ARM stimulus-funded instruments, with their new capabilities, will dramatically improve this situation and once again make progress possible on the shortwave problem. The new shortwave spectrometers will provide a reliable, calibrated record including the near infrared – and for other climatic regimes than SGP. The new scanning radars will provide the 3D cloud view, making it possible to tackle fully 3D situations. Thus, our main theme for the project is the understanding and closure of the surface spectral shortwave radiation problem in fully 3D cloud situations by combining the new ARM scanning radars and shortwave spectrometers with the arsenal of radiative transfer tools.

  12. In situ scanning tunneling microscopy study of the structure of the hydroxylated anodic oxide film formed on Cr(110) single-crystal surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Zuili, D.; Maurice, V.; Marcus, P. [Ecole Nationale Superieure de Chimie de Paris (France)

    1999-09-16

    The structure of hydroxylated oxide films (passive films) formed on Cr(110) in 0.5 M H{sub 2}SO{sub 4} at +0.35, +0.55, and +0.75 V/SHE has been investigated by in situ scanning tunneling microscopy (STM). Cathodic reduction pretreatments at {minus}0.54, {minus}0.64, and {minus}0.74 V/SHE destroy the well-defined topography of the single-crystal electrode and they have been excluded from the passivation procedure. Two different passive film structures have been observed, depending on the potential and time of passivation. At low potential (+0.35 V/SHE), the passive film, consisting mostly of chromium hydroxide, has a noncrystalline and granular structure whose roughness suggests local variations of thickness of ca. {+-} 0.5 nm. A similar structure is observed at higher potential (+0.55 V/SHE), but only for a short polarization time. For longer polarization at 0.55 V/SHE, and at higher potentials (+0.75 V/SHE), a crystalline structure is formed; the higher the potential, the faster the crystallization. It corresponds to the growth of a chromium oxide layer in the passive film. This chromium oxide layer is (0001) oriented. A structural model of the passive film is proposed, with termination of this oxide layer by a monolayer of hydroxyl groups or of chromium hydroxide in (1 {times} 1) epitaxy with the underlying oxide, and with surface steps resulting from the emergence of stacking faults of the Cr{sup 3+} planes in the oxide layer. Energy band models of the electronic structure of the semiconductive passive films show that the tunneling mechanism of the STM imaging involves empty electronic states located in the band gap of the passive film. The growth of the oxide layer in the passive film is governed by a combined reaction of dehydration of chromium hydroxide and oxidation of chromium: Cr(OH){sub 3} (film) + Cr (metal) {yields} Cr{sub 2}O{sub 3} (film) + 3 H{sup +} + 3 e{sup {minus}}.

  13. Grain boundary engineering of La{sub 0.7} Sr{sub 0.3} MnO{sub 3} films on silicon substrate: Scanning Tunneling Microscopy-Spectroscopy study

    Energy Technology Data Exchange (ETDEWEB)

    Joshi, Anupama [Department of Applied Physics, Defence Institute of Advanced Technology (DU), Girinagar, Pune 411025 (India); Nori, Rajashree [Centre of Excellence in Nanoelectronics, Department of Electrical Engineering, Indian Institute of Technology (IIT Bombay), Mumbai 400076 (India); Dhobale, Sandip [Department of Applied Physics, Defence Institute of Advanced Technology (DU), Girinagar, Pune 411025 (India); Ramgopal Rao, V. [Centre of Excellence in Nanoelectronics, Department of Electrical Engineering, Indian Institute of Technology (IIT Bombay), Mumbai 400076 (India); Kale, S.N., E-mail: sangeetakale2004@gmail.com [Department of Applied Physics, Defence Institute of Advanced Technology (DU), Girinagar, Pune 411025 (India); Datar, Suwarna, E-mail: suwarna.datar@gmail.com [Department of Applied Physics, Defence Institute of Advanced Technology (DU), Girinagar, Pune 411025 (India)

    2014-09-01

    We employed a Scanning Tunnelling Microscope (STM) to study the surface topography and spatially resolved local electronic properties like local density of states (LDOS) of nanostructured films of La{sub 0.7} Sr{sub 0.3} MnO{sub 3} (LSMO). The nanostructured thin films of LSMO on silicon substrate were prepared using Pulsed Laser Deposition (PLD) technique. The deposition conditions were tuned to yield two different morphologies; one with uniform columnar closely packed islands and other with larger grain distribution in random fashion. The Scanning Tunnelling Spectroscopy (STS) revealed the extent of variation of density of states (DOS) near the Fermi level. From the spectroscopic features obtained we found the occurrence of phase separation between conducting and semiconducting domains and its possible correlation with the properties of the system. Semiconducting nature was observed at the grain boundaries, which could be extremely promising in futuristic nano-devices.

  14. Scanning Gate Spectroscopy on Nanoclusters

    OpenAIRE

    Gurevich, L.; Canali, L.; Kouwenhoven, L.P.

    1999-01-01

    A gated probe for scanning tunnelling microscopy (STM) has been developed. The probe extends normal STM operations by means of an additional electrode fabricated next to the tunnelling tip. The extra electrode does not make contact with the sample and can be used as a gate. We report on the recipe used for fabricating the tunnelling tip and the gate electrode on a silicon nitride cantilever. We demonstrate the functioning of the scanning gate probes by performing single-electron tunnelling sp...

  15. Evidence for Time-Reversal Symmetry Breaking of the Superconducting State near Twin-Boundary Interfaces in FeSe Revealed by Scanning Tunneling Spectroscopy

    Science.gov (United States)

    Watashige, T.; Tsutsumi, Y.; Hanaguri, T.; Kohsaka, Y.; Kasahara, S.; Furusaki, A.; Sigrist, M.; Meingast, C.; Wolf, T.; Löhneysen, H. v.; Shibauchi, T.; Matsuda, Y.

    2015-07-01

    Junctions and interfaces consisting of unconventional superconductors provide an excellent experimental playground to study exotic phenomena related to the phase of the order parameter. Not only does the complex structure of unconventional order parameters have an impact on the Josephson effects, but it also may profoundly alter the quasiparticle excitation spectrum near a junction. Here, by using spectroscopic-imaging scanning tunneling microscopy, we visualize the spatial evolution of the LDOS near twin boundaries (TBs) of the nodal superconductor FeSe. The π /2 rotation of the crystallographic orientation across the TB twists the structure of the unconventional order parameter, which may, in principle, bring about a zero-energy LDOS peak at the TB. The LDOS at the TB observed in our study, in contrast, does not exhibit any signature of a zero-energy peak, and an apparent gap amplitude remains finite all the way across the TB. The low-energy quasiparticle excitations associated with the gap nodes are affected by the TB over a distance more than an order of magnitude larger than the coherence length ξa b. The modification of the low-energy states is even more prominent in the region between two neighboring TBs separated by a distance ≈7 ξa b . In this region, the spectral weight near the Fermi level (≈±0.2 meV ) due to the nodal quasiparticle spectrum is almost completely removed. These behaviors suggest that the TB induces a fully gapped state, invoking a possible twist of the order parameter structure, which breaks time-reversal symmetry.

  16. Role of the anion in the underpotential deposition of cadmium on a Rh(111) electrode: probed by voltammetry and in situ scanning tunneling microscopy.

    Science.gov (United States)

    Ou Yang, Liang-Yueh; Bensliman, Fahd; Shue, Chia-Haw; Yang, Yaw-Chia; Zang, Ze-Haw; Wang, Li; Yau, Shueh-Lin; Yoshimoto, Soichiro; Itaya, Kingo

    2005-08-11

    In situ scanning tunneling microscopy (STM) and cyclic voltammetry (CV) were employed to examine the underpotential deposition (UPD) of cadmium on a rhodium(111) electrode in sulfuric and hydrochloric acids. The (bi)sulfate and chloride anions in the electrolytes played a main role in controlling the number and arrangement of Cd adatoms. Deposition of Cd along with hydrogen adsorption occurred near 0.1 V (vs reversible hydrogen electrode) in either 0.05 M H2SO4 or 0.1 M HCl containing 1 mM Cd(ClO4)2. These coupled processes resulted in an erroneous coverage of Cd adatoms. The process of Cd deposition shifted positively to 0.3 V and thus separated from that of hydrogen in 0.05 M H2SO4 containing 0.5 M Cd2+. The amount of charge (80 microC/cm2) for Cd deposition in 0.5 M Cd2+ implied a coverage of 0.17 for the Cd adatoms, which agreed with in situ STM results. Regardless of [Cd2+], in situ STM imaging revealed a highly ordered Rh(111)-(6 x 6)-6Cd + HSO4- or SO42- structure in sulfuric acid,. In hydrochloric acid, in situ STM discerned a (2 x 2)-Cd + Cl structure at potentials where Cd deposition commenced. STM atomic resolution showed roughly one-quarter of a monolayer of Cd adatoms were deposited, ca. 50% more than in sulfuric acid. Dynamic in situ STM imaging showed potential dependent, reversible transformations between the (6 x 6) Cd adlattices and (square root 3 x square root 7)-(bi)sulfate structure, and between (2 x 2) and (square root 7 x square root 7)R19.1 degrees -Cl structures. The fact that different Cd structures observed in H2SO4 and HCl entailed the involvement of anions in Cd deposition, i.e. (bi)sulfate and chloride anions were codeposited with Cd adatoms on Rh(111).

  17. Comparison Study for the Probe of Scanning Tunneling Microscope Made in Our Own Laboratory%自制扫描隧道显微镜探针尖的比较研究

    Institute of Scientific and Technical Information of China (English)

    王晓秋; 苏杰

    2012-01-01

      A probe plays a crucial role in scanning tunneling microscope imaging. In this paper, The tungsten wire probe obtained using electrochemical etching method and the platinum-iridium probe through shear method in our own laboratory were analyzed via the image of grating by using two probes scan. The results show that, compared to platinum-iridium probe, although tungsten wire probe to be made is complex and difficult to control the reaction conditions, the tungsten wire probe which in sharp axisymmetric form to scan the sample topography is more subtle, and is not easy to lose topography information, and is appropriate as scanning probe. The study of scanning tunneling microscope probe provided a basis for the selection of probe.%  探针对扫描隧道显微镜成像起至关重要的作用。本文分别对电化学腐蚀法自制的钨丝探针和剪切法制得的铂铱探针进行扫描光栅图像比较分析。结果表明,相比铂铱探针,钨丝探针虽然制备繁琐,反应条件不易控制,但是尖锐轴对称形的钨丝探针扫描样品形貌更加细微,用作扫描隧道显微镜探针时扫描成像质量高。该研究为扫描隧道显微镜探针的选用提供了依据。

  18. Metalloprotein Adsorption on Au(111) and Polycrystalline Platinum Investigated by In Situ Scanning Tunnelling Microscopy with Molecular and Sub-Molecular Resolution

    DEFF Research Database (Denmark)

    Friis, Esben P.; Andersen, Jens Enevold Thaulov; Madsen, Lars Lithen;

    1998-01-01

    linking, facile ET routes through the protein, and tunnel enhancement by the low-lying redox level of the copper atom. The particular electronic-vibrational three-level con®guration in in situ STM of metalloproteins, ®nally, o€ers a new way of distinction between superexchange, coherent, and sequential ET...

  19. High-resolution photonic analysis with scanned probes

    Science.gov (United States)

    Wig, Andrew Gustaf

    Absorption spectroscopy is demonstrated to be feasible using a photon scanning tunneling microscope (PSTM) combined with a spectroscope. Methods of improving the spatial resolution and spectroscopic capabilities are studied in order to determine their potential practicability. Analysis of the photon scanning tunneling microscope (PSTM) and modifications made to the microscope are included with experimental results demonstrating certain image and spectral resolution capabilities. Results showing both the PSTM absorption spectra of gold island films and their independently acquired PSTM images are presented. An alternative scanning probe method involving photons is additionally examined. The new method is demonstrated to require specific improvements in order that it might provide a distinct improvement in resolution. The new type of scanning probe microscope is one utilizing nonlinear photonics: the nonlinear scanning tunneling microscope (NSTM). Basic results are described and two-photon fluorescence measurements are presented to demonstrate the principle of operation. In any scanned probe microscope or spectroscope, resolution is strongly dependent upon the characteristics of the signal as a function of distance to the sample and knowledge of these characteristics. The NSTM functionality is most dependent upon the sample-probe gap, but the gap also determines resolution in the PSTM. Hence measurements and calculations showing an analysis of the characteristics of the separation between the probe and sample surface are also presented.

  20. Step height measurement using a scanning tunneling microscope equipped with a crystalline lattice reference and interferometer; Koseiyo koha kanshokei wo sonaeta kessho koshi kijun dansa sokutei heiko bane STM

    Energy Technology Data Exchange (ETDEWEB)

    Fujii, T.; Suzuki, M. [Nikon Corp., Tokyo (Japan); Higuchi, T. [The University of Tokyo, Tokyo (Japan). Faculty of Engineering; Kogami, H.; Kawakatsu, H. [The University of Tokyo, Tokyo (Japan). Institute of Industrial Science

    1994-12-01

    A scanning tunneling microscope (STM) is a solid probe scanning type microscope having a high performance in the three dimensional space resolution. In this study, a technique has been developed for applying crystalline lattice reference measurement to step height measurement. An equipment has been developed which has a guide mechanism using a parallel spring for protecting mutual interference between individual axes and a light wave interferometer for calibration. Two STM are incorporated in this equipment for a step height sample and for a reference crystal. As a consequence of experiments only using STM for crystal, a movement of probe for step height measurement, i.e., a movement of graphite crystal, was measured as a distortion of crystal image obtained by scanning. It was confirmed that the distortion of crystal image can be modified by using control voltage applied to the step height sample, and that the movement of graphite, i.e., the movement of probe for step height measurement, can be measured using crystalline lattice as a scale. 7 refs., 4 figs.

  1. Short tunnels.

    NARCIS (Netherlands)

    Schreuder, D.A.

    1965-01-01

    Before dealing with the question of lighting short tunnels, it is necessary define what is meant by a tunnel and when it should be called 'short'. Confined to motorized road traffic the following is the most apt definition of a tunnel: every form of roofing-over a road section, irrespective of it le

  2. Self-assembly of F16ZnPc thin films and F16ZnPc-ZnPc heterostructures on deactivated Si surfaces studied by scanning tunneling microscopy.

    Science.gov (United States)

    Tan, Andrew; Wagner, Sean; Zhang, Pengpeng

    2017-02-07

    Using scanning tunneling microscopy, we show that hexadecafluorinated zinc phthalocyanine (F16ZnPc) molecules form two morphologically different self-assembled structures that both display point-on-line coincident epitaxial registration with the deactivated Si(111)-B 3×3 surface. The packing motif in these structures suggests that fluorination of conjugated organic molecules can lead to stronger molecule-substrate interaction, π-π intermolecular interaction, and side-to-side intermolecular repulsion. The delicate balance and interplay between these interactions determine the self-assembly behavior of fluorinated molecules. Furthermore, we demonstrate the formation of vertically and laterally stacked F16ZnPc-ZnPc heterojunctions, allowing for future spectroscopy investigation of molecular electronic structures and charge transfer behavior at organic-organic hetero-interfaces.

  3. Electronic characterization of LaAlO{sub 3}-SrTiO{sub 3} interfaces by scanning tunneling spectroscopy; Elektronische Charakterisierung von LaAlO{sub 3}-SrTiO{sub 3}-Grenzflaechen mittels Rastertunnelspektroskopie

    Energy Technology Data Exchange (ETDEWEB)

    Breitschaft, Martin

    2010-10-22

    When LaAlO{sub 3} is epitaxially grown on TiO{sub 2}-terminated SrTiO{sub 3}, an electrically conducting interface is generated. In this respect, the physical properties of the interface differ substantially from those of both LaAlO{sub 3} and SrTiO{sub 3}, which are electrically insulating in bulk form. This dissertation looks into the question of the microscopic structure of the conducting two-dimensional interface electron system. Comparing the electronic density of states of LaAlO{sub 3}-SrTiO{sub 3} interfaces measured by scanning tunneling spectroscopy with results of density functional theory, the interface electron system is found to be substantially coined by the hosting transition metal lattices. The comparison yields a detailed picture of the microscopic structure of the interface electron system. (orig.)

  4. Growth and structure of thin platinum films deposited on Co(0001) studied by low-energy electron diffraction, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and scanning tunneling microscopy

    Science.gov (United States)

    Cabeza, G. F.; Légaré, P.; Sadki, A.; Castellani, N. J.

    2000-06-01

    The growth of platinum deposited on Co(0001) at room temperature in the range of submonolayer coverage is described. The evolution of very thin Pt films has been studied using low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and scanning tunneling microscopy (STM). The LEED patterns suggested a coherent epitaxial growth mode for Pt on Co(0001). Evidence for an island growth mode has been confirmed by STM together with step decoration. However, the second and third monolayers start growing before the completion of the first Pt layer. The electronic structure of the Pt deposits exhibited original properties with low Fermi level density of states and valence-band broadening. This is in agreement with theoretical calculations presented in this work.

  5. Calculated and experimental low-loss electron energy loss spectra of dislocations in diamond and GaN

    CERN Document Server

    Jones, R; Gutiérrez-Sosa, A; Bangert, U; Heggie, M I; Blumenau, A T; Frauenheim, T; Briddon, P R

    2002-01-01

    First-principles calculations of electron energy loss (EEL) spectra for bulk GaN and diamond are compared with experimental spectra acquired with a scanning tunnelling electron microscope offering ultra-high-energy resolution in low-loss energy spectroscopy. The theoretical bulk low-loss EEL spectra, in the E sub g to 10 eV range, are in good agreement with experimental data. Spatially resolved spectra from dislocated regions in both materials are distinct from bulk spectra. The main effects are, however, confined to energy losses lying above the band edge. The calculated spectra for low-energy dislocations in diamond are consistent with the experimental observations, but difficulties remain in understanding the spectra of threading dislocations in GaN.

  6. - Tunneling Matrix Formalism for - and Two-Methyl Molecules Based on the Extended Permutation-Inversion Group Idea and its Application to the Analyses of the Methyl-Torsional Rotational Spectra

    Science.gov (United States)

    Ohashi, Nobukimi; Kobayashi, Kaori; Fujitake, Masaharu

    2016-06-01

    Recently we reanalyzed the microwave absorption spectra of the trans-ethyl methyl ether molecule, state by state, in the ground vibrational, O-methyl torsional, C-methyl torsional and skeletal torsional states with the use of an IAM-like tunneling matrix formalism based on an extended permutation-inversion (PI) group idea, whose results appeared in Journal of Molecular Spectroscopy recently. Since a single rho-axis does not exist in trans-ethyl methyl ether that has two methyl-tops and the IAM formalism is not available as in the case of the one methyl-top molecule, we adopted instead an IAM-like (in other word, partial IAM) formalism. We will show the outline of the present formalism and the results of the spectral analyses briefly. We also would like to review the IAM formalism for the one top molecules based on the extended PI group, and show the result of the application to the spectral analysis. If possible, we would like to compare the IAM and IAM-like formalisms based on the extended PI group with the ERHAM formalism developed by Groner, especially, in the form of Hamiltonian matrix elements, and discuss about similarity and difference.

  7. Temperature dependent tunneling study of CaFe1.96Ni0.04As2 single crystals

    Science.gov (United States)

    Dutta, Anirban; Thamizhavel, A.; Gupta, Anjan K.

    2014-04-01

    We report on temperature dependent scanning tunneling microscopy and spectroscopy studies on CaFe1.96Ni0.04As2 single crystals in 5.4 - 19.7 K temperature range across the normal metal - superconductor transition temperature, TC = 14K. The in-situ cleaved crystals show reasonably flat surface with signatures of atomic resolution. The tunnel spectra show significant spatial inhomogeneity below TC, which reduces significantly as the temperature goes above the TC. We discuss these results in terms of an inhomogeneous electronic phase that may exist due to the vicinity of this composition to the quantum critical point.

  8. Profiling and classification of French propolis by combined multivariate data analysis of planar chromatograms and scanning direct analysis in real time mass spectra.

    Science.gov (United States)

    Chasset, Thibaut; Häbe, Tim T; Ristivojevic, Petar; Morlock, Gertrud E

    2016-09-23

    Quality control of propolis is challenging, as it is a complex natural mixture of compounds, and thus, very difficult to analyze and standardize. Shown on the example of 30 French propolis samples, a strategy for an improved quality control was demonstrated in which high-performance thin-layer chromatography (HPTLC) fingerprints were evaluated in combination with selected mass signals obtained by desorption-based scanning mass spectrometry (MS). The French propolis sample extracts were separated by a newly developed reversed phase (RP)-HPTLC method. The fingerprints obtained by two different detection modes, i.e. after (1) derivatization and fluorescence detection (FLD) at UV 366nm and (2) scanning direct analysis in real time (DART)-MS, were analyzed by multivariate data analysis. Thus, RP-HPTLC-FLD and RP-HPTLC-DART-MS fingerprints were explored and the best classification was obtained using both methods in combination with pattern recognition techniques, such as principal component analysis. All investigated French propolis samples were divided in two types and characteristic patterns were observed. Phenolic compounds such as caffeic acid, p-coumaric acid, chrysin, pinobanksin, pinobanksin-3-acetate, galangin, kaempferol, tectochrysin and pinocembrin were identified as characteristic marker compounds of French propolis samples. This study expanded the research on the European poplar type of propolis and confirmed the presence of two botanically different types of propolis, known as the blue and orange types.

  9. A scanning tunneling microscopy investigation of the phases formed by the sulfur adsorption on Au(100) from an alkaline solution of 1,4-piperazine(bis)-dithiocarbamate of potassium

    Science.gov (United States)

    Martínez, Javier A.; Valenzuela B., José; Cao Milán, R.; Herrera, José; Farías, Mario H.; Hernández, Mayra P.

    2014-11-01

    Piperazine-dithiocarbamate of potassium (K2DTC2pz) was used as a new precursor for the spontaneous deposition of sulfur on the Au(100) surface in alkaline solution. Two new sulfur phases were studied by scanning tunneling microscopy (STM). These phases were formed by six sulfur atoms (S6 phase, hexamer) and by four sulfur atoms (S4 phase, tetramer with (√{ 2} ×√{ 2}) structure), and they were observed in coexistence with the well-known quasi-square patterns formed by eight sulfur atoms (S8 phase, octomer). A model was proposed where sulfur multilayers were formed by a (√{ 2} ×√{ 2}) phase adsorbed directly on the gold surface while one of the other structures: hexamers or octomers were deposited on top. Sulfur layers were formed on gold terraces, vacancies and islands produced by lifting reconstructed surface. Sequential high-resolution STM images allowed the direct observation of the dynamic of the octomers, while the (√{ 2} ×√{ 2}) structure remained static. Images also showed the reversible association/dissociation of the octomer.

  10. Atomic structure of the indium-induced Ge(001)(¤n¤x4) surface reconstruction determined by scanning tunneling microscopy and ¤ab initio¤ calculations

    DEFF Research Database (Denmark)

    Falkenberg, G.; Bunk, O.; Johnson, R.L.

    2002-01-01

    . Sci. 123/124, 104 (1998) for In on Si(001). For the (4x4) subunit, we propose a model that includes the main features of the (3x4) subunit together with additional mixed Ge-In dimers. The atomic positions were optimized using ab initio total-energy calculations. The calculated local densities......Using scanning-tunneling microscopy (STM) and first-principles total-energy calculations, we have determined the atomic geometry of the superstructures formed by the adsorption of up to 0.5 monolayer of indium on Ge(001) and annealing at temperatures above 200 degreesC. A strong interaction between...... indium adatoms and the germanium substrate atoms leads to the formation of two different In-Ge subunits on the Ge(001) surface. In the subsaturation regime separate (nx4) subunits are observed where n can be either 3 or 4 and the STM images resemble those of the Si(001)-(3x4)-In and -Al reconstructions...

  11. First results for custom-built low-temperature (4.2 K) scanning tunneling microscope/molecular beam epitaxy and pulsed laser epitaxy system designed for spin-polarized measurements

    Science.gov (United States)

    Foley, Andrew; Alam, Khan; Lin, Wenzhi; Wang, Kangkang; Chinchore, Abhijit; Corbett, Joseph; Savage, Alan; Chen, Tianjiao; Shi, Meng; Pak, Jeongihm; Smith, Arthur

    2014-03-01

    A custom low-temperature (4.2 K) scanning tunneling microscope system has been developed which is combined directly with a custom molecular beam epitaxy facility (and also including pulsed laser epitaxy) for the purpose of studying surface nanomagnetism of complex spintronic materials down to the atomic scale. For purposes of carrying out spin-polarized STM measurements, the microscope is built into a split-coil, 4.5 Tesla superconducting magnet system where the magnetic field can be applied normal to the sample surface; since, as a result, the microscope does not include eddy current damping, vibration isolation is achieved using a unique combination of two stages of pneumatic isolators along with an acoustical noise shield, in addition to the use of a highly stable as well as modular `Pan'-style STM design with a high Q factor. First 4.2 K results reveal, with clear atomic resolution, various reconstructions on wurtzite GaN c-plane surfaces grown by MBE, including the c(6x12) on N-polar GaN(0001). Details of the system design and functionality will be presented.

  12. Recent progress in vortex studies by tunneling spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kohen, A. [Institut des NanoSciences de Paris, UMR7588 au CNRS, Universite Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France)]. E-mail: Amir.Kohen@insp.jussieu.fr; Cren, T. [Institut des NanoSciences de Paris, UMR7588 au CNRS, Universite Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France); Noat, Y. [Institut des NanoSciences de Paris, UMR7588 au CNRS, Universite Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France); Proslier, T. [Institut des NanoSciences de Paris, UMR7588 au CNRS, Universite Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France); Giubileo, F. [Physics Department and INFM-SUPERMAT Laboratory, University of Salerno, via S. Allende, 84081 Baronissi (SA) (Italy); Bobba, F. [Physics Department and INFM-SUPERMAT Laboratory, University of Salerno, via S. Allende, 84081 Baronissi (SA) (Italy); Cucolo, A.M. [Physics Department and INFM-SUPERMAT Laboratory, University of Salerno, via S. Allende, 84081 Baronissi (SA) (Italy); Zhigadlo, N. [Solid State Physics Laboratory, ETH Zurich, CH-8093 Zurich (Switzerland); Kazakov, S.M. [Solid State Physics Laboratory, ETH Zurich, CH-8093 Zurich (Switzerland); Karpinski, J. [Solid State Physics Laboratory, ETH Zurich, CH-8093 Zurich (Switzerland); Sacks, W. [Institut des NanoSciences de Paris, UMR7588 au CNRS, Universite Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France); Roditchev, D. [Institut des NanoSciences de Paris, UMR7588 au CNRS, Universite Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France)

    2006-05-15

    Among the methods used to study the vortex state in superconductors, scanning tunneling spectroscopy (STS), is unique in its ability to measure in real space the variations in the local quasiparticle density of states. Thus, as opposed to magnetic imaging, STS gives direct access to the coherence length rather than to the penetration length. Here we discuss two novel methods which enhance the capabilities of STS as a tool for the study of the vortex state. In the first one, called Lazy Fisherman [A. Kohen et al., Appl. Phys. Lett. 86 (2005) 212503], the scanning tunneling microscope's tip is kept fixed at a selected location while the vortices are being moved by varying the applied magnetic field. By continuously acquiring the local tunneling conductance spectra, dI/dV(V), we detect the changes in the local density of states under the tip due to the vortex motion. With no need for scanning, the method permits one to extend the study of vortices to samples in which scanning is difficult or even impossible due to surface non-uniformity and allows one to detect faster vortex dynamics. To illustrate the approach we study single crystal samples of MgB{sub 2}. In the second STS method, we replace the commonly used normal metal STM tip by a superconducting (SC) tip which we produce either by mechanically breaking a Nb wire under vacuum in the STM chamber [A. Kohen et al., Physica C 49 (2005) 18] or by gluing a piece of a crystal of MgB{sub 2} [F. Giubileo et al., Phys. Rev. Lett. 87 (2001) 177008]. The use of a SC tip enhances the energy resolution of STS in comparison to that obtained with a normal metal tip. The method is illustrated by using Nb and MgB{sub 2} tips to perform a simultaneous topographic and spectroscopic imaging on 2H-NbSe{sub 2}.

  13. A scanning tunneling microscopy investigation of the phases formed by the sulfur adsorption on Au(100) from an alkaline solution of 1,4-piperazine(bis)-dithiocarbamate of potassium

    Energy Technology Data Exchange (ETDEWEB)

    Martínez, Javier A. [Instituto de Ciencia y Tecnología de Materiales (IMRE), Universidad de La Habana, Zapata y G, El Vedado, Plaza de la Revolución, La Habana 10400 (Cuba); Valenzuela B, José [Centro de Nanociencias y Nanotecnología (CNyN), Universidad Nacional Autónoma de México (UNAM) , km 107 Carretera Tijuana-Ensenada, Ensenada, BC 22860 (Mexico); Cao Milán, R. [Facultad de Química, Universidad de La Habana, Zapata y G, El Vedado, Plaza de la Revolución, La Habana 10400 (Cuba); Herrera, José [Instituto de Ciencia y Tecnología de Materiales (IMRE), Universidad de La Habana, Zapata y G, El Vedado, Plaza de la Revolución, La Habana 10400 (Cuba); Farías, Mario H. [Centro de Nanociencias y Nanotecnología (CNyN), Universidad Nacional Autónoma de México (UNAM) , km 107 Carretera Tijuana-Ensenada, Ensenada, BC 22860 (Mexico); Hernández, Mayra P., E-mail: mayrap@fisica.uh.cu [Instituto de Ciencia y Tecnología de Materiales (IMRE), Universidad de La Habana, Zapata y G, El Vedado, Plaza de la Revolución, La Habana 10400 (Cuba)

    2014-11-30

    Highlights: • New phases of sulfur on gold: hexamer and (√(2)×√(2)) were observed by STM. • Hexamers and (√(2)×√(2)) structures coexist with well-known octomers. • Formation of sulfur multilayer by K{sub 2}DTC{sub 2}pz hydrolysis under alkaline condition. • Top octomer layer have dynamic behavior while (√(2)×√(2)) and hexamer were static. • A model is presented to explain sulfur multilayer formation on Au(100). - Abstract: Piperazine-dithiocarbamate of potassium (K{sub 2}DTC{sub 2}pz) was used as a new precursor for the spontaneous deposition of sulfur on the Au(100) surface in alkaline solution. Two new sulfur phases were studied by scanning tunneling microscopy (STM). These phases were formed by six sulfur atoms (S{sub 6} phase, hexamer) and by four sulfur atoms (S{sub 4} phase, tetramer with (√(2)×√(2)) structure), and they were observed in coexistence with the well-known quasi-square patterns formed by eight sulfur atoms (S{sub 8} phase, octomer). A model was proposed where sulfur multilayers were formed by a (√(2)×√(2)) phase adsorbed directly on the gold surface while one of the other structures: hexamers or octomers were deposited on top. Sulfur layers were formed on gold terraces, vacancies and islands produced by lifting reconstructed surface. Sequential high-resolution STM images allowed the direct observation of the dynamic of the octomers, while the (√(2)×√(2)) structure remained static. Images also showed the reversible association/dissociation of the octomer.

  14. An in situ scanning tunneling microscopic study of electrodeposition of bismuth on Au(1 1 1) in a 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid: Precursor adsorption and underpotential deposition

    Energy Technology Data Exchange (ETDEWEB)

    Fu Yongchun; Su Yuzhuan; Zhang Haiming; Yan Jiawei; Xie Zhaoxiong [State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 (China); Mao Bingwei, E-mail: bwmao@xmu.edu.c [State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 (China)

    2010-11-30

    In this article, the electrodeposition of Bi on Au(1 1 1) surface in the underpotential region in BMIBF{sub 4} ionic liquid containing BiCl{sub 3} is studied by cyclic voltammetry and in situ scanning tunneling microscopy (STM). The cyclic voltammogram shows several cathodic and anodic peaks associated with underpotential deposition (UPD) of Bi and dissolution of the UPD deposit, respectively, in the potential region between -0.38 and -0.7 V versus Pt quasi-reference electrode. In situ STM results indicate there is a BiCl{sub 3} precursor adsorption stage prior to the Bi UPD. The adsorption of BiCl{sub 3} leads to the formation of unique hexagonal and trigonal supramolecular assembly with a Au(1 1 1)(10 x 10) structure. The initial stage of Bi UPD proceeds with the formation of Au(1 1 1)(7 x 7) R21.8{sup o} adlayer structure composed of Bi trigonal clusters at -0.5 V. A structural transformation occurred at -0.6 V resulting in a unique 'zipper-like' double-chain pattern composed of well-aligned Bi trigonal clusters which can be denoted by Au(1 1 1)(5 x 25{radical}3/3) structural model. The trigonal clusters composed of six Bi atoms seem to be the main characteristic elemental units of Bi UPD adlayer regardless of underpotential shift. These features are dramatically different from those observed in Bi(III)-containing acidic aqueous solutions as well as in chloroaluminated ionic liquid, but are similar to those of Sb UPD in BMIBF{sub 4} ionic liquid, which reveals profound solvent effects on the electrodeposition of semimetals.

  15. Investigations on the electronic surface properties of the stoichiometric superconductor LiFeAs using scanning tunneling microscopy and spectroscopy; Untersuchung der elektronischen Oberflaecheneigenschaften des stoechiometrischen Supraleiters LiFeAs mittels Rastertunnelmikroskopie und -spektroskopie

    Energy Technology Data Exchange (ETDEWEB)

    Schlegel, Ronny

    2014-09-29

    This work presents scanning tunneling microscopy and spectroscopy investigations on the stoichiometric superconductor lithium iron arsenide (LiFeAs). To reveal the electronic properties, measurements on defect-free surfaces as well as near defects have been performed. The former shows a shift of atomic position with respect to the applied bias voltage. Furthermore, temperature dependent spectroscopic measurements indicate the coupling of quasiparticles in the vicinity of the superconducting coherence peaks. LiFeAs surfaces influenced by atomic defects show a spacial variation of the superconducting gap. The defects can be characterized by their symmetry and thus can be assigned to a position in the atomic lattice. Detailed spectroscopic investigations of defects reveal their influence on the quasiparticle density of states. In particular, Fe-defects show a small effect on the superconductivity while As-defects strongly disturb the superconducting gap. Measurements in magnetic field have been performed for the determination of the Ginzburg-Landau coherence length ξ{sub GL}. For this purpose, a suitable fit-function has been developed in this work. This function allows to fit the differential conductance of a magnetic vortex at E{sub F}. The fit results in a coherence length of ξ{sub GL} = 3,9 nm which corresponds to an upper critical field of 21 Tesla. Besides measurements on a single vortex, investigation on the vortex lattice have been performed. The vortex lattice constant follows thereby the predicted behavior of a trigonal vortex lattice. However, for magnetic fields larger than 6 Tesla an increasing lattice disorder sets in, presumably due to vortex-vortex-interactions.

  16. Growth of an Ultrathin Zirconia Film on Pt3Zr Examined by High-Resolution X-ray Photoelectron Spectroscopy, Temperature-Programmed Desorption, Scanning Tunneling Microscopy, and Density Functional Theory.

    Science.gov (United States)

    Li, Hao; Choi, Joong-Il Jake; Mayr-Schmölzer, Wernfried; Weilach, Christian; Rameshan, Christoph; Mittendorfer, Florian; Redinger, Josef; Schmid, Michael; Rupprechter, Günther

    2015-02-05

    Ultrathin (∼3 Å) zirconium oxide films were grown on a single-crystalline Pt3Zr(0001) substrate by oxidation in 1 × 10(-7) mbar of O2 at 673 K, followed by annealing at temperatures up to 1023 K. The ZrO2 films are intended to serve as model supports for reforming catalysts and fuel cell anodes. The atomic and electronic structure and composition of the ZrO2 films were determined by synchrotron-based high-resolution X-ray photoelectron spectroscopy (HR-XPS) (including depth profiling), low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and density functional theory (DFT) calculations. Oxidation mainly leads to ultrathin trilayer (O-Zr-O) films on the alloy; only a small area fraction (10-15%) is covered by ZrO2 clusters (thickness ∼0.5-10 nm). The amount of clusters decreases with increasing annealing temperature. Temperature-programmed desorption (TPD) of CO was utilized to confirm complete coverage of the Pt3Zr substrate by ZrO2, that is, formation of a closed oxide overlayer. Experiments and DFT calculations show that the core level shifts of Zr in the trilayer ZrO2 films are between those of metallic Zr and thick (bulklike) ZrO2. Therefore, the assignment of such XPS core level shifts to substoichiometric ZrO x is not necessarily correct, because these XPS signals may equally well arise from ultrathin ZrO2 films or metal/ZrO2 interfaces. Furthermore, our results indicate that the common approach of calculating core level shifts by DFT including final-state effects should be taken with care for thicker insulating films, clusters, and bulk insulators.

  17. The interfacial and surface properties of thin Fe and Gd films grown on W(110) as studied by scanning tunneling microscopy, site-resolved photoelectron diffraction, and spin polarized photoelectron diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Tober, Eric D. [Univ. of California, Davis, CA (United States)

    1997-06-01

    Combined scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) measurements from Gd films grown on W(110) prepared with and without annealing have been used to provide a detailed picture of the growth of such films, permitting a quantitative structural explanation for previously-measured magnetic properties and the identification of a new two-dimensional structure for the first monolayer. The analysis of the film roughness of room-temperature-grown films as a function of coverage and lateral length scale reveals that the growing Gd surface follows scaling laws for a self-affine surface. Annealing these as-deposited films at elevated temperatures is found to drastically alter the morphology of the films, as seen by both STM and LEED. Nanometer-scale islands of relatively well-defined size and shape are observed under certain conditions. Finally, the first monolayer of Gd is observed to form a (7x14) superstructure with pseudo-(7x7) symmetry that is consistent with a minimally-distorted hexagonal two-dimensional Gd(0001) film. Furthermore, a new beamline and photoelectron spectrometer/diffractometer at the Advanced Light Source have been used to obtain full-solid-angle and site-specific photoelectron diffraction (PD) data from interface W atoms just beneath (1x1) Fe and (7x14) Gd monolayers on W(110) by utilizing the core level shift in the W 4f7/2 spectrum. A comparison of experiment with multiple scattering calculations permits determining the Fe adsorption site and the relative interlayer spacing to the first and second W layers. These Fe results are also compared to those from the very different Gd overlayer and from the clean W(110) surface. Such interface PD measurements show considerable promise for future studies. Finally, the rare-earth ferromagnetic system of Gd(0001) has been examined through the use of spin polarized photoelectron diffraction from the Gd 4s and 5s photoelectron multiplets.

  18. The interfacial and surface properties of thin Fe and Gd films grown on W(110) as studied by scanning tunneling microscopy, site-resolved photoelectron diffraction, and spin polarized photoelectron diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Tober, E.D. [Univ. of California, Davis, CA (US). Office of Graduate Studies

    1997-06-01

    Combined scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) measurements from Gd films grown on W(110) prepared with and without annealing have been used to provide a detailed picture of the growth of such films, permitting a quantitative structural explanation for previously-measured magnetic properties and the identification of a new two-dimensional structure for the first monolayer. The analysis of the film roughness of room-temperature-grown films as a function of coverage and lateral length scale reveals that the growing Gd surface follows scaling laws for a self-affine surface. Annealing these as-deposited films at elevated temperatures is found to drastically alter the morphology of the films, as seen by both STM and LEED. Nanometer-scale islands of relatively well-defined size and shape are observed under certain conditions. Finally, the first monolayer of Gd is observed to form a (7x14) superstructure with pseudo-(7x7) symmetry that is consistent with a minimally-distorted hexagonal two-dimensional Gd(0001) film. Furthermore, a new beamline and photoelectron spectrometer/diffractometer at the Advanced Light Source have been used to obtain full-solid-angle and site-specific photoelectron diffraction (PD) data from interface W atoms just beneath (1x1) Fe and (7x14) Gd monolayers on W(110) by utilizing the core level shift in the W 4f{sub 7/2} spectrum. A comparison of experiment with multiple scattering calculations permits determining the Fe adsorption site and the relative interlayer spacing to the first and second W layers. These Fe results are also compared to those from the very different Gd overlayer and from the clean W(110) surface. Such interface PD measurements show considerable promise for future studies. Finally, the rare-earth ferromagnetic system of Gd(0001) has been examined through the use of spin polarized photoelectron diffraction from the Gd 4s and 5s photoelectron multiplets.

  19. Femtosecond tunneling response of surface plasmon polaritons

    DEFF Research Database (Denmark)

    Keil, Ulrich Dieter Felix; Ha, Taekjip; Jensen, Jacob Riis;

    1998-01-01

    We obtain femtosecond (200 fs) time resolution using a scanning tunneling microscope on surface plasmon polaritons (SPPs) generated by two 100 fs laser beams in total internal reflection geometry. The tunneling gap dependence of the signal clearly indicates the tunneling origin of the signal...... and suggests that nanometer spatial resolution can be obtained together with femtosecond temporal resolution. This fast response, in contrast to the picosecond decay time of SPPs revealed by differential reflectivity measurements, can be attributed to a coherent superposition of SPPs rectified at the tunneling...

  20. Scanning tunnelling microscopy of suspended graphene.

    Science.gov (United States)

    Zan, Recep; Muryn, Chris; Bangert, Ursel; Mattocks, Philip; Wincott, Paul; Vaughan, David; Li, Xuesong; Colombo, Luigi; Ruoff, Rodney S; Hamilton, Bruce; Novoselov, Konstantin S

    2012-05-21

    Suspended graphene has been studied by STM for the first time. Atomic resolution on mono- and bi-layer graphene samples has been obtained after ridding the graphene surface of contamination via high-temperature annealing. Static local corrugations (ripples) have been observed on both types of structures.

  1. Nanofabrication with the Scanning Tunneling Microscope

    Energy Technology Data Exchange (ETDEWEB)

    Shedd, G.M.; Russell, P.E.

    1988-12-01

    The Precision Engineering Center has recently begun a research program into applications of STM to Nanotechnology. Few tools permit humans to control events and processes at the manometer level, and of those, the STM is the most well-suited to the task. A versatile new ultra-high-vacuum (UHV) STM is being built to study the use of STM for the manipulation of nanometer-scale particles. Part of the STM`s usefulness will be due to its being positioned directly beneath the focused ion beam (FIB). The interface of the STM with the FIB will allow the STM to take advantage of the FIB for long-range imaging and as a particle source; the FIB can in turn use the STM for in situ, high-resolution imaging of micromachined features.

  2. Applications of Scanning Tunneling Microscopy to Electrochemistry

    Science.gov (United States)

    1988-10-28

    3 electrode voltametry to be performed (61). Itaya ot. &l. have gained similar capabilities by modifying their aforementioned STH (Itaya, K.; Higaki...vs. NHE. f - 2.5 kHz ), and were imaged (at nanometer resolution) before and after the electrochemical treatment. The cyclic voltammograms in the H

  3. Study of the CH2I + O2 Reaction with a Step-Scan Fourier-Transform Infrared Absorption Spectrometer: Spectra of the Criegee Intermediate CH2OO and DIOXIRANE(?)

    Science.gov (United States)

    Huang, Yu-Hsuan; Lee, Yuan-Pern

    2014-06-01

    The Criegee intermediates are carbonyl oxides that play key roles in ozonolysis of unsaturated organic compounds. This mechanism was first proposed by Criegee in 1949, but the first direct observation of the simplest Criegee intermediate CH2OO in the gaseous phase has been reported only recently using photoionization mass spectrometry. Our group has reported the low-resolution IR spectra of CH2OO, produced from the reaction of CH2I + O2, with a second-generation step-scan Fourier-transfom IR absorption spectrometer. The spectral assignments were based on comparison of observed vibrational wavenumbers and rotational contours with theoretical predictions. Here, we report the IR absorption spectra of CH2OO at a resolution of 0.32 wn, showing partially rotationally-resolved structures. The origins of the νb{3}, νb{4}, νb{6}, and νb{8} vibrational modes of CH2OO are determined to be 1434.1, 1285.7, 909.2, and 847.3 wn, respectively. With the analysis of the vibration-rotational spectra, we provide a definitive assignment of these bands to CH2OO. The observed vibrational wavenumbers indicate a zwitterionic contribution to this singlet biradical showing a strengthened C-O bond and a weakened O-O bond. This zwitterionic character results to an extremely rapid self reaction via a cyclic dimer to form 2H2CO + O2 (1Δg). Another group of weak transient IR bands centered at 1231.5, 1213.3, and 899.8 wn are also observed. These bands might be contributed from dioxirane, which was postulated to be another important intermediate that might be isomerized from the Criegee intermediate in the reaction of O3 with 1-alkenes. O. Welz, J. D. Savee, D. L. Osborn, S. S.Vasu, C. J. Percival, D. E. Shallcross, and C. A. Taatjes, Science 335, 204 (2012). Y.-T. Su, Y.-H. Huang, H. A.Witek, and Y.-P. Lee, Science 340, 174 (2013).

  4. Towards a quantitative description of tunneling conductance of superconductors: Application to LiFeAs

    Science.gov (United States)

    Kreisel, A.; Nelson, R.; Berlijn, T.; Ku, W.; Aluru, Ramakrishna; Chi, Shun; Zhou, Haibiao; Singh, Udai Raj; Wahl, Peter; Liang, Ruixing; Hardy, Walter N.; Bonn, D. A.; Hirschfeld, P. J.; Andersen, Brian M.

    2016-12-01

    Since the discovery of iron-based superconductors, a number of theories have been put forward to explain the qualitative origin of pairing, but there have been few attempts to make quantitative, material-specific comparisons to experimental results. The spin-fluctuation theory of electronic pairing, based on first-principles electronic structure calculations, makes predictions for the superconducting gap. Within the same framework, the surface wave functions may also be calculated, allowing, e.g., for detailed comparisons between theoretical results and measured scanning tunneling topographs and spectra. Here we present such a comparison between theory and experiment on the Fe-based superconductor LiFeAs. Results for the homogeneous surface as well as impurity states are presented as a benchmark test of the theory. For the homogeneous system, we argue that the maxima of topographic image intensity may be located at positions above either the As or Li atoms, depending on tip height and the setpoint current of the measurement. We further report the experimental observation of transitions between As- and Li-registered lattices as functions of both tip height and setpoint bias, in agreement with this prediction. Next, we give a detailed comparison between the simulated scanning tunneling microscopy images of transition-metal defects with experiment. Finally, we discuss possible extensions of the current framework to obtain a theory with true predictive power for scanning tunneling microscopy in Fe-based systems.

  5. Semiconductor Surface Characterization by Scanning Probe Microscopies

    Science.gov (United States)

    2001-01-01

    potentiometry (STP)8 and ballistic electron emission microscopy (BEEM)9 which allow mapping of lateral surface potential and local subsurface Schottky...A.P.Fein. "Tunneling Spectroscopy of the Si(1 1 1)2xl Surface", Surf.Sci. 181, 295- 306, 1987. 8. P.Muralt, D.W.Pohl, "Scanning tunneling potentiometry

  6. Tunneling magnetic force microscopy

    Science.gov (United States)

    Burke, Edward R.; Gomez, Romel D.; Adly, Amr A.; Mayergoyz, Isaak D.

    1993-01-01

    We have developed a powerful new tool for studying the magnetic patterns on magnetic recording media. This was accomplished by modifying a conventional scanning tunneling microscope. The fine-wire probe that is used to image surface topography was replaced with a flexible magnetic probe. Images obtained with these probes reveal both the surface topography and the magnetic structure. We have made a thorough theoretical analysis of the interaction between the probe and the magnetic fields emanating from a typical recorded surface. Quantitative data about the constituent magnetic fields can then be obtained. We have employed these techniques in studies of two of the most important issues of magnetic record: data overwrite and maximizing data-density. These studies have shown: (1) overwritten data can be retrieved under certain conditions; and (2) improvements in data-density will require new magnetic materials. In the course of these studies we have developed new techniques to analyze magnetic fields of recorded media. These studies are both theoretical and experimental and combined with the use of our magnetic force scanning tunneling microscope should lead to further breakthroughs in the field of magnetic recording.

  7. Scanning tunneling microscopy study of in-plane graphene-hexagonal boron nitride heterostructures%石墨烯-六方氮化硼面内异质结构的扫描隧道显微学研究

    Institute of Scientific and Technical Information of China (English)

    刘梦溪; 张艳锋; 刘忠范

    2015-01-01

    石墨烯-六方氮化硼面内异质结构因可调控石墨烯的能带结构而受到广泛关注。本文介绍了在超高真空体系内,利用两步生长法在两类对石墨烯分别有强和弱电子掺杂的基底,即Rh(111)和Ir(111)上制备石墨烯-六方氮化硼单原子层异质结构。通过扫描隧道显微镜及扫描隧道谱对这两种材料的形貌和电子结构进行研究发现:石墨烯和六方氮化硼倾向于拼接生长形成单层的异质结构,而非形成各自分立的畴区;在拼接边界处,石墨烯和六方氮化硼原子结构连续无缺陷;拼接边界多为锯齿形型,该实验结果与密度泛函理论计算结果相符合;拼接界面处的石墨烯和六方氮化硼分别具有各自本征的电子结构,六方氮化硼对石墨烯未产生电子掺杂效应。%In-plane heterostructure of hexagonal boron nitride and graphene (h-BN-G) has become a research focus of graphene due to its predicted fascinating properties such as bandgap opening and magnetism, which hence has ignited the attempt of experimentally growing such in-plane two-dimensional (2D) hybrid materials. Many previous researches demonstrated the synthesis of such heterostructures on Cu foils via chemical vapor deposition (CVD) process. The obtained 2D hybrid materials would offer a possibility for fabricating atomically thin electronic devices. However, many fundamental issues are still unclear, including the in-plane atomic continuity, the edge type, and the electronic properties at the boundary of hybridized h-BN and graphene domain. To clarify these issues, we report the syntheses of h-BN-G monolayer heterostructures on strongly coupled Rh(111) substrate and weakly coupled Ir(111) substrate via a two-step growth process in an ultrahigh vacuum (UHV) system, respectively. With the aid of scanning tunneling microscopy (STM), it is revealed that graphene and h-BN could be linked together seamlessly on an atomic scale at the

  8. La0.67Ca0.33MnO3(001)薄膜表面结构的扫描隧道显微术研究%Study of La0.67 Ca0.33 MnO3 (001) thin film surface structure using scanning tunneling microscopy

    Institute of Scientific and Technical Information of China (English)

    刘锴; 王兵

    2011-01-01

    La0.67Ca0.33MnO3(O01) thin films have been grown with pulsed laser deposition method, and the surface structures and electronic states have been characterized using scanning tunneling microscopy/spectroscopy (STM/STS). In the MnO terminated surface, insulating ((√2)×(√2))R45° reconstruction surface and metallic (1 × 1 ) reconstruction surface are observed. In the (La,Ca)-O terminated surface, the surface presents the stripe structure. The results obtained from the variable temperature STM/STS show that the ((√~2) × (√~2))R45° reconstructed surface persists in insulating phase in a temperature range of 144-300 K, which may shield the signal of possible insulator-metal transition occurred in bulk in STS measurements.%利用 Scanning Tunneling Microscope(STM)和Scanning Tunneling Spectroscopy(STS)技术研究了La0.67Ca0.33MnO3(001)表面性质,研究发现表面呈现多相分离现象,在锰氧终端面观察到了绝缘性的(√2×√2)R45°重构表面和金属性的(1×1)重构表面,在镧钙氧终端面,观察到了表面呈现条纹状结构.La0.67Ca0.33MnO3(002)面(√2×√2)R45°重构表面电子态随温度的演化,表明(√2×√2)R45°重构作为一个绝缘相稳定在表面,可能掩盖了体相中相变信息.

  9. Carpal Tunnel Syndrome

    Science.gov (United States)

    ... arm. Just a passing cramp? It could be carpal tunnel syndrome. The carpal tunnel is a narrow passageway of ligament and ... difficult. Often, the cause is having a smaller carpal tunnel than other people do. Other causes include ...

  10. Investigation on the morphology of adsorbed benzotriazole film on copper surface by scanning tunneling microcopy%用扫描隧道显微镜研究铜表面苯并三氮唑吸附膜的结构形态

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    It is observed by scanning tunneling microscopy (STM) that the adsorbed Benzotriazole (BTA) on copper is long in shape and has an irregular rectangle. The growth of BTA on copper is in the form of polymeric chain and mainly in one dimension rather than two dimensions. The copper surface covered by BTA becomes flatter,smoother and the roughness was smaller than that of bare copper, so the corrosion is largely decreased. However,many grooves can be seen between BTA polymeric chains in which corrosion may exist to a degree.

  11. Nuclear Scans

    Science.gov (United States)

    Nuclear scans use radioactive substances to see structures and functions inside your body. They use a special ... images. Most scans take 20 to 45 minutes. Nuclear scans can help doctors diagnose many conditions, including ...

  12. Hawking radiation via tunnelling from general stationary axisymmetric black holes

    Institute of Scientific and Technical Information of China (English)

    Zhang Jing-Yi; Fan Jun-Hui

    2007-01-01

    Hawking radiation is viewed as a tunnelling process. In this way the emission rates of massless particles and massive particles tunnelling across the event horizon of general stationary axisymmetric black holes are calculated,separately. The emission spectra of these two different kinds of outgoing particles have the same functional form and both are consistent with an underlying unitary theory.

  13. Scanning Tunneling Spectroscopy on polycrystalline Cu(In,Ga)(S,Se){sub 2} thin-film solar cells; Rastertunnelspektroskopie an polykristallinen Cu(In,Ga)(S,Se){sub 2}-Duennschichtsolarzellen

    Energy Technology Data Exchange (ETDEWEB)

    Herber, U.

    2006-12-21

    In case of the investigated multinary Cu(In;Ga)Se{sub 2} system with its polycrystalline structure, the question for the lateral homogeneity of its electronic properties arises. By means of the here presented method, a photo-assisted tunneling spectroscopy, such lateral inhomogeneities of the Surface Photo Voltage (SPV) and the Photo-Induced Tunneling Current (PITC) are to be detected. Modulations of the bias voltage and/or the illumination intensity have been applied to a greater number of materials in tunneling spectroscopy. Within these field, disturbing current contributions, coupled via the tip-sample-capacitance, is a known problem. Electronic compensation by using an appropriate compensating circuit is a possible solution. As will be shown in this work, such procedure is very adequate to compensate stray signals generated by bias modulation. After the introduction and careful analysis of our technique in the first part the second part of the thesis deals with its application to a series of different CIGS samples. What becomes apparent is the aforementioned inhomogeneities in PITC signal to be an immanent property of these polycrystalline semiconductor systems. Besides lateral variations in the photocurrent amplitude, also inhomogeneities within its complex phase can be demonstrated. As becomes clear, it is impossible to draw conclusions about the participating capacity of the depletion region because of the dominating admittance of the tunneling junction. However, it is possible to gain a statistical distribution of the PITC by investigating a large number of positions on the sample. For small numbers of weak diodes, the distribution exhibits a distinct maximum at higher photocurrents. Metastable effects are observed by tracking PITC values over a longer period of time. (orig.)

  14. Giant tunnel-electron injection in nitrogen-doped graphene

    DEFF Research Database (Denmark)

    Lagoute, Jerome; Joucken, Frederic; Repain, Vincent

    2015-01-01

    Scanning tunneling microscopy experiments have been performed to measure the local electron injection in nitrogen-doped graphene on SiC(000) and were successfully compared to ab initio calculations. In graphene, a gaplike feature is measured around the Fermi level due to a phonon-mediated tunneling...... and at carbon sites. Nitrogen doping can therefore be proposed as a way to improve tunnel-electron injection in graphene....

  15. Inequality spectra

    Science.gov (United States)

    Eliazar, Iddo

    2017-03-01

    Inequality indices are widely applied in economics and in the social sciences as quantitative measures of the socioeconomic inequality of human societies. The application of inequality indices extends to size-distributions at large, where these indices can be used as general gauges of statistical heterogeneity. Moreover, as inequality indices are plentiful, arrays of such indices facilitate high-detail quantification of statistical heterogeneity. In this paper we elevate from arrays of inequality indices to inequality spectra: continuums of inequality indices that are parameterized by a single control parameter. We present a general methodology of constructing Lorenz-based inequality spectra, apply the general methodology to establish four sets of inequality spectra, investigate the properties of these sets, and show how these sets generalize known inequality gauges such as: the Gini index, the extended Gini index, the Rényi index, and hill curves.

  16. Tunneling electron induced luminescence from porphyrin molecules on monolayer graphene

    Energy Technology Data Exchange (ETDEWEB)

    Geng, Feng; Kuang, Yanmin; Yu, Yunjie; Liao, Yuan; Zhang, Yao; Zhang, Yang; Dong, Zhenchao, E-mail: zcdong@ustc.edu.cn

    2015-01-15

    Using epitaxially grown graphene on Ru(0001) as a decoupling layer, we investigate the evolution of tunneling electron induced luminescence from different number of layers of porphyrin molecules. Light emission spectra and photon maps, acquired via a combined optical setup with scanning tunneling microscopy (STM), indicate that the electronic decoupling effect of a monolayer (ML) graphene alone is still insufficient for generating molecule-specific emission from both the 1st- and 2nd-layer porphyrin molecules. Nevertheless, interestingly, the plasmonic emission is enhanced for the 1st-layer but suppressed for the 2nd-layer in comparison with the plasmonic emission on the monolayer graphene. Intrinsic intramolecular molecular fluorescence occurs at the 3rd-layer porphyrin. Such molecular thickness is about two MLs thinner than previous reports where molecules were adsorbed directly on metals. These observations suggest that the monolayer graphene does weaken the interaction between molecule and metal substrate and contribute to the reduction of nonradiative decay rates. - Highlights: • Showing molecularly resolved photon maps of graphene and porphyrins on it. • Revealing the influence of spacer thickness on molecular electroluminescence. • Graphene does weaken the interaction between molecules and metal substrate.

  17. Experimental determination of excitonic band structures of single-walled carbon nanotubes using circular dichroism spectra

    Science.gov (United States)

    Wei, Xiaojun; Tanaka, Takeshi; Yomogida, Yohei; Sato, Naomichi; Saito, Riichiro; Kataura, Hiromichi

    2016-10-01

    Experimental band structure analyses of single-walled carbon nanotubes have not yet been reported, to the best of our knowledge, except for a limited number of reports using scanning tunnelling spectroscopy. Here we demonstrate the experimental determination of the excitonic band structures of single-chirality single-walled carbon nanotubes using their circular dichroism spectra. In this analysis, we use gel column chromatography combining overloading selective adsorption with stepwise elution to separate 12 different single-chirality enantiomers. Our samples show higher circular dichroism intensities than the highest values reported in previous works, indicating their high enantiomeric purity. Excitonic band structure analysis is performed by assigning all observed Eii and Eij optical transitions in the circular dichroism spectra. The results reproduce the asymmetric structures of the valence and conduction bands predicted by density functional theory. Finally, we demonstrate that an extended empirical formula can estimate Eij optical transition energies for any (n,m) species.

  18. The study of laser induced dispersive fluorescence spectra of SO2 by time tomographic scanning%SO2气体激光诱导色散荧光时间断层扫描研究

    Institute of Scientific and Technical Information of China (English)

    张连水; 陈思远; 李明; 党伟; 赵魁芳

    2011-01-01

    The paper presented one study on the complicated de-excitation process of the first-excited band of SO2 molecule, including fluorescence radiation and collision relaxation, using gated enhanced optical multi-channel spectrum analyzer (OMA) and the quadruple harmonic output (266 nm) of a nanosecond pulsed Nd: YAG laser as excitation source.The time tomographic scanning results showed that the fluorescence spectrum envelopes centered in 305.6 nm and 337.2 nm and the regular fluorescence lines centered in 424.7 nm in the laser induced dispersive fluorescence spectra (LIDFS) were attributed to transitions to the different vibrational levels of ground electronic state X1A1 from low vibrational levels of B1B1, A1A2 and the ground vibrational level a3B1 respectively.The sensitive detection wavelength (425 nm) of SO2 gas was confirmed by the experiment.The harmonic frequencies of the symmetry stretch vibration (ω1 =1151.8 cm-1 ±0.6cm-1) and the bend vibration (ω2=517.8 cm-1 ±0.6 cm-1) of X1A1 state were also calculated from the experimental data.The anharmonic constants of stretch vibration mode and the bend vibration mode arex11 = 8±0.6 cm-1 andx22 = 9.2±0.6 cm-1 respectively.%以纳秒Nd:YAG激光器的四倍频(266 nm)为激发源,利用门选通增强光学多通道光谱分析仪(OMA),研究了SO2分子第一激发带粒子的荧光辐射与碰撞弛豫相结合的复杂退激发过程.通过对SO2分子第一激发带的激发及碰撞弛豫过程的时间断层扫描分析,可以将激光诱导色散荧光谱中以305.6 rnm、337.2 nm为中心的荧光包络和以424.7 nm为中心的规则序列分别归属于B1B1、A1A2低振动能级和a3B1基振动能级到基电子态X1A1不同振动能级的荧光跃迁,由此可以确定大气污染气体SO2的诱导荧光的灵敏检测波长为425 nm由规则序列的实验数据可以计算出SO2分子基电子态X1A1的对称振动和弯曲振动模式的基振动角频率分别为ω1=1151.8士0.6 cm-1和ω2=517.8

  19. Quantum theory of tunneling

    CERN Document Server

    Razavy, Mohsen

    2014-01-01

    In this revised and expanded edition, in addition to a comprehensible introduction to the theoretical foundations of quantum tunneling based on different methods of formulating and solving tunneling problems, different semiclassical approximations for multidimensional systems are presented. Particular attention is given to the tunneling of composite systems, with examples taken from molecular tunneling and also from nuclear reactions. The interesting and puzzling features of tunneling times are given extensive coverage, and the possibility of measurement of these times with quantum clocks are critically examined. In addition by considering the analogy between evanescent waves in waveguides and in quantum tunneling, the times related to electromagnetic wave propagation have been used to explain certain aspects of quantum tunneling times. These topics are treated in both non-relativistic as well as relativistic regimes. Finally, a large number of examples of tunneling in atomic, molecular, condensed matter and ...

  20. Road and Railroad Tunnels

    Data.gov (United States)

    Department of Homeland Security — Tunnels in the United States According to the HSIP Tiger Team Report, a tunnel is defined as a linear underground passageway open at both ends. This dataset is based...

  1. Transonic Dynamics Tunnel (TDT)

    Data.gov (United States)

    Federal Laboratory Consortium — The Transonic Dynamics Tunnel (TDT) is a continuous flow wind-tunnel facility capable of speeds up to Mach 1.2 at stagnation pressures up to one atmosphere. The TDT...

  2. Hypersonic Tunnel Facility (HTF)

    Data.gov (United States)

    Federal Laboratory Consortium — The Hypersonic Tunnel Facility (HTF) is a blow-down, non-vitiated (clean air) free-jet wind tunnel capable of testing large-scale, propulsion systems at Mach 5, 6,...

  3. The Tunnels of Samos

    Science.gov (United States)

    Apostol, Tom M. (Editor)

    1995-01-01

    This 'Project Mathematics' series video from CalTech presents the tunnel of Samos, a famous underground aquaduct tunnel located near the capital of Pithagorion (named after the famed Greek mathematician, Pythagoras, who lived there), on one of the Greek islands. This tunnel was constructed around 600 BC by King Samos and was built under a nearby mountain. Through film footage and computer animation, the mathematical principles and concepts of why and how this aquaduct tunnel was built are explained.

  4. Magnetic tunnel junctions (MTJs)

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    We review the giant tunnel magnetoresistance (TMR) in ferromagnetic-insulator-ferromagnetic junctions discovered in recent years, which is the magnetoresistance (MR) associated with the spin-dependent tunneling between two ferromagnetic metal films separated by an insulating thin tunnel barrier. The theoretical and experimental results including junction conductance, magnetoresistance and their temperature and bias dependences are described.

  5. Theory of dissociative tunneling ionization

    CERN Document Server

    Svensmark, Jens; Madsen, Lars Bojer

    2016-01-01

    We present a theoretical study of the dissociative tunneling ionization process. Analytic expressions for the nuclear kinetic energy distribution of the ionization rates are derived. A particularly simple expression for the spectrum is found by using the Born-Oppenheimer (BO) approximation in conjunction with the reflection principle. These spectra are compared to exact non-BO ab initio spectra obtained through model calculations with a quantum mechanical treatment of both the electronic and nuclear degrees freedom. In the regime where the BO approximation is applicable imaging of the BO nuclear wave function is demonstrated to be possible through reverse use of the reflection principle, when accounting appropriately for the electronic ionization rate. A qualitative difference between the exact and BO wave functions in the asymptotic region of large electronic distances is shown. Additionally the behavior of the wave function across the turning line is seen to be reminiscent of light refraction. For weak fiel...

  6. Vibration measurement and modal analysis for tunneller

    Institute of Scientific and Technical Information of China (English)

    HUANG Min; WU Miao; WEI Ren-zhi

    2001-01-01

    In this paper, the method of vibration measurement and modal analysis for AM~50 Tunneller machine is presented. When the machine was used for cutting man-made coal bed and real coal bed, the vibration of the machine was measured and the results of signal analysis show that the vibration characteristics under the two kinds of working situations are similar. The modal model of the machine is established, and then, the intrinsic vibration characteristics of AM50 tunneller are investigated by means of the method of experimental modal analysis. The vibration response simulation under a set of loading spectra measured is carried out by force response simulation software.

  7. Research on Effect of SpectraI Scanning Parameters on Quantitative AnaIysis ModeI of TotaI Acids and Amino Acid Nitrogen in Soy Sauce%光谱扫描参数对酱油总酸和氨基酸态氮定量分析模型的影响研究

    Institute of Scientific and Technical Information of China (English)

    胡亚云; 崔璐

    2015-01-01

    研究了适合进行酱油中总酸和氨基酸态氮定量分析的近红外光谱扫描参数。通过设定不同的分辨率和扫描次数,采用光程为1 mm的比色皿分别扫描各种扫描参数下的酱油透射光谱,利用PLS-交叉验证法建立酱油定量分析校正模型,结果表明:在光谱扫描频率范围为12000~4000 cm-1,分辨率为8 cm-1,扫描次数64次的参数条件下所建模型最优。%Study near infrared spectrum scanning parameters for total acids and amino acid nitrogen in soy sauce by quantitative analysis.By setting different resolution and scanning times,using the cuvette with optical path of 1 mm to scan transmission spectra of soy sauce under various parameters respectively,using PLS-cross validation method to establish quantitative analysis calibration model of soy sauce,the results show that:in the spectral scanning frequency range of 12000~4000 cm-1 ,the resolution of 8 cm-1 ,the scanning times of 64,the model is the best.

  8. Effect of tunnel structure on the specific capacitance of etched aluminum foil

    Institute of Scientific and Technical Information of China (English)

    Ning Peng; Li-Bo Liang; Ye-Dong He; Hong-Zhou Song; Xiao-Fei Yang; Xiao-Yu Cai

    2014-01-01

    The morphology of etched aluminum foil was observed using scanning electron microscopy, which led to the establishment of a cylindrical model and two merged models, considering the fixed weight loss of etching. The maximum of specific capacitance and the cor-responding optimum values for tunnel sizes at various anodization voltages were predicted. The increased size distribution and taper of tun-nels were demonstrated to decrease the specific capacitance, whereas the addition of polymeric additive into the tunnel widening solution was demonstrated to increase the capacitance. The formation of merged tunnels on the etched aluminum surface, irrespective of the presence of row-merged tunnels or cluster-merged tunnels, resulted in a dramatic decrease in the specific capacitance. It is concluded that, enhancing the uniformity of tunnel size and distribution and avoiding the formation of merged tunnels are the effective approach to achieving the higher capacitance for the tunnel etched and formed aluminum foil.

  9. Proton tunneling in solids

    Energy Technology Data Exchange (ETDEWEB)

    Kondo, J.

    1998-10-01

    The tunneling rate of the proton and its isotopes between interstitial sites in solids is studied theoretically. The phonons and/or the electrons in the solid have two effects on the tunneling phenomenon. First, they suppress the transfer integral between two neighbouring states. Second, they give rise to a finite lifetime of the proton state. Usually the second effect is large and the tunneling probability per unit time (tunneling rate) can be defined. In some cases, however, a coherent tunneling is expected and actually observed. (author)

  10. Variable density turbulence tunnel facility

    Science.gov (United States)

    Bodenschatz, E.; Bewley, G. P.; Nobach, H.; Sinhuber, M.; Xu, H.

    2014-09-01

    The Variable Density Turbulence Tunnel at the Max Planck Institute for Dynamics and Self-Organization in Göttingen, Germany, produces very high turbulence levels at moderate flow velocities, low power consumption, and adjustable kinematic viscosity between 10-4 m2/s and 10-7 m2/s. The Reynolds number can be varied by changing the pressure or flow rate of the gas or by using different non-flammable gases including air. The highest kinematic viscosities, and hence lowest Reynolds numbers, are reached with air or nitrogen at 0.1 bar. To reach the highest Reynolds numbers the tunnel is pressurized to 15 bars with the dense gas sulfur hexafluoride (SF6). Turbulence is generated at the upstream ends of two measurement sections with grids, and the evolution of this turbulence is observed as it moves down the length of the sections. We describe the instrumentation presently in operation, which consists of the tunnel itself, classical grid turbulence generators, and state-of-the-art nano-fabricated hot-wire anemometers provided by Princeton University [M. Vallikivi, M. Hultmark, S. C. C. Bailey, and A. J. Smits, Exp. Fluids 51, 1521 (2011)]. We report measurements of the characteristic scales of the flow and of turbulent spectra up to Taylor Reynolds number Rλ ≈ 1600, higher than any other grid-turbulence experiment. We also describe instrumentation under development, which includes an active grid and a Lagrangian particle tracking system that moves down the length of the tunnel with the mean flow. In this configuration, the properties of the turbulence are adjustable and its structure is resolvable up to Rλ ≈ 8000.

  11. MRI Scans

    Science.gov (United States)

    Magnetic resonance imaging (MRI) uses a large magnet and radio waves to look at organs and structures inside your body. Health care professionals use MRI scans to diagnose a variety of conditions, from ...

  12. Micro scanning probes

    CERN Document Server

    Niblock, T

    2001-01-01

    This thesis covers the design methodology, theory, modelling, fabrication and evaluation of a Micro-Scanning-Probe. The device is a thermally actuated bimorph quadrapod fabricated using Micro Electro Mechanical Systems technology. A quadrapod is a structure with four arms, in this case a planar structure with the four arms forming a cross which is dry etched out of a silicon diaphragm. Each arm has a layer of aluminium deposited on it forming a bimorph. Through heating each arm actuation is achieved in the plane of the quadrapod and the direction normal to it. Fabrication of the device has required the development of bulk micromachining techniques to handle post CMOS fabricated wafers and the patterning of thickly sputtered aluminium in bulk micro machined cavities. CMOS fabrication techniques were used to incorporate diodes onto the quadrapod arms for temperature measurement of the arms. Fine tungsten and silicon tips have also been fabricated to allow tunnelling between the tip and the platform at the centr...

  13. Inelastic electron tunneling spectroscopy: A route to the identification of the tip-apex structure

    Science.gov (United States)

    Vitali, Lucia; Borisova, Svetlana D.; Rusina, Galina G.; Chulkov, Evgueni V.; Kern, Klaus

    2010-04-01

    The vibrational spectrum of a tunneling junction on a clean Cu(111) surface has been characterized by vibrational density of states calculations and inelastic electron tunneling spectroscopy technique. We demonstrate that the achieved spectrum consists not only of vibrational modes excited by the tunneling electrons on the clean surface but also of modes characteristic of the structure of the tip apex. This allows to identify unequivocally the atomic structure of the tip, which is still the largest unknown parameter in a scanning tunneling microscope. This opens a new perspective in the interpretation of the measurements of vibrational modes with a scanning tunneling microscope. Additionally, it might have implications in the measurements of electron conductance through single atom or molecules contacted by the tip of scanning tunneling microscope.

  14. Parallel scanning probe arrays: their applications

    Directory of Open Access Journals (Sweden)

    Chang Liu

    2008-01-01

    Full Text Available Since the invention of the scanning tunneling microscope (STM1 and the atomic force microscope (AFM2, the field of scanning probe microscopy (SPM instruments has grown steadily and has had a profound influence in materials research, chemistry, biology, nanotechnology, and electronics3,4. Today, scanning probe instruments are used for metrology, characterization5, detection6, manipulation7, patterning8,9, and material modification. A wide range of scanning probe applications are available, taking advantage of various modes of tip–substrate interactions, including force, optics10,11, electrochemistry12, electromagnetics, electrostatics, thermal and mass transfer13,14, and vibration15,16.

  15. Resonance Enhanced Tunneling

    CERN Document Server

    Matsumoto, S; Matsumoto, Sh.

    2000-01-01

    Time evolution of tunneling in thermal medium is examined using the real-time semiclassical formalism previously developed. Effect of anharmonic terms in the potential well is shown to give a new mechanism of resonance enhanced tunneling. If the friction from environment is small enough, this mechanism may give a very large enhancement for the tunneling rate. The case of the asymmetric wine bottle potential is worked out in detail.

  16. Communication: Tunnelling splitting in the phosphine molecule

    Science.gov (United States)

    Sousa-Silva, Clara; Tennyson, Jonathan; Yurchenko, Sergey N.

    2016-09-01

    Splitting due to tunnelling via the potential energy barrier has played a significant role in the study of molecular spectra since the early days of spectroscopy. The observation of the ammonia doublet led to attempts to find a phosphine analogous, but these have so far failed due to its considerably higher barrier. Full dimensional, variational nuclear motion calculations are used to predict splittings as a function of excitation energy. Simulated spectra suggest that such splittings should be observable in the near infrared via overtones of the ν2 bending mode starting with 4ν2.

  17. Tunnelling splitting in the phosphine molecule

    CERN Document Server

    Sousa-Silva, Clara; Yurchenko, Sergey N

    2016-01-01

    Splitting due to tunnelling via the potential energy barrier has played a significant role in the study of molecular spectra since the early days of spectroscopy. The observation of the ammonia doublet led to attempts to find a phosphine analogous, but these have so far failed due to its considerably higher barrier. Full dimensional, variational nuclear motion calculations are used to predict splittings as a function of excitation energy. Simulated spectra suggest that such splittings should be observable in the near infrared via overtones of the $\

  18. Ulnar tunnel syndrome.

    Science.gov (United States)

    Bachoura, Abdo; Jacoby, Sidney M

    2012-10-01

    Ulnar tunnel syndrome could be broadly defined as a compressive neuropathy of the ulnar nerve at the level of the wrist. The ulnar tunnel, or Guyon's canal, has a complex and variable anatomy. Various factors may precipitate the onset of ulnar tunnel syndrome. Patient presentation depends on the anatomic zone of ulnar nerve compression: zone I compression, motor and sensory signs and symptoms; zone II compression, isolated motor deficits; and zone III compression; purely sensory deficits. Conservative treatment such as activity modification may be helpful, but often, surgical exploration of the ulnar tunnel with subsequent ulnar nerve decompression is indicated.

  19. Microsystem Aeromechanics Wind Tunnel

    Data.gov (United States)

    Federal Laboratory Consortium — The Microsystem Aeromechanics Wind Tunnel advances the study of fundamental flow physics relevant to micro air vehicle (MAV) flight and assesses vehicle performance...

  20. Quantum Tunnelling to the Origin and Evolution of Life.

    Science.gov (United States)

    Trixler, Frank

    2013-08-01

    Quantum tunnelling is a phenomenon which becomes relevant at the nanoscale and below. It is a paradox from the classical point of view as it enables elementary particles and atoms to permeate an energetic barrier without the need for sufficient energy to overcome it. Tunnelling might seem to be an exotic process only important for special physical effects and applications such as the Tunnel Diode, Scanning Tunnelling Microscopy (electron tunnelling) or Near-field Optical Microscopy operating in photon tunnelling mode. However, this review demonstrates that tunnelling can do far more, being of vital importance for life: physical and chemical processes which are crucial in theories about the origin and evolution of life can be traced directly back to the effects of quantum tunnelling. These processes include the chemical evolution in stellar interiors and within the cold interstellar medium, prebiotic chemistry in the atmosphere and subsurface of planetary bodies, planetary habitability via insolation and geothermal heat as well as the function of biomolecular nanomachines. This review shows that quantum tunnelling has many highly important implications to the field of molecular and biological evolution, prebiotic chemistry and astrobiology.

  1. Fast scanning mode and its realization in a scanning acoustic microscope.

    Science.gov (United States)

    Ju, Bing-Feng; Bai, Xiaolong; Chen, Jian

    2012-03-01

    The scanning speed of the two-dimensional stage dominates the efficiency of mechanical scanning measurement systems. This paper focused on a detailed scanning time analysis of conventional raster and spiral scan modes and then proposed two fast alternative scanning modes. Performed on a self-developed scanning acoustic microscope (SAM), the measured images obtained by using the conventional scan mode and fast scan modes are compared. The total scanning time is reduced by 29% of the two proposed fast scan modes. It will offer a better solution for high speed scanning without sacrificing the system stability, and will not introduce additional difficulties to the configuration of scanning measurement systems. They can be easily applied to the mechanical scanning measuring systems with different driving actuators such as piezoelectric, linear motor, dc motor, and so on. The proposed fast raster and square spiral scan modes are realized in SAM, but not specially designed for it. Therefore, they have universal adaptability and can be applied to other scanning measurement systems with two-dimensional mechanical scanning stages, such as atomic force microscope or scanning tunneling microscope.

  2. Scanning probe methods applied to molecular electronics

    OpenAIRE

    Pavliček, Niko

    2013-01-01

    Scanning probe methods on insulating films offer a rich toolbox to study electronic, structural and spin properties of individual molecules. This work discusses three issues in the field of molecular and organic electronics. A scanning tunneling microscopy (STM) head to be operated in high magnetic fields has been designed and built up. The STM head is very compact and rigid relying on a robust coarse approach mechanism. This will facilitate investigations of the spin properties of individ...

  3. Scanning probe microscopy competency development

    Energy Technology Data Exchange (ETDEWEB)

    Hawley, M.E.; Reagor, D.W.; Jia, Quan Xi [and others

    1998-12-31

    This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The project collaborators developed an ultra-high vacuum scanning tunneling microscope (UHV-STM) capability, integrated it with existing scanning probe microscopes, and developed new, advanced air-based scanning force techniques (SPMs). Programmatic, basic, and industrially related laboratory research requires the existence of SPMs, as well as expertise capable of providing local nano-scale information. The UHV-STM capability, equipped with load-lock system and several surface science techniques, will allow introduction, examination, and reaction of surfaces prepared under well-controlled vacuum conditions, including the examination of morphology and local bonding associated with the initial stages of film growth under controlled growth conditions. The resulting capabilities will enable the authors to respond to a variety of problems requiring local characterization of conducting and nonconducting surfaces in liquids, air, and UHV.

  4. Scan Statistics

    CERN Document Server

    Glaz, Joseph

    2009-01-01

    Suitable for graduate students and researchers in applied probability and statistics, as well as for scientists in biology, computer science, pharmaceutical science and medicine, this title brings together a collection of chapters illustrating the depth and diversity of theory, methods and applications in the area of scan statistics.

  5. Tunnel fire dynamics

    CERN Document Server

    Ingason, Haukur; Lönnermark, Anders

    2015-01-01

    This book covers a wide range of issues in fire safety engineering in tunnels, describes the phenomena related to tunnel fire dynamics, presents state-of-the-art research, and gives detailed solutions to these major issues. Examples for calculations are provided. The aim is to significantly improve the understanding of fire safety engineering in tunnels. Chapters on fuel and ventilation control, combustion products, gas temperatures, heat fluxes, smoke stratification, visibility, tenability, design fire curves, heat release, fire suppression and detection, CFD modeling, and scaling techniques all equip readers to create their own fire safety plans for tunnels. This book should be purchased by any engineer or public official with responsibility for tunnels. It would also be of interest to many fire protection engineers as an application of evolving technical principles of fire safety.

  6. Head CT scan

    Science.gov (United States)

    Brain CT; Cranial CT; CT scan - skull; CT scan - head; CT scan - orbits; CT scan - sinuses; Computed tomography - cranial; CAT scan - brain ... hold your breath for short periods. A complete scan usually take only 30 seconds to a few ...

  7. Proximity Scanning Transmission Electron Microscopy/Spectroscopy

    CERN Document Server

    Hwang, Ing-Shouh

    2016-01-01

    Here a new microscopic method is proposed to image and characterize very thin samples like few-layer materials, organic molecules, and nanostructures with nanometer or sub-nanometer resolution using electron beams of energies lower than 20 eV. The microscopic technique achieves high resolution through the proximity (or near-field) effect, as in scanning tunneling microscopy (STM), while it also allows detection of transmitted electrons for imaging and spectroscopy, as in scanning transmission electron microscopy (STEM). This proximity transmission electron microscopy (PSTEM) does not require any lens to focus the electron beam. It also allows detailed characterization of the interaction of low-energy electron with materials. PSTEM can operate in a way very similar to scanning tunneling microscopy, which provides high-resolution imaging of geometric and electronic structures of the sample surface. In addition, it allows imaging and characterization of the interior structures of the sample based on the detected...

  8. Spin-polarized scanning tunneling microscopy of magnetic nanostructures at the example of bcc-Co/Fe(110), Fe/Mo(110), and copper phthalocyanine/Fe(1110); Spinpolarisierte Rastertunnelmikroskopie magnetischer Nanostrukturen am Beispiel von bcc-Co/Fe(110), Fe/Mo(110) und Kupfer-Phthalocyanin/Fe(110)

    Energy Technology Data Exchange (ETDEWEB)

    Methfessel, Torsten

    2010-12-09

    This thesis provides an introduction into the technique of spin-polarized scanning tunnelling microscopy and spectroscopy as an experimental method for the investigation of magnetic nanostructures. Experimental results for the spin polarized electronic structure depending on the crystal structure of ultrathin Co layers, and depending on the direction of the magnetization for ultrathin Fe layers are presented. High-resolution measurements show the position-dependent spin polarization on a single copper-phthalocyanine molecule deposited on a ferromagnetic surface. Co was deposited by molecular beam epitaxy on the (110) surface of the bodycentered cubic metals Cr and Fe. In contrast to previous reports in the literature only two layers of Co can be stabilized in the body-centered cubic (bcc) structure. The bcc-Co films on the Fe(110) surface show no signs of epitaxial distortions. Thicker layers reconstruct into a closed-packed structure (hcp / fcc). The bcc structure increases the spin-polarization of Co to P=62 % in comparison to hcp-Co (P=45 %). The temperature-dependent spin-reorientation of ultrathin Fe/Mo(110) films was investigated by spin-polarized spectroscopy. A reorientation of the magnetic easy axis from the [110] direction along the surface normal to the in-plane [001] axis is observed at T (13.2{+-}0.5) K. This process can be identified as a discontinuous reorientation transition, revealing two simultaneous minima of the free energy in a certain temperature range. The electronic structure of mono- and double-layer Fe/Mo(110) shows a variation with the reorientation of the magnetic easy axis and with the direction of the magnetization. The investigation of the spin-polarized charge transport through a copper-phthalocyanine molecule on the Fe/Mo(110) surface provides an essential contribution to the understanding of spin-transport at the interface between metal and organic molecule. Due to the interaction with the surface of the metal the HOMO-LUMO energy

  9. Reactor Neutrino Spectra

    OpenAIRE

    Hayes, A. C.; Vogel, Petr

    2016-01-01

    We present a review of the antineutrino spectra emitted from reactors. Knowledge of these spectra and their associated uncertainties is crucial for neutrino oscillation studies. The spectra used to date have been determined either by converting measured electron spectra to antineutrino spectra or by summing over all of the thousands of transitions that make up the spectra, using modern databases as input. The uncertainties in the subdominant corrections to β-decay plague both methods, and we ...

  10. Aespoe Hard Rock Laboratory. The TASS-tunnel. Geological mapping

    Energy Technology Data Exchange (ETDEWEB)

    Hardenby, Carljohan (Vattenfall Power Consultant AB (Sweden)); Sigurdsson, Oskar (HAskGeokonsult AB (Sweden))

    2010-12-15

    The project entitled 'Sealing of tunnel at great depth' (Fintaetning av tunnel paa stort djup) needed a new tunnel in an area as undisturbed as possible and with cross-cutting water-bearing structures. The new tunnel, which was given the name TASS, was excavated on the -450 m level of SKB's Aespoe Hard Rock Laboratory (Aespoe HRL). The length of the tunnel is approximately 80 m and the theoretical tunnel area 19 m2. As is the case with all the other tunnels of the Aespoe HRL, the new tunnel has been geologically mapped. In addition, laser scanning combined with digital photography has been carried out. The tunnel was also used to test various types of explosives, borehole layouts and drilling techniques. The geological mapping of tunnel floor, walls and roof took place on four major occasions when a halt was made in tunnel excavation to allow for various tests. Before the mapping started on these occasions, laser scanning took place. The tunnel faces were mapped after each round (drilling, blasting and unloading). The present report describes the geological features of the tunnel and briefly how the laser scanning was performed. Water-bearing structures have been compared to similar structures in the neighbouring tunnels. The rock type names used here follow the old established Aespoe HRL nomenclature. Narrow (<0.1 m wide) dykes are normally mapped as fracture fillings. The dominating rock type is Aespoe diorite, which constitutes some 90 % of the rock mass. It is mostly mapped as fresh rock. . Minor constituents of the rock mass are fine-grained granite, hybrid rock, pegmatite, quartz veins/lenses and undifferentiated mafic rock. The mapping of fractures and deformation zones considers a number of parameters such as number of fractures, open/healed, width, length, description of fracture surfaces (roughness, planarity, etc), fracture filling, alteration and water. The deformation zones are discriminated into two main categories (&apos

  11. Experimental realization of single electron tunneling diode based on vertical graphene two-barrier junction

    OpenAIRE

    Xu, Rui; Bai, Ke-Ke; Nie, Jia-Cai; He, Lin

    2012-01-01

    Usually, graphene is used in its horizontal directions to design novel concept devices. Here, we report a single electron tunneling diode based on quantum tunneling through a vertical graphene two-barrier junction. The junction is formed by positioning a scanning tunnelling microscopy (STM) tip above a graphene nanoribbon that was deposited on a graphite surface. Because of the asymmetry of the two-barrier junction, the electrons can unidirectional transfer from the tip to the graphene nanori...

  12. Virtual photons in macroscopic tunneling

    OpenAIRE

    Aichmann, Horst; Nimtz, Guenter; Bruney, Paul

    2015-01-01

    Tunnelling processes are thought to proceed via virtual waves due to observed superluminal (faster than light) signal speeds. Some assume such speeds must violate causality. These assumptions contradict, for instance, superluminally tunnelled music and optical tunnelling couplers applied in fiber communication. Recently tunnelling barriers were conjectured to be cavities, wherein the tunnelled output signal is not causally related with the input. The tests described here resolve that tunnelli...

  13. Wind Tunnel Facility

    Data.gov (United States)

    Federal Laboratory Consortium — This ARDEC facility consists of subsonic, transonic, and supersonic wind tunnels to acquire aerodynamic data. Full-scale and sub-scale models of munitions are fitted...

  14. Wind Tunnel Testing Facilities

    Data.gov (United States)

    Federal Laboratory Consortium — NASA Ames Research Center is pleased to offer the services of our premier wind tunnel facilities that have a broad range of proven testing capabilities to customers...

  15. Water Tunnel Facility

    Data.gov (United States)

    Federal Laboratory Consortium — NETL’s High-Pressure Water Tunnel Facility in Pittsburgh, PA, re-creates the conditions found 3,000 meters beneath the ocean’s surface, allowing scientists to study...

  16. INCAS TRISONIC WIND TUNNEL

    Directory of Open Access Journals (Sweden)

    Florin MUNTEANU

    2009-09-01

    Full Text Available The 1.2 m x 1.2 m Trisonic Blowdown Wind Tunnel is the largest of the experimental facilities at the National Institute for Aerospace Research - I.N.C.A.S. "Elie Carafoli", Bucharest, Romania. The tunnel has been designed by the Canadian company DSMA (now AIOLOS and since its commissioning in 1978 has performed high speed aerodynamic tests for more than 120 projects of aircraft, missiles and other objects among which the twin jet fighter IAR-93, the jet trainer IAR-99, the MIG-21 Lancer, the Polish jet fighter YRYDA and others. In the last years the wind tunnel has been used mostly for experimental research in European projects such as UFAST. The high flow quality parameters and the wide range of testing capabilities ensure the competitivity of the tunnel at an international level.

  17. Counter Tunnel Project

    Science.gov (United States)

    2014-03-01

    the point clouds . This counter-tunnel effort was funded by the Joint Ground Robotics Enterprise (JGRE) from fiscal year 2010 through 2013, run...slide images against an iterative closest point (ICP) algorithm initialized using the centroids of the point clouds . The slide image algorithm performed...unnecessary for most of the time in the tunnels. However, the 3D point clouds made it possible to measure the height of objects lying in the path, detect

  18. Gravity Tunnel Drag

    CERN Document Server

    Concannon, Thomas

    2016-01-01

    The time it takes to fall down a tunnel through the center of the Earth to the other side takes approximately 42 minutes, but only when given several simplifying assumptions: a uniform density Earth; a gravitational field that varies linearly with radial position; a non-rotating Earth; a tunnel evacuated of air; and zero friction along the sides of the tunnel. Though several papers have singularly relaxed the first three assumptions, in this paper we relax the final two assumptions and analyze the motion of a body experiencing these types of drag forces in the tunnel. Under such drag forces, we calculate the motion of a transport vehicle through a tunnel of the Earth under uniform density, under constant gravitational acceleration, and finally under the more realistic Preliminary Reference Earth Model (PREM) density data. We find the density profile corresponding to a constant gravitational acceleration better models the motion through the tunnel compared to the PREM density profile, and the uniform density m...

  19. Neutrons and numerical methods. A new look at rotational tunneling

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, M.R.; Kearley, G.J. [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France)

    1997-04-01

    Molecular modelling techniques are easily adapted to calculate rotational potentials in crystals of simple molecular compounds. A comparison with the potentials obtained from the tunnelling spectra provides a stringent means for validating current methods of calculating Van der Waals, Coulomb and covalent terms. (author). 5 refs.

  20. Thyroid Scan and Uptake

    Science.gov (United States)

    ... Physician Resources Professions Site Index A-Z Thyroid Scan and Uptake Thyroid scan and uptake uses small ... Thyroid Scan and Uptake? What is a Thyroid Scan and Uptake? A thyroid scan is a type ...

  1. Scanning probe studies of the pilus nanowires in Geobacter sulfurreducens

    Science.gov (United States)

    Veazey, Joshua P.

    In microbial organisms like bacteria, pili (singular: pilus) are filament-like appendages that are nanometers in diameter and microns long. The sizes and structures of the different types of pili found in nature are adapted to serve one of many distinct functions for the organism from which they come. The pili expressed by the bacterium Geobacter sulfurreducens act as electrically conductive nanowires that provide conduits for electrons to leave the cell during its respiratory cycle. Biological experiments have suggested that long range electron transfer across micron distances may proceed along the protein matrix, rather than by metal cofactors (metal atoms bound to the protein). Protein conductivity across such distances would require a novel transport mechanism. In an effort to elucidate this mechanism, our lab has used two electronically sensitive scanning probe techniques: Scanning Tunneling Microscopy (STM) and Conductive Probe Atomic Force Microscopy (CP-AFM). I employed the high resolution imaging and electronic sensitivity of STM to resolve the molecular sub-structure and local electronic density of states (LDOS) at different points above pili from purified preparations, deposited onto a conducting substrate. The significant and stable tunneling currents achieved for biologically relevant voltages, in the absence of metal cofactors, demonstrated conduction between tip and substrate via the protein matrix. We observed periodicity of roughly 10 nm and 2.5 nm in topographs of the pili. In our acquisition of LDOS, we observed gap-like asymmetric energy spectra that were dependent upon the location of the tip above the pilus, suggestive of easier current flow out of one side of the cylindrical pilus and into the opposite side. Voltage-dependent STM imaging, which also contains information about the LDOS at each pixel, was consistent with this interpretation. The asymmetry in spectra observed on one pilus edge had a slightly larger magnitude than the other edge

  2. Biased impurity tunneling current emission spectrum in the presence of quasi-particle interaction

    Science.gov (United States)

    Maslova, N. S.; Arseyev, P. I.; Mantsevich, V. N.

    2016-09-01

    We performed theoretical investigations of the tunneling current noise spectra through single-level impurity in the presence of quasi-particle (electron-phonon) interaction by means of the non-equilibrium Green function formalism. We demonstrated a fundamental link between quantum noise in tunneling contact and light emission processes. We calculated tunneling current noise spectra through a single level impurity atom both in the presence and in the absence of quasi-particle interaction for a finite bias voltage and identified it as a source of experimentally observed light emission from bias STM contacts. The results turn out to be sensitive to the tunneling contact parameters. Our findings provide important insight into the nature of non-equilibrium electronic transport in tunneling junctions with quasi-particle interaction.

  3. Scanned probe microscopy for thin film superconductor development

    Energy Technology Data Exchange (ETDEWEB)

    Moreland, J. [National Institute of Standards and Technology, Boulder, CO (United States)

    1996-12-31

    Scanned probe microscopy is a general term encompassing the science of imaging based on piezoelectric driven probes for measuring local changes in nanoscale properties of materials and devices. Techniques like scanning tunneling microscopy, atomic force microscopy, and scanning potentiometry are becoming common tools in the production and development labs in the semiconductor industry. The author presents several examples of applications specific to the development of high temperature superconducting thin films and thin-film devices.

  4. Suppression of tunneling rate fluctuations in tunnel field-effect transistors by enhancing tunneling probability

    Science.gov (United States)

    Mori, Takahiro; Migita, Shinji; Fukuda, Koichi; Asai, Hidehiro; Morita, Yukinori; Mizubayashi, Wataru; Liu, Yongxun; O’uchi, Shin-ichi; Fuketa, Hiroshi; Otsuka, Shintaro; Yasuda, Tetsuji; Masahara, Meishoku; Ota, Hiroyuki; Matsukawa, Takashi

    2017-04-01

    This paper discusses the impact of the tunneling probability on the variability of tunnel field-effect transistors (TFETs). Isoelectronic trap (IET) technology, which enhances the tunneling current in TFETs, is used to suppress the variability of the ON current and threshold voltage. The simulation results show that suppressing the tunneling rate fluctuations results in suppression of the variability. In addition, a formula describing the relationship between the tunneling rate fluctuations and the electric field strength is derived based on Kane’s band-to-band tunneling model. This formula indicates that the magnitude of the tunneling rate fluctuations is proportional to the magnitude of the fluctuations in the electric field strength and a higher tunneling probability results in a lower variability. The derived relationship is universally valid for any technologies that exploit enhancement of the tunneling probability, including IET technology, channel material engineering, heterojunctions, strain engineering, etc.

  5. Restoration of images from the scanning-tunneling microscope

    Science.gov (United States)

    Kokaram, A. C.; Persad, N.; Lasenby, J.; Fitzgerald, W. J.; McKinnon, A.; Welland, M.

    1995-08-01

    During the acquisition of an image from any probe microscope instrument, various noise sources cause distortion in the observed image. It is often the case that impulsive disturbances cause bright groups of pixels to replace the actual image data in these locations. Furthermore, the images from a probe microscope show some amount of blurring caused both by the instrument function and the material properties. In almost all image-processing applications it is important to remove any impulsive distortion that may be present before deblurring can be attempted. We give a technique for detecting these impulses and reconstructing the image. This technique is superior to the standard global application of median filters for the case considered. The reconstruction is limited only to the affected regions and therefore results in a much sharper and more meaningful image. With the assumption of Gaussian blur it is then possible to propose several different deblurring methodologies. We present a novel Wiener-filter deblurring implementation and compare it to both maximum-entropy and Richardson-Lucy deblurring.

  6. Scanning Tunneling Microscopy, Atomic Force Microscopy, and Related Techniques

    Science.gov (United States)

    1992-02-26

    reducing the sixfold symmetry at the atomic Se surface to that of three-fold symmetry at the molecular WSe2 layer. Van Bakel et al. have imaged the...Technol. B 1991, 9, 1048-5 1. (D238) Akari, S.; Moller, R.; Dransfeld, K. App!. Phys. Let. 1991, 59, 243-5. (D239) Van Bakel , G.P.E.M.; De Hosson

  7. Construction of tunable supramolecular networks studied by scanning tunneling microscopy

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    In this review we describe a family of organic-based host frameworks which can accommodate guest molecules. The aim of the study is to test the adjustability of this class of mimic structures that may lead to new interesting functions. Emphasis of our research is placed upon four aspects: 1) thermal properties, 2) surface photochemistry, 3) fullerene adsorption, and 4) guest inclusion. It is envisioned that such approach of nanoporous molecular networks might be developed into a new family of useful soft frameworks for studies toward shape-selective catalysis, molecular recognition, self-assembly, and host-guest supramolecular chemistry.

  8. Helix Scan: A Scan Design for Diagnosis

    Institute of Scientific and Technical Information of China (English)

    WANG Fei; HU Yu; LI Xiaowei

    2007-01-01

    Scan design is a widely used design-for-testability technique to improve test quality and efficiency. For the scan-designed circuit, test and diagnosis of the scan chain and the circuit is an important process for silicon debug and yield learning. However, conventional scan designs and diagnosis methods abort the subsequent diagnosis process after diagnosing the scan chain if the scan chain is faulty. In this work, we propose a design-for-diagnosis scan strategy called helix scan and a diagnosis algorithm to address this issue. Unlike previous proposed methods, helix scan has the capability to carry on the diagnosis process without losing information when the scan chain is faulty. What is more, it simplifies scan chain diagnosis and achieves high diagnostic resolution as well as accuracy. Experimental results demonstrate the effectiveness of our design.

  9. Shifts and Dips in Inelastic Electron Tunneling Spectra Due to the Tunnel Junction Environment.

    Science.gov (United States)

    1981-05-27

    biochemistry,7𔄂 9 10 1water polution , electron beam irradiation, UV irradiation 12and lubrication 2 . Particularly promising applications have...partially oxidized the strip in air at 200 0C to form the alumina insulating barrier. Prior to the catalyst metal evaporation we cleaned the slide in

  10. Early times in tunneling

    CERN Document Server

    García-Calderón, G; Garcia-Calderon, Gaston; Villavicencio, Jorge

    2000-01-01

    Exact analytical solutions of the time-dependent Schr\\"odinger equation with the initial condition of an incident cutoff wave are used to investigate the traversal time for tunneling. The probability density starts from a vanishing value along the tunneling and transmitted regions of the potential. At the barrier width it exhibits, at early times, a distribution of traversal times that typically has a peak $\\tau_p$ and a width $\\Delta \\tau$. Numerical results for other tunneling times, as the phase-delay time, fall within $\\Delta \\tau$. The B\\"uttiker traversal time is the closest to $\\tau_p$. Our results resemble calculations based on Feynman paths if its noisy behaviour is ignored.

  11. Tunneling Through Black Rings

    Institute of Scientific and Technical Information of China (English)

    ZHAO Liu

    2007-01-01

    Hawking radiation of black ring solutions to 5-dimensional Einstein-Maxwell-dilaton theory is analyzed by use of the Parikh-Wilczek tunneling method. To get the correct tunneling amplitude and emission rate, we adopt and develop the Angheben-Nadalini-Vanzo-Zerbini covariant approach to cover the effects of rotation and electronic discharge all at once, and the effect of back reaction is also taken into account. This constitutes a unified approach to the tunneling problem. Provided the first law of thermodynamics for black rings holds, the emission rate is proportional to the exponential of the change of Bekenstein-Hawking entropy. Explicit calculation for black ring temperatures agrees exactly with the results obtained via the classical surface gravity method and the quasi-local formalism.

  12. Carpal tunnel syndrome caused by a giant cell tumour of the flexor tendon sheath.

    Science.gov (United States)

    Meek, Marcel F; Sheikh, Zahid A; Quinton, David N

    2014-02-01

    A 76-year-old woman developed right carpal tunnel syndrome after being conservatively treated for tenosynovitis of the flexor tendons with associated mild carpal tunnel syndrome. A magnetic resonance imaging scan showed a tumour in the carpal tunnel. Re-exploration showed that the median nerve was being compressed by a giant cell tumour of the flexor tendon sheaths. Appropriate imaging is advised in patients with additional findings (such as swelling) or in patients with secondary carpal tunnel syndrome and incomplete response to conservative treatment, to exclude a space-occupying lesion.

  13. Long distance tunneling

    CERN Document Server

    Ivlev, B I

    2005-01-01

    Quantum tunneling between two potential wells in a magnetic field can be strongly increased when the potential barrier varies in the direction perpendicular to the line connecting the two wells and remains constant along this line. A periodic structure of the wave function is formed in the direction joining the wells. The resulting motion can be coherent like motion in a conventional narrow band periodic structure. A particle penetrates the barrier over a long distance which strongly contrasts to WKB-like tunneling. The whole problem is stationary. The coherent process can be influenced by dissipation.

  14. Tunneling in axion monodromy

    Science.gov (United States)

    Brown, Jon; Cottrell, William; Shiu, Gary; Soler, Pablo

    2016-10-01

    The Coleman formula for vacuum decay and bubble nucleation has been used to estimate the tunneling rate in models of axion monodromy in recent literature. However, several of Coleman's original assumptions do not hold for such models. Here we derive a new estimate with this in mind using a similar Euclidean procedure. We find that there are significant regions of parameter space for which the tunneling rate in axion monodromy is not well approximated by the Coleman formula. However, there is also a regime relevant to large field inflation in which both estimates parametrically agree. We also briefly comment on the applications of our results to the relaxion scenario.

  15. Tunneling in Axion Monodromy

    CERN Document Server

    Brown, Jon; Shiu, Gary; Soler, Pablo

    2016-01-01

    The Coleman formula for vacuum decay and bubble nucleation has been used to estimate the tunneling rate in models of axion monodromy in recent literature. However, several of Coleman's original assumptions do not hold for such models. Here we derive a new estimate with this in mind using a similar Euclidean procedure. We find that there are significant regions of parameter space for which the tunneling rate in axion monodromy is not well approximated by the Coleman formula. However, there is also a regime relevant to large field inflation in which both estimates parametrically agree. We also briefly comment on the applications of our results to the relaxion scenario.

  16. Breaking through the tranfer tunnel

    CERN Multimedia

    Laurent Guiraud

    2001-01-01

    This image shows the tunnel boring machine breaking through the transfer tunnel into the LHC tunnel. Proton beams will be transferred from the SPS pre-accelerator to the LHC at 450 GeV through two specially constructed transfer tunnels. From left to right: LHC Project Director, Lyn Evans; CERN Director-General (at the time), Luciano Maiani, and Director for Accelerators, Kurt Hubner.

  17. Enhancement of Cross-Borehole Pulse Radar Signature on a Partially Water-Filled Tunnel

    Directory of Open Access Journals (Sweden)

    Ji-Hyun Jung

    2014-01-01

    Full Text Available Cross-borehole pulse radar has been employed to detect a deeply located empty tunnel. In this paper, effects of underground water collected in the bottom of an empty tunnel on cross-borehole pulse radar signatures are analyzed numerically. B-scan images, stacks of received pulses, are calculated by applying the finite-difference time-domain (FDTD method for 6 different heights of water from the bottom to the half height inside an empty tunnel. The most important features of an empty tunnel, the fastest time of peak (TOP and time of arrival (TOA extracted from the B-scan images, are slowed considerably depending on the increased height of water inside the tunnel. To compensate the weak TOP like that of an empty tunnel, a relation curve is formulated only utilizing measurable parameters of the fastest TOP and the fastest TOA. Then, a unified curve including the effects of two granites with the low and high dielectric properties is derived to cover widely varied dielectric properties of underground rocks. Based on the fastest TOP of an empty tunnel, the average difference between the fastest TOP of an empty tunnel and that of a partially water-filled tunnel decreases from 22.92% to 2.59% after enhancement.

  18. Lumbar spine CT scan

    Science.gov (United States)

    CAT scan - lumbar spine; Computed axial tomography scan - lumbar spine; Computed tomography scan - lumbar spine; CT - lower back ... your breath for short periods of time. The scan should take only 10 to 15 minutes.

  19. The acquisition of multidimensional NMR spectra within a single scan

    Science.gov (United States)

    Frydman, Lucio; Scherf, Tali; Lupulescu, Adonis

    2002-01-01

    A scheme enabling the complete sampling of multidimensional NMR domains within a single continuous acquisition is introduced and exemplified. Provided that an analyte's signal is sufficiently strong, the acquisition time of multidimensional NMR experiments can thus be shortened by orders of magnitude. This could enable the characterization of transient events such as proteins folding, 2D NMR experiments on samples being chromatographed, bring the duration of higher dimensional experiments (e.g., 4D NMR) into the lifetime of most proteins under physiological conditions, and facilitate the incorporation of spectroscopic 2D sequences into in vivo imaging investigations. The protocol is compatible with existing multidimensional pulse sequences and can be implemented by using conventional hardware; its performance is exemplified here with a variety of homonuclear 2D NMR acquisitions. PMID:12461169

  20. The near-field scanning thermal microscope

    Science.gov (United States)

    Wischnath, Uli F.; Welker, Joachim; Munzel, Marco; Kittel, Achim

    2008-07-01

    We report on the design, characterization, and performance of a near-field scanning thermal microscope capable to detect thermal heat currents mediated by evanescent thermal electromagnetic fields close to the surface of a sample. The instrument operates in ultrahigh vacuum and retains its scanning tunneling microscope functionality, so that its miniature, micropipette-based thermocouple sensor can be positioned with high accuracy. Heat currents on the order of 10-7W are registered in z spectroscopy at distances from the sample ranging from 1 to about 30nm. In addition, the device provides detailed thermographic images of a sample's surface.

  1. INCAS SUBSONIC WIND TUNNEL

    Directory of Open Access Journals (Sweden)

    Corneliu STOICA

    2009-09-01

    Full Text Available The INCAS Subsonic Wind Tunnel is a closed circuit, continuous, atmospheric pressure facility with a maximum speed of 110 m/s. The test section is octagonal ,of 2.5 m wide, 2.0 m high and 4 m long. The tunnel is powered by a 1200 kW, air cooled variable speed DC motor which drives a 12 blade, 3.5 m diameter fan and is equipped with a six component pyramidal type external mechanical balance with a 700 Kgf maximum lift capacity.The angle of attack range is between -45º and +45º while the yaw angle range is between -140º and +216º .The data acquisition system has been modified recently to allow the recording of all test data on a PC - type computer using LABVIEW and a PXI – type chassis containing specialized data acquisition modules.The tunnel is equipped with a variable frequency electrical supply system for powered models and a 10 bar compressed air supply for pneumatic flow control applications.In the recent years the subsonic wind tunnel has been intensively used for tests within several European projects (AVERT, CESAR and others.

  2. Scanning probe microscopy at video-rate

    Directory of Open Access Journals (Sweden)

    Georg Schitter

    2008-01-01

    Full Text Available Recent results have demonstrated the feasibility of video-rate scanning tunneling microscopy and video-rate atomic force microscopy. The further development of this technology will enable the direct observation of many dynamic processes that are impossible to observe today with conventional Scanning Probe Microscopes (SPMs. Examples are atom and molecule diffusion processes, the motion of molecular motors, real-time film growth, and chemical or catalytic reactions. Video-rate scanning probe technology might also lead to the extended application of SPMs in industry, e.g. for process control. In this paper we discuss the critical aspects that have to be taken into account for improving the imaging speed of SPMs. We point out the required instrumentation efforts, give an overview of the state of the art in high-speed scanning technology and discuss the required future developments for imaging at video-rates.

  3. Imaging standing surface plasmons by photon tunneling

    Science.gov (United States)

    Passian, A.; Lereu, A. L.; Wig, A.; Meriaudeau, F.; Thundat, T.; Ferrell, T. L.

    2005-04-01

    We present a direct method for optically exciting and imaging delocalized standing surface plasmons in thin metal films. We show theoretically that when imaging the field of the plasmons with a photon scanning tunneling microscope, the presence of the dielectric probe has a negligible effect on the surface modes of the metal film. We demonstrate that plasmon interference can be sustained in arbitrarily large regions of the metal film in comparison to the excitation wavelength. This knowledge can be important when seeking the relative distance between two scattering centers such as the presence of micron or submicron structures.

  4. Classical trajectories and quantum tunneling

    CERN Document Server

    Ivlev, B I

    2003-01-01

    The problem of inter-band tunneling in a semiconductor (Zener breakdown) in a nonstationary and homogeneous electric field is solved exactly. Using the exact analytical solution, the approximation based on classical trajectories is studied. A new mechanism of enhanced tunneling through static non-one-dimensional barriers is proposed in addition to well known normal tunneling solely described by a trajectory in imaginary time. Under certain conditions on the barrier shape and the particle energy, the probability of enhanced tunneling is not exponentially small even for non-transparent barriers, in contrast to the case of normal tunneling.

  5. Disorder effects in pnictides: a tunneling spectroscopy study

    Energy Technology Data Exchange (ETDEWEB)

    Noat, Y; Cren, T; Dubost, V; Lange, S; Debontridder, F; Roditchev, D [Institut des Nanosciences de Paris, CNRS UMR 7588, Universite Pierre et Marie Curie Paris 6, Campus Boucicaut, 140 rue de Lourmel, F-75015 Paris (France); Toulemonde, P; Marcus, J; Sulpice, A [Institut Neel, CNRS et Universite Joseph Fourier, 25 rue des Martyrs, BP 166, F-38042 Grenoble (France); Sacks, W, E-mail: yves.noat@insp.jussieu.f [Institut de Mineralogie et de Physique des Milieux Condenses, CNRS UMR 7590, Campus Boucicaut, 140 rue de Lourmel, F-75015 Paris (France)

    2010-11-24

    We present the synthesis and the tunneling spectroscopy study of superconducting FeSe{sub 0.5}Te{sub 0.5} (T{sub c} = 14 K), SmFeAsO{sub 0.85} (T{sub c} = 54 K) and SmFeAsO{sub 0.9}F{sub 0.1} (T{sub c} = 45 K). The samples were characterized by Rietveld refinement of x-ray diffraction patterns and transport as well as temperature-dependent magnetic measurements. Tunneling experiments on FeSe{sub 0.5}Te{sub 0.5} revealed a single superconducting gap {approx} 1 meV in BCS-like tunneling conductance spectra. In SmFeAsO{sub 0.85} and SmFeAsO{sub 0.9}F{sub 0.1}, however, more complex spectra were observed, characterized by two gap-like structures at {approx} 4 and {approx} 10 meV. These spectra are qualitatively understood assuming a two-band superconductor with a 's {+-}' order parameter. We show that, depending on the sign relation between the pairing amplitudes in the two bands, the interband quasiparticle scattering has a crucial effect on the shape of the tunneling spectra. On the other hand, single-gap spectra found in FeSe{sub 0.5}Te{sub 0.5} are more compatible with a disorder-induced 's '-wave gap, due to the Se-Te substitution.

  6. Reactor Neutrino Spectra

    CERN Document Server

    Hayes, A C

    2016-01-01

    We present a review of the antineutrino spectra emitted from reactors. Knowledge of these and their associated uncertainties are crucial for neutrino oscillation studies. The spectra used to-date have been determined by either conversion of measured electron spectra to antineutrino spectra or by summing over all of the thousands of transitions that makeup the spectra using modern databases as input. The uncertainties in the subdominant corrections to beta-decay plague both methods, and we provide estimates of these uncertainties. Improving on current knowledge of the antineutrino spectra from reactors will require new experiments. Such experiments would also address the so-called reactor neutrino anomaly and the possible origin of the shoulder observed in the antineutrino spectra measured in recent high-statistics reactor neutrino experiments.

  7. Wind Tunnel Management and Resource Optimization: A Systems Modeling Approach

    Science.gov (United States)

    Jacobs, Derya, A.; Aasen, Curtis A.

    2000-01-01

    complexity of developing a model that can be used for successfully implementing a standardized management planning tool. The objective of this study was to implement an Integrated Wind Tunnel Planning System to improve the operations within the aeronautics testing and research group, in particular Wind Tunnel Enterprise. The study included following steps: Conducted literature search and expert discussions (NASA and Old Dominion University faculty), Performed environmental scan of NASA Langley wind tunnel operations as foundation for problem definition. Established operation requirements and evaluation methodologies. Examined windtunnel operations to map out the common characteristics, critical components, and system structure. Reviewed and evaluated various project scheduling and management systems for implementation, Evaluated and implemented "Theory of Constraints (TOC)" project scheduling methodology at NASA Langley wind tunnel operations together with NASA staff.

  8. Tunneling and Transport in Nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Goldman, Allen M. [Univ. of Minnesota, Minneapolis, MN (United States)

    2016-08-16

    The goal of this program was to study new physical phenomena that might be relevant to the performance of conductive devices and circuits of the smallest realizable feature sizes possible using physical rather than biological techniques. Although the initial scientific work supported involved the use of scanning tunneling microscopy and spectroscopy to ascertain the statistics of the energy level distribution of randomly sized and randomly shaped quantum dots, or nano-crystals, the main focus was on the investigation of selected properties, including superconductivity, of conducting and superconducting nanowires prepared using electron-beam-lithography. We discovered a magnetic-field-restoration of superconductivity in out-of-equilibrium nanowires driven resistive by current. This phenomenon was explained by the existence of a state in which dissipation coexisted with nonvanishing superconducting order. We also produced ultra-small superconducting loops to study a predicted anomalous fluxoid quantization, but instead, found a magnetic-field-dependent, high-resistance state, rather than superconductivity. Finally, we developed a simple and controllable nanowire in an induced charged layer near the surface of a masked single-crystal insulator, SrTiO3. The layer was induced using an electric double layer transistor employing an ionic liquid (IL). The transport properties of the induced nanowire resembled those of collective electronic transport through an array of quantum dots.

  9. Tunneling and Transport in Nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Goldman, Allen M. [Univ. of Minnesota, Minneapolis, MN (United States)

    2016-08-16

    The goal of this program was to study new physical phenomena that might be relevant to the performance of conductive devices and circuits of the smallest realizable feature sizes possible using physical rather than biological techniques. Although the initial scientific work supported involved the use of scanning tunneling microscopy and spectroscopy to ascertain the statistics of the energy level distribution of randomly sized and randomly shaped quantum dots, or nano-crystals, the main focus was on the investigation of selected properties, including superconductivity, of conducting and superconducting nanowires prepared using electron-beam-lithography. We discovered a magnetic-field-restoration of superconductivity in out-of-equilibrium nanowires driven resistive by current. This phenomenon was explained by the existence of a state in which dissipation coexisted with nonvanishing superconducting order. We also produced ultra-small superconducting loops to study a predicted anomalous fluxoid quantization, but instead, found a magnetic-field-dependent, high-resistance state, rather than superconductivity. Finally, we developed a simple and controllable nanowire in an induced charged layer near the surface of a masked single-crystal insulator, SrTiO3. The layer was induced using an electric double layer transistor employing an ionic liquid (IL). The transport properties of the induced nanowire resembled those of collective electronic transport through an array of quantum dots.

  10. Vibration measurement and modal analysis of boom type tunneller

    Energy Technology Data Exchange (ETDEWEB)

    Min, H.; Gong, L.; Miao, W.; Wei, A. [China University of Mining & Technology, Jiangsu (China)

    2003-04-01

    The vibrations of an AM50 boom tunnelling machine have been measured in real time when cutting a man-made and a real coal bed. The vibration characteristics were similar in these working conditions, i.e. the man-made coal bed can be used as a realistic simulation of real cutting conditions. A modal model of the machine was then established and the intrinsic vibration characteristics were investigated by experimental modal analysis. Vibration response simulations under a set of measured load spectra and structural dynamics modification were also carried out using structural analysis software. The results not only facilitate the structural dynamics modification of the AM50 tunneller but also provide a foundation for optimising the design of new types of tunnelling machine.

  11. Educational Wind Tunnel

    Directory of Open Access Journals (Sweden)

    Juozas Bielskus

    2012-12-01

    Full Text Available The paper analyzes an educational wind tunnel produced by the Department of Building Energetics (DBE of Vilnius Gediminas Technical University. The equipment could be used for performing laboratory works and simple research. The article presents the projection of inflow and outlet velocity in the working chamber of DBE wind tunnel and carries out actual noise level measurement. The received data are compared with information on the level of noise generated by the fan considering instructions provided by the manufacturer. In order to assess the reliability of the computer program, simulation applying PHOENICS software has been conducted. The aim of modeling is to simulate a pilot model and to compare the obtained results with those of an analogous test presented in scientific articles.Article in Lithuanian

  12. Programmable ferroelectric tunnel memristor

    Directory of Open Access Journals (Sweden)

    Andy eQuindeau

    2014-02-01

    Full Text Available We report an analogously programmable memristor based on genuine electronic resistive switching combining ferroelectric switching and electron tunneling. The tunnel current through an 8 unit cell thick epitaxial Pb(Zr[0.2]Ti[0.8]O[3] film sandwiched between La[0.7]Sr[0.3]MnO[3] and cobalt electrodes obeys the Kolmogorov-Avrami-Ishibashi model for bidimensional growth with a characteristic switching time in the order of 10^-7 seconds. The analytical description of switching kinetics allows us to develop a characteristic transfer function that has only one parameter viz. the characteristic switching time and fully predicts the resistive states of this type of memristor.

  13. Carpal tunnel syndrome treatment

    Directory of Open Access Journals (Sweden)

    Emilio Filippucci

    2011-09-01

    Full Text Available Carpal tunnel syndrome, the most common peripheral neuropathy, results from compression of the median nerve at the wrist, and is a cause of pain, numbness and tingling in the upper extremities and an increasingly recognized cause of work disability. If carpal tunnel syndrome seems likely, conservative management with splinting should be initiated. Moreover, it has suggested that patients reduce activities at home and work that exacerbate symptoms. Pyridoxine and diuretics, since are largely utilised, are no more effective than placebo in relieving the symptoms. Non steroidal anti-inflammatory drugs and orally administered corticosteroids can be effective for short-term management (two to four weeks, but local corticosteroid injection may improve symptoms for a longer period. Injection is especially effective if there is no loss of sensibility or thenar-muscle atrophy and weakness, and if symptoms are intermittent rather than constant. If symptoms are refractory to conservative measures, the option of surgical therapy may be considered.

  14. [Carpal tunnel syndrome treatment].

    Science.gov (United States)

    De Angelis, Rossella; Salaffi, Fausto; Filippucci, Emilio; Grassi, Walter

    2006-01-01

    Carpal tunnel syndrome, the most common peripheral neuropathy, results from compression of the median nerve at the wrist, and is a cause of pain, numbness and tingling in the upper extremities and an increasingly recognized cause of work disability. If carpal tunnel syndrome seems likely, conservative management with splinting should be initiated. Moreover, it has suggested that patients reduce activities at home and work that exacerbate symptoms. Pyridoxine and diuretics, since are largely utilised, are no more effective than placebo in relieving the symptoms. Non steroidal anti-inflammatory drugs and orally administered corticosteroids can be effective for short-term management (two to four weeks), but local corticosteroid injection may improve symptoms for a longer period. Injection is especially effective if there is no loss of sensibility or thenar-muscle atrophy and weakness, and if symptoms are intermittent rather than constant. If symptoms are refractory to conservative measures, the option of surgical therapy may be considered.

  15. The beam dump tunnels

    CERN Multimedia

    Patrice Loïez

    2002-01-01

    In these images workers are digging the tunnels that will be used to dump the counter-circulating beams. Travelling just a fraction under the speed of light, the beams at the LHC will each carry the energy of an aircraft carrier travelling at 12 knots. In order to dispose of these beams safely, a beam dump is used to extract the beam and diffuse it before it collides with a radiation shielded graphite target.

  16. Carpal tunnel release

    DEFF Research Database (Denmark)

    Larsen, Morten Bo; Sørensen, A I; Crone, K L;

    2013-01-01

    A single-blind, randomized, controlled trial was done to compare the results of carpal tunnel release using classic incision, short incision, or endoscopic technique. In total, 90 consecutive cases were included. Follow-up was 24 weeks. We found a significantly shorter sick leave in the endoscopi...... incision could be found. There were no serious complications in either group. The results indicate that the endoscopic procedure is safe and has the benefit of faster rehabilitation and return to work....

  17. Lung gallium scan

    Science.gov (United States)

    Gallium 67 lung scan; Lung scan; Gallium scan - lung; Scan - lung ... Gallium is injected into a vein. The scan will be taken 6 to 24 hours after the gallium is injected. (Test time depends on whether your condition is acute or chronic .) ...

  18. Open Source Scanning Probe Microscopy Control Software Package Gxsm

    Energy Technology Data Exchange (ETDEWEB)

    Zahl P.; Wagner, T.; Moller, R.; Klust, A.

    2009-08-10

    Gxsm is a full featured and modern scanning probe microscopy (SPM) software. It can be used for powerful multidimensional image/data processing, analysis, and visualization. Connected toan instrument, it is operating many different avors of SPM, e.g., scanning tunneling microscopy(STM) and atomic force microscopy (AFM) or in general two-dimensional multi channel data acquisition instruments. The Gxsm core can handle different data types, e.g., integer and oating point numbers. An easily extendable plug-in architecture provides many image analysis and manipulation functions. A digital signal processor (DSP) subsystem runs the feedback loop, generates the scanning signals and acquires the data during SPM measurements. The programmable Gxsm vector probe engine performs virtually any thinkable spectroscopy and manipulation task, such as scanning tunneling spectroscopy (STS) or tip formation. The Gxsm software is released under the GNU general public license (GPL) and can be obtained via the Internet.

  19. Improved controlled atmosphere high temperature scanning probe microscope

    DEFF Research Database (Denmark)

    Hansen, Karin Vels; Wu, Yuehua; Jacobsen, Torben

    2013-01-01

    fuel cells and electrolyzer cells. Here, we report on advanced improvements of our original controlled atmosphere high temperature scanning probe microscope, CAHT-SPM. The new microscope can employ a broad range of the scanning probe techniques including tapping mode, scanning tunneling microscopy......, scanning tunneling spectroscopy, conductive atomic force microscopy, and Kelvin probe force microscopy. The temperature of the sample can be as high as 850 °C. Both reducing and oxidizing gases such as oxygen, hydrogen, and nitrogen can be added in the sample chamber and the oxygen partial pressure (pO2......To locally access electrochemical active surfaces and interfaces in operando at the sub-micron scale at high temperatures in a reactive gas atmosphere is of great importance to understand the basic mechanisms in new functional materials, for instance, for energy technologies, such as solid oxide...

  20. Heart PET scan

    Science.gov (United States)

    ... nuclear medicine scan; Heart positron emission tomography; Myocardial PET scan ... A PET scan requires a small amount of radioactive material (tracer). This tracer is given through a vein (IV), ...