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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. 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)

  4. 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.

  5. 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.

  6. 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 ?/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.

  7. 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.

  8. Investigation into scanning tunnelling luminescence microscopy

    CERN Document Server

    Manson-Smith, S K

    2001-01-01

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

  9. 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.

  10. Thermovoltages in vacuum tunneling investigated by scanning tunneling microscopy

    OpenAIRE

    HOFFMANN, D. H.; Rettenberger, Armin; Grand, Jean Yves; Läuger, K.; Leiderer, Paul; Dransfeld, Klaus; Möller, Rolf

    1995-01-01

    By heating the tunneling tip of a scanning tunneling microscope the thermoelectric properties of a variable vacuum barrier have been investigated. The lateral variation of the observed thermovoltage will be discussed for polycrystalline gold, stepped surfaces of silver, as well as for copper islands on silver.

  11. Fiber coupled ultrafast scanning tunneling microscope

    DEFF Research Database (Denmark)

    Keil, Ulrich Dieter Felix; Jensen, Jacob Riis

    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 substrate. By using a firmly attached fiber we achieve an excellent reproducibility and unconstrained positioning of the tip. We observe a transient signal with 2.9 ps pulse width in tunneling mode and 5 ps in contact mode. The instrument is applied to investigating the mode structure on a coplanar waveguide. The measurements show that the probe works as a transient voltage detector in contact and a capacitively coupled transient field detector in tunneling mode. We do not measure the transient voltage change in the ohmic tunneling current. In this sense, the spatial resolution for propagating electrical pulses is better in contact mode than in tunneling mode. ©1997 American Institute of Physics.

  12. Scanning tunneling spectroscopy of Pb thin films

    Energy Technology Data Exchange (ETDEWEB)

    Becker, Michael

    2010-12-13

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

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. Scanning tunnelling microscopy and spectroscopy of MgB2

    International Nuclear Information System (INIS)

    Experiments of the scanning tunnelling microscopy and spectroscopy (STM/STS) have been carried out on the layered superconductor MgB2 with Tc = 39 K. The measurements were done at 5 K using a Pt-Ir tip and the single-crystal grain. The STM images show characteristic hexagonal patterns with the distances of nearest neighbour atoms to be 0.3 - 0.35 nm and 0.15 - 0.2 nm, respectively, which are consistent with the Mg and B lattice sizes. The STS measurements clarify the superconducting gap 2? = 20 - 24 meV, which leads to the strong-coupling ratio 2?/kBTc = 5 - 6. The tunnelling spectra can be described by the correlated 2-gap model. These features are consistent with our previous break-junction measurements. The gap structure is homogeneous at least within the range of 200 nm x 200 nm

  20. Scanning tunneling spectroscopy studies of heavy fermion metals

    International Nuclear Information System (INIS)

    We report Scanning Tunneling Microscopy/Spectroscopy (STM/S) experiments on single crystals of the heavy fermion intermetallic compounds CeCoIn5, CeIrIn5, and YbRh2Si2. The tunneling experiments were conducted at temperatures down to 300 mK under ultra-high vacuum conditions. Methods have been established to facilitate in-situ sample cleaving. CeCoIn5 and CeIrIn5 exhibit unconventional superconductivity (SC) at ambient pressure. A gap compatible with d-wave symmetry of the order parameter was observed in the conductance spectra of CeCoIn5. The presence of a gap-like feature in a temperature range above Tc may indicate the existence of a precursor state to SC. Based on atomically resolved topography data, the possible influence of a modified surface structure on STS is discussed. For the case of YbRh2Si2, we speculate that the tunneling spectra reveal signatures of a Kondo resonance related to the Yb ions.

  1. 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.

  2. 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)

  3. Scanning tunnelling microscope studies of sputtering

    International Nuclear Information System (INIS)

    Experimental results are reported that improve our understanding of processes that initiate surface roughness from a single ion bombardment event. The results are from a scanning tunnelling microscopy (STM) study of the ion bombardment of silicon at implantation energies. Also reported is an atom by atom analysis of a single sputtering event-8 keV krypton on a cleaved crystal of PbS. In both cases a very low ion dose was used to minimize the overlap of cascades. Recent results on the bombardment of gold and graphite will also be reviewed. The results show that every impact leaves its mark on the surface, indicating that surface roughening processes can be nucleated at the atomic level. (author)

  4. 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.

  5. Scanning tunneling microscope (STM) - development programme at CSIO, Chandigarh

    International Nuclear Information System (INIS)

    A scanning tunneling microscope (STM) has been constructed as part of STM development programme at Central Scientific Instruments Organisation (CSIO). Design of its mechanics along with control and acquisition unit are described. Different aspects of scanning tunneling microscopy are also outlined. (author). 6 refs., 6 figs

  6. 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...

  7. 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.

  8. 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.

  9. 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 ...

  10. Scanning tunneling microspectroscopy of solids and surfaces

    International Nuclear Information System (INIS)

    Major progress has been made this year in our work on single crystals of Bi2Sr2CaCu2O8+y (BSCCO) grown in our laboratory in a transverse temperature gradient. We have obtained large crystals of improving quality and tunneling data which are superior to any we have seen elsewhere. In our first publication on this, we have identified a pair breaking process which appears near Tc and apparently is related to the absence of the Hebel-Slichter peak in 1/T1 vs T in this material. In more recent work much improved data reveal features in the tunnel conductance dI/dV which appear to agree with the ''proximity effect-superlattice'' model of the tunneling conductance of BSCCO described by Tachiki and coworkers. We devote a major portion of this report to this and other research topics, on which work is continuing, and briefly describe advances in Instrumentation that have occurred this year

  11. 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.

  12. 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...

  13. 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...

  14. 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...

  15. 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.

  16. Quantum size effects in ultrathin metallic islands: a scanning tunneling microscopy/spectroscopy study

    OpenAIRE

    Hong, I-Po

    2009-01-01

    This thesis reports measurements concerning quantum size effects of single crystalline metallic islands by using low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS). Different sample systems are presented in the following chapters. In chapter 2, several aspects of quantum well states (QWS) of Pb ultrathin islands grown on Si(111) substrate are reported. The differential conductance spectra of QWS can be understood by discrete energy levels with linewidth broadening beca...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-01-05

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

  18. 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.

  19. 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.

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

    CERN Document Server

    Bullock, E T

    2000-01-01

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

  2. 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.

  3. 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 ?/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 ?/5. Seismic data collected in an Arizona tunnel showed a superresolution limit of at least ?/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.

  4. Limits of perturbation theory: first principles simulations of scanning tunneling microscopy scans on Fe(100)

    Science.gov (United States)

    Hofer, W. A.; Redinger, J.; Biedermann, A.; Varga, P.

    2000-11-01

    Scanning tunneling microscopy (STM) scans on Fe(100) are compared with first principles calculations of the tunneling current based on the transfer Hamiltonian method. Experimentally, we find a reversal of corrugation for separations between sample and tip below 400 pm. In the simulations we can reproduce these topographies only in a distance range above 400 pm. The approach therefore fails to describe the observed corrugation reversal. We suggest that this failure is due to the quenching of surface states by the approaching STM tip.

  5. 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.

  6. 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 ?m diameter are dry etched in an SF? 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 Bi?Se? at temperatures ranging from 30 mK to 9 K.

  7. 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.

  8. Scanning tunnelling microscopy: application to field electron emission studies

    Energy Technology Data Exchange (ETDEWEB)

    Frolov, V.D.; Karabutov, A.V.; Konov, V.I.; Pimenov, S.M.; Prokhorov, A.M. [General Physics Institute, Moscow (Russian Federation)

    1999-04-07

    The principles of scanning tunnelling microscopy (STM) are extended to the study of field electron emission from metal, semiconducting and semi-insulating materials. A specially designed, high-vacuum STM device called a scanning tunnelling field emission microscope (STFEM) is constructed, and new measuring procedures are developed to examine complex physical properties of emission centres. Providing high bias voltages and fast mapping of large squares, the STFEM allows one to obtain reliable statistical data on surface properties, namely topography, emission intensity, surface potential distribution and local electroconductivity. Results from a study of low-field electron emission from CVD diamond films are described to illustrate the functional capabilities of the new STM device. It was found that the diamond films studied are composed of nanograined phases distinguished by their physical properties. It has also been noted that the low-field electron emission from the studied samples is associated with the interfaces of these phases. (author)

  9. 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.

  10. 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

  11. Distinction of Nuclear Spin States with the Scanning Tunneling Microscope

    OpenAIRE

    Natterer, Fabian Donat; Patthey, François; Brune, Harald

    2013-01-01

    We demonstrate rotational excitation spectroscopy with the scanning tunneling microscope for physisorbed hydrogen and its isotopes hydrogen-deuterid and deuterium. The observed excitation energies are very close to the gas phase values and show the expected scaling with moment of inertia. Since these energies are characteristic for the molecular nuclear spin states we are able to identify the para and ortho species of hydrogen and deuterium, respectively. We thereby demonstr...

  12. 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.

  13. 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

  14. Oxygen-free in situ scanning tunnelling microscopy

    DEFF Research Database (Denmark)

    Zhang, Jingdong; Ulstrup, Jens

    2007-01-01

    Scanning tunneling microscopy under full electrochemical potential control (in situ STM) has been used extensively as an efficient method to characterize microstructures at solid/liquid interfaces at the atomic and molecular levels. However, under ambient conditions oxygen may interfere in open 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 th...

  15. 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 Kon...

  16. 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.

  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. 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.

  19. 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

  20. 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.

  1. 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 ?/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.

  2. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Wang, T; Boer-Duchemin, E; Zhang, Y; Comtet, G; Dujardin, G, E-mail: Elizabeth.Boer-Duchemin@u-psud.fr [Institut des Sciences Moleculaire d' Orsay (ISMO), CNRS Universite Paris-Sud, 91405 Orsay (France)

    2011-04-29

    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 {mu}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.

  4. 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

  5. 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

  6. Measurement of turbulence spectra using scanning pulsed wind lidars

    DEFF Research Database (Denmark)

    Sathe, Ameya; Mann, Jakob

    2012-01-01

    Turbulent velocity spectra, as measured by a scanning pulsed wind lidar (WindCube), are analyzed. The relationship between ordinary velocity spectra and lidar derived spectra is mathematically very complex, and deployment of the three-dimensional spectral velocity tensor is necessary. The resulting scanning lidar spectra depend on beam angles, line-of-sight averaging, sampling rate, and the full three-dimensional structure of the turbulence being measured, in a convoluted way. The model captures the attenuation and redistribution of the spectral energy at high and low wave numbers very well. The model and measured spectra are in good agreement at two analyzed heights for the u and w components of the velocity field. An interference phenomenon is observed, both in the model and the measurements, when the diameter of the scanning circle divided by the mean wind speed is a multiple of the time between the beam measurements. For the v spectrum, the model and the measurements agree well at both heights, except at very low wave numbers, k1 <0.005 m?1. In this region, where the spectral tensor model has not been verified, the model overestimates the spectral energy measured by the lidar. The theoretical understanding of the shape of turbulent velocity spectra measured by scanning pulsed wind lidar is given a firm foundation.

  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 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.

  9. Observation of mode-like features in tunneling spectra of iron-based superconductors

    Science.gov (United States)

    Gong, Jing; Hou, Xing-Yuan; Zhu, Jun; Jie, Yun-Yin; Gu, Ya-Dong; Shen, Bing; Ren, Cong; Li, Chun-Hong; Shan, Lei

    2015-07-01

    We report scanning tunneling microscopy/spectroscopy (STM/STS) studies on iron-based superconductors of Ba1?xKxFe2As2 and nearly optimally doped Fe(Te,Se). Mode-like features were observed universally outside the superconducting gaps in the tunneling spectra, which are similar to our previous observations in other samples and can be ascribed to the interaction between electrons and spin excitations. Furthermore, an almost linear relationship between the superconducting gaps and the superconducting transition temperatures was noted and should also be taken into account in understanding the mechanism of iron-based superconductors. Project supported by the National Basic Research Program of China (Grant Nos. 2011CBA00110 and 2012CB821403), the National Natural Science Foundation of China (Grant Nos. 11174349 and 11322432), and the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant No. XDB07020300).

  10. 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.

  11. 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

  12. 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

  13. 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

  14. 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.

  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. Spin excitations and correlations in scanning tunneling spectroscopy

    Science.gov (United States)

    Ternes, Markus

    2015-06-01

    In recent years inelastic spin-flip spectroscopy using a low-temperature scanning tunneling microscope has been a very successful tool for studying not only individual spins but also complex coupled systems. When these systems interact with the electrons of the supporting substrate correlated many-particle states can emerge, making them ideal prototypical quantum systems. The spin systems, which can be constructed by arranging individual atoms on appropriate surfaces or embedded in synthesized molecular structures, can reveal very rich spectral features. Up to now the spectral complexity has only been partly described. This manuscript shows that perturbation theory enables one to describe the tunneling transport, reproducing the differential conductance with surprisingly high accuracy. Well established scattering models, which include Kondo-like spin-spin and potential interactions, are expanded to enable calculation of arbitrary complex spin systems in reasonable time scale and the extraction of important physical properties. The emergence of correlations between spins and, in particular, between the localized spins and the supporting bath electrons are discussed and related to experimentally tunable parameters. These results might stimulate new experiments by providing experimentalists with an easily applicable modeling tool.

  17. Electron-beam-assisted scanning tunneling microscopy of insulating surfaces

    Science.gov (United States)

    Bullock, Eugene Thomas

    2000-07-01

    Insulating materials are widely used in electronic devices. Bulk insulators and insulating films pose unique challenges for high resolution study since most commonly used charged particle surface analysis techniques are incompatible with insulating surfaces and materials. A, method of performing scanning tunneling microscopy (STM) on insulating surfaces has been investigated. The method is referred to as electron-beam assisted scanning tunneling microscopy (e-BASTM). It is proposed that by coupling the STM and the scanning electron microscopy (SEM) as one integrated device, that insulating materials may be studied, obtaining both high spatial resolution, and topographic and electronic resolution. The premise of the technique is based on two physical consequences of the interaction of an energetic electron beam (PE) with a material. First, when an electron beam is incident upon a material, low level material electrons are excited into conduction band states. For insulators, with very high secondary electron yields, the population of conduction band states could be quite significant. Second, for specific incident primary beam energies, the resulting electron yield will be equal to the incoming beam intensity. These are referred to as the cross over energies (E1 and E2). For a stationary primary beam at E2 the current entering the sample and the current leaving sample are equal so that a state of dynamic equilibrium is quickly reached whereby the charge density distribution local to primary beam, both at the surface and within the material, is fixed. Thus, if the surface of an insulator is illuminated with an energetic electron beam at E2, the surface will be locked to some potential and there will be filled conduction band states. Under these conditions, it may be possible to make STM measurements of material even though it is insulating. That is, from an STM point of view, it may be possible to make an insulator `act' like a conductor. In order to test the principle of e-BASTM, metals, thin insulating films, and bulk insulators have been examined. For metals, as expected, we observe no alteration of the tunneling signal due to the PE beam. However, with SiO 2, there is a significant increase in the tunneling current which can be directly attributed to the PE beam. For Al2O3 and CaF2 it is found that the surfaces are damaged too quickly by the PE beam for this technique to be applied suggesting that e-BASTM may only be suitable for a small class of materials. The STM (not e-BASTM) has been used to electrically stress thin films of SiO2 (native oxide thickness). The stressing is observed to create trapping states which have been connected to stress induced leakage currents (SILC) in metal/SiO2/Si devices. The effect of the stress is observed to depend on the polarization of the applied bias (positive or negative). The trapping site density is observed to reach levels on the order of 1013-1014 traps/cm2 which is about a factor of 10-100 higher than what has been previously been reported.

  18. Optical characterication of probes for photon scanning tunnelling microscopy

    DEFF Research Database (Denmark)

    Vohnsen, Brian; Bozhevolnyi, Sergey I.

    1999-01-01

    The photon scanning tunnelling microscope is a well-established member of the family of scanning near-field optical microscopes used for optical imaging at the sub-wavelength scale. The quality of the probes, typically pointed uncoated optical fibres, used is however difficult to evaluate in a direct manner and has most often been inferred from the apparent quality of recorded optical images. Complicated near-field optical imaging characteristics, together with the possibility of topographically induced artefacts, however, has increased demands for a more reliable probe characterization technique. Here we present experimental results obtained for optical characterization of two different probes by imaging of a well-specified near-field intensity distribution at various spatial frequencies. In particular, we observe that a sharply pointed dielectric probe can be highly suitable for imaging when using p-polarized light for the illumination. We conclude that the proposed scheme can be used directly for probe characterization and, subsequently, for determination of an optical transfer function, which could allow one to deduce from an experimentally obtained image of a weakly scattering sample the field distribution existing near the sample surface inthe absence of the probe.

  19. 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...

  20. 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...

  1. 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...

  2. 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.

  3. 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.

  4. Elevated Temperature Scanning Tunneling Microscopy of Ge on Si(100)

    Science.gov (United States)

    McKay, Michael; Drucker, Jeff

    2003-10-01

    The Ge/Si(100) system has been studied intensely in the past due to the fact that is a great model for observing the mechanisms involved in the Stranaski-Krastanov growth mode, described as layer-by-layer growth followed by the formation of islands, or dots. These mechanisms, driven by a 4.2lattice mismatch, are still not fully understood. Elevated temperature scanning tunneling microscopy (ET-STM) can assist us in better understanding these mechanisms by observing the kinetics of Ge on the surface of Si(100) at the atomic level. Currently, we have an ultra high vacuum ET-STM capable of depositing Ge via digermane on Si(100) substrates held at temperatures between 350 to 650 degrees Celsius. Preliminary results have resulted in 'movies' showing the growth of the wetting layers which then lead to the formation of Ge quantum dots. From these movies we are able to monitor aspects of Ge growth such as quantum dot volume over time, revealing critical radii as a function of growth temperature.

  5. 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

  6. 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)

  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. Effects of plasmon energetics on light emission induced by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    A theoretical model of plasmon and molecular luminescence induced by scanning tunneling microscopy using a molecule-covered tip on clean metal surfaces is developed. The effects of coupling between molecular exciton and interface plasmon on the luminescence spectra are investigated for variable energy of plasmon modes by means of the nonequilibrium Green's function method. It is found that spectral features arising from interference between the processes of energy absorption by the molecule and interface plasmons appear near the energy of the excitonic mode. For the energy of plasmon above (below) the energy of excitonic mode, an additional peak structure appears in the energy range slightly below (above) the energy of the excitonic mode. Prominent peak and dip structures observed in recent luminescence experiments are interpreted by the developed theory whereby its utility in the fields of plasmonics and nanophotonics is demonstrated. (fast track communication)

  9. 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...

  10. 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...

  11. 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

  12. 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...

  13. 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...

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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...

  1. 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.

  2. 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

  3. 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.

  4. 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)

  5. 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.

  6. 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

  7. 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...

  8. 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 ...

  9. 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 ...

  10. 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

  11. 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

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. 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

  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. Tetrairon(III) Single Molecule Magnet Studied by Scanning Tunneling Microscopy and Spectroscopy

    Science.gov (United States)

    Oh, Youngtek; Jeong, Hogyun; Lee, Minjun; Kwon, Jeonghoon; Yu, Jaejun; Mamun, Shariful Islam; Gupta, Gajendra; Kim, Jinkwon; Kuk, Young

    2011-03-01

    Tetrairon(III) single-molecule magnet (SMM) on a clean Au(111) has studied using scanning tunneling microscopy (STM) and spectroscopy (STS) to understand quantum mechanical tunneling of magnetization and hysteresis of pure molecular origin. Before the STM studies, elemental analysis, proton nuclear magnetic resonance (NMR) measurement and Energy Dispersive X- ray Spectroscopy (EDS) were carried out to check the robustness of the sample. The STM image of this molecule shows a hexagonal shape, with a phenyl ring at the center and surrounding six dipivaloylmethane ligands. Two peaks are observed at 0.5 eV, 1.5 eV in the STS results, agreeing well with the first principles calculations. Spin-polarized scanning tunneling microscopy (SPSTM) measurements have been performed with a magnetic tip to get the magnetization image of the SMM. We could observe the antiferromagnetic coupling and a centered- triangular topology with six alkoxo bridges inside the molecule while applying external magnetic fields.

  19. 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.

  20. 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...

  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. 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

  3. 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)

  4. 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)

  5. 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.

  6. 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.

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

    Science.gov (United States)

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

    2010-01-01

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

  8. 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.

  9. 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.

  10. 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.

  11. Defects, Tunneling, and EPR Spectra of Single-Molecule Magnets

    CERN Document Server

    Park, K; Dalal, N S; Hill, S; Rikvold, P A; Bhaduri, S; Christou, G; Hendrickson, D N; Park, Kyungwha

    2003-01-01

    We examine theoretically electron paramagnetic resonance (EPR) lineshapes as functions of resonance frequency, energy level, and temperature for single crystals of three different kinds of single-molecule nanomagnets (SMMs): Mn$_{12}$ acetate, Fe$_8$Br, and the $S=9/2$ Mn$_4$ compound. We use a density-matrix equation and consider distributions in the uniaxial (second-order) anisotropy parameter $D$ and the $g$ factor, caused by possible defects in the samples. Additionally, weak intermolecular exchange and electronic dipole interactions are included in a mean-field approximation. Our calculated linewidths are in good agreement with experiments. We find that the distribution in $D$ is common to the three examined single-molecule magnets. This could provide a basis for a proposed tunneling mechanism due to lattice defects or imperfections. We also find that weak intermolecular exchange and dipolar interactions are mainly responsible for the temperature dependence of the lineshapes for all three SMMs, and that ...

  12. 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.

  13. 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.

  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. 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.

  16. 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.

  17. 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

  18. 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.

  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. 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.

  1. 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.

  2. Analysis of ordered arrays of adsorbed lysozyme by scanning tunneling microscopy.

    OpenAIRE

    Haggerty, L; Lenhoff, A M

    1993-01-01

    Scanning tunneling microscopy (STM) has been used to observe lysozyme at a graphite surface directly in order to gain mechanistic information about the molecular events involved in protein adsorption. The experiments were performed using an insulated tip in an aqueous protein solution, allowing the time course of the adsorption process to be followed, including the evolution of ordered arrays. Ordered arrays of protein molecules were observed, with lattice spacings that varied with bulk prote...

  3. 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...

  4. 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...

  5. 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...

  6. 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...

  7. 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

  8. Scanning tunneling microscopy reveals LiMnAs is a room temperature anti-ferromagnetic semiconductor.

    Czech Academy of Sciences Publication Activity Database

    Wijnheijmer, A.P.; Martí, Xavier; Holý, V.; Cukr, Miroslav; Novák, Vít; Jungwirth, Tomáš; Koenraad, P.M.

    2012-01-01

    Ro?. 100, ?. 11 (2012), "112107-1"-"112107-4". ISSN 0003-6951 R&D Projects: GA MŠk LC510 Grant ostatní: FP7 - ERC Advanced Grant 0MSPIN(XE) 268066; 7 FP NAMASTE(XE) 214499; AV?R(CZ) Premium Academiae Institutional research plan: CEZ:AV0Z10100521 Keywords : antiferromagnetic semiconductors * scanning tunneling microscopy Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.794, year: 2012

  9. 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...

  10. 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 spectro...

  11. 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...

  12. Measurements with an ultrafast scanning tunnelling microscope on photoexcited semiconductor layers

    DEFF Research Database (Denmark)

    Keil, Ulrich Dieter Felix; Jensen, Jacob Riis

    1998-01-01

    Summary form only given. We demonstrate the use of a ultrafast scanning tunnelling microscopes (USTM) for detecting laser-induced field transients on semiconductor layers. In principle, the instrument can detect transient field changes thus far observed as far-field THz radiation in the near-field regime and resolve small signal sources. For photoexcited low temperature (LT) GaAs we can explain the signal by a diffusion current driven by the laser-induced carrier density gradient

  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. 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...

  15. RESOLUTION OF FIELD-ION MICROSCOPY VERSUS SCANNING TUNNELLING MICROSCOPY FOR OBTAINING SURFACE CHARGE DENSITY CORRUGATIONS

    OpenAIRE

    Kingham, D.; Garcia, N. (Nicolás)

    1984-01-01

    Our investigations of the resolution of the field-ion microscope (FIM) and the scanning tunnelling microscope, based on calculations of charge density above a structured metal surface represented by a jellium model, indicate that better resolution may be expected in the FIM. We suggest that FIM can be used to determine the corrugation of the charge density above a surface and hence to elucidate the structure of a surface unit cell.

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

    OpenAIRE

    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 reso...

  17. 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

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

    DEFF Research Database (Denmark)

    Andersen, Jens Enevold Thaulov; Bech-Nielsen, Gregers

    1994-01-01

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

  19. 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.

  20. 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 ...

  1. 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...

  2. 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 ...

  3. 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...

  4. 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.

  5. Multiple-scanning-probe tunneling microscope with nanoscale positional recognition function

    International Nuclear Information System (INIS)

    Over the past decade, multiple-scanning-probe microscope systems with independently controlled probes have been developed for nanoscale electrical measurements. We developed a quadruple-scanning-probe tunneling microscope (QSPTM) that can determine and control the probe position through scanning-probe imaging. The difficulty of operating multiple probes with submicrometer precision drastically increases with the number of probes. To solve problems such as determining the relative positions of the probes and avoiding of contact between the probes, we adopted sample-scanning methods to obtain four images simultaneously and developed an original control system for QSPTM operation with a function of automatic positional recognition. These improvements make the QSPTM a more practical and useful instrument since four images can now be reliably produced, and consequently the positioning of the four probes becomes easier owing to the reduced chance of accidental contact between the probes.

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. 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.))

  11. New directions in point-contact spectroscopy based on scanning tunneling microscopy techniques (Review Article)

    International Nuclear Information System (INIS)

    Igor Yanson showed 38 years ago for the first time a point-contact measurement where he probed the energy resolved spectroscopy of the electronic scattering inside the metal. Since this first measurement, the pointcontact spectroscopy (PCS) technique improved enormously. The application of the scanning probe microscopy (SPM) techniques in the late 1980s allowed achieving contacts with a diameter of a single atom. With the introduction of the mechanically controlled break junction technique, even spectroscopy on freely suspended chains of atoms could be performed. In this paper, we briefly review the current developments of PCS and show recent experiments in advanced scanning PCS based on SPM techniques. We describe some results obtained with both needle-anvil type of point contacts and scanning tunneling microscopy (STM). We also show our first attempt to lift up with a STM a chain of single gold atoms from a Au(110) surface.

  12. Nanomanipulation and nanofabrication with multi-probe scanning tunneling microscope: From individual atoms to nanowires

    Science.gov (United States)

    Qin, Shengyong; Kim, Tae-Hwan; Wang, Zhouhang; Li, An-Ping

    2012-06-01

    The wide variety of nanoscale structures and devices demands novel tools for handling, assembly, and fabrication at nanoscopic positioning precision. The manipulation tools should allow for in situ characterization and testing of fundamental building blocks, such as nanotubes and nanowires, as they are built into functional devices. In this paper, a bottom-up technique for nanomanipulation and nanofabrication is reported by using a 4-probe scanning tunneling microscope (STM) combined with a scanning electron microscope (SEM). The applications of this technique are demonstrated in a variety of nanosystems, from manipulating individual atoms to bending, cutting, breaking carbon nanofibers, and constructing nanodevices for electrical characterizations. The combination of the wide field of view of SEM, the atomic position resolution of STM, and the flexibility of multiple scanning probes is expected to be a valuable tool for rapid prototyping in the nanoscience and nanotechnology.

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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.

  18. 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.)

  19. 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 molecular and solvent reorganisation Gibbs energy, E-r. However, a large V-bias is frequently needed for stable imaging. This applies particularly to in situ STM of redox metalloproteins, emerging as a new app...

  20. Electronic properties of (Zn,CoO systems probed by scanning tunnelling spectroscopy

    Directory of Open Access Journals (Sweden)

    L. Moldovan

    2008-05-01

    Full Text Available The aim of this paper is to gain insight into theelectronic properties of (Zn,CoO system - a widebandgap Diluted Magnetic Semiconductors (DMSshowing room temperature (RT ferromagnetism undern-type doping conditions. On the experimental side, ultrahigh-vacuum scanning tunnelling microscopy andspectroscopy (STM and STS at variable temperature (Tare used to probe the local electronic structure of thesystem. It is presented the map of the local density ofstates (LDOS of polar ZnO surfaces. Then, it is possibleto decorate (incorporate Co atoms onto (into thesemiconductor.

  1. 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...

  2. Graphene, Polycyclic Aromatic Hydrocarbons and Topological Insulators : A scanning tunneling microscopy study

    DEFF Research Database (Denmark)

    Nilsson, Louis

    2013-01-01

    I denne afhandling præsenterer jeg resultater for graphen, polyaromatiske kulbrinter (PAH’er) og topologiske isolatorer. Hovedparten af afhandlingen fokuserer på graphen, hvor vi har undersøgt følgende: Groning af høj-kvalitets graphene på forskellige metaloverflader; Introduktion af et båndgap i graphen via hydrogenering af graphen; Graphens coating egenskaber på en metaloverflade mod forskellige gasser. Kapitlet omhandlende PAH’er fokuserer på coronene på Cu(100) og hydrogenering af dette system. Jeg præsenterer scanning tunnel mikroskopi (STM) afbildninger af hydrogenerede coronene molekyler med submolekylær opløsning. Vores topologiske isolator forskning er udført med krystaller af Bi2Se3, for hvilke vi undersøgte stabiliteten af de topologiske beskyttede tilstande i forhold til inducerede defekter.

  3. 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...

  4. 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...

  5. 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, 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 dissolv...

  6. 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. ...

  7. 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

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

    DEFF Research Database (Denmark)

    Andersen, Jens Enevold Thaulov Technical University of Denmark,

    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 crystallographic-surface structures. Within the wide range of new technologies, those images surface features, the electrochemical scanning tunneling microscope (ESTM) provides means of atomic resolution where the tip participates actively in the process of imaging. Two metallic surfaces influence ions trapped in the interface of imaging and the independent-electrochemical control opens new pathways of studying fundamentals of electrocrystallisation and of adsorption kinetics. In addition, the ESTM instrument itself may be applied as a tool of nanotechnology that allows manufac-ture of new products, e.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 the characteristic details of the images. A large proportion of the observed noise may be explained by the scanning actions of the feedback circuitry while a minor fraction of the image details may be explained by surface drift phenomena. As opposed to the method of deconvolution, conventional methods of filtering discard some of the recorded data, as to improve the signal-to-noise ratio. By deconvolution however, all data were maintained and it is demonstrated that images of atomic resolution were sharpened considerably and shadow effects were removed in images of lower resolution. Thus, the smooth features observed in high-resolution images of metallic nanocrystallites may be effectively deconvoluted, as to resolve more details of the crystalline morphology (see figure). Images of surface-crystalline metals indicate that more than a single atomic layer is involved in mediating the tunneling current 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.

  9. Scanning tunneling microscopy in TTF-TCNQ: Phase and amplitude modulated charge density waves

    DEFF Research Database (Denmark)

    Wang, Z.Z.; Gorard, J.C.

    2003-01-01

    Charge density waves (CDWs) have been studied at the surface of a cleaved tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) single crystal using a low temperature scanning tunneling microscope (STM) under ultrahigh-vacuum conditions, between 300 and 33 K with molecular resolution. All CDW phase transitions of TTF-TCNQ have been identified. The measurement of the modulation wave vector along the a direction provides evidence of the existence of domains comprising single plane wave modulated structures in the temperature regime where the transverse wave vector of the CDW is temperature dependent, as hinted by the theory more than 20 years ago.

  10. Note: Advancement in tip etching for preparation of tunable size scanning tunneling microscopy tips

    Science.gov (United States)

    Corbett, J. P.; Pandya, S. G.; Mandru, A.-O.; Pak, J.; Kordesch, M. E.; Smith, A. R.

    2015-02-01

    The two aspects of a scanning tunneling microscopy tip, the macroscopic profile and the nanoscale apex, can be tailored by controlling the tension during electrochemical etching and the solution-electrode contact area via acetone vapor. The apex diameter is shown to be proportional to the square root of the tension, and is demonstrated over apex diameters of 150-500 nm. The apex was found to be created in four distinct shapes where a secondary etching can reshape the tip into a single geometry. Improvement in tip height and stability of the profile are demonstrated versus a non-acetone fabrication control.

  11. 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...

  12. Probing High-Barrier Pathways of Surface Reactions by Scanning Tunneling Microscopy

    Science.gov (United States)

    Dürr, M.; Biedermann, A.; Hu, Z.; Höfer, U.; Heinz, T. F.

    2002-06-01

    The ability of scanning tunneling microscopy to probe the pathways of thermally activated high-barrier surface processes is frequently limited by competing low-barrier processes that can confuse measurement of the true initial and final configuration. We introduce an approach to circumvent this difficulty by driving the surface process with nanosecond laser heating. The method is applied to determine the pathway of recombinative desorption in the H/Si(001) system. The observed configuration of dangling bonds after laser heating reveals that the desorbed hydrogen molecules are not formed on single dimers, but rather from neighboring silicon dimers via an interdimer reaction pathway.

  13. Scanning Tunneling Spectroscopy of One-Dimensional Surface States on a Metal Surface

    Science.gov (United States)

    Biedermann, A.; Genser, O.; Hebenstreit, W.; Schmid, M.; Redinger, J.; Podloucky, R.; Varga, P.

    1996-05-01

    Scanning tunneling spectroscopy permits real-space observation of one-dimensional electronic states on a Fe(100) surface alloyed with Si. These states are localized along chains of Fe atoms in domain boundaries of the Fe(100) c\\(2×2\\)Si surface alloy, as confirmed by first-principles spin-polarized calculations. The calculated charge densities illustrate the d-like orbital character of the one-dimensional state and show its relationship to a two-dimensional state existing on the pure Fe(100) surface.

  14. Lattice mismatch dislocations in a preferentially sputtered alloy studied by scanning tunneling microscopy

    Science.gov (United States)

    Schmid, M.; Biedermann, A.; Stadler, H.; Varga, P.

    1992-08-01

    Scanning tunneling microscopy (STM) on a sputtered and annealed Pt25Ni75(111) single crystal reveals a network of subsurface lattice mismatch dislocations caused by platinum enrichment due to preferential sputtering and recoil mixing. Atomically resolved STM topographs are compared with simulations of these dislocations using embedded atom potentials. This allows one to estimate the depth of the dislocations, and thus the thickness of Pt enrichment, which is three monolayers on the 500 eV Xe+ sputtered and five monolayers on the Ar+ sputtered surface, compatible with the depth of radiation damage.

  15. 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.

  16. 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...

  17. 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...

  18. A hysteresis phenomenon in NMR spectra of molecular nanomagnets Fe8: a resonant quantum tunneling system

    International Nuclear Information System (INIS)

    A molecular nanomagnet Fe8 with a total spin S=10 in the ground state attracts much attention as a substance which exhibits the quantum tunneling of magnetization below 300 mK. We performed 1H NMR measurements for a single crystal of Fe8 in temperature range between 20 and 800 mK. The spectra below 300 mK strongly depend on the sequence of the applied field and those in the positive and negative fields are not symmetric about zero field, while they are symmetric above 300 mK. We discuss the origin of this hysteresis phenomenon, relating to the initial spin state of molecules, the resonant quantum tunneling and the nuclear spin relaxation process

  19. 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...

  20. 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.

  1. 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.)

  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. 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)

  5. 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

  6. 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

  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 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.

  9. 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

  10. 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...

  11. Many-body lines in tunneling spectra of Al/-GaAs junctions near resonant polaron threshold

    Science.gov (United States)

    Kotel'nikov, I. N.; Dizhur, S. E.; Shtrom, F. V.

    2003-06-01

    A remarkable change of LO-phonon line for tunneling from metal to 2DEG, in comparison with 3D-case, was observed. It was shown that the line shapes and the amplitudes of LO-phonon and zero-bias anomaly in tunneling spectra of Al/?-GaAs junctions depended on magnetic field in-plane of the 2DEG. The parameters of the lines were changed when threshold for resonant intersubband polaron in ?-layer was exceeded.

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

    DEFF Research Database (Denmark)

    Zhang, Jingdong; Kuznetsov, A.M.

    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 molecular and solvent reorganisation Gibbs energy, E-r. However, a large V-bias is frequently needed for stable imaging. This applies particularly to in situ STM of redox metalloproteins, emerging as a new approach to imaging of biological processes directly in aqueous medium. We provide first an extension of previous theoretical work on in situ STM of redox molecules, to large bias voltages, \\eV(bias)\\ > E-r. Large bias voltages give tunnelling contrasts independent of the overpotential over a broad range, as both the oxidised and reduced redox levels are located within the 'energy tip' between 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 cover a broad tunnelling current-overpotential range at a constant (large) bias voltage of +0.2 V. The current is found to be constant over a 0.25 V overpotential range, which covers roughly the range where the oxidised and reduced redox levels are located within the energy tip. STM contrast and apparent adsorbate coverage decrease outside this range. This could reflect in part redox processes of azurin, but also tip-induced disassembly of the azurin monolayer.

  13. 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.

  14. 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.

  15. Grain boundary assisted degradation and breakdown study in cerium oxide gate dielectric using scanning tunneling microscopy

    Science.gov (United States)

    Shubhakar, K.; Pey, K. L.; Kushvaha, S. S.; O'Shea, S. J.; Raghavan, N.; Bosman, M.; Kouda, M.; Kakushima, K.; Iwai, H.

    2011-02-01

    The presence of grain boundaries (GBs) in polycrystalline high-? (HK) gate dielectric materials affects the electrical performance and reliability of advanced HK based metal-oxide-semiconductor devices. It is important to study the role of GB in stress-induced-leakage current (SILC) degradation and time-dependent dielectric breakdown of polycrystalline HK gate stacks. In this work, we present nanoscale localized electrical study and uniform stressing analysis comparing the electrical conduction properties at grain and GB locations for blanket cerium oxide (CeO2)-based HK thin films using scanning tunneling microscopy. The results clearly reveal higher SILC degradation rate at GB sites and their vulnerability to early percolation, supporting the phenomenon of GB-assisted HK gate dielectric degradation and breakdown.

  16. 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

  17. 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.

  18. 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.

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

    DEFF Research Database (Denmark)

    Thirstrup, C.; Sakurai, 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 quasipoint source with a spatial extension similar to the size of a dangling bond. [S0031-9007(98)08376-8].

  20. Circularly polarized light emission in scanning tunneling microscopy of magnetic systems

    CERN Document Server

    Apell, S P; Johansson, P

    2000-01-01

    Light is produced when a scanning tunneling microscope is used to probe a metal surface. Recent experiments on cobalt utilizing a tungsten tip found that the light is circularly polarized; the sense of circular polarization depends on the direction of the sample magnetization, and the degree of polarization is of order 10 %. This raises the possibility of constructing a magnetic microscope with very good spatial resolution. We present a theory of this effect for iron and cobalt and find a degree of polarization of order 0.1 %. This is in disagreement with the experiments on cobalt as well as previous theoretical work which found order of magnitude agreement with the experimental results. However, a recent experiment on iron showed 0.0 ${\\pm}$2 %. We predict that the use of a silver tip would increase the degree of circular polarization for a range of photon energies.

  1. 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

  2. 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)

  3. 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.

  4. 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.

  5. Surface structure of manganese gallium quantum height islands on wurtzite studied by scanning tunneling microscopy

    Science.gov (United States)

    Pak, Jeongihm; Mandru, Andrada-Oana; Chinchore, Abhijit; Smith, Arthur R.

    2015-09-01

    Submonolayer deposition of manganese on gallium-rich, nitrogen polar surface using radio-frequency nitrogen plasma molecular beam epitaxy leads to the spontaneous formation of manganese gallium into two distinct quantum height islands, 5-layer and 6-layer islands. Atomically resolved scanning tunneling microscopy reveals the atomically flat but unstable 5-layer island surface and the 6-layer island surface with relatively stable row structures. We propose possible surface models for these islands' surfaces and discuss the clear structural differences explained with strains and partial relaxations. It is found that the 5-layer islands form under lateral strains and a relaxation process leading to non-uniform alternating strains results in the more energetically favorable row structures on the 6-layer island.

  6. Sticking and diffusion of atomically adsorbed H on Si(100) studied by scanning tunneling microscopy

    Science.gov (United States)

    Biedermann, A.; Hu, Z.; Heinz, T. F.

    1998-03-01

    In this paper, we examine the sticking and diffusion processes of the "hot" H-atoms during the adsorption process on Si(100) surfaces. From the site occupancy observed in high-resolution scanning tunneling microscope (STM) images we are able to draw conclusions about initial diffusion processes and site- dependent sticking effects. After adsorption of atomic hydrogen at room temperature the arrangment of the individual H-atoms appears to be statistical on large clean terraces. However, we find ordered patterns in regions near defects where static buckling ("frozen" antiparallel ordering of asymmetric dimer units) is present. This effect can be explained by a preference of the H-atoms to adsorb on the down-buckled side of the Si-dimers or to migrate there during the adsorption process. Annealing experiments are performed in order to determine the relation of this initial structure to the local equilibrium structure.

  7. Segregated carbon on Pt 10Ni 90(100) studied by scanning tunneling microscopy

    Science.gov (United States)

    Schmid, M.; Biedermann, A.; Varga, P.

    1993-09-01

    Scanning tunneling microscopy is used to study the arrangement of segregated carbon atoms with atomic resolution. Individual carbon atoms are visible only under special tip conditions, while they normally do not directly appear on STM topographs. Under all tip conditions, carbon atoms affect the corrugation of their metal neighbours, reducing the apparent height by 20 to 40 pm in the p(2 × 2) and 40 to 70 pm in the c(2 × 2) superstructure. Therefore the existence, structure and amount of carbon can be also derived from images without directly visible carbon atoms. A substrate lattice distortion in regions of the carbon c(2 × 2) superstructure was observed, exhibiting areas of the p4g structure known from earlier LEED studies of Ni(100).

  8. 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.

  9. 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.

  10. 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.

  11. The atomic structure of Pt on Si(1 1 1) studied by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Highlights: • Two kinds of ordered reconstruction surface were prepared on Pt/Si(1 1 1) surface. • The atomic structures were observed and verified by STM. • Calculation results confirmed the bonding energy between Si and Pt atoms. - Abstract: Two kinds of ordered reconstruction surface (?3 × ?3) R30° and (?7 × ?7) R19.1°, are prepared by depositing different amounts of Pt on Si(1 1 1). The atomic structure and electronic properties are studied by scanning tunneling microscopy and X-ray photoelectron spectroscopy. Then two models are built to explain the results. And the calculated results using density functional theory based first principle calculation show that the distance between Pt and Si atoms in (?7 × ?7) R19.1° structure is smaller than that in (?3 × ?3) R30° structure, which can increase the bonding energy between Pt and Si atoms

  12. 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

  13. 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.

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

    Science.gov (United States)

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

    2014-12-01

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

  15. Cytochrome C Dynamics at Gold and Glassy Carbon Surfaces Monitored by in Situ Scanning Tunnel Microscopy

    DEFF Research Database (Denmark)

    Andersen, Jens Enevold Thaulov; MØller, Per

    1995-01-01

    We have investigated the absorption of cytochrome c on gold and glassy carbon substrates by in situ scanning tunnel microscopy under potentiostatic control of both substrate and tip. Low ionic strength and potential ranges where no Faradaic current flows were used. Cyt c aggregates into flat composite structures of about 50 nm lateral extension at gold surfaces. The aggregates evolve in time, and structures resembling individual cyt c molecules can be distinguished in the space between the 50 nm structures. Cyt c aggregates also form at glassy carbon but have a different, unbroken character where cyt c both sticks well to the surface and exhibits notable mobility. The observations suggest that characteristic surface specific, internally mobile protein aggregates are formed at both surfaces and that in situ molecular resolution of the STM pictures may have been achieved.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Time-resolved scanning tunneling microscopy for studies of nanoscale magnetization dynamics

    Science.gov (United States)

    Loth, Sebastian

    2015-03-01

    The time resolution of the scanning tunneling microscope can be boosted greatly by use of electronic pump probe measurement schemes. Pulse shaping of the input pulses can even overcome bandwidth limitations of the instrument and enables sub-nanosecond time resolution. In this talk we will focus on applications of this technique for measurements of fast spin dynamics in nanomagnets. We use the probe tip of a low-temperature STM to arrange magnetic atoms into arrays of our own design. Thin insulating films decouple the atoms from the supporting metallic substrate so that the nanostructures show quantum-magnetic properties with discrete spin states. The time-domain information gained in pump probe spectroscopy quantifies the spin relaxation between metastable spin states. It enables isolating the interaction between the nanomagnet and its environment. In particular, we find that the magnetic atoms of a spin-polarized STM tip interact significantly with the surface even at moderate tunneling conditions. This interaction acts analogously to a highly localized magnetic field. It depends exponentially on the tip-nanomagnet distance and can reach a strength of several tesla. We use this atomically localized magnetic field to control the spin state mixing of a nanomagnet in an avoided level crossing of low-energy spin states. Furthermore, pump probe spectroscopy enables non-local measurements of magnetic states and highlights pathways to design and control magnetism at the single atom level.

  3. 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

  4. 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)

  5. 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.

  6. Low conductive support for thermal insulation of a sample holder of a variable temperature scanning tunneling microscope.

    Czech Academy of Sciences Publication Activity Database

    Hanzelka, Pavel; Vonka, J.; Musilová, V?ra

    2013-01-01

    Ro?. 84, ?. 8 (2013), 085103:1-6. ISSN 0034-6748 R&D Projects: GA MŠk ED0017/01/01; GA TA ?R TE01020233 Institutional support: RVO:68081731 Keywords : Thermal conductiviy * Scanning tunneling microscope Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering Impact factor: 1.584, year: 2013

  7. 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)

  8. 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)

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

    CERN Document Server

    Wiesendanger, Roland

    1994-01-01

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

  10. 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)

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

    International Nuclear Information System (INIS)

    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

  12. 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.

  13. 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

  14. 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)

  15. 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

  16. 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.

  17. 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.

  18. 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)

  19. Nanoscale patterning and selective chemistry of silicon surfaces by ultrahigh-vacuum scanning tunneling microscopy

    Science.gov (United States)

    Lyding, J. W.; Shen, T.-C.; Abeln, G. C.; Wang, C.; Tucker, J. R.

    1996-06-01

    Nanometer scale patterning of the 0957-4484/7/2/006/img1 monohydride surface has been achieved by using an ultrahigh-vacuum (UHV) scanning tunneling microscope (STM) to selectively desorb the hydrogen. After preparing high-quality H-passivated surfaces in the UHV chamber, patterning is achieved by operating the STM in field emission. The field-emitted electrons stimulate the desorption of molecular hydrogen, restoring clean 0957-4484/7/2/006/img2 in the patterned area. This depassivation mechanism seems to be related to the electron kinetic energy for patterning at higher voltages and electron current for low-voltage patterning. The patterned linewidth varies linearly with tip bias, achieving a minimum of less than 10 Å at -4.5 V. The linewidth dependence on electron dose is also studied. For positive tip biases up to 10 V no patterning occurs. The selective chemical reactivity of the patterned surface has been explored by oxygen and ammonia dosing. For the oxygen case, initial oxidation of the patterned area is observed. Ammonia dosing, on the other hand, repassivates the surface in a manner different from that of atomic hydrogen. In both cases the pattern resolution is retained and the surrounding H-passivated areas remain unaffected by the dosing.

  20. 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...

  1. Influence of a dielectric layer on photon emission induced by a scanning tunneling microscope.

    Science.gov (United States)

    Tao, X; Dong, Z C; Yang, J L; Luo, Y; Hou, J G; Aizpurua, J

    2009-02-28

    We investigate theoretically the influence of a dielectric layer on light emission induced by a scanning tunneling microscope through a combined approach of classical electrodynamics and first-principles calculations. The modification of the junction geometry upon the insertion of a dielectric layer is treated first by using the density functional theory to calculate the effective potential along the surface normal and then by solving a one-dimensional Schrodinger equation to obtain the exact distance between the tip and the substrate for a given current and bias voltage. The modified external field with the inclusion of a dielectric layer is evaluated by using the Fresnel formula. The local-field enhancement factor and radiated power are calculated by the boundary element method for two typical systems, W-tip/C(60)/Au(111) and W-tip/Al(2)O(3)/NiAl(110). The calculated results indicate that the insertion of a dielectric layer tends to reduce the light emission intensity considerably but hardly changes the spectral profile with no substantial peak shifts with respect to the layer-free situation, in agreement with experimental observations. The suppression of the radiated power is mainly due to the increase in the tip-metal separation and the resultant reduction in the electromagnetic coupling between the tip and metal substrate. PMID:19256618

  2. 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. PMID:24784617

  3. 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.

  4. 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.

  5. 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)

  6. 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

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. High-resolution mapping of plasmonic modes: photoemission and scanning tunnelling luminescence microscopies

    International Nuclear Information System (INIS)

    Photonic properties of dense metal nanostructures are currently under intense investigation because of the possible local enhancements of electromagnetic fields induced by plasmonic excitations. In this review paper, we present examples of plasmonic-field mappings based on multiphoton photoemission or STM-induced light emission, two techniques among those which offer today's best spatial resolutions for plasmon microscopy. By imaging the photoemitted electrons, using well-established electron optics, two-dimensional intensity maps reflecting the actual distribution of the optical near-field are obtained. The imaging technique involves no physical probe altering the measure. This approach provides full field spectroscopic images with a routine spatial resolution of the order of 20 nm (down to 2 nm with recent aberration corrected instruments). Alternatively, an unfamiliar property of the junction of scanning tunnelling microscope is its ability to behave as a highly localized source of light. It can be exploited to probe opto-electronic properties, in particular plasmonic fields, with ultimate subnanometre spatial resolution, an advantage balanced by a sometimes delicate deconvolution of local-probe influence.

  13. Scanning tunneling microscopy assisted by synchrotron radiation light for high-resolution element specific imaging

    International Nuclear Information System (INIS)

    Microscope having atomic resolution with chemical sensitivity is one of the ultimate microscopes for the material science. Scanning tunneling microscope (STM) assisted by the core-level excitation by synchrotron radiation (SR) may be a possible candidate of such an ultimate microscope. In this paper we will demonstrate that we can observe element specific images of surfaces in the spatial resolution of several tens of nanometer by measuring the photon induced current images taken with an STM tip detecting the secondary electrons produced by the electron-hole recombination after the core-level excitation. Importance of the chemical contrast-enhancement by dividing the SR-STM image taken at photon absorption edge top by that of at the edge bottom is demonstrated by the observation of transition metal micro patterns. Possibility of a nanometer scale chemical imaging such as C60 domain structure on Si(111) ?3 x ?3-Ag surface with an assistance of high-brilliant light sources is also suggested. (author)

  14. 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.

  15. 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)

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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

  8. 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.

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

    CERN Document Server

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

    2014-01-01

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

  10. 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.

  11. 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.

  12. 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.

  13. 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)

  14. Superconducting ?-ZrNCl{sub x} probed by scanning-tunnelling and break-junction spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Ekino, Toshikazu, E-mail: ekino@hiroshima-u.ac.jp [Hiroshima University, Graduate School of Integrated Arts and Sciences, Higashi-Hiroshima 739-8521 (Japan); Sugimoto, Akira [Hiroshima University, Graduate School of Integrated Arts and Sciences, Higashi-Hiroshima 739-8521 (Japan); Gabovich, Alexander M. [Institute of Physics, National Academy of Sciences of Ukraine, 46, Nauka Avenue, Kyiv 036680 (Ukraine); Zheng, Zhanfeng; Yamanaka, Shoji [Hiroshima University, Graduate School of Engineering, Higashi-Hiroshima 739-8527 (Japan)

    2013-11-15

    Highlights: •STM/STS combined with break-junction tunnelling spectroscopy (BJTS) on ?-ZrNCl. •STM image on the ab plane shows triangular atomic lattice spots with a period of 0.36 nm. •The gap peaks are widely distributed (?{sub p–p} = 9–28 meV)over the area of 100 nm{sup 2}. •Average gap ratio 2?/k{sub B}T{sub c} ? 10 is confirmed by both STS and BJTS. -- Abstract: Superconducting layered compound ?-ZrNCl{sub x} (x = 0.7) with the critical temperature T{sub c} = 13–14 K was investigated by means of scanning tunnelling microscopy/spectroscopy. The single-crystal domain facet of ?100 ?m{sup 2} in the c-axis-oriented polycrystal was used as a probing surface. The STM image at 4.9 K shows triangular atomic lattice spots with the period of ?0.36 nm, which agrees with the X-ray diffraction measurements. The STS measurements of the local conductance, dI/dV, exhibit broadened gap structures with a substantial distribution of the gap-edge values. Most frequently observed peak-to-peak value of ?20 mV is remarkably similar to the superconducting gap edge of the isostructural ?-HfNCl{sub x} with T{sub c} = 24 K. Temperature, T, dependence of the dI/dV shows that the gap structure disappears above T{sub c} ? 13 K. Fitting of the dI/dV curve by the broadened BCS density of states leads to the superconducting gap of 2?(4.9 K) = 11–13 meV. This is in accordance with our former break-junction data confirming the intrinsic character of the previously obtained extremely large gap to T{sub c} ratio 2?(0)/k{sub B}T{sub c} ? 10 (k{sub B} is the Boltzmann constant), thereby pointing to the unusual superconducting properties of this compound.

  15. 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 STM. Many of them exhibit noninteger step-height plateaus with different widths. Clear evidence was found for the existence of two different populations at the surface with distinct (narrowed or widen...

  16. 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...

  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. Scanning tunneling spectroscopy study of c-axis proximity effect in epitaxial bilayer manganite/cuprate thin films

    OpenAIRE

    Fridman, I.; Gunawan, L.; G. A. Botton; Wei, J. Y. T.

    2011-01-01

    Recent experimental studies have indicated novel superconducting proximity effects in thin-film heterostructures comprising ferromagnetic manganites and superconducting cuprates. To look for such effects microscopically, we performed scanning tunneling spectroscopy on La$_{2/3}$Ca$_{1/3}$MnO$_3$/YBa$_2$Cu$_3$O$_{7-\\delta}$ (LCMO/YBCO) bilayer thin films. $\\emph{c}$-axis oriented films of varying thickness were grown on SrTiO$_{3}$ substrates using pulsed laser-ablated deposi...

  19. 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...

  20. 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.

  1. 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.

  2. 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).

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

    International Nuclear Information System (INIS)

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

  4. 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...

  5. Break-junction tunneling spectra of MgB2: Influence of boron quality

    International Nuclear Information System (INIS)

    Tunneling spectra of a superconductor-insulator-superconductor (SIS) junction formed by the break-junction technique have been carried out for two different boron quality MgB2 samples. One is a polycrystalline MgB2 pellet (RRR ? 4) and the other is a high purity MgB2 wire (RRR ? 25) of approximately 150 ?m in diameter. Both samples exhibit a multiple-gap feature, which can be expressed by the correlated two-gap model. From the conductance fitting at 4.2 K, the pellet gap parameters are ? S = 2.2 ± 0.3 meV, ? M = 6.0 ± 1.5 meV and ? L = 10 meV, whereas the only clear and very reproducible gap in the wires is the small gap at ? S = 2.5 ± 0.1 meV. The wires show almost constant values for the fitting parameters of the two-gap model, in contrast with the pellets that show a large variation

  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. 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.

  9. Ultrathin Mn layers on Rh(001): Investigations using scanning tunneling microscopy and density functional calculations

    Science.gov (United States)

    Zelený, Martin; Natterer, Fabian D.; Biedermann, Albert; Hafner, Jürgen

    2010-10-01

    The structural and magnetic properties of ultrathin layers of Mn grown on Rh(001) surfaces have been investigated using scanning tunneling microscopy (STM) and ab initio density-functional calculations. STM shows perfect wetting of the Rh substrate by the first Mn monolayer (ML) accompanied by a high mobility of the Mn atoms and only little film-substrate intermixing. By way of contrast, the second monolayer is unstable against formation of multilayer islands at 300 K. However, this is only a transient effect and growth approaches a layer-by-layer mode in thicker films. At 170 K growth proceeds layer-by-layer throughout. The structure of the films is face-centered tetragonal (fct) without any indication of lateral lattice mismatch up to 20 ML thickness. The apparent height differences between terraces of different local thickness are consistent with an average axial ratio close to unity (near fcc) for 2-3-ML-thick films that decreases continuously to ?0.94 in thicker films. Detailed spin-polarized density-functional calculations have been performed for the bulk and the (001) surface of strained fct Mn, as well as for free-standing and supported Mn/Rh(001). The results demonstrate that structure and stability of surface and thin films are strongly influenced by antiferromagnetic (AFM) ordering. In-plane c(2×2) AFM is found at the surface while bulk and the deeper layers prefer layered AFM. The calculations reproduce and explain the growth instability of 2 ML films and reproduce qualitatively the thickness-dependent variation in the film structure while the tetragonal distortion imposed by the size mismatch is overestimated because with all known exchange-correlation functionals the size ratio of bulk Rh and Mn crystals is overestimated. The calculations show that interface alloying is slightly exothermic but kinetically hindered because of a high activation energy for exchange processes.

  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. 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.

  14. 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

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

    Science.gov (United States)

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

    2012-04-01

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

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

    International Nuclear Information System (INIS)

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

  17. 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.)

  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. A review and outlook for an anomaly of scanning tunnelling microscopy (STM): superlattices on graphite

    International Nuclear Information System (INIS)

    Since its invention in 1981, scanning tunnelling microscopy (STM) is well-known for its supreme imaging resolution enabling one to observe atomic-scale structures, which has led to the flourishing of nanoscience. As successful as it is, there still remain phenomena which are observed using STM but are beyond our understanding. Graphite is one of the surfaces which have been most extensively studied using STM. However, there are a number of unusual properties of graphite surfaces. First reported in the 1980s, superlattices on graphite have since been observed many times and by many groups, but as yet our understanding of this phenomenon is quite limited. Most of the observed superlattice phenomena are widely believed to be the result of a Moire rotation pattern, arising from the misorientation between two graphite layers, as verified experimentally. A Moire pattern is a lattice with larger periodicity resulting from the overlap of two lattices with smaller periodicities. As graphite layers are composed of hexagonal lattices with a periodicity of 0.246 nm, as observed using STM, when there are misoriented graphite layers overlapping each other, a Moire pattern with larger periodicity, depending on the misorientation angle, will be produced and appear as a superperiodic hexagonal structure on top of the graphite atomic lattice of the topmost surface layer. It is important to study graphite superlattices because, firstly, knowledge of this phenomenon will enable us to properly interpret STM images; secondly, it helps us to understand the correlation between electronic structures and atomic-structure rearrangement of graphite which is of tremendous aid for engineering material properties; thirdly, and perhaps most importantly, the observation of the phenomenon exhibits the capability of STM to produce images indicating the nature of internal defects which are below the surface. Over recent years, experimental and modelling techniques have been developed to study this anomalous regime of STM; however, there is a lack of a systematic classification of this scattered information. This review article thus serves the purpose of organizing all these results so as to enable a more comprehensive understanding of this phenomenon. We review the discovery of graphite superlattices, the observation of the associated properties, and the research efforts on this subject. An effort is made to envision the future experimental and theoretical research possibilities to unveil the mystery of this anomaly of STM. Applications of graphite superlattices are also proposed. (topical review)

  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. Time-resolved detection of surface plasmon polaritons with a scanning tunneling microscope

    DEFF Research Database (Denmark)

    Keil, Ulrich Dieter Felix; Ha, T.

    1998-01-01

    We present the time-resolved detection of surface plasmon polaritons with an STM. The results indicate that the time resolved signal is due to rectification of coherently superimposed plasmon voltages. The comparison with differential reflectivity measurements shows that the tip itself influences the decay of the plasmon-field coherence. Generation of the measured signal at the tunneling junction offers the possibility to observe ultrafast effects with a spatial resolution determined by the tunneling junction

  2. 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 di

  3. 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...

  4. 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 sweep, LSV, cyclic, CV, and square wave (SQWV) voltammetry. Multifarious electrochemical patterns were observed. Most attention was given to reductive desorption caused by insulin binding to the Au-surfac...

  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. 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

  7. 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.

  8. 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.

  9. 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

    We have studied the adsorption and electrocatalysis of the redox metalloenzyme blue copper nitrite reductase from Achromobacter xylosoxidans (AxCuNiR) on single-crystal Au(111)-electrode surfaces modified by a self-assembled monolayer of cysteamine. A combination of cyclic voltammetry and in situ 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 st...

  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. Electrospray deposition of fullerenes in ultra-high vacuum: in situ scanning tunneling microscopy and photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Satterley, Christopher J [School of Physics and Astronomy, University of Nottingham (United Kingdom); Perdigao, LuIs M A [School of Physics and Astronomy, University of Nottingham (United Kingdom); Saywell, Alex [School of Physics and Astronomy, University of Nottingham (United Kingdom); Magnano, Graziano [School of Physics and Astronomy, University of Nottingham (United Kingdom); Rienzo, Anna [School of Physics and Astronomy, University of Nottingham (United Kingdom); Mayor, Louise C [School of Physics and Astronomy, University of Nottingham (United Kingdom); Dhanak, Vinod R [SERC, Daresbury Lab, Warrington (United Kingdom); Beton, Peter H [School of Physics and Astronomy, University of Nottingham (United Kingdom); O' Shea, James N [School of Physics and Astronomy, University of Nottingham (United Kingdom)

    2007-11-14

    Electrospray deposition of fullerenes on gold has been successfully observed by in situ room temperature scanning tunneling microscopy and photoemission spectroscopy. Step-edge decoration and hexagonal close-packed islands with a periodicity of 1 nm are observed at low and multilayer coverages respectively, in agreement with thermal evaporation studies. Photoemission spectroscopy shows that fullerenes are being deposited in high purity and are coupling to the gold surface as for thermal evaporation. These results open a new route for the deposition of thermally labile molecules under ultra-high vacuum conditions for a range of high resolution surface science techniques.

  12. 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.

  13. 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

    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 spatial extension of MOP-C, about 5 nm in height, conditions could be found where tip/sample interaction is minimal and proteins could be imaged without detectable tip interference. The results indicate further that the structural sensitivity of (in situ) STM depends to a significant extent on associated electron transfer kinetics. In the present case, the heme group does not contribute significantly to the tunnelling current, apparently due to slow electron transfer kinetics. As a consequence, STM images of heme-containing and heme-free MOP-C did not reveal any notable differences in apparent height or physical extension. The apparent height of heme-containing MOP-C did not show any dependence on the substrate potential being varied around the redox potential of the protein. The mere presence of an accessible molecular energy level is not sufficient to result in detectable tunnelling current modulation. (c) 2006 Elsevier B.V. All rights reserved.

  14. 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.

  15. 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.

  16. 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.)

  17. 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.)

  18. 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 ...

  19. 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

  20. 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.

  1. Time-resolved detection of surface plasmon polaritons with a scanning tunneling microscope

    DEFF Research Database (Denmark)

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

    1998-01-01

    We present the time-resolved detection of surface plasmon polaritons with an STM. The results indicate that the time resolved signal is due to rectification of coherently superimposed plasmon voltages. The comparison with differential reflectivity measurements shows that the tip itself influences the decay of the plasmon-field coherence. Generation of the measured signal at the tunneling junction offers the possibility to observe ultrafast effects with a spatial resolution determined by the tunn...

  2. Perspectives for in situ Scanning Tunnel Microscopic Imaging of Proteins at HOPG surfaces

    DEFF Research Database (Denmark)

    Andersen, Jens Enevold Thaulov; Thuesen, Marianne Hallberg; Møller, Per; Ulstrup, Jens

    1996-01-01

    We have investigated the behaviour of the four-copper fungal metalloenzyme laccase (MW~68kDa) at highly oriented pyrolytic graphite (HOPG) surfaces by ex situ and in situ STM. The four copper atoms ar suited to stimulate long-range inelastic tunnel modes through the protein. The proteins forms crystalline or amorphous structures of micro-meter lateral extension during evaporation of aqueous laccase solution at low ionic strength. Individual molecular-size structures distinct from the HOPG backgr...

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. [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).

  8. 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

  9. Deposition of copper multilayers on Au(111) in sulfuric acid solution: An electrochemical scanning tunneling microscopy study

    Science.gov (United States)

    Madry, B.; Wandelt, K.; Nowicki, M.

    2015-07-01

    The co-adsorption of submono-, mono- and multi-layers of Cu with sulfate anions on a Au(111) electrode surface was investigated in electrochemical environment (0.1 mM CuSO4 + 0.1 M H2SO4) by cyclic voltammetry (CV) and in-situ scanning tunneling microscopy (STM). Correlated with the STM investigations the CV measurements indicate co-adsorption/-desorption processes of Cu of submono-, mono- and multi-layer coverages with sulfuric acid species on Au(111). The formation of a quasi-hexagonal Moiré superstructure on terraces of copper multilayers was observed in situ by STM. In detail the observed Moiré-structure is similar but not identical to the one observed on the (111) surface of bulk copper. High resolution STM images show the formation of a (?{ 3} ×?{ 7})-like sulfate structure on all multilayer copper terraces.

  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. 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

    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 STM. Many of them exhibit noninteger step-height plateaus with different widths. Clear evidence was found for the existence of two different populations at the surface with distinct (narrowed or widened) partial-splitting widths. All findings are fully confirmed by the MD simulations. The MD simulations extend the STM-, i.e., surface-, investigation to the subsurface region. Due to this additional insight, we can explain the different partial-splitting widths as the result of the interaction between the partial dislocations and the surface.

  12. 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.)

  13. 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.

  14. 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

  15. 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

  16. 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

  17. Observation of Buried Phosphorus Dopants near Clean Si(100)-(2x1) with Scanning Tunneling Microscopy

    CERN Document Server

    Brown, G W; Hawley, M E; Brown, Geoffrey W.; Grube, Holger; Hawley, Marilyn E.

    2004-01-01

    We have used scanning tunneling microscopy to identify individual phosphorus dopant atoms near the clean silicon (100)-(2x1) reconstructed surface. The charge-induced band bending signature associated with the dopants shows up as an enhancement in both filled and empty states and is consistent with the appearance of n-type dopants on compound semiconductor surfaces and passivated Si(100)-(2x1). We observe dopants at different depths and see a strong dependence of the signature on the magnitude of the sample voltage. Our results suggest that, on this clean surface, the antibonding surface state band acts as an extension of the bulk conduction band into the gap. The positively charged dimer vacancies that have been observed previously appear as depressions in the filled states, as opposed to enhancements, because they disrupt these surface bands.

  18. Growth mechanism of silicene on Ag (111 ) determined by scanning tunneling microscopy measurements and ab initio calculations

    Science.gov (United States)

    Bernard, R.; Borensztein, Y.; Cruguel, H.; Lazzeri, M.; Prévot, G.

    2015-07-01

    Scanning tunneling microscopy has been used to real-time study the growth of silicene on Ag (111 ) in the 200-533-K temperature range. We show that the growth mode depends strongly on the deposition temperature T . At T =300 K and above, the formation of silicene results from the exchange between surface Ag atoms and Si atoms, which are inserted in the substrate top layer. Density functional theory calculations confirm that Si insertion is thermodynamically favored, and we propose an energetic model for explaining the observed growth processes as a function of T . For T ?400 K , ordered structures are observed as soon as silicene domains are large enough. With increasing coverage, disordered and dotted phases progressively transform into stable (?{13 }×?{13 }) R 13 .9? and (4 ×4 ) structures.

  19. 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.)

  20. 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

  1. 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...

  2. 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.

  3. 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

  4. 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

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

    OpenAIRE

    Holm, Jesper; Mygind, Jesper

    2009-01-01

    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...

  6. 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...

  7. 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.

  8. 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.

  9. 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.

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

    DEFF Research Database (Denmark)

    Holm, Jesper; Mygind, Jesper

    1995-01-01

    A novel cryogenic scanning laser microscope with a spatial resolution of less than 5 µm has been designed for on-chip in situ investigations of the working properties of normal and superconducting circuits and devices. The instrument relies on the detection of the electrical response of the circuit to a very localized heating induced by irradiation with 675 nm wavelength light from a semiconductor laser. The hot spot is moved by a specially designed piezoelectric scanner sweeping the tip of a single-mode optical fiber a few µm above the circuit. Depending on the scanner design the scanning area can be as large as 50×500 µm2 at 4.2 K. The microscope can be operated in the temperature range 2–300 K using a standard temperature controller. The central microscope body is mounted inside the vacuum can of a dip-stick-type cryoprobe. A damped spring system is used to reduce interference from extraneous mechanical vibrations. The microscope is integrated in a personal-computer-based data acquisition and control setup. ©1995 American Institute of Physics.

  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. 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.

  13. In situ scanning tunneling microscopy study of cobalt thin film electrodeposited on Pt(1 1 1) electrode

    International Nuclear Information System (INIS)

    Thanks to the availability of single crystal electrodes and the advance of scanning probes, it is now possible to characterize the process of electrodeposition in real time and the atomic structure of ultrathin film. Reported here is an in situ scanning tunneling microscopy (STM) study of cobalt electrodeposition on an ordered Pt(1 1 1) electrode in a pH 3 chloride-containing medium. It was found to be a two-staged process, involving an underpotential deposition (UPD) stage and an overpotential deposition (OPD) occurring at potentials positive and negative of the Nernst potential of ?0.57 V (versus Ag/AgCl) calculated for 0.04 M CoCl2. Time-dependent STM imaging revealed Co nucleated mainly in one atom high islands on terraces and at steps in the UPD stage, followed by quasi layer-by-layer growth to form a smooth thin film up to five layers in thickness. The UPD layer comprised Co atoms arranging in disarray, possibly resulting from competitive adsorption of hydrogen at the Pt electrode. Starting from the second layer, the Co film assumed ordered microstructures featuring a long range undulation of atomic height. This moire structure consisted of Co(0 0 0 1) like plane stacked on the Pt(1 1 1) substrate with an in-plane interatomic spacing of 0.257 nm in the bilayer film. Due to different lattice constants of Co and Pt, the Co/Pt(1 1 1) was strained, but the degree of this interfacial strain gradually decreased with the thickness of Co deposit, as revealed by the diminish of the moire pattern when the Co film grew to more than five layer in thickness. Meanwhile, the morphology of the Co deposit became rougher with thickness, which suggests a Stranski–Krastanov growth

  14. 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

  15. 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.

  16. Local Measurement of Microwave Response with Local Tunneling Spectra Using Near Field Microwave Microscopy

    OpenAIRE

    Machida, Tadashi; Gaifullin, Marat B.; Ooi, Shuuichi; Kato, Takuya; Sakata, Hideaki; Hirata, Kazuto

    2010-01-01

    We have designed and built a near-field scanning microwave microscope, which has been used to measure the local microwave response and the local density-of-states (LDOS) in the area including the boundary between the gold deposited and the non-deposited region on highly-orientated pyrolytic graphite at a frequency of about 7.3 GHz. We have succeeded in measuring the spatial variation of both the LDOS and the surface resistance. It can be observed that the surface resistance ...

  17. 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.

  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. The ReactorSTM: Atomically resolved scanning tunneling microscopy under high-pressure, high-temperature catalytic reaction conditions

    Energy Technology Data Exchange (ETDEWEB)

    Herbschleb, C. T.; Tuijn, P. C. van der; Roobol, S. B.; Navarro, V.; Bakker, J. W.; Liu, Q.; Stoltz, D.; Cañas-Ventura, M. E.; Verdoes, G.; Spronsen, M. A. van; Bergman, M.; Crama, L.; Taminiau, I.; Frenken, J. W. M., E-mail: frenken@physics.leidenuniv.nl [Huygens-Kamerlingh Onnes Laboratory, Leiden University, P.O. box 9504, 2300 RA Leiden (Netherlands); Ofitserov, A.; Baarle, G. J. C. van [Leiden Probe Microscopy B.V., J.H. Oortweg 21, 2333 CH Leiden (Netherlands)

    2014-08-15

    To enable atomic-scale observations of model catalysts under conditions approaching those used by the chemical industry, we have developed a second generation, high-pressure, high-temperature scanning tunneling microscope (STM): the ReactorSTM. It consists of a compact STM scanner, of which the tip extends into a 0.5 ml reactor flow-cell, that is housed in a ultra-high vacuum (UHV) system. The STM can be operated from UHV to 6 bars and from room temperature up to 600 K. A gas mixing and analysis system optimized for fast response times allows us to directly correlate the surface structure observed by STM with reactivity measurements from a mass spectrometer. The in situ STM experiments can be combined with ex situ UHV sample preparation and analysis techniques, including ion bombardment, thin film deposition, low-energy electron diffraction and x-ray photoelectron spectroscopy. The performance of the instrument is demonstrated by atomically resolved images of Au(111) and atom-row resolution on Pt(110), both under high-pressure and high-temperature conditions.

  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

  1. 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.

  2. 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.

  3. High-resolution scanning tunneling microscopy imaging of Si(1?1?1)-7?×?7 structure and intrinsic molecular states

    International Nuclear Information System (INIS)

    We review our achievements in exploring the high resolution imaging of scanning tunneling microscopy (STM) on the surface and adsorbates in a ultra-high vacuum system, by modifying the STM tip or introducing a decoupled layer onto the substrate. With an ultra-sharp tip, the highest resolution of Si(1?1?1)-7?×?7 reconstruction can be achieved, in which all the rest atoms and adatoms are observed simultaneously with high contrast. Further functionalization of STM tips can realize selective imaging of inherent molecular states. The electronic states of perylene and metal–phthalocyanine molecules are resolved with special decorated tips on metal substrates at low temperature. Moreover, we present two kinds of buffer layer: an organic molecular layer and epitaxially grown graphene to decouple the molecular electronic structure from the influence of the underlying metallic substrate and allow the direct imaging of the intrinsic orbitals of the adsorbed molecules. Theoretical calculations and STM simulations, based on first-principle density function theory, are performed in order to understand and verify the mechanism of high-resolution images. We propose that our results provide impactful routes to pursue the goal of higher resolution, more detailed information and extensive properties for future STM applications. (topical review)

  4. Scanning tunneling microscopy morphological study of the first stages of growth of microwave chemical vapor deposited thin films

    International Nuclear Information System (INIS)

    Thin diamond films have been grown by the microwave chemical vapor deposition method on polished silicon substrates using a methane concentration of 1.5% in hydrogen and deposition times between 7 and 60 min. The films were studied in air by scanning tunneling microscopy (STM). For short deposition times we have found small isolated diamond crystals (100 nm wide and 20 nm high), growing on the scratches produced by the initial polishing of the silicon surface, along with a smooth granular structure. As the deposition time increases to 15 min, the granular structure shows a slight faceting whereas the crystal size increases appreciably. This deposition period is characterized by a lower growth rate than that observed for longer times, which is explained as due to the presumably high nondiamond component of the granular structure. At 30 min a continuous film is formed with predominant (111) faces. The same trend is found for samples grown after 60 min. STM images show that (111) surfaces are rougher than (100) ones supporting the 2x1 reconstruction of the (100) surface during diamond growth. 30 refs., 7 figs., 1 tab

  5. 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.

  6. Monitoring Si growth on Ag(111) with scanning tunneling microscopy reveals that silicene structure involves silver atoms

    Energy Technology Data Exchange (ETDEWEB)

    Prévot, G.; Bernard, R.; Cruguel, H.; Borensztein, Y. [Sorbonne Universités, UPMC Univ Paris 06, UMR 7588 Institut des NanoSciences de Paris, 4 place Jussieu, F-75005 Paris (France); CNRS, UMR 7588 Institut des NanoSciences de Paris, F-75005 Paris (France)

    2014-11-24

    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.

  7. Quantitative Evaluation of Dopant Concentration in Shallow Silicon p-n Junctions by Tunneling Current Mapping with Multimode Scanning Probe Microscopy

    Science.gov (United States)

    Bolotov, Leonid; Fukuda, Koichi; Arimoto, Hiroshi; Tada, Tetsuya; Kanayama, Toshihiko

    2013-04-01

    Quantitative evaluation of the dopant concentration across silicon p-n junctions has been performed on oxide-passivated surfaces by using tunneling current mapping in the constant-gap mode of a multimode scanning probe microscope (MSPM). A distinct difference between regions with different impurity concentrations was observed in tunneling current maps when a constant tunneling gap was maintained by using repulsive force acting on the MSPM probe. To extract impurity profiles, the results of three-dimensional device simulations within the current continuity model were compared with measured bias-dependent current profiles. The obtained impurity profiles showed agreement with the actual donor concentration in the p-n junction region. The results demonstrate the applicability of the method for quantitative analysis of the local impurity distribution in modern semiconductor devices with improved sensitivity and nanometer spatial resolution.

  8. Approach to surface structure determination with the scanning tunneling microscope: Multiple-gap imaging and electron-scattering quantum-chemistry theory

    International Nuclear Information System (INIS)

    We have successfully developed and tested a method of quantitative surface structure determination using scanning tunneling microscopy (STM). Image simulations of the c(2x2) S on Mo(100) chemisorption system were calculated as a function of surface and tip structure using electron-scattering quantum-chemistry STM theory. STM images with a wide range of tunneling gap resistance values were acquired in a ''multiple-gap'' mode which preserves information on the z separation and lateral registry between the images under different tunneling conditions. The best fit of a numerical comparison of the image simulations with experimental data simultaneously determined two structural parameters of the surface. The STM results differ from those of dynamical LEED by approximately 0.1 A, which we estimate to be the level of accuracy obtainable with the present implementation of the method

  9. In Situ Scanning Tunneling Microscopy Study of 5,6-Dimethyl Uracil on Au (111)

    Scientific Electronic Library Online (English)

    Frederico G. C., Cunha; Francisco C., Nart.

    2001-12-01

    Full Text Available Fenômenos de desordem e posterior reorganização de um filme de 5,6-dimetil uracil (5,6 - DMU), causados pela evolução de hidrogênio, foram estudados usando STM in situ e voltametria cíclica em solução de ácido sulfúrico sobre Au (111). Um filme estável com adsorsão física foi formado entre os limite [...] s da evolução de hidrogênio (a -0.3 V/SCE) e o levantamento da reconstrução (a 0.4 V/SCE) na concentração de solução usada neste estudo. A evolução do hidrogênio causou a formação de estruturas semelhantes a "bolhas" que desestabilizaram o filme desencadeando o processo de desordem que ocorre em toda a área estudada. Polarizando novamente o eletrodo em um potencial na região de estabilidade do filme, foi possível o acompanhamento, em tempo real, da reorganização do filme. Uma evolução anisotrópica do filme foi observada. Os degraus monoatômicos não se mostraram sítios preferenciais de nucleação. A estrutura de empacotamento molecular foi derivada a partir de imagens de STM de alta resolução e a existência de dois estados de adsorsão distintos foi estabelecida. Abstract in english 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.

  10. Grain boundary engineering of La0.7 Sr0.3 MnO3 films on silicon substrate: Scanning Tunneling Microscopy-Spectroscopy study

    International Nuclear Information System (INIS)

    We employed a Scanning Tunnelling Microscope (STM) to study the surface topography and spatially resolved local electronic properties like local density of states (LDOS) of nanostructured films of La0.7 Sr0.3 MnO3 (LSMO). The nanostructured thin films of LSMO on silicon substrate were prepared using Pulsed Laser Deposition (PLD) technique. The deposition conditions were tuned to yield two different morphologies; one with uniform columnar closely packed islands and other with larger grain distribution in random fashion. The Scanning Tunnelling Spectroscopy (STS) revealed the extent of variation of density of states (DOS) near the Fermi level. From the spectroscopic features obtained we found the occurrence of phase separation between conducting and semiconducting domains and its possible correlation with the properties of the system. Semiconducting nature was observed at the grain boundaries, which could be extremely promising in futuristic nano-devices

  11. Oxidation of arsenopyrite and deposition of gold on the oxidized surfaces: A scanning probe microscopy, tunneling spectroscopy and XPS study

    Science.gov (United States)

    Mikhlin, Yuri L.; Romanchenko, Alexander S.; Asanov, Igor P.

    2006-10-01

    We have used ex situ atomic force microscopy (AFM), scanning tunneling microscopy and spectroscopy (STM/STS) and X-ray photoelectron spectroscopy (XPS) to study the surfaces of natural arsenopyrite samples that were electrochemically polarized in 1 M HCl, or leached in acidic solutions containing ferric iron salts, and then reacted with aqueous gold (III) chloride at ambient temperatures. For arsenopyrite oxidized on a positive-going potential sweep, progressively increasing amounts of surface Fe(III)-O and As-O species, and of S/Fe and S/As ratios in a non-stoichiometric sulfidic layer were found. The products formed in the sweep to a potential of 0.6 V (Ag/AgCl) of the passivity region are shaped in about 100 nm protrusions of two sorts, which are arranged in micrometer-size separate areas, while they are largely mixed at higher, "transpassive" potentials. The quantities of surface alteration substances notably decrease after leaching in ferric chloride and ferric sulfate acidic solutions. Passivation of arsenopyrite was suggested to associate with the disordered, metal-deficient surface layer having moderate excess of sulfur rather than with the products of arsenopyrite oxidation. Exposure of arsenopyrite to 10 -5-10 -3 M AuCl4- (pH 2) solutions results in the deposition of 8-50 nm gold particles; only a small fraction of the gold is present as Au(I)-S species. The electrochemical oxidation at 0.6 V or ageing of arsenopyrite in air promotes the subsequent gold deposition; in contrast, the amount of Au deposited on arsenopyrite that was treated by leaching in ferric chloride and sulfate solutions was about 10 times smaller than with polished arsenopyrite samples. It has been concluded that reducing agents formed as intermediates of arsenopyrite decomposition facilitate the Au 0 cementation although other factors related to the surface state of the arsenopyrite play a role as well. A decrease in the tunneling current magnitudes with decreasing the Au 0 particle size has been revealed using STS. This effect along with the increase by 0.2-0.5 eV in the XPS Au 4f binding energies were tentatively ascribed to retarding the electron transitions by emerging electrostatic charge on gold nanoparticles (Coulomb blockade). Possible mechanisms for the effects, and their potential role in the deposition and hydrometallurgy of "invisible" gold are discussed.

  12. Wetting of GaN islands by excess Ga: Origin of different appearances of GaN islands in scanning tunneling microscopy

    International Nuclear Information System (INIS)

    We observe three different kinds of islands, namely the 'bare', 'ghost', and 'normal' islands, by scanning tunneling microscopy of GaN(0001) prepared under Ga-rich conditions with different excess Ga coverage. They correlate to three different growth regimes. The various morphologies of the islands are suggested to be due to different states of wetting of the surface by excess Ga. The dynamical behavior of the wetting process is followed, and an island size dependence of Ga wetting is noted

  13. In situ Control of Si/Ge Growth on Stripe-Patterned Substrates Using Reflection High-Energy Electron Diffraction and Scanning Tunneling Microscopy

    OpenAIRE

    Sanduijav B; Matei DG; Springholz G.

    2010-01-01

    Abstract Si and Ge growth on the stripe-patterned Si (001) substrates is studied using in situ reflection high-energy electron diffraction (RHEED) and scanning tunneling microscopy (STM). During Si buffer growth, the evolution of RHEED patterns reveals a rapid change of the stripe morphology from a multifaceted “U” to a single-faceted “V” geometry with {119} sidewall facets. This allows to control the pattern morphology and to stop Si buffer growth once a well-defined ...

  14. Scanning tunnelling microscopy images of the copper-containing amine oxidase from Arthrobacter globiformis in the holo and apo forms adsorbed on gold under ambient conditions

    OpenAIRE

    Contera, SA; Okajima, T; Iwasaki, H

    2002-01-01

    Dimeric Arthrobacter globiformis amine oxidase in the holo and apo forms adsorbed onto a Au (111) surface have been observed by scanning tunnelling microscopy (STM) under ambient conditions. Individual protein molecules denature as they adsorb onto a bare Au surface, although they keep a dual appearance. Tapping atomic force microscopy images of individual proteins correspond well with the STM ones in the lateral direction. STM voltage affects the distance between the units of the denatured p...

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

    Energy Technology Data Exchange (ETDEWEB)

    Zubkov, Evgeniy

    2013-09-01

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

  16. High Pressure Scanning Tunneling Microscopy Studies of Adsorbate Structure and Mobility during Catalytic Reactions. Novel Design of an Ultra High Pressure, High Temperature Scanning Tunneling Microscope System for Probing Catalytic Conversions

    International Nuclear Information System (INIS)

    The aim of the work presented therein is to take advantage of scanning tunneling microscope's (STM) capability for operation under a variety of environments under real time and at atomic resolution to monitor adsorbate structures and mobility under high pressures, as well as to design a new generation of STM systems that allow imaging in situ at both higher pressures (35 atm) and temperatures (350 C). The design of a high pressure, high temperature scanning tunneling microscope system, that is capable of monitoring reactions in situ at conditions from UHV and ambient temperature up to 1 atm and 250 C, is briefly presented along with vibrational and thermal analysis, as this system serves as a template to improve upon during the design of the new ultra high pressure, high temperature STM. Using this existing high pressure scanning tunneling microscope we monitored the co-adsorption of hydrogen, ethylene and carbon dioxide on platinum (111) and rhodium (111) crystal faces in the mTorr pressure range at 300 K in equilibrium with the gas phase. During the catalytic hydrogenation of ethylene to ethane in the absence of CO the metal surfaces are covered by an adsorbate layer that is very mobile on the time scale of STM imaging. We found that the addition of CO poisons the hydrogenation reaction and induces ordered structures on the single crystal surfaces. Several ordered structures were observed upon CO addition to the surfaces pre-covered with hydrogen and ethylene: a rotated (?19 x ?19)R23.4o on Pt(111), and domains of c(4 x 2)-CO+C2H3, previously unobserved (4 x 2)-CO+3C2H3, and (2 x 2)-3CO on Rh(111). A mechanism for CO poisoning of ethylene hydrogenation on the metal single crystals was proposed, in which CO blocks surface metal sites and reduces adsorbate mobility to limit adsorption and reaction rate of ethylene and hydrogen. In order to observe heterogeneous catalytic reactions that occur well above ambient pressure and temperature that more closely resemble industrial settings, a custom STM motor has been designed and constructed in-house. The new STM design features a much reduced size and a rigid coupling to the sample, and has been tested to show considerably higher resonance frequency than conventional tripod designs, providing the ability to image faster and yielding smaller susceptibility to noise. A flow reactor cell of much reduced volume for pressures up to 35 atmospheres has also been designed and constructed to house the new STM. The small volume reduces gas consumption and sensitivity to impurities in high pressure gases, as well as maximizes product concentration and reduces response time. The ability to flow reactant gases also allows for continuous monitoring of reaction mixture by mass spectrometry or gas chromatography, and permits correlation of structural information from STM and reaction kinetics. The reactor cell containing the STM is placed inside an UHV system to allow cleaning and characterization of sample before and after experiments, as well as continuous monitoring by mass spectrometry or gas chromatography through a leak valve. The new ultra high pressure system also allows in vacuo sample and tip exchange through a load lock, without exposing the system to impurities in air. This new ultra high pressure, high temperature STM system has been shown to perform with major improvements over the existing high pressure, high temperature STM system. Unlike the older system which requires extensive vibration damping setup in order to operate, the new system is shown to be less susceptible to noise, and be able to image atomic steps with no vibration isolation and atomically resolve highly ordered pyrolytic graphite with only spring suspension and a cut tip. Extensive vibrational analysis of the new system is presented, as well as an appendix of AutoCAD-generated design schematics for the major components of the system is included at the end

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

    International Nuclear Information System (INIS)

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

  18. Studying the dynamic behaviour of porphyrins as prototype functional molecules by scanning tunnelling microscopy close to room temperature.

    Science.gov (United States)

    Marbach, H; Steinrück, H-P

    2014-08-21

    Scanning tunnelling microscopy (STM) enables us to directly observe the dynamic behaviour of organic molecules on surfaces. While imaging atoms and molecules using STM is certainly fascinating by itself, corresponding temperature-dependent measurements allow for the quantitative determination of the energetics and kinetics of the underlying molecular surface processes. Herein, we review recent advances in the STM investigation of the dynamic behaviour of adsorbed porphyrins at and close to room temperature. Three different case studies are discussed, providing insight into the dynamics of diffusion, rotation, reaction, and molecular switching at surfaces, based on isothermal STM measurements. The reviewed examples demonstrate that variable temperature STM can be a suitable tool to directly monitor the dynamic behaviour of individual adsorbed molecules, at and close to room temperature. Free base porphyrins on Cu(111) proved to be particularly suitable for these studies due to the strong bonding interaction between the iminic nitrogen atoms in the porphyrin macrocycle and the Cu substrate atoms. As a consequence, the corresponding activation energies for surface diffusion, self-metalation reaction and conformational switching are of a magnitude that allows for monitoring the processes at and around room temperature, in contrast to most previous studies, which were performed at cryogenic temperatures. The kinetic analysis of the surface diffusion and self-metalation was performed using an Arrhenius approach, yielding the corresponding activation energies and preexponential factors. In contrast, the conformational switching process was analysed in the framework of transition state theory, based on the Eyring equation. This approach provides a more detailed insight into interpretable thermodynamic potentials, i.e., the enthalpic and entropic contributions to the activation barrier. The analysis shows that at room temperature the adsorption and switching behaviour of the investigated free base porphyrin on Cu(111) is dominated by entropic effects. Since the entropic energy contribution vanishes at low temperatures, the importance of experiments conducted at temperatures close to room temperature is emphasized. PMID:24867780

  19. 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.

    2003-01-01

    We have studied the adsorption and electrocatalysis of the redox metalloenzyme blue copper nitrite reductase from Achromobacter xylosoxidans (AxCuNiR) on single-crystal Au(111)-electrode surfaces modified by a self-assembled monolayer of cysteamine. A combination of cyclic voltammetry and in situ 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 on this surface could be detected. A strong cathodic catalytic wave appears in the presence of nitrite. The catalytic current follows a Michaelis-Menten pattern with a Michaelis constant of K-m approximate to 44 muM, which is close to the value for AxCuNiR in homogeneous solution. The apparent 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 coverage is low and the actual rate constant 120-220 s(-1) is much closer to the values in homogeneous solution. The results show that AxCuNiR can be brought to immobilization in a functional state on suitably modified, well-defined, atomically planar Au(111)-electrode surfaces. This would be important for forthcoming biotechnology at the monolayer and toward the single-molecule level.

  20. The nucleation and growth of uranium on the basal plane of graphite studied by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    For the first time, nanometer scale uranium clusters were created on the basal plane of highly oriented pyrolytic graphite by laser ablation under ultra-high vacuum conditions. The physical and chemical properties of these clusters were investigated by scanning tunneling microscopy (STM) as well as standard surface science techniques. Auger electron and X-ray photoelectron spectroscopies found the uranium deposit to be free of contamination and showed that no carbide had formed with the underlying graphite. Clusters with sizes ranging from 42 Angstrom 2 to 630 Angstrom 2 were observed upon initial room temperature deposition. Surface diffusion of uranium was observed after annealing the substrate above 800 K, as evidenced by the decreased number density and the increased size of the clusters. Preferential depletion of clusters on terraces near step edges as a result of annealing was observed. The activation energy for diffusion deduced from these measurements was found to be 15 Kcal/mole. Novel formation of ordered uranium thin films was observed for coverages greater than two monolayers after annealing above 900 K. These ordered films displayed islands with hexagonally faceted edges rising in uniform step heights characteristic of the unit cell of the P-phase of uranium. In addition, atomic resolution STM images of these ordered films indicated the formation of the ?-phase of uranium. The chemical properties of these surfaces were investigated and it was shown that these uranium films had a reduced oxidation rate in air as compared to bulk metal and that STM imaging in air induced a polarity-dependent enhancement of the oxidation rate

  1. Characterization of one-dimensional molecular chains of 4,4?-biphenyl diisocyanide on Au(111) by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    The morphology and electronic structure of vapor deposited 4,4?-biphenyldiisocyanide (BPDI) on a Au(111) surface were investigated using variable-temperature scanning tunneling microscopy. When deposited at room temperature, BPDI molecules form one-dimensional molecular chains similar to that recently observed for the structurally related 1,4-phenyl diisocyanide (PDI). Compared to PDI, the longer periodicity for the BPDI molecular chains is consistent with the addition of a second phenyl ring and supports a structural model in which the BPDI molecules lie parallel to the surface and interconnected by Au-adatoms. The molecular chains are mostly aligned along the [11-0] direction of the Au(111) substrate, but exhibit frequent changes in angle that are consistent with directions between fcc and hcp three-fold hollow sites. Dispersion-corrected density functional theory calculations for one-dimensional chains of BPDI molecules bound end-to-end via their isocyanide groups to Au-adatoms reproduce the observed periodicity of the chains and show that this morphology is energetically favored over upright binding with one free —NC group. The spatially resolved conductance (dI/dV) map for BPDI on Au(111) exhibits a feature centered at ?0.67 eV below the Fermi level which are delocalized along the chain with maxima at the Au-adatom and biphenyl positions. This occupied resonant feature is close to that previously observed for the PDI in both photoemission and conductance measurements and is attributed to an occupied interfacial state resulting from BPDI-Au interactions

  2. Improved TV-scanning method for recording time-resolved optical spectra of transients

    International Nuclear Information System (INIS)

    An improved method to record a time-resolved transient absorption or emission spectrum produced by a single pulse of radiation is described. A streak image of the spectrum is produced by an image-converter camera. The image is scanned by a TV camera, stored in a video-disk recorder, and transferred line by line to a computer. The computer can produce three-dimensional plots of absorbance or emission versus time and wavelength containing 100 x 100 data points. 19 figs

  3. Studies on switching mechanisms in Pd-nanodot embedded Nb{sub 2}O{sub 5} memristors using scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Hota, M.K., E-mail: mksan21@gmail.com [VLSI Engineering Laboratory, Department of Electronics and ECE, Indian Institute of Technology, Kharagpur 721302 (India); Bera, M.K., E-mail: m.k.bera.iitkgp@gmail.com [VLSI Engineering Laboratory, Department of Electronics and ECE, Indian Institute of Technology, Kharagpur 721302 (India); Verma, S. [Institute of Physics, Bhubaneswar 751005 (India); Maiti, C.K. [VLSI Engineering Laboratory, Department of Electronics and ECE, Indian Institute of Technology, Kharagpur 721302 (India)

    2012-08-31

    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 Nb{sub 2}O{sub 5} 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 Nb{sub 2}O{sub 5} memristors. The incorporation of Pd nanodots in Nb{sub 2}O{sub 5} 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: Black-Right-Pointing-Pointer STM technique has been applied to study the resistance switching. Black-Right-Pointing-Pointer Use of Pd nanodots enhances the switching in Nb{sub 2}O{sub 5} memristors. Black-Right-Pointing-Pointer Origin of switching is found to be due to multiple oxide states of Nb.

  4. Low energy x-ray spectra measured with a mercuric iodide energy dispersive spectrometer in a scanning electron microscope

    International Nuclear Information System (INIS)

    A mercuric iodide energy dispersive x-ray spectrometer, with Peltier cooling provided for the detector and input field effect transistor, has been developed and tested in a scanning electron microscope. X-ray spectra were obtained with the 15 keV electron beam. An energy resolution of 225 eV (FWHM) for Mn-K/sub ?/ at 5.9 keV and 195 eV (FWHM) for Mg-K line at 1.25 keV has been measured. Overall system noise level was 175 eV (FWHM). The detector system characterization with a carbon target demonstrated good energy sensitivity at low energies and lack of significant spectral artifacts at higher energies. 16 refs., 5 figs

  5. 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

    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 sweep, LSV, cyclic, CV, and square wave (SQWV) voltammetry. Multifarious electrochemical patterns were observed. Most attention was given to reductive desorption caused by insulin binding to the Au-surfaces via up to three disulfide groups per insulin monomer, presumably converted to single Au-S links. 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 followed the order Au(110) > Au(100) > Au(111) and differs from the reductive desorption order that records the Au-S bondingelement. Evenly distributed single molecules were scattered over large Au(111)-terraces, with intriguing molecular arrays disclosed near the terrace edges. In comparison, high-density molecular scale structures were observed both over the terraces and across terrace edges on Au(100). Larger rectangular structures also appeared (8-12% coverage). These are Au-islands from the lift of the reconstruction. Notably, 10 x 10 nm(2) patches of highly ordered much smaller structures, possibly from insulin decomposition emerged sporadically within the dense insulin adlayer. Insulin adsorbed in highest coverage on the Au(110) and followed the directional surface topology with insulin molecules aligned in the Au(110)-surface grooves, occasionally "spilling over" and merging into larger structures. 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 mapping of the insulin monomer/dimer-hexamer interconversion.

  6. Surface roughness and surface-induced resistivity of gold films on mica: Application of quantitative scanning tunneling microscopy

    Science.gov (United States)

    Munoz, Raúl C.; Vidal, Guillermo; Mulsow, Marcelo; Lisoni, Judit G.; Arenas, Claudio; Concha, Andres; Mora, Fernando; Espejo, Roberto; Kremer, Germán; Moraga, Luis; Esparza, Rolando; Haberle, Patricio

    2000-08-01

    We report measurements of the resistivity ?(T) of a gold film 70 nm thick deposited on mica preheated to 300 °C in UHV, performed between 4 and 300 K, and measurements of the surface topography of the same film performed with a scanning tunneling microscope (STM). From the roughness measured with the STM we determine the parameters ? (rms amplitude) and ? (lateral correlation length) corresponding to a Gaussian representation of the average height-height autocorrelation function (ACF). We use the parameters ? and ? to calculate the quantum reflectivity R and the increase in resistivity induced by electron-surface scattering on this film, according to a modified version of the theory of Sheng, Xing, and Wang (mSXW) [Munoz et al., J. Phys.: Condens. Matter 11, L299 (1999)]. The mSXW theory is able to select the appropriate scale of distance over which corrugations take place, leading to R~1 for corrugations taking place over scales of distances that are long when compared to a few Fermi wavelength ?F, and R<1 for corrugations taking place over scales of distances that are comparable to ?F (to within an order of magnitude). The reflectivity R determined by corrugations ocurring over a scale of distances comparable to ?F approaches zero for a certain angle. The resistivity ?(T) of the film increases by roughly a factor of 4 between 4 and 300 K, and so does the bulk resistivity ?0(T) predicted by mSXW theory. With the parameters ? and ? measured on our 70-nm film, we reproduced approximately the thickness and temperature dependence of the resistivity (between 4 and 300 K) of several gold films on mica reported by Sambles, Elsom, and Jarvis [Philos. Trans. R. Soc. London, Ser. A 304, 365 (1982)], without using any adjustable parameters. The results of this paper suggest that the relevant quantities controlling electron-surface scattering in continuous gold films of arbitrary thickness, are the parameters ? and ? describing the average ACF that characterizes the surface of the sample on a nanoscopic scale, in agreement with the accepted view regarding the conductivity of ultrathin films.

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

    Science.gov (United States)

    Klappenberger, Florian

    2014-02-01

    Functional molecular nanoarchitectures (FMNs) are highly relevant for the development of future nanotechnology devices. Profound knowledge about the atomically controlled construction of such nanoscale assemblies is an indispensable requirement to render the implementation of such components into a real product successful. For exploiting their full potential the architectures’ functionalities have to be characterized in detail including the ways to tailor them. In recent years a plethora of sophisticated constructs were fabricated touching a wide range of research topics. The present review summarizes important achievements of bottom-up fabricated, molecular nanostructures created on single crystal metal surfaces under ultra-high vacuum conditions. This selection focuses on examples where self-assembly mechanisms played a central role for their construction. Such systems, though typically quite complex, can be comprehensively understood by the STM+XS approach combining scanning tunneling microscopy (STM) with X-ray spectroscopy (XS) and being aided in the atomic interpretation by the appropriate theoretic analysis, often from density functional theory. The symbiosis of the techniques is especially fruitful because of the complementary character of the information accessed by the local microscopy and the space-averaging spectroscopy tools. STM delivers sub-molecular spatial-resolution, but suffers from limited sensitivity for the chemical and conformational states of the building-blocks. XS compensates these weaknesses with element- and moiety-specific data, which in turn would be hard to interpret with respect to structure formation without the topographic details revealed by STM. The united merit of this methodology allows detailed geometric information to be obtained and addresses both the electronic and chemical state of the complex organic species constituting such architectures. Thus, possible changes induced by the various processes such as surface interaction, thermal annealing, or molecular recognition can be followed with unprecedented level of detail. The well-understood nanoarchitecture construction protocols often rely on the ‘classic’ supramolecular interactions, namely hydrogen bonding and metal-organic coordination. Further examples include rarely encountered special cases where substrate-mediated processes or repulsive forces drive the emergence of order. The demonstrated functionalities include tuning of the electronic structure by confining surface state electrons and atomically defined arrays of magnetic complexes. Moreover, the high-quality templates can be utilized for imposing novel thin film growth modes or act as basic constituents of nanoswitches. Finally, the aptitude of the STM+XS approach for the emerging field of creating nanoarchitectures by on-surface covalent coupling is addressed.

  8. Surface species formed by the adsorption and dissociation of water molecules on Ru(0001) surface containing a small coverage of carbon atoms studied by scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Dept of Materials Science and Engineering UCB; Dept of Applied Science and Technology, UCB; Institut de Ciencia de Materials de Barcelona, Barcelona, Spain; Instituto de Ciencia de Materiales de Madrid, Madrid, Spain; Department of Mechanical Engineering, Yale University; Salmeron, Miquel; Shimizu, Tomoko K.; Mugarza, Aitor; Cerda, Jorge I.; Heyde, Markus; Qi, Yabing; Schwarz, Udo D.; Ogletree, D. Frank; Salmeron, Miquel

    2008-04-26

    The adsorption and dissociation of water on a Ru(0001) surface containing a small amount ({le} 3 %) of carbon impurities was studied by scanning tunneling microscopy (STM). Various surface species are formed depending on the temperature. These include molecular H{sub 2}O, H{sub 2}O-C complexes, H, O, OH and CH. Clusters of either pure H{sub 2}O or mixed H{sub 2}O-OH species are also formed. Each of these species produces a characteristic contrast in the STM images and can be identified by experiment and by ab initio total energy calculations coupled with STM image simulations. Manipulation of individual species via excitation of vibrational modes with the tunneling electrons has been used as supporting evidence.

  9. Probing the limits of Si:P ?-doped devices patterned by a scanning tunneling microscope in a field-emission mode

    Energy Technology Data Exchange (ETDEWEB)

    Rudolph, M.; Carr, S. M.; Ten Eyck, G.; Dominguez, J.; Carroll, M. S.; Bussmann, E. [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Subramania, G. [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, New Mexico 87131 (United States); Lilly, M. P. [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Pluym, T.

    2014-10-20

    Recently, a single atom transistor was deterministically fabricated using phosphorus in Si by H-desorption lithography with a scanning tunneling microscope (STM). This milestone in precision, achieved by operating the STM in the conventional tunneling mode, typically utilizes slow (?10{sup 2}?nm{sup 2}/s) patterning speeds. By contrast, using the STM in a high-voltage (>10?V) field-emission mode, patterning speeds can be increased by orders of magnitude to ?10{sup 4}?nm{sup 2}/s. We show that the rapid patterning negligibly affects the functionality of relatively large micron-sized features, which act as contacting pads for these devices. For nanoscale structures, we show that the resulting electrical transport is consistent with the donor incorporation chemistry constraining the electrical dimensions to a scale of 10?nm even though the pattering spot size is 40?nm.

  10. Probing the limits of Si:P ?-doped devices patterned by a scanning tunneling microscope in a field-emission mode

    International Nuclear Information System (INIS)

    Recently, a single atom transistor was deterministically fabricated using phosphorus in Si by H-desorption lithography with a scanning tunneling microscope (STM). This milestone in precision, achieved by operating the STM in the conventional tunneling mode, typically utilizes slow (?102?nm2/s) patterning speeds. By contrast, using the STM in a high-voltage (>10?V) field-emission mode, patterning speeds can be increased by orders of magnitude to ?104?nm2/s. We show that the rapid patterning negligibly affects the functionality of relatively large micron-sized features, which act as contacting pads for these devices. For nanoscale structures, we show that the resulting electrical transport is consistent with the donor incorporation chemistry constraining the electrical dimensions to a scale of 10?nm even though the pattering spot size is 40?nm.

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

    Energy Technology Data Exchange (ETDEWEB)

    Krueger, David

    2009-12-02

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

  12. Superconducting vortex profile from fixed point measurements The Lazy Fisherman tunnelling microscopy method

    OpenAIRE

    Kohen, A.; Cren, T.; Proslier, Th.; Noat, Y.; Giubileo, F.; Bobba, F.; Cucolo, A. M.; Zhigadlo, W. Sacks D. Roditchev N.; Kazakov, S. M.; Karpinski, J.

    2005-01-01

    We introduce a mode of operation for studying the vortex phase in superconductors using scanning tunnelling microscopy (STM). While in the conventional STM method, the tip is scanned over a sample in which a fixed vortex pattern is prepared, in our "Lazy Fisherman" method the STM tip is kept fixed at a selected location while the vortices are being moved by varying the applied magnetic field. By continuously acquiring the local tunnelling conductance spectra, dI/dV(V), we de...

  13. The study of in situ scanning tunnelling microscope characterization on GaN thin film grown by plasma assisted molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Yang, R.; Krzyzewski, T.; Jones, T. [Department of Chemistry, University of Warwick, Coventry CV4 7AL (United Kingdom)

    2013-03-18

    The epitaxial growth of GaN by Plasma Assisted Molecular Beam Epitaxy was investigated by Scanning Tunnelling Microscope (STM). The GaN film was grown on initial GaN (0001) and monitored by in situ Reflection High Energy Electron Diffraction and STM during the growth. The STM characterization was carried out on different sub-films with increased thickness. The growth of GaN was achieved in 3D mode, and the hexagonal edge of GaN layers and growth gradient were observed. The final GaN was of Ga polarity and kept as (0001) orientation, without excess Ga adlayers or droplets formed on the surface.

  14. Defeitos superficiais em 2H-WS2 observados por microscopia de tunelamento / Surface defects on 2H-WS2 detected by scanning tunnelling microscopy

    Scientific Electronic Library Online (English)

    F., Wypych; Th., Weber; R., Prins.

    1998-02-01

    Full Text Available [...] Abstract in english Scanning tunnelling microscopy (STM) was used to characterise the basal surface of fresh cleaved crystals of 2H-WS2. Although no impurity or stacking faults could be detected by X-ray diffraction, STM images obtained with negative bias voltage showed two kinds of defects. These defects were attribut [...] ed to an iodine derivative used as transport agent. In a flat surface free of defects, an image with atomic resolution was achieved with sulphur distances and angles as expected for hexagonal symmetry of 2H-WS2.

  15. Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy.

    Science.gov (United States)

    Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R

    2014-04-01

    Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without breaking vacuum, and convenient visual access to the sample and tip inside a superconducting magnet cryostat. A sample/tip handling system is optimized for both the molecular beam epitaxy growth system and the scanning tunneling microscope system. The sample/tip handing system enables in situ STM studies on epitaxially grown samples, and tip exchange in the superconducting magnet cryostat. The hybrid molecular beam epitaxy and low temperature scanning tunneling microscopy system is capable of growing semiconductor-based hetero-structures with controlled accuracy down to a single atomic-layer and imaging them down to atomic resolution. PMID:24784613

  16. Electrochemistry and in situ scanning tunnelling microscopy of pure and redox-marked DNA- and UNA-based oligonucleotides on Au(111)-electrode surfaces

    DEFF Research Database (Denmark)

    Hansen, Allan G; Salvatore, Princia; Karlsen, Kasper K; Nichols, Richard John; Wengel, Jesper; Ulstrup, Jens

    2013-01-01

    We have studied adsorption and electrochemical electron transfer of several 13- and 15-base DNA and UNA (unlocked nucleic acids) oligonucleotides (ONs) linked to Au(111)-electrode surfaces via a 5'-C6-SH group using cyclic voltammetry (CV) and scanning tunnelling microscopy in aqueous buffer under electrochemical potential control (in situ STM). 2,2',6',2''-Terpyridine (terpy) onto which the transition metal ions Fe(2+/3+), Os(2+/3+) and Ru(2+/3+) could be coordinated after UNA monolayer formati...

  17. Electrochemistry and in situ scanning tunnelling microscopy of pure and redox-marked DNA- and UNA-based oligonucleotides on Au(111)-electrode surfaces

    DEFF Research Database (Denmark)

    Hansen, Allan Glargaard; Salvatore, Princia; Karlsen, K.; Nichols, R.; Wengel, Jesper; Ulstrup, Jens

    2013-01-01

    We have studied adsorption and electrochemical electron transfer of several 13- and 15-base DNA and UNA (unlocked nucleic acids) oligonucleotides (ONs) linked to Au(111)-electrode surfaces via a 50-C6-SH group using cyclic voltammetry (CV) and scanning tunnelling microscopy in aqueous buffer under electrochemical potential control (in situ STM). 2,20,60,200-Terpyridine (terpy) onto which the transition metal ions Fe2+/3+, Os2+/3+ and Ru2+/3+ could be coordinated after UNA monolayer formation was...

  18. Surface imaging by scanning tunneling microscopy of C60/70 thin films on Au(111) with different C60/C70 ratios

    International Nuclear Information System (INIS)

    Fullerene thin films have been prepared on Au(111) substrates by sublimation from fullerene powders with different C60 / C70 ratios. Scanning tunneling microscopy (STM) images of the film surfaces show a hexagonal lattice built-up of two types of ball-shaped molecules (differing in diameter and corrugation). The ratio of smaller to larger balls compares well with the C60 / C70 ratio determined by high pressure liquid chromatography (HPLC) on hexane solutions of the respective fullerene powders. STM images show defects such as vacancies, interstitials and boundaries between different stacking domains (ABC and CBA). Dynamic displacement of C70 molecules and vacancies is observed. (orig.)

  19. Lateral ordering of PTCDA on the clean and the oxygen pre-covered Cu(100) surface investigated by scanning tunneling microscopy and low energy electron diffraction

    OpenAIRE

    Gärtner, Stefan; Fiedler, Benjamin; Bauer, Oliver; Marele, Antonela; Sokolowski, Moritz M

    2014-01-01

    We have investigated the adsorption of perylene-3,4,9,10-tetracarboxylic acid dianhydride (PTCDA) on the clean and on the oxygen pre-covered Cu(100) surface [referred to as (?2 × 2?2)R45° – 2O/Cu(100)] by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). Our results confirm the (4?2 × 5?2)R45° superstructure of PTCDA/Cu(100) reported by A. Schmidt et al. [J. Phys. Chem. 1995, 99,11770–11779]. However, contrary to Schmidt et al., we have no indication for a ...

  20. Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy

    International Nuclear Information System (INIS)

    Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without breaking vacuum, and convenient visual access to the sample and tip inside a superconducting magnet cryostat. A sample/tip handling system is optimized for both the molecular beam epitaxy growth system and the scanning tunneling microscope system. The sample/tip handing system enables in situ STM studies on epitaxially grown samples, and tip exchange in the superconducting magnet cryostat. The hybrid molecular beam epitaxy and low temperature scanning tunneling microscopy system is capable of growing semiconductor-based hetero-structures with controlled accuracy down to a single atomic-layer and imaging them down to atomic resolution

  1. Scanning tunneling microscope study of striated carbon ridges in few-layer epitaxial graphene formed on 4H-silicon carbide (0001xAF)

    Science.gov (United States)

    Harrison, S. E.; Capano, M. A.; Reifenberger, R.

    2010-02-01

    Atomically resolved scanning tunneling microscope images of carbon ridge defects found in few-layer graphene formed on the C-face (0001¯) of 4H-silicon carbide reveal a striated exterior surface formed from out-of-plane distortions of the hexagonal graphene lattice. While ridge formation is likely explained by compressive in-plane stresses coupled with the small values of the bending modulus for few-layer graphene, the striated structure along the ridges argues for a localized unidirectional stress in the material directed along the ridge length.

  2. Scanning tunneling microscope study of striated carbon ridges in few-layer epitaxial graphene formed on 4H-SiC(000-1)

    Science.gov (United States)

    Harrison, Sara; Capano, Michael; Reifenberger, Ron

    2010-03-01

    Scanning tunneling microscopy (STM) is used to study carbon ridge defects found in few-layer graphene formed on the C-face of 4H-SiC(000-1) at growth temperatures between 1475 C and 1550 C. STM images reveal that ridges are characterized by a striated exterior surface formed from out-of-plane distortions in the hexagonal graphene lattice. While ridge formation is likely explained by compressive in-plane stresses and small values of the bending modulus for few-layer graphene, the striated structure along the ridges argues for a localized unidirectional stress in the material directed along the ridge length.

  3. Self-Assembly of TBrPP-Co Molecules on an Ag/Si(111) Surface Studied by Scanning Tunneling Microscopy

    International Nuclear Information System (INIS)

    Self-assembly of TBrPP-Co molecules on a Si(111)-?3 × ?3 Ag substrate is studied by low-temperature scanning tunneling microscopy. With the same adsorbed amount (0.07 ML), the molecules deposited by low-temperature evaporation show three kinds of ordered structures whereas those deposited by high-temperature evaporation have size-dependent ordered structures. The distinct differences in the self-assembly structures and in the electron density of states inside the molecule near the Fermi energy demonstrate that the Br atoms of the molecule desorb at the higher evaporation temperature. (condensed matter: structure, mechanical and thermal properties)

  4. Collective Modes and Structural Modulation in Ni-Mn-Ga(Co) Martensite Thin Films Probed by Femtosecond Spectroscopy and Scanning Tunneling Microscopy

    Science.gov (United States)

    Schubert, M.; Schaefer, H.; Mayer, J.; Laptev, A.; Hettich, M.; Merklein, M.; He, C.; Rummel, C.; Ristow, O.; Großmann, M.; Luo, Y.; Gusev, V.; Samwer, K.; Fonin, M.; Dekorsy, T.; Demsar, J.

    2015-08-01

    The origin of the martensitic transition in the magnetic shape memory alloy Ni-Mn-Ga has been widely discussed. While several studies suggest it is electronically driven, the adaptive martensite model reproduced the peculiar nonharmonic lattice modulation. We used femtosecond spectroscopy to probe the temperature and doping dependence of collective modes, and scanning tunneling microscopy revealed the corresponding static modulations. We show that the martensitic phase can be described by a complex charge-density wave tuned by magnetic ordering and strong electron-lattice coupling.

  5. Glancing-incidence and - take-off X-ray fluorescence and scanning tunnelling microscopy of thin films under X-ray irradiation

    International Nuclear Information System (INIS)

    We have measured Au and Ni thin films on a quartz glass using both scanning tunnelling microscopy (STM) and glancing-incidence and -take-off x-ray fluorescence (GIT-XRF). The STM image shows that the film surface consists of grains of several tens of nanometres in size. Although the GIT-XRF method utilizes a total reflection phenomenon which occurs on a flat surface, a surface roughness of 10 nm does not affect the GIT-XRF analysis. Moreover, we demonstrate for the first time that STM observation is possible under x-ray irradiation. (Author)

  6. Power spectra and auto correlation analysis of hyperfine-induced long period oscillations in the tunneling current of coupled quantum dots

    International Nuclear Information System (INIS)

    We outline power spectra and auto correlation analysis performed on temporal oscillations in the tunneling current of coupled vertical quantum dots. The current is monitored for ?2325 s blocks as the magnetic field is stepped through a high bias feature displaying hysteresis and switching: hallmarks of the hyperfine interaction. Quasi-periodic oscillations of ?2 pA amplitude and of ?100 s period are observed in the current inside the hysteretic feature. Compared to the baseline current outside the hysteretic feature the power spectral density is enhanced by up to three orders of magnitude and the auto correlation displays clear long lived oscillations about zero

  7. A combined frequency modulation dynamic force microscopy (FM-DFM) and scanning tunneling microscopy (STM) study of a SiO2/Ru(0001) model system

    International Nuclear Information System (INIS)

    Silica based support materials play an important role in catalysis. A stable and well characterized crystalline silica film can act as a model system for bulk silica and help us to understand silica's properties in detail. In order to examine catalytically relevant processes on such model surfaces, a thorough investigation of defect sites of any form is eminent. Recently, a double-layer silica film could be prepared on Ru(0001). Here we used a combined frequency modulation dynamic force microscope (FM-DFM) and scanning tunneling microscope (STM) under low temperature and ultra-high vacuum conditions to unveil the thin film's structural and electronic surface properties. Atomically resolved images of the crystalline silica film grown on Ru(0001) are presented. Structural elements of the pristine film, as well as its defects, are highlighted. Based on atomic resolution FM-DFM and STM images a direct comparison with density functional theory calculation can be made. Theory as well as experiment favor a hexagonal honeycomb structure of the film. Spectroscopy measurements, i.e. scanning tunneling spectroscopy (STS) and Kelvin probe force microscopy (KPFM), provide first insights into electronic properties of the system.

  8. Investigation of surface defect states in CeO{sub 2-y} nanocrystals by Scanning?tunneling microscopy/spectroscopy and ellipsometry

    Energy Technology Data Exchange (ETDEWEB)

    Radovi?, Marko; Stojadinovi?, Bojan; Tomi?, Nataša; Golubovi?, Aleksandar; Doh?evi?-Mitrovi?, Zorana, E-mail: zordoh@ipb.ac.rs [Institute of Physics, Pregrevica 118, University of Belgrade, 11 000 Belgrade (Serbia); Matovi?, Branko [Institute for Nuclear sciences “Vin?a,” Materials Science Laboratory, University of Belgrade, 11 000 Belgrade (Serbia); Veljkovi?, Ivana [Institute for Multidisciplinary Research, Kneza Viseslava 1a, University of Belgrade, 11 000 Belgrade (Serbia)

    2014-12-21

    Synthesis process strongly influences the nanocrystalline CeO{sub 2-y} defective structure. The presence of surface defects, in the form of oxygen vacancies in different charge states (F centers), can change the electronic properties of ceria nanocrystals. Nanocrystalline CeO{sub 2-y} samples were synthesized using three different methods (precipitation, self-propagating room temperature, and hydrothermal synthesis). Raman spectroscopy was used to identify the presence of oxygen vacancies which presumably were formed at the nanoparticle surface. The defect concentration depended on the crystallite size of differently prepared CeO{sub 2-y} samples. Scanning tunneling microscopy/spectroscopy and ellipsometry were employed to investigate the electronic band structure of defective CeO{sub 2-y} nanocrystals. Scanning tunneling spectroscopy measurements demonstrated that inside the band gap of CeO{sub 2-y} nanocrystals, besides the filled 4 f states, appeared additional states which were related to occupied and empty F center defect states. From the ellipsometric measurements, using the critical points model, the energy positions of different F centers states and the values of the reduced band gap energies were determined. The analysis of obtained data pointed out that depending on the synthesis method, different types of F centers (F{sup +} and F{sup 0}) can be formed in the CeO{sub 2-y} nanocrystals. The formation of different F center defect states inside the ceria gap have a strong impact on the electrical, optical, and magnetic properties of ceria nanocrystals.

  9. Voltammetry and in situ scanning tunnelling spectroscopy of osmium, iron, and ruthenium complexes of 2,2?:6?,2??-terpyridine covalently linked to Au(111)-electrodes

    DEFF Research Database (Denmark)

    Salvatore, Princia; Hansen, Allan Glargaard

    2011-01-01

    We have studied self-assembled molecular monolayers (SAMs) of complexes between Os(ii)/(iii), Fe(ii)/(iii), and Ru(ii)/(iii) and a 2,2?,6?,2??-terpyridine (terpy) derivative linked to Au(111)-electrode surfaces via a 6-acetylthiohexyloxy substituent at the 4?-position of terpy. The complexes were prepared in situ by first linking the terpy ligand to the surface via the S-atom, followed by addition of suitable metal compounds. The metal-terpy SAMs were studied by cyclic voltammetry (CV), and in situ scanning tunnelling microscopy with full electrochemical potential control of substrate and tip (in situ STM). Sharp CV peaks were observed for the Os- and Fe complexes, with interfacial electrochemical electron transfer rate constants of 6–50 s?1. Well-defined but significantly broader peaks (up to 300 mV) were observed for the Ru-complex. Addition of 2,2?-bipyridine (bipy) towards completion of the metal coordination spheres induced voltammetric sharpening. In situ STM images of single molecular scale strong structural features were observed for the osmium and iron complexes. As expected from the voltammetric patterns, the surface coverage was by far the highest for the Ru-complex which was therefore selected for scanning tunnelling spectroscopy. These correlations displayed a strong peak around the equilibrium potential with systematic shifts with increasing bias voltage, as expected for a sequential two-step in situ ET mechanism.

  10. Investigation of surface defect states in CeO2-y nanocrystals by Scanning-tunneling microscopy/spectroscopy and ellipsometry

    Science.gov (United States)

    Radovi?, Marko; Stojadinovi?, Bojan; Tomi?, Nataša; Golubovi?, Aleksandar; Matovi?, Branko; Veljkovi?, Ivana; Doh?evi?-Mitrovi?, Zorana

    2014-12-01

    Synthesis process strongly influences the nanocrystalline CeO2-y defective structure. The presence of surface defects, in the form of oxygen vacancies in different charge states (F centers), can change the electronic properties of ceria nanocrystals. Nanocrystalline CeO2-y samples were synthesized using three different methods (precipitation, self-propagating room temperature, and hydrothermal synthesis). Raman spectroscopy was used to identify the presence of oxygen vacancies which presumably were formed at the nanoparticle surface. The defect concentration depended on the crystallite size of differently prepared CeO2-y samples. Scanning tunneling microscopy/spectroscopy and ellipsometry were employed to investigate the electronic band structure of defective CeO2-y nanocrystals. Scanning tunneling spectroscopy measurements demonstrated that inside the band gap of CeO2-y nanocrystals, besides the filled 4 f states, appeared additional states which were related to occupied and empty F center defect states. From the ellipsometric measurements, using the critical points model, the energy positions of different F centers states and the values of the reduced band gap energies were determined. The analysis of obtained data pointed out that depending on the synthesis method, different types of F centers (F+ and F0) can be formed in the CeO2-y nanocrystals. The formation of different F center defect states inside the ceria gap have a strong impact on the electrical, optical, and magnetic properties of ceria nanocrystals.

  11. Investigation of surface defect states in CeO2-y nanocrystals by Scanning?tunneling microscopy/spectroscopy and ellipsometry

    International Nuclear Information System (INIS)

    Synthesis process strongly influences the nanocrystalline CeO2-y defective structure. The presence of surface defects, in the form of oxygen vacancies in different charge states (F centers), can change the electronic properties of ceria nanocrystals. Nanocrystalline CeO2-y samples were synthesized using three different methods (precipitation, self-propagating room temperature, and hydrothermal synthesis). Raman spectroscopy was used to identify the presence of oxygen vacancies which presumably were formed at the nanoparticle surface. The defect concentration depended on the crystallite size of differently prepared CeO2-y samples. Scanning tunneling microscopy/spectroscopy and ellipsometry were employed to investigate the electronic band structure of defective CeO2-y nanocrystals. Scanning tunneling spectroscopy measurements demonstrated that inside the band gap of CeO2-y nanocrystals, besides the filled 4 f states, appeared additional states which were related to occupied and empty F center defect states. From the ellipsometric measurements, using the critical points model, the energy positions of different F centers states and the values of the reduced band gap energies were determined. The analysis of obtained data pointed out that depending on the synthesis method, different types of F centers (F+ and F0) can be formed in the CeO2-y nanocrystals. The formation of different F center defect states inside the ceria gap have a strong impact on the electrical, optical, and magnetic properties of ceria nanocrystals

  12. Ultrasonic lateral modulation imaging, speckle reduction, and displacement vector measurements using simple single-beam scanning or plural crossed-beam scanning with new spectra frequency division processing methods

    Directory of Open Access Journals (Sweden)

    Sumi C

    2012-10-01

    Full Text Available Chikayoshi Sumi, Yousuke IshiiDepartment of Information and Communication Sciences, Faculty of Science and Technology, Sophia University, Tokyo, JapanAbstract: The development of effective ultrasonic tissue displacement measurement methods increases the number of possible applications for various tissue displacement and strain measurements. These applications include measurements of spontaneous motions/deformations generated by heart motion; pulsations from phenomena such as blood flow (intracardiac, intravascular, and carotid; heart, blood vessel, and liver motion; and motion from artificial sources such as motions/deformations generated by applying static compression/stretching forces, vibration or acoustic radiation forces (breast and liver. For arbitrary orthogonal coordinate systems obtained using arbitrary transducer types (eg, linear, convex, sector, arc, or radial array types, or single aperture types with a mechanical scan, several lateral modulation (LM methods (eg, scanning with plural crossed or steered beams over a region of interest have been developed that can be used with new echo imaging methods for tissue displacement/deformation measurements. Specifically, by using such beamforming methods, in addition to highly accurate displacement vector and lateral displacement measurements, LM echo imaging with a high lateral carrier frequency and a high lateral resolution has been developed. Another new beamforming method, referred to as “a steering angle (ASTA method,” ie, scanning with a defined steering angle, is also described. In addition to conventional non-steered-beam scanning (ie, a version of ASTA and conventional steered-beam scanning with a variable steering angle (eg, sector, arc, radial scan, a simple, single-beam scanning method also permits the use of LM, which yields an accurate displacement vector measurement with fewer calculations than the original LM methods. This is accomplished by using a previously developed spectra frequency division method (SFDM. However, the lateral carrier frequency and the measurement accuracy acquired by using such a single-beam scanning method are lower than those achieved with the original LM scanning methods and should be increased (ie, by using a quasi-LM method. In this report, the effectiveness of the use of the new SFDMs is verified with experiments on agar phantoms, in which conventional non-steered, focused single-beam transmission/reception scanning is performed together with high-speed non-steered single plane-wave transmission and non-steered, focused single-beam reception scanning using a linear array-type transducer. For comparison, the original LMs, with their respective transmissions of crossed, steered focused beams and plane waves are also performed. Because the use of rectangular apodization functions (ie, no apodization yields a larger bandwidth in a lateral direction than the effective use of parabolic functions with the original LM method, it is shown that disregarding the lateral low-frequency spectra yields useful quasi-LM echo imaging with a high lateral frequency, and further significantly increases the measurement accuracy of a displacement vector. In addition, when no apodization is used with the original version of LM, disregarding the low-frequency lateral spectra is effective. In addition, the interchangeability of cosine and sine modulations performed after completing beamforming can also be used for single-beam scanning as well as for the original LM scanning method. Specifically, the cosine and sine modulations, respectively, are used for LM and quasi-LM imaging and displacement vector measurements. It is concluded that the appropriate use of the new SFDMs with simple single-beam scanning or with simple plural crossed-beam scanning with no apodization can achieve almost the same accuracy as the original LM scanning method using plural crossed beams with the effective apodization. Another new application of SFDM is also described: an incoherent superposition of the frequency-divided spectra reduces spec

  13. Electronic Structure on (001) Surface of BaFe2As2 Parent Compound Studied with Scanning Tunneling Spectroscopy

    Science.gov (United States)

    Jayasundara, D. R.; Li, A.; Xuan, Y.; O'Neal, J. P.; Pan, S. H.; Jin, R.; Plummer, E. W.; Jin, R.; Sefat, A. S.; McGuire, M. A.; Sales, B. C.; Mandrus, D.

    2009-03-01

    Doping can drive some metallic pnictide compounds to superconducting phase. The microscopic mechanism of this phase transition has still not been understood. Starting with the parent compound, we have used a UHV Low Temperature STM to study the density of states on the (001) surface of single crystal BaFe2As2. The tunneling spectrum varies depending on the local environment. All the spectrums have the same background with density of states depression near the Fermi energy, but some of them show different anomalies. We attribute some of these anomalies to surface states. These results may provide useful information to those surface techniques other than STM.

  14. Electronic disorder of P- and B-doped Si at the metal–insulator transition investigated by scanning tunnelling microscopy and electronic transport

    International Nuclear Information System (INIS)

    The (111)-2 × 1 surface of in situ cleaved heavily P- or B-doped Si is investigated by scanning tunnelling microscopy and spectroscopy at room temperature and at low temperature. P atoms have been identified on different sites of the Si(111)-2 × 1 surface by their characteristic voltage-dependent contrast for positive as well as negative buckling of the ?-bonded chains. The distributions of dopants per surface area and of nearest-neighbour distances are found to be in agreement with a random arrangement of dopants in Si up to doping levels well above the metal–insulator transition. In addition, P atoms have been identified by their depth-dependent contrast down to the third layer beneath the surface with a volume density in agreement with the bulk doping density. The random electronic disorder supports the view of an Anderson transition driven by disorder close to the critical concentration or critical uniaxial stress. (paper)

  15. Simulation of spin-polarized scanning tunneling microscopy on complex magnetic surfaces: The case of a Cr monolayer on Ag(111)

    CERN Document Server

    Palotás, Krisztián; Szunyogh, László

    2011-01-01

    We propose an atom-superposition-based method for simulating spin-polarized scanning tunneling microscopy (SP-STM) from first principles. Our approach provides bias dependent STM images in high spatial resolution, with the capability of using either constant current or constant height modes of STM. In addition, topographic and magnetic contributions can clearly be distinguished, which are directly comparable to results of SP-STM experiments in the differential magnetic mode. Advantages of the proposed method are that it is computationally cheap, it is easy to parallelize, and it can employ the results of any ab initio electronic structure code. Its capabilities are illustrated for the prototype frustrated hexagonal antiferromagnetic system, Cr monolayer on Ag(111) in a noncollinear magnetic $120^{\\circ}$ N\\'eel state. We show evidence that the magnetic contrast is sensitive to the tip electronic structure, and this contrast can be reversed depending on the bias voltage.

  16. Thermal stress in the scanning tunneling microscopy of the metallic heterostructure lead on copper(111); Thermospannung bei der Rastertunnelmikroskopie der metallischen Heterostruktur Blei auf Kupfer(111)

    Energy Technology Data Exchange (ETDEWEB)

    Langenkamp, Winfried

    2008-02-22

    The thermal stress, which arises, when tip and sample of a scanning tunneling microscope have different temperatures, was studied in the system lead on copper(111). Thereby atomic resolution on the 4 x 4 superstructure of the lead atoms of the first layer was reached. The thermal stress of lead island was studied because the electronic density of states here is in the greatest part determined by quantum pot states. The density of states as function of the energy can by approached as step function und is by this available for a mathematical modelling. As sum of the influence of the substrates and the influence by the quantum pot states it bas possible to develop a model. in which the thermal stress for lead islands on copper(111) can be described also quantitatively.

  17. Local stabilization of single-walled carbon nanotubes on Si(100)-2 x 1:H via nanoscale hydrogen desorption with an ultrahigh vacuum scanning tunnelling microscope

    International Nuclear Information System (INIS)

    An ultrahigh vacuum scanning tunnelling microscope (UHV-STM) was used to modify the interface between isolated ?10 A-diameter single-walled carbon nanotubes (SWNTs) and the hydrogen-passivated Si(100) surface. Room-temperature UHV-STM desorption of hydrogen at the SWNT/H-Si(100) interface resulted in the local mechanical stabilization of tubes originally perturbed by the rastered STM tip under nominal imaging conditions. For the section of the SWNT contacted by depassivated Si, a topographic depression of 1.5 A (1 A) was measured in the case of parallel (nearly perpendicular) alignment between the tube axis and the Si dimer rows, in agreement with existing first-principles calculations. The compatibility of hydrogen-resist UHV-STM nanolithography with SWNTs adsorbed on H-Si(100) would enable the atomically precise placement of single molecules in proximity to the tube for the bottom-up fabrication of molecular electronic devices

  18. Measurement of the quantum conductance of germanium by an electrochemical scanning tunneling microscope break junction based on a jump-to-contact mechanism.

    Science.gov (United States)

    Xie, Xufen; Yan, Jiawei; Liang, Jinghong; Li, Jijun; Zhang, Meng; Mao, Bingwei

    2013-10-01

    We present quantum conductance measurements of germanium by means of an electrochemical scanning tunneling microscope (STM) break junction based on a jump-to-contact mechanism. Germanium nanowires between a platinum/iridium tip and different substrates were constructed to measure the quantum conductance. By applying appropriate potentials to the substrate and the tip, the process of heterogeneous contact and homogeneous breakage was realized. Typical conductance traces exhibit steps at 0.025 and 0.05 G0. The conductance histogram indicates that the conductance of germanium nanowires is located between 0.02 and 0.15 G0 in the low-conductance region and is free from the influence of substrate materials. However, the distribution of conductance plateaus is too discrete to display distinct peaks in the conductance histogram of the high-conductance region. PMID:23704043

  19. Surface of room-temperature-stable electride [Ca24Al28O64]4+(e-)4: preparation and its characterization by atomic-resolution scanning tunneling microscopy.

    Science.gov (United States)

    Toda, Yoshitake; Kubota, Yousuke; Hirano, Masahiro; Hirayama, Hiroyuki; Hosono, Hideo

    2011-03-22

    The nanocage compound crystal [Ca24Al28O64]4+(e-)4 (C12A7:e-) is a room-temperature-stable electride. Although bulk C12A7:e- exhibits metallic conduction, the surface of an as-prepared sample or one prepared by mechanical fracture in ultrahigh vacuum is almost insulating and exhibits distinct non-ohmic contact. We studied whether the intrinsic surface of this electride exhibits metallic conduction or not by examining various conditions for preparing the intrinsic surface. A combination of sputtering with thermal annealing led to the emergence of metallic conductivity in a specific condition. Suitably prepared surfaces revealed ohmic contact even in an ambient atmosphere. Atomic-resolution scanning tunneling microscopy (STM) images of the surfaces were consistent with a structural model in which the cage structure in the bulk C12A7:e- electride is conserved at the surface. PMID:21361301

  20. Formation mechanism of low-dimensional superstructure of adenine molecules and its control by chemical modification: a low-temperature scanning tunneling microscopy study

    Science.gov (United States)

    Furukawa, Masashi; Tanaka, Hiroyuki; Kawai, Tomoji

    2000-01-01

    The formation mechanism of low-dimensional self-assemblies of adenine, one of the DNA base molecules, on Cu(111) surfaces and its control by chemical modification have been studied using low-temperature (ca. 70 K) scanning tunneling microscopy and molecular orbital calculation. We have elucidated that the most stable hydrogen-bonded dimer plays a very important role as nuclei in the self-assembly formation of the adenine molecule. It was observed that the nuclei hydrogen-bonded dimers diffuse on the substrate, and self-assemble themselves into two different characteristic superstructures, a 'one-dimensional chain structure' and a 'two-dimensional hexagonal structure', through two distinct kinds of hydrogen bond pattern at low coverage and low deposition rate. It was also found that chemically modified adenine with an alkyl chain, which prevents the formation of the nucleic dimer, forms randomly aggregated small clusters.

  1. The role of dimer formation in the self-assemblies of DNA base molecules on Cu(111) surfaces: A scanning tunneling microscope study

    Science.gov (United States)

    Furukawa, Masashi; Tanaka, Hiroyuki; Kawai, Tomoji

    2001-08-01

    For the purpose of understanding the self-assembly formation mechanism of DNA base molecules, guanine, adenine, cytosine, and thymine molecules were deposited on Cu(111) surfaces, and were observed using a low-temperature (?80 K) scanning tunneling microscope (STM). Single-molecular-scale STM images revealed that guanine, adenine, and cytosine molecules can form ordered one- and/or two-dimensional unique structures, but thymine molecules, however, randomly aggregate into small clusters. Semiempirical molecular orbital (MO) calculation indicates that there exists predominantly stable dimer structures for the former three molecules, while such phenomena cannot be observed among the possible thymine dimer and even trimer structures. Based on experimental and theoretical results, we have concluded that specific hydrogen-bonded nucleus formation is a decisive process in the two-dimensional self-assembly formation of DNA base molecules on Cu(111) surfaces.

  2. Contrast stability and "stripe" formation in Scanning Tunnelling Microscopy imaging of highly oriented pyrolytic graphite: The role of STM-tip orientations

    CERN Document Server

    Mándi, Gábor; Palotás, Krisztián

    2014-01-01

    Highly oriented pyrolytic graphite (HOPG) is an important substrate in many technological applications and is routinely used as a standard in Scanning Tunnelling Microscopy (STM) calibration, which makes the accurate interpretation of the HOPG STM contrast of great fundamental and applicative importance. We demonstrate by STM simulations based on electronic structure obtained from first principles that the relative local orientation of the STM-tip apex with respect to the HOPG substrate has a considerable effect on the HOPG STM contrast. Importantly for experimental STM analysis of HOPG, the simulations indicate that local tip-rotations maintaining a major contribution of the $d_{3z^2-r^2}$ tip-apex state to the STM current affect only the secondary features of the HOPG STM contrast resulting in "stripe" formation and leaving the primary contrast unaltered. Conversely, tip-rotations leading to enhanced contributions from $m\

  3. Iron on GaN(0001) pseudo-1?×?1 (1+1/(12) ) investigated by scanning tunneling microscopy and first-principles theory

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Wenzhi; Mandru, Andrada-Oana; Smith, Arthur R., E-mail: smitha2@ohio.edu [Department of Physics and Astronomy, Nanoscale and Quantum Phenomena Institute, Ohio University, Athens, Ohio 45701 (United States); Takeuchi, Noboru [Centro de Nanociencias y Nanotecnologia, Universidad Nacional Autonoma de Mexico Apartado Postal 14, Ensenada Baja California, Codigo Postal 22800 (Mexico); Al-Brithen, Hamad A. H. [Physics and Astronomy Department, King Abdulah Institute for Nanotechnology, King Saud University, Riyadh, Saudi Arabia, and National Center for Nano Technology, KACST, Riyadh (Saudi Arabia)

    2014-04-28

    We have investigated sub-monolayer iron deposition on atomically smooth GaN(0001) pseudo-1?×?1 (1+1/(12) ). The iron is deposited at a substrate temperature of 360?°C, upon which reflection high energy electron diffraction shows a transformation to a ?(3)×?(3)-R30° pattern. After cooling to room temperature, the pattern transforms to a 6?×?6, and scanning tunneling microscopy reveals 6?×?6 reconstructed regions decorating the GaN step edges. First-principles theoretical calculations have been carried out for a range of possible structural models, one of the best being a Ga dimer model consisting of 2/9 monolayer of Fe incorporated into 7/3 monolayer of Ga in a relaxed but distorted structure.

  4. Molecular beam epitaxy growth and post-growth annealing of FeSe films on SrTiO3: a scanning tunneling microscopy study

    International Nuclear Information System (INIS)

    Low temperature scanning tunneling microscopy and spectroscopy are used to investigate the atomic and electronic structure evolution of FeSe films grown on SrTiO3 as a function of post-growth annealing. Single unit cell FeSe films are found to bond strongly with the underlying substrate, and become superconductive with diminishing chemical bond disorders at the interface via post-annealing. For thicker FeSe films, post-annealing removes excess Se in the films and leads to a transition from semiconductor into metallic behaviors. In double and multilayer films, strain-induced complex textures are observed and suggested to be the main cause for the absent superconductivity. (paper)

  5. In situ video-scanning tunneling microscopy studies of the structure and dynamics of Cl adlayers on Au(1 0 0) electrodes

    International Nuclear Information System (INIS)

    The chloride adlayer on Au(1 0 0) electrodes in 0.01 M HCl solution was studied on the atomic scale by in situ high-speed scanning tunneling microscopy. In the potential regime 0–0.4 VAg/AgCl a hitherto not reported defective c(2 × 2) structure was observed. In addition to characteristic straight domain boundaries oriented along the [0 1 0] and [0 1 1] directions of the Au substrate, unusual chain-like adsorbate structures were found. These defects can exhibit open structures with locally lower coverage as well as more close-packed arrangements, in which the adsorbates deviate from the lattice sites and have a 15% reduced nearest neighbor spacing. Dynamic fluctuations within the adlayer occur on the time scale of seconds, much slower than in Cl adlayers on Cu(1 0 0). The increase in defect density observed toward more positive potentials suggests a change of the adsorbate–adsorbate interactions with potential

  6. Scanning Tunnelling Microscopy Images of the Copper-Containing Amine Oxidase from Arthrobacter Globiformis in the Holo and Apo Forms Adsorbed on Gold under Ambient Conditions

    Science.gov (United States)

    Antoranz Contera, Sonia; Okajima, Toshihide; Iwasaki, Hiroshi

    2002-06-01

    Dimeric Arthrobacter globiformis amine oxidase in the holo and apo forms adsorbed onto a Au (111) surface have been observed by scanning tunnelling microscopy (STM) under ambient conditions. Individual protein molecules denature as they adsorb onto a bare Au surface, although they keep a dual appearance. Tapping atomic force microscopy images of individual proteins correspond well with the STM ones in the lateral direction. STM voltage affects the distance between the units of the denatured proteins: negative voltages separate them while positive ones get them together. Disordered as well as ordered layers of apo and holo proteins have been resolved by STM at molecular detail level. Individual proteins lying on the layers present a compact and a distinct dimeric shape, apo dimers looking bigger than holo dimers.

  7. A 350 mK, 9 T scanning tunneling microscope for the study of superconducting thin films on insulating substrates and single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Kamlapure, Anand; Saraswat, Garima; Ganguli, Somesh Chandra; Bagwe, Vivas; Raychaudhuri, Pratap, E-mail: pratap@tifr.res.in [Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Rd., Colaba, Mumbai 400 005 (India); Pai, Subash P. [Excel Instruments, 28, Sarvodaya Industrial Premises, Off Mahakali Caves Road, Andheri (East), Mumbai 400 093 (India)

    2013-12-15

    We report the construction and performance of a low temperature, high field scanning tunneling microscope (STM) operating down to 350 mK and in magnetic fields up to 9 T, with thin film deposition and in situ single crystal cleaving capabilities. The main focus lies on the simple design of STM head and a sample holder design that allows us to get spectroscopic data on superconducting thin films grown in situ on insulating substrates. Other design details on sample transport, sample preparation chamber, and vibration isolation schemes are also described. We demonstrate the capability of our instrument through the atomic resolution imaging and spectroscopy on NbSe{sub 2} single crystal and spectroscopic maps obtained on homogeneously disordered NbN thin film.

  8. Determining exact location of Group V dopants below the Si(001):H surface from scanning tunnelling spectroscopy and density functional theory

    Science.gov (United States)

    Brazdova, Veronika; Sinthiptharakoon, Kitiphat; Studer, Philipp; Bowler, David R.; Rahnejat, Adam; Curson, Neil J.; Schofield, Steven; Fisher, Andrew J.

    2015-03-01

    Group V impurities in silicon provide a way to tailor properties of electronic materials. The magnetically quiet environment that silicon provides for the impurity spins has also lead to new applications in coherent quantum devices. In both the ultimate classical devices and in future quantum computers the exact position of the dopants near surfaces and interfaces will determine the functionality: the ability to control and monitor those positions is key in these technologies. We precisely determine the substitutional sites of neutral As dopants that lie between 4.2 A and 15.0 A below the hydrogenated Si(001) surface, using a combination of density functional theory and low-temperature scanning tunnelling microscopy. We describe the interaction of the donor-electron state with the surface. Supported by the EPSRC Grant COMPASSS.

  9. Design and performance of an ultra-high vacuum scanning tunneling microscope operating at dilution refrigerator temperatures and high magnetic fields.

    Science.gov (United States)

    Misra, S; Zhou, B B; Drozdov, I K; Seo, J; Urban, L; Gyenis, A; Kingsley, S C J; Jones, H; Yazdani, A

    2013-10-01

    We describe the construction and performance of a scanning tunneling microscope capable of taking maps of the tunneling density of states with sub-atomic spatial resolution at dilution refrigerator temperatures and high (14 T) magnetic fields. The fully ultra-high vacuum system features visual access to a two-sample microscope stage at the end of a bottom-loading dilution refrigerator, which facilitates the transfer of in situ prepared tips and samples. The two-sample stage enables location of the best area of the sample under study and extends the experiment lifetime. The successful thermal anchoring of the microscope, described in detail, is confirmed through a base temperature reading of 20 mK, along with a measured electron temperature of 250 mK. Atomically resolved images, along with complementary vibration measurements, are presented to confirm the effectiveness of the vibration isolation scheme in this instrument. Finally, we demonstrate that the microscope is capable of the same level of performance as typical machines with more modest refrigeration by measuring spectroscopic maps at base temperature both at zero field and in an applied magnetic field. PMID:24182125

  10. Simulation of the soft-landing and adsorption of C60 molecules on a graphite substrate and computation of their scanning-tunnelling-microscopy-like images

    International Nuclear Information System (INIS)

    A constant-temperature molecular dynamics (MD) simulation was performed to model the soft-landing and adsorption of C60 molecules on a graphite substrate with the C60s treated as soft molecules and released individually towards the substrate. The intra-molecular and intra-planar covalently bonding interactions were modelled by very accurate many-body potentials, and the non-bonding forces were derived from various pairwise potentials. The simulation extended over 1.6 million time steps covering a significant period of 160 picoseconds. The final alignment of the molecules on the surface agrees closely with that observed in an experiment based on scanning tunnelling microscopy (STM) on the same system, performed at room temperature and under ultrahigh-vacuum (UHV) conditions. Using a tungsten tip in a constant-current mode of imaging, we have also computed the STM-like images of one of the adsorbed molecules using a formulation of the STM tunnelling current based on Keldysh's non-equilibrium Green function formalism. Our aim has been to search for tip-induced states, which were speculated, on the basis of another STM-based experiment, performed in air, to form one of the possible origins of the extra features purported to have been observed in that experiment. We have not obtained any such states. (author)

  11. Manifestation of dynamic Jahn–Teller distortions and surface interactions in scanning tunnelling microscopy images of the fullerene anion C?60

    International Nuclear Information System (INIS)

    Using scanning tunnelling microscopy (STM), it is possible to observe detailed structure of the molecular orbitals (MOs) of fullerene anions C?60. However, understanding the experimental observations is not straightforward because of the inherent presence of Jahn–Teller (JT) interactions, which (in general) split the MOs in one of a number of equivalent ways. Tunnelling between equivalent distortions means that any observed STM image will be a superposition of images arising from the individual configurations. Interactions with the surface substrate must also be taken into account. We will show how simple ideas involving a symmetry analysis and Hückel molecular orbital theory can be used to understand observed STM images without need for the more usual but more complicated density functional calculations. In particular, we will show that when the fullerene ion is adsorbed with a pentagon, hexagon or double-bond facing the surface, STM images involving the lowest unoccupied molecular orbital (LUMO) can be reproduced by adding together just two images of squares of components of the LUMO, in ratios that depend on the strength of the JT effect and the surface interaction. It should always be possible to find qualitative matches to observed images involving any of these orientations by simply looking at images of the components, without doing any detailed calculations. A comparison with published images indicates that the JT effect in the C?60 ion favours D3d distortions. (paper)

  12. Cross-sectional scanning tunneling microscopy observation of atomic arrangement in triple period-A type ordered AlInAs alloy

    International Nuclear Information System (INIS)

    Atomic arrangements in a triple-period (TP)-A type ordered AlInAs layer were investigated by a cross-sectional scanning tunneling microscope (XSTM) for the first time. The distributions of cation atoms in the ordered layer were distinguished using the tunneling spectroscopy method. The XSTM image on the cleaved surface of the ordered AlInAs layer revealed the presence of ragged short-range ordering domains comprising periodic structures aligned along the [1-bar 1-bar 2-bar ] direction on the whole surface, separated by three-fold periodicity along the [111] direction. This three-fold periodic structure comprises units of In-In-Al and/or In-Al-Al. That is, the TP-A type ordered AlInAs layer comprises two kinds of three-fold periodic planes; one is composed of two InAs-like planes and one AlAs-like plane, and the other is composed of one InAs-like plane and two AlAs-like planes. In addition, a local two-fold ordered structure having alternating InAs-like and AlAs-like planes can be observed in the STM image

  13. Scanning tunneling spectroscopy and break junction spectroscopy on iron-oxypnictide superconductor NdFeAs(O{sub 0.9}F{sub 0.1})

    Energy Technology Data Exchange (ETDEWEB)

    Sugimoto, A., E-mail: asugimoto@hiroshima-u.ac.j [Graduate School of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima 739-8521 (Japan); Ekino, T.; Ukita, R.; Shohara, K. [Graduate School of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima 739-8521 (Japan); Okabe, H.; Akimitsu, J. [Department of Physics, Aoyama Gakuin University, Sagamihara 229-8558 (Japan); Gabovich, A.M. [Institute of Physics, National Academy of Sciences, Nauka Ave. 46, Kyiv 03680 (Ukraine)

    2010-11-01

    Iron-oxypnictide superconductor NdFeAs(O{sub 0.9}F{sub 0.1}) was studied using both low-temperature scanning tunneling microscopy/spectroscopy (STM/STS) and tunnel break junction (BJ) methods. STM topography showed granular and spot structures with a typical size of several nanometers, most probably governed by fluorine atom distribution. The majority of STS conductance, G, versus voltage, V, curves revealed V-shaped structures, whereas some of G(V) dependences possessed coherent gap peaks or kinks at gap energies. At the same time, G(V) dependences obtained by the BJ technique showed clear-cut coherence peaks with peak-to-peak distances V{sub pp} = 4{Delta}/e {approx} 25 mV at 4.2 K, where {Delta} is the superconducting energy gap, e > 0 is the elementary charge. This yields {Delta}(0) = 6-7 meV, so that the ratio 2{Delta}(0)/k{sub B}T{sub c} is about 3-4, k{sub B} being the Boltzmann constant. This value is consistent with the conventional weak-coupling s-wave Bardeen-Cooper-Schrieffer theory.

  14. Electrochemistry and in situ scanning tunnelling microscopy of pure and redox-marked DNA- and UNA-based oligonucleotides on Au(111)-electrode surfaces

    DEFF Research Database (Denmark)

    Hansen, Allan Glargaard; Salvatore, Princia

    2013-01-01

    We have studied adsorption and electrochemical electron transfer of several 13- and 15-base DNA and UNA (unlocked nucleic acids) oligonucleotides (ONs) linked to Au(111)-electrode surfaces via a 50-C6-SH group using cyclic voltammetry (CV) and scanning tunnelling microscopy in aqueous buffer under electrochemical potential control (in situ STM). 2,20,60,200-Terpyridine (terpy) onto which the transition metal ions Fe2+/3+, Os2+/3+ and Ru2+/3+ could be coordinated after UNA monolayer formation was attached to UNA via a flexible linker. The metal centres offer CV probes and in situ STM contrast markers, and the flexible UNA/linker a potential binder for intercalation. CV of pure and mercaptohexanol diluted ON monolayers displayed reductive desorption signals but also, presumably capacitive, signals at higher potentials. Distinct voltammetric signals arise on metal binding. Those from Ru-binding are by far the strongest and in accord with multiple site Ru-attachment. In situ STM disclosed molecular scale features in varying coverage on addition of the metal ions. The Ru-derivatives showed a bias voltage dependent broad maximum in the tunnelling current–overpotential correlation which could be correlated with theoretical frames for condensed matter conductivity of redox molecules. Together the data suggest that Ru-units are bound to both terpy and the UNA–DNA backbone.

  15. Design and performance of an ultra-high vacuum scanning tunneling microscope operating at dilution refrigerator temperatures and high magnetic fields

    Science.gov (United States)

    Misra, S.; Zhou, B. B.; Drozdov, I. K.; Seo, J.; Urban, L.; Gyenis, A.; Kingsley, S. C. J.; Jones, H.; Yazdani, A.

    2013-10-01

    We describe the construction and performance of a scanning tunneling microscope capable of taking maps of the tunneling density of states with sub-atomic spatial resolution at dilution refrigerator temperatures and high (14 T) magnetic fields. The fully ultra-high vacuum system features visual access to a two-sample microscope stage at the end of a bottom-loading dilution refrigerator, which facilitates the transfer of in situ prepared tips and samples. The two-sample stage enables location of the best area of the sample under study and extends the experiment lifetime. The successful thermal anchoring of the microscope, described in detail, is confirmed through a base temperature reading of 20 mK, along with a measured electron temperature of 250 mK. Atomically resolved images, along with complementary vibration measurements, are presented to confirm the effectiveness of the vibration isolation scheme in this instrument. Finally, we demonstrate that the microscope is capable of the same level of performance as typical machines with more modest refrigeration by measuring spectroscopic maps at base temperature both at zero field and in an applied magnetic field.

  16. Design and performance of an ultra-high vacuum scanning tunneling microscope operating at dilution refrigerator temperatures and high magnetic fields

    CERN Document Server

    Misra, Shashank; Drozdov, Ilya K; Seo, Jungpil; Gyenis, Andras; Kingsley, Simon C J; Jones, Howard; Yazdani, Ali

    2013-01-01

    We describe the construction and performance of a scanning tunneling microscope (STM) capable of taking maps of the tunneling density of states with sub-atomic spatial resolution at dilution refrigerator temperatures and high (14 T) magnetic fields. The fully ultra-high vacuum system features visual access to a two-sample microscope stage at the end of a bottom-loading dilution refrigerator, which facilitates the transfer of in situ prepared tips and samples. The two-sample stage enables location of the best area of the sample under study and extends the experiment lifetime. The successful thermal anchoring of the microscope, described in detail, is confirmed through a base temperature reading of 20 mK, along with a measured electron temperature of 250 mK. Atomically-resolved images, along with complementary vibration measurements, are presented to confirm the effectiveness of the vibration isolation scheme in this instrument. Finally, we demonstrate that the microscope is capable of the same level of perform...

  17. Chemical analysis of Pt[sub x]Ni[sub 1-x] alloy single crystal surfaces by scanning tunnelling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Biedermann, A. (Inst. fuer Allgemeine Physik, Technische Univ. Wien (Austria)); Schmid, M. (Inst. fuer Allgemeine Physik, Technische Univ. Wien (Austria)); Varga, P. (Inst. fuer Allgemeine Physik, Technische Univ. Wien (Austria))

    1994-05-01

    Two STM investigations are presented, in which irregular tip conditions enable direct access to chemical and structural information of a surface on an atomic scale, otherwise invisible for the STM. They allow a study of surface ordering of a Pt[sub 25]Ni[sub 75](111) crystal by chemical contrast between the alloy components, and a study of carbon superstructures on a Pt[sub 10]Ni[sub 90](100) surface by simultaneous imaging of substrate lattice and carbon atoms. All these images were obtained at very low tunnelling resistances and thus at small tip-sample distances. A chemical interaction between the probably adsorbate covered tip and the sample is proposed to explain these images. (orig.)

  18. Toward quantitative STM: Scanning tunneling microscopy study of structure and dynamics of adsorbates on transition metal surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Dunphy, J.C.

    1995-05-01

    STM was applied to chemisorbed S layers on Re(000l) and Mo(100) surfaces. As function of coverage on both these surfaces, S orders into several different overlayer structures, which have been studied by dynamic LEED. STM images of all these structures were obtained. Approximate location of S atoms in the structures was determined by inspecting the images, especially the regions containing defects. Results are in agreement with LEED except for the p(2{times}l) overlayer of sulfur on Mo(100). The STM images were compared to calculations made with Electron Scattering Quantum Chemistry (ESQC) theory. Variation of contrast in experimental images is explained as a result of changes in STM tip termination structure. STM image contrast is a result of changes in the interference between different paths for the tunneling electrons. The simplest structure on the Mo(100) surface was used as a model for developing and testing a method of quantitative structure determination with the STM. Experimental STM images acquired under a range of tunneling conditions were compared to theoretical calculations of the images as a function of surface structure to determine the structure which best fit. Results matched within approximately 0.1 Angstroms a LEED structural determination. At lower S coverage, diffusion of S atoms over the Re(0001) surface and the lateral interaction between these atoms were investigated by application of a new image analysis technique. The interaction between the S and a coadsorbed CO layer was also studied, and CO was found to induce compression of the S overlayer. A similar result was found for Au deposited on the sulfur covered Mo(100) surface. The interaction between steps on the Mo surface was found to be influenced by S adsorption and this observation was interpreted with the theory of equilibrium crystal shape. Design of an STM instrument which operates at cryogenic and variable sample temperatures, and its future applications, are described.

  19. Scanning tunneling spectroscopic (STS) studies of MBE-grown topological insulators of Bi2 Se 3 epitaxial films on Si(111)

    Science.gov (United States)

    Yeh, N.-C.; Teague, M. L.; Lin, W.-H.; Chu, H.; Xiu, F. X.; He, L.; Wang, K. L.

    2011-03-01

    We report STS studies of MBE-grown Bi 2 Se 3 epitaxial films on Si(111) with varying thicknesses. The films were atomically flat on the scale of hundreds of nanometers, with occasional atomic steps of one c-axis lattice constant. In the case of thick Bi 2 Se 3 films, the tunneling spectra were consistent with those found in single crystalline Bi 2 Se 3 , except that the Dirac point (EDirac = - 50 ~ -100 meV) of the MBE-film is generally much closer to the Fermi level (E = 0), in contrast to the large downshift of EDirac (= -400 ~ -200 meV) commonly found in single crystalline bulk grown Bi 2 Se 3 . The STS spectra of the thinner films deviate from those of the thicker samples, probably the result of strain. Fourier transformed (FT) STS data as a function of energy reveals several quasiparticle scattering interference wave-vectors that are consistent with the topologically protected surface states with chiral spin texture, although the overall FT-STS maps are simpler than those reported on the Bi 0.92 Sb 0.08 (111) surface due to simpler electronic band-structures of Bi 2 Se 3 . The effect of time reversal symmetry breaking on the FT-STS will be investigated by either magnetic doping or application of magnetic fields. This work was supported by a grant from FENA of FCRP and DARPA.

  20. Ultrahigh Vacuum Scanning Tunneling Microscopy and Spectroscopy of Single-Walled Carbon Nanotubes Interfaced with Silicon Surfaces

    Science.gov (United States)

    Albrecht, Peter; Lyding, Joseph

    2008-03-01

    The UHV-STM was used to examine SWNTs directly interfaced with hydrogen-passivated Si(100). Dry contact transfer (DCT) [1] enabled the UHV deposition of SWNTs with minimal disruption of the atomically flat Si(100)-2x1:H surface. Isolated, rather than bundled, SWNTs could be routinely located for atomically resolved imaging, tunneling I-V spectroscopy [2], lateral manipulation [3], and proximal substrate modification. Weakly adsorbed SWNTs initially unstable in the presence of the rastered STM tip could be stabilized by depassivating the underlying H-Si(100) surface via UHV-STM electron-stimulated H desorption [4], which in the case of one chiral semiconducting SWNT also promoted the local alignment of the zigzag symmetry direction on the underside of the tube with the clean Si dimer rows [5]. The growing body of first-principles simulations of the SWNT/Si(100) system [6] was drawn upon in our interpretation of such local perturbations. [1] APL 83, 5029 (2003). [2] Nanotechnology 18, 095204 (2007). [3] Small 3, 146 (2007). [4] Nanotechnology 18, 125302 (2007). [5] Small 3, 1402 (2007). [6] JAP 100, 124304 (2006).

  1. Evaluation of magnetic flux distribution from magnetic domains in [Co/Pd] nanowires by magnetic domain scope method using contact-scanning of tunneling magnetoresistive sensor

    Energy Technology Data Exchange (ETDEWEB)

    Okuda, Mitsunobu, E-mail: okuda.m-ky@nhk.or.jp; Miyamoto, Yasuyoshi; Miyashita, Eiichi; Hayashi, Naoto [NHK Science and Technology Research Laboratories, 1-10-11 Kinuta Setagaya, Tokyo 157-8510 (Japan)

    2014-05-07

    Current-driven magnetic domain wall motions in magnetic nanowires have attracted great interests for physical studies and engineering applications. The magnetic force microscope (MFM) is widely used for indirect verification of domain locations in nanowires, where relative magnetic force between the local domains and the MFM probe is used for detection. However, there is an occasional problem that the magnetic moments of MFM probe influenced and/or rotated the magnetic states in the low-moment nanowires. To solve this issue, the “magnetic domain scope for wide area with nano-order resolution (nano-MDS)” method has been proposed recently that could detect the magnetic flux distribution from the specimen directly by scanning of tunneling magnetoresistive field sensor. In this study, magnetic domain structure in nanowires was investigated by both MFM and nano-MDS, and the leakage magnetic flux density from the nanowires was measured quantitatively by nano-MDS. Specimen nanowires consisted from [Co (0.3)/Pd (1.2)]{sub 21}/Ru(3) films (units in nm) with perpendicular magnetic anisotropy were fabricated onto Si substrates by dual ion beam sputtering and e-beam lithography. The length and the width of the fabricated nanowires are 20??m and 150?nm. We have succeeded to obtain not only the remanent domain images with the detection of up and down magnetizations as similar as those by MFM but also magnetic flux density distribution from nanowires directly by nano-MDS. The obtained value of maximum leakage magnetic flux by nano-MDS is in good agreement with that of coercivity by magneto-optical Kerr effect microscopy. By changing the protective diamond-like-carbon film thickness on tunneling magnetoresistive sensor, the three-dimensional spatial distribution of leakage magnetic flux could be evaluated.

  2. Heterodimers formed through a partial anionic exchange process: scanning tunneling spectroscopy to monitor bands across the junction vis-à-vis photoinduced charge separation

    Science.gov (United States)

    Bera, Abhijit; Saha, Sudip K.; Pal, Amlan J.

    2015-10-01

    We report controlled formation of heterodimers and their charge separation properties. CdS|CdTe heterodimers were formed through an anionic exchange process of CdS nanostructures. With control over the duration of the anionic exchange process, bulk|dot, bulk|bulk, and then dot|bulk phases of the semiconductors could be observed to have formed. A mapping of density of states as derived from scanning tunneling spectroscopy (STS) brought out conduction and valence band-edges along the nanostructures and heterodimers. The CdS|CdTe heterodimers evidenced a type-II band-alignment between the semiconductors along with the formation of a depletion region at the interface. The width (of the depletion region) and the energy-offset at the interface depended on the size of the semiconductors. We report that the width that is instrumental for photoinduced charge separation in the heterodimers has a direct correlation with the performance of hybrid bulk-heterojunction solar cells based on the nanostructures in a polymer matrix.We report controlled formation of heterodimers and their charge separation properties. CdS|CdTe heterodimers were formed through an anionic exchange process of CdS nanostructures. With control over the duration of the anionic exchange process, bulk|dot, bulk|bulk, and then dot|bulk phases of the semiconductors could be observed to have formed. A mapping of density of states as derived from scanning tunneling spectroscopy (STS) brought out conduction and valence band-edges along the nanostructures and heterodimers. The CdS|CdTe heterodimers evidenced a type-II band-alignment between the semiconductors along with the formation of a depletion region at the interface. The width (of the depletion region) and the energy-offset at the interface depended on the size of the semiconductors. We report that the width that is instrumental for photoinduced charge separation in the heterodimers has a direct correlation with the performance of hybrid bulk-heterojunction solar cells based on the nanostructures in a polymer matrix. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05785j

  3. Scanning tunneling microscopy study of formate species synthesized from CO{sub 2} hydrogenation and prepared by adsorption of formic acid over Cu(111)

    Energy Technology Data Exchange (ETDEWEB)

    Fujitani, T.; Choi, Y.; Sano, M.; Kushida, Y.; Nakamura, J.

    2000-02-17

    The adsorption structure of formate species on Cu(111), prepared by two different methods, was studied using ultrahigh vacuum scanning tunneling microscopy (UHV-STM), that is, the synthesis by the hydrogenation of CO{sub 2} at atmospheric pressure and the adsorption of formic acid on an oxygen-precovered Cu(111). Linear chains of formate molecules were imaged by the hydrogenation of CO{sub 2} by STM at low formate coverage with the distance to the nearest neighbor of the formate species estimated to be 5.0 {+-} 0.2{angstrom}, twice that of the nearest Cu--Cu neighbor. The adsorption phase of formate thus grows linearly at the initial stage by an anisotropic attractive interaction between the formate species. The ordered structure of the formate species changed in the order of p(2 x 4), c(2 x 8), (7 x 7), p(2 x 3), (5 x 5), and c(2 x 4) with increasing formate coverage, indicating that various ordered structures appeared corresponding to the small change in the formate coverage. All the formate structures, except for (7 x 7) and (5 x 5), consisted of the same chain as observed at low coverage, with the distance between the formate chains, resulting in a lowering of the adsorption energy of the formate species as reported in the literature. On the other hand, (4 x 4) and (3 x 7/2) structures were observed upon exposing the Cu(111) surface to formic acid at 2 and 15 L, respectively, showing no chain structure of the formate species. At low formate coverage, no molecular image was observed, indicating that the formate species diffuses more rapidly than the scanning of the STM tip. Thus, the adsorption structure of formate on Cu(111) was found to be different depending on the preparation method. It is suggested that the difference in the adsorption structure strongly influences the rate constant of the previously reported formate decomposition.

  4. A low temperature ultrahigh vacuum scanning tunneling microscope with high-NA optics to probe optical interactions at the atomic scale

    Science.gov (United States)

    Zhang, Haigang; Smerdon, Joseph; Suzer, Ozgun; Kersell, Heath; Guest, Jeffrey

    2015-03-01

    The optical and photophysical properties of single molecules/atoms, defects, and nanoscale structures at surfaces hinge on structure at the atomic scale. In order to characterize and control this structure and unravel these correlations, we are developing a low temperature (LT) laser-coupled ultrahigh vacuum (UHV) scanning tunneling microscope (LT Laser UHV STM) based on the Pan-style STM scanner with integrated high-numerical-aperture (NA) optics for single particle spectroscopy measurements under the STM tip. Using slip-stick inertial piezo steppers, the sample stage can be coarsely translated in X and Y directions. For optical measurements, high-NA optics behind and above the sample focus laser excitation on and collect photons emitted from the tip-sample junction. The STM is cooled by a liquid helium bath surrounded by a liquid nitrogen jacket for operation near 5 K; two separate ultrahigh vacuum chambers are used for sample preparation and STM measurements, respectively. We will describe our progress in demonstrating this instrument and plans for experiments studying the correlation between structure and optical function in nanoscale systems. U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.

  5. Atomic structure of the indium-induced Ge(001)(¤n¤x4) surface reconstruction determined by scanning tunneling microscopy and ¤ab initio¤ calculations

    DEFF Research Database (Denmark)

    Falkenberg, G.; Bunk, O.

    2002-01-01

    Using scanning-tunneling microscopy (STM) and first-principles total-energy calculations, we have determined the atomic geometry of the superstructures formed by the adsorption of up to 0.5 monolayer of indium on Ge(001) and annealing at temperatures above 200 degreesC. A strong interaction between indium adatoms and the germanium substrate atoms leads to the formation of two different In-Ge subunits on the Ge(001) surface. In the subsaturation regime separate (nx4) subunits are observed where n can be either 3 or 4 and the STM images resemble those of the Si(001)-(3x4)-In and -Al reconstructions. An ordered arrangement of the subunits into a (7x4) reconstruction can be prepared at saturation coverage. The (3x4) subunits are well described by the pyramidlike model introduced by O. Bunk, G. Falkenberg, L. Seehofer, J. H. Zeysing, R. L. Johnson, M. Nielsen, R. Feidenhans'l, and E. Landermark, Appl. Surf. Sci. 123/124, 104 (1998) for In on Si(001). For the (4x4) subunit, we propose a model that includes the mainfeatures of the (3x4) subunit together with additional mixed Ge-In dimers. The atomic positions were optimized using ab initio total-energy calculations. The calculated local densities of states are in excellent agreement with the STM images.

  6. Molecular-beam epitaxy of monolayer and bilayer WSe2: a scanning tunneling microscopy/spectroscopy study and deduction of exciton binding energy

    Science.gov (United States)

    Liu, H. J.; Jiao, L.; Xie, L.; Yang, F.; Chen, J. L.; Ho, W. K.; Gao, C. L.; Jia, J. F.; Cui, X. D.; Xie, M. H.

    2015-09-01

    Interest in two-dimensional (2D) transition-metal dichalcogenides (TMDs) has prompted some recent efforts to grow ultrathin layers of these materials epitaxially using molecular-beam epitaxy (MBE). However, growths of monolayer (ML) and bilayer (BL) WSe2—an important member of the TMD family—by the MBE method remain uncharted, probably because of the difficulty in generating tungsten fluxes from the elemental source. In this work, we present a scanning tunneling microscopy and spectroscopy (STM/S) study of MBE-grown WSe2 ML and BL, showing atomically flat epifilm with no domain boundary (DB) defect. This contrasts epitaxial MoSe2 films grown by the same method, where a dense network of the DB defects is present. The STS measurements of ML and BL WSe2 domains of the same sample reveal not only the bandgap narrowing upon increasing the film thickness from ML to BL, but also a band-bending effect across the boundary (step) between ML and BL domains. This band-bending appears to be dictated by the edge states at steps of the BL islands. Finally, comparison is made between the STS-measured electronic bandgaps with the exciton emission energies measured by photoluminescence, and the exciton binding energies in ML and BL WSe2 (and MoSe2) are thus estimated.

  7. In-situ scanning tunneling microscope studies of the ripening process of InAs quantum dots on GaAs during growth in the MOVPE

    International Nuclear Information System (INIS)

    Quantum dots (QD) are highly interesting for a number of different applications, like single photon emitters or semiconductor lasers. For industrial applications these optoelectronic devices are mainly grown by metal organic vapour phase epitaxy (MOVPE) systems which allows mass fabrication. QD growth has been studied intensely, but the understanding of the mechanisms responsible for the formation of the QDs and especially of the ripening process is still poor. In order to investigate the dynamics of the ripening process and to clarify the theory of QD ripening we employed our novel in-situ scanning tunnelling microscope (STM) technique which allows measurements directly during MOVPE growth. In this presentation we will discuss the ripening process of InAs QDs on GaAs(001):Si at 475 C where the development of the surface was analysed directly with the in-situ STM. Ex-situ AFM measurements showed a big scattering of the data, due to different substrates and varying cooling rates, while the in-situ measurements showed clear trends in RMS roughness and size distributions. E.g. the dot density decreased proportional to e-1 while the average dot size increased. In comparison of different ripening theories our experimental result follows the classical Ostwald ripening theory for the InAs on GaAs(001):Si system

  8. In situ scanning tunneling microscopy imaging of electropolymerized poly(3,4-ethylenedioxythiophene) on an iodine-modified Au(1 1 1) single crystal electrode

    International Nuclear Information System (INIS)

    The electrochemical polymerization of 3,4-ethylenedioxythiophene (EDOT) on an iodine-modified Au(1 1 1) single crystal electrode in aqueous 0.10 M HClO4 was investigated by cyclic voltammetry (CV) and electrochemical scanning tunneling microscopy (EC-STM). The cyclic voltammetric and EC-STM data revealed the stability of the iodine adlayer provided a suitable potential range for EDOT electropolymerization was controlled at 1.20 V (vs. the reversible hydrogen electrode). EC-STM was used to examine the formation of the PEDOT adlayer on the iodine-modified Au(1 1 1) electrode. In situ electropolymerization of EDOT was carried out by slowly increasing the electrode potential to 1.20 V. This process resulted in the formation of single molecular chains of PEDOT with a diameter of 0.90 nm and lengths of 5–7 nm. Higher resolution STM images further revealed PEDOT nanostructures with bent polymer backbones at angles of 105°, 144° and 180°. The growth of PEDOT multi-layers was observed when the potential was held for a longer time.

  9. Scanning tunneling microscopy and electrochemical study of the surface structure of Pt(10,10,9) and Pt(11,10,10) electrodes prepared under different cooling conditions

    Science.gov (United States)

    Herrero, Enrique; Orts, José M.; Aldaz, Antonio; Feliu, Juan M.

    1999-10-01

    The effect of three surface electrochemical preparation techniques for single crystal surfaces on two platinum stepped surfaces [Pt(10,10,9) and Pt(11,10,10)] has been investigated by scanning tunneling microscopy and cyclic voltammetry. The preparation techniques consisted of a thermal treatment followed by a cooling step in (a) a hydrogen+argon atmosphere, (b) air (c) iodine vapor+air. For Pt(10,10,9) and Pt(11,10,10) surfaces, the hydrogen+argon treatment provides surfaces that have a very narrow distribution of terrace widths around the nominal value and monatomic steps. On the other hand, facetted surfaces with terrace widths and steps four to five times their nominal values are obtained when the cooling is in the presence of iodine vapor. The air treatment generates surfaces in which the terrace width is not as uniform as in the H 2+Ar case and some kink sites are created. The changes in the surface topography can be followed in the voltammetric profile of the surfaces recorded in a sulfuric acid solution.

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

    DEFF Research Database (Denmark)

    Nazmutdinov, R.R.; Manyurov, I.R.

    2007-01-01

    Adsorption of two forms, molecule and radical, of amino acid L-cysteine (Cys) on the Au-12 cluster that simulates the (111) face of single-crystal gold is studied in the framework of the density functional theory. Effects of solvation of adsorbed Cys particles and lateral interaction in a monolayer are analyzed. The simulation predicts a commensurate adsorption energetics of the molecule and radical, with a difference between the "on-top," "hollow," and "bridge" positions. An analysis of lateral electrostatic interactions points to the stability of a cluster comprising six Cys particles, which conforms to the size of a fragment observed experimentally. Adsorption calculations are used to build three-dimensional isosurfaces (STM images), where the tungsten needle of the scanning tunneling microscope is simulated by a tungsten atom or by small clusters. The calculated images are sensitive to both the Cys shape and the orientation of adsorbed Cys particles. Calculation results are compared with fresh in situ submolecular-resolution STM data. Simulated images (with commensurate contributions made by sulfur atom and amino group) built for Cys radical adsorbed in the "on-top" position give best conformance to experiment.

  11. Atomistic structure of a spinel Li4Ti5O12(111) surface elucidated by scanning tunneling microscopy and medium energy ion scattering spectrometry

    Science.gov (United States)

    Kitta, Mitsunori; Matsuda, Taishi; Maeda, Yasushi; Akita, Tomoki; Tanaka, Shingo; Kido, Yoshiaki; Kohyama, Masanori

    2014-01-01

    Spinel lithium titanate (Li4Ti5O12, LTO) is one of the promising anode materials for high-performance lithium-ion batteries (LIBs). It is crucial to investigate atomistic structures of LTO surfaces to understand the phenomena at LTO/electrolyte interfaces such as CO2-gas generation which greatly affects the performance and safety of LIBs. By applying scanning tunneling microscopy (STM) and medium energy ion scattering spectrometry (MEIS) to a LTO(111) film prepared from a TiO2 wafer, we found that there exist two kinds of Li-terminated (111) terraces bounded by steps with different heights. In the major terraces, the top hexagonal Li layer is stacked above the oxygen layer, while the top Li layer is stacked above the Ti-Li layer in the minor terraces. The relative stability between the two surface structures seems to depend on the atmosphere due to different stoichiometry. For the major terraces, the LTO surface should have electronic holes due to oxygen-rich stoichiometry, which is a possible origin of CO2 generation via redox interaction with electrolyte molecules.

  12. Lateral ordering of PTCDA on the clean and the oxygen pre-covered Cu(100 surface investigated by scanning tunneling microscopy and low energy electron diffraction

    Directory of Open Access Journals (Sweden)

    Stefan Gärtner

    2014-09-01

    Full Text Available We have investigated the adsorption of perylene-3,4,9,10-tetracarboxylic acid dianhydride (PTCDA on the clean and on the oxygen pre-covered Cu(100 surface [referred to as (?2 × 2?2R45° – 2O/Cu(100] by scanning tunneling microscopy (STM and low energy electron diffraction (LEED. Our results confirm the (4?2 × 5?2R45° superstructure of PTCDA/Cu(100 reported by A. Schmidt et al. [J. Phys. Chem. 1995, 99,11770–11779]. However, contrary to Schmidt et al., we have no indication for a dissociation of the PTCDA upon adsorption, and we propose a detailed structure model with two intact PTCDA molecules within the unit cell. Domains of high lateral order are obtained, if the deposition is performed at 400 K. For deposition at room temperature, a significant density of nucleation defects is found pointing to a strong interaction of PTCDA with Cu(100. Quite differently, after preadsorption of oxygen and formation of the (?2 × 2?2R45° – 2O/Cu(100 superstructure on Cu(100, PTCDA forms an incommensurate monolayer with a structure that corresponds well to that of PTCDA bulk lattice planes.

  13. A comparative scanning tunneling spectroscopy investigation of the (12110)-surface of decagonal Al-Ni-Co and the (100)-surface of its approximant Y-Al-Ni-Co

    Energy Technology Data Exchange (ETDEWEB)

    Maeder, Ruben; Widmer, Roland; Groening, Pierangelo; Ruffieux, Pascal; Groening, Oliver [Empa, Swiss Federal Laboratories for Materials Testing and Research, nanotech-surfaces Laboratory, Feuerwerkerstrasse 39, CH-3602 Thun (Switzerland); Steurer, Walter, E-mail: oliver.groening@empa.c [Laboratory of Crystallography, Department of Materials, ETH Zurich, Wolfgang-Pauli-Str. 10, CH-8093 Zurich (Switzerland)

    2010-07-15

    We present a low-temperature scanning tunneling spectroscopy study of the local density of states (LDOS) on the (12110)-surface of the decagonal quasicrystal d-Al-Ni-Co and the (100)-surface of its structurally closely related approximant Y-Al-Ni-Co in the range of {+-}1 eV around the Fermi energy. The LDOS of both surfaces are dominated by a large parabolic pseudogap centered at the Fermi energy, which can be attributed to the Hume-Rothery stabilization mechanism or to an orbital hybridization. Superimposed on this large pseudogap, a spatially varying fine structure is revealed, whose spatial distribution correlates with the structures of both of the surfaces. This fine structure shows narrow peaks and pseudogaps exhibiting typical energy widths between 50 and 150 meV. The spatial extent of these localized states is of the order of the width of the topographic features, which is about 0.45 nm. Our findings show that specific electronic states are localized on equivalent topographic features regardless of the presence of periodic or quasiperiodic long-range order. We interpret this result as an indication that the fine structure in the LDOS is dominated much more by the complex short-range order than by the presence of the quasiperiodic long-range order.

  14. Hydrogen-bond-assisted supramolecular assembly of 1,3,5-tris(5-carboxyamyloxy)benzene at the liquid-solid interface: an scanning tunneling microscopy study.

    Science.gov (United States)

    Yan, Cunji; Han, Li

    2013-02-01

    The well-ordered self-assembled structure of 1,3,5-tris(5-carboxyamyloxy)benzene (TCAB) on Au(111) has been studied by electrochemical scanning tunneling microscopy (ECSTM) in HClO4 solution. Close examination indicates that the complex supramolecular network is formed by the TCAB molecules with flat-lying adsorption geometry and mainly stabilized by the hydrogen bonding interactions between carboxyl groups, except for the molecule-substrate interactions. It is particularly noteworthy that two types of hydrogen bonds, the dimers and tetramers of carboxyl group, coexist at the interface to balance the molecule-molecule and molecule-substrate interactions as well as to minimize the surface energy. Interestingly, the propeller-like motifs in STM image are fabricated by the bent alkoxy chains from four neighboring molecules respectively, bonded together by the cyclic carboxyl group tetramers. Moreover, there are two propellers in one lattice of TCAB adlayer, rotating in the clockwise and counterclockwise directions, respectively. Careful inspection shows that two structure domains of the TCAB adlayer are mirror images of each other since the molecular self-organization breaks the reflection symmetry of the substrate underneath. Our results give a good example of the flexibility adopted by alkyl chains functionalized by carboxyl group for the supramolecular assemblies at the liquid-solid interface. PMID:23646606

  15. Temperature-Dependent Site Control of InAs/GaAs (001 Quantum Dots Using a Scanning Tunneling Microscopy Tip During Growth

    Directory of Open Access Journals (Sweden)

    Toujyou Takashi

    2010-01-01

    Full Text Available Abstract Site-controlled InAs nano dots were successfully fabricated by a STMBE system (in situ scanning tunneling microscopy during molecular beam epitaxy growth at substrate temperatures from 50 to 430°C. After 1.5 ML of the InAs wetting layer (WL growth by ordinal Stranski–Krastanov dot fabrication procedures, we applied voltage at particular sites on the InAs WL, creating the site where In atoms, which were migrating on the WL, favored to congregate. At 240°C, InAs nano dots (width: 20–40 nm, height: 1.5–2.0 nm were fabricated. At 430°C, InAs nano dots (width: 16–20 nm, height: 0.75–1.5 nm were also fabricated. However, these dots were remained at least 40 s and collapsed less than 1000 s. Then, we fabricated InAs nano dots (width: 24–150 nm, height: 2.8–28 nm at 300°C under In and As4 irradiations. These were not collapsed and considered to high crystalline dots.

  16. In situ Control of Si/Ge Growth on Stripe-Patterned Substrates Using Reflection High-Energy Electron Diffraction and Scanning Tunneling Microscopy

    Directory of Open Access Journals (Sweden)

    Sanduijav B

    2010-01-01

    Full Text Available Abstract Si and Ge growth on the stripe-patterned Si (001 substrates is studied using in situ reflection high-energy electron diffraction (RHEED and scanning tunneling microscopy (STM. During Si buffer growth, the evolution of RHEED patterns reveals a rapid change of the stripe morphology from a multifaceted “U” to a single-faceted “V” geometry with {119} sidewall facets. This allows to control the pattern morphology and to stop Si buffer growth once a well-defined stripe geometry is formed. Subsequent Ge growth on “V”-shaped stripes was performed at two different temperatures of 520 and 600°C. At low temperature of 520°C, pronounced sidewall ripples are formed at a critical coverage of 4.1 monolayers as revealed by the appearance of splitted diffraction streaks in RHEED. At 600°C, the ripple onset is shifted toward higher coverages, and at 5.2 monolayers dome islands are formed at the bottom of the stripes. These observations are in excellent agreement with STM images recorded at different Ge coverages. Therefore, RHEED is an efficient tool for in situ control of the growth process on stripe-patterned substrate templates. The comparison of the results obtained at different temperature reveals the importance of kinetics on the island formation process on patterned substrates.

  17. Termination-specific study of oxygen vacancy transition levels on SrTiO3(001) surfaces by scanning tunneling spectroscopy

    Science.gov (United States)

    Sitaputra, Wattaka; Sivadas, Nikhil; Skowronski, Marek; Xiao, Di; Feenstra, Randall

    2015-03-01

    We have studied the surface electronic structure of oxygen vacancies on SrTiO3(001) surfaces using scanning tunneling spectroscopy and DFT calculations with local spin density approximation (LSDA +U). With high dynamic range measurements, a mid-gap level associated with the surface oxygen vacancies was observed for SrO-terminated surfaces. TiO2-terminated surfaces, on the other hand, did not exhibit observable mid-gap states (this lack of signal is believed to be due to the nature of defect wavefunction involved, as well as possibly involving transport limitations in the STS measurements). Both vacuum-cleaved and MBE-grown surface have been studied. For the former, the Fermi level is pinned near mid-gap owing to disorder-induced surface states. The amount of surface disorder can be controlled in the case of epitaxially grown surfaces. Rougher MBE-grown surfaces were found to exhibit similar spectral characteristics to the cleaved surfaces, while a shift of the Fermi level toward the conduction band was observed for flatter grown surfaces. Notably, with a decreasing number of disorder-induced surface states, the Fermi level is found to be pinned within the observed band of oxygen vacancy levels. This research was supported by AFOSR Grant No. FA9550-12-1-0479, and it used resources of the National Energy Research Scientific Computing Center, supported by the Office of Science, US Department of Energy under Contract No. DEAC02-05CH11231.

  18. Epitaxial growth of CeO{sub 2}(111) film on Ru(0001): Scanning tunneling microscopy (STM) and x-ray photoemission spectroscopy (XPS) study

    Energy Technology Data Exchange (ETDEWEB)

    Hasegawa, Tomo; Shahed, Syed Mohammad Fakruddin; Sainoo, Yasuyuki [Institute of Multidisciplinary Research for Advanced Materials (IMRAM, Tagen), Tohoku University, 2-1-1, Katahira, Aoba-Ku, Sendai 980-0877 (Japan); Beniya, Atsushi; Isomura, Noritake; Watanabe, Yoshihide [Toyota Central R and D Labs., Inc., 41-1 Yokomichi, Nagakute, Aichi 480-1192 (Japan); Komeda, Tadahiro, E-mail: komeda@tagen.tohoku.ac.jp [Institute of Multidisciplinary Research for Advanced Materials (IMRAM, Tagen), Tohoku University, 2-1-1, Katahira, Aoba-Ku, Sendai 980-0877 (Japan); JST, CREST, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan)

    2014-01-28

    We formed an epitaxial film of CeO{sub 2}(111) by sublimating Ce atoms on Ru(0001) surface kept at elevated temperature in an oxygen ambient. X-ray photoemission spectroscopy measurement revealed a decrease of Ce{sup 4+}/Ce{sup 3+} ratio in a small temperature window of the growth temperature between 1070 and 1096 K, which corresponds to the reduction of the CeO{sub 2}(111). Scanning tunneling microscope image showed that a film with a wide terrace and a sharp step edge was obtained when the film was grown at the temperatures close to the reduction temperature, and the terrace width observed on the sample grown at 1060 K was more than twice of that grown at 1040 K. On the surface grown above the reduction temperature, the surface with a wide terrace and a sharp step was confirmed, but small dots were also seen in the terrace part, which are considerably Ce atoms adsorbed at the oxygen vacancies on the reduced surface. This experiment demonstrated that it is required to use the substrate temperature close to the reduction temperature to obtain CeO{sub 2}(111) with wide terrace width and sharp step edges.

  19. Voltammetry and single-molecule in situ scanning tunneling microscopy of laccases and bilirubin oxidase in electrocatalytic dioxygen reduction on Au(111) single-crystal electrodes

    DEFF Research Database (Denmark)

    Climent, Victor; Zhang, Jingdong

    2012-01-01

    Laccases (E.C. 1.10.3.2) are multicopper oxidases catalytically active in the oxidation of diphenolics and related compounds by molecular dioxygen. The laccases contain a single-copper type I center and a trinuclear cluster of a single-copper type II and a dinuclear type III center. The oxidation of four equivalents of substrate near the type I copper and the sequential transfer of electrons to the trinuclear cluster are coupled with four-electron reduction of O2 to H2O at the latter site. Extensive efforts have been given to kinetic and structural characterization of numerous laccases to elucidate the catalytic mechanism, where laccase (sub)monolayer voltammetry has been a core approach. In this report, we address voltammetry and electrocatalysis of O2 reduction of (sub)monolayers of several laccases in new ways. These are based on the use of single-crystal, atomically planar bare Au(111)-electrode surfaces or surfaces modified by thiol-based self-assembled molecular monolayers. These well-defined surfaces enable introducing electrochemical scanning tunneling microscopy directly in aqueous biological media in which the enzymes are operative (in situ STM), to the level of resolution of the single enzyme molecule in electrocatalytic action. Enzyme-electrode electronic contact and intramolecular electron transfer triggered by the electrode potential or by O2-substrate binding to the enzyme, followed at the single-molecule level, are the most important observations of this study. © 2011 American Chemical Society.

  20. The fundamental role of the disorder in the properties of cuprate superconductors and calculations of the scanning tunneling microscopy and resistivity measurements

    Energy Technology Data Exchange (ETDEWEB)

    Kasal, Raphael; Pinheiro, C.F.S.; Mello, E.V.L. de [Universidade Federal Fluminense (UFF), Niteroi, RJ (Brazil). Inst. de Fisica; Universidade Federal de Ouro Preto (UFOP), MG (Brazil)

    2011-07-01

    Full text. The stripes and other types of electronic disorders have been measured for years on cuprate superconductors but their precise role and influence in the physical properties of these materials has not yet been established. It is the purpose of the present work to propose a model of how the inhomogeneities arises and their influence in some of the superconducting properties and phase diagram. To achieve this goal we analyze an electronic phase separation transition that leads to an electronic granular structure in cuprates superconductors. The minimization of the Ginzburg-Landau free energy leads to the Cahn-Hilliard equation which describes the charge diffusion into regions or grains of low and high densities separated by potential barriers where some bound states are formed. The charge clustering process works as an effective hole attraction that may be the origin of local pair formation in the isolated grains. Consequently the superconducting transition appears in two steps: first with local intragrain superconducting amplitudes {Delta}{sub sc}(r-bar) and then, at lower temperature, the superconducting phase is attained by intergrain Josephson coupling. We demonstrate that this approach reproduces the main features of the phase diagram of the cuprates, with a clear interpretation of the pseudogap phase. The model reproduces also the details of the position dependent local density of states measured by scanning tunneling experiments and is able to calculate important macroscopic properties like the bulk resistivity. (author)

  1. Immobilization, hybridization, and oxidation of synthetic DNA on gold surface: Electron transfer investigated by electrochemistry and scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    McEwen, Gerald D.; Chen Fan [Biological Engineering Program, Department of Biological and Irrigation Engineering, Utah State University, 4105 Old Main Hill, Logan, UT 84322-4105 (United States); Zhou Anhong, E-mail: Anhong.Zhou@usu.edu [Biological Engineering Program, Department of Biological and Irrigation Engineering, Utah State University, 4105 Old Main Hill, Logan, UT 84322-4105 (United States)

    2009-06-08

    Fundamental understanding of interfacial electron transfer (ET) among electrolyte/DNA/solid-surface will facilitate the design for electrical detection of DNA molecules. In this report, the electron transfer characteristics of synthetic DNA (sequence from pathogenic Cryptosporidium parvum) self-assembled on a gold surface was electrochemically studied. The effects of immobilization order on the interface ET related parameters such as diffusion coefficient (D{sub 0}), surface coverage ({theta}{sub R}), and monolayer thickness (d{sub i}) were determined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). DNA surface density ({Gamma}{sub DNA}) was determined by the integration of the charge of the electro-oxidation current peaks during the initial cyclic voltammetry scans. It was found that the DNA surface densities at different modifications followed the order: {Gamma}{sub DNA} (dsS-DNA/Au) > {Gamma}{sub DNA} (MCH/dsS-DNA/Au) > {Gamma}{sub DNA} (dsS-DNA/MCH/Au). It was also revealed that the electro-oxidation of the DNA modified gold surface would involve the oxidation of nucleotides (guanine and adenine) with a 5.51 electron transfer mechanism and the oxidative desorption of DNA and MCH molecules by a 3 electron transfer mechanism. STM topography and current image analysis indicated that the surface conductivity after each surface modification followed the order: dsS-DNA/Au < MCH/dsS-DNA/Au < oxidized MCH/dsS-DNA/Au < Hoechst/oxidized MCH/dsS-DNA/Au. The results from this study suggested a combination of variations in immobilization order may provide an alternative approach for the optimization of DNA hybridization and the further development for electrical detection of DNA.

  2. Immobilization, hybridization, and oxidation of synthetic DNA on gold surface: Electron transfer investigated by electrochemistry and scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Fundamental understanding of interfacial electron transfer (ET) among electrolyte/DNA/solid-surface will facilitate the design for electrical detection of DNA molecules. In this report, the electron transfer characteristics of synthetic DNA (sequence from pathogenic Cryptosporidium parvum) self-assembled on a gold surface was electrochemically studied. The effects of immobilization order on the interface ET related parameters such as diffusion coefficient (D0), surface coverage (?R), and monolayer thickness (di) were determined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). DNA surface density (?DNA) was determined by the integration of the charge of the electro-oxidation current peaks during the initial cyclic voltammetry scans. It was found that the DNA surface densities at different modifications followed the order: ?DNA (dsS-DNA/Au) > ?DNA (MCH/dsS-DNA/Au) > ?DNA (dsS-DNA/MCH/Au). It was also revealed that the electro-oxidation of the DNA modified gold surface would involve the oxidation of nucleotides (guanine and adenine) with a 5.51 electron transfer mechanism and the oxidative desorption of DNA and MCH molecules by a 3 electron transfer mechanism. STM topography and current image analysis indicated that the surface conductivity after each surface modification followed the order: dsS-DNA/Au < MCH/dsS-DNA/Au < oxidized MCH/dsS-DNA/Au < Hoechst/oxidized MCH/dsS-DNA/Au. The results from this study suggested a combination of variations in immobilization order may provide an alternative approach for the optimization of DNA hybridization and the further development for electrical detection of DNA.

  3. Scanning tunneling microscopy: Superconductor materials. January 1984-June 1990 (A Bibliography from the INSPEC: Information Services for the Physics and Engineering Communities data base). Report for January 1984-June 1990

    International Nuclear Information System (INIS)

    This bibliography contains citations concerning the development and utilization of scanning tunneling microscopy (STM) in surface topography analysis of superconductor materials. The citations cover the principles, operation, and implementation of STM. Specific materials analyzed by STM include bismuth, strontium, calcium, copper, yttrium, and barium. Some organic materials for superconductors are also analyzed. A separate Published Search covers the use of STM for analysis of semiconducting materials. (Contains 113 citations fully indexed and including a title list.)

  4. High Pressure Scanning Tunneling Microscopy and High PressureX-ray Photoemission Spectroscopy Studies of Adsorbate Structure,Composition and Mobility during Catalytic Reactions on A Model SingleCrystal

    Energy Technology Data Exchange (ETDEWEB)

    Montano, M.O.

    2006-05-12

    Our research focuses on taking advantage of the ability of scanning tunneling microscopy (STM) to operate at high-temperatures and high-pressures while still providing real-time atomic resolution images. We also utilize high-pressure x-ray photoelectron spectroscopy (HPXPS) to monitor systems under identical conditions thus giving us chemical information to compare and contrast with the structural and dynamic data provided by STM.

  5. Study of Shortwave Spectra in Fully 3D Environment: Synergy Between Scanning Radars and Spectral Radiation Measurements

    Science.gov (United States)

    Wiscombe, Warren J.

    2012-01-01

    The main theme for our research is the understanding and closure of the surface spectral shortwave radiation problem in fully 3D cloud situations by combining the new ARM scanning radars, shortwave spectrometers, and microwave radiometers with the arsenal of radiative transfer tools developed by our group. In particular, we define first a large number of cloudy test cases spanning all 3D possibilities not just the customary uniform-overcast ones. Second, for each case, we define a "Best Estimate of Clouds That Affect Shortwave Radiation" using all relevant ARM instruments, notably the new scanning radars, and contribute this to the ARM Archive. Third, we test the ASR-signature radiative transfer model RRTMG_SW for those cases, focusing on the near-IR because of long-standing problems in this spectral region, and work with the developers to improve RRTMG_SW in order to increase its penetration into the modeling community.

  6. Automated analysis for large amount gaseous fission product gamma-scanning spectra from nuclear power plant and its data mining

    International Nuclear Information System (INIS)

    Based on the Linssi database and UniSampo/Shaman software, an automated analysis platform has been setup for the analysis of large amounts of gamma-spectra from the primary coolant monitoring systems of a CANDU reactor. Thus, a database inventory of gaseous and volatile fission products in the primary coolant of a CANDU reactor has been established. This database is comprised of 15,000 spectra of radioisotope analysis records. Records from the database inventory were retrieved by a specifically designed data-mining module and subjected to further analysis. Results from the analysis were subsequently used to identify the reactor coolant half-life of 135Xe and 133Xe, as well as the correlations of 135Xe and 88Kr activities. (author)

  7. Roadmap of scanning probe microscopy

    CERN Document Server

    2006-01-01

    Scanning tunneling microscopy - with its applications that span not only atomic resolution but also scanning tunneling spectroscopy, atom/molecule manipulation and nanostructuring, and inelastic electron tunneling spectroscopy - has achieved remarkable progress and become the key technology for surface science. Besides, atomic force microscopy is also rapidly developing and achieving remarkable progress and accomplishments such as true atomic resolution, atom/molecule identification, manipulation and nanostructuring. This book that predicts the future development for all of scanning probe micr

  8. Tunneling Splittings in Vibronic Structure of CH_3F^+ ( X^2E): Studied by High Resolution Photoelectron Spectra and AB Initio Theoretical Method

    Science.gov (United States)

    Mo, Yuxiang; Gao, Shuming; Dai, Zuyang; Li, Hua

    2013-06-01

    We report a combined experimental and theoretical study on the vibronic structure of CH_3F^+. The results show that the tunneling splittings of vibrational energy levels occur in CH_3F^+ due to the Jahn-Teller effect. Experimentally, we have measured a high resolution ZEKE spectrum of CH_3F up to 3500 cm^-^1 above the ground state. Theoretically, we performed an ab initio calculation based on the diabatic model. The adiabatic potential energy surfaces (APES) of CH_3F^+ have been calculated at the MRCI/CAS/avq(t)z level and expressed by Taylor expansions with normal coordinates as variables. The energy gradients for the lower and upper APES, the derivative couplings between them and also the energies of the APES have been used to determine the coefficients in the Taylor expansion. The spin-vibronic energy levels have been calculated by accounting all six vibrational modes and their couplings. The experimental ZEKE spectra were assigned based on the theoretical calculations. W. Domcke, D. R. Yarkony, and H. Köpple (Eds.), Conical Intersections: Eletronic Structure, Dynamics and Spectroscopy (World Scientific, Singapore, 2004). M. S. Schuurman, D. E. Weinberg, and D. R. Yarkony, J. Chem. Phys. 127, 104309 (2007).

  9. Linear least-squares fit evaluation of series of analytical spectra from planar defects: extension and possible implementations in scanning transmission electron microscopy.

    Science.gov (United States)

    Walther, T

    2006-08-01

    In a previous paper, a new technique was introduced to determine the chemistry of crystallographically well-defined planar defects (such as straight interfaces, grain boundaries, twins, inversion or antiphase domain boundaries) in the presence of homogeneous solute segregation or selective doping. The technique is based on a linear least-squares fit using series of analytical (electron energy-loss or energy-dispersive X-ray) spectra acquired in a transmission electron microscope that is operated in nano-probe mode with the planar defect centred edge-on. First, additional notes on the use of proper k-factors and determination of Gibbsian excess segregation are given in this note. Using simulated data sets, it is shown that the linear least-squares fit improves both the accuracy and the robustness to noise beyond that obtainable by independently repeated measurements. It is then shown how the method originally developed for a stationary nano-probe mode in transmission electron microscopy can be extended to a focused electron beam that scans a square region in scanning transmission electron microscopy. The necessary modifications to scan geometry and corresponding numerical evaluation are described, and three different practical implementations are proposed. PMID:16911077

  10. Ordered molecular assemblies of substituted bis(phthalocyaninato) rare earth complexes on Au(111): in situ scanning tunneling microscopy and electrochemical studies.

    Science.gov (United States)

    Ma, Houyi; Yang, Liang-Yueh Ou; Pan, Na; Yau, Shueh-Lin; Jiang, Jianzhuang; Itaya, Kingo

    2006-02-28

    Substituted bis(phthalocyaninato) rare earth complexes ML2 (M = Y and Ce; L = [Pc(OC8H17)8]2, where Pc = phthalocyaninato) were adsorbed onto single crystalline Au(111) electrodes from benzene saturated with either YL2 or CeL2 complex at room temperature. In situ scanning tunneling microscopy (STM) and cyclic voltammetry (CV) were used to examine the structures and the redox reactions of these admolecules on Au(111) electrodes in 0.1 mol dm(-3) HClO4. The CVs obtained with YL2- and CeL2-coated Au(111) electrodes respectively contained two and three pairs of redox peaks between 0 and 1.0 V (versus reversible hydrogen electrode). STM molecular resolution revealed that YL2 and CeL2 admolecules were imaged as spherical protrusions separated by 2.3 nm, which suggests that they were oriented with their molecular planes parallel to the unreconstructed Au(111)-(1 x 1). Both molecules when adsorbing from approximately micromolar benzene dosing solutions produced mainly ordered arrays characterized as (8 x 5 radical3)rect (theta = 0.0125). The redox reactions occurring between 0.2 and 1.0 V caused no change in the adlayer, but they were desorbed or oxidized at the negative and positive potential limits. The processes of adsorption and desorption at the negative potentials were reversible to the modulation of potential. Electrochemical impedance spectroscopy (EIS) and CV measurements showed that YL2 and CeL2 adlayers could block the adsorption of perchlorate anions and mediating electron transfer at the Au(111) electrode, leading to the enhancement of charge transfer for the ferro/ferricyanide redox couple. PMID:16489795

  11. Atom-resolved scanning tunneling microscopy investigations of molecular adsorption on MoS2 and CoMoS hydrodesulfurization catalysts

    DEFF Research Database (Denmark)

    Lauritsen, Jeppe Vang; Besenbacher, Flemming

    2015-01-01

    We present an atomic-scale investigation of the molecular interactions relevant to hydrodesulfurization (HDS) catalysis at the catalytically active edge sites of single-layer MoS2 and cobalt-promoted MoS2 (CoMoS) nanoparticles synthesized as model catalysts. Atom-resolved scanning tunneling microscopy observations of the adsorption of thiophene, pyridine, and various refractory alkyl-substituted dibenzothiophenes have allowed us to reveal their predominant adsorption modes, study possible active sites, and provide explanations for the observed selectivity in HDS reactions, which are relevant to the two identified HDS pathways – the direct desulfurization route and the hydrogenation route. Hydrogenation is proposed to occur through interaction with edge S–H groups when the molecules are adsorbed in a flat-lying configuration near the nanoparticle edges of single-layer MoS2 and CoMoS. This adsorption mode is directly observed with STM at low temperatures and is realized due to the interaction of the aromatic ?-system of the adsorbing molecule with metallic edge states (brim states) in MoS2 and CoMoS which change the adsorption properties of the edges compared to the inert basal plane. The model studies also demonstrate the strong effect of sterical hindrance on the adsorption onto sulfur vacancies on MoS2 edges in direct desulfurization of the most refractory compounds, but it is also established that certain corner sites may exist for MoS2 and the promoted CoMoS structures, which directly facilitate strong adsorption.

  12. Solvent- and guest-responsive supramolecular self-assembly of 1,3,5-tris(10-carboxydecyloxy) benzene by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • TCDB can entrap solvent molecules or ?-electron-conjugated guest molecules. • We calculate hydrogen bonding which is crucial to stabilize the assembly networks. • Structural properties rely on the solvent- and guest-responsive assembly. • Kinetics and thermodynamics explain the morphology character of polarity. - Abstract: Two-dimensional hydrogen-bonded networks formed in the self-assembly of 1,3,5-tris(10-carboxydecyloxy) benzene (TCDB) show regular solvent- and guest-induced supramolecular structural properties, which have been presented by scanning tunneling microscopy at the liquid–solid interface at ambient conditions. TCDB acting as a host template can entrap solvent molecules or ?-electron-conjugated guest molecules to fabricate the flexible co-adsorption architectures, which are subject to the balance between the hydrogen bonding of the host lattice and the van der Waals forces between the host and the guest molecules. Hydrogen bonding among TCDB molecules is crucial to stabilize the host networks to settle the system into a global minimum of Gibbs free energy. We also find a strong correlation between the structural parameters and the physical properties of the solvent. Statistical analysis shows that the unit cell volume of TCDB dissolved in nonpolar 1-phenylotane and n-tetradecane shrank significantly compared with that of host–guest system, which fully reflects the coadsorption effect of nonpolar solvent molecules. Our results identify that the kinetic effect of adsorption/desorption as well as the solvent viscosity comes into play in tuning the two-dimensional self-assembled structures. Furthermore, mechanical calculations demonstrate that TCDB incline to adsorb with a larger dipole configuration in nonpolar solvents due to its dissolvability. It is believed that the results are of significance to supramolecular host–guest chemistry and surface science

  13. Fourier-transform scanning tunnelling spectroscopy: the possibility to obtain constant-energy maps and band dispersion using a local measurement

    International Nuclear Information System (INIS)

    We present here an overview of the Fourier-transform scanning tunnelling spectroscopy technique (FT-STS). This technique allows one to probe the electronic properties of a two-dimensional system by analysing the standing waves formed in the vicinity of defects. We review both the experimental and theoretical aspects of this approach, basing our analysis on some of our previous results, as well as on other results described in the literature. We explain how the topology of the constant-energy maps can be deduced from the FT of dI/dV map images which exhibit standing waves patterns. We show that not only the position of the features observed in the FT maps but also their shape can be explained using different theoretical models of different levels of approximation. Thus, starting with the classical and well known expression of the Lindhard susceptibility which describes the screening of electron in a free electron gas, we show that from the momentum dependence of the susceptibility we can deduce the topology of the constant-energy maps in a joint-density-of-states approximation (JDOS). We describe how some of the specific features predicted by the JDOS are (or are not) observed experimentally in the FT maps. The role of the phase factors which are neglected in the rough JDOS approximation is described using the stationary-phase conditions. We present also the technique of the T-matrix approximation, which accurately takes into account these phase factors. This technique has been successfully applied to normal metals, as well as to systems with more complicated constant-energy contours. We present results recently obtained on graphene systems which demonstrate the power of this technique, and the usefulness of local measurements for determining the band structure, the map of the Fermi energy and the constant-energy maps.

  14. Evidence for Time-Reversal Symmetry Breaking of the Superconducting State near Twin-Boundary Interfaces in FeSe Revealed by Scanning Tunneling Spectroscopy

    Science.gov (United States)

    Watashige, T.; Tsutsumi, Y.; Hanaguri, T.; Kohsaka, Y.; Kasahara, S.; Furusaki, A.; Sigrist, M.; Meingast, C.; Wolf, T.; Löhneysen, H. v.; Shibauchi, T.; Matsuda, Y.

    2015-07-01

    Junctions and interfaces consisting of unconventional superconductors provide an excellent experimental playground to study exotic phenomena related to the phase of the order parameter. Not only does the complex structure of unconventional order parameters have an impact on the Josephson effects, but it also may profoundly alter the quasiparticle excitation spectrum near a junction. Here, by using spectroscopic-imaging scanning tunneling microscopy, we visualize the spatial evolution of the LDOS near twin boundaries (TBs) of the nodal superconductor FeSe. The ? /2 rotation of the crystallographic orientation across the TB twists the structure of the unconventional order parameter, which may, in principle, bring about a zero-energy LDOS peak at the TB. The LDOS at the TB observed in our study, in contrast, does not exhibit any signature of a zero-energy peak, and an apparent gap amplitude remains finite all the way across the TB. The low-energy quasiparticle excitations associated with the gap nodes are affected by the TB over a distance more than an order of magnitude larger than the coherence length ?a b. The modification of the low-energy states is even more prominent in the region between two neighboring TBs separated by a distance ?7 ?a b . In this region, the spectral weight near the Fermi level (?±0.2 meV ) due to the nodal quasiparticle spectrum is almost completely removed. These behaviors suggest that the TB induces a fully gapped state, invoking a possible twist of the order parameter structure, which breaks time-reversal symmetry.

  15. Tuning Structures and Electronic Spectra of Graphene Layers by Tilt Grain Boundaries

    OpenAIRE

    Yin, Long-Jing; Qiao, Jia-Bin; Wang, Wen-Xiao; Chu, Zhao-Dong; Zhang, Kai Fen; Dou, Rui-Fen; Gao, Chun Lei; Jia, Jin-Feng; Nie, Jia-Cai; He, Lin

    2013-01-01

    Despite the structures and properties of tilt grain boundaries of graphite surface and graphene have been extensively studied, their effect on the structures and electronic spectra of graphene layers has not been fully addressed. Here we study effects of one-dimensional tilt grain boundaries on structures and electronic spectra of graphene multilayers by scanning tunneling microscopy and spectroscopy. A tilt grain boundary of a top graphene sheet in graphene multilayers lead...

  16. Slope of the superconducting gap function in $Bi_2Sr_2CaCu_2O_{8+\\delta}$ measured by vacuum tunneling spectroscopy

    OpenAIRE

    J. E. Hirsch

    1999-01-01

    Reproducible scanning tunneling microscope (STM) spectra of $Bi_2Sr_2CaCu_2O_{8+\\delta}$ consistently exhibit asymmetric tunneling characteristics, with the higher peak conductance corresponding to a negatively biased sample. We consider various possible sources of this asymmetry that are not intrinsic to the superconducting state, including energy dependence of the normal state densities of states of sample and/or tip, existence of bandwidth cutoffs, unequal work functions ...

  17. Supramolecular nanostructures of 1,3,5-benzene-tricarboxylic acid at electrified Au(111)/0.05 M H2SO4 interfaces: an in situ scanning tunneling microscopy study.

    Science.gov (United States)

    Li, Z; Han, B; Wan, L J; Wandlowski, Th

    2005-07-19

    The potential-induced adsorption and self-assembly of 1,3,5-benzene-tricarboxylic acid (TMA) was investigated at the electrified Au(111)/0.05 M H2SO4 interface by in-situ scanning tunneling microscopy (STM) and surface enhanced infrared reflection absorption spectroscopy (SEIRAS) in combination with electrochemical techniques. Depending on the applied electric field, TMA forms five distinctly different, highly ordered supramolecular adlayers on Au(111) surfaces. We have elucidated their real-space structures at the molecular scale. In the potential range -0.25 V nucleation and growth processes. PMID:16008404

  18. Design of a 300 mK-14 T scanning tunneling microscopy system and characterization of quantum Hall systems with respect to Rashba spin splitting, exchange enhancement and Coulomb gap

    OpenAIRE

    Becker, Stefan

    2011-01-01

    This thesis consists of two main parts. The first part describes the design of an ultra-high vacuum system (UHV) for measurements with a scanning tunneling microscope (STM) at a base temperature of about 300 mK and in magnetic fields of up to 14 T. The system consists of two main UHV chambers for sample and STM tip preparations and a large cryostat with an inner single-shot helium-3 cooling stage, holding the home-built STM. Besides commercially obtained ion source, LEED/Auger system, and mas...

  19. Low temperature scanning tunneling microscopy and spectroscopy of single crystals of the high temperature superconductor Bi2Sr2CaCu2O8, cleaved ''in-situ'' and at room temperature

    International Nuclear Information System (INIS)

    A low-temperature scanning tunneling microscope is used for simultaneous topography and superconducting energy gap measurements of Bi2Sr2CaCu2O8+d (Bi2212) single crystals. The samples were cleaved either in situ at 4.2 K or at room temperature with the surface parallel to the a-b planes. The interpretation of the conductance data suggests a superconducting gap value along the c-direction 2?/kBTc?9 for the room temperature cleaved crystals and 2?/kBTc?6.7 for the low-temperature cleaved samples. ((orig.))

  20. Voltammetry and in situ scanning tunnelling spectroscopy of osmium, iron, and ruthenium complexes of 2,2':6',2''-terpyridine covalently linked to Au(111)-electrodes

    DEFF Research Database (Denmark)

    Salvatore, Princia; Hansen, Allan Glargaard

    2011-01-01

    We have studied self-assembled molecular monolayers (SAMs) of complexes between Os(ii)/(iii), Fe(ii)/(iii), and Ru(ii)/(iii) and a 2,2',6',2''-terpyridine (terpy) derivative linked to Au(111)-electrode surfaces via a 6-acetylthiohexyloxy substituent at the 4'-position of terpy. The complexes were prepared in situ by first linking the terpy ligand to the surface via the S-atom, followed by addition of suitable metal compounds. The metal-terpy SAMs were studied by cyclic voltammetry (CV), and in situ scanning tunnelling microscopy with full electrochemical potential control of substrate and tip (in situ STM). Sharp CV peaks were observed for the Os- and Fe complexes, with interfacial electrochemical electron transfer rate constants of 6-50 s(-1). Well-defined but significantly broader peaks (up to 300 mV) were observed for the Ru-complex. Addition of 2,2'-bipyridine (bipy) towards completion of the metal coordination spheres induced voltammetric sharpening. In situ STM images of single molecular scale strong structural features were observed for the osmium and iron complexes. As expected from the voltammetric patterns, the surface coverage was by far the highest for the Ru-complex which was therefore selected for scanning tunnelling spectroscopy. These correlations displayed a strong peak around the equilibrium potential with systematic shifts with increasing bias voltage, as expected for a sequential two-step in situ ET mechanism.