Recent advances in atomic-scale spin-polarized scanning tunneling microscopy.

Science.gov (United States)

Smith, Arthur R; Yang, Rong; Yang, Haiqiang; Dick, Alexey; Neugebauer, Joerg; Lambrecht, Walter R L

2005-02-01

The Mn3N2 (010) surface has been studied using spin-polarized scanning tunneling microscopy at the atomic scale. The principle objective of this work is to elucidate the properties and potential of this technique to measure atomic-scale magnetic structures. The experimental approach involves the use of a combined molecular beam epitaxy/scanning tunneling microscopy system that allows the study of atomically clean magnetic surfaces. Several key findings have been obtained. First, both magnetic and non-magnetic atomic-scale information has been obtained in a single spin-polarized image. Magnetic modulation of the height profile having an antiferromagnetic super-period of c = 12.14 A (6 atomic rows) together with a non-magnetic superstructure having a period of c/2 = 6.07 A (3 atomic rows) was observed. Methods of separation of magnetic and non-magnetic profiles are presented. Second, bias voltage-dependent spin-polarized images show a reversal of the magnetic modulation at a particular voltage. This reversal is clearly due to a change in the sign of the magnetic term in the tunnel current. Since this term depends on both the tip's as well as the sample's magnetic local density of states, the reversal can be caused by either the sample or the tip. Third, the shape of the line profile was found to vary with the bias voltage, which is related to the energy-dependent spin contribution from the 2 chemically inequivalent Mn sites on the surface. Overall, the results shown here expand the application of the method of spin-polarized scanning tunneling microscopy to measure atomic-scale magnetic structures. (c) 2005 Wiley-Liss, Inc.

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.

Imaging of buried phosphorus nanostructures in silicon using scanning tunneling microscopy

International Nuclear Information System (INIS)

Oberbeck, Lars; Reusch, Thilo C. G.; Hallam, Toby; Simmons, Michelle Y.; Schofield, Steven R.; Curson, Neil J.

2014-01-01

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.

Investigation of non-collinear spin states with scanning tunneling microscopy.

Science.gov (United States)

Wulfhekel, W; Gao, C L

2010-03-05

Most ferromagnetic and antiferromagnetic substances show a simple collinear arrangement of the local spins. Under certain circumstances, however, the spin configuration is non-collinear. Scanning tunneling microscopy with its potential atomic resolution is an ideal tool for investigating these complex spin structures. Non-collinearity can be due to topological frustration of the exchange interaction, due to relativistic spin-orbit coupling or can be found in excited states. Examples for all three cases are given, illustrating the capabilities of spin-polarized scanning tunneling microscopy.

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 i...

Solid-State Quantum Computer Based on Scanning Tunneling Microscopy

Energy Technology Data Exchange (ETDEWEB)

Berman, G. P.; Brown, G. W.; Hawley, M. E.; Tsifrinovich, V. I.

2001-08-27

We propose a solid-state nuclear-spin quantum computer based on application of scanning tunneling microscopy (STM) and well-developed silicon technology. It requires the measurement of tunneling-current modulation caused by the Larmor precession of a single electron spin. Our envisioned STM quantum computer would operate at the high magnetic field ({approx}10 T) and at low temperature {approx}1 K .

Solid-State Quantum Computer Based on Scanning Tunneling Microscopy

International Nuclear Information System (INIS)

Berman, G. P.; Brown, G. W.; Hawley, M. E.; Tsifrinovich, V. I.

2001-01-01

We propose a solid-state nuclear-spin quantum computer based on application of scanning tunneling microscopy (STM) and well-developed silicon technology. It requires the measurement of tunneling-current modulation caused by the Larmor precession of a single electron spin. Our envisioned STM quantum computer would operate at the high magnetic field (∼10 T) and at low temperature ∼1 K

Tunneling microscopy of 2H-MoS2: A compound semiconductor surface

OpenAIRE

Weimer, M.; Kramar, J.; Bai, C.; Baldeschwieler, J. D.

1988-01-01

Molybdenum disulfide, a layered semiconductor, is an interesting material to study with the tunneling microscope because two structurally and electronically different atomic species may be probed at its surface. We report on a vacuum scanning tunneling microscopy study of 2H-MoS2. Atomic resolution topographs and current images show the symmetry of the surface unit cell and clearly reveal two distinct atomic sites in agreement with the well-known x-ray crystal structure.

Dynamics of decanethiol self-assembled monolayers on Au(111) studied by Scanning tunnelling microscopy

NARCIS (Netherlands)

Wu, Hairong; Sotthewes, Kai; Kumar, Avijit; Vancso, Gyula J.; Schön, Peter Manfred; Zandvliet, Henricus J.W.

2013-01-01

We investigated the dynamics of decanethiol self-assembled monolayers on Au(111) surfaces using time-resolved scanning tunneling microscopy at room temperature. The expected ordered phases (β, δ, χ*, and ) and a disordered phase (ε) were observed. Current–time traces with the feedback loop disabled

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

International Nuclear Information System (INIS)

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

1993-01-01

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

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

DEFF Research Database (Denmark)

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

2002-01-01

The 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 simulati......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...

Scanning tunneling microscopy measurements of the spin Hall effect in tungsten films by using iron-coated tungsten tips

Science.gov (United States)

Xie, Ting; Dreyer, Michael; Bowen, David; Hinkel, Dan; Butera, R. E.; Krafft, Charles; Mayergoyz, Isaak

2018-05-01

Scanning tunneling microscopy experiments using iron-coated tungsten tips and current-carrying tungsten films have been conducted. An asymmetry of the tunneling current with respect to the change of the direction of the bias current through a tungsten film has been observed. It is argued that this asymmetry is a manifestation of the spin Hall effect in the current-carrying tungsten film. Nanoscale variations of this asymmetry across the tungsten film have been studied by using the scanning tunneling microscopy technique.

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

International Nuclear Information System (INIS)

Coleman, R.V.

1986-01-01

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

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.

Scanning tunneling microscopy measurements of the spin Hall effect in tungsten films by using iron-coated tungsten tips

Directory of Open Access Journals (Sweden)

Ting Xie

2018-05-01

Full Text Available Scanning tunneling microscopy experiments using iron-coated tungsten tips and current-carrying tungsten films have been conducted. An asymmetry of the tunneling current with respect to the change of the direction of the bias current through a tungsten film has been observed. It is argued that this asymmetry is a manifestation of the spin Hall effect in the current-carrying tungsten film. Nanoscale variations of this asymmetry across the tungsten film have been studied by using the scanning tunneling microscopy technique.

Epitaxial clusters studied by synchrotron x-ray diffraction and scanning tunneling microscopy

DEFF Research Database (Denmark)

Nielsen, M.; Feidenhans'l, R.; Rasmussen, F.B.

1998-01-01

Nanoscale clusters are often formed during heteroepitaxial crystal growth. Misfit between the lattice parameter of the substrate and the adsorbate stimulates the formation of regular clusters with a characteristic size. The well-known "hut-clusters" formed during the growth of Ge on Si(001) are a...... similar to the "hut clusters". We demonstrate that X-ray diffraction in combination with scanning tunneling microscopy can be used to determine the fundamental properties of such clusters. (C) 1998 Elsevier Science B.V. All rights reserved....

The possibility to determine a constant of spin-orbit interaction by scanning tunneling microscopy method

International Nuclear Information System (INIS)

Khotkevich, N.V.; Kolesnichenko, Yu.A.; Vovk, N.P.

2016-01-01

The electron tunneling from the quasi-two-dimensional (surface) states with the spin-orbit interaction into bulk-mode states is studied in the framework of a model of an infinitely thin inhomogeneous tunnel magnetic barrier. The influence of the scattering of quasi-two-dimensional electrons by a single magnetic defect on the tunnel current is analyzed. Analytic formulas for the conductance of a tunnel point-contact as a function of its distance from the defect are obtained. It is shown that the analysis of the local magnetization density around the defect by means of spin-polarized scanning tunneling microscopy allows finding the constant of spin orbit interaction.

Photothermal modulation of the gap distance in scanning tunneling microscopy

International Nuclear Information System (INIS)

Amer, N.M.; Skumanich, A.; Ripple, D.

1986-01-01

We have employed the photothermal effect to modulate the gap distance in a tunneling microscope. In this approach, optical heating induces the expansion and buckling of laser-illuminated sample surface. The surface displacement can be modulated over a wide frequency range, and its height (typically <1 A-circle) can be varied by changing the illumination intensity and modulation frequency. This novel method provides an alternative means for performing tunneling spectroscopy and microscopy, and for determining work functions of materials

Molecules on vicinal Au surfaces studied by scanning tunnelling microscopy

International Nuclear Information System (INIS)

Kroeger, J; Neel, N; Jensen, H; Berndt, R; Rurali, R; Lorente, N

2006-01-01

Using low-temperature scanning tunnelling microscopy and spectroscopy we investigated the adsorption characteristics of 3,4,9,10-perylenetetracarboxylic-dianhydride and fullerenes on Au(788), Au(433), and Au(778). On Au(788) and Au(778), 3,4,9,10-perylenetetracarboxylic-dianhydride exhibits three coexisting superstructures, which do not reflect the periodicity of the hosting substrate. The adsorption on Au(433) leads to the formation of molecule chains along the step edges after annealing the sample. Fullerene molecules on Au(788) arrange in a mesh of islands, which extends over several hundreds of nanometres with an extraordinarily high periodicity. A combination of fullerene adsorption and annealing leads to facetting of Au(433) and the formation of extraordinarily long fullerene stripes

Concept for room temperature single-spin tunneling force microscopy with atomic spatial resolution

Science.gov (United States)

Payne, Adam

A study of a force detected single-spin magnetic resonance measurement concept with atomic spatial resolution is presented. The method is based upon electrostatic force detection of spin-selection rule controlled single electron tunneling between two electrically isolated paramagnetic states. Single-spin magnetic resonance detection is possible by measuring the force detected tunneling charge noise on and off spin resonance. Simulation results of this charge noise, based upon physical models of the tunneling and spin physics, are directly compared to measured atomic force microscopy (AFM) system noise. The results show that the approach could provide single-spin measurement of electrically isolated defect states with atomic spatial resolution at room temperature.

Atomic-resolution single-spin magnetic resonance detection concept based on tunneling force microscopy

Science.gov (United States)

Payne, A.; Ambal, K.; Boehme, C.; Williams, C. C.

2015-05-01

A study of a force detected single-spin magnetic resonance measurement concept with atomic spatial resolution is presented. The method is based upon electrostatic force detection of spin-selection rule controlled single-electron tunneling between two electrically isolated paramagnetic states. Single-spin magnetic resonance detection is possible by measuring the force detected tunneling charge noise on and off spin resonance. Simulation results of this charge noise, based upon physical models of the tunneling and spin physics, are directly compared to measured atomic force microscopy system noise. The results show that the approach could provide single-spin measurement of electrically isolated qubit states with atomic spatial resolution at room temperature.

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

International Nuclear Information System (INIS)

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

From Graphite to Graphene via Scanning Tunneling Microscopy

Science.gov (United States)

Qi, Dejun

The primary objective of this dissertation is to study both graphene on graphite and pristine freestanding grapheme using scanning tunneling microscopy (STM) and density functional theory (DFT) simulation technique. In the experiment part, good quality tungsten metalic tips for experiment were fabricated using our newly developed tip making setup. Then a series of measurements using a technique called electrostatic-manipulation scanning tunneling microscopy (EM-STM) of our own development were performed on a highly oriented pyrolytic graphite (HOPG) surface. The electrostatic interaction between the STM tip and the sample can be tuned to produce both reversible and irreversible large-scale movement of the graphite surface. Under this influence, atomic-resolution STM images reveal that a continuous electronic transition between two distinct patterns can be systematically controlled. DFT calculations reveal that this transition can be related to vertical displacements of the top layer of graphite relative to the bulk. Evidence for horizontal shifts in the top layer of graphite is also presented. Excellent agreement is found between experimental STM images and those simulated using DFT. In addition, the EM-STM technique was also used to controllably and reversibly pull freestanding graphene membranes up to 35 nm from their equilibrium height. Atomic-scale corrugation amplitudes 20 times larger than the STM electronic corrugation for graphene on a substrate were observed. The freestanding graphene membrane responds to a local attractive force created at the STM tip as a highly conductive yet flexible grounding plane with an elastic restoring force.

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.

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

International Nuclear Information System (INIS)

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

2015-01-01

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

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

Energy Technology Data Exchange (ETDEWEB)

Morawski, Ireneusz [Peter Grünberg Institut (PGI-3) and JARA-Fundamentals of Future Information Technology, Forschungszentrum Jülich, 52425 Jülich (Germany); Institute of Experimental Physics, University of Wrocław, pl. M. Borna 9, 50-204 Wrocław (Poland); Spiegelberg, Richard; Korte, Stefan; Voigtländer, Bert [Peter Grünberg Institut (PGI-3) and JARA-Fundamentals of Future Information Technology, Forschungszentrum Jülich, 52425 Jülich (Germany)

2015-12-15

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

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

Science.gov (United States)

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

2015-01-01

Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees of freedom to control electronic devices. In particular, the behavior of graphene’s charge carriers in response to potentials from charged Coulomb impurities is predicted to differ significantly from that of most materials. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) can provide detailed information on both the spatial and energy dependence of graphene's electronic structure in the presence of a charged impurity. The design of a hybrid impurity-graphene device, fabricated using controlled deposition of impurities onto a back-gated graphene surface, has enabled several novel methods for controllably tuning graphene’s electronic properties.1-8 Electrostatic gating enables control of the charge carrier density in graphene and the ability to reversibly tune the charge2 and/or molecular5 states of an impurity. This paper outlines the process of fabricating a gate-tunable graphene device decorated with individual Coulomb impurities for combined STM/STS studies.2-5 These studies provide valuable insights into the underlying physics, as well as signposts for designing hybrid graphene devices. PMID:26273961

Scanning tunnel microscopy of semiconductor nanostructures

International Nuclear Information System (INIS)

Eder, C.

1997-09-01

In this work a scanning tunneling microscope (STM) is utilized as a surface sensitive tool for local characterization of internal potential profiles of GaAs/AlGaAs heterostructures. The STM is operated at variable temperatures under ambient conditions, i.e. either in air or in the variable temperature insert of a cryostat. Distinct local differences between current-voltage curves taken on inverted heterostructures, which were patterned by wet chemically etching, are found. The spectroscopic differences can be ascribed to the internal potential profile in the subsurface regions of the sample. Current imaging tunneling spectroscopy (CITS) is applied to study quantum wire regions. It is found that the magnitude of the CITS-current is an indirect measure of edge depletion zones, which are much larger at 4.2 K. Direct measurements of relevant energy levels in quantum structures were obtained by ballistic electron emission microscopy (BEEM). It is shown that this 3-terminal technique is an excellent tool for transport characterization of minibands formed in semiconductor superlattices. Furthermore, low dimensional electron gases are shown to act as very efficient collector electrodes at low temperatures. For the first time, BEEM experiments were performed at 4.2 K. The enhanced thermal resolution at 4.2 K allows an analysis of the relevant scattering processes. It is found that the collector current is strongly influenced by diffusive scattering at the metal/semiconductor interface. (author)

Infrared spectroscopy of molecular submonolayers on surfaces by infrared scanning tunneling microscopy: tetramantane on Au111.

Science.gov (United States)

Pechenezhskiy, Ivan V; Hong, Xiaoping; Nguyen, Giang D; Dahl, Jeremy E P; Carlson, Robert M K; Wang, Feng; Crommie, Michael F

2013-09-20

We have developed a new scanning-tunneling-microscopy-based spectroscopy technique to characterize infrared (IR) absorption of submonolayers of molecules on conducting crystals. The technique employs a scanning tunneling microscope as a precise detector to measure the expansion of a molecule-decorated crystal that is irradiated by IR light from a tunable laser source. Using this technique, we obtain the IR absorption spectra of [121]tetramantane and [123]tetramantane on Au(111). Significant differences between the IR spectra for these two isomers show the power of this new technique to differentiate chemical structures even when single-molecule-resolved scanning tunneling microscopy (STM) images look quite similar. Furthermore, the new technique was found to yield significantly better spectral resolution than STM-based inelastic electron tunneling spectroscopy, and to allow determination of optical absorption cross sections. Compared to IR spectroscopy of bulk tetramantane powders, infrared scanning tunneling microscopy (IRSTM) spectra reveal narrower and blueshifted vibrational peaks for an ordered tetramantane adlayer. Differences between bulk and surface tetramantane vibrational spectra are explained via molecule-molecule interactions.

Dynamic tunneling force microscopy for characterizing electronic trap states in non-conductive surfaces

Energy Technology Data Exchange (ETDEWEB)

Wang, R.; Williams, C. C., E-mail: clayton@physics.utah.edu [Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112 (United States)

2015-09-15

Dynamic tunneling force microscopy (DTFM) is a scanning probe technique for real space mapping and characterization of individual electronic trap states in non-conductive films with atomic scale spatial resolution. The method is based upon the quantum mechanical tunneling of a single electron back and forth between a metallic atomic force microscopy tip and individual trap states in completely non-conducting surface. This single electron shuttling is measured by detecting the electrostatic force induced on the probe tip at the shuttling frequency. In this paper, the physical basis for the DTFM method is unfolded through a physical model and a derivation of the dynamic tunneling signal as a function of several experimental parameters is shown. Experimental data are compared with the theoretical simulations, showing quantitative consistency and verifying the physical model used. The experimental system is described and representative imaging results are shown.

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

DEFF Research Database (Denmark)

Andersen, Jens Enevold Thaulov

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2005-02-01

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

Scanning tunneling microscopy

International Nuclear Information System (INIS)

Binnig, G.; Rohrer, H.

1983-01-01

Based on vacuum tunneling, a novel type of microscope, the scanning tunneling microscope (STM) was developed. It has an unprecedented resolution in real space on an atomic scale. The authors review the important technical features, illustrate the power of the STM for surface topographies and discuss its potential in other areas of science and technology. (Auth.)

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

International Nuclear Information System (INIS)

Aoki, T.; Shudo, K.; Sato, K.; Ohno, S.; Tanaka, M.

2010-01-01

Thermal structural changes of TiO x 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.

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.

The study of optimal conditions of electrochemical etching of tunnel electron microscopy tungsten tips

International Nuclear Information System (INIS)

Anguiano, E.; Aguilar, M.; Olivar, A.I.

1996-01-01

We present the experimental results obtained during the study made in the electrochemical etching of tunneling electron microscopy tungsten tips. The experiments was made using DC and two usual electrolytes: KOH and NaOH. For the tip preparation we used a electrochemical cell with stainless steel cathode and the tungsten wire as anode. the electrodes was introduced in a glass recipient containing the electrolytic solution. We study the effects of applied voltage, polish time, tip length and electrolyte concentration as process relevant parameters. The best condition for tip preparation was obtained with a metallurgical microscope and with a SEM.EDX and Auger analysis was made. The results shown the better tips was made with KOH as electrolyte with a limited concentration range (2-4 normal) and applied voltage (2-6 volts) (Author) 20 refs

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.

Scanning tunneling microscopy study of a newly proposed topological insulator ZrTe{sub 5}

Energy Technology Data Exchange (ETDEWEB)

Kuhn, Timo; Gragnaniello, Luca; Fonin, Mikhail [Universitaet Konstanz (Germany); Autes, Gabriel; Berger, Helmuth; Yazyev, Oleg [Institute of Condensed Matter Physics, Ecole Polytechnique Federale de Lausanne (EPFL), Lausanne (Switzerland); Manzoni, Giulia [Universita degli Studi di Trieste (Italy); Crepaldi, Alberto; Parmigiani, Fulvio [Elettra-Sincrotrone Trieste, Trieste (Italy)

2016-07-01

Topological insulators belong to a new kind of material class that posses robust gapless states inside the insulating bulk gap, which makes them promising candidates for achieving dissipationless transport devices. We present a Scanning tunneling microscopy (STM) and spectroscopy (STS) study on a layered material ZrTe{sub 5}, a promising candidate for a new topological insulator. The crystal structure could clearly be identified in topography images. STM measurements enabled direct imaging of standing waves at steps and defects. The standing waves show a clearly dispersive character. Furthermore STS measurements are in good agreement with density functional theory calculations and reveal Landau quantization with applied magnetic field. Comparison with data obtained by angle resolved photoemission spectroscopy allows for detailed insights into the electronic properties of this material.

Scanning tunneling microscopy studies of glucose oxidase on gold surface

International Nuclear Information System (INIS)

Losic, D.; Shapter, J.G.; Gooding, J.J.

2002-01-01

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2014-11-03

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

Covalently Immobilised Cytochrome C Imaged by In Situ Scanning Tunnelling Microscopy

DEFF Research Database (Denmark)

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

1997-01-01

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

Probing Single Nanometer-scale Particles with Scanning Tunneling Microscopy and Spectroscopies

International Nuclear Information System (INIS)

McCarty, G.S.; Love, J.C.; Kushmerick, J.G.; Charles, L.F.; Keating, C.D.; Toleno, B.J.; Lyn, M.E.; Castleman, A.W.; Natan, M.J.; Weiss, P.S.

1999-01-01

Scanning tunneling microscopy can be used to isolate single particles on surfaces for further study. Local optical and electronic properties coupled with topographic information collected by the scanning tunneling microscope (STM) give insight into the intrinsic properties of the species under study. Since each spectroscopic measurement is done on a single particle, each sample is 'monodisperse', regardless of the degree of heterogeneity of the original preparation. We illustrate this with three example systems - a metal cluster of known atomic structure, metal nanoparticles dispersed from colloid suspensions, and metallocarbohedrenes (Met-Cars) deposited with other reaction products. Au and Ag nanoparticles were imaged using a photon emission STM. The threshold voltage, the lowest bias voltage at which photons are produced, was determined for Au nanoparticles. Electronic spectra of small clusters of Ni atoms on MoS 2 were recorded. Preliminary images of Zr-based Met-Car-containing soot were obtained on Au and MoS 2 substrates and partial electronic spectra were recorded of these possible Met-Car particles

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

Supramolecular chemistry at the liquid/solid interface probed by scanning tunnelling microscopy

NARCIS (Netherlands)

Feyter, S. De; Uji-i, H.; Mamdouh, W.; Miura, A.; Zhang, J.; Jonkheijm, P.; Schenning, A.P.H.J.; Meijer, E.W.; Chen, Z.; Wurthner, F.; Schuurmans, N.; Esch, J. van; Feringa, B.L.; Dulcey, A.E.; Percec, V.; Schryver, F.C. De

2006-01-01

The liquid/solid interface provides an ideal environment to investigate self-assembly phenomena, and scanning tunnelling microscopy (STM) is one of the preferred methodologies to probe the structure and the properties of physisorbed monolayers on the nanoscale. Physisorbed monolayers are of

Molecular electronics of a single photosystem I reaction center: Studies with scanning tunneling microscopy and spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Lee, I.; Lee, J.W.; Warmack, R.J.; Allison, D.P.; Greenbaum, E. [Oak Ridge National Lab., TN (United States)

1995-03-14

Thylakoids and photosystem I (PSI) reaction centers were imaged by scanning tunneling microscopy. The thylakoids were isolated from spinach chloroplasts, and PSI reaction centers were extracted from thylakoid membranes. Because thylakoids are relatively thick nonconductors, they were sputter-coated with Pd/Au before imaging. PSI photosynthetic centers and chemically platinized PSI were investigated without sputter-coating. They were mounted on flat gold substrates that had been treated with mercaptoacetic acid to help bind the proteins. With tunneling spectroscopy, the PSI centers displayed a semiconductor-like response with a band gap of 1.8 eV. Lightly platinized (platinized for 1 hr) centers displayed diode-like conduction that resulted in dramatic contrast changes between images taken with opposite bias voltages. The electronic properties of this system were stable under long-term storage. 42 refs., 7 figs.

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

NARCIS (Netherlands)

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

2011-01-01

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

Frequency shift, damping, and tunneling current coupling with quartz tuning forks in noncontact atomic force microscopy

Science.gov (United States)

Nony, Laurent; Bocquet, Franck; Para, Franck; Loppacher, Christian

2016-09-01

A combined experimental and theoretical approach to the coupling between frequency-shift (Δ f ) , damping, and tunneling current (It) in combined noncontact atomic force microscopy/scanning tunneling microscopy using quartz tuning forks (QTF)-based probes is reported. When brought into oscillating tunneling conditions, the tip located at the QTF prong's end radiates an electromagnetic field which couples to the QTF prong motion via its piezoelectric tensor and loads its electrodes by induction. Our approach explains how those It-related effects ultimately modify the Δ f and the damping measurements. This paradigm to the origin of the coupling between It and the nc-AFM regular signals relies on both the intrinsic piezoelectric nature of the quartz constituting the QTF and its electrodes design.

Preparation of Chemically Etched Tips for Ambient Instructional Scanning Tunneling Microscopy

Science.gov (United States)

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

2010-01-01

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

Single-step electrochemical method for producing very sharp Au scanning tunneling microscopy tips

International Nuclear Information System (INIS)

Gingery, David; Buehlmann, Philippe

2007-01-01

A single-step electrochemical method for making sharp gold scanning tunneling microscopy tips is described. 3.0M NaCl in 1% perchloric acid is compared to several previously reported etchants. The addition of perchloric acid to sodium chloride solutions drastically shortens etching times and is shown by transmission electron microscopy to produce very sharp tips with a mean radius of curvature of 15 nm

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

Directory of Open Access Journals (Sweden)

Thomas König

2011-01-01

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

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

Science.gov (United States)

Lagoute, J; Kawahara, S L; Chacon, C; Repain, V; Girard, Y; Rousset, S

2011-02-02

Several tens of chromium layers were deposited at 250 °C on a Cr(001) surface and investigated by spin-polarized scanning tunneling microscopy (SP-STM), Auger electron spectroscopy (AES) and scanning tunneling spectroscopy (STS). Chromium is found to grow with a mound-like morphology resulting from the stacking of several monolayers which do not uniformly cover the whole surface of the substrate. The terminal plane consists of an irregular array of Cr islands with lateral sizes smaller than 20 × 20 nm(2). Combined AES and STS measurements reveal the presence of a significant amount of segregants prior to and after deposition. A detailed investigation of the surface shows that it consists of two types of patches. Thanks to STS measurements, the two types of area have been identified as being either chromium pure or segregant rich. SP-STM experiments have evidenced that the antiferromagnetic layer coupling remains in the chromium mounds after deposition and is not significantly affected by the presence of the segregants.

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

Energy Technology Data Exchange (ETDEWEB)

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

1999-08-01

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

Scanning tunneling microscopy and spectroscopy on GaN and InGaN surfaces

International Nuclear Information System (INIS)

Krueger, David

2009-01-01

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.)

Scanning tunneling microscopy - STM: history, principle, construction, and related techniques

International Nuclear Information System (INIS)

Ostadal, I.; Sobotik, P.

1998-01-01

The method of scanning tunneling microscopy (STM) is discussed. The principle of STM and some other related methods is highlighted, and spectroscopy using STM is dealt with. A brief summary is given of problems to be solved in microscope design, and the influence of these on the resolution obtained is presented. A comparison of STM with other methods used at present in the physics of thin films and surfaces confirms its irreplaceability

Simultaneous scanning tunneling microscopy and synchrotron X-ray measurements in a gas environment.

Science.gov (United States)

Mom, Rik V; Onderwaater, Willem G; Rost, Marcel J; Jankowski, Maciej; Wenzel, Sabine; Jacobse, Leon; Alkemade, Paul F A; Vandalon, Vincent; van Spronsen, Matthijs A; van Weeren, Matthijs; Crama, Bert; van der Tuijn, Peter; Felici, Roberto; Kessels, Wilhelmus M M; Carlà, Francesco; Frenken, Joost W M; Groot, Irene M N

2017-11-01

A combined X-ray and scanning tunneling microscopy (STM) instrument is presented that enables the local detection of X-ray absorption on surfaces in a gas environment. To suppress the collection of ion currents generated in the gas phase, coaxially shielded STM tips were used. The conductive outer shield of the coaxial tips can be biased to deflect ions away from the tip core. When tunneling, the X-ray-induced current is separated from the regular, 'topographic' tunneling current using a novel high-speed separation scheme. We demonstrate the capabilities of the instrument by measuring the local X-ray-induced current on Au(1 1 1) in 800 mbar Ar. Copyright © 2017 Elsevier B.V. All rights reserved.

Scanning Tunneling Microscopy Analysis of a Pentacene/Graphene/SiC(0001) system

Science.gov (United States)

Yost, Andrew; Suzer, Ozgun; Smerdon, Joseph; Chien, Teyu; Guest, Jeffrey

2014-03-01

A complete understanding of the structure of molecular assemblies, as well as an understanding of donor-acceptor interactions is crucial in the development of emergent molecular electronics technologies such as organic photovoltaics. The pentacene (C22H14) is a good electron donor in Pentacene-C60 system, which is a model system of an organic photovoltaic cell.. Here we present scanning tunneling microscopy studies of the pentacene(Pn) molecule on Graphene(G) that is epitaxially grown on SiC(0001). In addition to the morphologies reported in literature, several new structures of Pn on on G/SiC(0001) were observed with different periodicity and registry both in monolayer and bilayer coverages of molecules on the surface. Preliminary scanning tunneling spectroscopy of the molecular system is also discussed; well-isolated states and a large HOMO-LUMO gap indicate the Pn is weakly coupled to the grapheme and underlying substrate.

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

International Nuclear Information System (INIS)

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

2015-01-01

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

Scanning tunneling microscopy on iron-chalcogenide superconductor Fe(Se, Te) single crystal

International Nuclear Information System (INIS)

Ukita, R.; Sugimoto, A.; Ekino, T.

2011-01-01

We show scanning tunneling microscopy/spectroscopy (STM/STS) results of Fe(Se, Te). STM topography shows square arrangements of spots with the lattice spacing 0.37 nm. Te and Se atoms are randomly distributed in the STM topography. The STM topography of FeTe exhibits clusters of separated iron atoms. We have investigated the iron-chalcogenide superconductor Fe(Se, Te) using a low-temperature scanning tunneling microscopy/spectroscopy (STM/STS) technique. STM topography at 4.9 K shows clear regular square arrangements of spots with the lattice spacing ∼0.37 nm, from which what we observe are attributed to Se or Te atomic plane. In the topography, brighter and darker atomic spots are randomly distributed, which are most probably due to Te and Se atoms, respectively. For the FeTe compound, the topography exhibits clusters of the bright spots probably arising from separated iron atoms distributing over several Te lattice sites. The STS measurements clarify the existence of the large-size gap with 2Δ = 0.4-0.6 eV.

Dielectric breakdown of ultrathin aluminum oxide films induced by scanning tunneling microscopy

International Nuclear Information System (INIS)

Magtoto, N. P.; Niu, C.; Ekstrom, B. M.; Addepalli, S.; Kelber, J. A.

2000-01-01

Dielectric breakdown of 7-Aa-thick Al 2 O 3 (111) films grown on Ni 3 Al(111) under ultrahigh vacuum conditions is induced by increasing the bias voltage on the scanning tunneling microscopy tip under constant current feedback. Breakdown is marked by the precipitous retreat of the tip from the surface, and the formation of an elevated feature in the scanning tunneling microscopy image, typically greater than 5 nm high and ∼100 nm in diameter. Constant height measurements performed at tip/sample distances of 1 nm or less yield no tip/substrate physical interaction, indicating that such features do not result from mass transport. Consistent with this, current/voltage measurements within the affected regions indicate linear behavior, in contrast to a band gap of 1.5 eV observed at unaffected regions of the oxide surface. A threshold electric field value of 11±1 MV cm -1 is required to induce breakdown, in good agreement with extrapolated values from capacitance measurements on thicker oxides. (c) 2000 American Institute of Physics

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

Energy Technology Data Exchange (ETDEWEB)

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

2015-09-21

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

Simultaneous scanning tunneling microscopy and synchrotron X-ray measurements in a gas environment

NARCIS (Netherlands)

Mom, R.V.; Onderwaater, W.G.; Rost, M.J.; Jankowski, M.; Wenzel, S.; Jacobse, L.; Alkemade, P.F.A.; Vandalon, V.; van Spronsen, M.A.; van Weeren, M.; Crama, B.; van der Tuijn, P.; Felici, R.; Kessels, W.M.M.; Carlà, F.; Frenken, J.W.M.; Groot, I.M.N.

2017-01-01

A combined X-ray and scanning tunneling microscopy (STM) instrument is presented that enables the local detection of X-ray absorption on surfaces in a gas environment. To suppress the collection of ion currents generated in the gas phase, coaxially shielded STM tips were used. The conductive outer

Thermovoltages in vacuum tunneling investigated by scanning tunneling microscopy

OpenAIRE

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

1995-01-01

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

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.

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.

Energy gap and surface structure of superconducting diamond films probed by scanning tunneling microscopy

International Nuclear Information System (INIS)

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

2007-01-01

We have performed scanning tunneling microscopy/spectroscopy (STM/STS) experiments on (1 1 1)-oriented epitaxial films of heavily boron-doped diamond at T = 0.47 K. The STM topography shows two kinds of atomic structures: a hydrogenated 1 x 1 structure, C(1 1 1)1 x 1:H, and an amorphous structure. On the C(1 1 1)1 x 1:H region, the tunneling spectra show superconducting property with the energy gap Δ = 0.83 meV. The obtained gap ratio 2Δ/k B T c = 3.57 is consistent with the weak-coupling BCS theory

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

International Nuclear Information System (INIS)

Mauger, S. J. C.; Bocquel, J.; Koenraad, P. M.; Feeser, C. E.; Parashar, N. D.; Wessels, B. W.

2015-01-01

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

Simultaneously measured signals in scanning probe microscopy with a needle sensor: frequency shift and tunneling current.

Science.gov (United States)

Morawski, Ireneusz; Voigtländer, Bert

2010-03-01

We present combined noncontact scanning force microscopy and tunneling current images of a platinum(111) surface obtained by means of a 1 MHz quartz needle sensor. The low-frequency circuit of the tunneling current was combined with a high-frequency signal of the quartz resonator enabling full electrical operation of the sensor. The frequency shift and the tunneling current were detected simultaneously, while the feedback control loop of the topography signal was fed using one of them. In both cases, the free signal that was not connected to the feedback loop reveals proportional-integral controller errorlike behavior, which is governed by the time derivative of the topography signal. A procedure is proposed for determining the mechanical oscillation amplitude by utilizing the tunneling current also including the average tip-sample work function.

Ultrafast photoinduced carrier dynamics in GaNAs probed using femtosecond time-resolved scanning tunnelling microscopy

International Nuclear Information System (INIS)

Terada, Yasuhiko; Aoyama, Masahiro; Kondo, Hiroyuki; Taninaka, Atsushi; Takeuchi, Osamu; Shigekawa, Hidemi

2007-01-01

The combination of scanning tunnelling microscopy (STM) with optical excitation using ultrashort laser pulses enables us, in principle, to simultaneously obtain ultimate spatial and temporal resolutions. We have developed the shaken-pulse-pair-excited STM (SPPX-STM) and succeeded in detecting a weak time-resolved tunnelling current signal from a low-temperature-grown GaNAs sample. To clarify the underlying physics in SPPX-STM measurements, we performed optical pump-probe reflectivity measurements with a wavelength-changeable ultrashort-pulse laser. By comparing the results obtained from the two methods with an analysis based on the nonlinear relationship between the photocarrier density and tunnelling current, we obtained a comprehensive explanation that the photocarrier dynamics is reflected in the SPPX-STM signal through the surface photovoltage effect

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

DEFF Research Database (Denmark)

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

2003-01-01

Theories of in situ scanning tunnelling microscopy (STM) of molecules with redox levels near the substrate and tip Fermi levels point to 'spectroscopic' current-overpotential features. Prominent features require a narrow 'probing tip', i.e. a small bias voltage, eV(bias), compared...

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

International Nuclear Information System (INIS)

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

2014-01-01

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

Spin-filter scanning tunneling microscopy : a novel technique for the analysis of spin polarization on magnetic surfaces and spintronic devices

NARCIS (Netherlands)

Vera Marun, I.J.

2010-01-01

This thesis deals with the development of a versatile technique to measure spin polarization with atomic resolution. A microscopy technique that can measure electronic spin polarization is relevant for characterization of magnetic nanostructures and spintronic devices. Scanning tunneling microscopy

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

DEFF Research Database (Denmark)

Albrecht, Tim; Li, Wu; Haehnel, Wolfgang

2006-01-01

to the tunnelling current, apparently due to slow electron transfer kinetics. As a consequence, STM images of heme-containing and heme-free MOP-C did not reveal any notable differences in apparent height or physical extension. The apparent height of heme-containing MOP-C did not show any dependence on the substrate...... potential being varied around the redox potential of the protein. The mere presence of an accessible molecular energy level is not sufficient to result in detectable tunnelling current modulation. (c) 2006 Elsevier B.V. All rights reserved.......In the present work, we report the electrochemical characterization and in situ scanning tunnelling microscopy (STM) studies of monolayers of an artificial de novo designed heme protein MOP-C, covalently immobilized on modified Au(111) surfaces. The protein forms closely packed monolayers, which...

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

DEFF Research Database (Denmark)

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

2010-01-01

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

Spin-polarized tunneling with GaAs tips in scanning tunneling microscopy

NARCIS (Netherlands)

Prins, M.W.J.; Jansen, R.; Kempen, van H.

1996-01-01

We describe a model as well as experiments on spin-polarized tunneling with the aid of optical spin orientation. This involves tunnel junctions between a magnetic material and gallium arsenide (GaAs), where the latter is optically excited with circularly polarized light in order to generate

Scanning tunneling microscopy and spectroscopy of twisted trilayer graphene

Science.gov (United States)

Zuo, Wei-Jie; Qiao, Jia-Bin; Ma, Dong-Lin; Yin, Long-Jing; Sun, Gan; Zhang, Jun-Yang; Guan, Li-Yang; He, Lin

2018-01-01

Twist, as a simple and unique degree of freedom, could lead to enormous novel quantum phenomena in bilayer graphene. A small rotation angle introduces low-energy van Hove singularities (VHSs) approaching the Fermi level, which result in unusual correlated states in the bilayer graphene. It is reasonable to expect that the twist could also affect the electronic properties of few-layer graphene dramatically. However, such an issue has remained experimentally elusive. Here, by using scanning tunneling microscopy/spectroscopy (STM/STS), we systematically studied a twisted trilayer graphene (TTG) with two different small twist angles between adjacent layers. Two sets of VHSs, originating from the two twist angles, were observed in the TTG, indicating that the TTG could be simply regarded as a combination of two different twisted bilayers of graphene. By using high-resolution STS, we observed a split of the VHSs and directly imaged the spatial symmetry breaking of electronic states around the VHSs. These results suggest that electron-electron interactions play an important role in affecting the electronic properties of graphene systems with low-energy VHSs.

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; Pedersen, Marianne Vind

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...

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

DEFF Research Database (Denmark)

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

2003-01-01

Theories of in situ scanning tunnelling microscopy (STM) of molecules with redox levels near the substrate and tip Fermi levels point to 'spectroscopic' current-overpotential features. Prominent features require a narrow 'probing tip', i.e. a small bias voltage, eV(bias), compared...... a broad tunnelling current-overpotential range at a constant (large) bias voltage of +0.2 V. The current is found to be constant over a 0.25 V overpotential range, which covers roughly the range where the oxidised and reduced redox levels are located within the energy tip. STM contrast and apparent...... of previous theoretical work on in situ STM of redox molecules, to large bias voltages, \\eV(bias)\\ > E-r. Large bias voltages give tunnelling contrasts independent of the overpotential over a broad range, as both the oxidised and reduced redox levels are located within the 'energy tip' between the substrate...

Ballistic current transport studies of ferromagnetic multilayer films and tunnel junctions (invited)

International Nuclear Information System (INIS)

Rippard, W. H.; Perrella, A. C.; Buhrman, R. A.

2001-01-01

Three applications of ballistic electron microscopy are used to study, with nanometer-scale resolution, the magnetic and electronic properties of magnetic multilayer thin films and tunnel junctions. First, the capabilities of ballistic electron magnetic microscopy are demonstrated through an investigation of the switching behavior of continuous Ni 80 Fe 20 /Cu/Co trilayer films in the presence of an applied magnetic field. Next, the ballistic, hot-electron transport properties of Co films and multilayers formed by thermal evaporation and magnetron sputtering are compared, a comparison which reveals significant differences in the ballistic transmissivity of thin film multilayers formed by the two techniques. Finally, the electronic properties of thin aluminum oxide tunnel junctions formed by thermal evaporation and sputter deposition are investigated. Here the ballistic electron microscopy studies yield a direct measurement of the barrier height of the aluminum oxide barriers, a result that is invariant over a wide range of oxidation conditions. [copyright] 2001 American Institute of Physics

Nano-contact microscopy of supracrystals

Directory of Open Access Journals (Sweden)

Adam Sweetman

2015-05-01

Full Text Available Background: Highly ordered three-dimensional colloidal crystals (supracrystals comprised of 7.4 nm diameter Au nanocrystals (with a 5% size dispersion have been imaged and analysed using a combination of scanning tunnelling microscopy and dynamic force microscopy.Results: By exploring the evolution of both the force and tunnel current with respect to tip–sample separation, we arrive at the surprising finding that single nanocrystal resolution is readily obtained in tunnelling microscopy images acquired more than 1 nm into the repulsive (i.e., positive force regime of the probe–nanocrystal interaction potential. Constant height force microscopy has been used to map tip–sample interactions in this regime, revealing inhomogeneities which arise from the convolution of the tip structure with the ligand distribution at the nanocrystal surface.Conclusion: Our combined STM–AFM measurements show that the contrast mechanism underpinning high resolution imaging of nanoparticle supracrystals involves a form of nanoscale contact imaging, rather than the through-vacuum tunnelling which underpins traditional tunnelling microscopy and spectroscopy.

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

Science.gov (United States)

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

2014-04-01

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

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

Energy Technology Data Exchange (ETDEWEB)

Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R., E-mail: smitha2@ohio.edu [Department of Physics and Astronomy, Nanoscale and Quantum Phenomena Institute, Ohio University, Athens, Ohio 45701 (United States)

2014-04-15

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

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)

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

2014-01-01

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

Simplified tunnelling current calculation for MOS structures with ultra-thin oxides for conductive atomic force microscopy investigations

International Nuclear Information System (INIS)

Frammelsberger, Werner; Benstetter, Guenther; Stamp, Richard; Kiely, Janice; Schweinboeck, Thomas

2005-01-01

As charge tunnelling through thin and ultra-thin silicon dioxide layers is regarded as the driving force for MOS device degradation the determination and characterisation of electrically week spots is of paramount importance for device reliability and failure analysis. Conductive atomic force microscopy (C-AFM) is able to address this issue with a spatial resolution smaller than the expected breakdown spot. For the determination of the electrically active oxide thickness in practice an easy to use model with sufficient accuracy and which is largely independent of the oxide thickness is required. In this work a simplified method is presented that meets these demands. The electrically active oxide thickness is determined by matching of C-AFM voltage-current curves and a tunnelling current model, which is based on an analytical tunnelling current approximation. The model holds for both the Fowler-Nordheim tunnelling and the direct tunnelling regime with one single tunnelling parameter set. The results show good agreement with macroscopic measurements for gate voltages larger than approximately 0.5-1 V, and with microscopic C-AFM measurements. For this reason arbitrary oxides in the DT and the FNT regime may be analysed with high lateral resolution by C-AFM, without the need of a preselection of the tunnelling regime to be addressed

In silico simulations of tunneling barrier measurements for molecular orbital-mediated junctions: A molecular orbital theory approach to scanning tunneling microscopy

Energy Technology Data Exchange (ETDEWEB)

Terryn, Raymond J.; Sriraman, Krishnan; Olson, Joel A., E-mail: jolson@fit.edu; Baum, J. Clayton, E-mail: cbaum@fit.edu [Department of Chemistry, Florida Institute of Technology, 150 West University Boulevard, Melbourne, Florida 32901 (United States); Novak, Mark J. [Department of Chemistry and Applied Biological Sciences, South Dakota School of Mines and Technology, 501 E. Saint Joseph Street, Rapid City, South Dakota 57701 (United States)

2016-09-15

A new simulator for scanning tunneling microscopy (STM) is presented based on the linear combination of atomic orbitals molecular orbital (LCAO-MO) approximation for the effective tunneling Hamiltonian, which leads to the convolution integral when applied to the tip interaction with the sample. This approach intrinsically includes the structure of the STM tip. Through this mechanical emulation and the tip-inclusive convolution model, dI/dz images for molecular orbitals (which are closely associated with apparent barrier height, ϕ{sub ap}) are reported for the first time. For molecular adsorbates whose experimental topographic images correspond well to isolated-molecule quantum chemistry calculations, the simulator makes accurate predictions, as illustrated by various cases. Distortions in these images due to the tip are shown to be in accord with those observed experimentally and predicted by other ab initio considerations of tip structure. Simulations of the tunneling current dI/dz images are in strong agreement with experiment. The theoretical framework provides a solid foundation which may be applied to LCAO cluster models of adsorbate–substrate systems, and is extendable to emulate several aspects of functional STM operation.

In silico simulations of tunneling barrier measurements for molecular orbital-mediated junctions: A molecular orbital theory approach to scanning tunneling microscopy

International Nuclear Information System (INIS)

Terryn, Raymond J.; Sriraman, Krishnan; Olson, Joel A.; Baum, J. Clayton; Novak, Mark J.

2016-01-01

A new simulator for scanning tunneling microscopy (STM) is presented based on the linear combination of atomic orbitals molecular orbital (LCAO-MO) approximation for the effective tunneling Hamiltonian, which leads to the convolution integral when applied to the tip interaction with the sample. This approach intrinsically includes the structure of the STM tip. Through this mechanical emulation and the tip-inclusive convolution model, dI/dz images for molecular orbitals (which are closely associated with apparent barrier height, ϕ_a_p) are reported for the first time. For molecular adsorbates whose experimental topographic images correspond well to isolated-molecule quantum chemistry calculations, the simulator makes accurate predictions, as illustrated by various cases. Distortions in these images due to the tip are shown to be in accord with those observed experimentally and predicted by other ab initio considerations of tip structure. Simulations of the tunneling current dI/dz images are in strong agreement with experiment. The theoretical framework provides a solid foundation which may be applied to LCAO cluster models of adsorbate–substrate systems, and is extendable to emulate several aspects of functional STM operation.

An experimental study of furan adsorption and decomposition on vicinal palladium surfaces using scanning tunneling microscopy

Science.gov (United States)

Loui, A.; Chiang, S.

2018-04-01

The intact adsorption and decomposition of furan (C4H4O) on vicinal palladium surfaces with (111)-oriented terraces has been studied by scanning tunneling microscopy (STM) over a range of temperatures. STM images at 225 K show that furan molecules lie flat and prefer to adsorb at upper step edges. At 225 K, furan molecules adsorbed on "narrow" terraces of 20 to 45 Å in width appear to diffuse more readily than those adsorbed on "wide" terraces of 160 to 220 Å. A distinct population of smaller features appears in STM images on "narrow" terraces at 288 K and on "wide" terraces at 415 K and is identified with the C3H3 decomposition product, agreeing with prior studies which demonstrated that furan dissociates on Pd(111) to yield carbon monoxide (CO) and a C3H3 moiety in the 280 to 320 K range. Based on our direct visualization of this reaction using STM, we propose a spatial mechanism in which adsorption of furan at upper step edges allows catalysis of the dissociation, followed by diffusion of the product to lower step edges.

A scanning tunneling microscopy based potentiometry technique and its application to the local sensing of the spin Hall effect

Directory of Open Access Journals (Sweden)

Ting Xie

2017-12-01

Full Text Available A scanning tunneling microscopy based potentiometry technique for the measurements of the local surface electric potential is presented. A voltage compensation circuit based on this potentiometry technique is developed and employed to maintain a desired tunneling voltage independent of the bias current flow through the film. The application of this potentiometry technique to the local sensing of the spin Hall effect is outlined and some experimental results are reported.

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

DEFF Research Database (Denmark)

Hansen, Allan Glargaard; Salvatore, Princia; Karlsen, K.

2013-01-01

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......We have studied adsorption and electrochemical electron transfer of several 13- and 15-base DNA and UNA (unlocked nucleic acids) oligonucleotides (ONs) linked to Au(111)-electrode surfaces via a 50-C6-SH group using cyclic voltammetry (CV) and scanning tunnelling microscopy in aqueous buffer under...

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.

Spectroscopic scanning tunneling microscopy insights into Fe-based superconductors

International Nuclear Information System (INIS)

Hoffman, Jennifer E

2011-01-01

In the first three years since the discovery of Fe-based high T c superconductors, scanning tunneling microscopy (STM) and spectroscopy have shed light on three important questions. First, STM has demonstrated the complexity of the pairing symmetry in Fe-based materials. Phase-sensitive quasiparticle interference (QPI) imaging and low temperature spectroscopy have shown that the pairing order parameter varies from nodal to nodeless s± within a single family, FeTe 1-x Se x . Second, STM has imaged C4 → C2 symmetry breaking in the electronic states of both parent and superconducting materials. As a local probe, STM is in a strong position to understand the interactions between these broken symmetry states and superconductivity. Finally, STM has been used to image the vortex state, giving insights into the technical problem of vortex pinning, and the fundamental problem of the competing states introduced when superconductivity is locally quenched by a magnetic field. Here we give a pedagogical introduction to STM and QPI imaging, discuss the specific challenges associated with extracting bulk properties from the study of surfaces, and report on progress made in understanding Fe-based superconductors using STM techniques.

Structure, Mobility, and Composition of Transition Metal Catalyst Surfaces. High-Pressure Scanning Tunneling Microscopy and Ambient-Pressure X-ray Photoelectron Spectroscopy Studies

Energy Technology Data Exchange (ETDEWEB)

Zhu, Zhongwei [Univ. of California, Berkeley, CA (United States)

2013-12-06

Surface structure, mobility, and composition of transition metal catalysts were studied by high-pressure scanning tunneling microscopy (HP-STM) and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) at high gas pressures. HP-STM makes it possible to determine the atomic or molecular rearrangement at catalyst surfaces, particularly at the low-coordinated active surface sites. AP-XPS monitors changes in elemental composition and chemical states of catalysts in response to variations in gas environments. Stepped Pt and Cu single crystals, the hexagonally reconstructed Pt(100) single crystal, and Pt-based bimetallic nanoparticles with controlled size, shape and composition, were employed as the model catalysts for experiments in this thesis.

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

International Nuclear Information System (INIS)

Cummings, M.L.; Chien, T.Y.; Preissner, C.; Madhavan, V.; Diesing, D.; Bode, M.; Freeland, J.W.; Rose, V.

2012-01-01

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.

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.

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

Directory of Open Access Journals (Sweden)

Giulia Serrano

2015-02-01

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2013-08-15

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

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

International Nuclear Information System (INIS)

Sander, Dirk; Oka, Hirofumi; Corbetta, Marco; Stepanyuk, Valeri; Kirschner, Jürgen

2013-01-01

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

Electronic structure classifications using scanning tunneling microscopy conductance imaging

International Nuclear Information System (INIS)

Horn, K.M.; Swartzentruber, B.S.; Osbourn, G.C.; Bouchard, A.; Bartholomew, J.W.

1998-01-01

The electronic structure of atomic surfaces is imaged by applying multivariate image classification techniques to multibias conductance data measured using scanning tunneling microscopy. Image pixels are grouped into classes according to shared conductance characteristics. The image pixels, when color coded by class, produce an image that chemically distinguishes surface electronic features over the entire area of a multibias conductance image. Such open-quotes classedclose quotes images reveal surface features not always evident in a topograph. This article describes the experimental technique used to record multibias conductance images, how image pixels are grouped in a mathematical, classification space, how a computed grouping algorithm can be employed to group pixels with similar conductance characteristics in any number of dimensions, and finally how the quality of the resulting classed images can be evaluated using a computed, combinatorial analysis of the full dimensional space in which the classification is performed. copyright 1998 American Institute of Physics

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

International Nuclear Information System (INIS)

Satterley, Christopher J; Perdigao, LuIs M A; Saywell, Alex; Magnano, Graziano; Rienzo, Anna; Mayor, Louise C; Dhanak, Vinod R; Beton, Peter H; O'Shea, James N

2007-01-01

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

Insulating nanoparticles on YBa2Cu3O7-δ thin films revealed by comparison of atomic force and scanning tunneling microscopy

International Nuclear Information System (INIS)

Thomson, R.E.; Moreland, J.; Missert, N.; Rudman, D.A.; Sanders, S.C.; Cole, B.F.

1993-01-01

The surface topography of YBa 2 Cu 3 O 7-δ thin films has been studied with both atomic force microscopy (AFM) and scanning tunneling microscopy (STM). The AFM images reveal a high density of small distinct nanoparticles, 10--50 nm across and 5--20 nm high, which do not appear in STM images of the same samples. In addition, we have shown that scanning the STM tip across the surface breaks off these particles and moves them to the edge of the scanned area, where they can later be imaged with the AFM

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

International Nuclear Information System (INIS)

Liao, Q.; Zhang, H.J.; Wu, K.; Li, H.Y.; Bao, S.N.; He, P.

2010-01-01

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2016-02-08

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

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

International Nuclear Information System (INIS)

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

2016-01-01

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

Topography and local modification of the HoBa2Cu3O/sub 7-//sub x/(001) surface using scanning tunneling microscopy

International Nuclear Information System (INIS)

Heinzelmann, H.; Anselmetti, D.; Wiesendanger, R.; Guentherodt, H.; Kaldis, E.; Wisard, A.

1988-01-01

The topography of the (001) surface of a high T/sub c/ superconducting HoBa 2 Cu 3 O/sub 7-//sub x/ single crystal was investigated in air using scanning tunneling microscopy. We found large, flat terraces separated by growth steps. The heights of these steps correspond to multiples of the c-axis lattice constant of 11.7 A of the perovskite structure. These steps have been verified by atomic force microscopy. On a smaller scale the flat terraces showed some fine structure with a corrugation height of 4 to 5 A and a lateral extent of several nanometers. In addition, we succeeded in creating nanometer-sized structures by increasing the sample bias voltage and tunneling current

Double capping of molecular beam epitaxy grown InAs/InP quantum dots studied by cross-sectional scanning tunneling microscopy

International Nuclear Information System (INIS)

Ulloa, J. M.; Koenraad, P. M.; Gapihan, E.; Letoublon, A.; Bertru, N.

2007-01-01

Cross-sectional scanning tunneling microscopy was used to study at the atomic scale the double capping process of self-assembled InAs/InP quantum dots (QDs) grown by molecular beam epitaxy on a (311)B substrate. The thickness of the first capping layer is found to play a mayor role in determining the final results of the process. For first capping layers up to 3.5 nm, the height of the QDs correspond to the thickness of the first capping layer. Nevertheless, for thicknesses higher than 3.5 nm, a reduction in the dot height compared to the thickness of the first capping layer is observed. These results are interpreted in terms of a transition from a double capping to a classical capping process when the first capping layer is thick enough to completely cover the dots

Facile synthesis and electron transport properties of NiO nanostructures investigated by scanning tunneling microscopy

Directory of Open Access Journals (Sweden)

Govind Mallick

2017-08-01

Full Text Available Due to their unique chemical, thermal, electronic and photonic properties, low -dimensional transition metal oxides, especially NiO, have attracted great deal of attention for potential applications in a wide range of technologies, such as, sensors, electrochromic coatings and self-healing materials. However, their synthesis involves multi-step complex procedures that in addition to being expensive, further introduce impurities. Here we present a low cost facile approach to synthesize uniform size NiO nanoparticles (NPs from hydrothermally grown Ni(OH2. Detailed transmission electron microscopic analysis reveal the average size of NiO NPs to be around 29 nm. The dimension of NiO NP is also corroborated by the small area scanning tunneling microscope (STM measurements. Further, we investigate electron transport characteristics of newly synthesized Ni(OH2 and NiO nanoparticles on p-type Si substrate using scanning tunneling microscopy. The conductivity of Ni(OH2 and NiO are determined to be 1.46x10-3 S/cm and 2.37x10-5 S/cm, respectively. The NiO NPs exhibit a lower voltage window (∼0.7 V electron tunneling than the parent Ni(OH2.

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

DEFF Research Database (Denmark)

Tison, Yann; Nielsen, Kenneth; Mowbray, Duncan J.

2012-01-01

–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...

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

Study of Perylenetetracarboxylic Acid Dimethylimide Films by Cyclic Thermal Desorption and Scanning Probe Microscopy

Science.gov (United States)

Pochtennyi, A. E.; Lappo, A. N.; Il'yushonok, I. P.

2018-02-01

Some results of studying the direct-current (DC) conductivity of perylenetetracarboxylic acid dimethylimide films by cyclic oxygen thermal desorption are presented. The microscopic parameters of hopping electron transport over localized impurity and intrinsic states were determined. The bandgap width and the sign of major current carriers were determined by scanning probe microscopy methods (atomic force microscopy, scanning probe spectroscopy, and photoassisted Kelvin probe force microscopy). The possibility of the application of photoassisted scanning tunneling microscopy for the nanoscale phase analysis of photoconductive films is discussed.

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

International Nuclear Information System (INIS)

Hagmann, M.J.

1994-01-01

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 10 11 W/m 2 would be required at several wavelengths from 1 to 10 μm. 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

An ultrahigh-vacuum cryostat for simultaneous scanning tunneling microscopy and magneto-transport measurements down to 400 mK.

Science.gov (United States)

Liebmann, Marcus; Bindel, Jan Raphael; Pezzotta, Mike; Becker, Stefan; Muckel, Florian; Johnsen, Tjorven; Saunus, Christian; Ast, Christian R; Morgenstern, Markus

2017-12-01

We present the design and calibration measurements of a scanning tunneling microscope setup in a 3 He ultrahigh-vacuum cryostat operating at 400 mK with a hold time of 10 days. With 2.70 m in height and 4.70 m free space needed for assembly, the cryostat fits in a one-story lab building. The microscope features optical access, an xy table, in situ tip and sample exchange, and enough contacts to facilitate atomic force microscopy in tuning fork operation and simultaneous magneto-transport measurements on the sample. Hence, it enables scanning tunneling spectroscopy on microstructured samples which are tuned into preselected transport regimes. A superconducting magnet provides a perpendicular field of up to 14 T. The vertical noise of the scanning tunneling microscope amounts to 1 pm rms within a 700 Hz bandwidth. Tunneling spectroscopy using one superconducting electrode revealed an energy resolution of 120 μeV. Data on tip-sample Josephson contacts yield an even smaller feature size of 60 μeV, implying that the system operates close to the physical noise limit.

An ultrahigh-vacuum cryostat for simultaneous scanning tunneling microscopy and magneto-transport measurements down to 400 mK

Science.gov (United States)

Liebmann, Marcus; Bindel, Jan Raphael; Pezzotta, Mike; Becker, Stefan; Muckel, Florian; Johnsen, Tjorven; Saunus, Christian; Ast, Christian R.; Morgenstern, Markus

2017-12-01

We present the design and calibration measurements of a scanning tunneling microscope setup in a 3He ultrahigh-vacuum cryostat operating at 400 mK with a hold time of 10 days. With 2.70 m in height and 4.70 m free space needed for assembly, the cryostat fits in a one-story lab building. The microscope features optical access, an xy table, in situ tip and sample exchange, and enough contacts to facilitate atomic force microscopy in tuning fork operation and simultaneous magneto-transport measurements on the sample. Hence, it enables scanning tunneling spectroscopy on microstructured samples which are tuned into preselected transport regimes. A superconducting magnet provides a perpendicular field of up to 14 T. The vertical noise of the scanning tunneling microscope amounts to 1 pmrms within a 700 Hz bandwidth. Tunneling spectroscopy using one superconducting electrode revealed an energy resolution of 120 μeV. Data on tip-sample Josephson contacts yield an even smaller feature size of 60 μeV, implying that the system operates close to the physical noise limit.

Well-ordered structure of methylene blue monolayers on Au(111) surface: electrochemical scanning tunneling microscopy studies.

Science.gov (United States)

Song, Yonghai; Wang, Li

2009-02-01

Well-ordered structure of methylene blue (MB) monolayers on Au(111) surface has been successfully obtained by controlling the substrate potential. Electrochemical scanning tunneling microscopy (ECSTM) examined the monolayers of MB on Au(111) in 0.1 M HClO(4) and showed long-range ordered, interweaved arrays of MB with quadratic symmetry on the substrate in the potential range of double-layer charging. High-resolution ECSTM image further revealed the details of the MB monolayers structure of c(5 x 5 radical 3)rect and the flat-lying orientation of ad-molecules. The dependence of molecular organization on the substrate potential and the formation mechanism of well-ordered structure on Au(111) surface were investigated in detail. The obtained well-ordered structure at the interface between a metal and an aqueous electrolyte might possibly be used as high-density device for signal memory and templates for the advanced nanopatterning of surfaces. (c) 2008 Wiley-Liss, Inc.

Surface polymerization of (3,4-ethylenedioxythiophene) probed by in situ scanning tunneling microscopy on Au(111) in ionic liquids.

Science.gov (United States)

Ahmad, Shahzada; Carstens, Timo; Berger, Rüdiger; Butt, Hans-Jürgen; Endres, Frank

2011-01-01

The electropolymerization of 3,4-ethylenedioxythiophene (EDOT) to poly(3,4-ethylenedioxythiophene) (PEDOT) was investigated in the air and water-stable ionic liquids 1-hexyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate [HMIm]FAP and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) amide [EMIm]TFSA. In situ scanning tunnelling microscopy (STM) results show that the electropolymerization of EDOT in the ionic liquid can be probed on the nanoscale. In contrast to present understanding, it was observed that the EDOT can be oxidised in ionic liquids well below its oxidation potential and the under potential growth of polymer was visualized by in situ STM. These results serve as the first study to confirm the under potential growth of conducting polymers in ionic liquids. Furthermore, ex situ microscopy measurements were performed. Quite a high current of 670 nA was observed on the nanoscale by conductive scanning force microscopy (CSFM).

Scanning tunnelling microscopy of a foldamer prototype at the liquid/solid interface : water/Au(111) versus 1-octanol/graphite

NARCIS (Netherlands)

Klymchenko, Andrey S.; Schuurmans, Norbert; van der Auweraer, Mark; Feringa, Ben L.; van Esch, Jan; De Feyter, Steven

2006-01-01

We report the design and synthesis of a catechol based foldamer containing amide functionalized alkyl chains, and its monolayer formation at the liquid/solid interface. By scanning tunnelling microscopy, both at the 1-octanol/graphite interface as well as at the water/Au( 111) interface, the

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

Energy Technology Data Exchange (ETDEWEB)

Chang, Hao, E-mail: hc000211@ohio.edu [Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States); Nanoscale and Quantum Phenomena Institute, Physics & Astronomy Department, Ohio University, Athens, Ohio 45701 (United States); Cummings, Marvin; Shirato, Nozomi; Stripe, Benjamin; Preissner, Curt; Freeland, John W. [Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States); Rosenmann, Daniel [Center for Nanoscale Materials, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States); Kersell, Heath; Hla, Saw-Wai [Nanoscale and Quantum Phenomena Institute, Physics & Astronomy Department, Ohio University, Athens, Ohio 45701 (United States); Center for Nanoscale Materials, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States); Rose, Volker, E-mail: vrose@anl.gov [Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States); Center for Nanoscale Materials, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States)

2016-01-28

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

Magnetic tunnel junctions with monolayer hexagonal boron nitride tunnel barriers

Energy Technology Data Exchange (ETDEWEB)

Piquemal-Banci, M.; Galceran, R.; Bouzehouane, K.; Anane, A.; Petroff, F.; Fert, A.; Dlubak, B.; Seneor, P. [Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, Palaiseau 91767 (France); Caneva, S.; Martin, M.-B.; Weatherup, R. S.; Kidambi, P. R.; Robertson, J.; Hofmann, S. [Department of Engineering, University of Cambridge, Cambridge CB21PZ (United Kingdom); Xavier, S. [Thales Research and Technology, 1 avenue Augustin Fresnel, Palaiseau 91767 (France)

2016-03-07

We report on the integration of atomically thin 2D insulating hexagonal boron nitride (h-BN) tunnel barriers into Co/h-BN/Fe magnetic tunnel junctions (MTJs). The h-BN monolayer is directly grown by chemical vapor deposition on Fe. The Conductive Tip Atomic Force Microscopy (CT-AFM) measurements reveal the homogeneity of the tunnel behavior of our h-BN layers. As expected for tunneling, the resistance depends exponentially on the number of h-BN layers. The h-BN monolayer properties are also characterized through integration into complete MTJ devices. A Tunnel Magnetoresistance of up to 6% is observed for a MTJ based on a single atomically thin h-BN layer.

Transfer doping of single isolated nanodiamonds, studied by scanning probe microscopy techniques.

Science.gov (United States)

Bolker, Asaf; Saguy, Cecile; Kalish, Rafi

2014-09-26

The transfer doping of diamond surfaces has been applied in various novel two-dimensional electronic devices. Its extension to nanodiamonds (ND) is essential for ND-based applications in many fields. In particular, understanding the influence of the crystallite size on transfer doping is desirable. Here, we report the results of a detailed study of the electronic energetic band structure of single, isolated transfer-doped nanodiamonds with nanometric resolution using a combination of scanning tunneling spectroscopy and Kelvin force microscopy measurements. The results show how the band gap, the valence band maximum, the electron affinity and the work function all depend on the ND's size and nanoparticle surface properties. The present analysis, which combines information from both scanning tunneling spectroscopy and Kelvin force microscopy, should be applicable to any nanoparticle or surface that can be measured with scanning probe techniques.

Transfer doping of single isolated nanodiamonds, studied by scanning probe microscopy techniques

Science.gov (United States)

Bolker, Asaf; Saguy, Cecile; Kalish, Rafi

2014-09-01

The transfer doping of diamond surfaces has been applied in various novel two-dimensional electronic devices. Its extension to nanodiamonds (ND) is essential for ND-based applications in many fields. In particular, understanding the influence of the crystallite size on transfer doping is desirable. Here, we report the results of a detailed study of the electronic energetic band structure of single, isolated transfer-doped nanodiamonds with nanometric resolution using a combination of scanning tunneling spectroscopy and Kelvin force microscopy measurements. The results show how the band gap, the valence band maximum, the electron affinity and the work function all depend on the ND’s size and nanoparticle surface properties. The present analysis, which combines information from both scanning tunneling spectroscopy and Kelvin force microscopy, should be applicable to any nanoparticle or surface that can be measured with scanning probe techniques.

Transfer doping of single isolated nanodiamonds, studied by scanning probe microscopy techniques

International Nuclear Information System (INIS)

Bolker, Asaf; Kalish, Rafi; Saguy, Cecile

2014-01-01

The transfer doping of diamond surfaces has been applied in various novel two-dimensional electronic devices. Its extension to nanodiamonds (ND) is essential for ND-based applications in many fields. In particular, understanding the influence of the crystallite size on transfer doping is desirable. Here, we report the results of a detailed study of the electronic energetic band structure of single, isolated transfer-doped nanodiamonds with nanometric resolution using a combination of scanning tunneling spectroscopy and Kelvin force microscopy measurements. The results show how the band gap, the valence band maximum, the electron affinity and the work function all depend on the ND’s size and nanoparticle surface properties. The present analysis, which combines information from both scanning tunneling spectroscopy and Kelvin force microscopy, should be applicable to any nanoparticle or surface that can be measured with scanning probe techniques. (paper)

Local X-ray magnetic circular dichroism study of Fe/Cu(111) using a tunneling smart tip

Energy Technology Data Exchange (ETDEWEB)

DiLullo, Andrew; Shirato, Nozomi; Cummings, Marvin [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Kersell, Heath; Chang, Hao [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Ohio University, Athens, OH 45701 (United States); Rosenmann, Daniel; Miller, Dean; Freeland, John W. [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Hla, Saw-Wai [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Ohio University, Athens, OH 45701 (United States); Rose, Volker, E-mail: vrose@anl.gov [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States)

2016-01-28

A tunneling smart tip of a synchrotron X-ray scanning tunneling microscope provides simultaneously localized topographic, elemental and magnetic information. Localized spectroscopy with simultaneous topographic, elemental and magnetic information is presented. A synchrotron X-ray scanning tunneling microscope has been employed for the local study of the X-ray magnetic circular dichroism at the Fe L{sub 2,3}-edges of a thin iron film grown on Cu(111). Polarization-dependent X-ray absorption spectra have been obtained through a tunneling smart tip that serves as a photoelectron detector. In contrast to conventional spin-polarized scanning tunneling microscopy, X-ray excitations provide magnetic contrast even with a non-magnetic tip. Intensity variations in the photoexcited tip current point to chemical variations within a single magnetic Fe domain.

Band Alignment in MoS2/WS2 Transition Metal Dichalcogenide Heterostructures Probed by Scanning Tunneling Microscopy and Spectroscopy.

Science.gov (United States)

Hill, Heather M; Rigosi, Albert F; Rim, Kwang Taeg; Flynn, George W; Heinz, Tony F

2016-08-10

Using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS), we examine the electronic structure of transition metal dichalcogenide heterostructures (TMDCHs) composed of monolayers of MoS2 and WS2. STS data are obtained for heterostructures of varying stacking configuration as well as the individual monolayers. Analysis of the tunneling spectra includes the influence of finite sample temperature, yield information about the quasi-particle bandgaps, and the band alignment of MoS2 and WS2. We report the band gaps of MoS2 (2.16 ± 0.04 eV) and WS2 (2.38 ± 0.06 eV) in the materials as measured on the heterostructure regions and the general type II band alignment for the heterostructure, which shows an interfacial band gap of 1.45 ± 0.06 eV.

Real-Space Analysis of Scanning Tunneling Microscopy Topography Datasets Using Sparse Modeling Approach

Science.gov (United States)

Miyama, Masamichi J.; Hukushima, Koji

2018-04-01

A sparse modeling approach is proposed for analyzing scanning tunneling microscopy topography data, which contain numerous peaks originating from the electron density of surface atoms and/or impurities. The method, based on the relevance vector machine with L1 regularization and k-means clustering, enables separation of the peaks and peak center positioning with accuracy beyond the resolution of the measurement grid. The validity and efficiency of the proposed method are demonstrated using synthetic data in comparison with the conventional least-squares method. An application of the proposed method to experimental data of a metallic oxide thin-film clearly indicates the existence of defects and corresponding local lattice distortions.

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

International Nuclear Information System (INIS)

Tartaglini, E.; Verhagen, T.G.A.; Galli, F.; Trouwborst, M.L.; Aarts, J.; Van-Ruitebbeek, J.M.; Muller, R.; Shiota, T.

2013-01-01

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

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

DEFF Research Database (Denmark)

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

2006-01-01

The atomic-scale structure of naturally occurring screw dislocations intersecting a Au(111) surface has been investigated both experimentally by scanning tunneling microscopy (STM) and theoretically using molecular dynamics (MD) simulations. The step profiles of 166 dislocations were measured using...... STM. Many of them exhibit noninteger step-height plateaus with different widths. Clear evidence was found for the existence of two different populations at the surface with distinct (narrowed or widened) partial-splitting widths. All findings are fully confirmed by the MD simulations. The MD...... simulations extend the STM-, i.e., surface-, investigation to the subsurface region. Due to this additional insight, we can explain the different partial-splitting widths as the result of the interaction between the partial dislocations and the surface....

Tip-Loading, Force-Dependent Tunneling Behavior in Alkanethiol Self-Assembled Monolayers Studied Through Conducting Atomic Force Microscopy

International Nuclear Information System (INIS)

Lee, Min Hyung; Song, Hyun Wook

2013-01-01

The force-dependent tunneling transport in metal/alkanethiol/metal junctions was examined using CAFM. Tunneling current and current density through alkanethiol SAMs increased with increasing tip-loading force in CAFM, which suggests that a potential change in geometry of the molecules under the tip loads influences the transport properties of alkanethiol SAMs. Enhanced intermolecular tunneling transport in the tilted molecular configuration under tip-loading effect is likely responsible for such an increase in tunneling current density. We also demonstrated that through-bond tunneling is a more efficient pathway in alkanethiol SAMs than are intermolecular chain-to-chain pathways, by demonstrating a dependence of current density on the associated tunneling distances. We report a tip-loading, force-dependent tunneling behavior in alkanethiol SAMs using CAFM. A variable tip-loading force applies to alkanethiol SAMs with a standard AFM feedback, and current(I)-voltage(V) characteristics are simultaneously measured while varying the loading forces. In particular, we observe how a tip-loading force in CAFM influences the transport properties of alkanethiol SAMs

Cross-sectional scanning tunneling microscopy of antiphase boundaries in epitaxially grown GaP layers on Si(001)

Energy Technology Data Exchange (ETDEWEB)

Prohl, Christopher; Lenz, Andrea, E-mail: alenz@physik.tu-berlin.de [Technische Universität Berlin, Institut für Festkörperphysik, 10623 Berlin (Germany); Döscher, Henning; Kleinschmidt, Peter; Hannappel, Thomas [Helmholtz Center Berlin for Materials and Energy, 14109 Berlin (Germany)

2016-05-15

In a fundamental cross-sectional scanning tunneling microscopy investigation on epitaxially grown GaP layers on a Si(001) substrate, differently oriented antiphase boundaries are studied. They can be identified by a specific contrast and by surface step edges starting/ending at the position of an antiphase boundary. Moreover, a change in the atomic position of P and Ga atoms along the direction of growth is observed in agreement with the structure model of antiphase boundaries in the GaP lattice. This investigation opens the perspective to reveal the orientation and position of the antiphase boundaries at the atomic scale due to the excellent surface sensitivity of this method.

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...

Fabrication of magnetic tunnel junctions with a single-crystalline LiF tunnel barrier

Science.gov (United States)

Krishna Narayananellore, Sai; Doko, Naoki; Matsuo, Norihiro; Saito, Hidekazu; Yuasa, Shinji

2018-04-01

We fabricated Fe/LiF/Fe magnetic tunnel junctions (MTJs) by molecular beam epitaxy on a MgO(001) substrate, where LiF is an insulating tunnel barrier with the same crystal structure as MgO (rock-salt type). Crystallographical studies such as transmission electron microscopy and nanobeam electron diffraction observations revealed that the LiF tunnel barrier is single-crystalline and has a LiF(001)[100] ∥ bottom Fe(001)[110] crystal orientation, which is constructed in the same manner as MgO(001) on Fe(001). Also, the in-plane lattice mismatch between the LiF tunnel barrier and the Fe bottom electrode was estimated to be small (about 0.5%). Despite such advantages for the tunnel barrier of the MTJ, the observed tunnel magnetoresistance (MR) ratio was low (˜6% at 20 K) and showed a significant decrease with increasing temperature (˜1% at room temperature). The results imply that indirect tunneling and/or thermally excited carriers in the LiF tunnel barrier, in which the current basically is not spin-polarized, play a major role in electrical transport in the MTJ.

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

Science.gov (United States)

Sander, Dirk; Phark, Soo-Hyon; Corbetta, Marco; Fischer, Jeison A; Oka, Hirofumi; Kirschner, Jürgen

2014-10-01

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.

Photoelectrical properties of semiconductor tips in scanning tunneling microscopy

NARCIS (Netherlands)

Prins, M.W.J.; Jansen, R.; Groeneveld, R.H.M.; Gelder, Van A.P.; Kempen, van H.

1996-01-01

We describe a model as well as experiments on the electrical properties of a photoexcited tunnel junction between a metal and a semiconductor material, as is established in a scanning tunneling microscope. The model treats the case in which carrier transport is mediated by capture and relaxation in

Vacuum phonon tunneling.

Science.gov (United States)

Altfeder, Igor; Voevodin, Andrey A; Roy, Ajit K

2010-10-15

Field-induced phonon tunneling, a previously unknown mechanism of interfacial thermal transport, has been revealed by ultrahigh vacuum inelastic scanning tunneling microscopy (STM). Using thermally broadened Fermi-Dirac distribution in the STM tip as in situ atomic-scale thermometer we found that thermal vibrations of the last tip atom are effectively transmitted to sample surface despite few angstroms wide vacuum gap. We show that phonon tunneling is driven by interfacial electric field and thermally vibrating image charges, and its rate is enhanced by surface electron-phonon interaction.

Si Nanoribbons on Ag(110) Studied by Grazing-Incidence X-Ray Diffraction, Scanning Tunneling Microscopy, and Density-Functional Theory: Evidence of a Pentamer Chain Structure.

Science.gov (United States)

Prévot, Geoffroy; Hogan, Conor; Leoni, Thomas; Bernard, Romain; Moyen, Eric; Masson, Laurence

2016-12-30

We report a combined grazing incidence x-ray diffraction (GIXD), scanning tunneling microscopy (STM), and density-functional theory (DFT) study which clearly elucidates the atomic structure of the Si nanoribbons grown on the missing-row reconstructed Ag(110) surface. Our study allows us to discriminate between the theoretical models published in the literature, including the most stable atomic configurations and those based on a missing-row reconstructed Ag(110) surface. GIXD measurements unambiguously validate the pentamer model grown on the reconstructed surface, obtained from DFT. This pentamer atomistic model accurately matches the high-resolution STM images of the Si nanoribbons adsorbed on Ag(110). Our study closes the long-debated atomic structure of the Si nanoribbons grown on Ag(110) and definitively excludes a honeycomb structure similar to that of freestanding silicene.

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.

Atomic origin of the scanning tunneling microscopy images of charge-density-waves on 1T-TaSe{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Stoltz, D. [Kamerlingh Onnes Laboratory, Leiden University, P.O. Box 9504, 2300 RA Leiden (Netherlands)], E-mail: stoltz@physics.leidenuniv.nl; Bielmann, M.; Schlapbach, L. [Swiss Federal Lab for Materials Science and Technology (EMPA), CH-8600 Duebendorf (Switzerland); Bovet, M. [Institut de Physique, Universite de Neuchatel, CH-2000 Neuchatel (Switzerland); Berger, H. [Institut de Physique Appliquee, EPF, 1015 Lausanne (Switzerland); Goethelid, M. [Materialfysik, MAP, KTH-Electrum, SE-16440 Kista (Sweden); Stoltz, S.E. [MAX-Lab, Lund University, SE-22100 Lund (Sweden); Starnberg, H.I. [Department of Physics, Goeteborg University and Chalmers University of Technology, SE-412 96 Goeteborg (Sweden)

2008-07-01

We show atomically resolved scanning tunneling microscopy (STM) images of charge density waves (CDWs) at room temperature together with angle-resolved photoelectron band-mapping of 1T-TaSe{sub 2}. By comparing the results of these two techniques, we demonstrate the atomic structure of the CDW-features observed by the STM and atomic origin of the reconstructed band-structure in this material.

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, Max O. [Univ. of California, Berkeley, CA (United States)

2006-01-01

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.

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

International Nuclear Information System (INIS)

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

2014-01-01

Single molecule manipulations have been achieved on dichlorotin phthalocyanine(SnCl 2 Pc) molecules adsorbed on Cu (100) at room temperature. Scanning tunneling microscopy observations directly demonstrate that the individual SnCl 2 Pc molecules can be moved along the [100] direction on Cu(100) surface by employing a scanning tunneling microscope tip fixed at the special position of the molecules. The orientation of the molecule can be switched between two angles of ±28° with respect to the [011] surface direction in the same way. Dependences of the probability of molecular motion on the distances between the tip and the molecules reveal that the mechanism for such manipulation of a SnCl 2 Pc molecule is dominated by the repulsive interactions between the tip and the molecules. With the assistance of this manipulation process, a prototype molecular storage array with molecular orientation as information carrier and an artificial hydrogen bonded supramolecular structure have been constructed on the surface. (paper)

Variability in ACL tunnel placement: observational clinical study of surgeon ACL tunnel variability.

Science.gov (United States)

Wolf, Brian R; Ramme, Austin J; Wright, Rick W; Brophy, Robert H; McCarty, Eric C; Vidal, Armando R; Parker, Richard D; Andrish, Jack T; Amendola, Annunziato

2013-06-01

Multicenter and multisurgeon cohort studies on anterior cruciate ligament (ACL) reconstruction are becoming more common. Minimal information exists on intersurgeon and intrasurgeon variability in ACL tunnel placement. Purpose/ The purpose of this study was to analyze intersurgeon and intrasurgeon variability in ACL tunnel placement in a series of The Multicenter Orthopaedic Outcomes Network (MOON) ACL reconstruction patients and in a clinical cohort of ACL reconstruction patients. The hypothesis was that there would be minimal variability between surgeons in ACL tunnel placement. Cross-sectional study; Level of evidence, 3. Seventy-eight patients who underwent ACL reconstruction by 8 surgeons had postoperative imaging with computed tomography, and ACL tunnel location and angulation were analyzed using 3-dimensional surface processing and measurement. Intersurgeon and intrasurgeon variability in ACL tunnel placement was analyzed. For intersurgeon variability, the range in mean ACL femoral tunnel depth between surgeons was 22%. For femoral tunnel height, there was a 19% range. Tibial tunnel location from anterior to posterior on the plateau had a 16% range in mean results. There was only a small range of 4% for mean tibial tunnel location from the medial to lateral dimension. For intrasurgeon variability, femoral tunnel depth demonstrated the largest ranges, and tibial tunnel location from medial to lateral on the plateau demonstrated the least variability. Overall, surgeons were relatively consistent within their own cases. Using applied measurement criteria, 85% of femoral tunnels and 90% of tibial tunnels fell within applied literature-based guidelines. Ninety-one percent of the axes of the femoral tunnels fell within the boundaries of the femoral footprint. The data demonstrate that surgeons performing ACL reconstructions are relatively consistent between each other. There is, however, variability of average tunnel placement up to 22% of mean condylar depth

Ballistic hole magnetic microscopy

NARCIS (Netherlands)

Haq, E.; Banerjee, T.; Siekman, M.H.; Lodder, J.C.; Jansen, R.

2005-01-01

A technique to study nanoscale spin transport of holes is presented: ballistic hole magnetic microscopy. The tip of a scanning tunneling microscope is used to inject hot electrons into a ferromagnetic heterostructure, where inelastic decay creates a distribution of electron-hole pairs.

Direct observation for atomically flat and ordered vertical {111} side-surfaces on three-dimensionally figured Si(110) substrate using scanning tunneling microscopy

Science.gov (United States)

Yang, Haoyu; Hattori, Azusa N.; Ohata, Akinori; Takemoto, Shohei; Hattori, Ken; Daimon, Hiroshi; Tanaka, Hidekazu

2017-11-01

A three-dimensional Si{111} vertical side-surface structure on a Si(110) wafer was fabricated by reactive ion etching (RIE) followed by wet-etching and flash-annealing treatments. The side-surface was studied with scanning tunneling microscopy (STM) in atomic scale for the first time, in addition to atomic force microscopy (AFM), scanning electron microscopy (SEM), and low-energy electron diffraction (LEED). AFM and SEM showed flat and smooth vertical side-surfaces without scallops, and STM proved the realization of an atomically-flat 7 × 7-reconstructed structure, under optimized RIE and wet-etching conditions. STM also showed that a step-bunching occurred on the produced {111} side-surface corresponding to a reversely taped side-surface with a tilt angle of a few degrees, but did not show disordered structures. Characteristic LEED patterns from both side- and top-reconstructed surfaces were also demonstrated.

Apparent Barrier Height in Scanning Tunneling Microscopy Revisited

DEFF Research Database (Denmark)

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

1996-01-01

The apparent barrier height phi(ap), that is, the rate of change of the logarithm of the conductance with tip-sample separation in a scanning tunneling microscope (STM), has been measured for Ni, Pt, and Au single crystal surfaces. The results show that phi(ap) is constant until point contact...... is reached rather than decreasing at small tunneling gap distances, as previously reported. The findings for phi(ap) can be accounted for theoretically by including the relaxations of the tip-surface junction in an STM due to the strong adhesive forces at close proximity. These relaxation effects are shown...

Scanning tunneling microscopy and spectroscopy studies of the heavy-electron superconductor TlNi2Se2

Science.gov (United States)

Wilfert, Stefan; Schmitt, Martin; Schmidt, Henrik; Mauerer, Tobias; Sessi, Paolo; Wang, Hangdong; Mao, Qianhui; Fang, Minghu; Bode, Matthias

2018-01-01

We report on the structural and superconducting electronic properties of the heavy-electron superconductor TlNi2Se2 . By using a variable-temperature scanning tunneling microscopy (VT-STM) the coexistence of (√{2 }×√{2 }) R 45∘ and (2 ×1 ) surface reconstructions is observed. Similar to earlier observations on the "122" family of Fe-based superconductors, we find that their respective surface fraction strongly depends on the temperature during cleavage, the measurement temperature, and the sample's history. Cleaving at low temperature predominantly results in the (√{2 }×√{2 }) R 45∘ -reconstructed surface. A detailed analysis of the (√{2 }×√{2 }) R 45∘ -reconstructed domains identifies (2 ×1 ) -ordered dimers, tertramers, and higher order even multimers as domain walls. Higher cleaving temperatures and the warming of low-temperature-cleaved samples increases the relative weight of the (2 ×1 ) surface reconstruction. By slowly increasing the sample temperature Ts inside the VT-STM we find that the (√{2 }×√{2 }) R 45∘ surface reconstructions transforms into the (2 ×1 ) structure at Ts=123 K. We identify the polar nature of the TlNi2Se2 (001) surface as the most probable driving mechanism of the two reconstructions, as both lead to a charge density ρ =0.5 e- , thereby avoiding divergent electrostatic potentials and the resulting "polar catastrophe." Low-temperature scanning tunneling spectroscopy (STS) performed with normal metal and superconducting probe tips shows a superconducting gap which is best fit with an isotropic s wave. We could not detect any correlation between the local surface reconstruction, suggesting that the superconductivity is predominantly governed by TlNi2Se2 bulk properties. Correspondingly, temperature- and field-dependent data reveal that both the critical temperature and critical magnetic field are in good agreement with bulk values obtained earlier from transport measurements. In the superconducting state

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.)

Scanning tunneling spectroscopy study of DNA conductivity

Czech Academy of Sciences Publication Activity Database

Kratochvílová, Irena; Král, Karel; Bunček, M.; Nešpůrek, Stanislav; Todorciuc, Tatiana; Weiter, M.; Navrátil, J.; Schneider, Bohdan; Pavluch, J.

2008-01-01

Roč. 6, č. 3 (2008), s. 422-426 ISSN 1895-1082 R&D Projects: GA AV ČR KAN401770651; GA MŠk OC 137; GA AV ČR KAN400720701; GA AV ČR KAN200100801 Institutional research plan: CEZ:AV0Z10100520; CEZ:AV0Z40500505; CEZ:AV0Z40550506 Keywords : molecular electronics * DNA * scanning tunneling microscopy * conductivity * charge carrier transport Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.448, year: 2008

Measurement of the vortex-core radius by scanning tunneling microscopy

NARCIS (Netherlands)

Hartmann, U.; Golubov, Alexandre Avraamovitch; Drechsler, T.; Kupriyanov, M. Yu; Heiden, C.

1994-01-01

Using a scanning tunneling microscope operated in a spectroscopic mode we imaged flux-line lattices in niobium diselenide at various external magnetic fields. From the evaluation of a large number of tunneling-current profiles taken across the individual vortices we deduced the dependence of the

Hydrophilicity and Microsolvation of an Organic Molecule Resolved on the Sub-molecular Level by Scanning Tunneling Microscopy.

Science.gov (United States)

Lucht, Karsten; Loose, Dirk; Ruschmeier, Maximilian; Strotkötter, Valerie; Dyker, Gerald; Morgenstern, Karina

2018-01-26

Low-temperature scanning tunneling microscopy was used to follow the formation of a solvation shell around an adsorbed functionalized azo dye from the attachment of the first water molecule to a fully solvated molecule. Specific functional groups bind initially one water molecule each, which act as anchor points for additional water molecules. Further water attachment occurs in areas close to these functional groups even when the functional groups themselves are already saturated. In contrast, water molecules surround the hydrophobic parts of the molecule only when the two-dimensional solvation shell closes around them. This study thus traces hydrophilic and hydrophobic properties of an organic molecule down to a sub-molecular length scale. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Quantum-Sequencing: Biophysics of quantum tunneling through nucleic acids

Science.gov (United States)

Casamada Ribot, Josep; Chatterjee, Anushree; Nagpal, Prashant

2014-03-01

Tunneling microscopy and spectroscopy has extensively been used in physical surface sciences to study quantum tunneling to measure electronic local density of states of nanomaterials and to characterize adsorbed species. Quantum-Sequencing (Q-Seq) is a new method based on tunneling microscopy for electronic sequencing of single molecule of nucleic acids. A major goal of third-generation sequencing technologies is to develop a fast, reliable, enzyme-free single-molecule sequencing method. Here, we present the unique ``electronic fingerprints'' for all nucleotides on DNA and RNA using Q-Seq along their intrinsic biophysical parameters. We have analyzed tunneling spectra for the nucleotides at different pH conditions and analyzed the HOMO, LUMO and energy gap for all of them. In addition we show a number of biophysical parameters to further characterize all nucleobases (electron and hole transition voltage and energy barriers). These results highlight the robustness of Q-Seq as a technique for next-generation sequencing.

A nanoscale gigahertz source realized with Josephson scanning tunneling microscopy

Energy Technology Data Exchange (ETDEWEB)

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

2015-01-05

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

Scanning tunneling spectroscopy under large current flow through the sample.

Science.gov (United States)

Maldonado, A; Guillamón, I; Suderow, H; Vieira, S

2011-07-01

We describe a method to make scanning tunneling microscopy/spectroscopy imaging at very low temperatures while driving a constant electric current up to some tens of mA through the sample. It gives a new local probe, which we term current driven scanning tunneling microscopy/spectroscopy. We show spectroscopic and topographic measurements under the application of a current in superconducting Al and NbSe(2) at 100 mK. Perspective of applications of this local imaging method includes local vortex motion experiments, and Doppler shift local density of states studies.

Preparation of scanning tunneling microscopy tips using pulsed alternating current etching

International Nuclear Information System (INIS)

Valencia, Victor A.; Thaker, Avesh A.; Derouin, Jonathan; Valencia, Damian N.; Farber, Rachael G.; Gebel, Dana A.; Killelea, Daniel R.

2015-01-01

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

Preparation of scanning tunneling microscopy tips using pulsed alternating current etching

Energy Technology Data Exchange (ETDEWEB)

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

2015-03-15

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

Direct observation of atoms on surfaces by scanning tunnelling microscopy

International Nuclear Information System (INIS)

Baldeschwieler, J.D.

1989-01-01

The scanning tunnelling microscope is a non-destructive means of achieving atomic level resolution of crystal surfaces in real space to elucidate surface structures, electronic properties and chemical composition. Scanning tunnelling microscope is a powerful, real space surface structure probe complementary to other techniques such as x-ray diffraction. 21 refs., 8 figs

First Principles Study of Electron Tunneling through Ice

KAUST Repository

Cucinotta, Clotilde S.; Rungger, Ivan; Sanvito, Stefano

2012-01-01

With the aim of understanding electrochemical scanning tunnel microscopy experiments in an aqueous environment, we investigate electron transport through ice in the coherent limit. This is done by using the nonequilibrium Greens functions method, implemented within density functional theory, in the self-interaction corrected local density approximation. In particular, we explore different ice structures and different Au electrode surface orientations. By comparing the decay coefficient for different thicknesses to the ice complex band structure, we find that the electron transport occurs via tunneling with almost one-dimensional character. The slow decay of the current with the ice thickness is largely due to the small effective mass of the conduction electrons. Furthermore, we find that the calculated tunneling decay coefficients at the Fermi energy are not sensitive to the structural details of the junctions and are at the upper end of the experimental range for liquid water. This suggests that linear response transport measurements are not capable of distinguishing between different ordered ice structures. However, we also demonstrate that a finite bias measurement may be capable of sorting polar from nonpolar interfaces due to the asymmetry of the current-voltage curves for polar interfaces. © 2012 American Chemical Society.

First Principles Study of Electron Tunneling through Ice

KAUST Repository

Cucinotta, Clotilde S.

2012-10-25

With the aim of understanding electrochemical scanning tunnel microscopy experiments in an aqueous environment, we investigate electron transport through ice in the coherent limit. This is done by using the nonequilibrium Greens functions method, implemented within density functional theory, in the self-interaction corrected local density approximation. In particular, we explore different ice structures and different Au electrode surface orientations. By comparing the decay coefficient for different thicknesses to the ice complex band structure, we find that the electron transport occurs via tunneling with almost one-dimensional character. The slow decay of the current with the ice thickness is largely due to the small effective mass of the conduction electrons. Furthermore, we find that the calculated tunneling decay coefficients at the Fermi energy are not sensitive to the structural details of the junctions and are at the upper end of the experimental range for liquid water. This suggests that linear response transport measurements are not capable of distinguishing between different ordered ice structures. However, we also demonstrate that a finite bias measurement may be capable of sorting polar from nonpolar interfaces due to the asymmetry of the current-voltage curves for polar interfaces. © 2012 American Chemical Society.

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...

Surface structure and analysis with scanning tunneling microscopy and electron tunneling spectroscopy

International Nuclear Information System (INIS)

Coleman, R.V.

1992-01-01

This report discusses the following topics: charge-density waves in layer structures; charge-density waves in linear chain compounds; spectroscopy with the STM; STM studies of oxides; and development of atomic force microscopy. (LSP)

New approach towards imaging -DNA using scanning tunneling

Indian Academy of Sciences (India)

DNA; scanning tunneling microscopy; Langmuir Blodget technique; silanization. ... Scanning tunneling spectroscopy (STS) at different stages depict a broad distribution of defect states in the bandgap region of -Si(111) which ... Current Issue

Analysis and Calibration of in situ scanning tunnelling microscopy Images with atomic Resolution Influenced by Surface Drift Phenomena

DEFF Research Database (Denmark)

Andersen, Jens Enevold Thaulov; Møller, Per

1994-01-01

The influence of surface drift velocities on in situ scanning tunnelling microscopy (STM) experiments with atomic resolution is analysed experimentally and mathematically. Constant drift velocities much smaller than the speed of scanning can in many in situ STM experiments with atomic resolution ...... as well as the vectors of the non-distorted surface lattice can be determined. The calibration of distances can thus be carried out also when the image is influenced by drift. Results with gold surfaces and graphite surfaces are analysed and discussed....

A compact atomic force-scanning tunneling microscope for studying microelectronics and environmental aerosols

International Nuclear Information System (INIS)

Chen, G.

1996-06-01

This dissertation describes the characteristics and the construction of a compact atomic force/scanning tunneling microscope (AFM/STM). The basics and the method of preparing a tunneling junction between a chemically etched tunneling tip and a micro-manufactured cantilever is outlined by analyzing the forces between tunneling tip and cantilever as well as between force-sensing tip and sample surfaces. To our best knowledge this instrument is the first one using a commercial cantilever with only one piezoelectric tube carrying the whole tunneling sensor. The feedback control system has been optimized after a careful analysis of the electronic loop characteristics. The mode of operation has been determined by analyzing the dynamic characteristics of the scan heads and by investigating the time characteristics of the data acquisition system. The vibration isolation system has been calibrated by analyzing the characteristics of the damping setup and the stiffness of the scan head. The calculated results agree well with the measured ones. Also, a software package for data acquisition and real time display as well as for image processing and three-dimensional visualization has been developed. With this home-made software package, the images can be processed by means of a convolution filter, a Wiener filter and other 2-D FFT filters, and can be displayed in different ways. Atomic resolution images of highly oriented pyrolytic graphite (HOPG) and graphite surfaces have been obtained in AFM and STM mode. New theoretical explanations have been given for the observed anomalous STM and AFM images of graphite by calculating the asymmetric distribution of quantum conductance and tip-surface forces on a graphite surface. This not only resolved the theoretical puzzles of STM and AFM of graphite, but also revealed the relation between atomic force microscopy and scanning tunneling microscopy of graphite. Applications of STM and AFM to micro-electronic devices have been investigated

Surface structure of YBa2Cu3O7-x probed by reversed-bias scanning tunneling microscopy

International Nuclear Information System (INIS)

Edwards, H.L.; Markert, J.T.; Lozanne, A.L.d.

1994-01-01

We report the results of scanning tunneling microscopy studies on high-quality single crystals of YBa 2 Cu 3 O 7-x (YBCO) which were cleaved along a basal plane in situ at 20 K prior to measurement. The initial results of a systematic study of the YBCO surface are presented. Reversed-bias images of the CuO chain layer reveal modulations 3.3±0.3|b|=1.3±0.1 nm in wavelength which change phase by 180 degree under bias polarity reversal along solid chains, and are invariant under bias polarity reversal at a point defect. Regions of sharp unit-cell-sized square corrugations with disordered islands are also observed. We interpret these new results in terms of our previous model [H. L. Edwards, J. T. Markert, and A. L. de Lozanne, Phys. Rev. Lett. 69, 2967 (1992)] of the cleaved YBCO surface

Graphene quantum dots probed by scanning tunneling microscopy

Energy Technology Data Exchange (ETDEWEB)

Morgenstern, Markus; Freitag, Nils; Nent, Alexander; Nemes-Incze, Peter; Liebmann, Marcus [II. Institute of Physics B and JARA-FIT, RWTH Aachen University, Aachen (Germany)

2017-11-15

Scanning tunneling spectroscopy results probing the electronic properties of graphene quantum dots are reviewed. After a short summary of the study of squared wave functions of graphene quantum dots on metal substrates, we firstly present data where the Landau level gaps caused by a perpendicular magnetic field are used to electrostatically confine electrons in monolayer graphene, which are probed by the Coulomb staircase revealing the consecutive charging of a quantum dot. It turns out that these quantum dots exhibit much more regular charging sequences than lithographically confined ones. Namely, the consistent grouping of charging peaks into quadruplets, both, in the electron and hole branch, portrays a regular orbital splitting of about 10meV. At low hole occupation numbers, the charging peaks are, partly, additionally grouped into doublets. The spatially varying energy separation of the doublets indicates a modulation of the valley splitting by the underlying BN substrate. We outline that this property might be used to eventually tune the valley splitting coherently. Afterwards, we describe graphene quantum dots with multiple contacts produced without lithographic resist, namely by local anodic oxidation. Such quantum dots target the goal to probe magnetotransport properties during the imaging of the corresponding wave functions by scanning tunneling spectroscopy. (copyright 2017 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Tunneling Mode of Scanning Electrochemical Microscopy: Probing Electrochemical Processes at Single Nanoparticles.

Science.gov (United States)

Sun, Tong; Wang, Dengchao; Mirkin, Michael V

2018-06-18

Electrochemical experiments at individual nanoparticles (NPs) can provide new insights into their structure-activity relationships. By using small nanoelectrodes as tips in a scanning electrochemical microscope (SECM), we recently imaged individual surface-bound 10-50 nm metal NPs. Herein, we introduce a new mode of SECM operation based on tunneling between the tip and a nanoparticle immobilized on the insulating surface. The obtained current vs. distance curves show the transition from the conventional feedback response to electron tunneling between the tip and the NP at separation distances of less than about 3 nm. In addition to high-resolution imaging of the NP topography, the tunneling mode enables measurement of the heterogeneous kinetics at a single NP without making an ohmic contact with it. The developed method should be useful for studying the effects of nanoparticle size and geometry on electrocatalytic activity in real-world applications. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Spin-polarized scanning tunneling microscopy with quantitative insights into magnetic probes.

Science.gov (United States)

Phark, Soo-Hyon; Sander, Dirk

2017-01-01

Spin-polarized scanning tunneling microscopy and spectroscopy (spin-STM/S) have been successfully applied to magnetic characterizations of individual nanostructures. Spin-STM/S is often performed in magnetic fields of up to some Tesla, which may strongly influence the tip state. In spite of the pivotal role of the tip in spin-STM/S, the contribution of the tip to the differential conductance d I /d V signal in an external field has rarely been investigated in detail. In this review, an advanced analysis of spin-STM/S data measured on magnetic nanoislands, which relies on a quantitative magnetic characterization of tips, is discussed. Taking advantage of the uniaxial out-of-plane magnetic anisotropy of Co bilayer nanoisland on Cu(111), in-field spin-STM on this system has enabled a quantitative determination, and thereby, a categorization of the magnetic states of the tips. The resulting in-depth and conclusive analysis of magnetic characterization of the tip opens new venues for a clear-cut sub-nanometer scale spin ordering and spin-dependent electronic structure of the non-collinear magnetic state in bilayer high Fe nanoislands on Cu(111).

Visualizing period fluctuations in strained-layer superlattices with scanning tunneling microscopy

Science.gov (United States)

Kanedy, K.; Lopez, F.; Wood, M. R.; Gmachl, C. F.; Weimer, M.; Klem, J. F.; Hawkins, S. D.; Shaner, E. A.; Kim, J. K.

2018-01-01

We show how cross-sectional scanning tunneling microscopy (STM) may be used to accurately map the period fluctuations throughout epitaxial, strained-layer superlattices based on the InAs/InAsSb and InGaAs/InAlAs material systems. The concept, analogous to Bragg's law in high-resolution x-ray diffraction, relies on an analysis of the [001]-convolved reciprocal-space satellite peaks obtained from discrete Fourier transforms of individual STM images. Properly implemented, the technique enables local period measurements that reliably discriminate vertical fluctuations localized to within ˜5 superlattice repeats along the [001] growth direction and orthogonal, lateral fluctuations localized to within ˜40 nm along directions in the growth plane. While not as accurate as x-ray, the inherent, single-image measurement error associated with the method may be made as small as 0.1%, allowing the vertical or lateral period fluctuations contributing to inhomogeneous energy broadening and carrier localization in these structures to be pinpointed and quantified. The direct visualization of unexpectedly large, lateral period fluctuations on nanometer length scales in both strain-balanced systems supports a common understanding in terms of correlated interface roughness.

Spin polarized electron tunneling and magnetoresistance in molecular junctions.

Science.gov (United States)

Szulczewski, Greg

2012-01-01

This chapter reviews tunneling of spin-polarized electrons through molecules positioned between ferromagnetic electrodes, which gives rise to tunneling magnetoresistance. Such measurements yield important insight into the factors governing spin-polarized electron injection into organic semiconductors, thereby offering the possibility to manipulate the quantum-mechanical spin degrees of freedom for charge carriers in optical/electrical devices. In the first section of the chapter a brief description of the Jullière model of spin-dependent electron tunneling is reviewed. Next, a brief description of device fabrication and characterization is presented. The bulk of the review highlights experimental studies on spin-polarized electron tunneling and magnetoresistance in molecular junctions. In addition, some experiments describing spin-polarized scanning tunneling microscopy/spectroscopy on single molecules are mentioned. Finally, some general conclusions and prospectus on the impact of spin-polarized tunneling in molecular junctions are offered.

Transition between scanning tunneling microscopy images of alkane derivatives on graphite

International Nuclear Information System (INIS)

Hibino, Masahiro; Tsuchiya, Hiroshi

2015-01-01

Graphical abstract: - Highlights: • SAMs of dialkyl sulfides form at the liquid–graphite interface. • STM contrast of molecules change reversibly between zigzag and aligned bright spot patterns. • The free energy for contrast change is smaller than the thermal energy (RT). • STM contrast change is caused by electronic effects and registry of the alkyl chains. - Abstract: Self-assembled monolayers of alkylated sulfides containing two alkyl chains and a sulfur atom positioned at the center of the molecules were studied on a graphite surface using scanning tunneling microscopy (STM). STM images of the closed-packed alkyl chains that extend linearly from the sulfur atoms change reversibly between a zigzag pattern and an aligned bright spot pattern on a time scale of minutes. The observation times of the zigzag and aligned bright spot patterns indicate that the difference between the free energies of these two stable molecular configurations with respect to the graphite surface is smaller than their thermal energies in the presence of a solvent, and 10 times smaller than the theoretical free energy between parallel and perpendicular configurations of the alkyl chains on graphite under vacuum. The change in the contrast of the STM images occurred owing to the electronic effects that depend on the registry of the alkyl chains on the graphite surface, and not by the classical observation of transfer between parallel and perpendicular orientations of alkyl chains on the surface.

A perfect wetting of Mg monolayer on Ag(111) under atomic scale investigation: First principles calculations, scanning tunneling microscopy, and Auger spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Migaou, Amani; Guiltat, Mathilde; Payen, Kevin; Landa, Georges; Hémeryck, Anne, E-mail: anne.hemeryck@laas.fr [LAAS-CNRS, Université de Toulouse, CNRS, UPS, Toulouse (France); Sarpi, Brice; Daineche, Rachid; Vizzini, Sébastien [Aix Marseille University, IM2NP, Fac Sci St. Jérôme, F-13397 Marseille (France)

2016-05-21

First principles calculations, scanning tunneling microscopy, and Auger spectroscopy experiments of the adsorption of Mg on Ag(111) substrate are conducted. This detailed study reveals that an atomic scale controlled deposition of a metallic Mg monolayer perfectly wets the silver substrate without any alloy formation at the interface at room temperature. A liquid-like behavior of the Mg species on the Ag substrate is highlighted as no dot formation is observed when coverage increases. Finally a layer-by-layer growth mode of Mg on Ag(111) can be predicted, thanks to density functional theory calculations as observed experimentally.

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 π stacking. Two-dimensional delocalized electronic states are found on the K-deposited π stacking structure.

Attractive interaction between Mn atoms on the GaAs(110) surface observed by scanning tunneling microscopy.

Science.gov (United States)

Taninaka, Atsushi; Yoshida, Shoji; Kanazawa, Ken; Hayaki, Eiko; Takeuchi, Osamu; Shigekawa, Hidemi

2016-06-16

Scanning tunneling microscopy/spectroscopy (STM/STS) was carried out to investigate the structures of Mn atoms deposited on a GaAs(110) surface at room temperature to directly observe the characteristics of interactions between Mn atoms in GaAs. Mn atoms were paired with a probability higher than the random distribution, indicating an attractive interaction between them. In fact, re-pairing of unpaired Mn atoms was observed during STS measurement. The pair initially had a new structure, which was transformed during STS measurement into one of those formed by atom manipulation at 4 K. Mn atoms in pairs and trimers were aligned in the direction, which is theoretically predicted to produce a high Curie temperature.

Optimization of a tunneling barrier in magnetic tunneling junction by tilted-plasma oxidation

International Nuclear Information System (INIS)

Nam, C.H.; Shim, Heejae; Kim, K.S.; Cho, B.K.

2004-01-01

Oxidation of an AlO x insulating barrier in a magnetic tunneling junction (MTJ) was carried out by a tilted-plasma oxidation method. It was found that the tilted-plasma oxidation induced a gradual change in the extent of oxidation of an insulating layer, which consequently led to a gradual change in the tunneling magnetoresistance (TMR) and specific junction resistance (RA) of the MTJ. We found a linear relation in the TMR versus RA curve with positive and negative slopes for less- and overoxidized junctions, respectively, and a parabolic relation for optimally oxidized junctions. The crossover in the TMR versus RA curves provides an effective and useful way to optimize (and monitor) the oxidation condition of a tunneling barrier in MTJs especially of a tunneling barrier less than 10 A thick. The tunneling junctions were also investigated after thermal annealing at various temperatures. The observations after thermal annealing were found to be consistent with transmission electrons microscopy images and a scenario of the partial formation of an additional ultrathin tunneling barrier at the top surface of the bottom magnetic layer

Experimental verification of the rotational type of chiral spin spiral structures by spin-polarized scanning tunneling microscopy.

Science.gov (United States)

Haze, Masahiro; Yoshida, Yasuo; Hasegawa, Yukio

2017-10-16

We report on experimental verification of the rotational type of chiral spin spirals in Mn thin films on a W(110) substrate using spin-polarized scanning tunneling microscopy (SP-STM) with a double-axis superconducting vector magnet. From SP-STM images using Fe-coated W tips magnetized to the out-of-plane and [001] directions, we found that both Mn mono- and double-layers exhibit cycloidal rotation whose spins rotate in the planes normal to the propagating directions. Our results agree with the theoretical prediction based on the symmetry of the system, supporting that the magnetic structures are driven by the interfacial Dzyaloshinskii-Moriya interaction.

Giant tunnel-electron injection in nitrogen-doped graphene

DEFF Research Database (Denmark)

Lagoute, Jerome; Joucken, Frederic; Repain, Vincent

2015-01-01

Scanning tunneling microscopy experiments have been performed to measure the local electron injection in nitrogen-doped graphene on SiC(000) and were successfully compared to ab initio calculations. In graphene, a gaplike feature is measured around the Fermi level due to a phonon-mediated tunneling...... and at carbon sites. Nitrogen doping can therefore be proposed as a way to improve tunnel-electron injection in graphene....

Spin inelastic electron tunneling spectroscopy on local spin adsorbed on surface.

Science.gov (United States)

Fransson, J

2009-06-01

The recent experimental conductance measurements taken on magnetic impurities on metallic surfaces, using scanning tunneling microscopy technique and suggesting occurrence of inelastic scattering processes, are theoretically addressed. We argue that the observed conductance signatures are caused by transitions between the spin states that have opened due to, for example, exchange coupling between the local spins and the tunneling electrons, and are directly interpretable in terms of inelastic transitions energies. Feasible measurements using spin-polarized scanning tunneling microscopy that would enable new information about the excitation spectrum of the local spins are discussed.

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

Hybrid High-Temperature-Superconductor–Semiconductor Tunnel Diode

Directory of Open Access Journals (Sweden)

Alex Hayat

2012-12-01

Full Text Available We report the demonstration of hybrid high-T_{c}-superconductor–semiconductor tunnel junctions, enabling new interdisciplinary directions in condensed matter research. The devices are fabricated by our newly developed mechanical-bonding technique, resulting in high-T_{c}-superconductor–semiconductor tunnel diodes. Tunneling-spectra characterization of the hybrid junctions of Bi_{2}Sr_{2}CaCu_{2}O_{8+δ} combined with bulk GaAs, or a GaAs/AlGaAs quantum well, exhibits excess voltage and nonlinearity, similarly to spectra obtained in scanning-tunneling microscopy, and is in good agreement with theoretical predictions for a d-wave-superconductor–normal-material junction. Additional junctions are demonstrated using Bi_{2}Sr_{2}CaCu_{2}O_{8+δ} combined with graphite or Bi_{2}Te_{3}. Our results pave the way for new methods in unconventional superconductivity studies, novel materials, and quantum technology applications.

An extended model of electrons: experimental evidence from high-resolution scanning tunneling microscopy

International Nuclear Information System (INIS)

Hofer, Werner A

2012-01-01

In a recent paper we introduced a model of extended electrons, which is fully compatible with quantum mechanics in the formulation of Schrödinger. However, it contradicts the current interpretation of electrons as point-particles. Here, we show by a statistical analysis of high-resolution scanning tunneling microscopy (STM) experiments, that the interpretation of electrons as point particles and, consequently, the interpretation of the density of electron charge as a statistical quantity will lead to a conflict with the Heisenberg uncertainty principle. Given the precision in these experiments we find that the uncertainty principle would be violated by close to two orders of magnitude, if this interpretation were correct. We are thus forced to conclude that the density of electron charge is a physically real, i.e. in principle precisely measurable quantity, as derived in a recent paper. Experimental evidence to the contrary, in particular high-energy scattering experiments, is briefly discussed. The finding is expected to have wide implications in condensed matter physics, chemistry, and biology, scientific disciplines which are based on the properties and interactions of electrons.

Scanning probe microscopy experiments in microgravity

International Nuclear Information System (INIS)

Drobek, Tanja; Reiter, Michael; Heckl, Wolfgang M.

2004-01-01

The scanning probe microscopy setups are small, lightweight and do not require vacuum or high voltage supply. In addition, samples can be investigated directly without further preparation. Therefore, these techniques are well-suited for applications in space, in particular, for operation on the International Space Station (ISS) or for high resolution microscopy on planetary missions. A feasibility study for a scanning tunneling microscopy setup was carried out on a parabolic flight campaign in November 2001 in order to test the technical setup for microgravity applications. With a pocket-size design microscope, a graphite surface was imaged under ambient conditions. Atomic resolution was achieved although the quality of the images was inferior in comparison to laboratory conditions. Improvements for future scanning probe microscopy experiments in microgravity are suggested

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

DEFF Research Database (Denmark)

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

1998-01-01

The voltage between tip and sample in a scanning tunneling microscope (STM) results in a large electric field localized near the tip apex. The mechanical stress due to this field can cause appreciable deformation of both tip and sample on the scale of the tunnel gap. We derive an approximate...

Atom probe field ion microscopy and related topics: A bibliography 1989

International Nuclear Information System (INIS)

Miller, M.K.; Hawkins, A.R.; Russell, K.F.

1990-12-01

This bibliography includes references related to the following topics: atom probe field ion microscopy (APFIM), field ion spectroscopy (FIM), field emission microscopy (FEM), liquid metal ion sources (LMIS), scanning tunneling microscopy (STM), and theory. Technique-orientated studies and applications are included. This bibliography covers the period 1989. The references contained in this document were compiled from a variety of sources including computer searches and personal lists of publications

Scanning tunneling microscopy/spectroscopy on multi-layered cuprate superconductor Ba2Ca5Cu6O12 (O1-x Fx)2

International Nuclear Information System (INIS)

Sugimoto, A.; Shohara, K.; Ekino, T.; Watanabe, Y.; Harada, Y.; Mikusu, S.; Tokiwa, K.; Watanabe, T.

2009-01-01

Scanning tunneling microscopy/spectroscopy (STM/STS) measurements on multi-layered cuprate superconductor Ba 2 Ca 5 Cu 6 O 12 (O 1-x F x ) 2 are carried out. STM topographies show randomly distributed bright spot structures with a typical spot size of ∼0.8 nm. These bright spots are occupied about 28% per one unit cell of c-plane, which is comparable to the regular amount of apical oxygen of 20% obtained from element analysis. Tunneling spectra simultaneously show both the small and the large gap structures. These gap sizes at 4.9 K are about Δ ∼15 meV and ∼90 meV, respectively. The small gap structure disappears at the temperature close to T C , while the large gap persists up to ∼200 K. Therefore, these features correspond to the superconducting gap and pseudogap, respectively. These facts give evidence for some ordered state with large energy scale even in the superconducting state. For the superconducting gap, the ratio of 2Δ/K B T C = 4.9 is obtained with T C = 70 K, which is determined from temperature dependence of the tunneling spectra.

Optical characterication of probes for photon scanning tunnelling microscopy

DEFF Research Database (Denmark)

Vohnsen, Brian; Bozhevolnyi, Sergey I.

1999-01-01

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

Resonance tunneling electron-vibrational spectroscopy of polyoxometalates.

Science.gov (United States)

Dalidchik, F I; Kovalevskii, S A; Balashov, E M

2017-05-21

The tunneling spectra of the ordered monolayer films of decamolybdodicobaltate (DMDC) compounds deposited from aqueous solutions on HOPG were measured by scanning tunnel microscopy in air. The DMDC spectra, as well as the tunneling spectra of other polyoxometalates (POMs), exhibit well-defined negative differential resistances (NDRs). The mechanism of formation of these spectral features was established from the collection of revealed NDR dependences on the external varying parameters and found to be common to all systems exhibiting Wannier-Stark localization. A model of biresonance tunneling was developed to provide an explanation for the totality of experimental data, both the literature and original, on the tunneling POM probing. A variant of the tunneling electron-vibrational POM spectroscopy was proposed allowing the determination of the three basic energy parameters-energy gaps between the occupied and unoccupied states, frequencies of the vibrational transitions accompanying biresonance electron-tunneling processes, and electron-vibrational interaction constants on the monomolecular level.

Scanning Tunneling Microscopy Study of Carbon Tetrachloride Adsorption and Degradation on a Natural a-Fe2O3(0001) Surface in Ultrahigh Vacuum

Science.gov (United States)

Taeg Rim, Kwang; Fitts, Jeffrey; Adib, Kaveh; Camillone, Nicholas, III; Schlosser, Peter; Osgood, Richard, Jr.; Flynn, George; Joyce, Stephen

2001-03-01

Scanning tunneling microscopy and low energy electron diffraction have been used to study a natural a-Fe2O3(0001) surface and the adsorption and degradation of carbon tetrachloride on the reduced Fe3O4(111) terminated surface. A natural a-Fe2O3 (0001) surface was prepared by repeated cycles of Ar+ ion sputtering and annealing in vacuum or in O2 at 850 K. STM images and a LEED pattern indicate that an Fe3O4(111) terminated surface and a bi-phase can be formed depending on annealing conditions. The Fe3O4(111) terminated surface was dosed with CCl4 at room temperature, and flashed up to 590 K and 850 K. STM images show adsorbates on the surface at room temperature and the degradation products of CCl4 are isolated on the surface as the flashing temperature increases up to 850 K. Results from a companion temperature programmed desorption investigation are used in conjunction with the STM images to propose site specific reactions of CCl4 on the Fe3O4(111) terminated surface.

The comparison between limited open carpal tunnel release using direct vision and tunneling technique and standard open carpal tunnel release: a randomized controlled trial study.

Science.gov (United States)

Suppaphol, Sorasak; Worathanarat, Patarawan; Kawinwongkovit, Viroj; Pittayawutwinit, Preecha

2012-04-01

To compare the operative outcome of carpal tunnel release between limited open carpal tunnel release using direct vision and tunneling technique (group A) with standard open carpal tunnel release (group B). Twenty-eight patients were enrolled in the present study. A single blind randomized control trial study was conducted to compare the postoperative results between group A and B. The study parameters were Levine's symptom severity and functional score, grip and pinch strength, and average two-point discrimination. The postoperative results between two groups were comparable with no statistical significance. Only grip strength at three months follow up was significantly greater in group A than in group B. The limited open carpal tunnel release in the present study is effective comparable to the standard open carpal tunnel release. The others advantage of this technique are better cosmesis and improvement in grip strength at the three months postoperative period.

High Surface Area Tunnels in Hexagonal WO₃.

Science.gov (United States)

Sun, Wanmei; Yeung, Michael T; Lech, Andrew T; Lin, Cheng-Wei; Lee, Chain; Li, Tianqi; Duan, Xiangfeng; Zhou, Jun; Kaner, Richard B

2015-07-08

High surface area in h-WO3 has been verified from the intracrystalline tunnels. This bottom-up approach differs from conventional templating-type methods. The 3.67 Å diameter tunnels are characterized by low-pressure CO2 adsorption isotherms with nonlocal density functional theory fitting, transmission electron microscopy, and thermal gravimetric analysis. These open and rigid tunnels absorb H(+) and Li(+), but not Na(+) in aqueous electrolytes without inducing a phase transformation, accessing both internal and external active sites. Moreover, these tunnel structures demonstrate high specific pseudocapacitance and good stability in an H2SO4 aqueous electrolyte. Thus, the high surface area created from 3.67 Å diameter tunnels in h-WO3 shows potential applications in electrochemical energy storage, selective ion transfer, and selective gas adsorption.

Temperature dependent tunneling study of CaFe{sub 1.96}Ni{sub 0.04}As{sub 2} single crystals

Energy Technology Data Exchange (ETDEWEB)

Dutta, Anirban, E-mail: adatta@iitk.ac.in; Gupta, Anjan K. [Department of Physics, IIT Kanpur, Kanpur-208 016 (India); Thamizhavel, A. [Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai-400 005 (India)

2014-04-24

We report on temperature dependent scanning tunneling microscopy and spectroscopy studies on CaFe{sub 1.96}Ni{sub 0.04}As{sub 2} single crystals in 5.4 – 19.7 K temperature range across the normal metal - superconductor transition temperature, T{sub C} = 14K. The in-situ cleaved crystals show reasonably flat surface with signatures of atomic resolution. The tunnel spectra show significant spatial inhomogeneity below T{sub C}, which reduces significantly as the temperature goes above the T{sub C}. We discuss these results in terms of an inhomogeneous electronic phase that may exist due to the vicinity of this composition to the quantum critical point.

The tunnel effect and their more important application: The microscope of quantum tunneling

International Nuclear Information System (INIS)

Alvarez M, L.

1999-01-01

Thanks to a donation made by the Volunteered Japanese JICA Program, the University National Headquarters Manizales, in particular the group of Physics of the Plasma, it has acquired a equipment where it is possible to combine several microscopy techniques: STM (scanning tunneling microscopy), AFM (atomic forced microscopy), MFM (magnetic forced microscopy) and LFM (lateral forced microscopy). These techniques group under the generic name of probe microscopy (SPM). The objective of this article is to offer a basic understanding to the whole university community on one of the previously mentioned techniques, STM, with the goal of generating future collaborations among the diverse investigators of the Headquarters. In the first one it leaves it explains the physical phenomenon in which the STM is based, then it is exposed in a brief way the operation of the same one and finally some of its applications are mentioned

Catalytic monolayer voltammetry and in situ scanning tunneling microscopy of copper nitrite reductase on cysteamine-modified Au(111) electrodes

DEFF Research Database (Denmark)

Zhang, Jingdong; Welinder, A.C.; Hansen, Allan Glargaard

2003-01-01

electrochemical scanning tunneling microscopy (in situ STM) directly in aqueous acetate buffer, pH 6.0 has been used. High-resolution in situ STM shows that cysteamine packs into ordered domains with strip features of a periodic distance of 11.7 +/- 0.3 Angstrom. No voltammetric signals of the nitrite substrate...... 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...

The (2 × 2) tunnels structured manganese dioxide nanorods with α phase for lithium air batteries

Science.gov (United States)

Ghouri, Zafar Khan; Zahoor, Awan; Barakat, Nasser A. M.; Alsoufi, Mohammad S.; Bawazeer, Tahani M.; Mohamed, Ahmed F.; Kim, Hak Yong

2016-02-01

The (2 × 2) tunnels structured manganese dioxide nanorods with α phase (α-MnO2) are synthesized via simplistic hydrothermal method at low temperature. The obtained tunnels structured α-MnO2 nanorods are characterized by, Transmission electron microscopy, Scanning electron microscopy, and X-ray diffraction techniques. The oxygen reduction reaction (ORR) activity was studied by cyclic voltammetry and rotating ring-disc electrode voltammetry techniques in alkaline media. Moreover; the highly electrocatalytic tunnels structured α-MnO2 nanorods were then also applied as cathode in rechargeable Li-O2 cells. The Li-O2 cells exhibited initial discharge capacity as high as ∼4000 mAh/g with the tunnels structured α-MnO2 nanorods which was double the original capacity of the cells without any catalyst. Also we obtained 100% round trip efficiency upon cycling with limited capacity for more than 50 cycles.

Regular Scanning Tunneling Microscope Tips can be Intrinsically Chiral

International Nuclear Information System (INIS)

Tierney, Heather L.; Murphy, Colin J.; Sykes, E. Charles H.

2011-01-01

We report our discovery that regular scanning tunneling microscope tips can themselves be chiral. This chirality leads to differences in electron tunneling efficiencies through left- and right-handed molecules, and, when using the tip to electrically excite molecular rotation, large differences in rotation rate were observed which correlated with molecular chirality. As scanning tunneling microscopy is a widely used technique, this result may have unforeseen consequences for the measurement of asymmetric surface phenomena in a variety of important fields.

Regular scanning tunneling microscope tips can be intrinsically chiral.

Science.gov (United States)

Tierney, Heather L; Murphy, Colin J; Sykes, E Charles H

2011-01-07

We report our discovery that regular scanning tunneling microscope tips can themselves be chiral. This chirality leads to differences in electron tunneling efficiencies through left- and right-handed molecules, and, when using the tip to electrically excite molecular rotation, large differences in rotation rate were observed which correlated with molecular chirality. As scanning tunneling microscopy is a widely used technique, this result may have unforeseen consequences for the measurement of asymmetric surface phenomena in a variety of important fields.

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

International Nuclear Information System (INIS)

Tench, R.J.

1992-11-01

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 β-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

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

DEFF Research Database (Denmark)

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

2003-01-01

Charge density waves (CDWs) have been studied at the surface of a cleaved tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) single crystal using a low temperature scanning tunneling microscope (STM) under ultrahigh-vacuum conditions, between 300 and 33 K with molecular resolution. All CDW...

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

Science.gov (United States)

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

2014-11-01

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

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

International Nuclear Information System (INIS)

Forman, C J; Barker, P D; Wang, N; Durkan, C; Yang, Z Y; Mowat, C G; Jarvis, S

2013-01-01

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

Giant inelastic tunneling in epitaxial graphene mediated by localized states

NARCIS (Netherlands)

Cervenka, J.; Ruit, van de K.; Flipse, C.F.J.

2010-01-01

Local electronic structures of nanometer-sized patches of epitaxial graphene and its interface layer with SiC(0001) have been studied by atomically resolved scanning tunneling microscopy and spectroscopy. Localized states belonging to the interface layer of a graphene/SiC system show to have

Scanning probe microscopy in material science and biology

International Nuclear Information System (INIS)

Cricenti, A; Colonna, S; Girasole, M; Gori, P; Ronci, F; Longo, G; Dinarelli, S; Luce, M; Rinaldi, M; Ortenzi, M

2011-01-01

A review of the activity of scanning probe microscopy at our Institute is presented, going from instrumentation to software development of scanning tunnelling microscopy, atomic force microscopy and scanning near-field optical microscopy (SNOM). Some of the most important experiments in material science and biology performed by our group through the years with these SPM techniques will be presented. Finally, infrared applications by coupling a SNOM with a free electron laser will also be presented.

Investigation of the structural anisotropy in a self-assembling glycinate layer on Cu(100) by scanning tunneling microscopy and density functional theory calculations

Energy Technology Data Exchange (ETDEWEB)

Kuzmin, Mikhail [Surface Science Laboratory, Optoelectronics Research Centre, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere (Finland); Ioffe Physical Technical Institute, Russian Academy of Sciences, 26 Polytekhnicheskaya, St Petersburg 194021 (Russian Federation); Lahtonen, Kimmo; Vuori, Leena [Surface Science Laboratory, Optoelectronics Research Centre, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere (Finland); Sánchez-de-Armas, Rocío [Materials Theory Division, Department of Physics and Astronomy, Uppsala University, P.O. Box 516, S75120 Uppsala (Sweden); Hirsimäki, Mika, E-mail: mikahirsi@gmail.com [Surface Science Laboratory, Optoelectronics Research Centre, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere (Finland); Valden, Mika [Surface Science Laboratory, Optoelectronics Research Centre, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere (Finland)

2017-07-01

Highlights: • Deprotonation reaction of glycine and self-assembly of glycinate is observed on Cu. • Bias-dependent scanning tunneling microscopy indicates two glycinate geometries. • Density functional theory calculations confirm the two non-identical configurations. • Non-identical adsorption explains the anisotropy in adlayer’s electronic structure. - Abstract: Self-assembling organic molecule-metal interfaces exhibiting free-electron like (FEL) states offers an attractive bottom-up approach to fabricating materials for molecular electronics. Accomplishing this, however, requires detailed understanding of the fundamental driving mechanisms behind the self-assembly process. For instance, it is still unresolved as to why the adsorption of glycine ([NH{sub 2}(CH{sub 2})COOH]) on isotropic Cu(100) single crystal surface leads, via deprotonation and self-assembly, to a glycinate ([NH{sub 2}(CH{sub 2})COO–]) layer that exhibits anisotropic FEL behavior. Here, we report on bias-dependent scanning tunneling microscopy (STM) experiments and density functional theory (DFT) calculations for glycine adsorption on Cu(100) single crystal surface. We find that after physical vapor deposition (PVD) of glycine on Cu(100), glycinate self-assembles into an overlayer exhibiting c(2 × 4) and p(2 × 4) symmetries with non-identical adsorption sites. Our findings underscore the intricacy of electrical conductivity in nanomolecular organic overlayers and the critical role the structural anisotropy at molecule-metal interface plays in the fabrication of materials for molecular electronics.

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.

Theory of high-resolution tunneling spin transport on a magnetic skyrmion

OpenAIRE

Palotás, Krisztián; Rózsa, Levente; Szunyogh, László

2018-01-01

Tunneling spin transport characteristics of a magnetic skyrmion are described theoretically in magnetic scanning tunneling microscopy (STM). The spin-polarized charge current in STM (SP-STM) and tunneling spin transport vector quantities, the longitudinal spin current and the spin transfer torque are calculated in high spatial resolution within the same theoretical framework. A connection between the conventional charge current SP-STM image contrasts and the magnitudes of the spin transport v...

Investigations on tunneling and kissing bond defects in FSW joints for dissimilar aluminum alloys

Energy Technology Data Exchange (ETDEWEB)

Khan, Noor Zaman, E-mail: noor_0315@yahoo.com [Department of Mechanical Engineering, Jamia Millia Islamia (A Central University), New Delhi (India); Siddiquee, Arshad Noor; Khan, Zahid A. [Department of Mechanical Engineering, Jamia Millia Islamia (A Central University), New Delhi (India); Shihab, Suha K. [Department of Mechanical Engineering, Engineering College, Diyala University, Diyala (Iraq)

2015-11-05

In this paper an attempt has been made to investigate the effect of two Friction Stir Welding (FSW) parameters i.e. tool pin offset and tool plunge depth on the formation of defects such as tunnel (tunneling defect) and kissing bond (KB) during welding of dissimilar aluminum alloys. 4.75 mm thick plates of AA5083-H116 and AA6063-T6 were welded using a novel work-fixture developed in-house which, apart from clamping the plated also imparted continuous variation of offset on both side of the faying line. The tunneling defect was modeled as a function of offset and plunge depth. The welds were characterised using optical microscopy (OM), scanning electron microscopy (SEM) and mechanical testing. The causes of such defects have been analyzed and discussed and recommendations have been made to prevent their occurrence. The findings of the study have revealed that the tunneling defects are formed at all offset (including zero offset) values towards stronger material (advancing side). And the cross-section of the tunnel varied with the amount of offset. Further, KBs are formed at the interface for all pin offset values except 0.5 mm towards weaker material and high plunge depth resulting in the poor mechanical properties. - Highlights: • Two dissimilar aluminum alloys are welded using FSW. • Formation of kissing bond and tunneling defects are investigated. • Defects are formed at pin offsets towards stronger material and also without offset. • The size of tunnel reduces significantly by increasing the plunge depth. • Tool pin offset towards weaker material prevent tunneling defects.

Fire safety case study of a railway tunnel: Smoke evacuation

Directory of Open Access Journals (Sweden)

van Maele Karim

2007-01-01

Full Text Available When a fire occurs in a tunnel, it is of great importance to assure the safety of the occupants of the tunnel. This is achieved by creating smoke-free spaces in the tunnel through control of the smoke gases. In this paper, results are presented of a study concerning the fire safety in a real scale railway tunnel test case. Numerical simulations are performed in order to examine the possibility of natural ventilation of smoke in inclined tunnels. Several aspects are taken into account: the length of the simulated tunnel section, the slope of the tunnel and the possible effects of external wind at one portal of the tunnel. The Fire Dynamics Simulator of the National Institute of Standards and Technology, USA, is applied to perform the simulations. The simulations show that for the local behavior of the smoke during the early stages of the fire, the slope of the tunnel is of little importance. Secondly, the results show that external wind and/or pressure conditions have a large effect on the smoke gases inside the tunnel. Finally, some idea for the value of the critical ventilation velocity is given. The study also shows that computational fluid dynamics calculations are a valuable tool for large scale, real life complex fire cases. .

STM in liquids. A scanning tunneling microscopy exploration of the liquid-solid interface.

NARCIS (Netherlands)

Hulsken, B.

2008-01-01

This thesis reports of a series of atomic scale studies of the liquid-solid interface, carried out with a home-built liquid-cell Scanning Tunnelling Microscope (STM). The home-built liquid-cell STM is described in detail, and numerical simulations are performed to show that surfaces immersed in the

The Ehrlich–Schwoebel barrier on an oxide surface: a combined Monte-Carlo and in situ scanning tunneling microscopy approach

International Nuclear Information System (INIS)

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

2015-01-01

The controlled growth of epitaxial films of complex oxides requires an atomistic understanding of key parameters determining final film morphology, such as termination dependence on adatom diffusion, and height of the Ehrlich–Schwoebel (ES) barrier. Here, through an in situ scanning tunneling microscopy study of mixed-terminated La_5_/_8Ca_3_/_8MnO_3 (LCMO) films, we image adatoms and observe pile-up at island edges. Image analysis allows determination of the population of adatoms at the edge of islands and fractions on A-site and B-site terminations. A simple Monte-Carlo model, simulating the random walk of adatoms on a sinusoidal potential landscape using Boltzmann statistics is used to reproduce the experimental data, and provides an estimate of the ES barrier as ∼0.18 ± 0.04 eV at T = 1023 K, similar to those of metal adatoms on metallic surfaces. These studies highlight the utility of in situ imaging, in combination with basic Monte-Carlo methods, in elucidating the factors which control the final film growth in complex oxides. (paper)

The Ehrlich-Schwoebel barrier on an oxide surface: a combined Monte-Carlo and in situ scanning tunneling microscopy approach.

Science.gov (United States)

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

2015-11-13

The controlled growth of epitaxial films of complex oxides requires an atomistic understanding of key parameters determining final film morphology, such as termination dependence on adatom diffusion, and height of the Ehrlich-Schwoebel (ES) barrier. Here, through an in situ scanning tunneling microscopy study of mixed-terminated La5/8Ca3/8MnO3 (LCMO) films, we image adatoms and observe pile-up at island edges. Image analysis allows determination of the population of adatoms at the edge of islands and fractions on A-site and B-site terminations. A simple Monte-Carlo model, simulating the random walk of adatoms on a sinusoidal potential landscape using Boltzmann statistics is used to reproduce the experimental data, and provides an estimate of the ES barrier as ∼0.18 ± 0.04 eV at T = 1023 K, similar to those of metal adatoms on metallic surfaces. These studies highlight the utility of in situ imaging, in combination with basic Monte-Carlo methods, in elucidating the factors which control the final film growth in complex oxides.

The Ehrlich-Schwoebel barrier on an oxide surface: a combined Monte-Carlo and in situ scanning tunneling microscopy approach

Science.gov (United States)

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

2015-11-01

The controlled growth of epitaxial films of complex oxides requires an atomistic understanding of key parameters determining final film morphology, such as termination dependence on adatom diffusion, and height of the Ehrlich-Schwoebel (ES) barrier. Here, through an in situ scanning tunneling microscopy study of mixed-terminated La5/8Ca3/8MnO3 (LCMO) films, we image adatoms and observe pile-up at island edges. Image analysis allows determination of the population of adatoms at the edge of islands and fractions on A-site and B-site terminations. A simple Monte-Carlo model, simulating the random walk of adatoms on a sinusoidal potential landscape using Boltzmann statistics is used to reproduce the experimental data, and provides an estimate of the ES barrier as ˜0.18 ± 0.04 eV at T = 1023 K, similar to those of metal adatoms on metallic surfaces. These studies highlight the utility of in situ imaging, in combination with basic Monte-Carlo methods, in elucidating the factors which control the final film growth in complex oxides.

Sediment and Cavitation Erosion Studies through Dam Tunnels

Directory of Open Access Journals (Sweden)

Muhammad Abid

2016-01-01

Full Text Available This paper presents results of sediment and cavitation erosion through Tunnel 2 and Tunnel 3 of Tarbela Dam in Pakistan. Main bend and main branch of Tunnel 2 and outlet 1 and outlet 3 of Tunnel 3 are concluded to be critical for cavitation and sediment erosion. Studies are also performed for increased sediments flow rate, concluding 5 kg/sec as the critical value for sudden increase in erosion rate density. Erosion rate is concluded to be the function of sediment flow rate and head condition. Particulate mass presently observed is reasonably low, hence presently not affecting the velocity and the flow field.

Scanning tunneling microscopy: A powerful tool for surface analysis

International Nuclear Information System (INIS)

Walle, G.F.A. van de; Nelissen, B.J.; Soethout, L.L.; Kempen, H. van

1987-01-01

The invention of the Scanning Tunneling Microscope (STM) has opened a new area of surface analysis. A description of the principle of operation is given in this paper. Also the technical problems encountered and their solution are described. Two examples demonstrating the possibilities of the STM are presented: topographic and spectroscopic measurements on a stepped Ni (111) surface and photoconductive measurements on GaAs. (orig.)

The study of optimal conditions of electrochemical etching of tunnel electron microscopy tungsten tips; Estudio de las condiciones optimas para la preparacion electroquimica de puntas de tungsteno para el Microscopio de Efecto Tunel

Energy Technology Data Exchange (ETDEWEB)

Anguiano, E; Aguilar, M [Instituto de Ciencia de Materiales del SCIC, Madrid (Spain); Olivar, A I [Centro de Investigacion y de Estudios Avanzados del IPN Unidad Merida. Departamento de fisica Aplicada, Yucatan, Mexico (Mexico)

1997-12-31

We present the experimental results obtained during the study made in the electrochemical etching of tunneling electron microscopy tungsten tips. The experiments was made using DC and two usual electrolytes: KOH and NaOH. For the tip preparation we used a electrochemical cell with stainless steel cathode and the tungsten wire as anode. the electrodes was introduced in a glass recipient containing the electrolytic solution. We study the effects of applied voltage, polish time, tip length and electrolyte concentration as process relevant parameters. The best condition for tip preparation was obtained with a metallurgical microscope and with a SEM.EDX and Auger analysis was made. The results shown the better tips was made with KOH as electrolyte with a limited concentration range (2-4 normal) and applied voltage (2-6 volts) (Author) 20 refs.

Studying the Effect of Tunnel Depth Variation on the Specific Energy of TBM, Case Study: Karaj–Tehran (Iran Water Conveyance Tunnel

Directory of Open Access Journals (Sweden)

Majid Mirahmadi

2016-09-01

Full Text Available The tunnel-boring machine (TBM is a common piece of equipment used in tunneling projects. For planning a mechanical excavation project, prediction of TBM performance and the specification of design elements such as required forces are critical. The specific energy of excavation (SE, i.e. drilling energy consumption per unit volume of rock mass, is a crucial parameter for performance prediction of a TBM. In this study, the effect of variation of tunnel depth on SE by considering the post-failure behavior of rock mass was investigated. Several new relations between SE and tunnel depth are proposed according to the statistical analysis obtained from Karaj – Tehran Water Conveyance Tunnel real data. The results showed that there is a direct relation between both parameters and. Polynomial equations are proposed as the best expression of the correlation between these parameters.

Switching and sensing spin states of co-porphyrin in bimolecular reactions on Au111 using scanning tunneling microscopy.

Science.gov (United States)

Kim, Howon; Chang, Yun Hee; Lee, Soon-Hyeong; Kim, Yong-Hyun; Kahng, Se-Jong

2013-10-22

Controlling and sensing spin states of magnetic molecules at the single-molecule level is essential for spintronic molecular device applications. Here, we demonstrate that spin states of Co-porphyrin on Au(111) can be reversibly switched over by binding and unbinding of the NO molecule and can be sensed using scanning tunneling microscopy and spectroscopy (STM and STS). Before NO exposure, Co-porphryin showed a clear zero-bias peak, a signature of Kondo effect in STS, whereas after NO exposures, it formed a molecular complex, NO-Co-porphyrin, that did not show any zero-bias feature, implying that the Kondo effect was switched off by binding of NO. The Kondo effect could be switched back on by unbinding of NO through single-molecule manipulation or thermal desorption. Our density functional theory calculation results explain the observations with pairing of unpaired spins in dz(2) and ppπ* orbitals of Co-porphyrin and NO, respectively. Our study opens up ways to control molecular spin state and Kondo effect by means of enormous variety of bimolecular binding and unbinding reactions on metallic surfaces.

Analysis of oxygen and hydrogen adsorption on Nb(100) surface by scanning tunneling microscopy

International Nuclear Information System (INIS)

An, Bai; Wen, Mao; Fukuyama, Seiji; Yokogawa, Kiyoshi; Ichimura, Shingo; Yoshimura, Masamichi

2006-01-01

The surface structure of Nb(100) under the condition of cleaning, oxidation and hydrogen adsorption is observed by STM (scanning tunneling microscopy). The results obtained are followings; (1) (3 x 1)-O→(4 x 1)-O→c(2 x 2)-O→clean(1 x 1)structure was observed by atom level, and these atomic models of structures and STM images were verified by the first-principles calculations, (2) when the clean(1 x 1) structure exposed to hydrogen, dissociative adsorption of hydrogen was observed and Nb hydride cluster formed on the surface at room temperature. It was heated at about 450 - 670 K in UHV, the cluster decomposed into hydrogen and (1 x 1) structure with linear defect was formed. The c(2 x 2)-O structure by oxygen adsorption transformed into (1 x 1)-H structure with OH and Nb hydride cluster under hydrogen gas at room temperature. When it was heated in UHV at 640 K, OH desorbed from the surface and (1 x 1) structure with linear defect was generated. The surface of (3 x 1)-O structure was not changed by hydrogen. (S.Y.)

Confined states of individual type-II GaSb/GaAs quantum rings studied by cross-sectional scanning tunneling spectroscopy.

Science.gov (United States)

Timm, Rainer; Eisele, Holger; Lenz, Andrea; Ivanova, Lena; Vossebürger, Vivien; Warming, Till; Bimberg, Dieter; Farrer, Ian; Ritchie, David A; Dähne, Mario

2010-10-13

Combined cross-sectional scanning tunneling microscopy and spectroscopy results reveal the interplay between the atomic structure of ring-shaped GaSb quantum dots in GaAs and the corresponding electronic properties. Hole confinement energies between 0.2 and 0.3 eV and a type-II conduction band offset of 0.1 eV are directly obtained from the data. Additionally, the hole occupancy of quantum dot states and spatially separated Coulomb-bound electron states are observed in the tunneling spectra.

Single Electron Tunneling

International Nuclear Information System (INIS)

Ruggiero, Steven T.

2005-01-01

Financial support for this project has led to advances in the science of single-electron phenomena. Our group reported the first observation of the so-called ''Coulomb Staircase'', which was produced by tunneling into ultra-small metal particles. This work showed well-defined tunneling voltage steps of width e/C and height e/RC, demonstrating tunneling quantized on the single-electron level. This work was published in a now well-cited Physical Review Letter. Single-electron physics is now a major sub-field of condensed-matter physics, and fundamental work in the area continues to be conducted by tunneling in ultra-small metal particles. In addition, there are now single-electron transistors that add a controlling gate to modulate the charge on ultra-small photolithographically defined capacitive elements. Single-electron transistors are now at the heart of at least one experimental quantum-computer element, and single-electron transistor pumps may soon be used to define fundamental quantities such as the farad (capacitance) and the ampere (current). Novel computer technology based on single-electron quantum dots is also being developed. In related work, our group played the leading role in the explanation of experimental results observed during the initial phases of tunneling experiments with the high-temperature superconductors. When so-called ''multiple-gap'' tunneling was reported, the phenomenon was correctly identified by our group as single-electron tunneling in small grains in the material. The main focus throughout this project has been to explore single electron phenomena both in traditional tunneling formats of the type metal/insulator/particles/insulator/metal and using scanning tunneling microscopy to probe few-particle systems. This has been done under varying conditions of temperature, applied magnetic field, and with different materials systems. These have included metals, semi-metals, and superconductors. Amongst a number of results, we have

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 K3[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 WO3 form.

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

DEFF Research Database (Denmark)

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

2007-01-01

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...

Size dependence in tunneling spectra of PbSe quantum-dot arrays.

Science.gov (United States)

Ou, Y C; Cheng, S F; Jian, W B

2009-07-15

Interdot Coulomb interactions and collective Coulomb blockade were theoretically argued to be a newly important topic, and experimentally identified in semiconductor quantum dots, formed in the gate confined two-dimensional electron gas system. Developments of cluster science and colloidal synthesis accelerated the studies of electron transport in colloidal nanocrystal or quantum-dot solids. To study the interdot coupling, various sizes of two-dimensional arrays of colloidal PbSe quantum dots are self-assembled on flat gold surfaces for scanning tunneling microscopy and scanning tunneling spectroscopy measurements at both room and liquid-nitrogen temperatures. The tip-to-array, array-to-substrate, and interdot capacitances are evaluated and the tunneling spectra of quantum-dot arrays are analyzed by the theory of collective Coulomb blockade. The current-voltage of PbSe quantum-dot arrays conforms properly to a scaling power law function. In this study, the dependence of tunneling spectra on the sizes (numbers of quantum dots) of arrays is reported and the capacitive coupling between quantum dots in the arrays is explored.

Electromigration of single metal atoms observed by scanning tunneling microscopy

NARCIS (Netherlands)

Braun, K.-F.; Soe, W.H.; Flipse, C.F.J.

2007-01-01

The authors show in this letter that single metal atoms on a Ni(111) surface can be pushed by electromigration forces from a scanning tunneling microscope tip. This repulsive interaction is obsd. over a length scale of 6 nm. While for voltages above -300 mV the atoms are pulled by the microscope

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

Science.gov (United States)

Forman, C. J.; Wang, N.; Yang, Z. Y.; Mowat, C. G.; Jarvis, S.; Durkan, C.; Barker, P. D.

2013-05-01

Amyloid fibres displaying cytochrome b562 were probed using scanning tunnelling microscopy (STM) in vacuo. The cytochromes are electron transfer proteins containing a haem cofactor and could, in principle, mediate electron transfer between the tip and the gold substrate. If the core fibres were insulating and electron transfer within the 3D haem network was detected, then the electron transport properties of the fibre could be controlled by genetic engineering. Three kinds of STM images were obtained. At a low bias (<1.5 V) the fibres appeared as regions of low conductivity with no evidence of cytochrome mediated electron transfer. At a high bias, stable peaks in tunnelling current were observed for all three fibre species containing haem and one species of fibre that did not contain haem. In images of this kind, some of the current peaks were collinear and spaced around 10 nm apart over ranges longer than 100 nm, but background monomers complicate interpretation. Images of the third kind were rare (1 in 150 fibres); in these, fully conducting structures with the approximate dimensions of fibres were observed, suggesting the possibility of an intermittent conduction mechanism, for which a precedent exists in DNA. To test the conductivity, some fibres were immobilized with sputtered gold, and no evidence of conduction between the grains of gold was seen. In control experiments, a variation of monomeric cytochrome b562 was not detected by STM, which was attributed to low adhesion, whereas a monomeric multi-haem protein, GSU1996, was readily imaged. We conclude that the fibre superstructure may be intermittently conducting, that the cytochromes have been seen within the fibres and that they are too far apart for detectable current flow between sites to occur. We predict that GSU1996, being 10 nm long, is more likely to mediate successful electron transfer along the fibre as well as being more readily detectable when displayed from amyloid.

Commendable surface physics by means of scanning tunneling microscopy

International Nuclear Information System (INIS)

Besenbacher, F.; Laegsgaard, E.; Stensgard, I.

1995-01-01

The scanning tunneling microscope, developed at the Aarhus University (Denmark) allows taking several STM images per second, as opposite to other similar microscopes, where the typical scanning time is 0,5-1 min. This new system enables collecting of important information concerning dynamic processes on the surfaces. The Aarhus microscope is very stable, hence atomic resolution is achievable even on close-packed metallic surfaces, while it is difficult to achieve by means of the conventional STM. (EG)

Tunneling technologies for the collider ring tunnels

International Nuclear Information System (INIS)

Frobenius, P.

1989-01-01

The Texas site chosen for the Superconducting Super Collider has been studied, and it has been determined that proven, conventional technology and accepted engineering practice are suitable for constructing the collider tunnels. The Texas National Research Laboratory Commission report recommended that two types of tunneling machines be used for construction of the tunnels: a conventional hard rock tunnel boring machine (TBM) for the Austin chalk and a double shielded, rotary TBM for the Taylor marl. Since the tunneling machines usually set the pace for the project, efficient planning, operation, and coordination of the tunneling system components will be critical to the schedule and cost of the project. During design, tunneling rate prediction should be refined by focusing on the development of an effective tunneling system and evaluating its capacity to meet or exceed the required schedules. 8 refs., 13 figs

A scanning tunneling microscope for a dilution refrigerator.

Science.gov (United States)

Marz, M; Goll, G; Löhneysen, H v

2010-04-01

We present the main features of a home-built scanning tunneling microscope that has been attached to the mixing chamber of a dilution refrigerator. It allows scanning tunneling microscopy and spectroscopy measurements down to the base temperature of the cryostat, T approximately 30 mK, and in applied magnetic fields up to 13 T. The topography of both highly ordered pyrolytic graphite and the dichalcogenide superconductor NbSe(2) has been imaged with atomic resolution down to T approximately 50 mK as determined from a resistance thermometer adjacent to the sample. As a test for a successful operation in magnetic fields, the flux-line lattice of superconducting NbSe(2) in low magnetic fields has been studied. The lattice constant of the Abrikosov lattice shows the expected field dependence proportional to 1/square root of B and measurements in the scanning tunneling spectroscopy mode clearly show the superconductive density of states with Andreev bound states in the vortex core.

Report Tunneling Cost Reduction Study prepared for Fermilab

International Nuclear Information System (INIS)

Not Available

1999-01-01

Fermi National Accelerator Laboratories has a need to review the costs of constructing the very long tunnels which would be required for housing the equipment for the proposed Very Large Hadron Collider (VLHC) project. Current tunneling costs are high, and the identification of potential means of significantly reducing them, and thereby helping to keep overall project costs within an acceptable budget, has assumed great importance. Fermilab has contracted with The Robbins Company to provide an up-to-date appraisal of tunneling technology, and to review the potential for substantially improving currently the state-of-practice performance and construction costs in particular. The Robbins Company was chosen for this task because of its long and successful experience in hard rock mechanical tunnel boring. In the past 40 years, Robbins has manufactured over 250 tunneling machines, the vast majority for hard rock applications. In addition to also supplying back-up equipment, Robbins has recently established a division dedicated to the manufacture of continuous conveying equipment for the efficient support of tunneling operations. The study extends beyond the tunnel boring machine (TBM) itself, and into the critical area of the logistics of the support of the machine as it advances, including manpower. It is restricted to proven methods using conventional technology, and its potential for incremental but meaningful improvement, rather than examining exotic and undeveloped means of rock excavation that have been proposed from time to time by the technical community. This is the first phase of what is expected to be a number of studies in increasing depth of technical detail, and as such has been restricted to the issues connected with the initial 34 kilometer circumference booster tunnel, and not the proposed 500 kilometer circumference tunnel housing the VLHC itself. The booster tunnel is entirely sited within low to medium strength limestone and dolomite formations

Evaluation of the Influence Caused by Tunnel Construction on Groundwater Environment: A Case Study of Tongluoshan Tunnel, China

Directory of Open Access Journals (Sweden)

Jian Liu

2015-01-01

Full Text Available Problems related to water inflow during tunnel construction are challenging to designers, workers, and management departments, as they can threaten tunneling project from safety, time, and economic aspects. Identifying the impacts on groundwater environment resulting from tunnel drainage and making a correct assessment before tunnel construction is essential to better understand troubles that would be encountered during tunnel excavation and helpful to adopt appropriate countermeasures to minimize the influences. This study presents an indicator system and quantifies each indicator of Tongluoshan tunnel, which is located in southwest China with a length of 5.2 km and mainly passes through carbonate rocks and sandstones, based on field investigation and related technological reports. Then, an evaluation is made using fuzzy comprehensive assessment method, with a result showing that it had influenced the local groundwater environment at a moderate degree. Information fed back from environmental investigation and hydrologic monitoring carried out during the main construction period proves the evaluation, as the flow of some springs and streams located beside the tunnel route was found experiencing an apparent decline.

Strong quasi-particle tunneling study in the paired quantum Hall states

OpenAIRE

Nomura, Kentaro; Yoshioka, Daijiro

2001-01-01

The quasi-particle tunneling phenomena in the paired fractional quantum Hall states are studied. A single point-contact system is first considered. Because of relevancy of the quasi-particle tunneling term, the strong tunneling regime should be investigated. Using the instanton method it is shown that the strong quasi-particle tunneling regime is described as the weak electron tunneling regime effectively. Expanding to the network model the paired quantum Hall liquid to insulator transition i...

Doping dependent tunneling conductance in SDW ordered copper oxide superconductors

International Nuclear Information System (INIS)

Rout, G.C.; Panda, S.K.

2011-01-01

The model calculation reports the co-existences of s-wave superconductivity and spin density wave (SDW) in high-T c cuprates. The doping dependence of the phase diagram explains the experimental observations qualitatively. The calculated tunneling spectra explains the observed multiple peak structures. This calculation provides an alternative to BCS formalism to calculate order parameters from the spectra. It is observed that doping suppresses the long range anti-ferromagnetic order and induces superconducting phase for a suitable doping. In order to study this effect, we present a model study of the doping dependence of the tunneling conductance in high-T c systems. The system is described by the Hamiltonian consisting of spin density wave (SDW) and s-wave type superconducting interaction in presence of varying impurity concentrations. The gap equations are calculated by using Green's functions technique of Zubarev. The gap equations and the chemical potential are solved self-consistently. The imaginary part of the electron Green's functions shows the quasi-particle density of states which represent the tunneling conductance observed by the scanning tunneling microscopy (STM). We investigate the effect of impurity on the gap equations as well as on the tunneling conductance. The results will be discussed based on the experimental observations.

Doping dependent tunneling conductance in SDW ordered copper oxide superconductors

Energy Technology Data Exchange (ETDEWEB)

Rout, G.C., E-mail: gcr@iopb.res.in [Condensed Matter Physics Group, Dept. of Applied Physics and Ballistics, F.M. University, 756 019 Balasore, Orissa (India); Panda, S K [K.D. Science College, Pochilima, Hinjilicut, 761 101 Ganjam, Orissa (India)

2011-07-15

The model calculation reports the co-existences of s-wave superconductivity and spin density wave (SDW) in high-T{sub c} cuprates. The doping dependence of the phase diagram explains the experimental observations qualitatively. The calculated tunneling spectra explains the observed multiple peak structures. This calculation provides an alternative to BCS formalism to calculate order parameters from the spectra. It is observed that doping suppresses the long range anti-ferromagnetic order and induces superconducting phase for a suitable doping. In order to study this effect, we present a model study of the doping dependence of the tunneling conductance in high-T{sub c} systems. The system is described by the Hamiltonian consisting of spin density wave (SDW) and s-wave type superconducting interaction in presence of varying impurity concentrations. The gap equations are calculated by using Green's functions technique of Zubarev. The gap equations and the chemical potential are solved self-consistently. The imaginary part of the electron Green's functions shows the quasi-particle density of states which represent the tunneling conductance observed by the scanning tunneling microscopy (STM). We investigate the effect of impurity on the gap equations as well as on the tunneling conductance. The results will be discussed based on the experimental observations.

Doping dependent tunneling conductance in SDW ordered copper oxide superconductors

Energy Technology Data Exchange (ETDEWEB)

Rout, G.C., E-mail: gcr@iopb.res.in [Condensed Matter Physics Group, Dept. of Applied Physics and Ballistics, F.M. University, 756 019 Balasore, Orissa (India); Panda, S.K. [K.D. Science College, Pochilima, Hinjilicut, 761 101 Ganjam, Orissa (India)

2011-07-15

The model calculation reports the co-existences of s-wave superconductivity and spin density wave (SDW) in high-T{sub c} cuprates. The doping dependence of the phase diagram explains the experimental observations qualitatively. The calculated tunneling spectra explains the observed multiple peak structures. This calculation provides an alternative to BCS formalism to calculate order parameters from the spectra. It is observed that doping suppresses the long range anti-ferromagnetic order and induces superconducting phase for a suitable doping. In order to study this effect, we present a model study of the doping dependence of the tunneling conductance in high-T{sub c} systems. The system is described by the Hamiltonian consisting of spin density wave (SDW) and s-wave type superconducting interaction in presence of varying impurity concentrations. The gap equations are calculated by using Green's functions technique of Zubarev. The gap equations and the chemical potential are solved self-consistently. The imaginary part of the electron Green's functions shows the quasi-particle density of states which represent the tunneling conductance observed by the scanning tunneling microscopy (STM). We investigate the effect of impurity on the gap equations as well as on the tunneling conductance. The results will be discussed based on the experimental observations.

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

DEFF Research Database (Denmark)

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

2009-01-01

We have used L-Cysteine (Cys) as a model system to study the surface electronic structures of single molecules at the submolecular level in aqueous buffer solution by a combination of electrochemical scanning tunneling microscopy (in situ STM), electrochemistry including voltammetry and chronocou...

Structural Safety Assessment of Existing Multiarch Tunnel: A Case Study

Directory of Open Access Journals (Sweden)

Jinxing Lai

2017-01-01

Full Text Available Structural health assessment is one of the key activities in maintaining the performance of a tunnel during its service life. Due to the development of modern detection technology, comprehensive structural health assessment system is being established for operating tunnels. To evaluate the actual operational state of Shitigou tunnel, overall detection of the liner crack, tunnel seepage, and liner void was conducted by employing the modern detection technology, such as crack width monitoring technology, concrete strength monitoring technology, and electromagnetic wave nondestructive monitoring technology. Through the statistical analysis of the detection results, the distribution characteristic, development law, and damage grade of structural defects were obtained. Tunnel liner cracks are mainly located on the middle wall; serious water leakage is encountered on the side wall, middle wall, and vault; the strength of foundation and liner structure of left tunnel does not meet the design requirement; the liner voids are mostly located at the tunnel entrance section, especially, on the tunnel vault; and the proportion of influence factors of structural defects should be considered. The research results presented for this study can serve as references for effective design and health assessment of existing multiarch tunnel projects.

A functional renormalization group application to the scanning tunneling microscopy experiment

Directory of Open Access Journals (Sweden)

José Juan Ramos Cárdenas

2015-12-01

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

Directional scanning tunneling spectroscopy in MgB2

International Nuclear Information System (INIS)

Iavarone, M.; Karapetrov, G.; Koshelev, A.E.; Kwok, W.K.; Crabtree, G.W.; Hinks, D.G.; Cook, R.; Kang, W.N.; Choi, E.M.; Kim, H.J.; Lee, S.I.

2003-01-01

The superconductivity in MgB 2 has a two-band character with the dominating band having a 2D character and the second band being isotropic in the three dimensions. We use tunneling microscopy and spectroscopy to reveal the two distinct energy gaps at Δ 1 =2.3 meV and Δ 2 =7.1 meV. Different spectral weights of the partial superconducting density of states are a reflection of different tunneling directions in this multi-band system. The results are consistent with the existence of two-band superconductivity in the presence of strong interband superconducting pair interaction and quasiparticle scattering. The temperature evolution of the tunneling spectra shows both gaps vanishing at the bulk T c

Atomic site tunneling spectroscopy on high-Tc superconductors

International Nuclear Information System (INIS)

Hasegawa, T.; Nantoh, M.; Takagi, A.; Yamaguchi, W.; Ogino, M.; Kawasaki, M.

1994-01-01

Superconducting gap structures of Bi 2 Sr 2 CaCu 2 O y (BSCCO) and YBa 2 Cu 3 O y (YBCO) have been probed by scanning tunneling microscopy (STM) at cryogenic temperatures. The tunneling conductance curves observed on bulk single crystals of BSCCO and epitaxial thin films of YBCO revealed clear obershooting peaks and flat bottom regions around V=0 with quite low zero-bias conductances of ∝1%. Since the electron tunneling process in STM is essentially incoherent, the present observation is favored by the s-wave pairing mechanism. However, the conductance curves were found to be substantially smeared in comparison with the conventional spectra predicted in the BCS (isotropic s-wave) superconductors, suggesting gap anisotropy. (orig.)

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

DEFF Research Database (Denmark)

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

1998-01-01

A first-principles theory of inelastic tunneling between a model probe tip and an atom adsorbed on a surface is presented, extending the elastic tunneling theory of Tersoff and Hamann. The inelastic current is proportional to the change in the local density of states at the center of the tip due...... to the addition of the adsorbate. We use the theory to investigate the vibrational heating of an adsorbate below a scanning tunneling microscopy tip. We calculate the desorption rate of PI from Si(100)-H(2 X 1) as a function of the sample bias and tunnel current, and find excellent a,agreement with recent...

Three-dimensional scanning force/tunneling spectroscopy at room temperature

International Nuclear Information System (INIS)

Sugimoto, Yoshiaki; Ueda, Keiichi; Abe, Masayuki; Morita, Seizo

2012-01-01

We simultaneously measured the force and tunneling current in three-dimensional (3D) space on the Si(111)-(7 × 7) surface using scanning force/tunneling microscopy at room temperature. The observables, the frequency shift and the time-averaged tunneling current were converted to the physical quantities of interest, i.e. the interaction force and the instantaneous tunneling current. Using the same tip, the local density of states (LDOS) was mapped on the same surface area at constant height by measuring the time-averaged tunneling current as a function of the bias voltage at every lateral position. LDOS images at negative sample voltages indicate that the tip apex is covered with Si atoms, which is consistent with the Si-Si covalent bonding mechanism for AFM imaging. A measurement technique for 3D force/current mapping and LDOS imaging on the equivalent surface area using the same tip was thus demonstrated. (paper)

"We Actually Saw Atoms with Our Own Eyes": Conceptions and Convictions in Using the Scanning Tunneling Microscope in Junior High School

Science.gov (United States)

Margel, Hannah; Eylon, Bat-Sheva; Scherz, Zahava

2004-01-01

The feasibility and the potential contribution of the scanning tunneling microscopy (STM) in junior high school (JHS) as an instructional tool for learning the particulate nature of matter is described. The use and power of new technologies can probably be demonstrated by the scanning tunneling microscopy (STM).

Tracheal reconstruction by re-inforced Gore-Tex in esophageal submuscular tunneling: An experimental study

Directory of Open Access Journals (Sweden)

Hodjati Hossein

2011-01-01

Full Text Available Background: Tracheal reconstructions are aimed at rearranging or replacing parts of the tracheal tissue by different techniques. Here we introduce a new technique for tracheal reconstruction. Methods: In 10 adult dogs, after intubation with an endotracheal tube, a segment of trachea including seven tracheal rings was resected circumferentially. A submuscular tunnel was induced between mucosal and muscular layers of the adjacent esophagus lying right next to the trachea. The esophageal submuscular tunnel starts and ends exactly at the level of distal and proximal ends of tracheal resection, respectively. Inforced Gore-Tex passed through the esophageal submuscular tunnel the distal segment of trachea and end-to-end anastomosis were made between distal ends of Gore-Tex and trachea, then endotracheal tube removed and the same procedure was made for proximal ends of Gore-Tex and trachea. Afterward, the proximal and distal ends of the esophageal tunnel were approximated to proximal and distal tracheal parts over the anastomosis. Results: All dogs, except one due to anesthetic problem, survived and tolerated the operation; the first two dogs experienced postoperative fever, aspiration pneumonia, and died due to tracheoesophageal fistula. All survived animals were eating and barking well. We started to scarify dogs at least 6 and 12 weeks after operation for microscopy and pathologic examination. The Gore-Texes were patent and supported externally with fibrous connective tissue in esophageal tunneling, with in growth of respiratory epithelium on inner surfaces. Conclusion: Air tightness, good re-epithelialization, and relatively no limitation of esophageal length and no risk of luminal collapse are advantages of tracheal reconstruction by submuscular esophageal tunneling. This new method is worthy of further investigation, as it is technically feasible and easy to implement.

New approach towards imaging λ-DNA using scanning tunneling ...

Indian Academy of Sciences (India)

Wintec

spectroscopy (STS) at different stages depict a broad distribution of defect states in the bandgap ... DNA; scanning tunneling microscopy; Langmuir Blodget technique; silanization. 1. ... assembled monolayer (SAM) of C-8 silane gave stable.

Near-field optical microscopy with a scanning tunneling microscope

International Nuclear Information System (INIS)

Barbara, A.; Lopez-Rios, T.; Quemerais, P.

2005-01-01

A homemade apertureless near-field optical microscope using a scanning tunneling microscope (STM) is described. The experimental set-up simultaneously provides optical and topographic images of the sample. Technical details and features of the set-up are presented, together with results demonstrating the sub-wavelength resolution achieved as well as its sensitivity to dielectric contrasts. We show that the use of a STM permits to precisely control very small distances between the tip and the sample which is a great advantage to excite localized optical resonances between the tip and the surface

First principles studies of electron tunneling in proteins

Science.gov (United States)

Hayashi, Tomoyuki; Stuchebrukhov, Alexei A.

2014-01-01

A first principles study of electronic tunneling along the chain of seven Fe/S clusters in respiratory complex I, a key enzyme in the respiratory electron transport chain, is described. The broken-symmetry states of the Fe/S metal clusters calculated at both DFT and semi-empirical ZINDO levels were utilized to examine both the extremely weak electronic couplings between Fe/S clusters and the tunneling pathways, which provide a detailed atomistic-level description of the charge transfer process in the protein. One-electron tunneling approximation was found to hold within a reasonable accuracy, with only a moderate induced polarization of the core electrons. The method is demonstrated to be able to calculate accurately the coupling matrix elements as small as 10−4 cm−1. A distinct signature of the wave properties of electrons is observed as quantum interferences of multiple tunneling pathways. PMID:25383312

Spin-polarized scanning tunneling microscopy experiments on the rough surface of a polycrystalline NiFe film with a fine magnetic tip sensitive to a well-defined magnetization component

Directory of Open Access Journals (Sweden)

H. Matsuyama

2016-03-01

Full Text Available We developed a micrometer-sized magnetic tip integrated onto the write head of a hard disk drive for spin-polarized scanning tunneling microscopy (SP-STM in the modulated tip magnetization mode. Using SP-STM, we measured a well-defined in-plane spin-component of the tunneling current of the rough surface of a polycrystalline NiFe film. The spin asymmetry of the NiFe film was about 1.3% within the bias voltage range of -3 to 1 V. We obtained the local spin component image of the sample surface, switching the magnetic field of the sample to reverse the sample magnetization during scanning. We also obtained a spin image of the rough surface of a polycrystalline NiFe film evaporated on the recording medium of a hard disk drive.

Spin-polarized scanning tunneling microscopy experiments on the rough surface of a polycrystalline NiFe film with a fine magnetic tip sensitive to a well-defined magnetization component

Energy Technology Data Exchange (ETDEWEB)

Matsuyama, H., E-mail: matsu@phys.sci.hokudai.ac.jp [Department of Physics, Faculty of Science, Hokkaido University, Sapporo, Hokkaido 060-0810 (Japan); Nara, D.; Kageyama, R.; Honda, K.; Sato, T.; Kusanagi, K. [Department of Condensed Matter Physics, Graduate School of Science, Hokkaido University, Sapporo, Hokkaido 060-0810 (Japan); Srinivasan, E. [Creative Research Institution (CRIS), Hokkaido University, Sapporo, Hokkaido 001-0021 (Japan); Koike, K. [Department of Physics, Faculty of Science, Hokkaido University, Sapporo, Hokkaido 060-0810 (Japan); Creative Research Institution (CRIS), Hokkaido University, Sapporo, Hokkaido 001-0021 (Japan)

2016-03-15

We developed a micrometer-sized magnetic tip integrated onto the write head of a hard disk drive for spin-polarized scanning tunneling microscopy (SP-STM) in the modulated tip magnetization mode. Using SP-STM, we measured a well-defined in-plane spin-component of the tunneling current of the rough surface of a polycrystalline NiFe film. The spin asymmetry of the NiFe film was about 1.3% within the bias voltage range of -3 to 1 V. We obtained the local spin component image of the sample surface, switching the magnetic field of the sample to reverse the sample magnetization during scanning. We also obtained a spin image of the rough surface of a polycrystalline NiFe film evaporated on the recording medium of a hard disk drive.

Electronic-Reconstruction-Enhanced Tunneling Conductance at Terrace Edges of Ultrathin Oxide Films.

Science.gov (United States)

Wang, Lingfei; Kim, Rokyeon; Kim, Yoonkoo; Kim, Choong H; Hwang, Sangwoon; Cho, Myung Rae; Shin, Yeong Jae; Das, Saikat; Kim, Jeong Rae; Kalinin, Sergei V; Kim, Miyoung; Yang, Sang Mo; Noh, Tae Won

2017-11-01

Quantum mechanical tunneling of electrons across ultrathin insulating oxide barriers has been studied extensively for decades due to its great potential in electronic-device applications. In the few-nanometers-thick epitaxial oxide films, atomic-scale structural imperfections, such as the ubiquitously existed one-unit-cell-high terrace edges, can dramatically affect the tunneling probability and device performance. However, the underlying physics has not been investigated adequately. Here, taking ultrathin BaTiO 3 films as a model system, an intrinsic tunneling-conductance enhancement is reported near the terrace edges. Scanning-probe-microscopy results demonstrate the existence of highly conductive regions (tens of nanometers wide) near the terrace edges. First-principles calculations suggest that the terrace-edge geometry can trigger an electronic reconstruction, which reduces the effective tunneling barrier width locally. Furthermore, such tunneling-conductance enhancement can be discovered in other transition metal oxides and controlled by surface-termination engineering. The controllable electronic reconstruction can facilitate the implementation of oxide electronic devices and discovery of exotic low-dimensional quantum phases. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

DEFF Research Database (Denmark)

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

2000-01-01

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

Molecular modeling study on tunnel behavior in different histone deacetylase isoforms.

Directory of Open Access Journals (Sweden)

Sundarapandian Thangapandian

Full Text Available Histone deacetylases (HDACs have emerged as effective therapeutic targets in the treatment of various diseases including cancers as these enzymes directly involved in the epigenetic regulation of genes. However the development of isoform-selective HDAC inhibitors has been a challenge till date since all HDAC enzymes possess conserved tunnel-like active site. In this study, using molecular dynamics simulation we have analyzed the behavior of tunnels present in HDAC8, 10, and 11 enzymes of class I, II, and IV, respectively. We have identified the equivalent tunnel forming amino acids in these three isoforms and found that they are very much conserved with subtle differences to be utilized in selective inhibitor development. One amino acid, methionine of HDAC8, among six tunnel forming residues is different in isoforms of other classes (glutamic acid (E in HDAC10 and leucine (L in HDAC 11 based on which mutations were introduced in HDAC11, the less studied HDAC isoform, to observe the effects of this change. The HDAC8-like (L268M mutation in the tunnel forming residues has almost maintained the deep and narrow tunnel as present in HDAC8 whereas HDAC10-like (L268E mutation has changed the tunnel wider and shallow as observed in HDAC10. These results explained the importance of the single change in the tunnel formation in different isoforms. The observations from this study can be utilized in the development of isoform-selective HDAC inhibitors.

Observation and Manipulation of Polymers by Scanning Tunneling and Atomic Force Microscopy

Science.gov (United States)

1988-07-13

Observation and Manipulation of Polymers by Scanning Tunneling and Atomic Force Microscooy 12. PERSONAL AUTHOR(S) M.M. Dovek, T.R. Albrecht, S.W.J. Kuan, C.A...COUNT FIELD GOP SU8 -GROUP 19. ABSTRACT (Continue on reverse if ncosay and kIti1I by block numbor) ~AM\\~ v~~\\~A Dhe properties of monolayer films of...organic materi s are importantl i--V~ ety of technologies. We have employed the STM and AFM t study’ LanD~ ..-odgett films of a varie ’ty of polymers

A study for the KAERI research tunnel

Energy Technology Data Exchange (ETDEWEB)

Kim, J.; Hwang, Y. S.; Park, H. S.; Park, S. K.; Park, B. Y.; Bang, K. S.; Kuh, J. H.; Kang, K. H

1997-12-01

Major goal of the R and D on the KAERI Research Tunnel in 1997 are 1) concept development of the KAERI research tunnel and its major units 2) computer simulation of facilities 3) study on thermo-hydro mechanical coupling in the vicinity of a waste repository 4) effect of excavated distrubed zone. In addition supplementary site investigation to understand the distribution of stresses in the site was done along with long term monitoring of the water table. (author). 44 refs., 16 tabs., 36 figs

Theory of high-resolution tunneling spin transport on a magnetic skyrmion

Science.gov (United States)

Palotás, Krisztián; Rózsa, Levente; Szunyogh, László

2018-05-01

Tunneling spin transport characteristics of a magnetic skyrmion are described theoretically in magnetic scanning tunneling microscopy (STM). The spin-polarized charge current in STM (SP-STM) and tunneling spin transport vector quantities, the longitudinal spin current and the spin transfer torque, are calculated in high spatial resolution within the same theoretical framework. A connection between the conventional charge current SP-STM image contrasts and the magnitudes of the spin transport vectors is demonstrated that enables the estimation of tunneling spin transport properties based on experimentally measured SP-STM images. A considerable tunability of the spin transport vectors by the involved spin polarizations is also highlighted. These possibilities and the combined theory of tunneling charge and vector spin transport pave the way for gaining deep insight into electric-current-induced tunneling spin transport properties in SP-STM and to the related dynamics of complex magnetic textures at surfaces.

Study of tunneling transport in Si-based tunnel field-effect transistors with ON current enhancement utilizing isoelectronic trap

Science.gov (United States)

Mori, Takahiro; Morita, Yukinori; Miyata, Noriyuki; Migita, Shinji; Fukuda, Koichi; Mizubayashi, Wataru; Masahara, Meishoku; Yasuda, Tetsuji; Ota, Hiroyuki

2015-02-01

The temperature dependence of the tunneling transport characteristics of Si diodes with an isoelectronic impurity has been investigated in order to clarify the mechanism of the ON-current enhancement in Si-based tunnel field-effect transistors (TFETs) utilizing an isoelectronic trap (IET). The Al-N complex impurity was utilized for IET formation. We observed three types of tunneling current components in the diodes: indirect band-to-band tunneling (BTBT), trap-assisted tunneling (TAT), and thermally inactive tunneling. The indirect BTBT and TAT current components can be distinguished with the plot described in this paper. The thermally inactive tunneling current probably originated from tunneling consisting of two paths: tunneling between the valence band and the IET trap and tunneling between the IET trap and the conduction band. The probability of thermally inactive tunneling with the Al-N IET state is higher than the others. Utilization of the thermally inactive tunneling current has a significant effect in enhancing the driving current of Si-based TFETs.

Effect of Surface Blasting on Subway Tunnels- A Parametric Study

Directory of Open Access Journals (Sweden)

Hossein Entezari Zarch

2017-01-01

Full Text Available During wars and crises, the underground tunnels are used as a safe space. Therefore, the stability and safety of them under a blast is of particular importance. In this paper, the Finite Difference Method has been used to study the influence of the change in geotechnical parameters and depth on surface blasting on subway tunnels. Results showed that increasing the internal friction angle, modulus of elasticity and cohesion of the soil reduced the effects of blast loads on the vertical displacement and bending moment in the center of tunnel crown. Furthermore, the results showed that increasing the depth of the tunnel reduced the effects of blast loading. Comparing all parameters collectively showed that the increase in the modulus of elasticity of the soil and depth of the tunnel is the most effective in reducing the influence of the blast loads on the vertical displacement and bending moment of the tunnel crown, respectively.

Resolving amorphous solid-liquid interfaces by atomic force microscopy

International Nuclear Information System (INIS)

Burson, Kristen M.; Gura, Leonard; Kell, Burkhard; Büchner, Christin; Lewandowski, Adrian L.; Heyde, Markus; Freund, Hans-Joachim

2016-01-01

Recent advancements in liquid atomic force microscopy make it an ideal technique for probing the structure of solid-liquid interfaces. Here, we present a structural study of a two-dimensional amorphous silica bilayer immersed in an aqueous solution utilizing liquid atomic force microscopy with sub-nanometer resolution. Structures show good agreement with atomically resolved ultra-high vacuum scanning tunneling microscopy images obtained on the same sample system, owing to the structural stability of the silica bilayer and the imaging clarity from the two-dimensional sample system. Pair distance histograms of ring center positions are utilized to develop quantitative metrics for structural comparison, and the physical origin of pair distance histogram peaks is addressed by direct assessment of real space structures.

Tunnel magnetoresistance in alumina, magnesia and composite tunnel barrier magnetic tunnel junctions

International Nuclear Information System (INIS)

Schebaum, Oliver; Drewello, Volker; Auge, Alexander; Reiss, Guenter; Muenzenberg, Markus; Schuhmann, Henning; Seibt, Michael; Thomas, Andy

2011-01-01

Using magnetron sputtering, we have prepared Co-Fe-B/tunnel barrier/Co-Fe-B magnetic tunnel junctions with tunnel barriers consisting of alumina, magnesia, and magnesia-alumina bilayer systems. The highest tunnel magnetoresistance ratios we found were 73% for alumina and 323% for magnesia-based tunnel junctions. Additionally, tunnel junctions with a unified layer stack were prepared for the three different barriers. In these systems, the tunnel magnetoresistance ratios at optimum annealing temperatures were found to be 65% for alumina, 173% for magnesia, and 78% for the composite tunnel barriers. The similar tunnel magnetoresistance ratios of the tunnel junctions containing alumina provide evidence that coherent tunneling is suppressed by the alumina layer in the composite tunnel barrier. - Research highlights: → Transport properties of Co-Fe-B/tunnel barrier/Co-Fe-B magnetic tunnel junctions. → Tunnel barrier consists of MgO, Al-Ox, or MgO/Al-Ox bilayer systems. → Limitation of TMR-ratio in composite barrier tunnel junctions to Al-Ox values. → Limitation indicates that Al-Ox layer is causing incoherent tunneling.

Local crystallography analysis for atomically resolved scanning tunneling microscopy images

International Nuclear Information System (INIS)

Lin, Wenzhi; Li, Qing; Belianinov, Alexei; Gai, Zheng; Baddorf, Arthur P; Pan, Minghu; Jesse, Stephen; Kalinin, Sergei V; Sales, Brian C; Sefat, Athena

2013-01-01

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 FeTe 0.55 Se 0.45 . This study provides a new pathway to extract and quantify local properties for scanning probe microscopy images. (paper)

Long-range protein electron transfer observed at the single-molecule level: In situ mapping of redox-gated tunneling resonance

DEFF Research Database (Denmark)

Chi, Qijin; Farver, O; Ulstrup, Jens

2005-01-01

on the redox potential. Maximum resonance appears around the equilibrium redox potential of azurin with an on/off current ratio of approximate to 9. Simulation analyses, based on a two-step interfacial ET model for the scanning tunneling microscopy redox process, were performed and provide quantitative......A biomimetic long-range electron transfer (ET) system consisting of the blue copper protein azurin, a tunneling barrier bridge, and a gold single-crystal electrode was designed on the basis of molecular wiring self-assembly principles. This system is sufficiently stable and sensitive in a quasi...... constants display tunneling features with distance-decay factors of 0.83 and 0.91 angstrom(-1) in H2O and D2O, respectively. Redox-gated tunneling resonance is observed in situ at the single-molecule level by using electrochemical scanning tunneling microscopy, exhibiting an asymmetric dependence...

Water Tunnel Studies of Dynamic Wing Flap Effects

Science.gov (United States)

2016-06-01

NAVAL POSTGRADUATE SCHOOL MONTEREY, CALIFORNIA THESIS Approved for public release; distribution is unlimited WATER TUNNEL...Master’s Thesis 4. TITLE AND SUBTITLE WATER TUNNEL STUDIES OF DYNAMIC WING FLAP EFFECTS 5. FUNDING NUMBERS 6. AUTHOR(S) Edgar E. González 7. PERFORMING...ABSTRACT (maximum 200 words ) The flow features developing over a two-element NACA 0012 airfoil, with the rear portion serving as a trailing edge flap

Dynamics of a nanoscale Josephson junction probed by scanning tunneling microscopy

Energy Technology Data Exchange (ETDEWEB)

Ast, Christian R.; Jaeck, Berthold; Eltschka, Matthias; Etzkorn, Markus [Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany); Kern, Klaus [Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany); Institut de Physique de la Matiere Condensee, EPFL, Lausanne (Switzerland)

2015-07-01

The Josephson effect is an intriguing phenomenon as it presents an interplay of different energy scales, such as the Josephson energy ε{sub J} (critical current), charging energy ε{sub C}, and temperature T. Using a scanning tunneling microscope (STM) operating at a base temperature of 15 mK, we create a nanoscale superconductor-vacuum-superconductor tunnel junction in an extremely underdamped regime (Q>>10). We observe extremely small retrapping currents also owing to strongly reduced ohmic losses in the well-developed superconducting gaps. While formally operating in the zero temperature limit, i.e. the temperature T is smaller than the Josephson plasma frequency ω{sub J} (k{sub B}T<<ℎω{sub J}=√(8ε{sub J}ε{sub C})), experimentally other phenomena, such as stray photons, may perturb the Josephson junction, leading to an effectively higher temperature. The dynamics of the Josephson junction can be addressed experimentally by looking at characteristic parameters, such as the switching current and the retrapping current. We discuss the dynamics of the Josephson junction in the context of reaching the zero temperature limit.

Multilayered cuprate superconductor Ba2Ca5Cu6O12(O1-x,Fx) 2 studied by temperature-dependent scanning tunneling microscopy and spectroscopy

Science.gov (United States)

Sugimoto, Akira; Ekino, Toshikazu; Gabovich, Alexander M.; Sekine, Ryotaro; Tanabe, Kenji; Tokiwa, Kazuyasu

2017-05-01

Scanning tunneling microscopy/spectroscopy (STM/STS) measurements were carried out on a multilayered cuprate superconductor Ba2Ca5Cu6O12 (O1 -x,Fx )2. STM topography revealed random spot structures with the characteristic length ≤0.5 nm. The conductance spectra d I /d V (V ) show the coexistence of smaller gaps ΔS and large gaps (pseudogaps) ΔL. The pseudogap-related features in the superconducting state were traced with the spatial resolution of ˜0.07 nm. Here, I and V are the tunnel current and bias voltage, respectively. The temperature, T , dependence of ΔS follows the reduced Bardeen-Cooper-Schrieffer (BCS) dependence. The hallmark ratio 2 ΔS(T =0 ) /kBTc equals to 4.9, which is smaller than those of other cuprate superconductors. Here, Tc is the superconducting critical temperature and kB is the Boltzmann constant. The larger gap ΔL survives in the normal state and even increases with T above Tc. The T dependencies of the spatial distributions for both relevant gaps (Δ map), as well as for each gap separately (ΔS and ΔL), were obtained. From the histogram of Δ map, the averaged gap values were found to be Δ¯S=˜24 meV and Δ¯L=˜79 meV. The smaller gap ΔS shows a spatially homogeneous distribution while the larger gap ΔL is quite inhomogeneous, indicating that rather homogeneous superconductivity coexists with the patchy distributed pseudogap. The spatial variation length ξΔ L of ΔL correlates with the scale of the topography spot structures, being approximately 0.4 nm. This value is considerably smaller than the coherence length of this class of superconductors, suggesting that ΔL is strongly affected by the disorder of the apical O/F.

Dextrose-induced subsynovial connective tissue fibrosis in the rabbit carpal tunnel: A potential model to study carpal tunnel syndrome?

NARCIS (Netherlands)

Oh, S.; Ettema, A.M.; Zhao, C.; Zobitz, M.E.; Wold, L.E.; An, K.N.; Amadio, P.C.

2008-01-01

In this pilot study, hypertonic dextrose solution was used to induce fibrosis of the subsynovial connective tissue (SSCT) and create an animal model of potential use in the study of carpal tunnel syndrome (CTS). The SSCT of the carpal tunnel in 15 New Zealand white rabbits were injected with 0.05 ml

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

Science.gov (United States)

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

2009-12-01

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

Dynamic Tunnel Usability Study: Format Recommendations for Synthetic Vision System Primary Flight Displays

Science.gov (United States)

Arthur, Jarvis J., III; Prinzel, Lawrence J., III; Kramer, Lynda J.; Bailey, Randall E.

2006-01-01

A usability study evaluating dynamic tunnel concepts has been completed under the Aviation Safety and Security Program, Synthetic Vision Systems Project. The usability study was conducted in the Visual Imaging Simulator for Transport Aircraft Systems (VISTAS) III simulator in the form of questionnaires and pilot-in-the-loop simulation sessions. Twelve commercial pilots participated in the study to determine their preferences via paired comparisons and subjective rankings regarding the color, line thickness and sensitivity of the dynamic tunnel. The results of the study showed that color was not significant in pilot preference paired comparisons or in pilot rankings. Line thickness was significant for both pilot preference paired comparisons and in pilot rankings. The preferred line/halo thickness combination was a line width of 3 pixels and a halo of 4 pixels. Finally, pilots were asked their preference for the current dynamic tunnel compared to a less sensitive dynamic tunnel. The current dynamic tunnel constantly gives feedback to the pilot with regard to path error while the less sensitive tunnel only changes as the path error approaches the edges of the tunnel. The tunnel sensitivity comparison results were not statistically significant.

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

International Nuclear Information System (INIS)

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

2014-01-01

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

Microscopy image segmentation tool: Robust image data analysis

Energy Technology Data Exchange (ETDEWEB)

Valmianski, Ilya, E-mail: ivalmian@ucsd.edu; Monton, Carlos; Schuller, Ivan K. [Department of Physics and Center for Advanced Nanoscience, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093 (United States)

2014-03-15

We present a software package called Microscopy Image Segmentation Tool (MIST). MIST is designed for analysis of microscopy images which contain large collections of small regions of interest (ROIs). Originally developed for analysis of porous anodic alumina scanning electron images, MIST capabilities have been expanded to allow use in a large variety of problems including analysis of biological tissue, inorganic and organic film grain structure, as well as nano- and meso-scopic structures. MIST provides a robust segmentation algorithm for the ROIs, includes many useful analysis capabilities, and is highly flexible allowing incorporation of specialized user developed analysis. We describe the unique advantages MIST has over existing analysis software. In addition, we present a number of diverse applications to scanning electron microscopy, atomic force microscopy, magnetic force microscopy, scanning tunneling microscopy, and fluorescent confocal laser scanning microscopy.

Microscopy image segmentation tool: Robust image data analysis

Science.gov (United States)

Valmianski, Ilya; Monton, Carlos; Schuller, Ivan K.

2014-03-01

We present a software package called Microscopy Image Segmentation Tool (MIST). MIST is designed for analysis of microscopy images which contain large collections of small regions of interest (ROIs). Originally developed for analysis of porous anodic alumina scanning electron images, MIST capabilities have been expanded to allow use in a large variety of problems including analysis of biological tissue, inorganic and organic film grain structure, as well as nano- and meso-scopic structures. MIST provides a robust segmentation algorithm for the ROIs, includes many useful analysis capabilities, and is highly flexible allowing incorporation of specialized user developed analysis. We describe the unique advantages MIST has over existing analysis software. In addition, we present a number of diverse applications to scanning electron microscopy, atomic force microscopy, magnetic force microscopy, scanning tunneling microscopy, and fluorescent confocal laser scanning microscopy.

Microscopy image segmentation tool: Robust image data analysis

International Nuclear Information System (INIS)

Valmianski, Ilya; Monton, Carlos; Schuller, Ivan K.

2014-01-01

We present a software package called Microscopy Image Segmentation Tool (MIST). MIST is designed for analysis of microscopy images which contain large collections of small regions of interest (ROIs). Originally developed for analysis of porous anodic alumina scanning electron images, MIST capabilities have been expanded to allow use in a large variety of problems including analysis of biological tissue, inorganic and organic film grain structure, as well as nano- and meso-scopic structures. MIST provides a robust segmentation algorithm for the ROIs, includes many useful analysis capabilities, and is highly flexible allowing incorporation of specialized user developed analysis. We describe the unique advantages MIST has over existing analysis software. In addition, we present a number of diverse applications to scanning electron microscopy, atomic force microscopy, magnetic force microscopy, scanning tunneling microscopy, and fluorescent confocal laser scanning microscopy

Scanning/friction force microscopy study of YBa2Cu3O7-δ single crystals grown in BaZrO3 crucibles

International Nuclear Information System (INIS)

Lang, H.P.; Jess, P.; Hubler, U.

1996-01-01

Very pure YBa 2 Cu 3 O 7-δ (YBCO) single crystals grown in BaZrO 3 crucibles are studied in the as-grown and the oxidized state by scanning force (SFM), friction force (FFM) and scanning tunneling microscopies (STM). The images show clean terraces with step-heights of one unit cell along YBCO(001), i.e. 1.2 nm. Only close to step edges is material contrast observed by FFM indicating traces of flux. Some crystal surfaces exhibit over-layer features, such as star-like, ribbon-like and checkerboard-like structures, which exhibit friction contrast implying the presence of different materials on the surface. Tunneling spectroscopy at 4-7 K in high vacuum reveals a superconducting energy gap of 2Δ ∼ 26 meV

Rock mechanical conditions at the Aespoe HRL. A study of the correlation between geology, tunnel maintenance and tunnel shape

International Nuclear Information System (INIS)

Andersson, Christer; Soederhaell, Joergen

2001-12-01

Maintenance records including scaling, shotcreting and bolting have been kept since the excavation start of Aespoe HRL 1990 together with records of groundwater flow and all other activities taking place in the tunnels. When the facility was constructed one objective was to limit the rock support as much as possible. The reason for this was that it should be possible to go back and easily study the exposed rock surface. Support during the operational phase has only been carried out where and when necessary. This type of maintenance and its location is documented in the digital database each time. The maintenance records have been compiled and areas requiring more maintenance than average noted. An interview has also been held with one of the miners conducting scaling and bolting in the tunnel. His experiences together with the study of the database maintenance records led to the selection of certain areas in the tunnel to be studied by numerical modelling. The probable reason for the need of additional maintenance in all areas, not only these numerically modelled, has been investigated. Almost all maintenance in the main tunnel both during construction and the operational phase has been located in the widened curves of the access tunnel. The maintenance is also located in areas containing veins or intrusions of Smaaland granite or fine-grained granite. These areas are often located in fracture zones of different sizes or show an increasing fracture frequency. The areas numerically modelled indicate stress concentrations or unloaded stress conditions. The stress concentrations are created by the geometry of the niches and side-tunnels in relation to the in situ stress field. The angle between the tunnel and the major principal stress has an impact on the need for maintenance. The areas with the largest angles towards the principal stress direction need more maintenance than the areas almost parallel to the major principal stress direction. The maintenance work in

A temperature dependent tunneling study of the spin density wave gap in EuFe2As2 single crystals.

Science.gov (United States)

Dutta, Anirban; Anupam; Hossain, Z; Gupta, Anjan K

2013-09-18

We report temperature dependent scanning tunneling microscopy and spectroscopy measurements on single crystals of EuFe2As2 in the 15-292 K temperature range. The in situ cleaved crystals show atomic terraces with homogeneous tunnel spectra that correlate well with the spin density wave (SDW) transition at a temperature, TSDW ≈ 186 K. Above TSDW the local tunnel spectra show a small depression in the density of states (DOS) near the Fermi energy (EF). The gap becomes more pronounced upon entering the SDW state with a gap value ∼90 meV at 15 K. However, the zero bias conductance remains finite down to 15 K indicating a finite DOS at the EF in the SDW phase. Furthermore, no noticeable change is observed in the DOS at the antiferromagnetic ordering transition of Eu(2+) moments at 19 K.

The Beginner's Guide to Wind Tunnels with TunnelSim and TunnelSys

Science.gov (United States)

Benson, Thomas J.; Galica, Carol A.; Vila, Anthony J.

2010-01-01

The Beginner's Guide to Wind Tunnels is a Web-based, on-line textbook that explains and demonstrates the history, physics, and mathematics involved with wind tunnels and wind tunnel testing. The Web site contains several interactive computer programs to demonstrate scientific principles. TunnelSim is an interactive, educational computer program that demonstrates basic wind tunnel design and operation. TunnelSim is a Java (Sun Microsystems Inc.) applet that solves the continuity and Bernoulli equations to determine the velocity and pressure throughout a tunnel design. TunnelSys is a group of Java applications that mimic wind tunnel testing techniques. Using TunnelSys, a team of students designs, tests, and post-processes the data for a virtual, low speed, and aircraft wing.

Real-space observation of a right-rotating inhomogeneous cycloidal spin spiral by spin-polarized scanning tunneling microscopy in a triple axes vector magnet.

Science.gov (United States)

Meckler, S; Mikuszeit, N; Pressler, A; Vedmedenko, E Y; Pietzsch, O; Wiesendanger, R

2009-10-09

Using spin-polarized scanning tunneling microscopy performed in a triple axes vector magnet, we show that the magnetic structure of the Fe double layer on W(110) is an inhomogeneous right-rotating cycloidal spin spiral. The magnitude of the Dzyaloshinskii-Moriya vector is extracted from the experimental data using micromagnetic calculations. The result is confirmed by comparison of the measured saturation field along the easy axis to the respective value as obtained from Monte Carlo simulations. We find that the Dzyaloshinskii-Moriya interaction is too weak to destabilize the single domain state. However, it can define the sense of rotation and the cycloidal spiral type once the single domain state is destabilized by dipolar interaction.

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

International Nuclear Information System (INIS)

Bishara, E.M.El.

2009-01-01

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.

Typical Underwater Tunnels in the Mainland of China and Related Tunneling Technologies

Directory of Open Access Journals (Sweden)

Kairong Hong

2017-12-01

Full Text Available In the past decades, many underwater tunnels have been constructed in the mainland of China, and great progress has been made in related tunneling technologies. This paper presents the history and state of the art of underwater tunnels in the mainland of China in terms of shield-bored tunnels, drill-and-blast tunnels, and immersed tunnels. Typical underwater tunnels of these types in the mainland of China are described, along with innovative technologies regarding comprehensive geological prediction, grouting-based consolidation, the design and construction of large cross-sectional tunnels with shallow cover in weak strata, cutting tool replacement under limited drainage and reduced pressure conditions, the detection and treatment of boulders, the construction of underwater tunnels in areas with high seismic intensity, and the treatment of serious sedimentation in a foundation channel of immersed tunnels. Some suggestions are made regarding the three potential great strait-crossing tunnels—the Qiongzhou Strait-Crossing Tunnel, Bohai Strait-Crossing Tunnel, and Taiwan Strait-Crossing Tunnel—and issues related to these great strait-crossing tunnels that need further study are proposed. Keywords: Underwater tunnel, Strait-crossing tunnel, Shield-bored tunnel, Immersed tunnel, Drill and blast

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

Science.gov (United States)

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

1991-01-01

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

Interdot carrier's transfer via tunneling pathway studied from photoluminescence spectroscopy

International Nuclear Information System (INIS)

Rihani, J.; Sallet, V.; Yahyaoui, N.; Harmand, J.C.; Oueslati, M.; Chtourou, R.

2009-01-01

Self-assembled InAs quantum dots (QDs) on GaAs(0 0 1) substrate were grown by molecular beam epitaxy (MBE) at a growth temperature of 490 deg. C. Two different families of dots were observed in the atomic force microscopy (AFM) image and ambiguously identified in the photoluminescence (PL) spectra. Temperature-dependent PL study was carried out in the 8-270 K temperature range. The integrated-PL intensity behavior of the two QDs populations was fit with the help of a rate equations model. It is found that the evolutions of the integrated-PL intensity of the two QDs population were governed by two regimes. The first one occurs in the 8-210 K temperature range and reveals an unusual enhancement of the integrated-PL intensity of the larger QDs (LQDs) class. This was attributed to the carrier supplies from the smaller QDs (SQDs) class via the tunneling process. The second one occurs in the 210-270 K temperature range and shows a common quench of the PL signals of the two QDs families, reflecting the same thermal escape mechanism of carriers

Scanning Tunneling Spectroscopy of Potassium on Graphene

Science.gov (United States)

Cormode, Daniel; Leroy, Brian; Yankowitz, Matthew

2012-02-01

We investigate the effect of charged impurities on the electronic properties of large single crystal CVD grown graphene using scanning tunneling microscopy. Mono- and multilayer crystals were prepared by transferring graphene from copper onto exfoliated boron nitride flakes on 300 nm SiO2 substrates. The boron nitride provides an ultra flat surface for the graphene. Potassium atoms are controllably deposited on the graphene at low temperature by heating a nearby getter source. Scanning tunneling spectroscopy and transport measurements were performed in ultra high vacuum at 4.5 K. Transport measurements demonstrate the shifting of the Dirac point as the samples are doped, while STM measurements demonstrate the size, arrangement and local electronic influence of the potassium atoms.

Ag/ZnO hybrid systems studied with scanning tunnelling microscopy-based luminescence spectroscopy

International Nuclear Information System (INIS)

Pascua, Leandro; Freund, Hans-Joachim; Stavale, Fernando; Nilius, Niklas

2016-01-01

Coupled metal/oxide systems are prepared by depositing and embedding Ag nanoparticles into crystalline ZnO films grown on Au(111) supports. The morphology and optical properties of the compounds are investigated by topographic imaging and luminescence spectroscopy performed in a scanning tunnelling microscope (STM). The luminescence of bare ZnO is governed by the band-recombination and a Zn-vacancy related peak. After Ag deposition, two additional maxima are detected that are assigned to the in-plane and out-of-plane plasmon in Ag nanoparticles and have energies below and slightly above the oxide band-gap, respectively. Upon coating the particles with additional ZnO, the out-of-plane plasmon redshifts and loses intensity, indicating strong coupling to the oxide electronic system, while the in-plane mode broadens but remains detectable. The original situation can be restored by gently heating the sample, which drives the silver back to the surface. However, the optical response of pristine ZnO is not recovered even after silver evaporation at high temperature. Small discrepancies are explained with changes in the ZnO defect landscape, e.g., due to silver incorporation. Our experiments demonstrate how energy-transfer processes can be investigated in well-defined metal/oxide systems by means of STM-based spectroscopic techniques.

Ag/ZnO hybrid systems studied with scanning tunnelling microscopy-based luminescence spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Pascua, Leandro; Freund, Hans-Joachim [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin (Germany); Stavale, Fernando [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin (Germany); Centro Brasileiro de Pesquisas Físicas - CBPF/MCTI, Rua Xavier Sigaud 150, 22290-180 Rio de Janeiro (Brazil); Nilius, Niklas, E-mail: niklas.nilius@uni-oldenburg.de [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin (Germany); Institut für Physik, Carl von Ossietzky Universität Oldenburg, D-26111 Oldenburg (Germany)

2016-03-07

Coupled metal/oxide systems are prepared by depositing and embedding Ag nanoparticles into crystalline ZnO films grown on Au(111) supports. The morphology and optical properties of the compounds are investigated by topographic imaging and luminescence spectroscopy performed in a scanning tunnelling microscope (STM). The luminescence of bare ZnO is governed by the band-recombination and a Zn-vacancy related peak. After Ag deposition, two additional maxima are detected that are assigned to the in-plane and out-of-plane plasmon in Ag nanoparticles and have energies below and slightly above the oxide band-gap, respectively. Upon coating the particles with additional ZnO, the out-of-plane plasmon redshifts and loses intensity, indicating strong coupling to the oxide electronic system, while the in-plane mode broadens but remains detectable. The original situation can be restored by gently heating the sample, which drives the silver back to the surface. However, the optical response of pristine ZnO is not recovered even after silver evaporation at high temperature. Small discrepancies are explained with changes in the ZnO defect landscape, e.g., due to silver incorporation. Our experiments demonstrate how energy-transfer processes can be investigated in well-defined metal/oxide systems by means of STM-based spectroscopic techniques.

Spin- and energy-dependent tunneling through a single molecule with intramolecular spatial resolution.

Science.gov (United States)

Brede, Jens; Atodiresei, Nicolae; Kuck, Stefan; Lazić, Predrag; Caciuc, Vasile; Morikawa, Yoshitada; Hoffmann, Germar; Blügel, Stefan; Wiesendanger, Roland

2010-07-23

We investigate the spin- and energy-dependent tunneling through a single organic molecule (CoPc) adsorbed on a ferromagnetic Fe thin film, spatially resolved by low-temperature spin-polarized scanning tunneling microscopy. Interestingly, the metal ion as well as the organic ligand show a significant spin dependence of tunneling current flow. State-of-the-art ab initio calculations including also van der Waals interactions reveal a strong hybridization of molecular orbitals and substrate 3d states. The molecule is anionic due to a transfer of one electron, resulting in a nonmagnetic (S=0) state. Nevertheless, tunneling through the molecule exhibits a pronounced spin dependence due to spin-split molecule-surface hybrid states.

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.

Development of the safety control framework for shield tunneling in close proximity to the operational subway tunnels: case studies in mainland China.

Science.gov (United States)

Li, Xinggao; Yuan, Dajun

2016-01-01

China's largest cities like Beijing and Shanghai have seen a sharp increase in subway network development as a result of the rapid urbanization in the last decade. The cities are still expanding their subway networks now, and many shield tunnels are being or will be constructed in close proximity to the existing operational subway tunnels. The execution plans for the new nearby shield tunnel construction calls for the development of a safety control framework-a set of control standards and best practices to help organizations manage the risks involved. Typical case studies and relevant key technical parameters are presented with a view to presenting the resulting safety control framework. The framework, created through collaboration among the relevant parties, addresses and manages the risks in a systematic way based on actual conditions of each tunnel crossing construction. The framework consists of six parts: (1) inspecting the operational subway tunnels; (2) deciding allowed movements of the existing tunnels and tracks; (3) simulating effects of the shield tunneling on the existing tunnels; (4) doing preparation work; (5) monitoring design and information management; and (6) measures and activation mechanism of the countermeasures. The six components are explained and demonstrated in detail. In the end, discussions made involve construction and post-construction settlement of the operational tunnel, application of the remedial grouting to rectify excessive settlements of the operational tunnel, and use of the innovative tool of the optical fiber measurement for tunnel movement monitoring. It is concluded that the construction movement of the tunnel can be controlled within 15 mm when the shield machine is <7 m in excavation diameter. The post-construction settlement of the tunnel buried in the very soft ground is much greater than its construction settlement, and last several years until reaching a final stable state. Two cases are outlined to demonstrate the

Tunnel Boring Machine Performance Study. Final Report

Science.gov (United States)

1984-06-01

Full face tunnel boring machine "TBM" performance during the excavation of 6 tunnels in sedimentary rock is considered in terms of utilization, penetration rates and cutter wear. The construction records are analyzed and the results are used to inves...

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

Energy Technology Data Exchange (ETDEWEB)

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

2009-09-01

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

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

International Nuclear Information System (INIS)

1990-06-01

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

Spin-polarized scanning tunneling spectroscopy of self-organized nanoscale Co islands on Au(111) surfaces.

Science.gov (United States)

Schouteden, K; Muzychenko, D A; Van Haesendonck, C

2008-07-01

Magnetic monolayer and bilayer Co islands of only a few nanometer in size were grown by atomic deposition on atomically flat Au(111) films. The islands were studied in situ by scanning tunneling microscopy (STM) and spectroscopy at low temperatures. Spin-resolved tunneling spectroscopy, using an STM tip with a magnetic coating, revealed that the Co islands exhibit a net magnetization perpendicular to the substrate surface due to the presence of spin-polarized d-states. A random distribution of islands with either upward or downward pointing magnetization was observed, without any specific correlation of magnetization orientation with island size or island height.

Scanning tunneling microscopy and atomic force microscopy: application to biology and technology.

Science.gov (United States)

Hansma, P K; Elings, V B; Marti, O; Bracker, C E

1988-10-14

The scanning tunneling microscope (STM) and the atomic force microscope (AFM) are scanning probe microscopes capable of resolving surface detail down to the atomic level. The potential of these microscopes for revealing subtle details of structure is illustrated by atomic resolution images including graphite, an organic conductor, an insulating layered compound, and individual adsorbed oxygen atoms on a semiconductor. Application of the STM for imaging biological materials directly has been hampered by the poor electron conductivity of most biological samples. The use of thin conductive metal coatings and replicas has made it possible to image some biological samples, as indicated by recently obtained images of a recA-DNA complex, a phospholipid bilayer, and an enzyme crystal. The potential of the AFM, which does not require a conductive sample, is shown with molecular resolution images of a nonconducting organic monolayer and an amino acid crystal that reveals individual methyl groups on the ends of the amino acids. Applications of these new microscopes to technology are demonstrated with images of an optical disk stamper, a diffraction grating, a thin-film magnetic recording head, and a diamond cutting tool. The STM has even been used to improve the quality of diffraction gratings and magnetic recording heads.

Ultrafast terahertz control of extreme tunnel currents through single atoms on a silicon surface

DEFF Research Database (Denmark)

Jelic, Vedran; Iwaszczuk, Krzysztof; Nguyen, Peter H.

2017-01-01

scanning tunnelling microscopy (THz-STM) in ultrahigh vacuum as a new platform for exploring ultrafast non-equilibrium tunnelling dynamics with atomic precision. Extreme terahertz-pulse-driven tunnel currents up to 10(7) times larger than steady-state currents in conventional STM are used to image...... terahertz-induced band bending and non-equilibrium charging of surface states opens new conduction pathways to the bulk, enabling extreme transient tunnel currents to flow between the tip and sample.......Ultrafast control of current on the atomic scale is essential for future innovations in nanoelectronics. Extremely localized transient electric fields on the nanoscale can be achieved by coupling picosecond duration terahertz pulses to metallic nanostructures. Here, we demonstrate terahertz...

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

Science.gov (United States)

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

2009-02-17

Metallosupramolecular compounds have attracted a great deal of attention over the past two decades largely because of their unique, highly complex structural characteristics and their potential electronic, magnetic, optical, and catalytic properties. These molecules can be prepared with relative ease using coordination-driven self-assembly techniques. In particular, the use of electron-poor square-planar Pt(II) transition metals in conjunction with rigid, electron-rich pyridyl donors has enabled the spontaneous self-assembly of a rich library of 2D metallacyclic and 3D metallacage assemblies via the directional-bonding approach. With this progress in the preparation and characterization of metallosupramolecules, researchers have now turned their attention toward fully exploring and developing their materials properties. Assembling metallosupramolecular compounds on solid supports represents a vitally important step toward developing their materials properties. Surfaces provide a means of uniformly aligning and orienting these highly symmetric metallacycles and metallacages. This uniformity increases the level of coherence between molecules above that which can be achieved in the solution phase and provides a way to integrate adsorbed layers, or adlayers, into a solid-state materials setting. The dynamic nature of kinetically labile Pt(II)-N coordination bonds requires us to adjust deposition and imaging conditions to retain the assemblies' stability. Toward these aims, we have used scanning tunneling microscopy (STM) to image these adlayers and to understand the factors that govern surface self-assembly and the interactions that influence their structure and stability. This Account describes our efforts to deposit 2D rectangular and square metallacycles and 3D trigonal bipyramidal and chiral trigonal prism metallacages on highly oriented pyrolytic graphite (HOPG) and Au(111) substrates to give intact assemblies and ordered adlayers. We have investigated the effects

Geological Hazards analysis in Urban Tunneling by EPB Machine (Case study: Tehran subway line 7 tunnel

Directory of Open Access Journals (Sweden)

Hassan Bakhshandeh Amnieh

2016-06-01

Full Text Available Technological progress in tunneling has led to modern and efficient tunneling methods in vast underground spaces even under inappropriate geological conditions. Identification and access to appropriate and sufficient geological hazard data are key elements to successful construction of underground structures. Choice of the method, excavation machine, and prediction of suitable solutions to overcome undesirable conditions depend on geological studies and hazard analysis. Identifying and investigating the ground hazards in excavating urban tunnels by an EPB machine could augment the strategy for improving soil conditions during excavation operations. In this paper, challenges such as geological hazards, abrasion of the machine cutting tools, clogging around these tools and inside the chamber, diverse work front, severe water level fluctuations, existence of water, and fine-grained particles in the route were recognized in a study of Tehran subway line 7, for which solutions such as low speed boring, regular cutter head checks, application of soil improving agents, and appropriate grouting were presented and discussed. Due to the presence of fine particles in the route, foam employment was suggested as the optimum strategy where no filler is needed.

Combined spectroscopy and microscopy of supported MoS2 nanoparticles

DEFF Research Database (Denmark)

Nielsen, Jane Hvolbæk; Bech, Lone; Nielsen, Kenneth

2009-01-01

Supported molybdenum-sulfide nanoparticles are known catalysts for petroleum hydrodesulfurization as well as for electrochemical hydrogen evolution. In this study, we investigate molybdenum-sulfide nanoparticles supported on Au(111) using X-ray photoelectron spectroscopy (XPS) and scanning...... tunneling microscopy (STM), aiming to correlate spectroscopically determined chemical states with atomically resolved nanostructure. The results of this study allow us to conclude the following: (1) the XPS results from our model system are in good agreement with previously published results on supported Mo...

Interplay between Switching Driven by the Tunneling Current and Atomic Force of a Bistable Four-Atom Si Quantum Dot.

Science.gov (United States)

Yamazaki, Shiro; Maeda, Keisuke; Sugimoto, Yoshiaki; Abe, Masayuki; Zobač, Vladimír; Pou, Pablo; Rodrigo, Lucia; Mutombo, Pingo; Pérez, Ruben; Jelínek, Pavel; Morita, Seizo

2015-07-08

We assemble bistable silicon quantum dots consisting of four buckled atoms (Si4-QD) using atom manipulation. We demonstrate two competing atom switching mechanisms, downward switching induced by tunneling current of scanning tunneling microscopy (STM) and opposite upward switching induced by atomic force of atomic force microscopy (AFM). Simultaneous application of competing current and force allows us to tune switching direction continuously. Assembly of the few-atom Si-QDs and controlling their states using versatile combined AFM/STM will contribute to further miniaturization of nanodevices.

Atomic scale images of acceptors in III-V semiconductors. Band bending, tunneling paths and wave functions

Energy Technology Data Exchange (ETDEWEB)

Loth, S.

2007-10-26

This thesis reports measurements of single dopant atoms in III-V semiconductors with low temperature Scanning Tunneling Microscopy (STM) and Scanning Tunneling Spectroscopy (STS). It investigates the anisotropic spatial distribution of acceptor induced tunneling processes at the {l_brace}110{r_brace} cleavage planes. Two different tunneling processes are identified: conventional imaging of the squared acceptor wave function and resonant tunneling at the charged acceptor. A thorough analysis of the tip induced space charge layers identifies characteristic bias windows for each tunnel process. The symmetry of the host crystal's band structure determines the spatial distribution of the tunneling paths for both processes. Symmetry reducing effects at the surface are responsible for a pronounced asymmetry of the acceptor contrasts along the principal [001] axis. Uniaxial strain fields due to surface relaxation and spin orbit interaction of the tip induced electric field are discussed on the basis of band structure calculations. High-resolution STS studies of acceptor atoms in an operating p-i-n diode confirm that an electric field indeed changes the acceptor contrasts. In conclusion, the anisotropic contrasts of acceptors are created by the host crystal's band structure and concomitant symmetry reduction effects at the surface. (orig.)

Scanning tunneling spectroscopy of CdSe nanocrystals covalently bound to GaAs

DEFF Research Database (Denmark)

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

2003-01-01

We present scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) measurements of CdSe nanocrystals covalently attached to doped GaAs substrates using monolayers of 1,6-hexanedithiol. STM measurements showed the formation of stable, densely packed, homogeneous monolayers...... of nanocrystals. STS measurements showed rectifying behaviour, with high currents at the opposite sample bias to that previously observed for CdSe nanocrystals adsorbed on Si substrates. We explain the rectifying behaviour by considering the interaction between the electronic states of the nanocrystals...

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

Energy Technology Data Exchange (ETDEWEB)

Ernst, Stefan

2011-06-24

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

Quantum nature of protons in water probed by scanning tunneling microscopy and spectroscopy

Science.gov (United States)

Guo, Jing; Lü, Jing-Tao; Feng, Yexin; Chen, Ji; Peng, Jinbo; Lin, Zeren; Meng, Xiangzhi; Wang, Zhichang; Li, Xin-Zheng; Wang, En-Ge; Jiang, Ying; Jing-Tao Lü Team; Xin-Zheng Li Team

The complexity of hydrogen-bonding interaction largely arises from the quantum nature of light hydrogen nuclei, which has remained elusive for decades. Here we report the direct assessment of nuclear quantum effects on the strength of a single hydrogen bond formed at a water-salt interface, using tip-enhanced inelastic electron tunneling spectroscopy (IETS) based on a low-temperature scanning tunneling microscope (STM). The IETS signals are resonantly enhanced by gating the frontier orbitals of water via a chlorine-terminated STM tip, such that the hydrogen-bonding strength can be determined with unprecedentedly high accuracy from the redshift in the O-H stretching frequency of water. Isotopic substitution experiments combined with quantum simulations reveal that the anharmonic quantum fluctuations of hydrogen nuclei weaken the weak hydrogen bonds and strengthen the relatively strong ones. However, this trend can be completely reversed when the hydrogen bond is strongly coupled to the polar atomic sites of the surface.

Spectroscopic Imaging Scanning Tunneling Microscopy Studies of Electronic Structure in the Superconducting and Pseudogap Phases of Cuprate High-Tc Superconductors

Science.gov (United States)

Fujita, Kazuhiro; Schmidt, Andrew R.; Kim, Eun-Ah; Lawler, Michael J.; Lee, Dung Hai; Davis, J. C.; Eisaki, Hiroshi; Uchida, Shin-ichi

2012-01-01

One of the key motivations for the development of atomically resolved spectroscopic imaging scanning tunneling microscopy (SI-STM) has been to probe the electronic structure of cuprate high temperature superconductors. In both the d-wave superconducting (dSC) and the pseudogap (PG) phases of underdoped cuprates, two distinct classes of electronic states are observed using SI-STM. The first class consists of the dispersive Bogoliubov quasiparticles of a homogeneous d-wave superconductor. These are detected below a lower energy scale |E|=Δ0 and only upon a momentum space (k-space) arc which terminates near the lines connecting k=±(π/a0,0) to k=±(0,π/a0). Below optimal doping, this ``nodal'' arc shrinks continuously with decreasing hole density. In both the dSC and PG phases, the only broken symmetries detected in the |E|≤Δ0 states are those of a d-wave superconductor. The second class of states occurs at energies near the pseudogap energy scale |E|˜ Δ1 which is associated conventionally with the ``antinodal'' states near k=±(π/a0,0) and k=±(0,π/a0). We find that these states break the expected 90°-rotational (C4) symmetry of electronic structure within CuO2 unit cells, at least down to 180°-rotational (C2) symmetry (nematic) but in a spatially disordered fashion. This intra-unit-cell C4 symmetry breaking coexists at |E|˜Δ1 with incommensurate conductance modulations locally breaking both rotational and translational symmetries (smectic). The characteristic wavevector Q of the latter is determined, empirically, by the k-space points where Bogoliubov quasiparticle interference terminates, and therefore evolves continuously with doping. The properties of these two classes of |E|˜Δ1 states are indistinguishable in the dSC and PG phases. To explain this segregation of k-space into the two regimes distinguished by the symmetries of their electronic states and their energy scales |E|˜Δ1 and |E|≤Δ0, and to understand how this impacts the electronic

Inelastic electron tunneling spectroscopy of a single nuclear spin.

Science.gov (United States)

Delgado, F; Fernández-Rossier, J

2011-08-12

Detection of a single nuclear spin constitutes an outstanding problem in different fields of physics such as quantum computing or magnetic imaging. Here we show that the energy levels of a single nuclear spin can be measured by means of inelastic electron tunneling spectroscopy (IETS). We consider two different systems, a magnetic adatom probed with scanning tunneling microscopy and a single Bi dopant in a silicon nanotransistor. We find that the hyperfine coupling opens new transport channels which can be resolved at experimentally accessible temperatures. Our simulations evince that IETS yields information about the occupations of the nuclear spin states, paving the way towards transport-detected single nuclear spin resonance.

Giant electroresistance of super-tetragonal BiFeO3-based ferroelectric tunnel junctions.

Science.gov (United States)

Yamada, Hiroyuki; Garcia, Vincent; Fusil, Stéphane; Boyn, Sören; Marinova, Maya; Gloter, Alexandre; Xavier, Stéphane; Grollier, Julie; Jacquet, Eric; Carrétéro, Cécile; Deranlot, Cyrile; Bibes, Manuel; Barthélémy, Agnès

2013-06-25

Ferroelectric tunnel junctions enable a nondestructive readout of the ferroelectric state via a change of resistance induced by switching the ferroelectric polarization. We fabricated submicrometer solid-state ferroelectric tunnel junctions based on a recently discovered polymorph of BiFeO3 with giant axial ratio ("T-phase"). Applying voltage pulses to the junctions leads to the highest resistance changes (OFF/ON ratio >10,000) ever reported with ferroelectric tunnel junctions. Along with the good retention properties, this giant effect reinforces the interest in nonvolatile memories based on ferroelectric tunnel junctions. We also show that the changes in resistance scale with the nucleation and growth of ferroelectric domains in the ultrathin BiFeO3 (imaged by piezoresponse force microscopy), thereby suggesting potential as multilevel memory cells and memristors.

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.

Thermal stability analysis of thin film Ni-NiOx-Cr tunnel junctions

International Nuclear Information System (INIS)

Krishnan, S.; Emirov, Y.; Bhansali, S.; Stefanakos, E.; Goswami, Y.

2010-01-01

This research reports on the thermal stability of Ni-NiO x -Cr based Metal-Insulator-Metal (MIM) junction. Effect of annealing (250 to 400 o C) on the electrical and physical transport properties of this MIM stack was understood to determine the thermal budget allowable when using these diodes. MIM tunnel junctions were fabricated by sputtering and the NiO x was formed through reactive sputtering. The performance of the tunnel junctions after exposure to elevated temperatures was investigated using current-voltage measurements. This was correlated to the structural properties of the interfaces at different temperatures, characterized by Atomic Force Microscopy, X-ray Diffraction and Transmission Electron Microscopy (TEM). MIM tunnel junctions annealed up to 350 o C demonstrated satisfactory current-voltage characteristics and sensitivity. MIM junctions exhibited improved electrical performance as they were heated to 250 o C (sensitivity of 42 V -1 and a zero-bias resistance of ∼300 Ω) due to improved crystallization of the layers within the stack. At temperatures over 350 o C, TEM and Energy Dispersive Spectra confirmed a breakdown of the MIM structure due to interdiffusion.

A Study of Vertical Transport through Graphene toward Control of Quantum Tunneling.

Science.gov (United States)

Zhu, Xiaodan; Lei, Sidong; Tsai, Shin-Hung; Zhang, Xiang; Liu, Jun; Yin, Gen; Tang, Min; Torres, Carlos M; Navabi, Aryan; Jin, Zehua; Tsai, Shiao-Po; Qasem, Hussam; Wang, Yong; Vajtai, Robert; Lake, Roger K; Ajayan, Pulickel M; Wang, Kang L

2018-02-14

Vertical integration of van der Waals (vdW) materials with atomic precision is an intriguing possibility brought forward by these two-dimensional (2D) materials. Essential to the design and analysis of these structures is a fundamental understanding of the vertical transport of charge carriers into and across vdW materials, yet little has been done in this area. In this report, we explore the important roles of single layer graphene in the vertical tunneling process as a tunneling barrier. Although a semimetal in the lateral lattice plane, graphene together with the vdW gap act as a tunneling barrier that is nearly transparent to the vertically tunneling electrons due to its atomic thickness and the transverse momenta mismatch between the injected electrons and the graphene band structure. This is accentuated using electron tunneling spectroscopy (ETS) showing a lack of features corresponding to the Dirac cone band structure. Meanwhile, the graphene acts as a lateral conductor through which the potential and charge distribution across the tunneling barrier can be tuned. These unique properties make graphene an excellent 2D atomic grid, transparent to charge carriers, and yet can control the carrier flux via the electrical potential. A new model on the quantum capacitance's effect on vertical tunneling is developed to further elucidate the role of graphene in modulating the tunneling process. This work may serve as a general guideline for the design and analysis of vdW vertical tunneling devices and heterostructures, as well as the study of electron/spin injection through and into vdW materials.

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.

Quantum size effects on spin-tunneling time in a magnetic resonant tunneling diode

OpenAIRE

Saffarzadeh, Alireza; Daqiq, Reza

2009-01-01

We study theoretically the quantum size effects of a magnetic resonant tunneling diode (RTD) with a (Zn,Mn)Se dilute magnetic semiconductor layer on the spin-tunneling time and the spin polarization of the electrons. The results show that the spin-tunneling times may oscillate and a great difference between the tunneling time of the electrons with opposite spin directions can be obtained depending on the system parameters. We also study the effect of structural asymmetry which is related to t...

Proton tunneling in solids

Energy Technology Data Exchange (ETDEWEB)

Kondo, J.

1998-10-01

The tunneling rate of the proton and its isotopes between interstitial sites in solids is studied theoretically. The phonons and/or the electrons in the solid have two effects on the tunneling phenomenon. First, they suppress the transfer integral between two neighbouring states. Second, they give rise to a finite lifetime of the proton state. Usually the second effect is large and the tunneling probability per unit time (tunneling rate) can be defined. In some cases, however, a coherent tunneling is expected and actually observed. (author)

Proton tunneling in solids

International Nuclear Information System (INIS)

Kondo, J.

1998-01-01

The tunneling rate of the proton and its isotopes between interstitial sites in solids is studied theoretically. The phonons and/or the electrons in the solid have two effects on the tunneling phenomenon. First, they suppress the transfer integral between two neighbouring states. Second, they give rise to a finite lifetime of the proton state. Usually the second effect is large and the tunneling probability per unit time (tunneling rate) can be defined. In some cases, however, a coherent tunneling is expected and actually observed. (author)

Grain boundary engineering of La{sub 0.7} Sr{sub 0.3} MnO{sub 3} films on silicon substrate: Scanning Tunneling Microscopy-Spectroscopy study

Energy Technology Data Exchange (ETDEWEB)

Joshi, Anupama [Department of Applied Physics, Defence Institute of Advanced Technology (DU), Girinagar, Pune 411025 (India); Nori, Rajashree [Centre of Excellence in Nanoelectronics, Department of Electrical Engineering, Indian Institute of Technology (IIT Bombay), Mumbai 400076 (India); Dhobale, Sandip [Department of Applied Physics, Defence Institute of Advanced Technology (DU), Girinagar, Pune 411025 (India); Ramgopal Rao, V. [Centre of Excellence in Nanoelectronics, Department of Electrical Engineering, Indian Institute of Technology (IIT Bombay), Mumbai 400076 (India); Kale, S.N., E-mail: sangeetakale2004@gmail.com [Department of Applied Physics, Defence Institute of Advanced Technology (DU), Girinagar, Pune 411025 (India); Datar, Suwarna, E-mail: suwarna.datar@gmail.com [Department of Applied Physics, Defence Institute of Advanced Technology (DU), Girinagar, Pune 411025 (India)

2014-09-01

We employed a Scanning Tunnelling Microscope (STM) to study the surface topography and spatially resolved local electronic properties like local density of states (LDOS) of nanostructured films of La{sub 0.7} Sr{sub 0.3} MnO{sub 3} (LSMO). The nanostructured thin films of LSMO on silicon substrate were prepared using Pulsed Laser Deposition (PLD) technique. The deposition conditions were tuned to yield two different morphologies; one with uniform columnar closely packed islands and other with larger grain distribution in random fashion. The Scanning Tunnelling Spectroscopy (STS) revealed the extent of variation of density of states (DOS) near the Fermi level. From the spectroscopic features obtained we found the occurrence of phase separation between conducting and semiconducting domains and its possible correlation with the properties of the system. Semiconducting nature was observed at the grain boundaries, which could be extremely promising in futuristic nano-devices.

Study of the Integration of the CNU-TS-1 Mobile Tunnel Monitoring System.

Science.gov (United States)

Du, Liming; Zhong, Ruofei; Sun, Haili; Zhu, Qiang; Zhang, Zhen

2018-02-01

A rapid, precise and automated means for the regular inspection and maintenance of a large number of tunnels is needed. Based on the depth study of the tunnel monitoring method, the CNU-TS-1 mobile tunnel monitoring system (TS1) is developed and presented. It can efficiently obtain the cross-sections that are orthogonal to the tunnel in a dynamic way, and the control measurements that depend on design data are eliminated. By using odometers to locate the cross-sections and correcting the data based on longitudinal joints of tunnel segment lining, the cost of the system has been significantly reduced, and the interval between adjacent cross-sections can reach 1-2 cm when pushed to collect data at a normal walking speed. Meanwhile, the relative deformation of tunnel can be analyzed by selecting cross-sections from original data. Through the measurement of the actual tunnel, the applicability of the system for tunnel deformation detection is verified, and the system is shown to be 15 times more efficient than that of the total station. The simulation experiment of the tunnel deformation indicates that the measurement accuracy of TS1 for cross-sections is 1.1 mm. Compared with the traditional method, TS1 improves the efficiency as well as increases the density of the obtained points.

Study of the Integration of the CNU-TS-1 Mobile Tunnel Monitoring System

Directory of Open Access Journals (Sweden)

Liming Du

2018-02-01

Full Text Available A rapid, precise and automated means for the regular inspection and maintenance of a large number of tunnels is needed. Based on the depth study of the tunnel monitoring method, the CNU-TS-1 mobile tunnel monitoring system (TS1 is developed and presented. It can efficiently obtain the cross-sections that are orthogonal to the tunnel in a dynamic way, and the control measurements that depend on design data are eliminated. By using odometers to locate the cross-sections and correcting the data based on longitudinal joints of tunnel segment lining, the cost of the system has been significantly reduced, and the interval between adjacent cross-sections can reach 1–2 cm when pushed to collect data at a normal walking speed. Meanwhile, the relative deformation of tunnel can be analyzed by selecting cross-sections from original data. Through the measurement of the actual tunnel, the applicability of the system for tunnel deformation detection is verified, and the system is shown to be 15 times more efficient than that of the total station. The simulation experiment of the tunnel deformation indicates that the measurement accuracy of TS1 for cross-sections is 1.1 mm. Compared with the traditional method, TS1 improves the efficiency as well as increases the density of the obtained points.

Recognizing nitrogen dopant atoms in graphene using atomic force microscopy

DEFF Research Database (Denmark)

van der Heijden, Nadine J.; Smith, Daniel; Calogero, Gaetano

2016-01-01

Doping graphene by heteroatoms such as nitrogen presents an attractive route to control the position of the Fermi level in the material. We prepared N-doped graphene on Cu(111) and Ir(111) surfaces via chemical vapor deposition of two different molecules. Using scanning tunneling microscopy image...

Atomic force microscope-assisted scanning tunneling spectroscopy under ambient conditions.

Science.gov (United States)

Vakhshouri, Amin; Hashimoto, Katsushi; Hirayama, Yoshiro

2014-12-01

We have developed a method of atomic force microscopy (AFM)-assisted scanning tunneling spectroscopy (STS) under ambient conditions. An AFM function is used for rapid access to a selected position prior to performing STS. The AFM feedback is further used to suppress vertical thermal drift of the tip-sample distance during spectroscopy, enabling flexible and stable spectroscopy measurements at room temperature. © The Author 2014. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Scanning tunneling microscopy of the atomically smooth (001) surface of vanadium pentoxide V_2O_5 crystals

International Nuclear Information System (INIS)

Muslimov, A. E.; Butashin, A. V.; Kanevsky, V. M.

2017-01-01

The (001) cleavage surface of vanadium pentoxide (V_2O_5) crystal has been studied by scanning tunneling spectroscopy (STM). It is shown that the surface is not reconstructed; the STM image allows geometric lattice parameters to be determined with high accuracy. The nanostructure formed on the (001) cleavage surface of crystal consists of atomically smooth steps with a height multiple of unit-cell parameter c = 4.37 Å. The V_2O_5 crystal cleavages can be used as references in calibration of a scanning tunneling microscope under atmospheric conditions both along the (Ñ…, y) surface and normally to the sample surface (along the z axis). It is found that the terrace surface is not perfectly atomically smooth; its roughness is estimated to be ~0.5 Å. This circumstance may introduce an additional error into the microscope calibration along the z coordinate.

EXPERIMENTAL STUDY ON THE STABILITY OF SURROUNDING ROCK IN TUNNEL BLASTING CONSTRUCTION

Directory of Open Access Journals (Sweden)

Hongxian Fu

2018-04-01

Full Text Available In this study, criteria and blasting technologies are introduced in order to control the stability of surrounding rock of tunnel built using drill-and-blast safety. The paper is composed of three parts, namely, a blast vibration propagation law in roof surrounding rock in close proximity to tunnel face, two formulae to calculate particle critical vibration velocity of shotcrete and key structural element at the roof of tunnel, and innovative technologies of tunnel blasting. The blast vibration propagation law is the base to control the stability of surrounding rock during tunnel blasting. Based on Morhr-Coulomb criterion and the dynamic analysis, two formulae to calculate the critical particle vibration velocity are proposed. Based on a series of trial blasts using electronic detonators, two innovative blasting technologies are derived. One is the blast holes detonated one by one by using electronic detonator, and another is the blast holes detonated by combining initiation system of electronic detonators and nonel detonators. The use of electronic detonators in tunnel blasting not only leads to a smaller blast vibration but also to a smaller extent of the EDZ (excavation damaged zone.

Silicon Nano fabrication by Atomic Force Microscopy-Based Mechanical Processing

International Nuclear Information System (INIS)

Miyake, Sh.; Wang, M.; Kim, J.

2014-01-01

This paper reviews silicon nano fabrication processes using atomic force microscopy (AFM). In particular, it summarizes recent results obtained in our research group regarding AFM-based silicon nano fabrication through mechanochemical local oxidation by diamond tip sliding, as well as mechanical, electrical, and electromechanical processing using an electrically conductive diamond tip. Microscopic three-dimensional manufacturing mainly relies on etching, deposition, and lithography. Therefore, a special emphasis was placed on nano mechanical processes, mechanochemical reaction by potassium hydroxide solution etching, and mechanical and electrical approaches. Several important surface characterization techniques consisting of scanning tunneling microscopy and related techniques, such as scanning probe microscopy and AFM, were also discussed.

Microwave Frequency Comb from a Semiconductor in a Scanning Tunneling Microscope.

Science.gov (United States)

Hagmann, Mark J; Yarotski, Dmitry A; Mousa, Marwan S

2017-04-01

Quasi-periodic excitation of the tunneling junction in a scanning tunneling microscope, by a mode-locked ultrafast laser, superimposes a regular sequence of 15 fs pulses on the DC tunneling current. In the frequency domain, this is a frequency comb with harmonics at integer multiples of the laser pulse repetition frequency. With a gold sample the 200th harmonic at 14.85 GHz has a signal-to-noise ratio of 25 dB, and the power at each harmonic varies inversely with the square of the frequency. Now we report the first measurements with a semiconductor where the laser photon energy must be less than the bandgap energy of the semiconductor; the microwave frequency comb must be measured within 200 μm of the tunneling junction; and the microwave power is 25 dB below that with a metal sample and falls off more rapidly at the higher harmonics. Our results suggest that the measured attenuation of the microwave harmonics is sensitive to the semiconductor spreading resistance within 1 nm of the tunneling junction. This approach may enable sub-nanometer carrier profiling of semiconductors without requiring the diamond nanoprobes in scanning spreading resistance microscopy.

Effects of polymer corrosion inhibitor on widening etch tunnels of aluminum foil for capacitor

International Nuclear Information System (INIS)

Ban, Chaolei; He, Yedong; Shao, Xin; Wang, Zhishen

2014-01-01

Highlights: •With PSSA, the exterior surface dissolution of etched Al foil is suppressed. •With PSSA, the interior surface dissolution of etched Al foil is facilitated. •With PSSA, the tunnels are widened along the entire length. •With PSSA, the area and capacitance of etched Al foil are significantly improved. -- Abstract: We investigated the effects of polymeric corrosion inhibitor polystyrene sulfonic acid (PSSA) additive to 3% HNO 3 solution on widening tunnels of pre-etched aluminum foil by electrochemical DC etching for aluminum electrolytic capacitors, using scanning electron microscopy and polarization curves. With trace PSSA, the dissolution of exterior surface of etch tunnels of Al foil is suppressed and the dissolution of interior surface of etch tunnels of Al foil is facilitated, respectively. The tunnels transform from circular cone to circular column in shape and pits-merging on the surface is weakened, leading to significant increase in the surface area and specific capacitance of the Al foil. The amounts of reduced thickness and weight of Al foil during the widening process of etch tunnels can be decreased if PSSA is employed

Force and light tuning vertical tunneling current in the atomic layered MoS2.

Science.gov (United States)

Li, Feng; Lu, Zhixing; Lan, Yann-Wen; Jiao, Liying; Xu, Minxuan; Zhu, Xiaoyang; Zhang, Xiankun; Wu, Hualin; Qi, Junjie

2018-07-06

In this work, the vertical electrical transport behavior of bilayer MoS 2 under the coupling of force and light was explored by the use of conductive atomic force microscopy. We found that the current-voltage behavior across the tip-MoS 2 -Pt junction is a tunneling current that can be well fitted by a Simmons approximation. The transport behavior is direct tunneling at low bias and Fowler-Nordheim tunneling at high bias, and the transition voltage and tunnel barrier height are extracted. The effect of force and light on the effective band gap of the junction is investigated. Furthermore, the source-drain current drops surprisingly when we continually increase the force, and the dropping point is altered by the provided light. This mechanism is responsible for the tuning of tunneling barrier height and width by force and light. These results provide a new way to design devices that take advantage of ultrathin two-dimensional materials. Ultrashort channel length electronic components that possess tunneling current are important for establishing high-efficiency electronic and optoelectronic systems.

Adsorption of selenium atoms at the Si(1 1 1)-7 x 7 surface: A combination of scanning tunnelling microscopy and density functional theory studies

International Nuclear Information System (INIS)

Wu, S.Q.; Zhou Yinghui; Wu Qihui; Pakes, C.I.; Zhu Zizhong

2011-01-01

Graphical abstract: A selenium atom, which adsorbs at site close to a Si adatom and bonds with this Si adatom and one of its backbonding Si atoms on the Si(1 1 1)-7 x 7 surface, will break the Si-Si bond and consequently disorder the Si reconstruction surface. Research highlights: → STM and DFT are used to study the adsorption properties of Se atoms on a Si surface. → The adsorption site of Se atom on the Si surface has been identified. → The electronic effect of Se atom on the adsorbed Si surface has been ivestigaed. → The Se atom weakens the bond between two Si atom bonding with the Se atom. - Abstract: The adsorption of selenium (Se) atoms at the Si(1 1 1)-7 x 7 surface has been investigated using both scanning tunnelling microscopy (STM) and density functional theory calculations. A single Se atom prefers to adsorb at sites close to a Si adatom and bonds with this Si adatom and one of its backbonding Si atoms. The adsorption sites are referred to as A*-type sites in this article. The density of the conduction band (empty states) of the Si adatom increases as a result of the adsorption of a Se atom, which causes the Si adatom to become brighter in the empty state STM images. At the same time, the adsorption of the Se atom weakens the bonding between the Si adatom and its backbonding Si atom due to the charge transfer from them to the Se atom, and consequently destructs the ordered Si(1 1 1)-7 x 7 surface with increasing Se coverage.

Cyclic voltammetry and scanning electrochemical microscopy studies of methylene blue immobilized on the self-assembled monolayer of n-dodecanethiol

International Nuclear Information System (INIS)

Salamifar, Seyed Ehsan; Mehrgardi, Masoud Ayatollahi; Kazemi, Sayed Habib; Mousavi, Mir Fazllollah

2010-01-01

Electron transfer (ET) kinetics through n-dodecanethiol (C 12 SH) self-assembled monolayer on gold electrode was studied using cyclic voltammetry (CV), scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS). An SECM model for compensating pinhole contribution, was used to measure the ET kinetics of solution-phase probes of ferrocyanide/ferricyanide (Fe(CN) 6 4-/3- ) and ferrocenemethanol/ferrociniummethanol (FMC 0/+ ) through the C 12 SH monolayer yielding standard tunneling rate constant (k ET 0 ) of (4 ± 1) x 10 -11 and (3 ± 1) x 10 -10 cm s -1 for Fe(CN) 6 4-/3- and FMC 0/+ respectively. Decay tunneling constants (β) of 0.97 and 0.96 A -1 for saturated alkane thiol chains were obtained using Fe(CN) 6 4- and FMC respectively. Also, it was found that methylene blue (MB) molecules are effectively immobilized on the C 12 SH monolayer and can mediate the ET between the solution-phase probes and underlying gold substrate. SECM-mediated model was used to simultaneously measure the bimolecular ET between the solution-phase probes and the monolayer-immobilized MB molecules, as well as tunneling ET between the monolayer-immobilized MB molecules and the underlying gold electrode, allowing the measurement of k BI = (5 ± 1) x 10 6 and (4 ± 2) x 10 7 cm 3 mol -1 s -1 for the bimolecular ET and k ET/MB 0 =(1±0.3)x10 -3 and (7 ± 3) x 10 -2 s -1 for the standard tunneling rate constant of ET using Fe(CN) 6 4-/3- and FMC 0/+ probes respectively.

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

International Nuclear Information System (INIS)

Wang, Fei; Clément, Nicolas; Ducatteau, Damien; Troadec, David; Legrand, Bernard; Dambrine, Gilles; Théron, Didier; Tanbakuchi, Hassan

2014-01-01

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

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

DEFF Research Database (Denmark)

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

2011-01-01

High-resolution scanning tunneling microscope (STM) images of moiré-structured FeO films on Pt(111) were obtained in a number of different tip-dependent imaging modes. For the first time, the STM images are distinguished and interpreted unambiguously with the help of distinct oxygen...

Molecular assembly and electro polymerization of 3,4-ethylenedioxy thiophene on Au(100) single crystal electrode using in-situ electrochemical scanning tunneling microscopy

International Nuclear Information System (INIS)

Garcia, Jonyl L.; Tongol, Bernard John V.; ShuehLin Yau

2012-01-01

Electrochemical scanning tunneling microscopy (Ec-STM) is a powerful technique that can provide molecular-level information regarding electrode surface processes in-situ in electrolyte solvent under ambient conditions. In this study, the adsorption and electro polymerization of an industrially important conducting polymer precursor, 3,4-ethylenedioxy thiophene (EDOT), on Au (100) single crystal was probed using Ec-STM. The Au (100) single crystal electrode substrate used for this study was fabricated using the well-known Clavilier's flame melting procedure. Cyclic voltammetry (CV) was used along with Ec-STM to characterize the bare, EDOT-modified, and poly(EDOT)-modified Au (100) single crystal electrode. Time-dependent Ec-STM imaging at 0.550 V showed the formation of an EDOT self-assembled monolayer through 2-D surface dillusion. The resulting EDOT molecular assembly on Au (100) single crystal electrode was found to fit in a 4√2χ3√2 unit cell. Difference in apparent corrugation between molecular rows was attributed to different angular orientation with respect to the substrate. The electro polymerization of EDOT on Au (100) single crystal electrode was done by potentiostatic and potentiodynamic methods. Both methods suggested a solution-process mechanism for EDOT electro polymerization. (author)

Case study on ventilation method development for Bar-Boljare highway tunnels construction in Montenegro

Directory of Open Access Journals (Sweden)

Cvjetić Aleksandar S.

2017-01-01

Full Text Available Sometimes tunnel construction is a necessity regardless of its purpose due to many reasons, to mention some of them: limited space, safe operation, environmental protection etc. In those cases, one of the main aspects concerning an appropriate design of a tunnel construction is site ventilation. Ventilation is required during the construction of any tunnel regardless of technology used to construct it. Three major construction ventilation schemes are typically applied. Which one will be use are often in dependency of the site requirements. In this paper is presented case study on ventilation method development for the highway tunnels construction and it includes ventilation solutions for tunnels ‘Suka’, ‘Vežešnik’, ‘Mrke’ and ‘Vjeternik’ during construction phase. The tunnels are part of the Bar-Boljare highway which is also a part of the Trans-European Highway (THE through the Republic of Montenegro.

Simulation of the soft-landing and adsorption of C{sub 60} molecules on a graphite substrate and computation of their scanning-tunnelling-microscopy-like images

Energy Technology Data Exchange (ETDEWEB)

Rafii-Tabar, H. [Computational Nano-Science Research Group, Centre for Numerical Modelling and Process Analysis, School of Computing and Mathematical Sciences, University of Greenwich, Greenwich, London (United Kingdom); Jurczyszyn, L.; Stankiewicz, B. [Institute of Experimental Physics, University of Wroclaw, Wroclaw (Poland)

2000-07-03

A constant-temperature molecular dynamics (MD) simulation was performed to model the soft-landing and adsorption of C{sub 60} molecules on a graphite substrate with the C{sub 60}s treated as soft molecules and released individually towards the substrate. The intra-molecular and intra-planar covalently bonding interactions were modelled by very accurate many-body potentials, and the non-bonding forces were derived from various pairwise potentials. The simulation extended over 1.6 million time steps covering a significant period of 160 picoseconds. The final alignment of the molecules on the surface agrees closely with that observed in an experiment based on scanning tunnelling microscopy (STM) on the same system, performed at room temperature and under ultrahigh-vacuum (UHV) conditions. Using a tungsten tip in a constant-current mode of imaging, we have also computed the STM-like images of one of the adsorbed molecules using a formulation of the STM tunnelling current based on Keldysh's non-equilibrium Green function formalism. Our aim has been to search for tip-induced states, which were speculated, on the basis of another STM-based experiment, performed in air, to form one of the possible origins of the extra features purported to have been observed in that experiment. We have not obtained any such states. (author)

Thermovoltage in scanning tunnelling microscopy. Study of heterogeneous metal surfaces on atomic scale; Thermospannung in der Rastertunnelmikroskopie. Untersuchung heterogener Metalloberflaechen auf atomarer Skala

Energy Technology Data Exchange (ETDEWEB)

Weyers, B.

2005-07-01

In this thesis the thermovoltage has been studied via a tunnel barrier under different aspects. Au(111) has been chosen as substrate. The mean free path of the electrons on the Au(111) surface was determined by a comparison of the standing waves on stage edges with the theoretical prediction. The measurements were performed at different temperatures. Detailed studies were performed on Au(111), Cu(111), and Cu(110) in order to examine the question whether the cause for strong signal on the stage edges lies in the surface state itself or in the band gap. The mani theme of this thesis is the study of a binary metal system, in this case silver on Au(111).

Study of Scanning Tunneling Microscope control electronics

International Nuclear Information System (INIS)

Oliva, A.J.; Pancarobo, M.; Denisenko, N.; Aguilar, M.; Rejon, V.; Pena, J.L.

1994-01-01

A theoretical study of Scanning Tunneling Microscope control electronics is made. The knowledge of its behaviour allows us to determine accurately the region where the unstable operation could effect the measurements, and also to set the optimal working parameters. Each feedback circuitry compound is discussed as well as their mutual interaction. Different working conditions analysis and results are presented. (Author) 12 refs

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

Science.gov (United States)

Schoelz, James K.

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

Experimental study of drag reduction in flumes and spillway tunnels

Directory of Open Access Journals (Sweden)

Ying-kui Wang

2010-06-01

Full Text Available Experiments in an open flume model and spillway tunnel model were carried out using drag reduction techniques. Two drag reduction techniques were adopted in the experiments: polymer addition and coating. The drag reduction effect of a polyacrylamide (PAM solution and dimethyl silicone oil coating were studied in the flume model experiments, and the results were analyzed. Experiments were then carried out with a model of the Xiluodu Hydropower Station, the second largest dam in China. In order to reduce the resistance, the spillway tunnels were internally coated with dimethyl silicone oil. This is the first time that these drag reduction techniques have been applied to so large a hydraulic model. The experimental results show that the coating technique can effectively increase flood discharge. The outlet velocity and the jet trajectory distance are also increased, which enhances the energy dissipation of the spillway tunnel.

SPATIAL REPARTITION OF CURRENT FLUCTUATIONS IN A SCANNING TUNNELING MICROSCOPE

Directory of Open Access Journals (Sweden)

Jerome Lagoute

2011-05-01

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

Scanning probe microscope simulator for the assessment of noise in scanning probe microscopy controllers

International Nuclear Information System (INIS)

Wutscher, T.; Niebauer, J.; Giessibl, F. J.

2013-01-01

We present an electronic circuit that allows to calibrate and troubleshoot scanning probe microscopy (SPM) controllers with respect to their noise performance. The control signal in an SPM is typically highly nonlinear—the tunneling current in scanning tunneling microscopy (STM) varies exponentially with distance. The exponential current-versus-voltage characteristics of diodes allow to model the current dependence in STM. Additional inputs allow to simulate the effects of external perturbations and the reactions of the control electronics. We characterized the noise performance of the feedback controller using the apparent topography roughness of recorded images. For a comparison of different STM controllers, an optimal gain parameter was determined by exploring settling times through a rectangular perturbation signal. We used the circuit to directly compare the performance of two types of SPM controllers used in our laboratory

Cotunneling enhancement of magnetoresistance in double magnetic tunnel junctions with embedded superparamagnetic NiFe nanoparticles

International Nuclear Information System (INIS)

Dempsey, K.J.; Arena, D.; Hindmarch, A.T.; Wei, H.X.; Qin, Q.H.; Wen, Z.C.; Wang, W.X.; Vallejo-Fernandez, G.; Han, X.F.; Marrows, C.H.

2010-01-01

Temperature and bias voltage-dependent transport characteristics are presented for double magnetic tunnel junctions (DMTJs) with self-assembled NiFe nanoparticles embedded between insulating alumina barriers. The junctions with embedded nanoparticles are compared to junctions with a single barrier of comparable size and growth conditions. The embedded particles are characterized using x-ray absorption spectroscopy, transmission electron microscopy, and magnetometry techniques, showing that they are unoxidized and remain superparamagnetic to liquid helium temperatures. The tunneling magnetoresistance (TMR) for the DMTJs is lower than the control samples, however, for the DMTJs an enhancement in TMR is seen in the Coulomb blockade region. Fitting the transport data in this region supports the theory that cotunneling is the dominant electron transport process within the Coulomb blockade region, sequential tunneling being suppressed. We therefore see an enhanced TMR attributed to the change in the tunneling process due to the interplay of the Coulomb blockade and spin-dependent tunneling through superparamagnetic nanoparticles, and develop a simple model to quantify the effect, based on the fact that our nanoparticles will appear blocked when measured on femtosecond tunneling time scales.

Solvent-Dependent Self-Assembly of 4,7-Dibromo-5,6-bis(octyloxybenzo[c][1,2,5] Thiadiazole on Graphite Surface by Scanning Tunneling Microscopy

Directory of Open Access Journals (Sweden)

Bao Zha

2013-01-01

Full Text Available Solvent effect on self-assembly of 4,7-dibromo-5,6-bis(octyloxybenzo[c][1,2,5] thiadiazole (DBT on a highly oriented graphite (HOPG surface was investigated by scanning tunneling microscopy (STM by using 1-phenyloctane, 1-octanoic acid, and 1-octanol as the solvents. Two different patterns were obtained in 1-phenyloctane and 1-octanoic acid, suggesting that the self-assembly of DBT was solvent dependent. At the 1-phenyloctane/HOPG interface, a linear structure was revealed due to the intermolecular halogen bonding. When 1-octanoic acid and 1-octanol are used as the solvents, the coadsorption of solvent molecules resulting from the hydrogen bonding between DBT and solvent made an important contribution to the formation of a lamellar structure. The results demonstrate that solvents could affect the molecular self-assembly according to the variational intermolecular interactions.

Thermally oxidized Inconel 600 and 690 nickel-based alloys characterizations by combination of global photoelectrochemistry and local near-field microscopy techniques (STM, STS, AFM, SKPFM)

Science.gov (United States)

Mechehoud, F.; Benaioun, N. E.; Hakiki, N. E.; Khelil, A.; Simon, L.; Bubendorff, J. L.

2018-03-01

Thermally oxidized nickel-based alloys are studied by scanning tunnelling microscopy (STM), scanning tunnelling spectroscopy (STS), atomic force microscopy (AFM), scanning kelvin probe force microscopy (SKPFM) and photoelectro-chemical techniques as a function of oxidation time at a fixed temperature of 623 K. By photoelectrochemistry measurements we identify the formation of three oxides NiO, Fe2O3, Cr2O3 and determine the corresponding gap values. We use these values as parameter for imaging the surface at high bias voltage by STM allowing the spatial localization and identification of both NiO, Fe2O3 oxide phases using STS measurements. Associated to Kelvin probe measurements we show also that STS allow to distinguished NiO from Cr2O3 and confirm that the Cr2O3 is not visible at the surface and localized at the oxide/steel interface.

Joule heating and spin-transfer torque investigated on the atomic scale using a spin-polarized scanning tunneling microscope.

Science.gov (United States)

Krause, S; Herzog, G; Schlenhoff, A; Sonntag, A; Wiesendanger, R

2011-10-28

The influence of a high spin-polarized tunnel current onto the switching behavior of a superparamagnetic nanoisland on a nonmagnetic substrate is investigated by means of spin-polarized scanning tunneling microscopy. A detailed lifetime analysis allows for a quantification of the effective temperature rise of the nanoisland and the modification of the activation energy barrier for magnetization reversal, thereby using the nanoisland as a local thermometer and spin-transfer torque analyzer. Both the Joule heating and spin-transfer torque are found to scale linearly with the tunnel current. The results are compared to experiments performed on lithographically fabricated magneto-tunnel junctions, revealing a very high spin-transfer torque switching efficiency in our experiments.

Atomic force microscopy. A new method for atom identification and manipulation

International Nuclear Information System (INIS)

Abe, Masayuki; Sugimoto, Yoshiaki; Morita, Seizo

2007-01-01

Frequency modulation atomic force microscopy (FM-AFM) is a scanning probe technique that detects the interaction forces between the outermost atom of a sharp tip and the atoms at a surface to image the sample surface. It is expected that the FM-AFM can cover the research field which scanning tunneling microscopy does not provide. In this article, we would introduce FM-AFM experiments applied to site-specific force measurements and atom manipulation, including how to solve the problems to achieve precise FM-AFM measurements. (author)

Geochemical study of acid mine drainage of the Big Lick Tunnel area, Williamstown, PA

International Nuclear Information System (INIS)

Tollin, S.

1993-01-01

Acid mine drainage in the anthracite region of Pennsylvania continues to be a significant environmental problem. This study examines the acid mine outflow from the Big Lick Tunnel, north of Williamstown, Dauphin County, Pennsylvania. The tunnel drains abandoned mines on the north side of the Big Lick Mountain. Mining ceased in the area circa 1940, and the tunnel has been in operation since that time. The water, soil and stream bed sediment geochemistry has been studied to determine their changes in chemistry over distance. The pH, TDS and metal concentrations were the primary focus. Metal concentrations were determined using an ICP unit. Data indicates the pH of the outflow to range between 6.7 and 7.3 Fe and Mn concentrations are as high as 9.7 ppb. Extensive metal precipitation (''yellow boy'') occurs within the tunnel and for several hundred meters from the mouth of the tunnel. The combination of near neutral pH and high metal concentration suggest that the drainage is in contact with highly alkaline materials prior to discharge from the tunnel. The geology of the area does not suggest bedrock as the possible source of alkaline material. One hypothesis is that the acidic water is reacting with the concrete tunnel and being neutralized. Data also suggests that the Fe precipitates much quicker than the Mn, resulting in a zonation between Fe-rich and Mn-rich sediments along the length of the drainage

Cyclic voltammetry and scanning electrochemical microscopy studies of methylene blue immobilized on the self-assembled monolayer of n-dodecanethiol

Energy Technology Data Exchange (ETDEWEB)

Salamifar, Seyed Ehsan [Department of Chemistry, Tarbiat Modares University, P.O. Box 14115-175, Tehran (Iran, Islamic Republic of); Mehrgardi, Masoud Ayatollahi [Department of Chemistry, University of Isfahan, Isfahan (Iran, Islamic Republic of); Kazemi, Sayed Habib [Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan (Iran, Islamic Republic of); Mousavi, Mir Fazllollah, E-mail: mousavim@modares.ac.i [Department of Chemistry, Tarbiat Modares University, P.O. Box 14115-175, Tehran (Iran, Islamic Republic of)

2010-12-30

Electron transfer (ET) kinetics through n-dodecanethiol (C{sub 12}SH) self-assembled monolayer on gold electrode was studied using cyclic voltammetry (CV), scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS). An SECM model for compensating pinhole contribution, was used to measure the ET kinetics of solution-phase probes of ferrocyanide/ferricyanide (Fe(CN){sub 6}{sup 4-/3-}) and ferrocenemethanol/ferrociniummethanol (FMC{sup 0/+}) through the C{sub 12}SH monolayer yielding standard tunneling rate constant (k{sub ET}{sup 0}) of (4 {+-} 1) x 10{sup -11} and (3 {+-} 1) x 10{sup -10} cm s{sup -1} for Fe(CN){sub 6}{sup 4-/3-} and FMC{sup 0/+} respectively. Decay tunneling constants ({beta}) of 0.97 and 0.96 A{sup -1} for saturated alkane thiol chains were obtained using Fe(CN){sub 6}{sup 4-} and FMC respectively. Also, it was found that methylene blue (MB) molecules are effectively immobilized on the C{sub 12}SH monolayer and can mediate the ET between the solution-phase probes and underlying gold substrate. SECM-mediated model was used to simultaneously measure the bimolecular ET between the solution-phase probes and the monolayer-immobilized MB molecules, as well as tunneling ET between the monolayer-immobilized MB molecules and the underlying gold electrode, allowing the measurement of k{sub BI} = (5 {+-} 1) x 10{sup 6} and (4 {+-} 2) x 10{sup 7} cm{sup 3} mol{sup -1} s{sup -1} for the bimolecular ET and k{sub ET/MB}{sup 0}=(1{+-}0.3)x10{sup -3} and (7 {+-} 3) x 10{sup -2} s{sup -1} for the standard tunneling rate constant of ET using Fe(CN){sub 6}{sup 4-/3-} and FMC{sup 0/+} probes respectively.

Tunnel - history of

International Nuclear Information System (INIS)

1998-11-01

This book introduces history of tunnel in ancient times, the middle ages and modern times, survey of tunnel and classification of bedrock like environment survey of position, survey of the ground, design of tunnel on basic thing of the design, and design of tunnel of bedrock, analysis of stability of tunnel and application of the data, construction of tunnel like lattice girder and steel fiber reinforced shot crete, and maintenance control and repair of tunnel.

Sonographic diagnosis of carpal tunnel syndrome: a study in 200 hospital workers

Directory of Open Access Journals (Sweden)

Adham do Amaral e Castro

2015-10-01

Full Text Available AbstractObjective:To describe the prevalence of carpal tunnel syndrome in a sample of 200 healthy hospital workers, establishing the respective epidemiological associations.Materials and Methods:Two hundred individuals were submitted to wrist ultrasonography to measure the median nerve area. They were questioned and examined for epidemiological data, body mass index, carpal tunnel syndrome signs and symptoms, and submitted to the Boston carpal tunnel questionnaire (BCTQ to evaluate the carpal tunnel syndrome severity. A median nerve area ≥ 9 mm2 was considered to be diagnostic of carpal tunnel syndrome.Results:Carpal tunnel syndrome was diagnosed by ultrasonography in 34% of the sample. It was observed the association of carpal tunnel syndrome with age (p < 0.0001, paresthesia (p < 0.0001, Tinel's test (p < 0.0001, Phalen's test (p< 0.0001, BCTQ score (p < 0.0001, and years of formal education (p < 0.0001. Years of formal education was the only variable identified as an independent risk factor for carpal tunnel syndrome (95% CI = 1.03 to 1.24.Conclusion:The prevalence of carpal tunnel syndrome in a population of hospital workers was of 34%. The number of years of formal education was the only independent risk factor for carpal tunnel syndrome.

Automatic control study of the icing research tunnel refrigeration system

Science.gov (United States)

Kieffer, Arthur W.; Soeder, Ronald H.

1991-01-01

The Icing Research Tunnel (IRT) at the NASA Lewis Research Center is a subsonic, closed-return atmospheric tunnel. The tunnel includes a heat exchanger and a refrigeration plant to achieve the desired air temperature and a spray system to generate the type of icing conditions that would be encountered by aircraft. At the present time, the tunnel air temperature is controlled by manual adjustment of freon refrigerant flow control valves. An upgrade of this facility calls for these control valves to be adjusted by an automatic controller. The digital computer simulation of the IRT refrigeration plant and the automatic controller that was used in the simulation are discussed.

Multi-level communication of human retinal pigment epithelial cells via tunneling nanotubes.

Directory of Open Access Journals (Sweden)

Dierk Wittig

Full Text Available BACKGROUND: Tunneling nanotubes (TNTs may offer a very specific and effective way of intercellular communication. Here we investigated TNTs in the human retinal pigment epithelial (RPE cell line ARPE-19. Morphology of TNTs was examined by immunostaining and scanning electron microscopy. To determine the function of TNTs between cells, we studied the TNT-dependent intercellular communication at different levels including electrical and calcium signalling, small molecular diffusion as well as mitochondrial re-localization. Further, intercellular organelles transfer was assayed by FACS analysis. METHODOLOGY AND PRINCIPAL FINDINGS: Microscopy showed that cultured ARPE-19 cells are frequently connected by TNTs, which are not attached to the substratum. The TNTs were straight connections between cells, had a typical diameter of 50 to 300 nm and a length of up to 120 µm. We observed de novo formation of TNTs by diverging from migrating cells after a short time of interaction. Scanning electron microscopy confirmed characteristic features of TNTs. Fluorescence microscopy revealed that TNTs between ARPE-19 cells contain F-actin but no microtubules. Depolymerisation of F-actin, induced by addition of latrunculin-B, led to disappearance of TNTs. Importantly, these TNTs could function as channels for the diffusion of small molecules such as Lucifer Yellow, but not for large molecules like Dextran Red. Further, organelle exchange between cells via TNTs was observed by microscopy. Using Ca²⁺ imaging we show the intercellular transmission of calcium signals through TNTs. Mechanical stimulation led to membrane depolarisation, which expand through TNT connections between ARPE-19 cells. We further demonstrate that TNTs can mediate electrical coupling between distant cells. Immunolabelling for Cx43 showed that this gap junction protein is interposed at one end of 44% of TNTs between ARPE-19 cells. CONCLUSIONS AND SIGNIFICANCE: Our observations indicate that

Spin polarized tunnelling investigation of nanometre Co clusters by means of a Ni bulk tip

International Nuclear Information System (INIS)

Rastei, M V; Bucher, J P

2006-01-01

A massive Ni tip is used in spin polarized scanning tunnelling microscopy (SP STM) to explore the magnetization state of nanometre Co clusters, self-organized on the Au(111) surface. Constant current STM images taken at 4.6 K show a bimodal distribution of the cluster heights, accounting for the spin polarization of the STM junction. The spin polarization of the tunnel junction as a function of the bias voltage is found to depend on the local density of states of the sample examined. Changing the vacuum barrier parameters by bringing the tip closer to the surface leads to a reduction in the tunnelling magnetoresistance that may be attributed to spin flip effects. (letter to the editor)

Electron transfer kinetics of cytochrome c immobilized on a phenolic terminated thiol self assembled monolayer determined by scanning electrochemical microscopy

International Nuclear Information System (INIS)

Alizadeh, Vali; Mousavi, Mir Fazlollah; Mehrgardi, Masoud Ayatollahi; Kazemi, Sayed Habib; Sharghi, Hashem

2011-01-01

Highlights: → Preparing a thiolated phenolic self-assembled monolayer surface (SAM). → Application of this SAM to immobilize cytochrome C. → Scanning electrochemical microscopy used for these studies. → Determination of both tunneling electron transfer and bimolecular rate constants between the immobilized protein-substrate and probe. - Abstract: In the present manuscript, the electrochemical behavior of cytochrome c (cyt-c) immobilized onto a phenolic terminated self assembled monolayer (SAM) on a gold electrode is investigated using cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM). The tunneling electron transfer (ET) rate constant between the immobilized protein and the underlying electrode surface, and also the bimolecular ET rate constant between the immobilized protein and a probe has been obtained using approach curves that were obtained by SECM. The approach curves were recorded at different substrate overpotentials in the presence of various concentrations of ferrocyanide as a probe and various surface concentrations of cyt-c; then the standard tunneling ET and bimolecular rate constants are obtained as 3.4 ± 0.3 s -1 and (2.0 ± 0.5) x 10 7 cm 3 mol -1 s -1 , respectively.

Electron transfer kinetics of cytochrome c immobilized on a phenolic terminated thiol self assembled monolayer determined by scanning electrochemical microscopy

Energy Technology Data Exchange (ETDEWEB)

Alizadeh, Vali [Department of Chemistry, Tarbiat Modares University, P.O. Box 14115-175, Tehran (Iran, Islamic Republic of); Mousavi, Mir Fazlollah, E-mail: mousavim@modares.ac.ir [Department of Chemistry, Tarbiat Modares University, P.O. Box 14115-175, Tehran (Iran, Islamic Republic of); Mehrgardi, Masoud Ayatollahi [Department of Chemistry, University of Isfahan, Isfahan (Iran, Islamic Republic of); Kazemi, Sayed Habib [Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan (Iran, Islamic Republic of); Sharghi, Hashem [Department of Chemistry, Shiraz University, Shiraz (Iran, Islamic Republic of)

2011-07-01

Highlights: > Preparing a thiolated phenolic self-assembled monolayer surface (SAM). > Application of this SAM to immobilize cytochrome C. > Scanning electrochemical microscopy used for these studies. > Determination of both tunneling electron transfer and bimolecular rate constants between the immobilized protein-substrate and probe. - Abstract: In the present manuscript, the electrochemical behavior of cytochrome c (cyt-c) immobilized onto a phenolic terminated self assembled monolayer (SAM) on a gold electrode is investigated using cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM). The tunneling electron transfer (ET) rate constant between the immobilized protein and the underlying electrode surface, and also the bimolecular ET rate constant between the immobilized protein and a probe has been obtained using approach curves that were obtained by SECM. The approach curves were recorded at different substrate overpotentials in the presence of various concentrations of ferrocyanide as a probe and various surface concentrations of cyt-c; then the standard tunneling ET and bimolecular rate constants are obtained as 3.4 {+-} 0.3 s{sup -1} and (2.0 {+-} 0.5) x 10{sup 7} cm{sup 3} mol{sup -1} s{sup -1}, respectively.

Comparative study of donor-induced quantum dots in Si nano-channels by single-electron transport characterization and Kelvin probe force microscopy

International Nuclear Information System (INIS)

Tyszka, K.; Moraru, D.; Samanta, A.; Mizuno, T.; Tabe, M.; Jabłoński, R.

2015-01-01

We comparatively study donor-induced quantum dots in Si nanoscale-channel transistors for a wide range of doping concentration by analysis of single-electron tunneling transport and surface potential measured by Kelvin probe force microscopy (KPFM). By correlating KPFM observations of donor-induced potential landscapes with simulations based on Thomas-Fermi approximation, it is demonstrated that single-electron tunneling transport at lowest gate voltages (for smallest coverage of screening electrons) is governed most frequently by only one dominant quantum dot, regardless of doping concentration. Doping concentration, however, primarily affects the internal structure of the quantum dot. At low concentrations, individual donors form most of the quantum dots, i.e., “donor-atom” quantum dots. In contrast, at high concentrations above metal-insulator transition, closely placed donors instead of individual donors form more complex quantum dots, i.e., “donor-cluster” quantum dots. The potential depth of these “donor-cluster” quantum dots is significantly reduced by increasing gate voltage (increasing coverage of screening electrons), leading to the occurrence of multiple competing quantum dots

Study of the geometrical resonances of superconducting tunnel junctions

DEFF Research Database (Denmark)

Sørensen, O. Hoffmann; Finnegan, T.F.; Pedersen, Niels Falsig

1973-01-01

The resonant cavity structure of superconducting Sn-Sn-oxide-Sn tunnel junctions has been investigated via photon-assisted quasiparticle tunneling. We find that the temperature-dependent losses at 35 GHz are determined by the surface resistance of the Sn films for reduced temperatures between 0...

Probing defect states in polycrystalline GaN grown on Si(111) by sub-bandgap laser-excited scanning tunneling spectroscopy

Science.gov (United States)

Hsiao, F.-M.; Schnedler, M.; Portz, V.; Huang, Y.-C.; Huang, B.-C.; Shih, M.-C.; Chang, C.-W.; Tu, L.-W.; Eisele, H.; Dunin-Borkowski, R. E.; Ebert, Ph.; Chiu, Y.-P.

2017-01-01

We demonstrate the potential of sub-bandgap laser-excited cross-sectional scanning tunneling microscopy and spectroscopy to investigate the presence of defect states in semiconductors. The characterization method is illustrated on GaN layers grown on Si(111) substrates without intentional buffer layers. According to high-resolution transmission electron microscopy and cathodoluminescence spectroscopy, the GaN layers consist of nanoscale wurtzite and zincblende crystallites with varying crystal orientations and hence contain high defect state densities. In order to discriminate between band-to-band excitation and defect state excitations, we use sub-bandgap laser excitation. We probe a clear increase in the tunnel current at positive sample voltages during sub-bandgap laser illumination for the GaN layer with high defect density, but no effect is found for high quality GaN epitaxial layers. This demonstrates the excitation of free charge carriers at defect states. Thus, sub-bandgap laser-excited scanning tunneling spectroscopy is a powerful complimentary characterization tool for defect states.

Reliability analysis of idealized tunnel support system using probability-based methods with case studies

Science.gov (United States)

Gharouni-Nik, Morteza; Naeimi, Meysam; Ahadi, Sodayf; Alimoradi, Zahra

2014-06-01

In order to determine the overall safety of a tunnel support lining, a reliability-based approach is presented in this paper. Support elements in jointed rock tunnels are provided to control the ground movement caused by stress redistribution during the tunnel drive. Main support elements contribute to stability of the tunnel structure are recognized owing to identify various aspects of reliability and sustainability in the system. The selection of efficient support methods for rock tunneling is a key factor in order to reduce the number of problems during construction and maintain the project cost and time within the limited budget and planned schedule. This paper introduces a smart approach by which decision-makers will be able to find the overall reliability of tunnel support system before selecting the final scheme of the lining system. Due to this research focus, engineering reliability which is a branch of statistics and probability is being appropriately applied to the field and much effort has been made to use it in tunneling while investigating the reliability of the lining support system for the tunnel structure. Therefore, reliability analysis for evaluating the tunnel support performance is the main idea used in this research. Decomposition approaches are used for producing system block diagram and determining the failure probability of the whole system. Effectiveness of the proposed reliability model of tunnel lining together with the recommended approaches is examined using several case studies and the final value of reliability obtained for different designing scenarios. Considering the idea of linear correlation between safety factors and reliability parameters, the values of isolated reliabilities determined for different structural components of tunnel support system. In order to determine individual safety factors, finite element modeling is employed for different structural subsystems and the results of numerical analyses are obtained in

Study on the bearing capacity of embedded chute on shield tunnel segment

Science.gov (United States)

Fanzhen, Zhang; Jie, Bu; Zhibo, Su; Qigao, Hu

2018-05-01

The method of perforation and steel implantation is often used to fix and install pipeline, cables and other facilities in the shield tunnel, which would inevitably do damage to the precast segments. In order to reduce the damage and the resulting safety and durability problems, embedded chute was set at the equipment installation in one shield tunnel. Finite element models of segment concrete and steel are established in this paper. When water-soil pressure calculated separately and calculated together, the mechanical property of segment is studied. The bearing capacity and deformation of segment are analysed before and after embedding the chute. Research results provide a reference for similar shield tunnel segment engineering.

Experimental study of wind tunnel performance by a two-component laserDopplerAnemometer

Directory of Open Access Journals (Sweden)

M Pourmahabadian

2005-10-01

Full Text Available Background and Aims: This survey studies the wind tunnel performance by a two- componentlaser Doppler Anemometer, so some experiments were carried out to assess the performance of awind tunnel.Method: The tunnel was capable to produce air velocity of up to 40 m/s.. Measurements ofvelocity profiles have been made actors the test section of wind tunnel through the using a twocomponentfiber optic Laser Doppler anemometer. Measurements of velocity profiles andturbulence intensities have been made across the test section of the wind tunnel using a twocomponentfiber optic Laser Doppler anemometer (I.D.A for wind speeds ranging from 1 to3m/s.Results: Performance rests of velocity profiles at a given flow rate and various position of aerosolgenerator showed that although uniformity of flow dependent to the place of an atomizer (asaerosol generator but the variation of wind speed across the test section meets the wind speedrequirements, as specified by US EPAfor 3m/s only.Conclusion:At time which particles velocity reach to less than one micron, the air velocity relateson the similarity of particles and

Gate-controlled current and inelastic electron tunneling spectrum of benzene: a self-consistent study.

Science.gov (United States)

Liang, Y Y; Chen, H; Mizuseki, H; Kawazoe, Y

2011-04-14

We use density functional theory based nonequilibrium Green's function to self-consistently study the current through the 1,4-benzenedithiol (BDT). The elastic and inelastic tunneling properties through this Au-BDT-Au molecular junction are simulated, respectively. For the elastic tunneling case, it is found that the current through the tilted molecule can be modulated effectively by the external gate field, which is perpendicular to the phenyl ring. The gate voltage amplification comes from the modulation of the interaction between the electrodes and the molecules in the junctions. For the inelastic case, the electron tunneling scattered by the molecular vibrational modes is considered within the self-consistent Born approximation scheme, and the inelastic electron tunneling spectrum is calculated.

Study on water migration of tunnel surrounding rock in nuclear waste repository based on coupling theory

International Nuclear Information System (INIS)

Jiang Zhongming; Zhang Xinmin

2008-01-01

Excavation of tunnel changes not only the stresses and deformation of tunnel surrounding rock, but also disturbs the underground water environment in tunnel surrounding rock Water migration happens due to variation of pore water pressure and redistribution. Based on the mechanics of porous media, saturated and unsaturated hydro-mechanical coupling analysis method is employed to study the variation of the stresses, deformation and pore pressure of the surrounding rock. Case study indicates that the excavation of tunnel will induce redistribution of stress and pore water pressure. Redistribution of pore water pressure will seriously affect on evaluation of surrounding rock stability and diffusion of nucleon in the pore water. (authors)

Tunneling spectroscopy study of YBa2Cu3O7 thin films using a cryogenic scanning tunneling microscope

International Nuclear Information System (INIS)

Wilkins, R.; Amman, M.; Soltis, R.E.; Ben-Jacob, E.; Jaklevic, R.C.

1990-01-01

We have measured reproducible tunneling spectra on YBa 2 Cu 3 O 7 (T c ∼85 K) thin films (thickness ∼2 μm) with a cryogenic scanning tunneling microscope. We find that the I-V curves are generally of three types. The most common type, featured in a large majority of the data, shows a region of high conductance at zero bias. The amplitude of this region is inversely proportional to the tunneling resistance between the tip and sample. It is possible that this can be explained in terms of Josephson effects within the films, although an alternative is given based on electronic self-energy corrections. Data showing capacitive charging steps are analyzed in terms of two ultrasmall tunnel junctions in series.. Theoretical fits to the data give specific values of the junction parameters that are consistent with the assumed geometry of the tip probing an individual grain of the film. The third type of I-V curves exhibits negative differential resistance. We conclude that this phenomenon is probably due to tunneling to localized states in the surface oxide. We also present and discuss data with energy-gap-like behavior; the best example gives Δ to be about 27 mV

Study and fabrication of tunnel diodes made on germanium using a collective planar technique

International Nuclear Information System (INIS)

Vrahides, Michel

1973-01-01

The main results of the theory on tunnel diodes are presented in the first chapter. From these results are deduced the technological requirements that any fabrication process should meet to make tunnel diodes. These requirements show up that, among the three techniques for junction making (thermal diffusion of impurities, epitaxy, alloying), the last one is presently the best fitted to the fabrication of tunnel junctions. By analyzing the defects created by various alloying technologies presently used, together with a study of the benefits due to a use of chemical photolithography, evaporation under vacuum and masking by deposited oxide, it is possible to design a tentative scheme of a 0.5 ns tunnel diode. Then, in a second chapter, is presented the collective process for fabrication that has been used on monocrystalline, P-type, germanium wafers. 8 000 tunnel diodes may be positioned on a 1.5 inch diameter wafer by using that process. A description of the various apparatus used is also given. The experimental results are described in the third chapter. The influence of the various fabrication parameters on the electrical characteristics of the diodes are discussed. It is shown, by studying the fabrication yields and parameter spreading, that 80 per cent of the diodes exhibit a standard tunnel diode behaviour and that 90 per cent of these present a peak current dispersion less than ± 25 per cent. When measuring at the peak current drifts under temperature stresses, a good analogy with conventional tunnel diode is found. Some measurements of switching times have led to values as low as 0.6 nanoseconds. (author) [fr

Scanning tunneling microscopy of the atomically smooth (001) surface of vanadium pentoxide V{sub 2}O{sub 5} crystals

Energy Technology Data Exchange (ETDEWEB)

Muslimov, A. E., E-mail: amuslimov@mail.ru; Butashin, A. V.; Kanevsky, V. M. [Russian Academy of Sciences, Shubnikov Institute of Crystallography, Federal Research Centre “Crystallography and Photonics” (Russian Federation)

2017-01-15

The (001) cleavage surface of vanadium pentoxide (V{sub 2}O{sub 5}) crystal has been studied by scanning tunneling spectroscopy (STM). It is shown that the surface is not reconstructed; the STM image allows geometric lattice parameters to be determined with high accuracy. The nanostructure formed on the (001) cleavage surface of crystal consists of atomically smooth steps with a height multiple of unit-cell parameter c = 4.37 Å. The V{sub 2}O{sub 5} crystal cleavages can be used as references in calibration of a scanning tunneling microscope under atmospheric conditions both along the (Ñ…, y) surface and normally to the sample surface (along the z axis). It is found that the terrace surface is not perfectly atomically smooth; its roughness is estimated to be ~0.5 Å. This circumstance may introduce an additional error into the microscope calibration along the z coordinate.

Careful stoichiometry monitoring and doping control during the tunneling interface growth of an n + InAs(Si)/p + GaSb(Si) Esaki diode

Science.gov (United States)

El Kazzi, S.; Alian, A.; Hsu, B.; Verhulst, A. S.; Walke, A.; Favia, P.; Douhard, B.; Lu, W.; del Alamo, J. A.; Collaert, N.; Merckling, C.

2018-02-01

In this work, we report on the growth of pseudomorphic and highly doped InAs(Si)/GaSb(Si) heterostructures on p-type (0 0 1)-oriented GaSb substrate and the fabrication and characterization of n+/p+ Esaki tunneling diodes. We particularly study the influence of the Molecular Beam Epitaxy shutter sequences on the structural and electrical characteristics of InAs(Si)/GaSb(Si) Esaki diodes structures. We use real time Reflection High Electron Diffraction analysis to monitor different interface stoichiometry at the tunneling interface. With Atomic Force Microscopy, X-ray diffraction and Transmission Electron Microscopy analyses, we demonstrate that an "InSb-like" interface leads to a sharp and defect-free interface exhibiting high quality InAs(Si) crystal growth contrary to the "GaAs-like" one. We then prove by means of Secondary Ion Mass Spectroscopy profiles that Si-diffusion at the interface allows the growth of highly Si-doped InAs/GaSb diodes without any III-V material deterioration. Finally, simulations are conducted to explain our electrical results where a high Band to Band Tunneling (BTBT) peak current density of Jp = 8 mA/μm2 is achieved.

Monitoring pilot projects on bored tunnelling : The Second Heinenoord Tunnel and the Botlek Rail Tunnel

NARCIS (Netherlands)

Bakker, K.J.; De Boer, F.; Admiraal, J.B.M.; Van Jaarsveld, E.P.

1999-01-01

Two pilot projects for bored tunnelling in soft soil have been undertaken in the Netherlands. The monitoring was commissioned under the authority of the Centre for Underground Construction (COB). A description of the research related to the Second Heinenoord Tunnel and the Botlek Rail Tunnel will be

CCl 4 chemistry on the reduced selvedge of a α-Fe 2O 3(0 0 0 1) surface: a scanning tunneling microscopy study

Science.gov (United States)

Rim, Kwang Taeg; Fitts, Jeffrey P.; Müller, Thomas; Adib, Kaveh; Camillone, Nicholas; Osgood, Richard M.; Joyce, S. A.; Flynn, George W.

2003-09-01

Scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) were used to study the degradation of CCl 4 on the reduced selvedge of a natural single crystal α-Fe 2O 3(0 0 0 1) surface in ultrahigh vacuum. Before exposure to CCl 4, STM images indicate that approximately 85% of the reduced surface exhibits a Fe 3O 4(1 1 1) 2 × 2 termination, while the remaining 15% is terminated by 1 × 1 and superstructure phases. Images obtained after room temperature dosing with CCl 4 and subsequent flashing to 600 K reveal that chlorine atoms are adsorbed only on surface regions with the Fe 3O 4(1 1 1) 2 × 2 termination, not on 1 × 1 and superstructure regions. Chlorine atoms from dissociative adsorption of CCl 4 are observed to occupy two distinct positions located atop lattice protrusions and in threefold oxygen vacancy sites. However, in companion chemical labeling experiments, chlorine atoms provided by room temperature, dissociative Cl 2 adsorption on this surface are found to occupy sites atop lattice protrusions exclusively. The clear dissimilarity in STM feature shape and brightness at the two distinct chlorine adsorption sites arising from CCl 4 dissociation as well as the results of the Cl 2 chemical labeling experiments are best explained via reactions on a Fe 3O 4(1 1 1) 2 × 2 selvedge terminated by a 1/4 monolayer of tetrahedrally coordinated iron atoms. On this surface, adsorption atop an iron atom occurs for both the CCl 4 and Cl 2 dissociative reactions. A second adsorption site, assigned as binding to second layer iron atoms left exposed following surface oxygen atom abstraction resulting in the formation of phosgene (COCl 2), only appears in the case of reaction with CCl 4. The reaction mechanism and active site requirements for CCl 4 degradation on iron oxide surfaces are discussed in light of this evidence and in the context of our previously reported results from Auger electron spectroscopy (AES), LEED, temperature-programmed desorption

Geological Prediction Ahead of Tunnel Face in the Limestone Formation Tunnel using Multi-Modal Geophysical Surveys

Science.gov (United States)

Zaki, N. F. M.; Ismail, M. A. M.; Hazreek Zainal Abidin, Mohd; Madun, Aziman

2018-04-01

Tunnel construction in typical karst topography face the risk which unknown geological condition such as abundant rainwater, ground water and cavities. Construction of tunnel in karst limestone frequently lead to potentially over-break of rock formation and cause failure to affected area. Physical character of limestone which consists large cavity prone to sudden failure and become worsen due to misinterpretation of rock quality by engineer and geologists during analysis stage and improper method adopted in construction stage. Consideration for execution of laboratory and field testing in rock limestone should be well planned and arranged in tunnel construction project. Several tests including Ground Penetration Radar (GPR) and geological face mapping were studied in this research to investigate the performances of limestone rock in tunnel construction, measured in term of rock mass quality that used for risk assessment. The objective of this study is to focus on the prediction of geological condition ahead of tunnel face using short range method (GPR) and verified by geological face mapping method to determine the consistency of actual geological condition on site. Q-Value as the main indicator for rock mass classification was obtained from geological face mapping method. The scope of this study is covering for tunnelling construction along 756 meters in karst limestone area which located at Timah Tasoh Tunnel, Bukit Tebing Tinggi, Perlis. For this case study, 15% of GPR results was identified as inaccurate for rock mass classification in which certain chainage along this tunnel with 34 out of 224 data from GPR was identified as incompatible with actual face mapping.

Histological Observation of Regions around Bone Tunnels after Compression of the Bone Tunnel Wall in Ligament Reconstruction

International Nuclear Information System (INIS)

Maeda, Shintaro; Ishikawa, Hiroki; Tanigawa, Naoaki; Miyazaki, Kyosuke; Shioda, Seiji

2012-01-01

The objectives of this study were to investigate the time-course of influence of compression of bone tunnel wall in ligament reconstruction on tissue around the bone tunnel and to histologically examine the mechanism of preventing the complication of bone tunnel dilation, using rabbit tibia. A model in which the femoral origin of the extensor digitorum longus tendon was cut and inserted into a bone tunnel made proximal to the tibia was prepared in the bilateral hind legs of 20 Japanese white rabbits. In each animal, a tunnel was made using a drill only in the right leg, while an undersized bone tunnel was made by drilling and then dilated by compression using a dilator to the same tunnel size as that in the right leg. Animals were sacrificed at 0, 2, 4, 8 and 12 weeks after surgery (4 animals at each time point). Observation of bone tunnels by X-ray radiography showed osteosclerosis in the 2- and 4-week dilation groups. Osteosclerosis appeared as white lines around the bone tunnel on X-ray radiography. This suggests that dilation promotes callus formation in the bone tunnel wall and prevents the complication of bone tunnel enlargement after ligament reconstruction

Two-dimensional dopant profiling by electrostatic force microscopy using carbon nanotube modified cantilevers

International Nuclear Information System (INIS)

Chin, S.-C.; Chang, Y.-C.; Chang, C.-S.; Tsong, T T; Hsu, Chen-Chih; Wu, Chih-I; Lin, W-H; Woon, W-Y; Lin, L-T; Tao, H-J

2008-01-01

A two-dimensional (2D) dopant profiling technique is demonstrated in this work. We apply a unique cantilever probe in electrostatic force microscopy (EFM) modified by the attachment of a multiwalled carbon nanotube (MWNT). Furthermore, the tip apex of the MWNT was trimmed to the sharpness of a single-walled carbon nanotube (SWNT). This ultra-sharp MWNT tip helps us to resolve dopant features to within 10 nm in air, which approaches the resolution achieved by ultra-high vacuum scanning tunnelling microscopy (UHV STM). In this study, the CNT-probed EFM is used to profile 2D buried dopant distribution under a nano-scale device structure and shows the feasibility of device characterization for sub-45 nm complementary metal-oxide-semiconductor (CMOS) field-effect transistors

New Tunneling Features in Polar III-Nitride Resonant Tunneling Diodes

Directory of Open Access Journals (Sweden)

Jimy Encomendero

2017-10-01

Full Text Available For the past two decades, repeatable resonant tunneling transport of electrons in III-nitride double barrier heterostructures has remained elusive at room temperature. In this work we theoretically and experimentally study III-nitride double-barrier resonant tunneling diodes (RTDs, the quantum transport characteristics of which exhibit new features that are unexplainable using existing semiconductor theory. The repeatable and robust resonant transport in our devices enables us to track the origin of these features to the broken inversion symmetry in the uniaxial crystal structure, which generates built-in spontaneous and piezoelectric polarization fields. Resonant tunneling transport enabled by the ground state as well as by the first excited state is demonstrated for the first time over a wide temperature window in planar III-nitride RTDs. An analytical transport model for polar resonant tunneling heterostructures is introduced for the first time, showing a good quantitative agreement with experimental data. From this model we realize that tunneling transport is an extremely sensitive measure of the built-in polarization fields. Since such electric fields play a crucial role in the design of electronic and photonic devices, but are difficult to measure, our work provides a completely new method to accurately determine their magnitude for the entire class of polar heterostructures.

Tunneling progress on the Yucca Mountain Project

International Nuclear Information System (INIS)

Hansmire, W.H.; Munzer, R.J.

1996-01-01

The current status of tunneling progress on the Yucca Mountain Project (YMP) is presented in this paper. The Exploratory Studies Facility (ESF), a key part of the YMP, has been long in development and construction is ongoing. This is a progress report on the tunneling aspects of the ESF as of January 1, 1996. For purposes of discussion in this summary, the tunneling has progressed in four general phases. The paper describes: tunneling in jointed rock under low stress; tunneling through the Bow Ridge Fault and soft rock; tunneling through the Imbricate Fault Zone; and Tunneling into the candidate repository formation

Scanning tunnelling spectroscopy of low pentacene coverage on the Ag/Si(111)-(√3 x √3) surface

International Nuclear Information System (INIS)

Guaino, Ph; Cafolla, A A; McDonald, O; Carty, D; Sheerin, G; Hughes, G

2003-01-01

The low coverage S1 phase of pentacene deposited on Ag/Si(111)-(√3 x √3) has been investigated at room temperature by scanning tunnelling microscopy (STM) and scanning tunnelling spectroscopy (STS). Current-voltage data were acquired simultaneously with STM images for this phase. The normalized conductivity reveals two pronounced peaks at -1.10 and +2.25 V relative to the Fermi level. These peaks are attributed to resonant tunnelling through the highest occupied molecular orbital and lowest unoccupied molecular orbital molecular levels of the pentacene layer. The electronic properties of this interface are discussed in relation to results obtained for pentacene adsorbed on other metallic surfaces

Reversal of atomic contrast in scanning probe microscopy on (111) metal surfaces

Czech Academy of Sciences Publication Activity Database

Ondráček, Martin; González, C.; Jelínek, Pavel

2012-01-01

Roč. 24, 08 (2012), 084003/1-084003/7 ISSN 0953-8984 R&D Projects: GA ČR(CZ) GPP204/11/P578; GA ČR GAP204/10/0952; GA ČR GA202/09/0545; GA MŠk(CZ) ME10076 Grant - others:AVČR(CZ) M100100904 Institutional research plan: CEZ:AV0Z10100521 Keywords : atomic force microscopy * metallic surfaces * atomic contrast * scanning tunneling microscopy Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.355, year: 2012 http://iopscience.iop.org/0953-8984/24/8/084003

The scanning probe microscopy study of thin polymer films

International Nuclear Information System (INIS)

Harron, H.R.

1995-08-01

Scanning Tunnelling Microscopy and Atomic Force Microscopy were used systematically to investigate the morphology, uniformity, coverage and structure of the thin films of several commercially important insulating polymers. Despite the poorly conducting nature of the polymer sample, detailed and convincing images of this class of materials were achieved by STM without the need to coat the samples with a conductive layer. The polymer regions of the sample were further investigated by the use of surface profiling with 'line scans'. The fluctuations of the amplitude therein enabled important film characteristics to be assessed. An environmental stage was designed for the STM to enable the effect of various vapour-sample interactions to be observed during the imaging process. Using the data from the environmental stage in addition to the surface profiling with line scans, an insight into the conduction mechanism and image interpretation was gained. Results suggest that the water content of the sample and its immediate surroundings is an important factor in achieving reliable STM images in air. The initial study culminated with the observation by STM alone of the plasticizer induced crystallization of uncoated PC thin films. The 'amorphous' PC films were observed before crystallization and small ordered regions in roughly the same proportion as that predicted by diffraction studies [Prietschk, 1959 and Schnell, 1964] were imaged. This has never been observed by a microscopy technique. Furthermore, images of the crystalline film contained elongated units that were attributed to the lamellae formations that form the basic building blocks of polymer spherulites. The study continued with the AFM imaging of the growth of crystalline entities in a PC film, without the need for harsh sample treatment or metal coating. A method of casting and crystallizing the films was developed such that the growth was predominantly in two dimensions and consequently ideal for observation by

Electric double layer effect on observable characteristics of the tunnel current through a bridged electrochemical contact

DEFF Research Database (Denmark)

Kuznetsov, A.M.; Medvedev, I.G.; Ulstrup, Jens

2007-01-01

Scanning tunneling microscopy and electrical conductivity of redox molecules in conducting media (aqueous or other media) acquire increasing importance both as novel single-molecule science and with a view on molecular scale functional elements. Such configurations require full and independent el...

Theory of tunneling in metal--superconductor devices: Supercurrents in the superconductor gap at zero temperature

International Nuclear Information System (INIS)

Garcia, N.; Flores, F.; Guinea, F.

1988-01-01

Tunneling experiments in metal-oxide superconductor have shown the existence of ''leakage'' currents for applied voltages V smaller than one-half of the superconductor gap Δ. These currents are independent of temperature T. Recently experiments with scanning tunneling microscopy (STM) and squeezable tunnel junctions have shown that the observation of the superconductor gap depends strongly on the resistance in the junction. In fact only for resistances larger than ∼10 6 Ω the gap is clearly observable. These experiments have been explained in terms of the perturbative Hamiltonian formalism of Bardeen. However, it may happen that this theory while applicable for very large resistances may not be so for small tunnel resistances. We present here a nonperturbative theory in all orders of the transmitivity chemical bondTochemical bond 2 and show the existence of supercurrents for values of V 2 . We believe that experiments in STM and other junctions should be interpreted in the frame of this theory

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

Energy Technology Data Exchange (ETDEWEB)

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

2005-05-16

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

Air pollution at an urban traffic tunnel in Lisbon, Portugal-an INAA study

Energy Technology Data Exchange (ETDEWEB)

Almeida-Silva, M.; Canha, N. [Instituto Tecnologico e Nuclear, URSN, E.N. 10, 2686-953 Sacavem (Portugal); Freitas, M.C., E-mail: cfreitas@itn.pt [Instituto Tecnologico e Nuclear, URSN, E.N. 10, 2686-953 Sacavem (Portugal); Dung, H.M; Dionisio, I. [Instituto Tecnologico e Nuclear, URSN, E.N. 10, 2686-953 Sacavem (Portugal)

2011-11-15

In this study, the results of chemical concentrations inside and outside of a Lisbon (Portugal) traffic tunnel were compared, during one week. They were obtained by Instrumental Neutron Activation Analysis (INAA). The tunnel values largely exceed the Air Ambient legislated values and the Pearson Correlations Coefficients point out to soil re-suspension/dispersed road dust (As, Ce, Eu, Hf, Fe, Mo, Sc, Zn), traffic-markers (Ba, Cr), tire wear (Cr, Zn), break wear (Fe, Zn, Ba, Cu, Sb), exhaust and motor oil (Zn) and sea-spray (Br, Na). On all days these elements inside the tunnel were more enriched than outside; significant statistical differences were found for Co (p=0.005), Br (p=0.008), Zn (p=0.01) and Sb (p=0.005), while enrichment factors of As and Sc are statistically identical. The highest values were found for As, Br, Zn and Sb, for both inside and outside the tunnel.

Ab initio simulation study of defect assisted Zener tunneling in GaAs diode

Science.gov (United States)

Lu, Juan; Fan, Zhi-Qiang; Gong, Jian; Jiang, Xiang-Wei

2017-06-01

The band to band tunneling of defective GaAs nano-junction is studied by using the non-equilibrium Green's function formalism with density functional theory. Aiming at performance improvement, two types of defect-induced transport behaviors are reported in this work. By examining the partial density of states of the system, we find the substitutional defect OAs that locates in the middle of tunneling region will introduce band-gap states, which can be used as stepping stones to increase the tunneling current nearly 3 times higher at large bias voltage (Vb≥0.3V). Another type of defects SeAs and VGa (Ga vacancy) create donor and acceptor states at the edge of conduction band (CB) and valence band (VB)respectively, which can change the band bending of the junction as well as increase the tunneling field obtaining a 1.5 times higher ON current. This provides an effective defect engineering approach for next generation TFET device design.

A model study of tunneling conductance spectra of ferromagnetically ordered manganites

Science.gov (United States)

Panda, Saswati; Kar, J. K.; Rout, G. C.

2018-02-01

We report here the interplay of ferromagnetism (FM) and charge density wave (CDW) in manganese oxide systems through the study of tunneling conductance spectra. The model Hamiltonian consists of strong Heisenberg coupling in core t2g band electrons within mean-field approximation giving rise to ferromagnetism. Ferromagnetism is induced in the itinerant eg electrons due to Kubo-Ohata type double exchange (DE) interaction among the t2g and eg electrons. The charge ordering (CO) present in the eg band giving rise to CDW interaction is considered as the extra-mechanism to explain the colossal magnetoresistance (CMR) property of manganites. The magnetic and CDW order parameters are calculated using Zubarev's Green's function technique and solved self-consistently and numerically. The eg electron density of states (DOS) calculated from the imaginary part of the Green's function explains the experimentally observed tunneling conductance spectra. The DOS graph exhibits a parabolic gap near the Fermi energy as observed in tunneling conductance spectra experiments.

Luminescence of Quantum Dots by Coupling with Nonradiative Surface Plasmon Modes in a Scanning Tunneling Microscope

International Nuclear Information System (INIS)

Romero, M.J.; van de Lagemaat, J.

2009-01-01

The electronic coupling between quantum dots (QDs) and surface plasmons (SPs) is investigated by a luminescence spectroscopy based on scanning tunneling microscopy (STM). We show that tunneling luminescence from the dot is excited by coupling with the nonradiative plasmon mode oscillating at the metallic tunneling gap formed during the STM operation. This approach to the SP excitation reveals aspects of the SP-QD coupling not accessible to the more conventional optical excitation of SPs. In the STM, luminescence from the dot is observed when and only when the SP is in resonance with the fundamental transition of the dot. The tunneling luminescence spectrum also suggests that excited SP-QD hybrid states can participate in the excitation of QD luminescence. Not only the SP excitation regulates the QD luminescence but the presence of the dot at the tunneling gap imposes restrictions to the SP that can be excited in the STM, in which the SP cannot exceed the energy of the fundamental transition of the dot. The superior SP-QD coupling observed in the STM is due to the tunneling gap acting as a tunable plasmonic resonator in which the dot is fully immersed.

Study of grain boundary tunneling in barium-titanate ceramic films

CERN Document Server

Wong, H; Poon, M C

1999-01-01

The temperature and the electric-field dependences of the current-voltage characteristics and the low-frequency noise of barium-titanate ceramic films are studied. An abnormal field dependence is observed in the resistivity of BaTiO sub 3 materials with a small average grain size. In addition, experiments show that the low-frequency noise behaviors are governed by grain-boundary tunneling at room temperature and by trapping-detrapping of grain-boundary states at temperatures above the Curie point. Physical models for the new observations are developed. Results suggest that grain-boundary tunneling of carriers is as important as the double Schottky barrier in the current conduction in BaTiO sub 3 materials with small grain sizes.

Destructive quantum interference in spin tunneling problems

OpenAIRE

von Delft, Jan; Henley, Christopher L.

1992-01-01

In some spin tunneling problems, there are several different but symmetry-related tunneling paths that connect the same initial and final configurations. The topological phase factors of the corresponding tunneling amplitudes can lead to destructive interference between the different paths, so that the total tunneling amplitude is zero. In the study of tunneling between different ground state configurations of the Kagom\\'{e}-lattice quantum Heisenberg antiferromagnet, this occurs when the spi...

Tunnel magnetoresistance in asymmetric double-barrier magnetic tunnel junctions

International Nuclear Information System (INIS)

Useinov, N.Kh.; Petukhov, D.A.; Tagirov, L.R.

2015-01-01

The spin-polarized tunnel conductance and tunnel magnetoresistance (TMR) through a planar asymmetric double-barrier magnetic tunnel junction (DBMTJ) have been calculated using quasi-classical model. In DBMTJ nanostructure the magnetization of middle ferromagnetic metal layer can be aligned parallel or antiparallel with respect to the fixed magnetizations of the top and bottom ferromagnetic electrodes. The transmission coefficients of an electron to pass through the barriers have been calculated in terms of quantum mechanics. The dependencies of tunnel conductance and TMR on the applied voltage have been calculated in case of non-resonant transmission. Estimated in the framework of our model, the difference between the spin-channels conductances at low voltages was found relatively large. This gives rise to very high magnitude of TMR. - Highlights: • The spin-polarized conductance through the junction is calculated. • Dependencies of the tunnel conductance vs applied bias are shown. • Bias voltage dependence of tunnel magnetoresistance for the structure is shown

Magnetic Fluxtube Tunneling

Science.gov (United States)

Dahlburg, Russell B.; Antiochos,, Spiro K.; Norton, D.

1996-01-01

We present numerical simulations of the collision and subsequent interaction of two initially orthogonal, twisted, force free field magnetic fluxtubes. The simulations were carried out using a new three dimensional explicit parallelized Fourier collocation algorithm for solving the viscoresistive equations of compressible magnetohydrodynamics. It is found that, under a wide range of conditions, the fluxtubes can 'tunnel' through each other. Two key conditions must be satisfied for tunneling to occur: the magnetic field must be highly twisted with a field line pitch much greater than 1, and the magnetic Lundquist number must be somewhat large, greater than or equal to 2880. This tunneling behavior has not been seen previously in studies of either vortex tube or magnetic fluxtube interactions. An examination of magnetic field lines shows that tunneling is due to a double reconnection mechanism. Initially orthogonal field lines reconnect at two specific locations, exchange interacting sections and 'pass' through each other. The implications of these results for solar and space plasmas are discussed.

Case Study of Oriental Medicine Treatment with acupotomy Therpy of the Tarsal tunnel Syndrome

Directory of Open Access Journals (Sweden)

Lim Na-ra

2009-03-01

Full Text Available Purpose : In order to estimate clinical effects of Oriental Medicine Treatment with acupotomy therapy of Tarsal tunnel Syndrome Methods : From 5th November, 2008 to 8th November, 2008, 1 male patient diagnosed as Tarsal tunnel syndrome(clinical diagnosed was treated with general oriental medicine therapy (acupuncture, moxibustion, cupping, physical therapy, herbal medication and acupotomy. Results : The patient's Rt foot paresthesia, pain were remarkably improved. Conclusions : This study demonstrates that oriental medical treatment with acuputomy therapy has notable effect in improving symptoms of tarsal tunnel syndrome. as though we had not wide experience in this treatment, more research is needed.

Fermi surface investigation in the scanning tunneling microscopy of Bi2Sr2CaCu2O8

International Nuclear Information System (INIS)

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

2004-01-01

Within the ideal Fermi liquid picture, the impurity-induced spatial modulation of local density of states (LDOS) in the d-wave superconductor Bi 2 Sr 2 CaCu 2 O 8 is investigated at different superconducting (SC) gap sizes. These LDOS spectra are related to the finite-temperature dI/dV spectra in scanning tunneling microscopy (STM), when the Fermi distribution factor is deconvoluted away from dI/dV. We find stripe-like structures even in the zero gap case due to a local-nesting mechanism. This mechanism is different from the octet-scattering mechanism in the d-wave SC (dSC) state proposed by McElroy et al. [K. McElroy, R.W. Simmonds, J.E. Hoffman, D.H. Lee, J. Orenstein, H. Eisaki, S. Uchida, J.C. Davis, Nature 422 (2003) 592]. The zero gap LDOS is related to the normal state dI/dV. The zero gap spectra when Fourier-transformed into the reciprocal space, can reveal the information of the entire Fermi surface at a single measuring bias voltage, in contrast to the point-wise tracing out proposed by McElroy et al. This may serve as another way to check the reality of Landau quasiparticles in the normal state. We have also re-visited the octet-scattering mechanism in the dSC state and pointed out that, due to the Umklapp symmetry, there are additional peaks in the reciprocal space that experimentally yet to be found

Clinical Study on Five Cases of Carpal tunnel syndrome

Directory of Open Access Journals (Sweden)

Kim Il Hwan

2001-12-01

Full Text Available Objections : The purpose of the study was to evaluate the effectiveness of treating the carpal tunnel syndrome by using both the Herbal Acupuncture and herbal medicine therapy on five cases. Methods : For the Herbal Acupuncture, Jungseonguhhyl No. 1 and Hwanglyunhaedoktang were used. For the herbal medicine, Dangguihwalhyul-tang was used. The patients were treated once in every two days; the result was evaluated after ten treatments. Patients' conditions were monitored through their testimony, phalen's test, nerve conduction study and electromyography. Results : In all five cases, the patients showed improvement; in four cases, the patients no longer had most of the clinical symptoms. Based on the result of the nerve conduction study, for the four cases in which the patients no longer displayed most of the clinical symptoms, their nerve conduction rate improved; for the remaining one case, the patient's nerve conduction rate deteriorated. Conclusions : The results of this study demonstrate that combining the Herbal Acupuncture and herbal medicine therapy can have noticeable effects in treating the carpal tunnel syndrome; developing more variety of the herbal acupuncture would lead to even better treatment results.

Circularly polarized light emission in scanning tunneling microscopy of magnetic systems

International Nuclear Information System (INIS)

Apell, S.P.; Penn, D.R.; Johansson, P.

2000-01-01

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

Fermion tunneling from higher-dimensional black holes

International Nuclear Information System (INIS)

Lin Kai; Yang Shuzheng

2009-01-01

Via the semiclassical approximation method, we study the 1/2-spin fermion tunneling from a higher-dimensional black hole. In our work, the Dirac equations are transformed into a simple form, and then we simplify the fermion tunneling research to the study of the Hamilton-Jacobi equation in curved space-time. Finally, we get the fermion tunneling rates and the Hawking temperatures at the event horizon of higher-dimensional black holes. We study fermion tunneling of a higher-dimensional Schwarzschild black hole and a higher-dimensional spherically symmetric quintessence black hole. In fact, this method is also applicable to the study of fermion tunneling from four-dimensional or lower-dimensional black holes, and we will take the rainbow-Finsler black hole as an example in order to make the fact explicit.

Size-dependent energy levels of InSb quantum dots measured by scanning tunneling spectroscopy.

Science.gov (United States)

Wang, Tuo; Vaxenburg, Roman; Liu, Wenyong; Rupich, Sara M; Lifshitz, Efrat; Efros, Alexander L; Talapin, Dmitri V; Sibener, S J

2015-01-27

The electronic structure of single InSb quantum dots (QDs) with diameters between 3 and 7 nm was investigated using atomic force microscopy (AFM) and scanning tunneling spectroscopy (STS). In this size regime, InSb QDs show strong quantum confinement effects which lead to discrete energy levels on both valence and conduction band states. Decrease of the QD size increases the measured band gap and the spacing between energy levels. Multiplets of equally spaced resonance peaks are observed in the tunneling spectra. There, multiplets originate from degeneracy lifting induced by QD charging. The tunneling spectra of InSb QDs are qualitatively different from those observed in the STS of other III-V materials, for example, InAs QDs, with similar band gap energy. Theoretical calculations suggest the electron tunneling occurs through the states connected with L-valley of InSb QDs rather than through states of the Γ-valley. This observation calls for better understanding of the role of indirect valleys in strongly quantum-confined III-V nanomaterials.

FUNDAMENTAL TUNNELING PROCESSES IN MOSa SOLAR CELLS

OpenAIRE

Balberg , I.; Hanak , J.; Weakliem , H.; Gal , E.

1981-01-01

In previous studies of tunneling through a MOSa tunnel junction, where Sa was a-Si : H, it was shown that their characteristics resemble those of MOSc devices where Sc was crystalline silicon. In the present work we would like to report a demonstration of fundamental tunneling processes in such tunnel junctions. In particular, the transition from semiconductor controlled regime to tunneling controlled regime can be clearly distinguished. The present results represent one of the rare cases whe...

High resolution, high speed ultrahigh vacuum microscopy

International Nuclear Information System (INIS)

Poppa, Helmut

2004-01-01

The history and future of transmission electron microscopy (TEM) is discussed as it refers to the eventual development of instruments and techniques applicable to the real time in situ investigation of surface processes with high resolution. To reach this objective, it was necessary to transform conventional high resolution instruments so that an ultrahigh vacuum (UHV) environment at the sample site was created, that access to the sample by various in situ sample modification procedures was provided, and that in situ sample exchanges with other integrated surface analytical systems became possible. Furthermore, high resolution image acquisition systems had to be developed to take advantage of the high speed imaging capabilities of projection imaging microscopes. These changes to conventional electron microscopy and its uses were slowly realized in a few international laboratories over a period of almost 40 years by a relatively small number of researchers crucially interested in advancing the state of the art of electron microscopy and its applications to diverse areas of interest; often concentrating on the nucleation, growth, and properties of thin films on well defined material surfaces. A part of this review is dedicated to the recognition of the major contributions to surface and thin film science by these pioneers. Finally, some of the important current developments in aberration corrected electron optics and eventual adaptations to in situ UHV microscopy are discussed. As a result of all the path breaking developments that have led to today's highly sophisticated UHV-TEM systems, integrated fundamental studies are now possible that combine many traditional surface science approaches. Combined investigations to date have involved in situ and ex situ surface microscopies such as scanning tunneling microscopy/atomic force microscopy, scanning Auger microscopy, and photoemission electron microscopy, and area-integrating techniques such as x-ray photoelectron

Investigation of the structural anisotropy in a self-assembling glycinate layer on Cu(100) by scanning tunneling microscopy and density functional theory calculations

Science.gov (United States)

Kuzmin, Mikhail; Lahtonen, Kimmo; Vuori, Leena; Sánchez-de-Armas, Rocío; Hirsimäki, Mika; Valden, Mika

2017-07-01

Self-assembling organic molecule-metal interfaces exhibiting free-electron like (FEL) states offers an attractive bottom-up approach to fabricating materials for molecular electronics. Accomplishing this, however, requires detailed understanding of the fundamental driving mechanisms behind the self-assembly process. For instance, it is still unresolved as to why the adsorption of glycine ([NH2(CH2)COOH]) on isotropic Cu(100) single crystal surface leads, via deprotonation and self-assembly, to a glycinate ([NH2(CH2)COO-]) layer that exhibits anisotropic FEL behavior. Here, we report on bias-dependent scanning tunneling microscopy (STM) experiments and density functional theory (DFT) calculations for glycine adsorption on Cu(100) single crystal surface. We find that after physical vapor deposition (PVD) of glycine on Cu(100), glycinate self-assembles into an overlayer exhibiting c(2 × 4) and p(2 × 4) symmetries with non-identical adsorption sites. Our findings underscore the intricacy of electrical conductivity in nanomolecular organic overlayers and the critical role the structural anisotropy at molecule-metal interface plays in the fabrication of materials for molecular electronics.

Study on the measures of tunnels side-crossing bridge based on sheltering effects of isolation piles

Science.gov (United States)

Tang, Jian; Liu, Jun yan; Liu, Yan

2017-08-01

Based on the transit line 3, we studied the effect of the bridge piles crossed closely from the side by the shield tunnel. Using the three-dimensional finite element numerical analysis software Midas GTS/NX, we analyzed the effect of shield tunnel on pile deformation, statistics are obtained that under the condition of pile, subgrade reinforcement and ground changes. The calculation results show that in the condition of reinforcement, the new tunnel shield crossing through the pile caused longitudinal disturbance of the tunnel surrounding strata along the tunnel, where the soil over the area is within a certain range of pile and settlement deformation of surface subsidence occurs, changing the surface roughly to the shape of “V”. The maximum value appears above the shield tunnel and the value is high. In combination with engineering geology, hydrogeology and environment factors, this paper adopted isolation pile reinforcement to the pile, and the simulated results show that, pile settlement was significantly reduced under the condition of pile reinforcement. The calculation results show the rationality of the reinforcement scheme to a certain extent, which provides a theoretical basis for the similar tunnel.

Interaction between groundwater and TBM (Tunnel Boring Machine) excavated tunnels

OpenAIRE

Font Capó, Jordi

2012-01-01

A number of problems, e.g. sudden inflows are encountered during tunneling under the piezometric level, especially when the excavation crosses high transmissivity areas. These inflows may drag materials when the tunnel crosses low competent layers, resulting in subsidence, chimney formation and collapses. Moreover, inflows can lead to a decrease in head level because of aquifer drainage. Tunnels can be drilled by a tunnel boring machine (TBM) to minimize inflows and groundwater impacts, restr...

Study of the tunneling effect within lattices with cubic structure on varying temperature

International Nuclear Information System (INIS)

Frisone, F.

2008-01-01

In this theoretical study, it is underlined that the presence of micro-cracks in the lattice structure increases the probability of tunneling effect between two deuterons by some orders of magnitude with respect to non-deformed lattices. We have derived an expression to compute the tunneling probability within a micro-crack, and hypothesized a D + 2 -D + 2 binding mechanism. Finally, the overall indications provided by these theoretical simulations appear to suggest that the deformation of the crystalline lattice, at varying temperature, seems able to influence the process of tunneling between the deuterons in the metal, while the forced loading with D 2 has, in general, no evident positive effects in pure metals, but in some cases could, on the contrary, condition the phenomenon negatively. (authors)

Relativistic tunneling through two successive barriers

International Nuclear Information System (INIS)

Lunardi, Jose T.; Manzoni, Luiz A.

2007-01-01

We study the relativistic quantum mechanical problem of a Dirac particle tunneling through two successive electrostatic barriers. Our aim is to study the emergence of the so-called generalized Hartman effect, an effect observed in the context of nonrelativistic tunneling as well as in its counterparts and which is often associated with the possibility of superluminal velocities in the tunneling process. We discuss the behavior of both the phase (or group) tunneling time and the dwell time, and show that in the limit of opaque barriers the relativistic theory also allows the emergence of the generalized Hartman effect. We compare our results with the nonrelativistic ones and discuss their interpretation

Emission factors from road traffic from a tunnel study (Gubrist tunnel, Switzerland). Part 1 Concept and first results

Energy Technology Data Exchange (ETDEWEB)

Staehelin, Johannes; Brunner, Dominik; Baumle, Martin [Atmospheric Science, ETH-Hoenggerberg, Zuerich (Switzerland); Schlapfer, Kurt [Carbotech AG, Basel (Switzerland); Burgin, Toni; Meier, Markus [Amt fuer Technische Anlagen und Lufthygiene Kanton Zuerich ATAL, Zuerich (Switzerland); Steinemann, Urs [Ingenieurbuero Steinemann, Wollerau (Switzerland); Schneider, Stefan; Zahner, Christoph; Keiser, Stephan [Planungsbuero Jud AG, Zuerich (Switzerland); Stahel, Werner; Keller, Christian [Sem. for Statistics, ETH-Z, Zuerich (Switzerland)

1995-06-22

In the industrialized world a large part of the emission of the primary air pollutants (NO{sub x}, volatile organic compounds (VOC) and CO) originates from road traffic. Here we present the concept and first results of a tunnel study which took place from September 20th to September 26th, 1993, at the Gubrist tunnel (close to Zuerich, Switzerland) in which the emission factors of a large number of individual VOCs, total hydrocarbons (t-HC), CO, NO{sub x} and SO{sub 2} are determined. The first tentative results of the emission factors of NO{sub x}, CO, t-HC and 26 individual hydrocarbons (alkanes and aromatics in the volatility range from n-heptane to n-decane) for the average of all vehicles and the light duty vehicles at an average speed of 90 km/h are given

Learning from case studies and monitoring of Dutch tunnel projects

NARCIS (Netherlands)

Korff, M.

2017-01-01

Individuals and project-based organisations in the construction industry can learn in a (more) systematic way from case studies and the monitoring of underground construction works. Underground construction projects such as tunnels and excavations suffer as much or more from failure costs

Atomistic modeling trap-assisted tunneling in hole tunnel field effect transistors

Science.gov (United States)

Long, Pengyu; Huang, Jun Z.; Povolotskyi, Michael; Sarangapani, Prasad; Valencia-Zapata, Gustavo A.; Kubis, Tillmann; Rodwell, Mark J. W.; Klimeck, Gerhard

2018-05-01

Tunnel Field Effect Transistors (FETs) have the potential to achieve steep Subthreshold Swing (S.S.) below 60 mV/dec, but their S.S. could be limited by trap-assisted tunneling (TAT) due to interface traps. In this paper, the effect of trap energy and location on OFF-current (IOFF) of tunnel FETs is evaluated systematically using an atomistic trap level representation in a full quantum transport simulation. Trap energy levels close to band edges cause the highest leakage. Wave function penetration into the surrounding oxide increases the TAT current. To estimate the effects of multiple traps, we assume that the traps themselves do not interact with each other and as a whole do not modify the electrostatic potential dramatically. Within that model limitation, this numerical metrology study points to the critical importance of TAT in the IOFF in tunnel FETs. The model shows that for Dit higher than 1012/(cm2 eV) IO F F is critically increased with a degraded IO N/IO F F ratio of the tunnel FET. In order to have an IO N/IO F F ratio higher than 104, the acceptable Dit near Ev should be controlled to no larger than 1012/(cm2 eV) .

Switching behaviour of individual Ag-TCNQ nanowires: an in situ transmission electron microscopy study

Science.gov (United States)

Ran, Ke; Rösner, Benedikt; Butz, Benjamin; Fink, Rainer H.; Spiecker, Erdmann

2016-10-01

The organic semiconductor silver-tetracyanoquinodimethane (Ag-TCNQ) exhibits electrical switching and memory characteristics. Employing a scanning tunnelling microscopy setup inside a transmission electron microscope, the switching behaviour of individual Ag-TCNQ nanowires (NWs) is investigated in detail. For a large number of NWs, the switching between a high (OFF) and a low (ON) resistance state was successfully stimulated by negative bias sweeps. Fitting the experimental I-V curves with a Schottky emission function makes the switching features prominent and thus enables a direct evaluation of the switching process. A memory cycle including writing, reading and erasing features is demonstrated at an individual NW. Moreover, electronic failure mechanisms due to Joule heating are discussed. These findings have a significant impact on our understanding of the switching behaviour of Ag-TCNQ.

Revealing energy level structure of individual quantum dots by tunneling rate measured by single-electron sensitive electrostatic force spectroscopy.

Science.gov (United States)

Roy-Gobeil, Antoine; Miyahara, Yoichi; Grutter, Peter

2015-04-08

We present theoretical and experimental studies of the effect of the density of states of a quantum dot (QD) on the rate of single-electron tunneling that can be directly measured by electrostatic force microscopy (e-EFM) experiments. In e-EFM, the motion of a biased atomic force microscope cantilever tip modulates the charge state of a QD in the Coulomb blockade regime. The charge dynamics of the dot, which is detected through its back-action on the capacitavely coupled cantilever, depends on the tunneling rate of the QD to a back-electrode. The density of states of the QD can therefore be measured through its effect on the energy dependence of tunneling rate. We present experimental data on individual 5 nm colloidal gold nanoparticles that exhibit a near continuous density of state at 77 K. In contrast, our analysis of already published data on self-assembled InAs QDs at 4 K clearly reveals discrete degenerate energy levels.

Characterization of 10,12-pentacosadiynoic acid Langmuir–Blodgett monolayers and their use in metal–insulator–metal tunnel devices

Directory of Open Access Journals (Sweden)

Saumya Sharma

2014-11-01

Full Text Available The characterization of Langmuir–Blodgett thin films of 10,12-pentacosadiynoic acid (PDA and their use in metal–insulator–metal (MIM devices were studied. The Langmuir monolayer behavior of the PDA film was studied at the air/water interface using surface tension–area isotherms of polymeric and monomeric PDA. Langmuir–Blodgett (LB, vertical deposition and Langmuir–Schaefer (LS, horizontal deposition techniques were used to deposit the PDA film on various substrates (glass, quartz, silicon, and nickel-coated film on glass. The electrochemical, electrical and optical properties of the LB and LS PDA films were studied using cyclic voltammetry, current–voltage characteristics (I–V, and UV–vis and FTIR spectroscopies. Atomic force microscopy measurements were performed in order to analyze the surface morphology and roughness of the films. A MIM tunnel diode was fabricated using a PDA monolayer assembly as the insulating barrier, which was sandwiched between two nickel layers. The precise control of the thickness of the insulating monolayers proved critical for electron tunneling to take place in the MIM structure. The current–voltage characteristics of the MIM diode revealed tunneling behavior in the fabricated Ni–PDA LB film–Ni structures.

Asymmetric voltage behavior of the tunnel magnetoresistance in double barrier magnetic tunnel junctions

KAUST Repository

Useinov, Arthur

2012-06-01

In this paper, we study the value of the tunnel magnetoresistance (TMR) as a function of the applied voltage in double barrier magnetic tunnel junctions (DMTJs) with the left and right ferromagnetic (FM) layers being pinned and numerically estimate the possible difference of the TMR curves for negative and positive voltages in the homojunctions (equal barriers and electrodes). DMTJs are modeled as two single barrier junctions connected in series with consecutive tunneling (CST). We investigated the asymmetric voltage behavior of the TMR for the CST in the range of a general theoretical model. Significant asymmetries of the experimental curves, which arise due to different annealing regimes, are mostly explained by different heights of the tunnel barriers and asymmetries of spin polarizations in magnetic layers. © (2012) Trans Tech Publications.

Asymmetric voltage behavior of the tunnel magnetoresistance in double barrier magnetic tunnel junctions

KAUST Repository

Useinov, Arthur; Gooneratne, Chinthaka Pasan; Kosel, Jü rgen

2012-01-01

In this paper, we study the value of the tunnel magnetoresistance (TMR) as a function of the applied voltage in double barrier magnetic tunnel junctions (DMTJs) with the left and right ferromagnetic (FM) layers being pinned and numerically estimate the possible difference of the TMR curves for negative and positive voltages in the homojunctions (equal barriers and electrodes). DMTJs are modeled as two single barrier junctions connected in series with consecutive tunneling (CST). We investigated the asymmetric voltage behavior of the TMR for the CST in the range of a general theoretical model. Significant asymmetries of the experimental curves, which arise due to different annealing regimes, are mostly explained by different heights of the tunnel barriers and asymmetries of spin polarizations in magnetic layers. © (2012) Trans Tech Publications.

CURRENT ASSET TUNNELING AND FIRM PERFORMANCE IN AN EMERGING MARKET

OpenAIRE

Ratna Candra Sari; Zaki Baridwan

2014-01-01

This study examines the effect of current asset tunneling on firm performance from the emerging market perspective. Although tunneling activities is a common practices by businesses especially in Indonesia, there exist obstacles in the measurement of tunneling activity because it is difficult to proof the existence of such practices. In this study, we measure tunneling by using accounts receivables and develop tunneling detection criteria. In addition, this study examines the effect of tunnel...

Trap assisted tunneling and its effect on subthreshold swing of tunnel field effect transistors

OpenAIRE

Sajjad, Redwan N.; Chern, Winston; Hoyt, Judy L.; Antoniadis, Dimitri A.

2016-01-01

We provide a detailed study of the interface Trap Assisted Tunneling (TAT) mechanism in tunnel field effect transistors to show how it contributes a major leakage current path before the Band To Band Tunneling (BTBT) is initiated. With a modified Shockley-Read-Hall formalism, we show that at room temperature, the phonon assisted TAT current always dominates and obscures the steep turn ON of the BTBT current for common densities of traps. Our results are applicable to top gate, double gate and...

A combined optical, SEM and STM study of growth spirals

Indian Academy of Sciences (India)

Some novel results of a combined sequential study of growth spirals on the basal surface of the richly polytypic CdI2 crystals by optical microscopy, scanning electron microscopy (SEM) and scanning tunneling microscopy (STM) are presented and discussed. In confirmation of the known structural data, the STM pictures ...

Study of tunnelling through water-bearing fracture zones. Baseline study on technical issues with NE-1 as reference

International Nuclear Information System (INIS)

Yanting Chang; Swindell, Robert; Bogdanoff, Ingvar; Lindstroem, Beatrice; Termen, Jens; Starsec, Peter

2005-04-01

The Swedish Nuclear Fuel and Waste Management Co (SKB) is responsible for the management of Sweden's nuclear waste. SKB is investigating various designs for the construction of an underground deep repository for spent nuclear fuel at 500-600 m depths. For the construction of an access tunnel for such a deep repository, the possibility of encountering a water-bearing fracture zone cannot be discounted. Such a zone named NE-1 (deformation zone in accordance to SKB's terminology) was encountered during the construction of the Aespoe Hard Rock Laboratory (HRL) and difficulties with large water inflows were reported. With the aim to assess the feasibility of different technical solutions, SKB commissioned a baseline study into the passage of an access tunnel through a water-bearing fracture zone at three different depths (200 m, 400 m and 600 m). The objectives of this baseline study are to: Increase the knowledge of possible technical solutions for tunnelling through water-bearing fractures zones with the characteristics of the brittle deformation zone NE-1 at different depths, namely 200, 400 and 600 metres; Form a reference document to assist the engineering design and construction work for the passage through such a water-bearing fracture zone; To highlight the engineering parameters that should be obtained to facilitate design for the passage through water-bearing fracture zones.The study has been carried out in the following five stages: A. Compilation of the relevant data for deformation zone NE-1; B. Problem identification and proposal of technical solutions; C. Identification of hazards to be involved in the tunnel excavation; D. Recommendations and conclusions for further investigations; E. Documentation of the results in a final report. The analyses will be expressed in statistical/probabilistic terms where appropriate. In order to specify the precondition that will be valid for this study, a descriptive model of the water-bearing fracture zone is established

Study of tunnelling through water-bearing fracture zones. Baseline study on technical issues with NE-1 as reference

Energy Technology Data Exchange (ETDEWEB)

Yanting Chang; Swindell, Robert; Bogdanoff, Ingvar; Lindstroem, Beatrice; Termen, Jens [WSP Sweden, Stockholm (Sweden) ; Starsec, Peter [SGI, Linkoeping (Sweden)

2005-04-01

The Swedish Nuclear Fuel and Waste Management Co (SKB) is responsible for the management of Sweden's nuclear waste. SKB is investigating various designs for the construction of an underground deep repository for spent nuclear fuel at 500-600 m depths. For the construction of an access tunnel for such a deep repository, the possibility of encountering a water-bearing fracture zone cannot be discounted. Such a zone named NE-1 (deformation zone in accordance to SKB's terminology) was encountered during the construction of the Aespoe Hard Rock Laboratory (HRL) and difficulties with large water inflows were reported. With the aim to assess the feasibility of different technical solutions, SKB commissioned a baseline study into the passage of an access tunnel through a water-bearing fracture zone at three different depths (200 m, 400 m and 600 m). The objectives of this baseline study are to: Increase the knowledge of possible technical solutions for tunnelling through water-bearing fractures zones with the characteristics of the brittle deformation zone NE-1 at different depths, namely 200, 400 and 600 metres; Form a reference document to assist the engineering design and construction work for the passage through such a water-bearing fracture zone; To highlight the engineering parameters that should be obtained to facilitate design for the passage through water-bearing fracture zones.The study has been carried out in the following five stages: A. Compilation of the relevant data for deformation zone NE-1; B. Problem identification and proposal of technical solutions; C. Identification of hazards to be involved in the tunnel excavation; D. Recommendations and conclusions for further investigations; E. Documentation of the results in a final report. The analyses will be expressed in statistical/probabilistic terms where appropriate. In order to specify the precondition that will be valid for this study, a descriptive model of the water-bearing fracture zone is

Klein tunneling phenomenon with pair creation process

Science.gov (United States)

Wu, G. Z.; Zhou, C. T.; Fu, L. B.

2018-01-01

In this paper, we study the Klein tunneling phenomenon with electron-positron pair creation process. Pairs can be created from the vacuum by a supercritical single-well potential (for electrons). In the time region, the time-dependent growth pattern of the created pairs can be characterized by four distinct regimes which can be considered as four different statuses of the single well. We find that if positrons penetrate the single well by Klein tunneling in different statuses, the total number of the tunneling positrons will be different. If Klein tunneling begins at the initial stage of the first status i.e. when the sing well is empty, the tunneling process and the total number of tunneling positrons are similar to the traditional Klein tunneling case without considering the pair creation process. As the tunneling begins later, the total tunneling positron number increases. The number will finally settle to an asymptotic value when the tunneling begins later than the settling-down time t s of the single well which has been defined in this paper.

Frequency driven inversion of tunnel magnetoimpedance and observation of positive tunnel magnetocapacitance in magnetic tunnel junctions

International Nuclear Information System (INIS)

Parui, Subir; Ribeiro, Mário; Atxabal, Ainhoa; Llopis, Roger; Bedoya-Pinto, Amilcar; Sun, Xiangnan; Casanova, Fèlix; Hueso, Luis E.

2016-01-01

The relevance for modern computation of non-volatile high-frequency memories makes ac-transport measurements of magnetic tunnel junctions (MTJs) crucial for exploring this regime. Here, we demonstrate a frequency-mediated effect in which the tunnel magnetoimpedance reverses its sign in a classical Co/Al 2 O 3 /NiFe MTJ, whereas we only observe a gradual decrease in the tunnel magnetophase. Such effects are explained by the capacitive coupling of a parallel resistor and capacitor in the equivalent circuit model of the MTJ. Furthermore, we report a positive tunnel magnetocapacitance effect, suggesting the presence of a spin-capacitance at the two ferromagnet/tunnel-barrier interfaces. Our results are important for understanding spin transport phenomena at the high frequency regime in which the spin-polarized charge accumulation due to spin-dependent penetration depth at the two interfaces plays a crucial role.

Frequency driven inversion of tunnel magnetoimpedance and observation of positive tunnel magnetocapacitance in magnetic tunnel junctions

Energy Technology Data Exchange (ETDEWEB)

Parui, Subir, E-mail: s.parui@nanogune.eu, E-mail: l.hueso@nanogune.eu; Ribeiro, Mário; Atxabal, Ainhoa; Llopis, Roger [CIC nanoGUNE, 20018 Donostia-San Sebastian (Spain); Bedoya-Pinto, Amilcar [CIC nanoGUNE, 20018 Donostia-San Sebastian (Spain); Max Planck Institute of Microstructure Physics, D-06120 Halle (Germany); Sun, Xiangnan [CIC nanoGUNE, 20018 Donostia-San Sebastian (Spain); National Center for Nanoscience and Technology, 100190 Beijing (China); Casanova, Fèlix; Hueso, Luis E., E-mail: s.parui@nanogune.eu, E-mail: l.hueso@nanogune.eu [CIC nanoGUNE, 20018 Donostia-San Sebastian (Spain); IKERBASQUE, Basque Foundation for Science, 48011 Bilbao (Spain)

2016-08-01

The relevance for modern computation of non-volatile high-frequency memories makes ac-transport measurements of magnetic tunnel junctions (MTJs) crucial for exploring this regime. Here, we demonstrate a frequency-mediated effect in which the tunnel magnetoimpedance reverses its sign in a classical Co/Al{sub 2}O{sub 3}/NiFe MTJ, whereas we only observe a gradual decrease in the tunnel magnetophase. Such effects are explained by the capacitive coupling of a parallel resistor and capacitor in the equivalent circuit model of the MTJ. Furthermore, we report a positive tunnel magnetocapacitance effect, suggesting the presence of a spin-capacitance at the two ferromagnet/tunnel-barrier interfaces. Our results are important for understanding spin transport phenomena at the high frequency regime in which the spin-polarized charge accumulation due to spin-dependent penetration depth at the two interfaces plays a crucial role.

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

Science.gov (United States)

Molina-Mendoza, Aday J; Rodrigo, José G; Island, Joshua; Burzuri, Enrique; Rubio-Bollinger, Gabino; van der Zant, Herre S J; Agraït, Nicolás

2014-02-01

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.

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

Energy Technology Data Exchange (ETDEWEB)

Molina-Mendoza, Aday J., E-mail: aday.molina@uam.es [Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Rodrigo, José G.; Rubio-Bollinger, Gabino [Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Condensed Matter Physics Center (IFIMAC) and Instituto Universitario de Ciencia de Materiales “Nicolás Cabrera,” Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Island, Joshua; Burzuri, Enrique; Zant, Herre S. J. van der [Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (Netherlands); Agraït, Nicolás [Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Condensed Matter Physics Center (IFIMAC) and Instituto Universitario de Ciencia de Materiales “Nicolás Cabrera,” Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Instituto Madrileño de Estudios Avanzados en Nanociencia IMDEA-Nanociencia, E-28049 Madrid (Spain)

2014-02-15

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.

Tunneling study of SRF cavity-grade niobium

International Nuclear Information System (INIS)

Proslier, T.; Zasadzinski, J.; Cooley, L.; Pellin, M.; Norem, J.; Elam, J.; Antonine, C. Z.; Rimmer, R.; Kneisel, P.

2009-01-01

Niobium, with its very high H C1 , has been used in superconducting radio frequency (SRF) cavities for accelerator systems for 40 years with continual improvement. The quality factor of cavities (Q) is governed by the surface impedance R BCS , which depends on the quasiparticle gap, delta, and the superfluid density. Both of these parameters are seriously affected by surface imperfections (metallic phases, dissolved oxygen, magnetic impurities). Loss mechanism and surface treatments of Nb cavities found to improve the Q factor are still unsolved mysteries. We present here an overview of the capabilities of the point contact tunneling spectroscopy and Atomic layer deposition methods and how they can help understanding the High field Q-drop and the mild baking effect. Tunneling spectroscopy was performed on Nb pieces from the same processed material used to fabricate SRF cavities. Air exposed, electropolished Nb exhibited a surface superconducting gap Delta = 1.55 meV, characteristic of clean, bulk Nb, however the tunneling density of states (DOS) was broadened significantly. Nb pieces treated with the same mild baking used to improve the Q-slope in SRF cavities revealed a much sharper DOS. Good fits to the DOS are obtained using Shiba theory suggesting that magnetic scattering of quasiparticles is the origin of the degraded surface superconductivity and the Q-slope problem of Nb SRF cavities

Carpal Tunnel Syndrome

Science.gov (United States)

... a passing cramp? It could be carpal tunnel syndrome. The carpal tunnel is a narrow passageway of ... three times more likely to have carpal tunnel syndrome than men. Early diagnosis and treatment are important ...

Theory of superconducting tunneling without the tunneling Hamiltonian

International Nuclear Information System (INIS)

Arnold, G.B.

1987-01-01

When a tunneling barrier is nearly transparent, the standard tunneling (or transfer) Hamiltonian approximation fails. The author describes the theory which is necessary for calculating the tunneling current in these cases, and illustrate it by comparing theory and experiment on superconductor/insulator/superconductor (SIS) junctions have ultra-thin tunnel barriers. This theory accurately explains the subgap structure which appears in the dynamical resistance of such SIS junctions, including many observed details which no previous theory has reproduced. The expression for the current through an SIS junction with an ultrathin barrier is given by I(t) = Re{Sigma/sub n/ J/sub n/ (omega/sub o/)e/sup in omega/o/sup t/} where omega/sub o/ = 2eV/h is the Josephson frequency, V is the bias voltage, and the J/sub n/ are voltage dependent coefficients, one for each positive or negative integer, n, and n=0. The relative sign of the terms involving cos(n omega/sub o/t) and sin(n omega/sub o/t) agrees with experiment, in contrast to previous theories of Josephson tunneling

Quantum tunneling with friction

Science.gov (United States)

Tokieda, M.; Hagino, K.

2017-05-01

Using the phenomenological quantum friction models introduced by P. Caldirola [Nuovo Cimento 18, 393 (1941), 10.1007/BF02960144] and E. Kanai [Prog. Theor. Phys. 3, 440 (1948), 10.1143/ptp/3.4.440], M. D. Kostin [J. Chem. Phys. 57, 3589 (1972), 10.1063/1.1678812], and K. Albrecht [Phys. Lett. B 56, 127 (1975), 10.1016/0370-2693(75)90283-X], we study quantum tunneling of a one-dimensional potential in the presence of energy dissipation. To this end, we calculate the tunneling probability using a time-dependent wave-packet method. The friction reduces the tunneling probability. We show that the three models provide similar penetrabilities to each other, among which the Caldirola-Kanai model requires the least numerical effort. We also discuss the effect of energy dissipation on quantum tunneling in terms of barrier distributions.

Shock Tunnel Studies of Scramjet Phenomena 1993

Science.gov (United States)

Stalker, R. J.; Bakos, R. J.; Morgan, R. G.; Porter, L.; Mee, D.; Paull, A.; Tuttle, S.; Simmons, J. M.; Wendt, M.; Skinner, K.

1995-01-01

Reports by the staff of the University of Queensland on various research studies related to the advancement of scramjet technology and hypervelocity pulse test facilities are presented. These reports document the tests conducted in the reflected shock tunnel T4 and supporting research facilities that have been used to study the injection, mixing, and combustion of hydrogen fuel in generic scramjets at flow conditions typical of hypersonic flight. In addition, topics include the development of instrumentation and measurement technology, such as combustor wall shear and stream composition in pulse facilities, and numerical studies and analyses of the scramjet combustor process and the test facility operation. This research activity is Supplement 10 under NASA Grant NAGw-674.

Does flexible tunnel drilling affect the femoral tunnel angle measurement after anterior cruciate ligament reconstruction?

Science.gov (United States)

Muller, Bart; Hofbauer, Marcus; Atte, Akere; van Dijk, C Niek; Fu, Freddie H

2015-12-01

To quantify the mean difference in femoral tunnel angle (FTA) as measured on knee radiographs between rigid and flexible tunnel drilling after anatomic anterior cruciate ligament (ACL) reconstruction. Fifty consecutive patients that underwent primary anatomic ACL reconstruction with a single femoral tunnel drilled with a flexible reamer were included in this study. The control group was comprised of 50 patients all of who underwent primary anatomic ACL reconstruction with a single femoral tunnel drilled with a rigid reamer. All femoral tunnels were drilled through a medial portal to ensure anatomic tunnel placement. The FTA was determined from post-operative anterior-to-posterior (AP) radiographs by two independent observers. A 5° difference between the two mean FTA was considered clinically significant. The average FTA, when drilled with a rigid reamer, was 42.0° ± 7.2°. Drilling with a flexible reamer resulted in a mean FTA of 44.7° ± 7.0°. The mean difference of 2.7° was not statistically significant. The intraclass correlation coefficient for inter-tester reliability was 0.895. The FTA can be reliably determined from post-operative AP radiographs and provides a useful and reproducible metric for characterizing femoral tunnel position after both rigid and flexible femoral tunnel drilling. This has implications for post-operative evaluation and preoperative treatment planning for ACL revision surgery. IV.

Atomistic nature in band-to-band tunneling in two-dimensional silicon pn tunnel diodes

International Nuclear Information System (INIS)

Tabe, Michiharu; Tan, Hoang Nhat; Mizuno, Takeshi; Muruganathan, Manoharan; Anh, Le The; Mizuta, Hiroshi; Nuryadi, Ratno; Moraru, Daniel

2016-01-01

We study low-temperature transport properties of two-dimensional (2D) Si tunnel diodes, or Si Esaki diodes, with a lateral layout. In ordinary Si Esaki diodes, interband tunneling current is severely limited because of the law of momentum conservation, while nanoscale Esaki diodes may behave differently due to the dopants in the narrow depletion region, by atomistic effects which release such current limitation. In thin-Si lateral highly doped pn diodes, we find clear signatures of interband tunneling between 2D-subbands involving phonon assistance. More importantly, the tunneling current is sharply enhanced in a narrow voltage range by resonance via a pair of a donor- and an acceptor-atom in the pn junction region. Such atomistic behavior is recognized as a general feature showing up only in nanoscale tunnel diodes. In particular, a donor-acceptor pair with deeper ground-state energies is likely to be responsible for such a sharply enhanced current peak, tunable by external biases.

Study both films structure and fractal growth in the T-10 tokamak

International Nuclear Information System (INIS)

Khimchenko, L.N.; Budaev, V.P.; Guseva, M.I.; Kamneva, S.A.; Kolbasov, B.N.; Kuteev, B.V.; Martynenko, Yu.V.; Svechnikov, N.Yu.; Stankevich, V.G.; Loginov, B.A.; Romanov, P.B.

2005-01-01

In the paper results of films growth mechanism study, their internal structure are summarized. The mechanism leading to hydrogen capture effect on the first wall at over dusting stage is stated. Films internal structure have been studied with help of synchrotron radiation, electron paramagnetic resonance, IR reflection spectra, thermal gravimetric methods, spectroscopy in the vision spectrum range and UV vacuum range. Structure of the films surfaces have been examined with help of electron microscopy, probe scanning tunnel and atom-force microscopy, as well as miniature scanning tunnel microscope placed in the T-10 tokamak

Seismic prediction ahead of tunnel constructions

Science.gov (United States)

Jetschny, S.; Bohlen, T.; Nil, D. D.; Giese, R.

2007-12-01

To increase safety and efficiency of tunnel constructions, online seismic exploration ahead of a tunnel can become a valuable tool. Within the \\it OnSite project founded by the BMBF (German Ministry of Education and Research) within \\it GeoTechnologien a new forward looking seismic imaging technique is developed to e.g. determine weak and water bearing zones ahead of the constructions. Our approach is based on the excitation and registration of \\it tunnel surface waves. These waves are excited at the tunnel face behind the cutter head of a tunnel boring machine and travel into drilling direction. Arriving at the front face they generate body waves (mainly S-waves) propagating further ahead. Reflected S-waves are back- converted into tunnel surface waves. For a theoretical description of the conversion process and for finding optimal acquisition geometries it is of importance to study the propagation characteristics of tunnel surface waves. 3D seismic finite difference modeling and analytic solutions of the wave equation in cylindric coordinates revealed that at higher frequencies, i.e. if the tunnel diameter is significantly larger than the wavelength of S-waves, these surface waves can be regarded as Rayleigh-waves circulating the tunnel. For smaller frequencies, i.e. when the S-wavelength approaches the tunnel diameter, the propagation characteristics of these surface waves are then similar to S- waves. Field measurements performed by the GeoForschungsZentrum Potsdam, Germany at the Gotthard Base Tunnel (Switzerland) show both effects, i.e. the propagation of Rayleigh- and body-wave like waves along the tunnel. To enhance our understanding of the excitation and propagation characteristics of tunnel surface waves the transition of Rayleigh to tube-waves waves is investigated both analytically and by numerical simulations.

The Use Of Scanning Probe Microscopy To Investigate Crystal-Fluid Interfaces

International Nuclear Information System (INIS)

Orme, C A; Giocondi, J L

2007-01-01

Over the past decade there has been a natural drive to extend the investigation of dynamic surfaces in fluid environments to higher resolution characterization tools. Various aspects of solution crystal growth have been directly visualized for the first time. These include island nucleation and growth using transmission electron microscopy and scanning tunneling microscopy; elemental step motion using scanning probe microscopy; and the time evolution of interfacial atomic structure using various diffraction techniques. In this lecture we will discuss the use of one such in situ method, scanning probe microscopy, as a means of measuring surface dynamics during crystal growth and dissolution. We will cover both practical aspects of imaging such as environmental control, fluid flow, and electrochemical manipulation, as well as the types of physical measurements that can be made. Measurements such as step motion, critical lengths, nucleation density, and step fluctuations, will be put in context of the information they provide about mechanistic processes at surfaces using examples from metal and mineral crystal growth

Signatures of unstable semiclassical trajectories in tunneling

International Nuclear Information System (INIS)

Levkov, D G; Panin, A G; Sibiryakov, S M

2009-01-01

It was found recently that processes of multidimensional tunneling are generally described at high energies by unstable semiclassical trajectories. We study two observational signatures related to the instability of trajectories. First, we find an additional power-law dependence of the tunneling probability on the semiclassical parameter as compared to the standard case of potential tunneling. The second signature is a substantial widening of the probability distribution over final-state quantum numbers. These effects are studied using a modified semiclassical technique which incorporates stabilization of the tunneling trajectories. The technique is derived from first principles. We obtain expressions for the inclusive and exclusive tunneling probabilities in the case of unstable semiclassical trajectories. We also investigate the 'phase transition' between the cases of stable and unstable trajectories across certain 'critical' values of energy. Finally, we derive the relation between the semiclassical probabilities of tunneling from the low-lying and highly excited initial states. This puts on firm ground a conjecture made previously in the semiclassical description of collision-induced tunneling in field theory

Diesel bus emissions measured in a tunnel study.

Science.gov (United States)

Jamriska, Milan; Morawska, Lidia; Thomas, Steven; He, Congrong

2004-12-15

The emission factors of a bus fleet consisting of approximately 300 diesel-powered buses were measured in a tunnel study under well-controlled conditions during a 2-d monitoring campaign in Brisbane. Particle number and mass concentration levels of submicrometer particles and PM2.5 were monitored by SMPS and DustTrak instruments at the tunnel's entrance and exit, respectively. Correlation between DustTrak and TEOM response to diesel emissions was assessed, and the DustTrak results were recalculated into TEOM equivalent data. The mean value of the number and mass emission factors was (3.11+/-2.41) x 10(14) particles km(-1) for submicrometer particles and 583+/-451 mg km(-1) for PM2.5 (DustTrak), respectively. TEOM PM2.5 equivalent emission factor was 267+/-207 mg km(-1). The results are in good agreement with the emission factors determined from steady-state dynamometer testing of 12 buses from the same Brisbane City bus fleet. The results indicate that when carefully designed, both approaches, the dynamometer and on-road studies, can provide comparable results, applicable for the assessment of the effect of traffic emissions on airborne particle pollution. A brief overview of emission factors determined from other on-road and dynamometer studies reported in the literature as well as with the regulatory values used for the vehicle emission inventory assessment is presented and compared with the results obtained in this study.

CURRENT ASSET TUNNELING AND FIRM PERFORMANCE IN AN EMERGING MARKET

Directory of Open Access Journals (Sweden)

Ratna Candra Sari

2014-12-01

Full Text Available This study examines the effect of current asset tunneling on firm performance from the emerging market perspective. Although tunneling activities is a common practices by businesses especially in Indonesia, there exist obstacles in the measurement of tunneling activity because it is difficult to proof the existence of such practices. In this study, we measure tunneling by using accounts receivables and develop tunneling detection criteria. In addition, this study examines the effect of tunneling on firm performance and market reaction during the announcement of the related party transaction. The study finds that from the perspective of the being-tunneled companies, receivables to related parties negatively affect the company’s profit margin. Companies which announce related party transaction indicating tunneling obtain negative abnormal return during the announcement of the related party transaction.

Tunneling works. Tunnel koji

Energy Technology Data Exchange (ETDEWEB)

Higo, M [Hazam Gumi, Ltd., Tokyo (Japan)

1991-10-25

A mountain tunneling method for rock-beds used to be applied mainly to construction works in the mountains under few restrictions by environmental problems. However, construction works near residential sreas have been increasing. There are such enviromental problems due to tunneling works as vibration, noise, lowering of ground-water level, and influences on other structures. This report mainly describes the measurement examples of vibration and noise accompanied with blasting and the effects of the measures to lessen such influences. When the tunneling works for the railroad was carried out on the natural ground mainly composed of basalt, vibration of the test blasting was measured at three stations with piezoelectric accelerometers. Then, ordinary blasting, mutistage blasting, and ABM blasting methods were used properly besed on the above results, and only a few complaints were made. In the different works, normal noise and low-frequency sound were mesured at 22 stations around the pit mouth. As countermeasures for noise, sound-proof sheets, walls, and single and double doors were installed and foundto be effective. 1 ref., 6 figs., 1 tab.

Scanning microscopies of superconductors at very low temperatures

International Nuclear Information System (INIS)

Crespo, V.; Maldonado, A.; Galvis, J.A.; Kulkarni, P.; Guillamon, I.; Rodrigo, J.G.; Suderow, H.; Vieira, S.; Banerjee, S.; Rodiere, P.

2012-01-01

We discuss basics of Scanning Tunneling Microscopy and Spectroscopy (STM/S) of the superconducting state with normal and superconducting tips. We present a new method to measure the local variations in the Andreev reflection amplitude between a superconducting tip and the sample. This method is termed Scanning Andreev Reflection Spectroscopy (SAS). We also briefly discuss vortex imaging with STM/S under an applied current through the sample, and show the vortex lattice as a function of the angle between the magnetic field and sample’s surface.

STUDI KOMPUTASI BERBASIS DFT TERHADAP FENOMENA QUANTUM TUNNELING DALAM ISOMERISASI METILHIDROKSIKARBENA

Directory of Open Access Journals (Sweden)

Jumaidil Awal

2016-01-01

Full Text Available Density functional theory-based methods have been applied to predict the most possible one among the isomerizations of methylhydroxycarbene considering the probability of hydrogen tunneling occurrence. B3LYP/6-31+G(d,p and M08-SO/6-31+G(d,p methods were applied in all computations using GAMESS-US software. There were three steps of computation in this research. First, electronic structure computations of both equilibrium and transition compounds involved in all isomerization alternatives in order to obtain the optimum structures of the compounds. Second, vibrational computations of optimum transition structures to ensure that each of the respective structures is well on its potential energy surface. Third, tunneling analysis accomplished by intrinsic reaction coordinate (IRC computatuins for all isomerization alternatives followed by tunneling probabilitycalculation using the Wentzel-Kramers-Brillouin (WKB formula for methylhydroxycarbene isomerizations. The result of this research showed that the DFT methods successfully produced the optimum structure of each compound. Both DFT methods also successfully mapped all the intrinsic reaction coordinates. B3LYP/6-31+G(d,p method gave tunneling probabilities of 3.55 x 10-19 for the isomerization into acetaldehyde and 3.30 x 10-20 for that into vinyl alcohol. While M08-SO/6-31+G(d,p method gave tunneling probabilities of 2.38 x 10-23 for the isomerization into acetaldehyde and 4.79 x 10-23 for that into vinyl alcohol. Keywords: DFT, methylhydroxycarbene, hydrogen tunneling, isomerization

Analysis of an underground structure settlement risk due to tunneling- A case study from Tabriz, Iran

Directory of Open Access Journals (Sweden)

Mohammad Javad Vahdatirad

2010-05-01

Full Text Available The tunnel of the Tabriz urban railway line 2 (TURL2, Iran, will pass through an underground commercial center onits way. Too little distance between the tunnel crown and the underground structure foundation will probably cause collapseor excessive settlement during the tunnel construction based on studied geotechnical conditions of the region. In this paper,a method of risk level assessment for various types of structures, such as frame and masonry structures, and various typesof foundation, such as continuous and isolated, is well defined and the risk level is classified. Moreover, the value of theunderground commercial center structure settlement is estimated using both empirical and numerical methods. The settlementrisk level of the commercial center structure is determined based on presented definitions about risk classification ofvarious types of structures. Consequently, tunneling processes in this section need a special monitoring system and consolidationmeasures before the passage of a tunnel boring machine.

Surface damage through grazing incidence ions investigated by scanning tunneling microscopy

International Nuclear Information System (INIS)

Redinger, Alex

2009-01-01

Surface damage, caused by grazing incidence ions, is investigated with variable temperature scanning tunneling microscopy. The experiments are carried out on a Pt(111) crystal. The kinetic energy of noble gas ions is varied between 1-15 keV and the angle of incidence can be adjusted between θ = 78.5 and θ = 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 θ = 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

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

Investigation of Supramolecular Coordination Self-Assembly and Polymerization Confined on Metal Surfaces Using Scanning Tunneling Microscopy

Science.gov (United States)

Lin, Tao

Organic molecules are envisioned as the building blocks for design and fabrication of functional devices in future, owing to their versatility, low cost and flexibility. Although some devices such as organic light-emitting diode (OLED) have been already applied in our daily lives, the field is still in its infancy and numerous challenges still remain. In particular, fundamental understanding of the process of organic material fabrication at a molecular level is highly desirable. This thesis focuses on the design and fabrication of supramolecular and macromolecular nanostructures on a Au(111) surface through self-assembly, polymerization and a combination of two. We used scanning tunneling microscopy (STM) as an experimental tool and Monte Carlo (MC) and kinetic Monte Carlo (KMC) simulations as theoretical tools to characterize the structures of these systems and to investigate the mechanisms of the self-assembly and polymerization processes at a single-molecular level. The results of this thesis consist of four parts as below: Part I addresses the mechanisms of two-dimensional multicomponent supramolecular self-assembly via pyridyl-Fe-terpyridyl coordination. Firstly, we studied four types of self-assembled metal-organic systems exhibiting different dimensionalities using specifically-designed molecular building blocks. We found that the two-dimensional system is under thermodynamic controls while the systems of lower dimension are under kinetic controls. Secondly, we studied the self-assembly of a series of cyclic supramolecular polygons. Our results indicate that the yield of on-surface cyclic polygon structures is very low independent of temperature and concentration and this phenomenon can be attributed to a subtle competition between kinetic and thermodynamic controls. These results shed light on thermodynamic and kinetic controls in on-surface coordination self-assembly. Part II addresses the two-dimensional supramolecular self-assembly of porphyrin

Enhanced MRI in carpal tunnel syndrome

International Nuclear Information System (INIS)

Hayakawa, Katsuhiko; Nakane, Takashi; Kobayashi, Shigeru; Asai, Takahiro; Wada, Kunio; Yoshizawa, Hidezo

1998-01-01

In this study, we performed contrast-enhanced MRI in patients with idiopathic carpal tunnel syndrome and examined the morphologic change in the carpal tunnel. In the transverse section of the opening of carpal tunnel where scaphoid and pisiform bones are figured out, we measured and examined 4 items, viz. the soft carpal tunnel volume, flat rate of median nerve, position of median nerve and thickness of palmer ligaments composing the base of carpal tunnel, with an image analyzer attached to the MRI apparatus. Whereas the average carpal tunnel volume in 12 hands of normal controls was 166.8 mm 2 , that in 74 hands of carpal tunnel syndrome was 207.2 mm 2 , a significant increase compared with the normal controls. The flat rate of median nerve was 46% in the controls, but that was 37.5% in the carpal tunnel syndrome, a significant flattening was noted. We connected the peaks of the scaphoid node and pisiform bone with a line and named it standard line. When we observed the position of median nerve in the carpal tunnel, the nerve in 9 of 12 hands, 75%, lay below the standard line in the controls, but the nerve in 65 of 74 hands, 87.8%, lay above the standard line in the carpal tunnel syndrome, clearly showing that the median nerve had shifted to the palmar side. Regarding these morphologic changes of the carpal tunnel, the internal pressure of the carpal tunnel is considered to be raised with swelling of the soft tissues mainly composing the inside of carpal tunnel, thus the area of cross section of carpal tunnel to be increased, the median nerve to be shifted to the palmar side and the median nerve to be compressed by the transverse carpal ligament at that time. Although we can observe these morphological changes readily in MRI images, these images show only the results of carpal tunnel syndrome after all, and do not specify the direct causes. However, we believe that these facts are important factors in the manifestation of idiopathic carpal tunnel syndrome. (author)

Tunneling junction as an open system. Normal tunneling

International Nuclear Information System (INIS)

Ono, Y.

1978-01-01

The method of the tunneling Hamiltonian is reformulated in the case of normal tunneling by introducing two independent particle baths. Due to the baths, it becomes possible to realize a final stationary state where the electron numbers of the two electrodes in the tunneling system are maintained constant and where there exists a stationary current. The effect of the bath-system couplings on the current-voltage characteristics of the junction is discussed in relation to the usual expression of the current as a function of voltage. (Auth.)

Tunneling time, exit time and exit momentum in strong field tunnel ionization

International Nuclear Information System (INIS)

Teeny, Nicolas

2016-01-01

Tunnel ionization belongs to the fundamental processes of atomic physics. It is still an open question when does the electron tunnel ionize and how long is the duration of tunneling. In this work we solve the time-dependent Schroedinger equation in one and two dimensions and use ab initio quantum calculations in order to answer these questions. Additionally, we determine the exit momentum of the tunnel ionized electron from first principles. We find out results that are different from the assumptions of the commonly employed two-step model, which assumes that the electron ionizes at the instant of electric field maximum with a zero momentum. After determining the quantum final momentum distribution of tunnel ionized electrons we show that the two-step model fails to predict the correct final momentum. Accordingly we suggest how to correct the two-step model. Furthermore, we determine the instant at which tunnel ionization starts, which turns out to be different from the instant usually assumed. From determining the instant at which it is most probable for the electron to enter the tunneling barrier and the instant at which it exits we determine the most probable time spent under the barrier. Moreover, we apply a quantum clock approach in order to determine the duration of tunnel ionization. From the quantum clock we determine an average tunneling time which is different in magnitude and origin with respect to the most probable tunneling time. By defining a probability distribution of tunneling times using virtual detectors we relate both methods and explain the apparent discrepancy. The results found have in general an effect on the interpretation of experiments that measure the spectra of tunnel ionized electrons, and specifically on the calibration of the so called attoclock experiments, because models with imprecise assumptions are usually employed in order to interpret experimental results.

Tunneling time, exit time and exit momentum in strong field tunnel ionization

Energy Technology Data Exchange (ETDEWEB)

Teeny, Nicolas

2016-10-18

Tunnel ionization belongs to the fundamental processes of atomic physics. It is still an open question when does the electron tunnel ionize and how long is the duration of tunneling. In this work we solve the time-dependent Schroedinger equation in one and two dimensions and use ab initio quantum calculations in order to answer these questions. Additionally, we determine the exit momentum of the tunnel ionized electron from first principles. We find out results that are different from the assumptions of the commonly employed two-step model, which assumes that the electron ionizes at the instant of electric field maximum with a zero momentum. After determining the quantum final momentum distribution of tunnel ionized electrons we show that the two-step model fails to predict the correct final momentum. Accordingly we suggest how to correct the two-step model. Furthermore, we determine the instant at which tunnel ionization starts, which turns out to be different from the instant usually assumed. From determining the instant at which it is most probable for the electron to enter the tunneling barrier and the instant at which it exits we determine the most probable time spent under the barrier. Moreover, we apply a quantum clock approach in order to determine the duration of tunnel ionization. From the quantum clock we determine an average tunneling time which is different in magnitude and origin with respect to the most probable tunneling time. By defining a probability distribution of tunneling times using virtual detectors we relate both methods and explain the apparent discrepancy. The results found have in general an effect on the interpretation of experiments that measure the spectra of tunnel ionized electrons, and specifically on the calibration of the so called attoclock experiments, because models with imprecise assumptions are usually employed in order to interpret experimental results.

Quantum theory of tunneling

CERN Document Server

Razavy, Mohsen

2014-01-01

In this revised and expanded edition, in addition to a comprehensible introduction to the theoretical foundations of quantum tunneling based on different methods of formulating and solving tunneling problems, different semiclassical approximations for multidimensional systems are presented. Particular attention is given to the tunneling of composite systems, with examples taken from molecular tunneling and also from nuclear reactions. The interesting and puzzling features of tunneling times are given extensive coverage, and the possibility of measurement of these times with quantum clocks are critically examined. In addition by considering the analogy between evanescent waves in waveguides and in quantum tunneling, the times related to electromagnetic wave propagation have been used to explain certain aspects of quantum tunneling times. These topics are treated in both non-relativistic as well as relativistic regimes. Finally, a large number of examples of tunneling in atomic, molecular, condensed matter and ...

Does the graft-tunnel friction influence knee joint kinematics and biomechanics after anterior cruciate ligament reconstruction? A finite element study.

Science.gov (United States)

Wan, Chao; Hao, Zhixiu

2018-02-01

Graft tissues within bone tunnels remain mobile for a long time after anterior cruciate ligament (ACL) reconstruction. However, whether the graft-tunnel friction affects the finite element (FE) simulation of the ACL reconstruction is still unclear. Four friction coefficients (from 0 to 0.3) were simulated in the ACL-reconstructed joint model as well as two loading levels of anterior tibial drawer. The graft-tunnel friction did not affect joint kinematics and the maximal principal strain of the graft. By contrast, both the relative graft-tunnel motion and equivalent strain for the bone tunnels were altered, which corresponded to different processes of graft-tunnel integration and bone remodeling, respectively. It implies that the graft-tunnel friction should be defined properly for studying the graft-tunnel integration or bone remodeling after ACL reconstruction using numerical simulation.

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

International Nuclear Information System (INIS)

Lysenko, O; Novikov, N; Gontar, A; Grushko, V; Shcherbakov, A

2007-01-01

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

Distribution of tunnelling times for quantum electron transport

International Nuclear Information System (INIS)

Rudge, Samuel L.; Kosov, Daniel S.

2016-01-01

In electron transport, the tunnelling time is the time taken for an electron to tunnel out of a system after it has tunnelled in. We define the tunnelling time distribution for quantum processes in a dissipative environment and develop a practical approach for calculating it, where the environment is described by the general Markovian master equation. We illustrate the theory by using the rate equation to compute the tunnelling time distribution for electron transport through a molecular junction. The tunnelling time distribution is exponential, which indicates that Markovian quantum tunnelling is a Poissonian statistical process. The tunnelling time distribution is used not only to study the quantum statistics of tunnelling along the average electric current but also to analyse extreme quantum events where an electron jumps against the applied voltage bias. The average tunnelling time shows distinctly different temperature dependence for p- and n-type molecular junctions and therefore provides a sensitive tool to probe the alignment of molecular orbitals relative to the electrode Fermi energy.

Reciprocity theory of apertureless scanning near-field optical microscopy with point-dipole probes.

Science.gov (United States)

Esslinger, Moritz; Vogelgesang, Ralf

2012-09-25

Near-field microscopy offers the opportunity to reveal optical contrast at deep subwavelength scales. In scanning near-field optical microscopy (SNOM), the diffraction limit is overcome by a nanoscopic probe in close proximity to the sample. The interaction of the probe with the sample fields necessarily perturbs the bare sample response, and a critical issue is the interpretation of recorded signals. For a few specific SNOM configurations, individual descriptions have been modeled, but a general and intuitive framework is still lacking. Here, we give an exact formulation of the measurable signals in SNOM which is easily applicable to experimental configurations. Our results are in close analogy with the description Tersoff and Hamann have derived for the tunneling currents in scanning tunneling microscopy. For point-like scattering probe tips, such as used in apertureless SNOM, the theory simplifies dramatically to a single scalar relation. We find that the measured signal is directly proportional to the field of the coupled tip-sample system at the position of the tip. For weakly interacting probes, the model thus verifies the empirical findings that the recorded signal is proportional to the unperturbed field of the bare sample. In the more general case, it provides guidance to an intuitive and faithful interpretation of recorded images, facilitating the characterization of tip-related distortions and the evaluation of novel SNOM configurations, both for aperture-based and apertureless SNOM.