WorldWideScience
1

Scanning-tunnelling spectra of cuprates.  

Science.gov (United States)

The study of bosonic modes that couple to the charge carriers is a key element in understanding superconductivity. Using atomic-resolution scanning-tunnelling microscopy (STM) to extract the spectrum of these modes in the high-temperature superconductor Bi2Sr2CaCu2O(8+delta), Lee et al. find a mode whose frequency does not depend on doping but that changes on isotopic substitution of 16O with 18O. From this, they infer a role for lattice modes (phonons). However, examination of their data reveals a weaker, but distinct, feature that has all the characteristics of the magnetic excitation identified as the bosonic mode in other competing experiments. We therefore suggest that the lattice mode seen by Lee et al. is not relevant to superconductivity and is due to inelastic tunnelling through the insulating oxide layer. PMID:17344807

Hwang, Jungseek; Timusk, Thomas; Carbotte, Jules P

2007-03-01

2

Ultrafast scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

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

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

1995-09-01

3

Femtosecond scanning tunneling microscope  

Energy Technology Data Exchange (ETDEWEB)

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

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

1998-11-01

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.

The Concord Consortium

2011-12-11

5

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

6

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

7

Cryomagnetic scanning tunneling spectroscopy study of multi-gap spectra in superconducting 2H-NbSe2  

OpenAIRE

Scanning tunneling spectroscopy was performed on single crystals of superconducting 2H-NbSe2, at 300 mK and in a magnetic field, up to 5 T, applied parallel to the ab-plane. This novel field geometry allows the quasiparticle density-of-states spectrum to be measured under finite superfluid momentum, while avoiding contributions from the vortex-core bound states. At zero field, we observed a fully-gapped conductance spectrum with both gap-edge peaks and sub-gap kinks. These s...

Fridman, I.; Kloc, C.; Wei, J. Y. T.

2011-01-01

8

Theory of Scanning Tunneling Microscopy  

OpenAIRE

This lecture has been given at the 45th Spring School: Computing Solids: Models, Ab-initio Methods and Supercomputing organized at the Forschungszentrum J\\"ulich. The goal of this manuscript is to review the basics behind the theory accompanying Scanning Tunneling Microscopy.

Lounis, Samir

2014-01-01

9

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

10

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

CERN Document Server

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

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

2006-01-01

11

Scanning Tunneling Microscopy of Manganites  

Science.gov (United States)

We have built a scanning tunneling microscope (STM) which employs a mechanical coarse approach mechanism. We have tested the mechanical and electronic components of the system and calibrated the piezoelectric scanning mechanism by imaging highly ordered pyrolytic graphite (HOPG) at room temperature. Atomic resolution HOPG images were obtained when the STM was placed inside a vibration isolated liquid helium dewar. We have also scanned single crystals and thin-films of hole-doped manganese oxides (manganites) and obtained images on the scale of about 100 nm to about 10 nm. After obtaining satisfactory images at room temperature, we will cool the apparatus first down to liquid nitrogen temperature (77 K) and then down to liquid helium temperature (4.2 K) to investigate micrometer and nanometer scale phase separation in manganites.

Mazzaccari, Icon; Jeen, Hyoungjeen; Biswas, Amlan

2011-03-01

12

Low-temperature scanning tunneling spectroscopy  

International Nuclear Information System (INIS)

A scanning tunneling microscope (STM) was designed and built to operate at liquid helium temperature and was used to measure highly localized electron tunneling spectroscopy. Several instruments were built, all capable of operating in many different environments: air, vacuum, liquid helium and in a transfer gas. An adaptation of one particular design was made into an atomic force microscope capable of operating at low temperatures. Using a low temperature STM, three adsorbed molecular species (liquid crystals, sorbic acid, and carbon monoxide), deposited on a graphite substrate, have been imaged at 4.2K. The inelastic tunneling spectra of these adsorbates show strong peaks in dI/dV vs V curves at energies that correspond to known vibrational modes. The increase in conductance at the onset of inelastic tunneling was measured to be as high as 100 times. The spatial variation of the spectra was measured and was seen to change dramatically on the scale of angstroms, suggesting that individual molecular bonds could be measured. A theoretical model is presented to explain the contrast seen in the STM images of adsorbed molecules, thereby explaining why adsorbed molecules appear to be more conductive than the background. The microscope proved very useful for measuring the energy gap of high temperature superconductors. These materials often have submicron grain sizes. For LaSrCuO, YBaCuO, and BiCaSrCuO, the conductance curves showed a large energy gap suggesting a strongly ca large energy gap suggesting a strongly coupled superconductor. The conductance curves also indicated that intergrain tunneling may occur and that the background conductance varied linearly with the applied voltage. The crystalline structure of Bi2Sr2CaCu2O8+? was imaged by an STM operating in air and in ultra-high vacuum

13

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

14

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

15

Scanning Tunneling Microscopy of Semiconductors  

Science.gov (United States)

This dissertation consists of two parts. In the first part, we discuss the design and construction of two Scanning Tunneling Microscopes (STM) that were operated in air, liquid, and ultra-high vacuum (UHV). Atomic resolution images were achieved on both STMs. Two different configurations were adopted in our STMs: The first STM was constructed using internal viton O-ring vibration-isolation. It operates in air and in liquid with a vertical resolution of 0.4A. The second STM is UHV compatible with in situ sample change and cleavage facilities. It is able to operate without an internal isolation stage and provides a vertical resolution of 0.1A. In the second part of the dissertation, we present the results of studies of a variety of surfaces. We imaged the cleaved HgCdTe and HgMnTe surfaces in glycerin solvent. Using time-lapse images, we studied dynamical processes on these semiconductor surfaces: the filling-in of craters and the formation of steps. We estimate that the surface diffusion constant is in the range of 10^{-18 } m^2/sec. to 10 ^{-19} m^2/sec. We also studied InSb, InAs, and InP (110) surfaces in UHV. We obtained the first atomic resolution images on all three indium compound surfaces. A new c(4 x 6) surface reconstruction has been discovered on the cleaved InSb(110) surface. In addition to the first-layer structures, we have also studied STM imaging of second-layer structures. Our experimental results and theoretical results show that STM is indeed able to image the second-layer structures under special circumstances. We have studied steps on the cleaved (110) surfaces. Dimerization models have been proposed to explain the periodicity along (111) and (112) step edges. In addition to imaging the surface, we have developed several methods of manipulating and modifying surfaces by STM. For example: Dots as small as 8A radius can be controllably fabricated on the InSb(110) surface using a tunneling tip. Features on a gold surface can be selectively smoothed, and lines are able to be "chiseled" on the gold surface. These techniques may find important application in surface nano-lithography.

Liang, Yong

16

Investigation into scanning tunnelling luminescence microscopy  

International Nuclear Information System (INIS)

This work reports on the development of a scanning tunnelling luminescence (STL) microscope and its application to the study of Ill-nitride semiconductor materials used in the production of light emitting devices. STL microscopy is a technique which uses the high resolution topographic imaging capabilities of the scanning tunnelling microscope (STM) to generate high resolution luminescence images. The STM tunnelling current acts as a highly localised source of electrons (or holes) which generates luminescence in certain materials. Light generated at the STM tunnelling junction is collected concurrently with the height variation of the tunnelling probe as it is scanned across a sample surface, producing simultaneous topographic and luminescence images. Due to the very localised excitation source, high resolution luminescence images can be obtained. Spectroscopic resolution can be obtained by using filters. Additionally, the variation of luminescence intensity with tunnel current and with bias voltage can provide information on recombination processes and material properties. The design and construction of a scanning tunnelling luminescence microscope is described in detail. Operating under ambient conditions, the microscope has several novel features, including a new type of miniature inertial slider-based approach motor, large solid-angle light collection optical arrangement and a tip-height regulation system which requires the minimum of operator input. (author)e minimum of operator input. (author)

17

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

18

Theoretical Description of Scanning Tunneling Potentiometry  

OpenAIRE

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

19

Scanning tunneling microscope assembly, reactor, and system  

Science.gov (United States)

An embodiment of a scanning tunneling microscope (STM) reactor includes a pressure vessel, an STM assembly, and three spring coupling objects. The pressure vessel includes a sealable port, an interior, and an exterior. An embodiment of an STM system includes a vacuum chamber, an STM reactor, and three springs. The three springs couple the STM reactor to the vacuum chamber and are operable to suspend the scanning tunneling microscope reactor within the interior of the vacuum chamber during operation of the STM reactor. An embodiment of an STM assembly includes a coarse displacement arrangement, a piezoelectric fine displacement scanning tube coupled to the coarse displacement arrangement, and a receiver. The piezoelectric fine displacement scanning tube is coupled to the coarse displacement arrangement. The receiver is coupled to the piezoelectric scanning tube and is operable to receive a tip holder, and the tip holder is operable to receive a tip.

Tao, Feng; Salmeron, Miquel; Somorjai, Gabor A

2014-11-18

20

An ultrafast terahertz scanning tunnelling microscope  

Science.gov (United States)

Ultrafast studies of excitations on the nanometre scale are essential for guiding applications in nanotechnology. Efforts to integrate femtosecond lasers with scanning tunnelling microscopes (STMs) have yielded a number of ultrafast STM techniques, but the basic ability to directly modulate the STM junction bias while maintaining nanometre spatial resolution has been limited to ~10 ps (refs 7,8) and has required specialized probe or sample structures. Here, without any modification to the STM design, we modulate the STM junction bias by coupling terahertz pulses to the scanning probe tip of an STM and demonstrate terahertz-pulse-induced tunnelling in an STM. The terahertz STM (THz-STM) provides simultaneous subpicosecond (STM accesses an ultrafast tunnelling regime that opens the door to subpicosecond scanning probe microscopy of materials with atomic resolution.

Cocker, Tyler L.; Jelic, Vedran; Gupta, Manisha; Molesky, Sean J.; Burgess, Jacob A. J.; Reyes, Glenda De Los; Titova, Lyubov V.; Tsui, Ying Y.; Freeman, Mark R.; Hegmann, Frank A.

2013-08-01

21

Radio-frequency scanning tunnelling microscopy.  

Science.gov (United States)

The scanning tunnelling microscope (STM) relies on localized electron tunnelling between a sharp probe tip and a conducting sample to attain atomic-scale spatial resolution. In the 25-year period since its invention, the STM has helped uncover a wealth of phenomena in diverse physical systems--ranging from semiconductors to superconductors to atomic and molecular nanosystems. A severe limitation in scanning tunnelling microscopy is the low temporal resolution, originating from the diminished high-frequency response of the tunnel current readout circuitry. Here we overcome this limitation by measuring the reflection from a resonant inductor-capacitor circuit in which the tunnel junction is embedded, and demonstrate electronic bandwidths as high as 10 MHz. This approximately 100-fold bandwidth improvement on the state of the art translates into fast surface topography as well as delicate measurements in mesoscopic electronics and mechanics. Broadband noise measurements across the tunnel junction using this radio-frequency STM have allowed us to perform thermometry at the nanometre scale. Furthermore, we have detected high-frequency mechanical motion with a sensitivity approaching approximately 15 fm Hz(-1/2). This sensitivity is on par with the highest available from nanoscale optical and electrical displacement detection techniques, and the radio-frequency STM is expected to be capable of quantum-limited position measurements. PMID:17972882

Kemiktarak, U; Ndukum, T; Schwab, K C; Ekinci, K L

2007-11-01

22

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

23

New directions in scanning-tunneling microscopy  

International Nuclear Information System (INIS)

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

24

Scanning tunneling microscopy II further applications and related scanning techniques  

CERN Document Server

Scanning Tunneling Microscopy II, like its predecessor, presents detailed and comprehensive accounts of the basic principles and broad range of applications of STM and related scanning probe techniques. The applications discussed in this volume come predominantly from the fields of electrochemistry and biology. In contrast to those described in Vol. I, these sudies may be performed in air and in liquids. The extensions of the basic technique to map other interactions are described inchapters on scanning force microscopy, magnetic force microscopy, scanning near-field optical microscopy, together with a survey of other related techniques. Also described here is the use of a scanning proximal probe for surface modification. Togehter, the two volumes give a comprehensive account of experimental aspcets of STM. They provide essentialreading and reference material for all students and researchers involvedin this field.

Güntherodt, Hans-Joachim

1992-01-01

25

Scanning tunneling microscopy II further applications and related scanning techniques  

CERN Document Server

Scanning Tunneling Microscopy II, like its predecessor, presents detailed and comprehensive accounts of the basic principles and broad range of applications of STM and related scanning probe techniques. The applications discussed in this volume come predominantly from the fields of electrochemistry and biology. In contrast to those described in STM I, these studies may be performed in air and in liquids. The extensions of the basic technique to map other interactions are described in chapters on scanning force microscopy, magnetic force microscopy, and scanning near-field optical microscopy, together with a survey of other related techniques. Also described here is the use of a scanning proximal probe for surface modification. Together, the two volumes give a comprehensive account of experimental aspects of STM. They provide essential reading and reference material for all students and researchers involved in this field. In this second edition the text has been updated and new methods are discussed.

Güntherodt, Hans-Joachim

1995-01-01

26

Spin-polarized scanning tunnelling microscopy  

CERN Document Server

The recent experimental progress in spin-polarized scanning tunnelling microscopy (SP-STM) - a magnetically sensitive imaging technique with ultra-high resolution - is reviewed. The basics of spin-polarized electron tunnelling are introduced as they have been investigated in planar tunnel junctions for different electrode materials, i.e. superconductors, optically excited GaAs, and ferromagnets. It is shown that ferromagnets and antiferromagnets are suitable tip materials for the realization of SP-STM. Possible tip designs and modes of operations are discussed for both classes of materials. The results of recent spatially resolved measurements as performed with different magnetic probe tips and using different modes of operation are reviewed and discussed in terms of applicability to surfaces, thin films, and nanoparticles. The limits of spatial resolution, and the impact of an external magnetic field on the imaging process.

Bode, M

2003-01-01

27

Spin-polarized scanning tunnelling microscopy  

International Nuclear Information System (INIS)

The recent experimental progress in spin-polarized scanning tunnelling microscopy (SP-STM) - a magnetically sensitive imaging technique with ultra-high resolution - is reviewed. The basics of spin-polarized electron tunnelling are introduced as they have been investigated in planar tunnel junctions for different electrode materials, i.e. superconductors, optically excited GaAs, and ferromagnets. It is shown that ferromagnets and antiferromagnets are suitable tip materials for the realization of SP-STM. Possible tip designs and modes of operations are discussed for both classes of materials. The results of recent spatially resolved measurements as performed with different magnetic probe tips and using different modes of operation are reviewed and discussed in terms of applicability to surfaces, thin films, and nanoparticles. The limits of spatial resolution, and the impact of an external magnetic field on the imaging process

28

Potential barrier for tunneling electrons in STM [scanning tunneling microscope  

International Nuclear Information System (INIS)

The correct interpretation of vacuum-tunneling experiments achieved with the scanning tunneling microscope (STM) makes it necessary to know about the effective potential barrier that an electron leaving the surface sees. A variety of semiclassical and quantum-mechanical approaches are available to calculate the attractive potential between an external charged particle and a semi-infinite polarizable medium, but local effects are not negligible for the distances of interest, and a simple local formalism cannot be applied, either, so it is necessary to include, at the same time, local and non-local correlations effects. Consequently, the determination of this potential barrier is a difficult task and it remains an open problem. Recently some work has been performed going beyond the local density formalism (LDA). The tunneling current in a metal-vacuum-metal junction is very sensitive to the detailed form of the potential barrier between the electrodes, and specially sensitive are the positions of the transmission resonances which occur in the region close to the metal-vacuum interface where the momentum of the electron can be real, so the tunneling electrons can serve as a probe of this surface-interaction. Indeed, the STM has been used to study the distance-voltage characteristics (d-Va) in the constant current mode, and tunneling resonances, that is, peaks in the dJ/dVa curve have been observed in recent experiments, as predicted by Gundlach. Thuexperiments, as predicted by Gundlach. Thus, in order to estimate the shape of the potential barrier that electrons feel when they tunnel the vacuum region, the author has carried out theoretical calculations of the dI/dVa-Va characteristics for a W(110) tip on a AU(110) sample. 14 refs., 2 figs

29

Scanning tunneling spectroscopy study of DNA conductivity.  

Czech Academy of Sciences Publication Activity Database

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

Kratochvílová, Irena; Král, Karel; Bun?ek, M.; Nešp?rek, Stanislav; Todorciuc, Tatiana; Weiter, M.; Navrátil, J.; Schneider, Bohdan; Pavluch, J.

2008-01-01

30

A SCANNING TUNNELING MICROSCOPE FOR SURFACE MODIFICATION  

OpenAIRE

With the recent success for the scanning tunneling microscope (STM) has come question of whether the instrument might be used for material modifications lithography. We embarked on the design of an STM with this application in mind. Its features include a wide x-y piezoelectric scan range of 10 or more microns, plus coarse mechanical motion in the x direction to a new region on the sample while in vacuum. Coarse motion in the z direction is accomplished with a micrometer drive, while fine mov...

Mccord, M.; Pease, R.

1986-01-01

31

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

32

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

33

COMBINED FIELD ION AND SCANNING TUNNELING MICROSCOPE  

OpenAIRE

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

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

1987-01-01

34

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

Science.gov (United States)

Scanning tunneling spectroscopy (STS) was used to measure local differential conductance (dI/dV) spectra on nanometer-size graphene islands on an Ir(111) surface. Energy resolved dI/dV maps clearly show a spatial modulation, which we ascribe to a modulated local density of states due to quantum confinement. STS near graphene edges indicates a position dependence of the dI/dV signals, which suggests a reduced density of states near the edges of graphene islands on Ir(111). PMID:22587725

2012-01-01

35

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

OpenAIRE

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

Phark, Soo-hyon; Borme, Je?ro?me; Vanegas, Augusto Leo?n; Corbetta, Marco; Sander, Dirk; Kirschner, Ju?rgen

2012-01-01

36

Atomic structure of carbon nanotubes from scanning tunneling microscopy  

International Nuclear Information System (INIS)

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

37

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.

38

Scanning tunneling spectroscopy studies of heavy fermion metals  

Energy Technology Data Exchange (ETDEWEB)

We report Scanning Tunneling Microscopy/Spectroscopy (STM/S) experiments on single crystals of the heavy fermion intermetallic compounds CeCoIn{sub 5}, CeIrIn{sub 5}, and YbRh{sub 2}Si{sub 2}. 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. CeCoIn{sub 5} and CeIrIn{sub 5} 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 CeCoIn{sub 5}. The presence of a gap-like feature in a temperature range above T{sub c} 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 YbRh{sub 2}Si{sub 2}, we speculate that the tunneling spectra reveal signatures of a Kondo resonance related to the Yb ions.

Ernst, Stefan; Wirth, Steffen; Krellner, Cornelius; Geibel, Christoph; Steglich, Frank [Max-Planck-Institut fuer Chemische Physik fester Stoffe, Dresden (Germany); Fisk, Zachary [Department of Physics and Astronomy, University of California at Irvine (United States); Sarrao, John L.; Thompson, Joe D. [Los Alamos National Laboratory, Los Alamos (United States)

2010-07-01

39

Measuring voltage transients with an ultrafast scanning tunneling microscope  

DEFF Research Database (Denmark)

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

Keil, Ulrich Dieter Felix; Jensen, Jacob Riis

1997-01-01

40

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

International Nuclear Information System (INIS)

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

41

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

42

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

Science.gov (United States)

We have developed a new scanning-tunneling-microscopy-based spectroscopy technique to characterize infrared (IR) absorption of submonolayers of molecules on conducting crystals. The technique employs a scanning tunneling microscope as a precise detector to measure the expansion of a molecule-decorated crystal that is irradiated by IR light from a tunable laser source. Using this technique, we obtain the IR absorption spectra of [121]tetramantane and [123]tetramantane on Au(111). Significant differences between the IR spectra for these two isomers show the power of this new technique to differentiate chemical structures even when single-molecule-resolved scanning tunneling microscopy (STM) images look quite similar. Furthermore, the new technique was found to yield significantly better spectral resolution than STM-based inelastic electron tunneling spectroscopy, and to allow determination of optical absorption cross sections. Compared to IR spectroscopy of bulk tetramantane powders, infrared scanning tunneling microscopy (IRSTM) spectra reveal narrower and blueshifted vibrational peaks for an ordered tetramantane adlayer. Differences between bulk and surface tetramantane vibrational spectra are explained via molecule-molecule interactions. PMID:24093277

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

2013-09-20

43

Scanning Tunneling Microscopy at Metal Surfaces.  

Science.gov (United States)

An ultra-high vacuum scanning tunneling microscope has been used in the study and modification of metal surfaces. Its novel design features a dual sample and tip exchange mechanism, a packaged tip-amplifier assembly and an integrated cooling finger. Representative results for the well-known surfaces of graphite, gallium arsenide and gold are included. The (111) surface of gold films evaporated onto mica substrates was characterized using scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy and low energy electron diffraction. The step structure, native (22 x 1) reconstruction and its domain structure, and surface contamination of the Au(111) surface were investigated. Nucleation and layer-by-layer epitaxial growth of gold and silver on Au(111) and Ag(111) surfaces at room -temperature have also been studied under ultra-high vacuum conditions, from the initial stages up to the completion of several layers. Quantitative information, such as cluster size distributions and spatial correlation functions, was extracted from STM topographs, demonstrating generally applicable techniques. The results reveal the relation between the Au(111) (22 x 1) surface reconstruction and its domain structure, the absence of a reconstruction for Ag(111), and the nucleation and growth of the four possible substrate-overlayer metal combinations in this system. Furthermore, we report a study on the evolution of the surface topography of ion-bombarded gold films, from the initial stages of sputter damage to the removal of several layers. Energy-dependent sputter yields and crater size distributions are derived from STM images which show the progressing surface erosion. A duality in the behavior of surfaces prepared by deposition of atoms (evaporation) and deposition of vacancies (sputtering) is revealed. Another experiment investigates the room-temperature Stranski-Krastanov growth of the compound insulator silver bromide on the silver(111) surface, illustrating the effects of lattice mismatch and doping on the observed topography. Finally, several techniques for the nanometer -scale modification of metallic surfaces by voltage pulses or mechanical indentation are described. In particular, permanent hole patterns in graphite with 100 A resolution and chain-scission of ultra-thin polymer films are presented.

Lang, Christoph A.

44

Development and trial measurement of synchrotron-radiation-light-illuminated scanning tunneling microscope  

International Nuclear Information System (INIS)

Scanning tunneling microscope (STM) study is performed under synchrotron-radiation-light illumination. The equipment is designed so as to achieve atomic resolution even under rather noisy conditions in the synchrotron radiation facility. By measuring photoexcited electron current by the STM tip together with the conventional STM tunneling current, Si 2p soft-x-ray absorption spectra are successfully obtained from a small area of Si(111) surface. The results are a first step toward realizing a new element-specific microscope

45

Scanning tunneling microscopy, orbital-mediated tunneling spectroscopy, and ultraviolet photoelectron spectroscopy of metal(II) tetraphenylporphyrins deposited from vapor.  

Science.gov (United States)

Thin films of vapor-deposited Ni(II) and Co(II) complexes of tetraphenylporphyrin (NiTPP and CoTPP) were studied supported on gold and embedded in Al-Al(2)O(3)-MTPP-Pb tunnel diodes, where M = Ni or Co. Thin films deposited onto polycrystalline gold were analyzed by ultraviolet photoelectron spectroscopy (UPS) using He I radiation. Scanning tunneling microscopy (STM) and orbital-mediated tunneling spectroscopy (STM-OMTS) were performed on submonolayer films of CoTPP and NiTPP supported on Au(111). Inelastic electron tunneling spectroscopy (IETS) and OMTS were measured in conventional tunnel diode structures. The highest occupied pi molecular orbital of the porphyrin ring was seen in both STM-OMTS and UPS at about 6.4 eV below the vacuum level. The lowest unoccupied pi molecular orbital of the porphyrin ring was observed by STM-OMTS and by IETS-OMTS to be located near 3.4 eV below the vacuum level. The OMTS spectra of CoTPP had a band near 5.2 eV (below the vacuum level) that was attributed to transient oxidation of the central Co(II) ion. That is, it is due to electron OMT via the half-filled d(z)(2) orbital present in Co(II) of CoTPP. The NiTPP OMTS spectra show no such band, consistent with the known difficulty of oxidation of the Ni(II) ion. The STM-based OMTS allowed these two porphyrin complexes to be easily distinguished. The present work is the first report of the observation of STM-OMTS, tunnel junction OMTS, and UPS of the same compounds. Scanning tunneling microscope-based orbital-mediated tunneling provides more information than UPS or tunnel junction-based OMTS and does so with molecular-scale resolution. PMID:11457159

Scudiero, L; Barlow, D E; Mazur, U; Hipps, K W

2001-05-01

46

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

OpenAIRE

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

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

2007-01-01

47

A vertical coarse approach scanning tunneling microscope  

Science.gov (United States)

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

Drevniok, Benedict

48

Scanning Tunneling Microscopy and Spectroscopy of Graphene on Insulating Substrates  

OpenAIRE

Graphene is a truly two-dimensional material with exceptional electronic, mechanical, and optical properties. As such, it consists of surface only and can be probed by the well developed surface-science techniques as, e.g., scanning tunneling microscopy. This method bridges the gap between the surface science community and the electronic device community and might lead to novel combined approaches. Here, I review some of the scanning tunneling microscopy (STM) and spectrosco...

Morgenstern, Markus

2012-01-01

49

SPATIAL REPARTITION OF CURRENT FLUCTUATIONS IN A SCANNING TUNNELING MICROSCOPE  

OpenAIRE

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...

Jerome Lagoute; Tomaso Zambelli; Stephane Martin; Sebastien Gauthier

2011-01-01

50

AgBr microcrystals studied by scanning tunneling microscopy  

Science.gov (United States)

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

Gordon, W. S.; Szuba, S.

1997-06-01

51

Tunneling spectra simulation of interacting Majorana wires  

OpenAIRE

Recent tunneling experiments on InSb hybrid superconductor-semiconductor devices have provided hope for a stabilization of Majorana edge modes in a spin-orbit quantum wire subject to a magnetic field and superconducting proximity effect. Connecting the experimental scenario with a microscopic description poses challenges of different kind, such as accounting for the effect of interactions on the tunneling properties of the wire. We develop a density matrix renormalization gr...

Thomale, Ronny; Rachel, Stephan; Schmitteckert, Peter

2013-01-01

52

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

53

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

54

Wide bandwidth transimpedance preamplifier for a scanning tunneling microscope  

Science.gov (United States)

A new two-stage transimpedance preamplifier in feedback picoammeter setup for use in scanning tunneling microscopy is represented. The first stage consisting of a wide band field effect transistor input operational amplifier with resistive feedback has a transimpedance of 20 k? and a 3 dB bandwidth of 35 MHz. This setup is built to investigate sub ?s fluctuations in the tunneling current.

Demming, F.; Dickmann, K.; Jersch, J.

1998-06-01

55

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

56

Characterization of light emission from subphthalocyanine monolayers using scanning tunneling microscopy  

International Nuclear Information System (INIS)

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

57

Scanning tunneling microscopy of interface properties of Bi2Se3 on FeSe.  

Science.gov (United States)

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

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

2012-11-28

58

Tunneling spectra of layered strongly correlated d-wave superconductors  

CERN Document Server

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

Wen, T C R X G

2005-01-01

59

Inertial tip translator for a scanning tunneling microscope  

Science.gov (United States)

A two-dimensional micropositioning device for scanning tunneling microscope (STM) probes has been developed. This device uses the principle of piezoelectric inertial translation to produce a controlled stepping motion of the probe along vertical and horizontal axes over distances of several mm. The tip micropositioner is controlled by the same electrical signals that drive the scanning piezoelectric element, thus alleviating the need for additional electronic control elements. This device has been tested on STMs operating in air and in ultrahigh vacuum environments.

Brockenbrough, R. T.; Lyding, J. W.

1993-08-01

60

Scanning Tunneling Luminescence of Pentacene Nanocrystals  

OpenAIRE

Organic semiconductors are promising materials for future electronic and electroluminescence applications. A detailed understanding of organic layers and nano-sized crystals down to single molecules can address fundamental questions of contacting organic semiconductors at the nanometer limit and obtaining luminescence from them. In this thesis, electroluminescence spectra from pentacene, a policyclic hydrocarbon (acene), are discussed. The luminescenc...

Kabakchiev, Alexander

2010-01-01

61

Estimation and improvement of the spatial resolution of scanning tunneling microscope combined with synchrotron-radiation  

International Nuclear Information System (INIS)

In order to achieve the imaging of scanning tunneling microscope (STM) with chemical information, we have developed the STM system combined with synchrotron radiation (SR-STM). It is ascertained that an x-ray absorption spectra (XAS) can be observed by STM tip during the STM observation so far. The spatial resolution of the XAS measurement with the tip is, however, still unclear. Here, we present our recent trials to estimate the spatial resolution and improve it. (author)

62

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

OpenAIRE

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

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

2011-01-01

63

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

64

Scanning tunneling microscopy III theory of STM and related scanning probe methods  

CERN Document Server

Scanning Tunneling Microscopy III provides a unique introduction to the theoretical foundations of scanning tunneling microscopy and related scanning probe methods. The different theoretical concepts developed in the past are outlined, and the implications of the theoretical results for the interpretation of experimental data are discussed in detail. Therefore, this book serves as a most useful guide for experimentalists as well as for theoreticians working in the filed of local probe methods. In this second edition the text has been updated and new methods are discussed.

Güntherodt, Hans-Joachim

1996-01-01

65

Mechanism of nanoparticle manipulation by scanning tunnelling microscopy  

International Nuclear Information System (INIS)

Scanning tunnelling microscopy (STM) imaging was performed on gold surfaces with a large coverage of monodispersed silver nanoparticles soft-landed on the surface from the gas phase. In both ambient and ultra-high vacuum conditions, STM scanning was found to displace the particles out of the scanning area, due to weak adhesion of the particles to the substrate surface. Calculations based on contact mechanics and electrostatics show that the particles can overcome the force of adhesion to the surface and jump onto the STM tip beyond the tunnelling distance. The observation provides the possibility for patterning or arranging nanoparticles on a surface, which is demonstrated, and offers the potential for a multiplexed approach to create very precise surface patterns and particle arrangements

66

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

67

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.

68

Spatially resolved scanning tunneling spectroscopy on single-walled carbon nanotubes  

International Nuclear Information System (INIS)

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

69

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

70

Scanning Tunneling Microspectroscopy of Solids and Surfaces - Final Report; FINAL  

International Nuclear Information System (INIS)

Experimental and theoretical research on the bulk and surface properties of conductive solid state materials has been performed based on the techniques of scanning tunneling microscopy and scanning tunneling spectroscopy, often at cryogenic temperatures. The research has focused on the electronic properties, particularly the superconductivity, of high temperature superconductors and other layered systems. The superconducting electronic density of states N(E)=dI/dV of the high T(sub c) superconductor Bi(sub 2)Sr(sub 2)CaCu(sub 2)O(sub 8+(delta)) was measured with spatial resolution of 5 A at 4.2K. An internal superconducting proximity effect was inferred to operate between Cu and Bi based layers of the crystal in those regions where the Bi layers are metallic in nature. This research project supported the thesis research of several young scientists, and led to a significant number of published papers, presentations and reports

71

Scanning tunneling microscopy experiments on single molecular landers  

Science.gov (United States)

Molecular landers are molecules comprising of a central rigid molecular wire maintained above a metallic surface by organic spacers, which allows specific ultrahigh vacuum-scanning tunneling microscopy experiments to be performed at the single-molecule level. The understanding of the molecule-surface interactions, intramolecular mechanics, and the possibility to perform extremely precise tip-induced manipulation permit these molecules to be brought in contact with a nanoelectrode and the resulting electronic interaction to be analyzed in well controlled conditions. Author contributions: F.M. and A.G. designed research, performed research, contributed new reagents/analytic tools, analyzed data, and wrote the paper.This paper was submitted directly (Track II) to the PNAS office.Abbreviations: LT, low temperature; SAM, self-assembled monolayer; STM, scanning tunneling microscopy.

Moresco, Francesca; Gourdon, André

2005-06-01

72

Plasma etching of superconducting Niobium tips for scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

We have developed a reproducible technique for the fabrication of sharp superconducting Nb tips for scanning tunneling microscopy (STM) and scanning tunneling spectroscopy. Sections of Nb wire with 250??m diameter are dry etched in an SF{sub 6} plasma in a Reactive Ion Etcher. The gas pressure, etching time, and applied power are chosen to control the ratio of isotropic to anisotropic etch rates and produce the desired tip shape. The resulting tips are atomically sharp, with radii of less than 100?nm, mechanically stable, and superconducting. They generate good STM images and spectroscopy on single crystal samples of Au(111), Au(100), and Nb(100), as well as a doped topological insulator Bi{sub 2}Se{sub 3} at temperatures ranging from 30 mK to 9?K.

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

2014-07-07

73

Apparent diameter of carbon nanotubes in scanning tunnelling microscopy measurements  

International Nuclear Information System (INIS)

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

74

Electrical excitation of surface plasmons with a scanning tunneling microscope  

OpenAIRE

For the first time, using a equipment combining a scanning tunneling microscope (STM) and an invertedoptical microscope, we excite and directly image STM-excited broadband propagating surface plasmons ona thin gold film. The STM-excited propagating surface plasmons have been imaged both in real space andFourier space by leakage radiation microscopy. Broadband localized surface plasmons due to the tip-goldfilm coupled plasmon resonance have also been detected. Quantitatively, we compare the in...

Wang, Tao

2012-01-01

75

Imaging atoms and molecules on surfaces by scanning tunnelling microscopy  

International Nuclear Information System (INIS)

This review discusses nearly 30 years of scanning tunnelling microscopy (STM) work on high resolution imaging of numerous materials systems, giving a historical perspective on the field through the author's work. After a brief discussion of early STM and atomic force microscope (AFM) instrumentation development, the review discusses high resolution STM imaging on semiconductors, metals on semiconductors, Au(1 1 1), metal on metals including surface alloys, oxygen on metals, molecules adsorbed on metals, and AFM measurements of friction on graphite and mica.

76

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

77

Distinction of Nuclear Spin States with the Scanning Tunneling Microscope  

OpenAIRE

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

78

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

79

Scanning tunneling microscopy experiments on single molecular landers  

OpenAIRE

Molecular landers are molecules comprising of a central rigid molecular wire maintained above a metallic surface by organic spacers, which allows specific ultrahigh vacuum-scanning tunneling microscopy experiments to be performed at the single-molecule level. The understanding of the molecule–surface interactions, intramolecular mechanics, and the possibility to perform extremely precise tip-induced manipulation permit these molecules to be brought in contact with a nanoelectrode and the re...

Moresco, Francesca; Gourdon, Andre?

2005-01-01

80

Many-Impurity Effects in Fourier Transform Scanning Tunneling Spectroscopy  

OpenAIRE

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

81

Two-dimensional, remote micropositioner for a scanning tunneling microscope  

Energy Technology Data Exchange (ETDEWEB)

A simple walker is described that is suitable as the coarse positioner in a scanning tunneling microscope. The walker is fabricated from a single piece of piezoelectric ceramic and has feet coated with thin metal and insulating films. The walker can move in either of two orthogonal, horizontal directions on an insulated, metallized quartz substrate in steps that can be varied from 25 to 400 nm.

Mamin, H.J.; Abraham, D.W.; Ganz, E.; Clarke, J.

1985-11-01

82

Two-dimensional, remote micropositioner for a scanning tunneling microscope  

International Nuclear Information System (INIS)

A simple walker is described that is suitable as the coarse positioner in a scanning tunneling microscope. The walker is fabricated from a single piece of piezoelectric ceramic and has feet coated with thin metal and insulating films. The walker can move in either of two orthogonal, horizontal directions on an insulated, metallized quartz substrate in steps that can be varied from 25 to 400 nm

83

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

84

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

85

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

CERN Document Server

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

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

2003-01-01

86

Optical and Electrical Characterization at the Nanoscale by a Transparent Tip of a Scanning Tunneling Microscope  

OpenAIRE

A new type of scanning probe microscope, combining features of the scanning tunnelling microscope, the scanning tunnelling luminescence microscope with a transparent probe and the aperture scanning near-field optical microscope, is described. Proof-of-concept experiments were performed under ultrahigh vacuum conditions at varying temperature on GaAs/AlAs heterostructures.

Sychugov, Ilya; Omi, Hiroo; Murashita, Toru; Kobayashi, Yoshihiro

2009-01-01

87

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

R.K. Kale

2006-10-01

88

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

89

Spin-polarized scanning tunneling microscopy: breakthroughs and highlights.  

Science.gov (United States)

The principle of scanning tunneling microscopy, an imaging method with atomic resolution capability invented by Binnig and Rohrer in 1982, can be adapted for surface magnetism studies by using magnetic probe tips. The contrast mechanism of this so-called spin-polarized scanning tunneling microscopy, or SP-STM, relies on the tunneling magneto-resistance effect, i.e. the tip-sample distance as well as the differential conductance depend on the relative magnetic orientation of tip and sample. To illustrate the working principle and the unique capabilities of SP-STM, this compilation presents some key experiments which have been performed on various magnetic surfaces, such as the topological antiferromagnet Cr(001), a double-layer of Fe which exhibits a stripe- domain pattern with about 50 nm periodicity, and the Mn monolayer on W(110), where the combination of experiment and theory reveal an antiferromagnetic spin cycloid. Recent experimental results also demonstrate the suitability of SP-STM for studies of dynamic properties, such as the spin relaxation time of single magnetic nanostructures. PMID:22546192

Bode, Matthias

2012-01-01

90

Size-Dependent Energy Levels of InSb Quantum Dots Measured by Scanning Tunneling Spectroscopy.  

Science.gov (United States)

The electronic structure of single InSb quantum dots (QDs) with diameters between 3 and 7 nm was investigated using atomic force microscopy (AFM) and scanning tunneling spectroscopy (STS). In this size regime, InSb QDs show strong quantum confinement effects which lead to discrete energy levels on both valence and conduction band states. Decrease of the QD size increases the measured band gap and the spacing between energy levels. Multiplets of equally spaced resonance peaks are observed in the tunneling spectra. There, multiplets originate from degeneracy lifting induced by QD charging. The tunneling spectra of InSb QDs are qualitatively different from those observed in the STS of other III-V materials, for example, InAs QDs, with similar band gap energy. Theoretical calculations suggest the electron tunneling occurs through the states connected with L-valley of InSb QDs rather than through states of the ?-valley. This observation calls for better understanding of the role of indirect valleys in strongly quantum-confined III-V nanomaterials. PMID:25531244

Wang, Tuo; Vaxenburg, Roman; Liu, Wenyong; Rupich, Sara M; Lifshitz, Efrat; Efros, Alexander L; Talapin, Dmitri V; Sibener, S J

2015-01-27

91

Scanning tunneling spectroscopy of high-temperature superconductors  

CERN Document Server

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

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

2006-01-01

92

Scanning Tunneling Microscopy Contrast Mechanisms for TiO2  

Science.gov (United States)

Controlled dual mode scanning tunneling microscopy (STM) experiments and first-principles simulations show that the tunneling conditions can significantly alter the positive-bias topographic contrast of geometrically corrugated titania surfaces such as rutile TiO2(011)-(2×1). Depending on the tip-surface distance, two different contrasts can be reversibly imaged. STM simulations which either include or neglect the tip-electronic structure, carried out at three density functional theory levels of increasing accuracy, allow assignment of both contrasts on the basis of the TiO2(011)-(2×1) structure proposed by Torrelles et al. [Phys. Rev. Lett. 101, 185501 (2008)]. Finally, the mechanisms of contrast formation are elucidated in terms of the subtle balance between the surface geometry and the different vacuum decay lengths of the topmost Ti(3d) and O(2p) states probed by the STM-tip apex.

Woolcot, T.; Teobaldi, G.; Pang, C. L.; Beglitis, N. S.; Fisher, A. J.; Hofer, W. A.; Thornton, G.

2012-10-01

93

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

94

Versatile scanning tunneling microscopy with 120 ps time resolution  

Science.gov (United States)

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; Raphael Bindel, Jan; Pratzer, Marco; Morgenstern, Markus

2013-02-01

95

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

96

Kondo Effect in a Co-Porphyrin on Au(111) probed by Scanning Tunneling Spectroscopy  

Science.gov (United States)

Kondo effect is a core topic in condensed matter physics, exhibiting a localized state raised by the interaction between a single magnetic impurity and Fermi electrons in metals. We have studied Kondo effect in a Co-porphyrin on Au(111) using low-temperature scanning tunneling spectroscopy. A localized state is observed at Fermi level from the spectra measured above the Co atom. The spectra were fitted by Fano line shape, revealing the Kondo temperature of the system ˜ 400K. By taking spectra at points along some symmetry directions, decaying behavior of the Kondo effect could be analyzed. With the help of simulated d-electron orbital, the observed decaying behavior is accounted for. Our study implies that lattice reconstruction in a system can induce d-electron orbital distortion, resulting in magnetic asymmetries.

Kahng, Se-Jong; Kim, Howon; Jang, Won Jun; Heum Jeon, Jung; Son, Won-Joon; Han, Seungwu

2009-03-01

97

Spin-polarized scanning tunneling microscopy with antiferromagnetic probe tips.  

Science.gov (United States)

We have performed low temperature spin-polarized scanning tunneling microscopy (SP-STM) of two monolayers Fe on W(110) using tungsten tips coated with different magnetic materials. We observe stripe domains with a magnetic period of 50 +/- 5 nm. Employing Cr as a coating material we recorded SP-STM images with an antiferromagnetic probe tip. The advantage of its vanishing dipole field is most apparent in external magnetic fields. This new approach resolves the problem of the disturbing influence of a ferromagnetic tip in the investigation of soft magnetic materials and superparamagnetic particles. PMID:11863771

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

2002-02-01

98

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

99

Development of a scanning tunneling microscope combined with a synchrotron radiation light source  

International Nuclear Information System (INIS)

We have developed a scanning tunneling microscope (STM) combined with a synchrotron-radiation light source (SR-STM) aiming at elemental analysis in a spatial resolution of STM. Using SR-STM atomically resolved STM images under the irradiation and also X-ray adsorption spectra clearly showing an adsorption edge of a substrate were successfully obtained by detecting photo-emitted electrons with the STM tip. In order to focus the probing area of the photo-induced current, a glass-coated metal tip sharpened with focused ion beam was used as a probe. The present situation and prospects of the instrument are discussed in this review. (author)

100

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

101

Many-body transitions in a single molecule visualized by scanning tunnelling microscopy  

Science.gov (United States)

Many-body effects arise from the collective behaviour of large numbers of interacting particles, for example, electrons, and the properties of such a system cannot be understood considering only single or non-interacting particles. Despite the generality of the many-body picture, there are only a few examples of experimentally observing such effects in molecular systems. Measurements of the local density of states of single molecules by scanning tunnelling spectroscopy is usually interpreted in terms of single-particle molecular orbitals. Here, we show that the simple single-particle picture fails qualitatively to account for the resonances in the tunnelling spectra of different charge states of cobalt phthalocyanine molecules. Instead, these resonances can be understood as a series of many-body excitations of the different ground states of the molecule. Our theoretical approach opens an accessible route beyond the single-particle picture in quantifying many-body states in molecules.

Schulz, Fabian; Ijäs, Mari; Drost, Robert; Hämäläinen, Sampsa K.; Harju, Ari; Seitsonen, Ari P.; Liljeroth, Peter

2015-03-01

102

Nt_STM: A step forward in Scanning Tunneling Microscopy (STM) simulations  

Science.gov (United States)

We present the Nt_STM software suite designed to help analysis and interpretation of Scanning Tunneling Microscope (STM) images, via the simulation of STM data under different tip and bias conditions and facilitating their comparison against the experimental ones. The Nt_STM package includes two components: (i) an intuitive and directive Graphical User Interface (GUI) designed to build a precise model of the STM set-up and analyze the simulation results and, (ii) a powerful simulation engine (GREEN) allowing an efficient, yet accurate, calculation of the tunneling current necessary to generate current or topographic images, I(V) spectra as well as various properties such as band structures, Local Density Of State (LDOS), etc. The Nt_STM package, at its current version 2.0, gives the opportunity to access parallel computation, a new collection of objects and new Extended Hückel parameters.

Magoga, Michaël; Archambault, Fabien; Cerdá, Jorge I.

2012-06-01

103

Scanning electron and tunneling microscopy of palladium-barium emitters  

International Nuclear Information System (INIS)

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

104

Scanning tunnelling spectroscopy of low-dimensional semiconductor systems  

International Nuclear Information System (INIS)

The applicability of tunnelling spectroscopy by scanning tunnelling microscopy (STM) to semiconductor nanoobjects is addressed through two examples: chemically synthesized PbSe nanocrystals and cleaved InAs quantum dots (QDs) embedded in a GaAs matrix. In the case of free-standing nanocrystals on a metallic substrate, measurements of the conductance at low temperature provides the electronic structures of the nanocrystals in the conduction band and a broad transition range is found for the density of states as a function of the nanocrystal dimensions. Use of the scanning ability of the STM also allows the acquisition of spectroscopic images. At room temperature, current images obtained on cleaved InAs QDs for different samples voltages show the formation of standing wave patterns, which are identified as the probability density of the ground and first excited states. Such results open the opportunity to study the electronic structure of more complicated systems based on the assembly of semiconductor nanoobjects such as coupled QDs

105

Scanning electron and tunneling microscopy of palladium barium emitters  

Science.gov (United States)

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

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

2003-06-01

106

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

International Nuclear Information System (INIS)

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

107

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

108

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

Energy Technology Data Exchange (ETDEWEB)

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: Black-Right-Pointing-Pointer An experimental observation of force interactions in conventional STM. Black-Right-Pointing-Pointer Thermally excited vibration mode in an STM tip used as a shear force sensor. Black-Right-Pointing-Pointer Spectra analysis of the thermal fluctuations of the probe from tunneling current. Black-Right-Pointing-Pointer Shear strength of 7 Gpa for HOPG is obtained under compressive stress. Black-Right-Pointing-Pointer Stimulating ideas for the measurement of short-range forces at atomic scale.

Ding, X.D.; Wang, Y.Z.; Xiong, X.M.; Du, X.S. [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics Science and Engineering, Sun Yat-sen University, Guangzhou 510275, People' s Republic of China (China); Zhang, J.X., E-mail: gzdxd@sina.com [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics Science and Engineering, Sun Yat-sen University, Guangzhou 510275, People' s Republic of China (China)

2012-04-15

109

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.

110

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

111

In situ scanning tunnelling spectroscopy of inorganic transition metal complexes.  

Science.gov (United States)

Redox molecules with equilibrium potentials suitable for electrochemical control offer perspectives in nanoscale and single-molecule electronics. This applies to molecular but also towards higher sophistication such as transistor or diode function. Most recent nanoscale or single-molecule functional systems are, however, fraught with operational limitations such as cryogenic temperatures and ultra-high vacuum, or lack of electrochemical potential control. We report here cyclic voltammetry (CV) using single-crystal Au(111)- and Pt(111)-electrodes and electrochemical in situ scanning tunnelling microscopy (STM) of a class of Os(II)/(III)- and Co(II)/(III)-complexes, the former novel molecular electronics. The complexes are robust, with ligand groups suitable for linking the complexes to the Au(111)- and Pt(111)-surfaces via N- and S-donor atoms. The data reflect monolayer behaviour. Interfacial ET of the Os-complexes is fast, kET(0) > or = 10(6) s(-1), while the Co-complex reacts much more slowly, kET(0) approximately (1-3) x 10(3) s(-1). In STM of the Os-complexes shows a maximum in the tunnelling current/overpotential relation at constant bias voltage with up to 50-fold current rise. The peak position systematically the bias voltage and equilibrium potential, in keeping with theoretical frames for two-step electron transfer (ET) of in situ STM of redox molecules. The molecular conductivity behaves broadly similarly. The Co-complex also shows a tunnelling spectroscopic feature but much weaker than the Os-complexes. This can be ascribed much smaller interfacial ET rate constant, again caused by large intramolecular nuclear reorganization and weak electronic coupling to the substrate electrode. Overall the has mapped the properties of target molecules needed for stable electronic switching, possible importance in molecular electronics towards the single-molecule level, in room temperature condensed matter environment. PMID:16512377

Albrecht, Tim; Moth-Poulsen, Kasper; Christensen, Jørn B; Guckian, Adrian; Bjørnholm, Thomas; Vos, Johannes G; Ulstrup, Jens

2006-01-01

112

Edge scattering of surface plasmons excited by scanning tunneling microscopy.  

Science.gov (United States)

The scattering of electrically excited surface plasmon polaritons (SPPs) into photons at the edges of gold metal stripes is investigated. The SPPs are locally generated by the inelastic tunneling current of a scanning tunneling microscope (STM). The majority of the collected light arising from the scattering of SPPs at the stripe edges is emitted in the forward direction and is collected at large angle (close to the air-glass critical angle, ?(c)). A much weaker isotropic component of the scattered light gives rise to an interference pattern in the Fourier plane images, demonstrating that plasmons may be scattered coherently. An analysis of the interference pattern as a function of excitation position on the stripe is used to determine a value of 1.42 ± 0.18 for the relative plasmon wave vector (kSPP/k0) of the corresponding SPPs. From these results, we interpret the directional, large angle (?~?(c)) scattering to be mainly from plasmons on the air-gold interface, and the diffuse scattering forming interference fringes to be dominantly from plasmons on the gold-substrate interface. PMID:23787583

Zhang, Yang; Boer-Duchemin, Elizabeth; Wang, Tao; Rogez, Benoit; Comtet, Geneviève; Le Moal, Eric; Dujardin, Gérald; Hohenau, Andreas; Gruber, Christian; Krenn, Joachim R

2013-06-17

113

Detection of electronic nematicity using scanning tunneling microscopy  

Science.gov (United States)

Electronic nematic phases have been proposed to occur in various correlated electron systems and were recently claimed to have been detected in scanning tunneling microscopy (STM) conductance maps of the pseudogap states of the cuprate high-temperature superconductor Bi2Sr2CaCu2O8+? (Bi-2212). We investigate the influence of anisotropic STM tip structures on such measurements and establish, with a model calculation, the presence of a tunneling interference effect within an STM junction that induces energy-dependent symmetry-breaking features in the conductance maps. We experimentally confirm this phenomenon on different correlated electron systems, including measurements in the pseudogap state of Bi-2212, showing that the apparent nematic behavior of the imaged crystal lattice is likely not due to nematic order but is related to how a realistic STM tip probes the band structure of a material. We further establish that this interference effect can be used as a sensitive probe of changes in the momentum structure of the sample's quasiparticles as a function of energy.

da Silva Neto, Eduardo H.; Aynajian, Pegor; Baumbach, Ryan E.; Bauer, Eric D.; Mydosh, John; Ono, Shimpei; Yazdani, Ali

2013-04-01

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

Au(111) Autoepitaxy studied by scanning tunneling microscopy  

Science.gov (United States)

Using a scanning tunneling microscope in ultra-high vacuum, we have studied several stages of autoepitaxy on Au(111) from submonolayer up to twenty monolayer coverage at room temperature. The substrate, Au(111) epitaxially grown on mica. exhibits several hundred ångström wide atomatically flat terraces separated by monoatomic steps. At submonolayer coverages, the gold nucleates into single layer clusters arranged preferentially in rows along directions. As the metal coverage increases, cluster coalescence by growth is observed. Cluster size distributions and spatial correlation functions have been extracted from the STM data. Higher layers start forming before the lower ones are completely filled. The number of incomplete layers increases with deposition rate and total thickness of the film. Room temperature diffusion smooths the terrace structure over a period of several hours. This process is observed to accelerate with a moderate anneal.

Lang, C. A.; Dovek, M. M.; Nogami, J.; Quate, C. F.

1989-12-01

116

Scanning tunneling microscopy and spectroscopy at very low temperatures  

Science.gov (United States)

During past decades, an increasing number of laboratories is using cryogenic scanning tunneling microscopy and spectroscopy (STM/S) to probe different kinds of electronic systems. Measurements in a dilution refrigerator are particularly useful to study superconductors, because temperatures of order of 100 mK are well below most critical temperatures and effectively reduce thermally excited quasiparticles. The local electronic density of states is then obtained at atomic level with a resolution in energy of some tens of ?eV. Visualizing spatial variations of the local density of states allows characterizing vortex cores and the vortex lattice. Vortex core electronic features provide the anisotropy of the superconducting properties, and help understanding the influence of competing orders such as charge density waves. Here we will review results in dichalcogenide superconductors, in the magnetic borocarbide TmNi2B2C and in thin films, discussing in some detail a few relevant aspects of thermal depinning and melting in thin films.

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

2014-12-01

117

A combined scanning tunneling microscope-atomic layer deposition tool.  

Science.gov (United States)

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

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

2011-12-01

118

C58 on Au(111): A scanning tunneling microscopy study  

Science.gov (United States)

C58 fullerenes were adsorbed onto room temperature Au(111) surface by low-energy (˜6 eV) cluster ion beam deposition under ultrahigh vacuum conditions. The topographic and electronic properties of the deposits were monitored by means of scanning tunnelling microscopy (STM at 4.2 K). Topographic images reveal that at low coverages fullerene cages are pinned by point dislocation defects on the herringbone reconstructed gold terraces (as well as by step edges). At intermediate coverages, pinned monomers act as nucleation centres for the formation of oligomeric C58 chains and 2D islands. At the largest coverages studied, the surface becomes covered by 3D interlinked C58 cages. STM topographic images of pinned single adsorbates are essentially featureless. The corresponding local densities of states are consistent with strong cage-substrate interactions. Topographic images of [C58]n oligomers show a stripe-like intensity pattern oriented perpendicular to the axis connecting the cage centers. This striped pattern becomes even more pronounced in maps of the local density of states. As supported by density functional theory, DFT calculations, and also by analogous STM images previously obtained for C60 polymers [M. Nakaya, Y. Kuwahara, M. Aono, and T. Nakayama, J. Nanosci. Nanotechnol. 11, 2829 (2011)], 10.1166/jnn.2011.3898, we conclude that these striped orbital patterns are a fingerprint of covalent intercage bonds. For thick C58 films we have derived a bandgap of 1.2 eV from scanning tunnelling spectroscopy data confirming that the outermost C58 layer behaves as a wide band semiconductor.

Bajales, Noelia; Schmaus, Stefan; Miyamashi, Toshio; Wulfhekel, Wulf; Wilhelm, Jan; Walz, Michael; Stendel, Melanie; Bagrets, Alexej; Evers, Ferdinand; Ulas, Seyithan; Kern, Bastian; Böttcher, Artur; Kappes, Manfred M.

2013-03-01

119

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

OpenAIRE

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; Courtois, Herve?

2007-01-01

120

Scanning tunneling microscopy III theory of STM and related scanning probe methods  

CERN Document Server

While the first two volumes on Scanning Tunneling Microscopy (STM) and its related scanning probe (SXM) methods have mainly concentrated on intro­ ducing the experimental techniques, as well as their various applications in different research fields, this third volume is exclusively devoted to the theory of STM and related SXM methods. As the experimental techniques including the reproducibility of the experimental results have advanced, more and more theorists have become attracted to focus on issues related to STM and SXM. The increasing effort in the development of theoretical concepts for STM/SXM has led to considerable improvements in understanding the contrast mechanism as well as the experimental conditions necessary to obtain reliable data. Therefore, this third volume on STM/SXM is not written by theorists for theorists, but rather for every scientist who is not satisfied by just obtaining real­ space images of surface structures by STM/SXM. After a brief introduction (Chap. 1), N. D. Lang first co...

Güntherodt, Hans-Joachim

1993-01-01

121

Substrate effects on the surface topography of evaporated gold films: a scanning tunnelling microscopy investigation  

OpenAIRE

Direct observation of surface roughness on metal films is a longstanding problem in thin film characterization. In this work the high quality of scanning tunnelling microscopy (STM) was used for investigation of evaporated gold films. A scanning tunnelling microscope able to scan areas up to 0.8 × 0.8 micro m with high reproducibility is presented. The topography of 80 nm thick gold films grown under identical evaporation conditions was investigated as a function of the selected substrate ma...

Vancea, Johann; Reiss, Gu?nter; Schneider, F.; Bauer, K.; Hoffmann, Horst

1989-01-01

122

As-rich GaAs(001) surfaces observed during As4-irradition by scanning tunneling microscopy  

CERN Document Server

As-rich GaAs (001) surfaces are successfully observed during As4-irradition by a system in which scanning tunneling microscopy (STM) and molecular beam epitaxy can be performed simultaneously. With a substrate temperature of 440 C and an As4 partial pressure of 2x10-6 torr, reflection high energy electron diffraction patterns and reflectance anisotropy spectra confirm a c(4x4) As-stabilized surface. STM images clearly show alteration of the surface reconstructions while scanning. It is postulated that continual attachment / detachment of As molecules to and from the surface produces the observed dynamic behavior.

Tsukamoto, S; Orr, B G; Ohtake, A; Bell, G R; Koguchi, N; Tsukamoto, Shiro; Pristovsek, Markus; Orr, Bradford G.; Ohtake, Akihiro; Bell, Gavin R.; Koguchi, Nobuyuki

2002-01-01

123

Scanning tunneling microscopy and spectroscopy of phase change alloys  

Energy Technology Data Exchange (ETDEWEB)

Phase change random access memory (PCRAM) is a very promising candidate for the next generation of memories. In contrast to the standard Si-based RAM, PCRAM is a non-volatile storage system which exploits the high electrical contrast between the amorphous and the crystalline phase. However, the origin of this contrast is not well understood. Scanning tunneling microscopy gives insight into the local atomic structure and the electronic properties of phase change materials. Using the topography mode of STM, we realized images of Ge{sub 1}Sb{sub 2}Te{sub 4} on the nanometer down to the atomic scale, revealing the morphology as well as the complex atomic arrangement of the sputter-deposited material. The spectroscopy mode enabled us to analyse the local density of states in the amorphous and crystalline phase. The band gap varied continuously from 0.5 eV in the amorphous phase to 0.2 eV in the crystalline phase. The Fermi level moved from the center of the gap in the amorphous phase into the valence band within the crystalline phase.

Subramaniam, Dinesh; Pauly, Christian; Pratzer, Marco; Liebmann, Marcus; Morgenstern, Markus [II. Physikalisches Institut B, RWTH Aachen (Germany); Rausch, Pascal; Woda, Michael; Wuttig, Matthias [I. Physikalisches Institut A, RWTH Aachen (Germany)

2009-07-01

124

Scanning tunneling microscopy and spectroscopy of phase change alloys  

International Nuclear Information System (INIS)

Phase change random access memory (PCRAM) is a very promising candidate for the next generation of memories. In contrast to the standard Si-based RAM, PCRAM is a non-volatile storage system which exploits the high electrical contrast between the amorphous and the crystalline phase. However, the origin of this contrast is not well understood. Scanning tunneling microscopy gives insight into the local atomic structure and the electronic properties of phase change materials. Using the topography mode of STM, we realized images of Ge1Sb2Te4 on the nanometer down to the atomic scale, revealing the morphology as well as the complex atomic arrangement of the sputter-deposited material. The spectroscopy mode enabled us to analyse the local density of states in the amorphous and crystalline phase. The band gap varied continuously from 0.5 eV in the amorphous phase to 0.2 eV in the crystalline phase. The Fermi level moved from the center of the gap in the amorphous phase into the valence band within the crystalline phase.

125

Oxygen-free in situ scanning tunnelling microscopy  

DEFF Research Database (Denmark)

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

Zhang, Jingdong; Ulstrup, Jens

2007-01-01

126

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

127

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

CERN Document Server

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

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

2004-01-01

128

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

129

Scanning tunneling spectroscopy at surfaces of superconducting charge-transfer salts  

International Nuclear Information System (INIS)

Superconducting materials based on organic charge-transfer salts are regarded as candidates for unconventional superconductors because their properties strongly deviate from the BCS theory, similar to the high-temperature superconductors. We study ?-[ET]2Cu[N(CN)2]Br-crystals. Previous measurements showed a surface contamination of the crystals. Because of that we developed an in-situ cleaving mechanism for the preparation of clean surfaces. Measurements on these cleaved crystals show an improved signal-to-noise ratio in the measured I(U) spectra and atomic flat surfaces in the topographic images (nanometer scale in the height profile). All investigations were done under UHV-conditions (5 . 10-11 mbar) using a scanning tunneling microscope at 5 K.

130

Scanning tunneling spectroscopy at surfaces of superconducting charge-transfer salts  

Energy Technology Data Exchange (ETDEWEB)

Superconducting materials based on organic charge-transfer salts are regarded as candidates for unconventional superconductors because their properties strongly deviate from the BCS theory, similar to the high-temperature superconductors. We study ?-[ET]{sub 2}Cu[N(CN){sub 2}]Br-crystals. Previous measurements showed a surface contamination of the crystals. Because of that we developed an in-situ cleaving mechanism for the preparation of clean surfaces. Measurements on these cleaved crystals show an improved signal-to-noise ratio in the measured I(U) spectra and atomic flat surfaces in the topographic images (nanometer scale in the height profile). All investigations were done under UHV-conditions (5 . 10{sup -11} mbar) using a scanning tunneling microscope at 5 K.

Diehl, Sandra [Graduate School Materials Science, Mainz (Germany); SFB/TR 49 (Germany); Institut fuer Physik, Johannes Gutenberg-Universitaet Mainz (Germany); Methfessel, Torsten; Elmers, Hans-Joachim [SFB/TR 49 (Germany); Institut fuer Physik, Johannes Gutenberg-Universitaet Mainz (Germany); Mueller, Jens; Lang, Michael [SFB/TR 49 (Germany); Physikalisches Institut, Goethe-Universitaet, Frankfurt am Main (Germany)

2013-07-01

131

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

132

Development of a scanning tunneling microscope for in situ experiments with a synchrotron radiation hard-X-ray microbeam.  

Science.gov (United States)

A scanning tunneling microscope dedicated to in situ experiments under the irradiation of highly brilliant hard-X-rays of synchrotron radiation has been developed. In situ scanning tunneling microscopy (STM) observation was enabled by developing an accurate alignment system in ultrahigh vacuum. Despite the noisy conditions of the synchrotron radiation facility and the radiation load around the probe tip, STM images were successfully obtained at atomic resolution. Tip-current spectra were obtained for Ge nano-islands on a clean Si(111) surface by changing the incident photon energy across the Ge absorption edge. A current modification was detected at the absorption edge with a spatial resolution of the order of 10 nm. PMID:16495622

Saito, Akira; Maruyama, Junpei; Manabe, Ken; Kitamoto, Katsuyuki; Takahashi, Koji; Takami, Kazuhiro; Yabashi, Makina; Tanaka, Yoshihito; Miwa, Daigo; Ishii, Masashi; Takagi, Yasumasa; Akai-Kasaya, Megumi; Shin, Shik; Ishikawa, Tetsuya; Kuwahara, Yuji; Aono, Masakazu

2006-03-01

133

Scanning tunneling microscopy studies of glucose oxidase on gold surface  

International Nuclear Information System (INIS)

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

134

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

135

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

136

Electronic band dispersion of graphene nanoribbons via Fourier-transformed scanning tunneling spectroscopy  

Science.gov (United States)

The electronic structure of atomically precise armchair graphene nanoribbons of width N =7 (7-AGNRs) are investigated by scanning tunneling spectroscopy (STS) on Au(111). We record the standing waves in the local density of states of finite ribbons as a function of sample bias and extract the dispersion relation of frontier electronic states by Fourier transformation. The wave-vector-dependent contributions from these states agree with density functional theory calculations, thus enabling the unambiguous assignment of the states to the valence band, the conduction band, and the next empty band with effective masses of 0.41 ±0.08 me ,0.40 ±0.18 me , and 0.20 ±0.03 me , respectively. By comparing the extracted dispersion relation for the conduction band to corresponding height-dependent tunneling spectra, we find that the conduction band edge can be resolved only at small tip-sample separations and has not been observed before. As a result, we report a band gap of 2.37 ±0.06 eV for 7-AGNRs adsorbed on Au(111).

Söde, Hajo; Talirz, Leopold; Gröning, Oliver; Pignedoli, Carlo Antonio; Berger, Reinhard; Feng, Xinliang; Müllen, Klaus; Fasel, Roman; Ruffieux, Pascal

2015-01-01

137

Single-Atomic-Level Probe of Transient Carrier Dynamics by Laser-Combined Scanning Tunneling Microscopy  

Science.gov (United States)

The first application of laser-combined time-resolved scanning tunneling microscopy (STM) to single-atomic-level analysis was demonstrated. The dynamics of photoinduced holes, transiently trapped at the surface and recombined with the electrons tunneling from the STM tip to the in-gap states associated with single-(Mn,Fe)/GaAs(110) structures, was successfully probed on the atomic level for the first time. In addition, light-modulated scanning tunneling spectroscopy (LT-STS) was performed for energy-space analysis in conjunction with time-resolved measurement and shown useful for developing the laser-combined STM techniques for further advances.

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

2013-03-01

138

Imaging of buried phosphorus nanostructures in silicon using scanning tunneling microscopy  

International Nuclear Information System (INIS)

We demonstrate the locating and imaging of single phosphorus atoms and phosphorus dopant nanostructures, buried beneath the Si(001) surface using scanning tunneling microscopy. The buried dopant nanostructures have been fabricated in a bottom-up approach using scanning tunneling microscope lithography on Si(001). We find that current imaging tunneling spectroscopy is suited to locate and image buried nanostructures at room temperature and with residual surface roughness present. From these studies, we can place an upper limit on the lateral diffusion during encapsulation with low-temperature Si molecular beam epitaxy.

139

Development of a Millikelvin dual-tip Josephson scanning tunneling microscope  

Science.gov (United States)

In this thesis, I first describe the design and construction of a dual-tip millikelvin STM system. The STM is mounted on a dilution refrigerator and the setup includes vibration isolation, rf-filtered wiring, an ultra high vacuum (UHV) sample preparation chamber and sample transfer mechanism. Next I describe a novel superconducting tip fabrication technique. My technique involves dry-etching sections of 250 mum diameter Nb wire with an SF6 plasma in a reactive ion etcher. I present data taken with these tips on various samples at temperatures ranging from 30 mK to 9 K. My results demonstrate that the tips are superconducting, achieve good spectroscopic energy resolution, are mechanically robust over long time periods, and are atomically sharp. I also show data characterizing the performance of our system. This data is in the form of atomic resolution images, spectroscopy, noise spectra and simultaneous scans taken with both tips of the STM. I used these to examine the tip-sample stability, cross talk between the two tips, and to extract the effective noise temperature (˜185 mK) of the sample by fitting the spectroscopy data to a voltage noise model. Finally, I present spectroscopy data taken with a Nb tip on a Nb(100) sample at 30 mK. The enhanced spectroscopic resolution at this temperature allowed me to resolve peaks in the fluctuation-dominated supercurrent at sub-gap voltages. My analysis indicates that these peaks are due to the incoherent tunneling of Cooper pairs at resonant frequencies of the STM's electromagnetic environment. By measuring the response of the STM junction to microwaves, I identified the charge carriers in this regime as Cooper pairs with charge 2e. The amplitude of the response current scales as the square of the Bessel functions, indicating that the pair tunneling originates from photon assisted tunneling in the incoherent regime, rather than the more conventionally observed Shapiro steps in the coherent regime.

Roychowdhury, Anita

140

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

Science.gov (United States)

Metallosupramolecular compounds have attracted a great deal of attention over the past two decades largely because of their unique, highly complex structural characteristics and their potential electronic, magnetic, optical, and catalytic properties. These molecules can be prepared with relative ease using coordination-driven self-assembly techniques. In particular, the use of electron-poor square-planar Pt(II) transition metals in conjunction with rigid, electron-rich pyridyl donors has enabled the spontaneous self-assembly of a rich library of 2D metallacyclic and 3D metallacage assemblies via the directional-bonding approach. With this progress in the preparation and characterization of metallosupramolecules, researchers have now turned their attention toward fully exploring and developing their materials properties. Assembling metallosupramolecular compounds on solid supports represents a vitally important step toward developing their materials properties. Surfaces provide a means of uniformly aligning and orienting these highly symmetric metallacycles and metallacages. This uniformity increases the level of coherence between molecules above that which can be achieved in the solution phase and provides a way to integrate adsorbed layers, or adlayers, into a solid-state materials setting. The dynamic nature of kinetically labile Pt(II)-N coordination bonds requires us to adjust deposition and imaging conditions to retain the assemblies' stability. Toward these aims, we have used scanning tunneling microscopy (STM) to image these adlayers and to understand the factors that govern surface self-assembly and the interactions that influence their structure and stability. This Account describes our efforts to deposit 2D rectangular and square metallacycles and 3D trigonal bipyramidal and chiral trigonal prism metallacages on highly oriented pyrolytic graphite (HOPG) and Au(111) substrates to give intact assemblies and ordered adlayers. We have investigated the effects of varying the size, symmetry, and dimensionality of supramolecular adsorbates, the choice of substrate, the use of a molecular template, and the effects of chirality. Our systematic investigations provide insights into the various adsorbate-adsorbate and substrate-adsorbate interactions that largely determine the architecture of each assembly and affect their performance in a materials setting. Rational control over adlayer formation and structure will greatly enhance the potential of these supramolecules to be used in a variety of applications such as host-guest sensing/diagnostic systems, molecular electronic devices, and heterogeneous stereoselective synthesis and catalysis. PMID:19072706

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

2009-02-17

141

New potentiometry method in scanning tunneling microscopy: Exploiting the correlation of fluctuations  

Science.gov (United States)

We developed a new scanning tunneling microscopy technique to measure the surface potential. The new method exploits the tunneling voltage dependence of the tip-sample separation. The indirect measurement of the potential together with a differential measurement technique makes the new potentiometry insensitive to errors of the electronic setup and provides submicrovolt sensitivity limited by approximately thermal noise of the tunneling resistance. We illustrate the new technique by basic measurements performed under ultrahigh-vacuum conditions. In addition we present the coherence of tunneling current fluctuations and potential fluctuations which underlines the quality of the new technique: the coherence differs significantly from unity. We conclude that the tunneling resistance does not have thermal voltage fluctuations predicted by Nyquist's formula. Possible sources of residual voltage fluctuations such as single electron tunneling efffects are discussed.

Koslowski, B.; Baur, C.

1995-01-01

142

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

143

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

144

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

International Nuclear Information System (INIS)

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

145

Scanning tunneling microscopy on rough surfaces: deconvolution of constant current images  

OpenAIRE

This letter critically discusses the topographical information obtained by scanning tunneling microscopy (STM) on surfaces with a mesoscopic roughness, i.e., in the range of some nm's. In a foregoing publication [J. Appl. Phys. 67, 1156 (1990)], we already treated the evaluation of constant current images based on the knowledge of the real surface and the shape of the tunneling tip ('tip shape limited resolution'). Now we deal with the invers problem: the reconstruction of the real surface to...

Reiss, Gu?nter; Schneider, F.; Vancea, Johann; Hoffmann, Horst

1990-01-01

146

Design and Performance of a Practical Variable-Temperature Scanning Tunneling Potentiometry System  

OpenAIRE

We have constructed a scanning tunneling potentiometry system capable of simultaneously mapping the transport-related electrochemical potential of a biased sample along with its surface topography. Combining a novel sample biasing technique with a continuous current-nulling feedback scheme pushes the noise performance of the measurement to its fundamental limit - the Johnson noise of the STM tunnel junction. The resulting 130 nV voltage sensitivity allows us to spatially res...

Rozler, M.; Beasley, M. R.

2008-01-01

147

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

OpenAIRE

Scanning tunneling microscopy (STM) has been a fundamental tool to characterize many-body effects in condensed matter systems, from extended solids to quantum dots. STM of molecules decoupled from the supporting conductive substrate has the potential to extend STM characterization of many body effects to the molecular world as well. In this article, we describe a many-body tunneling theory for molecules decoupled from the STM substrate, and we report on the use of standard q...

Toroz, Dimitrios; Rontani, Massimo; Corni, Stefano

2011-01-01

148

Theory of a scanning tunneling microscope with a two-protrusion tip  

CERN Document Server

We consider a scanning tunneling microscope (STM) such that tunneling occurs through two atomically sharp protrusions on its tip. When the two protrusions are separated by at least several atomic spacings, the differential conductance of this STM depends on the electronic transport in the sample between the protrusions. Furthermore two-protrusion tips commonly occur during STM tip preparation. We explore possible applications to probing dynamical impurity potentials on a metallic surface and local transport in an anisotropic superconductor.

Flatté, M E; Flatte', Michael E; Byers, Jeff M

1995-01-01

149

Josephson scanning tunneling microscopy: A local and direct probe of the superconducting order parameter  

OpenAIRE

Direct measurements of the superconducting superfluid on the surface of vacuum-cleaved Bi2Sr2CaCu2O8(BSCCO) samples are reported. These measurements are accomplished via Josephson tunneling into the sample using a 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. Instrumen...

Kimura, Hikari; Barber Jr, R. P.; Ono, S.; Ando, Yoichi; Dynes, R. C.

2009-01-01

150

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

OpenAIRE

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 ...

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

2012-01-01

151

High precision mechanical approach mechanism for a low temperature scanning tunneling microscope  

Science.gov (United States)

A novel mechanical micropositioner has been developed for producing exact linear displacements in the nm range. Incorporated in a low temperature scanning tunneling microscope (STM), it is used as a coarse approach mechanism for the tunneling tip. The advantage of the design is the high accuracy of the linear motion and the absence of backlash. The design principle is discussed and its positioning accuracy and stability for STM imaging are demonstrated.

Rust, H.-P.; Buisset, J.; Schweizer, E. K.; Cramer, L.

1997-01-01

152

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

Science.gov (United States)

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

Majer, C.; Schindler, W.

2015-01-01

153

A Mechanism for Cutting Carbon Nanotubes with a Scanning Tunneling Microscope  

OpenAIRE

We discuss the local cutting of single-walled carbon nanotubes by a voltage pulse to the tip of a scanning tunneling microscope. The tip voltage ($\\mid V \\mid \\ge $~3.8 eV) is the key physical quantity in the cutting process. After reviewing several possible physical mechanisms we conclude that the cutting process relies on the weakening of the carbon-carbon bonds through a combination of localized particle-hole excitations induced by inelastically tunneling electrons and el...

Rubio, Angel; Apell, S. Peter; Venema, Liesbeth C.; Dekker, Cees

2000-01-01

154

Vacuum tunneling spectroscopy of superconducting Bi2Sr2CaCuO2O8 using scanning tunneling spectroscopy  

International Nuclear Information System (INIS)

The authors report STM spectroscopy measurements of in-situ cleaved Bi2Sr2CaCu2O8 single crystals at 4.8 Kelvin, where they achieved strong evidences for true vacuum tunneling. These careful experiments result in very reproducible spectroscopy s a function of position on the surface, and as a function of tip/sample spacing. The characteristic features of the tunneling spectra are a significant filling of the gap region, a large density of states at the gap edges and a weak dip about 70meV below the Fermi level. Such IV characteristics are not compatible with a single gap BCS-like s-wave theory. Furthermore, they report spatially resolved spectroscopy where they, observe regions with two distinct gap values. A double gap structure appears in the tunneling spectra acquired in the vicinity of the boundary between these regions. They believe the double gap structure they observe in this case does not reflect an intrinsic gap anisotropy, but seems rather related to crystalline inhomogeneities. This demonstrates the potential of the STM's spatial resolution to shed some light on the controversy among the tunneling spectroscopy of high temperature superconductors published so far

155

Characterization of local dielectric breakdown in ultrathin SiO2 films using scanning tunneling microscopy and spectroscopy  

Science.gov (United States)

Local dielectric breakdown of ultrathin SiO2 films grown on silicon substrates has been investigated by using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). We found that STM observation can reveal individual quasibreakdown spots created by hot-electron injection into the oxide, as well as features of the topography such as atomic steps on the oxide surface. STS was used to study the local electrical properties of the oxide films before and after electrical stressing. We observed a leakage current at the quasibreakdown spots that passed through defect levels in the ultrathin oxide films. We also found that several tunneling spectra obtained from near leakage sites showed clear negative differential resistance. This phenomenon was attributed to the conductance change in the leakage path due to electron charging effects. Moreover, we confirmed the stressing polarity dependence of the leakage-site creation, and that atomic steps on the oxide and at the SiO2/Si interface did not cause any serous problem in the quasibreakdown process.

Watanabe, Heiji; Baba, Toshio; Ichikawa, Masakazu

1999-05-01

156

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

Science.gov (United States)

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

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

2007-04-01

157

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

International Nuclear Information System (INIS)

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

158

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

159

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

OpenAIRE

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

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

2012-01-01

160

The Kondo effect of an adatom in graphene and its scanning tunneling spectroscopy  

International Nuclear Information System (INIS)

We study the Kondo effect of a single magnetic adatom on the surface of graphene. The unique linear dispersion relation near the Dirac points in graphene makes it easier for the magnetic atom to form a local magnetic moment, which simply means that the Kondo resonance can be observed in a wider parameter region than in the metallic host. Our study indicates that the Kondo resonance, whenever the chemical potential is tuned away from the Dirac points, can indeed occur ranging from the Kondo regime, to the mixed valence, even to the empty orbital regime defined in the conventional metal host. While the Kondo resonance appears as a sharp peak in the Kondo regime, it has a peak-dip structure and/or an anti-resonance in the mixed valence and empty orbital regimes, which result from the Fano resonance due to the significant background due to dramatic broadening of the impurity level in graphene. We also study the scanning tunneling microscopy (STM) spectra of the adatom and they show obvious particle–hole asymmetry when the chemical potential is tuned by the gate voltages applied to the graphene. Finally, we explore the influence of the direct tunneling channel between the STM tip and the graphene on the Kondo resonance and find that the lineshape of the Kondo resonance is unaffected, which can be attributed to an unusually large asymmetry factor in graphene. Our study indicates that graphene is an ideal platform to systematically study Kondo physics and these results aretudy Kondo physics and these results are useful to further stimulate relevant experimental studies on the system. (paper)

161

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

162

Photon emission at molecular resolution induced by a scanning tunneling microscope.  

Science.gov (United States)

The tip-surface region of a scanning tunneling microscope (STM) emits light when the energy of the tunneling electrons is sufficient to excite luminescent processes. These processes provide access to dynamic aspects of the local electronic structure that are not directly amenable to conventional STM experiments. From monolayer films of carbon-60 fullerenes on gold(110) surfaces, intense emission is observed when the STM tip is placed above an individual molecule. The diameter of this emission spot associated with carbon-60 is approximately 4 angstroms. These results demonstrate the highest spatial resolution of light emission to date with a scanning probe technique. PMID:17736824

Berndt, R; Gaisch, R; Gimzewski, J K; Reihl, B; Schlittler, R R; Schneider, W D; Tschudy, M

1993-11-26

163

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

164

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

Energy Technology Data Exchange (ETDEWEB)

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.

Galloway, H.C.

1995-12-01

165

DESIGN NOTE: Bias-controlled mechanism for a scanning tunnelling microscope  

Science.gov (United States)

In this paper we describe a simple and low-cost circuit that limits the tunnelling current in a scanning tunnelling microscope, in order to protect the sample against sparks when using a bias higher than 1 V. During the evolution of the spark, when the current exceeds a predetermined value, a fast feedback control mechanism reduces the bias immediately and prevents the spark from developing. We show that this mechanism provides a better scanning image in comparison to a system without such a mechanism.

Flaxer, Eli

2006-10-01

166

Scanning tunneling microscopy I general principles and applications to clean and adsorbate-covered surfaces  

CERN Document Server

Scanning Tunneling Microscopy I provides a unique introduction to a novel and fascinating technique that produces beautiful images of nature on an atomic scale. It is the first of three volumes that together offer a comprehensive treatment of scanning tunneling microscopy, its diverse applications, and its theoretical treatment. In this volume the reader will find a detailed description of the technique itself and of its applications to metals, semiconductors, layered materials, adsorbed molecules and superconductors. In addition to the many representative results reviewed, extensive references to original work will help to make accessible the vast body of knowledge already accumulated in this field.

Wiesendanger, Roland

1992-01-01

167

Scanning tunneling microscopy of initial nitridation processes on oxidized Si(100) surface with radical nitrogen  

CERN Document Server

We have investigated the initial nitridation processes on oxidized Si(100) with radical nitrogen at a substrate temperature of 850degC using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). It is found that the thin oxide layer suppresses the changes of original Si step structures during nitridation, and this effect critically depends on the growth conditions of the oxide layer. Comparison of the nitride island morphology to the case of the clean surface suggests that the migration of the precursor during nitridation is suppressed by the oxygen in the layer. (author)

Takahashi, R; Ikeda, H; Sakashita, M; Sakai, A; Yasuda, Y; Nakatsuka, O; Zaima, S

2003-01-01

168

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

International Nuclear Information System (INIS)

Previous measurements of tunnel conductance in heterostructures and experiments with Josephson junctions suggest quantum tunneling has a definite duration. The authors use semiclassical methods to determine the effects of this delay on the tunneling current in a laser-assisted STM. A planar-planar STM model is used with the exact multiple image potential, and the energy distribution for a free-electron metal. It is necessary to average over the phase at barrier entry, and iteration with back propagated solutions is required to obtain the transmission coefficients for evenly spaced phases and specified energies at barrier entry. The simulations suggest that the dependence of the tunneling current on the wavelength of illumination can serve as a basis for determining the duration of barrier traversal. A power flux density of 1011 W/m2 would be required at several wavelengths from 1 to 10 ?m. It is possible that thermal effects could be separated from the modeled phenomena by determining the time dependence of the tunneling current with a pulsed laser

169

Fabrication of tungsten tip for scanning tunneling microscope by the lever principle  

International Nuclear Information System (INIS)

A novel experimental setup was designed to fabricate tungsten tips for scanning tunneling microscope (STM), based on simple mechanical lever principle. The equipment can quickly separate the tip from electrolyte to avoid the further etching of the fine-shaped tungsten tip. The setup is advantageous for its simplicity over complex electronic control systems. The use result in scanning electron microscope demonstrates that the radius of the tip can reach 50 nm. The tip was applied to scan the surface of highly-oriented pyrolytic graphite, and the results were satisfactory. It is shown that the tip can be used for the scanning of atomically resolved images. (authors)

170

Element specific imaging by scanning tunneling microscope combined with synchrotron-radiation  

International Nuclear Information System (INIS)

In order to achieve the imaging of scanning tunneling microscope (STM) with chemical information, we have developed the STM system combined with synchrotron radiation (SR-STM). That is, we are trying to get the effect of the SR-light illumination by an STM tip during the STM observation. In the previous work, we have succeeded to observe the x-ray absorption spectra (XAS) of Si L edge by an STM tip in the constant current operation mode. In the measurement, the clear tip height change as a function of the irradiated photon energy is observed. This result suggests that the STM can be used as a element specific analysis. However, the spatial resolution of the XAS measurement with the SR-STM, i.e. the size of the area where the STM tip is detecting the photo-induced electrons was not evident. In this paper, we will report the recent trial to measure the spatial resolution of the XAS measurement by the SR-STM. (author)

171

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.

172

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

Science.gov (United States)

Chemically functionalized probes are required for tunneling measurements made via chemical contacts ("Recognition Tunneling"). Here, we describe the etching of gold STM probes suitable for chemical functionalization with moieties bearing thiol groups. Insulated with high density polyethylene, these probes may be used in aqueous electrolytes with sub pA leakage currents. The area of the exposed probe surface was characterized via the saturation current in an electroactive solution (0.1 M K(3)Fe(CN)(6)). Twenty five percent of the probes had an exposed region of 10 nm radius or less. PMID:22299981

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

2012-01-01

173

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

Science.gov (United States)

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

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

2013-12-01

174

Theoretical studies of scanning tunneling microsopy and electron transport through nanostructures  

Science.gov (United States)

In this dissertation, we present several studies that employ density functional theory (DFT) to investigate physical principles underlying electron transport in nanostructures. Scanning tunneling microscopy and spectroscopy (STM/STS) experiments have been modeled using DFT calculations within the Tersoff-Hamann approximation, and the conductance and nonlinear I-V characteristics of several molecules have been studied using a method that combines the scattering-state formalism with DFT calculation techniques. We start with an introduction to density functional theory methods in Chapter One, followed by an application of these methods to study changes induced in boron nitride (BN) nanotubes under a transverse electric field in Chapter Two. Our calculations show that sufficiently strong fields can induce significant gap reduction and provide a way of tuning BN nanotube band gaps for applications. It was found that the band gap modulation increases with the nanotube diameter and is nearly independent of chirality. In Chapter Three, we performed DFT calculations to investigate recent scanning tunneling microscopy and spectroscopy (STM/STS) experiments performed on C60 monomers adsorbed on Au(111) and Ag(100) substrates. Our calculations demonstrated that resonances in the STS spectra of C60 on Au(III) and Ag(100) originate from C60 HOMO, LUMO, and LUMO+1 states, and that the STM tip trajectory plays an important role in determining the spatial inhomogeneities of dI/dV images. Continuing the theme of combined STM/DFT studies in Chapter Four, we carried out an investigation of the elastic and inelastic tunneling properties of Gd C82 monomers adsorbed on Ag(100). Measurements show the dominant inelastic channel to be spatially localized in a particular region of the molecule, and calculations indicate that this channel arises from a vibrational cage mode. The observed inelastic tunneling localization is then explained as a consequence of strong localization of the electron-phonon coupling to this mode. To calculate transport properties across non-equilibrium aperiodic systems, we developed a method that combines DFT calculation techniques with the scattering-state formalism in Chapter Five. The semi-infinite nature of the leads is accounted for by using scattering-state wavefunctions to represent electron states and the chemical potential difference between the leads is reproduced by introducing shifts in the bulk-lead Hartree potential corresponding to the applied bias. This scattering-state method was then applied in Chapter Six to investigate a recent negative differential resistance (NDR) measurement, postulated to originate from current carried by a carbon atomic wire bridging carbon nanotube leads. Our calculations show that such junctions exhibit NDR and display clear even-odd behavior in the size of their currents, lending support to the postulate of carbon chain mediated NDR. In Chapter Seven, we applied our scattering-state method to study electron transport across a single hydrogen molecule sandwiched between Pd and Pt contacts. Substituting Pt contacts with Pd is found to result in a dramatic reduction in conductance, consistent with two recent break junction experiments. The computed drop in conductance is explained in terms of a qualitative change in transport behavior between the two systems. (Abstract shortened by UMI.)

Khoo, Khoonghong

175

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

176

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

DEFF Research Database (Denmark)

A first-principles theory of inelastic tunneling between a model probe tip and an atom adsorbed on a surface is presented, extending the elastic tunneling theory of Tersoff and Hamann. The inelastic current is proportional to the change in the local density of states at the center of the tip due to the addition of the adsorbate. We use the theory to investigate the vibrational heating of an adsorbate below a scanning tunneling microscopy tip. We calculate the desorption rate of PI from Si(100)-H(2 X 1) as a function of the sample bias and tunnel current, and find excellent a,agreement with recent experimental data. [S0163-1829(98)09036-5].

Stokbro, Kurt; Hu, Ben Yu-Kuang

1998-01-01

177

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

178

Scanning tunneling microscopy and in situ spectroscopy of ultra thin Ti films and nano sized TiO x dots induced by STM  

Science.gov (United States)

Scanning tunneling microscopy and scanning tunneling spectroscopy (STM/STS) of a titanium (Ti) amorphous film and titanium oxide dots were investigated at room temperature and in ambient air by scanning tunneling microscope (STM). A smooth amorphous Ti film (3 nm thick) with an area of 1 ?m×1 ?m was chosen and imaged by STM. Tunneling current versus bias spectra for the film are symmetric to the origin in the STS measurements. Ultra thin films were oxidized at different positions by applying different voltage pulses ranging from 3.5 to 5 V for a period of 5 s. The subsequent images of STM show that the higher the bias applied to the film, the larger the dot. The in situ STS measurements were used, for the first time, to study the contaminant-free TiO x dots just as induced by STM. The in situ corresponding tunneling current versus bias spectrum was preceded by formation of a dot and followed by imaging the dot. STS I- V curves exhibit that the formed TiO x dots are n-type semiconductors. A transformation from slight asymmetry to drastic asymmetry of STS curves and increase in band gap indicate that nano-TiO x dots exhibit metallic to semiconducting behaviors with increase in the voltage pulse applied to sample.

Yin, You; Jiang, Jianfei; Cai, Qiyu; Cai, Bingchu

2002-10-01

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

Thermal effects in a scanning tunneling microscope associated with laser excitation  

International Nuclear Information System (INIS)

Some near-field experimental methods use laser excitation inducing thermal effects that are often neglected or incompletely estimated (1,2). We particularly investigate the case of a Scanning Tunneling Microscope (STM). The thermal response of the tip and of the sample are studied and the thermal ability of the STM are defined

181

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

182

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

183

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

184

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)

185

Direct probing of the stacking order and electronic spectrum of rhombohedral trilayer graphene with scanning tunneling microscopy  

Science.gov (United States)

Recently, rhombohedral trilayer graphene (r-TLG) has attracted much attention because of its low-energy flat bands, which are predicted to result in many strongly correlated phenomena. However, there has been a need for more experimental evidence for these flat bands in the r-TLG, since the supporting substrates usually have strong destructive effects on the low-energy band structure of graphene systems. Here, we demonstrate that it is possible to directly probe the stacking order and electronic spectrum of the r-TLG on a graphite surface with scanning tunneling microscopy around a monoatomic step edge of the top graphene layer. The tunneling spectra of the r-TLG exhibit four adjacent peaks, which are generated by the low-energy flat bands, flanking the charge neutrality point. Based on these spectra, the true energy gap and the energy gap at the K point of the r-TLG are determined as about 9 and 23 meV, respectively. The observed features are well reproduced by a low-energy effective Hamiltonian.

Xu, Rui; Yin, Long-Jing; Qiao, Jia-Bin; Bai, Ke-Ke; Nie, Jia-Cai; He, Lin

2015-01-01

186

Scanning tunneling microscopy of films of amorphous carbon doped with copper  

International Nuclear Information System (INIS)

The results of experimental studies of the copper-doped hydrogenated amorphous carbon films by scanning tunneling microscopy and spectroscopy are reported. These results are indicative of the effect of spatial ordering of nanostructures in thin films based on carbon and copper. Geometric parameters of nanostructures were measured. In the context of the Simmons model, the work function was estimated to be equal to ? ? 0.05 eV. Oscillations in differential conductance with a period in a voltage of ?V = 200-400 mV were detected in tunneling contacts of Ir with the films. The origin of the observed oscillations is discussed

187

Transient measurements with an ultrafast scanning tunneling microscope on semiconductor surfaces  

OpenAIRE

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 id...

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

2006-01-01

188

A Mechanism for Cutting Carbon Nanotubes with a Scanning Tunneling Microscope  

CERN Document Server

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

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

2000-01-01

189

A comparison of SIR-B directional ocean wave spectra with aircraft scanning radar spectra  

Science.gov (United States)

Directional ocean wave spectra derived from Shuttle Imaging Radar-B (SIR-B) L-band imagery collected off the coast of Southern Chile on 11 and 12 October 1984 were compared with independent spectral estimates from two airborne scanning radars. In sea states with significant wave heights ranging from 3 to 5 meters, the SIR-B-derived sspectra at 18 deg and 25 deg off nadir yielded reasonable estimates of wavelengths, directions, and spectral shapes for all wave systems encountered, including a purely azimuth-traveling system. A SIR-B image intensity variance spectrum containing predominantly range-traveling waves closely resembles an independent aircraft estimate of the slope variance spectrum. The prediction of a U.S. Navy global spectral ocean wave model on 11 October 1984 exhibited no significant bias in dominant wave number but contained a directional bias of about 30 deg with respect to the mean of the aircraft and spacecraft estimates.

Beal, R. C.; Monaldo, F. M.; Tilley, D. G.; Irvine, D. E.; Walsh, E. J.; Jackson, F. C.; Hancock, D. W., III; Hines, D. E.

1986-01-01

190

EDITORIAL: Three decades of scanning tunnelling microscopy that changed the course of surface science Three decades of scanning tunnelling microscopy that changed the course of surface science  

Science.gov (United States)

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

Ramachandra Rao, M. S.; Margaritondo, Giorgio

2011-11-01

191

Scanning tunnelling microscopy of real time defect motion on surfaces  

International Nuclear Information System (INIS)

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

192

Scanning tunneling spectroscopy of MgB2 micr-owires  

Science.gov (United States)

We report scanning tunneling spectroscopy of polycrystalline MgB2 microwires using both normal metal-insulator-superconductor (N-I-S) and superconductor-insulator-superconductor (S-I-S) tunnel junctions. A segment of the micro-wire was affixed to a Pt-Ir STM tip and approached to a gold film in the first case, and to another segment of the micro-wire in the latter case. In each configuration we observe both gaps, ? _pi and ? _sigma, and for the S-I-S junctions we observe a directional dependence of the dI/dV on the relative orientation of the grains in each superconducting electrode. In particular, we found that for a certain orientation of the grains, which we infer to be perpendicular, tunneling between ?-bands and between ?-bands is strongly suppressed. We argue that these are matrix element effects, and discuss symmetry and fermi velocity contributions to these.

Heitmann, Thomas; Rzchowski, M. S.; Canfield, Paul; Finnemore, Douglas

2004-03-01

193

Field enhancement and rectification of surface plasmons detected by scanning tunneling microscopy  

Science.gov (United States)

We investigated surface plasmon (SP) waves in the junction of a scanning tunneling microscope (STM). The SP waves were generated on a 45-nm thin Au film and their near-field was locally probed by the tip of the STM. The temporal structure of the observed tunneling current signal revealed information on the physical mechanisms which regulate the interaction of the electric fields in play. We estimated the magnitude of the local electric field enhancement on surface nanostructures by taking advantage of the nonlinearity of the tunneling junction. The mapping of the plasmon field to the surface topography delivers experimental evidence for the localization of SP waves in narrow gaps of a few nanometers width and/or at grain boundaries. The results gained can directly be utilized (e.g., in the development of nanoscale geometries for high-energy electron sources where electrons are accelerated in the electric field of surface plasmons).

Lenner, Miklós; Rácz, Péter; Dombi, Péter; Farkas, Gy?z?; Kroó, Norbert

2011-05-01

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

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

International Nuclear Information System (INIS)

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

196

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

Science.gov (United States)

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

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

2012-07-01

197

Scanning tunneling microscopy of the cleaved surfaces of BI-containing superconductors  

International Nuclear Information System (INIS)

Scanning tunneling microscopy (STM) images of the cleaved surfaces of Bi2Sr2CaCu2O8 (2212), Bi2Sr2CuO6 (221), nd the Pb-substituted Bi1.5Pb0.5Sr2CuO6 (Pb-substituted 221) at room temperature have been obtained. On the 2212 (Tc = 85 K) compound, high resolution images show striations ? 10 angstrom to 30 angstrom wide. Similar striations of a periodicity of ? 27 angstrom are also observed on the 221 (Tc = 10 K) compound. On the Pb-substituted 221 (Tc = 25 K) compound, no periodic structure can be observed. On samples oriented with Laue reflection, the striations are observed to run parallel to the a or b axis of the crystal. These striations are likely to be associated with the undulations along the b axis of the Bi layer observed in recent transmission electron micrographs. For the 2212 compound, comparison of the dependence of scan line characteristics on tunneling bias with calculations on the density of states of each elemental component around the Fermi energy also suggests that tunneling occurs on the Bi face. The topographical and tunneling bias dependence results show that the Bi-rich surfaces of these new superconductors is essentially a termination of the bulk structure even though structural or chemical defects are common

198

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)

199

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

200

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

201

Negative Differential Resistance in the Scanning Tunneling Spectroscopy of Organic molecules  

CERN Document Server

The conductance-voltage spectrum of molecular nanostructures measured by scanning tunneling spectroscopy (STS) is generally assumed to reflect the local density of states of the molecule. This excludes the possibility of observing negative differential resistance (NDR). We report here the observation of NDR in the scanning tunneling microscope (STM) current-voltage (I-V) characteristics of self-assembled monolayer (SAM) of 4-p-Terphenylthiol molecules on gold substrate measured using a platinum probe. We argue that the NDR arises from narrow structures in the local density of states at the tip apex atom and show that depending on the electrostatic potential profile across the system, NDR could be observed in one or both bias directions.

Xue, Y; Hong, S; Reifenberger, R; Henderson, J I; Kubiak, C P; Xue, Yongqiang; Datta, Supriyo; Hong, Seunghun; Henderson, Jason I.; Kubiak, Cliff P.

1999-01-01

202

Structure of hydrated oligonucleotides studied by in situ scanning tunneling microscopy.  

OpenAIRE

We have used the scanning tunneling microscope (STM) to image several synthetic oligonucleotides adsorbed onto a positively charged Au(111) electrode. The molecules were deposited and imaged in aqueous electrolyte under potential control, a procedure that eliminated the problem of the substrate artifacts that had limited some previous STM studies. Experiments were carried out with two types of single-stranded molecules (11 and 20 bases long) and three types of double-stranded molecules (20 an...

Jing, T. W.; Jeffrey, A. M.; Derose, J. A.; Lyubchenko, Y. L.; Shlyakhtenko, L. S.; Harrington, R. E.; Appella, E.; Larsen, J.; Vaught, A.; Rekesh, D.

1993-01-01

203

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

CERN Document Server

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.

Krawiec, M; Jalochowski, M

2005-01-01

204

Nanoscale visualization of microcrystalline chlorophyll a investigated with scanning tunneling microscopy  

Science.gov (United States)

We have studied the topography of microcrystalline chlorophyll a films, that have been electrodeposited onto gold electrodes, using scanning tunneling microscopy (STM). The STM revealed that the films possess a polycrystalline structure with small grain sizes of 50 to 100 nm in diameter and a very rough surface topography with a surface roughness of 5 to 10 nm over surface areas of 1 × 1 ?m. The surface structure correlates with results from an earlier photocurrent study of microcrystalline chlorophyll a.

Boussaad, S.; de, J. A.; Rose; Leblanc, R. M.

1995-11-01

205

Scanning tunnelling microscope combined with synchrotron radiation for element specific analysis  

International Nuclear Information System (INIS)

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

206

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

OpenAIRE

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

Xue, Yongqiang; Datta, Supriyo

1999-01-01

207

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

OpenAIRE

Scanning tunneling microscope (STM) induced light emission from artificial atomic scale structures comprising silicon dangling bonds on hydrogen-terminated Si(001) surfaces has been mapped spatially and analyzed spectroscopically in the visible spectral range. The light emission is based on a novel mechanism involving optical transitions between a tip state and localized states on the sample surface. The wavelength of the photons can be changed by the bias voltage of the STM. The spatial reso...

Thirstrup, C.; Sakurai, M.; Stokbro, Kurt; Aono, M.

1999-01-01

208

Phase change of tetrahedral amorphous-carbon by low energy electrons in a scanning tunnelling microscope  

International Nuclear Information System (INIS)

Low energy electron-based energy deposition in tetrahedral amorphous-carbon thin films by a scanning tunnelling microscope leads to a local phase change of the carbon. Both the mass density and the electrical resistivity are reduced indicating a graphitization. We expose nano-sized surface areas to field emitted low energy electrons under high vacuum conditions and investigate the temperature and electron energy dependence of the carbon phase change process. Supplementary topography measurements are performed by atomic force microscopy.

209

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

OpenAIRE

Direct observation of electric potential and field variation near local scatterers like grain boundaries, triple points and voids in thin platinum films studied by scanning tunneling potentiometry is presented. The field is highest at a void, followed by a triple point and a grain boundary. The local field near a void can even be four orders of magnitude higher than the macroscopic field. This indicates that the void is the most likely place for an electromigration induced f...

Ramaswamy, Geetha; Raychaudhuri, A. K.

1998-01-01

210

Local transport measurements at mesoscopic length scales using scanning tunneling potentiometry  

OpenAIRE

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

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

2012-01-01

211

Scanning tunneling potentiometry (STP) studies of gold islands on a thin carbon film  

OpenAIRE

The technique of scanning tunneling microscopy (STM) has been used to study the spatial variation of the electric potential on thin film surfaces. Topography and potential distribution of the film surface are measured simultaneously. A lateral voltage gradient is obtained by applying a DC voltage bias to a metal film. With our experimental arrangement potential differences of a few my V can be distinguished. On the lateral scale, potential drops of about 500 my V can be localized within a dis...

Besold, J.; Reiss, Gu?nter; Hoffmann, Horst

1993-01-01

212

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

OpenAIRE

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 energ...

Irkhin, V. Yu; Katsnelson, M. I.

2005-01-01

213

Dissociation of individual molecules with electrons from the tip of a scanning tunneling microscope.  

Science.gov (United States)

The scanning tunneling microscope (STM) can be used to select a particular adsorbed molecule, probe its electronic structure, dissociate the molecule by using electrons from the STM tip, and then examine the dissociation products. These capabilities are demonstrated for decaborane(14) (B(10)H(14)) molecules adsorbed on a silicon(111)-(7 x 7) surface. In addition to basic studies, such selective dissociation processes can be used in a variety of applications to control surface chemistry on the molecular scale. PMID:17816830

Dujardin, G; Walkup, R E; Avouris, P

1992-03-01

214

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

OpenAIRE

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

Hirstein, Andreas

1998-01-01

215

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.)

216

Imaging of biomolecules with the scanning tunneling microscope: Problems and prospects  

Energy Technology Data Exchange (ETDEWEB)

The capabilities of the scanning tunneling microscope as a tool to study the morphology and structure of adsorbed biomolecules are reviewed in view of recent experimental results. Problems such as electrical conductivity of the biomolecules, fixation to the substrate and identification are analyzed in detail. In particular, the role of tip--surface interaction giving rise to repulsive forces is illustrated. It is concluded that fixation rather than conductivity is the major obstacle to the use of the STM for biological imaging.

Salmeron, M. (Lawrence Berkeley Laboratory, Berkeley, California 94720 (USA)); Beebe, T. (Lawrence Livermore National Laboratory, Livermore California 94550 (USA)); Odriozola, J. (Lawrence Berkeley Laboratory, Berkeley, California 94720 (USA)); Wilson, T. (Lawrence Livermore National Laboratory, Livermore, California 94550 (USA)); Ogletree, D.F. (Lawrence Berkeley Laboratory, Berkeley, California 94720 (USA)); Siekhaus, W. (Lawrence Livermore National Laboratory, Livermore, California 94550 (USA))

1990-01-01

217

Scanning tunneling microscopy on rough surfaces: tip-shape-limited resolution  

OpenAIRE

This paper discusses the reliability of scanning tunneling microscopy (STM) images of mesoscopically rough surfaces. The specific structure of these images represents a convolution between the real surface topography and the shape of the tip. In order to interpret these images quantitatively, the line scans of steep and high steps can be used to obtain an image of the tip itself. This image shows tip radii ranging typically from 5 to 15 nm and cone angles of about 30° over a length of 80 nm,...

Reiss, Gu?nter; Vancea, Johann; Wittmann, H.; Zweck, Josef; Hoffmann, Horst

1990-01-01

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

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

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

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

International Nuclear Information System (INIS)

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

222

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

DEFF Research Database (Denmark)

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

Giusca, Cristina E; Tison, Yann

2008-01-01

223

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

224

Note: Long range and accurate measurement of deep trench microstructures by a specialized scanning tunneling microscope  

Science.gov (United States)

A compact but practical scanning tunneling microscope (STM) with high aspect ratio and high depth capability has been specially developed. Long range scanning mechanism with tilt-adjustment stage is adopted for the purpose of adjusting the probe-sample relative angle to compensate the non-parallel effects. A periodical trench microstructure with a pitch of 10 ?m has been successfully imaged with a long scanning range up to 2.0 mm. More innovatively, a deep trench with depth and step height of 23.0 ?m has also been successfully measured, and slope angle of the sidewall can approximately achieve 67°. The probe can continuously climb the high step and exploring the trench bottom without tip crashing. The new STM could perform long range measurement for the deep trench and high step surfaces without image distortion. It enables accurate measurement and quality control of periodical trench microstructures.

Ju, Bing-Feng; Chen, Yuan-Liu; Zhang, Wei; Zhu, Wule; Jin, Chao; Fang, F. Z.

2012-05-01

225

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

Science.gov (United States)

Igor Yanson showed 38 yr 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 point contact spectroscopy (PCS) technique improved enormously. The application of the scanning probe microscopy (SPM) techniques in the late 1980 s 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.

Tartaglini, E.; Verhagen, T. G. A.; Galli, F.; Trouwborst, M. L.; Müller, R.; Shiota, T.; Aarts, J.; van Ruitenbeek, J. M.

2013-03-01

226

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

Science.gov (United States)

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

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

2012-06-01

227

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

Science.gov (United States)

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

Raigoza, Annette F; Webb, Lauren J

2012-11-28

228

Scanning tunneling microscope images of adenine and thymine at atomic resolution.  

Science.gov (United States)

The scanning tunneling microscope has been used to obtain images of DNA that reveal its major and minor grooves and the direction of helical coiling, but sufficient resolution has not yet been achieved to identify its bases. To determine if this technology is capable of identifying individual DNA bases, we have examined the molecular arrangements of adenine and thymine attached to the basal plane of highly oriented pyrolytic graphite. Both molecules form highly organized lattices following deposition on heated graphite. Lattice dimensions, structural periodicities, and the epitaxy of adenine and thymine molecules with respect to the basal plane of graphite have been determined. Images of these molecules at atomic resolution reveal that the aromatic regions are strongly detected in both molecules while the various side-groups are not well-resolved. These studies provide the first evidence that tunneling microscopy can be used to discriminate between purines and pyramidines. PMID:1808704

Allen, M J; Balooch, M; Subbiah, S; Tench, R J; Siekhaus, W; Balhorn, R

1991-09-01

229

Scanning tunneling microscopy of 1, 2, and 3 layers of electroactive compounds.  

Science.gov (United States)

Bilayer and trilayer organic films grown on Au(111) were studied by scanning tunneling microscopy (STM). Studies were carried out under UHV conditions with the sample cooled to either 80 or 100K. Cobalt(II)phthalocyanine [CoPc] was deposited from vapor onto Au(111), followed by vanadyl phthalocyanine, VOPc. CoPc coverages studied were 0.5 and 1 monolayer, while VOPc coverages were about 0.5 monolayer. Constant current images were acquired at high tunneling gap resistance, of the order of 30GOmega. Two different physical structures were observed for VOPc on CoPc, and each had a characteristic I(V) curve indicating significantly different unoccupied state density. It is also demonstrated that the transmission factor for two layers of VOPc is not simply the product of the transmission factors for each layer. PMID:12801656

Barlow, Dan; Scudiero, Louis; Hipps, K W

2003-01-01

230

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

231

Silicon Surface Conductance Investigated Using a Multiple-Probe Scanning Tunneling Microscope  

Science.gov (United States)

A custom-built multiple probe scanning tunneling microscope (STM) was used to perform measurements of the surface conductivity of Si(111)-7 × 7 and H-Si(111)-1 × 1 surfaces. Metallic contacts with points spaced probes, while a central STM tip imaged the region between the contacts. A novel imaging method measuring the fraction of the tunneling current flowing to each contact was used to image surface conductivity with nanometer resolution. Si(111)-7 × 7 was shown to be significantly more conductive than H-Si(111)-1 × 1. Additionally, the resistance of single atomic steps on the Si(111)-7 × 7 was imaged using this method.

Zikovsky, Janik; Salomons, Mark H.; Dogel, Stanislav A.; Wolkow, Robert A.

232

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

233

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

234

Adsorption of oxygen on Pt3Sn(111) studied by scanning tunneling microscopy and x-ray photoelectron diffraction  

International Nuclear Information System (INIS)

The adsorption of oxygen on the (111) surface of the Pt3Sn alloy was studied by means of scanning tunneling microscopy (STM) and x-ray photoelectron diffraction (XPD). As Auger electron spectroscopy, low-energy ion scattering, and x-ray photoelectron spectroscopy indicate, upon oxygen exposure (range 10000 L, with the sample at circa 770 K) Sn segregates to the surface and forms a two-dimensional tin-oxygen layer. In the x-ray photoemission spectra no pronounced chemical shift is visible that would indicate a thicker tin oxide layer. After exposure to 10000 L O2 at 770 K low-energy electron diffraction shows a streaky2x2 pattern with additional spots. Scanning tunneling microscopy images show a surface with a 2x2periodicity characterized by an high defect density. The corrugation of this surface is substantially higher than that of the clean surface. After annealing in vacuum at temperatures ranging from 600 to 800 K, a sharp 4x4 low-energy electron diffraction pattern can be observed. STM then reveals a superlattice of depressions, the remaining protrusions are slightly laterally displaced from their 2x2 positions. X-ray photoelectron diffraction intensities of the 4x4 phase show hardly any change for Pt 4f, whereas Sn3d azimuthal curves measured at higher polar angles are substantially modified after oxygen exposure. In order to understand the nature of the features observed in the STM images, the experimental XPD curves were compared with singimental XPD curves were compared with single and multiple scattering cluster calculations performed for various structural models. On the basis of these results we propose a model involving the reconstruction of the substrate surface

235

Adsorption of oxygen on Pt3Sn studied by scanning tunneling microscopy and x-ray photoelectron diffraction  

Science.gov (United States)

The adsorption of oxygen on the (111) surface of the Pt3Sn alloy was studied by means of scanning tunneling microscopy (STM) and x-ray photoelectron diffraction (XPD). As Auger electron spectroscopy, low-energy ion scattering, and x-ray photoelectron spectroscopy indicate, upon oxygen exposure (range 10000 L, with the sample at circa 770 K) Sn segregates to the surface and forms a two-dimensional tin-oxygen layer. In the x-ray photoemission spectra no pronounced chemical shift is visible that would indicate a thicker tin oxide layer. After exposure to 10000 L O2 at 770 K low-energy electron diffraction shows a streaky2×2 pattern with additional spots. Scanning tunneling microscopy images show a surface with a 2×2periodicity characterized by an high defect density. The corrugation of this surface is substantially higher than that of the clean surface. After annealing in vacuum at temperatures ranging from 600 to 800 K, a sharp 4×4 low-energy electron diffraction pattern can be observed. STM then reveals a superlattice of depressions, the remaining protrusions are slightly laterally displaced from their 2×2 positions. X-ray photoelectron diffraction intensities of the 4×4 phase show hardly any change for Pt 4f, whereas Sn3d azimuthal curves measured at higher polar angles are substantially modified after oxygen exposure. In order to understand the nature of the features observed in the STM images, the experimental XPD curves were compared with single and multiple scattering cluster calculations performed for various structural models. On the basis of these results we propose a model involving the reconstruction of the substrate surface.

Hoheisel, M.; Speller, S.; Heiland, W.; Atrei, A.; Bardi, U.; Rovida, G.

2002-10-01

236

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.

237

Scanning tunneling microscopy and spectroscopy on GaN and InGaN surfaces  

International Nuclear Information System (INIS)

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

238

Investigation of gold nanocrystals by ultrahigh vacuum cryogenic scanning tunneling microscopy  

Science.gov (United States)

Alkane thiol stabilized 28,000 amu Au nanocrystals (28k Au) supported on graphite and Au(111) substrates have been investigated using a newly-constructed cryogenic STM. STM measurements revealed that isolated nanocrystals are highly mobile on bare Au(111) and graphite, and cannot be imaged by STM even at cryogenic temperatures unless they are stabilized by inclusion in a nanocrystal film or by some surface defect. Using a Au substrate which was coated with a SAM of xylenedithiol to support the nanocrystals reduced their surface mobility to the point they could be imaged in isolation, but also reduced their overall binding to the surface. Tunneling spectroscopy performed in conjunction with the STM imaging revealed that the charging energy of adding a single electron to a 28k Au nanocrystal, which has a diameter of 1.7 nm, plays an important role in the nanocrystal's electronic properties, and leads to a series of steps in the measured current-versus-voltage spectra. The semi-classical model of double-junction tunneling through a small center conductor was used to model this phenomenon which is known as the Coulomb staircase. In some cases, a nanocrystal transferred to the tip and stabilized at its apex. Under these conditions, exceptionally clear Coulomb staircase tunneling behavior was observed. These spectra showed multiple charging steps and were in excellent agreement with the semi-classical model. Examination of the first derivative of the nanocrystal-on-tip spectra revealed small peaks in addition to the charging peaks. This additional structure was attributed to quantum size effect splitting of the electronic energy levels of the nanocrystal.

Harrell, Lee Elwyn

1998-11-01

239

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

OpenAIRE

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

1994-01-01

240

Low energy ion scattering and scanning tunneling microscopy for surface structure analysis  

International Nuclear Information System (INIS)

Low energy ion scattering (ISS) and scanning tunneling microscopy (STM) are powerful tools for the analysis of surface structures. Both techniques are operative in real space. The ion scattering techniques afford quantitative data on surface structure but as spatial averages only. STM provides non-averaged local information but it is not necessarily quantitative. STM provides detailed information on surface defects, e.g. steps, and mesoscopic structures. The two techniques will be compared in the case of (110) surfaces of Au and Pb. copyright 1996 American Institute of Physics

241

A MEASUREMENT OF A SURFACE SELF-DIFFUSION COEFFICIENT BY SCANNING TUNNELING MICROSCOPY  

OpenAIRE

A technique is described to measure a surface self-diffusion coefficient (D) of a metal (gold) by scanning tunneling microscopy. Micro-hills formed on a gold face show a shape evolution by a diffusion transport of kink site atoms. D is determined via a measurement of the hill apex radius as a function of time and includes corrections of image errors. The technique shows that STM can be used to study diffusion and it opens the possibility of measuring diffusion at lower temperatures where D co...

Drechsler, M.; Blackford, B.; Putnam, A.; Jericho, M.

1989-01-01

242

Time-correlations as a contrast mechanism in scanning-tunneling-microscopy-induced photon emission  

International Nuclear Information System (INIS)

We have developed an experimental technique based on scanning-tunneling microscope (STM) which permits to record simultaneously topography, STM-induced photon emission and a map of two-photon auto-correlations for time resolutions down to the sub-nanosecond range. In the case of a gold surface at air, we show that the tip-induced luminescence exhibits a photon-bunching phenomenon at a 10-ns time scale which depends both on bias and on local topography. The photon bunching was exclusively observed at specific bumps of the surface

243

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

OpenAIRE

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

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

1996-01-01

244

A scanning tunneling microscopy (STM) investigation of complex formation between cytochrome P450(cam) and putidaredoxin.  

OpenAIRE

We have previously reported the scanning tunnelling microscopy (STM) imaging under buffer of the heme monooxygenase cytochrome P450(cam) from Pseudomonas putida [Faraday Discuss. 116 (2000) 1]. We describe here the adsorption and STM imaging under buffer of complexes of a mutant of cytochrome P450(cam), K344C, and wild-type putidaredoxin (Pdx) on gold(111). The images of Pdx on its own on gold(111) are not uniform, presumably due to multiple orientations of protein adsorption because of the p...

Djuricic, D.; Hill, Ha; Lo, Kk; Wong, Ll

2002-01-01

245

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

246

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

OpenAIRE

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

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

2001-01-01

247

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,

248

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

CERN Document Server

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

Ramaswamy, G; Ramaswamy, Geetha

1998-01-01

249

Low-temperature scanning tunneling microscopy and spectroscopy measurements of ultrathin Pb films  

Science.gov (United States)

We have investigated the electronic properties of ultrathin Pb films by low temperature scanning tunneling microscopy and spectroscopy. Our results show that 30 nm thick Pb(111) films grown on atomically flat highly oriented pyrolytic graphite (HOPG) and on amorphous SiO2 are both in the strong-coupling limit with transition temperature and energy gap close to the bulk value. Conductance maps and spectroscopy in the vortex state reveal a bound state at the center of the vortices, which suggest that the films are in the clean limit. Measurements of 3 nm Pb films grown on HOPG show a clear crossover to the weak-coupling regime and dirty limit.

Moore, S. A.; Fedor, J.; Iavarone, M.

2015-04-01

250

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

OpenAIRE

Electron-electron interactions and excitons in carbon nanotubes are locally measured by combining Scanning tunneling spectroscopy and optical absorption in bundles of nanotubes. The largest gap deduced from measurements at the top of the bundle is found to be related to the intrinsic quasi-particle gap. From the difference with optical transitions, we deduced exciton binding energies of 0.4 eV for the gap and 0.7 eV for the second Van Hove singularity. This provides the firs...

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

2009-01-01

251

Single-bond formation and characterization with a scanning tunneling microscope  

Science.gov (United States)

A scanning tunneling microscope (STM) was used to manipulate the bonding of a carbon monoxide (CO) molecule and to analyze the structure and vibrational properties of individual products. Individual iron (Fe) atoms were evaporated and coadsorbed with CO molecules on a silver (110) surface at 13 kelvin. A CO molecule was transferred from the surface to the STM tip and bonded with an Fe atom to form Fe(CO). A second CO molecule was similarly transferred and bonded with Fe(CO) to form Fe(CO)(2). Controlled bond formation and characterization at the single-bond level probe chemistry at the spatial limit. PMID:10576735

Lee; Ho

1999-11-26

252

Different tips for high-resolution atomic force microscopy and scanning tunneling microscopy of single molecules  

Science.gov (United States)

We explore different tip functionalizations for atomic force microscopy (AFM), scanning tunneling microscopy (STM), and Kelvin probe force microscopy (KPFM) of organic molecules on thin insulating films. We describe in detail how tips terminated with single Br and Xe atoms can be created. The performance of these tips in AFM, STM, and KPFM imaging of single molecules is compared to other tip terminations, and the advantages and disadvantages of the different tips are discussed. The Br tip was found to be particularly useful for AFM and lateral manipulation, whereas the Xe tip excelled in STM and KPFM.

Mohn, Fabian; Schuler, Bruno; Gross, Leo; Meyer, Gerhard

2013-02-01

253

Hydrothermally-grown ZnO nanowire tips for scanning tunnelling microscopy.  

Science.gov (United States)

The probe tip is pivotal in determining the resolution and nature of features observed in the Scanning Tunnelling Microscope (STM). We have augmented a conventional Pt/Ir metallic tip with a hydrothermally grown ZnO nanowire (NW). Atomic resolution imaging of graphite is attained. Current-voltage (IV) characteristics demonstrate an asymmetry stemming from the unintentional n-type doping of the ZnO NW, whereas the expected Schottky barrier at the ZnO-Pt/Ir interface is shown to have negligible effect. Moreover the photoconductivity of the system is investigated, paving the way towards a photodetector capable of atomic resolution. PMID:22755064

Wong, H S; Tan, S C; Wang, N; Durkan, C

2012-03-01

254

Spin-polarized scanning tunneling microscopy. Influence of the tip on measurements  

International Nuclear Information System (INIS)

After a brief introduction of the spin-polarized scanning tunneling microscopy (SP-STM), its measurement techniques are described based on our recent experimental results. We have observed anomalously high spin contrast for epitaxially grown Mn(001)/Fe(001) samples. This phenomenon can be attributed to a single atom or a cluster of Mn attached to the apex of the thin film Fe tip. This interpretation is supported by a recent first-principle calculation of model magnetic tips. These results stress the importance of the identification of the magnetic tip and its precise control at an atomic level for the purpose of SP-STM measurement. (author)

255

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

256

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

International Nuclear Information System (INIS)

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

257

Tip-induced nanostructuring of alloy surfaces with an electrochemical scanning tunneling microscope  

Science.gov (United States)

Tip-induced nanostructuring with an electrochemical scanning tunneling microscope (EC-STM) was applied to alloy surfaces in order to resolve the reasons for the unusual stability of tip-induced metal clusters to anodic oxidation. Therefore Au thin films on glass and AuCu-alloy single crystals of different composition and surface orientation were used as substrates. The experiments give evidence that the three main factors for cluster formation and stability are the attractive interaction between tip and substrate, alloy formation during the cluster formation process as well as additional stabilization by adsorption of an underpotential deposition layer. Experimental results on the three aspects are presented and discussed.

Maupai, S.; Dakkouri, A. S.; Schmuki, P.

2005-12-01

258

Scanning tunnelling microscopy investigations of simple surface reactions on Rh(110)  

International Nuclear Information System (INIS)

The unique potential of scanning tunnelling microscopy (STM) as a tool for determining the elementary steps of surface catalytic reactions at an atomic scale is highlighted using selected representative results obtained in studies of adsorption and reactions on the Rh(110) surface. The Rh(110) surface was chosen as a prototype of a flexible catalyst, due to its propensity to reconstruct in the presence of adsorbates. Both dissociative adsorption of simple molecules and oxidation reactions involving adsorbed oxygen layers are considered. It was demonstrated that a combined approach where STM was used in conjunction with other experimental techniques and ab initio calculations yields a thorough description of the underlying reaction mechanism. (topical review)

259

Real-time scanning tunneling microscopy studies of thin film deposition and ion erosion  

OpenAIRE

In this thesis I present my research on the physics of some important processes in the production of thin films. I studied physical vapour deposition (PVD) and thin film modification through ion bombardment using a newly developed, high-speed scanning tunneling microscope (STM). The instrument has the special property that it can be tilted and azimuthally rotated to allow atom or ion beams a direct line-of-sight access to the region of the surface that is being imaged by the STM tip. With the...

Fokkema, Vincent

2011-01-01

260

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2008-09-09

261

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

Science.gov (United States)

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

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

2015-02-01

262

Dysprosium disilicide nanostructures on silicon(001) studied by scanning tunneling microscopy and transmission electron microscopy  

International Nuclear Information System (INIS)

The microstructure of self-assembled dysprosium silicide nanostructures on silicon(001) has been studied by scanning tunneling microscopy and transmission electron microscopy. The studies focused on nanostructures that involve multiple atomic layers of the silicide. Cross-sectional high resolution transmission electron microscopy images and fast Fourier transform analysis showed that both hexagonal and orthorhombic/tetragonal silicide phases were present. Both the magnitude and the anisotropy of lattice mismatch between the silicide and the substrate play roles in the morphology and epitaxial growth of the nanostructures formed

263

Minimizing image-processing artifacts in scanning tunneling microscopy using linear-regression fitting  

Science.gov (United States)

We present a method for removing noise from scanning tunneling microscopy images based on least-squares fitting of spatial data. Modeling the known structure of the surface, including isolated features and surface steps, allows for effective discrimination of signal from noise and produces minimal processing artifacts, even for very noisy images. This approach is effective for removing external noise due to vibrational or acoustic interference, and can also be applied to correct for tip-related height jumps as well as to flatten images warped by thermal effects or nonlinearity of the microscope scanner.

Fogarty, Daniel P.; Deering, Amanda L.; Guo, Song; Wei, Zhongqing; Kautz, Natalie A.; Kandel, S. Alex

2006-12-01

264

Molecular beam epitaxy growth and scanning tunneling microscopy study of TiSe$_2$ ultrathin films  

OpenAIRE

Molecular beam epitaxy is used to grow TiSe2 ultrathin films on graphitized SiC(0001) substrate. TiSe2films proceed via a nearly layer-by-layer growth mode and exhibit two dominant types of defects, identified as Se vacancy and interstitial, respectively. By means of scanning tunneling microscopy, we demonstrate that the well-established charge density waves can survive in single unit-cell (one triple layer) regime, and find a gradual reduction in their correlation length as...

Peng, Jun-ping; Guan, Jia-qi; Zhang, Hui-min; Song, Can-li; Wang, Lili; He, Ke; Xue, Qi-kun; Ma, Xu-cun

2014-01-01

265

Ultrahigh vacuum scanning force/scanning tunneling microscope: Application to high-resolution imaging of Si(111)7 × 7  

Science.gov (United States)

We present a combined scanning force/scanning tunneling microscope (SFM/STM) operating in ultrahigh vacuum using a fiber-optic laser interferometer to detect the lever deflection. As force microscope it operates in ac and dc mode with commercial (Si, Si3N4) or individually made (W) cantilevers. Samples and cantilevers can be inserted without breaking the vacuum using a load-lock system. The force sensor includes a novel three-dimensional micropositioner based on the piezoelectric slider principle. The system includes standard surface analytical techniques (low-energy electron diffraction/Auger, prepared for x-ray photoelectron spectroscopy) and is equipped for mass spectroscopic detection of reaction products from catalytic surfaces at elevated temperature. Tips are cleaned in situ using electron bombardment. By using tungsten cantilevers with a high spring constant (k=100-200 N/m), it is possible to switch directly between STM and SFM operation. As reference surface we have used the Si(111)7×7 reconstruction, prepared by in situ flashing to 1150 °C, which is imaged at atomic resolution using STM as well as ac-mode SFM.

Olsson, L.; Wigren, R.; Erlandsson, R.

1996-06-01

266

Variable-temperature independently driven four-tip scanning tunneling microscope  

International Nuclear Information System (INIS)

The authors have developed an ultrahigh vacuum (UHV) variable-temperature four-tip scanning tunneling microscope (STM), operating from room temperature down to 7 K, combined with a scanning electron microscope (SEM). Four STM tips are mechanically and electrically independent and capable of positioning in arbitrary configurations in nanometer precision. An integrated controller system for both of the multitip STM and SEM with a single computer has also been developed, which enables the four tips to operate either for STM imaging independently and for four-point probe (4PP) conductivity measurements cooperatively. Atomic-resolution STM images of graphite were obtained simultaneously by the four tips. Conductivity measurements by 4PP method were also performed at various temperatures with the four tips in square arrangement with direct contact to the sample surface

267

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

268

Variable-temperature independently driven four-tip scanning tunneling microscope.  

Science.gov (United States)

The authors have developed an ultrahigh vacuum (UHV) variable-temperature four-tip scanning tunneling microscope (STM), operating from room temperature down to 7 K, combined with a scanning electron microscope (SEM). Four STM tips are mechanically and electrically independent and capable of positioning in arbitrary configurations in nanometer precision. An integrated controller system for both of the multitip STM and SEM with a single computer has also been developed, which enables the four tips to operate either for STM imaging independently and for four-point probe (4PP) conductivity measurements cooperatively. Atomic-resolution STM images of graphite were obtained simultaneously by the four tips. Conductivity measurements by 4PP method were also performed at various temperatures with the four tips in square arrangement with direct contact to the sample surface. PMID:17552823

Hobara, Rei; Nagamura, Naoka; Hasegawa, Shuji; Matsuda, Iwao; Yamamoto, Yuko; Miyatake, Yutaka; Nagamura, Toshihiko

2007-05-01

269

Design criteria for scanning tunneling microscopes to reduce the response to external mechanical disturbances.  

Science.gov (United States)

We present a simple one-dimensional model to find design criteria for a scanning tunneling microscope (STM) minimizing the response of the tip-sample distance to external mechanical disturbances. The underlying concept-achieving a response that is in phase and same amplitude-goes beyond the conventional approach to construct the STM as stiff as possible. It introduces optimization conditions relating the resonance frequencies of the different components to the STM assembly, which can be implemented accordingly during the STM design process. In this way an improvement in the response to external disturbances of several orders of magnitude can be achieved. Calculations for three typical STM designs are presented along with the corresponding optimization criteria. For one of the designs an improvement in performance has been experimentally verified. The results can also be extended to other scanning probe techniques. PMID:19044422

Ast, Christian R; Assig, Maximilian; Ast, Alexandra; Kern, Klaus

2008-09-01

270

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

Science.gov (United States)

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

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

2014-01-01

271

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

International Nuclear Information System (INIS)

The morphological evolution of the surfaces of gold deposits grown from the vapour on smooth glass under nonequilibrium conditions and incident angle near substrate normal is studied at the nanometer level by scanning tunnelling microscopy. For an average film thickness equal to or greater than 500 nm, the interface thickness (?) reaches a steady state. Under these conditions, ? depends on the scan length (L) as ? ? L? with ? = 0.35 ± 0.05 for L > ds, where ds is the columnar size, and ? = 0.89 ± 0.05 for L s. These results indicate that the growing surface spontaneously reaches a steady state and it can be described as a self-affine fractal. The value of ? for L > ds agrees with the prediction of ballistic deposition models without restructuring, whereas that for L s exceeds the prediction of ballistic models including restructuring. (orig.)

272

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

CERN Document Server

We introduce a statistical correlation analysis method to obtain information on the local geometry and orientation of the tip used in scanning tunneling microscopy (STM) experiments based on large scale simulations. The key quantity is the relative brightness correlation of constant-current topographs between experimental and simulated data. This correlation can be analyzed statistically for a large number of modeled tip orientations and geometries. Assuming a stable tip during the STM scans and based on the correlation distribution, it is possible to determine the tip orientations that are most likely present in an STM experiment, and exclude other orientations. This is especially important for substrates such as highly oriented pyrolytic graphite (HOPG) since its STM contrast is strongly tip dependent, which makes interpretation and comparison of STM images very challenging. We illustrate the applicability of our method considering the HOPG surface in combination with tungsten tip models of two different ap...

Mándi, Gábor; Palotás, Krisztián

2015-01-01

273

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

274

Scanning tunneling microscopy and spectroscopy for cluster and small particle research  

International Nuclear Information System (INIS)

Scanning tunneling microscopy (STM) and spectroscopy (STS) are new methods to investigate atomic arrangements and electronic structures of clusters and small particles of atoms. In this paper we review recent developments in this field, in particular the work from our laboratory. We show studies of single adatoms, small clusters and larger particles of platinum and a trimer of aluminium imaged with atomic resolution on highly-oriented pyrolytic graphite. We find different isomeric structures for clusters of a specific size. Taking the substrate lattice as reference we determine bond lengths and angles for the clusters. We find that adsorbed Pt-particles have a strong influence on the substrate. Periodic charge density modulations on the graphite lattice surrounding the particles are observed. We also discuss recent STS experiments which showed Coulomb blockade in electron tunneling. A silicon-oxide-graphite tip-junction is used where a mesoscopic insulating area containing trap levels for temporary electron storage is responsible for the blockade of single electron transport. Such an ultra-small insulator capacitor shows large voltage steps in current-voltage characteristics and quantization of the tunneling current. (orig.)

275

A high-speed variable-temperature ultrahigh vacuum scanning tunneling microscope  

Science.gov (United States)

An ultrahigh vacuum scanning tunneling microscopy (STM) system capable of collecting constant-current STM images at rates exceeding 1 image/s at temperatures up to 900 K was designed, built, and tested. The microscope uses an inchworm to push a scanner assembly through a quartz tube towards the sample. When the scanner is within tunneling range of the surface, the inchworm is decoupled from the scanner, resulting in a small, rigid mechanical loop with a high resonant frequency. The cylindrical symmetry and the use of low thermal expansion materials reduces image distortion due to thermal drift. An analog proportional-integral controller with tilt correction is used to maintain a constant tunnel current. A personal computer running Microsoft WINDOWS '95 is used to control all other instrument functions, as well as for data acquisition, manipulation, and storage. Problems associated with the non real time nature of the operating system were overcome by collecting the STM images within a virtual device driver. By taking advantage of the WINDOWS '95 multimedia functions, the time required to display and save images was reduced below 5 ms using a standard personal computer with no special hardware other than data acquisition cards. Sample STM images of Pd(111) and halogens adsorbed on Cu(100) are presented.

Nakakura, C. Y.; Phanse, V. M.; Zheng, G.; Bannon, G.; Altman, E. I.; Lee, K. P.

1998-09-01

276

s-orbital continuum model accounting for the tip shape in simulated scanning tunneling microscope images  

Science.gov (United States)

In this paper we present a simple method accounting for tip size effects in scanning tunneling microscopy (STM) simulations. We consider the case where the tip atoms can be regarded as independent sources of s orbitals and compute the tunneling current using the Bardeen formula and the approximation of incoherent scattering. By averaging over the many possible tip configurations compatible with the effective external shape of the STM probe, we show that the tunneling current is proportional, within our model, to the convolution product between the local density of states of the system and a three-dimensional step function defined by the effective tip volume. The method is tested on three systems of current scientific interest, namely, a hexabenzocoronene molecule adsorbed on Cu(111), a reconstructed Au(677) surface, and a formate molecule adsorbed on Pt(111), which we study by means of large-scale density functional theory calculations and STM experiments. An excellent agreement between experimental and simulated STM images is found. It is shown that, under typical experimental conditions, our approach recovers the results of the well-known Tersoff-Hamann modeling in the case of spherical tips, while allowing for more versatility in the choice of the shape of the STM probe. Finally we present an application of our method to one-dimensional surface models mimicking a localized defect and a surface step, thereby offering a very simple framework for the discussion of the tip-induced broadening of the surface features in the STM imaging.

Gaspari, Roberto; Blankenburg, Stephan; Pignedoli, Carlo A.; Ruffieux, Pascal; Treier, Matthias; Fasel, Roman; Passerone, Daniele

2011-09-01

277

Current and voltage dependent interactions between a scanning tunneling microscopy tip and a freestanding graphene sample  

Science.gov (United States)

The two dimensional nature of graphene gives rise to a number of unique properties. Chief among them are the ability to manipulate the electronic properties using mechanical deformations, opening a new field of ``straintronics.'' Previous work from our group demonstrated the ability to manipulate a freestanding graphene sample with atomic precision using electromagnetic manipulation scanning tunneling microscopy (EM-STM). In the EM-STM technique, the tip bias is ramped over a predetermined range while maintaining a constant tunneling current. The resulting change in height of the tip is then recorded. Typical EM-STM measurements show quick movement of the sample between 0.1-1.0 V, and then slower movement after this point. The height of this final plateau is dependent on the tunneling current. To look for the cause of this current dependence z(I) curves taken at a constant tip bias were examined. It was found that at low tip bias (0.1-0.5 V) the sample drops between 10-20 nm, while at high tip bias (1.0-3.0 V) the sample only drops 2-3 nm. This current dependence is attributed to a drop in the electrostatic force as the tip approaches the sample and holes in the benzene rings become more important.

Schoelz, Kevin; Xu, Peng; Barber, Steven; Ackerman, Matt; Thibado, Paul

2013-03-01

278

Visualizing the Pt Doping Effect on Surface and Electronic Structure in Ir1-xPtxTe2 by Scanning Tunneling Microscopy and Spectroscopy  

Science.gov (United States)

We report on the Pt doping effect on surface and electronic structure in Ir1-xPtxTe2 by scanning tunneling microscopy (STM) and spectroscopy (STS). The surface prepared by cleavage at 4.2 K shows a triangular lattice of topmost Te atoms. The compounds that undergo structural transition have supermodulation with a fixed wave vector q = 2?/5am (where am is the lattice constant in the monoclinic phase) despite the different Pt concentrations. The superconducting compounds show patch structures. The surface of the compound that exhibits neither the superconductivity nor the structural transition shows no superstructure. In all doped samples, the dopant is observed as a dark spot in STM images. The tunneling spectra near the dopant show the change in the local density of state at approximately -200 mV. Such microscopic effects of the dopant give us the keys for establishing a microscopic model of this material.

Fujisawa, Yuita; Machida, Tadashi; Igarashi, Kei; Kaneko, Akihiro; Mochiku, Takashi; Ooi, Shuuichi; Tachiki, Minoru; Komori, Kazunori; Hirata, Kazuto; Sakata, Hideaki

2015-04-01

279

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

280

Scanning tunneling microscopy investigation of copper phthalocyanine and truxenone derivative binary superstructures on graphite.  

Science.gov (United States)

The binary self-assembly of copper phthalocyanine (CuPc) and 2,3,7,8,12,13-hexahexyloxy-truxenone (TrO23) at the solid/liquid interface of highly oriented pyrolytic graphite (HOPG) was investigated by using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Pseduohexagonal and linear patterned superstructures of CuPc are obtained by co-adsorbing with TrO23. High-resolution STM images reveal the structural details of the arrangement of TrO23 and CuPc in the binary assembly structures. The molecular ratio between CuPc and TrO23 in the adlayer can be modulated by the CuPc concentration in liquid phase. The electronic properties of CuPc and TrO23 in the co-adsorbed self-assembly are investigated by STS. The results presented here are helpful to the design and fabrication of multi-component functional molecular nanostructures. PMID:21254420

Liu, Jia; Wang, Dong; Wang, Jie-Yu; Pei, Jian; Wan, Li-Jun

2011-02-01

281

Critical Mechanisms of Nanoscopic Electrochemical Deposition Induced by the Scanning Tunneling Microscope  

Science.gov (United States)

For the first time, a new state of solid state matter was predicted and experimentally observed in the electrochemical environment under the tip of the Scanning Tunneling Microscope. Onset of the existence of the material was predicted to occur at a tip to substrate bias of 0.34 volts for the exemplary solvent, water, in excellent agreement with the approximately 0.2 volt measured value. The phenomenon, directly tied by the theory to the dipole moment of the solvent molecule thence its dielectric constant, was also predicted to be absent for solvents with low dielectric constant as was observed when carbon tetrachloride replaced water in the experiment. By solving Laplace's equation in prolate spheroidal coordinates, the STM tip could be modeled as a hyperbola of rotation in close proximity to the substrate and curvature of the electric field within the double layer predicted, in contrast to conventional electrochemistry modeling. Introduction of a highly polar solvent into the structured electric field predicted a local, three dimensional formation of electrophoretically formed solid (EPS) at the apex of the tip capable of joining the tip and substrate double layers when sufficient potential is applied (cong1 volt) for a given geometry. Thermodynamic and kinetic implications are examined predicting the exclusion of ions from the EPS region. In experimental proof of the region's existence, the tip of an STM was configured to tunnel into a conductive gold coated AFM cantilever while the z-piezo oscillated 2A to 20A at 10 Hz and 1000 Hz. Tunneling current oscillations reflected the frequency and amplitude of physical displacement between tip and substrate until sufficient potential was applied to form the EPS causing the cantilever to follow the oscillatory motion and thereby damping the tunneling current oscillations. Possible involvement of the EPS in previously demonstrated STM electrodeposition was also proposed. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.).

Jette, Bruce Donald

1993-01-01

282

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

International Nuclear Information System (INIS)

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

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2014-10-15

285

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. PMID:25362400

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

2014-10-01

286

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

287

Fermi surface investigation in the scanning tunneling microscopy of Bi2Sr2CaCu2O8  

International Nuclear Information System (INIS)

Within the ideal Fermi liquid picture, the impurity-induced spatial modulation of local density of states (LDOS) in the d-wave superconductor Bi2Sr2CaCu2O8 is investigated at different superconducting (SC) gap sizes. These LDOS spectra are related to the finite-temperature dI/dV spectra in scanning tunneling microscopy (STM), when the Fermi distribution factor is deconvoluted away from dI/dV. We find stripe-like structures even in the zero gap case due to a local-nesting mechanism. This mechanism is different from the octet-scattering mechanism in the d-wave SC (dSC) state proposed by McElroy et al. [K. McElroy, R.W. Simmonds, J.E. Hoffman, D.H. Lee, J. Orenstein, H. Eisaki, S. Uchida, J.C. Davis, Nature 422 (2003) 592]. The zero gap LDOS is related to the normal state dI/dV. The zero gap spectra when Fourier-transformed into the reciprocal space, can reveal the information of the entire Fermi surface at a single measuring bias voltage, in contrast to the point-wise tracing out proposed by McElroy et al. This may serve as another way to check the reality of Landau quasiparticles in the normal state. We have also re-visited the octet-scattering mechanism in the dSC state and pointed out that, due to the Umklapp symmetry, there are additional peaks in the reciprocal space that experimentally yet to be found

288

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

289

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

290

Temperature dependence of the superconducting proximity effect quantified by scanning tunneling spectroscopy  

Directory of Open Access Journals (Sweden)

Full Text Available Here, we present the first systematic study on the temperature dependence of the extension of the superconducting proximity effect in a 1–2 atomic layer thin metallic film, surrounding a superconducting Pb island. Scanning tunneling microscopy/spectroscopy (STM/STS measurements reveal the spatial variation of the local density of state on the film from 0.38 up to 1.8 K. In this temperature range the superconductivity of the island is almost unaffected and shows a constant gap of a 1.20 ± 0.03 meV. Using a superconducting Nb-tip a constant value of the proximity length of 17 ± 3 nm at 0.38 and 1.8 K is found. In contrast, experiments with a normal conductive W-tip indicate an apparent decrease of the proximity length with increasing temperature. This result is ascribed to the thermal broadening of the occupation of states of the tip, and it does not reflect an intrinsic temperature dependence of the proximity length. Our tunneling spectroscopy experiments shed fresh light on the fundamental issue of the temperature dependence of the proximity effect for atomic monolayers, where the intrinsic temperature dependence of the proximity effect is comparably weak.

A. St?pniak

2015-01-01

291

Temperature dependence of the superconducting proximity effect quantified by scanning tunneling spectroscopy  

Science.gov (United States)

Here, we present the first systematic study on the temperature dependence of the extension of the superconducting proximity effect in a 1-2 atomic layer thin metallic film, surrounding a superconducting Pb island. Scanning tunneling microscopy/spectroscopy (STM/STS) measurements reveal the spatial variation of the local density of state on the film from 0.38 up to 1.8 K. In this temperature range the superconductivity of the island is almost unaffected and shows a constant gap of a 1.20 ± 0.03 meV. Using a superconducting Nb-tip a constant value of the proximity length of 17 ± 3 nm at 0.38 and 1.8 K is found. In contrast, experiments with a normal conductive W-tip indicate an apparent decrease of the proximity length with increasing temperature. This result is ascribed to the thermal broadening of the occupation of states of the tip, and it does not reflect an intrinsic temperature dependence of the proximity length. Our tunneling spectroscopy experiments shed fresh light on the fundamental issue of the temperature dependence of the proximity effect for atomic monolayers, where the intrinsic temperature dependence of the proximity effect is comparably weak.

Stepniak, A.; Caminale, M.; Leon Vanegas, A. A.; Oka, H.; Sander, D.; Kirschner, J.

2015-01-01

292

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

International Nuclear Information System (INIS)

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.

293

Josephson scanning tunneling microscopy: A local and direct probe of the superconducting order parameter  

Science.gov (United States)

Direct measurements of the superconducting superfluid on the surface of vacuum-cleaved Bi2Sr2CaCu2O8+? (BSCCO) samples are reported. These measurements are accomplished via Josephson tunneling into the sample using a 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 wave function 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; Barber, R. P., Jr.; Ono, S.; Ando, Yoichi; Dynes, R. C.

2009-10-01

294

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

International Nuclear Information System (INIS)

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

295

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

296

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.)

297

Nanostructure fabrication using laser field enhancement in the near field of a scanning tunneling microscope tip  

Science.gov (United States)

The scanning tunneling microscope (STM) has been combined with laser excitation and was used for modification of metal surfaces in air. This technique enables processing of structures with a lateral resolution of approximately 10 nm. The form of the created features ranges from craters and ditches to hillocks. The process has been demonstrated on gold and gold/palladium substrates by utilization of tungsten, silver, and platin/iridium tips. Using pure silver tips or silver-coated tungsten tips, a transfer of tip atoms to the substrate occurred. In the case of uncoated tungsten tips, we observed substrate evaporation and surface grain reorganization at low laser intensities, respectively. No distortion of the employed tips during the structuring process was observed. Several future oriented applications are conceivable, such as, for example, high density data storage and fresnel optics for x rays.

Jersch, J.; Dickmann, K.

1996-02-01

298

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

CERN Document Server

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

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

2000-01-01

299

Development and research of synchrotron radiation light-illuminated scanning tunneling microscope  

International Nuclear Information System (INIS)

Scanning Tunneling Microscope (STM) is one of the most useful techniques for surface investigation. But it has a disadvantage of impossibility of element specific research. To solve this problem, there have been several attempts to detect photoemitted electrons by STM. In these studies, X-ray or laser was used to illuminate the sample during STM observation. However, to identify the sample elements, we have to tune the energy of light to excite the core electrons of the particular element and detect photoemitted electrons. Synchrotron Radiation (SR) light is suitable for the purpose. We have designed the new system of SR light-illuminated STM (SR-STM), and estimated the performance of this system. (author)

300

Scanning Tunneling and Electronic Microscopy of Diamond Irradiated by High Energy Ions  

International Nuclear Information System (INIS)

The surfaces of boron doped synthetic and natural diamonds have been investigated by scanning tunneling (STM) and electronic microscopy (SEM) before and after irradiation with 40 Ar (25 MeV), 84 Kr (210 MeV), 129 Xe (124 MeV) ions. The structures observed (STM) after irradiation showed craters ranging from 3 nm to 20 nm in diameters, which are deduced to be single ion tracks and multiple hits of ions at the nearest positions of the surface. In the case of argon ion irradiation the surface was very amorphous, but after xenon irradiation one could see parts of surface without amorphism. It can be explained by the influence of high inelastic energy losses. 20 refs., 5 figs

301

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

302

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

Energy Technology Data Exchange (ETDEWEB)

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 {proportional_to} 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, {alpha}{sup 2}F({omega}).

Stocker, Matthias; Pfeifer, Holger; Koslowski, Berndt; Ziemann, Paul [Institut fuer Festkoerperphysik, Universitaet Ulm, D-89069 Ulm (Germany)

2011-07-01

303

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

304

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

305

Adsorption geometry of Cu(111)-Cs studied by scanning tunneling microscopy  

CERN Document Server

Using scanning tunneling microscopy at low temperatures we investigated the adsorbate system Cu(111)-Cs for various cesium coverages. At low coverages we observe a hexagonally ordered Cs adsorption layer with a mutual adsorbate distance of 1.1 nm. This distance is discussed in terms of a commensurate adsorption superstructure which is stabilized by long-range adsorbate interactions mediated by Cu(111) surface state electrons. Intermediate coverages are characterized by incommensurate superstructures which are rotated with respect to the substrate lattice. The rotation behavior at 9K follows a general trend which is consistent with models of epitaxial rotation. With increasing coverage the adsorption layers are found to rotate toward alignment with the substrate.

Von Hofe, T; Berndt, R; Hofe, Th. von

2006-01-01

306

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

DEFF Research Database (Denmark)

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

Kalashnyk, Nataliya; Nielsen, Jakob T

2012-01-01

307

All low voltage lateral junction scanning tunneling microscope with very high precision and stability  

Science.gov (United States)

We describe the first lateral junction and fully low voltage scanning tunneling microscope, featuring very high precision, stability, compactness, and image quality (highly oriented pyrolytic graphite atomic resolution images). In its core, the tip and sample each sit on one of two parallel-mounted piezoelectric tube scanners so that the tip-sample gap is regulated along the scanners' pairing direction. The scanner's large lateral deflection provides a large gap regulation range even under low voltages, allowing exclusively using only low voltage (less than ±15 V) operational amplifiers to precisely implement the coarse (inertial slider) and fine approach, feedback control, and hence the entire electronics. Because the scanners are identical and adjacent, thermal drifts are minimal.

Hou, Yubin; Wang, Jihui; Lu, Qingyou

2008-11-01

308

Identification of nitrogen dopants in single-walled carbon nanotubes by scanning tunneling microscopy.  

Science.gov (United States)

Using scanning tunnelling microscopy and spectroscopy, we investigated the atomic and electronic structure of nitrogen-doped single walled carbon nanotubes synthesized by chemical vapor deposition. The insertion of nitrogen in the carbon lattice induces several types of point defects involving different atomic configurations. Spectroscopic measurements on semiconducting nanotubes reveal that these local structures can induce either extended shallow levels or more localized deep levels. In a metallic tube, a single doping site associated with a donor state was observed in the gap at an energy close to that of the first van Hove singularity. Density functional theory calculations reveal that this feature corresponds to a substitutional nitrogen atom in the carbon network. PMID:23829349

Tison, Yann; Lin, Hong; Lagoute, Jérôme; Repain, Vincent; Chacon, Cyril; Girard, Yann; Rousset, Sylvie; Henrard, Luc; Zheng, Bing; Susi, Toma; Kauppinen, Esko I; Ducastelle, François; Loiseau, Annick

2013-08-27

309

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

310

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

Science.gov (United States)

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

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

2013-12-01

311

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

CERN Document Server

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

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

2005-01-01

312

Scanning tunneling microscopy studies of the Fe3O4(001) surface using antiferromagnetic probes  

International Nuclear Information System (INIS)

We have studied the (001) surface of a Fe3O4 single crystal using low-energy electron diffraction (LEED), Auger electron spectroscopy (AES) and scanning tunneling microscopy (STM). The STM measurements were performed using a novel tip of antiferromagnetic MnNi alloy. Atomically resolved STM images provide evidence of a surface terminated at the octahedral plane, with rows of Fe cations running along the crystallographic axes. Two different kinds of Fe cations with a separation of 6 Aa were imaged, while the periodicity between Fe cations of the same kind is about 12 Aa. We propose an interpretation of the anomalous corrugation observed in terms of a spin polarized effect, resulting in magnetic contrast between Fe2+ and Fe3+ ions in octahedral coordination

313

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

Science.gov (United States)

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

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

2014-03-01

314

Surface modification of a-Si:H with a scanning tunneling microscope operated in air  

International Nuclear Information System (INIS)

A scanning tunneling microscope was applied to the lithographic microprocessing of amorphous materials in air. Phase transformations were induced in the thin-film a-Si:H on silicon by low-energy electron irradiation. Electronic characterization of the surface before and after the phase transformation indicated a change in the local conductivity directly below the tip. Submicrometer lines were formed on these thin films by application of multiple, 10-V, 35-?s voltage pulses between the tip and the sample. The lines were imaged with the STM in the imaging mode. The linewidths written on a-Si:H corresponded to the average tip radii used in the experiments, e.g., approximately 500--5000 A

315

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

316

Edge state on hydrogen-terminated graphite edges investigated by scanning tunneling microscopy  

CERN Document Server

The edge states that emerge at hydrogen-terminated zigzag edges embedded in dominant armchair edges of graphite are carefully investigated by ultrahigh-vacuum scanning tunneling microscopy (STM) measurements. The edge states at the zigzag edges have different spatial distributions dependent on the $\\alpha$- or $\\beta$-site edge carbon atoms. In the case that the defects consist of a short zigzag (or a short Klein) edge, the edge state is present also near the defects. The amplitude of the edge state distributing around the defects in an armchair edge often has a prominent hump in a direction determined by detailed local atomic structure of the edge. The tight binding calculation based on the atomic arrangements observed by STM reproduces the observed spatial distributions of the local density of states.

Kobayashi, Y; Enoki, T; Kusakabe, K; Kobayashi, Yousuke; Fukui, Ken-ichi; Enoki, Toshiaki; Kusakabe, Koichi

2006-01-01

317

Scanning Tunneling Microscopy of the Topological Crystalline Insulator SnTe  

Science.gov (United States)

Topological insulators are a new state of matter characterized by a bulk insulating gap and gapless surface states protected by time reversal symmetry. This is realized by spin orbit coupling induced band inversion with an odd number of Dirac cones. Recently, the topological classification of states has been extended to a new class of matter called topological crystalline insulators. In contrast to topological insulators, topological crystalline insulators arise from crystal symmetry and are characterized by surface states with an even number of Dirac cones. Here, we report molecular beam epitaxy growth of SnTe thin films, a material recently predicted and experimentally confirmed as a topological crystalline insulator. The film morphology and SnTe (001) surface states were characterized in-situ by low temperature scanning tunneling microscopy and spectroscopy will be discussed in relation to the predicated topological properties of this material.

Zhang, Duming; Zhang, Tong; Ha, Jeonghoon; Baek, Hongwoo; Kuk, Young; Sharifi, Fred; Stroscio, Joseph

2013-03-01

318

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 x 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 pi-pi* transition of the molecule. PMID:15847486

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

2005-04-01

319

Hydrogen adsorption on Ru(001) studied by Scanning TunnelingMicroscopy  

Energy Technology Data Exchange (ETDEWEB)

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

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

2008-01-18

320

Hydration-scanning tunneling microscopy as a reliable method for imaging biological specimens and hydrophilic insulators.  

Science.gov (United States)

The recently discovered high lateral conductivity of molecularly thin adsorbed water films enables investigation of biological specimens, and even of surfaces of hydrophilic insulators by scanning tunneling microscopy (STM). Here we demonstrate the capabilities of this method, which we call hydration-STM (HSTM), with images of various specimens taken in humid atmosphere: We obtained images of a glass coverslip, collagen molecules, tobacco mosaic virus, lipid bilayers and cryosectioned bovine achilles tendon on mica. To elucidate the physical mechanism of this conduction phenomenon we recorded current-voltage curves on hydrated mica. This revealed a basically ohmic behavior of the I-V curves without a threshold voltage to activate the current transport and indicates that electrochemistry probably does not dominate the surface conductivity. We assume that the conduction mechanism is due to structuring of water at the surface. PMID:9601531

Heim, M; Eschrich, R; Hillebrand, A; Knapp, H F; Cevc, G; Guckenberger, R

1996-01-01

321

A Direct Probe of Electronic Nematic Order; Symmetry Information in Scanning Tunneling Microscope Images  

CERN Document Server

An electronic nematic state spontaneously breaks a point-group symmetry of an underlying lattice. As a result, the nematic-isotropic transition accompanies a Fermi surface distortion. However, the anisotropic nature of the nematic state at a macroscopic scale can be easily wiped out when domains of different orientations of nematic order exist. We suggest that a spatial pattern of local density of states (LDOS) in the presence of a non-magnetic impurity can be a direct probe of the nematic order. We study various patterns of LDOS across the quantum phase transition between the isotropic and nematic phases. Especially the Fourier transformed local density of states (FT-LDOS), which can be deduced from scanning tunneling microscope images, represent a transparent symmetry of an electronic structure. The application of our results to the bilayer ruthenate, Sr$_3$Ru$_2$O$_7$ is also discussed.

Doh, H; Doh, Hyeonjin; Kee, Hae-Young

2007-01-01

322

Scanning tunneling microscopy of gate tunable topological insulator Bi2Se3 thin films  

Science.gov (United States)

Electrical-field control of the carrier density of topological insulators (TIs) has greatly expanded the possible practical use of these materials. However, the combination of low-temperature local probe studies and a gate tunable TI device remains challenging. We have overcome this limitation by scanning tunneling microscopy and spectroscopy measurements on in situ molecular-beam epitaxy grown Bi2Se3 films on SrTiO3 substrates with prepatterned electrodes. Using this gating method, we are able to tune the Fermi level of the top surface states within a range of ?250 meV on a 3-nm-thick Bi2Se3 device. We report field effect studies of the surface-state dispersion, band gap, and electronic structure at the Fermi level.

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

2013-03-01

323

Scanning tunneling microscopy of defects and electronic fluctuations in Cu-doped Bi2Se3  

Science.gov (United States)

We report scanning tunneling microscopy and spectroscopy studies of the topological insulator CuxBi2Se3. We have identified five different atomic-resolution signatures of Cu dopant-related point defects and correlated several of them to density functional theory simulations of the defects. Most interestingly, by investigating the dI/dV images of the known BiSe antisite defects as a function of bias, we show that local electronic structure can vary substantially over a length scale of 30nm, with amplitudes as large as ±50meV. The strong fluctuations appear to be caused by a variety of defects and may have consequences for the topological surface state, as revealed by quasiparticle scattering studies. Correlation of quasiparticle scattering with the various defects indicates that the surface state is robust to backscattering, though detailed analysis shows that some defects are more effective in producing stationary scattering states than others.

Mann, Christopher; West, Damien; Miotkowski, Ireneusz; Chen, Yong; Zhang, Shengbai; Shih, Chih-Kang

2013-03-01

324

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

325

How the vortex lattice of a superconductor becomes disordered: a study by scanning tunneling spectroscopy.  

Science.gov (United States)

Order-disorder transitions take place in many physical systems, but observing them in detail in real materials is difficult. In two- or quasi-two-dimensional systems, the transition has been studied by computer simulations and experimentally in electron sheets, dusty plasmas, colloidal and other systems. Here I show the different stages of defect formation in the vortex lattice of a superconductor while it undergoes an order-disorder transition by presenting real-space images of the lattice from scanning tunneling spectroscopy. When the system evolves from the ordered to the disordered state, the predominant kind of defect changes from dislocation pairs to single dislocations, and finally to defect clusters forming grain boundaries. Correlation functions indicate a hexatic-like state preceding the disordered state. The transition in the microscopic vortex distribution is mirrored by the well-known spectacular second peak effect observed in the macroscopic current density of the superconductor. PMID:25784605

Zehetmayer, M

2015-01-01

326

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

International Nuclear Information System (INIS)

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

327

Gallium nitride surface preparation optimised using in situ scanning tunnelling microscopy  

International Nuclear Information System (INIS)

Effective preparation of clean GaN surfaces is vital for surface studies, and also has a key role to play in the development of nitride-based electronic devices, due to the importance of forming good metal-semiconductor contacts. We identify the effect of two common surface cleaning treatments (annealing in ammonia, and sputtering in nitrogen followed by in vacuo annealing) on surface reconstruction, morphology and stoichiometry, by employing a combination of in situ RHEED and scanning tunnelling microscopy (STM), and ex situ X-ray photoelectron spectroscopy (XPS). We show how the defect densities in as-treated GaN surfaces may be reduced by growing thin layers of GaN by low-pressure MBE, a technique compatible with most experimental surface science systems. By using a combination of in situ etching and low-pressure growth, we show that it is possible to obtain very similar surface structures to those obtained by full-scale MBE

328

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

Science.gov (United States)

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

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

2014-12-01

329

Robust nodal structure of Landau level wave functions revealed by Fourier transform scanning tunneling spectroscopy.  

Science.gov (United States)

Scanning tunneling spectroscopy is used to study the real-space local density of states of a two-dimensional electron system in a magnetic field, in particular within higher Landau levels. By Fourier transforming the local density of states, we find a set of n radial minima at fixed momenta for the nth Landau levels. The momenta of the minima depend only on the inverse magnetic length. By comparison with analytical theory and numerical simulations, we attribute the minima to the nodes of the quantum cyclotron orbits, which decouple in a Fourier representation from the random guiding center motion due to disorder. Adequate Fourier filtering reveals the nodal structure in real space in some areas of the sample with relatively smooth potential disorder. PMID:23005665

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

2012-09-14

330

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

331

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

332

Scanning tunneling microscopy of charge-density waves in NbSe3  

International Nuclear Information System (INIS)

The charge-density wave (CDW) structure in NbSe3 due to the two independent CDWs has been imaged by scanning tunneling microscopy. As predicted by band structure considerations the CDW modulation is observed to be substantially localized on different chains for the separate CDWs. At 77K where only the high temperature CDW exists a relatively weak modulation with a single component along the /bar b/-axis is observed. At 4.2K the low temperature CDW contributes a much stronger /approximately/4/bar b/0 /times/ 2/rvec c/0 superlattice modulation. The combination of atomic resolution and CDW modulations allows an unambiguous identification of the chain structure to be made. 9 refs., 5 figs

333

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)

334

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.

335

Atomic structure of Mn wires on Si(001) resolved by scanning tunneling microscopy.  

Science.gov (United States)

At submonolayer coverage, Mn forms atomic wires on the Si(001) surface oriented perpendicular to the underlying Si dimer rows. While many other elements form symmetric dimer wires at room temperature, we show that Mn wires have an asymmetric appearance and pin the Si dimers nearby. We find that an atomic configuration with a Mn trimer unit cell can explain these observations as due to the interplay between the Si dimer buckling phase near the wire and the orientation of the Mn trimer. We study the resulting four wire configurations in detail using high-resolution scanning tunneling microscopy (STM) imaging and compare our findings with the STM images simulated by density functional theory. PMID:23083259

Fuhrer, A; Rueß, F J; Moll, N; Curioni, A; Widmer, D

2012-10-01

336

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

337

Studies of superconductors by low temperature scanning tunneling microscopy and spectroscopy  

International Nuclear Information System (INIS)

Scanning tunneling microscope which operates at very low temperature (0.45 K) under high magnetic field (14.5 T) (LT·HM-STM/STS) has been developed to be applied for the scanning tunneling spectroscopy (STS) study of superconductivity. Its spatial resolution is in the atomic scale under the high field and STS can be performed with high energy resolution. It was found with this unique instrument that Cooper pairs in Bi2Sr2CaCu2OX had d-character component from the observation of local distribution of state density near the superconductive and normal boundary. Vortex-line lattices were observed on 2H-NbSe2, Bi2Sr2CaCu2OX, YNi2B2C and CeRu2 up to now with LT·HM-STM/STS. Bound state of Cooper pairs confined in the core of magnetic flux of 2H-NbSe2 was observed up close to Hc2 and the behavior how the superconductivity decays there was followed. Since very clean surface is needed to observe superconducting magnetic line lattices it is only seven materials for which the STS flux observation was successfully performed by now. A new method has been developed to cleave or crack samples at low temperatures in vacuum or in helium atmosphere. The method lead to the successful observation of the four materials described above. It was observed that the flux lattice of YNi2B2C changes from triangular lattice to square one when magnetic field is increased. The magnetic flux lattice of Bi2Sr2CaCu2OX was observed under 11.5 T, which is the highest magnetic field under which magnetic flux has been observed in the real space. (S. Funahashi)

338

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 suppoe 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)

339

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

340

Scanning tunneling microscopy combined with hard X-ray microbeam of high brilliance from synchrotron radiation source  

International Nuclear Information System (INIS)

In situ scanning microscopy (STM) with highly brilliant hard X-ray irradiation was enabled at SPring-8. To obtain a good signal-to-noise ratio for elemental analysis, an X-ray beam with a limited size of ?10?m was aligned to a specially designed STM stage in ultrahigh vacuum. Despite various types of noises and a large radiation load around the STM probe, STM images were successfully observed with atomic resolution. The use of a new system for elemental analysis was also attempted, which was based on the modulation of tunneling signals rather than emitted electrons. Among tunneling signals, tunneling current was found to be better than tip height as a signal to be recorded, because the former reduces markedly the error of measurement. On a Ge nanoisland on a clean Si(111) surface, the modulation of tunneling current was achieved by changing the incident photon energy across the Ge absorption edge. (author)

341

Documentation and Visualization of AN As-Built Tunnel by Combining 3d Laser Scanning and Web Mapping  

Science.gov (United States)

A new way to document and visualize the as-built condition of an urban tunnel project with high accuracy is described in this paper, based on recent developments of laser scanning technology. In traditional surveying, the components of a tunnel are organized on the basis of the location of stations and offsets along the project alignment specified in the drawings. It is difficult for people without an engineering background to understand the information involved in surveying reports, drawings, and engineering data. However, in the interest of transparency, public agencies that commission construction projects have to make project information available to government officials and to the general public. This paper discusses the combined use of laser scanning technology and web mapping services to improve the documentation and visualization of an urban metro tunnel. Laser scanning technology is introduced to perform the surveyor's task, document the as-built condition, and geo-reference the construction elements. A set of panoramic pictures is generated by laser scanning that allows for taking measurements and extracting 3D coordinates. An XML file that contains geo-reference information is appended to each panoramic picture. Using application programming interface (API), this information is referenced to a web mapping service. A case study of the CTA Red line Tunnel in Chicago, IL demonstrates this method in a real life project.

Zhang, C.; Arditi, D.; Chen, Z.

2013-08-01

342

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

Czech Academy of Sciences Publication Activity Database

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

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

2013-01-01

343

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

344

Scanning-tunneling-microscopy study of the surface diffusion of sulfur on Re(0001)  

International Nuclear Information System (INIS)

Low coverages of sulfur chemisorbed on the rhenium (0001) surface were studied by scanning tunneling microscopy (STM). At one-quarter monolayer coverage, sulfur forms a p(2x2) ordered overlayer, consistent with low-energy electron-diffraction results. At lower coverages, some of the sulfur forms small islands of the p(2x2) structure. Between the islands, sulfur atoms diffuse over the surface as a lattice gas. In our conditions, the residence time of the sulfur atoms in each site is comparable to the STM scan rate, which gives rise to an apparently noisy image. However, a spatial corelation function was used to determine that this apparent noise is due to diffusing sulfur that maintains a local p(2x2) order. This order is due to a weak attractive interaction between the diffusing atoms at twice the Re lattice spacing and a repulsive interaction at closer distances. The strength of the attractive interaction was measured by fitting the results of the correlation function to an Ising model of the interaction of sulfur atoms on the surface. The energy barrier to diffusion was calculated from the sulfur residence time, and compares well with an extended Hueckel calculation

345

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

CERN Document Server

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

Wiesendanger, Roland

1994-01-01

346

Scanning-tunneling-microscopy study of the surface diffusion of sulfur on Re(0001)  

Energy Technology Data Exchange (ETDEWEB)

Low coverages of sulfur chemisorbed on the rhenium (0001) surface were studied by scanning tunneling microscopy (STM). At one-quarter monolayer coverage, sulfur forms a [ital p](2[times]2) ordered overlayer, consistent with low-energy electron-diffraction results. At lower coverages, some of the sulfur forms small islands of the [ital p](2[times]2) structure. Between the islands, sulfur atoms diffuse over the surface as a lattice gas. In our conditions, the residence time of the sulfur atoms in each site is comparable to the STM scan rate, which gives rise to an apparently noisy image. However, a spatial corelation function was used to determine that this apparent noise is due to diffusing sulfur that maintains a local [ital p](2[times]2) order. This order is due to a weak attractive interaction between the diffusing atoms at twice the Re lattice spacing and a repulsive interaction at closer distances. The strength of the attractive interaction was measured by fitting the results of the correlation function to an Ising model of the interaction of sulfur atoms on the surface. The energy barrier to diffusion was calculated from the sulfur residence time, and compares well with an extended Hueckel calculation.

Dunphy, J.C. (Center for Advanced Materials, Material Science Division, Lawrence Berkeley Laboratory, Berkeley, California 94720 (United States) Department of Physics, University of California, Berkeley, Berkeley, California 94720 (United States)); Sautet, P.; Ogletree, D.F.; Dabbousi, O.; Salmeron, M.B. (Center for Advanced Materials, Material Science Division, Lawrence Berkeley Laboratory, Berkeley, California 94720 (United States))

1993-01-15

347

Scanning tunneling microscopy in UHV with an X,Y,Z micropositioner  

Science.gov (United States)

The extremely high resolution of a scanning tunneling microscope (STM) or atomic force microscope allows the examination of local material faults like dislocations, grain boundaries, and cracks on an atomic scale. However, the visual field of a scanning probe microscope is small and, especially in UHV, it is difficult to position a probe tip directly above such faults since they are not very frequent on a specimen surface. Therefore, a STM for the quantitative examination of large areas in UHV was developed. A new three-dimensional micropositioner based on inertial slip-stick motion was built, where the vertical motion is achieved with a special seesaw-like construction. This device is very compact and allows positioning of the piezoscanner with steps down to 20 nm length. The microspositioner is designed with low weight drives and special materials for the bearings (ruby on sapphire) to avoid sticking in UHV. First applications of a STM built with this micropositioner are shown where atomic resolution is reached.

Göken, Mathias

1994-07-01

348

Eliashberg analysis of Bi2Sr2CaCu2O8+? intrinsic tunneling spectra  

Science.gov (United States)

Tunneling spectra of Bi2Sr2CaCu2O8+? intrinsic Josephson junctions with different doping are analyzed and reproduced using a d-wave Eliashberg formalism in a wide temperature range below Tc , from which the pairing glue spectral function ?2 F (?) composed of a low-energy resonance peak and a high-energy broad spectrum is obtained. As temperature increases toward Tc , the resonance peak shows continuous decrease both in energy and in height while the broad spectrum slightly increases in height. The calculated coupling constant demonstrates an important role for pairing by the broad spectrum that originates from spin fluctuations. The gap function extracted from the analysis bears a close resemblance to the recent Hubbard and t-J model simulations. We discuss the limitations of the d-wave Eliashberg approach used in our analysis.

Sui, Xiao-Hong; Tang, H.; Zhao, S. P.; Su, Zhao-Bin

2015-04-01

349

Scanning tunneling microscopy studies of an electron-doped high-Tc superconductor, praseodymium lanthanum cerium copper oxide  

Science.gov (United States)

It has been more than two decades since the first high temperature superconductor was discovered. In this time there has been tremendous progress in understanding these materials both theoretically and experimentally. Some important questions however remain to be answered; one of them is the temperature dependence of the superconducting gap which is in turn tied to question of the origin of the pseudogap and its connection with superconductivity. In this thesis, we present detailed Scanning Tunneling Microscopy (STM) spectroscopic studies of an electron doped superconductor, Pr0.88LaCe 0.12CuO4-delta (PLCCO). The electron doped compounds form an interesting venue for STM studies for many reasons. In the hole-doped materials, especially in the underdoped side of the phase diagram, there is mounting evidence of a second gap that survives to high temperatures (high temperature pseudogap) that may have a different origin from superconductivity. This complicates studies of the temperature dependence of the superconducting gap in these materials. In PLCCO however, there is little evidence for a high temperature pseudogap potentially allowing us to address the question of the temperature evolution of the superconducting gap without the complication of a second gap. Secondly, the low Tc of the optimally doped materials makes it easily accessible to temperature dependent STM studies. Finally, while hole-doped materials have been extensively studied by scanning tunneling microscopy (STM), there have been no detailed STM spectroscopic studies on the electron doped compounds. In the first part of the thesis, we investigate the effect of temperature on the superconducting gap of optimally doped PLCCO with Tc = 24K. STM spectroscopy data is analyzed to obtain the gap as a function of temperature from 5K to 35K. The gap is parameterized with a d-wave form and the STM spectra are fit at each temperature to extract the gap value. A plot of this gap value as a function of temperature shows clear deviations from what is expected from BCS theory. We find that similar to the hole-doped superconductors a fraction of the surface still shows a gap above Tc. The implications of our finding to the pseudogap phase are discussed. In the second part of the thesis, STM spectra are analyzed to determine the effect of impurities or vacancies on the local density of states. Electron doped superconductors require a post-annealing process to induce superconductivity. It is claimed that Cu vacancies in the CuO2 planes which suppress superconductivity are healed by this process. This implies that for the same doping, a sample with higher Tc should have fewer impurities compared to a sample with lower Tc. We studied two PLCCO samples with 12% Ce doping; one with higher Tc (24K) and the other with lower T c (21K). Through quasiparticle scattering study we find that there are more impurities in 21K samples than 24K sample, consistent with the picture of Cu vacancies in as grown samples. Finally, we present a discussion of the bosonic modes observed in the STM spectra and their connection to the spin excitations measured by neutron scattering.

Kunwar, Shankar

350

Scanning tunneling microscope design with a confocal small field permanent magnet  

International Nuclear Information System (INIS)

The field of ultra-sensitive measurements with scanning probes requires the design and construction of novel instruments. For example, the combination of radio frequency detection and scanning probe can be exploited to measure thermal properties and mechanical resonances at a very low scale. Very recent results by Komeda and Manassen (2008 Appl. Phys. Lett. 92 212506) on the detection of spin noise with the scanning tunneling microscopy (STM) have further expanded previous results reported by one of the authors of this manuscript (Messina et al 2007 J. Appl. Phys. 101 053916). In a previous publication, one of the authors used a new STM instrument (Messina et al J. Appl. Phys. 2007 101 053916 and Mannini et al 2007 Inorg. Chim. Acta 360 3837–42) to obtain the detection of electron spin noise (ESN) from individual paramagnetic adsorbates. The magnetic field homogeneity at the STM tip–sample region was limited. Furthermore, vacuum operation of the STM microscope was limited by the heat dissipation at the electromagnet and the radio frequency (RF) recovery electronics. We report here on a new STM head that incorporates a specially designed permanent magnet and in-built RF amplification system. The magnet provides both a better field homogeneity and freedom to operate the instrument in vacuum. The STM microscope is vacuum compatible, and vertical stability has been improved over the previous design (Messina et al 2007 J. Appl. Phys. 101 053916), despite the presence os. 101 053916), despite the presence of a heat dissipative RF amplifier in the close vicinity of the STM tip

351

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

352

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

Science.gov (United States)

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

Pasanai, K.

2014-05-01

353

Characterization of nanometer-sized, mechanically exfoliated graphene on the H-passivated Si(100) surface using scanning tunneling microscopy  

International Nuclear Information System (INIS)

We have developed a method for depositing graphene monolayers and bilayers with minimum lateral dimensions of 2-10 nm by the mechanical exfoliation of graphite onto the Si(100)-2 x 1:H surface. Room temperature, ultrahigh vacuum tunneling spectroscopy measurements of nanometer-sized single layer graphene reveal a size-dependent energy gap ranging from 0.1 to 1 eV. Furthermore, the number of graphene layers can be directly determined from scanning tunneling microscopy topographic contours. This atomistic study provides an experimental basis for probing the electronic structure of nanometer-sized graphene which can assist the development of graphene-based nanoelectronics

354

Novel selective etching reaction of carbon atoms on molybdenum carbide by oxygen at room temperature visualized by scanning tunneling microscopy  

Science.gov (United States)

We have succeeded in imaging each surface carbon atom on Mo 2C(0001) by scanning tunneling microscopy operated at low tunneling resistances and found a novel selective etching reaction of the surface carbon atoms by oxygen gas exposed at room temperature. On a carbon terminated Mo 2C(0001) surface with both (?3×?3)R30°-honeycomb and c(2×4)-zigzag row structures, the etching reaction selectively occurred on the c(2×4)-zigzag row structure, leading to exposure of the underlying (1×1) Mo layer. Energetically excited oxygen formed on the surface is probably responsible for this new reaction event.

Fukui, Ken-ichi; Lo, Rong-Li; Otani, Shigeki; Iwasawa, Yasuhiro

2000-07-01

355

Direct Probing of Transient Photocurrent Dynamics in p-WSe2 by Time-Resolved Scanning Tunneling Microscopy  

Science.gov (United States)

We have carried out time-resolved scanning tunneling microscopy on a layered semiconductor with an indirect bandgap, p-WSe2, and the dynamics of nonequilibrium photocurrent generated by ultrashort-pulse-laser excitation was analyzed. The photocurrent dynamics reflecting the flow of excited photocarriers at the surface, which is determined by the balance between the diffusion and tunneling rates, was successfully probed. Furthermore, the excess minority carriers transiently trapped at the surface for a few nanoseconds, which produce a transient surface photovoltage and cannot be detected by conventional methods, were directly observed and evaluated.

Yoshida, Shoji; Terada, Yasuhiko; Yokota, Munenori; Takeuchi, Osamu; Mera, Yutaka; Shigekawa, Hidemi

2013-01-01

356

Scanning tunneling microscopy studies on CeCoIn{sub 5} and CeIrIn{sub 5}  

Energy Technology Data Exchange (ETDEWEB)

High-quality single crystals of the heavy fermion superconductors CeCoIn{sub 5} and CeIrIn{sub 5} have been studied by means of low-temperature scanning tunneling microscopy. Methods were established to facilitate in situ sample cleaving. Spectroscopy in CeCoIn{sub 5} reveals a gap which persists to above T{sub c}, possibly evidencing a precursor state to superconductivity. Atomically resolved topographs show a rearrangement of the atoms at the crystal surface. This modification at the surface might influence the surface properties as detected by tunneling spectroscopy. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

Ernst, S.; Wirth, S.; Steglich, F. [Max Planck Institute for Chemical Physics of Solids, Dresden (Germany); Fisk, Z. [Department of Physics and Astronomy, University of California at Irvine, Irvine (United States); Sarrao, J.L.; Thompson, J.D. [Los Alamos National Laboratory, Los Alamos (United States)

2010-03-15

357

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.

358

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

International Nuclear Information System (INIS)

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

359

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

360

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.

Colaianni, Maria Loredana; Chorkendorff, Ib

1994-01-01

361

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

DEFF Research Database (Denmark)

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

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

2010-01-01

362

High-resolution scanning tunneling microscopy characterization of mixed monolayer protected gold nanoparticles.  

Science.gov (United States)

Gold nanoparticles protected by a binary mixture of thiolate molecules have a ligand shell that can spontaneously separate into nanoscale domains. Complex morphologies arise in such ligand shells, including striped, patchy, and Janus domains. Characterization of these morphologies remains a challenge. Scanning tunneling microscopy (STM) imaging has been one of the key approaches to determine these structures, yet the imaging of nanoparticles' surfaces faces difficulty stemming from steep surface curvature, complex molecular structures, and the possibility of imaging artifacts in the same size range. Images obtained to date have lacked molecular resolution, and only domains have been resolved. There is a clear need for images that resolve the molecular arrangement that leads to domain formation on the ligand shell of these particles. Herein we report an advance in the STM imaging of gold nanoparticles, revealing some of the molecules that constitute the domains in striped and Janus gold nanoparticles. We analyze the images to determine molecular arrangements on parts of the particles, highlight molecular "defects" present in the ligand shell, show persistence of the features across subsequent images, and observe the transition from quasi-molecular to domain resolution. The ability to resolve single molecules in the ligand shell of nanoparticles could lead to a more comprehensive understanding of the role of the ligand structure in determining the properties of mixed-monolayer-protected gold nanoparticles. PMID:24024977

Ong, Quy Khac; Reguera, Javier; Silva, Paulo Jacob; Moglianetti, Mauro; Harkness, Kellen; Longobardi, Maria; Mali, Kunal S; Renner, Christoph; De Feyter, Steven; Stellacci, Francesco

2013-10-22

363

Scanning Tunneling Microscope Study of Surface Diffusion and Dislocation Motion in Atomically Flat Gold Films.  

Science.gov (United States)

A simple scanning tunneling microscope (STM) which works well from room temperature to 4K is described. It is relatively easy to build, repair or modify, and works very reliably. With this STM, we study mass flow on (111)Au and find that the rate of decay of the area of monolayer islands produced by STM lithography is linear in time. We demonstrate by Monte Carlo simulations that a proper accounting of the detachment and reattachment rates of kink site atoms produces a linear decay. To observe the decay rate of a monolayer gold island, one needs a sample with large isolated grains with large facets showing atomically flat terraces separated by monatomic steps. We find that thermal evaporation of Au onto heated glass substrates satisfies these conditions. At room temperature in air, these films show low angle grain boundaries and other dislocation arrays which move under an applied stress introduced either by handling the sample or by crashing an STM tip on the sample surface.

Hwang, Jeeseong

364

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.

365

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

366

Topological superconductivity in metallic nanowires fabricated with a scanning tunneling microscope  

International Nuclear Information System (INIS)

We report on several low-temperature experiments supporting the presence of Majorana fermions in superconducting lead nanowires fabricated with a scanning tunneling microscope (STM). These nanowires are the connecting bridges between the STM tip and the sample resulting from indentation–retraction processes. We show here that by a controlled tuning of the nanowire region, in which superconductivity is confined by applied magnetic fields, the conductance curves obtained in these situations are indicative of topological superconductivity and Majorana fermions. The most prominent feature of this behavior is the emergence of a zero bias peak in the conductance curves, superimposed on a background characteristic of the conductance between a normal metal and a superconductor in the Andreev regime. The zero bias peak emerges in some nanowires when a magnetic field larger than the lead bulk critical field is applied. This field drives one of the electrodes into the normal state while the other, the tip, remains superconducting on its apex. Meanwhile a topological superconducting state appears in the connecting nanowire of nanometric size. (paper)

367

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; Olesen, Klaus G.

1997-01-01

368

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

Science.gov (United States)

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

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

2007-09-01

369

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

370

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

371

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

International Nuclear Information System (INIS)

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

372

Atomic-scale surface science phenomena studied by scanning tunneling microscopy  

Science.gov (United States)

Following the development of the scanning tunneling microscope (STM), the technique has become a very powerful and important tool for the field of surface science, since it provides direct real-space imaging of single atoms, molecules and adsorbate structures on surfaces. From a fundamental perspective, the STM has changed many basic conceptions about surfaces, and paved the way for a markedly better understanding of atomic-scale phenomena on surfaces, in particular in elucidating the importance of local bonding geometries, defects and resolving non-periodic structures and complex co-existing phases. The so-called "surface science approach", where a complex system is reduced to its basic components and studied under well-controlled conditions, has been used successfully in combination with STM to study various fundamental phenomena relevant to the properties of surfaces in technological applications such as heterogeneous catalysis, tribology, sensors or medical implants. In this tribute edition to Gerhard Ertl, we highlight a few examples from the STM group at the University of Aarhus, where STM studies have revealed the unique role of surface defects for the stability and dispersion of Au nanoclusters on TiO 2, the nature of the catalytically active edge sites on MoS 2 nanoclusters and the catalytic properties of Au/Ni or Ag/Ni surfaces. Finally, we briefly review how reaction between complex organic molecules can be used to device new methods for self-organisation of molecular surface structures joined by comparatively strong covalent bonds.

Besenbacher, F.; Lauritsen, J. V.; Linderoth, T. R.; Lægsgaard, E.; Vang, R. T.; Wendt, S.

2009-06-01

373

Analysis of synthetic DNAs and DNA-protamine complexes with the scanning tunneling microscope.  

Science.gov (United States)

Three duplex DNAs 22, 47, and 100 base-pairs in length have been imaged with the scanning tunneling microscope (STM) after deposition on highly oriented pyrolytic graphite (HOPG). Images of the 47 base-pair (bp) molecules are resolved sufficiently to identify the two phosphodiester strands, the direction of helical coiling (this molecule contains three turns of left-handed helix), and single-stranded ends. Length measurements indicate that all three DNA sequences have adopted an "A-like" conformation. DNA-protamine complexes were also prepared and imaged under similar conditions. Length measurements of the complexes demonstrate that the binding of bull protamine 1 to the 47-mer stabilizes the DNA in a B conformation and prevents the B to A transition that has been shown to occur as the DNA molecules dehydrate on the surface. Measurements of the diameter of the complex (3 nm) were also obtained and were found to be only slightly larger than the DNA molecule. This observation is consistent with the binding of the protamine molecule inside one of the grooves. PMID:8108673

Allen, M J; Tench, R J; Mazrimas, J A; Balooch, M; Siekhaus, W J; Balhorn, R

1993-06-01

374

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

International Nuclear Information System (INIS)

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

375

High-resolution microscopy of plasmon field distributions by scanning tunneling luminescence and photoemission electron microscopies  

Science.gov (United States)

The exploitation of plasmon resonances to promote the interaction between conjugated molecules and optical fields motivates intensive research. The objectives are to understand the mechanisms of plasmon-mediated interactions, and to realize molecularly- or atomically-precise metal nanostructures, combining field enhancements and optical antenna effects. In this review paper, we present examples of plasmonic-field mappings based on scanning tunneling microscope (STM)-induced light emission or multiphoton photoemission (PEEM), two techniques among those which offer today's best spatial resolutions for plasmon microscopy. An unfamiliar property of the junction of an STM is its ability to behave as a highly localized source of light. It can be exploited to probe optoelectronic properties, in particular plasmonic fields, with ultimate subnanometer spatial resolution, an advantage balanced by a sometimes delicate deconvolution of local-probe influence. Alternatively, local-probe disadvantages can be overcome by imaging the photoemitted electrons, using well-established electron optics. This allows obtaining two-dimensional intensity maps reflecting the unperturbed distribution of the optical near field. This approach provides full field spectroscopic images with a routine spatial resolution of the order of 20 nm (down to 5 nm with recent aberration corrected instruments).

Douillard, Ludovic; Charra, Fabrice

2012-10-01

376

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°. PMID:25362397

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

2014-10-01

377

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

Energy Technology Data Exchange (ETDEWEB)

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

Yoshida, Yasuo, E-mail: yyoshida@issp.u-tokyo.ac.jp; Yokosuka, Takuya; Hasegawa, Yukio, E-mail: hasegawa@issp.u-tokyo.ac.jp [The Institute of Solid State Physics, The University of Tokyo, Kashiwa 277-8581 (Japan); Yang, Hung-Hsiang [Department of Physics, National Taiwan University, Taipei 106, Taiwan (China); Huang, Hsu-Sheng; Guan, Shu-You; Su, Wei-Bin; Chang, Chia-Seng [Institute of Physics, Academia Sinica, Nankang, Taipei 11529, Taiwan (China); Yanagisawa, Susumu [Department of Physics and Earth Science Department, University of the Ryukyus, 1 Nishihara, Okinawa 903-0213 (Japan); Lin, Minn-Tsong [Department of Physics, National Taiwan University, Taipei 106, Taiwan (China); Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan (China); Hoffmann, Germar [The Institute of Solid State Physics, The University of Tokyo, Kashiwa 277-8581 (Japan); Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan (China)

2014-09-21

378

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

Science.gov (United States)

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 (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.

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

2013-05-01

379

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

380

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

International Nuclear Information System (INIS)

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

381

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

Science.gov (United States)

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 approximately 150 nm in thickness to ensure the conductivity of the fiber probe. The outer Au layer is kept approximately 13 nm in thickness to obtain a better combination of high electron injection efficiency and optical transparency. High-quality STM images, and STML corresponding to maximum quantum efficiencies of 7 x 10(-4) and 1 x 10(-4) photons/electron are obtained on Au(111)/mica and p-GaAs(110) surfaces at room temperature (RT), respectively. The outer Au layer on the Au/ITO-coated fiber probe shows an effective role in improving the quality of STM imaging, the tip apex geometry and durability of the fiber probe, the stability and reproducibility of STML and enhancing the intensity of plasmon-mediated STML from the Au(111) surface but it shows no effect in enhancing the intensity of STML from the GaAs(110) surface. PMID:20009175

Guo, Xinli; Fujita, Daisuke; Onish, Keiko

2010-01-29

382

Bias asymmetry in the conductance profile of magnetic ions on surfaces probed by scanning tunneling microscopy  

Science.gov (United States)

The conductance profiles of magnetic transition-metal atoms, such as Fe, Co, and Mn, deposited on surfaces and probed by a scanning tunneling microscope (STM), provide detailed information on the magnetic excitations of such nanomagnets. In general, the profiles are symmetric with respect to the applied bias. However, a set of recent experiments has shown evidence for inherent asymmetries when either a normal or a spin-polarized STM tip is used. In order to explain such asymmetries, here we expand our previously developed perturbative approach to electron-spin scattering to the spin-polarized case and to the inclusion of out of equilibrium spin populations. In the case of a magnetic STM tip, we demonstrate that the asymmetries are driven by the nonequilibrium occupation of the various atomic spin levels, an effect that is reminiscent of electron spin transfer. In contrast, when the tip is not spin polarized, such a nonequilibrium population cannot be built up. In this circumstance, we propose that the asymmetry simply originates from the transition metal ion density of states and from the uneven electronic coupling between the scattering magnetic atoms and both the tip and the substrate. These effects are included in the formalism as a nonvanishing real component to the spin-scattering self-energy.

Hurley, Aaron; Baadji, Nadjib; Sanvito, Stefano

2012-09-01

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, whicub>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

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

385

Scanning Tunneling Microscopy and Spectroscopy of Quasi-freestanding Graphene on SiC  

Science.gov (United States)

Epitaxial graphene on SiC(0001) is a promising approach for industrial-scale production of very high quality graphene. Recently, it has been demonstrated by angle-resolved photoelectron spectroscopy (Riedl et al., Phys. Rev. Lett 103, 246804 (2009)) that graphene can be prepared on SiC in almost undoped form by intercalating atomic hydrogen beneath the non-graphitic carbon-rich ``buffer layer.'' We present scanning tunneling microscopy and spectroscopy measurements of quasi-free-standing monolayer graphene on SiC(0001) obtained by atomic hydrogen intercalation. Small hydrogen-intercalated domains formed at the initial stages of quasi-free graphene nucleation exhibit a ( ?3 x?3 )R30 corrugation due to the sub-surface hydrogen. Local image potential state spectroscopy on these domains is used to observe changes in local doping due to intercalation. These states show the energetic shift ( 0.4 eV) with respect to the usual n-doped single-layer graphene on SiC(0001) that suggests that H-intercalated graphene is almost charge-neutral.

Guan, Tianshuai; Sandin, Andreas; Rowe; Dougherty, Daniel

2013-03-01

386

Scanning Tunneling Microscope Observation and Manipulation of DNA and DNA-Related Molecules in Aqueous Condition  

Science.gov (United States)

We have studied the structure of adsorbed DNA and DNA-related molecules, such as adenosine, adenosine triphosphate disodium (ATP-2Na) and short single-stranded DNA oligomer (3 to 20 base pairs) adsorbed on Au(111) substrate by scanning tunneling microscopy (STM). Adenosine and ATP are spontaneously adsorbed on the Au substrate in 1.0×10-4 mol/l solution, and are imaged clearly as densely packed clusters. The adenosine clusters have been observed as hydrogen-bonded dimers which tend to dissociate with a change in the pH towards the alkaline condition. The ATP cluster has a spherical shape with a diameter of 150 Å. In the case of DNA oligomers, clear STM images can be observed after pre-rinse treatment or electrochemical treatment. The images of all the DNA oligomers are round with a diameter of 30 to 50 Å. This reveals the aggregated structures of DNA at the Au-solution interface. The manipulation of these DNA oligomers can be achieved by the lateral pushing of the microscope tip.

Tano, Tomoko; Tomyo, Masatoshi; Tabata, Hitoshi; Kawai, Tomoji

1998-06-01

387

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

388

Scanning tunneling microscopy investigations of the epitaxial growth of ZrB2 on Si(111)  

International Nuclear Information System (INIS)

By means of Scanning Tunneling Microscopy (STM), elongated structures observed in ZrB2 thin films epitaxially grown on Si(111) have been determined to be ZrB2 crystallites misoriented from the dominant orientation of ZrB2(0001)//Si(111). The epitaxial relationships ZrB2(11 anti 2 0)//Si(111) and ZrB2(1 anti 1 00)//Si(111) were identified together with the in-plane ZrB2[0001]//Si[1 anti 1 0] orientation. The surface of these crystallites exhibits a well-defined ZrB2 (1 anti 1 00) - (2 x 6) surface re- construction, which is observed for the first time. The presence of large ZrB2(1 anti 1 00) facets indicates that this surface contributes significantly to the growth of misoriented ZrB2 crystallites as well as to their elongated shape. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

389

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

390

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1995-12-31

391

Scanning tunnelling microscopy of the nucleation and growth of sputter-deposited Cr on graphite  

Energy Technology Data Exchange (ETDEWEB)

In this paper, we present a study of the nucleation and growth stages of sputter-deposited Cr thin films on highly oriented pyrolytic graphite (HOPG) substrates using scanning tunnelling microscopy (STM) in air. Freshly cleaved HOPG surfaces and those modified by Ar{sup +} ion bombardment were used as substrates.For short deposition times, two-dimensional (2D) chromium clusters on the graphite substrate were observed. With an increase in deposition time, the formation of three-dimensional (3D) clusters occurred. The number of surface defect sites influences the number and size of clusters formed on the graphite substrate. The formation and surface diffusion of 2D and 3D clusters play a dominant role in the subsequent stages of the nucleation of chromium thin films. The results of our investigation show clearly that the most important contribution to the elementary mechanism of growth is the phase transition from 2D to 3D clusters and their condensation into larger 3D clusters. ((orig.))

Rakocevic, Z. [Institut za Nuklearne Nauke Boris Kidric, Belgrade (Yugoslavia); Strbac, S. [ICTM-Centre of Electrochemistry, University of Belgrade, P.O. Box 815, 11001 Belgrade (Yugoslavia); Bibic, N. [Institut za Nuklearne Nauke Boris Kidric, Belgrade (Yugoslavia); Perusko, D. [Institut za Nuklearne Nauke Boris Kidric, Belgrade (Yugoslavia); Nenadovic, T. [Institut za Nuklearne Nauke Boris Kidric, Belgrade (Yugoslavia)

1995-02-15

392

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2002-04-29

393

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

International Nuclear Information System (INIS)

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

394

Oscillatory CO oxidation on Pd(1 0 0) studied with in situ scanning tunneling microscopy  

Science.gov (United States)

We have studied the catalytic oxidation of CO on Pd(1 0 0) at atmospheric pressures, using a combined flow reactor and scanning tunneling microscope (STM). By switching from a CO-rich flow to an O 2-rich flow, and vice versa, we could reversibly oxidize and reduce the surface, as we have observed with the STM. Both during the initial oxidation and during the catalytic reaction on the oxide, the surface became rough. Coinciding with the formation of the palladium oxide there was a step up in the CO oxidation rate. Whereas the reaction rate on the metallic surface followed traditional Langmuir-Hinshelwood kinetics, the reaction rate on the oxide was proportional to the CO-pressure and did not depend on the O 2-pressure. We suggest that the high reaction rate on the oxide resulted from the low stability of the oxide, making it highly reactive, and that the reaction followed the Mars-Van Krevelen mechanism, in which the oxide is continually 'consumed' and reformed. The switching between the metallic surface and the oxide showed significant hysteresis in the CO-pressure for O 2-rich conditions. This resulted in a CO-pressure window where reaction was stable both on the metal and on the oxide. We have observed that the reaction switched spontaneously between these branches, leading to oscillations in the reaction rate. Our interpretation is in strong disagreement with well-established models for CO oxidation on Pt-group metal surfaces.

Hendriksen, B. L. M.; Bobaru, S. C.; Frenken, J. W. M.

2004-03-01

395

Oxygen driven reconstruction dynamics of Ni(977) measured by time-lapse scanning tunneling microscopy  

Science.gov (United States)

Time-lapse scanning tunneling microscopy (STM) has been used to observe the oxygen induced reconstruction behavior of Ni(977), a stepped metallic surface. Previous studies using helium atom diffraction resolved the macroscopic kinetics for the reversible step-doubling and -singling of this vicinal surface. Sequential STM imaging recorded at elevated temperature has now elucidated atomic-level mechanistic details for the merging of steps in the presence of small amounts of adsorbed oxygen, less than 2% of a monolayer. Point contact between neighboring steps decorated with chemisorbed oxygen facilitates rapid step coalescence by means of zippering. An optimal oxygen concentration of step edge saturation was found to enable the step merging to proceed most rapidly. Excess oxygen was found to hinder the coalescence of neighboring steps through the possible growth of overlayer structures on the terraces. At sufficiently high temperatures, the surface is driven back to single steps due to oxygen dissolution. The departure of oxygen from the surface through dissolution, as well as the associated presence of oxygen in the selvedge region, may both play a role in destabilizing the double steps. Local step density influences the coalescence behavior by defining the number of available step edge sites. The microscopic details made available by time-resolved STM imaging illuminate some of the mechanistic steps related to the initial stages of metallic oxidation, and the sensitivity of surface morphological transformations to local surface structure and adsorbate coverage.

Pearl, T. P.; Sibener, S. J.

2001-07-01

396

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

397

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

398

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

Science.gov (United States)

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

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

2014-04-01

399

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. PMID:25343608

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

2014-11-01

400

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

401

Self-assembly of organopolysilanes on graphite: a scanning tunneling microscopy study  

Science.gov (United States)

In this study the observation of self-assembled monolayers of poly(dimethylsilanes) and poly(di- n-hexylsilanes) on the basal plane of highly oriented pyrolytic graphite (HOPG) is reported. The layers were characterized by scanning tunneling microscopy (STM). Individual polysilane molecules, the polysilane backbone and the hydrocarbon side chains within an individual molecule could be identified. Measured atomic distances were found to correspond to the expected values. The polysilanes formed regular molecular patterns, such that the polysilane backbone chains were stretched out straight, aligned parallel to each other separated by the alkyl side groups. The molecules were found in the all-trans zigzag conformation, the dihedral angle of the silicon backbone chain atoms is proposed to be perpendicular to the graphite substrate. The relative orientation of the polysilane molecules on graphite and the relative orientation of the molecules to each other is different for each of the investigated polysilanes. The structural behaviour of polysilanes is of interest, since it may allow future investigations on the conductivity of ?-bonded polysilanes on the molecular scale.

Gröppel, M.; Roth, W.; Elbel, N.; von Seggern, H.

1995-01-01

402

Understanding scanning tunneling microscopy contrast mechanisms on metal oxides: a case study.  

Science.gov (United States)

A comprehensive analysis of contrast formation mechanisms in scanning tunneling microscopy (STM) experiments on a metal oxide surface is presented with the oxygen-induced (2?2×?2)R45° missing row reconstruction of the Cu(100) surface as a model system. Density functional theory and electronic transport calculations were combined to simulate the STM imaging behavior of pure and oxygen-contaminated metal tips with structurally and chemically different apexes while systematically varying bias voltage and tip-sample distance. The resulting multiparameter database of computed images was used to conduct an extensive comparison with experimental data. Excellent agreement was attained for a large number of cases, suggesting that the assumed model tips reproduce most of the commonly encountered contrast-determining effects. Specifically, we find that depending on the bias voltage polarity, copper-terminated tips allow selective imaging of two structurally distinct surface Cu sites, while oxygen-terminated tips show complex contrasts with pronounced asymmetry and tip-sample distance dependence. Considering the structural and chemical stability of the tips reveals that the copper-terminated apexes tend to react with surface oxygen at small tip-sample distances. In contrast, oxygen-terminated tips are considerably more stable, allowing exclusive surface oxygen imaging at small tip-sample distances. Our results provide a conclusive understanding of fundamental STM imaging mechanisms, thereby providing guidelines for experimentalists to achieve chemically selective imaging by properly selecting imaging parameters. PMID:24111487

Mönig, Harry; Todorovi?, Milica; Baykara, Mehmet Z; Schwendemann, Todd C; Rodrigo, Lucía; Altman, Eric I; Pérez, Rubén; Schwarz, Udo D

2013-11-26

403

Self-Organized Graphene Nanoribbons on SiC(0001) Studied with Scanning Tunneling Microscopy  

Science.gov (United States)

Graphene nanoribbons grown directly on nanofacets of SiC(0001) offer an attractive union of top-down and bottom-up fabrication techniques. Nanoribbons have been shown to form on the facets of templated silicon carbide substrates,ootnotetextSprinkle et al., Nat. Nanotech. 5, 727 (2010). but also appear spontaneously along step-bunches on vicinal SiC(0001) miscut slightly towards . These self-organized graphene nanoribbons were characterized with low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES) in ultra-high vacuum. Our measurements indicate that the graphene forms a continuous ``buffer layer'' across the SiC(0001) terraces during nanoribbon formation, with the zigzag edge of the buffer layer aligned parallel to the step-bunched nanofacets. Scanning tunneling microscopy/spectroscopy (STM/STS) was used to characterize the topography and electrical characteristics of the graphene nanoribbons. These measurements indicate that the graphene nanoribbons are highly-crystalline with predominantly zigzag edges.

Torrance, David; Zhang, Baiqian; Hoang, Tien; First, Phillip

2012-02-01

404

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

405

Aircraft and satellite measurement of ocean wave directional spectra using scanning-beam microwave radars  

Science.gov (United States)

A microwave radar technique for remotely measuring the vector wave number spectrum of the ocean surface is described. The technique which employs short-pulse, noncoherent radars in a conical scan mode near vertical incidence, is shown to be suitable for both aircraft and satellite application, the technique was validated at 10 km aircraft altitude, where we have found excellent agreement between buoy and radar-inferred absolute wave height spectra.

Jackson, F. C.; Walton, W. T.; Baker, P. L.

1985-01-01

406

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

407

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

408

Use of in situ scanning tunneling microscopy for the study of dye sensitization of semiconductor electrodes. Progress report, September 15, 1992--August 15, 1995  

Energy Technology Data Exchange (ETDEWEB)

In the three years of this contract, the authors have set up a state-of-the-art computer-controlled photoelectrochemical characterization laboratory with facilities to measure Mott-Schottky behavior, photocurrent spectra and photocurrent voltage curves on semiconductor electrodes. They have also set up a Bridgeman crystal growth furnace for preparing their own single crystals of SnS{sub 2} and other semiconductor materials for the photoelectrochemical studies. The first boules of SnS{sub 2} have recently been prepared. They have also modified a scanning tunneling microscope to perform photo-STM experiments to spatially resolve photocurrents on semiconductor surfaces. In addition, the acquisition of a Ti:sapphire laser system from the DOE-URI program will give us the power and flexibility in the light source to provide a better chance of single molecule detection. The results on sensitization will be summarized below.

Parkinson, B.

1995-12-31

409

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.

410

Nano-scale patterning on sulfur terminated GaAs (0 0 1) surface by scanning tunneling microscope  

International Nuclear Information System (INIS)

We perform nano-scale patterning on a sulfur (S) terminated GaAs (0 0 1) surface by a scanning tunneling microscope (STM) in ultra-high vacuum (UHV). A multi-layer of S deposited by using (NH4)2Sx solution is changed to a mono-layer after annealing at 560 deg. C for 15 h, which terminates the GaAs (0 0 1) surface. Groove structures with about 0.23 nm in depth and about 5 nm in width are patterned successfully on the S-terminated surface. We investigate dependences of both depth and width of the patterned groove on the tunneling current and the scanning speed of tip. It is observed that topmost S atoms are extracted together with first-layer Ga atoms, because of the larger binding energy of S-Ga bond

411

Scanning tunnelling microscopy and spectroscopy on organic PTCDA films deposited on sulfur passivated GaAs(001)  

Energy Technology Data Exchange (ETDEWEB)

Deposition of 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) on sulfur passivated gallium arsenide S-GaAs(001) surfaces is investigated by scanning tunnelling microscopy and scanning tunnelling spectroscopy. The surface morphology and the film structure are studied for the multilayer growth of the organic molecules. Spectroscopic results for both clean substrate and ordered areas of PTCDA are shown in this work. We have measured I-V plots at different tip-sample distances, avoiding deformation of the organic layer. Under proper experimental conditions, a gap value of 2.2eV has been measured on PTCDA crystals, in good agreement with the expected value for PTCDA (2.2-2.55eV)

Nicoara, N [Laboratorio de Nuevas MicroscopIas, Departamento de FIsica Materia Condensada C-III, Universidad Autonoma de Madrid, E-28049 Madrid (Spain); Custance, O [Laboratorio de Nuevas MicroscopIas, Departamento de FIsica Materia Condensada C-III, Universidad Autonoma de Madrid, E-28049 Madrid (Spain); Granados, D [Instituto de Microelectronica de Madrid-CSIC, E-28760 Madrid (Spain); GarcIa, J M [Instituto de Microelectronica de Madrid-CSIC, E-28760 Madrid (Spain); Gomez-RodrIguez, J M [Laboratorio de Nuevas MicroscopIas, Departamento de FIsica Materia Condensada C-III, Universidad Autonoma de Madrid, E-28049 Madrid (Spain); Baro, A M [Laboratorio de Nuevas MicroscopIas, Departamento de FIsica Materia Condensada C-III, Universidad Autonoma de Madrid, E-28049 Madrid (Spain); Mendez, J [Instituto de Ciencia de Materiales de Madrid-CSIC, E-28049 Madrid (Spain)

2003-10-01

412

Analysis of Scanning Tunneling Spectroscopy Experiments from First Principles the Test Case of C60 Adsorbed on Au(111)  

CERN Document Server

We report on the first principles determination of the conductance properties of Buckminster fullerene adsorbed on a gold surface, comparing them with recent Scanning Tunneling Microscopy/Spectroscopy (STM/S) experiments [J.Chem.Phys.116, 832 (2002)]. Our procedure has the two appealing features of being able to elucidate delicate aspects of STM/S results without resorting to ad hoc fittings or approximations and to provide a complete description of the phenomena involved when the tip approaches the adsorbate.

Pérez-Jiménez, A J; Louis, E; San Fabian, E; Vergés, J A

2002-01-01

413

Simultaneous study by scanning tunneling spectroscopy and transport measurements in adsorbate-induced two-dimensional systems  

Science.gov (United States)

An adsorbate-induced two-dimensional electron system at cleaved surfaces of InSb is investigated by low-temperature scanning tunneling microscope and spectroscopy combined with transport measurements in magnetic fields up to 10 T. The magnitude of the potential disorder obtained from the spatially averaged density of states agrees with that deduced from the analysis of the Shubnikov-de Haas oscillations.

Masutomi, Ryuichi; Okamoto, Tohru

2014-12-01

414

Scanning tunneling microscopy study of pinning-induced vortex lattice distortion in ion-irradiated NbSe2  

International Nuclear Information System (INIS)

We observe vortex pinning in 2.2 GeV Au-ion irradiated NbSe2 by scanning tunneling microscopy (STM) at 3 K. The ion irradiation generates columnar defects which act as pinning sites. At various external magnetic fields the vortex arrangement is clearly resolved but shows strong distortion. The location of individual defects is extracted from STM data and compared to the vortex arrangement. (orig.)

415

Simulated scanning tunneling microscopy images of few-layer-phosphorus capped by graphene and hexagonal boron nitride monolayers  

OpenAIRE

Elemental phosphorous is believed to have several stable allotropes that are energetically nearly degenerate, but chemically reactive. To prevent chemical degradation under ambient conditions, these structures may be capped by monolayers of hexagonal boron nitride ({\\em h}-BN) or graphene. We perform {\\em ab initio} density functional calculations to simulate scanning tunneling microscopy (STM) images of different layered allotropes of phosphorus and study the effect of capp...

Rivero, Pablo; Horvath, Cedric M.; Zhu, Zhen; Guan, Jie; Toma?nek, David; Barraza-lopez, Salvador

2014-01-01

416

Atomic origin of the scanning tunneling microscopy images of charge-density-waves on 1T-TaSe2  

International Nuclear Information System (INIS)

We show atomically resolved scanning tunneling microscopy (STM) images of charge density waves (CDWs) at room temperature together with angle-resolved photoelectron band-mapping of 1T-TaSe2. By comparing the results of these two techniques, we demonstrate the atomic structure of the CDW-features observed by the STM and atomic origin of the reconstructed band-structure in this material

417

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

Energy Technology Data Exchange (ETDEWEB)

We present a novel homebuilt scanning tunneling microscope (STM) with high quality atomic resolution. It is equipped with a small but powerful GeckoDrive piezoelectric motor which drives a miniature and detachable scanning part to implement coarse approach. The scanning part is a tiny piezoelectric tube scanner (industry type: PZT-8, whose d{sub 31} coefficient is one of the lowest) housed in a slightly bigger polished sapphire tube, which is riding on and spring clamped against the knife edges of a tungsten slot. The STM so constructed shows low back-lashing and drifting and high repeatability and immunity to external vibrations. These are confirmed by its low imaging voltages, low distortions in the spiral scanned images, and high atomic resolution quality even when the STM is placed on the ground of the fifth floor without any external or internal vibration isolation devices.

Wang, Qi; Wang, Junting; Lu, Qingyou, E-mail: qxl@ustc.edu.cn [High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026 (China); Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China); Hou, Yubin [High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026 (China)

2013-11-15

418

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

International Nuclear Information System (INIS)

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

419

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

Science.gov (United States)

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 (observed for all three fibre species containing haem and one species of fibre that did not contain haem. In images of this kind, some of the current peaks were collinear and spaced around 10 nm apart over ranges longer than 100 nm, but background monomers complicate interpretation. Images of the third kind were rare (1 in 150 fibres); in these, fully conducting structures with the approximate dimensions of fibres were observed, suggesting the possibility of an intermittent conduction mechanism, for which a precedent exists in DNA. To test the conductivity, some fibres were immobilized with sputtered gold, and no evidence of conduction between the grains of gold was seen. In control experiments, a variation of monomeric cytochrome b562 was not detected by STM, which was attributed to low adhesion, whereas a monomeric multi-haem protein, GSU1996, was readily imaged. We conclude that the fibre superstructure may be intermittently conducting, that the cytochromes have been seen within the fibres and that they are too far apart for detectable current flow between sites to occur. We predict that GSU1996, being 10 nm long, is more likely to mediate successful electron transfer along the fibre as well as being more readily detectable when displayed from amyloid. PMID:23571459

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

2013-05-01

420

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

International Nuclear Information System (INIS)

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

421

Scanning Tunneling Spectroscopy Studies of Transition Metal Oxides and Spin Light Emitting Diode Studies  

Science.gov (United States)

Studies of three transition metal oxide (TMO) materials and two types of spin light emitting diodes (LEDs) are contained in this dissertation. The studies of the samples processed into spin LEDs contained herein were all grown with molecular beam epitaxy (MBE), and utilize the same spin injector material, manganese arsenide (MnAs). We have demonstrated that MnAs is an efficient spin injector of spin polarized electrons into gallium arsenide (GaAs) and indium arsenide (InAs). It has also been shown that annealing MnAs grown on GaAs does not cause Mn ions to diffuse into GaAs; such diffusion would be detrimental to spin injection. A scanning tunneling spectroscopy (STS) modulation bias technique was used to examine and spatially map the local density of states (LDOS) of the surfaces of these TMOs with sub-nanometer resolution. Two of the TMO materials have possible photovoltaic/photocatalytic applications, while the other undergoes a metal-insulator transition (MIT) and is a promising material for high-speed field effect transistors. The distributions of energy gaps measured across the surface of the two solar materials were found to be consistent with their respective absorption measurements. This confirms that the utilization of the successful co-doping scheme/alteration of the growth parameters effectively reduced the energy gaps thereby increasing the solar efficiency of these materials. Also, the electronic structure of an intermediate metallic phase was measured with STS for the first time to our knowledge in the MIT TMO material examined herein.

Hatch, John B.

422

A compact sub-Kelvin ultrahigh vacuum scanning tunneling microscope with high energy resolution and high stability.  

Science.gov (United States)

We designed a scanning tunneling microscope working at sub-Kelvin temperatures in ultrahigh vacuum (UHV) in order to study the magnetic properties on the nanoscale. An entirely homebuilt three-stage cryostat is used to cool down the microscope head. The first stage is cooled with liquid nitrogen, the second stage with liquid (4)He. The third stage uses a closed-cycle Joule-Thomson refrigerator of a cooling power of 1 mW. A base temperature of 930 mK at the microscope head was achieved using expansion of (4)He, which can be reduced to ?400 mK when using (3)He. The cryostat has a low liquid helium consumption of only 38 ml/h and standing times of up to 280 h. The fast cooling down of the samples (3 h) guarantees high sample throughput. Test experiments with a superconducting tip show a high energy resolution of 0.3 meV when performing scanning tunneling spectroscopy. The vertical stability of the tunnel junction is well below 1 pm (peak to peak) and the electric noise floor of tunneling current is about 6fA/?Hz. Atomic resolution with a tunneling current of 1 pA and 1 mV was achieved on Au(111). The lateral drift of the microscope at stable temperature is below 20 pm/h. A superconducting spilt-coil magnet allows to apply an out-of-plane magnetic field of up to 3 T at the sample surface. The flux vortices of a Nb(110) sample were clearly resolved in a map of differential conductance at 1.1 K and a magnetic field of 0.21 T. The setup is designed for in situ preparation of tip and samples under UHV condition. PMID:22047298

Zhang, L; Miyamachi, T; Tomani?, T; Dehm, R; Wulfhekel, W

2011-10-01

423

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

OpenAIRE

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

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

2005-01-01

424

Control of charging in resonant tunneling through InAs nanocrystal quantum dots  

OpenAIRE

Tunneling spectroscopy of InAs nanocrystals deposited on graphite was measured using scanning tunneling microscopy, in a double-barrier tunnel-junction configuration. The effect of the junction symmetry on the tunneling spectra is studied experimentally and modeled theoretically. When the tip is retracted, we observe resonant tunneling through the nanocrystal states without charging. This is in contrast to previous measurements on similar nanocrystals anchored to gold by lin...

Katz, David; Millo, Oded; Kan, Shi-hai; Banin, Uri

2001-01-01

425

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

International Nuclear Information System (INIS)

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

426

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

Science.gov (United States)

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

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

2012-04-01

427

First principles theory of inelastic currents in a scanning tunneling microscope  

CERN Document Server

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

Stokbro, K; Thirstrup, C; Xie, X C; Hu, Ben Yu-Kuang

1998-01-01

428

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

Science.gov (United States)

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

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

2004-03-01

429

Scanning tunneling microscopy simulations of nitrogen- and boron-doped graphene and single-walled carbon nanotubes.  

Science.gov (United States)

We report on studies of electronic properties and scanning tunneling microscopy (STM) of the most common configurations of nitrogen- or boron-doped graphene and carbon nanotubes using density functional theory. Charge transfer, shift of the Fermi level, and localized electronic states are analyzed as a function of the doping configurations and concentrations. The theoretical STM images show common fingerprints for the same doping type for graphene, and metallic or semiconducting nanotubes. In particular, nitrogen is not imaged in contrast to boron. STM patterns are mainly shaped by local density of states of the carbon atoms close to the defect. STM images are not strongly dependent on the bias voltage when scanning the defect directly. However, the scanning of the defect-free side of the tube displays a perturbation compared to the pristine tube depending on the applied bias. PMID:20552993

Zheng, Bing; Hermet, Patrick; Henrard, Luc

2010-07-27

430

Co on Pt(111) studied by spin-polarized scanning tunneling microscopy and spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

In this thesis the electronic properties of the bare Pt(111) surface, the structural, electronic, and magnetic properties of monolayer and double-layer high Co nanostructures as well as the spin-averaged electronic structure of single Co atoms on Pt(111) were studied by low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS). The experiments on the bare Pt(111) surface and on single Co atoms have been performed in an STM facility operating at temperatures of down to 0.3 K and at magnetic fields of up to 14 T under ultra-high vacuum conditions. The facility has been taken into operation within the time period of this thesis and its specifications were tested by STS measurements. These characterization measurements show a very high stability of the tunneling junction and an energy resolution of about 100 {mu}eV, which is close to the thermal limit. The investigation of the electronic structure of the bare Pt(111) surface reveals the existence of an unoccupied surface state. By a comparison of the measured dispersion to first-principles electronic structure calculations the state is assigned to an sp-derived surface band at the lower boundary of the projected bulk band gap. The surface state exhibits a strong spin-orbit coupling induced spin splitting. The close vicinity to the bulk bands leads to a strong linear contribution to the dispersion and thus to a deviant appearance in the density of states in comparison to the surface states of the (111) surfaces of noble metals. A detailed study of Co monolayer and double-layer nanostructures on the Pt(111) surface shows that both kinds of nanostructures exhibit a highly inhomogeneous electronic structure which changes at the scale of only a few Aa due to a strong stacking dependence with respect to the Pt(111) substrate. With the help of first principles calculations the different spectroscopic appearance for Co atoms within the Co monolayer is assigned to a stacking dependent hybridization of Co states with the substrate states. Despite this electronic inhomogeneity, the magnetic domains and domain walls are clearly observed by spin-resolved STS. For both types of Co nanostructures the out-of-plane orientation of the magnetic moments is proven. Furthermore, new insights into the anisotropy of the Co nanostructures as well as a strong dependence of the coercivity on the local sample morphology for Co double-layer islands were found. The experiments performed on single Co atoms on the Pt(111) surface show that two groups of Co atoms are present on the surface. Each group can be characterized by a specific spectroscopic signature. An analysis of the spectroscopy and atom manipulation experiments proves that the spectroscopic differences are related to the two possible adsorption sites of the Co atoms on the Pt(111) substrate. (orig.)

Meier, F.K.

2006-07-01

431

NaCl multi-layer islands grown on Au(111)-(22x?3) probed by scanning tunneling microscopy  

International Nuclear Information System (INIS)

The growth of multi-layer NaCl islands on Au(111)-(22x?3) surfaces was investigated using scanning tunneling microscopy (STM). We observed that the aspect of the NaCl islands drastically differs depending on the tunneling conditions. It is therefore possible to observe the layers forming an NaCl island or to image the gold reconstruction below the first NaCl layer. Atomically resolved STM images obtained on the first NaCl layer demonstrate that NaCl grows as an epitaxial crystalline film on Au(111)-(22x?3). STM images also suggest that some NaCl layers can be non-crystalline.

432

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

International Nuclear Information System (INIS)

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

433

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

Energy Technology Data Exchange (ETDEWEB)

The domain structure of (FeCo)-Zr-O thin film was observed with spin-polarized scanning tunneling microscopy. A maze domain is characterized by a domain width of about 320 nm, and a wall energy of 4.97 erg cm{sup -2}. The tunneling magnetoresistance (TMR) profile is fitted by a tanh function, and a wall thickness of about 100 nm is obtained. This indicates that the TMR is proportional to the angle between the tip and the film magnetizations. Effective exchange and anisotropy constants are estimated at 3.88 x 10{sup -6} erg cm{sup -1} and 3.98 x 10{sup 5} erg cm{sup -3}, respectively.

Gao Youhui [Department of Physics, Beijing Normal University, No. 19, Xinjiekou Waidajie, Beijing 100875 (China)], E-mail: ygao@bnu.edu.cn; Shindo, Daisuke [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 1-1 Katahira, 2-Chome, Aobaku, Sendai 980-8577 (Japan); Ohnuma, Shigehiro; Fujimori, Hiroyasu [The Research Institute for Electric and Magnetic Materials, Sendai 982-0807 (Japan)

2008-09-15

434

Interfacial features of La0.7Sr0.3MnO3 probed by scanning tunneling microscopy  

International Nuclear Information System (INIS)

We present scanning tunneling microscopy (STM) and spectroscopy (STS) studies on artificial grain boundary (GB) resulting from the growth of Sr-substituted manganite on MgO bicrystal substrate. The width of the GB-the region between the two crystals- was found to be around 20-30 nm, wherein unusual structural and electronic features were observed in the topography and spectroscopy. Within the GB, structural features running parallel to the grain boundary were detected, which originate probably due to relaxation of stress. Tunneling conductivity within the GB at room temperature was found to be insulating-like, and could be strongly increased through the interaction between the tip and film. The puzzle of sharp versus diffused electronic phase separation between two different electronic phases appears to be linked to domains/antiphase boundaries versus disorder/strain

435

Graphene ripples as a realization of a two-dimensional Ising model: A scanning tunneling microscope study  

Science.gov (United States)

Ripples in pristine freestanding graphene naturally orient themselves in an array that is alternately curved-up and curved-down; maintaining an average height of zero. Using scanning tunneling microscopy (STM) to apply a local force, the graphene sheet will reversibly rise and fall in height until the height reaches 60%-70% of its maximum at which point a sudden, permanent jump occurs. We successfully model the ripples as a spin-half Ising magnetic system, where the height of the graphene plays the role of the spin. The permanent jump in height, controlled by the tunneling current, is found to be equivalent to an antiferromagnetic-to-ferromagnetic phase transition. The thermal load underneath the STM tip alters the local tension and is identified as the responsible mechanism for the phase transition. Four universal critical exponents are measured from our STM data, and the model provides insight into the statistical role of graphene's unusual negative thermal expansion coefficient.

Schoelz, J. K.; Xu, P.; Meunier, V.; Kumar, P.; Neek-Amal, M.; Thibado, P. M.; Peeters, F. M.

2015-01-01