WorldWideScience
 
 
1

Scanning tunneling spectroscopy  

International Nuclear Information System (INIS)

Scanning tunneling microscopy (STM) provides a means of directly imaging surface topography with atomic scale resolution. Scanning tunneling spectroscopy (STS) usually refers to the image-wise determination of the tunnel current variation with bias voltage for fixed tunnel gap width. Results can be related to the density of filled and empty surface electronic states. The association of energic features with spatially localized features is a unique capability. Other variations of STS are inelastic tunneling imaging and barrier spectroscopic imaging. All these techniques are described and representative examples given to provide a survey of STS.

1988-01-01

2

Josephson scanning tunneling microscopy  

CERN Document Server

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

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

2000-01-01

3

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

4

Scanning tunneling microscope nanoetching method  

Energy Technology Data Exchange (ETDEWEB)

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

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

1990-01-01

5

Scanning Tunneling Microscopy - image interpretation  

International Nuclear Information System (INIS)

The basic ideas of image interpretation in Scanning Tunneling Microscopy are presented using simple quantum-mechanical models and supplied with examples of successful application. The importance is stressed of a correct interpretation of this brilliant experimental surface technique

1998-01-01

6

Scanning Tunneling Spectroscopic Studies of Cuprate Superconductors  

CERN Document Server

Quasiparticle tunneling spectra of both hole-doped (p-type) and electron-doped (n-type) cuprates are studied using a low-temperature scanning tunneling microscope. The results reveal that neither the pairing symmetry nor the pseudogap phenomenon is universal among all cuprates, and that the response of n-type cuprates to quantum impurities is drastically different from that of the p-type cuprates. The only ubiquitous features among all cuprates appear to be the strong electronic correlation and the nearest-neighbor antiferromagnetic Cu^{2+}-Cu^{2+} coupling in the CuO_2 planes.

Yeh, N C; Vásquez, R P; Jung, C U; Lee, S I; Yoshida, K; Tajima, S

2002-01-01

7

Investigation into scanning tunnelling luminescence microscopy  

CERN Multimedia

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

8

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

9

Induced superconductivity in noncuprate layers of the Bi2Sr2CaCu2O8+? high-temperature superconductor: Modeling of scanning tunneling spectra  

Science.gov (United States)

We analyze how the coherence peaks observed in scanning tunneling spectroscopy (STS) of cuprate high-temperature superconductors are transferred from the cuprate layer to the oxide layers adjacent to the STS microscope tip. For this purpose, we have carried out a realistic multiband calculation for the superconducting state of Bi2Sr2CaCu2O8+? (Bi2212) assuming a short-range d-wave pairing interaction confined to the nearest-neighbor Cu dx2-y2 orbitals. The resulting anomalous matrix elements of the Green’s function allow us to monitor how pairing is then induced not only within the cuprate bilayer but also within and across other layers and sites. The symmetry properties of the various anomalous matrix elements and the related selection rules are delineated.

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

2011-01-01

10

New directions in scanning-tunneling microscopy  

International Nuclear Information System (INIS)

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

1989-01-01

11

Potential barrier for tunneling electrons in STM [scanning tunneling microscope  

International Nuclear Information System (INIS)

[en] 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. 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

1989-01-01

12

Scanning Tunneling Microscopy of a Luttinger Liquid  

CERN Document Server

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

Eggert, S

2000-01-01

13

Scanning tunneling microscopy of semiconductor surfaces  

Energy Technology Data Exchange (ETDEWEB)

This review describes advances in understanding the structural, electronic, and chemical properties of clean low-index semiconductor surfaces during the first decade following the advent of the scanning tunneling microscope (STM). The principles of STM are discussed together with the instrumentation required to perform STM measurements on semiconductor surfaces in ultrahigh vacuum. A comprehensive review of the structures of the clean, low-index surfaces of elemental and compound semiconductors is presented. These structures are discussed using the general physical principles that determine them

Kubby, J.A. [Xerox Wilson Center for Research and Technology, Xerox Corporation, Webster, NY (United States); Boland, J.J. [Department of Chemistry, University of North Carolina at Chapel Hill Chapel Hill, NC 27599-3290 (United States)

1996-11-28

14

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

CERN Multimedia

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

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

2006-01-01

15

Scanning tunneling microscopy/spectroscopy in iron-pnictide superconductor  

International Nuclear Information System (INIS)

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

2010-01-01

16

Scanning tunneling microscopy of marine hydrothermal sediments  

Energy Technology Data Exchange (ETDEWEB)

Scanning tunneling microscopy (STM) was employed to study the nanometer-scale morphology and topography of marine hydrothermal sediments collected from the Lau Basin and the North Fiji Basin during R/V Sonne cruise SO 35. The mineralogy and bulk chemistry of the sediments were determined prior to STM studies. Samples consist primarily of birnessite or a mixture of todorokite and birnessite. Because manganese oxides are wide bandgap semiconductors that cannot be readily imaged in their natural state, the particles were coated with an approximately 25-nm carbon layer prior to imaging. Low resolution STM images were acquired in the constant current mode. The birnessite surface is characterized by gently sloped topography and smaller scale knolls and depressions; less commonly distinct elongated growth patterns similar to fibrous todorokite crystals are observed. The surface of todorokite-birnessite particles is more homogeneous with the well-defined parallel ridge and valley topography of fibrous todorokite. Ridges and valleys are interrupted by 7-10-nm terraces and step-like features interpreted to represent edges of aligned tunnel structures. The authors observations are consistent with results of previous studies of hydrothermal manganese oxides and suggest that STM is useful for investigating the nanometer-scale surface characteristics of aggregates of wide bandgap semiconductor particles. However, because of 2-3-nm scale artifacts imparted by carbon coating, only features larger than approximately 5 nm can be confidently attributed to the underlying particles.

Koeppenkastrop, D.; Lewis, S.; De Carlo, E.H. (Univ. of Hawaii, Honolulu (United States))

1991-11-01

17

Scanning tunneling spectroscopy in an ionic liquid.  

Science.gov (United States)

Molecular redox levels can be used to modulate tunneling currents through single or small numbers of molecules and induce molecular electronic device function. While most of these devices require cryogenic conditions, room temperature operation has been demonstrated by using electrochemical gating in aqueous environments. The latter have, however, serious shortcomings with a view on their relatively high volatility and narrow stability ranges in terms of potential. Here we report the first-time use of an ionic liquid, 1-butyl-3-methylimidazoliumhexafluorophosphate (BMI), as an electrochemical gate in a Scanning Tunneling Microscope (STM) configuration. Ionic liquids are known to have a very low vapor pressure, and accessible potential ranges are in principle large, up to 6 V. In a proof-of-principle experiment, we show how a heteroleptic redox-active Os bisterpyridine complex (Ossac) can be brought to exhibit both transistor and diode function in this novel environment at room temperature. This renders ionic liquids an attractive gating medium for configurations where back-gating is difficult to implement (e.g., break-junction techniques) or experimental conditions prohibit the use of aqueous or organic electrolyte media (vacuum or high temperatures). From an applied perspective, they represent a step toward solid-state molecular electronics with electrochemical gating. PMID:16704254

Albrecht, Tim; Moth-Poulsen, Kasper; Christensen, Jørn B; Hjelm, Johan; Bjørnholm, Thomas; Ulstrup, Jens

2006-05-24

18

Direct, coherent and incoherent intermediate state tunneling and scanning tunnel microscopy (STM)  

International Nuclear Information System (INIS)

Theory and experiment in tunneling are still qualitative in nature, which hold true also for the latest developments in direct-, resonant-, coherent- and incoherent-tunneling. Those tunnel processes have recently branched out of the field of ''solid state tunnel junctions'' into the fields of scanning tunnel microscopy (STM), single electron tunneling (SET) and semiconducting resonant tunnel structures (RTS). All these fields have promoted the understanding of tunneling in different ways reaching from the effect of coherence, of incoherence and of charging in tunneling, to spin flip or inelastic effects. STM allows not only the accurate measurements of the tunnel current and its voltage dependence but, more importantly, the easy quantification via the (quantum) tunnel channel conductance and the distance dependence. This new degree of freedom entering exponentially the tunnel current allows an unique identification of individual tunnel channels and their quantification. In STM measurements large tunnel currents are observed for large distances d > 1 nm explainable by intermediate state tunneling. Direct tunneling with its reduced tunnel time and reduced off-site Coulomb charging bridges distances below 1 nm, only. The effective charge transfer process with its larger off-site and on-site charging at intermediate states dominates tunnel transfer in STM, biology and chemistry over distances in the nm-range. Intermediates state tunneling becomes variable range hopping conduction for distances larger than d > 2 nm, for larger densities of intermediate states n1(?) and for larger temperatures T or voltages U, still allowing high resolution imaging.

1997-01-01

19

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

International Nuclear Information System (INIS)

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

1994-01-01

20

Scanning tunneling microscopy of hexagonal BN grown on graphite  

Energy Technology Data Exchange (ETDEWEB)

The microscopic surface topography of thin BN{sub {ital x}} films grown on graphite by electron cyclotron resonance plasma chemical vapor deposition have been imaged with scanning tunneling microscopy in air. The scanning tunneling microscope has generated images of hexagonal BN with atomic resolution.

Fukumoto, H.; Hamada, T. (Department of Electrical Engineering, Hiroshima University, Higashihiroshima 724, Japan (JP)); Endo, T. (Hiroshima Denki Institute of Technology, Hiroshima 739-03, Japan (JP)); Osaka, Y. (Department of Electrical Engineering, Hiroshima University, Higashihiroshima 724, Japan (JP))

1991-06-15

 
 
 
 
21

Infrared Spectroscopy of Molecular Submonolayers on Surfaces by Infrared Scanning Tunneling Microscopy: Tetramantane on Au(111)  

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.

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

2013-09-01

22

The fabrication of reproducible superconducting scanning tunneling microscope tips  

CERN Document Server

Superconducting scanning tunneling microscope tips have been fabricated with a high degree of reproducibility. The fabrication process relies on sequential deposition of superconducting Pb and a proximity-coupled Ag capping layer onto a Pt/Ir tip. The tips were characterized by tunneling into both normal-metal and superconducting films. The simplicity of the fabrication process, along with the stability and reproducibility of the tips, clear the way for tunneling studies with a well-characterized, scannable superconducting electrode.

Naaman, O; Dynes, R C

2001-01-01

23

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

CERN Document Server

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

Howald, C; Kapitulnik, A

2001-01-01

24

Scanning Tunneling Microscopy Investigations of Metal Dichalcogenide Materials.  

Science.gov (United States)

Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) have been used to characterize the atomic level structure of electronic properties, reactivity and wear of metal dichalcogenide materials that are or have potential as solid state lubri...

C. M. Lieber

1993-01-01

25

Inelastic scanning tunneling spectroscopy: magnetic excitations on the nanoscale  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Inelastic scanning tunneling spectroscopy is used to study elementary excitations (magnons) in magnetic systems of various dimensions: from bulk to single magnetic atoms. The creation mechanism, the excitation probability, the spectrum and the lifetimes of magnons are investigated.

Balashov, Timofey

26

Doping and quantum confinement effects in single Si nanocrystals observed by scanning tunneling spectroscopy.  

UK PubMed Central (United Kingdom)

We have applied scanning tunneling spectroscopy in studies of the electronic level structure of surface-functionalized colloidal Si nanocrystals (Si-NCs) as a function of their size for various capping ligands. The energy gaps extracted from the tunneling spectra increase with decreasing NC size, manifesting the effect of quantum confinement. This is consistent with the blueshift revealed by photoluminescence (PL) from dodecene functionalized Si-NCs. The tunneling spectra measured on NCs functionalized with NH4Br or allylamine show band-edge shifts toward higher energies, akin to p-type doping. This behavior can be accounted for by the combined contributions of the ligands' dipole moments and charge transfer between a Si-NC and its surface groups. Concomitantly, size-independent PL spectra, which cannot be associated with NC band gap variations, were observed for the latter Si-NCs.

Wolf O; Dasog M; Yang Z; Balberg I; Veinot JG; Millo O

2013-06-01

27

Influence of tunneling voltage on the imaging of carbon nanotube rafts by scanning tunneling microscopy  

Science.gov (United States)

The influence of bias voltage on the quality of scanning tunneling microscopy images of carbon nanotube ``rafts'' was investigated in the range from -1 to 1 V in combination with scanning tunneling spectroscopy (STS) measurements. While for positive tip polarity only a slight voltage dependence was found in the image quality, for negative polarity a strong increase of the noise was observed with increasing voltage. STS showed that, for negative tip polarity, the tunneling current may be different in different locations by several orders of magnitude.

Biró, L. P.; Thiry, P. A.; Lambin, Ph.; Journet, C.; Bernier, P.; Lucas, A. A.

1998-12-01

28

Franck-condon fingerprinting of vibration-tunneling spectra.  

Science.gov (United States)

We introduce Franck-Condon fingerprinting as a method for assigning complex vibration-tunneling spectra. The B? state of thiophosgene (SCCl2) serves as our prototype. Despite several attempts, assignment of its excitation spectrum has proved difficult because of near-degenerate vibrational frequencies, Fermi resonance between the C-Cl stretching mode and the Cl-C-Cl bending mode, and large tunneling splittings due to the out-of-plane umbrella mode. Hence, the spectrum has never been fitted to an effective Hamiltonian. Our assignment approach replaces precise frequency information with intensity information, eliminating the need for double resonance spectroscopy or combination differences, neither of which have yielded a full assignment thus far. The dispersed fluorescence spectrum of each unknown vibration-tunneling state images its character onto known vibrational progressions in the ground state. By using this Franck-Condon fingerprint, we were able to determine the predominant character of several vibration-tunneling states and assign them; in other cases, the fingerprinting revealed that the states are strongly mixed and cannot be characterized with a simple normal mode assignment. The assigned transitions from vibration-tunneling wave functions that were not too strongly mixed could be fitted within measurement uncertainty by an effective vibration-tunneling Hamiltonian. A fit of all observed vibration-tunneling states will require a full resonance-tunneling Hamiltonian. PMID:23586664

Berrios, Eduardo; Sundaradevan, Praveen; Gruebele, Martin

2013-05-02

29

Franck-condon fingerprinting of vibration-tunneling spectra.  

UK PubMed Central (United Kingdom)

We introduce Franck-Condon fingerprinting as a method for assigning complex vibration-tunneling spectra. The B? state of thiophosgene (SCCl2) serves as our prototype. Despite several attempts, assignment of its excitation spectrum has proved difficult because of near-degenerate vibrational frequencies, Fermi resonance between the C-Cl stretching mode and the Cl-C-Cl bending mode, and large tunneling splittings due to the out-of-plane umbrella mode. Hence, the spectrum has never been fitted to an effective Hamiltonian. Our assignment approach replaces precise frequency information with intensity information, eliminating the need for double resonance spectroscopy or combination differences, neither of which have yielded a full assignment thus far. The dispersed fluorescence spectrum of each unknown vibration-tunneling state images its character onto known vibrational progressions in the ground state. By using this Franck-Condon fingerprint, we were able to determine the predominant character of several vibration-tunneling states and assign them; in other cases, the fingerprinting revealed that the states are strongly mixed and cannot be characterized with a simple normal mode assignment. The assigned transitions from vibration-tunneling wave functions that were not too strongly mixed could be fitted within measurement uncertainty by an effective vibration-tunneling Hamiltonian. A fit of all observed vibration-tunneling states will require a full resonance-tunneling Hamiltonian.

Berrios E; Sundaradevan P; Gruebele M

2013-08-01

30

Solid-state quantum computer based on scanning tunneling microscopy.  

UK PubMed Central (United Kingdom)

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

Berman GP; Brown GW; Hawley ME; Tsifrinovich VI

2001-08-01

31

Solid-State Quantum Computer Based on Scanning Tunneling Microscopy  

Energy Technology Data Exchange (ETDEWEB)

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

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

2001-08-27

32

Solid-State Quantum Computer Based on Scanning Tunneling Microscopy  

International Nuclear Information System (INIS)

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

2001-08-27

33

Three-terminal scanning tunneling spectroscopy of suspended carbon nanotubes  

CERN Document Server

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

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

2005-01-01

34

A scanning tunneling microscope for a dilution refrigerator  

Science.gov (United States)

We present the main features of a home-built scanning tunneling microscope that has been attached to the mixing chamber of a dilution refrigerator. It allows scanning tunneling microscopy and spectroscopy measurements down to the base temperature of the cryostat, T~30 mK, and in applied magnetic fields up to 13 T. The topography of both highly ordered pyrolytic graphite and the dichalcogenide superconductor NbSe2 has been imaged with atomic resolution down to T~50 mK as determined from a resistance thermometer adjacent to the sample. As a test for a successful operation in magnetic fields, the flux-line lattice of superconducting NbSe2 in low magnetic fields has been studied. The lattice constant of the Abrikosov lattice shows the expected field dependence ~1/B and measurements in the scanning tunneling spectroscopy mode clearly show the superconductive density of states with Andreev bound states in the vortex core.

Marz, M.; Goll, G.; Löhneysen, H. V.

2010-04-01

35

Scanning Tunneling Spectroscopy of Nanofeatures on Silver-Selenide Surface  

Science.gov (United States)

Scanning tunneling spectroscopy (STS) was performed to characterize nanofeatures on silver-selenide (Ag-Se) surface chemically modified by scanning tunneling microscopy (STM). Differential conductivity and gap-modulation images of the topologically modified surface show no structures, verifying no accumulation of Ag ions and chemically homogeneous surface. Moreover, current-voltage characteristics show that the Ag-Se surface is semiconductive. These characteristics change with the period of application of bias voltage, revealing the dynamical movement of Ag ions; lateral movement on the surface and migration into the matrix. These results suggest that these methods are powerful for chemically analyzing the fabricated nanofeatures.

Utsugi, Yasushi

1993-06-01

36

Electronic excitations and the tunneling spectra of metallic nanograins  

CERN Document Server

Tunneling-induced electronic excitations in a metallic nanograin are classified in terms of {em generations}: subspaces of excitations containing a specific number of electron-hole pairs. This yields a hierarchy of populated excited states of the nanograin that strongly depends on (a) the available electronic energy levels; and (b) the ratio between the electronic relaxation rate within the nano-grain and the bottleneck rate for tunneling transitions. To study the response of the electronic energy level structure of the nanograin to the excitations, and its signature in the tunneling spectrum, we propose a microscopic mean-field theory. Two main features emerge when considering an Al nanograin coated with Al oxide: (i) The electronic energy response fluctuates strongly in the presence of disorder, from level to level and excitation to excitation. Such fluctuations produce a dramatic sample dependence of the tunneling spectra. On the other hand, for excitations that are energetically accessible at low applied ...

Narvaez, G A; Kirczenow, George; Narvaez, Gustavo A.

2003-01-01

37

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

2012-10-31

38

Scanning tunneling microscopy of interface properties of Bi2Se3 on FeSe.  

UK PubMed Central (United Kingdom)

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.

Wang Y; Jiang Y; Chen M; Li Z; Song C; Wang L; He K; Chen X; Ma X; Xue QK

2012-11-01

39

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

International Nuclear Information System (INIS)

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

2006-08-04

40

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

Energy Technology Data Exchange (ETDEWEB)

Random telegraphic noise in scanning tunneling microscopy of dodecane thiol capped Au nanoparticles on highly oriented pyrolytic graphite surface has been investigated. The presence of nanoparticles gives rise to random switching of tunneling current between two discrete levels. The experimental power spectra of these current fluctuations show 1/f{sup 2} dependence. Analysis of the behavior of the power spectrum indicates that observed noise originates from Brownian motion of the trapped nanoparticle. Statistical analysis of the fluctuations shows exponential behaviour with time width {tau} {approx} 18 ms. The results suggest a method of producing an electrostatic trap analogus to laser tweezer.

Singh, Poonam; Dharmadhikari, C V [Centre for Advanced Studies in Materials Science and Solid State Physics, Department of Physics, University of Pune, Pune-411007 (India)

2007-04-15

 
 
 
 
41

Development of Scanning Tunneling Potentiometry for Semiconducting Samples  

Science.gov (United States)

We have developed a new setup of scanning tunneling potentiometry (STP) applicable to semiconducting samples, which cannot be studied by conventional STP since it measures the local electrostatic potential from a voltage that makes the tunneling current zero. In the new STP setup, the local potential below the tip and its spatial distribution are obtained by measuring the applied voltage that makes the tunneling current fixed at a nonzero value. Using a gold thin film sample we demonstrated the performance of the new STP setup and found that the local potential can be measured in the nonzero tunneling current mode with an energy sensitivity of ˜20 ?eV and nanometer-scale spatial resolution.

Hamada, Masayuki; Hasegawa, Yukio

2012-12-01

42

Commendable surface physics by means of scanning tunneling microscopy  

International Nuclear Information System (INIS)

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

1995-01-01

43

Scanning tunneling spectroscopy of suspended single-wall carbon nanotubes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have performed low-temperature scanning tunneling microscopy measurements on single-wall carbon nanotubes that are freely suspended over a trench. The nanotubes were grown by chemical vapor deposition on a Pt substrate with predefined trenches etched into it. Atomic resolution was obtained on the...

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

44

Spectroscopic Scanning Tunneling Microscopy Insights into Fe-based Superconductors  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In the first three years since the discovery of Fe-based high Tc superconductors, scanning tunneling microscopy (STM) and spectroscopy have shed light on three important questions. First, STM has demonstrated the complexity of the pairing symmetry in Fe-based materials. Phase-sensitive quasiparticle...

Hoffman, Jenny Eve

45

Mechanism of nanoparticle manipulation by scanning tunnelling microscopy  

Energy Technology Data Exchange (ETDEWEB)

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.

Grobelny, J [National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States); Tsai, D-H [National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States); Kim, D-I [National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States); Pradeep, N [National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States); Cook, R F [National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States); Zachariah, M R [National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States)

2006-11-14

46

Electron-beam-assisted Scanning Tunneling Microscopy Of Insulating Surfaces  

CERN Multimedia

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

47

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

CERN Multimedia

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

48

Coulomb blockade effect of molecularly suspended graphene nanoribbons investigated with scanning tunneling microscopy  

Science.gov (United States)

We present the study of the quantum tunneling through a vertical two-barrier structure sandwiching a graphene nanoribbon quantum object. Scanning tunneling microscopy measurements of the graphene nanoribbon show staircase I-U characteristics and oscillating dI/dU spectra. To identify the physical origin of the observed effect, we varied the tunneling resistance of the tip-ribbon junction and found a tip-to-ribbon distance dependent oscillating period change. Together with the numerical analysis, we confirm that the resonances in the spectroscopy arise from the Coulomb blockade effect. The study of the Coulomb blockade effect in graphene nanoribbons may be of potential usages for the fabrication of superthin quantum dot devices.

Zhong, Z. F.; Shen, H. L.; Cao, R. X.; Sun, L.; Li, K. P.; Hu, J.; Liu, Z.; Wu, D.; Wang, X. R.; Ding, H. F.

2013-09-01

49

Apparent diameter of carbon nanotubes in scanning tunnelling microscopy measurements  

Energy Technology Data Exchange (ETDEWEB)

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

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

2006-07-05

50

Apparent diameter of carbon nanotubes in scanning tunnelling microscopy measurements  

International Nuclear Information System (INIS)

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

2006-07-05

51

Scanning tunneling microscopy on Ga/Si(100)  

Science.gov (United States)

The Ga/Si(100) surface is investigated using scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and low-energy electron diffraction. Two distinct peaks are observed on the 2×2 Ga phase using STS, which are associated with one Ga unoccupied state and two Ga-Si occupied states, respectively. The latter peak is assigned to surface state bands observed using angle-resolved photoelectron spectroscopy [Surf. Sci. 242, 277 (1991)]. Regular arrays of Ga clusters are observed in STM images for the 8×1-Ga phase. The spacing between Ga cluster arrays is constant, whereas the spacing between the clusters along an array fluctuates. Adjacent arrays are out of phase in the direction perpendicular to the arrays. Steps are severely deformed by the formation of the 8×1-Ga phase. The initial stage and second-layer growths of the 8×1-Ga phase are observed. Ga clusters disrupt the 2×2-Ga phase.

Sakama, H.; Kawazu, A.; Sueyoshi, T.; Sato, T.; Iwatsuki, M.

1996-09-01

52

Scanning tunneling microscopy and potentiometry on a semiconductor heterojunction  

Energy Technology Data Exchange (ETDEWEB)

The potential distribution across the cleaved end face of a forward-biased GaAs double heterojunction laser diode was mapped using scanning tunneling potentiometry. Space-charge regions next to the heterojunction interface as well as the electron-hole recombination region within the active layer are outlined with nanometer resolution. The carrier injection zone in the active layer is observed as a function of junction voltage.

Muralt, P.; Meier, H.; Pohl, D.W.; Salemink, H.W.M.

1987-05-11

53

Evaporation of silicon nanoparticles under scanning tunneling microscope control  

Science.gov (United States)

A kinetic model is developed to describe the heating and evaporation of a spherical nanoparticle under the influence of a scanning tunneling microscope (STM). Simulations were performed for silicon nanoparticles of different sizes and for different STM parameters. Different kinetic features of evaporation are predicted and discussed. The lifetime of the nanoparticles is estimated and compared with original experimental data obtained for layers of silicon nanoparticles formed upon magnetron sputtering and deposited on a highly oriented pyrolytic graphite surface (HOPG).

Hager, Michaela; Berezin, Alexander S.; Zinkicheva, Tamara T.; Bohme, Diethard K.; Probst, Michael; Scheier, Paul; Nazmutdinov, Renat R.

2013-11-01

54

Migration of Metals on Graphite in Scanning Tunneling Microscopy  

Science.gov (United States)

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

Ohto, Masanori; Yamaguchi, Satoru; Tanaka, Keiji

1995-06-01

55

Rattling modes and the intrinsic vibrational spectrum of beetle-type scanning tunneling microscopes.  

UK PubMed Central (United Kingdom)

It is known that the vibrational spectra of beetle-type scanning tunneling microscopes with a total mass of approximately 3-4 g contain extrinsic 'rattling' modes in the frequency range extending from 500 to 1700 Hz that interfere with image acquisition. These modes lie below the lowest calculated eigenfrequency of the beetle and it has been suggested that they arise from the inertial sliding of the beetle between surface asperities on the raceway. In this paper we describe some cross-coupling measurements that were performed on three home-built beetle-type STMs of two different designs. We provide evidence that suggests that for beetles with total masses of 12-15 g all the modes in the rattling range are intrinsic. This provides additional support for the notion that the vibrational properties of beetle-type scanning tunneling microscopes can be improved by increasing the contact pressure between the feet of the beetle and the raceway.

Miwa JA; MacLeod JM; Moffat A; McLean AB

2003-12-01

56

Rattling modes and the intrinsic vibrational spectrum of beetle-type scanning tunneling microscopes.  

Science.gov (United States)

It is known that the vibrational spectra of beetle-type scanning tunneling microscopes with a total mass of approximately 3-4 g contain extrinsic 'rattling' modes in the frequency range extending from 500 to 1700 Hz that interfere with image acquisition. These modes lie below the lowest calculated eigenfrequency of the beetle and it has been suggested that they arise from the inertial sliding of the beetle between surface asperities on the raceway. In this paper we describe some cross-coupling measurements that were performed on three home-built beetle-type STMs of two different designs. We provide evidence that suggests that for beetles with total masses of 12-15 g all the modes in the rattling range are intrinsic. This provides additional support for the notion that the vibrational properties of beetle-type scanning tunneling microscopes can be improved by increasing the contact pressure between the feet of the beetle and the raceway. PMID:14609641

Miwa, J A; MacLeod, J M; Moffat, Antje; McLean, A B

2003-12-01

57

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

58

A scanning tunneling microscope for a dilution refrigerator.  

UK PubMed Central (United Kingdom)

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

Marz M; Goll G; Löhneysen Hv

2010-04-01

59

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; Tomaso Zambelli; Stephane Martin; Sebastien Gauthier

2001-01-01

60

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

Science.gov (United States)

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

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

2013-08-08

 
 
 
 
61

Apparent Barrier Height in Scanning Tunneling Microscopy Revisited  

DEFF Research Database (Denmark)

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

Olesen, L.; Brandbyge, Mads

1996-01-01

62

Tomography of molecular nanographene double layers using scanning tunneling microscopy  

Science.gov (United States)

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

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

2009-12-01

63

Safe fabrication of sharp gold tips for light emission in scanning tunnelling microscopy  

International Nuclear Information System (INIS)

Gold is the optimal tip metal for light emission in scanning tunnelling microscopy (LESTM) under ambient conditions. Sharp Au-tips of ?10 nm radius were produced reliably using a safe, two-step etching method in 20% (w/w) CaCl2 solution. Previous CaCl2-based methods have tended to produce blunter tips, while other etching techniques that do produce sharp Au-tips, do so with the use of toxic or hazardous electrolytes. The tips are characterised using scanning electron microscopy and their efficacy in LESTM is evidenced by high-resolution, simultaneous topographic and photon mapping of Au(1 1 1)- and polycrystalline Au-surfaces. Spectra of the optical emission exhibit only one or two peaks with etched tips in contrast to the more complex spectra typical of cut tips; this feature, together with the highly symmetric geometry of the tips, facilitates a definitive analysis of the light emission process.

2008-01-01

64

Scanning-tunneling-microscopy study of Pb on Si(111)  

Energy Technology Data Exchange (ETDEWEB)

Scanning-tunneling microscopy has been used to study temperature and coverage dependence of the structure of lead on the Si(111)-7{times}7 surface. For low Pb coverage, the Pb atoms favored the faulted sites. The ratio between the number of Pb atoms on faulted to unfaulted sites increased after sample annealing. An energy difference of 0.05 eV associated with a Pb atom on these two sites is estimated. The mobility of Pb atoms on Si(111) was observed at a temperature as low as 260 {degree}C for a coverage of 0.1 and 1 ML.

Tang, D.; Elsayed-Ali, H.E. [Physical Electronics Research Institute, Department of Electrical Computer Engineering, Old Dominion University, Norfolk, Virginia 23529 (United States); Wendelken, J.; Xu, J. [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

1995-07-15

65

Images of demineralized coal surfaces by scanning tunnelling microscopy  

Energy Technology Data Exchange (ETDEWEB)

Turkish Zonguldak bituminous coal was demineralized with HCl and HF. Mineral removal was followed by classical chemical analysis and FT-i.r. spectroscopy to determine the types of inorganics dissolved. Scanning tunnelling microscopy (STM) images of the surfaces of original and acid-treated Zonguldak coal were compared with those of an original semianthracite and a highly oriented pyrolytic graphite. It was concluded that STM has great potential for the investigation of the structural changes occurring on coal surfaces due to different treatments. 10 refs., 2 figs., 2 tabs.

Zareie, H.; Oztas, N.; Gundogan, M.; Piskin, E.; Yurum, Y. [Hacettepe University, Ankara (Turkey). Bioengineering Division

1996-05-01

66

Calibration of scanning tunneling microscope transducers using optical beam deflection  

Energy Technology Data Exchange (ETDEWEB)

An accurate, sensitive, easily implemented method of calibration of the elastic displacement of piezoelectric transducers used in scanning tunneling microscopes has been developed. The axial displacement for both static and harmonic excitation has been measured using laser beam deflection amplified by an optical magnification system. For harmonic excitation where lock-in amplifier detection can be utilized, displacements as small as 0.03 A have been measured. Measurements on PZT-5H and PZT-8 transducers over a range of five orders of magnitude in applied voltage demonstrate the power of the method in calibration of displacements from the subangstrom to the nonlinear region with an uncertainty of about 4%.

Wetsel, G. C., Jr.; McBride, S. E.; Warmack, R. J.; Van de Sande, B.

1989-08-07

67

In situ scanning tunneling microscopy of copper deposition with benzotriazole  

International Nuclear Information System (INIS)

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

1991-01-01

68

In situ scanning tunneling microscopy of copper deposition with benzotriazole  

Energy Technology Data Exchange (ETDEWEB)

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

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

1991-08-01

69

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

70

Scanning electron and tunneling microscopy of palladium-barium emitters  

International Nuclear Information System (INIS)

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

2003-06-15

71

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

72

Nanoscale characterization of redox and acid properties of keggin-type heteropolyacids by scanning tunneling microscopy and tunneling spectroscopy: effect of heteroatom substitution.  

Science.gov (United States)

Nanoscale characterization of acid and redox properties of Keggin-type heteropolyacids (HPAs) with different heteroatoms, H(n)MW(12)O(40) (M = P, Si, B, Co), was carried out by scanning tunneling microscopy (STM) and tunneling spectroscopy (TS) in this study. HPA samples were deposited on highly oriented pyrolytic graphite surfaces to obtain images and tunneling spectra by STM before and after pyridine adsorption. All HPA samples formed well-ordered 2-dimensional arrays on graphite before and after pyridine exposure. NDR (negative differential resistance) peaks were observed in the tunneling spectra. Those measured for fresh HPA samples appeared at less negative voltages with increasing reduction potential of the HPAs and with increases in the electronegativity of the heteroatom, but with decreases in the overall negative charge of the heteropolyanions. These results support the conclusion that more reducible HPA samples show NDR behavior at less negative applied voltages in their tunneling spectra. Introduction of pyridine into the HPA arrays increased the lattice constants of the 2-dimensional HPA arrays by ca. 6 A. Exposure to pyridine also shifted NDR peak voltages of H(n)MW(12)O(40) (M = P, Si, B, Co) samples to less negative values in the TS measurements. The NDR shifts of HPAs obtained before and after pyridine adsorption were correlated with the acid strengths of the HPAs, suggesting that tunneling spectra measured by STM could serve to probe acid properties of HPAs. These results show how one can relate the bulk acid and redox properties of HPAs to surface properties of nanostructured HPA monolayers determined by STM. PMID:11874367

Song, In K; Shnitser, Russell B; Cowan, Jennifer J; Hill, Craig L; Barteau, Mark A

2002-03-11

73

Nanoscale characterization of redox and acid properties of keggin-type heteropolyacids by scanning tunneling microscopy and tunneling spectroscopy: effect of heteroatom substitution.  

UK PubMed Central (United Kingdom)

Nanoscale characterization of acid and redox properties of Keggin-type heteropolyacids (HPAs) with different heteroatoms, H(n)MW(12)O(40) (M = P, Si, B, Co), was carried out by scanning tunneling microscopy (STM) and tunneling spectroscopy (TS) in this study. HPA samples were deposited on highly oriented pyrolytic graphite surfaces to obtain images and tunneling spectra by STM before and after pyridine adsorption. All HPA samples formed well-ordered 2-dimensional arrays on graphite before and after pyridine exposure. NDR (negative differential resistance) peaks were observed in the tunneling spectra. Those measured for fresh HPA samples appeared at less negative voltages with increasing reduction potential of the HPAs and with increases in the electronegativity of the heteroatom, but with decreases in the overall negative charge of the heteropolyanions. These results support the conclusion that more reducible HPA samples show NDR behavior at less negative applied voltages in their tunneling spectra. Introduction of pyridine into the HPA arrays increased the lattice constants of the 2-dimensional HPA arrays by ca. 6 A. Exposure to pyridine also shifted NDR peak voltages of H(n)MW(12)O(40) (M = P, Si, B, Co) samples to less negative values in the TS measurements. The NDR shifts of HPAs obtained before and after pyridine adsorption were correlated with the acid strengths of the HPAs, suggesting that tunneling spectra measured by STM could serve to probe acid properties of HPAs. These results show how one can relate the bulk acid and redox properties of HPAs to surface properties of nanostructured HPA monolayers determined by STM.

Song IK; Shnitser RB; Cowan JJ; Hill CL; Barteau MA

2002-03-01

74

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

International Nuclear Information System (INIS)

Scanning tunneling microscopy can be used to isolate single particles on surfaces for further study. Local optical and electronic properties coupled with topographic information collected by the scanning tunneling microscope (STM) give insight into the intrinsic properties of the species under study. Since each spectroscopic measurement is done on a single particle, each sample is 'monodisperse', regardless of the degree of heterogeneity of the original preparation. We illustrate this with three example systems - a metal cluster of known atomic structure, metal nanoparticles dispersed from colloid suspensions, and metallocarbohedrenes (Met-Cars) deposited with other reaction products. Au and Ag nanoparticles were imaged using a photon emission STM. The threshold voltage, the lowest bias voltage at which photons are produced, was determined for Au nanoparticles. Electronic spectra of small clusters of Ni atoms on MoS2 were recorded. Preliminary images of Zr-based Met-Car-containing soot were obtained on Au and MoS2 substrates and partial electronic spectra were recorded of these possible Met-Car particles

1999-01-01

75

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

76

Design of a high-speed electrochemical scanning tunneling microscope.  

UK PubMed Central (United Kingdom)

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

Yanson YI; Schenkel F; Rost MJ

2013-02-01

77

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

CERN Multimedia

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

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

1995-01-01

78

Scanning Tunneling Spectroscopy of Graphene on Hexagonal Boron Nitride  

Science.gov (United States)

Recent work has found hexagonal boron nitride (hBN) to be a good substrate for graphene devices due to its ability to screen charged impurities in the underlying substrate and increase graphene mobility. We investigated graphene on hBN heterostructures using scanning tunneling microscopy and spectroscopy. Because hBN has the same bond structure as graphene with a slightly longer lattice constant, a rotationally dependent Moir'e pattern is formed in graphene on hBN heterostructures. The Moir'e pattern creates a weak periodic potential for the charge carriers in graphene. We performed an experimental and theoretical investigation of its effect on the local density of states. We observed a Moir'e wavelength dependent modification of the local density of states in good agreement with theory predictions.

Yankowitz, Matthew; Xue, Jiamin; Cormode, Daniel; Sanchez-Yamagishi, Javier; Jarillo-Herrero, Pablo; Watanabe, K.; Taniguchi, T.; Jacquod, Philippe; Leroy, Brian

2012-02-01

79

Visualization of semiconductor surface etching with scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

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

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

1998-06-01

80

Ni nanocrystals on HOPG(0001): A scanning tunnelling microscope study.  

UK PubMed Central (United Kingdom)

The growth mode of small Ni clusters evaporated in UHV on HOPG has been investigated by scanning tunnelling microscopy. The size, the size distribution, and the shape of the clusters have been evaluated for different evaporation conditions and annealing temperatures. The total coverage of the surface strongly depends on the evaporation rate and time, whereas the influence of these parameters is low on the cluster size. Subsequent stepwise annealing has been performed. This results in a reduction of the total amount of the Ni clusters accompanied by a decreasing in the overall coverage of the surface. The diameter of the clusters appears to be less influenced by the annealing than is their height. Besides this, the cluster shape is strongly influenced, changing to a quasi-hexagonal geometry after the first annealing step, indicating single-crystal formation. Finally, a reproducible methodology for picking up individual clusters is reported [1].

Marz M; Sagisaka K; Fujita D

2013-01-01

 
 
 
 
81

Ni nanocrystals on HOPG(0001): A scanning tunnelling microscope study.  

Science.gov (United States)

The growth mode of small Ni clusters evaporated in UHV on HOPG has been investigated by scanning tunnelling microscopy. The size, the size distribution, and the shape of the clusters have been evaluated for different evaporation conditions and annealing temperatures. The total coverage of the surface strongly depends on the evaporation rate and time, whereas the influence of these parameters is low on the cluster size. Subsequent stepwise annealing has been performed. This results in a reduction of the total amount of the Ni clusters accompanied by a decreasing in the overall coverage of the surface. The diameter of the clusters appears to be less influenced by the annealing than is their height. Besides this, the cluster shape is strongly influenced, changing to a quasi-hexagonal geometry after the first annealing step, indicating single-crystal formation. Finally, a reproducible methodology for picking up individual clusters is reported [1]. PMID:23844347

Marz, Michael; Sagisaka, Keisuke; Fujita, Daisuke

2013-06-28

82

Scanning tunneling microscope with two-dimensional translator.  

UK PubMed Central (United Kingdom)

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

Nichols J; Ng KW

2011-01-01

83

Scanning tunneling microscope with two-dimensional translator.  

Science.gov (United States)

Since the invention of the scanning tunneling microscope (STM), it has been a powerful tool for probing the electronic properties of materials. Typically STM designs capable of obtaining resolution on the atomic scale are limited to a small area which can be probed. We have built an STM capable of coarse motion in two dimensions, the z- and x-directions which are, respectively, parallel and perpendicular to the tip. This allows us to image samples with very high resolution at sites separated by macroscopic distances. This device is a single unit with a compact design making it very stable. It can operate in either a horizontal or vertical configuration and at cryogenic temperatures. PMID:21280836

Nichols, J; Ng, K-W

2011-01-01

84

High-resolution scanning tunneling microscopy for molecules  

Energy Technology Data Exchange (ETDEWEB)

Scanning tunneling microscopy (STM) can detect individual molecular configuration with its high spatial resolution ability, but some intrinsical and extrinsic factors result in the complexities of STM imaging of single molecules. By combining STM experimental work and theoretical simulation with the local density approximation based on Bardeen perturbation method, we have explored the atomic-scale configuration of the following molecular systems: C{sub 60} molecules adsorbed on Si(1 1 1)-(7x7); alkanethiol self-assembly monolayers on Au(1 1 1); C{sub 60} molecule imaged by STM tip adsorbed with another C{sub 60} molecule; O{sub 2} molecule adsorbed on Ag(1 1 0) and CO molecule adsorbed on Cu(1 1 1) imaged by CO chemically modified STM tip. Some related problems including: molecule-substrate interactions, STM imaging mechanism, chemically modified STM tip, etc., are discussed.

Li Bin; Wang Haiqian; Yang Jinlong; Hou, J.G

2004-01-15

85

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

86

Profiling of cross-sectional a-Si:H solar cells using a scanning tunneling microscope  

International Nuclear Information System (INIS)

A scanning tunneling microscope in ultrahigh vacuum is used to measure the profile of electronic properties of cleaved amorphous silicon solar cells. Their exposed layers in a single and a tandem cell can be identified by their characteristic current-voltage dependencies (scanning tunneling spectroscopy). An 'Apparent Potential' is measured throughout the cells. The results for the tandem cell from SOLAREX, Inc. are shown.

1999-03-05

87

Optical characterication of probes for photon scanning tunnelling microscopy  

DEFF Research Database (Denmark)

The photon scanning tunnelling microscope is a well-established member of the family of scanning near-field optical microscopes used for optical imaging at the sub-wavelength scale. The quality of the probes, typically pointed uncoated optical fibres, used is however difficult to evaluate in a direct manner and has most often been inferred from the apparent quality of recorded optical images. Complicated near-field optical imaging characteristics, together with the possibility of topographically induced artefacts, however, has increased demands for a more reliable probe characterization technique. Here we present experimental results obtained for optical characterization of two different probes by imaging of a well-specified near-field intensity distribution at various spatial frequencies. In particular, we observe that a sharply pointed dielectric probe can be highly suitable for imaging when using p-polarized light for the illumination. We conclude that the proposed scheme can be used directly for probe characterization and, subsequently, for determination of an optical transfer function, which could allow one to deduce from an experimentally obtained image of a weakly scattering sample the field distribution existing near the sample surface inthe absence of the probe.

Vohnsen, Brian; Bozhevolnyi, Sergey I.

1999-01-01

88

Assigning Complex Vibration-Tunneling Spectra Using Franck-Condon Fingerprints  

Science.gov (United States)

We propose Franck-Condon fingerprinting as a method to assign complex vibration-tunneling spectra. The ˜{B} electronic excited state of Thiophosgene (SCCl_{2}) is our prototype case. Assignment of its spectrum has proven to be difficult because large tunneling splittings and near-degenerate vibrational frequencies. The dispersed fluorescence spectrum of each unkown vibration-tunneling state reveals its wavefunction character onto the known SCCl_{2} vibrational progressions in the ground states. This Franck-Condon fingerprint allows us to assign several vibration-tunneling states of SCCl_{2} in the ˜{B} electronic excited state. These assigned transitions could be fitted by an effective vibration-tunneling Hamiltonian within measurement uncertainty.

Berrios, Eduardo; Sundaradevan, Praveen; Gruebele, Martin

2013-06-01

89

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

Science.gov (United States)

We propose new simple and generalized multiple-gap models of quasiparticle tunneling across the high-Tc cuprate superconductor (HTSC)/insulator/normal metal (SIN) junction based on the two different mechanisms for tunneling at positive and negative bias voltages, and the gap inhomogeneity (i.e., multiple-gap) picture. The tunneling of electrons from the normal metal into the quasiparticle states in HTSC with the BCS-type density of states (DOSs) takes place at V>0, while the tunneling of Cooper pairs and large polarons from the HTSC with the BCS DOS and quasi-free state DOS (which appears only in the dissociation of polarons) into the normal metal occurs at V<0. We show that most of the unusual features of tunneling spectra such as nearly U- and V-shaped subgap features, peak-dip-hump structure (appearing systematically at V<0) and asymmetry of the conductance peaks and their temperature and doping dependences, and shoulder-like features inside the main conductance peaks arise naturally in our specific models of SIN tunneling. The experimental tunneling spectra of Bi2Sr2CaCu2O are adequately reproduced by using the specific multiple-gap models and taking into account the distribution of BCS and polaronic gap values.

Dzhumanov, S.; Ganiev, O. K.; Djumanov, Sh. S.

2013-10-01

90

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

91

Local potentiometry using a multiprobe scanning tunneling microscope.  

Science.gov (United States)

Scanning tunneling potentiometry (STP) is a powerful tool to analyze the conductance through thin conducting layers with lateral resolution in the nanometer range. In this work, we show how a commercial ultrahigh vacuum multiprobe system, equipped with four independent tips, can be used to perform STP experiments. Two tips are gently pushed into the surface applying a lateral current through the layer of interest. Simultaneously, the topography and the potential distribution across the metal film are measured with a third tip. The signal-to-noise ratio of the potentiometry signal may be enhanced by using a fourth tip, providing a reference potential in close vicinity of the studied area. Two different examples are presented. For epitaxial (111) oriented Bi films, grown on a Si(100)-(2 x 1) surface, an almost constant gradient of the potential as well as potential drops at individual Bi-domain boundaries were observed. On the surface of the Si(111)(3 x 3)-Ag superstructure the potential variation at individual monoatomic steps could be precisely resolved. PMID:19044354

Bannani, A; Bobisch, C A; Möller, R

2008-08-01

92

A fully automated, 'thimble-size' scanning tunnelling microscope.  

UK PubMed Central (United Kingdom)

A novel, fully automated high-stability, high-eigenfrequency scanning tunnelling microscope (STM) has been developed. Its key design feature is the application of two piezoelectric ceramic tubes, one for the x-y-z motion of the tip and one for a linear motor ('nano-worm') used for the coarse positioning of the tip relative to the specimen. By means of the nano-worm, the tip can be advanced in steps between 16 and 0.2 nm. The walking distance is greater than 2 mm, with a maximum speed of 2000 steps/s. The nano-worm positioning implies that this STM is fully controlled by electronic means, and that no mechanical coupling is needed, which makes operation of the STM extremely convenient. The axial-symmetry construction is rigid, small and temperature-compensated, yielding reduced sensitivity to mechanical and acoustic vibrations and temperature variations. The sample is simply placed on a piece of invar which surrounds the scanner tube and the nano-worm and is held by gravity alone. This allows for easy sample mounting. The performance of the microscope has been tested in air by imaging a variety of surfaces, including graphite and biological samples.

Laegsgaard E; Besenbacher F; Mortensen K; Stensgaard I

1988-12-01

93

An ultrahigh vacuum fast-scanning and variable temperature scanning tunneling microscope for large scale imaging.  

UK PubMed Central (United Kingdom)

We describe the design and performance of a fast-scanning, variable temperature scanning tunneling microscope (STM) operating from 80 to 700 K in ultrahigh vacuum (UHV), which routinely achieves large scale atomically resolved imaging of compact metallic surfaces. An efficient in-vacuum vibration isolation and cryogenic system allows for no external vibration isolation of the UHV chamber. The design of the sample holder and STM head permits imaging of the same nanometer-size area of the sample before and after sample preparation outside the STM base. Refractory metal samples are frequently annealed up to 2000 K and their cooldown time from room temperature to 80 K is 15 min. The vertical resolution of the instrument was found to be about 2 pm at room temperature. The coarse motor design allows both translation and rotation of the scanner tube. The total scanning area is about 8 x 8 microm(2). The sample temperature can be adjusted by a few tens of degrees while scanning over the same sample area.

Diaconescu B; Nenchev G; de la Figuera J; Pohl K

2007-10-01

94

An ultrahigh vacuum fast-scanning and variable temperature scanning tunneling microscope for large scale imaging.  

Science.gov (United States)

We describe the design and performance of a fast-scanning, variable temperature scanning tunneling microscope (STM) operating from 80 to 700 K in ultrahigh vacuum (UHV), which routinely achieves large scale atomically resolved imaging of compact metallic surfaces. An efficient in-vacuum vibration isolation and cryogenic system allows for no external vibration isolation of the UHV chamber. The design of the sample holder and STM head permits imaging of the same nanometer-size area of the sample before and after sample preparation outside the STM base. Refractory metal samples are frequently annealed up to 2000 K and their cooldown time from room temperature to 80 K is 15 min. The vertical resolution of the instrument was found to be about 2 pm at room temperature. The coarse motor design allows both translation and rotation of the scanner tube. The total scanning area is about 8 x 8 microm(2). The sample temperature can be adjusted by a few tens of degrees while scanning over the same sample area. PMID:17979422

Diaconescu, Bogdan; Nenchev, Georgi; de la Figuera, Juan; Pohl, Karsten

2007-10-01

95

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.

2005-02-15

96

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

Energy Technology Data Exchange (ETDEWEB)

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 T{sub c} = 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.

Kohen, A. [Groupe de Physique des Solides, UMR7588 au CNRS, Univ. Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France)]. E-mail: kohen@gps.jussieu.fr; Noat, Y. [Groupe de Physique des Solides, UMR7588 au CNRS, Univ. Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France); Proslier, T. [Groupe de Physique des Solides, UMR7588 au CNRS, Univ. Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France); Lacaze, E. [Groupe de Physique des Solides, UMR7588 au CNRS, Univ. Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France); Aprili, M. [Laboratoire de Spectroscopie en Lumiere Polarisee-CNRS ESPCI 10, rue Vauquelin 75005 Paris (France); Sacks, W. [Groupe de Physique des Solides, UMR7588 au CNRS, Univ. Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France); Roditchev, D. [Groupe de Physique des Solides, UMR7588 au CNRS, Univ. Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France)

2005-02-15

97

Fine structure in the tunneling spectra of electron-doped cuprates: no coupling to the magnetic resonance mode.  

UK PubMed Central (United Kingdom)

We reanalyze high-resolution scanning tunneling spectra of the electron-doped cuprate Pr(0.88)LaCe(0.12)CuO(4) (T(c) = 24 K). We find that the spectral fine structure below 35 meV is consistent with strong coupling to a bosonic mode at about 16 meV, in quantitative agreement with early tunneling spectra of Nd(1.85)Ce(0.15)CuO(4). Since the energy of the bosonic mode is significantly higher than that (9.5-11 meV) of the magnetic resonancelike mode observed by inelastic neutron scattering, the coupling feature at about 16 meV cannot arise from strong coupling to the magnetic mode. The present work thus demonstrates that the magnetic resonancelike mode cannot be the origin of high-temperature superconductivity in electron-doped cuprates.

Zhao GM

2009-12-01

98

Fine structure in the tunneling spectra of electron-doped cuprates: no coupling to the magnetic resonance mode.  

Science.gov (United States)

We reanalyze high-resolution scanning tunneling spectra of the electron-doped cuprate Pr(0.88)LaCe(0.12)CuO(4) (T(c) = 24 K). We find that the spectral fine structure below 35 meV is consistent with strong coupling to a bosonic mode at about 16 meV, in quantitative agreement with early tunneling spectra of Nd(1.85)Ce(0.15)CuO(4). Since the energy of the bosonic mode is significantly higher than that (9.5-11 meV) of the magnetic resonancelike mode observed by inelastic neutron scattering, the coupling feature at about 16 meV cannot arise from strong coupling to the magnetic mode. The present work thus demonstrates that the magnetic resonancelike mode cannot be the origin of high-temperature superconductivity in electron-doped cuprates. PMID:20366161

Zhao, Guo-meng

2009-12-04

99

Nonequilibrium theory of scanning tunneling spectroscopy via adsorbate resonances nonmagnetic and Kondo impurities  

CERN Multimedia

We report on a fully nonequilibrium theory of the scanning tunneling microscopy (STM) through resonances induced by impurity atoms adsorbed on metal surfaces. The theory takes into account the effect of the tunneling current and finite bias on the system and is valid for arbitrary intra-adsorbate electron correlation strength. It is thus applicable to the recent STM experiments on Kondo impurities.

Plihal, M

2001-01-01

100

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

International Nuclear Information System (INIS)

[en] 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

1986-01-01

 
 
 
 
101

Origin of the checkerboard pattern in scanning tunneling microscopy maps of underdoped cuprate superconductors  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The checkerboard pattern in the differential conductance maps on underdoped cuprates appears when the scanning tunneling microscopy is placed above the O sites in the outermost CuO2 plane. In this position the interference between tunneling paths through the apical ions above the neighboring Cu site...

Yang, KY; Chen, WQ; Rice, TM; Zhang, FC

102

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.

Yeh N.-C.; Teague M. L.; Wu R. T.-P.; Chu H.; Boyd D. A.; Bockrath M. W.; He L.; Xiu F.-X.; wang K.-L.

2012-01-01

103

ScanningTunneling Luminescence of Grain Boundaries in Cu(In,Ga)Se2  

Energy Technology Data Exchange (ETDEWEB)

At the Laboratory, photon emission in semiconductors has been mapped in the nanoscale using scanning tunneling microscopy (STM). In this Solar Program Review Meeting, we report on the latest results obtained in Cu(In,Ga)Se2 (CIGS) thin films by this adapted STM. Scanning tunneling luminescence (STL) spectroscopy suggests that photons are emitted near the surface of CIGS. STL is excited either by (1) diffusion of tunneling electrons and subsequent recombination with available holes in CIGS or (2) impact ionization by hot electrons. Which process becomes predominant depends on the voltage applied to the STM tip. Photon mapping shows electronically active, extended defects near the surface of CIGS thin films.

Romero, M. J.; Jiang, C.-S.; Al-Jassim, M. M.; Noufi, R.

2005-01-01

104

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

CERN Multimedia

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

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

2005-01-01

105

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

UK PubMed Central (United Kingdom)

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.

Li SS; Northrop BH; Yuan QH; Wan LJ; Stang PJ

2009-02-01

106

Quantitative Analysis of Scanning Tunneling Microscopy Images of Mixed Ligand Functionalized Nanoparticles.  

UK PubMed Central (United Kingdom)

Ligand-protected gold nanoparticles exhibit large local curvatures, features rapidly varying over small scales, and chemical heterogeneity. Their imaging by Scanning Tunneling Microscopy (STM) can, in principle, provide direct information on the architecture of their ligand shell, yet STM images require laborious analysis and are challenging to be interpreted. Here, we report a straightforward, robust and rigorous method for the quantitative analysis of the multiscale features contained in STM images of samples consisting of functionalized Au nanoparticles deposited onto Au/mica. The method relies on the analysis of the topographical power spectral density (PSD), and allows us to extract the characteristic length scales of the features exhibited by nanoparticles in STM images. For the mixed-ligand protected Au nanoparticles analyzed here the characteristic length scale is 1.2±0.1 nm, whereas for the homoligand Au NPs this scale is 0.75±0.05 nm. These length scales represent spatial correlations independent of scanning parameters, and hence the features in the PSD can be ascribed to a fingerprint of the STM contrast of ligand-protected nanoparticles. PSD spectra from images recorded at different laboratories using different microscopes and operators can be overlapped across most of the frequency range, proving that the features in the STM images of nanoparticles can be compared and reproduced.

Biscarini F; Ong QK; Albonetti C; Liscio F; Longobardi M; Mali KS; Ciesielski A; Reguera J; Renner C; De Feyter S; Samori P; Stellacci F

2013-10-01

107

CT-scanning study of cross-sectional area of the carpal tunnel in cases of carpal tunnel syndrome  

International Nuclear Information System (INIS)

[en] The cross-sectional area, transverse and anteroposterior diameter of the carpal tunnel were investigated by CT scanning in 68 cases of carpal tunnel syndrome (CTS) and in 100 normal controls of both sexes. The cross-sectional areas of the carpal tunnel in idiopathic CTS of both sexes were significantly smaller, whereas those in secondary CTS were larger than in normal controls. In female wrists with idiopathic CTS narrowing of distal carpal tunnel was attributed to short transverse diameter in wrists with normally shaped hook of the hamate, or to decreased anteroposterior diameter in wrists with abnormally short hook of the hamate. The smallest cross-sectional area in both types of CTS and in normal controls is located at the proximal border of distal carpal tunnel (D 1 level). This coincides with the thickest portion of the flexor retinaculum and, together with our operative findings, supports the conclusion that the essential compression on the median nerve takes place at the D 1 level in idiopathic CTS. (author)

1987-01-01

108

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

109

Conduction States with Vanishing Dimerization in Pt Nanowires on Ge(001) Observed with Scanning Tunneling Microscopy  

CERN Document Server

The low-energy electronic properties of one-dimensional nanowires formed by Pt atoms on Ge(001) are studied with scanning tunneling microscopy down to the millivolt-regime. The chain structure exhibits various dimerized elements at high tunneling bias, indicative of a substrate bonding origin rather than a charge density wave. Unexpectedly, this dimerization becomes vanishingly small when imaging energy windows close to the Fermi level with adequately low tunneling currents. Evenly spaced nanowire atoms emerge which are found to represent conduction states. Implications for the metallicity of the chains are discussed.

Schaefer, J; Preisinger, M; Claessen, R

2006-01-01

110

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 are useful to further stimulate relevant experimental studies on the system. (paper)

2013-01-01

111

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

112

Dopant enhanced etching of TiSe2 by scanning tunneling microscopy.  

UK PubMed Central (United Kingdom)

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.

Kidd TE; Gamb BI; Skirtachenko PI; Strauss LH

2010-07-01

113

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

114

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

115

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

116

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

Science.gov (United States)

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

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

2013-04-01

117

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

118

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

UK PubMed Central (United Kingdom)

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

Wulfhekel W; Gao CL

2010-02-01

119

Investigation of non-collinear spin states with scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

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

Wulfhekel, W [Physikalisches Institut, Universitaet Karlsruhe - TH, Wolfgang-Gaede Strasse 1, 76131 Karlsruhe (Germany); Gao, C L, E-mail: w.wulfhekel@pi.uni-karlsruhe.d [Max-Planck Institut fuer Mikrostrukturphysik, Weinberg 2, 06120 Halle (Germany)

2010-03-03

120

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

Science.gov (United States)

Most ferromagnetic and antiferromagnetic substances show a simple collinear arrangement of the local spins. Under certain circumstances, however, the spin configuration is non-collinear. Scanning tunneling microscopy with its potential atomic resolution is an ideal tool for investigating these complex spin structures. Non-collinearity can be due to topological frustration of the exchange interaction, due to relativistic spin-orbit coupling or can be found in excited states. Examples for all three cases are given, illustrating the capabilities of spin-polarized scanning tunneling microscopy. PMID:21389397

Wulfhekel, W; Gao, C L

2010-02-05

 
 
 
 
121

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)

2004-01-01

122

Ga-rich GaAs(001) surfaces observed during high-temperature annealing by scanning tunneling microscopy  

CERN Document Server

Ga-rich GaAs (001) surfaces are successfully observed during high-temperature annealing by scanning tunneling microscopy (STM). With a substrate temperature of 550 oC, reflection high-energy diffraction patterns and reflectance anisotropy spectra confirm a (4x2) Ga-stabilized surface. STM images clearly show alteration of the surface reconstructions while scanning. It is postulated that detaching and attaching of Ga adatoms may be the cause of these surface dynamics. For these conditions it is determined that zeta(4x4), zeta2(4x4) and zeta(4x6) reconstructions co-exist on the surface. The zeta2(4x4) reconstruction contains a Ga tetramer cluster and in more Ga-rich conditions, the zeta2(4x6) surface has a Ga octamer cluster.

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

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

UK PubMed Central (United Kingdom)

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

Morawski I; Voigtländer B

2010-03-01

124

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

Science.gov (United States)

We present combined noncontact scanning force microscopy and tunneling current images of a platinum(111) surface obtained by means of a 1 MHz quartz needle sensor. The low-frequency circuit of the tunneling current was combined with a high-frequency signal of the quartz resonator enabling full electrical operation of the sensor. The frequency shift and the tunneling current were detected simultaneously, while the feedback control loop of the topography signal was fed using one of them. In both cases, the free signal that was not connected to the feedback loop reveals proportional-integral controller errorlike behavior, which is governed by the time derivative of the topography signal. A procedure is proposed for determining the mechanical oscillation amplitude by utilizing the tunneling current also including the average tip-sample work function. PMID:20370181

Morawski, Ireneusz; Voigtländer, Bert

2010-03-01

125

The use of Scanning Tunneling Microscope as a novel characterization tool for metallic alloys  

International Nuclear Information System (INIS)

[en] A novel method is reported for characterizing the microstructure of metals and alloys by utilizing the surface imaging properties of a STM (Scanning Tunneling microscope). In the present work there is no need to take advantage of the high atomic resolution of the STM, instead only gross resolution is required. Twenty different samples having different grain sizes (caused by the mosaic structure) and ranging between 20 to 200 nm were prepared. These dimensions are far below the resolution limit of optical microscopes. The samples were first studied using line profile analysis of XRD spectra while focusing on two of the most characteristic properties of steel which are: grain size and the deviation from cubic symmetry. Some of the samples showed nonuniform XRD line broadening effects, which could be attributed to a tetragonal distortion. If it is true, the samples must consist of martensitic twinned structure, as a result of the typical y to a shear transformation in steels. The samples were then studied using the STM. In general, many 1000 nm x 1000 )zm STM scans were carried out on each sample. In all cases of irregular XRD line broadening, the STM identified bands and sub-bands in the images which fitted the usual twining structure in steels. In addition, the STM images were found to show individual domains, from which histograms of the grain dimensions for each sample were prepared and compared to the XRD data. An excellent agreement was observed between tile two sets of data of grain sizes. The present method is much simpler than that which employs the Transmission Electron Microscope (TEM) as it can be carried out in air and no special requirements on sample preparation is necessary. This work establishes the STM as a very useful characterization tool for studies in metallurgy and metal physics. (author)

1996-01-01

126

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

International Nuclear Information System (INIS)

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

2013-01-01

127

Spatially Resolved Low-Temperature Scanning Tunneling Spectroscopy on AuFe Spin-Glass Films.  

Science.gov (United States)

In this contribution, we will demonstrate the possibility to study size effects in thin films of AuFe spin-glass alloys by investigating the differential conductance near the Fermi level with low-temperature scanning tunneling spectroscopy (STS). As confi...

A. Depuydt G. Neuttiens N. S. Maslova S. V. Savinov V. I. Panov

1998-01-01

128

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have developed an ultra-stable low temperature scanning tunneling microscope (LTSTM) for application in atomic scale spectroscopy and atom manipulation experiments. The design is based on the Besocke type microscope allowing the installation of the LTSTM within a liquid helium bath (LHe) cryostat...

Hirstein, Andreas

129

Surface damage through grazing incidence ions investigated by scanning tunneling microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Surface damage, caused by grazing incidence ions, is investigated with variable temperature scanning tunneling microscopy. The experiments are carried out on a Pt(111) crystal. The kinetic energy of noble gas ions is varied between 1-15 keV and the angle of incidence can be adjusted between 78.5° an...

Redinger, Alex

130

Observation and investigation of graphite superlattice boundaries by scanning tunneling microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this article, we report on scanning tunneling microscopy (STM) observations of several different kinds of superlattice boundaries on highly-oriented pyrolytic graphite (HOPG) including an array of bead-like structures, a monolayer deep trench, a zig-zag shaped termination, and a plain boundary wi...

Pong, WT; Bendall, J; Durkan, C

131

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

UK PubMed Central (United Kingdom)

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

Andrei EY; Li G; Du X

2012-05-01

132

Scanning tunneling microscopy of copper electrodeposited in the presence of benzotriazole  

Energy Technology Data Exchange (ETDEWEB)

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

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

1988-12-01

133

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report a scanning-tunneling-microscope (STM) study of a stage-1 graphite intercalation compound (GIC) of approximate stoichiometry C6CuCl2. When the sample bias is positive with respect to the tip, we observe a hexagonal symmetry in which all the atoms of the graphite surface plane are imaged. Th...

OLK, C H; HEREMANS, J; DRESSELHAUS, M S; SPECK, J S; NICHOLLS, J T

134

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 granula...

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

135

Scanning tunneling spectroscopy on neutron irradiated MgB{sub 2} thin films  

Energy Technology Data Exchange (ETDEWEB)

Neutron irradiation was performed on MgB{sub 2} thin films grown by hybrid physical chemical vapor deposition. Samples irradiated with different neutron fluences, having different critical temperatures, were studied by scanning tunneling spectroscopy in order to investigate the effect of the introduced disorder on the superconducting and spectroscopic properties. A monotonic increase of the {pi} gap with increasing disorder was found.

Di Capua, Roberto [University of Napoli and CNR-INFM/Coherentia, Via Cinthia, Naples I-80126 (Italy)], E-mail: rdicapua@na.infn.it; Salluzzo, Marco; Vaglio, Ruggero [University of Napoli and CNR-INFM/Coherentia, Via Cinthia, Naples I-80126 (Italy); Ferdeghini, Carlo [CNR-INFM/LAMIA, Via Dodecaneso 33, Genova I-16146 (Italy); Ferrando, Valeria [CNR-INFM/LAMIA, Via Dodecaneso 33, Genova I-16146 (Italy); Pennsylvania State University, University Park, PA 16802 (United States); Putti, Marina [CNR-INFM/LAMIA, Via Dodecaneso 33, Genova I-16146 (Italy); Xi Xiaoxing [Pennsylvania State University, University Park, PA 16802 (United States); Aebersold, Hans U. [Paul Scherrer Institut, Villigen CH-5232 (Switzerland)

2007-09-01

136

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 ...

Chen Xi; He Ke; Ma Xucun; Xue Qikun

137

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.

Chen Xi; He Ke; Ma Xucun; Xue Qikun

2012-01-01

138

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report novel properties derived from scanning tunnelling spectroscopic (STS) studies of Dirac fermions in graphene and the surface state (SS) of a strong topological insulator (STI), Bi2Se3. For mono-layer graphene grown on Cu by chemical vapour deposition (CVD), strain-induced scalar and gauge p...

Yeh N.-C.; Teague M. L.; Wu R. T.-P.; Chu H.; Boyd D. A.; Bockrath M. W.; He L.; Xiu F.-X.; wang K.-L.

139

Local crystallography analysis for atomically resolved scanning tunneling microscopy images.  

UK PubMed Central (United Kingdom)

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

Lin W; Li Q; Belianinov A; Sales BC; Sefat A; Gai Z; Baddorf AP; Pan M; Jesse S; Kalinin SV

2013-10-01

140

Local crystallography analysis for atomically resolved scanning tunneling microscopy images.  

Science.gov (United States)

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

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

2013-09-24

 
 
 
 
141

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

142

Note: optical optimization for ultrasensitive photon mapping with submolecular resolution by scanning tunneling microscope induced luminescence.  

UK PubMed Central (United Kingdom)

We report the development of a custom scanning tunneling microscope equipped with photon collection and detection systems. The optical optimization includes the comprehensive design of aspherical lens for light collimation and condensing, the sophisticated piezo stages for in situ lens adjustment inside ultrahigh vacuum, and the fiber-free coupling of collected photons directly onto the ultrasensitive single-photon detectors. We also demonstrate submolecular photon mapping for the molecular islands of porphyrin on Ag(111) under small tunneling currents down to 10 pA and short exposure time down to 1.2 ms/pixel. A high quantum efficiency up to 10(-2) was also observed.

Chen LG; Zhang C; Zhang R; Zhang XL; Dong ZC

2013-06-01

143

Note: optical optimization for ultrasensitive photon mapping with submolecular resolution by scanning tunneling microscope induced luminescence.  

Science.gov (United States)

We report the development of a custom scanning tunneling microscope equipped with photon collection and detection systems. The optical optimization includes the comprehensive design of aspherical lens for light collimation and condensing, the sophisticated piezo stages for in situ lens adjustment inside ultrahigh vacuum, and the fiber-free coupling of collected photons directly onto the ultrasensitive single-photon detectors. We also demonstrate submolecular photon mapping for the molecular islands of porphyrin on Ag(111) under small tunneling currents down to 10 pA and short exposure time down to 1.2 ms/pixel. A high quantum efficiency up to 10(-2) was also observed. PMID:23822393

Chen, L G; Zhang, C; Zhang, R; Zhang, X L; Dong, Z C

2013-06-01

144

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

CERN Multimedia

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

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

2004-01-01

145

Combined cross sectional scanning tunneling microscopy and high resolution x-ray diffraction study for quantitative structural descriptions of type-II superlattice infrared detectors  

Science.gov (United States)

Thorough structural analysis is critical to understanding the effects of device design and modeling on type II superlattice (T2SL) based devices. In this work, structural parameters of T2SL infrared devices were uniquely determined by combining local structural parameters obtained by cross-sectional scanning tunneling microscopy (XSTM) with high resolution x-ray diffraction (HRXRD) spectra. The XSTM results were used to initialize and set tolerances for full dynamical simulation and simultaneous fitting of multiple HRXRD spectra. Using this method, we obtain unique, quantitative description of the superlattice structure, composition, and strain which can be used to evaluate the material effects on device performance.

Yakes, M. K.; Qadri, S. B.; Mahadik, N. A.; Yi, C.; Lubyshev, D.; Fastenau, J. M.; Liu, A. W. K.; Aifer, E. H.

2012-12-01

146

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

UK PubMed Central (United Kingdom)

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

Han MJ; Hao J; Christodoulatos C; Korfiatis GP; Wan LJ; Meng X

2007-05-01

147

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

Science.gov (United States)

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

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

2007-04-19

148

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

CERN Document Server

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

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

2006-01-01

149

Intrinsic tunneling spectra of Bi2(Sr(2-x)Lax)CuO(6+delta).  

Science.gov (United States)

We have measured intrinsic-tunneling spectra of a single CuO-layer La-doped Bi2(Sr(2-x)Lax)CuO(6+delta) (Bi2201-Lax). Despite a difference of a factor of 3 in the optimal superconducting critical temperatures for Bi2201-La0.4 and Bi2212 (32 and 95 K, respectively) and different spectral energy scales, we find that the pseudogap vanishes at a similar characteristic temperature T* approximately 230-300 K for both compounds. We find also that, in Bi2201-Lax, pseudogap humps are seen as sharp peaks and, in fact, even dominate the intrinsic spectra. PMID:12731942

Yurgens, A; Winkler, D; Claeson, T; Ono, S; Ando, Yoichi

2003-04-11

150

Intrinsic tunneling spectra of Bi2(Sr(2-x)Lax)CuO(6+delta).  

UK PubMed Central (United Kingdom)

We have measured intrinsic-tunneling spectra of a single CuO-layer La-doped Bi2(Sr(2-x)Lax)CuO(6+delta) (Bi2201-Lax). Despite a difference of a factor of 3 in the optimal superconducting critical temperatures for Bi2201-La0.4 and Bi2212 (32 and 95 K, respectively) and different spectral energy scales, we find that the pseudogap vanishes at a similar characteristic temperature T* approximately 230-300 K for both compounds. We find also that, in Bi2201-Lax, pseudogap humps are seen as sharp peaks and, in fact, even dominate the intrinsic spectra.

Yurgens A; Winkler D; Claeson T; Ono S; Ando Y

2003-04-01

151

Observation of zigzag and armchair edges of graphite using scanning tunneling microscopy and spectroscopy  

CERN Multimedia

The presence of structure-dependent edge states of graphite is revealed by both ambient- and ultra-highvacuum- (UHV) scanning tunneling microscopy (STM) / scanning tunneling spectroscopy (STS) observations. On a hydrogenated zigzag (armchair) edge, bright spots are (are not) observed together with (SQRT(3) by SQRT(3))R30 superlattice near the Fermi level (V_S = ?30 mV for a peak of the local density of states (LDOS)) under UHV, demonstrating that a zigzag edge is responsible for the edge states, although there is no appreciable difference between as-prepared zigzag and armchair edges in air. Even in hydrogenated armchair edge, however, bright spots are observed at defect points, at which partial zigzag edges are created in the armchair edge.

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

2005-01-01

152

Scanning tunneling spectroscopy and luminescent properties of ZnS:Mn, Cu,Cl thin films  

International Nuclear Information System (INIS)

Electrical and luminescent properties of ZnS:Mn,Cu,Cl thin films were investigated. Combined both studies: scanning tunneling microscopy and scanning tunneling spectroscopy were made. The current and differential conductance versus applied voltage were measured for the ZnS:Mn,Cu,Cl thin films. Additionally, the spectral and kinetic properties of the electroluminescent cells based on the ZnS:Mn,Cu,Cl thin films were measured. The maximum of electroluminescence lies at 586 nm. The electroluminescence was excited by regular wave voltage pulses with pulse length from 1 ?s to 1 ms. It was shown that time dependence of the electroluminescence is well explained assuming energy transfer between monomolecular centers. (author)

2003-01-01

153

Atomic-scale properties of semiconductor heterostructures probed by scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

The engineering of advanced semiconductor heterostructure materials and devices requires a detailed understanding of, and control over, the structure and properties of semiconductor materials and devices at the atomic to nanometer scale. Cross-sectional scanning tunneling microscopy has emerged as a unique and powerful method to characterize structural morphology and electronic properties in semiconductor epitaxial layers and device structures at these length scales. The basic experimental techniques in cross-sectional scanning tunneling microscopy are described, and some representative applications to semiconductor heterostructure characterization drawn from recent investigations in the authors laboratory are discussed. Specifically, they describe some recent studies of InP/InAsP and InAsP/InAsSb heterostructures in which nanoscale compositional clustering has been observed and analyzed.

Yu, E.T.; Zuo, S.L.; Bi, W.G.; Tu, C.W. [Univ. of California, San Diego, La Jolla, CA (United States). Dept. of Electrical and Computer Engineering; Biefeld, R.M.; Allerman, A.A. [Sandia National Labs., Albuquerque, NM (United States)

1998-05-01

154

Highly reproducible low temperature scanning tunneling microscopy and spectroscopy with in situ prepared tips.  

UK PubMed Central (United Kingdom)

An in situ tip preparation procedure compatible with ultra-low temperature and high magnetic field scanning tunneling microscopes is presented. This procedure does not require additional preparation techniques such as thermal annealing or ion milling. It relies on the local electric-field-induced deposition of material from the tip onto the studied surface. Subsequently, repeated indentations are performed onto the sputtered cluster to mechanically anneal the tip apex and thus to ensure the stability of the tip. The efficiency of this method is confirmed by comparing the topography and spectroscopy data acquired with either unprepared or in situ prepared tips on epitaxial graphene grown on Ru (0001). We demonstrate that the use of in situ prepared tips increases the stability of the scanning tunneling images and the reproducibility of the spectroscopic measurements.

Castellanos-Gomez A; Rubio-Bollinger G; Garnica M; Barja S; Vázquez de Parga AL; Miranda R; Agraït N

2012-11-01

155

Highly reproducible low temperature scanning tunneling microscopy and spectroscopy with in situ prepared tips.  

Science.gov (United States)

An in situ tip preparation procedure compatible with ultra-low temperature and high magnetic field scanning tunneling microscopes is presented. This procedure does not require additional preparation techniques such as thermal annealing or ion milling. It relies on the local electric-field-induced deposition of material from the tip onto the studied surface. Subsequently, repeated indentations are performed onto the sputtered cluster to mechanically anneal the tip apex and thus to ensure the stability of the tip. The efficiency of this method is confirmed by comparing the topography and spectroscopy data acquired with either unprepared or in situ prepared tips on epitaxial graphene grown on Ru (0001). We demonstrate that the use of in situ prepared tips increases the stability of the scanning tunneling images and the reproducibility of the spectroscopic measurements. PMID:22955323

Castellanos-Gomez, Andres; Rubio-Bollinger, Gabino; Garnica, Manuela; Barja, Sara; Vázquez de Parga, Amadeo L; Miranda, Rodolfo; Agraït, Nicolás

2012-07-31

156

Scanning tunneling spectroscopy of CdSe nanocrystals covalently bound to GaAs  

DEFF Research Database (Denmark)

We present scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) measurements of CdSe nanocrystals covalently attached to doped GaAs substrates using monolayers of 1,6-hexanedithiol. STM measurements showed the formation of stable, densely packed, homogeneous monolayers of nanocrystals. STS measurements showed rectifying behaviour, with high currents at the opposite sample bias to that previously observed for CdSe nanocrystals adsorbed on Si substrates. We explain the rectifying behaviour by considering the interaction between the electronic states of the nanocrystals and the bands in the substrate which are bent under the influence of the strong electric field between the closely separated semiconductor substrate and STM tip. The polarity of the forward bias direction is determined by the alignment of the CdSe electronic states with the semiconductor bands. (C) 2003 Elsevier Science B.V. All rights reserved.

Walzer, K.; Marx, E.

2003-01-01

157

Nanolithography on Graphene by Using Scanning Tunneling Microscopy in a Methanol Environment.  

UK PubMed Central (United Kingdom)

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

Kim C; Park J; Seo Y; Ahn J; Park IS

2013-09-01

158

Single pentagon in a hexagonal carbon lattice revealed by scanning tunneling microscopy  

International Nuclear Information System (INIS)

The electronic structure of a single pentagon in a hexagonal carbon lattice has been revealed on an atomic scale by scanning tunneling microscopy. The pentagon is located at the apex of the conical protuberance of the graphitic particle. The enhanced charge density localized at each carbon atom in the pentagon is identified, and the ringlike pattern of the (?3 x ?3)R30 degree superstructure of graphite is clearly observed around the pentagon. [copyright] 2001 American Institute of Physics.

2001-06-04

159

Single pentagon in a hexagonal carbon lattice revealed by scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

The electronic structure of a single pentagon in a hexagonal carbon lattice has been revealed on an atomic scale by scanning tunneling microscopy. The pentagon is located at the apex of the conical protuberance of the graphitic particle. The enhanced charge density localized at each carbon atom in the pentagon is identified, and the ringlike pattern of the ({radical}3{times}{radical}3)R30{degree} superstructure of graphite is clearly observed around the pentagon. {copyright} 2001 American Institute of Physics.

An, B.; Fukuyama, S.; Yokogawa, K.; Yoshimura, M.; Egashira, M.; Korai, Y.; Mochida, I.

2001-06-04

160

Measurements with an ultrafast scanning tunnelling microscope on photoexcited semiconductor layers  

DEFF Research Database (Denmark)

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

Keil, Ulrich Dieter Felix; Jensen, Jacob Riis

1998-01-01

 
 
 
 
161

Surface structure and analysis with scanning probe microscopy and electron tunneling spectroscopy. Final report  

Energy Technology Data Exchange (ETDEWEB)

This report summarizes the results accomplished during the funding period of this grant (June 1, 1995 to May 31, 1998). The projects are (1) room-temperature atomic force microscopy (AFM) studies of NbSe{sub 3} doped with various elements and (2) low-temperature scanning tunneling microscopy (STM) studies of NbSe{sub 3}. In addition, AFM was used to study the surface morphology and defects of GaAs films grown on Ge and Ge/Si substracts.

Hsu, Julia

1998-05-01

162

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

2005-01-01

163

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

164

Imaging of stacking faults in highly oriented pyrolytic graphite using scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

Scanning tunneling microscopy images of the (0001) plane of highly oriented pyrolytic graphite show defect regions consisting of an extensive network of partial dislocations that form extended and contracted nodes. The partial dislocations in hexagonal graphite enclose triangular regions ({similar to}1000 nm on a side) of faulted material comprised of rhombohedral graphite. Electronic and elastic interactions of the tip with the HOPG surface are proposed to explain the observed image contrast between hexagonal and rhombohedral graphite.

Snyder, S.R.; Foecke, T.; White, H.S.; Gerberich, W.W. (Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455 (United States))

1992-02-01

165

Dual-probe scanning tunneling microscope: Measuring a carbon nanotube ring transistor  

Science.gov (United States)

We have constructed a dual-probe scanning tunneling microscope (D-STM). We used multiwall carbon nanotubes [(NT), diameter: ~10 nm] as STM probes. The D-STM allows us to elucidate the electric property of a sample with a spatial resolution of ~1 nm. Using this system, we have measured the current-voltage curves of a single NT ring as a transistor. The curves show the possibility of nanometer-scale electronic circuits composed of NT devices.

Watanabe, Hiroyuki; Manabe, Chikara; Shigematsu, Taishi; Shimizu, Masaaki

2001-05-01

166

Scanning tunneling microscopy study of asymmetric Pd pincer complexes on a Cu(111) surface  

Energy Technology Data Exchange (ETDEWEB)

The adsorption of asymmetric Pd pincer complexes on a Cu(111) surface was investigated by means of ultra-high vacuum scanning tunneling microscopy. The structural asymmetry is manifested in the observation of two chiral enantiomers. To enable an unambiguous identification of individual constituents, three closely related complexes with small modifications are investigated in parallel. Thereby, methyl substituents determine attractive molecule-molecule interaction. Depending on their distribution, dimerization and tetramerization can be observed.

Chang, Shih-Hsin [Institute of Applied Physics and Microstructure Research Center Hamburg, University of Hamburg (Germany); Research Center for Applied Sciences, Academia Sinica, Taipei (China); Scarfato, Alessandro [Dipartimento di Fisica E.R. Caianiello, Universita degli Studi di Salerno (Italy); Fachbereich Chemie, Philipps-Universitaet Marburg (Germany); Kleeberg, Christian; Broering, Martin [Fachbereich Chemie, Philipps-Universitaet Marburg (Germany); Hoffmann, Germar; Wiesendanger, Roland [Institute of Applied Physics and Microstructure Research Center Hamburg, University of Hamburg (Germany)

2011-07-01

167

Modelling of the intramolecular structure of monolayer C60 molecules observed with scanning tunneling microscopy  

International Nuclear Information System (INIS)

Images of monolayer coverages of C60 on gold substrates, using scanning tunneling microscopy, reveal intermolecular arrangement and intramolecular features. In this paper the authors concentrate on the interpretation of these internal features, present a model showing that they arise from local charge density variations of high-lying ? orbitals on approximately every other carbon atom, and discuss also other possible mechanisms for this effect.

1990-12-01

168

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

169

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

UK PubMed Central (United Kingdom)

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

Sripirom J; Kuhn S; Jung U; Magnussen O; Schulte A

2013-01-01

170

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

CERN Multimedia

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

171

Scanning tunneling microscopy study and nanomanipulation of graphene-coated water on mica.  

UK PubMed Central (United Kingdom)

We study interfacial water trapped between a sheet of graphene and a muscovite (mica) surface using Raman spectroscopy and ultrahigh vacuum scanning tunneling microscopy (UHV-STM) at room temperature. We are able to image the graphene-water interface with atomic resolution, revealing a layered network of water trapped underneath the graphene. We identify water layer numbers with a carbon nanotube height reference. Under normal scanning conditions, the water structures remain stable. However, at greater electron energies, we are able to locally manipulate the water using the STM tip.

He KT; Wood JD; Doidge GP; Pop E; Lyding JW

2012-06-01

172

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

173

A 10 mK scanning tunneling microscope operating in ultra high vacuum and high magnetic fields.  

Science.gov (United States)

We present design and performance of a scanning tunneling microscope (STM) that operates at temperatures down to 10 mK providing ultimate energy resolution on the atomic scale. The STM is attached to a dilution refrigerator with direct access to an ultra high vacuum chamber allowing in situ sample preparation. High magnetic fields of up to 14 T perpendicular and up to 0.5 T parallel to the sample surface can be applied. Temperature sensors mounted directly at the tip and sample position verified the base temperature within a small error margin. Using a superconducting Al tip and a metallic Cu(111) sample, we determined an effective temperature of 38 ± 1 mK from the thermal broadening observed in the tunneling spectra. This results in an upper limit for the energy resolution of ?E = 3.5 kBT = 11.4 ± 0.3 ?eV. The stability between tip and sample is 4 pm at a temperature of 15 mK as demonstrated by topography measurements on a Cu(111) surface. PMID:23556826

Assig, Maximilian; Etzkorn, Markus; Enders, Axel; Stiepany, Wolfgang; Ast, Christian R; Kern, Klaus

2013-03-01

174

A 10 mK scanning tunneling microscope operating in ultra high vacuum and high magnetic fields.  

UK PubMed Central (United Kingdom)

We present design and performance of a scanning tunneling microscope (STM) that operates at temperatures down to 10 mK providing ultimate energy resolution on the atomic scale. The STM is attached to a dilution refrigerator with direct access to an ultra high vacuum chamber allowing in situ sample preparation. High magnetic fields of up to 14 T perpendicular and up to 0.5 T parallel to the sample surface can be applied. Temperature sensors mounted directly at the tip and sample position verified the base temperature within a small error margin. Using a superconducting Al tip and a metallic Cu(111) sample, we determined an effective temperature of 38 ± 1 mK from the thermal broadening observed in the tunneling spectra. This results in an upper limit for the energy resolution of ?E = 3.5 kBT = 11.4 ± 0.3 ?eV. The stability between tip and sample is 4 pm at a temperature of 15 mK as demonstrated by topography measurements on a Cu(111) surface.

Assig M; Etzkorn M; Enders A; Stiepany W; Ast CR; Kern K

2013-03-01

175

A hysteresis phenomenon in NMR spectra of molecular nanomagnets Fe8: a resonant quantum tunneling system  

International Nuclear Information System (INIS)

[en] A molecular nanomagnet Fe8 with a total spin S=10 in the ground state attracts much attention as a substance which exhibits the quantum tunneling of magnetization below 300 mK. We performed 1H NMR measurements for a single crystal of Fe8 in temperature range between 20 and 800 mK. The spectra below 300 mK strongly depend on the sequence of the applied field and those in the positive and negative fields are not symmetric about zero field, while they are symmetric above 300 mK. We discuss the origin of this hysteresis phenomenon, relating to the initial spin state of molecules, the resonant quantum tunneling and the nuclear spin relaxation process

2003-01-01

176

Scanning Tunneling Potentiometry: The Power of STM Applied to Electrical Transport  

Energy Technology Data Exchange (ETDEWEB)

Scanning Probe Microscopy brings up to date a constantly growing knowledge base of electrical and electromechanical characterization at the nanoscale. This comprehensive, two-volume set presents practical and theoretical issues of advanced scanning probe microscopy (SPM) techniques ranging from fundamental physical studies to device characterization, failure analysis, and nanofabrication. Volume 1 focuses on the technical aspects of SPM methods ranging from scanning tunneling potentiometry to electrochemical SPM, and addresses the fundamental physical phenomena underlying the SPM imaging mechanism. Volume 2 concentrates on the practical aspects of SPM characterization of a wide range of materials, including semiconductors, ferroelectrics, dielectrics, polymers, carbon nanotubes, and biomolecules, as well as on SPM-based approaches to nanofabrication and nanolithography.

Baddorf, Arthur P [ORNL

2006-01-01

177

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

CERN Multimedia

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

178

Quantitative analysis of Scanning Tunneling Microscopy images for surface structure determination: Sulfur on Re(0001)  

Energy Technology Data Exchange (ETDEWEB)

Scanning Tunneling Microscopy (STM) images of adsorbed atoms and molecules on single crystal substrates provide important information on surface structure and order. In many cases images are interpreted qualitatively based on other information on the system. To obtain quantitative information, a theoretical analysis of the STM image is required. A new method of calculating STM images is presented that includes a full description of the STM tip and surface structure. This method is applied to experimental STM images of sulfur adsorbed on Re(0001). Effects of adsorption site, adsorbate geometry, tip composition and tunnel gap resistance on STM image contrast are analyzed. The chemical identity of tip apex atom and substrate subsurface structure are both shown to significantly affect STM image contrast.

Ogletree, D.F.; Dunphy, J.C.; Salmeron, M.B. [Lawrence Berkeley Lab., CA (United States); Sautet, P. [ENS, Lyon (France). Lab. de Chemie Theoretique]|[Centre National de la Recherche Scientifique (CNRS), 69 - Villeurbanne (France). Inst. de Recherches sur la Catalyse

1993-02-01

179

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

UK PubMed Central (United Kingdom)

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 NbSe(2) 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 UR; Enayat M; White SC; Wahl P

2013-01-01

180

Study of Conduction Mechanism and Scanning Tunneling Spectrum of NANO-CaCO3  

Science.gov (United States)

We have experimentally found out that an obvious tunnel current begins to appear between nano-CaCO3 film and tip of STM when the bias voltage reaches 0.6V, above which there is a non-linear rise quickly. We further measure the scanning tunneling spectrum (STS) of nano-CaCO3 and analyze it compared to that of Au and Silicon. The results show that CaCO3, an insulating material, after nanometer processing presents a characteristic similarly to a metal, and the constraint to electrons is even smaller than a semiconductor. STS has not only well explained the spectroscopic mechanism of conducting performances of nano-CaCO3, but also expanded applications of STM to one of the most important research areas. Moreover, the method can be applied to the study of the structure of superconductive materials and energy spectrum characterization.

Wang, Y. F.; Yang, X. H.; Wang, S. F.; Xin, H. Z.; Liu, A. P.

 
 
 
 
181

MgB2 Energy Gap Determination by Scanning Tunneling Spectroscopy  

CERN Multimedia

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

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

2002-01-01

182

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

CERN Multimedia

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

Raza, H

2007-01-01

183

MgB2 energy gap determination by scanning tunnelling spectroscopy  

International Nuclear Information System (INIS)

We report scanning tunnelling spectroscopy (STS) measurements of the gap properties of both ceramic MgB2 and c-axis oriented epitaxial MgB2 thin films. Both show a temperature dependent zero bias conductance peak and evidence for two superconducting gaps. We report tunnelling spectroscopy of superconductor-insulator-superconductor (S-I-S) junctions formed in two ways in addition to normal metal-insulator-superconductor (N-I-S) junctions. We find a gap ? = 2.2-2.8 meV, with spectral features and temperature dependence that are consistent between S-I-S junction types. In addition, we observe evidence of a second, larger gap, ? 7.2 meV, consistent with a proposed two-band model.

2004-02-01

184

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

UK PubMed Central (United Kingdom)

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

Lee I; Lee JW; Warmack RJ; Allison DP; Greenbaum E

1995-03-01

185

Scanning tunneling microscopy and spectroscopy on GaN and InGaN surfaces  

International Nuclear Information System (INIS)

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

2009-01-01

186

Antenna-based ultrahigh vacuum microwave frequency scanning tunneling microscopy system.  

UK PubMed Central (United Kingdom)

The instrumental synthesis of high resolution scanning tunneling microscopy (STM) with the ability to measure differential capacitance with atomic scale resolution is highly desirable for fundamental metrology and for the study of novel physical characteristics. Microwave frequency radiation directed at the tip-sample junction in an STM system allows for such high-resolution differential capacitance information. This ability is particularly critical in ultrahigh vacuum environments, where the additional parameter space afforded by including a capacitance measurement would prove powerful. Here we describe the modifications made to a commercial scanning tunneling microscope to allow for broad microwave frequency alternating current scanning tunneling microscopy (ACSTM) in ultrahigh vacuum conditions using a relatively simple loop antenna and microwave difference frequency detection. The advantages of our system are twofold. First, the use of a removable antenna on a commercial STM prevents interference with other UHV processes while providing a simple method to retrofit any commercial UHV-STM with UHV-ACSTM capability. Second, mounting the microwave antenna on a translator allows for specific tuning of the system to replicate experimental conditions between samples, which is particularly critical in sensitive systems like organic thin films or single molecules where small changes in incident power can affect the results. Our innovation therefore provides a valuable approach to give nearly any commercial STM, be it an ambient or UHV system, the capability to measure atomic-scale microwave studies such as differential capacitance or even single molecule microwave response, and it ensures that experimental ACSTM conditions can be held constant between different samples.

Giridharagopal R; Zhang J; Kelly KF

2011-05-01

187

Intrinsic tunneling spectra of Bi_2(Sr_{2-x}La_x)CuO_6  

CERN Document Server

We have measured intrinsic-tunneling spectra of a single CuO-layer La-doped Bi_2Sr_{2-x}La_xCuO_{6+\\delta} (Bi2201-La_x). Despite a difference of a factor of three in the optimal superconducting critical temperatures for Bi2201-La_{0.4} and Bi2212 (32 and 95 K, respectively) and different spectral energy scales, we find that the pseudogap vanishes at a similar characteristic temperature T*\\approx 230-300K for both compounds. We find also that in Bi2201-La_x, PG humps are seen as sharp peaks and, in fact, even dominate the intrinsic spectra.

Yurgens, A; Claeson, T; Ono, S; Ando, Y; Ando, Yoichi

2002-01-01

188

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1998-12-31

189

Atomic resolution imaging of currents in nanoscopic quantum networks via scanning tunneling microscopy.  

UK PubMed Central (United Kingdom)

We propose a new method for atomic-scale imaging of spatial current patterns in nanoscopic quantum networks by using scanning tunneling microscopy (STM). By measuring the current flowing from the STM tip into one of the leads attached to the network as a function of tip position, one obtains an atomically resolved spatial image of "current riverbeds" whose spatial structure reflects the coherent flow of electrons out of equilibrium. We show that this method can be successfully applied in a variety of network topologies and is robust against dephasing effects.

Can T; Morr DK

2013-02-01

190

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

UK PubMed Central (United Kingdom)

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

Greenwood J; Baddeley CJ

2013-01-01

191

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

UK PubMed Central (United Kingdom)

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.

Tison Y; Lin H; Lagoute J; Repain V; Chacon C; Girard Y; Rousset S; Henrard L; Zheng B; Susi T; Kauppinen EI; Ducastelle F; Loiseau A

2013-08-01

192

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

CERN Document Server

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

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

2002-01-01

193

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

194

Scanning tunneling microscopy at 70 mK in the dichalcogenide superconductor TaSe2  

Science.gov (United States)

We present scanning tunneling microscopy and spectroscopy measurements of the layered dichalcogenide 2H-TaSe2, performed in a dilution refrigerator cryostat equipped with a three axis superconducting magnet. In this compound superconductivity and charge density wave (CDW) ordering coexist below 200mK. We find CDW order corresponding to hexagonal (2H) symmetry, but we also find areas where CDW order corresponding to trigonal (1T) symmetry appears. We study the superconducting density of states as a function of position and magnetic field at 70mK and relate the results to the CDW patterns.

Galvis, Jose; Suderow, Hermann; Vieira, Sebastian

2012-02-01

195

Identification of single-strand DNA by in situ scanning tunneling microscopy.  

UK PubMed Central (United Kingdom)

We report here in situ scanning tunneling microscopy imaging of hexaammineruthenium (II)/(III) (RuHex) binding to single-strand DNA oligonucleotide with 13 bases immobilized in a mixed monolayer on a single-crystal Au(111) surface. RuHex does not bind to the other component in the monolayer, mercaptohexanol. Images before and after addition of RuHex show a strong contrast increase, suggesting that single-stranded DNA is, indeed, conducting when a redox group is bound to the strand. When compared with previous results, the data also suggest that the mechanism of domain formation of the immobilized DNA is independent of the sequence.

Grubb M; Wackerbarth H; Ulstrup J

2006-06-01

196

Identification of single-strand DNA by in situ scanning tunneling microscopy.  

Science.gov (United States)

We report here in situ scanning tunneling microscopy imaging of hexaammineruthenium (II)/(III) (RuHex) binding to single-strand DNA oligonucleotide with 13 bases immobilized in a mixed monolayer on a single-crystal Au(111) surface. RuHex does not bind to the other component in the monolayer, mercaptohexanol. Images before and after addition of RuHex show a strong contrast increase, suggesting that single-stranded DNA is, indeed, conducting when a redox group is bound to the strand. When compared with previous results, the data also suggest that the mechanism of domain formation of the immobilized DNA is independent of the sequence. PMID:16771476

Grubb, Mikala; Wackerbarth, Hainer; Ulstrup, Jens

2006-06-21

197

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

CERN Multimedia

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 discuss the relevance of this study to recent experiments on carbon nanotube transistors and argue that the Fermi-level alignment will be different for carbon nanotube transistors with low resistance and high resistance contacts.

Xue, Y; Xue, Yongqiang; Datta, Supriyo

1999-01-01

198

Current-Voltage characterization of Individual as-grown Nanowires using a Scanning Tunneling Microscope.  

UK PubMed Central (United Kingdom)

Utilizing semiconductor nanowires for (opto)electronics requires exact knowledge of their current-voltage properties. We report accurate on-top imaging and I-V-characterization of individual as-grown nanowires, using a sub-nanometer resolution scanning tunneling microscope - with no need for additional microscopy tools, thus allowing versatile application. We form Ohmic contacts to InP and InAs nanowires without any sample processing, followed by quantitative measurements of diameter dependent I-V properties, with a very small spread in measured values compared to standard techniques.

Timm R; Persson O; Engberg DL; Fian A; Webb J; Wallentin J; Jönsson A; Borgstrom MT; Samuelson L; Mikkelsen A

2013-09-01

199

Tip effects in scanning tunnelling microscopy of atomic-scale magnetic structures  

CERN Multimedia

The spin-polarized scanning tunnelling microscope (STM) can in principle resolve not only the electronic, but also the magnetic surface structure. We model recent STM measurements achieving magnetic resolution on the atomic scale by a first-principles method. It is shown that the signature of a specific magnetic or non-magnetic STM tip can unambiguously be identified. It is also established that the model of Tersoff and Hamann would yield an electronic as well as magnetic contrast of the surface which is well below STM resolution.

Hofer, W A

2001-01-01

200

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

 
 
 
 
201

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

202

Magnetic Scanning Tunneling Microscopy with a Two-Terminal Non-Magnetic Tip Quantitative Results  

CERN Document Server

We report numerical simulation result of a recently proposed \\{P. Bruno, Phys. Rev. Lett {\\bf 79}, 4593, (1997)\\} approach to perform magnetic scanning tunneling microscopy with a two terminal non-magnetic tip. It is based upon the spin asymmetry effect of the tunneling current between a ferromagnetic surface and a two-terminal non-magnetic tip. The spin asymmetry effect is due to the spin-orbit scattering in the tip. The effect can be viewed as a Mott scattering of tunneling electrons within the tip. To obtain quantitative results we perform numerical simulation within the single band tight binding model, using recursive Green function method and Landauer-B\\"uttiker formula for conductance. A new model has been developed to take into account the spin-orbit scattering off the impurities within the single-band tight-binding model. We show that the spin-asymmetry effect is most prominent when the device is in quasi-ballistic regime and the typical value of spin asymmetry is about 5%.

Pareek, T P; Bruno, Patrick

2000-01-01

203

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

Energy Technology Data Exchange (ETDEWEB)

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

Kazmerski, Lawrence L. (Lakewood, CO)

1990-01-01

204

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

UK PubMed Central (United Kingdom)

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

Raad C; Graf KH; Ebert P

2010-01-01

205

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

Science.gov (United States)

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

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

2010-01-01

206

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

Energy Technology Data Exchange (ETDEWEB)

Several tens of chromium layers were deposited at 250 {sup 0}C on a Cr(001) surface and investigated by spin-polarized scanning tunneling microscopy (SP-STM), Auger electron spectroscopy (AES) and scanning tunneling spectroscopy (STS). Chromium is found to grow with a mound-like morphology resulting from the stacking of several monolayers which do not uniformly cover the whole surface of the substrate. The terminal plane consists of an irregular array of Cr islands with lateral sizes smaller than 20 x 20 nm{sup 2}. Combined AES and STS measurements reveal the presence of a significant amount of segregants prior to and after deposition. A detailed investigation of the surface shows that it consists of two types of patches. Thanks to STS measurements, the two types of area have been identified as being either chromium pure or segregant rich. SP-STM experiments have evidenced that the antiferromagnetic layer coupling remains in the chromium mounds after deposition and is not significantly affected by the presence of the segregants.

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

2011-02-02

207

Optical spectroscopy and scanning tunneling microscopy studies of molecular adsorbates and anisotropic ultrathin films. Final report  

Energy Technology Data Exchange (ETDEWEB)

The bonding, chemistry and ordering of molecular adsorbates on well defined single crystal surfaces and in ultrathin films was to be studied in an effort to develop sufficient fundamental understanding to allow the controlled preparation of anisotropic ultrathin films of organic monolayers. In this research the authors combine the use of optical probes (Raman spectroscopy, laser induced thermal desorption with Fourier transform mass spectrometry detection) with scanning tunneling microscopy (STM) and conventional methods of UHV surface science (Auger electron spectroscopy, x-ray photoelectron spectroscopy, low energy electron diffraction, and thermal desorption spectroscopy). The conventional surface probes provide well tested methods for the preparation and characterization of single crystal substrates. The optical probes used in the experiments provide powerful methods for the molecular identification of adsorbates in monolayers and ultrathin films. Scanning tunneling microscopy provides one with the ability to determine the detailed molecular level ordering of the molecular adsorbates. The emphasis of this research is on more complex molecular absorbates some of which are monomer precursors to ultrathin polymer films. Enhanced methods of Raman spectroscopy have been developed for the study of monolayer adsorbates on surfaces in ultrahigh vacuum environments. This report gives an overview of recent research results, including the construction of UHV variable temperature STM, analysis of STM images, growth and chemistry of intermetallic single crystal ultrathin films, and electron beam induced chemistry of tetracyanoquinodimethane.

Hemminger, J.C.

1998-09-01

208

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

Science.gov (United States)

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

Wang, Kangkang; Rosenmann, Daniel; Holt, Martin; Winarski, Robert; Hla, Saw-Wai; Rose, Volker

2013-06-01

209

Scanning tunneling microscopy and spectroscopy of sodium-chloride overlayers on the stepped Cu(311) surface: Experimental and theoretical study  

CERN Multimedia

The physical properties of ultrathin NaCl overlayers on the stepped Cu(311) surface have been characterized using scanning tunneling microscopy (STM) and spectroscopy, and density functional calculations. Simulations of STM images and differential conductance spectrum were based on the Tersoff-Hamann approximation for tunneling with corrections for the modified tunneling barrier at larger voltages and calculated Kohn-Sham states. Characteristic features observed in the STM images can be directly related to calculated electronic and geometric properties of the overlayers. The measured apparent barrier heights for the mono-, bi-, and trilayers of NaCl and the corresponding adsorption-induced changes in the work function, as obtained from the distance dependence of the tunneling current, are well reproduced by and understood from the calculated results. The measurements revealed a large reduction of the tunneling conductance in a wide voltage region, resembling a band gap. However, the simulated spectrum showed ...

Olsson, F E; Repp, J; Meyer, G

2005-01-01

210

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

UK PubMed Central (United Kingdom)

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

Wang K; Rosenmann D; Holt M; Winarski R; Hla SW; Rose V

2013-06-01

211

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

2004-12-01

212

Scanning tunneling spectroscopy at the [110]-[1 anti 10] cleaved edge of GaAs  

Energy Technology Data Exchange (ETDEWEB)

We report the first cross-sectional scanning tunneling spectroscopy (STS) study of zincblende[110]-[1 anti 10] cleaved edges with atomic resolution. The samples were prepared in-situ by a double cleavage procedure applied to 6.10{sup 18} cm{sup -3} Si-doped GaAs in UHV. In edge-approaching scans and for positive sample bias we observed a monotonically decreasing tunnel current within a few tens of nm from the edge. For negative bias we found the onset of this decrease within a few nm from the edge, followed by a considerable increase directly at the edge. Comparing these observations with scans over charged defects embedded in plane surfaces, we conclude that the edge contains a negative line charge density. The data suggests that the observed effect is not simply caused by tip-induced band bending and screening of bulk states confined within the 90 {sup circle} -edge geometry. Spectroscopic measurements on edges support the concept of a negatively charged quasi-1d electronic state localized along the edge. It is laterally confined within {proportional_to}2 lattice constants and is clearly observed in the local density of states derived from the STS data. To estimate the absolute value of its charge density we simulated the shape and spatial extension of the screening cloud of a negative line charge located at the center of the ''quarter-space'' geometry. By adjusting this potential to the spectroscopic data we find a line charge density of {proportional_to}0.7 electrons per unit cell.

Siewers, S.; Wenderoth, M.; Winking, L.; Kloth, P.; Ulbrich, R.G. [IV. Phys. Inst., Georg-August-Universitaet Goettingen (Germany)

2009-07-01

213

Influence of resonant tunneling on the imaging of atomic defects on InAs(110) surfaces by low-temperature scanning tunneling microscopy  

CERN Multimedia

We have used a low-temperature scanning tunneling microscope (STM) to study the surface of heavily doped semiconductor InAs crystals. The crystals are cleaved in situ along the (110) plane. Apart from atomically flat areas, we also observe two major types of atomic scale defects which can be identified as S dopant atoms and as As vacancies, respectively. The strong bias voltage dependence of the STM image of the impurities can be explained in terms of resonant tunneling through localized states which are present near the impurity.

Depuydt, A; Maslova, N S; Panov, V I; Rakov, V V; Savinov, S V

1998-01-01

214

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

International Nuclear Information System (INIS)

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

2009-08-19

215

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

International Nuclear Information System (INIS)

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

2010-01-01

216

Evidence from scanning tunneling spectroscopy for magnetic-field-enhanced collective modes in the high-TC superconductor YBa2Cu3O7-?  

Science.gov (United States)

We present scanning tunneling spectroscopic evidence for field-enhanced collective modes in YBa2Cu3O7-?. The observed spectra inside vortices exhibit two characteristic features: a pseudogap (VCO = 31.5+2.0 meV) larger than the superconducting gap (?SC = 20.0+1.0 meV) and a subgap (?' 7-10meV) smaller than ?SC. Outside vortices, the spectra display a gap of ?SC. As magnetic field increases, spectral weight rapidly shifts from ?SC to VCO and ?'. The vortex state also reveals energy-independent conductance modulations with peridocities of 3.6 and 7.1 lattice constants along the Cu-O bonding direction and 9.5 lattice constants along the nodal direction. The energy-independent modulations differ fundamentally from energy-dispersive modes due to Bogoliubov quasiparticle scattering interferences and originate from field-enhanced collective modes of pair-, charge- and spin-density waves.

Beyer, A. D.; Grinolds, M. S.; Teague, M. L.; Yeh, N.-C.; Tajima, S.

2010-03-01

217

Investigation of ascorbate-Cu (II) induced cleavage of DNA by scanning tunneling microscopy.  

UK PubMed Central (United Kingdom)

Scanning Tunneling Microscopy (STM) was used for the investigation of oxidative DNA damage. A PCR amplified fragment of human beta-globin gene was used as a model for time dependent cleavage reaction by ascorbate and copper. Cleavage reactions were carried out in a medium containing 0.5 microgram/20 microliters DNA, 20 nM Tris-HC1 pH, 7.8 and ascorbate-Cu (II) in the final concentrations of 1 mM and 30 microM, respectively. The mixtures were incubated at 37 degrees C for 5, 15 and 30 min. For STM studies, 3 pg/5 microliters DNA samples were deposited on the gold coated mica and dried in a water flow vacuum drier. The STM was operated in air at atmospheric pressure with a tip-to-substrate bias of 100 mV and tunneling currents of < 10 pA. Etched tips of Pt/Ir wires were used in a constant current mode. The degradated DNA structure can be distinguished from the intact DNA and the sizes of the degradation products can be identified in the STM micrographs. The size of fragments decreased from approximately 3000 A to 34 A in ascorbate-Cu (II) medium, after 30 min of incubation.

Zareie MH; Erdem G; Oner C; Oner R; O?ü? A; Pi?kin E

1996-07-01

218

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

DEFF Research Database (Denmark)

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

Haiss, W.; Albrecht, Tim

2007-01-01

219

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

CERN Multimedia

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

Zhao, S P; Wei, Y F

2007-01-01

220

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

 
 
 
 
221

Circularly polarized light emission in scanning tunneling microscopy of magnetic systems  

CERN Multimedia

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

Apell, S P; Johansson, P

2000-01-01

222

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

Energy Technology Data Exchange (ETDEWEB)

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

223

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

International Nuclear Information System (INIS)

[en] 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

1994-01-01

224

Formation of sulfur clusters on Re(0001) surfaces observed with the scanning tunneling microscope  

International Nuclear Information System (INIS)

We have studied the various structures formed by sulfur on Re(0001) single-crystal surfaces using a scanning tunneling microscope. At coverages of 0.25 monolayer and below, open lattices formed by single adatoms are formed, mostly with a (2x2) structure. Between 0.25 and 0.5 monolayer, phases consisting of three-, four-, or six-adatom clusters are observed. The sulfur trimers are formed first randomly in the (2x2) regions and then ordered as their coverage increases to saturation at 0.45 monolayer. In all cases sulfur atoms are adsorbed in threefold hollow sites. The formation of sulfur clusters above 0.25 monolayer is interpreted as evidence of substrate-mediated many-body forces

1991-07-15

225

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

1994-01-01

226

Analysis of scanning tunneling microscope topographs of graphite surfaces roughened by Ar+ ion bombardment  

International Nuclear Information System (INIS)

The scanning tunneling microscopy (STM) has been used to investigate graphite surfaces roughened by 5 keV Ar+ ion bombardment. The (0001) surfaces of several samples were etched with the same total ion dose but with different sputter rates for each surface. STM images taken after sputtering show that the roughness of the sputtered surfaces depended on the sputter rate and that the surface topography of each sample appeared self-similar over a large range of length scales. These experimental observations agree with predictions of the recently proposed Shadow Model. The two dimensional height-height correlation function is utilized as a means of quantitative analysis for STM topographs of sputtered surfaces

1989-12-02

227

Scanning-tunneling-microscopy study of faceting on high-step-density TaC surfaces  

International Nuclear Information System (INIS)

We have studied the morphologies of the TaC(310), (210), and (110) surfaces using scanning tunneling microscopy. Heating the crystals to high temperatures activates a faceting of these surfaces into a hill-and-valley structure consisting of enlarged (100) terraces and (010) step walls. Step-separation distributions obtained from these surfaces can be well fit by sharp Gaussians and are much narrower than predicted for the noninteracting terrace-step-kink model, indicating a strong repulsive interaction exists between steps on the faceted surfaces. This faceting is suggested to be driven by a decrease in the total step repulsive energy through a reduction of the total number of step pairs. copyright 1996 The American Physical Society.

1996-01-01

228

Surface structure and spectroscopy of charge-density wave materials using scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

The Scanning tunneling microscope (STM) has been used to study the effects of Fe doping on the charge-density wave (CDW) structure in NbSe{sub 3} and 1T-TaS{sub 2}. In NbSe{sub 3} small amounts of Fe reduce both CDW gaps by 25--30% and change the relative CDW amplitudes of the high and low temperature CDWs. The CDW amplitudes remain strong on all three chains of the surface unit cell with no evident disorder. In 1T-Fe{sub 0.05}Ta{sub 0.95}S{sub 2} the Fe introduces substantial disorder in the CDW pattern, but the local CDW amplitude remains strong. The CDW energy gap is reduced by approximately 50% and the resistive anomaly at the commensurate-incommensurate transition is removed. The STM in both the image and spectroscopy modes can detect subtle changes in CDW structure due to impurities.

Coleman, R.V.; Dai, Zhenxi; McNairy, W.W.; Slough, C.G.; Wang, Chen

1991-12-31

229

A New Interpretation of the Scanning Tunneling Microscope Image of Graphite  

Energy Technology Data Exchange (ETDEWEB)

In this work, highly-resolved scanning tunneling microscopy images of graphite basal plane are obtained and theoretical computations are performed to explain the resolution of only half the atoms in STM images of graphite. Our experimental and computational findings indicate that the bright elliptical spots observed in trigonal STM images of graphite may not correspond to carbon positions but to p-states localized above alternate carbon–carbon bonds. This interpretation is based on STM experiments that suggest that the elliptical shape of the bright spots may not be a tip artifact and on simulated STM images of a graphite using orthorhombic unit cells that are in excellent agreement with experimentally obtained images.

Zeinalipour-Yazdi, Constantinos D.; Pullman, David P.

2008-06-02

230

Surface structure and spectroscopy of charge-density wave materials using scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

The Scanning tunneling microscope (STM) has been used to study the effects of Fe doping on the charge-density wave (CDW) structure in NbSe{sub 3} and 1T-TaS{sub 2}. In NbSe{sub 3} small amounts of Fe reduce both CDW gaps by 25--30% and change the relative CDW amplitudes of the high and low temperature CDWs. The CDW amplitudes remain strong on all three chains of the surface unit cell with no evident disorder. In 1T-Fe{sub 0.05}Ta{sub 0.95}S{sub 2} the Fe introduces substantial disorder in the CDW pattern, but the local CDW amplitude remains strong. The CDW energy gap is reduced by approximately 50% and the resistive anomaly at the commensurate-incommensurate transition is removed. The STM in both the image and spectroscopy modes can detect subtle changes in CDW structure due to impurities.

Coleman, R.V.; Dai, Zhenxi; McNairy, W.W.; Slough, C.G.; Wang, Chen.

1991-01-01

231

Optical pump-probe scanning tunneling microscopy for probing ultrafast dynamics on the nanoscale  

Science.gov (United States)

The development of a method for exploring the ultrafast transient dynamics in small organized structures with high spatial resolution is expected to be a basis for further advances in current science and technology. Recently, we have developed a new microscopy technique by combining scanning tunneling microscopy (STM) with ultrashort-pulse laser technology, which enables the visualization of ultrafast carrier dynamics even on the single-atomic level. A nonequilibrium carrier distribution is generated using ultrashort laser pulses and its relaxation processes are probed by STM using the optical pump-probe method realized in STM by the pulse-picking technique. In this paper, the fundamentals of the new microscopy technique are overviewed.

Yoshida, S.; Terada, Y.; Yokota, M.; Takeuchi, O.; Oigawa, H.; Shigekawa, H.

2013-07-01

232

Structural study of a wholly aromatic polyamide with a rigid pendent group by scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

The scanning tunneling microscope was used to study nonconducting wholly aromatic polyamide chains deposited onto highly oriented pyrolytic graphite (HOPG) substrates. Images, taken in air, were analyzed to address questions concerning the attachment sites of rigid pendent groups to the polymeric molecular backbone as well as to answer general, larger morphological questions relating to such issues as possible helical coiling of chains, monomeric or dimeric, and multichain aggregation. Films were prepared from solutions of the polyamide dissolved in dimethylacetamide and differing in salt content to change the degree of association between chains and, therefore, the tendency of chains to form large bundles. Evidence was found for coiling of multimolecular chains and a tendency to form large ordered multimacromolecular assemblies.

Hawley, M.E.; Benicewicz, B.C. (Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico, 87545 (USA))

1991-03-01

233

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

234

Scanning tunneling microscopy reveals LiMnAs is a room temperature anti-ferromagnetic semiconductor  

Energy Technology Data Exchange (ETDEWEB)

We performed scanning tunneling microscopy and spectroscopy on a LiMnAs(001) thin film epitaxially grown on an InAs(001) substrate by molecular beam epitaxy. While the in situ cleavage exposed only the InAs(110) non-polar planes, the cleavage continued into the LiMnAs thin layer across several facets. We combined both topography and current mappings to confirm that the facets correspond to LiMnAs. By spectroscopy we show that LiMnAs has a band gap. The band gap evidenced in this study, combined with the known Neel temperature well above room temperature, confirms that LiMnAs is a promising candidate for exploring the concepts of high temperature semiconductor spintronics based on antiferromagnets.

Wijnheijmer, A. P.; Koenraad, P. M. [COBRA Inter-University Research Institute, Department of Applied Physics, Eindhoven University of Technology, P. O. Box 513, NL-5600 MB Eindhoven (Netherlands); Marti, X. [Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 121 16 Prague 2 (Czech Republic); Institute of Physics ASCR, v.v.i., Cukrovarnicka 10, 162 53 Prague 6 (Czech Republic); Holy, V. [Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 121 16 Prague 2 (Czech Republic); Cukr, M.; Novak, V. [Institute of Physics ASCR, v.v.i., Cukrovarnicka 10, 162 53 Prague 6 (Czech Republic); Jungwirth, T. [Institute of Physics ASCR, v.v.i., Cukrovarnicka 10, 162 53 Prague 6 (Czech Republic); School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom)

2012-03-12

235

Hydrogen-bond imaging and engineering with a scanning tunnelling microscope  

International Nuclear Information System (INIS)

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

2011-11-23

236

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

237

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

238

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

Energy Technology Data Exchange (ETDEWEB)

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

Dow, J.D.

1992-03-17

239

A theoretical model for single-molecule incoherent scanning tunneling spectroscopy  

International Nuclear Information System (INIS)

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

2008-11-05

240

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

 
 
 
 
241

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

242

Self-organized nanotemplating on misfit dislocation networks investigated by scanning tunneling microscopy.  

Science.gov (United States)

Self-ordering growth of nanoarrays on strained metallic interfaces is an attractive option for preparing highly ordered nanotemplates. The great potential of this natural templating approach is that symmetry, feature sizes, and density are predicted to depend on the interfacial stress in these strained layers, which can be adjusted by changing the substrate-thin film composition, temperature, and adlayer coverage. This bottom-up approach of growing nanostructured two-dimensional ordered arrays of clusters on the misfit dislocation networks of strained metallic thin films and surfaces requires a detailed understanding of the nucleation and film-adsorbate interaction processes. Here we show how high resolution, large scale, variable temperature scanning tunneling microscopy imaging can improve our understanding of these self-assembly processes. PMID:17479982

Diaconescu, Bogdan; Nenchev, Georgi; Jones, Joshua; Pohl, Karsten

2007-06-01

243

Self-organized nanotemplating on misfit dislocation networks investigated by scanning tunneling microscopy.  

UK PubMed Central (United Kingdom)

Self-ordering growth of nanoarrays on strained metallic interfaces is an attractive option for preparing highly ordered nanotemplates. The great potential of this natural templating approach is that symmetry, feature sizes, and density are predicted to depend on the interfacial stress in these strained layers, which can be adjusted by changing the substrate-thin film composition, temperature, and adlayer coverage. This bottom-up approach of growing nanostructured two-dimensional ordered arrays of clusters on the misfit dislocation networks of strained metallic thin films and surfaces requires a detailed understanding of the nucleation and film-adsorbate interaction processes. Here we show how high resolution, large scale, variable temperature scanning tunneling microscopy imaging can improve our understanding of these self-assembly processes.

Diaconescu B; Nenchev G; Jones J; Pohl K

2007-06-01

244

Height analysis of amorphous and crystalline ice structures on Cu(111) in scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

Scanning tunneling microscopy imaging of amorphous and crystalline D{sub 2}O ice on Cu(111) is discussed with respect to the apparent and the real heights of these structures above the metal surface. The apparent height increases linearly below the conduction band onset of amorphous ice and the first image state of crystalline ice, respectively. However, it largely underestimates the real height. For these voltages, histograms of the apparent height can be used to identify different layers. The dependence of the apparent height on voltage increases step-like up to the real height at the onsets of the first unoccupied electronic state. Apparent height spectroscopy is utilized to relate the apparent height to the real height of the different structures. The analysis reveals the layering during growth of porous amorphous ice between 0.1 and 1.4 BL and the dynamics of crystallization between 130 and 145 K.

Mehlhorn, Michael; Morgenstern, Karina [Institut fuer Festkoerperphysik, Abteilung ATMOS, Leibniz Universitaet Hannover, Appelstr. 2, D-30167 Hannover (Germany)], E-mail: morgenstern@fkp.uni-hannover.de

2009-09-15

245

In situ scanning tunneling microscopy investigation of subphthalocyanine and subnaphthalocyanine adlayers on a Au(111) electrode.  

UK PubMed Central (United Kingdom)

The adsorption behaviors of subphthalocyanine (SubPc) and subnaphthalocyanine (SubNc) on the Au(111) surface were investigated by electrochemical scanning tunneling microscopy (ECSTM). Two types of ordered adlayer structures of SubPc were observed at 550 mV versus the reversible hydrogen electrode (RHE). All of the SubPc molecules take the Cl-down adsorption configuration on Au(111) in both structures. The ordered adlayers exist in the potential range between 350 and 650 mV. The SubNc molecules adsorb on Au(111) in a less-ordered pattern than the SubPc molecules. The present work provides direct evidence for understanding the potential-controlled adsorption behaviors of SubPc and SubNc on the Au(111) surface.

Gu JY; Cui B; Chen T; Yan HJ; Wang D; Wan LJ

2013-01-01

246

Adsorption of diferrocenylacetylene on Au(111) studied by scanning tunneling microscopy.  

UK PubMed Central (United Kingdom)

Scanning tunneling microscopy images of diferrocenylacetylene (DFA) coadsorbed with benzene on Au(111) show individual and close-packed DFA molecules, either adsorbed alongside benzene or on top of a benzene monolayer. Images acquired over a range of positive and negative tip-sample bias voltages show a shift in contrast, with the acetylene linker appearing brighter than the ferrocenes at positive sample bias (where unoccupied states primarily contribute) and the reverse contrast at negative bias. Density functional theory was used to calculate the electronic structure of the gas-phase DFA molecule, and simulated images produced through two-dimensional projections of these calculations approximate the experimental images. The symmetry of both experimental and calculated molecular features for DFA rules out a cis adsorption geometry, and comparison of experiment to simulation indicates torsion around the inter-ferrocene axis between 90° and 180° (trans); the cyclopentadienyl rings are thus angled with respect to the surface.

Quardokus RC; Wasio NA; Forrest RP; Lent CS; Corcelli SA; Christie JA; Henderson KW; Kandel SA

2013-05-01

247

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

UK PubMed Central (United Kingdom)

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.

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

2012-09-01

248

Atomic force and scanning tunneling microscopy analysis of palladium and silver nanophase materials  

Energy Technology Data Exchange (ETDEWEB)

Atomic force and scanning tunneling microscopy images of nanophase palladium and silver materials taken on various length scales are presented. The samples show a conformational packing of individual nanometer-sized clusters. In the case of silver, islands of clusters are observed on micrometer length scales. The islands are very flat and separated by deep crevices. The grains (clusters) within the islands are closely packed with shapes adjusting to the neighboring grains. The islands are compact, either equiaxed or oblong in shape. Average island diameters of 200--300 nm and average grain sizes of 20--50 nm were measured. The height variations on the islands are between 5 and 15 nm. The crevices are between 200 and 400 nm deep. In the case of palladium, the clusters are more uniformly packed and do not appear to be agglomerated in islands. Palladium grain sizes typically of 15 nm were measured along with corrugations of 10 nm in the closely packed areas.

Sattler, K. (Department of Physics and Astronomy, University of Hawaii at Manoa, 2505 Correa Road, Honolulu, Hawaii 96822 (United States)); Raina, G. (Hawaii Institute of Geophysics, School of Ocean, Earth Sciences and Technology, University of Hawaii, 2525 Correa Road, Honolulu, Hawaii 96822 (United States)); Ge, M.; Venkateswaran, N.; Xhie, J. (Department of Physics and Astronomy, University of Hawaii at Manoa, 2505 Correa Road, Honolulu, Hawaii 96822 (United States)); Liao, Y.X.; Siegel, R.W. (Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439-4838 (United States))

1994-07-01

249

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

International Nuclear Information System (INIS)

[en] 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.)

1992-01-01

250

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

Energy Technology Data Exchange (ETDEWEB)

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 Au{sup 24+} 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.).

Kemmer, H.; Grafstroem, S.; Neitzert, M.; Woertge, M. (Heidelberg Univ. (Germany). Physikalisches Inst.); Neumann, R.; Trautmann, C.; Vetter, J.; Angert, N.

1992-02-01

251

Construction of a Versatile Ultra-Low Temperature Scanning Tunneling Microscope  

CERN Multimedia

We constructed a dilution-refrigerator (DR) based ultra-low temperature scanning tunneling microscope (ULT-STM) which works at temperatures down to 20 mK, in magnetic fields up to 6 T and in ultrahigh vacuum (UHV). Besides these extreme operation conditions, this STM has several unique features not available in other DR based ULT-STMs. One can load STM tips as well as samples with clean surfaces prepared in a UHV environment to an STM head keeping low temperature and UHV conditions. After then, the system can be cooled back to the base temperature within 3 hours. Due to these capabilities, it has a variety of applications not only for cleavable materials but also for almost all conducting materials. The present ULT-STM has also an exceptionally high stability in the presence of magnetic field and even during field sweep. We describe details of its design, performance and applications for low temperature physics.

Kambara, H; Niimi, Y; Fukuyama, H

2007-01-01

252

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

International Nuclear Information System (INIS)

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

1995-01-01

253

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1995-07-01

254

Imaging surface electronic structure of NiAl(110) using low-temperature scanning tunneling microscopy  

International Nuclear Information System (INIS)

The surface electronic structure of NiAl(110) is examined by means of scanning tunneling microscopy and spectroscopy at a temperature of 4 K. Topography and conductance images for a wide range of bias voltages reveal wavelike patterns around steps and defects. Fourier transforms of conductance images are used to map the surface electronic structure of NiAl(110). We interpret the patterns in the Fourier transforms in terms of surface resonances, and analyze the details of its dispersion relation E(k parallel). A comparison with density-functional-based calculations and photoemission experiments is presented, and alternative explanations for the appearance of structures in Fourier transforms of conductance images are discussed. (orig.)

2001-01-01

255

Imaging surface electronic structure of NiAl(110) using low-temperature scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

The surface electronic structure of NiAl(110) is examined by means of scanning tunneling microscopy and spectroscopy at a temperature of 4 K. Topography and conductance images for a wide range of bias voltages reveal wavelike patterns around steps and defects. Fourier transforms of conductance images are used to map the surface electronic structure of NiAl(110). We interpret the patterns in the Fourier transforms in terms of surface resonances, and analyze the details of its dispersion relation E(k {sub parallel}). A comparison with density-functional-based calculations and photoemission experiments is presented, and alternative explanations for the appearance of structures in Fourier transforms of conductance images are discussed. (orig.)

Song, Z.; Pascual, J.I.; Conrad, H.; Horn, K.; Rust, H.P. [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin (Germany)

2001-04-01

256

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

257

Scanning tunneling microscope investigation of carbon nanotubes produced by catalytic decomposition of acetylene  

Science.gov (United States)

A detailed scanning tunneling microscopy (STM) study of carbon nanotubes prepared by catalytic decomposition of acetylene over a supported transition metal catalyst is reported. Nanotubes with diameters in the 10-nm range and others with diameters as small as 1 nm were found. The mechanism of STM image formation and image deconvolution with respect to the tip shape are discussed, as well as the corrections which have to be applied when measuring by STM nanotube diameters in the ranges of 10 nm and of 1 nm, respectively. The behavior of a nanotube crossing steps on the graphite surface is analyzed. Modified height values measured on a single-wall nanotube in regions where it was subjected to strong mechanical stresses indicate changes in the electrical conductivity by several orders of magnitude. Carbon nanotubes are found to be good candidates to be used for STM tip shape characterization in the nm range.

Biró, L. P.; Lazarescu, S.; Lambin, Ph.; Thiry, P. A.; Fonseca, A.; Nagy, J. B.; Lucas, A. A.

1997-11-01

258

Study on the Structure of C-Phycocyanin in Spirulina platensis with Scanning Tunneling Microscope.  

UK PubMed Central (United Kingdom)

The C-phycocyanin (C-PC) trimmer was isolated from the blue-green alga Spirulina platensis, and scanning tunneling microscope (STM) was used to investigate its structure. High resolution STM images of C-PC were obtained. From the STM images, it could be observed that the C-PC molecules were disk-like in shape and the subunits of C-PC arranged in ring-like pattern with a channel in the center. After filter treatment, the folding of the polypeptide chains could be seen clearly. This is the first time to observe directly the topography of phycobiliprotein, and the results showed STM to be a powerful tool for the structural study of phycobiliproteins.

Zhang YZ; Shi DX; Zhou BC; Zeng CK; Pang SJ

1997-01-01

259

Study on the Structure of C-Phycocyanin in Spirulina platensis with Scanning Tunneling Microscope.  

Science.gov (United States)

The C-phycocyanin (C-PC) trimmer was isolated from the blue-green alga Spirulina platensis, and scanning tunneling microscope (STM) was used to investigate its structure. High resolution STM images of C-PC were obtained. From the STM images, it could be observed that the C-PC molecules were disk-like in shape and the subunits of C-PC arranged in ring-like pattern with a channel in the center. After filter treatment, the folding of the polypeptide chains could be seen clearly. This is the first time to observe directly the topography of phycobiliprotein, and the results showed STM to be a powerful tool for the structural study of phycobiliproteins. PMID:12215795

Zhang, Yu-Zhong; Shi, Dong-Xia; Zhou, Bai-Cheng; Zeng, Cheng-Kui; Pang, Shi-Jin

1997-01-01

260

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

International Nuclear Information System (INIS)

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

2011-01-01

 
 
 
 
261

Construction of a Dual-Tip Scanning Tunneling Microscope: a Prototype Nanotechnology Workstation.  

Science.gov (United States)

This dissertation describes the construction and performance of a dual-tip scanning tunneling microscope (STM). The microscope was built as a prototype nanotechnology workstation, a general purpose instrument designed to give a researcher the ability to investigate and manipulate nanometer scale structures. Chapter One describes the genesis and development of the concept of nanotechnology, from the atomic hypothesis of Democritus to modern developments in synthetic chemistry. Nanometer scale electronics (molecular electronics) is introduced and the state of the art in this field is described. The dual-tip scanning probe microscope is proposed as a way to address individual molecular electronic devices, a key goal in realizing nanometer scale electronic technology. Investigation of microtubules, a proposed nanometer scale intracellular biological information processing system, is also discussed. Chapter Two reviews the history and fundamental physics of STM, along with the related techniques of Field Ion Microscopy (FIM) and Ballistic Electon Emission Microscopy (BEEM). BEEM is used to introduce the physics of the dual -tip STM. Other dual-probe systems are also described. Chapter Three covers the design and construction of the dual-tip STM. Both hardware and software are described in detail. Chapter Four presents the results obtained with the dual-tip STM, including dual-tip images and noise measurements for the electronic circuitry. The last chapter, Chapter Five, contains suggested design changes for improving the performance of the dual -tip microscope and descriptions of experiments that can be performed with an improved instrument. Design and use of a nanotechnology workstation in the fields of semiconductor electronics, molecular electronics and cellular biology is discussed. Investigation of neurons grown on a silicon chip with a dual-tip STM system is proposed. Four Appendices present a noise model of the STM tunneling gap and preamplifier, describe calibration of the piezoelectric scanners that move the probe tips, and list the software that controls the system.

Voelker, Mark Alan

1993-01-01

262

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

263

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

International Nuclear Information System (INIS)

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

1979-01-01

264

Scanning tunneling microscopy study of the assembly and structure of filamentous virus M13 bound to graphite  

Science.gov (United States)

Viruses are an important class of biomaterials used for placing nano particles on inorganic substrates. To accomplish greater control over viral assembly on a substrate it is important to determine the in situ nanoscale structure of the viral protein coat. Scanning tunneling microscopy offers the unique potential for determining the structure and arrangement of the proteins of a virus adsorbed on a conducting substrate. In this work, I develop an experimental technique for isolating and studying M13 viruses that bind to graphite. Using scanning tunneling microscopy in ambient conditions I obtain the correct lateral dimension of the virus and the periodicity of its protein structure when it is bound to graphite. I also analyze the tunneling conductance fluctuations in these measurements and introduce a simple model for tunneling through an assembly of proteins to obtain an accurate estimation of the vertical dimension of a virus bound to a conducting substrate. I discuss broader implications of this scanning tunneling microscopy study for the in situ structure determination of other biomolecules.

Sharma, Prashant

2012-02-01

265

Investigation of cross-sectional area of the carpal canal by CT scanning as a factor causing carpal tunnel syndrome  

Energy Technology Data Exchange (ETDEWEB)

The cross-sectional area of the carpal tunnel in patients with carpal tunnel syndrome (CTS) and healthy controls was measured using CT scanning to investigate the relationship between the cross-sectional area and the occurrence of this syndrome. The cross-sectional area in patients with idiopathic CTS was significantly narrowed at the levels of proximal part (Pm) where scaphoid and pisiform bones were visualized and of the distal part (D/sub 1/, D/sub 2/) where the trapezium and hook of hamate were visualized, as compared with the controls, suggesting that the median nerve within the carpal tunnel is easily compressed at the level D/sub 1/. Narrowing of the cross-sectional area of the carpal tunnel can be estimated by measuring the transverse and antero-posterior diameters.

Ryo, Shoryu; Tajima, Tatsuya; Saito, Hidehiko (Niigata Univ. (Japan). School of Medicine)

1983-11-01

266

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

Science.gov (United States)

The influence of a high spin-polarized tunnel current onto the switching behavior of a superparamagnetic nanoisland on a nonmagnetic substrate is investigated by means of spin-polarized scanning tunneling microscopy. A detailed lifetime analysis allows for a quantification of the effective temperature rise of the nanoisland and the modification of the activation energy barrier for magnetization reversal, thereby using the nanoisland as a local thermometer and spin-transfer torque analyzer. Both the Joule heating and spin-transfer torque are found to scale linearly with the tunnel current. The results are compared to experiments performed on lithographically fabricated magneto-tunnel junctions, revealing a very high spin-transfer torque switching efficiency in our experiments. PMID:22107658

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

2011-10-27

267

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

UK PubMed Central (United Kingdom)

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

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

2011-10-01

268

Investigation of cross-sectional area of the carpal canal by CT scanning as a factor causing carpal tunnel syndrome  

International Nuclear Information System (INIS)

[en] The cross-sectional area of the carpal tunnel in patients with carpal tunnel syndrome (CTS) and healthy controls was measured using CT scanning to investigate the relationship between the cross-sectional area and the occurrence of this syndrome. The cross-sectional area in patients with idiopathic CTS was significantly narrowed at the levels of proximal part (Pm) where scaphoid and pisiform bones were visualized and of the distal part (D1, D2) where the trapezium and hook of hamate were visualized, as compared with the controls, suggesting that the median nerve within the carpal tunnel is easily compressed at the level D1. Narrowing of the cross-sectional area of the carpal tunnel can be estimated by measuring the transverse and antero-posterior diameters. (namekawa, k.)

1983-01-01

269

Adsorption and in situ scanning tunneling microscopy of cysteine on Au(111): Structure, energy, and tunneling contrasts.  

UK PubMed Central (United Kingdom)

The amino acid L-cysteine (Cys) adsorbs in highly ordered (3 square root of 3 x 6) R30 degrees lattices on Au(111) electrodes from 50 mM ammonium acetate, pH 4.6. We provide new high-resolution in situ scanning tunneling microscopy (STM) data for the L-Cys adlayer. The data substantiate previous data with higher resolution, now at the submolecular level, where each L-Cys molecule shows a bilobed feature. The high image resolution has warranted a quantum chemical computational effort. The present work offers a density functional study of the geometry optimized adsorption of four L-Cys forms-the molecule, the anion, the neutral radical, and its zwitterion adsorbed a-top-at the bridge and at the threefold hollow site of a planar Au(111) Au12 cluster. This model is crude but enables the inclusion of other effects, particularly the tungsten tip represented as a single or small cluster of W-atoms, and the solvation of the L-Cys surface cluster. The computational data are recast as constant current-height profiles as the most common in situ STM mode. The computations show that the approximately neutral radical, with the carboxyl group pointing toward and the amino group pointing away from the surface, gives the most stable adsorption, with little difference between the a-top and threefold sites. Attractive dipolar interactions screened by a dielectric medium stabilize around a cluster size of six L-Cys entities, as observed experimentally. The computed STM images are different for the different L-Cys forms. Both lateral and vertical dimensions of the radical accord with the observed dimensions, while those of the molecule and anion are significantly more extended. A-top L-Cys radical adsorption further gives a bilobed height profile resembling the observed images, with comparable contributions from sulfur and the amino group. L-Cys radical a-top adsorption therefore emerges as the best representation of L-Cys adsorption on Au(111).

Nazmutdinov RR; Zhang J; Zinkicheva TT; Manyurov IR; Ulstrup J

2006-08-01

270

Adsorption and in situ scanning tunneling microscopy of cysteine on Au(111): Structure, energy, and tunneling contrasts.  

Science.gov (United States)

The amino acid L-cysteine (Cys) adsorbs in highly ordered (3 square root of 3 x 6) R30 degrees lattices on Au(111) electrodes from 50 mM ammonium acetate, pH 4.6. We provide new high-resolution in situ scanning tunneling microscopy (STM) data for the L-Cys adlayer. The data substantiate previous data with higher resolution, now at the submolecular level, where each L-Cys molecule shows a bilobed feature. The high image resolution has warranted a quantum chemical computational effort. The present work offers a density functional study of the geometry optimized adsorption of four L-Cys forms-the molecule, the anion, the neutral radical, and its zwitterion adsorbed a-top-at the bridge and at the threefold hollow site of a planar Au(111) Au12 cluster. This model is crude but enables the inclusion of other effects, particularly the tungsten tip represented as a single or small cluster of W-atoms, and the solvation of the L-Cys surface cluster. The computational data are recast as constant current-height profiles as the most common in situ STM mode. The computations show that the approximately neutral radical, with the carboxyl group pointing toward and the amino group pointing away from the surface, gives the most stable adsorption, with little difference between the a-top and threefold sites. Attractive dipolar interactions screened by a dielectric medium stabilize around a cluster size of six L-Cys entities, as observed experimentally. The computed STM images are different for the different L-Cys forms. Both lateral and vertical dimensions of the radical accord with the observed dimensions, while those of the molecule and anion are significantly more extended. A-top L-Cys radical adsorption further gives a bilobed height profile resembling the observed images, with comparable contributions from sulfur and the amino group. L-Cys radical a-top adsorption therefore emerges as the best representation of L-Cys adsorption on Au(111). PMID:16922533

Nazmutdinov, Renat R; Zhang, Jingdong; Zinkicheva, Tamara T; Manyurov, Ibragim R; Ulstrup, Jens

2006-08-29

271

Fabrication of nanometer flat areas onto YBa2Cu3O7-x thin film surfaces by scanning tunneling microscope  

International Nuclear Information System (INIS)

A scanning tunneling microscope was used to mechanically ''mill'' nanometer flat areas of up to 1600 ?m2 on high temperature superconducting (HTS) films of YBa2Cu3O7-x which were originally formed by laser ablation. Flatness to a standard deviation of 2 nm in height was found to be characteristic of milled areas. It was subsequently possible to mill trenches and ditches onto these flat areas. Scanning tunneling measurements of the exposed layered structure of the milled HTS surface are also reported. Surface modifications are also possible by the application of voltage pulse to the tunneling tip. The combination of electrical pulses and milling offer a possibility of mixed electromechanical patterning of the film

1991-09-15

272

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

UK PubMed Central (United Kingdom)

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

Koepke JC; Wood JD; Estrada D; Ong ZY; He KT; Pop E; Lyding JW

2013-01-01

273

Sulfur-induced c(4×4) reconstruction of the Si(001) surface studied by scanning tunneling microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Scanning tunneling microscopy and low-energy electron diffraction have been used to study the adsorption and subsequent thermal desorption of molecular sulfur from the Si(001) surface. Room-temperature adsorption of sulfur resulted in the formation of an overlayer, displaying a high density of vacan...

Moriarty, P.; Koenders, L.; Hughes, Greg

274

Study of Scanning Tunneling Microscope control electronics. Estudio del Sistema de Control y Estabilidad en el microscopico de efecto tunel  

Energy Technology Data Exchange (ETDEWEB)

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

Oliva, A.J.; Pancarobo, M.; Denisenko, N.; Aguilar, M.; Rejon, V.; Pea, J.L. (Instituto de Ciencia de Materiales, CSIC, Universidad Autonoma de Madrid, Madrid (Spain))

1994-01-01

275

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

UK PubMed Central (United Kingdom)

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

Salerno M

2010-09-01

276

Investigation of the Tunneling Spectra in HgBr2-Intercalated Bi-2212 Single Crystals below and above Tc  

CERN Document Server

Interlayer tunneling spectroscopy measurements were performed on mesa arrays of Bi-2212 single crystals, intercalated with HgBr$_2$. Tunneling conductances were obtained over a wide temperature range to examine the spectral features, especially the behavior of the quasiparticle peaks corresponding to superconducting energy gaps (SGs). Experimental spectra showed that gap-like features are still present even for the temperatures far above the transition temperature, T$_c$. This evidence is consistent with the idea that the SG evolves into a pseudogap above T$_c$ for HgBr$_2$-intercalated Bi-2212 single crystals.

Kurter, C; Ozyuzer, L; Hinks, D G; Gray, K E

2007-01-01

277

H3PW12O40-functionalized tip for scanning tunneling microscopy.  

UK PubMed Central (United Kingdom)

Recent reports of C(60)-functionalized metal tips [Kelly, K. F., Sarkar, D., Hale, G. D., Oldenburg, S. J. & Halas, N. J. (1996) Science 273, 1371-1373] and carbon nanotube tips [Dai, H., Hafner, J. H., Rinzler, A. G., Colbert, D. T. & Smalley, R. E. (1996) Nature (London) 384, 147-151] demonstrate the potential of controlling the chemical identity and geometric structure of tip atoms in scanning tunneling microscopy (STM). This work reports the performance of a heteropolyacid (HPA)-functionalized Pt/Ir tip, which was formulated by contacting a mechanically formed tip with a solution of H(3)PW(12)O(40) molecules. Attachment of an H(3)PW(12)O(40) molecule on the metal tip was confirmed by observing the characteristic negative differential resistance (NDR) behavior of H(3)PW(12)O(40) in tunneling spectroscopy. Atomic resolution images of bare graphite as well as of H(6)P(2)W(18)O(62) HPA monolayers on graphite were successfully obtained with a Pt/Ir-HPA tip. In the H(3)PW(12)O(40) molecule on a metal tip, it is likely that a terminal oxygen of WO (an oxygen species projecting outward from the pseudospherical H(3)PW(12)O(40) molecule) serves as an atomically sharp and stable tip. Additionally, superimposed superperiodic structures commensurate with the underlying graphite lattice were regularly observed with the modified tips. This result suggests that tip functionalization with these metal oxide molecules may enhance resolution in a fashion analogous to functionalization with C(60).

Song IK; Kitchin JR; Barteau MA

2002-04-01

278

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

UK PubMed Central (United Kingdom)

Scanning tunnelling spectroscopy (STS) was used to study the Luttinger liquid behaviour of the purple bronze Li(0.9)Mo(6)O(17) in the temperature range 5 K < T < 300 K. In the entire temperature range the suppression of the density of states at the Fermi energy can be fitted very well by a model describing the tunnelling into a Luttinger liquid at ambient temperature. The power-law exponent extracted from these fits reveals a significant increase above 200 K. It changes from ? = 0.6 at low temperature to ? = 1.0 at room temperature.

Podlich T; Klinke M; Nansseu B; Waelsch M; Bienert R; He J; Jin R; Mandrus D; Matzdorf R

2013-01-01

279

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

Science.gov (United States)

Scanning tunnelling spectroscopy (STS) was used to study the Luttinger liquid behaviour of the purple bronze Li(0.9)Mo(6)O(17) in the temperature range 5 K < T < 300 K. In the entire temperature range the suppression of the density of states at the Fermi energy can be fitted very well by a model describing the tunnelling into a Luttinger liquid at ambient temperature. The power-law exponent extracted from these fits reveals a significant increase above 200 K. It changes from ? = 0.6 at low temperature to ? = 1.0 at room temperature. PMID:23221173

Podlich, T; Klinke, M; Nansseu, B; Waelsch, M; Bienert, R; He, J; Jin, R; Mandrus, D; Matzdorf, R

2012-12-05

280

Break-junction tunneling spectra of MgB2: Influence of boron quality  

International Nuclear Information System (INIS)

Tunneling spectra of a superconductor-insulator-superconductor (SIS) junction formed by the break-junction technique have been carried out for two different boron quality MgB2 samples. One is a polycrystalline MgB2 pellet (RRR ? 4) and the other is a high purity MgB2 wire (RRR ? 25) of approximately 150 ?m in diameter. Both samples exhibit a multiple-gap feature, which can be expressed by the correlated two-gap model. From the conductance fitting at 4.2 K, the pellet gap parameters are ? S = 2.2 ± 0.3 meV, ? M = 6.0 ± 1.5 meV and ? L = 10 meV, whereas the only clear and very reproducible gap in the wires is the small gap at ? S = 2.5 ± 0.1 meV. The wires show almost constant values for the fitting parameters of the two-gap model, in contrast with the pellets that show a large variation.

2005-10-01

 
 
 
 
281

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

282

Scanning tunnelling microscopy and spectroscopy of ultra-flat graphene on hexagonal boron nitride.  

UK PubMed Central (United Kingdom)

Graphene has demonstrated great promise for future electronics technology as well as fundamental physics applications because of its linear energy-momentum dispersion relations which cross at the Dirac point. However, accessing the physics of the low-density region at the Dirac point has been difficult because of disorder that leaves the graphene with local microscopic electron and hole puddles. Efforts have been made to reduce the disorder by suspending graphene, leading to fabrication challenges and delicate devices which make local spectroscopic measurements difficult. Recently, it has been shown that placing graphene on hexagonal boron nitride (hBN) yields improved device performance. Here we use scanning tunnelling microscopy to show that graphene conforms to hBN, as evidenced by the presence of Moiré patterns. However, contrary to predictions, this conformation does not lead to a sizeable band gap because of the misalignment of the lattices. Moreover, local spectroscopy measurements demonstrate that the electron-hole charge fluctuations are reduced by two orders of magnitude as compared with those on silicon oxide. This leads to charge fluctuations that are as small as in suspended graphene, opening up Dirac point physics to more diverse experiments.

Xue J; Sanchez-Yamagishi J; Bulmash D; Jacquod P; Deshpande A; Watanabe K; Taniguchi T; Jarillo-Herrero P; LeRoy BJ

2011-04-01

283

Scanning tunnelling microscopy and spectroscopy of ultra-flat graphene on hexagonal boron nitride.  

Science.gov (United States)

Graphene has demonstrated great promise for future electronics technology as well as fundamental physics applications because of its linear energy-momentum dispersion relations which cross at the Dirac point. However, accessing the physics of the low-density region at the Dirac point has been difficult because of disorder that leaves the graphene with local microscopic electron and hole puddles. Efforts have been made to reduce the disorder by suspending graphene, leading to fabrication challenges and delicate devices which make local spectroscopic measurements difficult. Recently, it has been shown that placing graphene on hexagonal boron nitride (hBN) yields improved device performance. Here we use scanning tunnelling microscopy to show that graphene conforms to hBN, as evidenced by the presence of Moiré patterns. However, contrary to predictions, this conformation does not lead to a sizeable band gap because of the misalignment of the lattices. Moreover, local spectroscopy measurements demonstrate that the electron-hole charge fluctuations are reduced by two orders of magnitude as compared with those on silicon oxide. This leads to charge fluctuations that are as small as in suspended graphene, opening up Dirac point physics to more diverse experiments. PMID:21317900

Xue, Jiamin; Sanchez-Yamagishi, Javier; Bulmash, Danny; Jacquod, Philippe; Deshpande, Aparna; Watanabe, K; Taniguchi, T; Jarillo-Herrero, Pablo; LeRoy, Brian J

2011-02-13

284

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

285

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

International Nuclear Information System (INIS)

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

2008-02-13

286

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

International Nuclear Information System (INIS)

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

1991-01-01

287

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

2013-09-18

288

Scanning tunneling microscopy investigation of self-assembled poly(3-hexylthiophene) monolayer  

Science.gov (United States)

Poly(3-hexylthiophene) (P3HT) monolayer has been investigated by scanning tunneling microscopy (STM). The monolayer was dominated by three kinds of ordered structure (I, II, and III), where the thiophene main chains lied parallel to one another, but high resolution STM images revealed that the arrangement of the hexyl side chains was different. In structure I, the hexyl side chains tilted at ~60° with respect to the main chain, and the interchain distance (distance between two parallel neighboring backbones) was ~1.41 nm. In structure II, the interchain distance was significantly larger at ~1.52 nm, and the hexyl side chains were liquid-like. Structure III exhibited similar interchain distance as structure II, but the hexyl side chains were perpendicular to the main chain and were interdigitated. In addition to these ordered domains, individual poly(3-hexylthiophene) chains in various special configurations were observed, and their unfolding into more stable structures was tracked by dynamic STM, which provides evidence that P3HT is a relatively flexible polymer.

Ma, Xiaojing; Guo, Yan; Wang, Tian; Su, Zhaohui

2013-07-01

289

Scanning tunneling microscope-quartz crystal microbalance study of temperature gradients at an asperity contact  

Science.gov (United States)

Investigations of atomic-scale friction frequently involve setups where a tip and substrate are initially at different temperatures. The temperature of the sliding interface upon contact has thus become a topic of interest. A method for detecting initial tip-sample temperature differences at an asperity contact is described, which consists of a scanning tunneling microscope (STM) tip in contact with the surface electrode of a quartz crystal microbalance (QCM). The technique makes use of the fact that a QCM is extremely sensitive to abrupt changes in temperature. In order to demonstrate the technique's capabilities, QCM frequency shifts were recorded for varying initial tip-substrate temperature differences as an STM tip was brought into and out of contact. The results are interpreted within the context of a recent model for thermal heat conduction at an asperity contact, and it is concluded that the transient frequency response is attributable to small changes in temperature close to the region of contact rather than a change in the overall temperature of the QCM itself. For the assumed model parameters, the results moreover reveal substantial temperature discontinuities at the boundary between the tip and the sample, for example, on the order of 10-15 °C for initial temperature differences of 20 °C.

Pan, L.; Krim, J.

2013-01-01

290

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

291

Characterization of ?-domains in C-terminal fragments of TDP-43 by scanning tunneling microscopy.  

UK PubMed Central (United Kingdom)

The TAR DNA-binding protein 43 (TDP-43) has been identified as a critical player in a range of neurodegenerative diseases, including frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS). Recent discoveries demonstrate the important role of carboxyl-terminal fragments of TDP-43 in its proteinopathy. Herein, we report the characterization of ?-domains in the C-terminal fragments of TDP-43 using scanning tunneling microscopy (STM). Careful comparison of the wild-type TDP-43 (Wt) and the three mutant TDP-43 peptides: an ALS-related mutant peptide: phosphorylated A315T mutant TDP-43 (A315T(p)) and two model peptides: A315T mutant TDP-43 (A315T), A315E mutant TDP-43 (A315E) reveals that A315T(p) has a longer core region of the ?-domain than Wt. A315E possesses the longest core region of the ?-domain and A315T(p) mutant TDP-43 has the second longest core region of the ?-domain. The core regions of the ?-domains for A315T and Wt TDP-43 have the same length. This observation provides a supportive evidence of a higher tendency in beta-sheet formation of A315T(p) containing TDP-43 fragment, and structural mechanism for the higher cytotoxicity and accelerated fibril formation of the A315T(p) mutation-containing TDP-43 peptide as compared with Wt TDP-43.

Xu M; Zhu L; Liu J; Yang Y; Wu JY; Wang C

2013-01-01

292

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

DEFF Research Database (Denmark)

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

Merte, Lindsay Richard; Grabow, Lars C.

2011-01-01

293

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

294

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

UK PubMed Central (United Kingdom)

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., F(0), F(+), F(2+) 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 F(2+)-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.

König T; Simon GH; Heinke L; Lichtenstein L; Heyde M

2011-01-01

295

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; Georg H. Simon; Lars Heinke; Leonid Lichtenstein; Markus Heyde

2011-01-01

296

Scanning tunneling microscope-quartz crystal microbalance study of temperature gradients at an asperity contact.  

UK PubMed Central (United Kingdom)

Investigations of atomic-scale friction frequently involve setups where a tip and substrate are initially at different temperatures. The temperature of the sliding interface upon contact has thus become a topic of interest. A method for detecting initial tip-sample temperature differences at an asperity contact is described, which consists of a scanning tunneling microscope (STM) tip in contact with the surface electrode of a quartz crystal microbalance (QCM). The technique makes use of the fact that a QCM is extremely sensitive to abrupt changes in temperature. In order to demonstrate the technique's capabilities, QCM frequency shifts were recorded for varying initial tip-substrate temperature differences as an STM tip was brought into and out of contact. The results are interpreted within the context of a recent model for thermal heat conduction at an asperity contact, and it is concluded that the transient frequency response is attributable to small changes in temperature close to the region of contact rather than a change in the overall temperature of the QCM itself. For the assumed model parameters, the results moreover reveal substantial temperature discontinuities at the boundary between the tip and the sample, for example, on the order of 10-15 °C for initial temperature differences of 20 °C.

Pan L; Krim J

2013-01-01

297

Fabrication and investigation of nanostructures on transition metal dichalcogenide surfaces using a scanning tunneling microscope.  

Science.gov (United States)

Nanometer-scale holes have been fabricated on the surfaces of the semiconducting transition metal dichalcogenides (TMDCs) molybdenum ditelluride (MoTe2) and molybdenum disulfide (MoS2) by applying voltage pulses from the tip of a scanning tunneling microscope (STM) operating in ultrahigh vacuum (UHV). It was found that the tip geometry (tip shape and sharpness) influences the formation and structure of the atomic-scale nanostructures. Threshold voltage ranges for the surface modification of MoTe2 (3.0 +/- 0.3 V) and MoS2 (3.4 +/- 0.3 V) were determined. Negative sample voltage pulses applied to a p-type MoTe2 surface produced much larger and deeper nanometer-scale holes when compared with those produced by positive voltage pulses. The existence of threshold voltages and the pulse polarity dependence of nanostructure fabrication suggests that an electric field evaporation mechanism is applicable. Support for this mechanism was obtained by nanostructuring metallic TMDC NbSe2, where both the produced features and the threshold voltages (3.0 +/- 0.3 V) were similar for both positive and negative voltage pulses. PMID:16732661

Park, J B; Jaeckel, B; Parkinson, B A

2006-06-01

298

Fabrication and investigation of nanostructures on transition metal dichalcogenide surfaces using a scanning tunneling microscope.  

UK PubMed Central (United Kingdom)

Nanometer-scale holes have been fabricated on the surfaces of the semiconducting transition metal dichalcogenides (TMDCs) molybdenum ditelluride (MoTe2) and molybdenum disulfide (MoS2) by applying voltage pulses from the tip of a scanning tunneling microscope (STM) operating in ultrahigh vacuum (UHV). It was found that the tip geometry (tip shape and sharpness) influences the formation and structure of the atomic-scale nanostructures. Threshold voltage ranges for the surface modification of MoTe2 (3.0 +/- 0.3 V) and MoS2 (3.4 +/- 0.3 V) were determined. Negative sample voltage pulses applied to a p-type MoTe2 surface produced much larger and deeper nanometer-scale holes when compared with those produced by positive voltage pulses. The existence of threshold voltages and the pulse polarity dependence of nanostructure fabrication suggests that an electric field evaporation mechanism is applicable. Support for this mechanism was obtained by nanostructuring metallic TMDC NbSe2, where both the produced features and the threshold voltages (3.0 +/- 0.3 V) were similar for both positive and negative voltage pulses.

Park JB; Jaeckel B; Parkinson BA

2006-06-01

299

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

300

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

Science.gov (United States)

Experimental data and theoretical notions are presented for 6-[1'-(6-mercapto-hexyl)-[4,4']bipyridinium]-hexane-1-thiol iodide (6V6) "wired" between a gold electrode surface and tip in an in situ scanning tunneling microscopy configuration. The viologen group can be used to "gate" charge transport across the molecular bridge through control of the electrochemical potential and consequently the redox state of the viologen moiety. This gating is theoretically considered within the framework of superexchange and coherent two-step notions for charge transport. It is shown here that the absence of a maximum in the Itunneling versus electrode potential relationship can be fitted by a "soft" gating concept. This arises from large configurational fluctuations of the molecular bridge linked to the gold contacts by flexible chains. This view is incorporated in a formalism that is well-suited for data analysis and reproduces in all important respects the 6V6 data for physically sound values of the appropriate parameters. This study demonstrates that fluctuations of isolated configurationally "soft" molecules can dominate charge transport patterns and that theoretical frameworks for compact monolayers may not be directly applied under such circumstances. PMID:17497912

Haiss, W; Albrecht, T; van Zalinge, H; Higgins, S J; Bethell, D; Höbenreich, H; Schiffrin, D J; Nichols, R J; Kuznetsov, A M; Zhang, J; Chi, Q; Ulstrup, J

2007-05-12

 
 
 
 
301

Voltammetry and in situ scanning tunneling microscopy of cytochrome C nitrite reductase on Au(111) electrodes.  

Science.gov (United States)

Escherichia coli cytochrome c nitrite reductase (NrfA) catalyzes the six-electron reduction of nitrite to perform an important role in the biogeochemical cycling of nitrogen. Here we describe NrfA adsorption on single-crystal Au(111) electrodes as an electrocatalytically active film in which the enzyme undergoes direct electron exchange with the electrode. The adsorbed NrfA has been imaged to molecular resolution by in situ scanning tunneling microscopy (in situ STM) under full electrochemical potential control and under conditions where the enzyme is electrocatalytically active. Details of the density and orientational distribution of NrfA molecules are disclosed. The submonolayer coverage resolved by in situ STM is readily reconciled with the failure to detect nonturnover signals in cyclic voltammetry of the NrfA films. The molecular structures show a range of lateral dimensions. These are suggestive of a distribution of orientations that could account for the otherwise anomalously low turnover number calculated for the total population of adsorbed NrfA molecules when compared with that determined for solutions of NrfA. Thus, comparison of the voltammetric signals and in situ STM images offers a direct approach to correlate electrocatalytic and molecular properties of the protein layer, a long-standing issue in protein film voltammetry. PMID:16935959

Gwyer, James D; Zhang, Jingdong; Butt, Julea N; Ulstrup, Jens

2006-08-25

302

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

International Nuclear Information System (INIS)

The oxidation of graphene layer on Ru(0 0 0 1) has been investigated by means of scanning tunneling microscopy. Graphene overlayer can be formed by decomposing ethyne on Ru(0 0 0 1) at a temperature of about 1000 K. The lattice mismatch between the graphene overlayer and the substrate causes a moire pattern with a superstructure in a periodicity of about 30 A. The oxidation of graphene/Ru(0 0 0 1) was performed by exposure the sample to O2 gas at 823 K. The results showed that, at the initial stage, the oxygen intercalation between the graphene and the Ru(0 0 0 1) substrate takes place at step edges, and extends on the lower steps. The oxygen intercalation decouples the graphene layer from the Ru(0 0 0 1) substrate. More oxygen intercalation yields wrinkled bumps on the graphene surface. The oxidation of graphene, or the removal of carbon atoms can be attributed to a process of the combination of the carbon atoms with atomic oxygen to form volatile reaction products. Finally, the Ru(0 0 0 1)-(2 x 1)O phase was observed after the graphene layer is fully removed by oxidation.

2010-10-15

303

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1994-07-01

304

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

International Nuclear Information System (INIS)

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

1994-01-01

305

Visualization of atomic processes on ruthenium dioxide using scanning tunneling microscopy.  

UK PubMed Central (United Kingdom)

The visualization of surface reactions on the atomic scale provides direct insight into the microscopic reaction steps taking place in a catalytic reaction at a (model) catalyst's surface. Employing the technique of scanning tunneling microscopy (STM), we investigated the CO oxidation reaction over the RuO2(110) and RuO2(100) surfaces. For both surfaces the protruding bridging O atoms are imaged in STM as bright features. The reaction mechanism is identical on both orientations of RuO2. CO molecules adsorb on the undercoordinated surface Ru atoms from where they recombine with undercoordinated O atoms to form CO2 at the oxide surface. In contrast to the RuO2(110) surface, the RuO2(100) surface stabilizes also a catalytically inactive c(2 x 2) surface phase onto which CO is not able to adsorb above 100 K. We argue that this inactive RuO2(100)-c(2 x 2) phase may play an important role in the deactivation of RuO2 catalysts in the electrochemical Cl2 evolution and other heterogeneous reactions.

Over H; Knapp M; Lundgren E; Seitsonen AP; Schmid M; Varga P

2004-02-01

306

Core-state manipulation of single Fe impurities in GaAs with a scanning tunneling microscope  

Science.gov (United States)

We demonstrate that a scanning tunneling microscope tip can be used to manipulate the tightly bound core (d-electron) state of single Fe ions embedded in GaAs. Increasing tip-sample voltage removes one d electron from the core of a single Fe, changing the dopant from the (Fe2+)- ionized acceptor state to the (Fe3+)0 isoelectronic state, which alters the spin moment and dramatically modifies the measured local electronic contrast in topographic maps of the surface. Evidence of internal transitions among the d states of the Fe core is also seen in topographic maps where dark anisotropic features emerge from the interference between two paths: the direct tip-sample tunneling and tunneling which excites a d-state core exciton of the Fe dopant.

Bocquel, J.; Kortan, V. R.; ?ahin, C.; Campion, R. P.; Gallagher, B. L.; Flatté, M. E.; Koenraad, P. M.

2013-02-01

307

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

308

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

309

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

Science.gov (United States)

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

Kline, Jeffrey Scott

310

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2011-12-01

311

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

Science.gov (United States)

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

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

2013-03-01

312

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

International Nuclear Information System (INIS)

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

2012-06-01

313

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

314

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

International Nuclear Information System (INIS)

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

2009-01-01

315

Scanning tunneling microscopy of charge density wave structure in 1T- TaS{sub 2}  

Energy Technology Data Exchange (ETDEWEB)

I have used a scanning tunneling microscope (STM) to image simultaneously the atomic lattice and the charge density wave (CDW) superstructure in tantalum disulfide (1T-TaS{sub 2}) over the temperature range of 370-77K. In the lowest temperature (commensurate) phase, present below 180K, the CDW is at an angle of 13.9{degrees} relative to the lattice and is uniformly commensurate. In the incommensurate phase, present above 353K, the CDW is aligned with the lattice. 1T-TaS{sub 2} exhibits two other phases; the triclinic (T) phase which is present between 223K and 283K upon warming the sample, and the nearly-commensurate (NC) phase which is present between 353K and 180K upon cooling the sample and between 283K and 353K upon warming the sample. In both of these phases, discommensurate models where the CDW is arranged in small commensurate domains have been proposed. In the NC phase the CDW is rotated between 10{degrees} and 12.5{degrees} relative to the atomic lattice. Such a rotated CDW would create an interference pattern with the underlying atomic lattice regardless of the existence of a true domain superstructure. Previous work on 1T-TaS{sub 2} has not adequately accounted for the possibility of this moire pattern. However, around each fundamental CDW peak in the Fourier transform of the real space STM images, several satellite spots are visible, which conclusively prove the existence of domains in the NC phase.

Thomson, R.E.

1991-11-01

316

Scanning tunneling microscopy of charge density wave structure in 1T- TaS sub 2  

Energy Technology Data Exchange (ETDEWEB)

I have used a scanning tunneling microscope (STM) to image simultaneously the atomic lattice and the charge density wave (CDW) superstructure in tantalum disulfide (1T-TaS{sub 2}) over the temperature range of 370-77K. In the lowest temperature (commensurate) phase, present below 180K, the CDW is at an angle of 13.9{degrees} relative to the lattice and is uniformly commensurate. In the incommensurate phase, present above 353K, the CDW is aligned with the lattice. 1T-TaS{sub 2} exhibits two other phases; the triclinic (T) phase which is present between 223K and 283K upon warming the sample, and the nearly-commensurate (NC) phase which is present between 353K and 180K upon cooling the sample and between 283K and 353K upon warming the sample. In both of these phases, discommensurate models where the CDW is arranged in small commensurate domains have been proposed. In the NC phase the CDW is rotated between 10{degrees} and 12.5{degrees} relative to the atomic lattice. Such a rotated CDW would create an interference pattern with the underlying atomic lattice regardless of the existence of a true domain superstructure. Previous work on 1T-TaS{sub 2} has not adequately accounted for the possibility of this moire pattern. However, around each fundamental CDW peak in the Fourier transform of the real space STM images, several satellite spots are visible, which conclusively prove the existence of domains in the NC phase.

Thomson, R.E.

1991-11-01

317

Submonolayer growth of Pd on Cu(111) studied by scanning tunneling microscopy  

DEFF Research Database (Denmark)

The growth mode of sub-monolayer amounts of Pd on Cu(111) in the temperature range - 80-300 degrees C has been investigated by scanning tunneling microscopy (STM), Rutherford backscattering spectroscopy (RBS) and Auger electron spectroscopy (AES). Below approximate to 100 degrees C, the Pd induced phase nucleates at ascending steps in fingered brims and, on large terraces, in fingered islands. The lack of order suggests that the brims and islands are a disordered alloy formed by exchange between Pd and Cu from the layer underneath. For temperatures exceeding approximate to 160 degrees C, Cu is dug out from the surface in extended, monolayer deep pits, and concurrently, the brims and islands increase in height by one layer. High-resolution STM images of brims and islands in this phase are interpreted as evidence for Cu capping. For Pd evaporation at temperatures of 220-300 degrees C, the surface is characterized by the appearance of individual Pd atoms substituted into the first layer and the presence of subsurface Pd. A short-range order that excludes the population of nearest-neighbour, in-plane sites is revealed by pair-correlation analysis. The Pd atoms form bands in the upper terrace next to steps. These bands are surprisingly stable against further diffusion, possibly due to an attractive interaction with second- and third-nearest (in-plane) neighbours and with subsurface Pd. The lack of any ordering is explained, based on a calculation of the surface energy. Once the population of nearest-neighbour sites is excluded, there is practically no energy gain by ordering. (C) 1998 Elsevier Science B.V. All rights reserved.

Lægsgaard, E.; Ruban, Andrei

1998-01-01

318

Charge-Dependent Atomic-Scale Structures of High-Index and (110) Gold Electrode Surfaces as Revealed by Scanning Tunneling Microscopy.  

Science.gov (United States)

The atomic and nanoscale structures of high-index gold surfaces in aqueous perchloric acid electrolyte as revealed by in-situ scanning tunneling microscopy (STM) under electrode potential control are reported with the objective of ascertaining systematica...

X. Gao G. J. Edens A. Hamelin M. J. Weaver

1994-01-01

319

First principles theory of inelastic currents in a scanning tunneling microscope  

CERN Multimedia

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

320

An approach to long-range electron transfer mechanisms in metalloproteins: in situ scanning tunneling microscopy with submolecular resolution.  

Science.gov (United States)

In situ scanning tunneling microscopy (STM) of redox molecules, in aqueous solution, shows interesting analogies and differences compared with interfacial electrochemical electron transfer (ET) and ET in homogeneous solution. This is because the redox level represents a deep indentation in the tunnel barrier, with possible temporary electronic population. Particular perspectives are that both the bias voltage and the overvoltage relative to a reference electrode can be controlled, reflected in spectroscopic features when the potential variation brings the redox level to cross the Fermi levels of the substrate and tip. The blue copper protein azurin adsorbs on gold(111) via a surface disulfide group. Well resolved in situ STM images show arrays of molecules on the triangular gold(111) terraces. This points to the feasibility of in situ STM of redox metalloproteins directly in their natural aqueous medium. Each structure also shows a central brighter contrast in the constant current mode, indicative of 2- to 4-fold current enhancement compared with the peripheral parts. This supports the notion of tunneling via the redox level of the copper atom and of in situ STM as a new approach to long-range electron tunneling in metalloproteins. PMID:9990032

Friis, E P; Andersen, J E; Kharkats, Y I; Kuznetsov, A M; Nichols, R J; Zhang, J D; Ulstrup, J

1999-02-16

 
 
 
 
321

Characterization and tunneling conductance spectra of N,N'-bis (9H-fluoren-9-ylidene)benzene-1,4-diamine thin films on graphite  

International Nuclear Information System (INIS)

N,N'-bis(9H-fluoren-9-ylidene)benzene-1,4-diamine was synthesized via the acetic acid-assisted Schiff base reaction between 9-fluorenone and p-phenylenediamine. The thin films were deposited from solution and characterized by contact angle measurements (CAM), X-ray photoelectron spectroscopy (XPS) and tunneling conductance spectroscopy (TCS). The tunneling conductance spectra, related to the potential and distance between the tip and substrate, were acquired at different tip-substrate separations and depicted significant trend under the action of electric field. Systematic analysis shows more information about electron transport through medium layers. The electric field plays an important role in tunneling conductance spectra. The tunneling conductance spectra data indicate the electric field dependence of electron transport.

2010-06-01

322

A review and outlook for an anomaly of scanning tunnelling microscopy (STM): superlattices on graphite  

International Nuclear Information System (INIS)

[en] Since its invention in 1981, scanning tunnelling microscopy (STM) is well-known for its supreme imaging resolution enabling one to observe atomic-scale structures, which has led to the flourishing of nanoscience. As successful as it is, there still remain phenomena which are observed using STM but are beyond our understanding. Graphite is one of the surfaces which have been most extensively studied using STM. However, there are a number of unusual properties of graphite surfaces. First reported in the 1980s, superlattices on graphite have since been observed many times and by many groups, but as yet our understanding of this phenomenon is quite limited. Most of the observed superlattice phenomena are widely believed to be the result of a Moire rotation pattern, arising from the misorientation between two graphite layers, as verified experimentally. A Moire pattern is a lattice with larger periodicity resulting from the overlap of two lattices with smaller periodicities. As graphite layers are composed of hexagonal lattices with a periodicity of 0.246 nm, as observed using STM, when there are misoriented graphite layers overlapping each other, a Moire pattern with larger periodicity, depending on the misorientation angle, will be produced and appear as a superperiodic hexagonal structure on top of the graphite atomic lattice of the topmost surface layer. It is important to study graphite superlattices because, firstly, knowledge of this phenomenon will enable us to properly interpret STM images; secondly, it helps us to understand the correlation between electronic structures and atomic-structure rearrangement of graphite which is of tremendous aid for engineering material properties; thirdly, and perhaps most importantly, the observation of the phenomenon exhibits the capability of STM to produce images indicating the nature of internal defects which are below the surface. Over recent years, experimental and modelling techniques have been developed to study this anomalous regime of STM; however, there is a lack of a systematic classification of this scattered information. This review article thus serves the purpose of organizing all these results so as to enable a more comprehensive understanding of this phenomenon. We review the discovery of graphite superlattices, the observation of the associated properties, and the research efforts on this subject. An effort is made to envision the future experimental and theoretical research possibilities to unveil the mystery of this anomaly of STM. Applications of graphite superlattices are also proposed. (topical review)

2005-11-07

323

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

DEFF Research Database (Denmark)

We have used L-Cysteine (Cys) as a model system to study the surface electronic structures of single molecules at the submolecular level in aqueous buffer solution by a combination of electrochemical scanning tunneling microscopy (in situ STM), electrochemistry including voltammetry and chronocoulometry, and density functional theory (DFT) computations. Cys molecules were assembled on single-crystal Au(110) surfaces to form a highly ordered monolayer with a periodic lattice structure of c(2 x 2) in which each unit contains two molecules; this conclusion is confirmed by the results of calculations based on a slab model for the metal surface. The ordered monolayer offers a platform for submolecular scale electronic mapping that is an issue of fundamental interest but remains a challenge in STM imaging science and surface chemistry. Single Cys molecules were mapped as three electronic subunits contributed mainly from three chemical moieties: thiol (-SH), carboxylic (-COOH), and amine (-NH2) groups. The contrastsof the three subunits depend on the environment (e.g., pH), which affects the electronic structure of adsorbed species. From the DFT computations focused on single molecules, rational analysis of the electronic structures is achieved to delineate the main factors that determine electronic contrasts in the STM images. These factors include the molecular orientation, the chemical nature of the elements or groups in the molecule, and the interaction of the elements with the substrate and tip. The computational images recast as constant-current-height profiles show that the most favorable molecular orientation is the adsorption of cysteine as a radical in zwitterionic form located on the bridge between the Au(I 10) atomic rows and with the amine and carboxyl group toward the solution bulk. The correlation between physical location and electronic contrast of the adsorbed molecules was also revealed by the computational data. The present study shows that cysteine packing in the adlayer on Au(110) from the liquid environment is in contrast to that from the ultrahigh-vacuum environment, suggesting solvent plays a role during molecular assembly.

Zhang, Jingdong; Chi, Qijin

2009-01-01

324

Scanning tunneling microscopy and spectroscopy at low temperatures of the (110) surface of Te doped GaAs single crystals  

CERN Multimedia

We have performed voltage dependent imaging and spatially resolved spectroscopy on the (110) surface of Te doped GaAs single crystals with a low temperature scanning tunneling microscope (STM). A large fraction of the observed defects are identified as Te dopant atoms which can be observed down to the fifth subsurface layer. For negative sample voltages, the dopant atoms are surrounded by Friedel charge density oscillations. Spatially resolved spectroscopy above the dopant atoms and above defect free areas of the GaAs (110) surface reveals the presence of conductance peaks inside the semiconductor band gap. The appearance of the peaks can be linked to charges residing on states which are localized within the tunnel junction area. We show that these localized states can be present on the doped GaAs surface as well as at the STM tip apex.

Depuydt, A; Maslova, N S; Panov, V I; Savinov, S V; Arseev, P I

1999-01-01

325

Layer-by-layer nanometer scale etching of two-dimensional substrates using the scanning tunneling microscope  

Energy Technology Data Exchange (ETDEWEB)

The scanning tunneling microscope can be used to sequentially etch single molecular layers from the surface of two-dimensional materials (i.e., SnSe{sub 2}, TiSe{sub 2}, and NbSe{sub 2}). Etching occurs by the nucleation and growth of holes in the region of the sample rastered by the tip under normal conditions of tunneling bias and current. In the case of etching NbSe{sub 2}, triangular etch pits are formed in the initial etching stages. The mechanism for the etching process is unknown at this point although four reasonable mechanisms are proposed. Several submicron complex structures have been prepared as well as a structure as small as 25 x 25 x 1.2 nm.

Parkinson, B. (E.I. DuPont de Nemours and Co., Wilmington, DE (USA))

1990-10-10

326

Layer-by-layer nanometer scale etching of two-dimensional substrates using the scanning tunneling microscope  

International Nuclear Information System (INIS)

The scanning tunneling microscope can be used to sequentially etch single molecular layers from the surface of two-dimensional materials (i.e., SnSe2, TiSe2, and NbSe2). Etching occurs by the nucleation and growth of holes in the region of the sample rastered by the tip under normal conditions of tunneling bias and current. In the case of etching NbSe2, triangular etch pits are formed in the initial etching stages. The mechanism for the etching process is unknown at this point although four reasonable mechanisms are proposed. Several submicron complex structures have been prepared as well as a structure as small as 25 x 25 x 1.2 nm.

1990-01-01

327

Energy gap evolution in the tunneling spectra of Bi2Sr2CaCu2O8+d  

CERN Document Server

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

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

2002-01-01

328

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

International Nuclear Information System (INIS)

[en] In this work the development and the construction of a scanning tunneling microscope (STM) are described, which is also able to measure relatively rough surfaces. Rough surfaces are considered to have an elevation of the gradient of 45o and more. Such measurements pose special requirements for the construction and especially for the signal processing and control of the STM. For the reconstruction of the sample surface by the raw data delivered by the STM the knowledge about the exact behavior of the STM is essential. For this reason the identification of the individual components is very important. Especially the mechanical behavior of the probe head which positions the sensor tip over the sample is a matter of particular interest. To calculate the exact position of the sensor tip a mechanical model is introduced. The unknown parameters of this model are determined using a laser vibrometer. Because of cost and space limitations the mechanical deflections of the piezoelectric actuators of the probe head aren't checked by range sensors. So an identification of the piezoelectric actuators is required. In particular, the hysteresis behavior of piezoelectric transducers represents a major challenge. Using the mathematical hysteresis model of Coleman and Hodgdon succeeds in solving this problem. To carry out an effective control, the behavior of the STM is modeled in a simulation. Using this model, the design of a fast controller is described. The controller improves the dynamic behavior of the STM and allows short measurement periods. The work includes detailed descriptions of the mechanical setup and electronics of the STM in the form of working drawings, schematics and PCB layouts. In addition instructions for two different methods of tip preparation are given. The presented methods and solutions are not limited to the STM, but can be directly transferred to other varieties of scanning probe microscopes. (author)[de] Die vorliegende Arbeit beschaeftigt sich mit der Entwicklung und dem Aufbau eines Rastertunnelmikroskops (RTM), welches in der Lage ist auch relativ raue Oberflaechen zu vermessen. Mit rau sind hier Oberflaechen mit einer Elevation des Gradienten von 45o und mehr gemeint. Solche Aufnahmen stellen spezielle Anforderungen an den Aufbau und vor allem an die Signalverarbeitung bzw. Regelung des RTMs. Um aus den Rohdaten, welche das RTM liefert, die tatsaechliche Form der Probenoberflaeche zu rekonstruieren ist das Wissen ueber das genaue Verhalten des RTMs unerlaesslich. Aus diesem Grund wird auf die Identifizierung der einzelnen Komponenten großer Wert gelegt. Erwaehnenswert ist hier vor allem das mechanische Verhalten des Tastkopfes, mit welchem die Sensorspitze ueber der Probe positioniert wird. Um die genaue Position der Spitze, welche die Topographie der Probenoberflaeche abrastert, zu berechnen, wird ein mechanisches Modell verwendet. Die unbekannten Parameter dieses Modells werden mithilfe einer Laservibrometer-Messung bestimmt. Da die mechanischen Auslenkungen der Piezoaktoren des Tastkopfes aus Kosten- und Platzgruenden nicht ueber Sensoren kontrolliert werden, ist eine vorhergehende Identifikation der Piezoaktoren erforderlich. Vor allem das Hysterese-Verhalten piezoelektrischer Wandler stellt eine große Herausforderung dar. Durch die Verwendung des mathematischen Hysteresemodells von Coleman und Hodgdon gelingt es dieses Problem zu loesen. Um eine effektive Regelung der Spitzenposition durchzufuehren, wird das Verhalten des RTMs in einem Simulationsmodell nachgebildet. Anhand dieses Modells wird der Entwurf eines schnellen Reglers beschrieben der die Dynamik des RTMs erhoeht und kurze Aufnahmezeiten ermoeglicht. Die Arbeit beinhaltet detaillierte Beschreibungen des mechanischen Aufbaus und der Elektronik des RTMs in Form von Werkzeichnungen, Schaltplaenen und Platinenlayouts. Des Weiteren wird auch eine Anleitung fuer zwei unterschiedliche Verfahren der Spitzenpraeparation gegeben. Die hier vorgestellten Methoden und Loesungen sind nicht nur auf das RTM beschraenkt, sondern lassen sich d

2010-01-01

329

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

CERN Multimedia

Based on a Fermi liquid picture, the temperature effect on the impurity-induced spatial modulation of local density of states (LDOS) is investigated for the d-wave superconductor Bi$_2$Sr$_2$CaCu$_2$O$_8$, in the context of scanning tunneling microscopy (STM). It is found that stripe-like structure exists even in the normal state due to a local-nesting mechanism, which is different from the octet scattering mechanism proposed by McElroy $et al$. {[Nature {\\bf 422}, 592 (2003)]} in the d-wave superconducting ($d$SC) state. The normal-state spectra, when Fourier-transformed into the reciprocal space, can reveal the information of the entire Fermi surface at a single measuring bias, in contrast to the point-wise tracing 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 spectra in the $d$SC state and pointed out that, due to the Umklapp symmetry of the lattice, there should exist additional peaks in the recipro...

Voo, K K; Chen, H Y; Mou, C Y

2003-01-01

330

Scanning Tunneling Microscopy in TTF-TCNQ direct proof of phase and amplitude modulated charge density waves  

CERN Document Server

Charge density waves (CDW) have been studied at the surface of a cleaved TTF-TCNQ single crystal using a low temperature scanning tunneling microscope (STM) under ultra high vacuum (UHV) conditions. All CDW phase transitions of TTF-TCNQ have been identified. The measurement of the modulation wave vector along the a direction provides the first evidence for the existence of domains comprising single plane wave modulated structures in the temperature regime where the transverse wave vector of the CDW is temperature dependent, as hinted by the theory more than 20 years ago.

Wang, Z Z Z; Girard, J C; Pasquier, C; Bechgaard, K; Wang, Zhao Z.Z.; Jerome, Denis; Girard, Jean Christophe; Pasquier, Claude; Bechgaard, Klaus

2003-01-01

331

Electronic structures of one-dimensional metal-molecule hybrid chains studied using scanning tunneling microscopy and density functional theory.  

UK PubMed Central (United Kingdom)

The electronic structures of self-assembled hybrid chains comprising Ag atoms and organic molecules were studied using scanning tunneling microscopy (STM) and spectroscopy (STS) in parallel with density functional theory (DFT). Hybrid chains were prepared by catalytic breaking of Br-C bonds in 4,4?-dibromo-p-terphenyl molecules, followed by spontaneous formation of Ag-C bonds on Ag(111). An atomic model was proposed for the observed hybrid chain structures. Four electronic states were resolved using STS measurements, and strong energy dependence was observed in STM images. These results were explained using first-principles calculations based on DFT.

Chung KH; Koo BG; Kim H; Yoon JK; Kim JH; Kwon YK; Kahng SJ

2012-05-01

332

Surface structures of layered compounds treated with alkali-metal hydroxide solutions studied by scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

Ordered 2x2 and {radical}3x{radical}3 superstructures with charge density modulation were observed by scanning tunneling microscopy (STM) on highly oriented pyrolytic graphite surfaces treated with MOH (M=Na, K) aqueous solutions. Charge transfer from intercalants to host graphite was observed, as previously seen on stage-1 alkali-metal intercalations. On the other hand, for the MoS2 crystal treated with the same solutions, the host MoS2 lattice was observed together with island structures with low charge density formed by intercalants. Some electronic states seemed to be formed between the MoS2 band gap. (orig.)

Miyake, Koji [Inst. of Materials Science, Univ. of Tsukuba (Japan); Shigekawa, Hidemi [Inst. of Materials Science, Univ. of Tsukuba (Japan)

1995-04-01

333

Scanning tunneling microscopy and spectroscopy of the chain layer in YBa2Cu3O7-x  

International Nuclear Information System (INIS)

The authors review the recent results on the surface structure and spectroscopy of the chain layer of YBa2Cu3O7-x obtained with a low temperature scanning tunneling microscope. Foremost is the discovery of a long wavelength (?1.3nm) modulation of the electronic density along the CuO chains, which has now been confirmed by neutron diffraction to also exist in the bulk. Spectroscopically, they observe an energy gap (20--25 meV) which disappears near oxygen vacancies. They also give experimental details not previously published.

1996-02-02

334

Diffusional kinetics of SiGe Dimers on Si(100) using atom-tracking scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

Quantitative measurements of the diffusion of adsorbed mixed Ge-Si dimers on the Si(100) surface have been made as a function of temperature using atom-tracking scanning tunneling microscopy. These mixed dimers are distinguishable from pure Si-Si dimers by their characteristic kinetics--a 180-degree rotation between two highly buckled configurations. At temperatures at which the mixed dimers diffuse, atomic-exchange events occur, in which the Ge atom in the adsorbed dimer exchanges with a substrate Si atom. Re-exchange can also occur when the diffusing Si-Si dimer revisits the original site of exchange.

QIN,X.R.; SWARTZENTRUBER,BRIAN S.; LAGALLY,M.G.

2000-06-14

335

Use of molybdenum telluride as a substrate for the imaging of biological molecules during scanning tunnelling microscopy.  

Science.gov (United States)

Scanning tunnelling microscopy was used to image biological molecules including supercoiled deoxyribonacetic acid and specific retrovirus enzymes, the reverse transcriptases of the avian myeloblastosis virus, the moloney murine leukaemia virus and the human immunodeficiency virus. Measurements were carried out on graphite and Group VI transition metal dichalcogenide layered crystals. Images obtained with graphite could not be unequivocally interpreted and attachment appears to occur solely at surface defect sites. The layered crystal MoTe2 shows different imaging properties. The bimolecules are clearly visible, distributed over the semiconductor surface, and the molecular shapes and dimensions show good correlation with structure predictions. PMID:7520674

Campbell, S A; Müller, D J; Jungblut, H; Giersig, M; Tomm, Y; Lewerenz, H J

1994-05-01

336

Use of molybdenum telluride as a substrate for the imaging of biological molecules during scanning tunnelling microscopy.  

UK PubMed Central (United Kingdom)

Scanning tunnelling microscopy was used to image biological molecules including supercoiled deoxyribonacetic acid and specific retrovirus enzymes, the reverse transcriptases of the avian myeloblastosis virus, the moloney murine leukaemia virus and the human immunodeficiency virus. Measurements were carried out on graphite and Group VI transition metal dichalcogenide layered crystals. Images obtained with graphite could not be unequivocally interpreted and attachment appears to occur solely at surface defect sites. The layered crystal MoTe2 shows different imaging properties. The bimolecules are clearly visible, distributed over the semiconductor surface, and the molecular shapes and dimensions show good correlation with structure predictions.

Campbell SA; Müller DJ; Jungblut H; Giersig M; Tomm Y; Lewerenz HJ

1994-05-01

337

Scanning tunneling spectroscopy study of electric-pulse-induced electronic inhomogeneities in GaTa4Se8  

Science.gov (United States)

We have recently discovered a bulk Electric Pulse Induced Insulator-Metal Transition and possible superconductivity in the cluster Mott Insulator GaTa4Se8 [1]. The transport measurements, conducted on single crystals, are consistent with a two-channel model, which suggests that the electric pulse generates electronic inhomogeneities in the bulk of the samples. Our Scanning Tunneling Microscopy/Spectroscopy experiments indeed confirmed that the observed drop in the electric resistance originates from an electronic phase separation with the coexistence of metallic- like and insulating like domains at the nanometer scale [1]. [1] Vaju et al. Advanced Materials, 20 2760 (2008), Microelectronics engineering in press, (2008)

Dubost, Vincent; Vaju, Cristian; Cren, Tristan; Corraze, Benoit; Debontridder, Francois; Janod, Etienne; Roditchev, Dimitri; Cario, Laurent

2009-03-01

338

Kink-induced buckled dimers on Si(001) and Ge(001) at room temperature studied by scanning tunneling microscopy  

Science.gov (United States)

The structure of kinks at monatomic steps on Si(001) and Ge(001) is investigated by high-resolution scanning tunneling microscopy at room temperature. In addition to previously known asymmetric-dimers at edges of the SA and SB steps running parallel and perpendicular to dimer rows in the upper terrace, respectively, we have found that kinks at both SA and SB steps induce buckled (asymmetric-appearing) dimers locally in the connecting dimer rows in the lower terrace. Influence of the kinks on the formation of a c(4×2) phase of asymmetric dimers at low temperatures is discussed.

Tochihara, Hiroshi; Sato, Tomoshige; Sueyoshi, Takashi; Amakusa, Takaaki; Iwatsuki, Masashi

1996-03-01

339

Scanning tunnelling spectroscopy on the local electronic structure of Gd rate at C{sub 82} peapods  

Energy Technology Data Exchange (ETDEWEB)

The electronic structure of Gd rate at C{sub 82} metallofullerene peapods is studied experimentally by using scanning tunnelling microscopy and spectroscopy (STM and STS). The spatial modulation of the nanotube electronic structure induced by Gd rate at C{sub 82} encapsulation has been observed depending on the position along the tube axis. Both STM and STS reveal a 1.2 nm periodicity which is consistent with the intermolecular distance of Gd rate at C{sub 82} inside single-wall carbon nanotubes. (Copyright copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Ohashi, Kazunori; Imazu, Naoki; Kitaura, Ryo; Shinohara, Hisanori [Department of Chemistry and Institute for Advanced Research, Nagoya University, Nagoya 464-8602 (Japan)

2010-12-15

340

Atomic resolved material displacement on graphite surfaces by scanning tunnelling microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Atomic scale modifications and subsequent atomic resolution imaging has been achieved on the highly oriented pyrolytic graphite surface in air. Application of short pulse voltages, above a minimum threshold voltage of 3.5 V, across the tunneling gap results in the displacement of a layer or more of ...

Moriarty, Philip; Hughes, Greg

 
 
 
 
341

Voltammetry and in situ scanning tunnelling microscopy of de novo designed heme protein monolayers on Au(111)-electrode surfaces.  

UK PubMed Central (United Kingdom)

In the present work, we report the electrochemical characterization and in situ scanning tunnelling microscopy (STM) studies of monolayers of an artificial de novo designed heme protein MOP-C, covalently immobilized on modified Au(111) surfaces. The protein forms closely packed monolayers, which remain electroactive upon immobilization. In situ STM images show circular structures indicating that MOP-C stands upright on the surface in accordance with the molecular design. Despite the large spatial extension of MOP-C, about 5 nm in height, conditions could be found where tip/sample interaction is minimal and proteins could be imaged without detectable tip interference. The results indicate further that the structural sensitivity of (in situ) STM depends to a significant extent on associated electron transfer kinetics. In the present case, the heme group does not contribute significantly to the tunnelling current, apparently due to slow electron transfer kinetics. As a consequence, STM images of heme-containing and heme-free MOP-C did not reveal any notable differences in apparent height or physical extension. The apparent height of heme-containing MOP-C did not show any dependence on the substrate potential being varied around the redox potential of the protein. The mere presence of an accessible molecular energy level is not sufficient to result in detectable tunnelling current modulation.

Albrecht T; Li WW; Haehnel W; Hildebrandt P; Ulstrup J

2006-10-01

342

Voltammetry and in situ scanning tunnelling microscopy of de novo designed heme protein monolayers on Au(111)-electrode surfaces.  

Science.gov (United States)

In the present work, we report the electrochemical characterization and in situ scanning tunnelling microscopy (STM) studies of monolayers of an artificial de novo designed heme protein MOP-C, covalently immobilized on modified Au(111) surfaces. The protein forms closely packed monolayers, which remain electroactive upon immobilization. In situ STM images show circular structures indicating that MOP-C stands upright on the surface in accordance with the molecular design. Despite the large spatial extension of MOP-C, about 5 nm in height, conditions could be found where tip/sample interaction is minimal and proteins could be imaged without detectable tip interference. The results indicate further that the structural sensitivity of (in situ) STM depends to a significant extent on associated electron transfer kinetics. In the present case, the heme group does not contribute significantly to the tunnelling current, apparently due to slow electron transfer kinetics. As a consequence, STM images of heme-containing and heme-free MOP-C did not reveal any notable differences in apparent height or physical extension. The apparent height of heme-containing MOP-C did not show any dependence on the substrate potential being varied around the redox potential of the protein. The mere presence of an accessible molecular energy level is not sufficient to result in detectable tunnelling current modulation. PMID:16580892

Albrecht, Tim; Li, Wen-Wu; Haehnel, Wolfgang; Hildebrandt, Peter; Ulstrup, Jens

2006-02-23

343

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

DEFF Research Database (Denmark)

In the present work, we report the electrochemical characterization and in situ scanning tunnelling microscopy (STM) studies of monolayers of an artificial de novo designed heme protein MOP-C, covalently immobilized on modified Au(111) surfaces. The protein forms closely packed monolayers, which remain electroactive upon immobilization. In situ STM images show circular structures indicating that MOP-C stands upright on the surface in accordance with the molecular design. Despite the large spatial extension of MOP-C, about 5 nm in height, conditions could be found where tip/sample interaction is minimal and proteins could be imaged without detectable tip interference. The results indicate further that the structural sensitivity of (in situ) STM depends to a significant extent on associated electron transfer kinetics. In the present case, the heme group does not contribute significantly to the tunnelling current, apparently due to slow electron transfer kinetics. As a consequence, STM images of heme-containing and heme-free MOP-C did not reveal any notable differences in apparent height or physical extension. The apparent height of heme-containing MOP-C did not show any dependence on the substrate potential being varied around the redox potential of the protein. The mere presence of an accessible molecular energy level is not sufficient to result in detectable tunnelling current modulation. (c) 2006 Elsevier B.V. All rights reserved.

Albrecht, Tim; Li, Wu

2006-01-01

344

Surface damage through grazing incidence ions investigated by scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

Surface damage, caused by grazing incidence ions, is investigated with variable temperature scanning tunneling microscopy. The experiments are carried out on a Pt(111) crystal. The kinetic energy of noble gas ions is varied between 1-15 keV and the angle of incidence can be adjusted between {theta} = 78.5 and {theta} = 90 measured with respect to the surface normal. The damage patterns of single ion impacts, on flat terraces and at step edges of monoatomic height, are investigated at low surface temperatures. Ions hitting a flat terrace are usually specular reflected. The energy transfer from the ion to the crystal atoms is small and only little damage is produced. In contrast, at ascending step edges, which are illuminated by the ion beam, large angle scattering events occur. Sputtering, adatom and vacancy production is induced. However, a significant fraction of the ions, which hit step edges, enter the crystal and are guided in between two atomic layers parallel to the surface via small angle binary collisions. This steering process is denoted as subsurface channeling. The energy loss per length scale of the channeled particles is low, which results in long ion trajectories (up to 1000A). During the steering process, the ions produce surface damage. Depending on the ion species and the ion energy, adatom and vacancies or surface vacancy trenches of monoatomic width are observed. The surface damage can be used to track the path of the ion. This makes the whole trajectory of single ions with keV energy visible. The number of sputtered atoms per incident ion at ascending step edges, i.e. the step edge sputtering yield, is measured experimentally for different irradiation conditions. For {theta} = 86 , the sputtering yield is determined from the fluence dependent retraction of pre-existing illuminated step edges. An alternative method for the step edge sputtering yield determination, is the analysis of the concentration of ascending steps and of the removed amount of material as a function of the ion fluence. This method is also applicable under less grazing angles of incidence. The investigations show that the sputtering yield at step edges depends on the azimuthal orientation of the impinging ions with respect to the surface. This change is attributed to the orientation dependence of subsurface channeling. The step edge sputtering yield at small adatom clusters is measured. In this case, the topmost layer (which forms the step edge) has a small lateral extension in ion beam direction. The evaluation shows that the step edge yield is, compared to step edges with a long upper terrace, decreased by a factor of three. The physical reason can be traced back to subsurface channeling. The ions are able to pass underneath the cluster and exit the crystal without a large scattering event. Little energy is transfered to the crystal which results in a low sputtering yield. The influence of adsorbates on sputtering and surface damage in grazing incidence ion erosion is studied for the case of oxygen and carbon monoxide. A partial surface coverage with adsorbates causes an enhancement of the erosion rate (the amount of removed material per ion fluence) by a factor of up to 40 compared to the clean case. The study is performed for 5 keV Ar{sup +} ions for various grazing angles between 81 and 87 and temperatures ranging from 400 K to 550 K. Finally, coarsening of ion beam induced ripple patterns is analyzed. For surface temperatures of 450 K or below coarsening is athermal and kinetic, unrelated to diffusion and surface free energy. Similar to the situation of sand dunes, coarsening takes place through annihilation reactions of mobile defects in the pattern. The defect velocity derived on the basis of a simple model agrees quantitatively with the velocity of monoatomic steps illuminated by the ion beam. (orig.)

Redinger, Alex

2009-07-10

345

Surface damage through grazing incidence ions investigated by scanning tunneling microscopy  

International Nuclear Information System (INIS)

[en] Surface damage, caused by grazing incidence ions, is investigated with variable temperature scanning tunneling microscopy. The experiments are carried out on a Pt(111) crystal. The kinetic energy of noble gas ions is varied between 1-15 keV and the angle of incidence can be adjusted between ? = 78.5 and ? = 90 measured with respect to the surface normal. The damage patterns of single ion impacts, on flat terraces and at step edges of monoatomic height, are investigated at low surface temperatures. Ions hitting a flat terrace are usually specular reflected. The energy transfer from the ion to the crystal atoms is small and only little damage is produced. In contrast, at ascending step edges, which are illuminated by the ion beam, large angle scattering events occur. Sputtering, adatom and vacancy production is induced. However, a significant fraction of the ions, which hit step edges, enter the crystal and are guided in between two atomic layers parallel to the surface via small angle binary collisions. This steering process is denoted as subsurface channeling. The energy loss per length scale of the channeled particles is low, which results in long ion trajectories (up to 1000A). During the steering process, the ions produce surface damage. Depending on the ion species and the ion energy, adatom and vacancies or surface vacancy trenches of monoatomic width are observed. The surface damage can be used to track the path of the ion. This makes the whole trajectory of single ions with keV energy visible. The number of sputtered atoms per incident ion at ascending step edges, i.e. the step edge sputtering yield, is measured experimentally for different irradiation conditions. For ? = 86 , the sputtering yield is determined from the fluence dependent retraction of pre-existing illuminated step edges. An alternative method for the step edge sputtering yield determination, is the analysis of the concentration of ascending steps and of the removed amount of material as a function of the ion fluence. This method is also applicable under less grazing angles of incidence. The investigations show that the sputtering yield at step edges depends on the azimuthal orientation of the impinging ions with respect to the surface. This change is attributed to the orientation dependence of subsurface channeling. The step edge sputtering yield at small adatom clusters is measured. In this case, the topmost layer (which forms the step edge) has a small lateral extension in ion beam direction. The evaluation shows that the step edge yield is, compared to step edges with a long upper terrace, decreased by a factor of three. The physical reason can be traced back to subsurface channeling. The ions are able to pass underneath the cluster and exit the crystal without a large scattering event. Little energy is transfered to the crystal which results in a low sputtering yield. The influence of adsorbates on sputtering and surface damage in grazing incidence ion erosion is studied for the case of oxygen and carbon monoxide. A partial surface coverage with adsorbates causes an enhancement of the erosion rate (the amount of removed material per ion fluence) by a factor of up to 40 compared to the clean case. The study is performed for 5 keV Ar+ ions for various grazing angles between 81 and 87 and temperatures ranging from 400 K to 550 K. Finally, coarsening of ion beam induced ripple patterns is analyzed. For surface temperatures of 450 K or below coarsening is athermal and kinetic, unrelated to diffusion and surface free energy. Similar to the situation of sand dunes, coarsening takes place through annihilation reactions of mobile defects in the pattern. The defect velocity derived on the basis of a simple model agrees quantitatively with the velocity of monoatomic steps illuminated by the ion beam. (orig.)

2009-01-01

346

Adsorbate structures and catalytic reactions studied in the torrpressure range by scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

High-pressure, high-temperature scanning tunneling microscopy (HPHTSTM) was used to study adsorbate structures and reactions on single crystal model catalytic systems. Studies of the automobile catalytic converter reaction [CO + NO {yields} 1/2 N{sub 2} + CO{sub 2}] on Rh(111) and ethylene hydrogenation [C{sub 2}H{sub 4} + H{sub 2} {yields} C{sub 2}H{sub 6}] on Rh(111) and Pt(111) elucidated information on adsorbate structures in equilibrium with high-pressure gas and the relationship of atomic and molecular mobility to chemistry. STM studies of NO on Rh(111) showed that adsorbed NO forms two high-pressure structures, with the phase transformation from the (2 x 2) structure to the (3 x 3) structure occurring at 0.03 Torr. The (3 x 3) structure only exists when the surface is in equilibrium with the gas phase. The heat of adsorption of this new structure was determined by measuring the pressures and temperatures at which both (2 x 2) and (3 x 3) structures coexisted. The energy barrier between the two structures was calculated by observing the time necessary for the phase transformation to take place. High-pressure STM studies of the coadsorption of CO and NO on Rh(111) showed that CO and NO form a mixed (2 x 2) structure at low NO partial pressures. By comparing surface and gas compositions, the adsorption energy difference between topsite CO and NO was calculated. Occasionally there is exchange between top-site CO and NO, for which we have described a mechanism for. At high NO partial pressures, NO segregates into islands, where the phase transformation to the (3 x 3) structure occurs. The reaction of CO and NO on Rh(111) was monitored by mass spectrometry (MS) and HPHTSTM. From MS studies the apparent activation energy of the catalytic converter reaction was calculated and compared to theory. STM showed that under high-temperature reaction conditions, surface metal atoms become mobile. Ethylene hydrogenation and its poisoning by CO was also studied by STM on Rh(111) and Pt(111). Poisoning was found to coincide with decreased adsorbate mobility. Under ethylene hydrogenation conditions, no order is detected by STM at 300 K, as hydrogen and ethylidyne, the surface species formed by gas-phase ethylene, are too mobile. When CO is introduced, the reaction stops, and ordered structures appear on the surface. For Rh(111), the structure is predominantly a mixed c(4 x 2), though there are some areas of (2 x 2). For Pt(111), the structure is hexagonal and resembles the Moire pattern seen when Pt(111) is exposed to pure CO. From these studies it is concluded that CO poisons by stopping adsorbate mobility. This lack of adsorbate mobility prevents the adsorption of ethylene from the gas phase by hindering the creation of adsorption sites.

Hwang, Kevin Shao-Lin

2003-05-23

347

The dissolution of Ag(111) electrodes investigated by in situ scanning tunnelling microscopy  

International Nuclear Information System (INIS)

The technique of in situ scanning tunnelling microscopy (in situ STM) has been exploited to examine the effect of oxidation-reduction cycles (ORCs) on the morphology of Ag(111) electrodes in 0.1 M KCI and 0.1 M KClO4 solutions. Ag(111) films were prepared by the evaporation of silver onto cleaved muscovite mica substrates at 220 deg C. The films were characterised by in-air STM by comparing them with silver deposited onto cleaved muscovite mica at room temperature. The results demonstrated that at elevated temperatures large monoatomically flat terraced regions were formed, indicating the presence of well ordered crystallites. Images of Ag(111) electrodes immersed in 0.1 M KCI and 0.1 M KClO4 solutions at double layer potentials demonstrated that the morphology was the same as for Ag(l II) films imaged in-air. Higher resolution images of the steps demonstrated they appeared fuzzy due to step atom mobility. Ag(111) electrodes were oxidised in 0.1 M KCI solutions by swept and pulsed ORCs of 1.22x10-3 C cm-2. For pulsed ORCs the reduction potential of the silver chloride was over the range -90 mV to -240 mV versus the SCE where it is known specific adsorption of chloride ions is predominant. For swept ORCs the final rest potential of the Ag(111) electrode was also chosen over the same range. In situ STM revealed discernable differences in the shape, size and distribution of the silver islands for the reformed surface between the two voltammetric methods. This remained evident for varying extents of silver dissolution. Ag(111) electrodes were oxidised in 0.1 M KCIO4 solutions by a single swept ORC of 0.77x10-3 C cm-2. The final rest potential of the Ag(111) working electrode was over the potential range of -36 mV to 114 mV versus the SCE where the silver islands of the reformed surface are believed to be unstable. Results show that a majority of silver islands of all sizes are stable with time, whereas the silver islands with irregular shapes tended to evolve to exhibit higher degrees of spherical geometry. Additionally, the position of the silver islands did not remain constant during the acquisition of STM images. Results from in situ STM demonstrated that the underlying step-terrace morphology of the Ag(111) electrodes did not remain constant with time. Both macroscale and nanoscale changes to the Ag(111) electrode surface were observed. It is concluded that this is due to the transport of material along and from step sites due to step atom to surface adatom promotion over the range of working electrode potentials investigated. The results in these studies have demonstrated that the technique of in situ STM can be used to probe the morphology and dynamics of roughened Ag(111) surfaces at both the nanoscopic and macroscopic scales. (author)

1998-01-01

348

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

UK PubMed Central (United Kingdom)

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

Ahmad S; Carstens T; Berger R; Butt HJ; Endres F

2011-01-01

349

Spin polarized and degenerate tunneling spectra in intrinsic Josephson junctions of Bi2212  

International Nuclear Information System (INIS)

Tunneling characteristics of HgBr2 intercalated superconducting Bi2212 single crystals have been obtained by using 10 x 10 mm2 intrinsic Josephson junction stacks, so called mesa structures. The spin degenerate current is driven along the c-axis with Au layer using point contact tunneling assembly at 4.2 K. The spin polarized current is also driven along the c-axis of crystals with Au/Co/Au multilayer. In order to understand the role of ferromagnetic layer (Co), quasiparticle branches are examined with and without magnetic field. The magnetic field evolution of switching currents are obtained for gaining further insight about the spin injection through the stack. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

2006-08-04

350

Fermi surface investigation in the scanning tunneling microscopy of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}  

Energy Technology Data Exchange (ETDEWEB)

Within the ideal Fermi liquid picture, the impurity-induced spatial modulation of local density of states (LDOS) in the d-wave superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} is investigated at different superconducting (SC) gap sizes. These LDOS spectra are related to the finite-temperature dI/dV spectra in scanning tunneling microscopy (STM), when the Fermi distribution factor is deconvoluted away from dI/dV. We find stripe-like structures even in the zero gap case due to a local-nesting mechanism. This mechanism is different from the octet-scattering mechanism in the d-wave SC (dSC) state proposed by McElroy et al. [K. McElroy, R.W. Simmonds, J.E. Hoffman, D.H. Lee, J. Orenstein, H. Eisaki, S. Uchida, J.C. Davis, Nature 422 (2003) 592]. The zero gap LDOS is related to the normal state dI/dV. The zero gap spectra when Fourier-transformed into the reciprocal space, can reveal the information of the entire Fermi surface at a single measuring bias voltage, in contrast to the point-wise tracing out proposed by McElroy et al. This may serve as another way to check the reality of Landau quasiparticles in the normal state. We have also re-visited the octet-scattering mechanism in the dSC state and pointed out that, due to the Umklapp symmetry, there are additional peaks in the reciprocal space that experimentally yet to be found.

Voo, K.K. [Department of Physics, National Tsing-Hua University, Hsinchu 300, Taiwan (China)]. E-mail: kkvoo@cc.nctu.edu.tw; Wu, W.C. [Department of Physics, 88, Sec. 4, Ting-Chou Rd., National Taiwan Normal University, Taipei 11650, Taiwan (China); Chen, H.Y. [Texas Center for Superconductivity and Department of Physics, University of Houston, Houston, TX 77204 (United States); Mou, C.Y. [Department of Physics, National Tsing-Hua University, Hsinchu 300, Taiwan (China); Physics Division, National Center for Theoretical Sciences, P.O. Box 2-131, Hsinchu 300, Taiwan (China)

2004-12-01

351

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

Science.gov (United States)

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

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

2003-11-01

352

[Scanning tunnelling microscopy and spectroscopy of ceramic grain boundaries]. [Annual report, September 1992--September 1993  

Energy Technology Data Exchange (ETDEWEB)

Objective is to study the local geometric and electronic structure at grain boundaries in oxides; this was motivated by the potential to use STM and tunneling spectroscopy on semiconducting ceramics. In order to understand the imaging of low conductivity materials, a number of transition metal oxides were examined: ZnO, TiO{sub 2}. Spatial resolution limits are considered. Conductance profiles across silicon grain boundaries are compared with those across more complex SrTiO{sub 3} grain boundaries. Calculations of space charge in complex oxides are presented. A SEM/STM was constructed which operates in ultrahigh vacuum and has large scale positioning capability (> 1 cm).

1993-10-01

353

Estudio de superficies usando un microscopio de efecto túnel (STM)/ A study of surfaces using a scanning tunneling microscope (STM)  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish Los microscopios de barrido se han convertido en las manos y los "ojos" de experimentadores de nuestro siglo, son herramientas necesarias en los laboratorios de educación e investigación para la caracterización a nanoescalas. El presente artículo presenta las modificaciones en la implementación electrónica (caracterización de los piezoeléctricos y sistema de barrido) y mecánica (diseño de un sistema de antivibración) de un microscopio de barrido de efecto túne (more) l que han permitido visualización y modificación de superficies a nanoescala. Se describe una metodología para la correcta visualización y caracterización de superficies usando el instrumento implementado, alcanzando la cuantificación bidimensional de características de hasta 1300nm², con resolución ~15nm. Esta metodología, determinada experimentalmente, tiene en cuenta parámetros críticos para la estabilización de la corriente túnel, como lo son la velocidad de barrido y las geometrías y dimensiones de las agujas del microscopio. La versatilidad del microscopio permite modificar y visualizar los defectos introducidos en muestras de HOPG al aplicar voltajes entre la punta del microscopio y la muestra. Los resultados aquí descritos permiten presentar fácilmente los conceptos de barrido topográfico y litografía. Abstract in english Sweeping/scanning microscopes have become an experimental scientist's hands and eyes in this century; they have become a powerful and necessary tool for nanoscale characterisation in education and research laboratories all around the world. This article presents the modifications made in the mechanical (isolation or designing an antivibration system) and electrical (piezoelectric and scanning system characterisation) implementation of a scanning tunnelling microscope (STM (more) ), thereby allowing nanoscale surfaces to be visualised and modified. A methodology for visualising and characterising surfaces using the aforementioned instrument is described, bidimensional quantification of up to 1,300 nm², with ~15 nm resolution being reached. This experimental methodology took critical parameters for tunnelling current stability into account, such as scanning speed and microscope tip geometry and dimensions. This microscope's versatility allowed defects in highly oriented pyrolytic graphite (HOPG) samples to be modified and visualised by applying a voltage between the tip and the sample. The concepts of topography scanning and lithography can be easily understood by using the instrument implemented here.

Ávila Bernal, Alba Graciela; Bonilla Osorio, Ruy Sebastián

2009-12-01

354

Estudio de superficies usando un microscopio de efecto túnel (STM) A study of surfaces using a scanning tunneling microscope (STM)  

Directory of Open Access Journals (Sweden)

Full Text Available Los microscopios de barrido se han convertido en las manos y los “ojos” de experimentadores de nuestro siglo, son herramien- tas necesarias en los laboratorios de educación e investigación para la caracterización a nanoescalas. El presente artículo pre- senta las modificaciones en la implementación electrónica (caracterización de los piezoeléctricos y sistema de barrido) y mecáni- ca (diseño de un sistema de antivibración) de un microscopio de barrido de efecto túnel que han permitido visualización y modi- ficación de superficies a nanoescala. Se describe una metodología para la correcta visualización y caracterización de superficies usando el instrumento implementado, alcanzando la cuantificación bidimensional de características de hasta 1300nm2, con re- solución ~15nm. Esta metodología, determinada experimentalmente, tiene en cuenta parámetros críticos para la estabilización de la corriente túnel, como lo son la velocidad de barrido y las geometrías y dimensiones de las agujas del microscopio. La ver- satilidad del microscopio permite modificar y visualizar los defectos introducidos en muestras de HOPG al aplicar voltajes entre la punta del microscopio y la muestra. Los resultados aquí descritos permiten presentar fácilmente los conceptos de barrido to- pográfico y litografía.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.

Ávila Bernal Alba Graciela; Bonilla Osorio Ruy Sebastián

2009-01-01

355

Surface structure and superconductivity in Ba(Fe0.93Co0.07)2As2 probed by scanning tunneling microscopy/spectroscopy  

International Nuclear Information System (INIS)

We present scanning tunneling microscopy/spectroscopy (STM/STS) on iron-based superconductor Ba(Fe0.93-Co0.07)2As2 single crystals. The STM topography shows that the low-temperature cleaved surface consists of two types of ordered atomic structures: (1) the 2x1 surface, formed by half of the Ba atoms remaining on the As layer, and (2) the ?2x?2 surface of the As layer from which Ba atoms are completely removed. The superconducting spectra with the energy gap (2??6.9kBTc) are observed only on the 2x1 surface. This value is approximately twice that for weak coupling s-wave BCS superconductors, indicating a strong pairing interaction similar to that observed in cuprate superconductors. We also find that vortices form a disordered structure and that the vortex core spectroscopy does not show a bound state, suggesting a strong disorder effect on the vortex pinning and quasiparticle scattering. (author)

2011-01-01

356

Electronic characterization of LaAlO3-SrTiO3 interfaces by scanning tunneling spectroscopy  

International Nuclear Information System (INIS)

When LaAlO3 is epitaxially grown on TiO2-terminated SrTiO3, an electrically conducting interface is generated. In this respect, the physical properties of the interface differ substantially from those of both LaAlO3 and SrTiO3, which are electrically insulating in bulk form. This dissertation looks into the question of the microscopic structure of the conducting two-dimensional interface electron system. Comparing the electronic density of states of LaAlO3-SrTiO3 interfaces measured by scanning tunneling spectroscopy with results of density functional theory, the interface electron system is found to be substantially coined by the hosting transition metal lattices. The comparison yields a detailed picture of the microscopic structure of the interface electron system. (orig.)

2010-01-01

357

Surface photovoltage of Ag on Si(111)-7 times 7 by scanning tunneling microscopy. Technical report No. 1  

Energy Technology Data Exchange (ETDEWEB)

Using a scanning tunneling microscope and light from a He-Ne laser, the authors have measured the surface photovoltage of the Si(111)-7 {times} 7 surface with coverages of Ag up to 1 monolayer. The data agree with a model for the photovoltage based on the recombination of photoexcited minority carriers with majority carriers thermally excited over the surface Schottky barrier. The surface Fermi level positions derived from these data are consistent for n and p type Si decreasing from 0.60 eV above the conduction band maximum for the clean surface to 0.40 eV near 1 monolayer coverage. Although the photovoltage data are spatially resolved on an atomic scale, they do not observe any spatial variation in the photovoltage on the clean surface or on surfaces partially covered by Ag islands.

Cahill, D.G.; Hamers, R.J.

1991-05-30

358

Si-capping of Ge nanohuts on Si(001) analyzed by scanning tunneling microscopy and the finite element method  

International Nuclear Information System (INIS)

Ge hut nanocrystals were grown on an Si(001) surface and Si-capped by gas-source molecular-beam epitaxy. Growth and capping at 430 deg. C were observed in real time by scanning tunneling microscopy, and analyzed by the finite element method. Observations made here of three-dimensional Si-cap growth (in the shape of pyramids and huts) on Ge, similar to the Ge growth on Si(001), are consistent with energetic arguments based on finite elements in the framework of linear elasticity. These observations are in contrast with the higher-temperature behavior, where Si preferentially sticks to the Ge nanocrystal facets, causing them to develop large flat (001) tops and a reduced height-base ratio.

2004-09-06

359

Investigation of Si-Au vicinal surfaces using scanning tunnelling microscopy and reflection high-energy electron diffraction.  

Science.gov (United States)

Silicon vicinal surfaces can be successfully used as substrates for the preparation of one-dimensional nanostructures. The quality of the structures prepared may be controlled using scanning tunnelling microscopy, as shown in this work. Additionally, it is possible to obtain valuable information using reflection high-energy electron diffraction. A typical way of employing reflection high-energy electron diffraction is to observe patterns of scattered electrons on a screen. However, it is possible to obtain more detailed information on the arrangement of atoms at the surface if azimuthal plots are collected. Azimuthal plots are measured by recording the intensity of specularly reflected electrons during the rotation of the sample around an axis perpendicular to its surface. So far, only flat surfaces have been examined in such a way. In this work, it is shown that such data, containing interesting features, can also be collected for vicinal surfaces. PMID:17100924

Mazurek, P; Paprocki, K; Mitura, Z

2006-10-01

360

Investigation of Si-Au vicinal surfaces using scanning tunnelling microscopy and reflection high-energy electron diffraction.  

UK PubMed Central (United Kingdom)

Silicon vicinal surfaces can be successfully used as substrates for the preparation of one-dimensional nanostructures. The quality of the structures prepared may be controlled using scanning tunnelling microscopy, as shown in this work. Additionally, it is possible to obtain valuable information using reflection high-energy electron diffraction. A typical way of employing reflection high-energy electron diffraction is to observe patterns of scattered electrons on a screen. However, it is possible to obtain more detailed information on the arrangement of atoms at the surface if azimuthal plots are collected. Azimuthal plots are measured by recording the intensity of specularly reflected electrons during the rotation of the sample around an axis perpendicular to its surface. So far, only flat surfaces have been examined in such a way. In this work, it is shown that such data, containing interesting features, can also be collected for vicinal surfaces.

Mazurek P; Paprocki K; Mitura Z

2006-10-01

 
 
 
 
361

Development of an ion beam alignment system for real-time scanning tunneling microscope observation of dopant-ion irradiation  

International Nuclear Information System (INIS)

[en] An ion beam alignment system has been developed in order to realize real-time scanning tunneling microscope (STM) observation of 'dopant-ion' irradiation that has been difficult due to the low emission intensity of the liquid-metal-ion-source (LMIS) containing dopant atoms. The alignment system is installed in our original ion gun and STM combined system (IG/STM) which is used for in situ STM observation during ion irradiation. By using an absorbed electron image unit and a dummy sample, ion beam alignment operation is drastically simplified and accurized. We demonstrate that sequential STM images during phosphorus-ion irradiation are successfully obtained for sample surfaces of Si(111)-7x7 at room temperature and a high temperature of 500 deg. C. The LMIS-IG/STM equipped with the developed ion beam alignment system would be a powerful tool for microscopic investigation of the dynamic processes of ion irradiation

2008-01-01

362

Energetics and bias-dependent scanning tunneling microscopy images of Si ad-dimers on Ge(001)  

Energy Technology Data Exchange (ETDEWEB)

We report an {ital ab initio} study of the energetics and scanning tunneling microscopy (STM) images of Si ad-dimers on Ge(001) and energetics of Ge ad-dimers on Si(001). As in the case of Si dimers on Si(001), we find for both systems that the {ital D} dimer configuration, lying between the substrate dimer rows and parallel to them, is highest in energy. Conversely, recent STM experiments for Si ad-dimers on Ge(001) deduce the {ital D} configuration to be most stable. Our theoretical STM images for this system find that both the {ital D} and {ital C} configurations (the latter also between the rows) have similar STM images for the experimental voltages. We propose an experimental test (low-bias STM imaging) which would unambiguously distinguish between the {ital D} and {ital C} configurations. {copyright} {ital 1999} {ital The American Physical Society}

Khare, S.V.; Kulkarni, R.V.; Stroud, D.; Wilkins, J.W. [Department of Physics, Ohio State University, Columbus, Ohio 43210 (United States)

1999-08-01

363

Observation of Buried Phosphorus Dopants near Clean Si(100)-(2x1) with Scanning Tunneling Microscopy  

CERN Multimedia

We have used scanning tunneling microscopy to identify individual phosphorus dopant atoms near the clean silicon (100)-(2x1) reconstructed surface. The charge-induced band bending signature associated with the dopants shows up as an enhancement in both filled and empty states and is consistent with the appearance of n-type dopants on compound semiconductor surfaces and passivated Si(100)-(2x1). We observe dopants at different depths and see a strong dependence of the signature on the magnitude of the sample voltage. Our results suggest that, on this clean surface, the antibonding surface state band acts as an extension of the bulk conduction band into the gap. The positively charged dimer vacancies that have been observed previously appear as depressions in the filled states, as opposed to enhancements, because they disrupt these surface bands.

Brown, G W; Hawley, M E; Brown, Geoffrey W.; Grube, Holger; Hawley, Marilyn E.

2004-01-01

364

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

UK PubMed Central (United Kingdom)

We have designed a supporting system to fix a sample holder of a scanning tunneling microscope in an UHV chamber at room temperature. The microscope will operate down to a temperature of 20 K. Low thermal conductance, high mechanical stiffness, and small dimensions are the main features of the supporting system. Three sets of four glass balls placed in vertices of a tetrahedron are used for thermal insulation based on small contact areas between the glass balls. We have analyzed the thermal conductivity of the contacts between the balls mutually and between a ball and a metallic plate while the results have been applied to the entire support. The calculation based on a simple model of the setup has been verified with some experimental measurements. In comparison with other feasible supporting structures, the designed support has the lowest thermal conductance.

Hanzelka P; Vonka J; Musilova V

2013-08-01

365

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

Science.gov (United States)

We have designed a supporting system to fix a sample holder of a scanning tunneling microscope in an UHV chamber at room temperature. The microscope will operate down to a temperature of 20 K. Low thermal conductance, high mechanical stiffness, and small dimensions are the main features of the supporting system. Three sets of four glass balls placed in vertices of a tetrahedron are used for thermal insulation based on small contact areas between the glass balls. We have analyzed the thermal conductivity of the contacts between the balls mutually and between a ball and a metallic plate while the results have been applied to the entire support. The calculation based on a simple model of the setup has been verified with some experimental measurements. In comparison with other feasible supporting structures, the designed support has the lowest thermal conductance. PMID:24007103

Hanzelka, Pavel; Vonka, Jakub; Musilova, Vera

2013-08-01

366

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

DEFF Research Database (Denmark)

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

Engbæk, Jakob; SchiØtz, Jakob

2006-01-01

367

Growth Mechanism of Sputtered Films of YBa2Cu3O7 Studied by Scanning Tunneling Microscopy.  

Science.gov (United States)

The surface microstructures of c-axis-oriented films of YBa(2)Cu(3)O(7), deposited by off-axis magnetron sputtering on MgO and SrTiO(3) single crystal (100) substrates, have been investigated with scanning tunneling microscopy and atomic force microscopy. There is strong evidence that the films nucleate as islands and grow by adding material to the edge of a spirally rising step. This results in columnar grains, each of which contains a screw dislocation at its center. This microstructure may be of significance in determining superconducting properties such as critical current, and represents a significant difference between thin films (especially those grown in situ) and bulk materials. PMID:17793141

Hawley, M; Raistrick, I D; Beery, J G; Houlton, R J

1991-03-29

368

Scanning tunneling microscopy study of GaAs(1 0 0) surface prepared by HCl-isopropanol treatment  

International Nuclear Information System (INIS)

[en] In this letter, scanning tunneling microscopy (STM) is utilized to investigate surface morphology and a local atomic structure of the GaAs(1 0 0) surfaces prepared by the HCl-isopropanol (HCl-iPA) treatment and annealing in ultrahigh vacuum (UHV). Low-energy electron diffraction (LEED) reveals that the (2x4) reconstruction appears on the HCl-iPA treated GaAs(1 0 0) surface after an UHV annealing at 300 deg. C. According to the STM images, this (2x4) structure is ? phase. Both LEED and STM suggest improvement in surface quality of the HCl-iPA GaAs(1 0 0) with increasing the annealing temperature in the range of 300-400 deg. C

2003-02-15

369

A 350 mK, 9 T scanning tunneling microscope for the study of superconducting thin films and single crystals  

CERN Multimedia

We report the construction and performance of a low temperature, high field scanning tunneling microscope (STM) operating down to 350mK and in magnetic fields up to 9T, with thin film deposition and in-situ cleaving capabilities. The main focus lies on the simple design of STM head allowing top loading of the sample and innovative sample holder design that allows us to get spectroscopic data on superconducting thin films grown in-situ on insulating substrates. Other design details on sample transport, chamber and vibration isolation scheme will also be described. We demonstrate the capability of our instrument through the atomic resolution imaging and spectroscopy on NbSe2 single crystal and spectroscopic maps obtained on homogeneously disordered NbN thin film.

Kamlapure, Anand; Ganguli, Somesh Chandra; Bagwe, Vivas; Raychaudhuri, Pratap; Pai, Subash P

2013-01-01

370

Capping process of InAs/GaAs quantum dots studied by cross-sectional scanning tunneling microscopy  

International Nuclear Information System (INIS)

The capping process of self-assembled InAs quantum dots (QDs) grown on GaAs(100) substrates by molecular-beam epitaxy is studied by cross-sectional scanning tunneling microscopy. GaAs capping at 500 deg. C causes leveling of the QDs which is completely suppressed by decreasing the growth temperature to 300 deg. C. At elevated temperature the QD leveling is driven in the initial stage of the GaAs capping process while it is quenched during continued overgrowth when the QDs become buried. For common GaAs growth rates, both phenomena take place on a similar time scale. Therefore, the size and shape of buried InAs QDs are determined by a delicate interplay between driving and quenching of the QD leveling during capping which is controlled by the GaAs growth rate and growth temperature.

2004-12-06

371

Measurement of the Mott insulating gap of Sr2IrO4 with a scanning tunneling microscope  

Science.gov (United States)

Recently the 5d transition metal oxide Sr2IrO4 has become a material of interest. This is due to comparable interaction strengths between crystal field splitting, the Coulomb interaction, and spin-orbit coupling, resulting in a Mott insulating ground state that has a finite resistance even at cryogenic temperatures. In order to fully understand this material it is important to measure the Mott insulating gap. A scanning tunneling microscope is an excellent tool for studying this material for its ability to directly measure this gap. Our preliminary results show this gap measured on single crystals to be ˜50 meV which is comparable to the activation energy of this sample. We will discuss our current STM results and compare our results with other optical conductivity data obtained from this material.

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

2012-02-01

372

Growth of Cu films on Si(111)-7 x 7 surfaces at low temperature: a scanning tunnelling microscopy study  

International Nuclear Information System (INIS)

Morphologies of Cu(111) films on Si(111)-7 x 7 surfaces prepared at low temperature are investigated by scanning tunnelling microscopy (STM) and reflection high-energy electron diffraction (RHEED). At the initial growth stage, Cu films are flat due to the formation of silicide at the interface that decreases the mismatch between Cu films and the Si substrate. Different from the usual multilayer growth of Cu/Cu(111), on the silicide layer a layer-by-layer growth is observed. The two dimensional (2D) growth is explained by the enhanced high island density at low deposition temperature. Increasing deposition rate produces films with different morphologies, which is the result of Ostwald ripening. (authors)

2007-01-01

373

Scanning tunneling microscope study of electrical transport properties of nanoscale Schottky contacts between manganese silicide nanostructures and Si(111)  

Science.gov (United States)

The electrical transport properties of three types of manganese silicide nanocontacts, including tabular island/Si(111), nanowire/Si(111), and three-dimensional island/Si(111), are investigated by a scanning tunneling microscope with tip contacting the silicide islands. All current-voltage curves measured on the islands exhibit Schottky diode-like rectifying behaviors. Compared to the macroscopic counterparts, the nanocontacts display low Schottky barrier heights and extremely large ideality factors. The interface structure of the nanocontacts has a significant influence on the current at forward bias. This influence can be attributed to the leakage current associated with the conductive dislocations induced by the lattice mismatch between the islands and the substrate.

Liu, Xiao-Yong; Zou, Zhi-Qiang; Sun, Li-Min; Li, Xu

2013-07-01

374

Network Topology and Subgap Resonances Observed by Fourier Transform Scanning Tunnelling Microscopy in Cuprate High-Temperature Superconductors  

CERN Multimedia

Fourier transform scanning tunneling microscopy on BSCCO subgap resonances has deciphered an octet of "quasi-particle" states that are consistent with the Fermi surface and energy gap observed by ARPES, but the origin of the high-intensity k-space octets and the sharply defined r-space checkerboard is unexplained. The filamentary ferroelastic nanodomain model that predicted the r-space checkerboard also explains the k-space octets and the origin of the apparent anisotropic surface d-wave gap by using strong electron-phonon interactions outside the CuO2 planes. The topological model identifies the factors that stabilize high-intensity k-space octets in the presence of a very high level of irregular r-space checkerboard noise.

Phillips, J C

2003-01-01

375

Scanning tunneling microscopy studies of the surfaces of a-Si:H and a-SiGe:H films  

Energy Technology Data Exchange (ETDEWEB)

The report contains a detailed description of the experimental complexities encountered in developing scanning tunneling microscope (STM) probing of atomic structure on the surface of freshly-grown hydrogenated-amorphous semiconductors. It also contains a speculative microscopic film-growth model that explains differences between the disorder in CVD grown a-Ge:H versus a-Si:H films. This model is derived from prior results obtained in the chemical analysis of GeH{sub 4} plasmas, combined with surface reaction and thermodynamic considerations. The neutral radical fragments of silane, disilane and germane dissociation in discharges, which dominate the vapor and film-growth reactions, have been deduced from detailed analysis of prior data and are reported. 4 refs., 7 figs.

Gallagher, A.; Ostrom, R.; Tannenbaum, D. (National Inst. of Standards and Technology, Boulder, CO (USA))

1991-06-01

376

Surface reconstruction of FeAl(110) studied by scanning tunnelling microscopy and angle-resolved photoemission spectroscopy  

Science.gov (United States)

The surface geometric and electronic structure of the FeAl(110) intermetallic alloy has been investigated by scanning tunnelling microscopy and angle-resolved photoemission spectroscopy (ARPES). Preferential sputtering results in depletion of Al in the surface region and subsequent annealing promotes surface segregation of Al and gives rise to new reconstructed phases. A bulk terminated surface structure is obtained after annealing the surface to 400 °C. However, an incommensurate phase develops above 800 °C with a stoichiometry consistent with an FeAl2 structure in the topmost layer. The ARPES measurements confirm the Al segregation with increased density of states (DOS) near the Fermi level. The increased DOS is believed to be due to hybridization between the Fe d and Al sp states. The increased intensity of the Al 2p core level for the incommensurate phase also confirms the higher Al surface concentration for this phase.

Kizilkaya, O.; Hite, D. A.; Zehner, D. M.; Sprunger, P. T.

2004-08-01

377

Scanning tunneling microscopy (STM) and lateral force microscopy (LFM) investigation of the structure and character of conductive polypyrrole film  

Energy Technology Data Exchange (ETDEWEB)

Polypyrrole doped with p-toluenesulfonate was electropolymerized onto highly oriented pyrolytic graphite (HOPG), glassy carbon (GC) and Pt electrode surfaces under the same experimental conditions. The resulting films were studied by scanning tunneling microscopy (STM) and lateral force microscopy (LFM). It is found that the topography of these thick films on HOPG, GC and Pt is very similar although their substrate surface morphology is completely different. Furthermore, the microstructure of these films generally transforms from disordered, amorphous and flocculent particles to ordered, homogeneous and oriented granules on exposure to air. In addition, the effect of different ions on surface morphology and the thermal stability of the polypyrrole films are also discussed in detail. ((orig.))

Li Jing (Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China)); Wang Erkang (Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China))

1994-09-15

378

Two-probe theory of scanning tunneling microscopy of single molecules: Zn(II)-etioporphyrin on alumina  

CERN Document Server

We explore theoretically the scanning tunneling microscopy of single molecules on substrates using a framework of two local probes. This framework is appropriate for studying electron flow in tip/molecule/substrate systems where a thin insulating layer between the molecule and a conducting substrate transmits electrons non-uniformly and thus confines electron transmission between the molecule and substrate laterally to a nanoscale region significantly smaller in size than the molecule. The tip-molecule coupling and molecule-substrate coupling are treated on the same footing, as local probes to the molecule, with electron flow modelled using the Lippmann-Schwinger Green function scattering technique. STM images are simulated for various positions of the stationary (substrate) probe below a Zn(II)-etioporphyrin I molecule. We find that these images have a strong dependence on the substrate probe position, indicating that electron flow can depend strongly on both tip position and the location of the dominant mol...

Buker, J; Buker, John; Kirczenow, George

2005-01-01

379

Asymmetric tunneling, Andreev reflection and dynamic conductance spectra in strongly correlated metals  

CERN Document Server

Landau Fermi liquid theory predicts that the differential conductivity between metallic point and metal is a symmetric function of voltage bias V. This symmetry holds if the particle-hole symmetry is preserved. We show that the situation can be different when one of the two metals is a strongly correlated one whose electronic system can be represented by a heavy fermion liquid. When the heavy fermion liquid undergoes fermion condensation quantum phase transition, the particle-hole symmetry is violated making both the differential tunneling conductivity and dynamic conductance asymmetric as a function of applied voltage. This asymmetry can be observed when the strongly correlated metal is either normal or superconducting. We show that at small values of $V the asymmetric part of the dynamic conductance is a linear function of V and inversely proportional to the maximum value of the gap and does not depend on temperature provided that metal is superconducting, when it becomes normal the asymmetric part diminish...

Shaginyan, V R

2006-01-01

380

Using a hybrid superconducting-ferromagnetic tip as a magnetic scanning tunneling microscope  

CERN Multimedia

Approaching a two-component tip made of a superconductor (S) and a ferromagnet (F) from a magnetic sample allows for two distinct tunneling processes between the ferromagnets, through S: i) Charge and spin are conserved; ii) Charge and spin are reversed, e.g. a Cooper pair flows from S, one electron going into F, the other into the sample. At subgap voltages, this allows two currents to flow from the tip : one is insensitive to the spin polarizations and allows for surface topography, the other directly tracks the relative spin polarizations of F and the sample. The whole device acts as a STM sensitive to the spin polarization at the Fermi level (MSTM). Its sensitivity is studied and optimized with respect to the tip geometry.

Feinberg, D

2002-01-01

 
 
 
 
381

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

Science.gov (United States)

The electropolymerization of 3,4-ethylenedioxythiophene (EDOT) to poly(3,4-ethylenedioxythiophene) (PEDOT) was investigated in the air and water-stable ionic liquids 1-hexyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate [HMIm]FAP and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) amide [EMIm]TFSA. In situ scanning tunnelling microscopy (STM) results show that the electropolymerization of EDOT in the ionic liquid can be probed on the nanoscale. In contrast to present understanding, it was observed that the EDOT can be oxidised in ionic liquids well below its oxidation potential and the under potential growth of polymer was visualized by in situ STM. These results serve as the first study to confirm the under potential growth of conducting polymers in ionic liquids. Furthermore, ex situ microscopy measurements were performed. Quite a high current of 670 nA was observed on the nanoscale by conductive scanning force microscopy (CSFM).The electropolymerization of 3,4-ethylenedioxythiophene (EDOT) to poly(3,4-ethylenedioxythiophene) (PEDOT) was investigated in the air and water-stable ionic liquids 1-hexyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate [HMIm]FAP and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) amide [EMIm]TFSA. In situ scanning tunnelling microscopy (STM) results show that the electropolymerization of EDOT in the ionic liquid can be probed on the nanoscale. In contrast to present understanding, it was observed that the EDOT can be oxidised in ionic liquids well below its oxidation potential and the under potential growth of polymer was visualized by in situ STM. These results serve as the first study to confirm the under potential growth of conducting polymers in ionic liquids. Furthermore, ex situ microscopy measurements were performed. Quite a high current of 670 nA was observed on the nanoscale by conductive scanning force microscopy (CSFM). Electronic supplementary information (ESI) available: In situ image of PEDOT in [HMIm]FAP and in situ studies of PEDOT grown in [EMIm]TFSA and redox behavior of PEDOT. See DOI: 10.1039/c0nr00579g

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

2011-01-01

382

Control of charging in resonant tunneling through InAs nanocrystal quantum dots  

CERN Multimedia

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 linker molecules, where charging took place. Charging is regained upon reducing the tip-nanocrystal distance, making the junctions more symmetric. The effect of voltage distribution between the junctions on the measured spectra is also discussed.

Katz, D; Kan, S H; Banin, U; Katz, David; Millo, Oded; Kan, Shi-Hai; Banin, Uri

2001-01-01

383

Nanographenes as active components of single-molecule electronics and how a scanning tunneling microscope puts them to work.  

UK PubMed Central (United Kingdom)

Single-molecule electronics, that is, realizing novel electronic functionalities from single (or very few) molecules, holds promise for application in various technologies, including signal processing and sensing. Nanographenes, which are extended polycyclic aromatic hydrocarbons (PAHs), are highly attractive subjects for studies of single-molecule electronics because the electronic properties of their flat conjugated systems can be varied dramatically through synthetic modification of their sizes and topologies. Single nanographenes provide high tunneling currents when adsorbed flat onto conducting substrates, such as graphite. Because of their chemical inertness, nanographenes interact only weakly with these substrates, thereby preventing the need for special epitaxial structure matching. Instead, self-assembly at the interface between a conducting solid, such as the basal plane of graphite, and a nanographene solution generally leads to highly ordered monolayers. Scanning tunneling spectroscopy (STS) allows the current-voltage characteristics to be measured through a single molecule positioned between two electrodes; the key to the success of STS is the ability to position the scanning tunneling microscopy (STM) tip freely with respect to the molecule in all dimensions, that is, both parallel and perpendicular to the surface. In this Account, we report the properties of nanographenes having sizes ranging from 0.7 to 3.1 nm and exhibiting various symmetry, periphery, and substitution types. The size of the aromatic system and the nature of its perimeter are two essential features affecting its HOMO-LUMO gap and charge carrier mobility in the condensed phase. Moreover, the extended pi area of larger substituted PAHs improves the degree of self-ordering, another key requirement for high-performance electronic devices. Self-assembly at the interface between an organic solution and the basal plane of graphite allows deposition of single molecules within the well-defined environment of a molecular monolayer. We have used STM and STS to investigate both the structures and electronic properties of these single molecules in situ. Indeed, we have observed key electronic functions, rectification and current control through single molecules, within a prototypical chemical field-effect transistor at ambient temperature. The combination of nanographenes and STM/STS, with the PAHs self-assembled in oriented molecular mono- or bilayers at the interface between an organic solution and the basal plane of graphite and contacted by the STM tip, is a simple, reliable, and versatile system for developing the fundamental concepts of molecular electronics. Our future targets include fast reversible molecular switches and complex molecular electronic devices coupled together from several single-molecule systems.

Müllen K; Rabe JP

2008-04-01

384

Low-temperature scanning tunneling microscopy of ring-like surface electronic structures around Co islands on InAs(110) surfaces.  

Science.gov (United States)

We report on the experimental observation by scanning tunneling microscopy at low temperature of ring-like features that appear around Co metal islands deposited on a clean (110) oriented surface of cleaved p-type InAs crystals. These features are visible in spectroscopic images within a certain range of negative tunneling bias voltages due to the presence of a negative differential conductance in the current-voltage dependence. A theoretical model is introduced, which takes into account non-equilibrium effects in the small tunneling junction area. In the framework of this model the appearance of the ring-like features is explained in terms of interference effects between electrons tunneling directly and indirectly (via a Co island) between the tip and the InAs surface. PMID:19928137

Muzychenko, D A; Schouteden, K; Savinov, S V; Maslova, N S; Panov, V I; Van Haesendonck, C

2009-08-01

385

Scanning tunneling microscopy study of oxide nucleation and oxidation-induced roughening at elevated temperatures on the Si(001)-(2×1) surface  

Science.gov (United States)

Room temperature scanning tunneling microscopy images of Si(001)-(2×1) surfaces exposed to O2 at pressures 1×10-8Pmox, with m>=2. This is consistent with a simple model in which two diffusing surface oxygen species are required to nucleate a stable oxide cluster.

Seiple, J. V.; Pelz, J. P.

1994-08-01

386

Development of Near-Field Microwave Microscope with the Functionality of Scanning Tunneling Spectroscopy  

Science.gov (United States)

We describe the details of an original near-field scanning microwave microscope, developed for simultaneous measurements of local density-of-states (LDOS) and local ohmic losses (LOL). Improving microwave detection systems, we have succeeded in distinguishing the LDOS and LOL even between two low resistance materials; gold and highly orientated pyrolitic graphite. The experimental data indicate that our microscope holds a capability to investigate both LDOS and LOL in nanoscale.

Machida, Tadashi; Gaifullin, Marat B.; Ooi, Shuuich; Kato, Takuya; Sakata, Hideaki; Hirata, Kazuto

2010-11-01

387

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1988-12-01

388

Non-collinear exchange coupling in Fe/Mn/Fe(0 0 1): insight from scanning tunneling microscopy  

International Nuclear Information System (INIS)

The film growth and morphology of epitaxial Mn films grown on Fe(0 0 1) single-crystal whiskers measured with scanning tunneling microscopy (STM) provides insight into the mechanism of interlayer exchange coupling in Fe/Mn/Fe(0 0 1) trilayers. The proximity model of Slonczewski for exchange coupling through an antiferromagnet predicts that the coupling angle between the ferromagnetic layers will oscillate around a mean value of 90 deg. with an amplitude that is very sensitive to the width of the thickness distribution of the spacer layer. We measure the thickness distribution with the STM and find that the coupling angle variation predicted by the proximity model is qualitatively consistent with the actual coupling angle variations in Fe/Mn/Fe(0 0 1) measured with scanning electron microscopy with polarization analysis (SEMPA). Going beyond the proximity model and allowing for a non-uniform magnetization of the thin Fe overlayer provides an improved explanation of the results. We contrast the behavior of Fe/Mn/Fe(0 0 1), where the proximity model appears applicable, to coupling through antiferro-magnetic Cr in Fe/Cr/Fe(0 0 1), where it is not, and discuss possible reasons for the difference.

2000-01-01

389

Non-collinear exchange coupling in Fe/Mn/Fe(0 0 1): insight from scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

The film growth and morphology of epitaxial Mn films grown on Fe(0 0 1) single-crystal whiskers measured with scanning tunneling microscopy (STM) provides insight into the mechanism of interlayer exchange coupling in Fe/Mn/Fe(0 0 1) trilayers. The proximity model of Slonczewski for exchange coupling through an antiferromagnet predicts that the coupling angle between the ferromagnetic layers will oscillate around a mean value of 90 deg. with an amplitude that is very sensitive to the width of the thickness distribution of the spacer layer. We measure the thickness distribution with the STM and find that the coupling angle variation predicted by the proximity model is qualitatively consistent with the actual coupling angle variations in Fe/Mn/Fe(0 0 1) measured with scanning electron microscopy with polarization analysis (SEMPA). Going beyond the proximity model and allowing for a non-uniform magnetization of the thin Fe overlayer provides an improved explanation of the results. We contrast the behavior of Fe/Mn/Fe(0 0 1), where the proximity model appears applicable, to coupling through antiferro-magnetic Cr in Fe/Cr/Fe(0 0 1), where it is not, and discuss possible reasons for the difference.

Pierce, D.T. E-mail: daniel.pierce@nist.gov; Davies, A.D.; Stroscio, J.A.; Tulchinsky, D.A.; Unguris, J.; Celotta, R.J

2000-12-01

390

Combined low-temperature scanning tunneling/atomic force microscope for atomic resolution imaging and site-specific force spectroscopy.  

Science.gov (United States)

We present the design and first results of a low-temperature, ultrahigh vacuum scanning probe microscope enabling atomic resolution imaging in both scanning tunneling microscopy (STM) and noncontact atomic force microscopy (NC-AFM) modes. A tuning-fork-based sensor provides flexibility in selecting probe tip materials, which can be either metallic or nonmetallic. When choosing a conducting tip and sample, simultaneous STM/NC-AFM data acquisition is possible. Noticeable characteristics that distinguish this setup from similar systems providing simultaneous STM/NC-AFM capabilities are its combination of relative compactness (on-top bath cryostat needs no pit), in situ exchange of tip and sample at low temperatures, short turnaround times, modest helium consumption, and unrestricted access from dedicated flanges. The latter permits not only the optical surveillance of the tip during approach but also the direct deposition of molecules or atoms on either tip or sample while they remain cold. Atomic corrugations as low as 1 pm could successfully be resolved. In addition, lateral drifts rates of below 15 pm/h allow long-term data acquisition series and the recording of site-specific spectroscopy maps. Results obtained on Cu(111) and graphite illustrate the microscope's performance. PMID:18377012

Albers, Boris J; Liebmann, Marcus; Schwendemann, Todd C; Baykara, Mehmet Z; Heyde, Markus; Salmeron, Miquel; Altman, Eric I; Schwarz, Udo D

2008-03-01

391

Combined low-temperature scanning tunneling/atomic force microscope for atomic resolution imaging and site-specific force spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

The authors present the design and first results of a low-temperature, ultrahigh vacuum scanning probe microscope enabling atomic resolution imaging in both scanning tunneling microscopy (STM) and noncontact atomic force microscopy (NC-AFM) modes. A tuning-fork-based sensor provides flexibility in selecting probe tip materials, which can be either metallic or nonmetallic. When choosing a conducting tip and sample, simultaneous STM/NC-AFM data acquisition is possible. Noticeable characteristics that distinguish this setup from similar systems providing simultaneous STM/NC-AFM capabilities are its combination of relative compactness (on-top bath cryostat needs no pit), in situ exchange of tip and sample at low temperatures, short turnaround times, modest helium consumption, and unrestricted access from dedicated flanges. The latter permits not only the optical surveillance of the tip during approach but also the direct deposition of molecules or atoms on either tip or sample while they remain cold. Atomic corrugations as low as 1 pm could successfully be resolved. In addition, lateral drifts rates of below 15 pm/h allow long-term data acquisition series and the recording of site-specific spectroscopy maps. Results obtained on Cu(111) and graphite illustrate the microscope's performance.

Schwarz, Udo; Albers, Boris J.; Liebmann, Marcus; Schwendemann, Todd C.; Baykara, Mehmet Z.; Heyde, Markus; Salmeron, Miquel; Altman, Eric I.; Schwarz, Udo D.

2008-02-27

392

Combined low-temperature scanning tunneling/atomic force microscope for atomic resolution imaging and site-specific force spectroscopy.  

UK PubMed Central (United Kingdom)

We present the design and first results of a low-temperature, ultrahigh vacuum scanning probe microscope enabling atomic resolution imaging in both scanning tunneling microscopy (STM) and noncontact atomic force microscopy (NC-AFM) modes. A tuning-fork-based sensor provides flexibility in selecting probe tip materials, which can be either metallic or nonmetallic. When choosing a conducting tip and sample, simultaneous STM/NC-AFM data acquisition is possible. Noticeable characteristics that distinguish this setup from similar systems providing simultaneous STM/NC-AFM capabilities are its combination of relative compactness (on-top bath cryostat needs no pit), in situ exchange of tip and sample at low temperatures, short turnaround times, modest helium consumption, and unrestricted access from dedicated flanges. The latter permits not only the optical surveillance of the tip during approach but also the direct deposition of molecules or atoms on either tip or sample while they remain cold. Atomic corrugations as low as 1 pm could successfully be resolved. In addition, lateral drifts rates of below 15 pm/h allow long-term data acquisition series and the recording of site-specific spectroscopy maps. Results obtained on Cu(111) and graphite illustrate the microscope's performance.

Albers BJ; Liebmann M; Schwendemann TC; Baykara MZ; Heyde M; Salmeron M; Altman EI; Schwarz UD

2008-03-01

393

Variable-temperature scanning tunneling microscopy. Final report, 21 Jul 88-20 Jul 91  

Energy Technology Data Exchange (ETDEWEB)

Variable temperature STM/STS has been used over the 4.2 K to 400 K temperature range to study CDW formation and spatial variations of the superconducting energy gap in Pb films. Topographic variations of the superconducting energy gap in Pb films show an intriguing transition from superconducting to normal behavior over distances much less than the bulk coherence length. More recently, effort has been focused on the development of a multi-chamber UHV-STM system that will couple a wide range of STM/STS capability with sample and tip preparation and characterization facilities. The first chamber of this system is fully functional and is being used to study and modify semiconductor surfaces. Other chambers will be specialized for STM nanolithography and cryogenic UHV-STM. This system accommodates UHV sample and tip transfer between chambers in addition to independent chamber operation modes. STM modification of H-passivated silicon surfaces has been accomplished using techniques developed by John Dagata at NIST. A unique STM lateral coarse translation system has been developed and used to locate and modify Si MOSFET structures fabricated for this project. Gratings written by STM within the gate region are being evaluated for the creation of finished devices that will exhibit quantum interference effects at higher temperatures than previously observed. Work is also underway to fabricate planar tunnel junction structures that utilize coulomb charging effects to realize logic functions.

Lyding, J.W.

1991-07-01

394

Interplay between Plasmon Luminescence and Vibrationally Resolved Molecular Luminescence Induced by Scanning Tunneling Microscopy  

CERN Document Server

Effects of the coupling between an exciton consisting of an electron and hole in a molecule and a surface plasmon (exciton-plasmon coupling) on the luminescence properties of the molecule and the surface plasmons are investigated using the nonequilibrium Green's function method. Molecular absorption and enhancement by molecular electronic and vibrational modes (molecular modes) lead to dip and peak structures in the luminescence spectra of the surface plasmons. It is considered that the corresponding structures can be seen in a recent experiment. Moreover we found that the re-absorption by the surface plasmons plays important roles in determining the luminescence spectral profiles.

Miwa, Kuniyuki; Kasai, Hideaki

2013-01-01

395

Note: Automated electrochemical etching and polishing of silver scanning tunneling microscope tips  

Science.gov (United States)

Fabrication of sharp and smooth Ag tips is crucial in optical scanning probe microscope experiments. To ensure reproducible tip profiles, the polishing process is fully automated using a closed-loop laminar flow system to deliver the electrolytic solution to moving electrodes mounted on a motorized translational stage. The repetitive translational motion is controlled precisely on the ?m scale with a stepper motor and screw-thread mechanism. The automated setup allows reproducible control over the tip profile and improves smoothness and sharpness of tips (radius 27 +/- 18 nm), as measured by ultrafast field emission.

Sasaki, Stephen S.; Perdue, Shawn M.; Perez, Alejandro Rodriguez; Tallarida, Nicholas; Majors, Julia H.; Apkarian, V. Ara; Lee, Joonhee

2013-09-01

396

Note: Automated electrochemical etching and polishing of silver scanning tunneling microscope tips.  

UK PubMed Central (United Kingdom)

Fabrication of sharp and smooth Ag tips is crucial in optical scanning probe microscope experiments. To ensure reproducible tip profiles, the polishing process is fully automated using a closed-loop laminar flow system to deliver the electrolytic solution to moving electrodes mounted on a motorized translational stage. The repetitive translational motion is controlled precisely on the ?m scale with a stepper motor and screw-thread mechanism. The automated setup allows reproducible control over the tip profile and improves smoothness and sharpness of tips (radius 27 ± 18 nm), as measured by ultrafast field emission.

Sasaki SS; Perdue SM; Perez AR; Tallarida N; Majors JH; Apkarian VA; Lee J

2013-09-01

397

Magnetic tunnel junctions of perpendicularly magnetized L10-MnGa/Fe/MgO/CoFe structures: Fe-layer-thickness dependences of magnetoresistance effect and tunnelling conductance spectra  

Science.gov (United States)

The tunnel magnetoresistance (TMR) effect and the bias voltage dependence of tunnelling conductance spectra were measured in L10 Mn-Ga/Fe/MgO/CoFe magnetic tunnel junctions (MTJs). The TMR ratio and bias-voltage dependences on annealing conditions and Fe-layer thickness were investigated. The TMR ratio showed an increase subsequent to Fe-layer deposition under the optimum annealing condition, and a maximum value of 24% was achieved in an MTJ with a perpendicularly magnetized Fe layer of thickness of 1.1 nm at room temperature; this corresponded to a 57% TMR ratio in the case of completely antiparallel magnetization configuration. In the tunnelling conductance spectra, an anomalous dip, the so-called zero-bias anomaly, was observed for all the samples. The zero-bias anomaly is speculated to have appeared because of an increase in magnon excitation at the magnetic layer/barrier interfaces according to the model by Zhang et al (1997 Phys. Rev. Lett. 79 3744). In our experiments magnitude of the zero-bias anomaly depended on both the annealing condition and the Fe-layer thickness. We discuss our observation of the variation in the Curie temperature of the magnetic layer at the barrier layer interface depending on the the preparation conditions of the Fe insertion layer, which caused the change in the magnitude of the zero-bias anomaly.

Kubota, T.; Ma, Q. L.; Mizukami, S.; Zhang, X. M.; Naganuma, H.; Oogane, M.; Ando, Y.; Miyazaki, T.

2013-04-01

398

Superconductivity and scanning tunneling microscopy (STM)/spectroscopy (STS) of transition metal oxide artificial lattices  

International Nuclear Information System (INIS)

[en] High Tc superconducting artificial lattices and superlattices have been constructed by a laser molecular beam epitaxy method. A layer-by-layer growth method controlled by RHEED and STM is a promising method for the construction of these artificial lattices. Formation and properties of superconducting artificial lattices and superconducting/ferromagnetic superlattices are presented as the typical examples. In order to investigate the electronic state of carrier doped strongly correlated electronic system, STM measurements have been performed on La2-xSrxCuO4, La2-xSrxNiO4, and La1-xSrxMnO3 thin films. Based on the similarities and the differences between the STM spectra of the three types of the films, electronic states of the strongly correlated system are discussed

1996-01-01

399

Electron transport across capped Au nanoclusters adsorbed in different configurations on highly oriented pyrolytic graphite substrate using scanning tunneling microscopy / spectroscopy  

International Nuclear Information System (INIS)

Comparison of electron transport across dodecanethiol capped Au nanoclusters adsorbed in different locations viz. in an agglomeration, on isolated particle either on the terrace or at the step edge of highly oriented pyrolytic graphite using scanning tunneling microscopy / spectroscopy is carried out. Current-distance measurements on these different locations shows different regimes suggesting different mechanisms for electron transport. Current-voltage measurements at these locations have been carried out and the results are discussed in the light of orthodox theory for electron transport in double-barrier tunnel junction.

2006-08-04

400

Electron transport across capped Au nanoclusters adsorbed in different configurations on highly oriented pyrolytic graphite substrate using scanning tunneling microscopy / spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

Comparison of electron transport across dodecanethiol capped Au nanoclusters adsorbed in different locations viz. in an agglomeration, on isolated particle either on the terrace or at the step edge of highly oriented pyrolytic graphite using scanning tunneling microscopy / spectroscopy is carried out. Current-distance measurements on these different locations shows different regimes suggesting different mechanisms for electron transport. Current-voltage measurements at these locations have been carried out and the results are discussed in the light of orthodox theory for electron transport in double-barrier tunnel junction.

Singh, Poonam; Dharmadhikari, C V [Centre for Advanced Studies in Materials Science and Solid State Physics, Department of Physics, University of Pune, Pune 411007 (India)

2007-04-15

 
 
 
 
401

Scanning tunneling spectroscopic (STS) studies of magnetically doped MBE-grown topological insulators (TIs)  

Science.gov (United States)

We conduct STS studies on MBE-grown heterostructures of non-magnetic TI (Bi2Se3) with a range of thicknesses (d = 1, 3, 5, 7 quintuple layers, QL) on top of 7-QL magnetically doped TI (Cr-doped Bi2Se3). For d = 1 and 3-QL, a spatially homogeneous magnetism-induced surface gap (as large as about 150 meV for d = 1-QL) is observed at 77 K, whereas gapless Dirac spectra are found for d = 5 and 7-QL, suggesting that the effective magnetic length for Cr-doped Bi2Se3 is approximately 4 ˜ 5-QL. These findings are further corroborated by ARPES and bulk electrical transport measurements. The magnetism-induced surface gap differs from those found in pure Bi2Se3 and (Bi0.5Sb0.5)2Te3 films of thicknesses smaller than 6-QL, because the latter are due to overlaps of wave functions between the surface and interface layers, which lead to Rashba-like spin-orbit splitting and spin-preserving quasiparticle interference wave-vectors. In contrast, STS studies of TIs with magnetism-induced surface gap do not yield any quasiparticle interferences for energies within the bulk Bi2Se3 gap. Finally, comparative STS studies of pure and magnetically doped TIs in high magnetic fields will be discussed.

Chu, Hao; Teague, Marcus; Chen, Chien-Chang; Woodward, Nicholas; Yeh, Nai-Chang; Kou, Xufeng; He, Liang; Lang, Murong; Wang, Kang Long

2013-03-01

402

In Situ Scanning Tunneling Microscopy Study of 5,6-Dimethyl Uracil on Au (111)  

Directory of Open Access Journals (Sweden)

Full Text Available The hydrogen evolution mediated 5,6-dimethyluracil (5,6-DMU) film disordering and subsequent reordering was studied in situ in sulfuric acid solution on Au (111) using STM and cyclic voltammetry. A stable, condensed physisorbed film was formed between the limits of the hydrogen evolution (at -0.3 V/SCE) and the lifting of the surface reconstruction (at 0.4 V/SCE) in the bulk solution concentration used in this study. The onset of hydrogen evolution led to the formation of "bubble" like structures which disrupted the stability of the film causing a disordering process which takes place within the whole scanned area. Stepping the potential back to the region of stability allowed the real time observation of the film reorganization. An anisotropic evolution of the film was found. The surface step edges were not found to be preferential nucleation sites. The molecular packing structure was inferred from high-resolution STM images and the existence of two distinct adsorbate states was established.

Cunha Frederico G. C.; Nart Francisco C.

2001-01-01

403

Dynamics of decanethiol self-assembled monolayers on Au(111) studied by time-resolved scanning tunneling microscopy.  

UK PubMed Central (United Kingdom)

We investigated the dynamics of decanethiol self-assembled monolayers on Au(111) surfaces using time-resolved scanning tunneling microscopy at room temperature. The expected ordered phases (?, ?, ?*, and ?) and a disordered phase (?) were observed. Current-time traces with the feedback loop disabled were recorded at different locations on the surface. The sulfur end group of the decanethiolate molecule exhibits a stochastic two-level switching process when the molecule is adsorbed in a (local) ? phase registry. This two-level process is attributed to the diffusion of the Au-thiolate complex between two adjacent adsorption sites. The irregular current jumps in the current-time traces recorded on the tails of decanethiolate molecules in the ordered ?, ?, and ?* phases are ascribed to wagging of the alkyl tails. Finally, the disordered phase is characterized by even larger current jumps, which indicates that the tail of the decanethiolate flips up occasionally and makes contact with the tip. Our experiments reveal that the massive dynamics of the self-assembled monolayer is due to diffusion of decanethiol-Au complexes, rather than the diffusion of decanethiolate molecules.

Wu H; Sotthewes K; Kumar A; Vancso GJ; Schön PM; Zandvliet HJ

2013-02-01

404

Atomic structures of silicene layers grown on ag(111): scanning tunneling microscopy and noncontact atomic force microscopy observations.  

UK PubMed Central (United Kingdom)

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

Resta A; Leoni T; Barth C; Ranguis A; Becker C; Bruhn T; Vogt P; Le Lay G

2013-08-01

405

Scanning tunneling microscopy of the surface topography and surface etching of nanoscale structures on the high-temperature superconductors  

International Nuclear Information System (INIS)

We report on the use of the scanning tunneling microscope (STM) for etching both single crystal and thin film, YBa2Cu3O7-x. Nanoscale features can be generated with the STM by ablation of atoms rastered by the microscope tip. The etching process can be controlled to remove layers of material which are multiples of the c axis (12 A). Various geometric features have been fabricated ranging from fine lines to square etch pits. The STM has also been used to study the growth mechanism and surface topography of thin films of YBa2Cu3O7-x produced by in situ laser deposition (Jc typically 1x106 A cm-2 at 77 K). Step features equal to the c axis of the material can be readily identified which form pinnacles or chip like morphologies at the surface. These surfaces can also be etched with the STM to reveal a more continuous substructure consistent with the high Jc's observed

1991-09-01

406

A scanning tunneling microscope study of single platinum atoms, platinum dimers and trimers on highly-oriented pyrolytic graphite  

International Nuclear Information System (INIS)

[en] We report a topographic study of platinum clusters on highly-oriented pyrolytic graphite (HOPG) using a scanning tunneling microscope operating in air. The particles were produced by evaporation of platinum onto the graphite-surface in high vacuum. The simultaneous finding of single platinum atoms, clusters and small particles on an otherwise clean and atomically flat surface shows that the platinum-HOPG surface interaction is strong enough to yield stable images of Pt atoms and yet is not strong enough to annihilate the Pt-Pt interaction. Small flat platinum clusters on HOPG can be imaged with atomic resolution of the cluster and the surrounding graphite lattice. We show the adsorption site distribution for the monomers. The Pt-dimers show a very broad bond length distribution on graphite with an average of 2.46 A. We found two types of Pt-trimers, one which is almost linear and one of triangular form. The average nearest neighbour distance of the trimers is 2.61 A. (orig.)

1991-01-01

407

A scanning tunneling microscope study of single platinum atoms, platinum dimers and trimers on highly-oriented pyrolytic graphite  

Energy Technology Data Exchange (ETDEWEB)

We report a topographic study of platinum clusters on highly-oriented pyrolytic graphite (HOPG) using a scanning tunneling microscope operating in air. The particles were produced by evaporation of platinum onto the graphite-surface in high vacuum. The simultaneous finding of single platinum atoms, clusters and small particles on an otherwise clean and atomically flat surface shows that the platinum-HOPG surface interaction is strong enough to yield stable images of Pt atoms and yet is not strong enough to annihilate the Pt-Pt interaction. Small flat platinum clusters on HOPG can be imaged with atomic resolution of the cluster and the surrounding graphite lattice. We show the adsorption site distribution for the monomers. The Pt-dimers show a very broad bond length distribution on graphite with an average of 2.46 A. We found two types of Pt-trimers, one which is almost linear and one of triangular form. The average nearest neighbour distance of the trimers is 2.61 A. (orig.).

Mueller, U.; Sattler, K.; Xhie, J.; Venkateswaran, N.; Raina, G. (Hawaii Univ., Manoa (USA))

1991-01-01

408

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

Science.gov (United States)

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

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

2013-01-01

409

Scanning tunneling microscope study of La- and Sb-doped BaSnO3 thin films  

Science.gov (United States)

The La-doped BaSnO3(BLSO) system was found to exhibit high electron mobility and high oxygen stability along with its transparency in visible spectrum. Additionally, we recently observed a significant difference in electron mobility values between BLSO and Sb-doped BSO (BSSO) epitaxial thin films. In order to elucidate the origin of the different mobility in BLSO and BSSO thin films, we have investigated a density of states (DOS) of BLSO and BSSO by scanning tunneling microscopy and spectroscopy. Our measurements were performed at 77 K in ultra-high vacuum of 2x10-10 Torr. We will compare the DOS of the conduction band of BLSO with that of BSSO. Only in the conduction band of BSSO, we found a specific peak that can be identified as due to the localized Sb impurity states. Our results provide strong evidence for the strong influence of localized Sb impurity states on the electron mobility. We will explain our data by anisotropy of scattering on the Fermi surface by resorting to band structure calculations of BLSO and BSSO.

Ju, Chan-Jong; Kim, Hoonmin; Kim, Useong; Park, Chulkwon; Char, Kookrin

2013-03-01

410

Molecular dynamics and energy landscape of decanethiolates in self-assembled monolayers on Au(111) studied by scanning tunneling microscopy.  

UK PubMed Central (United Kingdom)

The energetics and dynamics of the various phases of decanethiolate self-assembled monolayers on Au(111) surfaces were studied with scanning tunneling microscopy. We have observed five different phases of the decanethiolate monolayer on Au(111): four ordered phases (?, ?, ?*, and ?) and one disordered phase (?). We have determined the boundary free energies between the disordered and order phases by analyzing the thermally induced meandering of the domain boundaries. On the basis of these results, we are able to accurately predict the two-dimensional phase diagram of the decanethiolate/Au(111) system. The order-disorder phase transition of the ?* phase occurs at 295 K, followed by the order-disorder phase transition of the ? phase at 325 K. Above temperatures of 325 K, only the densely packed ? and disordered ? phases remain. Our findings are in good agreement with the phase diagram of the decanethiolate/Au(111) system that was put forward by Poirier et al. [Langmuir 2001, 17 (4), 1176-1183].

Sotthewes K; Wu H; Kumar A; Vancso GJ; Schön PM; Zandvliet HJ

2013-03-01

411

Effect of bromine and substituted alkyl chain on the interfacial self-assembly of bromobenzene derivatives by scanning tunneling microscopy.  

UK PubMed Central (United Kingdom)

The self-assemblies of four compounds, 1-bromo-4-(hexadecyloxy)benzene (BHB-16), 1-bromo-4-(octadecyloxy)benzene (BOB-18), 1-bromo-4-(pentadecyloxy)benzene (BPB-15) and 1,4-dibromo-2,5-(dioctadecyloxy)benzene (DDB-18), have been studied on highly oriented pyrolytic graphite (HOPG) under ambient conditions by scanning tunneling microscopy (STM), with the aim of understanding the influence of the molecular structure and functional groups on the arrangements. It is found that the bromine atoms of the four molecules are in bright contrast and can be identified in STM images. The neighbouring phenyl head groups of the BHB-16, BOB-18 and BPB-15 molecules in one lamella, with an anti-parallel orientation, are interdigitated with different offset distance, while the aromatic cores of DDB-18 molecules in the same row are in a parallel orientation. Moreover, an odd-even effect is observed in the self-assemblies of the former three molecules as expected. The STM images of the four molecules resemble the calculated HOMO electron density contours somewhat with positive surface bias voltage. On the basis of comparative analysis between the STM images, it is suggested that the electrostatic attractions between the neighbouring molecules play an important role in the self-assemblies of BHB-16, BOB-18 and BPB-15, while it is the van der Waals force and the non-covalent halogen-halogen interaction that dominate the structure of DDB-18 adlayer.

Li Y; Miao X; Liu G; Li Z; Xu L; Deng W

2012-01-01

412

Effect of bromine and substituted alkyl chain on the interfacial self-assembly of bromobenzene derivatives by scanning tunneling microscopy.  

Science.gov (United States)

The self-assemblies of four compounds, 1-bromo-4-(hexadecyloxy)benzene (BHB-16), 1-bromo-4-(octadecyloxy)benzene (BOB-18), 1-bromo-4-(pentadecyloxy)benzene (BPB-15) and 1,4-dibromo-2,5-(dioctadecyloxy)benzene (DDB-18), have been studied on highly oriented pyrolytic graphite (HOPG) under ambient conditions by scanning tunneling microscopy (STM), with the aim of understanding the influence of the molecular structure and functional groups on the arrangements. It is found that the bromine atoms of the four molecules are in bright contrast and can be identified in STM images. The neighbouring phenyl head groups of the BHB-16, BOB-18 and BPB-15 molecules in one lamella, with an anti-parallel orientation, are interdigitated with different offset distance, while the aromatic cores of DDB-18 molecules in the same row are in a parallel orientation. Moreover, an odd-even effect is observed in the self-assemblies of the former three molecules as expected. The STM images of the four molecules resemble the calculated HOMO electron density contours somewhat with positive surface bias voltage. On the basis of comparative analysis between the STM images, it is suggested that the electrostatic attractions between the neighbouring molecules play an important role in the self-assemblies of BHB-16, BOB-18 and BPB-15, while it is the van der Waals force and the non-covalent halogen-halogen interaction that dominate the structure of DDB-18 adlayer. PMID:22523963

Li, Yijing; Miao, Xinrui; Liu, Gang; Li, Zhuomin; Xu, Li; Deng, Wenli

2012-01-01

413

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

DEFF Research Database (Denmark)

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

Wang, Yun; Chi, Qijin

2009-01-01