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Sample records for scanning tunneling spectra

  1. Josephson scanning tunneling microscopy

    Science.gov (United States)

    Šmakov, Jurij; Martin, Ivar; Balatsky, Alexander V.

    2001-12-01

    We propose a set of scanning tunneling microscopy experiments in which the surface of a superconductor is scanned by a superconducting tip. Potential capabilities of such experimental setup are discussed. Most important anticipated results of such an experiment include the position-resolved measurement of the superconducting order parameter and the possibility to determine the nature of the secondary component of the order parameter at the surface. The theoretical description based on the tunneling Hamiltonian formalism is presented.

  2. Ultrafast scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

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

    1995-09-01

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

  3. Scanning Tunneling Microscopy

    Science.gov (United States)

    The Concord Consortium

    2011-12-11

    Use a virtual scanning tunneling microscope (STM) to observe electron behavior in an atomic-scale world. Walk through the principles of this technology step-by-step. First learn how the STM works. Then try it yourself! Use a virtual STM to manipulate individual atoms by scanning for, picking up, and moving electrons. Finally, explore the advantages and disadvantages of the two modes of an STM: the constant-height mode and the constant-current mode.

  4. 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.

  5. Introduction to scanning tunneling microscopy

    CERN Document Server

    Chen, C Julian

    2008-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-12-15

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

  7. Thermal radiation scanning tunnelling microscopy.

    Science.gov (United States)

    De Wilde, Yannick; Formanek, Florian; Carminati, Rémi; Gralak, Boris; Lemoine, Paul-Arthur; Joulain, Karl; Mulet, Jean-Philippe; Chen, Yong; Greffet, Jean-Jacques

    2006-12-01

    In standard near-field scanning optical microscopy (NSOM), a subwavelength probe acts as an optical 'stethoscope' to map the near field produced at the sample surface by external illumination. This technique has been applied using visible, infrared, terahertz and gigahertz radiation to illuminate the sample, providing a resolution well beyond the diffraction limit. NSOM is well suited to study surface waves such as surface plasmons or surface-phonon polaritons. Using an aperture NSOM with visible laser illumination, a near-field interference pattern around a corral structure has been observed, whose features were similar to the scanning tunnelling microscope image of the electronic waves in a quantum corral. Here we describe an infrared NSOM that operates without any external illumination: it is a near-field analogue of a night-vision camera, making use of the thermal infrared evanescent fields emitted by the surface, and behaves as an optical scanning tunnelling microscope. We therefore term this instrument a 'thermal radiation scanning tunnelling microscope' (TRSTM). We show the first TRSTM images of thermally excited surface plasmons, and demonstrate spatial coherence effects in near-field thermal emission. PMID:17151664

  8. Induced superconductivity in noncuprate layers of the Bi$_2$Sr$_2$CaCu$_2$O$_{8+\\delta}$ high-temperature superconductor: Modeling of scanning tunneling spectra

    OpenAIRE

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

    2010-01-01

    We analyze how the coherence peaks observed in Scanning Tunneling Spectroscopy (STS) of cuprate high temperature superconductors are transferred from the cuprate layer to the oxide layers adjacent to the STS microscope tip. For this purpose, we have carried out a realistic multiband calculation for the superconducting state of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\\delta}$ (Bi2212) assuming a short range d-wave pairing interaction confined to the nearest-neighbor Cu $d_{x^2-y^2}$ orbita...

  9. Scanning tunneling microscopy imaging of nanotubes

    International Nuclear Information System (INIS)

    Samples of carbon paper containing multiwalled carbon nanotube films are produced by current annealing. A scanning tunneling microscope is used to examine the structure of the modified carbon paper. X-, Y-, and V-shaped nanotubes are found

  10. Investigation into scanning tunnelling luminescence microscopy

    International Nuclear Information System (INIS)

    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 provide information on recombination processes and material properties. The design and construction of a scanning tunnelling luminescence microscope is described in detail. Operating under ambient conditions, the microscope has several novel features, including a new type of miniature inertial slider-based approach motor, large solid-angle light collection optical arrangement and a tip-height regulation system which requires the minimum of operator input. (author)e minimum of operator input. (author)

  11. 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.)

  12. Scanning tunneling microscope assembly, reactor, and system

    Energy Technology Data Exchange (ETDEWEB)

    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.

  13. Characterization of nanowires and molecular switches with scanning tunneling microscopy

    International Nuclear Information System (INIS)

    We consider the problem of finding the energy spectra, transmission and charge distribution on nanowires with scanning tunneling spectroscopy. Within this context, we first test the applicability of the method by comparing the output of our theory with available experimental results on In-based quantum wells patterned on nanowires. Then we study the correlation between density of states and electron transmission curves. Third, we investigate the induction of ultrafast electronic transitions due to the presence of a molecular switch or a scanning probe microscope tip

  14. New directions in scanning-tunneling microscopy

    International Nuclear Information System (INIS)

    The tunneling of electrons in scanning-tunneling microscopy (STM) has permitted imaging of the electronic distribution about individual atoms on surfaces. The need for use of conducting surfaces in STM limits its applicability, and new forms of scanning microscopy have emerged as a result of interest in poorly conducting samples. Atomic force microscopy has demonstrated that the force between a surface and a probe tip can be used to image selected materials. Now being developed are magnetic probe STM's and photon tunneling microscopes in which the probe is a sharpened optical fiber. Also of great interest presently is the measurement of differential conductance of surfaces using electron STM's. This method supplies spectral information and contrast enhancement in images. At present there remains much theoretical work to be carried out in order to better characterize related data on inelastic electron tunneling, and valuable insight may be gained from data being gathered on the local work function of materials. As matters stand today, the key problems lie in determining tip and contamination effects, preparation of samples, and understanding conductivity mechanisms in very thin materials on conducting substrates. Resolution of these problems and introduction of new forms of scanning microscopy may permit novel and important applications in biology as well as surface science

  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. An ultralow-temperature scanning tunnelling microscope

    International Nuclear Information System (INIS)

    We have developed a home-built ultralow-temperature scanning tunnelling microscope (STM) capable of continuous operation down to 70 mK, and in a magnetic field of up to 12 T. Extensive testing has shown that the STM is capable of very stable operation, including atomic resolution and spectroscopy with a high energy resolution. To test the microscope we have investigated the structural and electronic properties of the type-II superconductor NbSe2. (orig.)

  18. 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.

  19. Simulation of scanning tunneling spectroscopy of supported carbon nanotubes

    International Nuclear Information System (INIS)

    The angle and energy dependent transmission of wave packets was calculated through a jellium potential model of a scanning tunneling microscope (STM) junction containing different arrangements of carbon nanotubes. The total tunnel current as a function of STM bias was calculated by statistical averaging over a distribution of wave packets in the allowed energy window. Three tunneling situations were studied: (i) a STM tunnel junction with no nanotube present, (ii) one single wall nanotube in the STM junction, and (iii) a nanotube 'raft'. The effects of point contacts at the STM tip/nanotube, at the nanotube/substrate, and at both interfaces were also investigated. The theory allowed us to identify components of pure geometrical origin responsible for the asymmetry in the scanning tunneling spectroscopy (STS) spectrum of the carbon nanotubes with respect to bias voltage polarity. The calculations show that for tip negative bias the angular dependence of the transmission is determined by the tip shape. The particular tip shape introduces an asymmetry on the negative side of the STS spectrum. For tip positive bias the angular dependence of the transmission depends strongly on the nature of the nanosystem in the STM gap. While the transmission of the STM tunnel junction with no nanotube present can be well represented by a one dimensional model, all other geometries cause a large normal-transverse momentum mixing of the wave packet. A diffraction-grating-like behavior is t. A diffraction-grating-like behavior is seen in the angular dependence of the transmission of the nanotube raft. Point contacts between the nanotube and the substrate cause an asymmetry in the positive side of the STS spectrum. Calculated STS spectra are compared to experimental ones

  20. Bottom-Up Nanomanufacturing: Scanning Tunneling Microscope

    Science.gov (United States)

    This overview of nanotechnology is presented by the NaMCATE project."The scanning tunneling microscope (STM) is a type of electron microscope that shows three-dimensional images of a sample." This lesson explains how an STM works and the applications of the images it generates. It provides two learning activities titled Introduction to Atomic Force Microscopy and Study of the Morpho Butterfly Wing Structure Using AFM. Additionally, a powerpoint presentation is included.Users must create a free login in order to access materials.

  1. Atomic structure of carbon nanotubes from scanning tunneling microscopy

    International Nuclear Information System (INIS)

    The atomic structure of a carbon nanotube can be described by its chiral angle and diameter and can be specified by a pair of lattice indices (n,m). The electronic and mechanical properties are critically dependent on these indices. Scanning tunneling microscopy (STM) is a useful tool to investigate carbon nanotubes since the atomic structure as well as the electronic properties of individual molecules can be determined. This paper presents a discussion of the technique to obtain (n,m) indices of nanotubes from STM images in combination with current-voltage tunnel spectra. Image contrast, distortion effects, and determination of chiral angle and diameter are discussed. The procedure of (n,m) identification is demonstrated for a few single-walled carbon nanotubes

  2. 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.

  3. 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.

  4. Scanning tunneling spectroscopy in MgB2.

    Science.gov (United States)

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

    2001-05-01

    We present scanning tunneling microscopy measurements of the surface of superconducting MgB2 with a critical temperature of 39 K. In zero magnetic field the conductance spectra can be analyzed in terms of the standard BCS theory with a smearing parameter gamma. The value of the superconducting gap is 5 meV at 4.2 K, with no experimentally significant variation across the surface of the sample. The temperature dependence of the gap follows the BCS form, fully consistent with phonon-mediated superconductivity in this novel superconductor. The application of a magnetic field induces strong pair breaking as seen in the conductance spectra in fields up to 6 T. PMID:11328178

  5. 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)

  6. 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.

  7. Principles and Application of Heterodyne Scanning Tunnelling Spectroscopy

    Science.gov (United States)

    Matsuyama, Eiji; Kondo, Takahiro; Oigawa, Haruhiro; Guo, Donghui; Nemoto, Shojiro; Nakamura, Junji

    2014-10-01

    Detection of the extremely weak signals in spectroscopy over an extremely wide frequency region is central to diverse sciences, including materials science, biology, astronomy and chemistry. Here we show a new type of atomic-scale spectroscopy, heterodyne scanning tunnelling spectroscopy (HSTS), which is based on the innovative application of the nonlinear heterodyne-mixing detection at the metal-insulator-metal (MIM) heterojunction of STM tip-vacuum-sample. The principle of HSTS is identical to that of the Atacama Large Millimeter Array (ALMA) space telescope in terms of using heterojunction for detecting extremely weak signals by converting from terahertz region to lower frequency regions. The MIM detector of ALMA, which is composed of niobium-titanium-nitride (NbTiN) tip-insulator-NbTiN, is very similar in shape and size to that of HSTS. We successfully detect a heterodyne beat signal f3 (= |f2 - f1|) and intermodulation distortion via tunnelling current by superimposing two different AC signals, f1 and f2, onto the DC tunnelling current at a highly oriented pyrolytic graphite (HOPG) surface. We then obtain spectra of the localized electronic states of HOPG by using f3. HSTS can be performed with a high resolution and over a wide energy range, including the terahertz range.

  8. Shifts and dips in inelastic-electron-tunneling spectra due to the tunnel-junction environment

    International Nuclear Information System (INIS)

    In general, the tunnel-junction environment has proved to be surprisingly benign; tunneling spectra of molecules included within tunnel junctions are similar to infrared and Raman spectra of molecules not covered by a metal electrode. Peak shifts have been typically less than the linewidth of the peaks, and peaks intensities have been comparable to infrared and Raman intensities. Here we report a different situation for tunnel junctions containing molecules adsorbed on metal particles. Specifically, we find that different-top-metal electrodes give different tunneling spectra for CO on alumina-supported iron and rhodium particles. Though metals with similar atomic radii give similar spectra, metals with dissimilar atomic radii can give qualitatively different spectra. We also find anomalies concerning intensities. Specifically, for methyl isocyanide adsorbed on alumina-supported rhodium particles, the strongest peak in the infrared spectrum, the --NequivalentC stretching mode, appears as a dip in the tunneling spectrum

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

    International Nuclear Information System (INIS)

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

  10. Inherent Inhomogeneities in Tunneling Spectra of BSCCO Crystals in the Superconducting State

    OpenAIRE

    Howald, C.; Fournier, P.; Kapitulnik, A.

    2001-01-01

    Scanning Tunneling Spectroscopy on cleaved BSCCO(2212) single crystals reveal inhomogeneities on length-scales of $\\sim$30 $\\AA$. While most of the surface yields spectra consistent with a d-wave superconductor, small regions show a doubly gapped structure with both gaps lacking coherence peaks and the larger gap having a size typical of the respective pseudo-gap for the same sample.

  11. Scanning Tunneling Spectroscopy on the novel superconductor CaC6

    OpenAIRE

    Bergeal, N.; Dubost, V.; Noat, Y.; Sacks, W.; Roditchev, D.; Emery, N.; Herold, C.; Mareche, J-f; Lagrange, P.; Loupias, G.

    2006-01-01

    We present scanning tunneling microscopy and spectroscopy of the newly discovered superconductor CaC$_6$. The tunneling conductance spectra, measured between 3 K and 15 K, show a clear superconducting gap in the quasiparticle density of states. The gap function extracted from the spectra is in good agreement with the conventional BCS theory with $\\Delta(0)$ = 1.6 $\\pm$ 0.2 meV. The possibility of gap anisotropy and two-gap superconductivity is also discussed. In a magnetic f...

  12. Scanning tunneling spectroscopy on the novel superconductor CaC6.

    Science.gov (United States)

    Bergeal, N; Dubost, V; Noat, Y; Sacks, W; Roditchev, D; Emery, N; Hérold, C; Marêché, J-F; Lagrange, P; Loupias, G

    2006-08-18

    We present scanning tunneling microscopy and spectroscopy of the newly discovered superconductor CaC6. The tunneling conductance spectra, measured between 3 and 15 K, show a clear superconducting gap in the quasiparticle density of states. The gap function extracted from the spectra is in good agreement with the conventional BCS theory with Delta0=1.6+/-0.2 meV. The possibility of gap anisotropy and two-gap superconductivity is also discussed. In a magnetic field, direct imaging of the vortices allows us to deduce a coherence length in the ab plane xiab approximately 33 nm. PMID:17026267

  13. A vertical coarse approach scanning tunneling microscope

    Science.gov (United States)

    Drevniok, Benedict

    A Pan-style scanning tunneling microscope (STM), with a vertical coarse approach mechanism, was designed, built and tested. The microscope will be operated in ultra-high vacuum and also at cryogenic temperatures (8 K) inside a continuous flow cryostat. Fundamental differences in operating principle exist between the new microscope and the beetle-type inertial sliders [1] that have been the mainstay of the group for the last eight years. While Pan-style microscopes do already exist [2], they remain challenging to build, and an active area of research [3]. This system represents a bold departure from well-trodden paths, and will greatly expand the range of experiments that our group can perform. The operating principles of inertial piezoelectric motors are detailed. Design guidelines for a piezoelectric motor are given, and used in the design of the vertical coarse approach motor. A simple, inexpensive implementation for creating waveforms with an extremely fast fall time is discussed. Motor performance is tested, and a minimum step size of 20nm is found for frequencies ranging from 0 Hz to 3 kHz. The motor operates with high dynamic range: individual 20nm steps can be taken, as well as being able to move at a velocity of 0.4mm s-1. Little is known about the vibrational properties of Pan-style microscopes. Vibrational testing of the microscope revealed the expected scanner bending mode at 1.6 kHz (above the scanner bending mode of our beetles at 1.2 kHz), and a complicated response signal above this frequency. Custom extension springs for an eddy-current damping system are built and tested. A low resonant frequency of 1.8 Hz is found, which is ideal for the application. Initial testing of the STM in ambient conditions is performed on two different surfaces. A moire supermesh [4] with periodicity 3nm is observed on a highly-oriented pyrolytic graphite (HOPG) surface, and agrees well with previously published results. Using a flame-annealed Gold on mica surface, a low drift rate of 0.6nm s-1 is observed over a period of 13 minutes. Single-height atomic steps are observed on both surfaces. Additionally, the microscope is shown to be capable of zooming into different features on a surface, and scanning at different length scales.

  14. AgBr microcrystals studied by scanning tunneling microscopy

    Science.gov (United States)

    Gordon, W. S.; Szuba, S.

    1997-06-01

    Silver bromide crystals deposited on graphite were investigated with scanning tunneling microscope under ambient conditions. Different shape and size microcrystals, including cubic and octahedral forms and tabular grains, were observed and examined. Surface lattice parameters have been determined from high resolution images. In addition, the AgBr crystals were examined by scanning electron microscope.

  15. Transient measurements with an ultrafast scanning tunneling microscope

    DEFF Research Database (Denmark)

    Keil, Ulrich Dieter Felix; Jensen, Jacob Riis

    1998-01-01

    We use a photoconductively gated ultrafast scanning tunneling microscope to resolve laser-induced transients on transmission lines and photoconductors. The photoconductive switch on the tunneling probe is illuminated through a rigidly attached fiber. The use of the fiber enables us to scan across the transmission line while the change in delay time between pump beam (on the sample) and probe beam (on the probe) provides the temporal information. The investigated photoconductor sample is a low-temperature-grown GaAs layer placed on a sapphire substrate with a thin, semitransparent gold layer. In tunneling mode the probe is sensitive to laser-induced field changes in the semiconductor layer. Laser-induced transient signals of 2.2 ps widths are detected. As for the transmission lines, the signals can be explained by a capacitive coupling across the tunneling gap.

  16. Three-terminal scanning tunneling spectroscopy of suspended carbon nanotubes:

    OpenAIRE

    Leroy, B. J.; Kong, J.; Pahilwani, V. K.; Dekker, C.; Lemay, S. G.

    2005-01-01

    We have performed low-temperature scanning tunneling spectroscopy measurements on suspended single-wall carbon nanotubes with a gate electrode allowing three-terminal spectroscopy measurements. These measurements show well-defined Coulomb diamonds as well as side peaks from phonon-assisted tunneling. The side peaks have the same gate voltage dependence as the main Coulomb peaks, directly proving that they are excitations of these states.

  17. Three-terminal scanning tunneling spectroscopy of suspended carbon nanotubes

    CERN Document Server

    LeRoy, B J; Pahilwani, V K; Dekker, C; Lemay, S G

    2005-01-01

    We have performed low-temperature scanning tunneling spectroscopy measurements on suspended single-wall carbon nanotubes with a gate electrode allowing three-terminal spectroscopy measurements. These measurements show well-defined Coulomb diamonds as well as side peaks from phonon-assisted tunneling. The side peaks have the same gate voltage dependence as the main Coulomb peaks, directly proving that they are excitations of these states.

  18. Electrical characterization of nanocrystalline Si films by scanning tunnelling spectroscopy and beam-induced current in the scanning tunnelling microscope

    OpenAIRE

    Nogales Díaz, Emilio; Méndez Martín, Bianchi; Piqueras de Noriega, Javier; Plugaru, R.

    2003-01-01

    Nanocrystalline silicon films, with an average nanocrystal size of about 10 nm, obtained by boron implantation of amorphous silicon layers, have been studied by remote-beam-induced current (REBIC) in a scanning tunnelling microscope (STM) and by current imaging tunnelling spectroscopy. STM images reveal a cell structure with cell sizes of about 200 nm. STM-REBIC images display space-charge regions associated with the cell boundaries. The STM-REBIC contrast has been found to depend on the impl...

  19. Scanning tunneling microscopy of interface properties of Bi2Se3 on FeSe.

    Science.gov (United States)

    Wang, Yilin; Jiang, Yeping; Chen, Mu; Li, Zhi; Song, Canli; Wang, Lili; He, Ke; Chen, Xi; Ma, Xucun; Xue, Qi-Kun

    2012-11-28

    We investigate the heteroepitaxial growth of Bi(2)Se(3) films on FeSe substrates by low-temperature scanning tunneling microscopy/spectroscopy. The growth of Bi(2)Se(3) on FeSe proceeds via van der Waals epitaxy with atomically flat morphology. A striped moiré pattern originating from the lattice mismatch between Bi(2)Se(3) and FeSe is observed. Tunneling spectra reveal the spatially inhomogeneous electronic structure of the Bi(2)Se(3) thin films, which can be ascribed to the charge transfer at the interface. PMID:23110992

  20. Narrow Band Defect Luminescence from AI-doped ZnO Probed by Scanning Tunneling Cathodoluminescence

    OpenAIRE

    Likovich, Edward M.; Jaramillo, Rafael; Russell, Kasey Joe; Ramanathan, Shriram; Narayanamurti, Venkatesh

    2011-01-01

    We present an investigation of optically active near-surface defects in sputtered Al-doped ZnO films using scanning tunneling microscope cathodoluminescence (STM-CL). STM-CL maps suggest that the optically active sites are distributed randomly across the surface and do not correlate with the granular topography. In stark contrast to photoluminescence results, STM-CL spectra show a series of sharp, discrete emissions that characterize the dominant optically active defect, which we propose is a...

  1. Scanning Tunneling Spectroscopy of the superconducting proximity effect in a diluted ferromagnetic alloy

    OpenAIRE

    Cretinon, L.; Gupta, A. K.; Sellier, H.; Lefloch, F.; Faure, M.; Buzdin, A.; Courtois, H.

    2005-01-01

    We studied the proximity effect between a superconductor (Nb) and a diluted ferromagnetic alloy (CuNi) in a bilayer geometry. We measured the local density of states on top of the ferromagnetic layer, which thickness varies on each sample, with a very low temperature Scanning Tunneling Microscope. The measured spectra display a very high homogeneity. The analysis of the experimental data shows the need to take into account an additional scattering mechanism. By including in ...

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

    OpenAIRE

    Dubois, M.; Latil, Sylvain; Scifo, Lorette; Grévin, Benjamin; Rubio Secades, Ángel

    2006-01-01

    We report on a hybrid scheme to perform efficient and accurate simulations of scanning tunneling spectroscopy (STS) of molecules weakly bonded to surfaces. Calculations are based on a tight binding (TB) technique, including a self-consistent calculation of the electronic structure of the molecule, to predict STS conductance spectra. The use of a local basis makes our model easily applicable to systems with several hundreds of atoms. We performed first-principles density-functional calculation...

  3. Measurement of turbulence spectra using scanning pulsed wind lidars :

    OpenAIRE

    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 captu...

  4. 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.

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

    Science.gov (United States)

    Jäck, Berthold; Eltschka, Matthias; Assig, Maximilian; Hardock, Andreas; Etzkorn, Markus; Ast, Christian R.; Kern, Klaus

    2015-01-01

    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 1020 cm-2 s-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.

  6. 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...

  7. Node-like excitations in superconducting PbMo6S8 probed by scanning tunneling spectroscopy

    OpenAIRE

    Dubois, C.; Petrovic, A. P.; Santi, G.; Berthod, C.; Manuel, A. A.; Decroux, M.; Fischer, O.; Potel, M.; Chevrel, R.

    2007-01-01

    We present the first scanning tunneling spectroscopy study on the Chevrel phase PbMo6S8, an extreme type II superconductor with a coherence length only slightly larger than in high-Tc cuprates. Tunneling spectra measured on atomically flat terraces are spatially homogeneous and show well-defined coherence peaks. The low-energy spectral weight, the zero bias conductance and the temperature dependence of the gap are incompatible with a conventional isotropic s-wave interpretat...

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

    International Nuclear Information System (INIS)

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

  9. Scanning tunneling spectroscopy study of the proximity effect in a disordered two-dimensional metal.

    Science.gov (United States)

    Serrier-Garcia, L; Cuevas, J C; Cren, T; Brun, C; Cherkez, V; Debontridder, F; Fokin, D; Bergeret, F S; Roditchev, D

    2013-04-12

    The proximity effect between a superconductor and a highly diffusive two-dimensional metal is revealed in a scanning tunneling spectroscopy experiment. The in situ elaborated samples consist of superconducting single crystalline Pb islands interconnected by a nonsuperconducting atomically thin disordered Pb wetting layer. In the vicinity of each superconducting island the wetting layer acquires specific tunneling characteristics which reflect the interplay between the proximity-induced superconductivity and the inherent electron correlations of this ultimate diffusive two-dimensional metal. The observed spatial evolution of the tunneling spectra is accounted for theoretically by combining the Usadel equations with the theory of dynamical Coulomb blockade; the relevant length and energy scales are extracted and found in agreement with available experimental data. PMID:25167301

  10. 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.

  11. Scanning tunneling microscopy of carbon nanotubes: simulation and interpretation

    International Nuclear Information System (INIS)

    Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) are powerful techniques to investigate electronic and topographical properties of carbon nanotubes. The growing availability of experimental data enables us to study perfect tubules and to probe particular features of nanotubes such as topological (twists) or non-topological (pentagonal and heptagonal rings) modification of the hexagonal lattice and ending caps structures. We have recently proposed a general approach to interpret and predict STM and STS observations. Our formalism, which is based on a tight-binding framework, is sufficiently precise to be used routinely for various carbon sp2 geometries. Confronted with experimental results, our approach reveals to be a useful tool to help in the interpretation and prediction of STM and STS measurements

  12. 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.

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

    Science.gov (United States)

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

    2014-07-01

    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.

  14. 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.

  15. 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.

  16. Scanning tunneling microscopy and spectroscopy of Na intercalation in VSe2

    Science.gov (United States)

    Ekvall, I.; Brauer, H. E.; Olin, H.; Starnberg, H. I.; Wahlström, E.

    We have used an ultrahigh vacuum variable-temperature scanning tunneling microscope to study in situ Na intercalation in 1T-VSe2. At room temperature the clean surface showed large flat areas and a trigonal atomic arrangement. Tunneling spectroscopy revealed the known state at 100 mV below EF. At 60 K the clean surface showed a 4×4charge density wave and the spectra showed a CDW gap ? 80 mV. When evaporating <=1 ML Na at room temperature, the intercalated Na were distributed non-uniformly, giving bright areas of increased topographic height where Na was intercalated. In the intercalated material the VSe2 state was seen in the tunneling spectra, and was slightly shifted towards EF. Preliminary spectroscopy of the intercalated material at 60 K showed two different types of spectra. One type showed the VSe2 peak clearly, but had no sign of the CDW gap, while the other type showed a gap structure but did not resolve the VSe2 state. Presently, we can not tell whether these different spectra originate from the differences in the intercalated and non-intercalated areas or not.

  17. Broken Symmetries in Scanning Tunneling Images of Carbon Nanotubes

    OpenAIRE

    Kane, C. L.; Mele, E. J.

    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 stat...

  18. Scanning Tunneling Spectroscopy of Suspended Single-Wall Carbon Nanotubes

    OpenAIRE

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

    2004-01-01

    We have performed low-temperature scanning tunneling microscopy measurements on single-wall carbon nanotubes that are freely suspended over a trench. The nanotubes were grown by chemical vapor deposition on a Pt substrate with predefined trenches etched into it. Atomic resolution was obtained on the freestanding portions of the nanotubes. Spatially resolved spectroscopy on the suspended portion of both metallic and semiconducting nanotubes was also achieved, showing a Coulomb-staircase behavi...

  19. Scanning tunneling spectroscopy of thin films of carbon nanotubes

    Science.gov (United States)

    Poonia, Monika; Manjuladevi, V.; Gupta, Raj Kumar

    2013-06-01

    The thin films of single walled carbon nanotubes (CNT) were deposited on indium tin oxide (ITO) glass substrates. The films were characterized using scanning tunneling microscopy and spectroscopy. The topographic images reveal a high degree of orientational order in the arrangement of bundles of CNT onto the ITO substrates. We found a significant narrowing of the band gap of the CNT films on ITO as compared to that of ITO film on glass substrate.

  20. Subharmonic gap structure in superconducting scanning tunneling microscope junctions

    OpenAIRE

    Naaman, O.; Dynes, R. C.

    2003-01-01

    We observe a subharmonic gap sturucture (SGS) and the Josephson effect in superconducting scanning tunneling microscope junctions with resistances below 100 kOhm. The magnitude of the n=2 SGS is shown to scale with the square of the junction normal state conductance, in agreement with theory. We show by analyzing the Josephson effect in these junctions that the superconducting phase dynamics are strongly affected by thermal fluctuations. We estimate the linewidth of the Jose...

  1. Scanning tunneling microscopy studies of diamond films and optoelectronic materials

    Science.gov (United States)

    Perez, Jose M.

    1993-01-01

    In this report, we report on progress achieved from 12/1/92 to 10/1/93 under the grant entitled 'Scanning Tunneling Microscopy Studies of Diamond Films and Optoelectronic Materials'. We have set-up a chemical vapor deposition (CVD) diamond film growth system and a Raman spectroscopy system to study the nucleation and growth of diamond films with atomic resolution using scanning tunneling microscopy (STM). A unique feature of the diamond film growth system is that diamond films can be transferred directly to the ultrahigh vacuum (UHV) chamber of a scanning tunneling microscope without contaminating the films by exposure to air. The University of North Texas (UNT) provided $20,000 this year as matching funds for the NASA grant to purchase the diamond growth system. In addition, UNT provided a Coherent Innova 90S Argon ion laser, a Spex 1404 double spectrometer, and a Newport optical table costing $90,000 to set-up the Raman spectroscopy system. The CVD diamond growth system and Raman spectroscopy system will be used to grow and characterize diamond films with atomic resolution using STM as described in our proposal. One full-time graduate student and one full-time undergraduate student are supported under this grant. In addition, several graduate and undergraduate students were supported during the summer to assist in setting-up the diamond growth and Raman spectroscopy systems. We have obtained research results concerning STM of the structural and electronic properties of CVD grown diamond films, and STM and scanning tunneling spectroscopy of carbon nanotubes. In collaboration with the transmission electron microscopy (TEM) group at UNT, we have also obtained results concerning the optoelectronic material siloxene. These results were published in refereed scientific journals, submitted for publication, and presented as invited and contributed talks at scientific conferences.

  2. Technological applications of scanning tunneling microscopy at atmospheric pressure

    International Nuclear Information System (INIS)

    We present experimental evidence of the capability of the scanning tunneling microscope (STM) to image the microstructure of surfaces with atomic resolution even at atmospheric pressure. Some examples of different types of materials (metal single crystals, graphite, semiconductor, oxide and metal films) are shown. We propose the STM as a highly sensitive standard for surface roughness determination of industrial finishing at atmospheric pressure. In our opinion, these results may open new perspectives in technology and industrial applications

  3. Apparent diameter of carbon nanotubes in scanning tunnelling microscopy measurements

    International Nuclear Information System (INIS)

    Geometric effects influencing scanning tunnelling microscopy (STM) image formation of single wall carbon nanotubes (SWCNTs) were studied within the framework of a simple model potential. We focused on the geometrical effects which may influence the tunnelling probabilities and lead to discrepancies between the apparent height of the nanotubes measured by STM and their real geometrical diameter. We found that there are two main factors responsible for the underestimation of nanotubes diameter by measuring their height in STM images: (1) the curvature of the nanotube affects the cross sectional shape of the tunnelling channel; (2) the decay rate of tunnelling probabilities inside the tunnel gap increases with increasing curvature of the electrodes. For a nanotube with 1 nm diameter an apparent flattening of about 10%, due to these geometry-related effects, is predicted. Furthermore these effects are found to be dependent on the diameter of the tubes and tip-sample distances: an increasing flattening of the tubes is predicted for decreasing tube diameter and increasing tip-sample distance

  4. Tunneling Spectra of Skutterudite PrOs_4Sb_{12}

    CERN Document Server

    Asano, Y; Matsuda, Y; Kashiwaya, S

    2003-01-01

    The tunnel conductance in normal-metal / insulator / PrOs$_4$Sb$_{12}$ junctions is theoretically studied, where skutterudite PrOs$_4$Sb$_{12}$ is considered to be an unconventional superconductor. The conductance are calculated for several pair potentials which have been proposed in recent works. The results show that the conductance is sensitive to the relation between the direction of electric currents and the position of point nodes. We also show that the conductance spectra often deviate from the shape of the bulk density of states and that the sub gap spectra have peak structures in the case of the spin-triplet pair potentials. The results indicate that the tunnel conductance is a useful tool to obtain an information of the pairing symmetry.

  5. Characterization of single wall carbon nanotubes by scanning tunneling and scanning force microscopy

    International Nuclear Information System (INIS)

    In high-resolution scanning tunneling microscopy images of single-wall carbon nanotubes we often find complex superstructures superimposed onto the simple atomic pattern. They can be interpreted as a result of elastic scattering of the Fermi states at defects or impurities. A new combination of scanning tunneling and scanning force microscopy enables near-atomic point resolution in the resulting images. Using the force interaction as a feedback signal, the tubes can be identified without the need of a conducting substrate. This imaging mode is a crucial step for the characterization of electronic devices based on individual single-wall tubes. First results are presented showing that it is possible to obtain current images from tubes which are only locally connected to electrical contacts defined on insulating substrates

  6. 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.

  7. 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.

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

    International Nuclear Information System (INIS)

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

  9. Optical interactions in the junction of a scanning tunneling microscope

    Science.gov (United States)

    Kuk, Y.; Becker, R. S.; Silverman, P. J.; Kochanski, G. P.

    1990-07-01

    Surface bias voltages induced on a scanning-tunneling-microscope junction illuminated with laser radiation are spatially measured for both metal and semiconductor samples. A surface photovoltage of ~0.3 eV is observed for Si(111)-(7×7), with large reductions in the vicinity of surface (subsurface) defects having midgap states. These reductions, attributed to a change in the recombination rate, have a typical surface screening distance of 15-25 Å. A small, atomically varying signal of 3-5 mV is observed on both metal and semiconductor samples and demonstrated to arise not from variation in photovoltage but from spatial variations in rectification efficiency.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1988-12-01

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

  11. Scanning tunneling spectroscopy of epitaxial silver indium diselenide

    Science.gov (United States)

    Peña Martin, Pamela; Lyding, Joseph; Rockett, Angus

    2015-06-01

    We report on the measurement of the electronic properties of (112) AgInSe2 (AIS) by scanning tunneling microscopy (STM) and spectroscopy (STS). Current-voltage STS measurements show an average band gap of about 1.3 eV and n-type behavior. The IV data also shows band edge fluctuations and a region of states near the valence band edge that decay well into the gap. We compare STS determined band fluctuations in AIS to those previously measured in CuInSe2 (CIS) and find that the fluctuations are smaller in scale in AIS than CIS.

  12. Scanning tunneling luminescence of individual CdSe nanowires.

    Science.gov (United States)

    Lutz, Theresa; Kabakchiev, Alexander; Dufaux, Thomas; Wolpert, Christian; Wang, Zhe; Burghard, Marko; Kuhnke, Klaus; Kern, Klaus

    2011-08-22

    The local luminescence properties of individual CdSe nanowires composed of segments of zinc blende and wurtzite crystal structures are investigated by low-temperature scanning tunneling luminescence spectroscopy. Light emission from the wires is achieved by the direct injection of holes and electrons, without the need for coupling to tip-induced plasmons in the underlying metal substrate. The photon energy is found to increase with decreasing wire diameter due to exciton confinement. The bulk bandgap extrapolated from the energy versus diameter dependence is consistent with photon emission from the zinc blende-type CdSe sections. PMID:21678550

  13. Measurement of turbulence spectra using scanning pulsed wind lidars

    Science.gov (United States)

    Sathe, A.; Mann, J.

    2012-01-01

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

  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 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.

  15. A scanning tunneling microscope with a scanning range from hundreds of micrometers down to nanometer resolution

    Science.gov (United States)

    Kalkan, Fatih; Zaum, Christopher; Morgenstern, Karina

    2012-10-01

    A beetle type stage and a flexure scanning stage are combined to form a two stages scanning tunneling microscope (STM). It operates at room temperature in ultrahigh vacuum and is capable of scanning areas up to 300 ?m × 450 ?m down to resolution on the nanometer scale. This multi-scale STM has been designed and constructed in order to investigate prestructured metallic or semiconducting micro- and nano-structures in real space from atomic-sized structures up to the large-scale environment. The principle of the instrument is demonstrated on two different systems. Gallium nitride based micropillars demonstrate scan areas up to hundreds of micrometers; a Au(111) surface demonstrates nanometer resolution.

  16. Molecular tips for scanning tunneling microscopy: intermolecular electron tunneling for single-molecule recognition and electronics.

    Science.gov (United States)

    Nishino, Tomoaki

    2014-01-01

    This paper reviews the development of molecular tips for scanning tunneling microscopy (STM). Molecular tips offer many advantages: first is their ability to perform chemically selective imaging because of chemical interactions between the sample and the molecular tip, thus improving a major drawback of conventional STM. Rational design of the molecular tip allows sophisticated chemical recognition; e.g., chiral recognition and selective visualization of atomic defects in carbon nanotubes. Another advantage is that they provide a unique method to quantify electron transfer between single molecules. Understanding such electron transfer is mandatory for the realization of molecular electronics. PMID:24420248

  17. A combined scanning tunneling microscope-atomic layer deposition tool.

    Science.gov (United States)

    Mack, James F; Van Stockum, Philip B; Iwadate, Hitoshi; Prinz, Fritz B

    2011-12-01

    We have built a combined scanning tunneling microscope-atomic layer deposition (STM-ALD) tool that performs in situ imaging of deposition. It operates from room temperature up to 200 °C, and at pressures from 1 × 10(-6) Torr to 1 × 10(-2) Torr. The STM-ALD system has a complete passive vibration isolation system that counteracts both seismic and acoustic excitations. The instrument can be used as an observation tool to monitor the initial growth phases of ALD in situ, as well as a nanofabrication tool by applying an electric field with the tip to laterally pattern deposition. In this paper, we describe the design of the tool and demonstrate its capability for atomic resolution STM imaging, atomic layer deposition, and the combination of the two techniques for in situ characterization of deposition. PMID:22225221

  18. Scanning Tunneling Microscope with Two-Dimensional Coarse Approach

    Science.gov (United States)

    Nichols, John; Ng, Kwok-Wai

    2010-03-01

    Since the invention of the Scanning Tunneling Microscope (STM), it has been a powerful tool for probing the electronic properties of materials. Typically STM designs capable of obtaining resolution on the atomic scale are limited to a small area which can be probed. We have built a STM with a coarse approach in two dimensions, the z- and x- directions which are respectively parallel and perpendicular to the tip. This allows us to image samples with very high sensitivity at sites separated by macroscopic distances. This device is a single unit with a compact design making it very stable with the potential of use at cryogenic temperatures. This STM is capable of obtaining atomic resolution on HOPG. I will discuss the design of this STM and share images illustrating its capabilities.

  19. Scanning tunneling microscope with two-dimensional translator

    Science.gov (United States)

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

    2011-01-01

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

  20. Photovoltage on silicon surfaces measured by scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kuk, Y.; Becker, R.S.; Silverman, P.J.; Kochanski, G.P. (AT and T Bell Labs., Murray Hill, NJ (United States))

    In this paper surface bias voltages induced on a scanning tunnel microscope (STM) junction illuminated with laser radiation are spatially resolved for silicon surfaces. Surface photovoltages of {approximately}0.3 V for Si(111){minus}(7{times}7) and <0.1 V for Si(001){minus}(2{times}1) are observed with large reductions in the vicinity of surface/subsurface defects associated with midgap states. These reductions, attributed to a variation in the recombination rate, have typical surface screening lengths that are less than those found in the bulk. A small, atomically varying signal of 3-5 mV is also observed and is due to spatial variations in rectification efficiency rather than photovoltage.

  1. Nanoscale imaging of surface acoustic waves by scanning tunneling microscopy

    Science.gov (United States)

    Koch, R.; Yang, Jianshu

    2005-05-01

    The scanning tunneling microscope (STM) has proven to be a powerful technique for probing surface acoustic waves (SAWs) with high spatial resolution. Here we use our ultrahigh-vacuum SAW-STM to investigate a Rayleigh wave excited in LiNbO3 with emphasis laid on the SAW-induced signals at steps that are only a few atomic layers high. Our study reveals that on the length scale of a few nanometer the description of the amplitude and phase contrast by a plain geometrical model fails and a variety of other mechanisms decisively affect the SAW-induced signal. At steps the lateral surface movement due to the SAW may play an important role. For larger step inclination angles also the shape of the STM tip as well as tip-surface interactions become relevant, which may even drive a SAW-induced movement of the tip apex.

  2. Scanning Tunneling Studies on Insulators and Crystalline Gold.

    Science.gov (United States)

    Shen, Weidian

    Scanning tunneling microscope, invented by G. Binninig and H. Rohrer at IBM Zurich Research Laboratory in 1982, is a very powerful tool for surface science. With atomic scale resolution it has been used to study a variety of materials such as metals, metal films, semiconductors, superconductors, and layered materials. Samples for STM study must have at least moderate conductance in order to sustain a tunneling current. However, the ability to study insulators is of great importance too. In the first part of the thesis work, we have developed a high-vacuum low-temperature deposition method to deposit an Au film onto insulating surfaces. The Au films made in this method are sufficiently thin, smooth and featureless to a degree not anticipated and allow observation of substrate details. A variety of insulators, including fused silica, salt crystals, oxidized metals, silicon, plastics, ceramic high T_{rm c} superconductors, and membrane filters have been studied and good quality topographic images are obtained without the appearance of significant details attributable to Au films. Thus, we have extended the STM technique to application to all solid materials. In addition to topographic measurements, the scanning tunneling microscope with its local probing capability has been widely used in spectroscopic studies too. In this part of the thesis work, we studied the surface states on Au (111) surface and observed a surface state at about 0.4 eV below the Fermi level, which is in agreement with previous observations by photoemission. Furthermore, we studied the spatial distribution of that surface state, and obtained for the first time a spectroscopic image on Au (111) surface that reveals how the intensity of the state varies in the monatomic step region. In another application, the STM is used primarily to select and define the location of the experiment. We used this method to select an appropriate site for making a local point contact junction with an oxide layer to study the spectroscopic properties of a silicon wafer and a W -Si multilayer. This method also holds promise as a way to study local spectroscopy.

  3. 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...

  4. Node-like excitations in superconducting PbMo6S8 probed by scanning tunneling spectroscopy

    OpenAIRE

    Dubois, Ce?dric; Petrovic, Alexander; Santi, Gilles; Berthod, Christophe; Manuel, Alfred-adrien; Decroux, Michel Andre?; Fischer, Oystein; Potel, M.; Chevrel, R.

    2007-01-01

    We present a scanning tunneling spectroscopy study on the Chevrel phase PbMo6S8, an extreme type-II superconductor with a coherence length only slightly larger than in high-Tc cuprates. Tunneling spectra measured on atomically flat terraces are spatially homogeneous and show well-defined coherence peaks. The low-energy spectral weight, the zero bias conductance, and the temperature dependence of the gap are incompatible with a conventional isotropic s-wave interpretation, revealing the presen...

  5. Scanning Tunneling Spectroscopy on InAs-GaSb Esaki Diode Nanowire Devices during Operation.

    Science.gov (United States)

    Persson, Olof; Webb, James L; Dick, Kimberly A; Thelander, Claes; Mikkelsen, Anders; Timm, Rainer

    2015-06-10

    Using a scanning tunneling and atomic force microscope combined with in-vacuum atomic hydrogen cleaning we demonstrate stable scanning tunneling spectroscopy (STS) with nanoscale resolution on electrically active nanowire devices in the common lateral configuration. We use this method to map out the surface density of states on both the GaSb and InAs segments of GaSb-InAs Esaki diodes as well as the transition region between the two segments. Generally the surface shows small bandgaps centered around the Fermi level, which is attributed to a thin multielement surface layer, except in the diode transition region where we observe a sudden broadening of the bandgap. By applying a bias to the nanowire we find that the STS spectra shift according to the local nanoscale potential drop inside the wire. Importantly, this shows that we have a nanoscale probe with which we can infer both surface electronic structure and the local potential inside the nanowire and we can connect this information directly to the performance of the imaged device. PMID:25927249

  6. A scanning tunneling microscope capable of imaging specified micron-scale small samples

    Science.gov (United States)

    Tao, Wei; Cao, Yufei; Wang, Huafeng; Wang, Kaiyou; Lu, Qingyou

    2012-12-01

    We present a home-built scanning tunneling microscope (STM) which allows us to precisely position the tip on any specified small sample or sample feature of micron scale. The core structure is a stand-alone soft junction mechanical loop (SJML), in which a small piezoelectric tube scanner is mounted on a sliding piece and a "U"-like soft spring strip has its one end fixed to the sliding piece and its opposite end holding the tip pointing to the sample on the scanner. Here, the tip can be precisely aligned to a specified small sample of micron scale by adjusting the position of the spring-clamped sample on the scanner in the field of view of an optical microscope. The aligned SJML can be transferred to a piezoelectric inertial motor for coarse approach, during which the U-spring is pushed towards the sample, causing the tip to approach the pre-aligned small sample. We have successfully approached a hand cut tip that was made from 0.1 mm thin Pt/Ir wire to an isolated individual 32.5 × 32.5 ?m2 graphite flake. Good atomic resolution images and high quality tunneling current spectra for that specified tiny flake are obtained in ambient conditions with high repeatability within one month showing high and long term stability of the new STM structure. In addition, frequency spectra of the tunneling current signals do not show outstanding tip mount related resonant frequency (low frequency), which further confirms the stability of the STM structure.

  7. A scanning tunneling microscope capable of imaging specified micron-scale small samples.

    Science.gov (United States)

    Tao, Wei; Cao, Yufei; Wang, Huafeng; Wang, Kaiyou; Lu, Qingyou

    2012-12-01

    We present a home-built scanning tunneling microscope (STM) which allows us to precisely position the tip on any specified small sample or sample feature of micron scale. The core structure is a stand-alone soft junction mechanical loop (SJML), in which a small piezoelectric tube scanner is mounted on a sliding piece and a "U"-like soft spring strip has its one end fixed to the sliding piece and its opposite end holding the tip pointing to the sample on the scanner. Here, the tip can be precisely aligned to a specified small sample of micron scale by adjusting the position of the spring-clamped sample on the scanner in the field of view of an optical microscope. The aligned SJML can be transferred to a piezoelectric inertial motor for coarse approach, during which the U-spring is pushed towards the sample, causing the tip to approach the pre-aligned small sample. We have successfully approached a hand cut tip that was made from 0.1 mm thin Pt?Ir wire to an isolated individual 32.5 × 32.5 ?m(2) graphite flake. Good atomic resolution images and high quality tunneling current spectra for that specified tiny flake are obtained in ambient conditions with high repeatability within one month showing high and long term stability of the new STM structure. In addition, frequency spectra of the tunneling current signals do not show outstanding tip mount related resonant frequency (low frequency), which further confirms the stability of the STM structure. PMID:23277990

  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. Scanning Tunneling Microscopy Studies of Diamond Films and Optoelectronic Materials

    Science.gov (United States)

    Perez, Jose M.

    1996-01-01

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

  10. Scanning tunneling microscopy and spectroscopy of multiwall carbon nanotubes

    International Nuclear Information System (INIS)

    We report on the structural analysis of multiwall carbon nanotubes (MWNTs), produced by DC arc discharge in hydrogen gas, using a scanning tunneling microscope operated at ambient conditions. On a microscopic scale the images show tubes condensed in ropes as well as individual tubes which are separated from each other. Individual nanotubes exhibit various diameters (2.5-6 nm) and chiralities (0-30 degree sign ). For MWNTs rope, the outer portion is composed of highly oriented nanotubes with nearly uniform diameter (4-5 nm) and chirality. Strong correlation is found between the structural parameters and the electronic properties in which the MWNTs span the metallic-semiconductor regime. True atomic-resolution topographic STM images of the outer shell show hexagonal arrangements of carbon atoms that are equally visible by STM tip. This suggests that the stacking nature of MWNTs has no detectable effects on the electronic band structure of the tube shells. Unlike other MWNTs produced by arc discharge in helium gas, the length of the tubes are rather short (80-500 nm), which make it feasible to use them as a components for molecular electronic devices

  11. Graphene grain boundary resistivity revealed by scanning tunneling potentiometry

    Science.gov (United States)

    Durand, Corentin; Clark, Kendal W.; Zhang, Xiaoguang; Vlassiouk, Ivan V.; Li, An-Ping; Oak Ridge National Lab Team

    2014-03-01

    All large-scale graphene films contain extended topological defects dividing graphene into domains or grains. Here, we study grain boundary (GB) resistivity in CVD graphene on Cu subsequently transferred to a SiO2 substrate. By using a scanning tunneling potentiometry (STP) setup with a cryogenic four-probe STM, the spatial variation of the local electrochemical potential is resolved across individual GBs on a graphene surface in the presence of a current. The 2D distributions of electric field and conductivity were then numerically extracted by solving conduction equations. The derived conductivity of individual grains was compared to that measured with microscopic four-probe STM method to provide a model-independent determination of conductivity map for specific type of defect in graphene. The resistance of a GB is found to change with the width of the disordered transition region between adjacent grains. A quantitative modeling of boundary resistance reveals the increased electron Fermi wave vector within the boundary region, possibly due to boundary induced charge density variation.

  12. Oxygen-free in situ scanning tunnelling microscopy

    DEFF Research Database (Denmark)

    Zhang, Jingdong; Ulstrup, Jens

    2007-01-01

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

  13. Scanning Tunneling Microscopy of DNA-Carbon Nanotube Hybrids

    Science.gov (United States)

    Yarotski, Dzmitry; Kilina, Svetlana; Talin, Alec; Balatsky, Alexander; Tretiak, Sergei; Taylor, Antoinette

    2009-03-01

    Production of carbon nanotube-based (CNT) devices holds a great promise for bringing the size of electronic circuits down to molecular scales. Recently, yet another step has been made towards achieving this goal by developing a new method for metal-semiconductor CNT separation, which relies on wrapping the CNT with ssDNA molecule[1]. Though it was shown that the outcome of the separation process strongly depends on the DNA sequence, further investigations have to be conducted to determine detailed structure of the hybrids and their electronic properties. Here, we use STM to characterize structural and electronic properties of the CNT-DNA hybrids and compare experimental results to theoretical calculations. STM images reveal 3.3 nm DNA coiling period, which agrees very well with the theoretical predictions. Additional width modulations with characteristic lengths of 1.9 and 2.6 nm are observed along the molecule itself. Although scanning tunneling microscopy confirms the presence of DNA in the hybrid and visualizes its structure, further experimental work is required to reveal the dependence of electronic properties of hybrids on their internal structure. [1] M. Zheng et al., Science 302, 1545 (2004).

  14. Compact Scanning Tunneling Microscope for Spin Polarization Measurements

    Science.gov (United States)

    Kim, Seong Heon; Chen, Leujen; de Lozanne, Alex

    2012-02-01

    We have built a low temperature scanning tunneling microscope for spin-polarized studies. An important aspect of our design philosophy is to keep everything small, starting with a one-inch STM body that fits in the UHV bore of a small superconducting solenoid that provides up to 8 Tesla parallel to the tip. This, in turn, makes the liquid helium and liquid nitrogen dewars smaller and leads to a compact UHV chamber. The largest flange in the system is 10 inches in outer diameter. The benefits of a smaller system include lower consumption of cryogens and a reduced footprint. The STM has been tested from 300K to 77K and has achieved atomic resolution. A test at 4.2K will be done soon. We have imaged cobalt clusters deposited in situ using a simple and compact design for an electron-beam evaporator. We have developed new electronics for z-approach and a novel magnetically-coupled manipulator with an actuated grabber for tip and sample exchange.

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

    International Nuclear Information System (INIS)

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

  16. Atomic and electronic structure in collapsed carbon nanotubes evidenced by scanning tunneling microscopy

    OpenAIRE

    Giusca, Ce; Tison, Y.; Silva, Srp

    2007-01-01

    The electronic behavior of a radially collapsed armchair carbon nanotube encountered by scanning tunneling microscopy experiments is presented in a study that probes the electronic changes directly associated with the atomically resolved structural perturbations. The finite density of states obtained through scanning tunneling spectroscopy at the Fermi energy when the interspacing of the flattened faces does not allow for bond formation suggests that the electronic properties are slightly mod...

  17. 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 een 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

  18. Scanning Tunneling Microscopy and Spectroscopy of Rare Earth-Monopnictide Nanostructures Embedded in a Semiconducting Matrix

    Science.gov (United States)

    Kawasaki, Jason; Timm, Rainer; Buehl, Trevor; Lundgren, Edvin; Mikkelsen, Anders; Gossard, Arthur; Palmstrãm, Chris

    2011-03-01

    The atomic and electronic structure of molecular beam epitaxy (MBE)-grown rare earth-monopnictide nanostructures embedded within a III-V semiconductor matrix are examined via scanning tunneling microscopy (STM) and spectroscopy (STS). We examine several systems, including ErSb nanoparticles embedded in GaSb, ScAs nanoparticles embedded in GaAs, and ErAs nanoparticles and nanorods embedded in GaAs. Tunneling current I(V) and differential conductance dI/dV spectra show that for both ErAs nanoparticles and nanorods the local density of states (LDOS) exhibits a sharp but finite minimum at the Fermi level, demonstrating that both the particles and rods are semimetallic and not semiconducting. This observation lies in contrast to previous models of quantum confinement in ErAs. We also use STS to measure the LDOS across the ErAs/GaAs interface and discuss the formation of interface states and band bending at the interface. Finally, we discuss possible changes in the LDOS with varying nanoparticle size and varying levels of doping in the semiconductor matrix.

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

    Directory of Open Access Journals (Sweden)

    wang K.-L.

    2012-03-01

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

  20. 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.

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

    CERN Document Server

    Kong, J; Lemay, S G; Dekker, C

    2005-01-01

    We have developed a fabrication process for incorporating a gate electrode into suspended single-walled carbon nanotube structures for scanning tunneling spectroscopy studies. The nanotubes are synthesized by chemical vapor deposition directly on a metal surface. The high temperature ~800 C involved in the growth process poses challenging issues such as surface roughness and integrity of the structure which are addressed in this work. We demonstrate the effectiveness of the gate on the freestanding part of the nanotubes by performing tunneling spectroscopy that reveals Coulomb blockade diamonds. Our approach enables combined scanning tunneling microscopy and gated electron transport investigations of carbon nanotubes.

  2. 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.

  3. 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.

  4. Design and construction of a low temperature scanning tunneling microscope for studying high temperature superconductivity

    Science.gov (United States)

    Jayasundara, Dilushan R.

    2008-10-01

    The complexities associated with high temperature superconductivity (HTS) have challenged scientists for over two decades, and as a result, the need for microscopic measurements has grown steadily. The scanning tunneling microscope's (STM) ability to image both the surface structure, and the local density of states (LDOS) with subatomic resolution has therefore made it a valuable technique to study HTS. In this thesis, I will present the design and construction of our state-of-the-art cryogenic scanning tunneling microscope, from which we were able to obtain both topographic and spectroscopic data with high spatial and energy resolution. The STM experiments on Yittrium-Bi2212, with a doping concentration close to the critical doping, revealed a checkerboard like modulations in its LDOS maps. Evaluation of these modulations for their energy dependence was carried out using Fourier transform mapping technique. We found a continuous dispersion of the modulation wave vector with energy. Whereas the dispersion was substantial at lower energies, it became continuously smaller with increasing energy. In this thesis, I will also present the STM investigation of the newly discovered pnictide superconductors. For this we studied the Co-BaFe 2As2 superconductor, which has a Tc of 22K. The cleaved surface of Co-BaFe2As2 showed a 2a0 stripe modulation along the As-As bond direction and the differential conductance spectra obtained on this surface revealed a 6meV gap opening at the Fermi energy. The Value of the BCS reduced gap and the shape of the gap reveals that the superconductivity is unconventional.

  5. Electronic processes in scanning tunneling microscopy of carbon nanotubes

    International Nuclear Information System (INIS)

    An LCAO theory of the tunneling current between carbon materials (sp2) and a metallic tip is developed to simulate their differential conductance and STM images. The tunneling current is expressed by a series expansion of the resolvent operator which is computed with a recursion algorithm. The differential conductance of both chiral and achiral nanotubes is calculated. We emphasize the fact that electronic and geometrical effects must be interpreted with much attention in STM imaging of carbon nanotubes

  6. 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...

  7. Note: Long-range scanning tunneling microscope for the study of nanostructures on insulating substrates

    International Nuclear Information System (INIS)

    The scanning tunneling microscope (STM) is a powerful tool for studying the electronic properties at the atomic level, however, it is of relatively small scanning range and the fact that it can only operate on conducting samples prevents its application to study heterogeneous samples consisting of conducting and insulating regions. Here we present a long-range scanning tunneling microscope capable of detecting conducting micro and nanostructures on insulating substrates using a technique based on the capacitance between the tip and the sample and performing STM studies

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

    Science.gov (United States)

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

    2015-05-01

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

  9. 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...

  10. Scanning tunneling spectroscopy study of the proximity effect in a disordered two-dimensional metal

    OpenAIRE

    Serrier-garcia, L.; Cuevas, J. C.; Cren, T.; Brun, C.; Cherkez, V.; Debontridder, F.; Fokin, D.; Bergeret, F. S.; Roditchev, D.

    2014-01-01

    The proximity effect between a superconductor and a highly diffusive two-dimensional metal was revealed in a Scanning Tunneling Spectroscopy experiment. The in-situ elaborated samples consisted of superconducting single crystalline Pb islands interconnected by a non-superconducting atomically thin disordered Pb wetting layer. In the vicinity of each superconducting island the wetting layer acquires specific tunneling characteristics which reflect the interplay between the pr...

  11. Spin-polarized scanning tunneling microscopy at the solid/liquid interface

    Science.gov (United States)

    Majer, C.; Schindler, W.

    2015-01-01

    We show strong indications for spin-polarized tunneling between a magnetic tip of a scanning tunneling microscope and a magnetic substrate at a solid/liquid interface under electrochemical conditions at room temperature. As a model system Co islands of several 100 nm in diameter were electrochemically grown on Au(111). They show a perpendicular easy axis of the magnetization for two and three atomic layers of Co.

  12. Combined Scanning Nanoindentation and Tunneling Microscope Technique by Means of Semiconductive Diamond Berkovich Tip

    International Nuclear Information System (INIS)

    A combined Scanning Probe Microscope (SPM) - nanoindentation instrument enables submicron resolution indentation tests and in-situ scanning of structure surfaces. A newly developed technique is based on the scanning tunneling microscopy (STM) with integrated Berkovich diamond semiconductive tip. Diamond tips for a combined SPM were obtained using the developed procedure including the synthesis of the semiconductive borondoped diamond monocrystals by the temperature gradient method at high pressure - high temperature conditions and fabrication of the tips from these crystals considering their zonal structure. Separately grown semiconductive diamond single crystals were studied in order to find the best orientation of diamond crystals. Optimal scanning characteristics and experimental data errors were calculated by an analysis of the general functional dependence of the tunneling current from properties of the tip and specimen. Tests on the indentation and scanning of the gold film deposited on the silicon substrate employing the fabricated tips demonstrated their usability, acceptable resolution and sensitivity

  13. Scanning tunneling spectroscopy of single-wall carbon nanotubes on a polymerized gold substrate

    Science.gov (United States)

    Shao, F.; Zha, F. X.; Pan, C. B.; Shao, J.; Zhao, X. L.; Shen, X. C.

    2014-02-01

    The physics picture on scanning tunneling spectroscopy of single-wall carbon nanotubes (SWCNTs) was revisited recently [H. Lin et al., Nat. Mater. 9, 235 (2010), 10.1038/nmat2771] with an image potential model under the framework of the many-body theory whose description is different from that of conventional one-particle tight-binding theory. The model is explored further in the present study of SWCNTs with an ultrahigh-vacuum scanning tunneling microscope. In the experiments, two types of samples were measured. In one sample, the nanotubes were in intimate contact with the gold surface and the observed tunneling gaps of semiconductor nanotubes fit the prediction of the one-particle model. In the other sample, the nanotubes were isolated by a thin polymer (4-vinylpyridine) layer from the gold surface. The semiconducting SWCNTs in the latter sample show tunneling gaps several hundreds of milli-electron volts larger than the prediction of the one-particle model. The results can, however, be interpreted by the modified image potential model, which takes into account the surface dielectric mechanism. The consistent picture of the tunneling gaps of the different samples provides insight into the scanning tunneling spectroscopy of SWCNTs from the standpoint of many-body theory.

  14. Scanning tunneling spectroscopy at the single atom scale

    OpenAIRE

    Ternes, Markus

    2006-01-01

    Cette thèse rapporte des mesures faites à l'échelle de l'atome en utilisant la microscopie et la spectroscopie à balayage par effet tunnel (STM et STS). Différents systèmes d'échantillons ont été analysés avec des pointes conductrices normale et supraconductrices. Le chapitre 2 présente les aspects théoriques donc nous devons tenir compte afin d'avoir une analyse détaillée et une interprétation consistente des mesures de la STS. Dans le chapitre 3 la création d'un superréseau...

  15. 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

  16. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Galloway, H.C.

    1995-12-01

    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.

  18. Na intercalation of VSe2 studied by photoemission and scanning tunneling microscopy

    Science.gov (United States)

    Brauer, H. E.; Ekvall, Inger; Olin, H.; Starnberg, H. I.; Wahlströautm, Erik; Hughes, H. P.; Strocov, V. N.

    1997-04-01

    In situ Na intercalation of the layered compound VSe2 has been studied with photoemission and scanning tunneling microscopy. Core-level spectroscopy proves that Na deposited in UHV onto the VSe2 surface rapidly intercalates, leaving only small amounts at the surface. The scanning tunneling microscopy measurements show that the intercalated Na is not uniformly distributed between the VSe2 layers, but preferentially in two-dimensional islands. Thus the surface region is divided into intercalated and nonintercalated areas. Holelike features in the intercalated areas are interpreted as locally missing Na.

  19. 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

  20. Scanning tunneling microscopy investigation of atomic-scale carbon nanotube defects produced by Ar+ ion irradiation

    International Nuclear Information System (INIS)

    Multi-wall carbon nanotubes (MWCNTs) dispersed on graphite (HOPG) substrate were irradiated with Ar+ ions of 30 keV, using a dose of D = 5 x 1011 ions/cm2. The irradiated nanotubes were investigated by scanning tunneling microscopy (STM) and spectroscopy (STS) under ambient conditions. Atomic resolution STM images revealed individual nanotube defects, which appeared as 'hillocks' of 0.1-0.2 nm in height, due to the locally changed electronic structure. The results are in agreement with previous theoretical predictions. Electron density patterns (superstructures) were observed near the defect sites, which originated from the interference of incident waves and waves scattered by defects. The period of these superstructures is larger than the period determined by the atomic structure. After annealing at 450 deg. C in nitrogen atmosphere, the irradiated MWCNTs were investigated again. The effect of heat treatment on the irradiation-induced nanotube-defects was observed both on the STM images and on the recorded STS spectra

  1. 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.

  2. 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.

  3. 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 ...

  4. Scanning tunneling microscopy studies of light-induced switching of diarylethenes & functionalized graphene

    OpenAIRE

    Arramel,

    2012-01-01

    De controle over de structurele ordening van -geconjugeerde organische moleculen met op maat gemaakte chemische functies en fysische eigenschappen is een essentile voorwaarde voor de ontwikkeling van hoogwaardige elektronische apparaatjes op molecuulschaal. Een van de moleculaire testsystemen, de zogenaamde 'scanning probe microscopie', heeft bewezen een onmisbaar gereedschap in dit veld te zijn. De ontdekking van de 'scanning tunneling microscopy' (STM) in 1982 betekende in het bijz...

  5. 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

  6. Low Temperature Scanning Tunneling Spectroscopy of isolated Mn12-Ph Single Molecule Magnets

    Science.gov (United States)

    Reaves, K.; Han, P.; Iwaya, K.; Hitosugi, T.; Packwood, D.; Katzgraber, H. G.; Zhao, H.; Dunbar, K. R.; Kim, K.; Teizer, W.

    2015-03-01

    We study Mn12O12(C6H5COO)16(H2O)4 (Mn12-Ph) single-molecule magnets on a Cu(111) surface using scanning tunneling microscopy and scanning tunneling spectroscopy at cryogenic temperatures (T isolation and in thin films, deposited through in situ vacuum spray deposition onto clean Cu(111). The tunneling current of isolated Mn12-Ph, normalized with respect to the Cu background, shows a strong bias voltage dependence within the molecular interior. The qualitative features of these I vs.V curves differ by spatial location in several intriguing ways (e.g. fixed junction impedance with increasing bias voltages). We explore these normalized I vs. V curves and present a phenomenological explanation for the observed behaviors, corresponding to the physical and electronic structure within the molecule. Funding from WPI-AIMR.

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

    DEFF Research Database (Denmark)

    Keil, Ulrich Dieter Felix; Jensen, Jacob Riis

    1998-01-01

    We demonstrate: the use of an ultrafast scanning tunneling microscope on a semiconductor surface. Laser-induced transient signals with 1.8 ps rise time are detected, The investigated sample is a low-temperature grown GaAs layer plated on a sapphire substrate with a thin gold layer that serves as st bias contact, For comparison, the measurements are performed with the tip in contact to the sample as well as in tunneling above the surface, In contact and under bias, the transient signals are identified as a transient photocurrent, An additional signal is generated by a transient voltage induced by the nonuniform carrier density created by the absorption of the light (photo Dember effect). The transient depends in sign and in shape on the direction of optical excitation. This signal is the dominating transient in tunneling mode. The signals are explained by a capacitive coupling across the tunneling gap, (C) 1998 American Institute of Physics.

  8. 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...

  9. Superstructure formation and faceting in the Cu(210)-O system studied by scanning tunneling microscopy

    OpenAIRE

    Wee, Ats; Foord, Js; Egdell, Rg; Pethica, Jb

    1998-01-01

    The interaction of O on Cu(210) has been investigated by scanning tunneling microscopy. Adsorption at room temperature followed by high-temperature annealing leads to a series of mesoscopic superstructures ordered on different length scales ranging between 15 and 150 Å. By contrast, adsorption at high temperatures leads to the formation of a (2 × 1) superstructure similar to that found on Cu(110).

  10. 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.

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

    Science.gov (United States)

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

    2014-09-30

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Ocko, B.M.; Magnussen, O.M.; Wang, J.X.; Adzic, R.R.

    1993-12-31

    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.

  13. 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

  14. 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.

  15. 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)

  16. Local crystallography analysis for atomically resolved scanning tunneling microscopy images

    International Nuclear Information System (INIS)

    Scanning probe microscopy has emerged as a powerful and flexible tool for atomically resolved imaging of surface structures. However, due to the amount of information extracted, in many cases the interpretation of such data is limited to being qualitative and semi-quantitative in nature. At the same time, much can be learned from local atom parameters, such as distances and angles, that can be analyzed and interpreted as variations of local chemical bonding, or order parameter fields. Here, we demonstrate an iterative algorithm for indexing and determining atomic positions that allows the analysis of inhomogeneous surfaces. This approach is further illustrated by local crystallographic analysis of several real surfaces, including highly ordered pyrolytic graphite and an Fe-based superconductor FeTe0.55Se0.45. This study provides a new pathway to extract and quantify local properties for scanning probe microscopy images. (paper)

  17. Electronic effects in scanning tunnelling microscopy of metal-filled multiwalled carbon nanotubes

    International Nuclear Information System (INIS)

    We have used ultrahigh-vacuum scanning tunnelling microscopy to investigate the effects of Fe filling on the electronic structure of multiwalled carbon nanotubes (MWNTs). When imaged using constant current feedback, Fe-filled MWNTs exhibit striking contrast corrugations that strongly correlate to expected positions (from transmission electron microscopy) of the Fe fillings along the nanotubes. Furthermore, the corrugation in contrast corresponds to significant variations in local electronic structure as determined by tunnelling spectroscopy. These results suggest that inner cores of Fe-filled carbon nanotubes can exhibit considerable influence on the electronics of the outer shells of even large MWNTs

  18. Fermi surface contours obtained from scanning tunneling microscope images around surface point defects

    International Nuclear Information System (INIS)

    We present a theoretical analysis of the standing wave patterns in scanning tunneling microscope (STM) images, which occur around surface point defects. We consider arbitrary dispersion relations for the surface states and calculate the conductance for a system containing a small-size tunnel contact and a surface impurity. We find rigorous theoretical relations between the interference patterns in the real-space STM images, their Fourier transforms and the Fermi contours of two-dimensional electrons. We propose a new method for reconstructing Fermi contours of surface electron states, directly from the real-space STM images around isolated surface defects. (paper)

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. Locality and lateral modulations of quantum well states in Ag(100) thin films studied using a scanning tunneling microscope

    Science.gov (United States)

    Uchihashi, Takashi; Nakayama, Tomonobu

    2015-07-01

    We investigate Ag(100) thin films epitaxially grown on a Fe(100) substrate using a low-temperature scanning tunneling microscope. Fabrication of a wedge structure by evaporating Ag through a shadow mask allows us to observe a systematic evolution of quantum well (QW) states for layer thicknesses varying from 3 to 16 monolayers (ML). Close inspection of differential conductance spectra and images reveals significant modulations of QW states in the lateral directions, presumably due to the local defects at the Ag/Fe interface. The area where QW states are modulated extends over ~ 5 nm. In clear contrast, near a surface atomic step, QW states exhibit negligible changes at least up to 1 nm away from the step, leaving unmixed the two sets of neighboring QW states belonging to different thicknesses. The results are discussed in terms of a simple electron wave diffraction model.

  5. Experimental demonstration of a two-band superconducting state for lead using scanning tunneling spectroscopy.

    Science.gov (United States)

    Ruby, Michael; Heinrich, Benjamin W; Pascual, Jose I; Franke, Katharina J

    2015-04-17

    The type I superconductor lead (Pb) has been theoretically predicted to be a two-band superconductor. We use scanning tunneling spectroscopy (STS) to resolve two superconducting gaps with an energy difference of 150???eV. Tunneling into Pb(111), Pb(110), and Pb(100) crystals reveals a strong dependence of the two coherence peak intensities on the crystal orientation. We show that this is the result of a selective tunneling into the two bands at the energy of the two coherence peaks. This is further sustained by the observation of signatures of the Fermi sheets in differential conductance maps around subsurface defects. A modification of the density of states of the two bands by adatoms on the surface confirms the different orbital character of each of the two subbands. PMID:25933331

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

    International Nuclear Information System (INIS)

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

  7. a New Approach for Subway Tunnel Deformation Monitoring: High-Resolution Terrestrial Laser Scanning

    Science.gov (United States)

    Li, J.; Wan, Y.; Gao, X.

    2012-07-01

    With the improvement of the accuracy and efficiency of laser scanning technology, high-resolution terrestrial laser scanning (TLS) technology can obtain high precise points-cloud and density distribution and can be applied to high-precision deformation monitoring of subway tunnels and high-speed railway bridges and other fields. In this paper, a new approach using a points-cloud segmentation method based on vectors of neighbor points and surface fitting method based on moving least squares was proposed and applied to subway tunnel deformation monitoring in Tianjin combined with a new high-resolution terrestrial laser scanner (Riegl VZ-400). There were three main procedures. Firstly, a points-cloud consisted of several scanning was registered by linearized iterative least squares approach to improve the accuracy of registration, and several control points were acquired by total stations (TS) and then adjusted. Secondly, the registered points-cloud was resampled and segmented based on vectors of neighbor points to select suitable points. Thirdly, the selected points were used to fit the subway tunnel surface with moving least squares algorithm. Then a series of parallel sections obtained from temporal series of fitting tunnel surfaces were compared to analysis the deformation. Finally, the results of the approach in z direction were compared with the fiber optical displacement sensor approach and the results in x, y directions were compared with TS respectively, and comparison results showed the accuracy errors of x, y, z directions were respectively about 1.5 mm, 2 mm, 1 mm. Therefore the new approach using high-resolution TLS can meet the demand of subway tunnel deformation monitoring.

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

    Science.gov (United States)

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

    2014-09-01

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

  9. Nanolithography on graphene by using scanning tunneling microscopy in a methanol environment.

    Science.gov (United States)

    Kim, Chulsu; Park, Joonkyu; Seo, Yongho; Ahn, Jinho; Park, In-Sung

    2013-12-01

    Since it was discovered in 2004, graphene has attracted enormous attention as an emerging material for future devices, but it has been found that conventional lithographic processes based on polymer resist degrade its intrinsic performance. Recently, our group studied a resist-free scanning tunneling microscopy-based lithography in various atmospheres by injecting volatile liquids into a chamber. In this study, multilayer graphene was scanned and etched by controlling bias voltage under methanol pressure. We focused on improving patterning results in terms of depth and line width, while the previous study was performed to find an optimum gas environment for patterning on a graphite surface. Specifically, we report patterning outputs depending on conditions of voltage, current, and pressure. The optimum conditions for methanol environment etching were a gas pressure in the range of 41-50 torr, a -4 V tip bias, and a 2 nA tunneling current. PMID:24016389

  10. Probing Dirac Fermion Dynamics in Topological Insulator Bi$_2$Se$_3$ Films with Scanning Tunneling Microscope

    OpenAIRE

    Song, Can-li; Wang, Lili; He, Ke; Ji, Shuai-hua; Chen, Xi; Ma, Xu-cun; Xue, Qi-kun

    2015-01-01

    Scanning tunneling microscopy and spectroscopy have been used to investigate the femtosecond dynamics of Dirac fermions in the topological insulator Bi$_2$Se$_3$ ultrathin films. At two-dimensional limit, bulk electrons becomes quantized and the quantization can be controlled by film thickness at single quintuple layer level. By studying the spatial decay of standing waves (quasiparticle interference patterns) off steps, we measure directly the energy and film thickness depe...

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

    OpenAIRE

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

    2005-01-01

    We have developed a fabrication process for incorporating a gate electrode into suspended single-walled carbon nanotube structures for scanning tunneling spectroscopy studies. The nanotubes are synthesized by chemical vapor deposition directly on a metal surface. The high temperature ~800 C involved in the growth process poses challenging issues such as surface roughness and integrity of the structure which are addressed in this work. We demonstrate the effectiveness of the ...

  12. Scanning tunneling microscopy of chromium-filled carbon nanotubes: Tip effects and related topographic features

    International Nuclear Information System (INIS)

    We have used ultrahigh vacuum scanning tunneling microscopy (STM) to study chromium (Cr)-filled carbon nanotubes. STM micrographs show filled tubes to be less than 1 nm in height, while transmission electron microscopy indicates that Cr-filled naotubes are multiwalled with diameters generally over 10 nm. In this paper, we demonstrate that the small apparent heights are due to the STM tip status, which also accounts for the topographic anomalies observed

  13. Mapping of functionalized regions on carbon nanotubes by scanning tunneling microscopy

    OpenAIRE

    Nemes-incze, P.; Ko?nya, Z.; Kiricsi, I.; Pekker, A?; Horva?th, Z. E.; Kamara?s, K.; Biro?, L. P.

    2010-01-01

    Scanning tunneling microscopy (STM) gives us the opportunity to map the surface of functionalized carbon nanotubes in an energy resolved manner and with atomic precision. But this potential is largely untapped, mainly due to sample stability issues which inhibit reliable measurements. Here we present a simple and straightforward solution that makes away with this difficulty, by incorporating the functionalized multiwalled carbon nanotubes (MWCNT) into a few layer graphene - ...

  14. Observation of elastic deformations in single-walled carbon nanotubes by Scanning Tunneling Microscopy

    International Nuclear Information System (INIS)

    Scanning Tunneling Microscopy is used to obtain atomically resolved images of single-walled carbon nanotubes, in ropes of several tens to hundreds of tubes. The images confirm that in this environment strong elastic deformations of the tube lattice occur frequently. In particular, bent and twisted tubes have been identified. The observed distortions could play an important role in explaining the electronic transport properties of nanotubes

  15. Novel water overlayer growth on Pd(111) characterized with scanning tunneling microscopy and density functional theory

    OpenAIRE

    Cerda, J.; Michaelides, A.; Bocquet, M. L.; Feibelman, P. J.; Mitsui, T.; ROSE, M; Fomin, E.; Salmeron, M.

    2004-01-01

    Scanning tunneling microscopy (STM) images of water submonolayers on Pd(111) reveal quasiperiodic and isolated adclusters with internal structure that would ordinarily be ascribed to icelike puckered hexagonal units. However, density functional theory and STM simulations contradict this conventional picture, showing instead that the water adlayers are composed mainly of flat-lying molecules arranged in planar water hexagons. A new rule for two dimensional (2D) water growth is offered that gen...

  16. A Pathway between Bernal and Rhombohedral Stacked Graphene Layers with Scanning Tunneling Microscopy

    OpenAIRE

    Xu, P.; Yang, Y.; Qi, D.; Barber, S. D.; Ackerman, M. L.; Schoelz, J. K.; Bothwell, T. B.; Barraza-lopez, S.; Bellaiche, L.; Thibado, P. M.

    2015-01-01

    Horizontal shifts in the top layer of highly oriented pyrolytic graphite, induced by a scanning tunneling microscope (STM) tip, are presented. Excellent agreement is found between STM images and those simulated using density functional theory. First-principle calculations identify that the low-energy barrier direction of the top layer displacement is toward a structure where none of the carbon pz orbitals overlap, while the high-energy barrier direction is toward AA stacking...

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

    OpenAIRE

    Settnes, Mikkel; Power, Stephen R.; Petersen, Dirch H.; 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 tunnelling 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. The s...

  18. HIGH RESOLUTION ELECTRON BEAM INJECTION IN SEMICONDUCTORS USING A SCANNING TUNNELING MICROSCOPE

    OpenAIRE

    Alvarado, S.; Renaud, Ph; Meier, H.

    1991-01-01

    The tip of a scanning tunneling microscope is used as a source of ultralow-energy electrons to excite luminescence in model AlGaAs/GaAs(001) heterostructures. This beam injection technique has the advantage of providing a nanometer-sized charge generation volume. We demonstrate the application of this technique to determine minority charge carrier transport parameters such as the thermalization length of hot electrons and the diffusion length of minority electrons.

  19. Probing electron-electron interaction in quantum Hall systems with scanning tunneling spectroscopy

    OpenAIRE

    Becker, S.; Karrasch, C.; Mashoff, T.; Pratzer, M.; Liebmann, M.; Meden, V.; Morgenstern, M.

    2010-01-01

    Using low-temperature scanning tunneling spectroscopy applied to the Cs-induced two-dimensional electron system (2DES) on p-type InSb(110), we probe electron-electron interaction effects in the quantum Hall regime. The 2DES is decoupled from p-doped bulk states and exhibits spreading resistance within the insulating quantum Hall phases. In quantitative agreement with calculations we find an exchange enhancement of the spin splitting. Moreover, we observe that both the spatia...

  20. Electronic Band Dispersion of Graphene Nanoribbons via Fourier-Transformed Scanning Tunneling Spectroscopy

    OpenAIRE

    So?de, Hajo; Talirz, Leopold; Gro?ning, Oliver; Pignedoli, Carlo Antonio; Berger, Reinhard; Feng, Xinliang; Mu?llen, Klaus; Fasel, Roman; Ruffieux, Pascal

    2014-01-01

    Atomically precise armchair graphene nanoribbons of width $N=7$ (7-AGNRs) are investigated by scanning tunneling spectroscopy (STS) on Au(111). The analysis of energy-dependent standing wave patterns of finite length ribbons allows, by Fourier transformation, the direct extraction of the dispersion relation of frontier electronic states. Aided by density functional theory calculations, we assign the states to the valence band, the conduction band and the next empty band of 7...

  1. Robust Nodal Structure of Landau Level Wave Functions Revealed by Fourier Transform Scanning Tunneling Spectroscopy

    OpenAIRE

    Hashimoto, K.; Champel, T.; Florens, S.; Sohrmann, C.; Wiebe, J.; Hirayama, Y.; Roemer, R. A.; Wiesendanger, R.; Morgenstern, M.

    2012-01-01

    Scanning tunneling spectroscopy is used to study the real-space local density of states (LDOS) of a two-dimensional electron system in magnetic field, in particular within higher Landau levels (LL). By Fourier transforming the LDOS, we find a set of n radial minima at fixed momenta for the nth LL. The momenta of the minima depend only on the inverse magnetic length. By comparison with analytical theory and numerical simulations, we attribute the minima to the nodes of the qu...

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

    OpenAIRE

    Nig, Thomas K.; Simon, Georg H.; Lars Heinke; Leonid Lichtenstein; Markus Heyde

    2011-01-01

    Surfaces of thin oxide ?lms were investigated by means of a dual mode NC-AFM/STM. Apart from imaging the surface termination by NC-AFM with atomic resolution, point defects in magnesium oxide on Ag(001) and line defects in aluminum oxide on NiAl(110), respectively, were thoroughly studied. The contact potential was determined by Kelvin probe force microscopy (KPFM) and the electronic structure by scanning tunneling spectroscopy (STS). On magnesium oxide, different color centers, i.e., ...

  3. 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.

  4. Direct measurements of magnetostrictive process in amorphous wires using scanning tunneling microscopy

    OpenAIRE

    Costa, J. L.

    1995-01-01

    We demonstrate a versatile capability to measure directly the magnetostrictive properties through the magnetization process on a nanometric scale using a modified scanning tunneling microscope. Single 10 mm long, 125 ?m diam amorphouswires of both positive and negative magnetostriction have been studied and the data are compared with the hysteretic loops determined by both ac and SQUID magnetic measurements. This improved technique promises interesting possibilities, from both fundamental an...

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

    OpenAIRE

    Kingham, D.; Garcia, N.

    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.

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

    OpenAIRE

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

    2012-01-01

    Under mesoscopic conditions, the transport potential on a thin film with current is theoretically expected to bear spatial variation due to quantum interference. Scanning tunneling potentiometry is the ideal tool to investigate such variation, by virtue of its high spatial resolution. We report in this {\\it Letter} the first detailed measurement of transport potential under mesoscopic conditions. Epitaxial graphene at a temperature of 17K was chosen as the initial system for...

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

    OpenAIRE

    Ma?ndi, Ga?bor; Teobaldi, Gilberto; Palota?s, Krisztia?n

    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 dur...

  8. Scanning Tunneling Microscopy of Gate Tunable Topological Insulator Bi2Se3 Thin Films

    OpenAIRE

    Zhang, Tong; Levy, Niv; Ha, Jeonghoon; Kuk, Young; Stroscio, Joseph A.

    2013-01-01

    Electrical field control of the carrier density of topological insulators (TI) has greatly expanded the possible practical use of these materials. However, the combination of low temperature local probe studies and a gate tunable TI device remains challenging. We have overcome this limitation by scanning tunneling microscopy and spectroscopy measurements on in-situ molecular beam epitaxy growth of Bi2Se3 films on SrTiO3 substrates with pre-patterned electrodes. Using this ga...

  9. Simple model for scanning tunneling spectroscopy of noble metal surfaces with adsorbed Kondo impurities

    OpenAIRE

    Merino, J.; Gunnarsson, O.

    2003-01-01

    A simple model is introduced to describe conductance measurements between a scanning tunneling microscope (STM) tip and a noble metal surface with adsorbed transition metal atoms which display the Kondo effect. The model assumes a realistic parameterization of the potential created by the surface and a d3z2-r2 orbital for the description of the adsorbate. Fano lineshapes associated with the Kondo resonance are found to be sensitive to details of the adsorbate-substrate inter...

  10. Trapping and squeezing of vortices in voids directly observed by scanning tunneling microscopy and spectroscopy

    Science.gov (United States)

    Tominaga, Takaaki; Sakamoto, Takaki; Kim, Howon; Nishio, Takahiro; Eguchi, Toyoaki; Hasegawa, Yukio

    2013-05-01

    Using low-temperature scanning tunneling microscopy and spectroscopy, we have studied quantized magnetic fluxes (vortices) that penetrated nanosized superconductors with void structures inside. The void structures act as a pinning center for the vortices, and the trapped vortices are confined and squeezed inside. When multiple vortices are trapped in voids, a cluster of vortices and a giant vortex were formed as a result of the squeezing, depending on the depth and the size of the trapping potential.

  11. Interaction of bromine with Ni(110) studied by scanning tunnelling microscopy

    OpenAIRE

    Fishlock, Tw; Pethica, Jb; Oral, A.; Egdell, Rg; Jones, Fh

    1999-01-01

    The adsorption of bromine on Ni(110) has been studied by scanning tunnelling microscopy (STM). At low bromine coverage `butterfly' structures are observed in STM, built up from `pairs of pairs' of greyscale maxima. Two alternative models for the butterflies are discussed, the most plausible of which involves location of dissociated Br atoms in two-fold hollow sites flanked by pairs of Ni adatoms. At higher coverages the discrete butterfly structure breaks down and adatom pairs form a disorder...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-03-15

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

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

    Science.gov (United States)

    den Haan, A. M. J.; Wijts, G. H. C. J.; Galli, F.; Usenko, O.; van Baarle, G. J. C.; van der Zalm, D. J.; Oosterkamp, T. H.

    2014-03-01

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

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

    International Nuclear Information System (INIS)

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

  15. ScanRanker: Quality Assessment of Tandem Mass Spectra via Sequence Tagging

    OpenAIRE

    Ham, A. J.; Aerni, H. R.; Cheek, K.; Whitwell, C. W.; Caprioli, R. M.; Tabb, D. L.; Ma, Z.

    2011-01-01

    In shotgun proteomics, protein identification by tandem mass spectrometry relies on bioinformatics tools. Despite recent improvements in identification algorithms, a significant number of high quality spectra remain unidentified for various reasons. Here we present ScanRanker, an open-source tool that evaluates the quality of tandem mass spectra via sequence tagging with reliable performance in data from different instruments. The superior performance of ScanRanker enables it not only to find...

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

    DEFF Research Database (Denmark)

    Giusca, Cristina E; Tison, Yann

    2008-01-01

    Scanning Tunneling Microscopy and Spectroscopy have been used in an attempt to elucidate the electronic structure of nanotube systems containing two constituent shells. Evidence for modified electronic structure due to the inter-layer interaction in double-walled carbon nanotubes is provided by the experimental tunneling spectra and the contribution of the inner tube to the local density of states of the "composite" double-walled system is identified in agreement with previous theoretical calculations. An explicit correlation between the chirality of the two constituent tubes, the inter-wall interaction and the overall electronic structure for double-walled carbon nanotubes, is demonstrated by our experiments, showing that the effect the inner tube has on the overall electronic structure of double-walled nanotubes cannot be neglected, and is key to the opto-electronic properties of the system. We postulate that previous analysis of the opto-electronic properties on multiple-walled carbon nanotubes based purely on the outer layer chirality of the tube needs significant modification based on new understanding brought forth with our analysis.

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

    OpenAIRE

    Palacios, J. J.; Martin-moreno, L.; 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 ...

  18. Pseudo-gap in tunneling spectra as a signature of inhomogeneous superconductivity in oxide interfaces

    OpenAIRE

    Bucheli, D.; Caprara, S; M. Grilli

    2014-01-01

    We present a theory for the pseudo-gap state recently observed at the LaAlO3/SrTiO3 interface, based on superconducting islands embedded in a metallic background. Superconductivity within each island is BCS-like, and the local critical temperatures are randomly distributed, some of them necessarily exceeding the critical temperature for global percolation to the zero resistance state. Consequently, tunneling spectra display a suppression of the density of states and coherenc...

  19. 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.

  20. The effect of sputter deposition conditions on the growth mechanism of YBa2Cu3O7-? thin films studied by scanning tunnelling microscopy

    International Nuclear Information System (INIS)

    Surface topography of as-grown films of YBa2Cu3O7-? (YBCO) deposited by off-axis RF magnetron sputtering on MgO and SrTiO3 single-crystal (100) substrates, has been investigated by scanning tunnelling microscopy (STM)/scanning tunnelling spectroscopy (STS) operated in air at ambient temperature. Both c-axis- and a-axis-oriented YBCO films have been investigated. In the case of c axis thin films, we have directly observed spiral-shaped growth terraces, which emanate from screw dislocations of this layered superconducting oxide. The growth steps are generally seen to possess a step height close to or multiples of the unit cell height of the YBCO crystalline structure. In the case of a axis growth, the substrate as well as the deposition temperature determines the grain orientation. Furthermore, our STS data revealed that the surface layer of the film is semiconducting and the tunnelling spectrum varies its shape depending on the tip-to-sample distance. A superconducting gap appears clearly in the spectra when the STM tip is placed closer to the surface than the normal position of the scanning mode. This suggests that the semiconducting layer is confined in the topmost surface region of the as-prepared film, while the layer beneath it is superconducting in character. (author)

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

    OpenAIRE

    StorgardsStorgards, J.; Méndez Martín, Bianchi; Piqueras de Noriega, Javier; Storgards, M.; Dimroth, F.; Bett, A.W.

    2004-01-01

    The luminescence of GaSb and AlGaSb layers grown on GaAs substrates by metal organic vapour phase epitaxy has been studied by means of cathodoluminescence (CL) rising a scanning electron microscope. CL plane-view analysis reveals a distribution of defects, as misfit dislocations, in some of the structures. The luminescence bands observed in the GaSb layers are related to near band edge recombination and to an excess of Ga. In the case of AlGaSb/GaSb heterostructure emission bands related to t...

  2. 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 nanotube; the Schottky mechanism in (2) would result in I does not equal 0 only with V 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.

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

    Science.gov (United States)

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

    2015-03-01

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

  4. Dynamic probe of ZnTe(110) surface by scanning tunneling microscopy

    Science.gov (United States)

    Kanazawa, Ken; Yoshida, Shoji; Shigekawa, Hidemi; Kuroda, Shinji

    2015-02-01

    The reconstructed surface structure of the II–VI semiconductor ZnTe (110), which is a promising material in the research field of semiconductor spintronics, was studied by scanning tunneling microscopy/spectroscopy (STM/STS). First, the surface states formed by reconstruction by the charge transfer of dangling bond electrons from cationic Zn to anionic Te atoms, which are similar to those of IV and III–V semiconductors, were confirmed in real space. Secondly, oscillation in tunneling current between binary states, which is considered to reflect a conformational change in the topmost Zn–Te structure between the reconstructed and bulk-like ideal structures, was directly observed by STM. Third, using the technique of charge injection, a surface atomic structure was successfully fabricated, suggesting the possibility of atomic-scale manipulation of this widely applicable surface of ZnTe.

  5. Scanning tunneling spectrum of electrons confined in a rectangular quantum corral

    International Nuclear Information System (INIS)

    We obtained the scanning tunneling spectrum (STS) of an electron confined in a rectangular quantum corral by considering the electron to be in a quasi-stationary state. Because of non-hermiticity of the Hamiltonian, the electron has a complex eigenenergy. The imaginary part gives the peak width coming mainly from the electron tunneling through a corral barrier. Our STS is consistent with the experimental spectrum that had been measured for electrons confined in a rectangular quantum corral. We obtained peak widths against energy levels and components of the STS which are constructed with quasi-stationary eigenstates. It is shown that normalization of a wavefunction by considering its time evolution is decisive in obtaining the proper STS. Moreover, we specified the position dependence of STS in relation to the image of the surface local density of states.

  6. Highlighting functional groups in self-assembled overlayers with specific functionalized scanning tunnelling microscopy tips

    Science.gov (United States)

    Volcke, Cedric; Simonis, Priscilla; Thiry, Paul A.; Lambin, Philippe; Culot, Christine; Humbert, Christophe

    2005-11-01

    Overlayers of a fatty acid (palmitic and lauric acid) formed at the interface between a solution of this molecule in phenyloctane and the basal plane of graphite are studied by in situ scanning tunnelling microscopy. The layers organize into lamellae, which are formed by a close packing arrangement of molecules parallel to the graphite surface. Chemical modification of the STM tips used allowed identification of the functional group. Indeed, the gold tips used are functionalized with 4-mercaptobenzoic acid (4-MBA) and 4-mercaptotoluene (4-MT). The same functional group on a sample is then 'seen' as a dark and a bright spot when imaged with 4-MBA and 4-MT modified tips, respectively. This contrast distinction is related to interactions (or a lack of them) between the carboxyl group on the sample and molecules on the tip, which can facilitate (or hinder) the electron tunnelling.

  7. Scanning tunneling microscopy imaging of charged defects on clean Si(100)-(2×1)

    Science.gov (United States)

    Brown, G. W.; Grube, H.; Hawley, M. E.; Schofield, S. R.; Curson, N. J.; Simmons, M. Y.; Clark, R. G.

    2003-07-01

    We have used scanning tunneling microscopy (STM) to image charged defects on the clean (100)-(2×1) surface of p-type silicon. In the absence of ``C''-type defects, band bending can occur during STM imaging, allowing near surface charge to influence the state density contributing to the tunnel current. As in the case of cleavage faces of III-V semiconductor crystals, the charge-induced band bending produces long range enhancements superimposed on the periodic surface lattice. The charged defects observed in this work are of the types commonly observed elsewhere in clean Si(100)-(2×1) STM studies, however, not all defects of a given type appear charged. This would indicate subtle differences in defect structure that are not obvious at higher sample bias. This work demonstrates the ability to observe charged features on the clean Si(100) surface, which will be important for current and future research focused on producing atomic scale electronic structures.

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

    Science.gov (United States)

    Müllegger, Stefan; Das, Amal K; Mayr, Karlheinz; Koch, Reinhold

    2014-04-01

    We have upgraded a low-temperature scanning tunnelling microscope (STM) with a radio-frequency (RF) modulation system to extend STM spectroscopy to the range of low energy excitations (radical weakly physisorbed on Au(111). At 5 K thermal excitation of the adsorbed molecules is inhibited due to the lack of short-wavelength phonons of the substrate. We demonstrate resonant excitation of mechanical modes of single molecules by RF tunnelling at 115 MHz, which induces structural changes in the molecule ranging from controlled diffusion and modification of bond angles to bond breaking as the ultimate climax (resonance catastrophe). Our results pave the way towards RF-STM-based spectroscopy and controlled manipulation of molecular nanostructures on a surface. PMID:24594655

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

    Science.gov (United States)

    Müllegger, Stefan; Das, Amal K.; Mayr, Karlheinz; Koch, Reinhold

    2014-04-01

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

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

    CERN Document Server

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

    2006-01-01

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

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

    Science.gov (United States)

    Vasudevan, Rama K.; Tselev, Alexander; Gianfrancesco, Anthony G.; Baddorf, Arthur P.; Kalinin, Sergei V.

    2015-04-01

    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.

  12. Temperature-dependent scanning tunneling spectroscopy of 1T-TaS2

    Science.gov (United States)

    Kim, Ju-Jin; Ekvall, Inger; Olin, Håkan

    1996-07-01

    We have studied temperature-dependent tunneling spectroscopy of 1T-TaS2 from room temperature down to about 40 K. The spectra indicated an abrupt transition from the charge-density-wave-induced broad depletion to an opening of a deep pseudogap within 1 K of the nearly commensurate to commensurate transition temperature. The measured pseudogap was deep enough to form localized states at the Fermi level. In contrast to an inverse photoelectron spectroscopy study, our tunneling results indicate gap structures of two Hubbard subbands resulting from the band splitting of the Ta 5d band due to the electron correlation effect. We have also found an abrupt increase of thermoelectric voltage developing between the tip and sample at the transition temperature.

  13. Visualizing the native atomic defects in Bi2Se3 with scanning tunneling microscopy

    Science.gov (United States)

    Dai, Jixia; West, Damien; Wang, Xueyun; Wang, Yazhong; Kwok, Daniel; Cheong, Sang Wook; Zhang, Shengbai; Wu, Weida

    2015-03-01

    In topological insulators such as Bi2Se3 the existence of native atomic defects is one of the major bottlenecks for potential applications utilizing the topologically protected surface states. Native defects such as vacancies or antisites are believed to be responsible for the metallic transport observed in Bi2Se3. In this study, we examined a series of Bi2Se3 samples that were grown with different conditions using atomically resolving scanning tunneling microscopy. We have successfully identified several types of intrinsic defects, including Se vacancies and Bi-Se antisites. The individual defect images are corroborated by first principle calculations. The densities of these defects across different samples are correlated with their growth conditions. Preliminary results suggest the defect densities can account for the charge carrier density estimated from tunneling spectroscopy. In topological insulators such as Bi2Se3 the existence of native atomic defects is one of the major bottlenecks for potential applications utilizing the topologically protected surface states. Native defects such as vacancies or antisites are believed to be responsible for the metallic transport observed in Bi2Se3. In this study, we examined a series of Bi2Se3 samples that were grown with different conditions using atomically resolving scanning tunneling microscopy. We have successfully identified several types of intrinsic defects, including Se vacancies and Bi-Se antisites. The individual defect images are corroborated by first principle calculations. The densities of these defects across different samples are correlated with their growth conditions. Preliminary results suggest the defect densities can account for the charge carrier density estimated from tunneling spectroscopy. This work is supported by NSF Grant # DMR-0844807.

  14. Scanning tunneling microscopic analysis of Cu(In,Ga)Se2 epitaxial layers

    International Nuclear Information System (INIS)

    Scanning tunneling microscopy (STM) measurements have been made on single-crystal epitaxial layers of CuInSe2 grown on GaAs substrates. Results were obtained for as-grown, air-exposed, and cleaned surfaces; in situ cleaved surfaces; surfaces sputtered and annealed in the STM system; and samples prepared by a light chemical etch. Conventional constant-current topographs, current-voltage curves, and current imaging tunneling spectroscopy (CITS) scans were obtained. Topographic images show that the surfaces appear rough on the atomic scale and often exhibit regular features consistent with a previously proposed surface ad-dimer reconstruction. CITS scans show a spatially varying energy gap consistent with band-edge fluctuations on a scale of a few atomic spacings. Energy variations were observed in both band edges. Although quantitative description of the magnitude of these fluctuations is difficult, the fluctuations on the atomic scale appear much larger than observed by methods such as photoluminescence, which average over larger volumes.

  15. 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.)

  16. Valence loss spectra in STEM (Scanning Transmission Electron Microscope)

    International Nuclear Information System (INIS)

    The development of STEM (Scanning Transmission Electron Microscopy) has stimulated and renewed interest in the interaction of high-energy electron beams (of the order of 100 keV) with surfaces and small particles. One problem of interest in this field is the spatial resolution of an energy loss experiment. Here the problem of the impact parameter dependence of the energy loss probability is studied. Three magnitudes involved in the resolution, namely broadness of the beam, spatial extent of the electronic states that are excited, and the range of the Fourier (frequency) component of the Coulomb potential, are considered. It is pointed out that classical dielectric theory was shown to be a good tool to study the energy loss of STEM electrons. Finally the problem of targets of mixed geometries is studied. 51 refs, 15 figs

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

    Science.gov (United States)

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

    2012-01-01

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

  18. Signature of irradiation-induced defects in scanning-tunneling microscopy images of carbon nanotubes

    International Nuclear Information System (INIS)

    The structure and the stability of crystal defects induced by Ar ion irradiation on walls of carbon nanotubes are investigated by means of empirical and tight-binding models. The temporal evolution of the defects is simulated. The lifetimes of radiation-induced defects are calculated. The scanning-tunnel microscopy (STM) images of irradiated nanotubes with defects are simulated. It is found out that at low temperature, defects live long enough to be detected by STM and that different defects manifest themselves in STM images in different ways, which allows distinguishing defects experimentally

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

    OpenAIRE

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

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

    OpenAIRE

    Lin, Hong; Lagoute, Je?ro?me; Repain, Vincent; Chacon, Cyril; Girard, Yann; Lauret, Jean-se?bastien; Ducastelle, Franc?ois; 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...

  1. Probing hot-electron dynamics at surfaces with a cold scanning tunneling microscope

    OpenAIRE

    Burgi, L.; Jeandupeux, O.; Brune, H.; Kern, K.

    1999-01-01

    We report on a novel approach to measure the phase relaxation length and femtosecond lifetime of hot quasiparticles on metal surfaces. A 4 K scanning tunneling microscope has been used to study the spatial decay of interference patterns in the local density of states for surface state electrons on Ag(111) and Cu(111). This decay is governed by inelastic; electron-electron scattering. We find a (E - E-F)(-2) energy dependence of the lifetimes for both Ag and Cu, and our values are comparable t...

  2. Atomic arrangement of sulfur adatoms on Mo(001) at atmospheric pressure: A scanning tunneling microscopy study

    International Nuclear Information System (INIS)

    An ordered monolayer of chemisorbed sulfur adatoms on a Mo(001) surface is imaged in air, by means of scanning tunneling microscopy. The p(2 x 1) overlayer is observed, in agreement with low-energy electron-diffraction studies. The adsorption sites of the sulfur atoms on the molybdenum substrate are clarified, based on the measured corrugation amplitudes. Atomic resolution has also been obtained in the barrier height mode, by use of an ac synchronous detection, and with a better signal-to-noise ratio than in the constant current (topographic) mode

  3. Scanning tunneling spectroscopy on graphene nanoislands, iron nanoislands and phase change materials

    OpenAIRE

    Subramaniam, Dinesh

    2012-01-01

    This thesis is concerned with scanning tunnelling spectroscopy (STS) of graphene nanoisland on Ir(111), Fe nanoisland on W(110) and phase change materials Ge1Sb2Te4. Low-temperature STS is used to map the local density of states of graphene dots supported on Ir(111). Because of a band gap in the projected Ir band structure around the graphene K-point, the electronic properties of the quantum dots are dominantly graphene-like. Comparison with tight binding calculations on the honeycomb lattice...

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

    DEFF Research Database (Denmark)

    Christiansen, Jesper; Morgenstern, K.

    2002-01-01

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

  5. Scanning Tunneling Microscopy and Molecular Dynamics Simulations of Dislocations Intersecting a Ag(111) Surface

    CERN Document Server

    Christiansen, J; Schiøtz, J; Jacobsen, K W; Braun, K F; Rieder, K H; Laegsgaard, E; Besenbacher, F

    2002-01-01

    Using an interplay between molecular dynamics (MD) and scanning tunneling microscopy (STM) we have studied the intersection of dislocations with a Ag(111) surface, a model system for the more general situation of an extended crystal defect intersecting a metal surface. The broken translational symmetry at the surface permits the dissociation width of the dislocation to change significantly at the surface, which is clearly observed in both simulations and experiment. The near-surface structures obtained from the simulation are in good agreement with the STM data. Hereby a link is established between atomically resolved experimental surface structures and bulk structures inaccessible by STM.

  6. Controlled low-temperature molecular manipulation of sexiphenyl molecules on Ag(111) using scanning tunneling microscopy

    CERN Document Server

    Hla, S W; Wassermann, B; Rieder, K H; Hla, Saw-Wai; Braun, Kai-Felix; Wassermann, Bernhard; Rieder, Karl-Heinz

    2004-01-01

    A novel scanning tunneling microscope manipulation scheme for a controlled molecular transport of weakly adsorbed molecules is demonstrated. Single sexiphenyl molecules adsorbed on a Ag(111) surface at 6 K are shot towards single silver-atoms by excitation with the tip. To achieve atomically straight shooting paths, an electron resonator consisting of linear standing wave fronts is constructed. The sexiphenyl manipulation signals reveal a pi-ring flipping as the molecule moves from hcp to fcc site. Abinitio calculations show an incorporation of the Ag atom below the center of a pi-ring.

  7. 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.

  8. A scanning tunnelling microscopy investigation of the interaction of sulphur with semiconductor surfaces

    OpenAIRE

    Moriarty, Phillip

    1993-01-01

    UHV and ambient Scanning Tunnelling Microscopy (STM) have been used to investigate the interaction of sulphur with Si and GaAs (100) and (111) surfaces. The adsoiption of group VI elements on GaAs and other IE-V semiconductor surfaces is well known to passivate the surface, that is, reduce the number of mid-gap surface states. We find that in situ room temperature adsorption of sulphur on both Si(100)-(2xl) and S i(lll)-(7 x 7 ) surfaces, using an electrochemical cell, does not produce an ide...

  9. Etch-stop method for reliably fabricating sharp yet mechanically stable scanning tunneling microscope tips

    OpenAIRE

    Basnet, G.; Schoelz, J. K.; Xu, P.; Barber, S. D.; Ackerman, M. L.; Thibado, P. M.

    2015-01-01

    An extension of the direct-current, double-lamella drop-off technique for electrochemically etching tungsten scanning-tunneling-microscope tips is presented. The key fabrication step introduced here is the use of an etch stop as a simple but accurate way to optimize the contact area between the etchant and the wire. By restricting the etching process, the final cone angle of the tips can be made sharp and mechanically stable without a lot of finesse from the STM tip maker.

  10. Scanning Tunneling Microscopy of Defect States in the Semiconductor Bi$_2$Se$_3$

    OpenAIRE

    Urazhdin, S.; Bilc, D.; Tessmer, S. H.; Mahanti, S. D.; Kyratsi, Theodora; Kanatzidis, M. G.

    2001-01-01

    Scanning tunneling spectroscopy images of Bi$_2$Se$_3$ doped with excess Bi reveal electronic defect states with a striking shape resembling clover leaves. With a simple tight-binding model we show that the geometry of the defect states in Bi$_2$Se$_3$ can be directly related to the position of the originating impurities. Only the Bi defects at the Se sites five atomic layers below the surface are experimentally observed. We show that this effect can be explained by the inte...

  11. 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.

  12. Probing the Superconducting Proximity Effect in a Topological Insultor using Scanning Tunneling Microscopy

    Science.gov (United States)

    Dayton, Ian; Chung, Duck-Young; Chasapis, Thomas; Goodwin, Eric; Loloee, Reza; Kanatzidis, Mercouri; Tessmer, Stuart

    2015-03-01

    Topological insulators (TI) embody a new state of quantum matter characterized by topological invariants; this contrasts with superconductors (S), as superconductivity arises from a spontaneously broken symmetry of the underlying electron system. When a superconductor is placed on the surface of a topological insulator, the behavior of the superconducting condensate across the S/TI interface offers the opportunity to study the interplay between these two distinct quantum states. In this talk, we present our progress in applying cryogenic Scanning Tunneling Microscopy measurements to probe the local density of states in proximity to Pb/Bi2Se3 interfaces.

  13. Preparation of Superconducting Niobium Tips for Atomic-Resolution Scanning Tunneling Microscopy/Spectroscopy

    Science.gov (United States)

    Shimizu, Ryota; Hitosugi, Taro; Hashizume, Tomihiro; Fukuo, Noritaka; Hasegawa, Tetsuya

    2010-02-01

    We present a new reliable method to prepare superconducting niobium (Nb) tips for scanning tunneling microscopy/spectroscopy (STM/STS). Sharp Nb tips were fabricated by chemical etching using an electrolyte based on a hydrofluoric acid and hydrogen peroxide solution, followed by field evaporation utilizing field ion microscopy to remove Nb oxide layers from the tip apex. STM/STS measurements of Si(111) and Au(111) surfaces confirmed that the tips had atomic resolution capability together with bulk-like superconducting properties, indicating that the prepared Nb tips can be used as a unique probe for investigating local superconducting and magnetic properties on an atomic scale.

  14. Selective laser removal of the dimer layer from Si(100) surfaces revealed by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Scanning tunneling microscopy (STM) of laser-irradiated Si(100) surfaces shows that the dimerized outermost layer can be selectively removed by a pulsed Nd:YAG laser with a fluence below the melt threshold. The atoms in the laser-uncovered second layer are close to positions of a bulk terminated (1x1) structure, but with a slight pairing, while dimers retain a (2x1) configuration in the first layer. The pairing distance and fraction of the remaining dimers decrease with increasing laser exposures. The laser-uncovered layer also remains free of vacancies. copyright 1996 The American Physical Society

  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. Nanoscale Pattern Formation with the Scanning Tunneling Microscope on Polymer Thin Films

    Science.gov (United States)

    Tang, Sau; McGhie, Alistair; Suna, Andris

    1994-03-01

    Nanometer-scale structures can be routinely fabricated with voltage pulses applied through the sharp tip of the scanning tunneling microscope (STM) on thin (hydroxypropylcellulose. Structures were 20 30 Å in diameter in ambient atmosphere, and ˜200 Å in diameter in ultrahigh vacuum. Thermally induced structures can also be created with a modest power input (0.1 3 V tip bias voltages, 6 nA current, 10's of seconds duration for a ˜100 Å thick film). The structure formation mechanism appeared to include thermal effects from the current and its implications will be discussed.

  17. 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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-09-09

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

  19. Multiband coupling effect on density of states and tunneling conductance spectra of ferromagnetic material

    International Nuclear Information System (INIS)

    The electronic density of states (DOS) of ferromagnetic materials are theoretically studied within a two-band approach in one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) systems. In the two-band approximation, s-band and d-band coupling were considered. It has been found that if the coupling vanishes, the two bands can cross at some points in the energy spectra. When the coupling between bands is present, a gap is opened up at the corresponding point, thereby avoiding crossovers. The size of the gap depends on the size of the coupling strength. For any dimensionality, the DOS with no coupling behaves like a one-band model. When presenting the coupling strength, there is a change in the slope in the DOS, corresponding to those crossing points. In particular, this change is most prominent when the coupling strength is small and it almost disappears when the coupling strength is strong. With a large coupling strength, the energy band is extended. Finally, the measurable tunneling conductance spectra of a metal/ferromagnet junction within this approximation were clearly analyzed. - Highlights: • The density of states of a two-band ferromagnet were calculated. • There were crossing points, gaps, change in slope, and energy band extension occurring in the DOS. • The results show the relationship between DOS and tunneling conductance spectra

  20. Renormalization of the Graphene Dispersion Velocity Determined from Scanning Tunneling Spectroscopy

    Science.gov (United States)

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

    2012-09-01

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

  1. 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...

  2. Determination of horizontal and vertical design spectra based on ground motion records at Lali tunnel, Iran

    Science.gov (United States)

    Moradpouri, F.; Mojarab, M.

    2012-08-01

    Most acceleration diagrams show high levels of unpredictability, as a result, it is the best to avoid using diagrams of earthquake acceleration spectra, even if the diagrams recorded at the site in question. In order to design earthquake resistant structures, we, instead, suggest constructing a design spectrum using a set of spectra that have common characteristics to the recorded acceleration diagrams at a particular site and smoothing the associated data. In this study, we conducted a time history analysis and determined a design spectrum for the region near the Lali tunnel in Southwestern Iran. We selected 13 specific ground motion records from the rock site to construct the design spectrum. To process the data, we first applied a base-line correction and then calculated the signal-to-noise ratio ( R SN) for each record. Next, we calculated the Fourier amplitude spectra of the acceleration pertaining to the signal window (1), and the Fourier amplitude spectra of the associated noise (2). After dividing each spectra by the square root of the selected window interval, they were divided by each other (1 divided by 2), in order to obtain the R SN ratio (filtering was also applied). In addition, all data were normalized to the peak ground acceleration (PGA). Next, the normalized vertical and horizontal responses and mean response spectrum (50%) and the mean plus-one standard deviation (84%) were calculated for all the selected ground motion records at 5% damping. Finally, the mean design spectrum and the mean plus-one standard deviation were plotted for the spectrums. The equation of the mean and the above-mean design spectrum at the Lali tunnel site are also provided, along with our observed conclusions.

  3. 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.)

  4. Calibration of tip and sample temperature of a scanning tunneling microscope using a superconductive sample

    International Nuclear Information System (INIS)

    The temperature of the electrodes is a crucial parameter in virtually all tunneling experiments. The temperature not only controls the thermodynamic state of the electrodes but also causes thermal broadening, which limits the energy resolution. Unfortunately, the construction of many scanning tunneling microscopes inherits a weak thermal link between tip and sample in order to make one side movable. Such, the temperature of that electrode is badly defined. Here, the authors present a procedure to calibrate the tip temperature by very simple means. The authors use a superconducting sample (Nb) and a standard tip made from W. Due to the asymmetry in the density of states of the superconductor (SC)—normal metal (NM) tunneling junction, the SC temperature controls predominantly the density of states while the NM controls the thermal smearing. By numerically simulating the I-V curves and numerically optimizing the tip temperature and the SC gap width, the tip temperature can be accurately deduced if the sample temperature is known or measureable. In our case, the temperature dependence of the SC gap may serve as a temperature sensor, leading to an accurate NM temperature even if the SC temperature is unknown

  5. Analysis of SRB reentry acoustic environments. [aeroacoustic spectra determined from wind tunnel tests

    Science.gov (United States)

    Coffin, T.; Dandridge, R. E.; Haddock, U. W.

    1979-01-01

    Space shuttle solid rocket booster reentry aeroacoustic environments were estimated. Particular emphasis was given to the aft skirt/exit plane region for the Mach number regime 0.6 = or greater than M infinity = or less than 3.5. The analysis is based on the evaluation of wind tunnel model results in conjunction with Monte Carlo simulation of trajectory parameters. The experimental approach is described as well as the evaluation process utilized. Predicted environments are presented in terms of one-third octave band spectra representing space averaged values for critical regions on the solid rocket booster.

  6. 2D-isotope effects in NMR spectra of aqueous solutions and tunnel migration of protons

    International Nuclear Information System (INIS)

    Studied are the chemical shifts of protons and deuterium in aqueous solutions of inorganic salts, organic and inorganic acids and bases. In all studied systems occurs an exchange of protons and deuterons between hydroxyl groups, quick in NMR time scale, in the result of which the only signal from movable hydrogen atoms is observed in 1H and in 2D spectra as well. It is supposed that one of main mechanisms of proton exchange in the series of compounds is the tunnel process of proton transfer proceeding by the way of molecular and ion complexes formation

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

    Science.gov (United States)

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

    2015-04-01

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

  8. A compact combined ultrahigh vacuum scanning tunnelling microscope (UHV STM) and near-field optical microscope

    International Nuclear Information System (INIS)

    We have designed and constructed a hybrid scanning near-field optical microscope (SNOM)–scanning tunnelling microscope (STM) instrument which operates under ultrahigh vacuum (UHV) conditions. Indium tin oxide (ITO)-coated fibre-optic tips capable of high quality STM imaging and tunnelling spectroscopy are fabricated using a simple and reliable method which foregoes the electroless plating strategy previously employed by other groups. The fabrication process is reproducible, producing robust tips which may be exchanged under UHV conditions. We show that controlled contact with metal surfaces considerably enhances the STM imaging capabilities of fibre-optic tips. Light collection (from the cleaved back face of the ITO-coated fibre-optic tip) and optical alignment are facilitated by a simple two-lens arrangement where the in-vacuum collimation/collection lens may be adjusted using a slip-stick motor. A second in-air lens focuses the light (which emerges from the UHV system as a parallel beam) onto a cooled CCD spectrograph or photomultiplier tube. The application of the instrument to combined optical and electronic spectroscopy of Au and GaAs surfaces is discussed

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

    Science.gov (United States)

    Saad, Mahmoud M.; Abdallah, Tamer; Easawi, Khalid; Negm, Sohair; Talaat, Hassan

    2015-05-01

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

  10. High-stability cryogenic scanning tunneling microscope based on a closed-cycle cryostat

    Science.gov (United States)

    Hackley, Jason D.; Kislitsyn, Dmitry A.; Beaman, Daniel K.; Ulrich, Stefan; Nazin, George V.

    2014-10-01

    We report on the design and operation of a cryogenic ultra-high vacuum (UHV) scanning tunneling microscope (STM) coupled to a closed-cycle cryostat (CCC). The STM is thermally linked to the CCC through helium exchange gas confined inside a volume enclosed by highly flexible rubber bellows. The STM is thus mechanically decoupled from the CCC, which results in a significant reduction of the mechanical noise transferred from the CCC to the STM. Noise analysis of the tunneling current shows current fluctuations up to 4% of the total current, which translates into tip-sample distance variations of up to 1.5 picometers. This noise level is sufficiently low for atomic-resolution imaging of a wide variety of surfaces. To demonstrate this, atomic-resolution images of Au(111) and NaCl(100)/Au(111) surfaces, as well as of carbon nanotubes deposited on Au(111), were obtained. Thermal drift analysis showed that under optimized conditions, the lateral stability of the STM scanner can be as low as 0.18 Å/h. Scanning Tunneling Spectroscopy measurements based on the lock-in technique were also carried out, and showed no detectable presence of noise from the closed-cycle cryostat. Using this cooling approach, temperatures as low as 16 K at the STM scanner have been achieved, with the complete cool-down of the system typically taking up to 12 h. These results demonstrate that the constructed CCC-coupled STM is a highly stable instrument capable of highly detailed spectroscopic investigations of materials and surfaces at the atomic scale.

  11. High-stability cryogenic scanning tunneling microscope based on a closed-cycle cryostat

    Energy Technology Data Exchange (ETDEWEB)

    Hackley, Jason D.; Kislitsyn, Dmitry A.; Beaman, Daniel K.; Nazin, George V., E-mail: gnazin@uoregon.edu [Department of Chemistry and Biochemistry, 1253 University of Oregon, Eugene, Oregon 97403 (United States); Ulrich, Stefan [RHK Technology, Inc., 1050 East Maple Road, Troy, Michigan 48083 (United States)

    2014-10-15

    We report on the design and operation of a cryogenic ultra-high vacuum (UHV) scanning tunneling microscope (STM) coupled to a closed-cycle cryostat (CCC). The STM is thermally linked to the CCC through helium exchange gas confined inside a volume enclosed by highly flexible rubber bellows. The STM is thus mechanically decoupled from the CCC, which results in a significant reduction of the mechanical noise transferred from the CCC to the STM. Noise analysis of the tunneling current shows current fluctuations up to 4% of the total current, which translates into tip-sample distance variations of up to 1.5 picometers. This noise level is sufficiently low for atomic-resolution imaging of a wide variety of surfaces. To demonstrate this, atomic-resolution images of Au(111) and NaCl(100)/Au(111) surfaces, as well as of carbon nanotubes deposited on Au(111), were obtained. Thermal drift analysis showed that under optimized conditions, the lateral stability of the STM scanner can be as low as 0.18 Å/h. Scanning Tunneling Spectroscopy measurements based on the lock-in technique were also carried out, and showed no detectable presence of noise from the closed-cycle cryostat. Using this cooling approach, temperatures as low as 16 K at the STM scanner have been achieved, with the complete cool-down of the system typically taking up to 12 h. These results demonstrate that the constructed CCC-coupled STM is a highly stable instrument capable of highly detailed spectroscopic investigations of materials and surfaces at the atomic scale.

  12. High-stability cryogenic scanning tunneling microscope based on a closed-cycle cryostat

    International Nuclear Information System (INIS)

    We report on the design and operation of a cryogenic ultra-high vacuum (UHV) scanning tunneling microscope (STM) coupled to a closed-cycle cryostat (CCC). The STM is thermally linked to the CCC through helium exchange gas confined inside a volume enclosed by highly flexible rubber bellows. The STM is thus mechanically decoupled from the CCC, which results in a significant reduction of the mechanical noise transferred from the CCC to the STM. Noise analysis of the tunneling current shows current fluctuations up to 4% of the total current, which translates into tip-sample distance variations of up to 1.5 picometers. This noise level is sufficiently low for atomic-resolution imaging of a wide variety of surfaces. To demonstrate this, atomic-resolution images of Au(111) and NaCl(100)/Au(111) surfaces, as well as of carbon nanotubes deposited on Au(111), were obtained. Thermal drift analysis showed that under optimized conditions, the lateral stability of the STM scanner can be as low as 0.18 Å/h. Scanning Tunneling Spectroscopy measurements based on the lock-in technique were also carried out, and showed no detectable presence of noise from the closed-cycle cryostat. Using this cooling approach, temperatures as low as 16 K at the STM scanner have been achieved, with the complete cool-down of the system typically taking up to 12 h. These results demonstrate that the constructed CCC-coupled STM is a highly stable instrument capable of highly detailed spectroscopic investigations of materials and surfaces at the atomic scale

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

    Science.gov (United States)

    Lima, E. A.; Bruno, A. C.; Carvalho, H. R.; Weiss, B. P.

    2014-10-01

    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.

  14. Local spectroscopy and vortex-core imaging on chemically wet-etched surfaces of YBa2Cu3Oy by scanning tunneling microscopy/spectroscopy

    International Nuclear Information System (INIS)

    Low-temperature scanning tunneling microscopy/spectroscopy has been performed on chemically wet-etched surfaces of YBa2Cu3Oy (YBCO) single crystals. Chemically wet-etched YBCO surfaces are stable in ultrahigh vacuum environments, and superconducting gap spectra are observed with high spatial uniformity up to the bulk superconducting transition temperature, Tc. When a magnetic field was applied, local electronic modulations due to vortices were detected up to 80 K, enabling the real-space imaging of vortices in YBCO at high temperatures (c) and magnetic fields. Furthermore, local spectroscopy revealed spectra with a zero-bias anomaly due to weak impurities and the tendency of vortex pinning by these impurities.

  15. Scanning tunnel microscopic image of tungsten (100) and (110) real surfaces and nature of conduction electron reflection

    International Nuclear Information System (INIS)

    The electrically polished (100) and (110) surfaces of tungsten are studied with the aid of a scanning tunnel microscope at atmospheric pressure. The (110) surface consists of a large number of atomically plane terraces whereas the (100) surface is faceted. The scanning tunnel microscope data can explain such results of experiments on transverse electron focussing as the strong dependence of the probability for specular reflection of conduction electrons scattered by the (100) surface on the electron de Broglie wavelength and the absence of a dependence of the probability for specular reflection on the wavelength for the (110) surface

  16. Thermally processed titanium oxides film on Si(0 0 1) surface studied with scanning tunneling microscopy/spectroscopy

    International Nuclear Information System (INIS)

    Thermal structural changes of TiOx films built on a Si(0 0 1) surface were investigated at the nanometer scale with scanning tunneling microscopy. Electronic properties of individual clusters were classified by means of scanning tunneling spectroscopy. The differential conductance (dI/dV) near the Fermi energy showed that nano-clusters were transformed from semiconducting Ti-silicates into metallic Ti-silicides after heating to 970 K. Peaks of normalized differential conductance (dI/dV/(I/V)) of the clusters shifted after heating to about 1070 K, indicating exclusion of oxygen from the clusters.

  17. Tunnelling junctions with additional degrees of freedom: An extended toolbox of scanning probe microscopy

    Science.gov (United States)

    Wagner, Christian; Temirov, Ruslan

    2015-05-01

    Considering studies of molecular adsorption we review recent developments in the field of scanning probe microscopy and in particular in scanning tunnelling microscopy, concentrating on the progress that has been achieved by controlled decoration of the microscope tip. A view is presented according to which the tip decoration generally introduces additional degrees of freedom into the scanning junction and thus extends its functionality. In particular tips decorated with atomic point-like particles may attain the additional function of a force sensor which is realized through the degrees of freedom associated with the relative position of the decorating probe-particle with respect to the tip. It is shown how the force sensor function of such tips helps when studying large molecular adsorbates. Further prospects of more complex junctions equipped with numerous internal degrees of freedom are discussed. It is argued that the main problem impeding the utilization of such junctions is related to their control. An approach towards a higher degree of control is presented that is based on the analysis of single molecule manipulation experiments.

  18. Scanning tunneling microscopy studies of organic and inorganic materials for photovoltaics and photoelectrochemistry

    Science.gov (United States)

    Hiesgen, Renate; Meissner, Dieter

    1992-12-01

    Thin film solar cells require a structural control in nanometer dimensions. The only techniques currently available to investigate and control thin film preparation techniques in real space are based on scanning probe techniques as developed by Rohrer and Binning in 1981. However, the investigation of surface roughness on the ten to hundred nanometer range has proven to be especially complicated due to the convolution of tip and surface structures depending on the relative size dimensions of both the tip and the surface features. Special care is necessary to avoid multiple tip imaging as the major source of errors. Examples given in this paper include investigations of nanometer clusters of metals as used for semiconductor surface modifications in photoelectrochemical solar cells and of amorphous hydrocarbon films investigated as possible new materials for photovoltaics or as selective absorbers for solar thermal applications. More detailed investigations of molecular thin films for organic solar cells are presented. Here, besides information about the film structure, crystal growth mechanisms of organic crystalilites prepared by evaporation techniques also were investigated using scanning tunneling microscopy (STM) and scanning electron microscopy (SEM) techniques.

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

    Energy Technology Data Exchange (ETDEWEB)

    Cernota, Paul D.

    1999-08-01

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

  20. 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

  1. Memristor effect on bundles of vertically aligned carbon nanotubes tested by scanning tunnel microscopy

    Science.gov (United States)

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

    2013-12-01

    We report on the results of experimental study of an array of vertically aligned carbon nanotubes (VA CNTs) by scanning tunnel microscopy (STM). It is shown that upon the application of an external electric field to the STM probe/VA CNT system, individual VA CNTs are combined into bundles whose diameter depends on the radius of the tip of the STM probe. The memristor effect in VA CNTs is detected. For the VA CNT array under investigation, the resistivity ratio in the low- and high-resistance states at a voltage of 180 mV is 28. The results can be used in the development of structures and technological processes for designing nanoelectronics devices based on VA CNT arrays, including elements of ultrahigh-access memory cells for vacuum microelectronics devices.

  2. Molecular beam epitaxy growth and scanning tunneling microscopy study of TiSe2 ultrathin films

    Science.gov (United States)

    Peng, Jun-Ping; Guan, Jia-Qi; Zhang, Hui-Min; Song, Can-Li; Wang, Lili; He, Ke; Xue, Qi-Kun; Ma, Xu-Cun

    2015-03-01

    Molecular beam epitaxy is used to grow TiSe2 ultrathin films on a graphitized SiC(0001) substrate. TiSe2 films proceed via a nearly layer-by-layer growth mode and exhibit two dominant types of defects, identified as Se vacancy and interstitial, respectively. By means of scanning tunneling microscopy, we demonstrate that the well-established charge density waves can survive in a single unit-cell (one triple-layer) regime, and find a gradual reduction in their correlation length as the density of surface defects in TiSe2 ultrathin films increases. Our findings offer important insights into the nature of charge density waves in TiSe2, and also pave a material foundation for potential applications based on the collective electronic states.

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

    CERN Document Server

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

    2000-01-01

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

  4. 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.

  5. Heteroepitaxial growth of Co on W(110) investigated by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    We investigated the growth of Co submonolayers on bcc W(110) by scanning tunneling microscopy. Due to the strong Co-W bonding, monolayers of Co grow in equilibrium pseudomorphically on W(110) until the monolayer is almost completed. When excess atoms are deposited atop the pseudomorphic monolayer, it transforms to a close-packed (cp) monolayer with misfit dislocation lines parallel to [11-bar0] (Nishiyama-Wassermann orientation). The structure of the cp monolayer, as concluded from atomically resolved STM images, deviates from the rigid hard-sphere model of a cp (111) layer. Details of the structure are compared to a structure model previously proposed by van der Merwe et al. based on the embedded atom model (EAM)

  6. Different W cluster deposition regimes in pulsed laser ablation observed by in situ Scanning Tunneling Microscopy

    CERN Document Server

    Cattaneo, D; Casari, C S; Bassi, A L; Passoni, M; Bottani, C E

    2007-01-01

    We report on how different cluster deposition regimes can be obtained and observed by in situ Scanning Tunneling Microscopy (STM) by exploiting deposition parameters in a pulsed laser deposition (PLD) process. Tungsten clusters were produced by nanosecond Pulsed Laser Ablation in Ar atmosphere at different pressures and deposited on Au(111) and HOPG surfaces. Deposition regimes including cluster deposition-diffusion-aggregation (DDA), cluster melting and coalescence and cluster implantation were observed, depending on background gas pressure and target-to-substrate distance which influence the kinetic energy of the ablated species. These parameters can thus be easily employed for surface modification by cluster bombardment, deposition of supported clusters and growth of films with different morphologies. The variation in cluster mobility on different substrates and its influence on aggregation and growth mechanisms has also been investigated.

  7. 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.

  8. 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

  9. Graphene nanoribbons with zigzag and armchair edges prepared by scanning tunneling microscope lithography on gold substrates

    Science.gov (United States)

    Nemes-Incze, P.; Tapasztó, Levente; Magda, G. Zs.; Osváth, Z.; Dobrik, G.; Jin, X.; Hwang, C.; Biró, L. P.

    2014-02-01

    The properties of graphene nanoribbons are dependent on both the nanoribbon width and the crystallographic orientation of the edges. Scanning tunneling microscope lithography is a method which is able to create graphene nanoribbons with well defined edge orientation, having a width of a few nanometers. However, it has only been demonstrated on the top layer of graphite. In order to allow practical applications of this powerful lithography technique, it needs to be implemented on single layer graphene. We demonstrate the preparation of graphene nanoribbons with well defined crystallographic orientation on top of gold substrates. Our transfer and lithography approach brings one step closer the preparation of well defined graphene nanoribbons on arbitrary substrates for nanoelectronic applications.

  10. Laser desorption from and reconstruction on Si(100) surfaces studied by scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Jun; Overbury, S.H.; Wendelken, J.F.

    1995-07-01

    Laser irradiated Si(100) surfaces were studied with an ultrahigh-vacuum scanning tunneling microscopy (STM) system. Our observations indicate that only the dimerized outermost atomic layer is removed if the laser fluence is below the melting threshold with a photon energy larger than the band gap. The newly exposed layer, surprisingly, did not have a dimerized atomic structure, but rather, resembled that of a bulk-terminated structure. The uncovered layer remained atomically smooth (no vacancies) even after 90% of the outermost layer was removed. A possible explanation of these observations is that atom removal occurs by a preferential breakage of the atomic bonds in defect sites. When the laser fluence was increased to levels above the melting threshold, extensive surface roughening occurs.

  11. A theoretical model of scanning tunneling microscopy: Application to the graphite (0001) and Au(111) surfaces

    Science.gov (United States)

    Ou-Yang, Hui; Källebring, Bruno; Marcus, R. A.

    1993-05-01

    An expression for the scanning tunneling microscopy (STM) current between the tip and sample is presented using first-order perturbation theory for a two-Hamiltonian formalism (``reactants'' and ``products''). The calculated STM current depends on the square of the sample-tip matrix elements, averaged over a selection of random points in wave vector space. In the limit of low voltage and temperature, this averaging is over the Fermi surface of the sample. The model is applied to the graphite (0001) and Au(111) surfaces using a simple model (chain) of a tungsten tip and the tight-binding approximation. Comparisons with experiments and with the result for graphite obtained by Tersoff and Lang using a molybdenum tip are given. The theory is applied elsewhere to STM of adsorbates.

  12. Low temperature InSb(0 0 1) surface structure studied by scanning tunneling microscopy

    Science.gov (United States)

    Goryl, G.; Boelling, O.; Godlewski, S.; Kolodziej, J. J.; Such, B.; Szymonski, M.

    2007-09-01

    InSb(0 0 1) surface prepared by ion sputtering and thermal annealing has been studied in the temperature range from 77 K up to 300 K using scanning tunneling microscopy (STM). At 300 K the surface is c(8 × 2) reconstructed as indicated by low energy electron diffraction and STM images, and its structure appears to be consistent with the "?-model" recently proposed for this surface. Upon lowering of the temperature below 180 K a new phase appears on the surface. This phase is characterized by the surface structure period doubling along [1 1 0], lowering the surface symmetry from c2mm to p2, and appearance of structural domains. Possible origins of the new phase are discussed.

  13. Cross-sectional scanning tunneling microscopy of semiconductor vertical-cavity surface-emitting laser structure

    International Nuclear Information System (INIS)

    Scanning tunneling microscopy (STM) studies of a semiconductor vertical-cavity surface-emitting laser (VCSEL) device viewed in cross section on an atomic scale are reported. The strained layer In0.2Ga0.8As/GaAs multiple-quantum wells (MQWs) in the laser active region are imaged with atomic resolution. For the first time, the interface roughness of In0.2Ga0.8As/GaAs MQWs is revealed by imaging spectroscopically different individual indium and gallium atoms. It was found that STM images can directly map the interface electronic structure of Al0.67Ga0.33As/GaAs multiple layers in the Bragg reflectors of the VCSEL. The images reflect enhanced or reduced interface electron concentration in regions with a spatial extension of ?100 A. The bias effect is also discussed in the imaging of heterostructures

  14. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-01-18

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

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

    Science.gov (United States)

    Hsieh, Satcher; Hong, Jeongmin; Bokor, Jeffrey

    2014-03-01

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

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

    Science.gov (United States)

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

    1998-03-01

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

  18. 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.

  19. 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.

  20. 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.

  1. Scanning Tunneling Microscopy of Porphyrin-Based Molecules on TiO2 Surfaces

    Science.gov (United States)

    Inada, Mitsuru; Scifo, Lorette; Tanaka, Shukichi; Grevin, Benjamin; Suzuki, Hitoshi; Mashiko, Shinro

    2006-03-01

    The conformational features of bis(3,5-di-t-butyphenyl)(4-ethynylphenyl)(methylthiophenyl)porphyrin (EMTBPP) molecules on rutile TiO2(110)-(1 × 1) surfaces were investigated by scanning tunneling microscopy under ultrahigh vacuum conditions. The EMTBPP molecules are successively observed at single-molecule resolution. At lower coverage, the EMTBPP molecules seem to be selectively adsorbed to oxygen vacancy places in the oxygen row due to an attractive force between the center of the porphyrin ring and the oxygen vacancy. At higher coverages, periodical and orientational ordering of the EMTBPP molecules along the (1 × 1) surface structure occurs. The effects of molecule-substrate and intermolecular interactions on the conformational features are discussed.

  2. Long-range interaction between adatoms at the Cu(111) surface imaged by scanning tunnelling microscopy

    Science.gov (United States)

    Wahlström, E.; Ekvall, I.; Olin, H.; Walldén, L.

    We have used an ultra-high vacuum variable temperature scanning tunnelling microscope to study the Cu(111) surface at temperatures from 90 K to 300 K. After the sample is heated to 900 K, adatoms enriched at the surface. Around these adatoms ring-formed standing-wave features can be seen in the local density of states (LDOS). When more than one of the adatoms were imaged it became evident that the adatoms preferred lateral distances in which they shared LDOS standing-wave maximas. This means that adatoms were positioned at multiples of half the Fermi wavelength (15 Å) from each other. We ascribe the interaction that gave these results to the surface state electrons which form the LDOS standing waves. Furthermore the interaction was long-ranged (at least in the order of 80 Å), oscillatory with the pair distance, and present at high temperatures since the adatoms stick to the surface above room temperature.

  3. 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.

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

    DEFF Research Database (Denmark)

    Haiss, W.; Albrecht, Tim

    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 superexchange and coherent two-step notions for charge transport. It is shown here that the absence of a maximum in the I-tunneling versus electrode potential relationship can be fitted by a "soft" gating concept. This arises from large configurational fluctuations of the molecular bridge linked to the gold contacts by flexible chains. This view is incorporated in a formalism that is well-suited for data analysis and reproduces in all important respects the 6V6 data for physically sound values of the appropriate parameters. This study demonstrates that fluctuations of isolated configurationally "soft" molecules can dominate charge transport patterns and that theoretical frameworks for compact monolayers may not be directly applied under such circumstances.

  5. 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.

  6. Imaging charged defects on clean Si(100)-(2 x1) with scanning tunneling microscopy

    Science.gov (United States)

    Brown, G. W.; Grube, H.; Hawley, M. E.; Schofield, S. R.; Curson, N. J.; Simmons, M. Y.; Clark, R. G.

    2002-07-01

    Scanning tunneling microscopy (STM) has been used to image charged defects on the clean Si(100)-(2 x1) surface. Previous studies have shown that, in the absence of "C"-type defects, the surface does not pin the Fermi level, allowing near surface charge to influence the state density contributing to the tunneling current. As in the case of cleavage faces of III-V semiconductor crystals, the charge-induced band bending produces long-range enhancements superimposed on the periodic surface lattice. This is observed in empty-state STM images taken on n-type material. No band bending signature is seen in the filled-state images. This can be understood by considering the band structure at the surface, which has surface states within the band gap. The charged defects observed in this work are of the types commonly observed in clean Si(100)-(2 x1) STM studies, however, not all defects of a given type appear charged. This would indicate subtle differences in structure or the influence of impurities. Predictions for p-type material will also be made.

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

    Science.gov (United States)

    Toroz, Dimitrios; Rontani, Massimo; Corni, Stefano

    2011-01-01

    Scanning tunneling microscopy (STM) has been a fundamental tool to characterize many-body effects in condensed matter systems, from extended solids to quantum dots. STM of molecules decoupled from the supporting conductive substrate has the potential to extend STM characterization of many-body effects to the molecular world as well. In this paper, we describe a many-body tunneling theory for molecules decoupled from the STM substrate, and we report on the use of standard quantum chemical methods to calculate the quantities necessary to provide the "correlated" STM molecular image. The developed approach has been applied to 18 different molecules to explore the effects of their chemical nature and of their substituents, as well as to verify the possible contribution by transition metal centers. Whereas the bulk of calculations has been performed with the configuration interaction method with single and double excitations (CISD), because of the computational cost some tests have been also performed with the more accurate coupled cluster with single and double excitations (CCSD) method to quantify the importance of the computational level on many-body STM images. We have found that correlation induces a remarkable squeezing of the images, and that correlated images are not derived from Hartree-Fock HOMO or LUMO alone, but include contributions from other orbitals as well. Although correlation effects are too small to be resolved by present STM experiments for the studied molecules, our results provide hints for seeking out other species with larger, and possibly experimentally detectable, correlation effects.

  8. 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.

  9. Atomic-scale evidence for potential barriers and strong carrier scattering at graphene grain boundaries: a scanning tunneling microscopy study.

    Science.gov (United States)

    Koepke, Justin C; Wood, Joshua D; Estrada, David; Ong, Zhun-Yong; He, Kevin T; Pop, Eric; Lyding, Joseph W

    2013-01-22

    We use scanning tunneling microscopy and spectroscopy to examine the electronic nature of grain boundaries (GBs) in polycrystalline graphene grown by chemical vapor deposition (CVD) on Cu foil and transferred to SiO(2) substrates. We find no preferential orientation angle between grains, and the GBs are continuous across graphene wrinkles and SiO(2) topography. Scanning tunneling spectroscopy shows enhanced empty states tunneling conductance for most of the GBs and a shift toward more n-type behavior compared to the bulk of the graphene. We also observe standing wave patterns adjacent to GBs propagating in a zigzag direction with a decay length of ~1 nm. Fourier analysis of these patterns indicates that backscattering and intervalley scattering are the dominant mechanisms responsible for the mobility reduction in the presence of GBs in CVD-grown graphene. PMID:23237026

  10. 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

  11. REAL-SPACE OBSERVATION OF PEROXIDE-LIKE DIMERS ON A SODIUM TUNGSTEN BRONZE SURFACE BY SCANNING-TUNNELING-MICROSCOPY

    OpenAIRE

    Jones, F.; Rawlings, K.; Foord, J; P. Cox; EGDELL, R; Pethica, J

    1995-01-01

    Oxygen dimers on the (2×1) reconstructed surface of Na 0.65WO3(001) have been observed by scanning tunnelling microscopy, with an O-O separation (2.2 Å) that is significantly less than twice the ionic radius of the oxide ion (2.8 Å).

  12. Scanning tunneling microscope combined with synchrotron-radiation for elemental analysis

    International Nuclear Information System (INIS)

    Full text: We present a newly developed synchrotron-radiation-illuminated scanning-tunneling-microscope (SR-STM) at BL-19A in Photon Factory (KEK, Japan). Combining the energy tunability of SR light with the high-spatial resolution of STM, we aim to develop an element-specific microscope. That is, by detecting the photoelectrons from the specific core-levels excited by SR light with STM tip, we expect an elemental mapping of the surface with high spatial resolution. Figure shows an STM image of the Si(111) 7 x 7 surface by the SR- STM in a constant current mode (Vsample= - 1.2 V, It =240 pA) with and without SR light illuminating with the photon energy ranging from hv = 93 to 105 eV. As shown in the figure, atomically resolved imaging is attained even under the light illumination. The cross-sectional profile of the STM image is shown in the right of the figure. Light shade indicates the SR illumination during scanning over the area. When the surface is illuminated by the SR light, the tip height is obviously raised. Moreover, a sharp increase of the tip height is observed above the Si L adsorption edge ( ? 101 eV). These results demonstrate the possibility of elemental identification using this technique. The spatial resolution of the elemental mapping is approximately micron order at present. In order to improve it, we are now testing a tip-coating and some other trial techniques

  13. 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...

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

    Science.gov (United States)

    Salerno, Marco

    2010-09-01

    Different combinations of metal tips and oxide coatings have been tested for possible operation in electrochemical scanning tunneling microscopy. Silicon and magnesium oxides have been thermally evaporated onto gold and platinum-iridium tips, respectively. Two different thickness values have been explored for both materials, namely, 40 and 120 nm for silicon oxide and 20 and 60 nm for magnesium oxide. Alternatively, tungsten oxide has been grown on tungsten tips via electrochemical anodization. In the latter case, to seek optimal results we have varied the pH of the anodizing electrolyte between one and four. The oxide coated tips have been first inspected by means of scanning electron microscopy equipped with microanalysis to determine the morphological results of the coating. Second, the coated tips have been electrically characterized ex situ for stability in time by means of cyclic voltammetry in 1 M aqueous KCl supporting electrolyte, both bare and supplemented with K(3)[Fe(CN)(6)] complex at 10 mM concentration in milliQ water as an analyte. Only the tungsten oxide coated tungsten tips have shown stable electrical behavior in the electrolyte. For these tips, the uncoated metal area has been estimated from the electrical current levels, and they have been successfully tested by imaging a gold grating in situ, which provided stable results for several hours. The successful tungsten oxide coating obtained at pH=4 has been assigned to the WO(3) form. PMID:20886983

  15. 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

  16. 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.

  17. Molecular-resolution imaging of insulating macromolecules with the scanning tunneling microscope via a nontunneling, electric-field-induced mechanism

    Science.gov (United States)

    Tang, S. L.; McGhie, A. J.; Suna, A.

    1993-02-01

    The scanning tunneling microscope (STM) has been used to obtain molecular-resolution images of a film of hydroxypropylcellulose at least hundreds of angstroms thick in ultrahigh vacuum. Microfibrils with a periodicity of 34 Å were observed directly. The pulsing current used to obtain these images was drastically different from the stable direct current in conventional STM imaging of conducting substrates based on tunneling. An electric-field-induced impurity-mediated conduction in insulating thin-film materials is invoked to explain the occurrence of the pulsing current used for imaging. The experimental resolution in the images was shown to be consistent with the proposed mechanism.

  18. Domain wall in (FeCo)-Zr-O thin film profiled by spin-polarized scanning tunneling microscopy

    International Nuclear Information System (INIS)

    The domain structure of (FeCo)-Zr-O thin film was observed with spin-polarized scanning tunneling microscopy. A maze domain is characterized by a domain width of about 320 nm, and a wall energy of 4.97 erg cm-2. The tunneling magnetoresistance (TMR) profile is fitted by a tanh function, and a wall thickness of about 100 nm is obtained. This indicates that the TMR is proportional to the angle between the tip and the film magnetizations. Effective exchange and anisotropy constants are estimated at 3.88 x 10-6 erg cm-1 and 3.98 x 105 erg cm-3, respectively

  19. 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 imprntroller 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)

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

    CERN Document Server

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

    2006-01-01

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

  1. Characteristics of the (\\sqrt{3}×\\sqrt{3})R30\\circ Superstructure of Graphite by Scanning Tunneling Microscopy

    Science.gov (United States)

    An, Bai; Fukuyama, Seiji; Yokogawa, Kiyoshi; Yoshimura, Masamichi

    2000-07-01

    The bias-voltage- and the tunneling-current-dependent scanning tunneling microscopy (STM) images of the (\\sqrt{3}×\\sqrt{3})R30\\circ superstructure of graphite formed near defects produced by Ar+-irradiation on highly oriented pyrolytic graphite annealed at 1373 K were investigated. The (\\sqrt{3}×\\sqrt{3})R30\\circ superstructure of graphite is gradually changed to a triangular structure and the area of the superstructure becomes smaller with increasing bias voltage or decreasing tunneling current, namely, with increasing tip-sample distance. This result indicates that the STM image of the (\\sqrt{3}×\\sqrt{3})R30\\circ superstructure of graphite mainly depends on the tip-sample distance. It is suggested that the electronic superstructure induced by the defects on the surface of graphite decays faster than the electronic structure of normal graphite in vacuum.

  2. 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.

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

    DEFF Research Database (Denmark)

    Andersen, Jens Enevold Thaulov; Olesen, Klaus G.

    1997-01-01

    In situ scanning tunnelling microscopy (STM) imaging of cytochrome c (cyt c) on polycrystalline Pt surfaces and on Au(lll) was achieved first by covalent immobilisation of 3-aminopropyltriethoxysilane (3-APTS) brought to react with oxide present on the Pt surfaces. Covalently bound 3-APTS forms a further link to glutaric dialdehyde which immobilises the protein molecules. Cyt c is immobilised on Au(ll!) by reaction with N-acetylcystein and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. Imaging by in situ STM in a 20 mM phosphate buffer electrolyte with a Au/AuOx reference electrode could then be achieved, Protein was identified as hemispherical features on the surface with close to molecular resolution and with a quite different character compared both to the bare metal surfaces and to metal surfaces with only linker molecules attached. No subunits or side chains were visible, but the protein exhibited a grained surface appearance, possibly caused by mobile subunits or immobilising agent. (C) 1997 Elsevier Science S.A.

  4. Scanning tunnelling microscope fabrication of arrays of phosphorus atom qubits for a silicon quantum computer

    Science.gov (United States)

    O'Brien, J. L.; Schofield, S. R.; Simmons, M. Y.; Clark, R. G.; Dzurak, A. S.; Curson, N. J.; Kane, B. E.; McAlpine, N. S.; Hawley, M. E.; Brown, G. W.

    2002-10-01

    Recognition of the potentially massive computational power of a quantum computer has driven a considerable experimental effort to build such a device. Of the various possible physical implementations, silicon-based architectures are attractive for the long spin relaxation times involved, their scalability, and ease of integration with existing silicon technology. However, their fabrication requires construction at the atomic scale - an immense technological challenge. Here we outline a detailed strategy for the construction of a phosphorus in silicon quantum computer and demonstrate the first significant step towards this goal - the fabrication of atomically precise arrays of single phosphorus bearing molecules on a silicon surface. After using a monolayer hydrogen resist to passivate a silicon surface we apply pulsed voltages to a scanning tunnelling microscope tip to selectively desorb individual hydrogen atoms with atomic resolution. Exposure of this surface to the phosphorus precursor phosphine results in precise placement of single phosphorus atoms on the surface. We also describe preliminary studies into a process to incorporate these surface phosphorus atoms into the silicon crystal at the array sites.

  5. Scanning tunneling microscopy theory for an adsorbate: Application to adenine adsorbed on a graphite surface

    Science.gov (United States)

    Ou-Yang, Hui; Marcus, R. A.; Källebring, Bruno

    1994-05-01

    An expression is obtained for the current in scanning tunneling microscopy (STM) for a single adsorbate molecule. For this purpose the ``Newns-Anderson'' treatment (a ``discrete state in a continuum'' treatment) is used to obtain wave functions and other properties of the adsorbate/substrate system. The current is expressed in terms of the adsorbate-tip matrix elements, and an effective local density of states of the adsorbate/substrate system, at the adsorbate. As an example, the treatment is applied to the STM image of adenine adsorbed on a graphite surface, and the results are compared with experiment. The dependence of the image on the position of adenine with respect to the underlying graphite is considered. A discussion is given of the type of experimental STM data needed for suitable comparison of theory and experiment. In an analysis of the calculations, the role of each atom, its neighbors, next nearest neighbors, etc., in an adsorbed molecule is considered. The need for using in the present calculation more orbitals than only the HOMO and the LUMO of the adsorbate is also noted.

  6. Investigation of heteroepitaxial diamond films by atomic force and scanning tunneling microscopy

    International Nuclear Information System (INIS)

    We report on Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM) investigations on chemical vapour deposited heteroepitaxial diamond films. Besides the good macroscopic crystal morphology a statistical tilt up to ± 5.2 of the oriented crystallites has been found relative to the silicon substrates. By optimizing the process conditions, however, the crystal tilt of the films can be reduced, resulting in an improved film perfection. On crystallite (001)-surfaces a substructure of growth facets or islands has been found and high resolution STM images have established a 2 x 1 surface reconstruction on these growth facets. AFM and SEM were applied to study the morphology of diamond nuclei initially grown on the silicon substrate. Strong island like (Volmer-Weber) growth has been found, with a nucleus height to diameter ratio of 1:1. While the islands are growing in size with respect to time of nucleation, its aspect ratio does not change, due to the high surface free energy of the diamond relative to silicon. (orig.)

  7. 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.

  8. Defect formation by single ion impacts on highly oriented pyrolytic graphite observed by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    (0001) surfaces of highly oriented pyrolytic graphite (HOPG) were irradiated at 77K with 132Xe+ ions at energies between 50 keV and 900 keV. The ion fluences ranged between 1011 ions/cm2 and 1015 ions/cm2. Scanning tunneling microscopy (STM) was applied to image the irradiation induced defects at the surfaces. In case of orthogonal incidence and small ion fluence each incident ion induces one single hillock at the surface. These hillocks have typical lateral diameters of 2 nm and heights of several angstrom. In many cases measurements of the hillocks with atomic resolution show disordered atomic arrangements. The hillocks are interpreted as the local volume expansion due to surface-near self-interstitials generated in the collision cascades of the ions. The high mobility of these interstitials parallel to the (0001) planes leads to a formation of interstitial clusters which cause the larger hillocks. Irradiation at an angle of incidence of 75 degree with respect to the surface normal effects a higher density of hillocks due to the higher number of recoils stopped in the uppermost lattice planes. The hillocks are arranged in chains which are aligned in the direction of the incident beam. Each of these chains marks a single collision cascade

  9. Defect formation by single ion impacts on highly oriented pyrolytic graphite observed by scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Reimann, K.P.; Bolse, W.; Geyer, U.; Vom Minnigerode, G.; Lieb, K.P. [Univ. Goettingen (Germany). Physikalisches Inst.]|[Sonderforschungsbereich, Goettingen (Germany)

    1995-12-31

    (0001) surfaces of highly oriented pyrolytic graphite (HOPG) were irradiated at 77K with {sup 132}Xe{sup +} ions at energies between 50 keV and 900 keV. The ion fluences ranged between 10{sup 11} ions/cm{sup 2} and 10{sup 15} ions/cm{sup 2}. Scanning tunneling microscopy (STM) was applied to image the irradiation induced defects at the surfaces. In case of orthogonal incidence and small ion fluence each incident ion induces one single hillock at the surface. These hillocks have typical lateral diameters of 2 nm and heights of several {angstrom}. In many cases measurements of the hillocks with atomic resolution show disordered atomic arrangements. The hillocks are interpreted as the local volume expansion due to surface-near self-interstitials generated in the collision cascades of the ions. The high mobility of these interstitials parallel to the (0001) planes leads to a formation of interstitial clusters which cause the larger hillocks. Irradiation at an angle of incidence of 75{degree} with respect to the surface normal effects a higher density of hillocks due to the higher number of recoils stopped in the uppermost lattice planes. The hillocks are arranged in chains which are aligned in the direction of the incident beam. Each of these chains marks a single collision cascade.

  10. 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.

  11. 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.

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

    International Nuclear Information System (INIS)

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

  13. Scanning Tunneling Microscopy Study of Mechanically-Stacked Double Layer Graphene

    Science.gov (United States)

    Baek, Hongwoo; Ha, Jeonghoon; Hwang, Beomyong; Kwon, Jeonghoon; Stroscio, Joseph; Kuk, Young

    2012-02-01

    Bilayer graphene has drawn considerable attention due to deviation from Dirac Fermion picture such as anomalous quantum hall effect and a tunable band gap in their spectrum. While a pristine Bernal (AB) stacked bilayer graphene can be synthesized by mechanical exfoliation, growth on a SiC single crystal and epitaxial growth on metal substrates, separate control of the top and the bottom layers has seldom been performed. In this study, artificially modified 2D layers were demonstrated with individually stacked double layer graphene. Large-area graphene was grown on a Cu foil by chemical vapor deposition (CVD). CVD-grown graphene layers were transferred successively onto several insulating substrates with minimum chemical process for realizing bilayer graphene. Mechanically-stacked double layer graphene was mainly investigated using scanning tunneling microscopy and spectroscopy. The artificial bilayer graphene showed Moire patterns as determined by misalignment angle. In spatially resolved spectrums of local density of states, dependence on separation distance between two graphene layers and their corrugation was measured. In addition, we confirmed less charging effects of graphene on BN thin film than on SiO2 or SiN.

  14. Scanning tunneling microscopy of the annealing of a thin platinum film on highly oriented pyrolytic graphite

    International Nuclear Information System (INIS)

    Scanning tunneling microscopy (STM) was used to study morphological changes of a Pt thin film deposited on highly oriented pyrolytic graphite (HOPG) during an annealing process. In air, it was possible to image the morphology of the thin film with a vertical resolution of 0.5 A and a lateral resolution of 20 A. Surface structural change was observed after the annealing processes. When the annealing temperature was below 573 K, surface morphology changed only slightly. Between 573 and 873 K, the originally uniformly distributed rolling hills of Pt coagulated into larger clumps. Above 873 K, Pt crystal facets started to form on the surface. At 1123 K, a large portion of the surface turned into well defined Pt crystal facets. Above 1123 K, the Pt film started to crack and formed scattered crystals on the HOPG surface. A complementary X-ray diffraction measurement showed that the crystallized Pt film was preferentially oriented with the (111) plane parallel to the substrate graphite (0001) basal plane, indicating epitaxy of the Pt overlayer with the graphite substrate underneath. (orig.)

  15. Scanning tunneling microscopy study of metal-free phthalocyanine monolayer structures on graphite

    Science.gov (United States)

    Nilson, Katharina; Åhlund, John; Brena, Barbara; Göthelid, Emmanuelle; Schiessling, Joachim; Mârtensson, Nils; Puglia, Carla

    2007-09-01

    Low temperature scanning tunneling microscopy (STM) studies of metal-free phthalocyanine (H2Pc) adsorbed on highly oriented pyrolytic graphite (HOPG) have shown ordered arrangement of molecules for low coverages up to 1 ML. Evaporation of H2Pc onto HOPG and annealing of the sample to 670K result in a densely packed structure of the molecules. Arrangements of submonolayer, monolayer, and monolayer with additional adsorbed molecules have been investigated. The high resolution of our investigations has permitted us to image single molecule orientation. The molecular plane is found to be oriented parallel to the substrate surface and a square adsorption unit cell of the molecules is reported. In addition, depending on the bias voltage, different electronic states of the molecules have been probed. The characterized molecular states are in excellent agreement with density functional theory ground state simulations of a single molecule. Additional molecules adsorbed on the monolayer structures have been observed, and it is found that the second layer molecules adsorb flat and on top of the molecules in the first layer. All STM measurements presented here have been performed at a sample temperature of 70K.

  16. Probing Anistropic Excitonic Wavefunctions in Black Phosphorus using Scanning Tunneling Microscopy

    Science.gov (United States)

    Notis, Ayelet; Arguello, Carlos; Rosenthal, Ethan; Pasupathy, Abhay

    2015-03-01

    Black phosphorus is a layered, van der Waals semiconductor that has several structural similarities to graphite. Ultrathin black phosphorus (phosphorene) is conjectured to have a thickness-tunable bandgap and high carrier mobility, making it attractive for electronic and optical applications. Unlike graphene which is a true planar structure, phosphorene layers have a pronounced c-axis corrugation. This causes the electronic structure to be anisotropic, with different effective masses, carrier velocities and dielectric constants parallel and perpendicular to the direction of the corrugation. This has been predicted to lead to anisotropic wavefunctions for hydrogenic states and excitons in the material. In this talk, we present recent scanning tunneling microscopy and spectroscopy (STM and STS) studies investigating the topographic features and electronic structure of black phosphorus. We show that the primary charge defects are acceptors. By studying the local electronic structure in the vicinity of these defects that create hydrogenic states within the bandgap, we directly probe excitonic wavefunctions and their anisotropy in this material. We will describe spatially-resolved measurements of the bandgap and its inhomogeneity in the presence of defects.

  17. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1998-11-10

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

  19. 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.

  20. 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.

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

    Science.gov (United States)

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

    2015-03-01

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

  3. 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.

  4. Van Hove singularities in doped twisted graphene bilayers studied by scanning tunneling spectroscopy

    Science.gov (United States)

    Cherkez, V.; de Laissardière, G. Trambly; Mallet, P.; Veuillen, J.-Y.

    2015-04-01

    The effect of electron doping on the van Hove singularities (vHs) which develop in twisted graphene bilayers (tBLs) is studied for a broad range of rotation angles ? (1 .5?scanning tunneling microscopy and spectroscopy. Bilayer and trilayer graphene islands were grown on the 6H-SiC(000-1) (3 ×3 ) surface, which results in tBLs doped in the 1012cm-2 range by charge transfer from the substrate. For large angles, doping manifests in a strong asymmetry of the positions of the upper (in empty states) and lower (in occupied states) vHs with respect to the Fermi level. The splitting of these vHs energies is found essentially independent of doping for the whole range of ? values, but the center of theses vHs shifts towards negative energies with increasing electron doping. Consequently, the upper vHs crosses the Fermi level for smaller angles (around 3? ). The analysis of the data performed using tight-binding calculations and simple electrostatic considerations shows that the interlayer bias remains small (<100 mV ) for the doping level resulting from the interfacial charge transfer (?5 ×1012cm-2) .

  5. Magnetoresistance of oblique angle deposited multilayered Co/Cu nanocolumns measured by a scanning tunnelling microscope

    International Nuclear Information System (INIS)

    In this work we present the first magnetoresistance measurements on multilayered vertical Co(?6 nm)/Cu(?6 nm) and slanted Co(x nm)/Cu(x nm) (with x?6, 11, and 16 nm) nanocolumns grown by oblique angle vapour deposition. The measurements are performed at room temperature on the as-deposited nanocolumn samples using a scanning tunnelling microscope to establish electronic contact with a small number of nanocolumns while an electromagnet generates a time varying (0.1 Hz) magnetic field in the plane of the substrate. The samples show a giant magnetoresistance (GMR) response ranging from 0.2 to 2%, with the higher GMR values observed for the thinner layers. For the slanted nanocolumns, we observed anisotropy in the GMR with respect to the relative orientation (parallel or perpendicular) between the incident vapour flux and the magnetic field applied in the substrate plane. We explain the anisotropy by noting that the column axis is the magnetic easy axis, so the magnetization reversal occurs more easily when the magnetic field is applied along the incident flux direction (i.e., nearly along the column axis) than when the field is applied perpendicular to the incident flux direction

  6. Scanning tunneling microscopy of the initial stages of metal condensation on semiconductor surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Brodde, A.; Harazim, E.; Kliese, R.; Roettger, B.; Neddermeyer, H. (Inst. fuer Experimentalphysik, Ruhr-Univ., Bochum (Germany))

    1991-11-01

    After a brief description of the theoretical and experimental basis of scanning tunneling microscopy (STM) typical results from the initial stage of metal condensation on semiconductor surfaces will be presented. As substrates Si(111) and Si(100) are used. Their reconstruction is explained by the current atomic models and compared with STM images of the clean surfaces. While the 7x7 reconstruction of Si(111) can be prepared with a defect concentration in the order of 0.03% of a monolayer, Si(100) shows a higher density of imperfections by at least one order of magnitude. STM images from nonreactive systems (Ag/Si(111) and Ag/Si(100)) are described and from a reactive system (Fe/Si(111)), which forms well defined silicides. In case of Ag/Si and room temperature condensation the initial stage is characterized by a two-dimensional interface layer, which does not cover the substrates completely and the growth of rather regular three-dimensional Ag islands, whose shape is consistent with metallic character. After Fe deposition on Si(111) the surface is covered by islands, which due to their irregular size and shape indicate compound formation or intermixing with Si. After annealing Fe/Si(111) shows the development of well ordered Fe silicide layers. (orig.).

  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. Au/ITO dual-layer-coated optical fiber probe for multifunctional scanning tunneling microscopy

    International Nuclear Information System (INIS)

    We have fabricated an Au/ITO (indium-tin-oxide) dual-layer optical fiber probe with functions for high-quality scanning tunneling microscope (STM) imaging and near-field excitation and detection of STM-induced electroluminescence (STML). The inner ITO layer is kept ?150 nm in thickness to ensure the conductivity of the fiber probe. The outer Au layer is kept ?13 nm in thickness to obtain a better combination of high electron injection efficiency and optical transparency. High-quality STM images, and STML corresponding to maximum quantum efficiencies of 7 x 10-4 and 1 x 10-4 photons/electron are obtained on Au(111)/mica and p-GaAs(110) surfaces at room temperature (RT), respectively. The outer Au layer on the Au/ITO-coated fiber probe shows an effective role in improving the quality of STM imaging, the tip apex geometry and durability of the fiber probe, the stability and reproducibility of STML and enhancing the intensity of plasmon-mediated STML from the Au(111) surface but it shows no effect in enhancing the intensity of STML from the GaAs(110) surface.

  9. Au/ITO dual-layer-coated optical fiber probe for multifunctional scanning tunneling microscopy

    Science.gov (United States)

    Guo, Xinli; Fujita, Daisuke; Onish, Keiko

    2010-01-01

    We have fabricated an Au/ITO (indium-tin-oxide) dual-layer optical fiber probe with functions for high-quality scanning tunneling microscope (STM) imaging and near-field excitation and detection of STM-induced electroluminescence (STML). The inner ITO layer is kept ~150 nm in thickness to ensure the conductivity of the fiber probe. The outer Au layer is kept ~13 nm in thickness to obtain a better combination of high electron injection efficiency and optical transparency. High-quality STM images, and STML corresponding to maximum quantum efficiencies of 7 × 10-4 and 1 × 10-4 photons/electron are obtained on Au(111)/mica and p-GaAs(110) surfaces at room temperature (RT), respectively. The outer Au layer on the Au/ITO-coated fiber probe shows an effective role in improving the quality of STM imaging, the tip apex geometry and durability of the fiber probe, the stability and reproducibility of STML and enhancing the intensity of plasmon-mediated STML from the Au(111) surface but it shows no effect in enhancing the intensity of STML from the GaAs(110) surface.

  10. Solidification and epitaxial regrowth in surface nanostructuring with laser-assisted scanning tunneling microscope

    International Nuclear Information System (INIS)

    In this work, parallel molecular-dynamics simulation is conducted to study the long-time (up to 2 ns) behavior of argon crystal in surface nanostructuring with a laser-assisted scanning tunneling microscope. A large system consisting of more than 1x108 at. is explored. The study is focused on the solidification procedure after laser irradiation, which is driven by heat conduction in the material. Epitaxial regrowth is observed in the solidification. Atomic dislocation due to thermal strain-induced structural damages is observed as well in epitaxial regrowth. During solidification, the liquid is featured with decaying normal compressive stresses and negligible shear stresses. Two functions are designed to capture the structure and distinguish the solid and liquid regions. These functions work well in terms of reflecting the crystallinity of the material and identifying the atomic dislocations. The study of the movement of the solid-liquid interface reveals an accelerating moving speed in the order of 3-5 m/s. The spatial distribution of the moving speed at the solid-liquid interface indicates a nonuniform epitaxial regrowth in space. The bottom of the liquid solidifies slower than that at the edge

  11. Investigating individual arsenic dopant atoms in silicon using low-temperature scanning tunnelling microscopy

    International Nuclear Information System (INIS)

    We study subsurface arsenic dopants in a hydrogen-terminated Si(001) sample at 77 K, using scanning tunnelling microscopy and spectroscopy. We observe a number of different dopant-related features that fall into two classes, which we call As1 and As2. When imaged in occupied states, the As1 features appear as anisotropic protrusions superimposed on the silicon surface topography and have maximum intensities lying along particular crystallographic orientations. In empty-state images the features all exhibit long-range circular protrusions. The images are consistent with buried dopants that are in the electrically neutral (D0) charge state when imaged in filled states, but become positively charged (D+) through electrostatic ionization when imaged under empty-state conditions, similar to previous observations of acceptors in GaAs. Density functional theory calculations predict that As dopants in the third layer of the sample induce two states lying just below the conduction-band edge, which hybridize with the surface structure creating features with the surface symmetry consistent with our STM images. The As2 features have the surprising characteristic of appearing as a protrusion in filled-state images and an isotropic depression in empty-state images, suggesting they are negatively charged at all biases. We discuss the possible origins of this feature. (fast track communication)

  12. 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.

  13. 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.

  14. 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...

  15. Role of interband scattering in neutron irradiated MgB2 thin films by scanning tunneling spectroscopy measurements

    International Nuclear Information System (INIS)

    A series of MgB2 thin films systematically disordered by neutron irradiation have been studied by scanning tunneling spectroscopy. The c-axis orientation of the films allowed a reliable determination of the local density of states of the ? band. With increasing disorder, the conductance peak moves towards higher voltages and becomes lower and broader, indicating a monotonic increase of the ? gap and of the broadening parameter. These results are discussed in the framework of two-band superconductivity

  16. High-Percentage Success Method for Preparing and Pre-Evaluating Tungsten Tips for Atomic-Resolution Scanning Tunneling Microscopy

    OpenAIRE

    Schoelz, J. K.; Xu, P.; Barber, S. D.; Qi, D.; Ackerman, M. L.; Basnet, G.; Cook, C. T.; Thibado, P. M.

    2015-01-01

    A custom double-lamella method is presented for electrochemically etching tungsten wire for use as tips in scanning tunneling microscopy (STM). For comparison, tips were also manufactured in-house using numerous conventional methods and examined using an optical microscope. Both sets of tips were used to obtain STM images of highly-oriented pyrolytic graphite, the quality of which varied. The clarity of the STM images was found to be correlated to the optically-measured cone...

  17. Importance of charging in atomic resolution scanning tunneling microscopy: Study of a single phosphorus atom in a Si(001) surface

    Science.gov (United States)

    Radny, M. W.; Smith, P. V.; Reusch, T. C. G.; Warschkow, O.; Marks, N. A.; Wilson, H. F.; Curson, N. J.; Schofield, S. R.; McKenzie, D. R.; Simmons, M. Y.

    2006-09-01

    We present a detailed voltage-dependent scanning tunneling microscopy study of a single phosphorus atom in the Si(001) surface. Using density functional theory calculations we show that tip-induced charging results in reversible structural and electronic changes. These changes are caused by charge transfer from delocalized surface states to localized states associated with the presence of the phosphorus atom. While two stable geometric configurations are predicted, only the higher energy configuration is consistent with experiment.

  18. Layer by layer removal of Au atoms from passivated Au(111) surfaces using the scanning tunneling microscope: Nanoscale ``paint stripping''

    Science.gov (United States)

    Keel, J. M.; Yin, J.; Guo, Q.; Palmer, R. E.

    2002-04-01

    Layer by layer removal of gold atoms from the (111) surface of gold has been performed using the scanning tunneling microscope. The process is made possible by a chemisorbed self-assembled monolayer (SAM) of dodecanethiol molecules on the surface, which gives rise to a reduced bonding strength between the top two layers of gold atoms. The gold atoms and associated adsorbed molecules are peeled off and displaced laterally by the STM tip, and the size of the modified area (down to ˜10×10 nm) is more or less determined by the scan size.

  19. Scanning tunneling microscopy of the formation, transformation, and property of oligothiophene self-organizations on graphite and gold surfaces

    Science.gov (United States)

    Yang, Zhi-Yong; Zhang, Hui-Min; Yan, Cun-Ji; Li, Shan-Shan; Yan, Hui-Juan; Song, Wei-Guo; Wan, Li-Jun

    2007-01-01

    Two alkyl-substituted dual oligothiophenes, quarterthiophene (4T)-trimethylene (tm)-octithiophene (8T) and 4T-tm-4T, were used to fabricate molecular structures on highly oriented pyrolytic graphite and Au(111) surfaces. The resulted structures were investigated by scanning tunneling microscopy. The 4T-tm-8T and 4T-tm-4T molecules self-organize into long-range ordered structures with linear and/or quasi-hexagonal patterns on highly oriented pyrolytic graphite at ambient temperature. Thermal annealing induced a phase transformation from quasi-hexagonal to linear in 4T-tm-8T adlayer. The molecules adsorbed on Au(111) surface in randomly folded and linear conformation. Based on scanning tunneling microscopy results, the structural models for different self-organizations were proposed. Scanning tunneling spectroscopy measurement showed the electronic property of individual molecules in the patterns. These results are significant in understanding the chemistry of molecular structure, including its formation, transformation, and electronic properties. They also help to fabricate oligothiophene assemblies with desired structures for future molecular devices. PMID:17360417

  20. 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.

  1. Probing charge transport at the single-molecule level on silicon by using cryogenic ultra-high vacuum scanning tunneling microscopy

    OpenAIRE

    Guisinger, Nathan P.; Yoder, Nathan L.; Hersam, Mark C.

    2005-01-01

    A cryogenic variable-temperature ultra-high vacuum scanning tunneling microscope is used for measuring the electrical properties of isolated cyclopentene molecules adsorbed to the degenerately p-type Si(100)-2×1 surface at a temperature of 80 K. Current–voltage curves taken under these conditions show negative differential resistance at positive sample bias, in agreement with previous observations at room temperature. Because of the enhanced stability of the scanning tunneling microscope a...

  2. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Meinel, K.; Wolter, H.; Ammer, Ch.; Beckmann, A.; Neddermeyer, H. [Martin-Luther-Universitaet Halle - Wittenberg, Fachbereich Physik, D-06099 Halle (Germany)

    1997-06-02

    The adsorption of O on Ru(0001) at a temperature of 400 K is studied in detail by means of scanning tunnelling microscopy (STM). With increasing O coverage, an ordered p(2x2) structure develops, followed by a p(2x1) structure. While the p(2x2) structure grows via island formation, the p(2x1) structure is abruptly formed by a disorder - order phase transition. After completion of the p(2x2) structure at a coverage of 0.25 ML, the surface develops a rough structure where the (2x2) units remain visible but appear with different heights. As the origin of this phenomenon, we propose additional O-O interactions and/or subsurface O due to the increase in O coverage. At coverages between 0.3 monolayer (ML) and 0.35 ML, different preformations of the p(2x1) structure are observed. First, small fragments of p(2x1) rows develop, which are randomly distributed over the surface and rotated by 120 deg. with respect to each other. They grow in one dimension and induce a criss-cross arrangement of linear chains of O atoms. Two-dimensional ordering starts via pairing of the p(2x1) rows. At a critical O coverage slightly below 0.40 ML, suddenly large p(2x1) domains are formed in three orientations (rotated by 120 deg.), which coexist with remnants of the p(2x2) structure. At the saturation coverage of O (0.5 ML), the p(2x1) domains cover the surface completely. (author)

  4. Characterization and Properties of Oligothiophenes Using Scanning Tunneling Microscopy for Possible Use in Organic Electronics

    International Nuclear Information System (INIS)

    A scanning tunneling microscopy study has been made on a group of alkyl-substituted oligothiophenes. The self-assembled monolayers of this type of semi-conducting oligomers on graphite were observed and characterized. To control the self-assembly, it is important to first understand the forces that drive the spontaneous ordering of molecules at interfaces. For the identification of the forces, several substituted oligothiophenes were examined: carboxylic acid groups, methyl ester carboxylic acid, and iodine atoms at one end and benzyl esters at the other end of the oligomers this is in addition to the non-functionalized oligothiophehens, Self-assembled monolayers of these molecules were then examined by STM. A detailed analysis of the driving forces and parameters controlling the formation of the self-assembled 2- D crystal monolayers was carried out by performing modeling of the experimental observations. The theoretical calculations gave us a conclusive insight into the intermolecular interactions, which lead to the observed conformation of molecules on the surface. An attempt to react two iodinated oligomers on the surface after the formation of the monolayer has been done; a topochemical reaction studies using UV/Vis light irradiation has been preceded. The targeted reaction was achieved. This can be considered as a great step towards the formation of nano-wires and other organic electronic devices. The applicability of the above method of force-driven self organisation in different patterns was examined as template for building donor-nano structures for electronic devices. It was necessary to examine the stability of the formed templates in air. The monolayers were left to dry and STM images were taken; C60 was then added to the monolayer, and the complexation of the C60 (as acceptor) with the formed monolayer template was examined.

  5. 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.

  6. Scanning tunneling microscopy study of the electron transport properties of self-assembled monolayers of bis-phenyloxazoles

    Science.gov (United States)

    Park, Hayn; Lee, Whasil; Klare, Jennifer E.; Nuckolls, Colin; Heinz, Tony F.

    2004-03-01

    The self-assembly and electron transport properties of monothiol-terminated bis-phenyloxazole molecules have been studied by scanning tunneling microscopy and spectroscopy. The molecules were deposited on a clean Au(111) surface from solution and were studied under vacuum. In the as-deposited state, no long-range ordering was present. Upon annealing, however, an ordered monolayer was observed, characterized by well-defined columnar structures. The height of the corrugations was compatible with molecules aligned normal to the surface. This structure is attributed to the orthogonal terphenyl arms in the cruciform species study, which act to inhibit the molecules from assuming a prone position.[1] Scanning tunneling spectroscopy revealed a relatively high conductance, as expected for the conjugated electron system. Threshold features in the I-V characteristics were observed, indicative of resonant tunneling processes. The electronic properties of the molecules will be discussed in the context of the HOMO-LUMO gap deduced from complementary optical absorption data. [1] J. E. Klare et al., JACS 125, 6030 (2003).

  7. 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.)

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

    International Nuclear Information System (INIS)

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

  9. 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.

  10. 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 proe 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)

  11. 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.

  12. Three-dimensional Wentzel-Kramers-Brillouin approach for the simulation of scanning tunneling microscopy and spectroscopy

    Science.gov (United States)

    Palotás, Krisztián; Mándi, Gábor; Hofer, Werner A.

    2014-12-01

    We review the recently developed three-dimensional (3D) atom-superposition approach for simulating scanning tunneling microscopy (STM) and spectroscopy (STS) based on ab initio electronic structure data. In the method, contributions from individual electron tunneling transitions between the tip apex atom and each of the sample surface atoms are summed up assuming the one-dimensional (1D) Wentzel-Kramers-Brillouin (WKB) approximation in all these transitions. This 3D WKB tunneling model is extremely suitable to simulate spin-polarized STM and STS on surfaces exhibiting a complex noncollinear magnetic structure, i.e., without a global spin quantization axis, at very low computational cost. The tip electronic structure from first principles can also be incorporated into the model, that is often assumed to be constant in energy in the vast majority of the related literature, which could lead to a misinterpretation of experimental findings. Using this approach, we highlight some of the electron tunneling features on a prototype frustrated hexagonal antiferromagnetic Cr monolayer on Ag(111) surface. We obtain useful theoretical insights into the simulated quantities that is expected to help the correct evaluation of experimental results. By extending the method to incorporate a simple orbital dependent electron tunneling transmission, we reinvestigate the bias voltage- and tip-dependent contrast inversion effect on the W(110) surface. STM images calculated using this orbital dependent model agree reasonably well with Tersoff-Hamann and Bardeen results. The computational efficiency of the model is remarkable as the k-point samplings of the surface and tip Brillouin zones do not affect the computational time, in contrast to the Bardeen method. In a certain case we obtain a relative computational time gain of 8500 compared to the Bardeen calculation, without the loss of quality. We discuss the advantages and limitations of the 3D WKB method, and show further ways to improve and extend it.

  13. 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

  14. Nature of water and hydrogen reactions on transition metal surfaces studied by scanning tunneling microscopy

    Science.gov (United States)

    Tatarkhanov, Mouslim Magomedovich

    Scanning Tunneling Microscopy (STM) has already been established as a tool for the investigation of simple reaction mechanisms. In this work I present results of two parallel studies using STM: first, hydrogen on Ru(0001) surface and second, water on Ru(0001) and Pd(111). In both studies initial stages of adsorption up to saturation monolayer coverage were investigated by variable temperature scanning tunneling microscopy (VT STM). The first step of the hydrogen adsorption study was the identification and characterization of the various coverage structures on clean Ru(0001). Hydrogen was found to adsorb dissociatively forming ( 3x3 )R30°, 3 domains of (2x1), (2x2)-3H and (1x1) for increasing coverages of theta=0.3 ML, 0.5 ML, 0.75 ML and 0.1 ML respectively. Some of these structures were observed to coexist at intermediate coverage values. In addition effects of impurities such as oxygen and carbon on hydrogen adsorption has been discussed. Next, near saturation coverage the interesting mechanism of how H 2 dissociates and binds to the surface of Ru(0001) has been observed. We found that the H2 dissociation takes place only on Ru sites where the metal atom is not bound to any H atom. Such active sites are formed when at least 3 H-vacancies aggregate by thermal diffusion. Sites formed by single H-vacancies (i.e. unoccupied Ru sites) or pairs of adjoining vacancies were found to be unreactive toward H2. H-vacancies were observed as single entities diffusing on the surface at 50 K and able to form transient triangular shaped aggregations where H2 molecules dissociated. It was found that the diffusion and aggregation of the H-vacancies is essential in creation of active sites where dissociative adsorption of hydrogen occurs. The first step of water studies was the initial stages of growth of water on the hexagonal surfaces of Pd(111) and Ru(0001) in the temperature range between 40 K and 130 K. In addition, DFT calculations and STM image simulations were used to validate the models. Below 130 K water dissociation does not occur at any appreciable rate and only molecular films are formed. At these temperatures the kinetics of water growth leads to structures where the molecules bind to the metal substrate through the O-lone pair while making 3 H-bonds with neighboring molecules and form clusters of hexagonal units with a honeycomb structure. This bonding geometry imposes limitations to the size of the clusters, with unsaturated H-bonds confined to the cluster periphery. It is found that growth proceeds by attachement of water molecules to the edge of the clusters by H-bonds. These molecules bind only weakly to the metal substrate and can hop around the edges. Comparison of DFT and STM image calculations with experiments shows that on Pd the edge-attached molecules form two different structures, a metastable one where the molecule is elevated by 2.7 A with respect to the cluster molecules, and another where they are elevated by only 0.4 A. On Ru only the less elevated (0.4 A higher) edge-attached molecules are observed. In next final step, water structures on Ru(0001) were studied at temperatures above 140K. STM findings were backed by x-ray absorption spectroscopy. Additional DFT calculations and STM simulations provided validation of proposed models. It was found that while undissociated water layers are metastable below 140 K, heating above this temperature produces drastic transformations whereby a fraction of the water molecules partially dissociate and form mixed H 2O-OH structures. XPS and XAS revealed the presence of hydroxyl groups with their O-H bond essentiallymostly parallel to the surface. STM images show that the mixed H2O-OH structures consist of long narrow stripes aligned with the three crystallographic directions perpendicular to the close-packed atomic rows of the Ru(0001) substrate. The internal structure of the stripes is a honeycomb network of H-bonded water and hydroxyl species. We found that the metastable low temperature molecular phase can also be converted to a mixed H2O-OH phase through excitation

  15. Scanning tunneling microscopy investigations of hydrogen plasma-induced electron scattering centers on single-walled carbon nanotubes

    International Nuclear Information System (INIS)

    The authors report on the generation of localized defects on single-walled carbon nanotubes by means of a hydrogen electron cyclotron resonance plasma. The defects have been investigated using scanning tunneling microscopy (STM) and show an apparent topographic height in the STM of 1-3 A. In the vicinity of defects, characteristic superstructures could be observed and the patterns could be simulated using a simple model based on large momentum scattering of the valence electrons. The combination of low structural damage and high electronic activity opens the possibility to tune the electronic transport properties using such defects

  16. GaSb/GaAs quantum dot formation and demolition studied with cross-sectional scanning tunneling microscopy

    OpenAIRE

    Smakman, E. P.; Garleff, J. K.; Young, R. J.; Hayne, M.; Rambabu, P.; Koenraad, P. M.

    2012-01-01

    We present a cross-sectional scanning tunneling microscopy study of GaSb/GaAs quantum dots grown by molecular beam epitaxy. Various nanostructures are observed as a function of the growth parameters. During growth, relaxation of the high local strain fields of the nanostructures plays an important role in their formation. Pyramidal dots with a high Sb content are often accompanied by threading dislocations above them. GaSb ring formation is favored by the use of a thin GaAs first cap layer an...

  17. 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.

  18. Nucleation of oxides during dry oxidation of Si(001)-2x1 studied by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Morphological development of oxide islands on Si(001)-2x1 surfaces during the initial stage of dry oxidation has been studied using scanning tunneling microscopy. The oxidation was conducted at a substrate temperature of 560degC under an oxygen pressure of 6.7x10-5 Pa. The initial oxide islands grow one-dimensionally until the number of oxygen atoms within an island reaches four, at which point the growth is converted into a two-dimensional growth mode. (author)

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

    International Nuclear Information System (INIS)

    We analyze how a probing particle modifies the infrared electromagnetic near field of a sample. The particle, described by electric and magnetic polarizabilities, represents the tip of an apertureless scanning optical near-field microscope (SNOM). We show that the interaction with the sample can be accounted for by ascribing to the particle dressed polarizabilities that combine the effects of image dipoles with retardation. When calculated from these polarizabilities, the SNOM signal depends only on the fields without the perturbing tip. If the studied surface is not illuminated by an external source but heated instead, the signal is closely related to the projected electromagnetic local density of states (EM-LDOS). Our calculations provide the link between the measured far-field spectra and the sample's optical properties. We also analyze the case where the probing particle is hotter than the sample and evaluate the impact of the dressed polarizabilities on near-field radiative heat transfer. We show that such a heated probe above a surface performs a surface spectroscopy, in the sense that the spectrum of the heat current is closely related to the local electromagnetic density of states. The calculations agree well with available experimental data. - Highlights: • Polarizability of a dipolar particle changes close to a sample in near-field. • Signal detected in far field coming from a dipolar particle scattering of the near-field. • Calculation applied to plasmonic and thermal excitation. • Relation between signal and EM-LDOS is established. • Heat transfer between a dipolar particle and a sample is calculated

  20. First performance results of two novel spectroradiometers developed for fast scanning of solar spectra UV irradiance

    Science.gov (United States)

    Feister, Uwe; Kaifel, Anton K.; Grewe, Rolf-Dieter; Kaptur, Jasmine; Reutter, Oliver; Wohlfart, Michael; Gericke, Klaus

    2003-11-01

    Two recently developed different types of fast spectroradiometers measuring solar UV irradiance have been compared in a field campaign: i) the UV spectroradiometer on filter model basis (UV-SPRAFIMO) and ii) the modified version of the spectroradiometer SPECTRO 320D by Instrument Systems. The all-weather UV-SPRAFIMO instrument combines a UV filter radiometer with 5 narrow-band (FBHM ~ 2.0 to 2.5 nm) filters centered within +/- 0.01 nm at 303.5, 309.0, 314.5, 327.0 and 387.0 nm, and an advanced neural network-based model. It allows up to 5 measurements per second to be taken that are averaged within time intervals between 5 and 30 s. The neural networks model that is embedded in the PC-based processing software converts the 5 measured irradiances into a full spectrum from 280 to 450 nm at small wavelength steps (>= 0.05 nm). These spectra can be convoluted with user-defined slit function and integrated to broad-band and action-spectra-weighted irradiance values. Users can access the data stored in the internal data logger by a serial RS232 interface or by a modem and display them on a PC-based Graphical User Interface. The spectroradiometer SPECTRO320D consists of a grating double monochromator with a cooled (-20°C) PMT receiver. The modified instrument version run by DWD uses a Schreder type cosine diffuser that directs the solar global irradiance via quartz fiber optics onto the spectroradiometer's entrance slit. The spectroradiometer used at the campaign was installed in a thermostatted (22 +/- 0.02)°C aluminum box. The modified instrument version performs a spectral scan over the whole UV region in two subsequent parts, with a lower speed in the UV-B than in the UV-A to account for the exponential changes of solar irradiance with increasing wavelengths in the UV-B and for the almost linear change in the UV-A region. In the configuration applied in the comparison, i.e. wavelength steps of 0.2 nm within the scan range from 290 nm to 450 nm, the resulting scan time of the SPECTRO 320D was 23 s. The two spectroradiometers, which both have been absolutely calibrated in the DWD lab using FEL 1000 W halogen lamps traceable to the German Physikalisch-Technische Bundesanstalt (PTB), were used in a field campaign at Izana (Tenerife Island) at a height of 2409 m to compare measured spectral and integral values of solar irradiance. Results of that comparison and the instruments" characteristics revealed under those special field conditions will be discussed.

  1. Energy gap evolution in the tunneling spectra of Bi2Sr2CaCu2O8+d

    CERN Document Server

    Dipasupil, R M; Momono, N; Ido, M

    2002-01-01

    On the basis of the tunneling spectra of Bi2212, we report that there exist two kinds of pseudogaps; one with a characteristic energy comparable to the superconducting (SC) gap and another one that is 3 to 4 times larger. The smaller energy-scale pseudogap (SPG) develops progressively below temperature T*, which nearly scales with the SC gap amplitude D0, in addition to the larger energy-scale pseudogap (LPG). The SPG smoothly develops into the SC-state gap with no tendency to close at Tc.

  2. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Redinger, Alex

    2009-07-10

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

  4. 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.)

  5. Scanning tunneling microscopy and electrical transport in graphene and Au(111); Rastertunnelmikroskopie und elektrischer Transport in Graphen und Au(111)

    Energy Technology Data Exchange (ETDEWEB)

    Geringer, Viktor

    2010-12-02

    This thesis describes an investigation of morphologic and electronic properties of graphene. Using scanning tunneling microscopy (STM), a study of the crystallographic and morphologic structure of graphene on silicon dioxide was performed. The microscopic investigations with atomic resolution show strong variations of the surface corrugation of this system. Besides the substrate induced long range corrugation, graphene features an intrinsic short range corrugation with a preferential wave length of about 15 nm due to a partial decoupling from the substrate. A strong deformation of the graphene membrane induces effective vector and scalar potentials, which can modify the charge carrier transport in this system. In addition, complementary electrical transport measurements were performed, in order to determine macroscopically the effects of lithographical contaminations on the charge carrier transport in clean graphene. Electronic scattering could be observed by means of an energy dependent STM study on a graphene step edge and point impurities.The disorder breaks the lattice symmetry and couples the electronic states of two inequivalent K points in reciprocal space leading to a pronounced backscattering. In addition to graphene, a pseudo relativistic two-dimensional electronic system, the electronic scattering behavior of a classical two-dimensional system has been investigated. Using scanning tunneling spectroscopy a surprising effect of electron wave guiding in a periodic potential on the Au(111) surface was detected. STS measurements show, that electrons with an energy 20 times higher than the scattering potential can be channelled by this low potential (40 meV). (orig.)

  6. Measurements of neutron spectra and doses in the Tevatron tunnel for up to 800 GeV circulating proton beams

    International Nuclear Information System (INIS)

    Measurements of the neutron fluence and energy spectra in the Fermilab tunnel during Tevatron operation are described. Multi-sphere neutron moderators and /sup 6/Li I(Eu) scintillators, as well as other instruments, were used under various accelerator operating conditions. Comparison is made between neutron spectra derived from three unfolding codes and reasonable agreements is found. In addition to the usual slowing-down and thermal components, a prominent peak is evident at about 230 keV. About 30% of the fluence is between 0.1 and 1.0 MeV, with only --4% above 10 MeV. The median energy is about 60 keV and the average quality factor is close to seven. Upper limits are also given for the dose due to photons and minimum ionizing particles

  7. 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.

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

    International Nuclear Information System (INIS)

    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

  9. Local and global effects of quantum impurities on the quasi-particle tunneling spectra of p-type and n-type cuprate superconductors

    Science.gov (United States)

    Yeh, Nai-Chang; Chen, Ching-Tzu; Vasquez, Richard P.; Jung, Chang Uk; Kim, J. Y.; Park, Min-Seok; Kim, Heon-Jung; Lee, Sung-Ik; Yoshida, K.; Tajima, Setsuko

    2002-11-01

    We report scanning tunneling spectroscopic studies of the effects of quantum impurities on cuprate superconductors. The samples include p-type YBa2Cu3O7-? single crystals with spinless impurities of Zn2+ and Mg2+ ((Zn,Mg)-YBCO) and n-type infinite-layer system Sr0.9La0.1CuO2 with 1% magnetic Ni2+- or 1% non-magnetic Zn2+-impurities that substitute the Cu2+ in the CuO2 plane. The local effects of spinless impurities on the quasiparticles spectra of (Zn,Mg)-YBCO are analogous to those of Zn-substituted Bi2Sr2CaCu2O8+x, and the global effect is manifested by the suppression of the pairing potential ?d and of the spin excitation energy. In contrast, spectroscopic studies of Sr0.9La0.1CuO2 reveal momentum-independent spectra and superconducting gap ? , with (2?/kBTc) ~ 7 for Tc = 43 K and no pseudogap above Tc. The global response of Sr0.9La0.1CuO2 to quantum impurities is similar to that of s-wave superconductors, being insensitive to small concentrations of spinless impurities (Zn) while showing rapid degradation in Tc with increasing magnetic impurities (Ni). Moreover, the spectra of the Ni-substituted Sr0.9La0.1CuO2 reveal strong electron-hole asymmetry and long-range impurity effects, in contrast to the localized impurity effects in the p-type cuprates, and the introduction of Zn yield no reduction in either ? or Tc. The physical implications of these findings are discussed.

  10. 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.

  11. Charge transfer between semiconducting carbon nanotubes and their doped GaAs(110) and InAs(110) substrates detected by scanning tunnelling spectroscopy

    International Nuclear Information System (INIS)

    Ultrahigh vacuum (UHV) scanning tunnelling microscopy (STM) and spectroscopy (STS) have been used to examine the role of substrate doping and composition in determining the electronic behaviour of semiconducting single-walled carbon nanotubes (SWNT) deposited onto III-V(110) surfaces. Hybrid SWNT/III-V(110) systems were created through sample cleavage and subsequent nanotube transfer in UHV. Room temperature STS spectra indicate electron transfer from the n-GaAs substrate to the supported SWNT and from the SWNT to the p-GaAs substrate, resulting in the respective n-type and p-type doping of the nanotube upon adsorption. STS measurements on InAs(110) supported carbon nanotubes are less uniform, with selected SWNTs on the n-InAs(110) surface exhibiting distinct electronic changes when shifted into registration with the substrate lattice. No such orientation sensitivity is detected in nanotubes on GaAs surfaces. The potential for systematic modification of a SWNT's electronic behaviour through intentional substrate engineering could present a new avenue for the design and fabrication of nanotube-based device structures

  12. Atomic-Scale Characterization and Manipulation of Freestanding Graphene Using Adapted Capabilities of a Scanning Tunneling Microscope

    Science.gov (United States)

    Barber, Steven

    Graphene was the first two-dimensional material ever discovered, and it exhibits many unusual phenomena important to both pure and applied physics. To ensure the purest electronic structure, or to study graphene's elastic properties, it is often suspended over holes or trenches in a substrate. The aim of the research presented in this dissertation was to develop methods for characterizing and manipulating freestanding graphene on the atomic scale using a scanning tunneling microscope (STM). Conventional microscopy and spectroscopy techniques must be carefully reconsidered to account for movement of the extremely flexible sample. First, the acquisition of atomic-scale images of freestanding graphene using the STM and the ability to pull the graphene perpendicular to its plane by applying an electrostatic force with the STM tip are demonstrated. The atomic-scale images contained surprisingly large corrugations due to the electrostatic attractive force varying in registry with the local density of states. Meanwhile, a large range of control over the graphene height at a point was obtained by varying the tip bias voltage, and the application to strain engineering of graphene's so-called pseudomagnetic field is examined. Next, the effect of the tunneling current was investigated. With increasing current, the graphene sample moves away from the tip rather than toward it. It was determined that this must be due to local heating by the electric current, causing the graphene to contract because it has a negative coefficient of thermal expansion. Finally, by imaging a very small area, the STM can monitor the height of one location over long time intervals. Results sometimes exhibit periodic behavior, with a frequency and amplitude that depend on the tunneling current. These fluctuations are interpreted as low-frequency flexural phonon modes within elasticity theory. All of these findings set the foundation for employing a STM in the study of freestanding graphene.

  13. Scanning Tunneling Microscopy Observation of a Square Abrikosov Lattice in LuNi2B2C

    International Nuclear Information System (INIS)

    We present scanning tunneling microscopy measurements of the (001) surface of a LuNi2B 2C borocarbide single crystal at 4.2K. In zero field, the conductance versus voltage characteristics recorded at various locations on the sample reproducibly provide a gap value of 2.2meV. In a magnetic field of 1.5 and 0.375T, the recordings of the conductance as a function of position reveal a regular square vortex lattice tilted by 45 degree with respect to the crystalline a axis. This unusual result is correlated with an in-plane anisotropy of the upper critical field Hparallelc2(45 degree)/Hparallelc2(0)=0.92 at 4.2K and is analyzed within the framework of Ginzburg-Landau theory. copyright 1997 The American Physical Society

  14. Probing dirac fermion dynamics in topological insulator bi_{2}se_{3} films with a scanning tunneling microscope.

    Science.gov (United States)

    Song, Can-Li; Wang, Lili; He, Ke; Ji, Shuai-Hua; Chen, Xi; Ma, Xu-Cun; Xue, Qi-Kun

    2015-05-01

    Scanning tunneling microscopy and spectroscopy have been used to investigate the femtosecond dynamics of Dirac fermions in the topological insulator Bi_{2}Se_{3} ultrathin films. At the two-dimensional limit, bulk electrons become quantized and the quantization can be controlled by the film thickness at a single quintuple layer level. By studying the spatial decay of standing waves (quasiparticle interference patterns) off steps, we measure directly the energy and film thickness dependence of the phase relaxation length l_{?} and inelastic scattering lifetime ? of topological surface-state electrons. We find that ? exhibits a remarkable (E-E_{F})^{-2} energy dependence and increases with film thickness. We show that the features revealed are typical for electron-electron scattering between surface and bulk states. PMID:25978246

  15. Spatial resolution of imaging contaminations on the GaAs surface by scanning tunneling microscope-cathodoluminescence spectroscopy

    International Nuclear Information System (INIS)

    We obtained the luminescence image of the GaAs (1 1 0) surface by scanning tunneling microscope-cathodoluminescence (STM-CL) spectroscopy, where low-energy (?100 eV) electrons field emitted from the STM tip were used as a bright excitation source. The STM-CL image with high photon signal (1.25 x 104 cps) showed the dark image corresponding to the surface contamination in the STM image working as the nonradiative recombination centers of carriers. This dark image demonstrated the spatial resolution of about 100 nm in STM-CL spectroscopy of the GaAs (1 1 0) surface, which was determined by the field-emitted electron beam diameter

  16. Superlattice structure of an Ar monolayer on Ag(111) observed by low-temperature scanning tunneling microscopy

    Science.gov (United States)

    König, T.; Simon, G. H.; Rieder, K.-H.; Rust, H.-P.; Heyde, M.

    2008-11-01

    Scanning tunneling microscope (STM) images of a carefully prepared monolayer of Ar on Ag(111) reveal patterns of bright spots, which exhibit perfect ordering over large areas. The dimensions of the slightly oblique unit cell are 1137×2507pm2 , where the short side is aligned along the [-110] high-symmetry direction of the substrate, and the long side shows a regular division into two parts. In total six domains are observed. Analysis of this pattern, taking into account the tendency of noble gas overlayers to form hexagonal structures, which might be slightly stretched or compressed, leads to a structure for the Ar overlayer, which reproduces all the observed features. Surprisingly, it turns out that the bright STM spots correspond to Ag atoms which are not directly covered by Ar but surrounded by three Ar atoms from the adsorbate layer. A possible electronic origin for this unusual appearance is discussed.

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

    Science.gov (United States)

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

    2014-10-01

    The spin textures of ultra-thin magnetic layers exhibit surprising variety. The loss of inversion symmetry at the interface of the magnetic layer and substrate gives rise to the so-called Dzyaloshinskii-Moriya interaction which favors non-collinear spin arrangements with unique rotational sense. Here we review the application of spin-polarized scanning tunneling microscopy to such systems, which has led to the discovery of interface-induced chiral domain walls and spin spirals. Recently, different interface-driven skyrmion lattices have been found, and the writing as well as the deleting of individual skyrmions based on local spin-polarized current injection has been demonstrated. These interface-induced non-collinear magnetic states offer new exciting possibilities to study fundamental magnetic interactions and to tailor material properties for spintronic applications. PMID:25214495

  18. Probing Dirac Fermion Dynamics in Topological Insulator Bi2Se3 Films with a Scanning Tunneling Microscope

    Science.gov (United States)

    Song, Can-Li; Wang, Lili; He, Ke; Ji, Shuai-Hua; Chen, Xi; Ma, Xu-Cun; Xue, Qi-Kun

    2015-05-01

    Scanning tunneling microscopy and spectroscopy have been used to investigate the femtosecond dynamics of Dirac fermions in the topological insulator Bi2Se3 ultrathin films. At the two-dimensional limit, bulk electrons become quantized and the quantization can be controlled by the film thickness at a single quintuple layer level. By studying the spatial decay of standing waves (quasiparticle interference patterns) off steps, we measure directly the energy and film thickness dependence of the phase relaxation length l? and inelastic scattering lifetime ? of topological surface-state electrons. We find that ? exhibits a remarkable (E -EF)-2 energy dependence and increases with film thickness. We show that the features revealed are typical for electron-electron scattering between surface and bulk states.

  19. Scanning tunneling microscopy study of intermediates in the dissociative adsorption of closo-1,2-dicarbadodecaborane on Si(111)

    Energy Technology Data Exchange (ETDEWEB)

    Carpinelli, J.M. [Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996 (United States); Plummer, E.W. [Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996 (United States)]|[Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Byun, D.; Dowben, P.A. [Department of Physics, University of Nebraska, Lincoln, Nebraska 68588 (United States)

    1995-05-01

    {ital Closo}-1,2-dicarbadodecaborane (C{sub 2}B{sub 10}H{sub 12}) is a source compound found to be suitable for the deposition of a high resistivity form of boron-carbide (B{sub 5}C), and the fabrication of boron-rich semiconductor devices. A scanning tunneling microscope (STM) was used to image these molecular icosahedra on Si(111)-(7{times}7). Molecular decomposition (tip induced and otherwise) produced a boron-carbide/silicon interface with pronounced heterojunction electronic characteristics. In STM, this interface is characterized by a disordering of the Si(111)-(7{times}7) reconstruction. We suggest, based on Auger electron spectroscopy data and low-energy electron diffraction observations, that boron atoms from the dissociated source molecules substitutionally occupy selvedge sites, as in the boron-induced ({radical}3{times}{radical}3){ital R}30{degree} reconstruction of Si(111). {copyright} {ital 1995} {ital American} {ital Vacuum} {ital Society}

  20. Tailoring the local interaction between graphene layers in graphite at the atomic scale and above using scanning tunneling microscopy.

    Science.gov (United States)

    Wong, Hong Seng; Durkan, Colm; Chandrasekhar, Natarajan

    2009-11-24

    With recent developments in carbon-based electronics, it is imperative to understand the interplay between the morphology and electronic structure in graphene and graphite. We demonstrate controlled and repeatable vertical displacement of the top graphene layer from the substrate mediated by the scanning tunneling microscopy (STM) tip-sample interaction, manifested at the atomic level as well as over superlattices spanning several tens of nanometers. Besides the full-displacement, we observed the first half-displacement of the surface graphene layer, confirming that a reduced coupling rather than a change in lateral layer stacking is responsible for the triangular/honeycomb atomic lattice transition phenomenon, clearing the controversy surrounding it. Furthermore, an atomic scale mechanical stress at a grain boundary in graphite, resulting in the localization of states near the Fermi energy, is revealed through voltage-dependent imaging. A method of producing graphene nanoribbons based on the manipulation capabilities of the STM is also implemented. PMID:19795900

  1. 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.

  2. Scanning tunneling microscopy studies of heavy fermion compound CeCo(In1-xCdx)5

    Science.gov (United States)

    Gyenis, Andras; Aynajian, Pegor; da Silva Neto, Eduardo H.; Fisk, Zachary; Bauer, Eric D.; Yazdani, Ali

    2012-02-01

    Heavy fermion materials, such as those forming in actinide- or lanthanide-based compounds, have a rich variety of phases from unconventional superconductivity to antiferromagnetism to possibly exotic and non-Fermi liquid states. Central to all these ground states is the interaction between the magnetic impurities and the conduction electrons. In the Ce-based heavy fermions compounds (e.g. CeCoIn5), the ground state can be tuned by doping or isovalent substitution, for example, Cd doping tunes the system toward antiferromagnetism. We present scanning tunneling microscopy/spectroscopy.measurements on the Cd-doped CeCoIn5 heavy fermion compounds as a function of temperature. These results will be analyzed within the context of how tunning the chemical structure impacts the formation of heavy electron band and various ground states of this material system.

  3. 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.)

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

    International Nuclear Information System (INIS)

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

  5. Electronic properties of nanoporous TiO2 films investigated in real space by means of scanning tunnelling spectroscopy

    International Nuclear Information System (INIS)

    Nanoporous TiO2 films with a thickness between 100 nm and 8 ?m were studied by scanning tunnelling spectroscopy. The bias voltage of significantly increased differential conductivity, indicating the conduction and valence bands, was found to be strongly dependent on layer thickness and the underlying substrate material. This effect is traced back to the high resistivity of the oxide films and the formation of Schottky barriers at the TiO2-substrate contact. All films showed a strong hysteresis as a function of sweep direction of the bias voltage pointing towards the existence of a high number of localized electronic trap states. This effect is getting even more pronounced upon sample ageing. Laterally resolved measurements show that the major part of the surface exhibits similar I(V) characteristics with minor deviations, while smaller areas with significantly different response are identified. These areas are comparable in size to the individual crystals the material is composed of

  6. 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.

  7. Scanning Tunneling Microscopy and Spectroscopy of the commensurate charge density wave phase of 1T-TaS2

    Science.gov (United States)

    Luican-Mayer, Adina; Dilullo, Andrew; Li, Yang; Wai-Hla, Saw

    2015-03-01

    The 1T polymorph of TaS2, 1T-TaS2, has one of the richest phase diagrams among the transition metal dichalcogenides: It is metallic at higher temperatures; it has four temperature-dependent charge density wave (CDW) phases with different structures; at low temperatures it shows Mott insulator behavior and under pressure and doping it becomes superconducting. In this talk we focus on the low temperature commensurate charge density wave phase. Using scanning tunneling microscopy and spectroscopy, we explore the spatial variation of the electronic properties of the commensurate CDW phase at the atomic level. The role that defects play in the formation of this phase will also be discussed.

  8. Scanning Tunneling Microscopy Measurements of the Full Cycle of a Heterogeneous Asymmetric Hydrogenation Reaction on Chirally Modified Pt(111)

    DEFF Research Database (Denmark)

    Demers-Carpentier, Vincent; Goubert, Guillaume

    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.

  9. Line and Point Defects in MoSe2 Bilayer Studied by Scanning Tunneling Microscopy and Spectroscopy.

    Science.gov (United States)

    Liu, Hongjun; Zheng, Hao; Yang, Fang; Jiao, Lu; Chen, Jinglei; Ho, Wingkin; Gao, Chunlei; Jia, Jinfeng; Xie, Maohai

    2015-06-23

    Bilayer (BL) MoSe2 films grown by molecular-beam epitaxy (MBE) are studied by scanning tunneling microscopy and spectroscopy (STM/S). Similar to monolayer (ML) films, networks of inversion domain boundary (DB) defects are observed both in the top and bottom layers of BL MoSe2, and often they are seen spatially correlated such that one is on top of the other. There are also isolated ones in the bottom layer without companion in the top-layer and are detected by STM/S through quantum tunneling of the defect states through the barrier of the MoSe2 ML. Comparing the DB states in BL MoSe2 with that of ML film reveals some common features as well as differences. Quantum confinement of the defect states is indicated. Point defects in BL MoSe2 are also observed by STM/S, where ionization of the donor defect by the tip-induced electric field is evidenced. These results are of great fundamental interests as well as practical relevance of devices made of MoSe2 ultrathin layers. PMID:26051223

  10. Quantum Interference between Energy Absorption Processes of Molecular Exciton and Interface Plasmons on Luminescence Induced by Scanning Tunneling Microscopy

    Science.gov (United States)

    Miwa, Kuniyuki; Imasa, Hiroshi; Sakaue, Mamoru; Kasai, Hideaki; Kim, Yousoo

    2015-03-01

    Luminescence induced by the tunneling current of a scanning tunneling microscope (STM) from molecule-covered metal surfaces is attributed to radiative decays of molecules and interface plasmons localized near the tip-substrate gap region. Since the dynamics of molecule and interface plasmons strongly influence each other, the interplay between these dynamics gives rise to peculiar phenomena originating from quantum many-body effects. In this study, we develop the effective model of the system and investigate the luminescence properties using the nonequilibrium Green's function method. The results show that, in addition to the dynamics of molecule, energy reabsorption by interface plasmons have a critical role in determining the luminescence spectral profile of interface plasmons. The additional peak structure arises owing to the interference between these energy absorption processes. Origin of prominent peak and dip structures observed in recent experiments are identified by the developed theory. The details of the interference effects on the luminescence properties will be discussed. This work was supported by JSPS KAKENHI Grant Number 26886013.

  11. Mirror buckling of freestanding graphene membranes induced by local heating due to a scanning tunneling microscope tip

    Science.gov (United States)

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

    2014-03-01

    Scanning tunneling microscopy has been an invaluable tool in the study of graphene at the atomic scale. Several STM groups have managed to obtain atomic scale images of freestanding graphene membranes providing insight into the behavior of the stabilized ripple geometry. However, we found that the interaction between the STM tip and the freestanding graphene sample may induce additional effects. By varying the tunneling parameters, we can tune the position of the sample, in either a smooth or step like fashion. These phenomena were investigated by STM experiments, continuum elasticity theory and large scale molecular dynamics simulations. These results confirm that by increasing the tip bias, the electrostatic attraction between the tip and sample increases. When applied on a concave surface, this can result in mirror buckling which leads to a large scale movement of the sample. Interestingly, due in part to the negative coefficient of thermal expansion of graphene, buckling transitions can also be induced through local heating of the surface using the STM tip. Financial support by O.N.R. grant N00014-10-1-0181, N.S.F grant DMR-0855358, EU-Marie Curie IIF postdoc Fellowship/299855 (for M. N. A.), ESF-EuroGRAPHENE project CONGRAN, F.S.F (FWO-Vl), and Methusalem Foundation of the Flemish Government.

  12. Equivalence Principle: Tunnelling, Quantized Spectra and Trajectories from the Quantum HJ Equation

    OpenAIRE

    Faraggi, Alon E.; Matone, Marco

    1998-01-01

    A basic aspect of the recently proposed approach to quantum mechanics is that no use of any axiomatic interpretation of the wave function is made. In particular, the quantum potential turns out to be an intrinsic potential energy of the particle, which, similarly to the relativistic rest energy, is never vanishing. This is related to the tunnel effect, a consequence of the fact that the conjugate momentum field is real even in the classically forbidden regions. The quantum s...

  13. Visualizing the influence of an isolated Coulomb impurity on the Landau level spectrum in graphene using scanning tunneling microscopy

    Science.gov (United States)

    Luican-Mayer, Adina; Kharitonov, Maxim; Li, Guohong; Lu, Chihpin; Skachko, Ivan; Goncalves, Alem-Mar; Andrei, Eva Y.

    2013-03-01

    Charged impurities play a crucial role in determining the electronic properties of graphene. We report on experiments that elucidate the effect of an isolated charged impurity on the electronic spectrum of graphene in a magnetic field. Using scanning tunneling microscopy and gated graphene devices, we follow the evolution of quantized Landau levels with carrier density and find that the apparent strength of the impurity is controlled by the partial filling of the Landau levels. At low filling the impurity is cloaked and becomes essentially invisible. The cloaking effect diminishes with filling until, for fully occupied Landau levels, the impurity reaches its maximum strength causing a significant perturbation in the local density of states. In this regime we report the first observation of Landau level splitting due to lifting of the orbital degeneracy. Charged impurities play a crucial role in determining the electronic properties of graphene. We report on experiments that elucidate the effect of an isolated charged impurity on the electronic spectrum of graphene in a magnetic field. Using scanning tunneling microscopy and gated graphene devices, we follow the evolution of quantized Landau levels with carrier density and find that the apparent strength of the impurity is controlled by the partial filling of the Landau levels. At low filling the impurity is cloaked and becomes essentially invisible. The cloaking effect diminishes with filling until, for fully occupied Landau levels, the impurity reaches its maximum strength causing a significant perturbation in the local density of states. In this regime we report the first observation of Landau level splitting due to lifting of the orbital degeneracy. DOE-FG02-99ER45742 and NSF DMR 1207108, Alcatel- Lucent

  14. 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. 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.

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

    DEFF Research Database (Denmark)

    Andersen, Jens Enevold Thaulov; Thuesen, Marianne Hallberg

    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 background, and possibly arising from tip dislodging can also be imaged. The HOPG surface cracks at certain potentials on in situ potentiostatic control and releases nm size HOPG scrap bits. These are clearly different in shape from the ex situ imaged molecular-size structures. Laccase could not, however, be imaged by in situ STM, most likely due to structural incompatibility between hydrophobic HOPG surface and the strongly negatively charged protein, and to high protein surface mobility.

  16. 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

    2014-12-21

    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 Au(144) 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 Au(144)-MPCs and EC-STS experiments with laterally separated individual Au(144)-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 Au(144)-MPC. However, the resolution of the energy level spacing of the single clusters is strongly affected by the proximity of neighboring particles. PMID:25372883

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

    Science.gov (United States)

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

    2011-12-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1988-12-01

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

  19. 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.

  20. Spectra

    Science.gov (United States)

    The Exploratorium

    2012-06-26

    Learners construct a spectroscope out of a shoe box or mailing tube, diffraction grating, and other simple materials. They then use their spectroscope to observe spectra, the colors that make up light. Learners compare the spectra of various light sources. Use this activity to introduce learners to basic principles of light and color. Also, look at a related page about auroras to understand how distinguishing spectra of different atoms helps scientists understand the universe.

  1. Scanning tunneling spectroscopy characterization of the pseudogap and the x = 1/8 anomaly in La2-xSrxCuO4 thin films

    OpenAIRE

    Yuli, Ofer; Asulin, Itay; Koren, Gad; Millo, Oded

    2007-01-01

    Using scanning tunneling spectroscopy we examined the local density of states of thin c-axis La2-xSrxCuO4 films, over wide doping and temperature ranges. We found that the pseudogap exists only at doping levels lower than optimal. For x = 0.12, close to the 'anomalous' x = 1/8 doping level, a zero bias conductance peak was the dominant spectral feature, instead of the excepted V- shaped (c-axis tunneling) gap structure. We have established that this surprising effect cannot ...

  2. Spatial variation of the work function in nano-crystalline TiN films measured by dual-mode scanning tunneling microscopy

    Science.gov (United States)

    Bolotov, Leonid; Fukuda, Koichi; Tada, Tetsuya; Matsukawa, Takashi; Masahara, Meishoku

    2015-04-01

    We explored novel approach to measure spatial variation of work function (WF) on polycrystalline 20-nm-thick TiN films by using simultaneous measurements of tunneling current and interaction force in scanning tunneling microscopy. Upon processing at 860 °C in N2 atmosphere, the mean grain size increased from 3–5 to 20–30 nm. For multi-facet grains, facet-dependent variation of the WF was observed in the maps. Three WF values were ascribed to (001) and (111) crystal planes of cubic TiN. The area fraction of high-WF facets increased from ?55% for as-grown to 70% for processed films.

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

    DEFF Research Database (Denmark)

    Wang, Yun; Chi, Qijin

    2009-01-01

    Self-assembled monolayers (SAMs) formed by chemisorption of a branched-chain alkanethiol, 2-methyl-1-propanethiol, on Au(111) surfaces were studied by in situ scanning tunneling microscopy (STM) under electrochemical potential control and analyzed using extensive density functional theory (DFT) calculations. The SAM forms in the unusual (8 × ?3)-4 superlattice, producing a very complex STM image. Seventy possible structures were considered for the SAM, with the calculated lowest-energy configuration in fact predicting the details of the unusual observed STM image. The most stable structure involves two R?S?Au?S?R adatom-mediated motifs per surface cell, with steric-induced variations in the adsorbate alignment inducing the observed STM image contrasts. Observed pits covering 5.6 ± 0.5% of the SAM surface are consistent with this structure. These results provide the missing link from the structural motifs observed on surfaces at low coverage and on gold nanoparticles to the observed spectroscopic properties ofhigh-coverage SAMs formed by methanethiol. However, the significant role attributed to intermolecular steric packing effects suggests a lack of generality for the adatom-mediated motif at high coverage.

  4. Electronic and Magnetic Properties of Surface-Supported Hydrocarbon Radicals Studied by Low-Temperature Scanning Tunneling Microscopy

    International Nuclear Information System (INIS)

    Full text: The competition between screening of local spins and magnetic interactions of neighbouring spins determines many of the electronic and magnetic properties of dilute magnetic systems. We report on low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) experiments performed on linear chains of surface-supported hydrocarbon spin-1/2 radicals. The spin chains are prepared by self-assembly of the stable sp magnetic radicals a,g-bisdiphenylene-b-phenylallyl (BDPA) on a single-crystal metal surface under ultrahigh vacuum conditions. Below about 50 K the chains exhibit many of the characteristic properties of the Kondo effect observed by STM-based electron transport experiments at the atomic scale. We find strong evidence for a parallel alignment of neighbouring spins within the chains mediated by the electron gas of the supporting metal substrate. Spectroscopic imaging of radical chains reveals extended two-dimensional Kondo patterns. They span several nm2 across the substrate area even into regions of the pristine Au substrate, indicating the involvement of surface-state electrons from the substrate. The single adsorbed radicals exhibit a handedness as revealed by topographic STM imaging at the single-molecule level, which leads to an enantio-selective chain growth and the formation of structurally different domains of neighboring radical chains. (author)

  5. Charge-density waves in rubidium blue bronze Rb0.3 Mo O3 observed by scanning tunneling microscopy

    Science.gov (United States)

    Brun, C.; Girard, J. C.; Wang, Z. Z.; Marcus, J.; Dumas, J.; Schlenker, C.

    2005-12-01

    Using low-temperature scanning tunneling microscopy under ultrahigh vacuum, high-resolution topographical images were obtained on a cleaved (2¯01) surface of a rubidium blue bronze (Rb0.3MoO3) single crystal. Only molecular lattice was observed at room temperature. At temperatures of 63 and 78K , well below the charge density wave (CDW) transition temperature in Rb0.3MoO3 , underlying molecular lattice and CDW superlattice were observed simultaneously in topographical constant current images. The amplitude of the CDW modulation is about 0.1Å along b . On the Fourier transform of these images, both main Bragg spots (molecular lattice related) and satellite spots (CDW superlattice related) coexist unambiguously. The average projection of the CDW wave vector on the (2¯01) surface deduced by Fourier transform is consistent with the bulk value obtained previously by other techniques. Our results show clearly that the Peierls phase of the quasi-one-dimensional blue bronze can be studied by STM.

  6. Design of a new reactor-like high temperature near ambient pressure scanning tunneling microscope for catalysis studies

    Science.gov (United States)

    Tao, Franklin Feng; Nguyen, Luan; Zhang, Shiran

    2013-03-01

    Here, we present the design of a new reactor-like high-temperature near ambient pressure scanning tunneling microscope (HT-NAP-STM) for catalysis studies. This HT-NAP-STM was designed for exploration of structures of catalyst surfaces at atomic scale during catalysis or under reaction conditions. In this HT-NAP-STM, the minimized reactor with a volume of reactant gases of ~10 ml is thermally isolated from the STM room through a shielding dome installed between the reactor and STM room. An aperture on the dome was made to allow tip to approach to or retract from a catalyst surface in the reactor. This dome minimizes thermal diffusion from hot gas of the reactor to the STM room and thus remains STM head at a constant temperature near to room temperature, allowing observation of surface structures at atomic scale under reaction conditions or during catalysis with minimized thermal drift. The integrated quadrupole mass spectrometer can simultaneously measure products during visualization of surface structure of a catalyst. This synergy allows building an intrinsic correlation between surface structure and its catalytic performance. This correlation offers important insights for understanding of catalysis. Tests were done on graphite in ambient environment, Pt(111) in CO, graphene on Ru(0001) in UHV at high temperature and gaseous environment at high temperature. Atom-resolved surface structure of graphene on Ru(0001) at 500 K in a gaseous environment of 25 Torr was identified.

  7. 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)

  8. Admetal-induced substrate surface restructuring during metal-on-metal electrochemical deposition studied by in situ scanning tunneling microscopy

    Science.gov (United States)

    Maroun, F.; Morin, S.; Lachenwitzer, A.; Magnussen, O. M.; Behm, R. J.

    2000-07-01

    Based on time-dependent in situ scanning tunneling microscopy (STM) studies, we demonstrate that for Ni on Ag(111) and Ru on Au(111), electrochemical metal-on-metal deposition can result in pronounced substrate surface restructuring. For Ni/Ag(111), we observe that at low deposition flux and low coverage, Ni submonolayer islands at steps are partly embedded in the Ag terraces, whereas at higher deposition flux and higher coverage, substrate restructuring results in the formation of monolayer bays in the Ag terraces. We suggest that this restructuring process proceeds predominantly via step edge diffusion of Ag atoms. For Ru/Au(111), the formation of fjords and monolayer holes in the Au terraces is observed at low and high Ru coverage, respectively. The importance of the Au surface mobility for the restructuring process is demonstrated by comparing experiments in H 2SO 4 and HCl solutions, in which Au exhibits strongly different surface mobilities. For this system, restructuring involves Au diffusion along Au steps, Au atom detachment from the Au steps, and upward exchange diffusion. According to these observations and their comparison with similar findings for vacuum deposition, we conclude that this restructuring requires (i) a high substrate surface mobility and (ii) a stronger bonding of substrate atoms to deposit islands than to the substrate.

  9. Scanning tunneling spectroscopy investigation of the topological phase transition in (Bi1-xInx)2 Se3

    Science.gov (United States)

    Walkup, Daniel; Zhou, Wenwen; Zeljkovic, Ilija; Okada, Yoshinori; Ren, Zhensong; Scipioni, Kane; Wilson, Stephen; Madhavan, Vidya

    2015-03-01

    The three-dimensional topological insulator (Bi1-xInx)2 Se3 undergoes a phase transition to a trivial insulator as Bi atoms are replaced with In. This chemical substitution is expected to reduce the spin-orbit coupling, lift the bulk band inversion and thus destroy the Dirac surface states present in the end-member Bi2Se3. Although photoemission and transport measurements have provided evidence for this phase transition in thin films, the nature of the surface state transformation across the critical point remains unclear, especially near the transition point where the surface state penetration depth becomes comparable to film thicknesses. Here, we present scanning tunneling microscopy experiments on single crystals of (Bi1-xInx)2 Se3 for x ~ 0-10%. Using Landau Level spectroscopy, we map the surface state dispersion across the phase transition. Additionally, we use local density of states mapping to reveal the local influence of the In dopants near the critical point.

  10. Scanning tunneling microscopic studies of laser-induced modifications of Si(001)-(2 x 1) surface

    International Nuclear Information System (INIS)

    Scanning tunneling microscopic studies of Si(001)-2 x 1 surfaces excited with 532-nm laser pulses of intensities below melting and ablation thresholds have revealed two different modes of structural modifications, strongly depending on the intensity of laser lights. The excitation below 100 mJ/cm2 causes bond rupture at individual dimer-sites leading to the formation of vacancies selectively on the outermost layer. The bond rupture, which shows a strongly site-sensitive rate, forms efficiently vacancy-strings elongated along the surface dimer-rows. Selective removal of surface dimers results in the exposure of flat and defect-less underlying layer as reported previously, which is resistive to the excitation at this range of intensity. At intensities above 100 mJ/cm2, on the other hand, the excitation forms not only vacancies but also ad-dimers on terraces. The number density of ad-dimers is in proportion to the square of that for vacancies, indicating strongly that silicon atoms released by laser-induced bond rupture are associated with each other to form ad-dimers. The repeated irradiations at this range of intensities induce anisotropic growth of ad-dimer islands and of vacancy clusters on terrace regions, leading to multiply terraced structure. The primary processes of the structural modifications are discussed based on the quantitative analyses of the growth of vacancy and ad-dimer under excitation.

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

    Science.gov (United States)

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

    2014-11-01

    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.

  12. Atomic Structures of Silicene Layers Grown on Ag(111): Scanning Tunneling Microscopy and Noncontact Atomic Force Microscopy Observations

    Science.gov (United States)

    Resta, Andrea; Leoni, Thomas; Barth, Clemens; Ranguis, Alain; Becker, Conrad; Bruhn, Thomas; Vogt, Patrick; Le Lay, Guy

    2013-01-01

    Silicene, the considered equivalent of graphene for silicon, has been recently synthesized on Ag(111) surfaces. Following the tremendous success of graphene, silicene might further widen the horizon of two-dimensional materials with new allotropes artificially created. Due to stronger spin-orbit coupling, lower group symmetry and different chemistry compared to graphene, silicene presents many new interesting features. Here, we focus on very important aspects of silicene layers on Ag(111): First, we present scanning tunneling microscopy (STM) and non-contact Atomic Force Microscopy (nc-AFM) observations of the major structures of single layer and bi-layer silicene in epitaxy with Ag(111). For the (3 × 3) reconstructed first silicene layer nc-AFM represents the same lateral arrangement of silicene atoms as STM and therefore provides a timely experimental confirmation of the current picture of the atomic silicene structure. Furthermore, both nc-AFM and STM give a unifying interpretation of the second layer (?3 × ?3)R ± 30° structure. Finally, we give support to the conjectured possible existence of less stable, ~2% stressed, (?7 × ?7)R ± 19.1° rotated silicene domains in the first layer. PMID:23928998

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

    International Nuclear Information System (INIS)

    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

  14. Locally modified charge-density waves in Na intercalated VSe2 studied by scanning tunneling microscopy and spectroscopy

    Science.gov (United States)

    Ekvall, Inger; Brauer, Hans E.; Wahlström, Erik; Olin, Håkan

    1999-03-01

    We have observed local effects of the charge-density wave (CDW) in in situ Na-intercalated 1T-VSe2 using scanning tunneling microscopy and spectroscopy between 300 and 60 K. Na intercalates nonuniformly, and divides the sample into intercalated (I) and nonintercalated (NI) areas. Below the CDW transition temperature these areas displayed totally different CDW's. The NI areas seemed unaffected by Na, and showed a 4×4 CDW that did not differ from the CDW in pure VSe2. The intercalated areas showed a strong octahedral CDW (?1=0.99 nm, ?2=0.68 nm, ?70°, rotated 20° with respect to the atomic lattice) occurring in three different orientations. Additional spots in Fourier space at low temperatures were interpreted to originate from Na ordering in a 1.3×1.3 R45° structure. Spectroscopy showed a shift of the V 3d-derived state below the Fermi level (EF) upon intercalation. In the NI areas, a shift toward EF (-60 meV compared to -80 meV in pure VSe2) was observed, while the I areas showed a shift away from EF (-150 meV). The CDW energy gap was enlarged in the I areas (?~230 meV compared to ?~80 meV in pure VSe2), while it was never resolved in the NI areas.

  15. Multifractal spectra of scanning electron microscope images of SnO2 thin films prepared by pulsed laser deposition

    International Nuclear Information System (INIS)

    The concept of fractal geometry has proved useful in describing structures and processes in experimental systems. In this Letter, the surface topographies of SnO2 thin films prepared by pulsed laser deposition for various substrate temperatures were measured by scanning electron microscope (SEM). Multifractal spectra f(?) show that the higher the substrate temperature, the wider the spectrum, and the larger the ?f(?f=f(?min)-f(?max)). It is apparent that the nonuniformity of the height distribution increases with the increasing substrate temperature, and the liquid droplets of SnO2 thin films are formed on previous thin films. These results show that the SEM images can be characterized by the multifractal spectra

  16. Scanning tunneling microscopy and spectroscopy studies on structural and electronic properties of thin films of Co oxides and oxide precursor states on Ag(001)

    Energy Technology Data Exchange (ETDEWEB)

    Shantyr, R.; Hagendorf, Ch.; Neddermeyer, H

    2004-10-01

    The main aim of this work is the electronic characterization of various Co oxide and precursor states on Ag(001), which grow during reactive deposition by evaporating Co from a Knudsen cell in an O{sub 2} atmosphere. We have identified double-layer CoO(001) and monolayer and double-layer CoO(111), which show distinct differences in the I/U and (dI/dU)/(I/U) characteristics of scanning tunneling microscopy (STM)/scanning tunneling spectroscopy (STS). CoO(001) and, to some extent, also double-layer CoO(111) exhibit oxidic behavior. For CoO(001), the oxidic character is particularly recognized in the contrast dependence as a function of sample bias U.

  17. High resolution scanning tunnelling microscopy and extended x-ray-absorption fine structure study of the (533) silicide structure on Cu(001)

    OpenAIRE

    Lalmi, B.; Chorro, M.; Belkhou, R.

    2013-01-01

    Using low energy electron diffraction (LEED), scanning tunnelling microscopy (STM) and x-ray absorption spectroscopy (XAS) techniques, we have studied the first steps of silicon adsorption onto Cu (001) single crystal substrate. For low coverage (~ 0.5 ML) and after annealing at 100{\\deg}C, STM images and LEED patterns reveal the formation of an ordered quasi commensurate superstructure. From a quantitative analysis of XAS data, we extract the Si-Cu distance and detail the l...

  18. Coupling scanning tunneling microscope and supersonic molecular beams: a unique tool for in situ investigation of the morphology of activated systems.

    Science.gov (United States)

    Smerieri, M; Reichelt, R; Savio, L; Vattuone, L; Rocca, M

    2012-09-01

    We report here on a new experimental apparatus combining a commercial low temperature scanning tunneling microscope with a supersonic molecular beam. This setup provides a unique tool for the in situ investigation of the topography of activated adsorption systems and opens thus new interesting perspectives. It has been tested towards the formation of the O/Ag(110) added rows reconstruction and of their hydroxylation, comparing data recorded upon O(2) exposure at thermal and hyperthermal energies. PMID:23020379

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

    OpenAIRE

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

    1998-01-01

    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 attributed 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 symme...

  20. Observation of Fermi-energy dependent unitary impurity resonances in a strong topological insulator Bi2Se3 with scanning tunneling spectroscopy

    OpenAIRE

    Teague, M. L.; Chu, H.; Xiu, F. -x; He, L.; Wang, K. -l; Yeh, N. -c

    2012-01-01

    Scanning tunneling spectroscopic studies of Bi2Se3 epitaxial films on Si (111) substrates reveal highly localized unitary impurity resonances associated with non-magnetic quantum impurities. The strength of the resonances depends on the energy difference between the Fermi level ({E_F}) and the Dirac point ({E_D}) and diverges as {E_F} approaches {E_D}. The Dirac-cone surface state of the host recovers within ~ 2{\\AA} spatial distance from impurities, suggesting robust topolo...

  1. Scanning tunneling microscopy of coexisting 2D crystalline and 1D stacking-disordered phases at the chiral-liquid-crystal-graphite interface

    Science.gov (United States)

    Parks, Daniel C.; Clark, Noel A.; Walba, David M.; Beale, Paul D.

    1993-02-01

    Scanning tunneling microscopy study of monolayers of the chiral-liquid-crystal-forming molecule W7 shows the coexistence of two phases having unit cells of opposite chiral symmetry, one a 2D crystalline phase and the other a 1D stacking-disorder phase exhibiting the kind of structural ambivalence characteristic of bulk liquid crystals. The interrow interactions in the stacking-disorder phase can be described using a one-dimensional three-state Potts model with extended interrow interactions.

  2. 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.

  3. 3D nanostructuring of La0.7Sr0.3MnO3 thin film surfaces by scanning tunnelling microscopy

    OpenAIRE

    Liu, Yun; Monsen, A? F.; Boschker, J. E.; Wahlstro?m, E.; Borg, A.; Tybell, T.

    2009-01-01

    Nanoscale 3D surface modifications, by scanning tunneling microscopy under ambient conditions, of La0.7Sr0.3MnO3 thin films have been performed. It was demonstrated that there are well defined combinations of bias voltages and scan speeds which allow for controlled surface structuring. Lateral structures with sizes down to 1.5 nm are possible to obtain. Moreover, it is possible to reproducibly control the depth of etching with half a unit cell precision, enabling design of 3...

  4. 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.

  5. 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

  6. The use of computer simulation to investigate tip shape and point contact effects during scanning tunneling microscopy of supported nanostructures

    International Nuclear Information System (INIS)

    A recently developed computer code [1] is used to investigate effects which may arise during the STM investigation of supported nanostructures, like carbon nanotubes. The effects of tip geometry and point contact imaging are studied. The calculations show that while the magnitude of the tunnel current is determined by the tip-nanotube tunnel gap, the asymmetry of the tip ± current is influenced by the nanotube-support tunnel gap. The results obtained from simulation are compared with experimental data

  7. Scanning Tunneling Microscopy and Theoretical Study of Water Adsorption on Fe3O4: Implications for Catalysis

    Energy Technology Data Exchange (ETDEWEB)

    Rim, Kwang T.; Eom, Daejin; Chan, Siu-Wai; Flytzani-Stephanopoulos, Maria; Flynn, George; Wen, Xiaodong; Batista, Enrique R.

    2012-10-23

    The reduced surface of a natural Hematite single crystal a-Fe2O3(0001) sample has multiple surface domains with di!erent terminations, Fe2O3(0001), FeO(111), and Fe3O4(111). The adsorption of water on this surface was investigated via Scanning Tunneling Microscopy (STM) and first-principle theoretical simulations. Water species are observed only on the Fe-terminated Fe3O4(111) surface at temperatures up to 235 K. Between 235 and 245 K we observed a change in the surface species from intact water molecules and hydroxyl groups bound to the surface to only hydroxyl groups atop the surface terminating FeIII cations. This indicates a low energy barrier for water dissociation on the surface of Fe3O4 that is supported by our theoretical computations. Our first principles simulations con"rm the identity of the surface species proposed from the STM images, finding that the most stable state of a water molecule is the dissociated one (OH + H), with OH atop surface terminating FeIII sites and H atop under-coordinated oxygen sites. Attempts to simulate reaction of the surface OH with coadsorbed CO fail because the only binding sites for CO are the surface FeIII atoms, which are blocked by the much more strongly bound OH. In order to promote this reaction we simulated a surface decorated with gold atoms. The Au adatoms are found to cap the under-coordinated oxygen sites and dosed CO is found to bind to the Au adatom. This newly created binding site for CO not only allows for coexistence of CO and OH on the surface of Fe3O4 but also provides colocation between the two species. These two factors are likely promoters of catalytic activity on Au/Fe3O4(111) surfaces.

  8. 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.

  9. Growth of nanocrystalline MoO3 on Au(111) studied by in situ scanning tunneling microscopy

    International Nuclear Information System (INIS)

    The growth of nanocrystalline MoO3 islands on Au(111) using physical vapor deposition of Mo has been studied by scanning tunneling microscopy and low energy electron diffraction. The growth conditions affect the shape and distribution of the MoO3 nanostructures, providing a means of preparing materials with different percentages of edge sites that may have different chemical and physical properties than atoms in the interior of the nanostructures. MoO3 islands were prepared by physical vapor deposition of Mo and subsequent oxidation by NO2 exposure at temperatures between 450 K and 600 K. They exhibit a crystalline structure with a c(4x2) periodicity relative to unreconstructed Au(111). While the atomic-scale structure is identical to that of MoO3 islands prepared by chemical vapor deposition, we demonstrate that the distribution of MoO3 islands on the Au(111) surface reflects the distribution of Mo clusters prior to oxidation although the growth of MoO3 involves long-range mass transport via volatile MoO3 precursor species. The island morphology is kinetically controlled at 450 K, whereas an equilibrium shape is approached at higher preparation temperatures or after prolonged annealing at the elevated temperature. Mo deposition at or above 525 K leads to the formation of a Mo-Au surface alloy as indicated by the observation of embedded MoO3 islands after oxidation by NO3 islands after oxidation by NO2. Au vacancy islands, formed when Mo and Au dealloy to produce vacancies, are observed for these growth conditions

  10. Growth of nanocrystalline MoO3 on Au(111) studied by in situ scanning tunneling microscopy

    Science.gov (United States)

    Biener, Monika M.; Biener, Juergen; Schalek, Richard; Friend, Cynthia M.

    2004-12-01

    The growth of nanocrystalline MoO3 islands on Au(111) using physical vapor deposition of Mo has been studied by scanning tunneling microscopy and low energy electron diffraction. The growth conditions affect the shape and distribution of the MoO3 nanostructures, providing a means of preparing materials with different percentages of edge sites that may have different chemical and physical properties than atoms in the interior of the nanostructures. MoO3 islands were prepared by physical vapor deposition of Mo and subsequent oxidation by NO2 exposure at temperatures between 450 K and 600 K. They exhibit a crystalline structure with a c(4×2) periodicity relative to unreconstructed Au(111). While the atomic-scale structure is identical to that of MoO3 islands prepared by chemical vapor deposition, we demonstrate that the distribution of MoO3 islands on the Au(111) surface reflects the distribution of Mo clusters prior to oxidation although the growth of MoO3 involves long-range mass transport via volatile MoO3 precursor species. The island morphology is kinetically controlled at 450 K, whereas an equilibrium shape is approached at higher preparation temperatures or after prolonged annealing at the elevated temperature. Mo deposition at or above 525 K leads to the formation of a Mo-Au surface alloy as indicated by the observation of embedded MoO3 islands after oxidation by NO2. Au vacancy islands, formed when Mo and Au dealloy to produce vacancies, are observed for these growth conditions.

  11. 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

  12. 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 eifferent 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.

  13. Electronic phase diagram of NaFe1?xCoxAs investigated by scanning tunneling microscopy

    International Nuclear Information System (INIS)

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

  14. Target geometry dependence of electron energy loss spectra in scanning transmission electron microscopy (STEM).

    Science.gov (United States)

    Rivacoba, A; Aizpurua, J; Zabala, N

    1995-01-01

    In the frame of the Self-Energy formalism, we study the interaction between STEM electrons and small particles in the range of the valence electron excitations. We first calculate the energy loss probability for an isolated sphere and study the loss spectrum dependence on the size of the particle and on the relative impact parameter. Then we analyze the loss spectra in more realistic situations: (a) the effect of the coupling between the particle and supporting surface is studied in a simple geometrical model; and (b) we analyze the dependence of the losses on the geometrical shape of the target by considering hemispherical particle. Our results are in a good qualitative (and in simple cases, quantitative too) agreement with several experimental results which show anomalous excitations. We restate the suitability of the dielectric theory to study the surface excitations of these systems. PMID:8819881

  15. 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? 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. 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

  17. Scanning tunneling microscopy study of superconductivity, magnetic vortices, and possible charge-density wave in Ta4Pd3Te16

    Science.gov (United States)

    Fan, Q.; Zhang, W. H.; Liu, X.; Yan, Y. J.; Ren, M. Q.; Xia, M.; Chen, H. Y.; Xu, D. F.; Ye, Z. R.; Jiao, W. H.; Cao, G. H.; Xie, B. P.; Zhang, T.; Feng, D. L.

    2015-03-01

    Ta4Pd3Te16 is a newly discovered layered superconductor with quasi-one-dimensional (1D) structure. Recent thermal transport measurements show the possible existence of nodes in the superconducting gap. Here we report low-temperature scanning tunneling microscopy/spectroscopy study on Ta4Pd3Te16 single crystals. We observed stripelike structure composed of atom chains on the cleaved (1 ¯03 ) surface. There exists charge-density-wave (CDW)-like modulations along stripes with commensurate periods. Meanwhile, the tunneling conductance shows an s-wave-like superconducting gap. The magnetic vortex mapped at low field is highly anisotropic with a bound state in the core. At increased field, strong vortex overlapping is directly observed and the bound state is suppressed, indicating the delocalization of the superconducting quasiparticles. Our observations suggest that Ta4Pd3Te16 is of multiband superconductivity with strong 1D characters, which possibly coexist with CDW transition.

  18. Mapping the superconducting condensate surrounding a vortex in superconducting V3Si using a superconducting MgB2 tip in a scanning tunneling microscope

    Science.gov (United States)

    Bergeal, N.; Noat, Y.; Cren, T.; Proslier, Th.; Dubost, V.; Debontridder, F.; Zimmers, A.; Roditchev, D.; Sacks, W.; Marcus, J.

    2008-10-01

    As shown recently [Proslier , Europhys. Lett. 73, 962 (2006)], it is possible to map the superconducting (SC) condensate by measuring locally the Josephson tunneling current. We apply this technique to image the vortex lattice in V3Si which is used as the simplest example of a spatially varying quantum condensate. The Josephson scanning tunneling microscope (JSTM) maps revealed the vortex lattice with the Josephson effect being present outside the vortices and disappearing progressively toward the vortex core. The characteristic length scales of a vortex observed in the Josephson regime are compared to the ones obtained in the quasiparticle regime. We demonstrate that the JSTM allows a nanometer scale resolution of the SC condensate that may be applied to inhomogeneous phases such as high- Tc superconductors.

  19. 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.

  20. 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.

  1. 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.)

  2. Sr adatoms on As bridge positions on SrFe2As2 observed by scanning tunneling microscopy at 4.2 K

    International Nuclear Information System (INIS)

    We used a scanning tunneling microscope to image the surface of SrFe2As2 single crystals at 4.2 K. We found, besides the commonly reported row structures and some disordered areas, also maze-like regions. Atomically resolved images of the maze show that the atoms on the surface sit on As bridge positions of the underlying Fe2As2 layer. Examination of the corner positions within the maze-like reconstruction reveals the presence of adatoms rather than As dimers. Hence, the surface atoms on these samples are most likely to be Sr atoms.

  3. Temperature Effect and Fermi Surface Investigation in the Scanning Tunneling Microscopy of Bi$_2$Sr$_2$CaCu$_2$O$_8$

    OpenAIRE

    Voo, K. -K.; Wu, W. C.; Chen, H.-Y.; Mou, C. -Y.

    2003-01-01

    Based on a Fermi liquid picture, the temperature effect on the impurity-induced spatial modulation of local density of states (LDOS) is investigated for the d-wave superconductor Bi$_2$Sr$_2$CaCu$_2$O$_8$, in the context of scanning tunneling microscopy (STM). It is found that stripe-like structure exists even in the normal state due to a local-nesting mechanism, which is different from the octet scattering mechanism proposed by McElroy $et al$. {[Nature {\\bf 422}, 592 (2003...

  4. High resolution scanning tunneling spectroscopy of ultrathin iron silicide grown on Si(111): Origin of the c (4×8) long range order

    Science.gov (United States)

    Garreau, G.; Hajjar, S.; Gewinner, G.; Pirri, C.

    2005-05-01

    Thin iron silicide grown on Si(111) undergoes a p(2×2)?c(4×8) ordering process upon annealing that was studied by scanning tunneling spectroscopy. We identify unambiguously 3 nonequivalent Si adatom sites in the c(4×8) unit cell and a well localized electronic state that exhibits p1m spatial group symmetry as opposed to the 2 sites and p2mm symmetry revealed so far by standard topographs. Amazingly this electronic state originates in an atomic defect in the fifth subsurface layer, right at silicide-substrate interface and the c(4×8) periodicity reflects long range ordering of these defects.

  5. 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)

  6. Surface behavior and imaging of the lowest unoccupied molecular orbital of indolo[2,1-b]quinazoline-6,12-dione (tryptanthrin) via scanning tunneling microscopy

    Science.gov (United States)

    Sriraman, Krishnan; Novak, Mark J.; Baum, J. Clayton; Herron, Andrew; Olson, Joel A.

    2013-10-01

    Indolo[2,1-b]quinazoline-6,12-dione (tryptanthrin) was imaged at the solution-graphite interface using scanning tunneling microscopy. STM images of the molecular monolayers show clear lobe-to-lobe resolution of the lowest unoccupied molecular orbitals of the molecules, as well as a somewhat unusual parallel arrangement of the molecular dipoles. Evaluation of the dipole-dipole interactions reveals that the interactions of the closest molecule pairs are reduced due to a magic angle-like effect. These results represent an important step toward a more in-depth understanding of the behavior of tryptanthrins, which are of interest due to their potential as pharmaceutical compounds.

  7. Scanning tunneling microscopy of indolo[2,1-b]quinazolin-6,12-dione (tryptanthrin) on HOPG: Evidence of adsorption-induced stereoisomerization

    Science.gov (United States)

    Novak, Mark J.; Clayton Baum, J.; Buhrow, Jerry W.; Olson, Joel A.

    2006-10-01

    Scanning tunneling microscopy was used to observe monolayers of indolo[2,1-b]quinazolin-6,12-dione (tryptanthrin) at the solution-graphite interface. The monolayers were formed via physisorption from a saturated solution in 1-phenyloctane. Sub-molecular resolution was achieved allowing elucidation of the primary electronic features of the molecule. The adsorbed molecules form rows that are differentiable via the apparent heights of portions of each molecule, from row to row. The variation between the rows is attributed to adsorption-induced stereoisomerization of individual molecules, with each row comprised of one stereoisomer.

  8. 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.

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

    OpenAIRE

    Toujyou Takashi; Tsukamoto Shiro

    2010-01-01

    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 ...

  10. Photoelectron core-level spectroscopy and scanning-tunneling-microscopy study of the sulfur-treated GaAs(100) surface

    OpenAIRE

    Moriarty, P.; Murphy, B.; Roberts, L.; Cafolla, Attilio A.; Hughes, Greg; Koenders, L.; Bailey, P.

    1994-01-01

    A study of the adsorption of sulfur on the GaAs(100) surface after in situ thermal desorption of a protective As capping layer is presented. The sulfur flux was generated by the decomposition of silver sulfide in an UHV-compatible electrochemical cell. Use of As-capped samples provided a means to study the interaction of sulfur with both the c(2×8) and (4×1) surface reconstructions. Scanning-tunneling-microscopy images of the sulfur-covered surface indicated the formation of disordered surf...

  11. Atomistic structure of stacking faults in a commercial GaAs:Si wafer revealed by cross-sectional scanning tunneling microscopy

    International Nuclear Information System (INIS)

    A Frank-type stacking fault bounded by a partial dislocation, about a few nanometers in size, was observed in a commercial GaAs:Si wafer (with the Si concentration of ?1018 cm-3) annealed at the temperature of about 950 K, by cross-sectional scanning tunneling microscopy. There existed no charge around the stacking fault, unlike in heavily Si-doped GaAs. There was a localized energy level associated with the stacking fault, as expected theoretically in the pure stacking fault in which Si atoms do not exist

  12. Binding structures of propylene glycol stereoisomers on the Si(001)-2×1 surface: A combined scanning tunneling microscopy and theoretical study

    Science.gov (United States)

    Hahn, Jae Ryang; Bharath, Satyaveda C.; Jeong, Sukmin; Pearl, Thomas P.

    2011-01-01

    The binding configuration of propylene glycol stereoisomer molecules adsorbed on the Si(001)-2×1 surface was investigated using a combination of scanning tunneling microscopy (STM) and density functional theory calculations. Propylene glycol was found to adsorb dissociatively via two hydroxyl groups exclusively as a bridge between the ends of two adjacent dimers along the dimer row. The chirality was preserved during bonding to Si atoms and was identifiable with STM imaging. The large number of propylene glycol conformers in the gas phase was reduced to a single configuration adsorbed on the surface at low molecular coverage.

  13. 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

  14. The impact of structural relaxation on spin polarization and magnetization reversal of individual nano structures studied by spin-polarized scanning tunneling microscopy

    International Nuclear Information System (INIS)

    The application of low temperature spin-polarized scanning tunneling microscopy and spectroscopy in magnetic fields for the quantitative characterization of spin polarization, magnetization reversal and magnetic anisotropy of individual nano structures is reviewed. We find that structural relaxation, spin polarization and magnetic anisotropy vary on the nm scale near the border of a bilayer Co island on Cu(1?1?1). This relaxation is lifted by perimetric decoration with Fe. We discuss the role of spatial variations of the spin-dependent electronic properties within and at the edge of a single nano structure for its magnetic properties. (paper)

  15. Local electronic transport in La0.7Sr0.3MnO3 thin films studied by scanning tunneling potentiometry

    International Nuclear Information System (INIS)

    We have used a scanning tunneling microscope in potentiometry mode to investigate the local electric potential distribution in current carrying epitaxial La0.7Sr0.3MnO3 thin films, with magnetotransport properties similar to the ones of single crystals. Scans imaging simultaneously the surface topography and the potential distribution have been obtained with an unprecedented resolution. In textured La0.7Sr0.3MnO3/MgO, sharp potential steps coincide with some of the grain boundaries, whereas other grains are electrically well connected. The precise nature of the local electronic transport, the percolation of the current through the grain network, and the existence of phase separated insulating domains are then discussed

  16. A sub-Kelvin scanning tunneling microscope and its application to MgB2 AND CeCoIn5

    Science.gov (United States)

    Griggs, Cornelius E.

    A low temperature, high magnetic field, ultra high vacuum scanning tunneling microscope has been constructed. Such an environment places many constraints upon the design of the instrument, but also allows the study of many exotic phenomena, in particular superconductivity. The low temperatures permit high energy resolution, and the high field allows access to novel material phases. We have leveraged the rare ability to optically access the tunnel junction in order to study materials that are only available in very small sizes. Such samples would be difficult to study in many other low temperature systems. We have recorded the first superconducting spectroscopy in CeCoIn5 in the direction. CeCoIn5 shows a rich interplay of magnetism and superconductivity. The nodal direction has been confirmed, and evidence for multiband superconductivity is presented. We have also tunneled into the Meissner rim of MgB2 and observed the effect of a transverse current on the spectroscopy. The new STM has demonstrated its ability to measure novel materials in difficult configurations at low temperature.

  17. 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

  18. Semiconductor-metal nanostructures: Scanning tunneling microscopy investigation of the fullerene-gold and manganese-germanium-silicon system

    Science.gov (United States)

    Liu, Hui

    Nanostructures, assembled from a layer or cluster of atoms with size of the order of nanometers, have attracted much attention for decades, because it has been widely recognized that the properties of nanoscale materials are remarkably different from those of materials of large scale. As one of the most powerful techniques, Scanning Tunneling Microscopy (STM) has become an indispensable technique for studies in nanotechnology. This dissertation is focused on the investigation of the C60-Au system, which is relevant in photovoltaic applications and organic electronic devices, and the Mn-Ge-Si system which is central to the development of advanced spintronics system. The first part of the dissertation focuses on the C60-Au system. Exploring how fullerene molecules interact physically and electronically with each other and with other elements is highly relevant to the advancement of fullerene-based nanotechnology applications. The initial growth stage of C 60 thin film on graphite substrate has been investigated by STM at room temperature. It is observed that the C60 layer grows in a quasi-layer-by-layer mode and forms round 1st layer islands on the graphite surface. The fractal-dendritic growth of the 2nd layer islands has been successfully described by a combination of Monte Carlo simulation and molecular dynamics simulations. As a next step towards the application of fullerenes in device structures, the growth mechanisms of Au clusters on fullerene layers and co-deposition of Au and C60 were explored. The most prominent features of the growth of Au on C60 are the preferential nucleation of Au clusters at the graphite-first fullerene layer islands edge and the co-deposition of C60 and Au on graphite leading to the formation of highly organized structures, in which Au clusters are embedded in a ring of fullerene molecules with a constant width of about 4 nm. The second part of this dissertation concentrates on the Mn-Ge-Si system, a semiconductor/metal system, which is a potential building-block structure for the development of complex spin-electronic devices. In recent years the study of thin film magnetic materials and the doping of semiconductors with magnetically active dopant atoms has received increased attention due their potential applications in magnetic memory devices and spintronics. In particular, the importance of Mn-Ge-Si system emerges since it combines a technically relevant semiconductor surface with a metallic element with a large magnetic moment. The goal in this part is the early growth stage of Mn on a Si (100) 2x1surface, the formation of Mn-nanostructure and the interaction between Mn and Ge on the Si surface. The position of Mn atoms with respect to Si surface has been determined by high resolution STM images. It is found that Mn adatoms form relatively short monoatomic wires, with a typical length of 5 to about 20 atoms, which are oriented perpendicular to the Si-dimer rows. And at the same time, the modification of Si surface around Mn wires was observed. The formation of Mn silicide after annealing the sample was also studied. The stability of Mn wires during the growth of a Ge overlayer was investigated by comparing several STM images, which were taken at different bias voltages. Because of the different local density of states, Mn and Ge may be partially distinguished in STM images. It is turned out that Mn wires preserve their structures after the deposition of a small amount of Ge on the sample. And the growth of Ge at the early stage on Si surface has not been significantly influenced by the presence of Mn adatoms. In summary, an investigation of two semiconductor-metal nanostructures by STM has been reported in this dissertation.

  19. 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.

  20. 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.

  1. 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

  2. Estimating the roughness factor using Lidar scanning system : Comparison of tunnel surfaces before and after applied shotcrete

    OpenAIRE

    Selmer, Ann-Kristin

    2014-01-01

    This thesis gives a suggestion of a method for extracting the roughness factor for estimating the sprayed concrete volume in tunnel applications. The determination of the roughness factor today is based on experience and is usually done by guessing or based on the roughness factor used in the previous blasted round. This study includes creating a look-up-chart which could enable the contractor and engineer to have a better foundation and documentation on why the roughness factor is chosen as ...

  3. Dimer ordering of CuTtertBuPc molecules on the Ag/Si(111)-(?3x?3)R30 deg. surface: a scanning tunnelling microscopy/spectroscopy study

    International Nuclear Information System (INIS)

    The room temperature growth and ordering of copper(II) 2,9,16,23-tetra-tert-butyl-phthalocyanine (CuTtertBuPc) molecules on the Ag/Si(111)-(?3x?3)R30 deg. surface have been investigated using scanning tunnelling microscopy/spectroscopy (STM/STS). Results indicate a well-ordered molecular layer in which the phthalocyanine molecules have a flat orientation with the molecular plane lying parallel to the substrate and forming a dimer structure on the surface. STS data obtained from one monolayer (ML) of the CuTtertBuPc on the Ag/Si(111)-(?3x?3)R30 deg. surface show excellent agreement with valence-band x-ray photoemission and x-ray absorption spectra taken from thin films of CuTtertBuPc (10-20 ML) prepared in situ on the clean Si(111) substrate. Combining the spectroscopy results it was found that the highest occupied molecular orbital (HOMO) of the CuTtertBuPc is the half-occupied MO of b1g symmetry with mixed Cu 3d(x2-y2) and ligand 2p character which was confirmed by density functional theory calculations and x-ray emission spectroscopy data

  4. 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.

  5. 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

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

    International Nuclear Information System (INIS)

    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 NbSe2 single crystal and spectroscopic maps obtained on homogeneously disordered NbN thin film

  7. 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

  8. 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)

  9. Kinetic Monte Carlo simulations and cross-sectional scanning tunneling microscopy as tools to investigate the heteroepitaxial capping of self-assembled quantum dots

    Science.gov (United States)

    Keizer, J. G.; Koenraad, P. M.; Smereka, P.; Ulloa, J. M.; Guzman, A.; Hierro, A.

    2012-04-01

    The growth of self-assembled quantum dots has been intensively studied in the last decade. Despite substantial efforts, a number of details of the growth process remain unknown. The reason is the inability of current characterization techniques to image the growth process in real time. In this work, this limitation is alleviated by the use of kinetic Monte Carlo simulations in conjunction with cross-sectional scanning tunneling microscopy. The two techniques are used to study the method of strain engineering as a procedure to control the height of quantum dots. We show that fully three-dimensional kinetic Monte Carlo simulations can be matched with the experimentally obtained morphology of buried quantum dots and that combination of the two techniques provides details of the growth process that hitherto could not be obtained.

  10. Visualization of 0.1-?m-metal-oxide-semiconductor field-effect transistors by cross-sectional scanning tunneling microscopy

    International Nuclear Information System (INIS)

    The device structure of 0.1-?m-metal-oxide-semiconductor field-effect transistors (MOSFETs) has been examined by cross-sectional scanning tunneling microscopy (STM). Topographic STM images display the source/drain, gate, channel, gate oxide, and spacer of the MOSFETs in terms of height, where these regions appear as though they are a different height from each other. The bias voltage dependence of the STM images shows that the contrast observed by STM reflects the differences in carrier densities between the regions in addition to that in the corrugations. The dimensions of these regions as obtained from the images are consistent with the specifications of devices in feature size that we fabricated

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

    International Nuclear Information System (INIS)

    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

  12. End station for nanoscale magnetic materials study: Combination of scanning tunneling microscopy and soft X-ray magnetic circular dichroism spectroscopy

    International Nuclear Information System (INIS)

    We have constructed an end station for nanoscale magnetic materials study at the soft X-ray beamline HiSOR BL-14 at Hiroshima Synchrotron Radiation Center. An ultrahigh-vacuum scanning tunneling microscope (STM) was installed for an in situ characterization of nanoscale magnetic materials in combination with soft X-ray magnetic circular dichroism (XMCD) spectroscopy experiment. The STM was connected to the XMCD experimental station via damper bellows to isolate it from environmental vibrations, thus achieving efficient spatial resolution for observing Si(111) surface at atomic resolution. We performed an in situ experiment with STM and XMCD spectroscopy on Co nanoclusters on an Au(111) surface and explored its practical application to investigate magnetic properties for well-characterized nanoscale magnetic materials.

  13. 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.

  14. 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\

  15. 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

    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 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.

  16. Direct elemental and magnetic contrast of magnetic thin films and nanoparticles measured by synchrotron X-ray scanning tunneling microscopy and spectroscopy

    Science.gov (United States)

    Dilullo, Andrew; Shirato, N.; Cummings, M.; Kersell, H.; Hla, S.-W.; Rose, V.

    2015-03-01

    Synchrotron X-ray scanning tunneling microscopy (SX-STM) combines two of the most robust characterization instruments of materials science in a single setting and it can provide elemental fingerprinting of materials down to the atomic limits. Here, we show that the SX-STM can also be useful for the magnetic measurements with elemental specificity by combining tunneling microscopy and spectroscopy with the X-ray magnetic circular dichroism (XMCD) technique. The experiments are performed in the Advanced Photon Source beam line 4-ID-C using a custom-built SX-STM system. During the experiment, the circularly polarized synchrotron light is projected onto iron nanoclusters adsorbed on a cobalt thin film on Cu(111) surface, and the resulting photo-current is collected by a nano-fabricated SX-STM tip. The photocurrent intensity clearly reveals majority and minority spin states when measured at L2 and L3 edges of the magnetic materials. We will also discuss the enormous potential of this nascent technique in characterizations of materials at atomic limits.

  17. Experimental evidence for s-wave pairing symmetry in superconducting Cu(x)Bi2Se3 single crystals using a scanning tunneling microscope.

    Science.gov (United States)

    Levy, Niv; Zhang, Tong; Ha, Jeonghoon; Sharifi, Fred; Talin, A Alec; Kuk, Young; Stroscio, Joseph A

    2013-03-15

    Topological superconductors represent a newly predicted phase of matter that is topologically distinct from conventional superconducting condensates of Cooper pairs. As a manifestation of their topological character, topological superconductors support solid-state realizations of Majorana fermions at their boundaries. The recently discovered superconductor Cu(x)Bi(2)Se(3) has been theoretically proposed as an odd-parity superconductor in the time-reversal-invariant topological superconductor class, and point-contact spectroscopy measurements have reported the observation of zero-bias conductance peaks corresponding to Majorana states in this material. Here we report scanning tunneling microscopy measurements of the superconducting energy gap in Cu(x)Bi(2)Se(3) as a function of spatial position and applied magnetic field. The tunneling spectrum shows that the density of states at the Fermi level is fully gapped without any in-gap states. The spectrum is well described by the Bardeen-Cooper-Schrieffer theory with a momentum independent order parameter, which suggests that Cu(x)Bi(2)Se(3) is a classical s-wave superconductor contrary to previous expectations and measurements. PMID:25166563

  18. Investigations of titanium nanostructures on Si(111) 7x7 by means of scanning tunnelling microscopy and spectroscopy

    International Nuclear Information System (INIS)

    The aim of this paper were investigations of the growth of Ti nanostructures created by means of an electron gun on Si(111)-(7x7) with the coverage below 0.1 ML. Titanium was deposited on the Si substrate at 673 K. The Ti nanostructures after deposition and subsequent annealing processes were imaged in situ by means of UHV STM. The current imaging tunnelling spectroscopy (CITS) showed a contrast between the semiconducting substrate and Ti nanostructures. Some of the I V characteristics revealed the step-like character typical for the quantum size or Coulomb blockade effects. Annealing of the samples in the range of 673 K to 943 K led to appearing of the r19xr19 reconstruction. This reconstruction appeared at the cost of Ti nanostructures as a result of Ti atoms diffusion into Si sublayers.

  19. Investigations of titanium nanostructures on Si(111) 7×7 by means of scanning tunnelling microscopy and spectroscopy

    Science.gov (United States)

    Bazarnik, M.; C?giel, M.; Biskupski, P.; Mielcarek, S.; Czajka, R.

    2009-01-01

    The aim of this paper were investigations of the growth of Ti nanostructures created by means of an electron gun on Si(111)-(7×7) with the coverage below 0.1 ML. Titanium was deposited on the Si substrate at 673 K. The Ti nanostructures after deposition and subsequent annealing processes were imaged in situ by means of UHV STM. The current imaging tunnelling spectroscopy (CITS) showed a contrast between the semiconducting substrate and Ti nanostructures. Some of the I V characteristics revealed the step-like character typical for the quantum size or Coulomb blockade effects. Annealing of the samples in the range of 673 K to 943 K led to appearing of the r19×r19 reconstruction. This reconstruction appeared at the cost of Ti nanostructures as a result of Ti atoms diffusion into Si sublayers.

  20. Investigations of titanium nanostructures on Si(111) 7x7 by means of scanning tunnelling microscopy and spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Bazarnik, M; Cegiel, M; Czajka, R [Institute of Physics, Faculty of Technical Physics, Poznan University of Techgnology, ul. Nieszawska 13A, 60-965 Poznan (Poland); Biskupski, P; Mielcarek, S [Institute of Physics, Faculty of Physics, A. Mickiewicz University, ul. Umultowska 85, 61-614 Poznan (Poland)], E-mail: ryszard.czajka@put.poznan.pl

    2009-01-01

    The aim of this paper were investigations of the growth of Ti nanostructures created by means of an electron gun on Si(111)-(7x7) with the coverage below 0.1 ML. Titanium was deposited on the Si substrate at 673 K. The Ti nanostructures after deposition and subsequent annealing processes were imaged in situ by means of UHV STM. The current imaging tunnelling spectroscopy (CITS) showed a contrast between the semiconducting substrate and Ti nanostructures. Some of the I V characteristics revealed the step-like character typical for the quantum size or Coulomb blockade effects. Annealing of the samples in the range of 673 K to 943 K led to appearing of the r19xr19 reconstruction. This reconstruction appeared at the cost of Ti nanostructures as a result of Ti atoms diffusion into Si sublayers.

  1. 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.

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

    International Nuclear Information System (INIS)

    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)]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

  3. Win X-ray: A New Monte Carlo Program that Computes X-ray Spectra Obtained with a Scanning Electron Microscope

    Science.gov (United States)

    Gauvin, Raynald; Lifshin, Eric; Demers, Hendrix; Horny, Paula; Campbell, Helen

    2006-02-01

    A new Monte Carlo program, Win X-ray, is presented that predicts X-ray spectra measured with an energy dispersive spectrometer (EDS) attached to a scanning electron microscope (SEM) operating between 10 and 40 keV. All the underlying equations of the Monte Carlo simulation model are included. By simulating X-ray spectra, it is possible to establish the optimum conditions to perform a specific analysis as well as establish detection limits or explore possible peak overlaps. Examples of simulations are also presented to demonstrate the utility of this new program. Although this article concentrates on the simulation of spectra obtained from what are considered conventional thick samples routinely explored by conventional microanalysis techniques, its real power will be in future refinements to address the analysis of sample classifications that include rough surfaces, fine structures, thin films, and inclined surfaces because many of these can be best characterized by Monte Carlo methods. The first step, however, is to develop, refine, and validate a viable Monte Carlo program for simulating spectra from conventional samples.

  4. Win X-ray: a new Monte Carlo program that computes X-ray spectra obtained with a scanning electron microscope.

    Science.gov (United States)

    Gauvin, Raynald; Lifshin, Eric; Demers, Hendrix; Horny, Paula; Campbell, Helen

    2006-02-01

    A new Monte Carlo program, Win X-ray, is presented that predicts X-ray spectra measured with an energy dispersive spectrometer (EDS) attached to a scanning electron microscope (SEM) operating between 10 and 40 keV. All the underlying equations of the Monte Carlo simulation model are included. By simulating X-ray spectra, it is possible to establish the optimum conditions to perform a specific analysis as well as establish detection limits or explore possible peak overlaps. Examples of simulations are also presented to demonstrate the utility of this new program. Although this article concentrates on the simulation of spectra obtained from what are considered conventional thick samples routinely explored by conventional microanalysis techniques, its real power will be in future refinements to address the analysis of sample classifications that include rough surfaces, fine structures, thin films, and inclined surfaces because many of these can be best characterized by Monte Carlo methods. The first step, however, is to develop, refine, and validate a viable Monte Carlo program for simulating spectra from conventional samples. PMID:17481341

  5. Surface phase transition of Cu/Si(1 1 1)-(5 x 5) by scanning tunnelling microscopy and photoemission study

    International Nuclear Information System (INIS)

    The phase transition process from the Si(1 1 1)-(7 x 7) surface to the Cu/Si(1 1 1)-(5 x 5) surface structure has been studied by scanning tunnelling microscopy and synchrotron radiation photoemission spectroscopy. The nucleation and growth of Cu/Si(1 1 1)-(5 x 5) on the Si(1 1 1)-(7 x 7) surface progress gradually with the increase in Cu coverage. Cu deposition on the Si(1 1 1)-(7 x 7) surface at room temperature may only involve the saturation of the surface dangling bonds, whereas a new surface phase of Cu/Si(1 1 1)-(5 x 5) is formed upon annealing, which saturates at a Cu coverage of 0.9 ML. Our experiments clearly show the surface phase transition process of the (5 x 5) structure as a function of the Cu coverage and provide useful insight into the Cu/Si(1 1 1)-(5 x 5) structure

  6. Scanning tunnelling spectroscopy and ab initio calculations of single-walled carbon nanotubes interfaced with highly doped hydrogen-passivated Si(100) substrates

    International Nuclear Information System (INIS)

    The electronic properties of isolated single-walled carbon nanotubes (SWNTs) adsorbed onto n- and p-doped hydrogen-passivated Si(100) surfaces are studied by ultrahigh vacuum scanning tunnelling spectroscopy and ab initio density-functional methods. SWNTs identified as semiconductors (s-SWNTs) have well-defined conduction and valence band edges separated by a ?1 eV gap, with the mid-gap Fermi level implying that the s-SWNTs are undoped. Relative s-SWNT/H-Si(100) band alignments inferred from dI/dV plots are sensitive to the polarity of the substrate doping. Band structure calculations for a (12,4) s-SWNT corroborate experimental data: n-type (p-type) doping of the substrate leads to a shift of the surface bands lower (higher) in energy relative to those of the s-SWNT. The adsorption energy and charge transfer calculated for the (12,4) s-SWNT physisorbed onto H-Si(100) are considerably less than values reported for the same tube on unpassivated Si(100) and are registration independent. The atomistic results presented here have critical implications to hybrid electronic and photonic devices that rely upon a direct interface between a SWNT and a technologically relevant semiconductor such as Si or GaAs

  7. Two-dimensional silicide 5×3 structure on Cu(001) as seen by scanning tunneling microscopy and helium-atom scattering

    Science.gov (United States)

    Graham, A. P.; Hinch, B. J.; Kochanski, G. P.; McCash, E. M.; Allison, W.

    1994-11-01

    The incommensurate 5×3 structure, which is formed when silicon is deposited on copper(001) via a saturation exposure to silane at 420 K, has been examined with helium-atom scattering and scanning tunneling microscopy. The surface was found to be a two-dimensional copper-silicon alloy having large domains of a near perfect hexagonal structure with Cu2Si stoichiometry. The surface layer displays a rotation of one surface-lattice vector with respect to the substrate of 4.4°, and a high-order commensuration along the other surface-lattice vector, without rotation. The overlayer exhibited unequal densities of the four possible domains and it appears that the long-range order is influenced by the presence of steps on the copper(001) surface. The overall atomic density in the surface layer is 27.6% higher than on the unreconstructed surface. The driving force for the formation of the sheared hexagonal structure is believed to be the need to increase surface coordination and density together with a strongly directional in-plane bonding between Cu and Si atoms.

  8. 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.

  9. High-temperature scanning tunneling microscopy study of the ordering transition of an amorphous carbon layer into graphene on ruthenium(0001).

    Science.gov (United States)

    Günther, Sebastian; Dänhardt, Sebastian; Ehrensperger, Martin; Zeller, Patrick; Schmitt, Stefan; Wintterlin, Joost

    2013-01-22

    The ordering transition of an amorphous carbon layer into graphene was investigated by high-temperature scanning tunneling microscopy. A disordered C layer was prepared on a Ru(0001) surface by chemical vapor deposition of ethylene molecules at ~660 K. The carbon layer grows in the form of dendritic islands that have almost the same density as graphene. Upon annealing of the fully covered surface, residual hydrogen desorbs and a coherent but still disordered carbon layer forms, with almost the same carbon coverage as in graphene. The ordering of this layer into graphene at 920 to 950 K was monitored as a function of time. A unique mechanism was observed that involves small topographic holes in the carbon layer. The holes are mobile, and on the trajectories of the holes the disordered carbon layer is transformed into graphene. The transport of C atoms across the holes or along the hole edges provides a low-energy pathway for the ordering transition. This mechanism is prohibited in a dense graphene layer, which offers an explanation for the difficulty of removing defects from graphene synthesized by chemical methods. PMID:23214506

  10. A scanning tunneling microscopy study of the structure of thin oxide films grown on Ni(111) single crystal surfaces by anodic polarization in acid electrolyte

    Science.gov (United States)

    Maurice, V.; Talah, H.; Marcus, P.

    1994-03-01

    Scanning tunneling microscopy has been used to study ex situ (in air) the thin oxide films (passive films) grown on Ni(111) by anodic polarization at +550, +650 and +750 mV/SHE in 0.05 M H 2SO 4. Atomic resolution imaging demonstrates the crystalline character of the oxide film and the epitaxy with the substrate. Two levels of roughening with respect to the non-polarized surfaces are observed: on a mesoscopic scale and on the atomic scale. The roughening on the mesoscopic scale increases with higher polarization potentials. The observed roughness is attributed to the result of the competition between metal dissolution and nucleation and growth of the oxide film. The roughening on the atomic scale is independent of the polarization potential. It is evidenced by the formation of a stepped crystalline lattice whose parameters fit those of a (111)-oriented NiO surface. The presence of steps indicates a tilt of (8 ± 5)° of the surface of the film with respect to the (111) orientation. The possible epitaxial relationships resulting from the surface tilt are discussed. Local variations of the film thickness at the step edges are likely to result from the surface tilt and may constitute preferential sites for the local breakdown of passivity.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Unraveling the Intrinsic and Robust Nature of van Hove Singularities in Twisted Bilayer Graphene by Scanning Tunneling Microscopy and Theoretical Analysis

    Science.gov (United States)

    Brihuega, I.; Mallet, P.; González-Herrero, H.; Trambly de Laissardière, G.; Ugeda, M. M.; Magaud, L.; Gómez-Rodíguez, J. M.; Ynduráin, F.; Veuillen, J.-Y.

    2012-11-01

    Extensive scanning tunneling microscopy and spectroscopy experiments complemented by first-principles and parametrized tight binding calculations provide a clear answer to the existence, origin, and robustness of van Hove singularities (vHs) in twisted graphene layers. Our results are conclusive: vHs due to interlayer coupling are ubiquitously present in a broad range (from 1° to 10°) of rotation angles in our graphene on 6H-SiC(000-1) samples. From the variation of the energy separation of the vHs with the rotation angle we are able to recover the Fermi velocity of a graphene monolayer as well as the strength of the interlayer interaction. The robustness of the vHs is assessed both by experiments, which show that they survive in the presence of a third graphene layer, and by calculations, which test the role of the periodic modulation and absolute value of the interlayer distance. Finally, we clarify the role of the layer topographic corrugation and of electronic effects in the apparent moiré contrast measured on the STM images.

  16. Tip induced mechanical deformation of epitaxial graphene grown on reconstructed 6H-SiC(0001) surface during scanning tunneling and atomic force microscopy studies.

    Science.gov (United States)

    Meza, José Antonio Morán; Lubin, Christophe; Thoyer, François; Cousty, Jacques

    2015-06-26

    The structural and mechanical properties of an epitaxial graphene (EG) monolayer thermally grown on top of a 6H-SiC(0001) surface were studied by combined dynamic scanning tunneling microscopy (STM) and frequency modulation atomic force microscopy (FM-AFM). Experimental STM, dynamic STM and AFM images of EG on 6H-SiC(0001) show a lattice with a 1.9 nm period corresponding to the (6 × 6) quasi-cell of the SiC surface. The corrugation amplitude of this (6 × 6) quasi-cell, measured from AFM topographies, increases with the setpoint value of the frequency shift ?f (15-20 Hz, repulsive interaction). Excitation variations map obtained simultaneously with the AFM topography shows that larger dissipation values are measured in between the topographical bumps of the (6 × 6) quasi-cell. These results demonstrate that the AFM tip deforms the graphene monolayer. During recording in dynamic STM mode, a frequency shift (?f) map is obtained in which ?f values range from 41 to 47 Hz (repulsive interaction). As a result, we deduced that the STM tip, also, provokes local mechanical distortions of the graphene monolayer. The origin of these tip-induced distortions is discussed in terms of electronic and mechanical properties of EG on 6H-SiC(0001). PMID:26040291

  17. Tip induced mechanical deformation of epitaxial graphene grown on reconstructed 6H–SiC(0001) surface during scanning tunneling and atomic force microscopy studies

    Science.gov (United States)

    Morán Meza, José Antonio; Lubin, Christophe; Thoyer, François; Cousty, Jacques

    2015-06-01

    The structural and mechanical properties of an epitaxial graphene (EG) monolayer thermally grown on top of a 6H–SiC(0001) surface were studied by combined dynamic scanning tunneling microscopy (STM) and frequency modulation atomic force microscopy (FM-AFM). Experimental STM, dynamic STM and AFM images of EG on 6H–SiC(0001) show a lattice with a 1.9 nm period corresponding to the (6 × 6) quasi-cell of the SiC surface. The corrugation amplitude of this (6 × 6) quasi-cell, measured from AFM topographies, increases with the setpoint value of the frequency shift ?f (15–20 Hz, repulsive interaction). Excitation variations map obtained simultaneously with the AFM topography shows that larger dissipation values are measured in between the topographical bumps of the (6 × 6) quasi-cell. These results demonstrate that the AFM tip deforms the graphene monolayer. During recording in dynamic STM mode, a frequency shift (?f) map is obtained in which ?f values range from 41 to 47 Hz (repulsive interaction). As a result, we deduced that the STM tip, also, provokes local mechanical distortions of the graphene monolayer. The origin of these tip-induced distortions is discussed in terms of electronic and mechanical properties of EG on 6H–SiC(0001).

  18. Phosphorus and hydrogen atoms on the (0 0 1) surface of silicon: A comparative scanning tunnelling microscopy study of surface species with a single dangling bond

    Science.gov (United States)

    Reusch, T. C. G.; Curson, N. J.; Schofield, S. R.; Hallam, T.; Simmons, M. Y.

    2006-01-01

    We present a comparative scanning tunnelling microscopy (STM) study of two features on the Si(0 0 1) surface with a single dangling bond. One feature is the Si-P heterodimer—a single surface phosphorus atom substituted for one Si atom of a Si-Si dimer. The other feature is the Si-Si-H hemihydride—a single hydrogen atom adsorbed to one Si atom of a Si-Si dimer. Previous STM studies of both surface species have reported a nearly identical appearance in STM which has hampered an experimental distinction between them to date. Using voltage-dependent STM we are able to distinguish and identify both heterodimer and hemihydride on the Si(0 0 1) surface. This work is particularly relevant for the fabrication of atomic-scale Si:P devices by STM lithography on the hydrogen terminated Si(0 0 1):H surface, where it is important to monitor the distribution of single P dopants in the surface. Based on the experimental identification, we study the lateral P diffusion out of nanoscale reservoirs prepared by STM lithography.

  19. 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.

  20. 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.

  1. Ultra-high vacuum scanning tunnelling microscopy investigation of free radical adsorption to the Si(111)-7 x 7 surface

    International Nuclear Information System (INIS)

    Room-temperature ultra-high vacuum (UHV) scanning tunnelling microscopy (STM) has been employed to investigate free radical chemistry on the Si(111)-7 x 7 surface with atomic-scale spatial resolution. In particular, due to its single-site binding mechanism and extensive previous study on the Si(100)-2 x 1 surface, the nitroxyl free radical 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) was explored. UHV STM imaging of isolated molecules revealed that TEMPO covalently reacts with adatom dangling bonds with high affinity. By monitoring TEMPO adsorption as a function of surface coverage, TEMPO was also found to preferentially bind to centre adatom sites at the initial stages of adsorption. On the other hand, as the surface coverage increased, TEMPO molecules adsorbed to centre adatoms and corner adatoms approached a ratio of 1:1. At all surface coverage levels, TEMPO showed minimal preference for binding to either the faulted or unfaulted half of the unit cell. Consequently, upon saturation, the TEMPO adlayer exhibited long-range ordering and preserved the underlying 7 x 7 surface reconstruction. This study provides fundamental insight into free radical surface chemistry and suggests a direct pathway for forming nearly perfectly ordered organic adlayers on the Si(111)-7 x 7 surface

  2. High-sensitivity noncontact atomic force microscope/scanning tunneling microscope (nc AFM/STM) operating at subangstrom oscillation amplitudes for atomic resolution imaging and force spectroscopy

    Science.gov (United States)

    Oral, A.; Grimble, R. A.; Özer, H. Ö.; Pethica, J. B.

    2003-08-01

    We describe a new, highly sensitive noncontact atomic force microscope/scanning tunneling microscope (STM) operating in ultrahigh vacuum (UHV) with subangstrom oscillation amplitudes for atomic resolution imaging and force-distance spectroscopy. A novel fiber interferometer with ˜4×10-4 Å/?Hz noise level is employed to detect cantilever displacements. Subangstrom oscillation amplitude is applied to the lever at a frequency well below the resonance and changes in the oscillation amplitude due to tip-sample force interactions are measured with a lock-in amplifier. Quantitative force gradient images can be obtained simultaneously with the STM topography. Employment of subangstrom oscillation amplitudes lets us perform force-distance measurements, which reveal very short-range force interactions, consistent with the theory. Performance of the microscope is demonstrated with quantitative atomic resolution images of Si(111)(7×7) and force-distance curves showing short interaction range, all obtained with <0.25 Å lever oscillation amplitude. Our technique is not limited to UHV only and operation under liquids and air is feasible.

  3. Oxide film growth on Fe(111) and scanning tunneling microscopy induced high electric field stress in Fe2O3/Fe(111)

    International Nuclear Information System (INIS)

    Oxidation of Fe(111) at 300 and 500 K was studied using Auger electron spectroscopy, low energy electron diffraction and scanning tunneling microscopy (STM) under UHV conditions. Oxidation of the Fe(111) surface at oxygen partial pressures of 1-5x10-7 Torr resulted in the formation of Fe2O3 and Fe3O4 at 300 K. At 500 K, however, the predominant oxide phase was Fe3O4. STM images showed that the Fe(111) surface was uniformly covered with 5-15 nm wide oxide islands at room temperature oxidation, while oxidation at 500 K resulted in the formation of very large oxide islands (100-300 nm in width) interspersed with patches of uncovered substrate. High electric field stressing studies were carried out via STM under UHV conditions by increasing the bias voltage between the sample and the STM tip under constant current mode on iron oxide formed at both temperatures. Dielectric breakdown of the iron oxide formed at 300 K was induced after applying a high electric field. A critical bias voltage of 3.8±0.5 V was required to induce breakdown of iron oxide formed at 300 K at varying field strengths. No reproducible result was obtained from the high field stress studies of the iron oxide formed at 500 K

  4. Strain-induced structure transformations on Si(111) and Ge(111) surfaces: a combined density-functional and scanning tunneling microscopy study.

    Science.gov (United States)

    Zhachuk, R; Teys, S; Coutinho, J

    2013-06-14

    Si(111) and Ge(111) surface formation energies were calculated using density functional theory for various biaxial strain states ranging from -0.04 to 0.04, and for a wide set of experimentally observed surface reconstructions: 3 × 3, 5 × 5, 7 × 7 dimer-adatom-stacking fault reconstructions and c(2 × 8), 2 × 2, and ?3×?3 adatoms based surfaces. The calculations are compared with scanning tunneling microscopy data obtained on stepped Si(111) surfaces and on Ge islands grown on a Si(111) substrate. It is shown that the surface structure transformations observed in these strained systems are accounted for by a phase diagram that relates the equilibrium surface structure to the applied strain. The calculated formation energy of the unstrained Si(111)-9 × 9 dimer-adatom-stacking fault surface is reported for the first time and it is higher than corresponding energies of Si(111)-5 × 5 and Si(111)-7 × 7 dimer-adatom-stacking fault surfaces as expected. We predict that the Si(111) surface should adopt a c(2 × 8) reconstruction when tensile strain is above 0.03. PMID:23781810

  5. An ultra-precision scanning tunneling microscope Z-scanner for surface profile measurement of large amplitude micro-structures

    International Nuclear Information System (INIS)

    This paper presents an ultra-precision STM Z-scanner for surface profile measurement of micro-structures with large amplitudes on the order of several tens of micrometers. The Z-scanner consists of an STM probe, a long stroke PZT actuator with a full stroke of 70 µm, and a linear encoder. The linear encoder is employed to accurately measure a Z-directional displacement of a STM probe tracking a sample surface. The linear encoder yields a least significant bit resolution of 0.5 nm over the full stroke of the actuator. The peak-to-valley value of the Z-scanner nonlinearity is smaller than 10 nm over an effective measurement range of 50 µm. Experiments of surface profile measurement of samples with micro-structures were carried out by combining the Z-scanner and an X-directional PZT scanning stage, on which the sample is mounted. The feasibility of the developed ultra-precision Z-scanner has been confirmed from the measurement results

  6. 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/oxidizedzed 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.

  7. 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.

  8. 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.

  9. 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)

  10. 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.

  11. Self-assembled monolayers of radical molecules physisorbed on HOPG(0 0 0 1) substrate studied by scanning tunnelling microscopy and electron paramagnetic resonance techniques

    International Nuclear Information System (INIS)

    In this paper, we present a combined STM and EPR study on the adsorption and self-organization of monolayers formed from 2-(14-Carboxytetradecyl)-2-ethyl-4,4-dimethyl-3-oxazolidinyloxy (16DS) and 4',4'-Dimethylspiro(5?-cholestane-3,2'-oxazolidin)-3'-yloxy (CSL) adsorbed on a highly oriented pyrolitic graphite HOPG(0 0 0 1) substrate. Both 16DS and CSL molecules are persistent free radicals containing a paramagnetic doxyl group. The STM measurements of 16DS on HOPG(0 0 0 1) were performed at the liquid-solid interface while the studies of CSL on HOPG(0 0 0 1) were carried out under ultrahigh vacuum conditions. It was found that the 16DS molecules on the HOPG(0 0 0 1) surface form a highly-ordered monolayer with a domain structure. The high-resolution STM images show structural details of 16DS molecules on HOPG(0 0 0 1) revealing the paramagnetic doxyl group. In contrast, CSL molecules on HOPG(0 0 0 1) form a well-ordered monolayer without domain structure. The EPR results indicate that both compounds deposited on HOPG(0 0 0 1) substrate are not reduced and retain their paramagnetic character. We believe that the molecular systems described can be used in single spin detection experiments using an electron spin noise-scanning tunnelling microscopy (ESN-STM) technique. In particular, the possibility of obtaining contrast spin signals from the paramagnetic and diamagnetic parts of molecules increases the significance of our results.s.

  12. Strong uniaxial anisotropies of iron grown on UHV cleaved InAs(110) investigated by correlated scanning tunneling microscopy and ferromagnetic resonance

    Science.gov (United States)

    Spoddig, Detlef; Urban, Christian; You, Dai-Hyun; Köhler, Ulrich; Meckenstock, Ralf

    2006-04-01

    The magnetic properties of iron films grown under UHV condition are governed by the deposition condition and the substrate preparation. One way of producing almost perfect surface conditions with large terrace width and exact orientation is cleaving. With this method no additional cleaning process of the surface is needed. Here we present our investigations of iron films (thickness: 0.1-30 nm) grown on UHV cleaved InAs substrates using in situ scanning tunnel microscopy (STM) investigations combined with in situ magneto-optical Kerr effect (MOKE) and ex situ angle and frequency dependent conventional ferromagnetic resonance (FMR). The (110) InAs surface allows the investigation of three magnetic axes: in-plane easy (001), hard (111), and intermediate (110) axes of the iron layer. The (110) symmetry of the magnetic cubic crystalline anisotropy should lead to angles of 110° and 70° between the hard axes, respectively. STM images of the clean InAs(110) show 500 nm wide terraces with mono atomic steps predominately oriented parallel to the (001) direction. MOKE hysteresis loops were measured during the Fe deposition to prove the ferromagnetic state. The angle dependent in-plane FMR measurement revealed unexpected 90° symmetry. Deducing the anisotropy constants from the FMR resonance position, one finds a slightly increased bulk crystalline anisotropy and a uniaxial anisotropy of the same order of magnitude. This strong uniaxial anisotropy distorts the 110° symmetry to 90° symmetry. The correlation of frequency and angle dependent FMR and STM measurements evidences that the uniaxial anisotropy is due to the dislocations caused by the orientation of the terraces.

  13. Molecular oxygen adsorption behaviors on the rutile TiO2(110)-1×1 surface: an in situ study with low-temperature scanning tunneling microscopy.

    Science.gov (United States)

    Tan, Shijing; Ji, Yongfei; Zhao, Yan; Zhao, Aidi; Wang, Bing; Yang, Jinlong; Hou, J G

    2011-02-16

    A knowledge of adsorption behaviors of oxygen on the model system of the reduced rutile TiO(2)(110)-1×1 surface is of great importance for an atomistic understanding of many chemical processes. We present a scanning tunneling microcopy (STM) study on the adsorption of molecular oxygen either at the bridge-bonded oxygen vacancies (BBO(V)) or at the hydroxyls (OH) on the TiO(2)(110)-1×1 surface. Using an in situ O(2) dosing method, we are able to directly verify the exact adsorption sites and the dynamic behaviors of molecular O(2). Our experiments provide direct evidence that an O(2) molecule can intrinsically adsorb at both the BBO(V) and the OH sites. It has been identified that, at a low coverage of O(2), the singly adsorbed molecular O(2) at BBO(V) can be dissociated through an intermediate state as driven by the STM tip. However, singly adsorbed molecular O(2) at OH can survive from such a tip-induced effect, which implies that the singly adsorbed O(2) at OH is more stable than that at BBO(V). It is interesting to observe that when the BBO(V)s are fully filled with excess O(2) dosing, the adsorbed O(2) molecules at BBO(V) tend to be nondissociative even under a higher bias voltage of 2.2 V. Such a nondissociative behavior is most likely attributed to the presence of two or more O(2) molecules simultaneously adsorbed at a BBO(V) with a more stable configuration than singly adsorbed molecular O(2) at a BBO(V). PMID:21247169

  14. Tunnelling in chiral water clusters: Protons in concert

    Science.gov (United States)

    Drechsel-Grau, Christof; Marx, Dominik

    2015-03-01

    The transfer of protons across a high barrier only occasionally occurs through quantum-mechanical tunnelling. Low-temperature scanning tunnelling microscopy shows concerted tunnelling of four protons within chiral cyclic water tetramers supported on an inert surface.

  15. Traversal time for tunneling: Local aspects

    Science.gov (United States)

    Kotler, Zvi; Nitzan, Abraham

    1988-03-01

    The relationship between inelastic tunneling processes and the traversal time for tunneling is studied with emphasis on the local aspects of the tunneling time. Viewed in this framework, the local tunneling time is shown to be a dominant factor in determining the inelastic tunneling probability. It is shown that the Buttiker-Landauer semiclassical formalism, when generalized to the case of local interactions and applied to the calculation of inelastic tunneling probabilities, gives results identical to other perturbation theory calculations such as the Bardeen formula. Analytical results derived for square potential barrier are shown to hold also for strongly biased barriers. Application to inelastic tunneling in typical scanning tunneling microscope configuration are discussed.

  16. Effect of hydrogen adsorption on the quasiparticle spectra of graphene

    OpenAIRE

    Farjam, M.; Haberer, D.; Gru?neis, A.

    2011-01-01

    We use the non-interacting tight-binding model to study the effect of isolated hydrogen adsorbates on the quasiparticle spectra of single-layer graphene. Using the Green's function approach, we obtain analytic expressions for the local density of states and the spectral function of hydrogen-doped graphene, which are also numerically evaluated and plotted. Our results are relevant for the interpretation of scanning tunneling microscopy and angle-resolved photoemission spectro...

  17. A database for estimating organ dose for coronary angiography and brain perfusion CT scans for arbitrary spectra and angular tube current modulation

    International Nuclear Information System (INIS)

    Purpose: The purpose of this study was to develop a database for estimating organ dose in a voxelized patient model for coronary angiography and brain perfusion CT acquisitions with any spectra and angular tube current modulation setting. The database enables organ dose estimation for existing and novel acquisition techniques without requiring Monte Carlo simulations. Methods: The study simulated transport of monoenergetic photons between 5 and 150 keV for 1000 projections over 360° through anthropomorphic voxelized female chest and head (0° and 30° tilt) phantoms and standard head and body CTDI dosimetry cylinders. The simulations resulted in tables of normalized dose deposition for several radiosensitive organs quantifying the organ dose per emitted photon for each incident photon energy and projection angle for coronary angiography and brain perfusion acquisitions. The values in a table can be multiplied by an incident spectrum and number of photons at each projection angle and then summed across all energies and angles to estimate total organ dose. Scanner-specific organ dose may be approximated by normalizing the database-estimated organ dose by the database-estimated CTDIvol and multiplying by a physical CTDIvol measurement. Two examples are provided demonstrating how to use the tables to estimate relative organ dose. In the first, the change in breast and lung dose during coronary angiography CT scans is calculated for reduced kVp, anguans is calculated for reduced kVp, angular tube current modulation, and partial angle scanning protocols relative to a reference protocol. In the second example, the change in dose to the eye lens is calculated for a brain perfusion CT acquisition in which the gantry is tilted 30° relative to a nontilted scan. Results: Our database provides tables of normalized dose deposition for several radiosensitive organs irradiated during coronary angiography and brain perfusion CT scans. Validation results indicate total organ doses calculated using our database are within 1% of those calculated using Monte Carlo simulations with the same geometry and scan parameters for all organs except red bone marrow (within 6%), and within 23% of published estimates for different voxelized phantoms. Results from the example of using the database to estimate organ dose for coronary angiography CT acquisitions show 2.1%, 1.1%, and ?32% change in breast dose and 2.1%, ?0.74%, and 4.7% change in lung dose for reduced kVp, tube current modulated, and partial angle protocols, respectively, relative to the reference protocol. Results show ?19.2% difference in dose to eye lens for a tilted scan relative to a nontilted scan. The reported relative changes in organ doses are presented without quantification of image quality and are for the sole purpose of demonstrating the use of the proposed database. Conclusions: The proposed database and calculation method enable the estimation of organ dose for coronary angiography and brain perfusion CT scans utilizing any spectral shape and angular tube current modulation scheme by taking advantage of the precalculated Monte Carlo simulation results. The database can be used in conjunction with image quality studies to develop optimized acquisition techniques and may be particularly beneficial for optimizing dual kVp acquisitions for which numerous kV, mA, and filtration combinations may be investigated.

  18. Introduction to Scanning Probe Microscopy

    Science.gov (United States)

    Bullen, Heather

    This learning module teaches the principles behind scanning tunneling microscopy and atomic force microscopy. The module includes example applications and ample literature citations. Scanning tunneling (STM), atomic force (AFM), lateral (friction) force, magnetic force, chemical force and phase imaging are discussed.

  19. Scanning Gate Spectroscopy on Nanoclusters

    OpenAIRE

    Gurevich, L; Canali, L.; Kouwenhoven, L. P.

    1999-01-01

    A gated probe for scanning tunnelling microscopy (STM) has been developed. The probe extends normal STM operations by means of an additional electrode fabricated next to the tunnelling tip. The extra electrode does not make contact with the sample and can be used as a gate. We report on the recipe used for fabricating the tunnelling tip and the gate electrode on a silicon nitride cantilever. We demonstrate the functioning of the scanning gate probes by performing single-elec...

  20. 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.))