WorldWideScience
 
 
1

Scanning tunneling microscopic images and scanning tunneling spectra for coupled rectangular quantum corrals  

International Nuclear Information System (INIS)

Assuming that an electron confined by double ?-function barriers lies in a quasi-stationary state, we derived eigenstates and eigenenergies of the electron. Such an electron has a complex eigenenergy, and the imaginary part naturally leads to the lifetime of the electron associated with tunneling through barriers. We applied this point of view to the electron confined in a rectangular quantum corral (QC) on a noble metal surface, and obtained scanning tunneling microscopic images and a scanning tunneling spectrum consistent with experimental ones. We investigated the electron states confined in coupled QCs and obtained the coupled states constructed with bonding and anti-bonding states. Using those energy levels and wavefunctions we specified scanning tunneling microscope (STM) images and scanning tunneling spectra (STS) for the doubly and triply coupled QCs. In addition we pointed out the feature of resonant electron states associated with the same QCs at both ends of the triply coupled QCs.

2011-07-13

2

Scanning tunneling microscopic images and scanning tunneling spectra for coupled rectangular quantum corrals.  

Science.gov (United States)

Assuming that an electron confined by double ?-function barriers lies in a quasi-stationary state, we derived eigenstates and eigenenergies of the electron. Such an electron has a complex eigenenergy, and the imaginary part naturally leads to the lifetime of the electron associated with tunneling through barriers. We applied this point of view to the electron confined in a rectangular quantum corral (QC) on a noble metal surface, and obtained scanning tunneling microscopic images and a scanning tunneling spectrum consistent with experimental ones. We investigated the electron states confined in coupled QCs and obtained the coupled states constructed with bonding and anti-bonding states. Using those energy levels and wavefunctions we specified scanning tunneling microscope (STM) images and scanning tunneling spectra (STS) for the doubly and triply coupled QCs. In addition we pointed out the feature of resonant electron states associated with the same QCs at both ends of the triply coupled QCs. PMID:21690659

Mitsuoka, Shigenori; Tamura, Akira

2011-07-13

3

Scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

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.

Binnig, G.; Rohrer, H. (IBM Research Lab., Zurich (Switzerland))

1983-05-09

4

Tunneling spectra and superconducting gaps observed by scanning tunneling microscopy near the grain boundaries of FeSe0.3Te0.7 films  

Science.gov (United States)

We used scanning tunneling microscopy (STM) to study the tunneling spectra of FeSe0.3Te0.7 films with two orientations of the ab-planes and a connection ramp between them. We discovered that by pulsed laser deposition (PLD) method, the a- and b-axis of the FeSe0.3Te0.7 film deposited on an Ar-ion-milled magnesium oxide (MgO) substrate were rotated 45° with respect to those of MgO, whereas the a- and b-axis of the film grown on a pristine MgO substrate were parallel to those of MgO. With photolithography and this technique, we can prepare FeSe0.3Te0.7 films with two orientations on the same MgO substrate so that the connection between them forms a ramp at an angle of about 25° to the substrate plane. In the planar region, for either the 0° or 45° orientation, we observed tunneling spectra with a superconducting gap of about 5 meV and 1.78 meV, respectively. However, a much larger gap at about 18 meV was observed in the ramp region. Furthermore, we observed a small zero-bias conductance peak (ZBCP) inside the large gap at T = 4.3 K. The ZBCP becomes smaller with increasing temperature and disappeared at temperature above 7 K.

Lin, K. C.; Li, Y. S.; Shen, Y. T.; Wu, M. K.; Chi, C. C.

2013-12-01

5

Ultrafast scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

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

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

1995-09-01

6

Femtosecond scanning tunneling microscope  

Energy Technology Data Exchange (ETDEWEB)

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

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

1998-11-01

7

Josephson scanning tunneling microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2000-01-01

8

Scanning Tunneling Microscopy  

Science.gov (United States)

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

Consortium, The C.

2011-12-11

9

Photon scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

The Photon Scanning Tunneling Microscopy (PSTM) is the photon analogue of the electron Scanning Tunneling Microscope (STM). It uses the evanescent field due to the total internal reflection of a light beam in a Total Internal Reflection (TIR) prism. The sample, mounted on the base of the prism, modulates the evanescent field. A sharpened optical fiber probes this field, and the collected light is processed to generate an image of the topography and the chemical composition of the surface. We give, in this paper, a description of the microscope and discuss the influence of several parameters such as -- polarization of light, angle of incidence, shape of the end of the fiber -- on the resolution. Images of various samples -- glass samples, teflon spheres -- are presented. 8 refs., 7 figs.

Goudonnet, J.P.; Salomon, L.; De Fornel, F.; Chabrier, G. (Dijon Univ., 21 (France). Lab. de Physique du Solide); Warmack, R.J.; Ferrell, T.L. (Oak Ridge National Lab., TN (USA))

1990-01-01

10

Scanning tunneling microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A brief review of the state-of-the-art of scanning tunneling microscopy (STM) is presented with emphasis on materials problems. I shall discuss in particular the variety of materials, environrnents and temperatures that can be investigated. In addition to topographie studies, some examples of STM as local probe are given. It is proposed that STM be increasingly incorporated as a technique for investigation of real materials problems.

Gimzewski, J.

1993-01-01

11

Photon scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

An optical tunneling microscope is presented that operates in exactly the same way as the electron scanning tunneling microscope (ESTM). It takes advantage of evanescent fields generated by the total internal reflection (TIR) of light at the interface between materials of different optical densities. The photon scanning tunneling microscope (PSTM) employs an optically conducting probe tip to map spatial variations in the evanescent and scattered field intensity distributions adjacent to a sample surface, which forms or is placed on the TIR surface. These variations are due to the local topography, morphology, and optical activity of the surface and form the basis of imaging. Evanescent field theory is discussed and the evanescent field intensity as a function of surface-probe separation is calculated using several probe tip models. After a description of PSTM construction and operation, evanescent field intensity measurements are shown to agree with the model calculations. PSTM images of various sample surfaces demonstrate subwavelength resolution exceeding that of conventional optical microscopy, especially in the vertical dimension. Limitations and interpretation of PSTM images are discussed as well as the PSTMs applicability to other forms of surface analysis.

Reddick, R.C.; Warmack, R.J.; Chilcott, D.W.; Sharp, S.L.; Ferrell, T.L. (Health and Safety Research Division, Oak Ridge National Laboratory, Oak Ridge, TN (USA) Department of Physics and Astronomy, University of Tennessee, Knoxville, TN (USA))

1990-12-01

12

Scanning tunnel microscopy  

International Nuclear Information System (INIS)

The principles of operation of a scanning tunnel microscope (STM) and an atomic forces scanning microscope (AFSM) widely used for studying the surface of solid bodies with atomic resolution, are described. The STM basic element is a piesoelectric scanner, where the transverse piesoeffect is used. Three versions of the piesoelectric scanner design, which can move along three coordinates, are considered. The results of studies of surfaces of graphite, silicon and hallium arsenide, as well as large molecules and biological structures using STM are given. One of the most successful STM designs is a microscope based on atomic forces. It is a tandem of two piesoceramic scanners, one of them carrying a sample and the other one - the STM point. It is a great advantage that the AFSM can be used in nanometry and tests of dielectrics

1989-01-01

13

Scanning tunneling microscope nanoetching method  

Energy Technology Data Exchange (ETDEWEB)

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

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

1990-01-01

14

Introduction to scanning tunneling microscopy  

CERN Document Server

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.

Chen, C Julian

2008-01-01

15

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-12-15

16

Efficient and reliable method for the simulation of scanning tunneling images and spectra with local basis sets  

CERN Document Server

Based on Bardeen's perturbative approach to tunneling, we have found an expression for the current between tip and sample, which can be efficiently coded in order to perform fast ab initio simulations of STM images. Under the observation that the potential between the electrodes should be nearly flat at typical tunnel gaps, we have addressed the difficulty in the computation of the tunneling matrix elements by considering a vacuum region of constant potential delimited by two surfaces (each of them close to tip and sample respectively), then propagating tip and sample wave functions by means of the vacuum Green's function, to finally obtain a closed form in terms of convolutions. The current is then computed for every tip-sample relative position and for every bias voltage in one shot. The electronic structure of tip and sample is calculated at the same footing, within density functional theory, and independently. This allows us to carry out multiple simulations for a given surface with a database of differen...

Paz, O; Paz, Oscar; Soler, Jose M.

2006-01-01

17

Energy dissipation processes in scanning tunneling microscopy  

International Nuclear Information System (INIS)

Energy dissipation associated with assisted tunneling processes in scanning tunneling microscopy is analyzed and compared with the normal tunnel current. We find that, for high voltages, greater than one volt, the tunneling processes associated with electron-hole pair excitation control the increase in temperature at the microscope's interface

1986-08-15

18

Rapid Measurement of Inelastic Electron Tunneling Spectra.  

Science.gov (United States)

Inelastic electron tunneling spectroscopy is a versatile, high-sensitivity technique for obtaining vibrational spectra of absorbates on oxide surfaces, especially aluminum oxide. The theory and practice of tunneling spectroscopy have been reviewed extensi...

G. J. Gajda W. H. Weinberg

1985-01-01

19

Scanning Tunneling Spectroscopy in Anisotropic s-Wave Superconductors  

Science.gov (United States)

We discuss Scanning Tunneling Microscopy and Spectroscopy (STM/S) measurements at very low temperatures in single crystals of the non magnetic borocarbide superconductors RNi2B2C (R=Y, Lu, Tc=15.5 and 16.5 K) and in MgB2. The tunneling spectra in some regions of the surface show a clear reduction of the anisotropy of the superconducting gap.

Suderow, H.; Rodrigo, J. G.; Martinez-Samper, P.; Vieira, S.; Brison, J. P.; Lejay, P.; Canfield, P. C.; Lee, S. I.; Tajima, S.

20

Fluctuation Dominated Josephson Tunneling with a Scanning Tunneling Microscope  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We demonstrate Josephson tunneling in vacuum tunnel junctions formed between a superconducting scanning tunneling microscope tip and a Pb film, for junction resistances in the range 50-300 k$\\Omega$. We show that the superconducting phase dynamics is dominated by thermal fluctuations, and that the Josephson current appears as a peak centered at small finite voltages. In the presence of microwave fields (f=15.0 GHz) the peak decreases in magnitude and shifts to higher voltage...

Naaman, O.; Teizer, W.; Dynes, R. C.

2001-01-01

 
 
 
 
21

Single-electron tunneling. [Microwave scanning tunneling microscope  

Energy Technology Data Exchange (ETDEWEB)

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

Ruggiero, S.T.

1993-01-01

22

Thermovoltages in vacuum tunneling investigated by scanning tunneling microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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.

Hoffmann, D. H.; Rettenberger, Armin; Grand, Jean Yves; La?uger, K.; Leiderer, Paul; Dransfeld, Klaus; Mo?ller, Rolf

1995-01-01

23

Role of Inelastic Tunneling through the Barrier in Scanning Tunneling Microscope Experiments on Cuprates  

CERN Document Server

The tunneling path between the CuO2-layers in cuprate superconductors and a scanning tunneling microscope tip passes through a barrier made from other oxide layers. This opens up the possibility that inelastic processes in the barrier contribute to the tunneling spectra. Such processes cause one or possibly more peaks in the second derivative current-voltage spectra displaced by phonon energies from the density of states singularity associated with superconductivity. Calculations of inelastic processes generated by apical O-phonons show good qualitative agreement with recent experiments reported by Lee et al.[1]. Further tests to discriminate between these inelastic processes and coupling to planar phonons are proposed.

Pilgram, S; Sigrist, M

2006-01-01

24

Scanning tunneling spectroscopy of Pb thin films  

Energy Technology Data Exchange (ETDEWEB)

The present thesis deals with the electronic structure, work function and single-atom contact conductance of Pb thin films, investigated with a low-temperature scanning tunneling microscope. The electronic structure of Pb(111) thin films on Ag(111) surfaces is investigated using scanning tunneling spectroscopy (STS). Quantum size effects, in particular, quantum well states (QWSs), play a crucial role in the electronic and physical properties of these films. Quantitative analysis of the spectra yields the QWS energies as a function of film thickness, the Pb bulk-band dispersion in {gamma}-L direction, scattering phase shifts at the Pb/Ag interface and vacuum barrier as well as the lifetime broadening at anti {gamma}. The work function {phi} is an important property of surfaces, which influences catalytic reactivity and charge injection at interfaces. It controls the availability of charge carriers in front of a surface. Modifying {phi} has been achieved by deposition of metals and molecules. For investigating {phi} at the atomic scale, scanning tunneling microscopy (STM) has become a widely used technique. STM measures an apparent barrier height {phi}{sub a}, which is commonly related to the sample work function {phi}{sub s} by: {phi}{sub a}=({phi}{sub s}+{phi}{sub t}- vertical stroke eV vertical stroke)/2, with {phi}{sub t} the work function of the tunneling tip, V the applied tunneling bias voltage, and -e the electron charge. Hence, the effect of the finite voltage in STM on {phi}{sub a} is assumed to be linear and the comparison of {phi}{sub a} measured at different surface sites is assumed to yield quantitative information about work function differences. Here, the dependence of {phi}{sub a} on the Pb film thickness and applied bias voltage V is investigated. {phi}{sub a} is found to vary significantly with V. This bias dependence leads to drastic changes and even inversion of contrast in spatial maps of {phi}{sub a}, which are related to the QWSs in the Pb films. It is shown how accurate quantitative information about work function differences can be obtained and how these differences depend on the QWSs in the Pb thin films. The electron transport properties and mechanical characteristics of atom-sized metallic contacts are of fundamental interest in view of future nanoscale device technologies. Proximity probes like STM, metal break junctions, and related techniques, together with computational methods for simulating tip-sample interactions, have made it possible to address this question. While the importance of atomic structure and bonding for transport through single-atom junctions has repeatedly been emphasized, investigations of the influence of subsurface bonding properties have been rare. Here, the contact formation of a STM tip approaching Pb(111) thin films supported on Ag(111) substrates is investigated. Contacts on monolayer films are found to differ from contacts made on thicker Pb films. This behavior is explained in terms of different vertical bonding-strengths due to a charge-transfer induced surface dipole. Furthermore, the single-atom contact conductance on Pb(111) films beyond the first monolayer is determined. It is shown that analyses based on hitherto widely used conventional conductance histograms may overestimate the single-atom contact conductance by as much as 20%. (orig.)

Becker, Michael

2010-12-13

25

Fluctuation Dominated Josephson Tunneling with a Scanning Tunneling Microscope  

Energy Technology Data Exchange (ETDEWEB)

We demonstrate Josephson tunneling in vacuum tunnel junctions formed between a superconducting scanning tunneling microscope tip and a Pb film, for junction resistances in the range 50--300 k{Omega} . We show that the superconducting phase dynamics is dominated by thermal fluctuations, and that the Josephson current appears as a peak centered at small finite voltage. In the presence of microwave fields (f=15.0 GHz) the peak decreases in magnitude and shifts to higher voltages with increasing rf power, in agreement with theory.

Naaman, O.; Teizer, W.; Dynes, R. C.

2001-08-27

26

Nonlinear femtosecond laser induced scanning tunneling microscopy  

Science.gov (United States)

We demonstrate ultrafast laser driven nonlinear scanning tunneling microscopy (STM), under ambient conditions. The design is an adaptation of the recently introduced cross-polarized double beat method, whereby z-polarized phase modulated fields are tightly focused at a tunneling junction consisting of a sharp tungsten tip and an optically transparent gold film as substrate. We demonstrate the prerequisites for ultrafast time-resolved STM through an operative mechanism of nonlinear laser field-driven tunneling. The spatial resolution of the nonlinear laser driven STM is determined by the local field intensity. Resolution of 0.3 nm-10 nm is demonstrated for the intensity dependent, exponential tunneling range. The demonstration is carried out on a junction consisting of tungsten tip and gold substrate. Nano-structured gold is used for imaging purposes, to highlight junction plasmon controlled tunneling in the conductivity limit.

Dey, Shirshendu; Mirell, Daniel; Perez, Alejandro Rodriguez; Lee, Joonhee; Apkarian, V. Ara

2013-04-01

27

Scanning tunneling spectroscopy of single DNA molecules.  

Science.gov (United States)

We briefly present the results of recent experiments of transverse scanning tunneling spectroscopy of homogeneous poly(dG)-poly(dC) DNA molecules and discuss them in the light of theoretical investigation. A semiempirical theoretical model is adopted to describe the transverse tunneling current across a DNA molecule placed between a metallic gold substrate and a metallic STM tip. We show that the main trends in the positions and relative magnitudes of the conductance peaks can be explained by a minimal model of a double tunnel junction with the molecule-electrode couplings and the applied voltage explicitly taken into account. PMID:19572615

Ryndyk, Dmitry A; Shapir, Errez; Porath, Danny; Calzolari, Arrigo; Di Felice, Rosa; Cuniberti, Gianaurelio

2009-07-28

28

Shifts and Dips in Inelastic Electron Tunneling Spectra Due to the Tunnel Junction Environment.  

Science.gov (United States)

In general, the tunnel junction environment has proved to be surprisingly benign; tunneling spectra of molecules included within tunnel junctions are similar to infrared and Raman spectra of molecules not covered by a metal electrode. Peak shifts have bee...

A. Bayman P. K. Hansma W. C. Kaska

1981-01-01

29

Scanning Tunneling Spectroscope Use in Electrocatalysis Testing  

Directory of Open Access Journals (Sweden)

Full Text Available The relationship between the electrocatalytic properties of an electrode and its ability to transfer electrons between the electrode and a metallic tip in a scanning tunneling microscope (STM is investigated. The alkaline oxygen evolution reaction (OER was used as a test reaction with four different metallic glasses, Ni78Si8B14, Ni70Mo20Si5B5, Ni58Co20Si10B12, and Ni25Co50Si15B10, as electrodes. The electrocatalytic properties of the electrodes were determined. The electrode surfaces were then investigated with an STM. A clear relationship between the catalytic activity of an electrode toward the OER and its tunneling characteristics was found. The use of a scanning tunneling spectroscope (STS in electrocatalytic testing may increase the efficiency of the optimization of electrochemical processes.

Turid Knutsen

2010-06-01

30

Scanning tunneling microscopy studies on optical disc  

International Nuclear Information System (INIS)

The areas with and without data stampers are all observed carefully using scanning tunneling microscope (STM). Three-dimensional images of the disc surface clearly demonstrate the period, depth of the grooves and the shape of data stampers. Some phenomena of STM imaging are also discussed

1994-11-01

31

New directions in scanning-tunneling microscopy  

International Nuclear Information System (INIS)

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

1989-09-01

32

Tunneling spectra simulation of interacting Majorana wires  

Science.gov (United States)

Recent tunneling experiments on InSb hybrid superconductor-semiconductor devices have provided hope for a stabilization of Majorana edge modes in a spin-orbit quantum wire subject to a magnetic field and superconducting proximity effect. Connecting the experimental scenario with a microscopic description poses challenges of a different kind, such as accounting for the effect of interactions on the tunneling properties of the wire. We develop a density matrix renormalization group (DMRG) analysis of the tunneling spectra of interacting Majorana chains, which we explicate for the Kitaev chain model. Our DMRG approach allows us to calculate the spectral function down to zero frequency, where we analyze how the Majorana zero-bias peak is affected by interactions. For topological phase transitions between the topological and trivial superconducting phase in the Majorana wire, the bulk gap closure generically affects the proximity peaks and the Majorana peak.

Thomale, Ronny; Rachel, Stephan; Schmitteckert, Peter

2013-10-01

33

Tunneling Spectra of Individual Magnetic Endofullerene Molecules  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The manipulation of single magnetic molecules may enable new strategies for high-density information storage and quantum-state control. However, progress in these areas depends on developing techniques for addressing individual molecules and controlling their spin. Here we report success in making electrical contact to individual magnetic N@C60 molecules and measuring spin excitations in their electron tunneling spectra. We verify that the molecules remain magnetic by observ...

Grose, Jacob E.; Tam, Eugenia S.; Timm, Carsten; Scheloske, Michael; Ulgut, Burak; Parks, Joshua J.; Abruna, Hector D.; Harneit, Wolfgang; Ralph, Daniel C.

2008-01-01

34

PREFACE: Time-resolved scanning tunnelling microscopy Time-resolved scanning tunnelling microscopy  

Science.gov (United States)

Scanning tunnelling microscopy has revolutionized our ability to image, manipulate, and investigate solid surfaces on the length scale of individual atoms and molecules. The strength of this technique lies in its imaging capabilities, since for many scientists 'seeing is believing'. However, scanning tunnelling microscopy also suffers from a severe limitation, namely its poor time resolution. Recording a scanning tunnelling microscopy image typically requires a few tens of seconds for a conventional scanning tunnelling microscope to a fraction of a second for a specially designed fast scanning tunnelling microscope. Designing and building such a fast scanning tunnelling microscope is a formidable task in itself and therefore, only a limited number of these microscopes have been built [1]. There is, however, another alternative route to significantly enhance the time resolution of a scanning tunnelling microscope. In this alternative method, the tunnelling current is measured as a function of time with the feedback loop switched off. The time resolution is determined by the bandwidth of the IV converter rather than the cut-off frequency of the feedback electronics. Such an approach requires a stable microscope and goes, of course, at the expense of spatial information. In this issue, we have collected a set of papers that gives an impression of the current status of this rapidly emerging field [2]. One of the very first attempts to extract information from tunnel current fluctuations was reported by Tringides' group in the mid-1990s [3]. They showed that the collective diffusion coefficient can be extracted from the autocorrelation of the time-dependent tunnelling current fluctuations produced by atom motion in and out of the tunnelling junction. In general, current-time traces provide direct information on switching/conformation rates and distributions of residence times. In the case where these processes are thermally induced it is rather straightforward to map out the potential landscape of the system (often a molecule or an atom) under study [4, 5]. However, the dynamical processes might also be induced by the tunnelling process itself [6, 7]. In the field of molecular science, excited single molecule experiments have been especially performed [8]. As a nice example, we refer to the work of Sykes' group [9] on thioether molecular rotors. In addition, several groups explore the possibility of combining time-resolved scanning tunnelling microscopy with optical techniques [10, 11]. Although the majority of studies that have been performed so far focus on rather simple systems under nearly ideal and well-defined conditions, we anticipate that time-resolved scanning tunnelling microscopy can also be applied in other research areas, such as biology and soft condensed matter, where the experimental conditions are often less ideal. We hope that readers will enjoy this collection of papers and that it will trigger them to further explore the possibilities of this simple, but powerful technique. References [1] Besenbacher F, Laegsgaard E and Stengaard I 2005 Mater. Today 8 26 [2] van Houselt A and Zandvliet H J W 2010 Rev. Mod. Phys. 82 1593 [3] Tringides M C and Hupalo M 2010 J. Phys.: Condens. Matter 22 264002 [4] Ronci F, Colonna S, Cricenti A and Le Lay G 2010 J. Phys.: Condens. Matter 22 264003 [5] van Houselt A, Poelsema B and Zandvliet H J W 2010 J. Phys.: Condens. Matter 22 264004 [6] Sprodowski C, Mehlhorn M and Morgenstern K 2010 J. Phys.: Condens. Matter 22 264005 [7] Saedi A, Poelsema B and Zandvliet H J W 2010 J. Phys.: Condens. Matter 22 264007 [8] Sloan P A 2010 J. Phys.: Condens. Matter 22 264001 [9] Jewell A D, Tierney H L, Baber A E, Iski E V, Laha M M and Sykes E C H 2010 J. Phys.: Condens. Matter 22 264006 [10] Riedel D 2010 J. Phys.: Condens. Matter 22 264009 [11] Terada Y, Yoshida S, Takeuchi O and Shigekawa H 2010 J. Phys.: Condens. Matter 22 264008

Zandvliet, Harold J. W.; Lin, Nian

2010-07-01

35

A compact low temperature scanning tunneling microscope  

Energy Technology Data Exchange (ETDEWEB)

We describe the design and fabrication of a compact Low Temperature Scanning Tunneling Microscope (LT-STM) together with a dipper cryostat for cooling the STM down to liquid helium temperatures. The STM, based on the piezo-tube walker as coarse approach mechanism, is suspended inside a cryostat vacuum can using three soft helical springs. The can is dipped into a liquid helium storage container for cooling the STM. Its compact size makes it less susceptible to mechanical vibrations and so the STM works with atomic resolution with a simple spring suspension. We demonstrate the performance of this STM for atomic resolution imaging and tunneling spectroscopy by observing the 3 x3 charge modulation and the energy gap in the Charge Density Wave (CDW) phase of 2H-NbSe{sub 2} at liquid helium temperatures.

Gupta, Anjan Kumar; Sinha, Jaivardhan; Choudhary, Shyam Kumar; Singh, Udai Raj [Department of Physics, Indian Institute of Technology Kanpur, Kanpur 208016 (India)], E-mail: shyamkc@iitk.ac.in

2009-02-01

36

A compact low temperature scanning tunneling microscope  

International Nuclear Information System (INIS)

We describe the design and fabrication of a compact Low Temperature Scanning Tunneling Microscope (LT-STM) together with a dipper cryostat for cooling the STM down to liquid helium temperatures. The STM, based on the piezo-tube walker as coarse approach mechanism, is suspended inside a cryostat vacuum can using three soft helical springs. The can is dipped into a liquid helium storage container for cooling the STM. Its compact size makes it less susceptible to mechanical vibrations and so the STM works with atomic resolution with a simple spring suspension. We demonstrate the performance of this STM for atomic resolution imaging and tunneling spectroscopy by observing the 3 x3 charge modulation and the energy gap in the Charge Density Wave (CDW) phase of 2H-NbSe2 at liquid helium temperatures.

2009-02-01

37

Superconducting phonon spectroscopy using a low-temperature scanning tunneling microscope  

Science.gov (United States)

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

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

1989-01-01

38

Simulation of scanning tunneling spectroscopy of supported carbon nanotubes  

International Nuclear Information System (INIS)

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

2000-07-15

39

Laser lithography by photon scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

We have investigated the possibility of using a photon scanning tunneling microscopy (PSTM) for laser lithography. A contrast enhancement material (CEM) is coated onto a sample slide and coupled to the prism of a PSTM. The CEM becomes transparent above a laser (HeCd at a wavelength of 442 nm) intensity threshold attained due to the proximity of the probe tip. The same surface can then be inspected using the given experimental configuration by replacing the HeCd laser line with a non-exposing 633-nm HeNe laser line. Direct patterns can be produced by varying the exposure time and the shape of the probe tip.

Lee, I.; Warmack, R.J.; Ferrell, T.L. (Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831-6123 (United States))

1993-10-10

40

Laser lithography by photon scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

We have investigated the possibility of using a photon scanning tunneling microscope (PSTM) for laser lithography. A contrast enhancement material (CEM) is coated onto a sample slide and coupled to the prism of a PSTM. The CEM becomes transparent above a laser (HeCd at a wavelength of 442 nm) intensity threshold attained due to the proximity of the probe tip. The same surface can then be inspected using the given experimental configuration by replacing the HeCd laser line with a non-exposing 633-nm HeNe laser line. Direct patterns can be produced by varying the exposure time and the shape of the probe tip.

Lee, I.; Warmack, R.J.; Ferrell, T.L.

1993-06-01

 
 
 
 
41

COMBINED FIELD ION AND SCANNING TUNNELING MICROSCOPE  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Realizing the importance of characterizing a STM probe tip on an atomic scale, we have constructed a new instrument which combines a field ion microscope and scanning tunneling microscope. A complete STM set-up, which is similar to the one developed by Demuth, is mounted on an 8" O.D. flange and a FIM set-up is mounted on a 10" O.D. flange. FI images of the STM probe tip are observed using a 2" O.D. chevron channelplate-image intensifier screen assembly with liquid nitrogen cooling. A field n...

Sakurai, T.; Hashizurne, T.; Kamiya, I.; Hasegawa, Y.; Sakai, A.; Kobayashi, A.; Matsui, J.; Takahashi, S.; Kono, E.; Watanabe, H.

1987-01-01

42

Scanning tunneling microscopy of titanium silicide nanoislands  

International Nuclear Information System (INIS)

In this work, ultrathin titanium silicide layers were grown on Si(1 1 1) substrates, with the aim to stimulate spontaneous growth of nanostructures by self-assembly. Scanning tunneling microscopy was used as a primary tool for a close, in situ monitoring of the related surface processes. This method enabled a detailed observation of the formation and subsequent evolution of the silicide nanoislands as a function of deposition parameters and annealing treatments. Nanoisland shape and, possibly, phase transformations were analyzed in real time and space with atomic, or near atomic resolution. The results of these measurements are discussed, and plausible explanations offered

2004-11-15

43

Scanning tunneling microscopy of titanium silicide nanoislands  

Energy Technology Data Exchange (ETDEWEB)

In this work, ultrathin titanium silicide layers were grown on Si(1 1 1) substrates, with the aim to stimulate spontaneous growth of nanostructures by self-assembly. Scanning tunneling microscopy was used as a primary tool for a close, in situ monitoring of the related surface processes. This method enabled a detailed observation of the formation and subsequent evolution of the silicide nanoislands as a function of deposition parameters and annealing treatments. Nanoisland shape and, possibly, phase transformations were analyzed in real time and space with atomic, or near atomic resolution. The results of these measurements are discussed, and plausible explanations offered.

Goldfarb, I.; Grossman, S.; Cohen-Taguri, G.; Levinshtein, M

2004-11-15

44

Scanning tunnelling microscopy of bilayer manganites  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This thesis describes experimental work carried out on bilayer manganites with the general composition R_{2-2x}A_{1+2x}Mn_2O_7, where R is a trivalent rare earth cation and A is a divalent alkaline-earth cation. Experiments have been carried out primarily using Scanning Tunnelling Microscopy (STM) and Spectroscopy (STS); bulk electrical transport, MPMS and LEED measurements have also been made. The primary results are obtained from single crystal samples of PrSr_2Mn_2O_7. This compound pro...

Bryant, B. E. M.

2010-01-01

45

Scanning tunneling spectroscopy of epitaxial graphene nanoisland on Ir(111)  

Science.gov (United States)

Scanning tunneling spectroscopy (STS) was used to measure local differential conductance (dI/dV) spectra on nanometer-size graphene islands on an Ir(111) surface. Energy resolved dI/dV maps clearly show a spatial modulation, which we ascribe to a modulated local density of states due to quantum confinement. STS near graphene edges indicates a position dependence of the dI/dV signals, which suggests a reduced density of states near the edges of graphene islands on Ir(111).

2012-01-01

46

A millikelvin scanning tunneling microscope with two independent scanning systems  

CERN Document Server

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

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

2013-01-01

47

Measuring voltage transients with an ultrafast scanning tunneling microscope  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

2006-01-01

48

Scanning tunneling microscopy/spectroscopy in iron-pnictide superconductor  

International Nuclear Information System (INIS)

In order to study the electronic state and the mechanism of the superconductivity in high-Tc iron-based pnictide superconductors, scanning tunneling microscopy/spectroscopy (STM/STS) experiments have been performed on Ba(Fe0.93Co0.07)2As2 single crystals (Tc?24K). The STM topography on the cleaved surface shows the one-dimensional stripe-like structures with a periodicity of ?7.97 A which corresponds to twice the As-As (or Ba-Ba) distance. The tunneling spectra shows characteristic features of the superconductivity with the clear coherence peak and the superconducting energy gap 2??15.2meV. The estimated gap ratio 2?/kBTc?7.3 is about two times larger than the value of the weak coupling s-wave BCS superconductors, suggesting the unconventional superconductivity.

2010-12-01

49

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

CERN Document Server

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

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

2006-01-01

50

Identifying configuration and orientation of adsorbed molecules by inelastic electron tunneling spectra.  

Science.gov (United States)

Scanning tunneling microscopy (STM) topographical images and inelastic electron tunneling spectra (IETS) of a cis-2-butene molecule adsorbed on a Pd(110) surface have been simulated by first-principles calculations. Calculations have eliminated the ambiguity between the STM image and the adsorption orientation caused by the symmetry of the system and local chemical environment. A combination of STM images and IETS spectra has been shown to be particularly useful in determining the configuration of the molecule on the surface. PMID:20707581

Ren, Hao; Yang, Jinlong; Luo, Yi

2010-08-14

51

Scanning tunneling spectroscopy in MgB2.  

Science.gov (United States)

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

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

2001-05-01

52

Scanning tunnel microscopy of semiconductor nanostructures  

International Nuclear Information System (INIS)

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)

1997-01-01

53

Vibrational features in inelastic electron tunneling spectra  

CERN Document Server

A theoretical analysis of inelastic electron tunneling spectroscopy (IETS) experiments conducted on molecular junctions are presented, where the second derivative of the current with respect to voltage is usually plotted as a function of applied bias. Within the nonperturbative computational scheme, adequate for arbitrary parameters of the model, we consider the virtual conduction process in the off-resonance region. Here we study the influence of few crucial factors on the IETS spectra: the strength of the vibronic coupling, the phonon energy, and the device working temperature. It was also shown that weak asymmetry in the IETS signal with respect to bias polarity is obtained as a result of strongly asymmetric connection with the electrodes.

Walczak, K

2007-01-01

54

Vibrational features in inelastic electron tunneling spectra  

International Nuclear Information System (INIS)

A theoretical analysis of inelastic electron tunneling spectroscopy (IETS) experiments conducted on molecular junctions is presented, where the second derivative of the current with respect to voltage is usually plotted as a function of applied bias. Within the nonperturbative computational scheme, adequate for arbitrary parameters of the model, we consider the virtual conduction process in the off-resonance region. Here we study the influence of few crucial factors on the IETS spectra: the strength of the vibronic coupling, the phonon energy, and the device working temperature. It was also shown that weak asymmetry in the IETS signal with respect to bias polarity is obtained as a result of strongly asymmetric connection with the electrodes

2007-03-06

55

STM tunnelling spectroscopy in MgB2 thin films: the role of band structure in tunnelling spectra  

International Nuclear Information System (INIS)

A very peculiar feature of the recently discovered superconductor MgB2 is the multigap nature of the superconducting state, which is now commonly accepted in the scientific community and confirmed by a large number of experiments. We report a systematic scanning tunnelling spectroscopy (STS) study performed on high quality thin films of MgB2. Electron microscopy images and STM topography together with the STS investigation allow a direct correlation between tunnelling direction and the observed tunnelling spectra, confirming that the two-gap state is intrinsic to MgB2

2004-05-01

56

Measuring voltage transients with an ultrafast scanning tunneling microscope  

DEFF Research Database (Denmark)

We use an ultrafast scanning tunneling microscope to resolve propagating voltage transients in space and time. We demonstrate that the previously observed dependence of the transient signal amplitude on the tunneling resistance was only caused by the electrical sampling circuit. With a modified circuit, where the tunneling tip is directly connected to the current amplifier of the scanning tunneling microscope, this dependence is eliminated. Ail results can be explained with coupling through the geometrical capacitance of the tip-electrode junction. By illuminating the current-gating photoconductive switch with a rigidly attached fiber, the probe is scanned without changing the probe characteristics. (C) 1997 American Institute of Physics.

Keil, Ulrich Dieter Felix; Jensen, Jacob Riis

1997-01-01

57

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

International Nuclear Information System (INIS)

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

1994-01-01

58

Regular Scanning Tunneling Microscope Tips can be Intrinsically Chiral  

International Nuclear Information System (INIS)

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.

2011-01-07

59

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

Science.gov (United States)

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. PMID:24093277

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

2013-09-20

60

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

International Nuclear Information System (INIS)

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

1981-09-01

 
 
 
 
61

Bulk Cr tips for scanning tunneling microscopy and spin-polarized scanning tunneling microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A simple, reliable method for preparation of bulk Cr tips for Scanning Tunneling Microscopy (STM) is proposed and its potentialities in performing high-quality and high-resolution STM and Spin Polarized-STM (SP-STM) are investigated. Cr tips show atomic resolution on ordered surfaces. Contrary to what happens with conventional W tips, rest atoms of the Si(111)-7x7 reconstruction can be routinely observed, probably due to a different electronic structure of the tip apex. SP-S...

Bassi, A. Li; Casari, C. S.; Cattaneo, D.; Donati, F.; Foglio, S.; Passoni, M.; Bottani, C. E.; Biagioni, P.; Brambilla, A.; Finazzi, M.; Ciccacci, F.; Duo, L.

2007-01-01

62

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

Energy Technology Data Exchange (ETDEWEB)

A low-temperature scanning tunneling microscope (STM) was used to investigate the adsorption state of a single methyl isocyanide (MeNC) molecule on the Pt(111) surface at 4.7 K. We found that MeNC was resolved as a round-shaped protrusion in the STM image. The STM image of paired MeNC is highly protruded in comparison with that of isolated MeNC due to the charge transfer from Pt to MeNC. Inelastic electron tunneling spectroscopy with the STM system (STM-IETS) was also employed in order to reveal the adsorption state of individual MeNC molecules on Pt(111). The STM-IETS spectrum of MeNC exhibits peaks at 8, 48 and 375 mV. Referring to the vibrational spectra reported previously, we assigned these peaks to the frustrated translation mode, PtC stretching mode and CH{sub 3} stretching mode, respectively. The absence of other vibrational modes could be due to a reduction of the elastic tunneling current.

Katano, Satoshi [Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Kim, Yousoo; Hori, Masafumi; Kawai, Maki [Surface Chemistry Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 Japan (Japan); Trenary, Michael, E-mail: maki@riken.j, E-mail: skatano@riec.tohoku.ac.j [Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607-7061 (United States)

2010-06-01

63

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

International Nuclear Information System (INIS)

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

2010-06-01

64

Effective Background Removal Technique for Inelastic Electron Tunneling Spectra.  

Science.gov (United States)

Progress has been made in a number of areas. First, further improvements have been made in the measurement of inelastic electron tunneling spectra. Second, molecular beam scattering has been employed in out continuing investigation of the activated absorp...

G. J. Gajda W. H. Weinberg

1985-01-01

65

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

CERN Multimedia

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

Howald, C; Kapitulnik, A

2001-01-01

66

Scanning tunneling spectroscopy on the novel superconductor CaC6.  

Science.gov (United States)

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

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

2006-08-18

67

Observation of spin-polarized tunneling by scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

The tunneling magnetoresistance (TMR) in ferromagnet-vacuum-ferromagnet junction was studied by using an STM setup. After in situ cleaning of both of two ferromagnetic electrodes, up to 20% of TMR was observed. Such a signal was not observed for air gap nor nonmagnetic electrode. This technique is suitable for basic research of the TMR effect.

Kawagoe, Takeshi E-mail: tkawagoe@jrcat.or.jp; Suzuki, Yoshishige; Yuasa, Shinji

2002-02-01

68

Obtaining absolute acoustic spectra in an aerodynamic wind tunnel  

Science.gov (United States)

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

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

2011-05-01

69

Scanning tunneling microspectroscopy of solids and surfaces  

International Nuclear Information System (INIS)

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

1990-01-01

70

Scanning tunnelling spectroscopy of single molecule on a semiconductor surface  

Science.gov (United States)

Scanning tunnelling spectroscopy was performed on 1,3-cyclohexadiene molecules on Si(100) surface at 5K. Degenerated N-type semiconductor and platinum covered tungsten tips were used. For the first time a vibrational spectrum of chemisorbed molecule on semiconductor surface was obtained. The probe induced perturbations of the molecule electronic density of states and its vibrational properties were also investigated. Transition from tunnelling to contact regime between the probe and the molecule was successfully monitored.

Naydenov, Borislav; Ryan, Peter; Teague, Lucile; Boland, John

2006-03-01

71

The effect of the top metal electrode on tunneling spectra  

International Nuclear Information System (INIS)

We report experiments on the effect of the top metal electrode on the vibrational spectra of molecules adsorbed on metal particles within tunnel junctions. We find differences in the tunneling spectrum of CO bonded to iron particles with different top metal electrodes. The hydrocarbon vibrations of methyl isocyanide bonded to rhodium particles are not shifted due to different top metal electrodes. However, we find anomalies concerning intensities. Specifically for methyl isocyanide the N identical C stretching mode appears as a dip in the tunneling spectrum. (orig.)

1981-08-25

72

Tunneling spectra of layered strongly correlated d-wave superconductors  

CERN Document Server

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

Wen, T C R X G

2005-01-01

73

Characterization of light emission from subphthalocyanine monolayers using scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

Monolayers of subphthalocyanine were prepared by molecular beam epitaxy and self-assembled depositions on the Au (111) surface. Light emission from the monolayers was measured by photoexcitation as well as tunneling current excitation using scanning tunneling microscopy under ultrahigh vacuum. The photoexcited spectra of the monolayers deposited by both methods exhibited the fluorescence bands of {pi}-electronic transition of the subphthalocyanine macrocycle although their lifetime was very shortened due to quenching by the Au surface. The tunneling induced emission was taken from the self-assembled monolayers in which the subphthalocyanine molecules were chemically bound onto the surface by alkylthio substituents. The observed spectra were ascribed to the radiative decay of tip-induced surface plasmon of Au. The molecules in the self-assembled monolayers shifted the emission peak due to modification of the dielectric property and distance between the tip and surface.

Yanagi, Hisao [Faculty of Engineering, Kobe University, Rokkodai, Nada-ku, Kobe 657-8501 (Japan)]. E-mail: yanagi@kobe-u.ac.jp; Mukai, Hiroko [Faculty of Engineering, Kobe University, Rokkodai, Nada-ku, Kobe 657-8501 (Japan); Nair, Meenakshi [Venture Business Laboratory, Kobe University, Rokkodai, Nada-ku, Kobe 657-8501 (Japan)

2006-03-21

74

Characterization of light emission from subphthalocyanine monolayers using scanning tunneling microscopy  

International Nuclear Information System (INIS)

Monolayers of subphthalocyanine were prepared by molecular beam epitaxy and self-assembled depositions on the Au (111) surface. Light emission from the monolayers was measured by photoexcitation as well as tunneling current excitation using scanning tunneling microscopy under ultrahigh vacuum. The photoexcited spectra of the monolayers deposited by both methods exhibited the fluorescence bands of ?-electronic transition of the subphthalocyanine macrocycle although their lifetime was very shortened due to quenching by the Au surface. The tunneling induced emission was taken from the self-assembled monolayers in which the subphthalocyanine molecules were chemically bound onto the surface by alkylthio substituents. The observed spectra were ascribed to the radiative decay of tip-induced surface plasmon of Au. The molecules in the self-assembled monolayers shifted the emission peak due to modification of the dielectric property and distance between the tip and surface

2006-03-21

75

Scanning tunneling microscopy of interface properties of Bi2Se3 on FeSe  

International Nuclear Information System (INIS)

We investigate the heteroepitaxial growth of Bi2Se3 films on FeSe substrates by low-temperature scanning tunneling microscopy/spectroscopy. The growth of Bi2Se3 on FeSe proceeds via van der Waals epitaxy with atomically flat morphology. A striped moiré pattern originating from the lattice mismatch between Bi2Se3 and FeSe is observed. Tunneling spectra reveal the spatially inhomogeneous electronic structure of the Bi2Se3 thin films, which can be ascribed to the charge transfer at the interface.

2012-11-28

76

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

2006-01-01

77

Scanning tunneling microscopy of interface properties of Bi2Se3 on FeSe.  

Science.gov (United States)

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

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

2012-11-28

78

Intermediate metallic phase in VO2 observed with scanning tunneling spectroscopy.  

Science.gov (United States)

This investigation focuses on the formation of nanoscale puddles of an intermediate metallic phase (IMP) in the metal-insulator transition (MIT) temperature regime of single-crystalline vanadium dioxide (VO2) nanowires. The electronic structure of VO2 nanowires was examined with scanning tunneling spectroscopy. The evolution of the local density of states of individual nanowires throughout the MIT regime is presented with differential tunneling conductance spectra and images measured as the temperature was increased. Our results show that the formation of an IMP plays an important role in the MIT of intrinsic VO2. PMID:24909228

Hatch, John Byron; Whittaker-Brooks, Luisa; Wu, Tai-Lung; Long, Gen; Zeng, Hao; Sambandamurthy, G; Banerjee, Sarbajit; Luo, Hong

2014-07-21

79

Observation of random telegraphic noise in scanning tunneling microscopy of nanoparticles on highly oriented pyrolytic graphite  

International Nuclear Information System (INIS)

Random telegraphic noise in scanning tunneling microscopy of dodecane thiol capped Au nanoparticles on highly oriented pyrolytic graphite surface has been investigated. The presence of nanoparticles gives rise to random switching of tunneling current between two discrete levels. The experimental power spectra of these current fluctuations show 1/f2 dependence. Analysis of the behavior of the power spectrum indicates that observed noise originates from Brownian motion of the trapped nanoparticle. Statistical analysis of the fluctuations shows exponential behaviour with time width ? ? 18 ms. The results suggest a method of producing an electrostatic trap analogus to laser tweezer

2007-04-01

80

Commendable surface physics by means of scanning tunneling microscopy  

International Nuclear Information System (INIS)

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)

1995-06-01

 
 
 
 
81

Measuring charge trap occupation and energy level in CdSe/ZnS quantum dots using a scanning tunneling microscope  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We use a scanning tunneling microscope to probe single-electron charging phenomena in individual CdSe/ZnS (core/shell) quantum dots (QDs) at room temperature. The QDs are deposited on top of a bare Au thin film and form a double-barrier tunnel junction (DBTJ) between the tip, QD, and substrate. Analysis of room-temperature hysteresis in the current-voltage (IV) tunneling spectra, is consistent with trapped charge(s) presenting an additional potential barrier to tunneling, a measure of the Co...

Hummon, M. R.; Stollenwerk, A. J.; Narayanamurti, V.; Anikeeva, Polina; Panzer, Matthew J.; Wood, Vanessa Claire; Bulovic, Vladimir

2010-01-01

82

Imaging and manipulating organometallic molecules by scanning tunneling microscopy  

Science.gov (United States)

Using scanning tunneling microscopy (STM) we have explored complex surface adsorbed molecules, nanocars, on Au(111) and the parameters related to the direct translation of these molecules by the STM tip. Specifically, the molecules focused on here were functionalized with C60 or trans ruthenium complexes. With low tunneling currents the molecules could be imaged at room temperature. Increasing the tunneling current allowed us to bring the tip closer to individual molecules and reposition them on the surface. Below specific current and bias voltage conditions the molecules remained stationary, while in other cases the tip interaction was strong enough to drastically damage or eject the molecule from the field of view. High temperature scans revealed the effect of the wheel activation energy relative to the underlying surface as the different wheeled nanocars began diffusing at different temperatures confirming the manipulation measurements.

Slavonic, Corey J.

83

Molecular Transport Junctions: Propensity Rules for Inelastic Electron Tunneling Spectra  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We develop a series of propensity rules for interpreting Inelastic Electron Tunneling (IET) spectra of single-molecule transport junctions. IETS has no selection rules, such as those seen in optical, infrared and Raman spectra, because IETS features arise not from the field-dipole interaction characterizing these other spectroscopies, but from vibronic modification of the electronic levels. Expansion of the Landauer-Imry formula in Taylor series in molecular normal coordinat...

Troisi, Alessandro; Ratner, Mark A.

2006-01-01

84

Scanning tunnelling vibrational spectroscopy of single surface complexes and detection of single electron spins  

International Nuclear Information System (INIS)

New spectroscopic techniques employing the scanning tunnelling microscope are considered. The new methods allow measurements of the vibrational spectra of single surface complexes, determination of the nonequilibrium distributions of such complexes over vibrational levels, studies on the kinetics of vibrational transitions, determination of vibrational relaxation parameters, detection of single surface electron spins and studies on the dynamics of fast surface migration of species. The physical grounds and possible applications of the methods in chemical research are also discussed. The bibliography includes 80 references.

2001-08-31

85

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

2009-01-01

86

Electron-beam-assisted Scanning Tunneling Microscopy Of Insulating Surfaces  

CERN Document Server

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

Bullock, E T

2000-01-01

87

Excitation of propagating surface plasmons with a scanning tunnelling microscope  

International Nuclear Information System (INIS)

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

2011-04-29

88

Scanning Tunneling Microscopy methods for spectroscopic imaging of subsurface interfaces  

Science.gov (United States)

A new method for spatially-resolved, spectroscopic investigation of subsurface interface structure has been developed. The method, Ballistic Electron Emission Microscopy (BEEM), is based on Scanning Tunneling Microscopy (STM) techniques. BEEM combines STM vacuum tunneling with unique ballistic electron spectroscopy capabilities. BEEM enables, for the first time, direct imaging of subsurface interface electronic properties with nanometer spatial resolution. STM topographic images of surface structure and BEEM images of subsurface properties are obtained simultaneously. BEEM capabilities are demonstrated by investigation of important metal-semiconductor interfaces.

Bell, L. D.; Kaiser, W. J.

1988-01-01

89

Size dependence in tunneling spectra of PbSe quantum-dot arrays  

International Nuclear Information System (INIS)

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.

2009-07-15

90

Apparent diameter of carbon nanotubes in scanning tunnelling microscopy measurements  

International Nuclear Information System (INIS)

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

2006-07-05

91

Apparent diameter of carbon nanotubes in scanning tunnelling microscopy measurements  

Energy Technology Data Exchange (ETDEWEB)

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

Tapaszto, L [Research Institute for Technical Physics and Materials Science, H-1525 Budapest, PO Box 49 (Hungary); Mark, G I [Research Institute for Technical Physics and Materials Science, H-1525 Budapest, PO Box 49 (Hungary); Koos, A A [Research Institute for Technical Physics and Materials Science, H-1525 Budapest, PO Box 49 (Hungary); Lambin, P [Departement de Physique, FUNDP, 61 Rue de Bruxelles, B-5000 Namur (Belgium); Biro, L P [Research Institute for Technical Physics and Materials Science, H-1525 Budapest, PO Box 49 (Hungary)

2006-07-05

92

Migration of Metals on Graphite in Scanning Tunneling Microscopy  

Science.gov (United States)

Metals such as Au deposited on graphite substrates are found to migrate very easily when biased in scanning tunneling microscopes. Depending upon the film thickness and the tip voltage, a hillock surrounded by grooves or a hole surrounded by hillocks with a height of ˜±10 nm and a lateral dimension of ˜100 nm are formed. The mechanism of these surface-modification phenomena is discussed in light of electro- and thermomigration.

Ohto, Masanori; Yamaguchi, Satoru; Tanaka, Keiji

1995-06-01

93

A theoretical model for single molecule incoherent scanning tunneling spectroscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Single molecule scanning tunneling spectroscopy (STS), with dephasing due to elastic and inelastic scattering, is of some current interest. Motivated by this, we report an extended Huckel theory (EHT) based mean-field Non-equilibrium Green's function (NEGF) transport model with electron-phonon scattering treated within the self-consistent Born approximation (SCBA). Furthermore, a procedure based on EHT basis set modification is described. We use this model to study the effec...

Raza, Hassan

2007-01-01

94

Scanning Tunneling Spectroscopy in MgB 2  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present extensive Scanning Tunneling Spectroscopy (STM/S) measurements at low temperatures in the multiband superconductor MgB$_2$. We find a similar behavior in single crystalline samples and in single grains, which clearly shows the partial superconducting density of states of both the $\\pi$ and $\\sigma$ bands of this material. The superconducting gaps corresponding to both bands are not single valued. Instead, we find a distribution of superconducting gaps centered aro...

Martinez-samper, P.; Rodrigo, J. G.; Rubio-bollinger, G.; Suderow, H.; Vieira, S.; Lee, S.; Tajima, S.

2002-01-01

95

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

CERN Document Server

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

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

2003-01-01

96

Structure of YSi2 nanowires from scanning tunneling spectroscopy and ?rst-principles  

Energy Technology Data Exchange (ETDEWEB)

Exceptionally long and uniform YSi2 nanowires are formed via self-assembly of yttrium atoms on Si(001). The in-plane width of the thinnest wires is known to be quantized in odd multiples of the silicon lattice constant. Here, we identify a new class of YSi2 nanowires that violate the odd-multiple rule. The structure of the thinnest wire in this category is determined by comparing the normalized differential con- ductance spectra from scanning tunneling spectroscopy (STS) with the projected surface density of states (DOS) of various candidate models, obtained from ?rst-principles, by means of a R-factor analysis. The Pendry R-factor appears to be a useful indicator for selecting the best structure model from the tunneling spectra of individual nano objects.

Iancu, Violeta [University of Tennessee, Knoxville (UTK); Kent, Paul R [ORNL; Zeng, C. [University of Tennessee, Knoxville (UTK) & Oak Ridge National Laboratory (ORNL); Weitering, Hanno [University of Tennessee, Knoxville (UTK)

2009-01-01

97

Band mapping across a pn-junction in a nanorod by scanning tunneling microscopy.  

Science.gov (United States)

We map band-edges across a pn-junction that was formed in a nanorod. We form a single junction between p-type Cu2S and n-type CdS through a controlled cationic exchange process of CdS nanorods. We characterize nanorods of the individual materials and the single junction in a nanorod with an ultrahigh vacuum scanning tunneling microscope (UHV-STM) at 77 K. From scanning tunneling spectroscopy and correspondingly the density of states (DOS) spectra, we determine the conduction and valence band-edges at different points across the junction and the individual nanorods. We could map the band-diagram of nanorod-junctions to bring out the salient features of a diode, such as p- and n-sections, band-bending, depletion region, albeit interestingly in the nanoscale. PMID:24588335

Bera, Abhijit; Dey, Sukumar; Pal, Amlan J

2014-04-01

98

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

Directory of Open Access Journals (Sweden)

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.

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

2007-01-01

99

Quantum coherence of bulk electrons on metals revealed by scanning tunneling spectroscopy  

Science.gov (United States)

The quantum dynamics of electrons in bulk states is investigated by scanning tunneling microscopy and spectroscopy on a Ag(100) surface. By measuring conductance maps above a threshold voltage, we observe standing waves at step edges and defects. We interpret these to originate from electrons in a bulk band edge at the ? point. From the spatially decaying waves, the wave vector and the quantum coherence parameters—coherence length, lifetime, and linewidth—are determined as a function of energy. We measure a coherence length of about 5-7 Å, which is order of magnitudes lower than typically observed for surface or image-potential states. The energy of the band edge is extracted from the dispersion relation and agrees with the peak measured in scanning tunneling spectra at 1.9 eV above the Fermi energy. Theoretical calculations confirm the nature of the state elucidating the experimental findings.

Ohmann, Robin; Toher, Cormac; Meyer, Jörg; Nickel, Anja; Moresco, Francesca; Cuniberti, Gianaurelio

2014-05-01

100

Properties of annealed anodically etched porous Zn studied by scanning tunneling microscopy  

Science.gov (United States)

We have studied the annealing behavior of anodically etched porous Zn (p-Zn) as a function of annealing time. It is found that 10 min ambient air annealing of Zn yields efficient UV luminescence with a very weak deep-level defect-related luminescence. The emergence of the green luminescence band is observed with an increase of annealing time. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) have been performed on annealed p-Zn. STM studies reveal a more smooth surface for p-Zn annealed for a short period. STS analysis shows a good agreement with observed PL spectra, especially concerning the existence or absence of defect-related luminescence.

Chang, Sung-Sik; Kurokawa, Shu; Sakai, Akira

2003-07-01

 
 
 
 
101

SPATIAL REPARTITION OF CURRENT FLUCTUATIONS IN A SCANNING TUNNELING MICROSCOPE  

Directory of Open Access Journals (Sweden)

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.

Jerome Lagoute

2011-05-01

102

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

Science.gov (United States)

The tangled mechanism that produces optical pump-probe scanning tunneling microscopy spectra from semiconductors was analyzed by comparing model simulation data with experimental data. The nonlinearities reflected in the spectra, namely, the excitations generated by paired laser pulses with a delay time, the logarithmic relationship between carrier density and surface photovoltage (SPV), and the effect of the change in tunneling barrier height depending on SPV, were examined along with the delay-time-dependent integration process used in measurement. The optimum conditions required to realize reliable measurement, as well as the validity of the microscopy technique, were demonstrated for the first time. PMID:23929439

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

2013-10-01

103

A novel method achieving ultra-high geometrical resolution in scanning tunnelling microscopy  

International Nuclear Information System (INIS)

We report a new contrast mechanism in which scanning tunnelling micrographs of a certain class of molecules resemble chemists' structure formulae. The method is based on adding molecular hydrogen below its condensation temperature to the tunnelling junction of a low-temperature scanning tunnelling microscope. In the presence of hydrogen, the scanning tunnelling microscope contrast can be switched between the conventional mapping of the electronic local density of states and the new geometric imaging by selecting the appropriate bias voltage. Scanning tunnelling spectroscopy suggests that the coupling of the electron tunnelling current to an internal degree of freedom in the tunnelling junction is responsible for the geometric contrast. The new scanning tunnelling hydrogen microscopy (STHM) allows the chemical identification of certain molecular species by their structure

2008-05-01

104

Excitation of propagating surface plasmons with a scanning tunnelling microscope  

Energy Technology Data Exchange (ETDEWEB)

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

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

2011-04-29

105

Scanning tunneling spectroscopy of high-temperature superconductors  

CERN Document Server

Tunneling spectroscopy played a central role in the experimental verification of the microscopic theory of superconductivity in the classical superconductors. Initial attempts to apply the same approach to high-temperature superconductors were hampered by various problems related to the complexity of these materials. The use of scanning tunneling microscopy/spectroscopy (STM/STS) on these compounds allowed to overcome the main difficulties. This success motivated a rapidly growing scientific community to apply this technique to high-temperature superconductors. This paper reviews the experimental highlights obtained over the last decade. We first recall the crucial efforts to gain control over the technique and to obtain reproducible results. We then discuss how the STM/STS technique has contributed to the study of some of the most unusual and remarkable properties of high-temperature superconductors: the unusual large gap values and the absence of scaling with the critical temperature; the pseudogap and its ...

Fischer, O; Maggio-Aprile, I; Berthod, C; Renner, C; Fischer, Oystein; Kugler, Martin; Maggio-Aprile, Ivan; Berthod, Christophe; Renner, Christoph

2006-01-01

106

Local density of states and scanning tunneling currents in graphene  

Energy Technology Data Exchange (ETDEWEB)

We present exact analytical calculations of scanning tunneling currents in locally disordered graphene using a multimode description of the microscope tip. Analytical expressions for the local density of states (LDOS) are given for energies beyond the Dirac cone approximation. We show that the LDOS at the A and B sublattices of graphene are out of phase by {pi} implying that the averaged LDOS, as one moves away from the impurity, shows no trace of the 2q{sub F} (with q{sub F} the Fermi momentum) Friedel modulation. This means that a scanning tunneling microscopy (STM) experiment lacking atomic resolution at the sublattice level will not be able to detect the presence of the Friedel oscillations (this seems to be the case in the experiments reported in Brihuega et al 2008 Phys. Rev. Lett. 101 206802). The momentum maps of the LDOS for different types of impurities are given. In the case of the vacancy, 2q{sub F} features are seen in these maps. In all momentum space maps, K and K+K' features are seen. The K+K' features are different from what is seen around zero momentum. An interpretation for these features is given. The calculations reported here are valid for chemical substitution impurities, such as boron and nitrogen atoms, as well as for vacancies. It is shown that the density of states close to the impurity is very sensitive to the type of disorder: diagonal, non-diagonal, or vacancies. In the case of weakly coupled (to the carbon atoms) impurities, the LDOS presents strong resonances at finite energies, which leads to steps in the scanning tunneling currents and to suppression of the Fano factor.

Peres, N M R [Department of Physics and Center of Physics, University of Minho, P-4710-057, Braga (Portugal); Yang Ling; Tsai, S.-W. [Department of Physics and Astronomy, University of California, Riverside, CA 92521 (United States)], E-mail: peres@fisica.uminho.pt, E-mail: ling.yang@email.ucr.edu, E-mail: swtsai@physics.ucr.edu

2009-09-15

107

Spin-Polarized Scanning Tunneling Microscopy with Antiferromagnetic Probe Tips  

Science.gov (United States)

We have performed low temperature spin-polarized scanning tunneling microscopy (SP-STM) of two monolayers Fe on W(110) using tungsten tips coated with different magnetic materials. We observe stripe domains with a magnetic period of 50+/-5 nm. Employing Cr as a coating material we recorded SP-STM images with an antiferromagnetic probe tip. The advantage of its vanishing dipole field is most apparent in external magnetic fields. This new approach resolves the problem of the disturbing influence of a ferromagnetic tip in the investigation of soft magnetic materials and superparamagnetic particles.

Kubetzka, A.; Bode, M.; Pietzsch, O.; Wiesendanger, R.

2002-02-01

108

In situ scanning tunneling microscopy of copper deposition with benzotriazole  

Energy Technology Data Exchange (ETDEWEB)

In this paper, the submicron topography of Cu deposits is studied with scanning tunneling microscopy to investigate the effect of benzotriazole in the initial stages of deposition. The presence of benzotriazole results in a marked increase in over-potential for the deposition. It is found to eliminate the preferential growth of specific crystallographic planes and the formation of crystal facets. The number density of nuclei, determined from Fourier transforms of the surface profiles of 7 nm thick films, is found to increase with increasing overpotential of the deposition but is independent of the presence of the inhibitor.

Armstrong, M.J.; Muller, R.H. (Lawrence Berkeley Lab., Dept. of Chemical Engineering, Univ. of California at Berkeley, Berkeley, CA (US))

1991-08-01

109

In situ scanning tunneling microscopy of copper deposition with benzotriazole  

International Nuclear Information System (INIS)

In this paper, the submicron topography of Cu deposits is studied with scanning tunneling microscopy to investigate the effect of benzotriazole in the initial stages of deposition. The presence of benzotriazole results in a marked increase in over-potential for the deposition. It is found to eliminate the preferential growth of specific crystallographic planes and the formation of crystal facets. The number density of nuclei, determined from Fourier transforms of the surface profiles of 7 nm thick films, is found to increase with increasing overpotential of the deposition but is independent of the presence of the inhibitor

1991-08-01

110

Observation of diamond turned OFHC copper using Scanning Tunneling Microscopy  

Energy Technology Data Exchange (ETDEWEB)

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.

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

1988-12-01

111

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

CERN Multimedia

Scanning tunneling spectroscopy images of Bi$_2$Se$_3$ doped with excess Bi reveal defect states with a peculiar shape resembling clover leaves. We employ a simple tight-binding model to show that these states likely originate from the Bi substitutional defects five atomic layers below the surface, resulting from the interplay of defect and surface electronic structure. With first principles calculations we establish a quantitative picture of the contribution of the surface states to the near-gap differential conductance spectra of Bi$_2$Se$_3$. Our results may lead to a new interpretation of the defect electronic states observed in other semiconducting compounds with surface probe techniques.

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

2002-01-01

112

Influence of the quasiparticle lifetime effect on local tunneling spectra of high-T c superconductors  

International Nuclear Information System (INIS)

The local electronic states of optimally doped Bi2Sr2CaCu2O8-? and Ln-doped Bi2Sr2CuO6-? (Ln-Bi2201, Ln = La, Gd) were measured by low-temperature scanning tunneling spectroscopy. The spectra showed enhanced coherence peaks when the gap amplitude was relatively small, while the peaks in the spectra were gradually suppressed as the gap amplitude became larger. In the case of Ln-Bi2201, the spectra showed the enhancements of residual conductance reflecting the impurity scattering due to doped Ln ions. We demonstrate that these trends are systematically reproduced based on the conductance formula that takes account of the energy dependent damping factor corresponding to the quasiparticle lifetime. The consistency suggests that one of the main factors dominating the spectral line shapes is the energy dependence of the quasiparticle lifetime

2006-10-01

113

Density-matrix approach for the electroluminescence of molecules in a scanning tunneling microscope.  

Science.gov (United States)

The electroluminescence (EL) of molecules confined inside a nanocavity in the scanning tunneling microscope possesses many intriguing but unexplained features. We present here a general theoretical approach based on the density-matrix formalism to describe the EL from molecules near a metal surface induced by both electron tunneling and localized surface plasmon excitations simultaneously. It reveals the underlying physical mechanism for the external bias dependent EL. The important role played by the localized surface plasmon on the EL is highlighted. Calculations for porphyrin derivatives have reproduced corresponding experimental spectra and nicely explained the observed unusual large variation of emission spectral profiles. This general theoretical approach can find many applications in the design of molecular electronic and photonic devices. PMID:21635061

Tian, Guangjun; Liu, Ji-Cai; Luo, Yi

2011-04-29

114

Spin-polarized scanning tunneling spectroscopy of dislocation lines in Fe films on W(110)  

International Nuclear Information System (INIS)

We have studied the spin-resolved electronic properties of dislocation lines on the Fe double-layer (DL) on W(110) by spin-polarized scanning tunneling spectroscopy. The data reveal that the dislocation lines are ferromagnetically ordered with the magnetic contrast exhibiting a pronounced bias-dependence. By comparing tunneling spectra which were measured on the pseudomorphic DL and at different lateral separation from the dislocation line, we find a pronounced shift of a peak which originally appears at positive sample bias towards the Fermi level EF. In contrast, the binding energy of a peak just below EF remains constant but increases in intensity. This causes a pronounced modification of the bias voltage-dependent magnetic asymmetry

2006-09-01

115

Scanning electron and tunneling microscopy of palladium-barium emitters  

International Nuclear Information System (INIS)

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

2003-06-15

116

Scanning tunneling microscopy and spectroscopy of graphene on insulating substrates  

Energy Technology Data Exchange (ETDEWEB)

Graphene is a truly two-dimensional (2D) material with exceptional electronic, mechanical, and optical properties. As such, it consists of surface only and can be probed by the well-developed surface science techniques such as, e.g., scanning tunneling microscopy (STM). This method bridges the gap between the surface science community and the electronic device community and might lead to novel combined approaches. Here, I review some of the STM and scanning tunneling spectroscopy (STS) experiments on monolayer graphene samples. I will concentrate on graphene samples deposited on insulating substrates, since these are related to graphene device concepts. In particular, I will discuss the morphology of graphene on SiO{sub 2} and other emerging substrates, some nanomechanical manipulation experiments using STM, and spectroscopic results. The latter can map the disorder potentials as well as the interaction of the electrons with the disorder, which is most pronounced in the quantum Hall regime. Three-dimensional representation of a STM image of graphene; the atomic resolution is displayed as color code, while the rippling is shown in three dimensions (courtesy of M. Pratzer, RWTH Aachen). (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Morgenstern, Markus [II. Institute of Physics and JARA-FIT, RWTH Aachen, 52074 Aachen (Germany)

2011-11-15

117

Scanning electron and tunneling microscopy of palladium-barium emitters  

Energy Technology Data Exchange (ETDEWEB)

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

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

2003-06-15

118

Molecular Transport Junctions: Propensity Rules for Inelastic Electron Tunneling Spectra  

CERN Document Server

We develop a series of propensity rules for interpreting Inelastic Electron Tunneling (IET) spectra of single-molecule transport junctions. IETS has no selection rules, such as those seen in optical, infrared and Raman spectra, because IETS features arise not from the field-dipole interaction characterizing these other spectroscopies, but from vibronic modification of the electronic levels. Expansion of the Landauer-Imry formula in Taylor series in molecular normal coordinates gives a convenient, accurate perturbation-type formula for calculating both frequency and intensity of the IETS spectrum. Expansion in a Dyson-like form permits derivation of propensity rules, both symmetry-based and pathway-deduced, allowing correlation of structure and coupling geometry with the IETS spectrum. These propensity rules work very well for the calculated spectrum of four typical molecular bridges.

Troisi, A; Troisi, Alessandro; Ratner, Mark A.

2006-01-01

119

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

International Nuclear Information System (INIS)

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

2012-04-01

120

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

Directory of Open Access Journals (Sweden)

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

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

2006-01-01

 
 
 
 
121

Scanning tunneling co-ramp spectroscopy for reactive adsorbates  

Science.gov (United States)

We report the development of a spectroscopy for investigating reactive adsorbates, and its application to the study of chemisorbed methoxy on NiAl(110). Conventional scanning tunneling spectroscopy, a powerful tool to study stable adsorbates, is not applicable to the kinds that decompose or desorb upon the exposure to low-energy tunneling electrons. In order to find the electronic structure of these adsorbates, we developed a scanning spectroscopy that minimizes the exposure to external influences. The coramp spectroscopy (CRS), so named by us, involves synchronized ramping-up of bias V and the spatial position in a constant current mode, and recording the tip-sample separation s(V) at the same time. Numerical simulations of s(V) show that the information on the resonance can be extracted from the derivative of s(V). This technique was applied to the investigation of chemisorbed methoxy deposited by the injection of liquid methanol into NiAl(110) surface. It is shown that slow high-bias scans decompose methoxy through C-O bond scission or C-H bond dehydrogenation. Despite such reactivity of methoxy, CRS was successfully applied to reveal that methoxy has a resonance at 3.4 V. Simulations show that the resonance is well separated from the field emission resonances, and attributed to a nonbonding 2e orbital of chemisorbed methoxy. Our technique should be useful in the study of a wide range of molecular adsorbates, particularly, in the study of their unoccupied states where few techniques are available.

Choi, Eunyeoung; Lyo, In-Whan

2011-11-01

122

Design of a high-speed electrochemical scanning tunneling microscope  

Science.gov (United States)

In this paper, we present a bottom-up approach to designing and constructing a high-speed electrochemical scanning tunneling microscope (EC-STM). Using finite element analysis (FEA) calculations of the frequency response of the whole mechanical loop of the STM, we analyzed several geometries to find the most stable one that could facilitate fast scanning. To test the FEA results, we conducted measurements of the vibration amplitudes using a prototype STM setup. Based on the FEA analysis and the measurement results, we identified the potentially most disturbing vibration modes that could impair fast scanning. By modifying the design of some parts of the EC-STM, we reduced the amplitudes as well as increased the resonance frequencies of these modes. Additionally, we designed and constructed an electrochemical flow-cell that allows STM imaging in a flowing electrolyte, and built a bi-potentiostat to achieve electrochemical potential control during the measurements. Finally, we present STM images acquired during high-speed imaging in air as well as in an electrochemical environment using our newly-developed EC-STM.

Yanson, Y. I.; Schenkel, F.; Rost, M. J.

2013-02-01

123

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

Science.gov (United States)

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

Nishino, Tomoaki

2014-01-01

124

Visualization of semiconductor surface etching with scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

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

Weaver, J.H. [Minnesota Univ., Minneapolis, MN (United States). Dept. of Chemical Engineering and Material Sciences

1998-06-01

125

Superconducting phonon spectroscopy using a low-temperature scanning tunneling microscope  

International Nuclear Information System (INIS)

We report the first observation of phonon density of states effects in a superconductor using a low-temperature scanning tunneling microscope (STM). The phonon effects were observed using a STM spectroscopy method to measure dI/sub tunneling/ /dV vs V for the tunnel junction formed by the Au STM probe and a superconducting Pb sample

1989-03-06

126

Break-down of the density-of-states description of scanning tunneling spectroscopy in supported metal clusters  

CERN Document Server

Low-temperature scanning tunneling spectroscopy allows to probe the electronic properties of clusters at surfaces with unprecedented accuracy. By means of quantum transport theory, using realistic tunneling tips, we obtain conductance curves which considerably deviate from the cluster's density of states. Our study explains the remarkably small number of peaks in the conductance spectra observed in recent experiments. We demonstrate that the unambiguous characterization of the states on the supported clusters can be achieved with energy-resolved images, obtained from a theoretical analysis which mimics the experimental imaging procedure.

De Menech, M; García, M E; Menech, Mario De; Saalmann, Ulf; Garcia, Martin E.

2006-01-01

127

Andreev and Single-Particle Tunneling Spectra of Underdoped Cuprate Superconductors  

Energy Technology Data Exchange (ETDEWEB)

We study tunneling spectroscopy between a normal metal and an underdoped cuprate superconductor modeled by a phenomenological theory in which the pseudogap is a precursor to the undoped Mott insulator. In the low barrier tunneling limit, the spectra are enhanced by Andreev reflection only within a voltage region of the small superconducting energy gap. In the high barrier tunneling limit, the spectra show a large energy pseudogap associated with single particle tunneling. Our theory semiquantitatively describes the two gap behavior observed in tunneling experiments.

Rice, T.M.; Yang, K.-Y.; Huang, K.; Chen, W.-Q.; Zhang, F.-C.

2010-10-12

128

Andreev and Single-Particle Tunneling Spectra of Underdoped Cuprate Superconductors  

Science.gov (United States)

We study tunneling spectroscopy between a normal metal and an underdoped cuprate superconductor modeled by a phenomenological theory in which the pseudogap is a precursor to the undoped Mott insulator. In the low barrier tunneling limit, the spectra are enhanced by Andreev reflection only within a voltage region of the small superconducting energy gap. In the high barrier tunneling limit, the spectra show a large energy pseudogap associated with single particle tunneling. Our theory semi- quantitatively describes the two gap behavior observed in tunneling experiments.

Huang, Kun; Yang, Kai-Yu; Chen, Wei-Qiang; Rice, T. M.; Zhang, Fu-Chun

2011-03-01

129

Fixing the Energy Scale in Scanning Tunneling Microscopy on Semiconductor Surfaces  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

2013-01-01

130

Two-dimensional superstructure formation of fluorinated fullerene on Au(111): a scanning tunneling microscopy study.  

Science.gov (United States)

A two-dimensional fluorinated fullerene (C(60)F(36)) superstructure has been successfully formed on Au(111) and was investigated using scanning tunneling microscopy (STM) and density functional theory calculations. Although there exist three isomers (C(3), C(1), and T) in our molecular source, STM images of the molecules in the well-ordered region all appear identical, with 3-fold symmetry. This observation together with the differences in the calculated lowest unoccupied molecular orbital (LUMO) distribution among the three isomers suggests that a well-ordered monolayer consists of only the C(3) isomer. Because of the strong electron-accepting ability of C(60)F(36), the adsorption orientation can be explained by localized distribution of its LUMO, where partial electron transfer from Au(111) occurs. Intermolecular C-F···? electrostatic interactions are the other important factor in the formation of the superstructure, which determines the lateral orientation of C(60)F(36) molecules on Au(111). On the basis of scanning tunneling spectra obtained inside the superstructure, we found that the LUMO is located at 1.0 eV above the Fermi level (E(F)), while the highest occupied molecular orbital (HOMO) is at 4.6 eV below the E(F). This large energy gap with the very deep HOMO as well as uniform electronic structure in the molecular layer implies a potential for application of C(60)F(36) to an electron transport layer in organic electronic devices. PMID:22329735

Shimizu, Tomoko K; Jung, Jaehoon; Otani, Tetsuya; Han, Young-Kyu; Kawai, Maki; Kim, Yousoo

2012-03-27

131

Scanning Tunneling Microscopy Studies of Diamond Films and Optoelectronic Materials  

Science.gov (United States)

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

Perez, Jose M.

1996-01-01

132

Scanning tunneling microscope with long range lateral motion  

International Nuclear Information System (INIS)

We present our work on a recently built scanning tunneling microscope (STM), with coarse motion in two-dimensions. The tip of this STM can be translated a few millimeters in directions both parallel and perpendicular to the tip. This feature allows sampling of a larger area for experiments such as the study of how the electrical properties of charge density waves evolve between contacts, the proximity effect near a normal metal–superconducting interface, charge transport near the contact of a semiconductor interface, and for finding microscopically small samples like graphene. This STM is based on one of our previous one-dimensional designs. It utilizes orchestrated motion of six piezoelectric tubes in a slip–stick configuration in order to produce long range motion for the walker. This device is a single unit with a compact design making it very stable. It is stable enough to obtain atomic resolution on HOPG. It can operate in either a horizontal or vertical configuration and at cryogenic temperatures. It was designed entirely from non-magnetic materials for potential work in a magnetic field.

2012-06-01

133

Oxygen-free in situ scanning tunnelling microscopy  

DEFF Research Database (Denmark)

Scanning tunneling microscopy under full electrochemical potential control (in situ STM) has been used extensively as an efficient method to characterize microstructures at solid/liquid interfaces at the atomic and molecular levels. However, under ambient conditions oxygen may interfere in open in situ STM systems by diffusion through the solutions. Such interference can be serious for oxygen sensitive systems both for the target molecules themselves and for chemical linker molecules bound to the electrode surface for example, via Au-S bonding. This is strikingly illustrated in the present report. We present here oxygen-free in situ STM, in which the samples are contained in an argon atmosphere which removes oxygen in the system. Interference from oxygen is profoundly reduced in this setup and demonstrated by three examples. Two of these are in situ STM of the intermediate-size sulfur containing organic molecule cysteamine and the biomolecule homocysteine. The third example is the iron-sulfur protein ferredoxin (Pyrococcus furiosus). Monolayers of these molecules on Au(111) are imaged to molecular resolution and the images compared in the presence and absence of oxygen. In all the cases, the STM image quality of the monolayer structures has improved significantly in the absence of oxygen. Reasons for the drastic effects of dioxygen based on both chemical surface reactivity and electron scattering effects are discussed. These observations are important in general for STM of oxygen sensitive chemical and biological samples.

Zhang, Jingdong; Ulstrup, Jens

2007-01-01

134

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

CERN Document Server

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

Palotás, Krisztián; Szunyogh, László

2012-01-01

135

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

International Nuclear Information System (INIS)

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

1996-06-01

136

Nanostructural and local electronic properties of Fe/W(110) correlated by scanning tunneling spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

Epitaxial Fe(110) films grown on W(110) substrates exhibit, up to the second pseudomorphic monolayer, a peak in {ital dI}/{ital dU} spectra at 0.2 eV above the Fermi level as measured by scanning tunneling spectroscopy (STS). It is shown directly by STS on nanometer-scale wedges of Fe/W(110) that the density of empty states is diminished wherever the stressed Fe film begins to relax. The change in local differential conductivity can therefore be explained by a stress-induced change of electronic structure for the first two monolayers due to the large misfit between film and substrate. {copyright} {ital 1996 The American Physical Society.}

Bode, M.; Pascal, R.; Dreyer, M.; Wiesendanger, R. [Institute of Applied Physics and Microstructure Research Center, University of Hamburg, Jungiusstrasse 11, D-20355 Hamburg (Germany)

1996-09-01

137

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

Science.gov (United States)

A theoretical model of plasmon and molecular luminescence induced by scanning tunneling microscopy using a molecule-covered tip on clean metal surfaces is developed. The effects of coupling between molecular exciton and interface plasmon on the luminescence spectra are investigated for variable energy of plasmon modes by means of the nonequilibrium Green's function method. It is found that spectral features arising from interference between the processes of energy absorption by the molecule and interface plasmons appear near the energy of the excitonic mode. For the energy of plasmon above (below) the energy of excitonic mode, an additional peak structure appears in the energy range slightly below (above) the energy of the excitonic mode. Prominent peak and dip structures observed in recent luminescence experiments are interpreted by the developed theory whereby its utility in the fields of plasmonics and nanophotonics is demonstrated. PMID:24810264

Miwa, K; Sakaue, M; Gumhalter, B; Kasai, H

2014-06-01

138

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

Science.gov (United States)

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

Miwa, K.; Sakaue, M.; Gumhalter, B.; Kasai, H.

2014-06-01

139

Direct observation of adsorption-induced electronic states by low-temperature scanning tunneling microscopy  

International Nuclear Information System (INIS)

We have studied local density states of cobalt-phthalocyanine (CoPc) molecules on a Cu (1 0 0) surface by low-temperature scanning tunneling microscopy. Differential conductance (dI/dV) spectra of CoPc molecules had two peaks at 0.45 eV below and 0.1 eV above the Fermi level (E F). The dI/dV image revealed that Co atoms had large contribution to the state around 0.45 eV. The peak at 0.1 eV above E F was assigned to the states induced by the adsorption of molecules on surfaces. The porphyrin part of the CoPc molecules was found to contribute to this state. The lowest unoccupied molecular orbital was thought to hybridize with the electronic states of Cu (1 0 0) to generate the adsorption-induced state

2005-11-01

140

Local electronic properties of graphene on a BN substrate via scanning tunneling microscopy.  

Science.gov (United States)

The use of boron nitride (BN) as a substrate for graphene nanodevices has attracted much interest since the recent report that BN greatly improves the mobility of charge carriers in graphene compared to standard SiO(2) substrates. We have explored the local microscopic properties of graphene on a BN substrate using scanning tunneling microscopy. We find that BN substrates result in extraordinarily flat graphene layers that display microscopic Moire? patterns arising from the relative orientation of the graphene and BN lattices. Gate-dependent dI/dV spectra of graphene on BN exhibit spectroscopic features that are sharper than those obtained for graphene on SiO(2). We observe a significant reduction in local microscopic charge inhomogeneity for graphene on BN compared to graphene on SiO(2). PMID:21553853

Decker, Régis; Wang, Yang; Brar, Victor W; Regan, William; Tsai, Hsin-Zon; Wu, Qiong; Gannett, William; Zettl, Alex; Crommie, Michael F

2011-06-01

 
 
 
 
141

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

CERN Multimedia

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

Kohen, A; Proslier, T; Lacaze, E; Aprili, M; Sacks, W; Roditchev, D

2004-01-01

142

Nanostructural and local electronic properties of Fe/W(110) correlated by scanning tunneling spectroscopy  

International Nuclear Information System (INIS)

Epitaxial Fe(110) films grown on W(110) substrates exhibit, up to the second pseudomorphic monolayer, a peak in dI/dU spectra at 0.2 eV above the Fermi level as measured by scanning tunneling spectroscopy (STS). It is shown directly by STS on nanometer-scale wedges of Fe/W(110) that the density of empty states is diminished wherever the stressed Fe film begins to relax. The change in local differential conductivity can therefore be explained by a stress-induced change of electronic structure for the first two monolayers due to the large misfit between film and substrate. copyright 1996 The American Physical Society

1996-09-01

143

Design and performance of a beetle-type double-tip scanning tunneling microscope  

International Nuclear Information System (INIS)

A combination of a double-tip scanning tunneling microscope with a scanning electron microscope in ultrahigh vacuum environment is presented. The compact beetle-type design made it possible to integrate two independently driven scanning tunneling microscopes in a small space. Moreover, an additional level for coarse movement allows the decoupling of the translation and approach of the tunneling tip. The position of the two tips can be controlled from the millimeter scale down to 50 nm with the help of an add-on electron microscope. The instrument is capable of atomic resolution imaging with each tip

2006-09-01

144

Pseudogap formation and unusual quasiparticle tunneling in cuprate superconductors: Polaronic and multiple-gap effects on the tunneling spectra  

Energy Technology Data Exchange (ETDEWEB)

We propose new simple and generalized multiple-gap models of quasiparticle tunneling across the high-T{sub c} cuprate superconductor (HTSC)/insulator/normal metal (SIN) junction based on the two different mechanisms for tunneling at positive and negative bias voltages, and the gap inhomogeneity (i.e., multiple-gap) picture. The tunneling of electrons from the normal metal into the quasiparticle states in HTSC with the BCS-type density of states (DOSs) takes place at V>0, while the tunneling of Cooper pairs and large polarons from the HTSC with the BCS DOS and quasi-free state DOS (which appears only in the dissociation of polarons) into the normal metal occurs at V<0. We show that most of the unusual features of tunneling spectra such as nearly U- and V-shaped subgap features, peak-dip-hump structure (appearing systematically at V<0) and asymmetry of the conductance peaks and their temperature and doping dependences, and shoulder-like features inside the main conductance peaks arise naturally in our specific models of SIN tunneling. The experimental tunneling spectra of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+?} are adequately reproduced by using the specific multiple-gap models and taking into account the distribution of BCS and polaronic gap values.

Dzhumanov, S., E-mail: dzhumanov@inp.uz; Ganiev, O.K.; Djumanov, Sh.S.

2013-10-15

145

Scanning tunneling microscopy studies of glucose oxidase on gold surface  

International Nuclear Information System (INIS)

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

2002-02-01

146

A 3-d laser scanning system and scan data processing method for the monitoring of tunnel deformations  

Science.gov (United States)

The paper presents the mobile multi-sensor system Orthos Plus for the monitoring and mapping of tunnel walls, a scan data processing method for the evaluation of 3-d tunnel wall displacements from subsequent wall scans and, finally, a virtual reality tool supporting the interpretation of data. The measuring system consists of a 3-d laser scanner, a motorised total station and a digital camera that are integrated on a light metal frame that is installed on a mobile platform. It has been designed to perform tunnel measurements most efficiently and to meet the special requirements of tunnels under construction. The evaluation of 3-d displacements is based on a 3-d matching algorithm that takes advantage of the particular conditions of tunnel (shotcrete) surfaces. The virtual reality tool allows viewing of data in a 3-d virtual reality tunnel model and their animation in time and space in order supports understanding in an optimal way. The measuring system Orthos Plus has been developed in the course of a national research project, the 3-d matching method in the frame of the Austrian Christian Doppler Laboratory Spatial Data from Laser Scanning and Remote Sensing and the VR tool in the Austrian COMET K1 Competence Center VRVis Center (www.vrvis.at).

Chmelina, Klaus; Jansa, Josef; Hesina, Gerd; Traxler, Christoph

2012-11-01

147

Writing nanometer-scale symbols in gold using the scanning tunneling microscope  

Energy Technology Data Exchange (ETDEWEB)

The conditions required to electroetch nanometer-sized craters in flat gold substrates with a scanning tunneling microscope operating in air are identified. Reproducible nanometer-scale modifications of the substrate are possible. Letters and complex symbols with linewidths as small as 2 nm have been written. Experiments show that a good tunneling tip is not destroyed by the writing process.

Li, Y.Z.; Vazquez, L.; Piner, R.; Andres, R.P.; Reifenberger, R.

1989-04-10

148

Elucidating Complex Surface Reconstructions with Atomic-Resolution Scanning Tunneling Microscopy: Au(100)-Aqueous Electrochemical Interface.  

Science.gov (United States)

The utilization of scanning tunneling microscopy (STM) with high-quality atomic resolution for elucidating complex electrochemical surface reconstructions is illustrated for the Au(100)-aqueous interface. The reconstruction, triggered by negative surface ...

X. Gao A. Hamelin M. J. Weaver

1992-01-01

149

Superconducting Gap, Normal State Pseudogap and Tunnelling Spectra of Bosonic and Cuprate Superconductors  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We develop a theory of normal-metal - superconductor (NS) and superconductor - superconductor (SS) tunnelling in bosonic superconductors with strong attractive correlations taking into account coherence effects in single-particle excitation spectrum and disorder. The theory accounts for the existence of two energy scales, their temperature and doping dependencies, asymmetry and inhomogeneity of tunnelling spectra of underdoped cuprate superconductors.

Alexandrov, A. S.; Beanland, J.

2009-01-01

150

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

Directory of Open Access Journals (Sweden)

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

wang K.-L.

2012-03-01

151

Scanning tunneling spectroscopy on Mn12 single molecule magnets grafted on Au(111)  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report on the electronic properties of Mn12 molecules chemically grafted on the functionalized Au(111) surface studied by means of scanning tunneling microscopy/spectroscopy at room temperature. Reproducible current-voltage curves were obtained from Mn12 molecules showing a large region of low conductance around the Fermi energy. In agreement with the tunneling spectroscopy results the bias voltage variation upon scanning leads to apparent height changes of the Mn12 clusters. We discuss th...

2008-01-01

152

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

2007-01-01

153

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

Energy Technology Data Exchange (ETDEWEB)

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

Kawahara, Toshio [Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Takahashi, Takuya [Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Tanaka, Hiroyuki [Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Kawai, Tomoji [Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)]. E-mail: kawai@sanken.osaka-u.ac.jp

2006-05-30

154

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

International Nuclear Information System (INIS)

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

2006-05-30

155

Total synchronous fluorescence scan spectra of petroleum products  

Energy Technology Data Exchange (ETDEWEB)

Extending the two-dimensional synchronous fluorescence scan to a three-dimensional total synchronous fluorescence scan (TSFS) spectral measurement gives the total synchronous fluorescence characteristics of a multifluorophoric sample at various possible wavelength intervals ({delta}{lambda}), which could help to characterize multifluorophoric systems better. TSFS spectra of petroleum products such as diesel, kerosene, petrol, engine oil etc., available in the Indian market, are reported. Fluorescence in these samples is due to the presence of polycyclic aromatic hydrocarbons (PAHs) of various ring sizes. The TSFS contour plot profiles of the neat samples measured at right-angle geometry is a result of various energy-degrading photophysical processes such as inner filter effect, light attenuation, resonance energy transfer, collisional quenching etc. TSFS plots make it easy to obtain the optimized {delta}{lambda} of an unknown sample of analytical interest. TSFS and the excitation-emission matrix (EEM) techniques are similar, but the contour profiles generated are different. The response of the TSFS contour profiles to dilution is different from that in the EEM contour profiles. Thus, TSFS can provide an alternative way of presenting the fluorescence response of concentrated multifluorophoric samples. (orig.)

Patra, Digambara; Mishra, A.K. [Department of Chemistry, Indian Institute of Technology Madras, Chennai (India)

2002-07-01

156

Imaging the electron-boson coupling in superconducting FeSe films using a scanning tunneling microscope.  

Science.gov (United States)

Scanning tunneling spectroscopy has been used to reveal signatures of a bosonic mode in the local quasiparticle density of states of superconducting FeSe films. The mode appears below Tc as a "dip-hump" feature at energy ??4.7kBTc beyond the superconducting gap ?. Spectra on strained regions of the FeSe films reveal simultaneous decreases in ? and ?. This contrasts with all previous reports on other high-Tc superconductors, where ? locally anticorrelates with ?. A local strong coupling model is found to reconcile the discrepancy well, and to provide a unified picture of the electron-boson coupling in unconventional superconductors. PMID:24580624

Song, Can-Li; Wang, Yi-Lin; Jiang, Ye-Ping; Li, Zhi; Wang, Lili; He, Ke; Chen, Xi; Hoffman, Jennifer E; Ma, Xu-Cun; Xue, Qi-Kun

2014-02-01

157

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

Science.gov (United States)

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. PMID:24593405

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

158

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

International Nuclear Information System (INIS)

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

2014-02-01

159

A modular scanning tunneling microscope with an interchangeable elastic closed cell and external actuators  

Energy Technology Data Exchange (ETDEWEB)

We introduce a novel modular cell based scanning tunneling microscope with external piezoelectric actuators. A tip and a sample are contained in a closed interchangeable cell, consisting of a stiff top plate and a bottom part, fastened together by an elastic material. The bottom part, containing a scanning tip, is fastened to a base unit while the top plate, containing a sample, is capable of scanning motion by external piezoelectric actuators mounted in the same base unit. The actuators are pre-loaded by the deformation of the elastic material of the cell, giving an increased stability. This design is expected to simplify the scanning tunneling microscope (STM) operation in difficult environments greatly by enclosing only the tip and sample in a small cell-module, which is pluggable to a scanning mechanism and other supportive functionalities. A frequency characterization and an image scan showing atomic resolution of highly oriented graphite in air, at room temperature, is presented.

Bjarnason, Elias H. [Matvice, Dunhaga 3, 107 Reykjavik (Iceland)]. E-mail: ehb@raunvis.hi.is; Arnalds, Unnar B. [Matvice, Dunhaga 3, 107 Reykjavik (Iceland); Olafsson, Sveinn [Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavik (Iceland)

2006-05-30

160

A modular scanning tunneling microscope with an interchangeable elastic closed cell and external actuators  

International Nuclear Information System (INIS)

We introduce a novel modular cell based scanning tunneling microscope with external piezoelectric actuators. A tip and a sample are contained in a closed interchangeable cell, consisting of a stiff top plate and a bottom part, fastened together by an elastic material. The bottom part, containing a scanning tip, is fastened to a base unit while the top plate, containing a sample, is capable of scanning motion by external piezoelectric actuators mounted in the same base unit. The actuators are pre-loaded by the deformation of the elastic material of the cell, giving an increased stability. This design is expected to simplify the scanning tunneling microscope (STM) operation in difficult environments greatly by enclosing only the tip and sample in a small cell-module, which is pluggable to a scanning mechanism and other supportive functionalities. A frequency characterization and an image scan showing atomic resolution of highly oriented graphite in air, at room temperature, is presented

2006-05-30

 
 
 
 
161

Vacuum tunneling spectroscopy of superconducting Bi_2Sr_2CaCuO_2O_8 using scanning tunneling spectroscopy  

International Nuclear Information System (INIS)

The authors report STM spectroscopy measurements of in-situ cleaved Bi_2Sr_2CaCu_2O_8 single crystals at 4.8 Kelvin, where they achieved strong evidences for true vacuum tunneling. These careful experiments result in very reproducible spectroscopy s a function of position on the surface, and as a function of tip/sample spacing. The characteristic features of the tunneling spectra are a significant filling of the gap region, a large density of states at the gap edges and a weak dip about 70meV below the Fermi level. Such IV characteristics are not compatible with a single gap BCS-like s-wave theory. Furthermore, they report spatially resolved spectroscopy where they, observe regions with two distinct gap values. A double gap structure appears in the tunneling spectra acquired in the vicinity of the boundary between these regions. They believe the double gap structure they observe in this case does not reflect an intrinsic gap anisotropy, but seems rather related to crystalline inhomogeneities. This demonstrates the potential of the STM's spatial resolution to shed some light on the controversy among the tunneling spectroscopy of high temperature superconductors published so far

1994-01-22

162

Scanning Tunneling Microscope Nanolithography on SrRuO3 Thin Film Surfaces  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Liu, Yun; Zhang, Jia

2009-01-01

163

Scanning tunneling microscopy investigation of the TiO2 anatase (101) surface  

International Nuclear Information System (INIS)

We report the first scanning tunneling microscopy (STM) study of single-crystalline anatase. Atomically resolved images of the (101) surface are consistent with a bulk-truncated (1x1) termination. Step edges run predominantly in the [010], [bar 111], and [bar 11bar 11] directions. The surface is stable with very few point defects. Fourfold-coordinated Ti atoms at step edges are preferred adsorption sites and allow the identification of tunneling sites in STM

2000-12-15

164

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report on a novel scheme to perform efficient simulations of Scanning Tunneling Microscopy (STM) of molecules weakly bonded to surfaces. Calculations are based on a tight binding (TB) technique including self-consistency for the molecule to predict STM imaging and spectroscopy. To palliate the lack of self-consistency in the tunneling current calculation, we performed first principles density-functional calculations to extract the geometrical and electronic properties of ...

Dubois, M.; Latil, S.; Scifo, L.; Grevin, B.; Rubio, A.

2006-01-01

165

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report novel properties derived from scanning tunnelling spectroscopic (STS) studies of Dirac fermions in graphene and the surface state (SS) of a strong topological insulator (STI), Bi2Se3. For mono-layer graphene grown on Cu by chemical vapour deposition (CVD), strain-induced scalar and gauge potentials are manifested by the charging effects and the tunnelling conductance peaks at quantized energies, respectively. Additionally, spontaneous time-reversal symmetry breaking is evidenced by ...

-c, Yeh N.; Teague M. L.; -p, Wu R. T.; Chu H.; Boyd D. A.; Bockrath M. W.; He L.; -x, Xiu F.; -l, Wang K.

2012-01-01

166

Effect of polaronic pseudogap on tunneling spectra of high-Tc cuprate superconductors  

International Nuclear Information System (INIS)

We propose a model of quasi-particle tunneling across the high-Tc superconductor-insulator-normal metal junction based on the different mechanisms for tunneling of electrons at positive bias and dissociating polaronic Cooper pairs and large polarons at negative bias, and the gap inhomogeneity (i.e., multigap) picture. We show that the main features of the tunneling spectra such as low-bias U- and V-shaped features, asymmetry and high-bias dip-hump features, their temperature and doping dependences, and shoulders inside the conductance peaks observed in high-Tc cuprates arise naturally from the model. The experimental tunneling spectra of Ba2Sr2CaCu2O8+? are fitted quite well by taking into account the distribution of BCS and polaronic gap values. (author)

2012-01-01

167

Probing Nanoscale Electronic and Magnetic Interaction with Scanning Tunneling Spectroscopy  

DEFF Research Database (Denmark)

This thesis is concerned with fundamental research into electronic and magnetic interaction on the nanoscale. From small metallic and magnetic islands and layers to single atoms. The research revolves around magnetic interaction probed through the spectroscopic capabilities of the scanning tunneling microscope (STM). Especially at low temperatures the Kondo resonance is used to probe magnetic interaction with ferromagnetic islands and between two atoms. The latter showing a crossover between Kondo screened atoms and antiferromagnetically coupled atoms close to the quantum critical point. This is related to research in correlated electron materials such as studies of phase transitions in heavy fermion compounds and magnetic interaction in spintronic research. The capping of cobalt islands on Cu(111) with silver is investigated with STM and photoemission spectroscopy. It is shown that at low coverage the silver preferably nucleates on top of the bilayer high cobalt islands compared to directly on the Cu(111) substrate. Furthermore, the silver forms a combination of a reconstruction and a Moire pattern which is investigated with low-energy electron diraction and spectroscopic STM mapping at 6. The heterostructure is found to have very interesting electronic properties. The d-related state from the now buried cobalt island is visible through the silver capping layer, but the silver Moire pattern modulates the spin-polarized cobalt d-related state in amplitude, energy position and width. This is related to the d-band model for catalytic reactions. The largest change is in the amplitude of the state, however the "reversed" structure of cobalt on Ag(111) show similar properties, but with a large shift in energy instead of amplitude. The Kondo eect is used to probe magnetic interaction between the aforementioned silver-capped cobalt islands (and additionally gold-capped cobalt islands) and single cobalt atoms positioned on the Moire pattern. A split Kondo resonance due to the exchange interaction between the island and the atom is observed. In a more technical section of the thesis, it is shown how a gold-coated STM tip will make the tip apex susceptible to a single cobalt atom. The tip is indented either directly in a Au(111) surface or gold akes are picked up from cobalt islands on Cu(111). A change in the local barrier height (work function) of the tip-sample junction indicates that the apex is gold-coated and a single cobalt atom can be pickup up. The cobalt atom attached to the tip displays a Kondo resonance formed between the atom and the tip similar to the resonance displayed when the atom is on the surface with a clean tip. Here, this is used to show how a two-impurity Kondo system consisting of two cobalt atoms, one on the tip and one on the Au(111) sample, is undergoing a continuous crossover from Kondo screened atoms to antiferromagnetically coupled atoms when the atoms are moved from non-interacting to strongly interacting. In the Kondo screened regime, the Kondo temperature is believed to be constant, but the Fano line ii shape changes continuously from a dip to a peak. In the antiferromagnetic regime, inelastic spin-ip excitations reveal a splitting with a continuous increase in energy levels when pushing the atoms further together. This is supported by numerical renormalization group calculations. The crossover between the two regimes is furthermore interesting because it occurs in an area of the phase diagram close to the elusive quantum critical point, where the phase transition line meets absolute zero temperature. This freely positionable Kondo system on the tip represents a novel way to probe magnetic interaction with the possibility to continuously change the position of the probing Kondo system. The experiment is believed to be one of many applications possible and the method opens up for a new eld within STM. We expect that our work has direct impact in other research areas, such as for heavy fermion materials, a class of materials whose properties are governed by the competition between Kondo screening an

Bork, Jakob

2010-01-01

168

Tuning the electron transport at single donors in zinc oxide with a scanning tunnelling microscope  

Science.gov (United States)

In devices like the single-electron transistor the detailed transport properties of a nanostructure can be measured by tuning its energy levels with a gate voltage. The scanning tunnelling microscope in contrast usually lacks such a gate electrode. Here we demonstrate tuning of the levels of a donor in a scanning tunnelling microscope without a third electrode. The potential and the position of the tip are used to locally control band bending. Conductance maps in this parameter space reveal Coulomb diamonds known from three-terminal data from single-electron transistors and provide information on charging transitions, binding energies and vibrational excitations. The analogy to single-electron transistor data suggests a new way of extracting these key quantities without making any assumptions about the unknown shape of the scanning tunnelling microscope tip.

Zheng, Hao; Weismann, Alexander; Berndt, Richard

2014-01-01

169

Dopant enhanced etching of TiSe2 by scanning tunneling microscopy.  

Science.gov (United States)

The surfaces of pure and Mn doped TiSe(2) were etched using a scanning tunneling microscope. Both types of samples were found to etch easily when scanning was performed in ambient conditions. This process was enhanced at step edges or other surface defects. In pure samples, material was removed in a layer-by-layer fashion with a strong dependence on the scanning direction of the tip. Doped samples etched far more rapidly, to the point that stable scanning conditions were difficult to establish. Doped samples also showed a greater number of pits and other defects on their surface. A relatively small percentage of dopants was necessary to strongly impact the surface topography and stability. These results show that impurities can play a dominant role when using scanning tunneling microscopy to create surface nanostructures. PMID:20550168

Kidd, Timothy E; Gamb, Brett I; Skirtachenko, Polina I; Strauss, Laura H

2010-07-01

170

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

International Nuclear Information System (INIS)

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

2007-04-01

171

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

Energy Technology Data Exchange (ETDEWEB)

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.

Lysenko, O; Novikov, N; Gontar, A; Grushko, V; Shcherbakov, A [Institute for Superhard Materials, National Academy of Sciences, Kiev (Ukraine)

2007-04-15

172

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

Science.gov (United States)

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.

Lysenko, O.; Novikov, N.; Gontar, A.; Grushko, V.; Shcherbakov, A.

2007-04-01

173

Scanning tunneling spectroscopy on Mn12 single molecule magnets grafted on Au(111)  

International Nuclear Information System (INIS)

We report on the electronic properties of Mn12 molecules chemically grafted on the functionalized Au(111) surface studied by means of scanning tunneling microscopy/spectroscopy at room temperature. Reproducible current-voltage curves were obtained from Mn12 molecules showing a large region of low conductance around the Fermi energy. In agreement with the tunneling spectroscopy results the bias voltage variation upon scanning leads to apparent height changes of the Mn12 clusters. We discuss these findings in the light of the recent band structure calculations and electronic transport measurements on single Mn12 molecules

2008-03-01

174

Scanning tunneling spectroscopy on Mn{sub 12} single molecule magnets grafted on Au(111)  

Energy Technology Data Exchange (ETDEWEB)

We report on the electronic properties of Mn{sub 12} molecules chemically grafted on the functionalized Au(111) surface studied by means of scanning tunneling microscopy/spectroscopy at room temperature. Reproducible current-voltage curves were obtained from Mn{sub 12} molecules showing a large region of low conductance around the Fermi energy. In agreement with the tunneling spectroscopy results the bias voltage variation upon scanning leads to apparent height changes of the Mn{sub 12} clusters. We discuss these findings in the light of the recent band structure calculations and electronic transport measurements on single Mn{sub 12} molecules.

Fonin, M; Voss, S; Ruediger, U [Fachbereich Physik, Universitaet Konstanz, 78457 Konstanz (Germany); Burgert, M; Groth, U [Fachbereich Chemie, Universitaet Konstanz, 78457 Konstanz (Germany); Dedkov, Y S [Institut fuer Festkoerperphysik, Technische Universitaet Dresden, 01062 Dresden (Germany)], E-mail: Mikhail.Fonin@uni-konstanz.de

2008-03-15

175

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

International Nuclear Information System (INIS)

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

2006-07-01

176

Low-temperature scanning tunneling spectroscopy study of two-dimensional electron systems confined in semiconductor heterostructures  

International Nuclear Information System (INIS)

Low-temperature scanning tunneling spectroscopy under ultra-high vacuum was employed to investigate the two-dimensional electron system at the epitaxial surface of Sidoped In0.53Ga0.47As/In0.52Al0.48As(111)A quantum-well structures. The electron density in the near-surface region of the quantum well could be controlled through modulation doping. Spectra of the electronic local density of states in the conduction band showed a clear step-like energy dependence that reveals the subband states. In spectra acquired at some areas of nanometer size, peaks were observed near subband minima, indicating the existence of bound states

2007-04-01

177

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

Directory of Open Access Journals (Sweden)

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

Vassilis Gikas

2012-08-01

178

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

Science.gov (United States)

Driven by progress in sensor technology, computer software and data processing capabilities, terrestrial laser scanning has recently proved a revolutionary technique for high accuracy, 3D mapping and documentation of physical scenarios and man-made structures. Particularly, this is of great importance in the underground space and tunnel construction environment as surveying engineering operations have a great impact on both technical and economic aspects of a project. This paper discusses the use and explores the potential of laser scanning technology to accurately track excavation and construction activities of highway tunnels. It provides a detailed overview of the static laser scanning method, its principles of operation and applications for tunnel construction operations. Also, it discusses the planning, execution, data processing and analysis phases of laser scanning activities, with emphasis given on geo-referencing, mesh model generation and cross-section extraction. Specific case studies are considered based on two construction sites in Greece. Particularly, the potential of the method is examined for checking the tunnel profile, producing volume computations and validating the smoothness/thickness of shotcrete layers at an excavation stage and during the completion of excavation support and primary lining. An additional example of the use of the method in the geometric documentation of the concrete lining formwork is examined and comparisons against dimensional tolerances are examined. Experimental comparisons and analyses of the laser scanning method against conventional surveying techniques are also considered. PMID:23112655

Gikas, Vassilis

2012-01-01

179

Insulated gold scanning tunneling microscopy probes for recognition tunneling in an aqueous environment  

Science.gov (United States)

Chemically functionalized probes are required for tunneling measurements made via chemical contacts (“Recognition Tunneling”). Here, we describe the etching of gold STM probes suitable for chemical functionalization with moieties bearing thiol groups. Insulated with high density polyethylene, these probes may be used in aqueous electrolytes with sub pA leakage currents. The area of the exposed probe surface was characterized via the saturation current in an electroactive solution (0.1 M K3Fe(CN)6). Twenty five percent of the probes had an exposed region of 10 nm radius or less.

Tuchband, Michael; He, Jin; Huang, Shuo; Lindsay, Stuart

2012-01-01

180

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

International Nuclear Information System (INIS)

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

2013-01-01

 
 
 
 
181

Modification of tantalum surfaces by scanning tunneling microscopy in an electrochemical cell  

Energy Technology Data Exchange (ETDEWEB)

The morphological evolution of tantalum surfaces induced by scanning in an electrochemical cell have been investigated by scanning tunneling microscopy (STM). Repeated scanning over the same region was found to create a surface with a reduced peak-to-peak corrugation. This phenomenon was observed for negative tip biases only, and was also found to occur at a slower rate while scanning in air. X-ray photoelectron spectroscopy shows layers of Ta{sub 2}O{sub 5} deposited anodically on samples imaged with STM.

Thundat, T.; Nagahara, L.A.; Oden, P.I.; Lindsay, S.M. (Department of Physics, Arizona State University, Tempe, Arizona 85287 (USA)); George, M.A.; Glaunsinger, W.S. (Department of Chemistry, Arizona State University, Tempe, Arizona 85287 (USA))

1990-07-01

182

Note: Symmetric modulation methodology applied in improving the performance of scanning tunneling microscopy.  

Science.gov (United States)

A symmetric modulation methodology is proposed to combine robust control of external disturbance, rapid response to steep sidewalls with the high speed of a traditional scanning tunneling microscopy. The 1400 × 200 ?m(2) topography of a comb-like steep sidewalls micro-structure with the depth of 23 ?m was acquired at a high scanning speed of 120 ?ms(-1) and the detectable slope angle is up to 85°. The total measuring time was only 17 min. In addition, a 4 × 4 mm(2) aluminum dual-sinusoidal array has been successfully measured with a scanning speed up to 500 ?ms(-1). It improved the performance of the normal scanning tunneling microscope and enables efficient and stable measurement of large-area complex micro-structures, and thus can be introduced to engineering applications. PMID:24387483

Ju, Bing-Feng; Zhu, Wu-Le; Zhang, Wei

2013-12-01

183

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

Science.gov (United States)

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. PMID:20863138

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

2010-10-13

184

Observation of AlGaAs/GaAs multiquantum well structure by scanning tunneling microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have imaged an AlGaAs/GaAs multiquantum well structure by scanning tunneling microscopy (STM). In order to localize the structure the STM is integrated in a conventional scanning electron microscope. The observed surface structure has a periodicity of ?180 Å and shows an apparent corrugation of ?10 Å in the constant current mode. We discuss the possible mechanisms of the observed contrast, which we tentatively attribute to the different electrical properties of the two different layers.

1990-01-01

185

Note: A simple, convenient, and reliable method to prepare gold scanning tunneling microscope tips  

Energy Technology Data Exchange (ETDEWEB)

A simple method to prepare gold tips for scanning tunneling microscopy has been introduced. In this method, electrochemical etching without a hazardous electrolyte was employed. The setup uses basic laboratory instrumentation to control the etching process. This avoids purchasing complicated, expensive, and dedicated equipment for tip preparation. A procedure to optimize the etching parameters by setting the current limit is described. Etched tips were checked with both optical and scanning electron microscopy.

Qian Guoguang; Saha, Swatilekha; Lewis, K. M. [Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States)

2010-01-15

186

Note: A simple, convenient, and reliable method to prepare gold scanning tunneling microscope tips.  

Science.gov (United States)

A simple method to prepare gold tips for scanning tunneling microscopy has been introduced. In this method, electrochemical etching without a hazardous electrolyte was employed. The setup uses basic laboratory instrumentation to control the etching process. This avoids purchasing complicated, expensive, and dedicated equipment for tip preparation. A procedure to optimize the etching parameters by setting the current limit is described. Etched tips were checked with both optical and scanning electron microscopy. PMID:20113141

Qian, Guoguang; Saha, Swatilekha; Lewis, K M

2010-01-01

187

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present the design of a variable-temperature ultrahigh vacuum (UHV) scanning tunneling microscope which can be operated between 20 and 400 K. The microscope is mounted directly onto the heat exchanger of a He continuous flow cryostat without vibration isolation inside the UHV chamber. The coarse approach is performed with an inertial slider driven by the same piezo tube that is also used for scanning. The performance of the instrument is demonstrated by two different kinds of measurements:...

Mugele, Frieder; Rettenberger, Armin; Boneberg, Johannes; Leiderer, Paul

1998-01-01

188

Self-affine fractal vapour-deposited gold surfaces characterization by scanning tunnelling microscopy  

Energy Technology Data Exchange (ETDEWEB)

The morphological evolution of the surfaces of gold deposits grown from the vapour on smooth glass under nonequilibrium conditions and incident angle near substrate normal is studied at the nanometer level by scanning tunnelling microscopy. For an average film thickness equal to or greater than 500 nm, the interface thickness ([xi]) reaches a steady state. Under these conditions, [xi] depends on the scan length (L) as [xi] [proportional to] L[sup [alpha

Salvarezza, R.C.; Arvia, A.J. (Inst. de Investigaciones Fisicoquimicas Teoricas y Aplicadas (INIFTA), La Plata (Argentina)); Vazquez, L. (Inst. de Ciencia de Materiales, CSIC, Univ. Autonoma de Madrid (Spain)); Herrasti, P.; Ocon, P.; Vara, J.M. (Dept. Quimica Fisica Aplicada C-II, Univ. Autonoma de Madrid (Spain))

1992-12-15

189

Transient measurements with an ultrafast scanning tunneling microscope on semiconductor surfaces  

DEFF Research Database (Denmark)

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

Keil, Ulrich Dieter Felix; Jensen, Jacob Riis

1998-01-01

190

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

CERN Document Server

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

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

2013-01-01

191

Local crystallography analysis for atomically resolved scanning tunneling microscopy images  

Science.gov (United States)

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

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

2013-10-01

192

Local crystallography analysis for atomically resolved scanning tunneling microscopy images.  

Science.gov (United States)

Scanning probe microscopy has emerged as a powerful and flexible tool for atomically resolved imaging of surface structures. However, due to the amount of information extracted, in many cases the interpretation of such data is limited to being qualitative and semi-quantitative in nature. At the same time, much can be learned from local atom parameters, such as distances and angles, that can be analyzed and interpreted as variations of local chemical bonding, or order parameter fields. Here, we demonstrate an iterative algorithm for indexing and determining atomic positions that allows the analysis of inhomogeneous surfaces. This approach is further illustrated by local crystallographic analysis of several real surfaces, including highly ordered pyrolytic graphite and an Fe-based superconductor FeTe0.55Se0.45. This study provides a new pathway to extract and quantify local properties for scanning probe microscopy images. PMID:24060841

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

2013-10-18

193

Local crystallography analysis for atomically resolved scanning tunneling microscopy images  

International Nuclear Information System (INIS)

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

2013-10-18

194

Fixing the energy scale in scanning tunneling microscopy on semiconductor surfaces.  

Science.gov (United States)

In scanning tunneling experiments on semiconductor surfaces, the energy scale within the tunneling junction is usually unknown due to tip-induced band bending. Here, we experimentally recover the zero point of the energy scale by combining scanning tunneling microscopy with Kelvin probe force spectroscopy. With this technique, we revisit shallow acceptors buried in GaAs. Enhanced acceptor-related conductance is observed in negative, zero, and positive band-bending regimes. An Anderson-Hubbard model is used to rationalize our findings, capturing the crossover between the acceptor state being part of an impurity band for zero band bending and the acceptor state being split off and localized for strong negative or positive band bending, respectively. PMID:24313511

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

2013-11-22

195

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

International Nuclear Information System (INIS)

A low temperature scanning tunneling microscope device was constructed which allows a simultaneous spectroscopic and morphological measurement up to 4.2 K and 1T. Layers of niobium and NbSe_2 were measured and flux lines were determined. (WL)

1991-01-01

196

Preparation of Chemically Etched Tips for Ambient Instructional Scanning Tunneling Microscopy  

Science.gov (United States)

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…

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

2010-01-01

197

Scanning tunneling microscopy of copper electrodeposited in the presence of benzotriazole  

Energy Technology Data Exchange (ETDEWEB)

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

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

1988-12-01

198

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

Directory of Open Access Journals (Sweden)

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

Xue Qikun

2012-03-01

199

Nanolithography on SrRuO{sub 3} thin film surfaces by scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

Nanolithography on SrRuO{sub 3} (SRO) thin film surfaces has been performed by a scanning tunneling microscope under ambient conditions. The depth of etched lines increases with increasing bias voltage but it does not change significantly by increasing the tunneling current. The dependence of line-width on bias voltage from experimental data is in agreement with theoretical calculation based on field-induced evaporation mechanism. Moreover, a three-square nanostructure was successfully created, showing the capability of fabricating nanodevices in SRO thin films.

Liu Yun, E-mail: yun.liu@ntnu.n [Department of Physics, Norwegian University of Science and Technology, 7491 Trondheim (Norway); Zhang Jia [School of Mechanical Engineering, University of South China, Hengyang 421001 (China)

2010-04-01

200

Nanolithography on SrRuO3 thin film surfaces by scanning tunneling microscopy  

International Nuclear Information System (INIS)

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

2010-04-01

 
 
 
 
201

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

DEFF Research Database (Denmark)

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

Hansen, Ole; Ravnkilde, Jan Tue

1998-01-01

202

Single atom extraction by scanning tunneling microscope tip-crash and nanoscale surface engineering  

CERN Document Server

We report a novel atom extraction mechanism from the native substrate by means of a scanning tunneling microscope tip-crash on a Ag(111) surface at 5 K. Individual atoms are scattered on the surface when a silver coated tip is dipped into the substrate at low tunneling biases. Quantitative analyses reveal that the mechanical energy supplied by the tip-crash dominates the atom extraction process. Application of this procedure is demonstrated by constructing quantum structures using the extracted atoms on an atom-by-atom basis.

Hla, S W; Iancu, V; Deshpande, Abhay A; Hla, Saw Wai; Braun, Kai-Felix; Iancu, Violeta; Deshpande, Aparna

2004-01-01

203

A Mechanism for Cutting Carbon Nanotubes with a Scanning Tunneling Microscope  

CERN Document Server

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

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

2000-01-01

204

High order field emission resonances on W(110) and Fe/W(110) studied by scanning tunneling spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

Above metal surfaces a Rydberg-like series of states exists close to the vacuum level due to the potential well created by the attractive image potential and the surface projected bulk band gap. In scanning tunneling microscopy (STM) experiments these so-called image-potential states (IPS) experience a Stark shift, hence they are often called field emission resonances in this context. Neglecting the influence of the image potential, a simple triangular potential model can be applied to determine the effective electric field in the constant current spectroscopy of IPS. Whereas commercial STM electronics typically provide a maximum gap voltage of 10 V, we present scanning tunneling spectra of field emission resonances above the W(110) and Fe/W(110) surface up to the order of n=30 and voltages up to 20 V. The results will be discussed in terms of electric field determination, revealing that the assumption of a constant electric field is only applicable to voltages exceeding 10 V.

Emmenegger, Anika; Krause, Stefan; Kubetzka, Andre; Herzog, Gabriela; Wiesendanger, Roland [Institute of Applied Physics, University of Hamburg (Germany)

2009-07-01

205

Scanning tunnelling microscopy of real time defect motion on surfaces  

International Nuclear Information System (INIS)

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

2005-02-04

206

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)

Three decades ago, with a tiny tip of platinum, the scientific world saw the real space imaging of single atoms with unprecedented spatial resolution. This signalled the birth of one of the most versatile surface probes, based on the physics of quantum mechanical tunnelling: the scanning tunnelling microscope (STM). Invented in 1981 by Gerd Binnig and Heinrich Rohrer of IBM, Zurich, it led to their award of the 1986 Nobel Prize. Atoms, once speculated to be abstract entities used by theoreticians for mere calculations, can be seen to exist for real with the nano-eye of an STM tip that also gives real-space images of molecules and adsorbed complexes on surfaces. From a very fundamental perspective, the STM changed the course of surface science and engineering. STM also emerged as a powerful tool to study various fundamental phenomena relevant to the properties of surfaces in technological applications such as tribology, medical implants, catalysis, sensors and biology—besides elucidating the importance of local bonding geometries and defects, non-periodic structures and the co-existence of nano-scale phases. Atom-level probing, once considered a dream, has seen the light with the evolution of STM. An important off-shoot of STM was the atomic force microscope (AFM) for surface mapping of insulating samples. Then followed the development of a flurry of techniques under the general name of scanning probe microscopy (SPM). These techniques (STM, AFM, MFM, PFM etc) designed for atomic-scale-resolution imaging and spectroscopy, have led to brand new developments in surface analysis. All of these novel methods enabled researchers in recent years to image and analyse complex surfaces on microscopic and nanoscopic scales. All of them utilize a small probe for sensing the surface. The invention of AFM by Gerd Binnig, Calvin Quate and Christopher Gerber opened up new opportunities for characterization of a variety of materials, and various industrial applications could be envisaged. AFM observations of thin-film surfaces give us a picture of surface topography and morphology and any visible defects. The growing importance of ultra-thin films for magnetic recording in hard disk drive systems requires an in-depth understanding of the fundamental mechanisms occurring during growth. This special issue of Journal of Physics D: Applied Physics covers all of the different aspects of SPM that illustrate the achievements of this methodology: nanoscale imaging and mapping (Chiang, and Douillard and Charra), piezoresponse force microscopy (Soergel) and STM engineering (Okuyama and Hamada, and Huang et al). Chiang takes the reader on a journey along the STM imaging of atoms and molecules on surfaces. Jesse and Kalinin explore the band excitations that occur during the corresponding processes. Jia et al propose STM and molecular beam epitaxy as a winning experimental combination at the interface of science and technology. Douillard and Charra describe the high-resolution mapping of plasmonic modes using photoemission and scanning tunnelling microscopy. Cricenti et al demonstrate the importance of SPM in material science and biology. Wiebe et al have probed atomic scale magnetism, revealed by spin polarized scanning tunnelling microscopy. In addition, Simon et al present Fourier transform scanning tunnelling spectroscopy and the possibility to obtain constant energy maps and band dispersion using local measurements. Lackinger and Heckl give a perspective of the use of STM to study covalent intermolecular coupling reactions on surfaces. Okuyama and Hamada investigated hydrogen bond imaging and engineering with STM. Soergel describes the study of substrate-dependent self-assembled CuPc molecules using piezo force microscope (PFM). We are very grateful to the authors and reviewers for the papers in this special issue of Journal of Physics D: Applied Physics. Their contributions have provided a comprehensive picture of the evolution, status and potential of scanning probe microscopy, conveying to the readers the full excitement of this forefront do

Ramachandra Rao, M. S.; Margaritondo, Giorgio

2011-11-01

207

Direct evidence of arsenic(III)-carbonate complexes obtained using electrochemical scanning tunneling microscopy.  

Science.gov (United States)

Electrochemical scanning tunneling microscopy (ECSTM), ion chromatography (IC), and electrospray ionization-mass spectrometry/mass spectrometry were applied to investigate the interactions between arsenite [As(III)] and carbonate and arsenate [As(V)] and carbonate. The chemical species in the single and binary component solutions of As(III), As(V), and carbonate were attached to a Au(111) surface and then imaged in a 0.1 M NaClO4 solution at the molecular level by ECSTM. The molecules formed highly ordered adlayers on the Au(111) surface. High-resolution STM images revealed the orientation and packing arrangement of the molecular adlayers. Matching the STM images with the molecular models constructed using the Hyperchem software package indicated that As(III) formed two types of complexes with carbonate, including As(OH)2CO3- and As(OH)3(HCO3-)2. No complexes were formed between As(V) and carbonate. IC chromatograms of the solutions revealed the emergence of the new peak only in the aged As(III)-carbonate solution. MS spectra showed the presence of a new peak at m/z 187 in the aged As(III)-carbonate solution. The results obtained with the three independent methods confirmed the formation of As(OH)2CO3-. The results also indicated that As(OH)3 could be associated with HCO3- through a hydrogen bond. The knowledge of the formation of the As(III) and carbonate complexes will improve the understanding of As(III) mobility in the environment and removal of As(III) in water treatment systems. PMID:17441685

Han, Mei-Juan; Hao, Jumin; Christodoulatos, Christos; Korfiatis, George P; Wan, Li-Jun; Meng, Xiaoguang

2007-05-15

208

Atom-by-atom extraction using scanning tunneling microscope tip-cluster interaction  

CERN Document Server

We investigate atomistic details of a single atom extraction process realized by using scanning tunneling microscope (STM) tip-cluster interaction on a Ag(111) surface at 6 K. Single atoms are extracted from a silver cluster one atom at a time using small tunneling biases less than 35 mV and a threshold tunneling resistance of 47 kOhm. A combination of total energy calculations and molecular dynamics simulations shows a lowering of the atom extraction barrier upon approaching the tip to the cluster. Thus, a mere tuning of the proximity between the tip and the cluster governs the extraction process and is sufficient to extract an atom. The atomically precise control and reproducibility of the process are demonstrated by repeatedly extracting single atoms from a silver cluster on an atom-by-atom basis.

Deshpande, Abhay A; Kara, A; Acharya, D P; Vaughn, J; Rahman, T S; Hla, S W

2006-01-01

209

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

CERN Document Server

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

Yamashita, Mikio; Morita, Ryuji

2005-01-01

210

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

International Nuclear Information System (INIS)

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

2011-07-01

211

Temperature-dependent scanning tunneling spectroscopy on the Si(557)-Au surface  

Science.gov (United States)

Room-temperature and low-temperature (77 K) scanning tunneling spectroscopy and voltage-dependent scanning tunneling microscopy data are used to study the local electronic properties of the quasi-one-dimensional Si(557)-Au surface in real space. A gapped local electron density of states near the ?¯ point is observed at different positions of the surface, i.e., at protrusions arising from Si adatoms and step-edge atoms. Within the gap region, two distinct peaks are observed on the chain of localized protrusions attributed to Si adatoms. The energy gap widens on both types of protrusions after cooling from room temperature to T = 77 K. The temperature dependence of the local electronic properties can therefore not be attributed to a Peierls transition occurring for the step edge only. We suggest that more attention should be paid to finite-size effects on the one-dimensional segments.

Sauter, M.; Hoffmann, R.; Sürgers, C.; Löhneysen, H. v.

2014-02-01

212

Scanning tunnelling spectroscopy of quantized electron accumulation at InxGa1-xN surfaces  

International Nuclear Information System (INIS)

Electron tunnelling spectroscopy has been used to investigate quantized levels in electron accumulation layers at InGaN surfaces. The tunnelling spectra exhibit a plateau in the normalized conductance which widens with increasing Ga-content, corresponding to the band gap of InGaN. The measured InxGa1-xN band gaps (between ?0.65 eV for x=1 and 1.8 eV for x=0.43) are consistent with the band gaps determined by previous optical absorption and cathodoluminescence spectroscopy. Additional structures in the spectra reflect the two-dimensional electronic subbands in the surface quantum well. The subband energies depend on Ga-content, bulk doping level and the resultant shape of the surface potential well. The tunnelling spectra are compared with calculations of the potential well, the charge-profile and the subband energies. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

2006-01-01

213

Structure of YSi2 nanowires from scanning tunneling spectroscopy and first principles  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Exceptionally long and uniform YSi2 nanowires are formed via self-assembly on Si(001). The in-plane width of the thinnest wires is known to be quantized in odd multiples of the silicon lattice constant. Here, we identify a class of nanowires that violates the “odd multiple” rule. The structure of the thinnest wire in this category is determined by comparing scanning tunneling spectroscopy measurements with the calculated surface density of states of candidate models by means of the Pendry...

Iancu, V.; Kent, P. R. C.; Zeng, C. G.; Weitering, H. H.

2009-01-01

214

Low temperature scanning tunneling microscopy and spectroscopy in ultra-high-vacuum and high magnetic fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have developed an ultra-stable low temperature scanning tunneling microscope (LTSTM) for application in atomic scale spectroscopy and atom manipulation experiments. The design is based on the Besocke type microscope allowing the installation of the LTSTM within a liquid helium bath (LHe) cryostat in ultra-high-vacuum (UHV). The exclusive use of nonmagnetic materials allows STM-operation in magnetic fields up to 5 T without influencing the measurements. Compared to the frequently used "beet...

Hirstein, Andreas

1998-01-01

215

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Werner, Robert

2011-01-01

216

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Dunlap, D. D.; Garci?a, R.; Schabtach, E.; Bustamante, C.

1993-01-01

217

Scanning tunneling microscopy evidence of semicrystalline and helical conducting polymer structures  

Energy Technology Data Exchange (ETDEWEB)

Scanning tunneling microscopy images of strands, microislands, and thin films formed by the conducting polymers polypyrrole tosylate, polypyrrole tetrafluoroborate, and polythiophene tetrafluoroborate are presented. The polymer strands and microislands contain two types of helical structures with diameters of 1.5-1.8 nm, a simple helix, and 5-6 nm, a superhelix. The polymer films gradually transform from an ordered crystalline array located at the anode surface to an amorphous material at the air-polymer interface.

Yang, R.; Evans, D.F. (Univ. of Minnesota, Minneapolis (USA)); Christensen, L.; Hendrickson, W.A. (3M Co., St. Paul, MN (USA))

1990-07-26

218

Thickness-dependent thin-film resistivity: application of quantitative scanning-tunneling-microscopy imaging  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The dependence of thin-film resistivity on the thickness is known to be strongly influenced by the interaction of the conduction electrons with the surface. Great efforts have been made in recent years, mainly concerning the quantum-mechanical description of the surface scattering. Detailed discussions of this problem, however, suffer from the lack of information concerning the real topography of thin-film surfaces. The development of scanning tunneling microscopy (STM) now gives the chance o...

1990-01-01

219

Topographic and diffusion measurements of gold and platinum surfaces by scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

The authors have used the scanning tunneling microscope in air to investigate the topographic and diffusion properties of the surfaces formed by melting gold and platinum wires into spheres. Nanolithographic parameters, including thresholds for surface modification of the gold and platinum surfaces, have been studied and coefficients for self-diffusion have been determined. The data suggest diffusion rates at room temperature 1-2 orders of magnitude lower on platinum than on gold.

Sommerfeld, D.A.; Cambron, R.T.; Beebe, T.P. Jr. (Univ. of Utah, Salt Lake City (USA))

1990-12-27

220

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

2007-01-01

 
 
 
 
221

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2011-01-01

222

Selecting the tip electron orbital for scanning tunneling microscopy imaging with sub-ångström lateral resolution  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report on scanning tunneling microscopy (STM) studies performed with single crystalline W[001] tips on a graphite(0001) surface. Results of distance-dependent STM experiments with sub-ångström lateral resolution and density functional theory electronic structure calculations show how to controllably select one of the tip electron orbitals for high-resolution STM imaging. This is confirmed by experimental images reproducing the shape of the 5dxz,yz and 5dx2 ? y2 tungsten atomic orbitals...

Shvets, Igor; Bozhko, Sergey; Krasnikov, Sergey; Lubben, Olaf

2010-01-01

223

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

The spin-polarized scanning tunneling microscopy (sp-STM) is demonstrated between a magnetized tip and a magnetic substrate at the solid/liquid interface using the differential magnetic mode. The implementation of the sp-STM setup into the electrochemical STM is an important part. Special attention is paid to the magnetostriction effect of possible magnetic tips. As a model system extended Co islands are electrochemically grown on an Au(111) single crystal. An appropriate electrochemical envi...

Majer, Claudia

2013-01-01

224

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Haggerty, L.; Lenhoff, A. M.

1993-01-01

225

Pointed carbon fiber ultramicroelectrodes: a new probe option for electrochemical scanning tunneling microscopy.  

Science.gov (United States)

Carbon tips for in situ scanning tunneling microscopy studies in an electrochemical environment were prepared by electrochemical etching of carbon fibers and subsequent coating with electrodeposition paint and a silicone elastomer. The tips obtained were stable in acidic electrolyte and allowed high-resolution in situ imaging of the bare Au(111) electrode surface and of Au(111) covered by monolayers of the octyl-triazatriangulenium molecule. PMID:23286780

Sripirom, Jiyapa; Kuhn, Sonja; Jung, Ulrich; Magnussen, Olaf; Schulte, Albert

2013-01-15

226

Thickness determination of biological samples with a zeta-calibrated scanning tunneling microscope.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A single-tube scanning tunneling microscope has been zeta-calibrated by using atomic steps of crystalline gold and was used for measuring the thickness of two biological samples, metal-coated as well as uncoated. The hexagonal surface layer of the bacterium Deinococcus radiodurans with an open network-type structure shows thickness values that are strongly influenced by the substrate and the preparation method. In contrast, the thickness of the purple membrane of Halobacterium halobium with i...

1990-01-01

227

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Xue, Yongqiang; Datta, Supriyo

1999-01-01

228

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Vassilis Gikas

2012-01-01

229

Identification of DNA--cisplatin adducts in a blind trial of in situ scanning tunneling microscopy.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Scanning tunneling microscopy (STM) reveals nanometer scale details of hydrated DNA but the interpretation of the images is controversial because of substrate artifacts and the lack of a theory for image contrast. We demonstrate that we have overcome these problems by identifying five DNA samples by their STM images alone in a blinded trial. The samples were single-stranded and double-stranded DNA with and without covalent modification by the anti-tumor drug cisplatin. The cisplatin adducts w...

Jeffrey, A. M.; Jing, T. W.; Derose, J. A.; Vaught, A.; Rekesh, D.; Lu, F. X.; Lindsay, S. M.

1993-01-01

230

Potential applications of a scanning tunnelling microscope with a superconducting tip  

International Nuclear Information System (INIS)

We discuss the potential applications of the scanning tunnelling microscope (STM) with the superconducting tip. A number of set-ups are considered. The theoretical models are used to calculate the dependence of the measurable quantities on the bias voltage and other relevant parameters. Anticipated results include the position-resolved measurement of primary and secondary components of the superconducting order parameter on the surface, single-spin relaxation time measurements and, possibly, an effective spin-polarized STM. (author)

2002-03-01

231

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

Science.gov (United States)

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. PMID:24689625

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

2014-03-01

232

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

Science.gov (United States)

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.

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

2014-03-01

233

Topography and transport properties of oligo(phenylene ethynylene) molecular wires studied by scanning tunneling microscopy  

Science.gov (United States)

Conjugated phenylene(ethynylene) molecular wires are of interest as potential candidates for molecular electronic devices. Scanning tunneling microscopic study of the topography and current-voltage (I-V) characteristics of self-assembled monolayers of two types of molecular wires are presented here. The study shows that the topography and I-Vs, for small scan voltages, of the two wires are quite similar and that the electronic and structural changes introduced by the substitution of an electronegative N atom in the central phenyl ring of these wires does not significantly alter the self-assembly or the transport properties.

Dholakia, Geetha R.; Fan, Wendy; Koehne, Jessica; Han, Jie; Meyyappan, M.

2003-01-01

234

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

CERN Document Server

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

Schueler, M; Berakdar, J

2013-01-01

235

Analyzing multiple encounter as a possible origin of electron spin resonance signals in scanning tunneling microscopy on Si(111) featuring C and O defects  

Science.gov (United States)

The Si(111)7 × 7 surface exposed to 0.1 L of O2 and the carbonized Si(111) surface are investigated by electron spin resonance scanning tunneling microscopy (ESR-STM) using frequency sweeps and magnetic field sweeps. Only after oxidizing the clean Si(111)7 × 7 or by using the carbonized Si(111), spatially averaged ESR-STM spectra exhibit several peaks and dips around the frequencies corresponding to g = 2. The energy difference between these features is close to the known hyperfine splitting of A ? 9 MHz for vacancies in SiC interacting with next-nearest neighbor 29Si. Such spectra with peaks and dips can be qualitatively reproduced by introducing a primary encounter of the lead electrons with the localized spin correlating the two spins which afterwards evolve in different local hyperfine fields, thus, developing a relative spin angle prior to tunneling.

Manassen, Y.; Averbukh, M.; Morgenstern, M.

2014-05-01

236

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

International Nuclear Information System (INIS)

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

2010-07-01

237

Tunneling conductance spectra of a metal/ferromagnet junction within a two-band model  

Energy Technology Data Exchange (ETDEWEB)

We present a theory based on a scattering matrix approach to explain the tunneling spectroscopy of a metal/ferromagnet junction. The isotropic one-band free electron model was used to describe the energy dispersion relation of the electrons in a metal layer, while two-band approximation was used to examine the electronic dispersion relation within the ferromagnetic material. s-band and d-band coupling were considered using the two-band approximation. In this work, interfacial spin-flip scattering was neglected. The energy dispersion and tunneling conductance spectra were calculated to study the effect of the coupling strength between the two bands. With no coupling, the energy band will have the crossing point between the bands. In contrast, a gap is opened up at the crossing points. It was found that the size of the gap depends on the coupling strength. Some kinks occurred in the energy band corresponding to the crossing points. The rich features of conductance spectra occurring in the metallic regime have the effects more significant than those occurring in the tunneling regime. In both regimes the conductance spectrum becomes largest if the effective mass of free electrons in the majority of the bands in the ferromagnetic material is approximately in the same order as that of the free electrons in metals. - Highlights: Black-Right-Pointing-Pointer Tunneling conductance spectra of two-band ferromagnet/superconductor are calculated. Black-Right-Pointing-Pointer s-band and d-band of ferromagnet are mixed. Black-Right-Pointing-Pointer The conductance spectra consist of several kinks, depending on the coupling strength. Black-Right-Pointing-Pointer Two-band ferromagnet model is very essential.

Pasanai, K., E-mail: krisakronmsu@gmail.com [Department of Physics, Faculty of Science, Mahasarakham University, Khamriang Sub-District, Kantarawichai District, Maha Sarakham 44150 (Thailand); Pairor, P. [School of Physics, Institute of Science, Suranaree University of Technology, 111 University Avenue, Muang District, Nakhon Ratchasima 30000 (Thailand)

2013-02-15

238

Tunneling conductance spectra of a metal/ferromagnet junction within a two-band model  

International Nuclear Information System (INIS)

We present a theory based on a scattering matrix approach to explain the tunneling spectroscopy of a metal/ferromagnet junction. The isotropic one-band free electron model was used to describe the energy dispersion relation of the electrons in a metal layer, while two-band approximation was used to examine the electronic dispersion relation within the ferromagnetic material. s-band and d-band coupling were considered using the two-band approximation. In this work, interfacial spin-flip scattering was neglected. The energy dispersion and tunneling conductance spectra were calculated to study the effect of the coupling strength between the two bands. With no coupling, the energy band will have the crossing point between the bands. In contrast, a gap is opened up at the crossing points. It was found that the size of the gap depends on the coupling strength. Some kinks occurred in the energy band corresponding to the crossing points. The rich features of conductance spectra occurring in the metallic regime have the effects more significant than those occurring in the tunneling regime. In both regimes the conductance spectrum becomes largest if the effective mass of free electrons in the majority of the bands in the ferromagnetic material is approximately in the same order as that of the free electrons in metals. - Highlights: ? Tunneling conductance spectra of two-band ferromagnet/superconductor are calculated. ? s-band and d-band of ferromagnet are mixed. ? The conductance spectra consist of several kinks, depending on the coupling strength. ? Two-band ferromagnet model is very essential.

2013-02-01

239

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Palacios, J. J.; Martin-moreno, L.; Chiappe, G.; Louis, E.; Tejedor, C.

1994-01-01

240

ScanRanker: Quality Assessment of Tandem Mass Spectra via Sequence Tagging  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Ma, Ze-qiang; Chambers, Matthew C.; Ham, Amy-joan L.; Cheek, Kristin L.; Whitwell, Corbin W.; Aerni, Hans-rudolf; Schilling, Birgit; Miller, Aaron W.; Caprioli, Richard M.; Tabb, David L.

2011-01-01

 
 
 
 
241

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

DEFF Research Database (Denmark)

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

Giusca, Cristina E; Tison, Yann

2008-01-01

242

Vibrational spectroscopy of 4-mercaptopyridine on Au(111): A comparison of scanning tunneling spectroscopy and calculations  

Energy Technology Data Exchange (ETDEWEB)

Notion of the adsorption structure and vibrational properties is essential to understand electronic transport across molecules and, therefore, is an essential issue in the field of molecular electronics. Scanning tunnelling microscopy (STM), scanning tunnelling spectroscopy (STS), and especially inelastic electron tunnelling spectroscopy (IETS) is ideal to investigate these properties on a single-molecular basis. We employ these techniques to reveal the properties of 4-mercaptopyridine (4MPy) on Au(111) and compare those to, e.g., DFT calculations. We put emphasis on IETS where we find about 20 excitations in the energy range 0-200 meV. Results are compared to calculations based on the vibrational self-consistent field method and earlier experimental results. We conclude that 4MPy adsorbs at elbow sites, in the fcc region, and at step edges preferentially in a bridge configuration thereby ruling out a model proposed earlier which suggests that adsorption of a single 4MPy is accompanied by a Au ad-atom.

Maurer, Norbert; Tschetschetkin, Anna; Koslowski, Berndt; Ziemann, Paul [Institut fuer Festkoerperphysik (Germany); Respondek, Inga; Benoit, David M. [Nachwuchsgruppe Theorie SFB 569, Universitaet Ulm, Albert-Einstein-Allee 11, D-89081 Ulm (Germany)

2010-07-01

243

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

International Nuclear Information System (INIS)

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

2013-01-01

244

Electronic structure of single DNA molecules resolved by transverse scanning tunnelling spectroscopy.  

Science.gov (United States)

Attempts to resolve the energy-level structure of single DNA molecules by scanning tunnelling spectroscopy span over the past two decades, owing to the unique ability of this technique to probe the local density of states of objects deposited on a surface. Nevertheless, success was hindered by extreme technical difficulties in stable deposition and reproducibility. Here, by using scanning tunnelling spectroscopy at cryogenic temperature, we disclose the energy spectrum of poly(G)-poly(C) DNA molecules deposited on gold. The tunnelling current-voltage (I-V) characteristics and their derivative (dI/dV-V) curves at 78 K exhibit a clear gap and a peak structure around the gap. Limited fluctuations in the I-V curves are observed and statistically characterized. By means of ab initio density functional theory calculations, the character of the observed peaks is generally assigned to groups of orbitals originating from the different molecular components, namely the nucleobases, the backbone and the counterions. PMID:18037894

Shapir, Errez; Cohen, Hezy; Calzolari, Arrigo; Cavazzoni, Carlo; Ryndyk, Dmitry A; Cuniberti, Gianaurelio; Kotlyar, Alexander; Di Felice, Rosa; Porath, Danny

2008-01-01

245

Resonance tunneling spectroscopy of heteropoly compounds  

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-12-15

246

Resonance tunneling spectroscopy of heteropoly compounds  

Science.gov (United States)

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

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

2012-12-01

247

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

International Nuclear Information System (INIS)

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

2003-10-01

248

Molecularly resolved images of peptide-functionalized gold surfaces by scanning tunneling microscopy.  

Science.gov (United States)

Peptide-terminated monolayers were formed through a Huisgen cycloaddition reaction between an ?-helical peptide containing two propargylglycine unnatural functional groups 20 Å apart and an alkanethiol self-assembled monolayer (SAM) on a gold surface containing 25% surface density of reactive azide terminal groups. The azide- and peptide-terminated surfaces were imaged by scanning tunneling microscopy (STM) using a low tunneling current of 10 pA. On the peptide-terminated surface, oblong features ~30 Å long and ~20 Å wide were observed and attributed to individual surface-bound ?-helical peptides oriented parallel to the gold surface. These features covered an area of the surface corresponding to a density of 0.11 ± 0.01 peptides nm(-2), compared with a theoretical density of ~0.14 peptides nm(-2) for a fully reacted surface. Finally, no evidence of peptide aggregation was observed on either short (<10 nm) or long (~100 nm) length scales. PMID:23146081

Raigoza, Annette F; Webb, Lauren J

2012-11-28

249

Scanning tunneling microscopy/spectroscopy as an atomic-resolution dopant profiling method in Si  

International Nuclear Information System (INIS)

The ability of scanning tunneling microscopy and spectroscopy (STM/STS) as a dopant profiling method in Si is demonstrated. We have developed two different methods. One is a simultaneous measurement of potential and dopant atom distributions by conventional STM/STS. Actually acceptor and donor atoms were distinctly detected and the local potential variation was observed at p-n junctions on atomically-flat hydrogenated Si(111) substrates. The comparison between the measured dopant atom and potential distributions at a p-n junction revealed that the potential profile was significantly affected by the fluctuation of dopant atom distributions. The other is a quantitative measurement of carrier distributions by resonance electron tunneling (RET) spectroscopy. The RET peak energy of C60 molecules placed on oxidized Si(001) surfaces was measure by STS and the resulting value systematically varied depending on the doping level of the substrates, enabling us to measure carrier density profiles across p-n junctions

2008-03-01

250

Scanning tunneling microscopy/spectroscopy as an atomic-resolution dopant profiling method in Si  

Energy Technology Data Exchange (ETDEWEB)

The ability of scanning tunneling microscopy and spectroscopy (STM/STS) as a dopant profiling method in Si is demonstrated. We have developed two different methods. One is a simultaneous measurement of potential and dopant atom distributions by conventional STM/STS. Actually acceptor and donor atoms were distinctly detected and the local potential variation was observed at p-n junctions on atomically-flat hydrogenated Si(111) substrates. The comparison between the measured dopant atom and potential distributions at a p-n junction revealed that the potential profile was significantly affected by the fluctuation of dopant atom distributions. The other is a quantitative measurement of carrier distributions by resonance electron tunneling (RET) spectroscopy. The RET peak energy of C{sub 60} molecules placed on oxidized Si(001) surfaces was measure by STS and the resulting value systematically varied depending on the doping level of the substrates, enabling us to measure carrier density profiles across p-n junctions.

Nishizawa, M; Bolotov, L; Kanayama, T [MIRAI-Advanced Semiconductor Research Center (ASRC), National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305-8562 (Japan)], E-mail: m.nishizawa@aist.go.jp

2008-03-15

251

Scanning tunneling spectrum of electrons confined in a rectangular quantum corral  

International Nuclear Information System (INIS)

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

2009-06-03

252

MgB2 Energy Gap Determination by Scanning Tunneling Spectroscopy  

CERN Document Server

We report scanning tunneling spectroscopy (STS) measurements of the gap properties of both ceramic MgB2 and c-axis oriented epitaxial MgB2 thin films. Both show a temperature dependent zero bias conductance peak and evidence for two superconducting gaps. We report tunneling spectroscopy of superconductor-insulator-superconductor (S-I-S) junctions formed in two ways in addition to normal metal-insulator-superconductor (N-I-S) junctions. We find a gap delta=2.3-2.8 meV, with spectral features and temperature dependence that are consistent between S-I-S junction types. In addition, we observe evidence of a second, larger gap, delta=7.2 meV, consistent with a proposed two-band model.

Heitmann, T W; Kim, D M; Choi, J H; Giencke, J; Eom, C B; Regan, K A; Rogado, N S; Hayward, M A; He, T; Slusky, J S; Khalifah, P; Haas, M; Cava, R J; Larbalestier, D C; Rzchowski, M S

2002-01-01

253

Surface investigation of Ca1-xPrxFe2As2 by scanning tunneling microscopy  

Science.gov (United States)

Rare-earth-doped CaFe2As2 exhibits small volume-fraction superconductivity up to 49 K of unknown origin [1,2]. We use scanning tunneling microscopy to locally probe possible sources of this phase in Ca1-xPrxFe2As2. We encounter three kinds of surface morphologies and infer their chemical identities with local work function measurements. We also image Pr^3+ dopants as positive-energy resonances in tunneling conductance and examine their relationship with an observed inhomogeneous spectral gap. [1] B. Lv, L. Denga, M. Goocha, F. Weia, Y. Suna, J. K. Meena, Y.-Y. Xuea, B. Lorenza, and C.-W. Chu, Proc. Nat. Acad. Sci. 108, 15705 (2011). [2] S. R. Saha, N. P. Butch, T. Drye, J. Magill, S. Ziemak, K. Kirshenbaum, P. Y. Zavalij, J. W. Lynn, and J. Paglione, Phys. Rev. B 85, 024525 (2012)

Huang, Dennis; Zeljkovic, Ilija; Song, Can-Li; Lv, Bing; Chu, Ching-Wu; Hoffman, Jennifer E.

2013-03-01

254

Scanning tunneling microscopy of the subsurface structures of tungsten ditelluride and molybdenum ditelluride  

Science.gov (United States)

The surface structure of the van der Waals faces of tungsten ditelluride (WTe2) and molybdenum ditelluride (2H-MoTe2) have been studied with scanning tunneling microscopy (STM). The hexagonal symmetry observed on the 2H-MoTe2 surface is similar to that observed previously on other transition-metal dichalcogenides. On WTe2, which has a distorted layered structure due to the pairing of the metal atoms, the scanning tunneling micrographs distinctly show the dominance of the metal. Buckled, zig-zag chains of paired atomic rows, which are the signature of the tungsten layer, are observed. These results show for the first time that subsurface atoms can be imaged with the STM. The corrugated surface tellurium layer could not be identified unambiguously in two-dimensional scans. These results are surprising because a first-principles pseudofunction calculation of the surface-electronic charge density around the Fermi energy of the WTe2 surface shows that the calculated spatial distribution of the charge density at the surface has the characteristics of the topmost Te atoms. The experimental observations suggest that, unlike the case of graphite images, a direct comparison of the STM image of this surface with calculated surface charge density is not possible. These observations further suggest that the hexagonal symmetry observed in MoTe2 and other transition-metal dichalcogenides is also due to the metal layer rather than the surface chalcogenides.

Tang, S. L.; Kasowski, R. V.; Parkinson, B. A.

1989-05-01

255

Scanning tunneling microscopy and spectroscopy on GaN and InGaN surfaces  

International Nuclear Information System (INIS)

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

2009-01-01

256

Sub-barrier Coulomb effects on the interference pattern in tunneling ionization photoelectron spectra  

CERN Multimedia

We use a quantum trajectory-based semi-classical method to account for Coulomb interaction between the photoelectron and the parent ion in the classically forbidden, sub-barrier region during strong-field tunneling ionization processes. We show that---besides the well-known modification of the tunneling ionization probability---there is also an influence on the interference pattern in the photoelectron spectra. In the long-wavelength limit, the shift of the intra-cycle interference fringes caused by sub-barrier Coulomb effects in the laser polarization direction can be derived analytically. We compare our results with \\emph{ab initio} solutions of the time-dependent Schr\\"odinger equation and find good agreement in the long-wavelength regime, whereas the standard strong field approximation fails. We show that the nodal structure along low-order above-threshold ionization rings is also affected by sub-barrier Coulomb effects.

Yan, Tian-Min

2012-01-01

257

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1998-12-31

258

Bi-Sr-Ca-Cu-O surface studied by means of scanning tunnelling microscope  

International Nuclear Information System (INIS)

Surface topography of the high-Tc superconductor BiSrCaCu2Ox has been investigated by means of scanning tunnelling microscope. The measurements were performed on the natural surface of ceramics material in air at room temperature. It can be deduced from the surface images, that bulk orthorhombic crystal structure extends to the surface. The surface seems to be uniform metallic in character and not drastically contaminated. Regular steps observed on the surface correspond to the dimension of the unit cell in z direction or its multiples

1989-03-10

259

Structure of YSi(2) nanowires from scanning tunneling spectroscopy and first principles.  

Science.gov (United States)

Exceptionally long and uniform YSi(2) nanowires are formed via self-assembly on Si(001). The in-plane width of the thinnest wires is known to be quantized in odd multiples of the silicon lattice constant. Here, we identify a class of nanowires that violates the "odd multiple" rule. The structure of the thinnest wire in this category is determined by comparing scanning tunneling spectroscopy measurements with the calculated surface density of states of candidate models by means of the Pendry R-factor analysis. The relative stability of the odd and even wire systems is analyzed via first-principles calculations. PMID:19859579

Iancu, V; Kent, P R C; Zeng, C G; Weitering, H H

2009-09-21

260

Structure of YSi2 nanowires from scanning tunneling spectroscopy and first principles  

Science.gov (United States)

Exceptionally long and uniform YSi2 nanowires are formed via self-assembly on Si(001). The in-plane width of the thinnest wires is known to be quantized in odd multiples of the silicon lattice constant. Here, we identify a class of nanowires that violates the ``odd multiple'' rule. The structure of the thinnest wire in this category is determined by comparing scanning tunneling spectroscopy measurements with the calculated surface density of states of candidate models by means of the Pendry R-factor analysis. The relative stability of the odd and even wire systems is analyzed via first-principles calculations.

Iancu, V.; Kent, P. R. C.; Zeng, C. G.; Weitering, H. H.

2009-09-01

 
 
 
 
261

Scanning tunneling microscopy study of surface reconstruction induced by N adsorption on Cu (100) surface  

International Nuclear Information System (INIS)

The reconstructed structure of Cu (100) surface induced by atomic N adsorption is studied by using scanning tunneling microscopy (STM). The 2D structure of copper boundary between neighbouring N covered islands is found to be sensitive to the growth conditions, e.g. N+ bombardment time and annealing temperature. The copper boundary experiences a transition from nano-scale stripe to nano-particle when the substrate is continuously annealed at 623 K for a longer time. A well-defined copper-stripe network can be achieved by precisely controlling the growth conditions, which highlights the possibility of producing new templates for nanofabrication. (condensed matter: structure, thermal and mechanical properties)

2010-02-01

262

Scanning tunneling microscopy of a stage-1 CuCl2 graphite intercalation compound  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report a scanning-tunneling-microscope (STM) study of a stage-1 graphite intercalation compound (GIC) of approximate stoichiometry C6CuCl2. When the sample bias is positive with respect to the tip, we observe a hexagonal symmetry in which all the atoms of the graphite surface plane are imaged. This is in contrast to the threefold symmetry usually seen in atomic-resolution STM images of highly oriented pyrolytic graphite (HOPG), which we also observe on a reference sample of HOPG. The three...

Olk, C. H.; Heremans, J.; Dresselhaus, M. S.; Speck, J. S.; Nicholls, J. T.

1991-01-01

263

Probing the atomic structure of metallic nanoclusters with the tip of a scanning tunneling microscope.  

Science.gov (United States)

Preformed Co clusters with an average diameter of 2.5 nm are produced in the gas phase and are deposited under controlled ultra-high vacuum conditions onto a thin insulating NaCl film on Au(111). Relying on a combined experimental and theoretical investigation, we demonstrate visualization of the three-dimensional atomic structure of the Co clusters by high-resolution scanning tunneling microscopy (STM) using a Cl functionalized STM tip that can be obtained on the NaCl surface. More generally, use of a functionalized STM tip may allow for systematic atomic structure determination with STM of nanoparticles that are deposited on metal surfaces. PMID:24366289

Schouteden, Koen; Lauwaet, Koen; Janssens, Ewald; Barcaro, Giovanni; Fortunelli, Alessandro; Van Haesendonck, Chris; Lievens, Peter

2014-02-21

264

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

Science.gov (United States)

Coordination bonding between para-quarterphenyl-dicarbonitrile linkers and gadolinium on Ag(111) has been exploited to construct pentameric mononuclear supramolecules, consisting of a rare-earth center surrounded by five molecular linkers. By employing a scanning tunneling microscope tip, a manipulation protocol was developed to position individual pentamers on the surface. In addition, the tip was used to extract and replace individual linkers yielding tetrameric, pentameric, nonameric, and dodecameric metallosupramolecular arrangements. These results open new avenues toward advanced nanofabrication methods and rare-earth nanochemistry by combining the versatility of metal-ligand interactions and atomistic manipulation capabilities. PMID:24456175

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

2014-03-12

265

Surface damage through grazing incidence ions investigated by scanning tunneling microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Surface damage, caused by grazing incidence ions, is investigated with variable temperature scanning tunneling microscopy. The experiments are carried out on a Pt(111) crystal. The kinetic energy of noble gas ions is varied between 1-15 keV and the angle of incidence can be adjusted between 78.5° and 90° measured with respect to the surface normal. The damage patterns of single ion impacts, on flat terraces and at step edges of monoatomic height, are investigated at low surface temperatures...

Redinger, Alex

2009-01-01

266

Scanning tunneling microscope-based thermochemical hole burning on a series of charge transfer complexes  

International Nuclear Information System (INIS)

A thermochemical hole burning effect was observed on a series of 7, 7, 8, 8-tetra cyanoquinodimethane charge transfer complexes when applying a suitable voltage pulse using scanning tunneling microscope, which is attributed to the localized thermochemical decomposition of the complex induced by the current heating effect. The decomposition reaction evolves the low boiling point decomposition components of the charge transfer complex, leaving a nanometer-sized hole on the crystal surface. This effect demonstrates the possibility of creating a ultrahigh density thermochemical hole burning memory, in which information bit is recorded as a hole

2005-03-28

267

The mechanism of field emission for diamond films studied by scanning tunneling microscopy  

International Nuclear Information System (INIS)

Diamond films inherited with low electron affinity are prominent material for filed emission display devices. A close inspection of field emission efficiency at each local point by a scanning tunneling microscope (STM) for diamond films fabricated by chemical vapor deposition (CVD) method is fulfilled. We find that the emission character is better at the grain boundaries than on the center of the crystal. The temperature dependence on emission currents can be successfully portrayed by the semiconductor thermionic emission theory. The work function is almost temperature independent whereas the surface band bending increases as temperature decreases

2003-07-14

268

First-principles study on scanning tunneling microscopy images of hydrogen-terminated Si(110) surfaces  

CERN Document Server

Scanning tunneling microscopy images of hydrogen-terminated Si(110) surfaces are studied using first-principles calculations. Our results show that the calculated filled-state images and local density of states are consistent with recent experimental results, and the empty-state images appear significantly different from the filled-state ones. To elucidate the origin of this difference, we examined in detail the local density of states, which affects the images, and found that the bonding and antibonding states of surface silicon atoms largely affect the difference between the filled- and empty-state images.

Horie, S; Hirose, K; Katoh, J; Ono, T; Endo, K; Horie, Shinya; Arima, Kenta; Hirose, Kikuji; Katoh, Jun; Ono, Tomoya; Endo, Katsuyoshi

2005-01-01

269

Characterization of hot electron transmission tunneling through the gap potential in scanning hot electron microscopy  

Science.gov (United States)

With the emitter/gap-potential/tip structure, we have studied the hot electron (HE) transmission properties used in scanning hot electron microscopy (SHEM). The rational and practical gap potential profile between two electrodes has been constructed based on the electrostatic image force and the jellium model. The transmission probability calculated using the constructed potential profile in this paper differs from that using conventional profiles appreciably. Dependencies of the transmission probability on the gap separation, HE energy, and the tunnel voltage have been made clear.

Zhang, B. Y.; Furuya, K.

2001-05-01

270

Direct observation of long chain alkane bilayer films on graphite by scanning tunneling microscopy  

Science.gov (United States)

The interface between a solution of hexatriacontane (n-C 36H 74) in decane and the basal plane of graphite has been studied by scanning tunneling microscopy at room temperature. For the first time, we show that a second layer which is rotated by 60° with respect to the first layer may grow at the interface. We demonstrate that the carbon skeleton of the molecule is parallel to the graphite surface. We propose a model for the arrangement of the molecular layers and an explanation for the origin of the second layer rotation.

Watel, G.; Thibaudau, F.; Cousty, J.

1993-01-01

271

Observation and manipulation of tris(dibenzoylmethanato)ruthenium molecules by low temperature scanning tunnelling microscopy  

Science.gov (United States)

The behavior of tris(dibenzoylmethanato)ruthenium molecules has been studied using low temperature scanning tunneling microscopy after adsorption on Ag(111) and Cu(111). On both surfaces, the molecules present two adsorption geometries: a bi-lobed and a chiral threefold structure. This latter form can stand up to adopt a bi-lobed conformation which is oriented along the dense crystallographic directions. The molecular geometries after adsorption can be modified using the STM tip. In one of these modifications, a switch between two different conformations has been observed. The data recorded during the experiments show that this phenomenon is induced by the electric field in the STM junction.

Vernisse, L.; Guillermet, O.; Bonvoisin, J.; Coratger, R.

2014-01-01

272

Manipulation and Dynamics at the Atomic Scale: A Dual Use of the Scanning Tunneling Microscopy  

Science.gov (United States)

Atomic scale modification of surfaces may trigger off dynamical processes. This is shown here by using the tip of a scanning tunneling microscope to extract an individual atom in a controlled manner from a predefined site of the reconstructed Ge(111)- c(2 ×8) surface. By thermally activated hopping of neighboring adatoms to the vacant site, the produced single-atom vacancy diffuses on the surface. From statistical analysis of the adatom configurations observed around the vacancy, we determine tiny ( free energy between the configurations. A linear increase of the configuration free energy with the number of adatoms located at metastable T4 sites is reported.

Molinàs-Mata, Patrici; Mayne, Andrew J.; Dujardin, Gérald

1998-04-01

273

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

DEFF Research Database (Denmark)

Upon imaging, electrochemical scanning tunneling microscopy (ESTM), scanning electrochemical micro-scopy (SECM) and in situ STM resolve information on electronic structures and on surface topography. At very high resolution, imaging processing is required, as to obtain information that relates to crystallographic-surface structures. Within the wide range of new technologies, those images surface features, the electrochemical scanning tunneling microscope (ESTM) provides means of atomic resolution where the tip participates actively in the process of imaging. Two metallic surfaces influence ions trapped in the interface of imaging and the independent-electrochemical control opens new pathways of studying fundamentals of electrocrystallisation and of adsorption kinetics. In addition, the ESTM instrument itself may be applied as a tool of nanotechnology that allows manufac-ture of new products, e.g., nanoelectronics and single-molecule probing. In principle, the ESTM is capable of sub-atomic resolution but many details at this level of magnification need further treatment of recorded data before real information is obtained. Deconvolution of the data according to the instrument response may explain some of the characteristic details of the images. A large proportion of the observed noise may be explained by the scanning actions of the feedback circuitry while a minor fraction of the image details may be explained by surface drift phenomena. As opposed to the method of deconvolution, conventional methods of filtering discard some of the recorded data, as to improve the signal-to-noise ratio. By deconvolution however, all data were maintained and it is demonstrated that images of atomic resolution were sharpened considerably and shadow effects were removed in images of lower resolution. Thus, the smooth features observed in high-resolution images of metallic nanocrystallites may be effectively deconvoluted, as to resolve more details of the crystalline morphology (see figure). Images of surface-crystalline metals indicate that more than a single atomic layer is involved in mediating the tunneling current that generates the image. Tunneling through less-conductive molecules, such as organic molecules, DNA molecules or protein molecules, may be facilitated along channels of electronic conductivity or by transfer of protons generated electrochemically at the participating surfaces.

Andersen, Jens Enevold Thaulov Technical University of Denmark,

274

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

2012-01-01

275

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

Science.gov (United States)

By injecting low-energy minority carriers from the tip of a scanning tunneling microscope (STM) and analyzing the light emitted from the tip-sample gap of the STM, it is possible to study the optical and electronic properties of individual semiconductor nanostructures with an extremely high spatial resolution close to the atomic scale. This technique has been applied to investigate the transport properties of hot electrons injected into AlGaAs/GaAs quantum well structures and the optical properties of single self-assembled InAs/AlGaAs quantum dots. The physical principles, usefulness and future expectations of this novel technique are discussed. PMID:15180213

Tsuruoka, Tohru; Ushioda, Sukekatsu

2004-01-01

276

Formation of imine oligomers on Au under ambient conditions investigated by scanning tunneling microscopy.  

Science.gov (United States)

Scanning tunneling microscopy has been used to investigate the nucleophilic substitution reaction between melamine (1,3,5-triazine-2,4,6-triamine) and terephthalaldehyde on Au/mica following deposition from solution in ambient conditions. The reaction is observed to proceed at room temperature over a time scale of days with the formation of imine oligomers intermixed with melamine islands on the Au surface. The oligomers ultimately self-assemble into a porous arrangement. The mechanism and extent of the surface confined reactions are discussed. PMID:23252973

Greenwood, J; Baddeley, C J

2013-01-15

277

Electric field and potential around localized scatterers in thin metal films studied by scanning tunneling potentiometry  

CERN Document Server

Direct observation of electric potential and field variation near local scatterers like grain boundaries, triple points and voids in thin platinum films studied by scanning tunneling potentiometry is presented. The field is highest at a void, followed by a triple point and a grain boundary. The local field near a void can even be four orders of magnitude higher than the macroscopic field. This indicates that the void is the most likely place for an electromigration induced failure. The field build up near a scatterer strongly depends on the grain connectivity which is quantified by the average grain boundary reflection coefficient, estimated from the resistivity.

Ramaswamy, G; Ramaswamy, Geetha

1998-01-01

278

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

CERN Document Server

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

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

2004-01-01

279

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present a combined approach that relies on computational simulations and scanning tunneling microscopy (STM) measurements to reveal morphological properties and stability criteria of carbon nanotube-DNA (CNT-DNA) constructs. Application of STM allows direct observation of very stable CNT-DNA hybrid structures with the well-defined DNA wrapping angle of 63.4° and a coiling period of 3.3?nm. Using force field simulations, we determine how the DNA-CNT binding energy depends on the sequence...

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

2011-01-01

280

Scanning tunneling microscopy of mercapto-hexyl-oligonucleotides attached to gold.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

6-mercapto hexyl-oligonucleotides bind to a gold surface strongly enough to permit imaging by a scanning tunneling microscope (STM). STM images showed worm-like chains that were approximately 12-(A-wide for single-stranded DNA and 20-(A-wide for double-stranded DNA. The chain lengths corresponded to 3.4 +/- 0.4 A per basepair for double-stranded DNA and 2.2 +/- 0.4 A per base for single-stranded DNA. This unexpectedly short length for single-stranded DNA was confirmed using oligomers with bot...

Rekesh, D.; Lyubchenko, Y.; Shlyakhtenko, L. S.; Lindsay, S. M.

1996-01-01

 
 
 
 
281

Analyzing multiple encounter as a possible origin of electron spin resonance signals in scanning tunneling microscopy on Si(111) featuring C and O defects  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The Si(111)7 x 7 surface exposed to 0.1 L of O-2 and the carbonized Si(111) surface are investigated by electron spin resonance scanning tunneling microscopy (ESR-STM) using frequency sweeps and magnetic field sweeps. Only after oxidizing the clean Si(111)7 x 7 or by using the carbonized Si(111), spatially averaged ESR-STM spectra exhibit several peaks and dips around the frequencies corresponding to g = 2. The energy difference between these features is close to the known hyperfine splitting...

2014-01-01

282

Temperature and field dependence of MgB2 energy gaps from tunneling spectra  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have synthesized MgB2/Pb planar junctions to study the temperature and field dependence of the superconducting energy gap of MgB2. The major peak occurs at Delta of about 2 meV, and this corresponds to a 2Delta/kBTc value of 1.18. While this is significantly smaller than the BCS weak coupling value, there are features in the tunneling spectra indicating the possibility of another larger gap. By fitting the dI/dV curves with a simple model, the larger gap is estimated to b...

Badr, Mohamed H.; Ng, K. -w

2002-01-01

283

Scanning tunneling spectroscopy on vortex cores in high-T{sub c} superconductors  

Energy Technology Data Exchange (ETDEWEB)

Scanning tunneling spectroscopy (STS) with its unique capacity for tunneling spectroscopy with sub-nanometer spatial resolution, has opened new ways to look at the flux lines and their distribution in superconductors. In contrast to all other imaging techniques, which are sensitive to the local magnetic field, STM relies on local changes in the density of states near the Fermi level to generate a real space image of the vortex distribution. It is thus sensitive to the vortex cores, which in high temperature superconductors have a size approaching the interatomic distances. The small size of the vortex cores and the anisotropic character of the high temperature superconductors allow pinning to play a large role in determining the vortex core positions. Vortex hopping between different pinning sites, again down to a sub-nanometer scale, has been studied by STM imaging as a function of time. These studies give microscopic indications for quantum tunneling of vortices. Moreover, STM provides new insights into the detailed electronic vortex core structure, revealing localized quasiparticles. (orig.)

Hoogenboom, B.W.; Maggio-Aprile, I.; Fischer, Oe. [Geneva Univ. (Switzerland). Dept. de Physique de la Matiere Condensee; Renner, C. [NEC Research Inst., Princeton, NJ (United States)

2002-07-01

284

Scanning tunneling microscopy of ordered arrays of heteropolyacids deposited on a graphite surface  

Energy Technology Data Exchange (ETDEWEB)

Keggin-type heteropolyacids (water-soluble H{sub 3}PMo{sub 12}O{sub 40}, H{sub 4}PMo{sub 11}VO{sub 40}, and H{sub 8}PMo{sub 10}{sup {minus}}VCuO{sub 40} and water-insoluble K{sub 3}PMo{sub 12}O{sub 40}, x = 1, 2, 2.5, 3) deposited on highly oriented pyrolytic graphite (HOPG) surfaces were successfully imaged by scanning tunneling microscopy (STM). All of these heteropoly acids (HPAs) formed clear two-dimensional ordered arrays on graphite, and their periodicities were in good agreement with values determined by X-ray crystallography. Spatially resolved tunneling spectroscopy was used to demonstrate that the arrays imaged represented HPA monolayers, as the characteristic tunneling spectrum of graphite was obtained at high-symmetry interstitial sites in these arrays. STM permitted observation of the ordered structures of HPAs when deposited on a chemically inert surface, as well as the determination of the effects of changing framework and charge-compensating cations on these structures. The ubiquity of ordered array formation of these HPAs suggests that they can be utilized to create well-defined surfaces with more complex chemical functions than one typically encounters in studies of metal or oxide single-crystal surfaces. 36 refs., 6 figs., 2 tabs.

Song, I.K.; Kaba, M.S.; Barteau, M.A. [Univ. of Delaware, Newark, DE (United States)] [and others

1996-09-01

285

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

Science.gov (United States)

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

Kazmerski, Lawrence L. (Lakewood, CO)

1990-01-01

286

Atomic-scale patterning of hydrogen terminated Ge(001) by scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

In this paper we demonstrate atomic-scale lithography on hydrogen terminated Ge(001). The lithographic patterns were obtained by selectively desorbing hydrogen atoms from a H resist layer adsorbed on a clean, atomically flat Ge(001) surface with a scanning tunneling microscope tip operating in ultra-high vacuum. The influence of the tip-to-sample bias on the lithographic process have been investigated. Lithographic patterns with feature-sizes from 200 to 1.8 nm have been achieved by varying the tip-to-sample bias. These results open up the possibility of a scanning-probe lithography approach to the fabrication of future atomic-scale devices in germanium.

Scappucci, G; Lee, W C T; Simmons, M Y [School of Physics, University of New South Wales, Sydney, NSW 2052 (Australia); Capellini, G, E-mail: giordano.scappucci@unsw.edu.a, E-mail: michelle.simmons@unsw.edu.a [Dipartimento di Fisica, Universita di Roma Tre, Via della Vasca Navale 84, 00146 Roma (Italy)

2009-12-09

287

Fabrication of [001]-oriented tungsten tips for high resolution scanning tunneling microscopy.  

Science.gov (United States)

The structure of the [001]-oriented single crystalline tungsten probes sharpened in ultra-high vacuum using electron beam heating and ion sputtering has been studied using scanning and transmission electron microscopy. The electron microscopy data prove reproducible fabrication of the single-apex tips with nanoscale pyramids grained by the {011} planes at the apexes. These sharp, [001]-oriented tungsten tips have been successfully utilized in high resolution scanning tunneling microscopy imaging of HOPG(0001), SiC(001) and graphene/SiC(001) surfaces. The electron microscopy characterization performed before and after the high resolution STM experiments provides direct correlation between the tip structure and picoscale spatial resolution achieved in the experiments. PMID:24434734

Chaika, A N; Orlova, N N; Semenov, V N; Postnova, E Yu; Krasnikov, S A; Lazarev, M G; Chekmazov, S V; Aristov, V Yu; Glebovsky, V G; Bozhko, S I; Shvets, I V

2014-01-01

288

Four-probe measurements with a three-probe scanning tunneling microscope  

Science.gov (United States)

We present an ultrahigh vacuum (UHV) three-probe scanning tunneling microscope in which each probe is capable of atomic resolution. A UHV JEOL scanning electron microscope aids in the placement of the probes on the sample. The machine also has a field ion microscope to clean, atomically image, and shape the probe tips. The machine uses bare conductive samples and tips with a homebuilt set of pliers for heating and loading. Automated feedback controlled tip-surface contacts allow for electrical stability and reproducibility while also greatly reducing tip and surface damage due to contact formation. The ability to register inter-tip position by imaging of a single surface feature by multiple tips is demonstrated. Four-probe material characterization is achieved by deploying two tips as fixed current probes and the third tip as a movable voltage probe.

Salomons, Mark; Martins, Bruno V. C.; Zikovsky, Janik; Wolkow, Robert A.

2014-04-01

289

Four-probe measurements with a three-probe scanning tunneling microscope.  

Science.gov (United States)

We present an ultrahigh vacuum (UHV) three-probe scanning tunneling microscope in which each probe is capable of atomic resolution. A UHV JEOL scanning electron microscope aids in the placement of the probes on the sample. The machine also has a field ion microscope to clean, atomically image, and shape the probe tips. The machine uses bare conductive samples and tips with a homebuilt set of pliers for heating and loading. Automated feedback controlled tip-surface contacts allow for electrical stability and reproducibility while also greatly reducing tip and surface damage due to contact formation. The ability to register inter-tip position by imaging of a single surface feature by multiple tips is demonstrated. Four-probe material characterization is achieved by deploying two tips as fixed current probes and the third tip as a movable voltage probe. PMID:24784678

Salomons, Mark; Martins, Bruno V C; Zikovsky, Janik; Wolkow, Robert A

2014-04-01

290

Fabrication of [001]-oriented tungsten tips for high resolution scanning tunneling microscopy  

Science.gov (United States)

The structure of the [001]-oriented single crystalline tungsten probes sharpened in ultra-high vacuum using electron beam heating and ion sputtering has been studied using scanning and transmission electron microscopy. The electron microscopy data prove reproducible fabrication of the single-apex tips with nanoscale pyramids grained by the {011} planes at the apexes. These sharp, [001]-oriented tungsten tips have been successfully utilized in high resolution scanning tunneling microscopy imaging of HOPG(0001), SiC(001) and graphene/SiC(001) surfaces. The electron microscopy characterization performed before and after the high resolution STM experiments provides direct correlation between the tip structure and picoscale spatial resolution achieved in the experiments.

Chaika, A. N.; Orlova, N. N.; Semenov, V. N.; Postnova, E. Yu.; Krasnikov, S. A.; Lazarev, M. G.; Chekmazov, S. V.; Aristov, V. Yu.; Glebovsky, V. G.; Bozhko, S. I.; Shvets, I. V.

2014-01-01

291

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

Energy Technology Data Exchange (ETDEWEB)

Several tens of chromium layers were deposited at 250 {sup 0}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 x 20 nm{sup 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.

Lagoute, J; Kawahara, S L; Chacon, C; Repain, V; Girard, Y; Rousset, S, E-mail: jerome.lagoute@univ-paris-diderot.fr [Laboratoire Materiaux et Phenomenes Quantiques, Universite Paris Diderot et CNRS, UMR 7162, Case courrier 7021, 75205 Paris Cedex 13 (France)

2011-02-02

292

Differentiating amino acid residues and side chain orientations in peptides using scanning tunneling microscopy.  

Science.gov (United States)

Single-molecule measurements of complex biological structures such as proteins are an attractive route for determining structures of the large number of important biomolecules that have proved refractory to analysis through standard techniques such as X-ray crystallography and nuclear magnetic resonance. We use a custom-built low-current scanning tunneling microscope to image peptide structures at the single-molecule scale in a model peptide that forms ? sheets, a structural motif common in protein misfolding diseases. We successfully differentiate between histidine and alanine amino acid residues, and further differentiate side chain orientations in individual histidine residues, by correlating features in scanning tunneling microscope images with those in energy-optimized models. Beta sheets containing histidine residues are used as a model system due to the role histidine plays in transition metal binding associated with amyloid oligomerization in Alzheimer's and other diseases. Such measurements are a first step toward analyzing peptide and protein structures at the single-molecule level. PMID:24219245

Claridge, Shelley A; Thomas, John C; Silverman, Miles A; Schwartz, Jeffrey J; Yang, Yanlian; Wang, Chen; Weiss, Paul S

2013-12-11

293

Scanning tunneling microscopy studies of fluorinated graphene films and field-directed sputter sharpening  

Science.gov (United States)

Graphene fluoride is a two-dimensional fluorocarbon, and the wide-gap analogue of graphene. Among chemical derivatives of graphene, graphene fluoride is unique in its ease of synthesis and stability, as well as the extensive study of its bulk form, graphite fluoride. Only in the last few years, however, has graphene fluoride been isolated experimentally, and our understanding of its atomic and electronic structure, stability, reduction, and use as a platform for lithographic patterning is still limited. In this dissertation, an ultra-high vacuum scanning tunneling microscope (UHV-STM) is employed for the characterization of exfoliated double-sided graphene fluoride (ds-GF) and of single-sided graphene fluoride (ss-GF) on Cu foil. We explore the structure and stability of each material and, in particular, identify ss-GF as a stable, well-ordered, wide-gap semiconductor. This dissertation offers the first atomic-resolution study of this novel material, and the first UHV-STM measurement of its electronic structure. Furthermore, we develop the novel field-directed sputter sharpening (FDSS) technique for producing sharp metal probes with 1 -- 5 nm radii of curvature, a prerequisite for high-resolution scanning tunneling microscopy (STM) imaging and nanolithography. We show that FDSS offers significant improvements in lithographic patterning, and is applicable to a range of materials, including the hard metallic-ceramic hafnium diboride (HfB2). Finally, we explore the use of HfB2-coated W wires for STM imaging and spectroscopy.

Schmucker, Scott W.

294

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

Science.gov (United States)

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

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

295

An easy-to-implement filter for separating photo-excited signals from topography in scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

In order to achieve elemental and chemical sensitivity in scanning tunneling microscopy (STM), synchrotron x-rays have been applied to excite core-level electrons during tunneling. The x-ray photo-excitations result in tip currents that are superimposed onto conventional tunneling currents. While carrying important physical information, the varying x-ray induced currents can destabilize the feedback loop causing it to be unable to maintain a constant tunneling current, sometimes even causing the tip to retract fully or crash. In this paper, we report on an easy-to-implement filter circuit that can separate the x-ray induced currents from conventional tunneling currents, thereby allowing simultaneous measurements of topography and chemical contrasts. The filter and the schematic presented here can also be applied to other variants of light-assisted STM such as laser STM.

Wang Kangkang; Rosenmann, Daniel; Holt, Martin; Winarski, Robert; Hla, Saw-Wai [Center for Nanoscale Materials, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States); Rose, Volker [Center for Nanoscale Materials, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States); Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States)

2013-06-15

296

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

Directory of Open Access Journals (Sweden)

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

Berndt Koslowski

2011-09-01

297

The tip-sample water bridge and light emission from scanning tunnelling microscopy  

Energy Technology Data Exchange (ETDEWEB)

The light emission spectrum from a scanning tunnelling microscope (LESTM) is investigated as a function of relative humidity and shown to provide a novel and sensitive means for probing the growth and properties of a water meniscus on the nanometre scale. An empirical model of the light emission process is formulated and applied successfully to replicate the decay in light intensity and spectral changes observed with increasing relative humidity. The modelling indicates a progressive water filling of the tip-sample junction with increasing humidity or, more pertinently, of the volume of the localized surface plasmons responsible for light emission; it also accounts for the effect of asymmetry in structuring of the water molecules with respect to the polarity of the applied bias. This is juxtaposed with the case of a non-polar liquid in the tip-sample nanocavity where no polarity dependence of the light emission is observed. In contrast to the discrete detection of the presence/absence of a water bridge in other scanning probe experiments through measurement of the feedback parameter for instrument control, LESTM offers a means of continuously monitoring the development of the water bridge with sub-nanometre sensitivity. The results are relevant to applications such as dip-pen nanolithography and electrochemical scanning probe microscopy.

Boyle, Michael G; Mitra, J; Dawson, Paul, E-mail: j.mitra@qub.ac.u [Centre for Nanostructured Media, School of Mathematics and Physics, Queen' s University, Belfast BT7 1NN (United Kingdom)

2009-08-19

298

A new organic complex thin film for ultra-high-density data storage with a scanning tunneling microscope  

Energy Technology Data Exchange (ETDEWEB)

A new organic complex, tetrathiafulvalene/m-nitrobenzylidene propanedinitrile (TTF/m-NBP), was prepared to use as an ultra-high-density data-storage medium. A nanometer-scale recording technique was demonstrated with a scanning tunneling microscope (STM) under ambient conditions. The organic complex thin film was fabricated by using a vacuum thermal deposition method. The results of Fourier transform infrared spectra showed that the structure of the organic complex thin film was the same as that of a complex crystal. Data were recorded by applying voltage pulses between the tip and the substrate. Current-voltage (I-V) curves measured by the STM showed that the conductance of the recorded region is much higher than that of the unrecorded region, which indicated that the data were recorded by a local change of the electrical property of the film. The smallest recorded mark was 1.1 nm in diameter and the width of the pulse voltage has an influence upon the diameter of the recording marks. (orig.)

Chen, Y.W. [College of Chemistry, Peking University, 100871, Beijing (China); Li, J.C.; Xue, Z.Q. [Department of Electronics, Peking University, 100871, Beijing (China)

2003-08-01

299

Scanning tunneling microscopy investigation of atomic-scale carbon nanotube defects produced by Ar{sup +} ion irradiation  

Energy Technology Data Exchange (ETDEWEB)

Multi-wall carbon nanotubes (MWCNTs) dispersed on graphite (HOPG) substrate were irradiated with Ar{sup +} ions of 30 keV, using a dose of D = 5 x 10{sup 11} ions/cm{sup 2}. The irradiated nanotubes were investigated by scanning tunneling microscopy (STM) and spectroscopy (STS) under ambient conditions. Atomic resolution STM images revealed individual nanotube defects, which appeared as 'hillocks' of 0.1-0.2 nm in height, due to the locally changed electronic structure. The results are in agreement with previous theoretical predictions. Electron density patterns (superstructures) were observed near the defect sites, which originated from the interference of incident waves and waves scattered by defects. The period of these superstructures is larger than the period determined by the atomic structure. After annealing at 450 deg. C in nitrogen atmosphere, the irradiated MWCNTs were investigated again. The effect of heat treatment on the irradiation-induced nanotube-defects was observed both on the STM images and on the recorded STS spectra.

Osvath, Z. [Research Institute for Technical Physics and Materials, Sciences (MFA), H-1525 Budapest, P.O. Box 49 (Hungary)]. E-mail: osvath@mfa.kfki.hu; Vertesy, G. [Research Institute for Technical Physics and Materials, Sciences (MFA), H-1525 Budapest, P.O. Box 49 (Hungary); Tapaszto, L. [Research Institute for Technical Physics and Materials, Sciences (MFA), H-1525 Budapest, P.O. Box 49 (Hungary); Weber, F. [Research Institute for Technical Physics and Materials, Sciences (MFA), H-1525 Budapest, P.O. Box 49 (Hungary); Horvath, Z.E. [Research Institute for Technical Physics and Materials, Sciences (MFA), H-1525 Budapest, P.O. Box 49 (Hungary); Gyulai, J. [Research Institute for Technical Physics and Materials, Sciences (MFA), H-1525 Budapest, P.O. Box 49 (Hungary); Biro, L.P. [Research Institute for Technical Physics and Materials, Sciences (MFA), H-1525 Budapest, P.O. Box 49 (Hungary)

2006-07-15

300

Structure of an InAs(111)A-(2x2)S surface studied by scanning tunneling microscopy, photoelectron spectroscopy, and x-ray photoelectron diffraction  

International Nuclear Information System (INIS)

The structure of an InAs(111)A-(2x2)S surface has been studied by using scanning tunneling microscopy (STM), synchrotron radiation photoemission spectroscopy (SRPES), and x-ray photoelectron diffraction (XPD). Honeycomblike images are observed by STM measured at a bias voltage of -1.4 V. Similar images are also observed at +1.5 V, although the intensity of the alternative corner of a hexagon is depressed, resulting in a threefold symmetry. S 2s and As 3d XPD patterns show that sulfur atoms rarely exchange the fourfold arsenic sites. Three surface components are found in the In 4d spectra. On the other hand, no surface components are found in the As 3d spectra. Based on the STM, SRPES, and XPD results, a probable structure model for the (2x2)S surface is proposed. The experimental XPD patterns are in good agreement with the calculated ones

2000-05-15

 
 
 
 
301

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

DEFF Research Database (Denmark)

Experimental data and theoretical notions are presented for 6-[1'-(6-mercapto-hexyl)-[4,4']bipyridinium]-hexane-1-thiol iodide (6V6) "wired" between a gold electrode surface and tip in an in situ scanning tunneling microscopy configuration. The viologen group can be used to "gate" charge transport across the molecular bridge through control of the electrochemical potential and consequently the redox state of the viologen moiety. This gating is theoretically considered within the framework of superexchange and coherent two-step notions for charge transport. It is shown here that the absence of a maximum in the I-tunneling versus electrode potential relationship can be fitted by a "soft" gating concept. This arises from large configurational fluctuations of the molecular bridge linked to the gold contacts by flexible chains. This view is incorporated in a formalism that is well-suited for data analysis and reproduces in all important respects the 6V6 data for physically sound values of the appropriate parameters. This study demonstrates that fluctuations of isolated configurationally "soft" molecules can dominate charge transport patterns and that theoretical frameworks for compact monolayers may not be directly applied under such circumstances.

Haiss, W.; Albrecht, Tim

2007-01-01

302

Scanning tunneling microscopy. Final report, 1 Oct 87-30 Sep 90  

Energy Technology Data Exchange (ETDEWEB)

Scanning tunneling microscopy (STM) has been used to image and modify the surfaces of III-V, II-VI and group IV semiconductors. A tip-simulator based on a photocode was developed. The simulator allows the development of ultra-sensitive electronics for controlling STM tip movement. Various forms of 'nano-machining,' including chiselling, sanding, and sweeping of atoms on a surface, were developed. An STM design was modified to allow bending of long thin samples of Si(100) in UHV to permit the study of surface strain. A variety of studies were conducted on Au (in air) CdTe (in air), Hg(sub 1-x)Mn(sub x)Te (under glycerin), and Hg(sub 1-x)Cd(sub x)Te (in air and under glycerin).

Dow, J.D.

1992-03-17

303

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

Science.gov (United States)

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

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

2013-12-01

304

Interlocked grain growth of YBCO film on magnesium oxide as observed by scanning tunneling microscopy  

International Nuclear Information System (INIS)

Thin films of YBa2Cu3O7 on MgO deposited by RF magnetron sputtering to study their superconducting behavior, were examined by a Scanning Tunneling Microscope. The films were deposited at room temperature, sintered exsitu at 850 C, 900 C, 930 C, 950 C and 980 C for 30 minutes each and cooled at rate of 100 C per hour in oxygen ambient. Topographic images taken in air show that the films which were initially amorphous in nature, gradually transform to a layered grain structure with the increase of sintering temperature. Films sintered at temperatures above 900 C are c-axis oriented and have a coarse grain structure. These grains layers of neighboring grains. The mechanism of interlocking of layers from adjacent grains and its possible influence on the superconducting properties has been discussed

1993-03-01

305

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

Science.gov (United States)

Experimental advances allow for the inclusion of multiple probes to measure the transport properties of a sample surface. We develop a theory of dual-probe scanning tunneling microscopy using a Green's function formalism, and apply it to graphene. Sampling the local conduction properties at finite length scales yields real space conductance maps which show anisotropy for pristine graphene systems and quantum interference effects in the presence of isolated impurities. Spectral signatures in the Fourier transforms of real space conductance maps include characteristics that can be related to different scattering processes. We compute the conductance maps of graphene systems with different edge geometries or height fluctuations to determine the effects of nonideal graphene samples on dual-probe measurements. PMID:24655267

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

2014-03-01

306

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

DEFF Research Database (Denmark)

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

Kalashnyk, Nataliya; Nielsen, Jakob T

2012-01-01

307

A theoretical model for single-molecule incoherent scanning tunneling spectroscopy  

Science.gov (United States)

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

Raza, H.

2008-11-01

308

A theoretical model for single-molecule incoherent scanning tunneling spectroscopy  

International Nuclear Information System (INIS)

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

2008-11-05

309

Scanning tunneling microscopy study of the superconducting properties of three-atomic-layer Pb films  

Science.gov (United States)

Ultrathin Pb films with a thickness of three monolayers (ML) were prepared on ?-?3 ×?3 Pb/Si(111) (Pb-SIC) substrate by molecular beam epitaxy. Despite significant defect scattering, low temperature scanning tunneling microscopy reveals a high superconducting transition temperature Tc of 6.9 K, compared with the bulk Tc (7.2 K). By applying external magnetic field, magnetic vortices were directly imaged, which demonstrates the robustness of superconductivity. By comparing to nearly free-standing Pb films on graphitized SiC (0001) substrate, we suggest that the higher Tc of 3 ML Pb films on Pb-SIC originates from the combined effects of quantum confinement and substrate-enhanced electron-phonon coupling.

Wang, Yilin; Chen, Mu; Li, Zhi; Wang, Lili; He, Ke; Xue, Qi-Kun; Ma, Xucun

2013-12-01

310

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

CERN Multimedia

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

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

2007-01-01

311

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

International Nuclear Information System (INIS)

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

1995-05-15

312

Simultaneous scanning tunneling microscopy and stress measurements to elucidate the origins of surface forces.  

Science.gov (United States)

We have developed a new combined measurement system to investigate the underlying origins of forces on solid state surfaces from the viewpoint of atomic surface morphology. This system consists of two main parts: the measurements of force based on displacements and detailed atomic resolution observations of the surface morphology. The former involves a large sample cantilever and a capacitive detection method that provide sufficient resolution to detect changes of a few meV/atom or pN/atom at surfaces. For the latter, a scanning tunneling microscope was incorporated to observe structural changes occurring on the surface of the cantilever sample. Although this combined observation is not trivial, it was accomplished by carefully designing sample dimensions while suppressing the self-oscillation of the cantilever. To demonstrate the performance of this system a preliminary study of the room temperature adsorption of Br(2) on the clean Si(111)-7x7 surface is presented. PMID:17552837

Narushima, Tetsuya; Kinahan, Niall T; Boland, John J

2007-05-01

313

Graphene buckles under stress: An x-ray standing wave and scanning tunneling microscopy study  

Science.gov (United States)

Graphene on Ir(111) is studied using scanning tunneling microscopy (STM) and x-ray standing waves (XSW). The graphene layer has a corrugated shape due to the moiré pattern formed as a result of a spatially varying interaction strength between graphene and its substrate. The coherent fraction F(111) determined in XSW allows us to determine the amplitude of this intrinsic corrugation when the incoherent contributions of wrinkles, step edges, graphene edges, and contaminations are taken into account. The corrugation is found to depend on the stress state of the carbon sheet. Using density functional theory (DFT) calculations, we show that graphene can compensate stress by increasing its corrugation rather than by a reduction of the C-C bond length.

Runte, Sven; Lazi?, Predrag; Vo-Van, Chi; Coraux, Johann; Zegenhagen, Jörg; Busse, Carsten

2014-04-01

314

A theoretical model for single-molecule incoherent scanning tunneling spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

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

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

2008-11-05

315

An externally cooled beetle type scanning tunneling microscope for imaging in cryogenic liquids  

International Nuclear Information System (INIS)

We describe a variable temperature cryogenic scanning tunneling microscope designed for imaging and research in cryogenic liquids. It has an external Dewar type large scale cooling system with a temperature control range of roughly 85-110 K using pressure controlled liquid nitrogen cooling. The liquid nitrogen is kept in a closed chamber surrounding the STM and maintained at a pressure to suit the chosen temperature. Several gases have triple points in this temperature range and can therefore be liquified, such as argon, methane, silane and germane. The STM is based on a beetle type design built into a small cube vacuum chamber to fit into the cooling dewar. The system has been used for atomic resolution of highly oriented graphite submerged in a methane liquid at a temperature of 100 K

2006-05-30

316

An externally cooled beetle type scanning tunneling microscope for imaging in cryogenic liquids  

Energy Technology Data Exchange (ETDEWEB)

We describe a variable temperature cryogenic scanning tunneling microscope designed for imaging and research in cryogenic liquids. It has an external Dewar type large scale cooling system with a temperature control range of roughly 85-110 K using pressure controlled liquid nitrogen cooling. The liquid nitrogen is kept in a closed chamber surrounding the STM and maintained at a pressure to suit the chosen temperature. Several gases have triple points in this temperature range and can therefore be liquified, such as argon, methane, silane and germane. The STM is based on a beetle type design built into a small cube vacuum chamber to fit into the cooling dewar. The system has been used for atomic resolution of highly oriented graphite submerged in a methane liquid at a temperature of 100 K.

Arnalds, Unnar B. [Matvice, Dunhaga 3, 107 Reykjavik (Iceland)]. E-mail: uba@raunvis.hi.is; Bjarnason, Elias H. [Matvice, Dunhaga 3, 107 Reykjavik (Iceland); Jonsson, Kristjan [Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavik (Iceland); Olafsson, Sveinn [Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavik (Iceland)

2006-05-30

317

A development in the preparation of sharp scanning tunneling microscopy tips  

DEFF Research Database (Denmark)

An improved and reliable method for making sharp scanning tunneling microscopy (STM) tips is described. It is based on the widely used drop-off electrochemical etching procedure, here modified to improve the control of the tip shape. A second etching is applied not only to remove the oxide layer from the tip surface, but also to sharpen the STM tips further. A tip radius less than 20 nm can be obtained reproducibly. The quality of the produced tips was inspected with transmission electron microscopy, and micrographs of tips produced with different times of second etching are shown. To produce tips which are all without an oxide layer an electronic phase control unit is necessary. Even without this etch controller more than half the tips are oxide free, and then only standard laboratory equipment is used for the tip production. Review of Scientific Instruments is copyrighted by The American Institute of Physics.

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

1993-01-01

318

Scanning tunneling microscopy study of the relaxation mechanism of a Au(100) nanostructure.  

Science.gov (United States)

The three-dimensional shape relaxation of gold nanostructures was studied by scanning tunneling microscopy in real time and at ambient conditions. The nanostructures were fabricated on a Au(100) single crystal by a two step-process: electrochemical etching to produced a rough surface, followed by thermal annealing. The nanostructures can be described as mounds having small semicircular facets that shrink in time, peeling away layer by layer as a result of the sudden temperature change and evolving towards thermodynamic equilibrium. A model developed by Uwaha is used to describe the dynamic evolution of the peeling layers, where good agreement was found despite the presence of adsorbates due to ambient exposure. PMID:19205248

González-Carrazco, A; Valenzuela-Benavides, J

2008-12-01

319

Electronic states of Fe atoms and chains on InAs(110) from scanning tunneling spectroscopy  

Science.gov (United States)

The local density of states (DOS) on and around Fe single atoms and Fe chains deposited on the n-InAs(110) surface is studied by scanning tunneling spectroscopy at T?6K . The single atom shows two characteristic states in the filled as well as in the empty DOS which are attributed to an In-related and an Fe-related state. For chains longer than two atoms oriented along the [11¯0] direction, the In-related state results in a uniform state, while the Fe-related state splits up into an end state and inner states. The end state has a lower energy in the filled as well as in the empty DOS. Chains oriented along the [001] direction show an electronic structure which varies continuously along their axis, suggesting a position-dependent hybridization of each atom to the substrate.

Matsui, T.; Meyer, Chr.; Sacharow, L.; Wiebe, J.; Wiesendanger, R.

2007-04-01

320

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

CERN Document Server

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

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

2005-01-01

 
 
 
 
321

Observation of Ordered Arrays of Adsorbed Lysozyme by Scanning Tunneling Microscopy  

Science.gov (United States)

The lysozyme film formed on a Au(111) surface was observed at a molecular resolution by scanning tunneling microscopy (STM). The flat domains of this film was obtained by dipping the Au(111) surface into lysozyme solution (4 ?g/ml, pH=4.5 and room temperature) for 4 h. We observed a clear image of the stripes formed by lysozyme molecules. Two types of ordered stripes were confirmed. One was a simple stripe with a gap of 4.6 nm, and the other was a paired stripe with the periodicity of the pair is 6.2 nm. The latter case could be explained with a periodic bond chain model of the (110) surface of a lysozyme crystal.

Yamaguchi, Takahiro; Komeda, Tadahiro

2006-03-01

322

Scanning tunneling microscopy study of the superconducting properties of three-atomic-layer Pb films  

International Nuclear Information System (INIS)

Ultrathin Pb films with a thickness of three monolayers (ML) were prepared on ?-?(3)×?(3)Pb/Si(111) (Pb-SIC) substrate by molecular beam epitaxy. Despite significant defect scattering, low temperature scanning tunneling microscopy reveals a high superconducting transition temperature Tc of 6.9?K, compared with the bulk Tc (7.2?K). By applying external magnetic field, magnetic vortices were directly imaged, which demonstrates the robustness of superconductivity. By comparing to nearly free-standing Pb films on graphitized SiC (0001) substrate, we suggest that the higher Tc of 3 ML Pb films on Pb-SIC originates from the combined effects of quantum confinement and substrate-enhanced electron-phonon coupling

2013-12-09

323

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

Energy Technology Data Exchange (ETDEWEB)

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

Cernota, Paul D.

1999-08-01

324

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

Science.gov (United States)

We apply ultrahigh vacuum Scanning Tunneling Spectroscopy (STS) at ultra-low temperature to study proximity phenomena in metallic Cu in contact with superconducting Nb. In order to solve the problem of Cu-surface contamination, Cu(50 nm)/Nb(100 nm) structures are grown by respecting the inverted order of layers on SiO2/Si substrate. Once transferred into vacuum, the samples are cleaved at the structure-substrate interface. As a result, a contamination-free Cu-surface is exposed in vacuum. It enables high-resolution STS of superconducting correlations induced by proximity from the underlying superconducting Nb layer. By applying magnetic field, we generate unusual proximity-induced superconducting vortices and map them with a high spatial and energy resolution. The suggested method opens a way to access local electronic properties of complex electronic mesoscopic devices by performing ex situ STS under ultrahigh vacuum.

Stolyarov, V. S.; Cren, T.; Debontridder, F.; Brun, C.; Veshchunov, I. S.; Skryabina, O. V.; Rusanov, A. Yu.; Roditchev, D.

2014-04-01

325

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

Science.gov (United States)

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

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

2008-04-22

326

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

DEFF Research Database (Denmark)

Experimental advances allow for the inclusion of multiple probes to measure the transport properties of a sample surface. We develop a theory of dual-probe scanning tunneling microscopy using a Green's function formalism, and apply it to graphene. Sampling the local conduction properties at finite length scales yields real space conductance maps which show anisotropy for pristine graphene systems and quantum interference effects in the presence of isolated impurities. Spectral signatures in the Fourier transforms of real space conductance maps include characteristics that can be related to different scattering processes. We compute the conductance maps of graphene systems with different edge geometries or height fluctuations to determine the effects of nonideal graphene samples on dual-probe measurements. © 2014 American Physical Society.

Settnes, Mikkel; Power, Stephen R.

2014-01-01

327

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

DEFF Research Database (Denmark)

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

Nilsson, Louis

2013-01-01

328

Development of Novel System Combining Scanning Tunneling Microscope-Based Cathodoluminescence and Electroluminescence Nanospectroscopies  

Science.gov (United States)

Novel system equipped with conductive optical fiber probe scanning tunneling microscope (STM) and bipolar sample holder is a powerful tool to characterize light-emitting devices by several STM-based techniques at the same sample position, which can realize photoluminescence (PL), cathodoluminescence (CL), electroluminescence (EL), and electron beam induced current (EBIC) measurements with higher spatial resolutions than conventional techniques. In this study, we developed a STM-CL/EL system which combines STM-CL technique for high CL excitation power and high spatial resolution and STM-EL technique for local EL collection. We demonstrated spatially resolved STM-CL/EL spectroscopy of GaAs/AlGaAs heterostructure (110) cross-sections.

Watanabe, Kentaro; Nakamura, Yoshiaki; Kuboya, Shigeyuki; Katayama, Ryuji; Onabe, Kentaro; Ichikawa, Masakazu

2011-08-01

329

Nonequilibrium effects in the tunneling conductance spectra of small metallic particles  

CERN Document Server

The tunneling spectra of small metallic grains shows an unusual structure of the differential conductance peaks. Namely, resonance peaks appear in clusters, or develop substructure as the the gate voltage is changed. These features are manifestations of a nonequilibrium behavior which appears when the applied source-drain voltage is sufficiently large. Electron-electron Coulomb interaction as well as an attractive pairing interaction play an important role in determining the magnitude and energy scales of the phenomena. For normal grains each cluster of resonances is identified with one excited single-electron state of the metal particle, shifted as a result of the different nonequilibrium occupancy configurations of the other single-electron states. For superconducting grains in the odd charging state, the substructure of the resonance is explained by nonequilibrium ``gapless'' excitations associated with different energy levels occupied by the unpaired electron. The excitations are generated by inelastic co...

Agam, O

1997-01-01

330

Flare X-ray spectra observed by Diogenes scanning bragg spectrometer  

Science.gov (United States)

Diogeness is the uncollimated scanning flat crystal spectrometer observing flare X-ray spectra in four narrow wavelength bands in vicinity of Ca XIX, S XV and Si XIII He-like line "triplets" around 3.18 Å, 5.04 Å and 6.65 Å. In two spectral channels, the same emission lines around Ca XIX 3.178 Å resonance are scanned in opposite directions, being diffracted from precisely adjusted identical Quartz crystals mounted on the common shaft in so-called Dopplerometer configuration. During early phase of the CORONAS-F Mission, a number of big flares have been observed by Diogeness. In particular, tens of high resolution spectra have been measured during initial, maximum and decay phase of 25 August 2001 X5.3 flare. We present examples of these spectra, make prompt line identification, announcing observations of spectral features corresponding to transitions in Si XIV (Ly?) He-like ion. Early interpretation of the spectra measured indicates for substantial variations of average plasma temperature during the observed flare. Our measurements will be further analysed in detail together with the spectra obtained aboard Yohkoh using Bent Crystal Spectrometer observations.

Siarkowski, M.; Sylwester, J.; Plocieniak, S.; Kordylewski, Z.

2002-12-01

331

Scanning tunneling microscopy on unpinned GaN(11¯00) surfaces: Invisibility of valence-band states  

Science.gov (United States)

We investigated the origins of the tunnel current in scanning tunneling microscopy (STM) and spectroscopy experiments on GaN(11¯00) surfaces. By calculating the tunnel currents in the presence of a tip-induced band bending for unpinned n -type GaN(11¯00) surfaces, we demonstrate that only conduction-band states are observed at positive and negative voltage polarities independent of the doping concentration. Valence-band states remain undetectable because tunneling out of the electron-accumulation zone in conduction-band states dominates by four orders of magnitude. As a result band-gap sizes cannot be determined by STM on unpinned GaN(11¯00) surfaces. Appropriate band-edge positions and gap sizes can be determined on pinned surfaces.

Ebert, Ph.; Ivanova, L.; Eisele, H.

2009-08-01

332

Geometric and electronic structure of passive CuN monolayer on Cu(111) : a scanning tunneling microscopy and spectroscopy study  

Energy Technology Data Exchange (ETDEWEB)

An insulating CuN monolayer was grown on a Cu(111) surface; subsequently, the dynamic growth process, the reconstructed geometric structure and the electronic structure were studied using scanning tunneling microscopy. Confirmation of the atomic model of the pseudo-(100) layer, proposed by Higgs et al. and Driver et al. was made. In addition, we observed a small misalignment of the super cell away from the <110> direction of the Cu substrate, resulting in long range distortion. A large insulator-like band gap of {approx} 3.3 eV was measured through the CuN surface. The CuN monolayer can be used as a model surface on which the electronic structure of an atom or a molecule is explored by scanning tunneling microscopy. This electronic structure can not be perturbed by the metallic substrate, despite the tunneling of electrons through the surface layer.

Baek, Hongwoo; Jeon, Sangjun; Seo, Jungpil; Kuk, Young [Seoul National University, Seoul (Korea, Republic of); Seo, Jungpil [Princeton University, Princeton, NJ (United States)

2010-02-15

333

Systematic analyses of vibration noise of a vibration isolation system for high-resolution scanning tunneling microscopes.  

Science.gov (United States)

We designed and constructed an effective vibration isolation system for stable scanning tunneling microscopy measurements using a separate foundation and two vibration isolation stages (i.e., a combination of passive and active vibration isolation dampers). Systematic analyses of vibration data along the horizontal and vertical directions are present, including the vibration transfer functions of each stage and the overall vibration isolation system. To demonstrate the performance of the system, tunneling current noise measurements are conducted with and without the vibration isolation. Combining passive and active vibration isolation dampers successfully removes most of the vibration noise in the tunneling current up to 100 Hz. These comprehensive vibration noise data, along with details of the entire system, can be used to establish a clear guideline for building an effective vibration isolation system for various scanning probe microscopes and electron microscopes. PMID:21895246

Iwaya, Katsuya; Shimizu, Ryota; Hashizume, Tomihiro; Hitosugi, Taro

2011-08-01

334

Intrinsic Tunneling Spectra of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\\delta}$ near Optimal Doping  

CERN Document Server

We report tunneling spectra of near optimally doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\\delta}$ intrinsic Josephson junctions with area of 0.09 $\\mu$m$^2$, which avoid some fundamental difficulties in the previous tunneling experiments and allow a stable temperature-dependent measurement. A d-wave Eliashberg analysis shows that the spectrum at 4.2 K can be well fitted by considering electron couplings to a bosonic magnetic resonance mode and a broad high-energy continuum. Above $T_c$, the spectra show a clear pseudogap that persists up to 230 K, and a crossover can be seen indicating two different pseudogap phases existing above $T_c$. The intrinsic electron tunneling nature is discussed in the analysis.

Zhao, S P; Wei, Y F

2007-01-01

335

Pseudogap formation and unusual quasiparticle tunneling in cuprate superconductors: Polaronic and multiple-gap effects on the tunneling spectra  

International Nuclear Information System (INIS)

We propose new simple and generalized multiple-gap models of quasiparticle tunneling across the high-Tc cuprate superconductor (HTSC)/insulator/normal metal (SIN) junction based on the two different mechanisms for tunneling at positive and negative bias voltages, and the gap inhomogeneity (i.e., multiple-gap) picture. The tunneling of electrons from the normal metal into the quasiparticle states in HTSC with the BCS-type density of states (DOSs) takes place at V>0, while the tunneling of Cooper pairs and large polarons from the HTSC with the BCS DOS and quasi-free state DOS (which appears only in the dissociation of polarons) into the normal metal occurs at V2Sr2CaCu2O8+? are adequately reproduced by using the specific multiple-gap models and taking into account the distribution of BCS and polaronic gap values

2013-10-15

336

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

Science.gov (United States)

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

Pasanai, K.

2014-05-01

337

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

338

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

International Nuclear Information System (INIS)

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

2013-08-01

339

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

International Nuclear Information System (INIS)

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

2012-01-01

340

Spin-polarized scanning tunneling microscopy applied to nanoscale Fe islands  

Energy Technology Data Exchange (ETDEWEB)

The magnetic properties of single-crystal nanoscale Fe islands on W(110) have been studied by spin-polarized scanning tunnelling microscopy. All measurements have been done at room temperature by a modified commercial Omicron 'AFM/STM' using a 5 monolayer iron covered tungsten tip with an in-plane magnetic sensitivity. Preparation has been done by molecular beam epitaxy in UHV. We investigated islands with lateral dimensions of 200 by 400 nm{sup 2} and different heights from 3 to 8 nm. The observed domain structures are in line with previous results and with theoretical analysis. Variation of the thickness leads to different magnetic domain structures of the islands, which are dominated by the surface anisotropy with an easy axis along the [1 anti 10] direction. For islands with a thickness of 3.5 nm, the uniaxial surface anisotropy of Fe/W(110) leads to a single domain state. For thicker islands the magnetostatic energy becomes dominant due to the reduced anisotropy energy. This results in a multi domain configuration.

Subramaniam, Dinesh; Pratzer, Marco; Morgenstern, Markus [II. Institute of Physics B, RWTH Aachen, 52056 Aachen (Germany)

2007-07-01

 
 
 
 
341

Electrochemical deposition of platinum hydrosol on graphite observed by scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

Ligand stabilized metal colloids are discussed as promising candidates for metal catalyst precursors or even supported catalysts. The protective shell around the metal particles prevents their agglomeration and leads to a highly dispersed metal phase. A narrow metal particle size distribution, as revealed by transmission electron microscopy, is achieved by specific reduction techniques. These catalysts are generally prepared by adsorption, i.e., by adding the support material to the colloidal solution, followed by a drying step. Another way to prepared supported catalysts is electrophoretic deposition, which was recently demonstrated for a gold colloid. For conductive supports, such as carbon, an electrochemical deposition of colloids can be envisioned also. To our knowledge this has not been investigated yet. In this note the authors present, first, the results of a combined scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) study on the electrochemical deposition of platinum nanocolloids with an organic shell (hydrosol) onto highly oriented pyrolytic graphite (HOPG). 7 refs., 3 figs.

Shaikhutdinov, Sh.K.; Moeller, F.A.; Mestl, G.; Behm, R.J. [Universitaet Ulm (Germany)

1996-10-01

342

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

DEFF Research Database (Denmark)

High-resolution scanning tunneling microscope (STM) images of moiré-structured FeO films on Pt(111) were obtained in a number of different tip-dependent imaging modes. For the first time, the STM images are distinguished and interpreted unambiguously with the help of distinct oxygen-vacancy dislocation loops in the FeO moiré structure. The experimental STM results are compared with the results of electronic structure calculations within the DFT+U scheme for a realistic (sqrt(91)xsqrt(91)R5.2 moiré unit cell supported on Pt(111) as well as with the results from previous studies. We find that one type of STM imaging mode, showing both Fe and O atoms, agrees well with simulated STM images, indicating that the simple Tersoff-Hamann theory is partially valid for this imaging mode. In addition, we identify other distinct, element-specific imaging modes which reveal a strong dependence on the specific tip apex state and likely result from specific tip-sample chemical interactions. From the present STM results we show that several of the previously published conclusions for the FeO system have to be revisited.

Merte, Lindsay Richard; Grabow, Lars C.

2011-01-01

343

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

DEFF Research Database (Denmark)

Bulk copper electrodeposition onto technical gold surfaces in electrolytes of 0.05 M H2SO4 and 1 mM CuSO4 was investigated by in-situ scanning tunnelling microscopy at fixed overpotentials. At potentials between -60 and -30 mV the growth of bulk copper proceeds in cycles of nucleation, agglomeration and crystallization. Crystalline copper is seen as involving an intermediate stage in the progress of growth. The final stage in the growth involves an equilibrium of copper electrochemically dissolving and precipitating. The drift velocity was measured for a gold surface subjected to flame annealing and subsequently installed in the cell compartment. It was found that the drift velocity decays with time in an exponential-like manner, and a 70 min waiting time before experiments with atomic resolution is recommended. Atomic resolution on Au(111) has been obtained, and an apparent surface reconstruction was observed. It is suggested that in reality no reconstruction took place, and that the observation was due to a distortion of the image caused by a constant drift velocity. A mathematical expression which relates the observed surface structure to the drift velocity is presented.

Andersen, Jens Enevold Thaulov; Bech-Nielsen, Gregers

1994-01-01

344

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

Directory of Open Access Journals (Sweden)

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

Thomas König

2011-01-01

345

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

Science.gov (United States)

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

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

2014-04-01

346

Quantifying many-body effects by high-resolution Fourier transform scanning tunneling spectroscopy.  

Science.gov (United States)

High-resolution Fourier transform scanning tunneling spectroscopy (FT-STS) is used to study many-body effects on the surface state of Ag(111). Our results reveal a kink in the otherwise parabolic band dispersion of the surface electrons and an increase in the quasiparticle lifetime near the Fermi energy Ef. The experimental data are accurately modeled with the T-matrix formalism for scattering from a single impurity, assuming that the surface electrons are dressed by the electron-electron and electron-phonon interactions. We confirm the latter as the interaction responsible for the deviations from bare dispersion. We further show how FT-STS can be used to simultaneously extract real and imaginary parts of the self-energy for both occupied and unoccupied states with a momentum and energy resolution competitive with angle-resolved photoemission spectroscopy. From our quantitative analysis of the data we extract a Debye energy of ??D=14±1??meV and an electron-phonon coupling strength of ?=0.13±0.02, consistent with previous results. This proof-of-principle measurement advances FT-STS as a method for probing many body effects, which give rise to a rich array of material properties. PMID:24483688

Grothe, S; Johnston, S; Chi, Shun; Dosanjh, P; Burke, S A; Pennec, Y

2013-12-13

347

Film growth of germanium on Ru(0001) studies by scanning tunneling microscopy  

International Nuclear Information System (INIS)

Using in situ scanning tunneling microscopy, we observed that germanium deposited on the Ru(0001) surface near room temperature forms a two-dimensional wetting layer in the submonolayer regime, followed with growth of a segregated layer of Ge three-dimensional (3D) clusters of heights within about 1 nm. The growth of the first flat wetting layer can be understood in terms of optimal surface energy reduction by coating the Ru surface with a Ge layer which has a lower surface free energy. The nucleation and growth kinetics agrees with that derived from the conservative Ising model. Domains of a (?21x?21)R10.9 deg. superstructure are observed on the wetting layer. Formation of a layer consisting of 1-nm-high clusters above the wetting layer indicates that the Ge wetting layer is extremely inert so that Ge adatoms can migrate large distances on the top of the wetting layer. The 3D Ge clusters seem to have a relatively narrow size distribution

2004-12-15

348

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

Science.gov (United States)

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

Sinthiptharakoon, Kitiphat; Schofield, Steven R.; Studer, Philipp; Brázdová, Veronika; Hirjibehedin, Cyrus F.; Bowler, David R.; Curson, Neil J.

2014-01-01

349

Thermal dissociation of chemisorbed oxygen molecules on Ag(110): an investigation by scanning tunnelling microscopy  

International Nuclear Information System (INIS)

The thermal dissociation of oxygen molecules on Ag(110) was studied by means of scanning tunnelling microscopy. At temperatures around 170 K a fraction of the molecules dissociate to form pairs of O atoms on the unreconstructed surface. The atoms lie in the trenches between the close-packed Ag rows; the intrapair distance is two lattice constants. The O atoms are very reactive with CO at temperatures as low as 70 K. The preferential orientation of the pairs in the [001] direction contrasts with the finding in a previous study (Hahn J R, Lee H J and Ho W 2000 Phys. Rev. Lett. Vol. 85 1914) that electron-induced dissociation exclusively leads to [110]-oriented pairs. The trajectories of thermal and electron-induced dissociations must therefore be different. In the temperature range of the dissociation, several additional oxygen features occur on the surface. These include unreacted O2 molecules, the first nuclei of the added-row reconstruction, and two unidentified O-induced structures. (author)

2002-04-29

350

Thermal dissociation of chemisorbed oxygen molecules on Ag(110): an investigation by scanning tunnelling microscopy  

Energy Technology Data Exchange (ETDEWEB)

The thermal dissociation of oxygen molecules on Ag(110) was studied by means of scanning tunnelling microscopy. At temperatures around 170 K a fraction of the molecules dissociate to form pairs of O atoms on the unreconstructed surface. The atoms lie in the trenches between the close-packed Ag rows; the intrapair distance is two lattice constants. The O atoms are very reactive with CO at temperatures as low as 70 K. The preferential orientation of the pairs in the [001] direction contrasts with the finding in a previous study (Hahn J R, Lee H J and Ho W 2000 Phys. Rev. Lett. Vol. 85 1914) that electron-induced dissociation exclusively leads to [110]-oriented pairs. The trajectories of thermal and electron-induced dissociations must therefore be different. In the temperature range of the dissociation, several additional oxygen features occur on the surface. These include unreacted O{sub 2} molecules, the first nuclei of the added-row reconstruction, and two unidentified O-induced structures. (author)

Zambelli, T.; Barth, J.V.; Wintterlin, J. [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin (Germany)

2002-04-29

351

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

DEFF Research Database (Denmark)

The investigation of electron transport processes in nano-scale architectures plays a crucial role in the development of surface chemistry and nano-technology. Experimentally, an important driving force within this research area has been the concurrent refinements of scanning tunneling microscopy (STM) techniques. The theoretical treatment of the STM operation has traditionally been based on the Bardeen and Tersoff-Hamann methods which take as input the single-particle wave functions and eigenvalues obtained from finite cluster or slabs models of the surface-tip interface. Here, we present a novel STM simulation scheme based on non-equilibrium Green's functions (NEGF) and Wannier functions which is both accurate and very efficient. The main novelty of the scheme compared to the Bardeen and Tersoff-Hamann approaches is that the coupling to the infinite (macroscopic) electrodes is taken into account. As an illustrating example we apply the NEGF-STM method to the Si(001)(2x1):H surface with sub-surface P doping and discuss the results in comparison to the Bardeen and Tersoff-Hamann methods.

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

2010-01-01

352

Scanning tunneling microscopy study of polymerized carbon nanobells: Electronic effect and evidence of nitrogen incorporation  

Science.gov (United States)

Polymerized carbon nanobells has been grown by inducing nitrogen in the microwave plasma assisted chemical vapor deposition of carbon nanotubes. The nanobells consist of several tens of graphite layers with one end closed and the other open, and show characteristic field emission behavior with a turn-on field as low as 0.8 V/ mm. In this study, scanning tunneling microscopy/spectroscopy (STM/STS) is used to correlate the unique structure and field emission behavior and to confirm the previously proposed sidewall emission mechanism of the polymerized nanobells. Great contrast modulation along the axis of the tubes is revealed, while atomic-resolution STM images indicate that the bell surface is a nearly perfect carbon network. As enhanced local density of states is observed only on the nanobells, the corrugated morphology is of electronic nature. We discuss the enhanced localized states in terms of the pentagon defects, dangling bonds and enhanced interlayer coupling due to presence of nitrogen. Nitrogen-induced electronic states lies 0.3eV below the Fermi level, which can be used to explain the observed electron field emission behavior.

Sun, Hai-Lin; Jia, Jin-Feng; Shen, Quan-Tong; Zhong, Ding-Yong; Sun, Mu; Xue, Qi-Kun; Wang, En-Ge

2003-03-01

353

Electron--Vibron Interaction Effects on Scanning Tunneling Microscopy Current through Melamine Adsorbed on Cu(100)  

Science.gov (United States)

Electron transport through the melamine molecule was studied. Melamine molecules adsorbed on a Cu(100) surface were investigated by density functional theory (DFT) calculations with the dynamical matrix method. On the basis of calculation results, a model Hamiltonian for a system composed of scanning tunneling microscope (STM), a melamine molecule, and a Cu surface was proposed, taking into account electron--vibron (electron--molecular vibrations) interactions within the melamine molecule. Then, the electronic current was formulated by the nonequilibrium Green's function (NEGF) method. Results show that current is affected by the electron--vibron interactions defined in the melamine molecule through its controllable structural changes. The rectification and fluctuation of current are triggered by low-energy electron--vibron interactions. Furthermore, the electron--vibron interaction effect is found to be enhanced as temperature increases to where higher-energy vibrons begin to be excited at lower energies. However, current becomes uniform at higher temperatures, which shows an undesired sensitivity. The weakening of the electron--vibron interaction of the out-of-molecular-plane vibrational motion can transfer the melamine molecule in its tautomerization state into a current rectifier. The reduction or induction of the repulsion of lone pairs of consecutive N atoms causes the induction or reduction of the low-energy in-plane vibrational motion, which in turn causes the switching of the I--V characteristics between less stable melamine tautomers.

Sarhan, Abdulla; Sakaue, Mamoru; Nakanishi, Hiroshi; Kasai, Hideaki

2012-10-01

354

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

Directory of Open Access Journals (Sweden)

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

Daisuke Fujita and Keisuke Sagisaka

2008-01-01

355

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

Energy Technology Data Exchange (ETDEWEB)

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

Schiffmann, K. (Fraunhofer Inst. fuer Schicht- und Oberflaechentechnik (FhG-IST), Hamburg (Germany)); Jiang, X. (Fraunhofer Inst. fuer Schicht- und Oberflaechentechnik (FhG-IST), Hamburg (Germany))

1994-07-01

356

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

International Nuclear Information System (INIS)

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

1994-07-01

357

Surface valence charge distributions and scanning tunneling microscopy of WTe 2  

Science.gov (United States)

We have studied the surface electronic structures of the van der Waals surfaces of tungsten ditelluride (WTe 2) with first principles calculations of the spatial distribution of the surface valence charge densities and compared the results to images obtained with the scanning tunneling microscope (STM). The energy- and z(distance from the surface)-dependent calculations show that the valence charge density distribution above the Te surface could be derived from the surface Te layer, as we previously calculated, but the charge density distribution close to but below the Fermi energy has a distortion that coincidentally makes it appear to have a symmetry close to the paired, zig-zag and buckled rows of the W layer. These results dramatically illustrate that in highly covalent compounds, the surface valence charge density distribution does not necessarily follow the surface atomic positions even on ideal, unreconstructed surfaces. An alternative interpretation of the STM images of this surface is proposed in light of this new surface electronic structure. Our calculated and experimental results are also discussed with reference to recent STM results on other transition metal dichalcogenides.

Tang, S. L.; Kasowski, R. V.; Suna, A.; Parkinson, B. A.

1990-11-01

358

Unconventional superconductivity in ultrathin superconducting NbN films studied by scanning tunneling spectroscopy  

Science.gov (United States)

Using scanning tunneling spectroscopy, we address the problem of the superconductor-insulator phase transition in homogeneously disordered ultrathin (2-15 nm) films of NbN. Samples thicker than 8 nm, for which the Ioffe-Regel parameter kFl?5.6, manifest a conventional superconductivity: a spatially homogeneous BCS-like gap, vanishing at the critical temperature, and a disordered vortex lattice in magnetic field. Upon thickness reduction, however, while kFl lowers, the STS reveals striking deviations from the BCS scenario, among which a progressive decrease of the coherence peak height and small spatial inhomogeneities. In addition, the gap below TC develops on a spectral background, which becomes more and more “V-shaped” approaching the localization. The thinnest film (2.16 nm), while not being exactly at the superconductor-insulator transition (SIT) (TC?0.4TCbulk), showed unconventional signatures such as the vanishing of the coherence peaks and the absence of vortices. This behavior suggests a weakening of long-range phase coherence, when approaching the SIT in this quasi-2D limit.

Noat, Y.; Cherkez, V.; Brun, C.; Cren, T.; Carbillet, C.; Debontridder, F.; Ilin, K.; Siegel, M.; Semenov, A.; Hübers, H.-W.; Roditchev, D.

2013-07-01

359

Scanning tunneling microscopy and spectroscopy observations of the graphite edge state  

CERN Document Server

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

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

2006-01-01

360

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

DEFF Research Database (Denmark)

Escherichia coli cytochrome c nitrite reductase (NrfA) catalyzes the six-electron reduction of nitrite to perform an important role in the biogeochemical cycling of nitrogen. Here we describe NrfA adsorption on single-crystal Au(111) electrodes as an electrocatalytically active film in which the enzyme undergoes direct electron exchange with the electrode. The adsorbed NrfA has been imaged to molecular resolution by in situ scanning tunneling microscopy (in situ STM) under full electrochemical potential control and under conditions where the enzyme is electrocatalytically active. Details of the density and orientational distribution of NrfA molecules are disclosed. The submonolayer coverage resolved by in situ STM is readily reconciled with the failure to detect nonturnover signals in cyclic voltammetry of the NrfA films. The molecular structures show a range of lateral dimensions. These are suggestive of a distribution of orientations that could account for the otherwise anomalously low turnover number calculated for the total population of adsorbed NrfA molecules when compared with that determined for solutions of NrfA. Thus, comparison of the voltammetric signals and in situ STM images offers a direct approach to correlate electrocatalytic and molecular properties of the protein layer, a long-standing issue in protein film voltammetry.

Zhang, Jingdong; Ulstrup, Jens

2006-01-01

 
 
 
 
361

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

Science.gov (United States)

We describe the design, construction, and performance of an ultra-low temperature, high-field scanning tunneling microscope (STM) with two independent tips. The STM is mounted on a dilution refrigerator and operates at a base temperature of 30 mK with magnetic fields of up to 13.5 T. We focus on the design of the two-tip STM head, as well as the sample transfer mechanism, which allows in situ transfer from an ultra high vacuum preparation chamber while the STM is at 1.5 K. Other design details such as the vibration isolation and rf-filtered wiring are also described. Their effectiveness is demonstrated via spectral current noise characteristics and the root mean square roughness of atomic resolution images. The high-field capability is shown by the magnetic field dependence of the superconducting gap of CuxBi2Se3. Finally, we present images and spectroscopy taken with superconducting Nb tips with the refrigerator at 35 mK that indicate that the effective temperature of our tips/sample is approximately 184 mK, corresponding to an energy resolution of 16 ?eV. PMID:24784617

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

2014-04-01

362

Strong tip-sample coupling in thermal radiation scanning tunneling microscopy  

CERN Document Server

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

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

2014-01-01

363

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-11-15

364

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

Science.gov (United States)

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

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

2014-01-01

365

Unravelling the molecular structure and packing of a planar molecule by combining nuclear magnetic resonance and scanning tunneling microscopy.  

Science.gov (United States)

The determination of the molecular structure of a porphyrin is achieved by using nuclear magnetic resonance (NMR) and scanning tunneling microscopy (STM) techniques. Since macroscopic crystals cannot be obtained in this system, this combination of techniques is crucial to solve the molecular structure without the need for X-ray crystallography. For this purpose, previous knowledge of the flatness of the reagent molecules (a porphyrin and its functionalizing group, a naphthalimide) and the resulting molecular structure obtained by a force-field simulation are used. The exponents of the I-V curves obtained by scanning tunneling spectroscopy (STS) allow us to check whether the thickness of the film of molecules is greater than a monolayer, even when there is no direct access to the exposed surface of the metal substrate. Photoluminescence (PL), optical absorption, infrared (IR) reflectance and solubility tests are used to confirm the results obtained here with this NMR/STM/STS combination. PMID:24192713

Sáfar, Gustavo A M; Malachias, Angelo; Magalhães-Paniago, Rogério; Martins, Dayse C S; Idemori, Ynara M

2013-12-21

366

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

Science.gov (United States)

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

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

2014-01-01

367

In situ high-temperature scanning tunneling microscopy study of bilayer graphene growth on 6H-SiC(0001)  

International Nuclear Information System (INIS)

Using in situ high-temperature (1395 K), ultra-high vacuum, scanning tunneling microscopy (STM), we investigated the growth of bilayer graphene on 6H-SiC(0001). From the STM images, we measured areal coverages of SiC and graphene as a function of annealing time and found that graphene grows at the expense of SiC. Graphene domains were observed to grow, at comparable rates, at (I) graphene-free SiC step edges, (II) graphene–SiC interfaces, and (III) the existing graphene domain edges. Based upon our results, we suggest that the rate-limiting step controlling bilayer graphene growth is the desorption of Si from the substrate. - Highlights: ? Use of scanning tunneling microscopy at temperatures as high as 1395 K. ? Direct observation of graphene formation on SiC surfaces at the growth temperature. ? Identification of atomic-scale pathways for bilayer graphene growth.

2012-06-01

368

Size dependent bandgap of molecular beam epitaxy grown InN quantum dots measured by scanning tunneling spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

InN quantum dots (QDs) were grown on Si (111) by epitaxial Stranski-Krastanow growth mode using plasma-assisted molecular beam epitaxy. Single-crystalline wurtzite structure of InN QDs was verified by the x-ray diffraction and transmission electron microscopy. Scanning tunneling microscopy has been used to probe the structural aspects of QDs. A surface bandgap of InN QDs was estimated from scanning tunneling spectroscopy (STS) I-V curves and found that it is strongly dependent on the size of QDs. The observed size-dependent STS bandgap energy shifts with diameter and height were theoretical explained based on an effective mass approximation with finite-depth square-well potential model.

Kumar, Mahesh; Roul, Basanta [Materials Research Centre, Indian Institute of Science, Bangalore-560012 (India); Central Research Laboratory, Bharat Electronics, Bangalore-560013 (India); Rajpalke, Mohana K.; Bhat, Thirumaleshwara N.; Krupanidhi, S. B. [Materials Research Centre, Indian Institute of Science, Bangalore-560012 (India); Kalghatgi, A. T. [Central Research Laboratory, Bharat Electronics, Bangalore-560013 (India)

2011-12-01

369

Scanning tunneling microscopy investigation of electronic properties of cobalt nanoislands supported by Cu-9at.%Al(111)  

Science.gov (United States)

Growth and surface electronic states of Co nanoislands supported by Cu-9 at.%Al(111) are investigated by low temperature scanning tunneling microscopy. Deposition of about 0.25 monolayer of Co atoms causes the formation of flat Co nanoislands with thicknesses ranging from monolayer to triple layer. Scanning tunneling spectroscopy measurements reveal that a Tamm-type surface state exists on the Co islands and its energy varies with the thicknesses and stacking manners. In addition, density functional theory calculations conclude that the surface states of the mono- and bilayer nanoislands mainly originate from the hybridization between Co d bands and sp bands of the substrate and the Co d minority-spin bands, respectively.

Yu, Yinghui; Zhang, Yun; She, Limin; Wu, Ping; Huang, Min; Cao, Gengyu

2013-03-01

370

Scanning tunneling microscopy and small angle neutron scattering study of mixed monolayer protected gold nanoparticles in organic solvents  

Digital Repository Infrastructure Vision for European Research (DRIVER)

When a binary mixture of ligand molecules is used to coat gold nanoparticles, stripe-like domains can occur. These nanodomains confer nanoparticles unique structure-dependent properties. The domain structure has been characterized primarily using scanning tunneling microscopy (STM) in air and in vacuum. Here we show the first STM images of striped nanoparticles in a solvent, 1-phenyloctane. We achieve stable imaging conditions on dodecanethiol hexanethiol (C12 : C6) 2 : 1 protected gold nanop...

2014-01-01

371

Electroluminescence of a Polythiophene Molecular Wire Suspended between a Metallic Surface and the Tip of a Scanning Tunneling Microscope  

Science.gov (United States)

The electroluminescence of a polythiophene wire suspended between a metallic surface and the tip of a scanning tunneling microscope is reported. Under positive sample voltage, the spectral and voltage dependencies of the emitted light are consistent with the fluorescence of the wire junction mediated by localized plasmons. This emission is strongly attenuated for the opposite polarity. Both emission mechanism and polarity dependence are similar to what occurs in organic light emitting diodes (OLED) but at the level of a single molecular wire.

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

2014-01-01

372

Role of interband scattering in neutron irradiated MgB$_2$ thin films by Scanning Tunneling Spectroscopy measurements  

CERN Document Server

A series of MgB$_2$ thin films systematically disordered by neutron irradiation have been studied by Scanning Tunneling Spectroscopy. The c-axis orientation of the films allowed a reliable determination of local density of state of the $\\pi$ band. With increasing disorder, the conductance peak moves towards higher voltages and becomes lower and broader, indicating a monotonic increase of the $\\pi$ gap and of the broadening parameter. These results are discussed in the frame of two-band superconductivity.

Capua, R D; Ferdeghini, C; Ferrando, V; Orgiani, P; Putti, M; Salluzzo, M; Vaglio, R; Xi, X X

2006-01-01

373

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 wi...

Engbæk, Jakob; Schiøtz, Jakob; Dahl-madsen, Bjarke; Horch, Sebastian

2007-01-01

374

Scanning tunneling spectroscopy of Ni/W(110): bcc and fcc properties in the second atomic layer  

Science.gov (United States)

Nickel islands are grown on W(110) at elevated temperatures. Islands with a thickness of two layers are investigated with scanning tunneling microscopy. Spectroscopic measurements reveal that nanometer sized areas of the islands exhibit distinctly different apparent heights and d I/d Vspectra. Spin polarized and paramagnetic band structure calculations indicate that the spectral features are due to fcc(111) and bcc(110) orientations of the Ni film, respectively.

Schöneberg, Johannes; Weismann, Alexander; Berndt, Richard

2013-04-01

375

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

International Nuclear Information System (INIS)

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

2007-01-01

376

Cross-Sectional Scanning Tunneling Microscopy and Spectroscopy of Semimetallic ErAs Nanostructures Embedded in GaAs  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The growth and atomic/electronic structure of molecular beam epitaxy (MBE)-grown ErAs nanoparticles and nanorods embedded within a GaAs matrix are examined for the first time via cross-sectional scanning tunneling microscopy (XSTM) and spectroscopy (XSTS). Cross sections enable the interrogation of the internal structure and are well suited for studying embedded nanostructures. The early stages of embedded ErAs nanostructure growth are examined via these techniques and compa...

Kawasaki, Jason K.; Timm, Rainer; Buehl, Trevor E.; Lundgren, Edvin; Mikkelsen, Anders; Gossard, Arthur C.; Palmstrøm, Chris J.

2012-01-01

377

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

Science.gov (United States)

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

Chen, Ting; Sarid, Dror

378

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

Science.gov (United States)

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

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

2013-11-01

379

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

DEFF Research Database (Denmark)

The growth mode of sub-monolayer amounts of Pd on Cu(111) in the temperature range - 80-300 degrees C has been investigated by scanning tunneling microscopy (STM), Rutherford backscattering spectroscopy (RBS) and Auger electron spectroscopy (AES). Below approximate to 100 degrees C, the Pd induced phase nucleates at ascending steps in fingered brims and, on large terraces, in fingered islands. The lack of order suggests that the brims and islands are a disordered alloy formed by exchange between Pd and Cu from the layer underneath. For temperatures exceeding approximate to 160 degrees C, Cu is dug out from the surface in extended, monolayer deep pits, and concurrently, the brims and islands increase in height by one layer. High-resolution STM images of brims and islands in this phase are interpreted as evidence for Cu capping. For Pd evaporation at temperatures of 220-300 degrees C, the surface is characterized by the appearance of individual Pd atoms substituted into the first layer and the presence of subsurface Pd. A short-range order that excludes the population of nearest-neighbour, in-plane sites is revealed by pair-correlation analysis. The Pd atoms form bands in the upper terrace next to steps. These bands are surprisingly stable against further diffusion, possibly due to an attractive interaction with second- and third-nearest (in-plane) neighbours and with subsurface Pd. The lack of any ordering is explained, based on a calculation of the surface energy. Once the population of nearest-neighbour sites is excluded, there is practically no energy gain by ordering. (C) 1998 Elsevier Science B.V. All rights reserved.

Lægsgaard, E.; Ruban, Andrei

1998-01-01

380

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

International Nuclear Information System (INIS)

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

2009-01-01

 
 
 
 
381

Scanning Tunneling Microscope Observations of Fracture Surfaces of Polymeric, Silicate, and Metallic Glasses  

Science.gov (United States)

Scanning tunneling microscope (STM) observations of gold-coated polymer fracture surfaces show variety of nm-scale features. Observations are reported on poly(methyl methacrylate) (PMMA) fractured under three different loading conditions: in tension at room temperature, in tension at liquid nitrogen temperature, and in the double torsion geometry at room temperature (slow crack growth). Fracture surfaces of polystyrene and polycarbonate loaded in tension at room temperature are also investigated. Each of these surfaces show distinctive nm-scale features which we interpret in terms of crack growth instabilities. Nm-scale features on soda-lime glass and fused silica fracture surfaces formed during catastrophic crack growth are also investigated. Both materials show parallel ridges in the mirror zone. In addition, holes and protrusions are observed on a wide range of length scales. These features are similar to the larger features forming the mist region of many fracture surfaces. Evidence for crack-defect interactions is also observed on the nm-scale. Fractal dimension measurements made from STM images are reported. Soda-lime glass fractured at slow, stable crack velocities in ambient air show features which may be attributed to water-assisted crack growth. STM observations of fracture surfaces are reported for three metallic glasses: Fe_{78 }B_{13}Si _9, Ni_{56} Cr_{18}Si _{22}B_4 and Co_{69}Fe _4Ni_1B_ {12}Si_{12}. All three glasses display a macroscopic vein-like pattern of ridges resulting from a meniscus instability along the crack front. Extensive nm-scale structure is observed on the fracture surfaces of each material. Observations of the ridges consistent with the vein pattern show nm -scale steps which we attribute to shear band. Away from the ridges, nm-scale grooves are often observed. We attribute these grooves to micro-failure events in the process zone ahead of the advancing crack.

Kulawansa, Digala Mudiyanselage

382

Atomic-Resolution Scanning Tunneling Microscopy and Infrared Spectroscopy as Combined In-Situ Probes of Electrochemical Adlayer Structure: Carbon Monoxide on Rhodium(111).  

Science.gov (United States)

In-situ scanning tunneling microscopy (STM) has been combined with infrared reflection-absorption spectroscopy (IRRAS) to yield detailed atomic-level adlayer structures for saturated coverages of CO on ordered Rh(111) in aqueous solutions. Two distinctly ...

B. C. Schardt M. J. Weaver S. C. Chang S. L. Yau X. Gao

1991-01-01

383

Tunneling  

Science.gov (United States)

This web page illustrates the tunneling of a quantum wavepacket through potential barriers. Movies show the time-dependent properties of wavepackets interacting with various potential barriers and wells are shown. Issues related to energy and barrier width are considered, along with comparison to scattering by a potential well.

Michielsen, Kristel; De Raedt, Hans

2004-03-16

384

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

Energy Technology Data Exchange (ETDEWEB)

In this thesis the electronic properties of the bare Pt(111) surface, the structural, electronic, and magnetic properties of monolayer and double-layer high Co nanostructures as well as the spin-averaged electronic structure of single Co atoms on Pt(111) were studied by low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS). The experiments on the bare Pt(111) surface and on single Co atoms have been performed in an STM facility operating at temperatures of down to 0.3 K and at magnetic fields of up to 14 T under ultra-high vacuum conditions. The facility has been taken into operation within the time period of this thesis and its specifications were tested by STS measurements. These characterization measurements show a very high stability of the tunneling junction and an energy resolution of about 100 {mu}eV, which is close to the thermal limit. The investigation of the electronic structure of the bare Pt(111) surface reveals the existence of an unoccupied surface state. By a comparison of the measured dispersion to first-principles electronic structure calculations the state is assigned to an sp-derived surface band at the lower boundary of the projected bulk band gap. The surface state exhibits a strong spin-orbit coupling induced spin splitting. The close vicinity to the bulk bands leads to a strong linear contribution to the dispersion and thus to a deviant appearance in the density of states in comparison to the surface states of the (111) surfaces of noble metals. A detailed study of Co monolayer and double-layer nanostructures on the Pt(111) surface shows that both kinds of nanostructures exhibit a highly inhomogeneous electronic structure which changes at the scale of only a few Aa due to a strong stacking dependence with respect to the Pt(111) substrate. With the help of first principles calculations the different spectroscopic appearance for Co atoms within the Co monolayer is assigned to a stacking dependent hybridization of Co states with the substrate states. Despite this electronic inhomogeneity, the magnetic domains and domain walls are clearly observed by spin-resolved STS. For both types of Co nanostructures the out-of-plane orientation of the magnetic moments is proven. Furthermore, new insights into the anisotropy of the Co nanostructures as well as a strong dependence of the coercivity on the local sample morphology for Co double-layer islands were found. The experiments performed on single Co atoms on the Pt(111) surface show that two groups of Co atoms are present on the surface. Each group can be characterized by a specific spectroscopic signature. An analysis of the spectroscopy and atom manipulation experiments proves that the spectroscopic differences are related to the two possible adsorption sites of the Co atoms on the Pt(111) substrate. (orig.)

Meier, F.K.

2006-07-01

385

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

International Nuclear Information System (INIS)

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

2012-04-01

386

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

DEFF Research Database (Denmark)

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

Keil, Ulrich Dieter Felix; Jensen, Jacob Riis

1998-01-01

387

Surface reconstructions of the Sn/Si(111) system investigated by ion-scattering spectrometry and scanning tunneling microscopy  

Science.gov (United States)

We report the use of impact-collision ion scattering spectrometry (ICISS) and scanning tunneling microscopy (STM) to study the in-plane geometry of both the ?3 × ?3 and 2?3 × 2?3 reconstructions of Sn on Si(111). For the ?3 × ?3 reconstruction the Sn atoms are thought to sit in fourfold atop (T 4) sites, or threefold hollow (H 3) sites. ICISS polar angle scans show a definite agreement with computer simulations of the T 4 model. The ICISS scans also determine the spacing between Sn and Si layers. Previous STM work reported a twofold symmetric structure for the 2?3 × 2?3 reconstruction with three possible orientations. We use ICISS and STM to provide information on both the geometry and registration of atoms on the surface in order to solve the structure of this particular surface.

Worthington, M. S.; Stevens, J. L.; Chang, C. S.; Tsong, I. S. T.

1992-02-01

388

Scanning tunneling microscopy study on superconductivity of FeSe thin films  

Science.gov (United States)

Searching for superconducting materials with high transition temperature (TC) is one of the most exciting and challenging fields in physics and materials science. By using MBE technique, we are able to prepare stoichiometric and superconducting FeSe single crystalline films on various substrates, which enables us investigate superconductivity mechanism of FeSe thin films in well-controlled way [1-3]. Most importantly, by using low temperature scanning tunneling spectroscopy, a superconductive gap as large as 20 meV and the vortex state under high magnetic field are revealed in the single unit-cell thick FeSe films on SrTiO3(001) substrate [4]. Such a high Tc superconductor is further confirmed by recent transport measurement. The study not only demonstrates a powerful way for finding new superconductors and for raising TC, but also provides a well-defined platform for systematic study of the mechanism of unconventional superconductivity by using different superconducting materials and substrates. The study is collaborated with Professor Qi-Kun Xue, Department of Physics, Tsinghua University, China.[4pt] References:[0pt] [1] C. L. Song, Y. L.Wang, P. Cheng, Y. P. Jiang, W. Li, T. Zhang, Z. Li, K. He, L. L. Wang, J. F. Jia, H. H, Hung, C. J. Wu, X. C. Ma, X. Chen, and Q. K. Xue, Science 332, 1410 (2011).[0pt] [2] C. L. Song, Y. L. Wang, Y. P. Jiang, Z. Li, L. L. Wang, K. He, X. Chen, X. C. Ma, and Q. K. Xue, Phys. Rev. B 84, 020503 (2011).[0pt] [3] C. L. Song, Y. L. Wang, Y. P. Jiang, L. L. Wang, Ke He, Xi Chen, J. E. Hoffman, X. C. Ma, and Q. K. Xue, Phys. Rev. Lett. 109, 137004 (2012).[0pt] [4] Wang Qingyan, Li Zhi, Zhang Wenhao, Zhang Zuocheng, Zhang Jinsong, Li Wei, Ding Hao, Ou Yunbo, Deng Peng, Chang Kai, Wen Jing, Song Canli, He Ke, Ji Shuaihua, Jia Jinfeng, Wang Yayu, Wang Lili, Chen Xi, Ma Xucun, and Xue Qikun, Chin. Phys. Lett. 29, 037402 (2012).

Ma, Xucun

2013-03-01

389

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

DEFF Research Database (Denmark)

We have used L-Cysteine (Cys) as a model system to study the surface electronic structures of single molecules at the submolecular level in aqueous buffer solution by a combination of electrochemical scanning tunneling microscopy (in situ STM), electrochemistry including voltammetry and chronocoulometry, and density functional theory (DFT) computations. Cys molecules were assembled on single-crystal Au(110) surfaces to form a highly ordered monolayer with a periodic lattice structure of c(2 x 2) in which each unit contains two molecules; this conclusion is confirmed by the results of calculations based on a slab model for the metal surface. The ordered monolayer offers a platform for submolecular scale electronic mapping that is an issue of fundamental interest but remains a challenge in STM imaging science and surface chemistry. Single Cys molecules were mapped as three electronic subunits contributed mainly from three chemical moieties: thiol (-SH), carboxylic (-COOH), and amine (-NH2) groups. The contrastsof the three subunits depend on the environment (e.g., pH), which affects the electronic structure of adsorbed species. From the DFT computations focused on single molecules, rational analysis of the electronic structures is achieved to delineate the main factors that determine electronic contrasts in the STM images. These factors include the molecular orientation, the chemical nature of the elements or groups in the molecule, and the interaction of the elements with the substrate and tip. The computational images recast as constant-current-height profiles show that the most favorable molecular orientation is the adsorption of cysteine as a radical in zwitterionic form located on the bridge between the Au(I 10) atomic rows and with the amine and carboxyl group toward the solution bulk. The correlation between physical location and electronic contrast of the adsorbed molecules was also revealed by the computational data. The present study shows that cysteine packing in the adlayer on Au(110) from the liquid environment is in contrast to that from the ultrahigh-vacuum environment, suggesting solvent plays a role during molecular assembly.

Zhang, Jingdong; Chi, Qijin

2009-01-01

390

Investigations at the Solid-Liquid Interface by Scanning Tunneling Microscopy.  

Science.gov (United States)

Scanning tunneling microscopy (STM) has been used to investigate electrochemical processes at the solid-liquid interface. These investigations have been conducted in two specific areas, namely bioelectrochemistry and semiconductor electrochemistry. In the area of bioelectrochemistry, the STM was used to examine the morphology of the surface and determine the conditions necessary to electrochemically deposit a monolayer of nucleic acids. Parameters that were varied included: substrate material (graphite and gold), nucleic acid concentration (1.0-150 mug/ml), applied potential (between +2 and -2 V vs. Ag/AgCl) and potentiostatic pulse duration (10-180 s), and Tris buffer solution concentration (0.1-10 mM) and pH (7.3-8). Under most of the conditions studied, the deposited material was heterogeneously distributed over the surface as aggregates with small patches of isolated or loosely packed molecules. Conditions for repeatable homogeneous coverage were obtained by applying +1 V vs. Ag/AgCl to a gold substrate for one minute in a solution of 3 mM Tris buffer (pH 7.3) and a DNA concentration of 10 mug/ml. However, the homogeneous deposits consisted of a buffer salt complex with the nucleic acid. This salt complex prevented high resolution STM imaging of the nucleic acid. In the area of semiconductor electrochemistry, the STM was used to locally modify semiconducting surfaces on the nanometer scale. This was achieved by using the STM tip to either etch into the semiconductor surface or deposit gold onto the surface, while under solution. In the case of etching, the applied electric field existing between the tip and sample probably causes local oxidation of the surface. Subsequently, an etching solution removes the oxidized portion and leaves a depression in the sample. The oxide growth depended upon the length of time that the STM tip spent over a region. In the case of deposition, photoelectrochemical techniques were used to generate additional electrons in p-type GaAs(100). The STM tip bias was then used to bend the semiconductor bands to allow the photo -generated electrons to move toward the surface. This band bending occurred only beneath the STM tip and thus localized the gold deposition to this region. The size of the gold deposit depended upon the magnitude and duration of the potential applied to the STM tip.

Nagahara, Larry Akio

391

Fabrication, functionalization, and characterization of atomically precise organosilicon nanostructures: A scanning tunneling microscopy study  

Science.gov (United States)

An ultra-high vacuum (UHV) scanning tunneling microscope (STM) operating at room temperature has been used for the fabrication and characterization of organic nanostructures covalently bound to silicon surfaces. These nanostructures range from single molecules with diverse chemical functionalities, to one-dimensional molecular chains that can not only form dense and ordered monolayers, but also atomically precise structures in registry with a second molecular species, thus resulting in heteromolecular nanostructures. A technique called Multistep Feedback Controlled Lithography has been developed that allows the creation of atomically precise organic structures built of distinct chemical species. This technique has been experimentally demonstrated by the templated growth of styrene molecular chains in conjunction with a second molecular species, TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy). This approach can be widely used for fundamental studies and fabricating prototype devices that require atomically registered organic molecules mounted on silicon surfaces. A styrene variant, namely 4-bromostyrene, has been demonstrated to form dense self-assembled monolayers (SAMs) on Si(100) while maintaining structural order at the atomic scale, as revealed by UHV STM imaging. These SAMs can be effectively fabricated in UHV gas phase reactions as well as ambient liquid phase reactions. The chemical integrity of these SAMs was confirmed by X-ray photoelectron spectroscopy. This study shows that styrene derivatives can serve as effective organic molecules for the chemical functionalization of hydrogen passivated silicon surfaces. Another styrene derivative, namely 4-methoxystyrene, whose functional group possesses a rotational degree of freedom, has been used to study the stability and motion of individual molecules on the clean Si(100) surface. Using UHV STM imaging, this molecule and a specially synthesized analog molecule with its rotational freedom suppressed, have been used to study the correlation of molecular stability with its internal degrees of freedom. Additional UHV STM experiments performed with 3-methoxystyrene and 2-methoxystyrene molecules suggest that the extent of resonant interaction of the aromatic ring with the oxygen lone pairs influences the stability of these molecules on the surface. Overall this study suggests that the stability of surface mounted adsorbates can be controlled by engineering their intramolecular rotational degrees of freedom.

Basu, Rajiv

392

Scanning Tunneling Microscopy: Development ofTips for Contrast Enhanced Imaging and Imaging of Mixed Monolayers  

Science.gov (United States)

Scanning Tunneling Microscopy (STM) is a powerful tool for surface analysis which provides atomic resolution of samples. Of particular interest is the adsorption behavior of alkane and alkane derivatives on graphite substrates. Such studies are limited by the lack of chemical information provided by STM. Chemically Selective STM, wherein STM tips are chemically modified in order to provide enhanced contrast of chemicals on a surface is a solution to this limitation. While extremely promising this method has several limitations barring it from wider application. These limitations include the low population of modified tips that provide contrast enhancement and limited useful tip lifetime. Chapter 1 presents a general introduction to the materials and methods employed in this work. In Chapter 2 growth of carbon nanotubes (CNTs) on STM tips is explored as a new route to chemically modified STM tips. Growth of CNTs on tungsten followed by electrodeposition of ruthenium oxide to create a conductive path led to a working CNT STM tip. Chapter 3 presents a study of gold nanoparticle deposition on carbon nanotubes by thermal evaporation. Nanoparticles supported on CNTs are of interest in various area of study including catalysis and electrochemistry. It is demonstrated that evaporation is an effective route to CNT supported gold nanoparticles. Chapter 4 focuses on development of a new single-step electrochemical etching method for producing gold STM tips. Sharp gold STM tips are critical for chemically selective STM performed with self-assembled monolayer (SAM) modified tips. It is demonstrated that electrochemical etching in low concentrations of perchloric acid in aqueous sodium chloride solutions produces high quality tips. Chapter 5 discusses an in-situ voltage pulse treatment for inducing chemical contrast enhancement in STM images. This method, applied for the first time to a hydrogen bond donor, allows chemical contrast enhancement in STM images to be switched on or off and extend the useful life time and population of SAM modified STM tips. Chapter 6 describes an investigation of the adsorption behavior of an unsymmetrical alkyl ether and an unsymmetrical alkyl thioether, and the formation and structure of mixed monolayers of those two components.

Gingery, David Patrick

393

Scanning tunneling microscopy-based in situ measurement of fast tool servo-assisted diamond turning micro-structures  

Science.gov (United States)

We propose a new in situ measurement system based on scanning tunneling microscopy (STM) to realize spiral scanning of a micro-structure without removing it after fast tool servo (FTS) cutting. To avoid distortion of the machined and measured surface, the center alignment of the FTS tool and the STM tip was first implemented by an STM in situ raster scan of two circular grooves cut by the machine tool. To originally observe the machined surface, the trace of the STM tip is put in accord with that of the FTS by setting the same start and end points of cutting and scanning and the same feed rate, and both are triggered by the subdivided rotary encoder of the spindle of the diamond turning machine. The profile data of the in situ spiral scanning of the machined micro-lens array can be fed back to compensate the depth of the cut to guarantee sub-micron form accuracy after second machining. The efficient spiral scanning, proper matching and accurate evaluation results demonstrate that the proposed STM in situ measurement approach is of great significance to the fabrication process.

Ju, Bing-Feng; Zhu, Wu-Le; Yang, Shunyao; Yang, Keji

2014-05-01

394

Characterization and tunneling conductance spectra of N,N'-bis (9H-fluoren-9-ylidene)benzene-1,4-diamine thin films on graphite  

International Nuclear Information System (INIS)

N,N'-bis(9H-fluoren-9-ylidene)benzene-1,4-diamine was synthesized via the acetic acid-assisted Schiff base reaction between 9-fluorenone and p-phenylenediamine. The thin films were deposited from solution and characterized by contact angle measurements (CAM), X-ray photoelectron spectroscopy (XPS) and tunneling conductance spectroscopy (TCS). The tunneling conductance spectra, related to the potential and distance between the tip and substrate, were acquired at different tip-substrate separations and depicted significant trend under the action of electric field. Systematic analysis shows more information about electron transport through medium layers. The electric field plays an important role in tunneling conductance spectra. The tunneling conductance spectra data indicate the electric field dependence of electron transport.

2010-06-01

395

Electroluminescence of a polythiophene molecular wire suspended between a metallic surface and the tip of a scanning tunneling microscope.  

Science.gov (United States)

The electroluminescence of a polythiophene wire suspended between a metallic surface and the tip of a scanning tunneling microscope is reported. Under positive sample voltage, the spectral and voltage dependencies of the emitted light are consistent with the fluorescence of the wire junction mediated by localized plasmons. This emission is strongly attenuated for the opposite polarity. Both emission mechanism and polarity dependence are similar to what occurs in organic light emitting diodes (OLED) but at the level of a single molecular wire. PMID:24580491

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

2014-01-31

396

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

Science.gov (United States)

We describe a nanostencil lithography tool capable of operating at variable temperatures down to 30 K. The setup is compatible with a combined low-temperature scanning tunneling microscope/atomic force microscope located within the same ultra-high-vacuum apparatus. The lateral movement capability of the mask allows the patterning of complex structures. To demonstrate operational functionality of the tool and estimate temperature drift and blurring, we fabricated LiF and NaCl nanostructures on Cu(111) at 77 K. PMID:24593370

Steurer, Wolfram; Gross, Leo; Schlittler, Reto R; Meyer, Gerhard

2014-02-01

397

Electrostatic-interaction-induced molecular deposition of a hybrid bilayer on Au(111): a scanning tunneling microscopy study.  

Science.gov (United States)

Hybrid bilayers consisting of 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) and meso-tetra(4-pyridyl)porphine (TPyP) have been successfully constructed on Au(111) and investigated by electrochemical scanning tunneling microscopy (ECSTM). Under the guidance of the electrostatic interaction between negatively charged sulfonate groups and positively charged pyridyl groups, the underlying HPTS arrays act as templates for the deposition of cationic TPyPs, forming two types of TPyP/HPTS complex bilayers. The present work provides a feasible way to fabricate hybrid multilayers on the electrode surface via electrostatic interaction, which has great significance for the design of molecular nanodevices. PMID:24611792

Gu, Jing-Ying; Chen, Ting; Wang, Lin; Dong, Wei-Long; Yan, Hui-Juan; Wang, Dong; Wan, Li-Jun

2014-04-01

398

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

Science.gov (United States)

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

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

1993-01-01

399

Scanning tunnelling microscopy study of the charge-density wave in Hf-doped 1T-TaS2  

International Nuclear Information System (INIS)

The effect of doping with Hf atoms on the nearly commensurate (NC) charge-density-wave (CDW) structures of 1T-TaS2 was investigated using scanning tunnelling microscopy (STM) at room temperature, for levels of substitution of Hf for Ta up to 6.9%. It was found that the Hf atom introduces a point defect to the CDW superlattice at the CDW domain boundary for lower contents. For Hf contents higher than 1%, the CDW superlattice melted and a distorted structure was observed instead of the usual CDW superlattice. The change of the CDW structure observed by STM was compared with the change of the ?-T characteristics. (author)

2000-05-15

400

Charge-transfer effect at the interface of phthalocyanine-electrode contact studied by scanning tunneling spectroscopy.  

Science.gov (United States)

Scanning tunneling microscopy (STM) and spectroscopy (STS) are used in this work to investigate the charge-transfer effect at the molecule-substrate interface of substituted metal phthalocyanines. STS results revealed that the apparent energy gaps for both fluorinated phthalocyanines and unsubstituted phthalocyanines are essentially the same, which agree with the hybrid density functional calculations. More interestingly, there is a systematic shift of the energy level of valence bands, possibly as the result of charge-transfer effect at the molecule-substrate interface. PMID:16471672

Lei, Sheng-Bin; Deng, Ke; Yang, De-Liang; Zeng, Qing-Dao; Wang, Chen

2006-01-26

 
 
 
 
401

Scanning tunneling microscopy and spectroscopy of the chain layer in YBa2Cu3O7-x  

International Nuclear Information System (INIS)

The authors review the recent results on the surface structure and spectroscopy of the chain layer of YBa2Cu3O7-x obtained with a low temperature scanning tunneling microscope. Foremost is the discovery of a long wavelength (?1.3nm) modulation of the electronic density along the CuO chains, which has now been confirmed by neutron diffraction to also exist in the bulk. Spectroscopically, they observe an energy gap (20--25 meV) which disappears near oxygen vacancies. They also give experimental details not previously published

1996-02-02

402

Dynamics of Au (001) Surface in Electrolytes: In-Situ Coherent X-ray Scattering and Scanning Tunneling Microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We studied dynamics of Au (001) surface in situ in 0.1 M HClO4 electrolyte solution using both coherent x-ray scattering and scanning tunneling microscopy (STM). The surface of Au (001) is known to reconstruct at cathodic potentials; the reconstruction lifts at anodic potentials. In our in-situ STM experiments, the measurements focus on time-dependent progressions of surface morphology during slow potential sweep. In our in-situ coherent x-ray scattering measurements, we dem...

Pierce, M. S.; Komanicky, V.; Barbour, A.; Hennessy, D. C.; Su, J. -d; Sandy, A.; Zhu, C.; You, H.

2011-01-01

403

Connection of a Scanning Tunneling Microscope with a Molecular Beam Epitaxy Chamber and Analysis of the Vibration Isolation System  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A scanning tunneling microscope has been connected to a high vibrating commercial Molecular Beam Epitaxy (MBE) system, in order to study InGaAs layers grown on InP. An original and well efficient vibration isolation system has been designed and built: the microscope support, stiffly linked to a vibration free inert mass has been connected through a highly flexible bellow to the MBE system. The main characteristic of this design is a low transmission factor at low frequencies. A detailed analy...

Krapf, P.; Laine?, J. P.; Robach, Y.; Porte, L.

1995-01-01

404

Observation of photoactive yellow protein anchored to a modified Au(1 1 1) surface by scanning tunneling microscopy  

Science.gov (United States)

The adsorption of photoactive yellow protein (PYP) on a Au(1 1 1) surface and its fluorescence activity have been studied by electrochemical scanning tunneling microscopy (EC-STM) and fluorescence photometry. A stable, densely packed protein layer was observed after protein immobilization onto a Au(1 1 1) surface modified with a mixture of 3-mercaptopropanoic acid (3-MPA) and 11-mercaptoundecanoic acid (11-MUA) and subsequent formation of the amide bond with the use of N-hydroxysuccinimide and carbodiimide. Fluorescence photometry data indicate that covalent binding of PYP to the functionalized Au(1 1 1) surface does not interfere with the fluorescence properties of the native protein.

Rze?nicka, Izabela I.; Wurpel, George W. H.; Bonn, Mischa; van der Horst, Michael A.; Hellingwerf, Klaas J.; Matsunaga, Soichiro; Yamada, Taro; Kawai, Maki

2009-04-01

405

Low-dimensional NbO structures on the Nb(110) surface: scanning tunneling microscopy, electron spectroscopy and diffraction  

Digital Repository Infrastructure Vision for European Research (DRIVER)

X-ray photoelectron spectroscopy and diffraction (XPS, XPD) and scanning tunneling microscopy (STM) have been used for study of NbOx-structures on the Nb(110) surface. It is shown that niobium atoms are ordered to form a two-dimensional superstructure with equidistant spacing between the chains of niobium atoms. Chemical shifts of Nb3d- and O1s-levels demonstrate that the oxide layer corresponds to niobium monoxide NbO and the most part of oxygen in chemisorbed state is loca...

Razinkin, A. S.; Shalaeva, E. V.; Kuznetsov, M. V.

2008-01-01

406

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2012-01-01

407

Chain polymerization of diacetylene compound multilayer films on the topmost surface initiated by a scanning tunneling microscope tip.  

Science.gov (United States)

Chain polymerizations of diacetylene compound multilayer films on graphite substrates were examined with a scanning tunneling microscope (STM) at the liquid/solid interface of the phenyloctane solution. The first layer grew very quickly into many small domains. This was followed by the slow formation of the piled up layers into much larger domains. Chain polymerization on the topmost surface layer could be initiated by applying a pulsed voltage between the STM tip and the substrate, usually producing a long polymer of submicrometer length. In contrast, polymerizations on the underlying layer were never observed. This can be explained by a conformation model in which the polymer backbone is lifted up. PMID:17432888

Takajo, Daisuke; Okawa, Yuji; Hasegawa, Tsuyoshi; Aono, Masakazu

2007-05-01

408

Surface damage through grazing incidence ions investigated by scanning tunneling microscopy  

International Nuclear Information System (INIS)

Surface damage, caused by grazing incidence ions, is investigated with variable temperature scanning tunneling microscopy. The experiments are carried out on a Pt(111) crystal. The kinetic energy of noble gas ions is varied between 1-15 keV and the angle of incidence can be adjusted between ? = 78.5 and ? = 90 measured with respect to the surface normal. The damage patterns of single ion impacts, on flat terraces and at step edges of monoatomic height, are investigated at low surface temperatures. Ions hitting a flat terrace are usually specular reflected. The energy transfer from the ion to the crystal atoms is small and only little damage is produced. In contrast, at ascending step edges, which are illuminated by the ion beam, large angle scattering events occur. Sputtering, adatom and vacancy production is induced. However, a significant fraction of the ions, which hit step edges, enter the crystal and are guided in between two atomic layers parallel to the surface via small angle binary collisions. This steering process is denoted as subsurface channeling. The energy loss per length scale of the channeled particles is low, which results in long ion trajectories (up to 1000A). During the steering process, the ions produce surface damage. Depending on the ion species and the ion energy, adatom and vacancies or surface vacancy trenches of monoatomic width are observed. The surface damage can be used to track the path of the ion. This makes the whole trajectory of single ions with keV energy visible. The number of sputtered atoms per incident ion at ascending step edges, i.e. the step edge sputtering yield, is measured experimentally for different irradiation conditions. For ? = 86 , the sputtering yield is determined from the fluence dependent retraction of pre-existing illuminated step edges. An alternative method for the step edge sputtering yield determination, is the analysis of the concentration of ascending steps and of the removed amount of material as a function of the ion fluence. This method is also applicable under less grazing angles of incidence. The investigations show that the sputtering yield at step edges depends on the azimuthal orientation of the impinging ions with respect to the surface. This change is attributed to the orientation dependence of subsurface channeling. The step edge sputtering yield at small adatom clusters is measured. In this case, the topmost layer (which forms the step edge) has a small lateral extension in ion beam direction. The evaluation shows that the step edge yield is, compared to step edges with a long upper terrace, decreased by a factor of three. The physical reason can be traced back to subsurface channeling. The ions are able to pass underneath the cluster and exit the crystal without a large scattering event. Little energy is transfered to the crystal which results in a low sputtering yield. The influence of adsorbates on sputtering and surface damage in grazing incidence ion erosion is studied for the case of oxygen and carbon monoxide. A partial surface coverage with adsorbates causes an enhancement of the erosion rate (the amount of removed material per ion fluence) by a factor of up to 40 compared to the clean case. The study is performed for 5 keV Ar+ ions for various grazing angles between 81 and 87 and temperatures ranging from 400 K to 550 K. Finally, coarsening of ion beam induced ripple patterns is analyzed. For surface temperatures of 450 K or below coarsening is athermal and kinetic, unrelated to diffusion and surface free energy. Similar to the situation of sand dunes, coarsening takes place through annihilation reactions of mobile defects in the pattern. The defect velocity derived on the basis of a simple model agrees quantitatively with the velocity of monoatomic steps illuminated by the ion beam. (orig.)

2009-01-01

409

Adsorbate structures and catalytic reactions studied in the torrpressure range by scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

High-pressure, high-temperature scanning tunneling microscopy (HPHTSTM) was used to study adsorbate structures and reactions on single crystal model catalytic systems. Studies of the automobile catalytic converter reaction [CO + NO {yields} 1/2 N{sub 2} + CO{sub 2}] on Rh(111) and ethylene hydrogenation [C{sub 2}H{sub 4} + H{sub 2} {yields} C{sub 2}H{sub 6}] on Rh(111) and Pt(111) elucidated information on adsorbate structures in equilibrium with high-pressure gas and the relationship of atomic and molecular mobility to chemistry. STM studies of NO on Rh(111) showed that adsorbed NO forms two high-pressure structures, with the phase transformation from the (2 x 2) structure to the (3 x 3) structure occurring at 0.03 Torr. The (3 x 3) structure only exists when the surface is in equilibrium with the gas phase. The heat of adsorption of this new structure was determined by measuring the pressures and temperatures at which both (2 x 2) and (3 x 3) structures coexisted. The energy barrier between the two structures was calculated by observing the time necessary for the phase transformation to take place. High-pressure STM studies of the coadsorption of CO and NO on Rh(111) showed that CO and NO form a mixed (2 x 2) structure at low NO partial pressures. By comparing surface and gas compositions, the adsorption energy difference between topsite CO and NO was calculated. Occasionally there is exchange between top-site CO and NO, for which we have described a mechanism for. At high NO partial pressures, NO segregates into islands, where the phase transformation to the (3 x 3) structure occurs. The reaction of CO and NO on Rh(111) was monitored by mass spectrometry (MS) and HPHTSTM. From MS studies the apparent activation energy of the catalytic converter reaction was calculated and compared to theory. STM showed that under high-temperature reaction conditions, surface metal atoms become mobile. Ethylene hydrogenation and its poisoning by CO was also studied by STM on Rh(111) and Pt(111). Poisoning was found to coincide with decreased adsorbate mobility. Under ethylene hydrogenation conditions, no order is detected by STM at 300 K, as hydrogen and ethylidyne, the surface species formed by gas-phase ethylene, are too mobile. When CO is introduced, the reaction stops, and ordered structures appear on the surface. For Rh(111), the structure is predominantly a mixed c(4 x 2), though there are some areas of (2 x 2). For Pt(111), the structure is hexagonal and resembles the Moire pattern seen when Pt(111) is exposed to pure CO. From these studies it is concluded that CO poisons by stopping adsorbate mobility. This lack of adsorbate mobility prevents the adsorption of ethylene from the gas phase by hindering the creation of adsorption sites.

Hwang, Kevin Shao-Lin

2003-05-23

410

Infrared spectra and tunneling dynamics of the N{sub 2}–D{sub 2}O and OC–D{sub 2}O complexes in the v{sub 2} bend region of D{sub 2}O  

Energy Technology Data Exchange (ETDEWEB)

The rovibrational spectra of the N{sub 2}–D{sub 2}O and OC–D{sub 2}O complexes in the v{sub 2} bend region of D{sub 2}O have been measured in a supersonic slit jet expansion using a rapid-scan tunable diode laser spectrometer. Both a-type and b-type transitions were observed for these two complexes. All transitions are doubled, due to the heavy water tunneling within the complexes. Assuming the tunneling splittings are the same in K{sub a} = 0 and K{sub a} = 1, the band origins, all three rotational and several distortion constants of each tunneling state were determined for N{sub 2}–D{sub 2}O in the ground and excited vibrational states, and for OC–D{sub 2}O in the excited vibrational state, respectively. The averaged band origin of OC–D{sub 2}O is blueshifted by 2.241 cm{sup ?1} from that of the v{sub 2} band of the D{sub 2}O monomer, compared with 1.247 cm{sup ?1} for N{sub 2}–D{sub 2}O. The tunneling splitting of N{sub 2}–D{sub 2}O in the ground state is 0.16359(28) cm{sup ?1}, which is about five times that of OC–D{sub 2}O. The tunneling splittings decrease by about 26% for N{sub 2}–D{sub 2}O and 23% for OC–D{sub 2}O, respectively, upon excitation of the D{sub 2}O bending vibration, indicating an increase of the tunneling barrier in the excited vibrational state. The tunneling splittings are found to have a strong dependence on intramolecular vibrational excitation as well as a weak dependence on quantum number K{sub a}.

Zhu, Yu; Zheng, Rui; Li, Song; Yang, Yu; Duan, Chuanxi, E-mail: cxduan@phy.ccnu.edu.cn [College of Physical Science and Technology, Central China Normal University, Wuhan 430079 (China)

2013-12-07

411

Infrared spectra and tunneling dynamics of the N2-D2O and OC-D2O complexes in the v2 bend region of D2O.  

Science.gov (United States)

The rovibrational spectra of the N2-D2O and OC-D2O complexes in the v2 bend region of D2O have been measured in a supersonic slit jet expansion using a rapid-scan tunable diode laser spectrometer. Both a-type and b-type transitions were observed for these two complexes. All transitions are doubled, due to the heavy water tunneling within the complexes. Assuming the tunneling splittings are the same in K(a) = 0 and K(a) = 1, the band origins, all three rotational and several distortion constants of each tunneling state were determined for N2-D2O in the ground and excited vibrational states, and for OC-D2O in the excited vibrational state, respectively. The averaged band origin of OC-D2O is blueshifted by 2.241 cm(-1) from that of the v2 band of the D2O monomer, compared with 1.247 cm(-1) for N2-D2O. The tunneling splitting of N2-D2O in the ground state is 0.16359(28) cm(-1), which is about five times that of OC-D2O. The tunneling splittings decrease by about 26% for N2-D2O and 23% for OC-D2O, respectively, upon excitation of the D2O bending vibration, indicating an increase of the tunneling barrier in the excited vibrational state. The tunneling splittings are found to have a strong dependence on intramolecular vibrational excitation as well as a weak dependence on quantum number K(a). PMID:24320382

Zhu, Yu; Zheng, Rui; Li, Song; Yang, Yu; Duan, Chuanxi

2013-12-01

412

Infrared spectra and tunneling dynamics of the N2–D2O and OC–D2O complexes in the v2 bend region of D2O  

International Nuclear Information System (INIS)

The rovibrational spectra of the N2–D2O and OC–D2O complexes in the v2 bend region of D2O have been measured in a supersonic slit jet expansion using a rapid-scan tunable diode laser spectrometer. Both a-type and b-type transitions were observed for these two complexes. All transitions are doubled, due to the heavy water tunneling within the complexes. Assuming the tunneling splittings are the same in Ka = 0 and Ka = 1, the band origins, all three rotational and several distortion constants of each tunneling state were determined for N2–D2O in the ground and excited vibrational states, and for OC–D2O in the excited vibrational state, respectively. The averaged band origin of OC–D2O is blueshifted by 2.241 cm?1 from that of the v2 band of the D2O monomer, compared with 1.247 cm?1 for N2–D2O. The tunneling splitting of N2–D2O in the ground state is 0.16359(28) cm?1, which is about five times that of OC–D2O. The tunneling splittings decrease by about 26% for N2–D2O and 23% for OC–D2O, respectively, upon excitation of the D2O bending vibration, indicating an increase of the tunneling barrier in the excited vibrational state. The tunneling splittings are found to have a strong dependence on intramolecular vibrational excitation as well as a weak dependence on quantum number Ka

2013-12-07

413

Scanning tunneling microscopy of hundred-nanometer thick Nafion polymer covered Pt and highly ordered pyrolytic graphite  

Science.gov (United States)

The atom-scale structure and properties of the interface between polymer electrolyte and electronic conductor are of great interest for novel electrochemical power sources including fuel cell, lithium batteries, and supercapacitors. Scanning tunneling microscopy, a well-known tool for imaging electronically conducting surface, is used to investigate Nafion polymer electrolyte coated Pt or highly ordered pyrolytic graphite. Periodic atom-scale patterns at the interface between Nafion and highly ordered pyrolytic graphite are obtained. In addition, in situ, real-time visualization of the atom-scale interface structure is realized upon changing the electrochemical potential of the substrates. The results suggest that a highly convergent resonant tunneling electron wave can penetrate a thick (200-1000 nm) recast Nafion (polymer electrolyte) coating and reach the substrates. A theory based on electron resonant tunneling is established to explain this phenomenon. It is expected that this method can be applied for real-time atom-scale visualization of other polymer/conductor interfaces.

Zhou, Juanjuan; Zhou, Xiangyang

2013-06-01

414

Scanning tunnelling spectroscopy of atomic clusters deposited on oxidized silicon surfaces: induced surface dipole and resonant electron injection  

International Nuclear Information System (INIS)

We investigated the tunnelling conductance of atomic clusters (C60, Si6Hx, AsSi2Hx) deposited on oxidized p-type Si(100) surfaces using scanning tunnelling microscopy where the metal probe/vacuum barrier/cluster/oxide/silicon structures form an asymmetric double-barrier tunnel (ADBT) nanoscale junction. Atomic clusters were assembled onto ultra-thin (?0.3 nm) silicon oxide by either C60 sublimation or ion beam deposition of Si-clusters generated in an ion trap. Electron transfer to the clusters induced surface dipole and reduced junction current under reverse biasing conditions (negatively biased substrate) depending on cluster structure and composition, where the AsSi2Hx clusters created the strongest dipole. Conductance enhancement was observed for forward bias originating in resonance-like electron injection through the unoccupied orbital of the clusters, which was spatially localized within ?1 deg. nm diameter for C60. The resonance peak positions and the weak surface dipole indicated that the orbital energies of C60 and Si6Hx were beyond the forbidden energy gap of Si and shifted with respect to the silicon Fermi energy for heavily doped substrates. In contrast, the orbital energy of doped AsSi2Hx clusters was below the silicon Fermi level. These results demonstrate that the ADBT junction configuration reveals electronic coupling of the clusters to the semiconductor surfaces

2003-10-29

415

On the asymmetry of the inelastic tunneling spectra on magnetic materials  

Energy Technology Data Exchange (ETDEWEB)

Inelastic tunneling spectroscopy (ITS) is a valuable tool to study excitations in metallic systems. We have applied ITS to investigate low lying magnetic excitations. For tunneling between a non-magnetic tip and a ferromagnet, the excitations were found to be asymmetric with respect to the Fermi energy. For Fe(001) magnon creation was found predominantly for tunneling into the ferromagnet, while for opposite bias the excitation is much weaker. For fcc Co(001) strong magnon excitations were found for both positive and negative bias. Using ab-initio calculations of the spin-polarised DOS of the ferromagnets we show that this asymmetry is related to the spin-polarisation of the ferromagnet. This effect has strong implications for the efficiency of the spin transfer effect used in switching of MRAM cells.

Takacs, Albert F.; Balashov, Timofey [Physikalisches Institut, Universitaet Karlsruhe (TH), Wolfgang-Gaede Str. 1, 76131 Karlsruhe (Germany); Wulfhekel, Wulf [Physikalisches Institut, Universitaet Karlsruhe (TH), Wolfgang-Gaede Str. 1, 76131 Karlsruhe (Germany); MPI fuer Mikrostrukturphysik, Weinberg 2, 06108 Halle (Germany); Kirschner, Juergen; Ernst, Arthur; Bruno, Patrick [MPI fuer Mikrostrukturphysik, Weinberg 2, 06108 Halle (Germany); Daene, Markus [Martin-Luther- Universitaet Halle-Wittenberg, Fachbereich Physik, 06099 Halle (Germany)

2007-07-01