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Sample records for stm

  1. The Sounds of Nanoscience: Acoustic STM Analogues

    ERIC Educational Resources Information Center

    Euler, Manfred

    2013-01-01

    A hands-on model of scanning tunnelling microscopy (STM) is presented. It uses near-field imaging with sound and computer assisted visualization to create acoustic mappings of resonator arrangements. Due to the (partial) analogy of matter and sound waves the images closely resemble STM scans of atoms. Moreover, the method can be extended to build…

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

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

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

  3. Mergers, Acquisitions, and Access: STM Publishing Today

    NASA Astrophysics Data System (ADS)

    Robertson, Kathleen

    Electronic publishing is changing the fundamentals of the entire printing/delivery/archive system that has served as the distribution mechanism for scientific research over the last century and a half. The merger-mania of the last 20 years, preprint pools, and publishers' licensing and journals-bundling plans are among the phenomena impacting the scientific information field. Science-Technology-Medical (STM) publishing is experiencing a period of intense consolidation and reorganization. This paper gives an overview of the economic factors fueling these trends, the major STM publishers, and the government regulatory bodies that referee this industry in Europe, Canada, and the USA.

  4. Restructuring STM (Science, Technology, and Mathematics) Education for Entrepreneurship

    ERIC Educational Resources Information Center

    Ezeudu, F. O.; Ofoegbu, T. O.; Anyaegbunnam, N. J.

    2013-01-01

    This paper discussed the need to restructure STM (science, technology, and mathematics) education to reflect entrepreneurship. This is because the present STM education has not achieved its aim of making graduates self-reliant. Entrepreneurship education if introduced in the STM education will produce graduate who can effectively manage their…

  5. SSE software test management STM capability: Using STM in the Ground Systems Development Environment (GSDE)

    NASA Technical Reports Server (NTRS)

    Church, Victor E.; Long, D.; Hartenstein, Ray; Perez-Davila, Alfredo

    1992-01-01

    This report is one of a series discussing configuration management (CM) topics for Space Station ground systems software development. It provides a description of the Software Support Environment (SSE)-developed Software Test Management (STM) capability, and discusses the possible use of this capability for management of developed software during testing performed on target platforms. This is intended to supplement the formal documentation of STM provided by the SEE Project. How STM can be used to integrate contractor CM and formal CM for software before delivery to operations is described. STM provides a level of control that is flexible enough to support integration and debugging, but sufficiently rigorous to insure the integrity of the testing process.

  6. Manipulating interfacial hydrogens at palladium via STM.

    PubMed

    Tremblay, Jean Christophe; Blanco-Rey, María

    2015-06-01

    In this contribution, we provide a detailed dynamical analysis of the interfacial hydrogen migration mediated by scanning tunneling microscopy (STM). Contributions from the STM-current and from the non-adiabatic couplings are taken into account using only first principle models. The slight asymmetry of the tunnelling rates with respect to the potential bias sign inferred from experimental observations is reproduced by weighting the contributions of the metal acceptor-donor states for the propagation of the impinging electrons. The quasi-thermal inelastic collision mechanism is treated perturbatively. The influence of hydrogen pre-coverage is also investigated using new potential energy surfaces obtained from periodic density functional theory calculations. Fully quantum dynamical simulations of the system evolution are performed by solving the Pauli master equation, providing insight into the reaction mechanism of STM manipulation of subsurface hydrogens. It is observed that the hydrogen impurity favors resurfacing over occupation of the bulk and subsurface sites whenever possible. The present simulations give strong indication that the experimentally observed protuberances after STM-excitation are due to hydrogen accumulating in the vicinity of the surface. PMID:25948419

  7. Theoretical STM maps of curved graphene

    NASA Astrophysics Data System (ADS)

    Diniz, G. S.; Ulloa, S. E.

    2010-03-01

    We calculate the effect of curvature on the electronic states in monolayer graphene, considering a local ripple along different directions on the plane. The curvature introduces hybridization between σ and π bands and affects the electronic structure and associated wave functions, even opening a gap of the order of few meV at the Dirac point. Our calculation uses a non-orthogonal four-orbital tight-binding representation up to nearest-neighbors, which fully describes the electronic states of the structure. We focus this study on the analysis of theoretical STM maps for different ripple directions and radius of curvature. We discuss the appearance of a well defined pattern in the STM map near the Dirac point, which is strongly modified when the graphene is rippled along different directions, and discuss this effect in terms of a geometric Berry phase. Although it is difficult experimentally to produce and control a well defined direction for the graphene ripple, recent experiments suggest that this structure may be possible in suspended samples with stressors along the edges [1].[4pt] [1] W. Bao et al., Nature Nanotech. 4, 562 (2009).

  8. Near-Field Imaging with Sound: An Acoustic STM Model

    ERIC Educational Resources Information Center

    Euler, Manfred

    2012-01-01

    The invention of scanning tunneling microscopy (STM) 30 years ago opened up a visual window to the nano-world and sparked off a bunch of new methods for investigating and controlling matter and its transformations at the atomic and molecular level. However, an adequate theoretical understanding of the method is demanding; STM images can be…

  9. Tomography of Majorana fermions with STM tips

    NASA Astrophysics Data System (ADS)

    Chevallier, Denis; Klinovaja, Jelena

    2016-07-01

    We investigate numerically the possibility to detect the spatial profile of Majorana fermions (MFs) by using STM tips that are made of either normal or superconducting material. In both cases, we are able to resolve the localization length and the oscillation period of the MF wave function. We show that the tunneling between the substrate and the tip, necessary to get the information on the wave-function oscillations, has to be weaker in the case of a superconducting probe. In the strong tunneling regime, the differential conductance saturates making it more difficult to observe the exponential decay of MFs. The temperature broadening of the profile is strongly suppressed in the case of the superconducting tip resulting, generally, in better resolution.

  10. Photovoltaic characterization of semiconductors with STM

    NASA Astrophysics Data System (ADS)

    Hagen, T.; Grafström, S.; Kowalski, J.; Neumann, R.

    Surface photovoltage (SPV) provides information on the electronic structure of semiconductor surfaces. Several schemes for measuring SPV with the STM have been realized in the past, using both continuous and modulated illumination. In the latter case the signal also contains contributions due to thermal expansion and tip-sample stray capacitance. For measurements on metal-like surfaces such as Si(111)-(7×7)we apply a potentiometric method: the conductivity I./V.is used for distance control, while a second feedback loop adjusts the bias voltage for zero DC current, thus providing a direct measure of the SPV. Topography and SPV are imaged simultaneously and continuously. We present data obtained with this method as well as an experimental analysis of the competing effects observed under modulated illumination.

  11. Thermal behavior of the STM tip under laser irradiation

    NASA Astrophysics Data System (ADS)

    Reilly, Christopher G.

    This thesis discusses the thermal behavior of the STM tip under laser irradiation. The thermal expansion of the tip was researched with varying laser spot size, frequency, location, and power. In order to determine the thermal expansion of the STM tip, the behavior in both the time and frequency domain were investigated. By employing the FFT analysis, the noise of the thermal behavior in the frequency domain was greatly reduced when compared to the time domain behavior, allowing for higher resolution expansions. With noise reduced, a thermal expansion of 1 nm, equating to a 0.03 K average temperature rise across the tip was found. Besides the heating and expansion of the STM tip, the thermal diffusivity of the PtIr STM tip was calculated using the TET and Characteristic Point methods, and found to be within 3% of the expected value.

  12. Review of the STM range of pressure distribution products.

    PubMed

    Moody, M

    STM Healthcare is a division of the Recticel Group which has been actively involved in the production and use of polyurethane foams for the past 40 years, and is now one of Europe's leading manufacturers of polyurethane foam for insulation, packaging, filtration, aerospace, the automotive and furniture industries, domestic and specialist bedding and seating products. STM Healthcare is able to draw upon the wealth of experience and expertise of the manufacturing facilities, enabling products to be developed using the latest environmentally friendly specification foams best suited to the requirements of pressure-reduction technology. All STM Healthcare mattresses, cushions and Linknurse mattresses are manufactured with Safeguard combustion modified high resilience foams. (Linknurse is a licensed product name; products are manufactured by Recticel and distributed by STM). PMID:9830917

  13. Strong correlation effects in theoretical STM studies of magnetic adatoms

    NASA Astrophysics Data System (ADS)

    Dang, Hung T.; dos Santos Dias, Manuel; Liebsch, Ansgar; Lounis, Samir

    2016-03-01

    We present a theoretical study for the scanning tunneling microscopy (STM) spectra of surface-supported magnetic nanostructures, incorporating strong correlation effects. As concrete examples, we study Co and Mn adatoms on the Cu(111) surface, which are expected to represent the opposite limits of Kondo physics and local moment behavior, using a combination of density functional theory and both quantum Monte Carlo and exact diagonalization impurity solvers. We examine in detail the effects of temperature T , correlation strength U , and impurity d electron occupancy Nd on the local density of states. We also study the effective coherence energy scale, i.e., the Kondo temperature TK, which can be extracted from the STM spectra. Theoretical STM spectra are computed as a function of STM tip position relative to each adatom. Because of the multiorbital nature of the adatoms, the STM spectra are shown to consist of a complicated superposition of orbital contributions, with different orbital symmetries, self-energies, and Kondo temperatures. For a Mn adatom, which is close to half-filling, the STM spectra are featureless near the Fermi level. On the other hand, the quasiparticle peak for a Co adatom gives rise to strongly position-dependent Fano line shapes.

  14. Increased STM expression is associated with drought tolerance in Arabidopsis.

    PubMed

    Lee, Hong Gil; Choi, Yee-Ram; Seo, Pil Joon

    2016-08-20

    In higher plants, shoot apical meristem (SAM) maintains cell division activity in order to give rise to aerial plant organs. Several lines of evidence have suggested that plants ensure stem cell proliferation activity in response to various external stimuli, thereby contributing to plant adaptation and fitness. Here, we report that the abscisic acid (ABA)-inducible R2R3-type MYB96 transcription factor regulates transcript accumulation of SHOOT MERISTEMLESS (STM) possibly to contribute to plant adaptation to environmental stress. STM was up-regulated in MYB96-overexpressing activation-tagging myb96-ox plants, but down-regulated in MYB96-deficient myb96-1 mutant plants, even in the presence of ABA. Notably, the MYB96 transcription factor bound directly to the STM promoter. In addition, consistent with the role of MYB96 in drought tolerance, transgenic plants overexpressing STM (35S:STM-MYC) were more tolerant to drought stress. These observations suggest that the MYB96-STM module contributes to enhancing plant tolerance to drought stress. PMID:27448723

  15. Use of STM for analysis of surfaces of biological samples

    NASA Astrophysics Data System (ADS)

    Permjakov, N. K.; Ananyan, M. A.; Luskinovich, P. N.; Sorokovoi, V. I.; Saveliev, S. V.

    1999-04-01

    Scanning tunnelling microscopy (STM) was used to image the cell surfaces of the olfactory organ of the shark Carcharhinus longimanus and ectoderm of the frog Xenopus laevis blastulae of 1024 stages, as well as human low-density lipoproteins surface. The samples from two of these objects were prepared by using traditional techniques for scanning electron microscopy (SEM). The lipoprotein samples were prepared by drying in the air. A comparison of the STM images with the earlier obtained SEM images indicates that there are some earlier unknown details of the surface structures of receptor microvilli and support cell membranes of the olfactory organ of the shark. There was found a fold of membrane on the surface of the ectodermal frog embryo cells, which covered yolk granules. STM images of the lipoprotein surface were obtained without increasing conductivity treatment.

  16. Analysis of Batten disease candidate genes STP and STM

    SciTech Connect

    Munroe, P.B.; Mitchison, H.M.; Gardiner, R.M.

    1995-06-05

    We have sequenced a large proportion of the open reading frames (ORFs) of two phenol sulphotransferase gene transcripts (STP and STM) from three patients with Batten disease. This was done using reverse transcription and PCR amplification of total RNA followed by direct sequencing of the PCR products. No mutations or changes have been observed in either gene after sequencing 93% of the STP ORF and 72% of the STM ORF. Work is in the progress to finish sequencing both genes which will allow the confirmation or exclusion of these phenol sulphotransferases having a role in the development of Batten disease. 11 refs., 1 fig.

  17. STM investigation of pyridine interaction with heteropoly acid monolayers

    SciTech Connect

    Song, I.K.; Kaba, M.S.; Barteau, M.A.

    1996-10-31

    In this paper, scanning tunneling microscopy (STM) images and tunneling spectra of H{sub 3}PMo{sub 12}O{sub 40} and Cs{sub 3}PMo{sub 12}O{sub 40} deposited on graphite surfaces were obtained in air before and after pyridine adsorption on arrays of these heteropoly HPAs, and the interactions with pyridine were probed at the molecular level using STM. The interactions were subsequently confirmed by infrared spectroscopy. These studies demonstrate the selective interaction of pyridine with acid sites in these arrays and the dramatic alteration of array structure which results from this interaction. 46 refs., 8 figs.

  18. Comparison of dynamic lever STM and noncontact AFM

    NASA Astrophysics Data System (ADS)

    Guggisberg, M.; Bammerlin, M.; Lüthi, R.; Loppacher, C.; Battiston, F.; Lü, J.; Baratoff, A.; Meyer, E.; Güntherodt, H.-J.

    We investigate interaction effects which occur in scanning tunneling microscopy (STM) by performing local force spectroscopy with an oscillating tip while imaging Si(111)7×7 terraces in the dynamic lever STM mode (constant time-averaged current). It is found that true atomic resolution is achieved close to the minimum of the resonance frequency vs. distance curve and even closer to the sample. On the other hand true atomic resolution in noncontact AFM (constant frequency shift) is expected several nm away from this minimum, in the range where the frequency shift becomes more negative with decreasing distance.

  19. Mechanical stress contributes to the expression of the STM homeobox gene in Arabidopsis shoot meristems.

    PubMed

    Landrein, Benoît; Kiss, Annamaria; Sassi, Massimiliano; Chauvet, Aurélie; Das, Pradeep; Cortizo, Millan; Laufs, Patrick; Takeda, Seiji; Aida, Mitsuhiro; Traas, Jan; Vernoux, Teva; Boudaoud, Arezki; Hamant, Olivier

    2015-01-01

    The role of mechanical signals in cell identity determination remains poorly explored in tissues. Furthermore, because mechanical stress is widespread, mechanical signals are difficult to uncouple from biochemical-based transduction pathways. Here we focus on the homeobox gene SHOOT MERISTEMLESS (STM), a master regulator and marker of meristematic identity in Arabidopsis. We found that STM expression is quantitatively correlated to curvature in the saddle-shaped boundary domain of the shoot apical meristem. As tissue folding reflects the presence of mechanical stress, we test and demonstrate that STM expression is induced after micromechanical perturbations. We also show that STM expression in the boundary domain is required for organ separation. While STM expression correlates with auxin depletion in this domain, auxin distribution and STM expression can also be uncoupled. STM expression and boundary identity are thus strengthened through a synergy between auxin depletion and an auxin-independent mechanotransduction pathway at the shoot apical meristem. PMID:26623515

  20. NSS5/SP-STM2 Joint International Conference

    SciTech Connect

    Saw-Wai Hla

    2009-05-03

    The NSS5/SP-STM2 conference was held in Athens, Ohio July 15-19, 2008. The conference brought together a prestigious group of scientists from all over the globe to focus for 3 ½ days on a variety of nanoscience topics, particularly on nanoscale spectroscopy and spin-polarized scanning tunneling microscopy. The conference was attended by many young scientists as well as senior scientists. Attendees to the conference were drawn from more than 10 countries and included 28 invited speakers, who are the leading scientists in their respective research areas. Included among the invited speakers were 4 plenary speakers - eminent scientists in their fields. The conference was divided into two parallel sessions – the NSS5 session and the SP-STM2 session.

  1. STM study on the structures of SnSe surfaces

    NASA Astrophysics Data System (ADS)

    Kim, Tae Hoon; Kim, Sang-Ui; Thi Ly, Trinh; Duong, Anh Tuan; Cho, Sunglae; Rhim, S. H.; Kim, Jungdae

    SnSe is a 2 dimensional layered material, and each layer is coupled by van deer Waals forces allowing very easy cleaving though the layer surfaces. SnSe has been studied for various potential applications because of its high stability and elemental abundance in earth. Recently, it was also reported that bulk SnSe has an excellent thermoelectric property of ZT =2.6 at 923 K along the b axis (Zhao et al., Nature 508 373 (2014)). The surface of a single crystal SnSe was studied via a home-built low temperature scanning tunneling microscopy (STM). Clear atomic images of SnSe surfaces were observed at the filled and empty state measurements, and detail atomic structures were analyzed by comparing with DFT simulations. We found that the atomic image of SnSe surfaces measured by STM is not trivial to understand. Only Sn atoms were visible on STM topographic images for the both of filled and empty state probing. This work was supported by the National Research Foundation of Korea(NRF) [Nos. NRF-2013R1A1A1008724, NRF-2009-0093818, and NRF-2014R1A4A1071686].

  2. Sentinel-3 Surface Topography Mission (STM) User Data Products

    NASA Astrophysics Data System (ADS)

    Nogueira Loddo, Carolina; Scharroo, Remko; Wilson, Hilary; Bonekamp, Hans

    2015-04-01

    The Sentinel-3 Surface Topography Mission (STM) is a key component of the Copernicus Sentinel-3 mission, set to revolutionise operational oceanography with a suite of advanced surface topography data products over ocean and sea sea-ice. In addition the STM will collect data over all earth surfaces providing improved monitoring of River and Lake stage heights and inputs to the development of Digital Elevation Models. Sentinel-3 will be the first Earth Observation mission to provide 100% SAR altimetry coverage and LRM will be maintained as a backup operating mode. In order to fully exploit the SAR capability, and validating the algorithms evolution, lower level data products (L1A, L1B and L1B-S) will be made available to the users, in addition to the level 2 products. This poster provides an overview of the S-3 STM data products that will be generated operationally within the Sentinel-3 Payload Data Ground Segment by the Instrument Processing Facilities (IPFs), and disseminated to the users.

  3. STM/STS on proximity-coupled superconducting graphene

    NASA Astrophysics Data System (ADS)

    Ovadia, Maoz; Ji, Yu; Lee, Gil-Ho; Fang, Wenjing; Hoffman, Jennifer; Jarillo-Herrero, Pablo; Kong, Jing; Kim, Philip

    Graphene in good electrical contact with a superconductor has been observed to have an enhanced proximity effect. Application of a magnetic field is expected to generate an Abrikosov lattice of superconducting vortices, each containing Andreev bound states in its core. With our versatile, homebuilt, low temperature scanning tunneling force microscope (STM/SFM), we investigate the electronic properties of graphene on superconducting NbSe2 in a magnetic field and search for signatures of these vortex core states. This work was supported by the STC Center for Integrated Quantum Materials, NSF Grant No. DMR-1231319.

  4. STM observation of nitrided-Ga on Si

    SciTech Connect

    Nakada, Y.; Miwa, S.; Okumura, H. |

    1997-12-31

    To investigate the initial stage of GaN growth on Si, 0.2 Ga monolayers (ML) on Si (111) was nitrided and then the nitrided surfaces were observed by scanning tunneling microscopy (STM). An aggregation of islands whose longest edges had a direction rotated 15{degree} from Si [1{bar 1}0] direction was observed. The shape of islands looked like a pentagon. Surface roughness was estimated for several nitrided conditions. It was found that surface roughness becomes larger as the nitridation process proceeds.

  5. Video STM Studies of Adsorbate Diffusion at Electrochemical Interfaces

    NASA Astrophysics Data System (ADS)

    Tansel, T.; Magnussen, O. M.

    2006-01-01

    Direct in situ studies of the surface diffusion of isolated adsorbates at an electrochemical interface by high-speed scanning tunneling microscopy (video STM) are presented for sulfide adsorbates on Cu(100) in HCl solution. As revealed by a quantitative statistical analysis, the adsorbate motion can be described by thermally activated hopping between neighboring adsorption sites with an activation energy that increases linearly with electrode potential by 0.50 eV per V. This can be explained by changes in the adsorbate dipole moment during the hopping process and contributions from coadsorbates.

  6. Chemically Sensitive Imaging of MgP with STM

    NASA Astrophysics Data System (ADS)

    Yu, Arthur; Li, Shaowei; Czap, Greg; Ho, Wilson

    2014-03-01

    Since its invention, the STM has been limited by its lack of sensitivity to chemical structures in molecules. Recent advances in scanning probe microscopy techniques, such as non-contact AFM and scanning tunneling hydrogen microscopy have enabled imaging of the internal structure and bonding of aromatic molecules such as pentacene and PTCDA. Here, we present a novel method of using the STM to image magnesium porphyrin molecules adsorbed on Au(110) with chemical sensitivity. In our previous study, we have shown that hydrogen molecules weakly adsorb on Au(110), exhibiting both vibrational and rotational IETS spectra. Exploiting the sensitivity of the vibrational and rotational mode energies to the local chemical environment, we perform dI/dV and d2I/dV2 imaging at different bias voltages, highlighting the various parts of the MgP molecule. In particular, we are able to image the positions of the nitrogen atoms in MgP. d2I/dV2 spectral mapping reveals that the origin of the chemical sensitivity comes from an energy shift of the rotational peak as the tip is scanned across the molecule, indicating a changing potential landscape for the H2. Similar d2I/dV2 imaging with a CO terminated tip reveals no chemical sensitivity to nitrogen.

  7. Iodine adsorption on Ni(111): STM and DFT study

    NASA Astrophysics Data System (ADS)

    Komarov, N. S.; Pavlova, T. V.; Andryushechkin, B. V.

    2016-09-01

    Iodine adsorption on the Ni(111) surface has been studied in ultra-high vacuum conditions with scanning tunneling microscopy (STM), Auger electron spectroscopy (AES), low-energy electron diffraction (LEED) and density functional theory (DFT) calculations. At the first stage of adsorption, iodine was found to form a simple commensurate (√{ 3 } ×√{ 3 }) R 30∘ structure at the coverage of 0.33 ML. According to DFT calculations, all iodine atoms in the (√{ 3 } ×√{ 3 }) R 30∘ structure occupy fcc hollow sites. Increase of the coverage in the range of (0.333 ML <θ < 0.364 ML) results in the uniaxial compression of the iodine lattice and the formation of the high-order commensurate structure (11 ×√{ 3 } R 30∘). The mechanism of compression involves the formation and the development of the striped super-heavy domain wall network. Further iodine dosing gives rise to nucleation and growth of flat 2D islands of surface nickel iodide. Atomic resolution STM images of iodide islands, in addition to atomic modulation, exhibit clear visible moiré-like superstructures with a period about 26 Å. The origin of the moiré-patterns was explained by the incommensurability of lattices of the surface nickel iodide and underlying Ni(111).

  8. Space simulation techniques and facilities for SAX STM test campaign

    NASA Technical Reports Server (NTRS)

    Giordano, Pietro; Raimondo, Giacomo; Messidoro, Piero

    1994-01-01

    SAX is a satellite for X-Ray astronomy. It is a major element of the overall basic Science Program of the Italian Space Agency (ASI) and is being developed with the contribution of the Netherlands Agency for Aerospace Programs (NIVR). The scientific objectives of SAX are to carry out systematic and comprehensive observations of celestial X-Ray sources over the 0.1 - 300 KeV energy range with special emphasis on spectral and timing measurements. The satellite will also monitor the X-Ray sky to investigate long-term source variability and to permit localization and study of X-Ray transients. Alenia Spazio is developing the satellite that is intended for launch in the second half of 1995 in a low, near-equatorial Earth orbit. At system level a Structural Thermal Model (STM) has been conceived to verify the environmental requirements by validating the mechanical and thermal analytical models and qualifying satellite structure and thermal control. In particular, the following tests have been carried out in Alenia Spazio, CEA/CESTA and ESTEC facilities: Modal Survey, Centrifuge, Acoustic, Sinusoidal/Random Vibration and Thermal Balance. The paper, after a short introduction of the SAX satellite, summarizes the environmental qualification program performed on the SAX STM. It presents test objectives, methodologies and relevant test configurations. Peculiar aspects of the test campaign are highlighted. Problems encountered and solutions adopted in performing the tests are described as well. Furthermore, test results are presented and assessed.

  9. Single Crystal Synthesis and STM Studies of High Temperature Superconductors

    NASA Technical Reports Server (NTRS)

    Barrientos, Alfonso

    1997-01-01

    This is a final report for the work initiated in September of 1994 under the grant NAG8-1085 - NASA/OMU, on the fabrication of bulk and single crystal synthesis, specific heat measuring and STM studies of high temperature superconductors. Efforts were made to fabricate bulk and single crystals of mercury based superconducting material. A systematic thermal analysis on the precursors for the corresponding oxides and carbonates were carried out to synthesized bulk samples. Bulk material was used as seed in an attempt to grow single crystals by a two-step self flux process. On the other hand bulk samples were characterized by x-ray diffraction, electrical resistivity and magnetic susceptibility, We studied the specific heat behavior in the range from 80 to 300 K. Some preliminary attempts were made to study the atomic morphology of our samples. As part of our efforts we built an ac susceptibility apparatus for measuring the transition temperature of our sintered samples.

  10. Kondo effect and STM spectroscopy of Dirac electrons in graphene

    NASA Astrophysics Data System (ADS)

    Sengupta, Krishnendu

    2011-03-01

    We show that graphene, whose low-energy quasiparticles display Dirac like behavior, may exhibit a two-channel Kondo effect in the presence of magnetic impurities. We present a large N analysis for a generic spin S local moment coupled to Dirac electrons in graphene and demonstrate that the corresponding Kondo temperature can be tuned by an experimentally controllable applied gate voltage. We also study the STM spectra of these Dirac electrons in the presence of such impurities and demonstrate that such spectra depend qualitatively on the position of the impurity atom in the graphene matrix. More specifically, for impurity atoms atop the hexagon center, the zero-bias tunneling conductance, as measured by a STM, shows a peak; for those atop a graphene site, it shows a dip. We provide a qualitative theoretical explanation of this phenomenon and show that this unconventional behavior is a consequence of conservation/breaking of pseudospin symmetry of the Dirac quasiparticles by the impurity. We also predict that tuning the Fermi energy to zero by a gate voltage would not lead to qualitative change in the shape of the conductance spectra when the impurity is atop the hexagon center. A similar tuning of the Fermi energy for the impurity atop a site, however, would lead to a change in the tunneling conductance from a dip to a peak via an antiresonance. We discuss some recent experiments on a doped graphene sample that seem to have qualitative agreement with our theory and suggest further experiments to test our predictions. DST, India.

  11. Type II Secretion-Dependent Degradative and Cytotoxic Activities Mediated by Stenotrophomonas maltophilia Serine Proteases StmPr1 and StmPr2

    PubMed Central

    DuMont, Ashley L.; Karaba, Sara M.

    2015-01-01

    Stenotrophomonas maltophilia is an emerging opportunistic pathogen that primarily causes pneumonia and bacteremia in immunocompromised individuals. We recently reported that S. maltophilia strain K279a encodes the Xps type II secretion system and that Xps promotes rounding, actin rearrangement, detachment, and death in the human lung epithelial cell line A549. Here, we show that Xps-dependent cell rounding and detachment occur with multiple human and murine cell lines and that serine protease inhibitors block Xps-mediated rounding and detachment of A549 cells. Using genetic analysis, we determined that the serine proteases StmPr1 and StmPr2, which were confirmed to be Xps substrates, are predominantly responsible for secreted proteolytic activities exhibited by strain K279a, as well as the morphological and cytotoxic effects on A549 cells. Supernatants from strain K279a also promoted the degradation of type I collagen, fibrinogen, and fibronectin in a predominantly Xps- and protease-dependent manner, although some Xps-independent degradation of fibrinogen was observed. Finally, Xps, and predominantly StmPr1, degraded interleukin 8 (IL-8) secreted by A549 cells during coculture with strain K279a. Our findings indicate that while StmPr1 and StmPr2 are predominantly responsible for A549 cell rounding, extracellular matrix protein degradation, and IL-8 degradation, additional Xps substrates also contribute to these activities. Altogether, our data provide new insight into the virulence potential of the S. maltophilia Xps type II secretion system and its StmPr1 and StmPr2 substrates. PMID:26169274

  12. The Saccharomyces cerevisiae protein Stm1p facilitates ribosome preservation during quiescence

    SciTech Connect

    Van Dyke, Natalya; Chanchorn, Ekkawit; Van Dyke, Michael W.

    2013-01-11

    Highlights: Black-Right-Pointing-Pointer Stm1p confers increased resistance to the macrolide starvation-mimic rapamycin. Black-Right-Pointing-Pointer Stm1p maintains 80S ribosome integrity during stationary phase-induced quiescence. Black-Right-Pointing-Pointer Stm1p facilitates polysome formation following quiescence exit. Black-Right-Pointing-Pointer Stm1p facilitates protein synthesis following quiescence exit. Black-Right-Pointing-Pointer Stm1p is a ribosome preservation factor under conditions of nutrient deprivation. -- Abstract: Once cells exhaust nutrients from their environment, they enter an alternative resting state known as quiescence, whereby proliferation ceases and essential nutrients are obtained through internal stores and through the catabolism of existing macromolecules and organelles. One example of this is ribophagy, the degradation of ribosomes through the process of autophagy. However, some ribosomes need to be preserved for an anticipated recovery from nutrient deprivation. We found that the ribosome-associated protein Stm1p greatly increases the quantity of 80S ribosomes present in quiescent yeast cells and that these ribosomes facilitate increased protein synthesis rates once nutrients are restored. These findings suggest that Stm1p can act as a ribosome preservation factor under conditions of nutrient deprivation and restoration.

  13. Mechanical stress contributes to the expression of the STM homeobox gene in Arabidopsis shoot meristems

    PubMed Central

    Landrein, Benoît; Kiss, Annamaria; Sassi, Massimiliano; Chauvet, Aurélie; Das, Pradeep; Cortizo, Millan; Laufs, Patrick; Takeda, Seiji; Aida, Mitsuhiro; Traas, Jan; Vernoux, Teva; Boudaoud, Arezki; Hamant, Olivier

    2015-01-01

    The role of mechanical signals in cell identity determination remains poorly explored in tissues. Furthermore, because mechanical stress is widespread, mechanical signals are difficult to uncouple from biochemical-based transduction pathways. Here we focus on the homeobox gene SHOOT MERISTEMLESS (STM), a master regulator and marker of meristematic identity in Arabidopsis. We found that STM expression is quantitatively correlated to curvature in the saddle-shaped boundary domain of the shoot apical meristem. As tissue folding reflects the presence of mechanical stress, we test and demonstrate that STM expression is induced after micromechanical perturbations. We also show that STM expression in the boundary domain is required for organ separation. While STM expression correlates with auxin depletion in this domain, auxin distribution and STM expression can also be uncoupled. STM expression and boundary identity are thus strengthened through a synergy between auxin depletion and an auxin-independent mechanotransduction pathway at the shoot apical meristem. DOI: http://dx.doi.org/10.7554/eLife.07811.001 PMID:26623515

  14. STM-based methodologies for molecular identification and studies of chemical reaction mechanisms

    SciTech Connect

    Hamers, R.J.

    1995-12-01

    The use of STM to study chemical reactions has been hampered by the general inability to identify molecules and molecular fragments on surfaces. By combining the ability of the STM to probe local electronic structure with systematic study as a function of temperature and concepts from coordination chemistry, a priori chemical identification can be achieved, and this information can be used to elucidate new information about the mechanisms of chemical reactions. On silicon, this approach has been applied to study the decomposition of disilane, phosphine, and diborane. On metals, the delocalized bonding necessitates different approaches. We have also applied STM and tunneling spectroscopy to study the adsorption and decomposition of thiophene and related molecules on Ag(111) surfaces at 120 Kelvin. Here, voltage-dependent STM imaging is used to identify the rotational orientation of the molecules and to study polymerization at the molecular level. Methodologies for molecular identification will be discussed, with recent applications on semiconductors and metals.

  15. Ba termination of Ge(001) studied with STM

    NASA Astrophysics Data System (ADS)

    Curson, Neil; Koczorowski, Wojciech; Grzela, Tomasz; Radny, Marian; Schofield, Steven; Capellini, Giovanni; Czajka, Ryszard; Schroeder, Thomas

    2015-03-01

    We use controlled annealing to tune the interfacial properties of a sub-monolayer and monolayer coverages of Ba atoms deposited on Ge(001), enabling the generation of either of two fundamentally distinct interfacial phases, as revealed by scanning tunneling microscopy (STM). Firstly we identify the two key structural phases associated with this adsorption system, namely on-top adsorption and surface alloy formation, by performing a deposition and annealing experiment at a coverage low enough (0.15 ML) such that isolated Ba-related features can be individually resolved. Subsequently we investigate the monolayer coverage case, of interest for passivation schemes of future Ge based devices, for which we find that thermal evaporation of Ba onto a Ge(001) surface at room temperature results in on-top adsorption. This separation (lack of intermixing) between Ba and Ge layers is retained through successive annealing steps up to 770 K with a gradual ordering of the Ba layer at 570 K and above and a decrease in Ba layer density. Annealing above 770 K produces the 2-D surface alloy phase accompanied by strain relief through monolayer height trench formation. At 1070 K the surface morphology changes again but remains a 2-D surface alloy. WK and NJC acknowledge EPSRC grant EP/I02865X/1. WK, MWR and R.C. acknowledge the Polish Ministry of Science and Higher Education for support (Project No. N-N202-195840).

  16. Magnetic dipole-dipole sensing at atomic scale using electron spin resonance STM

    NASA Astrophysics Data System (ADS)

    Choi, T.; Paul, W.; Rolf-Pissarczyk, S.; MacDonald, A.; Yang, K.; Natterer, F. D.; Lutz, C. P.; Heinrich, A. J.

    Magnetometry having both high magnetic field sensitivity and atomic resolution has been an important goal for applications in diverse fields covering physics, material science, and biomedical science. Recent development of electron spin resonance STM (ESR-STM) promises coherent manipulation of spins and studies on magnetic interaction of artificially built nanostructures, leading toward quantum computation, simulation, and sensors In ESR-STM experiments, we find that the ESR signal from an Fe atom underneath a STM tip splits into two different frequencies when we position an additional Fe atom nearby. We measure an ESR energy splitting that decays as 1/r3 (r is the separation of the two Fe atoms), indicating that the atoms are coupled through magnetic dipole-dipole interaction. This energy and distance relation enables us to determine magnetic moments of atoms and molecules on a surface with high precision in energy. Unique and advantageous aspects of ESR-STM are the atom manipulation capabilities, which allow us to build atomically precise nanostructures and examine their interactions. For instance, we construct a dice cinque arrangement of five Fe atoms, and probe their interaction and energy degeneracy. We demonstrate the ESR-STM technique can be utilized for quantum magnetic sensors.

  17. Probing Single Molecules with a Tunable Femtosecond Laser Coupled RF-STM

    NASA Astrophysics Data System (ADS)

    Cao, Weicai

    Scanning Tunneling Microscope (STM) has become a powerful tool in nanoscience for imaging, manipulation and electronic spectroscopy. STM inelastic electron tunneling spectroscopy (IETS) first achieved chemical identification of molecular species by characterizing vibrational energies. Recently, with the STM itProbe and H2 rotational spectromicroscopy, molecular structure and chemical bonds are observed with the STM. Despite these successes in spatial resolution, various efforts have been made to combine fs laser with STM to overcome the temporal resolution limitation of STM, there is so far no clear evidence of simultaneous fs and A resolution. Electronic properties of organic molecules are of central importance to applications such as molecular electronics, organic LEDs, and solar cells. Properties of these molecules can be probed by the scanning tunneling microscope (STM) at the single molecule level and with sub-A spatial resolution. The molecular orbital of 4, 7-Di ([2, 20-bithiophen]-5-yl) benzo[c] [1, 2, 5] thiadiazole (4T-BTD) with intramolecular donor-acceptor-donor sites is probed with the electronic state dI/dV imaging and H2 rotational and vibrational spectromicroscopy. 1, 4-Phenylene Diisocyanide (PDI) is probed by imaging with a CO-terminated tip and H2. PDI can self-assemble on noble metal surfaces to form nanostructures, which could have potential applications in molecular electronics and catalysis. Further combination of a RF-STM with a tunable femtosecond laser enables the investigation of light-molecule interactions. In this dissertation, efforts are spent to setup a new tunable fs laser (220 nm˜1040 nm) to couple with the RF-STM. The effects of the femtosecond laser are followed by detecting photo induced electron emission and photochemistry. A new double lock-in technique is applied to detect the weak laser-induced signal in the tunneling regime. To sharpen the energy width and increase the lifetime of the excited states of molecules, thin

  18. Chen's derivative rule revisited: Role of tip-orbital interference in STM

    NASA Astrophysics Data System (ADS)

    Mándi, Gábor; Palotás, Krisztián

    2015-04-01

    On the occasion of its 25th anniversary, we revise Chen's derivative rule for electron tunneling [C. J. Chen, Phys. Rev. B 42, 8841 (1990), 10.1103/PhysRevB.42.8841] for the purpose of computationally efficient simulations of scanning tunneling microscopy (STM) based on first-principles electronic structure data. The revised model allows the weighting of tunneling matrix elements of different tip-orbital characters by an arbitrary energy-independent choice or based on energy-dependent weighting coefficients obtained by an expansion of the tip single-electron wave functions/density of states projected onto the tip-apex atom. Tip-orbital interference in the STM junction is included in the model by construction and can be analyzed quantitatively. As a further advantage, arbitrary tip geometrical orientations are included in the revised model by rotating the coordinate system of the tip apex using Euler angles and redefining the weighting coefficients of the tunneling matrix elements. We demonstrate the reliability of the model by applying it to two functionalized surfaces of recent interest where quantum interference effects play an important role in the STM imaging process: N-doped graphene and a magnetic Mn2H complex on the Ag(111) surface. We find that the proposed tunneling model is 25 times faster than the Bardeen method concerning computational time, while maintaining good agreement. Our results show that the electronic structure of the tip has a considerable effect on STM images, and the Tersoff-Hamann model does not always provide sufficient results in view of quantum interference effects. For both studied surfaces, we highlight the importance of interference between s and pz tip orbitals that can cause a significant contrast change in the STM images. Our method, thus, provides a fast and reliable tool for calculating STM images based on Chen's derivative rule, taking into account the electronic structure and local geometry of the tip apex.

  19. Effects of straw volume and Equex-STM on boar sperm quality after cryopreservation.

    PubMed

    Buranaamnuay, K; Tummaruk, P; Singlor, J; Rodriguez-Martinez, H; Techakumphu, M

    2009-02-01

    The present experiments were designed to study the effect of adding the detergent Equex-STM to freezing extender, and of straw volume (0.25 ml vs 0.5 ml), on boar sperm quality after cryopreservation. Three ejaculates from each of four purebred boars (three Landrace and one Yorkshire) were collected and frozen with a lactose-egg yolk extender containing glycerol with or without 1.5% Equex-STM. The extended semen was loaded into either 0.25- or 0.5-ml straws. The straws were placed in liquid nitrogen (LN(2)) vapour approximately 3 cm above the level of LN(2) for 20 min and then were plunged into LN(2). Thawing was achieved in warm water at 50 degrees C for 12 s and then was incubated in a 38 degrees C water-bath for 30 min before evaluating sperm quality. Results showed that the individual motility, viability and acrosomal normal apical ridge (NAR) were improved (p < 0.001) when Equex-STM was added to the freezing extender. There was no difference (p = 0.48) in sperm motility between 0.25- and 0.5-ml straws when Equex-STM was added. The percentages of viable and of NAR sperm in 0.5-ml straws were higher than those in 0.25-ml straws (p = 0.02, p = 0.0003 respectively). The percentages of membrane intact sperm evaluated using the short hypo-osmotic swelling test were not affected by straw volume or the adding of Equex-STM (p > 0.05). The results of these investigations suggested that Equex-STM exerts a beneficial effect on the quality of cryopreserved boar semen and this cryopreservation protocol was favourable for a 0.5-ml straw. PMID:18484955

  20. Cloning and characterization of a critical meristem developmental gene (EeSTM) from leafy spurge (Euphorbia esula)

    Technology Transfer Automated Retrieval System (TEKTRAN)

    SHOOTMERISTEMLESS (STM) encodes a member of the class I KNOX homeodomain protein family that is required for meristem development and maintenance. We have isolated both genomic and two different cDNA clones of STM from the perennial weed leafy spurge. A comparison to other class I KNOX genes indicat...

  1. Techniques Use by Science, Technology and Mathematics (STM) Teachers for Controlling Undesirable Classroom Behaviours in Anambra State Secondary Schools

    ERIC Educational Resources Information Center

    Chinelo, Okigbo Ebele; Nwanneka, Okoli Josephine

    2016-01-01

    This study investigated the techniques used by secondary school Science Technology and Mathematics (STM) teachers in controlling undesirable behaviours in their classrooms. It adopted descriptive survey design in which 178 Anambra State teachers teaching STM subjects in senior secondary were involved in the research. Two sections of questionnaire…

  2. What Do We Know about Explanations for Drop out/Opt out among Young People from STM Higher Education Programmes?

    ERIC Educational Resources Information Center

    Ulriksen, Lars; Madsen, Lene Moller; Holmegaard, Henriette T.

    2010-01-01

    In this paper we provide an overview of the literature on understandings of drop out/opt out from science, technology and mathematics (STM) higher education programmes. After outlining the literature on students leaving higher education programmes in general, we then explore the research on drop out/opt out from STM programmes in particular, with…

  3. STM study of morphology and electron transport features in cytochrome c and nanocluster molecule monolayers.

    PubMed

    Khomutov, G B; Belovolova, L V; Gubin, S P; Khanin, V V; Obydenov, A Yu; Sergeev-Cherenkov, A N; Soldatov, E S; Trifonov, A S

    2002-01-01

    The morphology and electron tunneling through single cytochrome c and nanocluster Pt(5)(CO)(7)[P(C(6)H(5))](4) molecules organized as monolayer Langmuir-Blodgett (LB) films on graphite substrate have been studied experimentally using scanning tunneling microscopy (STM) and spectroscopy techniques with sub-nanometer spatial resolution in a double barrier tunnel junction configuration STM tip-monomolecular film-conducting substrate at ambient conditions. STM images of the films revealed globular structures with characteristic diameters (approximately 3.5 nm for the protein molecule and approximately 1.2 nm for the nanocluster). The spectroscopic study by recording the tunneling current-bias voltage (I-V) curves revealed tunneling I-V characteristics with features as steps of different width and heights that are dependent on the STM tip position over the molecule in the monolayer, giving evidence for sequential discrete electron-tunneling effects with the combination of the single electron Coulomb-charging energy and the electronic energy level separation (molecular spectrum) in such immobilized metalloprotein and nanocluster structures that can be of interest for the development of bioelectronic and hybrid functional nanosystems. PMID:11786369

  4. A silver nanowire-based tip suitable for STM tip-enhanced Raman scattering.

    PubMed

    Fujita, Yasuhiko; Chiba, Rie; Lu, Gang; Horimoto, Noriko N; Kajimoto, Shinji; Fukumura, Hiroshi; Uji-i, Hiroshi

    2014-09-01

    A chemically synthesized silver nanowire was used for atomic-resolution STM imaging and tip-enhanced Raman scattering (TERS) spectroscopy, yielding excellent reproducibility. This TERS tip will open a new venue to surface analysis, such as molecular finger printing at nanoscales. PMID:24956261

  5. The Impact of Pointing on the Short-Term Memory (STM) of Heterophonic Homographs

    ERIC Educational Resources Information Center

    Vaknin-Nusbaum, Vered; Miller, Paul

    2014-01-01

    This study entailed two short-term memory (STM) experiments investigating the importance of vowel diacritics for the temporary retention of three distinct Hebrew word list types: heterophonic homographs, non-homographs and homophonic homographs. Eighty university students participated in each experiment, with half of them tested with word lists…

  6. S182 and STM2 gene missense mutations in sporadic alzheimer disease

    SciTech Connect

    Higuchi, Susumu; Matsushita, Sachio; Hasegawa, Yoshio; Muramatsu, Taro

    1996-07-26

    The linkage of genes S182 and STM2 to early-onset or late-onset sporadic Alzheimer disease (AD) was not found in a group of 97 clinically-diagnosed AD patients and 46 autopsy-confirmed AD cases, using PCR-RFLP methods. 7 refs.

  7. Chemical ordering and reconstruction of Pt 25Co 75(100): an LEED/STM study

    NASA Astrophysics Data System (ADS)

    Gauthier, Y.; Dolle, P.; Baudoing-Savois, R.; Hebenstreit, W.; Platzgummer, E.; Schmid, M.; Varga, P.

    1998-01-01

    The surface of a disordered Pt 25Co 75(100) alloy has been investigated using quantitative LEED, AES and UHV-STM at room temperature. Atomic-resolution images reveal that it reconstructs with close-packed rows shifted by half the interatomic distance, from hollow to bridge sites. The density of shifted rows increases with the surface Pt concentration, leading to (1 × 5), (1 × 6) and (1 × 7) patterns. Segregation and chemical ordering lead to the formation of c(2 × 2) domains between the shifted rows. Chemical resolution was achieved with STM: the apparent height of the Pt atoms in the STM topographs is about 0.1-0.4 Å above that of Co, whereas LEED shows that Pt atoms are geometrically ˜0.04 Å higher. The composition was determined down to the fourth layer. An oscillatory segregation profile is observed, with Pt-rich layers (< C1> = 62.6% Pt, < C3> = 53.5%) and Pt-depleted layers (< C2> = 6.9%, < C4> = 2.7%). Chemical ordering is present in the third layer and the four-layer surface slab stabilises with a structure and a composition quite similar to that of the L1 2 PtCo 3 phase. As regards the composition and ordering of the top layer, there is a remarkable agreement between chemically resolved STM analysis and LEED analysis.

  8. Origin of High-Resolution IETS-STM Images of Organic Molecules with Functionalized Tips.

    PubMed

    Hapala, Prokop; Temirov, Ruslan; Tautz, F Stefan; Jelínek, Pavel

    2014-11-28

    Recently, the family of high-resolution scanning probe imaging techniques using decorated tips has been complemented by a method based on inelastic electron tunneling spectroscopy (IETS). The new technique resolves the inner structure of organic molecules by mapping the vibrational energy of a single carbon monoxide (CO) molecule positioned at the apex of a scanning tunneling microscope (STM) tip. Here, we explain high-resolution IETS imaging by extending a model developed earlier for STM and atomic force microscopy (AFM) imaging with decorated tips. In particular, we show that the tip decorated with CO acts as a nanoscale sensor that changes the energy of its frustrated translation mode in response to changes of the local curvature of the surface potential. In addition, we show that high resolution AFM, STM, and IETS-STM images can deliver information about the charge distribution within molecules deposited on a surface. To demonstrate this, we extend our mechanical model by taking into account electrostatic forces acting on the decorated tip in the surface Hartree potential. PMID:25494078

  9. Recoding between Two Types of STM Representation Revealed by the Dynamics of Memory Search

    ERIC Educational Resources Information Center

    Leszczynski, Marcin; Myers, Nicholas E.; Akyurek, Elkan G.; Schubo, Anna

    2012-01-01

    Visual STM (VSTM) is thought to be related to visual attention in several ways. Attention controls access to VSTM during memory encoding and plays a role in the maintenance of stored information by strengthening memorized content. We investigated the involvement of visual attention in recall from VSTM. In two experiments, we measured…

  10. STM investigations of Au(1 1 1) electrodes coated with vitamin B 12 derivatives

    NASA Astrophysics Data System (ADS)

    Szőcs, E.; Durrer, L.; Luginbühl, R.; Simic, N.; Viana, A. S.; Abrantes, L. M.; Keese, R.; Siegenthaler, H.

    2006-01-01

    Vitamin B 12 derivatives immobilized at flame-annealed Au(1 1 1) electrode surfaces have been investigated in close correlation with their structural properties and spatial arrangement at the electrode substrate by scanning tunneling microscopy (STM) in air and in aqueous 0.1 M NaClO 4 solution. The investigated compounds were symmetrical (B 12C 10S-SC 10B 12) and nonsymmetrical (B 12C 10S-SC 10) dialkyl disulfide derivatives of vitamin B 12, attached to the electrode surfaces by the S-Au bond. The ex situ and in situ STM experiments show the formation of a surface layer, whose packing density and structure is presumably controlled by the spatial arrangement of the large cobyrinate head groups. In presence of the symmetrical B 12 compound, a disordered surface layer is observed. Voltammetric investigations show that, in 0.1 M NaClO 4, this layer becomes unstable at potentials approximately ⩽ -1000 mV vs. MSE and is almost completely removed at more negative potentials. The STM imaging properties of the nonsymmetrical B 12 surface layer show a significant dependence on the tunneling distance. In particular, at small tunneling distances, a highly regular hexagonal surface pattern is observed that suggests strongly the presence of an ordered surface assembly. Modeling of the B 12 head group has been performed to provide information for a structure-related interpretation of the high-resolution STM images. The investigations are first STM results obtained at such B 12 modified electrodes.

  11. Construction of Scanning Tunneling Microscope and Analysis of Vicinal SILICON(111) Surfaces with STM (SILICON(111), Vicinal Silicon(iii))

    NASA Astrophysics Data System (ADS)

    Wang, Xue-Sen

    1990-01-01

    Scanning Tunneling Microscopy (STM) has become a powerful technique in surface study. In this dissertation, basic theoretical and instrumentational aspects of STM are reviewed; the construction and testing of a UHV STM are described in detail. The structure of vicinal Si(111) surfaces were statistically investigated with this STM system. The surface morphology is strongly affected by the interaction between terrace and step structures. The (7 x 7) reconstruction domains are correlated across steps on thermally equilibrated surfaces. Energetic step repulsive interaction has been observed in addition to the entropic "repulsion" between wandering steps. This energetic repulsion is an important factor causing the ratio of the triple - to single-layer steps to increase with the misorientation angle. The height correlation measurement indicate that the surfaces can be categorized as "rough" surfaces. The Surface structure is also strongly affected by the annealing processes.

  12. STM/AFM investigations of β-MoTe 2, α-MoTe 2 and WTe 2

    NASA Astrophysics Data System (ADS)

    Hla, S. W.; Marinković, V.; Prodan, A.; Muševič, I.

    1996-05-01

    There is controversy in the literature concerning the correspondence of STM images to the atomic positions on some transition metal layered dichalcogenide surfaces. Although it is difficult to differentiate between metal and chalcogen atoms in these crystals with hexagonal symmetry, like α-MoTe 2, this can be done in cases of β-MoTe 2 and WTe 2 with changed metal-Te distances. Contrary to published STM images of WTe 2 our STM images of β-MoTe 2 show details which resemble the structure of both corrugated topmost Te and metal layers. The d z 2 orbitals of metal atoms protruding vertically upward may provide the tunneling current in this case. The detection of surface or sub-surface atoms depends on the tip electronic condition. The STM results are compared with those from AFM.

  13. Atom probe, AFM, and STM studies on vacuum-fired stainless steels.

    PubMed

    Stupnik, A; Frank, P; Leisch, M

    2009-04-01

    The surface morphology of grades 304L and 316LN stainless steels, after low-temperature bake-out process and vacuum annealing, has been studied by atomic force microscopy (AFM) and scanning tunnelling microscopy (STM). The local elemental composition on the surface before and after thermal treatment has been investigated by atom probe (AP) depth profiling measurements. After vacuum annealing, AFM and STM show significant changes in the surface structure and topology. Recrystallization and surface reconstruction is less pronounced on the 316LN stainless steel. AP depth profiling analyses result in noticeable nickel enrichment on the surface of grade 304L samples. Since hydrogen recombination is almost controlled by surface structure and composition, a strong influence on the outgassing behaviour by the particular surface microstructure can be deduced. PMID:19167824

  14. Ultrafast scanning tunneling microscopy (STM) using a photoexcited low-temperature-grown gallium arsenide tip

    SciTech Connect

    Donati, G.P.; Some, D.; Rodriguez, G.; Taylor, A.J.

    1998-08-01

    In the quest for atomic spatial and picosecond temporal resolutions, several groups have integrated an STM tip with an ultrafast optoelectronic switch that gates the tunneling current from the tip. The authors report a novel ultrafast STM tip consisting of a cleaved GaAs substrate with a 1-{micro}m thick epilayer of low-temperature-grown GaAs (LT-GaAs) deposited on the face. since LT-GaAs has a carrier lifetime of 1 ps, the photo-excitatin of the tip with an ultrafast above-bandgap pulse provides carriers for the tunneling current and photoconductively gates the current from the tip with picoseconds time resolution. The authors use this tip to detect picosecond voltage transients on a coplanar stripline.

  15. STM/STS study of metal-to-Mott-insulator transitions

    NASA Astrophysics Data System (ADS)

    Hanaguri, T.; Kohsaka, Y.; Iwaya, K.; Satow, S.; Kitazawa, K.; Takagi, H.; Azuma, M.; Takano, M.

    2004-08-01

    We performed low-temperature scanning tunneling microscopy/spectroscopy (STM/STS) on Ca 2- xNa xCuO 2Cl 2 and NiS 2- xSe x, which are filling and bandwidth-controlled Mott transition systems, respectively. STM images of Ca 2- xNa xCuO 2Cl 2 show inhomogeneous patch-like corrugations which are originated from the spatial variations of the local density of states. Such an electronic inhomogeneity is absent in NiS 2- xSe x, except in the close vicinity of the metal-insulator transition (MIT). These results suggest that the change in electronic states across the MIT is different between filling- and bandwidth-controlled Mott transition systems.

  16. Microwave Photon-Assisted Incoherent Cooper-Pair Tunneling in a Josephson STM

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    We observe photon-assisted Cooper-pair tunneling in an atomic-scale Josephson junction formed between a superconducting Nb tip and a superconducting Nb sample in a scanning tunneling microscope (STM) at 30 mK. High-resolution tunneling spectroscopy data show a zero-bias conduction peak and other sharp subgap peaks from coupling of the STM junction to resonances in the electromagnetic environment. The subgap peaks respond to incident microwave radiation by splitting into multiple peaks with the position and height depending on the frequency and amplitude of the microwaves. The interpeak spacing shows that the charge carriers are Cooper pairs rather than quasiparticles, and the power dependence reveals that the current originates from photon-assisted phase-incoherent tunneling of pairs rather than the more conventional phase-coherent tunneling of pairs that yields Shapiro steps.

  17. New STM Tip-induced Phases in 1T-TaS2

    NASA Astrophysics Data System (ADS)

    Ma, Liguo; Yu, Yijun; Lu, Xiu Fang; Yan, Ya Jun; Cho, Y. H.; Cheong, Sang-Wook; Chen, Xian Hui; Zhang, Yuanbo

    2015-03-01

    Transition metal dichalcogenide 1T-TaS2 is a layered material featuring a unique set of charge density wave (CDW) phases. The close proximity of the CDW phases in energy makes the material prone to external perturbation, and the intricate electron-phonon and electron-electron interactions often lead to electronic/structural phase transitions in 1T-TaS2. Here we report a new phase transition from the insulating commensurate CDW (also known as a Mott state) to a new metallic CDW state that is induced in 1T-TaS2 by voltage pulses from an STM tip at low temperatures. We study the topographic and spectroscopic properties of the metallic CDW phase in detail with STM and Scanning Tunneling Spectroscopy (STS).

  18. Nanomanipulation and nanofabrication with multi-probe STM: From individual atoms to nanowires

    SciTech Connect

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

    2012-01-01

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

  19. STM analysis of WTe 2 surfaces — correlation with crystal and electronic structures

    NASA Astrophysics Data System (ADS)

    Crossley, A.; Myhra, S.; Sofield, C. J.

    1994-10-01

    WTe 2 surfaces with [001] orientation have been studied in UHV by STM. The features in atomically resolved images exhibited an unequivocal dependence on the polarity of the tunnel voltage, and were in good agreement with results in the literature from calculations of the spatial dependence of the charge density across the unit cell. The analysis showed that "top" and "bottom" Te sites accounted for the observed features. Artefacts were observed; these are ascribed to tip effects, and are likely to have affected the interpretation of STM images in earlier studies. Vacancy defects located at the "top" Te sites in the surface were identified; the consequential redistribution of charge density and effects on the local electronic structure have been investigated.

  20. A low temperature surface preparation method for STM nano-lithography on Si(1 0 0)

    NASA Astrophysics Data System (ADS)

    Mol, J. A.; Beentjes, S. P. C.; Rogge, S.

    2010-06-01

    Registration markers are crucial in connecting scanning tunneling microscope (STM) lithographed nano- and atomic-scale devices to the outside world. In this paper we revisit an ultra high vacuum annealing method with a low thermal budget that is fully compatible with etched registration markers and results in clean 2 × 1 reconstructed Si(1 0 0) surfaces required for STM lithography. Surface contamination is prevented by chemically stripping and reforming a protective silicon oxide layer before transferring the sample to the vacuum system. This allows for annealing temperatures of only 900 °C, where normally carbon contaminants result in the formation of SiC clusters on the surface at annealing temperatures below 950 °C. Reactive ion etched marker structures with an etch depth of 60 nm and a typical lateral dimension of only 150 nm survive a 900 °C flash anneal.

  1. Ab initio calculations on twisted graphene/hBN: Electronic structure and STM image simulation

    NASA Astrophysics Data System (ADS)

    Correa, J. D.; Cisternas, E.

    2016-09-01

    By performing ab initio calculations we obtained theoretical scanning tunneling microscopy (STM) images and studied the electronic properties of graphene on a hexagonal boron-nitrite (hBN) layer. Three different stack configurations and four twisted angles were considered. All calculations were performed using density functional theory, including van der Waals interactions as implemented in the SIESTA ab initio package. Our results show that the electronic structure of graphene is preserved, although some small changes are induced by the interaction with the hBN layer, particularly in the total density of states at 1.5 eV under the Fermi level. When layers present a twisted angle, the density of states shows several van Hove singularities under the Fermi level, which are associated to moiré patterns observed in theoretical STM images.

  2. Elucidation of Isomerization Pathways of a Single Azobenzene Derivative Using an STM.

    PubMed

    Kazuma, Emiko; Han, Mina; Jung, Jaehoon; Oh, Junepyo; Seki, Takahiro; Kim, Yousoo

    2015-11-01

    The predominant pathway for the isomerization between cis- and trans-azobenzenes-either (i) inversion by the bending of an NNC bond or (ii) rotation by the torsion of two phenyl rings-continues to be a controversial topic. To elucidate each isomerization pathway, a strategically designed and synthesized azobenzene derivative was investigated on a Ag(111) surface. This was achieved by exciting the molecule with tunneling electrons from the tip of a scanning tunneling microscope (STM). Structural analyses of the molecularly resolved STM images reveal that both inversion and rotation pathways are available for isomerization on a metal surface and strongly depend on the initial adsorption structures of the molecule. On the basis of the potential energy diagrams for the isomerization, it is concluded that isomerization pathways on a metal surface are not simply related to the excited states. PMID:26722964

  3. Thermolabile phenol sulfotransferase gene (STM): Localization to human chromosome 16p11.2

    SciTech Connect

    Aksoy, I.A.; Her, C.; Weinshilboum, M.

    1994-09-01

    Thermolabile (TL) phenol sulfotransferase (PST) catalyzes the sulfate conjugation of phenolic monoamine neurotransmitters such as dopamine and serotonin. We recently cloned a cDNA for human liver TL PST and expressed it in COS-1 cells. We now report the chromosomal localization of the human TL PST gene (STM) as well as its partial sequence. DNA from NIGMS Human/Rodent Somatic Cell Hybrid Mapping Panels 1 and 2 was screened by use of the PCR, and the STM gene was mapped to chromosome 16. Regional localization to 16p11.2 was performed by PCR analysis of a high-resolution mouse/human somatic cell hybrid panel that contained defined portions of human chromosome 16. 15 refs., 2 figs.

  4. Josephson STM at mK temperatures: Coupling to the electronic environment

    NASA Astrophysics Data System (ADS)

    Dreyer, Michael; Dana, Rami; Liao, Wan-Ting; Lobb, Cris; Wellstood, Fred; Anderson, Bob

    Ultra-small Josephson junctions can couple to modes in the electronic environment. This leads to sub-gap peaks in the I(V) curve in addition to the phase diffuse supercurrent. The I(V) curve can - in principle - be explained by P(E) theory which describes the probability of tunneling at energy E. A recent study showed that antenna modes of the STM tips could be responsible for the observed sideband structures. In our case the explanation appears to be less simple. We employ a dual tip STM at a temperature of 30 mK. The I(V) spectra of the two tips show distinct patterns with only one shared mode. While the supercurrent branch for the ''inner'' tip is visible, it is obscured by a resonance for the ``outer'' tip. Possible causes and applications to other systems will be discussed. Support from NSF (DMR- 0605763) and Laboratory for Physical Sciences.

  5. In situ STM studies of Sb(111) electrodes in aqueous electrolyte solutions

    NASA Astrophysics Data System (ADS)

    Grozovski, V.; Kallip, S.; Lust, E.

    2013-07-01

    The in situ STM studies of Sb(111), which was cleaved at the temperature of liquid nitrogen inside the glove box, and of Sb(111), which was electrochemically polished in the KI + HCl aqueous solution, have been performed under negative polarizations from - 0.8 to - 0.15 V (versus Ag|AgCl in sat. KCl aqueous solution) in the 0.5 M Na2SO4 + 0.0003 M H2SO4 aqueous solution. The atomic resolution has been achieved. The in situ STM data show that there are no quick surface reconstruction processes and the surface structure of cleaved and electrochemically polished Sb(111) is stable within the potential region investigated, similarly for Bi(111) single crystal electrode, previously studied [S. Kallip, E. Lust, Electrochem. Comm. 7 (2005) 863].

  6. STM and ab initio study of holmium nanowires on a Ge(111) surface

    NASA Astrophysics Data System (ADS)

    Eames, C.; Bonet, C.; Probert, M. I. J.; Tear, S. P.; Perkins, E. W.

    2006-11-01

    A nanorod structure has been observed on the Ho/Ge(111) surface using scanning tunneling microscopy (STM). The rods do not require patterning of the surface or defects such as step edges in order to grow as is the case for nanorods on Si(111). At low holmium coverage the nanorods exist as isolated nanostructures while at high coverage they form a periodic 5×1 structure. We propose a structural model for the 5×1 unit cell and show using an ab initio calculation that the STM profile of our model structure compares favorably to that obtained experimentally for both filled and empty states sampling. The calculated local density of states shows that the nanorod is metallic in character.

  7. Bonding and reactivity of clean and chemically-modified semiconductor surfaces probed with STM

    SciTech Connect

    Hamers, R.J.

    1995-12-01

    Scanning tunneling microscopy has been used to directly study the interrelationships between chemical composition, chemical reactivity, electronic structure, and surface morphology at the atomic level on clean and chemically-modified semiconductor surfaces. Our work has focused recently on understanding the atomic-level interactions of dopants such as phosphorus and boron on the Si(001) surface, and the influence of these atoms on other chemical reactions such as the thermal decomposition of disilane to grow epitaxial silicon. Using STM to study how these atoms modify the surface in combination with tunneling spectroscopy to reveal the occupied and unoccupied molecular orbitals of these structures provides direct insight into the nature of chemical bonding on these surfaces. This talk will discuss the application of STM to understand chemical bonding at silicon surfaces.

  8. Mapping the first electronic resonances of a Cu phthalocyanine STM tunnel junction.

    PubMed

    Soe, W-H; Manzano, C; Wong, H S; Joachim, C

    2012-09-01

    Using a low temperature, ultrahigh vacuum scanning tunneling microscope (STM), dI/dV differential conductance maps were recorded at the tunneling resonance energies for a single Cu phthalocyanine molecule adsorbed on an Au(111) surface. We demonstrated that, contrary to the common assumption, such maps are not representative of the molecular orbital spatial expansion, but rather result from their complex superposition captured by the STM tip apex with a superposition weight which generally does not correspond to the native weight used in the standard Slater determinant basis set. Changes in the molecule conformation on the Au(111) surface further obscure the identification between dI/dV conductance maps and the native molecular orbital electronic probability distribution in space. PMID:22898492

  9. Morphological analysis of stainless steel scale like surface morphology using STM and AFM

    SciTech Connect

    Vignal, V.; Olive, J.M.; Desjardins, D.; Roux, J.C.; Genton, V.

    1997-12-19

    A combined atomic force microscopy (AFM) and scanning tunneling microscopy (STM) investigation of stainless steel like surface morphology formed either in electropolishing bath or in HNO{sub 3} medium is reported. A new numerical technique using the Nanoscope III software is proposed. The dimension, slope and orientation of scales can be easily determined. Moreover, grain boundaries structure and probable oxides present in the upper part of the film can be deduced.

  10. Toward quantitative STM: Scanning tunneling microscopy study of structure and dynamics of adsorbates on transition metal surfaces

    SciTech Connect

    Dunphy, J.C.

    1995-05-01

    STM was applied to chemisorbed S layers on Re(000l) and Mo(100) surfaces. As function of coverage on both these surfaces, S orders into several different overlayer structures, which have been studied by dynamic LEED. STM images of all these structures were obtained. Approximate location of S atoms in the structures was determined by inspecting the images, especially the regions containing defects. Results are in agreement with LEED except for the p(2{times}l) overlayer of sulfur on Mo(100). The STM images were compared to calculations made with Electron Scattering Quantum Chemistry (ESQC) theory. Variation of contrast in experimental images is explained as a result of changes in STM tip termination structure. STM image contrast is a result of changes in the interference between different paths for the tunneling electrons. The simplest structure on the Mo(100) surface was used as a model for developing and testing a method of quantitative structure determination with the STM. Experimental STM images acquired under a range of tunneling conditions were compared to theoretical calculations of the images as a function of surface structure to determine the structure which best fit. Results matched within approximately 0.1 Angstroms a LEED structural determination. At lower S coverage, diffusion of S atoms over the Re(0001) surface and the lateral interaction between these atoms were investigated by application of a new image analysis technique. The interaction between the S and a coadsorbed CO layer was also studied, and CO was found to induce compression of the S overlayer. A similar result was found for Au deposited on the sulfur covered Mo(100) surface. The interaction between steps on the Mo surface was found to be influenced by S adsorption and this observation was interpreted with the theory of equilibrium crystal shape. Design of an STM instrument which operates at cryogenic and variable sample temperatures, and its future applications, are described.

  11. Oxygen adsorption on the Al₉Co₂(001) surface: first-principles and STM study.

    PubMed

    Villaseca, S Alarcón; Loli, L N Serkovic; Ledieu, J; Fournée, V; Gille, P; Dubois, J-M; Gaudry, E

    2013-09-01

    Atomic oxygen adsorption on a pure aluminum terminated Al9Co2(001) surface is studied by first-principle calculations coupled with STM measurements. Relative adsorption energies of oxygen atoms have been calculated on different surface sites along with the associated STM images. The local electronic structure of the most favourable adsorption site is described. The preferential adsorption site is identified as a 'bridge' type site between the cluster entities exposed at the (001) surface termination. The Al-O bonding between the adsorbate and the substrate presents a covalent character, with s-p hybridization occurring between the states of the adsorbed oxygen atom and the aluminum atoms of the surface. The simulated STM image of the preferential adsorption site is in agreement with experimental observations. This work shows that oxygen adsorption generates important atomic relaxations of the topmost surface layer and that sub-surface cobalt atoms strongly influence the values of the adsorption energies. The calculated Al-O distances are in agreement with those reported in Al2O and Al2O3 oxides and for oxygen adsorption on Al(111). PMID:23883551

  12. Structure determination of chemisorbed chirality transfer complexes: Accelerated STM analysis and exchange-correlation functional sensitivity

    NASA Astrophysics Data System (ADS)

    Groves, M. N.; Goubert, G.; Rasmussen, A. M. H.; Dong, Y.; Lemay, J.-C.; Demers-Carpentier, V.; McBreen, P. H.; Hammer, B.

    2014-11-01

    Linking STM images to atomic positions determined by DFT calculations is an important step in characterizing the intermolecular interactions at play in many surface processes including asymmetric hydrogenation on heterogeneous catalysts. An accelerated data extraction method is used to collect STM information on the geometry of complexes formed between the two substrates, 2,2,2-trifluoroacetophenone (TFAP) and 3,3,3-methyltrifluoropyruvate (MTFP), and the chiral modifier (R)-(+)-1-(1-naphthyl)ethylamine ((R)-NEA) on Pt(111). We present new experimental data for complexes formed by MTFP and the (R)-NEA-1 conformer along with a new and enlarged set of reformulated STM data that extends what was reported in previously published studies of complexed MTFP and TFAP. Atomic geometries based on DFT calculations using PBE, M06-L, and optB88-vdW exchange-correlation functionals will also be presented. It will be shown that both substrates have well-defined complexation geometries when interacting with the modifier and that the relative complexation energies are not markedly sensitive to the functional employed.

  13. Fabrication and Characterization of CNT-Based Smart Tips for Synchrotron Assisted STM

    DOE PAGESBeta

    Yan, Hui; Cummings, Marvin; Camino, Fernando; Xu, Weihe; Lu, Ming; Tong, Xiao; Shirato, Nozomi; Rosenmann, Daniel; Rose, Volker; Nazaretski, Evgeny

    2015-01-01

    Determination of chemical composition along with imaging at the atomic level provides critical information towards fundamental understanding of the surface of materials and, hence, yields the capability to design new materials by tailoring their ultimate functionalities. Synchrotron X-ray assisted scanning tunneling microscopy (SX-STM) is a promising new technique to achieve real space chemically specific atomic mapping. Chemical sensitivity of SX-STM relies on excitation of core electrons by incident X-rays when their energy is tuned to an absorption edge of a particular element. However, along with core-level electrons, photoelectrons are also excited, which yield additional current and interfere with the tunnelingmore » current. To reduce the background photoelectron current and to improve ultimate resolution of SX-STM, we have developed and fabricated multiwalled carbon nanotubes (MWCNT) based “smart tips” using plasma enhanced chemical vapor deposition and focused ion beam milling. The newly developed CNT-based smart tips, characterized step by step by scanning electron microscopy (SEM) during the fabrication process, demonstrate good performance and provide opportunity for realizing atomic chemical mapping.« less

  14. In situ STM investigation of Ag(111) electrochemical roughening in perchlorate solutions

    NASA Astrophysics Data System (ADS)

    Aloisi, G.; Funtikov, A. M.; Guidelli, R.

    1993-11-01

    The surface structures generated by oxidation-reduction cycles (ORCs) on a well characterized silver (111) single crystal face have been examined by in situ STM. The ORCs, carried out in aqueous KClO 4, produce surface structures which span from atomic-scale clusters to large-scale features with linear dimensions of some hundreds of nanometers. While the surface structures produced by the ORC are stable at the most negative potentials, application of increasingly positive potentials causes a rearrangement of the surface with progressive predominance of the large-scale features over the small-scale ones, quite probably by a mechanism involving silver dissolution and redeposition of silver ions. This increase in dimensions is accompanied by a decrease in the SERS activity of the metal surface. The atomic-scale clusters, which are clearly visible by in situ STM at far negative potentials, are responsible for a substantial increase in Raman enhancement. Bumps with dimensions of the order of tens of nanometers, which are responsible for the excitation of local modes, are shown by in situ STM to persist at - 0.5 V/SCE. However, a further positive shift in potential causes a decrease both in their number and in the SERS activity.

  15. Growth and in vivo STM of III-V Compound Semiconductors

    NASA Astrophysics Data System (ADS)

    Bastiman, F.; Cullis, A. G.; Hopkinson, M.; Green, M.

    A combinational machine (MBSTM) capable of III-V molecular beam epitaxial deposition whilst performing scanning tunnelling microscopy (STM) is described. Epitaxial deposition `under the STM tip' heralds a new world of discovery in the field of III-V epitaxial growth. What is fashionably referred to as in vivo STM offers the potential to observe a medley of speculated transitions that until now have been glimpsed frozen in time. It is potentially possible to observe in real time and on the atomic scale GaAs surface processes such as reconstruction transformations, monolayer steps sweeping across the growth surface and, for eg (001) orientation, the structure evolution during heteroepitaxial InAs deposition through Stranski-Krastanow (S-K) wetting layer formation and quantum dot (QD) growth. To this end, an overview of the machine is given, detailing the crucial composition of the MBSTM chamber. Key aspects related to tip preparation, temperature regulation and deposition inception are detailed providing a picture of the future of III-V epitaxial research.

  16. An effect of couterion in STM imaging process of DNA on Cu(111)

    NASA Astrophysics Data System (ADS)

    Furukawa, Masashi; Nishimura, Makoto; Tanaka, Hiroyuki; Kawai, Tomoji

    2002-03-01

    In order to elucidate electrical conduction mechanism of DNA, which is still under debate over the last decade, we have performed local electronic structure measurement of single- and double-stranded DNA molecules adsorbed onto Cu(111) surfaces using scanning tunneling microscope (STM). Bias-voltage-dependent STM images (from -5 V to +5 V) have shown that the molecular corrugation height in STM increases gradually at positive bias voltage region (empty state). Despite the theoretical assumption in which their 1st-LUMO states are localized at π plane of DNA bases, one cannot conclude its origin as the existence of their LUMO states, based on the results of relevant control measurements, DNA base molecules/Cu(111) [1] and NaCl/Cu(111). In fact, we found almost identical bias dependencies in the latter case (NaCl/Cu(111)), indicating that the feature of π* states of DNA bases should be buried in an additional channel that opens up by the onset of its unoccupied overlayer state in the tunneling process [2]. This study implies a potential difficulty in direct comparison of the obtained data with those characterized by XAS, in which π* states is located at ca. -1 eV relative to the Fermi level [3]. [1]M. Furukawa et al., submitted to Surf. Sci. [2] J. Kliewer et al., Surf. Sci. 477 (2001) 250.; A. Carlsson et al., Phys. Rev. B. 56 (1997) 1593. [3] M. Furukawa et al., submitted to Phys. Rev. B.

  17. Genomic structure and expression of STM2, the chromosome 1 familial Alzheimer disease gene

    SciTech Connect

    Levy-Lahad, E.; Wang, Kai; Fu, Ying Hui

    1996-06-01

    Mutations in the gene STM2 result in autosomal dominant familial Alzheimer disease. To screen for mutations and to identify regulatory elements for this gene, the genomic DNA sequence and intron-exon structure were determined. Twelve exons including 10 coding exons were identified in a genomic region spanning 23, 737 bp. The first 2 exons encode the 5{prime}-untranslated region. Expression analysis of STM2 indicates that two transcripts of 2.4 and 2.8 kb are found in skeletal muscle, pancreas, and heart. In addition, a splice variant of the 2.4-kb transcript was identified that is the result of the use of an alternative splice acceptor site located in exon 10. The use of this site results in a transcript lacking a single glutamate. The promotor for this gene and the alternatively spliced exons leading to the 2.8-kb form of the gene remain to be identified. Expression of STM2 was high in skeletal muscle and pancreas, with comparatively low levels observed in brain. This expression pattern is intriguing since in Alzheimer disease, pathology and degeneration are observed only in the central nervous system. 19 refs., 2 figs., 3 tabs.

  18. Using L-STM to directly visualize enzymatic self-assembly/disassembly of nanofibers.

    PubMed

    Zheng, Zhen; Wang, Jihao; Chen, Peiyao; Xie, Maolin; Zhang, Lei; Hou, Yubin; Zhang, Xin; Jiang, Jun; Wang, Junfeng; Lu, Qingyou; Liang, Gaolin

    2016-08-18

    Self-assembly/disassembly is ubiquitous in nature and plays an important role in many biological events. But noninvasive characterization of this process in real time at molecular resolution remains challenging. Herein, using homebuilt liquid-phase scanning tunneling microscopy (L-STM) with ultrahigh stability, we directly visualized enzymatic self-assembly/disassembly of oligopeptide nanofibers in real time for the first time. Static high-resolution L-STM images clearly showed the molecular packing details in the supramolecular nanofiber and the diameter of the nanofiber was consistent with that of cryo transmission electron microscopy (cryo-TEM) observations. Moreover, the self-repairing behavior of the supramolecular nanofibers was also directly observed at high resolution for the first time. This work unprecedentedly revealed new insights into Nature-mimic self-assembly and disassembly at the molecular level. It also illustrates the potential of our homebuilt L-STM in studying delicate biological processes in physiological solution with high resolution. PMID:27492656

  19. How Authorship is Defined by Multiple Publishing Organizations and STM Publishers.

    PubMed

    da Silva, Jaime A Teixeira; Dobránszki, Judit

    2016-01-01

    The most important part of a biomedical scientific manuscript is undeniably the research data. Yet, scientists generate and validate that data, culminating, in most cases, in a scientific manuscript. Thus, authorship, specifically the contributions and attributed responsibilities of the authors, remains a central issue in science publishing. This article examines the definitions of authorship as defined by four publishing organizations--the Committee on Publication Ethics (COPE), the Council of Scientific Editors (CSE), the International Committee of Medical Journal Editors (ICMJE), and World Association of Medical Editors (WAME)-and 15 science, technology, and medicine (STM) publishers. The objective is to understand whether there is consistency among definitions. Five of these STM publishers rely specifically on the ICMJE definitions of authorship, while 12/15 are COPE members. The clarity, logic, realism, feasibility, and enforceability of these definitions will be discussed. Our analysis reveals that authorship definitions are inconsistent among the 15 STM publishers. Scientists have the inherent right to determine who is an author of an article according to the ethical guidelines of their institutes, but these may differ from the guidelines indicated by publishers, while editors and publishers have the right to verify authorship. PMID:26191641

  20. The ReactorSTM: Atomically resolved scanning tunneling microscopy under high-pressure, high-temperature catalytic reaction conditions

    NASA Astrophysics Data System (ADS)

    Herbschleb, C. T.; van der Tuijn, P. C.; Roobol, S. B.; Navarro, V.; Bakker, J. W.; Liu, Q.; Stoltz, D.; Cañas-Ventura, M. E.; Verdoes, G.; van Spronsen, M. A.; Bergman, M.; Crama, L.; Taminiau, I.; Ofitserov, A.; van Baarle, G. J. C.; Frenken, J. W. M.

    2014-08-01

    To enable atomic-scale observations of model catalysts under conditions approaching those used by the chemical industry, we have developed a second generation, high-pressure, high-temperature scanning tunneling microscope (STM): the ReactorSTM. It consists of a compact STM scanner, of which the tip extends into a 0.5 ml reactor flow-cell, that is housed in a ultra-high vacuum (UHV) system. The STM can be operated from UHV to 6 bars and from room temperature up to 600 K. A gas mixing and analysis system optimized for fast response times allows us to directly correlate the surface structure observed by STM with reactivity measurements from a mass spectrometer. The in situ STM experiments can be combined with ex situ UHV sample preparation and analysis techniques, including ion bombardment, thin film deposition, low-energy electron diffraction and x-ray photoelectron spectroscopy. The performance of the instrument is demonstrated by atomically resolved images of Au(111) and atom-row resolution on Pt(110), both under high-pressure and high-temperature conditions.

  1. The ReactorSTM: Atomically resolved scanning tunneling microscopy under high-pressure, high-temperature catalytic reaction conditions

    SciTech Connect

    Herbschleb, C. T.; Tuijn, P. C. van der; Roobol, S. B.; Navarro, V.; Bakker, J. W.; Liu, Q.; Stoltz, D.; Cañas-Ventura, M. E.; Verdoes, G.; Spronsen, M. A. van; Bergman, M.; Crama, L.; Taminiau, I.; Frenken, J. W. M.; Ofitserov, A.; Baarle, G. J. C. van

    2014-08-15

    To enable atomic-scale observations of model catalysts under conditions approaching those used by the chemical industry, we have developed a second generation, high-pressure, high-temperature scanning tunneling microscope (STM): the ReactorSTM. It consists of a compact STM scanner, of which the tip extends into a 0.5 ml reactor flow-cell, that is housed in a ultra-high vacuum (UHV) system. The STM can be operated from UHV to 6 bars and from room temperature up to 600 K. A gas mixing and analysis system optimized for fast response times allows us to directly correlate the surface structure observed by STM with reactivity measurements from a mass spectrometer. The in situ STM experiments can be combined with ex situ UHV sample preparation and analysis techniques, including ion bombardment, thin film deposition, low-energy electron diffraction and x-ray photoelectron spectroscopy. The performance of the instrument is demonstrated by atomically resolved images of Au(111) and atom-row resolution on Pt(110), both under high-pressure and high-temperature conditions.

  2. The EAL domain containing protein STM2215 (rtn) is needed during Salmonella infection and has cyclic di-GMP phosphodiesterase activity.

    PubMed

    Zheng, Yi; Sambou, Tounkang; Bogomolnaya, Lydia M; Cirillo, Jeffrey D; McClelland, Michael; Andrews-Polymenis, Helene

    2013-08-01

    Salmonella Typhimurium gene STM2215 (rtn) is conserved among many enterobacteriaceae. Mutants lacking STM2215 poorly colonized the liver and spleen in intraperitoneal infection of mice and poorly colonized the intestine and deeper tissues in oral infection. These phenotypes were complemented by a wild-type copy of STM2215 provided in trans. STM2215 deletion mutants grew normally in J774A.1 murine macrophages but were unable to invade Caco-2 colonic epithelial cells. Consistent with this finding, mutants in STM2215 produced lower levels of effectors of the TTSS-1. STM2215 is a predicted c-di-GMP phosphodiesterase, but lacks identifiable sensor domains. Biochemical analysis of STM2215 determined that it is located in the inner membrane and has c-di-GMP phosphodiesterase activity in vitro dependent on an intact EAL motif. Unlike some previously identified members of this family, STM2215 did not affect motility, was expressed on plates, and in liquid media at late exponential and early stationary phase during growth. Defined mutations in STM2215 revealed that neither the predicted periplasmic domain nor the anchoring of the protein to the inner membrane is necessary for the activity of this protein during infection. However, the EAL domain of STM2215 is required during infection, suggesting that its phosphodiesterase activity is necessary during infection. PMID:23734719

  3. The STM4195 Gene Product (PanS) Transports Coenzyme A Precursors in Salmonella enterica

    PubMed Central

    Ernst, Dustin C.

    2015-01-01

    ABSTRACT Coenzyme A (CoA) is a ubiquitous coenzyme involved in fundamental metabolic processes. CoA is synthesized from pantothenic acid by a pathway that is largely conserved among bacteria and eukaryotes and consists of five enzymatic steps. While higher organisms, including humans, must scavenge pantothenate from the environment, most bacteria and plants are capable of de novo pantothenate biosynthesis. In Salmonella enterica, precursors to pantothenate can be salvaged, but subsequent intermediates are not transported due to their phosphorylated state, and thus the pathway from pantothenate to CoA is considered essential. Genetic analyses identified the STM4195 gene product of Salmonella enterica serovar Typhimurium as a transporter of pantothenate precursors, ketopantoate and pantoate and, to a lesser extent, pantothenate. Further results indicated that STM4195 transports a product of CoA degradation that serves as a precursor to CoA and enters the biosynthetic pathway between PanC and CoaBC (dfp). The relevant CoA derivative is distinguishable from pantothenate, pantetheine, and pantethine and has spectral properties indicating the adenine moiety of CoA is intact. Taken together, the results presented here provide evidence of a transport mechanism for the uptake of ketopantoate, pantoate, and pantothenate and demonstrate a role for STM4195 in the salvage of a CoA derivative of unknown structure. The STM4195 gene is renamed panS to reflect participation in pantothenate salvage that was uncovered herein. IMPORTANCE This manuscript describes a transporter for two pantothenate precursors in addition to the existence and transport of a salvageable coenzyme A (CoA) derivative. Specifically, these studies defined a function for an STM protein in S. enterica that was distinct from the annotated role and led to its designation as PanS (pantothenate salvage). The presence of a salvageable CoA derivative and a transporter for it suggests the possibility that this

  4. Key Role of M.G. Nakhodkin’s Insight and Inspiration in Development of UHV STM-Related Techniques and Methods

    SciTech Connect

    Lyubinetsky, Igor

    2015-02-15

    In this contribution I briefly describe my joint efforts and experiences with M.G. Nakhodkin in the field of scanning tunneling microscopy (STM) including a construction of the home-built microscopes, application of this technique in various scientific endevours, as well as fruitfull and enlightening discusions. Our co-operation was focused on the novel aspects of STM probes preparation and conditioning, coupling the STM junction with laser irradiation, STM-based nanolithography, and also on collaboration at the international scale with M.G. Nakhodkin and members of his scientific group.

  5. Exploring routes to tailor the physical and chemical properties of oxides via doping: an STM study.

    PubMed

    Nilius, Niklas

    2015-08-01

    Doping opens fascinating possibilities for tailoring the electronic, optical, magnetic, and chemical properties of oxides. The dopants perturb the intrinsic behavior of the material by generating charge centers for electron transfer into adsorbates, by inducing new energy levels for electronic and optical excitations, and by altering the surface morphology and hence the adsorption and reactivity pattern. Despite a vivid scientific interest, knowledge on doped oxides is limited when compared to semiconductors, which reflects the higher complexity and the insulating nature of many oxides. In fact, atomic-scale studies, aiming at a mechanistic understanding of dopant-related processes, are still scarce.In this article, we review our scanning tunneling microscopy (STM) experiments on thin, crystalline oxide films with a defined doping level. We demonstrate how the impurities alter the surface morphology and produce cationic/anionic vacancies in order to keep the system charge neutral. We discuss how individual dopants can be visualized in the lattice, even if they reside in subsurface layers. By means of STM-conductance and x-ray photoelectron spectroscopy, we determine the electronic impact of dopants, including the energies of their eigen states and local band-bending effects in the host oxide. Electronic transitions between dopant-induced gap states give rise to new optical modes, as detected with STM luminescence spectroscopy. From a chemical perspective, dopants are introduced to improve the redox potential of oxide materials. Electron transfer from Mo-donors, for example, alters the growth behavior of gold and activates O2 molecules on a wide-gap CaO surface. Such results demonstrate the enormous potential of doped oxides in heterogeneous catalysis. Our experiments address the issue of doping from a fundamental viewpoint, posing questions on the lattice position, charge state, and electron-transfer potential of the impurity ions. Whether doped oxides are suitable

  6. Structural characterization and comparison of iridium, platinum and gold/palladium ultra-thin film coatings for STM of biomolecules

    SciTech Connect

    Sebring, R.; Arendt, P.; Imai, B.; Bradbury, E.M.; Gatewood, J.; Panitz, J.; Yau, P.

    1997-10-30

    Scanning tunneling microscopy (STM) is capable of atomic resolution and is ideally suited for imaging surfaces with uniform work function. A biological sample on a conducting substrate in air does not meet this criteria and requires a conductive coating for stable and reproducible STM imaging. In this paper, the authors describe the STM and transmission electron microscopy (TEM) characterization of ultra-thin ion-beam sputtered films of iridium and cathode sputtered gold/palladium and platinum films on highly ordered pyrolytic graphite (HOPG) which were developed for use as biomolecule coatings. The goals were the development of metal coatings sufficiently thin and fine grained that 15--20 {angstrom} features of biological molecules could be resolved using STM, and the development of a substrate/coating system which would allow complementary TEM information to be obtained for films and biological molecules. The authors demonstrate in this paper that ion-beam sputtered iridium on highly ordered pyrolytic graphite (HOPG) has met both these goals. The ion-beam sputtered iridium produced a very fine grained (< 10 {angstrom}) continuous film at 5--6 {angstrom} thickness suitable for stable air STM imaging. In comparison, cathode sputtered platinum produced 16 {angstrom} grains with the thinnest continuous film at 15 {angstrom} thickness, and the sputtered gold/palladium produced 25 {angstrom} grains with the thinnest continuous film at 18 {angstrom} thickness.

  7. Alumina supported model Pd Ag catalysts: A combined STM, XPS, TPD and IRAS study

    NASA Astrophysics Data System (ADS)

    Khan, N. A.; Uhl, A.; Shaikhutdinov, S.; Freund, H.-J.

    2006-05-01

    The bimetallic Pd-Ag model catalysts were prepared by physical vapor deposition on thin alumina films. The morphology and structure of the Pd-Ag particles were studied by STM, XPS, and by TPD and IRAS of CO. The results showed the formation of true alloy particles with Ag segregated at the surface. The addition of Ag first suppresses the most strongly bonded CO on threefold hollow sites of Pd. With further increasing Ag coverage, only isolated Pd atoms surrounded by Ag atoms are likely present on the surface. The results on CO adsorption suggest that the model Pd-Ag system mimics the structure of the real Pd-Ag catalysts.

  8. In-Situ TEM-STM Observations of SWCNT Ropes/Tubular Transformations

    NASA Technical Reports Server (NTRS)

    Sola, F.; Lebron-Colon, M.; Ferreira, P. J.; Fonseca, L. F.; Meador, M. A.; Marin, C.

    2010-01-01

    Single-walled carbon nanotubes (SWCNTs) prepared by the HiPco process were purified using a modified gas phase purification technique. A TEM-STM holder was used to study the morphological changes of SWCNT ropes as a function of applied voltage. Kink formation, buckling behavior, tubular transformation and eventual breakdown of the system were observed. The tubular formation was attributed to a transformation from SWCNT ropes to multi-walled carbon nanotube (MWCNT) structures. It is likely mediated by the patching and tearing mechanism which is promoted primarily by the mobile vacancies generated due to current-induced heating and, to some extent, by electron irradiation.

  9. Functional over-expression of the Stm1 protein, a G-protein-coupled receptor, in Schizosaccharomyces pombe.

    PubMed

    Chung, Kyung-Sook; Kim, Dong-Uk; Ryoo, Sung-Woo; Kang, Eun-Jung; Won, Misun; Kim, Lila; Jang, Young-Joo; Maeng, Pil-Jae; Kim, Sei-Chang; Yoo, Hyang-Sook; Hoe, Kwang-Lae

    2003-02-01

    We report here the first functional over-expression of the Stm1 protein, a G-protein-coupled receptor with seven-trans-membrane spanning regions, in a homologous expression system without internal modification of the open reading frame of Stm1. The entire coding sequence, except for the termination codon followed by a C-terminal His6 tag, has been cloned into the pREP1 vector. The functionally active Stm1-His6 was over-expressed in Schizosaccharomyces pombe under the control of the nmt1 (no message in thiamine) promoter. The expression after induction was 120 times as much as that of control before induction and it gave approximately 500 ng protein/2 x 10(7) cells. PMID:12882583

  10. Structural transformations of the Si(111)2 × 2-In surface induced by STM tip and thermal annealing

    NASA Astrophysics Data System (ADS)

    Saranin, A. A.; Numata, T.; Kubo, O.; Katayama, M.; Oura, K.

    1997-11-01

    We have investigated In deposition on to Si(111) 3× 3- In surface by using low-energy electron diffraction (LEED) and scanning tunnelling microscopy (STM). A 2 × 2 structure was formed at 50-100°C. Indium deposition at around 200°C on the 3× 3 surface or thermal annealing of the 2 × 2 surface resulted in the 4 × 1 structure formation but not through a 31× 31 phase, as takes place at higher temperatures. The difference between low and high temperature surface phase formation is discussed. We have found that the 2 × 2 structure converts into the 3× 3 one during STM observation. This process was explained by STM-induced In atoms diffusion and/or desorption. Possible atomic arrangement of the 2 × 2-In reconstruction was proposed.

  11. Irving Langmuir Prize in Chemical Physics Lecture: The Inner Machinery of Single Molecules: resolving the unresolved with the STM

    NASA Astrophysics Data System (ADS)

    Ho, Wilson

    2013-03-01

    The scanning tunneling microscope (STM) is a unique instrument that can probe and induce changes in a molecule with atomic scale resolution. Its operation is based on the current that flows between the tip and the substrate with the molecule sandwiched in between. Therefore, the STM can be used to understand the coupling of electrons to the different states and excitations in the molecule and to investigate the influence on them by its environment. From the spatial and energy dependences of the coupling to the charge, spin, and nuclear motions in the molecule, verification of and new insights into the quantum mechanical properties of molecules can be obtained, including the discovery of new conduction and energy transfer mechanisms. This understanding of electron-molecule interactions with the STM enables rational ways to control chemistry and the exploration of novel physical technologies based on molecules.

  12. Methanethiolate Adsorption Site on Au(111): A Combined STM/DFT Study at the Single-Molecule Level

    SciTech Connect

    Maksymovych, P.; Sorescu, D.C.; Yates, J.T.

    2006-10-26

    The chemisorptive bonding of methanethiolate (CH3S) on the Au(111) surface has been investigated at a single-molecule level using low-temperature scanning tunneling microscopy (LT-STM) and density functional theory (DFT). The CH3S species were produced by STM-tip-induced dissociation of methanethiol (CH3SH) or dimethyl disulfide (CH3SSCH3) at 5 K. The adsorption site of an isolated CH3S species was assigned by comparing the experimental and calculated STM images. We conclude that the S-headgroup of chemisorbed CH3S adsorbs on the 2-fold coordinated bridge site between two Au atoms, consistent with theoretical predictions for CH3S on the nondefective Au(111) surface. Our assignment is also supported by the freezing of the tip-induced rotational dynamics of a single CH3SH molecule upon conversion to CH3S via deprotonation.

  13. High-Resolution Electrochemical Scanning Tunneling Microscopy (EC-STM) Flow-Cell Studies.

    PubMed

    Lay, Marcus D; Sorenson, Thomas A; Stickney, John L

    2003-09-25

    Atomic-level studies involving an electrochemical scanning tunneling microscope (EC-STM) flow-cell are presented. Multiple electrochemical atomic layer epitaxy (EC-ALE) cycles of CdTe formation were observed. For a binary compound (i.e., CdTe), an EC-ALE cycle involves exposure of the substrate to a solution of the first precursor (CdSO4), followed by exposure to the second precursor (TeO2), while maintaining potential control. Interleaving blank rinses may also be used, but were omitted in the present studies. To allow the exchange of solutions, the EC-STM cell was modified to allow solution exchange via a single peristaltic pump. A selection valve was used to choose the solution to be introduced into the cell. There is evidence that the growth of the initial layer of CdTe on Au(111), the (√7 × √7)-CdTe monolayer, can be improved in homogeneity and morphology by repeatedly depositing and stripping the Cd atomic layer. Therefore, a new starting cycle, which should improve the quality of deposits formed via EC-ALE, has been developed. PMID:26317446

  14. Atomistic simulations of negatively charged donor states probed in STM experiments

    NASA Astrophysics Data System (ADS)

    Tankasala, Archana; Salfi, Joe; Rogge, Sven; Klimeck, Gerhard; Rahman, Rajib

    A single donor in silicon binding two electrons (D-) is important for electron spin readout and two-qubit operations in a donor based silicon (Si) quantum computer, and has recently been probed in Scanning Tunneling Microscope (STM) experiments for sub-surface dopants. In this work, atomistic configuration interaction technique is used to compute the two-electron states of the donor taking into account the geometry of the STM-vacuum-silicon-reservoir device. While 45 meV charging energy is obtained for D- in bulk Si, the electrostatics of the device reduces the charging energy to 30 meVs. It is also shown that the reduced charging energy enables spin triplet states to be bound to the donor. The exchange splitting between the singlet and triplet states can be tuned by an external electric field. The computed wavefunctions of the D- state helps to understand how the contribution of the momentum space valley states change with donor depth and electric field.

  15. STM study on the surface defects of SnSe induced by thermal annealing

    NASA Astrophysics Data System (ADS)

    Thi Ly, Trinh; Kim, Sang-Ui; Kim, Tae Hoon; Duong, Anh Tuan; Cho, Sunglae; Rhim, S. H.; Kim, Jungdae

    SnSe is a IV - VI semiconductor with 0.86 eV gap, and a single crystal SnSe usually exhibits a p-type characteristic. SnSe is one of 2D layered materials, and it has attracted researchers' attentions due to excellent physical properties for future applications. In particular, exceptionally high ZT value (ZT = ~2.6 at 923 K) was reported for SnSe single crystal (Zhao et al., Nature 508 373 (2014). Even though many researches on SnSe have proposed the possibilities of various applications so far, surprisingly little information is available regarding the microscopic structure of SnSe surfaces. We conducted a systematic study on the surface defect of SnSe induced by thermal annealing via a home-built low temperature scanning tunneling microscopy (STM). Various defects were characterized by STM/STS, and we found that Sn vacancy is a dominating intrinsic defect. The size of vacancy was changed after annealing process in UHV at different temperatures. This work was supported by the National Research Foundation of Korea(NRF) [Nos. NRF-2013R1A1A1008724, NRF-2009-0093818, and NRF-2014R1A4A1071686].

  16. Ti/CeOx(111) interfaces studied by XPS and STM

    NASA Astrophysics Data System (ADS)

    Zhou, Yinghui; Zhou, Jing

    2012-04-01

    Low coverage of Ti was deposited on the well-ordered CeOx(111) (1.5 < x < 2) thin films grown on Ru(0001) by physical vapor deposition at room temperature. The structure and interaction of Ti/ceria interfaces were investigated with X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) techniques under ultrahigh vacuum conditions. XPS data indicate that the deposition of Ti on both oxidized and reduced ceria surfaces causes the partial reduction of Ce from + 4 to + 3 state. Ti is formally in the + 4 state. STM data show the formation of small atomic-like titania features at 300 K, which coalesce to form chain structures upon heating. It is demonstrated in the study that the deposition of Ti can form mixed metal oxides at the interface and modify both electronic and structural properties of the ceria support. The structural study of Ti/ceria interfaces can be a key for understanding the higher catalytic activity of the Ti-CeOx mixed oxide catalysts as compared with the individual pure oxides.

  17. Superior properties of plasma-assisted room-temperature-grown graphene from STM studies

    NASA Astrophysics Data System (ADS)

    Teague, M. L.; Lin, W.-H.; Boyd, D. A.; Yeh, N.-C.; Lo, Y.-Y.; Wu, C.-I.; Chan, W.-Y.; Su, W.-B.; Chang, C.-S.

    2013-03-01

    We report scanning tunneling microscopic and spectroscopic (STM/STS) studies of large-area monolayer graphene grown at room temperature (RT) on Cu foils, Cu (100) and Cu (111) single crystals, and compare the properties of these samples with high-temperature (1000 °C) CVD-grown graphene. All RT-grown graphene exhibit highly ordered honeycomb structures over ~ 1 cm2 areas, smooth surface morphology, much reduced strain (< 0.1%) and additional Moire patterns for samples grown on single crystals. The structural quality and reduced strain obtained from STM studies are consistent with finds from Raman spectra. In contrast, high-temperature CVD-grown graphene revealed strongly distorted atomic structures and large strain, giving rise to giant pseudo-magnetic fields and charging effects as manifested by the conductance peaks at quantized energies and the strongly enhanced local conductance in highly strained regions. These strain-induced effects are believed to be responsible for the reduced electrical mobility in typical CVD-grown graphene. The superior structural and electronic properties demonstrated by our RT-grown graphene are promising for a wide range of applications. This work was supported by NSF through IQIM at Caltech.

  18. XPS and STM studies of the oxidation of hydrogen chloride at Cu(100) surfaces

    NASA Astrophysics Data System (ADS)

    Altass, Hatem; Carley, Albert F.; Davies, Philip R.; Davies, Robert J.

    2016-08-01

    The dissociative chemisorption of HCl on clean and oxidized Cu(100) surfaces has been investigated using x-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). Whereas the dissociation of HCl at the clean surface is limited to the formation of a (√ 2 × √ 2)-R45° Cl(a) monolayer, the presence of surface oxygen removes this barrier, leading to chlorine coverages up to twice that obtained at the clean surface. Additional features in the STM images that appear at these coverages are tentatively assigned to the nucleation of CuCl islands. The rate of reaction of the HCl was slightly higher on the oxidized surface but unaffected by the initial oxygen concentration or the availability of clean copper sites. Of the two distinct domains of adsorbed oxygen identified at room temperature on the Cu(100) surfaces, the (√ 2 × √ 2)-R45° structure reacts slightly faster with HCl than the missing row (√ 2 × 2 √ 2)-R45° O(a) structure. The results address the first stages in the formation of a copper chloride and present an interesting comparison with the HCl/O(a) reaction at Cu(110) surfaces, where oxygen also increased the extent of HCl reactions. The results emphasize the importance of the exothermic reaction to form water in the HCl/O(a) reaction on copper.

  19. Water adsorption on O(2x2)/Ru(0001) from STM experiments andfirst-principles calculations

    SciTech Connect

    Cabrera-Sanfelix, P.; Sanchez-Portal, D.; Mugarza, A.; Shimizu,T.K.; Salmeron, M.; Arnau, A.

    2007-10-15

    We present a combined theoretical and experimental study of water adsorption on Ru(0001) pre-covered with 0.25 monolayers (ML) of oxygen forming a (2 x 2) structure. Several structures were analyzed by means of Density Functional Theory calculations for which STM simulations were performed and compared with experimental data. Up to 0.25 monolayers the molecules bind to the exposed Ru atoms of the 2 x 2 unit cell via the lone pair orbitals. The molecular plane is almost parallel to the surface with its H atoms pointing towards the chemisorbed O atoms of the 2 x 2 unit cell forming hydrogen bonds. The existence of these additional hydrogen bonds increases the adsorption energy of the water molecule to approximately 616 meV, which is {approx}220 meV more stable than on the clean Ru(0001) surface with a similar configuration. The binding energy shows only a weak dependence on water coverage, with a shallow minimum for a row structure at 0.125 ML. This is consistent with the STM experiments that show a tendency of the molecules to form linear rows at intermediate coverage. Our calculations also suggest the possible formation of water dimers near 0.25 ML.

  20. Application of Machine Learning tools to recognition of molecular patterns in STM images

    NASA Astrophysics Data System (ADS)

    Maksov, Artem; Ziatdinov, Maxim; Fujii, Shintaro; Kiguchi, Manabu; Higashibayashi, Shuhei; Sakurai, Hidehiro; Kalinin, Sergei; Sumpter, Bobby

    The ability to utilize individual molecules and molecular assemblies as data storage elements has motivated scientist for years, concurrent with the continuous effort to shrink a size of data storage devices in microelectronics industry. One of the critical issues in this effort lies in being able to identify individual molecular assembly units (patterns), on a large scale in an automated fashion of complete information extraction. Here we present a novel method of applying machine learning techniques for extraction of positional and rotational information from scanning tunneling microscopy (STM) images of π-bowl sumanene molecules on gold. We use Markov Random Field (MRF) model to decode the polar rotational states for each molecule in a large scale STM image of molecular film. We further develop an algorithm that uses a convolutional Neural Network combined with MRF and input from density functional theory to classify molecules into different azimuthal rotational classes. Our results demonstrate that a molecular film is partitioned into distinctive azimuthal rotational domains consisting typically of 20-30 molecules. In each domain, the ``bowl-down'' molecules are generally surrounded by six nearest neighbor molecules in ``bowl-up'' configuration, and the resultant overall structure form a periodic lattice of rotational and polar states within each domain. Research was supported by the US Department of Energy.

  1. Low Temperature STM Experiments on Helical Edge States in InAs/GaSb

    NASA Astrophysics Data System (ADS)

    Du, Rui-Rui; Li, Tingxin; Mou, Xiaoyang; Du, Lingjie; Sullivan, Gerald

    2014-03-01

    Inverted InAs/GaSb quantum wells have been recently shown to be a 2D topological insulator hosting robust helical edge states. Attributing to the fact that the hybridized minigap in this system opens at a finite wavevector, the edge states here have a low Fermi velocity VF, and consequently their transport properties may reveal interesting interaction effects. Moreover, the VF in this system can be continuously tuned by electrostatic gates, providing an experimental knob for tuning the interactions. We report work in progress for STM/STS measurements of edge states in the tunneling regime, where the edge states are exposed at the cleaved edge/UHV interface. Experiments are performed in a 400 mK STM/vector magnet system with in situ sample cleavage and thin film deposition capabilities. Ref. I. Knez, R.-R. Du and G. Sullivan, Phys. Rev. Lett. 107, 136603 (2011); L-.J. Du, I. Knez, G. Sullivan, R-.R. Du, ArXiv:1306.1925 (2013). The work in PKU is supported by Basic Research Program of MOST; work in Rice is supported by NSF and DOE.

  2. Fabrication of Magnetic Probes for Spin-Polarized STM Studies of the Fe3O4 (001) and (111) Surfaces

    NASA Astrophysics Data System (ADS)

    Ceballos, S. F.; Mariotto, G.; Berdunov, N.; Murphy, S.; Jordan, K.; Shvets, I. V.

    2003-12-01

    Electrochemical etching in an aqueous solution (NaOH, HCl), using a teflon tubing to physically restrict the active etching region, has been developed to fabricate Scanning Tunneling Microscopy (STM) tips from a range of magnetic materials. Tips have been produced from polycrystalline MnNi, Cr, Fe and Ni with small radius of curvature, high aspect ratio and apexes in the 50-100 nm range. Atomic resolution STM images have been achieved on the Fe3O4 (001) and (111) surface using MnNi tips, which are interpreted in terms of a possible spin-polarized effect.

  3. Imaging, single atom contact and single atom manipulations at low temperature using the new ScientaOmicron LT-UHV-4 STM

    NASA Astrophysics Data System (ADS)

    Yang, Jianshu; Sordes, Delphine; Kolmer, Marek; Martrou, David; Joachim, Christian

    2016-01-01

    The performances of the new ScientaOmicron LT-UHV 4-STM microscope have been certified by a series of state-of-art STM experiments on an Au(1 1 1) surface at 4.3 K. During the STM operation of the 4 STM scanners (independently or in parallel with an inter tip apex front to front distance down to a few tens of nanometers), a ΔZ stability of about 2 pm per STM was demonstrated. With this LT-UHV 4-STM stability, single Au atom manipulation experiments were performed on Au(1 1 1) by recording the pulling, sliding and pushing manipulation signals per scanner. Jump to contact experiments lead to perfectly linear low voltage I-V characteristics on a contacted single Au ad-atom with no need of averaging successive I-V's. Our results show how this new instrument is exactly 4 times a very precise single tip LT-UHV-STM. Two tips surface conductance measurements were performed on Au(1 1 1) using a lock-in technique in a floating sample mode of operation to capture the Au(1 1 1) surface states via two STM tips dI/dV characteristics.

  4. Structural aspects of the fivefold quasicrystalline Al-Cu-Fe surface from STM and dynamical LEED Studies

    SciTech Connect

    Cai, T.; Shi, F.; Shen, Z.; Gierer, M.; Goldman, A.I.; Kramer, M.J.; Jenks, C.J.; Lograsso, T.A.; Delaney, D.W.; Thiel, P.A.; Van, M.A.

    2001-04-15

    We investigate the atomic structure of the fivefold surface of an icosahedral Al-Cu-Fe alloy, using scanning tunneling microscopy (STM) imaging and a special dynamical low energy-electron diffraction (LEED) method. STM indicates that the step heights adopt (primarily) two values in the ratio of tau, but the spatial distribution of these two values does not follow a Fibonacci sequence, thus breaking the ideal bulk-like quasicrystalline layer stacking order perpendicular to the surface. The appearance of screw dislocations in the STM images is another indication of imperfect quasicrystallinity. On the other hand, the LEED analysis, which was successfully applied to Al-Pd-Mn in a previous study, is equally successful for Al-Cu-Fe. Similar structural features are found for both materials, in particular for interlayer relaxations and surface terminations. Although there is no structural periodicity, there are clear atomic planes in the bulk of the quasicrystal, some of which can be grouped in recurring patterns. The surface tends to form between these grouped layers in both alloys. For Al-Cu-Fe, the step heights measured by STM are consistent with the thicknesses of the grouped layers favored in LEED. These results suggest that the fivefold Al-Cu-Fe surface exhibits a quasicrystalline layering structure, but with stacking defects.

  5. Electronic properties of precious-metal coated W tips in STM: Role of spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Yamashita, T.; Akiyama, T.; Nakamura, K.; Ito, T.; Rhim, S. H.; Freeman, A. J.

    2013-03-01

    Scanning tunneling microscopy (STM) has proved a versatile tool invigorating many physics at an atomic scale, where chemical identity and shape of the probe tip greatly affect resolution and sensitivity. There have been many efforts to functionalize STM tips: coating W tips with organic molecules and 3d transition metals, which facilitate the selective imaging with enhanced tunneling current. In this work, we model W(110) tips coated by precious metals such as Au, Ag, and Pt, in which large spin-orbit coupling significantly influences the electronic structure of the STM probe. Furthermore, we argue that this spin-orbit coupling can be used as a spin detecting STM probe without additional bias switching. The stability of the W(110) apex atom for each metal coating is also discussed. Supported at N. U. by the DOE (DE-FG02-05ER45372), and at Mie U. by the Young Researcher Overseas Visits Program for Vitalizing Brain Circulation (R2214) from the Japan Society for the Promotion of Science.

  6. Simultaneous noncontact AFM and STM of Ag:Si(111)-(3×3)R30∘

    NASA Astrophysics Data System (ADS)

    Sweetman, Adam; Stannard, Andrew; Sugimoto, Yoshiaki; Abe, Masayuki; Morita, Seizo; Moriarty, Philip

    2013-02-01

    The Ag:Si(111)-(3×3)R30∘ surface structure has attracted considerable debate concerning interpretation of scanning tunneling microscope (STM) and noncontact atomic force microscope (NC-AFM) images. In particular, the accepted interpretation of atomic resolution images in NC-AFM has been questioned by theoretical and STM studies. In this paper, we use combined NC-AFM and STM to conclusively show that the inequivalent trimer (IET) configuration best describes the surface ground state. Thermal-averaging effects result in a honeycomb-chained-trimer (HCT) appearance at room temperature, in contrast to studies suggesting that the IET configuration remains stable at higher temperatures [Zhang, Gustafsson, and Johansson, Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.74.201304 74, 201304(R) (2006) and J. Phys.: Conf. Ser.1742-658810.1088/1742-6596/61/1/264 61, 1336 (2007)]. We also comment on results obtained at an intermediate temperature that suggest an intriguing difference between the imaging mechanisms of NC-AFM and STM on structurally fluctuating samples.

  7. Nanoscale phosphorus atom arrays created using STM for the fabrication of a silicon based quantum computer.

    SciTech Connect

    O'Brien, J. L.; Schofield, S. R.; Simmons, M. Y.; Clark, R. G.; Dzurak, A. S.; Curson, N. J.; Kane, B. E.; McAlpine, N. S.; Hawley, M. E.; Brown, G. W.

    2001-01-01

    Quantum computers offer the promise of formidable computational power for certain tasks. Of the various possible physical implementations of such a device, silicon based architectures are attractive for their scalability and ease of integration with existing silicon technology. These designs use either the electron or nuclear spin state of single donor atoms to store quantum information. Here we describe a strategy to fabricate an array of single phosphorus atoms in silicon for the construction of such a silicon based quantum computer. We demonstrate the controlled placement of single phosphorus bearing molecules on a silicon surface. This has been achieved by patterning a hydrogen mono-layer 'resist' with a scanning tunneling microscope (STM) tip and exposing the patterned surface to phosphine (PH3) molecules. We also describe preliminary studies into a process to incorporate these surface phosphorus atoms into the silicon crystal at the array sites. Keywords: Quantum computing, nanotechriology scanning turincling microscopy, hydrogen lithography

  8. XPS/STM study of model bimetallic Pd-Au/HOPG catalysts

    NASA Astrophysics Data System (ADS)

    Bukhtiyarov, Andrey V.; Prosvirin, Igor P.; Bukhtiyarov, Valerii I.

    2016-03-01

    The preparation of model bimetallic Pd-Au/HOPG catalysts has been investigated using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) techniques. Initially, model "core-shell" type Pd-Au/HOPG catalysts with similar particle size distribution (5-8 nm), but with different densities of particle locations on the HOPG surface and Pd/Au atomic ratios are prepared. Further, their thermal stability is studied within a temperature range of 50-500 °C at UHV conditions. It has been shown that annealing the model catalysts at a temperature range of 300-400 °C leads to formation of Pd-Au alloyed particles. Enhancement of heating temperature up to 500 °C results in sintering of bimetallic nanoparticles. Contribution of different parameters controlling the properties of Pd-Au alloyed particles has been discussed.

  9. Image potential states mediated STM imaging of cobalt phthalocyanine on NaCl/Cu(100)

    NASA Astrophysics Data System (ADS)

    Qinmin, Guo; Zhihui, Qin; Min, Huang; Vladimir, N. Mantsevich; Gengyu, Cao

    2016-03-01

    The adsorption and electronic properties of isolated cobalt phthalocyanine (CoPc) molecule on an ultrathin layer of NaCl have been investigated. High-resolution STM images give a detailed picture of the lowest unoccupied molecular orbital (LUMO) of an isolated CoPc. It is shown that the NaCl ultrathin layer efficiently decouples the interaction of the molecules from the underneath metal substrate, which makes it an ideal substrate for studying the properties of single molecules. Moreover, strong dependence of the appearance of the molecules on the sample bias in the region of relatively high bias (> 3.1 V) is ascribed to the image potential states (IPSs) of NaCl/Cu(100), which may provide us with a possible method to fabricate quantum storage devices. Project supported by the National Natural Science Foundation of China (Grant Nos. 21203239 and 21311120059) and RFBR (Grant No. 13-02-91180).

  10. WTe 2 surfaces in UHV-STM image formation and analysis of point defect structures

    NASA Astrophysics Data System (ADS)

    Crossley, J. A. A.; Sofield, C. J.; Myhra, S.

    1997-05-01

    The layered semi-metallic T d phase of WTe 2 has been examined by STM in UHV. The effects of transient transfer of tip apex atom from/to the surface (W ↔ Te exchange) on the imaging conditions have been observed; the effects demonstrate the inadequacy of the Tersoff-Hamann approximation to the description of the tunnelling process. Two distinctly different point-defect configurations have been observed, assigned tentatively to vacancies in either "top" or "bottom" Te sites. Anomalous image conditions were observed frequently; these have been ascribed to delamination of the structure, and consequential transfer of the tunnelling to a delocalised internal gap, with the image representing the averaged tunnel current during relative displacements of two neighbouring Te planes.

  11. STM/STS study of graphene directly grown on h-BN films on Cu foils

    NASA Astrophysics Data System (ADS)

    Jang, Won-Jun; Wang, Min; Jang, Seong-Gyu; Kim, Minwoo; Park, Seong-Yong; Kim, Sang-Woo; Kahng, Se-Jong; Choi, Jae-Young; Song, Young; Lee, Sungjoo; Sanit Collaboration; Department Of Physics, Korea University Collaboration; Graphene Research Center, Samsung Advanced Institute Of Technology Collaboration

    2013-03-01

    Graphene-based devices on standard SiO2 substrate commonly exhibit inferior characteristics relative to the expected intrinsic properties of graphene, due to the disorder existing at graphene-SiO2 interface. Recently, it has been shown that exfoliated and chemical vapor deposition (CVD) graphene transferred onto hexagonal boron nitride (h-BN) possesses significantly reduced charge inhomogeneity, and yields improved device performance. Here we report the scanning tunneling microscopy (STM) and spectroscopy (STS) results obtained from a graphene layer directly grown on h-BN insulating films on Cu foils. STS measurements illustrate that graphene/h-BN film is charge neutral without electronic perturbation from h-BN/Cu substrate. Corresponding Author

  12. Design of mine-used DC carrier telephone based on STM32

    NASA Astrophysics Data System (ADS)

    Chen, Goufan; Zhou, Hui; Zhan, Minhua; Wang, Jian

    2016-01-01

    Abide by the design principles of mine intrinsically safe circuit, according to the need of underground communication in coal mine, the paper proposed a design scheme of DC carrier telephone which can dial. The design circuit of the telephone is introduced in detail. The telephone's voice signals are generated by the microphone. After enlarged then the voice signals are modulated to frequency signals by LM567 chip. The frequency signals are coupled by transformer and then transmitted by 12V DC power supply line to the other voice terminals. In the voice terminal the signals are demodulated by LM567 demodulation circuit and enlarged by LM386, then, the amplified audio signals are output from a speaker. The dialing circuit is designed based on the STM32 MCU. The dial information is transmitted to the other telephone terminals by CAN bus. The measured distance calls is greater than 2000m, volume is larger than 85dB, good results.

  13. Molecular design driving tetraporphyrin self-assembly on graphite: a joint STM, electrochemical and computational study

    NASA Astrophysics Data System (ADS)

    El Garah, M.; Santana Bonilla, A.; Ciesielski, A.; Gualandi, A.; Mengozzi, L.; Fiorani, A.; Iurlo, M.; Marcaccio, M.; Gutierrez, R.; Rapino, S.; Calvaresi, M.; Zerbetto, F.; Cuniberti, G.; Cozzi, P. G.; Paolucci, F.; Samorì, P.

    2016-07-01

    Tuning the intermolecular interactions among suitably designed molecules forming highly ordered self-assembled monolayers is a viable approach to control their organization at the supramolecular level. Such a tuning is particularly important when applied to sophisticated molecules combining functional units which possess specific electronic properties, such as electron/energy transfer, in order to develop multifunctional systems. Here we have synthesized two tetraferrocene-porphyrin derivatives that by design can selectively self-assemble at the graphite/liquid interface into either face-on or edge-on monolayer-thick architectures. The former supramolecular arrangement consists of two-dimensional planar networks based on hydrogen bonding among adjacent molecules whereas the latter relies on columnar assembly generated through intermolecular van der Waals interactions. Scanning Tunneling Microscopy (STM) at the solid-liquid interface has been corroborated by cyclic voltammetry measurements and assessed by theoretical calculations to gain multiscale insight into the arrangement of the molecule with respect to the basal plane of the surface. The STM analysis allowed the visualization of these assemblies with a sub-nanometer resolution, and cyclic voltammetry measurements provided direct evidence of the interactions of porphyrin and ferrocene with the graphite surface and offered also insight into the dynamics within the face-on and edge-on assemblies. The experimental findings were supported by theoretical calculations to shed light on the electronic and other physical properties of both assemblies. The capability to engineer the functional nanopatterns through self-assembly of porphyrins containing ferrocene units is a key step toward the bottom-up construction of multifunctional molecular nanostructures and nanodevices.Tuning the intermolecular interactions among suitably designed molecules forming highly ordered self-assembled monolayers is a viable approach to

  14. STM study on the self-assembly of oligothiophene-based organic semiconductors

    PubMed Central

    Urdanpilleta, Marta; El-Hosseiny, Erwaa; Koslowski, Berndt; Ziemann, Paul; Bäuerle, Peter

    2011-01-01

    Summary The self-assembly properties of a series of functionalized regioregular oligo(3-alkylthiophenes) were investigated by using scanning tunneling microscopy (STM) at the liquid–solid interface under ambient conditions. The characteristics of the 2-D crystals formed on the (0001) plane of highly ordered pyrolitic graphite (HOPG) strongly depend on the length of the π-conjugated oligomer backbone, on the functional groups attached to it, and on the alkyl substitution pattern on the individual thiophene units. Theoretical calculations were performed to analyze the geometry and electronic density of the molecular orbitals as well as to analyze the intermolecular interactions, in order to obtain models of the 2-D molecular ordering on the substrate. PMID:22259763

  15. Molecular design driving tetraporphyrin self-assembly on graphite: a joint STM, electrochemical and computational study.

    PubMed

    El Garah, M; Santana Bonilla, A; Ciesielski, A; Gualandi, A; Mengozzi, L; Fiorani, A; Iurlo, M; Marcaccio, M; Gutierrez, R; Rapino, S; Calvaresi, M; Zerbetto, F; Cuniberti, G; Cozzi, P G; Paolucci, F; Samorì, P

    2016-07-14

    Tuning the intermolecular interactions among suitably designed molecules forming highly ordered self-assembled monolayers is a viable approach to control their organization at the supramolecular level. Such a tuning is particularly important when applied to sophisticated molecules combining functional units which possess specific electronic properties, such as electron/energy transfer, in order to develop multifunctional systems. Here we have synthesized two tetraferrocene-porphyrin derivatives that by design can selectively self-assemble at the graphite/liquid interface into either face-on or edge-on monolayer-thick architectures. The former supramolecular arrangement consists of two-dimensional planar networks based on hydrogen bonding among adjacent molecules whereas the latter relies on columnar assembly generated through intermolecular van der Waals interactions. Scanning Tunneling Microscopy (STM) at the solid-liquid interface has been corroborated by cyclic voltammetry measurements and assessed by theoretical calculations to gain multiscale insight into the arrangement of the molecule with respect to the basal plane of the surface. The STM analysis allowed the visualization of these assemblies with a sub-nanometer resolution, and cyclic voltammetry measurements provided direct evidence of the interactions of porphyrin and ferrocene with the graphite surface and offered also insight into the dynamics within the face-on and edge-on assemblies. The experimental findings were supported by theoretical calculations to shed light on the electronic and other physical properties of both assemblies. The capability to engineer the functional nanopatterns through self-assembly of porphyrins containing ferrocene units is a key step toward the bottom-up construction of multifunctional molecular nanostructures and nanodevices. PMID:27376633

  16. The Sentinel-3 Surface Topography Mission (S-3 STM): Level 2 SAR Ocean Retracker

    NASA Astrophysics Data System (ADS)

    Dinardo, S.; Lucas, B.; Benveniste, J.

    2015-12-01

    The SRAL Radar Altimeter, on board of the ESA Mission Sentinel-3 (S-3), has the capacity to operate either in the Pulse-Limited Mode (also known as LRM) or in the novel Synthetic Aperture Radar (SAR) mode. Thanks to the initial results from SAR Altimetry obtained exploiting CryoSat-2 data, lately the interest by the scientific community in this new technology has significantly increased and consequently the definition of accurate processing methodologies (along with validation strategies) has now assumed a capital importance. In this paper, we present the algorithm proposed to retrieve from S-3 STM SAR return waveforms the standard ocean geophysical parameters (ocean topography, wave height and sigma nought) and the validation results that have been so far achieved exploiting the CryoSat-2 data as well as the simulated data. The inversion method (retracking) to extract from the return waveform the geophysical information is a curve best-fitting scheme based on the bounded Levenberg-Marquardt Least-Squares Estimation Method (LEVMAR-LSE). The S-3 STM SAR Ocean retracking algorithm adopts, as return waveform’s model, the “SAMOSA” model [Ray et al, 2014], named after the R&D project SAMOSA (led by Satoc and funded by ESA), in which it has been initially developed. The SAMOSA model is a physically-based model that offers a complete description of a SAR Altimeter return waveform from ocean surface, expressed in the form of maps of reflected power in Delay-Doppler space (also known as stack) or expressed as multilooked echoes. SAMOSA is able to account for an elliptical antenna pattern, mispointing errors in roll and yaw, surface scattering pattern, non-linear ocean wave statistics and spherical Earth surface effects. In spite of its truly comprehensive character, the SAMOSA model comes with a compact analytical formulation expressed in term of Modified Bessel functions. The specifications of the retracking algorithm have been gathered in a technical document (DPM

  17. STM and DFT study on formation and characterization of Ba-incorporated phases on a Ge(001) surface

    NASA Astrophysics Data System (ADS)

    Koczorowski, W.; Puchalska, A.; Grzela, T.; Jurczyszyn, L.; Schofield, S. R.; Czajka, R.; Curson, N. J.; Radny, M. W.

    2016-05-01

    We characterize the incorporation of Ba adatoms into the Ge(001) surface, resulting in the formation of one-dimensional structures with an internal 2 ×3 periodicity, after the deposition of Ba atoms at 970 K or at room temperature followed by a 770 K anneal. Scanning tunneling microscopy (STM) data were compared with theoretically simulated STM images generated by density functional theory electronic structure calculations. Excellent agreement between experiment and simulation was found when using an adopted structural model that assumes partial removal of the surface Ge dimers in the [1-10] surface direction and subsequent addition of a single Ba atom to the substrate second layer. Structural assignments for a number of defects observed within regions of the 2 ×3 reconstruction were also obtained.

  18. Photoemission and STM study of an In nanocluster array on the Si(111)-7×7 surface

    NASA Astrophysics Data System (ADS)

    Byun, J. H.; Ahn, J. R.; Choi, W. H.; Kang, P. G.; Yeom, H. W.

    2008-11-01

    The formation of nanoclusters for submonolayer indium on the Si(111)-7×7 surface was investigated by scanning tunneling microscopy (STM) and high-resolution photoelectron spectroscopy. The In 4d spectra indicate distinct bonding configurations for the well-known nanoclusters formed at 420 550 K and for the initial adsorbates at lower temperature. The STM imaging reveals a different type of clusters, with uniform shape and size, formed by the initial adsorbates. The spectral evolution of Si 2p indicates the importance of Si restatom sites for the formation of both initial clusters and nanoclusters in contrast to Si adatoms. The surface becomes semiconducting after the formation of the nanocluster array. For the well-developed nanoclusters, we found a surface state in valence bands at a binding energy of 0.6 eV. The origin of this surface state is discussed in comparison with a recent theoretical calculation.

  19. Self-assembled monolayers of methylselenolate on the Au(111) surface: A combined STM and DFT study

    NASA Astrophysics Data System (ADS)

    El-Kareh, L.; Mehring, P.; Caciuc, V.; Atodiresei, N.; Beimborn, A.; Blügel, S.; Westphal, C.

    2014-01-01

    In this study scanning tunneling microscopy (STM) and density functional theory (DFT) were used to investigate the structural formation of methylselenolate (CH3Se) self-assembled monolayers (SAMs) on the Au(111) surface. SAMs were prepared by two different methods, from solution and by exposing the Au(111) surface to gaseous dimethyldiselenide (DMDSe). For methylselenolate (MSe) on the Au(111) surface, our STM measurements revealed the presence of (4 × √3) and (3 × 2√3) rectangular striped phases. These structures were verified by DFT calculations. For both phases, the DFT calculations clearly found a bridge adsorption geometry for MSe on Au(111). Furthermore, they provide information about the electronic structure of the MSe-SAMs.

  20. Interaction measurements between a tip and a sample in proximity regions controlled by tunneling current in a UHV STM AFM

    NASA Astrophysics Data System (ADS)

    Arai, Toyoko; Tomitori, Masahiko

    1999-04-01

    The interaction force-distance curves between a tip and a sample surface in close proximity were measured by logarithmically changing a tunneling current passing through them with a ultrahigh vacuum scanning tunneling microscopy-atomic force microscopy (UHV STM-AFM). Since the tunneling current changes exponentially with the separation between the tip and the sample, the separation can be controlled precisely and linearly by modulating a logarithmic target value fed into the STM feedback circuit to be a triangular waveform. A piezoresistive cantilever with a conductive Si tip was used after cleaning the tip by heating it in the UHV chamber. As a preliminary result, force-separation curves with reversible and irreversible jumps in close proximity were presented.

  1. Performance mapping of the STM4-120 kinematic Stirling engine using a statistical design of experiments method

    SciTech Connect

    Powell, M.A.; Rawlinson, K.S.

    1992-12-31

    A kinetic Stirling cycle engine, the Stirling Thermal Motors (STM) STM4-120, was tested at the Sandia National Laboratories Engine Test Facility (ETF) from March 1989--August 1992. Sandia is interested in determining this engine`s potential for solar-thermal-electric applications. The last round of testing was conducted from July--August 1992 using Sandia-designed gas-fired heat pipe evaporators as the heat input system to the engine. The STM4-120 was performance mapped over a range of sodium vapor temperatures, cooling water temperatures, and cycle pressures. The resulting shaft power output levels ranged from 5--9 kW. The engine demonstrated high conversion efficiency (24--31%) even though the power output level was less than 40% of the rated output of 25 kW. The engine had been previously derated from 25 kW to 10 kW shaft power due to mechanical limitations that were identified by STM during parallel testing at their facility in Ann Arbor, MI. A statistical method was used to design the experiment, to choose the experimental points, and to generate correlation equations describing the engine performance given the operating parameters. The testing was trunacted due to a failure of the heat pipe system caused by entrainment of liquid sodium in the condenser section of the heat pipes. Enough data was gathered to generate the correlations and to demonstrate the experimental technique. The correlation is accurate in the experimental space and is simple enough for use in hand calculations and spreadsheet-based system models. Use of this method can simplify the construction of accurate performance and economic models of systems in which the engine is a component. The purpose of this paper is to present the method used to design the experiments and to analyze the performance data.

  2. New insight into the structure of saturated chlorine layer on Ag(1 1 1): LT-STM and DFT study

    NASA Astrophysics Data System (ADS)

    Andryushechkin, B. V.; Cherkez, V. V.; Gladchenko, E. V.; Zhidomirov, G. M.; Kierren, B.; Fagot-Revurat, Y.; Malterre, D.; Eltsov, K. N.

    2013-02-01

    Atomic structures formed on the Ag(1 1 1) surface as a result of molecular chlorine adsorption have been studied with a low-temperature scanning tunneling microscopy (LT-STM) in a combination with DFT calculations. We have found that saturated chlorine coverage on Ag(1 1 1) is a complex system consisting of two different structural phases: small anti-phase domains of a (3 × 3) reconstruction and nanoclusters Ag3Cl7.

  3. Effect of Cholesterol and Equex-STM Addition to an Egg Yolk Extender on Pure Spanish Stallion Cryopreserved Sperm

    PubMed Central

    Gil, Lidia; Galindo-Cardiel, Iván; Malo, C.; González, N.; Álvarez, C.

    2013-01-01

    Cholesterol and Equex-STM are frequently added to different commercial and experimental extenders improving postthawing sperm quality. Doses of 125–150 mM of cholesterol from pig liver and 0.5–0.7% of Equex-STM were evaluated in a standard eggyolk extender (Martin et al., 1979). Six ejaculates per stallion from six pure Spanish stallions (6–8 years old) were collected in Martin's extender (B) and different mixtures of 125 mM-0.5% (I), 125 mM-0.7% (II), 150 mM-0.5% (III), and 150 mM-0.7% (IV) were added to original Martin's extender. Samples were frozen in 0.5 mL straws (100 × 106 spermatozoa) and thawed (21 s., 37°C water bath). After thawing the following parameters were evaluated: viability (V), motility (computer assisted sperm analysis, CASA; % nonprogressive NP; % progressive MP), hipoosmotic swelling test (HOST), acrosome integrity (A), fluorescence test (FL), and resistance test (RT). Sperm quality was significantly affected by stallion (in the parameters V, VI, NP, MP, HOST, A, FL, and RT), extraction (VI, NP, MP, HOST, A, and FL), and the different combinations of Equex-STM-cholesterol (FL). We concluded that 0.5% of Equex-STM mixed with 125 mM of cholesterol has obtained better sperm quality results than those of original Martin's extender, showing a simple and economic improvement of this home-made practical seminal extender. PMID:24416597

  4. Performance mapping of the STM4-120 kinematic Stirling engine using a statistical design of experiments method

    SciTech Connect

    Powell, M.A.; Rawlinson, K.S.

    1992-01-01

    A kinetic Stirling cycle engine, the Stirling Thermal Motors (STM) STM4-120, was tested at the Sandia National Laboratories Engine Test Facility (ETF) from March 1989--August 1992. Sandia is interested in determining this engine's potential for solar-thermal-electric applications. The last round of testing was conducted from July--August 1992 using Sandia-designed gas-fired heat pipe evaporators as the heat input system to the engine. The STM4-120 was performance mapped over a range of sodium vapor temperatures, cooling water temperatures, and cycle pressures. The resulting shaft power output levels ranged from 5--9 kW. The engine demonstrated high conversion efficiency (24--31%) even though the power output level was less than 40% of the rated output of 25 kW. The engine had been previously derated from 25 kW to 10 kW shaft power due to mechanical limitations that were identified by STM during parallel testing at their facility in Ann Arbor, MI. A statistical method was used to design the experiment, to choose the experimental points, and to generate correlation equations describing the engine performance given the operating parameters. The testing was trunacted due to a failure of the heat pipe system caused by entrainment of liquid sodium in the condenser section of the heat pipes. Enough data was gathered to generate the correlations and to demonstrate the experimental technique. The correlation is accurate in the experimental space and is simple enough for use in hand calculations and spreadsheet-based system models. Use of this method can simplify the construction of accurate performance and economic models of systems in which the engine is a component. The purpose of this paper is to present the method used to design the experiments and to analyze the performance data.

  5. Performance mapping of the STM4-120 kinematic Stirling engine using a statistical design of experiments method

    NASA Astrophysics Data System (ADS)

    Powell, M. A.; Rawlinson, K. S.

    A kinetic Stirling cycle engine, the Stirling Thermal Motors (STM) STM4-120, was tested at the Sandia National Laboratories Engine Test Facility (ETF) from March 1989-August 1992. Sandia is interested in determining this engine's potential for solar-thermal-electric applications. The last round of testing was conducted from July-August 1992 using Sandia-designed gas-fired heat pipe evaporators as the heat input system to the engine. The STM4-120 was performance mapped over a range of sodium vapor temperatures, cooling water temperatures, and cycle pressures. The resulting shaft power output levels ranged from 5-9 kW. The engine demonstrated high conversion efficiency (24-31%) even though the power output level was less than 40% of the rated output of 25 kW. The engine had been previously derated from 25 kW to 10 kW shaft power due to mechanical limitations that were identified by STM during parallel testing at their facility in Ann Arbor, MI. A statistical method was used to design the experiment, to choose the experimental points, and to generate correlation equations describing the engine performance given the operating parameters. The testing was truncated due to a failure of the heat pipe system caused by entrainment of liquid sodium in the condenser section of the heat pipes. Enough data was gathered to generate the correlations and to demonstrate the experimental technique. The correlation is accurate in the experimental space and is simple enough for use in hand calculations and spreadsheet-based system models. Use of this method can simplify the construction of accurate performance and economic models of systems in which the engine is a component. The purpose of this paper is to present the method used to design the experiments and to analyze the performance data.

  6. Conformations of polyaniline molecules adsorbed on Au(111) probed by in situ STM and ex situ XPS and NEXAFS.

    PubMed

    Lee, YiHui; Chang, ChinZen; Yau, ShuehLin; Fan, LiangJen; Yang, YawWen; Yang, LiangYueh Ou; Itaya, Kingo

    2009-05-13

    In situ scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and near edge X-ray absorption fine structure (NEXAFS) have been used to examine the conformation of a monolayer of polyaniline (PAN) molecules produced on a Au(111) single-crystal electrode by anodization at 1.0 V [vs reversible hydrogen electrode (RHE)] in 0.10 M H(2)SO(4) containing 0.030 M aniline. The as-produced PAN molecules took on a well-defined linear conformation stretching for 500 A or more, as shown by in situ and ex situ STM. The XPS and NEXAFS results indicated that the linear PAN seen at 1.0 V assumed the form of an emeraldine salt made of PAN chains and (bi)sulfate anions. Shifting the potential from 1.0 to 0.7 V altered the shape of the PAN molecules from straight to crooked, which was ascribed to restructuring of the Au(111) electrified interface on the basis of voltammetric and XPS results. In situ STM showed that further decreasing the potential to 0.5 V transformed the crooked PAN threads into a mostly linear form again, with preferential alignment and formation of some locally ordered structures. PAN molecules could be reduced from emeraldine to leucoemeraldine as the potential was decreased to 0.2 V or less. In situ STM showed that the fully reduced PAN molecules were straight but mysteriously shortened to approximately 50 A in length. The conformation of PAN did not recuperate when the potential was shifted positively to 1.0 V. PMID:19361217

  7. STM studies of Co{sub x}NbSe{sub 2} and Mn{sub x}NbSe{sub 2}.

    SciTech Connect

    Iavarone, M.; Karapetrov, G.; Di Capua, R.; Koshelev, A. E.; Rosenmann, D.; Claus, H.; Kwok, W. K.; Nishizaki, T.; Kobayashi, N.; Univ. degli Studi del Molise; CNR-INFM Coherentia; Tohoku Univ.

    2009-01-01

    Cobalt and Manganese intercalated NbSe{sub 2} single crystals have been synthesized and characterized by DC magnetization and scanning tunnelling microscopy (STM) at low temperatures. We observed a pronounced peak effect in magnetization for both Co and Mn intercalated samples that we further investigated by low temperature STM. A structural phase transition of the vortex lattice (VL) has been observed for applied magnetic fields corresponding to the peak in magnetization.

  8. STM Study of Au(111) Surface-Grafted Paramagnetic Macrocyclic Complexes [Ni2L(Hmba)](+) via Ambidentate Coligands.

    PubMed

    Salazar, Christian; Lach, Jochen; Rückerl, Florian; Baumann, Danny; Schimmel, Sebastian; Knupfer, Martin; Kersting, Berthold; Büchner, Bernd; Hess, Christian

    2016-05-10

    Molecular anchoring and electronic properties of macrocyclic complexes fixed on gold surfaces have been investigated mainly by using scanning tunnelling microscopy (STM) and complemented with X-ray photoelectron spectroscopy (XPS). Exchange-coupled macrocyclic complexes [Ni2L(Hmba)](+) were deposited via 4-mercaptobenzoate ligands on the surface of a Au(111) single crystal from a mM solution of the perchlorate salt [Ni2L(Hmba)]ClO4 in dichloromethane. The combined results from STM and XPS show the formation of large monolayers anchored via Au-S bonds with a height of about 1.5 nm. Two apparent granular structures are visible: one related to the dinickel molecular complexes (cationic structures) and a second one related to the counterions ClO4(-) which stabilize the monolayer. No type of short and long-range order is observed. STM tip-interaction with the monolayer reveals higher degradation after 8 h of measurement. Spectroscopy measurements suggest a gap of about 2.5 eV between HOMO and LUMO of the cationic structures and smaller gap in the areas related to the anionic structures. PMID:27093097

  9. Graphene sheet versus two-dimensional electron gas: A relativistic Fano spin filter via STM and AFM tips

    NASA Astrophysics Data System (ADS)

    Seridonio, A. C.; Siqueira, E. C.; Souza, F. M.; Machado, R. S.; Lyra, S. S.; Shelykh, I. A.

    2013-11-01

    We explore theoretically the density of states (LDOS) probed by a scanning tunneling microscope (STM) tip of two-dimensional systems hosting an adatom and a subsurface impurity, both capacitively coupled to atomic force microscope (AFM) tips and traversed by antiparallel magnetic fields. Two kinds of setups are analyzed, a monolayer of graphene and a two-dimensional electron gas (2DEG). The AFM tips set the impurity levels at the Fermi energy, where two contrasting behaviors emerge: The Fano factor for the graphene diverges, while in the 2DEG it approaches zero. As result, the spin degeneracy of the LDOS is lifted exclusively in the graphene system, in particular, for the asymmetric regime of Fano interference. The aftermath of this limit is a counterintuitive phenomenon, which consists of a dominant Fano factor due to the subsurface impurity even with a stronger STM-adatom coupling. Thus we find a full polarized conductance, achievable just by displacing vertically the position of the STM tip. Our work proposes the Fano effect as the mechanism to filter spins in graphene. This feature arises from the massless Dirac electrons within the band structure and allows us to employ the graphene host as a relativistic Fano spin filter.

  10. STM studies of the growth of the Si/Cu(110) surface alloy

    NASA Astrophysics Data System (ADS)

    Polop, C.; Sacedón, J. L.; Martín-Gago, J. A.

    1998-05-01

    The stages of the growth of the surface alloy c(2×2)-Si/Cu(110) have been analysed on the basis of scanning tunneling microscopy images and low electron energy diffraction (LEED) patterns. The formation of this interface goes through several stages as the Si coverage is increased. For a Si coverage ca 0.1 monolayer (ML), structured islands are observed on the surface. They are aligned along the < 1¯12> surface direction which corresponds to the Si-Si bonding direction in the atomic model. These islands grow and coalesce upon Si coverage, forming extended alloy areas. Defects, consisting of grouped atomic vacancies, along the < 1¯10> surface direction are observed at this stage of growth which are reflected on the corresponding LEED pattern as diffuse c(2×2) spots enlarged along the <001> surface direction. Complete and free of defects alloy terraces are observed for a Si coverage ca 0.5 ML, that is, when the completion of the overlayer alloy is attained. Atomic resolution STM images show a c(2×2) atomic arrangement which can be explained as a near coplanar substitution of Cu by Si atoms. Throughout the text the relationship between the growth stages and the perfection of the alloy layer is discussed.

  11. Supramolecular order and structural dynamics: A STM study of 2H-tetraphenylporphycene on Cu(111)

    SciTech Connect

    Stark, Michael; Träg, Johannes; Ditze, Stefanie; Steinrück, Hans-Peter; Marbach, Hubertus; Brenner, Wolfgang; Jux, Norbert

    2015-03-14

    The adsorption of 2H-tetraphenylporphycene (2HTPPc) on Cu(111) was investigated by scanning tunneling microscopy (STM). At medium coverages, supramolecular ordered islands are observed. The individual 2HTPPc molecules appear as two pairs of intense protrusions which are separated by an elongated depression. In the islands, the molecules are organized in rows oriented along one of the close packed Cu(111) substrate rows; the structure is stabilized by T-type interactions of the phenyl substituents of neighboring molecules. Two types of rows are observed, namely, highly ordered rows in which all molecules exhibit the same orientation, and less ordered rows in which the molecules exhibit two perpendicular orientations. Altogether, three different azimuthal orientations of 2HTPPc are observed within one domain, all of them rotated by 15° ± 1° relative to one closed packed Cu direction. The highly ordered rows are always separated by either one or two less ordered rows, with the latter structure being the thermodynamically more stable one. The situation in the islands is highly dynamic, such that molecules in the less ordered rows occasionally change orientation, also complete highly ordered rows can move. The supramolecular order and structural dynamics are discussed on the basis of the specific molecule-substrate and molecule-molecule interactions.

  12. STM and XPS study of CeO2(111) reduction by atomic hydrogen

    NASA Astrophysics Data System (ADS)

    Shahed, Syed Mohammad Fakruddin; Hasegawa, Tomo; Sainoo, Yasuyuki; Watanabe, Yoshihide; Isomura, Noritake; Beniya, Atsushi; Hirata, Hirohito; Komeda, Tadahiro

    2014-10-01

    Reduction of CeO2(111)/Ru(0001) surface by atomic hydrogen was investigated using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). We observed the formation of oxygen vacancy trimers and hydroxyl trimers on the stoichiometric CeO2(111) surface when it was exposed to atomic hydrogen at room temperature. The reaction of an impinging hydrogen atom with a surface oxygen atom yields a hydroxyl species, which diffuse on the surface until stabilized by the formation of OH trimers. The hydrogen atoms were located at atop sites of the oxygen atoms in the topmost surface layer. A reaction between the hopping hydrogen atom and the hydroxyl species yields a water molecule, which is desorbed from the surface leaving an oxygen defect. The oxygen vacancies were also observed as a trimer of vacancies. XPS measurements showed an increase of a reduced Ce and hydroxyl species with an amount of exposed hydrogen atoms. The former was estimated by measuring the ratio of Ce3 +/Ce4 + in the Ce 3d components. Our study shows the formation of hydroxyl trimer species in atomic scale upon atomic hydrogen exposure to CeO2(111) surface which could offer new catalytic activity.

  13. Highly Ordered Organic Molecular Thin Films on Silicon Studied by STM and LEED

    NASA Astrophysics Data System (ADS)

    Wagner, Sean; Zhang, Pengpeng

    2014-03-01

    Achieving growth of long-range ordered organic molecular thin films on inorganic substrates continues to be a significant challenge for organic electronics applications. Here, we report the growth of highly ordered zinc phthalocyanine (ZnPc) thin films both in-plane and out-of-plane on the deactivated Si(111) surface by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). By adjusting the substrate temperature during deposition, the anisotropic step-flow growth mode can be accessed causing a reduction in the substrate symmetry which allows for the long-range in-plane ordering as well as the decrease of grain boundary density. Additionally, the ZnPc molecules are able to maintain a highly ordered configuration in multi-layers despite a gradual decrease in the molecule-substrate interaction, which is attributed to the strong interlayer π- π interaction. We appreciate the fruitful discussion with Prof. Richard Lunt. This research is funded by the DOE Office of Science Early Career Research Program (Grant number DE-SC0006400) through the Office of Basic Energy Sciences.

  14. STM observation of damage on HOPG induced by energetic ions escaped from thick botanic samples*

    NASA Astrophysics Data System (ADS)

    Liu, Feng; Wang, Yugang; Xue, Jianming; Wang, Sixue; Yan, Sha; Zhao, Weijiang

    2001-05-01

    The target samples of 30-100 μm thick slices of kidney bean dry seeds and 8 and 72 μm ethylene terephthalate (PET) films were irradiated by 40 keV N + ion beam. The current density was 8 μA/cm 2 and the fluency was in the range of 0.3-3×10 17 ions/cm 2. During ion irradiation, highly oriented pyrolytic graphite (HOPG) samples were placed behind the target samples to receive energetic ions. After irradiation, through scanning tunneling microscope (STM) observation, statistic number density of protrusion-like damage on HOPG surfaces have been obtained. The experimental results show that for 30 and 50 μm thick botanic slice samples, the number densities are 1.0-5.0×10 11 and 0.6-2×10 10/cm 2, respectively. It demonstrates that 40 keV N + ion irradiation can cause evident damage at a depth of 50 μm in dry kidney bean seed slices. Before and after low-energy ion irradiation, transmission spectra of MeV proton with low fluency rate were applied to examine those botanic samples and study the possible escaping mechanism of the energetic ions from them in the low-energy ion irradiation.

  15. FI-STM study of hydrogen adsorption on Si(100) surface

    NASA Astrophysics Data System (ADS)

    Hua, Lu; Xiang-dong, Wang; Motai, K.; Hashizume, T.; Sakurai, T.

    1992-11-01

    Chemisorption of atomic hydrogen on the Si(100)2 × 1 surface has been investigated in detail by using a field ion-scanning tunneling microscope (FI-STM). The results showed that the adsorption geometry changed from the 2 × 1 monohydride phase to the 1 × 1 dihydride phase with increasing exposure of hydrogen. The data of desorption of the hydrogen-saturated Si surface showed that on annealing at 670 K the surface becomes highly disordered: the 1 × 1 dihydride structure is eliminated and the 2 × 1 reconstructed monohydride is also hardly to identify. When the temperature rises to as high as 730 K, the surface is dominated by the 2 × 1 structure with missing dimer rows, and some adatom chains occur on the Si substrate terraces. We attribute the formation of these atomic chains to an epitaxial growth of Si atoms which are formed by the dissociation of SiHx (x = 1, 2, 3 or 4) compounds on the Si surface.

  16. Orbital signatures of Fano-Kondo line shapes in STM adatom spectroscopy

    NASA Astrophysics Data System (ADS)

    Frank, Sebastian; Jacob, David

    2015-12-01

    We investigate the orbital origin of the Fano-Kondo line shapes measured in STM spectroscopy of magnetic adatoms on metal substrates. To this end we calculate the low-bias tunnel spectra of a Co adatom on the (001) and (111) Cu surfaces with our density functional theory-based ab initio transport scheme augmented by local correlations. In order to associate different d orbitals with different Fano line shapes we only correlate individual 3 d orbitals instead of the full Co 3 d shell. We find that Kondo peaks arising in different d levels indeed give rise to different Fano features in the conductance spectra. Hence, the shape of measured Fano features allows us to draw some conclusions about the orbital responsible for the Kondo resonance, although the actual shape is also influenced by temperature, effective interaction, and charge fluctuations. Comparison with a simplified model shows that line shapes are mostly the result of interference between tunneling paths through the correlated d orbital and the s p -type orbitals on the Co atom. Very importantly, the amplitudes of the Fano features vary strongly among orbitals, with the 3 z2 orbital featuring by far the largest amplitude due to its strong direct coupling to the s -type conduction electrons.

  17. STM investigation of the superconducting state of BSCCO 2212 and borocarbide materials

    SciTech Connect

    Iavarone, M. |; Guptasarma, P.; Hinks, D.G.

    1997-10-01

    We present spectroscopic Scanning Tunneling Microscope (STM) measurements performed at 4.2 K on BSCCO 2212 single crystals and Y, Lu and Er based borocarbide compounds. The conductance versus voltage spectra on BSCCO 2212 reveal a reproducible dip feature near e{vert_bar}V{vert_bar} = 2{Delta}, for both voltage polarities pointing to a strong coupling origin of the feature. The conductance spectra obtained on YNi{sub 2}B{sub 2}C thin films and LuNi{sub 2}B{sub 2}C single crystals are similar and correspond to a BCS ratio of 3.2 indicating weak coupling superconductivity in these compounds. On Er Ni{sub 2}B{sub 2}C single crystals, the conductance spectra show a pronounced broadening compared to the spectra obtained on LuNi{sub 2}B{sub 2}C and YNi{sub 2}B{sub 2}C, which is attributed to the pair-breaking effect due to the Er magnetic ions.

  18. STM study of the superconducting proximity effect at 60 mK: influence of interface transparency.

    NASA Astrophysics Data System (ADS)

    Courtois, H.; Gupta, A. K.; Cretinon, L.; Moussy, N.; Pannetier, B.

    2002-03-01

    Proximity effect of a superconductor on a normal metal has a renewed interest recently. The effort, so far, has been to make the N-S interface as transparent and clean as possible to enhance the proximity effects. Here, we investigate the influence of interface transparency on the superconducting proximity effect of niobium on gold by probing the local density of states (DOS) at the surface of a thin gold layer deposited on a thick niobium film. This is achieved by measuring the tunneling spectra with a home-made STM operating in a upside-down dilution fridge at 60mK temperature footnote[1]N. Moussy, H. Courtois, and B. Pannetier, Rev. Sci. Instrum. 72, 128 (2001).. We observe BCS like spectra for the transparent interface since the gold layer thickness is much smaller than the coherence length. The interface transparency is adjusted by in situ argon etching of the Nb surface before depositing the gold layer. As a result of this semi-transparent interface, the BCS-like spectra evolve into a depression in the DOS near the Fermi energy (E_F) with a reduced energy scale as compared to the superconducting gap (Δ) together with some remnant features near Δ. We discuss the dependence of these two features on the interface transparency and the gold layer thickness and its possible implications.

  19. A New Ultra-Low Temperature, High Magnetic Field STM in an Ultra-Quiet Laboratory

    NASA Astrophysics Data System (ADS)

    Zhou, Brian B.; Misra, Shashank; Urban, Lukas; Seo, Jungpil; Gyenis, Andras; Kahng, Sejong; Yazdani, Ali

    2011-03-01

    We report progress in the construction of a new UHV STM capable of operating at the extremes of temperature (25 mK) and magnetic field (14 T), allowing atomically resolved studies in previously unexplored areas of phase space. Our novel design is based on a bottom-loading dilution refrigerator in which the entire dilution stage and mounted microscope are moved between measurement and sample transfer positions. Pumping for the dilution fridge and large magnetic fields introduce demanding challenges in vibration isolation, which we have addressed with an ultra-quiet laboratory setting and rigid microscope design. Our system is situated inside both acoustic and RF-shielded enclosures in complement with various stages of isolation for both pump and ambient vibration sources. We will discuss unique aspects of the microscope design, such as a two-in-one double sample holder, and assess preliminary system performance. Supported by the W. M. Keck Foundation. Infrastructure at Princeton Nanoscale Microscopy Laboratory is also supported by grants from DOE, NSF, and ARO.

  20. Beam tests of CALET with BBM electronics and STM at CERN-SPS

    NASA Astrophysics Data System (ADS)

    Tamura, Tadahisa

    We have been developing flight hardware of CALET (CALorimetric Electron Telescope) to observe electrons, gamma rays, and nuclei at the Japanese Experiment Module “Kibo” Exposed Facility (JEM-EF) on the International Space Station (ISS). The main calorimeter of CALET consists of a charge detector (CHD) to identify particles by charge, an imaging calorimeter (IMC) to determine incident angles and shower starting points, and a total absorption calorimeter (TASC) to measure energies and to discriminate electromagnetic particles from nuclei. We carried out beam experiments at CERN-SPS to confirm consistency between our simulation and beam test data. It is important for performance check and flight data analyses. We assembled a Beam Test Model detector by using BBM (Bread Board Model) of front end electronics and STM (Structure and Thermal Model) of CHD, IMC, and TASC for electron/proton runs in 2012. We made ion runs mainly to test CHD readout with BBM front end electronics in 2013. Basic results of the beam tests will be reported here.

  1. PTCDA molecules on a KBr/InSb system: a low temperature STM study.

    PubMed

    Such, B; Goryl, G; Godlewski, S; Kolodziej, J J; Szymonski, M

    2008-11-26

    We have used scanning tunnelling microscopy (STM) at 77 K to investigate 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) molecules adsorbed on an ultrathin (1-2 monolayer (ML)) film of KBr grown on a c(8 × 2)InSb(001) substrate. The molecules are stabilized both at the KBr steps and on the terraces. On the 1 ML film the PTCDA molecules appear predominantly as single entities, whereas on the 2 ML film formation of molecular clusters is preferred. Differences in the adsorption configurations indicate that the interaction between the molecules and the surface differs significantly for the cases of 1 and 2 ML films. We present images of the molecules obtained with sub-molecular resolution for both filled and empty state sampling modes. We argue that the highest occupied molecular orbital (the lowest unoccupied molecular orbital) is responsible for intramolecular contrast in filled (empty) state images of the molecules, even though they are deformed due to strong interaction with the substrate. PMID:21836286

  2. Structure and magnetism of cobalt intercalated graphene/Ir(111) via spin-polarized STM

    NASA Astrophysics Data System (ADS)

    Decker, Regis; Brede, Jens; Atodiresei, Nicolae; Caciuc, Vasile; Bluegel, Stefan; Wiesendanger, Roland

    2013-03-01

    The presence of intercalation compounds in graphite, i.e. impurities or layer(s) trapped between carbon sheets, can lead to changes in the transport, optical and catalytic properties compared to bulk graphite, or even superconductivity. Here, we present the local structure and magnetic properties of graphene on a magnetic substrate, resolved by spin-polarized STM. The magnetic substrate is obtained by the intercalation of a cobalt layer between graphene and an Ir(111) surface. The atomic structure of the graphene layer is dominated by a highly corrugated Moiré pattern, which arises due to the incommensurability and/or twisting angle of the graphene lattice and the Co/Ir(111) surface. Within the Moiré unit cell three different regions, i.e. top, fcc, and hcp regions are identified. Interestingly, these regions show very different electronic and magnetic signatures in the experiments, defining an atomic-scale magnetic Moiré pattern. The observed spin polarization is compared to density functional theory calculations. The calculations reveal that the bonding between the graphene layer and intercalated Co layer varies from weak to strong within the Moiré unit cell. Moreover, the interaction between the graphene and the intercalated cobalt layer leads to a spin dependent charge rearrangement, which induces magnetism in graphene as observed in experiment.

  3. Supramolecular order and structural dynamics: A STM study of 2H-tetraphenylporphycene on Cu(111).

    PubMed

    Stark, Michael; Träg, Johannes; Ditze, Stefanie; Brenner, Wolfgang; Jux, Norbert; Steinrück, Hans-Peter; Marbach, Hubertus

    2015-03-14

    The adsorption of 2H-tetraphenylporphycene (2HTPPc) on Cu(111) was investigated by scanning tunneling microscopy (STM). At medium coverages, supramolecular ordered islands are observed. The individual 2HTPPc molecules appear as two pairs of intense protrusions which are separated by an elongated depression. In the islands, the molecules are organized in rows oriented along one of the close packed Cu(111) substrate rows; the structure is stabilized by T-type interactions of the phenyl substituents of neighboring molecules. Two types of rows are observed, namely, highly ordered rows in which all molecules exhibit the same orientation, and less ordered rows in which the molecules exhibit two perpendicular orientations. Altogether, three different azimuthal orientations of 2HTPPc are observed within one domain, all of them rotated by 15° ± 1° relative to one closed packed Cu direction. The highly ordered rows are always separated by either one or two less ordered rows, with the latter structure being the thermodynamically more stable one. The situation in the islands is highly dynamic, such that molecules in the less ordered rows occasionally change orientation, also complete highly ordered rows can move. The supramolecular order and structural dynamics are discussed on the basis of the specific molecule-substrate and molecule-molecule interactions. PMID:25770514

  4. Nanopatterning of Donor/Acceptor Hybrid Supramolecular Architectures on HOPG: An STM Study

    PubMed Central

    Wang, Ling; Chen, Qing; Pan, Ge-Bo; Wan, Li-Jun; Zhang, Shiming; Zhan, Xiaowei; Northrop, Brian H.; Stang, Peter J.

    2009-01-01

    Hybrid supramolecular architectures have been fabricated with acceptor 1,4-bis(4-pyridylethynyl)-2,3-bis-dodecyloxy-benzene (PBP) and donor 2,6-bis(3,4,5-tris-dodecyloxy-phenyl)dithieno[3,2-b:2′,3′-d]thiophene (DTT) compounds on highly oriented pyrolytic graphite (HOPG) surfaces and their structures and molecular conductance are characterized by scanning tunneling microscopy/spectroscopy (STM/STS). Stable, one-component adlayers of PBP and DTT are also investigated. The coadsorption of two-component mixtures of PBP and DTT results in a variety of hybrid nanopattern architectures that differ from those of their respective one-component surface assemblies. Adjusting the acceptor/donor molar ratio in mixed adlayer assemblies results in dramatic changes in the structure of the hybrid nanopatterns. STS measurements indicate that the HOMO and LUMO energy levels of PBP and DTT on an HOPG surface are relatively insensitive to changes in the hybrid supramolecular architectures. These results provide important insight into the design and fabrication of two-dimensional hybrid supramolecular architectures. PMID:18783221

  5. A practical distributed Fiber Bragg grating temperature sensor system based on STM32 processor platform

    NASA Astrophysics Data System (ADS)

    Liu, Jinjun; Cheng, Yongxin; Wang, Guangyu; Zhang, Yanjun

    2015-10-01

    A practical distributed FBG temperature sensor system based on STM32 processor platform is presented in this paper and this FBG sensing system can realize single-channel and multi-point temperature measurement. Because the measured area has been divided into several parts, every part has several fiber Bragg gratings with the same wavelength. There is no need to get the temperature of each point, just get the temperature field information of the parts. In other words, if the temperature of points is varied, the largest varied temperature of the points in one part can be obtained as the temperature of this part. So in the system only use one light source, but more FBGs can be implanted in a fiber, which can effectively reduce costs and complexity. In signal processing system, the FFP-TF control circuit cans precise control without distortion of FFP-TF; high precision photoelectric detection circuit can achieve nW level optical power detection; wavelength demodulation algorithm can achieve system synchronization. The PC monitoring software based on VC++ is used to display the monitoring interface. The experiment results indicated that temperature precision is 1°C and the linearity is over 99.6%. All experiments can be reproducible. It has been seen in experiments that the system has the characteristics of the high measured stable, good reliability, low cost and can meet the needs of the engineering measurements.

  6. A Method for Studying Atomic Diffusion by STM Tip-Crash Induced Vacancy Island Coalescence

    NASA Astrophysics Data System (ADS)

    Lake, R. E.; Lange, A. P.; Ray, M. P.; Sosolik, C. E.

    2007-11-01

    The study of vacancy and adatom island motion on single crystal metals with the scanning tunneling microscope (STM) has explained many of the underlying atomic diffusion mechanisms responsible for movement of atoms on a surface. We present a new method for vacancy island creation at room temperature using a controlled mechanical tip-surface interaction. The method allows us to control the relative positions and initial sizes of vacancy islands with respect to one another and to surface defects. Complicated and closely spaced vacancy island configurations can also be engineered. This enhances our ability to collect statistics on the movement of the macro-scale vacancy islands and distinguish between mass transport channels. To demonstrate the technique, time series analysis of coalescence events on the surface of Ag(111) is presented. Diffusion coefficients of the Ag surface atoms obtained with this method are in general agreement with previous stochastic methods for creating vacancy islands such as low-dose sputtering [1]. [1] M. Eßer, K. Morgenstern, G. Rosenfeld, G. Comsa, Surf. Sci. 402-404, 341 (1998).

  7. An atomic scale STM study of the Fe 3O 4(0 0 1) surface

    NASA Astrophysics Data System (ADS)

    Ceballos, S. F.; Mariotto, G.; Jordan, K.; Murphy, S.; Seoighe, C.; Shvets, I. V.

    2004-01-01

    Despite the intensive investigation into the electronic properties of magnetite, fundamental issues related to the Verwey transition and the electronic transport mechanism are not fully understood. These issues are further complicated at the surface of magnetite crystals, due to the large number of possible surface terminations. The preparation procedure plays a fundamental role in determining the O/Fe ratio, and therefore the electronic properties of a magnetite crystal. We present a detailed investigation of the influence of the preparation conditions on the morphology of Fe 3O 4(0 0 1) single crystal surfaces using AES, LEED, and STM. We show that long anneals of single crystals in UHV cause segregation of contaminants to the surface and that a series of surface reconstructions is induced. A different preparation procedure gives rise to a clean surface exhibiting a ( 2× 2)R 45° reconstruction. This surface is terminated at the octahedral plane and has been imaged down to the atomic scale. This provides a useful test system to study the Verwey transition at the surface.

  8. Two-dimensional boron based nanomaterials: electronic, vibrational, Raman, and STM signatures

    NASA Astrophysics Data System (ADS)

    Massote, Daniel V. P.; Liang, Liangbo; Kharche, Neerav; Meunier, Vincent

    Because boron has only three electrons on its outer shell, planar mono-elemental boron nanostructures are expected to be much more challenging to assemble than their carbon counterparts. Several studies proposed schemes in which boron is stabilized to form flat semiconducting sheets consisting of a hexagonal lattice of boron atoms with partial hexagon filling (PRL 99 115501, ACSNano 6 7443-7453) . Other structures were proposed based on results from an evolutionary algorithm (PRL 112 085502). These structures are metallic and one even features a distorted Dirac cone near the Fermi level. Experimental evidence for 2D boron is still lacking but the recently proposed molecular synthesis of a flat all-boron molecule is a promising route to achieve this goal (Nat.Comms. 5 3113). Our research aims at providing a first-principles based description of these materials' properties to help in their identification. DFT is used to calculate phonon dispersion and associated Raman scattering spectra. We report some marked discrepancy between our findings and results from the recent literature and address the deviation using two methods for phonon dispersion. We also simulated STM images at various bias potentials to reveal the electronic symmetry of each material.

  9. In vivo vascular wall tissue characterization using a strain tensor measuring (STM) technique for flow-mediated vasodilation analyses

    NASA Astrophysics Data System (ADS)

    Mahmoud, Ahmed M.; Frisbee, Jefferson C.; D'Audiffret, Alexandre; Mukdadi, Osama M.

    2009-10-01

    Endothelial dysfunction is considered to be a key factor in the development of atherosclerosis, and the measurement of flow-mediated vasodilation (FMD) in brachial and other conduit arteries has become a common method to assess the status of endothelial function in vivo. Based on the direct relationship between the FMD response and local shear stress on the conduit brachial artery endothelium, we hypothesize that measuring relevant changes in the brachial wall strain tensor would provide a non-invasive tool for assessing vascular mechanics during post-occlusion reactive hyperemia. Direct measurement of the wall strain tensor due to FMD has not yet been reported in the literature. In this work, a noninvasive direct ultrasound-based strain tensor measuring (STM) technique is presented to assess changes in the mechanical parameters of the vascular wall during post-occlusion reactive hyperemia and/or FMD, including local velocities and displacements, diameter change, local strain tensor and strain rates. The STM technique utilizes sequences of B-mode ultrasound images as its input with no extra hardware requirement, and its algorithm starts with segmenting a region of interest within the artery and providing the acquisition parameters. Then a block matching technique based on speckle tracking is employed to measure the frame-to-frame local velocities. Displacements, diameter change, local strain tensor and strain rates are then calculated by integrating or differentiating velocity components. The accuracy of the STM algorithm was assessed in vitro using phantom studies, where an average error of 7% was reported using different displacement ranging from 100 µm to 1000 µm. Furthermore, in vivo studies using human subjects were performed to test the STM algorithm during pre- and post-occlusion. Good correlations (|r| >0.5, P < 0.05) were found between the post-occlusion responses of diameter change and local wall strains. Results indicate the validity and versatility of

  10. In vivo vascular wall tissue characterization using a strain tensor measuring (STM) technique for flow-mediated vasodilation analyses.

    PubMed

    Mahmoud, Ahmed M; Frisbee, Jefferson C; D'Audiffret, Alexandre; Mukdadi, Osama M

    2009-10-21

    Endothelial dysfunction is considered to be a key factor in the development of atherosclerosis, and the measurement of flow-mediated vasodilation (FMD) in brachial and other conduit arteries has become a common method to assess the status of endothelial function in vivo. Based on the direct relationship between the FMD response and local shear stress on the conduit brachial artery endothelium, we hypothesize that measuring relevant changes in the brachial wall strain tensor would provide a non-invasive tool for assessing vascular mechanics during post-occlusion reactive hyperemia. Direct measurement of the wall strain tensor due to FMD has not yet been reported in the literature. In this work, a noninvasive direct ultrasound-based strain tensor measuring (STM) technique is presented to assess changes in the mechanical parameters of the vascular wall during post-occlusion reactive hyperemia and/or FMD, including local velocities and displacements, diameter change, local strain tensor and strain rates. The STM technique utilizes sequences of B-mode ultrasound images as its input with no extra hardware requirement, and its algorithm starts with segmenting a region of interest within the artery and providing the acquisition parameters. Then a block matching technique based on speckle tracking is employed to measure the frame-to-frame local velocities. Displacements, diameter change, local strain tensor and strain rates are then calculated by integrating or differentiating velocity components. The accuracy of the STM algorithm was assessed in vitro using phantom studies, where an average error of 7% was reported using different displacement ranging from 100 microm to 1000 microm. Furthermore, in vivo studies using human subjects were performed to test the STM algorithm during pre- and post-occlusion. Good correlations (|r| >0.5, P < 0.05) were found between the post-occlusion responses of diameter change and local wall strains. Results indicate the validity and

  11. Os layers spontaneously deposited on the Pt(111) electrode : XPS, STM and GIF-XAS study.

    SciTech Connect

    Rhee, C. K.; Wakisaka, M.; Tolmachev, Y.; Johnston, C.; Haasch, R.; Attenkofer, K.; Lu, G. Q.; You, H.; Wieckowski, A.; Univ. of Illinois Champaigh-Urbana

    2003-01-01

    Scanning tunneling microscopy (STM) characterized adlayers of spontaneously deposited osmium on a Pt(111) electrode were investigated using ex-situ X-ray photoemission spectroscopy (XPS) and in-situ grazing incidence fluorescence X-ray absorption spectroscopy (GIF-XAS). After a single spontaneous deposition, monoatomic (or nearly monoatomic) nanoislands of osmium are formed. The island diameter varies from 2 to 5 nm depending on the Os coverage, which in turn is adjusted by varying the concentration of the Os precursor salt (OsCl3) in the deposition bath and/or by the deposition time. XPS reveals three oxidation states: a metallic Os (the 4f7/2 core level binding energy of 50.8 eV), Os(IV) (51.5 eV) and Os(VIII) (52.4 eV). The metallic osmium exists at potentials below 500 mV (vs. RHE) while above 500 mV osmium is oxidized to Os(IV). Electrodissolution of osmium begins above 900 mV and occurs simultaneously with platinum oxidation. At ca. 1200 mV V versus the RHE reference, the oxidation state of some small amounts of osmium that survive dissolution is the Os(VIII). We demonstrate, for the first time, that mixed or odd valencies of osmium exist on the platinum surface at potentials higher that 800 mV. In-situ GIF-XAS measurements of an Os LIII edge also reveal the presence of three Os oxidation states. Namely, below the electrode potential of 400 mV, the X-ray fluorescent energy at maximum absorption is 10.8765 keV, and is characteristic of the metallic Os. In the potential range between 500 and 1000 mV this energy is gradually shifted to higher values, assignable to higher valencies of osmium, like Os(IV). This tendency continues to higher potentials consistent with the third, highly oxidized osmium form present, most likely Os(VIII). The variation of the 'raw edge jump height' of Os with the electrode potential, which is equivalent to a drop in osmium surface concentration, demonstrates that the electrochemical stripping of Os begins below 1.0 V versus RHE, as

  12. Growth of nanocrystalline MoO3 on Au(111) studied by in-situ STM

    SciTech Connect

    Biener, M M; Biener, J; Schalek, R; Friend, C M

    2004-04-22

    The growth of nanocrystalline MoO{sub 3} islands on Au(111) using physical vapor deposition of Mo has been studied by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). The growth conditions affect the shape and distribution of the MoO{sub 3} nanostructures, providing a means of preparing materials with different percentages of edge sites that may have different chemical and physical properties than atoms in the interior of the nanostructures. MoO{sub 3} islands were prepared by physical vapor deposition of Mo and subsequent oxidation by NO{sub 2}exposure at temperatures between 450 K and 600 K. They exhibit a crystalline structure with a c(4x2) periodicity relative to unreconstructed Au(111). While the atomic-scale structure is identical to that of MoO{sub 3} islands prepared by chemical vapor deposition, we demonstrate that the distribution of MoO{sub 3} islands on the Au(111) surface reflects the distribution of Mo clusters prior to oxidation although the growth of MoO{sub 3} involves long-range mass transport via volatile MoO{sub 3} precursor species. The island morphology is kinetically controlled at 450 K, whereas an equilibrium shape is approached at higher preparation temperatures or after prolonged annealing at the elevated temperature. Mo deposition at or above 525 K leads to the formation of a Mo-Au surface alloy as indicated by the observation of embedded MoO{sub 3} islands after oxidation by NO{sub 2}. Au vacancy islands, formed when Mo and Au dealloy to produce vacancies, are observed for these growth conditions.

  13. Pd(1 1 0) surface oxide structures investigated by STM and DFT

    NASA Astrophysics Data System (ADS)

    Kralj, M.; Pertram, T.; Seriani, N.; Mittendorfer, F.; Krupski, A.; Becker, C.; Wandelt, K.

    2008-12-01

    The adsorption of oxygen on a Pd(1 1 0) surface has been studied with scanning tunneling microscopy (STM). The particular emphasis was given to the preparation of low oxygen coverages with the well known c(2 × 4)-O oxygen phase as a starting structure in the experiments. The oxygen content, surface morphology and structure were changed by annealing the sample to temperatures below the onset of oxygen desorption. The surface was characterized after cool-down to room temperature or temperatures in the range 100-140 K. At low temperatures we found a new oxygen adsorption structure characterized by a (3 × 2) periodicity. We also calculate the O/Pd(1 1 0) surface phase diagram by first-principles thermodynamics. For small coverages, near the low-coverage end of the large stability region of the c(2 × 4)-O structure it was found that a (2 × 3)-deep-O and a (2 × 3)-1D-O structures, which are degenerate in energy, are most stable. Conversely, at high chemical potentials, i.e. high coverages, a (7 × √3)-O structure becomes more stable. The formation of the metastable (3 × 2)-O phase is explained in terms of partial deoxidation via the interaction with residual hydrogen and by quenching of other types of restructuring at low temperatures since the (3 × 2)-O phase can be derived from the c(2 × 4)-O phase by slight rearrangement of oxygen atoms after the oxygen content was lowered from 1/2 to 1/3 of a monolayer. This is not the case with more stable structures of the same coverage which require an additional rearrangement of palladium atoms.

  14. STM and AFM; Which is Better for Surface Structural Analysis? Non- contact AFM Studies on Ge/Si(105) Surface

    NASA Astrophysics Data System (ADS)

    Hasegawa, Yukio

    2006-03-01

    Scanning tunneling microscopy (STM) has been utilized to determine surface atomic structure with its highly resolved images. Probing surface electronic states near the Fermi energy (EF), STM images, however, do not necessarily represent the atomic structure of surfaces. It has been believed that atomic force microscopy (AFM) provides us surface topographic images without being disturbed by the electronic states. In order to prove the surpassing performance, we performed noncontact (nc) AFM on the Ge/Si(105) surface [1], which is a facet plane of the ?hut? clusters formed on Ge-deposited Si(001) surface. It is found that STM images taken on the surface, either filled- or empty-state images, do not show all surface atoms because of the electronic effect; some surface atoms have dangling bond states below EF and other surface atoms have states above EF. [2]. In a nc-AFM image, on the other hand, all surface atoms having a dangling bond are observed [3], directly representing an atomic structure of the surface. Electronic information can also be obtained in AFM by using a Kelvin-probe method. From atomically resolved potential profile we obtained, charge transfer among the dangling bond states is directly demonstrated. These results clearly demonstrate that highly-resolved nc-AFM with a Kelvin-probe method is an ideal tool for analysis of atomic structures and electronic properties of surfaces. This work was done in collaboration with T. Eguchi, K. Akiyama, T. An, and M. Ono, ISSP, Univ. Tokyo and JST, Y. Fujikawa and T. Sakurai, IMR. Tohoku Univ. T. Hashimoto, AIST, Y. Morikawa, ISIR, Osaka Univ. K. Terakura, Hokkaido Univ., and M.G. Lagally, University of Wisconsin-Madison. [1] T. Eguchi et al., Phys. Rev. Lett. 93, 266102 (2004). [2] Y. Fujikawa et al., Phys. Rev. Lett. 88, 176101 (2002). [3] T. Eguchi and Y. Hasegawa, Phys. Rev. Lett. 89, 256105 (2002)

  15. Computer simulation of STM images of vertical heterostructures of graphene/hexagonal boron nitride with intercalated atoms

    NASA Astrophysics Data System (ADS)

    Kim, Gunn; Lee, Junsu

    Using density functional theory, we did computational simulations of scanning tunneling microscopy of vertical graphene/hexagonal boron nitride heterostructures with an intercalated atom (Li, K, Cr, Mn, Co or Cu). A plane-wave basis set was employed with a kinetic energy of 400 eV. The form of the Perdew-Burke-Ernzerhof type was utilized for the exchange-correlation energy functional. To obtain the more accurate result, the van der Waals interaction was also considered. In the computer-simulated scanning tunneling microscopy (STM) images in the Tersoff-Hamann scheme, we demonstrated that the single impurity atom between Gr and hBN sheets is detectable. We observed three different STM patterns on the graphene side. These can be classified by group 1 (Li, Co, and Cu), group 2 (Cr and Mn), and group 3 (K), which have hexagonal, circular, and wide bright spot patterns around the impurity atom, respectively. Although Co and Cu are both in group 1, the Co atom shows stronger d orbital character than the Cu atom. Interestingly, in the case of the Co atom, the simulated STM images are quite different at bias voltages of -0.1 V and +0.1 V. While C pz-Co dyz hybridization occurs at the bias voltage of -0.1 V, C pz-Co dxz hybridization occurs at the bias voltage of +0.1 V. GK and JL were supported by the Basic Science Research program (2013R1A2009131) through the National Research Foundation of Korea.

  16. Self-organization of surfactant molecules on solid surface: an STM study of sodium alkyl sulfonates [rapid communication

    NASA Astrophysics Data System (ADS)

    Yin, Xiu-Li; Wan, Li-Jun; Yang, Zheng-Yu; Yu, Jia-Yong

    2005-02-01

    Adsorption and self-organization of sodium alkyl sulfonates (STS and SHS) on HOPG have been studied by using in situ scanning tunneling microscopy (STM). Both SHS and STS molecules adsorb on HOPG surface and form long-range well-ordered monolayers. The molecular rows and the axes of alkyl chain of the molecules cross each other at angles of 60° and 90° in the STS and SHS layers, respectively. Molecular details such as sulfonate functional group (head) and alkyl chain are clearly imaged. The neighboring molecules in different rows form a "head to head" configuration. Structural models for the molecular arrangement of the two adlayers are proposed.

  17. Investigation of local tunneling current noise spectra on the silicon crystal surfaces by means of STM/STS

    SciTech Connect

    Mantsevich, V. N. Maslova, N. S.; Cao, G. Y.

    2015-08-15

    We report on a careful analysis of the local tunneling conductivity by means of ultra-high vacuum scanning tunneling microscopy/spectroscopy (STM/STS) technique in the vicinity of low-dimensional structures on the Si(111)–(7 × 7) and Si(110)–(16 × 2) surfaces. The power-law exponent α of low-frequency tunneling current noise spectra is investigated for different values of the tunneling contact parameters: relaxation rates, the localized state coupling, and the tunneling barrier width and height.

  18. Calculation of the temperature and thermal expansion of a STM tip heated by a short laser pulse

    NASA Astrophysics Data System (ADS)

    Geshev, P. I.; Klein, S.; Dickmann, K.

    A mathematical model for the calculation of the temperature field in a scanning tunneling microscope (STM) tip under laser illumination is developed. The duration of the laser pulse is a few nanoseconds or shorter. A Gaussian distribution of the laser light intensity in time and space is assumed. Two different mechanisms of tip heating are taken into account: 1. due to an enhanced electric field on the tip; 2. due to heating of the side surface of the tip by the focused spot of laser light. An average tip temperature is calculated using the heat conductivity equation. The enhanced electric field on the tip is calculated by the method of boundary integral equations.

  19. Spin polarized STM imaging of the Fe3O4 (0 0 1) surface using antiferromagnetic tips

    NASA Astrophysics Data System (ADS)

    Jordan, K.; Mariotto, G.; Ceballos, S. F.; Murphy, S.; Shvets, I. V.

    2005-04-01

    Spin polarized STM is used to image the charge ordered Fe3O4 (0 0 1) surface, using antiferromagnetic MnNi probes. Such a surface is characterized by the presence of Fe- Fe and Fe- Fe dimers. These dimers have different spin configurations, which are resolved using a MnNi probe. The surface is also imaged with paramagnetic W tips, which do not distinguish between the dimers, providing further evidence for a spin polarized contribution to the tunnel current with MnNi tips.

  20. The initial stages of the hydrogen-induced reconstruction of Pd(1 1 0) studied with STM

    NASA Astrophysics Data System (ADS)

    Kralj, Marko; Becker, Conrad; Wandelt, Klaus

    2006-09-01

    The hydrogen-induced reconstruction of the Pd(1 1 0) surface was investigated in situ with scanning tunneling microscopy (STM). Focusing on the initial stages of the restructuring, which ultimately leads to a stable (1 × 2) reconstructed surface, we find an exponential increase of the reconstructed surface area with hydrogen exposure, up to 8 Langmuir, which can be explained by an autocatalytic behavior. Moreover, the steps, especially those running along the [0 0 1] direction, play a distinctive role in the buildup of the (1 × 2) reconstruction.

  1. STM study of azobenzene self-assembly on Ag/Ge(1 1 1)-( √{3}×√{3})R30°

    NASA Astrophysics Data System (ADS)

    Wu, H.-C.; Chou, L.-W.; Lee, Y.-R.; Su, C.; Lin, J.-C.

    2009-10-01

    The adsorption and self-organization of trans-azobenzene (TAB) on Ag/Ge(1 1 1)-( √{3}×√{3})R30° (Ag/Ge(1 1 1)- √{3}) were studied by low temperature scanning tunneling microscopy (LT-STM) in ultrahigh vacuum (UHV). High-resolution STM images allow the observation of individual TAB molecules and the commensurate TAB chain domains formed via the hydrogen bond enhanced intermolecular interaction and molecule-substrate interaction on Ag/Ge(1 1 1)- √{3}. From in situ observation of the substrate lattice, the TAB monolayers were found to form a (2 × 1) structure. Some coexisting cis-azobenzene (CAB) molecules were observed on the domain boundary of TAB overlayer. The structural model and the molecule registry corresponding to STM images for the monolayer of TAB on Ag/Ge(1 1 1)- √{3} are proposed and discussed.

  2. STM probe on the surface electronic states of spin-orbit coupled materials

    NASA Astrophysics Data System (ADS)

    Zhou, Wenwen

    Spin-orbit coupling (SOC) is the interaction of an electron's intrinsic angular momentum (spin) with its orbital momentum. The strength of this interaction is proportional to Z4 where Z is the atomic number, so generally it is stronger in atoms with higher atomic number, such as bismuth (Z=83) and iridium (Z=77). In materials composed of such heavy elements, the prominent SOC can be sufficient to modify the band structure of the system and lead to distinct phase of matter. In recent years, SOC has been demonstrated to play a critical role in determining the unusual properties of a variety of compounds. SOC associated materials with exotic electronic states have also provided a fertile platform for studying emergent phenomena as well as new physics. As a consequence, the research on these interesting materials with any insight into understanding the microscopic origin of their unique properties and complex phases is of great importance. In this context, we implement scanning tunneling microscopy (STM) and spectroscopy (STS) to explore the surface states (SS) of the two major categories of SOC involved materials, Bi-based topological insulators (TI) and Ir-based transition metal oxides (TMO). As a powerful tool in surface science which has achieved great success in wide variety of material fields, STM/STS is ideal to study the local density of states of the subject material with nanometer length scales and is able to offer detailed information about the surface electronic structure. In the first part of this thesis, we report on the electronic band structures of three-dimensional TIs Bi2Te3 and Bi2Se 3. Topological insulators are distinct quantum states of matter that have been intensely studied nowadays. Although they behave like ordinary insulators in showing fully gapped bulk bands, they host a topologically protected surface state consisting of two-dimensional massless Dirac fermions which exhibits metallic behavior. Indeed, this unique gapless surface state is a

  3. Scrutinizing individual CoTPP molecule adsorbed on coinage metal surfaces from the interplay of STM experiment and theory

    NASA Astrophysics Data System (ADS)

    Houwaart, Torsten; Le Bahers, Tangui; Sautet, Philippe; Auwärter, Willi; Seufert, Knud; Barth, Johannes V.; Bocquet, Marie-Laure

    2015-05-01

    The cobalt tetraphenyl porphyrin (CoTPP) molecule and its adsorption on clean Cu and Ag surfaces are comparatively analyzed within the Density Functional Theory (DFT) framework. Different sets of exchange-correlation functionals - the Local Density Approximation (LDA) and the Gradient Generalized Approximation (along with the PBE functional and the semi-empirical Grimme's corrections of dispersion) - are compared. Two prominent structural adsorption properties are disclosed in all sets of calculations: an asymmetric saddle deformation of CoTPP with an enhanced tilting of the upwards bent pyrroles and a single adsorption site where the Co center occupies a bridge position and one molecular axis (along the direction of the lowered pair of opposite pyrroles) is aligned with the dense-packed < 1 1 bar 0 > substrate direction. The similarities between Cu(111) and Ag(111) surfaces extend to the interfacial electronic structure with similar electronic redistribution and molecular charging. However subtle differences between the two substrates are revealed with bias-dependent STM simulations, especially in the low-bias imaging range. The STM calculations underline the difficulty for the commonly used GGA + D2 DFT framework to quantitatively predict the energy positions of the frontier molecular orbitals (MOs).

  4. Development and performance of the nanoworkbench: A four tip STM for conductivity measurements down to submicrometer scales

    SciTech Connect

    Guise, Olivier; Marbach, Hubertus; Yates, John T. Jr.; Jung, Moon-Chul; Levy, Jeremy; Ahner, Joachim

    2005-04-01

    A multiple-tip ultrahigh vacuum (UHV) scanning tunneling microscope (MTSTM) with a scanning electron microscope (SEM) for imaging and molecular-beam epitaxy growth capabilities has been developed. This instrument (nanoworkbench) is used to perform four-point probe conductivity measurements at {mu}m spatial dimension. The system is composed of four chambers, the multiple-tip STM/SEM chamber, a surface analysis and preparation chamber, a molecular-beam epitaxy chamber, and a load-lock chamber for fast transfer of samples and probes. The four chambers are interconnected by a unique transfer system based on a sample box with integrated heating and temperature-measuring capabilities. We demonstrate the operation and the performance of the nanoworkbench with STM imaging on graphite and with four-point-probe conductivity measurements on a silicon-on-insulator (SOI) crystal. The creation of a local FET, whose dimension and localization are, respectively, determined by the spacing between the probes and their position on the SOI surface, is demonstrated.

  5. EC-STM study of the initial stages of the electrochemical Au(1 1 1)-Cd alloy formation

    NASA Astrophysics Data System (ADS)

    Schlaup, Christian; Horch, Sebastian

    2015-02-01

    We have studied the formation of an Au(1 1 1)-Cd alloy in a H2SO4 electrolyte by means of electrochemical STM (EC-STM). To this end, we first characterized the underpotential deposited (upd) Cd overlayers on Au(1 1 1) electrodes. We confirmed the existence of two upd phases on the reconstructed Au(1 1 1) surface, of which the first can be described with a (4 ×√{ 3}) unit cell and the second one with a (3 ×√{ 3}) unit cell in coexistence with a (2 ×√{ 3}) unit cell. At more negative potentials, an alloy with the Au(1 1 1) substrate is formed. In order to obtain a deeper insight into the alloying process, we had to avoid further Cd deposition at these potentials. This was achieved by exchanging the electrolyte after Cd deposition for a Cd-free solution under potential control. We found that the Au-Cd alloy exhibits an atomic structure with a close to square unit cell and locally interferes with the pattern of the Au(1 1 1) "herringbone" reconstruction. This Au-Cd alloy increases the overpotential for the hydrogen evolution reaction (HER) by about 130 mV.

  6. In situ electrochemical STM study of platinum nanodot arrays on highly oriented pyrolythic graphite prepared by electron beam lithography

    NASA Astrophysics Data System (ADS)

    Foelske-Schmitz, A.; Peitz, A.; Guzenko, V. A.; Weingarth, D.; Scherer, G. G.; Wokaun, A.; Kötz, R.

    2012-12-01

    Model electrodes consisting of platinum dots with a mean diameter of (30 ± 5) nm and heights of 3-5 nm upon highly oriented pyrolytic graphite (HOPG) were prepared by electron beam lithography and subsequent sputtering. The Pt nanodot arrays were stable during scanning tunnelling microscopy (STM) measurements in air and in sulphuric acid electrolyte, indicating the presence of "anchors", immobilising the dots on the HOPG surface. Electrochemical STM was used to visualise potential induced Pt, carbon and Pt-influenced carbon corrosion in situ in 0.5 M sulphuric acid under ambient conditions. Potentiostatic hold experiments show that the Pt dots start to disappear at electrode potentials of E > 1.4 V vs. SHE. With increasing time and potential a hole pattern congruent to the original dot pattern appears on the HOPG basal planes. Corrosion and peeling of the HOPG substrate could also be followed in situ. Dissolution of Pt dots appears to be accelerated for potential cycling experiments compared to the potential hold statistics.

  7. STM/STS Study of Surface Modification Effect on Bandgap Structure of Ti2C with -OH, -F, and -H

    NASA Astrophysics Data System (ADS)

    Jung, Seong Jun; Lai, Shen; Jeong, Taehwan; Lee, Sungjoo; Song, Young Jae

    In this presentation, we present Scanning Tunneling Microscopy (STM) and Spectroscopy (STS) study of bandgap structures of surface-modified Ti2C with -OH, -F, and -O in atomic scale. Since the discovery of new two dimensional (2D) materials like graphene, various 2D materials including transition metal dichalcogenide (TMD) have been intensively investigated. There are, however, still scientific issues to apply them to the device fabrications for controlling the appropriate bandgap structure with high field effect mobility. Recently another 2D materials of transition metal carbide (TMC), Ti2CTx with modifiable surface group Tx(-OH, -F, and -O) was suggested. [S. Lai et. al, Nanoscale (2015), DOI: 10.1039/C5NR06513E]. This 2D material shows that the mobility at room temperature is less sensitive to the measured transport bandgap, which can imply that Ti2CTx can be a strong candidate of 2D TMC for application to the future electronic devices. Surface modification on the electronic structure of Ti2C by -OH, -F, and -O is, therefore, investigated by STM and STS in atomic scale. More scientific results will be further discussed in the presentation. This research was supported by Basic Science Research Program through the National Research Foundation of Korea funded by the Korean government (Grant Numbers: 2015R1A1A1A05027585, 2011­0030046, IBS- R011­D1, 2014M3C1A3053024 and 2015M3A7B4050455).

  8. High resolution electrochemical STM : new structural results for underpotentially deposited Cu on Au(111) in acid sulfate solution.

    SciTech Connect

    Sieradzki, Karl; Vasiljevic, Natasa; Viyannalage, L.K.T.; Dimitrov, Nikolay

    2007-09-01

    Adsorption of sulfate assists Cu monolayer underpotential deposition (upd) on Au(111) in a unique way, rendering two distinct structural stages: (i) formation of a low-density Cu phase at coverage of 2/3 ML known as the ({radical}3 x {radical}3) R30{sup o} or honeycomb phase; (ii) formation of a complete monolayer, i.e., Cu-(1 x 1) phase pseudomorphic with respect to underlying Au(111) substrate. In this paper we present new structural in situ scanning tunneling microscopy (STM) results for this system. We show and discuss the STM imaging of the copper honeycomb superstructure probed underneath the co-adsorbed ({radical}3 x {radical}3)R30{sup o} sulfate adlayer in the low-density phase. High resolution imaging during the phase transition from the low to high density copper phase unambiguously shows the existence of an ordered sulfate structure p(2 x 2) on the pseudomorphic Cu-(1 x 1) layer. The new structure is seen during the co-existence of two copper phases as well as upon completion of the Cu-(1 x 1) monolayer. While supported by earlier chronocoulometric measurements in the same system, the new structural results raise questions that need to be addressed in a future work.

  9. Development of a toolbox of organic synthetic reactions that can be induced on individual molecules by STM

    SciTech Connect

    Ludwig Bartels

    2003-09-25

    OAK B262 Final Report DOE Grant No.: DE-FG03-01ER15263 ''Development of a toolbox of organic synthetic reactions that can be induced on individual molecules by STM'' Abstract Bommisetty V. Rao, Ki-Young Kwon, Robert Perry, Luke Nysen, Gregory Pavin, Qibin Zhang, Casey Dugger and Ludwig Bartels University of California at Riverside, Pierce Hall, Riverside, CA92521, email: Ludwig.Bartels@ucr.edu The key scientific objective of this project is the development of a set of reliable techniques for the addressal of specific bonds of individual molecules in order to assemble functional molecules on a metal surface at single-atom precision. Success in this direction will open up a conceptually novel route to single molecule chemistry, which can provide its products at any desired surface location without involving any lithographic steps at all. In the course of this project a number of halo-substituted aryls and alkyls where investigated with special concern to two properties: clean deposition of the reactants from the gas phase on metallic surfaces and STM-based addressability of individual substituents of them. In order to prevent contamination of the sample by deposition of solvent residue, a special depositions source was developed that uses a skimmed molecular beam. Exemplary substances studied were 1,3-iodobromobenzene (IBB), 3 bromopropionitrile (BPN) and 4,4'-dibromobiphenyl (DBB). In STM-induced reactions, IBB shows concerted activation of both halogens, which does not allow the individual addressal of one bond at a time. The concept of individual addressabilities of bonds in bi-substituted molecule was confirmed by use of BPN. This reactant is, however, strongly bound to the substrate and, hence, not very suitable for the assembly of larger aggregates, even if the nitrile group could be activated. We found individual activation of one of the bromines of DBB. This molecule lies flat on the surface and it is a promising candidate for the assembly of larger molecular

  10. In Situ Studies of Surface Mobility on Noble Metal Model Catalysts Using STM and XPS at Ambient Pressure

    SciTech Connect

    Butcher, Derek Robert

    2010-06-01

    High Pressure Scanning Tunneling Microscopy (HP-STM) and Ambient Pressure X-ray Photoelectron Spectroscopy were used to study the structural properties and catalytic behavior of noble metal surfaces at high pressure. HP-STM was used to study the structural rearrangement of the top most atomic surface layer of the metal surfaces in response to changes in gas pressure and reactive conditions. AP-XPS was applied to single crystal and nanoparticle systems to monitor changes in the chemical composition of the surface layer in response to changing gas conditions. STM studies on the Pt(100) crystal face showed the lifting of the Pt(100)-hex surface reconstruction in the presence of CO, H2, and Benzene. The gas adsorption and subsequent charge transfer relieves the surface strain caused by the low coordination number of the (100) surface atoms allowing the formation of a (1 x 1) surface structure commensurate with the bulk terminated crystal structure. The surface phase change causes a transformation of the surface layer from hexagonal packing geometry to a four-fold symmetric surface which is rich in atomic defects. Lifting the hex reconstruction at room temperature resulted in a surface structure decorated with 2-3 nm Pt adatom islands with a high density of step edge sites. Annealing the surface at a modest temperature (150 C) in the presence of a high pressure of CO or H2 increased the surface diffusion of the Pt atoms causing the adatom islands to aggregate reducing the surface concentration of low coordination defect sites. Ethylene hydrogenation was studied on the Pt(100) surface using HP-STM. At low pressure, the lifting of the hex reconstruction was observed in the STM images. Increasing the ethylene pressure to 1 Torr, was found to regenerate the hexagonally symmetric reconstructed phase. At room temperature ethylene undergoes a structural rearrangement to form ethylidyne. Ethylidyne preferentially binds at the three-fold hollow sites, which

  11. Yeast-based screening to identify modulators of G-protein signaling using uncontrolled cell division cycle by overexpression of Stm1.

    PubMed

    Chung, Kyung-Sook; Won, Misun; Lee, Jung-Joon; Ahn, Jiwon; Hoe, Kwang-Lae; Kim, Dong-Uk; Song, Kyung-Bin; Yoo, Hyang-Sook

    2007-05-01

    Stm1, a G-protein coupled receptor, which senses nutritional state drives cells to stop the proliferative cell cycle and enter meiosis under nutritionally deficient conditions in Schizosaccharomyces pombe. It was shown that overexpression of Stm1 led growth inhibition and uncontrolled mitotic haploidization presumably by the premature initiation of mitosis. Sty1 and Gpa2 seem to play important roles for Stm1 to deliver starvation signal to induce downstream function. Based on the observation that conversion of diploid to haploid by overexpression of Stm1 can be easily detected as pink or red colonies in the media containing low adenine, HTS drug screening system to identify modulators of GPCR was established and tested using 413 compounds. Four very potent modulators of GPCR including Biochanin A, which possess strong inhibitory activity against uncontrolled cell division, were identified in this screening. This study provides the yeast-based platform that allows robust cellular assays to identify novel modulators of G-protein signaling and MAP kinase pathway. PMID:17346842

  12. Fermionic scenario for the destruction of superconductivity in ultrathin MoC films evidenced by STM measurements

    NASA Astrophysics Data System (ADS)

    Szabó, P.; Samuely, T.; Hašková, V.; Kačmarčík, J.; Žemlička, M.; Grajcar, M.; Rodrigo, J. G.; Samuely, P.

    2016-01-01

    We use sub-Kelvin scanning tunneling spectroscopy to investigate the suppression of superconductivity in homogeneously disordered ultrathin MoC films. We observe that the superconducting state remains spatially homogeneous even on the films of 3-nm thickness. The vortex imaging suggests the global phase coherence in our films. Upon decreasing thickness, when the superconducting transition drops from 8.5 to 1.2 K, the superconducting energy gap Δ follows Tc perfectly. All this is pointing to a two-stage fermionic scenario of the superconductor-insulator transition (SIT) via a metallic state as an alternative to the direct bosonic SIT scenario with a Cooper-pair insulating state evidenced by the past decade STM experiments.

  13. Computing Ro in a population with heterogeneity in sexual activity and proportionate mixing using a STM-solver

    NASA Astrophysics Data System (ADS)

    Gutierrez A., Natalia A.

    2014-06-01

    A model to determinate the reproductive basic number, detonated Ro, for the case of population with heterogeneity in sexual activity and proportionate mixing is solved using computer algebra and SMT solvers. Specifically Maple and Z3 were used. The code for the solution of the model was written in Z3-Python, but it can also be played by Z3-SMT-Lib. Ro represents an algebraic synthesis of every epidemiological parameter. Numerical simulations were done to prove the effectiveness of the model and the code. The algebraic structure of Ro suggests the possible control measurements that should be implemented to avoid the propagation of the sexual transmitted diseases. The obtained results are important on the computational epidemiology field. As a future investigation, it is suggested to apply the STM solvers to analyze models for other kinds of epidemic diseases.

  14. Characteristics, finite element analysis, test description, and preliminary test results of the STM4-120 kinematic Stirling engine

    SciTech Connect

    Linker, K.L.; Rawlinson, K.S.; Smith, G.

    1991-10-01

    The Department of Energy's Solar Thermal Program has as one of its program elements the development and evaluation of conversion device technologies applicable to dish-electric systems. The primary research and development combines a conversion device (heat engine), solar receiver, and generator mounted at the focus of a parabolic dish concentrator. The Stirling-cycle heat engine was identified as the conversion device for dish-electric with the most potential for meeting the program's goals for efficiency, reliability, and installed cost. To advance the technology toward commercialization, Sandia National Laboratories has acquired a Stirling Thermal Motors, Inc., kinematic Stirling engine, STM4-120, for evaluation. The engine is being bench-tested at Sandia's Engine Test Facility and will be combined later with a solar receiver for on-sun evaluation. This report presents the engine characteristics, finite element analyses of critical engine components, test system layout, instrumentation, and preliminary performance results from the bench test.

  15. Intermolecular vs molecule–substrate interactions: A combined STM and theoretical study of supramolecular phases on graphene/Ru(0001)

    PubMed Central

    Roos, Michael; Uhl, Benedikt; Künzel, Daniela; Hoster, Harry E; Groß, Axel

    2011-01-01

    Summary The competition between intermolecular interactions and long-range lateral variations in the substrate–adsorbate interaction was studied by scanning tunnelling microscopy (STM) and force field based calculations, by comparing the phase formation of (sub-) monolayers of the organic molecules (i) 2-phenyl-4,6-bis(6-(pyridin-3-yl)-4-(pyridin-3-yl)pyridin-2-yl)pyrimidine (3,3'-BTP) and (ii) 3,4,9,10-perylene tetracarboxylic-dianhydride (PTCDA) on graphene/Ru(0001). For PTCDA adsorption, a 2D adlayer phase was formed, which extended over large areas, while for 3,3'-BTP adsorption linear or ring like structures were formed, which exclusively populated the areas between the maxima of the moiré structure of the buckled graphene layer. The consequences for the competing intermolecular interactions and corrugation in the adsorption potential are discussed and compared with the theoretical results. PMID:22003444

  16. Intermolecular vs molecule-substrate interactions: A combined STM and theoretical study of supramolecular phases on graphene/Ru(0001).

    PubMed

    Roos, Michael; Uhl, Benedikt; Künzel, Daniela; Hoster, Harry E; Groß, Axel; Behm, R Jürgen

    2011-01-01

    The competition between intermolecular interactions and long-range lateral variations in the substrate-adsorbate interaction was studied by scanning tunnelling microscopy (STM) and force field based calculations, by comparing the phase formation of (sub-) monolayers of the organic molecules (i) 2-phenyl-4,6-bis(6-(pyridin-3-yl)-4-(pyridin-3-yl)pyridin-2-yl)pyrimidine (3,3'-BTP) and (ii) 3,4,9,10-perylene tetracarboxylic-dianhydride (PTCDA) on graphene/Ru(0001). For PTCDA adsorption, a 2D adlayer phase was formed, which extended over large areas, while for 3,3'-BTP adsorption linear or ring like structures were formed, which exclusively populated the areas between the maxima of the moiré structure of the buckled graphene layer. The consequences for the competing intermolecular interactions and corrugation in the adsorption potential are discussed and compared with the theoretical results. PMID:22003444

  17. Nanoscale phosphorous atom arrays created using STM for the fabricaton of a silicon-based quantum computer

    NASA Astrophysics Data System (ADS)

    O'Brien, J. L.; Schofield, S. R.; Simmons, M. Y.; Clark, Robert G.; Dzurak, Andrew S.; Curson, N. J.; Kane, Bruce E.; McAlpine, N. S.; Hawley, Marilyn E.; Brown, Geoffrey W.

    2001-11-01

    Quantum computers offer the promise of formidable computational power for certain tasks. Of the various possible physical implementations of such a device, silicon based architectures are attractive for their scalability and ease of integration with existing silicon technology. These designs use either the electron or nuclear spin state of single donor atoms to store quantum information. Here we describe a strategy to fabricate an array of single phosphorus atoms in silicon for the construction of such a silicon based quantum computer. We demonstrate the controlled placement of single phosphorus bearing molecules on a silicon surface. This has been achieved by patterning a hydrogen mono-layer resist with a scanning tunneling microscope (STM) tip and exposing the patterned surface to phosphine (PH3) molecules. We also describe preliminary studies into a process to incorporate these surface phosphorus atoms into the silicon crystal at the array sites.

  18. Comparing XMCD and DFT with STM spin excitation spectroscopy for Fe and Co adatoms on Cu2N /Cu (100 )

    NASA Astrophysics Data System (ADS)

    Etzkorn, M.; Hirjibehedin, C. F.; Lehnert, A.; Ouazi, S.; Rusponi, S.; Stepanow, S.; Gambardella, P.; Tieg, C.; Thakur, P.; Lichtenstein, A. I.; Shick, A. B.; Loth, S.; Heinrich, A. J.; Brune, H.

    2015-11-01

    We report on the magnetic properties of Fe and Co adatoms on a Cu2N /Cu(100 ) -c (2 ×2 ) surface investigated by x-ray magnetic dichroism measurements and density functional theory (DFT) calculations including the local coulomb interaction. We compare these results with properties formerly deduced from STM spin excitation spectroscopy (SES) performed on the individual adatoms. In particular we focus on the values of the local magnetic moments determined by XMCD compared to the expectation values derived from the description of the SES data. The angular dependence of the projected magnetic moments along the magnetic field, as measured by XMCD, can be understood on the basis of the SES Hamiltonian. In agreement with DFT, the XMCD measurements show large orbital contributions to the total magnetic moment for both magnetic adatoms.

  19. Analysis of an Ordered, Comprehensive STM Mutant Library in Infectious Borrelia burgdorferi: Insights into the Genes Required for Mouse Infectivity

    PubMed Central

    Lin, Tao; Gao, Lihui; Zhang, Chuhua; Odeh, Evelyn; Jacobs, Mary B.; Coutte, Loïc; Chaconas, George; Philipp, Mario T.; Norris, Steven J.

    2012-01-01

    The identification of genes important in the pathogenesis of Lyme disease Borrelia has been hampered by exceedingly low transformation rates in low-passage, infectious organisms. Using the infectious, moderately transformable B. burgdorferi derivative 5A18NP1 and signature-tagged versions of the Himar1 transposon vector pGKT, we have constructed a defined transposon library for the efficient genome-wide investigation of genes required for wild-type pathogenesis, in vitro growth, physiology, morphology, and plasmid replication. To facilitate analysis, the insertion sites of 4,479 transposon mutants were determined by sequencing. The transposon insertions were widely distributed across the entire B. burgdorferi genome, with an average of 2.68 unique insertion sites per kb DNA. The 10 linear plasmids and 9 circular plasmids had insertions in 33 to 100 percent of their predicted genes. In contrast, only 35% of genes in the 910 kb linear chromosome had incapacitating insertions; therefore, the remaining 601 chromosomal genes may represent essential gene candidates. In initial signature-tagged mutagenesis (STM) analyses, 434 mutants were examined at multiple tissue sites for infectivity in mice using a semi-quantitative, Luminex-based DNA detection method. Examples of genes found to be important in mouse infectivity included those involved in motility, chemotaxis, the phosphoenolpyruvate phosphotransferase system, and other transporters, as well as putative plasmid maintenance genes. Availability of this ordered STM library and a high-throughput screening method is expected to lead to efficient assessment of the roles of B. burgdorferi genes in the infectious cycle and pathogenesis of Lyme disease. PMID:23133514

  20. Understanding the STM images of epitaxial graphene on a reconstructed 6H-SiC(0001) surface: the role of tip-induced mechanical distortion of graphene.

    PubMed

    Morán-Meza, José A; Cousty, Jacques; Lubin, Christophe; Thoyer, François

    2016-06-01

    Epitaxial graphene (EG) grown on an annealed 6H-SiC(0001) surface has been studied under ultra-high vacuum (UHV) conditions by using a combined dynamic-scanning tunneling microscope/frequency modulation-atomic force microscope (dynamic-STM/FM-AFM) platform based on a qPlus probe. STM and AFM images independently recorded present the same hexagonal lattice of bumps with a 1.9 nm lattice period, which agrees with density functional theory (DFT) calculations and experimental results previously reported, attributed to the (6 × 6) quasi-cell associated with the 6H-SiC(0001) reconstruction. However, topographic bumps in AFM images and maxima in the simultaneously recorded mean-tunneling-current map do not overlap but appear to be spaced typically by about 1 nm along the [11] direction of the (6 × 6) quasi-cell. A similar shift is observed between the position of maxima in dynamic-STM images and those in the simultaneously recorded frequency shift map. The origin of these shifts is discussed in terms of electronic coupling variations between the local density of states (LDOS) of EG and the LDOS of the buffer layer amplified by mechanical distortions of EG induced by the STM or AFM tip. Therefore, a constant current STM image of EG on a reconstructed 6H-SiC(0001) surface does not reproduce its real topography but corresponds to the measured LDOS modulations, which depend on the variable tip-induced graphene distortion within the (6 × 6) quasi-cell. PMID:27165124

  1. Road-Mapping the Way Forward for Sentinel-3 STM SAR-Mode Waveform Retracking over Water Surfaces

    NASA Astrophysics Data System (ADS)

    Benveniste, Jérôme; Cotton, David; Dinardo, Salvatore; Lucas, Bruno Manuel; Martin-Puig, Cristina; Ray, Chris; Clarizia, Maria Paola; Gommenginger, Christine

    2013-04-01

    . However, since the ultimate goal of the SAMOSA project is to deliver to the Sentinel-3 Surface Topography Mission Product and Algorithm Development (S-3 STM PAD) a Detailed Processing Model of a SAR ocean waveform re-tracker based on the best SAMOSA model to operationally re-track Sentinel-3 STM SAR-Mode L1b waveforms, the need for the full mathematical complexity of the SAMOSA2 model was re-evaluated. With this in mind, the SAMOSA team assessed a number of simplifications that can transform the SAMOSA2 model into a lighter, computationally more efficient, purely analytical formulation for input into the SAR re-tracker scheme for the Sentinel-3 STM PAD. The simplifications that have been considered involve the omission in the model of second order effects such as non-linear terms in the model, ocean surface skewness, and electromagnetic bias. Their impact has been evaluated. This SAMOSA3 model has the advantage to be a pure analytical solution, expressed by means of modified Bessel functions of first and second kind and returns no singularities for the full range of the gate bins. An extensive validation was performed. First equivalence between SAMOSA3, SAMOSA2 & SAMOSA1 models was confirmed and then a a sensitivity study on the input parameters and the re-tracking approach was carried out. Finally, the SAMOSA3 Model and re-tracker was applied to Cryosat-2 L1B SAR waveforms and the performance was studied as well as the sensitivity to mispointing. Two areas were chosen as representative of the high and low ocean dynamics regions, respectively the South Norwegian Sea and the Caspian Sea. Finally the SAMOSA3 output was validated against in situ wave buoy measurements. An overview of these results will be shown here.

  2. Inferring effective interactions from the local density of states: application to STM data from Bi_2Sr_2CaCu_2O_8 delta

    SciTech Connect

    Jamei, R.

    2010-04-06

    While the influence of impurities on the local density of states (LDOS) in a metal is notoriously non-local due to interference effects, low order moments of the LDOS in general can be shown to depend only on the local structure of the Hamiltonian. Specifically, we show that an analysis of the spatial variations of these moments permits one to 'work backwards' from scanning tunneling microscopy (STM) data to infer the local structure of the underlying effective Hamiltonian. Applying this analysis to STM data from the high temperature superconductor, Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}, we find that the variations of the electro-chemical potential are remarkably small (i.e., the disorder is, in a sense, weak) but that there are large variations in the local magnitude of the d-wave gap parameter.

  3. Simultaneous non-contact atomic force microscopy (nc-AFM)/STM imaging and force spectroscopy of Si(1 0 0)(2×1) with small oscillation amplitudes

    NASA Astrophysics Data System (ADS)

    Özer, H. Özgür; Atabak, Mehrdad; Ellialtıoğlu, Recai M.; Oral, Ahmet

    2002-03-01

    Si(1 0 0)(2×1) surface is imaged using a new non-contact atomic force microscopy (nc-AFM)/STM with sub-Ångström oscillation amplitudes using stiff tungsten levers. Simultaneous force gradient and STM images of individual dimers and atomic scale defects are obtained. We measured force-distance ( f- d) curves with different tips. Some of the tips show long force interactions, whereas some others resolve short-range interatomic force interactions. We observed that the tips showing short-range force interaction give atomic resolution in force gradient scans. This result suggests that short-range force interactions are responsible for atomic resolution in nc-AFM.

  4. Design, testing, and commercialization plans for the SAIC/STM 20 kW{sub e} solar dish/Stirling system

    SciTech Connect

    Beninga, K.J.; Davenport, R.L.; Johansson, S.N.

    1995-12-31

    As a part of the US Department of Energy`s (DOE) Utility-Scale Joint-Venture Program, Science Applications International Corporation (SAIC) and Stirling Thermal Motors (STM) have teamed to produce a solar dish/Stirling system for utility electricity generation. The 90 m{sup 2} dish concentrator consists of 16 stretched membrane mirror facets on a truss structure with an azimuth/elevation gear drive. The design modifies a faceted stretched membrane dish design developed previously by SAIC and WGA, Inc. in order to simplify the structure and reduce manufacturing costs, The Stirling engine used in the system is the STM 4-120 kinematic Stirling engine. It features variable swash plate control and a direct absorption solar receiver with hydrogen as the operating fluid. A prototype dish/Stirling system has been installed at a test site near Golden, Colorado and is now undergoing tests. The optical and thermal performance of the dish is being characterized using a Coldwater calorimeter and the optical Beam Characterization System (BCS) developed by Sandia National Labs in Albuquerque, New Mexico. After completion of the dish characterization tests, the STM engine will be installed on the dish and system power generation and efficiency will be measured. This paper presents a summary of the SAIC/STM dish/Stirling system design and gives results from initial testing of the system. Also described are SAIC`s plans for manufacturing and commercialization of the dish/Stirling system to utilities and other markets in the US and abroad.

  5. New sub-family of lysozyme-like proteins shows no catalytic activity: crystallographic and biochemical study of STM3605 protein from Salmonella Typhimurium

    SciTech Connect

    Michalska, Karolina; Brown, Roslyn N.; Li, Hui; Jedrzejczak, Robert; Niemann, George; Heffron, Fred; Cort, John R.; Adkins, Joshua N.; Babnigg, Gyorgy; Joachimiak, Andrzej

    2013-03-01

    Phage viruses that infect prokaryotes integrate their genome into the host chromosome; thus, microbial genomes typically contain genetic remnants of both recent and ancient phage infections. Often phage genes occur in clusters of atypical G+C content that reflect integration of the foreign DNA. However, some phage genes occur in isolation without other phage gene neighbors, probably resulting from horizontal gene transfer. In these cases, the phage gene product is unlikely to function as a component of a mature phage particle, and instead may have been co-opted by the host for its own benefit. The product of one such gene from Salmonella enterica serovar Typhimurium, STM3605, encodes a protein with modest sequence similarity to phage-like lysozyme (N-acetylmuramidase) but appears to lack essential catalytic residues that are strictly conserved in all lysozymes. Close homologs in other bacteria share this characteristic. The structure of the STM3605 protein was characterized by X-ray crystallography, and functional assays showed that it is a stable, folded protein whose structure closely resembles lysozyme. However, this protein is unlikely to hydrolyze peptidoglycan. Instead, STM3605 is presumed to have evolved an alternative function because it shows some lytic activity and partitions to micelles.

  6. Self-assembled monolayer of o-aminothiophenol on Fe(1 1 0) surface: a combined study by electrochemistry, in situ STM, and molecular simulations

    NASA Astrophysics Data System (ADS)

    Kong, De-Sheng; Yuan, Shi-Ling; Sun, Yu-Xi; Yu, Zhang-Yu

    2004-12-01

    Electrochemical measurements, in situ scanning tunneling microscopy (STM) observation, and molecular mechanics (MM) simulations were performed to study the physiochemical properties such as the corrosion-inhibition effect and the optimal packing structure of o-aminothiophenol (OATP) self-assembled monolayer (SAM) formed on Fe(1 1 0) surface in 0.1 M NaClO 4 solution. The formation of OATP SAMs drastically depressed the Faradaic processes at the Fe(1 1 0) surface and reduced the electrical double-layer capacitance at the electrode/electrolyte interface, revealing the anticorrosion property and the blocking behavior of OATP adlayers. Two-dimensional ordered molecular arrays of OATP on Fe(1 1 0) surface with a p(2 × 2) commensurate structure were observed by STM measurements. MM calculations showed that the p(2 × 2) packing pattern is indeed the preferable structure for OATP molecules adsorbed on Fe(1 1 0), in accordance with STM experiments. The OATP SAM on Fe(1 1 0) is ≈0.50 nm in thickness and with a dielectric constant of ˜7.0.

  7. Transmission measurement based on STM observation to detect the penetration depth of low-energy heavy ions in botanic samples

    NASA Technical Reports Server (NTRS)

    Liu, Feng; Wang, Yugang; Xue, Jianming; Wang, Sixue; Du, Guanhua; Zhao, Weijiang

    2003-01-01

    The penetration depth of low-energy heavy ions in botanic samples was detected with a new transmission measurement. In the measurement, highly oriented pyrolytic graphite (HOPG) pieces were placed behind the botanic samples with certain thickness. During the irradiation of heavy ions with energy of tens of keV, the energetic particles transmitted from those samples were received by the HOPG pieces. After irradiation, scanning tunneling microscope (STM) was applied to observe protrusion-like damage induced by these transmitted ions on the surface of the HOPG. The statistical average number density of protrusions and the minimum transmission rate of the low-energy heavy ions can be obtained. The detection efficiency of the new method for low-energy heavy ions was about 0.1-1 and the background in the measurement can be reduced to as low as 1.0 x 10(8) protrusions/cm2. With this method, the penetration depth of the energetic particles was detected to be no less than 60 micrometers in kidney bean slices when the slices were irradiated by 100 keVAr+ ion at the fluence of 5 x 10(16) ions/cm2. c2002 Elsevier Science Ltd. All rights reserved.

  8. Characterizing the electronic ground states of single-layer NbSe2 via STM/STS

    NASA Astrophysics Data System (ADS)

    Chen, Yi; Ugeda, Miguel; Bradley, Aaron; Zhang, Yi; Onishi, Seita; Ruan, Wei; Ojeda-Aristizabal, Claudia; Ryu, Hyejin; Edmonds, Mark; Tsai, Hsin-Zon; Riss, Alexander; Mo, Sung-Kwan; Lee, Dunghai; Zettl, Alex; Hussain, Zahid; Shen, Zhi-Xun; Crommie, Michael

    Layered transition metal dichalcogenides (TMDs) are ideal systems for exploring collective electronic phases such as charge density wave (CDW) order and superconductivity. In bulk NbSe2 the CDW sets in at TCDW = 33K and superconductivity sets in at Tc = 7.2K. Below Tc these electronic states coexist but their microscopic formation mechanisms remain controversial. Here we present an electronic characterization study of a single 2D layer of NbSe2 by means of low temperature scanning tunneling microscopy/spectroscopy (STM/STS), angle-resolved photoemission spectroscopy (ARPES), and electrical transport measurements. We demonstrate that the CDW order remains intact in 2D and exhibits a robust 3 x 3 superlattice. Superconductivity also still occurs but its onset is depressed to 1.6K. Our STS measurements at 5K reveal a CDW gap of Δ = 4 meV at the Fermi energy, which is accessible via STS due to the removal of bands crossing the Fermi surface in the 2D limit. Our observations are consistent with the predicted simplified (compared to bulk) electronic structure of single-layer NbSe2, thus providing new insight into CDW formation and superconductivity in this model strongly-correlated system.

  9. Observation of van Hove singularity and quasiparticle interference in KFe2 As2 superconductors revealed by STM/STS measurements

    NASA Astrophysics Data System (ADS)

    Wen, Hai-Hu; Fang, Delong; Du, Zengyi; Wang, Zhenyu; Yang, Huan; Ding, Xiaxin

    2015-03-01

    We have conducted STM/STS investigations on the KFe2As2 superconducting single crystals down to 0.45 K under magnetic field. Clear electronic standing waves have been observed allowing us to investigate the quasiparticle interference (QPI). Interestingly we observed a sharp peak of local density of states (LDOS) near the Fermi energy showing evidence of strongly enhanced DOS both below and above Tc. We demonstrate that this is induced by a van Hove singularity with the saddle point locating only 4 meV below the Fermi energy. Below Tc it is found that only 20% of the normal state DOS is gapped away by superconductivity, with the major part of DOS due to VHS ungapped. Combing with the ARPES data, we find that the VHS points locate on the (π,0) point, which gives strong constraint on the gap function and pairing mechanism. In the mixed state we clearly observed the mixture of vortices and the standing waves due to quasiparticle interference, giving support to above picture. In collaboration with X. Shi, P. Richard, T. Qian and H. Ding et al. in Institute of Physics, CAS.

  10. Direct interactions between metal nanoparticles and support: STM studies of Pd on TiO 2(1 1 0)

    NASA Astrophysics Data System (ADS)

    Bowker, Michael; Fourré, Elodie

    2008-05-01

    We have fabricated ultra-nanoparticulate model catalysts of Pd on TiO 2(1 1 0) using metal vapour deposition (MVD) to form particles in the size range 1-50 nm, which can be imaged at very high spatial resolution (and in some cases at atomic resolution) using scanning tunnelling microscopy (STM). Using these methods we are able to identify the atomic level mechanism responsible for certain phenomena in catalysis, for which molecular level models have previously been proposed from macroscopic measurements. In this paper we address two such phenomena, namely spillover and the so-called strong metal-support interaction (SMSI) effect. Oxygen spillover from Pd particles to the titania support occurs due to the fast adsorption of oxygen on Pd compared with titania, and is driven by reaction with Ti 3+ ions in the vicinity of the particles. The SMSI state is identified at atomic resolution as being due to the appearance of Ti at the surface of the Pd particles. These Ti layers are partially oxidised and form very well defined structures of two main types—a rectangular lattice and hexagonal unit cells of large dimension. These layers passivate the surface for the adsorption of CO.

  11. A combined STM and SPA-LEED study of the "explosive" nucleation and collective diffusion in Pb/Si(111)

    NASA Astrophysics Data System (ADS)

    Hattab, H.; Hupalo, M.; Hershberger, M. T.; Horn von Hoegen, M.; Tringides, M. C.

    2016-04-01

    A novel type of very fast nucleation was recently found in Pb/Si(111) with 4- to 7-layer high islands becoming crystalline in an "explosive" way, when the Pb deposited amount in the wetting layer is compressed to θc ~ 1.22 ML, well above the metallic Pb(111) density. This "explosive" nucleation is very different from classical nucleation when island growth is more gradual and islands grow in size by single adatom aggregation [8]. In order to identify the key parameters that control the nucleation we used scanning tunneling microscopy (STM) and spot profile analysis low energy electron diffraction (SPA-LEED). It was found that the number and duration of steps in iterative deposition used to approach θc and the flux rate have dramatic effects on the crystallization process. Larger depositions over shorter times induce greater spatial coverage fluctuations, so local areas can reach the critical coverage θc easier. This can trigger the collective motion of the wetting layer from far away to build the Pb islands "explosively". The SPA-LEED experiments show that even low flux experiments in iterative deposition experiments can trigger transfer of material to the superstable 7-layer islands, as seen from the stronger satellite rings close to the (00) spot.

  12. Characteristics, finite element analysis, test description, and preliminary test results of the STM4-120 kinematic Stirling engine

    SciTech Connect

    Linker, K.L.; Rawlinson, K.S.; Smith, G.

    1991-10-01

    The Department of Energy`s Solar Thermal Program has as one of its program elements the development and evaluation of conversion device technologies applicable to dish-electric systems. The primary research and development combines a conversion device (heat engine), solar receiver, and generator mounted at the focus of a parabolic dish concentrator. The Stirling-cycle heat engine was identified as the conversion device for dish-electric with the most potential for meeting the program`s goals for efficiency, reliability, and installed cost. To advance the technology toward commercialization, Sandia National Laboratories has acquired a Stirling Thermal Motors, Inc., kinematic Stirling engine, STM4-120, for evaluation. The engine is being bench-tested at Sandia`s Engine Test Facility and will be combined later with a solar receiver for on-sun evaluation. This report presents the engine characteristics, finite element analyses of critical engine components, test system layout, instrumentation, and preliminary performance results from the bench test.

  13. Studies of Mn12-Ph Single Molecule Magnets by LT-STM and Modeling of Magnetic Stability Under Perturbation

    NASA Astrophysics Data System (ADS)

    Reaves, K.; Han, P.; Iwaya, K.; Hitosugi, T.; Packwood, D.; Katzgraber, H. G.; Zhao, H.; Dunbar, K. R.; Kim, K.; Teizer, W.

    2014-03-01

    We study Mn12O12(C6H5COO)16 (H2O)4 (Mn12-Ph) single-molecule magnets on a Cu(111) surface using low temperature scanning tunneling microscopy, LT-STM. We report the observation of Mn12-Ph in isolation and in thin films, deposited through vacuum spray deposition onto clean Cu(111). The local tunneling current observed within the molecular structure shows a strong bias voltage dependency, which is distinct from that of the Cu surface. Furthermore, we identify an internal inhomogeneity in the bias behavior within a single molecule. To further understand the stability of the magnetic properties of the molecules while on the surface, we develop a theoretical model to study the stability of the net magnetic moment under deformation of the spin-spin interaction graph. We develop a spin Hamiltonian-type model to predict magnetic moments that are intrinsically robust under random shape deformations to the spin-graph structure. This spin moment is shown to be a weak topological invariant for molecules with sufficiently many spin centers, approximately 20 to 50. We thank the WPI program for financial and research support.

  14. Atomically Precise Prediction of 2D Self-Assembly of Weakly Bonded Nanostructures: STM Insight into Concentration-Dependent Architectures.

    PubMed

    El Garah, Mohamed; Dianat, Arezoo; Cadeddu, Andrea; Gutierrez, Rafael; Cecchini, Marco; Cook, Timothy R; Ciesielski, Artur; Stang, Peter J; Cuniberti, Gianaurelio; Samorì, Paolo

    2016-01-20

    A joint experimental and computational study is reported on the concentration-dependant self-assembly of a flat C3 -symmetric molecule on a graphite surface. As a model system a tripodal molecule, 1,3,5-tris(pyridin-3-ylethynyl)benzene, has been chosen, which can adopt either C3h or Cs symmetry when planar, as a result of pyridyl rotation along the alkynyl spacers. Density functional theory (DFT) simulations of 2D nanopatterns with different surface coverage reveal that the molecule can generate different types of self-assembled motifs. The stability of fourteen 2D patterns and the influence of concentration are analyzed. It is found that ordered, densely packed monolayers and 2D porous networks are obtained at high and low concentrations, respectively. A concentration-dependent scanning tunneling microscopy (STM) investigation of this molecular self-assembly system at a solution/graphite interface reveals four supramolecular motifs, which are in perfect agreement with those predicted by simulations. Therefore, this DFT method represents a key step forward toward the atomically precise prediction of molecular self-assembly on surfaces and at interfaces. PMID:26596683

  15. In-situ X-ray diffraction and STM studies of bromide adsorption on Au(111) electrodes

    SciTech Connect

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

    1996-03-28

    The structure of bromide adlayers at the Au(111)-aqueous solution interface has been studied by in-situ surface X-ray scattering (SXS) and scanning tunneling microscopy (STM). Both techniques show the existence of a hexagonal close-packed adlayer phase above a critical potential and are in good quantitative agreement on the adlayer structural parameters. The bromide-bromide spacing changes continuously between 4.24 A at the critical potential and 4.03 A at a potential 300 mV more positive. The adlayer is rotated relative to the substrate by an angle dependent on potential and bromide concentration. The potential- dependent adlayer density corresponding to these structural results agrees well with Br surface excess densities from published electrochemical measurements. At very positive potentials a bromide-induced step-flow etching of the Au substrate is observed. The results are used to compare the different techniques and to discuss the adlayer structure, the phase behavior, and the halide-gold chemical interaction. 49 refs., 8 figs.

  16. STM verification of the reduction of the Young's modulus of CdS nanoparticles at smaller sizes

    NASA Astrophysics Data System (ADS)

    Hazarika, A.; Peretz, E.; Dikovsky, V.; Santra, P. K.; Shneck, R. Z.; Sarma, D. D.; Manassen, Y.

    2014-12-01

    We demonstrate the first STM evaluation of the Young's modulus (E) of nanoparticles (NPs) of different sizes. The sample deformation induced by tip-sample interaction has been determined using current-distance (I-Z) spectroscopy. As a result of tip-sample interaction, and the induced surface deformations, the I-z curves deviates from pure exponential dependence. Normally, in order to analyze the deformation quantitatively, the tip radius must be known. We show, that this necessity is eliminated by measuring the deformation on a substrate with a known Young's modulus (Au(111)) and estimating the tip radius, and afterwards, using the same tip (with a known radius) to measure the (unknown) Young's modulus of another sample (nanoparticles of CdS). The Young's modulus values found for 3 NP's samples of average diameters of 3.7, 6 and 7.5 nm, were E ~ 73%, 78% and 88% of the bulk value, respectively. These results are in a good agreement with the theoretically predicted reduction of the Young's modulus due to the changes in hydrostatic stresses which resulted from surface tension in nanoparticles with different sizes. Our calculation using third order elastic constants gives a reduction of E which scales linearly with 1/r (r is the NP's radius). This demonstrates the applicability of scanning tunneling spectroscopy for local mechanical characterization of nanoobjects. The method does not include a direct measurement of the tip-sample force but is rather based on the study of the relative elastic response.

  17. STM studies of an atomic-scale gate electrode formed by a single charged vacancy in GaAs

    NASA Astrophysics Data System (ADS)

    Lee, Donghun; Daughton, David; Gupta, Jay

    2009-03-01

    Electric-field control of spin-spin interactions at the atomic level is desirable for the realization of spintronics and spin-based quantum computation. Here we demonstrate the realization of an atomic-scale gate electrode formed by a single charged vacancy on the GaAs(110) surface[1]. We can position these vacancies with atomic precision using the tip of a home-built, low temperature STM. Tunneling spectroscopy of single Mn acceptors is used to quantify the electrostatic field as a function of distance from the vacancy. Single Mn acceptors are formed by substituting Mn adatoms for Ga atoms in the first layer of the p-GaAs(110) surface[2]. Depending on the distance, the in-gap resonance of single Mn acceptors can shift as much as 200meV. Our data indicate that the electrostatic field decays according to a screened Coulomb potential. The charge state of the vacancy can be switched to neutral, as evidenced by the Mn resonance returning to its unperturbed position. Reversible control of the local electric field as well as charged states of defects in semiconductors can open new insights such as realizing an atomic-scale gate control and studying spin-spin interactions in semiconductors. http://www.physics.ohio-state.edu/sim jgupta [1] D. Lee and J.A. Gupta (in preparation) [2] D. Kitchen et al., Nature 442, 436-439 (2006)

  18. 1,3,5-Benzenetribenzoic Acid on Cu(111) and Graphene/Cu(111): A Comparative STM Study

    PubMed Central

    2016-01-01

    The self-assembly of 1,3,5-benzenetribenzoic acid (BTB) molecules on both Cu(111) and epitaxial graphene grown on Cu(111) were studied by scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) under ultrahigh vacuum conditions. On Cu(111), the BTB molecules were found to mainly arrange in close-packed structures through H-bonding between the (partially) deprotonated carboxylic acid groups. In addition, porous structures formed by intact BTB molecules-and also based on H-bonding-were observed. On graphene grown on Cu(111) the BTB molecules mainly form porous structures accompanied by small patches of disordered close-packed structures. Upon annealing, BTB adsorbed on Cu(111) is fully deprotonated and arranges in the close-packed structure while in contrast on graphene/Cu(111) the porous network is exclusively formed. This shows that the molecular self-assembly behavior is highly dependent on the first substrate layer: one graphene layer is sufficient to considerably alter the interplay of molecule substrate and intermolecular interactions in favor of the latter interactions. PMID:27588158

  19. Vibrational spectra of nanowires measured using laser doppler vibrometry and STM studies of epitaxial graphene : an LDRD fellowship report.

    SciTech Connect

    Biedermann, Laura Butler

    2009-09-01

    , their vibration spectra was more extensively studied. The thermal vibration spectra of Ag{sub 2}Ga nanoneedles was measured under both ambient and low-vacuum conditions. The operational deflection shapes of the vibrating Ag{sub 2}Ga nanoneedles was also measured, allowing confirmation of the eigenmodes of vibration. The modulus of the crystalline nanoneedles was 84.3 {+-} 1.0 GPa. Gas damping is the dominate mechanism of energy loss for nanowires oscillating under ambient conditions. The measured quality factors, Q, of oscillation are in line with theoretical predictions of air damping in the free molecular gas damping regime. In the free molecular regime, Q{sub gas} is linearly proportional to the density and diameter of the nanowire and inversely proportional to the air pressure. Since the density of the Ag{sub 2}Ga nanoneedles is three times that of the MWNTs, the Ag{sub 2}Ga nanoneedles have greater Q at atmospheric pressures. Our initial measurements of Q for Ag{sub 2}Ga nanoneedles in low-vacuum (10 Torr) suggest that the intrinsic Q of these nanoneedles may be on the order of 1000. The epitaxial carbon that grows after heating (000{bar 1}) silicon carbide (SiC) to high temperatures (1450-1600) in vacuum was also studied. At these high temperatures, the surface Si atoms sublime and the remaining C atoms reconstruct to form graphene. X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) were used to characterize the quality of the few-layer graphene (FLG) surface. The XPS studies were useful in confirming the graphitic composition and measuring the thickness of the FLG samples. STM studies revealed a wide variety of nanometer-scale features that include sharp carbon-rich ridges, moire superlattices, one-dimensional line defects, and grain boundaries. By imaging these features with atomic scale resolution, considerable insight into the growth mechanisms of FLG on the carbon-face of SiC is obtained.

  20. The structure and reactivity of adsorbates on stepped Rh and Pt surfaces investigated by LEED, HREELS, TPD, XPS and STM

    SciTech Connect

    Batteas, J.D. |

    1995-06-01

    Defects on surfaces such as steps play an important role in surface chemistry. In order to obtain an understanding of the influence of steps in surface chemical reactions, the structure and reactivity of small molecules (O{sub 2}, CO, H{sub 2}S, and C{sub 2}H{sub 4}) on atomically stepped surfaces of RH and Pt have been investigated. The detailed structures of CO and oxygen bonded to the Rh(110) surface were determined. The CO molecules bond near the short bridge sites with the CO molecular axis tilted approximately 24{degree} from the surface normal. Oxygen atoms are bound asymmetrically in the 3-fold fcc hollow-sites to the (111) facets of the steps. The interactions of CO and oxygen on the Rh(311) surface were examined. The reaction of CO with the ordered phases of O shows two distinct reaction channels, a low temperature reaction limited channel (200 K) and a high temperature diffusion limited channel (350 K). Models of the reaction geometry and dynamics are proposed. The thermal decomposition of ethylene was examined on the Rh(311) surface. The stable decomposition species (C{sub 2}H, CH and C{sub 2}) are formed near 300 K, approximately 100 K lower on the stepped Rh(311) than on the flatter Rh(111) surface. The formation of these species at lower temperatures is attributed to the stepped nature of the surface. Finally, in situ STM was used to examine surface structural changes of a stepped Pt(111) crystal under coadsorption of sulfur and CO. This is the first direct evidence for a new mechanism by which a surface covered with an unreactive, strongly chemisorbed overlayer can form new sites, for bonding and reactions to occur, by massive surface restructuring at the step edges. This new surface phenomenon answers some of the puzzles of metal surface catalysis and its implications are described. 278 refs.

  1. A safe vaccine (DV-STM-07) against Salmonella infection prevents abortion and confers protective immunity to the pregnant and new born mice.

    PubMed

    Negi, Vidya Devi; Nagarajan, Arvindhan G; Chakravortty, Dipshikha

    2010-01-01

    Pregnancy is a transient immuno-compromised condition which has evolved to avoid the immune rejection of the fetus by the maternal immune system. The altered immune response of the pregnant female leads to increased susceptibility to invading pathogens, resulting in abortion and congenital defects of the fetus and a subnormal response to vaccination. Active vaccination during pregnancy may lead to abortion induced by heightened cell mediated immune response. In this study, we have administered the highly attenuated vaccine strain DeltapmrG-HM-D (DV-STM-07) in female mice before the onset of pregnancy and followed the immune reaction against challenge with virulent S. Typhimurium in pregnant mice. Here we demonstrate that DV-STM-07 vaccine gives protection against Salmonella in pregnant mice and also prevents Salmonella induced abortion. This protection is conferred by directing the immune response towards Th2 activation and Th1 suppression. The low Th1 response prevents abortion. The use of live attenuated vaccine just before pregnancy carries the risk of transmission to the fetus. We have shown that this vaccine is safe as the vaccine strain is quickly eliminated from the mother and is not transmitted to the fetus. This vaccine also confers immunity to the new born mice of vaccinated mothers. Since there is no evidence of the vaccine candidate reaching the new born mice, we hypothesize that it may be due to trans-colostral transfer of protective anti-Salmonella antibodies. These results suggest that our vaccine DV-STM-07 can be very useful in preventing abortion in the pregnant individuals and confer immunity to the new born. Since there are no such vaccine candidates which can be given to the new born and to the pregnant women, this vaccine holds a very bright future to combat Salmonella induced pregnancy loss. PMID:20161765

  2. Direct probing of the structure and electron transfer of fullerene/ferrocene hybrid on Au(111) electrodes by in situ electrochemical STM.

    PubMed

    Chen, Ting; Wang, Dong; Gan, Li-Hua; Matsuo, Yutaka; Gu, Jing-Ying; Yan, Hui-Juan; Nakamura, Eiichi; Wan, Li-Jun

    2014-02-26

    The electron donor-acceptor dyads are an emerging class of materials showing important applications in nonlinear optics, dye-sensitized solar cells, and molecular electronics. Investigation of their structure and electron transfer at the molecular level provides insights into the structure-property relationship and can benefit the design and preparation of electron donor-acceptor dyad materials. Herein, the interface adstructure and electron transfer of buckyferrocene Fe(C60Me5)Cp, a typical electron donor-acceptor dyad, is directly probed using in situ electrochemical scanning tunneling microscopy (STM) combined with theoretical simulations. It is found that the adsorption geometry and assembled structure of Fe(C60Me5)Cp is significantly affected by the electrochemical environments. In 0.1 M HClO4 solution, Fe(C60Me5)Cp forms well-ordered monolayers and multilayers on Au(111) surfaces with molecular dimer as the building block. In 0.1 M NaClO4 solution, typical six-fold symmetric close-packed monolayer with vertically adsorbed Fe(C60Me5)Cp is formed. Upon electrochemical oxidation, the oxidized Fe(C60Me5)Cp shows higher brightness in an STM image, which facilitates the direct visualization of the interfacial electrochemical electron transfer process. Theoretical simulation indicates that the electrode potential-activated, one-electron transfer from Fe(C60Me5)Cp to the electrode leads to the change of the delocalization character of the frontier orbital in the molecule, which is responsible for the STM image contrast change. This result is beneficial for understanding the structure and property of single electron donor-acceptor dyads. It also provides a direct approach to study the electron transfer of electron donor-acceptor compounds at the molecular level. PMID:24483295

  3. Diguanylate Cyclases AdrA and STM1987 Regulate Salmonella enterica Exopolysaccharide Production during Plant Colonization in an Environment-Dependent Manner

    PubMed Central

    Cowles, Kimberly N.; Willis, David K.; Engel, Tyler N.; Jones, Jeffrey B.

    2015-01-01

    Increasing evidence indicates that despite exposure to harsh environmental stresses, Salmonella enterica successfully persists on plants, utilizing fresh produce as a vector to animal hosts. Among the important S. enterica plant colonization factors are those involved in biofilm formation. S. enterica biofilm formation is controlled by the signaling molecule cyclic di-GMP and represents a sessile lifestyle on surfaces that protects the bacterium from environmental factors. Thus, the transition from a motile, planktonic lifestyle to a sessile lifestyle may represent a vital step in bacterial success. This study examined the mechanisms of S. enterica plant colonization, including the role of diguanylate cyclases (DGCs) and phosphodiesterases (PDEs), the enzymes involved in cyclic di-GMP metabolism. We found that two biofilm components, cellulose and curli, are differentially required at distinct stages in root colonization and that the DGC STM1987 regulates cellulose production in this environment independent of AdrA, the DGC that controls the majority of in vitro cellulose production. In addition, we identified a new function for AdrA in the transcriptional regulation of colanic acid and demonstrated that adrA and colanic acid biosynthesis are associated with S. enterica desiccation tolerance on the leaf surface. Finally, two PDEs with known roles in motility, STM1344 and STM1697, had competitive defects in the phyllosphere, suggesting that regulation of motility is crucial for S. enterica survival in this niche. Our results indicate that specific conditions influence the contribution of individual DGCs and PDEs to bacterial success, perhaps reflective of differential responses to environmental stimuli. PMID:26655751

  4. Phase transition on the Si(001) clean surface prepared in UHV MBE chamber: a study by high-resolution STM and in situ RHEED

    PubMed Central

    2011-01-01

    The Si(001) surface deoxidized by short annealing at T ~ 925°C in the ultrahigh vacuum molecuar beam epitaxy chamber has been in situ investigated using high-resolution scanning tunneling microscopy (STM)and redegreesected high-energy electron diffraction (RHEED. RHEED patterns corresponding to (2 × 1) and (4 × 4) structures were observed during sample treatment. The (4 × 4) reconstruction arose at T ≲ 600°C after annealing. The reconstruction was observed to be reversible: the (4 × 4) structure turned into the (2 × 1) one at T ≳ 600°C, the (4 × 4) structure appeared again at recurring cooling. The c(8 × 8) reconstruction was revealed by STM at room temperature on the same samples. A fraction of the surface area covered by the c(8 × 8) structure decreased, as the sample cooling rate was reduced. The (2 × 1) structure was observed on the surface free of the c(8 × 8) one. The c(8 × 8) structure has been evidenced to manifest itself as the (4 × 4) one in the RHEED patterns. A model of the c(8 × 8) structure formation has been built on the basis of the STM data. Origin of the high-order structure on the Si(001) surface and its connection with the epinucleation phenomenon are discussed. PACS 68.35.B-·68.37.Ef·68.49.Jk·68.47.Fg PMID:21711733

  5. Transformation of self-assembly of a TTF derivative at the 1-phenyloctane/HOPG interface studied by STM--from a nanoporous network to a linear structure

    NASA Astrophysics Data System (ADS)

    Xu, Jing; Xiao, Xunwen; Deng, Ke; Zeng, Qingdao

    2016-01-01

    The self-assembly of a tetrathiafulvalene (TTF) derivative (EDTTF) and a 1,3,5-tris(10-carboxydecyloxy)-benzene (TCDB) heterobilayer nanostructure at the 1-phenyloctane/HOPG interface under ambient conditions has been studied by scanning tunneling microscopy (STM). EDTTF and TCDB could co-assemble into a brand new hexagonal network with one of the largest nano-cavities. Finally, the nanoporous network would transform into a more stable linear structure. Density functional theory (DFT) calculations have been performed to reveal the formation mechanism.The self-assembly of a tetrathiafulvalene (TTF) derivative (EDTTF) and a 1,3,5-tris(10-carboxydecyloxy)-benzene (TCDB) heterobilayer nanostructure at the 1-phenyloctane/HOPG interface under ambient conditions has been studied by scanning tunneling microscopy (STM). EDTTF and TCDB could co-assemble into a brand new hexagonal network with one of the largest nano-cavities. Finally, the nanoporous network would transform into a more stable linear structure. Density functional theory (DFT) calculations have been performed to reveal the formation mechanism. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07345f

  6. Hydration processes on metal surfaces studied by IR and STM: a model for the potential drop across the electric double layers

    NASA Astrophysics Data System (ADS)

    Nakamura, Masashi; Shingaya, Yoshitaka; Ito, Masatoki

    2002-04-01

    Four different hydration water molecules, a flat monomer, a tilted monomer, a tetramer cluster and an upright monomer, were observed on Ru(0 0 1). In situ scanning tunneling microscopy (STM) images of M(1 1 1)-√3×√7-(HSO -4+H 5O 2+) (M=Pt, Ir, Au, Ru(0 0 1)) in H 2SO 4 solution produced a zig-zag chain of hydration water molecules, revealing a large stabilization energy due to the formation of a hydrogen bonding network. Also 2×2-2CO + H 2O structure was observed on both Ru(0 0 1) electrode and Ru(0 0 1) ultra-high vacuum surfaces by STM and low energy electron diffraction. These model double layers including over-layer water molecules form a preferentially ordered structure in terms of hydrogen bonding at a negative electrode potential while also forming a disordered structure with a relatively random orientation in the over layer at a positive electrode potential. The preferential orientation of the large water dipole yields a strong electric field on the surface and lowers the frequencies of the adsorbed bisulfate S-O stretching or the CO stretching absorption band.

  7. Growth and analysis of polymorphic graphene with STM and LEEM-IV for applications in molecular self-assembly and organic electronics

    NASA Astrophysics Data System (ADS)

    Grady, Maxwell; Ohta, Taisuke; Diaconescu, Bogdan; Dai, Zhongwei; Pohl, Karsten

    Graphene has aroused tremendous interest due to its remarkable electronic and mechanical properties, and is of interest for use in organic electronic devices such as organic photovoltaic cells. We present an analysis of a novel graphene system grown on Ru (0001) in the presence of atomic hydrogen and carbon vapor using STM and LEEM-IV. Structural studies completed with STM show a wide array of moire superlattice sizes ranging from 0.9 to 3.0 nm. Preliminary LEEM and LEEM-IV results confirm the presence of ordered graphene atop the Ru (0001) surface. Investigation using LEEM-IV provides information about the carbon layer thickness; also, micro-LEED-IV determines the precise atomic reconstruction of the interface region. In this regard, we believe the hydrogen present in the system to be interstitial at the carbon-ruthenium interface thus passivating the ruthenium surface, decoupling, and lifting the carbon layer from the substrate. The structural polymorphism displayed by this system is of interest for the study of directed self-assembly. Control over moire size can aid in future work using graphene as a template for self-assembled growth of organic electronics. This work was performed in part at CINT (DE-AC04-94AL85000). Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US DOE NNSA (DE-AC04-94AL85000).

  8. Local density of states measurements via STM and TS on clean fresh cleaved HOPG and Gold thin films on HOPG under ambient conditions

    NASA Astrophysics Data System (ADS)

    Morean, Casey; Marijczuk, Roman; Senevirathne, Indrajith

    Highly Oriented Pyrolytic Graphite (HOPG) has many applications in physics and engineering thus understanding affiliated physical and chemical phenomena is important. This also makes HOPG an important and interesting system to study. This is an investigation of surfaces of HOPG and Au thin films (ranging about 20nm) via Scanning Tunneling Microscopy (STM) and Tunneling Spectroscopy (TS) with a Pt-Ir tip equipped Nanosurf Naio STM. In this investigation, clean fresh cleaved HOPG substrates were used. Surfaces of HOPG and Au sputter deposited at different film thicknesses were imaged via constant current mode to assess the surface consistency and roughness. Consistent atomic resolution images were obtained. The systems were then investigated via TS by applied tip voltage (V) vs. tunneling current (I) curves. These spectroscopic data were then used to assess the local density of states (LDOS) and the surface variation of LDOS. The discussion will attempt to assess the surface electronic environment of these systems in relation to the Au deposition and variation of Au thicknesses on HOPG. Since measurements were carried out in ambient conditions this adds to the complexity which will also be discussed. Lock Haven University Nanotechnology Program.

  9. The spatial distributions of large gap-like structure on Fe(Se,Te) single crystals observed by STM/STS

    NASA Astrophysics Data System (ADS)

    Sugimoto, Akira; Sakai, Yuta; Nagasaka, Kouhei; Ekino, Toshikazu

    2015-11-01

    The nanoscale spatial distributions of large gap-like structure on superconducting FeSe1-xTex were investigated by scanning tunneling microscopy/spectroscopy (STM/STS). The STM topography shows regular atomic lattice arrangements with the lattice spacing ∼0.38 nm, together with the randomly distributed large spots due to the excess Fe atoms. From the STS measurements, the small gap structures of Δ ∼ 7 meV were partly observed. On the other hand, the high-bias dI/dV curves exhibit the broad peak structures at the negative biases of VPG = -200 to -400 mV in the measured whole surface area. The average of these large gaps is |VPGave| ∼ 305 mV with the standard deviation of σ ∼ 48 mV. The spatial distributions of the VPG exhibit the domain structures consisting of the relatively smaller gaps (<250 meV), which correspond to the excess Fe positions. The small gap Δ ∼ 7 meV is also observed at those positions, suggesting that the excess Fe affects the electronic structures of FeSe1-xTex.

  10. High-sensitivity noncontact atomic force microscope/scanning tunneling microscope (nc AFM/STM) operating at subangstrom oscillation amplitudes for atomic resolution imaging and force spectroscopy

    NASA Astrophysics Data System (ADS)

    Oral, A.; Grimble, R. A.; Özer, H. Ö.; Pethica, J. B.

    2003-08-01

    We describe a new, highly sensitive noncontact atomic force microscope/scanning tunneling microscope (STM) operating in ultrahigh vacuum (UHV) with subangstrom oscillation amplitudes for atomic resolution imaging and force-distance spectroscopy. A novel fiber interferometer with ˜4×10-4 Å/√Hz noise level is employed to detect cantilever displacements. Subangstrom oscillation amplitude is applied to the lever at a frequency well below the resonance and changes in the oscillation amplitude due to tip-sample force interactions are measured with a lock-in amplifier. Quantitative force gradient images can be obtained simultaneously with the STM topography. Employment of subangstrom oscillation amplitudes lets us perform force-distance measurements, which reveal very short-range force interactions, consistent with the theory. Performance of the microscope is demonstrated with quantitative atomic resolution images of Si(111)(7×7) and force-distance curves showing short interaction range, all obtained with <0.25 Å lever oscillation amplitude. Our technique is not limited to UHV only and operation under liquids and air is feasible.

  11. XPS and STM study of SiC synthesized by acetylene and disilane reaction with the Si(1 0 0)2 × 1 surface

    NASA Astrophysics Data System (ADS)

    Santoni, A.; Frycek, R.; Castrucci, P.; Scarselli, M.; De Crescenzi, M.

    2005-05-01

    The SiC formation on a ordered Si(1 0 0) substrate at low temperatures (980-1180 K) and low total pressures (10 -6 mbar) has been investigated by in situ X-ray photoemission spectroscopy (XPS) and ex situ scanning tunneling microscopy (STM). SiC was grown by chemical vapor deposition (CVD) from C 2H 2 and Si 2H 6 as the precursor gases. At all the temperatures and in presence of both C 2H 2 and Si 2H 6 XPS data showed the formation of sub-stoichiometric Si 1- xC x alloys characterized by excess silicon. By exposing to C 2H 2 only, stoichiometric SiC could be synthesized up to 1080 K. At 1180 K the formation of a Si 1- xC x alloy was observed. STM analysis has pointed out the role of silicon from the gas phase in the growth mechanisms and it has shown that uniform films with low roughness and small nanostructures can be obtained by tuning the acetylene/disilane ratios independently from the temperature selected in the investigated range.

  12. Measurement of mesoscopic Si:P delta-doped devices fabricated by rapid STM hydrogen depassivation lithography via field-emission

    NASA Astrophysics Data System (ADS)

    Rudolph, M.; Carr, S. M.; Subramania, G.; Ten Eyck, G.; Dominguez, J.; Lilly, M. P.; Carroll, M. S.; Bussmann, E.

    2014-03-01

    Recently, a method to fabricate nanoelectronic and quantum devices has been developed that utilizes scanning tunneling microscopy (STM) to place dopants (P) into Si with deterministic atomic-precision. Dopant placement is achieved via STM hydrogen depassivation lithography (HDL). Typically HDL is performed in a low-voltage tunneling mode where electrons desorb one H at a time, which requires extremely slow scan rates. Here, we introduce a high-voltage field-emission HDL, increasing patterning scan rate by an order of magnitude. Using the field-emission mode, we fabricated several HDL-patterned Si:P delta-doped devices, including a microscale multi-terminal Hall Effect device and a nanoscale quantum point contact. Low temperature transport measurements of the Hall device reveal a dopant density of 1014 cm-2, resistance of 2 k Ω/square, and mobility of 30 cm2/Vs. The quantum point contact showed a blockaded voltage range of 80 mV, comparable to other similar devices patterned using conventional HDL. This work was performed, in part, at the Center for Integrated Nanotechnologies, a U.S. DOE, Office of Basic Energy Sciences user facility. The work was supported by the Sandia National Laboratories Directed Research and Development Program. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the U. S. Department of Energy under Contract No. DE-AC04-94AL85000.

  13. Complementary visualization of the pseudogap states in Bismuth2-Strontium2-Calcium-Copper2-Oxygen(8+delta): SI-STM study in real and momentum space

    NASA Astrophysics Data System (ADS)

    Kim, Chung Koo

    The high-temperature superconductivity has remained one of the most puzzling phenomena in contemporary condensed matter physics since its discovery in 1986. Despite enormous quantity of experimental results and theoretical proposals over 25 years, the pairing glue as well as the nature of the normal states are still not clearly identified. The enigmatic pseudogap phase, characterized by the loss of spectral weight above the superconducting transition temperature (Tc), is believed to be a key to understanding the superconductivity. This dissertation primarily investigates the underdoped BSCCO, a double layered cuprate perovskite which exhibits pseudogap over wide range. Spectroscopic-Imaging Scanning Tunneling Microscopy (SI-STM) is a unique probe in that it allows simultaneous access to complimentary spaces. For SI-STM can visualize the electronic structure of a physical system with atomic resolution and register in real space, with its Fourier-transform revealing the dispersion of quasiparticle excitations in momentum space. Three discoveries made with SI-STM are presented here. First, the real-space electronic nematicity observed within CuO2 unit cell demonstrates that the C4 rotational symmetry of the underlying crystal lattice is broken into the C2 symmetry in the electronic structure. Inequivalence of the orthogonal crystallographic axes narrows down the possible models for pseudogap in favor of stripe order. Momentum space provides two other discoveries. Ratio of the differential conductance data measured at opposite bias voltage, which amplifies the particle-hole symmetric dispersion of the Bogoliubov quasiparticle, shows that the pseudogap state retains the tri-partite electronic excitation structure present below Tc. The signature of the Cooper pairs without long-range phase coherence renders the pseudogap as a pre-cursor to the superconducting state. In contrast, the anti-nodal charge-ordering dominant in the raw data but washed out in the ratio map is

  14. On-surface synthesis of two-dimensional imine polymers with a tunable band gap: a combined STM, DFT and Monte Carlo investigation

    NASA Astrophysics Data System (ADS)

    Xu, Lirong; Yu, Yanxia; Lin, Jianbin; Zhou, Xin; Tian, Wei Quan; Nieckarz, Damian; Szabelski, Pawel; Lei, Shengbin

    2016-04-01

    Two-dimensional polymers are of great interest for many potential applications in nanotechnology. The preparation of crystalline 2D polymers with a tunable band gap is critical for their applications in nano-electronics and optoelectronics. In this work, we try to tune the band gap of 2D imine polymers by expanding the conjugation of the backbone of aromatic diamines both laterally and longitudinally. STM characterization reveals that the regularity of the 2D polymers can be affected by the existence of lateral bulky groups. Density functional theory (DFT) simulations discovered a significant narrowing of the band gap of imine 2D polymers upon the expansion of the conjugation of the monomer backbone, which has been confirmed experimentally by UV absorption measurements. Monte Carlo simulations help us to gain further insight into the controlling factors of the formation of regular 2D polymers, which demonstrated that based on the all rigid assumption, the coexistence of different conformations of the imine moiety has a significant effect on the regularity of the imine 2D polymers.Two-dimensional polymers are of great interest for many potential applications in nanotechnology. The preparation of crystalline 2D polymers with a tunable band gap is critical for their applications in nano-electronics and optoelectronics. In this work, we try to tune the band gap of 2D imine polymers by expanding the conjugation of the backbone of aromatic diamines both laterally and longitudinally. STM characterization reveals that the regularity of the 2D polymers can be affected by the existence of lateral bulky groups. Density functional theory (DFT) simulations discovered a significant narrowing of the band gap of imine 2D polymers upon the expansion of the conjugation of the monomer backbone, which has been confirmed experimentally by UV absorption measurements. Monte Carlo simulations help us to gain further insight into the controlling factors of the formation of regular 2D

  15. Clustering effects in a low coverage deposition of gold on the GaAs( 0 0 1 )-β2(2×4) surface: an STM-UHV and theoretical study

    NASA Astrophysics Data System (ADS)

    Amore Bonapasta, A.; Scavia, G.; Buda, F.

    2002-11-01

    A comparative study of gold deposition on the GaAs(0 0 1)-β2(2×4) surface based on scanning tunneling microscopy (STM)-ultra high vacuum (UHV) and Car-Parrinello calculations has been carried out. The theoretical results show that the preferential reactive sites of an isolated Au adatom on the GaAs surface drive a self-organizing process of further Au adatoms onto the surface, thus determining an Au clusterization onto the two-As-dimer cell. On the other hand, STM-UHV images reveal, for Au depositions <1 ML, a decorating effect of gold towards the GaAs(0 0 1)-β2(2×4) unit cell. In detail, gold clusters tend to cover the two-As-dimer cell without modifying the (2×4) reconstruction, in agreement with the theoretical results. Moreover, a fine comparison between the STM images of gold clusters and the theoretical results reveals that each of these clusters can be composed of four Au adatoms directly interacting with the two As dimers of the GaAs unit cell. An STM-UHV analysis of the surface for a deposition >1 ML suggests that gold clusterizes into 3D clusters rather than forming a 2D layer.

  16. A size, shape and concentration controlled self-assembling structure with host-guest recognition at the liquid-solid interface studied by STM.

    PubMed

    Shen, Mengqi; Luo, Zhouyang; Zhang, Siqi; Wang, Shuai; Cao, Lili; Geng, Yanfang; Deng, Ke; Zhao, Dahui; Duan, Wubiao; Zeng, Qingdao

    2016-06-01

    In the present investigation, we reported the fabrication of host networks formed by two newly prepared phenanthrene-butadiynylene macrocycles (PBMs) at the liquid-solid interface. Size, shape and concentration controlled experiments have been performed to investigate the PBMs/coronene (COR) host-guest system with the structural polymorphism phenomenon. Initially, PBM1 could form a regular linear network structure and PBM2 form a well-ordered nanoporous network structure. When the COR molecules were introduced, the self-assembled structure of PBM1 remained unchanged, while COR could be entrapped into the cavities of the PBM2 nanoporous network, and the co-assembly of the PBM2/COR host-guest systems underwent a structural transformation with the increase of concentration of COR. Scanning tunneling microscopy (STM) measurements and density functional theory (DFT) calculations are utilized to reveal the formation mechanism of the molecular nanoarrays controlled by the solution concentration. PMID:27241885

  17. RDS, LEED and STM of the P-rich and Ga-rich surfaces of GaP(1 0 0)

    NASA Astrophysics Data System (ADS)

    Töben, L.; Hannappel, T.; Möller, K.; Crawack, H.-J.; Pettenkofer, C.; Willig, F.

    2001-11-01

    Reflectance difference spectroscopy was measured in the metal organic chemical vapor deposition reactor and also in UHV at 20 K. It revealed a characteristic negative peak at the low energy side that was indicative of the specific surface reconstruction. This peak disappeared completely if the sample was kept within a narrow intermediate temperature range. At 20 K the negative peak appeared at 2.4 eV for the Ga-terminated (2×4)-reconstructed surface and at 2.6 eV for the P-terminated (2×1)/(2×2)-reconstructed surface. RDS for the two different surface reconstructions displayed strong structures also in the range of the bulk transitions. A characteristic zig-zag pattern was observed in the STM image of the P-terminated surface.

  18. STM imagery and density functional calculations of C60 fullerene adsorption on the 6H-SiC(0001)-3×3 surface

    NASA Astrophysics Data System (ADS)

    Ovramenko, T.; Spillebout, F.; Bocquet, F. C.; Mayne, A. J.; Dujardin, G.; Sonnet, Ph.; Stauffer, L.; Ksari, Y.; Themlin, J.-M.

    2013-04-01

    Scanning tunneling microscopy (STM) studies of the fullerene C60 molecule adsorbed on the silicon carbide SiC(0001)-3×3 surface, combined with density functional theory (DFT) calculations, show that chemisorption of individual C60 molecules occurs through the formation of one bond to one silicon adatom only in contrast to multiple bond formation on other semiconducting surfaces. We observe three stable adsorption sites with respect to the Si adatoms of the surface unit cell. Comprehensive DFT calculations give different adsorption energies for the three most abundant sites showing that van der Waals forces between the C60 molecule and the neighboring surface atoms need to be considered. The C60 molecules are observed to form small clusters even at low coverage indicating the presence of a mobile molecular precursor state and nonnegligible intermolecular interactions.

  19. STM, QCM, and the windshield wiper effect: a joint theoretical-experimental study of adsorbate mobility and lubrication at high sliding rates.

    PubMed

    Abdelmaksoud, M; Lee, S M; Padgett, C W; Irving, D L; Brenner, D W; Krim, J

    2006-11-01

    We have observed that when mobile adsorbed films of benzene, tricresyl phosphate, and tertiary-butyl phenyl phosphate are present on the surface electrode of a quartz crystal microbalance (QCM), oscillation of the QCM produces clearer scanning tunneling microscope (STM) images of the electrode surface. This is in contrast to an immobile overlayer of iodobenzene, where oscillation of the QCM does not affect image quality. This observation is attributed to a "windshield wiper effect", where at MHz frequencies the tip motion maintains a region of the surface where the absorbate concentration is reduced, which leads to a clearer image. A straightforward model is presented that supports this conclusion and that provides guidelines for effective lubrication of contacts operating at MHz frequencies. PMID:17073486

  20. Complete Genome sequence of Burkholderia phymatum STM815T, a broad host range and efficient nitrogen-fixing symbiont of Mimosa species

    PubMed Central

    Moulin, Lionel; Klonowska, Agnieszka; Caroline, Bournaud; Booth, Kristina; Vriezen, Jan A.C.; Melkonian, Rémy; James, Euan K.; Young, J. Peter W.; Bena, Gilles; Hauser, Loren; Land, Miriam; Kyrpides, Nikos; Bruce, David; Chain, Patrick; Copeland, Alex; Pitluck, Sam; Woyke, Tanja; Lizotte-Waniewski, Michelle; Bristow, Jim; Riley, Margaret

    2014-01-01

    Burkholderia phymatum is a soil bacterium able to develop a nitrogen-fixing symbiosis with species of the legume genus Mimosa, and is frequently found associated specifically with Mimosa pudica. The type strain of the species, STM 815T, was isolated from a root nodule in French Guiana in 2000. The strain is an aerobic, motile, non-spore forming, Gram-negative rod, and is a highly competitive strain for nodulation compared to other Mimosa symbionts, as it also nodulates a broad range of other legume genera and species. The 8,676,562 bp genome is composed of two chromosomes (3,479,187 and 2,697,374 bp), a megaplasmid (1,904,893 bp) and a plasmid hosting the symbiotic functions (595,108 bp). PMID:25197461

  1. The evaluation of surface diffusion coefficients of gold and platinum atoms at electrochemical interfaces from combined STM-SEM imaging and electrochemical techniques

    SciTech Connect

    Alonso, C.; Salvarezza, R.C.; Vara, J.M.; Arvia, A.J. ); Vazquez, L.; Bartolome, A.; Baro, A.M. )

    1990-07-01

    A simple method is presented for measuring the surface diffusion coefficients of Au and Pt atoms at electrodispersed electrodes of the same metals in contact with 0.5{ital M} H{sub 2}SO{sub 4}. The technique is based upon the time dependence of the surface roughness factor of electrodispersed metal overlayers. The method requires a model for the surface roughness of the metal structure. The model is deduced from microscopic measurements by a STM integrated into a conventional SEM microscope. This allows the relationship between the roughness factor and the area of the surface structure to be obtained. For Au and Pt in contact with an electrolyte solution, the values of our diffusion coefficients are higher than those reported in vacuum at the same temperature.

  2. Ultra-small oscillation amplitude nc-AFM/STM imaging, force and dissipation spectroscopy of Si(100)(2×1)

    NASA Astrophysics Data System (ADS)

    Özgür Özer, H.; Atabak, Mehrdad; Oral, Ahmet

    2002-12-01

    Si(100)(2×1) surface is imaged using a new nc-AFM (non-contact atomic force microscopy)/STM with sub-Ångstrom oscillation amplitudes using stiff hand-made tungsten levers. Simultaneous force gradient and scanning tunneling microscopy images of individual dimers and atomic scale defects are obtained. We measured force-distance and dissipation-distance curves with different tips. Some of the tips show long-range force interactions, whereas some others resolve short-range interatomic force interactions. We observed that the tips showing short-range force interaction give atomic resolution in force gradient scans. This result suggests that short-range force interactions are responsible for atomic resolution in nc-AFM. We also observed an increase in the dissipation as the tip is approached closer to the surface, followed by an unexpected decrease as we pass the inflection point in the energy-distance curve.

  3. Complete Genome sequence of Burkholderia phymatum STM815, a broad host range and efficient nitrogen-fixing symbiont of Mimosa species

    SciTech Connect

    Moulin, Lionel; Klonowska, Agnieszka; Caroline, Bournaud; Booth, Kristina; Vriezen, Jan A.C.; Melkonian, Remy; James, Euan; Young, Peter W.; Bena, Gilles; Hauser, Loren John; Land, Miriam L; Kyrpides, Nikos C; Bruce, David; Chain, Patrick S. G.; Copeland, A; Pitluck, Sam; Woyke, Tanja; Lizotte-Waniewski, Michelle; Bristow, James; Riley, Monica

    2014-01-01

    Burkholderia phymatum is a soil bacterium able to develop a nitrogen-fixing symbiosis with species of the legume genus Mimosa, and is frequently found associated specifically with Mimosa pudica. The type strain of the species, STM 815T, was isolated from a root nodule in French Guiana in 2000. The strain is an aerobic, motile, non-spore forming, Gram-negative rod, and is a highly competitive strain for nodulation compared to other Mimosa symbionts, as it also nodulates a broad range of other legume genera and species. The 8,676,562 bp genome is composed of two chromosomes (3,479,187 and 2,697,374 bp), a megaplasmid (1,904,893 bp) and a plasmid hosting the symbiotic functions (595,108 bp).

  4. STM sub-gap structure in cuprates is a consequence of density waves, according to Mean-Field Theory and CDMFT

    NASA Astrophysics Data System (ADS)

    Verret, Simon; Roy, Jyotirmoy; Sénéchal, David; Tremblay, A.-M. S.

    Much work has been done to find how the pseudogap is related to charge density waves in cuprates. In scanning tunneling microscopy (STM) measurements, the superconducting gap and pseudogap of cuprates are sometimes accompanied by a small sub-gap structure at very low energy. This was documented early in vortex cores studies, and has now been reported at zero field for YBCO.(1) Here, we show that this can be caused by density waves, first through a standard mean-field approach, and then with Cellular Dynamical Mean-Field Theory for the Hubbard model using an exact diagonalization solver. We comment on the implication of these results for the relation between pseudogap and charge order. (1) Jens Bruér et al. arXiv:1507.06775 Supported by NSERC, CIFAR and the Tier I Canada Research Chair Program.

  5. Atomic structures of Ag/Ge(1 1 1) √39 × √39 and 6 × 6 surfaces studied by STM: observations of bias dependent reconstruction transformations

    NASA Astrophysics Data System (ADS)

    Zhang, H. M.; Uhrberg, R. I. G.

    2003-05-01

    The 6×6 and √39×√39 phases on Ag/Ge(1 1 1) have been studied by scanning tunneling microscopy (STM). Four types of 6×6 configurations are found which all consist of a √3×√3 layer with six extra Ag adatoms per 6×6 unit cell. These reconstructions show either mirrored or complementary relations. We observe interesting transitions between the different 6×6 reconstructions. The √39×√39 surface appears to have five extra Ag atoms per unit cell. By using various tip biases, we show that the √39×√39 domain orientation can be changed. Surface structure models of the √39×√39 and 6×6 phases are proposed based on the HCT structure of the underlying √3×√3 surface.

  6. STM and x-ray diffraction temperature-dependent growth study of SrRuO{sub 3} PLD thin films

    SciTech Connect

    Hawley, M.E.; Jia, Q.X.; Brown, G.W.

    1996-12-31

    SrRuO{sub 3} (SRO) has recently found a number of applications in different fields, e.g. as a buffer layer for the growth of high temperature superconductor (HTS) YBa{sub 2}Cu{sub 3}O{sub 7-x} films and as a bottom electrode for ferroelectric or high dielectric constant thin film capacitors and nonvolatile data storage. The growth of high crystallinity SRO films with good structural and electrical properties is the prerequisite for each of these applications. In this paper we describe the affect of one growth parameters temperature (T), on the crystalline quality, epitaxial substrate relationship and resulting electrical properties. SRO films were deposited on LaAlO{sub 3} single crystal substrates by pulsed laser deposition at substrate temperatures (T{sub s}) ranging from room temperature (RT) up to 800{degrees}C with a nominal film thickness of 150 nm range. The resulting films were characterized by x-ray diffraction, 4-point transport, and STM. The films` microstructures, as revealed by STM, evolved from polygranular at RT to a layered plate-like structure at higher deposition temperatures, T{sub s}, Increasing T{sub s} was marked first by increasing grain size, then a stronger orientational relationship between film and substrate, finally followed by the development of increased connectivity between grains to an extended island or condensed layered state. The transition from polygranular to layered structure occurred at T{sub s} > 650{degrees}C. Increased conductivity paralleled the changes in microstructure. The surfaces of all of the films were relatively smooth; the oriented films are suitable for use as conductive templates in multilayer structures.

  7. A size, shape and concentration controlled self-assembling structure with host-guest recognition at the liquid-solid interface studied by STM

    NASA Astrophysics Data System (ADS)

    Shen, Mengqi; Luo, Zhouyang; Zhang, Siqi; Wang, Shuai; Cao, Lili; Geng, Yanfang; Deng, Ke; Zhao, Dahui; Duan, Wubiao; Zeng, Qingdao

    2016-06-01

    In the present investigation, we reported the fabrication of host networks formed by two newly prepared phenanthrene-butadiynylene macrocycles (PBMs) at the liquid-solid interface. Size, shape and concentration controlled experiments have been performed to investigate the PBMs/coronene (COR) host-guest system with the structural polymorphism phenomenon. Initially, PBM1 could form a regular linear network structure and PBM2 form a well-ordered nanoporous network structure. When the COR molecules were introduced, the self-assembled structure of PBM1 remained unchanged, while COR could be entrapped into the cavities of the PBM2 nanoporous network, and the co-assembly of the PBM2/COR host-guest systems underwent a structural transformation with the increase of concentration of COR. Scanning tunneling microscopy (STM) measurements and density functional theory (DFT) calculations are utilized to reveal the formation mechanism of the molecular nanoarrays controlled by the solution concentration.In the present investigation, we reported the fabrication of host networks formed by two newly prepared phenanthrene-butadiynylene macrocycles (PBMs) at the liquid-solid interface. Size, shape and concentration controlled experiments have been performed to investigate the PBMs/coronene (COR) host-guest system with the structural polymorphism phenomenon. Initially, PBM1 could form a regular linear network structure and PBM2 form a well-ordered nanoporous network structure. When the COR molecules were introduced, the self-assembled structure of PBM1 remained unchanged, while COR could be entrapped into the cavities of the PBM2 nanoporous network, and the co-assembly of the PBM2/COR host-guest systems underwent a structural transformation with the increase of concentration of COR. Scanning tunneling microscopy (STM) measurements and density functional theory (DFT) calculations are utilized to reveal the formation mechanism of the molecular nanoarrays controlled by the solution

  8. A comparison of the dose distributions between the brachytherapy 125I source models, STM1251 and Oncoseed 6711, in a geometry lacking radiation equilibrium scatter conditions.

    PubMed

    Tanaka, Kenichi; Kamo, Ken-ichi; Tateoka, Kunihiko; Asanuma, Osamu; Sato, Kaori; Takeda, Hiromitsu; Sakata, Koh-ichi; Takada, Jun

    2015-03-01

    The purpose of this study was to estimate the uncertainty in the dose distribution for the (125)I source STM1251, as measured with a radiophotoluminescent glass rod dosimeter and calculated using the Monte Carlo code EGS5 in geometry that included the source structure reported by Kirov et al. This was performed at a range of positions in and on a water phantom 18 cm in diameter and 16 cm in length. Some dosimetry positions were so close to the surface that the backscatter margin was insufficient for photons. Consequently, the combined standard uncertainty (CSU) at the coverage factor k of 1 was 11.0-11.2% for the measurement and 1.8-3.6% for the calculation. The calculation successfully reproduced the measured dose distribution within 13%, with CSU at k ≤ 1.6 (P > 0.3). Dose distributions were then compared with those for the (125)I source Oncoseed 6711. Our results supported the American Association of Physicists in Medicine Task Group No. 43 Updated Protocol (TG43U1) formalism, in which STM1251 dose distributions were more penetrating than those of Oncoseed 6711. This trend was also observed in the region near the phantom surface lacking the equilibrium radiation scatter conditions. In this region, the difference between the TG43U1 formalism and the measurement and calculation performed in the present study was not significant (P > 0.3) for either of the source models. Selection of the source model based on the treatment plans according to the TG43U1 formalism will be practical. PMID:25618137

  9. In situ STM study of the adsorption and electropolymerization of o-, m-, and p-ethylaniline molecules on Au(111) electrode.

    PubMed

    Chen, Sihzih; Hwuang, Chonzan; Tu, HsinLing; Wu, ChunGuey; Yau, ShuehLin; Fan, LiangJen; Yang, YawWen

    2010-08-28

    Cyclic voltammetry (CV) and in situ scanning tunneling microscopy (STM) were employed to study the adsorption and polymerization of the geometric isomers of ethylaniline (EA) on a Au(111) single-crystal electrode in 0.5 M H(2)SO(4). All three isomers, namely o-, m-, and p-EA, were adsorbed in highly ordered structures, identified as Au(111)-(4 x 2 square root(3))rect for m- and p-EA and (4 square root(3) x 4 square root(3))R30 degrees for o-EA, at the onset potentials (approximately 0.9 V [vs. reversible hydrogen electrode]) for electropolymerization. Raising the potential in excess of 0.9 V resulted in oxidation and polymerization of m- and o-EA, but decomposition of p-EA. Molecular-resolution STM imaging revealed that poly(m-EA) and poly(o-EA), denoted respectively as m- and o-PEA, exhibited distinctively different molecular shapes. More specifically, m-PEA molecules were predominantly linear and aligned preferentially in the 121 directions of the Au(111) surface; whereas o-PEA molecules were ill-defined in shape and in dimension. These differences in molecular conformation stemmed from unlike arrangements of adsorbed monomers at 0.9 V. Notably, m-EA were adsorbed in zigzags with two nearest neighbors separated by approximately 0.5 nm, which were spatially so similar to the backbones of m-PEA that m-EA molecules coupled readily when the potential was raised high enough to induce the oxidation of m-EA. In contrast, the arrangement of o-EA molecules was so different from the ideal configuration of its polymer that molecules coupled randomly to yield crooked polymer chains less than 20 nm in length. The effect of potential on the structure of m-PEA was examined also, revealing notable branching of linear m-PEA if the electrochemical potential was set at 1.1 V. PMID:20607178

  10. Electrochemical and in situ STM studies of anomalous phosphate adsorption induced on Zn UPD at Au( 1 1 1 ) in the presence of halide ions in aqueous phosphate solutions

    NASA Astrophysics Data System (ADS)

    Takahashi, Shin; Aramata, Akiko; Nakamura, Mitsuhiro; Hasebe, Kiyoshi; Taniguchi, Masahiro; Taguchi, Satoshi; Yamagishi, Akihiko

    2002-06-01

    Underpotential deposition (UPD) of Zn 2+ at Au(1 1 1) was studied in the phosphate solutions with and without halide ions (Cl -, Br -, and I -) by cyclic voltammetry and in situ STM for the evaluation of the anion adsorption induced on the Zn UPD. The order of the strength of anion adsorption induced on Zn UPD was found to be different from the order of specific adsorption strength of I ->Br ->Cl ->PO 43-⩾SO 42- at an Au substrate electrode. This anomalous tendency of anion adsorption induced on UPD Zn at Au seems to be identical with the cases of sulfate and phosphate adsorption induced on UPD Zn at a Pt electrode in the presence of chloride, being confirmed by radiotracer method. Such anomalous phosphate adsorption induced on Zn UPD was found to take place at Au(1 1 1) not only in the presence of chloride or bromide, but also even in the presence of iodide in the phosphate solution. The in situ STM images of Zn UPD were observed at Au(1 1 1) in the phosphate solution with iodide ions. At -200 mV (saturated calomel electrode; SCE) where the iodide adsorbs at substrate Au(1 1 1), the STM image was c(p× 3R30°) , and in the Zn UPD region, the STM image became ( 3× 3)R30° . The latter image is discussed to be assigned to the image in the absence of iodide, i.e., that the adsorbed anions induced at Zn UPD are phosphate species even in the solution containing iodide ions.

  11. Interaction of 2-mercaptopyrimidine and 4,4'-bipyridine and competition experiments between bipyridines and 1,10'-phenanthroline for the thiol layer on Au(1 1 1) by STM

    NASA Astrophysics Data System (ADS)

    Pinheiro, L. S.; Temperini, M. L. A.

    2001-02-01

    STM was employed to study the coadsorption of 4,4'-bipyridine (4bipy) and 2-mercaptopyrimidine (2MPy) on Au(1 1 1). The adsorption of 4bipy as a single layer was also analyzed. For the single layer STM reveals a molecular structure made of parallel periodic chains with a repeat distance of 11.5-11.7 Å. The mixed layer is formed with a ratio of two molecules of 2MPy to one of 4bipy. 4bipy assumes two different positions in relation to the 2MPy dimer. Competition between 4bipy, 2,2'-bipyridine and 1,10'-phenanthroline was investigated to obtain a qualitative view of the preference of the 2MPy assembly for these molecules. The mixed layers were grown on Au(1 1 1) from ternary molecular solutions containing either 2MPy+4bipy+2bipy or 2MPy+4bipy+phen. STM shows that the resulting layers are made of the 2MPy dimeric assembly plus one of the oligopyridines. A split of the 2MPy dimer or the formation of mixed domains with the three molecules present in the stock solution was not found.

  12. Coulomb blockade and charge ordering in a few layers of TTF-TCNQ investigated by low-temperature STM/STS

    NASA Astrophysics Data System (ADS)

    Jeon, Seokmin; Maksymovych, Petro

    In contrast to the vast effort on bulk crystal phases of the prototypical organic charge-transfer complex, TTF-TCNQ, study of low-dimensional phases has been limited to monolayer phases on substrates. In this state, however, none of the physics of the bulk phase is observed owing to the overwhelming effect of the substrate. We investigate the molecular structure and electronic properties of a few layers of TTF-TCNQ grown on Au(111) and Ag(111) using STM/STS at 4.3 K. By decoupling the molecular electronic state from the metal surface, we have made the first observation of the effect of confinement on the electronic properties of TTF-TCNQ. STS reveals a plethora of sharp features due to molecular orbitals, each influenced by charge-transfer between the molecules. We hypothesize the existence of a Mott-insulator state in 3-layer islands, with a Coulomb gap of ~1 eV. In contrast, the corresponding bulk phase is a Peierls insulator with a gap of ~20 meV. The root cause of the nanoscale phase is traced to simultaneous electron confinement and structural frustration, which dramatically modify the energy balance of self-ionization allowing for integer charge transfer. These studies open broad opportunities to explore correlated electron physics in molecular systems. This research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.

  13. A combined STM and SPA-LEED study of the “explosive” nucleation and collective diffusion in Pb/Si(111)

    SciTech Connect

    Hattab, H.; Hupalo, M.; Hershberger, M. T.; Horn von Hoegen, M.; Tringides, M. C.

    2015-08-20

    A novel type of very fast nucleation was recently found in Pb/Si(111) with 4- to 7-layer high islands becoming crystalline in an “explosive” way, when the Pb deposited amount in the wetting layer is compressed to θc ~ 1.22 ML, well above the metallic Pb(111) density. This “explosive” nucleation is very different from classical nucleation when island growth is more gradual and islands grow in size by single adatom aggregation [8]. In order to identify the key parameters that control the nucleation we used scanning tunneling microscopy (STM) and spot profile analysis low energy electron diffraction (SPA-LEED). It was found that the number and duration of steps in iterative deposition used to approach θc and the flux rate have dramatic effects on the crystallization process. Larger depositions over shorter times induce greater spatial coverage fluctuations, so local areas can reach the critical coverage θc easier. This can trigger the collective motion of the wetting layer from far away to build the Pb islands “explosively”. Here, the SPA-LEED experiments show that even low flux experiments in iterative deposition experiments can trigger transfer of material to the superstable 7-layer islands, as seen from the stronger satellite rings close to the (00) spot.

  14. A combined STM and SPA-LEED study of the “explosive” nucleation and collective diffusion in Pb/Si(111)

    DOE PAGESBeta

    Hattab, H.; Hupalo, M.; Hershberger, M. T.; Horn von Hoegen, M.; Tringides, M. C.

    2015-08-20

    A novel type of very fast nucleation was recently found in Pb/Si(111) with 4- to 7-layer high islands becoming crystalline in an “explosive” way, when the Pb deposited amount in the wetting layer is compressed to θc ~ 1.22 ML, well above the metallic Pb(111) density. This “explosive” nucleation is very different from classical nucleation when island growth is more gradual and islands grow in size by single adatom aggregation [8]. In order to identify the key parameters that control the nucleation we used scanning tunneling microscopy (STM) and spot profile analysis low energy electron diffraction (SPA-LEED). It was foundmore » that the number and duration of steps in iterative deposition used to approach θc and the flux rate have dramatic effects on the crystallization process. Larger depositions over shorter times induce greater spatial coverage fluctuations, so local areas can reach the critical coverage θc easier. This can trigger the collective motion of the wetting layer from far away to build the Pb islands “explosively”. Here, the SPA-LEED experiments show that even low flux experiments in iterative deposition experiments can trigger transfer of material to the superstable 7-layer islands, as seen from the stronger satellite rings close to the (00) spot.« less

  15. Electronic and geometric properties of Au nanoparticles on Highly Ordered Pyrolytic Graphite (HOPG) studied using X-ray Photoelectron Spectroscopy (XPS) and Scanning Tunneling Microscopy (STM).

    PubMed

    Lopez-Salido, Ignacio; Lim, Dong Chan; Dietsche, Rainer; Bertram, Nils; Kim, Young Dok

    2006-01-26

    Au nanoparticles grown on mildly sputtered Highly Ordered Pyrolytic Graphite (HOPG) surfaces were studied using Scanning Tunneling Microscopy (STM) and X-ray Photoelectron Spectroscopy (XPS). The results were compared with those of Ag nanoparticles on the same substrate. By varying the defect densities of HOPG and the Au coverages, one can create Au nanoparticles in various sizes. At high Au coverages, the structures of the Au films significantly deviate from the ideal truncated octahedral form: the existence of many steps between different Au atomic layers can be observed, most likely due to a high activation barrier of the diffusion of Au atoms across the step edges. This implies that the particle growth at room temperature is strongly limited by kinetic factors. Hexagonal shapes of Au structures could be identified, indicating preferential growth of Au nanostructures along the (111) direction normal to the surface. In the case of Au, XPS studies reveal a weaker core level shift with decreasing particle size compared to the 3d level in similarly sized Ag particles. Also taking into account the Auger analysis of the Ag particles, the core level shifts of the metal nanoparticles on HOPG can be understood in terms of the metal/substrate charge transfer. Ag is (partially) positively charged, whereas Au negatively charged on HOPG. It is demonstrated that XPS can be a useful tool to study metal-support interactions, which plays an important role for heterogeneous catalysis, for example. PMID:16471654

  16. On-surface synthesis of two-dimensional imine polymers with a tunable band gap: a combined STM, DFT and Monte Carlo investigation.

    PubMed

    Xu, Lirong; Yu, Yanxia; Lin, Jianbin; Zhou, Xin; Tian, Wei Quan; Nieckarz, Damian; Szabelski, Pawel; Lei, Shengbin

    2016-04-28

    Two-dimensional polymers are of great interest for many potential applications in nanotechnology. The preparation of crystalline 2D polymers with a tunable band gap is critical for their applications in nano-electronics and optoelectronics. In this work, we try to tune the band gap of 2D imine polymers by expanding the conjugation of the backbone of aromatic diamines both laterally and longitudinally. STM characterization reveals that the regularity of the 2D polymers can be affected by the existence of lateral bulky groups. Density functional theory (DFT) simulations discovered a significant narrowing of the band gap of imine 2D polymers upon the expansion of the conjugation of the monomer backbone, which has been confirmed experimentally by UV absorption measurements. Monte Carlo simulations help us to gain further insight into the controlling factors of the formation of regular 2D polymers, which demonstrated that based on the all rigid assumption, the coexistence of different conformations of the imine moiety has a significant effect on the regularity of the imine 2D polymers. PMID:27049517

  17. The creation of microscopic surface structures by interfacial diffusion of Au and Ag on Ag(110): A XPS and STM study

    NASA Astrophysics Data System (ADS)

    Schmid, Martin; Madix, Robert J.; Friend, C. M.

    2016-01-01

    Experiments on single crystal Au/Ag alloy surfaces may provide insight into the physical and chemical phenomena that determine the reactivity of complex alloy surfaces such as nanoporous gold or bimetallic nanoparticles. In this study, we report the highly unexpected observation that as soon as interfacial diffusion is feasible (400 K) thin gold films drastically restructure Ag(110) surfaces on the micrometer scale and create regular islands in a pattern which resembles the result of a sputter-etching process; bulk diffusion plays apparently no role during this phenomenon. Scanning tunneling microscopy (STM) reveals that the deposition of monolayer quantities of gold on the surface creates elongated islands, typically with a length of 1000 nm, a width of ~ 50 nm, and a height of ~ 30 lattice planes. The islands are predominantly elongated along the [1-10] direction and have a mutual distance of about 50 nm. Approximately, one monolayer of gold causes the relocation of ~ 11 ML of material. The islands are thermally unstable as further heating between 450 K and 600 K reduces the island structure significantly. The 'etching' of gold into the Ag(110) bulk material and the associated island formation can be rationalized with a simple kinetic model involving the diffusion of surface atoms only, illustrated with Monte Carlo simulations. A kinetic interpretation is also supported by the fact that those structures diminish after further annealing to higher temperatures. The observed large-scale reorganization underlines that even seemingly simple and well-defined surfaces may evolve in complex ways and that massive restructuring of surfaces can occur at temperatures well below the onset of bulk diffusion.

  18. STM-Induced Void Formation at the Al{sub 2}O{sub 3}/Ni{sub 3}Al(111) Interface

    SciTech Connect

    Magtoto, N.P.; Niu, C.; Anzaldura, M.; Kelber, J.A.; Jennison, D.R.

    2000-09-21

    Under UHV conditions at 300 K, the applied electric field and/or resulting current from an STM tip creates nanoscale voids at the interface between an epitaxial, 7.0 {angstrom} thick Al{sub 2}O{sub 3} film and a Ni{sub 3}Al(111) substrate. This phenomenon is independent of tip polarity. Constant current (1 nA) images obtained at +0.1 V bias and +2.0 bias voltage (sample positive) reveal that voids are within the metal at the interface and, when small, are capped by the oxide film. Void size increases with time of exposure. The rate of void growth increases with applied bias/field and tunneling current, and increases significantly for field strengths >5 MV/cm, well below the dielectric breakdown threshold of 12 {+-} 1 MV/cm. Slower rates of void growth are, however, observed at lower applied field strengths. Continued growth of voids, to {approximately}30 {angstrom} deep and {approximately}500 {angstrom} wide, leads to the eventual failure of the oxide overlayer. Density Functional Theory calculations suggest a reduction-oxidation (REDOX) mechanism: interracial metal atoms are oxidized via transport into the oxide, while oxide surface Al cations are reduced to admetal species which rapidly diffuse away. This is found to be exothermic in model calculations, regardless of the details of the oxide film structure; thus, the barriers to void formation are kinetic rather than thermodynamic. We discuss our results in terms of mechanisms for the localized pitting corrosion of aluminum, as our results suggest nanovoid formation requires just electric field and current, which are ubiquitous in environmental conditions.

  19. LT-STM/STS observation of definite superconducting gap states on the multistage crystal surface of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x}

    SciTech Connect

    Murakami, Hironaru; Aoki, Ryozo

    1996-12-31

    Low temperature STM/STS observations have been carried out on cleaved BSCCO crystal surfaces. The authors have succeeded in detection of a special layer, probably a CuO{sub 2} or Ca layer exposed on the surface. The STS spectrum which was reproducibly observed on this special site shows a considerably anisotropic but distinct superconducting gap structure with a definite and flat gap bottom region. This gap structure shows significantly different characteristic from another gap structure observed on the BiO layer, which shows a rounded shape at the gap bottom region without any indication of a finite gap state.

  20. Nondestructive room-temperature adsorption of 2,4,6-tri(2'-thienyl)-1,3,5-triazine on a Si-B interface: high-resolution STM imaging and molecular modeling.

    PubMed

    Makoudi, Y; Palmino, F; Duverger, E; Arab, M; Chérioux, F; Ramseyer, C; Therrien, B; Tschan, M J-L; Süss-Fink, G

    2008-02-22

    Organic nanostructures on semiconductors are currently investigated but the surfaces are known to interact strongly with molecules. To reduce the molecule-surface interaction, we used the Si(111)-B square root 3 x square root 3R30 degrees . Deposition of isolated 2,4,6-tri(2'-thienyl)-1,3,5-triazine, was achieved at room temperature without modification of their pi skeleton. This fascinating arrangement, observed by STM, has been validated by full density functional theory computations onto the entire system. The theoretical results give a clear explanation for the specific adsorption sites of molecules on the substrate. PMID:18352579

  1. Surface relaxation phenomena at electrified interfaces: Revealing adsorbate, potential, and solvent effects by combined x-ray diffraction, STM and DFT studies

    NASA Astrophysics Data System (ADS)

    Saracino, Martino; Broekmann, Peter; Gentz, Knud; Becker, Moritz; Keller, Hubert; Janetzko, Florian; Bredow, Thomas; Wandelt, Klaus; Dosch, Helmut

    2009-03-01

    Surface relaxation phenomena have been studied in an electrochemical environment using halide modified Cu(100) electrodes as model systems to unravel the impact of the chemical nature of the adsorbed halide, the applied potential, and the presence of solvent species on the surface interlayer spacings. Both, in situ STM and in situ x-ray scattering data point to lateral structures of the adsorbed halides on Cu(100) which are identical for both chloride and bromide. Under saturation conditions both halides form a p(1×1) adlayer on Cu(100) with reference to a conventional choice of the substrate fcc unit cell. The in situ x-ray scattering data clearly indicate that the copper-halide and the copper-copper interlayer spacings are much more affected by potential changes when bromide is adsorbed on the copper surface and are less affected when chloride is present. This difference in the potential dependence of both halides can be attributed to the larger polarizability of the bromide anion that is almost discharged on the copper surface at the highest applied potentials, while chloride remains largely ionic in the adsorbed state even at the highest applied potential. At the lowest applied potential of Ework=-150mV [vs reversible hydrogen electrode (RHE)] the Br-Cu and the topmost Cu-Cu layer distances are expanded by 0.150 and 0.058Å , respectively, with reference to their bulk analogs CuBr and Cu. These spacings continuously contract by up to 0.075 and 0.038Å when the electrode potential is increased to Ework=+50mV (RHE). Intriguingly, the second Cu layer experiences a potential-dependent buckling due to a different second-shell coordination of Cu by bromide while deeper Cu layers retain the bulk spacing at all potentials. Changes in the halide-copper and the copper-copper interlayer spacings are strongly correlated. An understanding of the in situ x-ray results is achieved by periodic quantum-chemical calculations at density-functional level that allow a modeling of

  2. Surface morphologies, electronic structures, and Kondo effect of lanthanide(III)-phthalocyanine molecules on Au(111) by using STM, STS and FET properties for next generation devices.

    PubMed

    Katoh, Keiichi; Komeda, Tadahiro; Yamashita, Masahiro

    2010-05-28

    The crystal structures of double-decker single-molecule magnets (SMMs) LnPc(2) (Ln = Tb(III) and Dy(III); Pc = phthalocyanine) and non-SMM YPc(2) were determined by using single crystal X-ray diffraction analysis. The compounds are isomorphous to each other. The compounds have metal-centers (M(3+) = Tb, Dy, and Y) sandwiched by two Pc ligands via eight isoindole-nitrogen atoms in a square-antiprism fashion. The twist angle between the two Pc ligands is 41.4 degrees. Scanning tunneling microscopy (STM) was used to investigate the compounds adsorbed on a Au(111) surface, deposited by using thermal evaporation in ultra-high vacuum. Both MPc(2) with eight-lobes and MPc with four-lobes, which has lost one Pc ligand, were observed. In the scanning tunneling spectroscopy (STS) images of TbPc molecules at 4.8 K, a Kondo peak with a Kondo temperature (T(K)) of approximately 250 K was observed near the Fermi level (V = 0 V). On the other hand, DyPc, YPc and MPc(2) exhibited no Kondo peak. In order to understand the observed Kondo effect, the energy splitting of sublevels in a crystal field should be taken into consideration. As the next step in our studies on the SMM/Kondo effect in Tb-Pc derivatives, we investigated the electronic transport properties of Ln-Pc molecules as the active layer in top- and bottom-contact thin-film organic field effect transistor (OFETs) devices. Tb-Pc molecule devices exhibit p-type semiconducting properties with a hole mobility (mu(H)) of approximately 10(-4) cm(2) V(-1) s(-1). Interestingly, the Dy-Pc based devices exhibited ambipolar semiconducting properties with an electron mobility (mu(e)) of approximately 10(-5) and a hole mobility (mu(H)) of approximately 10(-4) cm(2) V(-1) s(-1). This behavior has important implications for the electronic structure of the molecules. PMID:20396817

  3. STM studies of Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Inoue, Hiroyuki; Gyenis, Andras; Oh, Seong Woo; Li, Jian; Wang, Zhi Jun; Bernevig, Andrei; Ni, Ni; Yazdani, Ali

    Weyl semimetal exhibits a new gapless topological phase, which is characterized by an even number of band touching points of two non-degenerate bands in the bulk, called Weyl nodes. The surfaces of these compounds are expected to harbor topologically protected surface states with disconnected Fermi surfaces, called Fermi arcs, which connect surface projections of the Weyl nodes with opposing Chern numbers. Among the theoretically predicted Weyl semimetals, there have been several experimental reports on the presence of Fermi arcs in inversion-symmetry-broken monoarsenides, such as TaAs. In this talk, we will present atomic-scale imaging and spectroscopic mapping of the electronic properties of TaAs and other Weyl semimetal candidates. Such measurements have the potential to directly visualize the Fermi arc surface states of these compounds and to probe their properties. This work is supported by ARO and NSF.

  4. Isolation and characterization of Pseudomonas sp. STM 997 from soil sample having potentiality to degrade 3,6-dimethyl-1-keto-1,2,3,4-tetrahydrocarbazole: a novel approach.

    PubMed

    Chakraborty, Biswanath; Chakraborty, Suchandra; Basu, Anjan Kumar; Aditya, Bhrigu; Sinha, T P; Dhar, Tanima Modak; Saha, Chandan

    2012-12-01

    A pure colony of a bacterium from contaminated soil was isolated by exploiting 3,6-dimethyl-1-keto-1,2,3,4-tetrahydrocarbazole, a novel carbazole derivative, having indole moiety as well as 3-methyl functionality both in aromatic and hydro-aromatic moiety, as a sole source of carbon and energy. Taxonomical studies, biochemical analysis, and 16S rDNA sequence analysis indicated that the isolated strain has close similarity with Pseudomonas sp. Thin-layer chromatography followed by HPLC and mass spectroscopic study indicates that the isolated Pseudomonas sp. STM 997 degrades 3,6-dimethyl-1-keto-1,2,3,4-tetrahydrocarbazole, and this strain may be useful in the bioremediation of environments contaminated by the compounds containing carbazole moiety with methyl substituents at various reactive sites. This study also provides an evidence in favor of the suggested biodegradation of 3-methylcarbazole to carbazole in plants. PMID:22987067

  5. The evolution of the polycrystalline copper surface, first to Cu(111) and then to Cu(100), at a fixed CO₂RR potential: a study by operando EC-STM.

    PubMed

    Kim, Youn-Geun; Baricuatro, Jack Hess; Javier, Alnald; Gregoire, John Mathew; Soriaga, Manuel P

    2014-12-23

    A study based on operando electrochemical scanning tunneling microscopy (EC-STM) has shown that a polycrystalline Cu electrode held at a fixed negative potential, -0.9 V (vs SHE), in the vicinity of CO2 reduction reactions (CO2RR) in 0.1 M KOH, undergoes stepwise surface reconstruction, first to Cu(111) within 30 min, and then to Cu(100) after another 30 min; no further surface transformations occurred after establishment of the Cu(100) surface. The results may help explain the Cu(100)-like behavior of Cu(pc) in terms of CO2RR product selectivity. They likewise suggest that products exclusive to Cu(100) single-crystal electrodes may be generated through the use of readily available inexpensive polycrystalline Cu electrodes. The study highlights the dynamic nature of heterogeneous electrocatalyst surfaces and also underscores the importance of operando interrogations when structure-composition-reactivity correlations are intended. PMID:25489793

  6. Simulated structure and imaging of NTCDI on Si(1 1 1)-7 × 7 : a combined STM, NC-AFM and DFT study.

    PubMed

    Jarvis, S P; Sweetman, A M; Lekkas, I; Champness, N R; Kantorovich, L; Moriarty, P

    2015-02-11

    The adsorption of naphthalene tetracarboxylic diimide (NTCDI) on Si(1 1 1)-7 × 7 is investigated through a combination of scanning tunnelling microscopy (STM), noncontact atomic force microscopy (NC-AFM) and density functional theory (DFT) calculations. We show that NTCDI adopts multiple planar adsorption geometries on the Si(1 1 1)-7 × 7 surface which can be imaged with intramolecular bond resolution using NC-AFM. DFT calculations reveal adsorption is dominated by covalent bond formation between the molecular oxygen atoms and the surface silicon adatoms. The chemisorption of the molecule is found to induce subtle distortions to the molecular structure, which are observed in NC-AFM images. PMID:25414147

  7. Modulation of Biofilm-Formation in Salmonella enterica Serovar Typhimurium by the Periplasmic DsbA/DsbB Oxidoreductase System Requires the GGDEF-EAL Domain Protein STM3615

    PubMed Central

    Römling, Ute; Rhen, Mikael

    2014-01-01

    In Salmonella enterica serovar Typhimurium (S. Typhimurium), biofilm-formation is controlled by the cytoplasmic intracellular small-molecular second messenger cyclic 3′, 5′-di- guanosine monophosphate (c-di-GMP) through the activities of GGDEF and EAL domain proteins. Here we describe that deleting either dsbA or dsbB, respectively encoding a periplasmic protein disulfide oxidase and a cytoplasmic membrane disulfide oxidoreductase, resulted in increased biofilm-formation on solid medium. This increased biofilm-formation, defined as a red, dry and rough (rdar) colony morphotype, paralleled with enhanced expression of the biofilm master regulator CsgD and the biofilm-associated fimbrial subunit CsgA. Deleting csgD in either dsb mutant abrogated the enhanced biofilm-formation. Likewise, overexpression of the c-di-GMP phosphodiesterase YhjH, or mutationally inactivating the CsgD activator EAL-domain protein YdiV, reduced biofilm-formation in either of the dsb mutants. Intriguingly, deleting the GGDEF-EAL domain protein gene STM3615 (yhjK), previously not connected to rdar morphotype development, also abrogated the escalated rdar morphotype formation in dsb mutant backgrounds. Enhanced biofilm-formation in dsb mutants was furthermore annulled by exposure to the protein disulfide catalyst copper chloride. When analyzed for the effect of exogenous reducing stress on biofilm-formation, both dsb mutants initially showed an escalated rdar morphotype development that later dissolved to reveal a smooth mucoid colony morphotype. From these results we conclude that biofilm-development in S. Typhimurium is affected by periplasmic protein disulphide bond status through CsgD, and discuss the involvement of selected GGDEF/EAL domain protein(s) as signaling mediators. PMID:25153529

  8. STM imaging of electrically floating islands

    NASA Astrophysics Data System (ADS)

    Realpe, H.; Shamir, N.; Mintz, M. H.; Manassen, Y.

    2006-07-01

    Appearances and disappearances of Gd islands grown on top of a W(1 1 0) substrate were observed in time scales of hours after exposing the surface to a few Langmuirs of hydrogen. The phenomenon is presented and explained in terms of (temporary) creation of electrically floating islands, due to electrical decoupling of the island and substrate by the hydrogen that diffuses into the island/substrate interface. The disappearance of such an island is explained by forming a double barrier junction consisting of two tunneling barriers in series, causing, by charging, the potential of the island to become equal to that of the tip. The island then becomes "invisible" and the tip follows the corrugation of the surface under the substrate. The reappearance follows hydrogen mobility that retains the electrical conductivity of the island-substrate interface.

  9. STM studies of synthetic peptide monolayers

    SciTech Connect

    Bergeron, David J.; Clauss, Wilfried; Johnson, Alan T.; Pilloud, Denis L.; Leslie Dutton, P.

    1998-08-11

    We have used scanning probe microscopy to investigate self-assembled monolayers of chemically synthesized peptides. We find that the peptides form a dense uniform monolayer, above which is found a sparse additional layer. Using scanning tunneling microscopy, submolecular resolution can be obtained, revealing the alpha helices which constitute the peptide. The nature of the images is not significantly affected by the incorporation of redox cofactors (hemes) in the peptides.

  10. STM/STS observation of polyoxoanions on HOPG surfaces: the wheel-shaped [Cu20Cl(OH)24(H2O)12(P8W48O184)]25- and the ball-shaped [{Sn(CH3)2(H2O)}24{Sn(CH3)2}12(A-PW9O34)12]36-.

    PubMed

    Alam, Mohammad S; Dremov, Viacheslav; Müller, Paul; Postnikov, Andrei V; Mal, Sib Sankar; Hussain, Firasat; Kortz, Ulrich

    2006-04-01

    A combination of scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) techniques have been performed on the wheel-shaped [Cu20Cl(OH)24(H2O)12(P8W48O184)]25- and the ball-shaped [{Sn(CH3)2(H2O)}24{Sn(CH3)2}12(A-PW9O34)12]36- deposited on highly oriented pyrolytic graphite surfaces. Small, regular molecule clusters, as well as separated single molecules, were observed. The size of the molecules is in agreement with the data determined by X-ray crystallography. In STS measurements, we found a rather large contrast at the expected location of the Cu metal centers in our molecules, i.e., the location of the individual Cu ions in their organic matrix is directly addressable by STS. PMID:16562942

  11. Theoretical interpretation of donor wavefunctions STM images in silicon

    NASA Astrophysics Data System (ADS)

    Koiller, Belita; Saraiva, A. L.; Capaz, Rodrigo B.; Calderón, M. J.,; Salfi, J.; Voisin, B.; Bocquel, J.; Rogge, S.

    Single dopant wavefunctions in Si have recently been probed by scanning tunneling spectroscopy, revealing localized patterns of resonantly enhanced tunneling currents. We show that the shapes of the conducting splotches resemble cuts through Kohn-Luttinger (KL) hydrogenic envelopes, which modulate the interfering Bloch states of conduction electrons. All the non-monotonic features of the current profile are consistent with the charge density fluctuations observed between successive { 001 } atomic planes, including a counter-intuitive reduction of the symmetry - a heritage of the lowered point group symmetry at these planes. A model-independent analysis of the diffraction figure constrains the value of the electron wavevector to k0 = (0 . 82 +/- 0 . 03) (2 π /aSi) . Unlike prior measurements, averaged over a sizeable density of electrons, this estimate is obtained directly from isolated electrons. We further investigate the model-specific anisotropy of the wave function envelope, related to the effective mass anisotropy. This anisotropy appears in the KL variational wave function envelope as the ratio between Bohr radii b / a . Authors thank partial support by CNPq, FAPERJ in Bazil, by FIS2012-33521, MINECO in Spain and by ARC CE110001027 and ARO W911NF-08-1-0527 in Australia.

  12. Zn effect on STM imaging of brass surfaces

    NASA Astrophysics Data System (ADS)

    Wiame, Frédéric; Islam, Mazharul M.; Salgın, Bekir; Światowska, Jolanta; Costa, Dominique; Diawara, Boubakar; Maurice, Vincent; Marcus, Philippe

    2016-02-01

    The surface of brass has been characterized by combined experimental and theoretical approaches. The experimental scanning tunneling microscopy study performed on a Cu0.7Zn0.3(111) surface at room temperature showed terraces of up to several tens of nanometers in width, separated by monoatomic steps. Depending on the tunneling conditions, a disordered pattern or a sharp atomically-resolved hexagonal lattice was observed. The disordered pattern is attributed to the superposition of Friedel oscillations at the surface induced by the presence of Zn atoms. Comparison of simulated images, based on a simple model of randomly distributed point defects, shows a good agreement with experimental results. At atomic resolution, a chemical contrast has been demonstrated between Zn and Cu atoms at the surface showing the random distribution of isolated Zn atoms into the hexagonal lattice.

  13. Ba termination of Ge(001) studied with STM.

    PubMed

    Koczorowski, W; Grzela, T; Radny, M W; Schofield, S R; Capellini, G; Czajka, R; Schroeder, T; Curson, N J

    2015-04-17

    We use controlled annealing to tune the interfacial properties of a sub-monolayer and monolayer coverages of Ba atoms deposited on Ge(001), enabling the generation of either of two fundamentally distinct interfacial phases, as revealed by scanning tunneling microscopy. Firstly we identify the two key structural phases associated with this adsorption system, namely on-top adsorption and surface alloy formation, by performing a deposition and annealing experiment at a coverage low enough (∼0.15 ML) that isolated Ba-related features can be individually resolved. Subsequently we investigate the monolayer coverage case, of interest for passivation schemes of future Ge based devices, for which we find that the thermal evaporation of Ba onto a Ge(001) surface at room temperature results in on-top adsorption. This separation (lack of intermixing) between Ba and Ge layers is retained through successive annealing steps to temperatures of 470, 570, 670 and 770 K although a gradual ordering of the Ba layer is observed at 570 K and above, accompanied by a decrease in Ba layer density. Annealing above 770 K produces the 2D surface alloy phase accompanied by strain relief through monolayer height trench formation. An annealing temperature of 1070 K sees a further change in surface morphology but retention of the 2D surface alloy characteristic. These results are discussed in view of their possible implications for future semiconductor integrated circuit technology. PMID:25797886

  14. Ba termination of Ge(001) studied with STM

    NASA Astrophysics Data System (ADS)

    Koczorowski, W.; Grzela, T.; Radny, M. W.; Schofield, S. R.; Capellini, G.; Czajka, R.; Schroeder, T.; Curson, N. J.

    2015-04-01

    We use controlled annealing to tune the interfacial properties of a sub-monolayer and monolayer coverages of Ba atoms deposited on Ge(001), enabling the generation of either of two fundamentally distinct interfacial phases, as revealed by scanning tunneling microscopy. Firstly we identify the two key structural phases associated with this adsorption system, namely on-top adsorption and surface alloy formation, by performing a deposition and annealing experiment at a coverage low enough (∼0.15 ML) that isolated Ba-related features can be individually resolved. Subsequently we investigate the monolayer coverage case, of interest for passivation schemes of future Ge based devices, for which we find that the thermal evaporation of Ba onto a Ge(001) surface at room temperature results in on-top adsorption. This separation (lack of intermixing) between Ba and Ge layers is retained through successive annealing steps to temperatures of 470, 570, 670 and 770 K although a gradual ordering of the Ba layer is observed at 570 K and above, accompanied by a decrease in Ba layer density. Annealing above 770 K produces the 2D surface alloy phase accompanied by strain relief through monolayer height trench formation. An annealing temperature of 1070 K sees a further change in surface morphology but retention of the 2D surface alloy characteristic. These results are discussed in view of their possible implications for future semiconductor integrated circuit technology.

  15. STM Studies of TbTe3: Evidence for a Fully Incommensurate Charge Density Wave

    SciTech Connect

    Fang, A.; Ru, N.; Fisher, I.R.; Kapitulnik, A.; /Stanford U., Appl. Phys. Dept. /Stanford U., Phys. Dept.

    2010-02-15

    We observe unidirectional charge density wave ordering on the cleaved surface of TbTe{sub 3} with a Scanning Tunneling Microscope at {approx}6 K. The modulation wave-vector q{sub CDW} as determined by Fourier analysis is 0.71 {+-} 0.02 x2{pi}/c. Where c is one edge of the in-plane 3D unit cell. Images at different tip-sample voltages show the unit cell doubling effects of dimerization and the layer below. Our results agree with bulk X-ray measurements, with the addition of (1/3) x2{pi}/a ordering perpendicular to the CDW. Our analysis indicates that the CDW is incommensurate.

  16. Imaging epitaxial graphene on SiC(0001) using STM with functionalized W tips

    NASA Astrophysics Data System (ADS)

    Rhim, S. H.; Qi, Y.; Sun, G. F.; Liu, Y.; Weinert, M.; Li, L.

    2012-02-01

    Epitaxial graphene on SiC(0001) is studied using scanning tunneling microscopy with W tips functionalized by transition-metal (Cr, Fe) coatings, enabling the imaging of states within a few meV of the Fermi level that are not accessible with conventional W tips. First-principles modeling of these tips as pyramidal structures on W(110) indicates that an apex atom is stable for the Cr/W(110) tip but not for the Fe/W(110) or W/W(110) tips. Further calculations of the tunneling current show that the Cr- and Fe-coated tips can get significantly closer to the substrate than a bare W tip at a given current, and that the Cr (Fe) tip states contributing to the tunneling at low bias are spatially more localized than the W tip states. These characteristics lead to increased resolution, making possible the selective imaging of the complex electronic properties of the epitaxial graphene on SiC(0001)1,2.

  17. Visualized Multiprobe Electrical Impedance Measurements with STM Tips Using Shear Force Feedback Control

    PubMed Central

    Botaya, Luis; Coromina, Xavier; Samitier, Josep; Puig-Vidal, Manel; Otero, Jorge

    2016-01-01

    Here we devise a multiprobe electrical measurement system based on quartz tuning forks (QTFs) and metallic tips capable of having full 3D control over the position of the probes. The system is based on the use of bent tungsten tips that are placed in mechanical contact (glue-free solution) with a QTF sensor. Shear forces acting in the probe are measured to control the tip-sample distance in the Z direction. Moreover, the tilting of the tip allows the visualization of the experiment under the optical microscope, allowing the coordination of the probes in X and Y directions. Meanwhile, the metallic tips are connected to a current–voltage amplifier circuit to measure the currents and thus the impedance of the studied samples. We discuss here the different aspects that must be addressed when conducting these multiprobe experiments, such as the amplitude of oscillation, shear force distance control, and wire tilting. Different results obtained in the measurement of calibration samples and microparticles are presented. They demonstrate the feasibility of the system to measure the impedance of the samples with a full 3D control on the position of the nanotips. PMID:27231911

  18. Adsorption and thermal treatments of 1-dodecene on Si(100) investigated by STM

    DOE PAGESBeta

    Liu, H. W.; Fujikawa, Y.; Sadowski, J. T.; Xue, Q. -K.; Sakurai, T.

    2015-03-01

    We investigate the atomic behaviour of long-chain 1-dodecene adsorbed on Si(100) using a scanning tunnelling microscope with an exposure of 30 to 2.4 Langmuirs. Unlike previous reports on short-chain molecules, remarkable self-ordered assembly of molecules is not observed at room temperature, which is possibly attributed to the asymmetric molecular structure with long chains of 1-dodecene. After annealing at 500–580 °C, ordered patterns form with a c(4 × 4) structure, accompanied with thermal decomposition of molecules.

  19. AFM and STM studies of the carbonization and graphitization of polyimide films

    NASA Astrophysics Data System (ADS)

    Nysten, B.; Roux, J.-C.; Flandrois, S.; Daulan, C.; Saadaoui, H.

    1993-11-01

    Kapton polyimide and high-modulus polyimide (PPT) films were carbonized and graphitized at various temperatures from 600 to 3000 °C. Their surface was studied by atomic-force microscopy and/or by scanning tunneling microscopy in order to follow the modification of the large-scale morphology and the atomic structure as a function of the heat-treatment temperature (HTT). On the pristine Kapton films, the local order of the molecules is brought to the fore. With increasing HTT (600 to 1000 °C) the structure becomes more disordered while at larger scale a bumpy morphology appears. During graphitization, the bumpy morphology gradually disappears and is replaced by graphitized terraces whose size increases with HTT. At atomic scale, it is shown that the graphene layers progressively grow for HTT higher than 1800 °C. On the films treated between 1800 and 2400 °C, graphene layers containing point defects are imaged and (√3 × √3 )R 30° superstructures are observed near large defects. On the samples treated at 2400 and 2600 °C, moiré patterns are observed and are attributed to stacking faults (turbostratic structure).

  20. Embedded image processing engine using ARM cortex-M4 based STM32F407 microcontroller

    SciTech Connect

    Samaiya, Devesh

    2014-10-06

    Due to advancement in low cost, easily available, yet powerful hardware and revolution in open source software, urge to make newer, more interactive machines and electronic systems have increased manifold among engineers. To make system more interactive, designers need easy to use sensor systems. Giving the boon of vision to machines was never easy, though it is not impossible these days; it is still not easy and expensive. This work presents a low cost, moderate performance and programmable Image processing engine. This Image processing engine is able to capture real time images, can store the images in the permanent storage and can perform preprogrammed image processing operations on the captured images.

  1. Single Molecule Switches and Molecular Self-Assembly: Low Temperature STM Investigations and Manipulations

    SciTech Connect

    Iancu, Violeta

    2006-08-01

    This dissertation is devoted to single molecule investigations and manipulations of two porphyrin-based molecules, chlorophyll-a and Co-popphyrin. The molecules are absorbed on metallic substrates and studied at low temperatures using a scanning tunneling microscope. The electronic, structural and mechanical properties of the molecules are investigated in detail with atomic level precision. Chlorophyll-a is the key ingredient in photosynthesis processes while Co-porphyrin is a magnetic molecule that represents the recent emerging field of molecular spintronics. Using the scanning tunneling microscope tip and the substrate as electrodes, and the molecules as active ingredients, single molecule switches made of these two molecules are demonstrated. The first switch, a multiple and reversible mechanical switch, is realized by using chlorophyll-a where the energy transfer of a single tunneling electron is used to rotate a C-C bond of the molecule's tail on a Au(111) surface. Here, the det

  2. Theoretical analysis of STM experiments at rutile TiO 2 surfaces

    NASA Astrophysics Data System (ADS)

    Gülseren, O.; James, R.; Bullett, D. W.

    1997-04-01

    A first-principles atomic orbital-based electronic structure method is used to investigate the low index surfaces of rutile titanium dioxide (TiO 2). The method is relatively cheap in computational terms, making it attractive for the study of oxide surfaces, many of which undergo large reconstructions, and may be governed by the presence of oxygen vacancy defects. Calculated surface charge densities are presented for low-index surfaces of TiO 2, and the relation of these results to experimental scanning tunnelling microscopy images is discussed. Atomic resolution images at these surfaces tend to be produced at positive bias, probing states which largely consist of unoccupied Ti 3d bands, with a small contribution from O 2p. These experiments are particularly interesting since the O atoms tend to sit up to 1 Å above the Ti atoms, so providing a play-off between electronic and geometric structure in image formation.

  3. Local work function and STM tip-induced distortion of graphene on Ir(111)

    NASA Astrophysics Data System (ADS)

    Altenburg, S. J.; Berndt, R.

    2014-05-01

    The contact conductance and the apparent barrier height ϕ of graphene on Ir(111) are measured with a cryogenic scanning tunneling microscope. A strong dependence of ϕ on the tip-sample distance is found and explained by a local lifting of the graphene film by van-der-Waals forces. Variations of ϕ observed within the moiré unit cell of the graphene layer are interpreted in terms of differences in the local work function and the buckling of the graphene film. Comparison to results based on density functional theory indicates that a modulation of the charge transfer between graphene and Ir(111) is the origin of the work function variations.

  4. Micromechanisms of brittle fracture: STM, TEM and electron channeling analysis. Final report

    SciTech Connect

    Gerberich, W.W.

    1997-01-01

    The original thrust of this grant was to apply newly developed techniques in scanning tunneling and transmission electron microscopy to elucidate the mechanism of brittle fracture. This grant spun-off several new directions in that some of the findings on bulk structural materials could be utilized on thin films or intermetallic single crystals. Modeling and material evaluation efforts in this grant are represented in a figure. Out of this grant evolved the field the author has designated as Contact Fracture Mechanics. By appropriate modeling of stress and strain distribution fields around normal indentations or scratch tracks, various measures of thin film fracture or decohesion and brittle fracture of low ductility intermetallics is possible. These measures of fracture resistance in small volumes are still evolving and as such no standard technique or analysis has been uniformly accepted. For brittle ceramics and ceramic films, there are a number of acceptable analyses such as those published by Lawn, Evans and Hutchinson. For more dissipative systems involving metallic or polymeric films and/or substrates, there is still much to be accomplished as can be surmised from some of the findings in the present grant. In Section 2 the author reviews the funding history and accomplishments associated mostly with bulk brittle fracture. This is followed by Section 3 which covers more recent work on using novel techniques to evaluate fracture in low ductility single crystals or thin films using micromechanical probes. Basically Section 3 outlines how the recent work fits in with the goals of defining contact fracture mechanics and gives an overview of how the several examples in Section 4 (the Appendices) fit into this framework.

  5. Unraveling the electron pairing mechanism of FeSe by MBE and STM

    NASA Astrophysics Data System (ADS)

    Song, Canli

    Studies of high-transition-temperature superconductivity usually suffer from various imperfections in materials. Here we apply the state-of-the-art molecular beam epitaxy (MBE) to prepare controllably high-quality FeSe films on various substrates, and explore their superconducting properties using cryogenic scanning tunneling microscope. Single impurities, twin boundaries as well as strain are found in the MBE-grown FeSe films on graphene, and invariably suppress the superconductivity. Meanwhile, electronic nematicity and signatures of a bosonic mode, whose energy also decreases with strain, were identified. More significantly, we observed two disconnected superconducting domes at alkali-metal potassium (K)-dosed FeSe surface, stepping towards the mechanistic understanding of superconductivity in FeSe-derived superconductors. Our results are clarifying the secret of high-Tc superconductivity in FeSe-related superconductors, and by implications, in other unconventional superconductors, and guiding how to enhance Tc by interface engineering. This work was nancially supported by National Science Foundation and Ministry of Science and Technology of China.

  6. Adsorption of organic molecules on the TiO2(011) surface: STM study.

    PubMed

    Godlewski, Szymon; Tekiel, Antoni; Prauzner-Bechcicki, Jakub S; Budzioch, Janusz; Gourdon, Andre; Szymonski, Marek

    2011-06-14

    High resolution scanning tunneling microscopy has been applied to investigate adsorption and self-assembly of large organic molecules on the TiO(2)(011) surface. The (011) face of the rutile titania has been rarely examined in this context. With respect to possible industrial applications of rutile, quite often in a powder form, knowledge on behavior of organic molecules on that face is required. In the presented study we fill in the gap and report on experiments focused on the self-assembly of organic nanostructures on the TiO(2)(011) surface. We use three different kinds of organic molecules of potential interest in various applications, namely, PTCDA and CuPc representing flat, planar stacking species, and Violet Landers specially designed for new applications in molecular electronics. In order to reach a complete picture of molecular behavior, extended studies with different surface coverage ranging from single molecule up to 2 monolayer (ML) thick films are performed. Our results show that the adsorption behavior is significantly different from previously observed for widely used metallic templates. Creation of highly ordered molecular lines, quasi-ordered wetting layers, controlled geometrical reorientation upon thermal treatment, existence of specific adsorption geometries, and prospects for tip-induced molecule ordering and manipulation provide better understanding and add new phenomena to the knowledge on the (011) face of rutile titania. PMID:21682527

  7. STM tip-assisted engineering of molecular nanostructures: PTCDA islands on Ge(001):H surfaces

    PubMed Central

    Ahmad Zebari, Amir A; Kolmer, Marek

    2013-01-01

    Summary Islands composed of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) molecules are grown on a hydrogen passivated Ge(001):H surface. The islands are studied with room temperature scanning tunneling microscopy and spectroscopy. The spontaneous and tip-induced formation of the top-most layer of the island is presented. Assistance of the scanning probe seems to be one of the factors that facilitate and speed the process of formation of the top-most layer. PMID:24367762

  8. STM tip-assisted engineering of molecular nanostructures: PTCDA islands on Ge(001):H surfaces.

    PubMed

    Ahmad Zebari, Amir A; Kolmer, Marek; Prauzner-Bechcicki, Jakub S

    2013-01-01

    Islands composed of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) molecules are grown on a hydrogen passivated Ge(001):H surface. The islands are studied with room temperature scanning tunneling microscopy and spectroscopy. The spontaneous and tip-induced formation of the top-most layer of the island is presented. Assistance of the scanning probe seems to be one of the factors that facilitate and speed the process of formation of the top-most layer. PMID:24367762

  9. STM study of monolayer MoS2 synthesized by Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Mills, Adam; Chen, Chuanhui; Yu, Yifei; Cao, Linyui; Tao, Changgang

    2014-03-01

    Monolayer molybdenum disulfide (MoS2) , an atomically thin transition-metal dichalcogenide semiconductor with a direct band gap, as opposed to an indirect band gap in bulk MoS2, has recently captured a lot of research interest for its distinctive optical and electronic properties, and potential applications such as field effect transistors, optoelectronic devices and chemical sensors. Using scanning tunneling microscopy, we have investigated monolayer MoS2 synthesized by chemical vapor deposition. The structural and electronic properties of monolayer MoS2 grown on glassy carbon and other substrates will be presented. We will also discuss our preliminary scanning tunneling spectroscopy measurements on these samples.

  10. STM study of C60F18 high dipole moment molecules on Au(111)

    NASA Astrophysics Data System (ADS)

    Bairagi, K.; Bellec, A.; Chumakov, R. G.; Menshikov, K. A.; Lagoute, J.; Chacon, C.; Girard, Y.; Rousset, S.; Repain, V.; Lebedev, A. M.; Sukhanov, L. P.; Svechnikov, N. Yu.; Stankevich, V. G.

    2015-11-01

    Scanning tunneling microscopy and spectroscopy studies of C60F18 molecules deposited on Au(111) are reported and compared to C60 molecules both at liquid helium temperature and room temperature (RT). Whereas adsorption and electronic properties of C60F18 single molecules were studied at low temperature (LT), self-assemblies were investigated at RT. In both cases, the fluorine atoms of the C60F18 molecules are pointed towards the surface. Individual C60F18 molecules on Au(111) have a HOMO-LUMO gap of 2.9 eV. The self-assembled islands exhibit a close-packed hexagonal lattice with amorphous borders. The comparison with C60 molecules clearly demonstrates the influence of the C60F18 electric dipole moment (EDM) on the electronic properties of single molecules and on the thermodynamics of self-assembled islands. Besides, the apparent height value of a separate molecule increases in a self-assembly environment as a result of a depolarization phenomenon.

  11. STM study of PTCDA on Sn/Si(111)- 2 √{ 3 } × 2 √{ 3 }

    NASA Astrophysics Data System (ADS)

    Zhang, H. M.; Johansson, L. S. O.

    2016-03-01

    The electronic structures of perylene tetracarboxylic dianhydride on Sn/Si(111)- 2 √{ 3 } × 2 √{ 3 } have been studied by scanning tunneling microscopy and spectroscopy. Individual molecules have been investigated at 0.15 ML, while at 0.3 ML molecules formed short rods. At 0.6 ML, the molecular rods interacted with each other, coupling with the substrate and forming a new 4 √{ 3 } × 2 √{ 3 } super structure. At 0.9 ML, the surface was further reconstructed and consisted of strips with two and three rods of molecules. We found that these surface structures are strongly modified by the molecule/substrate and the intermolecular interactions. As a result, the HOMO-LUMO gaps of these molecules change with respect to the phases and the thickness. For a single molecular layer of the 4 √{ 3 } × 2 √{ 3 } phase, the HOMO-LUMO levels were split with a gap of approximately 2.1 eV, which is caused by charge transfer from the substrate to the molecules.

  12. Potential of lateral interactions of CO on Pt (111) fitted to recent STM images

    NASA Astrophysics Data System (ADS)

    Myshlyavtsev, Alexander V.; Stishenko, Pavel V.

    2015-12-01

    Monolayers of carbon monoxide (CO) on Pt(111) surfaces are one of the most studied adsorption systems. However, molecular models of this system still do not take into account the reliable potential of lateral interactions between adsorbed CO molecules. Recent advances in experimental technique have brought high-resolution real-space images of CO/Pt(111) monolayers. For example, Yang et al. (J. Phys. Chem. C 117 (2013) 16429-16437) found island structures for coverages from 0.11 to 0.25 ML. In this study we have shown that these island structures can be explained with long-range oscillating lateral interactions. Parameters of the proposed potential were fitted to experimental scanning tunneling microscopy images with a series of Monte Carlo simulations.

  13. STM study of PTCDA on Sn/Si(111)-23×23.

    PubMed

    Zhang, H M; Johansson, L S O

    2016-03-28

    The electronic structures of perylene tetracarboxylic dianhydride on Sn/Si(111)-23×23 have been studied by scanning tunneling microscopy and spectroscopy. Individual molecules have been investigated at 0.15 ML, while at 0.3 ML molecules formed short rods. At 0.6 ML, the molecular rods interacted with each other, coupling with the substrate and forming a new 43×23 super structure. At 0.9 ML, the surface was further reconstructed and consisted of strips with two and three rods of molecules. We found that these surface structures are strongly modified by the molecule/substrate and the intermolecular interactions. As a result, the HOMO-LUMO gaps of these molecules change with respect to the phases and the thickness. For a single molecular layer of the 43×23 phase, the HOMO-LUMO levels were split with a gap of approximately 2.1 eV, which is caused by charge transfer from the substrate to the molecules. PMID:27036469

  14. Tailored Organic Molecular Growth on Silicon Studied by STM and DFT

    NASA Astrophysics Data System (ADS)

    Wagner, Sean; Huang, Bing; Park, Changwon; Feng, Jiagui; Yoon, Mina; Zhang, Pengpeng

    2015-03-01

    Control of highly ordered organic molecular thin films with extended π systems is currently of intense interest for integrating molecules into modern electronics due to their tunable nature. Selection of molecules and substrates can lead to desired transport properties such as charge transfer, charge injection, exciton diffusion, etc., at the hetero-interface, which is crucial to the development of organic and molecular electronics. Combining scanning tunneling microscopy and density functional theory, we show that by appropriately choosing the coordinated transition-metal ion in metal phthalocyanine, the strength of the molecule-substrate interaction can be tailored, allowing for the molecular ordering and orientation at the hetero-interface with the silicon substrate to be tuned accordingly. This mechanism provides new control over the delicately balanced molecule-substrate and intermolecular interactions, offering a route towards well-ordered organic molecular growth. Experimental work is funded by the U. S. DOE Office of Science Early Career Research Program (DE-SC0006400) through the Office of Basic Energy Sciences. Theory work conducted at Oak Ridge National Laboratory is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. DOE.

  15. Direct visualization of photoinduced glassy dynamics on the amorphous silicon carbide surface by STM movies

    NASA Astrophysics Data System (ADS)

    Nguyen, Duc; Nienhaus, Lea; Haasch, Richard T.; Lyding, Joseph; Gruebele, Martin

    2015-03-01

    Glassy dynamics can be controlled by light irradiation. Sub- and above-bandgap irradiation cause numerous phenomena in glasses including photorelaxation, photoexpansion, photodarkening and pohtoinduced fluidity. We used scanning tunneling microscopy to study surface glassy dynamics of amorphous silicon carbide irradiated with above- bandgap 532 nm light. Surface clusters of ~ 4-5 glass forming unit in diameter hop mostly in a two-state fashion, both without and with irradiation. Upon irradiation, the average surface hopping activity increases by a factor of 3. A very long (~1 day) movie of individual clusters with varying laser power density provides direct evidence for photoinduced enhanced hopping on the glass surfaces. We propose two mechanisms: heating and electronic for the photoenhanced surface dynamics.

  16. The Impact of Information Technology and Networks: New Perspectives for Scientific, Technical and Medical (STM) Publishing

    NASA Astrophysics Data System (ADS)

    de Kemp, Arnoud

    1997-01-01

    This contribution can only be a small collection of ideas and experiences from my (personal) publishing point of view. The subject area assigned is very generic and there are indeed many developments going on, so I had to be very selective and restrictive, while avoiding redundancies as much as I could. I have included some metaphors and paradigms, such as the shift from print publications to electronic information. The traditional role of publishers in the information chain is compared with the new opportunities that electronic publishing is offering now and may offer in the foreseeable future. From DTP to DTD, unplugged and unbundled information, linearity, appropriateness, packaging and customizing, filters, intelligent agents, quality, integrity and authenticity are some of the items hidden in the text. The overall conclusion is: the Internet still can learn a lot from print...!

  17. The impact of information technology and networks: new perspectives for scientific, technical and medical (STM) publishing

    NASA Astrophysics Data System (ADS)

    De Kemp, Arnoud

    This contribution is a strongly abbreviated notation of a much longer presentation at the Workshop on Strategies and Techniques of Information for Astronomy, organized by the European Science Foundation in Strasbourg on 21/22 June 1996. The process of publishing will undergo dramatic changes due to the influences of information technology and networks. The publishing business as a whole will shift from traditional print- and paper-based organisations to a fully digital workflow from author to end-user. Electronic publishing has moved from pre-print activities to digital preprints on a variety of servers, but still most scientific documentation is printed and not only for archival purposes. In this short contribution, a plea is made for new rules in scientific communication that authors, editors, publishers, societies, libraries and users can recognize. In addition, in the electronic age we need more security for copyright, transactions over networks and against misuse in general.

  18. STM studies of topological phase transition in (Bi,In)2Se3

    NASA Astrophysics Data System (ADS)

    Zhang, Wenhan; Wang, Xueyun; Cheong, Sang-Wook; Wu, Weida; Weida Wu Team; Sang-Wook Cheong Collaboration

    Topological insulators (TI) are a class of materials with insulating bulk and metallic surface state, which is the result of band inversion induced by strong spin-orbit coupling (SOC). The transition from topological phase to non-topological phase is of great significance. In theory, topological phase transition is realized by tuning SOC strength. It is characterized by the process of gap closing and reopening. Experimentally it was observed in two systems: TlBi(S1-xSex)2 and (Bi1-xInx)2 Se3 where the transition is realized by varying isovalent elements doping concentration. However, none of the previous studies addressed the impact of disorder, which is inevitable in doped systems. Here, we present a systematic scanning tunneling microscopy/spectroscopy study on (Bi1-xInx)2 Se3 single crystals with different In concentrations across the transition. Our results reveal an electronic inhomogeneity due to the random distribution of In defects which locally suppress the topological surface states. Our study provides a new angle of understanding the topological transition in the presence of strong disorders. This work is supported by NSF DMR-1506618.

  19. Flexible information coding in human auditory cortex during perception, imagery, and STM of complex sounds.

    PubMed

    Linke, Annika C; Cusack, Rhodri

    2015-07-01

    Auditory cortex is the first cortical region of the human brain to process sounds. However, it has recently been shown that its neurons also fire in the absence of direct sensory input, during memory maintenance and imagery. This has commonly been taken to reflect neural coding of the same acoustic information as during the perception of sound. However, the results of the current study suggest that the type of information encoded in auditory cortex is highly flexible. During perception and memory maintenance, neural activity patterns are stimulus specific, reflecting individual sound properties. Auditory imagery of the same sounds evokes similar overall activity in auditory cortex as perception. However, during imagery abstracted, categorical information is encoded in the neural patterns, particularly when individuals are experiencing more vivid imagery. This highlights the necessity to move beyond traditional "brain mapping" inference in human neuroimaging, which assumes common regional activation implies similar mental representations. PMID:25603030

  20. Visualized Multiprobe Electrical Impedance Measurements with STM Tips Using Shear Force Feedback Control.

    PubMed

    Botaya, Luis; Coromina, Xavier; Samitier, Josep; Puig-Vidal, Manel; Otero, Jorge

    2016-01-01

    Here we devise a multiprobe electrical measurement system based on quartz tuning forks (QTFs) and metallic tips capable of having full 3D control over the position of the probes. The system is based on the use of bent tungsten tips that are placed in mechanical contact (glue-free solution) with a QTF sensor. Shear forces acting in the probe are measured to control the tip-sample distance in the Z direction. Moreover, the tilting of the tip allows the visualization of the experiment under the optical microscope, allowing the coordination of the probes in X and Y directions. Meanwhile, the metallic tips are connected to a current-voltage amplifier circuit to measure the currents and thus the impedance of the studied samples. We discuss here the different aspects that must be addressed when conducting these multiprobe experiments, such as the amplitude of oscillation, shear force distance control, and wire tilting. Different results obtained in the measurement of calibration samples and microparticles are presented. They demonstrate the feasibility of the system to measure the impedance of the samples with a full 3D control on the position of the nanotips. PMID:27231911

  1. Review Article: Structures of phthalocyanine molecules on surfaces studied by STM

    NASA Astrophysics Data System (ADS)

    Wang, Yongfeng; Wu, Kai; Kröger, Jörg; Berndt, Richard

    2012-12-01

    This review mainly focuses on progress recently achieved in the growth of phthalocyanine molecules on single-crystal surfaces of sub-monolayer up to few-monolayer thin films studied by scanning tunneling microscopy in our groups. On metallic surfaces such as Au(111), Ag(111) and Cu(111), molecular superstructures are determined by combining directional intermolecular interactions caused by symmetry reduction, molecule-substrate interactions and indirect long-range interactions due to quantum interference of surface state electrons. On semiconducting TiO2 surface, molecular assembling structures are dictated by the strong molecule-substrate interaction. However, on insulating NaCl film, molecule-molecule interaction dominates over the molecule-NaCl coupling, leading to molecular growth behavior. Knowledge obtained from these studies would help people better understand the physicochemical properties of the phthalocyanine molecules at surfaces so that their new applications could be further explored and uncovered in the future.

  2. STM study of the preparation of clean Ta(110) and the subsequent growth of two-dimensional Fe islands

    NASA Astrophysics Data System (ADS)

    Eelbo, T.; Zdravkov, V. I.; Wiesendanger, R.

    2016-11-01

    This report deals with the preparation of a clean Ta(110) surface, investigated by means of scanning tunneling microscopy/spectroscopy as well as by low-energy electron diffraction and Auger electron spectroscopy. The surface initially exhibits a surface reconstruction induced by oxygen contamination. This reconstruction can be removed by annealing at high temperatures under ultrahigh vacuum conditions. The reconstruction-free surface reveals a surface resonance at a bias voltage of about -500 mV. The stages of the transformation are presented and discussed. In a next step, Fe islands were grown on top of Ta(110) and investigated subsequently. An intermixing regime was identified for annealing temperatures of (550-590) K.

  3. STM/S study on the role of Arsenic in Iron-based Superconductivity at Atomic Scale

    NASA Astrophysics Data System (ADS)

    Pan, S. H.; Yin, J. X.; Wu, Zheng; Li, Ang; Wang, J. H.; Liang, X. J.; Zhang, C. L.; Dai, P. C.; Ting, C.-S.; Hu, J. P.; Wang, Z. Q.; Hor, H. P.; Chen, G. F.; Ding, Hong

    We use scanning tunneling microscopy /spectroscopy to investigate the role of Arsenic in superconducting Ba0.4K0.6Fe2As2 by directly breaking and repairing the local Fe-As structure. After the up-As-layer peeled away, the tunneling spectrum of the exposed Fe surface reveals a shallow incoherent gap, indicating a severe suppression of superconductivity without As covering. When an As-dimmer is placed on the same Fe surface, a localized topographic feature is formed due to p-d orbital hybridization and the superconducting coherent peaks recover locally with the superconducting gap size exactly the same as the Fe-layer with a complete As-coverage. These observations unravel the Fe-As interactions on an atomic scale and imply its essential roles in the Fe-based superconductivity.

  4. Field-emission resonances at tip/alpha,omega-mercaptoalkyl ferrocene/Au interfaces studied by STM.

    PubMed

    Müller-Meskamp, Lars; Karthäuser, Silvia; Zandvliet, Harold J W; Homberger, Melanie; Simon, Ulrich; Waser, Rainer

    2009-04-01

    The electrical properties of alpha,omega-mercaptoalkyl ferrocenes with different alkyl chain lengths embedded in a self-assembled host matrix of alkanethiols on Au(111) are studied by scanning tunneling microscopy and spectroscopy. Based on current-distance spectroscopy, as well as on the evaluation of Fowler-Nordheim tunneling current oscillations, the apparent barrier height of ferrocene is determined independently by two methods. The electronic coupling of the ferrocene moiety to the Au(111) substrate is shown to depend on the length of the alkane-spacer chain. In a double tunnel junction model our experimental findings are explained, addressing the role of the different molecular moieties of the mercaptoalkyl ferrocenes. PMID:19197965

  5. Generation of constant-amplitude radio-frequency sweeps at a tunnel junction for spin resonance STM

    NASA Astrophysics Data System (ADS)

    Paul, William; Baumann, Susanne; Lutz, Christopher P.; Heinrich, Andreas J.

    2016-07-01

    We describe the measurement and successful compensation of the radio-frequency transfer function of a scanning tunneling microscope over a wide frequency range (15.5-35.5 GHz) and with high dynamic range (>50 dB). The precise compensation of cabling resonances and attenuations is critical for the production of constant-voltage frequency sweeps for electric-field driven electron spin resonance (ESR) experiments. We also demonstrate that a well-calibrated tunnel junction voltage is necessary to avoid spurious ESR peaks that can arise due to a non-flat transfer function.

  6. Formation of low-dimensional GaN on trenched Si(5 5 12), probed by STM and XPS

    NASA Astrophysics Data System (ADS)

    Kumar, Mahesh; Kumar, Praveen; Devi, Pooja; Shivaprasad, S. M.

    2016-03-01

    We report the formation of self-assembled nanostructures of GaN, with controlled size and shape on the trenched planar Si (5 5 12) surface. Adsorbing low coverages of Ga on Si (5 5 12) forms 1D arrays of Ga adatoms. The Ga adsorbed Si surface is annealed to 300 °C, which results in the formation of Ga 2D nanoparticles (NPs). These Ga NPs were exposed to various fluence of energetic 2 keV {{{{N}}}2}+ ions followed by annealing which yields GaN nanostructures self-assembled along the < \\bar{1}10> direction. These studies were performed in ultrahigh vacuum using in situ scanning tunneling microscopy and ex situ x-ray photoelectron spectroscopy, to observe the structural and chemical evolution of the interface.

  7. Design, fabrication, and testing of a sodium evaporator for the STM4-120 kinematic Stirling engine

    NASA Astrophysics Data System (ADS)

    Rawlinson, K. S.; Adkins, D. R.

    1995-05-01

    This report describes the development and testing of a compact heat-pipe heat exchanger kW(e) designed to transfer thermal energy from hot combustion gases to the heater tubes of a 25-kW(e) Stirling engine. In this system, sodium evaporates from a surface that is heated by a stream of hot gases. The liquid metal then condenses on the heater tubes of a Stirling engine, where energy is transferred to the engine's helium working fluid. Tests on a prototype unit illustrated that a compact (8 cm times 13 cm times 16 cm) sodium evaporator can routinely transfer 15 kW(t) of energy at an operating vapor temperature of 760 C. Four of these prototype units were eventually used to power a 25-kW(e) Stirling engine system. Design details and test results from the prototype unit are presented in this report.

  8. Metal dependent motif transition in a self-assembled monolayer of bipyridine derivatives via coordination: An STM study

    NASA Astrophysics Data System (ADS)

    Wang, Yi; Yuan, Qunhui; Xu, Hongbo; Zhu, Xuefeng; Gan, Wei

    2016-07-01

    Low-dimensional molecular motifs with diversity developed via the on-surface chemistry are attracting growing interest for their potential in advanced nanofabrication. In this work, scanning tunneling microscopy was employed to investigate the in situ and ex situ metal coordinations between 4,4'-ditetradecyl-2,2'-bipyridine (bpy) and Zn(ii) or Cu(ii) ions at a highly oriented pyrolytic graphite (HOPG)/1-phenyloctane interface under ambient conditions. The results demonstrate that the bpy adopts a flat-lying orientation with its substituted alkyl chains in a tail-to-tail arrangement in a bpy monolayer. For the in situ coordination, the bpy/Zn(ii) and bpy/Cu(ii) complexes are aligned in edge-on fashions, wherein the bpy stands vertically on the HOPG surface and interdigitates at the alkyl chains. In the two-dimensional arrays of ex situ coordinated complexes, metal dependent motifs have been observed with Zn(ii) and Cu(ii), wherein the bipyridine moieties are parallel to the graphite surface. These results suggest that the desired on-surface coordination architectures may be achieved by the intentional selection of the metal centers.

  9. Effects of spin–orbit coupling and many-body correlations in STM transport through copper phthalocyanine

    PubMed Central

    Donarini, Andrea; Grifoni, Milena

    2015-01-01

    Summary The interplay of exchange correlations and spin–orbit interaction (SOI) on the many-body spectrum of a copper phtalocyanine (CuPc) molecule and their signatures in transport are investigated. We first derive a minimal model Hamiltonian in a basis of frontier orbitals that is able to reproduce experimentally observed singlet–triplet splittings. In a second step SOI effects are included perturbatively. Major consequences of the SOI are the splitting of former degenerate levels and a magnetic anisotropy, which can be captured by an effective low-energy spin Hamiltonian. We show that scanning tunneling microscopy-based magnetoconductance measurements can yield clear signatures of both these SOI-induced effects. PMID:26885457

  10. Effects of spin-orbit coupling and many-body correlations in STM transport through copper phthalocyanine.

    PubMed

    Siegert, Benjamin; Donarini, Andrea; Grifoni, Milena

    2015-01-01

    The interplay of exchange correlations and spin-orbit interaction (SOI) on the many-body spectrum of a copper phtalocyanine (CuPc) molecule and their signatures in transport are investigated. We first derive a minimal model Hamiltonian in a basis of frontier orbitals that is able to reproduce experimentally observed singlet-triplet splittings. In a second step SOI effects are included perturbatively. Major consequences of the SOI are the splitting of former degenerate levels and a magnetic anisotropy, which can be captured by an effective low-energy spin Hamiltonian. We show that scanning tunneling microscopy-based magnetoconductance measurements can yield clear signatures of both these SOI-induced effects. PMID:26885457

  11. Real-space observation of metal-insulator transition at complex oxide heterointerface with cross-sectional STM

    NASA Astrophysics Data System (ADS)

    Chiu, Ya-Ping; Lin, Jheng-Cyuan; Thanh, Tra-Vu; Lin, Tai-Te; Huang, Po-Cheng; Huang, Bo-Chao; Lin, Jiunn-Yuan; Chu, Ying-Hao

    We report the direct observation of tunable electronic property through visible light at LaAlO3 / SrTiO3 (LAO/STO) complex oxide heterointerface using cross-sectional scanning tunneling microscopy and spectroscopy (XSTM/S). Many researches have shown that for the interface to be conducting, the thickness of LAO should be equal to or greater than the critical value 4 unit cells (u.c.). With LAO surface modification by Au clusters, interfacial two-dimensional electron gas presents a giant optical switching effect under visible light illuminated. In this study, through the interaction between photons and electrons system, a direct observation of the evolution of electronic structures from insulating to conducting has been revealed in the LAO (3u.c.)/STO model using the technique of cross-sectional scanning tunneling microscopy and spectroscopy. Results clearly reveal the changes in the built-in electric field in LAO and the band bending in the STO adjacent to the interface after light illumination. National Sun Yat-sen University, Taiwan; Academia Sinica, Taiwan.

  12. STM-induced light emission from thin films of perylene derivatives on the HOPG and Au substrates

    PubMed Central

    2011-01-01

    We have investigated the emission properties of N,N'-diheptyl-3,4,9,10-perylenetetracarboxylic diimide thin films by the tunneling-electron-induced light emission technique. A fluorescence peak with vibronic progressions with large Stokes shifts was observed on both highly ordered pyrolytic graphite (HOPG) and Au substrates, indicating that the emission was derived from the isolated-molecule-like film condition with sufficient π-π interaction of the perylene rings of perylenetetracarboxylic diimide molecules. The upconversion emission mechanism of the tunneling-electron-induced emission was discussed in terms of inelastic tunneling including multiexcitation processes. The wavelength-selective enhanced emission due to a localized tip-induced surface plasmon on the Au substrate was also obtained. PMID:21711870

  13. 75 FR 49005 - In the Matter of Appiant Technologies, Inc., Cobalis Corp., FutureLink Corp., STM Wireless, Inc...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-08-12

    ...., Supermail International, Inc. (n/ k/a PBHG, Inc.), and Women First Healthcare, Inc.; Order of Suspension of... there is a lack of current and accurate information concerning the securities of Women First...

  14. Coupled study by TEM/EELS and STM/STS of electronic properties of C- and CN-nanotubes

    NASA Astrophysics Data System (ADS)

    Lin, Hong; Lagoute, Jérôme; Repain, Vincent; Chacon, Cyril; Girard, Yann; Lauret, Jean-Sébastien; Arenal, Raul; Ducastelle, François; Rousset, Sylvie; Loiseau, Annick

    2011-12-01

    Carbon nanotubes are the focus of considerable research efforts due to their fascinating physical properties. They provide an excellent model system for the study of one-dimensional materials and molecular electronics. The chirality of nanotubes can lead to very different electronic behaviour, either metallic or semiconducting. Their electronic spectrum consists of a series of Van Hove singularities defining a bandgap for semiconducting tubes and molecular orbitals at the corresponding energies. A promising way to tune the nanotubes electronic properties for future applications is to use doping by heteroatoms. Here we report on the experimental investigation of the role of many-body interactions in nanotube bandgaps, the visualization in direct space of the molecular orbitals of nanotubes and the properties of nitrogen doped nanotubes using scanning tunneling microscopy and transmission electron microscopy as well as electron energy loss spectroscopy.

  15. Force field analysis suggests a lowering of diffusion barriers in atomic manipulation due to presence of STM tip.

    PubMed

    Emmrich, Matthias; Schneiderbauer, Maximilian; Huber, Ferdinand; Weymouth, Alfred J; Okabayashi, Norio; Giessibl, Franz J

    2015-04-10

    We study the physics of atomic manipulation of CO on a Cu(111) surface by combined scanning tunneling microscopy and atomic force microscopy at liquid helium temperatures. In atomic manipulation, an adsorbed atom or molecule is arranged on the surface using the interaction of the adsorbate with substrate and tip. While previous experiments are consistent with a linear superposition model of tip and substrate forces, we find that the force threshold depends on the force field of the tip. Here, we use carbon monoxide front atom identification (COFI) to characterize the tip's force field. Tips that show COFI profiles with an attractive center can manipulate CO in any direction while tips with a repulsive center can only manipulate in certain directions. The force thresholds are independent of bias voltage in a range from 1 to 10 mV and independent of temperature in a range of 4.5 to 7.5 K. PMID:25910137

  16. Nature of Asymmetry in the Vibrational Line Shape of Single-Molecule Inelastic Electron Tunneling Spectroscopy with the STM

    NASA Astrophysics Data System (ADS)

    Xu, Chen; Chiang, Chi-lun; Han, Zhumin; Ho, W.

    2016-04-01

    Single molecule vibrational spectroscopy and microscopy was demonstrated in 1998 by inelastic electron tunneling with the scanning tunneling microscope. To date, the discussion of its application has mainly focused on the spatial resolution and the spectral energy and intensity. Here we report on the vibrational line shape for a single carbon monoxide molecule that qualitatively exhibits inversion symmetry when it is transferred from the surface to the tip. The dependence of the line shape on the molecule's asymmetric couplings in the tunnel junction can be understood from theoretical simulation and further validates the mechanisms of inelastic electron tunneling.

  17. Nature of Asymmetry in the Vibrational Line Shape of Single-Molecule Inelastic Electron Tunneling Spectroscopy with the STM.

    PubMed

    Xu, Chen; Chiang, Chi-Lun; Han, Zhumin; Ho, W

    2016-04-22

    Single molecule vibrational spectroscopy and microscopy was demonstrated in 1998 by inelastic electron tunneling with the scanning tunneling microscope. To date, the discussion of its application has mainly focused on the spatial resolution and the spectral energy and intensity. Here we report on the vibrational line shape for a single carbon monoxide molecule that qualitatively exhibits inversion symmetry when it is transferred from the surface to the tip. The dependence of the line shape on the molecule's asymmetric couplings in the tunnel junction can be understood from theoretical simulation and further validates the mechanisms of inelastic electron tunneling. PMID:27152811

  18. Generation of constant-amplitude radio-frequency sweeps at a tunnel junction for spin resonance STM.

    PubMed

    Paul, William; Baumann, Susanne; Lutz, Christopher P; Heinrich, Andreas J

    2016-07-01

    We describe the measurement and successful compensation of the radio-frequency transfer function of a scanning tunneling microscope over a wide frequency range (15.5-35.5 GHz) and with high dynamic range (>50 dB). The precise compensation of cabling resonances and attenuations is critical for the production of constant-voltage frequency sweeps for electric-field driven electron spin resonance (ESR) experiments. We also demonstrate that a well-calibrated tunnel junction voltage is necessary to avoid spurious ESR peaks that can arise due to a non-flat transfer function. PMID:27475577

  19. Exploration of complex multilayer film growth morphologies: STM analysis and predictive atomistic modeling for Ag on Ag(111)

    SciTech Connect

    Li, Maozhi; Chung, P.W.; Cox, E.; Jenks, C.J.; Thiel, P.A.; Evans, J.W.

    2008-01-03

    Scanning tunneling microscopy studies are integrated with development of a realistic atomistic model to both characterize and elucidate the complex mounded morphologies formed by deposition of Ag on Ag(111) at 150 and 180 K. Threefold symmetric lateral shapes of islands and mounds are shown to reflect the influence of a nonuniform step edge barrier inhibiting interlayer transport. Modeling of structure at the mound peaks leads to a sensitive estimate of the magnitude of this large barrier.

  20. An experimental UHV AFM-STM device for characterizing surface nanostructures under stress/strain at variable temperature.

    PubMed

    Nahas, Y; Berneau, F; Bonneville, J; Coupeau, C; Drouet, M; Lamongie, B; Marteau, M; Michel, J; Tanguy, P; Tromas, C

    2013-10-01

    A compression setup fully integrated in an ultra high vacuum chamber is presented. The system has been designed to combine in situ mechanical test together with near field microscopy at variable temperature, from 90 to 600 K. Compressive stress can be applied on the samples up to 500 MPa at different strain rates ranging from 10(-6) s(-1) to 10(-2) s(-1). The setup performances are highlighted through investigations on Au and Ni3(Al,Ta) single crystals. In particular, it is demonstrated that the high mechanical stability of the original apparatus allows us to follow in situ the evolution of the same area of interest over a large range of temperature and to keep the high spatial resolution offered by near field microscopy, even at high strain levels. PMID:24182173

  1. Metal dependent motif transition in a self-assembled monolayer of bipyridine derivatives via coordination: An STM study.

    PubMed

    Wang, Yi; Yuan, Qunhui; Xu, Hongbo; Zhu, Xuefeng; Gan, Wei

    2016-07-21

    Low-dimensional molecular motifs with diversity developed via the on-surface chemistry are attracting growing interest for their potential in advanced nanofabrication. In this work, scanning tunneling microscopy was employed to investigate the in situ and ex situ metal coordinations between 4,4'-ditetradecyl-2,2'-bipyridine (bpy) and Zn(ii) or Cu(ii) ions at a highly oriented pyrolytic graphite (HOPG)/1-phenyloctane interface under ambient conditions. The results demonstrate that the bpy adopts a flat-lying orientation with its substituted alkyl chains in a tail-to-tail arrangement in a bpy monolayer. For the in situ coordination, the bpy/Zn(ii) and bpy/Cu(ii) complexes are aligned in edge-on fashions, wherein the bpy stands vertically on the HOPG surface and interdigitates at the alkyl chains. In the two-dimensional arrays of ex situ coordinated complexes, metal dependent motifs have been observed with Zn(ii) and Cu(ii), wherein the bipyridine moieties are parallel to the graphite surface. These results suggest that the desired on-surface coordination architectures may be achieved by the intentional selection of the metal centers. PMID:27448898

  2. Design, fabrication, and testing of a sodium evaporator for the STM4-120 kinematic Stirling engine

    SciTech Connect

    Rawlinson, K.S.; Adkins, D.R.

    1995-05-01

    This report describes the development and testing of a compact heat-pipe heat exchanger kW(e) designed to transfer thermal energy from hot combustion gases to the heater tubes of a 25-kW(e) Stirling engine. In this system, sodium evaporates from a surface that is heated by a stream of hot gases. The liquid metal then condenses on the heater tubes of a Stirling engine, where energy is transferred to the engine`s helium working fluid. Tests on a prototype unit illustrated that a compact (8 cm {times} 13 cm {times} 16 cm) sodium evaporator can routinely transfer 15 kW(t) of energy at an operating vapor temperature of 760 C. Four of these prototype units were eventually used to power a 25-kW(e) Stirling engine system. Design details and test results from the prototype unit are presented in this report.

  3. Measuring Complementary Electronic Structure Properties of both Deposited and Gas Phase Clusters using STM, UPS, and PES: Size-Selected Clusters on Surfaces

    SciTech Connect

    Bowen, Kit H.

    2014-03-05

    In this project, we studied size-selected cluster interactions with surfaces, with other clusters on surfaces, and with external stimuli. These studies focused on mobility as a function of cluster size, surface morphologies as a function of composition and coverage, ion-induced modification and reactivity of clusters as a function of composition, the structural evolution of cluster cuboids culminating in the characterization of theoretically-predicted “baby crystal” clusters, and unusual fractal pattern formation due to deposition.

  4. Role of functionalized transition-metal coated W tips in STM imaging: Application to epitaxial graphene on SiC(0001)

    NASA Astrophysics Data System (ADS)

    Rhim, S. H.; Qi, Y.; Sun, G. F.; Liu, Y.; Weinert, M.; Li, L.

    2011-09-01

    Scanning tunneling microscopy using W tips functionalized with transition-metal (Cr, Fe) coatings is demonstrated to facilitate the imaging of states within a few millielectron volts (meV) of the Fermi level for epitaxial graphene on SiC(0001), which are not accessible with bare W tips. First-principles modeling of these probe tips as pyramidal structures on W(110) indicates that an apex atom is stable for the Cr/W(110) tip but not for the Fe/W(110) or W/W(110) tips. This difference in their atomic structures, together with the variation in the extent of the 3d and 5d orbitals, is found to be responsible for the capability of Cr and Fe functionalized tips to selectively image the complex electronic properties of epitaxial graphene on SiC(0001).

  5. An investigation of thin Zr films on 6H-SiC(0001) and GaN(0001) surfaces by XPS, LEED, and STM

    NASA Astrophysics Data System (ADS)

    Idczak, K.; Mazur, P.; Zuber, S.; Markowski, L.

    2016-04-01

    In this work, the results of the growth of zirconium films deposited under the ultrahigh vacuum at room temperature on the 6H-SiC(0001) and GaN(0001) surfaces were studied. Observed changes in the chemical composition, bonding environment, and surface reconstruction, and the effects of high-temperature annealing of the film are presented and discussed as well. In the performed experiment, the X-ray photoelectron spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy were used. The results show that for both investigated substrates, the grown films have eminently rich and varied compositions. Besides the metallic zirconium, there are also zirconium oxides, zirconium carbides, or zirconium nitrides. The growth process proceeds according to the Volmer-Weber mode. Moreover, the zirconium-semiconductor interface does not form typical Schottky contact, but some paths with a quasi-ohmic conduction character can be observed.

  6. Growth and ordering of Ni(II) diphenylporphyrin monolayers on Ag(111) and Ag/Si(111) studied by STM and LEED.

    PubMed

    Murphy, B E; Krasnikov, S A; Cafolla, A A; Sergeeva, N N; Vinogradov, N A; Beggan, J P; Lübben, O; Senge, M O; Shvets, I V

    2012-02-01

    The room temperature self-assembly and ordering of (5,15-diphenylporphyrinato)nickel(II) (NiDPP) on the Ag(111) and Ag/Si(111)-(√3 × √3)R30° surfaces have been investigated using scanning tunnelling microscopy and low-energy electron diffraction. The self-assembled structures and lattice parameters of the NiDPP monolayer are shown to be extremely dependent on the reactivity of the substrate, and probable molecular binding sites are proposed. The NiDPP overlayer on Ag(111) grows from the substrate step edges, which results in a single-domain structure. This close-packed structure has an oblique unit cell and consists of molecular rows. The molecules in adjacent rows are rotated by approximately 17° with respect to each other. In turn, the NiDPP molecules form three equivalent domains on the Ag/Si(111)-(√3 × √3)R30° surface, which follow the three-fold symmetry of the substrate. The molecules adopt one of three equivalent orientations on the surface, acting as nucleation sites for these domains, due to the stronger molecule-substrate interaction compared to the case of the Ag(111). The results are explained in terms of the substrate reactivity and the lattice mismatch between the substrate and the molecular overlayer. PMID:22223550

  7. Epitaxial growth of CeO2(111) film on Ru(0001): Scanning tunneling microscopy (STM) and x-ray photoemission spectroscopy (XPS) study

    NASA Astrophysics Data System (ADS)

    Hasegawa, Tomo; Shahed, Syed Mohammad Fakruddin; Sainoo, Yasuyuki; Beniya, Atsushi; Isomura, Noritake; Watanabe, Yoshihide; Komeda, Tadahiro

    2014-01-01

    We formed an epitaxial film of CeO2(111) by sublimating Ce atoms on Ru(0001) surface kept at elevated temperature in an oxygen ambient. X-ray photoemission spectroscopy measurement revealed a decrease of Ce4+/Ce3+ ratio in a small temperature window of the growth temperature between 1070 and 1096 K, which corresponds to the reduction of the CeO2(111). Scanning tunneling microscope image showed that a film with a wide terrace and a sharp step edge was obtained when the film was grown at the temperatures close to the reduction temperature, and the terrace width observed on the sample grown at 1060 K was more than twice of that grown at 1040 K. On the surface grown above the reduction temperature, the surface with a wide terrace and a sharp step was confirmed, but small dots were also seen in the terrace part, which are considerably Ce atoms adsorbed at the oxygen vacancies on the reduced surface. This experiment demonstrated that it is required to use the substrate temperature close to the reduction temperature to obtain CeO2(111) with wide terrace width and sharp step edges.

  8. Epitaxial growth of CeO{sub 2}(111) film on Ru(0001): Scanning tunneling microscopy (STM) and x-ray photoemission spectroscopy (XPS) study

    SciTech Connect

    Hasegawa, Tomo; Shahed, Syed Mohammad Fakruddin; Sainoo, Yasuyuki; Beniya, Atsushi; Isomura, Noritake; Watanabe, Yoshihide; Komeda, Tadahiro

    2014-01-28

    We formed an epitaxial film of CeO{sub 2}(111) by sublimating Ce atoms on Ru(0001) surface kept at elevated temperature in an oxygen ambient. X-ray photoemission spectroscopy measurement revealed a decrease of Ce{sup 4+}/Ce{sup 3+} ratio in a small temperature window of the growth temperature between 1070 and 1096 K, which corresponds to the reduction of the CeO{sub 2}(111). Scanning tunneling microscope image showed that a film with a wide terrace and a sharp step edge was obtained when the film was grown at the temperatures close to the reduction temperature, and the terrace width observed on the sample grown at 1060 K was more than twice of that grown at 1040 K. On the surface grown above the reduction temperature, the surface with a wide terrace and a sharp step was confirmed, but small dots were also seen in the terrace part, which are considerably Ce atoms adsorbed at the oxygen vacancies on the reduced surface. This experiment demonstrated that it is required to use the substrate temperature close to the reduction temperature to obtain CeO{sub 2}(111) with wide terrace width and sharp step edges.

  9. Quantum phase transition in Fe1 +x(Te,Se) induced by Single-atomic Impurities studied by STM/S

    NASA Astrophysics Data System (ADS)

    Yin, J. X.; Wu, Zheng; Huang, Xiong; Ye, Z. Y.; Wu, Rui; Liang, X. J.; Mao, H. Q.; Li, Jian; Ting, C.-S.; Hu, J. P.; Wang, Z. Q.; Hor, P.-H.; Ding, Hong; Pan, S. H.

    Previously we discovered a robust zero-energy bound state at an interstitial Fe impurity (IFIs) in Fe1 +x(Te,Se), which resembles the Majorana mode (Nature Physics 11, 543, (2015)). Here we report our comprehensive study, using scanning tunneling microscopy/spectroscopy technique, of the global effect of IFIs on the ground state of Fe1 +x(Te,Se) over a wide range of IFI concentration x. Our high resolution tunneling spectroscopy and quasi-particle interference data at very low temperature demonstrate that IFIs do not affect the electron pairing strength, while they cause significant dephasing effect, which eventually drives the ground state of the system from strong-coupling-superconductivity to diffusive-Bose-metal.

  10. STM study of electrical transport properties of one dimensional contacts between MnSi(~1.7) nanowires and Si(111) and (110) substrates.

    PubMed

    Liu, Xiao-Yong; Zou, Zhi-Qiang

    2015-05-15

    We demonstrate the formation of contact barriers at the interfaces between MnSi1.7 nanowires (NWs) and Si substrates by the current-voltage (I-V) curves measured by scanning tunneling microscope with the tip contacting the NWs. The NWs on Si(110) exhibit linear reverse bias I-V curves, which suggests a parallel Ohmic surface state conductance of the Si(110) surface. The NWs on Si(111) exhibit nonlinear reverse bias I-V behavior, which indicates a considerable amount of minority carrier recombination-generation current. The NW length-dependence study of the forward bias current clearly shows that the quantitative change in NW length leads to a qualitative change in electrical transport properties. We derive a characteristic length LC ≈ 200 nm and the corresponding aspect ratio of ∼12-18 for MnSi1.7 NWs according to the variation of current density with the NW length. PMID:25900852

  11. Squeezing and stretching Pd thin films: A high-resolution STM study of Pd/Au(111) and Pd/Cu(111) bimetallics

    NASA Astrophysics Data System (ADS)

    Blecher, Mishan E.; Lewis, Emily A.; Pronschinske, Alex; Murphy, Colin J.; Mattera, Michael F. G.; Liriano, Melissa L.; Sykes, E. Charles H.

    2016-04-01

    Pd bimetallic alloys are promising catalysts, especially for heterogeneous reactions involving hydrogen, as they exhibit increased activity and reduced demand for expensive precious metals. Using scanning tunneling microscopy, we examine the structure of Pd thin films on Cu(111) and Au(111) and demonstrate compression and expansion, respectively, of the bulk Pd lattice constant in the film. The relative binding strength of H to the two surfaces, inferred via tip-induced diffusion barriers, suggests that the strain in these systems may alter adsorbate binding and corroborates well-known trends in d-band shifts calculated by the density functional theory. Modification to the topography and activity of Pd films based on the choice of substrate metal illustrates the value of bimetallic systems for designing less expensive, tunable catalysts.

  12. Simultaneous current, force and dissipation measurements on the Si(111) 7×7 surface with an optimized qPlus AFM/STM technique

    PubMed Central

    Setvín, Martin; Feltz, Albrecht; Cháb, Vladimír; Jelínek, Pavel

    2012-01-01

    Summary We present the results of simultaneous scanning-tunneling and frequency-modulated dynamic atomic force microscopy measurements with a qPlus setup. The qPlus sensor is a purely electrical sensor based on a quartz tuning fork. If both the tunneling current and the force signal are to be measured at the tip, a cross-talk of the tunneling current with the force signal can easily occur. The origin and general features of the capacitive cross-talk will be discussed in detail in this contribution. Furthermore, we describe an experimental setup that improves the level of decoupling between the tunneling-current and the deflection signal. The efficiency of this experimental setup is demonstrated through topography and site-specific force/tunneling-spectroscopy measurements on the Si(111) 7×7 surface. The results show an excellent agreement with previously reported data measured by optical interferometric deflection. PMID:22496998

  13. Vacuum-aging effect on electronic structure of YBa2 Cu 3 O 6+x thin film: a STM/STS study

    NASA Astrophysics Data System (ADS)

    Liu, Y. H.; Xiong, J.; Yarotski, D.; Jia, Q.; Taylor, A. J.

    2011-03-01

    It is well known that oxygen plays a key role in the occurrence of superconductivity in high-temperature cuprate superconductors. Variation of oxygen content changes carrier concentration and directly affects electronic structure and superconducting properties of cuprate superconductors. Majority of previous studies relied on the intake process of oxygen to change the oxygen content in samples, while the reverse process, oxygen depletion, was rarely investigated. Nevertheless, the escape of oxygen from the surface of cuprate sample that was kept at room temperature under ultrahigh vacuum for extended period of time might lead to significant degradation of its superconducting properties due to the decrease of the carrier concentration. Here, we report this so-called vacuum-aging effect in YBa 2 Cu 3 O6 + x thin films grown by laser-MBE technique. In particular, we use variable-temperature scanning tunneling microscopy/spectroscopy to follow the evolution of superconductivity and pseudogap states in this material as a function of aging time and tip position on the surface.

  14. SU-F-BRE-16: VMAT Commissioning and Quality Assurance (QA) of An Elekta Synergy-STM Linac Using ICOM Test HarnessTM

    SciTech Connect

    Nguyen, A; Rajaguru, P; He, R; Yang, C; Kaurin, D; Paul, T; Plowman, A

    2014-06-15

    Purpose: To establish a set of tests based on the iCOM software that can be used to commission and perform periodic QA of VMAT delivery on the Elekta Synergy-S, commonly known as the Beam Modulator (BM). Methods: iCOM is used to create and deliver customized treatment fields to characterize the system in terms of 1) MLC positioning accuracy under static and dynamic delivery with full gantry rotation, 2) MLC positioning with known errors, 3) Maximum dose rate, 4) Maximum MLC speed, 5) Maximum gantry speed, 6) Synchronization: gantry speed versus dose rate, and 7) Synchronization: MLC speed versus dose rate. The resulting images were captured on the iView GT and exported in DICOM format to Dosimetry Check™ system for visual and quantitative analysis. For the initial commissioning phase, the system tests described should be supplemented with extensive patient QAs covering all clinically relevant treatment sites. Results: The system performance test suite showed that on our Synergy-S, MLC positioning was accurate under both static and dynamic deliveries. Intentional errors of 1 mm were also easily identified on both static and dynamic picket fence tests. Maximum dose rate was verified with stop watch to be consistently between 475-480 MU/min. Maximum gantry speed and MLC speed were 5.5 degree/s and 2.5 cm/s respectively. After accounting for beam flatness, both synchronization tests, gantry versus dose rate and MLC speed versus dose rate, were successful as the fields were uniform across the strips and there were no obvious cold/hot spots. Conclusion: VMAT commissioning and quality assurance should include machine characterization tests in addition to patient QAs. Elekta iCOM is a valuable tool for the design of customized VMAT field with specific MU, MLC leaf positions, dose rate, and indirect control of MLC and gantry speed at each of its control points.

  15. Upregulation of STM3175 Decreases Bacterial Motility and Swine Colonization in a qseC (preB) Mutant of Salmonella enterica serovar Typhimurium

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Inactivation of the QseC (PreB) sensor kinase decreases bacterial motility and pathogen colonization of the swine gastrointestinal tract for Salmonella enterica serovar Typhimurium (S. Typhimurium). In contrast, both the qseB [encoding the QseB (PreA) response regulator] and qseBC mutants had motil...

  16. STM study of Si(111)√3 × √3R30°B surface structure formed by HBO 2 irradiation

    NASA Astrophysics Data System (ADS)

    Miyake, Koji; Hata, Kenj; Shigekawa, Hidemi; Yoshizaki, Ryozo; Abe, Takeru; Ozawa, Takehiro; Nagamura, Toshihiko

    1996-11-01

    With irradiation of HBO 2 molecules onto the Si(111)-7 × 7 surface at ˜750°C, the √3 × √3 structure, where B atoms occupy the T 4 sites, was formed as predicted from previous electron diffraction measurements. In the initial stage, HBO 2 molecules were found to react with the unfolded half-units of the Si(111)-7 × 7 surface. When the √3 × √3 structure was heated at ˜900°C for 5 s, another √3 × √3 structure was formed. Upon comparison between the two structures, the high-temperature phase was attributed to the structure where B atoms occupy the S 5 sites.

  17. STM imaging of electronic waves on the surface of Bi2Te3: topologically protected surface states and hexagonal warping effects

    SciTech Connect

    Alpichshev, Zhanybek; Analytis, J.G.; Chu, J.-H.; Fisher, I.R.; Chen, Y.L.; Shen, Z.X.; Fang, A.; Kapitulnik, A.; /SIMES, Stanford /SLAC /Stanford U., Phys. Dept. /Stanford U., Appl. Phys. Dept.

    2010-06-02

    Scanning tunneling spectroscopy studies on high-quality Bi{sub 2}Te{sub 3} crystals exhibit perfect correspondence to ARPES data, hence enabling identification of different regimes measured in the local density of states (LDOS). Oscillations of LDOS near a step are analyzed. Within the main part of the surface band oscillations are strongly damped, supporting the hypothesis of topological protec- tion. At higher energies, as the surface band becomes concave, oscillations appear which disperse with a particular wave-vector that may result from an unconventional hexagonal warping term.

  18. Efficient Synthesis of Ir-Polyoxometalate Cluster Using a Continuous Flow Apparatus and STM Investigation of Its Coassembly Behavior on HOPG Surface.

    PubMed

    Zhang, Junyong; Chang, Shaoqing; Suryanto, Bryan H R; Gong, Chunhua; Zeng, Xianghua; Zhao, Chuan; Zeng, Qingdao; Xie, Jingli

    2016-06-01

    Taking advantage of a continuous-flow apparatus, the iridium(III)-containing polytungstate cluster K12Na2H2[Ir2Cl8P2W20O72]·37H2O (1) was obtained in a reasonable yield (13% based on IrCl3·H2O). Compound 1 was characterized by Fourier transform IR, UV-visible, (31)P NMR, electrospray ionization mass spectrometry (ESI-MS), and thermogravimetric analysis measurements. (31)P NMR, ESI-MS, and elemental analysis all indicated 1 was a new polytungstate cluster compared with the reported K14[(IrCl4)KP2W20O72] compound. Intriguingly, the successful isolation of 1 relied on the custom-built flow apparatus, demonstrating the uniqueness of continuous-flow chemistry to achieve crystalline materials. The catalytic properties of 1 were assessed by investigating the activity on catalyzing the electro-oxidation of ruthenium tris-2,2'-bipyridine [Ru(bpy)3](2+/3+). The voltammetric behavior suggested a coupled catalytic behavior between [Ru(bpy)3](3+/2+) and 1. Furthermore, on the highly oriented pyrolytic graphite surface, 1,3,5-tris(10-carboxydecyloxy) benzene (TCDB) was used as the two-dimensional host network to coassemble cluster 1; the surface morphology was observed by scanning tunneling microscope technique. "S"-shape of 1 was observed, indicating that the cluster could be accommodated in the cavity formed by two TCDB host molecules, leading to a TCDB/cluster binary structure. PMID:27163481

  19. Multistage nucleation of two-dimensional Si islands on Si(111)-7x7 during MBE growth: STM experiments and extended rate-equation model

    SciTech Connect

    Filimonov, Sergey; Cherepanov, Vasily; Voigtlaender, Bert; Hervieu, Yuri

    2007-07-15

    The submonolayer density of two-dimensional (2D) islands in Si/Si(111)-7x7 molecular beam epitaxy is measured using scanning tunneling microscopy. At a relatively low deposition temperature of 673 K, the density of 2D islands is a power function of the deposition flux N{sub 2D}{proportional_to}F{sup {chi}} with the exponent {chi}=0.24 being smaller than that predicted by the standard nucleation theory. The nonstandard scaling of the 2D island density is explained by the multistage character of the nucleation process on the Si(111)-7x7 surface which involves consecutive stages of formation of stable Si clusters, formation of pairs of clusters, and transformation of the cluster pairs to 2D islands. Using an extended rate-equation model, we analyze the temperature and growth rate dependencies of the density of single clusters, cluster pairs, and 2D islands and show that an activation barrier of {approx}1.26 eV delays the transformation of cluster pairs to 2D islands. The delayed transformation of cluster pairs to 2D islands is the reason for the nonstandard scaling of the 2D island density observed at low deposition temperatures.

  20. Structures of a 17,19-hexatriacontadiyne and sashlike polydiacetylene monolayer on MoS2(0001) studied by UHV-STM

    NASA Astrophysics Data System (ADS)

    Endo, O.; Sera, T.; Suhara, M.; Ozaki, H.; Mazaki, Y.

    2008-03-01

    We have observed a 17,19-hexatriacontadiyne (HTDY) monolayer on MoS2(0001) and sashlike polydiacetylene atomic sash (AS) molecules derived from the monolayer by scanning tunnelling microscopy under ultrahigh vacuum. HTDY molecules adsorbed at 150 K start to move around on the surface above 240 K to form relatively unstable columnar structures. The column is converted into the AS by UV irradiation. In most AS molecules on MoS2(0001), the alkyl chains are in all-trans conformation but their carbon planes are tilted to the polydiacetylene backbone. This conformer, which is one of the most stable structures for an isolated AS molecule, appears on MoS2(0001) because of very weak molecule-substrate interactions.

  1. Preparation of Chemically Etched Tips for Ambient Instructional Scanning Tunneling Microscopy

    ERIC Educational Resources Information Center

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

    2010-01-01

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

  2. The heterogeneity of verbal short-term memory impairment in aphasia.

    PubMed

    Majerus, Steve; Attout, Lucie; Artielle, Marie-Amélie; Van der Kaa, Marie-Anne

    2015-10-01

    Verbal short-term memory (STM) impairment represents a frequent and long-lasting deficit in aphasia, and it will prevent patients from recovering fully functional language abilities. The aim of this study was to obtain a more precise understanding of the nature of verbal STM impairment in aphasia, by determining whether verbal STM impairment is merely a consequence of underlying language impairment, as suggested by linguistic accounts of verbal STM, or whether verbal STM impairment reflects an additional, specific deficit. We investigated this question by contrasting item-based STM measures, supposed to depend strongly upon language activation, and order-based STM measures, supposed to reflect the operation of specific, serial order maintenance mechanisms, in a sample of patients with single-word processing deficits at the phonological and/or lexical level. A group-level analysis showed robust impairment for both item and serial order STM aspects in the aphasic group relative to an age-matched control group. An analysis of individual profiles revealed an important heterogeneity of verbal STM profiles, with patients presenting either selective item STM deficits, selective order STM deficits, generalized item and serial order STM deficits or no significant STM impairment. Item but not serial order STM impairment correlated with the severity of phonological impairment. These results disconfirm a strong version of the linguistic account of verbal STM impairment in aphasia, by showing variable impairment to both item and serial order processing aspects of verbal STM. PMID:26275964

  3. Picometer registration of zinc impurity states in Bi2Sr2CaCu2O8+δ for phase determination in intra-unit-cell Fourier transform STM

    NASA Astrophysics Data System (ADS)

    Hamidian, M. H.; Firmo, I. A.; Fujita, K.; Mukhopadhyay, S.; Orenstein, J. W.; Eisaki, H.; Uchida, S.; Lawler, M. J.; Kim, E.-A.; Davis, J. C.

    2012-05-01

    Direct visualization of electronic-structure symmetry within each crystalline unit cell is a new technique for complex electronic matter research (Lawler et al 2010 Nature 466 347-51, Schmidt et al 2011 New J. Phys. 13 065014, Fujita K et al 2012 J. Phys. Soc. Japan 81 011005). By studying the Bragg peaks in Fourier transforms of electronic structure images and particularly by resolving both the real and imaginary components of the Bragg amplitudes, distinct types of intra-unit-cell symmetry breaking can be studied. However, establishing the precise symmetry point of each unit cell in real space is crucial in defining the phase for such a Bragg-peak Fourier analysis. Exemplary of this challenge is the high-temperature superconductor Bi2Sr2CaCu2O8+δ for which the surface Bi atom locations are observable, while it is the invisible Cu atoms that define the relevant CuO2 unit-cell symmetry point. Here we demonstrate, by imaging with picometer precision the electronic impurity states at individual Zn atoms substituted at Cu sites, that the phase established using the Bi lattice produces a ˜2%(2π) error relative to the actual Cu lattice. Such a phase assignment error would not diminish reliability in the determination of intra-unit-cell rotational symmetry breaking at the CuO2 plane (Lawler et al 2010 Nature 466 347-51, Schmidt et al 2011 New J. Phys. 13 065014, Fujita K et al 2012 J. Phys. Soc. Japan 81 011005). Moreover, this type of impurity atom substitution at the relevant symmetry site can be of general utility in phase determination for the Bragg-peak Fourier analysis of intra-unit-cell symmetry.

  4. Proteomic Analysis of Salmonella enterica Serovar Typhimurium Isolated from RAW 264.7 Macrophages: identification of a novel protein that contributes to the replication of serovar Typhimurium inside macrophages

    SciTech Connect

    Shi, Liang; Adkins, Joshua N.; Coleman, James R.; Schepmoes, Athena A.; Dohnalkova, Alice; Mottaz, Heather M.; Norbeck, Angela D.; Purvine, Samuel O.; Manes, Nathan P.; Smallwood, Heather S.; Wang, Haixing H.; Forbes, John; Gros, Philippe; Uzzau, Sergio; Rodland, Karin D.; Heffron, Fred; Smith, Richard D.; Squier, Thomas C.

    2006-09-01

    ABSTRACT: To evade host resistance mechanisms, Salmonella enterica serovar Typhimurium (STM), a facultative intracellular pathogen, must alter its proteome following macrophage infection. To identify new colonization and virulence factors that mediate STM pathogenesis, we have isolated STM cells from RAW 264.7 macrophages at various time-points following infection and used a liquid chromatography-mass spectrometry (LC-MS)-based proteomic approach to detect the changes in STM protein abundances. Because host resistance to STM infection is strongly modulated by the expression of a functional host resistant regulator, i.e., natural resistance associated macrophage protein 1 (Nramp1, also called Slc11a1), we have also examined the effects of Nramp1 activity on the changes of STM protein abundances. A total of 315 STM proteins have been identified from isolated STM cells, which are largely house-keeping proteins whose abundances remain relatively constant during the time-course of infection. However, 39 STM proteins are strongly induced after infection, suggesting their involvement in modulating colonization and infection. Of the 39 induced proteins, 6 proteins are specifically modulated by Nramp1 activity, including STM3117, as well as STM3118-3119 whose time-dependent abundance changes were confirmed using Western blot analysis. Deletion of the gene encoding STM3117 resulted in a dramatic reduction in the ability of STM to colonize wild-type RAW 264.7 macrophages, demonstrating a critical involvement of STM3117 in promoting the replication of STM inside macrophages. The predicted function common for STM3117-3119 is biosynthesis and modification of the peptidoglycan layer of STM cell wall, emphasizing their important roles in the colonization of macrophages by Salmonella.

  5. Order short-term memory is not impaired in dyslexia and does not affect orthographic learning

    PubMed Central

    Staels, Eva; Van den Broeck, Wim

    2014-01-01

    This article reports two studies that investigate short-term memory (STM) deficits in dyslexic children and explores the relationship between STM and reading acquisition. In the first experiment, 36 dyslexic children and 61 control children performed an item STM task and a serial order STM task. The results of this experiment show that dyslexic children do not suffer from a specific serial order STM deficit. In addition, the results demonstrate that phonological processing skills are as closely related to both item STM and serial order STM. However, non-verbal intelligence was more strongly involved in serial order STM than in item STM. In the second experiment, the same two STM tasks were administered and reading acquisition was assessed by measuring orthographic learning in a group of 188 children. The results of this study show that orthographic learning is exclusively related to item STM and not to order STM. It is concluded that serial order STM is not the right place to look for a causal explanation of reading disability, nor for differences in word reading acquisition. PMID:25294996

  6. Calcium ion binding properties and the effect of phosphorylation on the intrinsically disordered Starmaker protein.

    PubMed

    Wojtas, Magdalena; Hołubowicz, Rafał; Poznar, Monika; Maciejewska, Marta; Ożyhar, Andrzej; Dobryszycki, Piotr

    2015-10-27

    Starmaker (Stm) is an intrinsically disordered protein (IDP) involved in otolith biomineralization in Danio rerio. Stm controls calcium carbonate crystal formation in vivo and in vitro. Phosphorylation of Stm affects its biomineralization properties. This study examined the effects of calcium ions and phosphorylation on the structure of Stm. We have shown that CK2 kinase phosphorylates 25 or 26 residues in Stm. Furthermore, we have demonstrated that Stm's affinity for calcium binding is dependent on its phosphorylation state. Phosphorylated Stm (StmP) has an estimated 30 ± 1 calcium binding sites per protein molecule with a dissociation constant (KD) of 61 ± 4 μM, while the unphosphorylated protein has 28 ± 3 sites and a KD of 210 ± 22 μM. Calcium ion binding induces a compaction of the Stm molecule, causing a significant decrease in its hydrodynamic radius and the formation of a secondary structure. The screening effect of Na(+) ions on calcium binding was also observed. Analysis of the hydrodynamic properties of Stm and StmP showed that Stm and StmP molecules adopt the structure of native coil-like proteins. PMID:26445027

  7. Order short-term memory is not impaired in dyslexia and does not affect orthographic learning.

    PubMed

    Staels, Eva; Van den Broeck, Wim

    2014-01-01

    This article reports two studies that investigate short-term memory (STM) deficits in dyslexic children and explores the relationship between STM and reading acquisition. In the first experiment, 36 dyslexic children and 61 control children performed an item STM task and a serial order STM task. The results of this experiment show that dyslexic children do not suffer from a specific serial order STM deficit. In addition, the results demonstrate that phonological processing skills are as closely related to both item STM and serial order STM. However, non-verbal intelligence was more strongly involved in serial order STM than in item STM. In the second experiment, the same two STM tasks were administered and reading acquisition was assessed by measuring orthographic learning in a group of 188 children. The results of this study show that orthographic learning is exclusively related to item STM and not to order STM. It is concluded that serial order STM is not the right place to look for a causal explanation of reading disability, nor for differences in word reading acquisition. PMID:25294996

  8. Nanofabrication with the Scanning Tunneling Microscope

    SciTech Connect

    Shedd, G.M.; Russell, P.E.

    1988-12-01

    The Precision Engineering Center has recently begun a research program into applications of STM to Nanotechnology. Few tools permit humans to control events and processes at the manometer level, and of those, the STM is the most well-suited to the task. A versatile new ultra-high-vacuum (UHV) STM is being built to study the use of STM for the manipulation of nanometer-scale particles. Part of the STM`s usefulness will be due to its being positioned directly beneath the focused ion beam (FIB). The interface of the STM with the FIB will allow the STM to take advantage of the FIB for long-range imaging and as a particle source; the FIB can in turn use the STM for in situ, high-resolution imaging of micromachined features.

  9. Transcriptional, Posttranscriptional, and Posttranslational Regulation of SHOOT MERISTEMLESS Gene Expression in Arabidopsis Determines Gene Function in the Shoot Apex1[OPEN

    PubMed Central

    Aguilar-Martínez, José Antonio; Uchida, Naoyuki; Townsley, Brad; West, Donnelly Ann; Yanez, Andrea; Lynn, Nafeesa; Kimura, Seisuke

    2015-01-01

    The activity of SHOOT MERISTEMLESS (STM) is required for the functioning of the shoot apical meristem (SAM). STM is expressed in the SAM but is down-regulated at the site of leaf initiation. STM is also required for the formation of compound leaves. However, how the activity of STM is regulated at the transcriptional, posttranscriptional, and posttranslational levels is poorly understood. We previously found two conserved noncoding sequences in the promoters of STM-like genes across angiosperms, the K-box and the RB-box. Here, we characterize the function of the RB-box in Arabidopsis (Arabidopsis thaliana). The RB-box, along with the K-box, regulates the expression of STM in leaf sinuses, which are areas on the leaf blade with meristematic potential. The RB-box also contributes to restrict STM expression to the SAM. We identified FAR1-RELATED SEQUENCES-RELATED FACTOR1 (FRF1) as a binding factor to the RB-box region. FRF1 is an uncharacterized member of a subfamily of four truncated proteins related to the FAR1-RELATED SEQUENCES factors. Internal deletion analysis of the STM promoter identified a region required to repress the expression of STM in hypocotyls. Expression of STM in leaf primordia under the control of the JAGGED promoter produced plants with partially undifferentiated leaves. We further found that the ELK domain has a role in the posttranslational regulation of STM by affecting the nuclear localization of STM. PMID:25524441

  10. Serial-Order Short-Term Memory Predicts Vocabulary Development: Evidence from a Longitudinal Study

    ERIC Educational Resources Information Center

    Leclercq, Anne-Lise; Majerus, Steve

    2010-01-01

    Serial-order short-term memory (STM), as opposed to item STM, has been shown to be very consistently associated with lexical learning abilities in cross-sectional study designs. This study investigated longitudinal predictions between serial-order STM and vocabulary development. Tasks maximizing the temporary retention of either serial-order or…

  11. The Contribution of Short-Term Memory for Serial Order to Early Reading Acquisition: Evidence from a Longitudinal Study

    ERIC Educational Resources Information Center

    Perez, Trecy Martinez; Majerus, Steve; Poncelet, Martine

    2012-01-01

    Early reading acquisition skills have been linked to verbal short-term memory (STM) capacity. However, the nature of this relationship remains controversial because verbal STM, like reading acquisition, depends on the complexity of underlying phonological processing skills. This longitudinal study addressed the relation between STM and reading…

  12. Evidence for a Specific Impairment of Serial Order Short-Term Memory in Dyslexic Children

    ERIC Educational Resources Information Center

    Perez, Trecy Martinez; Majerus, Steve; Mahot, Aline; Poncelet, Martine

    2012-01-01

    In order to better understand the nature of verbal short-term memory (STM) deficits in dyslexic children, the present study used the distinction between item and serial order retention capacities in STM tasks. According to recent STM models, storage of verbal item information depends very directly upon the richness of underlying phonological and…

  13. Functional Alterations in Order Short-Term Memory Networks in Adults With Dyslexia.

    PubMed

    Martinez Perez, Trecy; Poncelet, Martine; Salmon, Eric; Majerus, Steve

    2015-01-01

    Dyslexia is characterized not only by reading impairment but also by short-term memory (STM) deficits, and this particularly for the retention of serial order information. Here, we explored the functional neural correlates associated with serial order STM performance of adults with dyslexia for verbal and visual STM tasks. Relative to a group of age-matched controls, the dyslexic group showed abnormal activation in a network associated with order STM encompassing the right intraparietal and superior frontal sulcus, and this for both verbal and visual order STM conditions. This study highlights long-lasting alterations in non-language neural substrates and processes in dyslexia. PMID:27043828

  14. Explaining semantic short-term memory deficits: Evidence for the critical role of semantic control

    PubMed Central

    Hoffman, Paul; Jefferies, Elizabeth; Lambon Ralph, Matthew A.

    2011-01-01

    Patients with apparently selective short-term memory (STM) deficits for semantic information have played an important role in developing multi-store theories of STM and challenge the idea that verbal STM is supported by maintaining activation in the language system. We propose that semantic STM deficits are not as selective as previously thought and can occur as a result of mild disruption to semantic control processes, i.e., mechanisms that bias semantic processing towards task-relevant aspects of knowledge and away from irrelevant information. We tested three semantic STM patients with tasks that tapped four aspects of semantic control: (i) resolving ambiguity between word meanings, (ii) sensitivity to cues, (iii) ignoring irrelevant information and (iv) detecting weak semantic associations. All were impaired in conditions requiring more semantic control, irrespective of the STM demands of the task, suggesting a mild, but task-general, deficit in regulating semantic knowledge. This mild deficit has a disproportionate effect on STM tasks because they have high intrinsic control demands: in STM tasks, control is required to keep information active when it is no longer available in the environment and to manage competition between items held in memory simultaneously. By re-interpreting the core deficit in semantic STM patients in this way, we are able to explain their apparently selective impairment without the need for a specialised STM store. Instead, we argue that semantic STM patients occupy the mildest end of spectrum of semantic control disorders. PMID:21195105

  15. Development of liquid-metal-ion source low-energy ion gun/high-temperature ultrahigh vacuum scanning tunneling microscope combined system

    SciTech Connect

    Uchigasaki, M.; Kamioka, T.; Hirata, T.; Shimizu, T.; Lin, F.; Shinada, T.; Ohdomari, I.

    2005-12-15

    A liquid-metal-ion source low-energy ion gun/high-temperature ultrahigh vacuum scanning tunneling microscope combined system (LMIS-IG/STM) has been developed in order to investigate the ion beam modification process in situ based on our previous ion gun/STM combined system (IG/STM). Various kinds of metal ions can be irradiated with low acceleration energy of 0.01-5 keV during STM observation at 400-600 deg. C. As an example, real-time STM observation of Si(111)7x7 surface irradiated with Si{sup 2+} ions is demonstrated. The STM results have shown that the surface defects generated by Si{sup 2+} ion irradiation exhibit similar behavior of surface defects induced by Ar{sup +} irradiation with IG/STM.

  16. Scanning tunneling microscope assembly, reactor, and system

    DOEpatents

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

    2014-11-18

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

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

    SciTech Connect

    Ogletree, D.F.; Dunphy, J.C.; Salmeron, M.B.; Sautet, P. |

    1993-02-01

    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.

  18. Serial position encoding of signs.

    PubMed

    Miozzo, Michele; Petrova, Anna; Fischer-Baum, Simon; Peressotti, Francesca

    2016-09-01

    Reduced short-term memory (STM) capacity has been reported for sign as compared to speech when items have to be recalled in a specific order. This difference has been attributed to a more precise and efficient serial position encoding in verbal STM (used for speech) than visuo-spatial STM (used for sign). We tested in the present investigation whether the reduced STM capacity with signs stems from a lack of positional encoding available in verbal STM. Error analyses reported in prior studies have revealed that positions are defined in verbal STM by distance from both the start and the end of the sequence (both-edges positional encoding scheme). Our analyses of the errors made by deaf participants with finger-spelled letters revealed that the both-edges positional encoding scheme underlies the STM representation of signs. These results indicate that the cause of the STM disadvantage is not the type of positional encoding but rather the difficulties in binding an item in visuo-spatial STM to its specific position in the sequence. Both-edges positional encoding scheme could be specific of sign, since it has not been found in visuo-spatial STM tasks conducted with hearing participants. PMID:27244095

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

    SciTech Connect

    Kamioka, Takefumi; Sato, Kou; Kazama, Yutaka; Watanabe, Takanobu; Ohdomari, Iwao

    2008-07-15

    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.

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

    DOEpatents

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

    2008-04-22

    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.

  1. Equations of motion and fifth force in a general Kaluza-Klein space

    NASA Astrophysics Data System (ADS)

    Bejancu, Aurel

    2013-11-01

    In this paper we present a new point of view on space-time-matter (STM) theory. First, some weak points from earlier research papers on STM theory are presented. Then, we obtain in a covariant form the fully general equations of motion for STM theory. This enables us to classify the motions and to give a new definition of the fifth force in physics.

  2. Nitrogen-induced structures in epitaxial graphene on 6H-SiC(0001)

    NASA Astrophysics Data System (ADS)

    Sun, Guofeng; Rhim, Sung-Hyon; Qi, Yun; Weinert, Michael; Li, Lian

    2009-03-01

    Nitrogen-induced structures on epitaxial graphene grown on 6H- SiC(0001) are studied by scanning tunneling microscopy (STM) and first-principles calculations. Several defect structures produced by nitrogen incorporation are observed by STM. Calculations of the energetics of nitrogen substitution at various sites neighboring a carbon vacancy indicate that nitrogen prefers to be at the site nearest to the vacancy, consistent with the STM observations.

  3. Correlation of scanning-tunneling-microscope image profiles and charge-density-wave amplitudes

    NASA Astrophysics Data System (ADS)

    Giambattista, B.; Johnson, A.; McNairy, W. W.; Slough, C. G.; Coleman, R. V.

    1988-08-01

    Scanning-tunneling-microscope (STM) studies of 4Hb-TaS2 and 4Hb-TaSe2 at 4.2 K show systematic correlation between the charge-density-wave (CDW) amplitude and the STM deflection. The 4Hb phases have both weak and strong CDW's in the trigonal prismatic and octahedral sandwiches, respectively. Scans on opposite faces of the same cleave allow a comparison of the STM response to the two types of CDW.

  4. Atomic resolution images of graphite in air

    SciTech Connect

    Grigg, D.A.; Shedd, G.M.; Griffis, D.; Russell, P.E.

    1988-12-01

    One sample used for proof of operation for atomic resolution in STM is highly oriented pyrolytic graphite (HOPG). This sample has been imaged with many different STM`s obtaining similar results. Atomic resolution images of HOPG have now been obtained using an STM designed and built at the Precision Engineering Center. This paper discusses the theoretical predictions and experimental results obtained in imaging of HOPG.

  5. Correlates of nonmedical use of stimulants and methamphetamine use in a national sample

    PubMed Central

    Chen, Lian-Yu; Strain, Eric C.; Alexandre, Pierre Kébreau; Alexander, G. Caleb; Mojtabai, Ramin; Martins, Silvia S.

    2014-01-01

    Background Despite chemical similarities, ADHD stimulants and methamphetamine have distinct use patterns in the community. This study compared the characteristics of nonmedical ADHD stimulants users and methamphetamine users in a household sample. Methods In data from the 2009–2011 National Survey on Drug Use and Health, adult and adolescent stimulant users were categorized into three mutually exclusive subgroups: nonmedical ADHD stimulant users only (STM users), methamphetamine users (METH users), and both nonmedical ADHD stimulant and methamphetamine users (STM/METH users). Multivariate logistic regression analyses identified the substance comorbidity, mental health, and deviant behavior characteristics associated with these three groups. Results Compared to adolescent STM users, STM/METH users were more likely to be female, younger and uninsured while METH users were more likely to be younger, in a minority group and from a higher-income family. Compared to adult STM users, METH and STM/METH users were more likely to be male, older, uninsured, no longer married, and to be from rural areas. Adolescent METH users were more likely than STM users to report illegal drug use while adult METH users were less likely to report prescription drug use than their STM user counterparts. Overall, adult and adolescent STM/METH users were more likely to report substance use, mental health problems and deviant behaviors compared to STM users. Conclusion The characteristics of STM users differ from METH and STM/METH users, and their associations with substance use and psychiatric comorbidities differ by age. Findings have implications for understanding the risks for stimulant use in different age subgroups. PMID:24583271

  6. Scanning tunneling microscopy of chromium-filled carbon nanotubes: Tip effects and related topographic features

    NASA Astrophysics Data System (ADS)

    Zha, F.-X.; Czerw, R.; Carroll, D. L.; Kohler-Redlich, Ph.; Wei, B.-Q.; Loiseau, A.; Roth, S.

    2000-02-01

    We have used ultrahigh vacuum scanning tunneling microscopy (STM) to study chromium (Cr)-filled carbon nanotubes. STM micrographs show filled tubes to be less than 1 nm in height, while transmission electron microscopy indicates that Cr-filled naotubes are multiwalled with diameters generally over 10 nm. In this paper, we demonstrate that the small apparent heights are due to the STM tip status, which also accounts for the topographic anomalies observed.

  7. Phosphine adsorption and dissociation on the Si(001) surface: An ab initio survey of structures

    NASA Astrophysics Data System (ADS)

    Warschkow, O.; Wilson, H. F.; Marks, N. A.; Schofield, S. R.; Curson, N. J.; Smith, P. V.; Radny, M. W.; McKenzie, D. R.; Simmons, M. Y.

    2005-09-01

    We report a comprehensive ab initio survey of possible dissociation intermediates of phosphine (PH3) on the Si(001) surface. We assign three scanning tunneling microscopy (STM) features, commonly observed in room-temperature dosing experiments, to PH2+H , PH+2H , and P+3H species, respectively, on the basis of calculated energetics and STM simulation. These assignments and a time series of STM images which shows these three STM features converting into another, allow us to outline a mechanism for the complete dissociation of phosphine on the Si(001) surface. This mechanism closes an important gap in the understanding of the doping process of semiconductor devices.

  8. Ultrahigh vacuum scanning electron microscope system combined with wide-movable scanning tunneling microscope

    SciTech Connect

    Kaneko, A.; Homma, Y.; Hibino, H.; Ogino, T.

    2005-08-15

    A surface analysis system has been newly developed with combination of ultrahigh vacuum scanning electron microscope (SEM) and wide-movable scanning tunneling microscope (STM). The basic performance is experimentally demonstrated. These SEM and STM images are clear enough to obtain details of surface structures. The STM unit moves horizontally over several millimeters by sliding motion of PZT actuators. The motion resolution is proved to be submicrometers. The STM tip mounted on another PZT scanner can be guided to a specific object on the sample surface during SEM observation. In the observation of a Si(111) surface rapidly cooled from high temperature, the STM tip was accurately guided to an isolated atomic step and slightly moved along it during SEM observation. The STM observation shows an asymmetry of the (7x7)-transformed region along the step between the upper and lower terraces. (7x7) bands continuously formed along the edge of terraces, while (7x7) domains distributed on the terraces slightly far from the step. These experiments show the wide-movable STM unit resolves a gap of observation area between SEM and STM and the system enables a specific object found in the SEM image to be observed easily by STM.

  9. Two proprotein convertase subtilisin/kexin type 9 (PCSK9) paralogs from the tropical sea cucumber (Stichopus monotuberculatus): Molecular characterization and inducible expression with immune challenge.

    PubMed

    Ren, Chunhua; Chen, Ting; Jiang, Xiao; Sun, Hongyan; Qian, Jing; Hu, Chaoqun; Wang, Yanhong

    2016-09-01

    Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a multifunctional protein that widely exists in eukaryotic species. In this study, two PCSK9 paralogs, named StmPCSK9-1 and StmPCSK9-2, were identified from the tropical sea cucumber (Stichopus monotuberculatus). The cDNAs of StmPCSK9-1 and StmPCSK9-2 are 1330 kb and 1508 kb in size, respectively. The open reading frames (ORF) for StmPCSK9-1 and StmPCSK9-2 cDNAs are 1128 and 1167 bp in length, encoding the proteins of 375 and 388 amino acids with the deduced molecular weights of 38.76 and 41.07 kDa, respectively. In accord with other members in PCSK9 family, the two StmPCSK9 paralogs possessed the inhibitor_I9 and peptidase_S8 functional domains, seven active sites, a catalytic triad and two calcium binding sites. For the gene structure, the splicing of the two StmPCSK9 paralogs was relatively conserved. In addition, the mRNA expression of StmPCSK9-1 and StmPCSK9-2 was only detected in the sea cucumber intestine and coelomocytes, and the expression levels of both the two StmPCSK9 paralogs were higher in intestine. Moreover, StmPCSK9-2 was found to be a cytoplasm protein without signal peptide, and show no response to the immune challenge. On the contrary, StmPCSK9-1 was a secreted protein and the transcriptional expression of StmPCSK9-1 was significantly up-regulated by lipopolysaccharides (LPS) treatment and slightly down-regulated by polyriboinosinic polyribocytidylic acid [Poly (I:C)] challenge in in vitro experiments performed in the cultural primary coelomocytes, suggesting that the StmPCSK9-1 may play critical roles in the innate immune defense of sea cucumber, S. monotuberculatus, against bacterial and/or viral infections. PMID:27426522

  10. Overexpression of Salmonella enterica serovar Typhi recA gene confers fluoroquinolone resistance in Escherichia coli DH5α.

    PubMed

    Yassien, M A M; Elfaky, M A

    2015-11-01

    A spontaneous fluoroquinolone-resistant mutant (STM1) was isolated from its parent Salmonella enterica serovar Typhi (S. Typhi) clinical isolate. Unlike its parent isolate, this mutant has selective resistance to fluoroquinolones without any change in its sensitivity to various other antibiotics. DNA gyrase assays revealed that the fluoroquinolone resistance phenotype of the STM1 mutant did not result from alteration of the fluoroquinolone sensitivity of the DNA gyrase isolated from it. To study the mechanism of fluoroquinolone resistance, a genomic library from the STM1 mutant was constructed in Escherichia coli DH5α and two recombinant plasmids were obtained. Only one of these plasmids (STM1-A) conferred the selective fluoroquinolone resistance phenotype to E. coli DH5α. The chromosomal insert from STM1-A, digested with EcoRI and HindIII restriction endonucleases, produced two DNA fragments and these were cloned separately into pUC19 thereby generating two new plasmids, STM1-A1 and STM1-A2. Only STM1-A1 conferred the selective fluoroquinolone resistance phenotype to E. coli DH5α. Sequence and subcloning analyses of STM1-A1 showed the presence of an intact RecA open reading frame. Unlike that of the wild-type E. coli DH5α, protein analysis of a crude STM1-A1 extract showed overexpression of a 40 kDa protein. Western blotting confirmed the 40 kDa protein band to be RecA. When a RecA PCR product was cloned into pGEM-T and introduced into E. coli DH5α, the STM1-A11 subclone retained fluoroquinolone resistance. These results suggest that overexpression of RecA causes selective fluoroquinolone resistance in E. coli DH5α. PMID:26375447

  11. Current status of the state-and-transition framework

    Technology Transfer Automated Retrieval System (TEKTRAN)

    State-and-transition models (STM) have been widely adopted as a tool for explaining plant community dynamics and response to disturbance within rangeland ecosystems. Our understanding of the STM concepts has advanced substantially since they were introduced by Westoby et al. (1989) and modified by ...

  12. How Grammar Can Cope with Limited Short-Term Memory: Simultaneity and Seriality in Sign Languages

    ERIC Educational Resources Information Center

    Geraci, Carlo; Gozzi, Marta; Papagno, Costanza; Cecchetto, Carlo

    2008-01-01

    It is known that in American Sign Language (ASL) span is shorter than in English, but this discrepancy has never been systematically investigated using other pairs of signed and spoken languages. This finding is at odds with results showing that short-term memory (STM) for signs has an internal organization similar to STM for words. Moreover, some…

  13. A Single Brief Burst Induces GluR1-Dependent Associative Short-Term Potentiation: A Potential Mechanism for Short-Term Memory

    ERIC Educational Resources Information Center

    Erickson, Martha A.; Maramara, Lauren A.; Lisman, John

    2010-01-01

    Recent work showed that short-term memory (STM) is selectively reduced in GluR1 knockout mice. This raises the possibility that a form of synaptic modification dependent on GluR1 might underlie STM. Studies of synaptic plasticity have shown that stimuli too weak to induce long-term potentiation induce short-term potentiation (STP), a phenomenon…

  14. Visuospatial Support for Verbal Short-Term Memory in Individuals with Down Syndrome

    ERIC Educational Resources Information Center

    Duarte, Cintia Perez; Covre, Priscila; Braga, Ana Claudia; de Macedo, Elizeu Coutinho

    2011-01-01

    Individuals with Down syndrome (DS) tend to have impaired verbal short-term memory (STM), which persists even when visual support is provided for carrying out verbal tasks. Objective: The current study aims to investigate whether visuospatial support, rather than just visual, can compensate for verbal STM deficits in these individuals. The…

  15. Turning Simple Span into Complex Span: Time for Decay or Interference from Distractors?

    ERIC Educational Resources Information Center

    Lewandowsky, Stephan; Geiger, Sonja M.; Morrell, Daniel B.; Oberauer, Klaus

    2010-01-01

    We investigated the effects of the duration and type of to-be-articulated distractors during encoding of a verbal list into short-term memory (STM). Distractors and to-be-remembered items alternated during list presentation, as in the complex-span task that underlies much of working-memory research. According to an interference model of STM, known…

  16. Auditory Short-Term Memory Capacity Correlates with Gray Matter Density in the Left Posterior STS in Cognitively Normal and Dyslexic Adults

    ERIC Educational Resources Information Center

    Richardson, Fiona M.; Ramsden, Sue; Ellis, Caroline; Burnett, Stephanie; Megnin, Odette; Catmur, Caroline; Schofield, Tom M.; Leff, Alex P.; Price, Cathy J.

    2011-01-01

    A central feature of auditory STM is its item-limited processing capacity. We investigated whether auditory STM capacity correlated with regional gray and white matter in the structural MRI images from 74 healthy adults, 40 of whom had a prior diagnosis of developmental dyslexia whereas 34 had no history of any cognitive impairment. Using…

  17. The Generality of Working Memory Capacity: A Latent-Variable Approach to Verbal and Visuospatial Memory Span and Reasoning

    ERIC Educational Resources Information Center

    Kane, Michael J.; Hambrick, David Z.; Tuholski, Stephen W.; Wilhelm, Oliver; Payne, Tabitha W.; Engle, Randall W.

    2004-01-01

    A latent-variable study examined whether verbal and visuospatial working memory (WM) capacity measures reflect a primarily domain-general construct by testing 236 participants in 3 span tests each of verbal WM. visuospatial WM, verbal short-term memory (STM), and visuospatial STM. as well as in tests of verbal and spatial reasoning and general…

  18. Soluble flagellin coimmunization attenuates Th1 priming to Salmonella and clearance by modulating dendritic cell activation and cytokine production

    PubMed Central

    Flores‐Langarica, Adriana; Bobat, Saeeda; Marshall, Jennifer L.; Yam‐Puc, Juan Carlos; Cook, Charlotte N.; Serre, Karine; Kingsley, Robert A.; Flores‐Romo, Leopoldo; Uematsu, Satoshi; Akira, Shizuo; Henderson, Ian R.; Toellner, Kai M.

    2015-01-01

    Soluble flagellin (sFliC) from Salmonella Typhimurium (STm) can induce a Th2 response to itself and coadministered antigens through ligation of TLR5. These properties suggest that sFliC could potentially modulate responses to Th1 antigens like live STm if both antigens are given concurrently. After coimmunization of mice with sFliC and STm there was a reduction in Th1 T cells (T‐bet+IFN‐γ+ CD4 T cells) compared to STm alone and there was impaired clearance of STm. In contrast, there was no significant defect in the early extrafollicular B‐cell response to STm. These effects are dependent upon TLR5 and flagellin expression by STm. The mechanism for these effects is not related to IL‐4 induced to sFliC but rather to the effects of sFliC coimmunization on DCs. After coimmunization with STm and sFliC, splenic DCs had a lower expression of costimulatory molecules and profoundly altered kinetics of IL‐12 and TNFα expression. Ex vivo experiments using in vivo conditioned DCs confirmed the effects of sFliC were due to altered DC function during a critical window in the coordinated interplay between DCs and naïve T cells. This has marked implications for understanding how limits in Th1 priming can be achieved during infection‐induced, Th1‐mediated inflammation. PMID:26036767

  19. Task-evoked pupillometry provides a window into the development of short-term memory capacity

    PubMed Central

    Johnson, Elizabeth L.; Miller Singley, Alison T.; Peckham, Andrew D.; Johnson, Sheri L.; Bunge, Silvia A.

    2014-01-01

    The capacity to keep multiple items in short-term memory (STM) improves over childhood and provides the foundation for the development of multiple cognitive abilities. The goal of this study was to measure the extent to which age differences in STM capacity are related to differences in task engagement during encoding. Children (n = 69, mean age = 10.6 years) and adults (n = 54, mean age = 27.5 years) performed two STM tasks: the forward digit span test from the Wechsler Intelligence Scale for Children (WISC) and a novel eyetracking digit span task designed to overload STM capacity. Building on prior research showing that task-evoked pupil dilation can be used as a real-time index of task engagement, we measured changes in pupil dilation while participants encoded long sequences of digits for subsequent recall. As expected, adults outperformed children on both STM tasks. We found similar patterns of pupil dilation while children and adults listened to the first six digits on our STM overload task, after which the adults' pupils continued to dilate and the children's began to constrict, suggesting that the children had reached their cognitive limits and that they had begun to disengage from the task. Indeed, the point at which pupil dilation peaked at encoding was a significant predictor of WISC forward span, and this relationship held even after partialing out recall performance on the STM overload task. These findings indicate that sustained task engagement at encoding is an important component of the development of STM. PMID:24659980

  20. A Closer Look at Phonology as a Predictor of Spoken Sentence Processing and Word Reading

    ERIC Educational Resources Information Center

    Myers, Suzanne; Robertson, Erin K.

    2015-01-01

    The goal of this study was to tease apart the roles of phonological awareness (pA) and phonological short-term memory (pSTM) in sentence comprehension, sentence production, and word reading. Children 6- to 10-years of age (N = 377) completed standardized tests of pA ("Elision") and pSTM ("Nonword Repetition") from the…

  1. Two-Step Regulation of a Meristematic Cell Population Acting in Shoot Branching in Arabidopsis.

    PubMed

    Shi, Bihai; Zhang, Cui; Tian, Caihuan; Wang, Jin; Wang, Quan; Xu, Tengfei; Xu, Yan; Ohno, Carolyn; Sablowski, Robert; Heisler, Marcus G; Theres, Klaus; Wang, Ying; Jiao, Yuling

    2016-07-01

    Shoot branching requires the establishment of new meristems harboring stem cells; this phenomenon raises questions about the precise regulation of meristematic fate. In seed plants, these new meristems initiate in leaf axils to enable lateral shoot branching. Using live-cell imaging of leaf axil cells, we show that the initiation of axillary meristems requires a meristematic cell population continuously expressing the meristem marker SHOOT MERISTEMLESS (STM). The maintenance of STM expression depends on the leaf axil auxin minimum. Ectopic expression of STM is insufficient to activate axillary buds formation from plants that have lost leaf axil STM expressing cells. This suggests that some cells undergo irreversible commitment to a developmental fate. In more mature leaves, REVOLUTA (REV) directly up-regulates STM expression in leaf axil meristematic cells, but not in differentiated cells, to establish axillary meristems. Cell type-specific binding of REV to the STM region correlates with epigenetic modifications. Our data favor a threshold model for axillary meristem initiation, in which low levels of STM maintain meristematic competence and high levels of STM lead to meristem initiation. PMID:27398935

  2. Relations between Vocabulary Development and Verbal Short-Term Memory: The Relative Importance of Short-Term Memory for Serial Order and Item Information

    ERIC Educational Resources Information Center

    Majerus, Steve; Poncelet, Martine; Greffe, Christelle; Van der Linden, Martial

    2006-01-01

    Although many studies have shown an association between verbal short-term memory (STM) and vocabulary development, the precise nature of this association is not yet clear. The current study reexamined this relation in 4- to 6-year-olds by designing verbal STM tasks that maximized memory for either item or serial order information. Although…

  3. Lexical Learning in Bilingual Adults: The Relative Importance of Short-Term Memory for Serial Order and Phonological Knowledge

    ERIC Educational Resources Information Center

    Majerus, Steve; Poncelet, Martine; Van der Linden, Martial; Weekes, Brendan S.

    2008-01-01

    Studies of monolingual speakers have shown a strong association between lexical learning and short-term memory (STM) capacity, especially STM for serial order information. At the same time, studies of bilingual speakers suggest that phonological knowledge is the main factor that drives lexical learning. This study tested these two hypotheses…

  4. Verbal Short-Term Memory Reflects the Sublexical Organization of the Phonological Language Network: Evidence from an Incidental Phonotactic Learning Paradigm

    ERIC Educational Resources Information Center

    Majerus, Steve; Van der Linden; Martial; Mulder, Ludivine; Meulemans, Thierry; Peters, Frederic

    2004-01-01

    The nonword phonotactic frequency effect in verbal short-term memory (STM) is characterized by superior recall for nonwords containing familiar as opposed to less familiar phoneme associations. This effect is supposed to reflect the intervention of phonological long-term memory (LTM) in STM. However the lexical or sublexical nature of this LTM…

  5. Phonological and Sensory Short-Term Memory Are Correlates and Both Affected in Developmental Dyslexia

    ERIC Educational Resources Information Center

    Laasonen, Marja; Virsu, Veijo; Oinonen, Suvi; Sandbacka, Mirja; Salakari, Anita; Service, Elisabet

    2012-01-01

    We investigated whether poor short-term memory (STM) in developmental dyslexia affects the processing of sensory stimulus sequences in addition to phonological material. STM for brief binary non-verbal stimuli (light flashes, tone bursts, finger touches, and their crossmodal combinations) was studied in 20 Finnish adults with dyslexia and 24…

  6. Two-Step Regulation of a Meristematic Cell Population Acting in Shoot Branching in Arabidopsis

    PubMed Central

    Tian, Caihuan; Wang, Jin; Xu, Tengfei; Xu, Yan; Ohno, Carolyn; Sablowski, Robert; Heisler, Marcus G.; Theres, Klaus; Wang, Ying

    2016-01-01

    Shoot branching requires the establishment of new meristems harboring stem cells; this phenomenon raises questions about the precise regulation of meristematic fate. In seed plants, these new meristems initiate in leaf axils to enable lateral shoot branching. Using live-cell imaging of leaf axil cells, we show that the initiation of axillary meristems requires a meristematic cell population continuously expressing the meristem marker SHOOT MERISTEMLESS (STM). The maintenance of STM expression depends on the leaf axil auxin minimum. Ectopic expression of STM is insufficient to activate axillary buds formation from plants that have lost leaf axil STM expressing cells. This suggests that some cells undergo irreversible commitment to a developmental fate. In more mature leaves, REVOLUTA (REV) directly up-regulates STM expression in leaf axil meristematic cells, but not in differentiated cells, to establish axillary meristems. Cell type-specific binding of REV to the STM region correlates with epigenetic modifications. Our data favor a threshold model for axillary meristem initiation, in which low levels of STM maintain meristematic competence and high levels of STM lead to meristem initiation. PMID:27398935

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

    ERIC Educational Resources Information Center

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

    2004-01-01

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

  8. Ultra-Compact Multitip Scanning Probe Microscope with an Outer Diameter of 50 mm

    NASA Astrophysics Data System (ADS)

    Cherepanov, Vasily; Zubkov, Evgeny; Junker, Hubertus; Korte, Stefan; Blab, Marcus; Coenen, Peter; Voigtländer, Bert

    We present a multitip scanning tunneling microscope (STM) where four independent STM units are integrated on a diameter of 50 mm. The coarse positioning of the tips is done under the control of an optical microscope or an SEM in vacuum. The heart of this STM is a new type of piezoelectric coarse approach called Koala Drive which can have a diameter greater than 2.5 mm and a length smaller than 10 mm. Alternating movements of springs move a central tube which holds the STM tip or AFM sensor. This new operating principle provides a smooth travel sequence and avoids shaking which is intrinsically present for nanopositioners based on inertial motion with saw tooth driving signals. Inserting the Koala Drive in a piezo tube for xyz-scanning integrates a complete STM inside a 4 mm outer diameter piezo tube of <10 mm length. The use of the Koala Drive makes the scanning probe microscopy design ultra-compact and accordingly leads to a high mechanical stability. The drive is UHV, low temperature, and magnetic field compatible. The compactness of the Koala Drive allows building a four-tip STM as small as a single-tip STM with a drift of <0.2 nm/min and lowest resonance frequencies of 2.5 (xy) and 5.5 kHz (z). We present examples of the performance of the multitip STM designed using the Koala Drive.

  9. Short Term Memory, Working Memory, and Syntactic Comprehension in Aphasia

    PubMed Central

    Caplan, David; Michaud, Jennifer; Hufford, Rebecca

    2013-01-01

    Sixty one people with aphasia were tested on ten tests of short term memory (STM) and for the ability to use syntactic structure to determine the meanings of eleven types of sentences in three tasks – object manipulation, picture matching and picture matching with self-paced listening. Multilevel models showed relationships between measures of the ability to retain and manipulate item and order information in STM and accuracy and RT, and a greater relationship between these STM measures and accuracy and RT for several more complex sentence types in individual tasks. There were no effects of measures of STM that reflect the use of phonological codes or rehearsal on comprehension. There was only one effect of STM measures on self-paced listening times. There were double dissociations between performance on STM and individual comprehension tasks, indicating that normal STM is not necessary to perform normally on these tasks. The results are most easily related to the view that STM plays a facilitatory role in supporting the use of the products of the comprehension process to accomplish operations related to tasks. PMID:23865692

  10. From Graphite to Graphene via Scanning Tunneling Microscopy

    NASA Astrophysics Data System (ADS)

    Qi, Dejun

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

  11. Soluble flagellin coimmunization attenuates Th1 priming to Salmonella and clearance by modulating dendritic cell activation and cytokine production.

    PubMed

    Flores-Langarica, Adriana; Bobat, Saeeda; Marshall, Jennifer L; Yam-Puc, Juan Carlos; Cook, Charlotte N; Serre, Karine; Kingsley, Robert A; Flores-Romo, Leopoldo; Uematsu, Satoshi; Akira, Shizuo; Henderson, Ian R; Toellner, Kai M; Cunningham, Adam F

    2015-08-01

    Soluble flagellin (sFliC) from Salmonella Typhimurium (STm) can induce a Th2 response to itself and coadministered antigens through ligation of TLR5. These properties suggest that sFliC could potentially modulate responses to Th1 antigens like live STm if both antigens are given concurrently. After coimmunization of mice with sFliC and STm there was a reduction in Th1 T cells (T-bet(+) IFN-γ(+) CD4 T cells) compared to STm alone and there was impaired clearance of STm. In contrast, there was no significant defect in the early extrafollicular B-cell response to STm. These effects are dependent upon TLR5 and flagellin expression by STm. The mechanism for these effects is not related to IL-4 induced to sFliC but rather to the effects of sFliC coimmunization on DCs. After coimmunization with STm and sFliC, splenic DCs had a lower expression of costimulatory molecules and profoundly altered kinetics of IL-12 and TNFα expression. Ex vivo experiments using in vivo conditioned DCs confirmed the effects of sFliC were due to altered DC function during a critical window in the coordinated interplay between DCs and naïve T cells. This has marked implications for understanding how limits in Th1 priming can be achieved during infection-induced, Th1-mediated inflammation. PMID:26036767

  12. Extremely low-noise potentiometry with a scanning tunneling microscope

    NASA Astrophysics Data System (ADS)

    Pelz, J. P.; Koch, R. H.

    1989-03-01

    Novel ac biasing and detection techniques have been developed to allow a scanning tunneling microscope (STM) to measure spatial variations in electric potential on metallic surfaces with sub-μV sensitivity. When implemented with a room-temperature STM operating with minimal electrical shielding and no vibration isolation, the voltage sensitivity was limited by the thermal (Johnson) noise of the tunneling resistance.

  13. 40Gbit/s multi-lane distribution interface converter and its application to cost-effective optical transceiver for 40G SONET/SDH signals

    NASA Astrophysics Data System (ADS)

    Aisawa, S.; Ono, T.; Tomizawa, M.

    2011-12-01

    We create a 40Gbit/s multi-lane distribution (MLD) interface converter for STM-256 to STL-256.4 and OTU3 to OTL3.4. We successfully demonstrate a cost-effective optical transceiver for STM-256/OC-768/40G-POS by using our 40Gbit/s MLD interface converter prototype.

  14. Working Memory Capacity and Its Relation to Stroop Interference and Facilitation Effects in Individuals with Mild Cognitive Impairment

    ERIC Educational Resources Information Center

    Sung, Jee Eun; Kim, Jin Hee; Jeong, Jee Hyang; Kang, Heejin

    2012-01-01

    Purpose: The purposes of the study were to investigate (a) the task-specific differences in short-term memory (STM) and working memory capacity (WMC) in individuals with mild cognitive impairment (MCI) and normal elderly adults (NEAs), (b) the Stroop interference and facilitation effects, and (c) the relationship of STM and WMC to the Stroop…

  15. Individual Differences in Children's Working Memory and Writing Skill.

    ERIC Educational Resources Information Center

    Swanson, H. Lee; Berninger, Virginia W.

    1996-01-01

    Examined whether writing and working memory (WM) were related to general or process-specific system, whether WM tasks operated independently of phonological short-term memory (STM), and whether WM predicted writing variance beyond that predicted by reading. Found a four-factor model reflecting phonological STM, verbal WM span, executive…

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

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

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

  17. Engineering the emission of light from a scanning tunneling microscope using the plasmonic modes of a nanoparticle

    NASA Astrophysics Data System (ADS)

    Le Moal, Eric; Marguet, Sylvie; Canneson, Damien; Rogez, Benoît; Boer-Duchemin, Elizabeth; Dujardin, Gérald; Teperik, Tatiana V.; Marinica, Dana-Codruta; Borisov, Andrey G.

    2016-01-01

    The inelastic tunnel current in the junction formed between the tip of a scanning tunneling microscope (STM) and the sample can electrically generate optical signals. This phenomenon is potentially of great importance for nano-optoelectronic devices. In practice, however, the properties of the emitted light are difficult to control because of the strong influence of the STM tip. In this work, we show both theoretically and experimentally that the sought-after, well-controlled emission of light from an STM tunnel junction may be achieved using a nonplasmonic STM tip and a plasmonic nanoparticle on a transparent substrate. We demonstrate that the native plasmon modes of the nanoparticle may be used to engineer the light emitted in the substrate. Both the angular distribution and intensity of the emitted light may be varied in a predictable way by choosing the excitation position of the STM tip on the particle.

  18. Scanning tunneling microscope with three-dimensional interferometer for surface roughness measurement

    NASA Astrophysics Data System (ADS)

    Fujii, Toru; Yamaguchi, Masataka; Suzuki, Masatoshi

    1995-03-01

    The scanning tunneling microscope (STM) has been known for its high lateral resolution, but its unreliable vertical accuracy has prevented it from being widely used as a profiler for roughness and step height measurements. An STM equipped with an optical interferometer to calibrate STM tip feedback controlled motion in the Z direction along with interferometers for monitoring X and Y raster scanning has been developed. The resolution of the interferometer was 0.12 nm rms. Maximum line scanning distance is 250 μm and the motion in this direction is secured by a parallel spring mechanism. Step height and pitch measurements on a surface topography standard agree in nanometer scale with the certified value of the standard. The result of high accuracy roughness measurement with the STM supports the common observation that STM measurement gives larger roughness than interferometric measurement.

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

    SciTech Connect

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

    2007-05-15

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

  20. Probing electron transport and structural properties of nanostructures on Si with a quadraprobe scanning tunneling microscope

    SciTech Connect

    Kim, Tae Hwan; Wendelken, J F; Li, An-Ping

    2008-01-01

    The electron transport and structural properties of nanostructured materials have been examined with a newly developed low temperature quadraprobe scanning tunneling microscope (STM) system. The quadraprobe STM system, as a "nano" version of a four-probe station provides an integrated research platform with a low temperature four-probe STM, a molecular-beam epitaxy growth chamber, a high resolution scanning electron microscope, and a scanning Auger microscope. The four STM probes can be driven independently with sub-nanometer precision, enabling conventional STM imaging and four-point electrical transport study of surface electronic systems and nanostructured materials at temperatures down to 10 K. Self-assembled nanostructures grown on Si by doping with metal atoms (Au, Gd, Ag) have been fabricated and characterized in situ.

  1. Atomic-scale imaging of surfaces and interfaces. Materials Research Society Symposium Proceedings, volume 295

    NASA Astrophysics Data System (ADS)

    Biegelsen, David K.; Smith, David J.; Tong, S. Y.

    The gap between imagining and imaging is getting ever smaller. The Atomic-Scale Imaging of Surfaces and Interfaces, Symposium W at the 1992 MRS Fall Meeting in Boston, Massachusetts, brought together researchers using state-of-the-art imaging techniques capable of resolving atomic features. Methods represented were scanning tunneling microscopy (STM), atomic force microscopy (AFM), low energy electron microscopy (LEEM), transmission (TEM) and reflection (REM) electron microscopy, scanning electron microscopy (SEM), atom probe field ion microscopy (APFIM or POSAP), high and low energy external source electron holographies, and internal source electron holographies. Some highlights from the STM papers included discussions of the limitations and future potential of STM as well as current findings. Several papers presented work with STM at elevated temperatures. Jene Golovchenko reviewed STM work showing cooperative diffusion events (Pb on Ge) involving many tens of substrate atoms. Don Eigler focused on atomic manipulation and some of its uses to enable fundamental studies of small atomic clusters.

  2. The impact of aging and hearing status on verbal short-term memory.

    PubMed

    Verhaegen, Clémence; Collette, Fabienne; Majerus, Steve

    2014-01-01

    The aim of this study is to assess the impact of hearing status on age-related decrease in verbal short-term memory (STM) performance. This was done by administering a battery of verbal STM tasks to elderly and young adult participants matched for hearing thresholds, as well as to young normal-hearing control participants. The matching procedure allowed us to assess the importance of hearing loss as an explanatory factor of age-related STM decline. We observed that elderly participants and hearing-matched young participants showed equal levels of performance in all verbal STM tasks, and performed overall lower than the normal-hearing young control participants. This study provides evidence for recent theoretical accounts considering reduced hearing level as an important explanatory factor of poor auditory-verbal STM performance in older adults. PMID:24007209

  3. Dynamic soft tissue mobilisation increases hamstring flexibility in healthy male subjects

    PubMed Central

    Hopper, D; Deacon, S; Das, S; Jain, A; Riddell, D; Hall, T; Briffa, K; Vicenzino, B.

    2005-01-01

    Objectives: The purpose of this study was to investigate the effect of dynamic soft tissue mobilisation (STM) on hamstring flexibility in healthy male subjects. Methods: Forty five males volunteered to participate in a randomised, controlled single blind design study. Volunteers were randomised to either control, classic STM, or dynamic STM intervention. The control group was positioned prone for 5 min. The classic STM group received standard STM techniques performed in a neutral prone position for 5 min. The dynamic STM group received all elements of classic STM followed by distal to proximal longitudinal strokes performed during passive, active, and eccentric loading of the hamstring. Only specific areas of tissue tightness were treated during the dynamic phase. Hamstring flexibility was quantified as hip flexion angle (HFA) which was the difference between the total range of straight leg raise and the range of pelvic rotation. Pre- and post-testing was conducted for the subjects in each group. A one-way ANCOVA followed by pairwise post-hoc comparisons was used to determine whether change in HFA differed between groups. The α level was set at 0.05. Results: Increase in hamstring flexibility was significantly greater in the dynamic STM group than either the control or classic STM groups with mean (standard deviation) increase in degrees in the HFA measures of 4.7 (4.8), –0.04 (4.8), and 1.3 (3.8), respectively. Conclusions: Dynamic soft tissue mobilisation (STM) significantly increased hamstring flexibility in healthy male subjects. PMID:16118294

  4. Proteome of Salmonella Enterica SerotypeTyphimurium Grown in a Low Mg2+/pH Medium

    SciTech Connect

    Shi, Liang; Ansong, Charles; Smallwood, Heather S.; Rommereim, Leah M.; McDermott, Jason E.; Brewer, Heather M.; Norbeck, Angela D.; Taylor, Ronald C.; Gustin, Jean K.; Heffron, Fred; Smith, Richard D.; Adkins, Joshua N.

    2009-09-01

    The facultative intracellular pathogen Salmonella enterica serovar Typhimurium (STM) must replicate within host macrophages in order to establish systemic infection in susceptible mice. In an effort to identify new STM proteins that help the bacterium colonize macrophages, we have cultured STM cells with a low pH/low magnesium medium (MgM) under two different conditions termed MgM-Shock and MgM-Dilution and investigated the impacts of these culturing conditions on the STM proteome by using liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based proteomics. LC-MS/MS results showed that alteration of culturing conditions affected a group of STM proteins differently. Compared to MgM-Shock, MgM-Dilution induced more proteins of the Salmonella-pathogenecity island 2-type III secretion system (SPI2-T3SS). The abundances of the proteins used for cobalamin biosynthesis increased under MgM-Shock condition but decreased under MgM-Dilution condition, while those proteins used for thiamine or biotin biosynthesis were not affected under the former condition but increased under the latter condition. Western-blot (WB) analysis confirmed the LC-MS/MS results. Because cobalamin, thiamine and biotin play different roles in STM metabolism, differential induction of the proteins involved in their biosyntheses suggests that the metabolic states of STM cells under these conditions differ considerably. WB analysis also showed that the abundances of SPI2-T3SS proteins SsaQ and SseE and biotin biosynthesis proteins BioB and BioD increased after STM infection of RAW 264.7 macrophages. Deletion of the gene encoding BioB reduced the ability of STM to replicate inside the macrophages, demonstrating for the first time the involvement of a biotin synthesis protein in STM colonization of macrophages.

  5. Spectrotemporal Modulation Detection and Speech Perception by Cochlear Implant Users

    PubMed Central

    Won, Jong Ho; Moon, Il Joon; Jin, Sunhwa; Park, Heesung; Woo, Jihwan; Cho, Yang-Sun; Chung, Won-Ho; Hong, Sung Hwa

    2015-01-01

    Spectrotemporal modulation (STM) detection performance was examined for cochlear implant (CI) users. The test involved discriminating between an unmodulated steady noise and a modulated stimulus. The modulated stimulus presents frequency modulation patterns that change in frequency over time. In order to examine STM detection performance for different modulation conditions, two different temporal modulation rates (5 and 10 Hz) and three different spectral modulation densities (0.5, 1.0, and 2.0 cycles/octave) were employed, producing a total 6 different STM stimulus conditions. In order to explore how electric hearing constrains STM sensitivity for CI users differently from acoustic hearing, normal-hearing (NH) and hearing-impaired (HI) listeners were also tested on the same tasks. STM detection performance was best in NH subjects, followed by HI subjects. On average, CI subjects showed poorest performance, but some CI subjects showed high levels of STM detection performance that was comparable to acoustic hearing. Significant correlations were found between STM detection performance and speech identification performance in quiet and in noise. In order to understand the relative contribution of spectral and temporal modulation cues to speech perception abilities for CI users, spectral and temporal modulation detection was performed separately and related to STM detection and speech perception performance. The results suggest that that slow spectral modulation rather than slow temporal modulation may be important for determining speech perception capabilities for CI users. Lastly, test–retest reliability for STM detection was good with no learning. The present study demonstrates that STM detection may be a useful tool to evaluate the ability of CI sound processing strategies to deliver clinically pertinent acoustic modulation information. PMID:26485715

  6. Gaussian process style transfer mapping for historical Chinese character recognition

    NASA Astrophysics Data System (ADS)

    Feng, Jixiong; Peng, Liangrui; Lebourgeois, Franck

    2015-01-01

    Historical Chinese character recognition is very important to larger scale historical document digitalization, but is a very challenging problem due to lack of labeled training samples. This paper proposes a novel non-linear transfer learning method, namely Gaussian Process Style Transfer Mapping (GP-STM). The GP-STM extends traditional linear Style Transfer Mapping (STM) by using Gaussian process and kernel methods. With GP-STM, existing printed Chinese character samples are used to help the recognition of historical Chinese characters. To demonstrate this framework, we compare feature extraction methods, train a modified quadratic discriminant function (MQDF) classifier on printed Chinese character samples, and implement the GP-STM model on Dunhuang historical documents. Various kernels and parameters are explored, and the impact of the number of training samples is evaluated. Experimental results show that accuracy increases by nearly 15 percentage points (from 42.8% to 57.5%) using GP-STM, with an improvement of more than 8 percentage points (from 49.2% to 57.5%) compared to the STM approach.

  7. Spectroscopic scanning tunneling microscopy insights into Fe-based superconductors

    NASA Astrophysics Data System (ADS)

    Hoffman, Jennifer E.

    2011-12-01

    In the first three years since the discovery of Fe-based high Tc superconductors, scanning tunneling microscopy (STM) and spectroscopy have shed light on three important questions. First, STM has demonstrated the complexity of the pairing symmetry in Fe-based materials. Phase-sensitive quasiparticle interference (QPI) imaging and low temperature spectroscopy have shown that the pairing order parameter varies from nodal to nodeless s± within a single family, FeTe1-xSex. Second, STM has imaged C4 → C2 symmetry breaking in the electronic states of both parent and superconducting materials. As a local probe, STM is in a strong position to understand the interactions between these broken symmetry states and superconductivity. Finally, STM has been used to image the vortex state, giving insights into the technical problem of vortex pinning, and the fundamental problem of the competing states introduced when superconductivity is locally quenched by a magnetic field. Here we give a pedagogical introduction to STM and QPI imaging, discuss the specific challenges associated with extracting bulk properties from the study of surfaces, and report on progress made in understanding Fe-based superconductors using STM techniques.

  8. A novel functional module detection algorithm for protein-protein interaction networks

    PubMed Central

    Hwang, Woochang; Cho, Young-Rae; Zhang, Aidong; Ramanathan, Murali

    2006-01-01

    Background The sparse connectivity of protein-protein interaction data sets makes identification of functional modules challenging. The purpose of this study is to critically evaluate a novel clustering technique for clustering and detecting functional modules in protein-protein interaction networks, termed STM. Results STM selects representative proteins for each cluster and iteratively refines clusters based on a combination of the signal transduced and graph topology. STM is found to be effective at detecting clusters with a diverse range of interaction structures that are significant on measures of biological relevance. The STM approach is compared to six competing approaches including the maximum clique, quasi-clique, minimum cut, betweeness cut and Markov Clustering (MCL) algorithms. The clusters obtained by each technique are compared for enrichment of biological function. STM generates larger clusters and the clusters identified have p-values that are approximately 125-fold better than the other methods on biological function. An important strength of STM is that the percentage of proteins that are discarded to create clusters is much lower than the other approaches. Conclusion STM outperforms competing approaches and is capable of effectively detecting both densely and sparsely connected, biologically relevant functional modules with fewer discards. PMID:17147822

  9. A cryogen-free variable temperature scanning tunneling microscope capable for inelastic electron tunneling spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, Shuai; Huang, Di; Wu, Shiwei

    While low temperature scanning tunneling microscope (STM) has become an indispensable research tool in surface science, its versatility is yet limited by the shortage or high cost of liquid helium. The makeshifts include the use of alternative cryogen (such as liquid nitrogen) at higher temperature or the development of helium liquefier system usually at departmental or campus wide. The ultimate solution would be the direct integration of a cryogen-free cryocooler based on GM or pulse tube closed cycle in the STM itself. However, the nasty mechanical vibration at low frequency intrinsic to cryocoolers has set the biggest obstacle because of the known challenges in vibration isolation required to high performance of STM. In this talk, we will present the design and performance of our home-built cryogen-free variable temperature STM at Fudan University. This system can obtain atomically sharp STM images and high resolution dI/dV spectra comparable to state-of-the-art low temperature STMs, but with no limitation on running hours. Moreover, we demonstrated the inelastic tunneling spectroscopy (STM-IETS) on a single CO molecule with a cryogen-free STM for the first time.

  10. A cryogen-free low temperature scanning tunneling microscope capable of inelastic electron tunneling spectroscopy.

    PubMed

    Zhang, Shuai; Huang, Di; Wu, Shiwei

    2016-06-01

    The design and performance of a cryogen-free low temperature scanning tunneling microscope (STM) housed in ultrahigh vacuum (UHV) are reported. The cryogen-free design was done by directly integrating a Gifford-McMahon cycle cryocooler to a Besocke-type STM, and the vibration isolation was achieved by using a two-stage rubber bellow between the cryocooler and a UHV-STM interface with helium exchange gas cooling. A base temperature of 15 K at the STM was achieved, with a possibility to further decrease by using a cryocooler with higher cooling power and adding additional low temperature stage under the exchange gas interface. Atomically sharp STM images and high resolution dI/dV spectra on various samples were demonstrated. Furthermore, we reported the inelastic tunneling spectroscopy on a single carbon monoxide molecule adsorbed on Ag(110) surface with a cryogen-free STM for the first time. Being totally cryogen-free, the system not only saves the running cost significantly but also enables uninterrupted data acquisitions and variable temperature measurements with much ease. In addition, the system is capable of coupling light to the STM junction by a pair of lens inside the UHV chamber. We expect that these enhanced capabilities could further broaden our views to the atomic-scale world. PMID:27370453

  11. Design of a new reactor-like high temperature near ambient pressure scanning tunneling microscope for catalysis studies

    NASA Astrophysics Data System (ADS)

    Feng Tao, Franklin; Nguyen, Luan; Zhang, Shiran

    2013-03-01

    Here, we present the design of a new reactor-like high-temperature near ambient pressure scanning tunneling microscope (HT-NAP-STM) for catalysis studies. This HT-NAP-STM was designed for exploration of structures of catalyst surfaces at atomic scale during catalysis or under reaction conditions. In this HT-NAP-STM, the minimized reactor with a volume of reactant gases of ˜10 ml is thermally isolated from the STM room through a shielding dome installed between the reactor and STM room. An aperture on the dome was made to allow tip to approach to or retract from a catalyst surface in the reactor. This dome minimizes thermal diffusion from hot gas of the reactor to the STM room and thus remains STM head at a constant temperature near to room temperature, allowing observation of surface structures at atomic scale under reaction conditions or during catalysis with minimized thermal drift. The integrated quadrupole mass spectrometer can simultaneously measure products during visualization of surface structure of a catalyst. This synergy allows building an intrinsic correlation between surface structure and its catalytic performance. This correlation offers important insights for understanding of catalysis. Tests were done on graphite in ambient environment, Pt(111) in CO, graphene on Ru(0001) in UHV at high temperature and gaseous environment at high temperature. Atom-resolved surface structure of graphene on Ru(0001) at 500 K in a gaseous environment of 25 Torr was identified.

  12. Design of a new reactor-like high temperature near ambient pressure scanning tunneling microscope for catalysis studies

    NASA Astrophysics Data System (ADS)

    Tao, Franklin Feng; Nguyen, Luan; Zhang, Shiran

    2013-03-01

    Here, we present the design of a new reactor-like high-temperature near ambient pressure scanning tunneling microscope (HT-NAP-STM) for catalysis studies. This HT-NAP-STM was designed for exploration of structures of catalyst surfaces at atomic scale during catalysis or under reaction conditions. In this HT-NAP-STM, the minimized reactor with a volume of reactant gases of ~10 ml is thermally isolated from the STM room through a shielding dome installed between the reactor and STM room. An aperture on the dome was made to allow tip to approach to or retract from a catalyst surface in the reactor. This dome minimizes thermal diffusion from hot gas of the reactor to the STM room and thus remains STM head at a constant temperature near to room temperature, allowing observation of surface structures at atomic scale under reaction conditions or during catalysis with minimized thermal drift. The integrated quadrupole mass spectrometer can simultaneously measure products during visualization of surface structure of a catalyst. This synergy allows building an intrinsic correlation between surface structure and its catalytic performance. This correlation offers important insights for understanding of catalysis. Tests were done on graphite in ambient environment, Pt(111) in CO, graphene on Ru(0001) in UHV at high temperature and gaseous environment at high temperature. Atom-resolved surface structure of graphene on Ru(0001) at 500 K in a gaseous environment of 25 Torr was identified.

  13. Design of a new reactor-like high temperature near ambient pressure scanning tunneling microscope for catalysis studies.

    PubMed

    Tao, Franklin Feng; Nguyen, Luan; Zhang, Shiran

    2013-03-01

    Here, we present the design of a new reactor-like high-temperature near ambient pressure scanning tunneling microscope (HT-NAP-STM) for catalysis studies. This HT-NAP-STM was designed for exploration of structures of catalyst surfaces at atomic scale during catalysis or under reaction conditions. In this HT-NAP-STM, the minimized reactor with a volume of reactant gases of ∼10 ml is thermally isolated from the STM room through a shielding dome installed between the reactor and STM room. An aperture on the dome was made to allow tip to approach to or retract from a catalyst surface in the reactor. This dome minimizes thermal diffusion from hot gas of the reactor to the STM room and thus remains STM head at a constant temperature near to room temperature, allowing observation of surface structures at atomic scale under reaction conditions or during catalysis with minimized thermal drift. The integrated quadrupole mass spectrometer can simultaneously measure products during visualization of surface structure of a catalyst. This synergy allows building an intrinsic correlation between surface structure and its catalytic performance. This correlation offers important insights for understanding of catalysis. Tests were done on graphite in ambient environment, Pt(111) in CO, graphene on Ru(0001) in UHV at high temperature and gaseous environment at high temperature. Atom-resolved surface structure of graphene on Ru(0001) at 500 K in a gaseous environment of 25 Torr was identified. PMID:23556828

  14. Scanning tunneling microscope design with a confocal small field permanent magnet.

    SciTech Connect

    Messina, P.; Pearson, J.; Vasserman, I.; Sasaki, S.; Moog, E.; Fradin, F.

    2008-09-01

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

  15. Scanning tunneling microscopy on rough surfaces-quantitative image analysis

    NASA Astrophysics Data System (ADS)

    Reiss, G.; Brückl, H.; Vancea, J.; Lecheler, R.; Hastreiter, E.

    1991-07-01

    In this communication, the application of scanning tunneling microscopy (STM) for a quantitative evaluation of roughnesses and mean island sizes of polycrystalline thin films is discussed. Provided strong conditions concerning the resolution are satisfied, the results are in good agreement with standard techniques as, for example, transmission electron microscopy. Owing to its high resolution, STM can supply a better characterization of surfaces than established methods, especially concerning the roughness. Microscopic interpretations of surface dependent physical properties thus can be considerably improved by a quantitative analysis of STM images.

  16. Observation of diamond turned OFHC copper using Scanning Tunneling Microscopy

    SciTech Connect

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

    1988-12-01

    Diamond turned OFHC copper samples have been observed within the past few months using the Scanning Tunneling Microscope. Initial results have shown evidence of artifacts which may be used to better understand the diamond turning process. The STM`s high resolution capability and three dimensional data representation allows observation and study of surface features unobtainable with conventional profilometry systems. Also, the STM offers a better quantitative means by which to analyze surface structures than the SEM. This paper discusses findings on several diamond turned OFHC copper samples having different cutting conditions. Each sample has been cross referenced using STM and SEM.

  17. The study of in situ scanning tunnelling microscope characterization on GaN thin film grown by plasma assisted molecular beam epitaxy

    SciTech Connect

    Yang, R.; Krzyzewski, T.; Jones, T.

    2013-03-18

    The epitaxial growth of GaN by Plasma Assisted Molecular Beam Epitaxy was investigated by Scanning Tunnelling Microscope (STM). The GaN film was grown on initial GaN (0001) and monitored by in situ Reflection High Energy Electron Diffraction and STM during the growth. The STM characterization was carried out on different sub-films with increased thickness. The growth of GaN was achieved in 3D mode, and the hexagonal edge of GaN layers and growth gradient were observed. The final GaN was of Ga polarity and kept as (0001) orientation, without excess Ga adlayers or droplets formed on the surface.

  18. A cryogenic Quadraprobe scanning tunneling microscope system with fabrication capability for nanotransport research

    SciTech Connect

    Kim, T.-H.; Wang Zhouhang; Wendelken, John F.; Weitering, Hanno H.; Li Wenzhi; Li Anping

    2007-12-15

    We describe the development and the capabilities of an advanced system for nanoscale electrical transport studies. This system consists of a low temperature four-probe scanning tunneling microscope (STM) and a high-resolution scanning electron microscope coupled to a molecular-beam epitaxy sample preparation chamber. The four STM probes can be manipulated independently with subnanometer precision, enabling atomic resolution STM imaging and four-point electrical transport study of surface electronic systems and nanostructured materials at temperatures down to 10 K. Additionally, an integrated energy analyzer allows for scanning Auger microscopy to probe chemical species of nanostructures. Some testing results are presented.

  19. A Cryogenic Quadraprobe Scanning Tunneling Microscope System with Fabrication Capability for Nano-transport Research

    SciTech Connect

    Kim, Tae Hwan; Wang, Zhouhang; Wendelken, J F; Li, Wenzhi; Li, An-Ping; Bryant, Tracy H

    2007-01-01

    We describe the development and the capabilities of a Quadraprobe system, consisting of a low temperature four-probe scanning tunneling microscope (STM) and a high resolution scanning electron microscope (SEM), coupled to a molecular-beam epitaxy sample preparation chamber. The four STM probes can be manipulated independently with sub-nanometer precision, enabling atomic resolution STM imaging and four-point electrical transport study of surface electronic systems and nanostructured materials at temperatures down to 10 K. Additionally, the four scanning probes with automated motion controls allow for atom assembly to perform "bottom-up" fabrication of nanostructures. Some testing results are presented.

  20. Scanning Tunneling Microscopy analysis of space-exposed polymer films

    NASA Technical Reports Server (NTRS)

    Kalil, Carol R.; Young, Philip R.

    1993-01-01

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

  1. Adsorption of PTCDA on Si(001) - 2 × 1 surface

    NASA Astrophysics Data System (ADS)

    Suzuki, Takayuki; Yoshimoto, Yoshihide; Yagyu, Kazuma; Tochihara, Hiroshi

    2015-03-01

    Adsorption structures of the 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) molecule on the clean Si(001) - 2 × 1 surface were investigated using scanning tunneling microscopy (STM) experiments in conjunction with first principles theoretical calculations. Four dominant adsorption structures were observed in the STM experiments and their atomic coordinates on the Si(001) surface were determined by comparison between the experimental STM images and the theoretical simulations. Maximizing the number of the Si—O bonds is more crucial than that of the Si—C bonds in the PTCDA adsorption.

  2. Adsorption of PTCDA on Si(001) − 2 × 1 surface

    SciTech Connect

    Suzuki, Takayuki Yagyu, Kazuma; Tochihara, Hiroshi; Yoshimoto, Yoshihide

    2015-03-14

    Adsorption structures of the 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) molecule on the clean Si(001) − 2 × 1 surface were investigated using scanning tunneling microscopy (STM) experiments in conjunction with first principles theoretical calculations. Four dominant adsorption structures were observed in the STM experiments and their atomic coordinates on the Si(001) surface were determined by comparison between the experimental STM images and the theoretical simulations. Maximizing the number of the Si—O bonds is more crucial than that of the Si—C bonds in the PTCDA adsorption.

  3. Scanning Capacitace Microscope/Atomic Force Microscope/Scanning Tunneling Microscope Study of Ion-Implanted Silicon Surfaces

    NASA Astrophysics Data System (ADS)

    Tomiye, Hideto; Kawami, Hiroshi; Izawa, Michiyoshi; Yoshimura, Masamichi; Yao, Takafumi

    1995-06-01

    We have investigated the local electrical properties of ion-implanted Si using a combined scanning capacitance microscope (SCaM)/atomic force microscope (AFM)/scanning tunneling microscope (STM) with special attention paid to the effect of annealing. The STM image shows that the as-implanted area is insulating, while the unimplanted area is conductive, in an unannealed sample. Both STM and SCaM images clearly indicate that the implanted area is conductive with n-type behavior after annealing. However, the unimplanted area did not show p-type behavior but slightly n-type behavior due to the diffusion of P impurities during annealing.

  4. 1Surface structure of cleaved (001) USB2 single crystal surface

    SciTech Connect

    Chen, Shao-ping

    2009-01-01

    We have achieved what we believe to be the first atomic resolution STM images for a uranium compound USb2 taken at room temperature. The a, b, and c lattice parameters in the images confirm that the tetragonal USb2crystals cleave on the (00 I) basal plane as expected. Our calculations indicate a symmetric cut between Sb planes to be the most favorable cleavage plane and U atoms to be responsible for most ofthe density of states measured by STM. Since the spacing between Sb atoms and between U atoms is the same, STM topography only cannot unambiguously identify the surface atom species.

  5. Surface structure of cleaved (001) USb2 single crystal surface

    SciTech Connect

    Chen, Shao-ping

    2008-01-01

    We have achieved what we believe to be the first atomic resolution scanning tunneling microscopy (STM) images for a uranium compound USb2 taken at room temperature. The a, b, and c lattice parameters in the images confirm that the tetragonal USb2 crystals cleave on the (001) basal plane as expected. Our calculations indicate a symmetric cut between Sb planes to be the most favorable cleavage plane and U atoms to be responsible for most of the density of states measured by STM. Since the spacing between Sb atoms and between U atoms is the same, STM topography alone cannot unambiguously identify the surface atom species.

  6. Adsorption of PTCDA on Si(001) - 2 × 1 surface.

    PubMed

    Suzuki, Takayuki; Yoshimoto, Yoshihide; Yagyu, Kazuma; Tochihara, Hiroshi

    2015-03-14

    Adsorption structures of the 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) molecule on the clean Si(001) - 2 × 1 surface were investigated using scanning tunneling microscopy (STM) experiments in conjunction with first principles theoretical calculations. Four dominant adsorption structures were observed in the STM experiments and their atomic coordinates on the Si(001) surface were determined by comparison between the experimental STM images and the theoretical simulations. Maximizing the number of the Si-O bonds is more crucial than that of the Si-C bonds in the PTCDA adsorption. PMID:25770493

  7. Short myelitis lesions in aquaporin-4-IgG-positive neuromyelitis optica spectrum

    PubMed Central

    Flanagan, Eoin P.; Weinshenker, Brian G.; Krecke, Karl N.; Lennon, Vanda A.; Lucchinetti, Claudia F.; McKeon, Andrew; Wingerchuk, Dean M.; Shuster, Elizabeth A.; Jiao, Yujuan; Horta, Erika S.; Pittock, Sean J.

    2015-01-01

    Importance Short transverse myelitis (STM, <3 vertebral segments) is considered non-characteristic of neuromyelitis optica spectrum disorders (NMOSD). Poor recognition of the potential for STM to occur in NMOSD may lead to increased disability from delay in diagnosis and appropriate treatment. Objectives To determine the frequency of short lesions at the initial myelitis manifestation of NMOSD, and to compare the demographic, clinical and radiological characteristics of aquaporin-4-IgG (AQP4-IgG) seropositive and seronegative STM. Design, Setting, Participants We reviewed the records and images of Mayo Clinic AQP4-IgG positive NMOSD patients identified from 1996-2014. Inclusion criteria were: 1) first TM episode; 2) MRI performed ≤90 days from symptom onset; 3) Spinal cord T2-hyperintense lesion <3 vertebral segments; 4) AQP4-IgG seropositivity; 5) final diagnosis NMO or NMOSD. Patients with an initial longitudinally extensive transverse myelitis (LETM) were excluded (n=151). Patients with STM, seronegative for AQP4-IgG, among an Olmsted County population-based cohort of inflammatory demyelinating disorders of the central nervous system were used as a control group. Main Outcomes and Measures Delay to diagnosis in months, clinical and radiological characteristics and disability measured by ambulatory status. Results Twenty-five AQP4-IgG seropositive patients with an initial STM were included, representing 14% of initial myelitis episodes among NMOSD patients. The STM episode was: the first manifestation of NMOSD in 10 patients (40%); preceded by optic neuritis in 13 patients (52%); and preceded by a nausea and vomiting episode in 2 (8%). In comparison to the excluded NMOSD patients with an initial LETM, delay to diagnosis/treatment was greater when initial lesions were short (p=0.016). In AQP4-IgG positive STM cases subsequent myelitis episodes were longitudinally extensive in 92%. Attributes more common in aquaporin-4-IgG-positive STM patients than in 27

  8. Sensing Current and Forces with SPM

    SciTech Connect

    Park, Jeong Y.; Maier, Sabine; Hendriksen, Bas; Salmeron, Miquel

    2010-07-02

    Atomic force microscopy (AFM) and scanning tunneling microscopy (STM) are well established techniques to image surfaces and to probe material properties at the atomic and molecular scale. In this review, we show hybrid combinations of AFM and STM that bring together the best of two worlds: the simultaneous detection of atomic scale forces and conduction properties. We illustrate with several examples how the detection of forces during STM and the detection of currents during AFM can give valuable additional information of the nanoscale material properties.

  9. Structure of a zinc oxide ultra-thin film on Rh(100)

    SciTech Connect

    Yuhara, J.; Kato, D.; Matsui, T.; Mizuno, S.

    2015-11-07

    The structural parameters of ultra-thin zinc oxide films on Rh(100) are investigated using low-energy electron diffraction intensity (LEED I–V) curves, scanning tunneling microscopy (STM), and first-principles density functional theory (DFT) calculations. From the analysis of LEED I–V curves and DFT calculations, two optimized models A and B are determined. Their structures are basically similar to the planer h-BN ZnO(0001) structure, although some oxygen atoms protrude from the surface, associated with an in-plane shift of Zn atoms. From a comparison of experimental STM images and simulated STM images, majority and minority structures observed in the STM images represent the two optimized models A and B, respectively.

  10. Scanning tunneling microscopy on rough surfaces: Tip-shape-limited resolution

    NASA Astrophysics Data System (ADS)

    Reiss, G.; Vancea, J.; Wittmann, H.; Zweck, J.; Hoffmann, H.

    1990-02-01

    This paper discusses the reliability of scanning tunneling microscopy (STM) images of mesoscopically rough surfaces. The specific structure of these images represents a convolution between the real surface topography and the shape of the tip. In order to interpret these images quantitatively, the line scans of steep and high steps can be used to obtain an image of the tip itself. This image shows tip radii ranging typically from 5 to 15 nm and cone angles of about 30° over a length of 80 nm, and can in turn be used to recognize the limits of STM resolution on a rough surface: High-resolution transmission electron microscopy cross-section images of Au island films on a Au-Nb double layer are convoluted with the experimentally observed tip shape; the resulting line scans correspond very well with STM graphs of the same samples. Finally an overall criterion for the resolution of the STM on such surfaces is proposed.

  11. Mapping the excited states of single hexa-peri-benzocoronene oligomers.

    PubMed

    Soe, We-Hyo; Wong, Hon Seng; Manzano, Carlos; Grisolia, Maricarmen; Hliwa, Mohamed; Feng, Xinliang; Müllen, Klaus; Joachim, Christian

    2012-04-24

    Electronic states of a molecule are usually analyzed via their decomposition in linear superposition of multielectronic Slater determinants built up from monoelectronics molecular orbitals. It is generally believed that a scanning tunneling microscope (STM) is able to map those molecular orbitals. Using a low-temperature ultrahigh vacuum (LT-UHV) STM, the dI/dV conductance maps of large single hexabenzocoronene (HBC) monomer, dimer, trimer, and tetramer molecules were recorded. We demonstrate that the attribution of a tunnel electronic resonance to a peculiar π molecular orbital of the molecule (or σ intermonomer chemical bond) in the STM junction is inappropriate. With an STM weak-measurement-like procedure, a dI/dV resonance results from the conductance contribution of many molecular states whose superposition makes it difficult to reconstruct an apparent molecular orbital electron probability density map. PMID:22452387

  12. Selective scanning tunneling microscope light emission from rutile phase of VO2.

    PubMed

    Sakai, Joe; Kuwahara, Masashi; Hotsuki, Masaki; Katano, Satoshi; Uehara, Yoichi

    2016-09-28

    We observed scanning tunneling microscope light emission (STM-LE) induced by a tunneling current at the gap between an Ag tip and a VO2 thin film, in parallel to scanning tunneling spectroscopy (STS) profiles. The 34 nm thick VO2 film grown on a rutile TiO2 (0 0 1) substrate consisted of both rutile (R)- and monoclinic (M)-structure phases of a few 10 nm-sized domains at room temperature. We found that STM-LE with a certain photon energy of 2.0 eV occurs selectively from R-phase domains of VO2, while no STM-LE was observed from M-phase. The mechanism of STM-LE from R-phase VO2 was determined to be an interband transition process rather than inverse photoemission or inelastic tunneling processes. PMID:27460183

  13. A New Interpretation of the Scanning Tunneling Microscope Image of Graphite

    SciTech Connect

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

    2008-06-02

    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.

  14. A nanoscale gigahertz source realized with Josephson scanning tunneling microscopy

    SciTech Connect

    Jäck, Berthold Eltschka, Matthias; Assig, Maximilian; Etzkorn, Markus; Ast, Christian R.; Hardock, Andreas; Kern, Klaus

    2015-01-05

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

  15. Self-Construal Priming Affects Speed of Retrieval from Short-Term Memory

    PubMed Central

    MacDonald, Justin A.; Sandry, Joshua; Rice, Stephen

    2012-01-01

    We investigated the effects of collective or individual self-construal priming on recall in a short-term memory (STM) task. We primed participants to either their individual or their collective self-construals or a neutral control condition. Participants then completed a STM retrieval task using either random or patterned digit strings. Findings revealed that priming an individual self-construal resulted in faster retrieval of information from STM for both stimulus types. These results indicate that individual self-accessibility improves retrieval speed of digits from STM, regardless of set configuration. More broadly, the present findings extend prior research by adding further evidence of the effects of self-construal priming on cognitive information processing. PMID:23209632

  16. Detection Improvement for Electron Energy Spectra for Surface Analysis Using a Field Emission Scanning Tunneling Microscope

    NASA Astrophysics Data System (ADS)

    Hirade, Masato; Arai, Toyoko; Tomitori, Masahiko

    2003-07-01

    For identification of the atomic species on a sample surface with high spatial resolution, we developed a field emission scanning tunneling microscopy (FE-STM) combined with an energy analyzer to perform surface electron spectroscopy: the primary electrons are field-emitted from the STM tip to excite sample surfaces. The energy spectra of backscattered electrons obtained using this combined instrument exhibited the elemental features, though the energy peaks and their signal height in the spectra were affected by the electric field between the tip and the sample. In the present study, we have examined and improved the electric shield of an STM tip holder. The metal parts of the holder at a high voltage, which face the gap left for electrons to pass through, were shielded to reduce the electric field. We have successfully demonstrated the effect of the field reduction for surface electron spectroscopy with the FE-STM.

  17. Very low thermally induced tip expansion by vacuum ultraviolet irradiation in a scanning tunneling microscope junction

    NASA Astrophysics Data System (ADS)

    Riedel, D.; Delacour, C.; Mayne, A. J.; Dujardin, G.

    2009-10-01

    The thermal and photoelectronic processes induced when a vacuum ultraviolet (VUV) laser irradiates the junction of a scanning tunneling microscope (STM) are studied. This is performed by synchronizing the VUV laser shots with the STM scan signal. Compared to other wavelengths, the photoinduced thermal STM-tip expansion is not observed when the VUV radiation is freed from spurious emissions. Furthermore, we demonstrate that the purified VUV photoinduced transient signal detected in the tunnel current is entirely due to photoelectronic emission and not combined with thermionic processes. The ensuing photoelectron emission is shown to be independent of the tip-surface distance while varying linearly with the pure VUV laser intensity. These results illustrate a strong decoupling between phonons and photoelectrons which allows a very weak STM-tip expansion.

  18. Two stochastic mean-field polycrystal plasticity methods

    SciTech Connect

    Tonks, Michael

    2008-01-01

    In this work, we develop two mean-field polycrystal plasticity models in which the L{sup c} are approximated stochastically. Through comprehensive CPFEM analyses of an idealized tantalum polycrystal, we verify that the L{sup c} tend to follow a normal distribution and surmise that this is due to the crystal interactions. We draw on these results to develop the STM and the stochastic no-constraints model (SNCM), which differ in the manner in which the crystal strain rates D{sup c} are prescribed. Calibration and validation of the models are performed using data from tantalum compression experiments. Both models predict the compression textures more accurately than the FCM, and the SNCM predicts them more accurately than the STM. The STM is extremely computationally efficient, only slightly more expensive than the FCM, while the SNCM is three times more computationally expensive than the STM.

  19. A nanoscale gigahertz source realized with Josephson scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Jäck, Berthold; Eltschka, Matthias; Assig, Maximilian; Hardock, Andreas; Etzkorn, Markus; Ast, Christian R.; Kern, Klaus

    2015-01-01

    Using the AC Josephson effect in the superconductor-vacuum-superconductor tunnel junction of a scanning tunneling microscope (STM), we demonstrate the generation of GHz radiation. With the macroscopic STM tip acting as a λ/4-monopole antenna, we first show that the atomic scale Josephson junction in the STM is sensitive to its frequency-dependent environmental impedance in the GHz regime. Further, enhancing Cooper pair tunneling via excitations of the tip eigenmodes, we are able to generate high-frequency radiation. We find that for vanadium junctions, the enhanced photon emission can be tuned from about 25 GHz to 200 GHz and that large photon flux in excess of 1020 cm-2 s-1 is reached in the tunnel junction. These findings demonstrate that the atomic scale Josephson junction in an STM can be employed as a full spectroscopic tool for GHz frequencies on the atomic scale.

  20. Exact Solutions of the 5d Space-Time Universe and Their Implications

    NASA Astrophysics Data System (ADS)

    Fukui, Takao

    2008-09-01

    What can the exact solutions of the 5D STM Universe imply when they are compared to the field equations of a Corrected Metric Tensor Universe? The comparison implies the possibility of clarifying the meaning of the cosmological term.

  1. Scanning Tunneling Microscopy and Spectroscopy of Compound Semiconductor Heterojunctions

    NASA Astrophysics Data System (ADS)

    Gwo, Shang-, Jr.

    Scanning tunneling microscopy and spectroscopy (STM/S) were used to investigate the structural and electronic properties of III-V compound semiconductor heterojunctions in cross section. The most important properties of heterostructures can now be measured in real space with unprecedented resolution. By using prototypical Al_{0.3}Ga _{0.7}As/GaAs heterojunction and GaAs pn-junction systems, we demonstrate the unique capability of STM/S to precisely map out the detailed band structure across semiconductor junctions with nanometer resolution. An ultra-high vacuum STM system was designed and constructed in our laboratory for this work. The details of this system as well as the methodology used for the cross-sectional study are presented here. Because of its capability to provide valuable information on solid/solid interfaces, the cross-sectional STM/S characterization method reported here may have an important technological impact as device miniaturization continues.

  2. Selective scanning tunneling microscope light emission from rutile phase of VO2

    NASA Astrophysics Data System (ADS)

    Sakai, Joe; Kuwahara, Masashi; Hotsuki, Masaki; Katano, Satoshi; Uehara, Yoichi

    2016-09-01

    We observed scanning tunneling microscope light emission (STM-LE) induced by a tunneling current at the gap between an Ag tip and a VO2 thin film, in parallel to scanning tunneling spectroscopy (STS) profiles. The 34 nm thick VO2 film grown on a rutile TiO2 (0 0 1) substrate consisted of both rutile (R)- and monoclinic (M)-structure phases of a few 10 nm-sized domains at room temperature. We found that STM-LE with a certain photon energy of 2.0 eV occurs selectively from R-phase domains of VO2, while no STM-LE was observed from M-phase. The mechanism of STM-LE from R-phase VO2 was determined to be an interband transition process rather than inverse photoemission or inelastic tunneling processes.

  3. Cleaved thin-film probes for scanning tunneling microscopy.

    PubMed

    Siahaan, T; Kurnosikov, O; Barcones, B; Swagten, H J M; Koopmans, B

    2016-01-22

    We introduce an alternative type of probe for scanning tunneling microscopy (STM). Instead of using a needle-like tip made from a piece of metallic wire, a sharp-edged cleaved insulating substrate, which is initially covered by a thin conductive film, is used. The sharp tip is formed at the intersection of the two cleaved sides. Using this approach a variety of materials for STM probes can be used, and functionalization of STM probes is possible. The working principle of different probes made of metallic (Pt, Co, and CoB), indium-tin oxide, as well as Cu/Pt and Co/Pt multilayer films are demonstrated by STM imaging of clean Cu(001) and Cu(111) surfaces as well as the epitaxial Co clusters on Cu(111). PMID:26636763

  4. Structure of a zinc oxide ultra-thin film on Rh(100).

    PubMed

    Yuhara, J; Kato, D; Matsui, T; Mizuno, S

    2015-11-01

    The structural parameters of ultra-thin zinc oxide films on Rh(100) are investigated using low-energy electron diffraction intensity (LEED I-V) curves, scanning tunneling microscopy (STM), and first-principles density functional theory (DFT) calculations. From the analysis of LEED I-V curves and DFT calculations, two optimized models A and B are determined. Their structures are basically similar to the planer h-BN ZnO(0001) structure, although some oxygen atoms protrude from the surface, associated with an in-plane shift of Zn atoms. From a comparison of experimental STM images and simulated STM images, majority and minority structures observed in the STM images represent the two optimized models A and B, respectively. PMID:26547176

  5. Structure of a zinc oxide ultra-thin film on Rh(100)

    NASA Astrophysics Data System (ADS)

    Yuhara, J.; Kato, D.; Matsui, T.; Mizuno, S.

    2015-11-01

    The structural parameters of ultra-thin zinc oxide films on Rh(100) are investigated using low-energy electron diffraction intensity (LEED I-V) curves, scanning tunneling microscopy (STM), and first-principles density functional theory (DFT) calculations. From the analysis of LEED I-V curves and DFT calculations, two optimized models A and B are determined. Their structures are basically similar to the planer h-BN ZnO(0001) structure, although some oxygen atoms protrude from the surface, associated with an in-plane shift of Zn atoms. From a comparison of experimental STM images and simulated STM images, majority and minority structures observed in the STM images represent the two optimized models A and B, respectively.

  6. New filtering techniques to restore scanning tunneling microscopy images

    NASA Astrophysics Data System (ADS)

    Pancorbo, M.; Aguilar, M.; Anguiano, E.; Diaspro, A.

    1991-07-01

    An asymmetric transfer function — based on the symmetric one used in optical cases to correct blurring and defocusing effects in systems with circular aperture — is presented here to restore STM (scanning tunneling microscopy) images. A Wien filter is implemented that utilize this transfer function. In the STM case, the defocusing has two different origins depending on the scan direction that produce a set of two fitting parameters.

  7. Molecular structure of DNA by scanning tunneling microscopy.

    PubMed

    Cricenti, A; Selci, S; Felici, A C; Generosi, R; Gori, E; Djaczenko, W; Chiarotti, G

    1989-09-15

    Uncoated DNA molecules marked with an activated tris(l-aziridinyl) phosphine oxide (TAPO) solution were deposited on gold substrates and imaged in air with the use of a high-resolution scanning tunneling microscope (STM). Constant-current and gap-modulated STM images show clear evidence of the helicity of the DNA structure: pitch periodicity ranges from 25 to 35 angstroms, whereas the average diameter is 20 angstroms. Molecular structure within a single helix turn was also observed. PMID:2781279

  8. Molecular Structure of DNA by Scanning Tunneling Microscopy

    NASA Astrophysics Data System (ADS)

    Cricenti, A.; Selci, S.; Felici, A. C.; Generosi, R.; Gori, E.; Djaczenko, W.; Chiarotti, G.

    1989-09-01

    Uncoated DNA molecules marked with an activated tris(1-aziridinyl) phosphine oxide (TAPO) solution were deposited on gold substrates and imaged in air with the use of a high-resolution scanning tunneling microscope (STM). Constant-current and gap-modulated STM images show clear evidence of the helicity of the DNA structure: pitch periodicity ranges from 25 and 35 angstroms, whereas the average diameter is 20 angstroms. Molecular structure within a single helix turn was also observed.

  9. Design and Analysis of Complex D-Regions in Reinforced Concrete Structures

    ERIC Educational Resources Information Center

    Yindeesuk, Sukit

    2009-01-01

    STM design provisions, such as those in Appendix A of ACI318-08, consist of rules for evaluating the capacity of the load-resisting truss that is idealized to carry the forces through the D-Region. These code rules were primarily derived from test data on simple D-Regions such as deep beams and corbels. However, these STM provisions are taken as…

  10. Visual processing in reading disorders and attention-deficit/hyperactivity disorder and its contribution to basic reading ability

    PubMed Central

    Kibby, Michelle Y.; Dyer, Sarah M.; Vadnais, Sarah A.; Jagger, Audreyana C.; Casher, Gabriel A.; Stacy, Maria

    2015-01-01

    Whether visual processing deficits are common in reading disorders (RD), and related to reading ability in general, has been debated for decades. The type of visual processing affected also is debated, although visual discrimination and short-term memory (STM) may be more commonly related to reading ability. Reading disorders are frequently comorbid with ADHD, and children with ADHD often have subclinical reading problems. Hence, children with ADHD were used as a comparison group in this study. ADHD and RD may be dissociated in terms of visual processing. Whereas RD may be associated with deficits in visual discrimination and STM for order, ADHD is associated with deficits in visual-spatial processing. Thus, we hypothesized that children with RD would perform worse than controls and children with ADHD only on a measure of visual discrimination and a measure of visual STM that requires memory for order. We expected all groups would perform comparably on the measure of visual STM that does not require sequential processing. We found children with RD or ADHD were commensurate to controls on measures of visual discrimination and visual STM that do not require sequential processing. In contrast, both RD groups (RD, RD/ADHD) performed worse than controls on the measure of visual STM that requires memory for order, and children with comorbid RD/ADHD performed worse than those with ADHD. In addition, of the three visual measures, only sequential visual STM predicted reading ability. Hence, our findings suggest there is a deficit in visual sequential STM that is specific to RD and is related to basic reading ability. The source of this deficit is worthy of further research, but it may include both reduced memory for order and poorer verbal mediation. PMID:26579020

  11. Development and Application of Multiple-Probe Scanning Probe Microscopes

    SciTech Connect

    Nakayama, T.; Kubo, O.; Shingaya, Y.; Higuchi, S.; Hasegawa, T.; Jiang, C. S.; Okuda, T.; Kuwahara, Y.; Takami, K.; Aono, M.

    2012-04-03

    the research of advanced materials based on nanoscience and nanotechnology, it is often desirable to measure nanoscale local electrical conductivity at a designated position of a given sample. For this purpose, multiple-probe scanning probe microscopes (MP-SPMs), in which two, three or four scanning tunneling microscope (STM) or atomic force microscope (AFM) probes are operated independently, have been developed. Each probe in an MP-SPM is used not only for observing high-resolution STM or AFM images but also for forming an electrical contact enabling nanoscale local electrical conductivity measurement. The world's first double-probe STM (DP-STM) developed by the authors, which was subsequently modified to a triple-probe STM (TP-STM), has been used to measure the conductivities of one-dimensional metal nanowires and carbon nanotubes and also two-dimensional molecular films. A quadruple-probe STM (QP-STM) has also been developed and used to measure the conductivity of two-dimensional molecular films without the ambiguity of contact resistance between the probe and sample. Moreover, a quadruple-probe AFM (QP-AFM) with four conductive tuning-fork-type self-detection force sensing probes has been developed to measure the conductivity of a nanostructure on an insulating substrate. A general-purpose computer software to control four probes at the same time has also been developed and used in the operation of the QP-AFM. These developments and applications of MP-SPMs are reviewed in this paper.

  12. Memory integration in amnesia: prior knowledge supports verbal short-term memory.

    PubMed

    Race, Elizabeth; Palombo, Daniela J; Cadden, Margaret; Burke, Keely; Verfaellie, Mieke

    2015-04-01

    Short-term memory (STM) and long-term memory (LTM) have traditionally been considered cognitively distinct. However, it is known that STM can improve when to-be-remembered information appears in contexts that make contact with prior knowledge, suggesting a more interactive relationship between STM and LTM. The current study investigated whether the ability to leverage LTM in support of STM critically depends on the integrity of the hippocampus. Specifically, we investigated whether the hippocampus differentially supports between-domain versus within-domain STM-LTM integration given prior evidence that the representational domain of the elements being integrated in memory is a critical determinant of whether memory performance depends on the hippocampus. In Experiment 1, we investigated hippocampal contributions to within-domain STM-LTM integration by testing whether immediate verbal recall of words improves in MTL amnesic patients when words are presented in familiar verbal contexts (meaningful sentences) compared to unfamiliar verbal contexts (random word lists). Patients demonstrated a robust sentence superiority effect, whereby verbal STM performance improved in familiar compared to unfamiliar verbal contexts, and the magnitude of this effect did not differ from that in controls. In Experiment 2, we investigated hippocampal contributions to between-domain STM-LTM integration by testing whether immediate verbal recall of digits improves in MTL amnesic patients when digits are presented in a familiar visuospatial context (a typical keypad layout) compared to an unfamiliar visuospatial context (a random keypad layout). Immediate verbal recall improved in both patients and controls when digits were presented in the familiar compared to the unfamiliar keypad array, indicating a preserved ability to integrate activated verbal information with stored visuospatial knowledge. Together, these results demonstrate that immediate verbal recall in amnesia can benefit from two

  13. Spin microscope based on optically detected magnetic resonance

    SciTech Connect

    Berman, Gennady P.; Chernobrod, Boris M.

    2009-11-10

    The invention relates to scanning magnetic microscope which has a photoluminescent nanoprobe implanted in the tip apex of an atomic force microscope (AFM), a scanning tunneling microscope (STM) or a near-field scanning optical microscope (NSOM) and exhibits optically detected magnetic resonance (ODMR) in the vicinity of impaired electron spins or nuclear magnetic moments in the sample material. The described spin microscope has demonstrated nanoscale lateral resolution and single spin sensitivity for the AFM and STM embodiments.

  14. Spin microscope based on optically detected magnetic resonance

    SciTech Connect

    Berman, Gennady P.; Chernobrod, Boris M.

    2010-06-29

    The invention relates to scanning magnetic microscope which has a photoluminescent nanoprobe implanted in the tip apex of an atomic force microscope (AFM), a scanning tunneling microscope (STM) or a near-field scanning optical microscope (NSOM) and exhibits optically detected magnetic resonance (ODMR) in the vicinity of unpaired electron spins or nuclear magnetic moments in the sample material. The described spin microscope has demonstrated nanoscale lateral resolution and single spin sensitivity for the AFM and STM embodiments.

  15. Spin microscope based on optically detected magnetic resonance

    SciTech Connect

    Berman, Gennady P.; Chernobrod, Boris M.

    2010-07-13

    The invention relates to scanning magnetic microscope which has a photoluminescent nanoprobe implanted in the tip apex of an atomic force microscope (AFM), a scanning tunneling microscope (STM) or a near-field scanning optical microscope (NSOM) and exhibits optically detected magnetic resonance (ODMR) in the vicinity of unpaired electron spins or nuclear magnetic moments in the sample material. The described spin microscope has demonstrated nanoscale lateral resolution and single spin sensitivity for the AFM and STM embodiments.

  16. Spin microscope based on optically detected magnetic resonance

    SciTech Connect

    Berman, Gennady P.; Chernobrod, Boris M.

    2009-10-27

    The invention relates to scanning magnetic microscope which has a photoluminescent nanoprobe implanted in the tip apex of an atomic force microscope (AFM), a scanning tunneling microscope (STM) or a near-field scanning optical microscope (NSOM) and exhibits optically detected magnetic resonance (ODMR) in the vicinity of unpaired electron spins or nuclear magnetic moments in the sample material. The described spin microscope has demonstrated nanoscale lateral resolution and single spin sensitivity for the AFM and STM embodiments.

  17. A l-Lysine Transporter of High Stereoselectivity of the Amino Acid-Polyamine-Organocation (APC) Superfamily

    PubMed Central

    Kaur, Jagdeep; Olkhova, Elena; Malviya, Viveka Nand; Grell, Ernst; Michel, Hartmut

    2014-01-01

    Membrane proteins of the amino acid-polyamine-organocation (APC) superfamily transport amino acids and amines across membranes and play an important role in the regulation of cellular processes. We report the heterologous production of the LysP-related transporter STM2200 from Salmonella typhimurium in Escherichia coli, its purification, and functional characterization. STM2200 is assumed to be a proton-dependent APC transporter of l-lysine. The functional interaction between basic amino acids and STM2200 was investigated by thermoanalytical methods, i.e. differential scanning and isothermal titration calorimetry. Binding of l-lysine to STM2200 in its solubilized monomer form is entropy-driven. It is characterized by a dissociation constant of 40 μm at pH 5.9 and is highly selective; no evidence was found for the binding of l-arginine, l-ornithine, l-2,4-diaminobutyric acid, and l-alanine. d-Lysine is bound 45 times more weakly than its l-chiral form. We thus postulate that STM2200 functions as a specific transport protein. Based on the crystal structure of ApcT (Shaffer, P. L., Goehring, A., Shankaranarayanan, A., and Gouaux, E. (2009) Science 325, 1010–1014), a proton-dependent amino acid transporter of the APC superfamily, a homology model of STM2200 was created. Docking studies allowed identification of possible ligand binding sites. The resulting predictions indicated that Glu-222 and Arg-395 of STM2200 are markedly involved in ligand binding, whereas Lys-163 is suggested to be of structural and functional relevance. Selected variants of STM2200 where these three amino acid residues were substituted using single site-directed mutagenesis showed no evidence for l-lysine binding by isothermal titration calorimetry, which confirmed the predictions. Molecular aspects of the observed ligand specificity are discussed. PMID:24257746

  18. How do subvocal rehearsal and general attentional resources contribute to verbal short-term memory span?

    PubMed Central

    Morra, Sergio

    2015-01-01

    Whether rehearsal has a causal role in verbal STM has been controversial in the literature. Recent theories of working memory emphasize a role of attentional resources, but leave unclear how they contribute to verbal STM. Two experiments (with 49 and 102 adult participants, respectively) followed up previous studies with children, aiming to clarify the contributions of attentional capacity and rehearsal to verbal STM. Word length and presentation modality were manipulated. Experiment 1 focused on order errors, Experiment 2 on predicting individual differences in span from attentional capacity and articulation rate. Structural equation modeling showed clearly a major role of attentional capacity as a predictor of verbal STM span; but was inconclusive on whether rehearsal efficiency is an additional cause or a consequence of verbal STM. The effects of word length and modality on STM were replicated; a significant interaction was also found, showing a larger modality effect for long than short words, which replicates a previous finding on children. Item errors occurred more often with long words and correlated negatively with articulation rate. This set of findings seems to point to a role of rehearsal in maintaining item information. The probability of order errors per position increased linearly with list length. A revised version of a neo-Piagetian model was fit to the data of Experiment 2. That model was based on two parameters: attentional capacity (independently measured) and a free parameter representing loss of partly-activated information. The model could partly account for the results, but underestimated STM performance of the participants with smaller attentional capacity. It is concluded that modeling of verbal STM should consider individual and developmental differences in attentional capacity, rehearsal rate, and (perhaps) order representation. PMID:25798114

  19. Spin microscope based on optically detected magnetic resonance

    DOEpatents

    Berman, Gennady P.; Chernobrod, Boris M.

    2007-12-11

    The invention relates to scanning magnetic microscope which has a photoluminescent nanoprobe implanted in the tip apex of an atomic force microscope (AFM), a scanning tunneling microscope (STM) or a near-field scanning optical microscope (NSOM) and exhibits optically detected magnetic resonance (ODMR) in the vicinity of unpaired electron spins or nuclear magnetic moments in the sample material. The described spin microscope has demonstrated nanoscale lateral resolution and single spin sensitivity for the AFM and STM embodiments.

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

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

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

  1. Novel Two-Step Hierarchical Screening of Mutant Pools Reveals Mutants under Selection in Chicks.

    PubMed

    Yang, Hee-Jeong; Bogomolnaya, Lydia M; Elfenbein, Johanna R; Endicott-Yazdani, Tiana; Reynolds, M Megan; Porwollik, Steffen; Cheng, Pui; Xia, Xiao-Qin; McClelland, Michael; Andrews-Polymenis, Helene

    2016-04-01

    Contaminated chicken/egg products are major sources of human salmonellosis, yet the strategies used bySalmonellato colonize chickens are poorly understood. We applied a novel two-step hierarchical procedure to identify new genes important for colonization and persistence ofSalmonella entericaserotype Typhimurium in chickens. A library of 182S.Typhimurium mutants each containing a targeted deletion of a group of contiguous genes (for a total of 2,069 genes deleted) was used to identify regions under selection at 1, 3, and 9 days postinfection in chicks. Mutants in 11 regions were under selection at all assayed times (colonization mutants), and mutants in 15 regions were under selection only at day 9 (persistence mutants). We assembled a pool of 92 mutants, each deleted for a single gene, representing nearly all genes in nine regions under selection. Twelve single gene deletion mutants were under selection in this assay, and we confirmed 6 of 9 of these candidate mutants via competitive infections and complementation analysis in chicks.STM0580,STM1295,STM1297,STM3612,STM3615, andSTM3734are needed forSalmonellato colonize and persist in chicks and were not previously associated with this ability. One of these key genes,STM1297(selD), is required for anaerobic growth and supports the ability to utilize formate under these conditions, suggesting that metabolism of formate is important during infection. We report a hierarchical screening strategy to interrogate large portions of the genome during infection of animals using pools of mutants of low complexity. Using this strategy, we identified six genes not previously known to be needed during infection in chicks, and one of these (STM1297) suggests an important role for formate metabolism during infection. PMID:26857572

  2. Proteomic Investigation of the Time Course Responses of RAW 264.7 Macrophages to Infection with Salmonella enterica

    SciTech Connect

    Shi, Liang; Chowdhury, Saiful M.; Smallwood, Heather S.; Yoon, Hyunjin; Mottaz-Brewer, Heather M.; Norbeck, Angela D.; McDermott, Jason E.; Clauss, Therese RW; Heffron, Fred; Smith, Richard D.; Adkins, Joshua N.

    2009-08-01

    Macrophages plan important roles in controlling Salmonella-mediated systemic infection. To investigate the responses of macrophages to Salmonella infection, we infected RAW 264.7 macrophages with Salmonella enterica serovar Typhimurium (STM) and then performed a comparative liquid chromatography-tandem mass spectrometry [LC-MS(/MS)]-based proteomics analysis of the infected macrophages. A total of 1006 macrophage and 115 STM proteins were indentified from this study. Most of STM proteins were found at late stage of the time course of infection, consistent with the fact that STM proliferates inside RAW 264.7 macrophages. Majority of the identified macrophage proteins were house keeping-related, including cytoplasmic superoxide dismutase 1 (SOD1), whose peptide abundances were relatively constant during the time course of infection. Compared to those in no infection control, the peptide abundances of 244 macrophage proteins (or 24% of total indentified macrophage proteins) changed considerably after STM infection. The functions of these STM infection-affected macrophage proteins were diverse and ranged from production of antibacterial nitric oxide (i.e., inducible nitric oxide synthase or iNOS) or production of prostaglandin H2 (i.e., prostaglandin-endoperoxide synthase 2, also know as cyclooxygenase-2 or COX-2) to regulation of intracellular traffic (e.g., sorting nexin or SNX 5, 6 and 9), demonstrating a global impact of STM infection on macrophage proteome. Western-blot analysis not only confirmed the LC-MS(/MS) results of SOD1, COX-2 and iNOS, but also revealed that the protein abundances of mitochondrial SOD2 increased after STM infection, indicating an infection-induced oxidative stress in mitochondria.

  3. Discovery of Salmonella Virulence Factors Translocated via Outer Membrane Vesicles to Murine Macrophages.

    SciTech Connect

    Yoon, Hyunjin; Ansong, Charles; Adkins, Joshua N.; Heffron, Fred

    2011-06-01

    We have previously shown that the regulators SpvR, FruR, IHF, PhoP/PhoQ, SsrA/SsrB, SlyA, Hnr, RpoE, SmpB, CsrA, RpoS, Crp, OmpR/EnvZ, and Hfq are essential for Salmonella Typhimurium virulence in mice. Here we use quantitative LC-MS-based proteomics profiling of in-frame deletion mutants of these 14 regulators to identify proteins that are coordinately regulated by these virulence regulators and are thus presumably novel factors contributing to Salmonella pathogenesis. Putative candidate proteins from proteomics analysis were determined, which exhibited similar abundance profiles to those of Salmonella pathogenicity island (SPI)-2 type III secretion system (TTSS) proteins. A subset of 5 proteins including STM0082, STM1548, PdgL, STM1633, and STM3595 was selected for further analysis. All 5 proteins were expressed inside macrophage cells and STM0082 (SrfN) was secreted into host cytoplasm. Furthermore, deletion of STM0082 attenuated virulence in mice when administered intraperitoneally as determined by competitive index. srfN transcription was positively regulated by SsrAB, however, secretion was independent of SPI-2 TTSS as well as SPI-1 TTSS and flagella. Proteins including PagK and STM2585A, which are positively regulated by PhoP/PhoQ, have sec signal peptides as predicted for SrfN and were secreted into macrophage cytoplasm regardless of SPI-2 TTSS. Isolation of outer membrane vesicles (OMVs) revealed the presence of SrfN, PagK, and STM2585A inside vesicle compartments. This result is the first case showing delivery of virulence effectors via OMVs in S. Typhimurium. Moreover, Hfq regulation of SrfN translation suggests that small non-coding RNAs may be responsible for regulating effector protein expression.

  4. Ultrafast scanning probe microscopy

    SciTech Connect

    Botkin, D.; Weiss, S.; Ogletree, D.F.; Salmeron, M.; Chemla, D.S.

    1994-01-01

    The authors have developed a general technique which combines the temporal resolution of ultrafast laser spectroscopy with the spatial resolution of scanned probe microscopy (SPM). Using this technique with scanning tunneling microscopy (STM), they have obtained simultaneous 2 ps time resolution and 50 {angstrom} spatial resolution. This improves the time resolution currently attainable with STM by nine orders of magnitude. The potential of this powerful technique for studying ultrafast dynamical phenomena on surfaces with atomic resolution is discussed.

  5. Construction of silicon nanocolumns with the scanning tunneling microscope

    NASA Astrophysics Data System (ADS)

    Ostrom, R. M.; Tanenbaum, D. M.; Gallagher, Alan

    1992-08-01

    Voltage pulses to a scanning tunneling microscope (STM) are used to construct silicon columns of 30-100 Å diameter and up to 200 Å height on a silicon surface and on the end of a tungsten probe. These nanocolumns have excellent conductivity and longevity, and they provide an exceptional new ability to measure the shapes of nanostructures with a STM. This construction methodology and these slender yet robust columns provide a basis for nanoscale physics, lithography, and technology.

  6. The Value of Continuous ST-Segment Monitoring in the Emergency Department.

    PubMed

    Bovino, Leonie Rose; Funk, Marjorie; Pelter, Michele M; Desai, Mayur M; Jefferson, Vanessa; Andrews, Laura Kierol; Forte, Kenneth

    2015-01-01

    Practice standards for electrocardiographic monitoring recommend continuous ST-segment monitoring (C-STM) in patients presenting to the emergency department (ED) with signs and/or symptoms of acute coronary syndrome (ACS), but few studies have evaluated its use in the ED. We compared time to diagnosis and 30-day adverse events before and after implementation of C-STM. We also evaluated the diagnostic accuracy of C-STM in detecting ischemia and infarction. We prospectively studied 163 adults (preintervention: n = 78; intervention: n = 85) in a single ED and stratified them into low (n = 51), intermediate (n = 100), or high (n = 12) risk using History, ECG, Age, Risk factors, and Troponin (HEART) scores. The principal investigator monitored participants, activating C-STM on bedside monitors in the intervention phase. We used likelihood ratios (LRs) as the measure of diagnostic accuracy. Overall, 9% of participants were diagnosed with ACS. Median time to diagnosis did not differ before and after implementation of C-STM (5.55 vs. 5.98 hr; p = 0.43). In risk-stratified analyses, no significant pre-/postdifference in time to diagnosis was found in low-, intermediate-, or high-risk participants. There was no difference in the rate of 30-day adverse events before versus after C-STM implementation (11.5% vs. 10.6%; p = 0.85). The +LR and -LR of C-STM for ischemia were 24.0 (95% confidence interval [CI]: 1.4, 412.0) and 0.3 (95% CI: 0.02, 2.9), respectively, and for infarction were 13.7 (95% CI: 1.7, 112.3) and 0.7 (95% CI: 0.3, 1.5), respectively. Use of C-STM did not provide added diagnostic benefit for patients with signs and/or symptoms of myocardial ischemia in the ED. PMID:26509726

  7. High Pressure Scanning Tunneling Microscopy and High PressureX-ray Photoemission Spectroscopy Studies of Adsorbate Structure,Composition and Mobility during Catalytic Reactions on A Model SingleCrystal

    SciTech Connect

    Montano, M.O.

    2006-05-12

    Our research focuses on taking advantage of the ability of scanning tunneling microscopy (STM) to operate at high-temperatures and high-pressures while still providing real-time atomic resolution images. We also utilize high-pressure x-ray photoelectron spectroscopy (HPXPS) to monitor systems under identical conditions thus giving us chemical information to compare and contrast with the structural and dynamic data provided by STM.

  8. Scanning Tunneling Microscope Data Acquistion and Control System

    Energy Science and Technology Software Center (ESTSC)

    1995-02-01

    SHOESCAN is a PC based code that acquires and displays data for Scanning Tunneling Microscopes (STM). SHOESCAN interfaces with the STM through external electronic feedback and raster control circuits that are controlled by I/O boards on the PC bus. Data is displayed on a separate color monitor that is interfaced to the PC through an additional frame-grabber board. SHOESCAN can acquire a wide range of surface topographic information as well as surface electronic structure information.

  9. Shifting the Voltage Drop in Electron Transport Through a Single Molecule.

    PubMed

    Karan, Sujoy; Jacob, David; Karolak, Michael; Hamann, Christian; Wang, Yongfeng; Weismann, Alexander; Lichtenstein, Alexander I; Berndt, Richard

    2015-07-01

    A Mn-porphyrin was contacted on Au(111) in a low-temperature scanning tunneling microscope (STM). Differential conductance spectra show a zero-bias resonance that is due to an underscreened Kondo effect according to many-body calculations. When the Mn center is contacted by the STM tip, the spectrum appears to invert along the voltage axis. A drastic change in the electrostatic potential of the molecule involving a small geometric relaxation is found to cause this observation. PMID:26182113

  10. The first echinoderm poly-U-binding factor 60 kDa (PUF60) from sea cucumber (Stichopus monotuberculatus): Molecular characterization, inducible expression and involvement of apoptosis.

    PubMed

    Ren, Chunhua; Chen, Ting; Sun, Hongyan; Jiang, Xiao; Hu, Chaoqun; Qian, Jing; Wang, Yanhong

    2015-11-01

    Poly-U-binding factor 60 kDa (PUF60), also known as Ro RNA binding protein (RoBPI) and FBP interacting repressor (FIR), is a multifunctional protein that is involved in a variety of nuclear processes including pre-mRNA splicing, apoptosis and transcription regulation. In this study, the first echinoderm PUF60 named StmPUF60 was identified from sea cucumber (Stichopus monotuberculatus). The StmPUF60 cDNA is 4503 bp in length, containing a 5'-untranslated region (UTR) of 34 bp, a 3'-UTR of 2963 bp and an open reading frame (ORF) of 1506 bp that encoding a protein of 501 amino acids with a deduced molecular weight of 54.15 kDa and a predicted isoelectric point of 5.15. The putative StmPUF60 protein possesses all the main characteristics of known PUF60 proteins, including two RNA recognition motifs (RRM1 and RRM2), a C-terminal PUMP domain and two conserved nucleic acid-binding ribonucleoprotein sequences (RNP1 and RNP2). For the gene structure, StmPUF60 contains nine exons separated by eight introns. In addition, the highest level of StmPUF60 mRNA expression was noticed in the gonad, followed by coelomocytes, intestine, respiratory tree and body wall. In in vivo experiments, the expression of StmPUF60 mRNA in coelomocytes and intestine was significantly up-regulated by lipopolysaccharides (LPS) challenge, suggesting that the sea cucumber PUF60 might play critical roles in the innate immune defense against bacterial infections. Moreover, we further confirmed that overexpressed StmPUF60 could induce apoptosis, and this function of StmPUF60 may be one of the innate immune defense mechanisms for sea cucumber against pathogen infections. PMID:26362209

  11. Visual processing in reading disorders and attention-deficit/hyperactivity disorder and its contribution to basic reading ability.

    PubMed

    Kibby, Michelle Y; Dyer, Sarah M; Vadnais, Sarah A; Jagger, Audreyana C; Casher, Gabriel A; Stacy, Maria

    2015-01-01

    Whether visual processing deficits are common in reading disorders (RD), and related to reading ability in general, has been debated for decades. The type of visual processing affected also is debated, although visual discrimination and short-term memory (STM) may be more commonly related to reading ability. Reading disorders are frequently comorbid with ADHD, and children with ADHD often have subclinical reading problems. Hence, children with ADHD were used as a comparison group in this study. ADHD and RD may be dissociated in terms of visual processing. Whereas RD may be associated with deficits in visual discrimination and STM for order, ADHD is associated with deficits in visual-spatial processing. Thus, we hypothesized that children with RD would perform worse than controls and children with ADHD only on a measure of visual discrimination and a measure of visual STM that requires memory for order. We expected all groups would perform comparably on the measure of visual STM that does not require sequential processing. We found children with RD or ADHD were commensurate to controls on measures of visual discrimination and visual STM that do not require sequential processing. In contrast, both RD groups (RD, RD/ADHD) performed worse than controls on the measure of visual STM that requires memory for order, and children with comorbid RD/ADHD performed worse than those with ADHD. In addition, of the three visual measures, only sequential visual STM predicted reading ability. Hence, our findings suggest there is a deficit in visual sequential STM that is specific to RD and is related to basic reading ability. The source of this deficit is worthy of further research, but it may include both reduced memory for order and poorer verbal mediation. PMID:26579020

  12. Atomic scale study of corrugating and anticorrugating states on the bare Si(1 0 0) surface.

    PubMed

    Yengui, Mayssa; Pinto, Henry P; Leszczynski, Jerzy; Riedel, Damien

    2015-02-01

    In this article, we study the origin of the corrugating and anticorrugating states through the electronic properties of the Si(1 0 0) surface via a low-temperature (9 K) scanning tunneling microscope (STM). Our study is based on the analysis of the STM topographies corrugation variations when related to the shift of the local density of states (LDOS) maximum in the [Formula: see text] direction. Our experimental results are correlated with numerical simulations using the density-functional theory with hybrid Heyd-Scuseria-Ernzerhof (HSE06) functional to simulate the STM topographies, the projected density of states variations at different depths in the silicon surface as well as the three dimensional partial charge density distributions in real-space. This work reveals that the Si(1 0 0) surface exhibits two anticorrugating states at +0.8 and +2.8 V that are associated with a phase shift of the LDOS maximum in the unoccupied states STM topographies. By comparing the calculated data with our experimental results, we have been able to identify the link between the variations of the STM topographies corrugation and the shift of the LDOS maximum observed experimentally. Each surface voltage at which the STM topographies corrugation drops is defined as anticorrugating states. In addition, we have evidenced a sharp jump in the tunnel current when the second LDOS maximum shift is probed, whose origin is discussed and associated with the presence of Van Hove singularities. PMID:25524935

  13. Thalamo-Cortical Disruption Contributes to Short-Term Memory Deficits in Patients with Medial Temporal Lobe Damage.

    PubMed

    Voets, Natalie L; Menke, Ricarda A L; Jbabdi, Saad; Husain, Masud; Stacey, Richard; Carpenter, Katherine; Adcock, Jane E

    2015-11-01

    Short-term (STM) and long-term memory (LTM) have largely been considered as separate brain systems reflecting fronto-parietal and medial temporal lobe (MTL) functions, respectively. This functional dichotomy has been called into question by evidence of deficits on aspects of working memory in patients with MTL damage, suggesting a potentially direct hippocampal contribution to STM. As the hippocampus has direct anatomical connections with the thalamus, we tested the hypothesis that damage to thalamic nuclei regulating cortico-cortical interactions may contribute to STM deficits in patients with hippocampal dysfunction. We used diffusion-weighted magnetic resonance imaging-based tractography to identify anatomical subdivisions in patients with MTL epilepsy. From these, we measured resting-state functional connectivity with detailed cortical divisions of the frontal, temporal, and parietal lobes. Whereas thalamo-temporal functional connectivity reflected LTM performance, thalamo-prefrontal functional connectivity specifically predicted STM performance. Notably, patients with hippocampal volume loss showed thalamic volume loss, most prominent in the pulvinar region, not detected in patients with normal hippocampal volumes. Aberrant thalamo-cortical connectivity in the epileptic hemisphere was mirrored in a loss of behavioral association with STM performance specifically in patients with hippocampal atrophy. These findings identify thalamo-cortical disruption as a potential mechanism contributing to STM deficits in the context of MTL damage. PMID:26009613

  14. Thalamo-Cortical Disruption Contributes to Short-Term Memory Deficits in Patients with Medial Temporal Lobe Damage

    PubMed Central

    Voets, Natalie L.; Menke, Ricarda A. L.; Jbabdi, Saad; Husain, Masud; Stacey, Richard; Carpenter, Katherine; Adcock, Jane E.

    2015-01-01

    Short-term (STM) and long-term memory (LTM) have largely been considered as separate brain systems reflecting fronto-parietal and medial temporal lobe (MTL) functions, respectively. This functional dichotomy has been called into question by evidence of deficits on aspects of working memory in patients with MTL damage, suggesting a potentially direct hippocampal contribution to STM. As the hippocampus has direct anatomical connections with the thalamus, we tested the hypothesis that damage to thalamic nuclei regulating cortico-cortical interactions may contribute to STM deficits in patients with hippocampal dysfunction. We used diffusion-weighted magnetic resonance imaging-based tractography to identify anatomical subdivisions in patients with MTL epilepsy. From these, we measured resting-state functional connectivity with detailed cortical divisions of the frontal, temporal, and parietal lobes. Whereas thalamo-temporal functional connectivity reflected LTM performance, thalamo-prefrontal functional connectivity specifically predicted STM performance. Notably, patients with hippocampal volume loss showed thalamic volume loss, most prominent in the pulvinar region, not detected in patients with normal hippocampal volumes. Aberrant thalamo-cortical connectivity in the epileptic hemisphere was mirrored in a loss of behavioral association with STM performance specifically in patients with hippocampal atrophy. These findings identify thalamo-cortical disruption as a potential mechanism contributing to STM deficits in the context of MTL damage. PMID:26009613

  15. Analysis of Two Complementary Single-Gene Deletion Mutant Libraries of Salmonella Typhimurium in Intraperitoneal Infection of BALB/c Mice.

    PubMed

    Silva-Valenzuela, Cecilia A; Molina-Quiroz, Roberto C; Desai, Prerak; Valenzuela, Camila; Porwollik, Steffen; Zhao, Ming; Hoffman, Robert M; Andrews-Polymenis, Helene; Contreras, Inés; Santiviago, Carlos A; McClelland, Michael

    2015-01-01

    Two pools of individual single gene deletion (SGD) mutants of S. Typhimurium 14028s encompassing deletions of 3,923 annotated non-essential ORFs and sRNAs were screened by intraperitoneal (IP) injection in BALB/c mice followed by recovery from spleen and liver 2 days post infection. The relative abundance of each mutant was measured by microarray hybridization. The two mutant libraries differed in the orientation of the antibiotic resistance cassettes (either sense-oriented Kan(R), SGD-K, or antisense-oriented Cam(R), SGD-C). Consistent systemic colonization defects were observed in both libraries and both organs for hundreds of mutants of genes previously reported to be important after IP injection in this animal model, and for about 100 new candidate genes required for systemic colonization. Four mutants with a range of apparent fitness defects were confirmed using competitive infections with the wild-type parental strain: ΔSTM0286, ΔSTM0551, ΔSTM2363, and ΔSTM3356. Two mutants, ΔSTM0286 and ΔSTM2363, were then complemented in trans with a plasmid encoding an intact copy of the corresponding wild-type gene, and regained the ability to fully colonize BALB/c mice systemically. These results suggest the presence of many more undiscovered Salmonella genes with phenotypes in IP infection of BALB/c mice, and validate the libraries for application to other systems. PMID:26779130

  16. Salmonella contamination of cereal ingredients for animal feeds.

    PubMed

    Davies, R H; Wales, A D

    2013-10-25

    Cereal ingredients for animal feedstuffs may become contaminated by Salmonella on their farms of origin. This is often concentrated in multiple foci, owing to contamination by rodents and other wildlife which may be missed by routine sampling, and may involve serovars of particular public health significance, such as Salmonella Typhimurium (STM). The study examined such contamination in domestically-produced cereal ingredients in the United Kingdom. Cereal-producing farms with associated cattle or pig enterprises (43) and feedmills (6) were investigated, following the isolation of STM from their premises (feedmills) or STM DT104 from their livestock (farms) by routine surveillance. Cereal samples from feedmills yielded two STM isolates from the same premises, of the same phage types as were isolated from wild bird faeces at ingredient intake and product loading areas. Farm investigations identified numerous Salmonella serovars, including STM, on grain harvesting and handling equipment, in grain storage areas, and in wildlife samples. Mice were removed from one pig farm and shed Salmonella Derby and Salmonella Bovismorbificans for 10 months afterwards. Grain stores more than one kilometre away from livestock areas were rarely found to be contaminated with STM. The principal issues with Salmonella contamination of cereals appeared to be the use of livestock areas as temporary grain stores on cattle farms, and access to stored grain by wildlife and domestic animals. PMID:23915993

  17. Scanning tunnelling microscopy in extreme fields: very low temperature, high magnetic field, and extreme high vacuum

    NASA Astrophysics Data System (ADS)

    Sagisaka, Keisuke; Kitahara, Masayo; Fujita, Daisuke; Kido, Giyuu; Koguchi, Nobuyuki

    2004-06-01

    We present the performance of our newly developed very-low-temperature scanning tunnelling microscope (VLT-STM). This system can operate with high spatial and energy resolution at temperatures down to 350 mK, and in a magnetic field up to 11 T. The uniqueness of our VLT-STM is that the system possesses extreme-high-vacuum chambers (XHV) ({\\sim } 10^{-10} Pa). System operation ranges from sample preparation, such as cleaning and deposition, to observations in an extremely clean environment. XHV will have a significant impact within material sciences, particularly when treating a semiconductor surface. Test results have revealed STM images obtained below 1 K and with atomic resolution of highly oriented pyrolytic graphite (HOPG), Si(100) dimers, and Au(111) surfaces. Our Si(100) experiments are the first atomically-resolved STM images of the semiconductor surface obtained below 1 K. The results of those tests have conclusively determined its true ground state structure—a subject under debate for many years. Some of the STM images acquired in a high magnetic field are included in this paper. The XHV-VLT-STM system is state-of-the-art and a very powerful instrument for exploration of the nano-sciences.

  18. Analysis of Two Complementary Single-Gene Deletion Mutant Libraries of Salmonella Typhimurium in Intraperitoneal Infection of BALB/c Mice

    PubMed Central

    Silva-Valenzuela, Cecilia A.; Molina-Quiroz, Roberto C.; Desai, Prerak; Valenzuela, Camila; Porwollik, Steffen; Zhao, Ming; Hoffman, Robert M.; Andrews-Polymenis, Helene; Contreras, Inés; Santiviago, Carlos A.; McClelland, Michael

    2016-01-01

    Two pools of individual single gene deletion (SGD) mutants of S. Typhimurium 14028s encompassing deletions of 3,923 annotated non-essential ORFs and sRNAs were screened by intraperitoneal (IP) injection in BALB/c mice followed by recovery from spleen and liver 2 days post infection. The relative abundance of each mutant was measured by microarray hybridization. The two mutant libraries differed in the orientation of the antibiotic resistance cassettes (either sense-oriented KanR, SGD-K, or antisense-oriented CamR, SGD-C). Consistent systemic colonization defects were observed in both libraries and both organs for hundreds of mutants of genes previously reported to be important after IP injection in this animal model, and for about 100 new candidate genes required for systemic colonization. Four mutants with a range of apparent fitness defects were confirmed using competitive infections with the wild-type parental strain: ΔSTM0286, ΔSTM0551, ΔSTM2363, and ΔSTM3356. Two mutants, ΔSTM0286 and ΔSTM2363, were then complemented in trans with a plasmid encoding an intact copy of the corresponding wild-type gene, and regained the ability to fully colonize BALB/c mice systemically. These results suggest the presence of many more undiscovered Salmonella genes with phenotypes in IP infection of BALB/c mice, and validate the libraries for application to other systems. PMID:26779130

  19. Vesicular acetylcholine transporter knock-down mice show sexual dimorphism on memory.

    PubMed

    Capettini, Suellem B; Moraes, Márcio F D; Prado, Vânia F; Prado, Marco A M; Pereira, Grace S

    2011-04-25

    The key neural substrates involved in memory and cognitive tasks have been reported to receive important modulation from ovarian hormones. In fact, neurochemical systems associated with cognitive functions, such as the cholinergic system, are, at least in part, under modulation of estrogens. Here we show that vesicular acetylcholine transporter (VAChT) mutant mice, which express lower levels of the VAChT (VAChT KD) and reduced acetylcholine release, present sexual dimorphism on memory. We evaluate short- and long-term object recognition memories (STM and LTM) in both sexes. We have showed previously, and confirm here, that VAChT KDHET male mice present deficits in both STM and LTM object recognition memories in comparison with WT. In contrast, VAChT KDHET female mice present deficit in LTM, but not in STM. To test if the female hormones levels could be a determinant factor on sexual dimorphism observed, we submitted female mice to ovariectomy (OVX) or sham-surgery. After 1 week (1 w), we evaluate STM. Female hormone deprivation promotes STM impairment in VAChT KDHET, but not in WT female mice. Our results strongly suggest that the sexual dimorphism observed in VAChT KDHET mice on STM is due to modulation of cholinergic system by ovarian hormones. PMID:21329745

  20. Scanning tunnelling microscopy of charge-density waves in transition metal chalcogenides

    NASA Astrophysics Data System (ADS)

    Coleman, R. V.; Giambattista, B.; Hansma, P. K.; Johnson, A.; McNairy, W. W.; Slough, C. G.

    1988-11-01

    We have used scanning tunnelling microscopes (STMs) operating at liquid helium and liquid nitrogen temperatures to image the charge-density waves (CDWs) in transition metal chalcogenides. The layer structure dichalcogenides TaSe2, TaS2, NbSe2, VSe2, TiSe2 and TiS2 have been studied including representative polytype phases such as 1T, 2H and 4Hb. Experimental results are presented for the complete range of CDW amplitudes and structures observed in these materials. In most cases both the CDW and the surface atomic structure have been simultaneously imaged. Results on the trichalcogenide NbSe3 are also included.The formation of the CDW along with the associated periodic lattice distortion gaps the Fermi surface (FS) and modifies the local density-of-states (LDOS) detected by the tunnelling process. The tunnelling microscopes have been operated mostly in the constant current mode which maps the LDOS at the position of the tunnelling tip. The relative amplitudes and profiles of the CDW superlattice and the atomic lattice have been measured and confirm on an atomic scale the CDW structures predicted by X-ray, electron and neutron diffraction. The absolute STM deflections are larger than expected for the CDW induced modifications of the LDOS above the surface and possible enhancement mechanisms are reviewed.In the 2H trigonal prismatic coordination phases the CDWs involve a relatively small charge transfer and the atomic structure dominates the STM images. In the 1T octahedral coordination phases the charge transfer is large and the CDW structure dominates the STM image with an anomalously large enhancement of the STM profile. Systematic comparison of the STM profiles with band structure and FS information is included.In the case of the 4Hb mixed coordination phases at the lowest temperatures two nearly independent CDWs form in alternate sandwiches. STM studies on 4Hb crystals with both octahedral and trigonal prismatic surface sandwiches have been carried out. The STM

  1. Plasma soluble thrombomodulin levels are associated with mortality in the acute respiratory distress syndrome

    PubMed Central

    Calfee, Carolyn S.; Liu, Kathleen D.; Kangelaris, Kirsten; Hansen, Helen; Pawlikowska, Ludmila; Ware, Lorraine B.; Alkhouli, Mustafa F.; Abbot, Jason; Matthay, Michael A.

    2015-01-01

    Objective Thombomodulin (TM) is an activator of protein C and a biomarker for endothelial injury. We hypothesized that (1) elevated plasma levels would be associated with clinical outcomes and (2) polymorphisms in the TM gene would be associated with plasma levels. Patients We studied 449 patients enrolled in the Fluid and Catheter Treatment Trial (FACTT) for whom both plasma and DNA were available. We used logistic regression and receiver operator curves (ROC) to test for associations between soluble TM (sTM) and mortality at 60 days. Measurements and results Plasma sTM levels were higher in non-survivors than survivors at baseline [median 147 (IQR, 95–218) vs. 89 (56–129) ng/mL, p < 0.0001] and on day 3 after study enrollment [205 (146–302) vs. 127 (85–189), p < 0.0001]. The odds of death increased by 2.4 (95 %CI 1.5–3.8, p < 0.001), and by 2.8 (1.7–4.7, P < 0.001) for every log increase in baseline and day 3 sTM levels, respectively, after adjustment for age, race, gender, severity of illness, fluid management strategy, baseline creatinine, and non-pulmonary sepsis as the primary cause of ARDS. By ROC analysis, plasma sTM levels discriminated between non-survivors and survivors [AUC = 72 % (66–78 %) vs. AUC = 54 % for severity based on Berlin criteria). Addition of sTM improved discrimination based on APACHE III from 77 to 80 % (P < 0.03). sTM levels at baseline were not statistically different among subjects stratified by genotypes of tag SNPs in the TM gene. Conclusions Higher plasma sTM levels are associated with increased mortality in ARDS. The lack of association between the sTM levels and genetic variants suggests that the increased levels of sTM may reflect severity of endothelial damage rather than genetic heterogeneity. These findings underscore the importance of endothelial injury in ARDS pathogenesis and suggest that, in combination with clinical markers, sTM could contribute to risk stratification. PMID:25643902

  2. Remediation of language processing in aphasia: Improving activation and maintenance of linguistic representations in (verbal) short-term memory

    PubMed Central

    Kalinyak-Fliszar, Michelene; Kohen, Francine; Martin, Nadine

    2012-01-01

    Background Verbal short-term memory (STM) impairments are invariably present in aphasia. Word processing involves a minimal form of verbal STM, i.e., the time course over which semantic and phonological representations are activated and maintained until they are comprehended, produced, or repeated. Thus it is reasonable that impairments of word processing and verbal STM may co-occur. The co-occurrence of language and STM impairments in aphasia has motivated an active area of research that has revealed much about the relationship of these two systems and the effect of their impairment on language function and verbal learning (Freedman & Martin, 2001; Martin & Saffran, 1999; Trojano & Grossi, 1995). In keeping with this view a number of researchers have developed treatment protocols to improve verbal STM in order to improve language function (e.g., Koenig-Bruhin & Studer-Eichenberger, 2007). This account of aphasia predicts that treatment of a fundamental ability, such as STM, which supports language function, should lead to improvements that generalise to content and tasks beyond those implemented in treatment. Aims We investigated the efficacy of a treatment for language impairment that targets two language support processes: verbal short-term memory (STM) and executive processing, in the context of a language task (repetition). We hypothesised that treatment of these abilities would improve repetition abilities and performance on other language tasks that require STM. Method A single-participant, multiple-baseline, multiple-probe design across behaviours was used with a participant with conduction aphasia. The treatment involved repetition of words and nonwords under three “interval” conditions, which varied the time between hearing and repeating the stimulus. Measures of treatment effects included acquisition, maintenance, and follow-up data, effect sizes, and pre- and post-treatment performance on a test battery that varies the STM and executive function

  3. Atomic-Scale Imaging and Spectroscopy Using Scanning Tunneling Microscopy.

    NASA Astrophysics Data System (ADS)

    Youngquist, Michael George

    Advances in scanning tunneling microscopy (STM) instrumentation and applications are presented. An ultrahigh vacuum (UHV) scanning tunneling microscope incorporating computer-controlled two-dimensional sample translation and in vacuo tip and sample transfer was developed. Its performance is documented through large-area and atomic -resolution imaging of highly stepped Si(111) 7 x 7 reconstructed surfaces and physisorbed clusters on graphite. An STM with automated approach and intra-Dewar spring suspension was developed for operation in cryogenic liquids. A high performance digital signal processor (DSP) based control system was constructed, and software with advanced spectroscopic imaging and data processing capabilities was developed. The feasibility of individual-molecule vibrational spectroscopy via STM-detected inelastic electron tunneling is assessed. In preliminary experiments, a low-temperature STM was used for energy gap and phonon spectroscopy of superconducting Pb films. The first STM observation of phonon density of states effects in a superconductor is reported. A systematic UHV STM imaging and spectroscopy study of 2H-MoS_2 was conducted. Atom -resolved images from three distinct imaging modes are presented. Occasional appearance of negative differential resistance (NDR) in I vs. V measurements is traced to changing tip electronic structure rather than localized surface states. Other potential NDR mechanisms are discussed including electron trap charging and resonant tunneling through a double-barrier quantum well structure arising from layer separation in the MoS_2 crystal. DNA was imaged at atomic resolution with a UHV STM. Images show double-helical structure, base pairs, and atomic-scale substructure. Experimental STM profiles have atom-for-atom correlation with the A-DNA van der Waals surface. This work demonstrates the potential of the STM for characterization of large biomolecular structures. Impurity-pinned steps on silicon and gold surfaces

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

    SciTech Connect

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

    2014-10-15

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

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

    NASA Astrophysics Data System (ADS)

    Voelker, Mark Alan

    1993-01-01

    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

  6. The first echinoderm gamma-interferon-inducible lysosomal thiol reductase (GILT) identified from sea cucumber (Stichopus monotuberculatus).

    PubMed

    Ren, Chunhua; Chen, Ting; Jiang, Xiao; Luo, Xing; Wang, Yanhong; Hu, Chaoqun

    2015-01-01

    Gamma-interferon-inducible lysosomal thiol reductase (GILT) has been described as a key enzyme that facilitating the processing and presentation of major histocompatibility complex class II-restricted antigen in mammals. In this study, the first echinoderm GILT named StmGILT was identified from sea cucumber (Stichopus monotuberculatus). The StmGILT cDNA is 1529 bp in length, containing a 5'-untranslated region (UTR) of 87 bp, a 3'-UTR of 674 bp and an open reading frame (ORF) of 768 bp that encoding a protein of 255 amino acids with a deduced molecular weight of 27.82 kDa and a predicted isoelectric point of 4.73. The putative StmGILT protein possesses all the main characteristics of known GILT proteins, including a signature sequence, a reductase active site CXXC, twelve conserved cysteines, and two potential N-linked glycosylation sites. For the gene structure, StmGILT contains four exons separated by three introns. In the promoter region of StmGILT gene, an NF-κB binding site and an IFN-γ activation site were found. The thiol reductase activity of recombinant StmGILT protein was also demonstrated in this study. In addition, the highest level of mRNA expression was noticed in coelomocytes of S. monotuberculatus. In in vitro experiments performed in coelomocytes, the expression of StmGILT mRNA was significantly up-regulated by lipopolysaccharides (LPS), inactivated bacteria or polyriboinosinic polyribocytidylic acid [poly (I:C)] challenge, suggested that the sea cucumber GILT might play critical roles in the innate immune defending against bacterial and viral infections. PMID:25449705

  7. Short-term memory binding is impaired in AD but not in non-AD dementias.

    PubMed

    Della Sala, Sergio; Parra, Mario A; Fabi, Katia; Luzzi, Simona; Abrahams, Sharon

    2012-04-01

    Binding is a cognitive function responsible for integrating features within complex stimuli (e.g., shape-colour conjunctions) or events within complex memories (e.g., face-name associations). This function operates both in short-term memory (STM) and in long-term memory (LTM) and is severely affected by Alzheimer's disease (AD). However, forming conjunctions in STM is the only binding function which is not affected by healthy ageing or chronic depression. Whether this specificity holds true across other non-AD dementias is as yet unknown. The present study investigated STM conjunctive binding in a sample of AD patients and patients with other non-AD dementias using a task which has proved sensitive to the effects of AD. The STM task assesses the free recall of objects, colours, and the bindings of objects and colours. Patients with AD, frontotemporal dementia, vascular dementia, lewy body dementia and dementia associated with Parkinson's disease showed memory, visuo-spatial, executive and attentional deficits on standard neuropsychological assessment. However, only AD patients showed STM binding deficits. This deficit was observed even when memory for single features was at a similar level across patient groups. Regression and discriminant analyses confirmed that the STM binding task accounted for the largest proportion of variance between AD and non-AD groups and held the greatest classification power to identify patients with AD. STM conjunctive binding places little demands on executive functions and appears to be subserved by components of the memory network which are targeted by AD, but not by non-AD dementias. PMID:22289292

  8. Stochastic mean-field polycrystal plasticity methods

    NASA Astrophysics Data System (ADS)

    Tonks, Michael R.

    To accommodate multiple length scales, mean-field polycrystal plasticity models treat each material point as an aggregate of N crystals. The crystal velocity gradients Lc are approximated and then used to evaluate the crystal stresses T c. The Tc are averaged to determine the material point stress T. Commonly, the Lc are approximated with the fully constrained model (FCM) based on the Taylor hypothesis which equates Lc to the macro-scale velocity gradient L. Herein, we present two stochastic models that relax the FCM constraint. Through various applications we show that these computationally efficient stochastic models provide realistic response predictions. We first investigate the texture evolution in a planar polycrystal with our stochastic Taylor model (STM), in which we define L c as a realization of a normal distribution with mean equal to L. Our STM predictions agree with crystal plasticity finite element method (CPFEM) predictions, demonstrating the development of a steady-state texture that is not predicted by the FCM. The computational cost of the STM is comparable to the FCM, i.e. substantially less than the CPFEM. We develop the STM for 3-D polycrystals based on CPFEM analysis results which show that Lc follows a normal distribution. In addition to the STM, we develop the stochastic no-constraints model (SNCM), which differs from the STM in the manner with which the Lc distribution means are determined. Calibration and validation of the models are performed using tantalum compression experiment data. Both models predict the compression textures more accurately than the FCM, and the SNCM predicts them more accurately than the STM. The STM is slightly more computationally expensive than the FCM, while the SNCM is three times more expensive. Finally, we incorporate the STM in a finite element simulation of the Taylor impact of two tantalum specimens. Our simulation predictions mimic the texture and deformation data measured from a powder metallurgy

  9. Advances in Atomic Force Microscopy and Scanning Tunneling Microscopy

    NASA Astrophysics Data System (ADS)

    Albrecht, Thomas Robert

    The scanning tunneling microscope (STM) and the more recently developed atomic force microscope (AFM) are high resolution scanning probe microscopes capable of three dimensional atomic-scale surface profiling. In the AFM, minute forces acting between the tip of a flexible cantilever stylus and the surface of the sample cause deflections of the cantilever which are detected by a tunneling or optical sensor with subangstrom sensitivity. The AFM work presented here involves surface profiling via repulsive contact forces between 10^{-6} and 10^{-9} N in magnitude. In this contact profiling (repulsive) mode the AFM is capable of atomic resolution on both electrically conducting and insulating surfaces (unlike the STM). AFM instrumentation for room temperature and low temperature operation is discussed. The critical component of the AFM is the cantilever stylus assembly, which should have a small mass. Several microfabrication processes have been developed to produce thin film SiO_2 and Si_3N_4 microcantilevers with integrated sharp tips. Atomic resolution has been achieved with the AFM in air on a number of samples, including graphite, MoS _2, TaSe_2, WTe_2, TaS_2, and BN (the first insulator imaged with atomic resolution by any means). Various organic and molecular samples have been imaged with nanometer resolution. The difference between STM and AFM response is shown in images of TaS _2 (a charge density wave material), and in simultaneous STM/AFM images of lattice defects and adsorbates on graphite and MoS_2. A number of artifacts make STM and AFM image interpretation subtle, such as tip shape effects, frictional effects, and tracking in atomic grooves. STM images of moire patterns near grain boundaries confirm the importance of tip shape effects. Various surface modification and lithography techniques have been demonstrated with the STM and AFM, including an STM voltage pulse technique which reproducibly creates 40 A diameter holes on the surface of graphite, and a

  10. Determination of surface structure of cleaved (001) USb2 single crystal

    SciTech Connect

    Chen, Shao-ping; Hawley, Marilyn; Bauer, Eric D; Stockum, Phil B; Manoharan, Hari C

    2009-01-01

    We have achieved what we believe to be the first atomic resolution STM images for a uranium compound taken at room temperature. The a, b, and c lattice parameters in the images confirm that the USb{sub 2} crystals cleave on the (001) basal plane as expected. The a and b dimensions were equal, with the atoms arranged in a cubic pattern. Our calculations indicate a symmetric cut between Sb planes to be the most favorable cleavage plane and U atoms to be responsible for most of the DOS measured by STM. Some strange features associated with vacancies were observed in the STM win be discussed in conjunction with ab initio calculations. The purpose of this work is to demonstrate the power of scanning tunneling microscopy (STM) techniques combined with a theoretical underpinning to determine the surface atomic structure and properties of actinide materials, such as the quasi 2-dimensional uranium dipnictide USb{sub 2} single crystal, thereby contributing to the understanding of their surface structural and electronic properties. The members of this interesting UX{sub 2} (X=P, As, Sb, Bi) series of compounds display dual localized and itinerant 5f electron behavior within the same compound due to the hybridization of the 5f orbitals with the conduction band. With the exception of UO{sub 2}, which has to be studied at elevated temperature to generate enough carriers for STM imaging, STM techniques have not been applied successfully to the characterization of the surface atomic structure of any other single crystal actinide compound, to the best of our knowledge. However, STM has been used to a limited extent for the study of some cerium compounds. STM probes electronic properties at the atomic level and can directly provide information about the local density of filled and empty states (LDOS) states simultaneously. A STM topograph provides the local atomic arrangement and spacing of the atoms on the surface, local defect structures (e.g. steps, vacancies, and kink sites

  11. Structure of cleaved (001) USb2 single crystal

    SciTech Connect

    Chen, Shao-ping; Hawley, Marilyn; Bauer, Eric D; Stockum, Phil B; Manoharan, Hari C

    2009-01-01

    We have achieved what we believe to be the first atomic resolution STM images for a uranium compound taken at room temperature. The a, b, and c lattice parameters in the images confirm that the USb{sub 2} crystals cleave on the (001) basal plane as expected. The a and b dimensions were equal, with the atoms arranged in a cubic pattern. Our calculations indicate a symmetric cut between Sb planes to be the most favorable cleavage plane and U atoms to be responsible for most of the DOS measured by STM. Some strange features observed in the STM will be discussed in conjunction with ab initio calculations. The purpose of this work is to demonstrate the power of scanning tunneling microscopy (STM) techniques combined with a theoretical underpinning to determine the surface atomic structure and properties of actinide materials, such as the quasi 2-dimensional uranium dipnictide USb{sub 2} single crystal, thereby contributing to the understanding of their surface structural and electronic properties. The members of this interesting UX{sub 2} (X=P, As, Sb, Bi) series of compounds display dual localized and itinerant 5f electron behavior within the same compound due to the hybridization of the 5f orbitals with the conduction band. With the exception of UO{sub 2}, which has to be studied at elevated temperature to generate enough carriers for STM imaging, STM techniques have not been applied successfully to the characterization of the surface atomic structure of any other single crystal actinide compound, to the best of our knowledge. However, STM has been used to a limited extent for the study of some cerium compounds. STM probes electronic properties at the atomic level and can directly provide information about the local density of filled and empty states (LDOS) states simultaneously. A STM topograph provides the local atomic arrangement and spacing of the atoms on the surface, local defect structures (e.g. steps, vacancies, and kink sites) and the presence of contaminants

  12. How grammar can cope with limited short-term memory: simultaneity and seriality in sign languages.

    PubMed

    Geraci, Carlo; Gozzi, Marta; Papagno, Costanza; Cecchetto, Carlo

    2008-02-01

    It is known that in American Sign Language (ASL) span is shorter than in English, but this discrepancy has never been systematically investigated using other pairs of signed and spoken languages. This finding is at odds with results showing that short-term memory (STM) for signs has an internal organization similar to STM for words. Moreover, some methodological questions remain open. Thus, we measured span of deaf and matched hearing participants for Italian Sign Language (LIS) and Italian, respectively, controlling for all the possible variables that might be responsible for the discrepancy: yet, a difference in span between deaf signers and hearing speakers was found. However, the advantage of hearing subjects was removed in a visuo-spatial STM task. We attribute the source of the lower span to the internal structure of signs: indeed, unlike English (or Italian) words, signs contain both simultaneous and sequential components. Nonetheless, sign languages are fully-fledged grammatical systems, probably because the overall architecture of the grammar of signed languages reduces the STM load. Our hypothesis is that the faculty of language is dependent on STM, being however flexible enough to develop even in a relatively hostile environment. PMID:17537417

  13. Theoretical study of carbon-based tips for scanning tunnelling microscopy.

    PubMed

    González, C; Abad, E; Dappe, Y J; Cuevas, J C

    2016-03-11

    Motivated by recent experiments, we present here a detailed theoretical analysis of the use of carbon-based conductive tips in scanning tunnelling microscopy. In particular, we employ ab initio methods based on density functional theory to explore a graphitic, an amorphous carbon and two diamond-like tips for imaging with a scanning tunnelling microscope (STM), and we compare them with standard metallic tips made of gold and tungsten. We investigate the performance of these tips in terms of the corrugation of the STM images acquired when scanning a single graphene sheet. Moreover, we analyse the impact of the tip-sample distance and show that it plays a fundamental role in the resolution and symmetry of the STM images. We also explore in depth how the adsorption of single atoms and molecules in the tip apexes modifies the STM images and demonstrate that, in general, it leads to an improved image resolution. The ensemble of our results provides strong evidence that carbon-based tips can significantly improve the resolution of STM images, as compared to more standard metallic tips, which may open a new line of research in scanning tunnelling microscopy. PMID:26861537

  14. A low temperature ultrahigh vacuum scanning tunneling microscope with high-NA optics to probe optical interactions at the atomic scale

    NASA Astrophysics Data System (ADS)

    Zhang, Haigang; Smerdon, Joseph; Suzer, Ozgun; Kersell, Heath; Guest, Jeffrey

    2015-03-01

    The optical and photophysical properties of single molecules/atoms, defects, and nanoscale structures at surfaces hinge on structure at the atomic scale. In order to characterize and control this structure and unravel these correlations, we are developing a low temperature (LT) laser-coupled ultrahigh vacuum (UHV) scanning tunneling microscope (LT Laser UHV STM) based on the Pan-style STM scanner with integrated high-numerical-aperture (NA) optics for single particle spectroscopy measurements under the STM tip. Using slip-stick inertial piezo steppers, the sample stage can be coarsely translated in X and Y directions. For optical measurements, high-NA optics behind and above the sample focus laser excitation on and collect photons emitted from the tip-sample junction. The STM is cooled by a liquid helium bath surrounded by a liquid nitrogen jacket for operation near 5 K; two separate ultrahigh vacuum chambers are used for sample preparation and STM measurements, respectively. We will describe our progress in demonstrating this instrument and plans for experiments studying the correlation between structure and optical function in nanoscale systems. U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.

  15. Interface structure for growth of epitaxial graphene on SiC(0001)

    NASA Astrophysics Data System (ADS)

    Rhim, S. H.; Sun, G.; Li, L.; Weinert, M.

    2009-03-01

    In spite of the enormous effort devoted to the study of the epitaxial growth of graphene on SiC, there is not yet a consensus regarding the structure of the interface between graphene and the substrate. There have been a long standing discrepancy between low energy electron diffraction (LEED) and STM patterns regarding the periodicity of graphene on SiC(0001); the theoretical studies of the of 6√3x6√3 ootnotetextS. Kim, J. Ihm, H. J. Choi, and Y. W. Son, Phys. Rev. Lett. 100, 176802 (2008). or √3x√3 ootnotetextF. Varchon et al, Phys. Rev. Lett. 99, 126805 (2007); A. Mattausch and O. Pankratov, Phys. Rev. Lett. 99, 076802 (2007 periodicity, while describing some aspects, disagree in important details with scanning tunneling microscopy (STM) images. We present a combined theoretical and experimental study, employing density functional calculations and STM, to investigate this issue. We propose the formation of a defected graphene layer at the interface, and then subsequent growth of graphene. The calculated bias-dependent STM images are in good agreement with our STM images, and provide insight into the details of the interface structure.

  16. Kinin B1 receptor mediates memory impairment in the rat hippocampus.

    PubMed

    Dong-Creste, Káris Ester; Baraldi-Tornisielo, Ticiana; Caetano, Ariadiny Lima; Gobeil, Fernand; Montor, Wagner Ricardo; Viel, Tania Araujo; Buck, Hudson Sousa

    2016-04-01

    The bradykinin (BK) receptors B1R and B2R are involved in inflammatory responses and their activation can enhance tissue damage. The B2R is constitutively expressed and mediates the physiologic effects of BK, whereas B1R expression is induced after tissue damage. Recently, they have been involved with Alzheimer's disease, ischemic stroke and traumatic brain injury (TBI). In this study, we investigated the role of bradykinin in short and long-term memory consolidation (STM and LTM). It was observed that bilateral injection of BK (300 pmol/μl) disrupted the STM consolidation but not LTM, both evaluated by inhibitory avoidance test. The STM disruption due to BK injection was blocked by the previous injection of the B1R antagonist des-Arg10-HOE140 but not by the B2R antagonist HOE140. Additionally, the injection of the B1 agonist desArg9-BK disrupted STM and LTM consolidation at doses close to physiological concentration of the peptide (2.3 and 37.5 pmol, respectively) which could be reached during tissue injury. The presence of B1R located on glial cells around the implanted guide cannula used for peptide injection was confirmed by immunofluorescence. These data imply in a possible participation of B1R in the STM impairment observed in TBI, neuroinflammation and neurodegeneration. PMID:26669247

  17. Analysis and Prediction of Ice Shedding for a Full-Scale Heated Tail Rotor

    NASA Technical Reports Server (NTRS)

    Kreeger, Richard E.; Work, Andrew; Douglass, Rebekah; Gazella, Matthew; Koster, Zakery; Turk, Jodi

    2016-01-01

    When helicopters are to fly in icing conditions, it is necessary to consider the possibility of ice shed from the rotor blades. In 2013, a series of tests were conducted on a heated tail rotor at NASA Glenn's Icing Research Tunnel (IRT). The tests produced several shed events that were captured on camera. Three of these shed events were captured at a sufficiently high frame rate to obtain multiple images of the shed ice in flight that had a sufficiently long section of shed ice for analysis. Analysis of these shed events is presented and compared to an analytical Shedding Trajectory Model (STM). The STM is developed and assumes that the ice breaks off instantly as it reaches the end of the blade, while frictional and viscous forces are used as parameters to fit the STM. The trajectory of each shed is compared to that predicted by the STM, where the STM provides information of the shed group of ice as a whole. The limitations of the model's underlying assumptions are discussed in comparison to experimental shed events.

  18. Structural changes in a Schiff base molecular assembly initiated by scanning tunneling microscopy tip.

    PubMed

    Tomak, A; Bacaksiz, C; Mendirek, G; Sahin, H; Hur, D; Görgün, K; Senger, R T; Birer, Ö; Peeters, F M; Zareie, H M

    2016-08-19

    We report the controlled self-organization and switching of newly designed Schiff base (E)-4-((4-(phenylethynyl) benzylidene) amino) benzenethiol (EPBB) molecules on a Au (111) surface at room temperature. Scanning tunneling microscopy and spectroscopy (STM/STS) were used to image and analyze the conformational changes of the EPBB molecules. The conformational change of the molecules was induced by using the STM tip while increasing the tunneling current. The switching of a domain or island of molecules was shown to be induced by the STM tip during scanning. Unambiguous fingerprints of the switching mechanism were observed via STM/STS measurements. Surface-enhanced Raman scattering was employed, to control and identify quantitatively the switching mechanism of molecules in a monolayer. Density functional theory calculations were also performed in order to understand the microscopic details of the switching mechanism. These calculations revealed that the molecular switching behavior stemmed from the strong interaction of the EPBB molecules with the STM tip. Our approach to controlling intermolecular mechanics provides a path towards the bottom-up assembly of more sophisticated molecular machines. PMID:27378765

  19. The Historical Antecedents of the UPR School of Tropical Medicine.

    PubMed

    Mayo-Santana, Raúl; Peña-Carro, Lucy; Rabionet, Silvia E

    2016-06-01

    This article deals with the historical antecedents of the University of Puerto Rico (UPR) School of Tropical Medicine (STM) under the auspices of Columbia University. It presents a general view of the social, institutional and conceptual factors that were correlated with the establishment of the STM. The authors start by examining the historical continuities and discontinuities present during the imperial transitions between Spanish colonial and U.S. military medicine at the turn of the 20th century. The clarification of these changes is important for the proper understanding of the emergence of tropical medicine in Puerto Rico, marked by the identification of the biological determinant of the so called "peasants' anemia." The essay focuses on two institutional precursor events: the Puerto Rico Anemia Commissions (1904-1908) and the Institute of Tropical Medicine and Hygiene (1912-1914). Their nature and work paved the way for the establishment of the STM. The notions of tropical medicine and diseases are considered as historical concepts. The support of the Rockefeller Foundation to several significant public health activities in Puerto Rico is also examined. Finally, the social and health conditions which prevailed at the time of the creation of the STM have been summarized. In general, the article provides a sense of historical context deemed essential to understand the emergence and evolution of the STM. PMID:27232865

  20. Scanning Tunneling Microscopy Studies of Crystalline Hydrogenation of Graphene Grown on Cu(111)

    NASA Astrophysics Data System (ADS)

    Tjung, Steven J.; Gambrel, Grady A.; Hollen, Shawna M.; Gupta, Jay A.

    Because of the sensitivity of 2D material surfaces, chemical functionalization can be exploited to tune the electronic structure of these materials. For example, hydrogen bonding to carbon atoms in graphene tunes the material from a semi-metal to a wide-gap insulator. We developed a method for a reproducible epitaxial growth of graphene on Cu(111) in the ultra-high vacuum chamber of a scanning tunneling microscope (STM). We find that hydrogen atoms can be bonded to the graphene in a nanoscale region using a novel field-emission process, whereby physisorbed H2 is cracked in situ using the STM tip. This method produced crystalline surfaces of hydrogen-terminated graphene with 4.2Å lattice, which has proven difficult to produce using conventional atomic beam methods which typically produced disordered hydrogenation. Additionally, this hydrogenation process is reversible and we are able to recover the pristine graphene by H desorption during STM imaging at a high bias. STM images after the dehydrogenation process showed the same atomic lattice and Moiré pattern as the pristine graphene, with the exception of additional point defects. STM spectra show the suppression of the Cu surface state on the hydrogenated graphene, but the opening of a wide-gap was not observed. Funded by the Center for Emergent Materials at the Ohio State University, an NSF MRSEC (Grant No. DMR-1420451 and DMR-0820414).

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

    SciTech Connect

    Merte, L. R.; Grabow, Lars C.; Peng, Guowen; Knudsen, Jan; Zeuthen, Helene; Kudernatsch, Wilhelmine; Porsgaard, Soeren; Laegsgaard, E.; Mavrikakis, Manos; Besenbacher, Fleming

    2011-02-10

    High-resolution scanning tunneling microscope (STM) images of moire-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 moire structure. The experimental STM results are compared with the results of electronic structure calculations within the DFTþUscheme for a realistic (√91 x √ 91)R5.2º moire FeO 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 STMresults we show that several of the previously published conclusions for the FeO system have to be revisited.

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

    SciTech Connect

    Romero, M. J.; van de Lagemaat, J.

    2009-01-01

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

  3. Neural Organization of Linguistic Short-Term Memory is Sensory Modality-Dependent

    PubMed Central

    Pa, Judy; Wilson, Stephen M.; Pickell, Herbert; Bellugi, Ursula; Hickok, Gregory

    2009-01-01

    Despite decades of research, there is still disagreement regarding the nature of the information that is maintained in linguistic short-term memory (STM). Some authors argue for abstract phonological codes, whereas others argue for more general sensory traces. We assess these possibilities by investigating linguistic STM in two distinct sensory-motor modalities, spoken and signed language. Hearing bilingual participants (native in English and American Sign Language) performed equivalent STM tasks in both languages during fMRI scanning. Distinct, sensory-specific activations were seen during the maintenance phase of the task for spoken versus signed language. These regions have been previously shown to respond to non-linguistic sensory stimulation, suggesting that linguistic STM tasks recruit sensory-specific networks. However, maintenance-phase activations common to the two languages were also observed, implying some form of common process. We conclude that linguistic STM involves sensory-dependent neural networks, but suggest that sensory-independent neural networks may also exist. PMID:18457510

  4. Partially overlapping sensorimotor networks underlie speech praxis and verbal short-term memory: evidence from apraxia of speech following acute stroke

    PubMed Central

    Hickok, Gregory; Rogalsky, Corianne; Chen, Rong; Herskovits, Edward H.; Townsley, Sarah; Hillis, Argye E.

    2014-01-01

    We tested the hypothesis that motor planning and programming of speech articulation and verbal short-term memory (vSTM) depend on partially overlapping networks of neural regions. We evaluated this proposal by testing 76 individuals with acute ischemic stroke for impairment in motor planning of speech articulation (apraxia of speech, AOS) and vSTM in the first day of stroke, before the opportunity for recovery or reorganization of structure-function relationships. We also evaluated areas of both infarct and low blood flow that might have contributed to AOS or impaired vSTM in each person. We found that AOS was associated with tissue dysfunction in motor-related areas (posterior primary motor cortex, pars opercularis; premotor cortex, insula) and sensory-related areas (primary somatosensory cortex, secondary somatosensory cortex, parietal operculum/auditory cortex); while impaired vSTM was associated with primarily motor-related areas (pars opercularis and pars triangularis, premotor cortex, and primary motor cortex). These results are consistent with the hypothesis, also supported by functional imaging data, that both speech praxis and vSTM rely on partially overlapping networks of brain regions. PMID:25202255

  5. The electronic and structural properties of the silicon-gallium arsenide(110) interface

    NASA Astrophysics Data System (ADS)

    Dunstan, P. R.; Wilks, S. P.; Burgess, S. R.; Pan, M.; Williams, R. H.; Cammack, D. S.; Clark, S. A.

    1998-01-01

    The passivation properties of the Sisbnd GaAs(110) interface have been studied using scanning tunnelling microscopy/spectroscopy (STM/STS) and soft X-ray photoemission spectroscopy (SXPS). Silicon has been deposited at room temperature and STM images show the sub-monolayer growth of silicon islands on the GaAs substrate. The electrical properties of these islands together with the clean surface have been investigated using scanning tunnelling spectroscopy (STS). The spectroscopy clearly illustrates the difference in electrical properties between atomically flat regions of GaAs as compared to those containing defects or steps, i.e. where surface band bending occurs. We have investigated the use of sub-monolayer Si coverages to modify the electronic structure of the surface. Height variations of 3-4Åacross Si islands and 2Åacross steps on the GaAs surface have also been observed using the STM. STS spectra, collected simultaneously with the STM image, showed the Si to have semiconducting properties differing from that of crystalline Si and the GaAs substrate. Comparisons between the STM and STS results together with SXPS have provided a correlation between the structural, electrical and chemical nature of the Si/GaAs(110) interface.

  6. Comparative Genomics of Aeschynomene Symbionts: Insights into the Ecological Lifestyle of Nod-Independent Photosynthetic Bradyrhizobia

    PubMed Central

    Mornico, Damien; Miché, Lucie; Béna, Gilles; Nouwen, Nico; Verméglio, André; Vallenet, David; Smith, Alexander A.T.; Giraud, Eric; Médigue, Claudine; Moulin, Lionel

    2011-01-01

    Tropical aquatic species of the legume genus Aeschynomene are stem- and root-nodulated by bradyrhizobia strains that exhibit atypical features such as photosynthetic capacities or the use of a nod gene-dependent (ND) or a nod gene-independent (NI) pathway to enter into symbiosis with legumes. In this study we used a comparative genomics approach on nine Aeschynomene symbionts representative of their phylogenetic diversity. We produced draft genomes of bradyrhizobial strains representing different phenotypes: five NI photosynthetic strains (STM3809, ORS375, STM3847, STM4509 and STM4523) in addition to the previously sequenced ORS278 and BTAi1 genomes, one photosynthetic strain ORS285 hosting both ND and NI symbiotic systems, and one NI non-photosynthetic strain (STM3843). Comparative genomics allowed us to infer the core, pan and dispensable genomes of Aeschynomene bradyrhizobia, and to detect specific genes and their location in Genomic Islands (GI). Specific gene sets linked to photosynthetic and NI/ND abilities were identified, and are currently being studied in functional analyses. PMID:24704842

  7. Adlayer structures of anthracenthiol on Au(111) after removal of covering multilayers with probe scan

    NASA Astrophysics Data System (ADS)

    Azzam, Waleed

    2016-05-01

    Self-assembled monolayers (SAMs) of anthracene-2-thiol (AnT) on Au(111) have been investigated using scanning tunneling microscopy (STM). A preparation of AnT-SAMs from ethanolic solutions results in a deposition of multilayer films. As a result, the general features that have been frequently observed for different systems of thiol-modified gold surfaces are hidden in AnT-SAMs. The thin overlayers on top of the chemisorbed anthracenethiolate monolayer are removed by the STM-tip after a repetitive scanning over the same part of the SAM at nondestructive imaging conditions. After ∼2 h of consecutive and continuous STM scanning, smooth AnT-SAM surfaces were formed. The polished surfaces contain vacancy depressions rather than the elevated gold islands which are typically formed after the adsorption of purely aromatic thiols such as AnT on Au(111). The STM data showed the coexistence of two distinct stable commensurate phases, namely, α and β. High-resolution STM images revealed a (√{ 3 } × 8) structure for the α phase and a (√{ 7 } × 4) R11° structure for the β phase whose unit cells contain, respectively, four and two molecules. The β phase was found to be 50% less densely packed than the α phase. The lower molecular density of the β phase should be correlated with a significantly larger tilt angle of the AnT molecular backbone with respect to the surface normal.

  8. Marvels and Shadows: Science and Education at the University of Puerto Rico School of Tropical Medicine under the Auspices of Columbia University: An Introduction.

    PubMed

    Mayo-Santana, Raúl; Rabionet, Silvia E; Peña-Carro, Lucy; Serrano, Adelfa E

    2016-06-01

    This essay introduces a series of five historical articles on the scientific and educational contributions of the University of Puerto Rico School of Tropical Medicine (STM), under the auspices of Columbia University (1926-1949), to the fields of tropical medicine and public health. The articles will appear in several consecutive issues, and will address various themes as follows: 1) historical antecedents of the STM, particularly institutional precedents; 2) the educational legacy of the STM; 3) a history of the STM scientific journal ("The Puerto Rico Journal of Public Health and Tropical Medicine"); 4) the scientific practices and representations that prevailed at the institution; and, 5) a brief sociocultural history of malaria in Puerto Rico, mainly from the perspective of the STM's scientific and public health activities. The authors have systematically and comprehensively studied a wide variety of documents from different sources based on multiple archives in Puerto Rico, the United States and England. The authors treat the fluid meanings of the examined historical encounters from a research perspective that privilege complex reciprocal interactions, multiple adaptations and elaborate sociocultural constructs present in a collaborative exemplar of the modernity of medical science in a neocolonial tropical context. PMID:27232864

  9. Structural changes in a Schiff base molecular assembly initiated by scanning tunneling microscopy tip

    NASA Astrophysics Data System (ADS)

    Tomak, A.; Bacaksiz, C.; Mendirek, G.; Sahin, H.; Hur, D.; Görgün, K.; Senger, R. T.; Birer, Ö.; Peeters, F. M.; Zareie, H. M.

    2016-08-01

    We report the controlled self-organization and switching of newly designed Schiff base (E)-4-((4-(phenylethynyl) benzylidene) amino) benzenethiol (EPBB) molecules on a Au (111) surface at room temperature. Scanning tunneling microscopy and spectroscopy (STM/STS) were used to image and analyze the conformational changes of the EPBB molecules. The conformational change of the molecules was induced by using the STM tip while increasing the tunneling current. The switching of a domain or island of molecules was shown to be induced by the STM tip during scanning. Unambiguous fingerprints of the switching mechanism were observed via STM/STS measurements. Surface-enhanced Raman scattering was employed, to control and identify quantitatively the switching mechanism of molecules in a monolayer. Density functional theory calculations were also performed in order to understand the microscopic details of the switching mechanism. These calculations revealed that the molecular switching behavior stemmed from the strong interaction of the EPBB molecules with the STM tip. Our approach to controlling intermolecular mechanics provides a path towards the bottom-up assembly of more sophisticated molecular machines.

  10. Length Dependence of Tunneling Current Through Single Phenylene Oligomers Measured by Scanning Tunneling Microscopy at Low Temperature

    NASA Astrophysics Data System (ADS)

    Wakamatsu, Satoshi; Fujii, Shintaro; Akiba, Uichi; Fujihira, Masamichi

    2006-04-01

    The length dependence of tunneling current through single phenylene oligomers, i.e., benzenemethanethiol, 4-biphenylmethanethiol and [1,1':4',1''-terphenyl]-4-methanethiol, was determined experimentally by scanning tunneling microscopy (STM). The single phenylene oligomers were isolated in a self-assembled monolayer (SAM) matrix of a disulfide with two spherical bicyclo[2.2.2]octane moieties on Au(111). The STM measurement was conducted at a low temperature to prevent the thermal motions of the isolated molecules that occur at room temperature. The isolated single molecules inserted in the SAM matrix were observed as protrusions in an STM topography using a constant-current mode owing to their higher tunneling ability. The decay constant, β, of the tunneling current through single phenylene oligomers was estimated from the STM heights of the protrusions corresponding to the single phenylene oligomers using a bilayer tunnel junction model. The value of β for tunneling current through single phenylene oligomers was 5.5 ± 0.2 nm-1. In a constant-height mode, we measured the conductance of the isolated single molecules. We estimated an averaged single-molecular conductance of the isolated molecules of a biphenyl derivative to be ca. 2 nS. Here, one side of each isolated molecule was bound via an Au-S bond and the other phenyl end was physically in contact with an Au STM tip.

  11. Refinement of Strut-and-Tie Model for Reinforced Concrete Deep Beams.

    PubMed

    Panjehpour, Mohammad; Chai, Hwa Kian; Voo, Yen Lei

    2015-01-01

    Deep beams are commonly used in tall buildings, offshore structures, and foundations. According to many codes and standards, strut-and-tie model (STM) is recommended as a rational approach for deep beam analyses. This research focuses on the STM recommended by ACI 318-11 and AASHTO LRFD and uses experimental results to modify the strut effectiveness factor in STM for reinforced concrete (RC) deep beams. This study aims to refine STM through the strut effectiveness factor and increase result accuracy. Six RC deep beams with different shear span to effective-depth ratios (a/d) of 0.75, 1.00, 1.25, 1.50, 1.75, and 2.00 were experimentally tested under a four-point bending set-up. The ultimate shear strength of deep beams obtained from non-linear finite element modeling and STM recommended by ACI 318-11 as well as AASHTO LRFD (2012) were compared with the experimental results. An empirical equation was proposed to modify the principal tensile strain value in the bottle-shaped strut of deep beams. The equation of the strut effectiveness factor from AASHTTO LRFD was then modified through the aforementioned empirical equation. An investigation on the failure mode and crack propagation in RC deep beams subjected to load was also conducted. PMID:26110268

  12. Refinement of Strut-and-Tie Model for Reinforced Concrete Deep Beams

    PubMed Central

    Panjehpour, Mohammad; Chai, Hwa Kian; Voo, Yen Lei

    2015-01-01

    Deep beams are commonly used in tall buildings, offshore structures, and foundations. According to many codes and standards, strut-and-tie model (STM) is recommended as a rational approach for deep beam analyses. This research focuses on the STM recommended by ACI 318-11 and AASHTO LRFD and uses experimental results to modify the strut effectiveness factor in STM for reinforced concrete (RC) deep beams. This study aims to refine STM through the strut effectiveness factor and increase result accuracy. Six RC deep beams with different shear span to effective-depth ratios (a/d) of 0.75, 1.00, 1.25, 1.50, 1.75, and 2.00 were experimentally tested under a four-point bending set-up. The ultimate shear strength of deep beams obtained from non-linear finite element modeling and STM recommended by ACI 318-11 as well as AASHTO LRFD (2012) were compared with the experimental results. An empirical equation was proposed to modify the principal tensile strain value in the bottle-shaped strut of deep beams. The equation of the strut effectiveness factor from AASHTTO LRFD was then modified through the aforementioned empirical equation. An investigation on the failure mode and crack propagation in RC deep beams subjected to load was also conducted. PMID:26110268

  13. Developmental delays in phonological recoding among children and adolescents with Down syndrome and Williams syndrome.

    PubMed

    Danielsson, Henrik; Henry, Lucy; Messer, David; Carney, Daniel P J; Rönnberg, Jerker

    2016-08-01

    This study examined the development of phonological recoding in short-term memory (STM) span tasks among two clinical groups with contrasting STM and language profiles: those with Down syndrome (DS) and Williams syndrome (WS). Phonological recoding was assessed by comparing: (1) performance on phonologically similar and dissimilar items (phonological similarity effects, PSE); and (2) items with short and long names (word length effects, WLE). Participant groups included children and adolescents with DS (n=29), WS (n=25) and typical development (n=51), all with average mental ages around 6 years. The group with WS, contrary to predictions based on their relatively strong verbal STM and language abilities, showed no evidence for phonological recoding. Those in the group with DS, with weaker verbal STM and language abilities, showed positive evidence for phonological recoding (PSE), but to a lesser degree than the typical group (who showed PSE and WLE). These findings provide new information about the memory systems of these groups of children and adolescents, and suggest that STM processes involving phonological recoding do not fit with the usual expectations of the abilities of children and adolescents with WS and DS. PMID:27043367

  14. Tip induced mechanical deformation of epitaxial graphene grown on reconstructed 6H-SiC(0001) surface during scanning tunneling and atomic force microscopy studies

    NASA Astrophysics Data System (ADS)

    Morán Meza, José Antonio; Lubin, Christophe; Thoyer, François; Cousty, Jacques

    2015-06-01

    The structural and mechanical properties of an epitaxial graphene (EG) monolayer thermally grown on top of a 6H-SiC(0001) surface were studied by combined dynamic scanning tunneling microscopy (STM) and frequency modulation atomic force microscopy (FM-AFM). Experimental STM, dynamic STM and AFM images of EG on 6H-SiC(0001) show a lattice with a 1.9 nm period corresponding to the (6 × 6) quasi-cell of the SiC surface. The corrugation amplitude of this (6 × 6) quasi-cell, measured from AFM topographies, increases with the setpoint value of the frequency shift Δf (15-20 Hz, repulsive interaction). Excitation variations map obtained simultaneously with the AFM topography shows that larger dissipation values are measured in between the topographical bumps of the (6 × 6) quasi-cell. These results demonstrate that the AFM tip deforms the graphene monolayer. During recording in dynamic STM mode, a frequency shift (Δf) map is obtained in which Δf values range from 41 to 47 Hz (repulsive interaction). As a result, we deduced that the STM tip, also, provokes local mechanical distortions of the graphene monolayer. The origin of these tip-induced distortions is discussed in terms of electronic and mechanical properties of EG on 6H-SiC(0001).

  15. Attenuated mutant strain of Salmonella Typhimurium lacking the ZnuABC transporter contrasts tumor growth promoting anti-cancer immune response.

    PubMed

    Chirullo, Barbara; Ammendola, Serena; Leonardi, Leonardo; Falcini, Roberto; Petrucci, Paola; Pistoia, Claudia; Vendetti, Silvia; Battistoni, Andrea; Pasquali, Paolo

    2015-07-10

    Salmonella Typhimurium has been shown to be highly effective as antitumor agent. The aim of this study was to investigate the tumor targeting efficacy and the mechanism of action of a specific attenuated mutant strain of Salmonella Typhimurium (STM) devoid of the whole operon coding for the high-affinity zinc transporter ZnuABC, which is required for bacterial growth in environments poor in zinc and for conferring full virulence to different Gram-negative pathogens.We showed that STM is able to penetrate and replicate into tumor cells in in vitro and in vivo models. The subcutaneous administration of STM in mammary adenocarcinoma mouse model led to both reduction of tumor growth and increase in life expectancy of STM treated mice. Moreover, investigating the potential mechanism behind the favorable clinical outcomes, we provide evidence that STM stimulates a potent inflammatory response and a specific immune pattern, recruiting a large number of innate and adaptive immune cells capable to contrast the immunosuppressive environment generated by tumors. PMID:26158862

  16. Scanning tunneling microscopy-based in situ measurement of fast tool servo-assisted diamond turning micro-structures

    NASA Astrophysics Data System (ADS)

    Ju, Bing-Feng; Zhu, Wu-Le; Yang, Shunyao; Yang, Keji

    2014-05-01

    We propose a new in situ measurement system based on scanning tunneling microscopy (STM) to realize spiral scanning of a micro-structure without removing it after fast tool servo (FTS) cutting. To avoid distortion of the machined and measured surface, the center alignment of the FTS tool and the STM tip was first implemented by an STM in situ raster scan of two circular grooves cut by the machine tool. To originally observe the machined surface, the trace of the STM tip is put in accord with that of the FTS by setting the same start and end points of cutting and scanning and the same feed rate, and both are triggered by the subdivided rotary encoder of the spindle of the diamond turning machine. The profile data of the in situ spiral scanning of the machined micro-lens array can be fed back to compensate the depth of the cut to guarantee sub-micron form accuracy after second machining. The efficient spiral scanning, proper matching and accurate evaluation results demonstrate that the proposed STM in situ measurement approach is of great significance to the fabrication process.

  17. Phonological short-term memory in logopenic variant primary progressive aphasia and mild Alzheimer's disease.

    PubMed

    Meyer, Aaron M; Snider, Sarah F; Campbell, Rachael E; Friedman, Rhonda B

    2015-10-01

    It has been argued that individuals with logopenic variant primary progressive aphasia (lvPPA) have an impairment of the phonological loop, which is a component of the short-term memory (STM) system. In contrast, this type of impairment is not thought to be present in mild typical Alzheimer's disease (AD). Thus, one would predict that people with lvPPA would score significantly lower than a matched AD group on tasks that require phonological STM. In the current study, an lvPPA group was compared with a mild AD group that was matched on age, education, and general cognitive functioning. For a subset of the tasks that involved pseudowords, the AD and lvPPA groups were compared to a healthy control group that was matched on age and education. The lvPPA group was more impaired than the AD group on all of the tasks that required phonological STM, including the pseudoword tasks, but there were no significant differences between these groups on tasks that required visuospatial STM. Compared to the healthy controls, the lvPPA group performed significantly worse on the repetition and reading of pseudowords, while the AD group did not differ significantly from the controls on these tasks. These findings are consistent with the hypothesis that phonological STM is impaired in lvPPA. PMID:26232551

  18. Scanning Tunneling Microscopy Studies of Diamond Films and Optoelectronic Materials

    NASA Technical Reports Server (NTRS)

    Perez, Jose M.

    1996-01-01

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

  19. Theoretical study of carbon-based tips for scanning tunnelling microscopy

    NASA Astrophysics Data System (ADS)

    González, C.; Abad, E.; Dappe, Y. J.; Cuevas, J. C.

    2016-03-01

    Motivated by recent experiments, we present here a detailed theoretical analysis of the use of carbon-based conductive tips in scanning tunnelling microscopy. In particular, we employ ab initio methods based on density functional theory to explore a graphitic, an amorphous carbon and two diamond-like tips for imaging with a scanning tunnelling microscope (STM), and we compare them with standard metallic tips made of gold and tungsten. We investigate the performance of these tips in terms of the corrugation of the STM images acquired when scanning a single graphene sheet. Moreover, we analyse the impact of the tip-sample distance and show that it plays a fundamental role in the resolution and symmetry of the STM images. We also explore in depth how the adsorption of single atoms and molecules in the tip apexes modifies the STM images and demonstrate that, in general, it leads to an improved image resolution. The ensemble of our results provides strong evidence that carbon-based tips can significantly improve the resolution of STM images, as compared to more standard metallic tips, which may open a new line of research in scanning tunnelling microscopy.

  20. Atomic structure of the Ag / Ge ( 111 ) - ( √{ 3 } × √{ 3 } ) surface: From scanning tunneling microscopy observation to theoretical study

    NASA Astrophysics Data System (ADS)

    Chou, L.-W.; Wu, H. C.; Lee, Y.-R.; Jiang, J.-C.; Su, C.; Lin, J.-C.

    2009-12-01

    The atomic structure of the Ag / Ge ( 111 ) - ( √{ 3 } × √{ 3 } ) R 30 ° surface is studied by scanning tunneling microscopy (STM) and the density functional theory (DFT) calculations. Our STM images have shown a structure which is different from the widely accepted honeycomb-chained-triangle (HCT) model before. The structure is similar to the inequivalent triangle (IET) model found for the Ag / Si ( 111 ) - ( √{ 3 } × √{ 3 } ) R 30 ° surface. This model proposed two types of silver triangles with different sizes in the unit cell, corresponding to the bright spots and the dark spots in the STM image. A distinguishable hexagonal pattern of the IET structure was well disclosed in the temperature range from 100 to 473 K in our STM studies for Ag / Ge ( 111 ) - ( √{ 3 } × √{ 3 } ) R 30 ° . Furthermore, the result of the DFT calculations showed that the IET structure is 0.20 eV energetically more stable than the HCT model. Besides, the Ge triangles, which were not disclosed in earlier STM research, are found in this study.