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1

Strong-coupling analysis of scanning tunneling spectra in Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+\\delta}$  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study a series of spectra measured in the superconducting state of optimally-doped Bi-2223 by scanning tunneling spectroscopy. Each spectrum, as well as the average of spectra presenting the same gap, is fitted using a strong-coupling model taking into account the band structure, the BCS gap, and the interaction of electrons with the spin resonance. After describing our measurements and the main characteristics of the strong-coupling model, we report the whole set of para...

Berthod, C.; Fasano, Y.; Maggio-aprile, I.; Piriou, A.; Giannini, E.; Castro, G. Levy; Fischer, Ø.

2013-01-01

2

Scanning tunneling microscopy  

International Nuclear Information System (INIS)

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

3

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

International Nuclear Information System (INIS)

Highlights: •We prepared FeSe0.3Te0.7 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 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

4

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

5

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

6

Scanning tunneling microscope nanoetching method  

Science.gov (United States)

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

7

Photon scanning tunneling microscopy  

International Nuclear Information System (INIS)

The PSTM is shown to be the photon analogue of the electron STM. In the PSTM, externally-supplied plane waves undergo total internal reflection at a dielectric interface. This creates an exponentially-decaying evanescent field adjacent to the interface. Photons can be made to tunnel to a nearby optically conducting fiber optic tip. The transmitted light signal is strongly dependence upon the tip to interface distance and can be regulated by feedback control to stabilize this distance. Perturbations caused by irregularities in the interface can therefore be imaged by scanning the tip laterally in the same way as STM. Subwavelength lateral and vertical resolution is demonstrated. Lateral resolution is governed by the decay of the evanescent field and the probe shape. Vertical resolution is governed by electrical and mechanical noise. Controllable parameters include the angle of incidence, wavelength, polarization, index of refraction, and probe shape. Direct imaging of standing waves caused by the interference of two coherent surface waves at the interface will also be shown

8

The scanning tunneling microscope  

International Nuclear Information System (INIS)

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

9

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

10

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

11

Scanning Tunneling Optical Resonance Microscopy  

Science.gov (United States)

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

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

2003-01-01

12

Thermal radiation scanning tunnelling microscopy  

Science.gov (United States)

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

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

2006-12-01

13

Lorentz Force Feedback Scanning Tunneling Microscope  

Science.gov (United States)

Previously, we measured inelastic electron tunneling spectra (IETS) of molecules adsorbed on metal surfaces using a novel, crossed-wire technique.[1,2] In this geometry, the oxide barrier film typically used in a conventional metal-insulator-metal junction (MIM) junction is replaced by a rare-gas (neon) film. Although inelastic tunneling data obtained in this geometry demonstrate the ability to identify adsorbed molecules by their vibrational fingerprint, the technique does not provide any imaging capability. Presently, we have designed a new device based on the crossed-wire technique, that allows for both identification and imaging of single molecules adsorbed on metallic surfaces. The device overcomes the rigorous stability requirements necessary to measure molecular vibrational modes, by relying on the rare-gas film to maintain the tip-sample spacing. Unlike the scanning tunneling microscope (STM),[3] the Lorentz Force Feedback Scanning Tunneling Microscope (LFSTM) modulates the tip-sample spacing using an external magnetic field, allowing for precise, vertical positioning of the tip. Scanning the tip (or rather the sample) across the surface is accomplished by standard piezo bending elements. 1. D. T. Zimmerman, M. B. Weimer, and G. Agnolet, Appl. Phys. Lett. 75, 2500 (1999). 2. D. T. Zimmerman and G. Agnolet, Rev. Sci. Instrum. 72, 1781 (2001). 3. The success of the STM to image and identify single molecules was first demonstrated by Ho and co-workers [B. C. Stipe, M. A. Rezaei, and W. Ho, Science 280, 1732 (1998).

Sharp, Darrell L.; Zimmerman, Darin T.; Agnolet, Glenn

2002-03-01

14

Scanning tunnelling microscopy in biotechnology.  

Science.gov (United States)

The scanning tunnelling microscope (STM) is capable of atomic resolution of highly conductive materials. Whether biological molecules can be visualized to the same extent remains an open question, but remarkable progress in the past year confirms the possibility of seeing the fine structure of nucleic acids, proteins, membranes and viruses, and provides evidence that their dynamic interactions can be monitored under conditions approximating to those of the native environment. PMID:1366618

Arscott, P G; Bloomfield, V A

1990-06-01

15

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

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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. Calcula...

Pilgram, S.; Rice, T. M.; Sigrist, M.

2006-01-01

16

Scanning tunneling microscopy in air  

Science.gov (United States)

The paper examines the application of scanning tunneling microscopy (STM) to the study of the microtopography of irregular surfaces and to the imaging of biological objects and atomic structural changes of surfaces in air. A resolution of 0.1 A was obtained for probing normal to the surface and a resolution of 2 A was obtained in the plane of the surface. By way of illustration, attention is given to STM images of the relief of silver films spray-deposited in high vacuum and to an STM image of clusters of the reverse transcriptase of the bird myeloleucosis in a liquid medium on the surface of a gold film.

Vasil'Ev, S. I.; Leonov, V. B.; Panov, V. I.; Savinov, S. V.

17

Scanning tunneling microscopy of dye thin films  

International Nuclear Information System (INIS)

The Rhodamine 6G films on a metal and a semiconductor substrates were studied by scanning tunneling microscopy and spectral ellipsometry techniques. Scanning tunneling microscopy of dye on a metal substrate allowed obtaining interlayer surface profile with atomic spatial resolution 0.08 nm

18

Scanning Tunneling Microscope For Use In Vacuum  

Science.gov (United States)

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

Abel, Phillip B.

1993-01-01

19

Investigation into scanning tunnelling luminescence microscopy  

CERN Document Server

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

Manson-Smith, S K

2001-01-01

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

Fiber coupled ultrafast scanning tunneling microscope  

DEFF Research Database (Denmark)

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

Keil, Ulrich Dieter Felix; Jensen, Jacob Riis

1997-01-01

22

Scanning scene tunnel for city traversing.  

Science.gov (United States)

This paper proposes a visual representation named scene tunnel for capturing urban scenes along routes and visualizing them on the Internet. We scan scenes with multiple cameras or a fish-eye camera on a moving vehicle, which generates a real scene archive along streets that is more complete than previously proposed route panoramas. Using a translating spherical eye, properly set planes of scanning, and unique parallel-central projection, we explore the image acquisition of the scene tunnel from camera selection and alignment, slit calculation, scene scanning, to image integration. The scene tunnels cover high buildings, ground, and various viewing directions and have uniformed resolutions along the street. The sequentially organized scene tunnel benefits texture mapping onto the urban models. We analyze the shape characteristics in the scene tunnels for designing visualization algorithms. After combining this with a global panorama and forward image caps, the capped scene tunnels can provide continuous views directly for virtual or real navigation in a city. We render scene tunnel dynamically by view warping, fast transmission, and flexible interaction. The compact and continuous scene tunnel facilitates model construction, data streaming, and seamless route traversing on the Internet and mobile devices. PMID:16509375

Zheng, Jiang Yu; Zhou, Yu; Milli, Panayiotis

2006-01-01

23

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

24

Theoretical Description of Scanning Tunneling Potentiometry  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A theoretical description of scanning tunneling potentoimetry (STP) measurement is presented to address the increasing need for a basis to interpret experiments on macrscopic samples. Based on a heuristic understanding of STP provided to facilitate theoretical understanding, the total tunneling current related to the density matrix of the sample is derived within the general framework of quantum transport. The measured potentiometric voltage is determined implicitly as the v...

Wang, Weigang; Beasley, Malcolm R.

2010-01-01

25

Tunneling and Scanning Tunnel Microscopy: a Critical Review  

Science.gov (United States)

Electron tunneling across the surface potential barrier has been applied for many years to probe surface atomic and electronic structure. This had led, for example, to the development of the field emission microscope, and more recently, of electron tunneling spectroscopy of insulating barriers in MIM structures. Some four years ago, Binning, Rohrer and coworkers developed the first vacuum tunneling microscope with atomic resolution. In this device, electrons tunnel across a vacuum gap between a sample surface and a scanning tip. Since then, a growing number of research groups have constructed such devices. The STM has provided detailed insight into the atomic structure of surfaces. The feasibility of scanning tunnel spectroscopy (STS) has been demonstrated, though fewer results have been reported. However, before the full potential of the twin techniques of STM and STS can be realized, two problems have to be resolved: (1) A more quantitative, but tractable theory, has to be developed to permit an unambiguous interpretation of the data. (2) A more reliable procedure for the preparation of the tip has to be developed to assure the quantitative reproducibility of the data. A critical review of tunneling theory and the transfer Hamiltonian formalism is presented. Inelastic and elastic resonant tunneling are discussed. The construction and operation of the STM are briefly described. The transfer Hamiltonian theory of the device is reviewed. The concept of surface corrugation is also discussed. Recent results by Kuk on the dependence of the observed corrugation amplitude on the atomic structure of the scanning tip are analyzed. Lastly, image potential states and their significance in the STS study of the electronic structure of the surface barrier are considered.

Feuchtwang, T. E.; Cutler, P. H.

1987-02-01

26

The tunneling spectra and superconducting gaps observed by using scanning tunneling microscope near the grain-boundary of FeSe0.3Te0.7 films  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We used STM to study the tunneling spectra of FeSe0.3Te0.7 films with two orientations of ab-planes and the connection ramp between them. We have discovered that, using pulse laser deposition (PLD) method, the a- and b-axis of the FeSe0.3Te0.7 film deposited on Ar-ion-milled Magnesium Oxide (MgO) substrate are rotated 45 degree with respect to those of MgO, while the a- and b-axis of the film grown on pristine MgO substrate are parallel to those of MgO. With photolithography...

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

2013-01-01

27

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

28

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

29

Scanning tunneling microscopy studies of organic conductors  

Energy Technology Data Exchange (ETDEWEB)

Scanning tunneling microscopy (STM) studies of a series of single crystals of organic conductors reveal topographical and electronic structure of specific crystal planes, these planes exhibiting molecularly flat large areas. For example, scanning tunneling microscopy (STM) images of the (001) face of the organic conductors (TMTSF)[sub 2]X (TMTSF = tetramethyltetraselenafulvalene; X = ClO[sub 4-], ReO[sub 4-]) reveal significant differences in the local density of states associated with the transverse band structure in these two compounds. STM studies of the (001) and (010) faces of ([eta]-C[sub 5]Me[sub 5])[sub 2]Ru([eta][sup 6],[eta][sup 6]-2[sub 2](1,4)cyclophane)[sup 2+]TCNQ[sub 4][sup 2-] reveal tunneling current corrugation attributed to tunneling into the conduction band of a antiferromagnetic 2k[sub F] charge density wave (CDW) structure. The CDWs also exhibit antiphase modulation at a/2 with respect to adjacent stacks, consistent with appreciable interstack Coulomb interactions and contributions from the magnetic 4k[sub F] structure. (orig.)

Li Shulong (Dept. of Chemical Engineering and Materials Science, Univ. of Minnesota, Minneapolis (United States)); White, H.S. (Dept. of Chemical Engineering and Materials Science, Univ. of Minnesota, Minneapolis (United States)); Ward, M.D. (Dept. of Chemical Engineering and Materials Science, Univ. of Minnesota, Minneapolis (United States))

1993-03-15

30

Scanning tunnelling spectroscopy of electron resonators  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The electronic structure of artificial Mn atom arrays on Ag(111) is characterized in detail with scanning tunnelling spectroscopy and spectroscopic imaging at low temperature. We demonstrate the degree to which variations in geometry may be used to control spatial and spectral distributions of surface state electrons confined within the arrays, how these are influenced by atoms placed within the structure and how the ability to induce spectral features at specific energies m...

Berndt, Richard; Kliewer, Joerg; Crampin, S.

2001-01-01

31

Heisenberg, uncertainty, and the scanning tunneling microscope  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We show by a statistical analysis of high-resolution scanning tunneling microscopy (STM) experiments, that the interpretation of the density of electron charge as a statistical quantity leads to a conflict with the Heisenberg uncertainty principle. Given the precision in these experiments we find that the uncertainty principle would be violated by close to two orders of magnitude, if this interpretation were correct. We are thus forced to conclude that the density of electro...

Hofer, Werner A.

2011-01-01

32

Scanning Tunneling Microscopy of a Luttinger Liquid  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Explicit predictions for Scanning Tunneling Microscopy (STM) on interacting one-dimensional electron systems are made using the Luttinger liquid formalism. The STM current changes with distance from an impurity or boundary in a characteristic way, which reveals the spin-charge separation and the interaction strength in the system. The current exhibits Friedel-like oscillations, but also carries additional modulated behavior as a function of voltage and distance, which shows ...

Eggert, Sebastian

1999-01-01

33

Scanning Tunneling Optical Resonance Microscopy Developed  

Science.gov (United States)

The ability to determine the in situ optoelectronic properties of semiconductor materials has become especially important as the size of device architectures has decreased and the development of complex microsystems has increased. Scanning Tunneling Optical Resonance Microscopy, or STORM, can interrogate the optical bandgap as a function of its position within a semiconductor micro-structure. This technique uses a tunable solidstate titanium-sapphire laser whose output is "chopped" using a spatial light modulator and is coupled by a fiber-optic connector to a scanning tunneling microscope in order to illuminate the tip-sample junction. The photoenhanced portion of the tunneling current is spectroscopically measured using a lock-in technique. The capabilities of this technique were verified using semiconductor microstructure calibration standards that were grown by organometallic vapor-phase epitaxy. Bandgaps characterized by STORM measurements were found to be in good agreement with the bulk values determined by transmission spectroscopy and photoluminescence and with the theoretical values that were based on x-ray diffraction results.

Bailey, Sheila G.; Raffaelle, Ryne P.; Lau, Janis E.; Jenkins, Phillip P.; Castro, Stephanie L.; Tin, Padetha; Wilt, David M.; Pal, Anna Maria; Fahey, Stephen D.

2004-01-01

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

Atom oscillations in the scanning tunneling microscope  

International Nuclear Information System (INIS)

Time scales of the atomic oscillations between surface and tip in the scanning tunneling microscope (STM) are investigated by semiclassical methods and by the numerical integration of the time-dependent Schroedinger equation. It is shown that the upper limit of the time interval of stationary decay across the barrier is very small, and complete tunneling can be explained only by the resonance phenomenon of quantum coherence oscillations. The occurrence of these resonances at the variation of the bias voltage is studied for the first two isomeric states of a Xe atom in a sample-tip potential of double-well shape. The resonant bias voltages for these two states prove to coincide, and at the first common resonance the effect of temperature is discussed. The results provide a new frame for understanding the mechanism of atom transfer in STM. (author) 5 Figs., 10 Refs

36

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

37

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

38

Scanning Tunneling Microscopy/Spectroscopy of Vortices in LiFeAs  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We investigate vortices in LiFeAs using scanning tunneling microscopy/spectroscopy. Zero-field tunneling spectra show two superconducting gaps without detectable spectral weight near the Fermi energy, evidencing fully-gapped multi-band superconductivity. We image vortices in a wide field range from 0.1 T to 11 T by mapping the tunneling conductance at the Fermi energy. A quasi-hexagonal vortex lattice at low field contains domain boundaries which consist of alternating vorti...

Hanaguri, T.; Kitagawa, K.; Matsubayashi, K.; Mazaki, Y.; Uwatoko, Y.; Takagi, H.

2012-01-01

39

Bottom-Up Nanomanufacturing: Scanning Tunneling Microscope  

Science.gov (United States)

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

2011-09-22

40

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.

 
 
 
 
41

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

42

Scanning tunneling spectroscopy studies of heavy fermion metals  

International Nuclear Information System (INIS)

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

43

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

44

Scanning tunneling microscope study of cadmium telluride  

International Nuclear Information System (INIS)

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

45

Scanning tunneling microscopy studies of topological insulators  

Science.gov (United States)

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

Zhao, Kun; Lv, Yan-Feng; Ji, Shuai-Hua; Ma, Xucun; Chen, Xi; Xue, Qi-Kun

2014-10-01

46

Scanning tunneling microscopy studies of topological insulators.  

Science.gov (United States)

Scanning tunneling microscopy (STM), with surface sensitivity, is an ideal tool to probe the intriguing properties of the surface state of topological insulators (TIs) and topological crystalline insulators (TCIs). We summarize the recent progress on those topological phases revealed by STM studies. STM observations have directly confirmed the existence of the topological surface states and clearly revealed their novel properties. We also discuss STM work on magnetic doped TIs, topological superconductors and crystalline symmetry-protected surface states in TCIs. The studies have greatly promoted our understanding of the exotic properties of the new topological phases, as well as put forward new challenges. STM will continue to play an important role in this rapidly growing field from the point view of both fundamental physics and applications. PMID:25214502

Zhao, Kun; Lv, Yan-Feng; Ji, Shuai-Hua; Ma, Xucun; Chen, Xi; Xue, Qi-Kun

2014-10-01

47

Imaging graphite in air by scanning tunneling microscopy - Role of the tip  

Science.gov (United States)

Atomically resolved images of highly oriented pyrolytic graphite (HOPG) in air at point contact have been obtained. Direct contact between tip and sample or contact through a contamination layer provides a conduction mechanism in addition to the exponential tunneling mechanism responsible for scanning tunneling microscopy (STM) imaging. Current-voltage (I-V) spectra were obtained while scanning in the current imaging mode with the feedback circuit interrupted in order to study the graphite imaging mechanism. Multiple tunneling tips are probably responsible for images without the expected hexagonal or trigonal symmetry. The observations indicate that the use of HOPG for testing and calibration of STM instrumentation may be misleading.

Colton, R. J.; Baker, S. M.; Driscoll, R. J.; Youngquist, M. G.; Baldeschwieler, J. D.; Kaiser, W. J.

1988-01-01

48

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

49

Principles and Application of Heterodyne Scanning Tunnelling Spectroscopy  

Science.gov (United States)

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

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

2014-10-01

50

Principles and application of heterodyne scanning tunnelling spectroscopy.  

Science.gov (United States)

Detection of the extremely weak signals in spectroscopy over an extremely wide frequency region is central to diverse sciences, including materials science, biology, astronomy and chemistry. Here we show a new type of atomic-scale spectroscopy, heterodyne scanning tunnelling spectroscopy (HSTS), which is based on the innovative application of the nonlinear heterodyne-mixing detection at the metal-insulator-metal (MIM) heterojunction of STM tip-vacuum-sample. The principle of HSTS is identical to that of the Atacama Large Millimeter Array (ALMA) space telescope in terms of using heterojunction for detecting extremely weak signals by converting from terahertz region to lower frequency regions. The MIM detector of ALMA, which is composed of niobium-titanium-nitride (NbTiN) tip-insulator-NbTiN, is very similar in shape and size to that of HSTS. We successfully detect a heterodyne beat signal f3 (= |f2 - f1|) and intermodulation distortion via tunnelling current by superimposing two different AC signals, f1 and f2, onto the DC tunnelling current at a highly oriented pyrolytic graphite (HOPG) surface. We then obtain spectra of the localized electronic states of HOPG by using f3. HSTS can be performed with a high resolution and over a wide energy range, including the terahertz range. PMID:25342108

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

2014-01-01

51

Principles and Application of Heterodyne Scanning Tunnelling Spectroscopy  

Science.gov (United States)

Detection of the extremely weak signals in spectroscopy over an extremely wide frequency region is central to diverse sciences, including materials science, biology, astronomy and chemistry. Here we show a new type of atomic-scale spectroscopy, heterodyne scanning tunnelling spectroscopy (HSTS), which is based on the innovative application of the nonlinear heterodyne-mixing detection at the metal-insulator-metal (MIM) heterojunction of STM tip–vacuum–sample. The principle of HSTS is identical to that of the Atacama Large Millimeter Array (ALMA) space telescope in terms of using heterojunction for detecting extremely weak signals by converting from terahertz region to lower frequency regions. The MIM detector of ALMA, which is composed of niobium–titanium–nitride (NbTiN) tip-insulator-NbTiN, is very similar in shape and size to that of HSTS. We successfully detect a heterodyne beat signal f3 (= |f2 ? f1|) and intermodulation distortion via tunnelling current by superimposing two different AC signals, f1 and f2, onto the DC tunnelling current at a highly oriented pyrolytic graphite (HOPG) surface. We then obtain spectra of the localized electronic states of HOPG by using f3. HSTS can be performed with a high resolution and over a wide energy range, including the terahertz range. PMID:25342108

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

2014-01-01

52

Nanofabrication with the Scanning Tunneling Microscope.  

Science.gov (United States)

We have developed a technique to use the scanning tunneling microscope (STM) to create nanometer-scale structures. We use the STM tip as a localized source of electrons to decompose an organometallic gas, leaving metal atoms on the substrate. By scanning the STM tip over the surface of the substrate, we can create any desired pattern. We have used the technique in two different STM/vacuum system combinations. The first system which we designed and built to quickly test this deposition scheme, operated in high vacuum. Using this system, we deposited cadmium, aluminum, tungsten, and carbon lines with linewidths down to 10 nm, onto silicon and copper substrates. Using other organometallic gases, we etched 20 nm pits in silicon substrates. We measured the two-probe electrical resistivity of some of the wires as a function of temperature. The first system was not able to produce high -purity metal lines, nor was it possible to align the structures with pre-existing contact pads. To remedy these problems, we built a new, ultra-high-vacuum (UHV), scanning electron microscope (SEM)/STM combination. The system combines a conventional, high vacuum SEM with a separate UHV chamber for the STM. This instrument has a range of magnifications from 25x to 25,000,000x. The combination allows us to access any area on a substrate within a 2 mm x 2 mm area with the STM tip. Using this instrument, we have written wires with 95% nickel content on silicon substrates. This is by far the highest purity level achieved to date using this technique. Since the wires were aligned with a four -probe contact pad pattern, we were able to measure their four-point resistivity. This measurement, made on a 190 nm linewidth wire, confirmed the high nickel content of the wires. By varying the tip-to-sample voltage bias, we can adjust the linewidth of the deposited lines. Working at lower bias voltages, we have fabricated nickel wires down to a linewidth of 35 nm although we have not yet succeeded in making these narrow wires electrically continuous. This technique shows great promise for the fabrication of novel devices.

Ehrichs, Edward Erling

53

Scanning tunneling microscopy of self-assembled viral nanostructures  

Science.gov (United States)

We use scanning tunneling microscopy to investigate self-assembled monolayers of M13 bacteriophages on graphite surface. The bacteriophages we use have gold binding peptide motifs on their outer protein coat (˜1?m long, ˜10 nm diameter) allowing us to self-assemble gold nanoparticles on graphite. Using scanning tunneling microscopy we are able to resolve sub-molecular structure of the protein coat of M13 bacteriophage. Scanning tunneling spectroscopy allows us to study the binding of gold nanoparticles to the peptide motif on the bacteriophage.

Anacleto, Benjamin; Steinsultz, Nat; Sharma, Prashant

2010-03-01

54

Resolving catalytic phenomena with scanning tunnelling microscopy.  

Science.gov (United States)

Scanning tunnelling microscopy (STM) has proved to be an invaluable tool for investigating surface reactions and catalysis at the atomic scale on model catalysts. We show that good models of nanoparticulate catalyst surfaces can now be fabricated and imaged by the use of surface science methodology. In this paper the application of STM to some particular problems in catalysis is addressed. Specifically, these are: (i) Sintering. It is shown that sintering is a complex process, and, at least for separated nanoparticles anchored to a support, it occurs in a surface-mediated Ostwald ripening manner. That is, a reduction in particle number density and an increase in average particle size occurs by loss of atoms from the edge of nanoparticles, which then diffuse across the support to another particle. The net effect of such diffusion is that big particles get bigger at the expense of small ones, which eventually disappear. (ii) Spillover. By imaging individual nanoparticles, at elevated temperature, in the presence of gas phase oxygen, spillover of oxygen to the support is seen to occur directly. It happens because the dissociation probability of oxygen on Pd is much higher than that on titania, and spillover occurs by reaction with reduced titanium cations to grow new layers of titania around the metal nanoparticle, eventually totally encapsulating it. (iii) The so-called 'strong metal-support interaction' (SMSI). By the use of atomically-resolving STM this is shown to be due to the formation of an alloy-like mixed layer of Pd and Ti, which results in a surface of much reduced reactivity. PMID:17612718

Bowker, Michael

2007-07-21

55

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

56

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

57

Tunneling spectra for quasi-one-dimensional organic superconductors  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The tunneling conductance spectra of a normal-metal/insulator/quasi-one-dimensional superconductor is calculated by using the Blonder-Tinkham-Klapwijk formulation. The pairing symmetry of the superconductor is assumed to be $p$, $d$, and $f$-wave. It is found that there is a well defined zero energy peak in electron tunneling along the direction parallel to the chains or normal to these when the transmitted quasiparticles feel different sign of the pair potential. The actual...

Stefanakis, N.

2002-01-01

58

Structural monitoring of tunnels using terrestrial laser scanning:  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In recent years terrestrial laser scanning is rapidly evolving as a surveying technique for the monitoring of engineering objects like roof constructions, mines, dams, viaducts and tunnels. The advantage of laser scanning above traditional surveying methods is that it allows for the rapid acquisition of millions of scan points representing the whole surface of the object considered. Still it is a big challenge to obtain accuracies and precisions in the millimeter level when quantifying deform...

Lindenbergh, R. C.; Uchanski, L.; Bucksch, A.; Gosliga, R.

2009-01-01

59

Transient measurements with an ultrafast scanning tunneling microscope  

DEFF Research Database (Denmark)

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

Keil, Ulrich Dieter Felix; Jensen, Jacob Riis

1998-01-01

60

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

 
 
 
 
61

Visualization of electron orbitals in scanning tunneling microscopy  

Science.gov (United States)

Scanning tunneling microscopy (STM) is one of the main techniques for direct visualization of the surface electronic structure and chemical analysis of multi-component surfaces at the atomic scale. This review is focused on the role of the tip orbital structure and tip-surface interaction in STM imaging with picometer spatial resolution. Fabrication of STM probes with well-defined structure and selective visualization of individual electron orbitals in the STM experiments with controlled tunneling gap and probe structure are demonstrated.

Chaika, A. N.

2014-08-01

62

Probing superconductors. Spectroscopic-imaging scanning tunneling microscopy  

International Nuclear Information System (INIS)

Discovery of high-temperature superconductivity in a cuprate triggered developments of various spectroscopic tools which have been utilized to elucidate electronic states of this mysterious compound. Particularly, angle-resolved photoemission spectroscopy and scanning-tunneling microscopy/spectroscopy are improved considerably. It is now possible to map the superconducting gap in both momentum and real spaces using these two techniques. Here we review spectroscopic-imaging scanning tunneling microscopy which is able to explore momentum-space phase structure of the superconducting gap, as well as real-space structure. Applications of this technique to a cuprate and an iron-based superconductor are discussed. (author)

63

Atomic scale variation of electron tunneling into a Luttinger liquid ? : High resolution scanning tunneling spectroscopy study on Au/Ge(001)  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Au-induced atomic wires on the Ge(001) surface were recently claimed to be an ideal 1D metal and their tunneling spectra were analyzed as the manifestation of a Tomonaga-Luttinger liquid (TLL) state. We reinvestigate this system for atomically well-ordered areas of the surface with high resolution scanning tunneling microscopy and spectroscopy (STS). The local density-of-states maps do not provide any evidence of a metallic 1D electron channel along the wires. Moreover, the ...

Park, Jewook; Nakatsuji, Kan; Kim, Tae-hwan; Song, Sun Kyu; Komori, Fumio; Yeom, Han Woong

2014-01-01

64

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

65

Electronic Properties of Added Rows on TiO2(110) Surface Observed by Scanning Tunneling Spectroscopy  

Science.gov (United States)

The electronic properties of added rows on TiO2(110) surface have been studied in real space with atomic resolution by scanning tunneling spectroscopy. It is found that no vacant Ti 3d state is observed near the Fermi level in the tunneling spectra, and accordingly the tunneling conductance is lowest at the added row sites. On the other hand, a peak of vacant states appears at 1.2 eV above the Fermi level in the spectra obtained at a hill by which an added row is terminated.

Sakai, Yoshiyuki; Ehara, Shaw

2000-11-01

66

'Oxide-free' tip for scanning tunneling microscopy  

Science.gov (United States)

A new tip for scanning tunneling microscopy and a tip repair procedure that allows one to reproducibly obtain atomic images of highly oriented pyrolytic graphite with previously inoperable tips are reported. The tips are shown to be relatively oxide-free and highly resistant to oxidation. The tips are fabricated with graphite by two distinct methods.

Colton, R. J.; Baker, S. M.; Baldeschwieler, J. D.; Kaiser, W. J.

1987-01-01

67

Design and calibration of a vacuum compatible scanning tunneling microscope  

Science.gov (United States)

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

Abel, Phillip B.

1990-01-01

68

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2005-01-01

69

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...

Hong, I-po

2009-01-01

70

Scanning Auger microscopy study of W tips for scanning tunneling microscopy  

International Nuclear Information System (INIS)

Tungsten tips used in scanning tunneling microscopy (STM) (prepared via electrochemical etching with a 2 N KOH or NaOH solution) have been studied with state of the art scanning Auger microscopy (SAM) with chemical lateral resolution of 10 nm. The experiments were focused on the investigation of the W tips' apex shape and surface composition, for tips as etched, or after various postetching treatments performed for cleaning, sharpening, and surface oxide removal purposes. Ultrasonic cleaning likely bend the tip apex. Hydrofluoride etching successfully removes the native WO3 oxide layer, but this happens at the expense of the tip sharpness. Ion sputtering in ultrahigh vacuum is not always effective in sharpening and cleaning the tungsten tip apex, and we sometimes observed the formation of needle like nanotips, mostly composed of WO3. Direct resistive annealing of the tip (operated in the STM at 10 V, 50 nA set-point sample bias voltage and current, respectively) to remove the oxide layer, produces a coiling of the tip apex. In this case, atom transfer from the sample to the tip is directly demonstrated with Auger spectra taken at the tip apex

71

Tunneling rates in electron transport through double-barrier molecular junctions in a scanning tunneling microscope  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The scanning tunneling microscope enables atomic-scale measurements of electron transport through individual molecules. Copper phthalocyanine and magnesium porphine molecules adsorbed on a thin oxide film grown on the NiAl(110) surface were probed. The single-molecule junctions contained two tunneling barriers, vacuum gap, and oxide film. Differential conductance spectroscopy shows that electron transport occurs via vibronic states of the molecules. The intensity of spectral peaks correspondi...

Nazin, G. V.; Wu, S. W.; Ho, W.

2005-01-01

72

Comparison of scanning tunneling microscope-light emission and photoluminescence from porphyrin films using ultra-high vacuum scanning tunneling microscopy  

Science.gov (United States)

In order to study the interaction between molecules and photon fields, including plasmonic and external laser fields, we have carried out in situ measurements of photoluminescence (PL) from porphyrin molecules on Au substrates with and without a scanning tunneling microscope (STM) tip. Measurements were performed in a ultra-high vacuum scanning tunneling microscope chamber during irradiation by a He-Cd laser with incident power varying in the 10-3 to 10-7 W range. At an incident power of around 10-7 W, the spectra depend strongly on the presence of STM tip, which is associated with STM light emission from molecules. We estimated the ratio of quantum efficiency of scanning tunneling microscope-induced light emission (STML) from molecules to PL on the basis of the STML/PL intensity ratio observed experimentally at a laser power of 7.5 × 10-8 W, with the use of a 40 ?m laser beam diameter and an effective area of 2 nm for STML. The estimated quantum efficiency for an electron in STML is roughly 1010 times larger than that for one photon of PL. This anomalous enhancement will be discussed on the basis of plasmon-enhanced light emission from molecules in a STM nano-cavity.

Nishitani, Ryusuke; Liu, Hongwen; Iwasaki, Hiroshi

2012-01-01

73

Analysis of scanning tunneling optical spectroscopy for narrow gap semiconductors  

Science.gov (United States)

Narrow gap semiconductors (such as: Hg_1-xCd_xTe, Hg_1-xZn_xTe, and Hg_1-xZn_xSe) have been of interest for many years because of their use as infrared detectors. Due to gravity induced convective flows, these alloys are inherently difficult to grow homogeneously in bulk and therefore a microgravity growth environment seems promising. To evaluate the quality of these crystals it is necessary to characterize them, and an important aspect of this is the study of local stoichiometry x(r). Scanning tunneling optical spectroscopy involves measuring the spectral response of the photoexcited tunneling current using the scanning tunneling microscope and allows x(r) to be determined from the photon energy at which the tunneling current changes significantly (i.e. from the local bandgap Eg(x)). In this study we construct a simple model, using the Bardeen equation, and calculate the tunneling current versus photon energy for different tip-sample voltages and intensities of illumination.

Patterson, J. D.; Mantovani, J. G.

1997-03-01

74

Low-current Scanning Tunneling Microscope for Nanoscale Imaging  

Directory of Open Access Journals (Sweden)

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

R.K. Kale

2006-10-01

75

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

76

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

77

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.

78

Crystal-edge scanning tunnelling spectroscopy on aluminium-doped magnesium diboride  

Science.gov (United States)

We report on the first scanning tunnelling spectroscopy measurements on the edge of aluminium-doped magnesium diboride (Mg1-xAlxB2,x = 0.085) single crystals. To target their edge (~30 µm thick) we have developed a low temperature STM facility featuring a home built compact STM head coupled to an inertially driven carriage. This allows linear submicronic positioning over millimetric distances. We demonstrate the capabilities of our system by showing reproducible tunnelling spectra obtained both parallel and perpendicular to the crystalline c axis. Tunnelling on the edge reveals the gap originating in the highly 2D ? band but in contrast with pure MgB2 does not show the signature of the ? gap.

Dubois, C.; Jenkins, N.; Manuel, A. A.; Zhigadlo, N. D.; Karpinski, J.; Fischer, Ø.

2006-08-01

79

Plasma etching of superconducting Niobium tips for scanning tunneling microscopy  

Science.gov (United States)

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

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

2014-07-01

80

Spin-polarized quantum confinement in nanostructures: Scanning tunneling microscopy  

Science.gov (United States)

Experimental investigations of spin-polarized electron confinement in nanostructures by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) are reviewed. To appreciate the experimental results on the electronic level, the physical basis of STM is elucidated with special emphasis on the correlation between differential conductance, as measured by STS, and the electron density of states, which is accessible in ab initio theory. Experimental procedures which allow one to extract the electron dispersion relation from energy-dependent and spatially resolved STM and STS studies of electron confinement are reviewed. The role of spin polarization in electron confinement is highlighted by both experimental and theoretical insights, which indicate variation of the spin polarization in sign and magnitude on the nanometer scale. This review provides compelling evidence for the necessity to include spatial-dependent spin-resolved electronic properties for an in-depth understanding and quantitative assessment of electron confinement in magnetic nanostructures and interaction between magnetic adatoms.

Oka, Hirofumi; Brovko, Oleg O.; Corbetta, Marco; Stepanyuk, Valeri S.; Sander, Dirk; Kirschner, Jürgen

2014-10-01

 
 
 
 
81

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

International Nuclear Information System (INIS)

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

82

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

83

Many-Impurity Effects in Fourier Transform Scanning Tunneling Spectroscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Fourier transform scanning tunneling spectroscopy (FTSTS) is a useful technique for extracting details of the momentum-resolved electronic band structure from inhomogeneities in the local density of states due to disorder-related quasiparticle scattering. To a large extent, current understanding of FTSTS is based on models of Friedel oscillations near isolated impurities. Here, a framework for understanding many-impurity effects is developed based on a systematic treatment o...

Kodra, O.; Atkinson, W. A.

2005-01-01

84

Sub-Kelvin scanning tunneling microscopy on magnetic molecules  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Zhang, Lei

2012-01-01

85

Distinction of Nuclear Spin States with the Scanning Tunneling Microscope  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Natterer, Fabian Donat; Patthey, Franc?ois; Brune, Harald

2013-01-01

86

Scanning tunneling spectroscopy with superconducting tips of Al  

International Nuclear Information System (INIS)

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

87

Scanning tunneling microscopy of an ionic crystal: ferritin core.  

Science.gov (United States)

Ferritin molecules were imaged directly in air by scanning tunneling microscopy (STM). The lateral dimensions were close to the values determined by electron microscopy, and the vertical dimension was much reduced. Several clusters of partially naked ferritin cores displayed a hexagonal structure of lattice constant 4.9 +/- 0.5 A. It is thus shown that the STM can be used to image thin ionic crystals at high resolution. PMID:1440982

Yang, J; Takeyasu, K; Somlyo, A P; Shao, Z

1992-09-01

88

Technological applications of scanning tunneling microscopy at atmospheric pressure  

International Nuclear Information System (INIS)

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

89

Spectroscopic scanning tunneling microscopy insights into Fe-based superconductors  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In the first three years since the discovery of Fe-based high Tc superconductors, scanning tunneling microscopy (STM) and spectroscopy have shed light on three important questions. First, STM has demonstrated the complexity of the pairing symmetry in Fe-based materials. Phase-sensitive quasiparticle interference (QPI) imaging and low temperature spectroscopy have shown that the pairing order parameter varies from nodal to nodeless s\\pm within a single family, FeTe1-xSex. Sec...

Hoffman, Jennifer E.

2012-01-01

90

Nonmonotonic inelastic tunneling spectra due to surface spin excitations in ferromagnetic junctions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The paper addresses inelastic spin-flip tunneling accompanied by surface spin excitations (magnons) in ferromagnetic junctions. The inelastic tunneling current is proportional to the magnon density of states which is energy-independent for the surface waves and, for this reason, cannot account for the bias-voltage dependence of the observed inelastic tunneling spectra. This paper shows that the bias-voltage dependence of the tunneling spectra can arise from the tunneling mat...

Tkachov, G.

2004-01-01

91

A scanning tunneling microscope for a dilution refrigerator.  

Science.gov (United States)

We present the main features of a home-built scanning tunneling microscope that has been attached to the mixing chamber of a dilution refrigerator. It allows scanning tunneling microscopy and spectroscopy measurements down to the base temperature of the cryostat, T approximately 30 mK, and in applied magnetic fields up to 13 T. The topography of both highly ordered pyrolytic graphite and the dichalcogenide superconductor NbSe(2) has been imaged with atomic resolution down to T approximately 50 mK as determined from a resistance thermometer adjacent to the sample. As a test for a successful operation in magnetic fields, the flux-line lattice of superconducting NbSe(2) in low magnetic fields has been studied. The lattice constant of the Abrikosov lattice shows the expected field dependence proportional to 1/square root of B and measurements in the scanning tunneling spectroscopy mode clearly show the superconductive density of states with Andreev bound states in the vortex core. PMID:20441363

Marz, M; Goll, G; Löhneysen, H v

2010-04-01

92

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

93

A study of surfaces using a scanning tunneling microscope (STM  

Directory of Open Access Journals (Sweden)

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

Alba Graciela Ávila Bernal

2010-05-01

94

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

95

Theory and feasibility tests for a seismic scanning tunnelling macroscope  

Science.gov (United States)

We propose a seismic scanning tunnelling macroscope (SSTM) that can detect subwavelength scatterers in the near-field of either the source or the receivers. Analytic formulas for the time reverse mirror (TRM) profile associated with a single scatterer model show that the spatial resolution limit to be, unlike the Abbe limit of ?/2, independent of wavelength and linearly proportional to the source-scatterer separation as long as the scatterer is in the near-field region. This means that, as the scatterer approaches the source, imaging of the scatterer with super-resolution can be achieved. Acoustic and elastic simulations support this concept, and a seismic experiment in an Arizona tunnel shows a TRM profile with super-resolution adjacent to the fault location. The SSTM is analogous to the optical scanning tunnelling microscopes having subwavelength resolution. Scaled to seismic frequencies, it is theoretically possible to extract 100 Hz information from 20 Hz data by the imaging of near-field seismic energy.

Schuster, Gerard T.; Hanafy, Sherif; Huang, Yunsong

2012-09-01

96

Tomography of molecular nanographene double layers using scanning tunneling microscopy  

Science.gov (United States)

Double layers of a nanographene with defined molecular structure have been self-assembled at the interface between a molecular solution and the basal plane of graphite. Bias-dependent scanning tunnel microscopy allowed nondestructive imaging of the first or the second or both layers. While the first molecular layer can be well recognized at low negative or high positive sample biases, it is the other way around—at high negative or low positive sample biases—for the second molecular layer. This is attributed to the dependence of the resonant tunneling conditions for the molecules in the first and second layers on the position of the molecules within the tip-substrate gap. The effect may be used for a nanotomography of molecular multilayers.

Seifert, C.; Skuridina, D.; Dou, X.; Müllen, K.; Severin, N.; Rabe, J. P.

2009-12-01

97

Apparent Barrier Height in Scanning Tunneling Microscopy Revisited  

DEFF Research Database (Denmark)

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

Brandbyge, Mads; SØrensen, Mads Reinholdt

1996-01-01

98

Versatile scanning tunneling microscopy with 120ps time resolution  

CERN Document Server

We describe a fully ultra-high vacuum compatible scanning tunneling microscope (STM) optimized for radio-frequency signals. It includes in-situ exchangeable tips adapted to high frequency cabling and a standard sample holder, which offer access to the whole range of samples typically investigated by STM. We demonstrate a time resolution of 120 ps using the nonlinear I(V)-characteristic of the surface of highly oriented pyrolithic graphite. We provide atomically resolved images in pulse mode related to a spatially varying nonlinearity of the local density of states of the sample, thus, demonstrating the possible spatial resolution of the instrument in pulse mode. Analysis of the noise reveals that changes in the tunneling junction of 50 pA are dynamically detectable at 120 ps time resolution.

Saunus, Christian; Pratzer, Marco; Morgenstern, Markus; 10.1063/1.4790180

2013-01-01

99

Challenges in cross-sectional scanning tunneling microscopy on semiconductors  

International Nuclear Information System (INIS)

Cross sectional scanning tunneling microscopy (X-STM) has now become a well established method for the investigation of the structural and electronic properties of semiconductor nano-structures down to the scale of individual impurity atoms. Nevertheless, some aspects still remain challenging, for example in the sample preparation by cleavage as well as in the quantitative interpretation of the results. We present a brief overview of the techniques and geometries employed to cleave different semiconductors such as the lll-V materials, mainly GaAs, and the elementary semiconductors Si and Ge. Furthermore, we discuss the inevitable impact of the surface on the properties of the addressed impurities. This is mainly an issue when the surface reconstruction creates electronic surface states in the band gap. But also the unreconstructed GaAs(110) surface significantly modifies the symmetry of acceptor wave functions and the binding energy of donors and acceptors in the first few atomic layers. The impact of the tip will be addressed as a third quite important challenge, which is frequently neglected in the analysis of X-STM data. On surfaces with an unpinned Fermi level, the presence of the STM tip and the voltage applied to the tunneling contact significantly modifies the spectral positions of the observed electronic states and bands. Furthermore, different band bending situations open up qualitatively different tunneling paths to address individual electronic states in the sample. Detailed knowledge of the tunneling mechanism and of the tip properties, mainly apex radius and work function, is required in order to correctly extract the energetic levels from the tunneling spectroscopy data

100

Tunneling spectra of strongly coupled superconductors: Role of dimensionality  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We investigate numerically the signatures of collective modes in the tunneling spectra of superconductors. The larger strength of the signatures observed in the high-Tc superconductors, as compared to classical low-Tc materials, is explained by the low dimensionality of these layered compounds. We also show that the strong-coupling structures are dips (zeros in the d2I/dV2 spectrum) in d-wave superconductors, rather than the steps (peaks in d2I/dV2) observed in classical s-w...

Berthod, Christophe

2010-01-01

 
 
 
 
101

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

102

Observation of Liquid Crystals on Graphite by Scanning Tunneling Microscopy  

Science.gov (United States)

Molecules of liquid crystals adsorbed on graphite were observed by scanning tunneling microscopy (STM). Liquid crystals of both smectic and nematic phases provided periodic STM images of 3-nm-spacing lines, seemingly composed of molecules with their axes vertical to the line. Detailed investigation of the images revealed that several different patterns existed in smectic liquid crystal. On the other hand, nematic liquid crystal exhibited one reproducible pattern. Monolayer, multilayer, and dimer-based molecular arrangements are discussed. Models for the molecular arrangement of the nematic liquid crystal are proposed.

Shigeno, Masatsugu; Mizutani, Wataru; Suginoya, Mitsuru; Ohmi, Manabu; Kajimura, Koji; Ono, Masatoshi

1990-01-01

103

Scanning Tunneling Microscopy analysis of space-exposed polymer films  

Science.gov (United States)

The characterization of the surface of selected space-exposed polymer films by Scanning Tunneling Microscopy (STM) is reported. Principles of STM, an emerging new technique for materials analysis, are reviewed. The analysis of several films which received up to 5.8 years of low Earth orbital (LEO) exposure onboard the NASA Long Duration Exposure Facility (LDEF) is discussed. Specimens included FEP Teflon thermal blanket material, Kapton film, and several experimental polymer films. Ultraviolet and atomic oxygen-induced crazing and erosion are described. The intent of this paper is to demonstrate how STM is enhancing the understanding of LEO space environmental effects on polymer films.

Kalil, Carol R.; Young, Philip R.

1993-01-01

104

Fourier Transformed Scanning Tunneling Peaks in the $d$-density wave phase  

CERN Document Server

In this brief note we repeat an earlier calculation of the Fourier transformed scanning tunneling spectra of the $d$-density wave (DDW) phase using a different band structure, which is more realistic and consistent with the angle resolved photoemission spectroscopy (ARPES) data. We note that four peaks, which used to be located at $(\\pm \\pi/4,0)$ and $(0, \\pm \\pi/4)$, are still present, but at positive energies their wavevectors shift to the neighborhood of $(\\pm 2 \\pi/5,0)$, $(0, \\pm 2\\pi/5)$ and slowly disperse with energy. The implications for the sensitivity with respect to the band structure are discussed.

Bena, C; Hu, J; Nayak, C; Bena, Cristina; Chakravarty, Sudip; Hu, Jiangping; Nayak, Chetan

2004-01-01

105

Selective surface modifications with a scanning tunneling microscope  

Science.gov (United States)

A combination scanning tunneling microscope (STM) and scanning electron microscope has been used to selectively pattern and image Si(111) and Si(001) surfaces in a SEM chamber. Both positive and negative STM tip polarities produce marks on the surface with linewidths as small as 20 nm. We have transferred these patterns to the silicon substrate via selective wet chemical etching. We demonstrate a well-defined voltage threshold for patterning at negative tip bias. The modifications are consistent with a model based on hydrogen depassivation and electric field mediated deposition. The physical mechanism for positive tip bias patterning is shown to be different than that for negative bias. At positive bias, the patterning is consistent with selective surface contamination.

Konsek, S. L.; Coope, R. J. N.; Pearsall, T. P.; Tiedje, T.

1997-04-01

106

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.

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

2011-04-01

107

Measurement of turbulence spectra using scanning pulsed wind lidars  

DEFF Research Database (Denmark)

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

Sathe, Ameya; Mann, Jakob

2012-01-01

108

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.

109

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

110

Inelastic electron tunneling spectroscopy with a dilution refrigerator based scanning tunneling microscope  

International Nuclear Information System (INIS)

This paper presents the design and operations of a compact cryogenic scanning tunneling microscope system combined with a dilution refrigerator. We obtained a minimum temperature of 260 mK at the sample position. Taking advantage of low-temperature measurement for the spectroscopy, inelastic electron tunneling spectroscopy (IETS) at 4.4 K was demonstrated for the octanethiol molecules in a self-assembled monolayer. The spectrum showed many vibrational features as in the case of a high-resolution electron energy loss spectroscopy. We discuss the resolution of the IET signals focusing on its changes with the modulation voltage and the sample temperature. IETS at 260 mK is also presented with similar quality as in the case of 4.4 K, indicating that the vibration-dumping methods for the operation of the dilution refrigerator described in this paper are adequate

111

Measurement of Tunneling Current of Self-Assembled Viologen Derivative Molecules Using Scanning Tunneling Microscopy  

Science.gov (United States)

The electrical properties of viologen derivatives with various lengths were studied using self-assembly and ultrahigh-vacuum scanning tunneling microscopy (UHV-STM). In addition, in this study, we produced the vertical junction structure of an STM tip/molecule/Au(111) substrate using an STM tip. We used Au(111) as the base substrate. Also, the current-voltage (I-V) and differential conductance (dI/dV--V) characteristics were measured while the electrical properties of the self-assembled viologen derivatives were scanned by scanning tunneling spectroscopy (STS). We investigated electron movement, which is caused by height variation, because we can observe height variation between the barrier height of organic materials and the STM tip from the energy gap (Eg) of organic materials. The effective barrier heights of viologen derivative N-methyl-N'-(8-mercaptooctyl)-4,4'-bipyridinium (VC8SH), N-methyl-N'-(10-mercaptodecyl)-4,4'-bipyridinium (VC10SH), N-methyl-N'-di(8-mercaptooctyl)-4,4'-bipyridinium (HSC8VC8SH), and N-methyl-N'-di(10-mercaptodecyl)-4,4'-bipyridinium (HSC10VC10SH) self-assembled monolayers (SAMs) were calculated from the decay constant (?) to be 0.81, 0.46, 0.28, and 0.26 Å-1, respectively.

Lee, Nam-Suk; Shin, Hoon-Kyu; Qian, Dong-Jin; Kwon, Young-Soo

2007-04-01

112

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

Energy Technology Data Exchange (ETDEWEB)

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

McCarty, G.S.; Love, J.C.; Kushmerick, J.G.; Charles, L.F.; Keating, C.D.; Toleno, B.J.; Lyn, M.E.; Castleman, A.W.; Natan, M.J.; Weiss, P.S. [The Pennsylvania State University, Department of Chemistry (United States)], E-mail: stm@psu.edu

1999-12-15

113

Imaging of single uncoated DNA molecules by scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

Scanning tunneling microscope images of DNA molecules adsorbed onto highly oriented pyrolytic graphite have been obtained. Three methods of deposition and sample preparation have been utilized. In the first method, a highly concentrated solution of DNA is sonicated, and a drop is deposited on freshly cleaved graphite. Under these conditions, the molecules tend to align in a parallel fashion, forming liquid-crystalline phases. In the second method, a solution of DNA is deposited directly on the graphite surface without sonication. In this case, ammonium acetate, a volatile salt, is used to decrease the amount of the residual salt crystals left after drying. In the third method, a solution containing lysed phage particles and DNA is adsorbed onto a graphite surface. The molecules are seen either isolated or in small bundles. The values of height, periodicity, and thickness observed and the handedness of the molecules are consistent with those expected for DNA. In all cases, the molecules were identified by their characteristic periodic structure and because, at higher magnification, no graphite-like structure was detectable on the surface of the molecules. Often the DNA molecules appear to adsorb in areas of the graphite that have many steps and defects. A mechanism that explains the magnitude of the tunneling currents measured in DNA is proposed. This mechanism, in turn, suggests a general method by which large insulating molecules can be rendered conductive.

Keller, D.; Bustamante, C.; Keller, R.W. (Univ. of New Mexico, Albuquerque (USA))

1989-07-01

114

Atomic-Scale Devices in Silicon by Scanning Tunneling Microscopy  

Science.gov (United States)

The ability to control matter at the atomic scale and build devices with atomic precision is one of the core challenges of nanotechnology. In this chapter, we outline a complete fabrication strategy for building atomic-scale devices in silicon with atomic precision in all three-dimensions. Using scanning tunneling microscopy (STM)-based lithography we have imaged and placed phosphorus dopant atoms in precise locations on a silicon surface before encapsulating them with silicon using low temperature molecular beam epitaxy to activate the dopants. Etched registration markers allow us to locate and align external electrical contacts to the buried STM-patterned dopant atoms so that we can perform electron transport measurements outside the microscope at cryogenic temperatures. Using this unique strategy we discuss the realization of conducting nanoscale wires, tunnel junctions and all epitaxial single electron transistors. Finally we provide an outlook to achieving truly single atom device architectures toward our ultimate goal of realizing a silicon-based quantum computer.

Miwa, J. A.; Simmons, M. Y.

115

Images of 16S ribosomal RNA by scanning tunnelling microscopy.  

Science.gov (United States)

We report the use of scanning tunnelling microscopy (STM) to study surface topographies of complex nucleic acid structures. From low-resolution STM images of uncoated 16S ribosomal RNA, we demonstrate the possibility of determining several objective parameters (molecular mass and radius of gyration) in order to characterize and identify the molecules observed. These parameters were compared with values obtained by other physical methods and the radius of gyration was found to be the most reliable. At high resolution, it was possible to measure the main dimensions of selected V-form particles more precisely than with electron microscopy. Images of the more compact form have been also obtained that show different domains in the macromolecular structure. PMID:1960712

Flamion, P J; Cachia, C; Schreiber, J P; David, T; Lesniewska, E; Goudonnet, J P

1991-09-01

116

Control systems for scanning tunneling microscopes with tube scanners  

Science.gov (United States)

The design of the control system for a scanning tunneling microscope is described. The control system was optimized for a tube scanner instrument and for constant-current-mode operation. The optimization process included measurement of the transient and frequency responses of the instrument, design of the appropriate control electronics, and development of software consistent with the characteristics of the instrument and electronics. The limiting factor for tube scanner performance was found to be the transient settling time rather than the lowest mechanical resonant frequency of the tube. The settling time for the mechanical resonances of the tube scanner was reduced from 100 to 1 ms by potting the device with silicone rubber. After the potting procedure, the sensitivity of the tube scanner was essentially unchanged.

DiLella, D. P.; Wandass, J. H.; Colton, R. J.; Marrian, C. R. K.

1989-06-01

117

Imaging and Manipulation of Single Molecules by Scanning Tunneling Microscopy  

Science.gov (United States)

The scanning tunneling microscope (STM) is not only used to image single atoms and molecules on a surface, but also to manipulate them in a controlled way. This work aims to summarize the pioneering and most representative examples in this active research field. After an introduction into the basics of the method, the topographic and electronic origin of the images and the resulting "chemical contrast" are discussed. In addition to imaging, molecular orbitals and the chemical nature of adsorbates can be identified by spectroscopy, even if their images are equivalent. Different types of molecular manipulation are presented, including examples for all three possible driving forces: Interatomic forces without a bias voltage, electron-induced manipulation and electric-field induced processes. The lateral manipulation of molecules, including the hopping and rolling of a molecular wheel, and vertical pulling experiments are discussed. The latter ones lead to particular configurations that allow conductance measurements of single molecules between two electrodes.

Grill, Leonhard

2013-12-01

118

Construction of a versatile ultralow temperature scanning tunneling microscope.  

Science.gov (United States)

We constructed a dilution-refrigerator (DR)-based ultralow temperature scanning tunneling microscope (ULT-STM) which works at temperatures down to 30 mK, in magnetic fields up to 6 T and in ultrahigh vacuum (UHV). Besides these extreme operation conditions, this STM has several unique features not available in other DR-based ULT-STMs. One can load STM tips as well as samples with clean surfaces prepared in an UHV environment to a STM head keeping low temperature and UHV conditions. After then, the system can be cooled back to near the base temperature within 3 h. Due to these capabilities, it has a variety of applications not only for cleavable materials but also for almost all conducting materials. The present ULT-STM has also an exceptionally high stability in the presence of magnetic field and even during field sweep. We describe details of its design, performance, and applications for low temperature physics. PMID:17672762

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

2007-07-01

119

Scanning tunneling microscopy and tunneling luminescence of the surface of GaN films grown by vapor phase epitaxy  

CERN Document Server

We report scanning tunneling microscopy (STM) images of surfaces of GaN films and the observation of luminescence from those films induced by highly spatially localized injection of electrons or holes using STM. This combination of scanning tunneling luminescence (STL) with STM for GaN surfaces and the ability to observe both morphology and luminescence in GaN is the first step to investigate possible correlations between surface morphology and optical properties.

Garni, B; Perkins, N; Liu, J; Kuech, T F; Lagally, M G; Ma, Jian; Liu, Jutong

1995-01-01

120

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

Science.gov (United States)

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

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

2007-03-01

 
 
 
 
121

Electron-beam-assisted scanning tunneling microscopy of insulating surfaces  

Science.gov (United States)

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

Bullock, Eugene Thomas

2000-07-01

122

Direct control and characterization of a Schottky barrier by scanning tunneling microscopy  

Science.gov (United States)

Scanning tunneling microscopy (STM) methods are used to directly control the barrier height of a metal tunnel tip-semiconductor tunnel junction. Barrier behavior is measured by tunnel current-voltage spectroscopy and compared to theory. A unique surface preparation method is used to prepare a low surface state density Si surface. Control of band bending with this method enables STM investigation of semiconductor subsurface properties.

Bell, L. D.; Kaiser, W. J.; Hecht, M. H.; Grunthaner, F. J.

1988-01-01

123

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. A...

Mu?nnich, Gerhard; Donarini, Andrea; Wenderoth, Martin; Repp, Jascha

2013-01-01

124

Complex magnetic order on the atomic scale revealed by spin-polarized scanning tunneling microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Abstract A fundamental understanding of magnetic phenomena requires the determination of spin structures down to the atomic scale. The direct visualization of atomic-scale spin structures has been accomplished by combining the atomic resolution capability of Scanning Tunnelling Microscopy (STM) with spin sensitivity, based on vacuum tunnelling of spin-polarized electrons. The resulting technique, Spin-Polarized Scanning Tunnelling Microscopy (SP-STM), nowadays provides unprecedente...

2008-01-01

125

Combined scanning force microscopy and scanning tunneling spectroscopy of an electronic nano-circuit at very low temperature  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We demonstrate the combination of scanning force microscopy and scanning tunneling spectroscopy in a local probe microscope operating at very low temperature (60 mK). This local probe uses a quartz tuning fork ensuring high tunnel junction stability. We performed the spatially-resolved spectroscopic study of a superconducting nano-circuit patterned on an insulating substrate. Significant deviations from the BCS prediction are observed.

Senzier, Julien; Luo, Pengshun S.; Courtois, Herv

2006-01-01

126

Long-range Scanning Tunneling Microscope for the study of nanostructures on insulating substrates  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The Scanning Tunneling Microscope is a powerful tool for studying the electronic properties at the atomic level, however it's relatively small scanning range and the fact that it can only operate on conducting samples prevents its application to study heterogeneous samples consisting on 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 techniq...

Molina-mendoza, Aday; Rodrigo, Jose? Gabriel; Island, Joshua; Burzuri, Enrique; Rubio-bollinger, Gabino; Zant, Herre S. J.; Agrai?t, Nicola?s

2013-01-01

127

Compact Scanning Tunneling Microscope for Spin Polarization Measurements  

Science.gov (United States)

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

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

2012-02-01

128

Scanning tunneling spectroscopy studies on heavy fermion superconductors  

Energy Technology Data Exchange (ETDEWEB)

Scanning tunneling spectroscopy (STS) is a powerful tool for mapping the local electronic density of states of conducting sample surfaces. Of particular interest are experiments with superconducting (SC) materials, as information about the SC energy gap can directly be obtained. The application of STS to heavy fermion (HF) superconductors is expected to make a valuable contribution to the understanding of this class of materials. Fundamental properties such as the symmetry of the SC order parameter or, possibly, excitations due to the SC pairing interaction might be revealed. This work reports on STM measurements carried out at low temperatures (320 mK) and under UHV conditions. A magnetic field of up to 12 T could be applied to confirm superconductivity of clean samples. For the materials investigated here, spectroscopic features in the order of a few hundred {mu}eV are expected, calling for an excellent energy resolution during STS. The sufficiently high resolution of our STM has been verified by resolving the sub-meV SC energy gap of aluminum. Clean sample surfaces were prepared by in situ cleaving of the single crystals. Preliminary STS measurements were conducted on single crystalline samples of the HF superconductors CeCoIn{sub 5} and CeCu{sub 2}Si{sub 2}.

Ernst, Stefan; Wirth, Steffen; Jeevan, Hirale; Geibel, Christoph; Steglich, Frank [Max Planck Institute for Chemical Physics of Solids, Dresden (Germany); Fisk, Zachary [Department of Physics and Astronomy, UC Irvine, CA (United States)

2008-07-01

129

Scanning tunneling spectroscopy studies on heavy fermion superconductors  

International Nuclear Information System (INIS)

Scanning tunneling spectroscopy (STS) is a powerful tool for mapping the local electronic density of states of conducting sample surfaces. Of particular interest are experiments with superconducting (SC) materials, as information about the SC energy gap can directly be obtained. The application of STS to heavy fermion (HF) superconductors is expected to make a valuable contribution to the understanding of this class of materials. Fundamental properties such as the symmetry of the SC order parameter or, possibly, excitations due to the SC pairing interaction might be revealed. This work reports on STM measurements carried out at low temperatures (320 mK) and under UHV conditions. A magnetic field of up to 12 T could be applied to confirm superconductivity of clean samples. For the materials investigated here, spectroscopic features in the order of a few hundred ?eV are expected, calling for an excellent energy resolution during STS. The sufficiently high resolution of our STM has been verified by resolving the sub-meV SC energy gap of aluminum. Clean sample surfaces were prepared by in situ cleaving of the single crystals. Preliminary STS measurements were conducted on single crystalline samples of the HF superconductors CeCoIn5 and CeCu2Si2

130

Simplified Besocke scanning tunneling microscope with linear approach geometry  

Science.gov (United States)

Besocke-style scanning tunneling microscopes are used in low and variable temperature applications because they are compact and the tip-sample spacing is insensitive to thermal drift. It is demonstrated that the economical Besocke design can be simplified even further if a linear approach geometry is used. In this geometry, the sample has only to be moved along two orthogonal axes and just 11 wires are required to control both tip-sample approach and image acquisition. This simplifies the control electronics, increases the reliability of the microscope and, if the microscope is operated in a cryostat, it weakens the thermal link between low and room temperature. Nevertheless, all of the advantages of the Besocke design are retained including thermal compensation of the tip-sample spacing. A self-aligning mechanism is also described that automatically locates the sample relative to the scanner before tip-sample approach. This feature is particularly useful because the microscope is designed for remote operation in a cryostat where there is restricted visual access. Graphite was used as a test surface and images are presented of ?-site corrugation and moiré supermeshes.

Ball, S. J.; Contant, G. E.; McLean, A. B.

2004-12-01

131

Atom manipulation with the scanning tunneling microscope: nanostructuring and femtochemistry  

Science.gov (United States)

We briefly survey our recent studies on the 'soft'lateral manipulation of atoms and small molecules with the scanning tunneling microscope (STM), whereby mainly the tip-surface forces are employed. Repulsive (pushing) as well as discontinuous (pulling) and continuous (sliding)attractive manipulation modes could be distinguished on Cu(211) for CO molecules and metal atoms, respectively. In the case of pulling of Cu atoms on Cu(111) even finer details could be discerned: the adparticle may show various movement patterns visiting different surface sites upon applying different tip forces. Lateral manipulation also allows modifications of the Cu(211) substrate itself in an atom-by-atom manner by releasing atoms from sixfold coordinated kink sites and even sevenfold coordinated regular step sites. Furthermore, investigations concerning controled vertical manipulation with emphasis on 'picking-up' single CO molecules are reported. The mechanism behind vertical transfer of CO molecules relates to ultrafast chemical processes. Vertical manipulation implies, besides extending the possibilities for the build-up of nanostructures, the important possibility of creating structurally and compositionally well-defined tips, which may eventually lead to chemical sensitivity with the STM.

Meyer, G.; Bartels, L.; Rieder, K.-H.

1999-01-01

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.

133

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

134

Many-Impurity Effects in Fourier Transform Scanning Tunneling Spectroscopy  

CERN Document Server

Fourier transform scanning tunneling spectroscopy (FTSTS) is a useful technique for extracting details of the momentum-resolved electronic band structure from inhomogeneities in the local density of states due to disorder-related quasiparticle scattering. To a large extent, current understanding of FTSTS is based on models of Friedel oscillations near isolated impurities. Here, a framework for understanding many-impurity effects is developed based on a systematic treatment of the variance Delta rho^2(q,omega) of the Fourier transformed local density of states rho(q,\\omega). One important consequence of this work is a demonstration that the poor signal-to-noise ratio inherent in rho(q,omega) due to randomness in impurity positions can be eliminated by configuration averaging Delta rho^2(q,omega). Furthermore, we develop a diagrammatic perturbation theory for Delta rho^2(q,omega) and show that an important bulk quantity, the mean-free-path, can be extracted from FTSTS experiments.

Kodra, O

2005-01-01

135

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

136

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

137

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

International Nuclear Information System (INIS)

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

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. PMID:24810264

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

2014-06-01

139

Scanning Tunneling Microscopy of Insulators and Biological Specimens Based on Lateral Conductivity of Ultrathin Water Films  

Science.gov (United States)

Scanning tunneling microscopy is based on the flow of an electrical current and thus cannot be used to directly image insulating material. It has been found, however, that a very thin film of water (about one monolayer) adsorbed to a surface exhibits a surprisingly high conductivity that is sufficient to allow scanning tunneling microscope imaging at currents below 1 picoampere. Hydrophilic insulators, such as glass and mica, can thus be imaged in humid air. The same is true for biological specimens deposited on such surfaces, as demonstrated by the scanning tunneling microscope imaging of plasmid DNA on mica.

Guckenberger, Reinhard; Heim, Manfred; Cevc, Gregor; Knapp, Helmut F.; Wiegrabe, Winfried; Hillebrand, Anton

1994-12-01

140

Field emission characteristics of the scanning tunneling microscope for nanolithography  

Energy Technology Data Exchange (ETDEWEB)

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

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

1996-07-01

 
 
 
 
141

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 almo 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

142

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

International Nuclear Information System (INIS)

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

143

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

144

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

145

Reversible hydrogenation and band gap opening of graphene and graphite surfaces probed by scanning tunneling spectroscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The effect of hydrogenation on the topography and the electronic properties of graphene and graphite surfaces are studied by scanning tunneling microscopy and spectroscopy. The surfaces are chemically modified using Ar/H2 plasma. Analyzing thousands of scanning tunneling spectroscopy measurements we determine that the hydrogen chemisorption on the surface of graphite/graphene opens on average an energy band gap of 0.4 eV around the Fermi level. We find that although the plas...

Castellanos-gomez, Andres; Wojtaszek, Magdalena; Arramel; Tombros, Nikolaos; Wees, Bart J.

2012-01-01

146

Networks of ABA and ABC stacked graphene on mica observed by scanning tunneling microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Graphene flakes are prepared on freshly cleaved mica by exfoliation and studied by scanning tunneling microscopy in ultra high vacuum. On few-layer graphene, a triangular network of partial dislocations separating ABC stacked and ABA stacked graphene was found similar to the networks occasionally visible on freshly cleaved HOPG. We found differences in the electronic structure of ABC and ABA stacked areas by scanning tunneling spectroscopy, i.e., a pronounced peak at 0.25 eV...

Hattendorf, Silke; Georgi, Alexander; Liebmann, Marcus; Morgenstern, Markus

2012-01-01

147

Atom-Resolved Luminescence of Si(111)-7×7 Induced by Scanning Tunneling Microscopy  

Science.gov (United States)

Photon emission induced by scanning tunneling microscopy (STM), i.e., scanning tunneling luminescence (STL), is widely believed to reveal the inherent optical properties of nanostructures with high spatial resolution comparable to that of STM. We investigated STL of Si(111)-7×7 using silver STM tips. The photon emission via inherent electronic transitions of Si(111)-7×7 is strongly enhanced by surface plasmon localized in the tunnel junction, allowing the surface atomic configurations to be clearly visualized by luminescence mapping. The STL maps suggest that the local optical properties of non-equivalent adatoms are different.

Imada, Hiroshi; Ohta, Masashi; Yamamoto, Naoki

2010-04-01

148

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

149

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

Energy Technology Data Exchange (ETDEWEB)

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.

Molina-Mendoza, Aday J., E-mail: aday.molina@uam.es [Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Rodrigo, José G.; Rubio-Bollinger, Gabino [Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Condensed Matter Physics Center (IFIMAC) and Instituto Universitario de Ciencia de Materiales “Nicolás Cabrera,” Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Island, Joshua; Burzuri, Enrique; Zant, Herre S. J. van der [Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (Netherlands); Agraït, Nicolás [Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Condensed Matter Physics Center (IFIMAC) and Instituto Universitario de Ciencia de Materiales “Nicolás Cabrera,” Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Instituto Madrileño de Estudios Avanzados en Nanociencia IMDEA-Nanociencia, E-28049 Madrid (Spain)

2014-02-15

150

Long-range Scanning Tunneling Microscope for the study of nanostructures on insulating substrates  

CERN Document Server

The Scanning Tunneling Microscope is a powerful tool for studying the electronic properties at the atomic level, however it's relatively small scanning range and the fact that it can only operate on conducting samples prevents its application to study heterogeneous samples consisting on 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.

Molina-Mendoza, Aday; Rubio-Bollinger, Gabino; Agraït, Nicolás

2013-01-01

151

Virtual Scanning Tunneling Microscopy: A local spectroscopic probe of high mobility 2D electron systems  

Science.gov (United States)

Many scanning probe techniques have been utilized in recent years to measure local properties of high mobility two-dimensional (2D) electron systems in GaAs. However, most techniques lack the ability to tunnel into the buried 2D system and measure local spectroscopic information. We report scanning gate measurements on a bilayer GaAs/AlGaAs heterostructure that allows for a local modulation of tunneling between two 2D electron layers. We call this technique Virtual Scanning Tunneling Microscopy (VSTM) [1] as the influence of the scanning gate is analogous to an STM tip, except at a GaAs/AlGaAs interface instead of a surface. We present measurements that highlight the spatial resolution and spectroscopic capabilities of the technique. [1] A. Sciambi, M. Pelliccione et al., Appl. Phys. Lett. 97, 132103 (2010).

Pelliccione, Matthew; Bartel, John; Sciambi, Adam; Pfeiffer, Loren; West, Ken; Goldhaber-Gordon, David

2013-03-01

152

Fabrication and characterization of artificial nanostructures with a scanning tunneling microscope  

Science.gov (United States)

A homemade variable temperature scanning tunneling microscope (STM) was used to fabricate nanostructures on metal surfaces and to probe their electronic, magnetic, and vibrational properties via imaging and local spectroscopy. The main goal of the research presented in this dissertation was to gain insights into the physics and chemistry at the nanoscale for possible future application to molecular electronics and spintronics. The use of a STM as an atomic-scale reactor and analyzer was demonstrated by building single molecules from the bottom up and characterizing the reactants and products. Individual CO molecules adsorbed on a Ag(110) surface was vertically transferred onto the apex of the STM tip and subsequently placed down on top of the Fe and Cu adatoms to form single Fe and Cu carbonyls. Inelastic electron tunneling spectroscopy with the STM (STM-IETS) enabled vibrational analyses of the reactants and products as well as structural characterization. Spatial mapping of the CO vibrational intensities revealed a marked difference between the bonding geometries of the Fe and Cu carbonyls. Bonding geometries and vibrational properties of various metal carbonyls (CrCO, MnCO, FeCO, PdCO, CuCO, AgCO, and AuCO) on a NiAl(110) surface were compared by STM-IETS. Electronic states of magnetic atoms (Mn, Fe, and Co) on a NiAl(110) surface were probed by scanning tunneling spectroscopy. Resonance peaks characteristic of each magnetic species were observed in the unoccupied density of states. Comparison of the measured dI/dV spectra with calculations by density functional theory revealed spin splitting in the unoccupied resonance states with s and p characters. Magnitude of the resonance splitting for the adatoms scaled with the calculated values of magnetic moments. Magnetic dimers, trimers, and chains were assembled from individual magnetic atoms. Controlled atom manipulation with the STM enables 'atom-by-atom' construction of nanostructures where neighboring atoms can be systematically substituted with elements of different magnetic properties. The spin-split resonance structures of the fabricated nanostructures exhibited signatures of their internal magnetic coupling. This novel approach probes the evolution of electronic and magnetic properties of nanostructures as functions of size and constituents.

Lee, Hyojune

153

Scanning Tunneling Spectroscopy Study of TiO2(110) Surface  

Science.gov (United States)

The electronic states of a (110) surface of a single crystal TiO2 sample were studied in real space with atomic resolution by scanning tunneling spectroscopy. We found that the inversion of the dominant tunneling current site occurs in the positive sample voltage region above 1.9 V@. According to the discrete-variational (DV)-X? calculations of the surface electronic states, atomic alignments observed in the scanning tunneling microscopy image at a higher tunneling bias voltage are of six-fold coordinated titanium ion rows while those at a lower voltage are of five-fold coordinated Ti rows. A broad peak was observed in the empty state region of a differential conductance spectrum, which is considered to originate from the intrinsic surface states of TiO2(110).

Sakai, Yoshiyuki; Ehara, Shaw

2000-06-01

154

Electron transfer processes in scanning tunneling spectroscopy through small supported particles  

Energy Technology Data Exchange (ETDEWEB)

Mechanism of the staircase like I-V curve observed recently in scanning tunneling spectroscopy (STS) of a metal fine particle supported on an oxide covered substrate is clarified based on theoretical simulations. It is discussed how the step structures are influenced by the coupling of the fine particle charge to the remaining degrees of freedom, such as induced charge in the surrounding medium. Relation between the characteristic features of single eletron tunneling (SET) and the STS of microclusters is discussed. (orig.).

Tsukada, M. (Tokyo Univ. (Japan). Dept. of Physics)

1991-01-01

155

Electron transfer processes in scanning tunneling spectroscopy through small supported particles  

International Nuclear Information System (INIS)

Mechanism of the staircase like I-V curve observed recently in scanning tunneling spectroscopy (STS) of a metal fine particle supported on an oxide covered substrate is clarified based on theoretical simulations. It is discussed how the step structures are influenced by the coupling of the fine particle charge to the remaining degrees of freedom, such as induced charge in the surrounding medium. Relation between the characteristic features of single eletron tunneling (SET) and the STS of microclusters is discussed. (orig.)

156

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

157

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

158

Compact design of a low temperature XY stage scanning tunneling microscope  

Science.gov (United States)

We describe the design and development of a compact low temperature XY stage scanning tunneling microscope dedicated to operation at low temperatures, in high magnetic fields, and in an ultrahigh vacuum environment. The system features a homemade compact scanning tunneling microscope (STM) head coupled to an inertially driven horizontal slider which allows a two-dimensional coarse positioning of the tip over 6×3mm2 with submicronic resolution. We also describe the geometry used to avoid coupling between the three-dimensional coarse and fine movements. To demonstrate the mechanical stability of the STM we display atomic resolution and large scale imaging. We illustrate the capabilities of our system by performing scanning tunneling spectroscopy on PbMo6S8 microcrystals.

Dubois, C.; Bisson, P. E.; Manuel, A. A.; Fischer, Ø.; Reymond, S.

2006-04-01

159

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

160

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

International Nuclear Information System (INIS)

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

 
 
 
 
161

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

Room-temperature and low-temperature (77 K) scanning tunneling spectroscopy (STS) and voltage-dependent scanning tunneling microscopy (STM) 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 Gamma-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...

Sauter, M.; Hoffmann, R.; Surgers, C.; Lohneysen, H. V.

2014-01-01

162

Networks of ABA and ABC stacked graphene on mica observed by scanning tunneling microscopy  

Science.gov (United States)

Graphene flakes are prepared on freshly cleaved mica by exfoliation and studied by scanning tunneling microscopy in ultra high vacuum. On few-layer graphene, a triangular network of partial dislocations separating ABC stacked and ABA stacked graphene was found similar to the networks occasionally visible on freshly cleaved HOPG. We found differences in the electronic structure of ABC and ABA stacked areas by scanning tunneling spectroscopy, i.e., a pronounced peak at 0.25 eV above the Fermi level exclusively in the ABA areas, which is shown to be responsible for the different apparent heights observed in STM images.

Hattendorf, S.; Georgi, A.; Liebmann, M.; Morgenstern, M.

2013-04-01

163

Scanning tunneling spectroscopy on Bi2SrCaCuO6+?  

International Nuclear Information System (INIS)

Scanning tunneling microscopy and scanning tunneling spectroscopy (STS) measurements were performed on Bi2SrCaCuO6 whose superconducting transition temperature Tc is about 80 K. The superconducting gap obtained by the STS measurements was found to be about 40 meV. This value is close to that of optimally doped Bi2Sr2CaCu2O8 which has similar Tc. The observed spatial inhomogeneity of the gap value was much smaller than that of Bi2Sr2CuO6.

164

Study of dynamic processes on semiconductor surfaces using time-resolved scanning tunneling microscopy  

International Nuclear Information System (INIS)

The time resolution of a conventional scanning tunneling microscope can be improved by many orders of magnitude by recording open feedback loop current-time traces. The enhanced time resolution comes, however, at the expense of the ability to obtain spatial information. In this paper, we first consider the Ge(111)-c(2 x 8) surface as an example of how surface dynamics can show up in conventional STM images. After a brief introduction to the time-resolved scanning tunneling microscopy technique, its capabilities will be demonstrated by addressing the dynamics of a dimer pair of a Pt modified Ge(001).

165

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

166

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

167

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

168

Tunneling spectra of break junctions involving Nb3Sn  

Science.gov (United States)

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

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

2014-10-01

169

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.

170

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

171

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

172

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

173

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.

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

2010-01-01

174

Scanning Tunneling Microscopy Study and Nanomanipulation of Graphene-Coated Water on Mica  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study interfacial water trapped between a sheet of graphene and a muscovite (mica) surface using Raman spectroscopy and ultra-high vacuum scanning tunneling microscopy (UHV-STM) at room temperature. We are able to image the graphene-water interface with atomic resolution, revealing a layered network of water trapped underneath the graphene. We identify water layer numbers with a carbon nanotube height reference. Under normal scanning conditions, the water structures remai...

He, Kevin T.; Wood, Joshua D.; Doidge, Gregory P.; Pop, Eric; Lyding, Joseph W.

2012-01-01

175

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

International Nuclear Information System (INIS)

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.

176

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)

177

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

International Nuclear Information System (INIS)

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

178

Partial sequencing of a single DNA molecule with a scanning tunnelling microscope.  

Science.gov (United States)

The scanning tunnelling microscope is capable of the real-space imaging and spectroscopy of molecules on an atomic scale. Numerous attempts have been made to use the scanning tunnelling microscope to sequence single DNA molecules, but difficulties in preparing samples of long-chain DNA molecules on surfaces, and problems in reproducing results have limited these experiments. Here, we report single-molecule DNA sequencing with a scanning tunnelling microscope by using an oblique pulse-injection method to deposit the molecules onto a copper surface. First, we show that guanine bases have a distinct electronic state that allows them to be distinguished from the other nucleic acid bases. Then, by comparing data on M13mp18, a single-stranded phage DNA, with a known base sequence, the 'electronic fingerprint' of guanine bases in the DNA molecule is identified. These results show that it is possible to sequence individual guanine bases in real long-chain DNA molecules with high-resolution scanning tunnelling microscope imaging and spectroscopy. PMID:19662015

Tanaka, Hiroyuki; Kawai, Tomoji

2009-08-01

179

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-09-30

180

Process dependent morphology of the Si/SiO2 interface measured with scanning tunneling microscopy  

Science.gov (United States)

A new experimental technique to determine Si/SiO2 interface morphology is described. Thermal oxides of silicon are chemically removed, and the resulting surface topography is measured with scanning tunneling microscopy. Interfaces prepared by oxidation of Si (100) and (111) surfaces, followed by postoxidation anneal (POA) at different temperatures, have been characterized. Correlations between interface structure, chemistry, and electrical characteristics are described.

Hecht, Michael H.; Bell, L. D.; Grunthaner, F. J.; Kaiser, W. J.

1988-01-01

 
 
 
 
181

Investigating Intermolecular Interactions via Scanning Tunneling Microscopy: An Experiment for the Physical Chemistry Laboratory  

Science.gov (United States)

A scanning tunneling microscope (STM) project designed as a module for the undergraduate physical chemistry laboratory is described. The effects of van der Waals interactions on the condensed-phase structure are examined by the analysis of the pattern of the monolayer structures.

Pullman, David; Peterson, Karen I.

2004-01-01

182

Electronic properties of graphene: a perspective from scanning tunneling microscopy and magnetotransport  

International Nuclear Information System (INIS)

This review covers recent experimental progress in probing the electronic properties of graphene and how they are influenced by various substrates, by the presence of a magnetic field and by the proximity to a superconductor. The focus is on results obtained using scanning tunneling microscopy, spectroscopy, transport and magnetotransport techniques. (review article)

183

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

184

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

185

Luminescence of Quantum Dots by Coupling with Nonradiative Surface Plasmon Modes in a Scanning Tunneling Microscope  

International Nuclear Information System (INIS)

The electronic coupling between quantum dots (QDs) and surface plasmons (SPs) is investigated by a luminescence spectroscopy based on scanning tunneling microscopy (STM). We show that tunneling luminescence from the dot is excited by coupling with the nonradiative plasmon mode oscillating at the metallic tunneling gap formed during the STM operation. This approach to the SP excitation reveals aspects of the SP-QD coupling not accessible to the more conventional optical excitation of SPs. In the STM, luminescence from the dot is observed when and only when the SP is in resonance with the fundamental transition of the dot. The tunneling luminescence spectrum also suggests that excited SP-QD hybrid states can participate in the excitation of QD luminescence. Not only the SP excitation regulates the QD luminescence but the presence of the dot at the tunneling gap imposes restrictions to the SP that can be excited in the STM, in which the SP cannot exceed the energy of the fundamental transition of the dot. The superior SP-QD coupling observed in the STM is due to the tunneling gap acting as a tunable plasmonic resonator in which the dot is fully immersed.

186

Nanoscale ferroelectric field-effect writing and reading using scanning tunnelling spectroscopy.  

Science.gov (United States)

Control of the density of mobile charge carriers using electric fields is widely used in a variety of metal-insulator-semiconductor structures and is the governing principle behind the operation of field-effect transistors. Ferroelectric materials possessing a switchable and non-volatile polarization field can be used as insulating layers, revealing new opportunities for device applications. Advances in material processing and in particular complex oxide thin-film growth mean that high-quality field-effect devices can be based on ferroelectric/metallic oxide heterostructures. In addition, advances in local probe techniques such as atomic force microscopy allow them to be used in the imaging and study of small ferroelectric domain structures in bulk crystals and thin films. Meanwhile, scanning tunnelling microscopy and spectroscopy have established themselves as powerful techniques for atomic manipulation and nanometre-resolution electron tunnelling spectroscopy. Here, a scanning tunnelling microscope is used to investigate the ferroelectric field effect in all-perovskite heterostructures. Scanning tunnelling spectroscopy allows us to probe the local electronic properties of the polarized channel of a ferroelectric field-effect device as a function of the field orientation. This technique can be used to read and write ferroelectric field-induced regions with a size as low as 20 nm. PMID:15834416

Kuffer, Olivier; Maggio-Aprile, Ivan; Fischer, Øystein

2005-05-01

187

Superconducting LiFeAs as seen by scanning tunneling microscopy/spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-07-01

188

Superconducting LiFeAs as seen by scanning tunneling microscopy/spectroscopy  

International Nuclear Information System (INIS)

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

189

Ultrasensitive immunoassay for prostate specific antigen using scanning tunneling microscopy-based electrical detection  

Science.gov (United States)

We characterized a vertically configured electrical detection system that used scanning tunneling microscopy (STM) to detect antigen-antibody binding. This technique could be used to easily construct a multiple measurement system in a protein chip. We utilized immunocomplexes comprised of our model protein, prostate specific antigen (PSA), corresponding antibody fragments, and gold nanoparticle-antibody conjugates. The electrical tunneling current between the STM tip and these complexes exhibited a peaklike pulse, the frequency of which depended on the surface density of the bound complexes. We could therefore quantitatively measure PSA concentrations as low as 10fg/mL using periodogram analysis of this peak frequency.

Choi, Jeong-Woo; Oh, Byung-Keun; Jang, Yong-Hark; Kang, Da-Yeon

2008-07-01

190

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

191

Scanning tunnelling miscroscopy/spectroscopy and X-ray absorption spectroscopy studies of Co adatoms and anoislands on highly oriented pyrolytic graphite  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this paper, the scanning tunneling microscopy, scanning tunneling spectroscopy and X-ray absorption spectroscopy of cobalt adatoms and nanoislands were studied on a highly oriented pyrolytic graphite. Local electronic structure were observed by STS.

Wong, P. K. J.; Leonardus, L.; Jong, M. P.; Siekman, M. H.; Zandvliet, H. J. W.; Wiel, W. G.

2010-01-01

192

Origin of fine structure in tunneling spectra of BiSrCaCuO films  

International Nuclear Information System (INIS)

The tunneling spectroscopy studies have been carried out on BSCCO textured films (2212 and 2223 phases) at T = 4.2K using the point junction technique with a silver or lead needle as an injector electrode. The tunneling spectra recorded in superconductive state have demonstrated the gap structures corresponding to S-I-S and S-I-N tunneling junctions. The energy gap peaks of the metaloxide correspond to the tunneling along ab plane in the CuO2 layer. The effect of the series resistance of the deteriorated surface layer which is responsible for the gap broadening in addition to that due to the finite lifetime of quasiparticles is discussed in connection with the determination of the energy gap. The tunneling spectra of Bi-22212 revealing the sharp gap peaks and a reproducible structure above the gap have been investigated in detail. The gap of Pb was also observed in the spectra of BSCCO-Pb junctions suggesting that a S-I-N junction has been formed between the needle and the normal surface of the film. Above the gap, some fine structure independent on magnetic field up to 0.5 T was observed. The most distinct feature was a pronounced dip at the energy of 70 meV which amplitude varied with junction resistance and bias polarity. This feature is consistent with the results of studies on single crystals. The authors assume this dip is due to the effects of layered structure of metaloxide, the interlayer pairing. The observed V-shaped conductance curve in sub-gap ved V-shaped conductance curve in sub-gap region is also consistent with this model. The remaining weak peculiarities the authors consider to be due to the electron-phonon interaction. The problem of Eliashberg function reconstruction from these data is discussed

193

Three-dimensional approach to scanning tunneling spectroscopy and application to Shockley states  

International Nuclear Information System (INIS)

The problem of the interpretation of scanning tunneling spectroscopy (STS) data is analytically solved using a three-dimensional (3D) transfer Hamiltonian approach. We present an analytical model capable of including both the electronic structure of the sample and the symmetry of the tip states (s, pz, dz2, ...) and we discuss the role of these 3D aspects in tunneling. We applied this model to the case of Shockley states. This system, allowing a full analytical treatment, led us to a detailed simulation and comprehension of the tunneling process. A procedure for the recovery of the sample local density of states from STS measurements is then proposed and applied to both the simulated and the experimental STS data of Shockley states. Comparing this approach with other methods proposed in the literature, the importance of considering the 3D aspects in treating and interpreting STS data is demonstrated.

194

Scanning tunneling microscopic and scanning tunneling spectroscopic studies of nanostructure and surface energy properties of stainless steel Kh18N10T. 1. Measurements at interfaces with air and 0.1 N HCl solution  

International Nuclear Information System (INIS)

Stainless steel Cr18Ni10Ti has been investigated by the electrochemical scanning tunneling microscopy (ESTM) and electrochemical scanning tunneling spectroscopy (ESTS) at the border with the air, and when controlled potential of the sample and needle in 0.01 N HCl solution. Local spectral dependencies of tunnel current from tunnel voltage (It, Ut) at the air and in the solution in the range of potential of stable properties have been analyzed, and local values of tunnel conductivity (G0), coefficient of probability of tunnel electron transition from the specimen to the needle (?), and slope of logarithmic dependence (?=Ut/ln(It)) have been calculated. It is demonstrated that local energetic properties of steel Cr18Ni10Ti surface at the atomic level are determined by interference of nearest atoms (matrix effect)

195

Scanning Tunneling Spectroscopy in the Superconducting State and Vortex Cores of the ?-Pyrochlore KOs2O6  

Science.gov (United States)

We performed the first scanning tunneling spectroscopy measurements on the pyrochlore superconductor KOs2O6 (Tc=9.6K) in both zero magnetic field and the vortex state at several temperatures above 1.95 K. This material presents atomically flat surfaces, yielding spatially homogeneous spectra which reveal fully gapped superconductivity with a gap anisotropy of 30%. Measurements performed at fields of 2 and 6 T display a hexagonal Abrikosov flux line lattice. From the shape of the vortex cores, we extract a coherence length of 31 40 Å, in agreement with the value derived from the upper critical field Hc2. We observe a reduction in size of the vortex cores (and hence the coherence length) with increasing field which is consistent with the unexpectedly high and unsaturated upper critical field reported.

Dubois, C.; Santi, G.; Cuttat, I.; Berthod, C.; Jenkins, N.; Petrovi?, A. P.; Manuel, A. A.; Fischer, Ø.; Kazakov, S. M.; Bukowski, Z.; Karpinski, J.

2008-08-01

196

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.

197

Analysis of scanning tunneling optical spectroscopy applied to narrow-gap semiconductors  

Science.gov (United States)

Homogeneous II-VI narrow gap semiconducting alloys are of interest because of their use in infrared detectors. These compound semiconductor materials are inherently difficult to grow in bulk due to gravity induced convective flows. A microgravity growth environment has therefore been considered. In order to evaluate the quality of crystals grown in space compared to those grown on the ground, it is necessary to characterize both. One important aspect of this characterization is the study of stoichiometry, x. A characterization scheme using scanning tunneling optical spectroscopy (STOS) involves determining the spectral response of the photoexcited tunneling current for a semiconductor. By measuring the photoenhanced tunneling current versus photon energy, the band gap Eg of the semiconductor material can be determined. Such measurements determine Eg equals Eg(x) locally, and thus x can be determined as a function of position provided Eg(x) is known. We consider a one dimensional model, involving a simple analysis of absorption of photons, production of photoelectrons, diffusion of photoelectrons to the surface, and tunneling of these electrons to the STM probe. Our results of photoenhanced tunneling current versus photon energy are qualitatively similar to experiment. After our results are presented, we list questions that need to be considered for an improved version of our analysis which is planned.

Patterson, James D.; Mantovani, James G.

1997-07-01

198

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

Science.gov (United States)

Knowledge of and control over the curvature of ripples in freestanding graphene are desirable for fabricating and designing flexible electronic devices, and recent progress in these pursuits has been achieved using several advanced techniques such as scanning tunnelling microscopy. The electrostatic forces induced through a bias voltage (or gate voltage) were used to manipulate the interaction of freestanding graphene with a tip (substrate). Such forces can cause large movements and sudden changes in curvature through mirror buckling. Here we explore an alternative mechanism, thermal load, to control the curvature of graphene. We demonstrate thermal mirror buckling of graphene by scanning tunnelling microscopy and large-scale molecular dynamic simulations. The negative thermal expansion coefficient of graphene is an essential ingredient in explaining the observed effects. This new control mechanism represents a fundamental advance in understanding the influence of temperature gradients on the dynamics of freestanding graphene and future applications with electro-thermal-mechanical nanodevices. PMID:25230052

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

2014-01-01

199

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

Science.gov (United States)

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

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

2014-12-01

200

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

Science.gov (United States)

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

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

2014-09-01

 
 
 
 
201

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

International Nuclear Information System (INIS)

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

202

Radio Frequency Scanning Tunneling Spectroscopy for Single-Molecule Spin Resonance  

Science.gov (United States)

We probe nuclear and electron spins in a single molecule even beyond the electromagnetic dipole selection rules, at readily accessible magnetic fields (few mT) and temperatures (5 K) by resonant radio-frequency current from a scanning tunneling microscope. We achieve subnanometer spatial resolution combined with single-spin sensitivity, representing a 10 orders of magnitude improvement compared to existing magnetic resonance techniques. We demonstrate the successful resonant spectroscopy of the complete manifold of nuclear and electronic magnetic transitions of up to ?Iz=±3 and ?Jz=±12 of single quantum spins in a single molecule. Our method of resonant radio-frequency scanning tunneling spectroscopy offers, atom-by-atom, unprecedented analytical power and spin control with an impact on diverse fields of nanoscience and nanotechnology.

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

2014-09-01

203

Observation and manipulation of hexa-adamantyl-hexa-benzocoronene molecules by low temperature scanning tunneling microscopy.  

Science.gov (United States)

Large molecules made of a central hexa-adamantyl-hexa-benzocoronene plateau surrounded by six adamantyl groups have been investigated by low temperature scanning tunneling microscopy and scanning tunneling spectroscopy coupled with image calculations and molecular mechanics. The structure of large self-assembled domains reveals that the intermolecular interactions between adamantyl peripheral groups dominate film growth. At very low coverage, the molecules can exhibit a certain instability for negative bias voltages which induces a partial rotation. Manipulations of single objects using the STM tip are used to create small clusters of two or three molecules. The formed structures can be obtained and manipulated provided that the flexible adamantyl moieties of neighbouring molecules are brought in close contact promoting a robust mechanical anchoring. PMID:25244027

Calmettes, Bastien; Vernisse, Loranne; Guillermet, Olivier; Benjalal, Youness; Bouju, Xavier; Coudret, Christophe; Coratger, Roland

2014-10-01

204

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)

205

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

206

Radio frequency scanning tunneling spectroscopy for single-molecule spin resonance.  

Science.gov (United States)

We probe nuclear and electron spins in a single molecule even beyond the electromagnetic dipole selection rules, at readily accessible magnetic fields (few mT) and temperatures (5 K) by resonant radio-frequency current from a scanning tunneling microscope. We achieve subnanometer spatial resolution combined with single-spin sensitivity, representing a 10 orders of magnitude improvement compared to existing magnetic resonance techniques. We demonstrate the successful resonant spectroscopy of the complete manifold of nuclear and electronic magnetic transitions of up to ?I_{z}=±3 and ?J_{z}=±12 of single quantum spins in a single molecule. Our method of resonant radio-frequency scanning tunneling spectroscopy offers, atom-by-atom, unprecedented analytical power and spin control with an impact on diverse fields of nanoscience and nanotechnology. PMID:25302884

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

2014-09-26

207

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

208

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

209

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

International Nuclear Information System (INIS)

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

210

Theory of scanning tunneling microscopy probe of impurity states in a d-wave superconductor  

CERN Document Server

Scanning tunneling microscopy can provide a probe for the detailed study of quasiparticle states in high-T_c superconductors. We propose that it can also be used to acquire specific information about impurity-induced quasiparticle states and the superconducting order-parameter structure. In particular, the local density of states is found to be sensitive to impurity-induced resonances and to the symmetry of the order parameter.

Salkola, M I; Scalapino, D J

1996-01-01

211

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

Measurements on an ultrafast scanning tunneling microscope with simultaneous spatial and temporal resolution are presented. We show images of picosecond pulses propagating on a coplanar waveguide and resolve their mode structures. The influence of transmission line discontinuities on the mode structure is investigated. It is also demonstrated how common and differential modes of electrical pulses are generated. The capacitive coupling between the tip and the transmission line is explained in ...

Jensen, Jacob Riis; Keil, Ulrich Dieter Felix; Hvam, Jørn Ma?rcher

2006-01-01

212

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

Science.gov (United States)

We have developed a method of atomic force microscopy (AFM)-assisted scanning tunneling spectroscopy (STS) under ambient conditions. An AFM function is used for rapid access to a selected position prior to performing STS. The AFM feedback is further used to suppress vertical thermal drift of the tip-sample distance during spectroscopy, enabling flexible and stable spectroscopy measurements at room temperature. PMID:25145648

Vakhshouri, Amin; Hashimoto, Katsushi; Hirayama, Yoshiro

2014-12-01

213

Image-processing and pattern recognition of scanning tunneling microscope data  

International Nuclear Information System (INIS)

Scanning Tunneling Microscopy (STM) gives information on the topography, chemical composition and electronic structure of metal and semiconductor surfaces down to the atomic scale. The experimental data can be filtered using a Wiener or least-square filter to eliminate blurring, to suppress noise, and, in addition, to correct spatial distortions by correlating typical picture elements. The application of mask filters in Fourier space, however, can easily falsify processed images. (Auth.)

214

Measurements with an ultrafast scanning tunnelling microscope on photoexcited semiconductor layers  

DEFF Research Database (Denmark)

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

Keil, Ulrich Dieter Felix; Jensen, Jacob Riis

1998-01-01

215

Scanning tunnelling microscope combined with synchrotron radiation for element specific analysis  

Energy Technology Data Exchange (ETDEWEB)

Scanning tunnelling microscopy (STM) combined with synchrotron radiation (SR) has been developed. By means of detecting the photoelectrons excited by the SR light with an STM tip, X-ray absorption spectrum (XAS) of the sample surface was successfully obtained during the STM observation. The results suggest the possibilities of the element specific surface analysis by an STM with a microscopic spatial resolution. Several trials for estimating and improving the spatial resolution of the XAS measurement are now undergoing.

Okuda, Taichi [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-0851 (Japan)]. E-mail: okudat@issp.u-tokyo.ac.jp; Eguchi, Toyoaki [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-0851 (Japan); Matsushima, Takeshi [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-0851 (Japan); Hamada, Masayuki [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-0851 (Japan); Ma, Xiao-Dong [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-0851 (Japan); Kataoka, Akira [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-0851 (Japan); Harasawa, Ayumi [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-0851 (Japan); Kinoshita, Toyohiko [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-0851 (Japan); Hasewgawa, Yukio [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-0851 (Japan)

2005-06-15

216

Local probing and manipulation of molecules and nanoscale contacts with scanning tunneling microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this thesis single molecules, metal-organic complexes and single adatoms are characterized on a metal surface by means of scanning tunneling microscopy (STM). Specifically the organic molecule 4-[trans-2-(pyrid-4-yl-vinyl)] benzoic acid (PVBA) is primarily in the focus. The molecule has two functional groups, a pyridyl and a carboxylic group connected by a vinyl group giving rise to versatile electronic properties and interaction mechanisms. The PVBA molecules are deposited by molecular be...

Ohmann, Robin

2010-01-01

217

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

2014-03-15

218

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

International Nuclear Information System (INIS)

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

219

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

220

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

 
 
 
 
221

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

222

Mapping the Electron Transport of Graphene Boundaries Using Scanning Tunneling Potentiometry  

Science.gov (United States)

The symmetry of the graphene honeycomb lattice is a key element for determining many of graphene's unique electronic properties. Topological lattice defects, such as grain boundaries and step edges, break the sublattice symmetry and can affect the electronic properties, especially the transport of graphene. A complete understanding of the physical and electronic properties of defects and boundaries of graphene is needed for future applications. Using a scanning tunneling potentiometry method with a low temperature four-probe scanning tunneling microscope, two-dimensional maps of electrochemical potentials have been measured across individual grain boundaries of graphene films on SiO2, as well as across 1ML to 1ML substrate steps and 1ML to 2ML transitions of graphene on SiC. An Atomic Force Microscope (AFM) is implemented to image the grain boundary that forms between coalesced individual graphene flakes on insulating surfaces where as a Scanning Tunneling Microscopy (STM) is implemented for characterizing the SiC grown graphene samples. Results of the influence that various boundaries have on the electronic transport of graphene will be presented.

Clark, Kendal; Zhang, Xiaoguang; Vlassiouk, Ivan; He, Guowei; Gu, Gong; Feenstra, Randall; Li, An-Ping

2013-03-01

223

Scanning tunneling microscopy study of Fe, Co and Cr growth on Re(0001)  

Science.gov (United States)

Atomically flat terraces of the Re(0001) surface with a contaminant density below 0.5% have been obtained by oxygen annealing followed by a flash to higher temperature. This Re(0001) single crystal has been used as a substrate for the deposition of Fe, Co and Cr atoms. Scanning Tunneling Microscopy experiments characterize the growth mode for the submonolayer coverage regime. Co, Cr and Fe atoms self-assemble to form monolayer high islands. Despite a large lattice mismatch between film and substrate, Co and Fe grow pseudomorphically up to half a monolayer. Cr islands are pseudomorphic only for a size below 10 nm. Higher coverage leads to reconstructed islands with an element-dependent reconstruction pattern. Scanning Tunneling Spectroscopy measurements at 8 K reveal the electronic properties of Fe and Re. Differential conductance measurements on the Re(0001) show the presence of standing waves, possibly due to a rhenium surface state. Atomic resolution images of Fe attached to a Re step edge lead to the conclusion that the Fe atoms occupy hcp hollow sites. A Néel magnetic ordered state of the Fe hcp monolayer is revealed with Spin-Polarized Scanning Tunneling Microscopy and Magnetic Atom Manipulation Imaging.

Ouazi, S.; Pohlmann, T.; Kubetzka, A.; von Bergmann, K.; Wiesendanger, R.

2014-12-01

224

Probing ultrafast spin dynamics with optical pump-probe scanning tunnelling microscopy  

Science.gov (United States)

Studies of spin dynamics in low-dimensional systems are important from both fundamental and practical points of view. Spin-polarized scanning tunnelling microscopy allows localized spin dynamics to be characterized and plays important roles in nanoscale science and technology. However, nanoscale analysis of the ultrafast dynamics of itinerant magnetism, as well as its localized characteristics, should be pursued to advance further the investigation of quantum dynamics in functional structures of small systems. Here, we demonstrate the optical pump-probe scanning tunnelling microscopy technique, which enables the nanoscale probing of spin dynamics with the temporal resolution corresponding, in principle, to the optical pulse width. Spins are optically oriented using circularly polarized light, and their dynamics are probed by scanning tunnelling microscopy based on the optical pump-probe method. Spin relaxation in a single quantum well with a width of 6 nm was observed with a spatial resolution of ~1 nm. In addition to spin relaxation dynamics, spin precession, which provides an estimation of the Landé g factor, was observed successfully.

Yoshida, Shoji; Aizawa, Yuta; Wang, Zi-Han; Oshima, Ryuji; Mera, Yutaka; Matsuyama, Eiji; Oigawa, Haruhiro; Takeuchi, Osamu; Shigekawa, Hidemi

2014-08-01

225

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

226

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.

Tison, Yann

2008-01-01

227

Combined Scanning Electron and Multi-tip Scanning Tunneling Microscopy as a Method for Charge Transport Measurements at the Nanometer Range  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In dieser Arbeit werden Ladungstransportmessungen im Nanometerbereich unter Ultrahochvakuum-Bedingungen präsentiert. Für diese Messungen ist eine Kombinationsapparatur aus Rasterelektronenmikroskop (engl. Scanning Electron Microscope, SEM) und Rastertunnelmikroskop (engl. Scanning Tunneling Microscope, STM) benutzt worden. Um neben vertikalen auch laterale Transportmessungen durchführen zu können, ist ein 2-Spitzen-STM entwickelt worden, welches in dieser Arbeit vorgestellt wird. Das Desi...

Jaschinsky, Philipp

2007-01-01

228

Theory of spin dynamics of magnetic adatoms traced by time-resolved scanning tunneling spectroscopy  

CERN Document Server

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

Schüler, Michael; Berakdar, Jamal

2012-01-01

229

Deformation and hyperfine structures of dendrimers investigated by scanning tunneling microscopy.  

Science.gov (United States)

Scanning tunneling microscopy (STM) is known to provide the highest spatial resolution in real space imaging of materials, and its applications are most common among conductive and semiconductive systems. The high tunneling barrier of insulators diminishes the tunneling probability and thus compromises STM's resolution. This work introduces a simple method to approach this problem, by using STM for high-resolution imaging of insulating materials such as the fourth and fifth generations of poly(amidoamine) hydroxyl-terminated dendrimers. The tunneling barrier is lowered by precoordination with Cu(II) or Pt(II) ions, enabling intramolecular hyperfine features be resolved with 0.2 nm resolution. The spatial distribution, size, and overall number of hyperfine features are consistent with the location of dendrimer termini. The immobilization process deforms dendrimers from the spherical geometry in solution phase to asymmetrical domes in ambient. The ultrahigh vacuum (UHV) environment leads to a higher degree of deformation with reduction of volume. The high-resolution images enable the determination of fundamental parameters of individual dendrimers, including axis, height, asymmetry, and volume. From STM spectroscopy and prior knowledge of dendritic systems, the STM imaging mechanism under UHV is consistent with metal(0) nanoparticles encapsulated by dendrimers, while ambient imaging is most likely via metal-ion-facilitated charge transport. The results from this investigation bring us one step closer toward structural characterization at atomistic level and should enable direct comparison of dendrimer structures with simulations, and deepen our understanding of charge transport in dendrimer systems. PMID:19278254

Fleming, Christopher J; Liu, Ying X; Deng, Zhao; Liu, Gang-Yu

2009-04-23

230

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.

231

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

International Nuclear Information System (INIS)

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

232

Spin-polarized scanning tunneling microscopy of half-metallic ferromagnets: Non-quasiparticle contributions  

CERN Document Server

The role of the many-body (spin-polaronic) effects in the scanning tunneling spectroscopy of half-metallic ferromagnets (HMF) is considered. It is shown that the non-quasiparticle (NQP) states exist in the majority or minority spin gap in the presence of arbitrary external potential and, in particular, at the surfaces and interfaces. Energy dependence of the NQP density of states is obtained in various models of HMF, an important role of the hybridization nature of the energy gap being demonstrated. The corresponding temperature dependence of spin polarization is calculated. It is shown that the NQP states result in a sharp bias dependence of the tunneling conductance near zero bias. Asymmetry of the NQP states with respect to the Fermi energy provides an opportunity to separate phonon and magnon peaks in the inelastic spectroscopy by STM.

Irkhin, V Y

2006-01-01

233

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

CERN Document Server

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

Raza, H

2007-01-01

234

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

Science.gov (United States)

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

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

2005-11-01

235

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

CERN Document Server

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

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

2006-01-01

236

Haptic-STM: A human-in-the-loop interface to a scanning tunneling microscope  

Science.gov (United States)

The operation of a haptic device interfaced with a scanning tunneling microscope (STM) is presented here. The user moves the STM tip in three dimensions by means of a stylus attached to the haptic instrument. The tunneling current measured by the STM is converted to a vertical force, applied to the stylus and felt by the user, with the user being incorporated into the feedback loop that controls the tip-surface distance. A haptic-STM interface of this nature allows the user to feel atomic features on the surface and facilitates the tactile manipulation of the adsorbate/substrate system. The operation of this device is demonstrated via the room temperature STM imaging of C60 molecules adsorbed on an Au(111) surface in ultra-high vacuum.

Perdigão, Luís M. A.; Saywell, Alex

2011-07-01

237

Scanning tunneling microscopy characterization of the geometric and electronic structure of hydrogen-terminated silicon surfaces  

Science.gov (United States)

Scanning tunneling microscopy (STM) methods are used to characterize hydrogen-terminated Si surfaces prepared by a novel method. The surface preparation method is used to expose the Si-SiO2 interface. STM images directly reveal the topographic structure of the Si-SiO2 interface. The dependence of interface topography on oxide preparation conditions observed by STM is compared to the results of conventional surface characterization methods. Also, the electronic structure of the hydrogen-terminated surface is studied by STM spectroscopy. The near-ideal electronic structure of this surface enables direct tunnel spectroscopy measurements of Schottky barrier phenomena. In addition, this method enables probing of semiconductor subsurface properties by STM.

Kaiser, W. J.; Bell, L. D.; Hecht, M. H.; Grunthaner, F. J.

1988-01-01

238

Construction and performance of a dilution-refrigerator based spectroscopic-imaging scanning tunneling microscope  

Science.gov (United States)

We report on the set-up and performance of a dilution-refrigerator based spectroscopic imaging scanning tunneling microscope. It operates at temperatures below 10 mK and in magnetic fields up to 14T. The system allows for sample transfer and in situ cleavage. We present first-results demonstrating atomic resolution and the multi-gap structure of the superconducting gap of NbSe2 at base temperature. To determine the energy resolution of our system we have measured a normal metal/vacuum/superconductor tunneling junction consisting of an aluminum tip on a gold sample. Our system allows for continuous measurements at base temperature on time scales of up to ?170 h.

Singh, U. R.; Enayat, M.; White, S. C.; Wahl, P.

2013-01-01

239

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

International Nuclear Information System (INIS)

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

240

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

 
 
 
 
241

Valence loss spectra in STEM (Scanning Transmission Electron Microscope)  

International Nuclear Information System (INIS)

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

242

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

International Nuclear Information System (INIS)

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

243

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,

244

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

International Nuclear Information System (INIS)

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

245

Adsorption of HgCl2 molecules on Au(111) surfaces studied by scanning tunneling microscopy  

Science.gov (United States)

We have studied the adsorption of HgCl2 on Au surfaces by scanning tunneling microscopy (STM). HgCl2 was found to form a stable, ordered overlayer on Au(111) surface in ambient conditions and it was imaged with molecular resolution. We suggest that the revealed structure is (?7 ×?7 )R19.1°-2HgCl2. This model supposes that the HgCl2 molecule bends in the adsorption to have a 123° angle between Cl-Hg bonds. In addition, the adsorption capacity of Au(111) surface for HgCl2 was determined to be 2:7.

Laakso, A.; Lahtinen, J.; Levlin, M.; Hautojärvi, P.

2001-08-01

246

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

CERN Document Server

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

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

2005-01-01

247

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

International Nuclear Information System (INIS)

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

248

Parallel stranded DNA under scanning tunnelling microscope: the main characteristics of the double helix.  

Science.gov (United States)

Using the scanning tunnelling microscopy we have directly observed the parallel stranded DNA of 43 bp in length, containing alternating AT-stretches. The double helix is right-handed and has the same width of each grooves equal to 17.4 A. The average pitch of the helical turn is about 34 A. The parallel double helix possesses no more than 8.6 bases per one turn. The diameter of the parallel stranded DNA molecule is 17-18 A. We conclude that in parallel DNA double helix the angle between N-glycoside bounds in trans-Crick-Watson base pairs is close to 180 degrees. PMID:1841276

Tchurikov, N A; Zhu, J D; Li, M Q; Chernov, B K

1991-01-01

249

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

250

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

Directory of Open Access Journals (Sweden)

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

L. Moldovan

2008-05-01

251

Electrochemical scanning tunneling spectroscopy of redox-active molecules bound by Au-C bonds.  

Science.gov (United States)

A comparison of the electrochemical gating of molecular conduction by a redox [Os(bipyridine)(pyridine)Cl] complex tethered to Au(111) with two different metal-molecule junctions in a scanning tunneling microscope nanogap is presented. The same redox molecular structure was tethered by mercaptobenzoic acid or reduction of the aryldiazonium salt of p-aminobenzoic acid, resulting in a Au-S or Au-C bond, respectively. A two-step electron-transfer mechanism with vibrational relaxation of the redox molecule is apparent in each case. PMID:19954234

Ricci, Alejandra M; Calvo, Ernesto J; Martin, Santiago; Nichols, Richard J

2010-03-01

252

Electrochemical scanning tunneling microscopy and spectroscopy for single-molecule investigation.  

Science.gov (United States)

The technique of electrochemical scanning tunneling microscopy (ECSTM) and spectroscopy (ECSTS) for studying electron transport through single redox molecules is here described. Redox molecules of both biological and organic nature have been studied by this technique with the aim of understanding the transport mechanisms ruling the flow of electrons via a single molecule placed in a nanometer-sized gap between two electrodes while elucidating the role of the redox density of states brought about by the molecule. The obtained results provide unique clues to single-molecule transport behavior and support the concept of single-molecule electrochemical gating. PMID:23546676

Alessandrini, Andrea; Facci, Paolo

2013-01-01

253

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

Nilsson, Louis

2013-01-01

254

Scanning Tunneling Microscope Image of Thioguanine Molecules on Au(111) Surface  

Science.gov (United States)

We have studied 6-thioguanine, a substituent of deoxyribonucleic acid (DNA) bases, adsorbed on a Au(111) surface by scanning tunneling microscopy (STM) under ambient condition in air. Observation of the STM image of the molecule suggests that thioguanine is bound to the Au substrate through the Au-S bond formation described in STM studies of alkanethiolate molecules. Our STM images obtained under ambient condition are much more similar to those of a planar two-dimensional hydrogen-bonded array of guanine molecules on a MoS2 substrate rather than those of a disordered array of guanine on a Au substrate in solution.

Katsumata, Shunji; Ide, Atsushi

1994-06-01

255

Self-assembly of manganese phthalocyanine on Pb(111) surface: A scanning tunneling microscopy study  

Science.gov (United States)

The self-assembled structure of submonolayer manganese phthalocyanine (MnPc) on Pb(111) surface is investigated by using low-temperature scanning tunneling microscopy (STM). A "holelike" superlattice, which is superimposed on the self-assembled nearly quadratic network, is observed. High resolution STM images reveal that there are two distinct azimuthal orientations of MnPc molecules. It is found that by taking the two different orientations the self-assembly can further be optimized energetically by maximizing intermolecular orbital overlapping. It is this intralayer energy minimization process that leads to the characteristic holelike superlattice.

Hao, Dan; Song, Canli; Ning, Yanxiao; Wang, Yilin; Wang, Lili; Ma, Xu-Cun; Chen, Xi; Xue, Qi-Kun

2011-04-01

256

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

DEFF Research Database (Denmark)

Measurements on an ultrafast scanning tunneling microscope with simultaneous spatial and temporal resolution are presented. We show images of picosecond pulses propagating on a coplanar waveguide and resolve their mode structures. The influence of transmission line discontinuities on the mode structure is investigated. It is also demonstrated how common and differential modes of electrical pulses are generated. The capacitive coupling between the tip and the transmission line is explained in terms of two contributions: a long range and a local coupling. We also show how these contributions affect the imaging of the propagating pulses. (C) 1997 American Institute of Physics.

Jensen, Jacob Riis; Keil, Ulrich Dieter Felix

1997-01-01

257

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

Science.gov (United States)

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

Zhang, Xin; Luo, Hong

2013-12-01

258

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2005-02-01

259

Direct observation of C 60 LB film with scanning tunneling microscopy  

Science.gov (United States)

We report the direct imaging of monolayer LB film of C 60. The LB film was prepared onto an Au(100) surface by the vertical dipping method for scanning tunneling microscopy (STM) measurements. Ordered arrays of C 60 molecules and close-packed molecular aggregation in the film are shown on the STM images. The calculated diameters along two mutually perpendicular directions in the arrays are 0.635±0.013 and 0.572±0.024 nm, respectively. Our results demonstrate that the molecular shape of C 60 is easily compressed into an ellipsoid while forming the LB film.

Guo, Jun; Xu, Yu; Li, Yuliang; Yang, Chun; Yao, Youxin; Zhu, Daoben; Bai, Chunli

1992-07-01

260

Controlled manipulation of single atoms and small molecules with the scanning tunneling microscope  

Science.gov (United States)

We briefly survey our progress on manipulation of single atoms and small molecules and formation of prototypic nanostructures with our simple versatile temperature variable scanning tunneling microscope (STM). Lateral manipulation, i.e. sliding of species along the surface is demonstrated on the Cu(211) surface for carbon monoxide- and ethene-molecules, lead-atoms and lead-dimers. We show furthermore, that we can also manipulate substrate atoms and are even able to release native Cu-atoms from high coordinated substrate sites. Vertical manipulation, i.e. controlled transfer of species between tip and surface and vice versa is discussed for xenon atoms and propene molecules.

Meyer, Gerhard; Rieder, Karl-Heinz

1997-04-01

 
 
 
 
261

Note: A quartz cell with Pt single crystal bead electrode for electrochemical scanning tunneling microscope measurements  

Science.gov (United States)

In this paper, we provide and demonstrate a design of a unique cell with Pt single crystal bead electrode for electrochemical scanning tunneling microscope (ECSTM) measurements. The active metal Pt electrode can be protected from air contamination during the preparation process. The transparency of the cell allows the tip and bead to be aligned by direct observation. Based on this, a new and effective alignment method is introduced. The high-quality bead preparations through this new cell have been confirmed by the ECSTM images of Pt (111).

Xia, Zhigang; Wang, Jihao; Hou, Yubin; Lu, Qingyou

2014-09-01

262

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

Science.gov (United States)

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

Gao, Min; Pan, Yi; Xu, Wenyan; Huang, Li; Wang, Yeliang; Lin, Yuan; Gao, H.-J.

2014-09-01

263

Scanning tunneling microscopy study of the CeTe3 charge density wave  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have studied the nature of the surface charge distribution in CeTe3. This is a simple, cleavable, layered material with a robust one-dimensional incommensurate charge density wave (CDW). Scanning tunneling microscopy (STM) has been applied on the exposed surface of a cleaved single crystal. At 77 K, the STM images show both the atomic lattice of surface Te atoms arranged in a square net and the CDW modulations oriented at 45 degrees with respect to the Te net. Fourier tra...

Tomic, A.; Rak, Zs; Veazey, J. P.; Mahanti, S. D.; Tessmer, S. H.; Malliakas, C. D.; Kanatzidis, M. G.

2008-01-01

264

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

This study utilizes Auger-electron spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy (STM) to examine sulfur coverages above theta(S)=0.25 on the Cu(100) surface. These large sulfur coverages are observed to induce a restructuring of the copper surface through the removal of copper atoms from terrace sites. The layer produced at room temperature by H2S exposures is composed of small Cu-S aggregates which do not exhibit long-range order, but which orient in the [...

Colaianni, Maria Loredana; Chorkendorff, Ib

2009-01-01

265

Scanning tunneling microscopy image modeling for zigzag-edge graphene nanoribbons  

Science.gov (United States)

Based on the nonequilibrium Green's function with tight-binding approximation scheme, we study the scanning tunneling microscopy (STM) current from a semi-infinite quantum wire to carbon sites of a zigzag-edge graphene nanoribbon (ZGNR) via an adatom on it. We find that although the existence of local edge states, only the even order number carbon chains near the edge provide good conducting channels, and the STM image should be alternative with dark-bright fringes. This effect has not been shown in previous studies by treating a ZGNR in its entirety, and it may be useful for the STM experimental characterization on graphene samples.

Chen, Xiongwen; Wan, Haiqing; Song, Kehui; Tang, Dongsheng; Zhou, Guanghui

2011-06-01

266

Scanning tunneling microscopy study of higher-order Si(100)-c(8 x 8) surface reconstruction  

International Nuclear Information System (INIS)

We have studied the higher-order Si(100)-c(8 x 8) surface reconstruction using scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). Our high resolution STM images show that long range ordering of rectangular cells are the building blocks of this reconstruction. We identify Si-Si ad-dimers and determine that three pairs of ad-dimers constitute each rectangular cell. The ad-dimer direction is parallel to the longer side of these rectangular cells. We propose a new dimer model to explain this reconstruction

267

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.

268

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

Science.gov (United States)

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

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

2012-01-01

269

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

International Nuclear Information System (INIS)

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

270

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

Energy Technology Data Exchange (ETDEWEB)

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

Stocker, Matthias; Pfeifer, Holger; Koslowski, Berndt, E-mail: berndt.koslowski@uni-ulm.de [Institute of Solid State Physics, University of Ulm, D-89069 Ulm (Germany)

2014-05-15

271

Efficient method for fast simulation of scanning tunneling microscopy with a tip effect.  

Science.gov (United States)

On the basis of Bardeen's perturbation theory on electron tunneling and inspired by Paz et al.'s study, a new expression for the tunneling current between the scanning tunneling microscopy (STM) tip and sample has been obtained, and it provides us with an efficient method to simulate STM images. The method can be implemented in any code of first-principles computing software, which offers the wave functions of the tip and sample, calculated independently at the same footing, as input. By calculating the integral with fast Fourier transform (FFT), simulating the STM image of a given sample surface by a database of different tips on a PC turns out to be not a time-consuming work. Compared with Paz et al.'s method, our method abandons the application of the vacuum Green function and possesses better computing efficiency, fewer parameters, and more reasonable simulated results especially at lower computing cost. Simple tip-sample systems, such as H-H and Pd2-Ag2, are taken as benchmarks to test our method. The topographic images of a CO molecule adsorbed on a Cu(111) surface obtained by using a tungsten tip and a CO-terminated tip are also simulated, and the simulated results are in good agreement with the experimental ones. PMID:24708199

Zhang, Ruiqi; Hu, Zhenpeng; Li, Bin; Yang, Jinlong

2014-10-01

272

A stable scanning tunneling microscope designed for investigations of organic thin films in air  

Science.gov (United States)

A new and stable scanning tunneling microscope (STM) system has been constructed for the investigation of thin organic films in air. The STM unit is made of Macor, which is machinable ceramic and has a small thermal expansion coefficient and a high mechanical stiffness. Three-dimensional coarse position adjustment (within 3 ?m) is carried out using five stacked piezoelectric transducers (PZTs). A cross-type configuration is used to prevent the thermal effect of the x- and y-direction displacement mechanism. In order to achieve high resolution, x-, y-, and z-direction displacements are performed using a tube-type PZT. The z direction of the tube PZT has a high mechanical resonant frequency of 24.4 kHz. Therefore, this STM unit is mechanically rigid, and allows stable operation under mechanical disturbances (sound and mechanical vibration). Moreover, this STM unit can be controlled for 24 h or longer by using an ordinary operational amplifier, because thermal effects are compensated. The STM system can also be used to obtain information on the spatially resolved local tunneling barrier height, which is sensitive to the chemical structure of the sample. The capabilities of this newly designed STM are demonstrated with experiments investigating the morphology and tunneling barrier height of stearic acid thin films on indium-tin-oxide substrates.

Sasaki, A.; Iwata, F.; Katsumata, A.; Akiyama, T.; Fujiyasu, H.

1997-02-01

273

In situ manipulation of scanning tunneling microscope tips without tip holder.  

Science.gov (United States)

A design for a manipulator system for manipulating bare scanning tunneling microscopy (STM) tips without any tip holder is presented. The extremely stiff and rigid system consists of an ultrahigh vacuum compatible fully three-dimensionally movable gripper module driven by stepping motors and piezomotors. The tips are clamped by hardened tool steel gripper jaws, which are controlled by a stepping motor through levers. The system allows the reproducible manipulation of bare tungsten tips made of wires with diameters of 0.25 nm and having length of only up to 3 mm without damaging the tip or the STM. The tip manipulators' advantage is that the total mass of the scanning piezotube is reduced by removing the mass of a separate tip holder. Thereby, it becomes possible to further increase the resonance frequencies of the STM. PMID:20113106

Raad, C; Graf, K H; Ebert, Ph

2010-01-01

274

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

275

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

Energy Technology Data Exchange (ETDEWEB)

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 [National Institute for Nanotechnology, National Research Council of Canada, Edmonton, Alberta T6G 2M9 (Canada); Martins, Bruno V. C.; Zikovsky, Janik; Wolkow, Robert A., E-mail: rwolkow@ualberta.ca [National Institute for Nanotechnology, National Research Council of Canada, Edmonton, Alberta T6G 2M9 (Canada); Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1 (Canada)

2014-04-15

276

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

277

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

International Nuclear Information System (INIS)

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

278

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

International Nuclear Information System (INIS)

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.

279

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

International Nuclear Information System (INIS)

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

280

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

International Nuclear Information System (INIS)

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

 
 
 
 
281

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

International Nuclear Information System (INIS)

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

282

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

Energy Technology Data Exchange (ETDEWEB)

Highlights: Black-Right-Pointing-Pointer Nanoscale alumina was fabricated on NiAl(1 0 0) surface with a STM tip. Black-Right-Pointing-Pointer Varied powers (bias Multiplication-Sign current) give two distinct modes of oxidation. Black-Right-Pointing-Pointer In the high-power mode alumina forms on the surface near the tip. Black-Right-Pointing-Pointer In the low-power mode alumina grows along direction [0 0 1] or [0 1 0] of NiAl(1 0 0). Black-Right-Pointing-Pointer 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 Multiplication-Sign 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 ( Less-Than-Over-Equal-To 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.

Lin, C.W.; Wang, C.T. [Department of Physics and Center for Nano Science and Technology, National Central University, 300 Jhongda Road, Jhongli 32001, Taiwan (China); Luo, M.F., E-mail: mfl28@phy.ncu.edu.tw [Department of Physics and Center for Nano Science and Technology, National Central University, 300 Jhongda Road, Jhongli 32001, Taiwan (China)

2013-01-01

283

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

Science.gov (United States)

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

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

2014-10-01

284

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

Science.gov (United States)

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

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

2014-10-01

285

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

International Nuclear Information System (INIS)

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

286

A separation of the refractive index and topography in photon-scanning tunneling microscopy: Simulations and experiments  

International Nuclear Information System (INIS)

In order to separate the purely optical and topographic information from images in constant-gap mode simultaneously, we proposed the atomic force/photon-scanning tunneling microscopy (AF/PSTM). In this paper, we focus on the principle of separation of the refractive index image from the images of photon-scanning tunneling microscopy. We prove the formula of refractive index imaging by using a three-dimensional finite-difference time-domain method. The formula indicates that the refractive index of a sample is approximately proportional to photon tunneling information (?I/I-bar)2. From the viewpoint of practical use, we simulated the refractive index images for the realistic experiments. We present line scans along two orthogonal directions and the transmitted intensity as a function of the tip position under the constant-gap mode. The experimental results are presented and are in good agreement with the numerical results

287

A separation of the refractive index and topography in photon-scanning tunneling microscopy: Simulations and experiments  

Energy Technology Data Exchange (ETDEWEB)

In order to separate the purely optical and topographic information from images in constant-gap mode simultaneously, we proposed the atomic force/photon-scanning tunneling microscopy (AF/PSTM). In this paper, we focus on the principle of separation of the refractive index image from the images of photon-scanning tunneling microscopy. We prove the formula of refractive index imaging by using a three-dimensional finite-difference time-domain method. The formula indicates that the refractive index of a sample is approximately proportional to photon tunneling information ({delta}I/I-bar){sup 2}. From the viewpoint of practical use, we simulated the refractive index images for the realistic experiments. We present line scans along two orthogonal directions and the transmitted intensity as a function of the tip position under the constant-gap mode. The experimental results are presented and are in good agreement with the numerical results.

Wang Xiaoqiu [Department of Physics, Dalian University of Technology, Dalian 116024 (China) and Department of Physics, Dalian University, Dalian 116622 (China)]. E-mail: wangxqdl@sina.com; Zhang Jian [Department of Physics, Dalian University of Technology, Dalian 116024 (China); Li Yinli [Department of Physics, Dalian University of Technology, Dalian 116024 (China); Jian Guoshu [Department of Physics, Dalian University of Technology, Dalian 116024 (China); Suen Wei [Department of Physics, Dalian University of Technology, Dalian 116024 (China); Pan Shi [Department of Physics, Dalian University of Technology, Dalian 116024 (China); Wu Shifs [Department of Physics, Dalian University of Technology, Dalian 116024 (China)

2005-08-15

288

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

289

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

International Nuclear Information System (INIS)

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

290

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

International Nuclear Information System (INIS)

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

291

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

292

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

International Nuclear Information System (INIS)

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.

293

Nanosecond Scanning Tunneling Microscopy: resolving spin dynamics at the atomic scale  

Science.gov (United States)

With the advent of nanoelectronics, functional electronic elements advance towards atomic dimensions and analysis techniques need to keep pace. Scanning tunneling microscopes (STM) have evolved into standard tools to measure the static electronic properties of nanostructures, molecules and atoms. Here we show how the STM can be used to access the equally important dynamical properties on time scales ranging from pico- to nanoseconds. We combine inelastic electron tunneling spectroscopy (IETS) with an all-electronic pump-probe measurement scheme and record the dynamical evolution of magnetic atoms on surfaces in the time domain [1]. We focus on the dynamics of electron spin relaxation in transition metal atoms placed onto a copper nitride decoupling layer on Cu(100). On this surface Fe atoms experience large magneto-crystalline anisotropy [2] that enables long spin lifetimes. At the same time the quantum mechanical nature of the discrete spin states allows for an additional path of spin relaxation: quantum tunneling of magnetization. We probe the dynamic behavior associated with this process and find that placing a Cu atom close to a Fe atom boosts the uniaxial anisotropy energy and creates a long-lived spin state with relaxation times in excess of 200 ns. The ability to probe individual nanostructures with atomic spatial and nanosecond temporal resolution opens a new avenue to explore spin dynamics and other dynamical phenomena on the intrinsic length scale of the underlying interactions. [4pt] [1] S. Loth, M. Etzkorn, C. P. Lutz, D. M. Eigler, A. J. Heinrich, Science 329 1628 (2010). [0pt] [2] C.F. Hirjibehedin, et al., Science 317, 1199 (2007).

Loth, Sebastian

2011-03-01

294

Determination of the DOS in Nb(110) from scanning tunneling spectroscopy  

International Nuclear Information System (INIS)

We investigate the electronic structure of Nb(110)/Al2O3(0001) by means of scanning tunneling spectroscopy (STS) at 6.2 K. To enable a comprehensive analysis of the local electronic structure of niobium, we employ standard I-V as well as I-z and dI/dz-z spectroscopy. The experimental results will be discussed in the framework of a recently developed method for recovering the electronic density of states (DOS) from STS data. Based on the one-dimensional WKB approximation this method should enable recovering the DOS of the sample semi-quantitatively, and it should allow principally a deconvolution of tip and sample DOS. In this contribution we first elucidate the effect of data evaluation on the recovered DOS separating contributions from the bulk and the surface. We then try to deconvolute the DOS of tip and sample at least partially by comparing I-V data and differential barrier measurements taken at different locations of the sample with the same tunneling tip

295

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-09-01

296

Scanning tunneling microscopy with chemically modified tips: orientation-sensitive observation of ether oxygens  

Science.gov (United States)

Diethers, CH 3(CH 2) 15O(CH 2) nO(CH 2) 15CH 3 ( n=10,11; C 16OC nOC 16), adsorbed onto highly ordered pyrolytic graphite were observed with scanning tunneling microscopy (STM) using unmodified tips and tips chemically modified with 4-mercaptobenzoic acid (4MBA). Pairs of bright lines corresponding to the ether oxygens were observed with the modified but not the unmodified tips. Using the modified tips, one of the oxygens of C 16OC 10OC 16 appears brighter than the other one, whereas no difference in the brightness of the two oxygens of C 16OC 11OC 16 is observed in the STM images. The relative difference in the brightness for the ether oxygens appear to result from the facilitation of electron tunneling by hydrogen bond interactions between the ether oxygens of the samples and the carboxyl group of 4MBA on the tips. These results demonstrate that the STM observation using chemically modified tips can reveal the orientation of the ether oxygens and furthermore the molecular orientation of the sample molecules.

Nishino, Tomoaki; Bühlmann, Philippe; Ito, Takashi; Umezawa, Yoshio

2001-09-01

297

Scanning Tunneling Microscopy Studies of Layered Correlated Electron Systems: Transition Metal Dichalcogenides and Iridates  

Science.gov (United States)

Strongly correlated electron problems, including high temperature superconductivity, colossal magneto-resistivity, charge-density wave, heavy fermion phenomena, etc., have been major research focuses in condensed-matter physics for the past several decades. Involvements of and competitions between different degrees of freedom and energy scales present considerable difficulties for understanding these problems. In this thesis, I have used home-built variable-temperature high resolution (spatial and energy) spectroscopic imaging scanning tunneling microscopes (SI-STM) to study the topography and the local single-particle tunneling spectroscopy in a family of two-dimensional charge-density wave (2D-CDW) materials (TaSe 2, TaS2, and NbSe2) and in a newly discovered 5d Mott insulator Sr2IrO4 with strong spin-orbit coupling. In the 2D-CDW materials, we have shown the strong lattice distortion and weak electron modulation accompanying CDW transition, directly opposite to Peierls mechanism. We have also discovered that the 2D-CDW transitions in TaSe 2 and TaS2 show involvement of the orbital degree of freedom, shedding light on a long standing puzzle with their electrical resistivity anomalies. In the novel 5d Mott insulator Sr2IrO4 we have found a large insulating gap of 620 meV, indicating a stronger-than-expected correlation effect for a 5d electron system.

Dai, Jixia

298

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

Science.gov (United States)

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

Yamada, Toshishige; Kwak, Dochan (Technical Monitor)

2000-01-01

299

Control and characterization of cyclopentene unimolecular dissociation on Si(100) with scanning tunneling microscopy.  

Science.gov (United States)

Dissociation of individual cyclopentene molecules on the Si(100) surface is induced and investigated using cryogenic ultrahigh vacuum scanning tunneling microscopy (STM). Using a secondary feedback loop during elevated tunneling current and sample biasing conditions, the cyclopentene dissociation products are isolated and then characterized with atomic-scale spatial resolution. Using multibias STM and density functional theory, the cyclopentene dissociation products are shown to consist of a C(5)H(7) fragment and an individual H atom. The C(5)H(7) fragment contains a C=C double bond and is bound to the Si(100) surface via a single Si-C covalent bond, while the individual H atom can be induced to hop between two sites on a single silicon dimer with the STM tip. This study shows that the use of feedback control during STM-induced single molecule reactions allows transient reaction products to be captured and thus more thoroughly studied. While demonstrated here for cyclopentene on Si(100), this feedback-controlled approach can likely be applied to a wide array of chemical reactions on semiconductor surfaces. PMID:19572713

Yoder, Nathan L; Fakonas, James S; Hersam, Mark C

2009-07-29

300

New insights into nanomagnetism: spin-polarized scanning tunneling microscopy and spectroscopy studies  

Science.gov (United States)

We perform low-temperature spin-polarized scanning tunneling microscopy (SP-STM) and spectroscopy measurements in magnetic fields to gain new insights into nanomagnetism. We use the magnetic field to change and control magnetizations of a sample and a magnetic tip, and measure the magnetic hysteresis loops of individual Co nano-islands on Cu(111). We also exploit the high spatial resolution of SP-STM in magnetic fields to measure maps of the differential conductance within a single Co nano-island. In connection with ab initio calculations, we find that the spin polarization is not homogeneous but spatially modulated within the nano-island. We ascribe the spatial variation of the spin polarization to spin-dependent electron confinement within the Co nano-island.

Oka, Hirofumi; Rodary, Guillemin; Wedekind, Sebastian; Ignatiev, Pavel A.; Niebergall, Larissa; Stepanyuk, Valeri S.; Sander, Dirk; Kirschner, Jürgen

2011-10-01

 
 
 
 
301

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 Br2 on the clean Si(111)-7×7 surface is presented.

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

2007-05-01

302

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

DEFF Research Database (Denmark)

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

Andersen, Jens Enevold Thaulov; MØller, Per

1995-01-01

303

An ultrahigh vacuum scanning tunneling microscope for use at variable temperature from 10 to 400 K  

DEFF Research Database (Denmark)

We report on the construction of an ultrahigh vacuum (UHV) scanning tunneling microscope (STM) specially designed for operation in the entire range of sample temperatures between 10 and 400 K. The sample is cooled by means of a liquid helium continuous-flow cryostat, while the supporting manipulator and the surrounding devices remain at room temperature. This allows rapid variation of the sample temperature. The standard instruments for surface preparation and analysis and the STM are contained in a single UHV chamber. By rotation of the manipulator the sample can be positioned in front of any of these instruments without changing the sample temperature. The performance of the microscope is demonstrated by two examples of images of xenon adsorbed on platinum(111) showing: (a) the evolution of the morphology of a submonolayer of xenon from adsorption at 17 K up to desorption at about 90 K and (b) atomically resolved images of the hexagonal incommensurate rotated phase for xenon at monolayer completion.

Horch, Sebastian; Zeppenfeld, Peter

1994-01-01

304

Temperature dependence of the xenon-layer morphology on platinum (111) studied with scanning tunneling microscopy  

DEFF Research Database (Denmark)

The temperature induced changes in the morphology of a xenon sub-monolayer adsorbed on a platinum (111) surface have been investigated using a variable temperature scanning tunneling microscope (STM). The morphology changes of Xe layers adsorbed at 17K and annealed in the temperature range between 17 and 34K were compared to the morphologies of Xe layers adsorbed at different temperatures in the same range. Effects of the single Xe atom diffusivity on Pt(lll) as well as of the 2D evaporation rate of the Xe islands could be observed. The corresponding activation energies were estimated to be 0.7 kcal/mol (31 meV) and 1.5 kcal/mol (64 meV), respectively.

Horch, Sebastian; Zeppenfeld, Peter

1995-01-01

305

Hydrogen-bond imaging and engineering with a scanning tunnelling microscope  

Science.gov (United States)

The scanning tunnelling microscope (STM) has been a valuable tool in surface science for the study of structures and electronic states of metal surfaces. The recent advance of STM as a state-of-the-art technique to probe and manipulate individual molecules has made it possible to investigate molecular dynamics and chemical reactions at the surface in a single-molecule limit. In this review paper, we present an overview of our recent work of H-bond imaging, manipulating and engineering at a metal surface. From individual water molecules, a variety of H-bonded structures including water clusters, hydroxyl clusters and water-hydroxyl complexes are assembled on Cu(1 1 0), whose properties and dynamics are studied in real space in collaboration with density-functional-theory calculations.

Okuyama, Hiroshi; Hamada, Ikutaro

2011-11-01

306

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

Science.gov (United States)

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

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

2011-02-01

307

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

International Nuclear Information System (INIS)

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

308

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

309

Scanning tunneling microscopy of surface modifications induced by UNILAC heavy-ion irradiation  

International Nuclear Information System (INIS)

The processes and modifications induced by the passage of heavy ions through solids have for a long time been the subject of intensive research. Scanning tunneling microscopy (STM) provides a novel access to highly resolved imaging of ion tracks, complementing classical methods such as electron microscopy, X-ray and neutron scattering analysis. Our investigations concentrated on STM of surface modifications of highly oriented pyrolytic graphite (HOPG), and polycarbonate foil. All samples were irradiated at the GSI heavy-ion accelerator UNILAC with highly charged ions, having kinetic energies of several GeV. The impacts of 15 MeV/u Au24+ ions on HOPG created little hills (rather than craters). Within the damaged surface areas the graphite lattice is disturbed to an extent which no longer allows atomic resolution. Single submicron pores in a polymer foil, created by etching ion tracks, became accessible to STM by covering the surface with a thin gold layer. (orig.)

310

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

311

Connecting scanning tunneling spectroscopy to device performance for polymer:fullerene organic solar cells.  

Science.gov (United States)

Scanning tunneling microscopy and spectroscopy have been used to measure the local photovoltaic performance of prototypical polymer:fullerene (MDMO-PPV:PCBM) bulk heterojunction films with approximately 10 nm resolution. Fullerene-rich clusters are found to act as sinks, extracting electrons from a shell layer of a homogeneously mixed polymer:fullerene matrix, surrounding the fullerene cluster. The experimental results were quantitatively modeled with a drift-diffusion model that in first order accounts for the specific morphology. The same model has subsequently been used to calculate performance indicators of macroscopic solar cells as a function of film composition and characteristic size of the phase separation. As such, a first step has been set toward a quantitative correlation between nanoscopic and macroscopic device photovoltaic performance. PMID:20184387

Maturová, Klára; Janssen, René A J; Kemerink, Martijn

2010-03-23

312

Interpretation of scanning tunneling and atomic force microscopy images of TCNQ salts  

International Nuclear Information System (INIS)

The surfaces of the TCNQ salts TTF-TCNQ, Qn(TCNQ)2, 4EP(TCNQ)2 and TEA(TCNQ)2 (TCNQ=tetracyanoquinodimethane, TTF=tetrathiafulvalene, Qn=quinolinium, 4EP=4-ethyl-N-methylpyridinium, TEA=triethylammonium) were examined by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The STM and AFM images of these salts were interpreted on the basis of the ?(r0, ef), and ?(r0) plots of their molecular layers calculated with the extended Hueckel tight-binding electronic structure method. The present work shows that a close interplay between experiment and theory is necessary for the rational surface analysis with STM and AFM. (orig.)

313

Interpretation of scanning tunneling and atomic force microscopy images of TCNQ salts  

Energy Technology Data Exchange (ETDEWEB)

The surfaces of the TCNQ salts TTF-TCNQ, Qn(TCNQ)[sub 2], 4EP(TCNQ)[sub 2] and TEA(TCNQ)[sub 2] (TCNQ=tetracyanoquinodimethane, TTF=tetrathiafulvalene, Qn=quinolinium, 4EP=4-ethyl-N-methylpyridinium, TEA=triethylammonium) were examined by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The STM and AFM images of these salts were interpreted on the basis of the [rho](r[sub 0], e[sub f]), and [rho](r[sub 0]) plots of their molecular layers calculated with the extended Hueckel tight-binding electronic structure method. The present work shows that a close interplay between experiment and theory is necessary for the rational surface analysis with STM and AFM. (orig.)

Magonov, S.N. (Freiburger Materialforschungszentrum (FMF), Albert-Ludwigs Univ., Freiburg (Germany)); Bar, G. (Freiburger Materialforschungszentrum (FMF), Albert-Ludwigs Univ., Freiburg (Germany)); Cantow, H.F. (Freiburger Materialforschungszentrum (FMF), Albert-Ludwigs Univ., Freiburg (Germany)); Ren, J. (North Carolina State Univ., Raleigh (United States). Dept. of Chemistry); Whangbo, M.H. (North Carolina State Univ., Raleigh (United States). Dept. of Chemistry)

1994-01-31

314

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.

315

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

316

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

Science.gov (United States)

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

Ciesielski, Artur; El Garah, Mohamed; Haar, Sébastien; Kova?í?ek, Petr; Lehn, Jean-Marie; Samorì, Paolo

2014-11-01

317

Scanning tunneling microscopy investigation of the structure of methanethiolate on Ag(111).  

Science.gov (United States)

Scanning tunneling microscopy (STM) has been used to investigate the structure of the ordered methanethiolate overlayer formed on Ag(111) by reaction at room temperature with dimethyl disulfide. High-resolution images show an ordered structure with three inequivalent atomic-scale protrusions within each ( radical7 x radical7)R19 degrees surface unit mesh which can be reconciled with methanethiolate species on a regular lateral submesh, similar to that proposed in the multilayer ( radical7 x radical7)R19 degrees -S sulfide phase previously reported. STM imaging during dynamic dosing also provides evidence for a significant change in the outermost layer Ag atom density, consistent with a reconstructed surface model. Possible models for this reconstruction are presented and discussed in the light of available information. PMID:16042455

Yu, Miao; Driver, S M; Woodruff, D P

2005-08-01

318

Intrinsic granularity in nanocrystalline boron-doped diamond films measured by scanning tunneling microscopy  

Science.gov (United States)

We report on low-temperature scanning tunneling microscopy/spectroscopy experiments performed on superconducting boron-doped nanocrystalline diamond (NCD) thin films prepared by chemical-vapor deposition methods. The most representative sample reveals the observed superconducting gap (?) highly modulated over a length scale on the order of ˜30nm , which is much shorter than the typical diamond grain size. The sample local and macroscopic behavior favors for the ? modulation as being an intrinsic property of the NCD granules. On the other hand, ? shows its temperature dependence [?(T)] consistent with the results obtained by Fominov and Feigel’man [Phys. Rev. B 63, 094518 (2001)], who studied theoretically the behavior of the superconducting gap of a BCS superconductor in contact with a normal layer by solving the one-dimensional Usadel equations on the superconducting side of the superconducting to normal interface.

Willems, B. L.; Dao-, V. H.; Vanacken, J.; Chibotaru, L. F.; Moshchalkov, V. V.; Guillamón, I.; Suderow, H.; Vieira, S.; Janssens, S. D.; Williams, O. A.; Haenen, K.; Wagner, P.

2009-12-01

319

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

International Nuclear Information System (INIS)

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

320

Circularly polarized light emission in scanning tunneling microscopy of magnetic systems  

CERN Document Server

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

Apell, S P; Johansson, P

2000-01-01

 
 
 
 
321

Controlled Vertical and Lateral Manipulation of Single Atoms and Molecules with the Scanning Tunneling Microscope  

Science.gov (United States)

We report on the successful controlled vertical manipulation of single Xe atoms with the scanning tunneling microscope (STM) at a temperature of 15 K. In transferring Xe atoms from the Cu(211) substrate to the STM tip and releasing them back to the surface we used a technique similar to that employed previously by Eigler and collaborators. We demonstrate that with the well defined Xe-tip the substrate is imaged with appreciably better resolution. We show further that nanostructures built at 15 K with CO molecules by employing lateral manipulation are much more stable than those produced at 30 K, on which we reported previously. As an important consequence such structures can be produced quicker and with larger precision.

Neu, Björn; Meyer, Gerhard; Rieder, Karl-Heinz

322

Manipulation of Atoms and Molecules with the Low-Temperature Scanning Tunneling Microscope  

Science.gov (United States)

The controlled manipulation with a scanning tunneling microscope (STM) down to the scale of small molecules and single atoms allows the buildup of molecular and atomic nanostructures. In the case of the lateral manipulation of adsorbed species, in which only tip/particle forces are used, three different manipulation modes (pushing, pulling, sliding) can be discerned. Vertical manipulation of Xe and CO is demonstrated, leading to the formation of functionalized tips, which can be used for improved imaging and even to perform vibrational spectroscopy on single molecules. Furthermore, we describe how we have reproduced a full chemical reaction with single molecules, whereby all basic steps, namely, preparation of the reactants, diffusion and association, are induced with the STM tip.

Meyer, Gerhard; Moresco, Francesca; Hla, Saw Wai; Repp, Jascha; Braun, Kai-Felix; Fölsch, Stefan; Rieder, Karl Heinz

2001-06-01

323

Scanning Tunneling Microscopy Manipulation of Complex Organic Molecules on Solid Surfaces  

Science.gov (United States)

Organic molecules adsorbed on solid surfaces display a fascinating variety of new physical and chemical phenomena ranging from self-assembly and molecular recognition to nonlinear optical properties and current rectification. Both the fundamental interest in these systems and the promise of technological applications have motivated a strong research effort in understanding and controlling these properties. Scanning tunneling microscopy (STM) and, in particular, its ability to manipulate individual adsorbed molecules, has become a powerful tool for studying the adsorption geometry and the conformation and dynamics of single molecules and molecular aggregates. Here we review selected case studies demonstrating the enormous capabilities of STM manipulations to explore basic physiochemical properties of adsorbed molecules. In particular, we emphasize the role of STM manipulations in studying the coupling between the multiple degrees of freedom of adsorbed molecules, the phenomenon of molecular molding, and the possibility of creating and breaking individual chemical bonds in a controlled manner, i.e., the concept of single-molecule chemistry.

Otero, Roberto; Rosei, Federico; Besenbacher, Flemming

2006-05-01

324

Adsorbate-Induced Alloy Phase Separation: A Direct View by High-Pressure Scanning Tunneling Microscopy  

Science.gov (United States)

The influence of high pressures of carbon monoxide (CO) on the stability of a Au/Ni(111) surface alloy has been studied by high-pressure scanning tunneling microscopy. We show that CO induces a phase separation of the surface alloy at high pressures, and by means of time-lapsed STM movies we find that Ni atoms are removed from the surface layer during the process. Density functional theory calculations reveal the thermodynamic driving force for the phase separation to be the Au-induced compression of the CO overlayer with a resulting CO-CO repulsion. Furthermore, the atomistic mechanism of the process is shown to be kink-site carbonyl formation and evaporation which is found to be enhanced by the presence of Au.

Vestergaard, Ebbe K.; Vang, Ronnie T.; Knudsen, Jan; Pedersen, Thorbjørn M.; An, Toshu; Lægsgaard, Erik; Stensgaard, Ivan; Hammer, Bjørk; Besenbacher, Flemming

2005-09-01

325

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

Energy Technology Data Exchange (ETDEWEB)

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 T{sub c} of 6.9?K, compared with the bulk T{sub c} (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 T{sub c} of 3 ML Pb films on Pb-SIC originates from the combined effects of quantum confinement and substrate-enhanced electron-phonon coupling.

Wang, Yilin; Li, Zhi; Wang, Lili; He, Ke; Ma, Xucun, E-mail: xcma@iphy.ac.cn [State Key Laboratory for Surface Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Chen, Mu [State Key Laboratory for Surface Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084 (China); Xue, Qi-Kun [State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084 (China)

2013-12-09

326

Hydrogen-bond imaging and engineering with a scanning tunnelling microscope  

International Nuclear Information System (INIS)

The scanning tunnelling microscope (STM) has been a valuable tool in surface science for the study of structures and electronic states of metal surfaces. The recent advance of STM as a state-of-the-art technique to probe and manipulate individual molecules has made it possible to investigate molecular dynamics and chemical reactions at the surface in a single-molecule limit. In this review paper, we present an overview of our recent work of H-bond imaging, manipulating and engineering at a metal surface. From individual water molecules, a variety of H-bonded structures including water clusters, hydroxyl clusters and water-hydroxyl complexes are assembled on Cu(1 1 0), whose properties and dynamics are studied in real space in collaboration with density-functional-theory calculations.

327

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-04-28

328

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 ?-? 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

329

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

330

Regulating the interactions of adsorbates on surfaces by scanning tunneling microscopy manipulation.  

Science.gov (United States)

Scanning tunneling microscopy (STM) manipulation has received wide attention in the surface science community since the pioneering work of Eigler to construct surface nanostructures in an atom by atom fashion. Lots of scientists have been inspired and devoted to study the surface issues with the help of STM manipulations and great achievements have been obtained. In this Minireview, we mainly describe the recent progress in applying STM manipulations to regulate the inter-adsorbate and adsorbate-substrate interactions on solid surfaces. It was shown that this technique could not only differentiate intermolecular interactions but also construct molecular nanostructures by regulating different kinds of inter-adsorbate interactions or adsorbate-substrate interactions. PMID:24888547

Sun, Qiang; Xu, Wei

2014-09-15

331

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

International Nuclear Information System (INIS)

In this work, we report a detailed analysis of the atomic and electronic structures of transition metal scanning tunneling microscopy tips: Rh, Pd, W, Ir, and Pt pyramidal models, and transition metal (TM) atom tips supported on the W surface, by means of ab initio density-functional theory methods. The d electrons of the apex atoms of the TM tips (Rh, Pd, W, Ir, and Pt tetrahedral structures) show different behaviors near the Fermi level and, especially for the W tip, dz2 states are shown to be predominant near the Fermi level. The electronic structures of larger pyramidal TM tip structures with a single apex atom are also reported. Their obtained density of states are thoroughly discussed in terms of the different d-electron occupations of the TM tips. (paper)

332

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

333

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

Science.gov (United States)

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

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

2011-12-01

334

In-gap states of In2O3 single crystals investigated by scanning tunneling spectroscopy  

International Nuclear Information System (INIS)

The influence of intrinsic point defects on the electronic structure of n-type In2O3 single crystals grown by two methods, namely chemical vapor transport and from the melt, was examined by scanning tunneling spectroscopy. This method is a very surface sensitive technique for measuring the local density of states. So far not resolved states within the fundamental band gap have been observed. The gap states have been studied at different crystals and after several annealing treatments in an oxidizing atmosphere. The spectroscopic results will be compared to state of the art DFT-calculations revealing hints on the origin of the gap states of In2O3 to be due to oxygen vacancies as well as indium and oxygen interstitials. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

335

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

CERN Document Server

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

336

Dislocation network at InN/GaN interface revealed by scanning tunneling microscopy  

International Nuclear Information System (INIS)

For heteroepitaxy of InN on GaN(0001) by molecular-beam epitaxy, the lattice misfit strain is relieved by misfit dislocations (MDs) formed at the interface between InN and GaN. Imaging by scanning tunneling microscopy (STM) of the surfaces of thin InN epifilms reveals line feature parallel to . Their contrast becomes less apparent for thicker epifilms. From the interline spacing as well as a comparison with transmission electron microscopy studies, it is suggested that they correspond to the MDs beneath the surface. The STM contrast originates from both the surface distortion caused by the local strain at MDs and the electronic states of the defects

337

Study of an organic nonlinear optical material for nanoscale data storage by scanning tunneling microscope  

Science.gov (United States)

In this paper, organic thin films of a nonlinear optical (NLO) material ((E)-1-ferrocenyl-2-(l-methyl-4-pyridiniumyl) ethylene iodide) were prepared by a vacuum deposition method. The typical I V curve of the film exhibits a favorable room-temperature bistability. Further recording experiments have been performed with a scanning tunneling microscope, which confirmed that the thin film of the donor ? acceptor NLO material could certainly be applied for nanoscale data storage. The average size of the recorded marks is about 1.5 nm. Mechanism analyses suggest that the formation of the recording dots is due to the local change of electrical property of the thin film, and the intermolecular charge transfer induced by an electric field is proposed as the reason for the change.

Qin, Z. B.; Wen, Y. Q.; Shang, Y. L.; Song, Y. L.; Wan, Y. Z.

2007-05-01

338

Selectivity mechanism of all ultra high vacuum scanning tunneling microscopy based selective area growth  

Science.gov (United States)

We describe a selective area growth based on ultra-high-vacuum (UHV)-scanning-tunneling-microscopy (STM) lithography. After nitridation of GaAs surfaces and selective depassivation by UHV-STM, an array of uniform 6.4±0.8-nm high GaAs dots was successfully grown on the depassivated areas (50 nm×50 nm) using trimethylgallium (TMG) and tertiarybutylarsine. On the side walls of dots, (114) or (117) facets appeared. It was found that unintentional growth on the nitrided mask surface is due to TMG decomposition on the nitrided surface. The unintentional growth can be suppressed by using an amorphous-like nitrided surface and by increasing the thickness of the nitrided surface layer, and consequently the selectivity is improved.

Kasu, Makoto; Makimoto, Toshiki; Kobayashi, Naoki

1998-06-01

339

Structure investigation of Cellobiohydrolase I from Trichoderma pseudokoningii S38 with a scanning tunneling microscope  

Science.gov (United States)

Cellobiohydrolase I (CBH I) was isolated from a cellulolytic fungal strain Trichoderma pseudokoningii S38, and its ultrastructure was investigated with a scanning tunneling microscope (STM). The STM images showed that the shape of intact CBH I was tadpole-like, consisting of a big head and a long tail. It could be deduced that the head domain was the core protein for the catalytic function, and the long tail was the cellulose binding domain for substrate binding. Thus, for this enzyme molecule, functional differentiation is reflected in the structure peculiarities. This is the first direct observation of the three-dimensional structure of intact CBH I from real space at nanometer scale. The functional mechanism is also discussed.

Zhang, Y. Z.; Liu, J.; Gao, P. J.; Ma, L. P.; Shi, D. X.; Pang, S. J.

340

Selective internal manipulation of a single molecule by scanning tunneling microscopy  

Science.gov (United States)

We have studied the adsorption of the polyaromatic molecule 1,4?-paratriphenyldimethylacetone, which we have nicknamed Trima. The originality of this linear molecule is that it was designed and synthesized to have two functionalities. First, chemisorb itself to the surface by its two ends rather like a bridge. Second, the central part of the molecule could then be rotated by injecting electrons with the tip of the scanning tunneling microscope (STM). The length of the molecule corresponds exactly to the spacing between five dimers in a row on the Si(100)-2×1 surface. We found that the molecule adsorbs as expected on the clean silicon surface by using complementary STM and synchrotron radiation studies. Manipulation of individual molecules with the STM tip showed selective internal modifications that were highly voltage dependent. These manipulations were found to be compatible with an electronic excitation of the ?-?* transition of the molecule.

Soukiassian, Laetitia; Mayne, Andrew J.; Comtet, Geneviève; Hellner, Lucette; Dujardin, Gérald; Gourdon, André

2005-04-01

 
 
 
 
341

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

342

Scanning Tunneling Microscopy and Spectroscopy of Conjugated Oligomers at the Liquid-Solid Interface  

Science.gov (United States)

Self-assembly - the spontaneous organization of molecules into stable, structurally well-defined aggregates - has been put forward as a possible paradigm for generating nanoscale templates under ambient conditions. A very convenient method for the formation of extended two-dimensional (2D) networks is physisorption at the liquid-solid interface. The preparation is relatively simple and scanning tunneling microscopy (STM) allows a detailed investigation of the structural aspects of the 2D patterns. A deep understanding and control of the spatial orientation and packing of pi-conjugated oligomers in self-assembled systems is indispensable for the development of future nanodevices. By means of STM, we have investigated the self-assembly of achiral and chiral pi-conjugated small organic molecules at the organic liquid-solid interface with submolecular resolution. In addition, by means of scanning tunneling spectroscopy (STS) we have investigated with molecular and submolecular resolution the electronic properties of isolated and stacked conjugated molecules at the liquid-solid interface. In the first part, we focus on the control of 2D molecular self-assembly of pi-conjugated systems driven by the molecular shape and/or by directional non-convalent interactions such as hydrogen bonding. Examples include alkylated molecules with a rhombus or triangle shaped pi-conjugated core, hydrogen bond forming p-phenylene vinylenes, and oligothiophenes. In the second part, we report on bias dependent imaging and STS experiments revealing information on the electronic properties of electron donor-acceptor-donor triads, and isolated and stacked oligothiophenes.

de Feyter, Steven

2006-03-01

343

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

International Nuclear Information System (INIS)

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

344

Imaging superconducting vortex cores and lattices with a scanning tunneling microscope  

Science.gov (United States)

The observation of vortices in superconductors was a major breakthrough in developing the conceptual background for superconducting applications. Each vortex carries a flux quantum, and the magnetic field decreases radially from the center. Techniques used to make magnetic field maps, such as magnetic decoration, give vortex lattice images in a variety of systems. However, strong type II superconductors allow penetration of the magnetic field over large distances, of the order of the magnetic penetration depth ?. Superconductivity survives up to magnetic fields where, for imaging purposes, there is no magnetic contrast at all. Static and dynamic properties of vortices are largely unknown at such high magnetic fields. Reciprocal space studies using neutron scattering have been employed to obtain insight into the collective behavior. But the microscopic details of vortex arrangements and their motion remain difficult to obtain. Direct real-space visualization can be made using scanning tunneling microscopy and spectroscopy (STM/S). Instead of using magnetic contrast, the electronic density of states describes spatial variations of the quasiparticle and pair wavefunction properties. These are of the order of the superconducting coherence length ?, which is much smaller than ?. In principle, individual vortices can be imaged using STM up to the upper critical field where vortex cores, of size ?, overlap. In this review, we describe recent advances in vortex imaging made with scanning tunneling microscopy and spectroscopy. We introduce the technique and discuss vortex images that reveal the influence of the Fermi surface distribution of the superconducting gap on the internal structure of vortices, the collective behavior of the lattice in different materials and conditions, and the observation of vortex lattice melting. We consider challenging lines of work, which include imaging vortices in nanostructures, multiband and heavy fermion superconductors, single layers and van der Waals crystals, studying current-driven dynamics and the liquid vortex phases.

Suderow, H.; Guillamón, I.; Rodrigo, J. G.; Vieira, S.

2014-06-01

345

Imaging by in situ Scanning Tunnelling Microscopy and its Nanotechnological Perspectives  

DEFF Research Database (Denmark)

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

Andersen, Jens Enevold Thaulov

2002-01-01

346

Scanning Tunneling Microscopy and Spectroscopy: I. Semimetals and Semiconductors. I. Atom-Resolved Imaging of DNA.  

Science.gov (United States)

The topographic and electronic structure of semimetal and semiconductor surfaces were investigated using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS), respectively. The long-range morphology and atomic -scale characteristics of cleaved materials, including highly oriented pyrolitic graphite (HOPG), boronated pyrolitic graphite (BPG), titanium disulfide, and gallium arsenide (GaAs), were revealed by STM performed in ultrahigh vacuum (UHV). Atom-resolved constant current topographs and current -imaging data, as well as barrier height information, are presented. Both point and line defects were observed on these surfaces. Visual evidence of coulombic screening caused by adsorption of charged species on n-GaAs(110) is provided. On BPG samples, containing up to 0.5% boron, boron substituent atoms appeared as protrusions approximately 3 A in diameter, with a density consistent with the known concentration. The BPG surface contained numerous line defects, including large-angle grain boundaries, and monolayer -deep etch pits. The effects of stress on the morphology of an annealed vicinal Si(111) wafer were explored. The height and orientation of step bunches, as well as terrace widths, on the (7 x 7) surface were determined. Line fault defects at step kinks were observed; theories for the origin and structure of these features based on stress relief are proposed. Current imaging tunneling spectroscopy (CITS) revealed differences between the adatom sites of the (7 x 7) surface. Atom-resolved barrier height images were also obtained. The measured barrier height was seen to depend strongly on the "cleanliness" of the STM tip. In addition, atom-resolved STM images of duplex DNA supported on a HOPG surface were obtained in UHV. These images revealed double-helical structure, major and minor groove alternation, base pairs, and atomic-scale substructure. The DNA dimensions derived from the STM data were in agreement with dimensions from x-ray crystallography for "random sequence" A-DNA. Cross-sectional profiles of the experimental STM data showed excellent correlation with the atomic contours of the van der Waals surface of A-DNA. Barrier height cross-sections showed general correlation with the atomic -scale topography over the phosphate-sugar backbone but distinct anticorrelation over the base pair region.

Driscoll, Robert James

1993-01-01

347

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

348

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

International Nuclear Information System (INIS)

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 direction of the Cu substrate, resulting in long range distortion. A large insulator-like band gap of ? 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.

349

A sub-Kelvin facility for cross-sectional scanning tunneling spectroscopy of metal-semiconductor heterostructures  

Energy Technology Data Exchange (ETDEWEB)

We investigate III-V semiconductors with magnetic dopants by spin-resolved scanning tunneling spectroscopy in order to achieve an atomic-scale understanding of magnetism in these systems. The method of choice for ex-situ grown heterostructures is cross-sectional scanning tunneling microscopy which enables to study their bulk properties by looking at nonpolar surfaces prepared by cleavage under ultra high vacuum conditions. For these experiments we have planned and constructed a low-temperature scanning tunneling microscopy facility with the possibility to move the sample laterally. The main chamber being commercially available consists of a Joule-Thomson cryostat with a scanning tunneling microscope. It has a base temperature of less than 1 K using {sup 4}He. There are two additional home built vacuum chambers for in-situ sample and tip preparation. These chambers include several electron beam evaporators, a customized sample heating manipulator, an electron beam heater and a sputter gun. The whole system is attached to a frame and supported by passive air damping legs. We show first test measurements.

Loeptien, Peter; Meier, Focko; Zhou, Lihui; Wiebe, Jens; Wiesendanger, Roland [Institute of Applied Physics, University of Hamburg (Germany)

2011-07-01

350

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

Science.gov (United States)

Different combinations of metal tips and oxide coatings have been tested for possible operation in electrochemical scanning tunneling microscopy. Silicon and magnesium oxides have been thermally evaporated onto gold and platinum-iridium tips, respectively. Two different thickness values have been explored for both materials, namely, 40 and 120 nm for silicon oxide and 20 and 60 nm for magnesium oxide. Alternatively, tungsten oxide has been grown on tungsten tips via electrochemical anodization. In the latter case, to seek optimal results we have varied the pH of the anodizing electrolyte between one and four. The oxide coated tips have been first inspected by means of scanning electron microscopy equipped with microanalysis to determine the morphological results of the coating. Second, the coated tips have been electrically characterized ex situ for stability in time by means of cyclic voltammetry in 1 M aqueous KCl supporting electrolyte, both bare and supplemented with K3[Fe(CN)6] complex at 10 mM concentration in milliQ water as an analyte. Only the tungsten oxide coated tungsten tips have shown stable electrical behavior in the electrolyte. For these tips, the uncoated metal area has been estimated from the electrical current levels, and they have been successfully tested by imaging a gold grating in situ, which provided stable results for several hours. The successful tungsten oxide coating obtained at pH=4 has been assigned to the WO3 form.

Salerno, Marco

2010-09-01

351

Resistivity of Endotaxial Silicide Nanowires Measured with a Scanning Tunneling Microscope  

Science.gov (United States)

In this project, a novel method is presented for measuring the resistivity of nanoscale metallic conductors (nanowires) using a variable-spacing 2-point method with a modified ultrahigh vacuum scanning tunneling microscope. An auxiliary field emission imaging method that allows for scanning insulating surfaces using a large gap distance (20nm) is also presented. Using these methods, the resistivity of self-assembled endotaxial FeSi2 nanowires (NWs) on Si(110) was measured. The resistivity was found to vary inversely with NW width, being rhoNW = 200 muO cm at 12 nm and 300 muO cm at 2 nm. The increase at small w is attributed to boundary scattering, and is fit to the Fuchs-Sondheimer model, yielding values of rho0 = 150 muO cm and lambda = 2.4 nm, for specularity parameter p = 0.5. These results are attributed to a high concentration of point defects in the FeSi2 structure, with a correspondingly short inelastic electron scattering length. It is remarkable that the defect concentration persists in very small structures, and is not changed by surface oxidation.

Tobler, Samuel

352

Chiral recognition in dimerization of adsorbed cysteine observed by scanning tunnelling microscopy.  

Science.gov (United States)

Stereochemistry plays a central role in controlling molecular recognition and interaction: the chemical and biological properties of molecules depend not only on the nature of their constituent atoms but also on how these atoms are positioned in space. Chiral specificity is consequently fundamental in chemical biology and pharmacology and has accordingly been widely studied. Advances in scanning probe microscopies now make it possible to probe chiral phenomena at surfaces at the molecular level. These methods have been used to determine the chirality of adsorbed molecules, and to provide direct evidence for chiral discrimination in molecular interactions and the spontaneous resolution of adsorbates into extended enantiomerically pure overlayers. Here we report scanning tunnelling microscopy studies of cysteine adsorbed to a (110) gold surface, which show that molecular pairs formed from a racemic mixture of this naturally occurring amino acid are exclusively homochiral, and that their binding to the gold surface is associated with local surface restructuring. Density-functional theory calculations indicate that the chiral specificity of the dimer formation process is driven by the optimization of three bonds on each cysteine molecule. These findings thus provide a clear molecular-level illustration of the well known three-point contact model for chiral recognition in a simple bimolecular system. PMID:11859364

Kühnle, Angelika; Linderoth, Trolle R; Hammer, Bjørk; Besenbacher, Flemming

2002-02-21

353

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

Science.gov (United States)

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

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

2004-01-01

354

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

355

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

356

Superconducting ?-ZrNClx probed by scanning-tunnelling and break-junction spectroscopy  

International Nuclear Information System (INIS)

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 (?p–p = 9–28 meV)over the area of 100 nm2. •Average gap ratio 2?/kBTc ? 10 is confirmed by both STS and BJTS. -- Abstract: Superconducting layered compound ?-ZrNClx (x = 0.7) with the critical temperature Tc = 13–14 K was investigated by means of scanning tunnelling microscopy/spectroscopy. The single-crystal domain facet of ?100 ?m2 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 ?-HfNClx with Tc = 24 K. Temperature, T, dependence of the dI/dV shows that the gap structure disappears above Tc ? 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 Tc ratio 2?(0)/kBTc ? 10 (kB is the Boltzmann constant), thereby pointing to the unusual superconducting properties of this compound

357

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

Science.gov (United States)

We present a method to characterize sub-10 nm capacitors and tunnel junctions by interferometric scanning microwave microscopy (iSMM) at 7.8 GHz. At such device scaling, the small water meniscus surrounding the iSMM tip should be reduced by proper tip tuning. Quantitative impedance characterization of attofarad range capacitors is achieved using an 'on-chip' calibration kit facing thousands of nanodevices. Nanoscale capacitors and tunnel barriers were detected through variations in the amplitude and phase of the reflected microwave signal, respectively. This study promises quantitative impedance characterization of a wide range of emerging functional nanoscale devices. PMID:25213481

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

2014-10-10

358

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

International Nuclear Information System (INIS)

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

359

Measurements of the superconducting gap of La-Sr-Cu-O with a scanning-tunneling microscope  

International Nuclear Information System (INIS)

We report the first tunneling measurements made on the new high-transition-temperature perovskite superconductors. These were obtained using an ultrahigh-vacuum low-temperature scanning-tunneling microscope. The superconducting gap of a La/sub 1.85/Sr/sub 0.15/CuO/sub 4-//sub y/ sample is 12 +- 3 mV, and the onset T/sub c/ is 40 K, from which 2?/k/sub B/T/sub c/ = 7 +- 2. The possibility that this surprisingly high ratio may be due to a mechanism other than superconductivity is discussed

360

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

Science.gov (United States)

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

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

2014-10-01

 
 
 
 
361

Luttinger liquid behaviour of Li0.9Mo6O17 studied by scanning tunnelling microscopy  

International Nuclear Information System (INIS)

Scanning tunnelling spectroscopy (STS) was used to study the Luttinger liquid behaviour of the purple bronze Li0.9Mo6O17 in the temperature range 5 K < T < 300 K. In the entire temperature range the suppression of the density of states at the Fermi energy can be fitted very well by a model describing the tunnelling into a Luttinger liquid at ambient temperature. The power-law exponent extracted from these fits reveals a significant increase above 200 K. It changes from ? = 0.6 at low temperature to ? = 1.0 at room temperature.

362

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.

363

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

International Nuclear Information System (INIS)

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

364

Scanning tunneling microscopy studies of surface structures of icosahedral aluminum-copper-iron quasicrystals  

Science.gov (United States)

We investigate the atomic structure of fivefold surface of icosahedral (i-) Al-Cu-Fe quasicrystal using scanning tunneling microscopy (STM) under ultra high vacuum (UHV). Annealing the sputtered surface at appropriate temperature produces a step-terrace structure on the surface. Our STM analysis indicates that the terraces are separated with primarily two stepheights in the ratio of t=5+1 /2 , a characteristic ratio in quasiperiodic structures. The measurements agree with the results from dynamical low energy electron diffraction (LEED) calculations. The spatial distribution of stepheights along the fivefold axis does not follow the quasiperiodic Fibonacci sequence. The existence of such stacking defects in the bulk structure is confirmed with the screw dislocations often observed in the STM scans. The first atomic resolution STM images on this type of material are obtained. The flat terraces are dominated with "ten-petal flower-like" motif, locally arranged with fivefold symmetry. Similar structural features can be identified in the atomically-dense planes generated from one of the available bulk structure models. Based on these results, we conclude that the fivefold i-AlCuFe surface corresponds to a two-dimensional cut of the bulk material. After examining the clean surface, we investigate the nucleation and growth of aluminium metallic thin films on the quasicrystalline i-Al-Cu-Fe fivefold surface. Upon deposition at room temperature, aluminium adatoms nucleate as pentagonal "starfish" with uniform size and in the same orientation. The same structure features are observed for different fluxes at low coverages. Based on the experimental results and the available bulk structure model, we identify the specific nucleation sites on the substrate and develop a model for the formation of the pentagonal starfish.

Cai, Tanhong

2001-07-01

365

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

DEFF Research Database (Denmark)

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

Chorkendorff, Ib

1994-01-01

366

Self-organized atomic gold nanowires on Ge(001) revealed by scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

Atomic nanowires have become objects of intense research, as they host a wealth of physical phenomena not encountered in three-dimensional solids. They are synthesized by self-organization of metal adatoms on suitable semiconducting substrates that guide chain formation. Thus far, examples for quasi one-dimensional (1D) systems have been found where the Fermi surface hosts a charge density wave (CDW). This can be observed below room temperature in systems on Si(111) or high-index variants thereof. However, the ease of CDW condensation points at still significant coupling to the second dimension. In the search for better defined 1D systems, we have identified self-organized Au-induced chains on Ge(001) which grow in a long-range c(8 x 2) phase and exhibit metallic behavior. In using scanning tunneling microscopy, we find that the wires are spaced by several Ge lattice constants, while their electron density is strictly confined laterally. In turn, the metallic charge cloud is spread out very evenly in chain direction, as seen for a large range of bias values. Such exceptional degree of confinement may open a pathway to study non-Fermi liquid physics. The talk will review the various structural ingredients of this exceptional 1D electron system.

Blumenstein, Christian; Meyer, Sebastian; Schaefer, Joerg; Claessen, Ralph [Physikal. Institut, Universitaet Wuerzburg (Germany)

2009-07-01

367

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

Science.gov (United States)

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)-(2×1):H surface with sub-surface P doping and discuss the results in comparison to the Bardeen and Tersoff-Hamann methods.

Lin, Haiping; Rauba, Janosch M. C.; Thygesen, Kristian S.; Jacobsen, Karsten W.; Simmons, Michelle Y.; Hofer, Werner A.

2010-12-01

368

Ultrafast Electron Emission and Molecular Dynamics in a Scanning Tunneling Microscope  

Science.gov (United States)

In pursuit of measurements at the limits of space and time relevant to chemistry, we have developed the cross-polarized double beat (CPDB) method. This method employs phase modulation in a Mach-Zehnder type interferometer to enable signal modulation without intensity modulation of the incident light. The method is applied to a scanning tunneling microscope (STM) tip, where the ultrafast induced electron emission properties are measured. The mechanism of electron emission is found to be the result of a nonlinear excitation of the surface plasmon, followed by a Fowler-Nordheim type field emission. This is determined through analysis of the dependence of the current on laser power, incident polarization, and delay time (in a pump-probe type measurement). We have also discovered latent time information in traditional STM measurements on Zinc(II) Etioporphyrin. The Jahn-Teller active electron of the anion couples the vibrational and electronic densities, allowing complete reconstruction of its vibrational superposition from the topography and electroluminescent spectrum. ZnEtio- also undergoes a spin flip transition which allows it to be used as a tunable molecular switch.

Perdue, Shawn Michael

369

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

370

Imaging Molecular Interaction of NO on Cu(110) with a Scanning Tunneling Microscope.  

Science.gov (United States)

Molecular interaction on metal surfaces is one of the central issues of surface science for the microscopic understanding of heterogeneous catalysis. In this Personal Account, I review the recent studies on NO/Cu(110) employing a scanning tunneling microscope (STM) to probe and control the molecule-molecule interaction on the surface. An individual NO molecule was observed as a characteristic dumbbell-shaped protrusion, visualizing the 2?* orbital. By manipulating the intermolecular distance with the STM, the overlap of the 2?* orbital between two NO molecules was controlled. The interaction causes the formation of the bonding and antibonding orbitals below and above the Fermi level, respectively, as a function of the intermolecular distance. The 2?* orbital also plays a role in the reaction of NO with water molecules. A water molecule donates a H-bond to NO, giving rise to the down-shift of the 2?* level below the Fermi level. This causes electron transfer from the substrate to NO, weakening, and eventually rupturing, the N-O bond. The facile bond cleavage by water molecules has implications for the catalytic reduction of NO under ambient conditions. PMID:25092114

Okuyama, Hiroshi

2014-10-01

371

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

Science.gov (United States)

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

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

2012-06-01

372

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2008-05-12

373

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

International Nuclear Information System (INIS)

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

374

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

375

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

376

Electrical Conductivity of Organic and Inorganic Nanowires Measured by Multi-probe Scanning Tunneling Microscopes  

Science.gov (United States)

Since 1998 [1], the authors and co-workers have developed multi-probe scanning tunneling microscopes (MPSTMs), in which two, three or four probes are operated independently. All probes of the MPSTMs can observe STM images independently, but the main role of the multiple probes is to be used as nanoscale electrodes that can contact any points selected in an observed STM image. It is therefore possible to measure electrical conductivity at the nanoscale through the multiple probes. By using MPSTMs and related methods, we measured the electrical conductivity of organic and inorganic nanowires, i.e., single-wall carbon nanotubes (SWCNTs), erbium disilicide (ErSi2) metallic nanowires, and single polydiacetylene (PDA) molecular wires. For a SWCNT and an ErSi2 nanowire, ballistic conduction was observed at lengths less than about 500 and 20 nm, respectively, at room temperature. For a PDA molecular wire, polaron formation due to charge injection caused by applying a voltage to an STM tip placed close to the PDA molecular wire was observed, and when the voltage exceeded a critical value, the PDA molecular wire changed into a metallic state. [1] M. Aono, C.-S. Jiang, T. Nakayama, T. Okuda, S. Qiao, M. Sakurai, C. Thirstrup, Z.-H. Wu: Oyo Buturi (Applied Physics) 67, 1361 (1998) (in Japanese); A brief English abstract is available on INSPEC.

Aono, Masakazu

2006-03-01

377

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

378

Interfacial Electronic and Magnetic Coupling in Organic-metal System Studied by Scanning Tunneling Microscopy  

Science.gov (United States)

Organic materials have drawn much attention in spintronics studies because of their tunable properties by functional groups and potential to achieve molecular magnets. An important factor influencing these properties is the interfacial effect. In organic-metal systems, different interfaces lead to strong modulation of electronic structures and even magnetic behaviors like spin coupling. In our study, Mn-phthalocyanine (MnPc) deposited on Cu(111) surface have been measured by scanning tunneling microscopy (STM) and spectroscopy (STS) at 4.5 K. With different deposition amount, MnPc are adsorbed as isolated molecules or in an ordered assembled structure. From STS curves, assembled MnPc possess a broadened state near the onset of Cu(111) surface state comparing to islolated ones. According to ab initio calculation, distance between the central Mn atom and the substrate in assembled molecules is reduced due to intermolecular interaction and affects the electronic structures. Magnetic behaviors of MnPc on ferromagnetic metal substrate are further investigated by spin-polarized STM (SP-STM). Spin contrast of isolated molecules on Co nanoislands on Cu(111) is found near the Fermi level in STS maps, which is considered to be ferromagnetic coupling between MnPc and Co islands.

Chu, Yu-Hsun; Hsu, C. H.; Hsu, P. J.; Hsieh, W. J.; Lu, C. I.; Chen, S. W.; Butler, C. J.; Kaun, Chao-Cheng; Lin, Minn-Tsong

2012-02-01

379

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

Energy Technology Data Exchange (ETDEWEB)

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

Guo Xinli; Fujita, Daisuke; Onish, Keiko, E-mail: guo.xinli@seu.edu.cn [Advanced Nano Characterization Center, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan)

2010-01-29

380

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-04-15

 
 
 
 
381

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

International Nuclear Information System (INIS)

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

382

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

Science.gov (United States)

Using ultrahigh-vacuum low-temperature scanning tunneling microscopy and spectroscopy combined with first principles density functional theory calculations, we have investigated structural and electronic properties of pristine and potassium (K)-deposited picene thin films formed in situ on a Ag(111) substrate. At low coverages, the molecules are uniformly distributed with the long axis aligned along the [11bar 2] direction of the substrate. At higher coverages, ordered structures composed of monolayer molecules are observed, one of which is a monolayer with tilted and flat-lying molecules resembling a (1bar 10) plane of the bulk crystalline picene. Between the molecules and the substrate, the van der Waals interaction is dominant with negligible hybridization between their electronic states; a conclusion that contrasts with the chemisorption exhibited by pentacene molecules on the same substrate. We also observed a monolayer picene thin film in which all molecules were standing to form an intermolecular ? stacking. Two-dimensional delocalized electronic states are found on the K-deposited ? stacking structure.

Yoshida, Yasuo; Yang, Hung-Hsiang; Huang, Hsu-Sheng; Guan, Shu-You; Yanagisawa, Susumu; Yokosuka, Takuya; Lin, Minn-Tsong; Su, Wei-Bin; Chang, Chia-Seng; Hoffmann, Germar; Hasegawa, Yukio

2014-09-01

383

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

International Nuclear Information System (INIS)

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

384

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

DEFF Research Database (Denmark)

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

Tison, Yann; Nielsen, Kenneth

2012-01-01

385

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

386

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

387

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.

Thygesen, Kristian Sommer; Jacobsen, Karsten Wedel

2010-01-01

388

A new variable temperature solution-solid interface scanning tunneling microscope  

Science.gov (United States)

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

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

2014-10-01

389

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

International Nuclear Information System (INIS)

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

390

Versatile bottom-up construction of diverse macromolecules on a surface observed by scanning tunneling microscopy.  

Science.gov (United States)

The heterocoupling of organic building blocks to give complex multicomponent macromolecules directly at a surface holds the key to creating advanced molecular devices. While "on-surface" synthesis with prefunctionalized molecules has recently led to specific one- and two- component products, a central challenge is to discover universal connection strategies that are applicable to a wide range of molecules. Here, we show that direct activation of C-H bonds intrinsic to ?-functional molecules is a highly generic route for connecting different building blocks on a copper surface. Scanning tunneling microscopy (STM) reveals that covalent ?-functional macromolecular heterostructures, displaying diverse compositions, structures and topologies, are created with ease from seven distinct building blocks (including porphyrins, pentacene and perylene). By exploiting differences in C-H bond reactivity in the deposition and heating protocols we also demonstrate controlled synthesis of specific products, such as block copolymers. Further, the symmetry and geometry of the molecules and the surface also play a critical role in determining the outcome of the covalent bond forming reactions. Our "pick-mix-and-link" strategy opens up the capability to generate libraries of multivariate macromolecules directly at a surface, which in conjunction with nanoscale probing techniques could accelerate the discovery of functional interfaces. PMID:25191836

Haq, Sam; Hanke, Felix; Sharp, John; Persson, Mats; Amabilino, David B; Raval, Rasmita

2014-09-23

391

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

392

Scanning tunneling microscopy observation of self-assembled monolayers of strapped porphyrins.  

Science.gov (United States)

In this paper, we reveal that the free-base and zinc strapped porphyrins possessing long alkyl chains, C 24OPP-HQ and Zn(C 24OPP-HQ), respectively, can be arranged on surfaces. We used scanning tunneling microscopy (STM) to observe alkyl-chain-assisted self-assembled monolayers (SAMs) of these strapped porphyrins at the solid-liquid interface. STM images revealed that the strapped benzene moiety was detectable on the porphyrin core: that is, the strapped porphyrins could be differentiated from nonstrapped analogues. We compared the population of the nonstrapped porphyrin (C 24OPP) and either of the strapped porphyrins C 24OPP-HQ or Zn(C 24OPP-HQ) in the mixed SAMs. We then confirmed that Zn(C 24OPP-HQ) is more favorably incorporated in the mixed SAMs than C 24OPP-HQ. From (1)H NMR spectroscopic and X-ray crystallographic analyses, we concluded that the factors increasing the population of Zn(C 24OPP-HQ) in the mixed SAMs are the enhanced rigidity of the porphyrin core by the zinc coordination and the flat structure of the porphyrin moiety in the saddle conformation. This study demonstrates that strapped porphyrins possessing long alkyl chains are available to arrange the functional modules on the surface via chemical modification on the strapped moiety. PMID:18922028

Ikeda, Taichi; Asakawa, Masumi; Miyake, Koji; Goto, Midori; Shimizu, Toshimi

2008-11-18

393

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

International Nuclear Information System (INIS)

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

394

Scanning tunneling microscopy/spectroscopy on perovskite oxide thin films deposited in situ.  

Science.gov (United States)

Complex oxide surfaces and interfaces, consisting of two or more cations and oxygen anions, have attracted a great deal of attention because their properties are crucial factors in the performance of catalysts, fuel cells, and Li-ion batteries. However, atomic-scale investigations of these oxide surfaces have been hindered because of the difficulties in surface preparation. Here, we demonstrate atomic-scale surface studies of complex perovskite oxides and the initial growth processes in oxide epitaxial films deposited on (?13?×??13)-R33.7° reconstructed SrTiO3 (001) substrates using a scanning tunneling microscope integrated with a pulsed laser deposition system. The atomically ordered, reconstructed SrTiO3 (001) surface is stable under the typical conditions necessary for the growth of oxide thin films, and hence is considered suitable for the study of the initial growth processes in oxide films. The atomic-scale microscopic/spectroscopic characterizations performed here shed light on the microscopic origin of electronic properties observed in complex oxides and their heterostructures. PMID:25224101

Hitosugi, Taro; Shimizu, Ryota; Ohsawa, Takeo; Iwaya, Katsuya

2014-10-01

395

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

CERN Document Server

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

Meinel, K; Ammer, C; Beckmann, A; Neddermeyer, H

1997-01-01

396

Covalently Immobilised Cytochrome C Imaged by In Situ Scanning Tunnelling Microscopy  

DEFF Research Database (Denmark)

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

Andersen, Jens Enevold Thaulov; Foverskov, Carl Erik

1997-01-01

397

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

Science.gov (United States)

Using ultrahigh-vacuum low-temperature scanning tunneling microscopy and spectroscopy combined with first principles density functional theory calculations, we have investigated structural and electronic properties of pristine and potassium (K)-deposited picene thin films formed in situ on a Ag(111) substrate. At low coverages, the molecules are uniformly distributed with the long axis aligned along the [112¯] direction of the substrate. At higher coverages, ordered structures composed of monolayer molecules are observed, one of which is a monolayer with tilted and flat-lying molecules resembling a (11¯0) plane of the bulk crystalline picene. Between the molecules and the substrate, the van der Waals interaction is dominant with negligible hybridization between their electronic states; a conclusion that contrasts with the chemisorption exhibited by pentacene molecules on the same substrate. We also observed a monolayer picene thin film in which all molecules were standing to form an intermolecular ? stacking. Two-dimensional delocalized electronic states are found on the K-deposited ? stacking structure. PMID:25240362

Yoshida, Yasuo; Yang, Hung-Hsiang; Huang, Hsu-Sheng; Guan, Shu-You; Yanagisawa, Susumu; Yokosuka, Takuya; Lin, Minn-Tsong; Su, Wei-Bin; Chang, Chia-Seng; Hoffmann, Germar; Hasegawa, Yukio

2014-09-21

398

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

Science.gov (United States)

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

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

1996-06-01

399

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

International Nuclear Information System (INIS)

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

400

Local low-energy electrical excitation of localized and propagating surface plasmons with a scanning tunneling microscope  

Science.gov (United States)

The highly confined nature of the fields from surface plasmons makes them excellent candidates for future nano-optical devices. Most often, optical excitation is used to excite surface plasmons. However, a local, low energy, electrical method for surface plasmon excitation would be preferable for device applications. The scanning tunneling microscope (STM) is an ideal, low energy, local source of electrons that can excite both localized (LSP) and propagating surface plasmons (SPP). Its local nature, along with the ability to precisely position the excitation source and the absence of any background light from the excitation are essential for our experiments. We have used this technique to locally excite surface plasmons on a variety of metal structures. In our setup, the STM is coupled to an inverted optical microscope and the resulting emitted light is collected through the glass substrate. In such a configuration, both the light emitted from localized plasmons as well as the leakage radiation from propagating surface plasmons may be recorded. Both real plane (spatial information) and Fourier plane (angular information) images may be obtained, as well as emission spectra. In this article we will present the results of STM-SPP excitation on thin Au films on glass and investigate the effect of Au film thickness on the SPP propagation length. These results demonstrate the unique features of STM-excited SPPs: the STM plasmon source may be considered equivalent to a series of oscillating vertical point dipoles, and the resulting plasmons consist of a 2D circular wave with a broadband spectrum. These properties are then exploited to study how SPPs scatter into photons from super and sub-wavelength sized holes. It is found that the larger the hole diameter, the more directional the scattering light. From a type of SPP-Young's experiment we determine that the orientation of the electric field is maintained when SPPs are scattered into photons at holes.

Boer-Duchemin, Elizabeth; Wang, Tao; Le Moal, Eric; Rogez, Benoît; Comtet, Geneviève; Dujardin, Gérald

2014-05-01

 
 
 
 
401

Harmonic oscillator wave functions of a self-assembled InAs quantum dot measured by scanning tunneling microscopy.  

Science.gov (United States)

InAs quantum dots embedded in an AlAs matrix inside a double barrier resonant tunneling diode are investigated by cross-sectional scanning tunneling spectroscopy. The wave functions of the bound quantum dot states are spatially and energetically resolved. These bound states are known to be responsible for resonant tunneling phenomena in such quantum dot diodes. The wave functions reveal a textbook-like one-dimensional harmonic oscillator behavior showing up to five equidistant energy levels of 80 meV spacing. The derived effective oscillator mass of m* = 0.24m0 is 1 order of magnitude higher than the effective electron mass of bulk InAs that we attribute to the influence of the surrounding AlAs matrix. This underlines the importance of the matrix material for tailored QD devices with well-defined properties. PMID:23777509

Teichmann, Karen; Wenderoth, Martin; Prüser, Henning; Pierz, Klaus; Schumacher, Hans W; Ulbrich, Rainer G

2013-08-14

402

Newly developed low-temperature scanning tunneling microscope and its application to the study of superconducting materials  

International Nuclear Information System (INIS)

A newly developed scanning tunneling microscope (STM) capable of operating at room temperature, 77 K, and 4.2 K is presented. This compact STM has a highly symmetric and rigid tunneling unit designed as an integral frame except the coarse and fine adjustment parts. The tunneling unit is incorporated into a small vacuum chamber that is usually pumped down to 2x10-4 Pa to avoid water contamination. The fine mechanic adjustment makes the tip approach the sample in 5 nm steps. The coarse adjustment not only changes the distance between the tip and the sample, but also adjusts the tip to be normal to the surface of the sample. With this low-temperature STM atomic resolution images of Bi-2212 single-crystal and large-scale topographies of a YBa2Cu3O7 thin film are observed at 77 K

403

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

CERN Document Server

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

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

2006-01-01

404

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

405

Silicon nanoelectronic devices fabricated by ultra-high vacuum, scanning tunneling microscope nanolithography  

Science.gov (United States)

As the critical dimension and density of MOSFETs continues to scale in accordance with Moore's Law, alternatives to conventional CMOS technology are being investigated. One such alternative is based on scanning tunneling microscope (STM) H-resist nanolithography. This technique involves the patterning of the hydrogen passivated silicon surfaces under ultra-high vacuum (UHV) conditions. Hydrogen atoms are selectively removed from the surface via electron stimulated desorption, yielding highly reactive bare silicon dangling bonds. These function as adsorption sites for subsequent chemical vapor deposition (CVD) reactions with dopant precursor molecules such as PH3, B2H6, and AsH3. The extreme high resolution of the STM allows the creation of atom-scale dopant patterns. Low temperature Si overgrowth serves to electrically activate dopants while limiting dopant redistribution. The low charged-defect density provided by complete epitaxial encapsulation could allow the fabrication of a solid state quantum computer based on phosphorus single-atom nuclear or electron spin quantum bits. In contrast to other approaches, this technique is compatible with conventional silicon microfabrication and large scale integration is plausible. Electrical and magnetotransport measurements are carried out at low temperature on various device geometries. Two-dimensional unpatterned delta-doped samples yield ohmic conduction and sharp positive magnetoconductance: a characteristic of a weakly localized electron gas. The 2D electron density (˜ 1 x 1014 cm-2) is significantly higher than modulation-doped structures. This allows the lateral patterning of low-dimensional devices without the formation of undesirable carrier depletion regions. STM-patterned nanowires 12-200 nm wide and 750 nm long patterned by STM nanolithography are electrically connected to the outside world using ion implanted contacts. Nanowires ? 30 nm wide exhibit ohmic conduction. Magnetoconductance curves are analyzed in terms of weak localization theory. Nonlinear conduction resembling coulomb blockade is observed in a 12 nm wide nanowire and may be due to the formation on unintentional tunnel barriers at the nanowire contacts. The fabrication process outlined within may be extended toward the fabrication of single electron transistors (SETs).

Kline, Jeffrey Scott

406

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

407

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

International Nuclear Information System (INIS)

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.

408

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.

409

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

Science.gov (United States)

We report on a theoretical interpretation of scanning tunneling potentiometry (STP), formulated within the Keldysh non-equilibrium Green?s function description of quantum transport. By treating the probe tip as an electron point source/sink, it is shown that this approach provides an intuitive bridge between existing theoretical interpretations of scanning tunneling microscopy and STP. We illustrate this through ballistic transport simulations of the potential drop across an opaque graphene grain boundary, where atomistic features are predicted that might be imaged through high resolution STP measurements. The relationship between the electrochemical potential profile measured and the electrostatic potential drop across such a nanoscale defect is also explored in this model system.

Bevan, Kirk H.

2014-10-01

410

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

411

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

Science.gov (United States)

We report on a theoretical interpretation of scanning tunneling potentiometry (STP), formulated within the Keldysh non-equilibrium Green's function description of quantum transport. By treating the probe tip as an electron point source/sink, it is shown that this approach provides an intuitive bridge between existing theoretical interpretations of scanning tunneling microscopy and STP. We illustrate this through ballistic transport simulations of the potential drop across an opaque graphene grain boundary, where atomistic features are predicted that might be imaged through high resolution STP measurements. The relationship between the electrochemical potential profile measured and the electrostatic potential drop across such a nanoscale defect is also explored in this model system. PMID:25248965

Bevan, Kirk H

2014-10-17

412

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

413

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