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Sample records for scanning tunneling spectra

  1. 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.

  2. Scanning tunneling microscope nanoetching method

    Science.gov (United States)

    Li, Yun-Zhong (West Lafayette, IN); Reifenberger, Ronald G. (West Lafayette, IN); Andres, Ronald P. (West Lafayette, IN)

    1990-01-01

    A method is described for forming uniform nanometer sized depressions on the surface of a conducting substrate. A tunneling tip is used to apply tunneling current density sufficient to vaporize a localized area of the substrate surface. The resulting depressions or craters in the substrate surface can be formed in information encoding patterns readable with a scanning tunneling microscope.

  3. Evidence of strong correlations at the van Hove singularity in the scanning tunneling spectra of superconducting Bi2Sr2CaCu2O8+? single crystals

    Science.gov (United States)

    Nieminen, Jouko; Suominen, Ilpo; Das, Tanmoy; Markiewicz, R. S.; Bansil, A.

    2012-06-01

    We present realistic multiband calculations of scanning tunneling spectra in Bi2Sr2CaCu2O8+? over a wide doping range. Our modeling incorporates effects of a competing pseudogap and pairing gap as well as effects of strong electronic correlations, which are included by introducing self-energy corrections in the one-particle propagators. The calculations provide a good description of the two-gap features seen in experiments at low energies and the evolution of the van Hove singularity (VHS) with doping, and suggest a possible quantum critical point near the point where the VHS crosses the Fermi level.

  4. Scanning tunneling spectra and low energy ion scattering studies of the Verwey transition in MBE Fe3O4 (100) thin film

    International Nuclear Information System (INIS)

    The (100) surface magnetite Fe3O4 thin film was studied by a UHV low-temperature scanning tunneling microscope and by an ion scattering spectroscopy. The tunneling spectra revealed a widening of the gap with decreasing temperature, which may be related to the metal-insulator phase transition in this material. A strong effect of this phase transition on ion scattering from such a surface was observed. The temperature dependence of a scattered ion yield, R+(T), revealed two minima at around 100 K and at 125 K under Ne+ bombardment with the primary energy up to 6 keV. The disappearance of the high-temperature minimum at a bombarding energy of 6.5 keV gave a further evidence for the ion in the velocity dependence of the character of the R+(T) curve, which has been first observed for a MBE Fe3O4 (111) film surface. (author)

  5. The scanning tunneling microscope

    International Nuclear Information System (INIS)

    A newly conceived microscope, based on a pure quantum phenomenon, is an ideal tool to study atom by atom the topography and properties of surfaces. Applications are presented: surface ''reconstruction'' of silicon, lamellar compound study, etc... Spectroscopy by tunnel effect will bring important information on electronic properties; it is presented with an application on silicon

  6. Tunneling spectra and superconducting gaps observed by scanning tunneling microscopy near the grain boundaries of FeSe{sub 0.3}Te{sub 0.7} films

    Energy Technology Data Exchange (ETDEWEB)

    Lin, K.C., E-mail: d943333@oz.nthu.edu.tw [Department of Physics, National Tsing Hua University, Hsinchu 300, Taiwan (China); Institute of Physics, Academia Sinica, Nankang, Taipei 115, Taiwan (China); Li, Y.S. [Institute of Physics, Academia Sinica, Nankang, Taipei 115, Taiwan (China); Shen, Y.T. [Department of Physics, National Tsing Hua University, Hsinchu 300, Taiwan (China); Wu, M.K. [Institute of Physics, Academia Sinica, Nankang, Taipei 115, Taiwan (China); Department of Physics, National Dong Hwa University, Hualien 974, Taiwan (China); Chi, C.C. [Department of Physics, National Tsing Hua University, Hsinchu 300, Taiwan (China)

    2013-12-15

    Highlights: •We prepared FeSe{sub 0.3}Te{sub 0.7} films with two orientations on the same MgO substrate by the pulsed laser deposition technique. •The STM tunneling spectra in the grains with two orientations and boundary between them. •Different superconducting gaps were observed in different orientations and their boundary. -- Abstract: We used scanning tunneling microscopy (STM) to study the tunneling spectra of FeSe{sub 0.3}Te{sub 0.7} films with two orientations of the ab-planes and a connection ramp between them. We discovered that by pulsed laser deposition (PLD) method, the a- and b-axis of the FeSe{sub 0.3}Te{sub 0.7} film deposited on an Ar-ion-milled magnesium oxide (MgO) substrate were rotated 45° with respect to those of MgO, whereas the a- and b-axis of the film grown on a pristine MgO substrate were parallel to those of MgO. With photolithography and this technique, we can prepare FeSe{sub 0.3}Te{sub 0.7} films with two orientations on the same MgO substrate so that the connection between them forms a ramp at an angle of about 25° to the substrate plane. In the planar region, for either the 0° or 45° orientation, we observed tunneling spectra with a superconducting gap of about 5 meV and 1.78 meV, respectively. However, a much larger gap at about 18 meV was observed in the ramp region. Furthermore, we observed a small zero-bias conductance peak (ZBCP) inside the large gap at T = 4.3 K. The ZBCP becomes smaller with increasing temperature and disappeared at temperature above 7 K.

  7. Scanning Tunneling Optical Resonance Microscopy

    Science.gov (United States)

    Bailey, Sheila; Wilt, Dave; Raffaelle, Ryne; Gennett, Tom; Tin, Padetha; Lau, Janice; Castro, Stephanie; Jenkins, Philip; Scheiman, Dave

    2003-01-01

    Scanning tunneling optical resonance microscopy (STORM) is a method, now undergoing development, for measuring optoelectronic properties of materials and devices on the nanoscale by means of a combination of (1) traditional scanning tunneling microscopy (STM) with (2) tunable laser spectroscopy. In STORM, an STM tip probing a semiconductor is illuminated with modulated light at a wavelength in the visible-to-near-infrared range and the resulting photoenhancement of the tunneling current is measured as a function of the illuminating wavelength. The photoenhancement of tunneling current occurs when the laser photon energy is sufficient to excite charge carriers into the conduction band of the semiconductor. Figure 1 schematically depicts a proposed STORM apparatus. The light for illuminating the semiconductor specimen at the STM would be generated by a ring laser that would be tunable across the wavelength range of interest. The laser beam would be chopped by an achromatic liquid-crystal modulator. A polarization-maintaining optical fiber would couple the light to the tip/sample junction of a commercial STM. An STM can be operated in one of two modes: constant height or constant current. A STORM apparatus would be operated in the constant-current mode, in which the height of the tip relative to the specimen would be varied in order to keep the tunneling current constant. In this mode, a feedback control circuit adjusts the voltage applied to a piezoelectric actuator in the STM that adjusts the height of the STM tip to keep the tunneling current constant. The exponential relationship between the tunneling current and tip-to-sample distance makes it relatively easy to implement this mode of operation. The choice of method by which the photoenhanced portion of the tunneling current would be measured depends on choice of the frequency at which the input illumination would be modulated (chopped). If the frequency of modulation were low enough (typically piezoelectric tip-height actuator could be measured by use of a lock-in amplifier locked to the modulation (chopping) signal. However, at a high modulation frequency (typically in the kilohertz range or higher), the feedback circuit would be unable to respond. In this case, the photoenhanced portion of the tunneling current could be measured directly. For this purpose, the tunneling current would be passed through a precise resistor and the voltage drop would be measured by use of the lock-in amplifier.

  8. 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.

  9. Low-temperature scanning tunneling spectroscopy

    International Nuclear Information System (INIS)

    A scanning tunneling microscope (STM) was designed and built to operate at liquid helium temperature and was used to measure highly localized electron tunneling spectroscopy. Several instruments were built, all capable of operating in many different environments: air, vacuum, liquid helium and in a transfer gas. An adaptation of one particular design was made into an atomic force microscope capable of operating at low temperatures. Using a low temperature STM, three adsorbed molecular species (liquid crystals, sorbic acid, and carbon monoxide), deposited on a graphite substrate, have been imaged at 4.2K. The inelastic tunneling spectra of these adsorbates show strong peaks in dI/dV vs V curves at energies that correspond to known vibrational modes. The increase in conductance at the onset of inelastic tunneling was measured to be as high as 100 times. The spatial variation of the spectra was measured and was seen to change dramatically on the scale of angstroms, suggesting that individual molecular bonds could be measured. A theoretical model is presented to explain the contrast seen in the STM images of adsorbed molecules, thereby explaining why adsorbed molecules appear to be more conductive than the background. The microscope proved very useful for measuring the energy gap of high temperature superconductors. These materials often have submicron grain sizes. For LaSrCuO, YBaCuO, and BiCaSrCuO, the conductance curves showed a large energy gap suggesting a strongly coupled superconductor. The conductance curves also indicated that intergrain tunneling may occur and that the background conductance varied linearly with the applied voltage. The crystalline structure of Bi2Sr2CaCu2O8+δ was imaged by an STM operating in air and in ultra-high vacuum

  10. 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...

  11. Scanning Tunneling Microscope For Use In Vacuum

    Science.gov (United States)

    Abel, Phillip B.

    1993-01-01

    Scanning tunneling microscope with subangstrom resolution developed to study surface structures. Although instrument used in air, designed especially for use in vacuum. Scanning head is assembly of small, mostly rigid components made of low-outgassing materials. Includes coarse-positioning mechanical-translation stage, on which specimen mounted by use of standard mounting stub. Tunneling tip mounted on piezoelectric fine-positioning tube. Application of suitable voltages to electrodes on piezoelectric tube controls scan of tunneling tip across surface of specimen. Electronic subsystem generates scanning voltages and collects data.

  12. Single-electron tunneling. [Microwave scanning tunneling microscope

    Energy Technology Data Exchange (ETDEWEB)

    Ruggiero, S.T.

    1993-01-01

    Pictures using the low-temperature microwave scanning tunneling microscope, have been made of particles and tunneling IV characteristics determined. Strong, sometimes periodic negative differential resistance was observed in small-particle systems. Au and Ag droplets and particles were studied. 4 figs.

  13. 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 films. It is shown how accurate quantitative information about work function differences can be obtained and how these differences depend on the QWSs in the Pb thin films. The electron transport properties and mechanical characteristics of atom-sized metallic contacts are of fundamental interest in view of future nanoscale device technologies. Proximity probes like STM, metal break junctions, and related techniques, together with computational methods for simulating tip-sample interactions, have made it possible to address this question. While the importance of atomic structure and bonding for transport through single-atom junctions has repeatedly been emphasized, investigations of the influence of subsurface bonding properties have been rare. Here, the contact formation of a STM tip approaching Pb(111) thin films supported on Ag(111) substrates is investigated. Contacts on monolayer films are found to differ from contacts made on thicker Pb films. This behavior is explained in terms of different vertical bonding-strengths due to a charge-transfer induced surface dipole. Furthermore, the single-atom contact conductance on Pb(111) films beyond the first monolayer is determined. It is shown that analyses based on hitherto widely used conventional conductance histograms may overestimate the single-atom contact conductance by as much as 20%. (orig.)

  14. Scanning probe microscopy atomic force microscopy and scanning tunneling microscopy

    CERN Document Server

    Voigtländer, Bert

    2015-01-01

    This book explains the operating principles of atomic force microscopy and scanning tunneling microscopy. The aim of this book is to enable the reader to operate a scanning probe microscope successfully and understand the data obtained with the microscope. The chapters on the scanning probe techniques are complemented by the chapters on fundamentals and important technical aspects. This textbook is primarily aimed at graduate students from physics, materials science, chemistry, nanoscience and engineering, as well as researchers new to the field.

  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. Ultraviolet light emission from Si in a scanning tunneling microscope

    OpenAIRE

    Schmidt, Patrick; Berndt, Richard; Vexler, Mikhail I.

    2007-01-01

    Ultraviolet and visible radiation is observed from the contacts of a scanning tunneling microscope with Si(100) and (111) wafers. This luminescence relies on the presence of hot electrons in silicon, which are supplied, at positive bias on n- and p-type samples, through the injection from the tip, or, at negative bias on p-samples, by Zener tunneling. Measured spectra reveal a contribution of direct optical transitions in Si bulk. The necessary holes well below the valence band edge are injec...

  17. Evidence of strong correlations at the Van Hove singularity in the scanning-tunneling spectra of superconducting Bi2Sr2CaCu2O8+? single crystals

    Science.gov (United States)

    Bansil, Arun; Nieminen, Jouko; Suominen, Ilpo; Das, Tanmoy; Markiewicz, Robert

    2012-02-01

    We present realistic multiband calculations of scanning tunneling spectra in Bi2Sr2CaCu2O8+? over a wide doping range. Our modeling incorporates effects of a competing pseudogap and pairing gap as well as effects of strong electronic correlations, which are included by introducing self-energy corrections in the one-particle propagators. The calculations provide a good description of the two-gap features seen in experiments at low energies. In particular, the Van Hove singularity (VHS) in the underlying electronic states is found to split into a prominent incoherent feature at high energies and a weaker coherent part near the Fermi level which is strongly involved in gap formation. The progressive hybridization of the localized VHS into the Fermi surface with increasing doping is suggestive of Kondo physics which has been proposed previously for cuprates and heavy fermion compounds.

  18. 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.

  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. Contrast mechanisms in photothermal scanning tunneling microscopy

    Science.gov (United States)

    Probst, O.; Grafström, S.; Fritz, J.; Dey, S.; Kowalski, J.; Neumann, R.; Wörtge, M.; Zu Putlitz, G.

    1994-08-01

    By irradiation of the tunneling junction of a scanning tunneling microscope with intensity-modulated laser light a gap-width modulation due to thermal expansion of tip and sample was produced. Photothermal images were obtained by spatial mapping of the resulting modulation of the tunneling current or its logarithm. The various mechanisms responsible for the observed contrast are discussed quantitatively. In case of a highly corrugated gold film on mica the contrast arises mainly from either the current variations caused by the non-zero reaction time of the current control loop or from a geometry factor. In both cases the images reflect certain properties of the sample topography. On the other hand, for a liquid-crystal film adsorbed on graphite a contrast on a molecular scale was found which is attributed to variations of the effective barrier height.

  1. Scanning tunneling microscopy of biological molecules

    International Nuclear Information System (INIS)

    Scanning Tunnelling Microscopy (STM) has been used to image a number of biological molecules including thrombospondin and glycoprotein 88 (GP88). In this paper, STM images which clearly resolve the morphology of these molecules are presented. Ultimately, it is hoped that STM will provide information about the interaction between these molecules after overcoming problems associated with sample preparation and reproducibility of results which are discussed. 4 refs., 2 figs

  2. Superconducting phonon spectroscopy using a low-temperature scanning tunneling microscope

    Science.gov (United States)

    Leduc, H. G.; Kaiser, W. J.; Hunt, B. D.; Bell, L. D.; Jaklevic, R. C.

    1989-01-01

    The low-temperature scanning tunneling microscope (STM) system described by LeDuc et al. (1987) was used to observe the phonon density of states effects in a superconductor. Using techniques based on those employed in macroscopic tunneling spectroscopy, electron tunneling current-voltage (I-V) spectra were measured for NbN and Pb, and dI/dV vs V spectra were measured using standard analog derivative techniques. I-V measurements on NbN and Pb samples under typical STM conditions showed no evidence for multiparticle tunneling effects.

  3. Simulation of scanning tunneling spectroscopy of supported carbon nanotubes

    International Nuclear Information System (INIS)

    The angle and energy dependent transmission of wave packets was calculated through a jellium potential model of a scanning tunneling microscope (STM) junction containing different arrangements of carbon nanotubes. The total tunnel current as a function of STM bias was calculated by statistical averaging over a distribution of wave packets in the allowed energy window. Three tunneling situations were studied: (i) a STM tunnel junction with no nanotube present, (ii) one single wall nanotube in the STM junction, and (iii) a nanotube 'raft'. The effects of point contacts at the STM tip/nanotube, at the nanotube/substrate, and at both interfaces were also investigated. The theory allowed us to identify components of pure geometrical origin responsible for the asymmetry in the scanning tunneling spectroscopy (STS) spectrum of the carbon nanotubes with respect to bias voltage polarity. The calculations show that for tip negative bias the angular dependence of the transmission is determined by the tip shape. The particular tip shape introduces an asymmetry on the negative side of the STS spectrum. For tip positive bias the angular dependence of the transmission depends strongly on the nature of the nanosystem in the STM gap. While the transmission of the STM tunnel junction with no nanotube present can be well represented by a one dimensional model, all other geometries cause a large normal-transverse momentum mixing of the wave packet. A diffraction-grating-like behavior is seen in the angular dependence of the transmission of the nanotube raft. Point contacts between the nanotube and the substrate cause an asymmetry in the positive side of the STS spectrum. Calculated STS spectra are compared to experimental ones

  4. A millikelvin scanning tunneling microscope with two independent scanning systems

    CERN Document Server

    Roychowdhury, A; Anderson, J R; Lobb, C J; Wellstood, F C; Dreyer, M

    2013-01-01

    We describe the design, construction and operation of a scanning tunneling microscope (STM) with two tips that can independently acquire simultaneous scans of a sample. The STM is mounted on a dilution refrigerator and the setup includes vibration isolation, rf-filtered wiring, an ultra high vacuum (UHV) sample preparation chamber and sample transfer mechanism. We present images and spectroscopy taken with superconducting Nb tips with the refrigerator at 35 mK that indicate that the effective temperature of our tips/sample is approximately 184 mK, corresponding to an energy resolution of 16 $\\mu$eV. Atomic resolution topographic images of an Au(100) surface taken with the inner and outer tips were found to have root mean square roughness of 1.75 $\\pm$ 0.01 pm and 3.55 $\\pm$ 0.03 pm respectively.

  5. First-principles study of tunnel current between scanning tunneling microscopy tip and hydrogen-adsorbed Si(001) surface

    CERN Document Server

    Ono, T; Endo, K; Hirose, K; Ono, Tomoya; Horie, Shinya; Endo, Katsuyoshi; Hirose, Kikuji

    2006-01-01

    A scanning tunneling microscopy (STM) image of a hydrogen-adsorbed Si(001) surface is studied using first-principles electron-conduction calculation. The resultant STM image and scanning tunneling spectroscopy spectra are in agreement with experimental results. The contributions of the $\\pi$ states of bare dimers to the tunnel current are markedly large, and the $\\sigma$ states of the dimers rarely affect the STM images. The tunnel currents do not pass through the centers of the dimers but go through the edges of the dimers with local loop currents. In addition, when the tip exists above the hydrogen-adsorbed dimer, there are certain contributions from the $\\pi$ state of the adjacing bare dimers to the tunnel current. This leads to the STM image in which the hydrogen-adsorbed dimers neighboring bare dimers look higher than those surrounded by hydrogen-adsorbed dimers. These results are consistent with the experimental images observed by STM.

  6. Atomic and Molecular Manipulation with a Scanning Tunneling Microscope

    OpenAIRE

    Sperl, Alexander

    2011-01-01

    In this thesis structural, electronic, chemical properties and dynamic processes of adsorbed nanostructures on metal surfaces are investigated with a low-temperature scanning tunneling microscope (STM).

  7. Scanning tunneling microscope study of cadmium telluride

    International Nuclear Information System (INIS)

    Layered samples of cadmium telluride grown epitaxially on gallium arsenide substrates have been investigated by means of scanning tunneling microscopy (STM). The surface geometric and electronic structures are both of interest. Techniques were developed to remove the native oxide by etching, or to create a fresh surface by cleaving, and to protect them from oxidation by employing mineral or paraffin oil media. STM studies were conducted within the protective medium. These techniques were adapted and tested for both etched and cleaved samples of Si, CdTe and HgTe. The current-voltage characteristics of the CdTe surface were investigated during dynamic changes of the tunnel current and barrier height while the probe-to-sample separation (gap) was static. Recorded values are shown for current versus bias for several constant gap values. A range of bias values has been employed to test a possible solution for the problem of interference between the contributions from geometric and electronic structure factors

  8. Scanning tunneling microscopy studies of topological insulators

    International Nuclear Information System (INIS)

    Scanning tunneling microscopy (STM), with surface sensitivity, is an ideal tool to probe the intriguing properties of the surface state of topological insulators (TIs) and topological crystalline insulators (TCIs). We summarize the recent progress on those topological phases revealed by STM studies. STM observations have directly confirmed the existence of the topological surface states and clearly revealed their novel properties. We also discuss STM work on magnetic doped TIs, topological superconductors and crystalline symmetry-protected surface states in TCIs. The studies have greatly promoted our understanding of the exotic properties of the new topological phases, as well as put forward new challenges. STM will continue to play an important role in this rapidly growing field from the point view of both fundamental physics and applications. (topical review)

  9. Scanning tunneling microscopy and spectroscopy of nanostructures

    Science.gov (United States)

    Schneider, Wolf-Dieter

    2002-08-01

    Recent advances in low-temperature scanning tunneling microscopy and spectroscopy have provided new opportunities for investigating locally the geometric and electronic properties of nanostructures on surfaces. Four examples are chosen from our laboratory, which illustrate the power and the potential of this local approach. (i) Light emission from individual C 60 molecules on a Au(1 1 0) surface--challenges for an optical spectroscopic analysis on the scale of single molecules. (ii) Kondo effect of a single magnetic Ce adatom on Ag(1 1 1)--new perspectives for probing magnetic nanostructures. (iii) Two-dimensional self-assembly of supramolecular structures on metal surfaces--a step towards understanding and control of supramolecular aggregation. (iv) MgO on Ag(0 0 1): insulator at the ultrathin limit--new frontiers for the development of oxide heterostructure-based nanodevices.

  10. Scanning tunneling spectroscopy of proximity superconductivity in epitaxial multilayer graphene

    Science.gov (United States)

    Natterer, Fabian D.; Ha, Jeonghoon; Baek, Hongwoo; Zhang, Duming; Cullen, William G.; Zhitenev, Nikolai B.; Kuk, Young; Stroscio, Joseph A.

    2016-01-01

    We report on spatial measurements of the superconducting proximity effect in epitaxial graphene induced by a graphene-superconductor interface. Superconducting aluminum films were grown on epitaxial multilayer graphene on SiC. The aluminum films were discontinuous, with networks of trenches in the film morphology reaching down to exposed graphene terraces. Scanning tunneling spectra measured on the graphene terraces show a clear decay of the superconducting energy gap with increasing separation from the graphene-aluminum edges. The spectra were well described by BCS theory. The decay length for the superconducting energy gap in graphene was determined to be greater than 400 nm. Deviations in the exponentially decaying energy gap were also observed on a much smaller length scale of tens of nanometers.

  11. Spin-polarized scanning tunneling spectroscopy of individual magnetic adatoms

    Science.gov (United States)

    Yayon, Yosef; Brar, Victor; Crommie, Michael; Senapati, Lax; Erwin, Steve

    2007-03-01

    An important goal in condensed matter physics is the ability to measure the spin-polarization state of a single magnetic atom or impurity. We have used spin-polarized scanning tunneling spectroscopy (SP-STS) to probe the local spin-dependent electronic structure of isolated Fe and Cr adatoms deposited onto magnetic Co islands on a copper surface. Individual Fe and Cr atoms prepared in this way show strong spin-polarized contrast in their dI/dV spectra. The spectra of Fe and Cr adatoms differ in that Fe atoms couple ferromagnetically to the Co islands while Cr adatoms couple antiferromagnetically to the islands. dI/dV spatial mapping reveals spin-dependent contrast in the spatial features of individual Fe and Cr atoms. Density functional theory calculations support our interpretation of the experimental results.

  12. Energy gaps measured by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    A scanning tunneling microscope (STM) has been used to measure energy gaps in the charge-density-wave (CDW) phases of the layer-structure dichalcogenides and in the high-temperature superconductor Bi2Sr2CaCu2O8. Measured values of ?CDW at 4.2 K for 2H-TaSe2, 2H-TaS2, and 2H-NbSe2 are 80, 50, and 34 meV giving values of 2?CDW/kBTc equal to 15.2, 15.4, and 23.9, indicating strong coupling in these CDW systems. Measured values of ?CDW at 4.2 K in 1T-TaSe2 and 1T-TaS2 are ?150 meV for both materials giving 2?CDW/kBTc?5.8. STM scans of Bi2Sr2CaCu2O8 at 4.2 K resolve atoms on the BiOx layer and show possible variations in electronic structure. The energy gap determined from I versus V and dI/dV versus V curves is in the range 30--35 meV giving values of 2?/kBTc?8. Spectroscopy measurements with the STM can exhibit large zero-bias anomalies which complicate the analysis of the energy-gap structure, but adequate separation has been accomplished

  13. Measuring voltage transients with an ultrafast scanning tunneling microscope

    DEFF Research Database (Denmark)

    Keil, Ulrich Dieter Felix; Jensen, Jacob Riis

    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-gating photoconductive switch with a rigidly attached fiber, the probe is scanned without changing the probe characteristics. (C) 1997 American Institute of Physics.

  14. Scanning tunneling microscopy and inelastic electron tunneling spectroscopy studies of methyl isocyanide adsorbed on Pt(111)

    International Nuclear Information System (INIS)

    A low-temperature scanning tunneling microscope (STM) was used to investigate the adsorption state of a single methyl isocyanide (MeNC) molecule on the Pt(111) surface at 4.7 K. We found that MeNC was resolved as a round-shaped protrusion in the STM image. The STM image of paired MeNC is highly protruded in comparison with that of isolated MeNC due to the charge transfer from Pt to MeNC. Inelastic electron tunneling spectroscopy with the STM system (STM-IETS) was also employed in order to reveal the adsorption state of individual MeNC molecules on Pt(111). The STM-IETS spectrum of MeNC exhibits peaks at 8, 48 and 375 mV. Referring to the vibrational spectra reported previously, we assigned these peaks to the frustrated translation mode, PtC stretching mode and CH3 stretching mode, respectively. The absence of other vibrational modes could be due to a reduction of the elastic tunneling current.

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

    OpenAIRE

    Jerome Lagoute; Tomaso Zambelli; Stephane Martin; Sebastien Gauthier

    2011-01-01

    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...

  16. Obtaining absolute acoustic spectra in an aerodynamic wind tunnel

    Science.gov (United States)

    Quayle, Alexander R.; Dowling, Ann P.; Graham, W. R.; Babinsky, H.

    2011-05-01

    Cost effective methods for identifying and reducing sources of noise have become essential in the design of many modern transport vehicles. Whilst closed-section wind tunnels can readily evaluate aerodynamic performance, obtaining accurate acoustic spectra is often a major challenge because of the poor signal to noise ratios available. In this paper, methods of obtaining absolute spectra from the non-acoustically treated Markham wind tunnel at the University of Cambridge are discussed. Initial measurements with a small monopole source compare well with simulations and show that it is possible to obtain similar spectra from two nested acoustic arrays. However, a series of further experiments with simplified landing gear models show very different spectra from each array. By comparing measurements with simulations, it is shown that negative side lobes affect beamforming source maps. Measurements of an 'empty tunnel' cross spectral matrix allow the removal of sidelobes, providing much greater consistency between spectra. Finally, a dipole beamforming vector is used to account for the directivity of the landing gear noise, leading to good agreement between absolute spectra from the differently sized arrays. This analysis demonstrates that data from a phased array in a hard-walled, aerodynamic wind tunnel can provide meaningful acoustic spectra from low-noise models.

  17. Tunneling spectra of layered strongly correlated d-wave superconductors

    CERN Document Server

    Wen, T C R X G

    2005-01-01

    The tunneling spectra of layered d-wave superconductors close to the Mott insulator transition show signatures of strong correlations, namely the bias sign asymmetry, the generic lack of evidence for the Van Hove singularity and, in some cases, the absence of coherence peaks, and thus deviate from the weak coupling BCS paradigm. We show that such spectra are reproduced by a recently proposed mean field theory of strongly correlated d-wave superconductors and establish the connection between tunneling and ARPES experiments in materials like the cuprate superconductors. In particular, we discuss the tunneling spectra in terms of the strong renormalization of the electron dispersion around (0,\\pi) and (\\pi,0) and the momentum space anisotropy of electronic states.

  18. Applications of terrestrial laser scanning for tunnels: a review

    Directory of Open Access Journals (Sweden)

    Weixing Wang

    2014-10-01

    Full Text Available In recent years, the use of terrestrial laser scanning (TLS technique in engineering surveys is gaining an increasing interest due to the advantages of non-contact, rapidity, high accuracy, and large scale. Millions of accurate 3D points (mm level accuracy can be delivered by this technique with a high point density in a short time (up to 1 million points per second, which makes it a potential technique for large scale applications in engineering environments such as tunnels, bridges, and heritage buildings. Tunnels, in particular those with long lengths, create great challenges for surveyors to obtain the satisfactory scanned data. This paper presents a short history of TLS techniques used for tunnels. A general overview of TLS techniques is given, followed by a review of several applications of TLS for tunnels. These applications are classified as: detecting geological features of drilling tunnels, monitoring the geometry of tunnels during excavation, making deformation measurements, and extracting features. The review emphasizes how TLS techniques can be used to measure various aspects of tunnels. It is clear that TLS techniques are not yet a common tool for tunnel investigations, but there is still a huge potential to excavate.

  19. Scanning tunneling spectroscopy of novel superconductors

    OpenAIRE

    Jenkins, Nathan

    2009-01-01

    Ce travail a été axé sur l'étude de la supraconductivité non conventionnelle en utilisant à effet tunnel (STM). La première partie de ce travail était de construire un STM capable de mesurer des supraconducteurs sous champs magnétiques élevés et à basses temperatures. La deuxième section a appliqué ce microscope à l'étude de MgB2, un supraconducteur récemment découvert avec une température critique élevé. Les effets des impuretés et des champs magnétiques ont été étudiés. La troisième partie ...

  20. Quadrupolar Echo Spectra of the Tunneling CD 3Group

    Science.gov (United States)

    Olejniczak, Z.; Detken, A.; Manz, B.; Haeberlen, U.

    Deuteron NMR spectra of both single crystal and powder samples of acetylsalicylic acid-CD 3were measured using the quadrupolar-echo technique. The experiments were done in the temperature range 17-100 K, with a special emphasis on the range 20- 30 K, in which the observable tunneling frequency decreases rapidly from its low-temperature value of 2.7 down to 1.2 MHz. In the tunneling regime, modulations of the line intensities and phases as a function of the echo time ? are observed in the single-crystal spectra. The modulation frequency is equal to the orientation-dependent displacement of the inner satellite pairs (? lines) from the Larmor frequency. These effects were confirmed in numerical simulations and fully explain the phase-modulation effects observed previously in quadrupolar-echo spectra of methyl-deuterated methanol and para-xylene guest molecules in some inclusion compounds. By measuring the temperature and orientation dependence of the quadrupolar lineshapes, it was found that the echo spectra are more sensitive to the value of the tunneling frequency than the spectra obtained from the free induction decay. It is pointed out that, because of the modulation effects, special care must be taken when structural parameters are to be extracted from quadrupolar-echo spectra, in particular from spectra of powder samples.

  1. Majorana fermion fingerprints in spin-polarised scanning tunneling microscopy

    OpenAIRE

    Kotetes, Panagiotis; Mendler, Daniel; Heimes, Andreas; Schön, Gerd

    2015-01-01

    We calculate the spatially resolved tunneling conductance of topological superconductors (TSCs) based on ferromagnetic chains, measured by means of spin-polarised scanning tunneling microscopy (SPSTM). Our analysis reveals novel signatures of MFs arising from the interplay of their strongly anisotropic spin-polarisation and the magnetisation content of the tip. We focus on the deep Yu-Shiba-Rusinov (YSR) limit where only YSR bound states localised in the vicinity of the adatoms govern the low...

  2. 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.

  3. Broken Symmetries in Scanning Tunneling Images of Carbon Nanotubes

    CERN Document Server

    Kane, C L

    1999-01-01

    Scanning tunneling images of carbon nanotubes frequently show electron distributions which break the local sixfold symmetry of the graphene sheet. We present a theory of these images which relates these anisotropies to the off diagonal correlations in the single particle density matrix, and allows one to extract these correlations from the observed images. The theory is applied to images of the low energy states reflected at the end of a tube or by point defects, and to states propagating on defect free semiconducting tubes. The latter exhibit a novel switching of the anisotropy in the tunneling image with the sign of the tunneling bias.

  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...

  5. Scanning Tunneling Luminescence of Pentacene Nanocrystals

    OpenAIRE

    Kabakchiev, Alexander

    2010-01-01

    Organic semiconductors are promising materials for future electronic and electroluminescence applications. A detailed understanding of organic layers and nano-sized crystals down to single molecules can address fundamental questions of contacting organic semiconductors at the nanometer limit and obtaining luminescence from them. In this thesis, electroluminescence spectra from pentacene, a policyclic hydrocarbon (acene), are discussed. The luminescenc...

  6. Plasma etching of superconducting Niobium tips for scanning tunneling microscopy

    OpenAIRE

    Roychowdhury, A.; Dana, R; Dreyer, M.; Anderson, J. R.; C. J. Lobb; F.C. Wellstood

    2014-01-01

    We report a reproducible technique for the fabrication of sharp superconducting Nb tips for scanning tunneling microscopy (STM) and scanning tunneling spectroscopy. Sections of Nb wire with 250 $\\mu$m diameter are dry etched in an SF$_6$ plasma in a Reactive Ion Etcher. The gas pressure, etching time and applied power are chosen to produce a self-sharpening effect to obtain the desired tip shape. The resulting tips are atomically sharp, with radii of less than 100 nm, and generate good STM im...

  7. PROBING OF OSCILLATING SURFACES BY A SCANNING ACOUSTIC TUNNELING MICROSCOPE

    OpenAIRE

    Hesjedal, T; Chilla, E; FROHLICH, H

    1995-01-01

    The scanning acoustic tunneling microscope (SATM) which is based on a scanning tunneling microscope, is capable of detecting the amplitude and the phase of high-frequency surface acoustic waves (SAWs) as well as the surface topography. For our experiments the SAWs have been excited by interdigital transducers on YZ-LiNbO3 samples. A thin gold film with a thickness of about 100 nm has been deposited on its surface. The read-out of the high-frequency acoustic wave field is performed by a mixing...

  8. Scanning tunneling microscopy and spectroscopy studies of superconducting boron-doped diamond films

    OpenAIRE

    Terukazu Nishizaki, Yoshihiko Takano, Masanori Nagao, Tomohiro Takenouchi, Hiroshi Kawarada and Norio Kobayashi

    2006-01-01

    We report on scanning tunneling microscopy/spectroscopy (STM/STS) experiments on (1 1 1)-oriented epitaxial films of heavily boron-doped diamond grown by using the microwave plasma-assisted chemical vapor deposition method. STM/STS measurements were performed by 3He-refrigerator based STM under ultra-high vacuum. The STM topography on the film surface shows a corrugation (with a typical size of ~1 ?m) and grain-like microstructures (~5–20 nm). The tunneling conductance spectra do not show lar...

  9. Magnon dispersion and life times of thin Ni films studied with inelastic scanning tunneling spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Yamada, Toyo Kazu; Urban, Nicolai; Balashov, Timofey; Takacs, Albert; Wulfhekel, Wulf [Physikalisches Institut, Universitaet Karlsruhe (Germany); Buczek, Pawel; Sandratskii, Leonid; Ernst, Arthur [Max-Planck-Institut fuer Mikrostrukturphysik, Halle (Germany)

    2009-07-01

    Ni films of thickness between 4 and 12 monolayers were grown epitaxially on a Cu(100) substrate. Using inelastic scanning tunneling spectroscopy at 4 K magnons in the Ni film were studied. In the thin films, the magnons are confined and thus quantized along the surface normal. For a film of n monolayers, n magnon modes normal to the surface are expected. In the experiments these modes appear as peaks in the inelastic tunnelling spectra. By measuring the peak position and widths the magnon energies and lifetimes can be obtained. The observed lifetimes strongly depend on the momentum of the magnons in agreement with non-adiabatic dynamic susceptibility calculations.

  10. 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 ?/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.

  11. Design and calibration of a vacuum compatible scanning tunneling microscope

    Science.gov (United States)

    Abel, Phillip B.

    1990-01-01

    A vacuum compatible scanning tunneling microscope was designed and built, capable of imaging solid surfaces with atomic resolution. The single piezoelectric tube design is compact, and makes use of sample mounting stubs standard to a commercially available surface analysis system. Image collection and display is computer controlled, allowing storage of images for further analysis. Calibration results from atomic scale images are presented.

  12. 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 in...

  13. 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.

  14. Excitation of propagating surface plasmons with a scanning tunnelling microscope

    International Nuclear Information System (INIS)

    Inelastic electron tunnelling excitation of propagating surface plasmon polaritons (SPPs) on a thin gold film is demonstrated. This is done by combining a scanning tunnelling microscope (STM) with an inverted optical microscope. Analysis of the leakage radiation in both the image and Fourier planes unambiguously shows that the majority (up to 99.5%) of the detected photons originate from propagating SPPs with propagation lengths of the order of 10 ?m. The remaining photon emission is localized under the STM tip and is attributed to a tip-gold film coupled plasmon resonance as evidenced by the bimodal spectral distribution and enhanced emission intensity observed using a silver STM tip for excitation.

  15. 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.

  16. Time-resolved scanning tunnelling microscopy for molecular science

    International Nuclear Information System (INIS)

    Time-resolved scanning tunnelling microscopy (STM) and its application in molecular science are reviewed. STM can image individual atoms and molecules and thus is able to observe the results of molecular processes such as diffusion, desorption, configuration switching, bond-breaking and chemistry, on the atomic scale. This review will introduce time-resolved STM, its experimental limitations and implementations with particular emphasis on thermally activated and tunnelling current induced molecular processes. It will briefly examine the push towards ultrafast imaging. In general, results achieved by time-resolved STM demonstrate the necessity of both space and time resolution for fully characterizing molecular processes on the atomic scale.

  17. Manifestation of the Verwey Transition in the Tunneling Spectra of Magnetite Nanocrystals

    CERN Document Server

    Poddar, P; Markovich, G M; Sharoni, A; Katz, D; Wizansky, T; Millo, O; Poddar, Pankaj; Fried, Tcipi; Markovich, Gil; Sharoni, Amos; Katz, David; Wizansky, Tommer; Millo, Oded

    2003-01-01

    Tunneling transport measurements performed on single particles and on arrays of Fe3O4 (magnetite) nanocrystals provide strong evidence for the existence of the Verwey metal-insulator transition at the nanoscale. The resistance measurements on nanocrystal arrays show an abrupt increase of the resistance around 100 K, consistent with the Verwey transition, while the current-voltage characteristics exhibit a sharp transition from an insulator gap to a peak structure around zero bias voltage. The tunneling spectra obtained on isolated particles using a Scanning Tunneling Microscope reveal an insulator-like gap structure in the density of states below the transition temperature that gradually disappeared with increasing temperature, transforming to a small peak structure at the Fermi energy. These data provide insight into the roles played by long- and short-range charge ordering in the Verwey transition.

  18. Spatially resolved scanning tunneling spectroscopy on single-walled carbon nanotubes

    International Nuclear Information System (INIS)

    Scanning tunneling microscope spectroscopy is used to study in detail the electronic band structure of carbon nanotubes as well as to locally investigate electronic features of interesting topological sites such as nanotube ends and bends. From a large number of measurements of the tunneling density-of-states (DOS) nanotubes can be classified, according to predictions, as either semiconducting (two-third of the total number of tubes) or metallic (one-third). The energy subband separations in the tunneling DOS compare reasonably well to theoretical calculations. At nanotube ends, spatially resolved spectra show additional sharp conductance peaks that shift in energy as a function of position. Spectroscopy measurements on a nanotube kink suggest that the kink is a heterojunction between a semiconducting and a metallic nanotube

  19. Plasma etching of superconducting Niobium tips for scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Roychowdhury, A. [Laboratory for Physical Sciences, College Park, Maryland 20740 (United States); Center for Nanophysics and Advanced Materials, Department of Physics, University of Maryland, College Park, Maryland 20742 (United States); Dana, R.; Dreyer, M. [Laboratory for Physical Sciences, College Park, Maryland 20740 (United States); Anderson, J. R.; Lobb, C. J.; Wellstood, F. C. [Center for Nanophysics and Advanced Materials, Department of Physics, University of Maryland, College Park, Maryland 20742 (United States)

    2014-07-07

    We have developed a reproducible technique for the fabrication of sharp superconducting Nb tips for scanning tunneling microscopy (STM) and scanning tunneling spectroscopy. Sections of Nb wire with 250 μm diameter are dry etched in an SF₆ plasma in a Reactive Ion Etcher. The gas pressure, etching time, and applied power are chosen to control the ratio of isotropic to anisotropic etch rates and produce the desired tip shape. The resulting tips are atomically sharp, with radii of less than 100 nm, mechanically stable, and superconducting. They generate good STM images and spectroscopy on single crystal samples of Au(111), Au(100), and Nb(100), as well as a doped topological insulator Bi₂Se₃ at temperatures ranging from 30 mK to 9 K.

  20. 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.

  1. Scanning Tunneling Microspectroscopy of Solids and Surfaces - Final Report; FINAL

    International Nuclear Information System (INIS)

    Experimental and theoretical research on the bulk and surface properties of conductive solid state materials has been performed based on the techniques of scanning tunneling microscopy and scanning tunneling spectroscopy, often at cryogenic temperatures. The research has focused on the electronic properties, particularly the superconductivity, of high temperature superconductors and other layered systems. The superconducting electronic density of states N(E)=dI/dV of the high T(sub c) superconductor Bi(sub 2)Sr(sub 2)CaCu(sub 2)O(sub 8+(delta)) was measured with spatial resolution of 5 A at 4.2K. An internal superconducting proximity effect was inferred to operate between Cu and Bi based layers of the crystal in those regions where the Bi layers are metallic in nature. This research project supported the thesis research of several young scientists, and led to a significant number of published papers, presentations and reports

  2. Plasma etching of superconducting Niobium tips for scanning tunneling microscopy

    International Nuclear Information System (INIS)

    We have developed a reproducible technique for the fabrication of sharp superconducting Nb tips for scanning tunneling microscopy (STM) and scanning tunneling spectroscopy. Sections of Nb wire with 250??m diameter are dry etched in an SF6 plasma in a Reactive Ion Etcher. The gas pressure, etching time, and applied power are chosen to control the ratio of isotropic to anisotropic etch rates and produce the desired tip shape. The resulting tips are atomically sharp, with radii of less than 100?nm, mechanically stable, and superconducting. They generate good STM images and spectroscopy on single crystal samples of Au(111), Au(100), and Nb(100), as well as a doped topological insulator Bi2Se3 at temperatures ranging from 30 mK to 9?K.

  3. Scanning tunneling spectroscopy with superconducting tips of Al

    OpenAIRE

    Guillamon, Isabel; Suderow, Hermann; Vieira, Sebastian; Rodiere, Pierre

    2007-01-01

    We present Scanning Tunneling Spectroscopy measurements at 0.1 K using tips made of Al. At zero field, the atomic lattice and charge density wave of 2HNbSe2 are observed, and under magnetic fields the peculiar electronic surface properties of vortices are precisely resolved. The tip density of states is influenced by the local magnetic field of the vortex, providing for a new probe of the magnetic field at nanometric sizes.

  4. Scanning tunneling spectroscopy with superconducting tips of Al

    International Nuclear Information System (INIS)

    We present scanning tunneling spectroscopy measurements at 0.1 K using tips made of Al. At zero field, the atomic lattice and charge density wave of 2H-NbSe2 are observed, and under magnetic fields the peculiar electronic properties of vortices are precisely resolved. The tip density of states is influenced by the local magnetic field of the vortex, providing a new probe for the magnetic field at nanometric sizes

  5. Study on tube scanner of photon scanning tunneling microscopy

    International Nuclear Information System (INIS)

    The formula of defection of the tube scanner for PSTM (Photon Scanning Tunneling Microscopy) is derived. The deflection range, its linear and the X-Z coupling are analyzed. A useful method has been developed to make optical fiber probe tips with smooth surface. A new experimental method to measure the deflection of PZT (piezoeletic tube) is reported. The experimental data are consistent with theory results. Therefore, some key problems in both theory and technique for PSTM can be resolved

  6. Sub-Kelvin scanning tunneling microscopy on magnetic molecules

    OpenAIRE

    Zhang, Lei

    2012-01-01

    Magnetic molecules have attracted lots interest. In this work, an ultra-stable and low noise scanning tunneling microscopy operating at 400 mK using He-3 (930 mK using He-4) has been developed. The magnetic behavior of different magnetic molecules on substrates, especially the exchange interaction between the magnetic ions, the magnetic anisotropy on the surface, the magnetic excitations as well as the Kondo effect, were studied by using STM.

  7. Imaging atoms and molecules on surfaces by scanning tunnelling microscopy

    International Nuclear Information System (INIS)

    This review discusses nearly 30 years of scanning tunnelling microscopy (STM) work on high resolution imaging of numerous materials systems, giving a historical perspective on the field through the author's work. After a brief discussion of early STM and atomic force microscope (AFM) instrumentation development, the review discusses high resolution STM imaging on semiconductors, metals on semiconductors, Au(1 1 1), metal on metals including surface alloys, oxygen on metals, molecules adsorbed on metals, and AFM measurements of friction on graphite and mica.

  8. The electroluminescence and scanning tunneling microscopy of single molecules

    OpenAIRE

    Buker, John William

    2009-01-01

    The scanning tunneling microscopy (STM) of single molecules has become a prominent experimental method in the field of molecular electronics. It has been found that in STM experiments, when an electric current flows through a single molecule, the molecule may luminesce. This electroluminescence, in conjunction with traditional STM data, provides a potentially important additional degree of freedom for understanding nanoscale systems. This thesis describes exploratory theoretical work on the n...

  9. Studies of Novel Nanostructures by Cross- sectional Scanning Tunneling Microscopy

    OpenAIRE

    Ouattara, Lassana

    2006-01-01

    This thesis presents structural and morphological studies of semiconductor nanostructures, namely quantum dots, nanowires and a dilute ferromagnetic semiconductor. These nanostructures are investigated on the atomic scale using cross-sectional scanning tunneling microscopy (XSTM). Indium arsenide (InAs) quantum dots in both an indium phosphide (InP) and GaAs matrix are studied. The InAs/InP quantum dots are shown to be vertically aligned and I present experimental and theoretical investigatio...

  10. Investigation of graphite surfaces by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Scanning Tunneling Microscopy experiments on pyrolytic graphite at low voltages VT ? 0 reveal an anomalous surface corrugation. It can be understood from the energy dependent corrugation of the local density of states near EF, in good qualitative agreement with theory. The high lateral resolution of < 2 A and the observed giant corrugations seem to be adequately described by models which consider the special structure of the Fermi surface of graphite and its elastic properties. (orig.)

  11. A study of surfaces using a scanning tunneling microscope (STM

    Directory of Open Access Journals (Sweden)

    Alba Graciela Ávila Bernal

    2010-05-01

    Full Text Available Sweeping/scanning microscopes have become an experimental scientist’s hands and eyes in this century; they have become a powerful and necessary tool for nanoscale characterisation in education and research laboratories all around the world. This arti- cle presents the modifications made in the mechanical (isolation or designing an anti-vibration system and electrical (piezoelec- tric and scanning system characterisation implementation of a scanning tunnelling microscope (STM, thereby allowing nanosca- le surfaces to be visualised and modified. A methodology for visualising and characterising surfaces using the aforementioned instrument is described, bidimensional quantification of up to 1,300 nm2, with ~15 nm resolution being reached. This experi- mental methodology took critical parameters for tunnelling current stability into account, such as scanning speed and microscope tip geometry and dimensions. This microscope’s versatility allowed defects in highly oriented pyrolytic graphite (HOPG samples to be modified and visualised by applying a voltage between the tip and the sample. The concepts of topography scanning and lithography can be easily understood by using the instrument implemented here.

  12. Tip preparation for usage in an ultra-low temperature UHV scanning tunneling microscope

    Directory of Open Access Journals (Sweden)

    S. Ernst, S. Wirth, M. Rams, V. Dolocan and F. Steglich

    2007-01-01

    Full Text Available This work deals with the preparation and characterization of tungsten tips for the use in UHV low-temperature scanning tunneling microscopy and spectroscopy (STM and STS, respectively. These specific environments require in situ facilities for tip conditioning, for further sharpening of the tips, as well as for reliable tip characterization. The implemented conditioning methods include direct resistive annealing, annealing by electron bombardment, and self-sputtering with noble gas ions. Moreover, results from in situ tip characterization by field emission and STM experiments were compared to ex situ scanning electron microscopy. Using the so-prepared tips, high resolution STM images and tunneling spectra were obtained in a temperature range from ambient down to 350 mK, partially with applied magnetic field, on a variety of materials.

  13. Low-current Scanning Tunneling Microscope for Nanoscale Imaging

    Directory of Open Access Journals (Sweden)

    R.K. Kale

    2006-10-01

    Full Text Available Advances in the nanotechnology, which is still in its infancy, will depend on our ability todesign, build, replicate, and mass-produce usable nanoscale systems. At sub-nanometer lengthscales, scanning tunneling microscopy (STM and the related techniques, collectively calledscanning probe microscopies, replace the optical microscopy for real-space imaging andmanipulation of materials. STM operation is based on measurement of current due to tunnelingof electrons across a finite potential barrier between the probe and the sample. In conventionalSTM, tunneling current of tens of nA and probe-sample distance of a few Å are maintained.These conditions, while necessary for atomic-scale imaging under ultra high vacuum environment,are not suited to handle nanostructures. Quantum structures deposited on a flat substrate usuallypresent a non-metallic sample, and the roughness levels involved are much too high forconventional STM. STM operation with low tunneling current (few pA and larger tunneling gap(several nm is preferred to overcome these difficulties. This paper presents experimental workand theoretical considerations for developing an atmospheric low-current STM (LC-STM.Researchers from diverse fields can build their own LC-STM for routine imaging and spectroscopy.Several design details are included keeping this aspect in mind.

  14. 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.

  15. 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.

  16. 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

    2013-10-01

    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. PMID:23929439

  17. Optical and Electrical Characterization at the Nanoscale by a Transparent Tip of a Scanning Tunneling Microscope

    OpenAIRE

    Sychugov, Ilya; Omi, Hiroo; Murashita, Toru; Kobayashi, Yoshihiro

    2009-01-01

    A new type of scanning probe microscope, combining features of the scanning tunnelling microscope, the scanning tunnelling luminescence microscope with a transparent probe and the aperture scanning near-field optical microscope, is described. Proof-of-concept experiments were performed under ultrahigh vacuum conditions at varying temperature on GaAs/AlAs heterostructures.

  18. STM beyond vacuum tunnelling: scanning tunnelling hydrogen microscopy as a route to ultra-high resolution

    OpenAIRE

    Weiss, Christian

    2012-01-01

    Direct imaging is a fast and reliable method for the characterization of surfaces. When it comes to small surface structures in the size of the features e.g. in todays computer processors, classical optical imaging methods fail in resolving these structures. With the invention of the scanning tunnelling microscope (STM) for the first time it became possible to image the structure of surfaces with atomic precision. However, the STM fails in resolving complex chemical structures like e.g. organ...

  19. STM beyond vacuum tunneling : scanning tunneling hydrogen microscopy as a route to ultra-high resolution

    OpenAIRE

    Weiss, Christian

    2012-01-01

    Direct imaging is a fast and reliable method for the characterization of surfaces. When it comes to small surface structures in the size of the features e.g. in todays computer processors, classical optical imaging methods fail in resolving these structures. With the invention of the scanning tunnelling microscope (STM) for the first time it became possible to image the structure of surfaces with atomic precision. However, the STM fails in resolving complex chemical structures ...

  20. Direct observation of reverse transcriptases by scanning tunneling microscopy.

    Science.gov (United States)

    Lewerenz, H J; Jungblut, H; Campbell, S A; Giersig, M; Müller, D J

    1992-09-01

    First images on a nanometer scale of reverse transcriptases (RT) of the human immunodeficiency virus (HIV-1) and of the Moloney murine leukemia virus (MuLV) obtained by scanning tunneling microscopy (STM) are reported. The common feature of the observed molecules is a ring-type or horseshoe shape with hole diameters of approximately 30 A. The STM images are compared with high resolution transmission electron microscopy (TEM) and existing structure predictions. The similarities of the structural data obtained by STM and TEM and their agreement with the structure prediction for the RT of HIV-1 shows the principal possibility to image such biomolecules by STM. PMID:1280957

  1. Pb on Mo(110) studied by scanning tunneling microscopy

    Science.gov (United States)

    Krupski, A.

    2009-07-01

    Scanning tunneling microscopy (STM) has been used to investigate the growth behavior of ultrathin Pb films on the Mo(110) surface at room temperature. The analysis of STM measurements indicates that for a coverage ?1ML , the three-dimensional growth of the Pb islands with strongly preferred atomic scale “magic height” and flat top is observed. At coverages between 1ML3ML , the island height distribution shows peaks at relative heights corresponding to N=(2,4,6,7,and9) of Pb atomic layers.

  2. 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.

  3. 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...... parameters. We use the method to calculate theoretical STM images of the monohydrate Si(100)-H(2x1) surface with missing hydrogen defects at -2V and find an enhanced corrugation due to the electric field, in good agreement with experimental images....

  4. Scanning tunneling microscopy at millikelvin temperatures: Design and construction

    Science.gov (United States)

    Gubrud, Mark Avrum

    This dissertation reports on work toward the realization of a state-of-the-art scanning tunneling microscopy and spectroscopy facility operating at milliKelvin temperatures in a dilution refrigerator. Difficulties that have been experienced in prior efforts in this area are identified. Relevant issues in heat transport and in the thermalization and electrical filtering of wiring are examined, and results are applied to the design of the system. The design, installation and characterization of the pumps, plumbing and mechanical vibration isolation, and the design and installation of wiring and fabrication and characterization of electrical filters are described.

  5. Scanning tunneling microscopy current--voltage characteristics of carbon nanotubes

    International Nuclear Information System (INIS)

    Scanning tunneling microscopy (STM) has been used to obtain images and current--voltage (I--V) curves of carbon nanotubes produced by arc discharge of carbon electrodes. The STM I--V curves indicate that carbon nanotubes with diameters from 2.0 to 5.1 nm have a metallic density of states. Using STM, we also observe nanometer-size graphene sheets which are four graphite layers thick. The STM images of carbon nanotubes are in good agreement with transmission electron microscope images. copyright 1995 American Vacuum Society

  6. Scanning tunneling microscopy of individual molecules: beyond imaging

    Science.gov (United States)

    Gimzewski, J. K.; Jung, T. A.; Cuberes, M. T.; Schlittler, R. R.

    1997-10-01

    We discuss several concepts of handling molecule-adsorbent and hetero-molecular structures on an individual molecular basis. Molecular recognition using scanning tunneling microscopy underpins the fundamental progress made. "Beyond imaging" implies repositioning, patterning, and exploring the functionality of individual molecules. Using porphyrin- and fullerene-based systems, we discuss issues such as conformational analysis, supramolecular systems, patterning, and the fabrication of a molecular adding machine. These examples form the beginnings of a bottom-up approach to fabrication and "sciengineering" from a molecule-by-molecule perspective.

  7. Lateral extension of quantum well states: scanning tunneling spectroscopy study

    Science.gov (United States)

    Manna, Sujit; Kirschner, Jürgen

    2014-03-01

    Quantum well states(QWS) in thin metal films have been extensively studied mostly by laterally averaging techniqes such as photoemission or inverse photoemission.A complementary approach is opened by scanning tunneling spectroscopy(STS) and microscopy(STM), which extends the range of this extremely surface sensitive device into the interior of the sample, and make it possible to image features of a buried interface with lateral resolution on the atomic scale. We present low temperature STS results of ocuupied sp-QWS localized in Ag(111) films. For thin film with local varying thickness,we recall the fundamental question-how the transition of QWS takes place,and at what length scale? We demonstrate that the QWS of thin Ag(111) films are highly perturbed within the proximity of a step edge.Atomic resolved scanning tunneling microscopy/spectroscopy indicates that the energy of these states has a strong distance dependence within the proximity of the step edge with large energetic shift equaling up to ~ 200meV. For an Ag layer of 30ML thick, we obtain a lateral extension of the QWS in the order of ~ 10Å. This spatial extension of QWS can be understood within the context of electron scattering within the proximity of the buried interface.

  8. Scanning electron and tunneling microscopy of palladium-barium emitters

    International Nuclear Information System (INIS)

    The results of study of metal-alloyed palladium-barium emitters' of modern very high frequency high-powered electronic vacuum tubes by scanning electron microscopy (SEM) and scanning tunneling microscopy/spectroscopy (STM/STS) are presented. Since the Pd/Ba foil surface is fairly smooth and is not oxidized in air STM/STS investigations are carried out in air in normal laboratory environment. SEM and STM images show that the emitter surface has a complex porous structure. The cathode surface study by STS in tunneling gap modulation mode allowed to take a map of phase distribution with various work function values and high lateral resolution. Obtained images demonstrate the presence of three phases on the Pd/Ba emitter surface, viz. barium-oxygen compounds, intermetallic, and palladium. As it is seen from presented STS image the phase with a low work function value (barium oxides) is concentrated along boundaries of the substance inclusions with work function corresponding to the intemetallic compound Pd5Ba. This supports the model of low work function areas obtained via Ba segregation from the intermetallic compound and oxidation. The presented methods may be used in the Pd/Ba cathode manufacturing process for increasing the yield of electronic devices in microwave tube production and optimize the emitters' characteristics

  9. Scanning electron and tunneling microscopy of palladium barium emitters

    Science.gov (United States)

    Baiburin, V. B.; Volkov, U. P.; Semenov, S. V.; Semenov, A. S.

    2003-06-01

    The results of study of metal-alloyed palladium-barium emitters' of modern very high frequency high-powered electronic vacuum tubes by scanning electron microscopy (SEM) and scanning tunneling microscopy/spectroscopy (STM/STS) are presented. Since the Pd/Ba foil surface is fairly smooth and is not oxidized in air STM/STS investigations are carried out in air in normal laboratory environment. SEM and STM images show that the emitter surface has a complex porous structure. The cathode surface study by STS in tunneling gap modulation mode allowed to take a map of phase distribution with various work function values and high lateral resolution. Obtained images demonstrate the presence of three phases on the Pd/Ba emitter surface, viz. barium-oxygen compounds, intermetallic, and palladium. As it is seen from presented STS image the phase with a low work function value (barium oxides) is concentrated along boundaries of the substance inclusions with work function corresponding to the intemetallic compound Pd 5Ba. This supports the model of low work function areas obtained via Ba segregation from the intermetallic compound and oxidation. The presented methods may be used in the Pd/Ba cathode manufacturing process for increasing the yield of electronic devices in microwave tube production and optimize the emitters' characteristics.

  10. A local view of the Kondo effect: scanning tunneling spectroscopy

    International Nuclear Information System (INIS)

    The fascinating many-body physics involved in the interaction of a single magnetic impurity with the conduction electrons of its nonmagnetic metallic host is reflected in un conventional phenomena in magnetism, transport properties and the specific heat. Characteristic low-energy excitations, termed the Kondo resonance, are generally believed to be responsible for this striking behaviour. However, in spite of an intense research for over more than 30 years, a direct spectroscopic observation of the Kondo resonance on individual magnetic adatoms withstood experimental efforts hitherto. Recently for the first time, two such scanning tunneling spectroscopy (STS)/scanning tunneling microscopes (STM) experiments spatially resolved the electronic properties of individual magnetic adatoms displaying the Kondo effect. In particular, the observed Fano lineshape of the Kondo resonance reveals unambiguously the details of the quantum mechanical interference between the localized orbital and the conduction electrons on an atomic length scale. This achievement of the detection of individual magnetic atoms with atomic resolution opens new perspectives for probing magnetic nanostructures

  11. Measurement of shear strength for HOPG with scanning tunneling microscopy by thermal excitation method.

    Science.gov (United States)

    Ding, X D; Wang, Y Z; Xiong, X M; Du, X S; Zhang, J X

    2012-04-01

    An experimental observation of force interactions in scanning tunneling microscopy (STM) is presented. A technique for measuring force interactions between a conventional STM probe and a sample by spectra analysis of its thermal fluctuations from tunneling current in STM is developed theoretically and experimentally. Thermally excited fluctuation of the STM probe is exactly discerned in air and then force gradient is determined from its corresponding eigen-frequency with a formula similar to that for a small-amplitude atomic force microscopy (AFM). The observed force interactions are consistent with forces in dynamic AFM. Shear strength of 7 GPa for highly oriented pyrolytic graphite (HOPG) under compressive stress is obtained from the experiment and using the elastic theory. We believe that this technique is of scientific significance as it enables accurate measurement of short-range force interactions at atomic scale under true STM conditions. PMID:22446198

  12. Scanning Tunneling Microscopy Studies of the Topological Insulator Candidate YbB6

    Science.gov (United States)

    Zhu, Zhihuai; He, Y.; Kim, D.-J.; Fisk, Z.; Hoffman, J. E.

    2015-03-01

    We report scanning tunneling microscopy studies of YbB6, a proposed topological insulator candidate with moderate correlation. The in-situ cleaved sample surface has two dominant morphologies: atomic square lattices and disordered rows, which likely correspond to Yb and B terminations, respectively. Spatially resolved dI / dV maps show enhanced tunneling due to the local perturbation of the tip-induced band bending. The dI / dV spectra reveal a bulk gap with distinct in-gap features near the Fermi level on different terminations. Our study presents nanoscale evidence for the interplay between surface structure, correlation and topological properties. The work at Harvard was supported by NSF-DMR-1410480 and NSERC (ZHZ).

  13. Scanning tunneling microscopy and spectroscopy studies of superconducting boron-doped diamond films

    Directory of Open Access Journals (Sweden)

    Terukazu Nishizaki, Yoshihiko Takano, Masanori Nagao, Tomohiro Takenouchi, Hiroshi Kawarada and Norio Kobayashi

    2006-01-01

    Full Text Available We report on scanning tunneling microscopy/spectroscopy (STM/STS experiments on (1 1 1-oriented epitaxial films of heavily boron-doped diamond grown by using the microwave plasma-assisted chemical vapor deposition method. STM/STS measurements were performed by 3He-refrigerator based STM under ultra-high vacuum. The STM topography on the film surface shows a corrugation (with a typical size of ~1 ?m and grain-like microstructures (~5–20 nm. The tunneling conductance spectra do not show large spatial dependence and superconductivity is observed independent of the surface structures. The tunneling spectra are analyzed by the Dynes function and the superconducting energy gap is estimated to be ?=0.87 meV at T=0.47 K, corresponding to 2?/kBTc=3.7. The relatively large value of the broadening parameter ?=0.38 meV is discussed in terms of the inelastic electron scattering processes.

  14. Fully low voltage and large area searching scanning tunneling microscope

    International Nuclear Information System (INIS)

    We present a novel scanning tunneling microscope (STM), which allows the tip to travel a large distance (millimeters) on the sample and take images (to find microscopic targets) anywhere it reaches without losing atomic resolution. This broad range searching capability, together with the coarse approach and scan motion, is all done with only one single piezoelectric tube scanner as well as with only low voltages (<15 V). Simple structure, low interference and high precision are thus achieved. To this end, a pillar and a tube scanner are mounted in parallel on a base with one ball glued on the pillar top and two balls glued on the scanner top. These three balls form a narrow triangle, which supports a triangular slider piece. By inertial stepping, the scanner can move the slider toward the pillar (coarse approach) or rotate the slider about the pillar (travel along sample surface). Since all the stepping motions are driven by the scanner's lateral bending which is large per unit voltage, high voltages are unnecessary. The technology is also applicable to scanning force microscopes (SFM) such as atomic force microscopes (AFM), etc

  15. Majorana fermion fingerprints in spin-polarised scanning tunnelling microscopy

    Science.gov (United States)

    Kotetes, Panagiotis; Mendler, Daniel; Heimes, Andreas; Schön, Gerd

    2015-11-01

    We calculate the spatially resolved tunnelling conductance of topological superconductors (TSCs) based on ferromagnetic chains, measured by means of spin-polarised scanning tunnelling microscopy (SPSTM). Our analysis reveals novel signatures of MFs arising from the interplay of their strongly anisotropic spin-polarisation and the magnetisation content of the tip. We focus on the deep Yu-Shiba-Rusinov (YSR) limit where only YSR bound states localised in the vicinity of the adatoms govern the low-energy as also the topological properties of the system. Under these conditions, we investigate the occurrence of zero/finite bias peaks (ZBPs/FBPs) for a single or two coupled TSC chains forming a Josephson junction. Each TSC can host up to two Majorana fermions (MFs) per edge if chiral symmetry is preserved. Here we retrieve the conductance for all the accessible configurations of the MF number of each chain. Our results illustrate innovative spin-polarisation-sensitive experimental routes for arresting the MFs by either restoring or splitting the ZBP in a predictable fashion via: (i) weakly breaking chiral symmetry, e.g. by the SPSTM tip itself or by an external Zeeman field and (ii) tuning the superconducting phase difference of the TSCs, which is encoded in the 4?-Josephson coupling of neighbouring MFs.

  16. Cleaved thin-film probes for scanning tunneling microscopy.

    Science.gov (United States)

    Siahaan, T; Kurnosikov, O; Barcones, B; Swagten, H J M; Koopmans, B

    2016-01-22

    We introduce an alternative type of probe for scanning tunneling microscopy (STM). Instead of using a needle-like tip made from a piece of metallic wire, a sharp-edged cleaved insulating substrate, which is initially covered by a thin conductive film, is used. The sharp tip is formed at the intersection of the two cleaved sides. Using this approach a variety of materials for STM probes can be used, and functionalization of STM probes is possible. The working principle of different probes made of metallic (Pt, Co, and CoB), indium-tin oxide, as well as Cu/Pt and Co/Pt multilayer films are demonstrated by STM imaging of clean Cu(001) and Cu(111) surfaces as well as the epitaxial Co clusters on Cu(111). PMID:26636763

  17. Imaging chemical disorder in cuprates using scanning tunneling microscopy

    Science.gov (United States)

    Zeljkovic, Ilija; Huang, Dennis; Song, Can-Li; Chang, Tay-Rong; Jeng, Horng-Tay; Xu, Zhijun; Wen, Jinsheng; Gu, Genda; Nieminen, Jouko; Bansil, Arun; Markiewicz, Robert; Hoffman, Jennifer

    2013-03-01

    High-Tc cuprate superconductors are chemically, electronically and structurally inhomogeneous at the nanoscale. Although a body of theoretical work has predicted that local and global superconductivity may be dramatically impacted by particular dopant configurations, the exact positions of dopants introduced into cuprates to induce superconductivity are generally unknown. Here we use scanning tunneling microscopy to reveal the intra-unit-cell location of two different types of oxygen dopants in Bi2+ySr2-yCaCu2O8+x. Furthermore, we show the relationship between these interstitial oxygen dopants, oxygen vacancies, and a global structural buckling known as the supermodulation. We compare our findings to theoretical simulations. This research was supported by NSF Career grant DMR-0847433 and the New York Community Trust-George Merck Fund.

  18. A high stability and repeatability electrochemical scanning tunneling microscope

    International Nuclear Information System (INIS)

    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 SO42? image on Au (111) work electrode is demonstrated to show the performance of the ECSTM

  19. 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.

  20. Metal-silicene interaction studied by scanning tunneling microscopy.

    Science.gov (United States)

    Li, Zhi; Feng, Haifeng; Zhuang, Jincheng; Pu, Na; Wang, Li; Xu, Xun; Hao, Weichang; Du, Yi

    2016-01-27

    Ag atoms have been deposited on 3??×??3 silicene and???3??×???3 silicene films by molecular beam epitaxy method in ultrahigh vacuum. Using scanning tunneling microscopy and Raman spectroscopy, we found that Ag atoms do not form chemical bonds with both 3??×??3 silicene and???3??×???3 silicene films, which is due to the chemically inert surface of silicene. On 3??×??3 silicene films, Ag atoms mostly form into stable flat-top Ag islands. In contrast, Ag atoms form nanoclusters and glide on silicene films, suggesting a more inert nature. Raman spectroscopy suggests that there is more sp (2) hybridization in???3??×???3 than in???7??×???7/3??×??3 silicene films. PMID:26704018

  1. Metallocene Molecular Clusters Studied with Scanning Tunneling Microscopy and Spectroscopy

    Science.gov (United States)

    Kwon, Jeonghoon; Ham, Ungdon; Lee, Minjun; Lim, Seong Joon; Kuk, Young

    2014-03-01

    Atomic spins and molecular magnets have been actively reported using Scanning Tunneling Microscope(STM) in recent studies. One can even assemble an artificial magnet by STM manipulation. Manganocene((C5H5)2 Mn), a sandwich complex of metallocene, is composed of one manganese atom and two cyclopentadianyl ligands. This molecule is known to reveal not only high spin number S = 5/2 at room temperature but also two structural states: monomer and molecular chain. In this presentation, we report STM images and spectroscopic results of these monomers and dimers. We try to map the molecular electronic state and the spin texture. The molecule is adsorbed on an insulating layer to decouple the spin state from the metallic substrate. We will present that manganocene can become a basic element of a spin chain.

  2. Cleaved thin-film probes for scanning tunneling microscopy

    Science.gov (United States)

    Siahaan, T.; Kurnosikov, O.; Barcones, B.; Swagten, H. J. M.; Koopmans, B.

    2016-01-01

    We introduce an alternative type of probe for scanning tunneling microscopy (STM). Instead of using a needle-like tip made from a piece of metallic wire, a sharp-edged cleaved insulating substrate, which is initially covered by a thin conductive film, is used. The sharp tip is formed at the intersection of the two cleaved sides. Using this approach a variety of materials for STM probes can be used, and functionalization of STM probes is possible. The working principle of different probes made of metallic (Pt, Co, and CoB), indium-tin oxide, as well as Cu/Pt and Co/Pt multilayer films are demonstrated by STM imaging of clean Cu(001) and Cu(111) surfaces as well as the epitaxial Co clusters on Cu(111).

  3. Scanning tunnelling microscopy study of Au growth on Mo(110)

    Science.gov (United States)

    Krupski, A.

    2011-02-01

    Scanning tunnelling microscopy (STM) has been used to investigate the growth behaviour of ultra-thin Au films up to two monolayers thick on a Mo(110) surface at room temperature. An analysis of STM measurements indicates that the layer-by-layer growth for the first two layers of Au is observed. For submonolayer coverage gold prefers to nucleates along the [001¯] and [11¯1] directions and creates one atom high islands on Mo terraces. The average diameter of the observed gold islands is about 12 ± 5 nm. In the completed first layer, no ordered regions were observed. In addition, when the coverage increases to 1.2 ML, the decoration of the substrate steps by one atom high Au islands can be distinguished. As the sample is post-annealed to 800 K, the rearrangement of an existing film did occur and a Au-Mo surface alloy is formed.

  4. High-resolution scanning tunneling microscopy for molecules

    International Nuclear Information System (INIS)

    Scanning tunneling microscopy (STM) can detect individual molecular configuration with its high spatial resolution ability, but some intrinsical and extrinsic factors result in the complexities of STM imaging of single molecules. By combining STM experimental work and theoretical simulation with the local density approximation based on Bardeen perturbation method, we have explored the atomic-scale configuration of the following molecular systems: C60 molecules adsorbed on Si(1 1 1)-(7x7); alkanethiol self-assembly monolayers on Au(1 1 1); C60 molecule imaged by STM tip adsorbed with another C60 molecule; O2 molecule adsorbed on Ag(1 1 0) and CO molecule adsorbed on Cu(1 1 1) imaged by CO chemically modified STM tip. Some related problems including: molecule-substrate interactions, STM imaging mechanism, chemically modified STM tip, etc., are discussed

  5. Oxygen-free in situ scanning tunnelling microscopy

    DEFF Research Database (Denmark)

    Zhang, Jingdong; Ulstrup, Jens

    2007-01-01

    situ STM systems by diffusion through the solutions. Such interference can be serious for oxygen sensitive systems both for the target molecules themselves and for chemical linker molecules bound to the electrode surface for example, via Au-S bonding. This is strikingly illustrated in the present......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 in...... report. We present here oxygen-free in situ STM, in which the samples are contained in an argon atmosphere which removes oxygen in the system. Interference from oxygen is profoundly reduced in this setup and demonstrated by three examples. Two of these are in situ STM of the intermediate-size sulfur...

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

    DEFF Research Database (Denmark)

    Bork, Jakob

    mapping at 6. The heterostructure is found to have very interesting electronic properties. The d-related state from the now buried cobalt island is visible through the silver capping layer, but the silver Moire pattern modulates the spin-polarized cobalt d-related state in amplitude, energy position and......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...... tunneling microscope (STM). Especially at low temperatures the Kondo resonance is used to probe magnetic interaction with ferromagnetic islands and between two atoms. The latter showing a crossover between Kondo screened atoms and antiferromagnetically coupled atoms close to the quantum critical point. This...

  7. Visualization of semiconductor surface etching with scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Full text: Etching, or the process of producing a pattern, is central to a great many technologies. In the world of thin films and multilayers, etching (material removal) plays a complementary role to growth (material addition), and product fabrication is likely to include both etching and growth. This talk will review recent progress made in understanding surface etching of semiconductors. Emphasis will be on atomic-scale changes in surface morphology as revealed through scanning tunneling microscopy. We will consider a specific case, the etching of Si by halogens, where the parameters that are controlled are the flux and the fluence of the halogen beam and the reaction temperature of the substrate. The talk will highlight the kinds of information that can be gained and the new insights that are provided. Studies such as these are being extended to include the effects of photon irradiation, ion impact, and electron impact, as they pertain to plasma processing of semiconductors

  8. Scanning tunneling microscope with two-dimensional translator

    Science.gov (United States)

    Nichols, J.; Ng, K.-W.

    2011-01-01

    Since the invention of the scanning tunneling microscope (STM), it has been a powerful tool for probing the electronic properties of materials. Typically STM designs capable of obtaining resolution on the atomic scale are limited to a small area which can be probed. We have built an STM capable of coarse motion in two dimensions, the z- and x-directions which are, respectively, parallel and perpendicular to the tip. This allows us to image samples with very high resolution at sites separated by macroscopic distances. This device is a single unit with a compact design making it very stable. It can operate in either a horizontal or vertical configuration and at cryogenic temperatures.

  9. Scanning tunneling microscopy studies of diazo dye monolayers on HOPG

    Science.gov (United States)

    Fritz, J.; Probst, O.; Dey, S.; Grafström, S.; Kowalski, J.; Neumann, R.

    1995-05-01

    We report on scanning tunneling microscopy (STM) studies of monolayers of the diazo dye 4-[4-(N,N-dimethylamino)phenylazo]azobenzene (D2, summation formula C 20H 19N 5) on the basal plane of highly oriented pyrolytic graphite (HOPG). Monolayers of the dye were prepared by vapour deposition or by dissolving the molecules in the liquid crystal octylcyanobiphenyl (8CB). The STM images show a double-row structure exhibiting different types of lattice defects and various domains. High-resolution images allow the identification of individual molecules and the observation of intramolecular contrast. The different orientations of the rows can be explained by a commensurate registry of the molecules with the substrate. A model for the unit cell is proposed.

  10. Thermal expansion of scanning tunneling microscopy tips under laser illumination

    Science.gov (United States)

    Grafström, S.; Schuller, P.; Kowalski, J.; Neumann, R.

    1998-04-01

    The periodic thermal expansion of scanning tunneling microscopy (STM) tips arising under irradiation with power-modulated laser light has been investigated. The expansion was determined by comparison with a calibrated piezomotion measured in an STM, which was operated in the constant-current mode, and instrumental effects were corrected for. The experimental data concerning the frequency response of the thermal expansion for various geometries of the tip and for different positions of the laser focus are compared with theoretical results which were derived from a numerical solution of the equation of heat conduction. A very good agreement is found. The results are also interpreted in terms of simplified analytical expressions. Furthermore, the theoretical data are used to derive the response of the tip to fast transients of the light power as in the case of pulsed irradiation.

  11. 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.

  12. C58 on Au(111): a scanning tunneling microscopy study.

    Science.gov (United States)

    Bajales, Noelia; Schmaus, Stefan; Miyamashi, Toshio; Wulfhekel, Wulf; Wilhelm, Jan; Walz, Michael; Stendel, Melanie; Bagrets, Alexej; Evers, Ferdinand; Ulas, Seyithan; Kern, Bastian; Böttcher, Artur; Kappes, Manfred M

    2013-03-14

    C58 fullerenes were adsorbed onto room temperature Au(111) surface by low-energy (~6 eV) cluster ion beam deposition under ultrahigh vacuum conditions. The topographic and electronic properties of the deposits were monitored by means of scanning tunnelling microscopy (STM at 4.2 K). Topographic images reveal that at low coverages fullerene cages are pinned by point dislocation defects on the herringbone reconstructed gold terraces (as well as by step edges). At intermediate coverages, pinned monomers act as nucleation centres for the formation of oligomeric C58 chains and 2D islands. At the largest coverages studied, the surface becomes covered by 3D interlinked C58 cages. STM topographic images of pinned single adsorbates are essentially featureless. The corresponding local densities of states are consistent with strong cage-substrate interactions. Topographic images of [C58]n oligomers show a stripe-like intensity pattern oriented perpendicular to the axis connecting the cage centers. This striped pattern becomes even more pronounced in maps of the local density of states. As supported by density functional theory, DFT calculations, and also by analogous STM images previously obtained for C60 polymers [M. Nakaya, Y. Kuwahara, M. Aono, and T. Nakayama, J. Nanosci. Nanotechnol. 11, 2829 (2011)], we conclude that these striped orbital patterns are a fingerprint of covalent intercage bonds. For thick C58 films we have derived a bandgap of 1.2 eV from scanning tunnelling spectroscopy data confirming that the outermost C58 layer behaves as a wide band semiconductor. PMID:23514509

  13. Fixing the Energy Scale in Scanning Tunneling Microscopy on Semiconductor Surfaces

    OpenAIRE

    Münnich, Gerhard; Donarini, Andrea; Repp, Jascha

    2013-01-01

    In scanning tunneling experiments on semiconductor surfaces, the energy scale within the tunneling junction is usually unknown due to tip-induced band bending. Here, we experimentally recover the zero point of the energy scale by combining scanning tunneling microscopy with Kelvin probe force spectroscopy. With this technique, we revisit shallow acceptors buried in GaAs. Enhanced acceptor-related conductance is observed in negative, zero, and positive band-bending regimes. An Anderson-Hubbard...

  14. Characterization of GaSb-based heterostructures by scanning electron microscope cathodoluminescence and scanning tunnelling microscope

    Energy Technology Data Exchange (ETDEWEB)

    Storgards, J [Departamento de FIsica de Materiales, Facultad de Ciencias FIsicas, Universidad Complutense de Madrid, 28040 Madrid (Spain); Mendez, B [Departamento de FIsica de Materiales, Facultad de Ciencias FIsicas, Universidad Complutense de Madrid, 28040 Madrid (Spain); Piqueras, J [Departamento de FIsica de Materiales, Facultad de Ciencias FIsicas, Universidad Complutense de Madrid, 28040 Madrid (Spain); Chenot, M [Fraunhofer Institute for Solar Energy Systems, 79110 Freiburg (Germany); Dimroth, F [Fraunhofer Institute for Solar Energy Systems, 79110 Freiburg (Germany); Bett, A W [Fraunhofer Institute for Solar Energy Systems, 79110 Freiburg (Germany)

    2004-01-21

    The luminescence of GaSb and AlGaSb layers grown on GaAs substrates by metal organic vapour phase epitaxy has been studied by means of cathodoluminescence (CL) using a scanning electron microscope. CL plane-view analysis reveals a distribution of defects, as misfit dislocations, in some of the structures. The luminescence bands observed in the GaSb layers are related to near band edge recombination and to an excess of Ga. In the case of AlGaSb/GaSb heterostructure emission bands related to the ternary compound and to donor-acceptor recombination are detected. In addition, with the aid of a scanning tunnelling microscope (STM), local electronic properties, such as conductance and surface energy gap, were studied in sample cross-sections. The results obtained from imaging and spectroscopy modes of STM enabled us to image the single AlGaSb layer.

  15. Characterization of GaSb-based heterostructures by scanning electron microscope cathodoluminescence and scanning tunnelling microscope

    International Nuclear Information System (INIS)

    The luminescence of GaSb and AlGaSb layers grown on GaAs substrates by metal organic vapour phase epitaxy has been studied by means of cathodoluminescence (CL) using a scanning electron microscope. CL plane-view analysis reveals a distribution of defects, as misfit dislocations, in some of the structures. The luminescence bands observed in the GaSb layers are related to near band edge recombination and to an excess of Ga. In the case of AlGaSb/GaSb heterostructure emission bands related to the ternary compound and to donor-acceptor recombination are detected. In addition, with the aid of a scanning tunnelling microscope (STM), local electronic properties, such as conductance and surface energy gap, were studied in sample cross-sections. The results obtained from imaging and spectroscopy modes of STM enabled us to image the single AlGaSb layer

  16. 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 in situ STM systems by diffusion through the solutions. Such interference can be serious for oxygen sensitive systems both for the target molecules themselves and for chemical linker molecules bound to the electrode surface for example, via Au-S bonding. This is strikingly illustrated in the present report. We present here oxygen-free in situ STM, in which the samples are contained in an argon atmosphere which removes oxygen in the system. Interference from oxygen is profoundly reduced in this setup and demonstrated by three examples. Two of these are in situ STM of the intermediate-size sulfur containing organic molecule cysteamine and the biomolecule homocysteine. The third example is the iron-sulfur protein ferredoxin (Pyrococcus furiosus). Monolayers of these molecules on Au(111) are imaged to molecular resolution and the images compared in the presence and absence of oxygen. In all the cases, 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 sensitive chemical and biological samples.

  17. Scanning tunnelling microscopy observations of biomolecules on layered materials.

    Science.gov (United States)

    Jungblut, H; Campbell, S A; Giersig, M; Müller, D J; Lewerenz, H J

    1992-01-01

    Scanning tunnelling microscopy (STM) has been performed on the reverse transcriptases of the human immunodeficiency virus (HIV-1) and the moloney murine leukaemia virus (MuLV). The biological molecules are adsorbed on n-type semiconducting MoTe2. The p66 (66 kD) subunit of the RT of HIV-1 is imaged by STM. Both STM and processed transmission electron microscopy (TEM) data show a spherical and horseshoe-like shape of external diameter ca. 65 A, depending on the angle of observation. The STM results show a larger diameter which is related to the curvature radius of the tip of the probing needle. The RTs of HIV-1 and MuLV exhibit a circular hole of ca. 20 A diameter in accordance with structure predictions and functioning considerations. The surface-molecule interaction is discussed in terms of the electronic properties of the semiconductor surface including the influence of small defect sites at the layered crystal surface. PMID:1285040

  18. Spectroscopic scanning tunneling microscopy insights into Fe-based superconductors

    International Nuclear Information System (INIS)

    In the first three years since the discovery of Fe-based high Tc superconductors, scanning tunneling microscopy (STM) and spectroscopy have shed light on three important questions. First, STM has demonstrated the complexity of the pairing symmetry in Fe-based materials. Phase-sensitive quasiparticle interference (QPI) imaging and low temperature spectroscopy have shown that the pairing order parameter varies from nodal to nodeless s± within a single family, FeTe1-xSex. Second, STM has imaged C4 ? C2 symmetry breaking in the electronic states of both parent and superconducting materials. As a local probe, STM is in a strong position to understand the interactions between these broken symmetry states and superconductivity. Finally, STM has been used to image the vortex state, giving insights into the technical problem of vortex pinning, and the fundamental problem of the competing states introduced when superconductivity is locally quenched by a magnetic field. Here we give a pedagogical introduction to STM and QPI imaging, discuss the specific challenges associated with extracting bulk properties from the study of surfaces, and report on progress made in understanding Fe-based superconductors using STM techniques.

  19. Scanning Tunneling Microscopy Studies of Diamond Films and Optoelectronic Materials

    Science.gov (United States)

    Perez, Jose M.

    1996-01-01

    We present a summary of the research, citations of publications resulting from the research and abstracts of such publications. We have made no inventions in the performance of the work in this project. The main goals of the project were to set up a Chemical Vapor Deposition (CVD) diamond growth system attached to an UltraHigh Vacuum (UHV) atomic resolution Scanning Tunneling Microscopy (STM) system and carry out experiments aimed at studying the properties and growth of diamond films using atomic resolution UHV STM. We successfully achieved these goals. We observed, for the first time, the atomic structure of the surface of CVD grown epitaxial diamond (100) films using UHV STM. We studied the effects of atomic hydrogen on the CVD diamond growth process. We studied the electronic properties of the diamond (100) (2x1) surface, and the effect of alkali metal adsorbates such as Cs on the work function of this surface using UHV STM spectroscopy techniques. We also studied, using STM, new electronic materials such as carbon nanotubes and gold nanostructures. This work resulted in four publications in refereed scientific journals and five publications in refereed conference proceedings.

  20. Scanning tunneling microscopy and spectroscopy of phase change alloys

    Energy Technology Data Exchange (ETDEWEB)

    Subramaniam, Dinesh; Pauly, Christian; Pratzer, Marco; Liebmann, Marcus; Morgenstern, Markus [II. Physikalisches Institut B, RWTH Aachen (Germany); Rausch, Pascal; Woda, Michael; Wuttig, Matthias [I. Physikalisches Institut A, RWTH Aachen (Germany)

    2009-07-01

    Phase change random access memory (PCRAM) is a very promising candidate for the next generation of memories. In contrast to the standard Si-based RAM, PCRAM is a non-volatile storage system which exploits the high electrical contrast between the amorphous and the crystalline phase. However, the origin of this contrast is not well understood. Scanning tunneling microscopy gives insight into the local atomic structure and the electronic properties of phase change materials. Using the topography mode of STM, we realized images of Ge{sub 1}Sb{sub 2}Te{sub 4} on the nanometer down to the atomic scale, revealing the morphology as well as the complex atomic arrangement of the sputter-deposited material. The spectroscopy mode enabled us to analyse the local density of states in the amorphous and crystalline phase. The band gap varied continuously from 0.5 eV in the amorphous phase to 0.2 eV in the crystalline phase. The Fermi level moved from the center of the gap in the amorphous phase into the valence band within the crystalline phase.

  1. Scanning tunneling microscopy and spectroscopy of phase change alloys

    International Nuclear Information System (INIS)

    Phase change random access memory (PCRAM) is a very promising candidate for the next generation of memories. In contrast to the standard Si-based RAM, PCRAM is a non-volatile storage system which exploits the high electrical contrast between the amorphous and the crystalline phase. However, the origin of this contrast is not well understood. Scanning tunneling microscopy gives insight into the local atomic structure and the electronic properties of phase change materials. Using the topography mode of STM, we realized images of Ge1Sb2Te4 on the nanometer down to the atomic scale, revealing the morphology as well as the complex atomic arrangement of the sputter-deposited material. The spectroscopy mode enabled us to analyse the local density of states in the amorphous and crystalline phase. The band gap varied continuously from 0.5 eV in the amorphous phase to 0.2 eV in the crystalline phase. The Fermi level moved from the center of the gap in the amorphous phase into the valence band within the crystalline phase.

  2. Electroluminescence properties of organic nanostructures studied by scanning tunnelling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kuhnke, Klaus; Kabakchiev, Alexander; Lutz, Theresa [Max-Planck Institute for Solid State Research, Stuttgart (Germany); Kern, Klaus [Max-Planck Institute for Solid State Research, Stuttgart (Germany); Institut de Physique des Nanostructures, Ecole Politechnique Federale de Lausanne (Switzerland)

    2012-04-15

    The control of light emission on the scale of individual quantum systems, like molecules or quantum dots, is a field of intense current research. One way to induce light emission from these systems is the local charge injection through the tip of a scanning tunnelling microscope (STM). Studies which employ this method have to address one basic question: Does the detected luminescence provide information precisely from the molecule into which charge is injected by the STM tip apex or are the luminescence properties determined by a larger volume? In this article, we focus on the investigation of organic nanocrystals and discuss the relation between the local excitation, the intermolecular coupling and the influence of the STM as a measuring instrument. Choosing pentacene as an organic emitter, we present results, which suggest that the STM-induced luminescence cannot be attributed simply to the emission by a single molecule. We discuss how information about locality can be obtained and comment on the present experimental limitations and possible future improvements. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  3. Substrate effects on the surface topography of evaporated gold films: a scanning tunnelling microscopy investigation

    OpenAIRE

    Vancea, Johann; Reiss, Günter; Schneider, F; Bauer, K.; Hoffmann, Horst

    1989-01-01

    Direct observation of surface roughness on metal films is a longstanding problem in thin film characterization. In this work the high quality of scanning tunnelling microscopy (STM) was used for investigation of evaporated gold films. A scanning tunnelling microscope able to scan areas up to 0.8 × 0.8 micro m with high reproducibility is presented. The topography of 80 nm thick gold films grown under identical evaporation conditions was investigated as a function of the selected substrate mat...

  4. As-rich GaAs(001) surfaces observed during As4-irradition by scanning tunneling microscopy

    CERN Document Server

    Tsukamoto, S; Orr, B G; Ohtake, A; Bell, G R; Koguchi, N; Tsukamoto, Shiro; Pristovsek, Markus; Orr, Bradford G.; Ohtake, Akihiro; Bell, Gavin R.; Koguchi, Nobuyuki

    2002-01-01

    As-rich GaAs (001) surfaces are successfully observed during As4-irradition by a system in which scanning tunneling microscopy (STM) and molecular beam epitaxy can be performed simultaneously. With a substrate temperature of 440 C and an As4 partial pressure of 2x10-6 torr, reflection high energy electron diffraction patterns and reflectance anisotropy spectra confirm a c(4x4) As-stabilized surface. STM images clearly show alteration of the surface reconstructions while scanning. It is postulated that continual attachment / detachment of As molecules to and from the surface produces the observed dynamic behavior.

  5. The atomic force (AFM), scanning tunneling (STM) and scanning force (SFM) microscopies

    International Nuclear Information System (INIS)

    This work deals with the atomic force (AFM), scanning tunneling (STM) and scanning force (SFM) microscopies. These analysis methods are based on different physical principles. Nevertheless, in all of them, a probe is situated at a few angstroms or at the direct contact of the studied sample and carries out a controlled scanning of the sample surface. Their physical principles and their running ways are described. Their potentialities and limits are given too. With these analysis methods, and more particularly with the AFM can be observed the crystal structure of isolated biological molecules and the tri dimensional structure of biological molecules which are inserted in artificial membranes. One of the future prospect of the AFM in biology is the direct observation of living cells. Indeed, it will offer the opportunity to follow, with time and in space, the individual cells behaviour and their morphological modifications. Others uses and developments of the AFM concerns the in situ analysis of mechanisms which govern the crystal growth or the direct viewing of a protein enzymatic activity. (O.M.). 37 refs., 7 figs

  6. Evidence of s-Wave Subdominant Order Parameter in YBCO from Break Junction Tunneling Spectra

    OpenAIRE

    Akimenko, A. I.; Bobba, F.; Giubileo, F.; Gudimenko, V.; Scarfato, A.; Cucolo, A. M.

    2006-01-01

    The tunneling spectra of YBa2Cu3O7 break-junctions have been investigated for the tunneling direction close to the node one. The zero-bias conductance peak (ZBCP) and Josephson current have been studied with temperature and magnetic field. The observed deep splitting of ZBCP which starts at Ts

  7. Fabrication and characterization of scanning tunneling microscopy superconducting Nb tips having highly enhanced critical fields

    Energy Technology Data Exchange (ETDEWEB)

    Kohen, A. [Groupe de Physique des Solides, UMR7588 au CNRS, Univ. Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France)]. E-mail: kohen@gps.jussieu.fr; Noat, Y. [Groupe de Physique des Solides, UMR7588 au CNRS, Univ. Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France); Proslier, T. [Groupe de Physique des Solides, UMR7588 au CNRS, Univ. Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France); Lacaze, E. [Groupe de Physique des Solides, UMR7588 au CNRS, Univ. Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France); Aprili, M. [Laboratoire de Spectroscopie en Lumiere Polarisee-CNRS ESPCI 10, rue Vauquelin 75005 Paris (France); Sacks, W. [Groupe de Physique des Solides, UMR7588 au CNRS, Univ. Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France); Roditchev, D. [Groupe de Physique des Solides, UMR7588 au CNRS, Univ. Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France)

    2005-02-15

    We report a simple method for the fabrication of Niobium superconducting (SC) tips for scanning tunneling microscopy which allow atomic resolution. The tips, formed in situ by the mechanical breaking of a niobium wire, reveal a clear SC gap of 1.5 meV and a critical temperature T{sub c} = 9.2 {+-} 0.3 K, as deduced from Superconductor Insulator Normal metal (SIN) and Superconductor Insulator Superconductor (SIS) spectra. These match the values of bulk Nb samples. We systematically find an enhanced value of the critical magnetic field in which superconductivity in the tip is destroyed (around 1 T for some tips) up to five times larger than the critical field of bulk Nb (0.21 T). Such enhancement is attributed to a size effect at the tip apex.

  8. Simulation of spin-polarized scanning tunneling spectroscopy on complex magnetic surfaces: Case of a Cr monolayer on Ag(111)

    CERN Document Server

    Palotás, Krisztián; Szunyogh, László

    2012-01-01

    We propose a computationally efficient atom-superposition-based method for simulating spin-polarized scanning tunneling spectroscopy (SP-STS) on complex magnetic surfaces based on the sample and tip electronic structure obtained from first principles. By directly calculating bias-integrated terms, we avoid numerical errors of the differentiation of the tunneling current with respect to the bias voltage in determining the differential conductance (dI/dV). The capabilities of our approach are illustrated for a Cr monolayer on a Ag(111) surface in a noncollinear magnetic state. We find evidence that the simulated tunneling spectra and magnetic asymmetries are sensitive to the tip electronic structure, and we analyze the contributing terms. Related to SP-STS experiments, we show how to simulate two-dimensional differential conductance maps and qualitatively correct effective spin polarization maps on a constant current contour above a magnetic surface. Moreover, we derive alternative expressions for dI/dV and sug...

  9. 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.

  10. Tunneling spectra for single molecules of HEX-fluorescent dye attached to DNA adsorbed on Cu(1 1 1) surfaces

    International Nuclear Information System (INIS)

    We used the scanning tunneling microscope (STM) to examine single-stranded deoxyribonucleic acid (DNA) oligomers deposited on a metal surface. Because STM can be used to study the electrical properties of materials via the tunneling spectra, we used it to visualize DNA oligomers at the single molecule resolution. The 5'-hexachloro-fluorescein phosphoramidite (HEX)-labeled oligomers (sequence, AGCTTC) were observed on an atomically flat Cu(1 1 1) surface. At large tip-sample distances at large set-point biases, the lowest unoccupied molecular orbit (LUMO) peak of the empty state can be observed for the dye molecules on the tunneling spectra. When this distance becomes small, similar spectra as for the Cu substrate were observed for the dye molecule on the LUMO-related peak. Cu gave peaks at small bias voltages in the filled state. From comparison of these peaks on each subunit of the molecules, the measured values of dI/dV on HEX were smaller to those on Cu because of the large size of the HEX molecule, but the normalized values of dI/dV/(I/V) were apparently equal. We believe that the tunneling current is able to pass through the HEX molecules to the Cu substrate, thus reflecting the density of the Cu(1 1 1) surface. Molecular size therefore affects the intensity of dI/dV. LUMO-related peaks sometimes cannot be observed for HEX because of conformational differences, but Cu peaks can almost always be observed for HEX molecules. These peaks for the counter ions are almost the same as those for the Cu substrate. Thus, tunneling spectra can assist in the molecular mapping of DNA

  11. Scanning tunneling microscopy and spectroscopy of single wall carbon nanotubes

    Science.gov (United States)

    Lagoute, Jérôme

    2010-03-01

    Carbon nanotubes (CNTs) are fascinating candidates for fundamental studies of one dimensional materials as well as for future molecular electronics applications. Their electronic structure is directly linked to their chirality which controls their semiconducting of metallic character. The link between local electronic and atomic structure is a crucial parameter which can be investigated in detail by using Scanning tunnelling microscopy (STM) and spectroscopy (STS). STS measurements are dominated by a series of Van Hove singularities (VHS) which are usually successfully described by a tight-binding model. The energy position of these singularities and the related wavefunctions which can be seen as the molecular orbitals of CNTs are two fundamental characteristics of CNTs which will be discussed in details here. The experimental visualization of the wavefunctions associated to the VHS will be presented. They exhibit a symmetry breaking in semiconducting and metallic tubes which is well described by a tight-binding model. The energy position of the VHS will then be discussed in details. The recent experimental evidence of the major role of excitons in the optical transitions in CNTs has enlightened the importance of many-body effects in the electronic structure of CNTs. In STS experiments, the electronic gaps of semiconducting tubes supported by a metallic substrate are close to the optical transitions although STS is not sensitive to the excitons and should exhibit much larger VHS separation. We will discuss this issue and show the importance of many-body effects and tube-substrate interaction in the electronic bandgaps of semiconducting tubes.

  12. Scanning tunneling microscopy studies of glucose oxidase on gold surface

    International Nuclear Information System (INIS)

    Full text: Three immobilization methods have been used for scanning tunneling microscopy (STM) studies of glucose oxidase (GOD) on gold. They are based on a) physical adsorption from solution, b) microcontact printing and c) covalent bonding onto self-assembled monolayers (SAM) of 3-mercaptopropionic acid (MPA). The STM images are used to provide information about the organization of individual GOD molecules and more densely packed monolayers of GOD on electrode surfaces, thus providing information of the role of interfacial structure on biosensor performance. The use of atomically flat gold substrates enables easy distinction of deposited enzyme features from the flat gold substrate. Microcontact printing is found to be a more reliable method than adsorption from solution for preparing individual GOD molecules on the gold surface STM images of printed samples reveal two different shapes of native GOD molecules. One is a butterfly shape with dimensions of 10 ± 1 nm x 6 ± 1 nm, assigned to the lying position of molecule while the second is an approximately spherical shape with dimensions of 6.5 ± 1 nm x 5 ± 1nm assigned to a standing position. Isolated clusters of 5 to 6 GOD molecules are also observed. With monolayer coverage, GOD molecules exhibit a tendency to organize themselves into a two dimensional array with adequate sample stability to obtain high-resolution STM images. Within these two-dimensional arrays are clearly seen repeating clusters of five to six enzyme molecules in a unit STM imaging of GOD monolayers covalently immobilized onto SAM (MPA) are considerably more difficult than when the enzyme is adsorbed directly onto the metal. Cluster structures are observed both high and low coverage despite the fact that native GOD is a negatively charged molecule. Copyright (2002) Australian Society for Electron Microscopy Inc

  13. Field emission characteristics of the scanning tunneling microscope for nanolithography

    Energy Technology Data Exchange (ETDEWEB)

    Mayer, T.M.; Adams, D.P.; Marder, B.M. [Sandia National Laboratories, Albuquerque, New Mexico 87185-1413 (United States)

    1996-07-01

    We present a systematic study of the performance of scanning tunneling microscope (STM)-based, low energy electron beam lithography, using simulations of field emission from STM tips, emphasizing realistic conditions of tip geometry and operation. We calculate the potentials and electric field for a hemispherical model emitter in an axially symmetric system. Emission current density at the tip is calculated using the Fowler{endash}Nordheim equation, and current density at the sample is obtained by calculating trajectories of emitted electrons. We characterize the beam diameter at the sample as a function of emitter radius, tip{endash}sample bias, emission current, resist thickness, and tip work function. The beam diameter is primarily affected by the tip{endash}sample gap, increasing at larger gaps, characteristic of high bias and large tip curvature. For optimal tip radius the beam diameter increases linearly with bias from approximately 2 nm at 5 V to 25 nm at 50 V. Beam diameter is nearly independent of emission current over the range 0.05{endash}50 nA. Dielectric resist films cause an increase in beam diameter due to increased tip{endash}substrate gap. Beam diameter is very sensitive to tip work function, increasing dramatically for low work function tips. Tips comprised of asperities on flat surfaces produce significantly smaller beams compared to {open_quote}{open_quote}standard{close_quote}{close_quote} tips of the same emitter radius. However, for low bias ({lt}15 V) beam diameter becomes insensitive to tip geometry. We compare these simulations to selected experimental results to evaluate the limitations to performance and assess the feasibility of routine sub-10 nm structure fabrication using STM-based low energy electron beam lithography. {copyright} {ital 1996 American Vacuum Society}

  14. 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...

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

    OpenAIRE

    K. Braun; Kern, A. M.; 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 ar...

  16. Two-photon Induced Hot Electron Transfer to a Single Molecule in a Scanning Tunneling Microscope

    OpenAIRE

    Wu, Shiwei; Ho, Wilson

    2010-01-01

    The junction of a scanning tunneling microscope (STM) operating in the tunneling regime was irradiated with femtosecond laser pulses. A photo-excited hot electron in the STM tip resonantly tunnels into an excited state of a single molecule on the surface, converting it from the neutral to the anion. The electron transfer rate depends quadratically on the incident laser power, suggesting a two-photon excitation process. This nonlinear optical process is further confirmed by t...

  17. 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...

  18. Spectroscopy of surface adsorbed molecules (scanning tunneling microscopy). Progress report, May 1, 1985-April 30, 1986

    International Nuclear Information System (INIS)

    A review of the scanning tunneling microscopy program is given. This article contains a description of the design and fabrication of the microscope in addition to description of studies which use the microscope: studies of charge-density waves and studies of tunnel junctions doped with metals and semiconductors. 48 refs., 26 figs

  19. 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.

  20. The Density of States of hole-doped Manganites A Scanning Tunneling Microscopy\\/Spectroscopy study

    CERN Document Server

    Biswas, A K; Raychaudhuri, A K; Bhat, H L; Biswas, Amlan; Elizabeth, Suja

    1999-01-01

    Variable temperature scanning tunneling microscopy/spectroscopy studies on single crystals and epitaxial thin films of hole-doped manganites, which show colossal magnetoresistance, have been done. We have investigated the variation of the density of states, at and near the Fermi energy ($E_f$), as a function of temperature. Simple calculations have been carried out, to find out the effect of temperature on the tunneling spectra and extract the variation of density of states with temperature, from the observed data. We also report here, atomic resolution images, on the single crystals and larger range images showing the growth patterns on thin films. Our investigation shows unambiguously that there is a rapid variation in density of states for temperatures near the Curie temperature ($T_c$). While for temperatures below $T_c$, a finite DOS is observed at $E_f$, for temperatures near $T_c$ a hard gap opens up in the density of states near $E_f$. For temperatures much higher than $T_c$, this gap most likely give...

  1. To probe quantum criticality with scanning tunneling spectroscopy

    OpenAIRE

    Tran, Minh-Tien; Kim, Ki-Seok

    2009-01-01

    We investigate the role of quantum coherence in tunneling conductance, where quantum criticality turns out to suppress Fano resonance. Based on the nonequilibrium noncrossing approximation, we show that the linear tunneling conductance exhibits weak Fano line-shape with sharp cusp at zero energy in the multichannel Kondo effect, resulting from incoherence associated with quantum criticality of impurity dynamics. In particular, shift of the peak position in the Fano resonance...

  2. Scanning tunnelling microscopy on organic field-effect transistors based on intrinsic pentacene

    OpenAIRE

    Roelofs, W.S. Christian; Charrier, Dimitri S. H.; Dzwilewski, Andrzej; Janssen, Rene A. J.; de Leeuw, Dago M.; Kemerink, Martijn

    2014-01-01

    The full potential of scanning tunnelling microscopy (STM) and scanning tunnelling spectroscopy for in-situ characterization of organic semiconductors has so far not been accessible. Here, we demonstrate that the underlying problem, the low intrinsic conductivity, can be overcome by working in a field-effect geometry. We present high resolution surface topographies obtained by STM on pentacene organic field-effect transistors (OFETs). By virtue of the OFET geometry, the hole accumulation laye...

  3. Surface confined metallosupramolecular architectures: formation and scanning tunneling microscopy characterization.

    Science.gov (United States)

    Li, Shan-Shan; Northrop, Brian H; Yuan, Qun-Hui; Wan, Li-Jun; Stang, Peter J

    2009-02-17

    Metallosupramolecular compounds have attracted a great deal of attention over the past two decades largely because of their unique, highly complex structural characteristics and their potential electronic, magnetic, optical, and catalytic properties. These molecules can be prepared with relative ease using coordination-driven self-assembly techniques. In particular, the use of electron-poor square-planar Pt(II) transition metals in conjunction with rigid, electron-rich pyridyl donors has enabled the spontaneous self-assembly of a rich library of 2D metallacyclic and 3D metallacage assemblies via the directional-bonding approach. With this progress in the preparation and characterization of metallosupramolecules, researchers have now turned their attention toward fully exploring and developing their materials properties. Assembling metallosupramolecular compounds on solid supports represents a vitally important step toward developing their materials properties. Surfaces provide a means of uniformly aligning and orienting these highly symmetric metallacycles and metallacages. This uniformity increases the level of coherence between molecules above that which can be achieved in the solution phase and provides a way to integrate adsorbed layers, or adlayers, into a solid-state materials setting. The dynamic nature of kinetically labile Pt(II)-N coordination bonds requires us to adjust deposition and imaging conditions to retain the assemblies' stability. Toward these aims, we have used scanning tunneling microscopy (STM) to image these adlayers and to understand the factors that govern surface self-assembly and the interactions that influence their structure and stability. This Account describes our efforts to deposit 2D rectangular and square metallacycles and 3D trigonal bipyramidal and chiral trigonal prism metallacages on highly oriented pyrolytic graphite (HOPG) and Au(111) substrates to give intact assemblies and ordered adlayers. We have investigated the effects of varying the size, symmetry, and dimensionality of supramolecular adsorbates, the choice of substrate, the use of a molecular template, and the effects of chirality. Our systematic investigations provide insights into the various adsorbate-adsorbate and substrate-adsorbate interactions that largely determine the architecture of each assembly and affect their performance in a materials setting. Rational control over adlayer formation and structure will greatly enhance the potential of these supramolecules to be used in a variety of applications such as host-guest sensing/diagnostic systems, molecular electronic devices, and heterogeneous stereoselective synthesis and catalysis. PMID:19072706

  4. Development of a Millikelvin dual-tip Josephson scanning tunneling microscope

    Science.gov (United States)

    Roychowdhury, Anita

    In this thesis, I first describe the design and construction of a dual-tip millikelvin STM system. The STM is mounted on a dilution refrigerator and the setup includes vibration isolation, rf-filtered wiring, an ultra high vacuum (UHV) sample preparation chamber and sample transfer mechanism. Next I describe a novel superconducting tip fabrication technique. My technique involves dry-etching sections of 250 mum diameter Nb wire with an SF6 plasma in a reactive ion etcher. I present data taken with these tips on various samples at temperatures ranging from 30 mK to 9 K. My results demonstrate that the tips are superconducting, achieve good spectroscopic energy resolution, are mechanically robust over long time periods, and are atomically sharp. I also show data characterizing the performance of our system. This data is in the form of atomic resolution images, spectroscopy, noise spectra and simultaneous scans taken with both tips of the STM. I used these to examine the tip-sample stability, cross talk between the two tips, and to extract the effective noise temperature (˜185 mK) of the sample by fitting the spectroscopy data to a voltage noise model. Finally, I present spectroscopy data taken with a Nb tip on a Nb(100) sample at 30 mK. The enhanced spectroscopic resolution at this temperature allowed me to resolve peaks in the fluctuation-dominated supercurrent at sub-gap voltages. My analysis indicates that these peaks are due to the incoherent tunneling of Cooper pairs at resonant frequencies of the STM's electromagnetic environment. By measuring the response of the STM junction to microwaves, I identified the charge carriers in this regime as Cooper pairs with charge 2e. The amplitude of the response current scales as the square of the Bessel functions, indicating that the pair tunneling originates from photon assisted tunneling in the incoherent regime, rather than the more conventionally observed Shapiro steps in the coherent regime.

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

    DEFF Research Database (Denmark)

    Stokbro, Kurt; Hu, Ben Yu-Kuang; Thirstrup, C.; Xie, X.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 to...... the addition of the adsorbate. We use the theory to investigate the vibrational heating of an adsorbate below a scanning tunneling microscopy tip. We calculate the desorption rate of PI from Si(100)-H(2 X 1) as a function of the sample bias and tunnel current, and find excellent a,agreement with...

  6. Imaging of buried phosphorus nanostructures in silicon using scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Oberbeck, Lars [Centre for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052 (Australia); TOTAL Marketing Services, New Energies, La Défense 10, 92069 Paris La Défense Cedex (France); Reusch, Thilo C. G.; Hallam, Toby; Simmons, Michelle Y., E-mail: n.curson@ucl.ac.uk, E-mail: michelle.simmons@unsw.edu.au [Centre for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052 (Australia); Schofield, Steven R. [Centre for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052 (Australia); London Centre for Nanotechnology, UCL, London WC1H 0AH (United Kingdom); Department of Physics and Astronomy, UCL, London WC1E 6BT (United Kingdom); Curson, Neil J., E-mail: n.curson@ucl.ac.uk, E-mail: michelle.simmons@unsw.edu.au [Centre for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052 (Australia); London Centre for Nanotechnology, UCL, London WC1H 0AH (United Kingdom); Department of Electronic and Electrical Engineering, UCL, London WC1E 7JE (United Kingdom)

    2014-06-23

    We demonstrate the locating and imaging of single phosphorus atoms and phosphorus dopant nanostructures, buried beneath the Si(001) surface using scanning tunneling microscopy. The buried dopant nanostructures have been fabricated in a bottom-up approach using scanning tunneling microscope lithography on Si(001). We find that current imaging tunneling spectroscopy is suited to locate and image buried nanostructures at room temperature and with residual surface roughness present. From these studies, we can place an upper limit on the lateral diffusion during encapsulation with low-temperature Si molecular beam epitaxy.

  7. Imaging of buried phosphorus nanostructures in silicon using scanning tunneling microscopy

    International Nuclear Information System (INIS)

    We demonstrate the locating and imaging of single phosphorus atoms and phosphorus dopant nanostructures, buried beneath the Si(001) surface using scanning tunneling microscopy. The buried dopant nanostructures have been fabricated in a bottom-up approach using scanning tunneling microscope lithography on Si(001). We find that current imaging tunneling spectroscopy is suited to locate and image buried nanostructures at room temperature and with residual surface roughness present. From these studies, we can place an upper limit on the lateral diffusion during encapsulation with low-temperature Si molecular beam epitaxy.

  8. 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.

  9. Electronic structure and tunneling resonance spectra of nanoscopic aluminum islands

    OpenAIRE

    Narvaez, Gustavo A.; Kirczenow, George

    2002-01-01

    The electronic structure of nanoscopic oxide-coated aluminum islands is investigated using a tight-binding model that incorporates the geometry, chemistry and disorder of the particle. The oxide coat is found to significantly increase the volume accessible to electrons at the Fermi level. The level statistics agree with random matrix theory predictions. States near the Fermi level show pronounced clustering regardless of disorder. It is suggested that the observed clusters of tunneling resona...

  10. Visualizing Surface States of Topological Insulators with Scanning Tunneling Microscopy

    Science.gov (United States)

    Roushan, Pedram

    2011-12-01

    Topological insulators are materials that have a bulk band gap similar to commonly known insulators, but have conducting states on their edge or surface. The bulk band gap is generated because of the strong spin-orbit coupling inherent to these systems, which also modifies the band in a fundamental way, leading to unconventional spin-polarized Dirac fermions on the boundary of the insulator. In this thesis, we present our scanning tunneling spectroscopy studies of topological surface states in Bi1- xSbx, Sb, Bi 2Te3 and Bi2 Se3. Due to their helical spin texture, the surface states of topological insulators are distinct from the well-known conventional surface states of noble metals. A key predicted feature of these metallic surface states is their immunity to localization and ability to overcome barriers caused by material imperfections. These predictions can be examined by studying the scattering of surface states from random alloying disorder. We have mapped the interference of the surface states in Bi0.9 Sb0.1 and demonstrated that despite strong atomic scale disorder, backscattering between states of opposite momentum and opposite spin is absent, resulting from the helical spin texture of the surface states. Furthermore, we have measured transmission and reflection of the topological surface states of Sb by atomic terraces. In contrast to surface states of noble metals, these surface states penetrate such barriers with high probability. These results experimentally demonstrate the fundamental difference of these surface states in comparison to other known surface states, and show their potential to be used for spin-based electronics and nano-scale devices. In recent years, the topological surface states of Bi 2Te3 and Bi2 Se3, the "second generation" topological insulators, has become the focus of intense research. The single Dirac cone surface states on these compounds constitutes the simplest manifestation of 3D topological insulators. Many of the interesting theoretical proposals that utilize topological insulator surfaces require the chemical potential to lie at or near the surface Dirac point, and consequently bulk doping is commonly used to tune the chemical potential to the Dirac point. We have studied the surface states of Bi2Te3 and Bi 2Se3 in the presence of magnetic and non-magnetic dopants. Bulk doping results in strong nano-scale spatial fluctuations of the surface states' energy and momentum. In spite of these fluctuations, Dirac electrons show a remarkable robustness to backscattering that can be understood based on their helical spin texture, which is preserved even in the presence of magnetic dopants or bulk magnetism. While we show that these strong spatial fluctuations influence the transmission of topological surface states, we find no evidence for their localization by bulk or surface disorder. In the vicinity of the Dirac point, the energy and momentum fluctuations we observed would result in spatially alternating spin helicity. This could possibly limit the mobility of topological surface state near the Dirac point. Our findings suggest that utilization of helical Dirac fermions on topological insulators requires methods of tuning the chemical potential which do not involve chemical doping.

  11. 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.

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

    International Nuclear Information System (INIS)

    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

  13. 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.

  14. Scanning tunneling microscopy and spectroscopy study of FeAs based crystals with magnetic and superconducting order

    International Nuclear Information System (INIS)

    Coexisting superconducting and magnetic phases in layered pnictides has attracted much attention after discovery of superconductivity in various pnictides. We present temperature dependent scanning tunneling microscopy and spectroscopy studies of FeAs-based 122 layered crystals with magnetic and superconducting orders. The topographic images show a atomically flat surfaces with some signatures of atomic resolution. The tunnel spectra in parent compounds, EuFe2As2 and SrFe2As2, show a homogeneous gap-like feature in the local electronic density of states (DOS) at low temperatures below the corresponding spin density wave (SDW) transition temperature. In CaFe1.96Ni0.04As2 crystals, having both SDW ordering (below 125 K) and superconductivity (Tc = 15K), we see significant inhomogeneities in superconducting phase, which slowly disappear as we go above Tc. We divide the spectra below Tc into three categories: gap-like but with only one coherence peak either below the Fermi energy or above. The third category spectra show no gap feature. With increasing temperature the inhomogeneities disappear and we see homogeneous SDW-gap-like spectra as seen in parent compounds. We discuss these results in terms of an inhomogeneous electronic phases that may exist due to the vicinity of this composition to the quantum critical point. (author)

  15. Spin polarised scanning tunneling probe for helical Luttinger liquids

    OpenAIRE

    Das, Sourin; Rao, Sumathi

    2010-01-01

    We propose a three terminal spin polarized stm setup for probing the helical nature of the Luttinger liquid edge state that appears in the quantum spin Hall system. We show that the three-terminal tunneling conductance strongly depends on the angle ($\\theta$) between the magnetization direction of the tip and the local orientation of the electron spin on the edge while the two terminal conductance is independent of this angle. We demonstrate that chiral injection of an electron into the helic...

  16. Local imaging of high mobility two-dimensional electron systems with virtual scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Correlated electron states in high mobility two-dimensional electron systems (2DESs), including charge density waves and microemulsion phases intermediate between a Fermi liquid and Wigner crystal, are predicted to exhibit complex local charge order. Existing experimental studies, however, have mainly probed these systems at micron to millimeter scales rather than directly mapping spatial organization. Scanning probes should be well-suited to study the spatial structure of these states, but high mobility 2DESs are found at buried semiconductor interfaces, beyond the reach of conventional scanning tunneling microscopy. Scanning techniques based on electrostatic coupling to the 2DES deliver important insights, but generally with resolution limited by the depth of the 2DES. In this letter, we present our progress in developing a technique called “virtual scanning tunneling microscopy” that allows local tunneling into a high mobility 2DES. Using a specially designed bilayer GaAs/AlGaAs heterostructure where the tunnel coupling between two separate 2DESs is tunable via electrostatic gating, combined with a scanning gate, we show that the local tunneling can be controlled with sub-250?nm resolution

  17. Local imaging of high mobility two-dimensional electron systems with virtual scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Pelliccione, M. [Department of Applied Physics, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305 (United States); Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Department of Physics, University of California, Santa Barbara, Santa Barbara, California 93106 (United States); Bartel, J.; Goldhaber-Gordon, D. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, California 94305 (United States); Sciambi, A. [Department of Applied Physics, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305 (United States); Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Pfeiffer, L. N.; West, K. W. [Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544 (United States)

    2014-11-03

    Correlated electron states in high mobility two-dimensional electron systems (2DESs), including charge density waves and microemulsion phases intermediate between a Fermi liquid and Wigner crystal, are predicted to exhibit complex local charge order. Existing experimental studies, however, have mainly probed these systems at micron to millimeter scales rather than directly mapping spatial organization. Scanning probes should be well-suited to study the spatial structure of these states, but high mobility 2DESs are found at buried semiconductor interfaces, beyond the reach of conventional scanning tunneling microscopy. Scanning techniques based on electrostatic coupling to the 2DES deliver important insights, but generally with resolution limited by the depth of the 2DES. In this letter, we present our progress in developing a technique called “virtual scanning tunneling microscopy” that allows local tunneling into a high mobility 2DES. Using a specially designed bilayer GaAs/AlGaAs heterostructure where the tunnel coupling between two separate 2DESs is tunable via electrostatic gating, combined with a scanning gate, we show that the local tunneling can be controlled with sub-250?nm resolution.

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

    DEFF Research Database (Denmark)

    Bork, Jakob

    2010-01-01

    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 tunneling microscope (STM). Especially at low temperatures the Kondo resonance is used to probe magnetic interaction with ferromagnetic islands and between two atoms. The latter showing a crossover between Kondo screened atoms and antiferromagnetically coupled atoms close to the quantum critical point. 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. The heterostructure is found to have very interesting electronic properties. The d-related state from the now buried cobalt island is visible through the silver capping layer, but the silver Moire pattern modulates the spin-polarized cobalt d-related state in amplitude, energy position and width. This is related to the d-band model for catalytic reactions. The largest change is in the amplitude of the state, however the "reversed" structure of cobalt on Ag(111) show similar properties, but with a large shift in energy instead of amplitude. The Kondo eect is used to probe magnetic interaction between the aforementioned silver-capped cobalt islands (and additionally gold-capped cobalt islands) and single cobalt atoms positioned on the Moire pattern. A split Kondo resonance due to the exchange interaction between the island and the atom is observed. In a more technical section of the thesis, it is shown how a gold-coated STM tip will make the tip apex susceptible to a single cobalt atom. The tip is indented either directly in a Au(111) surface or gold akes are picked up from cobalt islands on Cu(111). A change in the local barrier height (work function) of the tip-sample junction indicates that the apex is gold-coated and a single cobalt atom can be pickup up. The cobalt atom attached to the tip displays a Kondo resonance formed between the atom and the tip similar to the resonance displayed when the atom is on the surface with a clean tip. Here, this is used to show how a two-impurity Kondo system consisting of two cobalt atoms, one on the tip and one on the Au(111) sample, is undergoing a continuous crossover from Kondo screened atoms to antiferromagnetically coupled atoms when the atoms are moved from non-interacting to strongly interacting. In the Kondo screened regime, the Kondo temperature is believed to be constant, but the Fano line ii shape changes continuously from a dip to a peak. In the antiferromagnetic regime, inelastic spin-ip excitations reveal a splitting with a continuous increase in energy levels when pushing the atoms further together. This is supported by numerical renormalization group calculations. The crossover between the two regimes is furthermore interesting because it occurs in an area of the phase diagram close to the elusive quantum critical point, where the phase transition line meets absolute zero temperature. This freely positionable Kondo system on the tip represents a novel way to probe magnetic interaction with the possibility to continuously change the position of the probing Kondo system. The experiment is believed to be one of many applications possible and the method opens up for a new eld within STM. We expect that our work has direct impact in other research areas, such as for heavy fermion materials, a class of materials whose properties are governed by the competition between Kondo screening an

  19. A Mechanism for Cutting Carbon Nanotubes with a Scanning Tunneling Microscope

    OpenAIRE

    Rubio, Angel; Apell, S. Peter; Venema, Liesbeth C.; Dekker, Cees

    2000-01-01

    We discuss the local cutting of single-walled carbon nanotubes by a voltage pulse to the tip of a scanning tunneling microscope. The tip voltage ($\\mid V \\mid \\ge $~3.8 eV) is the key physical quantity in the cutting process. After reviewing several possible physical mechanisms we conclude that the cutting process relies on the weakening of the carbon-carbon bonds through a combination of localized particle-hole excitations induced by inelastically tunneling electrons and el...

  20. Scanning Tunneling Microscope Nanolithography on SrRuO3 Thin Film Surfaces

    OpenAIRE

    Liu, Yun; Zhang, Jia

    2009-01-01

    Nanoscale lithography on SrRuO3 (SRO) thin film surfaces has been performed by scanning tunneling microscopy under ambient conditions. The depth of etched lines increases with increasing bias voltage but it does not change significantly by increasing the tunneling current. The dependence of line width on bias voltage from experimental data is in agreement with theoretical calculation based on field-induced evaporation. Moreover, a three-square nanostructure was successfully ...

  1. Scanning tunnelling spectroscopy of the vortex state in NbSe2 using a superconducting tip

    OpenAIRE

    Rodrigo, J. G.; Crespo, V.; Vieira, S.

    2007-01-01

    The vortex electronic structure in the multiband superconductor NbSe2 is studied by means of Scanning Tunneling Spectroscopy (STS) using a superconducting tip. The use of a superconducting tip (Pb) as a probe provides an enhancement of the different features related to the DOS of NbSe2 in the tunneling conductance curves. This use allows the observation of rich patterns of electronic states in the conductance images around the vortex cores in a wide range of temperature, as ...

  2. Visualizing electron correlation by means of ab-initio scanning tunneling spectroscopy images of single molecules

    OpenAIRE

    Toroz, Dimitrios; Rontani, Massimo; Corni, Stefano

    2011-01-01

    Scanning tunneling microscopy (STM) has been a fundamental tool to characterize many-body effects in condensed matter systems, from extended solids to quantum dots. STM of molecules decoupled from the supporting conductive substrate has the potential to extend STM characterization of many body effects to the molecular world as well. In this article, we describe a many-body tunneling theory for molecules decoupled from the STM substrate, and we report on the use of standard quantum chemical me...

  3. Effects of temperature and other experimental variables on single molecule vibrational spectroscopy with the scanning tunneling microscope

    International Nuclear Information System (INIS)

    Inelastic electron tunneling spectroscopy (IETS) was performed on single molecules with a variable temperature scanning tunneling microscope. The peak intensity, width, position, and line shape of single molecule vibrational spectra were studied as a function of temperature, modulation bias, bias polarity, and tip position for the (C--H,C--D) stretching vibration of acetylene (C2H2,C2D2) on Cu(001). The temperature broadening of vibrational peaks was found to be a consequence of Fermi smearing as in macroscopic IETS. The modulation broadening of vibrational peaks assumed the expected form for IETS. Extrapolation of the peak width to zero temperature and modulation suggested an intrinsic width of ?4 meV due primarily to instrumental broadening. The inelastic tunneling cross section at negative bias was reduced by a factor of 1.7 for the C--H stretch mode. Low energy modes of other molecules did not show such a reduction. There was no evidence of a tip-induced Stark shift in the peak positions. The spatial variation of the inelastic signal was measured to determine the junction stability necessary for the acquisition of single molecule vibrational spectra

  4. CT-scanning study of cross-sectional area of the carpal tunnel in cases of carpal tunnel syndrome

    International Nuclear Information System (INIS)

    The cross-sectional area, transverse and anteroposterior diameter of the carpal tunnel were investigated by CT scanning in 68 cases of carpal tunnel syndrome (CTS) and in 100 normal controls of both sexes. The cross-sectional areas of the carpal tunnel in idiopathic CTS of both sexes were significantly smaller, whereas those in secondary CTS were larger than in normal controls. In female wrists with idiopathic CTS narrowing of distal carpal tunnel was attributed to short transverse diameter in wrists with normally shaped hook of the hamate, or to decreased anteroposterior diameter in wrists with abnormally short hook of the hamate. The smallest cross-sectional area in both types of CTS and in normal controls is located at the proximal border of distal carpal tunnel (D 1 level). This coincides with the thickest portion of the flexor retinaculum and, together with our operative findings, supports the conclusion that the essential compression on the median nerve takes place at the D 1 level in idiopathic CTS. (author)

  5. The Kondo effect of an adatom in graphene and its scanning tunneling spectroscopy

    International Nuclear Information System (INIS)

    We study the Kondo effect of a single magnetic adatom on the surface of graphene. The unique linear dispersion relation near the Dirac points in graphene makes it easier for the magnetic atom to form a local magnetic moment, which simply means that the Kondo resonance can be observed in a wider parameter region than in the metallic host. Our study indicates that the Kondo resonance, whenever the chemical potential is tuned away from the Dirac points, can indeed occur ranging from the Kondo regime, to the mixed valence, even to the empty orbital regime defined in the conventional metal host. While the Kondo resonance appears as a sharp peak in the Kondo regime, it has a peak-dip structure and/or an anti-resonance in the mixed valence and empty orbital regimes, which result from the Fano resonance due to the significant background due to dramatic broadening of the impurity level in graphene. We also study the scanning tunneling microscopy (STM) spectra of the adatom and they show obvious particle–hole asymmetry when the chemical potential is tuned by the gate voltages applied to the graphene. Finally, we explore the influence of the direct tunneling channel between the STM tip and the graphene on the Kondo resonance and find that the lineshape of the Kondo resonance is unaffected, which can be attributed to an unusually large asymmetry factor in graphene. Our study indicates that graphene is an ideal platform to systematically study Kondo physics and these results are useful to further stimulate relevant experimental studies on the system. (paper)

  6. Tunneling spectra of break junctions involving Nb3Sn

    Science.gov (United States)

    Ekino, Toshikazu; Sugimoto, Akira; Sakai, Yuta; Gabovich, Alexander M.; Akimitsu, Jun

    2014-10-01

    The electronic gap structure of Nb3Sn was measured by the break-junction (BJ) tunneling technique. The superconducting gap values are estimated to be in the range 2? = 4-5.5 meV at T = 4.2 K as follows from the observed distinct conductance peaks. In addition to the superconducting gap structure, we observed reproducible hump-like structures at the biases of about ±20 and ±50 mV. Such a coexistence of gap and hump structures resembles the situation found in the high-Tc copper-oxide superconductors. Above the superconducting critical temperature Tc ˜ 18 K, the humps appear as the only gap-like structures. Their possible origin is discussed in connection to the structural phase transition occurring in Nb3Sn.

  7. Oxidation of a Single Carbon Monoxide Molecule Manipulated and Induced with a Scanning Tunneling Microscope

    International Nuclear Information System (INIS)

    A carbon monoxide molecule (CO) was positioned with a scanning tunneling microscope (STM) at various distances from an oxygen atom (O) on the Ag(110) surface at 13K. At the closest separation, carbon dioxide (CO2) production was induced by tunneling electrons. Direct reaction of a CO desorbed from the STM tip with an O atom on Ag(110) illustrates another catalytic oxidation mechanism. Inelastic electron tunneling spectroscopy with the STM was used to monitor the vibrations of CO in its different environment

  8. Effects of the finite duration of quantum tunneling in laser-assisted scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Previous measurements of tunnel conductance in heterostructures and experiments with Josephson junctions suggest quantum tunneling has a definite duration. The authors use semiclassical methods to determine the effects of this delay on the tunneling current in a laser-assisted STM. A planar-planar STM model is used with the exact multiple image potential, and the energy distribution for a free-electron metal. It is necessary to average over the phase at barrier entry, and iteration with back propagated solutions is required to obtain the transmission coefficients for evenly spaced phases and specified energies at barrier entry. The simulations suggest that the dependence of the tunneling current on the wavelength of illumination can serve as a basis for determining the duration of barrier traversal. A power flux density of 1011 W/m2 would be required at several wavelengths from 1 to 10 ?m. It is possible that thermal effects could be separated from the modeled phenomena by determining the time dependence of the tunneling current with a pulsed laser

  9. 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.

  10. Thin films of metal oxides on metal single crystals: Structure and growth by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Detailed studies of the growth and structure of thin films of metal oxides grown on metal single crystal surfaces using Scanning Tunneling Microscopy (STM) are presented. The oxide overlayer systems studied are iron oxide and titanium oxide on the Pt(III) surface. The complexity of the metal oxides and large lattice mismatches often lead to surface structures with large unit cells. These are particularly suited to a local real space technique such as scanning tunneling microscopy. In particular, the symmetry that is directly observed with the STM elucidates the relationship of the oxide overlayers to the substrate as well as distinguishing, the structures of different oxides

  11. 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.

  12. 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. PMID:23112655

  13. Construction of a four tip scanning tunneling microscope/scanning electron microscope combination and conductivity measurements of silicide nanowires

    International Nuclear Information System (INIS)

    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 with a gate has provided the resistance of the nanowire. From the dimensions of the nanowire the resistivity was calculated. The obtained resistivity was found to be in agreement with literature values. In addition, the contact resistances of the tunneling tips on the silicide nanowires were determined.

  14. Quasiparticle spectra of 2 H -NbSe2 : Two-band superconductivity and the role of tunneling selectivity

    Science.gov (United States)

    Noat, Y.; Silva-Guillén, J. A.; Cren, T.; Cherkez, V.; Brun, C.; Pons, S.; Debontridder, F.; Roditchev, D.; Sacks, W.; Cario, L.; Ordejón, P.; García, A.; Canadell, E.

    2015-10-01

    We have studied the superconducting state of 2 H -NbSe2 by scanning tunneling spectroscopy along two different crystal orientations, the c and the a /b axes. Along the c axis a large gap is dominant in the spectra, while a smaller gap is measured along the a /b axis. We show that these spectra are accurately described by the McMillan model where the small gap is induced through the coupling to the band associated with the large gap. In order to assign the small and large gaps to specific parts of the 2 H -NbSe2 Fermi surface, the electronic structure was studied using first-principles calculations. While we cannot exclude the possibility of intrinsic anisotropy of the gaps, we propose that the large gap opens in the Fermi surface cylinders located around the corner K points while the sheets located around ? are associated with the small gap. An additional component of the Fermi surface, a selenium based pocket, plays an essential role in the tunneling process. The role of the charge density wave occurring in this material is also discussed. Finally, we are able to give a coherent description of the observed characteristics of the tunneling spectra of 2 H -NbSe2 as well as the differences with 2 H -NbS2 where no charge density wave state is present. Further experimental work, such as high-resolution ARPES, would be very useful to confirm our interpretation. The approach and modeling developed here could also be relevant for other compounds of the dichalcogenide family.

  15. 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...

  16. Correlation of scanning-tunneling-microscope image profiles and charge-density-wave amplitudes

    International Nuclear Information System (INIS)

    Scanning-tunneling-microscope (STM) studies of 4Hb-TaS2 and 4Hb-TaSe2 at 4.2 K show systematic correlation between the charge-density-wave (CDW) amplitude and the STM deflection. The 4Hb phases have both weak and strong CDW's in the trigonal prismatic and octahedral sandwiches, respectively. Scans on opposite faces of the same cleave allow a comparison of the STM response to the two types of CDW

  17. Combined Scanning Tunneling and Atomic Force Microscopy and Spectroscopy on Molecular Nanostructures

    OpenAIRE

    Herden, Tobias

    2014-01-01

    Several key aspects in the exciting field of surface science on the nanoscale were addressed during this thesis. The common denominator of this work is the microscope used for the experiments; the combined scanning tunneling and atomic force microscope (STM and AFM). These scanning probe methods allow the study of electronic, magnetic and mechanical properties on surfaces down to the level of an individual atom.In the scope of this thesis and a previous diploma thesis, I designed and built a ...

  18. Fixing the Energy Scale in Scanning Tunneling Microscopy on Semiconductor Surfaces

    Science.gov (United States)

    Münnich, Gerhard; Donarini, Andrea; Wenderoth, Martin; Repp, Jascha

    2013-11-01

    In scanning tunneling experiments on semiconductor surfaces, the energy scale within the tunneling junction is usually unknown due to tip-induced band bending. Here, we experimentally recover the zero point of the energy scale by combining scanning tunneling microscopy with Kelvin probe force spectroscopy. With this technique, we revisit shallow acceptors buried in GaAs. Enhanced acceptor-related conductance is observed in negative, zero, and positive band-bending regimes. An Anderson-Hubbard model is used to rationalize our findings, capturing the crossover between the acceptor state being part of an impurity band for zero band bending and the acceptor state being split off and localized for strong negative or positive band bending, respectively.

  19. Imaging surfaces with reflected electrons from a field emission scanning tunnelling microscope: image contrast mechanisms

    International Nuclear Information System (INIS)

    Electrons backscattered from a scanning tunnelling microscope operating in the field emission mode have been collected to produce images of a rough Si(111) surface. We have obtained a spatial resolution of about 40 nm in such images. Comparison between backscattered electron images and topographic images reveals that edge enhancement and shadowing are important contrast mechanisms. (author)

  20. 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; Jacobsen, Karsten Wedel; Simmons, M.Y.; Hofer, W.A.

    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...

  1. 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.

  2. Streamlined Inexpensive Integration of a Growth Facility and Scanning Tunneling Microscope for in situ Characterization

    CERN Document Server

    Xu, P; Barber, S D; Cook, C T; Ackerman, M L; Thibado, P M

    2015-01-01

    The integration of a scanning tunneling microscope chamber with a sample growth facility using non-custom, commercially available parts is described. The facility also features a newly-designed magnetic wobble stick to increase the reliability of sample transfer in a cost-effective manner.

  3. Characterization and manipulation of individual defects in insulating hexagonal boron nitride using scanning tunnelling microscopy

    Science.gov (United States)

    Wong, Dillon; Velasco, Jairo; Ju, Long; Lee, Juwon; Kahn, Salman; Tsai, Hsin-Zon; Germany, Chad; Taniguchi, Takashi; Watanabe, Kenji; Zettl, Alex; Wang, Feng; Crommie, Michael F.

    2015-11-01

    Defects play a key role in determining the properties and technological applications of nanoscale materials and, because they tend to be highly localized, characterizing them at the single-defect level is of particular importance. Scanning tunnelling microscopy has long been used to image the electronic structure of individual point defects in conductors, semiconductors and ultrathin films, but such single-defect electronic characterization remains an elusive goal for intrinsic bulk insulators. Here, we show that individual native defects in an intrinsic bulk hexagonal boron nitride insulator can be characterized and manipulated using a scanning tunnelling microscope. This would typically be impossible due to the lack of a conducting drain path for electrical current. We overcome this problem by using a graphene/boron nitride heterostructure, which exploits the atomically thin nature of graphene to allow the visualization of defect phenomena in the underlying bulk boron nitride. We observe three different defect structures that we attribute to defects within the bulk insulating boron nitride. Using scanning tunnelling spectroscopy we obtain charge and energy-level information for these boron nitride defect structures. We also show that it is possible to manipulate the defects through voltage pulses applied to the scanning tunnelling microscope tip.

  4. Spatio-temporal imaging of voltage pulses with an ultrafast scanning tunneling microscope

    DEFF Research Database (Denmark)

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

    1997-01-01

    Measurements on an ultrafast scanning tunneling microscope with simultaneous spatial and temporal resolution are presented. We show images of picosecond pulses propagating on a coplanar waveguide and resolve their mode structures. The influence of transmission line discontinuities on the mode...... affect the imaging of the propagating pulses. (C) 1997 American Institute of Physics....

  5. Surface x-ray scattering and scanning tunneling microscopy studies at the Au(111) electrode

    International Nuclear Information System (INIS)

    This chapter reviews Surface X-ray Scattering and Scanning Tunneling Microscopy results carried out at the Au(111) surface under electrochemical conditions. Results are presented for the reconstructed surface, and for bromide and thallium monolayers. These examples are used to illustrate the complementary nature of the techniques

  6. Local investigation of magnetic structures in superconductors by a low-temperature scanning tunneling microscope

    International Nuclear Information System (INIS)

    A low temperature scanning tunneling microscope device was constructed which allows a simultaneous spectroscopic and morphological measurement up to 4.2 K and 1T. Layers of niobium and NbSe2 were measured and flux lines were determined. (WL)

  7. DEVELOPMENT OF THE FIELD ION-SCANNING TUNNELING MICROSCOPE AND ITS APPLICATIONS

    OpenAIRE

    Kamiya, I.; Sakurai, T.

    1989-01-01

    A scanning tunneling microscope (STM) equipped with a field ion microscope (FIM) which operates at room temperature has been constructed and operated successfully to obtain atomically resolved STM images with 100% reproductibility. This instrument, which we call the FI-STM, has been employed for the quantitative study of the Si(100) "2xn" phase.

  8. Spin-sensitive tunneling through individual terbium-phthalocyanine molecules by spin-polarized scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Terbium-Phthalocyanine double-decker molecules (TbPc2) belong to the class of single-molecule magnets, which could serve as the smallest building blocks of future information technology devices such as for quantum computers and data storage. Because of its high blocking temperature (>10 K), TbPc2 attracted considerable interests in recent years. Here, we locally address TbPc2 adsorbed on a ferromagnetic surface (Co nanoislands) with spin-polarized scanning tunneling microscopy. We detect a significant spin contrast by tunneling through TbPc2 molecules with intramolecular resolution. Thereby, the spin-polarization depends on the energy and the position within the molecule. We present our experimental data and discuss the origin of the magnetic contrast observed.

  9. Scanning tunnelling microscopy of real time defect motion on surfaces

    International Nuclear Information System (INIS)

    Full text: The Interface Physics group uses various types of Scanning Probe Microscopy to investigate the structure and dynamic behaviour of surfaces and interfaces. Topics that they are working on at present include surface diffusion, surface phase transitions, gas-surface interactions, nanotribology, and nanobiology. For example, from accurate measurements of the statistics of the observed jump lengths and of the waiting times between successive jumps, it has been deduced that the mobility of indium atoms on a copper surface is caused by the rapid, two-dimensional diffusion of a very low density of monatomic vacancies (missing copper atoms), through the first copper layer. Due to their ultrahigh diffusion rate, these vacancies remain 'invisible' for the STM at room temperature. It is important to realize that the slide-puzzle diffusion mechanism is also active when there is no embedded indium in the copper surface. The indium merely serves as a low density of 'tracer' particles, which enable us to follow the rearrangements continually taking place in the surface. What we learn from these observations is that not only adatoms, but also the atoms in a close-packed terrace of a metal surface are mobile at relatively low temperatures, e.g. room temperature. Copyright (2005) Australian Institute of Physics

  10. High frequency transmission to a junction of a scanning tunneling microscope

    Science.gov (United States)

    Hervé, M.; Peter, M.; Wulfhekel, W.

    2015-08-01

    We report on an easy method to calibrate the transmission of radio-frequency (rf) voltages to the tunneling junction of a scanning tunneling microscope. The transmission strongly depends on frequency, as the cabling shows frequency dependent damping and the impedance mismatch between the cable and the tunneling junction induces reflections. To first order, the current-voltage characteristic of the junction induces a rf tunneling current of the same frequency as the rf voltage. Omnipresent non-linearities of the current-voltage characteristic of the junction to second order, however, generate an additional rectified DC. A direct comparison between this current and the second derivative of the current-voltage curve allows to determine the rf transmission to the tunneling junction. The transmission data up to 2 GHz were used to compensate the rf damping such that at every frequency a constant amplitude at the tunneling junction could be realized expanding the bandwidth of the experiment from less then 100 MHz to 2 GHz.

  11. Superconducting LiFeAs as seen by scanning tunneling microscopy/spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Pohle, Rico; Scheffler, Martha; Schlegel, Ronny; Haenke, Torben; Baumann, Danny; Bachmann, Anne; Bombor, Dirk; Sykora, Steffen; Harnagea, Luminita; Wurmehl, Sabine; Hess, Christian; Buechner, Bernd [Institut fuer Festkoerperforschung IFW Dresden (Germany)

    2012-07-01

    Among the entire class of iron-based superconductors the material LiFeAs is of particular interest since an absence of nesting between electron and hole pockets suggests an unconventional type of pairing in this material. Using Scanning Tunnelling Microscopy (STM) and Spectroscopy (STS) we investigate topographic properties of the surface as well as the temperature dependency of the superconducting gap. The good agreement of our results with model calculations for the tunnelling conductance allows us to draw conclusions about the low energy properties of the superconducting system. Furthermore, we compare our results with Transport- and NMR-measurements.

  12. A Mechanism for Cutting Carbon Nanotubes with a Scanning Tunneling Microscope

    CERN Document Server

    Rubio, A; Venema, L C; Dekker, C; Rubio, Angel; Venema, Liesbeth C.; Dekker, Cees

    2000-01-01

    We discuss the local cutting of single-walled carbon nanotubes by a voltage pulse to the tip of a scanning tunneling microscope. The tip voltage ($\\mid V reviewing several possible physical mechanisms we conclude that the cutting process relies on the weakening of the carbon-carbon bonds through a combination of localized particle-hole excitations induced by inelastically tunneling electrons and elastic deformation due to the electric field between tip and sample. The carbon network releases part of the induced mechanical stress by forming topological defects that act as nucleation centers for the formation of dislocations that dynamically propagate towards bond-breaking.

  13. Nanolithography on SrRuO3 thin film surfaces by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Nanolithography on SrRuO3 (SRO) thin film surfaces has been performed by a scanning tunneling microscope under ambient conditions. The depth of etched lines increases with increasing bias voltage but it does not change significantly by increasing the tunneling current. The dependence of line-width on bias voltage from experimental data is in agreement with theoretical calculation based on field-induced evaporation mechanism. Moreover, a three-square nanostructure was successfully created, showing the capability of fabricating nanodevices in SRO thin films.

  14. Scanning tunneling microscopy on rough surfaces: Deconvolution of constant current images

    Science.gov (United States)

    Reiss, G.; Schneider, F.; Vancea, J.; Hoffmann, H.

    1990-08-01

    This letter critically discusses the topographical information obtained by scanning tunneling microscopy (STM) on surfaces with a mesoscopic roughness, i.e., in the range of some nm's. In a foregoing publication [J. Appl. Phys. 67, 1156 (1990)], we already treated the evaluation of constant current images based on the knowledge of the real surface and the shape of the tunneling tip (``tip shape limited resolution''). Now we deal with the invers problem: the reconstruction of the real surface topography based on the corresponding STM image and the tip shape, using a simple, straightforward formalism.

  15. Superconducting LiFeAs as seen by scanning tunneling microscopy/spectroscopy

    International Nuclear Information System (INIS)

    Among the entire class of iron-based superconductors the material LiFeAs is of particular interest since an absence of nesting between electron and hole pockets suggests an unconventional type of pairing in this material. Using Scanning Tunnelling Microscopy (STM) and Spectroscopy (STS) we investigate topographic properties of the surface as well as the temperature dependency of the superconducting gap. The good agreement of our results with model calculations for the tunnelling conductance allows us to draw conclusions about the low energy properties of the superconducting system. Furthermore, we compare our results with Transport- and NMR-measurements.

  16. Scanning tunneling spectroscopy of the vortex state in NbSe2 using a superconducting tip

    International Nuclear Information System (INIS)

    The vortex electronic structure in the multiband superconductor NbSe2 is studied by means of scanning tunneling spectroscopy (STS) using a superconducting tip. The use of a superconducting tip (Pb) as a probe provides an enhancement of the different features related to the DOS of NbSe2 in the tunneling conductance curves. This use allows the observation of rich patterns of electronic states in the conductance images around the vortex cores in a wide range of temperature, as well as the simultaneous acquisition of Josephson current images in the vortex state

  17. 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.

  18. Capacitance spectroscopy in quantum dots Addition spectra and decrease of tunneling rates

    CERN Document Server

    Palacios, J; Chiappe, G; Louis, E; Tejedor, C

    1994-01-01

    A theoretical study of single electron capacitance spectroscopy in quantum dots is presented. Exact diagonalizations and the unrestricted Hartree-Fock approximation have been used to shed light over some of the unresolved aspects. The addition spectra of up to 15 electrons is obtained and compared with the experiment. We show evidence for understanding the decrease of the single electron tunneling rates in terms of the behavior of the spectral weight function. (To appear in Phys. Rev. B (Rapid Comm.))

  19. 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 envisaged. AFM observations of thin-film surfaces give us a picture of surface topography and morphology and any visible defects. The growing importance of ultra-thin films for magnetic recording in hard disk drive systems requires an in-depth understanding of the fundamental mechanisms occurring during growth. This special issue of Journal of Physics D: Applied Physics covers all of the different aspects of SPM that illustrate the achievements of this methodology: nanoscale imaging and mapping (Chiang, and Douillard and Charra), piezoresponse force microscopy (Soergel) and STM engineering (Okuyama and Hamada, and Huang et al). Chiang takes the reader on a journey along the STM imaging of atoms and molecules on surfaces. Jesse and Kalinin explore the band excitations that occur during the corresponding processes. Jia et al propose STM and molecular beam epitaxy as a winning experimental combination at the interface of science and technology. Douillard and Charra describe the high-resolution mapping of plasmonic modes using photoemission and scanning tunnelling microscopy. Cricenti et al demonstrate the importance of SPM in material science and biology. Wiebe et al have probed atomic scale magnetism, revealed by spin polarized scanning tunnelling microscopy. In addition, Simon et al present Fourier transform scanning tunnelling spectroscopy and the possibility to obtain constant energy maps and band dispersion using local measurements. Lackinger and Heckl give a perspective of the use of STM to study covalent intermolecular coupling reactions on surfaces. Okuyama and Hamada investigated hydrogen bond imaging and engineering with STM. Soergel describes the study of substrate-dependent self-assembled CuPc molecules using piezo force microscope (PFM). We are very grateful to the authors and reviewers for the papers in this special issue of Journal of Physics D: Applied Physics. Their contributions have provided a comprehensive picture of the evolution, status and potential of scanning probe microscopy, conveying to the readers the full excitement of this forefront do

  20. 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. PMID:26861537

  1. Thermal mirror buckling in freestanding graphene locally controlled by scanning tunnelling microscopy

    Science.gov (United States)

    Neek-Amal, M.; Xu, P.; Schoelz, J. K.; Ackerman, M. L.; Barber, S. D.; Thibado, P. M.; Sadeghi, A.; Peeters, F. M.

    2014-09-01

    Knowledge of and control over the curvature of ripples in freestanding graphene are desirable for fabricating and designing flexible electronic devices, and recent progress in these pursuits has been achieved using several advanced techniques such as scanning tunnelling microscopy. The electrostatic forces induced through a bias voltage (or gate voltage) were used to manipulate the interaction of freestanding graphene with a tip (substrate). Such forces can cause large movements and sudden changes in curvature through mirror buckling. Here we explore an alternative mechanism, thermal load, to control the curvature of graphene. We demonstrate thermal mirror buckling of graphene by scanning tunnelling microscopy and large-scale molecular dynamic simulations. The negative thermal expansion coefficient of graphene is an essential ingredient in explaining the observed effects. This new control mechanism represents a fundamental advance in understanding the influence of temperature gradients on the dynamics of freestanding graphene and future applications with electro-thermal-mechanical nanodevices.

  2. Creation of stable molecular junctions with a custom-designed scanning tunneling microscope

    International Nuclear Information System (INIS)

    The scanning tunneling microscope break junction (STMBJ) technique is a powerful approach for creating single-molecule junctions and studying electrical transport in them. However, junctions created using the STMBJ technique are usually mechanically stable for relatively short times (<1 s), impeding detailed studies of their charge transport characteristics. Here, we report a custom-designed scanning tunneling microscope that enables the creation of metal–single molecule–metal junctions that are mechanically stable for more than 1 minute at room temperature. This stability is achieved by a design that minimizes thermal drift as well as the effect of environmental perturbations. The utility of this instrument is demonstrated by performing transition voltage spectroscopy—at the single-molecule level—on Au–hexanedithiol–Au, Au–octanedithiol–Au and Au–decanedithiol–Au junctions.

  3. Manipulating individual dichlorotin phthalocyanine molecules on Cu(100) surface at room temperature by scanning tunneling microscopy

    Science.gov (United States)

    Li, Chao; Xiang, Feifei; Wang, Zhongping; Liu, Xiaoqing; Jiang, Danfeng; Wang, Guang; Zhang, Xueao; Chen, Wei; Wang, Li

    2014-12-01

    Single molecule manipulations have been achieved on dichlorotin phthalocyanine(SnCl2Pc) molecules adsorbed on Cu (100) at room temperature. Scanning tunneling microscopy observations directly demonstrate that the individual SnCl2Pc molecules can be moved along the [100] direction on Cu(100) surface by employing a scanning tunneling microscope tip fixed at the special position of the molecules. The orientation of the molecule can be switched between two angles of ±28° with respect to the [011] surface direction in the same way. Dependences of the probability of molecular motion on the distances between the tip and the molecules reveal that the mechanism for such manipulation of a SnCl2Pc molecule is dominated by the repulsive interactions between the tip and the molecules. With the assistance of this manipulation process, a prototype molecular storage array with molecular orientation as information carrier and an artificial hydrogen bonded supramolecular structure have been constructed on the surface.

  4. Negative Differential Resistance in the Scanning Tunneling Spectroscopy of Organic molecules

    CERN Document Server

    Xue, Y; Hong, S; Reifenberger, R; Henderson, J I; Kubiak, C P; Xue, Yongqiang; Datta, Supriyo; Hong, Seunghun; Henderson, Jason I.; Kubiak, Cliff P.

    1999-01-01

    The conductance-voltage spectrum of molecular nanostructures measured by scanning tunneling spectroscopy (STS) is generally assumed to reflect the local density of states of the molecule. This excludes the possibility of observing negative differential resistance (NDR). We report here the observation of NDR in the scanning tunneling microscope (STM) current-voltage (I-V) characteristics of self-assembled monolayer (SAM) of 4-p-Terphenylthiol molecules on gold substrate measured using a platinum probe. We argue that the NDR arises from narrow structures in the local density of states at the tip apex atom and show that depending on the electrostatic potential profile across the system, NDR could be observed in one or both bias directions.

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

    DEFF Research Database (Denmark)

    Andersen, Jens Enevold Thaulov

    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 to.......g., nanoelectronics and single-molecule probing. In principle, the ESTM is capable of sub-atomic resolution but many details at this level of magnification need further treatment of recorded data before real information is obtained. Deconvolution of the data according to the instrument response may explain some of...... current that generates the image. Tunneling through less-conductive molecules, such as organic molecules, DNA molecules or protein molecules, may be facilitated along channels of electronic conductivity or by transfer of protons generated electrochemically at the participating surfaces....

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

    OpenAIRE

    Thomas König; Simon, Georg H; Lars Heinke; Leonid Lichtenstein; Markus Heyde

    2011-01-01

    Surfaces of thin oxide ?lms 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., ...

  7. Magnetic Tunnel Junctions and Superconductor/Ferromagnet Hybrids Investigated by Low-Temperature Scanning Laser Microscopy

    OpenAIRE

    Werner, Robert

    2011-01-01

    Low-temperature scanning laser microscopy (LTSLM) allows the investigation of local properties in thin film structures in a broad temperature range. Depending on the sample under investigation, LTSLM can map various kinds of physical properties such as the current distribution or the magnetic microstructure. In this thesis, the correlation between local and integral magnetotransport properties in thin-film superconductor/ferromagnet (S/F) hybrids and magnetic tunnel junctions are investigated...

  8. Thermal mirror buckling in freestanding graphene locally controlled by scanning tunneling microscopy

    OpenAIRE

    Neek-Amal, M.; Xu, P.; Schoelz, J. K.; Ackerman, M. L.; Barber, S. D.; Thibado, P. M.; Sadeghi, A.; Peeters, F. M.

    2014-01-01

    Knowledge of and control over the curvature of ripples in freestanding graphene are desirable for fabricating and designing flexible electronic devices, and recent progress in these pursuits has been achieved using several advanced techniques such as scanning tunneling microscopy. The electrostatic forces induced through a bias voltage (or gate voltage) were used to manipulate the interaction of freestanding graphene with a tip (substrate). Such forces can cause large moveme...

  9. Scanning Tunneling Microscopy Evidence for the Dissociation of Carbon Monoxide on Ruthenium Steps

    DEFF Research Database (Denmark)

    Tison, Yann; Nielsen, Kenneth; Mowbray, Duncan J.; Bech, Lone; Holse, Christian; Vallejo, Federico Calle; Andersen, Kirsten; Mortensen, Jens J.; Jacobsen, Karsten W.; Nielsen, Jane H.

    2012-01-01

    In heterogeneous catalysis, identifying the active site for key reaction steps is an important contribution for the optimization of industrial synthesis. The structure sensitivity of CO dissociation on a metal catalyst, which is the rate-limiting step for the methanation and the Fischer–Tropsch processes under certain conditions, has been debated for years. Here, scanning tunneling microscopy (STM) and density functional theory (DFT) are used to clarify the role of monatomic steps in the splitti...

  10. Submonolayer growth of Pd on Cu(111) studied by scanning tunneling microscopy

    DEFF Research Database (Denmark)

    Lægsgaard, E.; Ruban, Andrei; Stensgaard, I.

    1998-01-01

    The growth mode of sub-monolayer amounts of Pd on Cu(111) in the temperature range - 80-300 degrees C has been investigated by scanning tunneling microscopy (STM), Rutherford backscattering spectroscopy (RBS) and Auger electron spectroscopy (AES). Below approximate to 100 degrees C, the Pd induced phase nucleates at ascending steps in fingered brims and, on large terraces, in fingered islands. The lack of order suggests that the brims and islands are a disordered alloy formed by exchange between...

  11. Note: Fabrication and characterization of molybdenum tips for scanning tunneling microscopy and spectroscopy

    International Nuclear Information System (INIS)

    We present a method for the preparation of bulk molybdenum tips for Scanning Tunneling Microscopy and Spectroscopy and we assess their potential in performing high resolution imaging and local spectroscopy by measurements on different single crystal surfaces in UHV, namely, Au(111), Si(111)-7 × 7, and titanium oxide 2D ordered nanostructures supported on Au(111). The fabrication method is versatile and can be extended to other metals, e.g., cobalt

  12. Local Tunneling Magnetoresistance probed by Low-Temperature Scanning Laser Microscopy

    OpenAIRE

    Werner, Robert; Weiler, Mathias; Petrov, Aleksandr Yu.; Davidson, Bruce A; Gross, Rudolf; Kleiner, Reinhold; Goennenwein, Sebastian T. B.; Koelle, Dieter

    2011-01-01

    Tunneling magnetoresistance (TMR) in a vertical manganite junction was investigated by low-temperature scanning laser microscopy (LTSLM) allowing to determine the local relative magnetization M orientation of the two electrodes as a function of magnitude and orientation of the external magnetic field H. Sweeping the field amplitude at fixed orientation revealed magnetic domain nucleation and propagation in the junction electrodes. For the high-resistance state an almost sing...

  13. Electroluminescence from a polythiophene molecular wire suspended in a plasmonic scanning tunneling microscope junction

    OpenAIRE

    Reecht, Gaël; Scheurer, Fabrice; Speisser, Virginie; Dappe, Yannick J.; Mathevet, Fabrice; Schull, Guillaume

    2014-01-01

    The electroluminescence of a polythiophene wire suspended between two metallic electrodes is probed using a scanning tunneling microscope. Under positive sample voltage, the spectral and voltage dependencies of the emitted light are consistent with the fluorescence of the wire junction mediated by localized plasmons. This emission is strongly attenuated for the opposite polarity. Both emission mechanism and polarity dependence are similar to what occurs in organic light emit...

  14. 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 dis...

  15. 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...

  16. Clean porphyrin films on a silver (111) surface:a Scanning Tunneling Microscopy study

    OpenAIRE

    Comanici, Karmen

    2007-01-01

    In the work at hand a detailed scanning tunneling microscopy study of films of different porphyrin derivates on a Ag(111) surface has been performed under ultra high vacuum conditions at room temperature. The key focus was put on the porphyrin monolayer regime, the corresponding self-assembled phases and their electronic structure. Thermal sublimation in vacuum was the applied method to prepare films of various porphyrin molecules. With this method, it was possible to obtain films with high p...

  17. Scanning tunnelling microscopy study of phosphorus dopants on the Si(001)2x1 surface

    International Nuclear Information System (INIS)

    Full text: We report an atomic resolution scanning tunnelling microscopy study of phosphorus dopant surface segregation on the silicon (001)2x1 surface. An understanding of the surface segregation of dopants in Si is of fundamental interest and technological importance for the fabrication of a P in Si based quantum computer. Although there are a number of studies of surface segregation of boron in Si, a detailed study of P segregation has not yet been reported

  18. Fermi-level alignment at metal-carbon nanotube interfaces: application to scanning tunneling spectroscopy

    OpenAIRE

    Xue, Yongqiang; Datta, Supriyo

    1999-01-01

    At any metal-carbon nanotube interface there is charge transfer and the induced interfacial field determines the position of the carbon nanotube band structure relative to the metal Fermi-level. In the case of a single-wall carbon nanotube (SWNT) supported on a gold substrate, we show that the charge transfers induce a local electrostatic potential perturbation which gives rise to the observed Fermi-level shift in scanning tunneling spectroscopy (STS) measurements. We also discuss the relevan...

  19. Scanning tunneling microscopy of an ion-bombarded PbS(001) surface

    International Nuclear Information System (INIS)

    Freshly cleaved (001) surfaces of single crystalline PbS were bombarded by 8 keV Kr+ ions at a dose of 3 x 1012 cm-2. Atomically resolved scanning tunneling microscopy (STM) images were taken showing damaged areas due to individual ion impacts. Analysis of a STM image shows a shallow impact crater, a stacking fault, displacement of Pb2+ and S2- ions from their regular surface sites, and migration of interstitials to the surface

  20. H3PW12O40-functionalized tip for scanning tunneling microscopy

    OpenAIRE

    Song, In K.; Kitchin, John R.; Barteau, Mark A.

    2002-01-01

    Recent reports of C60-functionalized metal tips [Kelly, K. F., Sarkar, D., Hale, G. D., Oldenburg, S. J. & Halas, N. J. (1996) Science 273, 1371–1373] and carbon nanotube tips [Dai, H., Hafner, J. H., Rinzler, A. G., Colbert, D. T. & Smalley, R. E. (1996) Nature (London) 384, 147–151] demonstrate the potential of controlling the chemical identity and geometric structure of tip atoms in scanning tunneling microscopy (STM). This work reports the performance of a heteropolyacid (HPA)-functionali...

  1. Nuclear and electronic resonance spectroscopy of single molecules by radio-frequency scanning tunnelling microscopy

    OpenAIRE

    Müllegger, Stefan; Tebi, Stefano; Das, Amal K.; Schöfberger, Wolfgang; Faschinger, Felix; Koch, Reinhold

    2014-01-01

    The ongoing miniaturization in nanoscience and -technology challenges the sensitivity and selectivity of experimental analysis methods to the ultimate level of single atoms and molecules. A promising new approach, addressed here, focuses on the combination of two well-established complementary techniques that have proven to be very successful in their own fields: (i) low-temperature scanning tunneling microscopy (STM), offering high spatial resolution for imaging and spectroscopy together wit...

  2. Structure of hydrated oligonucleotides studied by in situ scanning tunneling microscopy.

    OpenAIRE

    Jing, T W; Jeffrey, A. M.; DeRose, J. A.; Lyubchenko, Y L; Shlyakhtenko, L S; Harrington, R. E.; Appella, E.; LARSEN, J.; Vaught, A; Rekesh, D

    1993-01-01

    We have used the scanning tunneling microscope (STM) to image several synthetic oligonucleotides adsorbed onto a positively charged Au(111) electrode. The molecules were deposited and imaged in aqueous electrolyte under potential control, a procedure that eliminated the problem of the substrate artifacts that had limited some previous STM studies. Experiments were carried out with two types of single-stranded molecules (11 and 20 bases long) and three types of double-stranded molecules (20 an...

  3. Coadsorption phases of CO and oxygen on Pd(111) studied by scanning tunneling microscopy

    OpenAIRE

    Méndez, J.; Kim, S.; Cerdá, J.; Wintterlin, J.; Ertl, G

    2005-01-01

    The adsorption of CO on an oxygen precovered Pd(111) surface was investigated between 60 and 300 K. Applied methods were variable temperature scanning tunneling microscopy (STM) and video STM to analyze the coadsorption structures. The STM data are compared with simulated STM images for the various surface phases in order to identify the appropiate structural model for each case. Low-energy electron diffraction and reaction isotherms by means of mass spectrometry were used to correlate the ph...

  4. Masking generates contiguous segments of metal-coated and bare DNA for scanning tunneling microscope imaging.

    OpenAIRE

    Dunlap, D D; García, R.; Schabtach, E; Bustamante, C.

    1993-01-01

    To date, no microscopic methods are available to confirm scanning tunneling microscope (STM) images of DNA. The difficulties encountered in repeating these images may be attributed to inadequate distribution of molecules on the substrate, poor adhesion to the substrate, or the low conductivity of the molecules. However, these factors are difficult to assess in an STM experiment where they may act simultaneously. A method to isolate these factors involves partly masking the deposited molecules...

  5. Scanning tunneling microscopy and spectroscopy of functional molecules on metal surfaces

    OpenAIRE

    Ge, Xin

    2007-01-01

    This thesis is committed to the study of functional molecules adsorbed on metal surfaces by means of Low Temperature Scanning Tunneling Microscopy. It includes two main parts. In the first part the adsorption geometry of lander molecule (C90H98) on different metal surfaces is discussed. Three conformations as well as chiral structures of lander molecules on the terrace of Cu(100) are observed by STM. Electron scattering quantum chemical calculated results are compared with our experimental da...

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

    DEFF Research Database (Denmark)

    Haiss, W.; Albrecht, Tim; van Zalinge, H.; Higgins, S.J.; Bethell, D.; Hobenreich, H.; Schiffrin, D.J.; Nichols, Richard John; Kuznetsov, A.M.; Zhang, Jingdong; Chi, Qijin; Ulstrup, Jens

    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 transport across the molecular bridge through control of the electrochemical potential and consequently the redox state of the viologen moiety. This gating is theoretically considered within the framework of sup...

  7. Note: Fabrication and characterization of molybdenum tips for scanning tunneling microscopy and spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Carrozzo, P.; Tumino, F.; Facibeni, A.; Passoni, M.; Casari, C. S.; Li Bassi, A. [Dipartimento di Energia, Politecnico di Milano, via Ponzio 34/3, I-20133 Milan (Italy)

    2015-01-15

    We present a method for the preparation of bulk molybdenum tips for Scanning Tunneling Microscopy and Spectroscopy and we assess their potential in performing high resolution imaging and local spectroscopy by measurements on different single crystal surfaces in UHV, namely, Au(111), Si(111)-7 × 7, and titanium oxide 2D ordered nanostructures supported on Au(111). The fabrication method is versatile and can be extended to other metals, e.g., cobalt.

  8. Phase change of tetrahedral amorphous-carbon by low energy electrons in a scanning tunnelling microscope

    International Nuclear Information System (INIS)

    Low energy electron-based energy deposition in tetrahedral amorphous-carbon thin films by a scanning tunnelling microscope leads to a local phase change of the carbon. Both the mass density and the electrical resistivity are reduced indicating a graphitization. We expose nano-sized surface areas to field emitted low energy electrons under high vacuum conditions and investigate the temperature and electron energy dependence of the carbon phase change process. Supplementary topography measurements are performed by atomic force microscopy.

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

    DEFF Research Database (Denmark)

    Settnes, Mikkel; Power, Stephen R.; Petersen, Dirch Hjorth; Jauho, Antti-Pekka

    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 finite length scales yields real space conductance maps which show anisotropy for pristine graphene systems and quantum interference effects in the presence of isolated impurities. Spectral signatures in the ...

  10. Scanning tunnelling microscopy and electronic structure of Mn clusters on Ag(111)

    Energy Technology Data Exchange (ETDEWEB)

    Kliewer, J.; Berndt, R. [Christian-Albrechts-Universitaet zu Kiel, Institut fuer Experimentelle und Angewandte Physik, Kiel (Germany); Minar, J.; Ebert, H. [University of Munich, Dept. Chemie und Biochemie, Muenchen (Germany)

    2006-01-01

    Small Mn clusters (Mn{sub 1}-Mn{sub 4}) are prepared by manipulation of Mn adatoms on Ag(111) with the tip of a scanning tunnelling microscope. The apparent heights of the clusters are observed to increase monotonously from 1.6 A for a monomer to 2.2 A for a tetramer. Self-consistent calculations of the electronic structure of these clusters are in encouraging agreement with the experimental data. (orig.)

  11. Tip preparation for usage in an ultra-low temperature UHV scanning tunneling microscope

    OpenAIRE

    S. Ernst, S. Wirth, M. Rams, V. Dolocan and F. Steglich

    2007-01-01

    This work deals with the preparation and characterization of tungsten tips for the use in UHV low-temperature scanning tunneling microscopy and spectroscopy (STM and STS, respectively). These specific environments require in situ facilities for tip conditioning, for further sharpening of the tips, as well as for reliable tip characterization. The implemented conditioning methods include direct resistive annealing, annealing by electron bombardment, and self-sputtering with noble gas ions. Mor...

  12. Atomic resolution scanning tunneling microscopy in a cryogen free dilution refrigerator at 15 mK

    Energy Technology Data Exchange (ETDEWEB)

    Haan, A. M. J. den, E-mail: arthur.denhaan@gmail.com; Wijts, G. H. C. J.; Galli, F.; Oosterkamp, T. H. [Department of Interface Physics, Leiden University, Niels Bohrweg 2, 2333CA Leiden (Netherlands); Usenko, O. [Leiden Cryogenics, Kenauweg 11, 2331BA Leiden (Netherlands); Baarle, G. J. C. van; Zalm, D. J. van der [Leiden Spin Imaging (LSI), J.H. Oortweg 21, 2333CH Leiden (Netherlands)

    2014-03-15

    Pulse tube refrigerators are becoming more common, because they are cost efficient and demand less handling than conventional (wet) refrigerators. However, a downside of a pulse tube system is the vibration level at the cold-head, which is in most designs several micrometers. We implemented vibration isolation techniques which significantly reduced vibration levels at the experiment. These optimizations were necessary for the vibration sensitive magnetic resonance force microscopy experiments at milli-kelvin temperatures for which the cryostat is intended. With these modifications we show atomic resolution scanning tunneling microscopy on graphite. This is promising for scanning probe microscopy applications at very low temperatures.

  13. Nanocatalysis by the Tip of a Scanning Tunneling Microscope Operating Inside a Reactor Cell

    Science.gov (United States)

    McIntyre, B. J.; Salmeron, M.; Somorjai, G. A.

    1994-09-01

    The platinum-rhodium tip of a scanning tunneling microscope that operates inside of an atmospheric-pressure chemical reactor cell has been used to locally rehydrogenate carbonaceous fragments deposited on the (111) surface of platinum. The carbon fragments were produced by partial dehydrogenation of propylene. The reactant gas environment inside the cell consisted of pure H_2 or a 1:9 mixture of CH_3CHCH_2 and H_2 at 300 kelvin. The platinum-rhodium tip acted as a catalyst after activation by short voltage pulses. In this active state, the clusters in the area scanned by the tip were reacted away with very high spatial resolution.

  14. Local Ionization Dynamics Traced by Photoassisted Scanning Tunneling Microscopy: A Theoretical Approach

    CERN Document Server

    Schueler, M; Berakdar, J

    2013-01-01

    For tracing the spatiotemporal evolution of electronic systems, we suggest and analyze theoretically a setup that exploits the excellent spatial resolution based on scanning tunneling microscopy techniques combined with the temporal resolution of femtosecond pump-probe photoelectron spectroscopy. As an example, we consider the laser-induced, local vibrational dynamics of a surface-adsorbed molecule. The photoelectrons released by a laser pulse can be collected by the scanning tip and utilized to access the spatiotemporal dynamics. Our proof-of-principle calculations are based on the solution of the time-dependent Schrooedinger equation supported by the ab initio computation of the matrix elements determining the dynamics.

  15. A 10Â mK scanning tunneling microscope operating in ultra high vacuum and high magnetic fields

    Science.gov (United States)

    Assig, Maximilian; Etzkorn, Markus; Enders, Axel; Stiepany, Wolfgang; Ast, Christian R.; Kern, Klaus

    2013-03-01

    We present design and performance of a scanning tunneling microscope (STM) that operates at temperatures down to 10 mK providing ultimate energy resolution on the atomic scale. The STM is attached to a dilution refrigerator with direct access to an ultra high vacuum chamber allowing in situ sample preparation. High magnetic fields of up to 14 T perpendicular and up to 0.5 T parallel to the sample surface can be applied. Temperature sensors mounted directly at the tip and sample position verified the base temperature within a small error margin. Using a superconducting Al tip and a metallic Cu(111) sample, we determined an effective temperature of 38 ± 1 mK from the thermal broadening observed in the tunneling spectra. This results in an upper limit for the energy resolution of ?E = 3.5kBT = 11.4 ± 0.3 ?eV. The stability between tip and sample is 4 pm at a temperature of 15 mK as demonstrated by topography measurements on a Cu(111) surface.

  16. A 10 mK scanning tunneling microscope operating in ultra high vacuum and high magnetic fields.

    Science.gov (United States)

    Assig, Maximilian; Etzkorn, Markus; Enders, Axel; Stiepany, Wolfgang; Ast, Christian R; Kern, Klaus

    2013-03-01

    We present design and performance of a scanning tunneling microscope (STM) that operates at temperatures down to 10 mK providing ultimate energy resolution on the atomic scale. The STM is attached to a dilution refrigerator with direct access to an ultra high vacuum chamber allowing in situ sample preparation. High magnetic fields of up to 14 T perpendicular and up to 0.5 T parallel to the sample surface can be applied. Temperature sensors mounted directly at the tip and sample position verified the base temperature within a small error margin. Using a superconducting Al tip and a metallic Cu(111) sample, we determined an effective temperature of 38 ± 1 mK from the thermal broadening observed in the tunneling spectra. This results in an upper limit for the energy resolution of ?E = 3.5 kBT = 11.4 ± 0.3 ?eV. The stability between tip and sample is 4 pm at a temperature of 15 mK as demonstrated by topography measurements on a Cu(111) surface. PMID:23556826

  17. Building a 3d Reference Model for Canal Tunnel Surveying Using Sonar and Laser Scanning

    Science.gov (United States)

    Moisan, E.; Charbonnier, P.; Foucher, P.; Grussenmeyer, P.; Guillemin, S.; Koehl, M.

    2015-04-01

    Maintaining canal tunnels is not only a matter of cultural and historical preservation, but also a commercial necessity and a security issue. This contribution adresses the problem of building a full 3D reference model of a canal tunnel by merging SONAR (for underwater data recording) and LASER data (for the above-water parts). Although both scanning devices produce point clouds, their properties are rather different. In particular, SONAR data are very noisy and their processing raises several issues related to the device capacities, the acquisition setup and the tubular shape of the tunnel. The proposed methodology relies on a denoising step by meshing, followed by the registration of SONAR data with the geo-referenced LASER data. Since there is no overlap between point clouds, a 3-step procedure is proposed to robustly estimate the registration parameters. In this paper, we report a first experimental survey, which concerned the entrance of a canal tunnel. The obtained results are promising and the analysis of the method raises several improvement directions that will help obtaining more accurate models, in a more automated fashion, in the limits of the involved technology.

  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. Fabrication of nanoscale alumina on NiAl(1 0 0) with a scanning tunneling microscope

    International Nuclear Information System (INIS)

    Highlights: ? Nanoscale alumina was fabricated on NiAl(1 0 0) surface with a STM tip. ? Varied powers (bias × current) give two distinct modes of oxidation. ? In the high-power mode alumina forms on the surface near the tip. ? In the low-power mode alumina grows along direction [0 0 1] or [0 1 0] of NiAl(1 0 0). ? The grown alumina strips have minimal width about 3 nm. - Abstract: Nanoscale alumina was fabricated on NiAl (1 0 0) surface using a scanning tunneling microscope in an ultrathin vacuum condition. With the tunneling current greater than 0.4 nA and the power (bias voltage × tunneling current) greater than 0.24 nW, Al and pre-adsorbed O atoms were activated to form alumina (with thickness 0.25–1.0 nm) on the surface directly vicinal to the tip; the width and thickness of the grown alumina strips are controllable by the current and bias. With an evidently smaller power and a smaller bias (?1.0 V), crystalline alumina were grown along direction [0 0 1] or [0 1 0] of NiAl(1 0 0) in the tip-scanned area of either O-chemisorbed or oxidized surfaces, independent of the direction of tip movement. The alumina strips grown through the latter mode have minimal width near 3 nm.

  20. Resonance tunneling spectroscopy of heteropoly compounds

    Science.gov (United States)

    Dalidchik, F. I.; Budanov, B. A.; Kolchenko, N. N.; Balashov, E. M.; Kovalevskii, S. A.

    2012-12-01

    The electron tunneling spectra of phosphomolybdic and phosphomolybdovanadic acids have been measured using a scanning tunneling microscope. A new mechanism of negative differential resistance (NDR) formation in tunneling nanocontacts is established, which is general for all systems featuring the Wannier-Stark localization effect. A two-center inelastic resonance tunneling model is constructed, which allows the values of both electron and vibrational energy parameters to be determined from the measured spectra.

  1. Resonance tunneling spectroscopy of heteropoly compounds

    Energy Technology Data Exchange (ETDEWEB)

    Dalidchik, F. I., E-mail: domfdal@mail.ru; Budanov, B. A.; Kolchenko, N. N.; Balashov, E. M.; Kovalevskii, S. A. [Russian Academy of Sciences, Semenov Institute of Chemical Physics (Russian Federation)

    2012-12-15

    The electron tunneling spectra of phosphomolybdic and phosphomolybdovanadic acids have been measured using a scanning tunneling microscope. A new mechanism of negative differential resistance (NDR) formation in tunneling nanocontacts is established, which is general for all systems featuring the Wannier-Stark localization effect. A two-center inelastic resonance tunneling model is constructed, which allows the values of both electron and vibrational energy parameters to be determined from the measured spectra.

  2. Electromagnetic properties of scanning tunneling microscope tip-sample gap in the terahertz frequency range

    Science.gov (United States)

    Uehara, Yoichi; Katano, Satoshi; Kuwahara, Masashi; Suzuki, Tetsu

    2015-08-01

    We have investigated electromagnetic properties of the tip-sample gap of a scanning tunneling microscope (STM) in the terahertz (THz) spectral range. Light in the STM is emitted from the current source excited by tunneling electrons through dipole radiation processes. The antenna factor that measures the efficiency of the dipole radiation contains a factor proportional to the square of the angular frequency ? of the STM light. Hence, it might occur that STM light emissions in the THz spectral range become undetectably weak. The antenna factors for samples of Au and TiO2, whose plasma frequencies are in the UV and THz spectral ranges, respectively, were investigated as a function of the radius a of curvarure of the W tip. We have found that the effect of ?2 in the antenna factor can be compensated for using a tip having an a of approximately 1500 nm.

  3. Electronic effects in scanning tunneling microscopy: Moiré pattern on a graphite surface

    Science.gov (United States)

    Rong, Zhao Y.; Kuiper, Pieter

    1993-12-01

    We observed by scanning tunneling microscopy (STM) a hexagonal superlattice on graphite with a period of 66 Å. Direct measurement of the angle between lattice vectors confirmed that the superlattice is a Moiré pattern caused by a 2.1° rotation of the topmost (0001) plane with respect to the bulk. The STM corrugation of 2.6 Å is not due to physical buckling, but to differences in electronic structure between AA-stacked, normal AB-stacked, and rhombohedral CAB-stacked graphite. The high tunneling current of AA-stacked regions is in agreement with the high density of states at the Fermi level calculated for AA graphite. The Moiré pattern changes, both the amplitude and the shape, with bias voltage. The observation provides a basis for a comparative study of surface electronic structures with different subsurface layer configuration, which is a vital test of our understanding of STM.

  4. Thermal mirror buckling transitions in a pristine freestanding graphene membrane investigated by scanning tunneling microscopy

    Science.gov (United States)

    Schoelz, Kevin; Meunier, Vincent; Kumar, Pradeep; Neek-Amal, Mehdhi; Thibado, Paul; Peeters, Francois

    2015-03-01

    Freestanding graphene membranes are not flat, but rather display an array of ripples with alternating curvature. By applying a local force using a scanning tunneling microscope tip, we can pull out these ripples, causing the graphene membrane to reversibly rise and fall. By increasing the tunneling current and exploiting the negative coefficient of thermal expansion, we can increase the strain in the graphene membrane causing an irreversible transition from this flexible state to a rigid configuration. This transition typically happens when the graphene membrane reaches 60-70% of the total graphene height. We successfully model this transition as the transition of a spin-half Ising magnet where the ripples are modeled as Ising spins. The buckling transition can be interpreted as the transition from an antiferromagnetic state, to a ferromagnetic state. In addition, four critical exponents are measured. These results provide insight into the role of the negative thermal expansion of graphene.

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

    International Nuclear Information System (INIS)

    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 La0.625Ca0.375MnO3 grown on (001) SrTiO3 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

  6. Imaging by in situ Scanning Tunnelling Microscopy and its Nanotechnological Perspectives

    DEFF Research Database (Denmark)

    Andersen, Jens Enevold Thaulov

    2002-01-01

    resolution at Au(111) in electrolyte, imaging of bulk-metal electrocrystallisation, imaging of pulse plating and imaging of single-molecule metalloproteins in the adsorbed state. Methods of covalent immobilisation of proteins, which enables imaging by in situ STM were developed. The combination of......The development of in situ Scanning Tunneling Microscopy (in situ STM) and the implementation to scientific investigations is documented. The term ‘in situ’ that is added to the STM refers to an advanced development of the microscope, which encompasses tip coating and bipotentiostatic control of...... bipotentiostat construction were evaluated. After the fulfilment of the instrument manufacturing process followed application of the system to scientific investigations. The generation of an image by in situ STM is founded on the principle of electron tunneling but the application of the instrument to aqueous...

  7. Scanning tunneling microscopy simulations of poly(3-dodecylthiophene) chains adsorbed on highly oriented pyrolytic graphite

    CERN Document Server

    Dubois, M; Latil, S; Rubio, A; Scifo, L

    2006-01-01

    We report on a novel scheme to perform efficient simulations of Scanning Tunneling Microscopy (STM) of molecules weakly bonded to surfaces. Calculations are based on a tight binding (TB) technique including self-consistency for the molecule to predict STM imaging and spectroscopy. To palliate the lack of self-consistency in the tunneling current calculation, we performed first principles density-functional calculations to extract the geometrical and electronic properties of the system. In this way, we can include, in the TB scheme, the effects of structural relaxation upon adsorption on the electronic structure of the molecule. This approach is applied to the study of regioregular poly(3-dodecylthiophene) (P3DDT) polymer chains adsorbed on highly oriented pyrolytic graphite (HOPG). Results of spectroscopic calculations are discussed and compared with recently obtained experimental dat

  8. Radio-frequency excitation of single molecules by scanning tunnelling microscopy

    International Nuclear Information System (INIS)

    We have upgraded a low-temperature scanning tunnelling microscope (STM) with a radio-frequency (RF) modulation system to extend STM spectroscopy to the range of low energy excitations (<1 meV). We studied single molecules of a stable hydrocarbon π-radical weakly physisorbed on Au(111). At 5 K thermal excitation of the adsorbed molecules is inhibited due to the lack of short-wavelength phonons of the substrate. We demonstrate resonant excitation of mechanical modes of single molecules by RF tunnelling at 115 MHz, which induces structural changes in the molecule ranging from controlled diffusion and modification of bond angles to bond breaking as the ultimate climax (resonance catastrophe). Our results pave the way towards RF-STM-based spectroscopy and controlled manipulation of molecular nanostructures on a surface. (paper)

  9. A variable-temperature scanning tunneling microscope capable of single-molecule vibrational spectroscopy

    International Nuclear Information System (INIS)

    The design and performance of a variable-temperature scanning tunneling microscope (STM) is presented. The microscope operates from 8 to 350 K in ultrahigh vacuum. The thermally compensated STM is suspended by springs from the cold tip of a continuous flow cryostat and is completely surrounded by two radiation shields. The design allows for in situ dosing and irradiation of the sample as well as for the exchange of samples and STM tips. With the STM feedback loop off, the drift of the tip-sample spacing is approximately 0.001 Angstrom/min at 8 K. It is demonstrated that the STM is well-suited for the study of atomic-scale chemistry over a wide temperature range, for atomic-scale manipulation, and for single-molecule inelastic electron tunneling spectroscopy (IETS). copyright 1999 American Institute of Physics

  10. An EHT based model for Single Molecule Incoherent Resonant Scanning Tunneling Spectroscopy

    CERN Document Server

    Raza, H

    2007-01-01

    We report Extended Huckel theory (EHT) based mean-field incoherent Non-equilibrium Green's function (NEGF) transport model, for single molecule scanning tunneling spectroscopy (STS), with dephasing due to elastic and inelastic scattering within the self-consistent Born approximation (SCBA) and report a procedure for tip modeling based on EHT basis set modification. We use this model to study the effect of the temperature dependent elastic dephasing, due to low energy phonon modes in far-infrared range for which hf is much less than kT, on the resonant conduction through highest occupied molecular orbital (HOMO) level. Furthermore, we report inelastic off-resonant tunneling results, showing peak in second derivative due to one phonon mode. Finally, we suggest that dephasing should be included in room temperature molecular transport calculations.

  11. Aluminum corrosion: Correlations of corrosion rate with surface coverage and tunneling spectra of organic inhibitors

    Science.gov (United States)

    Shu, Q. Q.; Love, P. J.; Bayman, A.; Hansma, P. K.

    Thin films of evaporated aluminum form a convenient model system for studying corrosion and corrosion inhibition on aluminum because (1) corrosion can be conveniently and continuously monitored by both electrical resistance measurements and optical transmission, (2) surface coverage of inhibitor species can be measured by either radiotracer techniques or tunneling spectroscopy and (3) the nature of surface adsorbed species can be determined with tunneling spectroscopy. The corrosion rate for these films is of order 20 ?m/year in pure water at flow rates of order 20 cm/s. The corrosion is inhibited by roughly one order of magnitude by monolayer surface coverages of the surface species that result when acetic acid, benzoic acid, cupferron or ethylene glycol are added to the water. At surface coverages of order 1/100 of a monolayer, the corrosion rate is increased by roughly an order of magnitude for the first three additives but not for ethylene glycol. From the previous studies of tunneling spectra, it is clear that the acetic and benzoic acids lose a proton to become benzoate and acetate ions on the surface. The ethylene glycol loses the protons from both of its OH groups during bonding. The spectrum of the adsorbed cupferron species is presented but not analyzed.

  12. Scanning tunneling microscopy and spectroscopy on GaN and InGaN surfaces

    International Nuclear Information System (INIS)

    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.)

  13. Fermi-level alignment at metal-carbon nanotube interfaces application to scanning tunneling spectroscopy

    CERN Document Server

    Xue, Y; Xue, Yongqiang; Datta, Supriyo

    1999-01-01

    At any metal-carbon nanotube interface there is charge transfer and the induced interfacial field determines the position of the carbon nanotube band structure relative to the metal Fermi-level. In the case of a single-wall carbon nanotube (SWNT) supported on a gold substrate, we show that the charge transfers induce a local electrostatic potential perturbation which gives rise to the observed Fermi-level shift in scanning tunneling spectroscopy (STS) measurements. We also discuss the relevance of this study to recent experiments on carbon nanotube transistors and argue that the Fermi-level alignment will be different for carbon nanotube transistors with low resistance and high resistance contacts.

  14. Scanning tunneling spectroscopy studies of angle-dependent van Hove singularities on twisted graphite surface layer

    Science.gov (United States)

    Zhang, Xin; Luo, Hong

    2013-12-01

    Slightly misoriented surface graphene layer on highly ordered pyrolytic graphite (HOPG) can result in Moiré patterns (MP). Two van Hove singularity (VHS) peaks in the density of states are observed with scanning tunneling spectroscopy on a series of the MPs with different periods on HOPG surface, flanking the Fermi energy. The energy difference between the two VHS peaks (?EVHS) is linearly proportional to the sine of interlayer rotation angle. A similar relation between ?EVHS and MP periods has recently been reported on twisted graphene layers. Compared to the case of twisted graphene layers, the Fermi velocity of MPs on a HOPG surface is found to be larger, and the interlayer hopping is enhanced.

  15. Measuring many-body effects in carbon nanotubes with a scanning tunneling microscope

    OpenAIRE

    Lin, Hong; Lagoute, Jérôme; Repain, Vincent; Chacon, Cyril; Girard, Yann; Lauret, Jean-Sébastien; Ducastelle, François; Loiseau, Annick; Rousset, Sylvie

    2009-01-01

    Electron-electron interactions and excitons in carbon nanotubes are locally measured by combining Scanning tunneling spectroscopy and optical absorption in bundles of nanotubes. The largest gap deduced from measurements at the top of the bundle is found to be related to the intrinsic quasi-particle gap. From the difference with optical transitions, we deduced exciton binding energies of 0.4 eV for the gap and 0.7 eV for the second Van Hove singularity. This provides the firs...

  16. Illuminating structural transformation of Ir(110): A high-temperature scanning tunneling microscopy study

    International Nuclear Information System (INIS)

    High-temperature scanning tunneling microscope investigation of Ir(110) reveals that the originally {331} faceted room-temperature surface flattens upon heating to form (1x3)+(1x1) and eventually (1x2) missing row reconstructed terraces at about 800 K, thus finally resolving a long-standing controversy on its equilibrium configuration. The surprising structural transformations can be explained by a surface stress related mechanism that is consistent also with the reconstruction behavior of the other low index planes of the noble metals

  17. Real-time scanning tunneling microscopy studies of thin film deposition and ion erosion

    OpenAIRE

    Fokkema, Vincent

    2011-01-01

    In this thesis I present my research on the physics of some important processes in the production of thin films. I studied physical vapour deposition (PVD) and thin film modification through ion bombardment using a newly developed, high-speed scanning tunneling microscope (STM). The instrument has the special property that it can be tilted and azimuthally rotated to allow atom or ion beams a direct line-of-sight access to the region of the surface that is being imaged by the STM tip. With the...

  18. Scanning Tunneling Microscopy Study of Square Manganese Tetramers on Mn3N2 (001)

    OpenAIRE

    De Yang, Rong; Yang, Haiqiang; Smith, Arthur R.

    2005-01-01

    We have investigated the growth of antiferromagnetic Mn3N2(001) on MgO (001) by molecular beam epitaxy and scanning tunneling microscopy . The images show smooth terraces and atomic steps. On some of the terraces a unique and new reconstruction is seen, resolved as square Mn tetramers in a c(4x2) structural arrangement. Two domains of the tetramer reconstruction, rotated by 90$^\\circ$ to each other, occur. A model is presented for this square Mn tetramer reconstruction, in w...

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

    OpenAIRE

    Redinger, Alex

    2009-01-01

    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 78.5° and 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. ...

  20. 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.)

  1. Charge ordering in stoichiometric FeTe: Scanning tunneling microscopy and spectroscopy

    Science.gov (United States)

    Li, Wei; Yin, Wei-Guo; Wang, Lili; He, Ke; Ma, Xucun; Xue, Qi-Kun; Chen, Xi

    2016-01-01

    We use scanning tunneling microscopy and spectroscopy to reveal a unique stripy charge order in a parent phase of iron-based superconductors in stoichiometric FeTe epitaxy films. The charge order has unusually the same—usually half—period as the spin order. We also found highly anisotropic electron band dispersions being large and little along the ferromagnetic (crystallographic b ) and antiferromagnetic (a ) directions, respectively. Our data suggest that the microscopic mechanism is likely of the Stoner type driven by interatomic Coulomb repulsion Vi j, and that Vi j and charge fluctuations, so far much neglected, are important to the understanding of iron-based superconductors.

  2. Visible Light Emission from Atomic Scale Patterns Fabricated by the Scanning Tunneling Microscope

    DEFF Research Database (Denmark)

    Thirstrup, C.; Sakurai, M.; Stokbro, Kurt; Aono, M.

    1999-01-01

    Scanning tunneling microscope (STM) induced light emission from artificial atomic scale structures comprising silicon dangling bonds on hydrogen-terminated Si(001) surfaces has been mapped spatially and analyzed spectroscopically in the visible spectral range. The light emission is based on a novel...... mechanism involving optical transitions between a tip state and localized states on the sample surface. The wavelength of the photons can be changed by the bias voltage of the STM. The spatial resolution of the photon maps is as good as that of STM topographic images and the photons are emitted from a...

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

    OpenAIRE

    Svetlana Kilina; Dzmitry A. Yarotski; A. Alec Talin; Sergei Tretiak; Antoinette J. Taylor; Balatsky, Alexander V.

    2011-01-01

    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 an...

  4. Multilevel memristor effect in metal-semiconductor core-shell nanoparticles tested by scanning tunneling spectroscopy

    Science.gov (United States)

    Chakrabarti, Sudipto; Pal, Amlan J.

    2015-05-01

    We have grown gold (Au) and copper-zinc-tin-sulfide (CZTS) nanocrystals and Au-CZTS core-shell nanostructures, with gold in the core and the semiconductor in the shell layer, through a high-temperature colloidal synthetic approach. Following usual characterization, we formed ultrathin layers of these in order to characterize the nanostructures in an ultrahigh-vacuum scanning tunneling microscope. Scanning tunneling spectroscopy of individual nanostructures showed the memristor effect or resistive switching from a low- to a high-conducting state upon application of a suitable voltage pulse. The Au-CZTS core-shell nanostructures also show a multilevel memristor effect with the nanostructures undergoing two transitions in conductance at two magnitudes of voltage pulse. We have studied the reproducibility, reversibility, and retentivity of the multilevel memristors. From the normalized density of states (NDOS), we infer that the memristor effect is correlated to a decrease in the transport gap of the nanostructures. We also infer that the memristor effect occurs in the nanostructures due to an increase in the density of available states upon application of a voltage pulse.We have grown gold (Au) and copper-zinc-tin-sulfide (CZTS) nanocrystals and Au-CZTS core-shell nanostructures, with gold in the core and the semiconductor in the shell layer, through a high-temperature colloidal synthetic approach. Following usual characterization, we formed ultrathin layers of these in order to characterize the nanostructures in an ultrahigh-vacuum scanning tunneling microscope. Scanning tunneling spectroscopy of individual nanostructures showed the memristor effect or resistive switching from a low- to a high-conducting state upon application of a suitable voltage pulse. The Au-CZTS core-shell nanostructures also show a multilevel memristor effect with the nanostructures undergoing two transitions in conductance at two magnitudes of voltage pulse. We have studied the reproducibility, reversibility, and retentivity of the multilevel memristors. From the normalized density of states (NDOS), we infer that the memristor effect is correlated to a decrease in the transport gap of the nanostructures. We also infer that the memristor effect occurs in the nanostructures due to an increase in the density of available states upon application of a voltage pulse. Electronic supplementary information (ESI) available: Additional figures. See DOI: 10.1039/c5nr01161b

  5. Investigations of the superconducting proximity effect in normal conducting and ferromagnetic materials using scanning tunneling spectroscopy

    International Nuclear Information System (INIS)

    The superconducting proximity effect (SPE) describes the mutual influence of a normal conductor and a superconductor in electrical contact. Due to the Anderson reflection at the interface the single electron based current in the normal conductor can be transformed into a dissipation free current due to Cooper pairs. Theoretical expectations on the local quasi particle density of states on layered systems with aluminum (BCS superconductor), gold and silver were compared with scanning tunneling microscopy measurements. Palladium was also studied using the proximity effect with respect to a strong electron-phonon coupling with simultaneous ferromagnetism. Another topic was the study of superconductor/ferromagnetic layer structures.

  6. Electronic structure of nanoscale iron oxide particles measured by scanning tunneling and photoelectron spectroscopies

    OpenAIRE

    Preisinger, M.; Krispin, M.; Rudolf, T; Horn, S.; Strongin, D. R.

    2005-01-01

    We have investigated the electronic structure of nano-sized iron oxide by scanning tunnelling microscopy (STM) and spectroscopy (STS) as well as by photoelectron spectroscopy. Nano particles were produced by thermal treatment of Ferritin molecules containing a self-assembled core of iron oxide. Depending on the thermal treatment we were able to prepare different phases of iron oxide nanoparticles resembling gamma-Fe2O3, alpha-Fe2O3, and a phase which apparently contains both gamma-Fe2O3 and a...

  7. 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 with the...... substrate 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...

  8. A low temperature scanning tunneling microscope for electronic and force spectroscopy

    International Nuclear Information System (INIS)

    In this article, we describe and test a novel way to extend a low temperature scanning tunneling microscope with the capability to measure forces. The tuning fork that we use for this is optimized to have a high quality factor and frequency resolution. Moreover, as this technique is fully compatible with the use of bulk tips, it is possible to combine the force measurements with the use of superconductive or magnetic tips, advantageous for electronic spectroscopy. It also allows us to calibrate both the amplitude and the spring constant of the tuning fork easily, in situ and with high precision

  9. 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.

  10. Spin-polarized scanning tunneling microscopy. Influence of the tip on measurements

    International Nuclear Information System (INIS)

    After a brief introduction of the spin-polarized scanning tunneling microscopy (SP-STM), its measurement techniques are described based on our recent experimental results. We have observed anomalously high spin contrast for epitaxially grown Mn(001)/Fe(001) samples. This phenomenon can be attributed to a single atom or a cluster of Mn attached to the apex of the thin film Fe tip. This interpretation is supported by a recent first-principle calculation of model magnetic tips. These results stress the importance of the identification of the magnetic tip and its precise control at an atomic level for the purpose of SP-STM measurement. (author)

  11. A 30 mK, 13.5 T scanning tunneling microscope with two independent tips

    OpenAIRE

    Roychowdhury, A.; Gubrud, M. A.; Dana, R; Anderson, J. R.; C. J. Lobb; F. C. Wellstood; Dreyer, M.

    2013-01-01

    We describe the design, construction, and performance of an ultra-low temperature, high-field scanning tunneling microscope (STM) with two independent tips. The STM is mounted on a dilution refrigerator and operates at a base temperature of 30 mK with magnetic fields of up to 13.5 T. We focus on the design of the two-tip STM head, as well as the sample transfer mechanism, which allows \\textit{in situ} transfer from an ultra high vacuum (UHV) preparation chamber while the STM...

  12. Construction of a Versatile Ultra-Low Temperature Scanning Tunneling Microscope

    OpenAIRE

    Kambara, H.; Matsui, T.; Niimi, Y.; Fukuyama, H.

    2007-01-01

    We constructed a dilution-refrigerator (DR) based ultra-low temperature scanning tunneling microscope (ULT-STM) which works at temperatures down to 30 mK, in magnetic fields up to 6 T and in ultrahigh vacuum (UHV). Besides these extreme operation conditions, this STM has several unique features not available in other DR based ULT-STMs. One can load STM tips as well as samples with clean surfaces prepared in a UHV environment to an STM head keeping low temperature and UHV con...

  13. Total quantitative recording of elemental maps and spectra with a scanning microprobe

    International Nuclear Information System (INIS)

    A system of data recording and analysis has been developed by means of which simultaneously all data from a scanning instrument such as a microprobe can be quantitatively recorded and permanently stored, including spectral outputs from several detectors. Only one scanning operation is required on the specimen. Analysis is then performed on the stored data, which contain quantitative information on distributions of all elements and spectra of all regions

  14. 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. PMID:17155496

  15. Investigation of the Tunneling Spectra in HgBr2-Intercalated Bi-2212 Single Crystals below and above Tc

    OpenAIRE

    Kurter, C.; Mazur, D.; Ozyuzer, L.; Hinks, D. G.; Gray, K E

    2007-01-01

    Interlayer tunneling spectroscopy measurements were performed on mesa arrays of Bi-2212 single crystals, intercalated with HgBr$_2$. Tunneling conductances were obtained over a wide temperature range to examine the spectral features, especially the behavior of the quasiparticle peaks corresponding to superconducting energy gaps (SGs). Experimental spectra showed that gap-like features are still present even for the temperatures far above the transition temperature, T$_c$. Th...

  16. Scanning tunneling microscopy and spectroscopy for cluster and small particle research

    International Nuclear Information System (INIS)

    Scanning tunneling microscopy (STM) and spectroscopy (STS) are new methods to investigate atomic arrangements and electronic structures of clusters and small particles of atoms. In this paper we review recent developments in this field, in particular the work from our laboratory. We show studies of single adatoms, small clusters and larger particles of platinum and a trimer of aluminium imaged with atomic resolution on highly-oriented pyrolytic graphite. We find different isomeric structures for clusters of a specific size. Taking the substrate lattice as reference we determine bond lengths and angles for the clusters. We find that adsorbed Pt-particles have a strong influence on the substrate. Periodic charge density modulations on the graphite lattice surrounding the particles are observed. We also discuss recent STS experiments which showed Coulomb blockade in electron tunneling. A silicon-oxide-graphite tip-junction is used where a mesoscopic insulating area containing trap levels for temporary electron storage is responsible for the blockade of single electron transport. Such an ultra-small insulator capacitor shows large voltage steps in current-voltage characteristics and quantization of the tunneling current. (orig.)

  17. Nanocatalysis by the tip of a scanning tunneling micrscope operating inside a reactor cell

    Energy Technology Data Exchange (ETDEWEB)

    McIntyre, B.J.; Salmeron, M.; Somorjai, G.A. (Lawrence Berkeley Lab., CA (United States))

    1994-09-02

    The platinum-rhodium tip of a scanning tunneling microscope that operates inside of an atmospheric-pressure chemical reactor cell has been used to locally rehydrogenate carbonaceous fragments deposited on the (111) surface of platinum. The carbon fragments were produced by partial dehydrogenation of propylene. The reactant gas environment inside the cell consisted of pure H[sub 2] or a 1:9 mixture of CH[sub 3]CHCH[sub 2] and H[sub 2] at 300 kelvin. The platinum-rhodium tip acted as a catalyst after activation by short voltage pulses. In this active state, the clusters in the area scanned by the tip were reacted away with very high spatial resolution.

  18. What is the orientation of the tip in a scanning tunneling microscope?

    CERN Document Server

    Mándi, Gábor; Palotás, Krisztián

    2015-01-01

    We introduce a statistical correlation analysis method to obtain information on the local geometry and orientation of the tip used in scanning tunneling microscopy (STM) experiments based on large scale simulations. The key quantity is the relative brightness correlation of constant-current topographs between experimental and simulated data. This correlation can be analyzed statistically for a large number of modeled tip orientations and geometries. Assuming a stable tip during the STM scans and based on the correlation distribution, it is possible to determine the tip orientations that are most likely present in an STM experiment, and exclude other orientations. This is especially important for substrates such as highly oriented pyrolytic graphite (HOPG) since its STM contrast is strongly tip dependent, which makes interpretation and comparison of STM images very challenging. We illustrate the applicability of our method considering the HOPG surface in combination with tungsten tip models of two different ap...

  19. Investigation of surface relief accompanying Widmanstatten ferrite formation by scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Bo, X.Z.; Fang, H.S.; Wang, J.J.; Wang, Z.H. [Tsinghua Univ., Beijing (China). Dept. of Materials Science and Engineering

    1998-06-12

    There are two types of surface relief associated with phase transformation, i.e., N-like type (Invariant Plane Strain -- IPS) and tent-shaped type (non-IPS). Although many scientists investigated the surface relief accompanying Widmanstaetten ferrite (WF) formation by light optical microscopy (LOM), controversy still exists on its formation mechanism. Up to now, most research concerning surface relief has been done by LOM, scanning electron microscopy (SEM) and transmission electron microscopy (replica), which either do not have enough vertical or lateral resolution. Scanning tunneling microscopy (STM) invented in the 1980s, which has high vertical resolution (0.01 nm) and lateral resolution (0.1 nm), has proved to be very suitable to investigate the surface relief quantitatively.

  20. Wind Tunnel Testing of a One-Dimensional Laser Beam Scanning and Laser Sheet Approach to Shock Sensing

    Science.gov (United States)

    Tokars, Roger; Adamovsky, Grigory; Anderson, Robert; Hirt, Stefanie; Huang, John; Floyd, Bertram

    2012-01-01

    A 15- by 15-cm supersonic wind tunnel application of a one-dimensional laser beam scanning approach to shock sensing is presented. The measurement system design allowed easy switching between a focused beam and a laser sheet mode for comparison purposes. The scanning results were compared to images from the tunnel Schlieren imaging system. The tests revealed detectable changes in the laser beam in the presence of shocks. The results lend support to the use of the one-dimensional scanning beam approach for detecting and locating shocks in a flow, but some issues must be addressed in regards to noise and other limitations of the system.

  1. Study of the resistive switching of vertically aligned carbon nanotubes by scanning tunneling microscopy

    Science.gov (United States)

    Ageev, O. A.; Blinov, Yu. F.; Il'in, O. I.; Konoplev, B. G.; Rubashkina, M. V.; Smirnov, V. A.; Fedotov, A. A.

    2015-04-01

    The effect of an external electric field on the electromechanical properties and regularities of the resistive switching of a vertically aligned carbon nanotube (VA CNT) has been studied experimentally using scanning tunneling microscopy. It has been shown that the VA CNT resistivity ratio in the high- and low-resistance states is higher than 25 as the distance between the scanning tunneling microscope (STM) probe and the VA CNT is 1 nm at a voltage of 8 V and depends on the voltage applied between the probe and the VA CNT. The proposed mechanism of resistive switching of VA CNTs is based on an instantaneous deformation and induction of a VA CNT internal electric field as a result of the sharp change in the time derivative of the external electric field strength. The obtained results can be used for the design and fabrication of resistive energy-efficient memory elements with a high density of storage cells on the basis of vertically aligned carbon nanotubes.

  2. Spin-polarized scanning tunneling microscopy and spectroscopy study of chromium on a Cr(001) surface

    International Nuclear Information System (INIS)

    Several tens of chromium layers were deposited at 250 0C on a Cr(001) surface and investigated by spin-polarized scanning tunneling microscopy (SP-STM), Auger electron spectroscopy (AES) and scanning tunneling spectroscopy (STS). Chromium is found to grow with a mound-like morphology resulting from the stacking of several monolayers which do not uniformly cover the whole surface of the substrate. The terminal plane consists of an irregular array of Cr islands with lateral sizes smaller than 20 x 20 nm2. Combined AES and STS measurements reveal the presence of a significant amount of segregants prior to and after deposition. A detailed investigation of the surface shows that it consists of two types of patches. Thanks to STS measurements, the two types of area have been identified as being either chromium pure or segregant rich. SP-STM experiments have evidenced that the antiferromagnetic layer coupling remains in the chromium mounds after deposition and is not significantly affected by the presence of the segregants.

  3. Atomic-scale mapping of electronic structures across heterointerfaces by cross-sectional scanning tunneling microscopy

    Science.gov (United States)

    Chiu, Ya-Ping; Huang, Bo-Chao; Shih, Min-Chuan; Huang, Po-Cheng; Chen, Chun-Wei

    2015-09-01

    Interfacial science has received much attention recently based on the development of state-of-the-art analytical tools that can create and manipulate the charge, spin, orbital, and lattice degrees of freedom at interfaces. Motivated by the importance of nanoscale interfacial science that governs device operation, we present a technique to probe the electronic characteristics of heterointerfaces with atomic resolution. In this work, the interfacial characteristics of heteroepitaxial structures are investigated and the fundamental mechanisms that pertain in these systems are elucidated through cross-sectional scanning tunneling microscopy (XSTM). The XSTM technique is employed here to directly observe epitaxial interfacial structures and probe local electronic properties with atomic-level capability. Scanning tunneling microscopy and spectroscopy experiments with atomic precision provide insight into the origin and spatial distribution of electronic properties across heterointerfaces. The first part of this report provides a brief description of the cleavage technique and spectroscopy analysis in XSTM measurements. The second part addresses interfacial electronic structures of several model heterostructures in current condensed matter research using XSTM. Topics to be discussed include high-?‘s/III-V’s semiconductors, polymer heterojunctions, and complex oxide heterostructures, which are all material systems whose investigation using this technique is expected to benefit the research community. Finally, practical aspects and perspectives of using XSTM in interface science are presented.

  4. Optical spectroscopy and scanning tunneling microscopy studies of molecular adsorbates and anisotropic ultrathin films. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Hemminger, J.C.

    1998-09-01

    The bonding, chemistry and ordering of molecular adsorbates on well defined single crystal surfaces and in ultrathin films was to be studied in an effort to develop sufficient fundamental understanding to allow the controlled preparation of anisotropic ultrathin films of organic monolayers. In this research the authors combine the use of optical probes (Raman spectroscopy, laser induced thermal desorption with Fourier transform mass spectrometry detection) with scanning tunneling microscopy (STM) and conventional methods of UHV surface science (Auger electron spectroscopy, x-ray photoelectron spectroscopy, low energy electron diffraction, and thermal desorption spectroscopy). The conventional surface probes provide well tested methods for the preparation and characterization of single crystal substrates. The optical probes used in the experiments provide powerful methods for the molecular identification of adsorbates in monolayers and ultrathin films. Scanning tunneling microscopy provides one with the ability to determine the detailed molecular level ordering of the molecular adsorbates. The emphasis of this research is on more complex molecular absorbates some of which are monomer precursors to ultrathin polymer films. Enhanced methods of Raman spectroscopy have been developed for the study of monolayer adsorbates on surfaces in ultrahigh vacuum environments. This report gives an overview of recent research results, including the construction of UHV variable temperature STM, analysis of STM images, growth and chemistry of intermetallic single crystal ultrathin films, and electron beam induced chemistry of tetracyanoquinodimethane.

  5. Scanning tunneling microscopy studies of graphene and hydrogenated graphene on Cu(111)

    Science.gov (United States)

    Hollen, Shawna M.; Gambrel, Grady; Tjung, Steven; Santagata, Nancy M.; Johnston-Halperin, Ezekiel; Gupta, Jay A.

    2015-03-01

    Because of the innate sensitivity of 2D material surfaces, it is increasingly important to understand and characterize surface functionalization and interactions with environmental elements, such as substrate, metallic contacts, and adatoms. We developed a method for reproducible, epitaxial growth of pristine graphene islands on Cu(111) in UHV and use scanning tunneling microscopy and spectroscopy (STM) to study the interaction of these graphene islands with the Cu substrate. Tunneling spectroscopy measurements of the electronic surface states over the graphene islands indicate a lower local work function, decreased coupling to bulk Cu states, and a decreased electron effective mass. Additionally, we developed a novel field electron dissociation technique to form hydrogen-terminated graphene at low temperatures and in UHV. This method produced what may be the first STM images of crystalline hydrogenated graphene. The pristine graphene island is then recovered by scanning at a high tip-sample bias. The hydrogenation and its reversibility suggest writing lateral 2D devices using the STM tip. Toward this end, we are developing the capability to repeat the hydrogenation on working graphene devices. This research is supported by the Center for Emergent Materials NSF-funded MRSEC (DMR-0820414)

  6. Bulk crystalline copper electrodeposition on polycrystalline gold surfaces observed by in-situ scanning tunneling microscopy

    DEFF Research Database (Denmark)

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

    1994-01-01

    Bulk copper electrodeposition onto technical gold surfaces in electrolytes of 0.05 M H2SO4 and 1 mM CuSO4 was investigated by in-situ scanning tunnelling microscopy at fixed overpotentials. At potentials between -60 and -30 mV the growth of bulk copper proceeds in cycles of nucleation, agglomerat......Bulk copper electrodeposition onto technical gold surfaces in electrolytes of 0.05 M H2SO4 and 1 mM CuSO4 was investigated by in-situ scanning tunnelling microscopy at fixed overpotentials. At potentials between -60 and -30 mV the growth of bulk copper proceeds in cycles of nucleation......, agglomeration and crystallization. Crystalline copper is seen as involving an intermediate stage in the progress of growth. The final stage in the growth involves an equilibrium of copper electrochemically dissolving and precipitating. The drift velocity was measured for a gold surface subjected to flame...... reconstruction was observed. It is suggested that in reality no reconstruction took place, and that the observation was due to a distortion of the image caused by a constant drift velocity. A mathematical expression which relates the observed surface structure to the drift velocity is presented....

  7. Scanning magnetic tunnel junction microscope for high-resolution imaging of remanent magnetization fields

    International Nuclear Information System (INIS)

    Scanning magnetic microscopy is a new methodology for mapping magnetic fields with high spatial resolution and field sensitivity. An important goal has been to develop high-performance instruments that do not require cryogenic technology due to its high cost, complexity, and limitation on sensor-to-sample distance. Here we report the development of a low-cost scanning magnetic microscope based on commercial room-temperature magnetic tunnel junction (MTJ) sensors that typically achieves spatial resolution better than 7?µm. By comparing different bias and detection schemes, optimal performance was obtained when biasing the MTJ sensor with a modulated current at 1.0 kHz in a Wheatstone bridge configuration while using a lock-in amplifier in conjunction with a low-noise custom-made preamplifier. A precision horizontal (x–y) scanning stage comprising two coupled nanopositioners controls the position of the sample and a linear actuator adjusts the sensor-to-sample distance. We obtained magnetic field sensitivities better than 150 nT/Hz1/2 between 0.1 and 10?Hz, which is a critical frequency range for scanning magnetic microscopy. This corresponds to a magnetic moment sensitivity of 10–14 A m2, a factor of 100 better than achievable with typical commercial superconducting moment magnetometers. It also represents an improvement in sensitivity by a factor between 10 and 30 compared to similar scanning MTJ microscopes based on conventional bias-detection schemes. To demonstrate the capabilities of the instrument, two polished thin sections of representative geological samples were scanned along with a synthetic sample containing magnetic microparticles. The instrument is usable for a diversity of applications that require mapping of samples at room temperature to preserve magnetic properties or viability, including paleomagnetism and rock magnetism, nondestructive evaluation of materials, and biological assays. (paper)

  8. Scanning tunneling microscopy and spectroscopy of sodium-chloride overlayers on the stepped Cu(311) surface: Experimental and theoretical study

    CERN Document Server

    Olsson, F E; Repp, J; Meyer, G

    2005-01-01

    The physical properties of ultrathin NaCl overlayers on the stepped Cu(311) surface have been characterized using scanning tunneling microscopy (STM) and spectroscopy, and density functional calculations. Simulations of STM images and differential conductance spectrum were based on the Tersoff-Hamann approximation for tunneling with corrections for the modified tunneling barrier at larger voltages and calculated Kohn-Sham states. Characteristic features observed in the STM images can be directly related to calculated electronic and geometric properties of the overlayers. The measured apparent barrier heights for the mono-, bi-, and trilayers of NaCl and the corresponding adsorption-induced changes in the work function, as obtained from the distance dependence of the tunneling current, are well reproduced by and understood from the calculated results. The measurements revealed a large reduction of the tunneling conductance in a wide voltage region, resembling a band gap. However, the simulated spectrum showed ...

  9. An approach to long-range electron transfer mechanisms in metalloproteins: In situ scanning tunneling microscopy with submolecular resolution

    OpenAIRE

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

    1999-01-01

    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 ca...

  10. Scanning Tunneling Microscopy of Dirac Fermions at mK Temperatures

    Science.gov (United States)

    Stroscio, Joseph

    2011-03-01

    Since the beginning of the last century new frontiers in physics have emerged when advances in instrumentation achieved lower experimental operating temperatures. Notable examples include the discovery of superconductivity and the integer and fractional quantum Hall effects. New experimental techniques are continually adapted in order to meet new experimental challenges. A case in point is scanning tunneling microscopy (STM) which has seen a wealth of new measurements emerge as cryogenic STM instruments have been developed in the last two decades. In this talk I describe the design, development and performance of a scanning probe microscopy facility operating at a base temperature of 10 mK in magnetic fields up to 15 T. The microscope is cooled by a custom designed, fully ultra-high vacuum (UHV) compatible dilution refrigerator (DR) and is capable of in-situ tip and sample exchange. Sub-picometer stability at the tip-sample junction is achieved through three independent vibration isolation stages and careful design of the dilution refrigerator. The system can be connected to, or disconnected from, a network of interconnected auxiliary UHV chambers used for sample and probe tip preparation. Current measurements are focusing on Dirac fermions in graphene and in topological insulators. The history of the fractional quantum Hall states in semiconductor heterostructures suggests that studying graphene at lower temperatures and higher magnetic fields may reveal new quantum phases of matter. Scanning tunneling spectroscopy of graphene at mK temperatures reveals the detailed structure of the degenerate Landau levels in graphene, resolving the full quartet of states corresponding to the lifting of the spin and valley dengeneracies. When the Fermi level lies inside the four-fold Landau manifold, significant electron correlation effects result in enhanced valley splitting and spin splitting. New many-body states are observed at fractional filling factors of 7/2, 9/2, and 11/2.

  11. Terthiophene on Au(111: A scanning tunneling microscopy and spectroscopy study

    Directory of Open Access Journals (Sweden)

    Berndt Koslowski

    2011-09-01

    Full Text Available Terthiophene (3T molecules adsorbed on herringbone (HB reconstructed Au(111 surfaces in the low coverage regime were investigated by means of low-temperature scanning tunneling microscopy (STM and spectroscopy (STS under ultra-high vacuum conditions. The 3T molecules adsorb preferentially in fcc regions of the HB reconstruction with their longer axis oriented perpendicular to the soliton walls of the HB and at maximum mutual separation. The latter observation points to a repulsive interaction between molecules probably due to parallel electrical dipoles formed during adsorption. Constant-separation (I-V and constant-current (z-V STS clearly reveal the highest occupied (HOMO and lowest unoccupied (LUMO molecular orbitals, which are found at −1.2 eV and +2.3 eV, respectively. The HOMO–LUMO gap corresponds to that of a free molecule, indicating a rather weak interaction between 3T and Au(111. According to conductivity maps, the HOMO and LUMO are inhomogeneously distributed over the adsorbed 3T, with the HOMO being located at the ends of the linear molecule, and the LUMO symmetrically with respect to the longer axis of the molecule at the center of its flanks. Analysis of spectroscopic data reveals details of the contrast mechanism of 3T/Au(111 in STM. For that, the Shockley-like surface state of Au(111 plays an essential role and appears shifted outwards from the surface in the presence of the molecule. As a consequence, the molecule can be imaged even at a tunneling bias within its HOMO–LUMO gap. A more quantitative analysis of this detail resolves a previous discrepancy between the fairly small apparent STM height of 3T molecules (1.4–2.0 nm, depending on tunneling bias and a corresponding larger value of 3.5 nm based on X-ray standing wave analysis. An additionally observed linear decrease of the differential tunneling barrier at positive bias when determined on top of a 3T molecule is compared to the bias independent barrier obtained on bare Au(111 surfaces. This striking difference of the barrier behavior with and without adsorbed molecules is interpreted as indicating an adsorption-induced dimensionality transition of the involved tunneling processes.

  12. Scanning tunneling microscope design with a confocal small field permanent magnet

    International Nuclear Information System (INIS)

    The field of ultra-sensitive measurements with scanning probes requires the design and construction of novel instruments. For example, the combination of radio frequency detection and scanning probe can be exploited to measure thermal properties and mechanical resonances at a very low scale. Very recent results by Komeda and Manassen (2008 Appl. Phys. Lett. 92 212506) on the detection of spin noise with the scanning tunneling microscopy (STM) have further expanded previous results reported by one of the authors of this manuscript (Messina et al 2007 J. Appl. Phys. 101 053916). In a previous publication, one of the authors used a new STM instrument (Messina et al J. Appl. Phys. 2007 101 053916 and Mannini et al 2007 Inorg. Chim. Acta 360 3837–42) to obtain the detection of electron spin noise (ESN) from individual paramagnetic adsorbates. The magnetic field homogeneity at the STM tip–sample region was limited. Furthermore, vacuum operation of the STM microscope was limited by the heat dissipation at the electromagnet and the radio frequency (RF) recovery electronics. We report here on a new STM head that incorporates a specially designed permanent magnet and in-built RF amplification system. The magnet provides both a better field homogeneity and freedom to operate the instrument in vacuum. The STM microscope is vacuum compatible, and vertical stability has been improved over the previous design (Messina et al 2007 J. Appl. Phys. 101 053916), despite the presence of a heat dissipative RF amplifier in the close vicinity of the STM tip

  13. Modeling of Electronic Transport in Scanning Tunneling Microscope Tip-Carbon Nanotube Systems

    Science.gov (United States)

    Yamada, Toshishige; Kwak, Dochan (Technical Monitor)

    2000-01-01

    A model is proposed for two observed current-voltage (I-V) patterns in a recent experiment with a scanning tunneling microscope tip and a carbon nanotube. We claim that there are two mechanical contact modes for a tip (metal) -nanotube (semiconductor) junction (1) with or (2) without a tiny vacuum gap (0.1 - 0.2 nm). With the tip grounded, the tunneling case in (1) would produce large dI/dV with V > 0, small dI/dV with V < 0, and I = 0 near V = 0 for an either n- or p-nanotube; the Schottky mechanism in (2) would result in I does not equal 0 only with V < 0 for an n-nanotube, and the bias polarities would be reversed for a p-nanotube. The two observed I-V patterns are thus entirely explained by a tip-nanotube contact of the two types, where the nanotube must be n-type.

  14. Electron-phonon coupling in C{sub 60} as revealed by scanning tunneling spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Franke, Katharina J.; Schulze, Gunnar; Pascual, Jose Ignacio [Freie Universitaet Berlin (Germany); Frederiksen, Thomas; Arnau, Andres [Donostia International Physics Center, Donostia (Spain); Monturet, Sergio [Universite Paul Sabatier, Toulouse (France); Lorente, Nicolas [Centro de Investigaciones en Nanociencia y Nanotecnologia, Bellaterra (Spain)

    2008-07-01

    Electron-phonon coupling is of major importance for charge transport through single molecule tunneling junctions. In most experimental implementations of molecular junctions the electronic coupling of the molecular orbitals with substrate states leads to a significant broadening, thus obscuring electron-phonon coupling effects. Here, we investigate the electronic structure of single C{sub 60} molecules adsorbed on top of a self-assembled pattern of alternating tetraphenyladamantane and C{sub 60}. Scanning tunnelling spectroscopy reveals that these molecules exhibit properties similar to the free molecule, such as a large gap of 3.7 eV and a narrow LUMO resonance of only {approx}60 meV line width. The LUMO resonance is followed by a broad weaker peak at about 240 meV higher energy. By density functional calculations including the Jahn-Teller effect, we show that this broad feature is induced by a complex coupling of the C{sub 60} vibrational eigenmodes with the LUMO resonance.

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

    Directory of Open Access Journals (Sweden)

    A. St?pniak

    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.

  16. 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.

  17. Josephson scanning tunneling microscopy -- a local and direct probe of the superconducting order parameter

    Energy Technology Data Exchange (ETDEWEB)

    Kimura, Hikari; Dynes, Robert; Barber Jr., Richard. P.; Ono, S.; Ando, Y.

    2009-09-01

    Direct measurements of the superconducting superfluid on the surface of vacuum-cleaved Bi2Sr2CaCu2O8+delta (BSCCO) samples are reported. These measurements are accomplished via Josephson tunneling into the sample using a novel scanning tunneling microscope (STM) equipped with a superconducting tip. The spatial resolution of the STM of lateral distances less than the superconducting coherence length allows it to reveal local inhomogeneities in the pair wavefunction of the BSCCO. Instrument performance is demonstrated first with Josephson measurements of Pb films followed by the layered superconductor NbSe2. The relevant measurement parameter, the Josephson ICRN product, is discussed within the context of both BCS superconductors and the high transition temperature superconductors. The local relationship between the ICRN product and the quasiparticle density of states (DOS) gap are presented within the context of phase diagrams for BSCCO. Excessive current densities can be produced with these measurements and have been found to alter the local DOS in the BSCCO. Systematic studies of this effect were performed to determine the practical measurement limits for these experiments. Alternative methods for preparation of the BSCCO surface are also discussed.

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

    Science.gov (United States)

    Stepniak, A.; Caminale, M.; Leon Vanegas, A. A.; Oka, H.; Sander, D.; Kirschner, J.

    2015-01-01

    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.

  19. Strongly compressed Bi (111) bilayer films on Bi2Se3 studied by scanning tunneling microscopy

    Science.gov (United States)

    Zhang, K. F.; Yang, Fang; Song, Y. R.; Liu, Canhua; Qian, Dong; Gao, C. L.; Jia, Jin-Feng

    2015-09-01

    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 Bi2Se3. 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.

  20. Detailed analysis of scanning tunneling microscopy images of the Si(001) reconstructed surface with buckled dimers

    CERN Document Server

    Okada, H; Endo, K; Hirose, K; Mori, Y

    2000-01-01

    The adequate interpretation of scanning tunneling microscopy (STM) images of the clean Si(001) surface is presented. We have performed both STM observations and {\\it ab initio} simulations of STM images for buckled dimers on the clean Si(001) surface. By comparing experimental results with theoretical ones, it is revealed that STM images depend on the sample bias and the tip-sample separation. This enables us to elucidate the relationship between the corrugation in STM images and the atomic structure of buckled dimers. Moreover, to elucidate these changes, we analyze details of the spatial distributions of the $\\pi$, $\\pi^{\\ast}$ surface states and $\\sigma$, $\\sigma^{\\ast}$ Si-Si bond states in the local density of states which contribute to STM images.

  1. 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.

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

    International Nuclear Information System (INIS)

    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

  3. Construction of a Versatile Ultra-Low Temperature Scanning Tunneling Microscope

    CERN Document Server

    Kambara, H; Niimi, Y; Fukuyama, H

    2007-01-01

    We constructed a dilution-refrigerator (DR) based ultra-low temperature scanning tunneling microscope (ULT-STM) which works at temperatures down to 20 mK, in magnetic fields up to 6 T and in ultrahigh vacuum (UHV). Besides these extreme operation conditions, this STM has several unique features not available in other DR based ULT-STMs. One can load STM tips as well as samples with clean surfaces prepared in a UHV environment to an STM head keeping low temperature and UHV conditions. After then, the system can be cooled back to the base temperature within 3 hours. Due to these capabilities, it has a variety of applications not only for cleavable materials but also for almost all conducting materials. The present ULT-STM has also an exceptionally high stability in the presence of magnetic field and even during field sweep. We describe details of its design, performance and applications for low temperature physics.

  4. Ex situ elaborated proximity mesoscopic structures for ultrahigh vacuum scanning tunneling spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Stolyarov, V. S. [UMR 7588, Institut des Nanosciences de Paris, UPMC Univ Paris 06, Sorbonne Universités, F-75005 Paris (France); CNRS, UMR 7588, Institut des Nanosciences de Paris, F-75005 Paris (France); Institute of Solid State Physics RAS, 142432 Chernogolovka (Russian Federation); Moscow Institute of Physics and Technology, 141700 Dolgoprudny (Russian Federation); Kazan Federal University, 420008 Kazan (Russian Federation); Moscow State University, 119991 Moscow (Russian Federation); Cren, T., E-mail: tristan.cren@upmc.fr; Debontridder, F.; Brun, C. [UMR 7588, Institut des Nanosciences de Paris, UPMC Univ Paris 06, Sorbonne Universités, F-75005 Paris (France); CNRS, UMR 7588, Institut des Nanosciences de Paris, F-75005 Paris (France); Veshchunov, I. S. [Université de Bordeaux, LP2N, 351 cours de la Libération, F-33405 Talence (France); Institute of Solid State Physics RAS, 142432 Chernogolovka (Russian Federation); Skryabina, O. V. [Institute of Solid State Physics RAS, 142432 Chernogolovka (Russian Federation); Rusanov, A. Yu. [LLC “Applied radiophysics” 142432 Chernogolovka (Russian Federation); Roditchev, D. [UMR 7588, Institut des Nanosciences de Paris, UPMC Univ Paris 06, Sorbonne Universités, F-75005 Paris (France); CNRS, UMR 7588, Institut des Nanosciences de Paris, F-75005 Paris (France); LPEM-UMR 8213, CNRS, ESPCI-ParisTech, UPMC, 10 rue Vauquelin, F-75005 Paris (France)

    2014-04-28

    We apply ultrahigh vacuum Scanning Tunneling Spectroscopy (STS) at ultra-low temperature to study proximity phenomena in metallic Cu in contact with superconducting Nb. In order to solve the problem of Cu-surface contamination, Cu(50?nm)/Nb(100?nm) structures are grown by respecting the inverted order of layers on SiO{sub 2}/Si substrate. Once transferred into vacuum, the samples are cleaved at the structure-substrate interface. As a result, a contamination-free Cu-surface is exposed in vacuum. It enables high-resolution STS of superconducting correlations induced by proximity from the underlying superconducting Nb layer. By applying magnetic field, we generate unusual proximity-induced superconducting vortices and map them with a high spatial and energy resolution. The suggested method opens a way to access local electronic properties of complex electronic mesoscopic devices by performing ex situ STS under ultrahigh vacuum.

  5. Ultra-high vacuum compatible optical chopper system for synchrotron x-ray scanning tunneling microscopy

    Science.gov (United States)

    Chang, Hao; Cummings, Marvin; Shirato, Nozomi; Stripe, Benjamin; Rosenmann, Daniel; Preissner, Curt; Freeland, John W.; Kersell, Heath; Hla, Saw-Wai; Rose, Volker

    2016-01-01

    High-speed beam choppers are a crucial part of time-resolved x-ray studies as well as a necessary component to enable elemental contrast in synchrotron x-ray scanning tunneling microscopy (SX-STM). However, many chopper systems are not capable of operation in vacuum, which restricts their application to x-ray studies with high photon energies, where air absorption does not present a significant problem. To overcome this limitation, we present a fully ultra-high vacuum (UHV) compatible chopper system capable of operating at variable chopping frequencies up to 4 kHz. The lightweight aluminum chopper disk is coated with Ti and Au films to provide the required beam attenuation for soft and hard x-rays with photon energies up to about 12 keV. The chopper is used for lock-in detection of x-ray enhanced signals in SX-STM.

  6. Scanning Tunneling Microscopy Reveals Single-Molecule Insights into the Self-Assembly of Amyloid Fibrils

    DEFF Research Database (Denmark)

    Kalashnyk, Nataliya; Nielsen, Jakob T

    2012-01-01

    Many severe diseases are associated with amyloid fibril deposits in the body caused by protein misfolding. Structural information on amyloid fibrils is accumulating rapidly, but little is known about the assembly of peptides into fibrils at the level of individual molecules. Here we investigate self-assembly of the fibril-forming tetrapeptides KFFE and KVVE on a gold surface under ultraclean vacuum conditions using scanning tunneling microscopy. Combined with restrained molecular dynamics modeling, we identify peptide arrangements with interesting similarities to fibril structures. By resolving individual peptide residues and revealing conformational heterogeneities and dynamics, we demonstrate how conformational correlations may be involved in cooperative fibril growth. Most interestingly, intermolecular interactions prevail over intramolecular interactions, and assembly of the phenyl-rich KFFE peptide appears not to be dominated by ?-? interactions. This study offers interesting perspectives for obtaining fundamental single-molecule insights into fibril formation using a surface science approach to study idealized model systems.

  7. Measurement of Quantized Conductance in Gallium Using a Scanning Tunneling Microscope

    Science.gov (United States)

    Lewis, B. B.; Vandervoort, K. G.

    1998-03-01

    A scanning tunneling microscope was employed to form nanometer diameter wires in gallium in various states. Nanowires form when objects come in and out of contact, much like the filaments that form when you step on a piece of gum and pull your foot away. When nanowires form, quantized steps in conductance occur and can be measured. The low melting point of gallium was utilized to study the quantized conductance dependence on the physical state of the metal. For temperatures adequately below gallium's melting point, quantized effects are seen that correspond to other studies performed on gold, copper, and aluminum. At temperatures near the melting point of gallium, there appears to be a weaker quantum effect. By varying the type of STM tip, the dependence on the contact metal was observed. Statistical analysis of conductance steps was performed and will be discussed.

  8. 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; Jacobsen, Karsten Wedel; Simmons, M.Y.; Hofer, W.A.

    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...... (STM) techniques. The theoretical treatment of the STM operation has traditionally been based on the Bardeen and Tersoff-Hamann methods which take as input the single-particle wave functions and eigenvalues obtained from finite cluster or slabs models of the surface-tip interface. Here, we present a...... account. As an illustrating example we apply the NEGF-STM method to the Si(001)(2x1):H surface with sub-surface P doping and discuss the results in comparison to the Bardeen and Tersoff-Hamann methods....

  9. 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

    2015-09-01

    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.

  10. 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. PMID:23829349

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

    International Nuclear Information System (INIS)

    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, dz2 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. (paper)

  12. Scanning tunneling microscope based nanoscale optical imaging of molecules on surfaces

    Science.gov (United States)

    Zhang, Chao; Chen, Liuguo; Zhang, Rui; Dong, Zhenchao

    2015-08-01

    We provide an overview of the development of a merged system of low-temperature ultrahigh-vacuum scanning tunneling microscope (STM) with photon collection and detection units for optical imaging at the nanoscale. Focusing on our own work over the past ten years, the paper starts from a brief introduction of the STM induced luminescence (STML) technique and the challenge for nanoscale optical imaging, and then describes the design and instrumentation on the photon collection and detection system. The powerful potentials of the technique are illustrated using several selected examples from STML to tip enhanced Raman scattering that are mainly related to photon mapping. Such photon maps could reveal not only the local electromagnetic properties and the nature of optical transitions in the junction, but also exhibit spatial imaging resolution down to sub-molecular and sub-nanometer scale. The paper is concluded with a brief overlook on the future development of the STML technique.

  13. 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.; Foverskov, Carl Erik; Møller, Per; Ulstrup, Jens

    1997-01-01

    further link to glutaric dialdehyde which immobilises the protein molecules. Cyt c is immobilised on Au(ll!) by reaction with N-acetylcystein and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. Imaging by in situ STM in a 20 mM phosphate buffer electrolyte with a Au/AuOx reference electrode could then be......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 a...... achieved, Protein was identified as hemispherical features on the surface with close to molecular resolution and with a quite different character compared both to the bare metal surfaces and to metal surfaces with only linker molecules attached. No subunits or side chains were visible, but the protein...

  14. Voltammetry and In Situ Scanning Tunneling Microscopy of Cytochrome c Nitrite Reductase on Au(111)-Electrodes

    DEFF Research Database (Denmark)

    Gwyer, James; Zhang, Jingdong; Butt, Julea; Ulstrup, Jens

    2006-01-01

    density and orientational distribution of NrfA molecules are disclosed. The submonolayer coverage resolved by in situ STM is readily reconciled with the failure to detect nonturnover signals in cyclic voltammetry of the NrfA films. The molecular structures show a range of lateral dimensions. These are...... suggestive of a distribution of orientations that could account for the otherwise anomalously low turnover number calculated for the total population of adsorbed NrfA molecules when compared with that determined for solutions of NrfA. Thus, comparison of the voltammetric signals and in situ STM images offers...... enzyme undergoes direct electron exchange with the electrode. The adsorbed NrfA has been imaged to molecular resolution by in situ scanning tunneling microscopy (in situ STM) under full electrochemical potential control and under conditions where the enzyme is electrocatalytically active. Details of the...

  15. Electronic structure of nanoscale iron oxide particles measured by scanning tunneling and photoelectron spectroscopies

    CERN Document Server

    Preisinger, M; Rudolf, T; Horn, S; Strongin, D R

    2005-01-01

    We have investigated the electronic structure of nano-sized iron oxide by scanning tunnelling microscopy (STM) and spectroscopy (STS) as well as by photoelectron spectroscopy. Nano particles were produced by thermal treatment of Ferritin molecules containing a self-assembled core of iron oxide. Depending on the thermal treatment we were able to prepare different phases of iron oxide nanoparticles resembling gamma-Fe2O3, alpha-Fe2O3, and a phase which apparently contains both gamma-Fe2O3 and alpha-Fe2O3. Changes to the electronic structure of these materials were studied under reducing conditions. We show that the surface band gap of the electronic excitation spectrum can differ from that of bulk material and is dominated by surface effects.

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

    DEFF Research Database (Denmark)

    Zhang, Jingdong; Chi, Qijin; Nazmutdinov, R. R.; Zinkicheva, T. T.; Bronshtein, M. D.

    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...... based on a slab model for the metal surface. The ordered monolayer offers a platform for submolecular scale electronic mapping that is an issue of fundamental interest but remains a challenge in STM imaging science and surface chemistry. Single Cys molecules were mapped as three electronic subunits...... analysis of the electronic structures is achieved to delineate the main factors that determine electronic contrasts in the STM images. These factors include the molecular orientation, the chemical nature of the elements or groups in the molecule, and the interaction of the elements with the substrate and...

  17. InAs/GaAs(001) molecular beam epitaxial growth in a scanning tunnelling microscope

    International Nuclear Information System (INIS)

    The growth on InAs on GaAs(001) has attracted great interest and investigation over the past few decades primarily due to the opto-electronic properties of the self-assembled quantum dot (QD) arrays formed. Scanning tunnelling microscopy (STM) has been extensively employed to investigate the complicated and spontaneous mechanism of QD growth via molecular beam epitaxy (MBE). Classically, combined MBE-STM requires quenching the sample after growth and transferring it to an arsenic-free high vacuum chamber which houses the STM system. However, without access to the phenomenon as a dynamic process a basic understanding remains elusive. In order to access surface dynamics, MBE and STM must be combined into a single element. The system herein discussed allows the operation of MBE sources in an STM system relating to InAs/GaAs(001) surfaces.

  18. Scanning tunnelling microscopy study of atomic hydrogen adsorption on the Si(111) 7 x 7 surface

    International Nuclear Information System (INIS)

    We studied initial atomic hydrogen adsorption onto Si(111) 7 x 7 adatoms by scanning tunnelling microscopy in an ultrahigh vacuum. Adatom reaction probabilities were measured as a function of atomic hydrogen exposure time for room-temperature and hightemperature surfaces. Hydrogen uptake was well represented by Langmuir adsorption at 361 and 414 K, while depression of uptake was seen at 481 K after one of six adatoms was terminated by hydrogen. Hydrogen adsorption had positive adsorption correlations between adjacent centre adatoms and corner adatoms across the 7 x 7 half unit. These correlations were enhanced at 481 K. In accordance with the positive reaction correlation between these adjacent adatoms, the average number of reacted adatoms in adjacent 7 x 7 half units was also enhanced as the number of reacted adatoms increased in the half unit

  19. 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.

  20. 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.

  1. Atomic species identification at the (101) anatase surface by simultaneous scanning tunnelling and atomic force microscopy.

    Science.gov (United States)

    Stetsovych, Oleksandr; Todorovi?, Milica; Shimizu, Tomoko K; Moreno, César; Ryan, James William; León, Carmen Pérez; Sagisaka, Keisuke; Palomares, Emilio; Matolín, Vladimír; Fujita, Daisuke; Perez, Ruben; Custance, Oscar

    2015-01-01

    Anatase is a pivotal material in devices for energy-harvesting applications and catalysis. Methods for the accurate characterization of this reducible oxide at the atomic scale are critical in the exploration of outstanding properties for technological developments. Here we combine atomic force microscopy (AFM) and scanning tunnelling microscopy (STM), supported by first-principles calculations, for the simultaneous imaging and unambiguous identification of atomic species at the (101) anatase surface. We demonstrate that dynamic AFM-STM operation allows atomic resolution imaging within the material's band gap. Based on key distinguishing features extracted from calculations and experiments, we identify candidates for the most common surface defects. Our results pave the way for the understanding of surface processes, like adsorption of metal dopants and photoactive molecules, that are fundamental for the catalytic and photovoltaic applications of anatase, and demonstrate the potential of dynamic AFM-STM for the characterization of wide band gap materials. PMID:26118408

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

    DEFF Research Database (Denmark)

    Settnes, Mikkel; Power, Stephen R.

    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 finite length scales yields real space conductance maps which show anisotropy for pristine graphene systems and quantum interference effects in the presence of isolated impurities. Spectral signatures in the Fourier transforms of real space conductance maps include characteristics that can be related to different scattering processes. We compute the conductance maps of graphene systems with different edge geometries or height fluctuations to determine the effects of nonideal graphene samples on dual-probe measurements. © 2014 American Physical Society.

  3. 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.

  4. Low temperature scanning tunneling spectroscopy on high quality Nb(110) films

    International Nuclear Information System (INIS)

    High quality Nb(110) films were prepared by evaporation onto (0001)oriented sapphire substrates at 850 C and analyzed in situ by Low Temperature Scanning Tunneling Spectroscopy (LT-STS). In this way, the superconducting gap in the quasi-particle density of states (DOS) of Nb(110) is investigated. The incomplete opening of this gap at 5.3 K can be attributed to the somewhat higher tip temperature of ? 7 K. Significant structures in the I-V data positioned symmetrically around zero energy and matching nicely known phonon energies of Nb indicate strong coupling behavior of this superconductor. These results suggest attempting an evaluation of the corresponding Eliashberg function, ?2F(?).

  5. Investigation of laser-induced effects in molecular layers by scanning tunneling microscopy

    Science.gov (United States)

    Grafström, S.; Schuller, P.; Kowalski, J.; Neumann, R.

    Aiming at the detection of laser-induced currents caused by resonant optical excitation of adsorbed molecules with a scanning tunneling microscope, we have developed a method that provides access to very small laser-induced effects normally hidden in the thermal background. An optical compensation setup based on two lasers with different wavelengths for controlling very precisely the thermal signal, together with a special scheme for signal averaging and interpolation, provides access to laser-induced signals down to <100 fA. We apply this method to molecular films consisting of islands of the dye perylene-tetracarboxylic-dianhydride (PTCDA) embedded in the liquid crystal octylcyanobiphenyl (8CB). Under complete compensation of the background, a statistically significant residual laser-induced current has been observed on the PTCDA islands with a magnitude of 125 fArms at a modulated laser intensity of 3.5 kWrms/cm2.

  6. Surface structure of niobium-dioxide overlayer on niobium(100) identified by scanning tunneling microscopy

    Science.gov (United States)

    Li, Y.; An, B.; Xu, X.; Fukuyama, S.; Yokogawa, K.; Yoshimura, M.

    2001-05-01

    The surface structures of an oxide overlayer on Nb(100) single crystal formed by numerous cycles of Ar-ion sputtering and flash annealing at 1973 K in an ultra-high-vacuum chamber have been investigated by scanning tunneling microscopy. Flat terraces with a monatomic step height of Nb(100) are observed; where two orthogonal domains are alternately evident. A ladder-like (3×10) structure of Nb(100) with no long-range order is identified at atomic resolution in the domain on the terrace. The ladder-like (3×10) structure is interpreted to be a modulated NbO2(010) overlayer on the Nb(100) surface and an atomic structural model of the ladder-like (3×10) structure is proposed.

  7. A theoretical model for single-molecule incoherent scanning tunneling spectroscopy

    International Nuclear Information System (INIS)

    Single-molecule scanning tunneling spectroscopy (STS), with dephasing due to elastic and inelastic scattering, is of some current interest. Motivated by this, we report an extended Hueckel theory (EHT)-based mean-field non-equilibrium Green's function (NEGF) transport model with electron-phonon scattering treated within the self-consistent Born approximation (SCBA). Furthermore, a procedure based on EHT basis set modification is described. We use this model to study the effect of the temperature-dependent dephasing due to low lying modes in the far-infrared range for which ??BT, on the resonant conduction through the highest occupied molecular orbital (HOMO) level of a phenyl dithiol molecule bonded to fcc-Au(111) contact. We finally propose to include dephasing in room temperature molecular resonant conduction calculations.

  8. A theoretical model for single-molecule incoherent scanning tunneling spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Raza, H [NSF Network for Computational Nanotechnology and School of Electrical and Computer Engineering, Purdue University, West Lafayette, IN 47907 (United States); School of Electrical and Computer Engineering, Cornell University, Ithaca, NY 14853 (United States)], E-mail: hr89@cornell.edu

    2008-11-05

    Single-molecule scanning tunneling spectroscopy (STS), with dephasing due to elastic and inelastic scattering, is of some current interest. Motivated by this, we report an extended Hueckel theory (EHT)-based mean-field non-equilibrium Green's function (NEGF) transport model with electron-phonon scattering treated within the self-consistent Born approximation (SCBA). Furthermore, a procedure based on EHT basis set modification is described. We use this model to study the effect of the temperature-dependent dephasing due to low lying modes in the far-infrared range for which {Dirac_h}{omega}<

  9. A theoretical model for single-molecule incoherent scanning tunneling spectroscopy

    Science.gov (United States)

    Raza, H.

    2008-11-01

    Single-molecule scanning tunneling spectroscopy (STS), with dephasing due to elastic and inelastic scattering, is of some current interest. Motivated by this, we report an extended Hückel theory (EHT)-based mean-field non-equilibrium Green's function (NEGF) transport model with electron-phonon scattering treated within the self-consistent Born approximation (SCBA). Furthermore, a procedure based on EHT basis set modification is described. We use this model to study the effect of the temperature-dependent dephasing due to low lying modes in the far-infrared range for which \\hbar \\omega \\ll k_{\\mathrm {B}}T , on the resonant conduction through the highest occupied molecular orbital (HOMO) level of a phenyl dithiol molecule bonded to fcc-Au(111) contact. We finally propose to include dephasing in room temperature molecular resonant conduction calculations.

  10. Interfacial self-assembly of amino acids and peptides: Scanning tunneling microscopy investigation

    Science.gov (United States)

    Xu, Li-Ping; Liu, Yibiao; Zhang, Xueji

    2011-12-01

    Proteins play important roles in human daily life. To take advantage of the lessons learned from nature, it is essential to investigate the self-assembly of subunits of proteins, i.e., amino acids and polypeptides. Due to its high resolution and versatility of working environment, scanning tunneling microscopy (STM) has become a powerful tool for studying interfacial molecular assembly structures. This review is intended to reflect the progress in studying interfacial self-assembly of amino acids and peptides by STM. In particular, we focus on environment-induced polymorphism, chiral recognition, and coadsorption behavior with molecular templates. These studies would be highly beneficial to research endeavors exploring the mechanism and nanoscale-controlling molecular assemblies of amino acids and polypeptides on surfaces, understanding the origin of life, unravelling the essence of disease at the molecular level and deeming what is necessary for the ``bottom-up'' nanofabrication of molecular devices and biosensors being constructed with useful properties and desired performance.

  11. Hydrogen adsorption on Ru(001) studied by Scanning TunnelingMicroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Tatarkhanov, Mous; Rose, Franck; Fomin, Evgeny; Ogletree, D.Frank; Salmeron, Miquel

    2008-01-18

    The adsorption of hydrogen on Ru(001) was studied by scanning tunneling microscopy at temperatures around 50 K. Hydrogen was found to adsorb dissociatively forming different ordered structures as a function of coverage. In order of increasing coverage {theta} in monolayers (ML) these were ({radical}3 x {radical}3)r30{sup o} at {theta} = 0.3 ML; (2 x 1) at {theta} = 0.50 ML, (2 x 2)-3H at {theta} = 0.75, and (1 x 1) at {theta} = 1.00. Some of these structures were observed to coexist at intermediate coverage values. Close to saturation of 1 ML, H-vacancies (unoccupied three fold fcc hollow Ru sites) were observed either as single entities or forming transient aggregations. These vacancies diffuse and aggregate to form active sites for the dissociative adsorption of hydrogen.

  12. Surface structure and spectroscopy of charge-density wave materials using scanning tunneling microscopy

    International Nuclear Information System (INIS)

    The Scanning tunneling microscope (STM) has been used to study the effects of Fe doping on the charge-density wave (CDW) structure in NbSe3 and 1T-TaS2. In NbSe3 small amounts of Fe reduce both CDW gaps by 25--30% and change the relative CDW amplitudes of the high and low temperature CDWs. The CDW amplitudes remain strong on all three chains of the surface unit cell with no evident disorder. In 1T-Fe0.05Ta0.95S2 the Fe introduces substantial disorder in the CDW pattern, but the local CDW amplitude remains strong. The CDW energy gap is reduced by approximately 50% and the resistive anomaly at the commensurate-incommensurate transition is removed. The STM in both the image and spectroscopy modes can detect subtle changes in CDW structure due to impurities

  13. Scanning tunneling microscopy of charge-density waves in NbSe3

    International Nuclear Information System (INIS)

    The charge-density wave (CDW) structure in NbSe3 due to the two independent CDWs has been imaged by scanning tunneling microscopy. As predicted by band structure considerations the CDW modulation is observed to be substantially localized on different chains for the separate CDWs. At 77K where only the high temperature CDW exists a relatively weak modulation with a single component along the /bar b/-axis is observed. At 4.2K the low temperature CDW contributes a much stronger /approximately/4/bar b/0 /times/ 2/rvec c/0 superlattice modulation. The combination of atomic resolution and CDW modulations allows an unambiguous identification of the chain structure to be made. 9 refs., 5 figs

  14. A scanning tunneling microscope break junction method with continuous bias modulation

    Science.gov (United States)

    Beall, Edward; Yin, Xing; Waldeck, David H.; Wierzbinski, Emil

    2015-09-01

    Single molecule conductance measurements on 1,8-octanedithiol were performed using the scanning tunneling microscope break junction method with an externally controlled modulation of the bias voltage. Application of an AC voltage is shown to improve the signal to noise ratio of low current (low conductance) measurements as compared to the DC bias method. The experimental results show that the current response of the molecule(s) trapped in the junction and the solvent media to the bias modulation can be qualitatively different. A model RC circuit which accommodates both the molecule and the solvent is proposed to analyze the data and extract a conductance for the molecule.Single molecule conductance measurements on 1,8-octanedithiol were performed using the scanning tunneling microscope break junction method with an externally controlled modulation of the bias voltage. Application of an AC voltage is shown to improve the signal to noise ratio of low current (low conductance) measurements as compared to the DC bias method. The experimental results show that the current response of the molecule(s) trapped in the junction and the solvent media to the bias modulation can be qualitatively different. A model RC circuit which accommodates both the molecule and the solvent is proposed to analyze the data and extract a conductance for the molecule. Electronic supplementary information (ESI) available: Additional current-time traces recorded for mesitylene, 2,4-dichlorotoluene, and 3,4-dichlorotoluene under different bias modulation frequencies, determined solvent capacitance values, and traces recorded under various geometrical constraints in the experimental cell. See DOI: 10.1039/c5nr04649a

  15. Cross sectional scanning tunneling microscopy and spectroscopy of fractured oxide surfaces and heterostructure interfaces

    International Nuclear Information System (INIS)

    Recently, interfaces between novel oxide materials have become a playground for manipulation of new functionalities. At interfaces, the broken symmetry and the spatially confined environment have been shown to modify the local interactions and generate wholly new electronic phases (e.g. magnetism, metallicity, superconductivity etc.) distinct from the composite bulk materials. However, to date our understanding of these interface driven phases is still limited. While there exist powerful spatially resolved tools for visualizing the chemical and magnetic structure of an interface, a direct observation of electronic behavior across the interface presents a major experimental challenge. After the success of creating flat fractured surfaces on Nb-doped SrTiO3 (Nb:STO) accessible to scanning tunneling microscopy (STM), we have further harnessed the high-sensitivity to electronic local density of states (LDOS) of the scanning tunneling spectroscopy (STS) in cross-sectional geometry to visualize complex oxide interface electronic properties. By extending XSTM/S to the interface between colossal magnetoresistant manganite La2/3Ca1/3MnO3 (LCMO) and semiconducting Nb:STO, we were able to map the LDOS across the boundary to unambiguously visualize the interface by the location of the valence band and elucidate the fundamental issue of band alignment at a complex oxide heterointerface. Use of the Center for Nanoscale Materials was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. (author)

  16. Imaging by in situ Scanning Tunnelling Microscopy and its Nanotechnological Perspectives

    DEFF Research Database (Denmark)

    Andersen, Jens Enevold Thaulov

    2002-01-01

    The development of in situ Scanning Tunneling Microscopy (in situ STM) and the implementation to scientific investigations is documented. The term ‘in situ’ that is added to the STM refers to an advanced development of the microscope, which encompasses tip coating and bipotentiostatic control of the tip and working electrode. In collaboration with Danish Micro Engineering A/S, the instrument was constructed and tested in laboratory environments. The system was successfully developed, as to meet international-market requirements. Within the frame of the work, procedures of tip coating and bipotentiostat construction were evaluated. After the fulfilment of the instrument manufacturing process followed application of the system to scientific investigations. The generation of an image by in situ STM is founded on the principle of electron tunneling but the application of the instrument to aqueous conditions introduces an influence of electrochemical currents to the image interpretation. The corresponding technique where the image is exclusively generated by electrochemical currents is denoted as Scanning Electrochemical Microscopy (SECM). The combined current contributions are considered in the interpretation of the imaging procedure. Other methods of in situ Scanning Probe Microscopy (in situ SPM), such as in situ Scanning Force Microscopy (in situ AFM) are considered for the sake of comparison and they are applied to imaging of non-conducting systems. Major results include demonstration of atomic resolution at Au(111) in electrolyte, imaging of bulk-metal electrocrystallisation, imaging of pulse plating and imaging of single-molecule metalloproteins in the adsorbed state. Methods of covalent immobilisation of proteins, which enables imaging by in situ STM were developed. The combination of simultaneous imaging and electrochemical manipulation offers unprecedented possibilities of device construction at the nanometer level. The present work is therefore intended as a promotion of in situ STM as a tool of nanotechnology that allows device fabrication of sub-nanometer tolerances. Novel applications and disclosures are included in the presentation with emphasis on thiol self-assembled monolayers (SAM’s), on electrochemical-surface manipulations and on imaging of proteins. Evidence of the validity of successful imaging of adsorbed metalloproteins is presented and perspectives of nano-biotechnology are evaluated. It is thus documented that in situ STM constitutes an indispensable tool of nanotechnology. Keywords are imaging and control. The manufacture of nanotechnological devices is exemplified by construction of a ‘nanotypewriter’ that exploits a novel feature of electrochemistry. The nanotypewriter is patented in Denmark and U.S.A.

  17. Variations of x-ray spectra in water phantom during CT scanning. Simulation study

    International Nuclear Information System (INIS)

    Computed tomography (CT) is indispensable in diagnostic radiology today. The specifications of the patient dose undergoing CT examinations has a significant problem because the dose distribution is non-uniform and many dosimeters have to be used to obtain each organ dose. Detector response is based on the absorbed dose in detector materials and the dose must be converted to that in water to obtain the patient dose. The correction for the detector response in patient dosimetry needs the x-ray spectra in tissue equivalent phantoms. The variations of x-ray spectra in water phantoms during CT scanning were calculated with the Monte Carlo method. The results indicate that x-ray spectra in water phantoms are quite different from incident x-ray spectra and dependent on the position in water phantoms, phantom sizes and incident x-ray spectra. The variations of x-ray spectra are attributed to the beam-hardening due to the photoelectric effect and the beam softening due to the compton scattering. (T. Tanaka)

  18. Investigation of cross-sectional area of the carpal canal by CT scanning as a factor causing carpal tunnel syndrome

    International Nuclear Information System (INIS)

    The cross-sectional area of the carpal tunnel in patients with carpal tunnel syndrome (CTS) and healthy controls was measured using CT scanning to investigate the relationship between the cross-sectional area and the occurrence of this syndrome. The cross-sectional area in patients with idiopathic CTS was significantly narrowed at the levels of proximal part (Pm) where scaphoid and pisiform bones were visualized and of the distal part (D1, D2) where the trapezium and hook of hamate were visualized, as compared with the controls, suggesting that the median nerve within the carpal tunnel is easily compressed at the level D1. Narrowing of the cross-sectional area of the carpal tunnel can be estimated by measuring the transverse and antero-posterior diameters. (namekawa, k.)

  19. 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)

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

    International Nuclear Information System (INIS)

    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)

  1. Scanning Tunneling Microscopy study on exfoliated single-layer MoSe2

    Science.gov (United States)

    Zhou, Xiaodong; Dadgar, Ali; Ross, Frances M.; Pasupathy, Abhay N.

    2015-03-01

    Monolayer transitional metal dichalcogenides (TMDs) MX2 (M = Mo, W, Ti etc; X = S, Se, Te) are a new platform for exploring new electronic and optical phenomena and functionality. However, much remains to be understood about their chemical and local electronic properties when taken to the monolayer limit. We will discuss a scanning tunneling microscopy (STM) study on exfoliated single-layer MoSe2 using a 4-probe STM system. The ability to carry out scanning electron microscopy (SEM) in our system allows us to easily locate and measure single-layer MoSe2 flakes that are mechanically exfoliated on a SiO2/Si substrate and are only a few micrometers in lateral size. Using a combination of imaging and spectroscopy, we will discuss the chemical purity and nature of defect states in this monolayer material. Using a electrostatic back gate, we will describe measurements of the single-particle electronic bandgap as a function of the chemical potential.

  2. 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...

  3. 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; Horch, Sebastian

    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 using...

  4. New insights into nano-magnetism by spin-polarized scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Sander, Dirk, E-mail: sander@mpi-halle.de [Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, D-06120 Halle/Saale (Germany); Oka, Hirofumi; Corbetta, Marco; Stepanyuk, Valeri; Kirschner, Jürgen [Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, D-06120 Halle/Saale (Germany)

    2013-08-15

    Highlights: ? We measure the magnetization reversal of individual nm small Co island by spin-STM. ? We identify an inhomogeneous magnetic anisotropy within a single Co island. ? The magnetic anisotropy near the rim is negligible as compared to 0.148 meV/atom at the island center. ? A crossover of the magnetization reversal from an exchange-spring behavior to domain wall formation is suggested. ? The impact of the observed spatial variation of the spin-dependent electronic properties on reversal is discussed. -- Abstract: We study the magnetization reversal and the position dependence of the spin-dependent electronic properties of nm small bilayer Co islands on Cu(1 1 1) by spin-polarized scanning tunneling microscopy in magnetic fields at low temperatures of 8 K. The analysis of the energy barrier of magnetization reversal from measurements of the switching field suggests a crossover of the magnetization reversal mode with increasing island size around 7500 atoms from exchange-spring behavior to domain wall formation. The quantitative analysis of the island size dependence of the energy barrier indicates an inhomogeneous magnetic anisotropy of the island. The island rim is magnetically soft, whereas the center shows a pronounced effective anisotropy of 0.148 meV/atom. We speculate that this inhomogeneity of the magnetic anisotropy might be a consequence of the spatial dependence of the spin-dependent electronic properties. We measure a spin-polarization and a tunnel magneto resistance ratio of opposite sign at the rim as compared to the island center.

  5. H3PW12O40-functionalized tip for scanning tunneling microscopy.

    Science.gov (United States)

    Song, In K; Kitchin, John R; Barteau, Mark A

    2002-04-30

    Recent reports of C(60)-functionalized metal tips [Kelly, K. F., Sarkar, D., Hale, G. D., Oldenburg, S. J. & Halas, N. J. (1996) Science 273, 1371-1373] and carbon nanotube tips [Dai, H., Hafner, J. H., Rinzler, A. G., Colbert, D. T. & Smalley, R. E. (1996) Nature (London) 384, 147-151] demonstrate the potential of controlling the chemical identity and geometric structure of tip atoms in scanning tunneling microscopy (STM). This work reports the performance of a heteropolyacid (HPA)-functionalized Pt/Ir tip, which was formulated by contacting a mechanically formed tip with a solution of H(3)PW(12)O(40) molecules. Attachment of an H(3)PW(12)O(40) molecule on the metal tip was confirmed by observing the characteristic negative differential resistance (NDR) behavior of H(3)PW(12)O(40) in tunneling spectroscopy. Atomic resolution images of bare graphite as well as of H(6)P(2)W(18)O(62) HPA monolayers on graphite were successfully obtained with a Pt/Ir-HPA tip. In the H(3)PW(12)O(40) molecule on a metal tip, it is likely that a terminal oxygen of WO (an oxygen species projecting outward from the pseudospherical H(3)PW(12)O(40) molecule) serves as an atomically sharp and stable tip. Additionally, superimposed superperiodic structures commensurate with the underlying graphite lattice were regularly observed with the modified tips. This result suggests that tip functionalization with these metal oxide molecules may enhance resolution in a fashion analogous to functionalization with C(60). PMID:11904387

  6. Organic Molecular Thin Films: Growth, Structure, and Manipulation Studied by Scanning Tunneling Microscopy

    Science.gov (United States)

    Stock, Taylor J. Z.

    Room temperature scanning tunneling microscopy (RT-STM) has been used to observe the growth modes, morphologies and crystal structures of sub-monolayer (ML) to multilayer thin films of phthalocyanines (H2Pc and CuPc), C60 fullerenes, and CuPc:C60 composites, grown on the Cu(111) surface. In addition to imaging these films, STM has been used to manipulate the various molecules via hot tunneling electron injection. At sub-ML coverage the phthalocyanines are mobile on the Cu(111) and form a diffuse 2D gas. Molecules in this mobile phase can be immobilized on the substrate through exposure to tunneling electrons at a bias voltage exceeding a threshold value. The bias threshold value and strength of the induced molecular immobilization is dependent on the particular phthalocyanine molecule/substrate combination. At approximately one ML coverage the phthalocyanine molecules become sterically confined and lie flat on the Cu(111), forming an ordered 2D lattice. As coverage is increased beyond 1ML in the Cu(111)-CuPc system, the molecule-substrate interaction diminishes in strength and the intermolecular interaction becomes dominant, causing the molecular crystal lattice parameters to evolve towards the bulk α-phase. This trend continues for the layer-by-layer growth of three complete ML, and then gives way to 3D island growth at a coverage of 4 ML. The 3D island growth mode of the pure CuPc films is dramatically suppressed by the inclusion of C60 during deposition. X-ray diffraction (XRD) and STM studies reveal that the CuPc molecular packing is altered upon C 60 inclusion, producing disordered CuPc-C60 interfaces. The ordered molecular stacking of CuPc is found to be disrupted completely when C60 concentration reaches 30 wt.%. This disorder in the CuPc:C 60 composites is explained in terms of the relative strengths of the intermolecular interactions. Furthermore, an understanding of these relative interaction strengths is exploited to grow ordered composite films, through selective sequential depositions.

  7. Mirror Buckling Transitions in Freestanding Graphene Membranes Induced through Scanning Tunneling Microscopy

    Science.gov (United States)

    Schoelz, James K.

    Graphene has the ability to provide for a technological revolution. First isolated and characterized in 2004, this material shows promise in the field of flexible electronics. The electronic properties of graphene can be tuned by controlling the shape of the membrane. Of particular interest in this endeavor are the thermal ripples in graphene membranes. Years of theoretical work by such luminaries as Lev Landau, Rudolf Peierls, David Mermin and Herbert Wagner have established that 2D crystals should not be thermodynamically stable. Experimental research on thin films has supported this finding. Yet graphene exists, and freestanding graphene films have been grown on large scales. It turns out that coupling between the bending and stretching phonons can stabilize the graphene in a flat, albeit rippled phase. These ripples have attracted much attention, and recent work has shown how to arrange these ripples in a variety of configurations. In this thesis, I will present work done using a scanning tunneling microscope (STM) to interact with freestanding graphene membranes. First I will present STM images of freestanding graphene and show how these images show signs of distortion under the electrostatic influence of the STM tip. This electrostatic attraction between the STM tip and the graphene sample can be used to pull on the graphene sample. At the same time, by employing Joule heating in order to heat graphene using the tunneling current, and exploiting the negative coefficient of thermal expansion, a repulsive thermal load can be generated. By repeatedly pulling on the graphene using the electrostatic potential, while sequentially increasing the setpoint current we can generate a thermal mirror buckling event. Slowly heating the graphene using the tunneling current, prepares a small convex region of graphene under the tip. By increasing thermal stress, as well as pulling using the out of plane electrostatic force, the graphene suddenly and irreversibly switches the sign of its curvature. This event is discovered using STM measurements and supplemented by molecular dynamics simulations. Finally, I will show how to characterize this transition using the famed Ising model. The ripples are modeled as individual Ising spins, which at low temperature exhibit antiferromagnetic coupling. By heating the graphene membrane, the strain increases, changing the antiferromagnetic coupling to ferromagnetic coupling, which characterizes the irreversible transition from a soft, flexible state to a rigid configuration.

  8. 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.

  9. Spatial homogeneity and doping dependence of quasiparticle tunneling spectra in cuprate superconductors

    CERN Document Server

    Yeh, N C; Hammerl, G; Mannhart, J; Tajima, S; Yoshida, K; Schmehl, A; Schneider, C W; Schulz, R R

    2001-01-01

    Scanning tunneling spectroscopy (STS) studies reveal long-range (~100 nm) spatial homogeneity in optimally and underdoped superconducting YBa_2Cu_3O_{7-\\delta} (YBCO) single crystals and thin films, and macroscopic spatial modulations in overdoped (Y_{0.7}Ca_{0.3})Ba_2Cu_3O_{7-\\delta} (Ca-YBCO) epitaxial films. In contrast, STS on an optimally doped YBa_2(Cu_{0.9934}Zn_{0.0026}Mg_{0.004})_3O_{6.9} single crystal exhibits strong spatial modulations and suppression of superconductivity over a microscopic scale near the Zn or Mg impurity sites, and the global pairing potential is also reduced relative to that of optimally doped YBCO, suggesting strong pair-breaking effects of the non-magnetic impurities. The spectral characteristics are consistent with d_{x^2-y^2} pairing symmetry for the optimally and underdoped YBCO, and with (d_{x^2-y^2}+s) for the overdoped Ca-YBCO. The doping-dependent pairing symmetry suggests interesting changes in the superconducting ground state, and is consistent with the presence of n...

  10. Sensitivity Analysis of X-ray Spectra from Scanning Electron Microscopes

    Energy Technology Data Exchange (ETDEWEB)

    Miller, Thomas Martin [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Patton, Bruce W. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Weber, Charles F. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Bekar, Kursat B. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2014-10-01

    The primary goal of this project is to evaluate x-ray spectra generated within a scanning electron microscope (SEM) to determine elemental composition of small samples. This will be accomplished by performing Monte Carlo simulations of the electron and photon interactions in the sample and in the x-ray detector. The elemental inventories will be determined by an inverse process that progressively reduces the difference between the measured and simulated x-ray spectra by iteratively adjusting composition and geometric variables in the computational model. The intended benefit of this work will be to develop a method to perform quantitative analysis on substandard samples (heterogeneous phases, rough surfaces, small sizes, etc.) without involving standard elemental samples or empirical matrix corrections (i.e., true standardless quantitative analysis).

  11. Quantitative impedance characterization of sub-10 nm scale capacitors and tunnel junctions with an interferometric scanning microwave microscope

    International Nuclear Information System (INIS)

    We present a method to characterize sub-10 nm capacitors and tunnel junctions by interferometric scanning microwave microscopy (iSMM) at 7.8 GHz. At such device scaling, the small water meniscus surrounding the iSMM tip should be reduced by proper tip tuning. Quantitative impedance characterization of attofarad range capacitors is achieved using an ‘on-chip’ calibration kit facing thousands of nanodevices. Nanoscale capacitors and tunnel barriers were detected through variations in the amplitude and phase of the reflected microwave signal, respectively. This study promises quantitative impedance characterization of a wide range of emerging functional nanoscale devices. (paper)

  12. Tip-induced excitation of a single vortex in nano-size superconductors using scanning tunneling microscopy.

    Science.gov (United States)

    Nishio, Takahiro; Lin, Shizeng; An, Toshu; Eguchi, Toyoaki; Hasegawa, Yukio

    2010-11-19

    A single vortex is excited into nano-size Pb superconducting island structures by a local current injection from a probe tip of a scanning tunneling microscope. For the excitation, a sufficient amount and duration of the pulsed current are required. Injecting the current at peripheral sites is more effective than the center for the vortex excitation. Time-dependent Ginzburg-Landau calculations suggest that a current-induced normal-state area, which can be nucleated by the tunneling current exceeding the critical current and expanded by the Joule heating, reduces the required magnetic field for the vortex penetration and excites a vortex into the islands. PMID:20972314

  13. Tip-induced excitation of a single vortex in nano-size superconductors using scanning tunneling microscopy

    International Nuclear Information System (INIS)

    A single vortex is excited into nano-size Pb superconducting island structures by a local current injection from a probe tip of a scanning tunneling microscope. For the excitation, a sufficient amount and duration of the pulsed current are required. Injecting the current at peripheral sites is more effective than the center for the vortex excitation. Time-dependent Ginzburg-Landau calculations suggest that a current-induced normal-state area, which can be nucleated by the tunneling current exceeding the critical current and expanded by the Joule heating, reduces the required magnetic field for the vortex penetration and excites a vortex into the islands.

  14. Combining scanning tunneling microscopy and synchrotron radiation for high-resolution imaging and spectroscopy with chemical, electronic, and magnetic contrast

    International Nuclear Information System (INIS)

    The combination of high-brilliance synchrotron radiation with scanning tunneling microscopy opens the path to high-resolution imaging with chemical, electronic, and magnetic contrast. Here, the design and experimental results of an in-situ synchrotron enhanced x-ray scanning tunneling microscope (SXSTM) system are presented. The system is designed to allow monochromatic synchrotron radiation to enter the chamber, illuminating the sample with x-ray radiation, while an insulator-coated tip (metallic tip apex open for tunneling, electron collection) is scanned over the surface. A unique feature of the SXSTM is the STM mount assembly, designed with a two free-flex pivot, providing an angular degree of freedom for the alignment of the tip and sample with respect to the incoming x-ray beam. The system designed successfully demonstrates the ability to resolve atomic-scale corrugations. In addition, experiments with synchrotron x-ray radiation validate the SXSTM system as an accurate analysis technique for the study of local magnetic and chemical properties on sample surfaces. The SXSTM system's capabilities have the potential to broaden and deepen the general understanding of surface phenomena by adding elemental contrast to the high-resolution of STM. -- Highlights: ? Synchrotron enhanced x-ray scanning tunneling microscope (SXSTM) system designed. ? Unique STM mount design allows angular DOF for tip alignment with x-ray beam. ? System demonstrates ability to resolve atomic corrugations on HOPG. ? Studies show chemical sensitivity with STM tip from photocurrent and tunneling. ? Results show system's ability to study local magnetic (XMCD) properties on Fe films.

  15. Development, design and signal processing of a scanning tunneling microscope for measurement of rough surfaces

    International Nuclear Information System (INIS)

    In this work the development and the construction of a scanning tunneling microscope (STM) are described, which is also able to measure relatively rough surfaces. Rough surfaces are considered to have an elevation of the gradient of 45o and more. Such measurements pose special requirements for the construction and especially for the signal processing and control of the STM. For the reconstruction of the sample surface by the raw data delivered by the STM the knowledge about the exact behavior of the STM is essential. For this reason the identification of the individual components is very important. Especially the mechanical behavior of the probe head which positions the sensor tip over the sample is a matter of particular interest. To calculate the exact position of the sensor tip a mechanical model is introduced. The unknown parameters of this model are determined using a laser vibrometer. Because of cost and space limitations the mechanical deflections of the piezoelectric actuators of the probe head aren't checked by range sensors. So an identification of the piezoelectric actuators is required. In particular, the hysteresis behavior of piezoelectric transducers represents a major challenge. Using the mathematical hysteresis model of Coleman and Hodgdon succeeds in solving this problem. To carry out an effective control, the behavior of the STM is modeled in a simulation. Using this model, the design of a fast controller is described. The controller improves the dynamic behavior of the STM and allows short measurement periods. The work includes detailed descriptions of the mechanical setup and electronics of the STM in the form of working drawings, schematics and PCB layouts. In addition instructions for two different methods of tip preparation are given. The presented methods and solutions are not limited to the STM, but can be directly transferred to other varieties of scanning probe microscopes. (author)

  16. 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 ?lms 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 classi?cation 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 ?lms beyond imaging the topography of the surface atoms.

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

    DEFF Research Database (Denmark)

    Lin, H.P.; Rauba, J.M.C.

    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 (STM) techniques. The theoretical treatment of the STM operation has traditionally been based on the Bardeen and Tersoff-Hamann methods which take as input the single-particle wave functions and eigenvalues obtained from finite cluster or slabs models of the surface-tip interface. Here, we present a novel STM simulation scheme based on non-equilibrium Green's functions (NEGF) and Wannier functions which is both accurate and very efficient. The main novelty of the scheme compared to the Bardeen and Tersoff-Hamann approaches is that the coupling to the infinite (macroscopic) electrodes is taken into account. As an illustrating example we apply the NEGF-STM method to the Si(001)(2x1):H surface with sub-surface P doping and discuss the results in comparison to the Bardeen and Tersoff-Hamann methods.

  18. A New Scanning Tunneling Microscope Reactor Used for High Pressure and High Temperature Catalysis Studies

    Energy Technology Data Exchange (ETDEWEB)

    Tao, Feng; Tang, David C.; Salmeron, Miquel; Somorjai, Gabor A.

    2008-05-12

    We present the design and performance of a home-built high-pressure and high-temperature reactor equipped with a high-resolution scanning tunneling microscope (STM) for catalytic studies. In this design, the STM body, sample, and tip are placed in a small high pressure reactor ({approx}19 cm{sup 3}) located within an ultrahigh vacuum (UHV) chamber. A sealable port on the wall of the reactor separates the high pressure environment in the reactor from the vacuum environment of the STM chamber and permits sample transfer and tip change in UHV. A combination of a sample transfer arm, wobble stick, and sample load-lock system allows fast transfer of samples and tips between the preparation chamber, high pressure reactor, and ambient environment. This STM reactor can work as a batch or flowing reactor at a pressure range of 10{sup -13} to several bars and a temperature range of 300-700 K. Experiments performed on two samples both in vacuum and in high pressure conditions demonstrate the capability of in situ investigations of heterogeneous catalysis and surface chemistry at atomic resolution at a wide pressure range from UHV to a pressure higher than 1 atm.

  19. Copper intercalation at the interface of graphene and Ir(111) studied by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    We report on the intercalation of a submonolayer of copper at 775 K underneath graphene epitaxially grown on Ir(111) studied by means of low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) at 77 K. Nucleation and growth dynamics of Cu below graphene have been investigated, and, most importantly, the intercalation mechanism has been identified. First, LEED patterns reveal the pseudomorphic growth of Cu on Ir under the topmost graphene layer resulting in a large Cu in-plane lattice parameter expansion of about 6% compared to Cu(111). Second, large-scale STM topographs as a function of Cu coverage show that Cu diffusion on Ir below graphene exhibits a low energy barrier resulting in Cu accumulation at Ir step edges. As a result, the graphene sheet undergoes a strong edges reshaping. Finally, atomically-resolved STM images reveal a damaged graphene sheet at the atomic scale after metal intercalation. Point defects in graphene were shown to be carbon vacancies. According to these results, a Cu penetration path beneath graphene is proposed to occur via metal aided defect formation with no or poor self healing of the graphene sheet. This work illustrates the fact that Cu intercalation is harmful for graphene grown on Ir(111) at the atomic scale

  20. A new variable temperature solution-solid interface scanning tunneling microscope

    Science.gov (United States)

    Jahanbekam, Abdolreza; Mazur, Ursula; Hipps, K. W.

    2014-10-01

    We present a new solution-solid (SS) interface scanning tunneling microscope design that enables imaging at high temperatures with low thermal drift and with volatile solvents. In this new design, distinct from the conventional designs, the entire microscope is surrounded in a controlled-temperature and controlled-atmosphere chamber. This allows users to take measurements at high temperatures while minimizing thermal drift. By incorporating an open solution reservoir in the chamber, solvent evaporation from the sample is minimized; allowing users to use volatile solvents for temperature dependent studies at high temperatures. The new design enables the user to image at the SS interface with some volatile solvents for long periods of time (>24 h). An increase in the nonlinearity of the piezoelectric scanner in the lateral direction as a function of temperature is addressed. A temperature dependent study of cobalt(II) octaethylporphyrin (CoOEP) at the toluene/Au(111) interface has been performed with this instrument. It is demonstrated that the lattice parameters remain constant within experimental error from 24 °C to 75 °C. Similar quality images were obtained over the entire temperature range. We report the unit cell of CoOEP at the toluene/Au(111) interface (based on two molecules per unit cell) to be A = (1.36 ± 0.04) nm, B = (2.51 ± 0.04) nm, and ? = 97° ± 2°.

  1. Scanning tunneling microscopy study of the possible topological surface states in BiTeCl.

    Science.gov (United States)

    Yan, Y J; Ren, M Q; Liu, X; Huang, Z C; Jiang, J; Fan, Q; Miao, J; Xie, B P; Xiang, F; Wang, X; Zhang, T; Feng, D L

    2015-12-01

    Recently, the non-centrosymmetric bismuth tellurohalides such as BiTeCl are being studied as possible candidates for topological insulators. While some photoemission studies showed that BiTeCl is an inversion asymmetric topological insulator, others showed that it is a normal semiconductor with Rashba splitting. Meanwhile, first-principle calculations have failed to confirm the existence of topological surface states in BiTeCl so far. Therefore, the topological nature of BiTeCl requires further investigation. Here we report a low-temperature scanning tunneling microscopy study on the surface states of BiTeCl single crystals. On the tellurium (Te) -terminated surfaces with relatively low defect density, evidence for topological surface states is observed in the quasi-particle interference patterns, both in the anisotropy of the scattering vectors and the fast decay of the interference near the step edges. Meanwhile, on the samples with much higher defect densities, we observed surface states that behave differently. Our results may help to resolve the current controversy on the topological nature of BiTeCl. PMID:26491022

  2. Interaction of scanning tunneling microscopy tip with mesoscopic islands at the atomic-scale

    International Nuclear Information System (INIS)

    Performing atomic-scale simulations, we study the interaction of the scanning tunneling microscopy (STM) tip with mesoscopic islands at zero bias voltage. Our calculations reveal tip-induced shape transitions in Co islands on Cu(100) as the tip approaches the surface. The structure of the islands and of the tip are found to depend strongly on the tip-substrate distance. A significant influence of the tip on atomic diffusion on the top and at the edges of the islands is demonstrated. The size-dependent strain relief in the islands caused by the tip and by the substrate is found to play a key role in atomistic processes on islands. Our results show that, for certain tip-surface separations, the hopping diffusion of Co adatoms on the top of Co islands and the upward mass transport at the edge of the islands can be strongly enhanced. Our findings point out the possibility of manipulating atomic motion on mesoscopic islands using the STM tip. (letter to the editor)

  3. 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.

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

    DEFF Research Database (Denmark)

    Christensen, Finn Erland; Besenbacher, Flemming

    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 reveal that the surfaces consist of islands with different topographic features. The microroughness is found to be in the range from 7 to 1 5 Å, and the characteristic length scale for this microroughness is estimated to be between 0.03 and 0.06 m. For the thin foil mirrors it is found 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. The results can be used as a guide when selecting the best coating process in the production of x-ray mirrors.

  5. 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.

  6. Theoretical characterisation of point defects on a MoS2 monolayer by scanning tunnelling microscopy.

    Science.gov (United States)

    González, C; Biel, B; Dappe, Y J

    2016-03-11

    Different S and Mo vacancies as well as their corresponding antisite defects in a free-standing MoS2 monolayer are analysed by means of scanning tunnelling microscopy (STM) simulations. Our theoretical methodology, based on the Keldysh nonequilibrium Green function formalism within the density functional theory (DFT) approach, is applied to simulate STM images for different voltages and tip heights. Combining the geometrical and electronic effects, all features of the different STM images can be explained, providing a valuable guide for future experiments. Our results confirm previous reports on S atom imaging, but also reveal a strong dependence on the applied bias for vacancies and antisite defects that include extra S atoms. By contrast, when additional Mo atoms cover the S vacancies, the MoS2 gap vanishes and a bias-independent bright protrusion is obtained in the STM image. Finally, we show that the inclusion of these point defects promotes the emergence of reactive dangling bonds that may act as efficient adsorption sites for external adsorbates. PMID:26862020

  7. Probing the location of displayed cytochrome b562 on amyloid by scanning tunnelling microscopy

    International Nuclear Information System (INIS)

    Amyloid fibres displaying cytochrome b562 were probed using scanning tunnelling microscopy (STM) in vacuo. The cytochromes are electron transfer proteins containing a haem cofactor and could, in principle, mediate electron transfer between the tip and the gold substrate. If the core fibres were insulating and electron transfer within the 3D haem network was detected, then the electron transport properties of the fibre could be controlled by genetic engineering. Three kinds of STM images were obtained. At a low bias (562 was not detected by STM, which was attributed to low adhesion, whereas a monomeric multi-haem protein, GSU1996, was readily imaged. We conclude that the fibre superstructure may be intermittently conducting, that the cytochromes have been seen within the fibres and that they are too far apart for detectable current flow between sites to occur. We predict that GSU1996, being 10 nm long, is more likely to mediate successful electron transfer along the fibre as well as being more readily detectable when displayed from amyloid. (paper)

  8. Oxidation of graphene on Ru(0 0 0 1) studied by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    The oxidation of graphene layer on Ru(0 0 0 1) has been investigated by means of scanning tunneling microscopy. Graphene overlayer can be formed by decomposing ethyne on Ru(0 0 0 1) at a temperature of about 1000 K. The lattice mismatch between the graphene overlayer and the substrate causes a moire pattern with a superstructure in a periodicity of about 30 A. The oxidation of graphene/Ru(0 0 0 1) was performed by exposure the sample to O2 gas at 823 K. The results showed that, at the initial stage, the oxygen intercalation between the graphene and the Ru(0 0 0 1) substrate takes place at step edges, and extends on the lower steps. The oxygen intercalation decouples the graphene layer from the Ru(0 0 0 1) substrate. More oxygen intercalation yields wrinkled bumps on the graphene surface. The oxidation of graphene, or the removal of carbon atoms can be attributed to a process of the combination of the carbon atoms with atomic oxygen to form volatile reaction products. Finally, the Ru(0 0 0 1)-(2 x 1)O phase was observed after the graphene layer is fully removed by oxidation.

  9. Scanning Tunneling Spectroscopy of Transition Metal Dichalcogenides: Quasiparticle Gap, Critical Point Energies and Heterojunction Band Offsets

    Science.gov (United States)

    Shih, Chih-Kang

    2015-03-01

    As an emergent atomically thin electronic and photonic materials material, transition metal dichalcogenides (TMDs) has triggered intensive research activities toward understanding of their electronic structures. Here I will introduce a comprehensive form of scanning tunneling spectroscopy (STS) which allows us to probe details quasi-particle electronic structures of TMDs. More specifically, we show that not only the quasi-particle band gaps but also the critical point energy locations and their origins in the Brillouin Zone (BZ) can be revealed using this comprehensive form of STS. By using this new method, we unravel the systematic trend of the critical point energies for TMDs due to atomic orbital couplings, spin-orbital coupling and the interlayer coupling. Moreover, by combining the micro-beam X-ray photoelectron spectroscopy (micro-XPS) and STS, we determine the band offsets in planar heterostructures formed between dissimilar single layer TMDs (MoS2, WSe2, and WS2). We show that both commutativity and transitivity of heterojunction band offset hold within the experimental uncertainty. Other Contributors: (i) Chendong Zhang, Yuxuan Chen, and Amber Johnson at the University of Texas at Austin; (ii) Ming-Yang Li, Jing-Kai Huang, Lain-Jong Li, Chih-Piao Chuu and Mei-Yin Chou at the Institute of Atomic and Molecular Sciences, Academia Sinica, Taiwan.

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

    DEFF Research Database (Denmark)

    Merte, Lindsay Richard; Grabow, Lars C.

    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 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 type of STM imaging mode, showing both Fe and O atoms, agrees well with simulated STM images, indicating that the simple Tersoff-Hamann theory is partially valid for this imaging mode. In addition, we identify other distinct, element-specific imaging modes which reveal a strong dependence 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.

  11. Copper intercalation at the interface of graphene and Ir(111) studied by scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Sicot, M., E-mail: muriel.sicot@univ-lorraine.fr; Fagot-Revurat, Y.; Kierren, B.; Vasseur, G.; Malterre, D. [Institut Jean Lamour, UMR 7198, CNRS Université de Lorraine, BP 70239, 54506 Vandoeuvre lès Nancy (France)

    2014-11-10

    We report on the intercalation of a submonolayer of copper at 775?K underneath graphene epitaxially grown on Ir(111) studied by means of low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) at 77?K. Nucleation and growth dynamics of Cu below graphene have been investigated, and, most importantly, the intercalation mechanism has been identified. First, LEED patterns reveal the pseudomorphic growth of Cu on Ir under the topmost graphene layer resulting in a large Cu in-plane lattice parameter expansion of about 6% compared to Cu(111). Second, large-scale STM topographs as a function of Cu coverage show that Cu diffusion on Ir below graphene exhibits a low energy barrier resulting in Cu accumulation at Ir step edges. As a result, the graphene sheet undergoes a strong edges reshaping. Finally, atomically-resolved STM images reveal a damaged graphene sheet at the atomic scale after metal intercalation. Point defects in graphene were shown to be carbon vacancies. According to these results, a Cu penetration path beneath graphene is proposed to occur via metal aided defect formation with no or poor self healing of the graphene sheet. This work illustrates the fact that Cu intercalation is harmful for graphene grown on Ir(111) at the atomic scale.

  12. Scanning Tunneling Microscopy Evidence for the Dissociation of Carbon Monoxide on Ruthenium Steps

    DEFF Research Database (Denmark)

    Tison, Yann; Nielsen, Kenneth

    2012-01-01

    In heterogeneous catalysis, identifying the active site for key reaction steps is an important contribution for the optimization of industrial synthesis. The structure sensitivity of CO dissociation on a metal catalyst, which is the rate-limiting step for the methanation and the Fischer–Tropsch processes under certain conditions, has been debated for years. Here, scanning tunneling microscopy (STM) and density functional theory (DFT) are used to clarify the role of monatomic steps in the splitting of CO on a stepped Ru(0 1 54) crystal, which displays alternating steps with either 4-fold or 3-fold symmetry. After CO doses at elevated temperatures, the STM images reveal step decorations characteristic of atomic oxygen resulting from CO dissociation on every second step. The comparison of the STM images with the results of DFT calculations shows that the step decoration occurs on the steps displaying the 4-fold symmetry. We conclude that the active sites for CO dissociation on ruthenium are located on the 4-foldsymmetry monatomic steps.

  13. Evidences of electrochemical graphene functionalization and substrate dependence by Raman and scanning tunneling spectroscopies

    Science.gov (United States)

    Daniels, Kevin M.; Daas, B. K.; Srivastava, N.; Williams, C.; Feenstra, R. M.; Sudarshan, T. S.; Chandrashekhar, M. V. S.

    2012-06-01

    Electrochemical functionalization and possible hydrogenation of treated epitaxial graphene samples on 6H-SiC are presented. To attract H+ ions to react with the exposed working cathode, a 10% sulfuric acid electrolyte was used with a Pt counter anode. Functionalization was determined using Raman spectroscopy and measured by a marked increase in I(D)/I(G) ratio and introduction of C-H bond peak at ˜2930 cm-1. There was also a marked increase in fluorescence background, which clearly differentiates functionalization from lattice damage in the graphene. Quantifying the fluorescence, we estimate that H-incorporation as high as 50% was achieved based on results on hydrocarbons, although other functional groups cannot be excluded. We further distinguished these functionalization signatures from lattice damage through measurements on nanocrystalline graphene on a and m plane SiC, which displayed very different surface morphologies and no measureable fluorescence. Finally, we show that the extent of functionalization is strongly substrate dependent by using samples cut from three semi-insulating 6H-SiC substrates with similar resistivity but orientations varying from on-axis (˜0.02°), 0.5° to 1.0° off-axis. This functionalization was found to be thermally reversible at ˜1000 °C. Scanning tunneling spectroscopy indicates the presence of sp3-like localized states not present in the starting graphene, further supporting the assertion that functionalization has occurred.

  14. Scanning tunneling microscopy and spectroscopy observations of the graphite edge state

    CERN Document Server

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

    2006-01-01

    We measured the electronic local density of states (LDOS) of graphite surfaces near monoatomic step edges, which consist of either the zigzag or armchair edge, with the scanning tunneling microscopy (STM) and spectroscopy (STS) techniques. The STM data reveal that the $(\\sqrt{3} \\times \\sqrt{3}) R 30^{\\circ}$ and honeycomb superstructures coexist over a length scale of 3-4 nm from both the edges. By comparing with density-functional derived non-orthogonal tight-binding calculations, we show that the coexistence is due to a slight admixing of the two types of edges at the graphite surfaces. In the STS measurements, a clear peak in the LDOS at negative bias voltages from -100 to -20 mV was observed near the zigzag edges, while such a peak was not observed near the armchair edges. We concluded that this peak corresponds to the graphite "edge state" theoretically predicted by Fujita \\textit{et al.} [J. Phys. Soc. Jpn. {\\bf 65}, 1920 (1996)] with a tight-binding model for graphene ribbons. The existence of the edg...

  15. Theoretical characterisation of point defects on a MoS2 monolayer by scanning tunnelling microscopy

    Science.gov (United States)

    González, C.; Biel, B.; Dappe, Y. J.

    2016-03-01

    Different S and Mo vacancies as well as their corresponding antisite defects in a free-standing MoS2 monolayer are analysed by means of scanning tunnelling microscopy (STM) simulations. Our theoretical methodology, based on the Keldysh nonequilibrium Green function formalism within the density functional theory (DFT) approach, is applied to simulate STM images for different voltages and tip heights. Combining the geometrical and electronic effects, all features of the different STM images can be explained, providing a valuable guide for future experiments. Our results confirm previous reports on S atom imaging, but also reveal a strong dependence on the applied bias for vacancies and antisite defects that include extra S atoms. By contrast, when additional Mo atoms cover the S vacancies, the MoS2 gap vanishes and a bias-independent bright protrusion is obtained in the STM image. Finally, we show that the inclusion of these point defects promotes the emergence of reactive dangling bonds that may act as efficient adsorption sites for external adsorbates.

  16. Scanning tunneling microscopy/spectroscopy of picene thin films formed on Ag(111)

    Energy Technology Data Exchange (ETDEWEB)

    Yoshida, Yasuo, E-mail: yyoshida@issp.u-tokyo.ac.jp; Yokosuka, Takuya; Hasegawa, Yukio, E-mail: hasegawa@issp.u-tokyo.ac.jp [The Institute of Solid State Physics, The University of Tokyo, Kashiwa 277-8581 (Japan); Yang, Hung-Hsiang [Department of Physics, National Taiwan University, Taipei 106, Taiwan (China); Huang, Hsu-Sheng; Guan, Shu-You; Su, Wei-Bin; Chang, Chia-Seng [Institute of Physics, Academia Sinica, Nankang, Taipei 11529, Taiwan (China); Yanagisawa, Susumu [Department of Physics and Earth Science Department, University of the Ryukyus, 1 Nishihara, Okinawa 903-0213 (Japan); Lin, Minn-Tsong [Department of Physics, National Taiwan University, Taipei 106, Taiwan (China); Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan (China); Hoffmann, Germar [The Institute of Solid State Physics, The University of Tokyo, Kashiwa 277-8581 (Japan); Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan (China)

    2014-09-21

    Using ultrahigh-vacuum low-temperature scanning tunneling microscopy and spectroscopy combined with first principles density functional theory calculations, we have investigated structural and electronic properties of pristine and potassium (K)-deposited picene thin films formed in situ on a Ag(111) substrate. At low coverages, the molecules are uniformly distributed with the long axis aligned along the [112{sup ¯}] direction of the substrate. At higher coverages, ordered structures composed of monolayer molecules are observed, one of which is a monolayer with tilted and flat-lying molecules resembling a (11{sup ¯}0) plane of the bulk crystalline picene. Between the molecules and the substrate, the van der Waals interaction is dominant with negligible hybridization between their electronic states; a conclusion that contrasts with the chemisorption exhibited by pentacene molecules on the same substrate. We also observed a monolayer picene thin film in which all molecules were standing to form an intermolecular ? stacking. Two-dimensional delocalized electronic states are found on the K-deposited ? stacking structure.

  17. 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.

  18. Scanning tunneling microscopy images of ruthenium submonolayers spontaneously deposited on a Pt(111) electrode

    Energy Technology Data Exchange (ETDEWEB)

    Herrero, E.; Feliu, J.M. [Univ. de Alicante (Spain). Dept. de Quimica Fisica; Wieckowski, A. [Univ. of Illinois, Urbana, IL (United States). Dept. of Chemistry

    1999-07-20

    Recently, a major effort has been reported toward producing high activity surfaces made of platinum/ruthenium composites as a catalyst for methanol electro-oxidation. Scanning tunneling microscopy (STM) was used to examine spontaneously deposited ruthenium adlayers on the well-defined Pt(111) electrode. Stable and STM discernible structures were obtained after a brief cyclic voltammetric treatment of the ruthenium deposit. As demonstrated previously, the electrochemically stabilized Pt/Ru electrodes are active catalysts in methanol electrooxidation. The STM data indicate that the deposit is arranged in nanometer size islands of which the detailed structural characterization is presented. Maximum ruthenium coverage is no higher than 20%, which confirms the previous results obtained by the use of Auger electron spectroscopy. While most of the islands are monatomic, a fraction of the islands, approximately 10% of the total ruthenium coverage, displays a second monolayer deposit over the first monolayer. This is a new discovery showing an unexpected tendency of the spontaneously deposited ruthenium at such a low coverage to nucleate in a bilayer configuration. The hydrogen underpotential deposition process does not affect the spatial distribution of the islands, but ruthenium is reductively removed from the surface under hydrogen evolution conditions.

  19. Scanning tunneling microscopy investigation of the surface structures of natural MoS 2

    Science.gov (United States)

    Ha, Jeong Sook; Roh, Hee-Sook; Park, Seong-Ju; Yi, Jae-Yel; Lee, El-Hang

    1994-08-01

    Scanning tunneling microscope (STM) images of natural MoS 2 revealed protrusions with a diameter of 30-40 Å and ring-type structures with two different diameters of 40 and 80 Å on the surface. The STM images were taken varying the tip bias voltage from -0.04 to -1.1 eV. Ring-type structures existed in the whole range of tip bias voltages used, but the ring intensity which was subtracted by the background drastically decreased at tip bias voltages beyond -0.9 eV. Atomic force microscope (AFM) images of the same MoS 2 sample did not show such structures. In order to understand the origin of the ring-type structures observed on the natural MoS 2 surface, the impurities in the sample were analyzed by using glow discharge mass spectrometry (GDMS). The concentrations of the major impurities such as V and Ti were comparable to the average number density of ring structures on the sample. STM and AFM images suggest that the ring-type structures appear as an electronic effect due to the sinuous band structure caused by two kinds of band bending near the impurities included in the MoS 2 sample.

  20. Scanning-tunneling-microscopy studies of the S-induced reconstruction of Cu(100)

    DEFF Research Database (Denmark)

    Colaianni, Maria Loredana; Chorkendorff, Ib

    1994-01-01

    This study utilizes Auger-electron spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy (STM) to examine sulfur coverages above theta(S)=0.25 on the Cu(100) surface. These large sulfur coverages are observed to induce a restructuring of the copper surface through the removal of copper atoms from terrace sites. The layer produced at room temperature by H2S exposures is composed of small Cu-S aggregates which do not exhibit long-range order, but which orient in the [001] and [010] directions. Heating above 873 K causes tetramer sulfur unit cells to form in a poorly ordered overlayer. Annealing to 1173 K produces a well-ordered (root 17X root 17)R14 degrees structure which shows four sulfur atoms per unit cell in the STM images. Since the sulfur coverage of the (root 17X root 17)R14 degrees structure has been previously measured to contain a total of eight sulfur atoms per unit cell, a structural model is proposed that is consistent with the coverage and STM measurements.

  1. A 30 mK, 13.5 T scanning tunneling microscope with two independent tips

    Energy Technology Data Exchange (ETDEWEB)

    Roychowdhury, Anita [Laboratory for Physical Sciences, College Park, Maryland 20742 (United States); Center for Nanophysics and Advanced Materials, Department of Physics, University of Maryland, College Park, Maryland 20740 (United States); Gubrud, M. A.; Dana, R.; Dreyer, M. [Laboratory for Physical Sciences, College Park, Maryland 20742 (United States); Anderson, J. R.; Lobb, C. J.; Wellstood, F. C. [Center for Nanophysics and Advanced Materials, Department of Physics, University of Maryland, College Park, Maryland 20740 (United States)

    2014-04-15

    We describe the design, construction, and performance of an ultra-low temperature, high-field scanning tunneling microscope (STM) with two independent tips. The STM is mounted on a dilution refrigerator and operates at a base temperature of 30 mK with magnetic fields of up to 13.5 T. We focus on the design of the two-tip STM head, as well as the sample transfer mechanism, which allows in situ transfer from an ultra high vacuum preparation chamber while the STM is at 1.5 K. Other design details such as the vibration isolation and rf-filtered wiring are also described. Their effectiveness is demonstrated via spectral current noise characteristics and the root mean square roughness of atomic resolution images. The high-field capability is shown by the magnetic field dependence of the superconducting gap of Cu{sub x}Bi{sub 2}Se{sub 3}. Finally, we present images and spectroscopy taken with superconducting Nb tips with the refrigerator at 35 mK that indicate that the effective temperature of our tips/sample is approximately 184 mK, corresponding to an energy resolution of 16 ?eV.

  2. Self-Organized Graphene Nanoribbons on SiC(0001) Studied with Scanning Tunneling Microscopy

    Science.gov (United States)

    Torrance, David; Zhang, Baiqian; Hoang, Tien; First, Phillip

    2012-02-01

    Graphene nanoribbons grown directly on nanofacets of SiC(0001) offer an attractive union of top-down and bottom-up fabrication techniques. Nanoribbons have been shown to form on the facets of templated silicon carbide substrates,ootnotetextSprinkle et al., Nat. Nanotech. 5, 727 (2010). but also appear spontaneously along step-bunches on vicinal SiC(0001) miscut slightly towards . These self-organized graphene nanoribbons were characterized with low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES) in ultra-high vacuum. Our measurements indicate that the graphene forms a continuous ``buffer layer'' across the SiC(0001) terraces during nanoribbon formation, with the zigzag edge of the buffer layer aligned parallel to the step-bunched nanofacets. Scanning tunneling microscopy/spectroscopy (STM/STS) was used to characterize the topography and electrical characteristics of the graphene nanoribbons. These measurements indicate that the graphene nanoribbons are highly-crystalline with predominantly zigzag edges.

  3. Atomic-scale surface science phenomena studied by scanning tunneling microscopy

    Science.gov (United States)

    Besenbacher, F.; Lauritsen, J. V.; Linderoth, T. R.; Lægsgaard, E.; Vang, R. T.; Wendt, S.

    2009-06-01

    Following the development of the scanning tunneling microscope (STM), the technique has become a very powerful and important tool for the field of surface science, since it provides direct real-space imaging of single atoms, molecules and adsorbate structures on surfaces. From a fundamental perspective, the STM has changed many basic conceptions about surfaces, and paved the way for a markedly better understanding of atomic-scale phenomena on surfaces, in particular in elucidating the importance of local bonding geometries, defects and resolving non-periodic structures and complex co-existing phases. The so-called "surface science approach", where a complex system is reduced to its basic components and studied under well-controlled conditions, has been used successfully in combination with STM to study various fundamental phenomena relevant to the properties of surfaces in technological applications such as heterogeneous catalysis, tribology, sensors or medical implants. In this tribute edition to Gerhard Ertl, we highlight a few examples from the STM group at the University of Aarhus, where STM studies have revealed the unique role of surface defects for the stability and dispersion of Au nanoclusters on TiO 2, the nature of the catalytically active edge sites on MoS 2 nanoclusters and the catalytic properties of Au/Ni or Ag/Ni surfaces. Finally, we briefly review how reaction between complex organic molecules can be used to device new methods for self-organisation of molecular surface structures joined by comparatively strong covalent bonds.

  4. Scanning tunneling microscope-quartz crystal microbalance study of temperature gradients at an asperity contact.

    Science.gov (United States)

    Pan, L; Krim, J

    2013-01-01

    Investigations of atomic-scale friction frequently involve setups where a tip and substrate are initially at different temperatures. The temperature of the sliding interface upon contact has thus become a topic of interest. A method for detecting initial tip-sample temperature differences at an asperity contact is described, which consists of a scanning tunneling microscope (STM) tip in contact with the surface electrode of a quartz crystal microbalance (QCM). The technique makes use of the fact that a QCM is extremely sensitive to abrupt changes in temperature. In order to demonstrate the technique's capabilities, QCM frequency shifts were recorded for varying initial tip-substrate temperature differences as an STM tip was brought into and out of contact. The results are interpreted within the context of a recent model for thermal heat conduction at an asperity contact, and it is concluded that the transient frequency response is attributable to small changes in temperature close to the region of contact rather than a change in the overall temperature of the QCM itself. For the assumed model parameters, the results moreover reveal substantial temperature discontinuities at the boundary between the tip and the sample, for example, on the order of 10-15 °C for initial temperature differences of 20 °C. PMID:23387679

  5. Scanning tunneling spectroscopy reveals a silicon dangling bond charge state transition

    Science.gov (United States)

    Labidi, Hatem; Taucer, Marco; Rashidi, Mohammad; Koleini, Mohammad; Livadaru, Lucian; Pitters, Jason; Cloutier, Martin; Salomons, Mark; Wolkow, Robert A.

    2015-07-01

    We report the study of single dangling bonds (DBs) on a hydrogen-terminated silicon (100) surface using a low-temperature scanning tunneling microscope. By investigating samples prepared with different annealing temperatures, we establish the critical role of subsurface arsenic dopants on the DB electronic properties. We show that when the near-surface concentration of dopants is depleted as a result of 1250 °C flash anneals, a single DB exhibits a sharp conduction step in its I(V) spectroscopy that is not due to a density of states effect but rather corresponds to a DB charge state transition. The voltage position of this transition is perfectly correlated with bias-dependent changes in the STM images of the DB at different charge states. Density functional theory calculations further highlight the role of subsurface dopants on DB properties by showing the influence of the DB-dopant distance on the DB state. We discuss possible theoretical models of electronic transport through the DB that could account for our experimental observations.

  6. A 30 mK, 13.5 T scanning tunneling microscope with two independent tips

    International Nuclear Information System (INIS)

    We describe the design, construction, and performance of an ultra-low temperature, high-field scanning tunneling microscope (STM) with two independent tips. The STM is mounted on a dilution refrigerator and operates at a base temperature of 30 mK with magnetic fields of up to 13.5 T. We focus on the design of the two-tip STM head, as well as the sample transfer mechanism, which allows in situ transfer from an ultra high vacuum preparation chamber while the STM is at 1.5 K. Other design details such as the vibration isolation and rf-filtered wiring are also described. Their effectiveness is demonstrated via spectral current noise characteristics and the root mean square roughness of atomic resolution images. The high-field capability is shown by the magnetic field dependence of the superconducting gap of CuxBi2Se3. Finally, we present images and spectroscopy taken with superconducting Nb tips with the refrigerator at 35 mK that indicate that the effective temperature of our tips/sample is approximately 184 mK, corresponding to an energy resolution of 16 ?eV

  7. A 30 mK, 13.5 T scanning tunneling microscope with two independent tips

    Science.gov (United States)

    Roychowdhury, Anita; Gubrud, M. A.; Dana, R.; Anderson, J. R.; Lobb, C. J.; Wellstood, F. C.; Dreyer, M.

    2014-04-01

    We describe the design, construction, and performance of an ultra-low temperature, high-field scanning tunneling microscope (STM) with two independent tips. The STM is mounted on a dilution refrigerator and operates at a base temperature of 30 mK with magnetic fields of up to 13.5 T. We focus on the design of the two-tip STM head, as well as the sample transfer mechanism, which allows in situ transfer from an ultra high vacuum preparation chamber while the STM is at 1.5 K. Other design details such as the vibration isolation and rf-filtered wiring are also described. Their effectiveness is demonstrated via spectral current noise characteristics and the root mean square roughness of atomic resolution images. The high-field capability is shown by the magnetic field dependence of the superconducting gap of CuxBi2Se3. Finally, we present images and spectroscopy taken with superconducting Nb tips with the refrigerator at 35 mK that indicate that the effective temperature of our tips/sample is approximately 184 mK, corresponding to an energy resolution of 16 ?eV.

  8. Engineering the emission of light from a scanning tunneling microscope using the plasmonic modes of a nanoparticle

    Science.gov (United States)

    Le Moal, Eric; Marguet, Sylvie; Canneson, Damien; Rogez, Benoît; Boer-Duchemin, Elizabeth; Dujardin, Gérald; Teperik, Tatiana V.; Marinica, Dana-Codruta; Borisov, Andrey G.

    2016-01-01

    The inelastic tunnel current in the junction formed between the tip of a scanning tunneling microscope (STM) and the sample can electrically generate optical signals. This phenomenon is potentially of great importance for nano-optoelectronic devices. In practice, however, the properties of the emitted light are difficult to control because of the strong influence of the STM tip. In this work, we show both theoretically and experimentally that the sought-after, well-controlled emission of light from an STM tunnel junction may be achieved using a nonplasmonic STM tip and a plasmonic nanoparticle on a transparent substrate. We demonstrate that the native plasmon modes of the nanoparticle may be used to engineer the light emitted in the substrate. Both the angular distribution and intensity of the emitted light may be varied in a predictable way by choosing the excitation position of the STM tip on the particle.

  9. Two-photon-induced hot-electron transfer to a single molecule in a scanning tunneling microscope

    International Nuclear Information System (INIS)

    The junction of a scanning tunneling microscope (STM) operating in the tunneling regime was irradiated with femtosecond laser pulses. A photoexcited hot electron in the STM tip resonantly tunnels into an excited state of a single molecule on the surface, converting it from the neutral to the anion. The electron-transfer rate depends quadratically on the incident laser power, suggesting a two-photon excitation process. This nonlinear optical process is further confirmed by the polarization measurement. Spatial dependence of the electron-transfer rate exhibits atomic-scale variations. A two-pulse correlation experiment reveals the ultrafast dynamic nature of photoinduced charging process in the STM junction. Results from these experiments are important for understanding photoinduced interfacial charge transfer in many nanoscale inorganic-organic structures.

  10. Realizing a Four-Step Molecular Switch in Scanning Tunneling Microscope Manipulation of Single Chlorophyll-a Molecules

    CERN Document Server

    Iancu, V; Iancu, Violeta; Hla, Saw-Wai

    2006-01-01

    Single chlorophyll-a molecules, a vital resource for the sustenance of life on Earth, have been investigated by using scanning-tunneling-microscope manipulation and spectroscopy on a gold substrate at 4.6 K. The chlorophyll-a binds on Au(111) via its porphyrin unit while the phytyl-chain is elevated from the surface by a support of four CH3 groups. By injecting tunneling electrons from the STM-tip, we are able to bend the phytyl-chain, which enable switching of four molecular conformations in a controlled manner. Statistical analyses and structural calculations reveal that all reversible switching mechanisms are initiated by a single tunnelling-electron energy-transfer process, which induces bond rotation within the phytyl-chain.

  11. Scanning magnetic tunnel junction (MTJ) microscopy: High-resolution magnetic imaging of geologic samples

    Science.gov (United States)

    Lascu, I.; Harrison, R. J.

    2014-12-01

    We describe a Micromagnetics, Inc. magnetic tunnel junction (MTJ) scanning microscope developed for the University of Cambridge Nanopaleomagnetism Lab. The MTJ sensor used contains a thin film multilayer structure, whose core consists of two ferromagnetic electrodes, separated by an insulating layer. One of the electrodes is magnetically pinned via exchange bias to an antiferromagnetic layer, while the other is free to react to an external magnetic field. The magnetization of the pinned layer is fixed in a perpendicular direction, so this ferromagnetic junction can be used as a low-field magnetic sensor. The magnetoresistance of the junction is dependent on the magnetic orientation of the electrodes, and is quantified as the percent change between the low and high resistance states. The higher its value, the more sensitive the device is, which makes the MTJ sensor (magnetoresistance exceeding 200%) particularly attractive for detecting small-scale magnetic structures. The MTJ sensor does not require the use of cryogens, enabling straightforward, low-cost operation of the microscope. The lack of cryogen technology means the sensor can be brought close to the sample surface, routinely allowing for sample-to-sensor distances of 15-20 ?m. Scan height depends on factors such as scanning mode (if using a static or vibrating stage), sample surface configuration, or sensor configuration (i.e., proximity of the sensor to the tip of the die). This renders the MTJ microscope capable of producing magnetic images that may resolve features as small as 15 ?m, and of detecting field intensities lower than 1 ?T. This technology is particularly useful for detecting stray fields from micro-regions of interest preserving the original paleomagnetic signature within a bulk sample that may also contain remagnetised regions. Examples include ancient or altered rocks, extraterrestrial materials, samples containing inclusions or exsolution structures, and in general specimens characterised by spatial heterogeneity. In addition, the high-resolution capability of the MTJ microscope makes it extremely useful for investigating sedimentary archives formed under low accumulation conditions (e.g., speleothems, stromatolites, Fe-Mn nodules) that hold a detectable environmental magnetic signal.

  12. Metastable de-excitation spectroscopy and scanning tunneling microscopy study of the 2×4 and 2×7 reconstructions of Ho on Si(001)

    Science.gov (United States)

    Pratt, Andrew; Woffinden, Charles; Bonet, Christopher; Tear, Steve

    2008-10-01

    Ho silicide nanostructures were formed by the deposition of submonolayer coverages of Ho onto a clean Si(001) 2×1 surface at various substrate temperatures. Depending on the deposition temperature and coverage, the substrate surrounding the nanostructures reconstructs into either a 2×4 or 2×7 structure or a combination of the two. We use metastable de-excitation spectroscopy (He23S) to complement scanning tunneling microscopy (STM) to study these reconstructions revealing the electronic similarities between the 2×4 and 2×7 phases. The presence in the spectra of features due to hybridized Si3s3p-Ho6s5d bonds at the surface suggest that prominent maxima in the corresponding STM images are due to Ho atoms and that these reconstructions form as a precursor to nanowire formation.

  13. Use of in situ scanning tunneling microscopy for the study of dye sensitization of semiconductor electrodes. Progress report, September 15, 1992--August 15, 1995

    Energy Technology Data Exchange (ETDEWEB)

    Parkinson, B.

    1995-12-31

    In the three years of this contract, the authors have set up a state-of-the-art computer-controlled photoelectrochemical characterization laboratory with facilities to measure Mott-Schottky behavior, photocurrent spectra and photocurrent voltage curves on semiconductor electrodes. They have also set up a Bridgeman crystal growth furnace for preparing their own single crystals of SnS{sub 2} and other semiconductor materials for the photoelectrochemical studies. The first boules of SnS{sub 2} have recently been prepared. They have also modified a scanning tunneling microscope to perform photo-STM experiments to spatially resolve photocurrents on semiconductor surfaces. In addition, the acquisition of a Ti:sapphire laser system from the DOE-URI program will give us the power and flexibility in the light source to provide a better chance of single molecule detection. The results on sensitization will be summarized below.

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

    International Nuclear Information System (INIS)

    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. (paper)

  15. Design and properties of a cryogenic dip-stick scanning tunneling microscope with capacitive coarse approach control.

    Science.gov (United States)

    Schlegel, R; Hänke, T; Baumann, D; Kaiser, M; Nag, P K; Voigtländer, R; Lindackers, D; Büchner, B; Hess, C

    2014-01-01

    We present the design, setup, and operation of a new dip-stick scanning tunneling microscope. Its special design allows measurements in the temperature range from 4.7 K up to room temperature, where cryogenic vacuum conditions are maintained during the measurement. The system fits into every (4)He vessel with a bore of 50 mm, e.g., a transport dewar or a magnet bath cryostat. The microscope is equipped with a cleaving mechanism for cleaving single crystals in the whole temperature range and under cryogenic vacuum conditions. For the tip approach, a capacitive automated coarse approach is implemented. We present test measurements on the charge density wave system 2H-NbSe2 and the superconductor LiFeAs which demonstrate scanning tunneling microscopy and spectroscopy data acquisition with high stability, high spatial resolution at variable temperatures and in high magnetic fields. PMID:24517774

  16. Local secondary-electron emission spectra of graphite and gold surfaces obtained using the Scanning Probe Energy Loss Spectrometer (SPELS)

    International Nuclear Information System (INIS)

    Secondary-electron emission (SEE) spectra have been obtained with the Scanning Probe Energy Loss Spectrometer at a tip-sample distance of only 50 nm. Such short working distances are required for the best theoretical spatial resolution (<10 nm). The SEE spectra of graphite, obtained as a function of tip bias voltage, are shown to correspond to unoccupied states in the electronic band structure. The SEE spectra of thin gold films demonstrate the capability of identifying (carbonaceous) surface contamination with this technique.

  17. Analysis of Scanning Tunneling Spectroscopy Experiments from First Principles the Test Case of C60 Adsorbed on Au(111)

    CERN Document Server

    Pérez-Jiménez, A J; Louis, E; San Fabian, E; Vergés, J A

    2002-01-01

    We report on the first principles determination of the conductance properties of Buckminster fullerene adsorbed on a gold surface, comparing them with recent Scanning Tunneling Microscopy/Spectroscopy (STM/S) experiments [J.Chem.Phys.116, 832 (2002)]. Our procedure has the two appealing features of being able to elucidate delicate aspects of STM/S results without resorting to ad hoc fittings or approximations and to provide a complete description of the phenomena involved when the tip approaches the adsorbate.

  18. Alkali-metal adsorption on silicon surfaces studied by field ion-scanning tunneling microscopy (FI sbnd STM)

    Science.gov (United States)

    Hashizume, Tomihiro; Hasegawa, Y.; Sakurai, T.

    1991-06-01

    Adsorption of alkali metals (Li, K, Cs) on the Si(111) and Si(100) surfaces has been investigated by field ion-scanning tunneling microscopy (FI sbnd STM). The FI sbnd STM data suggest that alkali-metal atoms absorb quite differently between the (111) and (100) surface: almost completely ionized on the (111)7 × 7 surface, while there is small charge transfer on the (100)2 × 1 surface.

  19. Enhancement and termination of the superconducting proximity effect due to atomic-scale defects visualized by scanning tunneling microscopy

    OpenAIRE

    Kim, Howon; Lin, Shi-Zeng; Graf, Matthias J.; Kato, Takeo; Hasegawa, Yukio

    2014-01-01

    Using low-temperature scanning tunneling microscopy and spectroscopy, we have studied the proximity effect at the interfaces between superconducting Pb island structures and metallic Pb-induced striped-incommensurate phase formed on a Si(111) substrate. Our real-space observation revealed that the step structures on the two-dimensional metallic layer exhibit significant roles on the propagation of the superconducting pair correlation; the proximity effect is terminated by th...

  20. From Soccer-Ball and Rugby-Ball to Giant Fullerene Molecules:. a Scanning Tunneling Microscopy and Spectroscopy Study

    Science.gov (United States)

    Chen, Ting; Sarid, Dror

    Thin films of carbon fullerene molecules, Cn, prepared on metallic substrates are studied by scanning tunneling microscopy (STM) and atomic force microscopy (AFM) under both ambient and ultrahigh vacuum conditions. The STM and AFM images provide real-space atomic-resolution views of these fascinating molecules and their monolayer growth on metal surfaces which reflect both the intermolecular interactions and interactions with the underlying substrates.

  1. Generalised effective mass theory of sub-surface scanning tunnelling microscopy: application to weakly bound impurity states

    Science.gov (United States)

    Roy, Mervyn; Maksym, P. A.

    2014-06-01

    We apply our generalised effective mass theory of sub-surface scanning tunnelling microscopy (STM) (Phys. Rev. B 19, 195304 (2010)) to simulate STM images of electronic states localised around sub-surface Si dopant atoms in GaAs. In the case of these shallow impurity-states, we demonstrate that electrostatic effects from image-charges and from the STM tip have a strong influence on the sub-surface state and hence the simulated image.

  2. Generalised effective mass theory of sub-surface scanning tunnelling microscopy: application to weakly bound impurity states

    International Nuclear Information System (INIS)

    We apply our generalised effective mass theory of sub-surface scanning tunnelling microscopy (STM) (Phys. Rev. B 19, 195304 (2010)) to simulate STM images of electronic states localised around sub-surface Si dopant atoms in GaAs. In the case of these shallow impurity-states, we demonstrate that electrostatic effects from image-charges and from the STM tip have a strong influence on the sub-surface state and hence the simulated image.

  3. Voltammetry and In Situ Scanning Tunnelling Microscopy of De Novo Designed Heme Protein Monolayers on Au(111)-Electrode Surfaces

    DEFF Research Database (Denmark)

    Albrecht, Tim; Li, Wu; Haehnel, Wolfgang; Hildebrandt, Peter; Ulstrup, Jens

    2006-01-01

    In the present work, we report the electrochemical characterization and in situ scanning tunnelling microscopy (STM) studies of monolayers of an artificial de novo designed heme protein MOP-C, covalently immobilized on modified Au(111) surfaces. The protein forms closely packed monolayers, which remain electroactive upon immobilization. In situ STM images show circular structures indicating that MOP-C stands upright on the surface in accordance with the molecular design. Despite the large spatia...

  4. Atomic Scale Visualization of Quantum Interference on a Weyl Semimetal Surface by Scanning Tunneling Microscopy/Spectroscopy

    OpenAIRE

    Zheng, Hao; Xu, Su-Yang; Bian, Guang; Guo, Cheng; Chang, Guoqing; Sanchez, Daniel S.; Belopolski, Ilya; Lee, Chi-Cheng; Huang, Shin-Ming; Zhang, Xiao; Sankar, Raman; Alidoust, Nasser; Chang, Tay-Rong; WU Fan; Neupert, Titus

    2015-01-01

    Weyl semimetals may open a new era in condensed matter physics, materials science and nanotech after graphene and topological insulators. We report the first atomic scale view of the surface states of a Weyl semimetal (NbP) using scanning tunneling microscopy/spectroscopy. We observe coherent quantum interference patterns that arise from the scattering of quasiparticles near point defects on the surface. The measurements reveal the surface electronic structure both below and above the chemica...

  5. High vacuum tip-enhanced Raman spectroscope based on a scanning tunneling microscope

    Science.gov (United States)

    Fang, Yurui; Zhang, Zhenglong; Sun, Mengtao

    2016-03-01

    In this paper, we present the construction of a high-vacuum tip-enhanced Raman spectroscopy (HV-TERS) system that allows in situ sample preparation and measurement. A detailed description of the prototype instrument is presented with experimental validation of its use and novel ex situ experimental results using the HV-TERS system. The HV-TERS system includes three chambers held under a 10-7 Pa vacuum. The three chambers are an analysis chamber, a sample preparation chamber, and a fast loading chamber. The analysis chamber is the core chamber and contains a scanning tunneling microscope (STM) and a Raman detector coupled with a 50 × 0.5 numerical aperture objective. The sample preparation chamber is used to produce single-crystalline metal and sub-monolayer molecular films by molecular beam epitaxy. The fast loading chamber allows ex situ preparation of samples for HV-TERS analysis. Atomic resolution can be achieved by the STM on highly ordered pyrolytic graphite. We demonstrate the measurement of localized temperature using the Stokes and anti-Stokes TERS signals from a monolayer of 1,2-benzenedithiol on a gold film using a gold tip. Additionally, plasmonic catalysis can be monitored label-free at the nanoscale using our device. Moreover, the HV-TERS experiments show simultaneously activated infrared and Raman vibrational modes, Fermi resonance, and some other non-linear effects that are not observed in atmospheric TERS experiments. The high spatial and spectral resolution and pure environment of high vacuum are beneficial for basic surface studies.

  6. Visualizing surface states of topological insulators using spectroscopic mapping with the scanning tunneling microscope

    Science.gov (United States)

    Roushan, Pedram

    2011-03-01

    In topological insulators, the spin texture of the surface states makes them distinct from conventional two-dimensional electron states, and leads to novel properties for these states. These surface states are expected to be immune to localization and to overcome barriers caused by material imperfections. We have used scanning tunneling microscopy and spectroscopy to study the topological surface states in Bi 0.9 Sb 0.1 , Sb, and Bi 2 Te 3 . By mapping the interference of the surface states scattering off random alloying disorder in Bi 0.9 Sb 0.1 , we have demonstrated that despite strong atomic scale disorder, backscattering between states of opposite momentum and opposite spin is absent, resulting from the spin texture. Furthermore, we have measured the transmission and reflection of topological surface states of Sb through atomic terraces. In contrast to Schottky surface states of noble metals, these surface states penetrate such barriers with high probability. To examine the possibility of disorder induced localization, we investigated the surface states of Bi 2 Te 3 in the presence of local defects. In the presence of magnetic dopants, we have observed an interference pattern throughout a broad range of energies, even in the region of linear dispersion near the Dirac point. We discuss the results of a statistical analysis of these patterns which can help to learn about the tendency toward localization for these surface states and how this trend is affected as the energy is tuned to the Dirac point. *Work was done in collaboration with J. Seo, H. Beidenkopf, L. Gorman, Y. S. Hor, C. Parker, D. Hsieh, and A. Richardella, M. Z. Hasan, R. Cava, and A. Yazdani. Supported by NSF-DMR, and MRSEC through PCCM. Infrastructure at Princeton Nanoscale Microscopy Laboratory are also supported by grants from DOE, and the W.M. Keck foundation.

  7. Submonolayer growth of Pd on Cu(111) studied by scanning tunneling microscopy

    DEFF Research Database (Denmark)

    Lægsgaard, E.; Ruban, Andrei

    1998-01-01

    The growth mode of sub-monolayer amounts of Pd on Cu(111) in the temperature range - 80-300 degrees C has been investigated by scanning tunneling microscopy (STM), Rutherford backscattering spectroscopy (RBS) and Auger electron spectroscopy (AES). Below approximate to 100 degrees C, the Pd induced phase nucleates at ascending steps in fingered brims and, on large terraces, in fingered islands. The lack of order suggests that the brims and islands are a disordered alloy formed by exchange between Pd and Cu from the layer underneath. For temperatures exceeding approximate to 160 degrees C, Cu is dug out from the surface in extended, monolayer deep pits, and concurrently, the brims and islands increase in height by one layer. High-resolution STM images of brims and islands in this phase are interpreted as evidence for Cu capping. For Pd evaporation at temperatures of 220-300 degrees C, the surface is characterized by the appearance of individual Pd atoms substituted into the first layer and the presence of subsurface Pd. A short-range order that excludes the population of nearest-neighbour, in-plane sites is revealed by pair-correlation analysis. The Pd atoms form bands in the upper terrace next to steps. These bands are surprisingly stable against further diffusion, possibly due to an attractive interaction with second- and third-nearest (in-plane) neighbours and with subsurface Pd. The lack of any ordering is explained, based on a calculation of the surface energy. Once the population of nearest-neighbour sites is excluded, there is practically no energy gain by ordering. (C) 1998 Elsevier Science B.V. All rights reserved.

  8. Characterization and Properties of Oligothiophenes Using Scanning Tunneling Microscopy for Possible Use in Organic Electronics

    International Nuclear Information System (INIS)

    A scanning tunneling microscopy study has been made on a group of alkyl-substituted oligothiophenes. The self-assembled monolayers of this type of semi-conducting oligomers on graphite were observed and characterized. To control the self-assembly, it is important to first understand the forces that drive the spontaneous ordering of molecules at interfaces. For the identification of the forces, several substituted oligothiophenes were examined: carboxylic acid groups, methyl ester carboxylic acid, and iodine atoms at one end and benzyl esters at the other end of the oligomers this is in addition to the non-functionalized oligothiophehens, Self-assembled monolayers of these molecules were then examined by STM. A detailed analysis of the driving forces and parameters controlling the formation of the self-assembled 2- D crystal monolayers was carried out by performing modeling of the experimental observations. The theoretical calculations gave us a conclusive insight into the intermolecular interactions, which lead to the observed conformation of molecules on the surface. An attempt to react two iodinated oligomers on the surface after the formation of the monolayer has been done; a topochemical reaction studies using UV/Vis light irradiation has been preceded. The targeted reaction was achieved. This can be considered as a great step towards the formation of nano-wires and other organic electronic devices. The applicability of the above method of force-driven self organisation in different patterns was examined as template for building donor-nano structures for electronic devices. It was necessary to examine the stability of the formed templates in air. The monolayers were left to dry and STM images were taken; C60 was then added to the monolayer, and the complexation of the C60 (as acceptor) with the formed monolayer template was examined.

  9. 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.

  10. Scanning tunneling microscopy of charge density wave structure in 1T- TaS{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Thomson, R.E.

    1991-11-01

    I have used a scanning tunneling microscope (STM) to image simultaneously the atomic lattice and the charge density wave (CDW) superstructure in tantalum disulfide (1T-TaS{sub 2}) over the temperature range of 370-77K. In the lowest temperature (commensurate) phase, present below 180K, the CDW is at an angle of 13.9{degrees} relative to the lattice and is uniformly commensurate. In the incommensurate phase, present above 353K, the CDW is aligned with the lattice. 1T-TaS{sub 2} exhibits two other phases; the triclinic (T) phase which is present between 223K and 283K upon warming the sample, and the nearly-commensurate (NC) phase which is present between 353K and 180K upon cooling the sample and between 283K and 353K upon warming the sample. In both of these phases, discommensurate models where the CDW is arranged in small commensurate domains have been proposed. In the NC phase the CDW is rotated between 10{degrees} and 12.5{degrees} relative to the atomic lattice. Such a rotated CDW would create an interference pattern with the underlying atomic lattice regardless of the existence of a true domain superstructure. Previous work on 1T-TaS{sub 2} has not adequately accounted for the possibility of this moire pattern. However, around each fundamental CDW peak in the Fourier transform of the real space STM images, several satellite spots are visible, which conclusively prove the existence of domains in the NC phase.

  11. Scanning tunneling microscopy of charge density wave structure in 1T- TaS sub 2

    Energy Technology Data Exchange (ETDEWEB)

    Thomson, R.E.

    1991-11-01

    I have used a scanning tunneling microscope (STM) to image simultaneously the atomic lattice and the charge density wave (CDW) superstructure in tantalum disulfide (1T-TaS{sub 2}) over the temperature range of 370-77K. In the lowest temperature (commensurate) phase, present below 180K, the CDW is at an angle of 13.9{degrees} relative to the lattice and is uniformly commensurate. In the incommensurate phase, present above 353K, the CDW is aligned with the lattice. 1T-TaS{sub 2} exhibits two other phases; the triclinic (T) phase which is present between 223K and 283K upon warming the sample, and the nearly-commensurate (NC) phase which is present between 353K and 180K upon cooling the sample and between 283K and 353K upon warming the sample. In both of these phases, discommensurate models where the CDW is arranged in small commensurate domains have been proposed. In the NC phase the CDW is rotated between 10{degrees} and 12.5{degrees} relative to the atomic lattice. Such a rotated CDW would create an interference pattern with the underlying atomic lattice regardless of the existence of a true domain superstructure. Previous work on 1T-TaS{sub 2} has not adequately accounted for the possibility of this moire pattern. However, around each fundamental CDW peak in the Fourier transform of the real space STM images, several satellite spots are visible, which conclusively prove the existence of domains in the NC phase.

  12. What is the orientation of the tip in a scanning tunneling microscope?

    Science.gov (United States)

    Mándi, Gábor; Teobaldi, Gilberto; Palotás, Krisztián

    2015-05-01

    The atomic structure and electronic properties of the tip apex can strongly affect the contrast of scanning tunneling microscopy (STM) images. This is a critical issue in STM imaging given the, to date unsolved, experimental limitations in precise control of the tip apex atomic structure. Definition of statistically robust procedures to indirectly obtain information on the tip apex structure is highly desirable as it would open up for more rigorous interpretation and comparison of STM images from different experiments. To this end, here we introduce a statistical correlation analysis method to obtain information on the local geometry and orientation of the tip used in STM experiments based on large scale simulations. The key quantity is the relative brightness correlation of constant-current topographs between experimental and simulated data. This correlation can be analyzed statistically for a large number of modeled tip orientations and geometries. Assuming a stable tip during the STM scans and based on the correlation distribution, it is possible to determine the tip orientations that are most likely present in an STM experiment, and exclude other orientations. This is especially important for substrates such as highly oriented pyrolytic graphite (HOPG) since its STM contrast is strongly tip dependent, which makes interpretation and comparison of STM images very challenging. We illustrate the applicability of our method considering the HOPG surface in combination with tungsten tip models of two different apex geometries and 18,144 different orientations. We calculate constant-current profiles along the direction of the HOPG(0 0 0 1) surface in the | V | ? 1V bias voltage range, and compare them with experimental data. We find that a blunt tip model provides better correlation with the experiment for a wider range of tip orientations and bias voltages than a sharp tip model. Such a combination of experiments and large scale simulations opens up the way for obtaining more detailed information on the structure of the tip apex and more reliable interpretation of STM data in the view of local tip geometry effects.

  13. Low-temperature scanning tunneling microscopy study on the electronic properties of a double-decker DyPc2 molecule at the surface.

    Science.gov (United States)

    Zhang, Yajie; Liao, Peilin; Kan, Jinglan; Yin, Cen; Li, Na; Liu, Jing; Chen, Qiwei; Wang, Yongfeng; Chen, Wei; Xu, Guo Qin; Jiang, Jianzhuang; Berndt, Richard; Wu, Kai

    2015-10-28

    To fully achieve potential applications of the double-decker molecules containing rare earth elements as single-molecule magnets in molecular spintronics, it is crucial to understand the 4f states of the rare earth atoms sandwiched in the double-decker molecules by metal electrodes. In this study, low-temperature scanning tunneling microscopy and spectroscopy were employed to investigate the isolated double-decker DyPc2 molecule adsorbed on Au(111) via its differential conductance measurements. The experimental results revealed that the differential conductance maps acquired at a constant height mode simply depicted the authentic molecular orbitals; moreover, the differential conductance maps achieved at a constant current mode could not directly probe the 4f states of the sandwiched Dy atom. This was consistent with the spectra obtained over the molecule center around the Fermi level, indicative of no Kondo feature. Upon decreasing the tip-molecule distance, the CH-mode images presented high-resolution structure but no information of the 4f states. All results indicated that the Dy atom barely contributed to the tunneling current because of the absence of coupling with the microscope tip, echoing the inaccessibility of the Dy 4f states in the double-decker DyPc2 molecule. PMID:26411704

  14. 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 with the substrate states. Despite this electronic inhomogeneity, the magnetic domains and domain walls are clearly observed by spin-resolved STS. For both types of Co nanostructures the out-of-plane orientation of the magnetic moments is proven. Furthermore, new insights into the anisotropy of the Co nanostructures as well as a strong dependence of the coercivity on the local sample morphology for Co double-layer islands were found. The experiments performed on single Co atoms on the Pt(111) surface show that two groups of Co atoms are present on the surface. Each group can be characterized by a specific spectroscopic signature. An analysis of the spectroscopy and atom manipulation experiments proves that the spectroscopic differences are related to the two possible adsorption sites of the Co atoms on the Pt(111) substrate. (orig.)

  15. Characterization and tunneling conductance spectra of N,N'-bis (9H-fluoren-9-ylidene)benzene-1,4-diamine thin films on graphite

    Energy Technology Data Exchange (ETDEWEB)

    Xin Hongliang; Li Zhuomin; He Tianxian; Miao Xinrui [College of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Deng Wenli, E-mail: wldeng@scut.edu.cn [College of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China)

    2010-06-01

    N,N'-bis(9H-fluoren-9-ylidene)benzene-1,4-diamine was synthesized via the acetic acid-assisted Schiff base reaction between 9-fluorenone and p-phenylenediamine. The thin films were deposited from solution and characterized by contact angle measurements (CAM), X-ray photoelectron spectroscopy (XPS) and tunneling conductance spectroscopy (TCS). The tunneling conductance spectra, related to the potential and distance between the tip and substrate, were acquired at different tip-substrate separations and depicted significant trend under the action of electric field. Systematic analysis shows more information about electron transport through medium layers. The electric field plays an important role in tunneling conductance spectra. The tunneling conductance spectra data indicate the electric field dependence of electron transport.

  16. Studies on switching mechanisms in Pd-nanodot embedded Nb2O5 memristors using scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Current imaging tunneling spectrum obtained from scanning tunneling microscopy has been used to probe the formation and/or rupture of conductive filaments responsible for bipolar switching in Pd nano-dots embedded Nb2O5 memristors. Filamentary conduction mechanism has been confirmed by scanning tunneling microscopy study using a Pt–Ir tip that enabled performing electroforming and reset operations at the nanoscale. The back and forth transition between the fully oxidized and metallic sub-oxide states of niobium under applied bias, as observed from X-ray photoelectron spectroscopy, is believed to be the source of bipolar switching in Nb2O5 memristors. The incorporation of Pd nanodots in Nb2O5 matrix plays a critical role by acting as an oxygen ion reservoir and/or by polarizing a large volume of oxygen vacancies. The formation and/or rupture of the conducting filaments through trapping–detrapping phenomena are found to boost the memristive switching performance. - Highlights: ► STM technique has been applied to study the resistance switching. ► Use of Pd nanodots enhances the switching in Nb2O5 memristors. ► Origin of switching is found to be due to multiple oxide states of Nb.

  17. 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 experiment is happening--thus turning the STM from a remote, batch surface modifier into a real-time, user-guided surface modifier.

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

    DEFF Research Database (Denmark)

    Zhang, Jingdong; Chi, Qijin

    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 chronocoulometry, and density functional theory (DFT) computations. Cys molecules were assembled on single-crystal Au(110) surfaces to form a highly ordered monolayer with a periodic lattice structure of c(2 x 2) in which each unit contains two molecules; this conclusion is confirmed by the results of calculations based on a slab model for the metal surface. The ordered monolayer offers a platform for submolecular scale electronic mapping that is an issue of fundamental interest but remains a challenge in STM imaging science and surface chemistry. Single Cys molecules were mapped as three electronic subunits contributed mainly from three chemical moieties: thiol (-SH), carboxylic (-COOH), and amine (-NH2) groups. The contrastsof the three subunits depend on the environment (e.g., pH), which affects the electronic structure of adsorbed species. From the DFT computations focused on single molecules, rational analysis of the electronic structures is achieved to delineate the main factors that determine electronic contrasts in the STM images. These factors include the molecular orientation, the chemical nature of the elements or groups in the molecule, and the interaction of the elements with the substrate 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, suggesting solvent plays a role during molecular assembly.

  19. I Situ Electrochemical Scanning Tunneling Microscopy Study of Dealloying and Stress Corrosion Cracking of Copper - Alloys.

    Science.gov (United States)

    Chen, Jin-Syung Fred

    The mechanism of stress corrosion cracking (SCC) of Cu-30Au in 0.6 M NaCl was investigated by a series of experiments, in which samples were dealloyed (i.e., selective removal of copper atoms) by potentiostatic anodic polarization at zero applied stress (i) for varying lengths of time (10 seconds to 30 minutes) and then impact bent, and (ii) for 30 minutes followed by a period of time (5 seconds to 10 minutes) at the open circuit potential and then impact bent. The results indicate that dealloying at zero applied stress produces a surface porous layer that is capable, for a brief period of time (15 seconds at open circuit potential, aging or coarsening reverses the ability of the surface layer to induce cleavage. In addition, samples were dealloyed and simultaneously stressed at various nominal values. At low values of applied stress, failure occurred by brittle intergranular cracking (IGSCC); and at high values of stress, failure occurred by brittle transgranular cracking (TGSCC). The results indicate that the mechanism of IGSCC is identical to that of TGSCC and can best be described by a modification of the "film-induced cleavage" model. The implication of the aging phenomenon to the film-induced cleavage model of stress corrosion cracking is also discussed. An electrochemical scanning tunneling microscope (ESTM) was built and used to study the in-situ dealloying process of thin-film Cu-Au alloys. Thin-films of Cu-75 at%Au alloy were prepared by thermal evaporation of the bulk alloy and deposition of the vapor onto heated mica. The surface structure of the thin film thus grown consists of terrace of well defined (111) planes separated by atomic height steps. The results from in-situ ESTM indicate that if applied potentials were lower than the critical potential (E_{rm c}), dissolution of Cu preferentially occurred at the low coordination sites, namely, sites of defects, kinks and ledges. Surface diffusion of the remaining Au atoms then occurred. This exposed underlying Cu atoms at low coordination sites to the solution. Their dissolution promoted further surface diffusion of Au atoms. (Abstract shortened by UMI.).

  20. A Scanning Tunneling Microscope at the Milli-Kelvin, High Magnetic Field Frontier

    Science.gov (United States)

    Zhou, Brian B.

    The ability to access lower temperatures and higher magnetic fields has precipitated breakthroughs in our understanding of physical matter, revealing novel effects such as superconductivity, the integer and fractional quantum Hall effects, and single spin magnetism. Extending the scanning tunneling microscope (STM) to the extremity of the B-T phase space provides unique insight on these phenomena both at the atomic level and with spectroscopic power. In this thesis, I describe the design and operation of a full-featured, dilution refrigerator-based STM capable of sample preparation in ultra-high vacuum (UHV) and spectroscopic mapping with an electronic temperature of 240 mK in fields up to 14 T. I detail technical solutions to overcome the stringent requirements on vibration isolation, electronic noise, and mechanical design necessary to successfully integrate the triad of the STM, UHV, and dilution refrigeration. Measurements of the heavy fermion superconductor CeCoIn5 ( Tc = 2.3 K) directly leverage the resulting combination of ultra-low temperature and atomic resolution to identify its Cooper pairing to be of dx2-y2 symmetry. Spectroscopic and quasiparticle interference measurements isolate a Kondo-hybridized, heavy effective mass band near the Fermi level, from which nodal superconductivity emerges in CeCoIn5 in coexistence with an independent pseudogap. Secondly, the versatility of this instrument is demonstrated through measurements of the three-dimensional Dirac semimetal Cd3As2 up to the maximum magnetic field. Through high resolution Landau level spectroscopy, the dispersion of the conduction band is shown to be Dirac-like over an unexpectedly extended regime, and its two-fold degeneracy to be lifted in field through a combination of orbital and Zeeman effects. Indeed, these two experiments on CeCoIn5 and Cd3 As2 glimpse the new era of nano-scale materials research, spanning superconductivity, topological properties, and single spin phenomena, made possible by the advance of STM instrumentation to the milli-Kelvin, high magnetic field frontier.

  1. 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 rhenium atoms, leading to weaker metal - support interactions in the bimetallic sample than what is observed for the monometallic sample. Cobalt does not catalyse the reduction of rhenium and more than six hours reduction at 450{sup o}C is required for complete reduction of accessible rhenium. The influence of pretreatment temperature on the metal function of a commercial Pt-Re/Al{sub 2}O{sub 3} reforming catalyst (EUROPT-4) was studied by X-ray absorption spectroscopy. By simultaneously examining the rhenium L{sub III} and platinum L{sub III} EXAFS data, the bimetallic interaction and the metal - support interaction can be distinguished from the overall spectrum. The results show that if the catalyst is dried in air at temperatures {<=} 500{sup o}C before reduction at 480{sup o}C, bimetallic particles of platinum and rhenium are formed. Drying at higher temperatures and in absence of air inhibits the transport of mobile (rhenium) species on the surface causing no intimate contact between the two metals. Platinum L{sub III} EXAFS data show that the average particle size of the bimetallic particles on the alumina surface is less than 10 A. The results from the rhenium L{sub III} EXAFS analysis confirm that rhenium is not completely reduced to metallic rhenium after reduction, with a significant fraction of the rhenium present in low, positive oxidation states and in intimate contact with the support. The EXAFS data are consistent with a structural model of flat rhenium metal particles with smaller platinum particles situated at the boundary of the rhenium particles. Ethene adsorption and subsequent dehydrogenation on the hexagonally reconstructed Pt(100)-hex-R0.7{sup o} surface has been investigated using scanning tunnelling microscopy (STM) and low energy electron diffraction (LEED). The results show that heterogeneous nucleation of the (1x1) domains occur when the hexagonal reconstruction is lifted during ethene adsorption on Pt(100). The (1x1) domains are highly anisotropic, and tend to grow in the [N 1] direction of the hexagonal reconstruction. The diffusion barrier associated with step edges parallel to the [N 1] direction is shown to be an important factor for the anisotropic behaviour of the adsorption process. The Pt(111) and the Pt(100)-hex-R0.7{sup o} surfaces were both saturated with ethene at room temperature followed by heating to 900 K. LEED patterns and STM images of the platinum surfaces after heating consistently show that graphite formation is more pronounced on Pt(111) than on Pt(100). The adsorbate formed on the Pt(100) surface during ethene exposure appears to desorb completely, leaving a clean hexagonally reconstructed surface when heated in UHV to temperatures above 900 K.

  2. Scanning tunneling microscopy-based in situ measurement of fast tool servo-assisted diamond turning micro-structures

    Science.gov (United States)

    Ju, Bing-Feng; Zhu, Wu-Le; Yang, Shunyao; Yang, Keji

    2014-05-01

    We propose a new in situ measurement system based on scanning tunneling microscopy (STM) to realize spiral scanning of a micro-structure without removing it after fast tool servo (FTS) cutting. To avoid distortion of the machined and measured surface, the center alignment of the FTS tool and the STM tip was first implemented by an STM in situ raster scan of two circular grooves cut by the machine tool. To originally observe the machined surface, the trace of the STM tip is put in accord with that of the FTS by setting the same start and end points of cutting and scanning and the same feed rate, and both are triggered by the subdivided rotary encoder of the spindle of the diamond turning machine. The profile data of the in situ spiral scanning of the machined micro-lens array can be fed back to compensate the depth of the cut to guarantee sub-micron form accuracy after second machining. The efficient spiral scanning, proper matching and accurate evaluation results demonstrate that the proposed STM in situ measurement approach is of great significance to the fabrication process.

  3. Strong tip–sample coupling in thermal radiation scanning tunneling microscopy

    International Nuclear Information System (INIS)

    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 such a heated probe above a surface performs a surface spectroscopy, in the sense that the spectrum of the heat current is closely related to the local electromagnetic density of states. The calculations agree well with available experimental data. - Highlights: • Polarizability of a dipolar particle changes close to a sample in near-field. • Signal detected in far field coming from a dipolar particle scattering of the near-field. • Calculation applied to plasmonic and thermal excitation. • Relation between signal and EM-LDOS is established. • Heat transfer between a dipolar particle and a sample is calculated

  4. Spin-polarized scanning tunneling microscopy and spectroscopy of ultrathin Fe/Mo (110) films using W/Au/Co tips

    Science.gov (United States)

    Prokop, J.; Kukunin, A.; Elmers, H. J.

    2006-01-01

    We report on magnetic contrast observed in low-temperature spin-polarized scanning tunneling microscopy (SP-STM) of Fe nanowires deposited on Mo(110) using tungsten tips covered by Au/Co thin films. Due to the spin reorientation transition of Co films on Au an out-of-plane magnetic sensitivity is obtained for tips with thin cobalt films (up to 8 monolayers of Co), while for thicker Co coverages an in-plane magnetization component can be probed. Using W/Au/Co tips with out-of-plane magnetic sensitivity we show that the one (ML) and two (DL) atomic layers thick Fe nanowires prepared using step flow growth on a Mo(110) crystal are perpendicularly magnetized. The reorientation of the tip sensitivity axis has been confirmed by SP-STM measurements of thicker Fe/Mo(110) films, where an in-plane easy axis has been observed for islands thicker than 3 ML. Spin-resolved spectra were measured using the W/Au/Co tips for ML, DL and thicker Fe/Mo films. The spectra reveal strong characteristic peaks at 0.4eV for ML Fe, and at -0.08eV and 0.78eV for DL Fe. Peak positions and intensities depend on the relative orientation of tip and sample magnetization. Spin-resolved spectroscopic data obtained for different tips are compared.

  5. 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.

  6. 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.

  7. Use of molybdenum telluride as a substrate for the imaging of biological molecules during scanning tunnelling microscopy.

    Science.gov (United States)

    Campbell, S A; Müller, D J; Jungblut, H; Giersig, M; Tomm, Y; Lewerenz, H J

    1994-05-01

    Scanning tunnelling microscopy was used to image biological molecules including supercoiled deoxyribonacetic acid and specific retrovirus enzymes, the reverse transcriptases of the avian myeloblastosis virus, the moloney murine leukaemia virus and the human immunodeficiency virus. Measurements were carried out on graphite and Group VI transition metal dichalcogenide layered crystals. Images obtained with graphite could not be unequivocally interpreted and attachment appears to occur solely at surface defect sites. The layered crystal MoTe2 shows different imaging properties. The bimolecules are clearly visible, distributed over the semiconductor surface, and the molecular shapes and dimensions show good correlation with structure predictions. PMID:7520674

  8. Scanning Tunneling Microscopy Measurements of the Full Cycle of a Heterogeneous Asymmetric Hydrogenation Reaction on Chirally Modified Pt(111)

    DEFF Research Database (Denmark)

    Demers-Carpentier, Vincent; Goubert, Guillaume; Masini, Federico; Dong, Yi; Rasmussen, Anton Michael Havelund; Hammer, Bjørk; McBreen, Peter H.

    2012-01-01

    The hydrogenation of a prochiral substrate, 2,2,2-trifluoroacetophenone (TFAP), on Pt(111) was studied using room-temperature scanning tunneling microscopy (STM) measurements. The experiments were carried out both on a clean surface and on a chirally modified surface, using chemisorbed (R)-(+)-1-(1-naphthyl)ethylamine, ((R)-NEA), as the modifier. On the nonmodified surface, introduction of H2 at a background pressure of ?1 × 10–6 mbar leads to the rapid break-up of TFAP dimer structures followed...

  9. Scanning tunneling microscopy observation and theoretical calculation of the adsorption of adenine on Si(100)2 × 1 surfaces

    Science.gov (United States)

    Kasaya, Megumi; Tabata, Hitoshi; Kawai, Tomoji

    1995-11-01

    Scanning tunneling microscopy (STM) images of adenine molecules on Si(100)2 × 1 surfaces have shown for the first time that the adenine is adsorbed on a Si dimer row. The double bright molecular images are located on the neighboring two Si dimer rows and have ellipsoidal shapes. An extended Hückel molecular orbital calculation of the adenine adsorbed on the Si cluster gives the form of the hybridized orbital in this system. This calculation explains the adsorption site and the surface local density of states corresponding to the observed STM images.

  10. Low-dimensional NbO structures on the Nb(110) surface: scanning tunneling microscopy, electron spectroscopy and diffraction

    OpenAIRE

    Razinkin, A. S.; Shalaeva, E. V.; Kuznetsov, M. V.

    2008-01-01

    X-ray photoelectron spectroscopy and diffraction (XPS, XPD) and scanning tunneling microscopy (STM) have been used for study of NbOx-structures on the Nb(110) surface. It is shown that niobium atoms are ordered to form a two-dimensional superstructure with equidistant spacing between the chains of niobium atoms. Chemical shifts of Nb3d- and O1s-levels demonstrate that the oxide layer corresponds to niobium monoxide NbO and the most part of oxygen in chemisorbed state is loca...

  11. Scanning-Tunneling Microscope Imaging of Single-Electron Solitons in a Material with Incommensurate Charge-Density Waves

    Science.gov (United States)

    Brazovskii, Serguei; Brun, Christophe; Wang, Zhao-Zhong; Monceau, Pierre

    2012-03-01

    We report on scanning-tunneling microscopy experiments in a charge-density wave (CDW) system allowing visually capturing and studying in detail the individual solitons corresponding to the self-trapping of just one electron. This “Amplitude Soliton” is marked by vanishing of the CDW amplitude and by the ? shift of its phase. It might be the realization of the spinon—the long-sought particle (along with the holon) in the study of science of strongly correlated electronic systems. As a distinct feature we also observe one-dimensional Friedel oscillations superimposed on the CDW which develop independently of solitons.

  12. Adsorbate structures and catalytic reactions studied in the torrpressure range by scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Hwang, Kevin Shao-Lin

    2003-05-23

    High-pressure, high-temperature scanning tunneling microscopy (HPHTSTM) was used to study adsorbate structures and reactions on single crystal model catalytic systems. Studies of the automobile catalytic converter reaction [CO + NO {yields} 1/2 N{sub 2} + CO{sub 2}] on Rh(111) and ethylene hydrogenation [C{sub 2}H{sub 4} + H{sub 2} {yields} C{sub 2}H{sub 6}] on Rh(111) and Pt(111) elucidated information on adsorbate structures in equilibrium with high-pressure gas and the relationship of atomic and molecular mobility to chemistry. STM studies of NO on Rh(111) showed that adsorbed NO forms two high-pressure structures, with the phase transformation from the (2 x 2) structure to the (3 x 3) structure occurring at 0.03 Torr. The (3 x 3) structure only exists when the surface is in equilibrium with the gas phase. The heat of adsorption of this new structure was determined by measuring the pressures and temperatures at which both (2 x 2) and (3 x 3) structures coexisted. The energy barrier between the two structures was calculated by observing the time necessary for the phase transformation to take place. High-pressure STM studies of the coadsorption of CO and NO on Rh(111) showed that CO and NO form a mixed (2 x 2) structure at low NO partial pressures. By comparing surface and gas compositions, the adsorption energy difference between topsite CO and NO was calculated. Occasionally there is exchange between top-site CO and NO, for which we have described a mechanism for. At high NO partial pressures, NO segregates into islands, where the phase transformation to the (3 x 3) structure occurs. The reaction of CO and NO on Rh(111) was monitored by mass spectrometry (MS) and HPHTSTM. From MS studies the apparent activation energy of the catalytic converter reaction was calculated and compared to theory. STM showed that under high-temperature reaction conditions, surface metal atoms become mobile. Ethylene hydrogenation and its poisoning by CO was also studied by STM on Rh(111) and Pt(111). Poisoning was found to coincide with decreased adsorbate mobility. Under ethylene hydrogenation conditions, no order is detected by STM at 300 K, as hydrogen and ethylidyne, the surface species formed by gas-phase ethylene, are too mobile. When CO is introduced, the reaction stops, and ordered structures appear on the surface. For Rh(111), the structure is predominantly a mixed c(4 x 2), though there are some areas of (2 x 2). For Pt(111), the structure is hexagonal and resembles the Moire pattern seen when Pt(111) is exposed to pure CO. From these studies it is concluded that CO poisons by stopping adsorbate mobility. This lack of adsorbate mobility prevents the adsorption of ethylene from the gas phase by hindering the creation of adsorption sites.

  13. 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 of material as a function of the ion fluence. This method is also applicable under less grazing angles of incidence. The investigations show that the sputtering yield at step edges depends on the azimuthal orientation of the impinging ions with respect to the surface. This change is attributed to the orientation dependence of subsurface channeling. The step edge sputtering yield at small adatom clusters is measured. In this case, the topmost layer (which forms the step edge) has a small lateral extension in ion beam direction. The evaluation shows that the step edge yield is, compared to step edges with a long upper terrace, decreased by a factor of three. The physical reason can be traced back to subsurface channeling. The ions are able to pass underneath the cluster and exit the crystal without a large scattering event. Little energy is transfered to the crystal which results in a low sputtering yield. The influence of adsorbates on sputtering and surface damage in grazing incidence ion erosion is studied for the case of oxygen and carbon monoxide. A partial surface coverage with adsorbates causes an enhancement of the erosion rate (the amount of removed material per ion fluence) by a factor of up to 40 compared to the clean case. The study is performed for 5 keV Ar{sup +} ions for various grazing angles between 81 and 87 and temperatures ranging from 400 K to 550 K. Finally, coarsening of ion beam induced ripple patterns is analyzed. For surface temperatures of 450 K or below coarsening is athermal and kinetic, unrelated to diffusion and surface free energy. Similar to the situation of sand dunes, coarsening takes place through annihilation reactions of mobile defects in the pattern. The defect velocity derived on the basis of a simple model agrees quantitatively with the velocity of monoatomic steps illuminated by the ion beam. (orig.)

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

    International Nuclear Information System (INIS)

    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 ? = 78.5 and ? = 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 ? = 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 of material as a function of the ion fluence. This method is also applicable under less grazing angles of incidence. The investigations show that the sputtering yield at step edges depends on the azimuthal orientation of the impinging ions with respect to the surface. This change is attributed to the orientation dependence of subsurface channeling. The step edge sputtering yield at small adatom clusters is measured. In this case, the topmost layer (which forms the step edge) has a small lateral extension in ion beam direction. The evaluation shows that the step edge yield is, compared to step edges with a long upper terrace, decreased by a factor of three. The physical reason can be traced back to subsurface channeling. The ions are able to pass underneath the cluster and exit the crystal without a large scattering event. Little energy is transfered to the crystal which results in a low sputtering yield. The influence of adsorbates on sputtering and surface damage in grazing incidence ion erosion is studied for the case of oxygen and carbon monoxide. A partial surface coverage with adsorbates causes an enhancement of the erosion rate (the amount of removed material per ion fluence) by a factor of up to 40 compared to the clean case. The study is performed for 5 keV Ar+ ions for various grazing angles between 81 and 87 and temperatures ranging from 400 K to 550 K. Finally, coarsening of ion beam induced ripple patterns is analyzed. For surface temperatures of 450 K or below coarsening is athermal and kinetic, unrelated to diffusion and surface free energy. Similar to the situation of sand dunes, coarsening takes place through annihilation reactions of mobile defects in the pattern. The defect velocity derived on the basis of a simple model agrees quantitatively with the velocity of monoatomic steps illuminated by the ion beam. (orig.)

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

    DEFF Research Database (Denmark)

    Haiss, W.; Albrecht, Tim; van Zalinge, H.; Higgins, S.J.; Bethell, D.; Hobenreich, H.; Schiffrin, D.J.; Nichols, Richard John; Kuznetsov, A.M.; Zhang, Jingdong; Chi, Qijin; Ulstrup, Jens

    2007-01-01

    maximum in the I-tunneling versus electrode potential relationship can be fitted by a "soft" gating concept. This arises from large configurational fluctuations of the molecular bridge linked to the gold contacts by flexible chains. This view is incorporated in a formalism that is well-suited for data...

  16. Spin polarized and degenerate tunneling spectra in intrinsic Josephson junctions of Bi2212

    Energy Technology Data Exchange (ETDEWEB)

    Ozdemir, M.; Ozyuzer, L. [Department of Physics, Izmir Institute of Technology, Izmir, 35430 (Turkey); Kurter, C. [Materials Science Division, Argonne National Laboratory, Argonne, IL 60439 (United States)

    2007-07-01

    Tunneling characteristics of HgBr{sub 2} intercalated superconducting Bi2212 single crystals have been obtained by using 10 x 10 mm{sup 2} intrinsic Josephson junction stacks, so called mesa structures. The spin degenerate current is driven along the c-axis with Au layer using point contact tunneling assembly at 4.2 K. The spin polarized current is also driven along the c-axis of crystals with Au/Co/Au multilayer. In order to understand the role of ferromagnetic layer (Co), quasiparticle branches are examined with and without magnetic field. The magnetic field evolution of switching currents are obtained for gaining further insight about the spin injection through the stack. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  17. Manifestation of the Verwey Transition in the Tunneling Spectra of Magnetite Nanocrystals

    OpenAIRE

    Poddar, Pankaj; Fried, Tcipi; Markovich, Gil; Sharoni, Amos; Katz, David; Wizansky, Tommer; Millo, Oded

    2003-01-01

    Tunneling transport measurements performed on single particles and on arrays of Fe3O4 (magnetite) nanocrystals provide strong evidence for the existence of the Verwey metal-insulator transition at the nanoscale. The resistance measurements on nanocrystal arrays show an abrupt increase of the resistance around 100 K, consistent with the Verwey transition, while the current-voltage characteristics exhibit a sharp transition from an insulator gap to a peak structure around zero...

  18. Density of states and tunneling spectra in two-dimensional d-wave superconductors

    Science.gov (United States)

    Zhou, C.; Schulz, H. J.

    1992-04-01

    The quasiparticle density of states is discussed in the framework of d-wave superconductivity, and the corresponding superconductor-insulator-superconductor tunneling conductivity ?(V) is obtained. We find a quadratic increase of ?(V) at low voltage and two maxima at higher voltage. These features are in qualitative agreement with recent experimental findings of Forro et al. An s-wave state also gives rise to a double-peak structure, but no quadratic low-voltage behavior is found.

  19. Scattering of electrically excited surface plasmon polaritons by gold nanoparticles studied by optical interferometry with a scanning tunneling microscope

    Science.gov (United States)

    Wang, Tao; Rogez, Benoît.; Comtet, Geneviève; Le Moal, Eric; Abidi, Wafa; Remita, Hynd; Dujardin, Gérald; Boer-Duchemin, Elizabeth

    2015-07-01

    We study the scattering of electrically excited surface plasmon polaritons (SPP) from individual nanostructures. The tunneling electrons from a scanning tunneling microscope (STM) are used to excite an out-going, circular SPP wave on a thin (50-nm) gold film on which isolated gold nanoparticles (NPs) have been deposited. Interaction of the excited SPPs with the NPs leads to both in-plane (SPP-to-SPP) and out-of-plane (SPP-to-photon) scattering. We use SPP leakage radiation microscopy to monitor the interference between the incident and in-plane scattered SPP waves in the image plane. By changing the location of the STM tip, the distance of the pointlike SPP source to the scatterers can be varied at will, which constitutes a key advantage over other existing techniques. As well, the out-of-plane scattered radiation interferes with the direct light emission from the STM tip in the back focal plane (Fourier plane). This confirms the mutual coherence of the light and SPP emission resulting from the inelastic tunneling of an electron in the STM junction. We use this effect to demonstrate that SPP-to-photon scattering at NPs is highly directional.

  20. Local secondary-electron emission spectra of graphite and gold surfaces obtained using the Scanning Probe Energy Loss Spectrometer (SPELS).

    Science.gov (United States)

    Lawton, J J; Pulisciano, A; Palmer, R E

    2009-11-25

    Secondary-electron emission (SEE) spectra have been obtained with the Scanning Probe Energy Loss Spectrometer at a tip-sample distance of only 50 nm. Such short working distances are required for the best theoretical spatial resolution (thin gold films demonstrate the capability of identifying (carbonaceous) surface contamination with this technique. PMID:21832485

  1. Scanning tunnelling microscopy imaging and spectroscopy of p-type degenerate 4H-SiC(0001)

    International Nuclear Information System (INIS)

    In this work we present scanning tunnelling microscopy (STM) imaging and spectroscopy of a highly p-doped wide bandgap semiconducting 4H-SiC(0001) surface. Whereas n- and p-doped 6H-SiC or n-doped 4H-SiC surfaces can be relatively easily imaged with the STM, the p-doped 4H-SiC cannot be imaged due to the absence of any surface conductivity. This is very surprising given the presence of a p-doped, degenerate epitaxial layer. The behaviour can be explained by the formation of a Schottky barrier either between the tip and the surface or between the surface and the sample holder, depending on the polarity of the applied voltage. We found that prolonged and repeated exposures of the SiC surface to a Si atomic flux followed by thermal annealing are required before the surface conductivity is sufficient to allow STM images to be recorded. The result is the deposition of overlayers of Si, with structures similar to Si(111) 7 x 7, Si(113) 3 x 2, and Si(110) 16 x 2 rather than the expected stable SiC(0001) 3 x 3 reconstruction. We have further demonstrated the ability of scanning tunnelling spectroscopy to distinguish between the Si and the SiC phases based on the difference in their bandgaps

  2. Scanning tunnelling microscopy imaging and spectroscopy of p-type degenerate 4H-SiC(0001)

    Science.gov (United States)

    Laikhtman, A.; Baffou, G.; Mayne, A. J.; Dujardin, G.

    2005-07-01

    In this work we present scanning tunnelling microscopy (STM) imaging and spectroscopy of a highly p-doped wide bandgap semiconducting 4H-SiC(0001) surface. Whereas n- and p-doped 6H-SiC or n-doped 4H-SiC surfaces can be relatively easily imaged with the STM, the p-doped 4H-SiC cannot be imaged due to the absence of any surface conductivity. This is very surprising given the presence of a p-doped, degenerate epitaxial layer. The behaviour can be explained by the formation of a Schottky barrier either between the tip and the surface or between the surface and the sample holder, depending on the polarity of the applied voltage. We found that prolonged and repeated exposures of the SiC surface to a Si atomic flux followed by thermal annealing are required before the surface conductivity is sufficient to allow STM images to be recorded. The result is the deposition of overlayers of Si, with structures similar to Si(111) 7 × 7, Si(113) 3 × 2, and Si(110) 16 × 2 rather than the expected stable SiC(0001) 3 × 3 reconstruction. We have further demonstrated the ability of scanning tunnelling spectroscopy to distinguish between the Si and the SiC phases based on the difference in their bandgaps.

  3. 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; Friis, Esben P.; Andersen, Jens Enevold Thaulov; Ulstrup, Jens

    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 net......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...

  4. Preparation of theoretical scanning tunneling microscope images of adsorbed molecules: a theoretical study of benzene on the Cu(110) surface

    International Nuclear Information System (INIS)

    Full text: Since its development in 1982, the Scanning Tunneling Microscope (STM) has developed into a powerful tool for the study of surfaces and adsorbates. However, the utility of the technique can be further enhanced through the development of techniques for generating theoretical STM images. This is particularly true when studying molecules adsorbed on a substrate, as the results are often interpreted superficially due to an inadequate understanding of the orbital overlap probed in the experiment. A method of preparing theoretical scanning tunneling microscope (STM) images using comparatively inexpensive desktop computers and the commercially available CRYSTAL98 package is presented through a study of benzene adsorbed on the Cu(110) surface. Density Functional Theory (DFT) and Hartree-Fock (HF) methods are used to model clean Cu(110) slabs of various thicknesses and to simulate the adsorption of benzene onto these slabs. Eight possible orientations of benzene on the Cu(110) surface are proposed, and the optimum orientation according to the calculations is presented. Theoretical STM images of the Cu(110) surface and benzene adsorbed on the Cu(110) surface are compared with experimental STM images of the system from a published study. Significant differences are observed and are examined in detail

  5. Monte Carlo Simulation of Complete X-Ray Spectra for Use in Scanning Electron Microscopy Analysis

    International Nuclear Information System (INIS)

    Full Text: The interactions of keV electrons and photons with matter can be simulated accurately with the aid of the Monte Carlo (MC) technique. In scanning electron microscopy x-ray analysis (SEM-EDX) such simulations can be used to perform quantitative analysis using a Reverse Monte Carlo method even if the samples have irregular geometry. Alternatively the MC technique can generate spectra of standards for use in quantization with partial least squares regression. The feasibility of these alternatives to the more classical ZAF or phi-rho-Z quantification methods has been proven already. In order to be applicable for these purposes the MC-code needs to generate accurately only the characteristic K and L x-ray lines, but also the Bremsstrahlung continuum, i.e. the complete x-ray spectrum need to be simulated. Currently two types of MC simulation codes are available. Programs like Electron Flight Simulator and CASINO simulate characteristic x-rays due to electron interaction in a fast and efficient way but lack provision for the simulation of the continuum. On the other hand, programs like EGS4, MCNP4 and PENELOPE, originally developed for high energy (MeV- GeV) applications, are more complete but difficult to use and still slow, even on todays fastest computers. We therefore started the development of a dedicated MC simulation code for use in quantitative SEM-EDX work. The selection of the most appropriate cross section for the different interactions will be discussed and the results obtained will be compared with those obtained with existing MC programs. Examples of the application of MC simulations for quantitative analysis of samples with various composition will be given

  6. Design and performance of an ultra-high vacuum scanning tunneling microscope operating at dilution refrigerator temperatures and high magnetic fields

    OpenAIRE

    Misra, Shashank; Zhou, Brian B.; 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 ...

  7. Preeminent role of the Van Hove singularity in the strong-coupling analysis of scanning tunneling spectroscopy for two-dimensional cuprates

    CERN Document Server

    de Castro, G L; Fischer, O; Castro, Giorgio Levy de; Berthod, Christophe; Fischer, Oystein

    2007-01-01

    In two dimensions the non-interacting density of states displays a Van Hove singularity (VHS) which introduces an intrinsic electron-hole asymmetry, absent in three dimensions. We show that due to this VHS the strong-coupling analysis of tunneling spectra in high-$T_c$ superconductors must be reconsidered. Based on a microscopic model which reproduces the experimental data with great accuracy, we elucidate the peculiar role played by the VHS in shaping the tunneling spectra, and show that more conventional analyses of strong-coupling effects can lead to severe errors.

  8. Preeminent Role of the Van Hove Singularity in the Strong-Coupling Analysis of Scanning Tunneling Spectroscopy for Two-Dimensional Cuprate Superconductors

    Science.gov (United States)

    Levy de Castro, Giorgio; Berthod, Christophe; Piriou, Alexandre; Giannini, Enrico; Fischer, Øystein

    2008-12-01

    In two dimensions the noninteracting density of states displays a van Hove singularity (VHS) which introduces an intrinsic electron-hole asymmetry, absent in three dimensions. We show that due to this VHS the strong-coupling analysis of tunneling spectra in high-Tc superconductors must be reconsidered. Based on a microscopic model which reproduces the experimental data with excellent accuracy, we elucidate the peculiar role played by the VHS in shaping the tunneling spectra, and show that more conventional analysis of strong-coupling effects can lead to severe errors.

  9. [Scanning tunnelling microscopy and spectroscopy of ceramic grain boundaries]. [Annual report, September 1992--September 1993

    Energy Technology Data Exchange (ETDEWEB)

    1993-10-01

    Objective is to study the local geometric and electronic structure at grain boundaries in oxides; this was motivated by the potential to use STM and tunneling spectroscopy on semiconducting ceramics. In order to understand the imaging of low conductivity materials, a number of transition metal oxides were examined: ZnO, TiO{sub 2}. Spatial resolution limits are considered. Conductance profiles across silicon grain boundaries are compared with those across more complex SrTiO{sub 3} grain boundaries. Calculations of space charge in complex oxides are presented. A SEM/STM was constructed which operates in ultrahigh vacuum and has large scale positioning capability (> 1 cm).

  10. 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.

  11. Estudio de superficies usando un microscopio de efecto túnel (STM) / A study of surfaces using a scanning tunneling microscope (STM)

    Scientific Electronic Library Online (English)

    Alba Graciela, Ávila Bernal; Ruy Sebastián, Bonilla Osorio.

    2009-12-01

    Full Text Available Los microscopios de barrido se han convertido en las manos y los "ojos" de experimentadores de nuestro siglo, son herramientas necesarias en los laboratorios de educación e investigación para la caracterización a nanoescalas. El presente artículo presenta las modificaciones en la implementación elec [...] trónica (caracterización de los piezoeléctricos y sistema de barrido) y mecánica (diseño de un sistema de antivibración) de un microscopio de barrido de efecto túnel que han permitido visualización y modificación de superficies a nanoescala. Se describe una metodología para la correcta visualización y caracterización de superficies usando el instrumento implementado, alcanzando la cuantificación bidimensional de características de hasta 1300nm², con resolución ~15nm. Esta metodología, determinada experimentalmente, tiene en cuenta parámetros críticos para la estabilización de la corriente túnel, como lo son la velocidad de barrido y las geometrías y dimensiones de las agujas del microscopio. La versatilidad del microscopio permite modificar y visualizar los defectos introducidos en muestras de HOPG al aplicar voltajes entre la punta del microscopio y la muestra. Los resultados aquí descritos permiten presentar fácilmente los conceptos de barrido topográfico y litografía. Abstract in english Sweeping/scanning microscopes have become an experimental scientist's hands and eyes in this century; they have become a powerful and necessary tool for nanoscale characterisation in education and research laboratories all around the world. This article presents the modifications made in the mechani [...] cal (isolation or designing an antivibration system) and electrical (piezoelectric and scanning system characterisation) implementation of a scanning tunnelling microscope (STM), thereby allowing nanoscale surfaces to be visualised and modified. A methodology for visualising and characterising surfaces using the aforementioned instrument is described, bidimensional quantification of up to 1,300 nm², with ~15 nm resolution being reached. This experimental methodology took critical parameters for tunnelling current stability into account, such as scanning speed and microscope tip geometry and dimensions. This microscope's versatility allowed defects in highly oriented pyrolytic graphite (HOPG) samples to be modified and visualised by applying a voltage between the tip and the sample. The concepts of topography scanning and lithography can be easily understood by using the instrument implemented here.

  12. One-Dimensional Nature of InAs/InP Quantum Dashes Revealed by Scanning Tunneling Spectroscopy.

    Science.gov (United States)

    Papatryfonos, Konstantinos; Rodary, Guillemin; David, Christophe; Lelarge, François; Ramdane, Abderrahim; Girard, Jean-Christophe

    2015-07-01

    We report on low-temperature cross-sectional scanning tunneling microscopy and spectroscopy on InAs(P)/InGaAsP/InP(001) quantum dashes, embedded in a diode-laser structure. The laser active region consists of nine InAs(P) quantum dash layers separated by the InGaAsP quaternary alloy barriers. The effect of the p-i-n junction built-in potential on the band structure has been evidenced and quantified on large-scale tunneling spectroscopic measurements across the whole active region. By comparing the tunneling current onset channels, a consistent energy shift has been measured in successive quantum dash or barrier layers, either for the ground state energy of similar-sized quantum dashes or for the conduction band edge of the barriers, corresponding to the band-bending slope. The extracted values are in good quantitative agreement with the theoretical band structure calculations, demonstrating the high sensitivity of this spectroscopic measurement to probe the electronic structure of individual nanostructures, relative to local potential variations. Furthermore, by taking advantage of the potential gradient, we compared the local density of states over successive quantum dash layers. We observed that it does not vanish while increasing energy, for any of the investigated quantum dashes, in contrast to what would be expected for discrete level zero-dimensional (0D) structures. In order to acquire further proof and fully address the open question concerning the quantum dash dimensionality nature, we focused on individual quantum dashes obtaining high-energy-resolution measurements. The study of the local density of states clearly indicates a 1D quantum-wirelike nature for these nanostructures whose electronic squared wave functions were subsequently imaged by differential conductivity mapping. PMID:26076402

  13. Cluster formation in laser-induced ablation and evaporation of solids observed by laser ionization time-of-flight mass-spectrometry and scanning tunneling microscopy

    International Nuclear Information System (INIS)

    This paper reports on laser ionization time-of-flight mass analysis (LIMA) which used pulses (5ns) of a frequency-quadrupled Nd-YAG laser (266 nm) focused onto spots of 4--100 ?m diameter to ablate material, and a reflection time of flight tube to mass-analyze the plume. The observed mass spectra for Si, Pt, SiC, and UO2 varied in the distribution of ablation products among atoms, molecules and clusters, depending on laser power density and target material. Cleaved surfaces of highly oriented pyrolytic graphite (HOPG) positioned at room temperature either 10 cm away from materials ablated at 10-5 Torr by 1-3 excimer laser (308 nm) pulses of 20 ns duration or 1 m away from materials vaporized at 10-8 Torr by 10 Nd-Glass laser pulses of 1 ms duration were analyzed by Scanning Tunneling Microscopy (STM) in air with Angstrom resolution. Clusters up to 30 Angstrom in diameter were observed

  14. Observation of two-gap superconductivity in SrFe1.85Co0.15As2 single crystals by scanning tunneling microscopy and spectroscopy

    International Nuclear Information System (INIS)

    Superconducting properties of SrFe1.85Co0.15As2 single crystals and their parent material, SrFe2As2, were investigated by scanning tunneling microscopy and spectroscopy (STM/S). In the parent material, we modeled surface conditions on the in situ cleaved single crystals, based on the observation of 2x1 stripe patterns and ?2x?2 square-lattice patterns in the atomic-resolution topography images and with the help of local density of states measurements. In the STM/S studies on SrFe1.85Co0.15As2, a robust superconducting gap (2?large=17.3 meV) was observed in the conductance spectra measured along a line on the SrFe1.85Co0.15As2 surface. Moreover, an additional small gap-like (2?small=2.9 meV) structure was simultaneously observed. Our observation corroborates the two-gap structures in iron-based superconductors.

  15. Cluster formation in laser-induced ablation and evaporation of solids observed by laser ionization time-of-flight mass spectrometry and scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Tench, R.J.; Balooch, M.; Bernardez, L.; Allen, M.J.; Siekhaus, W.J. (Lawrence Livermore National Lab., CA (USA)); Olander, D.R.; Wang, W. (Lawrence Berkeley Lab., CA (USA))

    1990-01-01

    Laser ionization time-of-flight mass analysis (LIMA) used pulses (5ns) of a frequency-quadrupled Nd-YAG laser (266 nm) focused onto spots of 4--100 {mu}m diameter to ablate material, and a reflectron time of flight tube to mass-analyze the plume. The observed mass spectra for Si, Pt, SiC, and UO{sub 2} varied in the distribution of ablation products among atoms, molecules and clusters, depending on laser power density and target material. Cleaved surfaces of highly oriented pyrolytic graphite (HOPG) positioned at room temperature either 10 cm away from materials ablated at 10{sup {minus}5} Torr by 1--3 excimer laser (308 nm) pulses of 20 ns duration or 1 m away from materials vaporized at 10{sup {minus}8} Torr by 10 Nd-Glass laser pulses of 1 ms duration were analyzed by Scanning Tunneling Microscopy (STM) in air with {angstrom} resolution. Clusters up to 30 {angstrom} in diameter were observed. 8 refs., 4 figs.

  16. Line and Point Defects in MoSe2 Bilayer Studied by Scanning Tunneling Microscopy and Spectroscopy.

    Science.gov (United States)

    Liu, Hongjun; Zheng, Hao; Yang, Fang; Jiao, Lu; Chen, Jinglei; Ho, Wingkin; Gao, Chunlei; Jia, Jinfeng; Xie, Maohai

    2015-06-23

    Bilayer (BL) MoSe2 films grown by molecular-beam epitaxy (MBE) are studied by scanning tunneling microscopy and spectroscopy (STM/S). Similar to monolayer (ML) films, networks of inversion domain boundary (DB) defects are observed both in the top and bottom layers of BL MoSe2, and often they are seen spatially correlated such that one is on top of the other. There are also isolated ones in the bottom layer without companion in the top-layer and are detected by STM/S through quantum tunneling of the defect states through the barrier of the MoSe2 ML. Comparing the DB states in BL MoSe2 with that of ML film reveals some common features as well as differences. Quantum confinement of the defect states is indicated. Point defects in BL MoSe2 are also observed by STM/S, where ionization of the donor defect by the tip-induced electric field is evidenced. These results are of great fundamental interests as well as practical relevance of devices made of MoSe2 ultrathin layers. PMID:26051223

  17. Mirror buckling of freestanding graphene membranes induced by local heating due to a scanning tunneling microscope tip

    Science.gov (United States)

    Schoelz, J. K.; Neek Amal, M.; Xu, P.; Barber, S. D.; Ackerman, M. L.; Thibado, P. M.; Sadeghi, A.; Peeters, F. M.

    2014-03-01

    Scanning tunneling microscopy has been an invaluable tool in the study of graphene at the atomic scale. Several STM groups have managed to obtain atomic scale images of freestanding graphene membranes providing insight into the behavior of the stabilized ripple geometry. However, we found that the interaction between the STM tip and the freestanding graphene sample may induce additional effects. By varying the tunneling parameters, we can tune the position of the sample, in either a smooth or step like fashion. These phenomena were investigated by STM experiments, continuum elasticity theory and large scale molecular dynamics simulations. These results confirm that by increasing the tip bias, the electrostatic attraction between the tip and sample increases. When applied on a concave surface, this can result in mirror buckling which leads to a large scale movement of the sample. Interestingly, due in part to the negative coefficient of thermal expansion of graphene, buckling transitions can also be induced through local heating of the surface using the STM tip. Financial support by O.N.R. grant N00014-10-1-0181, N.S.F grant DMR-0855358, EU-Marie Curie IIF postdoc Fellowship/299855 (for M. N. A.), ESF-EuroGRAPHENE project CONGRAN, F.S.F (FWO-Vl), and Methusalem Foundation of the Flemish Government.

  18. Atomic-Scale Control of Surface Reconstruction on Ge(001) by Scanning Tunneling Microscopy at 80 K

    Science.gov (United States)

    Takagi, Yasumasa; Nakatsuji, Kan; Yamada, Masamichi; Komori, Fumio

    2004-03-01

    The reconstruction of a clean Ge(001) surface is controlled at the atomic scale by the temporal change in the sample bias voltage during scanning tunneling microscopy (STM) observation at 80 K. A positive voltage pulse on the c(4×2)-reconstructed region flips the buckled dimers only in the dimer row right under the STM tip apex, and creates a wire of p(2×2) reconstruction extending along the dimer row. An artificial superstructure is made on the c(4×2) surface by inverting the buckling of the target dimer rows periodically and forming p(2×2) wires side by side. A negative voltage pulse on the p(2×2) region creates a local c(4×2)-reconstructed area near the point of pulse. Its size can be reduced to 1.6 nm × 2.8 nm by manipulating the voltage of the pulse.

  19. Scanning tunneling microscopy investigation of growth of self-assembled indium and aluminum nanostructures on inert substrates

    International Nuclear Information System (INIS)

    The growth and surface morphology of indium and aluminum nanostructures on highly oriented pyrolytic graphite (HOPG) and molybdenum disulphide (MoS2) surfaces were investigated using scanning tunneling microscopy in ultra-high vacuum. Mostly triangular and hexagonal In islands with (111) orientation were obtained along the steps of HOPG at room temperature (RT). Triangular, round-shape and large irregular In islands were found on MoS2 surfaces at different growth conditions. Al island chains as well as isolated triangular islands were found on HOPG whereas nanoparticles and ramified Al islands were obtained on MoS2 at RT. The shapes of these self-assembled metal nanostructures were controlled by varying growth conditions. The different shapes of nanostructures on these inert substrates can be explained in terms of differences in energetic and kinetic properties of atoms and clusters of each elements as well as the nature of substrates.

  20. Scanning tunneling microscopy investigation of growth of self-assembled indium and aluminum nanostructures on inert substrates

    Energy Technology Data Exchange (ETDEWEB)

    Kushvaha, S.S., E-mail: kushvahas@imre.a-star.edu.s [Department of Physics, National University of Singapore, 2 Science Drive 3, 117542 (Singapore); Xu, H.; Xiao, W.; Zhang, H.L.; Wee, A.T.S. [Department of Physics, National University of Singapore, 2 Science Drive 3, 117542 (Singapore); Wang, X.-S., E-mail: phywxs@nus.edu.s [Department of Physics, National University of Singapore, 2 Science Drive 3, 117542 (Singapore)

    2009-06-30

    The growth and surface morphology of indium and aluminum nanostructures on highly oriented pyrolytic graphite (HOPG) and molybdenum disulphide (MoS{sub 2}) surfaces were investigated using scanning tunneling microscopy in ultra-high vacuum. Mostly triangular and hexagonal In islands with (111) orientation were obtained along the steps of HOPG at room temperature (RT). Triangular, round-shape and large irregular In islands were found on MoS{sub 2} surfaces at different growth conditions. Al island chains as well as isolated triangular islands were found on HOPG whereas nanoparticles and ramified Al islands were obtained on MoS{sub 2} at RT. The shapes of these self-assembled metal nanostructures were controlled by varying growth conditions. The different shapes of nanostructures on these inert substrates can be explained in terms of differences in energetic and kinetic properties of atoms and clusters of each elements as well as the nature of substrates.

  1. Scanning Tunneling Microscopy Measurements of the Full Cycle of a Heterogeneous Asymmetric Hydrogenation Reaction on Chirally Modified Pt(111)

    DEFF Research Database (Denmark)

    Demers-Carpentier, Vincent; Goubert, Guillaume

    2012-01-01

    The hydrogenation of a prochiral substrate, 2,2,2-trifluoroacetophenone (TFAP), on Pt(111) was studied using room-temperature scanning tunneling microscopy (STM) measurements. The experiments were carried out both on a clean surface and on a chirally modified surface, using chemisorbed (R)-(+)-1-(1-naphthyl)ethylamine, ((R)-NEA), as the modifier. On the nonmodified surface, introduction of H2 at a background pressure of ?1 × 10–6 mbar leads to the rapid break-up of TFAP dimer structures followed by the gradual removal of all TFAP-related images. During the latter step, some monomers display an extra protrusion compared to TFAP in dimer structures. They are attributed to a half-hydrogenated intermediate. The introduction of H2 to a mixture of (R)-NEA and TFAP on Pt(111) leads to the removal of TFAP without any change in the population of the modifier, as required for an efficient chirally modified catalyst.

  2. Scanning Tunneling Microscopy Observation of a Square Abrikosov Lattice in LuNi2B2C

    International Nuclear Information System (INIS)

    We present scanning tunneling microscopy measurements of the (001) surface of a LuNi2B 2C borocarbide single crystal at 4.2K. In zero field, the conductance versus voltage characteristics recorded at various locations on the sample reproducibly provide a gap value of 2.2meV. In a magnetic field of 1.5 and 0.375T, the recordings of the conductance as a function of position reveal a regular square vortex lattice tilted by 45 degree with respect to the crystalline a axis. This unusual result is correlated with an in-plane anisotropy of the upper critical field Hparallelc2(45 degree)/Hparallelc2(0)=0.92 at 4.2K and is analyzed within the framework of Ginzburg-Landau theory. copyright 1997 The American Physical Society

  3. Determination of carbide structures on an Mo(110) surface by scanning tunneling microscopy and low energy electron diffraction

    Science.gov (United States)

    Yu, De-Wei; Wu, Yi-Hsueh; Lin, Rong-Bin; Lo, Rong-Li

    2008-04-01

    Surface properties of transition metals can be modified considerably by forming carbide overlayers. In this study we fabricated molybdenum carbide overlayers by carburizing the Mo(110) surface with ethylene (C2H4) and successfully determined their real space structures by using low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). With various carburization recipes, three carbon-terminated structures {\\scriptsize \\bigl (\\matrix {5 & 0 \\cr {-2} & 6 }\\bigr)} , (12 × 4)-2C, and (4 × 4) of coverages 1/30,1/24, and 1/16 monolayer (ML) were formed on the surface, respectively. Since the carbide overlayers were formed at high temperatures, inward diffusion of carbon atoms played a key role in structure formation.

  4. Determination of carbide structures on an Mo(110) surface by scanning tunneling microscopy and low energy electron diffraction

    International Nuclear Information System (INIS)

    Surface properties of transition metals can be modified considerably by forming carbide overlayers. In this study we fabricated molybdenum carbide overlayers by carburizing the Mo(110) surface with ethylene (C2H4) and successfully determined their real space structures by using low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). With various carburization recipes, three carbon-terminated structures ((5)/-2/(0)/6), (12 x 4)-2C, and (4 x 4) of coverages 1/30,1/24, and 1/16 monolayer (ML) were formed on the surface, respectively. Since the carbide overlayers were formed at high temperatures, inward diffusion of carbon atoms played a key role in structure formation

  5. Electronic properties of nanoporous TiO2 films investigated in real space by means of scanning tunnelling spectroscopy

    International Nuclear Information System (INIS)

    Nanoporous TiO2 films with a thickness between 100 nm and 8 ?m were studied by scanning tunnelling spectroscopy. The bias voltage of significantly increased differential conductivity, indicating the conduction and valence bands, was found to be strongly dependent on layer thickness and the underlying substrate material. This effect is traced back to the high resistivity of the oxide films and the formation of Schottky barriers at the TiO2-substrate contact. All films showed a strong hysteresis as a function of sweep direction of the bias voltage pointing towards the existence of a high number of localized electronic trap states. This effect is getting even more pronounced upon sample ageing. Laterally resolved measurements show that the major part of the surface exhibits similar I(V) characteristics with minor deviations, while smaller areas with significantly different response are identified. These areas are comparable in size to the individual crystals the material is composed of

  6. Kinetic energy barriers on the GaN(0001) surface: A nucleation study by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Island nucleation of GaN on its (0001) surface is studied by scanning tunneling microscopy. A comparison is made between surfaces with and without excess Ga and among surfaces with different excess Ga coverages. Evidence is provided for the change of step characteristics of GaN(0001) by excess Ga adlayers, where the Ehrlich-Schwoebel effect is seen to be mediated by excess Ga coverage. For single Ga adlayer covered GaN(0001) surfaces, nucleation island densities are evaluated, which are used to derive the kinetic barriers of adatom diffusion on a terrace. A barrier of less than 1 eV is obtained for the system, and the Ga adlayers make GaN growth surfactant mediated

  7. Atomic-scale structure of a SrTiO3 bicrystal boundary studied by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    An atomically flat and well ordered c(6x2)(001) surface of a [100] tilted (2x12 degree) artificial SrTiO3 bicrystal was prepared by thermal annealing in oxygen and ultrahigh vacuum, and characterized with low-energy electron diffraction and scanning tunneling microscopy. The real-space images of the boundary show that the bicrystal boundary is not straight, but zigzagged along the [100] and [010] crystal axis, and grooved with a depth of several atomic steps down to the bulk. We attribute the observed boundary structure to strong thermal etching and crystal faceting effects. A simple model is proposed for the path of superconducting currents of high-Tc thin films crossing such a bicrystal boundary. The model yields a 1/tan(?) dependence of the critical current crossing the bicrystal boundary, which explains very well the reported experimental data. copyright 1997 The American Physical Society

  8. In situ scanning tunneling microscopy study of selective dissolution of Au3Cu and Cu3Au (0 0 1)

    International Nuclear Information System (INIS)

    We present an electrochemical study of Au3Cu (0 0 1) single crystal surfaces in 0.1 mol dm-3 H2SO4 and 0.1 mol dm-3 H2SO4 + 0.1 mmol dm-3 HCl, and of Cu3Au (0 0 1) in 0.1 mol dm-3 H2SO4. 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.

  9. In-gap states of In{sub 2}O{sub 3} single crystals investigated by scanning tunneling spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Braun, Dorothee; Fornari, Roberto [Humboldt-Universitaet zu Berlin, Institut fuer Physik (Germany); Leibniz-Institut fuer Kristallzuechtung, Berlin (Germany); Scherer, Valentina; Janowitz, Christoph; Manzke, Recardo [Humboldt-Universitaet zu Berlin, Institut fuer Physik (Germany); Galazka, Zbigniew [Leibniz-Institut fuer Kristallzuechtung, Berlin (Germany)

    2014-01-15

    The influence of intrinsic point defects on the electronic structure of n-type In{sub 2}O{sub 3} single crystals grown by two methods, namely chemical vapor transport and from the melt, was examined by scanning tunneling spectroscopy. This method is a very surface sensitive technique for measuring the local density of states. So far not resolved states within the fundamental band gap have been observed. The gap states have been studied at different crystals and after several annealing treatments in an oxidizing atmosphere. The spectroscopic results will be compared to state of the art DFT-calculations revealing hints on the origin of the gap states of In{sub 2}O{sub 3} to be due to oxygen vacancies as well as indium and oxygen interstitials. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  10. Reproducible Fabrication of Scanning Tunneling Microscope Tips / Fabricación reproducible de puntas de barrido para microscopios de efecto túnel

    Scientific Electronic Library Online (English)

    Rodrigo, Bernal; Alba, Ávila.

    2008-05-01

    Full Text Available La fabricación reproducible de puntas de barrido para microscopios de efecto túnel es demostrada usando un método electroquímico. Las puntas son hechas a partir de alambre de tungsteno de 0.5 mm de diámetro. Controlando las condiciones de fabricación: la inmersión en la solución electrolítica, rango [...] s de voltaje-corriente y duración del proceso se logra realizar puntas con relaciones de aspecto de 0.68 y radios de punta de 330 nm en el mejor caso. Abstract in english Reproducible fabrication of Scanning Tunneling Microscope tips is carried out following an electrochemical procedure widely reported. Tips are made from 0.5 diameter tungsten wire. Controlling fabrication parameters (immersion in the electrochemical solution, current-voltage ranges, duration of the [...] process, among others) we achieve aspect ratios of 0.68 and tip radii of 330 nm in the best case.

  11. 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.; Reimers, Jeffrey R.; Zhang, Jingdong; Ulstrup, Jens

    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......) calculations. The SAM forms in the unusual (8 × √3)-4 superlattice, producing a very complex STM image. Seventy possible structures were considered for the SAM, with the calculated lowest-energy configuration in fact predicting the details of the unusual observed STM image. The most stable structure involves...... two R−S−Au−S−R adatom-mediated motifs per surface cell, with steric-induced variations in the adsorbate alignment inducing the observed STM image contrasts. Observed pits covering 5.6 ± 0.5% of the SAM surface are consistent with this structure. These results provide the missing link from the...

  12. Single molecule manipulation at low temperature and laser scanning tunnelling photo-induced processes analysis through time-resolved studies

    International Nuclear Information System (INIS)

    This paper describes, firstly, the statistical analysis used to determine the processes that occur during the manipulation of a single molecule through electronically induced excitations with a low temperature (5 K) scanning tunnelling microscope (STM). Various molecular operation examples are described and the ability to probe the ensuing molecular manipulation dynamics is discussed within the excitation context. It is, in particular, shown that such studies can reveal reversible manipulation for tuning dynamics through variation of the excitation energy. Secondly, the photo-induced process arising from the irradiation of the STM junction is also studied through feedback loop dynamics analysis, allowing us to distinguish between photo-thermally and photo-electronically induced signals.

  13. Catalytic monolayer voltammetry and in situ scanning tunneling microscopy of copper nitrite reductase on cysteamine-modified Au(111) electrodes

    DEFF Research Database (Denmark)

    Zhang, Jingdong; Welinder, A.C.; Hansen, Allan Glargaard; Christensen, Hans Erik Mølager; Ulstrup, Jens

    2003-01-01

    electrochemical scanning tunneling microscopy (in situ STM) directly in aqueous acetate buffer, pH 6.0 has been used. High-resolution in situ STM shows that cysteamine packs into ordered domains with strip features of a periodic distance of 11.7 +/- 0.3 Angstrom. No voltammetric signals of the nitrite substrate...... catalytic rate constant based on a dense monolayer is k(cat) = 6-10 s(-1). This is significantly lower than two reported values of 185 s(-1) and 1400-1900 s(-1) for AxCuNiR in homogeneous solution. In situ STM of adsorbed AxCuNiR on the cysteamine-modified Au(111) surface suggests, however, that the...... forthcoming biotechnology at the monolayer and toward the single-molecule level....

  14. 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.; Ulstrup, Jens

    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....... SQWV suggested the Au-S bond strength order Au(111) > Au(110) > Au(100) based on the reductive desorption potentials. The voltammetric diversity was paralleled by different in situ STM insulin adsorption modes on the three surfaces. Single-molecule resolution was achieved in all cases. The coverage....... Adsorption, Au-S binding, and insulin unfolding are all parts of insulin surface behaviour and reflected in both voltammetry and in situ STM. In spite of these complications, the data show that molecular scale resolution has been achieved and offer other perspectives of insulin surface science such as single-molecule...

  15. Two-probe theory of scanning tunneling microscopy of single molecules: Zn(II)-etioporphyrin on alumina

    CERN Document Server

    Buker, J; Buker, John; Kirczenow, George

    2005-01-01

    We explore theoretically the scanning tunneling microscopy of single molecules on substrates using a framework of two local probes. This framework is appropriate for studying electron flow in tip/molecule/substrate systems where a thin insulating layer between the molecule and a conducting substrate transmits electrons non-uniformly and thus confines electron transmission between the molecule and substrate laterally to a nanoscale region significantly smaller in size than the molecule. The tip-molecule coupling and molecule-substrate coupling are treated on the same footing, as local probes to the molecule, with electron flow modelled using the Lippmann-Schwinger Green function scattering technique. STM images are simulated for various positions of the stationary (substrate) probe below a Zn(II)-etioporphyrin I molecule. We find that these images have a strong dependence on the substrate probe position, indicating that electron flow can depend strongly on both tip position and the location of the dominant mol...

  16. Scanning-tunneling-microscopy analysis of the charge-density-wave structure in NbSe3

    Science.gov (United States)

    Ren, J.; Whangbo, M.-H.

    1992-08-01

    93Nb NMR and scanning-tunneling-microscopy (STM) studies lead to different conclusions on the question of which chains are involved in the formation of the two charge-density waves (CDW's) in NbSe3. To resolve this conflict, we calculated the STM images of a single NbSe3 layer and analyzed the local densities of states (LDOS) of Nb and Se atoms in the vicinity of the Fermi level. The conflict arises from the fact that 93Nb NMR and STM measurements probe the LDOS of different atoms (Nb and Se atoms, respectively) at the Fermi level. Concerning the question of which chains are responsible for the CDW formation in NbSe3, however, the conclusion of the 93Nb NMR studies is appropriate because the major character of the electrons at the Fermi level is the Nb atoms of type-I and -III chains.

  17. Electronic characterization of LaAlO3-SrTiO3 interfaces by scanning tunneling spectroscopy

    International Nuclear Information System (INIS)

    When LaAlO3 is epitaxially grown on TiO2-terminated SrTiO3, an electrically conducting interface is generated. In this respect, the physical properties of the interface differ substantially from those of both LaAlO3 and SrTiO3, 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 LaAlO3-SrTiO3 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.)

  18. Tunnel spectra of junctions involving BSCCO and other cuprates: Superconducting and charge-density-wave gapping

    International Nuclear Information System (INIS)

    We have calculated quasiparticle current-voltage characteristics J(V) for non-symmetric CDWS-I-N tunnel junctions between a partially gapped charge-density wave (CDW) s-wave superconductor and a normal metal (I stands for an insulator), as well as for symmetric CDWS-I-CDWS junctions. Relevant parameters of CDWS are considered spatially inhomogeneous in accordance with experimental data for various cuprates, especially Bi2Sr2CaCu2O8+? (BSCCO). The calculated dependences G(V) dJ(V)/dV demonstrate conspicuous dip-hump structures (DHSs) at low temperatures, T, and pseudogap shallow well at high T > Tc above the critical temperature. In CDWS-I-N junctions, DHSs were shown to be observed for either one or both voltage polarities, depending on the CDW order parameter phase. Similar symmetric DHSs were found for CDWS-I-CDWS junctions. J(V) for break-junctions made of BSCCO were measured. Qualitative agreement was reached between our theoretically calculated and experimental G(V) dependences

  19. Controlled assembly and single electron charging of monolayer protected Au144 clusters: an electrochemistry and scanning tunneling spectroscopy study

    Science.gov (United States)

    Bodappa, Nataraju; Fluch, Ulrike; Fu, Yongchun; Mayor, Marcel; Moreno-García, Pavel; Siegenthaler, Hans; Wandlowski, Thomas

    2014-11-01

    Single gold particles may serve as room temperature single electron memory units because of their size dependent electronic level spacing. Here, we present a proof-of-concept study by electrochemically controlled scanning probe experiments performed on tailor-made Au particles of narrow dispersity. In particular, the charge transport characteristics through chemically synthesized hexane-1-thiol and 4-pyridylbenzene-1-thiol mixed monolayer protected Au144 clusters (MPCs) by differential pulse voltammetry (DPV) and electrochemical scanning tunneling spectroscopy (EC-STS) are reported. The pyridyl groups exposed by the Au-MPCs enable their immobilization on Pt(111) substrates. By varying the humidity during their deposition, samples coated by stacks of compact monolayers of Au-MPCs or decorated with individual, laterally separated Au-MPCs are obtained. DPV experiments with stacked monolayers of Au144-MPCs and EC-STS experiments with laterally separated individual Au144-MPCs are performed both in aqueous and ionic liquid electrolytes. Lower capacitance values were observed for individual clusters compared to ensemble clusters. This trend remains the same irrespective of the composition of the electrolyte surrounding the Au144-MPC. However, the resolution of the energy level spacing of the single clusters is strongly affected by the proximity of neighboring particles.Single gold particles may serve as room temperature single electron memory units because of their size dependent electronic level spacing. Here, we present a proof-of-concept study by electrochemically controlled scanning probe experiments performed on tailor-made Au particles of narrow dispersity. In particular, the charge transport characteristics through chemically synthesized hexane-1-thiol and 4-pyridylbenzene-1-thiol mixed monolayer protected Au144 clusters (MPCs) by differential pulse voltammetry (DPV) and electrochemical scanning tunneling spectroscopy (EC-STS) are reported. The pyridyl groups exposed by the Au-MPCs enable their immobilization on Pt(111) substrates. By varying the humidity during their deposition, samples coated by stacks of compact monolayers of Au-MPCs or decorated with individual, laterally separated Au-MPCs are obtained. DPV experiments with stacked monolayers of Au144-MPCs and EC-STS experiments with laterally separated individual Au144-MPCs are performed both in aqueous and ionic liquid electrolytes. Lower capacitance values were observed for individual clusters compared to ensemble clusters. This trend remains the same irrespective of the composition of the electrolyte surrounding the Au144-MPC. However, the resolution of the energy level spacing of the single clusters is strongly affected by the proximity of neighboring particles. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr03793f

  20. Lattice-Assisted Spectroscopy: A Generalized Scanning Tunneling Microscope for Ultracold Atoms.

    Science.gov (United States)

    Kantian, A; Schollwöck, U; Giamarchi, T

    2015-10-16

    We propose a scheme to measure the frequency-resolved local particle and hole spectra of any optical lattice-confined system of correlated ultracold atoms that offers single-site addressing and imaging, which is now an experimental reality. Combining perturbation theory and time-dependent density matrix renormalization group simulations, we quantitatively test and validate this approach of lattice-assisted spectroscopy on several one-dimensional example systems, such as the superfluid and Mott insulator, with and without a parabolic trap, and finally on edge states of the bosonic Su-Schrieffer-Heeger model. We highlight extensions of our basic scheme to obtain an even wider variety of interesting and important frequency resolved spectra. PMID:26550881

  1. Local optical absorption spectra of MoS2 monolayers obtained using scanning near-field optical microscopy measurements

    Science.gov (United States)

    Nozaki, Junji; Mori, Shohei; Miyata, Yasumitsu; Maniwa, Yutaka; Yanagi, Kazuhiro

    2016-03-01

    We obtained local optical absorption spectra of MoS2 with a spatial resolution of approximately 200 nm using scanning near-field optical microscopy with a supercontinuum laser light source, and we found that the absorption spectra exhibited a significant site dependence on the MoS2 monolayer crystal. We found clear relationships between local optical absorption spectra and photoluminescence intensities. At a site that exhibited a weak photoluminescence, the intensity of the A exciton optical absorption was also weak, and its line shape was significantly deformed, which suggests the influence of n-doping. The results indicate a significant inhomogeneity in the n-doping levels on a single sheet.

  2. Development of Near-Field Microwave Microscope with the Functionality of Scanning Tunneling Spectroscopy

    Science.gov (United States)

    Machida, Tadashi; Gaifullin, Marat B.; Ooi, Shuuich; Kato, Takuya; Sakata, Hideaki; Hirata, Kazuto

    2010-11-01

    We describe the details of an original near-field scanning microwave microscope, developed for simultaneous measurements of local density-of-states (LDOS) and local ohmic losses (LOL). Improving microwave detection systems, we have succeeded in distinguishing the LDOS and LOL even between two low resistance materials; gold and highly orientated pyrolitic graphite. The experimental data indicate that our microscope holds a capability to investigate both LDOS and LOL in nanoscale.

  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. 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 si...

  5. Interplay between Plasmon Luminescence and Vibrationally Resolved Molecular Luminescence Induced by Scanning Tunneling Microscopy

    CERN Document Server

    Miwa, Kuniyuki; Kasai, Hideaki

    2013-01-01

    Effects of the coupling between an exciton consisting of an electron and hole in a molecule and a surface plasmon (exciton-plasmon coupling) on the luminescence properties of the molecule and the surface plasmons are investigated using the nonequilibrium Green's function method. Molecular absorption and enhancement by molecular electronic and vibrational modes (molecular modes) lead to dip and peak structures in the luminescence spectra of the surface plasmons. It is considered that the corresponding structures can be seen in a recent experiment. Moreover we found that the re-absorption by the surface plasmons plays important roles in determining the luminescence spectral profiles.

  6. 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.

  7. 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 ?m 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.

  8. Scanning tunneling microscopy of charge-density waves in NbSe3

    International Nuclear Information System (INIS)

    The charge-density wave (CDW) structure in NbSe3 due to the two independent CDW's has been imaged by scanning microscopy. As predicted by band-structure considerations, the CDW modulation is observed to be substantially localized on different chains for the separate CDW's. AT 77 K where only the high-temperature CDW exists, a relatively weak modulation with a single component along the b axis is observed. At 4.2 K the low-temperature CDW contributes a much stronger ?4b0 x 2c0 superlattice modulation

  9. Underpotential deposition of Cu on iodine-modified Au(1 1 1): an in situ scanning tunneling microscopy study

    Science.gov (United States)

    Martínez-Ruiz, A.; Valenzuela-Benavides, J.; Morales de la Garza, L.; Batina, N.

    2001-04-01

    The electrochemical deposition of Cu on iodine-modified Au(1 1 1) surfaces has been investigated by in situ electrochemical scanning tunneling microscopy (ECSTM) and cyclic voltammetry (CV) in sulfuric acid solutions. In situ ECSTM studies reveal different iodine adlayer structures before and during the process of copper underpotential deposition (UPD). At the beginning of the cathodic scan and for potentials higher than the onset of UPD a c( p×?3 R-30°) iodine structure is observed on wide terraces. For lower potentials this iodine structure transforms to a more compact (3×3) structure characterized by two different structural variations (symmetric and asymmetric) sometimes observed coexisting in the same terrace. Charge transfer analysis from CV measurements reveals that the amount of copper deposited at these potentials is not sufficient to account for this structure in the framework of a hard-ball structural model. During the UPD process itself other iodine structures are also observed as a function of copper deposition, together with an additional compression of the iodine adlayer associated with the formation of a CuI bilayer, in agreement with previously reported X-ray diffraction data. At the end of the UPD process a Cu(1×1) monolayer is formed with a lattice parameter equal to that of Au(1 1 1). The same course of structural changes was also observed during the anodic scan where stripping of the copper layer takes place, returning to the initial iodine c( p×?3 R-30°) structure. Our results strongly suggest that the iodine adlayer is constantly present as the top layer during the process of electrodeposition and stripping of Cu with no noticeable loss of iodine in the process. The observed structures are discussed in terms of iodine-copper interactions.

  10. Superconductivity and scanning tunneling microscopy (STM)/spectroscopy (STS) of transition metal oxide artificial lattices

    International Nuclear Information System (INIS)

    High Tc superconducting artificial lattices and superlattices have been constructed by a laser molecular beam epitaxy method. A layer-by-layer growth method controlled by RHEED and STM is a promising method for the construction of these artificial lattices. Formation and properties of superconducting artificial lattices and superconducting/ferromagnetic superlattices are presented as the typical examples. In order to investigate the electronic state of carrier doped strongly correlated electronic system, STM measurements have been performed on La2-xSrxCuO4, La2-xSrxNiO4, and La1-xSrxMnO3 thin films. Based on the similarities and the differences between the STM spectra of the three types of the films, electronic states of the strongly correlated system are discussed

  11. Imaging of ferroelectric vinylidene fluoride and trifluoroethylene copolymer films by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    In this paper, we reported the possibility to image non-conducting P(VDF-TrFE) copolymer films by STM. The films had the thickness of ?25.0 nm and were spin-coated onto Au or graphite substrates. For films deposited on Au substrates, STM images showed grain structures of ?100 nm, much larger than the grains of bare Au substrate. With increased scan rate, the film surface was damaged by STM tip and extreme protrusions and holes were observed. For films deposited on graphite substrates, we only obtained an image of very flat plane and could not observe the topography of the film surface. It seemed that the tip had pierced through the uppermost P(VDF-TrFE) layers and only imaged the layers nearest to the substrate. Asymmetrical current-voltage curves were observed from copolymer films deposited on HOPG. Experimental results were discussed

  12. Control of charging in resonant tunneling through InAs nanocrystal quantum dots

    CERN Document Server

    Katz, D; Kan, S H; Banin, U; Katz, David; Millo, Oded; Kan, Shi-Hai; Banin, Uri

    2001-01-01

    Tunneling spectroscopy of InAs nanocrystals deposited on graphite was measured using scanning tunneling microscopy, in a double-barrier tunnel-junction configuration. The effect of the junction symmetry on the tunneling spectra is studied experimentally and modeled theoretically. When the tip is retracted, we observe resonant tunneling through the nanocrystal states without charging. This is in contrast to previous measurements on similar nanocrystals anchored to gold by linker molecules, where charging took place. Charging is regained upon reducing the tip-nanocrystal distance, making the junctions more symmetric. The effect of voltage distribution between the junctions on the measured spectra is also discussed.

  13. In Situ Scanning Tunneling Microscopy Study of 5,6-Dimethyl Uracil on Au (111

    Directory of Open Access Journals (Sweden)

    Cunha Frederico G. C.

    2001-01-01

    Full Text Available The hydrogen evolution mediated 5,6-dimethyluracil (5,6-DMU film disordering and subsequent reordering was studied in situ in sulfuric acid solution on Au (111 using STM and cyclic voltammetry. A stable, condensed physisorbed film was formed between the limits of the hydrogen evolution (at -0.3 V/SCE and the lifting of the surface reconstruction (at 0.4 V/SCE in the bulk solution concentration used in this study. The onset of hydrogen evolution led to the formation of "bubble" like structures which disrupted the stability of the film causing a disordering process which takes place within the whole scanned area. Stepping the potential back to the region of stability allowed the real time observation of the film reorganization. An anisotropic evolution of the film was found. The surface step edges were not found to be preferential nucleation sites. The molecular packing structure was inferred from high-resolution STM images and the existence of two distinct adsorbate states was established.

  14. Electron transport across capped Au nanoclusters adsorbed in different configurations on highly oriented pyrolytic graphite substrate using scanning tunneling microscopy / spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Poonam; Dharmadhikari, C V [Centre for Advanced Studies in Materials Science and Solid State Physics, Department of Physics, University of Pune, Pune 411007 (India)

    2007-04-15

    Comparison of electron transport across dodecanethiol capped Au nanoclusters adsorbed in different locations viz. in an agglomeration, on isolated particle either on the terrace or at the step edge of highly oriented pyrolytic graphite using scanning tunneling microscopy / spectroscopy is carried out. Current-distance measurements on these different locations shows different regimes suggesting different mechanisms for electron transport. Current-voltage measurements at these locations have been carried out and the results are discussed in the light of orthodox theory for electron transport in double-barrier tunnel junction.

  15. Two-dimensional TiO x nanostructures on Au(111): a scanning tunneling microscopy and spectroscopy investigation

    Science.gov (United States)

    Tumino, F.; Carrozzo, P.; Mascaretti, L.; Casari, C. S.; Passoni, M.; Tosoni, S.; Bottani, C. E.; Li Bassi, A.

    2015-12-01

    We investigated the growth of titanium oxide two-dimensional nanostructures on Au(111), produced by Ti evaporation and post-deposition oxidation. Scanning tunneling microscopy and spectroscopy (STM and STS) and low-energy electron diffraction measurements characterized the morphological, structural and electronic properties of the observed structures. Five distinct TiO x phases were identified: the honeycomb and pinwheel phases appear as monolayer films wetting the gold surface, while nanocrystallites of the triangular, row and needle phases grow mainly over the honeycomb or pinwheel layers. Density Functional Theory investigation of the honeycomb structure supports a (2× 2) structural model based on a Ti-O bilayer having Ti 2 O 3 stoichiometry. The pinwheel phase was observed to evolve, for increasing coverage, from single triangular crystallites to a well-ordered film forming a (4\\sqrt{7}× 4\\sqrt{7})R19.1^\\circ superstructure, which can be interpreted within a moiré-like model. Structural characteristics of the other three phases were disclosed from the analysis of high-resolution STM measurements. STS measurements revealed a partial metallization of honeycomb and pinwheel and a semiconducting character of row and triangular phases.

  16. Organization of adenine on Ag(111) and correlated interfacial electronic structure measured with low temperature scanning tunneling microscopy

    Science.gov (United States)

    Pearl, Thomas P.; Andrews, Katie M.; Davis, Bryce F.

    2010-03-01

    Low temperature scanning tunneling microscopy and spectroscopy has been used to observe the organization of the nucleobase adenine on the Ag(111) surface as well as to resolve modifications to Ag(111) surface electronic structure. Multiple hydrogen bonding interactions between adenine adsorbates dictate the formation of dimers on the surface as well as long range order of molecular domains, which have limited commensuration with the Ag(111) lattice. Differential conductance spectroscopy recorded at 15 K reveals an upward energetic shift of the Shockley-type surface state native to Ag(111) from a band edge of -67 meV on the clean surface to+82.5 meV recorded over adenine islands. Differential conductance maps show free-electron like scattering in the adenine domains. Dispersion of the parallel wave vector of scattered electrons in the adenine domains is compared to the dispersion for electron scattering in bare silver and the ratio of effective masses for electrons in those bands is 1.1 ± 0.05. It is hypothesized that this shift occurs due to a combination of effects brought on by the adsorption of adenine including changes in work function and dipole-induced screening of the first image potential.

  17. Adenine monolayers on the Au(111) surface: Structure identification by scanning tunneling microscopy experiment and ab initio calculations

    Science.gov (United States)

    Lukas, Maya; Kelly, Ross E. A.; Kantorovich, Lev N.; Otero, Roberto; Xu, Wei; Laegsgaard, Erik; Stensgaard, Ivan; Besenbacher, Flemming

    2009-01-01

    From an interplay between scanning tunneling microscopy (STM) and ab initio density functional theory (DFT) we have identified and characterized two different self-assembled adenine (A) structures formed on the Au(111) surface. The STM observations reveal that both structures have a hexagonal geometry in which each molecule forms double hydrogen bonds with three nearest neighbors. One of the A structures, with four molecules in the primitive cell, has p2gg space group symmetry, while the other one, with two molecules in the cell, has p2 symmetry. The first structure is observed more frequently and is found to be the dominating structure after annealing. Experimental as well as theoretical findings indicate that the interaction of A molecules with the gold surface is rather weak and smooth across the surface. This enabled us to unequivocally characterize the observed structures, systematically predict all structural possibilities, based on all known A-A dimers, and provisionally optimize positions of the A molecules in the cell prior to full-scale DFT calculations. The theoretical method is a considerable improvement compared to the approach suggested previously by Kelly and Kantorovich [Surf. Sci. 589, 139 (2005)]. We propose that the less ordered p2gg symmetry structure is observed more frequently due to kinetic effects during island formation upon deposition at room temperature.

  18. Design and performance of a cryogenic scanning tunneling microscope in high magnetic field for 2D layered materials study

    Science.gov (United States)

    Chuang, Tien-Ming; Chung, Pei-Fang; Guan, Syu-You; Yu, Shan-An; Liu, Che-An; Hsu, Chia-Sheng; Su, Chih-Chuan; Sankar, Raman; Chou, Fang-Cheng

    2015-03-01

    We will describe the design and performance of a cryogenic scanning tunneling microscope (STM) system in a high magnetic field. A Pan-type STM is mounted on a homemade low vibration 4He pot refrigerator, which can be operated in continuous flow mode at T ~ 1.6K and in a magnetic field of up to 9 Tesla. A cleavage device at T =4.2K stage is used to cleave the 2D layered materials before inserting into STM as well as functioning as the radiation shield. The liquid helium boil rate of 4.6 liters per day is achieved due to our careful design, which allows the measurement at base temperature up to 10 days. We will demonstrate its capability of measuring atomically registered energy resolved spectroscopic maps in both real space and momentum space by our recent results on Rashba BiTeI. This work is supported by Ministry of Science and Technology, Taiwan and Kenda Foundation, Taiwan.

  19. Exciton dynamics of C60-based single-photon emitters explored by Hanbury Brown-Twiss scanning tunnelling microscopy

    Science.gov (United States)

    Merino, P.; Große, C.; Ros?awska, A.; Kuhnke, K.; Kern, K.

    2015-09-01

    Exciton creation and annihilation by charges are crucial processes for technologies relying on charge-exciton-photon conversion. Improvement of organic light sources or dye-sensitized solar cells requires methods to address exciton dynamics at the molecular scale. Near-field techniques have been instrumental for this purpose; however, characterizing exciton recombination with molecular resolution remained a challenge. Here, we study exciton dynamics by using scanning tunnelling microscopy to inject current with sub-molecular precision and Hanbury Brown-Twiss interferometry to measure photon correlations in the far-field electroluminescence. Controlled injection allows us to generate excitons in solid C60 and let them interact with charges during their lifetime. We demonstrate electrically driven single-photon emission from localized structural defects and determine exciton lifetimes in the picosecond range. Monitoring lifetime shortening and luminescence saturation for increasing carrier injection rates provides access to charge-exciton annihilation dynamics. Our approach introduces a unique way to study single quasi-particle dynamics on the ultimate molecular scale.

  20. Monitoring Si growth on Ag(111) with scanning tunneling microscopy reveals that silicene structure involves silver atoms

    International Nuclear Information System (INIS)

    Using scanning tunneling microscopy (STM), the elaboration of the so-called silicene layer on Ag(111) is monitored in real time during Si evaporation at different temperatures. It is shown that the growth of silicene is accompanied by the release of about 65% of the surface Ag atoms from the Si covered areas. We observe that Si islands develop on the Ag terraces and Si strips at the Ag step edges, progressively forming ordered (4×4), (?(13)×?(13)) R13.9°, and dotted phases. Meanwhile, displaced Ag atoms group to develop additional bare Ag terraces growing round the Si islands from the pristine Ag step edges. This indicates a strong interaction between Si and Ag atoms, with an important modification of the Ag substrate beneath the surface layer. This observation is in contradiction with the picture of a silicene layer weakly interacting with the unreconstructed Ag substrate, and strongly indicates that the structure of silicene on Ag(111) corresponds either to a Si-Ag surface alloy or to a Si plane covered with Ag atoms